Created by E.Ö., SUPSI, on 27.11.2025
Although hail events are relatively infrequent, they pose a significant risk when they occur, as they can directly impact the mechanical stability of PV modules, including the glass and solar cells. The likelihood and severity of hail damage depend on location, with Alpine foothills identified as higher-risk areas (see Alpine PV Stressors). Hailstones can vary considerably in both size and speed, which directly influences the impact energy delivered to PV panels. Natural hailstones may have diameters ranging from 5 mm to 100 mm, with terminal velocities between 10 m/s and 50 m/s [1]. Larger or faster-moving hailstones can crack or shatter the module glass, potentially causing electrical failures, reducing performance, and compromising long-term reliability. The severity of hail-induced damage depends on multiple factors, including hail size, shape, density, impact velocity, and module orientation [2]. Modules located in regions prone to severe hailstorms are particularly at risk, and repeated impacts over time can exacerbate initial micro-cracks, leading to more pronounced failures.
Hail-induced degradation primarily occurs through a few mechanisms. Direct impacts can fracture or shatter the front glass, which diminishes the mechanical protection of the solar cells (Figure 1). Even when the glass remains intact, the transmitted forces can cause micro-cracks in the solar cells, resulting in increased electrical resistance, performance losses, and potential hot spot formation. Additionally, severe hail impacts may deform module frames that are not designed for sufficient impact resistance, further compromising the structural integrity of the module.
Figure 1: PV module damaged by a hailstorm in the Locarno area (July 24, 2023) [1].
Mitigation Strategies
- Thicker glass: Use fully tempered thick glass to improve impact resistance and reduce the likelihood of cracking from hail.
- Glass-glass module design: Modules with glass on both front and back provide additional structural support, helping to absorb and distribute impact forces.
- Protective installation: Install modules at an angle or in configurations that deflect hail impacts, reducing direct stress on the glass surface.
- Reinforced frames and mounts: Strengthen frames and mounting systems to better absorb and distribute forces from hail impacts, minimizing deformation.
- Mechanical durability testing: Testing hail impact conditions before installation to verify module resilience under expected site-specific stresses.
- Compliance with regional standards: In areas with severe hail risk, consider modules meeting more stringent standards, such as the Swiss VKF, which requires resistance to hailstones up to 40 mm or more [3].
References
[1] V. Steinbauer, J. Kaufmann, R. Zurbriggen, T. Bühler, and M. Herwegh, “Tracing hail stone impact on external thermal insulation composite systems (ETICS) – An evaluation of standard admission impact tests by means of high-speed-camera recordings,” Int. J. Impact Eng., vol. 109, pp. 354–365, 2017, doi: 10.1016/j.ijimpeng.2017.07.016.
[2] D. Forni, M. Caccivio, D. Chudy, and E. Cadoni, «An experimental investigation of ice ball impact behaviour to improve PV panel hailstone safety,» International Journal of Impact Engineering, vol. 202, p. 105315, 2025, doi: 10.1016/j.ijimpeng.2025.105315
[3] E. Cadoni, D. Forni, M. Dotta, G. Bellenda, and M. Caccivio, “Advanced characterisation of photovoltaics for hail resistance,” Mater. Lett., vol. 354, p. 135371, 2024, doi: 10.1016/j.matlet.2023.135371.
