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O. Isabella

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As crystalline silicon (c-Si) solar cells approach their theoretical efficiency limit, the perovskite/silicon (PerSi) tandem technology offers a promising solution for further improving the efficiency of photovoltaic (PV) modules. However, as perovskite cells are facing stability issues, it is unclear whether PerSi modules will have a larger lifetime energy yield (LEY) than c-Si modules. In this work, we present a novel methodology to simulate the LEY of PerSi tandem devices, accounting for environmental stress factor-dependent degradation across four different climates. Our approach combines a physics-based analytical degradation model for components shared with c-Si modules and a scenario-based degradation model for the perovskite top cell. This method enables us to identify the tolerable degradation rate (ktol) of the perovskite cell under different scenarios and climatic conditions. We find that ktol is lowest when degradation occurs in the short-circuit current, reaching a minimum value of 1.2% per year in Delft (the Netherlands). Additionally, we demonstrate that ktol inversely depends on the module lifetime, reaching values up 7.6% per year in Lagos (Nigeria). Moreover, we show that module efficiency (ηmod) significantly impacts ktol. For instance, increasing ηmod from 28.0% to 32.9% raises ktol by approximately 50%. Additionally, we propose a simplified model that can predict ktol without the computationally intensive simulations, which has a root-mean-square error of 0.34% per year. Lastly, environmental impact assessments reveal that PerSi modules are more sustainable in all impact categories when the degradation rate is 80% of ktol for LEY. ...

Multispectral, penumbra-aware irradiance modeling for agrivoltaic orchards

Light-simulation tools—exemplified by Radiance—are widely used for quantitative daylight studies and are increasingly adopted in agrivoltaics (agri-PV) to handle complex geometry via ray tracing. Yet, beyond typical workflows three practical limitations persist: spectrally resolved skies are restricted to the visible band; soft-shadow (penumbra) rendering relies on runtime-intensive solar-disk sampling; and fast, integrated canopy models remain scarce. We present a Radiance-compatible Python framework that adds: (i) atmosphere-specific sun–sky generation across the solar spectrum; (ii) efficient, equal-area sampling of the solar disk; and (iii) a simple canopy reconstruction tailored to narrow-trained orchards. To improve spectral fidelity, resolution, and range, we couple SMARTS-derived spectra to a Perez-based sky, leveraging Radiance's multispectral rendering. We deterministically sample the sun's finite extent using a Fibonacci lattice, yielding stable penumbra without prohibitive runtimes. The canopy model parameterizes porosity and seasonal development at a daily rate. Canopy representation matters: opaque–static models, common in agri-PV simulations, systematically underestimate light levels and miss spatiotemporal patterns needed to diagnose suboptimal conditions. Comparatively, a porous–dynamic model led to ≈26% higher seasonal light levels, with gains attaining ≈100% early in the season and converging to ≈16% after foliage matured. While penumbra is limited under conventional PV modules, penumbra-capable renderings enable exploration of design pathways—narrower cell layouts (half-cell and beyond) with greater module–canopy separation—that smooth lighting extremes. ...
Perovskite/silicon (PS) technology includes three main configurations: two-terminal (2T), three-terminal (3T), and four-terminal (4T). Previous studies have made various comparisons between these configurations, significantly advancing our understanding of these devices. While these studies mostly focus on simulations on cell level, we perform bandgap energy ((Formula presented.)) optimization at the module level for different configurations under outdoor conditions. Using opto-electrical simulations, we predict the energy yield of each module at four geographical locations, with varying values of (Formula presented.). The optimal (Formula presented.) for the 2T, 3T, and 4T modules are 1.62, 1.80, and 1.82 eV, respectively. We also perform a loss analysis to explore the differences in power losses among the configurations. These loss differences can be attributed to the configurations having different optimal (Formula presented.) values (affecting the thermalization losses) or different module designs (affecting the interconnection losses). Among all losses, mismatch losses play the most critical role in optimizing the bandgap. Overall, all optimized configurations have similar energy yields (all differences within 1.5%) across all locations. Finally, we compare the robustness of the different configurations against different scenarios of perovskite degradation. Our results show that the 4T module is the least sensitive to degradation in the perovskite subcell. ...
