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© 2019 Elsevier Ltd This study investigates the effect of soiling on the cooling capacity of the wind and its consequences for the performance of photovoltaic modules. Cooling and electrical characteristics were measured on a glass-glass module for wind speeds up to 4 ms−1 and soiling levels up to 41 gm−2. Soiling can promote the cooling of photovoltaic modules and affects the influence of wind on module performance. Soiling may result in less external heating of the module's surface because of the higher albedo of a soiled module compared to a clean one. Also, soiling results in a decrease of the amount of heat to be evacuated by the wind whereas the capacity of the wind to evacuate heat is not affected; the surplus in cooling capacity can be used to cool the module to a lower temperature than if the module were clean. Soiling had a negative effect on the short-circuit current and the maximum power whereas no direct effect on the open-circuit voltage was observed, but soiling did stimulate the positive effect wind has on the voltage. The study sheds more light on the physical processes that occur on and near the surface of a soiled photovoltaic module. ispartof: SUSTAINABLE ENERGY TECHNOLOGIES AND ASSESSMENTS vol:34 pages:116-125 status: published

Nowadays, material manufacturers are engineering module materials to optimize the energy production of the PV modules. One of the elements which can be influenced is the optical scattering of a material. In this study, we quantified the effect of a scattering front encapsulant on the energy production of PV modules. First, a wavelength-dependent scattering model was developed in the ray-tracing software PVlighthouse. This model was used to find the optimal scattering conditions, looking at the photo-generated current for a glass-glass PV module with flat front surface. It was shown that a gain of +0.63 mA/cm2 can be obtained for optimal scattering conditions. The scattering is mostly beneficial when the light strikes the module surface at a perpendicular angle. The outcome of the optimization study was implemented in IMEC’s energy yield simulation framework. This framework was used to estimate the energy gain of PV module with scattering front encapsulant when installed in Kuwait’s desert. It was shown that an energy production gain of 1.8% can be expected in case of a glass-glass module with flat front surface and ARC coating.

Currently, photovoltaic (PV) installations target a maximization of annual energy yield. However, as the grid penetration of PV is increasing, PV electricity generation will need to match better with local load profiles. Especially the seasonal variabilities remain challenging. While wind and PV tend to have complementary seasonal variability, wind turbine installation faces limitations especially in densely populated areas. In this paper, we discuss how this challenge may be addressed with climateand consumption-specific PV module technology. In particular, we demonstrate how the temperature coefficient of a PV system can impact the energy yield throughout the year. In colder climates, higher temperature coefficients allow for a better energy balance, favoring production in colder seasons without a significant reduction of yearly energy yield. Simulations for locations at high latitude, and colder climates, indicate that higher temperature coefficients and improved low-light behavior not only enable a higher energy yield in cold seasons, but also negligible losses in the overall yearly energy yield compared to lower temperature coefficients and slightly better low-light behavior. Simulations show that these results can be obtained using commercial PV modules. More broadly, they indicate how PV module technology may be optimized depending on the location and climate. (C) 2020 Elsevier Ltd. All rights reserved. This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 751159. The work in this paper was partially funded by the Kuwait Foundation for the Advancement of Sciences under project number CN18-15 EE-01. Govaerts, J (corresponding author), IMEC, Kapeldreef 75, Leuven, Belgium. Jonathan.Govaerts@imec.be

Computational Fluid Dynamics (CFD) and wind tunnel experiments were used to study wind flow over PV modules attached to inclined surfaces. Wind velocities were investigated at various positions on a test module, for five wind speeds varying from 1 to 5 m s−1. After validation the CFD model was used to study the effects air gaps and wall cavities under the module have on the airflow over the module. Data were measured for two air gaps, 3.5 cm and 5.5 cm thick, and for three cavity depths ranging from 0 cm to 9 cm. The 3.5 cm air gap resulted in lower near-surface wind speeds over the PV module. This will result in less wind-generated cooling of the module, and consequently, in a lower electrical performance. The wall cavities did not affect the magnitude of the wind speed over the module but generated an increased deflection of the wind towards the lateral sides of the module. They also created clockwise and anti-clockwise eddies next to the PV setup and in the cavity itself. The study shows that in CFD simulations for PV applications, even small irregularities in the PV setup should be included in the model to predict reliable results.

