Statistical methods to determine dominant degradation modes of fielded PV modules

The purpose of this analysis is to identify the most influential degradation modes in the fielded photovoltaic (PV) modules in two different climatic conditions using statistical techniques. This study is based on the measured I-V data and visual inspection data on sampled modules in five different power plants located in Arizona (hot-dry climate) and in New York (cold-dry climate). Statistical tests such as Pearson correlation and hypothesis testing were carried out on degradation rates to identify the parameter(s) that are affected the most. The parameters were also correlated to the visual defects observed in the field to identify the most dominant defect affecting power degradation. Analysis indicates that power is affected the most in hot-dry climate due to solder bond issues leading to high series resistance increase, while encapsulant delamination defect is being predominant in cold-dry climate leading to higher Isc drop and noticeable Voc loss due to triggering of bypass diodes.