"uuid","repository link","title","author","contributor","publication year","abstract","subject topic","language","publication type","publisher","isbn","issn","patent","patent status","bibliographic note","access restriction","embargo date","faculty","department","research group","programme","project","coordinates"
"uuid:c54f3785-0af4-43fe-ba50-7e0c320155d1","http://resolver.tudelft.nl/uuid:c54f3785-0af4-43fe-ba50-7e0c320155d1","Failure anticipation scheme in distribution systems based on wave distortions and Montecarlo methods","Bhandia, R. (TU Delft Intelligent Electrical Power Grids); de Jesus Chavez, Jose (TU Delft Intelligent Electrical Power Grids; Tecnologico de Monterrey); Cvetkovic, M. (TU Delft Intelligent Electrical Power Grids); Garcia-Vite, Pedro M. (Tecnológico Nacional de México Campus de Cd. Madero); Popov, M. (TU Delft Intelligent Electrical Power Grids); Palensky, P. (TU Delft Electrical Sustainable Energy)","","2024","Anticipating failures is vital for maintaining a reliable power supply. Advanced measurement devices in the grid generate vast data that contains valuable information on grid operations. Initial signatures of an incipient failure are often reflected in this data in the form of electrical waveform distortions. Conventional protection schemes are not equipped to analyze these distortions and anticipate failures. There is a considerable research gap for a simple yet robust and universal failure anticipation and diagnosis scheme. This paper proposes a universal Failure Anticipation and Diagnosis Scheme (FADS) to detect incipient failures in AC distribution grids. The method comprises three short stages, helping the operator make an informed decision. In the first stage, the FADS scheme leverages the fundamental properties of electrical sinusoid waveforms to detect distortions. In the second stage, the distortion data is processed through pre-determined thresholds set in accordance with the system's regular operation. In the third stage, depending on the system, the FADS uses the extent of the violations of these thresholds and ranks the severity of the danger posed to grid operations. The classification helps determine if the waveform distortions are the signature of an incipient failure. The proposed FADS method's reliability, robustness and effectiveness are evaluated in incipient failure conditions of field events modelled in real-time simulations on standardized IEEE distribution feeders. The FADS is a high-speed distortion detector, is quite sensitive, and the method has high selectivity because of its nature.","Incipient faults detection; Failure anticipation; Situational awareness; Signature analysis; Distribution systems","en","review","","","","","","","","","","Electrical Sustainable Energy","Intelligent Electrical Power Grids","","",""
"uuid:9661b26e-8f7d-414f-a743-9b46e0718d6b","http://resolver.tudelft.nl/uuid:9661b26e-8f7d-414f-a743-9b46e0718d6b","Cosimulating Integrated Energy Systems with Heterogeneous Digital Twins: Matching a Connected World","Palensky, P. (TU Delft Electrical Sustainable Energy); Mancarella, Pierluigi (University of Melbourne; The University of Manchester); Hardy, Trevor (Pacific Northwest National Laboratory); Cvetkovic, M. (TU Delft Intelligent Electrical Power Grids)","","2024","Energy system integration promises in-creased resiliency and the unlocking of synergies, while also contributing to our goal of decarbonization. It is enabled by both old and new technologies, glued together with data and digital services. Hydrolyzers, heat pumps, distributed renewable generation, smart buildings, and the digital grid edge are all currently the subject of integration with the power system and the energy sector at large. To plan and operate such a multidisciplinary and multisectoral system properly, insight, tools, and expertise are all needed. This is exactly where the state of the art fails to deliver: tools for integrated energy systems (IESs) are still in their infancy, and many times, even academia treats these sectors separately, producing experts in each of them but not across.","","en","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2024-07-12","","Electrical Sustainable Energy","Intelligent Electrical Power Grids","","",""
"uuid:b20ef73f-46ff-44c0-84c6-38bc0c2ddbf5","http://resolver.tudelft.nl/uuid:b20ef73f-46ff-44c0-84c6-38bc0c2ddbf5","Will SiOx-pinholes for SiOx/poly-Si passivating contact enhance the passivation quality?","Yang, G. (TU Delft Photovoltaic Materials and Devices); Gram, Remon (Student TU Delft); Procel Moya, P.A. (TU Delft Photovoltaic Materials and Devices); Han, C. (TU Delft Photovoltaic Materials and Devices); Yao, Z. (TU Delft Photovoltaic Materials and Devices); Singh, M. (TU Delft Photovoltaic Materials and Devices); Zhao, Y. (TU Delft Photovoltaic Materials and Devices); Mazzarella, L. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy); Isabella, O. (TU Delft Photovoltaic Materials and Devices)","","2023","Passivating contacts based on poly-Si have enabled record-high c-Si solar cell efficiencies due to their excellent surface passivation quality and carrier selectivity. The eventual existence of pinholes within the ultra-thin SiOx layer is one of the key factors for carrier collection, beside the tunneling mechanism. However, pinholes are usually believed to have negative impact on the passivation quality of poly-Si passivating contacts. This work studied the influence of the pinhole density on the passivation quality of ion-implanted poly-Si passivating contacts by decoupling the pinhole generation from the dopants diffusion process by means of two annealing steps: (1) a pre-annealing step at high temperature after the intrinsic poly-Si deposition to visualize the formation of pinholes and (2) a post-annealing step for dopants activation/diffusion after ion-implantation. The pinhole density is quantified in the range of 1✕106 to 3✕108 cm2 by the TMAH selective etching approach. The passivation quality is discussed with respect to the pinhole density and the post-annealing thermal budget (TB) for dopants diffusion. The study shows that a moderate pinhole density does not induce doping profile variations that can be detectable by the coarse spatial resolution of ECV measurements. It is surprising that the existence of pinholes in a moderate density within our thickness fixed SiOx layer can effectively enhance the passivation qualities for both n+ and p+ poly-Si passivating contacts. We speculate the reason is due to the enhanced field-effect passivation at the pinhole surrounding. In fact, the variation of the passivation quality depends on the balance between a strengthened field-effect passivation and an excessive local Auger recombination, being both effects induced by the higher and deeper level of dopants diffused into the c-Si surface through the pinholes.","Poly-Si passivating Contacts; Pinhole density; Thermal diffusion budget; Enhanced passivation","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:34cc5b72-0d69-4842-888d-52d31c218a72","http://resolver.tudelft.nl/uuid:34cc5b72-0d69-4842-888d-52d31c218a72","Energy Loss Analysis of Two-Terminal Tandem PV Systems under Realistic Operating Conditions—Revealing the Importance of Fill Factor Gains","Blom, Y. (TU Delft Photovoltaic Materials and Devices); Vogt, M.R. (TU Delft Photovoltaic Materials and Devices); Ruiz Tobon, C.M. (TU Delft Photovoltaic Materials and Devices); Santbergen, R. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy); Isabella, O. (TU Delft Photovoltaic Materials and Devices)","","2023","The tandem PV technology can potentially increase the efficiency of PV modules over 30%. To design efficient modules, a quantification of the different losses is important. Herein, a model for quantifying the energy loss mechanisms in PV systems under real-world operating conditions with a level of detail back to the components and their fundamental properties is presented. Totally, 17 losses are defined and divided into four categories (fundamental, optical, electrical, and system losses). As example, a system based on a > 29% two-terminal perovskite/silicon tandem cell is considered. The loss distribution at standard test conditions is compared to four geographical locations. The results show that the thermalization, reflection, and inverter losses increase by 1.2%, 1.1%, and 1.4%, respectively, when operating outdoors. Additionally, it is quantified how fill factor gains partly compensate the current mismatch losses. For example, a mismatch of 7.0% in photocurrent leads to a power mismatch of 1.2%. Therefore, the power mismatch should be used as indicator for mismatch losses instead of a current mismatch. Finally, herein, it is shown that solar tracking increases not only the in-plane irradiance but also the efficiency of the tandem module.","energy loss analysis; fill factor gains; outdoors simulation; perovskite/silicon; tandem PV","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:adf37e38-675b-4208-ae78-7b675978d6c3","http://resolver.tudelft.nl/uuid:adf37e38-675b-4208-ae78-7b675978d6c3","Exploring Stability and Accuracy Limits of Distributed Real-Time Power System Simulations via System-of-Systems Cosimulation","Barbierato, Luca (Politecnico di Torino); Pons, Enrico (Politecnico di Torino); Bompard, Ettore Francesco (Politecnico di Torino); Subramaniam Rajkumar, Vetrivel (TU Delft Intelligent Electrical Power Grids); Palensky, P. (TU Delft Electrical Sustainable Energy); Bottaccioli, Lorenzo (Politecnico di Torino); Patti, Edoardo (Politecnico di Torino)","","2023","Electromagnetic transients (EMT) is the most accurate, but computationally expensive method of analyzing power system phenomena. Thereby, interconnecting several real-time simulators can unlock scalability and system coverage, but leads to a number of new challenges, mainly in time synchronization, numerical stability, and accuracy quantification. This study presents such a cosimulation, based on digital real-time simulators (DRTS), connected via Aurora 8B/10B protocol. Such a setup allows to analyze complex and hybrid system-of-systems whose resulting numerical phenomena and artifacts have been poorly investigated and understood so far. We experimentally investigate the impact of IEEE 1588 precision time protocol synchronization assessing both time and frequency domains. The analysis of the experimental results is encouraging and show that numerical stability can be maintained even with complex system setups. Growing shares of inverter-based renewable power generation require larger and interconnected EMT system studies. This work helps to understand the phenomena connected to such DRTS advanced cosimulation setups.","Cosimulation; digital real-time simulators (DRTSs); numerical stability; power system assessments; system-of-systems (SoS)","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Intelligent Electrical Power Grids","","",""
"uuid:9b73bee5-b8cf-46c1-b4b9-f3fb9d3b4e07","http://resolver.tudelft.nl/uuid:9b73bee5-b8cf-46c1-b4b9-f3fb9d3b4e07","Developing an energy rating for bifacial photovoltaic modules","Vogt, M.R. (TU Delft Photovoltaic Materials and Devices); Pilis, Giorgos (Student TU Delft); Zeman, M. (TU Delft Electrical Sustainable Energy); Santbergen, R. (TU Delft Photovoltaic Materials and Devices); Isabella, O. (TU Delft Photovoltaic Materials and Devices)","","2023","The photovoltaic (PV) module energy rating standard series IEC 61853 does not cover bifacial PV modules. However, the market share of bifacial PV modules has dramatically increased in recent years and is projected to grow. This work demonstrates how Parts 3 and 4 of the IEC 61853 standard could be extended to bifacial modules. First, we develop an irradiance model that uses the data already given in the standard IEC 61853-4 to calculate the irradiance on the rear side of the module. Second, we propose a way to extend the energy yield calculation algorithm IEC 61853-3 to include bifacial modules and make it available to the PV community. This rear irradiance and bifacial energy yield calculation procedure is tested using real outdoor measurements for a nine-month period with a root mean square difference between measured and simulated energy yield of 4.65%. To conclude, we investigate the impact of different climates and normalization on the bifacial module energy rating results.","bifacial PV module; energy rating; energy yield; IEC61853; PV module; PV module performance; view factor","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:f354b443-9433-4f92-be0d-0919495192a5","http://resolver.tudelft.nl/uuid:f354b443-9433-4f92-be0d-0919495192a5","Dynamic operation of water electrolyzers: A review for applications in photovoltaic systems integration","Martinez Lopez, V.A. (TU Delft Photovoltaic Materials and Devices); Ziar, H. (TU Delft Photovoltaic Materials and Devices); Haverkort, J.W. (TU Delft Energy Technology); Zeman, M. (TU Delft Electrical Sustainable Energy); Isabella, O. (TU Delft Photovoltaic Materials and Devices)","","2023","This review provides a comprehensive overview of the dynamics of low-temperature water electrolyzers and their influence on coupling the three major technologies, alkaline, Proton Exchange Membrane (PEM) and, Anion Exchange Membrane (AEM) with photovoltaic (PV) systems. Hydrogen technology is experiencing considerable interest as a way to accelerate the energy transition. With no associated CO2 emissions and fast response, water electrolyzers are an attractive option for producing green hydrogen on an industrial scale. This can be seen by the ambitious goals and large-scale projects being announced for hydrogen, especially with solar energy dedicated entirely to drive the process. The electrical response of water electrolyzers is extremely fast, making the slower variables, such as temperature and pressure, the limiting factors for variable operation typically associated with PV-powered electrolysis systems. The practical solar-to-hydrogen efficiency of these systems is in the range of 10% even with a very high coupling factor exceeding 99% for directly coupled systems. The solar-to-hydrogen efficiency can be boosted with a battery, potentially sacrificing the cost. The intermittency of solar irradiance, rather than its variability is the biggest challenge for PV-hydrogen systems regarding operation and degradation.","","en","review","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:0115a6a1-da19-4e7d-8967-170f054e2750","http://resolver.tudelft.nl/uuid:0115a6a1-da19-4e7d-8967-170f054e2750","Cyber Attacks on Power Grids: Causes and Propagation of Cascading Failures","Subramaniam Rajkumar, Vetrivel (TU Delft Intelligent Electrical Power Grids); Stefanov, Alexandru (TU Delft Intelligent Electrical Power Grids); Presekal, A. (TU Delft Intelligent Electrical Power Grids); Palensky, P. (TU Delft Electrical Sustainable Energy); Rueda, José L. (TU Delft Intelligent Electrical Power Grids)","","2023","Cascading effects in the power grid involve an uncontrolled, successive failure of elements. The root cause of such failures is the combined occurrence of multiple, statistically rare events that may result in a blackout. With increasing digitalisation, power systems are vulnerable to emergent cyber threats. Furthermore, such threats are not statistically limited and can simultaneously occur at multiple locations. In the absence of real-world attack information, however, it is imperative to investigate if and how cyber attacks can cause power system cascading failures. Hence, in this work we present a fundamental analysis of the connection between the cascading failure mechanism and cyber security. We hypothesise and demonstrate how cyber attacks on power grids may cause cascading failures and a blackout. To do so, we perform a systematic survey of major historic blackouts caused by physical disturbances, and examine the cascading failure mechanism. Subsequently, we identify critical cyber-physical factors that can activate and influence it. We then infer and discuss how cyber attack vectors can enable these factors to cause and accelerate cascading failures. A synthetic case-study and software-based simulation results prove our hypothesis. This analysis enables future research into cyber resilience of power grids.","","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Intelligent Electrical Power Grids","","",""
"uuid:99863cbd-fb5b-461b-b0ad-779242fb70c5","http://resolver.tudelft.nl/uuid:99863cbd-fb5b-461b-b0ad-779242fb70c5","Towards Real-Time Distinction of Power System Faults and Cyber Attacks","Abedi, A. (TU Delft Intelligent Electrical Power Grids); Subramaniam Rajkumar, Vetrivel (TU Delft Intelligent Electrical Power Grids); Stefanov, Alexandru (TU Delft Intelligent Electrical Power Grids); Palensky, P. (TU Delft Electrical Sustainable Energy)","","2023","This paper presents a methodology to distinguish between three-phase faults and GOOSE cyber attacks, aimed at opening the circuit breakers in the power grid. We propose a scheme that utilizes Phasor Measurement Unit (PMU)-enabled monitoring of power grid states, and communication network packet logs in the substation. In this scheme, by leveraging both cyber and physical data correlations and applying a Seasonal Autoregressive Moving Average (SARMA) model, we successfully distinguish between 3-phase faults and cyber attacks. The proposed scheme is tested using the benchmark IEEE 9-bus system, and can distinguish cyber attacks from faults in less than 0.2s. This demonstrates the usefulness of the proposed scheme for power system cyber security analytics.","","en","conference paper","IEEE","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2024-03-25","","Electrical Sustainable Energy","Intelligent Electrical Power Grids","","",""
"uuid:a9e4a3de-3ad2-4e17-8889-0d670d6f4caa","http://resolver.tudelft.nl/uuid:a9e4a3de-3ad2-4e17-8889-0d670d6f4caa","Closed-loop simulation testing of a probabilistic DR framework for Day Ahead Market participation applied to Battery Energy Storage Systems","van der Heijden, T.J.T. (TU Delft Water Resources); Palensky, P. (TU Delft Electrical Sustainable Energy); van de Giesen, N.C. (TU Delft Water Resources); Abraham, E. (TU Delft Water Resources)","","2023","In this manuscript, we test the operational performance decrease of a probabilistic framework for Demand Response (DR). We use Day Ahead Market (DAM) price scenarios generated by a Combined Quantile Regression Deep Neural Network (CQR-DNN) and a Non-parametric Bayesian Network (NPBN) to maximise profit of a Battery Energy Storage System (BESS) participating on the DAM for energy arbitrage. We apply the generated forecast time series to a stochastic Model Predictive Control (MPC), and compare the performance using a point and perfect forecast. For the probabilistic forecasts, we test two control strategies; 1) minimising the Conditional Value at Risk (CVaR) for making costs, and 2) minimising the expected value of the cost. We apply the MPC in a closed-loop simulation setting and perform a sensitivity analysis of the profit by changing the ratio between battery capacity and the max power, the cluster reduction method, and the number of scenarios used by the MPC. We show that the proposed framework works, but the approach does not increase profit compared to a deterministic point forecast. This can possibly be explained by the deterministic forecast capturing the shape of the price curve with less noise than a probabilistic forecast without enough scenarios. We show that the value of a good forecast becomes smaller as the charging time of the battery becomes larger, due to the battery being unable to exploit small price differences optimally.","Demand Response; probabilistic forecasting; scenario generation; stochastic programming; battery energy storage systems; day ahead market","en","conference paper","IEEE","","","","","Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2024-03-01","","Electrical Sustainable Energy","Water Resources","","",""
"uuid:0da1d025-a22a-4fc0-96ae-25294022412c","http://resolver.tudelft.nl/uuid:0da1d025-a22a-4fc0-96ae-25294022412c","Impact of Dynamic Tariffs for Smart EV Charging on LV Distribution Network Operation","Verbist, Flore (Student TU Delft); Panda, Nanda Kishor (TU Delft Intelligent Electrical Power Grids); Vergara Barrios, P.P. (TU Delft Intelligent Electrical Power Grids); Palensky, P. (TU Delft Electrical Sustainable Energy)","","2023","With a growing share of electric vehicles (EVs) in our distribution grids, the need for smart charging becomes indispensable to minimise grid reinforcement. To circumvent the associated capacity limitations, this paper evaluates the effectiveness of different levels of network constraints and different dynamic tariffs, including a dynamic network tariff. A detailed optimisation model is first developed for public charging electric vehicles in a representative Dutch low voltage (LV) distribution network, susceptible to congestion and voltage problems by 2050 without smart charging of EVs. Later, a detailed reflection is made to assess the influence of the modelled features on the distribution system operator (DSO), charge point operator (CPO) costs, and the EVs' final state-of-charge (SOC) for both mono- (V1G) and bi-directional (V2G) charging. Results show that the dynamic network tariff outperforms other flat tariffs by increasing valley-filling. Consequently, compared to regular day-ahead pricing, a significant reduction in the frequency of congestion in the lines is achieved. In addition, V2G ensures the joint optimum for different stakeholders causing adequate EV user satisfaction, decreased CPO costs compared to conventional charging and fewer violations of grid constraints for the DSOs.","dynamic tariffs; EV; flexibility; OPF; smart charging; V2G","en","conference paper","IEEE","","","","","Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2024-03-25","","Electrical Sustainable Energy","Intelligent Electrical Power Grids","","",""
"uuid:a5b4a4c2-c438-43d6-aa77-0e2be9aea1b6","http://resolver.tudelft.nl/uuid:a5b4a4c2-c438-43d6-aa77-0e2be9aea1b6","Stable passivation of cut edges in encapsulated n-type silicon solar cells using Nafion polymer","Chen, N. (TU Delft Photovoltaic Materials and Devices; International Solar Energy Research Center (ISC)); Tune, Daniel (International Solar Energy Research Center (ISC)); Buchholz, Florian (International Solar Energy Research Center (ISC)); Roescu, Razvan (International Solar Energy Research Center (ISC)); Zeman, M. (TU Delft Electrical Sustainable Energy); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Mihailetchi, Valentin D. (International Solar Energy Research Center (ISC))","","2023","In this study, the edge passivation effectiveness and long-term stability of Nafion polymer in n-type interdigitated back contact (IBC) solar cells are investigated. For new module technologies such as half-cut, triple-cut, or shingled modules, cutting of the cells introduces unpassivated edges with a high recombination rate and this limits the module power. These cut edges can be “repassivated” after cutting and in this work Nafion polymer is used to achieve this. First, different edge types, namely emitter edges (n+/n/p+) and back surface field (BSF) edges (n+/n/n+), as well as different cutting techniques such as laser cut and cleave (L&C), thermal laser separation (TLS), and mechanical cleaving are evaluated. It is found that TLS and mechanical cleaving enable good repassivation on both BSF and emitter edges. Second, industrial-size IBC solar cells are made to assess the effect of the edge repassivation on performance. On 1/4-cut M2 size IBC cells with two emitter edges, efficiency is improved by over 0.3%abs. However, an efficiency improvement was not observed for similar cells with BSF edges, due to an insufficient passivation at the bulk edges. Last, the real-world stability of the Nafion repassivation is evaluated in industrially relevant module stacks by laminating the repassivated wafers with ethylvinylacetate (EVA) or polyolefin elastomer (POE) encapsulants and then exposing them to industry standard testing of 1000 h under damp heat conditions (85 °C, 85% relative humidity). The tests reveal that the repassivation is stable in EVA encapsulants but not in POE.","Edge passivation; Laser cut; Cut loss; Silicon solar cell; Back contact; Nafion","en","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2023-12-12","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:dcdd37f4-e686-422c-8287-39c6d0bdb548","http://resolver.tudelft.nl/uuid:dcdd37f4-e686-422c-8287-39c6d0bdb548","Voltage Stability improvement based on firing angle control of SVCs in wind integrated system with ANN","Mishra, Rajan Kumar (Silicon Institute of Technology, Bhubaneswar); Panda, Ramprasad (Silicon Institute of Technology, Bhubaneswar); Panda, Nanda Kishor (TU Delft Electrical Sustainable Energy; TU Delft Intelligent Electrical Power Grids)","","2023","The widening gap between energy generation and demand on a global scale, coupled with the imperative to reduce emissions, has necessitated the development of largescale sustainable energy solutions. Among the various renewable energy options, Wind Power stands out as a viable source capable of generating substantial amounts of electricity. However, the unpredictable nature of wind availability and its fluctuations pose challenges for grid operators in effectively harnessing and distributing the generated wind power. This issue becomes more pronounced when transmitting wind power through local grids to distant load centers. Voltage instability at local buses emerges as a significant concern in wind-integrated power systems. To address these challenges, dynamic compensation at multiple locations has proven to be an effective solution. Various alternative approach to controlling the firing of Static Var Compensators (SVCs) connected to the network is proposed in the present work. The traditional method, which relies on a classical control approach, is computationally intensive and time-consuming. To overcome this limitation, we propose the utilization of a trained Neural Network for simultaneous control of the firing angles of all SVCs, accommodating various system conditions such as change in load and wind generation fluctuations. Porposed method has been evaluated on both a modified IEEE-30 bus system and a 28-bus Indian system.","ANN; Distributed Computing; Restoration; Smart Grid; SVC firing","en","conference paper","Institute of Electrical and Electronics Engineers (IEEE)","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2024-05-06","","Electrical Sustainable Energy","Intelligent Electrical Power Grids","","",""
"uuid:bf76c6cb-36ac-4e62-ac07-97773d5dd57d","http://resolver.tudelft.nl/uuid:bf76c6cb-36ac-4e62-ac07-97773d5dd57d","Future Dutch Electricity Grid: Assessing the Potential of Overplanting in Photovoltaic Systems","Reis, F.R. (TU Delft Intelligent Electrical Power Grids); Rueda, José L. (TU Delft Intelligent Electrical Power Grids); Palensky, P. (TU Delft Electrical Sustainable Energy); Gonzalez-Longatt, Francisco (University of Exeter)","","2023","This paper concerns with the determination of a suitable level of overplanting for photovoltaic systems. For this purpose, six futuristic operational scenarios for the Dutch electrical power system are generated for year 2050. A synthetic model is developed by using DIgSILENT Power Factory 2022 SP3 to investigate the steady-state systemic performance in each operational scenario, taking into account three cases with different levels of overplanting. Power flow calculations are conducted to reflect on the resulting voltage profiles and active power losses as well as on the implications on the required network upgrades (e.g. addition of lines, transformers, and reactive power compensation devices).","power system; national scenario; overplanting; photovoltaic systems; power flow","en","conference paper","IEEE","","","","","Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2024-05-16","","Electrical Sustainable Energy","Intelligent Electrical Power Grids","","",""
"uuid:513b5e4f-880f-42da-bcc3-b48e0383331d","http://resolver.tudelft.nl/uuid:513b5e4f-880f-42da-bcc3-b48e0383331d","Cyber Forensic Analysis for Operational Technology Using Graph-Based Deep Learning","Presekal, A. (TU Delft Intelligent Electrical Power Grids); Stefanov, Alexandru (TU Delft Intelligent Electrical Power Grids); Subramaniam Rajkumar, Vetrivel (TU Delft Intelligent Electrical Power Grids); Palensky, P. (TU Delft Electrical Sustainable Energy)","","2023","The cyber attacks in Ukraine in 2015 and 2016 demonstrated the vulnerability of electrical power grids to cyber threats. They highlighted the significance of Operational Technology (OT) communication-based anomaly detection. Many anomaly detection methods are based on real-time traffic monitoring, i.e., Intrusion Detection Systems (IDS) that may produce false positives and degrade the OT communication performance. Security Operations Center (SOC) needs intelligent tools to conduct forensic analysis on generated IDS alarms and identify the attack locations. Therefore, in this paper, we propose a novel, graph-based forensic analysis method for anomaly detection in power systems using OT communication network traffic throughput. It employs a hybrid deep learning model involving Graph Convolutional Long Short-Term Memory and a Convolutional Neural Network. The proposed method aids SOC with continuous OT security monitoring and post-mortem investigations. Results indicate that the proposed method is able to pinpoint the locations of cyber attacks on power grid OT networks with an AUC score above 75%.","Anomaly Detection; Attack Graph; CNN; Cyber Security; Digital Forensics; Graph; GNN; LSTM; Operational Technology","en","conference paper","IEEE","","","","","Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2024-06-06","","Electrical Sustainable Energy","Intelligent Electrical Power Grids","","",""
"uuid:248d4da7-4d4d-4c73-8c08-e79228384f01","http://resolver.tudelft.nl/uuid:248d4da7-4d4d-4c73-8c08-e79228384f01","A stochastic MPC framework for the control of pumping stations in polder systems with regard for uncertainty in inflow and hourly electricity prices","van der Heijden, T.J.T. (TU Delft Civil Engineering & Geosciences); van de Giesen, N.C. (TU Delft Water Resources); Palensky, P. (TU Delft Electrical Sustainable Energy); Abraham, E. (TU Delft Water Resources)","","2023","The Netherlands is a low-lying country situated in the Rhine-Meuse delta. A significant portion of the Netherlands is located below sea level, making the proper management of local and national waterways essential. Polders are used to manage groundwater levels, drain excess rainwater, and store water during times of drought. These polders often have pumping stations that pump water into drainage canals, like the Noordzeekanaal-Amsterdam-Rijnkanaal (NZK-ARK), which receives water from the Rhine river and four local water authorities and connects to the North Sea at IJmuiden through a pumping station and a series of undershot gates.
The operators of the NZK-ARK utilize Model Predictive Control (MPC) to schedule the discharge of water through the gates and pumps. The combination of the pump and gate discharge allows the NZK-ARK to discharge excess water to the North Sea when the sea water level is both higher and lower than the water level in the canal. However, traditional MPC can lead to suboptimal schedules when uncertainty is introduced, resulting from, for example, incoming discharge, fluctuating electricity prices, and the availability of renewable energy. Stochastic MPC allows for the consideration of uncertainty in decision-making, optimizing control actions based on a range of potential scenarios. In the future, the objectives for the control system of the gates and pumps may become more complex and may need to take into account factors like renewable energy availability and electricity prices. Ensuring the effective and efficient management of water in the Netherlands is critical, and the use of polders for water storage and control of groundwater tables, and techniques like MPC and stochastic MPC play important roles in achieving this goal.
In this study, we present a framework that combines probabilistic forecasting, scenario generation and reduction, and stochastic MPC to minimize energy costs associated with pumping at the NZK-ARK. This framework is based on probabilistic forecasts of electricity prices and incoming discharge and is specifically designed for use at the NZK-ARK. By considering the uncertainty present in electricity prices and incoming discharge, our framework allows for the optimization of control actions through the use of stochastic MPC. The ultimate goal of this approach is to reduce energy costs at the NZK-ARK by effectively managing the discharge of water through the pumps and gates while complying with local constraints.","","en","conference paper","","","","","","","","","Civil Engineering & Geosciences","Electrical Sustainable Energy","Water Resources","","",""
"uuid:dfebbfd1-95be-4258-bee5-a43bb7a53128","http://resolver.tudelft.nl/uuid:dfebbfd1-95be-4258-bee5-a43bb7a53128","Opportunities of digitalization","Winiwarter, Wilfried; Palensky, P. (TU Delft Electrical Sustainable Energy)","Winiwarter, Wilfried (editor); Bruckman, Viktor J. (editor)","2023","","","en","book chapter","","","","","","","","","","Electrical Sustainable Energy","","","",""
"uuid:254e67c8-8ba2-404a-b2e3-c487ca51210e","http://resolver.tudelft.nl/uuid:254e67c8-8ba2-404a-b2e3-c487ca51210e","Wide-Area Damping of Sub-Synchronous Oscillations Excited by Large Wind Power Plants","van Vledder, C.A. (TU Delft Intelligent Electrical Power Grids); Rueda, José L. (TU Delft Intelligent Electrical Power Grids); Stefanov, Alexandru (TU Delft Intelligent Electrical Power Grids); Palensky, P. (TU Delft Electrical Sustainable Energy); Anaya-Lara, Olimpo (Norwegian University of Science and Technology (NTNU)); Kruimer, B. (DNV Energy Systems); Gonzalez-Loderiro, Francisco (University of Exeter)","","2023","Power electronic interfaced generation (PEIG) has become significantly dominant in the electrical power grid. This development is leading to a decrease in systemic inertia and damping against electrical oscillations. This causes the introduction of new and faster dynamic phenomena. One of these phenomena is sub-synchronous control interaction (SSCI), occurring as sub-synchronous oscillations (SSOs) in the system. Several real-world events reported so far have been related with large wind power plants (WPPs) and the improper tuning of the grid side converter (GSC) of (type-4) fully rated converter (FR C) wind turbines. As other PEl G have similar topologies and control systems, it is a very relevant topic. Weak grid conditions often contribute to the risks of SSO events. This paper proposes supplementary wide-area damping (WAD) to the control system of the GSC, focused on damping excursions of the phase locked loop (PLL). Signals measured by a remote phasor measurement unit (PMU) are communicated to the control system, which uses it for dynamic damping control. The effects of the WAD are tested by comparing the results of linearization-based eigenvalue analysis with and without the addition of WAD. Supplementary analysis conducted by using time-domain simulations and Prony analysis confirm the positive effect of WAD. Numerical tests are performed in DlgSILENT PowerFactory 2023 SP2 on a modified IEEE-39 bus test system.","Sub-synchronous oscillations; observability; phasor measurement units; control interaction; wide area monitoring and control","en","conference paper","IEEE","","","","","Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2024-05-16","","Electrical Sustainable Energy","Intelligent Electrical Power Grids","","",""
"uuid:40cd3659-a1a9-43ff-9aa9-fa5bf427c8bd","http://resolver.tudelft.nl/uuid:40cd3659-a1a9-43ff-9aa9-fa5bf427c8bd","Hybrid Energy Storage System Based on a Multioutput Multilevel Converter","Lizana, Ricardo (Universidad Católica de la Santísima Concepción); Rivera, Sebastian (TU Delft Electrical Sustainable Energy; TU Delft DC systems, Energy conversion & Storage; Universidad Católica de la Santísima Concepción); Figueroa, Fidel (Universidad Católica de la Santísima Concepción); Flores-Bahamonde, Freddy (Universidad Andres Bello); Rodriguez, Jose (Universidad San Sebastian Santiago); Goetz, Stefan M. (University of Cambridge; Duke University)","","2023","Energy storage systems (ESSs) allow improving the stability and efficiency of the electrical grids with a high penetration of renewable energy sources. Moreover, the use of Hybrid ESSs (HESSs) enables storage solutions with both high-energy and high-power densities, by combining different storage technologies such as diverse battery chemistries, ultracapacitors, or hydrogen fuel cells to name a few. In this article, an HESS-based multioutput multilevel (MOM) converter is presented. The proposed topology enables decoupled control of each ac converter voltage output. The internal switching states further allow the use of different storage units and high-quality multilevel voltage in each ac output. The mathematical model of the proposed topology and the defined operation region of the system, besides a model-predictive control strategy, are developed. Finally, simulation and experimental results validate the performance of the proposed topology.","Energy storage system (ESS); modular multilevel series parallel converter (MMSPC); multioutput multilevel (MOM) converter","en","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2023-10-19","","Electrical Sustainable Energy","DC systems, Energy conversion & Storage","","",""
"uuid:24c00e56-8ae5-4f5e-be6c-2c53b4e24603","http://resolver.tudelft.nl/uuid:24c00e56-8ae5-4f5e-be6c-2c53b4e24603","Update Scheduling for ADMM-based Energy Sharing in Virtual Power Plants Considering Massive Prosumer Access","Feng, Cheng (Tsinghua University); Zheng, Kedi (Tsinghua University); Zhou, Yangze (Zhejiang University); Palensky, P. (TU Delft Electrical Sustainable Energy); Chen, Qixin (Tsinghua University)","","2023","With the proliferation of distributed energy resources (DERs), electricity consumers in virtual power plants (VPPs) are transitioning into prosumers and are encouraged to share surplus energy with peers. Nevertheless, large-scale energy sharing among thousands of prosumers may encounter communication-related challenges. Communication network congestion may result in a significant increase in the negotiation waiting time to reach a sharing agreement, and potentially risks exceeding the deadline of negotiation before the market gate closes, rendering energy sharing ineffective. This paper proposes an online partial-update algorithm for the alternating direction method of multipliers (ADMM)-based energy sharing. By restricting the update connection between the VPP and the prosumers, the algorithm selects a subset of the prosumers participating in ADMM updates each round, hence eliminating the excessively long waiting time caused by communication congestion. Considering the delay induced by massive prosumer communication access requests, a method for determining the optimal number of prosumers participating in updates is provided. To fully utilize the limited update opportunities, a fair and efficient prosumer update scheduling policy is designed. The VPP schedules the participation of prosumers in updates such that the convergence-critical prosumers receive higher priority, yet every prosumer is granted sufficient update opportunities. Additionally, the extra computation and communication overheads brought by the prosumer scheduling are minimized, allowing the whole algorithm to be executed in real time. Numerical studies are conducted to validate the effectiveness of the algorithm and its performance in reducing the overall convergence time.","Energy Sharing; Virtual Power Plant; ADMM; Machine type Communications; Access Delay; Update Scheduling; Distributed Energy Resource","en","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2024-02-23","","Electrical Sustainable Energy","","","",""
"uuid:971c7c1a-bc35-499e-bd2a-08d362760d55","http://resolver.tudelft.nl/uuid:971c7c1a-bc35-499e-bd2a-08d362760d55","A GNN-Based Generative Model for Generating Synthetic Cyber-Physical Power System Topology","Liu, Y. (TU Delft Intelligent Electrical Power Grids); Xie, H. (TU Delft Intelligent Electrical Power Grids); Presekal, A. (TU Delft Intelligent Electrical Power Grids); Stefanov, Alexandru (TU Delft Intelligent Electrical Power Grids); Palensky, P. (TU Delft Electrical Sustainable Energy)","","2023","Synthetic networks aim at generating realistic projections of real-world networks while concealing the actual system information. This paper proposes a scalable and effective approach based on graph neural networks (GNN) to generate synthetic topologies of Cyber-Physical power Systems (CPS) with realistic network feature distribution. In order to comprehensively capture the characteristics of real CPS networks, we propose a generative model, namely Graph-CPS, based on graph variational autoencoder and graph recurrent neural networks. The method hides the sensitive topological information while maintaining the similar feature distribution of the real networks. We used multiple power and communication networks to prove and assess the effectiveness of the proposed method with experimental results.","Cyber-physical systems; graph neural networks; synthetic networks","en","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2024-02-14","","Electrical Sustainable Energy","Intelligent Electrical Power Grids","","",""
"uuid:019d5385-8339-435c-86ea-367636181573","http://resolver.tudelft.nl/uuid:019d5385-8339-435c-86ea-367636181573","Specifications of a Simulation Framework for Virtualized Intelligent Electronic Devices in Smart Grids Covering Networking and Security Requirements","Kabbara, N. (Électricité de France S.A.; Universiteit Utrecht); Mwangi, A.W. (Universiteit Utrecht); Gibescu, Madeleine (Universiteit Utrecht); Abedi, A. (TU Delft Intelligent Electrical Power Grids); Stefanov, Alexandru (TU Delft Intelligent Electrical Power Grids); Palensky, P. (TU Delft Electrical Sustainable Energy)","","2023","As power system's operational technology converges with innovative information and communication technologies, the need for extensive resilience testing for scenarios covering the electrical grid, networking bottlenecks, as well as cyber security threats, become a necessity. This paper proposes a comprehensive, multi-disciplinary simulation framework to test virtualized intelligent electronic devices (vIEDs), considering 1) functional requirements, 2) performance and quality of service of the underlying communication network using software-defined networking, and 3) cyber security intrusion detection schemes. This work serves as a reference for researchers interested in the grid modernization of information and communication infrastructure for future power systems. Six different cyber security attack surfaces have been identified within the framework scope. It was observed that migration of vIEDs due to device maintenance or external anomalies is interesting from an operational perspective yet still poses significant security threats. Therefore, both host-based and network-based intrusion detection schemes were analyzed. Also, the setup has been mapped to an offshore wind case study demonstrating its potential and possible scenarios to simulate.","virtualized intelligent electronic devices; software-defined networking; intrusion detection; IT/OT; simulation framework; cyber-physical power systems","en","conference paper","IEEE","","","","","Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2024-02-09","","Electrical Sustainable Energy","Intelligent Electrical Power Grids","","",""
"uuid:c2e7fd95-6dd7-40b4-bec8-be81da613638","http://resolver.tudelft.nl/uuid:c2e7fd95-6dd7-40b4-bec8-be81da613638","Development of Reliable Power Electronic Systems using Real Time Digital Twin Based Power Hardware-in-the-Loop Testbed","Shekhar, A. (TU Delft DC systems, Energy conversion & Storage); Rituraj, G. (TU Delft DC systems, Energy conversion & Storage); van der Sande, Robin (TU Delft DC systems, Energy conversion & Storage); Ahmadi, M. (TU Delft DC systems, Energy conversion & Storage); Deshmukh, R.S. (TU Delft DC systems, Energy conversion & Storage); Bauer, P. (TU Delft DC systems, Energy conversion & Storage); Nougain, V. (TU Delft Intelligent Electrical Power Grids); Lekić, A. (TU Delft Intelligent Electrical Power Grids); Palensky, P. (TU Delft Electrical Sustainable Energy)","","2023","Reliable Power Electronic Systems (PES) are vital for enabling energy transition technologies of the future. Power hardware-in-the-Loop (PHIL) test bed can be used to validate such systems cost-effectively and time-efficiently. In general, the Real Time Digital Twin (RTDT) is a virtual representation of the PES and its operating environment that mimics its behavior in real-time to provide adequate flexibility to the test bed. The workflow of alternating between the prototype and twin, for instance, overcomes the dilemma of needing 100 % details (due to fast dynamics), but optimization during design choices requires cheap flexibility. In this paper, some use cases in applications of RTDT-based PHIL test bed such as fault tolerant converters, power electronic interface for green technologies, survivable all-electric ships, mission profile-based reliability testing, protection of multi terminal dc systems and reconfigurable hybrid ac-dc links is discussed. Furthermore, the co-simulation potential of real-time platforms is briefly described.","","en","conference paper","IEEE","","","","","Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2024-02-09","","Electrical Sustainable Energy","DC systems, Energy conversion & Storage","","",""
"uuid:26093a92-63e0-4130-a27d-a9fda998942c","http://resolver.tudelft.nl/uuid:26093a92-63e0-4130-a27d-a9fda998942c","The Illuminator: An Open Source Energy System Integration Development Kit","Fu, A. (TU Delft Intelligent Electrical Power Grids); Saini, Raghav (Student TU Delft); Koornneef, R.N. (TU Delft ESP LAB); van der Meer, A.A. (TU Delft Intelligent Electrical Power Grids); Palensky, P. (TU Delft Electrical Sustainable Energy); Cvetkovic, M. (TU Delft Intelligent Electrical Power Grids)","","2023","This paper introduces a flexible and extendable easy-to-use energy system integration development kit: the Illuminator. The Illuminator illustrates challenges arising from the energy transition. Hence, it is suitable in education and for demonstration. It also acts as a sandbox for testing new research concepts, and particularly, distributed energy coordination algorithms in real and non-real time. The Illuminator technology is primarely a modular software platform developed to run on a Raspberry Pi (RasPi) cluster. It is open-source, available at GitHub and developed in Python. The Illuminator comprises models of common energy technologies, such as photovoltaic (PV) panels, wind turbines, batteries, and hydrogen systems. The uniqueness of the Illuminator is in its modularity and flexibility to reconfigure scenarios and cases on the fly, even by non-experts in a plug-and-play fashion. This paper introduces the Illuminator and shows its performance in a simple case study.","Energy system integration; open source; education; energy transition; demonstration","en","conference paper","IEEE","","","","","Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2024-02-09","","Electrical Sustainable Energy","Intelligent Electrical Power Grids","","",""
"uuid:42fcf01b-29f9-462d-a834-3f0158640409","http://resolver.tudelft.nl/uuid:42fcf01b-29f9-462d-a834-3f0158640409","Optimal Energy Scheduling of Flexible Industrial Prosumers via Reinforcement Learning","van den Bovenkamp, Nick (Student TU Delft; Sunrock Investments B.V); Giraldo, Juan S. (TNO); Salazar Duque, Edgar Mauricio (Eindhoven University of Technology); Vergara Barrios, P.P. (TU Delft Intelligent Electrical Power Grids); Konstantinou, Charalambos (King Abdullah University of Science and Technology (KAUST)); Palensky, P. (TU Delft Electrical Sustainable Energy)","","2023","This paper introduces an energy management system (EMS) aiming to minimize electricity operating costs using reinforcement learning (RL) with a linear function approximation. The proposed EMS uses a Q-learning with tile coding (QLTC) algorithm and is compared to a deterministic mixed-integer linear programming (MILP) with perfect forecast information. The comparison is performed using a case study on an industrial manufacturing company in the Netherlands, considering measured electricity consumption, PV generation, and wholesale electricity prices during one week of operation. The results show that the proposed EMS can adjust the prosumer's power consumption considering favorable prices. The electricity costs obtained using the QLTC algorithm are 99% close to those obtained with the MILP model. Furthermore, the results demonstrate that the QLTC model can generalize on previously learned control policies even in the case of missing data and can deploy actions 80% near to the MILP's optimal solution.","Q-learning; tile coding; energy management system; mixed-integer linear programming","en","conference paper","IEEE","","","","","Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2024-02-09","","Electrical Sustainable Energy","Intelligent Electrical Power Grids","","",""
"uuid:35b96fc1-1f61-4cfe-87c0-df1822d36ecf","http://resolver.tudelft.nl/uuid:35b96fc1-1f61-4cfe-87c0-df1822d36ecf","Voltage/Current Doubler Converter for Electric Vehicle Wireless Charging Employing Bipolar Pads","Grazian, F. (TU Delft Electrical Sustainable Energy; TU Delft DC systems, Energy conversion & Storage); Soeiro, Thiago B. (TU Delft Electrical Sustainable Energy; TU Delft DC systems, Energy conversion & Storage); Bauer, P. (TU Delft Electrical Sustainable Energy; TU Delft DC systems, Energy conversion & Storage)","","2023","Light-duty electric vehicles (EVs) typically have a rated voltage of either 400 or 800 V. Especially when considering public parking infrastructures or owners with multiple EVs, e.g., car rental companies, EV wireless chargers must efficiently deliver electric power to both battery options. For this purpose, this article proposes an advanced and compact version of the previously defined voltage/current doubler (V/I-D) converter, here comprising two coupled series-compensated bipolar pads (BPPs). The presented system can efficiently charge EVs with both battery voltage classes at the same power level without affecting the current rating of the converter's circuit components. The control scheme is implemented at the power source side in terms of switching frequency and input voltage, and only passive semiconductor devices are employed on board the EV. The equivalent circuit is analyzed, focusing on the BPPs' undesired cross-coupling and its effect on the power transfer. Methods to compensate for the cross-coupling are proposed regarding the BPP design and operating strategy. At 7.2 kW and aligned BPPs, the dc-to-dc efficiency of 96.34% and 96.53% have been measured at 400 and 800 V, respectively. The proposed method has been experimentally validated at different misalignment profiles while considering battery voltages 300-400 V and 600-800 V, which proves that the V/I -D converter is a universal charging solution for EV batteries.","Battery voltage; bipolar pads (BPPs); compensation networks; cross-coupling; electric vehicles (EVs); inductive power transfer (IPT); wireless charging","en","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2023-10-16","","Electrical Sustainable Energy","DC systems, Energy conversion & Storage","","",""
"uuid:247bffe5-0355-457c-ad6f-1e524dde05c0","http://resolver.tudelft.nl/uuid:247bffe5-0355-457c-ad6f-1e524dde05c0","Charging Infrastructure and Grid Integration for Electromobility","Rivera, Sebastian (Universidad de los Andes, Chile); Goetz, Stefan M. (University of Cambridge); Kouro, Samir (Universidad Técnica Federico Santa María); Lehn, Peter W. (University of Toronto); Pathmanathan, Mehanathan (University of Toronto); Bauer, P. (TU Delft Electrical Sustainable Energy; TU Delft DC systems, Energy conversion & Storage); Mastromauro, Rosa Anna (University of Florence)","","2023","Electric vehicle (EV) charging infrastructure will play a critical role in decarbonization during the next decades, energizing a large share of the transportation sector. This will further increase the enabling role of power electronics converters as an energy transition technology in the widespread adoption of clean energy sources and their efficient use. However, this deep transformation comes with challenges, some of which are already unfolding, such as the slow deployment of charging infrastructure and competing charging standards, and others that will have a long-term impact if not addressed timely, such as the reliability of power converters and power system stability due to loss of system inertia, just to name a few. Nevertheless, the inherent transition toward power systems with higher penetration of power electronics and batteries, together with a layer of communications and information technologies, will also bring opportunities for more flexible and intelligent grid integration and services, which could increase the share of renewable energy in the power grid. This work provides an overview of the existing charging infrastructure ecosystem, covering the different charging technologies for different EV classes, their structure, and configurations, including how they can impact the grid in the future.","Batteries; Charging infrastructure; Charging stations; Costs; electric mobility; Electric vehicle charging; electric vehicles (EVs); EV charging; grid integration; Power electronics; Standards; Voltage control; weak-grid chargers","en","journal article","","","","","","Invited paper","","","","Electrical Sustainable Energy","DC systems, Energy conversion & Storage","","",""
"uuid:c09cc323-4a75-4929-99c0-ced0d6a27386","http://resolver.tudelft.nl/uuid:c09cc323-4a75-4929-99c0-ced0d6a27386","Comprehensive Study on Transformer Fault Detection via Frequency Response Analysis","Kakolaki, Seyed Ebrahim Hosseini (Ferdowsi University of Mashhad); Hakimian, Vahid (Tarbiat Modares University); Sadeh, Javad (Ferdowsi University of Mashhad); Rakhshani, E. (TU Delft Electrical Sustainable Energy; TU Delft Intelligent Electrical Power Grids)","","2023","The sudden outage of a transformer due to a fault can cause irreparable damage to the electricity industry. Hence, by conducting momentarily inspections of the transformer's condition, faults can be promptly detected, and the transformer can be disconnected from the power grid to prevent subsequent failures in this equipment. Detecting faults at an early stage can also result in reduced repair costs. One recent promising technique for fault detection is Frequency Response Analysis (FRA), which compares the transformer's response in healthy and faulty conditions for understanding the occurrence of transformer faults. This paper presents a comprehensive and accurate modeling approach for the behavior of the transformer at different frequencies, followed by an exposition of the requirements for implementing this method in order to find the fault type, severity, and location. Additionally, various methods for analyzing the results of frequency response are introduced and discussed. In this regard, attempts have been made to introduce advanced complementary methods to address the weaknesses and limitations of the frequency response method. Finally, the concepts are summarized, and suggestions for further research with applications in this field are presented and compared.","Artificial intelligence; Circuit faults; Configuration-transfer function pair; Fault detection; Frequency response; Frequency response analysis; Hybrid model; Integrated circuit modeling; Ladder model; Online frequency response analysis; Online services; Power transformer insulation; Transformer fault detection; Transformers; Windings","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Intelligent Electrical Power Grids","","",""
"uuid:7d468279-37bc-4a79-8bfb-8f74879d0e06","http://resolver.tudelft.nl/uuid:7d468279-37bc-4a79-8bfb-8f74879d0e06","Split-based sequential sampling for realtime security assessment","Bugaje, A.-.A.B. (TU Delft Intelligent Electrical Power Grids; Imperial College London); Cremer, Jochen (TU Delft Electrical Sustainable Energy; TU Delft Intelligent Electrical Power Grids); Strbac, Goran (Imperial College London)","","2023","Machine learning (ML) for real-time security assessment requires a diverse training database to be accurate for scenarios beyond historical records. Generating diverse operating conditions is highly relevant for the uncertain future of emerging power systems that are completely different to historical power systems. In response, for the first time, this work proposes a novel split-based sequential sampling approach based on optimisation that generates more diverse operation scenarios for training ML models than state-of-the-art approaches. This work also proposes a volume-based coverage metric, the convex hull volume (CHV), to quantify the quality of samplers based on the coverage of generated data. This metric accounts for the distribution of samples across multidimensional space to measure coverage within the physical network limits. Studies on IEEE test cases with 6, 68 and 118 buses demonstrate the efficiency of the approach. Samples generated using the proposed split-based sampling cover 37.5% more volume than random sampling in the IEEE 68-bus system. The proposed CHV metric can assess the quality of generated samples (standard deviation of 0.74) better than a distance-based coverage metric which outputs the same value (standard deviation of <0.001) for very different data distributions in the IEEE 68-bus system. As we demonstrate, the proposed split-based sampling is relevant as a pre-step for training ML models for critical tasks such as security assessment.","Database generation; Machine learning; Power system operation; Sampling; Security assessment","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Intelligent Electrical Power Grids","","",""
"uuid:a1a9781a-1029-4622-9d39-d7a2c5024a68","http://resolver.tudelft.nl/uuid:a1a9781a-1029-4622-9d39-d7a2c5024a68","Industrially viable diffused IBC solar cells using APCVD dopant glass layers","Kuruganti, V.V. (International Solar Energy Research Center (ISC)); Wurmbrand, Daniel (Universität Konstanz); Buck, Thomas (International Solar Energy Research Center (ISC)); Seren, Sven (SCHMID Group, Freudenstadt); Zeman, M. (TU Delft Electrical Sustainable Energy); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Geml, Fabian (Universität Konstanz); Plagwitz, Heiko (Universität Konstanz); Terheiden, Barbara (Universität Konstanz); Mihailetchi, Valentin D. (International Solar Energy Research Center (ISC))","","2023","Even though interdigitated back contact (IBC) architecture produces the most efficient solar cells, it is difficult to make them cost-effective and industrially viable. Therefore, single-sided atmospheric pressure chemical vapor deposition (APCVD) is investigated for the fabrication of IBC solar cells because it reduces the overall thermal budget, simplifies wet bench processing, and requires no additional masking layer. For the fabrication of a full APCVD IBC solar cell, a very lightly doped front surface field (FSF) of 650 Ω/sq, a heavier doped back surface field (BSF) of 100 Ω/sq and a moderately doped emitter of 250 Ω/sq was used. The high-temperature annealing step is partially done in an oxygen (O2) environment to (i) drive in dopants, (ii) prevent the formation of a boron-rich layer in case of p+ doped c-Si, and (iii) grow an in-situ SiO2 at the Si/dopant glass interface. The etch rate difference between the in-situ grown SiO2 and the doped glass layer is utilized to etch the doped glass completely. The retained in-situ SiO2 after etching is capped with plasma-enhanced chemical vapor deposited (PECVD) SiNx for the passivation of both polarities of IBC solar cells. A full APCVD IBC solar cell precursors (i.e. before metallization) obtained implied open-circuit voltage (iVoc) of 714 mV and emitter saturation current density (J0s) of 17 fA/cm2. At the device level, a full APCVD IBC solar cell achieved a conversion efficiency of 22.8% with Voc of 696 mV and short-circuit current density JSC of 41.3 mA/cm2. These parameters are comparable to the commercially available full-tube diffused ZEBRA® IBC solar cells.","","en","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2023-07-01","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:a4ffa499-f887-4e30-811a-5ad375fde044","http://resolver.tudelft.nl/uuid:a4ffa499-f887-4e30-811a-5ad375fde044","Individual yield nowcasting for residential PV systems","Grzebyk, Daniel (Student TU Delft; Solar Monkey); Alcañiz Moya, A. (TU Delft Photovoltaic Materials and Devices); Donker, Jaap (Solar Monkey); Zeman, M. (TU Delft Electrical Sustainable Energy); Ziar, H. (TU Delft Photovoltaic Materials and Devices); Isabella, O. (TU Delft Photovoltaic Materials and Devices)","","2023","Due to the inherent uncertainty in photovoltaic (PV) energy generation, an accurate power forecasting is essential to ensure a reliable operation of PV systems and a safe electric grid. Machine learning (ML) techniques have gained popularity on the development of this task due to its increased accuracy. Most literature, however, focuses only on less than 5 PV systems during training process, which does not ensure generalization to unseen systems. When in presence of a large feet, regional forecasts are the norm. Nevertheless, none of these approaches are usable when it comes to monitoring residential PV systems. In this work, we propose a single ML model that is able to predict the individual power of a large fleet of 1102 PV systems. XGBoost algorithm was selected as the most suitable algorithm for the task of PV yield nowcasting due to its performance and ease of use. This algorithm obtains Mean Absolute Error (MAE) of 0.877 kWh (considering an average system size of 4.44 kWp) and Mean Absolute Percentage Error (MAPE) of 23% for hourly data aggregated to daily values. XGBoost predictions for individual PV systems are on average two times better than currently used commercial software. We discuss the lack of a suitable loss function that can combine absolute and relative errors for residential PV yield forecasting. We also point out the lack of an adequate metric to compute the error made on the predictions and provide hints on developing a suitable one.","Forecasting; Loss function; Machine learning; Nowcasting; Photovoltaics; Solar yield prediction; XGBoost","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:4694d842-4904-4c03-9b12-af8041d98da5","http://resolver.tudelft.nl/uuid:4694d842-4904-4c03-9b12-af8041d98da5","Crystalline silicon solar cells with thin poly-SiOx carrier-selective passivating contacts for perovskite/c-Si tandem applications","Singh, M. (TU Delft Photovoltaic Materials and Devices); Amarnath, A. (TU Delft EKL Processing); Wagner, Fabian (Student TU Delft); Zhao, Y. (TU Delft Photovoltaic Materials and Devices); Yang, G. (TU Delft Photovoltaic Materials and Devices); Mazzarella, L. (TU Delft Photovoltaic Materials and Devices); Weeber, A.W. (TU Delft Photovoltaic Materials and Devices; TNO Energy Transition); Zeman, M. (TU Delft Electrical Sustainable Energy); Isabella, O. (TU Delft Photovoltaic Materials and Devices)","","2023","Single junction crystalline silicon (c-Si) solar cells are reaching their practical efficiency limit whereas perovskite/c-Si tandem solar cells have achieved efficiencies above the theoretical limit of single junction c-Si solar cells. Next to low-thermal budget silicon heterojunction architecture, high-thermal budget carrier-selective passivating contacts (CSPCs) based on polycrystalline-SiOx (poly-SiOx) also constitute a promising architecture for high efficiency perovskite/c-Si tandem solar cells. In this work, we present the development of c-Si bottom cells based on high temperature poly-SiOx CSPCs and demonstrate novel high efficiency four-terminal (4T) and two-terminal (2T) perovskite/c-Si tandem solar cells. First, we tuned the ultra-thin, thermally grown SiOx. Then we optimized the passivation properties of p-type and n-type doped poly-SiOx CSPCs. Here, we have optimized the p-type doped poly-SiOx CSPC on textured interfaces via a two-step annealing process. Finally, we integrated such bottom solar cells in both 4T and 2T tandems, achieving 28.1% and 23.2% conversion efficiency, respectively.","","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:f941f2c8-8790-4cfb-a8bb-f53b4707347a","http://resolver.tudelft.nl/uuid:f941f2c8-8790-4cfb-a8bb-f53b4707347a","Coordinated tuning of MMC-HVDC interconnection links and PEM electrolyzers for fast frequency support in a multiarea electrical power system","Giannakopoulos, G. (TU Delft Electrical Sustainable Energy; TU Delft Intelligent Electrical Power Grids); Perilla Guerra, A.D. (TU Delft Electrical Sustainable Energy; TU Delft Intelligent Electrical Power Grids); Rueda, José L. (TU Delft Electrical Sustainable Energy; TU Delft Intelligent Electrical Power Grids); Palensky, P. (TU Delft Electrical Sustainable Energy; TU Delft Intelligent Electrical Power Grids); Gonzalez-Longatt, Francisco (University of South-Eastern Norway)","","2023","Modernization of power systems leads to more power electronic interfaced units in the generation, demand, and transmission. Examples are remotely installed renewable energy sources, loads with constant power, or high voltage direct current (HVDC) corridors. These changes significantly affect the frequency stability margins of the system and thus special control techniques should be applied in the converters of the new installed units so as to shoulder the frequency regulation in case of commonly occurred active power imbalances. The response of such units has to be cooperative in order to avoid problems such as insufficient reactions or overshoots. In this chapter, a coordinative tuning approach of the active power gradient control scheme applied to the controllers of modular multilevel converter (MMC)-based HVDC links and proton exchange membrane electrolyzers with the provision of fast frequency support in a multiarea hybrid HVDC-HVAC power system with responsive demand units is proposed. This tuning uses an optimization approach based on mean variance mapping optimization and is able to minimize the frequency excursions in all interconnected areas participating in the frequency regulation even without communication between the system nodes. This technique has shown great results in terms of quality and convergence rate within a short number of fitness evaluations achieving a set of frequency responses within acceptable limits set by operators even in case of the loss of the largest generating unit in the weakest system area. It has also revealed the applicability of such a method in more complex systems and the necessity for sophisticated tuning methods according to the application needs and the system characteristics.","Active power gradient; Fast active power-frequency support; Mean variance optimization; MMC-HVDC links; PEM electrolyzers","en","book chapter","Elsevier","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2023-09-04","","Electrical Sustainable Energy","Intelligent Electrical Power Grids","","",""
"uuid:87e10b67-06b1-4627-9a6b-84a194999c3e","http://resolver.tudelft.nl/uuid:87e10b67-06b1-4627-9a6b-84a194999c3e","Strategies for realizing high-efficiency silicon heterojunction solar cells","Zhao, Y. (TU Delft Photovoltaic Materials and Devices); Procel Moya, P.A. (TU Delft Photovoltaic Materials and Devices); Han, C. (TU Delft Photovoltaic Materials and Devices); Cao, L. (TU Delft Photovoltaic Materials and Devices); Yang, G. (TU Delft Photovoltaic Materials and Devices); Özkol, E. (TU Delft Photovoltaic Materials and Devices); Alcañiz, Alba; Kovačević, K. (TU Delft Electrical Engineering, Mathematics and Computer Science); Limodio, G. (TU Delft QN/Kavli Nanolab Delft); Santbergen, R. (TU Delft Photovoltaic Materials and Devices); Smets, A.H.M. (TU Delft Photovoltaic Materials and Devices); Weeber, A.W. (TU Delft Photovoltaic Materials and Devices; TNO); Zeman, M. (TU Delft Electrical Sustainable Energy); Mazzarella, L. (TU Delft Photovoltaic Materials and Devices); Isabella, O. (TU Delft Photovoltaic Materials and Devices)","","2023","Silicon heterojunction (SHJ) solar cells have achieved a record efficiency of 26.81% in a front/back-contacted (FBC) configuration. Moreover, thanks to their advantageous high VOC and good infrared response, SHJ solar cells can be further combined with wide bandgap perovskite cells forming tandem devices to enable efficiencies well above 33%. In this study, we present strategies to realize high-efficiency SHJ solar cells through combined theoretical and experimental studies, starting from the optimization of Si-based thin-film layers to the implementation of electrodes with reduced indium and silver usage. Advanced opto-electrical simulations, which enable comprehensive theoretical understandings of the main physical mechanisms governing carriers’ collection and light management, provide clear pathways for device designs and experimental optimizations. We present the fabricated FBC-SHJ solar cells in both monofacial and bifacial configurations with the best efficiencies of 24.18% and 23.25%, respectively. We point out that to achieve optimum device performance, the compositional materials should be holistically optimized and evaluated as part of the contact stacks with adjacent layers. As an outlook beyond the classical FBC-SHJ solar cell architecture, we propose various novel SHJ-based solar cell architectures. Their potential performance was assessed and compared via rigorous opto-electrical simulations and a maximal efficiency of 27.60% was simulated for FBC-SHJ solar cells featuring localized contacts.","","en","journal article","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:1a8ad15d-48dc-4b5d-a08d-7b337bae28c8","http://resolver.tudelft.nl/uuid:1a8ad15d-48dc-4b5d-a08d-7b337bae28c8","Congestion management in electricity distribution networks: Smart tariffs, local markets and direct control","Hennig, R.J. (TU Delft Technology, Policy and Management; TU Delft Energie and Industrie); De Vries, Laurens (TU Delft Technology, Policy and Management; TU Delft Energie and Industrie); Tindemans, Simon H. (TU Delft Electrical Sustainable Energy; TU Delft Intelligent Electrical Power Grids)","","2023","Increasing peaks from high-power loads such as EVs and heat pumps lead to congestion of electric distribution grids. The inherent flexibility of these loads could be used to resolve congestion events. Possible options for this are smart network tariffs, market-based approaches, and direct control of flexible loads by the network operator. In most instances, these approaches are looked at in isolation, without considering potential connections and trade-offs between them. In this contribution, we aim to bridge this gap by presenting an overarching design framework for congestion management mechanisms. We classify proposals based on design choices and qualitatively discuss their benefits and risks based on an extensive literature analysis. As there is no one-size-fits-all solution, we map possible risks and discuss the pros and cons of different mechanisms for various problem types. We caution against using market-based mechanisms for local congestion, as they can be susceptible to undesired strategic behavior of market actors.","Congestion management; Distribution networks; Dynamic tariffs; Flexibility markets; Load control","en","journal article","","","","","","","","","Technology, Policy and Management","Electrical Sustainable Energy","Energie and Industrie","","",""
