Standard Test Conditions

Standard Test Conditions (STC) provide a common reference for comparing the performance of photovoltaic modules. Since actual conditions vary constantly, manufacturers measure each module under a set of fixed laboratory conditions to determine its rated power. STC specifies three key parameters: an irradiance of 1000 W/m², a cell temperature of 25 °C, and a standard solar spectrum known as AM 1.5. These values represent idealized conditions that allow different modules to be evaluated on a common basis.

A module’s rated power—often referred to as Pₘₚₚ under STC—reflects the power it can deliver when tested under these specific conditions. In practice, photovoltaic modules rarely operate under STC conditions, as the intensity of solar radiation, temperature, and spectral composition vary throughout the day. Understanding STC ratings allows for the comparison of products, while acknowledging that actual performance depends on the environmental conditions encountered in the field.

STC defines not only irradiance and cell temperature, but also the spectral distribution of solar radiation, specified by the AM1.5G spectrum. This spectrum is a standardized representation of typical solar radiation under clear skies.