Academic literature on the topic 'Soiling in PV'

Soiling severely hinders the ability of solar photovoltaic (PV) modules to absorb incident solar radiation, causing significant deterioration of module performances. In this study, the thermal profiles and the electrical power outputs of PV modules were evaluated in order to establish the impact of soiling under tropical field conditions. Two case-study PV installations in the Universityof Nigeria were considered. Assessments of the PV systems, undertaken both when soiled and after they had been cleaned, involved the measurement of electrical power outputs and the acquisition of infrared (IR) thermograms. It was found that soiling had noticeable impacts on both module surface temperature distributions and their power outputs. The IR images, which showed spatial distributions of module surface temperatures, revealed the occurrence of hotspots on the modules when soiled. Furthermore, as a result of soiling, up to four-fold declines in module electrical efficiencies were observed. These declines were more significant in theground-mounted PV system at the University Staff Primary School compared to the roofmounted system at the University Energy Research Centre. Simple cleaning of the modules led to the disappearance of hotspots and significant improvements in output, showing that it is an effective means of maintaining PV modules performance and recovering the performance potentials lost due to soiling. Keywords: solar PV, PV soiling, infrared thermography, module failure, PV performance

Across the world, the geographical conditions are varied, and the characteristics of dust depend on the local environmental conditions. The solar power generators must incorporate the soiling losses in their estimation for power output and therefore a methodology was developed to estimate the soiling correction factor. After extensive research, a comprehensive review was presented on the effect of soiling on performance of PV plants along with case studies of soiling experiments around the world. A soiling experiment was designed to develop the soiling correction factor. A methodology to calculate the soiling correction factor, which can be implemented in any location, was developed by analyzing the data from the soiling experiment. The effect of rainfall, humidity and wind on soiling was analyzed and documented. The performance of one 20 kWp PV plant was monitored to study the effect of weather-related parameters on the performance. The soiling correction factor varied from -1.36% to 3.67% during the period between June 2018 and June 2019 in Chennai. It was observed that the average PV conversion efficiency of the 20-kW plant was 11.75% and the average PR was 75%. It was observed that the correlation between module temperature and DC power; between humidity and DC power; between GTI and DC power varied every month. The soiling factor developed could be incorporated into the short-term day ahead solar forecasting model. The developed methodology could be applied at the any large-scale solar power plant around the world for yield assessment, designing as well as operational forecasting purposes.

This work attempts to shed some light on the impact of organic soiling due to pollen on solar photovoltaic (PV) power generation. Apart from introducing several soiling-related pollen features, the previous works reporting soiling by pollen have been reviewed. Local observations from late winter to early spring showed that a rooftop PV system experienced both uniform and non-uniform soiling issues, which were mainly caused by pollen from nearby cypress specimens. In addition, this work publishes preliminary results regarding an artificial soiling test performed with pollen. In this test, soda lime float glass coupons were artificially soiled with fresh cypress pollen. A linear relationship was found between the pollen mass density (ρA) and the glass averaged transmittance (TAVE) for values up to 9.1 g/m2. In comparison with other artificial soiling tests performed with different soiling agents, the transmittance loss caused by pollen cypress deposition was relatively high and spectrally selective.

Photovoltaic (PV) module operation is critical in PV systems for optimum generation of electrical power. Modules installed in the field suffer uneven soiling caused by bird droppings and dust build-up on their front surface. This study investigated the impact of partial shading caused by non-uniform soiling on the electrical characteristics of multi-crystalline silicon (mc-Si) modules and strings, and compared this with simulated I-V parameters. Light and heavy uneven soiling on mc-Si solar cells resulted in current mismatch which can be simulated. The effects of partial soiling on the I-V characteristics of mc-Si module strings were experimentally measured and agreed with the simulated results.

