Solar photovoltaic (PV) energy has the potential to become a major source of electricity production worldwide. However, the deployment of this renewable energy source comes with several challenges. Besides societal, political, and grid-limiting, several technical limitations decrease the trust in this technology. Within this context arises the Trust-PV project, whose objective is to improve the performance and reliability of photovoltaic systems.

This work contributes to this European project by exploring different power prediction models for several types of PV systems. Considering the broadness of the topic, four parts or blocks are identified. The first part deals with machine learning models to forecast the yield of residential PV systems. The second block focuses on analytical models used during the design phase. The third part is dedicated to systems floating on water. Lastly, a metric to assess the tolerance towards shading of different modules is developed in the fourth block.

Starting with the first block of machine learning techniques for PV power forecasting, Chapter 2 introduces the topic by reviewing a large number of manuscripts. The chapter performs a broad classification of the reviewed literature with the objective to identify trends and gaps in the field. Among the identified trends, one can highlight the high percentage of predictions for the day ahead, the generally low number of systems employed to train the models, and the concentration of systems in mild climates.

The latter points may stem from researchers primarily using the systems available within their institutions. To promote collaboration, Chapter 3 presents a developed website that lists PV power open source databases. The website aims to encourage researchers to train and test their models with different data sources.

One consequence of the concentration of systems in mild climates is that the effect of climate on machine learning models remains underexplored in the literature. Chapter 4 addresses this gap by studying how machine learning models behave for systems located in different climatic zones. The results show that weather homogeneity affects the accuracy of the models. Models developed for systems located in uniform climates - like desert areas - achieve in general higher accuracy than the models developed for systems in highly varying climates - like tropical areas.

Chapter 5 addresses another challenge: creating a single machine learning model able to monitor the performance of a large fleet of residential PV systems. The developed model surpasses in accuracy an analytical reference model but is limited by a fundamental characteristic of machine learning methods: the focus on large errors which resulted in the overlooking of smaller systems. Consequently, Chapter 6 develops a different approach based on the peer-to-peer methodology. In this approach, the power output of similar neighboring systems is compared to identify any malfunctions. The method is tested for the residential fleet of PV systems and proves effective for detecting faults.

Moving on to the second block of analytical power predictions, Chapter 7 presents the PVMD toolbox, a state-of-the-art analytical simulation framework that can predict the power of systems that do not exist yet. The abilities of the toolbox are tested for residential systems in the same chapter and the results show the negative influence that inaccurate input irradiance data has on the predictions.

This importance of accurate irradiance data affects all kinds of PV systems, but especially large-scale ones. Therefore, to monitor them, a proper allocation of irradiance sensors is essential. Hence, in Chapter 8, a software tool is developed to identify the optimal number of irradiance sensors and their position in a PV farm. The tool’s strengths are more prominent in plants located on terrains with significant elevation changes.

The third block focuses on PV systems that are installed on floating platforms rather than on land. Chapter 9 introduces the topic by examining three factors influenced by proximity to water that can impact the production of a floating PV system in a French quarry lake: movement fluctuations, dust accumulation, and module temperature. The results reveal a limited influence of all factors on the production for the period of study therefore facilitating the deployment of floating systems.

The block continues by studying the effect of sea waves for a system located in the North Sea. The simulation results from Chapter 10 reveal that wave fluctuations can have a negative yet limited effect on the DC and AC yield of floating PV systems. These results are further elaborated in Chapter 11, where the model is improved by considering the fluid-structure interaction. This advanced model enables to study the effect of various platform characteristics on the power mismatch losses. The results reveal a trade-off between mechanical stability and mismatch losses.

Finally, the last part deals with the power lost when a PV module is partially shaded. Chapter 12 develops a simulation tool to efficiently calculate the shading tolerability of a PV module given its datasheet. The shading tolerability is a metric that quantifies the resilience towards shading of a PV module, that is how much power is lost when the module is partially shaded. The developed tool is used to create a database of shading tolerability of commercial PV modules, to compare the resilience of different modules towards shading. ... Read more

With an estimated global share of greenhouseemissions of 35%, the building sectormust be the target of significant transformation. These next decades represent one of the best opportunities for a giant energy consumer to become an efficient energy prosumer. Of the many technical possibilities available that can help in this objective, building integrated photovoltaic systems is becoming one of the most salient because of their versatility of application and simplicity of operation. However, to achieve their projected market growth, BIPV products must overcome technical, financial, and social barriers.

The interrelationship between these barriers creates requirements that are sometimes in conflict with each other. Research suggests that the most important parameters for the financial viability of a BIPV system (studied in North America) are its electrical performance and its effective lifetime. However, the social acceptance of BIPV systems, among architects and other consumers, increases when photovoltaic modules are provided with a variety of colors, resulting in losses in their electrical output. Furthermore, a BIPV system can present an installation layout in which its modules operate at high values of temperature, which hinders their useful lifetime.

Significant research has been done to tackle these requirements, striving to find a balance in which each, however contradictory, is met. This thesis seeks to add to this body of research through modeling and experimental efforts focused on creating techniques and concepts to improve the aesthetics and thermal behavior of photovoltaic modules.

After an introductory chapter, Chapter 2 presents an overview of the efforts done so far to improve aesthetics and passively cool photovoltaic modules. The challenges and barriers that remain from a technical perspective are outlined, and the base modeling approach deployed to tackle them is introduced. Chapter 3 presents how this model can be complemented by auxiliary algorithms to find ways to provide color directly to c-Si solar cells by using interference optical filters. The chapter also provides insight into ways of stabilizing color and the beneficial impact that a color optical filter has on the operating temperature of a c-Si solar cell.