Journal article (2026) - Yifeng Zhao, Esma Ugur, Arsalan Razzaq, Thomas G. Allen, Paul Procel Moya, Katarina Kovačević, Yi Zheng, Luana Mazzarella, Olindo Isabella, More Authors
The monolithic integration of perovskite top cells on textured crystalline silicon affords efficient tandem devices with strong prospects for large-scale applications. Such integration has primarily relied on state-of-the-art recombination junctions, which typically comprise transparent conductive oxides and molecular self-assembled monolayer (SAM) contacts. However, the potential influence of bottom cell nanoroughness, which may vary based on specific processing routes and technologies, has received far less attention. Here, we systematically engineered the top surface nanoroughness of silicon heterojunction solar cells to examine its impact on monolithic perovskite–silicon tandem solar cells. We employed two approaches: (i) varying the thickness of (n)-type hydrogenated nanocrystalline silicon ((n)nc-Si:H) layers or (ii) applying a plasma treatment using a hydrogen and carbon dioxide gas mixture before the deposition of (n)nc-Si:H layers. Both methods enhanced the conductivity and crystallinity of (n)nc-Si:H layers and increased the surface nanoroughness, with plasma treatment enabling the efficient realization of distinct nanoroughness in thin (n)nc-Si:H (15-nm-thick) layers. Our results reveal that the surface nanoroughness imposed by (n)nc-Si:H layers influences the SAM anchoring, leading to increased work function shifts and improved SAM/perovskite interface quality, thereby impacting the overall tandem device performance. Notably, tandem devices incorporating higher-nanoroughness bottom cells achieved increased fill factors, dominating the observed tandem efficiency enhancements, with a peak efficiency of 32.6% enabled by a 30-second-long plasma treatment. ...

Physics-based modelling, sensitivity-driven quantification, surrogate-model prediction, and design-guided mitigation strategies

Journal article (2026) - Sathya Shanka Vasuki, Jack Levell, Teddy Simanjuntak, Rudi Santbergen, Olindo Isabella
Offshore floating photovoltaics (OFPVs) emerge as a promising solution to overcome land constraints associated with inland renewable energy deployment. However, as OFPVs are still a developing technology, several performance-related uncertainties persist. The reduction in energy yield caused by wave-induced losses (WIL) is one such critical uncertainty that needs to be understood, quantified and minimised. To address this need, this work introduces a physics-based modelling framework that couples validated hydrodynamic simulations with opto-electrical analysis to accurately estimate WIL. An extensive sensitivity analysis is then carried out, performing over 100 simulations by systematically varying both design and environmental parameters. The results show that WIL ranges between 1%–30% on an hourly basis and exhibits a nonlinear dependence on both parameter groups. The resulting dataset is then used to develop S [Figure presented] IFT 1.0 - a surrogate model capable of predicting WIL across a wide range of design and operating conditions, achieving an average absolute RMSE of 3% relative to the physics-based model. The insights from S [Figure presented] IFT 1.0 are finally used to provide practical measures that minimise WIL at a system design level. Overall, this work provides a complete pathway to model, quantify, predict, and minimise WIL, promoting confident and scalable OFPV deployment. ...
Photovoltaic (PV) system performance is linked to climatic conditions in which the system operates. This leads to the Köppen-Geiger-Photovoltaic (KGPV) climate classification. KGPV is created by overlaying four irradiation levels with the commonly used Köppen-Geiger climate zones. Potential drawbacks of this approach are that the climate features are not considered in a combined manner in the sorting process and that the KGPV zones inherent a dependence on precipitation. We propose a machine-learning approach to address this deficiencies and improve PV climate classification. First, supervised learning is used to evaluate the correlation between climate features and a PV system's specific energy yield. We find that the inclusion of the darkest and brightest irradiation months as well as UV irradiation improves accuracy, while wind speed, relative humidity, precipitation and annual mean daily temperature difference have little impact on accuracy. Subsequently, k-means clustering combined with comprehensive qualitative analysis, identifies a PV classification based on seven climate features and 21 clusters. A mountainous climate characterized by moderate to low temperature and high irradiation is uncovered compared to KGPV. Moreover, this new PV climate classification reduces the sum of squared errors by 58 % compared to KGPV clearly signifying a more accurate PV climate classification approach. ...
