PV Fundamentals

Direct conversion of light (photons) into electricity, generating a DC voltage in a semiconductor when photons free electrons across a p-n junction.

Irradiance is instantaneous power per unit area (W/m²); irradiation (insolation) is energy accumulated over time (Wh/m² or kWh/m²).

1000 W/m² irradiance, 25 °C cell temperature, and air mass 1.5 (AM1.5). Module nameplate ratings are given at STC.

The number of hours per day during which irradiance would average 1000 W/m²; equals daily irradiation in kWh/m² divided by 1 kW/m².

The relative path length of sunlight through the atmosphere compared to straight overhead; AM1.5 is the standard for terrestrial PV ratings.

Direct (beam) radiation comes straight from the sun, diffuse radiation is scattered by the atmosphere, and reflected (albedo) radiation bounces off surfaces. Global = direct + diffuse + reflected.