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.@en

The motivation of this study stems from the reality that 2.2 million households in South Africa remain unelectrified, with the majority residing in informal settlements—communities that are remnants of the apartheid era, designed to enforce racially segregated living. While existing off-grid solutions provide basic electricity access to these households, they fail to meet the growing demand for higher levels of electricity access that local residents desire and can afford. This project aims to address this gap between the limited supply capacity of current off-grid solutions and the enhanced electricity services that communities are eager to receive.

Through site visits and consultations with local developers, specific design considerations and unique challenges were identified. These efforts revealed the limitations of existing open-source design tools, which do not comprehensively address the entire system’s design requirements for the proposed solution of a PV-powered DC microgrid. Consequently, a new framework was developed, integrating open-source tools and custom Python scripts based on established methodologies.

The comprehensive design framework was applied to the informal settlements of Oudtshoorn and Daveyton, demonstrating its ability to generate feasible, scalable, and adaptable microgrid designs. Overall, this project provides a solid foundation for advancing electrification efforts in underserved communities.

As photovoltaic (PV) technology enters the terawatt era, reliability, sustainability, and circularity in the solar industry can no longer be optional considerations for manufacturing solar modules. Despite two decades of intense solar manufacturing, the PV industry still predominantly operates within a linear economic structure, characterized by energy-intensive production and limited sustainability practices. One significant challenge associated with crystalline PV modules is the encapsulation process, which occurs within costly and unwieldy laminator machines. While laminating PV modules offers long-term stability and performance, it also imposes significant limitations on the disassembly, repairability, and recyclability of valuable PV module materials. The development of sustainable PV designs and manufacturing processes is crucial for transitioning to a circular economy. In response to this problem, Biosphere Solar, a startup company based in Delft, is developing a novel solar module design that eliminates the need for lamination. Their focus is on creating an easily disassembled solar module to facilitate repair, reuse, and ultimately achieving full recyclability with low-energy input. It is crucial to recognize that transitioning to non-laminated modules presents challenges in manufacturing. This thesis aims to identify and address barriers encountered in manufacturing laminate-free PV modules compared to traditional PV panels. First, becoming acquainted with laminated PV lines provided insights into the challenges to be encountered. The analysis of the laminate-free product primarily examines the module components, and materials diverging from laminated panels, such as adhesives, solder pastes, fillers, and edge sealants, assessing their trade-offs and configurations in terms of manufacturability. The product analysis has facilitated the definition of a manufacturing process flow, which is constructed based on assembly operations that both align with and diverge from standard PV manufacturing practices. This is complemented by an exploration of non-standardized processing methods, considering the associated boundary conditions in the assembly. The main challenges encountered include the metal paste dispensing, low-temperature soldering, and fluid filling processes, with multiple units installed and a necessity for a specific design tailored to this application. This study demonstrates competitiveness with respect to laminate PV line scales, particularly evident in larger-scale operations. Technically, a 30% reduction in energy consumption for machinery and up to 50% factory area savings can be achieved. The electrical consumption of the laminator(s) alone, for production volumes up to 300MW, can range between 20% and 50%, with a footprint share of up to 10% of the total manufacturing space. Economically, capital costs also demonstrate promise and have the potential to outperform laminated PV modules, especially in a highly automated setup line. Savings between 20-30% for equipment costs and up to 50% for building infrastructure costs are achievable. Nevertheless, the main factors offsetting these mitigated capital costs are the operational expenses associated with the bill of materials and the manpower required to produce this specific product. These material expenses can be up to 4-5 times higher than for a laminated panel, and up to twice the investment in manufacturing labour. This assessment lays the foundation for future research leveraging the trade-offs explored to refine choices and achieve optimal results.

Photovoltaic (PV) systems are often exposed to mismatch conditions caused by partial shading, different mounting angles, dust accumulation, cell degradation, etc. Among various techniques, PV to Virtual Bus Parallel Differential Power Processing (PV2VB P-DPP) has been proposed to overcome the mismatch among PV strings. This thesis focuses on the dynamic behavior of the PV2VB P-DPP configuration in order to analyze the system stability and design appropriate controllers. Configuration needs to control two different types of converters: 1- P-DPP converters (inner control loop) and 2- the Central Converter (outer control loop). Moreover, since the selection of capacitance for the virtual bus is a tradeoff between several factors, such as cost, stability, reliability, current ripple, and so on, this thesis provides a methodology to identify an acceptable range for the capacitance of the virtual bus.
This project used the state space representation to model the system owing to its simplicity and ability to provide a uniform and convenient starting point for linearization, stability evaluation, control design, and simulation. Since the system’s large signal model is nonlinear and difficult to work with, we linearized the state space equations (to achieve the small-signal model of a PV2VB P-DPP system consisting of any number of strings and converted them into the Laplace form to perform system analysis and controller design. Considering Gain and Phase Margin as the main design criteria, proportional control (Kp ) and integral control (Ki) were tuned for PI controllers using the SISO tool MATLAB toolbox for a PV system consisting of two PV strings. The system stability depends on two main aspects: the value of the virtual bus capacitor (CVB) and the voltage magnitude in the virtual bus (vV B ). The complete developed model has been implemented in MATLAB.
For the simulated PV2VB P-DPP system, a gain margin of 15.7 dB, a phase margin of 121 degrees, and a settling time of 0.8 s have been achieved for the outer control loop (central converter) by setting Ki and Kp to 5s^−1 and 0.5, respectively. On top of that, a gain margin of infinity dB, a phase margin of 91.2 degrees, and a settling time of 1 ms have been achieved for the inner control loop (DPP converter) by setting Ki and Kp to 10s^−1 and 0.1, respectively. Finally, it is shown that the virtual bus capacitor should be selected within the range 50µF- 5mF in order to make the system have higher stability margin. However, the final selected value of capacitance for the virtual bus is equal to 1.2 mF owing to other constraints, such as the expected ripple current.

