Integrating renewable offshore wind generation into global power grids is a critical issue in the energy industry. Modular Multilevel Converter (MMC)-based High Voltage Direct Current (HVDC) grids are the most effective and promising technical solution for the new offshore wind energy power system connections. These grids offer scalability, controllability, and reliability advantages, but their stable and compliant operation requires implementing MMC control strategies and controllers. This thesis investigates the intricacies of HVDC technologies, focusing on MMC control strategies and controllers. The research explores grid following and grid forming converter control strategies, essential for ensuring stable and compliant operation of MMC-based HVDC grids. The research elaborates on the Model Predictive Control (MPC), which is a promising control strategy for MMC-based HVDC grids. The MPC controller makes the control strategies respond faster, emphasizing constraints and cost functions. Furthermore, a comparative analysis of Proportional Integral (PI)-based and MPC-based controllers is conducted across various scenarios, highlighting the advantages of MPC-based controllers over PI-based controllers regarding response time and stability. Lastly, a large stability analysis is conducted using the direct Lyapunov method to evaluate the effectiveness of the control strategies and controllers during transient events. This analysis provides insights into the stability and performance of MMC-based HVDC grids under different operating conditions and disturbances. This thesis illustrates the capabilities of grid-forming control strategy through Model Predictive controllers for FPGA-based MMC-MTDC networks on RSCAD/RTDS®. The outcomes of this thesis contribute to advancing HVDC technologies and control strategies, with implications for enhancing the stability and efficiency of MMC-based HVDC grids. The findings of this thesis have significant potential in the energy industry, particularly in integrating renewable offshore wind generation into global power grids.

In 2019 the European Aviation Environmental Report stated showed a relative increase in CO2 emissions of 16% compared to 2005 to 2017. It also stated that an increase of 42% is expected according to current models. Aviation is thus a big sector of the global warming problem. The solution to this is to go full electric. There are already more electric aircraft who decline the use of fuel for aircraft. This project thus attempts to design an electrical architecture for one of these airplanes. This thesis in particular shows the power demand for most the loads on the plane using mostly linear extrapolations, and voltage to current ratio on the system. It also talk about a state of the art electrical motor, and its characteristics, estimated to be available by the year 2038

Electret transducers utilize the electric field generated by an electret, a dielectric with a quasi-permanent embedded charge, to induce charge on an electrode. When the electret is moved relative to the electrode, the induced charge magnitude on the electrode changes, generating a current that can be used to convert mechanical energy into electrical energy. Micro-electret transducers are promising alternatives to conventional electromagnetic transducers for small-scale energy harvesting as they can achieve a high voltage output at low frequencies, can be miniaturized effectively, and can be manufactured using microfabrication methods. One-dimensional electrostatic models have been developed to predict the power output of electret transducers. However, for micro-electret transducers, fringing fields play a large role in the electrostatic domain. To be able to more accurately predict the output characteristics of micro-electret transducers, a two-dimensional (2D) electrostatic model is proposed. To verify the 2D model, a novel micro-electret transducer is designed. The novel electret design allows the micro-electret transducer to embed charges of only one polarity, increasing the power output of the electret transducer. The novel 2D model more accurately predicts the power output characteristics of the micro-electret transducer with the voltage output deviating 57%, compared with 317% by the conventional model predictions. Furthermore, the novel unipolar micro-electret transducer achieves double the power output and better charge stability compared with conventional electret transducers.

