Field test results on the stability of crystalline silicon photovoltaic modules manufactured in the 1990s

The long-term stability of crystalline silicon (p-Si and c-Si) photovoltaic (PV) modules manufactured in the 1990s has been studied. Approximately 2,000 modules were investigated after nearly 10 years of exposure. About 150 of these modules were evaluated by indoor I-V measurements and analyzed to determine their degradation tendency. An average performance loss of less than 0.5%/year was estimated. We found three dominant degradation modes for crystalline Si PV modules, which represent the main problems for achieving 30-year lifetimes. Visual defects caused by delamination between the cells and the potent EVA were observed. In addition, two dominant degradation modes without visual features were found by analysis of the I-V data. One is accompanied by a decrease in the fill factor (FF), the other is accompanied by a decrease in both the short circuit current (I/sub sc/) and the open circuit voltage (V/sub oc/). The degradation in FF was analyzed.