Abstract This article presents an evaluation of the performance of PV modules with the variation of some technical and environmental parameters: The PV module tilt angle, and the impact of soiling on the power output of PV module, and the transmittance of the PV glass surfaces. The experiments were achieved in Helwan City (Egypt) at the premises of the Faculty of Engineering of Helwan University. For the soiling part, it comprises two experiments: Transmittance of PV glass surfaces, and the power output of PV modules. For the transmittance experiment, it has been achieved using a simplified method, where three PV glass surfaces were placed at three different tilt angles (0°, 15°, and 30°) and left exposed to the outdoor environment without cleaning for a period of 25 days during the summer season. For the experiment concerning the impact of soiling on the power output, a set of PV modules connected in series have been exposed for a period of 75 days to the outdoor environment without cleaning. Finally, for the PV module tilt angle experiment, another set of PV modules have been used for that purpose, where four different tilt angles were experimented: 0°, 15°, 30°, and 45°. The present research recommends that more studies are needed in the same context, taking into consideration correlating the technical and environmental parameters in one single experiment and during different times of the year. This would be helpful in having overarching perspective regarding the electrical performance of PV modules under different circumstances of tilt angles and soiling patterns within the area of Helwan (Egypt).

The shadow effect caused by nearby objects or the lack of cleaning significantly affects the performance of photovoltaics (PV) installations. This article analyses the bypass diode electrical behaviour and the thermal response of a PV crystalline module under shading or soiling conditions. PV cells of different substrings were covered progressively to simulate the effect of shading or soiling while a programmable electronic DC load was connected to a PV module to set an operating voltage. Three different tests were made to different PV crystalline technology. The paper characterizes in real conditions the I–V curve, bypass diode current, and front and back side PV cell temperature with contact sensor and infrared (IR) thermography, respectively. The results showed that the operation voltage established in the PV module defines the electrical bypass diode current and thermal response under normal operating conditions, shading or soiling. To show the bypass diode behaviour in such conditions, I–V curves were obtained, pointing out the value of the current that flows through bypass diodes in the whole voltage range.

Soiling losses of photovoltaic (PV) panels due to dust lead to a significant decrease in solar energy yield and result in economic losses; this hence poses critical challenges to the viability of PV in smart grid systems. In this paper, these losses are quantified under Qatar’s harsh environment. This quantification is based on experimental data from long-term measurements of various climatic parameters and the output power of PV panels located in Qatar University’s Solar facility in Doha, Qatar, using a customized measurement and monitoring setup. A data processing algorithm was deliberately developed and applied, which aimed to correlate output power to ambient dust density in the vicinity of PV panels. It was found that, without cleaning, soiling reduced the output power by 43% after six months of exposure to an average ambient dust density of 0.7 mg/m3. The power and economic loss that would result from this power reduction for Qatar’s ongoing solar PV projects has also been estimated. For example, for the Al-Kharasaah project power plant, similar soiling loss would result in about a 10% power decrease after six months for typical ranges of dust density in Qatar’s environment; this, in turn, would result in an 11,000 QAR/h financial loss. This would pose a pressing need to mitigate soiling effects in PV power plants.

Soiling refers to the accumulation of dust on PV modules which plays a small but significant role in degrading solar photovoltaics system efficiency. Its effect cannot be generalized because the severity is location and environment dependent. Currently, there are limited studies available on the soiling effect in the hot and humid Malaysian tropical climate. This paper presents an experimental-based approach to investigate the effect of soiling on PV module performance in a tropical climate. The experiment involved a full day exposure of a polycrystalline PV module in the outdoors with accelerated artificial dust loading and an indoor experiment for testing variable dust dimensions. The findings show that for the worst case, the module’s output can be reduced by as much as 20%.

Soiling refers to the accumulation of dust on PV modules which plays a small but significant role in degrading solar photovoltaics system efficiency. Its effect cannot be generalized because the severity is location and environment dependent. Currently, there are limited studies available on the soiling effect in the hot and humid Malaysian tropical climate. This paper presents an experimental-based approach to investigate the effect of soiling on PV module performance in a tropical climate. The experiment involved a full day exposure of a polycrystalline PV module in the outdoors with accelerated artificial dust loading and an indoor experiment for testing variable dust dimensions. The findings show that for the worst case, the module’s output can be reduced by as much as 20%.