"uuid:be7b5fcd-5f63-437a-aa36-2ea85f81b1ee","http://resolver.tudelft.nl/uuid:be7b5fcd-5f63-437a-aa36-2ea85f81b1ee","Generating quality datasets for real-time security assessment: Balancing historically relevant and rare feasible operating conditions","Bugaje, A.-.A.B. (TU Delft Intelligent Electrical Power Grids; Imperial College London); Cremer, Jochen (TU Delft Electrical Sustainable Energy; TU Delft Intelligent Electrical Power Grids); Strbac, Goran (Imperial College London)","","2023","This paper presents a novel, unified approach for generating high-quality datasets for training machine-learned models for real-time security assessment in power systems. Synthetic data generation methods that extrapolate beyond historical data can be inefficient in generating feasible and rare operating conditions (OCs). The proposed approach balances the trade-off between historically relevant OCs and rare but feasible OCs. Unlike conventional methods that rely on historical records or generic sampling, our approach results in datasets that generalise well beyond similar distributions. The proposed approach is validated through experiments on the IEEE 118-bus system, where a decision tree model trained on data generated using our approach achieved 97% accuracy in predicting the security label of rare OCs, outperforming baseline approaches by 41% and 20%. This work is crucial for deploying reliable machine-learned models for real-time security assessment in power systems undergoing decarbonisation and integrating renewable energy sources.","Data generation; Dynamic security assessment; Machine learning; Power system operation","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Intelligent Electrical Power Grids","","",""
"uuid:45205755-7213-4468-8fa5-2dd62d61e316","http://resolver.tudelft.nl/uuid:45205755-7213-4468-8fa5-2dd62d61e316","Zero-sequence current suppression control for fault current damper based on model predictive control","Shetgaonkar, A.D. (TU Delft Intelligent Electrical Power Grids); Popov, M. (TU Delft Intelligent Electrical Power Grids); Palensky, P. (TU Delft Electrical Sustainable Energy); Lekić, A. (TU Delft Intelligent Electrical Power Grids)","","2023","In a multi-terminal direct current (MTdc) system based on a modular multilevel converter (MMC), high-speed and large interruption capability direct current circuit breakers (dc CBs) are required for dc fault interruption. However, commercializing these breakers is challenging, especially offshore, due to the large footprint of the surge arrester. Hence, a supplementary control is required to limit the rate of current rise along with the fault current limiter. Furthermore, the operation of the dc CB is not frequent. Thus, it can lead to delays in fault interruption. This study proposes the indirect model predictive control (MPC)-based zero-sequence current control. This control provides dc fault current suppression by continuously controlling the zero-sequence current component using circulating current suppression control (CCSC) and by providing feedback to the outer voltage loop and inner current loop of MMCs. The proposed control is simulated for pole-to-pole and pole-to-ground faults at the critical fault location of an MTdc system. The simulation is performed in Real Time Digital Simulator (RTDS) environment, which shows that the predictive control reduces the rate of rise of the fault current, providing an additional 3 ms after the dc fault occurrence to the dc CB to clear the fault. Besides, the energy absorbed by the dc CB's surge arrester during the pole-to-pole and pole-to-ground fault remains the same with the proposed control.","Dc circuit breakers; Model predictive control; Multiterminal HVdc grids; RTDS","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Intelligent Electrical Power Grids","","",""
"uuid:7564223b-643f-44c5-b9d9-c8bffdbb933f","http://resolver.tudelft.nl/uuid:7564223b-643f-44c5-b9d9-c8bffdbb933f","Screen Printed Fire-Through Contact Formation for Polysilicon-Passivated Contacts and Phosphorus-Diffused Contacts","Chaudhary, A. (International Solar Energy Research Center (ISC)); Hos, Jan (International Solar Energy Research Center (ISC)); Lossen, Jan (International Solar Energy Research Center (ISC)); Huster, Frank (Universität Konstanz); Kopecek, Radovan (International Solar Energy Research Center (ISC)); van Swaaij, R.A.C.M.M. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2022","In this article, we investigate the passivation quality and electrical contact properties for samples with a 150 nm thick n+ polysilicon layer in comparison to samples with a phosphorus diffused layer. High level of passivation is achieved for the samples with n+ polysilicon layer and an interfacial oxide underneath it. The contact properties with screen-printed fire-through silver paste are excellent (no additional recombination from metallization and specific contact resistivity (ρc) ≤ 2 mΩ·cm2) for the samples with the polysilicon layers. Fast-firing peak temperature was varied during the contact formation process; this was done to see the trend in the contact properties with the change in the thermal budget. The differences in the J0met and ρc for the two different kinds of samples are explained with the help of high-resolution scanning electron microscope imaging. Finally, we prepare M2-sized n-passivated emitter rear totally (PERT) diffused solar cells with a 150 nm thick n+ polysilicon based passivated rear contact. The best cell achieved an efficiency of 21.64%, with a Voc of 686 mV and fill factor of 80.2%.","Conductivity; Cross-sectional scanning electron microscope (SEM); Metallization; metallization; passivated contacts; Passivation; Phosphorus; phosphorus-doped layer; Photovoltaic cells; polysilicon; screen printing; Silicon; Silver","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:830cdd42-4a2f-4fa5-997c-41ca6a91a7df","http://resolver.tudelft.nl/uuid:830cdd42-4a2f-4fa5-997c-41ca6a91a7df","Mapping the photovoltaic potential of the roads including the effect of traffic","Ferri, Carlotta (Student TU Delft); Ziar, H. (TU Delft Photovoltaic Materials and Devices); Nguyen, T.T. (TU Delft Transport and Planning); van Lint, J.W.C. (TU Delft Transport and Planning); Zeman, M. (TU Delft Electrical Sustainable Energy); Isabella, O. (TU Delft Photovoltaic Materials and Devices)","","2022","After developing the methodology, we applied it to the case of the Netherlands highways. We show that the average irradiation on the Dutch highway network is around 880 kWh/m2/y, 35% less than the potential of an optimally tilted conventional PV system in the south of the Netherlands. Covering the entire 1600 km of the Dutch highways network with solar road modules of poly c-Si, mono c-Si and CIGS would respectively generate 5.2 TWh/y, 6.6 TWh/y, and 3.4 TWh/y of DC electricity. This could be used to fully power the Dutch national public lighting demand. Moreover, to include the effect of traffic on these values, a model was developed to account for the energy potential reduction due to vehicles shading. Using real traffic data from two of the top-four busiest roads in the Netherlands, the A12 and A16, it was found that traffic accounts for an average of 3% reduction of solar road irradiation and DC yield potential. The maximum reduction of 9% was observed in particular locations, such as bridges and nearby ramp roads. The result of such mapping methodology could serve as a useful tool for research advisory, private industry, and governmental projects.","Photovoltaic (PV) technology; Solar potential map; Solar road; Traffic shading; Urban PV","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:8c0d305d-cb5b-4d4a-b9c9-794fa1abdbde","http://resolver.tudelft.nl/uuid:8c0d305d-cb5b-4d4a-b9c9-794fa1abdbde","Oxygen-alloyed poly-Si passivating contacts for high-thermal budget c-Si heterojunction solar cells","Yang, G. (TU Delft Photovoltaic Materials and Devices); Han, C. (TU Delft Photovoltaic Materials and Devices); Procel Moya, P.A. (TU Delft Photovoltaic Materials and Devices); Zhao, Y. (TU Delft Photovoltaic Materials and Devices); Singh, M. (TU Delft Photovoltaic Materials and Devices); Mazzarella, L. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy); Isabella, O. (TU Delft Photovoltaic Materials and Devices)","","2022","Crystalline silicon solar cells with passivating contacts based on doped poly-Si exhibit high optical parasitic losses. Aiming at minimizing these losses, we developed the oxygen-alloyed poly-Si (poly-SiOx) as suitable material for passivating contacts. From passivation point of view, poly-SiOx layers show excellent passivation quality and carrier selectivity for both n-type (iVOC,flat = 740 mV, contact resistance ρc = 0.7 mΩ/cm2, iVOC,textured = 723 mV) and p-type (iVOC,flat = 709 mV, ρc = 0.5 mΩ/cm2). Optically, due to the incorporation of oxygen, the absorption coefficient of poly-SiOx becomes much lower than that of doped poly-Si at long wavelength. Both n-type and p-type poly-SiOx layers are concurrently deployed in front/back-contacted (FBC) solar cells with a front indium tin oxide (ITO) layer to facilitate the lateral transport of carriers and minimize cell's reflection. A high cell FF of 83.5% obtained in double-side flat FBC solar cell indicates an efficient carrier collection by these passivating contacts. An active-area cell efficiency of 21.0% featuring JSC,EQE = 39.7 mA/cm2 is obtained in front-side textured poly-SiOx FBC cell, with the potential of further improvement in both VOC and FF. The optical advantage of poly-SiOx over poly-Si as passivating contact is also observed with a 19.7% interdigitated back-contacted (IBC) solar cell endowed with poly-SiOx emitter and back surface field. Compared to the reference 23.0% IBC solar cell with poly-Si passivating contacts, the one based on poly-SiOx passivating contacts shows higher IQE at wavelengths above 1100 nm. This indicates that for both FBC and IBC cells, poly-SiOx passivating contacts hold potential in enhancing the cell JSC by maximizing the cell spectral response.","","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:4d78313f-452a-4986-9ea0-9f19517e4cfe","http://resolver.tudelft.nl/uuid:4d78313f-452a-4986-9ea0-9f19517e4cfe","A Carrier-based Two-Phase-Clamped DPWM Strategy With Zero-Sequence Voltage Injection for Three-Phase Quasi-Two-Stage Buck-Type Rectifiers","Xu, J. (Shanghai Jiao Tong University); Soeiro, Thiago B. (TU Delft DC systems, Energy conversion & Storage; TU Delft Electrical Sustainable Energy); Wu, Y. (TU Delft DC systems, Energy conversion & Storage); Gao, Fei (Shanghai Jiao Tong University); Wang, Y. (TU Delft Statistics; Shanghai Jiao Tong University); Tang, Houjun (Shanghai Jiao Tong University); Bauer, P. (TU Delft DC systems, Energy conversion & Storage)","","2022","A three-phase buck-type rectifier features a step-down ac-dc conversion function, which is considered as a prominent solution for electric vehicle chargers and telecommunication systems integrated to the grid above 380 V line to line. However, traditional solutions for those applications employ cascaded architectures with an ac-dc boost-type stage and a dc-dc buck-type stage, which may suffer from high switching losses and large dc-link capacitor volume. To relieve this issue, a straightforward carrier-based two-phase-clamped discontinuous pulsewidth modulation (DPWM) strategy with generalized zero-sequence voltage injection is proposed in this article for the commonly employed cascaded circuit. This method can stop the switching actions in the front-end stage during two-third of the grid period, which can yield to the best switching loss reduction. The operations of the front- and back-end converter stages become highly coupled to each other, which reduces the size requirement of the capacitor in the dc link. Therefore, the equivalent circuit behaves as a quasi-two-stage buck-type rectifier allowing an enhancement of the system power density by improving power conversion efficiency and by reducing the volume of passive components and heat sink. The proposed carrier-based two-phase-clamped DPWM strategy is described, analyzed, validated, and compared with different pulsewidth modulation methods on PLECS-based simulation and a 5-kW prototype.","buck-type rectifier; Capacitors; Carrier-based; discontinuous pulsewidth modulation (DPWM); Phase modulation; Pulse width modulation; Switches; Switching loss; Voltage; Voltage control; zero-sequence voltage injection","en","journal article","","","","","","","","","","Electrical Sustainable Energy","DC systems, Energy conversion & Storage","","",""
"uuid:7f006d2e-ae05-4a44-899c-fbafe2afaf78","http://resolver.tudelft.nl/uuid:7f006d2e-ae05-4a44-899c-fbafe2afaf78","Comparative Performance of Inverted-Based Generation using Synchonverter during Transient Stability Conditions","Gonzalez-Longatt, Francisco (University of South-Eastern Norway); Rueda, José L. (TU Delft Electrical Sustainable Energy; TU Delft Intelligent Electrical Power Grids); Palensky, P. (TU Delft Electrical Sustainable Energy; TU Delft Intelligent Electrical Power Grids); Chamorro, Harold R. (KTH Royal Institute of Technology); Abdellah, Kouzou (Université de Djelfa)","","2022","Inverter-based generation (IBG) is critical in achieving a dependable and resilient electrical system while meeting the net-zero emission goal. The enormous integration of IBG tends to produce various issues, including reduced rotational inertia and reduced short circuit levels. Several scientific publications agree that the voltage source converters (VSCs) empowered by the so-called grid forming (GFM) control may provide a lasting answer for reaching the future net-zero IBG-dominated power systems. This paper presents a comparative analysis of the dynamic performance between IBR using synchronverter and a traditional synchronous generator (SG), where the specific concern is the transient stability conditions. DIgSILENT PowerFactory has been used for time-domain simulations using a test system, and numerical simulations considering an N-l event prove the significant benefit of GFN converter controls in providing active power during a voltage sag induced by a short circuit condition, allowing the system to endure longer short circuit durations.","contingency; grid-following; gridforming; power electronic converter; short circuit; transient stability","en","conference paper","Institute of Electrical and Electronics Engineers (IEEE)","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2023-01-02","","Electrical Sustainable Energy","Intelligent Electrical Power Grids","","",""
"uuid:ff2f7ba0-269c-48e8-8a02-5714a86dafac","http://resolver.tudelft.nl/uuid:ff2f7ba0-269c-48e8-8a02-5714a86dafac","Time-varying, ray tracing irradiance simulation approach for photovoltaic systems in complex scenarios with decoupled geometry, optical properties and illumination conditions","Calcabrini, A. (TU Delft Photovoltaic Materials and Devices); Cardose, Ruben (Student TU Delft); Gribnau, David (Student TU Delft); Babal, Pavel (Kipp & Zonen); Manganiello, P. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy); Isabella, O. (TU Delft Photovoltaic Materials and Devices)","","2022","The accurate computation of the irradiance incident on the surface of photovoltaic modules is crucial for the simulation of the energy yield of a photovoltaic system. Depending on the geometrical complexity of the surroundings, different approaches are commonly employed to calculate the irradiance on the photovoltaic system. In this article, we introduce a backward ray tracing simulation approach to calculate the irradiance on photovoltaic systems in geometrically complex scenarios. We explain how the repetition of time-consuming simulation steps can be avoided with the proposed approach by storing a selection of the results from the most computationally expensive parts of the problem, and we show that the irradiance calculated with the proposed approach is in good agreement with the results of Radiance, a well-established irradiance simulation tool. Furthermore, we present an experimental validation carried out using a pyranometer and a reference cell over a period of 6 months in a complex scenario, which shows errors lower than 5% in the calculation of the daily irradiation. Finally, we compare high-resolution spectral simulations with measurements taken with a spectroradiometer under different sky conditions. The proposed approach is particularly well-suited for the simulation of bifacial and tandem photovoltaic modules in complex urban environments, for it enables the efficient simulation of high-resolution spectral irradiance in scenarios with time-varying reflectance properties.","bifacial PV; irradiance modelling; ray tracing; spectral irradiance; tandem PV; urban PV","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:3ab26b5a-e0fa-4f87-854c-8c145de82d50","http://resolver.tudelft.nl/uuid:3ab26b5a-e0fa-4f87-854c-8c145de82d50","Study on the Effect of Irradiance Variability on the Efficiency of the Perturb-and-Observe Maximum Power Point Tracking Algorithm","Martinez Lopez, V.A. (TU Delft Photovoltaic Materials and Devices); Žindžiūtė, U. (Student TU Delft); Ziar, H. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy); Isabella, O. (TU Delft Photovoltaic Materials and Devices)","","2022","Irradiance variability is one of the main challenges for using photovoltaic energy. This variability affects the operation of maximum power point trackers (MPPT) causing energy losses. The logic of the Perturb-and-Observe MPPT algorithm is particularly sensitive to quick irradiance changes. We quantified the existing relation between irradiance variations and efficiency loss of the logic of the Perturb-and-Observe MPPT algorithm, along with the sensitivity of the MPPT to its control parameters. If the algorithm parameters are not tuned properly, its efficiency will drop to nearly 2%. Irradiance variability causes a systematic energy loss of the algorithm that can only be quantified by ignoring the hardware components. With this, we aim to improve the energy yield estimation by providing an additional efficiency loss to be considered in the calculations.","maximum power point tracking (MPPT); solar power generation; energy efficiency; perturb-and-observe (P&O)","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:5930295f-509c-438a-8c14-fed8db0cfdec","http://resolver.tudelft.nl/uuid:5930295f-509c-438a-8c14-fed8db0cfdec","Transition to Digitalized Paradigms for Security Control and Decentralized Electricity Market","Bellizio, Federica (Imperial College London); Xu, Wangkun (Imperial College London); Qiu, Dawei (Imperial College London); Ye, Yujian (Southeast University); Papadaskalopoulos, Dimitrios (Imperial College London); Cremer, Jochen (TU Delft Electrical Sustainable Energy; TU Delft Intelligent Electrical Power Grids); Teng, Fei (Imperial College London); Strbac, Goran (Imperial College London)","","2022","Digitalization is one of the key drivers for energy system transformation. The advances in communication technologies and measurement devices render available a large amount of operational data and enable the centralization of such data storage and processing. The greater access to data opens up new opportunities for a more efficient and decentralized management of the energy system. At the distribution level of the energy system, local electricity markets (LEMs) provide new degrees of flexibility by trading and balancing the energy locally and offering ancillary services to the wider transmission and distribution system operators. Maximizing the grid impact from this flexibility calls for novel data analytics and artificial intelligence techniques to enhance the system's security and reduce the energy costs of local prosumers. At the same time, however, relying on data-based approaches increases the risk of cyberattacks, and robust countermeasures are, therefore, needed as an integral aspect of digitalization efforts. This article discusses the key role of centralized data analytics to fully benefit from the advantages of LEMs in terms of system's security enhancement and energy costs' reduction. Data-driven paradigms are investigated that allow for flexibility from decentralized markets, mitigate the physical security risks, and devise defensive strategies shielding the system from cyber threats.","Artificial intelligence (AI); Computational modeling; Computer crime; Control systems; cybersecurity; digitalization; local electricity markets (LEMs); Optimized production technology; Power system dynamics; Real-time systems; Security; system security.","en","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2023-07-31","","Electrical Sustainable Energy","Intelligent Electrical Power Grids","","",""
"uuid:7db5467a-411e-4c31-b036-108a8a1a63fb","http://resolver.tudelft.nl/uuid:7db5467a-411e-4c31-b036-108a8a1a63fb","Concepts for heat utilization and passive cooling techniques to improve reliability and performance of Building Integrated Photovoltaics (BIPV)","Ortiz Lizcano, J.C. (TU Delft Photovoltaic Materials and Devices); Calcabrini, A. (TU Delft Photovoltaic Materials and Devices); Santbergen, R. (TU Delft Photovoltaic Materials and Devices); Procel Moya, P.A. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy); Isabella, O. (TU Delft Photovoltaic Materials and Devices)","","2022","When integrated into urban environments, photovoltaic (PV) systems usually present operational temperatures that are significantly higher than those shown by rack-mounted systems. High operating temperatures are associated with reduced reliability of PV modules and significantly impact the electrical performance of solar cells. Utilizing the heat produced on PV modules or reducing operating temperatures can bolster their application within the building sector. We present the three main concepts studied to achieve these goals. First, a PV is a chimney concept that allows the use of the heat generated by the modules. Simulations for a PV chimney installed on a building in the Netherlands showed that although the heat quality produced inside its cavity was low, the potential use of the air mass flow for ventilation applications is promising. Additionally, we present two passive cooling solutions that can reduce the operating temperatures of PV modules: Optical filters and phase change materials. Experimental measurements in Delft showed that these solutions reduce the operating temperature of PV modules between 4 °C to 20 °C, particularly under high irradiance hours.","","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:f84d558e-9899-4ac0-91a8-298869612ec2","http://resolver.tudelft.nl/uuid:f84d558e-9899-4ac0-91a8-298869612ec2","Ray-optics study of gentle non-conformal texture morphologies for perovskite/silicon tandems","Santbergen, R. (TU Delft Photovoltaic Materials and Devices); Vogt, M.R. (TU Delft Photovoltaic Materials and Devices); Mishima, Ryota (KANEKA Belgium N.V.; Kaneka Corporation); Hino, Masashi (Kaneka Corporation); Uzu, Hisashi (Kaneka Corporation); Adachi, Daisuke (Kaneka Corporation); Yamamoto, Kenji (Kaneka Corporation); Zeman, M. (TU Delft Photovoltaic Materials and Devices; TU Delft Electrical Sustainable Energy); Isabella, O. (TU Delft Photovoltaic Materials and Devices)","","2022","We investigate gentle front side textures for perovskite/silicon tandem solar cells. These textures enhance the absorption of sunlight, yet are sufficiently gentle to allow deposition of an efficient perovskite top cell. We present a tandem solar cell with such gentle texture, fabricated by Kaneka corporation, with an efficiency as high as 28.6%. We perform an extensive ray-optics study, exploring non-conformal textures at the front and rear side of the perovskite layer. Our results reveal that a gentle texture with steepness of only 23° can be more optically efficient than conventional textures with more than double that steepness. We also show that the observed anti-reflective effect of such gentle textures is not based a double bounce, but on light trapping by total internal reflection. As a result, the optical effects of the encapsulation layers play an important role, and have to be accounted for when evaluating the texture design for perovskite/silicon tandems.","","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:f97f5df1-6fa2-43bf-b37a-9a13e3dc4042","http://resolver.tudelft.nl/uuid:f97f5df1-6fa2-43bf-b37a-9a13e3dc4042","Controllable Simultaneous Bifacial Cu-Plating for High-Efficiency Crystalline Silicon Solar Cells","Han, C. (TU Delft Photovoltaic Materials and Devices; Shenzhen Institute of Wide-bandgap Semiconductors); Yang, G. (TU Delft Photovoltaic Materials and Devices); Procel Moya, P.A. (TU Delft Photovoltaic Materials and Devices; Universidad San Francisco de Quito); O'Connor, D. (TU Delft Photovoltaic Materials and Devices); Zhao, Y. (TU Delft Photovoltaic Materials and Devices); Gopalakrishnan, Anirudh (Student TU Delft); Zhang, Xiaodan (Nankai University); Zeman, M. (TU Delft Electrical Sustainable Energy); Mazzarella, L. (TU Delft Photovoltaic Materials and Devices); Isabella, O. (TU Delft Photovoltaic Materials and Devices)","","2022","Bifacial (BF) copper-plated crystalline silicon solar cell is an attractive topic to concurrently reduce silver consumption and maintain good device performance. However, it is still challenging to realize a high aspect ratio (AR) of the metal fingers. Herein, a new type of hybrid-shaped Cu finger is electromagnetically fabricated in a BF plating process. Cyclic voltammetry is employed to disclose the electrochemical behaviors of cupric ions in monofacial and simultaneous BF Cu-plating processes, such that the controllability of the plating process could be assessed. The optimal hybrid Cu finger is composed of a rectangular bottom part and a round top part, such that an utmost effective AR value of 1.73 is reached. In BF Cu-plating, two sub-three-electrode electrochemical cells are employed to realize equal metal finger heights on both sides of the wafer. Compared to our low thermal-budget screen-printing metallization, the Cu-plated silicon heterojunction devices show both optical and electrical advantages (based on lab-scale tests). The champion BF Cu-plated device shows a front-side efficiency of 22.1% and a bifaciality factor of 0.99.","bifacial silicon heterojunction solar cells; Cu-plating; finger shapes; simultaneous electroplating","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:7f6a4faa-1fb0-41f7-8ac8-801e9f7a1250","http://resolver.tudelft.nl/uuid:7f6a4faa-1fb0-41f7-8ac8-801e9f7a1250","Towards bifacial silicon heterojunction solar cells with reduced TCO use","Han, C. (TU Delft Photovoltaic Materials and Devices; Shenzhen Institute of Wide-bandgap Semiconductors); Santbergen, R. (TU Delft Photovoltaic Materials and Devices); van Duffelen, Max (Student TU Delft); Procel Moya, P.A. (TU Delft Photovoltaic Materials and Devices; Universidad San Francisco de Quito); Zhao, Y. (TU Delft Photovoltaic Materials and Devices); Yang, G. (TU Delft Photovoltaic Materials and Devices); Zhang, Xiaodan (Nankai University); Zeman, M. (TU Delft Electrical Sustainable Energy); Mazzarella, L. (TU Delft Photovoltaic Materials and Devices); Isabella, O. (TU Delft Photovoltaic Materials and Devices)","","2022","Reducing indium consumption, which is related to the transparent conductive oxide (TCO) use, is a key challenge for scaling up silicon heterojunction (SHJ) solar cell technology to terawatt level. In this work, we developed bifacial SHJ solar cells with reduced TCO thickness. We present three types of In2O3-based TCOs, tin-, fluorine-, and tungsten-doped In2O3 (ITO, IFO, and IWO), whose thickness has been optimally minimized. These are promising TCOs, respectively, from post-transition metal doping, anionic doping, and transition metal doping and exhibit different opto-electrical properties. We performed optical simulations and electrical investigations with varied TCO thicknesses. The results indicate that (i) reducing TCO thickness could yield larger current in both monofacial and bifacial SHJ devices; (ii) our IWO and IFO are favorable for n-contact and p-contact, respectively; and (iii) our ITO could serve well for both n-contact and p-contact. Interestingly, for the p-contact, with the ITO thickness reducing from 75 nm to 25 nm, the average contact resistivity values show a decreasing trend from 390 mΩ cm2 to 114 mΩ cm2. With applying 25-nm-thick front IWO in n-contact, and 25-nm-thick rear ITO use in p-contact, we obtained front side efficiencies above 22% in bifacial SHJ solar cells. This represents a 67% TCO reduction with respect to a reference bifacial solar cell with 75-nm-thick TCO on both sides.","bifacial solar cell; silicon heterojunction solar cell; TCO reduction; transparent conductive oxide (TCO)","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:8267bb89-248a-4e62-b41d-994f0f5fc83d","http://resolver.tudelft.nl/uuid:8267bb89-248a-4e62-b41d-994f0f5fc83d","Influence of Silicon Substrate Surface Finish on the Screen-Printed Silver Metallization of Polysilicon-Based Passivating Contacts","Chaudhary, A. (International Solar Energy Research Center (ISC)); Hoß, Jan (International Solar Energy Research Center (ISC)); Lossen, Jan (International Solar Energy Research Center (ISC)); Huster, Frank (Universität Konstanz); Kopecek, Radovan (International Solar Energy Research Center (ISC)); van Swaaij, R.A.C.M.M. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2022","Passivated contact based on a thin interfacial oxide and a highly doped polysilicon layer has emerged as the next evolutionary step to increase the efficiencies of industrial silicon solar cells. To take maximum advantage from this layer stack, it is vital to limit the losses at the metal polysilicon interface, which can be quantified as metal polysilicon recombination current density (J 0met) and contact resistivity. In cell concepts, wherein a large variety of silicon substrate surface finish can be obtained, it is essential to know how the surface finish affects the J 0met and contact resistivity. Herein, commercially available fire through silver paste and the metal-polysilicon recombination current densities and contact resistivity are used for three different silicon substrate surface finishes, namely: planar or saw damage etched (SDE), chemically polished in acidic solution and alkaline pyramidal textured. Contact resistivity values below 3 mΩ cm2 with J 0met in order of the recombination current density of the doped region (J 0pass) are obtained for samples with planar surface for both 150 and 200 nm n+ polysilicon layer thicknesses. The results presented in this work show that the samples with flat substrate morphology outperform the samples with textured surfaces.","cross-sectional scanning electron microscope; metallization; passivated contacts; polysilicon; screen printing; silicon substrate surface morphology","en","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2023-07-01","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:f0f1d83a-a5ee-47ac-a5a7-469e974c50f4","http://resolver.tudelft.nl/uuid:f0f1d83a-a5ee-47ac-a5a7-469e974c50f4","Raman spectroscopy of silicon with nanostructured surface","Kadlečíková, Magdaléna (Slovak University of Technology); Vančo, Ľubomír (Slovak University of Technology); Breza, Juraj (Slovak University of Technology); Mikolášek, Miroslav (Slovak University of Technology); Hušeková, Kristína (Slovak Academy of Sciences); Fröhlich, Karol (Slovak Academy of Sciences); Procel Moya, P.A. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy); Isabella, O. (TU Delft Photovoltaic Materials and Devices)","","2022","We compared the morphology and Raman response of nanoscale shaped surfaces of Si substrates versus monocrystalline Si. Samples were structured by reactive ion etching, and four of them were covered by a RuO2-IrO2 layer. Raman bands, centred at approx. 520 cm–1, belonging to samples processed by etching the Si surface have intensities higher by approximately one order of magnitude than those of reference non-etched samples. For nanostructured samples, the rise in the Raman signal was 12–14 ×, which is in agreement with the model of the electric field at the tips of Si due to their geometry. This phenomenon is related to the high absorption of excitation radiation. Nanostructured surfaces of samples containing a layer of RuO2-IrO2 give rise to the phenomenon of surface enhancement of the Raman response most likely due to the charge transfer at the interface between silicon and conductive oxides. The nanostructured surface of Si without a metal layer behaves as a SERS substrate and detects the analytes at a low concentration.","Black silicon; Nanolayer RuO-IrO; SERS","en","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2023-07-01","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:06e5fd64-e32c-40fc-947c-0049a7cc3d97","http://resolver.tudelft.nl/uuid:06e5fd64-e32c-40fc-947c-0049a7cc3d97","Exploring the benefits, challenges, and feasibility of integrating power electronics into c-Si solar cells","van Nijen, D.A. (TU Delft Photovoltaic Materials and Devices); Manganiello, P. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy); Isabella, O. (TU Delft Photovoltaic Materials and Devices)","","2022","Power electronics traditionally plays a crucial role in conditioning the power of photovoltaic (PV) modules and connecting the systems to the electricity grid. Recently, PV module designs with more sub-module power electronics are gaining increased attention. These designs can offer higher reliability and improved resilience against non-uniform illumination. In this review, we explore an innovative method to facilitate sub-module power electronics, which is to integrate the power components into crystalline silicon (c-Si) PV cells. This approach has the potential to enable numerous design innovations. However, the fabrication processes of the integrated power electronics should be compatible with the PV cell fabrication methods. Moreover, only a limited amount of additional processing steps can be added with respect to standard solar cell manufacturing processes to achieve a cost-effective design. After reviewing previous research on this topic, we propose various new design possibilities for PV-cell-integrated diodes, transistors, capacitors, and inductors. Furthermore, we discuss the technical trade-offs and challenges that need to be overcome for successful industry adoption.","crystalline silicon; partial shading; photovoltaics; photovoltatronics; power electronics; shading tolerance; solar energy; urban PV","en","review","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:520c1006-fadc-4dff-80be-dd21687b7bba","http://resolver.tudelft.nl/uuid:520c1006-fadc-4dff-80be-dd21687b7bba","Introducing a comprehensive physics-based modelling framework for tandem and other PV systems","Vogt, M.R. (TU Delft Photovoltaic Materials and Devices); Ruiz Tobon, C.M. (TU Delft Photovoltaic Materials and Devices); Alcañiz Moya, A. (TU Delft Photovoltaic Materials and Devices); Procel Moya, P.A. (TU Delft Photovoltaic Materials and Devices); Blom, Y. (TU Delft Photovoltaic Materials and Devices); Nour El Din, A. (TU Delft Energie and Industrie); Stark, T. (Student TU Delft); Wang, Z. (Student TU Delft); Goma, E. Garcia (Student TU Delft); Etxebarria, J. G. (Student TU Delft); Ziar, H. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy); Santbergen, R. (TU Delft Photovoltaic Materials and Devices); Isabella, O. (TU Delft Photovoltaic Materials and Devices)","","2022","We introduce a novel simulation tool capable of calculating the energy yield of a PV system based on its fundamental material properties and using self-consistent models. Thus, our simulation model can operate without measurements of a PV device. It combines wave and ray optics and a dedicated semiconductor simulation to model the optoelectronic PV device properties resulting in the IV-curve. The system surroundings are described via spectrally resolved ray tracing resulting in a cell resolved irradiance distribution, and via the fluid dynamics-based thermal model, in the individual cell temperatures. A lumped-element model is used to calculate the IV-curves of each solar cell for every hour of the year. These are combined factoring in the interconnection to obtain the PV module IV-curves, which connect to the inverter for calculating the AC energy yield. In our case study, we compare two types of 2 terminal perovskite/silicon tandem modules with STC PV module efficiencies of 27.7% and 28.6% with a reference c-Si module with STC PV module efficiency of 20.9%. In four different climates, we show that tandem PV modules operate at 1–1.9 °C lower yearly irradiance weighted average temperatures compared to c-Si. We find that the effect of current mismatch is significantly overestimated in pure optical studies, as they do not account for fill factor gains. The specific yields in kWh/kWp of the tandem PV systems are between −2.7% and +0.4% compared to the reference c-Si system in all four simulated climates. Thus, we find that the lab performance of the simulated tandem PV system translates from the laboratory to outdoors comparable to c-Si systems.","Energy yield modelling; Operating temperature; Opto-electric device simulation; Pervoskite/silicon tandem; Specific yield; Tandem PV systems","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:af39307a-147e-4240-b106-5c4a1fe21f53","http://resolver.tudelft.nl/uuid:af39307a-147e-4240-b106-5c4a1fe21f53","Effects of (i)a-Si: H deposition temperature on high-efficiency silicon heterojunction solar cells","Zhao, Y. (TU Delft Photovoltaic Materials and Devices); Procel Moya, P.A. (TU Delft Photovoltaic Materials and Devices; University San Francisco de Quito); Smets, A.H.M. (TU Delft Photovoltaic Materials and Devices); Mazzarella, L. (TU Delft Photovoltaic Materials and Devices); Han, C. (TU Delft Photovoltaic Materials and Devices); Yang, G. (TU Delft Photovoltaic Materials and Devices); Cao, L. (TU Delft Photovoltaic Materials and Devices); Yao, Z. (TU Delft Photovoltaic Materials and Devices); Weeber, A.W. (TU Delft Photovoltaic Materials and Devices; TNO); Zeman, M. (TU Delft Electrical Sustainable Energy); Isabella, O. (TU Delft Photovoltaic Materials and Devices)","","2022","Excellent surface passivation induced by (i)a-Si:H is critical to achieve high-efficiency silicon heterojunction (SHJ) solar cells. This is key for conventional single-junction cell applications but also for bottom cell application in tandem devices. In this study, we investigated the effects of (i)a-Si:H deposition temperature on passivation quality and SHJ solar cell performance. At the lower end of temperatures ranging from 140°C to 200°C, it was observed with Fourier-transform infrared spectroscopy (FTIR) that (i)a-Si:H films are less dense, thus hindering their surface passivation capabilities. However, with additional hydrogen plasma treatments (HPTs), those (i)a-Si:H layers deposited at lower temperatures exhibited significant improvements and better passivation qualities than their counterparts deposited at higher temperatures. On the other hand, even though we observed the highest VOCs for cells with (i)a-Si:H deposited at the lowest temperature (140°C), the related FFs are poorer as compared to their higher temperature counterparts. The optimum trade-off between VOC and FF for the SHJ cells was found with temperatures ranging from 160°C to 180°C, which delivered independently certified efficiencies of 23.71%. With a further improved p-layer that enables a FF of 83.3%, an efficiency of 24.18% was achieved. Thus, our study reveals two critical requirements for optimizing the (i)a-Si:H layers in high-efficiency SHJ solar cells: (i) excellent surface passivation quality to reduce losses induced by interface recombination and simultaneously (ii) less-defective (i)a-Si:H bulk to not disrupt the charge carrier collections.","FTIR; intrinsic amorphous silicon; passivation; silicon heterojunction solar cells","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:ff23bdf0-e489-43cf-a734-862d514985f5","http://resolver.tudelft.nl/uuid:ff23bdf0-e489-43cf-a734-862d514985f5","Effect of Climate on Photovoltaic Yield Prediction Using Machine Learning Models","Alcañiz Moya, A. (TU Delft Photovoltaic Materials and Devices); Lindfors, Anders V. (Finnish Meteorological Institute (FMI)); Zeman, M. (TU Delft Electrical Sustainable Energy); Ziar, H. (TU Delft Photovoltaic Materials and Devices); Isabella, O. (TU Delft Photovoltaic Materials and Devices)","","2022","Machine learning is arising as a major solution for the photovoltaic (PV) power prediction. Despite the abundant literature, the effect of climate on yield predictions using machine learning is unknown. This work aims to find climatic trends by predicting the power of 48 PV systems around the world, equally divided into four climates. An extensive data gathering process is performed and open-data sources are prioritized. A website www.tudelft.nl/open-source-pv-power-databases has been created with all found open data sources for future research. Five machine learning algorithms and a baseline one have been trained for each PV system. Results show that the performance ranking of the algorithms is independent of climate. Systems in dry climates depict on average the lowest Normalized Root Mean Squared Error (NRMSE) of 47.6 %, while those in tropical present the highest of 60.2 %. In mild and continental climates the NRMSE is 51.6 % and 54.5 %, respectively. When using a model trained in one climate to predict the power of a system located in another climate, on average systems located in cold climates show a lower generalization error, with an additional NRMSE as low as 5.6 % depending on the climate of the test set. Robustness evaluations were also conducted that increase the validity of the results.","climate; forecasting; Köppen-Geiger; machine learning; photovoltaics","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:6501e113-6e58-4e62-908a-d4abdde56576","http://resolver.tudelft.nl/uuid:6501e113-6e58-4e62-908a-d4abdde56576","Achieving 23.83% conversion efficiency in silicon heterojunction solar cell with ultra-thin MoOx hole collector layer via tailoring (i)a-Si:H/MoOx interface","Cao, L. (TU Delft Photovoltaic Materials and Devices); Procel Moya, P.A. (TU Delft Photovoltaic Materials and Devices; Universidad San Francisco de Quito); Alcañiz Moya, A. (TU Delft Photovoltaic Materials and Devices); Yan, J. (TU Delft Photovoltaic Materials and Devices); Tichelaar, F.D. (TU Delft QN/Afdelingsbureau; Kavli institute of nanoscience Delft); Özkol, E. (TU Delft Photovoltaic Materials and Devices); Zhao, Y. (TU Delft Photovoltaic Materials and Devices); Han, C. (TU Delft Photovoltaic Materials and Devices); Yang, G. (TU Delft Photovoltaic Materials and Devices); Yao, Z. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy); Santbergen, R. (TU Delft Photovoltaic Materials and Devices); Mazzarella, L. (TU Delft Photovoltaic Materials and Devices); Isabella, O. (TU Delft Photovoltaic Materials and Devices)","","2022","Thin films of transition metal oxides such as molybdenum oxide (MoOx) are attractive for application in silicon heterojunction solar cells for their potential to yield large short-circuit current density. However, full control of electrical properties of thin MoOx layers must be mastered to obtain an efficient hole collector. Here, we show that the key to control the MoOx layer quality is the interface between the MoOx and the hydrogenated intrinsic amorphous silicon passivation layer underneath. By means of ab initio modelling, we demonstrate a dipole at such interface and study its minimization in terms of work function variation to enable high performance hole transport. We apply this knowledge to experimentally tailor the oxygen content in MoOx by plasma treatments (PTs). PTs act as a barrier to oxygen diffusion/reaction and result in optimal electrical properties of the MoOx hole collector. With this approach, we can thin down the MoOx thickness to 1.7 nm and demonstrate short-circuit current density well above 40 mA/cm2 and a champion device exhibiting 23.83% conversion efficiency.","dipole; fundamental study; industrial approach; numerical modelling; plasma treatment; silicon heterojunction solar cells; tailoring MoO; ultra-thin MoO","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:739f8e1d-5c84-43c4-87a0-791ea224d6eb","http://resolver.tudelft.nl/uuid:739f8e1d-5c84-43c4-87a0-791ea224d6eb","Thermal Stable High-Efficiency Copper Screen Printed Back Contact Solar Cells","Chen, N. (TU Delft Photovoltaic Materials and Devices; International Solar Energy Research Center (ISC)); Rudolph, Dominik (International Solar Energy Research Center (ISC)); Peter, Christoph (International Solar Energy Research Center (ISC)); Zeman, M. (TU Delft Electrical Sustainable Energy); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Rosen, Yitzchak (Copprint Technologies Ltd.); Grouchko, Michael (Copprint Technologies Ltd.); Shochet, Ofer (Copprint Technologies Ltd.); Mihailetchi, Valentin D. (International Solar Energy Research Center (ISC))","","2022","The high usage of silver in industrial solar cells may limit the growth of the solar industry. One solution is to replace Ag with copper. A screen printable Cu paste is used herein to metallize industrial interdigitated back contact (IBC) solar cells. A novel metallization structure is proposed for making solar cells. Cu paste is applied to replace the majority of the Ag used in IBC cells as busbars and fingers. Cu paste is evaluated for use as fingers, and solar cells are made to test conversion efficiency and reliability. The Cu paste achieves comparably low resistivity, and Cu paste printed cells demonstrate similar efficiency to Ag paste printed cells, with an average efficiency of 23%, and only 4.5 mg W−1 of Ag usage. Also, the solar cells are stable and no Cu in-diffusion is observed under damp heat (85 °C, 85% relative humidity) and thermal stress (200 °C) for 1000 h, respectively. All processes used in this study can be carried out with industrial equipment. These findings reveal a new application for Cu pastes and point to a new direction for reducing Ag utilization and cost.","back contacts; copper paste; screen printing; silver reduction; solar cells; thermal stability","en","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2023-07-01","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:3131fb15-c758-4d66-9027-363813eedf45","http://resolver.tudelft.nl/uuid:3131fb15-c758-4d66-9027-363813eedf45","Low-breakdown-voltage solar cells for shading-tolerant photovoltaic modules","Calcabrini, A. (TU Delft Photovoltaic Materials and Devices); Procel Moya, P.A. (TU Delft Photovoltaic Materials and Devices); Kambhampati, V. (TU Delft Wind Energy); Manganiello, P. (TU Delft Photovoltaic Materials and Devices); Muttillo, M. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy); Isabella, O. (TU Delft Photovoltaic Materials and Devices)","","2022","The integration of photovoltaic (PV) technology in urban environments poses new challenges for the design of PV modules. In particular, the poor shading tolerance of conventional PV modules strongly limits the energy performance of urban PV systems. In this work, we analyze how interdigitated back-contact solar cells with low-breakdown voltages can help improve the shading tolerance of PV modules. Through detailed simulations, we show that the breakdown voltage can be tuned without significantly degrading the efficiency of the solar cell. Simulation results indicate that, under partial shading conditions, cells with a 0.3-V breakdown voltage could boost by 20% the annual yield of conventional crystalline silicon PV modules with three bypass diodes. These findings are supported by a four-month-long monitoring campaign of PV modules with different breakdown characteristics, which shows a specific yield gain of about 4% in PV modules with six bypass diodes.","breakdown voltage; IBC solar cells; partial shading; shading tolerance; urban photovoltaics","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:7893135f-e004-47b0-a22b-cd47d51fc2c1","http://resolver.tudelft.nl/uuid:7893135f-e004-47b0-a22b-cd47d51fc2c1","Device operation of P-ion-implanted n-BaSi2/p-Si heterojunction solar cells","Aonuki, S. (University of Tsukuba); Yamashita, Yudai (University of Tsukuba); Limodio, G. (TU Delft Photovoltaic Materials and Devices); Narita, Shunsuke (University of Tsukuba); Takayanagi, Kaori (University of Tsukuba); Iwai, Ai (University of Tsukuba); Toko, Kaoru (University of Tsukuba); Zeman, M. (TU Delft Electrical Sustainable Energy); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Suemasu, Takashi (University of Tsukuba)","","2022","We formed phosphorous(P)-ion-implanted n-BaSi2 films on p-Si(111) substrates and demonstrated solar-cell functionality of the n-BaSi2/p-Si heterojunction under AM1.5 illumination. The BaSi2 films were grown by molecular beam epitaxy, followed by implantation of P ions to the BaSi2 films using PF3 gas at an energy of 10 keV and a dose of 1 × 1014 cm−2. Subsequent postannealing was conducted at 500°C in Ar for different durations (t = 30–480 s) to activate the P atoms. The diffusion coefficient for P atoms in BaSi2 was evaluated from the depth profiles of P atoms by secondary-ion mass spectrometry. The activation energies of lattice and grain boundary diffusion were found to be 1.1 ± 0.6 and 2.5 ± 0.6 eV, respectively. From the analysis of Raman and photoluminescence spectra, the ion implantation damage was recovered by the postannealing. For one treated sample with t = 120 s, the internal quantum efficiency reached 67% at a wavelength of 870 nm. This is the highest ever achieved for n-BaSi2/p-Si heterojunction solar cells. Ion implantation is thus applicable to BaSi2 films grown by any other method. This achievement thereby opens a new route for the formation of BaSi2 solar cells.","BaSi; ion implantation; solar cell","en","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2023-05-15","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:3f261f1a-b0fa-4dad-a7f8-1e384cf40937","http://resolver.tudelft.nl/uuid:3f261f1a-b0fa-4dad-a7f8-1e384cf40937","Erratum to: Sub-gap defect density characterization of molybdenum oxide: An annealing study for solar cell applications (Nano Research, (2020), 13, 12, (3416-3424), 10.1007/s12274-020-3029-9)","Scire, D. (TU Delft Photovoltaic Materials and Devices; Università degli Studi di Palermo); Procel Moya, P.A. (TU Delft Photovoltaic Materials and Devices); Gulino, Antonino (University of Catania); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy); Crupi, Isodiana (Università degli Studi di Palermo)","","2022","Ref. [56] was unfortunately wrong, Instead of [56] Corless, R. M.; Gonnet, G. H.; Hare, D. E. G.; Jeffrey, D. J.; Knuth, D. E. On the Lambert W function. Adv. Comput. Math. 1996, 5, 329–359. It should be changed to Biswas, R. K.; Khan, P.; Mukherjee, S.; Mukhopadhyay, A. K.; Ghosh, J.; Muraleedharan, K. Study of short range structure of amorphous Silica from PDF using Ag radiation in laboratory XRD system, RAMAN and NEXAFS. J. Non. Cryst. Solids 2018, 488, 1–9. Some entries in Table 2 were unfortunately misprinted.","","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:82c0c594-bd7d-4888-bd39-9a4be00f5a96","http://resolver.tudelft.nl/uuid:82c0c594-bd7d-4888-bd39-9a4be00f5a96","Experimental study on solar heat battery using phase change materials for parabolic dish collectors","Senthil, Ramalingam (SRM University); Priya, Inbaraj Infanta Mary (SRM University); Gupta, Mukund (University of Washington); Rath, C. (TU Delft Electrical Sustainable Energy); Ghosh, Nilanshu (KTH Royal Institute of Technology)","","2021","Energy consumption has increased with the population increase, and fossil fuel dependency has risen and causing pollutions. Solar energy is suitable to provide society's thermo-electric needs. Thermal energy storage-based concentrated solar receivers are aimed at store heat energy and transportable to the applications. A cavity receiver with two-phase change materials (PCM) is experimentally investigated using a parabolic dish collector to act as the solar heat battery. The selected PCMs are MgCl2.6H2O and KNO3-NaNO3. PCMs are chosen and placed as per the temperature zones of the receiver. The outdoor test was conducted to determine the conical receiver's storage performance using cascaded PCMs. The complete melting of PCM attains at an average receiver surface temperature of 230°C. The complete melting of the PCM in the receiver took around 30 minutes at average radiation around 700 W/m2, and heat stored is approximately 5000 kJ. The estimated number of cavity receivers to be charged on a sunny day is about 10-15 according to the present design and selected PCMs, for later use.","Cascaded PCM; Heat battery; Parabolic dish; Phase change material; Solar energy; Thermal energy storage","en","journal article","","","","","","","","","","Electrical Sustainable Energy","","","",""
"uuid:7f3fcc21-20ae-4109-b994-f30724eef445","http://resolver.tudelft.nl/uuid:7f3fcc21-20ae-4109-b994-f30724eef445","A Multi-layer Modelling Framework for Techno-Socio-Economical Penetration of Photovoltaics","Verkou, M.H. (TU Delft Photovoltaic Materials and Devices); Ahmad, Z. (TU Delft Photovoltaic Materials and Devices); Ziar, H. (TU Delft Photovoltaic Materials and Devices); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2021","Urban areas rely on the wide implementation of X-Integrated Photovoltaic (X-IPV) systems to provide green electricity for the sustainable electrification. In this research, a modelling framework to accurately predicting their output energy yield and asses their impact on the low voltage distribution grid has been developed. This tool can compute a densely populated urban area at a pace of 2.5 seconds per building. In this contribution, we present the results of a pilot project executed in a Dutch neighborhood of 4873 separate roof owners located in the city of Amsterdam, the Netherlands.","PV energy yield; X-IPV; framework; grid impact; low voltage","en","conference paper","IEEE","","","","","Accepted author manuscript","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:58af890d-7a45-4f81-8b85-b6f7a269c2be","http://resolver.tudelft.nl/uuid:58af890d-7a45-4f81-8b85-b6f7a269c2be","Room-temperature sputtered tungsten-doped indium oxide for improved current in silicon heterojunction solar cells","Han, C. (TU Delft Photovoltaic Materials and Devices; Shenzhen Institute of Wide-bandgap Semiconductors); Zhao, Y. (TU Delft Photovoltaic Materials and Devices); Mazzarella, L. (TU Delft Photovoltaic Materials and Devices); Santbergen, R. (TU Delft Photovoltaic Materials and Devices); Bento Montes, A.R. (TU Delft Photovoltaic Materials and Devices; University of Lisbon); Procel Moya, P.A. (TU Delft Photovoltaic Materials and Devices); Yang, G. (TU Delft Photovoltaic Materials and Devices); Zhang, Xiaodan (Nankai University); Zeman, M. (TU Delft Electrical Sustainable Energy); Isabella, O. (TU Delft Photovoltaic Materials and Devices)","","2021","The window layers limit the performance of silicon heterojunction (SHJ) solar cells with front and back contacts. Here, we optimized tungsten-doped indium oxide (IWO) film deposited by radio frequency magnetron sputtering at room temperature. The opto-electrical properties of the IWO were manipulated when deposited on top of thin-film silicon layers. The optimal IWO on glass shows carrier density and mobility of 2.1 × 1020 cm−3 and 34 cm2 V−1s−1, respectively, which were tuned to 2.0 × 1020 cm−3 and 47 cm2 V−1s−1, as well as 1.9 × 1020 cm−3 and 42 cm2 V−1s−1, after treated on i/n/glass and i/p/glass substrates, respectively. Using the more realistic TCO data that were obtained on thin-film silicon stacks, optical simulation indicates a promising visible-to-near-infrared optical response in IWO-based SHJ device structure, which was demonstrated in fabricated devices. Additionally, by adding an additional magnesium fluoride layer on device, the champion IWO-based SHJ device showed an active area cell efficiency of 22.92%, which is an absolute 0.98% efficiency gain compared to the ITO counterpart, mainly due to its current gain of 1.48 mA/cm2.","Improved near-infrared response; Room temperature transparent electrode; Silicon heterojunction solar cell; Tungsten-doped indium oxide","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:0a2d8fbe-0db3-4f82-a878-a30bbbb66dcc","http://resolver.tudelft.nl/uuid:0a2d8fbe-0db3-4f82-a878-a30bbbb66dcc","Critical Components Identification for Cyber-Physical Power Systems Considering Time-Varying Operational States","Liu, Y. (TU Delft Intelligent Electrical Power Grids; TU Delft Electrical Sustainable Energy); Semertzis, I. (TU Delft Intelligent Electrical Power Grids; TU Delft Electrical Sustainable Energy); Stefanov, Alexandru (TU Delft Intelligent Electrical Power Grids; TU Delft Electrical Sustainable Energy); Palensky, P. (TU Delft Intelligent Electrical Power Grids; TU Delft Electrical Sustainable Energy)","Palensky, Peter (editor); Srivastava, Anurag (editor)","2021","The security issues of Cyber-Physical power Systems (CPS) have attracted widespread attention from scholars. Vulnerability assessment emerges as an effective method to identify the critical components and thus increase the system resilience. While efforts have been made to study the vulnerability features of power systems under the occurrence of a single, discrete disturbance or failure at a specific time instant, this paper focuses on identifying the critical components of the cyber-physical system considering time-varying operational states. To investigate the potentially ever-changing CPS vulnerability features, in this paper we construct a database of cascading failure chains using quasi-dynamic simulations to capture the vulnerability relationships among components under time-varying operational states. Then, by adopting sequential mining algorithms, we mine the most frequent cascading failure patterns and identify the critical components based on the data mining results. Simulation studies are conducted on IEEE 39-bus and IEEE RTS-96 systems to evaluate the effectiveness of the proposed method for the identification of critical components at both cyber and physical layers.","Cyber-Physical Systems; Data Mining Algorithms; Vulnerability Assessment; Power Systems","en","conference paper","Association for Computing Machinery (ACM)","","","","","","","","","Electrical Sustainable Energy","Intelligent Electrical Power Grids","","",""
"uuid:e1b28dfa-307d-4500-a878-476c2ec293fd","http://resolver.tudelft.nl/uuid:e1b28dfa-307d-4500-a878-476c2ec293fd","Passivation Enhancement of Poly-Si Carrier-Selective Contacts by Applying ALD Al_2O_3 Capping Layers","Yang, G. (TU Delft Photovoltaic Materials and Devices); Van de Loo, Bas (SoLayTec); Stodolny, Maciej (New Energies Research and Technology, Tha Hague); Limodio, G. (TU Delft Photovoltaic Materials and Devices); Melskens, Jimmy (TNO Energy Transition); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Weeber, A.W. (TNO Energy Transition); Zeman, M. (TU Delft Electrical Sustainable Energy); Kessels, W. M.M. (Eindhoven University of Technology)","","2021","Hydrogenation of polycrystalline silicon (poly-Si) passivating contacts is crucial for maximizing their passivation performance. This work presents the application of Al2O3 prepared by atomic layer deposition as a hydrogenating capping layer. Several important questions related to this application of Al2O3 are addressed by comparing results from Al2O3 single layers, SiNx single layers, and Al2O3/SiNx double layers to different poly-Si types. We investigate the effect of the Al2O3 thickness, the poly-Si thickness, the poly-Si doping type, and the postdeposition annealing treatment on the passivation quality of poly-Si passivating contacts. Especially, the Al2O3/SiNx stack greatly enhances the passivation quality of both n+ and p+ doped as well as intrinsic poly-Si layers. The Al2O3 layer thickness is crucial for the single-layer approach, whereas the Al2O3/SiNx stack is less sensitive to the thickness of the Al2O3 layer. A thicker Al2O3 layer is needed for effectively hydrogenating p+ compared to n+ poly-Si passivating contact. The capping layers can hydrogenate poly-Si layers with thicknesses up to at least 600 nm. The hydrogenation-enhanced passivation for n+ poly-Si is found to be more thermally stable in comparison to p+ poly-Si. These results provide guidelines on the use of Al2O3 capping layers for poly-Si contacts to significantly improve their passivation performance.","Atomic layer deposition (ALD) Al2O3; hydrogenation; passivation quality; polycrystalline silicon (poly-Si) passivating contacts; thermal stability","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:7e39bbc2-46f3-43f0-a580-964cd5e733ce","http://resolver.tudelft.nl/uuid:7e39bbc2-46f3-43f0-a580-964cd5e733ce","A Comprehensive Workflow for High Resolution 3D Solar Photovoltaic Potential Mapping in Dense Urban Environment: A Case Study on Campus of Delft University of Technology","Zhou, Y. (TU Delft Photovoltaic Materials and Devices); Verkou, M.H. (TU Delft Electrical Engineering, Mathematics and Computer Science); Zeman, M. (TU Delft Electrical Sustainable Energy); Ziar, H. (TU Delft Photovoltaic Materials and Devices); Isabella, O. (TU Delft Photovoltaic Materials and Devices)","","2021","Photovoltaic (PV) technology is the most promising renewable energy source to be integrated on urban building surfaces. Modeling and simulating urban PV systems pose more challenges than the conventional ones installed in open field due to rich urban morphology. Herein, a comprehensive workflow to estimate urban solar PV potential is developed where TU Delft campus is used as a case study. This workflow only requires light detection and ranging data and building footprints as data inputs, and multiple levels of result can be delivered including accurate geo-referenced 3D building models, annual solar irradiation map, annual DC/AC yield maps and classified roof segments according to the specific yield of mounted PV system. The study reports a total of ≈8.1 GWh year−1 of PV energy which can be collected from campus building roofs and facades. Given the total electricity demand on the entire campus being 82.6 GWh/year, this PV potential can cover roughly 10% of the current electricity demand. The results constitute an initial assessment of solar PV potential on TU Delft campus buildings that is currently being used to prioritize PV integration on buildings and accelerate the transition toward a climate-neutral campus.","building integrated PV; complex geometry; electrical energy yield simulation; modeling; photovoltaic potential; solar mapping; urban PV","en","journal article","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:3821f578-9a06-4346-bc4e-6029da5ce933","http://resolver.tudelft.nl/uuid:3821f578-9a06-4346-bc4e-6029da5ce933","Colored optic filters on c-Si IBC solar cells for building integrated photovoltaic applications","Ortiz Lizcano, J.C. (TU Delft Photovoltaic Materials and Devices); Procel Moya, P.A. (TU Delft Photovoltaic Materials and Devices; Universidad San Francisco de Quito); Calcabrini, A. (TU Delft Photovoltaic Materials and Devices); Yang, G. (TU Delft Photovoltaic Materials and Devices); Ingenito, Andrea (CSEM SA); Santbergen, R. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy); Isabella, O. (TU Delft Photovoltaic Materials and Devices)","","2021","Building Integrated Photovoltaic systems can produce a significant portion of the energy demand of urban areas. Despite their potential, they remain a niche technology that architects and project engineers still find esthetically limited. The dark blue or black color of standard photovoltaic panels is considered inappropriate for restoration projects of historic buildings and represents a major constraint on the development of new projects. This work will provide insight into how the use of optic filters can offer new pathways for architectural acceptance of photovoltaic panels. Optic filters selectively reflect or transmit light by interference and can be designed and fabricated using cost-effective and industrially compatible processes. By using in-house developed ray tracing software coupled with TCAD Sentaurus, more than 400 colors were obtained, and their impact on the opto-electrical performance of interdigitated back-contacted solar cells was studied. Results show a maximum efficiency loss of 1.6% absolute at the perpendicular incidence of light on the range of obtained colors when compared with a standard dark blue solar cell. Simulations for different angles of incidence showed that the current reduction on the standard device could be modeled using a cosine relationship. The colored cells, however, deviated significantly from this relationship. We propose that the angular behavior of any cell (colored or standard) could be simulated by modifying the effective irradiance with scaling factors equal to the ratios of the photogenerated current at any angle with respect to the value at normal incidence. We demonstrate that this approach accurately models the effect of the color filter and allows for an easy transition from a bare cell to an encapsulated one. Due to the spectral effect of the filter, we developed both a spectrally resolved optical model and a two-dimensional finite volume transient thermal model. In case of the optical model, we demonstrate an accuracy in the prediction of the reflectance produced by the color with values of mean bias error (MBE) between 2.0% and 3.9%. As for the thermal model, it was validated by first analyzing a standard model under conditions of nominal operating cell temperature and then comparing its results with published scientific literature. Later, we compare its prediction against 2 weeks of measurements. In both cases the thermal model proves an adequate accuracy, yielding differences below 1.5°C with respect to other scientific works and an MBE value of 0.89°C as well as a root-mean-square error value of 2.10°C for the entire measurement period. With the validated models, we studied the effect of the encapsulation on the color perception. We present two options of color filters. The first one produces relatively low reflectance losses and presents relative annual direct current (DC) energy losses of up to 6.4% for Delft, in the Netherlands, and up to 5.9% for Alice Springs in Australia. However, this first option has very poor color brightness. The second studied filter produces highly saturated bright colors. Improving brightness can increase the annual DC relative losses up to 13.7% and 13.5% for Delft and Alice Springs, respectively. Overall, we demonstrate that colored filters based on multilayer optical stacks are a versatile option for coloring cells that allow a good compromise between esthetics and performance.","BIPV; c-Si Solar Cells; color perception; colored modules; performance assessment; solar energy","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:c81ddf8a-59ae-47fe-94a1-103b749b1411","http://resolver.tudelft.nl/uuid:c81ddf8a-59ae-47fe-94a1-103b749b1411","A fully reconfigurable series-parallel photovoltaic module for higher energy yields in urban environments","Calcabrini, A. (TU Delft Photovoltaic Materials and Devices); Muttillo, M. (TU Delft Photovoltaic Materials and Devices); Weegink, Raoul (Student TU Delft); Manganiello, P. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy); Isabella, O. (TU Delft Photovoltaic Materials and Devices)","","2021","Photovoltaic modules in the urban environment are very often exposed to uneven illumination conditions. The electrical interconnection between solar cells in a photovoltaic module limits the power that a solar module can generate under partial shading conditions. In this article, we introduce a PV module that is able to dynamically reconfigure the interconnection between its solar cells to minimise conduction and mismatch losses according to the irradiance distribution on its surface. Using an accurate simulation framework, it is determined that a reconfigurable PV module can generate over 12% more energy than a standard PV module with fixed topology and six bypass diodes, and as much energy as a fixed series-parallel module with six parallel strings, but at significantly lower currents. Simulation results are validated experimentally using a photovoltaic module with six reconfigurable blocks of cells controlled by a switching matrix on a high-performance solar flash simulator.","Partial shading; Reconfigurable PV module; Reconfiguration algorithm; Shading tolerance; Urban PV","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:1fd8a201-be6b-41b8-9f19-f72f683e250e","http://resolver.tudelft.nl/uuid:1fd8a201-be6b-41b8-9f19-f72f683e250e","Design and optimization of hole collectors based on nc-SiOx:H for high-efficiency silicon heterojunction solar cells","Zhao, Y. (TU Delft Photovoltaic Materials and Devices); Procel Moya, P.A. (TU Delft Photovoltaic Materials and Devices); Han, C. (TU Delft Photovoltaic Materials and Devices; Shenzhen Institute of Wide-bandgap Semiconductors); Mazzarella, L. (TU Delft Photovoltaic Materials and Devices); Yang, G. (TU Delft Photovoltaic Materials and Devices); Weeber, A.W. (TU Delft Photovoltaic Materials and Devices; TNO Energy Transition); Zeman, M. (TU Delft Electrical Sustainable Energy); Isabella, O. (TU Delft Photovoltaic Materials and Devices)","","2021","Low activation energy (Ea) and wide bandgap (Eg) are essential for (p)-contacts to achieve effective hole collection in silicon heterojunction (SHJ) solar cells. In this work, we study Plasma-Enhanced Chemical Vapor Deposition p-type hydrogenated nanocrystalline silicon oxide, (p)nc-SiOx:H, combined with (p)nc-Si:H as (p)-contact in front/back-contacted SHJ solar cells. We firstly determine the effect of a plasma treatment at the (i)a-Si:H/(p)-contact interface on the thickness-dependent Ea of (p)-contacts. Notably, when the (p)nc-Si:H layer is thinner than 20 nm, the Ea decreases by applying a hydrogen plasma treatment and a very-high-frequency (i)nc-Si:H treatment. Such an interface treatment also significantly reduces the contact resistivity of the (p)-contact stacks (ρc,p), resulting in an improvement of 6.1%abs in fill factor (FF) of the completed cells. Thinning down the (i)a-Si:H passivating layer to 5 nm leads to a low ρc,p (144 mΩ⋅cm2) for (p)-contact stacks. Interestingly, we observe an increment of FF from 72.9% to 78.3% by using (p)nc-SiOx:H layers featuring larger differences between their optical gap (E04) and Ea, which tend to enhance the built-in potential at the c-Si/(i)a-Si:H interface. Furthermore, we observe clear impacts on ρc,p, open-circuit voltage, and FF by optimizing the thicknesses of (p)-contact that influence its Ea. In front junction cells, the vertical and lateral collection of holes is affected by ρc,p of (p)-contact stacks. This observation is also supported by TCAD simulations which reveal different components of lateral contributions. Lastly, we obtain both front and rear junction cells with certified FF well-above 80% and the best efficiency of 22.47%.","Activation energy (E); Contact resistivity (ρ); Hydrogenated nanocrystalline silicon oxide (nc-SiO:H); Interface treatment; Optoelectrical properties; Silicon heterojunction (SHJ)","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:1f88b072-83a2-4aab-9af9-821f7fc39ab9","http://resolver.tudelft.nl/uuid:1f88b072-83a2-4aab-9af9-821f7fc39ab9","Simulation study of the electrical yield of various PV module topologies in partially shaded urban scenarios","Calcabrini, A. (TU Delft Photovoltaic Materials and Devices); Weegink, Raoul (Student TU Delft); Manganiello, P. