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 (Isc), open-circuit voltage, and fill factor for these modules shows that the performance degradation is mainly attributed to the Isc loss. The possible causes of the module performance deterioration are also discussed.