La salissure des modules photovoltaïques (PV) dégrade grandement leurs performances dans les environnements désertiques. Les études précédentes en extérieur ont tendance à trouver de faibles corrélations entre les taux de salissure et les paramètres météorologiques. On pensait que l'une des raisons était le long intervalle de mesure - jours ou semaines - des techniques traditionnelles de mesure des salissures sur le terrain. Dans la présente étude, un «microscope de souillure extérieur» (OSM) a été développé pour mesurer le dépôt et le détachement de particules de poussière individuelles, toutes les 10 minutes, dans des conditions extérieures, de jour comme de nuit. En utilisant une paire d'OSM graissés et non graissés, il était en outre possible de séparer les salissures en trois vitesses de flux de poussière de composants - dépôt, rebondissement immédiat et remise en suspension retardée. Les OSM ont été utilisés pour mesurer les taux de flux dans des expériences sur le terrain à Doha, au Qatar. La nouvelle méthode a révélé des effets explicatifs de paramètres environnementaux qui avaient auparavant été obscurcis par de longs intervalles de mesure des salissures et des taux de flux de poussière confondus. L'OSM pouvait également mesurer l'apparition et la croissance de gouttelettes de condensation microscopiques dans des conditions de terrain et de laboratoire. De telles expériences, ainsi que des mesures isothermes et des analyses de composition, ont démontré que la condensation sur les surfaces sales au terrain d’études était fortement influencée par la présence de matière hygroscopique dans la poussière autre que NaCl. En raison de cette matière, la condensation microscopique peut persister à la surface même si elle est bien supérieure à la température du point de rosée. Les résultats de l'étude suggèrent que la souillure des modules photovoltaïques pourrait être atténuée en tirant parti des variations naturelles des conditions météorologiques au cours de la journée
Soiling of photovoltaic (PV) modules greatly degrades their performance in desert environments. Previous field studies have tended to find weak correlations between the soiling rate and weather parameters. It was thought that one reason was the long measurement interval — days or weeks — of conventional field soiling measurement techniques. In the present study, an “outdoor soiling microscope” (OSM) was developed able to measure deposition and detachment of individual dust particles, every 10 minutes, in outdoor conditions, day and night. By using a greased and ungreased pair of OSMs, it was further possible to separate soiling into three component dust flux rates — deposition, immediate rebound, and delayed resuspension. OSMs were used to measure flux rates in field experiments in Doha, Qatar. The novel method revealed explanatory effects of environmental parameters that had previously been obscured by limits of conventional long soiling measurement intervals and confounded dust flux rates. The OSM could also measure the onset and growth of microscopic condensation droplets in field and laboratory settings. Such experiments, along with isotherm measurements and composition analysis, demonstrated that condensation on soiled surfaces at the test site was strongly influenced by the presence of hygroscopic matter in the dust other than NaCl. Because of such matter, microscopic condensation could persist on both hydrophilic and hydrophobic surfaces well above the dew-point temperature. Results of the study suggest that soiling of PV modules might be mitigated by taking advantage of natural time-of-day variations in weather conditions

