Degradation rate of eight photovoltaic plants: results during six years of continuous monitoring

The results of six years of continuous monitoring are presented in this paper that refer to eight outdoors PhotoVoltaic (PV) plants. The monitored plants are based on different technologies: mono-crystalline silicon (m-Si), poli-crystalline silicon (p-Si), string ribbon silicon, Copper Indium Gallium Selenide (CIGS) thin film and Cadmium Telluride (CdTe) thin film. Mono-crystalline silicon modules and thin-film modules are used both in fixed installation and on x-y tracking systems. The results are expressed in terms of degradation rate of the efficiency of each PV plant, which is estimated from the measurements provided by a multi-channel data-acquisition system that senses both electrical and environmental quantities. A comparison with the electrical characterization of each plant obtained by means of the transient charge of a capacitive load is also proposed. The capacitive-load technique has been implemented immediately after the installation of the PV plants and after 78 months of operation. The obtained results show that both the m-Si plants in fixed installation and on the tracking system had a negligible degradation, while p-Si and string-ribbon Si exhibited a moderate degradation. Higher was the degradation obtained for the thin-film based plants, with a worst behaviour of the plants installed on the tracking systems.