Hail Damage Investigation in Heterojunction Silicon Photovoltaic Modules: A Real-World Case Study

Most photovoltaic (PV) modules are guaranteed for 25-30 years. However, severe climatic events, particularly hail, can lead premature damage. In this article, a residential PV system in Padova, Italy, was studied after exposure to a severe storm with hailstones up to 16 cm in diameter, which is more than two times larger than the standard size of test stones employed for module validation (7.5 cm, as per IEC 61215-2-2021). The goals are: 1) to demonstrate the relevance of hail testing beyond what currently required by the standards; 2) to demonstrate the presence of latent damage even in the absence of broken glass or of reduced performance; and 3) to discuss the associated risks. Forward bias electroluminescence (EL) and infrared (IR) radiation investigations were conducted in dark to minimize the impact of environmental influences. In the worst case, complete glass breakage results in solar cell fragmentation, which induces nonuniformity in current flow and thermal radiation, increasing losses, compromising electrical insulation, and requiring immediate replacement. In addition, dark and outdoor light current-voltage characteristics reveal significant decrease in output power, as well as increased leakage current. Remarkably, latent or invisible damage, detectable by reduced EL intensity and higher IR radiation, poses safety issues even in modules whose protective glass withstood the mechanical impact of hail. Modules with intact glass exhibit a decreased shunt resistance, with a negligible reduction in the output power with respect to a completely intact module. The results underline the necessity of inspecting the entire PV system following hailstorms, to detect any latent damages and promptly replace the damaged modules, even in the absence of glass breakage or reduction in the output power, to ensure long-term reliability.