This thesis presents experimental research on a phenomenon that has been widely observed in photovoltaic systems in recent years. Hot-spots, most commonly reported as areas of extreme temperature within PV modules, have been identified as a critical issue in the industry. This is primarily due to the fact that solar cells are subjected to various mismatches and time-varying stresses in real-world operation, affecting their long-term reliability. Moreover, hot-spots are mostly invisible to the naked eye and require special inspection such as EL and IR imaging for detection, making them challenging to solve. The use of low-temperature lamination techniques on the front sheet and encapsulation increases the risk of hot-spots within Solarge’s polymer-based lightweight modules, with permanent damage being observed after exceeding temperatures beyond 160°C. Therefore, robust design criteria were needed to pass the hot-spot certification test, which was developed keeping in mind the thermal limits of failure for the polymer module. This study provides an overview of contemporary cell technologies, encompassing Passivated Emitter and Rear Cell (PERC) and Interdigitated Back Contact (IBC), in the context of reverse bias characterization. The methodology involves comprehending hot-spot behavior across various configurations, beginning from single-cell laminates to strings, followed by module-level testing. The experiments include the assessment of various commonly used industry wafer sizes to evaluate cell breakdown properties and performance using IV curve analysis. Notably, two electrical processes contribute largely to the power dissipation in a solar cell in reverse: zener and avalanche breakdown. The investigation revealed cell breakdown voltages of -5.2V for IBC cells and -19.6V for PERC cells. These findings were consistent with values provided by manufacturers, reinforcing the widely accepted nature of the cells. The main objective of the investigation of a string or a module of cells in series without bypass diodes was to identify cells with lower performance, which increases the vulnerability to the emergence of hot-spots. The hot-spot endurance test was conducted on a standard polymer module, in accordance with the IEC 61215 guidelines, revealing essential parameters that significantly impact the resulting temperatures. A notable observation that emerged was the linear correlation between string length and power dissipation. This trend became evident when temperature values exceeded 165.84°C, accompanied by power dissipation of 150–200 watts and heat flux (Q˙) ranging from 0.52 to 0.69 W/cm2 for string lengths up to 24 cells in series. This led to irreparable damage to the module and the failure of the endurance test. Therefore, to pass the test, the string length was confined to less than 20 to stay below the thermal threshold. In addition, the findings included broader observations delving into intricate topics of hot-spot characteristics such as shape, frequency of occurrence, location, shading ratios, orientation, and various other relevant parameters. Hot-spot detection can be used to assess module health and enable proactive maintenance strategies. Understanding the phenomena of cell breakdown and power dissipation assists in the development of safer modules. Finally, this study aims to emphasize the importance of design considerations and offers the potential for optimized module architectures for the industry.

This study explores the effects and severity of microcracks within Solarge’s innovative lightweight polymer-based photovoltaic modules, aiming to recommend a grading criterion specific to the company’s product range. Unlike the traditional PV modules which predominantly employ a glass and aluminum frame, Solarge utilizes lightweight, fully recyclable polymers. The uniqueness of Solarge’s composition presents a novel landscape in terms of durability and degradation trajectories. A pivotal concern arises from the introduction of microcracks, which inherently diminish a PV module’s power output. Leveraging Solarge’s extensive database of current-voltage measurements and electroluminescence images, an initial analysis discerned the emergence of small diagonal and v-type cracks post-production, predominantly after the lamination process. Subsequent experimental methodologies, encompassing mechanical loading and temperature cycling on these modules, demonstrated the growth of these existing cracks into diverse and more complex formations. This evolution of stressors significantly compromised module performance. A categorization system classifying cracks into noncritical (Category 1), critical (Category 2), and very critical (Category 3) was developed, with associated power losses identified for each. Using linear regression, predictive models for crack progression in each category were established. The study culminated in the formulation of a grading criterion proposed to Solarge, aiming to refine their quality assurance.

The use of DC microgrids in combination with photovoltaic (PV) energy generation sources results in higher efficiencies by avoiding AC to DC conversion. Moreover, bipolar DC grids allow for more system flexibility and increased reliability at the cost of an additional conductor when compared to unipolar DC. However, maximum power point tracking (MPPT) converters are still required in order to optimize the power delivered to the microgrid by PV systems. The development of more efficient and cost-effective DC-DC MPPT converters will be proven vital considering the expected growth in solar PV installation as a consequence of the relentlessly increasing global energy demand.

