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Over the course of their lifetime, photovoltaic (PV) modules develop defects and experience performance degradation due to local environmental stresses. The defect type and rate of degradation depend upon cell technology, module construction type, module manufacturing quality control, installer workmanship, and the installed environment. Defects can be purely cosmetic, can cause performance degradation and/or can cause safety risks. Testing labs and other applied researchers typically report the type and number/distribution of defects observed in each PV plant they have investigated. Simply reporting the observed number of defect types and their percent distribution in a plant is of little use to stakeholders, unless each defect is quantitatively correlated with the corresponding degradation rate per year or safety risk. A quantitative correlation can be achieved using a risk priority number (RPN) approach to assess the risk associated with module defects and determine the appropriate action, such as panel removal for safety reasons or warranty claims for material defects. Understanding the climate dependence of degradation rates and defects is valuable for predicting power output and assessing the financial risk of future projects in specific climatic regions. In this study, the influence of climatic condition on RPN for different types of defects, including encapsulant discoloration and solder bond degradation, has been analyzed. The performance degradation rate data and visual inspection data obtained from seven crystalline-silicon PV plants, aged between 3 and 18 years, were used to calculate the RPN for each defect in three climatic conditions (hot-dry, cold-dry, and temperate). The RPN data were, in turn, used to identify the defects with the greatest effect on performance in each of the three climatic regions
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