The Azimuth Project Solar radiation (Rev #5, changes)

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Solar output

The total solar output to space is 3.84 $\times$ 1024 watts, but only a tiny fraction hits the Earth. At the top of the atmosphere, energy is received with a flux, or power density of 1366$\pm$2 W/m2, a value known as the solar constant. About 7% is ultraviolet (wavelength 0.2-0.4 $\mu$m), 41% visible light (0.4-0.7 $\mu$m) and 51% near-infra-red ($\gt$0.7$\mu$m).

Because the radiation hits the Earth at an angle, and not at all at night, the average global power density is 342 W/m2 at the top of the atmosphere. (This is one quarter of 1366 W/m2, since the area of a sphere is four times the area of its circular shadow.)

About 18% of the incoming energy is absorbed directly by ozone and water vapour. This almost entirely removes wavelengths shorter than 0.285 $\mu$m while those longer than 0.295 $\mu$m reach the ground. About 30% of incoming solar radiation is reflected directly back into space by the atmosphere, clouds, and the earth’s surface. The remaining 70% heats the surface (approximately 50% goes there) and atmosphere (approximately 20% goes there).