PV performance during low irradiance and rainy weather conditions
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With data made available by a photovoltaic (PV) test facility located on top of an office building of the Utrecht University the performance of ten PV modules during time periods of low irradiance and precipitation was analysed. Using values for direct irradiance by Bird’s SPCTRAL2 model and measured climatic conditions a weather classification system was designed in order to categorize time periods and make a comparison between rainy and non-rainy time periods possible. Results show that precipitation induces a blue shift in the solar spectrum increasing the short-circuit current (ISC) of the modules (a-Si and CdTe in particular). Furthermore it is shown that precipitation causes module temperature to drop resulting in an increase in open-circuit voltage (VOC) for all modules. In terms of the performance ratio (PR) it is shown that almost all modules perform better under rainy than under non-rainy weather conditions, but it is noted that incorrect measurements of module temperature most likely overestimate the PR for some of the investigated modules.