In this master thesis, the design and implementation of a high-voltage switch using series-connected Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) is discussed. A high-voltage switch is needed for applications such as high-voltage DC converters. Multilevel modular converters (MMCs) can also aid in the voltage-blocking capabilities of converters. MMCs use multiple submodules to block the full voltage. Every submodule thus only blocks a part of the full voltage. Each submodule needs multiple components that can be expensive, like voltage sensors and gate drive circuitry. By having the submodules block a higher voltage, fewer components are needed. By implementing a higher voltage blocking switch into such a submodule, cost and components can be spared by having a lower total amount of submodules. Current technologies of high-voltage switches are MOSFETs, insulated gate bipolar transistors, thyristors or electro-mechanical switches. MOSFETs have the advantage of being faster and have lower losses than the other technologies. The downside of using MOSFETs is that the voltage-blocking capability is lower than the other technologies. This could be solved by connecting multiple MOSFETs in series for a higher blocking voltage. To do this, care has to be taken that the MOSFETs turn on- and off at the same time. They also need to share the voltage equally to take full advantage of the blocking voltage of each MOSFET. A cost-effective way to implement a high-voltage switch using series-connected MOSFETs is to use capacitive coupling. In this method, the gate charge needed to turn the MOSFETs on is stored in capacitors. When the first MOSFET is turned on, the other series-connected MOSFETs will also turn on. This method has the downside that the switch can only be turned on for a limited amount of time (a few microseconds) and that the voltage balancing is dependent on the load, the switching frequency and the parasitics of the circuit. For this reason, a single high-voltage MOSFET was used in this project, even though it can be slower and more lossy than the series-connected switch. An MMC submodule was made using a full-bridge configuration. Additionally required components such as a gate signal generator, power supply, voltage- and current sensors, and fault protection were also designed, built and tested. In this way, a functioning MMC submodule was created that can be used with a capacitor or an isolated transformer as its source.

As the electricity sector transitions towards a low-carbon future, an increasing proportion of synchronous generation in the power system is replaced with inverter-based resources (IBRs). The result is a reduction in the available rotational inertia in the grid, depleting its ability to withstand and arrest frequency changes following disturbances. Consequently, disturbances such as a loss of generation or load have an increasingly larger impact on the system, resulting in higher frequency deviations and increased rate of change of frequency (RoCoF). On two occasions in 2021, the Continental Europe Synchronous Area (CESA) experienced system splitting events caused by cascading trips of several transmission system elements. In both cases, system defence plans were activated in order to preserve the integrity of the overall system. The amount of disconnected load was limited on both occasions, however, should similar events occur in the future with even lower rotational inertia in the grid, the impact could be more severe. This raises the question of whether the existing defence measures are sufficient to maintain system integrity and stable system operation. Currently in CESA, containment of system frequency excursions following a severe loss of generation is achieved through low-frequency demand disconnection (LFDD) at a frequency below 49Hz. Due to the reduction in traditional synchronous generation and system inertia, the frequency stability of the system is expected to deteriorate, leading to an elevated impact of major disturbances, a rising probability of forced disconnections at frequencies below 49 Hz, and the potential for cascading loss of generation and blackout events. The objective of this research is to explore the potential impact of reduced system inertia and increased penetration of renewable generation on the performance of the traditional LFDD scheme. In conjunction, additional proactive measures are proposed and investigated with the aim to reduce the probability of LFDD disconnections, by taking actions at frequency thresholds between 50 and 49Hz, as well as to improve the performance of the LFDD scheme in the event that disconnections are required. As a test case, the LFDD scheme as currently applied by one of the distribution system operators in the Netherlands is considered. This project is therefore categorised in two primary research directions: (i) improving selection criteria for LFDD load shedding locations, and (ii) improving LFDD performance using alternative load shedding schemes. Key topics explored in this research include: (i) the use of system strength and real-time DER generation as input parameters to load bus selection criteria for LFDD, and (ii) proactive RoCoF-based disconnection of pre-determined consumers above 49Hz. The findings of this study indicate that adapting the current LFDD implementation based on the local system strength and the level of active DER generation at LFDD buses can improve frequency response and reduce instability following LFDD switching operations. Furthermore, proactive RoCoF-based demand side load management techniques above 49Hz prove effective in reducing frequency deviation during the most severe events while avoiding LFDD over-shedding for smaller contingencies.

In 2018 it was estimated that the aviation industry produced approximately 1.04 billion tons of CO2. This was an estimated 2.5% of the total CO2 emitted that year. In order to slow down global warming, big changes need to be made to the transportation industry. This change has already begun with commercialization of electric cars. The next step is clear: fully electric, zero emission air crafts. This projects goal is design a high power propulsion system for an electric aircraft set to launch in the year 2040. This project attempts at predicting how this propulsion system might look like, specifically the electrical architecture. This thesis looks at the battery energy storage system, the wiring system and how to deal with high-voltage phenomena at low pressure. Several simulations are performed to justify design choices and give a visual representation of the different design options.

