What does BP Solar say about how modules are rated?
PV modules are rated at a well-defined set of conditions known as Standard Test Conditions (STC). These conditions include the temperature of the PV cells (25°C), the intensity of radiation (1kW/square meter) and the spectral distribution of the light (air mass 1.5 or AM1.5, which is the spectrum of sunlight that has been filtered by the passing through 1.5 thickness of the earths atmosphere). These conditions correspond to noon on a clear sunny day with the sun about 60° above the horizon. The PV modules are tested in a chamber known as a flash simulator. This device contains a flash bulb and filter designed to mimic sunlight as closely as possible. It is accurate within about 3.1%. Because the flash takes place in only 50 milliseconds, the cells do not heat up appreciably. This allows the electrical characteristics of the module to be measured at a single temperature, the ambient temperature of the module/ factory. Since the temperature is usually close to 25°C, a minor adjustment co
