- A group of researchers led by the Case Western Reserve University in the United States has developed a field survey protocol for the monitoring of PV module backsheets.
“We performed the protocol on both ground-mounted arrays and rooftop systems. It is suitable for both,” the research’s corresponding author, Laura S. Bruckman, told pv magazine. “It can be used by non-professional workforce as well.”
The protocol is intended as a low-cost standardized guide for research groups conducting surveys at PV sites. “The colorimeter that we used is relatively inexpensive and can be used to monitor the PV systems,” Bruckman said. “Commonly used hand-held Fourier transform infrared (FTIR) spectroscopy instruments are more expensive.”
The protocol utilizes the Köppen Geiger Climatic Zone (KGCZ) classification as the approximate indicator of local climates. It offers a uniform data structure and naming convention for measurements from the surveyed sites, while standardizing terminology and assets.
Eight different types of airside layer backsheet materials were considered: Poly(vinylidene fluoride) (PVDF); acrylic PVDF; poly(tetrafluoroethylene-co-hexafluoropropylene-co-vinylidene fluoride) (THV); poly(vinyl fluoride) (PVF); poly(ethylene terephthalate) (PET); fluoroethylene vinyl ether (FEVE); polyethylene naphthalate (PEN); and glass.
Through the proposed protocol, the research team analyzed PV backsheet degradation across 41 sites, with exposure times ranging from 1 to 38 years. The survey revealed that backsheet degradation has a “non-uniform” spatial and temporal distribution, with elevated edge degradation being observed for all materials and climatic zones.
“Edge modules experience the combined effect of elevated junction box temperature and the ‘Edge Effect’ and thus had a less significant difference than the center modules,” the scientists explained, noting that the anisotropy they detected in edge modules is dominated by the increased rear-side irradiance and thus has a lower variance compared to the modules in the middle of the rows.
They also explained that the degradation rates can vary within different parts of the same site, block, row, sub-row, or module depending on the local micro-climate around the material.
“We observed a non-uniform module degradation in the field, which stresses the necessity of detailed, localized analysis and a limitation of lab-accelerated aging,” they added. “Moreover, comparing the behavior of materials across various climate zones revealed inconsistent trends, suggesting that macro-climate alone may not provide sufficient weather information for comprehensive backsheet degradation analysis.”
