Spread of flame testing of glass - backsheet c-Si solar modules: Degradation progression and effect of module laminate materials

Recent changes to the flammability test set in UL 1703 have raised the opportunity for using glass - backsheet c-Si modules on rooftop installations. For this module type, passing the Spread of Flame test can be problematic. This paper describes work undertaken to identify the progression of degradation in the module during the course of the test, and to understand which variables in module design can affect the process. Small and full size modules were prepared with different laminate material combinations, and these were flame tested while recording video, thermocouple and thermal imaging data. From these data sets, we have developed a physical model of events leading to failure, with critical steps consisting of A) stress generation in the glass due to thermal expansion B) glass cracking, and C) escape of volatiles through glass cracks followed by ignition above the glass and into the laminate. Glass cracking has been found to be the single most important factor in spread of flame testing. Encapsulant degree of cure is also important in determining flame performance.