© 2018 Elsevier Ltd PV module testing under standard conditions is an important and well-established procedure, which plays a vital role in module rating. However, PV modules rarely operate at standard conditions therefore their field performance should be predicted based on long term outdoor monitoring or by means of models – so called energy yield models, which combine PV module characteristics with varying environmental conditions. The present work employs a bottom-up, physics-based energy yield modelling approach, which accounts to the interacting optical, thermal and electrical mechanisms in a detailed manner. Additionally, measured data is used for the accurate calibration of the models. Such an approach permits to explore the influence of cell- and module technology details on energy yield under any specific environmental conditions. The present work employs such a method to evaluate the influence of Silicon solar cell technology on energy yield under desert and moderate climates, where the interplay of different irradiance and ambient temperature levels result in a challenging PV performance prediction problem. The purpose of this work is to identify the best-suited solar cell technologies and to understand the underlying mechanisms, which lead to superior PV performance under specific climate conditions. The study is performed by means of physics-based exploratory energy yield simulations with detailed resolution of the thermal effects. Our comparison of four different cell technologies in monofacial modules highlights that superior illumination-dependent performance can contribute to annual energy yield enhancement under both moderate and desert climates amounting to 1.75% and 0.4%, respectively; while a 0.04%/°C advantage in relative temperature coefficient increases annual energy yield (by 1.2%) only under a desert climate. ispartof: SOLAR ENERGY vol:173 pages:728-739 status: published

The influence of mounting setup on the wind flow field, temperature pattern, and electrical performance of building-integrated (BIPV) and building-applied (BAPV) photovoltaic modules was investigated using wind tunnel experiments. Tests were done with an inclined 3 × 2 module for four air gap thicknesses varying from 0 cm (BIPV) to 5.5 cm (BAPV) and five freestream approaching wind speeds from 1 to 5 m s−1. Wind speed and temperature were measured along the central line of the module, on the top (illuminated) as well as on the back (shaded) side. Short-circuit current and open-circuit voltage were determined from I-V measurements, and the maximum power was calculated. The wind and temperature patterns and the electrical performance were considerably affected by the mounting setup. The BAPV configurations were always better cooled by the wind than the BIPV setup because of the additional cooling in the air gap. Although a better cooling does not automatically guarantee a higher electrical performance, the BAPV configurations showed the highest performances in the test. In addition, the development of a boundary layer above and (in the case of BAPV) below the module and the trapping of heat into it, created a surface temperature gradient that significantly affected the electrical performance of the individual solar cells in the module. This is important because in most PV modules, solar cells are connected in series. Since the operational temperature influences mainly the open-circuit voltage, the open-circuit voltage of the whole module, and hereby the power output, will be determined by the behavior of each individual solar cell. In the tests reported here, the BAPV module with the thickest air gap (5.5 cm in this study) was the best performing configuration.

The continuous growth of photovoltaic installations globally carries hope for a sustainable future but also imposes challenges on all levels of energy production and distribution. Grid operators and designers have to cooperate more closely with monitoring service providers in order to sustain a flexible scheme of energy exchange. The basis of these calculations is accurate energy yield estimation models, which are able to capture all effects of the environment. Especially for locations with highly dynamic irradiance and environmental conditions, this remains a tough challenge. All photovoltaic energy yield models presented in this work aim at accommodating the inherent dynamism of these challenging locations at small time scales. A detailed, physics based electro-thermal energy yield model is validated along with other state-of-the-art models and performs 25% more accurately. Additionally, the results from the dynamic modeling are transferred to a neural network model, increasing the accuracy further up to six times better than any parametric solution.

Currently, most of the state-of-the-art energy yield prediction and evaluation models reported in the literature assume a uniform photovoltaic (PV) module temperature and air flow. However, during realistic wind flow conditions, local temperature variations occur over PV modules due to forced convection. This study aims to investigate how spatial temperature differences over the surface of a PV module that are caused by wind affect the convection of heat over the module, and how this influences the energy production by the module. A PV module composed of 2 rows of 9 solar cells each was placed horizontally in a wind tunnel. It has then been tested at free-stream wind velocities of 1, 2, 3 and 5 m/s. Surface temperatures and ambient air temperatures have been measured along the module and vertical temperature gradients have been determined. The electrical characteristics of each individual cell in the PV module have also been measured. Substantial differences in performance between the solar cells caused by local variations in module temperature have been observed. These data have been used to calculate the heat transfer coefficient along the module. To illustrate the importance of including, in energy yield evaluation models, the temperature variations that occur between the cells of a same module, we have constructed an energy yield evaluation model for a standard 60-cell PV module illuminated at 1000 W/m2 and calculated the power output for (1) a uniform heat transfer coefficient over the module, and (2) a realistic distribution of the heat transfer coefficient based on the wind tunnel experiments. Differences up to 4.3% have been observed, indicating that local variations in temperature within a PV module need to be taken into account for accurate energy yield evaluations. Using this improved modelling, the absolute errors remaining in the E-yield estimations can be reduced.

