A methodology for testing, characterization and prediction of edge seal performance in PV modules

A critical failure mechanism of PV modules is the degradation in performance as a result of exposure to temperature and humidity during a typical product lifetime of over 25 years. The time to failure of a PV module attributable to moisture ingress under given field conditions involves multiple factors, including encapsulant and edge seal moisture barrier performance as well as the degradation rate of particular solar cells when exposed to moisture. The aim of the work presented here is to establish a conservative estimate of field lifetime by examining the time to breakthrough of moisture across the edge seal. Establishing a lifetime model for the edge seal independent of the characteristics of the encapsulant and solar cells facilitates the design optimization of the cells and encapsulant. For the accelerated testing of edge seal materials in standard temperature- and humidity-controlled chambers, a novel test configuration is proposed that is amenable to varying dimensions of the edge seal and is decoupled from encapsulated components. A theoretical framework that accounts for the presence of desiccants is developed for analyzing the moisture ingress performance of the edge seal. Also developed is an approach to analyzing test data from accelerated testing which incorporates temperature dependence of the material properties of the edge seal. The proposed equations and functional forms have been validated by demonstrating fits to experimental test data. These functional forms and equations allow the prediction of edge seal performance in field conditions characterized by historical meteorological data. In the specific case of the edge seal used in certain MiaSolé glass–glass modules, this work has confirmed that the edge seal can prevent moisture ingress well beyond the intended service lifetime in the most aggressive climate conditions evaluated.

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