Chapter 4 expands on the findings of Chapter 3 and discusses that the application of the color optical filter on the front glass of a PV module provides better benefits, particularly in terms of better color saturation and more vivid hues. In addition, it provides guidelines for how colorimetry can be added to the modeling effort to improve the quality of color matching and color stability of a color photovoltaic module based on optical filters. Furthermore it demonstrates that it is possible to achieve colorful designs with relative DC energy losses below 10%.

Chapter 5 argues that optical filters can also be designed to provide thermal control to photovoltaic modules. Furthermore, this thermal control can be achieved by taking advantage of the harmonic reflectance produced by simple designs. It shows that the analysis of a thermal management solution must always consider their benefits related to extended lifetime. A simple optical thermal filter, despite its lossy nature (in terms of electrical output), can still provide a net benefit in terms of energy yield when this benefit is accounted for.

Chapter 6 presents the huge cooling potential provided by phase change material (PCM). This work is entirely experimental and demonstrates that a single type of PCM can be used in different locations, with different installation layouts, to provide substantial temperature reductions and increase the electrical output of photovoltaic modules with great consistency, even during the wintermonths.

Chapter 7 presents the novel concept of a photovoltaic chimney, developed with the purpose of studying the potential use of the thermal energy produced by photovoltaic modules. The concept was analyzed using common modeling approaches to calculate mass flow and heat production, offering quick ways to create sensitivity analysis for earlier stages of design. These initial stages of the model can be used to have insight into the quality (or lack thereof) of the heat produced and its potential use to improve the ventilation of buildings.

Chapter 8 completes this dissertation, highlighting its main conclusions and providing details on potential areas that can drive future research.
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As a key pillar of the long-term decarbonization efforts, Photovoltaic (PV) is expected to grow significantly, driven by continuous technology development, cost reduction, and long-term climate action strategies targeting net-zero greenhouse gas (GHG) emissions by 2050. A major advantage of PV over other renewable energy sources is its ability to be integrated seamlessly into the urban environment without demanding additional land use. With the ongoing urbanization, the expansion of decentralized solar energy solutions will be essential in facilitating the transition to a green energy future. However, despite these incentives, designing, allocating, and maintaining urban PV systems present challenges.

This dissertation explores potential solutions to these challenges from various perspectives, aiming to improve understanding of the dynamics between PV systems and the urban environment. To achieve this, simulation models are developed and implemented to evaluate large-scale urban PV potential while incorporating social and climate concerns. Meanwhile, experimental approaches are taken to investigate the multifunctional capabilities of PVs that can be integrated into the future urban infrastructure. ... Read more

Power electronics (PE) plays a crucial role in optimizing the performance of photovoltaic (PV) systems. At present, module and sub-module level PE is increasingly being adopted in global PV installations. Typically, PE for sub-module purposes is installed in the PV junction box. However, in this dissertation another approach is investigated: integrating power electronics into or onto crystalline silicon (c-Si) PV cells. This approach has the potential to contribute to the development of shade-tolerant PV modules, increase the reliability of PV module-integrated PE, reduce the volume and weight of the PV system, and support the development of autonomous devices powered by low-power and low-current PV cells. Specifically, the aim of this dissertation is to study the integration of different PE components into c-Si solar cells, and identify the most promising approaches. The dissertation is structured in two parts.

In Part 1, the objective is to gain a comprehensive understanding of the impedance of c-Si solar cells. To this end, Chapter 2 reports a characterization of the impedance of eight single-cell laminates. Each laminate contains a different commercially available c-Si solar cell, featuring various cell architectures, namely Aluminium Back Surface Field (Al-BSF), Passivated Emitter and Rear Contact (PERC), Tunnel Oxide Passivated Contact (TOPCon), Interdigitated Back Contact (IBC), and Silicon Heterojunction (SHJ). It is found that the two main factors contributing to a high PN junction capacitance (C_j) at maximum power point (MPP) are (1) a low wafer dopant concentration and (2) a high MPP voltage. Furthermore, the studied cell laminates exhibit inductances between 63 and 130 nH. Following this, the impedance of PN junctions is further investigated in Chapter 3. Specifically, PN homojunction devices are investigated through Technology Computer-Aided Design (TCAD) simulations. This methodology allows to study the junction impedance in a detailed way, which may be difficult to do experimentally due to noise and reactance of metal contacts. Through analysis of the impedance data it is revealed that the PN junction exhibits the behaviour of a parallel resistor-capacitor circuit (RC-loop) at low frequencies, but undergoes relaxation in both PN junction resistance R_j and capacitance C_j as frequency increases. While various publications on solar-cell impedance model the low-high (LH) junction using an RC-loop, the findings presented in this chapter indicate that such a model does not accurately represent the underlying physics. Instead, this approach is likely compensating for the frequency-dependent behavior of R_j and C_j. Finally, in Chapter 4, the PN junction impedance of modern c-Si solar cells is studied across varying temperature and illumination conditions. In the tested conditions, the range in which the area-specific MPP R_j varies is similar for different cell architectures, despite their different properties. Conversely, the range in which the areal MPP C_j varies is significantly affected by the substrate dopant concentration and MPP voltage of the cell.