The objective of this thesis is to design a DC-DC MPPT converter for bipolar DC microgrids based on gallium nitride (GaN) high-electron-mobility transistors (HEMTs). GaN transistors are wide-bandgap semiconductor devices that can operate at very high switching frequencies due to their superior electron mobility compared to other semiconductor materials used in electronic switching. Increasing the operational frequency of an electronic converter allows for smaller passive components, which in turn has the potential to result in system size and cost reductions. A complete electrical and thermal analysis of the performance of these components is simulated and presented in this report, and the implications of employing these devices for the selected application are evaluated. The design overview of the DC-DC MPPT converter using these GaN HEMTs is also showcased in this work, as well as the results obtained from testing the assembled DC-DC MPPT converter for bipolar DC microgrids. The main conclusions of this work aim to clarify the advantages of GaN devices in MPPT applications, as well as demonstrate a design solution to the integration of MPPT converters to DC microgrids. The project was developed in collaboration with the company DC Opportunities, and the designed converter was assembled and tested in their laboratory.

The remarkable expansion of the PV industry can be attributed to cost reductions and technological advancements, resulting in solar energy becoming an appealing and sustainable option. However, there is a growing concern regarding the environmental impact of disposing decommissioned solar panels. To address this issue, Biosphere Solar, a startup based in Delft, is actively engaged in developing recyclable and repairable solar panels, embracing a circular and sustainable approach. Their ongoing research is centered on solar modules made without EVA lamination, with the goal of facilitating easier disassembly. A crucial aspect of achieving disassembly of solar cells involves exploring modular interconnections that allow for the disconnection of interconnections between solar cells.

Although modular interconnections are already employed in batteries, electrical switches, and communication systems, their potential application in connecting solar cells has not been extensively explored. This thesis explores various interconnection approaches aimed at facilitating modular interconnections within PV modules constructed using interdigitated-back-contact (IBC) solar cells, following the structure established by Biosphere Solar for PV modules. The objective is to allow for the replacement of damaged solar cells without adversely affecting neighboring functional cells. Four distinct concepts were investigated, each utilizing the dog-bone contact wire to connect IBC solar cells in series. These concepts include a desolderable interconnection using a single dog-bone wire soldered with SnBi (a low melting temperature solder alloy), desoldering between the contact regions of two dog-bones connected through the fusion of tin coatings at overlapping areas, interconnection mechanisms based on contact pressure within a polymer-based cell-bed, and a contact pressure interconnection mechanism based on magnetic force. Both contact pressure interconnection mechanisms involve two dog-bones to create a series connection between a pair of solar cells.

After evaluating the technical feasibility of the aforementioned concepts, prototypes were developed, each incorporating the specified approaches. Furthermore, two reference prototypes were fabricated to establish benchmarks for comparison. Both prototypes employ conventional interconnections with a single dog-bone and SnAgCu solder alloy. The difference lies in the module build-up: one follows the Biosphere Solar approach (without EVA), while the other adheres to the traditional module build-up (with EVA and lamination). For the sake of simplicity, the reference prototype constructed using the Biosphere Solar approach and utilizing the SnAgCu solder alloy is referred to as the ’SnAgCu’ prototype, while the one built using EVA lamination is referred to as the ’EVA’ prototype.

I-V measurements revealed that the prototypes with single dog-bone based interconnection soldered using the SnBi solder alloy and two dog-bones with molten joint connections achieved the highest efficiencies (21.51% and 21.17%, respectively) compared to the other prototypes based on concepts explored for creating modular interconnections. The improved cell-bed design, which has a screw-based mechanism, showed an increase in efficiency (20.68%) compared to the slider-based mechanism (18.46%). The prototype with magnetic force-based interconnections achieved an efficiency of 19.94%. The two reference prototypes had efficiencies of 21.58% (SnAgCu) and 21.98% (EVA).

All prototypes, except for the one utilizing the slider-based interconnection in the cell-bed, underwent thermal cycle tests. Toward the conclusion of the thermal cycle testing, the prototypes featuring desolderable interconnection mechanisms (a single dog-bone soldered using the SnBi solder alloy and two dog-bones with soldered contact regions) exhibited the highest efficiencies compared to the other prototypes developed to explore potential concepts for modular interconnections.

Photovoltaic (PV) modules have considerable difficulty when exposed to shading since even partial blockages can significantly reduce energy production. To make the PV module shade-resilience, sub-module maximum power point tracking(MPPT) can be done for each string in the module. One way of doing it is by using converters at the sub-module level, which can track the string's maximum power point(MPP) by varying its duty cycle. In conventional converter design, inductors are the bulkiest and costliest component used, which eventually makes the application of sub-module MPPT less cost-effective. However, a literature study found that solar cell generates self-impedance under biasing, which opens up the idea for cell-level integration of power electronics. This thesis aims to validate the possibility of using the self-inductance generated in the solar cell for partially designing the DC/DC converter on the solar cell such that MPPT can be performed at the sub-module level. To accomplish this objective, two distinct strategies have been examined: The utilization of solar cell self-inductance for designing a conventional boost converter on a solar cell surface and the integration of a planar coil onto a solar cell for partially designing a DC/DC boost converter.

