Herein, the application of a comprehensive modeling framework that can help optimize the design of multilayered optical filters for coloring photovoltaic (PV) modules is presented based on crystalline silicon solar cells. To overcome technical issues related to the implementation of color filters (CFs) on PV modules, like glare and color instability, colorimetry metrics, such as the hue, chroma, luminance color space, and the quantitative concept of difference between two colors are extensively deployed. It is showcased in this work that designing colored modules with high hue and chroma stability is possible by using a front-side texturing with edged geometry, like V-shaped grooves and inverted pyramids, while obtaining colors with relatively high luminance values, indicating good brightness. Furthermore, it is argued that adapting the rear surface of the front glass with a random textured layout where the CF is applied can improve color and luminance stability without significant loss of chroma while eliminating glare. Finally, the models can be used to optimize the number of layers for a given CF, reducing unnecessary optical losses. Compared to a standard PV module, performance simulation of optimized, bright-colored PV modules predicts relative energy yield losses ranging from 7% to 25%.

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The deployment of photovoltaic (PV) systems in urban environments has the potential to supply a significant share of the urban energy demand and help us reduce greenhouse emissions in the hope of alleviating the consequences of climate change. Moreover, recent advancements in the integration of PV technology into multi-functional architectural elements, offer the possibility to deploy solar cells almost on every surface of the urban fabric. In this dissertation, the solar energy potential of the urban environments and approaches for improving the performance of urban PV systems are investigated. The first part of this thesis is focused on computational models to evaluate the solar radiation reaching a PV system in complex geometric environments. The second part, delves into the effects of partial shading on the electrical output of PV systems and proposes strategies to increase the shading tolerance of PV modules....@en

Reconfigurable photovoltaic modules are a promising approach to improve the energy yield of partially shaded systems. So far, the feasibility of this concept has been evaluated through simulations or simplified experiments. In this work, we analyse the outdoor performance of a full-scale prototype of a series-parallel photovoltaic module with six reconfigurable blocks. Over a 4-month-long period, its performance was compared to a reference photovoltaic module with static interconnections and six bypass diodes. The results show that under partial shading, the reconfigurable module produced 10.2% more energy than the reference module. In contrast, under uniform illumination the energy yield of the reconfigurable PV module was 1.9% lower due to the additional losses introduced by its switching matrix. Finally, a modification in the reconfiguration algorithm is proposed to reduce the output current–voltage range of the module and simplify the design of module-level power converters while limiting the shading tolerance loss.

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The integration of photovoltaic (PV) technology in urban environments poses new challenges for the design of PV modules. In particular, the poor shading tolerance of conventional PV modules strongly limits the energy performance of urban PV systems. In this work, we analyze how interdigitated back-contact solar cells with low-breakdown voltages can help improve the shading tolerance of PV modules. Through detailed simulations, we show that the breakdown voltage can be tuned without significantly degrading the efficiency of the solar cell. Simulation results indicate that, under partial shading conditions, cells with a 0.3-V breakdown voltage could boost by 20% the annual yield of conventional crystalline silicon PV modules with three bypass diodes. These findings are supported by a four-month-long monitoring campaign of PV modules with different breakdown characteristics, which shows a specific yield gain of about 4% in PV modules with six bypass diodes.

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The accurate computation of the irradiance incident on the surface of photovoltaic modules is crucial for the simulation of the energy yield of a photovoltaic system. Depending on the geometrical complexity of the surroundings, different approaches are commonly employed to calculate the irradiance on the photovoltaic system. In this article, we introduce a backward ray tracing simulation approach to calculate the irradiance on photovoltaic systems in geometrically complex scenarios. We explain how the repetition of time-consuming simulation steps can be avoided with the proposed approach by storing a selection of the results from the most computationally expensive parts of the problem, and we show that the irradiance calculated with the proposed approach is in good agreement with the results of Radiance, a well-established irradiance simulation tool. Furthermore, we present an experimental validation carried out using a pyranometer and a reference cell over a period of 6 months in a complex scenario, which shows errors lower than 5% in the calculation of the daily irradiation. Finally, we compare high-resolution spectral simulations with measurements taken with a spectroradiometer under different sky conditions. The proposed approach is particularly well-suited for the simulation of bifacial and tandem photovoltaic modules in complex urban environments, for it enables the efficient simulation of high-resolution spectral irradiance in scenarios with time-varying reflectance properties.