In Part 2, the aim is to assess the feasibility of leveraging solar-cell impedance at the input of a power converter, and to explore various methods for integrating additional PE components into solar cells. In Chapter 5, the feasibility of integrating different PE components into c-Si solar cells is explored. First of all, diodes exhibit high ease of integration into PV cells and successfully integrated designs have already been demonstrated in prior work. Alternatively, the integration of transistors is more complex. Since transistor fabrication processes require lithographic steps, it is necessary for cost-effective integration to combine as many processing steps as possible with PV fabrication. Regarding passive component integration, it is found that the self-capacitance of modern c-Si solar cells is sufficiently large to replace the input capacitor of an exemplary boost converter. However, for thin-film capacitor integration, it is challenging to achieve a sufficiently high areal capacitance. Moreover, the self-inductance of a solar-cell string could potentially be leveraged to replace the inductor at the input of a power converter. By analyzing this approach for an exemplary boost converter, it was found that high switching frequencies in the MHz range are required. Alternatively, the required switching frequency may be reduced through the integration of planar inductors. It was found that the area of PV cells is sufficiently large to facilitate the integration of planar coils exhibiting inductance values that are useful for power conversion. Finally, general challenges that should be considered for successful PE-PV integration are appropriate thermal management, opto-electric behaviour under illumination, and repairability. The inductor integration is further studied in Chapter 6. Specifically, it is explored whether large-area planar air-core inductors can yield the required inductor properties to support sub-module power conversion in PV modules. First, it is shown how the interplay between the different design parameters, such as track spacing, track width, number of turns, and middle gap size, play an important role in the inductor properties. This analysis includes changes due to high-frequency effects, which significantly impact the results. The coil geometries that are simulated yield inductance values between 0.3 and 3.2 μH. Considering the power losses, the applicability of such inductors in sub-module power converters is discussed. Finally, in Chapter 7, the concept of COSMOS (COmbined Solar cell and MOSFET) devices is introduced and a process flow is proposed in which back-contact TOPCon solar cells and lateral power MOSFETs are simultaneously fabricated on a single substrate. This process is successfully employed to manufacture both n-type solar cells with integrated p-channel MOSFETs (PMOS) and p-type solar cells with integrated n-channel MOSFETs (NMOS). Notably, efficiencies exceeding 20% are achieved for both n-type and p-type solar cells, highlighting the potential of COSMOS solar cells. Furthermore, two main integration challenges are identified. Firstly, the off-state leakage currents of the MOSFETs increase due to illumination. Secondly, specific topologies of monolithic integration lead to increased off-state leakage currents. ... Read more

This thesis introduces and develops advanced Differential Power Processing (DPP) architectures to enhance the performance and efficiency of photovoltaic (PV) systems by addressing mismatches among PV modules and strings. The work focuses on mitigating power losses due to voltage and current mismatches due to factors such as partial shading, panel misalignment, dust, and degradation. The research proposes novel architectures designed to reduce component voltage and power ratings, potentially lowering costs while maintaining high efficiency.

PV to Virtual Bus Parallel Differential Power Processing (PV2VB PDPP) Architecture: A new PV2VB PDPP architecture is introduced, leveraging a virtual bus as the input for string-level converters (SLCs). This design allows for reduced components’ voltage ratings by operating the virtual bus at a lower voltage than the main bus or PV strings. The architecture employs Dual Active Bridge converters connected to Bridgeless converters as SLCs to provide isolation and handle both positive and negative outputs. Experimental results demonstrate system efficiency ranging from 96.4% to 99%.

Dynamic Analysis and Stability: The thesis includes a comprehensive dynamic analysis of the PV2VB PDPP architecture, deriving small-signal models, transfer functions, and frequency responses. These analyses aid in understanding the system’s dynamic behavior, enabling effective controller design and stability studies. Experimental validation confirms fast stabilization of the virtual bus voltage (0.6 seconds) and intermediate bus voltages (15 milliseconds), ensuring efficient Maximum Power Point Tracking (MPPT) for each PV string.

Battery Integration in PV2VB PDPP Architecture: The work extends the PDPP architecture to include battery integration at the virtual bus, facilitating energy storage and management while performing MPPT. The battery integration reduces component voltage ratings and allows for efficient charging and discharging control by the central converter. Experimental evaluations show system efficiencies between 95.5% and 99%.

PV to Virtual Bus Series-Parallel Differential Power Processing (PV2VB SPDPP) Architecture: To address mismatches in both series-connected modules and parallel-connected strings, a PV2VB SPDPP architecture is proposed. This architecture uses a combination of SLCs and module-integrated converters (MICs), processing only a fraction of the total power. By leveraging virtual buses for both SLCs and MICs, the architecture reduces voltage and power stress on components, improving cost-effectiveness and reliability. Real-time simulations validate the system’s ability to balance power flow, ensure stable operation, and optimize PV module performance under mismatch conditions.
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Silicon heterojunction (SHJ) technology is gaining increasing attention due to its lowtemperature and simple fabrication process. Intrinsic hydrogenated amorphous silicon
((i)a-Si:H) serves as a passivation layer, providing excellent chemical passivation, while
doped a-Si:H offers good field passivation and selective contact. Thanks to these features,
SHJ has achieved a high conversion efficiency of 27.09%, approaching the theoretical
limit for silicon-based solar cells. However, achieving excellent passivation performance
results in optical and electrical losses, as the band gap of doped a-Si:H causes parasitic
absorption. One strategy to address this issue is to replace the doped layer with transition
metal oxides (TMOs), which can enable selective contact due to their high or low work
functions. Few researchers have integrated TMOs in silicon-based solar cells to replace
silicon-based doped thin films as selective contact layers. Wide-bandgap TMOs improve
the optical performance of the cells. However, interface reaction between TMOs and the
silicon substrate becomes an issue limiting the electronic properties of the device.

In this research, we first present three different interface engineering methods: no
plasma treatment (noPT), plasma treatment (PT), and plasma treatment with boron
(PTB). We applied these methods to SHJ solar cells with MoOx (2.9 < x < 3) as the hole
transport layer (HTL).MoOx thin-film is deposited by thermal evaporation. The methods
were implemented at theMoOx/(i)a-Si:H interface. Additionally, to address sustainability
concerns related to indium consumption and fully exploit the optical advantages of
MoOx, we propose bifacial SHJ solar cells withMoOx as the HTL to reduce the thickness
indium doped tin oxide (ITO) films. Furthermore, to test the capability of these interface
engineering methods with other TMO materials, we usedWOx (2.9 < x < 3) and V2Ox (2.9
< x < 3) as the hole transport films in SHJ solar cells. The TMO thin-films are deposited by
thermal evaporation. The specific results are summarized as follows.