The degradation of perovskite solar cells due to reverse bias (RB) is one of the remaining challenges hindering the commercialization of the technology. To overcome this challenge, a thorough understanding of and control over the breakdown (BD) voltage are crucial. A prerequisite for this is that the community “speaks the same language,” that is, that the reported BD voltages are comparable. A review of literature data shows that the impact of measurement parameters is often unknown and seems to depend strongly on sample properties. It follows that standardization is the only way to reach comparability. Here, a set of measurement parameters to fill this gap is proposed. Additionally, various definitions of a “BD voltage” are used in parallel without any way of relating them to each other; this metric and its determination need to be considered as well. After a thorough discussion of the available definitions, the use of the point of maximum curvature is introduced. Its main advantage is the possible connection to an analytical description of the BD mechanism. In this way, a starting point for scientists new to the field of RB stability is provided, and the ground for a broader discussion in the community is prepared. ...
Silicon is a promising alternative to the conventional graphite anodes due to its high theoretical capacity and favorable lithiation potential for lithium-ion batteries (LIBs) with liquid as well as solid-state electrolytes. However, lithiation-induced extreme volume change causes severe mechanochemical deformation and continuous formation of solid-electrolyte interphase leads to cell failure. One of the strategies to mitigate this problem is alloying silicon with a suitable element that can alter the surface electrochemistry and/or lithiation pathways, and acts as mechanical buffer. Nonetheless, these benefits come with a compromise on the specific capacity, which strongly influences the mass loading of the electrodes, highlighting the need to deconvolute the intertwined influence of composition and mass loading when designing high performance electrodes. In this work, we systematically studied the influence of composition and mass loading in monolithic amorphous silicon and non-stoichiometric silicon nitride (SiNx) electrodes on their electrochemical performance as LIB anodes. The incorporation of nitrogen in the electrode matrix clearly improves the electrochemical stability at the expense of reduced specific capacity, while higher mass loading accelerates capacity fading, most critically in amorphous silicon electrodes. Postmortem analysis reveals that such capacity fading in the electrodes with higher mass loading can be related to delamination due to evolved tensile stress during the charge–discharge cycle. Yet, nitrogen-rich SiNx monolithic electrodes accommodate strain more effectively. These findings demonstrate that while pristine Si delivers high specific capacity and long-term stability in thin films, thicker (>1 µm) monolithic electrodes benefit from higher nitrogen content in SiNx, which provides more stable cycling and sustained capacity. ...
Advanced and emerging photovoltaic (PV) technologies play a crucial role in meeting the increasing global energy demand sustainably. Simulations are essential for predicting system behavior and improving our understanding of complex PV architectures. This work extends an existing modeling framework designed for novel PV systems, offering a modular and flexible workflow suitable for diverse research applications. The framework computes PV performance from first-principles physics, removing the need for module datasheets. It comprises two pre-processing steps and six simulation steps. The first steps determine the optical behavior of the modules, followed by irradiance modeling and temperature calculations. The final steps evaluate the electrical characteristics and the conversion to alternating current at the full-system level. The framework incorporates detailed energy loss analysis and includes advanced features such as partial shading, reverse-bias effects, and photon recycling. Two applications demonstrate its capabilities: comparing module configurations in urban settings and optimizing multi-junction PV system design. Results show that Smart modules enhance shade resilience, delivering approximately (Formula presented.) higher energy yields. Additionally, the optimal perovskite bandgap for perovskite/silicon tandem devices is found to be 1.60–1.62 eV. These outcomes highlight the framework's value for future PV system research and development. The developed software can be found at: https://github.com/YBlom1999/PVMD_Toolbox. ...
Journal article (2026) - Afshin Nazer, Olindo Isabella, Hani Vahedi, Patrizio Manganiello
This article introduces a parallel differential power processing (PDPP) architecture for photovoltaic (PV)/battery applications. The PV to Virtual Bus (PV2VB) architecture enables the integration of a battery and manages its power while performing maximum power point tracking on the PV strings. In the proposed PV2VB PDPP architecture, the battery is positioned at the virtual bus, acting as the input for all string-level converters (SLCs). By selecting a lower voltage for the battery at the virtual bus compared to the PV string or the main bus voltages, component voltage ratings can be reduced. The architecture employs dual active bridge converters connected to bridgeless (BL) converters as SLCs to generate both positive and negative output voltages while providing isolation. These SLCs track the maximum power point of each PV string, while the central converter manages battery charging and discharging. Experimental results confirm the performance and effectiveness of the proposed PV2VB PDPP architecture, achieving efficiencies between 95.5% and 99%. ...