EU carbon emission targets related to climate change has set in motion a process of transition towards an environmentally clean and sustainable power system. A central focus on this process is the transition from fossil fuel based energy sources to clean Renewable Energy Sources (RES). However, the intermittency of RES (e.g. solar and wind) presents a formidable challenge to achieve a stable and reliable supply-demand balance in grid oper- ations. To achieve high levels of RES deployment, increasing the power system flexibility will be central to accommodate large fluctuations in supply and to cope with peak demand. Prospects of electricity storage technologies have emerged as a potential key technology to manage high levels of RES in the power system. Recent projections on the cost of electricity storage show a high decrease in the next five years ([1],[2], [3]). As the commercial maturity of batteries might become a reality within the next decade, many questions remain on the role of batteries in the power system, where batteries should be located? What capacity will be optimal? What kind of battery services are the most valuable? How do batteries contribute to the large deployment of distributed RES installations? Significant research has been done on estimating sizing and sitting of storage in power systems. Yet, most of this research treat storage capacity as continuous instead of discrete, i.e. allocating storage by percentages of a total allowed capacity, wherever necessary in the grid. Despite these previous studies have provided interesting contributions on the value of storage in the power system, many of them lack the modelling of power flows, technical limits, or voltage considerations. This thesis focuses on battery flexibility in medium voltage grids. Specifically, how to define cost-effective strategies to deploy batteries in a medium voltage grid? What is the optimal battery location in a distribution grid? And how do the technical limits of the power grid influence the allocation of storage? To address these questions, an optimization model was developed to simulate half-hourly operational decisions for a distribution grid. The model is multi-period and includes: power flows, diverse technical consideration for different battery sizes, high RES penetration levels, time of use electricity prices (half-hour dynamic prices), load data of actual customers and battery costs. To decide on the battery location, the model employs binary variables to determine the investment and sitting of the battery in a distribution grid. That is, the model is a mixed integer linear program with multi-period features which provides an investment analysis for the cost-effective sitting of batteries in a time horizon of 10 years. The model is implemented to the IEEE 33 bus test system. Results show that in general battery location and size strategies are driven by multiple factors, which can be either fixed or dynamic, like thermal limits and power load consumption, respectively. Some relevant findings are: First, flexibility in terms of power arbitrage delivers costs reductions of around 4% when RES production is low, compared to a No-Batteries case. Moreover, when RES production is high, the reductions in total costs can ramp up to 12% below the No-Batteries case. Also, this model decides to al- i locate batteries only if they are economically feasible for a 10-year time horizon. These results indicate a potential revenue up to 2.1 million pounds (GBP) based on the investment in batteries. And they are based on battery cost prices from 2008, together with several optimistic projections for the next decade. Furthermore, depending on battery size, RES penetration, RES generation and technical limits, batteries tend to be located for buses at the entrance of branches with high loads. Likewise, line limits and voltage limits proved to be decisive in the election of buses and the number of batteries placed. On one hand, results show that optimal allocation strategies depend on grid topology features and technical limits, on the other hand, they also have a high dependency on time- varying and unsteady factors (e.g. power generation and loads). The optimal location strategies tend to change and adapt to the dynamics of the system. Moreover, with the exception of the slack bus, every bus in the system turned out to be an optimal location, at least once. These results indicate that batteries might be useful in every bus of the dis- tribution grid, but only if each battery is operated in coordination and cooperation with one another. These insights support the idea of designing local electricity markets. Based on a reflection of this work, we recommend a market design that retrieves day-ahead and intraday DSO-reports of the battery operations and the flexibility that is available in the distribution grid. And also a subsequent structure of market incentives and penalties that maximizes the value of flexibility while keeping non-optimal operations to a minimum. In short, this thesis contributes with a novel modelling approach that can shed some lights on the optimal battery allocation problem for distribution grids. Moreover, it pro- vides insights on how location affects the value of storage, how optimal locations are affected by multiple technical factors. And finally, it also provide some reflections on the need to collectively, cooperatively and coordinately operate the storage resources in the grid by considering market-based solutions.

