Thinner, Taller Solar Modules Prone To Breakages: NREL Report

By Chitrika Grover/ Updated On Fri, Dec 13th, 2024

Glass breakage has always been a concern, but until recently, the cause has been obvious. Several changes have caused an increased risk of glass breakage changes to solar PV module design and materials. A recent study by NREL showed that some glass always break into small pieces, in a pattern that shows a clear starting point. NREL’s report, “Glass Breakage Is Changing,” identified cases of glass in solar panels (photovoltaic [PV] modules) breaking differently and more often than it did five years ago.

Change in Thickness

Most solar PV modules in power plants now use two pieces of glass. Based on a brief comparison of glass thickness, the report found: “When modules were small or had a single sheet of glass, 3.2-mm glass was common. But now, thin-film and crystalline silicon double-glass modules almost always use glass thinner than 3.2 mm—usually just 2 mm—to reduce weight and material use. This change in thickness affects multiple risk factors for breakage…In our experience, the power plants with spontaneous glass breakage problems use modules with two pieces of glass that are thinner than 3 mm.”

NREL study found, “It’s possible to make modules with 2-mm glass that are not vulnerable to spontaneous breakage, so we have been investigating other recent changes to design, materials, and assembly. So far, they haven’t found a single factor that is enough to explain the recent cases of glass breakage. Interactions among these factors probably explain observed failures.”

Trend Toward Thinner Glass Usage In PV Modules

Solar PV module data sheets are not usually specific about the heat treatment of glass. The study suggested ASTM C1048 as one of the available standards for heat-treated glass. A common misconception is that 2-mm glass cannot be tempered, but with the right equipment, 2-mm glass can be heat-treated to make fully tempered glass or fully tempered safety glass.

Based on NREL study: “The 2-mm glass in PV modules is almost always fully tempered according to the threshold in this standard, at least 69 MPa of surface compression. We have not yet seen 2-mm fully tempered safety glass in a PV module, but remember that the surface compression required to be safety glass is higher in thinner glass. Depending on the conditions, the same piece of 2-mm fully tempered glass may break with either a low-energy or a high-energy fracture pattern. That’s because thin, fully tempered glass is sometimes strong enough to bear heavy loads before it breaks. If low-energy cracks happen in the field, accelerated tests that cause high-energy cracks probably aren’t driving the same chain of mechanisms. Even though we’ve found that 2-mm glass in PV modules is usually fully tempered per ASTM C1048, it tends to have a lower surface compression than the 3.2-mm glass used in PV modules. Even so, changes to heat treatment alone are not enough to explain recent breakage problems.”