Journal article (2026) - U. Bothra, S.H.G. Weemaes, T.M. Rijsman, Alberto Poli, Siemen Brinksma, O. Isabella
The current industrial standard photovoltaic (PV) modules are dominated by crystalline-silicon (c-Si) PV technology, which cannot be easily recycled. This has generated worldwide concerns regarding the scarcity of critical raw materials and large waste streams of PV modules in the coming years. To overcome this problem, a lot of ongoing research focuses on upscaling the recycling process of present c-Si module designs by chemical, thermal and mechanical processes. Alternative research focuses on the development of new PV modules with enhanced circularity by design. In this work, we propose a new circular PV module design based on liquid-encapsulation technology in which silicon solar cells are encapsulated with a suitable liquid and an edge sealant instead of a polymer sheet. Our optical studies show that the selected liquids exhibit similar optical performance to ethylene vinyl acetate (EVA) due to their comparable refractive indices. We fabricate one-cell prototypes and observe comparable efficiency of liquid-encapsulated and EVA-encapsulated modules, signifying recyclable module design without an additional efficiency loss. To validate the module performance, we also simulate the optical performance of modules with different encapsulation materials. Furthermore, the new modules retained more than 95% of their efficiency after inducing accelerated ageing through damp heat, thermal cycling and humidity freeze tests, indicating the liquids as an excellent encapsulant material for PV. In the end, we disassemble the liquid-filled PV module and show the recovered components, which can directly be reused in new products. Therefore, this modular design bypasses the recycling process. Even more promising, the liquid encapsulation can improve the stability of perovskite/c-Si tandem solar cells due to the moisture barrier, which will be studied in the future. Adding further possibilities, in principle, with additional engineering, the liquid encapsulation could be used in a heat loop to turn the PV module into a photovoltaic-thermal (PV-T) module, thereby boosting the efficiency potential beyond that of traditional PV concept. ...
Photovoltaic (PV) to virtual bus parallel differential power processing (PDPP) architecture can mitigate mismatch losses among PV strings. This article presents a comprehensive dynamic analysis by deriving a small-signal model of the PDPP architecture based on its state space model. Subsequently, the corresponding transfer functions and frequency response are obtained, offering valuable insights into the dynamic behavior of the architecture. To validate the accuracy of the derived model, the frequency response has also been achieved by observed data from both PLECS simulation and experiment through system identification. Besides, this article discusses the design considerations of the discrete controllers' parameters for both virtual and intermediate bus voltages and studies the stability of the architecture. Experimental measurements confirm the ability of the central controller to stabilize the virtual bus voltage to the desired level within 0.6 seconds, while the intermediate bus voltages settle within 15 ms, enabling proper maximum power point tracking of each PV string. ...
Journal article (2025) - Daniele Scirè, Roberto Macaluso, Mauro Mosca, Maria Pia Casaletto, Olindo Isabella, Miro Zeman, Isodiana Crupi
This study presents a comprehensive analysis of the optical and electronic properties of thin films of molybdenum oxide and tungsten oxide to implement hole-selective contact for heterojunction solar cells. These contacts are currently viewed as an alternative for the fabrication of doping-free solar cells. However, the spreading of this technology is still limited due to the development of S-shaped J-V curves, which affect the electrical performance of the cells, and further optimization in the material deposition process is therefore crucial to overcome these challenges. To improve transition metal oxide-based heterojunction technology, this work investigates the impact of oxygen vacancies on electrical performance, particularly their role in S-shaped J-V curves. Defect density evaluation through nondestructive techniques like photothermal deflection spectroscopy together with a detailed experimental characterization is presented in this paper to highlight the structural and optical properties of the films. Prototypes of solar cells incorporating hole-selective contacts with tungsten and molybdenum oxide are prepared to show S-shaped J-V characteristics under AM 1.5 illumination. An equivalent circuit modeling was used for understanding the electrical characteristics of the prototypes. Furthermore, this approach offers insights into the optimization of the performances of devices. ...

