From the magazine

Solar glass is not supposed to break on its own – but increasingly, it does. Since about 2021, scientists, operators, and testing labs have been seeing glass breakage on solar modules with no apparent cause, such as impacts or extreme weather. This novel failure mode has been researched to some extent, but as its scientific name suggests, “spontaneous glass breakages” still occur without warning.

Spontaneous glass breakage in glass-glass modules is the most significant reliability issue affecting modules today, according to Kiwa PVEL. “We are aware of it occurring in multiple countries, with multiple module model types, mounted to multiple tracker/racking solutions,” the lab wrote in its 2025 PV scorecard.

Tristan Erion-Lorico, vice president of sales and marketing at Kiwa PVEL, said the phenomenon is directly related to the industry’s cost-saving efforts.

“Generally speaking, we have thinned the glass, frames, and encapsulant and gone to more aggressive mounting,” ­Erion-Lorico told pv magazine. “That probably all works on paper, where the ‘perfect module’ should be reliable over the expected lifetime. However, we have eroded the safety margins, and now microscopic defects along the glass edges or surface, improperly placed silicone or frame adhesive, edge pinch, pressure from the busbars, etc., can result in module breakage.”

In the second quarter of 2025, Kiwa PVEL’s mechanical stress sequence testing recorded a historic high, with about one-third of the modules’ glass breaking. In the last quarter of the year, the results got a bit better, with about one-quarter of the samples failing. But those are still unprecedented results in decades of commercial module manufacturing.

“While our test doesn’t provide the same breakage pattern as modules suffering spontaneous breakage in the field, it is a good indication of modules’ mechanical durability,” Erion-Lorico said. “A module that breaks after static mechanical load (SML) or dynamic mechanical load (DML) tests is likely not going to last 30 years in the field.”

XXL issue

New PV modules in power plants are now larger than ever. With glass on both sides representing more than half of a module’s weight, it is not surprising that manufacturers found room to cut costs by reducing its thickness. While previous PV module generations had 3.2 mm glass, current modules usually have around 2.0 mm.

“The shift to thinner glass is driven entirely by the customer. Glass manufacturers have had to invest significantly in new equipment to cater to this changed demand,” said Pradeep Kheruka, chairman of Borosil and Borosil Renewables, an Indian multinational solar glass manufacturer. “Glass manufacturers can safely handle large, thin glass, but as modules are now larger and heavier than in the past, they require specialized installation equipment.”

Kheruka added that responsibility for glass breakage is shared among different actors. “High pressure on the front and back glass from thick soldered joints is one factor that module manufacturers must address, while issues such as improper sealant filling leading to contact between the aluminum frame and the glass, or poorly finished holes in the backsheet, can also contribute,” he explained.

Not only tempering

The US National Laboratory of the Rockies (NLR), formerly known as the National Renewable Energy Laboratory (NREL), surveyed potential causes of spontaneous glass breakage in late 2024. A range of contributing factors was identified, including reduced thermal strengthening in thinner modules, microscopic flaws at edges and surfaces, lamination-induced stresses such as edge pinch, increasing module size without corresponding changes to mounting and frames, and contact between the glass and the frame or trapped debris.

For a recent 2026 paper, NLR focused on the first cause and developed a non-destructive method to measure the glass surface directly on finished solar panels. Using this novel method, researchers collected data from numerous mass-produced panels from commercial fields, where glass has spontaneously broken. “We confirm that most 2.0 mm glass in PV modules is fully tempered, however, it remains weaker than traditional 3.2 mm glass. Our results show a clear correlation between lower surface stress and increased susceptibility to spontaneous breakage. This is an important consideration for modules that are supposed to survive in various environments for more than 30 years,” explained NLR module reliability researcher Elizabeth Palmiotti.

Palmiotti added that recent research found that although 2.0 mm glass can meet the threshold for fully tempered glass under certain glass standards, its surface compressive stress is generally lower, and the compressive layer itself is thinner.

“The thickness of this protective layer scales with general thickness. So, 2.0 mm glass inherently has a thinner layer of protection than 3.2 mm glass, meaning the same defect may break a thinner glass but not the thicker one,” she added, explaining it becomes more susceptible to defects caused by edge defects, impacts, and contact with the frame.

Looking for standards

Henry Hieslmair, principal engineer for solar at DNV, an independent assurance and risk management provider, said investors are concerned about spontaneous glass breakage. “The general observation is that as safety margins are reduced, smaller and more nuanced factors begin to play a much larger role,” he said. Farid Samara, senior engineer for solar mounting at DNV, added that when projects with thinner glass and large module formats come to his desk, he usually requires a much deeper review of the module. “Module manufacturers often argue that structural testing should be the responsibility of tracker suppliers, while tracker manufacturers make the opposite claim,” he said.

This blame game ultimately points to a deeper issue: a lack of a clear, PV-specific standard for glass.

“There currently is no PV glass specific standard, meaning glass manufacturers and module manufacturers are not reporting their glass properties in any meaningful way,” NLR’s Palmiotti noted. “Having the community align on definitions for glass surface stress would be a huge step.”

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