Long-term performance modelling of amorphous silicon photovoltaic module

Output performance of the conversion efficiency of an amorphous silicon (a-Si) photovoltaic (PV) module under outdoor conditions has been evaluated for a period of two years. A simplistic model for the change in the module efficiency simultaneously taking into account the light-induced degradation and thermal-recovery effects is applied to the experimental results, yielding several physical parameters describing the degradation and recovery processes. The validity of the model and involved parameters are verified by a good fit between experimental results and model predictions regarding another identical a-Si module which was installed at a different time. By using a modeled seasonal temperature variation, the model is extended to predict the module efficiency for a further long-term period. We showed that the module efficiency becomes almost completely stable after two years of sunlight exposure and then follows a steady seasonal variation.