Chapter 3 explores using MoOx as a HTL to address these issues. By tailoring the
interface betweenMoOx and (i)a-Si:H using interface engineeringmethods, the oxygen
content in MoOx layers has been successfully optimized. The PTB method reduces
the formation of SiOx layer resulting in improved electronic properties and low contact
resistivity. PTB treated samples showed the best performance, with high open-circuit
voltage (VOC) and fill factor (FF). This approach achieved a certified conversion efficiency
of 23.83% with an ultra-thinMoOx layer of 1.7 nm. Notably, a short-circuit current density
(JSC) above 40 mA/cm² has been achieved.

Chapter 4 explores reducing indium consumption by optimizing n-contacts as electron
collector layer andMoOx as a hole collector layer. Bifacial SHJ solar cells withMoOx
as the HTL and various electron transport layers (ETL) were fabricated and optimized
using optical simulations. The results showed that bilayer ((n)nc-Si:H/a-Si:H) and trilayer
((n)nc-SiOx:H/nc-Si:H/a-Si:H) better than monolayer (a-Si:H) in electronic and optical
performance. The use of ultra-thin transparent conductive oxide (TCO) layers combined
withMgF2 as double layer antireflection coatings (DLARC) significantly reduced TCO consumption whilemaintaining high performance. Devices exhibiting 10-nm thick indium
tungsten oxide (IWO) on both side and bilayer n-contact achieved certified efficiencies
of 21.66% and 20.66% when measured from theMoOx and n-contact side, respectively.
This device realizes 90% TCO-reduction. The best-performing bifacial cells exhibited
conversion efficiencies of 23.25% and 22.75% measuring from front and back side, respectively.
The bifaciality factor of the champion device is 0.96. It demonstrates over 67%
reduction in TCO usage compared to traditional SHJ solar cells. This study successfully
shows that reducing TCO thickness and optimizing the interface withMoOx can lead to
high-efficiency bifacial SHJ solar cells, contributing to sustainability challenges related to
indium consumption.

Chapter 5 investigates the application of TMOs likeWOx, and V2Ox as HTLs combined
with interface engineering methods in SHJ solar cells. The study aims to investigate the
applicability of interface engineering methods to other TMOs. X-ray photoelectron
spectroscopy (XPS) is employed to measure oxygen content and defects within TMO films.
The XPS results demonstrate that PTB resulted in higher oxygen content and fewer oxygen
vacancies. The optimal WOx thickness was found to be 2 nm, achieving a champion
cell with 23.30% efficiency with PTB and improved FF of over 80%. Similarly, with PTB
method, the highest efficiency of 22.04% has been realized with 3-nmthick V2Ox layer.
The PTB method effectively controlled interface reactions, leading to better electronic
properties of TMOs. The study concludes that the PTB method offers suitable interface
conditions for depositing TMOs, enhancing SHJ solar cell performance.

Our findings in this study may provide valuable insights into applying TMOs in SHJ
solar cells to achieve high performance. With optimized interface engineeringmethods,
we can significantly reduce the optimal thickness of TMOs and achieve world-record
efficiency. Furthermore, by applying TMOs in bifacial SHJ solar cells, we can decrease the
thickness of indium-based TCOs, realizing both high efficiency and high bifaciality factor.
This approach makes it possible to develop sustainable and efficient solar cells. ... Read more

Due to increasing population growth and industrialization, the energy demand is soaring around the world. In order to meet this energy demand and continuing with business as usual, there is an increased need for fossil fuels. Burning of fossil fuels such as coal, gas and oil lead to emission of carbon dioxide in atmosphere. Emission of carbon dioxide rises the earth’s surface temperature and is leading to global warming. In order to tackle this crisis, an alternative to fossil fuels need to be investigated. In this regard, renewable energy sources are key as they can be replenished. Solar energy is one of the fastest growing and promising renewable energy sources.

Photovoltaics (PV) modules or solar panels have been installed across the world, converting solar energy into electrical energy. The PV market is dominated by single junction crystalline silicon (c-Si) solar cells. In order to improve the efficiency of single junction solar cells beyond their efficiency limit, tandemsolar cells, which stack one solar cell on top of another, are being actively explored by researchers. In this work, we have focused on perovskite/c-Si tandem solar cells.

Since direct contact of metal with semiconductor leads to recombination, the concept of carrier-selective passivating contacts (CSPCs), which separates the absorber from the metal by a thin passivating layer, becomes important. The most common type of CSPCs are doped hydrogenated amorphous silicon (a-Si:H) on intrinsic amorphous silicon, as in the case of silicon heterojunction (SHJ) solar cells. The other type of CSPCs are polycrystalline silicon (poly-Si) on ultrathin silicon oxide (SiOx) as in the case of poly-Si solar cells. Depending on the fabrication temperature of CSPCs, the former comes under low temperature CSPCs while the latter is a type of high temperature CSPCs. While low temperature CSPCs have been successfully integrated in perovskite/c-Si tandem solar cells, research involving high temperature CSPCs is less developed. In this work, high temperature CSPCs are studied, optimized and integrated in perovskite/c-Si tandem solar cells. In addition, the performance of tandem solar cells is evaluated not only in terms of efficiency but also energy yield which is more relevant for outdoor environment. In addition to poly-Si, this work explores novel materials such as polycrystalline silicon oxide (poly-SiOx) and polycrystalline silicon carbide (poly- SiCx) as high temperature CSPCs... ... Read more

