Ageing effect on the performance of a-Si photovoltaic modules in a grid connected system: experimental data and simulation results

To test performance and ageing of amorphous silicon photovoltaic (a-Si PV) modules, an Italian Electric Company (AEM Spa-Torino) has installed a PV system (12 kWp) connected to a three-phase grid. As is well-known, the performance of a PV field depends on irradiance, module temperature and ageing. In order to separate the ageing effect from the irradiance and temperature influence, it is necessary to know the beginning of life (BOL) performance, at the irradiance and module temperature, measured during the life of the PV field. The deviations, between the experimental data and the BOL performance, provide the ageing of the PV modules. This paper proposes a simulation procedure that gives the BOL performance and allows determination of the monthly and yearly ageing of the PV field. The simulation results, related to the 12 kWp field, are reported. This procedure can be also applied to stand alone PV systems with modules of different technologies.