The solar PV modules are influenced by a variety of loss mechanisms by which the energy yield is affected. A PV system is the sum of individual PV modules which should ideally operate similarly, however, inhomogeneous soiling, mismatching, and degradation, which are the main focus in this study, lead to dissimilarities in PV modules operating behavior and thus, lead to losses which will be assessed intensively in terms of energy yield. The dissimilarities in PV modules are referred to the ambient conditions or the PV modules characteristics which result in different modules’ maximum power point (MPP) and thus, different currents generated by each PV modules which cause the mismatching. However, the weakest PV module current governs the string current, and the weakest string voltage governs the voltage. Power optimizers are electronic devices connected to the PV modules which adjust the voltages of the PV modules in order to obtain the same current as the weakest module and thus, extract the modules’ MPP. Hence, the overall performance of the PV plant is enhanced. On the other hand, the power optimizers add additional cost to the plant’s investment cost and thus, the extra energy yield achieved by utilizing the power optimizers must be sufficient to compensate the additional cost of the power optimizers. This is assessed by designing three systems, a reference system with SMA inverters, a system utilizes Tigo power optimizers and SMA inverters, and a system utilizes SolarEdge power optimizers and inverters. The study considers four different locations which are Borlänge, Madrid, Abu Dhabi, and New Delhi. An Excel model is created and validated to emulate the inhomogeneous soiling and to evaluate the economic feasibility of the power optimiz ers. The model’s inputs are obtained from PVsyst and the precipitation data is obtained from Meteoblue and SMHI database. The economic model is based on the relation between Levelized Cost of Electricity (LCOE) which will be used to derive the discount rate. Graphs representing the discounted payback period as a function of the feed-in tariff for different discount rates is created in order to obtain the discounted payback period. The amount of extra energy yielded by the Tigo and the SolarEdge systems is dependent on the soiling accumulated on the PV modules. Relative to the reference system, 6.5 % annual energy gain by the systems utilizing the power optimizers in soiling conditions, up to 2.1 % in the degradation conditions, and up to 9.7 % annual energy gain at 10 % mismatching rate. The extra energy yield is dependent on the location, however, the Tigo and the SolarEdge systems have yielded more energy than the reference system in all cases except one case when the mismatch losses is set to zero. The precipitation pattern is very influential, and a scare precipitation leads to a reduction in the energy yield, in this case, the Tigo and the SolarEdge systems overall performance is enhanced and the extra energy gain becomes greater. The Tigo system yield slightly more energy than the SolarEdge system in most cases, however, during the plant’s lifetime, the SolarEdge system could become more efficient than the Tigo system which is referred to the system’s sizing ratio. The degradation of the system or the soiling accumulation decreases the irradiation and thus, a slightly oversized PV array become suitable and deliver an optimal power to the inverters. The SolarEdge system is feasible in all scenarios in terms of LCOE and discounted payback period, although its slightly lower performance relative to the Tigo system, this is referred to its low initial cost in comparison to the other systems. The Tigo system is mostly infeasible although it yields more energy than the reference and the SolarEdge systems, this is referred iii to its relatively high initial cost. However, feed- in tariffs higher than 20 € cent / kWh make all systems payback within less than 10 years. The results have overall uncertainty within ± 6.5 % including PVsyst, Excel model, and the precipitation uncertainties. The uncertainty in the degradation and the mismatching calculations is limited to PVsyst uncertainty which is ± 5 %. The uncertainties in LCOE in the location of New Delhi, since it is the worst-case scenario, are 5.1 % and 4 % for the reference and the systems utilizing power optimizers, respectively. Consequently, accommodating the uncertainties to the benefits gained by utilizing power optimizers indicates that the energy gain would oscillate in the range of 6 % - 6.9 % for the soiling calculations, 2 % - 2.2 % for the degradation simulations, and 9.2 % - 10.2 % for the mismatching simulations at 10 % mismatchrate.

abstract: This is a two-part thesis: Part 1 characterizes soiling losses using various techniques to understand the effect of soiling on photovoltaic modules. The higher the angle of incidence (AOI), the lower will be the photovoltaic (PV) module performance. Our research group has already reported the AOI investigation for cleaned modules of five different technologies with air/glass interface. However, the modules that are installed in the field would invariably develop a soil layer with varying thickness depending on the site condition, rainfall and tilt angle. The soiled module will have the air/soil/glass interface rather than air/glass interface. This study investigates the AOI variations on soiled modules of five different PV technologies. It is demonstrated that AOI effect is inversely proportional to the soil density. In other words, the power or current loss between clean and soiled modules would be much higher at a higher AOI than at a lower AOI leading to excessive energy production loss of soiled modules on cloudy days, early morning hours and late afternoon hours. Similarly, the spectral influence of soil on the performance of the module was investigated through reflectance and transmittance measurements. It was observed that the reflectance and transmittances losses vary linearly with soil density variation and the 600-700 nm band was identified as an ideal band for soil density measurements. Part 2 of this thesis performs statistical risk analysis for a power plant through FMECA (Failure Mode, Effect, and Criticality Analysis) based on non-destructive field techniques and count data of the failure modes. Risk Priority Number is used for the grading guideline for criticality analysis. The analysis was done on a 19-year-old power plant in cold-dry climate to identify the most dominant failure and degradation modes. In addition, a comparison study was done on the current power plant (framed) along with another 18-year-old (frameless) from the same climate zone to understand the failure modes for cold-dry climatic condition.
Dissertation/Thesis
Masters Thesis Engineering 2015