Hydrogen is not only the most common element in the universe, but also a versatile molecule which is an option to decarbonize sectors that are not easily electrified or are energy intensive, such as long-distance transport, chemical industry, and metallurgy among others. Hydrogen gas is typically obtained from fossil fuels, and only a small fraction is produced nowadays from electrolysis, or the process of using water and electricity to produce gaseous hydrogen.
If the electricity for powering the electrolysis process comes from renewable sources, the produced gas will have no associated greenhouse emissions. This is the so-called green hydrogen, which is the base for decarbonization of carbon intensive industries. This work investigates the potential of stand-alone green hydrogen production from solar energy, covering the whole design process, from an allocation and feasibility analysis, to system control. To do so, this thesis is separated in two parts. The first part focuses on the preliminary assessment phase of photovoltaic (PV) systems and the solar resource, while the second covers the integration of PV and electrolysis systems finalizing with a control strategy for these systems.
Chapter 2 presents a methodology for analyzing potential sites for PV deployment, including information on the degradation of the site. This provides the designer with additional information beyond the purely technical and economical layers that are typically considered in this type of study. The more degraded a site is, the more suitable it is for deploying new PV projects, avoiding pristine natural areas. This, combined with mitigation measures can minimize the environmental impact of new PV projects.
An analysis of the efficiency loss of PV systems is discussed in Chapter 3. In particular, the efficiency loss caused exclusively by quick variations in irradiance, as a consequence of passing clouds. These abrupt and quick changes affect not only the solar modules, but components downstream, such as the maximum power point tracker. The implemented algorithm might be sensitive to these changes and move the operating point of the PV module away from its maximum power point, leading to energy loss.
Predicting quick changes of irradiance is a topic covered in Chapter 4. Using sky images and artificial intelligence, it is possible to predict ultra-short-term irradiance. The proposed method is an ensemble of models, each trained on a particular sky condition. Because each model is highly specialized, once the sky condition is determined, the model that performs best on each sky type is employed, leading to lower prediction errors, more precise predictions and lower training data needed. Yet, an accurate prediction is a topic for further research.
The integration of PV with hydrogen systems is introduced in Chapter 5, which presents a literature review on integration methods for PV and electrolyzers as well as the main challenges for operating these systems in a variable manner.
Moving to the design phase, Chapter 6 proposes a sizing procedure, based on Particle Swarm Optimization to minimize the energy that cannot be used by the hydrogen equipment (electrolyzer and compressor), aiming at the maximum energy utilization in the system. Horizontally-placed PV modules provide a good compromise between efficiency, hydrogen production and cost.
Once the system has been designed, Chapter 7 puts together all the topics covered in this dissertation proposing a control strategy for an optimally-sized stand-alone PV electrolyzer systems, without electrical storage. The control is based on prediction of irradaince changes using sky-images. From Chapter 4 it was clear that the prediction using sky images is far from perfect, yet this is needed for control. To solve this problem, the strategy proposed in Chapter 7 relies on information on the uncertainty of the prediction and uses fuzzy logic to account for imperfect predictions. This strategy can effectively smooth power changes without the need of additional storage components. ... Read more

Photovoltaics will play a pivotal role in achieving a low-carbon-emission society. Remarkable advancements in the efficiency of crystalline Si (c-Si) solar cells, combined with standardized processes along the whole value chain, have enabled cost-competitive solar electricity production. In order to further decrease the cost of photovoltaic, significant efforts must be dedicated to further enhancing the efficiency of solar cells. The implementation passivating and carrier-selective contacts in recent years has led to a remarkable increase in the conversion efficiency of c-Si solar cells. Solar cells, such as silicon heterojunction (SHJ) and poly-Si/SiOx-based technologies are prime examples of the efficacy of these contacts, as cell efficiencies above 26% have been demonstrated. These achievements can be attributed to the excellent surface passivation properties of the intrinsic amorphous hydrogenated silicon (a-Si:H(i )) and the ultra-thin SiOx interlayers, coupled with the high carrier-selectivity exhibited by the doped Si-based layers. However, a significant limitation associated with these passivating and carrier-selective contacts is related to their optical parasitic absorption losses within the layers. These losses stem from the free-carrier absorption in a-Si:H layers of SHJ solar cells and poly-Si layers, which possess relatively narrow bandgaps, making them prone to absorbing the ultraviolet (UV) portion of sunlight. Consequently, these parasitic absorption losses diminish the amount of light reaching the c-Si absorber, ultimately restricting the short-circuit current (J sc) output of the solar cell. To mitigate these losses, wide-bandgap metal oxide layers, such as MoOx and TiOx, have been proposed as promising alternatives to replace these highly doped Si-based contacts. These metal oxides possess distinct carrier-selective characteristics, primarily due to their differences in work function (WF) with respect to the c-Si, leading to induced band bending within the absorber. Despite significant progress in recent years, several challenges still exist, as metal oxide contacts often suffer from carrier-selectivity issues due to material instability and interface reactions with adjacent layers. This thesis explores several possible strategies to minimize the parasitic absorption losses in passivating and carrier-selective contacts. A considerable portion of the research is devoted to understanding and enhancing the contact properties of the MoOx layer. The focus on MoOx is driven by the challenges it faces with carrier-selectivity, stemming from its low thermal stability and its susceptibility to band alignment issues when combined with various passivating interlayers. An innovative MoOx contact is introduced, incorporating ultra-thin surface passivating interlayers based on Al2O3 films. These ultra-thin interlayers offer substantial advantages, including enhanced surface passivation, minimal parasitic absorption, and improved transport of majority carriers. Additionally, MoOx and TiOx contacts, deposited by pulsed laser deposition (PLD) are also explored for c-Si solar cells... ... Read more