Conventional high voltage test sources, i.e., transformers (cascaded and resonant), impulse generators, and rectifier circuits generate 50 Hz/60 Hz sinusoidal, lightning and switching impulses, and DC respectively. For arbitrary wave shapes, function generator and HV amplifier setup are available up to 50 kV and few kHz signal bandwidths. Superimposed signals (impulses or transients on a sinusoidal or DC) are generated from a careful design of superposition of two voltage sources. The demand of these unconventional test sources is increasing as new electric stresses are introduced in the current electrical power network due to the rise of power electronics. This motivates the search for a novel high voltage test source which can generate arbitrary wave shapes with larger signal bandwidth at higher voltage level. Modular multilevel converter (MMC) topology is a promising solution for high power applications because of its high efficiency, modular structure, and reduced filter requirement. Hence, the idea of a MMC-based high voltage test source is proposed for arbitrary wave shape generation. Such a converter-based test source can also be adapted as a mobile test system for site acceptance and diagnostic testing and opens an entire new high voltage research area. This master’s thesis demonstrates the proof of concept of a MMC-based high voltage test source using a mathematical and simulation model. The first step is to identify critical differences between existing MMC applications versus high voltage testing applications. Based on this analysis, control methodology and converter parameter design are adapted for high voltage testing application. Since a power electronic converter generates an output signal with harmonics, a filter is required to obtain a smooth signal that can be applied to the test objects. The quality of the generated signal is measured in terms of the peak value and the slope of the output voltage. Also, the protection system and DC source requirements are investigated briefly for a comprehensive picture of the MMC-based high voltage test system. The thesis demonstrates the feasibility of the MMC-based high voltage test source with a proof of principle on paper and with simulations. Recommendations are given for the next steps to realize a high voltage test source for arbitrary wave shape generation.

Efficiency improvements of solar cells, growth in photovoltaic cells manufacturing, and declining prices of solar modules are just a few of the factors that have allowed solar power to break records (320 GW) in global cumulative installed capacity in 2016. In the energy systems of the future, solar energy will be the predominant energy source. However, the growth in solar power brings new technical challenges to overcome. Power intermittency, grid flexibility, and surplus electricity are just a few of the challenges that must be addressed for the power systems of the future. In the light of these challenges, this thesis provides new insights in the use of solar energy to produce hydrogen via a PEM electrolyzer. In order to achieve this goal, a hybrid power system model of hydrogen production using solar power was developed. The system consists of a PV array, a battery bank, a PEM electrolyzer, hydrogen tank, and a power control unit. The results are structured in two parts. First, simulations of three configurations between the panel and the electrolyzer: (i) direct coupling, (ii) including an MPPT, and (iii) including a battery. Second, simulations of several component sizes of PV modules, battery bank, and electrolyzer stack. These simulations were analyzed for yearly irradiance data from Delft. An analysis of energy yields, hydrogen production, system efficiency, and the impact on the electrolyzer lifetime, is performed for each of the configurations. Additionally, Wawa, a lab-scale solar-to-hydrogen system has been designed, built and tested. Wawa provides a practical hands-on understanding the hydrogen production via PEM electrolysis using solar power. Based on the simulation results, it is clear that the lifetime of the electrolyzer can be positively affected by including a battery as an energy buffer. An additional conclusion is that the shape of the irradiance curve plays an important role when sizing the components of the system. Hopefully, this research will motivate students to address more research on how solar-to-hydrogen systems can help to develop the power systems of the future.

