#UV Light and Solar Panels

Ultraviolet light (280 - 400 nm) is one of the most discussed and most misunderstood parts of the solar spectrum in residential PV contexts. UV makes up approximately 5% of total AM1.5G solar irradiance at Earth's surface - a small share, but one with an outsized role in long-term panel durability.

Standard silicon solar cells convert UV into electricity with relatively low efficiency. External quantum efficiency (EQE) in the UV band typically falls between 20 - 40%, compared to the 85 - 90% peak the same cells achieve at 600 - 700 nm. The physics reason is silicon's 1.12 eV bandgap: UV photons carry roughly three times the energy silicon needs, and the surplus is lost as heat through thermalization rather than converted to current.

UV also drives the slow degradation of EVA encapsulant through photo-oxidation - causing the yellowing that reduces light transmission to cells over years of exposure. Field data from high-UV climates (Sinha et al., NREL/ASU, IEEE Journal of Photovoltaics, 2020) shows encapsulant browning contributes 0.37% per year of short-circuit current loss. IEC 61215:2021 requires panels to withstand 15 kWh/m² of UV preconditioning - including 5 kWh/m² in the UVB band specifically - before any electrical performance testing.

Understanding what UV actually does to a solar panel helps separate meaningful durability considerations from marketing claims about UV-resistant coatings.

UV degradation rates have direct warranty implications. Manufacturers typically warrant less than 0.5% annual power loss - but field data from high-UV desert climates shows some panels degrading at 0.8 - 1.0% per year once encapsulant browning accelerates (NREL, 2020). A panel rated 400 W at commissioning could measure 360 W after 15 years at that rate, still within the 80% end-of-life warranty floor but meaningfully below the modeled output used in the original financial case.