Among the various tests called for in [4.11] is ahail test, for which hailstones 25 mm in diameter and with an impact speed of 23 m/s are normally used. Unfortunately, these parameters are not compatible in all cases with the conditions that obtain in severe hailstorms. A severe hailstorm on 23 July 2009 in the Swiss Mittelland region damaged some buildings, and hailstones measuring up to 5 cm in diameter were observed. Figures 4.114 and 4.115 display the damage that this storm inflicted on two solar modules. Although PV modules are indisputably more hail resistant than solar collectors used for heat reclamation, in areas with frequent hail, modules with greater hail resistance should be used such as devices that have been tested with hailstones that are 35 mm in diameter.
Figure 4.110 Close-up of the delamination in the Arco Solar M55 device shown in Figure 4.109