Large-scale deployment of photovoltaic (PV) technology is imperative for realizing a future sustainable and electrified energy system. Over the past decades, technological advancements that enhance the efficiency of PV technologies have been one of the crucial aspects for significantly reducing the cost of PV-generated electricity. Among various crystalline silicon (c-Si) PV technologies, silicon heterojunction (SHJ) solar cells, which have achieved the highest efficiency of single-junction c-Si solar cells, hold great promise for advancing the energy transition facilitated by PV technologies even further. Moreover, notable efficiency enhancements, which are well beyond the theoretical efficiency limit of single-junction c-Si solar cells, have been experimentally demonstrated by combining SHJ solar cells with semi-transparent perovskite solar cells in tandem configurations. This thesis focuses on addressing the challenges of efficient deployments of doped hydrogenated nanocrystalline silicon-based (nc-Si:H-based) layers for high-efficiency front/back-contacted (FBC) SHJ solar cells and applications of FBC-SHJ bottom-cells in two-terminal (2T) and four-terminal (4T) tandem devices with perovskite top-cells, supported by advanced opto-electrical simulations. ... Read more

In the efficiency-driven photovoltaic (PV) industry, the market dominating crystalline silicon (c-Si) technology has been developing towards PV devices with carrier-selective passivating contacts (CSPCs). Especially, the silicon heterojunction (SHJ) solar cell, based on hydrogenated amorphous silicon (a-Si:H) contact stacks, and the poly-Si solar cell, based on ultrathin SiOx/poly-Si passivating contacts, pave the way for power conversion efficiencies above 26%, approaching the theoretical limit of the c-Si solar cell. In case of front/back-contacted (FBC) architectures, to minimize the optical parasitic absorption at the emitter and/or surface field side(s), thin doped silicon layers are normally applied, which exhibit high sheet resistance. Accordingly, transparent conductive oxide (TCO) layers are required to ensure sufficient lateral carrier transport towards the metal electrodes. However, problems still exist in contacting schemes for high-efficiency solar cell design towards future multi-terawatt production of PV modules, regarding the development of TCO layer with high carrier mobility (μ), its integration into specific device structures, and more importantly, the material availability. In this work, we present three types of TCO materials. They are tin-, fluorine- and tungsten-doped indium oxide layers, namely, ITO, IFO, and IWO. RF magnetron sputtering approach has been utilized to deposit the films. The TCOs are integrated into both low thermal-budget SHJ and high thermal-budget poly-Si solar cells. Further, to address the sustainability implication related to indiumconsumption, we propose a strategy of bifacial SHJ solar cell with reduced TCO use. Meanwhile, to reduce silver (Ag) consumption, as well as to reach good solar cell performance in our laboratory, we have developed a platformfor bifacial copper (Cu)-platingmetallization approach. Specific results are summarized as follows... ... Read more

The coming years will see humanity facing significant challenges to ensure its continued survival. The threat of global warming to humans and the environment – exacerbated by rapidly growing population and energy demand – requires quick and decisive actions. Among them, increasing the generation of electricity from renewable resources is paramount to mitigate the effects of climate change. Photovoltaic (PV) energy conversion can be one of main technologies that propels the transition from fossil fuels towards a more sustainable future.
In recent years, the deployment of photovoltaic systems has increased at an astounding pace, with more than 100 GWp of power installed during each of the last three years. However, further expansion of PV installations cannot solely rely on increasing industrial production, but should also be supported by research aimed at increasing the efficiency of PV devices and reduce their manufacturing costs. One of the key aspects of photovoltaic energy conversion is absorption of light. By increasing the amount of solar energy that is absorbed inside PV devices, the efficiency of solar cells can be boosted. This is particularly true for thin-film structures, which due to their limited thickness struggle to effectively absorb photons. Light management indicates all the techniques aimed at maximising light absorption inside photovoltaic devices and is the main topic of this manuscript. The goal of this work is to investigate and optimise light management approaches – based on periodic structures – applied to different thin-film device technologies, and through this analysis provide guidelines for the design of photovoltaic devices and gain an insight into their optical performance.
After describing the theoretical background in chapter 1 and the methodology in chapter 2, chapter 3 begins the study of light management approaches by investigating nanowire arrays applied to thin-film nano-crystalline silicon solar cells. A proof-of-concept device was manufactured to ensure the feasibility of the proposed novel approach. Then, simulations were used to optimise the nanowire array structure. Results showed the good anti-reflective and scattering properties of nanowires, which are able to significantly boost absorption in the nano-crystalline silicon active layer.
In chapter 4, the analysis shifts to periodic metasurfaces and the achievement of perfect absorption in amorphous silicon solar cells. By tuning the size and arrangement of the dielectric nanostructures that make up the metasurface, near 100% absorption can be achieved in the spectral region where amorphous silicon struggles to efficiently absorb incident photons. With respect to flat devices the performance is significantly increased, despite a reduction of used material of more than 50%.
In chapter 5, a thorough investigation of periodic gratings for Cu(In,Ga)Se2 solar cells (CIGS) is carried out, complete with the selection of appropriate supporting materials to reduce the device thickness with a minimal sacrifice in performance. The accuracy of 3-dimensional rigorous modelling in predicting the performance of real CIGS devices was demonstrated for the first time. Then, a full study of 1-D and 2-D gratings was conducted – together with an analysis of device architectures that employ more transparent materials at the front and highly reflective metals at the back side. Results showed a marked increase in light absorption, mostly owing to a lower device reflectance and to reduced parasitic absorption in all supporting layers. The high optical performance was maintained when the thickness of the CIGS layer was reduced by 60%, which is crucial to reduce the utilisation of indium in the device and of the costs associated with it.
In chapter 6, the concept of front/back pyramidal textures with different geometries is introduced and fully explored. Its application to (nano-)crystalline silicon absorbers or to supporting layers is compared, showing a preference for the former. After careful study of the decoupled texture geometry, an optimised
optical performance beyond the traditional Lambertian scattering limit was achieved.
In chapter 7 the concept of double front and back textures is analysed further, by applying it to cheap and abundant barium silicide (BaSi2). The optical potential of of this novel PV material was first characterised with spectroscopy measurements, then assessed in both single- and multi-junction configurations with the aid of rigorous optical simulations. Results showed that BaSi2 outperforms thin-film silicon absorbers, owing to its higher absorption coefficient. This highlights the promise of this novel material, which can be an ideal candidate for both single- and double-junction thin-film devices. ... Read more