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy); Isabella, O. (TU Delft Photovoltaic Materials and Devices)","","2021","Urban environments present a great potential to generate electricity with photovoltaic technology. However, this electricity cannot be fully harvested using conventional solar modules that have been designed for open landscapes. In urban environments, photovoltaic modules can often be subject to partial shading caused by trees and building structures. Therefore, new photovoltaic module concepts and designs must be explored to increase the shading tolerance of PV modules. This study proposes a simple yet effective approach to compare the potential of different module topologies for maximising the electrical yield of partially shaded photovoltaic systems. Using this approach, the annual electrical performance of various PV module topologies in different urban environments and climates is simulated and compared to determine the potential benefit of using photovoltaic modules with new topologies. Results suggest that the shading tolerance of conventional solar modules can be significantly improved by adding only a few bypass diodes or parallel interconnections. It is shown that the yield of a partially shaded PV system endowed with conventional solar modules could be increased as much as 25% when shading is caused by nearby obstructions.","Bypass diodes; Partial shading; PV module topology; Shading tolerance; Urban PV systems","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:2948096a-7074-45e0-a013-26ebe35c342e","http://resolver.tudelft.nl/uuid:2948096a-7074-45e0-a013-26ebe35c342e","Comparing optical performance of a wide range of perovskite/silicon tandem architectures under real-world conditions","Singh, M. (TU Delft Photovoltaic Materials and Devices); Santbergen, R. (TU Delft Photovoltaic Materials and Devices); Syifai, Indra (Student TU Delft); Zeman, M. (TU Delft Electrical Sustainable Energy); Isabella, O. (TU Delft Photovoltaic Materials and Devices)","","2021","Since single junction c-Si solar cells are reaching their practical efficiency limit. Perovskite/c-Si tandem solar cells hold the promise of achieving greater than 30% efficiencies. In this regard, optical simulations can deliver guidelines for reducing the parasitic absorption losses and increasing the photocurrent density of the tandem solar cells. In this work, an optical study of 2, 3 and 4 terminal perovskite/c-Si tandem solar cells with c-Si solar bottom cells passivated by high thermal-budget poly-Si, poly-SiOx and poly-SiCx is performed to evaluate their optical performance with respect to the conventional tandem solar cells employing silicon heterojunction bottom cells. The parasitic absorption in these carrier selective passivating contacts has been quantified. It is shown that they enable greater than 20 mA/cm2 matched implied photocurrent density in un-encapsulated 2T tandem architecture along with being compatible with high temperature production processes. For studying the performance of such tandem devices in real-world irradiance conditions and for different locations of the world, the effect of solar spectrum and angle of incidence on their optical performance is studied. Passing from mono-facial to bi-facial tandem solar cells, the photocurrent density in the bottom cell can be increased, requiring again optical optimization. Here, we analyse the effect of albedo, perovskite thickness and band gap as well as geographical location on the optical performance of these bi-facial perovskite/c-Si tandem solar cells. Our optical study shows that bi-facial 2T tandems, that also convert light incident from the rear, require radically thicker perovskite layers to match the additional current from the c-Si bottom cell. For typical perovskite bandgap and albedo values, even doubling the perovskite thickness is not sufficient. In this respect, lower bandgap perovskites are very interesting for application not only in bi-facial 2T tandems but also in related 3T and 4T tandems.","Bi-facial; C-Si; Optical modelling; Perovskite; Photocurrent; Tandem","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:3a34c5d0-b8d6-40f8-9f5e-f64ce220d353","http://resolver.tudelft.nl/uuid:3a34c5d0-b8d6-40f8-9f5e-f64ce220d353","Solar cells based on n+-AZO/p-BaSi2 heterojunction: Advanced opto-electrical modelling and experimental demonstration","Yamashita, Yudai (University of Tsukuba); Ruiz Tobon, C.M. (TU Delft Photovoltaic Materials and Devices); Santbergen, R. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Suemasu, Takashi (University of Tsukuba)","","2021","We performed advanced opto-electrical simulations on thin-film BaSi2 solar cells. First, absorption spectra of BaSi2-pn homojunction solar cells on Si substrate were calculated based on flat and/or pyramidally-textured surfaces, wherein 20-nm-thick n+-BaSi2 was the topmost electron transport layer. By changing the front surface structure from flat to texture, the reflectance decreased in the wavelength (λ) range 700–1200 nm and the photocurrent density (Jph) delivered by the photogenerated carriers in the 500-nm thick p-BaSi2 layer increased by 1.2 mA/cm2. Simulations revealed that the key factor inhibiting light absorption in the p-BaSi2 layer was parasitic absorption in the n+-BaSi2 and in the c-Si substrate. To solve these optical issues, we propose a new device structure, Al-doped n+-ZnO (AZO, 50 nm)/i-ZnO (20 nm)/p-BaSi2 (500 nm) heterojunction solar cell (HJSC). In this device structure, the parasitic absorption reduced drastically, and Jph reached 30.23 mA/cm2. Furthermore, by replacing the Si substrate with a glass substrate, the light trapping worked more effectively, and the absorber layer thickness required for Jph to saturate was reduced to 1 μm, yielding 32.06 mA/cm2. Based on these simulation results, we manufactured n+-AZO/p-BaSi2 HJSC. The internal quantum efficiency exceeded 30% at λ = 600 nm, meaning that we demonstrated the operation of n+-AZO/p-BaSi2 HJSC for the first time. We investigated origins of small efficiencies compared to those simulated, and found that the passivation of defects in the p-BaSi2 layer and the reduction of carrier recombination at the i-ZnO/p-BaSi2 interface would significantly improve the solar cell performance.","Al-doped zinc oxide; Barium disilicide; Electron affinity; Parasitic absorption; Recombination","en","journal article","","","","","","","","2023-05-21","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:13ce9faa-6f18-473a-a222-6b92d98b511a","http://resolver.tudelft.nl/uuid:13ce9faa-6f18-473a-a222-6b92d98b511a","Advancement in screen printed fire through silver paste metallisation of polysilicon based passivating contacts","Chaudhary, A. (TU Delft Photovoltaic Materials and Devices; International Solar Energy Research Center (ISC)); Hoß, Jan (International Solar Energy Research Center (ISC)); Lossen, Jan (International Solar Energy Research Center (ISC)); van Swaaij, R.A.C.M.M. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy)","Tous, Loic (editor); Beaucarne, Guy (editor); Lossen, Jan (editor); Schubert, Gunnar (editor)","2021","We have metallised n+ polysilicon passivated layer structures deposited by Low Pressure Chemical Vapor Deposition (LPCVD) with silver pastes. We analysed recombination at the metal contacts by photoluminescence imaging of metallised lifetime samples and found for the best paste, metal semiconductor recombination current density values (J0met) below 70 fA/cm2, with contact resistivity below 2 mΩcm2. To our knowledge, these are among the lowest values reported so far for full size M2 wafers with 150 nm thin polysilicon layer and wet chemical thin oxide. We also studied the effect of the peak firing temperature on the J0met and contact resistivity in this work. Further, we performed Scanning Electron Microscopy to further understand the silver polysilicon interface.","","en","conference paper","American Institute of Physics","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:09fbae4d-0804-47a6-b62e-ae6bc65e9735","http://resolver.tudelft.nl/uuid:09fbae4d-0804-47a6-b62e-ae6bc65e9735","Ultra-thin electron collectors based on nc-Si:H for high-efficiency silicon heterojunction solar cells","Zhao, Y. (TU Delft Photovoltaic Materials and Devices); Mazzarella, L. (TU Delft Photovoltaic Materials and Devices); Procel Moya, P.A. (TU Delft Photovoltaic Materials and Devices; University San Francisco de Quito); Han, C. (TU Delft Photovoltaic Materials and Devices; Shenzhen Institute of Wide-bandgap Semiconductors); Tichelaar, F.D. (TU Delft QN/Afdelingsbureau; Kavli institute of nanoscience Delft); Yang, G. (TU Delft Photovoltaic Materials and Devices); Weeber, A.W. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy; TNO Energy Transition); Isabella, O. (TU Delft Photovoltaic Materials and Devices)","","2021","Low parasitic absorption and high conductivity enable (n)-type hydrogenated nanocrystalline silicon [(n)nc-Si:H], eventually alloyed with oxygen [(n)nc-SiOx:H], to be deployed as window layer in high-efficiency silicon heterojunction (SHJ) solar cells. Besides the appropriate opto-electrical properties of these nanocrystalline films, reduction of their thickness is sought for minimizing parasitic absorption losses. Many strategies proposed so far reveal practical limits of the minimum (n)-layer thickness that we address and overcome in this manuscript. We demonstrated the successful application of an ultra-thin layer of only 3-nm-thick based on (n)nc-Si:H PECVD plasma growth conditions without the use of additional contact or buffer layers. For simplicity, we still name (n)nc-Si:H this ultra-thin layer and the solar cell endowed with it delivers a certified efficiency η of 22.20%. This cell shows a 0.61 mA/cm2 overall JSC gain over the (n)a-Si:H counterpart mainly owing to the higher transparency of (n)nc-Si:H, while maintaining comparable VOC > 714 mV and FF > 80%. Our optimized (n)nc-Si:H layer yields low absorption losses that are commonly measured for (n)nc-SiOx:H films. In this way, we are able to avoid the detrimental effect that oxygen incorporation has on the electrical parameters of these functional layers. Further, by applying a MgF2/ITO double-layer anti-reflection coating, a cell with 3-nm-thick (n)nc-Si:H exhibits a JSC,EQE up to 40.0 mA/cm2. By means of EDX elemental mapping, we additionally identified the (n)nc-Si:H/ITO interface as critical for electron transport due to unexpected oxidation. To avoid this interfacial oxidation, insertion of a 2-nm-thick (n)a-Si:H on the 3-nm-thick (n)nc-Si:H contributes to FF gains of 1.4%abs. (FF increased from 78.6% to 80.0%), and showing further room for improvements.","(n)-type window layers; hydrogenated nanocrystalline silicon; hydrogenated nanocrystalline silicon oxide; opto-electrical properties; ultra-thin (n)-contact","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:7924a429-5a8e-45b3-aab8-e0a072b0bb73","http://resolver.tudelft.nl/uuid:7924a429-5a8e-45b3-aab8-e0a072b0bb73","A silicon carbide-based highly transparent passivating contact for crystalline silicon solar cells approaching efficiencies of 24%","Köhler, Malte (Forschungszentrum Jülich GmbH; Rheinisch-Westfälische Technische Hochschule); Pomaska, Manuel (Forschungszentrum Jülich GmbH); Procel Moya, P.A. (TU Delft Electrical Sustainable Energy; TU Delft Photovoltaic Materials and Devices; University San Francisco de Quito); Santbergen, R. (TU Delft Electrical Sustainable Energy; TU Delft Photovoltaic Materials and Devices); Lambertz, Andreas (Forschungszentrum Jülich GmbH); Duan, Weiyuan (Forschungszentrum Jülich GmbH); Eberst, Alexander (Forschungszentrum Jülich GmbH; Rheinisch-Westfälische Technische Hochschule); Luysberg, Martina (Forschungszentrum Jülich GmbH); Isabella, O. (TU Delft Electrical Sustainable Energy; TU Delft Photovoltaic Materials and Devices)","","2021","A highly transparent passivating contact (TPC) as front contact for crystalline silicon (c-Si) solar cells could in principle combine high conductivity, excellent surface passivation and high optical transparency. However, the simultaneous optimization of these features remains challenging. Here, we present a TPC consisting of a silicon-oxide tunnel layer followed by two layers of hydrogenated nanocrystalline silicon carbide (nc-SiC:H(n)) deposited at different temperatures and a sputtered indium tin oxide (ITO) layer (c-Si(n)/SiO2/nc-SiC:H(n)/ITO). While the wide band gap of nc-SiC:H(n) ensures high optical transparency, the double layer design enables good passivation and high conductivity translating into an improved short-circuit current density (40.87 mA cm−2), fill factor (80.9%) and efficiency of 23.99 ± 0.29% (certified). Additionally, this contact avoids the need for additional hydrogenation or high-temperature postdeposition annealing steps. We investigate the passivation mechanism and working principle of the TPC and provide a loss analysis based on numerical simulations outlining pathways towards conversion efficiencies of 26%.","","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:b3675013-08af-4673-9a0a-eaa8d2eeec5a","http://resolver.tudelft.nl/uuid:b3675013-08af-4673-9a0a-eaa8d2eeec5a","Characterization of the defect density states in MoOx for c-Si solar cell applications","Scire, D. (Università degli Studi di Palermo); Macaluso, Robert (Università degli Studi di Palermo); Mosca, Mauro (Università degli Studi di Palermo); Mirabella, S. (University of Catania); Gulino, Antonino (University of Catania); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy); Crupi, I. (Università degli Studi di Palermo)","","2021","Thin layers of MoOx have been deposited by thermal evaporation followed by post-deposition annealing. The density of states distributions of the MoOx films were extracted deconvoluting the absorption spectra, measured by a photothermal deflection spectroscopy setup, including the small polaron contribution. Results revealed a sub-band defect distribution centered 1.1 eV below the conduction band; the amplitude of this distribution was found to increase with post-deposition annealing temperature and film thickness.","c-Si solar cell; Density of states; Molybdenum oxide; Photovoltaic; Small polaron; Transition metal oxide","en","journal article","","","","","","Accepted author manuscript","","2023-06-20","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:e4e49ecf-d594-4bf6-932f-e2c703d857ef","http://resolver.tudelft.nl/uuid:e4e49ecf-d594-4bf6-932f-e2c703d857ef","Simulating Interior Radiant Energy for the Design and Prototyping of an Indoor Solar PV Lamp","Verkou, M.H. (TU Delft Photovoltaic Materials and Devices); Ziar, H. (TU Delft Photovoltaic Materials and Devices); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2020","The increasing development of photovoltaic (PV) technologies allows for more feasible PV products, that can split the fixed big electrical infrastructure into smaller mobile systems, suitable for future smart buildings. This research, investigates opportunities for interior PV (IPV) products, that harvest indoor ambient light. The outcome is a working prototype of a standalone indoor solar lamp. An indoor light simulation model is presented and validated for two rooms in Delft with absolute error of 10% compared to measurements over five days per room. The prototype consists of a tailor-made, foil-to-foil laminated PV module, consisting of 36 pieces of laser cut SunPower interdigitated back contact (IBC) cells. At standard test conditions, a maximum DC output of 35.9 Wp was measured, corresponding to a module efficiency of 20.3%. Furthermore, a charge controller with maximum power point tracking algorithm was used to charge a 12 V polymer lithium-ion battery pack. The combination of pyroelectric infrared (PIR) motion sensor detector and a light sensor module assures a conservative use of a 2.4 W strip of light emitting diodes (LED). Keywords: Indoor photovoltaics (IPV), interior light simulation, RADIANCE, PV module design, prototyping, SunPower IBC technology, laser cutting","","en","conference paper","","","","","","Article can be accessed by making a free account on the following page: https://www.eupvsec-proceedings.com/proceedings?paper=49608","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:7aa643e0-6be4-483a-8bca-98a3deb43c0c","http://resolver.tudelft.nl/uuid:7aa643e0-6be4-483a-8bca-98a3deb43c0c","Review of Packaging Schemes for Power Module","Hou, F. (TU Delft Electronic Components, Technology and Materials; National Center for Advanced Packaging; Chinese Academy of Sciences); Wang, W. (TU Delft DC systems, Energy conversion & Storage; Shenzhen Institute of Wide-bandgap Semiconductors); Cao, Liqiang (National Center for Advanced Packaging; Chinese Academy of Sciences); Li, Jun (National Center for Advanced Packaging; Chinese Academy of Sciences); Su, Meiying (National Center for Advanced Packaging; Chinese Academy of Sciences); Lin, Tingyu (National Center for Advanced Packaging); Zhang, Kouchi (TU Delft Electronic Components, Technology and Materials); Ferreira, Jan Abraham (TU Delft Electrical Sustainable Energy; University of Twente)","","2020","SiC devices are promising for outperforming Si counterparts in high-frequency applications due to its superior material properties. Conventional wirebonded packaging scheme has been one of the most preferred package structures for power modules. However, the technique limits the performance of a SiC power module due to parasitic inductance and heat dissipation issues that are inherent with aluminum wires. In this article, low parasitic inductance and high-efficient cooling interconnection techniques for Si power modules, which are the foundation of packaging methods of SiC ones, are reviewed first. Then, attempts on developing packaging techniques for SiC power modules are thoroughly overviewed. Finally, scientific challenges in the packaging of SiC power module are summarized.","High-efficient cooling; low parasitic inductance; packaging schemes; scientific challenges; SiC power module","en","review","","","","","","","","","","Electrical Sustainable Energy","Electronic Components, Technology and Materials","","",""
"uuid:641f564c-8189-4f57-958c-d542a9d25d7c","http://resolver.tudelft.nl/uuid:641f564c-8189-4f57-958c-d542a9d25d7c","Implantation-based passivating contacts for crystalline silicon front/rear contacted solar cells","Limodio, G. (TU Delft Photovoltaic Materials and Devices); Yang, G. (TU Delft Photovoltaic Materials and Devices); De Groot, Yvar (Student TU Delft); Procel, Paul; Mazzarella, L. (TU Delft Photovoltaic Materials and Devices); Weber, Arthur W.; Isabella, O. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2020","In this work, we develop SiOx/poly-Si carrier-selective contacts grown by low-pressure chemical vapor deposition and boron or phosphorus doped by ion implantation. We investigate their passivation properties on symmetric structures while varying the thickness of poly-Si in a wide range (20-250 nm). Dose and energy of implantation as well as temperature and time of annealing were optimized, achieving implied open-circuit voltage well above 700 mV for electron-selective contacts regardless the poly-Si layer thickness. In case of hole-selective contacts, the passivation quality decreases by thinning the poly-Si layer. For both poly-Si doping types, forming gas annealing helps to augment the passivation quality. The optimized doped poly-Si layers are then implemented in c-Si solar cells featuring SiO2/poly-Si contacts with different polarities on both front and rear sides in a lean manufacturing process free from transparent conductive oxide (TCO). At cell level, open-circuit voltage degrades when thinner p-type poly-Si layer is employed, while a consistent gain in short circuit current is measured when front poly-Si thickness is thinned down from 250 to 35 nm (up to +4 mA/cm2). We circumvent this limitation by decoupling front and rear layer thickness obtaining, on one hand, reasonably high current (JSC-EQE = 38.2 mA/cm2) and, on the other hand, relatively high VOC of approximately 690 mV. The best TCO-free device using Ti-seeded Cu-plated front contact exhibits a fill factor of 75.2% and conversion efficiency of 19.6%.","doping; ion implantation; passivating contacts; poly-silicon; silicon solar cells","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:8e512997-74f7-483c-86a0-ea3e81329126","http://resolver.tudelft.nl/uuid:8e512997-74f7-483c-86a0-ea3e81329126","The role of heterointerfaces and subgap energy states on transport mechanisms in silicon heterojunction solar cells","Procel Moya, P.A. (TU Delft Photovoltaic Materials and Devices); Xu, Haiyuan (Student TU Delft); Saez, Aurora (Student TU Delft); Ruiz Tobon, C.M. (TU Delft Photovoltaic Materials and Devices); Mazzarella, L. (TU Delft Photovoltaic Materials and Devices); Zhao, Y. (TU Delft Photovoltaic Materials and Devices); Han, C. (TU Delft Photovoltaic Materials and Devices); Yang, G. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy); Isabella, O. (TU Delft Photovoltaic Materials and Devices)","","2020","The contact resistivity is a key parameter to reach high conversion efficiency in solar cells, especially in architectures based on the so-called carrier-selective contacts. The importance of contact resistivity relies on the evaluation of the quality of charge collection from the absorber bulk through adjacent electrodes. The electrode usually consists of a stack of layers entailing complex charge transport processes. This is especially the case of silicon heterojunction (SHJ) contacts. Although it is known that in thin-film silicon, the transport is based on subgap energy states, the mechanisms of charge collection in SHJ systems is not fully understood yet. Here, we analyse the physical mechanisms driving the exchange of charge among SHJ layers with the support of rigorous numerical simulations that reasonably replicate experimental results. We observe a connection between recombination and collection of carriers. Simulation results reveal that charge transport depends on the alignment and the nature of energy states at heterointerfaces. Our results demonstrate that transport based on direct energy transitions is more efficient than transport based on subgap energy states. Particularly, for positive charge collection, energy states associated to dangling bonds support the charge exchange more efficiently than tail states. The conditions for optimal carrier collection rely on the Fermi energy of the layers, in terms of activation energy of doped layers and carrier concentration of transparent conductive oxide. We observe that fill factor (FF) above 86% concurrently with 750-mV open circuit voltage can be attained in SHJ solar cells with ρc lower than 45 mΩ·cm2 for p-contact and 20 mΩ·cm2 for the n-contact. Furthermore, for achieving optimal contact resistivity, we provide engineering guidelines that are valid for a wide range of silicon materials from amorphous to nanocrystalline layers.","charge collection; contact resistivity; interdigitated back contact (IBC); optoelectrical simulations; silicon heterojunction solar cells; trap-assisted tunnelling; tunnelling","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:c4679735-1360-4cbd-bd15-737825bbbd5c","http://resolver.tudelft.nl/uuid:c4679735-1360-4cbd-bd15-737825bbbd5c","Interdigitated back-contacted structure: A different approach towards high-efficiency ultrathin copper indium gallium (di)selenide solar cells","Rezaei, N. (TU Delft Photovoltaic Materials and Devices); Procel Moya, P.A. (TU Delft Photovoltaic Materials and Devices); Simor, Marcel (TNO/Solliance); Vroon, Zeger (TNO); Zeman, M. (TU Delft Electrical Sustainable Energy); Isabella, O. (TU Delft Photovoltaic Materials and Devices)","","2020","An interdigitated back-contacted (IBC) configuration is proposed for submicron copper indium gallium (di)selenide (CIGS). In a modelling platform, the structure was opto-electrically optimized for maximum efficiency. The results are compared with a reference front/back-contacted (FBC) solar cell with similar absorber thickness and exhibiting 11.9% efficiency. The electrical passivation at the front side is accomplished by an Al2O3 layer, which is endowed with negative fixed charges. The results indicate that with an optimal geometry and engineered bandgap grading, the efficiency of the new IBC structure can reach 17%. Additionally, with a reasonably low defect density in the absorber layer, efficiencies as high as 19.7% and open-circuit voltage comparable with that of the record solar cell are possible with the IBC structure.","bandgap grading; CIGS solar cells; electrical modelling; IBC; light management","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:0401b271-f7c0-49e3-a5a0-2e376e4c04da","http://resolver.tudelft.nl/uuid:0401b271-f7c0-49e3-a5a0-2e376e4c04da","A quick-scan method to assess photovoltaic rooftop potential based on aerial imagery and LiDAR","de Vries, Tim N.C. (Student TU Delft); Bronkhorst, Joris (Student TU Delft); Vermeer, Martijn (Student TU Delft); Donker, Jaap C.B. (Solar Monkey); Briels, Sven A. (Readar B.V.); Ziar, H. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy); Isabella, O. (TU Delft Photovoltaic Materials and Devices)","","2020","A quick-scan yield prediction method has been developed to assess rooftop photovoltaic (PV) potential. The method has three main parts. For each roof, first (i) virtual 3D roof segments were reconstructed using aerial imagery, then, (ii) PV modules were automatically fitted onto roof segments using a fitting algorithm and finally, (iii) expected annual yield was calculated. For each roof, the annual yield was calculated by three different quick yield calculation approaches. Two approaches are commercial software packages of Solar Monkey (SM) and Photovoltaic Geographical Information System (PVGIS) whereas the other one is the simplified skyline-based approach developed in photovoltaic material and devices (PVMD) group of Delft University of Technology. To validate the quick-scan method, a set of 145 roofs and 215 roof segments were chosen in urban areas in the Netherlands. For the chosen roofs, the number of fitted modules and calculated yield were compared with the actual modular layout and the measured yield of existing PV systems. Results showed a satisfactory agreement between the quick-scan yield prediction and measured annual yield per roof, with relative standard deviations of 7.2%, 9.1%, and 7.5% respectively for SM, PVGIS, and PVMD approaches. It was concluded that the obstacle-including approaches (e.g. SM and PVMD) outperformed the approaches which neglect the shading by surrounding obstacles (e.g. PVGIS). Results also showed that 3D roof segments had added value as input for the quick-scan PV yield prediction methods since the precision of yield prediction was significantly lower using only 2D land register data of buildings.","Annual energy yield; Automatic PV system design; Module fitting; PV potential; PV systems; Quick-scan; Rooftop PV; Urban PV; Yield prediction","en","journal article","","","","","","Accepted author manuscript","","2022-09-08","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:f6b71db8-d0db-41d4-9bda-ba3cb02c3936","http://resolver.tudelft.nl/uuid:f6b71db8-d0db-41d4-9bda-ba3cb02c3936","Doped hydrogenated nanocrystalline silicon oxide layers for high-efficiency c-Si heterojunction solar cells","Zhao, Y. (TU Delft Photovoltaic Materials and Devices); Mazzarella, L. (TU Delft Photovoltaic Materials and Devices); Procel Moya, P.A. (TU Delft Photovoltaic Materials and Devices); Han, C. (TU Delft Photovoltaic Materials and Devices; Nankai University; Shenzhen Institute of Wide-bandgap Semiconductors); Yang, G. (TU Delft Photovoltaic Materials and Devices); Weeber, A.W. (TU Delft Photovoltaic Materials and Devices; ECN Solar Energy); Zeman, M. (TU Delft Electrical Sustainable Energy); Isabella, O. (TU Delft Photovoltaic Materials and Devices)","","2020","Hydrogenated nanocrystalline silicon oxide (nc-SiOx:H) layers exhibit promising optoelectrical properties for carrier-selective-contacts in silicon heterojunction (SHJ) solar cells. However, achieving high conductivity while preserving crystalline silicon (c-Si) passivation quality is technologically challenging for growing thin layers (less than 20 nm) on the intrinsic hydrogenated amorphous silicon ((i)a-Si:H) layer. Here, we present an evaluation of different strategies to improve optoelectrical parameters of SHJ contact stacks founded on highly transparent nc-SiOx:H layers. Using plasma-enhanced chemical vapor deposition, we firstly investigate the evolution of optoelectrical parameters by varying the main deposition conditions to achieve layers with refractive index below 2.2 and dark conductivity above 1.00 S/cm. Afterwards, we assess the electrical properties with the application of different surface treatments before and after doped layer deposition. Noticeably, we drastically improve the dark conductivity from 0.79 to 2.03 S/cm and 0.02 to 0.07 S/cm for n- and p-contact, respectively. We observe that interface treatments after (i)a-Si:H deposition not only induce prompt nucleation of nanocrystals but also improve c-Si passivation quality. Accordingly, we demonstrate fill factor improvement of 13.5%abs from 65.6% to 79.1% in front/back-contacted solar cells. We achieve conversion efficiency of 21.8% and 22.0% for front and rear junction configurations, respectively. The optical effectiveness of contact stacks based on nc-SiOx:H is demonstrated by averagely 1.5 mA/cm2 higher short-circuit current density thus nearly 1%abs higher cell efficiency as compared with the (n)a-Si:H.","carrier-selective-contacts (CSCs); hydrogenated nanocrystalline silicon oxide (nc-SiO:H); interface treatments; optoelectrical properties; silicon heterojunction (SHJ)","en","journal article","","","","","","green","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:fd50c5da-8b48-4d4d-bc15-a8898aba5fbd","http://resolver.tudelft.nl/uuid:fd50c5da-8b48-4d4d-bc15-a8898aba5fbd","Photovoltatronics: Intelligent PV-based devices for energy and information applications","Ziar, H. (TU Delft Photovoltaic Materials and Devices); Manganiello, P. (TU Delft Photovoltaic Materials and Devices); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2020","At present, electrification and digitalization are two significant trends in the energy sector. Large-scale introduction of variable renewable energy sources, energy storage and power-electronics components, all based on direct current (DC), is fundamentally changing the electrical energy system of today that is based on alternating current (AC). This trend leads to a complex hybrid AC/DC power system with the extensive deployment of information and communication technologies (ICT) to keep the system stable and reliable. Photovoltaics (PV) is a technology that will play an essential role in local generation of clean electricity in expanding urban areas. To take full advantage of PV in the urban environment, PV technology must become intelligent. In this article, we identify, describe, and label a new research field that deals with intelligent PV and its application in components with multiple functionalities. We denote this field photovoltatronics. We review photovoltatronics research areas and introduce new directions for each area. Photovoltatronics brings together disciplines of energy and informatics. Since photons and electrons are carriers of both energy and information, photovoltatronics is the field that designs and delivers autonomous devices for electricity generation and information communication. It introduces a pathway from harvesting energy of photons (h?) to creating bits of information (01) through the energy of photo-generated electrons (eV). We show that ~10 keV energy is at least needed for transceiving one bit of information in the energy-information chain of the photovoltatronics, while the ultimate efficiency of the chain can reach up to 33.4%. We show that the number of publications related to photovoltatronics is exponentially increasing and the publication rate of combined research areas has been doubled in the present decade and reached 3.4% as a clear sign of its emergence.","","en","review","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:e54a817f-99e8-4dc0-b25b-eea054dab016","http://resolver.tudelft.nl/uuid:e54a817f-99e8-4dc0-b25b-eea054dab016","Strategy to mitigate the dipole interfacial states in (i)a-Si:H/MoOxpassivating contacts solar cells","Mazzarella, L. (TU Delft Photovoltaic Materials and Devices); Alcañiz Moya, A. (TU Delft Electrical Engineering, Mathematics and Computer Science); Kawa, Eliora (Student TU Delft); Procel Moya, P.A. (TU Delft Photovoltaic Materials and Devices); Zhao, Y. (TU Delft Photovoltaic Materials and Devices); Han, C. (TU Delft Photovoltaic Materials and Devices); Yang, G. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy); Isabella, O. (TU Delft Photovoltaic Materials and Devices)","","2020","Electrical simulations show that the dipole formed at (i)a-Si:H/MoOx interface can explain electrical performance degradation. We experimentally manipulate this interface by a plasma treatment (PT) to mitigate the dipole strength without harming the optical response. The optimal PT + MoOx stack results in strongly improved electrical parameters as compared to the one featuring only MoOx and to the silicon heterojunction reference cell. Optical simulations and experimentally measured currents suggest that the additional PT is responsible of very limited parasitic absorption overcompensated by the thinner MoOx used (3.5 nm) and by the lower losses in the (i)a-Si:H layer underneath.","(i)a-Si:H/MoOx solar cells; Dipole layer; Enhanced stability","en","conference paper","Institute of Electrical and Electronics Engineers (IEEE)","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:08bd60cd-7858-4bb5-abbf-43670c63c99f","http://resolver.tudelft.nl/uuid:08bd60cd-7858-4bb5-abbf-43670c63c99f","A Simulation Study of Reconfigurable Modules for Higher Yields in Partially Shaded PV Systems","Calcabrini, A. (TU Delft Photovoltaic Materials and Devices); Weegink, Raoul (Student TU Delft); Zeman, M. (TU Delft Electrical Sustainable Energy); Isabella, O. (TU Delft Photovoltaic Materials and Devices)","","2020","Photovoltaic systems in urban environments are usually partially shaded, thus the need for shade tolerant solar panels in the urban environment. We present the design of a series-parallel reconfigurable photovoltaic module. Given a specific irradiance distribution on its surface, it can change the interconnections between its solar cells to maximize the output power. First, we analyze the main trade-offs involved in the design of such module; then we propose an algorithm to choose the optimal module configuration; finally, we simulate the performance of different solar module architectures inferring the potential gain in annual energy yield.","Reconfigurable PV module; Shade tolerant PV; Urban Integrated PV","en","conference paper","Institute of Electrical and Electronics Engineers (IEEE)","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:4994d790-ca51-4b19-8357-f24974e0b650","http://resolver.tudelft.nl/uuid:4994d790-ca51-4b19-8357-f24974e0b650","Optical characterization of poly-SiOx and poly-SiCx carrier-selective passivating contacts","Singh, M. (TU Delft Photovoltaic Materials and Devices); Santbergen, R. (TU Delft Photovoltaic Materials and Devices); Mazzarella, L. (TU Delft Photovoltaic Materials and Devices); Madrampazakis, A. (External organisation); Yang, G. (TU Delft Photovoltaic Materials and Devices); Vismara, R. (TU Delft Photovoltaic Materials and Devices); Remes, Z. (Institute of physics AS CR); Weeber, A.W. (TU Delft Photovoltaic Materials and Devices; ECN part of TNO); Zeman, M. (TU Delft Electrical Sustainable Energy); Isabella, O. (TU Delft Photovoltaic Materials and Devices)","","2020","The optical modelling for optimizing high-efficiency c-Si solar cells endowed with poly-SiOx or poly-SiCx carrier-selective passivating contacts (CSPCs) demands a thorough understanding of their optical properties, especially their absorption coefficient. Due to the mixed phase nature of these CSPCs, spectroscopic ellipsometry is unable to accurately detect the weak free carrier absorption (FCA) at long wavelengths. In this work, the absorption coefficient of doped poly-SiOx and poly-SiCx layers as function of oxygen and carbon content, respectively, was obtained for wavelengths (300–2000 nm) by means of two alternative techniques. The first approach, photothermal deflection spectroscopy (PDS), was used for layers grown on quartz substrates and is appealing from the point of view of sample fabrication. The second, a novel inverse modelling (IM) approach based on reflectance and transmittance measurements, was instead used for layers grown on textured c-Si wafer substrates to mimic symmetrical samples. Although the absorption coefficients obtained from these two techniques slightly differ due to the different used substrates, we could successfully measure weak FCA in our CSPCs layers. Using an in-house developed multi-optical regime simulator and comparing modelled reflectance and transmittance with measured counterparts from symmetrical samples, we confirmed that with increasing doping concentration FCA increases; and found that the absorption coefficients obtained from IM can now be used to perform optical simulations of these CSPCs in solar cells.","Absorption coefficients; Carrier-selective passivating contacts; Photothermal deflection spectroscopy; Poly-SiC; Poly-SiO; Reflection-transmission","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:03e83c1f-ae35-47e6-873e-438b99177278","http://resolver.tudelft.nl/uuid:03e83c1f-ae35-47e6-873e-438b99177278","The long road to universal electrification: A critical look at present pathways and challenges","Narayan, N.S. (TU Delft Management Support; TU Delft DC systems, Energy conversion & Storage); Vega Garita, V.E. (TU Delft DC systems, Energy conversion & Storage); Qin, Z. (TU Delft DC systems, Energy conversion & Storage); Popovic-Gerber, Jelena (University of Twente); Bauer, P. (TU Delft DC systems, Energy conversion & Storage); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2020","Nearly 840 million people still lack access to electricity, while over a billion more have an unreliable electricity connection. In this article, the three different electrification pathways-grid extension, centralized microgrids, and standalone solar-based solutions, such as pico-solar and solar home systems (SHS)-are critically examined while understanding their relative merits and demerits. Grid extension can provide broad scale access at low levelized costs but requires a certain electricity demand threshold and population density to justify investments. To a lesser extent, centralized (off-grid) microgrids also require a minimum demand threshold and knowledge of the electricity demand. Solar-based solutions are the main focus in terms of off-grid electrification in this article, given the equatorial/tropical latitudes of the un(der-)electrified regions. In recent times, decentralized solar-based off-grid solutions, such as pico-solar and SHS, have shown the highest adoption rates and promising impetus with respect to basic lighting and electricity for powering small appliances. However, the burning question is-from lighting a million to empowering a billion-can solar home systems get us there?The two main roadblocks for SHS are discussed, and the requirements from the ideal electrification pathway are introduced. A bottom-up, interconnected SHS-based electrification pathway is proposed as the missing link among the present electrification pathways.","Microgrids; Multi-tier framework; Rural electrification; SDG 7; Solar home systems","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Management Support","","",""
"uuid:1d7eae95-3bad-48ae-8464-ff9174dd1470","http://resolver.tudelft.nl/uuid:1d7eae95-3bad-48ae-8464-ff9174dd1470","Transparent silicon carbide/tunnel SiO2 passivation for c-Si solar cell front side: Enabling Jsc > 42 mA/cm2 and iVoc of 742 mV","Pomaska, Manuel (Forschungszentrum Jülich GmbH); Köhler, Malte (Forschungszentrum Jülich GmbH); Procel Moya, P.A. (TU Delft Photovoltaic Materials and Devices); Zamchiy, Alexandr (Russian Academy of Sciences); Singh, Aryak (Forschungszentrum Jülich GmbH); Kim, Do Yun (Forschungszentrum Jülich GmbH); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy); Li, Shenghao (Forschungszentrum Jülich GmbH; Sun Yat-sen University)","","2020","N-type microcrystalline silicon carbide (μc-SiC:H(n)) is a wide bandgap material that is very promising for the use on the front side of crystalline silicon (c-Si) solar cells. It offers a high optical transparency and a suitable refractive index that reduces parasitic absorption and reflection losses, respectively. In this work, we investigate the potential of hot wire chemical vapor deposition (HWCVD)–grown μc-SiC:H(n) for c-Si solar cells with interdigitated back contacts (IBC). We demonstrate outstanding passivation quality of μc-SiC:H(n) on tunnel oxide (SiO2)–passivated c-Si with an implied open-circuit voltage of 742 mV and a saturation current density of 3.6 fA/cm2. This excellent passivation quality is achieved directly after the HWCVD deposition of μc-SiC:H(n) at 250°C heater temperature without any further treatments like recrystallization or hydrogenation. Additionally, we developed magnesium fluoride (MgF2)/silicon nitride (SiNx:H)/silicon carbide antireflection coatings that reduce optical losses on the front side to only 0.47 mA/cm2 with MgF2/SiNx:H/μc-SiC:H(n) and 0.62 mA/cm2 with MgF2/μc-SiC:H(n). Finally, calculations with Sentaurus TCAD simulation using MgF2/μc-SiC:H(n)/SiO2/c-Si as front side layer stack in an IBC solar cell reveal a short-circuit current density of 42.2 mA/cm2, an open-circuit voltage of 738 mV, a fill factor of 85.2% and a maximum power conversion efficiency of 26.6%.","antireflecting coating; excellent passivation; heterojunction; hot wire CVD; lean process; refractive index; silicon carbide; tunnel oxide","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:6083e347-0e00-4560-8d25-00a61c7e4229","http://resolver.tudelft.nl/uuid:6083e347-0e00-4560-8d25-00a61c7e4229","Point defects in BaSi2 thin films for photovoltaic applications studied by positron annihilation spectroscopy","Bento Montes, A.R. (TU Delft Photovoltaic Materials and Devices); Eijt, S.W.H. (TU Delft RST/Fundamental Aspects of Materials and Energy); Tian, Y. (TU Delft Photovoltaic Materials and Devices); Gram, R. (Student TU Delft); Schut, H. (TU Delft RST/Neutron and Positron Methods in Materials); Suemasu, T. (University of Tsukuba); Usami, N. (Nagoya University); Zeman, M. (TU Delft Electrical Sustainable Energy); Serra, J. (University of Lisbon); Isabella, O. (TU Delft Photovoltaic Materials and Devices)","","2020","Barium di-silicide (BaSi2) is a very promising absorber material for high-efficiency thin-film solar cells, due to its suitable bandgap, high light absorption coefficient, and long minority-carrier lifetime. In this study, we compare the nanostructure, layer composition, and point defects of BaSi2 thin films deposited by Radio Frequency (RF) sputtering, Thermal Evaporation (TE), and Molecular Beam Epitaxy (MBE), using Doppler Broadening Positron Annihilation Spectroscopy (DB-PAS) depth profiling, Raman spectroscopy, and x-ray diffraction. Our DB-PAS study on thermally annealed RF-sputter deposited and on TE-deposited BaSi2 layers, in a comparison with high quality BaSi2 films produced by MBE, points to the presence of vacancy-oxygen complexes and Si or Ba mono-vacancies, respectively, in the (poly)crystalline BaSi2 films. The degree of near-surface oxidation increases, going from MBE and TE to the industrially applicable RF-sputtered deposition synthesis. The use of a-Si capping layers on the thermally annealed RF-sputtered BaSi2 films leads to a clear reduction in sub-surface oxidation and improves the quality of the BaSi2 films, as judged from DB-PAS.","","en","journal article","","","","","","","","2021-03-01","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:8a002ec8-ce8f-49cb-91f2-774de6ab0b66","http://resolver.tudelft.nl/uuid:8a002ec8-ce8f-49cb-91f2-774de6ab0b66","Toward BaSi2/Si Heterojunction Thin-Film Solar Cells: Insights into Heterointerface Investigation, Barium Depletion, and Silicide-Mediated Silicon Crystallization","Tian, Y. (TU Delft Photovoltaic Materials and Devices); Bento Montes, A.R. (TU Delft Photovoltaic Materials and Devices; University of Lisbon); Vančo, Ľubomír (Slovak University of Technology); Čaplovičová, Mária (Slovak University of Technology); Vogrinčič, Peter (Slovak University of Technology); Šutta, Pavol (University of West Bohemia); Satrapinskyy, Leonid (Comenius University); Zeman, M. (TU Delft Electrical Sustainable Energy); Isabella, O. (TU Delft Photovoltaic Materials and Devices)","","2020","The knowledge of the structural and compositional details of Si/BaSi2/Si heterostructure annealed at high temperature is a prerequisite for BaSi2 application in heterojunction thin-film solar cells. For this purpose, Si/BaSi2/Si heterostructures deposited by magnetron sputtering with different Si layer thickness are submitted to systematic structural and compositional characterizations. Results reveal a BaSi2/Si heterointerfacial variation caused by surface oxidation and Ba diffusion at the high temperature. Its effects on the optical and electrical properties of Si/BaSi2/Si heterostructure are presented. The outcomes of this work can be extended to BaSi2 deposited by other techniques, and generate substantial advantages in BaSi2 development ranging from improvement on material qualities and eventual deployment in thin-film solar cells.","BaSi; heterostructures; photovoltaics; thin films","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:dd7e6a5a-561c-40d1-8411-596fdd80ac60","http://resolver.tudelft.nl/uuid:dd7e6a5a-561c-40d1-8411-596fdd80ac60","Realizing the Potential of RF-Sputtered Hydrogenated Fluorine-Doped Indium Oxide as an Electrode Material for Ultrathin SiO x/Poly-Si Passivating Contacts","Han, C. (TU Delft Photovoltaic Materials and Devices); Yang, G. (TU Delft Photovoltaic Materials and Devices); Montes, Ana (University of Lisbon); Procel Moya, P.A. (TU Delft Photovoltaic Materials and Devices); Mazzarella, L. (TU Delft Photovoltaic Materials and Devices); Zhao, Y. (TU Delft Electrical Engineering, Mathematics and Computer Science); Eijt, S.W.H. (TU Delft RST/Fundamental Aspects of Materials and Energy); Schut, H. (TU Delft RST/Neutron and Positron Methods in Materials); Zhang, Xiaodan (Nankai University); Zeman, M. (TU Delft Electrical Sustainable Energy); Isabella, O. (TU Delft Photovoltaic Materials and Devices)","","2020","In high-efficiency silicon solar cells featuring carrier-selective passivating contacts based on ultrathin SiOx/poly-Si, the appropriate implementation of transparent conductive oxide (TCO) layers is of vital importance. Considerable deterioration in passivation quality occurs for thin poly-Si-based devices owing to the sputtering damage during TCO deposition. Curing treatment at temperatures above 350 °C can recover such degradation, whereas the opto-electrical properties of the TCO are affected as well, and the carrier transport at the poly-Si/TCO contact is widely reported to degrade severely in such a procedure. Here, we propose straightforward approaches, post-deposition annealing at 400 °C in nitrogen, hydrogen, or air ambience, are proposed to tailor material properties of high-mobility hydrogenated fluorine-doped indium oxide (IFO:H) film. Structural, morphological, and opto-electrical properties of the IFO:H films are investigated as well as their inherent electron scattering and doping mechanisms. Hydrogen annealing treatment proves to be the most promising strategy. The resulting layer exhibits both optimal opto-electrical properties (carrier density = 1.5 × 1020 cm-3, electron mobility = 108 cm2 V-1 s-1, and resistivity = 3.9 × 10-4 ω cm) and remarkably low contact resistivities (∼20 mω cm2 for both n- and p-contacts) in poly-Si solar cells. Even though the presented cells are limited by the metallization step, the obtained IFO:H-base solar cell show an efficiency improvement from 20.1 to 20.6% after specific hydrogen treatment, demonstrating the potential of material manipulation and contact engineering strategy in high-efficiency photovoltaic devices endowed with TCOs.","carrier-selective passivating contacts; hydrogen annealing; hydrogenated fluorine-doped indium oxide (IFO:H); transparent conductive oxide (TCO); ultrathin SiO /poly-Si passivating contacts","en","journal article","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:27585952-6127-457f-87eb-eb82014bd919","http://resolver.tudelft.nl/uuid:27585952-6127-457f-87eb-eb82014bd919","Strategy to mitigate the dipole interfacial states in (i)a-Si:H/MoOx passivating contacts solar cells","Mazzarella, L. (TU Delft Photovoltaic Materials and Devices); Alcañiz Moya, A. (TU Delft Photovoltaic Materials and Devices); Procel Moya, P.A. (TU Delft Photovoltaic Materials and Devices; Universidad San Francisco de Quito); Kawa, Eliora (Student TU Delft); Zhao, Y. (TU Delft Photovoltaic Materials and Devices); Tiringer, U. (TU Delft (OLD) MSE-6); Han, C. (TU Delft Photovoltaic Materials and Devices; Shenzhen Institute of Wide-bandgap Semiconductors); Yang, G. (TU Delft Photovoltaic Materials and Devices); Taheri, P. (TU Delft (OLD) MSE-6); Zeman, M. (TU Delft Electrical Sustainable Energy); Isabella, O. (TU Delft Photovoltaic Materials and Devices)","","2020","Molybdenum oxide (MoOx) is attractive for applications as hole-selective contact in silicon heterojunction solar cells for its transparency and relatively high work function. However, the integration of MoOx stacked on intrinsic amorphous silicon (i)a-Si:H layer usually exhibits some issues that are still not fully solved resulting in degradation of electrical properties. Here, we propose a novel approach to enhance the electrical properties of (i)a-Si:H/MoOx contact. We manipulate the (i)a-Si:H interface via plasma treatment (PT) before MoOx deposition minimizing the electrical degradation without harming the optical response. Furthermore, by applying the optimized PT, we can reduce the MoOx thickness down to 3.5 nm with both open-circuit voltage and fill factor improvements. Our findings suggest that the PT mitigates the decrease of the effective work function of the MoOx (WFMoOx) thin layer when deposited on (i)a-Si:H. To support our hypothesis, we carry out electrical simulations inserting a dipole at the (i)a-Si:H/MoOx interface accounting the attenuation of WFMoOx caused by both MoOx thickness and dipole. Our calculations confirm the experimental trends and thus provide deep insight in critical transport issues. Temperature-dependent J-V measurements demonstrate that the use of PT improves the energy alignment for an efficient hole transport.","(i)a-Si:H/MoO hole transport contact; interfacial dipole layer; plasma treatment; TCAD electrical modeling","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:c73f2f9a-15ad-4490-9707-688e99c41817","http://resolver.tudelft.nl/uuid:c73f2f9a-15ad-4490-9707-688e99c41817","Sub-gap defect density characterization of molybdenum oxide: An annealing study for solar cell applications","Scire, D. (TU Delft Photovoltaic Materials and Devices; Università degli Studi di Palermo); Procel Moya, P.A. (TU Delft Photovoltaic Materials and Devices); Gulino, Antonino (University of Catania); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy); Crupi, Isodiana (Università degli Studi di Palermo)","","2020","The application of molybdenum oxide in the photovoltaic field is gaining traction as this material can be deployed in doping-free heterojunction solar cells in the role of hole selective contact. For modeling-based optimization of such contact, knowledge of the molybdenum oxide defect density of states (DOS) is crucial. In this paper, we report a method to extract the defect density through nondestructive optical measures, including the contribution given by small polaron optical transitions. The presence of defects related to oxygen-vacancy and of polaron is supported by the results of our opto-electrical characterizations along with the evaluation of previous observations. As part of the study, molybdenum oxide samples have been evaluated after post-deposition thermal treatments. Quantitative results are in agreement with the result of density functional theory showing the presence of a defect band fixed at 1.1 eV below the conduction band edge of the oxide. Moreover, the distribution of defects is affected by post-deposition treatment. [Figure not available: see fulltext.]","density of states; molybdenum oxide; polaron theory; silicon heterojunction solar cell","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:a53d0d39-7a86-4213-8347-27c9141816f4","http://resolver.tudelft.nl/uuid:a53d0d39-7a86-4213-8347-27c9141816f4","Analysis of Transition Metal Oxides based Heterojunction Solar Cells with S-shaped J-V curves","Scire, D. (Università degli Studi di Palermo); Bonadonna, Marco (Università degli Studi di Palermo); Zhao, Y. (TU Delft Photovoltaic Materials and Devices); Procel Moya, P.A. (TU Delft Photovoltaic Materials and Devices); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy); Macaluso, Robert (Università degli Studi di Palermo); Mosca, Mauro (Università degli Studi di Palermo); Crupi, Isodiana (Università degli Studi di Palermo)","","2020","The use of transition metal oxides for the selective carrier contact in the crystalline silicon solar cells technology is rising to interest for the excellent optoelectrical properties of these materials whose implementation, however, can result in lousy performing cells due to an S-shaped electrical characteristic. In this paper, we fabricated solar cells showing S-shaped J-V curve and carried out an analysis of the reasons of such behavior using a model involving the series of a standard cell equivalent circuit with a Schottky junction in order to explain these atypical performances. A good matching between the experimental measurements and the adopted theoretical model was obtained. The extracted parameters are listed and analyzed to shade light on the reasons behind the low-performance cells.","heterojunction; pulsed laser deposition; s-shape; solar cells; transition metal oxides","en","conference paper","IEEE","","","","","Accepted author manuscript","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:735f81c8-772f-4961-92b9-362c21b747a6","http://resolver.tudelft.nl/uuid:735f81c8-772f-4961-92b9-362c21b747a6","Accurate Soiling Ratio Determination with Incident Angle Modifier for PV Modules","Nepal, Pramod (Student TU Delft); Korevaar, Marc (Kipp & Zonen); Ziar, H. (TU Delft Photovoltaic Materials and Devices); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2019","The deposition of dust, soil, and microfibers resulting from the surroundings, as well as the growth of minute pollens like moss and fungi, contributes toward photovoltaic (PV) module soiling. Soiling is a widely recognized factor that significantly reduces the power production by acting as a barrier for effective light absorption by the module. The estimated loss in the irradiance and power can be determined with the help of a soiling ratio (SR) parameter, which is the ratio of the short-circuit current (Isc) or the maximum power produced (Pmax) by a soiled module to a clean one. The measured SR is normally not constant throughout a day but changes with the position of the Sun and the amount of dust on the module. This paper proposes an empirical equation to determine the SR at any instant of time of the day based on the Sun's angle of incidence on the module and a single SR value measured at the mid of the day. First, an indoor experiment was done to examine the angular loss dependence of two totally different dust colors for the same SR at normal light incidence. Next, in an outdoor experiment, the SR of an artificially soiled module was measured over the course of the day for three conditions of high, medium, and low daily average irradiance due to variation in cloudiness. Then, an empirical equation is introduced based on an incident angle modifier for soiled and cleaned PV modules. The proposed equation was further used to determine the SR. Finally, the average residuals between the measured and the modeled SRs were determined with the help of root-mean-square deviation. The results showed that the modeled SR was determined with a deviation of ±0.21% and ±0.28%, respectively, for high-and medium-irradiance days, whereas the deviation increased to ±1.04% in the case of low irradiance due to clouds.","Angle of incidence (AOI); Angular loss (AL); Incident angle modifier (IAM); Module soiling; Photovoltaic (PV) module; Soiling ratio (SR); Solar power generation; Transmission loss (t).","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:2faccb01-5eff-49f4-969b-9a3efb01be40","http://resolver.tudelft.nl/uuid:2faccb01-5eff-49f4-969b-9a3efb01be40","A simplified skyline-based method for estimating the annual solar energy potential in urban environments","Calcabrini, A. (TU Delft Photovoltaic Materials and Devices); Ziar, H. (TU Delft Photovoltaic Materials and Devices); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2019","Architects, engineers and urban planners have today at their disposal several tools for simulating the energy yield of photovoltaic systems. These tools are based on mathematical models that perform repetitive calculations to determine the annual irradiation received by solar panels; hence when photovoltaic systems are installed in complex urban environments, the simulations become highly computationally demanding. Here we present a simplified and yet accurate model for the direct calculation of the annual irradiation and energy yield of photovoltaic systems in urban environments. Our model is based on the correlation between the solar radiation components and the shape of the skyline profile. We show how calculations can be simplified by quantifying the skyline using two indicators: the sky view factor and the sun coverage factor. Model performance is evaluated in different climates using measured data from different photovoltaic systems. Results indicate that the proposed model significantly reduces the required computation time while preserving a high estimation accuracy.","","en","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:eff781c6-20a1-4d24-9c7f-f35320db95c4","http://resolver.tudelft.nl/uuid:eff781c6-20a1-4d24-9c7f-f35320db95c4","Understanding the nano-photonics absorption limit in both front-side and front/rear-side textured slabs","Ahmadpanahi, S.H. (TU Delft Photovoltaic Materials and Devices); Vismara, R. (TU Delft Photovoltaic Materials and Devices); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2019","Surface texturing is one of the main techniques to enhance light absorption in solar cells. In thin film devices, periodic texturing can be used to excite the guided resonances supported by the structure. Therefore, total absorption is enhanced largely due to the excitation of these resonances. Although the maximum absorption enhancement limit in both bulk and photonic structures is known already, the weight of each resonance type in this limit is not yet clear. In this contribution, we extend the temporal couple-mode theory, deriving a closed formula to distinguish the contribution of Fabry-Perot and wave-guided modes within the absorption limit for 1-D grating structures. Secondly, using this analytical approach, we can clearly address cases of bulk and thin absorber thicknesses. Our results, supported by rigorous electromagnetic calculation, show that absorption enhancement in a 1-D grating structure can be much higher than the nano-photonic limit (2πn) reported by Yu et al. Thirdly, beyond the framework put forward by Yu et al., we extended our theory to describe the absorption enhancement in double side textured slabs. We have found that when the periods of top and bottom gratings are aliquant, absorption is enhanced in a wider frequency range. We provide rigorous numerical calculations to support our theoretical approach.","","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:3a163d8f-0c6c-4836-b963-03972b641041","http://resolver.tudelft.nl/uuid:3a163d8f-0c6c-4836-b963-03972b641041","Fast and accurate ray-casting-based view factor estimation method for complex geometries","Sönmez, Furkan Fatih (Student TU Delft); Ziar, H. (TU Delft Photovoltaic Materials and Devices); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2019","The concept of view factor has various applications in engineering problems, ranging from heat management to bifacial photovoltaics. Analytical solutions for view factor calculations are difficult to obtain and normally numerical methods are used. For complex geometries, when several surfaces are arbitrarily arranged in a threedimensional environment, conventional numerical approaches such as Monte Carlo method will take a lot of simulation time. To tackle this challenge, we have developed a simple and yet accurate view factor estimation
method based on ray-casting. In our method, the view factor is determined by sending out rays, evenly distributed in all directions from the target surface, and consequently counting the number of rays intercepted by each of the other surfaces present in the environment under study. Then, a simple algebraic procedure enables the estimation of a large number of view factors
simultaneously. The results have been compared with exact and numerical solutions, proving that we have devised a fast and accurate view factor estimation method. This can be used to determine the view factors in environments generated via Light Detection And Ranging (LiDAR). The
method has the potential to be applied in several scientific researches and engineering studies including heat transfer and solar energy.","Albedo; Bifacial photovoltaics; Building integrated photovoltaics; Computer simulation; Configuration factor; Ray casting; Reflected irradiance; Shape factor; Sky view factor (SVF); Solar energy; View factor","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:149de32b-8502-483a-bb69-70a3e32120cd","http://resolver.tudelft.nl/uuid:149de32b-8502-483a-bb69-70a3e32120cd","Geometrical optimisation of core-shell nanowire arrays for enhanced absorption in thin crystalline silicon heterojunction solar cells","Vismara, R. (TU Delft Photovoltaic Materials and Devices); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Ingenito, A. (TU Delft Photovoltaic Materials and Devices; Swiss Federal Institute of Technology); Si, F.T. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2019","Background: Elongated nanostructures, such as nanowires, have attracted significant attention for application in silicon-based solar cells. The high aspect ratio and characteristic radial junction configuration can lead to higher device performance, by increasing light absorption and, at the same time, improving the collection efficiency of photo-generated charge carriers. This work investigates the performance of ultra-thin solar cells characterised by nanowire arrays on a crystalline silicon bulk. Results: Proof-of-concept devices on a p-type mono-crystalline silicon wafer were manufactured and compared to flat references, showing improved absorption of light, while the final 11.8% (best-device) efficiency was hindered by sub-optimal passivation of the nanowire array. A modelling analysis of the optical performance of the proposed solar cell architecture was also carried out. Results showed that nanowires act as resonators, amplifying interference resonances and exciting additional wave-guided modes. The optimisation of the array geometrical dimensions highlighted a strong dependence of absorption on the nanowire cross section, a weaker effect of the nanowire height and good resilience for angles of incidence of light up to 60°. Conclusion: The presence of a nanowire array increases the optical performance of ultra-thin crystalline silicon solar cells in a wide range of illumination conditions, by exciting resonances inside the absorber layer. However, passivation of nanowires is critical to further improve the efficiency of such devices.","Heterojunction; Nanowires; Optical modelling; Photovoltaics; Silicon","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:30601b5d-2387-4c96-a512-d878b706bb48","http://resolver.tudelft.nl/uuid:30601b5d-2387-4c96-a512-d878b706bb48","High temperature oxidation pre-treatment of textured c-Si wafers passivated by a-Si:H","Limodio, G. (TU Delft Photovoltaic Materials and Devices); D'Herouville, G. (Student TU Delft); Mazzarella, L. (TU Delft Photovoltaic Materials and Devices); Zhao, Y. (TU Delft Photovoltaic Materials and Devices); Yang, G. (TU Delft Photovoltaic Materials and Devices); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2019","This work shows an alternative surface cleaning method for c-Si wafers to replace the standard chemical procedures as RCA or HNO 3 which involve hazardous chemicals or unstable processes. The method consists in a high-temperature oxidation treatment (HTO) performed in a classical tube furnace that incorporates organic and metal particles present on the c-Si surfaces in the growing SiO 2 layer. The result is as a reliable pre-treatment method for obtaining less defective c-Si surfaces ready for solar cell fabrication after SiO 2 removal. To test the surface passivation quality obtained with our alternative cleaning method, we grow amorphous silicon (a-Si:H) layers by plasma enhanced chemical vapor deposition on both sides of the c-Si wafer and systematically compare the effective carrier lifetime (τ eff ) and implied V OC (iV oc ) to the wafer treated with the standard cleaning in our laboratory. We optimize HTO treatment time reaching τ eff of ∼6 ms and iV oc of 721 mV for the best sample. We ascribe the improved passivation quality using HTO to two concurrent factors. Firstly, the encapsulation of defects into SiO 2 layer that is then etched prior a-Si:H deposition and secondly, to modification of the pyramids’ morphology that facilitates the surface passivation. SEM pictures and reflection measurements support the latter hypothesis.","Amorphous silicon passivation; Defect encapsulation; Silicon heterojunction solar cells; Thermal oxidation","en","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:8f0eef73-9d56-4bc3-abf6-2ec9ffc10c7b","http://resolver.tudelft.nl/uuid:8f0eef73-9d56-4bc3-abf6-2ec9ffc10c7b","Photovoltaic chimney: Thermal modeling and concept demonstration for integration in buildings","Ortiz Lizcano, J.C. (TU Delft Photovoltaic Materials and Devices); Haghighi, Z. (TU Delft Climate Design and Sustainability); Wapperom, Sander (Student TU Delft); Infante Ferreira, C.A. (TU Delft Engineering Thermodynamics); Isabella, O. (TU Delft Photovoltaic Materials and Devices); van den Dobbelsteen, A.A.J.F. (TU Delft Climate Design and Sustainability); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2019","This work presents the concept of a photovoltaic (PV)-powered solar chimney. We modeled and experimentally studied the integration of a PV system within a naturally ventilated façade (NVF), attempting to use the inherent cavity as a ventilation channel to transfer heat. Thermodynamic models were created to study the thermal and, therefore, the electrical performance of a PV system installed at different positions within the cavity of the NVF. An experimental setup of the PV chimney was manufactured to validate the computational models. Results show low root mean square error (RMSE) values for the prediction of the mass flow and the temperature of the different materials considered in the chimney. A basic sensitivity analysis was performed to find the best position of the PV modules within the chimney for a three-story household in the Netherlands. Optimization showed that with a cavity depth of 0.2 m with PV modules located at the front layer, the electric annual yield is maximized. For the same cavity depth, placing the modules in the middle significantly increases heat flow production, albeit with a reduction on electrical performance.","PV façade; PV integration; solar chimney; thermal model","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:a0a5dd9b-f411-4b25-a5c6-22094fced256","http://resolver.tudelft.nl/uuid:a0a5dd9b-f411-4b25-a5c6-22094fced256","High-Mobility Hydrogenated Fluorine-Doped Indium Oxide Film for Passivating Contacts c-Si Solar Cells","Han, C. (TU Delft Photovoltaic Materials and Devices; Nankai University; Shenzhen Institute of Wide-bandgap Semiconductors); Mazzarella, L. (TU Delft Photovoltaic Materials and Devices); Zhao, Y. (TU Delft Photovoltaic Materials and Devices); Yang, G. (TU Delft Photovoltaic Materials and Devices); Procel Moya, P.A. (TU Delft Photovoltaic Materials and Devices); Tijssen, M. (TU Delft Photovoltaic Materials and Devices); Bento Montes, A.R. (TU Delft Photovoltaic Materials and Devices); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2019","Broadband transparent conductive oxide layers with high electron mobility (μe) are essential to further enhance crystalline silicon (c-Si) solar cell performances. Although metallic cation-doped In2O3 thin films with high μe (>60 cm2 V-1 s-1) have been extensively investigated, the research regarding anion doping is still under development. In particular, fluorine-doped indium oxide (IFO) shows promising optoelectrical properties; however, they have not been tested on c-Si solar cells with passivating contacts. Here, we investigate the properties of hydrogenated IFO (IFO:H) films processed at low substrate temperature and power density by varying the water vapor pressure during deposition. The optimized IFO:H shows a remarkably high μe of 87 cm2 V-1 s-1, a carrier density of 1.2 × 1020 cm-3, and resistivity of 6.2 × 10-4 ω cm. Then, we analyzed the compositional, structural, and optoelectrical properties of the optimal IFO:H film. The high quality of the layer was confirmed by the low Urbach energy of 197 meV, compared to 444 meV obtained on the reference indium tin oxide. We implemented IFO:H into different front/back-contacted solar cells with passivating contacts processed at high and low temperatures, obtaining a significant short-circuit current gain of 1.53 mA cm-2. The best solar cell shows a conversion efficiency of 21.1%.","electron mobility; hydrogenated fluorine-doped indium oxide (IFO:H); passivating contacts; silicon heterojunction (SHJ); transparent conductive oxide (TCO)","en","journal article","","","","","","green","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:4ee12aa2-d3b4-4d8a-9f4d-6c7783e05ebf","http://resolver.tudelft.nl/uuid:4ee12aa2-d3b4-4d8a-9f4d-6c7783e05ebf","Effective Passivation of Black Silicon Surfaces via Plasma-Enhanced Chemical Vapor Deposition Grown Conformal Hydrogenated Amorphous Silicon Layer","Özkol, E. (TU Delft Photovoltaic Materials and Devices); Procel Moya, P.A. (TU Delft Photovoltaic Materials and Devices); Zhao, Y. (TU Delft Photovoltaic Materials and Devices); Mazzarella, L. (TU Delft Photovoltaic Materials and Devices); Medlin, Rostislav (University of West Bohemia); Šutta, Pavol (University of West Bohemia); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2019","Solar cells based on black silicon (b-Si) are proven to be promising in photovoltaics (PVs) by exceeding 22% efficiency. To reach high efficiencies with b-Si surfaces, the most crucial step is the effective surface passivation. Up to now, the highest effective minority carrier lifetimes are achieved with atomic layer-deposited Al2O3 or thermal SiO2. Plasma-enhanced chemical vapor deposition (PECVD)-grown hydrogenated amorphous silicon (a-Si:H) passivation of b-Si is seldom reported due to conformality problems. In this current study, b-Si surfaces superposed on standard pyramidal textures, also known as modulated surface textures (MSTs), are successfully passivated by PECVD-grown conformal layers of a-Si:H. It is shown that under proper plasma-processing conditions, the effective minority carrier lifetimes of samples endowed with front MST and rear standard pyramidal textures can reach up to 2.3 ms. A route to the conformal growth is described and developed by transmission electron microscopic (TEM) images. Passivated MST samples exhibit less than 4% reflection in a wide spectral range from 430 to 1020 nm.","black silicon; conformal growth; hydrogenated amorphous silicon; plasma-enhanced chemical vapor deposition; surface passivation","en","journal article","","","","","","green","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:b990650e-8721-4e18-b285-808d27496f36","http://resolver.tudelft.nl/uuid:b990650e-8721-4e18-b285-808d27496f36","Optimization of Three-Terminal Perovskite/Silicon Tandem Solar Cells","Santbergen, R. (TU Delft Photovoltaic Materials and Devices); Uzu, Hisashi (Kaneka Corporation); Yamamoto, Kenji (Kaneka Corporation); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2019","We use simulations to optimize perovskite/silicon tandem solar cells in a novel three-terminal configuration, with one terminal at the front and two at the rear. We consider configurations in which the top cell has either the inverted or the same polarity as the bottom cell. Our goal is to minimize the optical losses, to compare the performance of both configurations and to determine the realistically achievable efficiency. Optical simulations show that if the hole-transporting material is in front of the perovskite, it gives rise to parasitic absorption losses. If it is behind the perovskite, these losses are avoided, however, at the cost of increased reflection losses. We systematically minimize these reflection losses. This increases the tandem's total implied photocurrent density from 34.4 to 41.1 mA/cm 2 . To determine the corresponding power conversion efficiency of these three-terminal tandems, electrical circuit simulations are performed based on existing 22.7% efficient perovskite and 24.9% efficient silicon cells. These simulations show that tandem efficiencies up to 32.0% can be obtained.","Equivalent circuit; light trapping; modeling; perovskite; photovoltaic cell; simulation; tandem","en","journal article","","","","","","Accepted author manuscript","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:3d92d77a-38dd-4337-ae0e-05cef49f3dee","http://resolver.tudelft.nl/uuid:3d92d77a-38dd-4337-ae0e-05cef49f3dee","Quantifying the Benefits of a Solar Home System-Based DC Microgrid for Rural Electrification","Narayan, N.S. (TU Delft DC systems, Energy conversion & Storage); Chamseddine, Ali (Student TU Delft); Vega Garita, V.E. (TU Delft DC systems, Energy conversion & Storage); Qin, Z. (TU Delft DC systems, Energy conversion & Storage); Popovic, J. (Klimop Energy B.V.); Bauer, P. (TU Delft DC systems, Energy conversion & Storage); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2019","Off-grid solar home systems (SHSs) currently constitute a major source of providing basic electricity needs in un(der)-electrified regions of the world, with around 73 million households having benefited from off-grid solar solutions by 2017. However, in and of itself, state-of-the-art SHSs can only provide electricity access with adequate power supply availability up to tier 2, and to some extent, tier 3 levels of the Multi-tier Framework (MTF) for measuring household electricity access. When considering system metrics of loss of load probability (LLP) and battery size, meeting the electricity needs of tiers 4 and 5 is untenable through SHSs alone. Alternatively, a bottom-up microgrid composed of interconnected SHSs is proposed. Such an approach can enable the so-called climb up the rural electrification ladder. The impact of the microgrid size on the system metrics like LLP and energy deficit is evaluated. Finally, it is found that the interconnected SHS-based microgrid can provide more than 40% and 30% gains in battery sizing for the same LLP level as compared to the standalone SHSs sizes for tiers 4 and 5 of the MTF, respectively, thus quantifying the definite gains of an SHS-based microgrid over standalone SHSs. This study paves the way for visualizing SHS-based rural DC microgrids that can not only enable electricity access to the higher tiers of the MTF with lower battery storage needs but also make use of existing SHS infrastructure, thus enabling a technologically easy climb up the rural electrification ladder.","Battery storage; DC microgrids; Energy sharing; Multi-tier framework; Rural electrification; Solar home systems","en","journal article","","","","","","","","","","Electrical Sustainable Energy","DC systems, Energy conversion & Storage","","",""
