Assessing power degradation and reliability of crystalline silicon solar modules with snail trails

Reliability and lifetime of crystalline silicon solar modules are very important for photovoltaic system performance. That the snail trails occasionally occurred on photovoltaic modules has not yet been solved. In this paper, the influence of the snail trails on the power degradation was investigated in detail by six years' tracking test and the extended reliability tests. The results show that the average power degradation of the modules with snail trails is 5.90%, while the average power degradation of modules without snail trails is 5.64% over a 6-year operation period. This reveals that the snail trail has a little impact on the performance of solar modules because the snail trail only affects the transmission of the sunlight. Electroluminescence images prove that there is no relationship between snail trails and micro-cracks. To assess the impact of snail trails on the long-term reliability of solar modules, we applied extended reliability tests based on the international standard IEC 61215. The extended reliability tests of solar modules with snail trails reveal that the average power degradation is 1.77% and 0.68% after the damp heat test over 1250 h and the thermal cycling test of 500 cycles, respectively. These results suggest that the long-term reliability and durability of solar modules are not affected by snail trails. The SEM and EDS prove that Ag finger below snail trails has no change, and no corrosion could be identified. The result of XPS indicates that there exists the silver oxide in the EVA affected by snail trails. The results obtained in this paper prove that the warranty period up to 25 years for solar modules with snail trails may be realized under real conditions.