Module front glass

The front glass protects the solar cells from the outside environment while letting as much light as possible through to them. In single-glass modules the front superstrate is 3.2 mm thick. Dual-glass modules use front glass 2.0 or 2.5 mm thick with a back glass behind the cells. Thermally tempered glass has much higher surface compressive stress than the annealed or lightly hardened front glass used on thin-film CdTe modules, so non-tempered glass breaks at lower impact stress. Tempered glass shatters into small fragments, while on non-tempered glass the impact point is easy to find. Glass breakage can come from hail, stones and other impacts, bad clamping, transport, installation stress, mounting structure defects, or thermal stress from hot spots and burn marks. Broken glass often leads to broken hot cells. Glass corrosion or abrasion shows as a hazy, milky or rougher surface with changed colour and transparency. It can make the glass soil more easily, and sandstorms can abrade and weaken it. Dust on the glass lowers its transmittance and array current. Fungal biofilms can stay stuck to the glass after rain until it is cleaned on purpose. Snow left on the module surface blocks irradiance. Patchy snow causes current mismatch between strings and substrings.