Analysis of the Long-Term Performance Degradation of Crystalline Silicon Photovoltaic Modules in Tropical Climates

The long-Term performance degradation of five different types of commercial crystalline silicon (c-Si) photovoltaic (PV) modules (one sample for each type) in the tropics, or more specifically the tropical rainforest climate 'Af' by the Köppen climate classification (Singapore), is investigated over a period of seven years, based on outdoor I-V measurements at 10-s intervals. The degradation rates of these c-Si PV modules, based on the temperature-corrected performance ratio, range from-0.03 to-0.47%/year, which satisfy the products' performance warranty. Further analysis of the short-circuit current (I_sc), open-circuit voltage, and fill factor for these modules shows that the performance degradation is mainly attributed to the I_sc loss. The possible causes of the module performance deterioration are also discussed.