Modeling Outdoor Service Lifetime Prediction of PV Modules: Effects of Combined Climatic Stressors on PV Module Power Degradation

Photovoltaic modules are exposed to a variety of climatic loads during outdoor operation. Over time, these loads trigger a number of degradation modes within the modules leading to performance loss. This paper quantifies the impact of combined climatic loads on the module's maximum power output using a mathematical approach. Three degradation precursor reactions, namely, hydrolysis, photodegradation, and thermomechanical degradation, are assumed to be necessary for service lifetime prediction. For each reaction, an empirical kinetics model is proposed and validated with indoor test measurements. A generalized model to quantify the effects of combined climatic loads is proposed. The generalized model is calibrated and validated using outdoor test measurements. The model is then applied to predict the annual degradation rates and a 20% performance loss of three identical monocrystalline modules installed in three benchmarking climates: maritime (Gran Canaria, Spain), arid (Negev, Israel), and alpine (Zugspitze, Germany) using real monitored meteorological data. A degradation of 0.74%/year corresponding to 21.4 years operation time was predicted as the highest for an arid environment, compared with 0.50%/year and 0.3%/year degradation for maritime and alpine environments, respectively. The proposed models will find applications in outdoor predictions as well as in the combined stress accelerated tests to develop test designs.