A
solar thermal collector collects
heat by
absorbing sunlight. A collector is a device for capturing solar radiation. Solar radiation is energy in the form of
electromagnetic radiation from the
infrared (long) to the
ultraviolet (short) wavelengths. The quantity of solar energy striking the Earth's surface (
solar constant) averages about 1,000 watts per square meter under clear skies, depending upon weather conditions, location and orientation.