Multi-stress durability testing to better predict outdoor performance of PV modules

Abstract

Photovoltaic modules in the outdoor environment are subjected to a wide range of stresses which can operate simultaneously and sequentially and can vary based on climate and installation.These stresses can include temperature, temperature variation, localized heating, humidity, moisture (rain, snow, humidity, condensation), weathering, mechanical stress, abrasion and internal electric fields. These multiple stress make prediction of service lifetime challenging. Frequently resistance to an extended single stress is improperly used to assess durability. We have used sequential and simultaneous multistress exposure of materials and modules to better predict the synergistic effects of these stresses on module performance. We have also assessed the change in component materials properties to better understand performance changes. Finally, we compare these results to inspection of modules from the field to validate the test methods proposed.

Motivation, benefits, and challenges for new photovoltaic material & module developments

“…Backsheets based on PVF and PET have been used for more than 30 years and have served as good standards for performance and durability in PV applications. Field studies have confirmed its outstanding long-term performance relative to other backsheet materials [106,129].…”

“…Several 'extended testing' procedures were proposed from different test houses, manufacturers, reinsurance and engineering companies, see e.g. [105], DuPont [106] and the Product qualification Program of PVEL [107] having both eight parallel test sequences, but different ones.…”

“…Field-specific errors have also been observed for other materials. Gambogi et al have observed PVDF cracks in backsheets of modules in the field-a failure pattern that could be replicated by sequential interior exposures [106,149]. These cracking effects have been associated with a change in phase of the PVDF material.…”

“…MAST starts with exposure of the samples to 1000 h of damp heat, and 1000 h in a UVA chamber followed by sequence of 200 thermal cycles and additional 1000 h in the UVA chamber [162]. This test sequence mimics the amount of approximately 25 years' worth of humidity, UV and mechanical stress seen in the field [106,155,158,162]. Using this approach cracking of PA and PVDF based backsheets was successfully replicated.…”

Development of high-efficiency bifacial photovoltaic module and simulation method for its power generation

“…In addition, glass is difficult to deteriorate due to UV and hygrothermal stress unlike normal PET. 9,10) And A lower water vapor transmission rate than the normal type backsheet prevent acetic acid from producing. 11,12) Figures 5-7 show the result of a 5400 Pa mechanical load test after 3000 h of damp heat test (DH), a thermal cycle test (TC) of 600 cycles, and combination test repeated three times that involved a thermal cycle test and humidity freeze test (HF).…”