"uuid:71e33863-97ba-4488-a0c4-21ee7ebc41a6","http://resolver.tudelft.nl/uuid:71e33863-97ba-4488-a0c4-21ee7ebc41a6","Exploring the boundaries of Solar Home Systems (SHS) for off-grid electrification: Optimal SHS sizing for the multi-tier framework for household electricity access","Narayan, N.S. (TU Delft DC systems, Energy conversion & Storage); Chamseddine, Ali (Student TU Delft); Vega Garita, V.E. (TU Delft DC systems, Energy conversion & Storage); Qin, Z. (TU Delft DC systems, Energy conversion & Storage); Popovic, J. (Klimop Energy B.V.); Bauer, P. (TU Delft DC systems, Energy conversion & Storage); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2019","With almost 1.1 billion people lacking access to electricity, solar-based off-grid products like Solar Home Systems (SHS) have become a promising solution to provide basic electricity needs in un(der)-electrified regions. Therefore, optimal system sizing is a vital task as both oversizing and undersizing a system can be detrimental to system cost and power availability, respectively. This paper presents an optimal SHS sizing methodology that minimizes the loss of load probability (LLP), excess energy dump, and battery size while maximizing the battery lifetime. A genetic algorithm-based multi-objective optimization approach is utilized to evaluate the optimal SHS sizes. The potential for SHS to cater to every tier of the Multi-tier framework (MTF) for measuring household electricity access is examined. The optimal system sizes for standalone SHS are found for different LLP thresholds. Results show that beyond tier 2, the present day SHS sizing needs to be expanded significantly to meet the load demand. Additionally, it is deemed untenable to meet the electricity needs of the higher tiers of MTF purely through standalone SHS without compromising one or more of the system metrics. A way forward is proposed to take the SHS concept all the way up the energy ladder such that load demand can also be satisfied at tier 4 and 5 levels.","Battery lifetime; Battery sizing; Multi objective optimization; Multi-tier framework; Optimal sizing; Solar Home Systems","en","journal article","","","","","","","","","","Electrical Sustainable Energy","DC systems, Energy conversion & Storage","","",""
"uuid:b9b7ec4a-5b2f-4494-b152-429f14ff1454","http://resolver.tudelft.nl/uuid:b9b7ec4a-5b2f-4494-b152-429f14ff1454","Inverted pyramidally-textured PDMS antireflective foils for perovskite/silicon tandem solar cells with flat top cell","Hou, Fuhua (Nankai University; Key Laboratory of Photoelectronic Thin Film Devices and Technology of Tianjin; Collaborative Innovation Center of Chemical Science and Engineering); Han, C. (TU Delft Photovoltaic Materials and Devices; Nankai University; Key Laboratory of Photoelectronic Thin Film Devices and Technology of Tianjin; Collaborative Innovation Center of Chemical Science and Engineering); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Yan, Lingling (Nankai University; Key Laboratory of Photoelectronic Thin Film Devices and Technology of Tianjin; Collaborative Innovation Center of Chemical Science and Engineering); Shi, Biao (Nankai University; Key Laboratory of Photoelectronic Thin Film Devices and Technology of Tianjin; Collaborative Innovation Center of Chemical Science and Engineering); Chen, Junfan (Nankai University; Key Laboratory of Photoelectronic Thin Film Devices and Technology of Tianjin; Collaborative Innovation Center of Chemical Science and Engineering); An, Sichong (Nankai University; Key Laboratory of Photoelectronic Thin Film Devices and Technology of Tianjin; Collaborative Innovation Center of Chemical Science and Engineering); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2019","Perovskite/silicon tandem solar cells (TSCs) have the potential to achieve power conversion efficiency exceeding 30%. To be compatible with high-efficiency solution-deposited perovskite top cell, a planar front surface for silicon bottom cell is generally required. However, flat front surfaces result in large light reflection losses and thus reduce the performance of tandem device. To boost light absorption, we design light management antireflective foils made from polydimethylsiloxane (PDMS) polymer carrying random-pyramidal textures with three different pyramid size ranges (1–3 µm, 3–8 µm, 8–15 µm). The optical properties, together with the reflection behavior applied to perovskite/silicon tandem solar cells have been systematically studied. One of the PDMS layer exhibited a relatively strong light-scattering property with a high average haze ratio originated from synergistic effect of the appropriate pyramid size and the uneven random pyramid distribution. Consequently, the short-circuit current density of the tandem device was improved by 1.72 mA/cm2 and thus its efficiency increased from 19.38% to 21.93%, after laminating the PDMS-based antireflection coating (ARC) onto the front surface of tandem device. Furthermore, this work provides a facile and cost-effective way to introduce light-management foils and indicates a broad strategy to enhance the performance of solar cells with planar front surface.","Antireflection coating; Light management; PDMS layer; Perovskite/silicon tandem solar cell; Pyramidal texture","en","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:a9a9d517-de8c-4932-be9b-ff06257eedcd","http://resolver.tudelft.nl/uuid:a9a9d517-de8c-4932-be9b-ff06257eedcd","Front and rear contact Si solar cells combining high and low thermal budget Si passivating contacts","Limodio, G. (TU Delft Photovoltaic Materials and Devices); Yang, G. (TU Delft Photovoltaic Materials and Devices); Ge, H. (Student TU Delft); Procel Moya, P.A. (TU Delft Photovoltaic Materials and Devices); de Groot, Y. (Student TU Delft); Mazzarella, L. (TU Delft Photovoltaic Materials and Devices); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2019","In this work we develop a rear emitter silicon solar cell integrating carrier-selective passivating contacts (CSPCs) with different thermal budget in the same device. The solar cell consists of a B-doped poly-Si/SiOx hole collector and an i/n hydrogenated amorphous silicon (a-Si:H) stack acting as electron collector placed on the planar rear and textured front side, respectively. We investigate the passivation properties of both CSPCs on symmetric structures by optimizing the interdependency among annealing temperature, time and environment. The optimized B-doped poly-Si/SiOx reaches a saturation current density of ~10 fA/cm2 on n-type wafers and an implied open circuit voltage (iVOC) of 716 mV. Furthermore, the i/n a-Si:H stack shows an effective carrier lifetime above 4 ms and iVOC of ~705 mV for cell-relevant layers thickness. After a post-deposition annealing in H2, lifetime is above 10 ms and iVOC = 708 mV. Finally, we optimize the optoelectronic properties of indium-based transparent conductive oxide (Indium Tin Oxide ITO and hydrogenated indium oxide IO:H) to reduce parasitic absorption with a gain in short circuit current density of 0.23 mA/cm2. In conclusion, the optimized layer stacks are implemented at device level obtaining a device with VOC = 704 mV, fill factor of 73.8%, a short circuit current of 39.7 mA/cm2 and 21.0% aperture-area conversion efficiency.","Amorphous silicon; Ion-implantation; Poly-silicon passivating contacts; Silicon solar cells","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:0f0fec5a-7a1d-4c1a-ad7c-fd55ace555df","http://resolver.tudelft.nl/uuid:0f0fec5a-7a1d-4c1a-ad7c-fd55ace555df","Designing a hybrid thin-film/wafer silicon triple photovoltaic junction for solar water splitting","Perez Rodriguez, P. (TU Delft Photovoltaic Materials and Devices); Vijselaar, Wouter (University of Twente); Huskens, Jurriaan (University of Twente); Stam, Machiel (Student TU Delft); Falkenberg, M. (Hamburg University of Applied Sciences); Zeman, M. (TU Delft Electrical Sustainable Energy); Smith, W.A. (TU Delft ChemE/Materials for Energy Conversion and Storage); Smets, A.H.M. (TU Delft Photovoltaic Materials and Devices)","","2019","Solar fuels are a promising way to store solar energy seasonally. This paper proposes an earth-abundant heterostructure to split water using a photovoltaic-electrochemical device (PV-EC). The heterostructure is based on a hybrid architecture of a thin-film (TF) silicon tandem on top of a c-Si wafer (W) heterojunction solar cell (a-Si:H (TF)/nc-Si:H (TF)/c-Si(W)) The multijunction approach allows to reach enough photovoltage for water splitting, while maximizing the spectrum utilization. However, this unique approach also poses challenges, including the design of effective tunneling recombination junctions (TRJ) and the light management of the cell. Regarding the TRJs, the solar cell performance is improved by increasing the n-layer doping of the middle cell. The light management can be improved by using hydrogenated indium oxide (IOH) as transparent conductive oxide (TCO). Finally, other light management techniques such as substrate texturing or absorber bandgap engineering were applied to enhance the current density. A correlation was observed between improvements in light management by conventional surface texturing and a reduced nc-Si:H absorber material quality. The final cell developed in this work is a flat structure, using a top absorber layer consisting of a high bandgap a-Si:H. This triple junction cell achieved a PV efficiency of 10.57%, with a fill factor of 0.60, an open-circuit voltage of 2.03 V and a short-circuit current density of 8.65 mA/cm 2 . When this cell was connected to an IrO x /Pt electrolyser, a stable solar-to-hydrogen (STH) efficiency of 8.3% was achieved and maintained for 10 hours.","electrolysis; heterostructures; hydrogen fuel; multijunction; open-circuit voltage; photovoltaic","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:74d39e7f-f4d1-4a42-9e49-2c107547795a","http://resolver.tudelft.nl/uuid:74d39e7f-f4d1-4a42-9e49-2c107547795a","Numerical Simulations of IBC Solar Cells Based on Poly-Si Carrier-Selective Passivating Contacts","Procel Moya, P.A. (TU Delft Photovoltaic Materials and Devices); Yang, G. (TU Delft Photovoltaic Materials and Devices); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2019","This paper presents an analysis of physical mechanisms related to operation and optimization of interdigitated back contact (IBC) poly-silicon-based devices. Concepts of carrier selectivity and tunneling are used to identify the parameters that impact on the fill factor. Then, based on technology computer-aided design (TCAD) numerical simulations, we describe the device performance in terms of transport and passivation. A validation of the model is performed by matching measured and simulated R, T, and external quantum efficiency spectra and electrical parameters. As result of such process, the opto-electrical losses of the reference device are identified. Then, we execute a study of the impact of process parameters on the performance of the IBC device under analysis. Assuming a uniform SiO 2 layer, simulation results reveal that both n-type and p-type poly-Si contacts can be theoretically perfect (i.e., approx. lossless), if assuming no interface recombination but considering tunneling of both carrier types. In other words, there exists an optimum oxide thickness (1 nm) for which majority carriers tunneling works already very well, and minority tunneling is still low enough to not result in significant recombination. Moreover, SiO 2 thickness up to maximum 1.6 nm is crucial to achieve high efficiency. Regarding rear geometry analysis, the efficiency curve as a function of emitter width peaks at 70% of pitch coverage. Further, it is shown that diffused dopants inside crystalline silicon make the device resilient to passivation quality. Finally, the calibrated model is used to perform an optimization study aiming at calculating the performance limit. The estimated performance limit is 27.3% for a 100-μm-thick bulk, 20-nm-thick poly-silicon layers, silver as rear contact, and double ARC.","IBC solar cells; passivating contacts; poly-silicon; semiconductors device modeling","en","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:6591b652-d1aa-4cf0-b77d-50072204ae9f","http://resolver.tudelft.nl/uuid:6591b652-d1aa-4cf0-b77d-50072204ae9f","Solar harvesting based on perfect absorbing all-dielectric nanoresonators on a mirror","Vismara, R. (TU Delft Photovoltaic Materials and Devices); Länk, Nils Odebo (Chalmers University of Technology); Verre, Ruggero (Chalmers University of Technology); Käll, Mikael (Chalmers University of Technology); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2019","The high-index all-dielectric nanoantenna system is a platform recently used for multiple applications, from metalenses to light management. These systems usually exhibit low absorption/scattering ratios and are not efficient photon harvesters. Nevertheless, by exploiting far-field interference, all-dielectric nanostructures can be engineered to achieve near-perfect absorption in specific wavelength ranges. Here, we propose – based on electrodynamics simulations – that a metasurface composed of an array of hydrogenated amorphous silicon nanoparticles on a mirror can achieve nearly complete light absorption close to the bandgap. We apply this concept to a realistic device, predicting a boost of optical performance of thin-film solar cells made of such nanostructures. In the proposed device, high-index dielectric nanoparticles act not only as nanoatennas able to concentrate light but also as the solar cell active medium, contacted at its top and bottom by transparent electrodes. By optimization of the exact geometrical parameters, we predict a system that could achieve initial conversion efficiency values well beyond 9% – using only the equivalent of a 75-nm thick active material. The device absorption enhancement is 50% compared to an unstructured device in the 400 nm − 550 nm range and more than 300% in the 650 nm − 700 nm spectral region. We demonstrate that such large values are related to the metasurface properties and to the perfect absorption mechanism.","","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:aa71a7dd-eaab-4ab1-96c9-4e65ad19cc81","http://resolver.tudelft.nl/uuid:aa71a7dd-eaab-4ab1-96c9-4e65ad19cc81","Electrochemical Oxidation of Organic Pollutants Powered by a Silicon-Based Solar Cell","Perez Rodriguez, P. (TU Delft Photovoltaic Materials and Devices); Maqueira Gonzalez, Carlos (Student TU Delft); Doekhi-Bennani, Y. (TU Delft Sanitary Engineering); Rietveld, L.C. (TU Delft Sanitary Engineering); Zeman, M. (TU Delft Electrical Sustainable Energy); Smets, A.H.M. (TU Delft Photovoltaic Materials and Devices)","","2018","Currently available (photo-)electrochemical technologies for water treatment establish a trade-off between low-pollutant concentration and costs. This paper aims at decoupling these two variables by designing a photo-oxidation device using earth abundant materials and an electronic-free approach. The proposed device combines a graphite/graphite electrochemical system with a silicon-based solar cell that provides the necessary electrical power. First, the optimum operational voltage for the graphite/graphite electrochemical system was found to be around 1.6 V. That corresponded closely to the voltage produced by an a-Si:H/a-Si:H tandem solar cell of approximately 1.35 V. This configuration was shown to provide the best pollutant degradation in relation to the device area, removing 70% of the initial concentration of phenol and 90% of the methylene blue after 4 h of treatment. The chemical oxygen demand (COD) removal of these two contaminants after 4 h of treatment was also promising, 55 and 30%, respectively. Moreover, connecting several solar cells in series led to higher pollutant degradation but lower COD removal, suggesting that the degradation of the intermediate components is a limiting factor. This is expected to be due to the higher currents achieved by the series-connected configuration, which would favor other reactions such as polymerization over the degradation of intermediate species.","","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:b17f8b3f-9c44-48be-90e3-ab494e596c54","http://resolver.tudelft.nl/uuid:b17f8b3f-9c44-48be-90e3-ab494e596c54","Solar Powered E-Bike Charging Station with AC, DC and Contactless Charging","Chandra Mouli, G.R. (TU Delft DC systems, Energy conversion & Storage); van Duijsen, P.J. (TU Delft DC systems, Energy conversion & Storage); Velzeboer, Tim (Student TU Delft); Ganesan Nair, Gireesh (Student TU Delft); Zhao, Yunpeng (Student TU Delft); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Bauer, P. (TU Delft DC systems, Energy conversion & Storage); Jamodkar, A.; Silvester, S. (TU Delft Applied Ergonomics and Design); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2018","Charging electric vehicles from solar energy provides a sustainable means of transportation. This paper shows the design of solar powered e-bike charging station that provides AC, DC and contactless charging of e-bikes. The DC charger allows direct DC charging of the e-bike from the DC power of the photovoltaic panels (PV) without the need for an external AC charger adapter. In case of the contactless charger, the bike can be charged without the use of any cables providing maximum convenience to the user. Finally, the charging station has an integrated battery that allows for both grid-connected and off-grid operation","","en","conference paper","EPE","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2021-12-01","","Electrical Sustainable Energy","DC systems, Energy conversion & Storage","","",""
"uuid:307d09bc-969f-4d30-976d-653a5bf6bb8a","http://resolver.tudelft.nl/uuid:307d09bc-969f-4d30-976d-653a5bf6bb8a","Harvesting Roadway Solar Energy-Performance of the Installed Infrastructure Integrated PV Bike Path","Shekhar, A. (TU Delft DC systems, Energy conversion & Storage); Kumaravel, Vinod Kumar (Sungevity International); Klerks, Stan (TNO); de Wit, Sten (TNO); Prasanth, V. (TU Delft DC systems, Energy conversion & Storage); Narayan, N.S. (TU Delft DC systems, Energy conversion & Storage); Bauer, P. (TU Delft DC systems, Energy conversion & Storage); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2018","Solar road technology provides an opportunity to harvest the vast, albeit dispersed, photovoltaic (PV) energy, while maximizing the land utilization. Deriving experience from the pioneering 70-m solar bike path installed in the Netherlands, this paper highlights the operational challenges and performance parameters using the first-year measured data. The theoretically predicted energy yield is compared with the measured energy yield. Based on the best performing module, the benchmark annual energy yield is set to 85–90 kWh/m<formula><tex>$^2$</tex></formula> specific to the installation site. It is shown that this value can be bettered by about 1.5 times if different cell technology such as monocrystalline is used. With different installation sites around the world, thermal behavior as well as annual energy yield changes. Theoretical proof is offered that it is not unreasonable to expect an annual energy yield in the upwards of 150 kWh/m<formula><tex>$^2$</tex></formula> with solar road energy harvesting technology. For example, the annual yield is found to be 213 kWh/m<formula><tex>$^2$</tex></formula> if the same model is simulated for a solar road PV installation in India, which increased further with the use of monocrystalline to almost 300 kWh/m<formula><tex>$^2$</tex></formula>.","Annual energy yield; energy harvester; infrastructure integrated photovoltaics (IIPV); module temperature; photovoltaics (PV); roadway; solar pavement; solar powered street; solar road (SR)","en","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","","","Electrical Sustainable Energy","DC systems, Energy conversion & Storage","","",""
"uuid:b9ca8466-ce5f-45fa-8f6a-b081b215272c","http://resolver.tudelft.nl/uuid:b9ca8466-ce5f-45fa-8f6a-b081b215272c","Electroluminescence and Dark Lock-In Thermography for the Quality Assessment of Metal-Wrap-Through Solar Devices","Ruggeri, Edoardo (University of Cambridge); van Aken, Bas (ECN, Petten); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2018","Imaging techniques, like electroluminescence and dark lock-in thermography, are valuable quality control tools as they yield quantitative and spatially resolved information about the device. In this paper, we isolated some of the conductive foil–cell interconnections of back-contact solar cells to study the appearance of these intentional failures in electroluminescence, dark lock-in thermography, and series resistance images. It has been found that isolated emitter-to-foil contacts are clearly visible in the three imaging techniques, as they show characteristic features that deviate from the features typical of functioning emitter-to-foil dots. Isolated base-to-foil contacts are instead invisible in the images obtained by electroluminescence and only hardly visible in the images obtained by the other two techniques. Only after a large amount of contacts are isolated, a local current redistribution or drastic series resistance increase is noticeable. Two graphical methods for the automatic identification of isolated emitter-to-foil contacts in electroluminescence, dark lock-in thermography, and series resistance images were also designed, showing a success rate of 97% in the investigated cells. Such techniques could represent useful tools for implementation in inline quality control processes. Moreover, the techniques and conclusions drawn in this paper can be extended to a large number of other conventional and emerging photovoltaic technologies.","Electrical resistance measurement; electroluminescence; failure analysis; infrared imaging; radiation imaging; solar energy","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:b948a63c-2e14-4fc7-87fa-5bfb261077a0","http://resolver.tudelft.nl/uuid:b948a63c-2e14-4fc7-87fa-5bfb261077a0","Distinguishing Fabry-Perot from guided resonances in thin periodically-textured silicon absorbers","Ahmadpanahi, S.H. (TU Delft Photovoltaic Materials and Devices); Vismara, R. (TU Delft Photovoltaic Materials and Devices); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2018","Periodic texturing is one of the main techniques for light-trapping in thin-film solar cells. Periodicity allows for the excitation of guided modes in the structure and, thus, largely enhances absorption. Understanding how much a guided resonance can increase the absorption is therefore of great importance. There is a common method to understand if an absorption peak is due to the excitation of a guided mode, using dispersion diagrams. In such graphs, a resonance is identified as the intersection of a guided-mode-line of a uniform waveguide (with the same optical thickness as the grating structure) with the center of a Brillouin zone of the grating. This method is unfortunately not reliable when the grating height is comparable with the thickness of the wave-guide, or when the thickness of the wave-guide is much larger than the wavelength. In this work, we provide a novel approach to calculate the contribution of a guided resonance to the total absorption in a periodic waveguide, without using the dispersion diagram. In this method, the total electric field in the periodic structure is described by its spatial frequencies, using a Fourier expansion. Fourier coefficients of the electric field were used to calculate the absorption of each diffraction order of the grating. Rigorous numerical calculations are provided to support our theoretical approach. This work paves the way for a deeper understanding of light behavior inside a periodic structure and, consequently, for developing more efficient light-trapping techniques for solar cells applications.","","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:0ea3ea0d-5da1-4a09-8ee8-73dc3cdff54d","http://resolver.tudelft.nl/uuid:0ea3ea0d-5da1-4a09-8ee8-73dc3cdff54d","A photovoltaic window with sun-tracking shading elements towards maximum power generation and non-glare daylighting","Gao, Y. (TU Delft Photovoltaic Materials and Devices; Nanjing University; Changzhou Institute of Technology Research for Solid State Lighting); Dong, J. (Chinese Academy of Sciences); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Santbergen, R. (TU Delft Photovoltaic Materials and Devices); Tan, H. (Nanjing University); Zeman, M. (TU Delft Electrical Sustainable Energy); Zhang, Kouchi (TU Delft Electronic Components, Technology and Materials)","","2018","Vertical space bears great potential of solar energy especially for congested urban areas, where photovoltaic (PV) windows in high-rise buildings can contribute to both power generation and daylight harvest. Previous studies on sun-tracking PV windows strayed into the trade-off between tracking performance and mutual shading, failing to achieve the maximum energy generation. Here we first build integrated models which couple the performance of sun-tracking PV windows to the rotation angles. Secondly, one-degree-of-freedom (DOF) and two-DOF sun tracking are mathematically proven to be not able to gain either maximum power generation or non-glare daylighting under reasonable assumptions. Then we derive the optimum rotation angles of the variable-pivot-three-degree-of-freedom (VP-3-DOF) sun-tracking elements and demonstrate that the optimum VP-3-DOF sun tracking can achieve the aforementioned goals. When the restriction of the proposed model is relaxed, the same performance can be achieved by the optimum one-DOF sun tracking with extended PV slats and particular design of cell layout, requiring less complicated mechanical structures. Simulation results of nine global cities show that the annual energy generation and average module efficiency are improved respectively by 27.40% and 19.17% via the optimum VP-3-DOF sun tracking over the conventional perpendicular sun tracking. The proposed optimum sun-tracking methods also reveal better protection against sun glare. The optimum VP-3-DOF sun tracking is also demonstrated to be applicable to horizontal PV windows, as those applied in the sun roof of a glass greenhouse.","photovoltaics; partial shading effects; sun-tracking methods; BIPV; solar energy","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:d3513ff3-80b5-4a3f-bda4-597dd81ec2d1","http://resolver.tudelft.nl/uuid:d3513ff3-80b5-4a3f-bda4-597dd81ec2d1","Oxidation-Induced Structure Transformation: Thin-Film Synthesis and Interface Investigations of Barium Disilicide toward Potential Photovoltaic Applications","Tian, Y. (TU Delft Photovoltaic Materials and Devices); Vismara, R. (TU Delft Photovoltaic Materials and Devices); van Doorene, S. (TU Delft Photovoltaic Materials and Devices); Šutta, Pavol (University of West Bohemia); Vančo, L’ubomír (Slovak University of Technology); Veselý, Marian (Slovak University of Technology); Vogrinčič, Peter (Slovak University of Technology); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2018","Barium disilicide (BaSi2) has been regarded as a promising absorber material for high-efficiency thin-film solar cells. However, it has confronted issues related to material synthesis and quality control. Here, we fabricate BaSi2 thin films via an industrially applicable sputtering process and uncovered the mechanism of structure transformation. Polycrystalline BaSi2 thin films are obtained through the sputtering process followed by a postannealing treatment. The crystalline quality and phase composition of sputtered BaSi2 are characterized by Raman spectroscopy and X-ray diffraction (XRD). A higher annealing temperature can promote crystallization of BaSi2, but also causes an intensive surface oxidation and BaSi2/SiO2 interfacial diffusion. As a consequence, an inhomogeneous and layered structure of BaSi2 is revealed by Auger electron spectroscopy (AES) and transmission electron microscopy (TEM). The thick oxide layer in such an inhomogeneous structure hinders further both optical and electrical characterizations of sputtered BaSi2. The structural transformation process of sputtered BaSi2 films then is studied by the Raman depth-profiling method, and all of the above observations come to an oxidation-induced structure transformation mechanism. It interprets interfacial phenomena including surface oxidation and BaSi2/SiO2 interdiffusion, which lead to the inhomogeneous and layered structure of sputtered BaSi2. The mechanism can also be extended to epitaxial and evaporated BaSi2 films. In addition, a glimpse toward future developments in both material and device levels is presented. Such fundamental knowledge on structural transformations and complex interfacial activities is significant for further quality control and interface engineering on BaSi2 films toward high-efficiency solar cells.","barium disilicide; sputtering; annealing; structure transformation; interface; photovoltaic","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:f8322ca2-fb42-4f37-8e83-4d8b7c53304f","http://resolver.tudelft.nl/uuid:f8322ca2-fb42-4f37-8e83-4d8b7c53304f","Constructing accurate equivalent electrical circuit models of lithium iron phosphate and lead-acid battery cells for solar home system applications","Yu, Y. (TU Delft Electrical Engineering, Mathematics and Computer Science); Narayan, N.S. (TU Delft DC systems, Energy conversion & Storage); Vega Garita, V.E. (TU Delft DC systems, Energy conversion & Storage); Popovic, J. (TU Delft DC systems, Energy conversion & Storage); Qin, Z. (TU Delft DC systems, Energy conversion & Storage); Wagemaker, M. (TU Delft RST/Storage of Electrochemical Energy); Bauer, P. (TU Delft DC systems, Energy conversion & Storage); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2018","The past few years have seen strong growth of solar-based off-grid energy solutions such as Solar Home Systems (SHS) as a means to ameliorate the grave problem of energy poverty. Battery storage is an essential component of SHS. An accurate battery model can play a vital role in SHS design. Knowing the dynamic behaviour of the battery is important for the battery sizing and estimating the battery behaviour for the chosen application at the system design stage. In this paper, an accurate cell level dynamic battery model based on the electrical equivalent circuit is constructed for two battery technologies: the valve regulated lead-acid (VRLA) battery and the LiFePO4 (LFP) battery. Series of experiments were performed to obtain the relevant model parameters. This model is built for low C-rate applications (lower than 0.5 C-rate) as expected in SHS. The model considers the non-linear relation between the state of charge (SOC) and open circuit voltage (VOC) for both technologies. Additionally, the equivalent electrical circuit model for the VRLA battery was improved by including a 2nd order RC pair. The simulated model differs from the experimentally obtained result by less than 2%. This cell level battery model can be potentially scaled to battery pack level with flexible capacity, making the dynamic battery model a useful tool in SHS design.","Battery testing; Dynamic battery model; Electric equivalent circuit battery model; LiFePO4; Solar home systems; VRLA","en","journal article","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","DC systems, Energy conversion & Storage","","",""
"uuid:80150942-549b-449f-9dda-070c365da451","http://resolver.tudelft.nl/uuid:80150942-549b-449f-9dda-070c365da451","Quenching Mo optical losses in CIGS solar cells by a point contacted dual-layer dielectric spacer: A 3-D optical study","Rezaei, N. (TU Delft Photovoltaic Materials and Devices); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Vroon, Zeger (TNO/Solliance); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2018","A 3-D optical modelling was calibrated to calculate the light absorption and the total reflection of fabricated CIGS solar cells. Absorption losses at molybdenum (Mo) / CIGS interface were explained in terms of plasmonic waves. To quench these losses, we assumed the insertion of a lossless dielectric spacer between Mo and CIGS, whose optical properties were varied. We show that such a spacer with low refractive index and proper thickness can significantly reduce absorption in Mo in the long wavelength regime and improve the device’s rear reflectance, thus leading to enhanced light absorption in the CIGS layer. Therefore, we optimized a realistic two-layer MgF2 / Al2O3 dielectric spacer to exploit (i) the passivation properties of ultra-thin Al2O3 on the CIGS side for potential high open-circuit voltage and (ii) the low refractive index of MgF2 on the Mo side to reduce its optical losses. Combining our realistic spacer with optically-optimized point contacts increases the implied photocurrent density of a 750 nm-thick CIGS layer by 10% for the wavelengths between 700 and 1150 nm with respect to the reference cell. The elimination of plasmonic resonances in the new structure leads to a higher electric field magnitude at the bottom of CIGS layer and justifies the improved optical performance.","Photovoltaic; Thin films; optical properties; Surface plasmons","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:3fbba0fd-9d2b-465d-b5f9-707cae10656b","http://resolver.tudelft.nl/uuid:3fbba0fd-9d2b-465d-b5f9-707cae10656b","Evolution and role of vacancy clusters at grain boundaries of ZnO:Al during accelerated degradation of Cu(In, Ga)Se-2 solar cells revealed by positron annihilation","Shi, W. (TU Delft RST/Fundamental Aspects of Materials and Energy); Theelen, Mirjam (TNO); Illiberi, Andrea (TNO); van der Sar, S.J. (TU Delft Applied Sciences); Butterling, M. (TU Delft RST/Fundamental Aspects of Materials and Energy); Schut, H. (TU Delft RST/Neutron and Positron Methods in Materials); Zeman, M. (TU Delft Electrical Sustainable Energy); Brück, E.H. (TU Delft RST/Fundamental Aspects of Materials and Energy); Eijt, S.W.H. (TU Delft RST/Fundamental Aspects of Materials and Energy)","","2018","Positron annihilation lifetime spectroscopy (PALS) and Doppler broadening positron annihilation spectroscopy DB-PAS) depth profiling demonstrate pronounced growth of vacancy clusters at the grain boundaries of as-deposited Al-doped ZnO films deposited as transparent conductive oxide (TCO) on Cu(In, Ga)Se2 (CIGS) solar cells upon accelerated degradation at 85 ◦C/85% relative humidity. Quantitative fractions of positrons trapped either in the vacancy clusters at the grain boundaries or in Zn monovacancies inside the grains of ZnO:Al were obtained by detailed analysis of the PALS data using a positron trapping model. The time and depth dependence of the positron Doppler depth profiles can be accurately described using a planar diffusion model, with an extracted diffusion coefficient of 35 nm2/hour characteristic for in-diffusion of molecules such as H2O andCO2 into ZnO:Al TCO films via the grain boundaries, where they react with the ZnO:Al. This leads to increased open volume at the grain boundaries that imposes additional transport barriers and may lead to charge carrier trapping and nonradiative recombination. Simultaneously, a pronounced increase in series resistance and a strong reduction in efficiency of the ZnO:Al capped CIGS solar cells is observed on a remarkably similar timescale. This strongly indicates that these atomic-scale processes of molecular in-diffusion and creation of open volume at the grain boundaries play a key role in the degradation of the solar cells. PhySH: Solar Cells, Positron Annihilation Spectroscopy, Grain Boundaries, Vacancies, Thin Films, Diffusion, Electrical Properties, Solid State Chemistry, Optoelectronics","PhySH: Solar Cells; Positron Annihilation Spectroscopy; Grain Boundaries; Vacancies; Thin Films; Diffusion; Electrical Properties; Solid State Chemistry; Optoelectronics","en","journal article","","","","","","","","","Applied Sciences","Electrical Sustainable Energy","RST/Fundamental Aspects of Materials and Energy","","",""
"uuid:0f14b3c8-68c3-4c95-81c7-ba7cb93bba96","http://resolver.tudelft.nl/uuid:0f14b3c8-68c3-4c95-81c7-ba7cb93bba96","Distinguishing Fabry-Perot from guided resonances in thin periodically-textured silicon absorber","Ahmadpanahi, S.H. (TU Delft Photovoltaic Materials and Devices); Vismara, R. (TU Delft Photovoltaic Materials and Devices); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2018","Total electric field in a periodic thin-film structure is described by its Fourier coefficients. These coefficients can be used to calculate the share of different resonances in total absorption in the structure.","","en","conference paper","OSA - The Optical Society","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:fc0175a0-1dea-4823-aade-9a50d9b77bb4","http://resolver.tudelft.nl/uuid:fc0175a0-1dea-4823-aade-9a50d9b77bb4","Evolution and role of vacancy clusters at grain boundaries of ZnO:Al during accelerated degradation of Cu(In, Ga)Se2 solar cells revealed by positron annihilation","Shi, W. (TU Delft RST/Fundamental Aspects of Materials and Energy); Theelen, Mirjam (TNO/Solliance); Illiberi, Andrea (TNO/Solliance); van der Sar, S.J. (TU Delft RST/Medical Physics & Technology); Butterling, M. (TU Delft RST/Fundamental Aspects of Materials and Energy; TU Delft RST/Neutron and Positron Methods in Materials); Schut, H. (TU Delft RST/Neutron and Positron Methods in Materials); Zeman, M. (TU Delft Electrical Sustainable Energy); Brück, E.H. (TU Delft RST/Fundamental Aspects of Materials and Energy); Eijt, S.W.H. (TU Delft RST/Fundamental Aspects of Materials and Energy)","","2018","Positron annihilation lifetime spectroscopy (PALS) and Doppler broadening positron annihilation spectroscopy (DB-PAS) depth profiling demonstrate pronounced growth of vacancy clusters at the grain boundaries of as-deposited Al-doped ZnO films deposited as transparent conductive oxide (TCO) on Cu(In,Ga)Se2 (CIGS) solar cells upon accelerated degradation at 85∘C/85% relative humidity. Quantitative fractions of positrons trapped either in the vacancy clusters at the grain boundaries or in Zn monovacancies inside the grains of ZnO:Al were obtained by detailed analysis of the PALS data using a positron trapping model. The time and depth dependence of the positron Doppler depth profiles can be accurately described using a planar diffusion model, with an extracted diffusion coefficient of 35nm2/hour characteristic for in-diffusion of molecules such as H2O and CO2 into ZnO:Al TCO films via the grain boundaries, where they react with the ZnO:Al. This leads to increased open volume at the grain boundaries that imposes additional transport barriers and may lead to charge carrier trapping and nonradiative recombination. Simultaneously, a pronounced increase in series resistance and a strong reduction in efficiency of the ZnO:Al capped CIGS solar cells is observed on a remarkably similar timescale. This strongly indicates that these atomic-scale processes of molecular in-diffusion and creation of open volume at the grain boundaries play a key role in the degradation of the solar cells.","Solar Cells; Positron Annihilation Spectroscopy; Grain Boundaries; Vacancies; Thin Films; Diffusion; Electrical properties; Solid State Chemistry; Optoelectronics; PhySH:","en","journal article","","","","","","","","","","Electrical Sustainable Energy","RST/Fundamental Aspects of Materials and Energy","","",""
"uuid:6d12fafa-8b72-4573-949b-52204fe0cc6e","http://resolver.tudelft.nl/uuid:6d12fafa-8b72-4573-949b-52204fe0cc6e","An optical study of back contacted CIGS solar cells","Rezaei, N. (TU Delft Photovoltaic Materials and Devices); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Vroon, Zeger (Brightlands Materials Center); Zeman, M. (TU Delft Photovoltaic Materials and Devices; TU Delft Electrical Sustainable Energy)","","2018","An optical investigation of ultra-thin CIGS solar cells and guidelines for elimination of optical losses is presented. Then, a novel back contacted structure for CIGS solar cells is suggested and optimized for best implied photocurrent density.","","en","conference paper","OSA - The Optical Society","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:d5510f06-8797-4cde-9923-aad12d0edff1","http://resolver.tudelft.nl/uuid:d5510f06-8797-4cde-9923-aad12d0edff1","Selection map for PV module installation based on shading tolerability and temperature coefficient","Ziar, H. (TU Delft Photovoltaic Materials and Devices); Mishra, Sandeep (Student TU Delft); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2018","","","en","poster","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:77fab707-f091-406a-8c08-3b0abb970331","http://resolver.tudelft.nl/uuid:77fab707-f091-406a-8c08-3b0abb970331","Comprehensive approach to accurate Albedo modelling for solar engineering applications","Ziar, H. (TU Delft Photovoltaic Materials and Devices); Sönmez, Furkan Fatih; Isabella, O. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2018","","","en","poster","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:769a34e5-e8dc-4306-9914-0425caf11b95","http://resolver.tudelft.nl/uuid:769a34e5-e8dc-4306-9914-0425caf11b95","The Dutch PV Portal 2.0","Schepel, Veikko (Student TU Delft); Tozzi, Arianna (Student TU Delft); Ziar, H. (TU Delft Photovoltaic Materials and Devices); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2018","","","en","poster","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:6cddf1c4-24ce-45df-b6c7-cd461676eab7","http://resolver.tudelft.nl/uuid:6cddf1c4-24ce-45df-b6c7-cd461676eab7","Decoupled textures for broadband absorption enhancement beyond Lambertian light trapping limit in thin-film silicon-based solar cells","Vismara, R. (TU Delft Photovoltaic Materials and Devices); Dane Linssen, N. P. (Student TU Delft); Wang, Ken X. (Stanford University; Huazhong University of Science and Technology); Fan, Shanhui (Stanford University); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy)","Freundlich, Alex (editor); Topic, Marko (editor); Yamada, Akira (editor)","2018","We present a modelling study of thin silicon based solar cells endowed with periodic and decoupled front/back textures. After careful optimization, the proposed device models exhibit absorption beyond the Lambertian light trapping limit for a wide range of light angles of incidence. The advanced light management scheme is applied to (nano)crystalline silicon solar cells, where the benefits of texturing the absorber rather than the supporting layers is clear and to barium (di)silicide solar cells, which could achieve an implied photocurrent densityof41.1 mA/cm2 for a thickness of only 2 \mum.","barium silicide; Lambertian scattering; light trapping; nano-crystalline silicon; periodic gratings; thin-film silicon","en","conference paper","Institute of Electrical and Electronics Engineers (IEEE)","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:de32adb4-a4a5-45a9-89da-7d37378be078","http://resolver.tudelft.nl/uuid:de32adb4-a4a5-45a9-89da-7d37378be078","The Need for a New Parameter on PV Modules Datasheet: Shading Tolerability","Ziar, H. (TU Delft Photovoltaic Materials and Devices); Mishra, Sandeep (Student TU Delft); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy)","Freundlich, Alex (editor); Topic, Marko (editor); Yamada, Akira (editor)","2018","This paper suggests a measurable parameter, the so-called Shading Tolerability (ST), to be added on PV modules datasheet. Using this parameter, PV modules can be compared and classified regarding the ability to oppose shading effects. The parameter is extracted based on mathematical and probability analysis, then measured using a Large Area Steady State Solar (LASSS) simulator. Outdoor measurements proved a correlation between ST and Performance Ratio (PR) of PV modules. ST was also found to be independent of the ambient temperature, which indicates that it is a characteristic parameter of a PV module. Finally, a selection map for PV module installation at different climate conditions based on ST and temperature coefficient for maximum power (\gamma)is presented.","partial shading; Photovoltaic (PV) module; selection map; shading tolerability (ST); temperature coefficient","en","conference paper","Institute of Electrical and Electronics Engineers (IEEE)","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:bc66f5e5-dd4f-4cbb-9988-5d3ebd5d5630","http://resolver.tudelft.nl/uuid:bc66f5e5-dd4f-4cbb-9988-5d3ebd5d5630","Improving the Back Surface Field on an Amorphous Silicon Carbide Thin Film Photocathode for Solar Water Splitting","Perez Rodriguez, P. (TU Delft Photovoltaic Materials and Devices); Cardenas-Morcoso, Drialys (Universitat Jaume I); Digdaya, I.A. (TU Delft ChemE/Materials for Energy Conversion and Storage); Mangel Raventos, A. (TU Delft Photovoltaic Materials and Devices); Procel Moya, P.A. (TU Delft Photovoltaic Materials and Devices); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Gimenez, Sixto (Universitat Jaume I); Zeman, M. (TU Delft Electrical Sustainable Energy); Smith, W.A. (TU Delft ChemE/Materials for Energy Conversion and Storage); Smets, A.H.M. (TU Delft Photovoltaic Materials and Devices)","","2018","Amorphous silicon carbide (a-SiC:H) is a promising material for photoelectrochemical water splitting owing to its relatively small band-gap energy and high chemical and optoelectrical stability. This work studies the interplay between charge-carrier separation and collection, and their injection into the electrolyte, when modifying the semiconductor/electrolyte interface. By introducing an n-doped nanocrystaline silicon oxide layer into a p-doped/intrinsic a-SiC:H photocathode, the photovoltage and photocurrent of the device can be significantly improved, reaching values higher than 0.8V. This results from enhancing the internal electric field of the photocathode, reducing the Shockley-Read-Hall recombination at the crucial interfaces because of better charge-carrier separation. In addition, the charge-carrier injection into the electrolyte is enhanced by introducing a TiO2 protective layer owing to better band alignment at the interface. Finally, the photocurrent was further enhanced by tuning the absorber layer thickness, arriving at a thickness of 150nm, after which the current saturates to 10mAcm-2 at 0V vs. the reversible hydrogen electrode in a 0.2m aqueous potassium hydrogen phthalate (KPH) electrolyte at pH4.","Charge carrier injection; Hydrogen; Silicon carbide; Titanium dioxide; Water splitting","en","journal article","","","","","","Accepted Author Manuscript","","2019-04-25","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:a36fdf28-a85f-4a2a-8ef3-f2064bdbc419","http://resolver.tudelft.nl/uuid:a36fdf28-a85f-4a2a-8ef3-f2064bdbc419","Poly-crystalline silicon-oxide films as carrier-selective passivating contacts for c-Si solar cells","Yang, G. (TU Delft Photovoltaic Materials and Devices); Guo, Peiqing (Student TU Delft); Procel Moya, P.A. (TU Delft Photovoltaic Materials and Devices); Weeber, A.W. (TU Delft Photovoltaic Materials and Devices; ECN, Petten); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2018","The poly-Si carrier-selective passivating contacts (CSPCs) parasitically absorb a substantial amount of light, especially in the form of free carrier absorption. To minimize these losses, we developed CSPCs based on oxygen-alloyed poly-Si (poly-SiOx) and deployed them in c-Si solar cells. Transmission electron microscopy analysis indicates the presence of nanometer-scale silicon crystals within such poly-SiOx layers. By varying the O content during material deposition, we can manipulate the crystallinity of the poly-SiOx material and its absorption coefficient. Also, depending on the O content, the bandgap of the poly-SiOx material can be widened, making it transparent for longer wavelength light. Thus, we optimized the O alloying, doping, annealing, and hydrogenation conditions. As a result, an extremely high passivation quality for both n-type poly-SiOx (J0 = 3.0 fA/cm2 and iVoc = 740 mV) and p-type poly-SiOx (J0 = 17.0 fA/cm2 and iVoc = 700 mV) is obtained. A fill factor of 83.5% is measured in front/back-contacted solar cells with both polarities made up of poly-SiOx. This indicates that the carrier transport through the junction between poly-SiOx and c-Si is sufficiently efficient. To demonstrate the merit of poly-SiOx layers' high transparency at long wavelengths, they are deployed at the back side of interdigitated back-contacted (IBC) solar cells. A preliminary cell efficiency of 19.7% is obtained with much room for further improvement. Compared to an IBC solar cell with poly-Si CSPCs, a higher internal quantum efficiency at long wavelengths is observed for the IBC solar cell with poly-SiOx CSPCs, thus demonstrating the potential of poly-SiOx in enabling higher JSC.","","en","journal article","","","","","","Accepted Author Manuscript","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:9c8d745a-4ca4-446e-8458-651f0c249ea0","http://resolver.tudelft.nl/uuid:9c8d745a-4ca4-446e-8458-651f0c249ea0","Advanced light management techniques for two-terminal hybrid tandem solar cells","Blanker, A.J. (TU Delft Photovoltaic Materials and Devices); Berendsen, P.P.A. (TU Delft Photovoltaic Materials and Devices); Phung, N. (External organisation); Vroon, Z.E.A.P. (TNO/Solliance); Zeman, M. (TU Delft Electrical Sustainable Energy); Smets, A.H.M. (TU Delft Photovoltaic Materials and Devices)","","2018","Multi-junction solar cells are considered for various applications, as they tackle various loss mechanisms for single junction solar cells. These losses include thermalization and non-absorption below the band gap. In this work, a tandem configuration comprising copper-indium-gallium-di-selenide (CIGS) and hydrogenated amorphous silicon (a-Si:H) absorber layers is studied. Two main challenges are addressed in this work. Firstly, the natural roughness of CIGS is unfavorable for monolithically growing a high quality a-Si:H top cell. Some sharp textures in the CIGS induce shunts in the a-Si:H top junction, limiting the electrical performance of such a configuration. To smoothen this interface, the possibility of mechanically polishing the intermediate i-ZnO layer has been explored. The second challenge that is addressed, is the significant current mismatch in these tandem architectures. To enhance absorption in the current-limiting top cell, the ZnO:Al front electrode was textured by means of wet-etching the entire tandem stack. We demonstrated that one can manipulate the morphology of the random textures by varying the growth conditions of the ZnO:Al, leading to better light management in these devices.","Amorphous silicon; CIGS; Light management; Polishing; Texturing; Two-terminal tandem cells","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:e3d4408c-72a0-48f4-ae58-5f7f2898ff45","http://resolver.tudelft.nl/uuid:e3d4408c-72a0-48f4-ae58-5f7f2898ff45","Maximizing annual yield of bifacial photovoltaic noise barriers","Faturrochman, G.J. (Solar Energy Application Centre); de Jong, M.M. (Solar Energy Application Centre); Santbergen, R. (TU Delft Photovoltaic Materials and Devices); Folkerts, W. (Solar Energy Application Centre); Zeman, M. (TU Delft Electrical Sustainable Energy); Smets, A.H.M. (TU Delft Photovoltaic Materials and Devices)","","2018","In this work we consider noise barriers with integrated photovoltaic modules. The novelty is that bifacial modules are considered. A full scale bifacial photovoltaic noise barrier was built and its power output was monitored. In addition we developed an advanced numerical model for predicting this power output for given weather conditions. Excellent agreement was found between the measured power output and the model prediction. Next we used this model to demonstrate the effects of the orientation, tilt, location, cell position and bypass-diode configuration on the annual energy yield of bifacial photovoltaic noise barriers.","Annual energy yield; Bifacial; BIPV; Noise barrier; Photovoltaic","en","journal article","","","","","","","","2020-02-13","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:ea55ccaf-b8c4-47dc-80fa-8654164144d0","http://resolver.tudelft.nl/uuid:ea55ccaf-b8c4-47dc-80fa-8654164144d0","High-efficiency black IBC c-Si solar cells with poly-Si as carrier-selective passivating contacts","Yang, G. (TU Delft Photovoltaic Materials and Devices); Guo, Peiqing (Student TU Delft); Procel Moya, P.A. (TU Delft Photovoltaic Materials and Devices); Limodio, G. (TU Delft Photovoltaic Materials and Devices); Weeber, A.W. (TU Delft Photovoltaic Materials and Devices; ECN Solar Energy); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2018","In this work, we present the application of poly-Si carrier-selective passivating contacts (CSPCs) as both polarities in interdigitated back-contacted (IBC) solar cell architectures. We compared two approaches to form a gap between the back-surface field (BSF) and emitter fingers. It is proved that the gaps prepared by both approaches are efficient in preventing carriers’ recombination. To minimize the reflection losses, we developed a novel modulated surface texturing (MST) structure as anti-reflection coating (ARC). It is obtained by superposing a nano-textured SiO2 layer on the conventional micro-textured pyramids, which are passivated with a-Si:H / SiNx:H layers. This approach decouples the light harvesting from the Si surface passivation, which potentially results in the highest possible optical and electrical performances of the solar cells. The reflectance (R) of the MST-ARC is very close to that of the high-aspect ratio nano-structured silicon (black-Silicon), achieving R < 1% between 450 and 1000 nm. The J0 of MST-ARC passivated Si surface (6.3 fA/cm2) is the same as that of standard a-Si:H/SiNx:H layers passivated pyramidally-textured Si surface. By applying this novel MST-ARC in our IBC solar cell, the highest JSC observed in a device is 42.2 mA/cm2 with a VOC as high as 701 mV. A spectral response enhancement in case of the MST-ARC cell is observed over the whole wavelength range with respect to the cell with standard SiNx:H ARC. The highest efficiency achieved in this work is 23.0%, with the potential to reach 24.0% in short term by using more conductive metal fingers.","Carrier selective passivating contact; IBC c-Si solar cells; Light in-coupling; Poly-silicon","en","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:98c7e658-2d10-415d-ada2-ae205777da33","http://resolver.tudelft.nl/uuid:98c7e658-2d10-415d-ada2-ae205777da33","Theoretical evaluation of contact stack for high efficiency IBC-SHJ solar cells","Procel Moya, P.A. (TU Delft Photovoltaic Materials and Devices); Yang, G. (TU Delft Photovoltaic Materials and Devices); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2018","In this work we present a theoretical analysis of charge carriers transport mechanisms in IBC-SHJ solar cells. The concepts of contact and transport selectivity are correlated through the band bending at c-Si interface and are used to identify thin-film silicon parameters affecting fill factor (FF) and open-circuit voltage (VOC). Additionally, the transport of carriers is associated to energy barriers at the conduction band for electrons and at the valence band for holes. In case of p-type contact, the transport of holes is mainly affected by activation energy and band gap of the p-type layer and work function of the TCO. In case of n-type contact, the activation energy and work function of the doped layer impact the most on transport of electrons. Selective transport is improved by maximizing the collection of majority carrier in each doped contact stack while blocking minority carriers. In particular, low activation energy values of doped layers are crucial to minimize energy barriers for majority carriers and increase the band bending at c-Si interface. Simulation results based on TCAD Sentaurus reveal that the FF increases as the activation energy of the doped layers is reduced. Also, for the p-type contact, the bandgap of p-type layer strongly affects the band bending at c-Si interface. Particularly, widening the bandgap of p-type layer enhances passivation and transport in terms of VOC and FF but work function mismatch between the p-type layer and the related transparent conductive oxide (TCO) strongly increases as bandgap increases. This possibly makes the device less performant because it is more sensitive to activation energy of the p-layer in combination with the choice of the proper TCO. Considering realistic deposited layers, a wide bandgap p-type layer, in combination with low activation energy, potentially improves hole collection leading to maximal simulated FF = 86.8% and VOC = 754 mV for a conversion efficiency η = 27.2%.","Fill Factor and passivation; IBC silicon heterojunction solar cell; Numerical simulations; Thin film silicon alloys; Transport mechanisms","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:e1ff3160-1158-4bad-8e5d-23b740237c7f","http://resolver.tudelft.nl/uuid:e1ff3160-1158-4bad-8e5d-23b740237c7f","Estimating battery lifetimes in Solar Home System design using a practical modelling methodology","Narayan, N.S. (TU Delft DC systems, Energy conversion & Storage); Papakosta, Thekla (Student TU Delft); Vega Garita, V.E. (TU Delft DC systems, Energy conversion & Storage); Qin, Z. (TU Delft DC systems, Energy conversion & Storage); Popovic, J. (TU Delft DC systems, Energy conversion & Storage); Bauer, P. (TU Delft DC systems, Energy conversion & Storage); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2018","The rapid increase in the adoption of Solar Home Systems (SHS) in recent times hopes to ameliorate the global problem of energy poverty. The battery is a vital but usually the most expensive part of an SHS; owing to the least lifetime among other SHS components, it is also the first to fail. Estimating battery lifetime is a critical task for SHS design. However, it is also a complex task due to the reliance on experimental data or modelling cell level electrochemical phenomena for specific battery technologies and application use-case. Another challenge is that the existing electrochemical models are not application-specific to Solar Home Systems. This paper presents a practical, non-empirical battery lifetime estimation methodology specific to the application and the available candidate battery choices. An application-specific SHS simulation is carried out, and the battery activity is analyzed. A practical dynamic battery lifetime estimation method is introduced, which captures the fading capacity of the battery dynamically through every micro-cycle. This method was compared with an overall non-empirical battery lifetime estimation method, and the dynamic lifetime estimation method was found to be more conservative but practical. Cyclic ageing of the battery was thus quantified and the relative lifetimes of 4 battery technologies are compared, viz. Lead-acid gel, Flooded lead-acid, Nickel-Cadmium (NiCd), and Lithium Iron Phosphate (LiFePO4) battery. For the same SHS use-case, State-of-Health (SOH) estimations from an empirical model for LiFePO4 is compared with those obtained from the described methodology, and the results are found to be within 2.8%. The relevance of this work in an SHS application is demonstrated through a delicate balance between battery sizing and lifetime. Based on the intended application and battery manufacturer's data, the practical methodology described in this paper can potentially help SHS designers in estimating battery lifetimes and therefore making optimal SHS design choices.","Battery lifetime model; Battery sizing; Cyclic ageing; Dynamic battery lifetime estimation; Solar Home Systems","en","journal article","","","","","","","","","","Electrical Sustainable Energy","DC systems, Energy conversion & Storage","","",""
"uuid:97a8d929-886d-4ea5-b90b-64921c250946","http://resolver.tudelft.nl/uuid:97a8d929-886d-4ea5-b90b-64921c250946","Effects of amorphous Si capping layer on sputtered BaSi2 film properties","Tian, Y. (TU Delft Photovoltaic Materials and Devices); Bento Montes, A.R. (TU Delft Photovoltaic Materials and Devices); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy)","Donoval, Daniel (editor); Breza, Juraj (editor); Vavrinsky, Erik (editor)","2018","Regarded as a promising absorber material for solar cell applications, Barium disilicide (BaSi2) is still confronted with issues related to surface oxidation. Here, we use a-Si.H deposited by plasma-enhanced chemical vapor deposition as capping layer to prevent surface oxidation of sputtered BaSi2 films. Based on crystalline quality and optical properties characterizations, thin a-Si.H capping cannot sufficiently prevent surface oxidation. Conversely, oxidation of a-Si.H layer in turn promotes Ba diffusion and Si isolation. Applying a thicker a-Si.H capping layer (more than 20 nm) can suppress such effect. The multi-materials capping layer can also be regarded as potential strategy to prevent surface oxidation of BaSi2.","","en","conference paper","Institute of Electrical and Electronics Engineers (IEEE)","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:22e524c8-3d23-4a87-a9db-9044853d7a7d","http://resolver.tudelft.nl/uuid:22e524c8-3d23-4a87-a9db-9044853d7a7d","Quantification of Shading Tolerability for Photovoltaic Modules","Ziar, H. (TU Delft Photovoltaic Materials and Devices; University of Tehran); Asaei, Behzad (University of Tehran); Farhangi, Shahrokh (University of Tehran); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Korevaar, M.A.N. (Kipp & Zonen); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2017","Despite several decades of research in the field of photovoltaic (PV) systems, shading tolerance has still not been properly addressed. PV modules are influenced by shading concerning many factors, such as number and configuration of cells in the module, electrical and thermal characteristics of the cells, number and type of bypass circuits, electrical characteristics of bypass elements, and shading profile features. Along with the random nature of shading profile over the lifetime of a PV system, it is difficult to choose the best module for a location which is most of the time sunny, partly cloudy, or cloudy. This paper suggests a measurable parameter, the so-called shading tolerability (ST), to classify PV modules regarding the ability to oppose shading effects. Based on mathematical and probability analysis, the ST parameter is extracted and then measured using a large area steady state solar simulator. Finally, the results of on-field experiments are presented as a proof for the shading quantification method and its significant contribution to performance ratio improvement.","Bypass diode; maximum power point tracking (MPPT); partial shading; performance ratio (PR); photovoltaic (PV) technology","en","journal article","","","","","","Accepted Author Manuscript","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:fcea6bff-8764-4c2c-acbf-5c07bab643e5","http://resolver.tudelft.nl/uuid:fcea6bff-8764-4c2c-acbf-5c07bab643e5","Design and comparison of a 10-kW interleaved boost converter for PV application using Si and SiC devices","Chandra Mouli, G.R. (TU Delft DC systems, Energy conversion & Storage); Schijffelen, Jos H. (Power Research Electronics BV); Bauer, P. (TU Delft DC systems, Energy conversion & Storage); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2017","Grid-connected photovoltaic (PV) inverters have a dc/dc converter connected to the PV for executing the maximum power point tracking. The design of an interleaved boost converter (IBC) with three switching legs for a 10-kW PV inverter is presented in this paper. This paper shows how the use of silicon carbide (SiC) switches and powdered iron core inductors enables the operation of the converter at a higher switching frequency and when increasing the converter power density. The IBC is designed using a 1.2-kV SiC MOSFET and Schottky diodes and Kool Mμ powdered iron inductors. The design is compared with an IBC built with a silicon (Si) IGBT, fast recovery Si diodes, and ferrite cores. The use of SiC devices reduces the switching loses drastically and there are no reverse recovery losses, resulting in improved efficiency. The higher frequency and higher saturation flux density of the powdered iron core enable the reduction in core size by three times. A 10-kW prototype is built and tested for both the Si and SiC designs and compared with theoretical estimations.","Interleaved boost converter (IBC); Photovoltaic (PV) systems; Powered iron core; Silicon carbide (SiC)","en","journal article","","","","","","Accepted Author Manuscript","","","","Electrical Sustainable Energy","DC systems, Energy conversion & Storage","","",""
"uuid:65eb8f3f-d6c7-4e86-b9a5-0cb1727a6ae0","http://resolver.tudelft.nl/uuid:65eb8f3f-d6c7-4e86-b9a5-0cb1727a6ae0","Understanding the Present and the Future Electricity Needs: Consequences for Design of Future Solar Home Systems for Off-Grid Rural Electrification","den Heeten, Thomas (External organisation); Narayan, N.S. (TU Delft DC systems, Energy conversion & Storage); Diehl, J.C. (TU Delft Design for Sustainability); Verschelling, Jeroen (Kamworks Ltd.); Silvester, S. (TU Delft Applied Ergonomics and Design); Popovic, J. (TU Delft DC systems, Energy conversion & Storage); Bauer, P. (TU Delft DC systems, Energy conversion & Storage); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2017","Solar Home Systems (SHSs) can fulfil the basic energy needs of the globally unelectrified population. With costs as one of the biggest barriers for SHS uptake, optimizing the system size with energy needs is crucial. Where most solutions focus only on the present needs, this work also addresses the future energy needs. The methodology includes extensive mapping of the current electricity needs in rural Cambodia through data analysis on existing SHSs in the field. Additionally, a 2-month field research was carried out in Cambodia to assess the qualitative state of electricity usage and investigate the future (2021) energy needs. A data analysis was performed on 111 SHSs (100 Wp, 1200 Wh).