abstract: The deposition of airborne dust, especially in desert conditions, is very problematic as it leads to significant loss of power of photovoltaic (PV) modules on a daily basis during the dry period. As such, PV testing laboratories around the world have been trying to set up soil deposition stations to artificially deposit soil layers and to simulate outdoor soiling conditions in an accelerated manner. This thesis is a part of a twin thesis. The first thesis, authored by Shanmukha Mantha, is associated with the designing of an artificial soiling station. The second thesis (this thesis), authored by Darshan Choudhary, is associated with the characterization of the deposited soil layers. The soil layers deposited on glass coupons and one-cell laminates are characterized and presented in this thesis. This thesis focuses on the characterizations of the soil layers obtained in several soiling cycles using various techniques including current-voltage (I-V), quantum efficiency (QE), compositional analysis and optical profilometry. The I-V characterization was carried out to determine the impact of soil layer on current and other performance parameters of PV devices. The QE characterization was carried out to determine the impact of wavelength dependent influence of soil type and thickness on the QE curves. The soil type was determined using the compositional analysis. The compositional data of the soil is critical to determine the adhesion properties of the soil layers on the surface of PV modules. The optical profilometry was obtained to determine the particle size and distribution. The soil layers deposited using two different deposition techniques were characterized. The two deposition techniques are designated as “dew” technique and “humidity” technique. For the same deposition time, the humidity method was determined to deposit the soil layer at lower rates as compared to the dew method. Two types of deposited soil layers were characterized. The first type layer was deposited using a reference soil called Arizona (AZ) dust. The second type layer was deposited using the soil which was collected from the surface of the modules installed outdoor in Arizona. The density of the layers deposited using the surface collected soil was determined to be lower than AZ dust based layers for the same number of deposition cycles.
Dissertation/Thesis
Masters Thesis Engineering 2016

