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Investigations on Characteristic Parameters and Power Degradation of Amorphous Silicon Solar Modules Based on Long-Term Outdoor Testing

Two types of amorphous silicon PV modules have been exposed for out door testing, under severe natural environmental conditions, for a period of three years. The tests were conducted to measure the current-voltage (I-V) curve as a function of solar radiation and ambient temperature. Test results were analyzed under consideration of the presented equivalent circuit, for a hydrogenated amorphous silicon solar cell or module (a-Si:H), with the respective mathematical model. The test system and procedure are explained. Based on continuous measurements, climatic conditions of the test site are presented. Test results show that the shunt resistance R sh and series resistance R s , represented in the equivalent circuit of the amorphous module, change their initial values remarkably represented in the equivalent circuit of the amorphous module, change their initial values remarkably as a function of the exposure time. Relation between the variation of R sh , R s and the degradation of the module is illustrated. Extensive degradation in the peak power, the efficiency, and fill factor of each amorphous module type, especially during the first 1.5 years of the test period, were measured. Contrary to some previous studies, the degradation does not stabilize totally after one year of operation.