Comparison of breakdown-voltage of contemporary and veteran photovoltaic backsheets

The ability of designated electrically insulating materials in a module, including the backsheet, to act as insulators is a key safety requirement for photovoltaic technology. The recently developed test standards IEC TS 62788-2 (including a method for direct-current breakdown-voltage) and IEC TS 62788-7-2 (for ultraviolet [UV] weathering) are examined for the first time together in this study. Thirty-six contemporary backsheets were compared using the breakdown-voltage test, before and after UV weathering, according to the recent A3 test condition. Twenty-eight backsheets, extracted from a variety of veteran photovoltaic modules, were also examined using the breakdown test. Additional characterizations were performed to interpret the breakdown-voltage results, including: surface and cross-sectional optical microscopy failure analysis; cross-sectional scanning electron (SEM) microscopy with EDS energy-dispersive X-ray spectroscopy (EDX) failure analysis; Fourier-transform infrared spectroscopy (FTIR) to identify the base resin and its chemical integrity; and differential scanning calorimetry (DSC) to identify phase transitions that might adversely affect degradation during weathering. The electrical insulation for the backsheets is discussed relative to: the industry safety requirement; features observed to facilitate the degradation of insulation; the validity of the artificial UV weathering test; the validity of the sheet geometry used for specimens in this study; and the validity of subsequent mechanical testing.