With the growing competition of utility-scale photovoltaic (PV) plants to provide electricity to the grid, accurate energy yield simulation is becoming essential. Apart from irradiance, forced convection can have an equally significant impact on solar cell temperature, which in turn affects the power output, hence the energy yield. As a consequence, the wind must be taken into account for an accurate estimation of PV installations' energy yield. However, no earlier studies have systematically investigated the impact of wind on precise energy yield simulation. In this study, we investigate how sensitive is PV module's output to forced convection. First, we reveal a significant deviation between the simulated PV module's energy yield and cell temperature compared to experimental results in case dynamic wind effects are neglected. Secondly, for controlled incremental forced convection with a steady state scenario, we show that for higher wind speed the change of PV module's cell temperature and power output is small with different forced convection. Whereas, for the low wind speed, small changes of forced convection imply a larger variation of the PV module's cell temperature and power output. This shows that for high wind speed region energy yield estimation is less sensitive on modelling errors. Whereas for the low wind speed region it is highly sensitive. This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 751159. Chowdhury, MG (corresponding author), Katholieke Univ Leuven, ELECTA ESAT MICAS, Kasteelpk Arenberg 10, B-3001 Leuven, Belgium ; IMEC, Kapeldreef 75, B-3001 Heverlee, Belgium ; Imec Partner EnergyVille, Thor Pk 8320, B-3600 Genk, Belgium.

Chapter 4 gives a summary composed from [1], and consistent with more general overview papers [2,3]. First, Section 4.1 describes recombination at Si surfaces theoretically to clarify two key passivation approaches: chemical and field effect passivation. Then, Section 4.2 quantifies the chemical and field effect passivation of Al2O3, i.e., its interface trap density and fixed charge density, respectively. Finally, Section 4.3 provides a larger picture by comparing Al2O3 to other Si surface layers, and showing that Al2O3 surface passivation can also be applied to passivate thin film photovoltaics.

Chapter 4 gives a summary based on one of the authors' earlier articles (Vermang (2012)), and consistent with more general overview papers. First, Section 4.1 describes recombination at Si surfaces theoretically to clarify two key passivation approaches: chemical and field effect passivation. Then, Section 4.2 quantifies the chemical and field effect passivation of Al2O3, i.e., its interface trap density and fixed charge density, respectively. Finally, Section 4.3 provides a larger picture by comparing Al2O3 to other Si surface layers, and showing that Al2O3 surface passivation can also be applied to passivate thin film photovoltaics.

Numerous models have been developed to predict the power output of photovoltaic (PV) systems as a function of insolation and ambient conditions. However, the effect of wind on module temperature, and hence performance, is only poorly incorporated into these models, and spatially distributed and (fast-varying) transient wind effects have not yet been studied in detail. In this paper, spatial distribution of temperature over a 156 × 156 mm PV mini-module is studied together with fine-time-scale temporal evolution. Tests were performed on a 2 × 3 mini-module mounted in a wind tunnel. Results show that the temperature differences can amount to 21 °C and more, depending on the wind speed and the location on the module. Apart from cooling caused by heat convection, a temperature increase generated by wind friction also occurs at the module’s surface although it remains very low compared to the cooling caused by convection.

Non-uniform operating conditions of photovoltaic modules have a huge impact on the energy generation of PV installations. To increase the energy yield of PV modules under non-uniform conditions, innovative module topologies have been proposed. However, a complete exploration of these topologies cannot be performed on the field, given the huge cost/time investment required for the realization of all potential topologies, as well as the large time required for comprehensively testing them in a real installation. Thus, it is more efficient and effective to compare them through simulations. An accurate and versatile simulation approach is proposed here which allows exploration of different PV module topologies under realistic time- and spatially-varying shading scenarios. The latter are created by matching measured weather data with simulated non-uniform and dynamic operating scenarios created by using the software SketchUp. The use of a physics-based bottom-up modeling approach for the different PV module topologies allows for accurate evaluation of the energy generated by each topology in the given operating conditions. Simulation results are presented that substantiate the feasibility of the methodology. Four relevant PV module topologies are compared, showing the better performance of reconfigurable topologies when uniform operating conditions are not dominant.