Single junction solar cells have a theoretical efficiency limit of 33.1% due to spectral mismatch. To overcome this, multi-junction devices are generally fabricated with two or more junctions, so as to achieve better energy conversion efficiency by optimum spectral utilization. The c-Si bottom cell of a thin-film Si triple-/quadruple-junction device does not utilize the low energy photons (below 1.1 eV). The photons in the range of 0.7-1.1 eV, have an available current density of 15.9 mA/cm^2. A fraction of this current density would be large enough to not limit the output current of these thin-film Si-based multi-junction devices. Ge, belonging to the same group IV as Si and being heavier than it, forms weaker covalent bonds. Hence, it has a lower bandgap energy, making it the preferred choice of material. In this work, a low bandgap material such as a Ge-based absorber layer is fabricated that can be used in the bottom cell of a thin-film Si-based quadruple-junction device. This thesis will focus on the influence of a set of deposition parameters on the various properties of the Ge:H films. This will result in a set of Ge:H films from which a specific few are used as absorber layers to analyze the performance of a single-junction cell. The fabrication of the Ge:H films is carried out on a CASCADE setup which is based on the RF-PECVD technique. A processing range is identified to be in the range of 1-5 mbar pressure with RF powers ranging between 5-25 W for a fixed electrode distance of 20mm. nc-Ge:H are processed in the range of 20-25 W for pressures of 2 mbar and higher at a high dilution of 400. A strong correlation is found between the refractive index of the films and the presence of GeOx. The films with low refractive index possibly indicate a porous network with high void density show substantial oxygen contamination and vice-versa. Water vapour in the ambient is responsible for the oxidation. The oxygen contamination significantly impacts the properties of the films. The E04 optical bandgap increases with oxygen contamination which hinders the development of a low-bandgap absorber layer, while the Eact decreases to values as low as around 50 eV . Generally, the pre-exponential factor (sigma_o) decreases significantly by 1-5 orders of magnitude which outweighs the decrease in Eact, resulting in the decrease in dark conductivity by 1-3 orders of magnitude. Consequently, highest photo/dark conductivity ratios of 5-6 are obtained for these films. Amongst the films without oxygen contamination, the lowest E04 optical bandgap reported is 1.2 eV, with a Etauc bandgap of 0.93 and a photo/dark conductivity ratio around 3.4. Most of the single-junction cells processed at absorber layer thicknesses of 100nm and above show resistor-like behaviour. The substantially high values of Rs losses associated to the Rsh degrade the cell parameters significantly. Although, for low absorber layer thickness of around 50nm, the closest resemblance to a cell-behaviour is observed. Therefore, there is a scope for improvement with regards to processing of these single-junction cells.

Lunar dust presents a serious problem for future lunar rovers. Due to the charged nature of this fine dust, it tends to stick to sensitive elements like solar panels. It is clear that a system needs to be implemented in order to remove lunar dust to keep the output power of the solar panel at a satisfactory level. This paper develops the proof of concept electronics for a method sometimes called an electrodynamic screen, that uses electrostatic fields to sweep away the dust adhered to the surface of the solar panel. The electronics for this system needs to produce a high voltage three phase pulse wave in order to drive the electrodes placed on top of the solar panel. The design of the electrodes themselves are not part of this thesis, but it is the main subject of the companion thesis produced by other members of our group.

Many countries in the world face the problem of fruit frost during spring, which results in the loss of harvested crops. Solutions exist to prevent the fruit to freeze, however this requires that the temperature is known. Therefore, a smart autonomous temperature sensor network is designed that is capable of acquiring a 3D temperature profile of a fruit orchard to detect fruit frost. This thesis discusses the design of the energy harvesting and control module, which is one of the three sub-modules of the system. The goal is to sustain the energy demands of the sensor in a durable way, in order to operate for 20 years without requiring maintenance. To achieve this, several ambient energy sources and their harvesting techniques are investigated and simulated to examine the energy that can be harvested. This resulted in the use of solar energy, harvested by a solar cell and controlled by a maximum power point tracking module. Next, different energy storage implementations are considered to store the harvested energy temporarily. The use of a 5 F supercapacitor is concluded. Furthermore, an energy monitoring circuit is designed to measure the energy stored in the supercapacitor. Full system reliability simulations are done to verify the complete design by utilising the solar irradiance and temperature data of the past ten years. From these simulations is concluded that the design can sustain the energy demands of the sensor at all times.

