Degradation analysis of a photovoltaic generator after operating for 15 years in southern Brazil

Photovoltaic modules long-term reliability is a key requirement to keep this technology a commercially interesting option for energy production. The investment return on PV generation system depends, among other factors, on the peculiarities of the system on efficiency reduction caused by environmental action. Technical standards suggest laboratory tests for the qualification and a better understanding on module degradation behavior. Nevertheless, some degradation modes can only be observed after years of field operation. This paper presents the main signs of degradation on crystalline silicon photovoltaic modules caused by outdoor exposure after a period of 15 years in an installation in the city of Porto Alegre, the southernmost state capital city in Brazil. The electric analysis demonstrated that the modules kept 90.5% of their initial power, with an average of degradation rate of 0.7% per year. Some techniques helped the evaluation of defects caused by exposure of the arrays for long periods of operation, such as electroluminescence imaging and I-V curve testing. The most frequent defects found were browning (encapsulant darkening) and cell encapsulant delamination, leading to the anti-reflective layer deterioration. The junction box of one of the modules was detached, allowing the entrance of moisture and resulting in the disconnection of some of the module cells. The electroluminescence technique also provided a better understanding on modes of degradation. Despite the observed evidences of degradation along these 15 years, it can be said that the system remains within the expected operation limits.