Degradation analysis of photovoltaic modules after operating for 22 years. A case study with comparisons

•PV module degradation after 22 years of operation are evaluated.•Several degradations rates are presented.•A comparison with other three studies is presented.•Severe defects have been found in the last years of operation.•Those severe defects explain the increase in degradation rates. The analysis of degradation mechanisms of photovoltaic (PV) modules is key to ensure its current lifetime and the economic feasibility of PV systems. Field operation is the best way to observe and detect all type of degradation mechanisms. This paper presents the main signs of degradation on 56 m-Si PV modules caused by outdoor exposure after a period of 22 years in Seville, Spain. Results are compared with other research works conclusions that analyse the degradation of identical PV cells and same manufacturer, after an exposure period of 12, 15 and 17 years. The analysis was conducted by visual inspection, infrared thermography, electroluminescence (EL) and electrical performance evaluation. The mean peak power degradation has been 30,9% in the 22 operation years, equivalent to 1,4% per year, which corresponds mainly to a loss in short-circuit current and, in a less degree, to loss in fill factor and open circuit voltage. The most significant defects found were severe browning, milky pattern and oxidation of the metallization grid. Those defects seem turns severe failures when exposure period is more than about 20 years and could explain the high degradation rate based on a comparison performed with other research works.