[Image above] Solar installers and volunteers work to construct a community solar array in Norwood, Colo. The installation of solar panels in the Great Plains region of the United States is hindered by the increasing frequency and severity of hailstorms, which puts the modules at risk of damage. Credit: U.S. Department of Energy, Flickr
Even as governments and companies around the world race to embrace solar energy to reduce their carbon emissions and help curb climate change, the increasing frequency and severity of hailstorms stymies installation in hail-prone regions that could greatly benefit from this emerging energy source, such as the Great Plains of the United States and the Pampas in northern and central Argentina.
To improve the resistance of photovoltaic modules to hail damage, thicker front glass panels is an excellent approach, as shown in a study by researchers in India and Hong Kong. Their study, which was summarized in a September 2023 CTT, found that front glass panels with the standard thickness of 3.2 mm could not withstand the impact of larger hailstones. In contrast, 4-mm-thick panels successfully reduced or nullified the hail damage.
Yet paradoxically, the recent trend in solar panel manufacturing is to make the glass thinner than before. This decision has led to an increase in spontaneous glass breakage even under normal conditions of use, as detailed in the Renewable Energy Test Center’s sixth annual PV Module Index Report.
The report, which published in June 2024, discussed the phenomenon of spontaneous glass breakage with Teresa Barnes, who manages the Photovoltaic Reliability and System Performance group at the National Renewable Energy Laboratory.
In the interview, Barnes notes that when she first started working on solar module reliability seven or eight years ago, she mostly heard about glass breakage in cases of sloppy operations or maintenance practices. Now, though, “People are seeing glass breakage for no apparent reason, often before commissioning,” she says.
While these field reports are anecdotal, they mirror reports coming from the testing labs.
“It used to be the case that modules would pass the IEC 61215 static load test with a big safety factor. Today, modules are either barely passing the base static load test or they are not passing with higher safety factors. Some new module designs are simply not passing the minimum static load test,” Barnes says.
The reason that thinner glass panels experience this failure mode more often than standard or thicker panels is because it cannot be fully tempered, Barnes explains.
“… [Any] manufacturer can temper glass that is 3 mm or thicker because it is relatively easy to get the thermal differential to build the stress profile you need,” she says. “However, it is more difficult to fully temper glass below a thickness of 3 mm. If you do not have a good temper on the glass, it is relatively easier for the glass to break.”
In addition, Barnes notes that the way people are cleaning or grinding around the edges of the glass may be causing more defects rather than fewer defects, “perhaps making this thinner glass even more sensitive to breakage.” Plus, the concurrent trend of developing ultralarge modules results in the glass bearing more of the load, “which may be bad because we have made the glass weaker,” Barnes says.
Fortunately, it appears that manufacturers are becoming more aware of the drawbacks that come with ultrathin module design. Barnes says that at this year’s PV Module Reliability Workshop, hosted annually by the National Renewable Energy Laboratory, manufacturers reported a trend back toward thicker frames and wider mounting rails to help optimize how loads are balanced out.
Ultimately, though, many of these design decisions will come down to the business model, Barnes says.
“People flipping and selling projects will always have different priorities than those who own and operate projects for the long term. If you are the person who will be caught holding the bag when a hailstorm comes, maybe you are willing to pay a little more for hail-hardened solar modules—because that decision helps make the system pencil over a long lifetime,” she says.
You can download the full 2024 PV Module Index Report at this link.