|Solar flux: at sphere of radius 1 AU (150,000,000 km), with the sun at its center, through each square meter of that sphere's surface pass 1370 watts (joules per second) of energy.|
In Carnot cycle models of surface sections of the earth, as used in human thermodynamics, ecological thermodynamics, etc., the solar flux is the measure of Qin (or Qhot) of heat input during the isothermal expansion step of the heat engine cycle, in which the working body (system) does work, in the form, predominately of pressure-volume expansion work, on the surroundings (environment).
1. Kaufmann, William J. (1994). Universe (pg. 86). W.H. Freeman and Co.
2. Sunlight – Wikipedia.