Solar photovoltaic cells are destined to become an important contributor in the renewable energy sector, also for small electrical systems inside buildings. They can be used to mobilise the electrical infrastructure, by providing an independent energy source for medium-consumption products, like decorative lighting. This thesis shows all aspects of designing and building an interior, solar powered lamp. First, the ideal position for indoor light harvesting has been investigated extensively, by recreating two typical Dutch rooms with 3D modelling software Blender. The light simulation tool RADIANCE was then used to compute the irradiance at various spots in the room, considering three standard sky types. Weather data from the KNMI was used to classify the sky conditions for every hour during two weeks in November, and the results were compared with pyranometer measurements, showing an error of 20% on a daily basis, and 5% over a five day period. The same simulation method was applied to predict the PV energy yield of four common solar cell technologies for a full year, for multiple room orientations and positions on a wall. Based on these results, three concepts were designed, corresponding to three specific room positions with different indoor light characteristics. Ultimately, one concept was chosen to be build as a prototype, with tailor-made, foil-to-foil laminated PV module, consisting of laser cut SunPower interdigitated back contact (IBC) cell technology. At standard test conditions, the measured short-circuit current was 2.37 A, with an open-circuit voltage of 21.5 V and a maximum power point of 35.9 W_p, resulting in an efficiency of 20.3%. Furthermore, a charge controller with maximum power point tracking algorithm was used to charge a 12V 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). ... Read more

Building Integrated Photovoltaics (BIPV) has the potential to play a major role in the ongoing transition towards nearly zero energy buildings. However, the BIPV market is still a niche market, representing only 1% of the global PV share. One of the main barriers that hinder the deployment of BIPV is the lack of aesthetic flexibility. Architects and designers are often reluctant to embed PV systems in buildings due to their unsuitable color.
In this thesis, the use of interference filters (IFs) as color coating solution for PV modules is proposed. IFs are optical devices designed to selectively reflect a narrow portion of the visible solar spectrum while transmitting the remaining part. The structural coloration provided by the filter is highly dependent on the angle of incidence of the light. This angular dependence could be an issue for BIPV applications, since color homogeneity is often an important requirement. The objective of this work is to model, fabricate and assess the opto-electrical performance of colored crystalline silicon (c-Si) PV modules based on interference filters, with the final goal of increasing the aesthetics of this technology.
First, the angular resilience challenge is addressed. Simulation results show that texturing the glass surface significantly improves the color stability, thanks to diffuse reflection of light. Very high angular resilience up to 80º can be achieved with a double-side texture profile made of hemispherical grooves. Secondly, five interference filters deposited on different glass substrates are used to fabricate 10 x 10 cm² c-Si colored mini-modules. The optical characterization of the demonstrators
allows to partially validate the optical model and confirm the good angular resilience of the textured surfaces. Finally, the electrical performance of the mini-modules is evaluated. I-V measurements show that IFs only affect the short-circuit current of the mini-modules due to optical losses. Depending on the color and the topology of the surface, absolute efficiency losses range from 0,95% to 4,6%. ... Read more

Bifacial PV modules and floating PV systems are two fast-growing technologies in the photovoltaic sector. Bifacial PV modules make use of the irradiance that is incident on both faces of the module, leading to higher energy yields. Several techniques are used in order to enhance this bifaciality effect, one of them being the use of reflectors. On the other hand, floating PV systems offer multiple advantages with respect to conventional in-land PV systems such as land saving (a big issue for vastly populated areas), higher efficiencies and lower water evaporation rates. The advantages that these technologies provide as well as the big market opportunities that they offer, make them very attractive for new investors.
The uncertainties related to floating PV and bifacial modules are higher compared to conventional power plants. In order to minimize these uncertainties, accurate modelling tools are essential. The most widespread software suites such as PVSyst or System Advisor Model, offer limited flexibility to the user. Therefore, the user is not able to adapt the simulation to very specific cases such as the addition of reflectors to the system. Additionally, they perform simulations only at module level, without performing an analysis at cell level.
Aiming to fill this gap, a Toolbox that is able to model and simulate the annual energy yield of a PV module, considering the physical effects from cell to module level, was developed by the Pho- tovoltaic Devices and Materials group of TU Delft. This Toolbox allows the integration of the work done by different members of the group and it offers great simulation flexibility to the user. The goal of this thesis is to continue the work carried out by former PVMD members and create a new and improved version of the Toolbox.
During this thesis project, several improvements were carried out in the optical models of the Tool- box. Multiple mistakes were discovered and corrected, and new features that improve the Toolbox were added, making it suitable for its use in real projects. Besides that, the thermal part has been improved by adding the option to utilize a thermal model developed in COMSOL Multiphysics that allows to study the temperature distribution in a bifacial PV module. Finally, the Toolbox was ap- plied to the INNOZOWA project, where several simulations were carried out to find the ideal design of a floating PV plant that consists of bifacial PV modules and reflectors. It was found that the chosen design for this type of system can provide a bifacial gain of 18%. ... Read more