SHS users were found to have a mean energy consumption of 310 Wh/day, with σ = 159 Wh. Most energy was consumed at night. The field research showed a clear demand for more energy and more appliances. The appliances attached to SHS in the future will be more diverse in power consumption and usage duration, resulting in a wide variety of energy consumption and high power peaks, causing fast and deep battery discharges. Three load profiles are presented. Solutions are discussed that can be applied to ensure the SHSs fit with future energy needs.","energy consumption; energy matching; load profile; low-income countries; solar home system; rural electrification","en","conference paper","Cape Peninsula University of Technology","","","","","","","","","Electrical Sustainable Energy","DC systems, Energy conversion & Storage","","",""
"uuid:5aca51b4-4506-4859-9102-fbc9932a0d5d","http://resolver.tudelft.nl/uuid:5aca51b4-4506-4859-9102-fbc9932a0d5d","Electron tomography analysis of 3D interfacial nanostructures appearing in annealed Si rich SiC films","Xie, L (Uppsala University); Jarolímek, K. (TU Delft Photovoltaic Materials and Devices); Kocevski, V. (Uppsala University); Rusz, J. (Uppsala University); Zeman, M. (TU Delft Electrical Sustainable Energy); van Swaaij, R.A.C.M.M. (TU Delft Photovoltaic Materials and Devices); Leifer, K (Uppsala University)","","2017","The optical and electrical properties of Si rich SiC (SRSC) solar cell absorber layers will strongly depend on interfacial layers between the Si and the SiC matrix and in this work, we analyze hitherto undiscovered interfacial layers. The SRSC thin films were deposited using a plasma-enhanced chemical vapor deposition (PECVD) technique and annealed in a nitrogen environment at 1100 °C. The thermal treatment leads to metastable SRSC films spinodally decomposed into a Si–SiC nanocomposite. After the thermal treatment, the coexistence of crystalline Si and SiC nanostructures was analysed by high resolution transmission electron microscopy (HRTEM) and electron diffraction. From the quantitative extraction of the different plasmon signals from electron energy-loss spectra, an additional structure, amorphous SiC (a-SiC) was found. Quantitative spectroscopic electron tomography was developed to obtain three dimensional (3D) plasmonic maps. In these 3D spectroscopic maps, the Si regions appear as network structures inside the SiC matrix where the a-SiC appears as an interfacial layer separating the matrix and Si network. The presence of the a-SiC interface can be explained in the framework of the nucleation and growth model.","","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:9806e6e3-6c62-4782-947a-c1caa8791ab4","http://resolver.tudelft.nl/uuid:9806e6e3-6c62-4782-947a-c1caa8791ab4","Thin-film amorphous silicon germanium solar cells with p-and n-type hydrogenated silicon oxide layers","Si, F.T. (TU Delft Photovoltaic Materials and Devices); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2017","Mixed-phase hydrogenated silicon oxide (SiOx:H) is applied to thin-film hydrogenated amorphous silicon germanium (a-SiGe:H) solar cells serving as both p-doped and n-doped layers. The bandgap of p-SiOx:H is adjusted to achieve a highly-transparent window layer while also providing a strong electric field. Bandgap grading of n-SiOx:H is designed to obtain a smooth transition of the energy band edge from the intrinsic to n-doped layer, without the need of an amorphous buffer layer. With the optimized optical and electrical structure, a high conversion efficiency of 9.41% has been achieved. Having eliminated other doped materials without sacrificing performance, the sole use of SiOx:H in the doped layers of a-SiGe:H cells opens up great flexibility in the design of high-efficiency multi-junction thin-film silicon-based solar cells.","Hydrogenated amorphous silicon germanium; Hydrogenated silicon oxide; Light management; Parasitic losses","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:a7603bb2-0be8-4b32-af92-a3c7f85f253f","http://resolver.tudelft.nl/uuid:a7603bb2-0be8-4b32-af92-a3c7f85f253f","Migration of Open Volume Deficiencies in Hydrogenated Amorphous Silicon during Annealing","Melskens, J. (TU Delft Photovoltaic Materials and Devices; Eindhoven University of Technology); Eijt, S.W.H. (TU Delft RST/Fundamental Aspects of Materials and Energy); Schouten, M. (TU Delft Photovoltaic Materials and Devices); Vullers, A.S. (TU Delft Photovoltaic Materials and Devices; TU Delft RST/Fundamental Aspects of Materials and Energy); Mannheim, Awital (External organisation); Schut, H. (TU Delft RST/Neutron and Positron Methods in Materials); Macco, Bart (Eindhoven University of Technology); Zeman, M. (TU Delft Photovoltaic Materials and Devices; TU Delft Electrical Sustainable Energy); Smets, A.H.M. (TU Delft Photovoltaic Materials and Devices)","","2017","The nanostructure of hydrogenated amorphous silicon (a-Si:H) is studied by means of doppler broadening positron annihilation spectroscopy (DB-PAS) and Fourier transform infrared (FTIR) spectroscopy. The evolution of open volume deficiencies is monitored during annealing, demonstrating that small vacancies and other small vacancy clusters that are initially present in the a-Si:H nanostructure agglomerate into larger vacancy clusters. The migration of open volume deficiencies is less pronounced for a-Si:H deposited at higher hydrogen-to-silane gas flow rate ratio, R. FTIR spectroscopy reveals the presence of a peculiar peak in the refractive index in the infrared - and hence the calculated mass density - which occurs just before H effusion from the films starts. The combined results of DB-PAS and FTIR spectroscopy indicate that a stress buildup caused by the accumulation of H2 in agglomerating vacancies during annealing can explain the sudden mass density increase. At higher temperatures, stress is released with the onset of H effusion. The H effusion consists of a two-stage process involving small open volume deficiencies and nanosized voids, contrasting earlier interpretations. The reduced amount of hydrogen migration and enhanced hydrogen passivation degree are suggested as key factors to the reduced light-induced degradation associated with increased R values.","Annealing; defects; hydrogenated amorphous silicon (a-Si:H); nanostructure; vacancies","en","journal article","","","","","","Accepted Author Manuscript","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:582bd686-c970-45d4-a2a0-e2d56dacd42b","http://resolver.tudelft.nl/uuid:582bd686-c970-45d4-a2a0-e2d56dacd42b","New insights into the nanostructure of innovative thin film solar cells gained by positron annihilation spectroscopy","Eijt, S.W.H. (TU Delft RST/Fundamental Aspects of Materials and Energy); Shi, W. (TU Delft RST/Fundamental Aspects of Materials and Energy); Mannheim, A.; Butterling, M. (TU Delft RST/Fundamental Aspects of Materials and Energy); Schut, H. (TU Delft RST/Neutron and Positron Methods in Materials); Egger, W (Universität der Bundeswehr München); Dickmann, M. (Universität der Bundeswehr München); Hugenschmidt, C (Technische Universität München); Shakeri, B. (University of Maine); Meulenberg, R.W. (University of Maine); Callewaert, V. (Universiteit Antwerpen); Saniz, R (Universiteit Antwerpen); Partoens, B (Universiteit Antwerpen); Barbiellini, B (Northeastern University); Bansil, A (Northeastern University); Melskens, J. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy); Smets, A.H.M. (TU Delft Photovoltaic Materials and Devices); Kulbak, M. (Weizmann Institute of Science); Hodes, G. (Weizmann Institute of Science); Cahen, D. (Weizmann Institute of Science); Brück, E.H. (TU Delft RST/Fundamental Aspects of Materials and Energy)","","2017","Recent studies showed that positron annihilation methods can provide key insights into the nanostructure and electronic structure of thin film solar cells. In this study, positron annihilation lifetime spectroscopy (PALS) is applied to investigate CdSe quantum dot (QD) light absorbing layers, providing evidence of positron trapping at the surfaces of the QDs. This enables one to monitor their surface composition and electronic structure. Further, 2D-Angular Correlation of Annihilation Radiation (2D-ACAR) is used to investigate the nanostructure of divacancies in photovoltaic-high-quality a-Si:H films. The collected momentum distributions were converted by Fourier transformation to the direct space representation of the electron-positron autocorrelation function. The evolution of the size of the divacancies as a function of hydrogen dilution during deposition of a-Si:H thin films was examined. Finally, we present a first positron Doppler Broadening of Annihilation Radiation (DBAR) study of the emerging class of highly efficient thin film solar cells based on perovskites.","","en","journal article","","","","","","","","","","Electrical Sustainable Energy","RST/Fundamental Aspects of Materials and Energy","","",""
"uuid:7440b130-533f-4627-b577-9a40a4350dea","http://resolver.tudelft.nl/uuid:7440b130-533f-4627-b577-9a40a4350dea","Surface passivation of n -type doped black silicon by atomic-layer-deposited SiO2/Al2O3 stacks","van de Loo, B.W.H. (Eindhoven University of Technology); Ingenito, A. (TU Delft Photovoltaic Materials and Devices); Verheijen, M.P.A.M. (Eindhoven University of Technology); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy); Kessels, W. M.M. (Eindhoven University of Technology)","","2017","Black silicon (b-Si) nanotextures can significantly enhance the light absorption of crystalline silicon solar cells. Nevertheless, for a successful application of b-Si textures in industrially relevant solar cell architectures, it is imperative that charge-carrier recombination at particularly highly n-type doped black Si surfaces is further suppressed. In this work, this issue is addressed through systematically studying lowly and highly doped b-Si surfaces, which are passivated by atomic-layer-deposited Al2O3 films or SiO2/Al2O3 stacks. In lowly doped b-Si textures, a very low surface recombination prefactor of 16 fA/cm2 was found after surface passivation by Al2O3. The excellent passivation was achieved after a dedicated wet-chemical treatment prior to surface passivation, which removed structural defects which resided below the b-Si surface. On highly n-type doped b-Si, the SiO2/Al2O3 stacks result in a considerable improvement in surface passivation compared to the Al2O3 single layers. The atomic-layer-deposited SiO2/Al2O3 stacks therefore provide a low-temperature, industrially viable passivation method, enabling the application of highly n- type doped b-Si nanotextures in industrial silicon solar cells.","","en","journal article","","","","","","","","2018-06-01","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:4be2157b-7c9c-4f84-a4e1-02039aa94ea6","http://resolver.tudelft.nl/uuid:4be2157b-7c9c-4f84-a4e1-02039aa94ea6","Back-contacted BaSi2 solar cells: An optical study","Vismara, R. (TU Delft Photovoltaic Materials and Devices); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2017","We present the optical investigation of a novel back-contacted architecture for solar cells based on a thin barium (di)silicide (BaSi2) absorber. First, through the analysis of absorption limits of different semiconducting materials, we show the potential of BaSi2 for photovoltaic applications. Then, the proposed back contacted BaSi2 solar cell design is investigated and optimized. An implied photocurrent density of 40.3 mA/cm2 in a 1-μm thick absorber was achieved, paving the way for novel BaSi2-based thin-film solar cells.","Photovoltaic; Diffraction gratings; Bragg reflectors; Solar energy","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:eb705425-f20e-408a-97a4-b9d5e8ee4b98","http://resolver.tudelft.nl/uuid:eb705425-f20e-408a-97a4-b9d5e8ee4b98","GenPro4 Optical Model for Solar Cell Simulation and Its Application to Multijunction Solar Cells","Santbergen, R. (TU Delft Photovoltaic Materials and Devices); Meguro, Tomomi (Kaneka Corporation); Suezaki, Takashi (Kaneka Corporation); Koizumi, Gensuke (Kaneka Corporation); Yamamoto, Kenji (Kaneka Corporation); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2017","We present a new version of our optical model for solar cell simulation: GenPro4. Its working principles are briefly explained. The model is suitable for quickly and accurately simulating a wide range of wafer-based and thin-film solar cells. Especially adjusting layer thicknesses to match the currents in multijunction devices can be done with a minimum of computational cost. To illustrate this, a triple junction thin-film silicon solar cell is simulated. The simulation results show very good agreement with external quantum efficiency measurements. The application of an MgF2 antireflective coating or an antireflective foil with pyramid texture is considered. Their effects on the implied photocurrents of top, middle, and bottom cells are investigated in detail.","Geometrical optics; modeling; thin film PV device properties and modeling","en","journal article","","","","","","Accepted author manuscript","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:fb3b02cb-216e-40be-a1d7-6ba8504e5120","http://resolver.tudelft.nl/uuid:fb3b02cb-216e-40be-a1d7-6ba8504e5120","Charging Electric Vehicles from Solar Energy: Integrated Converter and Charging Algorithms","Chandra Mouli, G.R. (TU Delft DC systems, Energy conversion & Storage); Van Der Meer, Dennis (External organisation); Bauer, P. (TU Delft DC systems, Energy conversion & Storage); Zeman, M. (TU Delft Electrical Sustainable Energy); Schijffelen, Jos H. (Power Research Electronics BV); van den Heuvel, Mike (Power Research Electronics BV); Kardolus, Menno (Power Research Electronics BV)","","2017","","Electric vehicles; PV system; EV charging; silicon carbide; smart charging; solar energy; MILP","en","abstract","","","","","","","","","","Electrical Sustainable Energy","DC systems, Energy conversion & Storage","","",""
"uuid:2769099a-7cb4-4eeb-bf07-0e9681a4ffbe","http://resolver.tudelft.nl/uuid:2769099a-7cb4-4eeb-bf07-0e9681a4ffbe","Too Many Junctions?: A Case Study of Multijunction Thin-Film Silicon Solar Cells","Si, F.T. (TU Delft Photovoltaic Materials and Devices); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2017","The benefit of two-terminal multijunction solar cells in regard to the number
of junctions (subcells) is critically evaluated. The optical and electrical losses
inherent in the construction of multijunction cells are analyzed using information
from thin-film silicon photovoltaics as a representative case. Although
the multijunction approach generally reduces the thermalization and nonabsorption losses, several types of losses rise with the number of subcells.
Optical reflection and parasitic absorption are slightly increased by adding
supporting layers and interfaces. The output voltages decline because of the
tunnel recombination junctions, and more importantly of the illumination
filtered and reduced by the top subcell(s). The loss mechanisms consume
the potential gains in efficiency of multijunction cells. For thin-film silicon,
the triple-junction is confirmed to be the best performing structure. More
generally, only when each component subcell shows a high ratio between the
output voltage and the bandgap of the absorber material, a multijunction cell
with a large number of subcells can be beneficial. Finally, the high voltage
and low current density of multijunction cells with a large number of subcells
make them difficult to optimize and manufacture, vulnerable to any changes
in the solar spectrum, and thus less practical for the ordinary terrestrial
applications.","Loss analysis; multijunction solar cells; photovoltaic cells; thin-film silicon; two-terminal monolithic cells","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:38b5c23c-a349-4624-b7a3-e6ce98175c84","http://resolver.tudelft.nl/uuid:38b5c23c-a349-4624-b7a3-e6ce98175c84","Quadruple-Junction Thin-Film Silicon Solar Cells Using Four Different Absorber Materials","Si, F.T. (TU Delft Photovoltaic Materials and Devices); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy); Tan, H. (TU Delft Photovoltaic Materials and Devices)","","2017","We fabricated and studied quadruple-junction wide-gap a-Si:H/narrow-gap a-Si:H/a-SiGex:H/nc-Si:H thin-film silicon solar cells. It is among the first attempts in thin-film photovoltaics to make a two-terminal solar cell with four different absorber materials. Several tunnel recombination junctions were tested, and the n-SiOx:H/p-SiOx:H structure was proven to be a generic solution for the three pairs of neighboring subcells. The proposed combination of absorbers led to a more reasonable spectral utilization than the counterpart containing two nc-Si:H subcells. Besides, the use of high-mobility transparent conductive oxide and modulated surface texture significantly enhances the total light absorption in the absorber layers. This work paved the way toward high-efficiency quadruple-junction cells, and a practical estimation of the achievable efficiency was given.
0,emitter = 11.5 fA/cm2 and J0,BSF = 4.5 fA/cm2) and have been deployed in FSF-based IBC c-Si solar cells using a simple self-aligned patterning process. Applying an optimized passivation of FSF by PECVD a-Si:H/SiNx layer (J0,FSF = 6.5 fA/cm2) leads to a cell with efficiency of 22.1% (VOC = 709 mV, JSC = 40.7 mA/cm2, FF = 76.6%). Since over 83% FF has been reached with adjusted metallization technology on similar IBC structures, we believe 23% efficiency is within reach on the short term. Further improvement, especially at JSC level, is expected by deploying less absorbing carrier-selective passivating contacts based on poly-Si or wide bandgap poly-SiOx layers (J0 ~ 10 fA/cm2).","IBC c-Si solar cell; passivating contact; poly-crystalline silicon oxide alloys","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:22312cf3-5d27-40d1-bebe-4496612eab27","http://resolver.tudelft.nl/uuid:22312cf3-5d27-40d1-bebe-4496612eab27","Calculation of irradiance distribution on PV modules by combining sky and sensitivity maps","Santbergen, R. (TU Delft Photovoltaic Materials and Devices); Muthukumar, V.A. (TU Delft Photovoltaic Materials and Devices; Solar Energy Application Centre); Valckenborg, R.M.E. (Solar Energy Application Centre); van de Wall, W.J.A. (Wallvision BV); Smets, A.H.M. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2017","Photovoltaic (PV) modules receive both direct light from the sun and scattered light from the sky, ground and nearby objects. The calculation of incident irradiance becomes complex when nearby objects cast shadows or reflect sunlight onto the PV modules. In this paper a flexible irradiance model is presented that takes all these effects into account by combining a so-called sky map, obtained from the Perez model, with a sensitivity map, generated using a ray tracing software. This irradiation model is validated for a PV facade that combines PV modules with mirror reflectors and is shown to be a flexible tool to accurately predict the irradiance distribution.","Irradiance; Model","en","journal article","","","","","","","","2019-04-22","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:9dc89b86-b554-4593-8f17-cd83db6b8633","http://resolver.tudelft.nl/uuid:9dc89b86-b554-4593-8f17-cd83db6b8633","Light-Induced Effects on the a-Si: H/c-Si Heterointerface","Vasudevan, R.A. (TU Delft Photovoltaic Materials and Devices); Poli, Isabella (External organisation); Deligiannis, D. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy); Smets, A.H.M. (TU Delft Photovoltaic Materials and Devices)","","2016","Light-induced effects on the minority carrier lifetime of silicon heterojunction structures are studied through multiple-exposure photoconductance decay (MEPCD). MEPCD monitors the effect of the measurement flash from a photoconductance decay setup on a sample over thousands of measurements. Varying the microstructure of the intrinsic hydrogenated amorphous silicon (a-Si:H) used for passivation of n-Type crystalline silicon (c-Si) showed that passivating films rich in voids produce light-induced improvement, while denser films result in samples that are susceptible to light-induced degradation. Light-induced degradation is linked to an increase in dangling bond density at the a-Si:H/c-Si interface, while light-induced improvements are linked to charging at the a-Si:H/c-Si interface. Furthermore, doped a-Si:H is added to make samples with an emitter and back surface field (BSF). These doped layers have a significant effect on the light-induced kinetics on minority carrier lifetime. Emitter samples exhibit consistent light-induced improvement, while BSF samples exhibit light-induced degradation. This is explained through negative charging at the BSF and positive charging at the emitter. Full precursors with a BSF and emitter exhibit different kinetics based on which side is being illuminated. This suggests that the light-induced charging at the a-Si:H/c-Si interface can only occur when a-Si:H has sufficient generation.","Hydrogenated amorphous silicon (a-Si:H); light-induced degradation (LID); silicon heterojunction (SHJ)","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:81bcedd1-f973-48dc-9bb4-7f5ff33a9aac","http://resolver.tudelft.nl/uuid:81bcedd1-f973-48dc-9bb4-7f5ff33a9aac","IBC c-Si solar cells based on ion-implanted poly-silicon passivating contacts","Yang, G. (TU Delft Photovoltaic Materials and Devices); Ingenito, A. (TU Delft Photovoltaic Materials and Devices); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2016","Ion-implanted poly-crystalline silicon (poly-Si), in combination with a tunnel oxide layer, is investigated as a carrier-selective passivating contact in c-Si solar cells based on an interdigitated back contact (IBC) architecture. The optimized poly-Si passivating contacts enable low interface recombination, resulting in implied VOC (iVOC) of about 720 mV and 704 mV for n-type and p-type, respectively, before any hydrogenation step. It is found that high-quality passivation can be obtained when confining the dopants within the poly-Si layers and realizing a shallow diffusion of dopants into the c-Si bulk, meaning a sharp decrease in doping concentration in the c-Si at the poly-Si/c-Si interface. The doping profile at the poly-Si/c-Si interface can be influenced by poly-Si layer thickness, poly-Si ion-implantation parameters, and post-implantation annealing conditions. The detailed discussion on the passivation properties of the poly-Si passivating contacts and their preparation conditions are presented in this paper. In addition, IBC solar cells with/without front surface field (FSF) are fabricated, with the optimized poly-Si passivating contacts as back surface field, BSF (n-type poly-Si), and emitter (p-type poly-Si). The best cell shows an efficiency of 21.2% (VOC=692 mV, JSC=39.2 mA/cm2, FF=78.3%, and pFF=83.5%).","Ion-implantation; Poly-silicon; Passivating contact; IBC c-Si solar cells","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:03f18640-79f5-4fc1-8c86-8b9ae63b7949","http://resolver.tudelft.nl/uuid:03f18640-79f5-4fc1-8c86-8b9ae63b7949","Optimizing Silicon Oxide Embedded Silicon Nanocrystal Inter-particle Distances","van Sebille, M. (TU Delft Photovoltaic Materials and Devices); Allebrandi, J.S. (TU Delft Photovoltaic Materials and Devices); Quik, J. (TU Delft Photovoltaic Materials and Devices); van Swaaij, R.A.C.M.M. (TU Delft Photovoltaic Materials and Devices); Tichelaar, F.D. (TU Delft QN/Zandbergen Lab); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2016","We demonstrate an analytical method to optimize the stoichiometry and thickness of multilayer silicon oxide films in order to achieve the highest density of non-touching and closely spaced silicon nanocrystals after annealing. The probability of a nanocrystal nearest-neighbor distance within a limited range is calculated using the stoichiometry of the as-deposited film and the crystallinity of the annealed film as input parameters. Multiplying this probability with the nanocrystal density results in the density of non-touching and closely spaced silicon nanocrystals. This method can be used to estimate the best as-deposited stoichiometry in order to achieve optimal nanocrystal density and spacing after a subsequent annealing step.","Inter-particle distance; Silicon nanocrystal; Silicon oxide; Spacing; Stoichiometry","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:7d68fafb-7d0e-4cc1-a858-67beb9b7175b","http://resolver.tudelft.nl/uuid:7d68fafb-7d0e-4cc1-a858-67beb9b7175b","Solar fuel production by using PV/PEC junctions based on earth-abundant materials","Perez Rodriguez, P. (TU Delft Photovoltaic Materials and Devices); Digdaya, I.A. (TU Delft ChemE/Materials for Energy Conversion and Storage); Mangel Raventos, A. (TU Delft Photovoltaic Materials and Devices); Falkenberg, M. (TU Delft Photovoltaic Materials and Devices); Vasudevan, R.A. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy); Smith, W.A. (TU Delft ChemE/Materials for Energy Conversion and Storage); Smets, A.H.M. (TU Delft Photovoltaic Materials and Devices)","","2016","One of the main problems of renewable energies is storage of the energy carrier. For long-term storage, solar fuels seem to be a good option. Direct solar water splitting could play an important role in the production of these solar fuels. One of the main challenges of this process is the charge separation and collection at the interfaces. The knowledge on photovoltaic (PV) junctions can be used to tackle this challenge. In this work, the use of doped layers to enhance the electric field in an a-SiC:H photocathode, and the use of thin-film silicon multijunction devices to achieve a stand-alone solar water splitting device are discussed. Using a p-i-n structure as a-SiC:H photocathode, a current density of 10mA/cm2 is achievable. The p-i-n structure proposed also indicates the suitability of traditional PV structures for solar water splitting. In addition, hybrid devices, including a silicon heterojunction PV device, are proposed. A combination of the a-SiC:H photocathode with a nc-Si:H/c-Si is demonstrated and potential STH efficiencies of 7.9% have been achieved. Furthermore, a purely PV approach such as a triple junction a-Si:H/nc-Si:H/nc-Si:H solar cell is demonstrated, with solar-to-hydrogen (STH) efficiencies of 9.8%.","Cathodes; Photovoltaic cells; Junctions; Current measurement; PIN photodiodes; Semiconductor device measurement; Silicon","en","conference paper","IEEE","","","","","Accepted Author Manuscript","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:a0a06b84-c562-4aa9-a934-575a2bf7272e","http://resolver.tudelft.nl/uuid:a0a06b84-c562-4aa9-a934-575a2bf7272e","Artifact Interpretation of Spectral Response Measurements on Two-Terminal Multijunction Solar Cells","Si, F.T. (TU Delft Photovoltaic Materials and Devices); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2016","Multijunction solar cells promise higher power-conversion efficiency than the single-junction. With respect to two-terminal devices, an accurate measurement of the spectral response requires a delicate adjustment of the light- and voltage-biasing; otherwise it can result in artifacts in the data and thus misinterpretation of the cell properties. In this paper, the formation of measurement artifacts is analyzed by modeling the measurement process, that is, how the current–voltage characteristics of the component subcells evolve with the photoresponse to the incident spectrum. This enables the examination on the operation conditions of the subcells, offering additional information for the study of artifacts. In particular, the influence of shunt resistance, bias-light intensity, and bias voltage on the measurement is examined. Having observed the dynamics and vulnerability of the measurement, the proper ways to configure and interpret a measurement are discussed in depth. As a practical example, simulations of the measurements on a quadruple-junction thin-film silicon solar cell demonstrate that the modeling can be used to interpret eventual irregularities in the measured spectral response. The application of such tool is especially meaningful taking account of the diverse and rapid development of novel hybrid multijunction solar cells, in which the role of reliable characterizations is essential.","measurement artifacts; multijunction solar cells; photovoltaic devices; quantum efficiency; spectral response measurements","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:048d8b61-3665-40f5-a1a1-b8f0389d7b0f","http://resolver.tudelft.nl/uuid:048d8b61-3665-40f5-a1a1-b8f0389d7b0f","Minimizing optical losses in monolithic perovskite/c-Si tandem solar cells with a flat top cell","Santbergen, R. (TU Delft Photovoltaic Materials and Devices); Mishima, Ryoto (Kaneka Corporation); Meguro, Tomomi (Kaneka Corporation); Hino, Masashi (Kaneka Corporation); Uzu, Hisashi (Kaneka Corporation); Blanker, A.J. (TU Delft Photovoltaic Materials and Devices); Yamamoto, Kenji (Kaneka Corporation); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2016","In a monolithic perovskite/c-Si tandem device, the perovskite top cell has to be deposited onto a flat c-Si bottom cell without anti-reflective front side texture, to avoid fabrication issues. We use optical simulations to analyze the reflection losses that this induces. We then systematically minimize these losses by introducing surface textures in combination with a so-called burial layer to keep the perovskite top cell flat. Optical simulations show that, even with a flat top cell, the monolithic perovskite/c-Si tandem device can reach a matched photocurrent density as high as 19.57 mA/cm2.","Solar energy; Photovoltaic; Thin films","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:860be8f4-09a9-44dd-9716-0955bdd7f8bc","http://resolver.tudelft.nl/uuid:860be8f4-09a9-44dd-9716-0955bdd7f8bc","Advanced light management based on periodic textures for Cu(In,Ga)Se2 thin-film solar cells","Onwudinanti, Chidozie (Student TU Delft); Vismara, R. (TU Delft Photovoltaic Materials and Devices); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Grenet, Louis (French Alternative Energies and Atomic Energy Commission); Emieux, Fabrice (French Alternative Energies and Atomic Energy Commission); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2016","We have used 3-D optical modelling to investigate light management concepts based on periodic textures and material optimization for photovoltaic devices based on Cu(In,Ga)Se2 (CIGS) absorber material. At first, calibration of the software based on the characterization of a reference (1500-nm thick) CIGS device was carried out. The effects of 1-D and 2-D symmetric gratings on the cell were then investigated, showing significant improvement in anti-reflection effect and in absorptance in the active layer, achieved by excitation of guided modes in the absorber. In addition, device configurations endowed with alternative back reflector and front transparent conductive oxide (TCO) were tested with the goal to quench parasitic absorption losses at front and back side. The use of In2O3:H (IOH) as front and back TCO, combined with an optimized 2-D grating structure, led to a 25% increase of the optical performance with respect to an equally-thick flat device. Most of the performance increase was kept when the absorber thickness was reduced from 1500 nm to 600 nm.","","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:8b8e325a-9e4d-493f-a382-b26c85c806f1","http://resolver.tudelft.nl/uuid:8b8e325a-9e4d-493f-a382-b26c85c806f1","Decoupled front/back dielectric textures for flat ultra-thin c-Si solar cells","Isabella, O. (TU Delft Photovoltaic Materials and Devices); Vismara, R. (TU Delft Photovoltaic Materials and Devices); Ingenito, A. (TU Delft Photovoltaic Materials and Devices); Rezaei, N. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2016","The optical analysis of optically-textured and electrically-flat ultra-thin crystalline silicon (c-Si) slabs is presented. These slabs were endowed with decoupled front titanium-dioxide (TiO2) / back silicon-dioxide (SiO2) dielectric textures and were studied as function of two types of back reflectors: standard silver (Ag) and dielectric modulated distributed Bragg reflector (MDBR). The optical performance of such systems was compared to that of state-of-the-art flat c-Si slabs endowed with so-called front Mie resonators and to those of similar optical systems still endowed with the same back reflectors and decoupled front/back texturing but based on textured c-Si and dielectric coatings (front TiO2 and back SiO2). Our optimized front dielectric textured design on 2-µm thick flat c-Si slab with MDBR resulted in more photo-generated current density in c-Si with respect to the same optical system but featuring state-of-the-art Mie resonators ( + 6.4%), mainly due to an improved light in-coupling between 400 and 700 nm and light scattering between 700 and 1050 nm. On the other hand, the adoption of textured dielectric layers resulted in less photo-generated current density in c-Si up to −20.6% with respect to textured c-Si, depending on the type of back reflector taken into account.","Diffraction and gratings; Silicon","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:4a3d986d-ec49-4b1e-8ac2-393885d9d026","http://resolver.tudelft.nl/uuid:4a3d986d-ec49-4b1e-8ac2-393885d9d026","Transmission Expansion Planning of Transnational Offshore Grids: A Techno-Economic and Legal Approach Case Study of the North Sea Offshore Grid","Shariat Torbaghan, S.","Van der Meijden, M.A.M.M. (promotor); Gibescu, M. (promotor)","2016","The new energy policy of the European Union (EU) with the core objectives of competitiveness, reliability and sustainability, has driven Europe into a transition towards a low carbon & sustainable electricity supply systems. Under the new policy, the European energy systems are pursing two major objectives. First is to shift the focus from national to regional or (perhaps) a European level with the ultimate goal of introducing regional markets that facilitates cross-border power trades. Second, is to incorporate large renewable energy sources into the power systems to best exploit the energy resources. In this regards, special attention is oriented towards the development of the offshore gird in the North Sea region where offshore wind is abundant and has potential to become major energy source in the area. This thesis looks into transmission expansion planing in the North Sea region. It presents a market based approach to solve a long-term transmission expansion planning for a meshed VSC-HVDC offshore grid that connect regional markets. The main goal here is to determine the grid design that enables harnessing the offshore wind energy most efficiently, at the same time, creating capacity for conducting cross-border power exchange. Development of an offshore grid in the North Sea can encounter various technical, legal and economic barriers. Consequently advanced planning frameworks are required that enables accounting for these issues. The methodology proposed here provides a framework to investigate the impact of each of these factors on the development of offshore infrastructures. More precisely, the contributions of this thesis can be summarized as follows: Static Transmission Expansion Planning framework (STEP) In Chapter 5, I have proposed a multiple time-period static transmission expansion planning framework that is applicable to VSC-HVDC meshed grids. I have shown that the analytical solution to the problem gives the pricing mechanism that expresses the relationship between the electricity price of different zones and the congestion charges associated with the interconnectors between them. It is an extension of the work of Schweppe et al. that has been proven for and applied to VSC-HVDC grids. The proposed formulation includes investment recovery through congestion revenues as an implicit strict equality constraint. It, therefore, computes the expansion plan, such that the investment capital will be fully paid off through congestion revenues by the end of the chosen lifetime of the infrastructure. The framework determines the topology, transmission capacities and the power flows through the offshore grid, and the resulting distribution of social welfare among the price zones. By combining both flow-constraints and investment recovery-constraints and working with historical market data, the framework can deliver useful results that demonstrate how onshore price zones could benefit from an optimal grid design. Iterative clustering methods for computation feasibility The optimization framework proposed in Chapter 5 was intended to be driven by historical market-data in the form of hourly regional cost curves. The dimensionality of the search space and the computational intensity of the proposed optimization algorithm make the problem intractable. It was desirable to identify and work with only a subset from the total set of operating states. I developed an iterative algorithm that combines an unsupervised clustering technique with the proposed optimization tool to cope with the computational burden of the large-scale optimization problem. Automatic space transformation and clustering were performed to select a subset of representative hourly operating states. The number of samples in the subset was adjusted in order to match the congestion-induced revenues to that of the full data set. This ensured that essential information was not lost. The framework, thus, balances the need for reasonable computation times against the benefits of a model that allows multiple time-periods (as defined by zonal prices and wind power production combinations) and obtains realistic results. Several clustering algorithms (including K-means) and feature reduction techniques (such as Principal Component Analysis (PCA)) have been used in investment planning analysis. Their combination has also been explored in literature. However, this is the first time that an unsupervised PCA/clustering technique has been combined with an optimization tool to refine the clustering results. StaticWind and Transmission Expansion Planning framework (SWTEP) Chapter 6 describes a novel co-optimization wind and transmission expansion framework applicable to VSC-HVDC meshed grids. This is an extension of the static framework presented in Chapter 5 that adds wind to the TEP formulation, while implementing support schemes, which inherently induce a deviation from perfect competition. This results in a fundamental contradiction between the structure of the competitive market and the nature of support policies. The novelty of the work presented in Chapter 6 is that it has limited the market distortion by excluding the support payments from the market clearing process. To do so, I have proposed a formulation that divides the initial investment of the offshore wind infrastructure into subsidized and unsubsidized parts. Thus, the objective of the optimization problem was to maximize sum of incremental social welfare of all regions at all times, minus the aggregated investment cost of offshore transmission infrastructure and the investment cost of building the offshore wind farms that has not been covered through the support payments. The proposed framework enables the impact of implementing two types of feed-in premium support schemes (i.e., generation-based and capacity-based) to be accounted for in the final development of the grid. The goal of this chapter was to investigate the performance of the two feed-in support policies to verify if investment recovery would be fulfilled under a certain support scheme design. In addition, an ‘optimal’ support level and offshore wind support tariff rate were determined. The analytical solution to the optimization problems confirms the complete recovery of the investment cost of transmission infrastructure. In addition, under the assumption that no offshore wind was curtailed, the revenues collected from market sales of offshore wind farms can pay off the unsubsidized part of the wind farm investment, regardless of the payment basis (generation-based or capacity-based). Dynamic Transmission Expansion Planning framework (DTEP) In Chapter 7, I have proposed a market-based, multiple stage, multi-time period dynamic transmission expansion planning framework for a meshed offshore grid to connect upcoming offshore wind farms to multiple onshore markets. The main contribution of this framework is that it enables accounting for delays in the construction and implementation of offshore infrastructures, including wind farms and transmission systems. Delays can occur mainly due to legal barriers associated with differing permitting criteria in an international context, but also due to market maturity and supply chain issues. The timing of delays in grid, market and wind farm developments are set exogenously in the model. This is an extension of the work presented in Chapter 5 in which the whole offshore grid was assumed to be built in one instant. The final results include the optimal grid topology, transmission capacities, construction timing and the resulting remuneration and distribution of the social welfare increase and financial benefit among the various onshore price zones. The analytical solution to the optimization problem gives the pricing mechanism that is consistent with the AC onshore counterpart. The proposed market mechanism facilitates the integration of a multi-terminal VSC-HVDC offshore grid into the existing AC grid. In addition, the analytical solution confirms the investment recovery through congestion revenues, regardless of the number of investors that are involved. In the case of multiple investors, an independent financial entity is required that collects the transmission revenues from the grid operators and distributes them appropriately amongst the investors. Under this regulatory assumption, the investment recovery of every cable of every interconnector will be completely fulfilled within the desired economic lifetime.","long term planning; optimization; wind energy; HVDC transmission; electricity markets; support schemes; policy recommendation","en","doctoral thesis","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:7fd7e28a-f700-4da6-8daa-bc554de71390","http://resolver.tudelft.nl/uuid:7fd7e28a-f700-4da6-8daa-bc554de71390","Integration of High-Tc Superconducting Cables in the Dutch Power Grid of the Future","Zuijderduin, R.","Smit, J.J. (promotor); Chevchenko, O.A. (promotor)","2016","Worldwide there is an increasing need for a more sustainable form of electrical power delivery with a growing share of renewable energy generation. In the distribution and transmission network, large-scale and small-scale wind and solar power plants will be introduced, in proportion to the annual economic growth. The transmission and distribution network will be expanded, focusing on the electricity transport, however, there will also be a need for exchanges with neighboring countries. Alternative solutions are needed in order to support the changes of the future grid. High temperature superconductors are an alternative to conventional conductors, due to their high current density and very low AC loss, and therefore deserve more attention. The purpose of this study is to explore ways to integrate high-temperature superconducting cables in a future network and to compare their favorable technical properties with, e.g., the conventional XLPE cable. The development of 2nd generation high temperature superconducting tapes results in a high tape quality, making it very attractive for use in superconducting power transmission cables. At the same time, the network requirements placed on the grid, based on society needs are changing, such as low magnetic field emissions, reducing space requirements, lower losses, minimizing visual intrusion, etc. Our study shows that superconducting cables compared to conventional cables score better on these societal requirements. From our comparison of three practical low and high temperature superconductors we can conclude that Yttrium Barium Copper Oxide is the most suitable superconductor for use in transmission cables. Our techno-economic analysis shows that superconducting cables become already competitive with conventional cable in the AC transmission, such as XLPE cables. Possible future problems concerning the transport capacity in the power grid where high temperature superconducting cables can offer a solution have been identified. For one promising location, we have formulated the requirements for the design of a high-temperature superconducting cable. Next, we propose two types of cable systems (with cold and warm dielectric). For both types we describe the core, the electrical insulation, the screen, the cryostat, the cooling system, etc. Also for the distribution grid a techno-economic investigation is conducted. To assess the feasibility of the application in distribution grids, we have experimentally demonstrated a reduction of AC conductor losses from 1 W/m to 0.1 W/m. We also carried out an experimental investigation to improve the developed cryostat design for a 6 km long cable connection. Despite these substantial technical improvements our economic study showed that the high-temperature superconducting distribution cable is not yet competitive with the present conventional distribution cable systems except for niche locations where additional advantages e.g. magnetic emission, reduced space usage, power density weighs more heavily. Besides the HVAC grid the Netherlands has HVDC interconnections with neighboring countries and there are initiatives for the use of DC high voltage connections to wind farms further out to sea. In our study, we make reference to a suitable location, where the above mentioned attractive features of the superconducting cable are applicable as well. We advised a modified design of a HTS HVDC cable which enables a possible upgrade of the transmission capacity of the HVDC link at such location. The main results from the investigation are that: Based on our techno-economic analysis HTS cables offer the most competitive solution in transmission grids. Introduction of such cables will reduce HTS tape price, which in turn will stimulate further applications. Conceptual designs of competitive HTS AC and DC transmission cables are formulated along with that for HTS AC distribution cable. Novel designs allow for much longer length between cooling stations. Our experimental research has shown that HTS cable core losses may be reduced by a factor 10 (down to 0.11 W/m/phase at 3 kArms, 77 K, 50 Hz). Dedicated low friction cable cryostat was developed and successfully tested for 47 meters length. Patented multi-layer thermal insulation improves the cable cryostat heat leak from 1 W/m to 0.1 W/m.","Superconductivity; Cables; HTS; Transmission","en","doctoral thesis","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:77aa69ee-6f17-4b44-9b0f-b0bb5f144292","http://resolver.tudelft.nl/uuid:77aa69ee-6f17-4b44-9b0f-b0bb5f144292","Economic Viability Study of an On-Road Wireless Charging System with a Generic Driving Range Estimation Method","Shekhar, A.; Prasanth, V.; Bauer, P.; Bolech, M.","","2016","The economic viability of on-road wireless charging of electric vehicles (EVs) strongly depends on the choice of the inductive power transfer (IPT) system configuration (static or dynamic charging), charging power level and the percentage of road coverage of dynamic charging. In this paper, a case study is carried out to determine the expected investment costs involved in installing the on-road charging infrastructure for an electric bus fleet. Firstly, a generic methodology is described to determine the driving range of any EV (including electric buses) with any gross mass and frontal area. A dynamic power consumption model is developed for the EV, taking into account the rolling friction, acceleration, deceleration, aerodynamic drag, regenerative braking and Li-ion battery behavior. Based on the simulation results, the linear dependence of the battery state of charge (SoC) on the distance traveled is proven. Further, the impact of different IPT system parameters on driving range is incorporated. Economic implications of a combination of different IPT system parameters are explored for achieving the required driving range of 400 km, and the cost optimized solution is presented for the case study of an electric bus fleet. It is shown that the choice of charging power level and road coverage are interrelated in the economic context. The economic viability of reducing the capacity of the on-board battery as a trade-off between higher transport efficiency and larger on-road charging infrastructure is presented. Finally, important considerations, like the number of average running buses, scheduled stoppage time and on-board battery size, that make on-road charging an attractive option are explored. The cost break-up of various system components of the on-road charging scheme is estimated, and the final project cost and parameters are summarized. The specific cost of the wireless on-road charging system is found to be more expensive than the conventional trolley system at this point in time. With decreasing battery costs and a higher number of running buses, a more economically-viable system can be realized.","analysis; contactless; charging; cost; driving range, dynamic; economic; electric vehicle (EV); extension; emissions; inductive power transfer (IPT); static; viability; wireless; OA-Fund TU Delft","en","journal article","MDPI","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:c07dbb22-09c1-432b-a48a-4b122568143e","http://resolver.tudelft.nl/uuid:c07dbb22-09c1-432b-a48a-4b122568143e","Analysis of the Mechanisms Determining the Thermal and Electrical Properties of Epoxy Nanocomposites for High Voltage Applications","Tsekmes, I.A.","Smit, J.J. (promotor)","2016","The addition of microsized fillers to polymers, in order to tailor their properties, has been extensively used in many industrial applications since the 1960s. The same approach applies to the field of electrical insulation. Epoxy resin is a widely used polymer in the electrical power sector, but it is usually loaded with microsized fillers, such as aluminum oxide and silicon dioxide, mainly to increase its thermal conductivity, improve its mechanical properties, and to decrease cost. Polymers with microsized fillers are called microcomposites. In the mid-1990s, a new type of polymeric composites for high voltage applications, the so-called nanocomposites, emerged. The main characteristic of these composites is the small filler size, which is smaller than 100 nm at least in one dimension. Since then, there has been a growing interest in the performance of polymeric nanocomposites for high voltage applications, including epoxy nanocomposites. The performance of nanocomposites is mainly related to the tremendous effective internal surface area of these materials because of the high surface-tovolume ratio of nanofillers. After 20 years of research, a significant amount of data has been generated which reflects the potential of nanodielectrics. It has been shown that nanofillers are capable of contributing to the improvement of both the thermal and electrical properties of polymers. However, the laboratory performance of nanocomposites is inconsistent and unpredictable. These are the main factors which inhibit the applicability of nanodielectrics. Important challenges in the field of epoxy nanocomposites should be overcome before nanodielectrics can be produced on an industrial level. The most important challenge is related to the dubious reproducibility of the nanocomposite performance which is closely related to sample homogeneity. Thus, the effectiveness of separating the nanoparticles from each other and the homogeneous incorporation of them into the polymer matrix are expected to affect the performance of nanocomposites. However, the extent to which the behavior of nanocomposites is influenced by sample homogeneity is not well defined. In this thesis, a number of epoxy nanocomposites and mesocomposites were synthesized aiming at the analysis of the parameters which influence their thermal and electrical properties. The analysis includes the thermal and electrical conductivity, dielectric response, and breakdown strength under both AC and DC electric fields. The experimental results demonstrate the important role of interfaces in the behavior of epoxy nanocomposites. Based on the experimental results, important parameters for determining the performance of nanocomposites are suggested to be the polymer re-organization and water uptake. The former is related to the influence of nanofillers on the polymer structure, i.e., the areas in the vicinity of nanofillers are assumed to exhibita different behavior from the rest of the polymer matrix. The uptake of water is related mainly to the hydrophilic nature of nanofillers and plays a significant role in the electrical performance of nanocomposites. Apart from the aforementioned mechanisms, the presence of structural imperfections should not be neglected as they affect both the thermal and electrical properties of epoxy nanocomposites. Additionally to the experimental part, models were developed for both the relative permittivity and thermal conductivity of nanocomposites. The models are based on the two aforementioned parameters; polymer re-organization in the vicinity of nanofillers and water uptake due to the hydrophilicity of nanofillers. The main characteristic of both models is the use of the same structure which strengthens the validity of the assumptions. The experimental results are in good agreement with the model results. Also, a large part of the thesis is devoted to the evaluation of the influence of sample homogeneity on the performance of nanocomposites. For this purpose, nanocomposites with different synthesis techniques were fabricated. The results suggest that the thermal conductivity, dielectric response, and breakdown strength (AC and DC) of epoxy nanocomposites are not significantly influenced by the nanoparticle distribution. This observation suggests that high levels of reproducibility can be achieved when the particles are similarly dispersed and differently distributed. Finally, hybrid composites which combine both microsized and nanosized fillers were fabricated, tested, and analyzed. This type of composites is more likely to be employed in industry as epoxy resin in its pure form is rarely used for high voltage applications. It is usually reinforced with high loadings of microparticles. Microcomposites reinforced only with a small amount of nanofillers, i.e., less than 1 % by volume, show a significant thermal and electrical improvement.","epoxy nanocomposites; electrical properties; thermal properties; thermal conductivity; dielectric response; electrical conductivity; breakdown strength; epoxy microcomposites","en","doctoral thesis","","","","","","","","2016-01-31","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:604f0968-bafc-48e6-99ab-995f3ae9aa31","http://resolver.tudelft.nl/uuid:604f0968-bafc-48e6-99ab-995f3ae9aa31","Emission efficiency limit of Si nanocrystals","Limpens, R.; Luxembourg, S.L.; Weeber, A.W.; Gregorkiewicz, T.","","2016","One of the important obstacles on the way to application of Si nanocrystals for development of practical devices is their typically low emissivity. In this study we explore the limits of external quantum yield of photoluminescence of solid-state dispersions of Si nanocrystals in SiO2. By making use of a low-temperature hydrogen passivation treatment we demonstrate a maximum emission quantum efficiency of approximately 35%. This is the highest value ever reported for this type of material. By cross-correlating PL lifetime with EQE values, we obtain a comprehensive understanding of the efficiency limiting processes induced by Pb-defects. We establish that the observed record efficiency corresponds to an interface density of Pb-centers of 1.3?×?1012?cm12, which is 2 orders of magnitude higher than for the best Si/SiO2 interface. This result implies that Si nanocrystals with up to 100% emission efficiency are feasible.","nanoparticles; quantum dots; surfaces, interfaces and thin films","en","journal article","Nature Publishing Group","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:96ea4b6c-5ae9-4148-b10d-339a9e418253","http://resolver.tudelft.nl/uuid:96ea4b6c-5ae9-4148-b10d-339a9e418253","Design and application of ion-implanted polySi passivating contacts for interdigitated back contact c-Si solar cells","Yang, G. (TU Delft Photovoltaic Materials and Devices); Ingenito, A. (TU Delft Photovoltaic Materials and Devices); van Hameren, Nienke (Student TU Delft); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy; TU Delft Photovoltaic Materials and Devices)","","2016","Ion-implanted passivating contacts based on poly-crystalline silicon (polySi) are enabled by tunneling oxide, optimized, and used to fabricate interdigitated back contact (IBC) solar cells. Both n-type (phosphorous doped) and p-type (boron doped) passivating contacts are fabricated by ion-implantation of intrinsic polySi layers deposited via low-pressure chemical vapor deposition and subsequently annealed. The impact of doping profile on the passivation quality of the polySi doped contacts is studied for both polarities. It was found that an excellent surface passivation could be obtained by confining as much as possible the implanted-and-activated dopants within the polySi layers. The doping profile in the polySi was controlled by modifying the polySi thickness, the energy and dose of ion-implantation, and the temperature and time of annealing. An implied open-circuit voltage of 721 mV for n-type and 692 mV for p-type passivating contacts was achieved. Besides the high passivating quality, the developed passivating contacts exhibit reasonable high conductivity (Rsh n-type = 95 Ω/□ and Rsh p-type = 120 Ω/□). An efficiency of 19.2% (Voc = 673 mV, Jsc = 38.0 mA/cm2, FF = 75.2%, and pseudo-FF = 83.2%) was achieved on a front-textured IBC solar cell with polySi passivating contacts as both back surface field and emitter. By improving the front-side passivation, a VOC of 696 mV was also measured.","","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:986461ea-efa5-423e-890d-7b2e528f3f4e","http://resolver.tudelft.nl/uuid:986461ea-efa5-423e-890d-7b2e528f3f4e","System design for a solar powered electric vehicle charging station for workplaces","Chandra Mouli, G.R. (TU Delft DC systems, Energy conversion & Storage); Bauer, P. (TU Delft DC systems, Energy conversion & Storage); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2016","This paper investigates the possibility of charging battery electric vehicles at workplace in Netherlands using solar energy. Data from the Dutch Meteorological Institute is used to determine the optimal orientation of PV panels for maximum energy yield in the Netherlands. The seasonal and diurnal variation in solar insolation is analyzed to determine the energy availability for EV charging and the necessity for grid connection. Due to relatively low solar insolation in Netherlands, it has been determined that the power
rating of the PV array can be oversized by 30% with respect to power rating of the converter. Various dynamic EV charging profiles are compared with an aim to minimize the grid dependency and to maximize the usage of solar power to directly charge the EV. Two scenarios are considered – one where the EVs have to be charged only on weekdays and the second case where EV have to be charged all 7 days/week. A priority mechanism is proposed to facilitate the charging of multiple EV from a single EV–PV charger. The feasibility of integrating a local storage to the EV–PV charger to make it grid independent is evaluated. The optimal storage size that reduces the grid dependency by 25% is evaluated.","Batteries; Electric vehicles; Energy storage; Photovoltaic systems; Solar energy","en","journal article","","","","","","","","","","Electrical Sustainable Energy","DC systems, Energy conversion & Storage","","",""
"uuid:45493fb4-9e7a-4e02-b961-7675e201c5a6","http://resolver.tudelft.nl/uuid:45493fb4-9e7a-4e02-b961-7675e201c5a6","Economic and CO2 Emission Benefits of a Solar Powered Electric Vehicle Charging Station for Workplaces in the Netherlands","Chandra Mouli, G.R. (TU Delft DC systems, Energy conversion & Storage); Leendertse, Mark (Student TU Delft); Prasanth, V. (TU Delft DC systems, Energy conversion & Storage); Bauer, P. (TU Delft DC systems, Energy conversion & Storage); Silvester, S. (TU Delft Applied Ergonomics and Design); van de Geer, S.G. (TU Delft Design Aesthetics); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2016","The paper analyses the economic and environmental benefits of charging electric vehicles (EV) at workplaces in the Netherlands using photovoltaic panels (PV). A 10kW EV-PV charging system is used to charge the electric cars directly from photovoltaic panels. The cost of using a gasoline vehicle is compared with that of an electric vehicle that is charged from the grid or from solar panels. It is found that charging EV from PV results in huge savings in fuel cost, taxes and lower CO2 emissions. A comparison is made for solar panels installed on rooftops and as a solar carport and the impact of feed-in tariffs on PV generation revenues is evaluated.","Petroleum; Automobiles; Employment; Finance; Electric vehicles","en","conference paper","IEEE","","","","","Accepted Author Manuscript","","","","Electrical Sustainable Energy","DC systems, Energy conversion & Storage","","",""
"uuid:d794f4b1-3a78-402f-92ee-a6e533fcdd56","http://resolver.tudelft.nl/uuid:d794f4b1-3a78-402f-92ee-a6e533fcdd56","Estimation of ripple and inductance roll off when using powdered iron core inductors","Chandra Mouli, G.R. (TU Delft DC systems, Energy conversion & Storage); Schijffelen, Jos (Power Research Electronics BV); Bauer, P. (TU Delft DC systems, Energy conversion & Storage); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2016","Magnetic cores like powdered iron cores have a variable permeability, which is dependent on the magnetic motive force of the inductor windings. When inductors are designed using such materials, the inductance varies as a function of the inductor current. This causes a non-linear current to flow through the inductor. In this paper, mathematical derivation of the inductancecurrent relationship is derived for such inductors. The model is applied for a KoolMmu(r) powdered iron core and the results are verified experimentally using an interleaved boost converter.","","en","conference paper","VDE Verlag GMBH","","","","","Accepted Author Manuscript","","","","Electrical Sustainable Energy","DC systems, Energy conversion & Storage","","",""
"uuid:b1686764-5a01-42cb-8d35-1b0b575a5f46","http://resolver.tudelft.nl/uuid:b1686764-5a01-42cb-8d35-1b0b575a5f46","A rapid method of estimating the solar irradiance spectra with potential lighting applications","Gao, Y. (TU Delft Photovoltaic Materials and Devices; TU Delft Beijing Delft Institute of Intelligent Science and Technology; State Key Laboratory of Solid State Lighting); Dong, J. (TU Delft Beijing Delft Institute of Intelligent Science and Technology; State Key Laboratory of Solid State Lighting); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy); Zhang, G (TU Delft Electronic Components, Technology and Materials)","","2016","Diverse solar irradiance spectra can be observed under different conditions of time, date, location, weather, etc. Since the solar irradiance spectrum is required by certain scientific and engineering applications, obtaining accurate spectral data is essential. Measurements by spectrophotometers are able to achieve accurate real-time data with high resolution, but at high expense. While in some engineering applications, the requirements on accuracy and resolution are much lower than that in a typical scientific research. Therefore, a rapid method of estimating the solar spectrum is proposed based on an available spectral model in this paper. In order to achieve fast estimation, we simplify the input parameters of this model into five key inputs, including latitude and longitude, altitude, date and time, sky and ground type. The first three parameters are easy to obtain from GPS and the internet. Sky and ground types include common types of sky and ground, which can be input manually or processed automatically by analyzing a digital image of target sky or ground. The automatic input is realized through dominant color extraction or by training an artificial neural network. Results show that the proposed rapid method can generate different spectral power distributions based on distinct input conditions. Two device frameworks are also proposed to implement the rapid method, which is applicable to many fields. LED lighting is one of the most prominent applications. Users can easily share local sunlight with each other through an APP in mobile phones","","en","conference paper","","","","","","","","2017-12-01","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:77dfef04-3d71-4c01-bff0-09e38fc53d03","http://resolver.tudelft.nl/uuid:77dfef04-3d71-4c01-bff0-09e38fc53d03","Implementation of Dynamic Charging and V2G using Chademo and CCS/Combo DC charging standard","Chandra Mouli, G.R. (TU Delft DC systems, Energy conversion & Storage); Kaptein, Johan (ABB B.V. EV Charging Infrastructure); Bauer, P. (TU Delft DC systems, Energy conversion & Storage); Zeman, M. (TU Delft Electrical Sustainable Energy)","","2016","Dynamic charging of electric vehicles (EV) refers to charging the EV using variable charging power. This is important for applications where the EV is charged from intermittent renewable energy sources like wind or solar. Dynamic charging can be implemented using three standards - AC charging, DC charging via Chademo and CCS/COMBO. This paper compares the charging standards in their implementation of dynamic charging and vehicle to grid (V2X) and brings out its influence on the charging system design, response time, flexibility in charging from renewable sources and buffer capacity that is required. Experimental results of dynamic charging using Chademo and CCS/COMBO are presented for different compatible EV that shows the fundamental difference between the two standards.","Pins; Batteries; Pulse width modulation; Standards; Europe; Protocols","en","conference paper","IEEE","","","","","Accepted Author Manuscript","","","","Electrical Sustainable Energy","DC systems, Energy conversion & Storage","","",""
"uuid:0f54dce2-5131-4957-96df-e8c45fbfb35b","http://resolver.tudelft.nl/uuid:0f54dce2-5131-4957-96df-e8c45fbfb35b","Temperature dependency of the silicon heterojunction lifetime model based on the amphoteric nature of dangling bonds","Vasudevan, R.A. (TU Delft Photovoltaic Materials and Devices); Poli, I. (Student TU Delft); Deligiannis, D. (TU Delft Photovoltaic Materials and Devices); Zeman, M. (TU Delft Electrical Sustainable Energy); Smets, A.H.M. (TU Delft Photovoltaic Materials and Devices)","","2016","This work adapts a model to simulate the carrier injection dependent minority carrier lifetime of crystalline silicon passivated with hydrogenated amorphous silicon at elevated temperatures. Two existing models that respectively calculate the bulk lifetime and surface recombination velocity are used and the full temperature dependency of these models are explored. After a thorough description of these temperature dependencies, experimental results using this model show that the minority carrier lifetime changes upon annealing of silicon heterojunction structures are not universal. Furthermore, comparisons of the temperature dependent model to using the room temperature model at elevated temperatures is given and significant differences are observed when using temperatures above 100 °C. This shows the necessity of taking temperature effects into account during in-situ annealing experiments.","","en","journal article","","","","","","","","","","Electrical Sustainable Energy","Photovoltaic Materials and Devices","","",""
"uuid:b74a7682-1559-4c81-9a11-f77d1c5ac9e8","http://resolver.tudelft.nl/uuid:b74a7682-1559-4c81-9a11-f77d1c5ac9e8","Solar road operating efficiency and energy yield - An integrated approach towards inductive power transfer","Shekhar, A.; Klerks, S.; Bauer, P.; Prasanth, V.","","2015","One of the first of its kind, a pilot project involving the instalment of solar roads in Krommenie, was successfully implemented by the consortium of the province of North Holland, TNO, Ooms and Imtech. Seen as a living lab for knowledge gathering in this nascent application area, with a potential of widening the proliferation of PV technologies, the testing of the operating performance of the installed solar road stretch is ongoing. In this context, the theoretical model for energy yield of the solar road is developed to facilitate the future comparative analysis with the real-time measured data. A combination of Inductive Power Transfer (IPT) to solar roads has been suggested for convenient charging of e-bikes in stands.","energy yield; inductive power transfer (IPT); module; photovoltaic modules; PV; solar; solar roads","en","conference paper","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:67575ea8-bcde-494a-82a7-005f17f9b5f9","http://resolver.tudelft.nl/uuid:67575ea8-bcde-494a-82a7-005f17f9b5f9","On computing the maximum parsimony score of a phylogenetic network","Fischer, M.; Van Iersel, L.J.J.; Kelk, S.; Scornavacca, C.","","2015","Phylogenetic networks are used to display the relationship among different species whose evolution is not treelike, which is the case, for instance, in the presence of hybridization events or horizontal gene transfers. Tree inference methods such as maximum parsimony need to be modified in order to be applicable to networks. In this paper, we discuss two different definitions of maximum parsimony on networks, “hardwired” and “softwired,” and examine the complexity of computing them given a network topology and a character. By exploiting a link with the problem Multiterminal Cut, we show that computing the hardwired parsimony score for 2-state characters is polynomial-time solvable, while for characters with more states this problem becomes NP-hard but is still approximable and fixed parameter tractable in the parsimony score. On the other hand we show that, for the softwired definition, obtaining even weak approximation guarantees is already difficult for binary characters and restricted network topologies, and fixed-parameter tractable algorithms in the parsimony score are unlikely. On the positive side we show that computing the softwired parsimony score is fixed-parameter tractable in the level of the network, a natural parameter describing how tangled reticulate activity is in the network. Finally, we show that both the hardwired and the softwired parsimony scores can be computed efficiently using integer linear programming. The software has been made freely available","phylogenetic trees; phylogenetic networks; parsimony; complexity; approximability; fixed-parameter tractability; software","en","journal article","SIAM","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:3944aa5b-2268-4b90-bbe4-c2c302d256bb","http://resolver.tudelft.nl/uuid:3944aa5b-2268-4b90-bbe4-c2c302d256bb","Thin-film photovoltaics 2014 (Editorial)","Di Marco, G.; Galogero, G.; Di Carlo, A.; Lombardo, S.; Palmisano, L.; Isabella, O.","","2015","","","en","journal article","Hindawi","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:d02b8d84-4a30-4bbc-a490-f7f3f2949671","http://resolver.tudelft.nl/uuid:d02b8d84-4a30-4bbc-a490-f7f3f2949671","Modeling intelligent energy systems","Palensky, P.","","2015","","","en","lecture notes","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:c9dd9b11-a7c0-45bf-93a2-18273a16d56a","http://resolver.tudelft.nl/uuid:c9dd9b11-a7c0-45bf-93a2-18273a16d56a","Design and Modeling of High Performance Permanent Magnet Synchronous Machines","Van der Geest, M.","Ferreira, J.A. (promotor)","2015","The electrification of transportation, and especially aerospace transportation, increases the demand for high performance electrical machines. Those machines often need to be fault-tolerant, cheap, highly efficient, light and small, and interface well with the inverter. In addition, the development time and cost are usually limited, with little room for later changes. Meeting those expectations requires an accurate and flexible design and optimization approach. This thesis will present such an approach, as well as discuss various modeling methods needed to speed up the optimization and finalize the details of the design. The design process of a brushless permanent magnet synchronous machine (PMSM) for a starter/generator application serves as an example throughout the thesis. A multi-objective optimization method is discussed first, demonstrating the insights that can be gained with such a method. Next, the rotor eddy current losses cannot be neglected in high speed machines, but their computation is numerically complex. Therefore, an alternate and faster method is also presented. Another potential loss source in high speed machines are winding AC losses. A computationally efficient method to compute unequal current sharing among parallel strands is proposed and tested. Next, the consequences, detection and mitigation of inter-turn faults are extensively discussed. Short circuit current densities over 400 A/mm² are experimentally demonstrated, highlighting the need for a good fault detection scheme. One potential detection scheme is introduced and tested, and found to be capable of detecting faults across 0.4% of the winding. With the models and knowledge obtained at this point, the actual starter/generator is designed. Particular to this design is a temporary starting torque four times larger than the nominal generator torque and the need to be able to withstand terminal short circuits. Key to meeting those specifications is a carefully chosen per-unit inductance, as this strongly affects machine and inverter size. Experiments on a prototype demonstrate satisfactory machine performance in all operating conditions. Finally, after having confirmed the used models, a design study into the specific power density limits of PMSMs is performed and the results are presented in detail.","","en","doctoral thesis","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:c2a2c9d9-e83d-43b0-a96d-75993464771c","http://resolver.tudelft.nl/uuid:c2a2c9d9-e83d-43b0-a96d-75993464771c","Managing Risks in Electrical Infrastructure Assets from a Strategic Perspective","Zhuang, Q.","Smit, J.J. (promotor)","2015","Should risks always be quantified before being managed? The answer is “yes” in the opinion of most asset managers in today’s electricity transmission and distribution companies, but “no” in modern theories of risk management. When the risks refer to reliability hazards of high-voltage assets, the answer to the above question is “yes, it should be, but not yet”. The first part of this thesis studies a typical cause of this situation: when data and knowledge on high-voltage assets are insufficient. Specifically, statistical methods were developed for analyzing life data of limit quantity and poor quality. For other types of data, the reliability data model and the knowledge maturity model were developed, as the tools to evaluate the progress towards risk-based asset management. When the risks on electrical infrastructure assets are long-term and stakeholder-oriented, the answer to the above question is probably “no”. In the second part of this thesis, these risks are modelled as “strategic risks”. Through adapting the theory of Klinke and Renn, the author identifies six types of strategic risks. Then, through developing our version of system diagram, the author provides asset managers with an analytical tool to manage the complexities and uncertainties caused by these strategic risks.","electrical infrastructure; asset management; strategic risk management; high voltage","en","doctoral thesis","Next Generation Infrastructures Foundation","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:847f7430-26d3-4034-bc9c-32f394bd9495","http://resolver.tudelft.nl/uuid:847f7430-26d3-4034-bc9c-32f394bd9495","Materials and Light Management for High-Efficiency Thin-Film Silicon Solar Cells","Tan, H.","Zeman, M. (promotor)","2015","Direct conversion of sunlight into electricity is one of the most promising approaches to provide sufficient renewable energy for humankind. Solar cells are such devices which can efficiently generate electricity from sunlight through the photovoltaic effect. Thin-film silicon solar cells, a type of photovoltaic (PV) devices which deploy the chemical-vapor-deposited hydrogenated amorphous silicon (a-Si:H) and nanocrystalline silicon (nc-Si:H) and their alloys as the absorber layers and doped layers, are one of the promising PV technologies. Compared to other PV technologies, thin-film silicon solar cells have several important advantages such as the use of abundant and non-toxic materials, low processing temperature, short energy payback time and mature large-area manufacturing techniques. Despite the many advantages, thin-film silicon (TF-Si) technology is suffering from the drop in the PV market share due to the relatively low efficiency compared to c-Si, CIGS, and CdTe solar cells. This thesis is devoted to the development of advanced materials and novel light-trapping structures to increase the power conversion efficiency of thin-film silicon solar cells. To achieve maximal light absorption in the absorber layers, implementation of light-trapping structures is crucial for thin-film silicon solar cells. The status of light-trapping techniques is briefly summarized in chapter 1, together with the background knowledge for thin-film silicon solar cells. To design an effective light-trapping scheme for solar cells, both the optical performance and the influence on the electrical performance of solar cells have to be considered. The light-trapping structure itself should not give additional parasitic absorption losses, or this loss should be minimized. The morphology of the light-trapping substrate should be suitable for the growth of high-quality materials. Meanwhile, absorption losses in the supporting layers such as front electrodes, doped layers, and back reflectors should be minimized. In chapter 2, the fabrication of plasmonic back reflectors (BRs) based on self-assembled Ag nanoparticles and their application in a-Si:H solar cells are presented. It has been experimentally demonstrated that the optimized plasmonic back reflector can provide light trapping performance comparable to state-of-the-art random textures, without obvious deterioration of open-circuit voltage (Voc) and/or fill factor (FF). This conclusion is based on the fair comparison with high performance n-i-p solar cells and state-of-the-art p-i-n solar cells deposited on Asahi-VU substrates. The combined optical and electrical design of plasmonic back reflectors follows in chapter 3. The design rules of plasmonic back reflectors based on self-assembled Ag nanoparticles are discussed in detail. The shape of Ag NPs, the thickness of ZnO:Al spacer layers, materials on top of Ag NPs, and nanoparticle size are crucial for the performance of plasmonic BRs. By following the design ruless, an 8.4% efficiency plasmonic a-Si:H solar cell has been achieved. The application of the plasmonic back reflector in low bandgap nc-Si:H solar cells is discussed in chapter 4. The light trapping performance in nc-Si:H solar cells is improved by using the plasmonic BRs with a broad angular scattering and low parasitic absorption loss through tuning the size of silver nanoparticles. The nc-Si:H solar cells deposited on the improved plasmonic BRs demonstrate a high photocurrent comparable to the one achieved by the state-of-the-art textured Ag/ZnO BR. The commonly observed deterioration of fill factor is avoided by using nc-SiOx:H as the n-layer for solar cells deposited on plasmonic BRs. In chapter 5, micro-textures on glass with large opening angles and smooth U-shape morphology are proposed and applied to nc-Si:H solar cells for the first time. The micro-textures can provide both efficient light trapping and suitable morphology for the growth of high-quality nc-Si:H materials under a high deposition rate. A higher Voc and FF can be achieved in reference to the cells using nano-textured substrates. For thick solar cells (i-layer thicker than 2 µm), high Voc and FF values are maintained. Particularly, the Voc only drops from 564 to 541 mV as solar cell thickness increases from 1 to 5 ?m. The use of micro-textures paves the road to develop multijunction solar cells with a higher efficiency as will be shown in chapter 7. High-efficiency multijunction thin-film silicon solar cells require both high Voc and high blue spectral response in the top a-Si:H cell. In chapter 6, the mixed-phase p-SiOx films are investigated and used as window layer in high Voc a-Si:H p-i-n solar cells. The use of p-SiOx as window layer results in a higher Voc and a better spectral response than the standard p-SiC based window layer. Consequently, a-Si:H solar cells with Voc >1 V and FF >70% have been obtained. A high initial efficiency of 14.4% has been achieved in a-Si:H/nc-Si:H tandem solar cells deposited on the Asahi-VU substrates. Chapter 7 presents the implementation of highly transparent modulated-surface-textured (MST) front electrodes as light-trapping structures in multijunction TF-Si solar cells. The MST substrates comprise a micro-textured glass as developed in chapter 5, a thin layer of hydrogenated indium oxide (IOH), and a sub-micron nano-textured ZnO layer grown by low-pressure chemical vapor deposition (LPCVD ZnO). The MST front electrode has a good transparency and conductance, can provide efficient light trapping for each subcell and a suitable morphology for the growth of high-quality silicon layers. Efficiencies of 14.8% (initial) and 12.5% (stable) have been achieved for a-Si:H/nc-Si:H tandem solar cells with the MST front electrode and the high-performance a-Si:H top cells as developed in chapter 6, surpassing efficiencies obtained on state-of-the-art LPCVD ZnO. A short summary of this thesis is given in chapter 8. Perspectives to further improve the performance of thin-film silicon solar cells are suggested and discussed. The light-trapping performance of modulated-surface-textured front electrodes can be further improved by replacing the wet-etched glass with honeycomb textures, without sacrifice in electrical performance of solar cells. The honeycomb textures can be easily applied to superstrate configuration by mature UV-NIL technique. In the end, the hybrid a-Si:H/organic multijunction device configuration is proposed to avoid the use of thick nc-Si:H solar cells. A high efficiency of 11.6% has been achieved in the hybrid tandem configuration with a total absorber layer thickness less than 500 nm. By deploying the triple-junction structure, a high efficiency of 13.2% has been obtained while the thickness of absorber layers stack is below 1µm. With further efforts on this concept, performance comparable to the traditional devices based on a-Si:H and nc-Si:H can be expected while the total processing time is much shorter and the cost for manufacturing and materials is lower.","thin-film silicon solar cells","en","doctoral thesis","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:df935358-0d87-4b27-8350-ac292e442862","http://resolver.tudelft.nl/uuid:df935358-0d87-4b27-8350-ac292e442862","Online Companion for Robust Unit Commitment with Dispatchable Wind: An LP Reformulation of the Second-stage","Morales-España, G.; Davidson, M.; Ramírez-Elizondo, L.; De Weerdt, M.M.","","2015","This document is an online companion for the paper ""Robust Unit Commitment with Dispatchable Wind: An LP Reformulation of the Second-stage"".","robust optimization; dispatchable wind; unit commitment","en","report","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy / Software and Computer Technology","","","",""