This thesis presents a practical topology for achieving highly efficient dual-side wireless power transfer (WPT). Traditional WPT systems with a diode rectifier on the secondary side lack flexibility in load matching, requiring the integration of an additional dc/dc converter at the back end. However, this approach leads to increased power losses and costs. In contrast, this thesis proposes the use of an active rectifier comprising MOSFETs, replacing the diode rectifier. By employing a dual active bridge topology with dual-side control, optimal load tracking is achieved by tuning one side and communicating the desired duty cycle or phase angle to the other side. To address practical challenges, two key aspects are considered. Firstly, synchronization is established between the generated current on the secondary side and the new active rectifier, enabling efficient load tracking and the potential for zero voltage switching (ZVS). This is accomplished using a printed circuit board (PCB) equipped with zero current crossing detection (ZCCD), validated with an 85kHz test signal. The PCB triggers the PWM output of the secondary side microcontroller with a latency of less than < 50ns, utilizing the trip-zone digital compare sub-block integrated into the TMS320F28379D. Secondly, seamless wireless communication between the primary and secondary sides is essential. While the secondary side can measure the current and voltage across the load to adjust its duty cycle for optimal conditions, the primary side lacks this information. Therefore, the secondary side transmits the new duty cycle to the primary side to ensure consistent power flow. The nRF24L01+ wifi module is utilized as a dual-purpose transmitter and receiver for achieving wireless communication. Validation of this wireless communication is performed by remotely controlling an external LED, connected to the receiver side, from a distance of approximately 5m.accurately to the transmitted values. Additionally, a mathematical modeling approach is used to optimize power delivery and mitigate high-frequency noise by incorporating two parallel MLCC capacitors on a custom PCB near the nRF24L01+ module.

Since the introduction of SF6 in the 1950s, gas-insulated high voltage circuit breakers and Gas-insulated switchgear (GIS) have improved considerably, in particular concerning required drive energy for operation, compactness, and reliability. Nevertheless, high voltage insulation design has become increasingly challenging in recent years. Customer demands for reducing the physical footprint of HV equipment has led to an increase in operational field stress and therefore, much higher pressure on tolerances and increased susceptibility to defects. Dielectric design is based on how electrostatic fields are distributed and how much stress they can generate. In the course of conducting the intensive theoretical and experimental investigations on the dielectric design of insulation systems applied to high voltage power and pulsed power applications, it is becoming necessary to consider the influence of phenomena that have not been considered before. On top of that, as SF6 is one of the greenhouse gases listed in the Kyoto Protocol, SF6 usage regulations have been implemented in many industries. In Europe, SF6 is regulated under the F-Gas directive, which bans or restricts its use for several purposes. Several studies have indicated that CO2 is a viable alternative to SF6 for the transmission and distribution of electricity. In this context, this project aims to investigate a potential new phenomenon, the occurrence of secondary discharges caused by propagating streamer or leader discharges in HV gas insulation. Learning more about such phenomena can help us improve the dielectric design or perhaps explain the occurrence of breakdowns reported in high voltage equipment for which no obvious cause could be found. Specifically, CO2/O2 mixtures will be studied, and its results compared to SF6. Breakdown in gaseous insulation is caused by propagating discharges that are external in ambient air, e.g. on a bushing, or inside high-pressure insulation, e.g. across the surface of a GIS insulator. During the propagation of such discharges and flashovers (streamer or leader), transient electric field enhancement may occur, leading the local fields to exceed the inception fields at other locations. This can result in secondary discharges. Dielectric experiments using Image Intensifier and Photomultiplier tubes (PMT) have been conducted at three different pressure ranges; SF6 and CO2/O2 were selected as the insulation mediums. A negative polarity electric field is expected to trigger the secondary discharge. An analysis of images obtained from optical investigations and time lag records obtained from PMT signals suggested that secondary discharges can occur at low pressures (0.2MPa) in both SF6 and CO2/O2. At higher pressures (0.4 to 0.6MPa), no secondary discharges were detected. The reason for this is that, at higher pressures, the breakdown field is higher leading to a faster propagation of discharge across that gap. Hence, the formative time lag of the discharge is very short (some 100푛푠 or less) and this short time is not sufficient for secondary discharge inception.

