How Are PV Modules Efficiencies are rated in the Factory?
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 or 77 F.), the intensity of radiation (1 kW/square meter), and the spectral distribution of the light (air mass 1.5 or AM 1.5, which is the spectrum of sunlight that has been filtered by passing through 1.5 thicknesses of the earth’s atmosphere). These conditions correspond to noonon a clear sunny day with the sun about 60 degrees above the horizon, the PV module directly facing the sun, and an air temperature of 0 C (32 F). In production, 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