Several promising photovoltaic (PV) concepts are supported by transistors. Along with the growth of PV capacity in the urban environment, issues related to partial shading highlight the interest in more shade-tolerant PV systems. An example of technologies improving a PV module’s energy yield under partial shading is the submodule power optimizer, including a power converter that operates sub-module maximum power point tracking (MPPT). Alternately, reconfigurable PV modules enable dynamic reconfiguration of the solar cells’ interconnections to optimize the energy yield depending on the irradiance distribution. Both technologies make use of transistors as fundamental components. Integrating the latter into the solar cell wafer might be a solution for cost reduction and reliability improvement and thus support such concepts. Moreover, that kind of transistor integration can have applications in solar cell-embedded electronic and digital devices.

In this thesis, a lateral metal-oxide-semiconductor field-effect transistor (MOSFET) and an interdigitated back-contacted (IBC) solar cell are integrated into the same crystalline silicon (c-Si) wafer. A combined process flow is developed to manufacture both components with a minimum number of additional steps compared to single-component manufacturing processes. One criterion for this is a high similarity in the design of the device. Therefore, a tunneling oxide passivated contact (TOPCon) solar cell structure is used, involving polycrystalline silicon (poly-Si) at the device’s backside. Similarly, the MOSFET’s gate is made of a highly doped poy-Si film. Ion implantation is used as a common doping process.

Both solar cells and transistors that were manufactured with the combined process flow are first characterized separately. The highest efficiencies obtained for n-type and p-type solar cells are 20.29% and 20.66%, respectively. This is achieved thanks to multiple combined passivation approaches including TOPCon, wet poly-Si etching, a front-side hydrogenated amorphous silicon (a-Si:H) film, and hydrogenated silicon nitride on both sides of the device. Different MOSFET layouts are explored to make the device able to handle relatively large currents. It is found that introducing several drain-source pairs in parallel is more efficient than increasing the channel width to reduce the on-resistance. The on-resistance is further minimized with a gate length reduction and wet chemical poly-Si etching. As expected, the comparison of PMOS and NMOS (MOSFETs built on n-type and p-type wafers, respectively) shows better on-performance for the latter. A minimum on-resistance value of 1 Ω is then obtained. However, a higher leakage current consistently seems to come along with reduced on-resistance; i.e., higher on-performance is coupled with lower off-performance. Finally, experiments are performed combining both components. Under illumination, the MOSFET exhibits lower off-performance due to the photovoltaic effect. However, this effect does not affect the on-performance of the component. The monolithically connected components exhibit I-V characteristics that depend on the applied MOSFET’s gate potential. In the on-mode, the solar cell maintains more than 95% of the conversion efficiency compared to the efficiency measured with the same solar cell without the transistor. However, a non-zero current is obtained in the off-mode, exhibiting low transistor blocking capability. Nevertheless, the large difference in characteristics obtained between the on- and off-modes proves the feasibility of integrating a solar cell and a transistor on the same substrate with a minimum number of additional processing
steps.

The aim of this thesis project is to investigate how different PV-deployment strategies can help reinforce energy security and reduce GHG emissions in Ukraine. The author addresses several sub-questions related to energy security, the current status of Ukraine's electricity and heat sector, and the potentials and yields of renewable energy sources in Ukraine. To answer this question, the author uses literature review and simulations using optimization software. Three different deployment strategies are considered: utility-scale PV systems, distributed PV systems, and a combination of both. The simulations are based on hourly data for solar irradiance, temperature, wind speed, and load demand for 2018 in Ukraine. The results are evaluated based on several key performance indicators (KPIs) linked to energy security such as import dependency, diversity, as well as GHG emissions reduction potential.

The author finds that a combination of utility-scale and distributed PV systems can provide the most effective solution for reinforcing energy security while also reducing GHG emissions in Ukraine. The simulations also show that improvements in grid infrastructure is crucial for achieving these results.
Overall, the author concludes that deploying both utility-scale and distributed PV systems can provide a cost-effective way to reinforce energy security while also reducing GHG emissions in Ukraine.

The considerable increase in the number of devices needing connectivity, such as mobile phones and Internet of Things (IoT) devices, has led to an exponential rise in data volumes during the last years, that will surely continue over the next decade. Therefore, it will be increasingly challenging to provide sufficient RF resources. A novel alternative to RF communications is Visible Light Communication (VLC). VLC is a communication technology that uses visible light as an information carrier. The use of VLC for indoor applications has been rapidly growing during the last years – Light Fidelity (LiFi) technology is an example of VLC application – with photodiodes being the most widely used receiving devices. However, looking at both indoor and outdoor communication, photovoltaic (PV) cells represent a relevant alternative for detecting the information. One of the advantages of using a PV cell as receiver is the huge sensitive area for detection of the information that simplifies alignment between transmitter and receiver.

Different light sources can be used in VLC. Typically, either LEDs or LASERs are considered, depending on the characteristics of the link (such as distance, type of receiver, indoor/outdoor application). These light sources differ in terms of spectrum, directionality, optical power density and bandwidth. The performance of the whole VLC link strongly depends on the characteristics of the light source, since it affects the ability of the receiver, such as a PV-device, to detect the information when it overlaps with the ambient light, that can reach very high values, especially in outdoor applications where the ambient light is the sunlight. Therefore, the modelling and analysis of the performance of different light sources in a PV-based VLC link will pave the way towards the realisation of a PV-based communication system of the future; and it is the focus of this thesis project.