The current energy scenario requires not only the conversion of renewable energy sources into electrical energy, but also a way to store it to match the demand and supply. In particular, solar energy can be used to stabilize energy conversion and energy supply by converting the energy in other diverse ways. And important possibility are photo electrochemical (PEC) reactions for water splitting and water treatment. To be able to directly drive these kind of reactions using solar energy, the interactions between the different elements must be studied in detail. In particular, the semiconductor/electrolyte interface seems to play a very important role in these kinds of devices. Moreover, each of these reactions needs specific conditions in terms of current and voltage, and thus specific semiconductor device architectures would be needed. In these two cases, both a study of the reaction, focusing on the semiconductor/ electrolyte interface, and a device optimization was performed. ... Read more

Electric vehicles are only sustainable if the electricity used to charge them comes from renewable sources and not from fossil fuel based power plants. The goal of this PhD thesis is to develop a highly efficient, V2G-enabled smart charging system for electric vehicles at workplaces, that is powered by solar energy. The thesis focusses on three research elements – power converter, charging algorithms and system design.  A 10kW EV charger has been developed that enables the direct DC charging of EV from PV without converting to AC. The charger is bidirectional, so energy from the EV battery can also be fed to the grid for vehicle to grid (V2G). The charger can realize four different power flows: PV → EV, EV → Grid, Grid → EV, PV → Grid. The 10kW modules are modularly built and can be operated without solar input as a bidirectional EV charger as well. Further, several DC charger modules can be operated paralleled for fast charging up to 150kW. The charger is based on silicon carbide and quasi-resonant technology which results in high efficiency (>96%) for both full load and partial load. The integrated EV-PV solution has a lower component count, three times higher power density and lower cost than using separate EV charger and PV inverter exchanging power over AC. The charger is compatible with the CHAdeMO and CCS/Combo charging standard and is designed for implementing smart charging. New smart charging algorithms developed in the project integrate several applications together: PV forecast, EV user preferences, multiplexing of EVs, V2G demand, energy prices, regulation prices and distribution network constraints. For two case studies simulated for Netherlands and Texas, the proposed algorithms reduced the net costs by up to 427% and 651% when compared to average rate charging, respectively.
... Read more

Low powered electric vehicles and electricity generation with the help of renewable energy technology are two kind of technological advancements which are taking place to meet growing global energy demand while reducing greenhouse gas emissions together at the same time. Achieving these objectives indicate shift from energy demand followed by fossil fuels to renewables. Renewable energy technology and plug-in vehicle electrification adoption have substantial problems associated with it, however there are ways to exploit their potential in order to develop sustainability in the field of electricity and transportation.

This thesis aims at designing the Roadside Photovoltaic (PV) system that act as a major supply of electrical power to charge Electric Bikes (E-bikes). The expansion and rapid growth in E-bikes is tremendous in the Netherlands, therefore the charging of E-bikes is chosen as an application to build the Roadside PV system for campus located at Mekelweg, Delft. The E-bike dynamic consumption is modelled to calculate the driving efficiency of an E-bike, and thus this model is used to compute the state of charge of incoming E-bikes in order to determine the daily consumption of charging station. Furthermore, for maximizing the energy yield of the PV system, the optimal orientation of module is analysed. The mounting and placement of these optimally oriented modules beside the road is decided such that the overall effect of shading is minimal. Moreover, as it is a Roadside PV, the system is compared with the solar road technology to see the difference of how the system behaves when placed optimally beside the roads on poles instead horizontally on roads. Finally, performance of entire grid-tied Roadside PV system with storage is determined according to chosen application. ... Read more

Among the advantages of crystalline silicon hetero-junction (SHJ) there is the possibility to use a thin c-Si wafer that is bendable, but still has a power conversion efficiency higher than commercially avail- able thin film (TF) modules. Nowadays, all the photovoltaic applications on curved surfaces use TF technologies, however their low power conversion efficiency requires a large area, which is not always available. Therefore, the entry of SHJ technology in the environment-integrated applications will de- crease the required PV area being a competitor of TF wherever the surface available is scarce and the the shape curved and not complex.

A structure that would benefit the advent of SHJ modules is the infotainment spot, which is a solar- powered device that provides useful information and entertainment to the user through an interactive screen. Such a device was realized for the first time by Weeda et al. [1] in TUDelft, but the CIGS module that powered the device made the structure bulky, unattractive and unwieldy. In this thesis the experience of Kaneka Corp., which holds the world’s record of highest conversion efficiency for c-Si hetero-junction, was used to design the PV module that powers the stand-alone system of a new infotainment spot.

In order to calculate the irradiation on the surface of the infotainment spot the Optical Model developed by Santbergen et al. [2] was used because allows flexibility in choosing the design and the location separately. However, this model does not include the surrounding, thus in this thesis three new ap- proaches to include the influence of the surrounding environment were proposed and validated through experimental measurements. Moreover, two of these new approaches have the possibility to study the irradiance also in indoor places. After that, its power was simulated knowing the irradiance values, the temperature of the PV module, computed with a thermal-energy balance, and other meteorological data. Lastly, a load profile was developed to simulate the system performance throughout the year. All these information served to find the best pair of number of SHJ cells to interconnect and battery capacity and basically it is a trade-off between system reliability and system size. The study indicated that in Osaka the infotainment spot would need 42 series connected half-cut solar cells that power a 12 푉 system with a storage capacity of 150 퐴ℎ in order to make the system completely autonomous and operable the whole year. The thesis ended with a working prototype of the Solar-Powered Infotainment Spot 2.0. ... Read more