Developing Methodology for Prediction of Long-Term Performance of PV Backsheets

Due to the intensified pressure from cost reduction and eco-friendly, polymeric materials that lack field history of reliability are being used as photovoltaic (PV) backsheets. Some of these materials have passed IEC61215 and other relevant qualification tests, but later have been identified with widespread failures in the field. Therefore, it's urgent to develop more reliable methodologies for accurately predicting long-term performance of PV backsheets. In this work, a reliability-based methodology has been developed based on the understanding of effect of environmental factors on degradation, the linkage between the accelerated laboratory testing and the outdoor performance and the statistical prediction modeling. The laboratory exposure of PPE films was performed on the NIST SPHERE (Simulated Photodegradation via High Energy Radiant Exposure) using a factorial design consisting of different levels of UV intensity, UV wavelength, temperature and relative humidity. The outdoor exposures were performed in Florida, Arizona and Maryland. The chemical and optical degradation of the backsheets were quantified. A physical-based statistical model for predicting the long-term performance of a commercial PPE backsheet (polyethylene terephthalate (PET)/PET/ethylene-vinyl acetate (EVA)) was developed and further validated by the outdoor exposures.