From accurate cell performance simulation to energy yield prediction

Journal article (2025) - P. Procel, Y. Zhou, M. Verkou, M. Leonardi, Y. Blom, M. R. Vogt, R. Santbergen, M. Zeman, O. Isabella, More authors...
Recent conversion efficiency breakthroughs in double-junction (tandem) perovskite/crystalline silicon solar cells demand advanced opto-thermo-electrical simulations, that are critical for translating laboratory results into realistic photovoltaic module and system performance. A holistic framework is here developed and presented, combining cell-level simulations, spectral analysis, PV module and PV system modelling. After validating the deployed physics models against measured cells and modules, hourly spectral irradiances for Delft, the Netherlands, and Catania, Italy, are generated and clustered into representative “blue-rich” and “red-rich” spectra. The effects of spectral variations on the current-matching and energy yield of tandem modules are quantified. Realistic module architectures are simulated, integrating dynamic temperature and spectrum data. Temperature coefficients are derived as a function of both irradiance and module temperature, significantly improving upon traditional indoor-derived values. Results show that standard indoor-derived coefficients under-/overestimate values in realistic conditions, highlighting the ultimate need for location-specific power matrixes. This study offers a robust pathway to predict tandem module energy yields across seasons and climates, supporting optimized design choices for industrial production and future PV installations. ...
Sequential thermal evaporation is an emerging technique for obtaining perovskite (PVK) photoactive materials for solar cell applications. Advantages include solvent-free processing, accurate stoichiometry control, and scalable processing. Nevertheless, the power conversion efficiency (PCE) of PVK solar cells (PSCs) fabricated by evaporation still lags behind that of solution-processed PSCs. Here, based on multi-cycle sequential thermal evaporation, we systematically investigate the effects of the post-deposition annealing temperature on the PVK properties in terms of surface morphology, opto-electronic properties, and device performance. We find that the average grain size increases to almost 1 μm and charge carrier mobilities exceed 50 cm2 V−1 s−1 when the annealing temperature is increased to 170 °C. We introduce a trace of PbCl2 to the multi-cycle sequential deposition to improve the absorber crystallinity at a lower annealing temperature of 150 °C, as evidenced by the XRD and PL analyses. The resulting PSC in a p–i–n structure yields a PCE of 18.5% with a cell area of 0.09 cm2. With the same deposition parameters, the cell area is scaled up to 0.36 cm2, achieving champion PCEs of 17.06%. This indicates the great potential of this technology for the commercialization of PSCs in the future. ...

Albedo change and radiative forcing dynamics

Integrating photovoltaic (PV) systems in urban areas enhances local renewable electricity production but also reduces surface albedo due to the lower reflectivity of PV panels. This albedo reduction increases Earth's energy absorption, resulting in positive radiative forcing (RF), while the displacement of fossil fuels by PV electricity leads to negative RF through avoided CO2 emissions. This study quantifies the net RF impact of urban rooftop PV deployment using a novel workflow. This proposed workflow combines: (1) a geometric spectral albedo (GSA) model, using LiDAR data and geo-referenced material maps to simulate albedo changes before and after PV integration; and (2) a simplified skyline-based PV model, using LiDAR-derived roof geometry to estimate annual PV electricity generation. The method is applied to the city of Delft, the Netherlands, and the average simulated albedo of Delft is 0.1584, differing by 6.12 % from MODIS observations (0.1493). Full PV integration on all rooftops reduces the city-wide albedo to 0.1557, corresponding to a positive RF of 3.53×10−8 W/m2. This can be offset in about 40 days by negative RF from PV electricity, assuming a grid carbon intensity of 454 gCO2-eq/kWh. However, under a low-carbon grid scenario (30 gCO2-eq/kWh), the payback time increases to 623 days, indicating that positive RF from albedo reduction becomes more relevant in future decarbonized scenarios. This study contributes to understanding the climatic implications of urban PV deployment and offers insights into the realistic potential of PV systems in mitigating climate change. ...
