The thermomechanical reliability of backsheet structures in photovoltaic (PV) modules is one of the biggest challenges in improving PV modules reliability. Backsheet structures are composites made of layers of polymer, and their resistance against mechanical failure is highly dependent on its ability to deform plastically. During operation, the backsheet structures are laminated to the back of a PV module and exposed to a wide range of temperature and humidity level. The plastic behavior of backsheets is influenced by factors including microstructure, lamination process, and the operation conditions (e.g. relative humidity, temperature). In particular, the interactions between the polymer layers of the backsheet can impose mechanical constraint on each other and reduce plastic deformation.<br/><br/>In our study, we used a wide selection of backsheets with polymers including ethylene-vinyl acetate (EVA), polyethylene terephthalate (PET), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), ethylene tetrafluoroethylene (ETFE). We employed characterization techniques to measure relevant mechanical properties such as strength, storage and loss moduli, and tearing energy. We exposed the backsheets to damp heat (85°C/85% relative humidity) for up to 3,000 hours to investigate the effect of degradation in high temperature and humidity. In addition, we subjected the backsheets to simulated lamination conditions and studied the processing effects on tearing properties. Furthermore, we analyzed the interactions among the polymer layers and their effect on the plastic deformation behavior and tearing energy of the overall backsheet structure. We report on the role of degradation, microstructure, and mechanical constraint on thermomechanical behaviors, including stiffness, plastic deformation, and tearing energy.

Reliability of polymer backsheet structures in photovoltaic modules

253rd National Meeting (2017)

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