The project goals were achieved by first reviewing the characteristics of light sources, to understand their advantages and drawbacks in (PV-based) VLC. This was followed by the development of models of the VLC data-link, with a focus on the light source, which took into account various factors such as the type of light source, its location relative to the receiver, and its dynamic behaviour. This was followed by the realisation of a test setup, to characterise different light sources, and the models were then used to simulate the light distribution from the actual light sources. Finally, the framework was used to simulate a LED-based solar simulator and an outdoor VLC data-link.

Kelp Blue is a company whose top priority is the well-being of the planet. Through the cultivation of giant kelp on offshore farms, they create several sustainable products, new job opportunities in regions where they are needed, enhance biodiversity in the water, and above all, sequester tons of CO2 from the air. The start-up is still in its research and development phase, but plans to be building farms on a large scale in just a few years. Despite their knowledge in engineering, the company still needs consulting on certain elements. Therefore the company invited a group of students from the Delft University of Technology to Lüderitz, Namibia for a consultancy project. The project involved creating a procedure for the company to scale up in a sustainable manner. The students decided that this complex problem should be divided into sub-problems. One workstream focused on reducing the carbon emissions during upscaling, while the other workstream focused on analyzing and improving the company’s current design and installation of the farms. Following, both parts of the project are shortly summarized: Part I: Improving the company’s current design Kelp Blue is currently in the pilot phase, in which they’re installing their first large giant kelp farms. Before, they were focusing on the complete installation, including planting the kelp on the submerged netting structure, and the review of this. For the company’s commercial phase, where they want to be able to place farms daily on a large scale, designs were still developed and analyzed. For the commercial phase, this workstream made a new design and installation method. It required an installation where buoys would need to be submerged, the structure locked in place at the desired depth, without the use of scuba divers or remote operated vehicles. Despite the fact that these requirements were challenging, an outstanding result was achieved. The main problem was divided into subproblems, and for each of those a suitable solution was created. Hopes are that the company will consider the given advice as helpful and maybe implement some parts of (or the whole) new design. Part II: Reducing carbon emissions during upscaling First, interviews and desk research were conducted to get a good idea of the challenge of sustainability. This included reading reports, speaking with employees, policy makers and experts with experience within the area. With this information, the challenge could be mapped out and the solution space became clear in terms of legislation and technical possibilities. Climate information was also requested that could later be used to run simulations. During the determination of the possible solutions, research was done on the realistic possibilities, where eventually the use of either solar or wind energy was most appropriate. After conducting a multi-criteria analysis that was put together with the management of Kelp Blue, investing in a solar plant proved to be the most appropriate solution.

Energy consumption keeps increasing, and more than three-quarters of the EU’s green-house gas emissions stem from it. Hence, it is important to reduce or stop burning fossil fuels to limit the temperature rise to 1.5∘C according to the Paris agreement target. Nowadays, renewable energy sources and distributed generation are increasingly integrated into the electric power system to achieve the ambitious target of the energy transition. Renewable energy sources are inherently fluctuating in their power. Whereas the grid is stable. The interface between these two can be made smooth based on a medium-frequency DC-DC converter. The advantages of increasing frequency are high power density, significant weight and size reduction, dynamic power flow control, and power quality management. All these are possible mainly because of advancements in power electronics in the recent decade. However, these power electronics induce harmonics across insulations, which are fast rising voltages and are repetitive. The dielectric strength of insulations under these fast-rising pulses is to be understood. This thesis project studied oil impregnated paper behavior under pulsed stresses.

To test the Oil Impregnated Paper samples, a source capable of generating repeating pulses with fast rising and lower overshoots is required. This source comprises an AC- DC converter that will power the H-bridge. The pulses from the H-bridge are then fed into a 1:50 pulse transformer to step up the voltage, which is then delivered across OIP (Oil Impregnated Papers) through test components that regulate the pulse’s rising time and overshoot. The process began with identifying critical factors to consider while developing a pulse generator. Following that, a random transformer prototype is created along with another transformer to extract the parameters, which are then modeled in the circuit simulator and COMSOL to predict the pulse. An algorithm was created to optimize the transformer design. Finally, this design method creates a pulse transformer that generates the necessary output.

The OIP samples are then tested at frequency 50𝑘𝐻𝑧 and at various voltages with a rise time 𝑇𝑟 ≈ 1.3𝜇 𝑠. A lifetime curve was obtained using the data of ageing tests at five field strengths. The results showed that the lifetime was reduced with the increase in frequency. At lower fields, a transition was seen, indicating a shift in the ageing process.