In the past, the phenomenon of dust deposition on the glass cover of photovoltaic modules has been studied mainly in the Middle East, but little is known about the phenomenon in Central Europe. This paper focuses on the magnitude of the problem in Belgium (Koppen climate classification: Cfb). A variety of measurements were performed to determine the effect of dust settlement on the power output of photovoltaic modules. The physical properties of the collected dust were examined using a scanning electron microscope (SEM). A potential solution for the phenomenon, namely the usage of special coatings on the cover glass, was investigated. The results show that the problem of dust settlement on photovoltaic modules in Belgium is not as severe as in the Middle East. Nonetheless the problem exists and results in a constant power loss between 3% and 4% for the optimal tilt angle in Belgium which is 35° and with periods of regular rainfall. Please note that these results do not reflect a one year energy loss, further experiments are needed. Rain seems to have little cleaning effect on smaller dust particles (2–10 μm), but on bigger particles (pollen, approx. 60 μm) the cleaning effect is clearly visible. The use of special coatings on the glass have a potential reduction in power loss caused by dust settlement. However, at this moment, the extra cost associated with these coatings is not justified for photovoltaic modules in Belgium. Cleaning panels should only be done when soft tap water or demineralized water is available.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 1936-1938, The ongoing growth of renewable energy installations is slowly shifting the energy mix for grids worldwide. Photovoltaic (PV) installations in specific have increased their share and PV currently covers more than 6% of the peak electricity demand in Europe. These growing numbers give hope for a sustainable future but also showcase the increasing challenges that the PV industry will have to face. With such a big number of PV installations on the grid, each with different size and characteristics, it is crucial to develop tools and methods for efficient monitoring and problem detection. The kind of dynamism, which occurs in time scales much shorter than 1 hour, requires PV models that inherently incorporate the dynamic effects of the PV system, like thermal transients and response time constants, also scalable both spatially and temporally. State of the art parametric models are unsuitable for fine time resolutions or non-uniform environmental conditions. In this work a novel PV model is presented, suitable for non-uniform, fast varying conditions on small time scales, for online monitoring and control of the PV plant. The model is validated on a 62.5 kWp installation for a period of 4 months and retains a root-mean-square (RMS) error of less than 5% even for time periods down to 10 seconds.

Atomic layer deposition (ALD) of thin Al2O3 (≤10 nm) films is used to improve the rear surface passivation of large-area screen-printed p-type Si passivated emitter and rear cells (PERC). A blister-free stack of Al2O3/SiOx/SiNx is developed, leading to an improved back reflection and a rear recombination current (J0,rear) of 92 ± 6 fA/cm2. The Al2O3/SiOx/SiNx stack is blister-free if a 700°C anneal in N2 is performed after the Al2O3 deposition and prior to the SiOx/SiNx capping. A clear relationship between blistering density and lower open-circuit voltage (VOC) due to increased rear contacting area is shown. In case of the blister-free Al2O3/SiOx/SiNx rear surface passivation stack, an average cell efficiency of 19.0% is reached and independently confirmed by FhG-ISE CalLab. Compared with SiOx/SiNx-passivated PERC, there is an obvious gain in VOC and short-circuit current (JSC) of 5 mV and 0.2 mA/cm2, respectively, thanks to improved rear surface passivation and rear internal reflection. Copyright © 2012 John Wiley & Sons, Ltd.

Atomic layer deposition (ALD) of thin Al2O3 (

This work investigates the formation of blisters during annealing an Al 2 O 3 film grown by atomic layer deposition (ALD) on Si. This blistering phenomenon is shown to occur under an external load in the presence of a tensile residual stress: the total membrane stress is a super-imposition of the residual stress of the pre-stressed film and a concomitant stress due to change of blister profile. In the case of this Si/Al 2 O 3 system, the film is indeed pre-stressed and the hydrostatic pressure is caused by (i) the effusion of H 2 and H 2 O and (ii) Al 2 O 3 being a diffusion barrier.