Evaluation of Technology-Dependent Maximum Power Point Current and Voltage Degradation in a Temperate Climate

In this paper the maximum power point current and voltage degradation of eight different photovoltaic technologies (27 systems) installed in a temperate climate is studied. The plant was installed in 2010 and seven years of production are considered. A performance loss over time has been observed for all systems. Most systems show a stronger relative decrease in current compared to voltage. The connection between performance losses broken down into these two parameters can lead to findings of which degradation modes appear in the PV system. Depending on the predominant performance loss parameter, specific degradation modes were suspected and several PV plant inspections, including IV curve measurements and electroluminescence as well as infrared imagery, took place to confirm these hypotheses. Degradation in current was detected in all systems and can be connected to hot cells, fractured cells, soiling as well as other root causes. A decrease in voltage was not observed for crystalline systems but is severe for copper indium (gallium) selenide as well as amorphous silicon systems and is suspected to be caused by a reduction in the conductivity of the metal contacts and a decreasing ability of the photovoltaic active material to separate the charge carriers. The outcomes of this study might contribute to O&M related improvements of failure detection