Module Glass Impacts Hail Resiliency
kWh analytics’ fifth annual Solar Risk Assessment is out now, featuring hail risk insights from Cherif Kedir, president & CEO of RETC.
RETC
Modules made with tempered glass are approximately 2x as resilient to hail impacts as those with heat-strengthened glass
After the Midway Solar farm in West Texas suffered >$70 million in hail damage in 2019, RETC developed the industry’s first-ever commercial beyond-qualification test program for severe hail. Our Hail Durability Test (HDT) program subjects PV modules to higher kinetic energy (KE) values than basic product safety and qualification tests to investigate impact resistance at the threshold of damage, just over this threshold, and at material failure.
Comparative HDT data can help project stakeholders differentiate PV product designs based on hail resilience and better understand hail effects in real-world applications. As evidence, RETC conducted a statistical analysis of more than three years of HDT results, a dataset that includes many different module sizes, power ratings, bills of materials, and manufacturers. Specifically, we analyzed the probability of module glass breakage as a function of effective KE for two standard crystalline silicon (c-Si) PV module packages: 1.) 3.2 mm glass superstrate with a polymer substrate, and 2.) 2.0 mm glass superstrate with a 2.0 mm glass substrate.
Figure 1. Comparative freezer iceball resiliency curves for common c-Si PV module packages.
The results in Figure 1 show that PV modules with 3.2 mm tempered front glass over a polymer backsheet are approximately twice as resilient to impact as dual-glass modules with 2.0 mm heat-strengthened glass when considering the KE associated with a 50% probability of breakage. The delta between the two probability curves in Figure 1 is largely a function of glass thickness and strengthening. Whereas 3.2 mm solar glass is heat tempered, 2.0 mm solar glass is heat strengthened only to control material costs. Glass manufacturers often describe heat-tempered glass as twice as strong as heat-strengthened glass. RETC’s aggregated HDT data support this characterization.
Deploying hail-resilient PV modules in hail-prone regions is one way to mitigate a leading cause of severe weather losses. Using RETC’s HDT data to identify and select hail-resilient modules, stakeholders can significantly reduce financial risk exposure in hail-prone regions. Moreover, hail risk mitigation specialists such as VDE Americas can use these impact resiliency data to inform probabilistic financial loss estimates that also consider site-specific hailstorm severity and frequency, tracker-specific defensive stow capabilities, and operator-specific weather-alert response protocols.