"uuid:ee1e27b9-6ba5-4ef2-8023-96e7f6fb89a6","http://resolver.tudelft.nl/uuid:ee1e27b9-6ba5-4ef2-8023-96e7f6fb89a6","A method for texturing a glass surface","Yang, G.; Van Swaaij, R.A.C.M.M.; Isabella, O.","","2015","The present invention relates to a new method of texturing a glass surface. In further aspects, the present invention relates to the resulting textured glass surface; to a photovoltaic device comprising the textured glass surface; and, to use of the textured glass surface for scattering light.","","en","patent","European Patent Office","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:59648f91-b0e7-4487-836e-d4234417cee5","http://resolver.tudelft.nl/uuid:59648f91-b0e7-4487-836e-d4234417cee5","Revision of TRV Requirements for the Application of Generator Circuit-Breakers","Palazzo, M.; Popov, M.; Marmolejo, A.; Delfanti, M.","","2015","The requirements imposed on generator circuitbreakers greatly differ from the requirements imposed on other transmission and distribution circuit-breakers. Due to the location of installation between the generator and the associated step-up transformer, a generator circuit-breaker must meet high technical requirements with respect to rated normal currents, short-circuit currents, fault currents due to out-of-phase conditions and transient recovery voltages. The question whether the transient recovery voltage requirements laid down in IEEE Std C37.013-1997 (R2008) and in its amendment IEEE Std C37.013a-2007 are still adequate for the application of generator circuit-breakers in modern power stations is considered in the present work. In order to quantify the transient recovery voltage requirements for the application of generator circuit-breakers a comprehensive survey of different fault conditions occurring in several power stations has been performed. The fault transients’ simulations have been performed by means of the Electromagnetic Transients Program (EMTP).","fault current; generator circuit-breaker; transient recovery voltage","en","conference paper","University of Zagreb","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:c5d1966b-227e-46a6-8892-3bbfc33a9fc9","http://resolver.tudelft.nl/uuid:c5d1966b-227e-46a6-8892-3bbfc33a9fc9","A system for measuring an optical spectral response and/or IV data of a photoelectric device under test","Elshinawy, M.; Heirman, S.G.M.; Melsken, J.; Fischer, M.","","2015","A system for measuring an optical spectral response or property and/or IV data of a device or object under test (9), comprising in optically coupled sequence: a broadband light source (1) for emitting light of a prede- fined spectrum, a slit and/or light guide (2), a wavelength dispersive device (3), a spatial light modulator (5) for re- ceiving the emitted light and controlling an intensity and spectrum of light reflected by said modulator (5), focusing optics (6, 7, 8, 12, 13, 14) for the reflected light directed towards a reference detector (15) and towards the device or object under test (9), wherein the spatial light modulator (5) is embodied as a beamsplitter and is combined with a fil- ter (4) for suppression of second and higher order frequen- cies of the primary frequencies in the reflected light.","","en","patent","European Patent Office","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:a7b97b7f-cff0-4f99-ba02-307c59e26eaf","http://resolver.tudelft.nl/uuid:a7b97b7f-cff0-4f99-ba02-307c59e26eaf","Size control, quantum confinement, and oxidation kinetics of silicon nanocrystals synthesized at a high rate by expanding thermal plasma","Han, L.; Zeman, M.; Smets, A.H.M.","","2015","The growth mechanism of silicon nanocrystals (Si NCs) synthesized at a high rate by means of expanding thermal plasma chemical vapor deposition technique are studied in this letter. A bimodal Gaussian size distribution is revealed from the high-resolution transmission electron microscopy images, and routes to reduce the unwanted large Si NCs are discussed. Photoluminescence and Raman spectroscopies are employed to study the size-dependent quantum confinement effect, from which the average diameters of the small Si NCs are determined. The surface oxidation kinetics of Si NCs are studied using Fourier transform infrared spectroscopy and the importance of postdeposition passivation treatments of hydrogenated crystalline silicon surfaces are demonstrated.","","en","journal article","American Institute of Physics","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:dbae57fb-db7a-464c-9a37-5e960afa27a5","http://resolver.tudelft.nl/uuid:dbae57fb-db7a-464c-9a37-5e960afa27a5","Tight MIP formulations of the power-based unit commitment problem","Morales-Espana, G.A.; Gentile, C.; Ramos, A.","","2015","This paper provides the convex hull description for the basic operation of slow- and quick-start units in power-based unit commitment (UC) problems. The basic operating constraints that are modeled for both types of units are (1) generation limits and (2) minimum up and down times. Apart from this, the startup and shutdown processes are also modeled, using (3) startup and shutdown power trajectories for slow-start units, and (4) startup and shutdown capabilities for quick-start units. In the conventional UC problem, power schedules are used to represent the staircase energy schedule; however, this simplification leads to infeasible energy delivery, as stated in the literature. To overcome this drawback, this paper provides a power-based UC formulation drawing a clear distinction between power and energy. The proposed constraints can be used as the core of any power-based UC formulation, thus tightening the final mixed-integer programming UC problem. We provide evidence that dramatic improvements in computational time are obtained by solving different case studies, for self-UC and network-constrained UC problems.","convex hull; unit commitment (UC); mixed-integer programming (MIP); tight formulation; slow-start units; quick-start units","en","journal article","Springer","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:6a9e06e1-d7ba-411b-b8f9-7f373fcb9c50","http://resolver.tudelft.nl/uuid:6a9e06e1-d7ba-411b-b8f9-7f373fcb9c50","Thermal management of High-Current Bidirectional Isolated DC-DC Converters","Wang, Y.","Ferreira, J.A. (promotor)","2015","","high current; DAB; thermal management; transformer design; loss modeling","en","doctoral thesis","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:14a05032-4be5-4524-9c1a-2d19bda16fd4","http://resolver.tudelft.nl/uuid:14a05032-4be5-4524-9c1a-2d19bda16fd4","UMBRELLA project - Deliverable D 7.4 “Workshop results on solutions for maximising power transits”","Electrical Sustainable Energy Department ","","2015","In the present deliverable, the results of the workshop ‘UMBRELLA Workshop on Optimized Solutions’ and ‘UMBRELLA Workshop on System State Modelling and Toolbox Design’ are summarized. The workshops were both hosted at ENTSO-E’s premises on October 22, 2013 and October 23rd, 2014 with a total number of 15 and 33 registered participants respectively, including experts from industry, academia and regulatory bodies.","","en","report","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:73005fd1-6612-46f4-a511-87b5b93136cf","http://resolver.tudelft.nl/uuid:73005fd1-6612-46f4-a511-87b5b93136cf","The implications of aerospace requirements on the design-space of a permanent magnet starter/generator system","Brink, E.; Gerber, M.; De Boer, A.; Van der Geest, M.; Zeilstra, D.","","2015","Starter/generator units based on PM machines are generally not considered due to their inherent safety risks. This technology can, however, prove advantageous for aerospace applications where mass, volume, efficiency and low maintenance costs play a significant role. A safety analysis is performed in order to identify the safety and mitigation measures required to realise such a system which conforms to aerospace requirements. These measures define the design-space and boundary conditions within which a design may be realised. It is found that not all the measures are unique to PM based SGUs and that their degree of influence on the mass and volume is highly dependent on the starting and generating specifications.","","en","conference paper","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:8c2a26a9-b5c0-4cbc-a135-2108ad48e6a6","http://resolver.tudelft.nl/uuid:8c2a26a9-b5c0-4cbc-a135-2108ad48e6a6","The influence of interfaces and water uptake on the dielectric response of epoxy-cubic boron nitride composites","Tsekmes, I.A.; Morshuis, P.H.F.; Smit, J.J.; Kochetov, R.","","2015","In this study, epoxy-cubic boron nitride composites are fabricated, and their dielectric response is investigated. They exhibit the same trend as epoxy composites reinforced with other filler types. Thus, at low filler concentrations, they exhibit a lower relative permittivity than neat epoxy. As the fill grade further increases, the relative permittivity of the composites increases as well. It is suggested that two competing mechanisms, namely polymer re-organization and water uptake, mainly determine the dielectric response of epoxy composites. The former is related to the decrease while the latter to the increase of the relative permittivity. The experimental results clearly verify that water uptake strongly depends on the filler concentration and not only affects the dielectric response of epoxy composites but also it is one of the main mechanisms which dictate their dielectric behavior.","","en","journal article","Springer","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:f80e4ee9-433a-4d56-88e3-1f2f0c27e1aa","http://resolver.tudelft.nl/uuid:f80e4ee9-433a-4d56-88e3-1f2f0c27e1aa","MVMO-based approach for optimal placement and tuning of supplementary damping controller","Rueda Torres, J.L.; Gonzalez-Longatt, F.","","2015","This paper introduces an approach based on the Swarm Variant of the Mean-Variance Mapping Optimization (MVMO-S) to solve the multi-scenario formulation of the optimal placement and coordinated tuning of power system supplementary damping controllers (POCDCs). The effectiveness of the approach is evaluated based on the classical IEEE 39-bus (New England) test system. Numerical results include performance comparisons with other metaheuristic optimization techniques, namely, comprehensive learning particle swarm optimization (CLPSO), genetic algorithm with multi-parent crossover (GA-MPC), differential evolution DE algorithm with adaptive crossover operator, linearized biogeography-based optimization with reinitialization (LBBO), and covariance matrix adaptation evolution strategy (CMA-ES).","coordinated control; damping controllers; metaheuristics; small-signal stability","en","journal article","Engg Journals Publications","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:13d60d5e-3d68-4ac7-b2b6-a867cc393231","http://resolver.tudelft.nl/uuid:13d60d5e-3d68-4ac7-b2b6-a867cc393231","Hydrogenated amorphous silicon: Nanostructure and defects","Melskens, J.","Zeman, M. (promotor); Bruck, E.H. (promotor); Smets, A.H.M. (promotor)","2015","Since the first report on the fabrication of hydrogenated amorphous silicon (a-Si:H) in 1965, this material has found many applications, for instance in the fabrication of solar cells, sensors and transistors. An especially notable example in the context of this thesis is thin-film silicon solar cells, which have attracted a lot of attention. This is largely due to the fact that this type of photovoltaic technology can be implemented on flexible substrates and is a potentially cheap and lightweight product. However, a-Si:H-based solar cells suffer from light-induced degradation (LID) which can only partially be recovered by annealing. This issue, which has become known as the Staebler-Wronski effect (SWE), is obviously an undesirable material property in the context of photovoltaic applications. Although the solar cell conversion efficiency of thin-film silicon solar cells has seen significant gains over the years, research efforts are still ongoing to achieve further improvements. A significant portion of these improvements has come from the development of new materials or improvements in existing materials. This type of fundamental research is inherently linked to the understanding of the nanostructure and the defects therein to enable further material quality improvements. In this thesis it is aimed to fundamentally improve the understanding of the a-Si:H nanostructure and the defects in this material to finally enable a reduction or even elimination of the SWE. Unfortunately, the SWE has proven to be a notoriously difficult problem due to the complexity of the a-Si:H nanostructure, which is the cause of the lacking consensus on the nature of the defects in this material. Because of this complication, there is a two-stage research approach in this thesis and it is not directly aimed to fabricate more stable a-Si:H. The first objective is to improve the fundamental understanding of the nanostructure and the defects in a-Si:H. Only secondly and using this newly gained knowledge, the SWE and the nature of metastable defects are studied to pave the way towards a reduction of the SWE","","en","doctoral thesis","Delft University of Technology","","","","","","","2017-02-25","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:ccd8c8ea-493e-45af-b04e-a27d0d7bfc77","http://resolver.tudelft.nl/uuid:ccd8c8ea-493e-45af-b04e-a27d0d7bfc77","Surface passivation and optical design of silicon heterojunction solar cells","Zhang, D.","Zeman, M. (promotor); Van Swaaij, R.A.C.M.M. (promotor)","2015","It has been predicted that due to the population growth the energy demand is increasing faster and faster. It has been well recognized that depleting fossil-fuel resources will not fulfill the energy need of the future world. Not to mention the problem of global warming caused by its combustion, and of energy security as a result of geopolitical developments. People have never stopped seeking for alternative energy sources. With the aid of rapid technology development renewable-energy sources with its unique characteristics of environmental compatibility and continual replenishment, become more and more appealing. Amongst all renewable energy sources solar energy is considered inexhaustible and very abundant and therefore much research is being carried out, aiming at making full use of it. A solar cell is a photovoltaic device that directly converts solar energy to electrical energy, a very versatile form of energy. Thanks to fast technologic progress and the price drop of some source materials, solar cells have been becoming cheaper. There are two ways to reduce the cost of electricity produced by solar cells: one is to increase the energy conversion efficiency mainly by means of reducing optical and electrical losses; the second is to lower the production cost by reducing the material cost and by simplifying the manufacturing process. So far crystalline-silicon (c-Si) based solar cells dominate the photovoltaic (PV) market, but there are two important challenges with conventional c-Si solar cells: (i) the relatively high material cost from the c-Si wafer and (ii) the high processing cost due to the relatively long processing time and high thermal budget. Worldwide researchers have been working on different solutions. For instance, the material cost can be reduced by the use of low-quality wafers and by slicing the ingot into thinner wafers. The use of laser doping, for instance, can replace the diffusion process in order to reduce thermal budget. Another solution, which led to the second generation of solar cells, is thin-film technology. Thin-film Si solar cells use only hundreds of nanometers or several micrometers thick Si layers and the processing temperature is only around 200 °C. However, the efficiency of thin-film silicon solar cells is relatively low especially after light-induced degradation. By combining advanced c-Si and thin-film Si technologies the silicon heterojunction (SHJ) solar cell has been developed. This type of solar cell consists of a c-Si wafer with layers of hydrogenated amorphous silicon (a Si:H) to passivate the surface and create emitter and back surface field (BSF) at front and back side respectively. These layers can be of intrinsic material (i-layer) or of p or n-type doped material (p-layer or n-layer). The SHJ solar cell has proved to be a high-efficiency concept and can be made with relatively simple and low-temperature processes. This thesis describes the development of the process to make SHJ solar cells in our facility. For this process first a reproducible wafer cleaning process has been developed. Different thin-film deposition technologies, e.g. plasma enhanced chemical vapor deposition (PECVD), sputtering and metal evaporation, have been used for fabricating the device. The properties of the layers have been characterized by techniques including transmittance and reflectance measurements, activation energy and dark conductivity measurements, and carrier lifetime measurements. For device characterization mainly current density versus voltage measurement, external quantum efficiency measurements, and reflectance measurements have been performed. In addition to experimental work, optical simulations have been carried out for optical analysis and design of the device. In order to simulate the optical effects of layers with thicknesses in the nanometer scale the interference of light was modelled using thin-film optics, while geometrical optics is used for modelling light scattering on the micrometer-scale surface morphology. The research in this thesis focusses on several aspects of SHJ solar cells including the deposition and optimization of the indium tin oxide (ITO) front contact, the intrinsic hydrogenated amorphous silicon (a-Si:H) passivating layer, and the emitter materials, and the optical design of the device structure. The influence of ITO sputtering conditions on the passivation of c-Si wafers by a-Si:H layers is studied in Chapter 3. A low sputtering power is favorable in order to maintain a high passivation of the c-Si/a-Si:H interface, as characterized by a long minority carrier lifetime. The degradation of the passivation caused by sputtering can be reduced by sputtering the ITO at a raised substrate temperature or by post-annealing after ITO deposition. However, the substrate temperature during sputtering can degrade the passivation if it is higher than a threshold value. Based on our results we suggest that the sputtering power for ITO deposition should be as low as possible, provided the plasma is stable and a reasonable deposition rate is maintained. The substrate temperature should be kept below a threshold value of 130 °C, avoiding any degradation of the passivation. One-hour post-annealing is an effective way to recover the degradation of the passivation caused by the sputtering process at the room temperature. However, any degradation caused by annealing during sputtering cannot be recovered by post-annealing probably due to irreversible hydrogen effusion. Since passivation of the c-Si by a-Si:H is sensitive to ITO sputtering, the device can perform better without an ITO layer on the rear side when metal fully covers the rear. In Chapter 4 we show that the intrinsic a-Si:H layer (i-layer) thickness has no significant influence on the optical performance of SHJ solar cells within the thickness range we investigated. However, the influence on the electrical performance is quite noticeable. There is an absolute fill factor (FF) decrease of 3% when the thickness of the i-layer increases from 3 to 7 nm in the emitter or from 1 to 5 nm in the back surface field (BSF). The influence of the i-layer thickness in the emitter on the passivation or open-circuit voltage (Voc) is different from in the BSF. In the BSF a thinner i-layer can be used or this layer can even be omitted without a noticeable effect on the Voc, while a gain in FF is obtained, because the n-type a-Si:H layer (n-layer) in the BSF can passivate the n-type c-Si surface well enough. In the emitter, a thicker i-layer has to be used to guarantee a good passivation quality. Surface recombination velocities of the wafer passivated by different a-Si:H layer stacks are also deduced from the carrier lifetime measurements, confirming the good passivating property of the n-layer and degradation of i-layer passivation after the p-type a-Si:H layer (p-layer) is applied. Annealing can improve the passivation of the n-layer and the i/n stack, but deteriorates the passivation of the i/p stack. Compared to homojunction c-Si solar cells, one main disadvantage of SHJ solar cells is the parasitic absorption loss caused by the ITO and the a-Si:H layers. The conventional method to design the anti-reflective (AR) coating, which is based on minimization of the reflectance, cannot be applied to this specific layer structure at the front of the SHJ solar cell. The reason is that a fraction of the light gained by applying an AR coating may be absorbed by the ITO and the a-Si:H layers. In Chapter 5 we show that for SHJ solar cells the current output can be estimated by examining the light absorption in the c-Si absorber using optical simulations. Using our advanced optical simulation program, a double-layer AR coating consisting of a SiOx layer and the ITO is designed for the SHJ solar cell and implemented in experimental SHJ solar cells. For a SHJ solar cell with a textured c-Si surface and utilizing this double-layer AR coating a short-circuit current density (Jsc) of 40.5 mA/cm2 is achieved. In order to reduce the parasitic absorption of the emitter in SHJ solar cells, one effective method is to use wide-gap silicon alloy materials. In Chapter 6 we demonstrate a SHJ solar cell with a p-type a-SiC:H emitter. Compared to the p-type a-Si:H emitter, the p-type a-SiC:H increases the current output of the solar cell by reducing not only parasitic absorption in the emitter, but also the reflection of the device. The reduction of reflection is due to the fact that the refractive index of p-type a-SiC:H is in between that of ITO and intrinsic a-Si:H. Since the electrical performance of the cell with a p-type a-SiC:H emitter is comparable to that with a p-type a-Si:H emitter, the optical benefit makes the p-type a-SiC:H a very promising alternative to p-type a-Si:H as the emitter material. Finally, a 4-cm2 SHJ solar cell employing the p-type a-SiC:H emitter was made, which shows a Jsc of 40.3 mA/cm2, a Voc of 682 mV, a FF of 75.5% and a conversion efficiency of 20.8%.","silicon heterojunction; solar cells; surface passivation; emitter; antireflective coating","en","doctoral thesis","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:1f3a0f5f-4036-44bf-97d3-5f7d483209aa","http://resolver.tudelft.nl/uuid:1f3a0f5f-4036-44bf-97d3-5f7d483209aa","Novel Concepts for Silicon Based Photovoltaics and Photoelectrochemistry","Han, L.","Zeman, M. (promotor); Smets, A.H.M. (promotor)","2015","Long term concerns about climate change and fossil fuel depletion will require a transition towards energy systems powered by solar radiation or other renewable sources. Novel concepts based on silicon materials and devices are investigated for applications in the next generation photovoltaic (PV) devices and photoelectrochemical (PEC) water splitting for solar energy conversion and storage. Expanding thermal plasma chemical vapor deposition (ETP-CVD), a remote plasma synthesis method, is verified as an efficient process for the fabrication of free-standing silicon nanocrystals (Si NCs) on an industrial scale. The unique physical, mechanical and electrical properties of Si NCs might open routes to new PV concepts to breach the so-called Shockley-Queisser limit using mechanisms like multiple exciton generation and up- or down-conversion of the incident spectrum. Under intensive laser illumination conditions, the thermal heating effects of Si NCs become the dominant mechanism for the transverse optical (TO) mode red-shifts of the first order Si-Si peak in reference to the bulk c-Si in the Raman spectrum. The free-standing Si NCs can be heated to their melting points by a well-focused laser, and the temperature can be determined by the measured ratio of Anti-Stokes-to-Stokes TO mode intensities. In contrast, Si NCs in various matrices can hardly be heated using the same amount of laser power due to good thermal conductivity. If the free-standing Si NCs are further heated, the intensity of the blackbody radiation in Raman spectrum starts to compete with that of the TO mode. Various PEC/PV configurations for solar water splitting structures are discussed in this thesis to directly store the solar energy in the form of hydrogen fuels. In Chapter 4, the a-Si:H/a-Si:H double-junction solar cell is demonstrated as the simplest and easiest option to meet the requirements for the integration with gradient-doped W:BiVO4 photoanode, by considering the stability in aqueous solutions, simple fabrication process, matching spectral response, voltage and current density. The optimization steps of the a-Si:H/a-Si:H solar cells are carried out in both experiments and simulations, by varying the top i-layer thickness in reference to the AM 1.5 spectrum and the spectrum transmitted through the BiVO4 photoanode respectively. The stability of the a-Si:H/a-Si:H solar cell shows less sensitive light-induced degradation kinetics under the spectrum transmitted through the BiVO4 photoanode from that under the standard AM 1.5 spectrum. In Chapter 5, the performance of the front BiVO4 photoanode is further improved, comparing with the studies in Chapter 4, by improving photon absorption and carrier collection. Photon absorption is enhanced by the application of light trapping techniques on the BiVO4 photoanode using textured TCO glass substrates. The carrier collection is optimized based on our new findings on diffusion length of the photogenerated charge carriers in an undoped BiVO4. By ingenious design of the gradient W-dopant profile, the thickness of the film is extended without deteriorating the carrier separation efficiency. The catalytic limitation is overcome by electrodepositing a thin film of cobalt phosphate as water oxidation catalysts on the surface of BiVO4. The optimized front photoanode is combined with three types of solar cells to form a hybrid PEC/PV solar water-splitting. The collaboration of a BiVO4/a-Si:H/nc-Si:H photoanode demonstrates the best performance concerning the better solar spectrum utilization of nc-Si:H up to 1100 nm near-infra-red region. A 5.2% solar-to-hydrogen conversion efficiency, which is the highest ratio of metal-oxide based photoanodes ever reported, has been achieved by this PEC/PV configuration. Besides the photoanode device for oxygen evolution reaction, a photocathode based on thin-film silicon technology is designed and optimized as well, to form an unbiased photoanode /photocathode aiming to revolutionize solar water splitting. Photon absorption is enhanced by state-of-the-art implementation of light trapping techniques on the a-SiC:H photoanode using a glass substrate with integrated micro-textured photonic structures. The light traveling length is prolonged in the high quality grown nc-Si:H benefiting from the scattering morphology on the glass substrate. The carrier collection is boosted by our unprecedented design of the gradient boron dopant profile from the a-SiC:H p-layer to the i-layer. Novel spectral utilization techniques are applied in the device for the integrated PV junctions, supported by a theoretical optical model. A benchmark photocurrent density of -5.1 mA cm-2 at 0 V vs. RHE is achieved in the a-SiC:H/a-Si:H/nc-Si:H configuration. It is note-worthy to address that this photocathode does not contain a passivation layer nor any catalyst. The efficient operation of a photocathode also requires metal catalysts to facilitate charge-transfer reactions at the interface between the semiconducting light absorbers and the electrolyte. Atomic layer deposition (ALD) is employed to fabricate the Pt nanoparticles and thin films as the hydrogen-evolution catalysts under varied conditions. Using MeCpPtMe3 and ozone as the precursors and substrate temperatures as low as 200 °C, a growth rate as fast as 1.1 Å/cycle is achieved. The electro-catalytic activity of ALD-grown Pt thin films on glassy carbon electrodes shows comparable performance for the hydrogen-evolution reaction as that of Pt films deposited using electron-beam evaporation.","solar cells; solar water splitting; thin-film silicon","en","doctoral thesis","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:8feecef1-9d0a-42a2-a305-ccdb902dfceb","http://resolver.tudelft.nl/uuid:8feecef1-9d0a-42a2-a305-ccdb902dfceb","New bearingless generator with buoyant rotor for large direct-drive wind turbines","Bang, D.; Jang, G.W.; Hwang, S.H.; Han, P.W.; Kim, J.W.; Koo, D.H.; Polinder, H.; Ferreira, J.A.","","2014","","bearingless; Buoyant rotor; generator direct-drive; wind turbines","en","conference paper","EWEA","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:5238d48c-722c-4928-9ab8-b05ff771228e","http://resolver.tudelft.nl/uuid:5238d48c-722c-4928-9ab8-b05ff771228e","Upcoming Role of Condition Monitoring in Risk-Based Asset Management for the Power Sector","Mehairjan, R.P.Y.; Zhuang, Q.; Djairam, D.; Smit, J.J.","","2014","The electrical power sector is stimulated to evolve under the pressures of the energy transition, the deregulation of electricity markets and the introduction of intelligent grids. In general, engineers believe that technologies such as monitoring, control and diagnostic devices, can realize this evolvement smoothly. Unfortunately, the contributions of these emerging technologies to business strategies remain difficult to quantify in straightforward metrics. Consequently, decisions to invest on these technologies are still taken in an ad hoc manner. This is far from the risk-based approach commonly recommended for asset management (AM). The paper introduces risk-based management as a guiding principle for maintenance management. Then, the triple-level AM model (strategic, tactical and operational) as the foundation to define risk-based AM is described. Afterwards, two categories of risks, one triggered by technical stimuli and the other by non-technical stimuli are introduced. It is shown that the main challenge of managing risks with technical stimuli is to have the ability to understand the technical cause of failures, which is located at the operational level within the triple-level AM model. One method to quantitatively understand the technical cause of failures is by means of condition diagnostic and monitoring technologies. Therefore, the aim of this paper is to clarify the potential contribution of condition diagnostic and monitoring technologies to risk-based decision making for the power sector. This paper shows that, in practice, the implementation of condition diagnostic and monitoring technologies is mainly driven by purely technical asset based considerations without evaluating the contribution to, for instance, risks. This paper provides a list of aspects in which condition diagnostic and monitoring may contribute to risk evaluation with technical stimuli. The listed aspects (which are: (1) asset specific condition data, (2) timely condition data and (3) predictive condition data) can be regarded as input for the probability of failure and as influencing input for the consequence of failure, hence benefiting quantitative risk studies and AM activities (such as condition assessment/maintenance or replacement). Finally, these benefits can be evaluated afterwards in a risk-based AM planning stage, so that asset managers can justify investments on necessary technical improvements of condition monitoring systems.","asset management; maintenance; risk management; condition monitoring; electricity networks","en","conference paper","Springer","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:448b63f4-2128-409e-bbd8-866e720116ed","http://resolver.tudelft.nl/uuid:448b63f4-2128-409e-bbd8-866e720116ed","Doped nanocrystalline silicon oxide for use as (intermediate) reflecting layers in thin-film silicon solar cells","Babal, P.","Zeman, M. (promotor)","2014","In summary, this thesis shows the development and nanostructure analysis of doped silicon oxide layers. These layers are applied in thin-film silicon single and double junction solar cells. Concepts of intermediate reflectors (IR), consisting of silicon and/or zinc oxide, are applied in tandem cells. Multi-stack Bragg reflector IRs are tested in tandem cells, increasing the top cell current output. Finally, mechanical polishing is applied on intermediate reflectors, creating asymmetrically textured IRs. Doped silicon oxide layers have proven their versatility as multipurpose layers in thin-film silicon solar cells. In chapter 3, the search for device grade n- and p-doped silicon oxide material is described. The nanostructure of silicon oxide films with a wide array of optical and electrical properties is studied in detail by TEM, Raman, FTIR and XPS. Silicon oxide is found to be a very heterogeneous material with complex nanostructure. Both the amorphous and crystalline phases of silicon oxide are studied in detail. Differences are found between the p- and n-doped materials. It is found that the n-doped material has a nanostructure of silicon crystal grains embedded in an amorphous silicon oxide matrix. The p-doped material, however, contains silicon filaments in an amorphous silicon oxide matrix. These filaments are of intrinsic amorphous silicon with crystalline silicon grains. Intrinsic amorphous silicon is mainly responsible for good conductivity in both n-doped and p-doped silicon oxide, however, minimum crystalline content is also required. Finally, the relations between each phase and element content is related to optical and electrical properties. N-doped silicon oxide used as a back reflector in single junction solar cells reflects unabsorbed light back into the absorber layer, increasing its current output. The blue part of the spectrum is absorbed in one pass, therefore the response in the red part of the spectrum is expected to increase. However, an increase in the blue part of the spectrum is observed as well and is the topic of chapter 4. This increase is attributed to a combination of factors, but mostly to the prevention of a native oxide formation on the standard a-Si:H n-layer. The standard n-layer is covered with the n-doped silicon oxide layer which prevents the standard layer from oxidizing in ambient air. The silicon oxide also provides a better contact interface with silver. Other factors increasing the blue response include: 1. The lower activation energy of n-doped silicon oxide in comparison with the standard a-Si:H n-layer. 2. The changing of the band states due to the larger bandgap of n-doped silicon oxide in reference to n-doped a-Si:H. 3. The thinner a-Si:H n-layer as the one in the reference cell is twice as thick. 4. The lower parasitic plasmonic absorption in the silver back contact due to the common interface with silicon oxide. P-doped silicon oxide exhibits anti-reflective properties, increasing cell current output in the blue part of the spectrum as well. An initial efficiency of 11.4% is achieved with the application of both p- and n-doped silicon oxide layers in a single junction a-Si:H solar cell. Intermediate reflector concepts are explored in chapter 5. Distributed Bragg Reflectors (DBR) have tunable reflective properties and are an interesting candidate for intermediate reflectors in tandem cells. They exhibit nearly the same reflectance range under various angles of incidence. DBRs can be easily designed with the help of optical simulation software such as ASA. The design sequence is as follows: 1. The desired reflectance range inside a solar cell is simulated by varying the thickness of each material. 2. This stack is then simulated in a glass – air environment. 3. The stack is deposited on a glass substrate. 4. The measured reflectance is compared with the air – glass simulation. If a good fit is achieved, the DBR will give the desired simulated reflectance inside the cell. DBRs greatly enhance the top cell current in a tandem cell, reaching up to 13,5 mA/cm2 in a 175 nm-thick a-Si:H layer. Current matching and lowering of Voc remain issues. Texture control in the IR is important in order to provide good light scattering for both the top and bottom cells of a tandem and to provide a good substrate for the growth of a defect-free nanocrystalline absorber layer. An approach to modify the texture of ZnO serving as an asymmetric IR in a tandem cell is developed. Because of the excellent performance of the top amorphous silicon cell deposited on an Asahi VU substrate, it is beneficial to keep this substrate texture for the top cell and integrate different textures (with larger surface features) in the layers processed after the top cell. Two approaches to create an asymmetrically-textured IR are chosen: wet etching and mechanical polishing. The wet etching approach is done with two dilution levels of HCl. Then the IR interface facing the top cell has a typical Asahi VU texture while the IR interface facing the bottom cell has larger surface features beneficial for long-wavelength scattering. The second approach is about applying mechanical polishing to silicon oxide and ZnO IRs. This approach successfully flattened the Asahi-induced texture, leaving it in the IR interface facing the top cell and on the other flat side allowing higher-quality nc-Si:H growth.","silicon oxide","en","doctoral thesis","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electric Sustainable Energy","","","",""
"uuid:66ecfa5a-68a4-4ff0-b4d1-4f4611ac3131","http://resolver.tudelft.nl/uuid:66ecfa5a-68a4-4ff0-b4d1-4f4611ac3131","Opto-electrical approaches for high efficiency and ultra-thin c-Si solar cells","Ingenito, A.; Isabella, O.; Zeman, M.","","2014","The need for cost reduction requires using less raw material and cost-effective processes without sacrificing the conversion efficiency. For keeping high the generated photo-current, an advanced light trapping scheme for ultra-thin silicon wafers is here proposed, exhibiting absorptances up to 99% of 4n2 classical absorption limit for wafer thinner than 35 ?m. Such excellent optical performance does not reflect optimal electronic properties due to high recombination rate of the nano-textured surface. Therefore, we propose a passivation method involving both wet etching and high quality passivation coating of the nano-textured surface. For wet etching time longer than 30 s recombination rate of the nano-textured surface reduced more than three time with respect to the un-etched one while keeping the averaged reflectance below 2% (between 300 and 1050 nm). Electrical simulations based on such findings indicate that for wafer thinner than 35 ?m conversion efficiency higher than 25% can be achieved.","","en","conference paper","IEEE","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:60d6698d-7978-46dd-99aa-7fa431aa561b","http://resolver.tudelft.nl/uuid:60d6698d-7978-46dd-99aa-7fa431aa561b","Magnet and device for magnetic density separation","Polinder, H.; Rem, P.C.","","2014","A planar magnet for magnetic density separation, comprising an array of pole pieces succeeding in longitudinal direction of a mounting plane, each pole piece having a body extending transversely along the mounting plane with a substantially constant cross section that includes a top segment that is curved to distribute the magnetic field associated with the top surface of the pole piece such that its strength transverse to the mounting plane is substantially uniformly distributed in planes parallel to the mounting plane, the curved top segments having a width (w) in longitudinal direction of the mounting plane and a maximum height (h) transverse to the mounting plane, wherein the top segments of successive pole pieces are unequal in height and/or width.","","en","patent","European Patent Office","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:242a6d68-c0e2-43b9-b466-7c2e36b4fe48","http://resolver.tudelft.nl/uuid:242a6d68-c0e2-43b9-b466-7c2e36b4fe48","Response of low voltage networks with high penetration of photovoltaic systems to transmission network faults","Skaloumpakas, K.; Boemer, J.C.; Van Ruitenbeek, E.; Gibescu, M.","","2014","The installed capacity of photovoltaic (PV) systems connected to low voltage (LV) networks in Germany has increased to more than 25 GW. Current grid codes still mandate these PV systems to disconnect in case of voltage dips below 0.8 p.u. The resulting response of LV distribution systems with high penetration of PV systems to faults in the transmission network is investigated for an integrated power system model that comprises all relevant voltage levels. Sensitivity studies with respect to the pre-fault power flow, various steady state and fault ride-through (FRT) control modes were performed. Our simulations for a realistic 2022 scenario show that a lack of FRT capability can cause the distribution system load to increase by 35-70 % of its peak value. It was found that for under-excited operation of PV systems prior to the fault, an overvoltage can occur post-fault at some busbars in the distribution system. Therefore, we conclude that new LV-connected PV systems and other DG installations should be requested to perform FRT.","","en","conference paper","IEEE","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:fb175261-43a4-44ee-ad4b-ee586ccdd1aa","http://resolver.tudelft.nl/uuid:fb175261-43a4-44ee-ad4b-ee586ccdd1aa","Wet-chemical Treatment for Improved Surface Passivation of Textured Silicon Heterojunction Solar Cells","Deligiannis, D.; Alivizatos, S.; Ingenito, A.; Zhang, D.; Van Sebille, M.; Van Swaaij, R.A.C.M.M.; Zeman, M.","","2014","Silicon heterojunction (SHJ) solar cells constantly gain more attention due to their low cost and relatively high efficiency. An important aspect of these solar cells is the incorporation of intrinsic hydrogenated amorphous silicon (a-Si:H) layers at each side of the c-Si wafer, which has increased the efficiency potential due to the excellent surface passivation. By applying a randomly textured instead of a double-side polished wafer, optical enhancement is achieved resulting in significant reflection reduction and high short-circuit current densities (Jsc). However, texturing-induced defects lead to an a-Si:H/c-Si interface with increased recombination, which limits the open circuit voltage (Voc) of the SHJ device after using the same cleaning treatment as for the flat wafer. Thus, a one-to-one transfer of process parameters from flat to textured c-Si substrate is not necessarily appropriate and a different wet-chemical treatment is needed. In this work, a chemical treatment is demonstrated, which leads to an improved surface passivation.","silicon heterojunction; passivation; nitric acid; cleaning; wafer texturing","en","journal article","Elsevier","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:167a5735-0105-4254-810f-cf6d4a0ce713","http://resolver.tudelft.nl/uuid:167a5735-0105-4254-810f-cf6d4a0ce713","Optimized back Reflectors for Rear Diffused c-Si Solar Cells","Ingenito, A.; Ortiz Lizcano, J.C.; Luxembourg, S.L.; Santbergen, R.; Weeber, A.; Isabella, O.; Zeman, M.","","2014","At present, research in c-Si solar cells is focused on increasing the efficiency while reducing the amount of used materials. Since silicon wafer and metal contribute up to 50% to the cost of a module, it is crucial to reduce the amount of these materials to fabricate cost-effective modules. In particular, for reducing the consumption of metal, the rear back contact can be patterned leaving ample metal-free regions that are well passivated. This is the concept of open-rear-metallization, typically found in solar cell concepts such as n-Pasha. In this contribution we compare a Distributed Bragg Reflector (DBR), white paint and white foil as cost-effective back reflectors for rear diffused c-Si solar cells.","back reflector; distributed Bragg reflector; white paint; absorption","en","journal article","Elsevier","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:aaa42ebd-13d5-4e91-b9fc-299c88629314","http://resolver.tudelft.nl/uuid:aaa42ebd-13d5-4e91-b9fc-299c88629314","Quantum confinement and band offsets in amorphous silicon quantum wells","Jarolimek, K.; De Groot, R.A.; De Wijs, G.A.; Zeman, M.","","2014","Quantum wells (QWs) are nanostructures consisting of alternating layers of a low and high band-gap semiconductor. The band gap of QWs can be tuned by changing the thickness of the low band-gap layer, due to quantum confinement effects. Although this principle is well established for crystalline materials, there is still controversy for QWs fabricated from amorphous materials: How strong are the confinement effects in amorphous QWs, where, because of the disorder, the carriers are localized to start with? We prepare an atomistic model of QWs based on a-Si:H to gain insight into this problem. The electronic structure of our atomistic QWs model is described with first-principles density functional theory, allowing us to study the confinement effects directly. We find that the quantum confinement effect is rather weak, compared to experimental results on a similar system.","","en","journal article","American Physical Society","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:1f300dde-5527-411d-8b1f-54148e190ed6","http://resolver.tudelft.nl/uuid:1f300dde-5527-411d-8b1f-54148e190ed6","Paper relief architecture","Latka, J.F.","","2014","The article presents two contemporary projects of paper structures relief architecture designed and built by Shigeru Ban Architects and Voluntary Architect Network. Author of the article took part in design and construction process of one of the projects. The project of Yaan Nursery School, which was built from November 2013 till March 2014 is presented in comparison to another project realized by Shigeru Ban and VAN in the city of Chengdu after the Sichuan Earthquake in 2008. The article gives the introduction of paper components in architecture and its history and shows both projects with their differences as well as evolution of the approaches to structural solutions. The age difference between the projects is 5 years. The attempt of determination of the quality of paper as a construction material is made by comparison of their condition and the process of wear and tear of the older building. At the end of the article thoughts of the author about both projects, their implementations and pros and cons are presented.","paper in architecture; relief; emergency architecture; paper tubes; Shigeru Ban Architects","en","conference paper","International Association for Shell and Spatial Structures (IASS)","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:0ce31d69-2964-4716-934e-289e95260145","http://resolver.tudelft.nl/uuid:0ce31d69-2964-4716-934e-289e95260145","Cross-bonding cable and box model based on pulse reflection measurement","De Regt, J.J.; Hoogendorp, G.; Wagenaars, P.; Wouters, P.A.A.F.; Popov, M.; Van der Sluis, L.; Steennis, E.F.","","2014","Transients from lightning strikes can enter underground cables at overhead line to power cable transitions. Possible overvoltages on these surges at cross-bonding connections of the cable screens are of major concern. A model is developed for modelling overvoltages from transient signal propagation through a combined cross-bonding cable and box. This model is applied to the first Dutch 400 kV cable connection. Such model incorporates model parameters whose values depend on design details of the cross-bonding box. The values for these model parameters are extracted from the measured transmission and reflection signal on steep pulses injected into the actual cross-bonding box configuration. The model combines transmission line description for the cross-bonding cables with mainly inductive behaviour of the cross-bonding box. The obtained results are verified by measurements. The model is applied to investigate overvoltages induced at the cross-bonding cable and box on 1.2/50 ?s impulse voltage injection representing a lightning impulse voltage applied to the core conductor of the cross-bonding cable. Furthermore, the effectiveness of surge arresters to reduce overvoltages at the cross-bonding cable screen is demonstrated by simulations with this model in PSCAD.","overvoltage protection; overhead line conductors; lightning protection; power overhead lines; arresters; underground cables; power system transients; pulse measurement","en","journal article","Institution of Engineering and Technology (IET)","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:a9b1c2fe-4e25-48da-b009-9927350b457a","http://resolver.tudelft.nl/uuid:a9b1c2fe-4e25-48da-b009-9927350b457a","Quadruple-junction thin-film silicon-based solar cells with high open-circuit voltage","Si, F.T.; Kim, D.; Santbergen, R.; Tan, H.; Van Swaaij, R.A.C.M.M.; Smets, A.H.M.; Isabella, O.; Zeman, M.","","2014","","","en","journal article","American Instutute of Physics","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:91ea86fd-f880-4b64-9b56-39a89902d2f9","http://resolver.tudelft.nl/uuid:91ea86fd-f880-4b64-9b56-39a89902d2f9","Analysis of North Sea Offshore Wind Power Variability","Buatois, A.; Gibescu, M.; Rawn, B.G.; Van der Meijden, M.A.M.M.","","2014","This paper evaluates, for a 2030 scenario, the impact on onshore power systems in terms of the variability of the power generated by 81 GW of offshore wind farms installed in the North Sea. Meso-scale reanalysis data are used as input for computing the hourly power production for offshore wind farms, and this total production is analyzed to identify the largest aggregated hourly power variations. Based on publicly available information, a simplified representation of the coastal power grid is built for the countries bordering the North Sea. Wind farms less than 60 km from shore are connected radially to the mainland, while the rest are connected to a hypothetical offshore HVDC (High-Voltage Direct Current) power grid, designed such that wind curtailment does not exceed 1% of production. Loads and conventional power plants by technology and associated cost curves are computed for the various national power systems, based on 2030 projections. Using the MATLAB-based MATPOWER toolbox, the hourly optimal power flow for this regional hybrid AC/DC grid is computed for high, low and medium years from the meso-scale database. The largest net load variations are evaluated per market area and related to the extra load-following reserves that may be needed from conventional generators.","offshore wind; meso-scale models; hybrid AC-DC optimal power flow; wind power variability; DC offshore grid","en","journal article","MDPI","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:648a1baa-6964-49dc-8cea-9e472c67bb4a","http://resolver.tudelft.nl/uuid:648a1baa-6964-49dc-8cea-9e472c67bb4a","Collection System Cable Routing and Wake Losses Optimization in Offshore Wind Farms","Fragoso Rodrigues, S.M.; Bauer, P.; Bosman, P.A.N.; Pierik, J.","","2014","Offshore wind farms with high installed capacities and located further from the shore are starting to be built by northern European countries. Furthermore, it is expected that by 2020, several dozens of large offshore wind farms will be built in the Baltic, Irish and North seas. These wind farms will be constituted of a considerable number of turbines packed together. Due to shadowing effects between turbines, the power production is reduced, resulting in a decreased wind farm efficiency. Moreover, the collection system length and complexity rapidly increase with the number of wind turbines installed, resulting in higher investment costs and power losses. Hence, when large wind farms are considered, wake losses and collection system total length are important aspects that need to be optimized. Nonetheless, designing a large offshore wind project is a very complex task. In the development phase, an enormous amount of time is used to generate feasible wind farm designs. For example, the manual layout optimization and cable routing are highly time consuming. Amongst others, this drawback leads to offshore wind projects with very high investments costs. In fact, electricity generated offshore is, up to today, substantially more expensive when compared to onshore wind or combined cycle gas turbines. Wind farm layout optimization is a possible solution to further increase the efficiency of wind projects leading to lower prices of energy generated offshore. Moreover, investment costs would be reduced if the collection system could be automatically designed via optimization tools. The aim of this work is to obtain optimized offshore wind farm layouts with enhanced energy production while considering the seabed constraints, e.g. maximum sea depth, inappropriate soil types and large seabed gradients. Through the use of optimization tools it is also desired to alleviate the designer teams of mundane manual layout optimization and cable routing. The optimized wind farm layout obtained presents higher energy yield. Although, the collection system total length is higher than for the standard case, the overall system efficiency is improved. Moreover, installation costs of the collection system were reduced through the avoidance of challenging areas of the wind farm. The wind turbine support structures costs were also reduced since deep areas of the seabed were avoided. In this work it is presented a novel optimization tool to obtain optimized offshore wind farm layouts while taking into consideration the seabed profile. Due to the increased offshore activity in recent years, as well as the expected installation in the coming years, this tool becomes very important and relevant for the offshore field.","Collection System Routing; Covariance Matrix Adaptation Evolutionary Strategy; Offshore Wind Energy; Wake losses; Wind Farm Layout Optimization","en","conference paper","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:aff41ea8-7aa1-44b2-bd81-0cdd60c8e98d","http://resolver.tudelft.nl/uuid:aff41ea8-7aa1-44b2-bd81-0cdd60c8e98d","Enhancing the driving field for plasmonic nanoparticles in thin-film solar cells","Santbergen, R.; Hairen, T.; Zeman, M.; Smets, A.H.M.","","2014","The scattering cross-section of a plasmonic nanoparticle is proportional to the intensity of the electric field that drives the plasmon resonance. In this work we determine the driving field pattern throughout a complete thin-film silicon solar cell. Our simulations reveal that by tuning of the thicknesses of silicon and transparent conductive oxide layers the driving field intensity experienced by an embedded plasmonic nanoparticle can be enhanced up to a factor of 14. This new insight opens the route towards more efficient plasmonic light trapping in thin-film solar cells.","plasmonics; interference; solar energy","en","journal article","Optical Society of America","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:4bc56c84-fc33-4ef0-b84a-03e0b06ea665","http://resolver.tudelft.nl/uuid:4bc56c84-fc33-4ef0-b84a-03e0b06ea665","UMBRELLA Deliverable D 7.3 “Workshop results on innovative operational tools”","Electrical Sustainable Energy Department ","","2014","In the present deliverable, the results of the second common ‘Workshop on intermediate results’, co-organized by UMBRELLA and iTesla projects are summarized. The workshop was hosted at ENTSO-E’s premises on January 14th, 2014 with a total number of some 80 registered participants including experts from industry, academia and regulatory bodies.","","en","report","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:10d2436b-f0f0-436c-999f-9bdff4600182","http://resolver.tudelft.nl/uuid:10d2436b-f0f0-436c-999f-9bdff4600182","Improved cost of energy comparison of permanent magnet generators for large offshore wind turbines","Hart, K.; McDonald, A.; Polinder, H.; Corr, E.; Carroll, J.","","2014","This paper investigates geared and direct-drive permanent magnet generators for a typical offshore wind turbine, providing a detailed comparison of various wind turbine drivetrain configurations in order to minimise the Cost of Energy. The permanent magnet generator topologies considered include a direct-drive machine and single stage, two-stage or three-stage gearbox driven generators. The cost of energy calculations are based on initial capital costs, the costs of manufacture, installation, operations and maintenance, with particular focus on improved calculations of the annual energy yield with better availability estimations and gearbox loss modelling.","cost of energy; permanent magnet generator; direct-drive; gearbox; wind turbine","en","conference paper","EWEA","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:01387120-a39a-477f-acea-e5b902b018fa","http://resolver.tudelft.nl/uuid:01387120-a39a-477f-acea-e5b902b018fa","Design study of a 10 MW MgB2 superconductor direct drive wind turbine generator","Abrahamsen, A.B.; Magnusson, N.; Liu, D.; Stehouwer, E.; Hendriks, B.; Polinder, H.","","2014","A superconducting direct drive generator based on field windings of MgB2 superconducting tape is proposed as a solution by mounting the generator in front of the blades using a king-pin nacelle design for offshore turbines with power ratings larger than 10 MW as investigated in the INNWIND.EU project.","superconducting generator; direct drive generator; offshore wind turbine; nacelle integration","en","conference paper","EWEA","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:de73f389-6203-4ff4-acaa-269bb89b081a","http://resolver.tudelft.nl/uuid:de73f389-6203-4ff4-acaa-269bb89b081a","Integrated Automotive High-Power LED-Lighting Systems in 3D-MID Technology","Thomas, W.","Ferreira, J.A. (promotor)","2014","The growing energy consumption of lighting as well as rising luminous efficacies and -fluxes of high-power Light Emitting Diodes (LEDs) have contributed to the widespread use of LEDs in modern lighting systems. One of the most prominent users of the LED-technology is automotive (exterior) lighting. It benefits from LEDs’ high efficiencies and long lifetimes, but furthermore uses their small size as key feature to obtain new degrees of freedom in placing light elements. Although automotive LED-lighting is at the leading edge regarding 3D LED-lighting systems, their current construction is not optimised towards complex design requirements. This thesis deals with decreasing the complexity and improving the degrees of freedom in the design of three-dimensional high-power LED-lighting systems with power electronic LED-driver by enhancing the level of function integration. Three main challenges are identified for the proposed concept and are investigated throughout the thesis. These are the integration of the power electronic LED-driver, of spatial - and electrical-functions as well as of thermal management functions into the three-dimensional multifunctional component.","Power Electronics; LED; Light Emitting Diode; Automotive; Integration of Power Electronics; 3D-MID; 3D-Moulded Interconnect Device; 3D-Molded Interconnect Device; Three-dimensional circuit carrier","en","doctoral thesis","Cuvillier Verlag","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:9b0a88cf-c2c6-43d3-810d-b64a211ab419","http://resolver.tudelft.nl/uuid:9b0a88cf-c2c6-43d3-810d-b64a211ab419","Multi-Terminal DC Networks: System Integration, Dynamics and Control","Teixeira Pinto, R.","Ferreira, J.A. (promotor)","2014","When large amounts of electricity need to be transported for long distances, or when underground or submarine cables are involved, using direct current high-voltage transmission systems is more efficient and cost effective than using traditional high-voltage alternating current transmission. Therefore, the main thesis objective is to study to what extent can multi-terminal dc networks provide an optimal platform to foster the integration of remotely located renewable resources, with particular focus on the integration of offshore wind farms in the North Sea. In this thesis, five main challenges were identified before high-voltage multi-terminal dc networks – which can promote the inclusion of remotely located renewable sources while strengthening the existing ac power system networks – can finally become widespread: system integration, power flow control, dynamic behaviour, stability and fault behaviour. These challenges are investigated through a comprehensive literature review, a series of detailed simulation models, and an experimental laboratory setup of a three-node multi-terminal dc network. A novel strategy to control the power flow in multi-terminal dc networks – called Distributed Voltage Control – was developed in this thesis. In the experimental setup, three voltage-source converters were successfully operated in a parallel-radial multi-terminal dc network with a symmetric monopolar configuration. Lastly, a real-time digital simulator was used to emulate the behaviour of an offshore wind farm. Real measurements from the Dutch offshore wind farm Egmond aan Zee were used to validate the Distributed Voltage Control strategy, which successfully controlled the power flow inside the three-terminal low-voltage dc network with high overall precision, while providing the complete system with a fast dynamic response.","DC networks; HVDC transmission; voltage-source converters; control theory; distributed voltage control strategy; optimisation algorithms; power electronics; offshore wind energy; real-time digital simulator","en","doctoral thesis","CPI Koninklijke Wöhrmann","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:2a967778-6cb1-45a2-ab90-9cbe1ad030da","http://resolver.tudelft.nl/uuid:2a967778-6cb1-45a2-ab90-9cbe1ad030da","The Power Sandwich: A Three-Dimensional Power Electronics Assembly Technology","Josifovic, I.","Ferreira, J.A. (promotor)","2014","Current PCB power converter construction technologies are based on the utilization of nonstandardized building blocks. Utilization of passive components with various shapes, poor thermal properties and mixed technology mounting (THT and SMT) represents fundamental limit for reaching high power density, effective thermal management, particular form-factor and a low-cost fully automated assembly of power electronic converters. The thesis develops a power electronics construction technology, which utilizes heightstandardized SMT passive components with enhanced thermal properties. This ultimately enables to achieve fully automated SMT assembly at low cost, high power densities and desired form-factor of power converters.","power electronics; power density; 3D Assembly; power sandwich","en","doctoral thesis","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:baa1f82f-e3b7-465d-901f-d85c1001369f","http://resolver.tudelft.nl/uuid:baa1f82f-e3b7-465d-901f-d85c1001369f","Electrical Power Converter","Ferreira, J.A.","","2014","Electrical power converter for converting electrical power of a power source connected or connectable at an input to electrical DC-power at an output, wherein between the input and the output a first circuit of submodules is provided, wherein said first circuit of submodules and the power source form a primary power loop and wherein each submodule comprises an energy storage component and each submodule is connected to a controller to drive the submodules in order to arrange that the electrical power at the output is DC-power, wherein the first circuit of submodules is provided with a parallel second electrical circuit so as to arrange that the first circuit and the parallel second circuit form a secondary power loop to enable the flow of local currents between the energy storage components of the submodules, wherein at the converter's output a blocking circuit is provided tuned to the operating frequency of the secondary power loop and that the secondary power loop is embodied as a current bypass circuit for the primary power loop so as to prevent that power from the converter flows to the input.","","en","patent","European Patent Office","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:f2e60853-b77d-4790-8868-cfbb2684d4f7","http://resolver.tudelft.nl/uuid:f2e60853-b77d-4790-8868-cfbb2684d4f7","Life-cycle assessment of high-voltage assets using statistical tool","Chmura, L.A.","Smit, J.J. (promotor); Morshuis, P.H.F. (promotor)","2014","Nowadays, utilities are confronted with assets reaching or even exceeding their designed life. This in turn, implies the occurrence of upcoming replacements to assure reliable network operation. In this thesis, the application of statistical tools for life-time and residual life assessment of high-voltage assets installed in a power network is presented. More specifically, future failure behaviour is estimated by statistical distribution fitting to the life-data of different assets types. Further focus is put on the obstacles hindering the interpretation of the life-data. The results presented in this thesis are continuation of the cooperation between the Dutch utility Liander and Delft University of Technology, investigating the applicability of statistical tools as a mean to support the replacement and spare parts policies for component populations being in operation. For the latter, assessment of the life-time, as accurate as possible is necessary. This in turn, is based on the limited, incomplete and imperfect data. In order to provide systematic methodology, the thesis works out the limits of the statistical tools applicability, for the condition assessment of populations of high-voltage assets. Particularly, the exceptional failure occurrence, influence of operational condition and possible discontinuities of the failure rate function are of interest. Based on the study-cases, ways to overcome hurdles met during statistical analysis are presented. First of all, based on the real examples of failure data of high-voltage assets, the robustness of the statistical analysis for incomplete life and imperfect data containing singularities is elaborated. Second of all, the fact of varying load of the components population and its influence on the process of statistical analysis is investigated and the results are put forward. In the end, the validity of the statistical analysis is discussed. In particular, the continuous behaviour of the failure rate function is interesting. It has been shown that due to gradual load increase over time, the sudden break in failure rate function and in the failure prediction is not expected to occur. The above mentioned study-cases have been used to determine the extent to which the statistical tools, in particular Weibull curve fitting methodology, can be applied to the life-time assessment of power network components. In particular, the derivation and extrapolation of the time-dependent failure rate function together with its confidence limits is possible and of relevance for the management of the assets and further decision making. Thus, the gap between the statistical tools used to analyse the imperfect data of the populations and decision making processes with respect to these populations, is closed by the study-cases presentation. It has been shown that the statistical analysis is a robust methodology for the asset life-time assessment. More specifically, it can provide answers to the questions with respect to the replacement and spare parts policies of the high-voltage assets installed in power network.","Statistics; failures; high-voltage; assets; asset management; Weibull distribution","en","doctoral thesis","","","","","","","","2016-01-16","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:59991074-c939-48e7-aa10-5f64e4551d86","http://resolver.tudelft.nl/uuid:59991074-c939-48e7-aa10-5f64e4551d86","Strengthening future electricity grid of the Netherlands by integration of HTS transmission cables","Zuijderduin, R.; Chevtchenko, O.; Smit, J.J.; Aanhaanen, G.; Ross, R.","","2014","The electricity grid of the Netherlands is changing. There is a call of society to use more underground cables, less overhead lines (OHL) and to reduce magnetic emissions. At the same time, parts of the future transmission grid need strengthening depending on the electricity demand in the coming decades [1]. Novel high temperature superconductor (HTS) AC transmission cables can play a role in strengthening the grid. The advantages as compared to alternatives, are: economic, underground, higher power capacity, lower losses, reduced magnetic field emissions in (existing) OHL, compact: less occupation of land and less permits needed, a