An efficient, compact, and lightweight three-phase AC-DC power factor correction (PFC) converter becomes a necessity for the On-board chargers (OBCs) of the electric vehicle (EV) in conventional grid-to-vehicle (G2V) and vehicle-to-grid (V2G) charging scenarios. The commercially available OBCs have very limited power density despite the moderate efficiency under specific power levels.
In this dissertation, the integrated triangular current mode (iTCM) control is implemented to improve the power density (kW/L) and specific power (kW/kg) of the three-phase PFC converter (the front stage of OBCs) while maintaining high efficiency. Zero voltage switching (ZVS) turn-on is realized in the iTCM control with a higher switching frequency to reduce the LCL filter size without sacrificing the efficiency.
By adding an LC branch between the bridge leg and the mid-point of the DC link, the high-frequency and low-frequency current is split to minimize the inductor loss and to achieve a better inductor design. Analytical modeling and simulation in PLECS are firstly conducted to verify the idea of iTCM. Besides, the capacitor-current feedback achaotive damping method is implemented to prevent instability from the LC and LCL filters. Finally, the designed 11 kW three-phase AC-DC PFC converter, including the input LCL filter, achieves an efficiency of 98.61%, a power density of 6.5 kW/L and a specific power per weight of 0.72 kW/kg.
The proposed three-phase iTCM control is validated in a 3 kW SiC MOSFET-based AC-DC converter. The current and voltage waveform of iTCM, TCM and CCM is verified in the hardware platform with (DSP)-TMS320F28379D. The efficiency of the iTCM control achieves 96.38%, which improves by around 1% compared to CCM at the same power density level.

To tackle the effect of climate change while meeting the ever-growing demand of energy, a high scale of integration of renewable energy resources has been performed in the past decade. Solar Photovoltaics have played a monumental role in this process, thus contributing in the fulfillment of the energy demand. The scalability and the flexibility of use has led to a significant development in the technologies implemented for assimilation of Solar PV. In addition, the development in power electronics has made the process of integration seamless. Due to Solar PV's dependency on irradiation there is an ever growing need for establishment of an improved control on power converters.
The aim of this thesis is to implement Maximum Power Point Tracking and Droop control algorithms on PV powered DC-DC Converters while considering the dynamics of Solar PV. Mathematical modelling is used to model the PV generator to consider its dynamics along with the dynamics of the converters to establish control. The output of these converters is connected to a DC Microgrid. After completion of the modelling process, the internal control design was performed followed by the implementation of both the algorithms. The project was performed at the lab of the company DC-Opportunities.
The findings of this research are presented in the current document. Its goal is to outline the procedure taken from the start of the project and the literature review all the way through the design and testing of the power electronic converters. Finally, suggestions for the future are offered, which might serve as a roadmap for more advancements.