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When integrated into urban environments, photovoltaic (PV) systems usually present operational temperatures that are significantly higher than those shown by rack-mounted systems. High operating temperatures are associated with reduced reliability of PV modules and significantly impact the electrical performance of solar cells. Utilizing the heat produced on PV modules or reducing operating temperatures can bolster their application within the building sector. We present the three main concepts studied to achieve these goals. First, a PV is a chimney concept that allows the use of the heat generated by the modules. Simulations for a PV chimney installed on a building in the Netherlands showed that although the heat quality produced inside its cavity was low, the potential use of the air mass flow for ventilation applications is promising. Additionally, we present two passive cooling solutions that can reduce the operating temperatures of PV modules: Optical filters and phase change materials. Experimental measurements in Delft showed that these solutions reduce the operating temperature of PV modules between 4 °C to 20 °C, particularly under high irradiance hours.

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In this manuscript, we discuss the relevance of the reverse characteristics of solar cells in the energy yield of partially shaded photovoltaic modules. We characterize the reverse IV curves of commercially available cells and we simulate the energy yield of photovoltaic modules using an experimentally validated simulation framework. Results suggest that cells with low breakdown voltages can boost the energy yield up to 74% in modules that are heavily shaded. Also, yield gains larger than 1% can be achieved for modules that are partially shaded only 7% of the time.@en

Photovoltaic modules in the urban environment are very often exposed to uneven illumination conditions. The electrical interconnection between solar cells in a photovoltaic module limits the power that a solar module can generate under partial shading conditions. In this article, we introduce a PV module that is able to dynamically reconfigure the interconnection between its solar cells to minimise conduction and mismatch losses according to the irradiance distribution on its surface. Using an accurate simulation framework, it is determined that a reconfigurable PV module can generate over 12% more energy than a standard PV module with fixed topology and six bypass diodes, and as much energy as a fixed series-parallel module with six parallel strings, but at significantly lower currents. Simulation results are validated experimentally using a photovoltaic module with six reconfigurable blocks of cells controlled by a switching matrix on a high-performance solar flash simulator.@en

Urban environments present a great potential to generate electricity with photovoltaic technology. However, this electricity cannot be fully harvested using conventional solar modules that have been designed for open landscapes. In urban environments, photovoltaic modules can often be subject to partial shading caused by trees and building structures. Therefore, new photovoltaic module concepts and designs must be explored to increase the shading tolerance of PV modules. This study proposes a simple yet effective approach to compare the potential of different module topologies for maximising the electrical yield of partially shaded photovoltaic systems. Using this approach, the annual electrical performance of various PV module topologies in different urban environments and climates is simulated and compared to determine the potential benefit of using photovoltaic modules with new topologies. Results suggest that the shading tolerance of conventional solar modules can be significantly improved by adding only a few bypass diodes or parallel interconnections. It is shown that the yield of a partially shaded PV system endowed with conventional solar modules could be increased as much as 25% when shading is caused by nearby obstructions.

