Hail impact

Hail is ice that forms in convective thunderstorms and falls when its weight overcomes the storm updraft. It hits modules as a sudden mechanical impact. Hail impacts break module glass and crack cells. Cracked cells without broken glass are called invisible damage. Qualification testing only requires modules to survive 25 mm ice balls. Reported damage comes from larger hail, and damage is typically expected once hailstones are bigger than 4 cm. Hail damage is random and can be concentrated in certain blocks or subarrays. Sometimes only the rear glass breaks, which makes inspection harder. Aerial photo and IR surveys find broken glass. EL imaging is the best way to confirm cell cracks, which show a distinctive hail pattern. Cracks may not appear in IR images or IV curves until several years of aging. Watch modules closely in the years after a hail event. To reduce risk, choose modules suited to the site's hail risk. Thicker, heat-strengthened or tempered front glass resists impacts better, and thin glass/glass modules resist less. On single-axis trackers, a hail stow triggered early by weather alerts reduces damage. The steeper tilt shrinks the exposed glass area and turns more hits into glancing blows.

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• sentence 5: support check: partial - Aerial photographic and IR surveys identify broken glass and EL is best for invisible cracks with hail-distinctive patterns, but the passage says surveys identify visible and degraded modules, not specifically that IR finds broken glass, and EL is said to be 'best diagnosed' rather than 'confirm'. -->