Fraunhofer CSP highlighted the impact of larger modules, thinner glass, and manufacturing changes on glass reliability
Testing just a handful of modules may not capture variations in glass strength across production batches
Statistical testing and greater industry cooperation are needed to address PV module glass failures
Solar modules have grown in size over the years, but the glass used in them has become thinner. Manufacturers have also changed module frames and mounting designs. With repeated reports of glass breakage in operating PV systems, these developments have brought mechanical reliability into focus.
At the TaiyangNews Reliable PV Module Design Conference 2026, Fraunhofer CSP Head Ralph Gottschalg discussed the issue from the perspective of glass strength and testing. His presentation looked at the different factors that can contribute to a fracture, rather than treating every case of broken glass as the result of a single cause.
In the glass industry, fracture strength is evaluated statistically, since not all glass breaks at the same stress level. Gottschalg noted that conventional IEC mechanical load tests usually involve just one or two PV modules, making it difficult to assess variations in glass strength. He also pointed to gaps in testing standards for glass thinner than 3 mm. Fraunhofer CSP tested 19 specimens of 2 mm glass using four-point bending tests. The estimated strength at the 5% quantile was 114.6 MPa, with a 95% confidence interval of 101-130 MPa.
Gottschalg also highlighted changes in module size and glass thickness. Earlier modules typically measured around 1.7 m² and used 3.2 mm thick glass. Newer modules can have an area of 2.4-2.8 m², with glass thickness ranging from 1.6 mm to 2.0 mm. The frame and mounting arrangement also influence the mechanical support available to the glass. Gottschalg noted that the combined effect of these changes needs attention.
One example he used was flying debris striking a module. The impact might be the final event that breaks the glass, but the glass may already have a lower fracture strength because of its manufacturing history. A similar impact might leave another module undamaged. This makes it difficult to draw conclusions from the impact alone.
Glass failures can also lead to lengthy discussions between manufacturers, project owners, installers, and insurers. Each party may commission its own investigation, even when the problems are similar. He says that bringing these findings together would be more useful. It would help determine which modules are affected, what precautions are needed, and whether replacements are justified.
For future module designs, he proposed using field experience to improve mechanical tests and set acceptance limits based on glass strength distributions. He also wanted manufacturers to specify mounting requirements, mechanical limits, and maintenance restrictions more clearly in their datasheets. These details matter to project owners, particularly when certain operating practices may need to change after installation.