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Building Integrated Photovoltaic systems can produce a significant portion of the energy demand of urban areas. Despite their potential, they remain a niche technology that architects and project engineers still find esthetically limited. The dark blue or black color of standard photovoltaic panels is considered inappropriate for restoration projects of historic buildings and represents a major constraint on the development of new projects. This work will provide insight into how the use of optic filters can offer new pathways for architectural acceptance of photovoltaic panels. Optic filters selectively reflect or transmit light by interference and can be designed and fabricated using cost-effective and industrially compatible processes. By using in-house developed ray tracing software coupled with TCAD Sentaurus, more than 400 colors were obtained, and their impact on the opto-electrical performance of interdigitated back-contacted solar cells was studied. Results show a maximum efficiency loss of 1.6% absolute at the perpendicular incidence of light on the range of obtained colors when compared with a standard dark blue solar cell. Simulations for different angles of incidence showed that the current reduction on the standard device could be modeled using a cosine relationship. The colored cells, however, deviated significantly from this relationship. We propose that the angular behavior of any cell (colored or standard) could be simulated by modifying the effective irradiance with scaling factors equal to the ratios of the photogenerated current at any angle with respect to the value at normal incidence. We demonstrate that this approach accurately models the effect of the color filter and allows for an easy transition from a bare cell to an encapsulated one. Due to the spectral effect of the filter, we developed both a spectrally resolved optical model and a two-dimensional finite volume transient thermal model. In case of the optical model, we demonstrate an accuracy in the prediction of the reflectance produced by the color with values of mean bias error (MBE) between 2.0% and 3.9%. As for the thermal model, it was validated by first analyzing a standard model under conditions of nominal operating cell temperature and then comparing its results with published scientific literature. Later, we compare its prediction against 2 weeks of measurements. In both cases the thermal model proves an adequate accuracy, yielding differences below 1.5°C with respect to other scientific works and an MBE value of 0.89°C as well as a root-mean-square error value of 2.10°C for the entire measurement period. With the validated models, we studied the effect of the encapsulation on the color perception. We present two options of color filters. The first one produces relatively low reflectance losses and presents relative annual direct current (DC) energy losses of up to 6.4% for Delft, in the Netherlands, and up to 5.9% for Alice Springs in Australia. However, this first option has very poor color brightness. The second studied filter produces highly saturated bright colors. Improving brightness can increase the annual DC relative losses up to 13.7% and 13.5% for Delft and Alice Springs, respectively. Overall, we demonstrate that colored filters based on multilayer optical stacks are a versatile option for coloring cells that allow a good compromise between esthetics and performance.

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Photovoltaic systems in urban environments are usually partially shaded, thus the need for shade tolerant solar panels in the urban environment. We present the design of a series-parallel reconfigurable photovoltaic module. Given a specific irradiance distribution on its surface, it can change the interconnections between its solar cells to maximize the output power. First, we analyze the main trade-offs involved in the design of such module; then we propose an algorithm to choose the optimal module configuration; finally, we simulate the performance of different solar module architectures inferring the potential gain in annual energy yield.

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Architects, engineers and urban planners have today at their disposal several tools for simulating the energy yield of photovoltaic systems. These tools are based on mathematical models that perform repetitive calculations to determine the annual irradiation received by solar panels; hence when photovoltaic systems are installed in complex urban environments, the simulations become highly computationally demanding. Here we present a simplified and yet accurate model for the direct calculation of the annual irradiation and energy yield of photovoltaic systems in urban environments. Our model is based on the correlation between the solar radiation components and the shape of the skyline profile. We show how calculations can be simplified by quantifying the skyline using two indicators: the sky view factor and the sun coverage factor. Model performance is evaluated in different climates using measured data from different photovoltaic systems. Results indicate that the proposed model significantly reduces the required computation time while preserving a high estimation accuracy.

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We report on an advanced modelling approach to accurately predict the energy yield of custom environment / urban integrated photovoltaic systems (E/UIPV). Several submodels are here presented, and their mutual interaction discussed. The flexibility of our software platform allows to exhaustively simulate custom horizons in combination with rigid/flexible PV modules and in presence of albedo component. In this respect, a modelling example predicts AC-side yield with <1% error on annual basis with respect to actual data. In addition, our platform can also deal with colored/bifacial modules and soiling losses for PV energy yield potential or performance prediction.

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In recent decades, the modeling of the current-voltage (I-V) characteristics of photovoltaic (PV) module still attracts much attention of researchers. Commonly, the I-V characteristic of the Si solar cells or PV modules is modeled by the single diode model or double diode model. Compared with the single diode model, the double diode model can obtain higher accuracy, especially under low irradiance conditions. However, more model parameters should be extracted in the double diode model, which makes it more complex. In this abstract, a simplified double diode model is presented and the method to identify the model parameters is briefly explained. The proposed approach can simplify the modeling and parameter extraction of the double diode model.@en