TSI

Total solar irradiance (abbreviated as TSI) is the quantity of radiant energy that comes from the Sun (total intensity of radiation) received by a 1 m² surface area at the top of the Earth's atmosphere, when it is located at one atmospheric unit (1,96.10⁸ km) from the sun and as long as the ray's trajectory is perpendicular to this surface.

Total solar irradiance varies over time (see the graphic below) by an interval between approximately 1.365 and 1.367 Watt/m².