Degradation of photovoltaic module backsheet materials in desert climate

To improve the Photovoltaic (PV) module design for desert climates, it is important to understand the typical failure mechanism observed and the main cause of failure. This paper reports on PV backsheet degradation in desert climates. Field inspections reveal that backsheet degradation was found to be one of the most frequent PV system failures observed at the Outdoor Test Facility (OTF) in addition to hotspots, snail trails, and encapsulant yellowing. Degradation of two different polyamide (PA) and two different polyethylene terephthalate (PET) backsheets were investigated in real outdoor testing conditions. The observation of material changes due to degradation was studied using scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. Backsheet crack initiation, propagation, and chalking were monitored. We found that the embrittlement of the PA-based and PET-backsheet materials is caused by a combination of prolonged exposure to high ultraviolet (UV) radiation, high operating temperature cycling, and relative humidity resulting in cracking of the top UV-blocker layer and subsequent chemical and physical degradation of the underlying layers. The PET-2 showed only chalking powder with no backsheet cracking, which indicates an early stage of backsheet degradation. The green spot observed on the PA backsheet was found to be antlerite (greenish hydrous copper sulfate mineral Cu3 (SO4) (OH) 4) resulting from the reaction of the chalking and the solar cell interconnections.