There is a rapid increase in the off-shore wind farms and the interconnection between countries which results in an increased energy transfer over longer distances. High voltage DC (HVDC) cables can transfer this energy in a reduced cost and efficient way in contrast with high voltage AC (HVAC) along with many other benefits. For the HVDC cables extruded cross linked polyethylene (XLPE) insulation is preferred over the mass impregnated paper oil cable due to advantages such as low costs, simplicity, no use of oil and high operating temperatures. One of the main degradation mechanism for such insulation type is weak electrical conduction of charges due to the material conductivity. Due to a local inhomogeneity of the insulation the ow of these charges is non-uniform. This results in the charge owing inside of a region not equal to the charge owing out of that region which causes a local charge build up. These charges are known as space charges. These create region(s) of high electrical stress which can result in partial breakdown or in some cases complete breakdown of the insulation material as well. Hence, space charge accumulation in cable insulation material governs the failure behaviour and life time of the cable. This thesis look into the possibility of carrying out an off-line space charge measurements for real-sized HVDC polymeric cable insulation samples using the electrostatic probe technique. The first objective is to develop a calibrated sample using which it is possible to carry out the space charge measurement. Secondly, the possibility to convert the measurements obtained from the sample into the space charge distribution is looked into. A calibrated sample (prototype) is prepared and both the objectives are evaluated using it.

The development in technology and increased public interest has attributed to an unprecedented growth of E-mobility in recent years. Electric vehicles (EVs) even though viewed as emission free and environmental friendly can still contribute towards indirect emissions if charged by using traditional fossil fuels. The integration of renewable energy sources is hence paramount to approach a completely carbon free future of E-mobility integration in the transportation sector. This thesis project aims at designing and implementing a photovoltaic (PV) based charging station for a fleet of ten EVs in the TU Delft campus. The complete solar powered charging station for EVs is hence called as E-Hub, which aims to facilitate the development of e-mobility in the TU Delft campus by providing charging facilities that can be scaled up along with a competitive business model. At first, the driving pattern of EV owners in the Netherlands is analysed to categorize employees and visitors. The driving pattern is used to estimate the load profile and the yearly charging demand for the EV fleet in the TU Delft campus. Calendar effects such as holidays and vacations are taken into account to accurately predict the charging demand. A thorough PV system design is carried out to meet the estimated charging demand, followed by a practical and economic feasibility study. The components required for the E-hub are listed along with an estimation of the initial investment. Later an optimisation model is used to develop power management algorithms for optimum economical performance based on the designed technical framework. Nine charging strategies are considered for both summer and winter conditions. The performance of each strategy is analysed under the estimated load profile and designed PV system. The model is also extended to explore the integration of battery systems and its effect on the technical and economical performance of the E-Hub. This battery system can hence function as a virtual power plant to supply power back to the grid in times of peak load and facilitate in stabilization of the grid. A proof of concept is then built to test the developed power management algorithms in the Electrical Sustainable Power Lab (EWI, TU Delft). The Eneco SolarEdge and Tesla Powerwall (ESTP) set-up is used to study the power flow and a system is designed to dynamically control and monitor the ESTP set-up. It was concluded that such a system is technically and economically feasible and can be implemented in the university to provide an environmentally friendly charging infrastructure to electrical vehicles.

To follow the rapid advance of the Energy Transition, the technology and application of the renewable energy resources and energy storage devices have been developed in an unstoppable speed. When the application of energy storage technology starts to prosper gradually over the world, there are some problems showing up while lots of advantages are being advocated. There are plenty of batteries staying unused or being wasted for over half of the lifetime of the system, especially for the behind-the-meter energy storage system. The business models are usually built just for one or two primary services for customers and grid that makes only a limited part of time occupied, leaving the essential untapped values aside. And also, it is common that the energy storage system is coupled with PV panels or wind turbines. In this case, how to increase the on-site solar energy self-consumption becomes an attractive issue considering the sizeable financial benefit it can bring. What is more, when putting the attention on the neighborhood or community level where there is more than one participator in this picture, how to create the extra value or bonus benefit using the existed system and equipment can be an interesting topic. This report will focus on the grid-size battery installed behind the meter within a commercial community. A methodology of the energy hub with two different lays providing all kinds of services will be proposed. As the result, the value of grid-size energy storage in enabling a community-level energy hub for both battery-owner and neighbors will be explored to cope with all the above problems. There will be a case study conducted in the selected Zuid-Oost Amsterdam region. In the end, how much benefit the energy hub can create for not only the battery-owner but also for the whole community and society will be discussed.

