ABSTRACT
This work describes the development of an algorithm to model the variation in seasonal performance of amorphous silicon (a-Si) photovoltaic devices. The model is designed to use local environmental data such as ambient temperature, solar irradiation and windspeed in order to first calculate average module temperature. Spectral irradiation data is then used together with module cover reflection effects in order to calculate 'useful' irradiation reaching the solar cell. An equivalent circuit specific to a-Si is used to obtain an IV characteristic curve from which maximum power point and hence efficiency can be calculated. Environmental data measured at Loughborough, UK is used to present a series of results that demonstrate an overall seasonal variation in performance corresponding to 20% of performance. The individual loss mechanisms contributing to this variation are then separated and quantified. It was found that the main contribution to the seasonal variation in performance in our environment is the low intensity of the light in winter time.