Tese de mestrado integrado, Engenharia da Energia e do Ambiente, Universidade de Lisboa, Faculdade de Ciências, 2019
A acumulação de partículas na superfície de painéis solares é um fenómeno transversal a todas as tecnologias fotovoltaicas. Este fenómeno é designado por Soiling, e têm como principal consequência a redução da eficiência fotovoltaica dos painéis. Esta tese tem como por objetivo a caracterização e quantificação das perdas causadas pelo efeito do soiling em painéis solares. Para tal, serão estudados cinco módulos instalados nos arredores de Paris com o intuito de obter uma taxa de degradação da potência para cada painel. O impacto do Soiling será estudado através da análise da eficiência dos painéis durante períodos secos, com um foco especial no maior período seco de que existem registos, durante o qual todos os módulos sofreram um decréscimo de eficiência para um intervalo de confiança superior a noventa por cento. Os painéis encontram-se no Observatório SIRTA [1], orientados a Sul a uma inclinação fixa de vinte e sete graus. Situados em terreno aberto, a cerca de vinte centímetros do solo, os painéis estão inseridos numa área rodeada por extensos relvados, caracterizada por uma fraca intensidade rodoviária. Para a realização deste estudo, foi disponibilizada uma ampla gama de dados amostrados em intervalos de dez minutos, permitindo uma precisa análise intra-diária da eficiência fotovoltaica. Dados como a temperatura, potência, corrente e tensão dos painéis, irradiância, temperatura ambiente, pluviosidade, velocidade do vento, humidade relativa, entre muitos outros, possibilitaram não só o estudo do impacto do soiling na performance dos painéis, como também várias outras análises acessórias relevantes. A tese inicia-se por uma abordagem aos principais fatores que afectam a taxa de deposição de partículas nos módulos, assim como os seus variados impactos na eficiência dos painéis. Esta secção visa introduzir o leitor aos conceitos básicos indispensáveis à compreensão da tese, e igualmente fornecer uma contextualização alargada de modo a facilitar a interpretação dos resultados apresentados. Seguem-se depois os métodos e objetivos, o capítulo central desta tese, o qual explica em detalhe todo o processo que culminou na quantificação do impacto do soiling na performance dos painéis estudados. Este capítulo encontra-se dividido em aproximadamente três partes. A primeira, relativa ao processamento inicial dos dados, envolve o cálculo da temperatura dos módulos, a sua eficiência de conversão e subsequente correção térmica. Grande parte desta seção é dedicada estimação das temperaturas dos módulos, as quais serão necessárias para preencher eventuais lacunas devido a falhas dos sensores térmicos. Estas temperaturas serão obtidas através da implementação de dois modelos térmicos capazes de simular a temperatura dos módulos. O primeiro, já existente na literatura, requer apenas a introdução da temperatura ambiente, irradiância, e a temperatura nominal de operação das células solares. Embora este valor seja geralmente fornecido pelo fabricante, este último foi calculado experimentalmente, assegurando que o modelo fosse fornecido com temperaturas nominais de operação de células reais, medidas nas suas verdadeiras condições de operação. O segundo modelo, baseado na modelação /dos fluxos de calor entre o painel e o ambiente, foi criado de raiz com o intuito de aumentar a precisão das estimativas. A estabilidade e desempenho destes modelos será avaliada, comparando a sua precisão e fiabilidade sob diferentes condições. De seguida, a eficiência dos painéis será calculada e corrigida para uma temperatura base de vinte e cinco graus Celcius. Esta correção é indispensável à análise da degradação do desempenho dos painéis, uma vez que remove o efeito da temperatura na eficiência, permitindo o cálculo das taxas de degradação de potência normalizadas. A qualidade desta correção será também estudada de modo a garantir a validade dos resultados. O segundo passo centra-se no reprocessamento dos valores de eficiência por forma a facilitar a deteção de eventuais perdas, permitindo obter uma taxa de degradação da potência fiável. Para tal, a eficiência diária acumulada dos painéis será calculada, com o objetivo de simplificar a análise através da redução das variações intra-diárias, obtendo uma série mais representativa das variações de eficiência. Nesta fase serão também filtrados valores anormais de eficiência, resultantes de erros de medição ou condições de fraca iluminação, detrimentais ao estudo em curso. Será ainda feita uma análise da relação entre a dispersão dos valores diários de eficiência e as condições climatéricas, uma vez que estas podem dificultar a análise dos impactos do soiling, afetando a extração e significância estatística das taxas de degradação de eficiência. O terceiro e último passo consiste na identificação dos períodos secos, ou intervalos durante os quais a chuva não foi suficientemente forte por forma a interferir com a acumulação de partículas nos painéis, e portanto ideais para o cálculo das taxas de degradação da eficiência. Estas serão baseadas no declive da recta resultante de uma regressão linear das eficiências durante estes períodos. O uso de uma regressão linear na previsão de perdas pelo efeito do soiling é baseado em estudos de natureza semelhante, os quais concluíram que o declínio do desempenho fotovoltaico observado durante períodos secos é aproximadamente linear, decrescendo continuamento durante períodos sem chuva e regressando a níveis normais após um episódio de precipitação [2]. Estes factos sugerem que os efeitos do soiling no desempenho de um Sistema PV podem ser estimados adotando um modelo linear de perdas de eficiência entre eventos significativos de precipitação. A quantificação destas perdas foi feita para dois tipos de períodos. Inicialmente, apenas períodos durante os quais a precipitação diária não excedeu os cinco milímetros foram estudados. Isto consistiu no cálculo das taxas de degradação da eficiência para estes intervalos. De seguida, este limiar foi fixado num valor mais conservador, assegurando que nenhum processo de limpeza possa ter acontecido, e as taxas de degradação recalculadas. Uma ênfase especial foi dada ao mais longo período seco de que existem registos, durante o qual todos os painéis registaram uma diminuição inequívoca de eficiência. A taxa de degradação média de potência durante este intervalo foi de -0.042 %/Dia, um valor que se encontra de acordo com vários outros estudos semelhantes [2,3]. Devido à sua incomparável duração, estendendo-se por trinta e sete dias, uma especial atenção foi dada a este intervalo, uma vez que este foi o mais longo período de acumulação ininterrupta de partículas. Por fim, foi feita uma breve análise estatística das regressões lineares, visando validar os resultados. As regressões lineares foram testadas unidireccionalmente, de modo a determinar a probabilidade de um painel registar um decréscimo de eficiência durante este período. Para tal, foram calculados os intervalos de confiança de cada regressão baseados na distribuição t de student, focando-se exclusivamente no intervalo superior, revelando o revelando o nível de confiança com o qual se pode afirmar que perdas devidas ao efeito do soiling estão presentes em cada painel. Os resultados indicaram que todos os painéis sofreram uma queda de eficiência para um intervalo de confiança superior a noventa porcento durante este período mais longo, e de noventa e cinco por cento para quatro dos painéis.
Soiling can be one of the major causes of power loss on photovoltaic systems. Despite this, these remain largely ignored. This study analyzed the soiling-induced efficiency degradation of five different solar modules, aiming to characterize and quantify the impact of soiling on the performance of these systems. This was accomplished through the analysis of the module efficiencies over dry periods, during which rain was insufficient to effectively clean the panels. Results showed that all panels registered an efficiency decrease within a ninety percent confidence interval during the longest dry period, with an average power degradation rate of -0.042 %/Day, suggesting a stable trend of soiling induced efficiency degradation. All other periods exhibited non-significant trends, likely due to the high day-to-day efficiency fluctuations which persisted despite the thermal correction of the efficiency values. The accuracy of two thermal models was tested, aiming to obtain the most reliable module temperature records to be employed in the thermal correction procedure. The first, already existent in the literature and based on the panels’ NOCT yielded the best results, with an average error of 3.55 ºC. The second, based on the precise modelling of the panels’ heat fluxes, proved less practical and reliable, yielding a slightly average error in the order of 3.9 ºC. Finally, the impact of the diffuse radiation on the dispersion of the daily efficiency values was studied, revealing that the latter is proportional to the diffuse ratio. This was achieved through the analysis of the monthly standard deviation for different day types, so as to bypass the effect of seasonal variations. Results suggest that solar panel cleaning can be neglected in the region of Palaiseau, as soiling losses are rendered insignificant due to the combination of moderate panel inclinations and the natural cleaning provided by the high frequency of rainfall events.

