Solar Irradiance

Solar irradiance is the power per unit area, or surface power density, received from the Sun in the form of electromagnetic radiation within the wavelength range of the measuring instrument, expressed in watts per square metre. When integrated over a period of time it becomes solar irradiation, also called solar radiation, solar exposure, solar insolation, or insolation, expressed in joules per square metre. Irradiance can be measured either in space, where it depends on distance from the Sun, the solar cycle, and longer-term variation, or at the Earth's surface, where it additionally depends on the tilt of the measuring surface, the height of the Sun above the horizon, and atmospheric conditions. Solar irradiance strongly influences plant and animal life and is used to predict the energy output of solar power installations, to calculate the heating and cooling needs of buildings, to model climate and forecast weather, and to support passive cooling and space exploration.