[Image above] A solar panel that sustained damage during a hailstorm. If solar energy is to be a reliable source of energy for people in hail-prone regions, the resistance of photovoltaic modules to hail damage must be improved. Credit: National Renewable Energy Laboratory
By Laurel Sheppard
Hail is an expected hazard for farmers growing crops in the Great Plains region of the United States. What is not expected is the severity of the hailstorms in the last few years.
“Usually, the storms on average will fall in that 15–25% range of damage. And the last three out of the last four years, a lot of them fall into that 50–100% of damage,” says crop insurance agent Steve Skupa in a Nebraska Public Media article.
Scientists are increasingly pointing to climate change as the reason for this increased severity. In brief, hail forms when raindrops are carried upward into colder areas of the atmosphere, where they freeze. As more liquid freezes on the hailstone’s surface, the hailstone increases in size.
Warmer air holds more moisture. Combined with warming temperatures, the potential for strong updrafts to form increases—leading more water to be carried upward into the higher altitudes where it can freeze into giant hailstones.
A Scientific American article notes that too much warming may instead stymie the formation of severe hailstorms, for example, by melting hailstones before they hit the ground. But in regions such as the Great Plains and the Pampas in northern and central Argentina, the “balancing act” between various hail formation factors tips in the favor of giant hailstones.
The frequency of abnormally large hailstones is now common enough that researchers proposed a new size classification for hail in 2020. The new classification, “gargantuan,” defines hailstones that are six inches in diameter or more.
Yet even as hailstorms grow increasingly more frequent and severe, more people are moving into areas vulnerable to hail. Ironically, that puts the budding industry of solar energy—which is driven by a need to mitigate the effects of climate change—more at risk.
The impact of hail on solar panels
U.S. solar installations are expected to jump 52% to nearly 32 GW in 2023, according to the latest U.S. Solar Market Insight report released by the Solar Energy Industries Association and Wood Mackenzie. But when these installations occur in hail-prone regions, the photovoltaic (PV) panels are put at risk.
For example, in May 2019, a 178-MW solar plant in Pecos County, Texas, suffered $70 million in hail damage when more than 400,000 PV modules were damaged. More recently, in June 2023, hail significantly damaged a solar farm in Nebraska.
Hail can crack or even shatter the glass in PV modules, resulting in considerable power loss and shortening the panel’s lifespan. In some cases, the panels may have microcracks that are not obvious to the naked eye but can decrease short-circuit current and increase series resistance. This electrical hiccup can lead to the formation of hotspots and possibly even fire. Electrical separation can also occur, making a section of a cell inactive.
Protecting solar panels from hail: The role of glass thickness
If solar energy is to be a reliable source of energy for people in hail-prone regions, the resistance of PV modules to hail damage must be improved. In a recent study, researchers from Vellore Institute of Technology and Waaree Energies Ltd. in India and the City University of Hong Kong explored the role that front glass thickness plays in improved hail resistance.
For their study, they used PV modules with three different thicknesses of front glass (2.8 mm, 3.2 mm, and 4 mm). Investigations were carried out following the guidelines prescribed by the IEC 61215–2:2016 and IS 14286:2019 standards. Specifically, the size, weight, and speed of the hailstones were varied within the limits given by these standards.
- Hailstone size: 25–55 mm
- Hailstone weight: 7.5–80 gm
- Hailstone speed: 23–34 m/s.
At least three rounds of hail tests were completed on each PV module, with the thickest sample undergoing four rounds. Eleven hailstones were shot at the panels in each round.
After each round of testing, the modules were analyzed in several ways.
- Standard test condition (measures module performance)
- Insulation test (determines if there is sufficient insulation for safety)
- Wet leakage current test (often required for certification)
- Electric power output
- Electroluminescence inspection (identifies microcracks)
Results showed that while hail reduces the power output, having a thicker glass panel greatly reduces this effect. The thickest panel (4 mm) only lost 1.1% power output, in contrast to a reduction of 21.8% and 11.74% for the 2.8-mm and 3.2-mm-thick panels, respectively.
The 2.8-mm and 3.2-mm-thick panels also showed severe cracks at the point of impact, and both only survived the first impact of the 45-mm hailstone without the glass breaking. In contrast, the 4-mm-thick panel withstood impact from the 55-mm hailstone, though it did experience some microcracks, which could lead to electrical separation that makes a section of the cell inactive.
Additionally, the 4-mm-thick panel experienced the smallest reduction in wet leakage current resistance, with the value dropping by only 27.23% compared to the 2.8-mm (55.25%) and 3.2-mm (46.81%) panels.
Currently, 3.2 mm is the standard thickness for glass front panels in commercial PV modules. Based on the results of this study, this thickness is not suitable for use in hail-prone regions.
So, “for hail-prone zones, the installer should go for PV modules with a front glass thickness of 4 mm to reduce or nullify the hail damage,” the researchers write.
They acknowledge that PV modules with thicker front panels may be more costly, in which case “solar PV plant owners could decide whether to pay the additional cost or seek support from alternative options, like enhancing the insurance coverage for risk events.”
The paper, published in Renewable Energy, is “Analysis of the hail impacts on the performance of commercially available photovoltaic modules of varying front glass thickness” (DOI: 10.1016/j.renene.2022.12.061).