abstract: This study evaluates two photovoltaic (PV) power plants based on electrical performance measurements, diode checks, visual inspections and infrared scanning. The purpose of this study is to measure degradation rates of performance parameters (Pmax, Isc, Voc, Vmax, Imax and FF) and to identify the failure modes in a "hot-dry desert" climatic condition along with quantitative determination of safety failure rates and reliability failure rates. The data obtained from this study can be used by module manufacturers in determining the warranty limits of their modules and also by banks, investors, project developers and users in determining appropriate financing or decommissioning models. In addition, the data obtained in this study will be helpful in selecting appropriate accelerated stress tests which would replicate the field failures for the new modules and would predict the lifetime for new PV modules. The study was conducted at two, single axis tracking monocrystalline silicon (c-Si) power plants, Site 3 and Site 4c of Salt River Project (SRP). The Site 3 power plant is located in Glendale, Arizona and the Site 4c power plant is located in Mesa, Arizona both considered a "hot-dry" field condition. The Site 3 power plant has 2,352 modules (named as Model-G) which was rated at 250 kW DC output. The mean and median degradation of these 12 years old modules are 0.95%/year and 0.96%/year, respectively. The major cause of degradation found in Site 3 is due to high series resistance (potentially due to solder-bond thermo-mechanical fatigue) and the failure mode is ribbon-ribbon solder bond failure/breakage. The Site 4c power plant has 1,280 modules (named as Model-H) which provide 243 kW DC output. The mean and median degradation of these 4 years old modules are 0.96%/year and 1%/year, respectively. At Site 4c, practically, none of the module failures are observed. The average soiling loss is 6.9% in Site 3 and 5.5% in Site 4c. The difference in soiling level is attributed to the rural and urban surroundings of these two power plants.
Dissertation/Thesis
M.S.Tech Engineering 2013

A solar micro inverter is a small-size inverter designed for single solar PV module instead of group of solar PV modules. Each module is equipped with a micro inverter to convert the DC electricity into AC electricity and the micro inverter is placed/installed below the module. The advantages of micro inverters are: reduced effect of shading losses, module degradation and soiling losses, enabled module independence, different rating of micro inverter can be connected in parallel to achieve the desired capacity, additional modules can be included at time which allows the good scalability, string design and sizing are avoided, failure of any micro inverter does not affect the overall power generation, individual MPPT controller for each module increases the power generation, any orientation and tilt angle allows higher design flexibility, lower DC voltage increasing the safety, easy to design, handle and install, requires less maintenance, draws attention of design engineers, contractors, etc.

The Amonix system is a high concentration PV system that utilizes acrylic Fresnel lenses to focus the sun’s rays onto dispersed PV cells. The Fresnel lenses become soiled with dust over time which decreases power performance. Because of the effect soiling has upon the system performance, Amonix and the University of Nevada, Las Vegas (UNLV) have defined a long term soiling investigation and cleaning methodology. The test and measurement procedure for determining Fresnel lens soiling rate characterization is discussed. Lens soiling rate data is presented for different sites that show the soiling rate is a direct function of the angle of the lens. This paper also discusses the test and measurement procedure of the first phase of an on-going Fresnel lens cleaning investigation. An assessment of the soiling rate upon power production is also presented.