Journal article (2025) - Zain Ul-Abdin, Olindo Isabella, Rudi Santbergen
In this study, a modeling methodology is presented for evaluating the performance of a hybrid system integrating different types of solar collectors, namely photovoltaic (PV), glazed flat plate solar thermal (ST) and unglazed photovoltaic-thermal (PVT) collectors to harvest solar energy. Further, the system is integrated with a seasonal storage that is an aquifer thermal energy storage (ATES) system, a heat exchanger and a heat pump (HP) to provide heating, including space heating (SH), domestic hot water (DHW), as well as cooling. The investigation considers various operational modes depending on the climate conditions and building characteristics. The study focuses on comparison of solar collectors in realistic scenarios, examining heating type and insulation levels. Real energy consumption data considering five residential buildings in Amsterdam is employed for the analysis. Annual simulations for the considered buildings are conducted for SH and DHW coverage, along with cooling. The results indicate that ATES combined with glazed ST collectors demonstrates superior heat storage while HP with PV/ST combination and floor heating achieves an average coefficient of performance (COP) of 6.09 for both SH and DHW. In contrast, HP combined with PVTs shows the lowest performance, with a COP of around 5 when used with radiator heating. Additionally, majority of the demand is covered using HP storage mode with seasonal storage and HP while building insulation plays a crucial role. ...
The impedance of solar cells can be leveraged for a variety of innovative applications. However, for the continued advancement of such applications, it is crucial to understand how the impedance varies during practical operation. This work characterizes the impedance of modern crystalline silicon solar cells across different bias voltages and under varying illumination and temperature conditions. It is found that for a given bias voltage, variations in temperature have a notably stronger impact on PN junction impedance than changes in irradiance. However, during maximum power point (MPP) tracking, variations in irradiance have a larger influence on the PN junction impedance than temperature variations. This is related to the shifting operating voltage during operation. Furthermore, it is shown that the capacitance during practical operation can strongly vary for different solar cells. For instance, the areal MPP capacitance values of the two cells tested in this study at 0.1 sun irradiance and a temperature of 30 °C were 0.283 μF/cm2 and 20.2 μF/cm2, a 71-fold difference. Conversely, the range of the MPP diffusion resistance was found to be highly similar for different cells. The results of this study enhance the understanding of solar-cell impedance and have a broad applicability. ...
Journal article (2025) - Youri Blom, Daniel Jimenez Pelarda, Tabitha Minett, Ismail Kaaya, Nikoleta Kyranaki, Rudi Santbergen, Olindo Isabella, Malte Ruben Vogt
Increasing the operating lifetime of photovoltaic (PV) modules is a key factor in further reducing their levelized cost of electricity. Analytical degradation models typically use the external relative humidity (RH) as a stress factor, rather than the moisture concentration inside the module. This study presents a Finite Element Method (FEM) model, built in COMSOL Multiphysics, to simulate the moisture ingress inside a PV module. We explore the effects of different encapsulant and backsheet materials, as well as various climatic conditions, on moisture penetration. Overall, the impact of the climate has a larger impact on the moisture ingress than the choice of material, implying that the PV module design should be adjusted for different climates. As FEM simulations are computationally intensive, we also present an analytical model, based on empirically determined characteristics, to simulate the moisture ingress. This reconstruction can be done with a deviation lower than 0.05 for all conditions. Finally, our findings indicate that the relative moisture content (RMC) within the module serves as a more accurate stress factor than outdoor RH. Degradation rates over time found in literature are captured more accurately when deploying RMC. ...
Photovoltaic modules are typically not optimized for conditions of partial shading. One proposed approach to improve their shade tolerance is to implement maximum power point tracking on different strings of cells within the modules. However, this approach increases the demand for sub-module power converters, which poses a challenge. To address this, researchers have suggested integrating power electronic components directly into the module laminate, or even within the solar cells themselves. Despite these advancements, limited research has focused on integrating the most bulky component: the inductor. This study investigates through simulations whether planar air-core inductors can yield the required properties to support sub-module power conversion. The simulated inductors have an area that is as large as an industrial crystalline silicon solar cell. 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, plays an important role in the inductor properties at high frequency. The coil geometries that are simulated yield inductance values between 0.3 μH and 3.2 μH. Subsequently, the feasibility of implementing these inductors into an exemplary DC–DC boost converter is evaluated. To adequately reduce the ripple current, a significant switching frequency of at least several hundred kHz is required. Additionally, at 500 kHz, an inductor thickness of around 0.5 mm is necessary to keep the ohmic losses in the inductor below 2% of the total generated power in standard test conditions. While demonstrating feasible combinations, these findings also present significant challenges. ...