As PV capacity in urban areas keeps increasing, non-uniform illumination of panels will become more prevalent. This could cause the partial shading to become more frequent, reducing PV system performance. Some ways to solve this problem is by the use of module-level maximum power point tracking (MPPT), micro inverters, or reconfigurable modules. To this end, the integration of metal-oxidesemiconductor field-effect transistor (MOSFET) on solar cells could play an important role in future methods to prevent this issue. This integration of a MOSFET allows for module level, and potentially sub-module level, MPPT, as well as the application of reconfigurable modules to circumvent this issue. This thesis aims to optimize the MOSFET dimensions and fabrication process to be able to handle the short circuit current and open circuit voltage of a PV module, and to analyze the optoelectrical effects under direct illumination of the MOSFET performance. In this thesis report, a flowchart is proposed on how to fabricate a working power MOSFET while combining the fabrication techniques used in the Integrated Circuits and Photovoltaics industries. This process closely resembles the fabrication of solar cells and uses similar techniques used to fabricate interdigitated back contacted (IBC) solar cells. It is shown that It is shown that the use of wider devices can reduce channel resistance from 167Ω for a PMOS device with a width of 500𝜇m down to 20Ω for a device with a width of 5000𝜇m. For NMOS devices a similar relationship can be seen where the channel resistance is 49Ω for a width of 500𝜇m and 8.1Ω for a device width of 5000𝜇m. The current density of the devices drop from 115𝜇𝐴/𝜇𝑚 for an NMOS device with a width of 500𝜇m to less than 80𝜇𝐴/𝜇𝑚 for a 5000𝜇m wide device. For PMOS this density drop is smaller where the drop is from 33𝜇𝐴/𝜇𝑚 to 27𝜇𝐴/𝜇𝑚. A study on the effects of implantation energy and scattering layer thicknesses showed that both lower energies and thicker layers yield higher drain currents and lower channel resistance. A possible explanation for this is that a shift in the threshold voltage increased the overdrive voltage and therefore the drain current. In the investigation of the effects of direct illumination on the electrical characteristics of the device it was found that the threshold voltage increases for PMOS devices from -0.21V under no illumination to -0.06V under full spectrum illumination at 1000𝑊/𝑚2 and decreases for NMOS devices from 0.06V under no illumination to -0.15V under full spectrum illumination at 1000𝑊/𝑚2. Furthermore the off state gate leakage current increases by factor 33 under illumination at 1000𝑊/𝑚2 for NMOS devices and by a factor of 107 for PMOS devices. The electron mobility of the NMOS transistor increases with incident light, improving the drain current gate voltage relationship. The channel resistance for the NMOS devices improved between 5-13%, depending on the intensity of the illumination, while the channel resistance of the PMOS increases up to 2%.A similar effect for the hole mobility of the PMOS was not observed. Similarly, the channel resistance of the NMOS transistor improved, possibly due to the shift in threshold voltage or improved electron mobility. This improvement in performance was not recognized for PMOS transistors, however. A flowchart has been proposed for a process in which a MOSFET is fabricated on the backside of an Interdigitated Back Contacted (IBC) solar cell while combining as many steps as possible from their respective flowcharts to reduce complexity and costs, possibly leading the best balance between MOSFET and IBC fabrication.As PV capacity in urban areas keeps increasing, non-uniform illumination of panels will become more prevalent. This could cause the partial shading to become more frequent, reducing PV system performance. Some ways to solve this problem is by the use of module-level maximum power point tracking (MPPT), micro inverters, or reconfigurable modules. To this end, the integration of metal-oxidesemiconductor field-effect transistor (MOSFET) on solar cells could play an important role in future methods to prevent this issue. This integration of a MOSFET allows for module level, and potentially sub-module level, MPPT, as well as the application of reconfigurable modules to circumvent this issue. This thesis aims to optimize the MOSFET dimensions and fabrication process to be able to handle the short circuit current and open circuit voltage of a PV module, and to analyze the optoelectrical effects under direct illumination of the MOSFET performance. In this thesis report, a flowchart is proposed on how to fabricate a working power MOSFET while combining the fabrication techniques used in the Integrated Circuits and Photovoltaics industries. This process closely resembles the fabrication of solar cells and uses similar techniques used to fabricate interdigitated back contacted (IBC) solar cells. It is shown that It is shown that the use of wider devices can reduce channel resistance from 167Ω for a PMOS device with a width of 500𝜇m down to 20Ω for a device with a width of 5000𝜇m. For NMOS devices a similar relationship can be seen where the channel resistance is 49Ω for a width of 500𝜇m and 8.1Ω for a device width of 5000𝜇m. The current density of the devices drop from 115𝜇𝐴/𝜇𝑚 for an NMOS device with a width of 500𝜇m to less than 80𝜇𝐴/𝜇𝑚 for a 5000𝜇m wide device. For PMOS this density drop is smaller where the drop is from 33𝜇𝐴/𝜇𝑚 to 27𝜇𝐴/𝜇𝑚. A study on the effects of implantation energy and scattering layer thicknesses showed that both lower energies and thicker layers yield higher drain currents and lower channel resistance. A possible explanation for this is that a shift in the threshold voltage increased the overdrive voltage and therefore the drain current. In the investigation of the effects of direct illumination on the electrical characteristics of the device it was found that the threshold voltage increases for PMOS devices from -0.21V under no illumination to -0.06V under full spectrum illumination at 1000𝑊/𝑚2 and decreases for NMOS devices from 0.06V under no illumination to -0.15V under full spectrum illumination at 1000𝑊/𝑚2. Furthermore the off state gate leakage current increases by factor 33 under illumination at 1000𝑊/𝑚2 for NMOS devices and by a factor of 107 for PMOS devices. The electron mobility of the NMOS transistor increases with incident light, improving the drain current gate voltage relationship. The channel resistance for the NMOS devices improved between 5-13%, depending on the intensity of the illumination, while the channel resistance of the PMOS increases up to 2%.A similar effect for the hole mobility of the PMOS was not observed. Similarly, the channel resistance of the NMOS transistor improved, possibly due to the shift in threshold voltage or improved electron mobility. This improvement in performance was not recognized for PMOS transistors, however. A flowchart has been proposed for a process in which a MOSFET is fabricated on the backside of an Interdigitated Back Contacted (IBC) solar cell while combining as many steps as possible from their respective flowcharts to reduce complexity and costs, possibly leading the best balance between MOSFET and IBC fabrication. As PV capacity in urban areaskeeps increasing, non-uniform illumination of panels will become more prevalent.This could cause the partial shading to become more frequent, reducing PVsystem performance. Some ways to solve this problem is by the use ofmodule-level maximum power point tracking (MPPT), micro inverters, orreconfigurable modules. To this end, the integration ofmetal-oxidesemiconductor field-effect transistor (MOSFET) on solar cells couldplay an important role in future methods to prevent this issue. Thisintegration of a MOSFET allows for module level, and potentially sub-modulelevel, MPPT, as well as the application of reconfigurable modules to circumventthis issue. This thesis aims to optimize the MOSFET dimensions and fabricationprocess to be able to handle the short circuit current and open circuit voltageof a PV module, and to analyze the optoelectrical effects under directillumination of the MOSFET performance. In this thesis report, a flowchart isproposed on how to fabricate a working power MOSFET while combining thefabrication techniques used in the Integrated Circuits and Photovoltaicsindustries. This process closely resembles the fabrication of solar cells anduses similar techniques used to fabricate interdigitated back contacted (IBC)solar cells. It is shown that It is shown that the use of wider devices canreduce channel resistance from 167Ω for a PMOS device with a width of 500𝜇m down to 20Ω for a devicewith a width of 5000𝜇m.For NMOS devices a similar relationship can be seen where the channelresistance is 49Ω for a width of 500𝜇mand 8.1Ω for a device width of 5000𝜇m.The current density of the devices drop from 115𝜇𝐴/𝜇𝑚 for an NMOSdevice with a width of 500𝜇mto less than 80𝜇𝐴/𝜇𝑚 for a 5000𝜇m wide device. For PMOSthis density drop is smaller where the drop is from 33𝜇𝐴/𝜇𝑚 to 27𝜇𝐴/𝜇𝑚. A study on theeffects of implantation energy and scattering layer thicknesses showed thatboth lower energies and thicker layers yield higher drain currents and lowerchannel resistance. A possible explanation for this is that a shift in thethreshold voltage increased the overdrive voltage and therefore the draincurrent. In the investigation of the effects of direct illumination on theelectrical characteristics of the device it was found that the thresholdvoltage increases for PMOS devices from -0.21V under no illumination to -0.06Vunder full spectrum illumination at 1000𝑊/𝑚2 and decreases for NMOSdevices from 0.06V under no illumination to -0.15V under full spectrumillumination at 1000𝑊/𝑚2. Furthermore the off stategate leakage current increases by factor 33 under illumination at 1000𝑊/𝑚2 for NMOS devices and bya factor of 107 for PMOS devices. The electron mobility of the NMOS transistorincreases with incident light, improving the drain current gate voltagerelationship. The channel resistance for the NMOS devices improved between5-13%, depending on the intensity of the illumination, while the channelresistance of the PMOS increases up to 2%.A similar effect for the hole mobilityof the PMOS was not observed. Similarly, the channel resistance of the NMOStransistor improved, possibly due to the shift in threshold voltage or improvedelectron mobility. This improvement in performance was not recognized for PMOStransistors, however. A flowchart has been proposed for a process in which aMOSFET is fabricated on the backside of an Interdigitated Back Contacted (IBC)solar cell while combining as many steps as possible from their respectiveflowcharts to reduce complexity and costs, possibly leading the best balancebetween MOSFET and IBC fabrication.    

