An experimental investigation of ice ball impact behaviour to improve PV panel hailstone safety

Hailstorms are becoming more frequent and intense due to climate change, particularly in alpine regions. PV module resistance to hail impacts is being improved, as outlined by standards like IEC 61215 (25 mm hailstones at 80 km/h) and Swiss VKF (30 mm minimum or larger). Increasing hailstone size and speed, increased safety margins are needed and it can be achieved with upgraded hail test stands. Initially, the impact of hail simulated by standards with an ice ball must be examined. Impact velocity, impact angle ($0°$ and $45°$), and duration were studied for ice balls with diameter ranging from 25 to 90 mm at speeds of 25, 50, 75 and 100 m/s and temperatures ranging from $-4$ to $-28°$C. Experimental data were analysed using dimensionless peak force and corresponding time as a function of dimensionless velocity and impact angle. Furthermore, compressive and indirect tensile strengths were studied in quasi-static and high strain rate regimes as a function of temperature. Based on these results, empirical relationships defined as functions of the impact velocity, sample size, dynamic tensile strength, density, and elastic wave speed of ice were analysed and compared with findings in the literature.