35 years of photovoltaics: Analysis of the TISO-10-kW solar plant, lessons learnt in safety and performance – Part 2

The TISO-10-kW plant, installed in 1982 in Lugano (Switzerland), is made of 288 Arco Solar modules and is the first grid-connected PV plant in Europe. In a joint publication (Part 1), we presented the results of the electrical characterization performed in 2017 after 35 years of operation. Power degradation rates were different among modules, and two groups could clearly be distinguished: Group 1, with a remarkably low mean degradation rate of 0.20%/year, and Group 2, with a mean degradation of 0.69%/year. After 35 years in a temperate climate, ~60% of the modules (~70% if considering a 3% measurement uncertainty) still exhibit a performance higher than 80% of their initial value. In this paper, we identify the mechanisms responsible for performance degradation. An extensive characterization of the modules was performed, based on a detailed visual inspection, IV curve measurements, electroluminescence and infrared imaging. When possible, we attempt to correlate module performance losses to specific failure mechanisms. We find that encapsulant aging is the main cause for the increase in the degradation rates over the last 7 years, discussed in Part 1, and we assigned the performance losses in the different groups to changes in the encapsulant used for the lamination. Potential safety threats are also investigated, by measuring the frame continuity, the functionality of the by-pass diodes, and the modules insulation. Finally, we discuss how the analysis of a 35-years-old PV module technology could serve the industry in order to target PV module lifetimes of 40+ years.