possibility to keep 380 kV voltage level in the grid for as long as needed. The main obstacles are: the relatively high price of HTS tapes and insufficient maturity of the HTS cable technology. In the paper we focus on a 34 km long connection in the transmission grid (to be strengthened in three of the four of TenneT scenarios [1]), present the network study results, derive the requirements for corresponding HTS transmission cable system and compare HTS system to the alternatives (OHLs and XLPE cables).","superconductivity","en","conference paper","IOP","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:fabc0cb6-e868-4bf4-84c2-f45cfc7d6642","http://resolver.tudelft.nl/uuid:fabc0cb6-e868-4bf4-84c2-f45cfc7d6642","Design of an MgB2 race track coil for a wind generator pole demonstration","Abrahamsen, A.B.; Magnusson, N.; Jensen, B.B.; Liu, D.; Polinder, H.","","2014","An MgB2 race track coil intended for demonstrating a down scaled pole of a 10 MW direct drive wind turbine generator has been designed. The coil consists of 10 double pancake coils stacked into a race track coil with a cross section of 84 mm x 80 mm. The length of the straight section is 0.5 m and the diameter of the end sections is 0.3 m. Expanded to a straight section of 3.1 m it will produce about 1.5 T magnetic flux density in the air gap of the 10 MW 32 pole generator and about 3.0 T at the edge of the superconducting coil with an operation current density of the coil of 70 A/mm2.","","en","conference paper","IOP","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:33aa3243-5ad0-4bad-89ef-433126b741a3","http://resolver.tudelft.nl/uuid:33aa3243-5ad0-4bad-89ef-433126b741a3","Feasibility study of a superconducting motor for electrical helicopter propulsion","Simons, C.A.B.A.E.; Sanabria-Walter, C.; Polinder, H.","","2014","During the past decades, superconducting electrical machines have become more suitable to replace conventional iron based designs, because of their lower weight and higher torque density. These properties make them good candidates for use in More Electric Aircraft (MEA). Especially helicopter propulsion systems could benefit from the increased performance. This paper describes the feasibility study of a superconducting motor to be used for helicopter propulsion as part of a More Electric Aircraft (MEA). For this, the armature, field windings and cryostat are designed, aiming at meeting the difficult specifications. Since superconductors have virtually no electrical resistance when cooled down below a certain critical temperature, they can be used to build high field and low weight coils for electrical machines. Especially the possibility to not use iron can make the superconducting motor lighter with a higher power density compared with conventional Permanent Magnet (PM) motors.","","en","conference paper","IOP","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:42184015-8cac-4be2-8084-a221744d0452","http://resolver.tudelft.nl/uuid:42184015-8cac-4be2-8084-a221744d0452","Feasibility Study of a 10 MW MgB2 Fully Superconducting Generator for Offshore Wind Turbines","Kostopoulos, D.; Liu, D.; Genani, G.; Polinder, H.","","2013","Offshore wind is considered a vital component of the future large scale renewable generation portfolio. Intense R&D effort is occurring in both the technology and the supply chain aiming at cost reduction. The drivetrain of wind turbines is an area of continuous evolution with currently no one standard configuration in the industry. It is anticipated that in order to upscale offshore wind turbines in the 10+ MW power range innovation is necessary in this subsystem. A possible solution could be the adoption of superconductivity technology. The potential benefits are multiple comprising weight, dimension and cost reduction in both capital and operating costs. In this paper a rough analytical design is presented of an MgB2 fully superconducting wind turbine generator (WTG). An analytical current sheet distribution is adopted to calculate the magnetic field of the generator and a finite element method (FEM) analysis is used to verify the field calculation. The objective of this work is to assess the technical feasibility of this generator topology and attempt to extract more general conclusions regarding the potential application of superconducting drivetrains in offshore wind turbines.","","en","conference paper","European Wind Energy Association","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:2d1e21d4-3bc3-4f15-815e-888b2583f743","http://resolver.tudelft.nl/uuid:2d1e21d4-3bc3-4f15-815e-888b2583f743","Modular Approach for the Optimal Wind Turbine Micro Siting Problem through CMA-ES Algorithm (abstract)","Rodrigues, S.; Bauer, P.; Pierik, J.","","2013","Although, only in recent years, northern European countries started to install large offshore wind farms, it is expected that by 2020, several dozens of far and large offshore wind farms (FLOWFs) will be built. These FLOWFs will be constituted of a considerable amount of wind turbines (WTs) packed together, leading to an energy density increase. However, due to shadowing effects between WTs, power production is reduced, resulting in a revenues decrease. Therefore, when FLOWFs are considered, wake losses reduction is an important optimization goal. This work presents a modular approach to optimize the energy yield of FLOWFs through an evolutionary algorithm. The method consists of a modular strategy where the site wind rose information is used in different steps, which accelerates the calculation of the wake losses. The main contribution of this paper is the use of surrogate models to optimize the layout of offshore wind farms. Although, the surrogates models do not make use of the entire wind information set, they preserve the main problem trend. At the end, the results obtained are tested for their sensitivity regarding the wind data and the turbine locations.","","en","conference paper","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:b3303f46-c311-48fa-9758-78bcccbc2960","http://resolver.tudelft.nl/uuid:b3303f46-c311-48fa-9758-78bcccbc2960","Micro-textures for efficient light trapping and improved electrical performance in thin-film nanocrystalline silicon solar cells","Tan, H.; Psomadaki, E.; Isabella, O.; Fischer, M.; Babal, P.; Vasudevan, R.A.; Zeman, M.; Smets, A.H.M.","","2013","","","en","journal article","American Instutute of Physics","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:3bd97b56-3edb-4071-8d5e-fe901b9d6e23","http://resolver.tudelft.nl/uuid:3bd97b56-3edb-4071-8d5e-fe901b9d6e23","Electricity yield simulation of complex BIPV systems","Sprenger, W.","Zeman, M. (promotor)","2013","Building-integrated photovoltaic systems (BIPV) are able to improve the energy balance of buildings. However, this improvement can be analyzed quantitatively only if the electricity yield generated by the BIPV system is calculated. This PhD thesis presents a simulation program that calculates the electricity yield generated by BIPV systems, including those made of geometrically complex BIPV modules. The simulation is based on a combination of a ray-tracing procedure with the resultant I-V curves of electrically connected PV cells. For the annual electricity yield, multi-core cluster computers are applied to perform the simulation on the basis of 5-minute meteorological data throughout a year. The ray-tracing technique is applied to calculate inhomogeneous irradiation, the consequence of shading or reflections from surrounding objects, and the quantitative relevance of reflections from the ground. The temperatures of the PV cells are calculated by taking the physical principles of heat conduction, heat convection and thermal radiation into account. The cell I-V curves are calculated depending on the temperature and the irradiance. After the virtual interconnection of the PV cells in the simulation, the effect of inverter efficiency and its dependence on the generator voltage are calculated, finally leading to the AC power of the BIPV system. All parts of the simulation are validated by comparison with measurements, and the accuracy of the simulation is quantified with the help of statistical measures. Finally, the simulation program is applied to calculate the electricity yield generated by two BIPV systems.","BIPV","en","doctoral thesis","Fraunhofer-Verlag","","","","","","","2023-10-10","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:b2c68eba-cd2c-4f3c-8c68-2e9a06172135","http://resolver.tudelft.nl/uuid:b2c68eba-cd2c-4f3c-8c68-2e9a06172135","Analysis of Switching Transient Overvoltages in the Power System of Floating Production Storage and Offloading Vessel","Xue, H.; Popov, M.","","2013","Large transient overvoltages are normally caused by vacuum circuit breaker (VCB) switching operation during disconnection of induction motors. In this paper VCBs, cables, generators, busbars, induction motors and surge arresters are modeled by making use of ATP-EMTP. Switching transient overvoltages of four typical induction motors are analyzed under starting, full load and light load working conditions in a power system of a Floating Production Storage and Offloading (FPSO) vessel. A suitable protection against the switching transient overvoltage is proposed and the results are presented.","switching transient overvoltage; ATP-EMTP; FPSO; VCBs; induction motors; surge protection","en","conference paper","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:e636b149-ff5e-40b7-8e41-b2258e50e8b1","http://resolver.tudelft.nl/uuid:e636b149-ff5e-40b7-8e41-b2258e50e8b1","An Efficient Algorithm for Fault Location on Mixed Line-Cable Transmission Corridors","Popov, M.; Rietveld, G.; Radojevic, Z.; Terzija, V.","","2013","This paper presents a fault location algorithm that can be used to accurately locate the fault at any place along mixed line-cable transmission corridors. The algorithm is an impedance based line/cable parameter dependent algorithm. The fault location algorithm is derived using distributed line model, modal transformation theory and Discrete Fourier Transform. The algorithm can be used as an on-line, or off-line application in practice. The proposed solution has the ability to locate the fault whether it is on the overhead line or on the underground power cable. The paper presents the results of the initial algorithm testing through the use of ATP simulations. Some results are validated by experimental measurements.","fault location; mixed line-cable transmission corridors; numerical algorithms; measurements; errors","en","conference paper","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:b6947c9d-75c0-4771-9516-368d007625c1","http://resolver.tudelft.nl/uuid:b6947c9d-75c0-4771-9516-368d007625c1","Lightning Induced Overvoltages in Mixed 380 kV OHL-Cable-OHL connections","Hoogendorp, G.; Popov, M.; Van der Sluis, L.","","2013","Transmission of electric energy at high voltage levels is mainly performed by overhead lines. Nowadays, an increasing amount of power grid operators are replacing overhead transmission lines by underground cables. Cable presence in power systems may have consequences for the behavior of the total system, since cables have much larger capacitance than overhead lines. In the Netherlands, a new mixed 380 kV connection is under construction, in which four underground cable sections are embedded between overhead lines. In this paper, the behavior of this mixed line-cable-line configuration is studied during lightning events. The study is performed by using a transient simulation model of this mixed 380 kV system, which is developed in PSCAD.","cable; transient model; lightning","en","conference paper","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:2fc02d51-2a1f-44ab-acf4-21aa85b95dac","http://resolver.tudelft.nl/uuid:2fc02d51-2a1f-44ab-acf4-21aa85b95dac","Plasmonic silicon solar cells: Impact of material quality and geometry","Pahud, C.; Isabella, O.; Naqavi, A.; Haug, F.J.; Zeman, M.; Herzig, H.P.; Ballif, C.","","2013","We study n-i-p amorphous silicon solar cells with light-scattering nanoparticles in the back reflector. In one configuration, the particles are fully embedded in the zinc oxide buffer layer; In a second configuration, the particles are placed between the buffer layer and the flat back electrode. We use stencil lithography to produce the same periodic arrangement of the particles and we use the same solar cell structure on top, thus establishing a fair comparison between a novel plasmonic concept and its more traditional counterpart. Both approaches show strong resonances around 700 nm in the external quantum efficiency the position and intensity of which vary strongly with the nanoparticle shape. Moreover, disagreement between simulations and our experimental results suggests that the dielectric data of bulk silver do not correctly represent the reality. A better fit is obtained by introducing a porous interfacial layer between the silver and zinc oxide. Without the interfacial layer, e.g. by improved processing of the nanoparticles, our simulations show that the nanoparticles concept could outperform traditional back reflectors.","","en","journal article","Optical Society of America","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:484448ad-566b-4905-9e46-29cc727095d6","http://resolver.tudelft.nl/uuid:484448ad-566b-4905-9e46-29cc727095d6","Coordinated Agent-Based Control for On-line Voltage Instability Prevention","Baalbergen, J.F.","Van der Sluis, L. (promotor); Gibescu, M. (promotor)","2013","Service interruptions have a significant impact on society and therefore the main objective of power system planning and operation is to ensure that they do not happen. Because voltage instability is one of the dynamic phenomena that may result in a system-wide blackout, this type of stability problem has been an important research topic for many years. Grid developments, like the increase of Renewable and Distributed Generation (RDG) and the impact of deregulation, in combination with the steadily increasing electricity demand, will have its impact on the vulnerability of the power system to voltage stability problems. On the other hand, developments in power system monitoring and control such as the use of accurate Phasor Measurement Units and the development of Smart Grid control concepts, introduce new possibilities for voltage instability prevention. In this work the impact of having a large share of RDG capacity on voltage stability is investigated and a new Hierarchical Agent-Based Voltage Instability Prevention (HABVIP) system for online voltage instability emergency control is proposed. The control philosophy uses the maximum loadability index to determine the amount of active and reactive power load relief necessary to restore stability. The intelligence for this control is provided by agents located in the substations: the substation agents. The load relief is obtained by: increase of local generation, virtual load shedding via adjusting the load tap changers set point, intelligent load control and increasing the reactive power output of Static Var Compensators. The control of the actuators is provided by agents located in the actuators: the actor agents. Verification of the system is done by off-line simulations and by building a real-time hardware in the loop demonstration model.","power systems; voltage stability; smart-grid","en","doctoral thesis","","","","","","","","2013-06-07","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:94cac88a-be85-44b1-b4da-a573669a908a","http://resolver.tudelft.nl/uuid:94cac88a-be85-44b1-b4da-a573669a908a","Designing optimized nano textures for thin-film silicon solar cells","Jäger, K.; Fischer, M.; Van Swaaij, R.A.C.M.M.; Zeman, M.","","2013","Thin-film silicon solar cells (TFSSC), which can be manufactured from abundant materials solely, contain nano-textured interfaces that scatter the incident light. We present an approximate very fast algorithm that allows optimizing the surface morphology of two-dimensional nano-textured interfaces. Optimized nano-textures scatter the light incident on the solar cell stronger leading to a higher short-circuit current density and thus efficiency. Our algorithm combines a recently developed scattering model based on the scalar scattering theory, the Perlin-noise algorithm to generate the nano textures and the simulated annealing algorithm as optimization tool. The results presented in this letter allow to push the efficiency of TFSSC towards their theoretical limit.","","en","journal article","Optical Society of America","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:36b0cd17-f1ca-46bc-b13a-c8d3afdb7436","http://resolver.tudelft.nl/uuid:36b0cd17-f1ca-46bc-b13a-c8d3afdb7436","Improved light trapping in microcrystalline silicon solar cells by plasmonic back reflector with broad angular scattering and low parasitic absorption","Tan, H.; Sivec, L.; Yan, B.; Santbergen, R.; Zeman, M.; Smets, A.H.M.","","2013","We show experimentally that the photocurrent of thin-film hydrogenated microcrystalline silicon (?c-Si:H) solar cells can be enhanced by 4.5?mA/cm2 with a plasmonic back reflector (BR). The light trapping performance is improved using plasmonic BR with broader angular scattering and lower parasitic absorption loss through tuning the size of silver nanoparticles. The ?c-Si:H solar cells deposited on the improved plasmonic BR demonstrate a high photocurrent of 26.3?mA/cm2 which is comparable to the state-of-the-art textured Ag/ZnO BR. The commonly observed deterioration of fill factor is avoided by using ?c-SiOx:H as the n-layer for solar cells deposited on plasmonic BR.","elemental semiconductors; hydrogen; nanoparticles; photoconductivity; plasmonics; radiation pressure; semiconductor thin films; silicon; silver; solar cells; thin film devices","en","journal article","American Institute of Physics","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:29b6b47d-8cd6-4099-950f-bd4f1f50cf16","http://resolver.tudelft.nl/uuid:29b6b47d-8cd6-4099-950f-bd4f1f50cf16","Ultrahigh throughput plasma processing of free standing silicon nanocrystals with lognormal size distribution","Dogan, I.; Kramer, N.J.; Westermann, R.H.J.; Dohnalova, K.; Smets, A.H.M.; Verheijen, M.A.; Greogorkiewicz, T.; Van de Sanden, M.C.M.","","2013","We demonstrate a method for synthesizing free standing silicon nanocrystals in an argon/silane gas mixture by using a remote expanding thermal plasma. Transmission electron microscopy and Raman spectroscopy measurements reveal that the distribution has a bimodal shape consisting of two distinct groups of small and large silicon nanocrystals with sizes in the range 2–10?nm and 50–120?nm, respectively. We also observe that both size distributions are lognormal which is linked with the growth time and transport of nanocrystals in the plasma. Average size control is achieved by tuning the silane flow injected into the vessel. Analyses on morphological features show that nanocrystals are monocrystalline and spherically shaped. These results imply that formation of silicon nanocrystals is based on nucleation, i.e., these large nanocrystals are not the result of coalescence of small nanocrystals. Photoluminescence measurements show that silicon nanocrystals exhibit a broad emission in the visible region peaked at 725?nm. Nanocrystals are produced with ultrahigh throughput of about 100?mg/min and have state of the art properties, such as controlled size distribution, easy handling, and room temperature visible photoluminescence.","crystal morphology; elemental semiconductors; nanofabrication; nanostructured materials; nucleation; photoluminescence; plasma materials processing; Raman spectra; semiconductor growth; silicon; transmission electron microscopy","en","journal article","American Institute of Physics","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:3e2cb6d7-3ba2-4b45-af71-2fa106b5d189","http://resolver.tudelft.nl/uuid:3e2cb6d7-3ba2-4b45-af71-2fa106b5d189","Optimal Usage of Multiple Energy Carriers in Residential Systems: Unit Scheduling and Power Control","Ramirez-Elizondo, L.M.","Van der Sluis, L. (promotor)","2013","The world’s increasing energy demand and growing environmental concerns have motivated scientists to develop new technologies and methods to make better use of the remaining resources of our planet. The main objective of this dissertation is to develop a scheduling and control tool at the district level for small-scale systems with multiple energy carriers and to apply exergy-related concepts for the optimization of these systems. The tool is based on the energy hub approach and provides insights and techniques that can be used to evaluate new district energy scenarios. The topics that are presented include the multicarrier unit commitment framework, the multi-carrier exergy hub approach, a hierarchical multi-carrier control architecture, a comparison of multi-carrier power applications and the implementation of a multi-carrier energy management system in a real infrastructure.","optimization; multiple energy-carriers; renewables; sustainable energy","en","doctoral thesis","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:a887bf7a-0a43-4793-b10c-8d82e424ca2b","http://resolver.tudelft.nl/uuid:a887bf7a-0a43-4793-b10c-8d82e424ca2b","Dangling-bond defect in a-Si:H: Characterization of network and strain effects by first-principles calculation of the EPR parameters","Pfanner, G.; Freysoldt, C.; Neugebauer, J.; Inam, F.; Drabold, D.; Jarolimek, K.; Zeman, M.","","2013","The performance of hydrogenated amorphous silicon (a-Si:H) solar cells is severely affected by the light-induced formation of metastable defects in the material (Staebler-Wronski effect). The common notion is that the dangling-bond (db) defect, a threefold coordinated silicon atom, plays a key role in the underlying mechanisms. To support the characterization of this defect by electron paramagnetic resonance (EPR), we present in this work a first-principles study of the EPR parameters for a structural ensemble of the db defect. We show that the a-Si:H dangling bond is a network defect for which charge and spin localization substantially depend on the actual coordination of the db atom and the local geometric and electronic structure of the immediate surrounding. It consequently differs by its very nature from its crystalline counterpart, which is typically related to the presence of a vacancy. The application of hydrostatic strain to our models yields further insights into the dependence of the hyperfine interaction on the structural characteristics of the defect. The observed trends are shown to result from the interplay between delocalization and sp hybridization.","","en","journal article","American Physical Society","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:8ef37eca-6931-47f5-b2c4-794739e6edc6","http://resolver.tudelft.nl/uuid:8ef37eca-6931-47f5-b2c4-794739e6edc6","Low Cost Small Wind Turbine Generators for Developing Countries","Ani, S.O.","Ferreira, J.A. (promotor)","2013","Wind energy accounts for an increasing percentage of the energy supplied to the electricity network. Electricity generation from wind is now cheaper than other renewables and almost cost competitive with other conventional sources of electricity generation. However, this impressive growth is largely due to advances in large wind turbines, particularly off-shore wind turbines. Small wind turbines on the other hand have not been developing at such an impressive rate. In the past few years, an annual growth rate of about 30% has been recorded in the installed large wind power capacity while the average growth of small wind turbines was 9%. This is despite its huge potentials in providing electricity to more than 1 billion people living mostly in developing countries without electricity. The objective of this thesis is to develop suitable low cost generators for small wind turbine application. A low cost generator solution is necessary to make small wind turbines an attractive option for remote areas of developing countries which are considered areas with the greatest potentials for such systems. To fulfill this objective, this thesis addresses three major problems identified as being responsible for the continued low penetration of small wind turbines in developing countries: 1) high cost of current systems; 2) maintainability of systems; and 3) energy yield and low wind speed operation. In addressing these challenges, this thesis focuses on the generator which is a major component of small wind turbines.","small wind turbines; axial flux permanent magnet generator; automotive alternator","en","doctoral thesis","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:c339d122-01a6-4a60-aaad-ddbfbb9a437d","http://resolver.tudelft.nl/uuid:c339d122-01a6-4a60-aaad-ddbfbb9a437d","Optical model for multilayer structures with coherent, partly coherent and incoherent layers","Santbergen, R.; Smets, A.H.M.; Zeman, M.","","2013","We present a novel approach for modeling the reflectance, transmittance and absorption depth profile of thin-film multilayer structures such as solar cells. Our model is based on the net-radiation method adapted for coherent calculations and is highly flexible while using a simple algorithm. We demonstrate that as a result arbitrary multilayer structures with coherent, partly coherent and incoherent layers can be simulated more accurately at much lower computational cost.","","en","journal article","Optical Society of America","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:c07d8cb6-62e9-4657-bc6e-eafb966a7733","http://resolver.tudelft.nl/uuid:c07d8cb6-62e9-4657-bc6e-eafb966a7733","The role of oxide interlayers in back reflector configurations for amorphous silicon solar cells","Demontis, V.; Sanna, C.; Melskens, J.; Santbergen, R.; Smets, A.H.M.; Damiano, A.; Zeman, M.","","2013","Thin oxide interlayers are commonly added to the back reflector of thin-film silicon solar cells to increase their current. To gain more insight in the enhancement mechanism, we tested different back reflector designs consisting of aluminium-doped zinc oxide (ZnO:Al) and/or hydrogenated silicon oxide (SiOx:H) interlayers with different metals (silver, aluminium, and chromium) in standard p-i-n a-Si:H solar cells. We use a unique inverse modeling approach to show that in most back reflectors the internal metal reflectance is lower than expected theoretically. However, the metal reflectance is increased by the addition of an oxide interlayer. Our experiments demonstrate that SiOx:H forms an interesting alternative interlayer because unlike the more commonly used ZnO:Al it can be deposited by plasma-enhanced chemical vapour deposition and it does not reduce the fill factor. The largest efficiency enhancement is obtained with a double interlayer of SiOx:H and ZnO:Al.","aluminium; inverse problems; plasma CVD; silicon; solar cells; zinc compounds","en","journal article","American Institute of Physics","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:03ae8b9c-6d4d-4653-8071-4b667f559e52","http://resolver.tudelft.nl/uuid:03ae8b9c-6d4d-4653-8071-4b667f559e52","Light management in thin-film silicon solar cells","Isabella, O.","Zeman, M. (promotor)","2013","Solar energy can fulfil mankind’s energy needs and secure a more balanced distribution of primary sources of energy. Wafer-based and thin-film silicon solar cells dominate todays’ photovoltaic market because silicon is a non-toxic and abundant material and high conversion efficiencies are achieved with silicon-based solar cells. To stay competitive with bulk crystalline silicon and other thin-film solar cell technologies, thin-film silicon solar cells have to achieve a conversion efficiency level of 20% on a laboratory scale. In this respect, light management techniques are essential for enhancing the efficiency of such solar devices since the energy of solar radiation is effectively used, absorption in the absorber layers is maximized and optical losses are minimized. Among several light management techniques presented in Chapter 2, light trapping is especially important for fabricating thinner cells with high efficiency and stable performance. The most basic light trapping scheme is given by the random texture at internal interfaces coupled with an efficient back reflector. The aim of this doctoral thesis is to introduce, analyse, model and employ in real solar devices novel types of textures and back reflectors. After Chapter 3, in which deposition techniques, characterization setups and modelling tools are introduced and discussed, four thematic chapters are reported. They are focussed, respectively, on periodic diffraction gratings and modulated surface textures as light scatterers, and dielectric distributed Bragg reflectors and Flattened Light-Scattering Substrates as efficient rear reflectors. In Chapter 4, transparent rectangular-like 1-D periodic gratings that were used as angle-selective scattering substrates in pin solar cells are described. These gratings were characterized from both morphological and optical perspectives. By making use of the Harvey-Shack scattering model, it was found that the geometrical parameters and the shape of such gratings play a considerable role in light scattering. Afterwards, such 1-D gratings were for the first time employed in the fabrication of pin single junction a-Si:H solar cells. These devices delivered up to +13.4% higher short-circuit current density than the solar cell with flat interfaces and exhibited, for wavelengths longer than 550 nm, a spectral response slightly higher than that of the solar cell deposited on the reference randomly-textured substrate. In order to find an optimal combination of period and height of rectangular-like 1-D gratings, and to explore the potential of 2-D gratings, 3-D optical modelling was employed. Solar-cell structures on 1-D (2-D) grating textures with different periods and heights were simulated. The best combinations led to a percentage increase of +25.5% (+32.5%) in the short-circuit current density with respect to the flat cell. In the framework of wave guide theory, this result indicates that solar cells on 2-D gratings can be optically better than random textures based on the same transparent conductive oxide. The recent possibility to texture transparent substrates over large areas opens the way for the industrial optimization of thin-film silicon solar cells on periodic gratings. In Chapter 5, modulated surface texturing is introduced for efficient light scattering at long wavelengths for multi-junction solar-cell applications. Based on the combination of two or more classes of textures on the same substrate, this concept paves the way for the realization of textures showing increased broadband light scattering. Different types of modulated surface textures were fabricated on etched glass, on 1-D gratings and on etched polycrystalline silicon wafers. The possibility to optimize the optical performance by manipulating the surface texturing was demonstrated by using wet etching processes. Single junction solar cells deposited on such modulated surface textures showed initial conversion efficiencies up to 9.74% and exhibited very good yield despite severe surface roughness. From these experiments, the best modulated surface texture could be selected, namely a combination of etched glass with large micrometer-scale features and etched ZnO:Al with nanometer-scale features. The same type of etched glass coated with textured ZnO:B was used as substrate for the fabrication of a tandem micromorph silicon device at IMT-PVLAB (Switzerland). The result was a state-of-the-art solar cell (11.6% initial conversion efficiency), where the redistribution of the light absorption between top and bottom cell occurred with a broadband increase in the (red) spectral response. Given such proofs of concept, the next step will be implementation of replicated modulated surface textures coated with low absorption front transparent conductive oxide for triple junction solar cells. In Chapter 6, Distributed Bragg reflectors are studied as dielectric mirrors for thin-film silicon solar-cells applications. Physical properties like photonic band gap, condition of omni-directionality and modulation were analysed and practical rules for appropriate design were reviewed. Distributed Bragg reflectors based on pairs of a-SiNx:H and a-Si:H and optimized for high internal reflectance in solar cells were designed employing advanced optical modelling. Afterwards, using a continuous plasma-assisted process at low temperature, these mirrors were fabricated, optically characterized and finally applied at the rear side of flat and textured single junction solar cells. From spectral and electrical measurements, solar cells with Distributed Bragg reflectors performed as well as the reference cells with Ag reflector. Future studies on these dielectric mirrors will focus on two main objectives: the concurrent usage of omni-directionality and modulation concepts for multi-junction applications and the development of patterning methods that do not make use of photolithography. In Chapter 7, Flattened Light Scattering Substrates are optimized for high efficiency single, double and triple junction solar cells. This type of substrate, based on 2-D photonic crystals proposed by AIST (Japan), is specifically developed for effective diffuse internal reflectance at long wavelengths and for deposition of high quality nc-Si:H. The study was based on a hybrid opto-electrical model that allowed to efficiently simulate both the optical situation and the electrical performance of thin-film multi-junction silicon solar cells. A potential initial conversion efficiency of 11.6%, 14.2%, and 16.0% for single, double, and triple junction solar cells on the optimized Flattened Light Scattering Substrates, respectively, was reported. Further studies on this matter will involve the modelling of asymmetric 2-D photonic crystals, usage of low-absorption supporting materials and application in multi-junctions with intermediate reflectors.","thin-film silicon; solar cells; light management; light scattering; light trapping; absorption; optical modelling; electrical modelling; diffraction gratings; Modulated Surface Textures; Photonic Crystals; Flattened Light-Scattering Substrates","en","doctoral thesis","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:9c1615f4-dfc2-4729-9b6b-cdded210e01d","http://resolver.tudelft.nl/uuid:9c1615f4-dfc2-4729-9b6b-cdded210e01d","Low Friction Cryostat for HTS Power Cable of Dutch Project","Chevtchenko, O.; Zuijderduin, R.; Smit, J.; Willen, D.; Lentge, H.; Thidemann, C.; Traeholt, C.","","2012","Particulars of 6 km long HTS AC power cable for Amsterdam project are: a cable has to fit in an annulus of 160 mm, with only two cooling stations at the cable ends [1]. Application of existing solutions for HTS cables would result in excessively high coolant pressure drop in the cable, possibly affecting public acceptance of the project. In order to solve this problem, a model cryostat was developed consisting of alternating rigid and flexible sections and hydraulic tests were conducted using sub-cooled liquid nitrogen. In the 47 m-long cryostat, containing a full-size HTS cable model, measured pressure drop amounts 11 mbar at the mass flow rate of 0.3 kg/s and temperature 65 K. For a 6 km-long HTS cable this gives a pressure drop below 2 bar, which is acceptable. In order to achieve this result, the cryostat was manufactured from alternating straight rigid sections and corrugated flexible sections. A flexible dummy HTS cable was inserted into this cryostat and sub-cooled liquid nitrogen was circulated in the annulus between the dummy cable surface and the inner cryostat surface. In the paper details are presented of the cryostat, of the measurement setup, of the experiment and of the results.","long HTS AC power cable; Dutch project; model cryostat; alternating rigid and flexible sections; hydraulic measurements; low friction; Reynolds number; friction factor","en","journal article","Elsevier","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:8c42112a-822b-45c8-b7e0-0766580de680","http://resolver.tudelft.nl/uuid:8c42112a-822b-45c8-b7e0-0766580de680","AC HTS Transmission Cable for Integration into the Future EHV Grid of the Netherlands","Zuijderduin, R.; Chevtchenko, O.; Smit, J.J.; Aanhaanen, G.; Melnik, I.; Geschiere, A.","","2012","Due to increasing power demand, the electricity grid of the Netherlands is changing. The future grid must be capable to transmit all the connected power. Power generation will be more decentralized like for instance wind parks connected to the grid. Furthermore, future large scale production units are expected to be installed near coastal regions. This creates some potential grid issues, such as: large power amounts to be transmitted to consumers from west to east and grid stability. High temperature superconductors (HTS) can help solving these grid problems. Advantages to integrate HTS components at Extra High Voltage (EHV) and High Voltage (HV) levels are numerous: more power with less losses and less emissions, intrinsic fault current limiting capability, better control of power flow, reduced footprint, etc. Today's main obstacle is the relatively high price of HTS. Nevertheless, as the price goes down, initial market penetration for several HTS components is expected by year 2015 (e.g.: cables, fault current limiters). In this paper we present a design of intrinsically compensated EHV HTS cable for future grid integration. Discussed are the parameters of such cable providing an optimal power transmission in the future network.","national transmission grid; potential bottlenecks; high temperature superconducting cables; compensation of reactive power; intrinsically compensated cable","en","journal article","Elsevier","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:8e4d760b-90db-4862-af54-1d0caa59a771","http://resolver.tudelft.nl/uuid:8e4d760b-90db-4862-af54-1d0caa59a771","A dynamic aggregate model for the simulation of short term power fluctuations","De Tommasi, L.; Gibescu, M.; Brand, A.J.","","2012","An important aspect related to wind energy integration into the electrical power system is the fluctuation of the generated power due to the stochastic variations of the wind speed across the area where wind turbines are installed. Simulation models are useful tools to evaluate the impact of the wind power on the power system stability and on the power quality. Aggregate models reduce the simulation time required by detailed dynamic models of multiturbine systems. In this paper, a new behavioral model representing the aggregate contribution of several variable-speed-pitchcontrolled wind turbines is introduced. It is particularly suitable for the simulation of short term power fluctuations due to wind turbulence, where steady-state models are not applicable. The model relies on the output rescaling of a single turbine dynamic model. The single turbine output is divided into its steady state and dynamic components, which are then multiplied by different scaling factors. The smoothing effect due to wind incoherence at different locations inside a wind farm is taken into account by filtering the steady state power curve by means of Gaussian filter as well as applying a proper damping on the dynamic part. The model has been developed to be one of the building-blocks of a model of a large electrical system, therefore a significant reduction of simulation time has been pursued. Comparison against a full model obtained by repeating a detailed single turbine model, shows that a proper trade-off between accuracy and computational speed has been achieved.","wind farm; variable speed wind turbine; wind power fluctuations; multiturbine model; aggregate model","en","journal article","Elsevier","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:6667bd3d-f47c-498c-89ae-d7816a56a210","http://resolver.tudelft.nl/uuid:6667bd3d-f47c-498c-89ae-d7816a56a210","Rotor losses in laminated magnets and an anisotropic carbon fiber sleeve","Van der Geest, M.; Wolmarans, J.J.; Polinder, H.; Ferreira, J.A.; Zeilstra, D.","","2012","High speed fault tolerant permanent magnet machines have strong asynchronous airgap harmonics, making them susceptible to rotor eddy-current losses. These losses can be reduced by using novel high resistivity materials like plastic bonded magnets and carbon fiber reinforced retaining sleeves. This paper examines by numerical studies the consequences for the losses of using these materials. The effect of laminating the magnets and the losses in the anisotropic sleeve are analysed with 3D simulations, using simplifications determined with 2D simulations. The anisotropic resistivity of the sleeve roughly doubles the losses compared to an isotropic sleeve, while laminating the magnets in n slices reduces the losses by 1/n1.8.","carbon fiber, magnet lamination, rotor losses, 3D FEM","en","conference paper","Institution of Engineering and Technology","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:f06a121d-86fb-4384-b3a8-7fb203d04daf","http://resolver.tudelft.nl/uuid:f06a121d-86fb-4384-b3a8-7fb203d04daf","Low AC Loss in a 3 kA HTS Cable of the Dutch Project","Chevtchenko, O.; Zuijderduin, R.; Smit, J.; Willen, D.; Lentge, H.; Thidemann, C.; Traeholt, C.; Melnik, I.; Geschiere, A.","","2012","are: a cable has to fit in an annulus of 160 mm, with two cooling stations at the cable ends only. Existing solutions for HTS cables would lead to excessively high coolant pressure drop in the cable, potentially affecting public acceptance of the project. A way out would be to substantially reduce AC losses from 1 down to about 0.1 W/m per phase at rated current of 3 kArms, frequency of 50 Hz and temperature of 77 K. In this paper we discuss a strategy towards this ambitious goal, a concept design of the single phase cable 3 kA conductor made of YBCO tapes and present corresponding experimental and simulation data supporting the developed approach leading directly to this goal. HTS cable model was made that show a drastically reduced AC loss. The low loss was achieved by using appropriate pitch angles for two-layer cable conductor of relatively large diameter, by minimizing the gaps between the HTS tapes, and by using narrow HTS tapes that conform well to the roundness of the underlying former. AC loss of 0.12 W/m at 3 kArms was measured at a frequency of 60 Hz and at a temperature of 77 K.","long HTS AC power cable; Dutch project; 3 kA class YBCO cable conductor; single phase model; very low AC losses at 60 Hz and 77 K; concept; experiment; simulation","en","journal article","Elsevier","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:231e660e-03cc-44b6-a6d2-4ce08bde12db","http://resolver.tudelft.nl/uuid:231e660e-03cc-44b6-a6d2-4ce08bde12db","Advanced Light Management Approaches for Thin-Film Silicon Solar Cells","Zeman, M.; Isabella, O.; Jäger, K.; Santbergen, R.; Solntsev, S.; Topic, M.; Krc, J.","","2012","Light management is important for improving the performance of thin-film solar cells. Advanced concepts of efficient light scattering and trapping inside the cell structures need to be investigated. An important tool for design and optimisation of the concepts present optical modelling and simulation. In the article a model of light scattering at textured surfaces, which is based on first order Born approximation and the Fraunhofer diffraction, is presented. Another approach presents rigorous solving of Maxwell's equations for electromagnetic waves in two- or three-dimensions. An example of a three-dimensional simulation, employing the finite element method, of an amorphous silicon solar cell with periodically textured interfaces is shown. The second part of the article focuses on experimental results related to three advanced light management approaches: i) modulated surface morphologies for enhanced scattering and anti-reflection, ii) metal nano-particles introducing plasmonic scattering, and iii) one-dimensional photonic crystals (Bragg stacks) for back reflectors. Improvements in output performance of amorphous silicon solar cells are demonstrated and discussed.","thin-film silicon solar cells; light trapping; optical modelling; modulated surface texture; metal nano-particles; plasmonics; photonic crystal","en","journal article","Elsevier","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:5acc250d-d8cd-4724-b53d-472faa4fb8e8","http://resolver.tudelft.nl/uuid:5acc250d-d8cd-4724-b53d-472faa4fb8e8","Electrical Model of Balanced AC HTS Power Cable","Zuijderduin, R.; Chevtchenko, O.; Smit, J.J.; Willen, D.; Melnik, I.; Geschiere, A.","","2012","The future electricity grid will be more sustainable and it will have more power transmission and distribution capability with more electrical power added from decentralized sources on distribution level and from wind parks and other large sources on transmission level. More interconnections and more underground transmission and distribution will be put up. Use of high temperature superconducting (HTS) power cables provides solutions to many of the future grid problems caused by these trends. In this paper we present an electrical model of a balanced 6 km-long three phase triaxial HTS power cable for the Dutch project being developed by a consortium of Alliander, Ultera and TUD. The cable currents in all three phases are balanced by selecting proper twist pitches and insulation thickness. The paper focuses on determining inductances, capacitances and AC losses of the balanced cable. Using the developed model, we also determine the voltage drop as function of the cable length, the neutral current and the effect of the imbalanced capacitances on the current distribution of the Dutch distribution cable. The model is validated and it can be used for accurate simulation of the electrical behaviour of triaxial HTS cables in electrical grids.","high temperature superconducting power cable; Dutch HTS cable project; cable electrical parameters; balancing of inductances and capacitances; zero neutral current; modelling","en","journal article","Elsevier","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:b43601b8-62af-4be5-b7e6-c9e455519c04","http://resolver.tudelft.nl/uuid:b43601b8-62af-4be5-b7e6-c9e455519c04","Integration of HTS Cables in the Future Grid of the Netherlands","Zuijderduin, R.; Chevchenko, O.; Smit, J.J.; Aanhaanen, G.; Melnik, I.; Geschiere, A.","","2012","ue to increasing power demand, the electricity grid of the Netherlands is changing. The future transmission grid will obtain electrical power generated by decentralized renewable sources, together with large scale generation units located at the coastal region. In this way electrical power has to be distributed and transmitted over longer distances from generation to end user. Potential grid issues like: amount of distributed power, grid stability and electrical loss dissipation merit particular attention. High temperature superconductors (HTS) can play an important role in solving these grid problems. Advantages to integrate HTS components at transmission voltages are numerous: more transmittable power together with less emissions, intrinsic fault current limiting capability, lower ac loss, better control of power flow, reduced footprint, less magnetic field emissions, etc. The main obstacle at present is the relatively high price of HTS conductor. However as the price goes down, initial market penetration of several HTS components (e.g.: cables, fault current limiters) is expected by year 2015. In the full paper we present selected ways to integrate EHV AC HTS cables depending on a particular future grid scenario in the Netherlands.","national transmission grid; potential bottlenecks; high temperature superconducting cables","en","journal article","Elsevier","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:50643dcc-4f58-4bb1-92da-2d49b02cc5a7","http://resolver.tudelft.nl/uuid:50643dcc-4f58-4bb1-92da-2d49b02cc5a7","Operation and Power Flow Control of Multi-Terminal DC Networks for Grid Integration of Offshore Wind Farms Using Genetic Algorithms","Teixeira Pinto, R.; Fragoso Rodrigues, S.; Wiggelinkhuizen, E.; Scherrer, R.; Bauer, P.; Pierik, P.","","2012","For achieving the European renewable electricity targets, a significant contribution is foreseen to come from offshore wind energy. Considering the large scale of the future planned offshore wind farms and the increasing distances to shore, grid integration through a transnational DC network is desirable for several reasons. This article investigates a nine-node DC grid connecting three northern European countries—namely UK, The Netherlands and Germany. The power-flow control inside the multi-terminal DC grid based on voltage-source converters is achieved through a novel method, called distributed voltage control (DVC). In this method, an optimal power flow (OPF) is solved in order to minimize the transmission losses in the network. The main contribution of the paper is the utilization of a genetic algorithm (GA) to solve the OPF problem while maintaining an N-1 security constraint. After describing main DC network component models, several case studies illustrate the dynamic behavior of the proposed control method.","HVDC transmission; voltage-source converters; power electronics; DC networks; offshore wind energy; control theory; optimal power flow; genetic algorithms","en","journal article","MDPI","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:4220e3ee-bdcb-4a46-ade1-470d3c2ad6da","http://resolver.tudelft.nl/uuid:4220e3ee-bdcb-4a46-ade1-470d3c2ad6da","On the Scalar Scattering Theory for Thin-Film Solar Cells","Jäger, K.","Zeman, M. (promotor)","2012","Nano-textured interfaces between two media of different refractive indices scatter light. The angular distribution and the intensity of the scattered light are deter- mined by the geometry of the nano-textures and the difference of the refractive indices of the two media. Thin-film silicon solar cells (TFSSC), which convert sunlight directly into electricity, have nano-textured interfaces. These interfaces scatter the light incident on the solar cell. The scattering leads to a longer average path length of the photons in the absorber layer of the solar cell. Therefore more light can be absorbed and thus converted to electricity. To introduce nano-textured interfaces into the solar cells, usually transparent conductive oxide (TCO) layers are used. Some TCO materials obtain nano-textured surfaces during the production process, while others are made rough by post processing, e.g. by etching. Nano-textures have been successfully implemented in TFSSC for almost 30 years by academia and industry; however, theoretical investigations on the relation between the nano-textures and the scattered electromagnetic fields have only been performed for about ten years. It is very important to investigate how the nano-textures can be optimized for scattering. In this thesis a scattering model is developed to tackle this important problem. The scattering model is based on the scalar scattering theory, i.e. it neglects the vector- character of the electromagnetic field and thus the light. Despite this strong assumption we have demonstrated that the model is suitable for simulating descriptive parameters of the scattered field in both reflection and transmission. The model is based on the fact that the transmitted field behind the nano-texture and the scattered field are related via Fourier transforms. By making simple assumptions for the transmitted field the model can be implemented using Fast Fourier trans- form algorithms, i.e. the model is very fast. The scattering model is formulated such that in principle it works for rough interfaces between arbitrary materials. We successfully evaluated it for several of these interfaces. We further showed that the model is also able to produce first predictions for the scattering parameters at oblique incidence. However, in this case the deviations between measured and simulated values are larger. Combining the scattering model with the ASA opto-electrical device simulator allows predicting how the nano-textures affect the performance of solar-cells. This combination can also be used to perform the major motivation for the development of scattering models: To investigate how the morphology of the nano- textures can be optimised. For this optimisation we use the “simulated annealing” optimisation algorithm. The optimisation and a subsequent evaluation reveal that the lateral feature size of the nano-textures is crucial for scattering into large angles: The smaller the lateral feature size, the more light is scattered into large angles. If, however, the lateral feature size becomes too small, less light is scattered since the nano texture then appears as effective medium. The vertical feature size hardly influences the shape of the scattered field. Nonetheless, it determines the fraction of the total light that is scattered away from the specular direction. If the rms-roughness, a measure for the vertical modulation of the texture, is kept constant, a nano- texture with the optimal lateral feature size is preferable to a texture that consists of a superposition of textures with different lateral feature sizes. However, due to the effect of the nano-textures on the electrical properties of the solar cells, a superposition of a texture consisting of large lateral and vertical features with another texture with small lateral and vertical features is preferable to a texture consisting of small lateral but large vertical features, i.e. sharp spikes. The results of our work give the direction to push absorption in solar cells towards the theoretical limits.","thin-film silicon solar cells; scattering model; transparent conducting oxides; photovol","en","doctoral thesis","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:f59a54ac-5fa7-40ac-aa60-e0757459b224","http://resolver.tudelft.nl/uuid:f59a54ac-5fa7-40ac-aa60-e0757459b224","Modulated surface textures for enhanced scattering in thin-film silicon solar cells","Isabella, O.; Battaglia, C.; Ballif, C.; Zeman, M.","","2012","Nano-scale randomly textured front transparent oxides are superposed on micro-scale etched glass substrates to form modulated surface textures. The resulting enhanced light scattering is implemented in single and double junction thin-film silicon solar cells.","","en","conference paper","Optical Society of America","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:ee26b80e-03f2-45a1-92b1-9b57f36a0594","http://resolver.tudelft.nl/uuid:ee26b80e-03f2-45a1-92b1-9b57f36a0594","3-D modeling of triple junction solar cells on 2-D gratings with optimized intermediate and back reflectors","Isabella, O.; Elshinawy, M.A.A.; Solntsev, S.; Zeman, M.","","2012","Superstrate thin-film silicon triple-junction solar cells on 2-D gratings were optimized using opto-electrical modeling. Tuning the thickness of intermediate and back reflectors and the band gap of the middle cell resulted in 17% initial efficiency.","","en","conference paper","Optical Society of America","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:5fc0ea1d-54ee-4371-8048-dcfadb7bc10d","http://resolver.tudelft.nl/uuid:5fc0ea1d-54ee-4371-8048-dcfadb7bc10d","Inductive and Wireless Energy Transfer in Residential Applications","Van der Pijl, F.F.A.","Ferreira, J.A. (promotor)","2012","The thesis considers contactless electromagnetic energy transfer, applied to residential and office environments. The objective is to investigate and design a (partially) contactless residential energy distribution network system for multiple electrical devices with a highly improved end-user flexibility. A special focus is system efficiency.","","en","doctoral thesis","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:1a2044c6-bbc9-43f1-b233-b75d60eb2811","http://resolver.tudelft.nl/uuid:1a2044c6-bbc9-43f1-b233-b75d60eb2811","UMBRELLA Deliverable D 7.2 “Workshop results on innovative operational tools”","Electrical Sustainable Energy Department ","","2012","This deliverable presents the results of the first common workshop, co-organized by UMBRELLA and iTesla projects. The workshop title is ‘Innovative tools needed for future and stable system operation’. The main focus of this common workshop is on the information exchange about the objectives, dissemination, key drivers of UMBRELLA and iTesla and results of previous studies, namely TradeWind , EWIS , and PEGASE projects. The workshop was hosted at ENTSO-E’s premises on June 21, 2012 with the total number of registered participants of 50, including experts from industry, academia and regulatory bodies.","","en","report","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:7aaf4288-8eff-4270-b4cb-0996c4fb4058","http://resolver.tudelft.nl/uuid:7aaf4288-8eff-4270-b4cb-0996c4fb4058","Solar simulator","Roest, S.J.M.","","2012","Solar simulator comprising at least at least one high-intensity discharge (HID) lamp type,and at least one halogen lamp type, which lamps are applied simultaneously and are provided with infrared filter means to provide a mixture of light approximating radiated sunlight,wherein the infrared filter means are embodied as heat reflective foil mounted on a trans- parent substrate. The heat reflective foil is preferably provided with a repetitive pattern of perforations.","","en","patent","European Patent Office","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:4c16dc3e-afc3-4fb5-9bb7-8de580f4b41f","http://resolver.tudelft.nl/uuid:4c16dc3e-afc3-4fb5-9bb7-8de580f4b41f","Design considerations for permanent magnet direct drive generators for wind energy applications","Jassal, A.K.; Polinder, H.; Damen, M.E.C.; Versteegh, K.","","2012","Permanent Magnet Direct Drive (PMDD) generators offer very high force density, high efficiency and low number of components. Due to these advantages, PMDD generators are getting popular in the wind energy industry especially for offshore application. Presence of permanent magnets gives magnetic field for free but there are many design considerations which must be taken into account for a good design. The design considerations presented in this paper are rotor eccentricity, short circuit current estimation, voltage reflection at generator terminals due to high frequency switching and forces during magnet assembly. Simplified analytical methods which give quick results have been developed and then simulations have been performed to validate the analytical models. FEMM 4.0 which is a Finite Element (FE) solver was used for validation of various magnetic force models. MATLAB® Simulink was used for short circuit and voltage reflection validation. It was deduced that the analytical methods give good estimation of these effects and can thus be included at an early design stage.","design considerations; generator; permanent magnets; wind-energy","en","journal article","Science Publishing Corporation","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:e414d365-0d1d-4818-a581-5502e586c402","http://resolver.tudelft.nl/uuid:e414d365-0d1d-4818-a581-5502e586c402","Long term performance of gas-insulated switchgear operating under tropical conditions","Pharmatrisanti, A.","Smit, J.J. (promotor)","2012","For the past two decades, electricity utilities have struggled to provide high quality electrical power to their customers while keeping on spending effectively the expenses for operating and maintaining the power system. Unfortunately, under tropical conditions, operation circumstances affect the equipment so that either its lifetime is cut shorter or its failure rate is higher. One of the affected equipment is GIS installations. Because of its important function in a power network, a need to investigate how the tropical circumstances affect the GIS installations has raised. This thesis focuses on the assessment and the understanding of how the tropical circumstances influence GIS long term performance. This knowledge is hence applied to develop a maintenance methodology for these circumstances to enable better tropical GIS performance. In order to improve the maintenance methodology, the degradation mechanisms need to be identified. FMECA method is applied so that parameters which indicate premature function loss can be defined and hence being monitored. Furthermore these degradation processes have to be controlled to attain a better GIS performance. This means that the processes have to be measured. In order to do so, series of experiments were conducted under both homogeneous and inhomogeneous electric field conditions. Gas pressure, gas humidity and gas temperature as well as electrical stresses were varied to measure the change of the electrical withstand of the insulating gas. Next, the health index and degradation level of the equipment are assessed. A model, namely condition and life assessment are introduced. This concept utilizes knowledge rules and norms obtained from field experiences as well as experimental results. To complete the model, a weighting factor is introduced to represent how high the influence of parameter or GIS system is. From our experiment we learn that the major factors of influence are the following parameters: gas pressure moisture content decomposition products For these parameters the respective weighting factors were determined through experiments. In asset management strategy, prioritizing work delivery is as important as determining health and degradation levels. This can be fulfilled by conducting risk assessment both to equipment and utility’s business values. A model of risk assessment is introduced. Verification of the models is carried out by using of data of a utility which installations are operated under tropical circumstances. In addition to the verification, an example of how the models are used is given as well.","gas-insulated substations; tropical influences; long term performance","en","doctoral thesis","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:248286d2-8cd6-4a54-a9f3-8d417eb9d678","http://resolver.tudelft.nl/uuid:248286d2-8cd6-4a54-a9f3-8d417eb9d678","New materials in high voltage technology","Smit, J.J.; Andritsch, T.; Chevtchenko, O.A.","","2012","Assets in high voltage technology have to meet harsh service conditions over long lifetimes of 40 years or more. Due to environmental concerns, substitution of conventional insulating materials becomes a necessity. Because robustness and sustainability are serious requirements, only few new materials are really breaking through. At present some promising material technologies emerge with great potential applicability in high voltage engineering. This paper discusses especially nanocomposites and high temperature superconductors.","high voltage technologies, nanocomposites, superconductors","en","journal article","Springer-Verlag","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:06821c6f-82cf-41f6-a6d9-5a03512747ac","http://resolver.tudelft.nl/uuid:06821c6f-82cf-41f6-a6d9-5a03512747ac","Responses of simple optical standing wave sensors","De Haan, V.O.; Santbergen, R.; Tijssen, M.; Zeman, M.","","2012","Optical standing wave sensors have been manufactured by amorphous silicon deposition. The responses of these sensors, when subjected to standing waves, have been calculated and measured. It is shown that the responses are different depending on the way the standing wave is created. The responses also depend on the thickness and material properties of the layers used to create the sensors. Quantitative agreement between measurements and model calculations can be obtained by including alignment errors, incoherent light interaction and scaling factors. The simple construction of the sensors allows for a broad application range.","","en","journal article","Optical Society of America","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:102870f0-d0d6-47d4-942a-6dc353a03633","http://resolver.tudelft.nl/uuid:102870f0-d0d6-47d4-942a-6dc353a03633","Thin film surface processing by ultrashort laser pulses (USLP)","Scorticati, D.; Skolski, J.Z.P.; Romer, G.R.B.E.; Huis in 't Veld, A.J.; Workum, M.J.; Theelen, M.J.; Zeman, M.","","2012","In this work, we studied the feasibility of surface texturing of thin molybdenum layers on a borosilicate glass substrate with Ultra-Short Laser Pulses (USLP). Large areas of regular diffraction gratings were produced consisting of Laserinduced periodic surface structures (LIPSS). A short pulsed laser source (230 fs-10 ps) was applied using a focused Gaussian beam profile (15-30 ?m). Laser parameters such as fluence, overlap (OL) and Overscans (OS), repetition frequency (100 200 kHz), wavelength (1030 nm, 515 nm and 343 nm) and polarization were varied to study the effect on periodicity, height and especially regularity of LIPSS obtained in layers of different thicknesses (150-400 nm). The aim was to produce these structures without cracking the metal layer and with as little ablation as possible. It was found that USLP are suitable to reach high power densities at the surface of the thin layers, avoiding mechanical stresses, cracking and delamination. A possible photovoltaic (PV) application could be found in texturing of thin film cells to enhance light trapping mechanisms.","Ultra Short Laser Pulses; surface processing; molybdenum; thin film; ripples; LIPSS; ps laser","en","conference paper","International Society for Optical Engineering (SPIE)","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:afa63e50-f9f8-48f3-9243-5bcf05fec461","http://resolver.tudelft.nl/uuid:afa63e50-f9f8-48f3-9243-5bcf05fec461","Invariance Kernels of Single-Input Planar Nonlinear Systems","Maggiore, B.; Rawn, B.G.; Lehn, P.","","2012","The problem of determining invariance kernels for planar single-input nonlinear systems is considered. If K is a closed set, its invariance kernel is the largest subset of K with the property of being positively invariant for arbitrary measurable input signals. It is shown that the boundary of the invariance kernel is a concatenation of solutions of two so-called extremal vector fields. Moreover, only the solutions through a finite number of special points are of interest. This result makes it possible to devise an algorithm which determines the invariance kernel of a simply connected set in a finite number of steps","invariance and viability kernels; extremal vector fields; switched systems; differential inclusions","en","journal article","Society for Industrial and Applied Mathematics (SIAM)","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Department of Electrical Sustainable Energy","","","",""
"uuid:bceb6955-eb0c-4ef9-9364-5abda6204655","http://resolver.tudelft.nl/uuid:bceb6955-eb0c-4ef9-9364-5abda6204655","A scattering model for nano-textured interfaces and its application in opto-electrical simulations of thin-film silicon solar cells","Jäger, K.; Fischer, M.; Van Swaaij, R.A.C.M.M.; Zeman, M.","","2012","We present a scattering model based on the scalar scattering theory that allows estimating far field scattering properties in both transmission and reflection for nano-textured interfaces. We first discuss the theoretical formulation of the scattering model and validate it for nano-textures with different morphologies. Second, we combine the scattering model with the opto-electric asa simulation software and evaluate this combination by simulating and measuring the external parameters and the external quantum efficiency of solar cells with different interface morphologies. This validation shows that the scattering model is able to predict the influence of nano-textured interfaces on the solar cell performance. The scattering model presented in this manuscript can support designing nano-textured interfaces with optimized morphologies.","interface structure; semiconductor thin films; silicon; solar cells; texture; thin film devices","en","journal article","American Institute of Physics","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:78c2d4f7-af49-493a-939b-548baaabda1e","http://resolver.tudelft.nl/uuid:78c2d4f7-af49-493a-939b-548baaabda1e","UMBRELLA project - Deliverable D 7.1 ""Website, Basic communication plan and dissemination strategy""","Electrical Sustainable Energy Department ","","2012","In the present deliverable, the dissemination strategy of the UMBRELLA project is discussed. The strategy is focused on the website, newsletter, workshops and attendance of conferences.","","en","report","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:aa1f5549-c354-4030-8459-5086f41e2b19","http://resolver.tudelft.nl/uuid:aa1f5549-c354-4030-8459-5086f41e2b19","Growth and Characterization of Thin Film Nanocrystalline Silicon Materials and Solar Cells","Agbo, S.N.","Zeman, M. (promotor)","2012","The need for electrical energy is growing fast as a result of the expanding world population and economic activities. On top of this the energy need of each individual is also growing. At present the growth in energy demand is not matched by the growth in energy generation because of insufficient energy production. This energy gap therefore needs to be bridged. In addition, most conventional means of energy generation are not environmentally-friendly and in turn affect human lives. Solar energy is one of the alternatives for renewable energy generation. It can be extracted directly in electrical form from solar radiation using photovoltaic (PV) solar cells or solar concentrators. The PV market is dominated by crystalline-silicon based solar cells. However, thin-film silicon solar cells are becoming increasingly important, because they are deposited at relatively low temperatures and as such offer the possibility to produce flexible and light-weight solar panels. The latter can be applied on for instance the roofs of factory buildings. Thin film nanocrystalline silicon (nc-Si:H) is an important material for application in thin-film silicon solar cells. It has been mainly developed because unlike amorphous silicon (a-Si:H) it is stable against light-induced degradation, and because with this material the solar cells have an extended spectral response up to the infrared wavelength region. Because of this extended response nc-Si:H films are used in combination with a-Si:H to form multi-junction solar cells, leading to an increased solar-cell efficiency. The focus of this thesis is on the development and characterization of nc-Si:H layers and solar cells. In chapter 3 we present results of research on how the deposition parameters during the growth affect nc-Si:H material properties and device performance when using radio frequency plasma enhanced chemical vapor deposition. Particular attention is paid to p-type and intrinsic films and their application in nc-Si:H solar cells. For the p-layer development, the effects of deposition power, the substrate roughness, and doping are investigated. Intrinsic layer investigation focused on the effect of substrate temperature, deposition power, deposition pressure, and the gas-flow ratio. Intrinsic layers deposited at the amorphous-to-nanocrystalline transition during growth are investigated in detail. At this transition nc-Si:H films with favorable properties for application in thin film solar cells can be made. Within our growth regime, this transition shows high sensitivity to the deposition parameters hence narrowing the process window. We show that materials deposited at the amorphous-to-nanocrystalline transition, but at different deposition settings, can have similar crystalline mass fraction while showing different electrical properties. In chapter 4 we present how seed layers are used to enhance crystal nucleation at the onset of nc-Si:H growth. By this approach, uniform and rapid evolution of the crystalline mass fraction as a function of thickness is obtained. Our results show a possibility to grow thin-film nc-Si:H without the usual amorphous incubation layer. A depth profile Raman technique that enables the ex-situ investigation of the crystalline mass fraction depth profile in nc-Si:H films is presented. This approach reveals different growth phases in the development of nc-Si:H. From transmission electron microscopy (TEM) analyses, we observe that crystal sizes are not affected by seed layers. However, horizontal cracks are observed to dominate the early growth of nc-Si:H in p-i-n solar cells and this effect is reduced upon seeding. For the n-i-p cells the appearance of these cracks is not affected by seeding. X-ray diffraction (XRD) results indicate that the use of seed layers does not affect the crystal size, but affects the preferential orientation of the crystals. Solar-cell external parameters show that seeding of p-i-n solar cells leads to an increase in solar cell efficiency, mainly due to increase in the short-circuit current density. The investigation of seeding on the crystallinity development is further extended in chapter 5. Here, we show that different substrates have different profile for the development of the crystalline mass fraction. For the three substrates investigated, we found a gradual development of the crystalline mass fraction, starting from the amorphous incubation layer. By means of seeding, rapid nucleation is observed as indicated by the high value of the crystalline mass fraction from the onset of growth. The effect of the substrate is reduced as all three substrates show a similar development profile of the crystalline mass fraction upon seeding. In the last chapter of this thesis, the possibility to use Raman spectroscopy to determine the preferred crystal orientation in nc-Si:H is demonstrated. The preferred orientation of crystals in nc-Si:H can give insight into the film growth mechanism and is often determined from transmission electron microscopy and x-ray diffraction. The method presented in this thesis is based on the fact that molecular vibrations in films under polarized light give rise to polarization-dependent Raman scattering intensity, depending on the grain crystal orientation of the irradiated material. This approach has been tested on a series of nc-Si:H samples and the results comparable with x-ray diffraction results.","thin film nanocrystalline silicon; solar energy","en","doctoral thesis","CPI","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical sustainable energy","","","",""