With the integration of solar panels in urban areas, where shading is a common issue, it is desired to realize more shade-resilient designs. A DC-DC boost converter is an electronic device that can be used for maximum power point tracking (MPPT). When implementing MPPT at sub-module level, the shade resilience of the module can be increased. This thesis aims to investigate the feasibility of implementing planar inductors into c-Si solar cells using the numerical simulation software COMSOL Multiphysics®. Through simulations, the inductance and resistance values for various planar coil geometries were obtained. Subsequently, the feasibility of using these coils in a sub-module DC-DC boost converter was investigated. For this study, a specific case was assumed where a Gen 2 Cell - 160 mm c-Si cell is used with a DC-DC boost converter with a duty cycle of 0.5 and a current ripple of 20%. Given the parameters from these devices, the minimum required inductance of 1.20 μH for a frequency of 200 kHz and 2.40 μH for a frequency of 100 kHz were obtained. The series resistances that can be added to the solar cell while still maintaining high efficiency, range from 1.0 mΩ to 4.8 mΩ, for a 1% to a 5% power loss, respectively. This is all for single-cell power conversion. Two different approaches have been examined; the screen-printed coil(s) approach and the screen printing thickness exceeding coil(s) approach. The former studies coils that do not exceed the maximum thickness achievable with screen printing. As such, these coils could be simpler to implement into a solar cell production line than coils with a higher thickness. In this research, for thicknesses below 300 μm a best-case scenario is studied where the skin effect is neglected. The latter studies a larger range of thicknesses, not taking any specific production method into account, but the skin and proximity effect is taken into account. The screen-printed approach is limited to a thickness range of 10 μm to 200 μm, thus simulated by the 2D model. For the air-core single-cell inductors for DC-DC boost converter applications, the inductance and resistance values were either below the 1.20 μH threshold or above the 4.8 mΩ threshold, respectively. These thresholds change depending on the number of series-connected cells. The inductance of a planar inductor can be boosted up to 200% when adding a magnetic material in a sandwich structure, however, this will also increase the costs of the application. In a boosted-inductance case, the 3-turn coil with a thickness of 200 μm, and a 5% power loss is the only configuration that is feasible for a 200 kHz DC-DC boost converter application, with an inductance of 1.569 μH and a resistance of 3.45 mΩ. By increasing the number of coils per cell, the power dissipation in the coils can be reduced. Using this approach, six feasible topologies can be created. One of those is the nine parallel-connected 8-turn coils with a thickness of 200 μm, reaching an inductance of 1.210 μH and a resistance of 3.186 mΩ, allowing for a 200 kHz DC-DC boost converter application without any magnetic inductance increase. All six options are feasible for integration on a single cell using screen printing, however, the actual resistances will be higher due to the skin and proximity effect, and single-cell integration will be too expensive for industrial applications. When studying thicknesses above the screen printing limit, only the 4-turn coil with a thickness of 300 μm, a magnetically increased inductance of 2.718 μH, and a resistance of 4.01 mΩ, is feasible for the 100 and 200 kHz frequencies. This case however does neglect the skin effect. For the 3D model and thicknesses above 400 μm, the skin effect significantly impacts the resistance. When series connecting multiple cells to a single coil, the only feasible option is the eight-cell connected 8-turn coil for a thickness of 200 μm and 300 μm, both reaching a magnetically increased inductance of 10.431 μH and resistance of 23.33 mΩ and 15.56 mΩ, respectively.