In-field monitoring of eight photovoltaic plants: Degradation rate over seven years of continuous operation

The results of more than seven years (October 2010-December 2017) 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. Thin-film and m-Si 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. In addition, three of the monitored plants have been characterized at module level and the estimated degradation rates have been compared to the values obtained with the monitoring system. The main outcome of this work can be summarized in a higher degradation rate of thin-film based PV modules with respect to silicon-based PV modules.