A next step in the energy transition is to produce green fuels from sunlight. One way to achieve this is via high voltage photovoltaic (PV) devices which can directly drive electrolysis reactions to produce hydrogen or other chemical fuels. Group IV based multijunction (MJ) PV devices are a candidate to function as these high voltage devices. This work is focused on improving the efficiency of crystalline silicon/nanocrystalline silicon/amorphous silicon (c-Si/nc-Si/a-Si) triple junction (3J) solar cells through better current matching. On top of that, the low bandgap material germanium tin (GeSn:H) is characterized as it shows potential for use as bottom junction in multijunction photovoltaic devices. Several methods were tried to improve current matching in the 3J PV devices. Varying the nc-Si middle absorber thickness was successful at improving the shortcircuit current density (J 𝑠𝑐 ) in the middle junction, which was the current limiting junction. A range between 35μm ncSi absorber thickness is effective at keeping the middle junction J𝑠𝑐 high while keeping opencircuit voltage (V𝑜𝑐 ) and fill factor (FF) losses at an acceptable level. Varying the n-type nanocrystalline silicon oxide (n-nc-SiO𝑥) intermediate reflective layer (IRL) thickness was also effective at improving the J𝑠𝑐 of the middle junction. Introducing a silver IRL between the n-layer of the middle junction and the player of the bottom junction was ineffective, as was introducing various transparent conductive oxides (TCOs). The J𝑠𝑐 of the middle junction did not increase with the introduction of these layers. In the case of the TCOs, the shunt resistance decreased drastically resulting in decreased V𝑜𝑐 s and FFs. The best performing device in this thesis was manufactured using a 400nm a-Si:H absorber, a 4.5μm i-nc-Si:H absorber and a 60nm n-nc-SiO𝑥 intermediate reflective layer. This device had a V𝑜𝑐 of 1.947V, FF of 0.789, a J𝑠𝑐 of 9.51mA/cm2 and an efficiency of 14.6%, which, to the best of our knowledge, is the highest conversion efficiency achieved to date with this device architecture. Introducing tetramethyltin (TMT) to process GeSn:H films resulted in carbonization of the films. Carbon passivates Ge dangling bonds better than hydrogen. This reduces the defect density, leading to higher activation energy (E𝑎𝑐𝑡) with high TMT injection rates. A high germane flow rate resulted in dense, relatively defectfree films with a high photoconductivity, low bandgap and near intrinsic semiconductor properties. A high germane flow of around 2 sccm is therefore recommended. Varying the pressure in the deposition chamber offers some control over postprocessing oxidation, where higher pressure results in less oxidation. Changing the radiofrequency power offers a tradeoff between film growth rate and film quality.

Due to the current trend of urbanization more people will come and live in cities than ever before. This increases the need to monitor the urban environment, to be able to improve the living conditions of the urban dwellers. Our project combines the need to monitor the local environment, with a portable, self-powered and wireless weather station. The final design consists of a solar powered and WiFi-connected weather station with autonomous functionality for one year. For our research, the focus was on the Netherlands. Part of such a project is the power management which will be dealt with in this thesis. In the thesis, different maximum power point tracking algorithms will be discussed and compared. Furthermore, some more research is done in the hardware design, the use of different evaluation boards and battery configurations. Finally, a prototype using the incremental conductance algorithm is constructed and tested. Simulations lead to an efficiency of around 80%, which means autonomous functionality for a minimum of one year. The physical system had a lower efficiency, but autonomous functionality for one year was still achieved.

Fruit-frost during spring is one of the main causes of damage to the harvest of fruit in orchards. Various systems using different methods of preventing spring-frost are available on the market. To determine when these systems should be activated, the temperature in the orchard needs to be determined. In this project, a self-sustaining autonomous temperature sensor network is designed, which is capable of making a 3D temperature map of the orchard. The system is used to warn farmers when the threat of fruit-frost occurs and to gather data on the spatial variation of the temperature in the orchard. In this thesis, the focus is put on designing the smart measurement and control system. This includes choosing an appropriate control unit and temperature sensors. Also, the software for the control unit is designed, which allows for a smart measurement scheme that balances energy usage and measurement frequency. Finally, an estimation of the energy usage of the subsystem is given based on theoretical analysis.