Experimental Evaluation of Energy Degradation of Photovoltaic Plants after 20+ Operation Years

In the context of the ever-growing importance of renewable energy sources, the long-term reliability assessment of PhotoVoltaic (PV) systems emerges as a critical aspect of ensuring sustainable energy production with cost-effective technologies. Nowadays, the first PV plants, installed at early 2000s, have achieved more than 20 years of operation: this reflects their predicted lifetime. Hence, evaluating their efficiency at the end of the estimated lifetime can provide important information regarding the real performance in accordance with the manufacturers' declaration. Actually, this study evaluates the performance of two PV arrays, installed at early 2000s at the university campus of Politecnico di Torino (Turin, Italy, latitude = 45 degrees N), characterised by monocrystalline silicon (mSi) modules and different inverters configurations. In particular, all the modules of the PV plants were tested under natural sunlight, and their performances were corrected to Standard Test Conditions (STC), according to the International Standards. This work estimated the measured power deviations, which were compared to the quantities predicted by the manufacturers after these operation years, and the average yearly degradation rates. The results revealed that the minimum performances guaranteed by the manufacturers of the modules (yearly degradation rate of about -0.8%) are satisfied, with only a few exceptions. Finally, a visual inspection was carried out to identify visible defects among the modules.