Spectral Effects

Sunlight is composed of many different wavelengths, and their distribution constitutes the solar spectrum. Under Standard Test Conditions (STC), this spectrum is fixed (AM1.5G). Under real outdoor conditions, however, the spectrum varies throughout the day and year, depending on factors such as the Sun’s position, atmospheric humidity, and cloud cover.

Photovoltaic modules do not respond equally to all wavelengths. Certain wavelengths generate electricity more efficiently than others; thus, when the spectrum changes, the electricity output by the module also varies. These variations are generally small compared to the effects of irradiance or temperature, but they nevertheless influence energy production—particularly under conditions of low sun angle, high diffuse component, or marked seasonal variations.