"uuid:b30a4354-3fa9-4ab3-845a-67810295fafe","http://resolver.tudelft.nl/uuid:b30a4354-3fa9-4ab3-845a-67810295fafe","Thermal ideality factor of hydrogenated amorphous silicon p-i-n solar cells","Kind, R.; Van Swaaij, R.A.C.M.M.; Rubinelli, F.A.; Solntsev, S.; Zeman, M.","","2011","The performance of hydrogenated amorphous silicon (a-Si:H) p-i-n solar cells is limited, as they contain a relatively high concentration of defects. The dark current voltage (JV) characteristics at low forward voltages of these devices are dominated by recombination processes. The recombination rate depends on the concentration of active recombination centers and the recombination efficacy of each of these centers. The first factor causes the ideality factor of the devices to be non-integer and to vary with voltage. The temperature dependence of the dark current can be expressed by its activation energy. For microcrystalline silicon solar cells the activation energy varies with voltage with a so-called thermal ideality factor of 2. This value was derived for devices with a spatially uniform defect distribution and reflects the recombination efficacy. Here we present results of a thickness series of a-Si:H p-i-n solar cells. We have matched the experimental curves with computer simulations, and show that the voltage-dependent ideality factor curve can be used to extract information on the cross sections for electron and hole capture. Also, the activation energy is used as a measure for the mobility gap, resulting in a mobility gap for a-Si:H of 1.69?eV. We find a thermal ideality factor close to 2 for all samples. This is explained with a theoretical derivation, followed by a comparison between the internal electric field strength and the spatial variation of the defect density in the intrinsic layer. The thermal ideality factor is shown to be insensitive to the defect distribution and the recombination profile in the device. It is, therefore, an appropriate parameter to characterize a-Si:H p-i-n devices, providing direct insight on the recombination efficacy.","amorphous semiconductors; crystal defects; dark conductivity; electron mobility; electron traps; electron-hole recombination; elemental semiconductors; hole mobility; hole traps; hydrogen; silicon; solar cells","en","journal article","American Institute of Physics","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:3221d00a-4964-4d42-abb7-f9c45b4006e7","http://resolver.tudelft.nl/uuid:3221d00a-4964-4d42-abb7-f9c45b4006e7","An Intelligent Algorithm for Smart Grid Protection Applications","Xyngi, I.","Van der Sluis, L. (promotor)","2011","","","en","doctoral thesis","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:a3b18301-fe72-4586-8277-68bd253a6345","http://resolver.tudelft.nl/uuid:a3b18301-fe72-4586-8277-68bd253a6345","Atomistic Models of Amorphous Semiconductors","Jarolimek, K.","Zeman, M. (promotor); De Groot, R.A. (promotor); De Wijs, G.A. (promotor)","2011","Crystalline silicon is probably the best studied material, widely used by the semiconductor industry. The subject of this thesis is an intriguing form of this element namely amorphous silicon. It can contain a varying amount of hydrogen and is denoted as a-Si:H. It completely lacks the neat long range order of the crystal, yet its structure is not random. Almost all silicon atoms have four neighbors and the average bond angle is identical to the tetrahedral angle in the crystal. Order is thus preserved over several bond lengths. The motivations to study a-Si:H are two-fold. Firstly some of its properties are different from the crystalline form and we do not understand them completely. For example, the electronic properties degrade after exposure to intense light, but can be recovered reversibly by heat treatment. The microscopic process of this is not known. Secondly, research on a-Si:H is motivated by its applications. These are mostly large area devices such as liquid crystal displays and solar cells. The latter are in use already today, the former are waiting to be widely used in future. Amorphous semiconductors can be deposited over large areas from vapor. On the other hand, the size of c-Si devices is limited by the much smaller size of the wafers. The production of a-Si:H is also cheaper and consumes less energy. Unlike its crystalline counterpart a-Si:H has a direct band gap, leading to an increased light absorption. Consequently, a-Si:H solar cells are ~ 1000 times thinner than c-Si cells, resembling more a foil than a semiconductor device. The methods used in the thesis are computational, largely relying on algorithms and powerful computers. The structural models are atomistic, where the interaction between electrons and nuclei is treated on the level of Density Functional Theory. This is a first-principles methods, meaning that it does not use any adjustable parameters. The chemical bonding, even of complex structures is described accurately. Calculation of total energies and forces allows us to find equilibrium structures and perform molecular dynamics calculations. The models of a-Si:H are prepared by cooling a melt to room temperature. This method resembles the preparation of glasses. We find that the structure is strongly in influenced by the cooling rate. Using slower cooling rates we improved existing models that contained excessive strain and a high defect concentration. Using a cooling rate of ~ 0.02 K/fs we were even able to prepare small defect-free models. The structure was in good agreement with available neutron scattering data. Calculated density of states shows a pronounced band gap. After the generation of structural models we turn our attention to defects. Defects in an amorphous solid are defined as atoms that deviate from the normal coordination. We find 3-fold and 5-fold coordinated Si atoms and 2-fold coordinated H atoms. We focus only on the 3-fold coordinated Si, also called the dangling bond (DB), that is believed to be the major defect in a-Si:H. We have calculated formation of the DB defect in the negative, neutral and positive charge state. By averaging over 25 distinct DB models we find a considerable spread in the energies of 0.2 eV. Another related property of a defect is its correlation energy U. A positive value of U means that we have to invest energy to add an extra electron to the defect. The size and sign of U are still a subject of controversy. On average we find a positive U value of 0.1 eV. Four models, however, have a negative correlation energy, suggesting large relaxations in the defect structure. Amorphous silicon readily forms compounds with nitrogen and carbon. We have investigated silicon-rich nitride (a-SiN:H) at two different densities of 2.0 and 3.0 g/cm3. Features in the pair-distribution functions can be related to ""square structures"". These are planar structures consisting of two Si in opposite corners of a square and two N in the remaining corners. The dense phase shows signs of phase separation into silicon and stoichiometric nitride. Both valence and conduction band edges are dominated by Si states. This is corroborated by the fact that by increasing the nitrogen content the band gap of the nitride can be varied from 1.8 to 5.3 eV. Recently there has been a considerable interest in man-made materials. Examples are multilayers (ML) formed by two semiconductors with a different band gap. By adjusting the thickness of the small band gap material (the well) one can tune the band gap of the ML due to quantum confinement effects. This concept is well established in crystalline semiconductors. The existence of quantum confinement in amorphous structures is, however, being still debated. Using models prepared previously we have constructed a model of a silicon/nitride ML. This allowed us to study confinement effects directly without using transport or optical measurements that can obscure the observations. Comparing our model to an experimental system with the same composition gave almost identical band gaps. This confirmed the existence of quantum confinement in a amorphous multilayer. The calculation of band offsets between the materials revealed that there is almost no barrier for the electrons and the confinement originated solely from holes.","amorphous; semiconductor; density functional theory; molecular dynamics; amorphous silicon","en","doctoral thesis","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:60aecb01-f735-490c-b282-b8d40260c2ee","http://resolver.tudelft.nl/uuid:60aecb01-f735-490c-b282-b8d40260c2ee","Standing waves in fiber-optic interferometers","De Haan, V.; Santbergen, R.; Tijssen, M.; Zeman, M.","","2011","A study is presented giving the response of three types of fiber-optic interferometers by which a standing wave through an object is investigated. The three types are a Sagnac, Mach–Zehnder and Michelson–Morley interferometer. The response of the Mach–Zehnder interferometer is similar to the Sagnac interferometer. However, the Sagnac interferometer is much harder to study because of the fact that one input port and output port coincide. Further, the Mach–Zehnder interferometer has the advantage that the output ports are symmetric, reducing the systematic effects. Examples of standing wave light absorption in several simple objects are given. Attention is drawn to the influence of standing waves in fiber-optic interferometers with weak-absorbing layers incorporated. A method is described for how these can be theoretically analyzed and experimentally measured. Further experiments are needed for a thorough comparison between theory and experiment.","coherent optical effects; fiber optics; waves","en","journal article","Optical Society of America","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:71e642a0-087c-49fc-b8f8-320d9e8739c1","http://resolver.tudelft.nl/uuid:71e642a0-087c-49fc-b8f8-320d9e8739c1","Angular resolved scattering by a nano-textured ZnO/silicon interface","Schulte, M.; Bittkau, K.; Jäger, K.; Ermes, M.; Zeman, M.; Pieters, B.E.","","2011","Textured interfaces in thin-film silicon solar cells improve the efficiency by light scattering. A technique to get experimental access to the angular intensity distribution (AID) at textured interfaces of the transparent conductive oxide (TCO) and silicon is introduced. Measurements are performed on a sample with polished microcrystalline silicon layer deposited onto a rough TCO layer. The AID determined from the experiment is used to validate the AID obtained by a rigorous solution of Maxwell’s equations. Furthermore, the applicability of other theoretical approaches based on scalar scattering theory and ray tracing is discussed with respect to the solution of Maxwell’s equations.","elemental semiconductors; II-VI semiconductors; light scattering; solar cells; zinc compounds","en","journal article","American Institute of Physics","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:ca3611d9-c2f1-4230-9eeb-2c186275f97b","http://resolver.tudelft.nl/uuid:ca3611d9-c2f1-4230-9eeb-2c186275f97b","Modelling of the thermal conductivity in polymer nanocomposites and the impact of the interface between filler and matrix","Kochetov, R.; Korobko, A.V.; Andritsch, T.; Morshuis, P.H.F.; Picken, S.J.; Smit, J.J.","","2011","In this paper the thermal conductivity of epoxy-based composite materials is analysed. Two and three-phase Lewis–Nielsen models are proposed for fitting the experimental values of the thermal conductivity of epoxy-based polymer composites. Various inorganic nano- and microparticles were used, namely aluminium oxide, aluminium nitride, magnesium oxide and silicon dioxide with average particle size between 20 nm and 20?m. It is shown that the filler–matrix interface plays a dominant role in the thermal conduction process of the nanocomposites. The two-phase model was proposed as an initial step for describing systems containing 2 constituents, i.e. an epoxy matrix and an inorganic filler. The three-phase model was introduced to specifically address the properties of the interfacial zone between the host polymer and the surface modified nanoparticles.","","en","journal article","IOP Publishing","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:65a36cc5-3ed4-4970-b3cc-4934c62db82a","http://resolver.tudelft.nl/uuid:65a36cc5-3ed4-4970-b3cc-4934c62db82a","Effect of ion bombardment on the a-Si:H based surface passivation of c-Si surfaces","Illiberi, A.; Kudlacek, P.; Smets, A.H.M.; Creatore, M.; Van de Sanden, M.C.M.","","2011","We have found that controlled Ar ion bombardment enhances the degradation of a-Si:H based surface passivation of c-Si surfaces. The decrease in the level of surface passivation is found to be independent on the ion kinetic energy (7–70 eV), but linearly proportional to the ion flux (6×1014–6×1015?ions?cm?2?s?1). This result suggests that the ion flux determines the generation rate of electron–hole pairs in a-Si:H films, by which metastable defects are created at the H/a-Si:c-Si interface. Possible mechanisms for the ion induced generation of electron–hole pairs are discussed.","amorphous semiconductors; electron-hole recombination; elemental semiconductors; ion beam effects; passivation; semiconductor thin films; silicon","en","journal article","American Institute of Physics","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:0502f8f9-fd8e-4f0f-b6a2-b8440d98df96","http://resolver.tudelft.nl/uuid:0502f8f9-fd8e-4f0f-b6a2-b8440d98df96","Optical scattering properties of a nano-textured ZnO-silicon interface","Jäger, K.; Schulte, K.; Bittkau, K.; Ermes, A.M.; Zeman, M.; Pieters, B.E.","","2011","The scattering properties of transparent conductive oxide (TCO) layers are fundamentally related to the performance of thin film silicon solar cells. In this study we introduce an experimental technique to access light scattering properties at textured TCO-silicon interfaces. Therefore we prepared a sample with a polished microcrystalline silicon layer, which is deposited onto a rough TCO layer. We used the measured results to validate calculations obtained with rigorous diffraction theory, i.e. a numerical solution of Maxwell’s equations. Furthermore we evaluated four approximate models based on the scalar scattering theory and ray tracing and compared them to the rigorous diffraction theory.","scattering, surface-textured TCO, microcrystalline silicon, ZnO, FDTD, scalar scattering theory, ray tracing","en","conference paper","SPIE","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:3fbb1fd0-7e3c-4e90-8b82-b44d7941e22e","http://resolver.tudelft.nl/uuid:3fbb1fd0-7e3c-4e90-8b82-b44d7941e22e","Influence of ITO deposition and post annealing on HIT solar cell structures","Zhang, D.; Tavakoliyaraki, A.; Wu, Y.; Van Swaaij, R.A.C.M.M.; Zeman, M.","","2011","Heterojunction silicon with intrinsic thin layer (HIT) solar cells that combine advanced thin-film hydrogenated amorphous silicon (a-Si:H) and crystalline silicon (c-Si) technologies are promising because of the high performance at low cost. Due to the low conductivity of a-Si:H, indium tin oxide (ITO) needs to be used as a front contact layer on top of a-Si:H in order to collect photogenerated currents. The thin a-Si:H layer requires the ITO deposition to be soft so that the passivation is maintained after deposition. Otherwise, the passivation degradation resulting from ITO deposition should be recovered by some post processing. In this contribution, we investigate how the power density and the temperature during ITO deposition as well as post annealing influence the passivation quality of HIT solar cells as characterised by the open-circuit voltage (Voc) and minority carrier lifetime. Firstly, ITO sputtering with lower power density can reduce the degradation of the passivation quality after ITO deposition. Secondly, we have investigated the simultaneous annealing during ITO deposition at elevated temperature. On one hand, simultaneous annealing can recover some of the degradation resulting from sputtering. On the other hand, there is a temperature threshold above which degradation of the passivation is observed, probably by hydrogen effusion. Thirdly, we observe that post annealing can fully recover the degradation resulting from ITO sputtering at room temperature (RT).","heterojunction silicon solar cell; ITO; annealing","en","journal article","Elsevier","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:18bae434-75f6-4ab7-8e2e-b04735bf0f60","http://resolver.tudelft.nl/uuid:18bae434-75f6-4ab7-8e2e-b04735bf0f60","Adaptive control method and adaptive controller for controlling energy supplied to a resonant tank","Van der Pijl, F.F.A.; Ferreira, J.A.; Bauer, P.; Castilla, M.","","2011","The invention relates to an adaptive controlling method for controlling energy- supplied by an electrical source (14) to a resonance tank (Cr, Lr) that is connectable to an electric load (13a, 13b). The method comprises the step of determining an energy amount to be supplied to the tank (Cr, Lr), based on information of energy in the resonance tank (Cr, Lr.).","","en","patent","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:8d94b97f-a44b-480e-a312-bb3686622f9a","http://resolver.tudelft.nl/uuid:8d94b97f-a44b-480e-a312-bb3686622f9a","Manipulating the Hydrogenated Amorphous Silicon Growing Surface","Wank, M.A.","Zeman, M. (promotor); Van de Sanden, M.C.M. (promotor)","2011","Our modern lifestyle is currently fueled by two billion years of accumulated energy reserves. For several years now there has been a strong rise in research interest and more recently also implementation of renewable energy sources in the European Union. Driving factors for these developments are the increasing awareness of global warming in our society, the limited nature of current fossil fuel sources, the need for energy security & independence and the opportunity to develop new technologies and business opportunities. Obtaining energy from solar radiation via solar cells based on cyrstalline silicon has seen continuous development since the demonstration of the first photovoltaic devices in the 1950’s. These types of solar cells are still the dominant technology today, but other solar cell technologies are about to make the transition from research labs into significant production volumes. One of these technologies is the hydrogenated amorphous silicon (a-Si:H) thin film solar cell, which promises to be a cheap alternative to the crystalline silicon solar cell, albeit at a reduced energy conversion efficiency. The deposition technique used to grow a-Si:H thin films in this work is the expanding thermal plasma chemical vapor deposition (ETP-CVD). Main benefit of ETP-CVD are the high growth rates of more than 1 nm/s that can be achieved, which is very beneficial for the growth of the thick intrinsic absorber layer in a solar cell. Substrate temperatures of >300ºC are required to obtain dense a-Si:H films suitable for solar cell application – temperatures that leads to degradation of previously deposited p-doped layers in a typical p-i-n solar cell. In order to reduce the temperature load during deposition, ion bombardment was employed with the goal to provide the growing film surface with kinetic energy from the bombarding ions, thereby allowing to deposit dense a-Si:H films at substrate temperatures around 200ºC. The results discussed in chapter 4 and 5 show that significant progress towards this goal has been achieved, as demonstrated by solar cells with > 7% initial efficiency at a growth rate of 1 nm/s and substrate temperatures between 200 – 180ºC for the intrinsic layer. To achieve this we have utilised two different types of substrate biasing, sinusoidal RF biasing and pulse-shaped biasing, with focus on the latter. Both biasing techniques result in ion bombardment of the film surface during deposition. Both biasing techniques enable the deposition of solar-grade intrinsic a-Si:H at substrate temperatures below the 350ºC required for unbiased deposition. In chapter 3 we demonstrate how RF substrate biasing leads to the growth of vacancy-dominated material up to 50ºC below the temperature required for unbiased deposition. This conclusion is based on FTIR analysis where a transition form vacancy- to void-dominated material is observed. We investigated the dependence of this transition on the reactor pressure. Ion bombardment at a DC bias voltage VDC of 14 V has hardly any effect on the transition, yet an increase in void fraction was observed for all temperatures and increasing pressures. Ion bombardment at VDC = 20 V for the high pressure series resulted in an increase of the transition from 9% total hydrogen concentration unbiased to 13% total hydrogen concentration biased. This is attributed to a reduced incorporation of ionic clusters and polymers into the film. The second type of substrate biasing utilized in this work is the pulseshaped biasing, PSB. As shown in chapter 4, with PSB we are able to obtain accurate control over the ion energy distribution in a range of 0 - 200 eV without the formation of a strong secondary plasma typically present for RF substrate biasing. Control over the ion energy was confirmed by retarding field energy analyzer measurements for conductive substrates, and non-conductive substrates covered with a conductive surface layer which is connected to the sample holder. For intrinsic a-Si:H deposited with PSB at a growth rate of 1 nm/s and substrate temperatures in the range of 180 - 200ºC we can distinguish roughly between two regions: region I < 4.8 eV of deposited energy per Si atom (eV/Si atom) and region II > 4.8 eV/Si atom. In region I we observe an increase in material density due to a decrease in nanovoid concentration as deduced from FTIR analysis. At the transition between region I and II around 4.8 eV/Si atom the densest material with low nanovoid concentration is obtained. The increase in material density and the reduction in surface roughness in region I are attributed to an increase in surface mobility of mobile species as well as surface atom displacement. Above 4.8 eV/Si atom we see an increase in Urbach energy which is related to bulk atom displacement in subsurface layers at higher ion energies. We report unique experimental evidence which indicates that the band gap is not correlated to the total hydrogen concentration, cH, as usually reported in literature, but instead to the presence of nanovoids in the film, asdetermined from the cHSM mode. Intrinsic a-Si:H deposited with PSB under the same conditions as the films from chapter 4 have also been implemented in p-i-n solar cells. These cells are discussed in chapter 5 and a reproducible record initial energy conversion efficiencies of 7.4% was obtained for cells grown by ETP-CVD at such high growth rates of 1 nm/s and low substrate temperatures of 200ºC. This efficiency was obtained for cells grown around deposited energies of around 1 eV/Si atom. The open-circuit voltage has a maximum of 0.82 V around 1 eV/Si atom and decreases at higher deposited energies per Si atom, which is attributed to the low band gap at higher deposited energy. The short-circuit current density reaches a maximum around 4.8 eV/Si atom and decreases at higher deposited energies, which is attributed to a reduced hole collection determined from external quantum efficiency measurements. The fill factor decreases above 1 eV/Si atom which we attribute to a lower mobility-lifetime product due to an increase in charge carrier recombination. This indicates defect formation at deposited energies above 1.7 eV/Si atom, significantly below the reported increase in Urbach energy around 4.8 eV/Si atom reported in chapter 4. Chapter 6 discusses the development of the a-Si:H surface roughness as function of several parameters like substrate temperature, RF substrate biasing and hydrogen dilution at growth rates of 0.1 nm/s. Important for this analysis was the spectroscopic ellipsometry technique, which allows to monitor the surface roughness development in-situ during film deposition. In the first section, from depositions with and without RF substrate biasing at different substrate temperatures the presence of a hydrogen-rich layer was suggested, which is removed/densified upon externally induced ion bombardment. In the second section of chapter 6, the surface roughness development was investigated as function of hydrogen dilution. We observe a discrepancy in the surface roughness development between spectroscopic ellipsometry and AFM measurements. We interpret this as another indication of the presence of a hydrogen rich/low density overlayer. At higher hydrogen dilutions, we obtain a thicker overlayer dominated by lower hydrides. From additional PSB experiments at two different dilutions we conclude that the hydrogen rich/low density layer is densified by the induced ion bombardment and/or excess hydrogen is removed.","amorphous silicon solar cells; plasma deposition","en","doctoral thesis","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:9233cfdf-f5c7-4faa-9867-7ec2bfacb9ac","http://resolver.tudelft.nl/uuid:9233cfdf-f5c7-4faa-9867-7ec2bfacb9ac","Optical modeling of thin-film silicon solar cells with submicron periodic gratings and nonconformal layers","Solntsev, S.; Zeman, M.","","2011","In thin-film silicon solar cells (TFSC) efficient light management is essential in order to increase energy conversion efficiency. The application of nano-scale periodic gratings (PG) is a promising method to enhance absorption in the absorber layers of TFSC since they can efficiently scatter the incident light. Carefully designed gratings give a possibility to increase the photocurrent over a wavelength range where silicon exhibits a weak absorption. Maxwell's equations solver was employed to carry out optical simulations of TFSC with PG. Atomic force microscopy (AFM) measurements demonstrate that film deposition smoothens the morphology of PG. In the simulations we used the results of AFM measurements to define the morphology of interfaces between the layers of TFSC. An optimum smoothing of interface roughness was determined that resulted in maximum absorption in thin-film silicon solar cells.","photovoltaics; solar cells; thin film; simulation; light management","en","journal article","Elsevier","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:ec337933-769c-40bf-8156-a33135023ea6","http://resolver.tudelft.nl/uuid:ec337933-769c-40bf-8156-a33135023ea6","Novel Topology of Saturated-core Fault Current Limiter","Cvoric, D.","Ferreira, J.A. (promotor)","2010","Increasing levels of fault currents in utility grids are expected to result in mechanical and thermal overstresses of different power system components. To cope with these increased levels, expensive upgrades and replacements of currently employed Circuit Breakers might be required in the near future. Fault Current Limiters (FCLs) are expected to play an important role in the protection of future energy systems. They limit a fault current to a predetermined level and have no influence on the system during normal operation. A number of different FCL types have been proposed in literature. FCLs based on core-saturation effect have a number of crucial operation advantages over other FCL types: they have no fault reaction delay and no post-fault recovery delay; they have high reliability, low losses and can limit any number of consecutive faults. By introducing FCLs in power systems, above-mentioned expensive upgrades can be avoided. This thesis introduces a novel design of saturated-core FCLs which solves the problem of excessive weight of these devices. The new design utilizes design principle of insertion of an air gap in a core, typically used in design of inductors. Because of gap presence, the size of the core is approximately reduced by 70% in comparison to typical FCL design. The gap is inserted in such a way that it is a part of ac magnetic circuit but not a part of dc magnetic circuit. Thus, it is still possible to drive the core to saturation during normal operation. The new design uses one three-leg core per phase, where ac and dc windings are placed on outer legs. Based on the new core design, two FCL topologies are introduced: single-phase and three-phase FCL. Single-core FCL uses three cores for three phases whereas three-phase design utilizes only one core for all three phases. Therefore, the later topology reduces the amount of magnetic material further by more or less 66%. The drawback of three-phase FCL is that it limits only single-phase faults. The full voltage 10 kV/400 A prototype of three-phase FCL is built and tested. The measurements align very well with simulation results; they validate 3D FE transient model, built in Ansys, and prove the principle of operation.","fault current limiters; saturation; FE modeling; protection; power systems; renewable sources; smart grids","en","doctoral thesis","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy (EPP Group)","","","",""
"uuid:2f22c04f-49ac-4d04-bcfd-2f4849823ce5","http://resolver.tudelft.nl/uuid:2f22c04f-49ac-4d04-bcfd-2f4849823ce5","Modeling and optimization of white paint back reflectors for thin-film silicon solar cells","Lipovek, B.; Kr?, J.; Isabella, O.; Zeman, M.; Topi?, M.","","2010","Diffusive dielectric materials such as white paint have been demonstrated as effective back reflectors in the photovoltaic technology. In this work, a one-dimensional (1D) optical modeling approach for simulation of white paint films is developed and implemented in a 1D optical simulator for thin-film solar cells. The parameters of white paint, such as the paint film thickness, the pigment volume concentration (PVC), and the pigment/binder refractive index ratio (RIR), are examined and optimized to achieve the required optical properties for back reflector application. The simulation trends indicate that white paint back reflectors with sufficient film thickness and higher PVC and RIR values exhibit improved reflectivity characteristics which results in an increased long-wavelength quantum efficiency of thin-film silicon solar cells. The simulation results based on the 1D model agree very well with the experimental data obtained from reflectance measurements of various white paint compositions and quantum efficiency measurements of amorphous silicon solar cells with white paint back reflectors.","elemental semiconductors; optical elements; optical films; paints; pigments; reflectivity; silicon; solar cells","en","journal article","American Institute of Physics","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:cf0627a5-f66b-4588-b90e-4a8b089ca635","http://resolver.tudelft.nl/uuid:cf0627a5-f66b-4588-b90e-4a8b089ca635","Hydrogenated amorphous silicon deposited under accurately controlled ion bombardment using pulse-shaped substrate biasing","Wank, M.A.; Van Swaaij, R.A.C.M.M.; Kudlacek, P.; Van de Sanden, M.C.M.; Zeman, M.","","2010","We have applied pulse-shaped biasing to the expanding thermal plasma deposition of hydrogenated amorphous silicon at substrate temperatures ? 200?°C and growth rates around 1 nm/s. Substrate voltage measurements and measurements with a retarding field energy analyzer demonstrate the achieved control over the ion energy distribution for deposition on conductive substrates and for deposition of conductive materials on nonconductive substrates. Presence of negative ions/particles in the Ar–H2–SiH4 plasma is deduced from a voltage offset during biasing. Densification of the material at low Urbach energies is observed at a deposited energy <4.8?eV/Si atom and attributed to an increase in surface mobility of mobile species as well as well as surface atom displacement. The subsequent increase in Urbach energy >4.8?eV/Si atom is attributed to bulk atom displacement in subsurface layers. We make the unique experimental abservation of a decreasing Tauc band gap at increasing total hydrogen concentration—this allows to directly relate the band gap of amorphous silicon to the presence of nanovoids in the material.","amorphous semiconductors; carrier mobility; densification; elemental semiconductors; energy gap; hydrogen; plasma deposition; semiconductor growth; semiconductor thin films; silicon, voids (solid)","en","journal article","American Institute of Physics","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:6703c457-e5b8-41b9-af80-6c6e66226e15","http://resolver.tudelft.nl/uuid:6703c457-e5b8-41b9-af80-6c6e66226e15","Epoxy Based Nanodielectrics for High Voltage DC Applications: Synthesis, Dielectric Properties and Space Charge Dynamics","Andritsch, T.M.","Smit, J.J. (promotor)","2010","Main goal of the research described in this PhD thesis was to determine the influences of filler size, material and distribution on the DC breakdown strength, permittivity and space charge behaviour of nanocomposites. This should lay the groundwork for tailored insulation materials for HVDC applications. Examples for this are medical and industrial X-ray imaging, radar and cable terminations. In the course of this project a manufacturing process was devised, which enabled the fabrication of epoxy based nanocomposites with a good dispersion of different types of nanoparticles. Models from literature, which explain the behaviour nanodielectrics exhibit, are discussed: electric double-layer model, intensity model, multi-core model and the interphase volume model. Based on these theories, a new model was devised for explaining the behaviour of epoxy based nanocomposites: the polymer chain alignment model. The underlying idea of this model is that the restructuring of the base polymer on the molecular scale, due to the presence of surface modified nanoparticles, plays a fundamental part in the properties of the bulk material. Each modified particle will act as centre for crosslinking of the polymer, leading to a rigid layer of polymer chains around each particle. These rigid layers have a much lower permittivity than both host and filler material, thus their presence can easily be identified by dielectric spectroscopy, since the relative permittivity of the bulk material decreases. In literature it is shown, that the strong bonding of particles and host material due to the surface modification gives rise to improved resistance to partial discharges and electrical treeing. More energy is needed to break these bonds than it would be the case in unmodified polymers. The particles themselves can also act as recombination centres for electrons and holes, which travel between or along polymer chains. This has an effect on the space charge dynamics. Agglomerations of nanoparticles can nullify these effects however: it is explained how agglomerations can act as charge traps, lead to field enhancements and cause interfacial polarization. Claims from theory are tested with three measurement methods: short term DC breakdown tests, dielectric spectroscopy and space charge measurement. It is shown that nanocomposites exhibit improved DC breakdown strength for very low fillgrades of 0.5 to 2 % by weight. Compared to the unmodified base material improvements of up to 80 % could be measured. Dielectric spectroscopy reveals that the relative permittivity in nanocomposites is lower than of the host and filler materials, with a minimum at a fillgrade of approximately 2 % by weight. For higher fillgrades the permittivity of the composite increases depending on the ratio between the permittivity values of filler and host material. Above 2 wt.% the permittivity of the filler material starts to overshadow the low permittivity of the rigid layers around the particles. Results from space charge measurement with the pulsed electro-acoustic method show that the quality of particle dispersion has an impact on the charge intake. Based on these measurements it is concluded that particle agglomerations act as charge traps, while the amount of charges in nanocomposites with good particle dispersion is lower than in the unmodified epoxy. This confirms that the particles indeed act as recombination centres, actively mitigating charge buildup inside the material. These results show why nanocomposites are very interesting for HVDC equipment. Space charges are a limiting factor for DC applications. Their reduction improves the reliability of the insulation system. The increased DC breakdown strength enables more compact high voltage equipment, respectively the utilization at higher field strengths. The work presented here is a stepping stone on the way to industrial applications of nanostructured insulation material and fundament for further investigations on topics like nanofluids.","nanodielectrics; polymer insulation; dielectric spectroscopy; space charges; DC breakdown strength; high voltage","en","doctoral thesis","","","","","","","","2010-11-02","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:c7b269f0-fb2d-41d0-8519-a5030910585c","http://resolver.tudelft.nl/uuid:c7b269f0-fb2d-41d0-8519-a5030910585c","Atomistic models of hydrogenated amorphous silicon nitride from first principles","Jarolimek, K.; De Groot, R.A.; De Wijs, G.A.; Zeman, M.","","2010","We present a theoretical study of hydrogenated amorphous silicon nitride (a-SiNx:H), with equal concentrations of Si and N atoms (x=1), for two considerably different densities (2.0 and 3.0?g/cm3). Densities and hydrogen concentration were chosen according to experimental data. Using first-principles molecular-dynamics within density-functional theory the models were generated by cooling from the liquid. Where both models have a short-range order resembling that of crystalline Si3N4 because of their different densities and hydrogen concentrations they show marked differences at longer length scales. The low-density nitride forms a percolating network of voids with the internal surfaces passivated by hydrogen. Although some voids are still present for the high-density nitride, this material has a much denser and uniform space filling. The structure factors reveal some tendency for the nonstoichiometric high-density nitride to phase separate into nitrogen rich and poor areas. For our slowest cooling rate (0.023 K/fs) we obtain models with a modest number of defect states, where the low (high) density nitride favors undercoordinated (overcoordinated) defects. Analysis of the structural defects and electronic density of states shows that there is no direct one-to-one correspondence between the structural defects and states in the gap. There are several structural defects that do not contribute to in-gap states and there are in-gap states that do only have little to no contributions from (atoms in) structural defects. Finally an estimation of the size and cooling rate effects on the amorphous network is reported.","","en","journal article","American Physical Society","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:46d98fd6-d8d4-47e3-96b5-c672f23505cd","http://resolver.tudelft.nl/uuid:46d98fd6-d8d4-47e3-96b5-c672f23505cd","Distributed Power Flow Controller","Yuan, Z.","Ferreira, J.A. (promotor)","2010","In modern power systems, there is a great demand to control the power flow actively. Power flow controlling devices (PFCDs) are required for such purpose, because the power flow over the lines is the nature result of the impedance of each line. Due to the control capabilities of different types of PFCDs, the trend is that mechanical PFCDs are gradually being replaced by Power electronics (PE) PFCDs. Among all PE PFCDs, the Unified Power Flow Controller (UPFC) is the most versatile device. However, the UPFC is not widely applied in utility grids, because the cost of such device is much higher than the rest of PFCDs and the reliability is relatively low due to its complexity. The objective of this thesis is to develop a new PFCD that offers the same control capability as the UPFC, at a reduced cost and with an increased reliability. The new device, so-called Distributed Power Flow Controller (DPFC), is invented and presented in this thesis. The DPFC is a further development of the UPFC. It has been shown that the DPFC fulfills all three of the listed goals. This thesis starts with the review the state-of-art of current PFCDs, followed by the research at the DPFC device level, including the operation principle, the modeling and control, and experimental demonstrations. At the end, the thesis presents the research at the system level, which includes the DPFC applications to improve power system controllability and stability, and the feasibility of the DPFC for real networks.","power flow; ac-dc converter; power system; power electronics","en","doctoral thesis","","","","","","","","2010-10-18","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:5c08c434-3a97-44fa-a9b1-3dd60fea5bbe","http://resolver.tudelft.nl/uuid:5c08c434-3a97-44fa-a9b1-3dd60fea5bbe","Modulated surface textures for enhanced light trapping in thin-film silicon solar cells","Isabella, O.; Kr?, J.; Zeman, M.","","2010","Substrates with a modulated surface texture were prepared by combining different interface morphologies. The spatial frequency surface representation method is used to evaluate the surface modulation. When combining morphologies with appropriate geometrical features, substrates exhibit an increased scattering level in a broad wavelength region. We demonstrate that the improved scattering properties result from a superposition of different light scattering mechanisms caused by the different geometrical features integrated in a modulated surface texture.","elemental semiconductors; interface structure; light scattering; semiconductor thin films; silicon; solar cells; surface morphology; surface texture","en","journal article","American Institute of Physics","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:667b8567-2267-41a6-a4e4-a425a1b8d4bf","http://resolver.tudelft.nl/uuid:667b8567-2267-41a6-a4e4-a425a1b8d4bf","Cryostat for a high-temperature superconducting power cable","Chevtchenko, O.A.; Smit, J.J.; Geschiere, A.","","2010","Cryostat for a high-temperature superconducting power cable, comprising concentric tubes, an annular region between said tubes, wherein a multilayer thermal insulation and getter material for supporting high vacuum conditions are provided in said annular region, and wherein the multilayer insulation comprises reflective layers separated by fibrous spacer material, wherein the fibrous spacer material comprises activated carbon micro-fibers and/or activated carbon nano-fibers. Beneficially the getter material is at least in part embodied in the activated carbon fibers of the fibrous spacer material.","","en","patent","European Patent Office","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:7845316c-13a0-4743-b651-7ff529fc5324","http://resolver.tudelft.nl/uuid:7845316c-13a0-4743-b651-7ff529fc5324","Formation of thin-film crystalline silicon on glass observed by in-situ XRD","Westra, J.M.; Vavrunkova, V.; Sutta, P.; Van Swaaij, R.A.C.M.M.; Zeman, M.","","2010","Thin-film poly-crystalline silicon (poly c-Si) on glass obtained by crystallization of an amorphous silicon (a-Si) film is a promising material for low cost, high efficiency solar cells. Our approach to obtain this material is to crystallize a-Si films on glass by solid phase crystallization (SPC). As the grain size of SPC poly c-Si films will be smaller than that of multi-crystalline wafers, lower solar cell efficiencies are expected for this technology. Despite the smaller grain size, a 2-micron-thick polycrystalline silicon solar cell with light trapping was shown to have a conversion efficiency of more than 10% [1]. Obtainable efficiencies up to 15% are expected for solar cells made using SPC of a-Si:H films. Expanding thermal plasma chemical vapor deposition (ETP-CVD) was used to prepare hydrogenated a-Si films; this technique is chosen because the deposition rates are much higher than with plasma enhanced CVD. A-Si:H films with different hydrogen contents were annealed using temperatures ranging from 500 °C to 700 °C. The evaluation of the films after annealing treatments revealed that the hydrogen content and bonding configuration did not influence the structural properties of the crystallized films significantly. The average crystallite size in the fully crystallized films was between 100 and 150 nm. Full crystallization of 1 micrometer thick films was achieved within 20 minutes for annealing at 625 °C and 650 °C. During annealing at 600 °C crystallization is much slower, and no crystallization is observed at 500 °C. The relation between the annealing temperature and the rate with which the films are fully crystallized is of great importance to develop a solar cell technology, to limit the thermal budget and processing time.","x-ray diffraction; silicon; crystallization; solar cells","en","journal article","Elsevier","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:c1ba2f21-65c9-4c22-9f70-54a0fd7cf4bb","http://resolver.tudelft.nl/uuid:c1ba2f21-65c9-4c22-9f70-54a0fd7cf4bb","Hydrogenated amorphous silicon solar cells deposited from silane diluted with hydrogen","Van Elzakker, G.","Zeman, M. (promotor)","2010","","","en","doctoral thesis","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:ed4c407d-e3a6-46ff-91df-b4adfe9cd20d","http://resolver.tudelft.nl/uuid:ed4c407d-e3a6-46ff-91df-b4adfe9cd20d","A Wind Farm Electrical Systems Evaluation with EeFarm-II","Pierik, J.; Axelsson, U.; Eriksson, E.; Salomonsson, D.; Bauer, P.; Czech, B.","","2010","EeFarm-II is used to evaluate 13 different electrical systems for a 200 MW wind farm with a 100 km connection to shore. The evaluation is based on component manufacturer data of 2009. AC systems are compared to systems with DC connections inside the wind farm and DC connection to shore. Two options have the best performance for this wind farm size and distance: the AC system and the system with a DC connection to shore. EeFarm-II is a user friendly computer program for wind farm electrical and economic evaluation. It has been built as a Simulink Library in the graphical interface of Matlab-Simulink. EeFarm-II contains models of wind turbines, generators, transformers, AC cables, inductors, nodes, splitters, PWM converters, thyristor converters, DC cables, choppers and statcoms.","offshore wind farm electrical systems; offshore wind farm design; offshore wind farm economics","en","journal article","MDPI AG","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:2135fefe-4449-46e6-bd99-4f37e38c4bbc","http://resolver.tudelft.nl/uuid:2135fefe-4449-46e6-bd99-4f37e38c4bbc","A scattering model for surface-textured thin films","Jäger, K.; Zeman, M.","","2009","We present a mathematical model that relates the surface morphology of randomly surface-textured thin films with the intensity distribution of scattered light. The model is based on the first order Born approximation [see e.g., M. Born and E. Wolf, Principles of Optics, 7th ed. (Cambridge University Press, Cambridge, England, 1999) ] and on Fraunhofer scattering. Scattering data of four transparent conductive oxide films with different surface textures were used to validate the model and good agreement between the experimental and calculated intensity distribution was obtained.","aluminium; boron; Fraunhofer diffraction; II-VI semiconductors; semiconductor thin films; surface morphology; wide band gap semiconductors; zinc compounds","en","journal article","American Institute of Physics","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:e86bc59d-28f8-4f40-adef-9a606ac5d355","http://resolver.tudelft.nl/uuid:e86bc59d-28f8-4f40-adef-9a606ac5d355","Design Challenges and Potentials of HTS Synchronous Motor for Superbus","Ani, S.O.; Polinder, H.; Ferreira, J.A.; Ockels, W.J.","","2009","This paper discusses the possibilities of applying high temperature superconducting (HTS) synchronous motor to Superbus, an alternative and sustainable type of public transportation developed at TU Delft. Two important factors within the Superbus drive that influence the operating range are weight and efficiency: increasing the weight results in larger roll resistance while the better the efficiency the larger the range. HTS rotating machines offer several advantages such as weight reduction and increased efficiency which can be exploited for special applications such as Superbus, where weight and volume reduction is important. In order to highlight the design challenges and potentials achievable by using HTS motor in Superbus an overview of the different approaches in the design of HTS machines is presented. Different rotor and stator topologies available in literature are discussed and comparison is made with conventional machines. The losses expected from the HTS motor are presented in comparison with conventional machines. It is concluded that it seems possible to achieve a reduction in losses and volume of about half compared with conventional machines.","","en","conference paper","IEEE","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:a1472a3d-e274-478b-bac4-9e710ac60f2b","http://resolver.tudelft.nl/uuid:a1472a3d-e274-478b-bac4-9e710ac60f2b","Optimization of condition-based asset management using a predictive health model","Bajracharya, G.; Koltunowicz, T.; Negenborn, R.R.; Papp, Z.; Djairam, D.; De Schutter, B.; Smit, J.J.","","2009","In this paper, a model predictive framework is used to optimize the operation and maintenance actions of power system equipment based on the predicted health sate of this equipment. In particular, this framework is used to predict the health state of transformers based on their usage. The health state of a transformer is hereby given by the hot-spot temperature of the paper insulation of the transformer and is predicted using the planned loading of the transformer. The actual loading of the transformer is subsequently optimized using these predictions. If you want to cite this report, please use the following reference instead: G. Bajracharya, T. Koltunowicz, R.R. Negenborn, Z. Papp, D. Djairam, B. De Schutter, J. J. Smit. Optimization of condition-based asset management using a predictive health model. In Proceedings of the 16th International Symposium on High Voltage Engineering (ISH 2009), Cape Town, South Africa, August 2009.","","en","report","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:c8c7bcd2-3ff3-4390-96bd-51954799aefc","http://resolver.tudelft.nl/uuid:c8c7bcd2-3ff3-4390-96bd-51954799aefc","On the surface roughness development of hydrogenated amorphous silicon deposited at low growth rates","Wank, M.A.; Van Swaaij, R.A.C.M.M.; Van de Sanden, M.C.M.","","2009","The surface roughness evolution of hydrogenated amorphous silicon (a-Si:H) films has been studied using in situ spectroscopic ellipsometry for a temperature range of 150–400?°C. The effect of external rf substrate biasing on the coalescence phase is discussed and a removal/densification of a hydrogen-rich layer is suggested to explain the observed roughness development in this phase. After coalescence we observe two distinct phases in the roughness evolution and highlight trends which are incompatible with the idea of dominant surface diffusion. Alternative, nonlocal mechanisms such as the re-emission effect are discussed, which can partly explain the observed incompatibilities.","amorphous semiconductors; elemental semiconductors; ellipsometry; hydrogen; hydrogenation; plasma CVD; semiconductor growth; semiconductor thin films; silicon; surface diffusion; surface roughness","en","journal article","American Institute of Physics","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:50fcccc2-31e3-422f-8473-b5b07419b9ad","http://resolver.tudelft.nl/uuid:50fcccc2-31e3-422f-8473-b5b07419b9ad","Optimization of maintenance for power system equipment using a predictive health model","Bajracharya, G.; Koltunowicz, T.; Negenborn, R.R.; Papp, Z.; Djairam, D.; De Schutter, B.; Smit, J.J.","","2009","In this paper, a model-predictive control based framework is proposed for modeling and optimization of the health state of power system equipment. In the framework, a predictive health model is proposed that predicts the health state of the equipment based on its usage and maintenance actions. Based on the health state, the failure rate of the equipment can be estimated. We propose to use this predictive health model to predict the effects of different maintenance actions. The effects of maintenance actions over a future time window are evaluated by a cost function. The maintenance actions are optimized using this cost function. The proposed framework is applied in the optimization of the loading of transformers based on the thermal degradation of the paper insulation.","maintenance optimization; model-predictive optimization; power system maintenance; power transformer; predictive health management","en","conference paper","IEEE","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:2c657a7e-87ff-4cca-a481-758f794e7677","http://resolver.tudelft.nl/uuid:2c657a7e-87ff-4cca-a481-758f794e7677","Experimental and theoretical analysis of vacuum circuit breaker prestrike effect on a transformer","Popov, M.; Smeets, R.P.P.; Van der Sluis, L.; De Herdt, H.; Declerq, J.","","2009","The work presented in this paper deals with the investigation of circuit breaker prestrike effect that occurs during energizing a distribution transformer. An experimental test setup that consists of a supply transformer, a vacuum circuit breaker (VCB), a cable and a test transformer is built, and the prestrikes in the VCB are recorded. The test transformer is a prototype distribution transformer, with installed measuring points along transformer windings in each phase. Voltage oscillations are measured along the windings and transformer terminals. The transformer is modeled by lumped parameters extracted from telegrapher's equations in discrete form. Voltage oscillations during switching-in operations are recorded and calculated with and without a cable installed between the VCB and the transformer. Computed voltages show good agreement with the measured voltages. Described method can be used by transformer manufacturers to estimate voltage wave forms during switching or lightning, to provide useful information for insulation coordination studies, and to investigate resonance effects in transformer windings.","modeling; switching tests; transformer; vacuum circuit breaker","en","journal article","IEEE","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:907aa1cf-4c67-4e8d-a522-13216abbf56c","http://resolver.tudelft.nl/uuid:907aa1cf-4c67-4e8d-a522-13216abbf56c","Application of Hybrid Modeling for Calculating Interturn Voltages in Transformer Windings","Hoogendorp, G.; Popov, M.; Van der Sluis, L.","","2009","This letter deals with the hybrid modeling of transformers and the determination of interturn voltage distribution in transformers with layer-type windings. The hybrid model uses a combination of a multiconductor transmission-line model and a single transmission-line model. The good agreement between computed and measured voltage waveforms shows that this model can be used for the computation of interturn voltages with full success. Analysis is performed by making use of a step function with 100-ns rise time.","hybrid model; modified Fourier transform; very fast transients","en","journal article","IEEE","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:d76e5f66-9f82-4c99-b526-1a6f4f388861","http://resolver.tudelft.nl/uuid:d76e5f66-9f82-4c99-b526-1a6f4f388861","Smart grids put into practice","Veldman, E.; Geldtmeijer, D.A.M.; Slootweg, J.G.","","2009","The transition towards a more sustainable energ y supply system causes changes in the supply and demand of energ y. It requires a more flexible and efficient operation of the electricity distribution grids. It calls for a smart grid with intelligent control embedded in the grids to incorporate electricity storage and controllable loads. This will ensure cost-effective development of an efficient and reliable electricity system that allows the integration of distributed generation. To realize this smart grid, a holistic approach is needed. The issues which need to be addressed to make smart grids a successful reality are addressed in this chapter. It is illustrated that these aspects are much broader than developing and implementing technologies: a holistic approach involving all parties affected by the required paradigm shift is needed.","","en","conference paper","Economics of Infrastructures, Delft University of Technology","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:670be6d3-c674-448b-bf3f-9325269aa266","http://resolver.tudelft.nl/uuid:670be6d3-c674-448b-bf3f-9325269aa266","Transient stability analysis of a distribution network with distributed generators","Xyngi, I.; Ishchenko, A.; Popov, M.; Van der Sluis, L.","","2009","This letter describes the transient stability analysis of a 10-kV distribution network with wind generators, microturbines, and CHP plants. The network being modeled in Matlab/Simulink takes into account detailed dynamic models of the generators. Fault simulations at various locations are investigated. For the studied cases, the critical clearing times are calculated. Results obtained from several case studies are presented and discussed.","critical clearing time; distributed generation; distribution network; power system protection","en","journal article","IEEE","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:af7990b5-59d8-4709-a712-1a512b045e82","http://resolver.tudelft.nl/uuid:af7990b5-59d8-4709-a712-1a512b045e82","First-principles study of hydrogenated amorphous silicon","Jarolimek, K.; De Groot, R.A.; De Wijs, G.A.; Zeman, M.","","2009","We use a molecular-dynamics simulation within density-functional theory to prepare realistic structures of hydrogenated amorphous silicon. The procedure consists of heating a crystalline structure of Si64H8 to 2370 K, creating a liquid and subsequently cooling it down to room temperature. The effect of the cooling rate is examined. We prepared a total of five structures which compare well to experimental data obtained by neutron-scattering experiments. Two structures do not contain any structural nor electronic defects. The other samples contain a small number of defects which are identified as dangling and floating bonds. Calculations on a bigger sample (Si216H27) show similar properties (radial distribution functions, band gap, and tail states) compared to the Si64H8 sample. Finally the vibrational density of states is calculated and compared to inelastic neutron-scattering measurements.","","en","journal article","American Physical Society","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:4d8fec26-1d05-4911-8850-d5815a3c466d","http://resolver.tudelft.nl/uuid:4d8fec26-1d05-4911-8850-d5815a3c466d","Modulated photonic-crystal structures as broadband back reflectors in thin-film solar cells","Krc, J.; Zeman, M.; Luxembourg, S.L.; Topic, M.","","2009","A concept of a modulated one-dimensional photonic-crystal (PC) structure is introduced as a back reflector for thin-film solar cells. The structure comprises two PC parts, each consisting of layers of different thicknesses. Using layers of amorphous silicon and amorphous silicon nitride a reflectance close to 100% is achieved over a broad wavelength region (700–1300 nm). Based on this concept, a back reflector was designed for thin-film microcrystalline silicon solar cells, using n-doped amorphous silicon and ZnO:Al. Simulations show that the short-circuit current of the cell with a modulated PC back reflector closely resembles that of a cell with an ideal reflector.","amorphous semiconductors; elemental semiconductors; photonic crystals; semiconductor thin films; silicon; silicon compounds; solar cells","en","journal article","American Institute of Physics","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:1c13fbb8-4061-4904-b13b-e336a6f054ab","http://resolver.tudelft.nl/uuid:1c13fbb8-4061-4904-b13b-e336a6f054ab","Possible Solutions to Overcome Drawbacks of Direct-Drive Generator for Large Wind Turbines","Bang, D.; Polinder, H.; Shrestha, G.; Ferreira, J.A.","","2009","","","en","conference paper","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:5d968993-b1b8-4004-923d-6b5914b9fbe0","http://resolver.tudelft.nl/uuid:5d968993-b1b8-4004-923d-6b5914b9fbe0","Investigation on the Possible Use of Magnetic Bearings in Large Direct Drive Wind Turbines","Shrestha, G.; Polinder, H.; Bang, D.; Jassal, A.K.; Ferreira, J.A.","","2009","A direct drive generator used in wind turbine has high energy yield compared to other drivetrain topologies and low maintenance is expected as the technology matures. On the other hand direct drive generator weight and size increases rapidly when scaled up to larger units. This paper will investigate the possibility of weight reduction of large direct drive generator using magnetic bearings without compromising maintenance. Three different configurations using magnetic bearings i.e. single magnetic bearing concept, flexible rotor and hybrid concept have been analyzed. The results show that a combination of magnetic bearings and mechanical bearing with stiff radial structure and axial flexibility i.e. hybrid concept has the possibility to reduce weight of direct drive machine significantly compared to conventional design.","direct drive; magnetic bearing; generator; wind turbine","en","conference paper","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:edfaf4ed-63ce-442e-b2ff-5b738a13fa1b","http://resolver.tudelft.nl/uuid:edfaf4ed-63ce-442e-b2ff-5b738a13fa1b","Operation of grid-connected DFIG under unbalanced grid voltage condition","Zhou, Y.; Bauer, P.; Ferreira, J.A.; Pierik, J.","","2009","Doubly fed induction generator (DFIG) still shares a large part in today's wind power market. It provides the benefits of variable speed operation cost-effectively, and can control its active and reactive power independently. Crowbar protection is often adopted to protect the rotor-side voltage source converter (VSC) from transient overcurrent during grid voltage dip. But under unbalanced grid voltage condition, the severe problems are not the transient overcurrent, but the electric torque pulsation and dc voltage ripple in the back-to-back VSCs. This paper develops dynamic models in MATLAB/Simulink, validates it through experiments, investigates the behavior of DFIG during unbalanced grid voltage condition, and proposes new controllers in separated positive and negative sequence. Methods to separate positive and negative sequence components in real time are also developed, and their responses to unsymmetrical voltage dip are compared. Simulation results prove that the separated positive and negative sequence controllers limit the torque pulsation and dc voltage ripple effectively.","control; doubly fed induction generator (DFIG); operation; unbalanced","en","journal article","IEEE","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:2b6ada05-dc85-43ba-8e7e-d6fe20e30a21","http://resolver.tudelft.nl/uuid:2b6ada05-dc85-43ba-8e7e-d6fe20e30a21","Determination of the mobility gap of intrinsic ?c-Si:H in p-i-n solar cells","Pieters, B.E.; Stiebig, H.; Zeman, M.; Van Swaaij, R.A.C.M.M.","","2009","Microcrystalline silicon (?c-Si:H) is a promising material for application in multijunction thin-film solar cells. A detailed analysis of the optoelectronic properties is impeded by its complex microstructural properties. In this work we will focus on determining the mobility gap of ?c-Si:H material. Commonly a value of 1.1?eV is found, similar to the bandgap of crystalline silicon. However, in other studies mobility gap values have been reported to be in the range of 1.48–1.59?eV, depending on crystalline volume fraction. Indeed, for the accurate modeling of ?c-Si:H solar cells, it is paramount that key parameters such as the mobility gap are accurately determined. A method is presented to determine the mobility gap of the intrinsic layer in a p-i-n device from the voltage-dependent dark current activation energy. We thus determined a value of 1.19?eV for the mobility gap of the intrinsic layer of an ?c-Si:H p-i-n device. We analyze the obtained results in detail through numerical simulations of the ?c-Si:H p-i-n device. The applicability of the method for other than the investigated devices is discussed with the aid of numerical simulations.","elemental semiconductors; energy gap; hydrogen; silicon; solar cells","en","journal article","American Institute of Physics","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:2b4c2763-586a-4806-a612-524fd3efe8c0","http://resolver.tudelft.nl/uuid:2b4c2763-586a-4806-a612-524fd3efe8c0","Common-mode DC-bus filter design for variable-speed drive system via transfer ratio measurements","Zhao, D.; Ferreira, J.A.; Roc'h, A.; Leferink, F.","","2009","Filters used in electromagnetic interference suppression are often described in literature on drive systems and have become a standard solution in industry. The effect of the commercial off-the-shelf filter depends significantly on how it is installed. A model that includes the installation parameters is made first and then the parameters of the model are extracted by transfer ratio measurements. One possibility is to include the filter on the dc-bus inside the converter. The differential mode DC-bus filter is well known, but the common-mode DC-bus filter has received little attention. Our model is used to show that the common-mode DC-bus filter can achieve the same or even better suppression of common-mode noise by careful design. The transfer ratio is used to evaluate the performance of filter design.","electromagnetic compatibility; electromagnetic interference; filters; variable-speed drives","en","journal article","IEEE","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:95f1600f-1d5f-4bc3-82ee-89dd490a12ba","http://resolver.tudelft.nl/uuid:95f1600f-1d5f-4bc3-82ee-89dd490a12ba","Using copulas for modeling stochastic dependence in power system uncertainty analysis","Papaefthymiou, G.; Kurowicka, D.","","2009","The increasing penetration of renewable generation in power systems necessitates the modeling of this stochastic system infeed in operation and planning studies. The system analysis leads to multivariate uncertainty analysis problems, involving non-Normal correlated random variables. In this context, the modeling of stochastic dependence is paramount for obtaining accurate results; it corresponds to the concurrent behavior of the random variables, having a major impact to the aggregate uncertainty (in problems where the random variables correspond to spatially spread stochastic infeeds) or their evolution in time (in problems where the random variables correspond to infeeds over specific time-periods). In order to investigate, measure and model stochastic dependence, one should transform all different random variables to a common domain, the rank/uniform domain, by applying the cumulative distribution function transformation. In this domain, special functions, copulae, can be used for modeling dependence. In this contribution the basic theory concerning the use of these functions for dependence modeling is presented and focus is given on a basic function, the Normal copula. The case study shows the application of the technique for the study of the large-scale integration of wind power in the Netherlands.","copula; correlation; Monte Carlo simulation; stochastic dependence; stochastic generation; uncertainty analysis; wind power","en","journal article","IEEE","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:98b18423-8ca4-4afe-8f01-1a15fa2de407","http://resolver.tudelft.nl/uuid:98b18423-8ca4-4afe-8f01-1a15fa2de407","Toward the Next Level of PCB Usage in Power Electronic Converters","De Jong, E.C.W.; Ferreira, B.J.A.; Bauer, P.","","2008","A means for power electronics to exploit the level of 3-D packaging already being implemented in compact consumer products, such as digital cameras, is investigated in order to increase its power density. The increase in functionality and usage of printed circuit board (PCB) in power electronic converters is highlighted and improvements proposed to boost PCB usage to the next level. The material and manufacturing cost of an embedded planar transformer in a PCB-assembled power converter has been substantially reduced by introducing flexible-foil PCB to create the many windings without increasing the remaining number of (expensive) rigid PCB layers. Aspects such as the required folding pattern and its PCB material usage receive qualitative and quantitative attention. Furthermore, increasing of PCB functionality as regards integration of passives, geometrical packaging, and 3-D thermal management enhancement has been addressed. Not only is it shown that the integration of passives into a single, multifunctional PCB transformer structure is feasible but also that the same integral PCB can be used to geometrically package the remaining bulky, low-frequency, discrete components to create a power-dense converter and enhance the 3-D thermal magement. A power density improvement of 66% (from 150 to 250 W/L) is achieved by the technology demonstrator.","design methodology; geometrical packaging; optimization methods; packaging; power conversion; power density; power supplies; printed circuits; printed circuit layout","en","journal article","IEEE","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:147f0aa6-3146-45a0-86c7-24d6cd8ae2e0","http://resolver.tudelft.nl/uuid:147f0aa6-3146-45a0-86c7-24d6cd8ae2e0","Statistical Approach in Power Cables Diagnostic Data Analysis","Cichecki, P.; Jongen, R.A.; Gulski, E.; Smit, J.J.; Quak, B.; Petzold, F.; De Vries, F.","","2008","","cable insulation; data analysis; partial discharges; statistical analysis","en","journal article","IEEE","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:f93c0b2f-fe53-4568-9b0e-fa18b61b27b3","http://resolver.tudelft.nl/uuid:f93c0b2f-fe53-4568-9b0e-fa18b61b27b3","On-site Testing and PD Diagnosis of High Voltage Power Cables","Gulski, E.; Cichecki, P.; Wester, F.; Smit, J.J.; Bodega, R.; Hermans, T.J.W.H.; Seitz, P.P.; Quak, B.; De Vries, F.","","2008","In addition to after-laying of new-installed high voltage (HV) power cables the use of on-site non-destructive on-site testing and diagnosis of service aged power cables is becoming an important issue to determine the actual condition of the cable systems and to determine the future performances. In this paper based on field experience an overview is presented on on-site testing and partial discharge diagnosis of HV power cables with regard to on-site testing methods: energizing, diagnostic aspects, possibilities and implications for new and service aged power cables.","high voltage power cables; on-site testing; ac over-voltages; partial discharges; diagnosis; condition assessment","en","journal article","IEEE","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:e8de3a0b-c4c9-4e48-adaf-2017ea925ad2","http://resolver.tudelft.nl/uuid:e8de3a0b-c4c9-4e48-adaf-2017ea925ad2","Improved Analytical Model of a Permanent-Magnet Brushless DC Motor","Kumar, P.; Bauer, P.","","2008","In this paper, we develop a comprehensive model of a permanent-magnet brushless DC (BLDC) motor. An analytical model for determining instantaneous air-gap field density is developed. This instantaneous field distribution can be further used to determine the cogging torque, induced back electromotive force, and iron losses in the motor. The advantage of analytical models is that they can be readily used for optimization of BLDC motor because they are fast.","air-gap field; BLDC motor; magnetization; permanent magnets","en","journal article","IEEE","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:8df50036-b0ab-42a2-ae0a-32dede396f76","http://resolver.tudelft.nl/uuid:8df50036-b0ab-42a2-ae0a-32dede396f76","Progressive design methodology for complex engineering systems based on multiobjective genetic algorithms and linguistic decision making","Kumar, P.; Bauer, P.","","2008","This work focuses on a design methodology that aids in design and development of complex engineering systems. This design methodology consists of simulation, optimization and decision making. Within this work a framework is presented in which modelling, multi-objective optimization and multi criteria decision making techniques are used to design an engineering system. Due to the complexity of the designed system a three-step design process is suggested. In the first step multi-objective optimization using genetic algorithm is used. In the second step a multi attribute decision making process based on linguistic variables is suggested in order to facilitate the designer to express the preferences. In the last step the fine tuning of selected few variants are performed. This methodology is named as progressive design methodology. The method is applied as a case study to design a permanent magnet brushless DC motor drive and the results are compared with experimental values.","BLDC motors; PDM; Voltage source inverter; Genetic algorithms; Linguistic variables; Multi attribute decision making; Multi-objective optimization (MOOP)","en","journal article","Springer","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:388bdf8c-26ee-4711-bf88-14ce82c8f3bb","http://resolver.tudelft.nl/uuid:388bdf8c-26ee-4711-bf88-14ce82c8f3bb","MCMC for Wind Power Simulation","Papaefthymiou, G.; Klöckl, B.","","2008","This paper contributes a Markov chain Monte Carlo (MCMC) method for the direct generation of synthetic time series of wind power output. It is shown that obtaining a stochastic model directly in the wind power domain leads to reduced number of states and to lower order of the Markov chain at equal power data resolution. The estimation quality of the stochastic model is positively influenced since in the power domain, a lower number of independent parameters is estimated from a given amount of recorded data. The simulation results prove that this method offers excellent fit for both the probability density function and the autocorrelation function of the generated wind power time series. The method is a first step toward simple stochastic black-box models for wind generation.","Monte Carlo simulation; Markov chain; wind energy conversion; wind turbine generator","en","journal article","IEEE","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:13ecde36-8156-47ee-b165-d0c6477e23c5","http://resolver.tudelft.nl/uuid:13ecde36-8156-47ee-b165-d0c6477e23c5","Analytical Approach to Grid Operation With Phase Shifting Transformers","Verboomen, J.; Van Hertem, D.; Schavemaker, P.H.; King, W.L.; Belmans, R.","","2008","Analytical expressions are derived to gain insight in the operating principles of phase shifting transformers (PSTs) in a highly meshed grid. To this extent, the dc load flow algorithm is adapted to account for such devices. This leads to a linear expression for the relation between PST settings and the active power flow in the lines. Based on these equations, the total transfer capacity (TTC) can be described mathematically, which allows for optimization. Furthermore, the linear least squares method is used to distribute a cross-border transport evenly over the interconnectors. Both criteria are demonstrated by two examples","dc load flow; load flow control; phase shifting transformer; total transfer capacity","en","journal article","IEEE","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:eb770cbe-bfe3-4f6d-b0de-347bd6ce43de","http://resolver.tudelft.nl/uuid:eb770cbe-bfe3-4f6d-b0de-347bd6ce43de","Bipolar Pulse-Drive Electronics for a Josephson Arbitrary Waveform Synthesizer","Van den Brom, H.E.; Houtzager, E.; Brinkmeier, B.E.R.; Chevtchenko, O.A.","","2008","AJosephson arbitrary waveform synthesizer (JAWS) has been developed in order to generate quantum-based ac voltage signals. The key component of this JAWS is a modified commercial 30-Gb/s pattern generator that can generate ternary patterns (containing the values +1, 0, and ?1, resulting in bipolar pulses). The new pulse-drive electronics have been successfully tested by driving Josephson arrays with bipolar current pulses from 1 to 30 Gb/s in order to study their current–voltage characteristics and the spectra of the JAWS signals.","AC Josephson voltage standard; Josephson junction array; metrology; pulse-driven Josephson junction; pulse pattern generator","en","journal article","IEEE","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:6ae01098-ac49-4dcc-9c4f-381f33f0cd96","http://resolver.tudelft.nl/uuid:6ae01098-ac49-4dcc-9c4f-381f33f0cd96","Charge deep-level transient spectroscopy study of high-energy-electron-beam-irradiated hydrogenated amorphous silicon","Klaver, A.; Nádady, V.; Zeman, M.; Swaaiij, R.A.C.M.M.","","2006","We present a study of changes in the defect density of states in hydrogenated amorphous silicon (a-Si:H) due to high-energy electron irradiation using charged deep-level transient spectroscopy. It was found that defect states near the conduction band were removed, while in other band gap regions the defect-state density increased. A similar trend is observed for a-Si:H which has been subjected to light soaking, but in that case the majority of defect states are created around midgap, whereas with electron-beam degradation more defect states are created near the valence-band tail.","silicon; hydrogen,; elemental semiconductors; amorphous semiconductors; deep level transient spectroscopy; electron beam effects; defect states; conduction bands; energy gap; valence bands","en","journal article","American Institute of Physics","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""
"uuid:85f8169b-3e5b-4a39-a9df-80842ed6811a","http://resolver.tudelft.nl/uuid:85f8169b-3e5b-4a39-a9df-80842ed6811a","Polymeric amorphous carbon as p-type window within amorphous silicon solar cells","Khan, R.U.A.; Silva, S.R.P.; Van Swaaij, R.A.C.M.M.","","2003","Amorphous carbon (a-C) has been shown to be intrinsically p-type, and polymeric a-C (PAC) possesses a wide Tauc band gap of 2.6 eV. We have replaced the p-type amorphous silicon carbide layer of a standard amorphous silicon solar cell with an intrinsic ultrathin layer of PAC. The thickness of the p layer had to be reduced from 9 to 2.5 nm in order to ensure sufficient conduction through the PAC film. Although the resulting external parameters suggest a decrease in the device efficiency from 9.2% to 3.8% due to a reduced value of open-circuit voltage, the spectral response shows an improvement in the 400–500-nm wavelength range, as a consequence of the wider band gap of the PAC layer.","carbon; amorphous state; optical windows; silicon; hydrogen; amorphous semiconductors; solar cells; energy gap; semiconductor device measurement; elemental semiconductors","en","journal article","American Institute of Physics","","","","","","","","Electrical Engineering, Mathematics and Computer Science","Electrical Sustainable Energy","","","",""