Cracking propensity of UV-aged transparent backsheets for bifacial photovoltaic modules and their effects on barrier properties

Abstract

Recently, bifacial photovoltaic (PV) modules have attracted more and more interest due to their potential advantage in energy yield. Transparent polymer backsheets are crucial for protecting the bifacial modules from environmental exposure to guarantee a service lifetime of PV modules of at least 25 years. However, harsh service environments often lead to the premature degradation of polymer backsheets and the loss of their protection performance. To date, understanding on the risk of failure of transparent PV backsheet is still very limited. In this study, commercial single-layer polyethylene terephthalate (PET) samples were used as the model transparent backsheet. A sequential UV exposure-fragmentation test was then conducted to evaluate their risk of failure. Changes in its key protection performance (including oxygen and water vapor barrier properties) were characterized before and after fragmentation tests. In addition, systematic characterizations of its chemical structures, crystalline structures, and mechanical properties were conducted. Moreover, to understand the correlation between their cracking patterns and barrier properties, finite element simulation was also performed. We hope that this work can provide a scientific basis for the reliability evaluation and optimization of transparent backsheets toward more durable bifacial PV modules.