Physics of solar radiation
The sun radiates energy in the form of a black body with a surface temperature of 6,000C for spectrum in the wavelength range from 300 up to 470 nm. Nine percent of the energy in the ultraviolet region, and 91% of the energy is in the visible part of the spectrum (380780 nm) and infrared. Figure 7.1 shows a typical spectral distribution of the energy reaching the surface of the earth. The peak intensity of the solar energy that reaches the upper limits of the atmosphere of the earth is about 2200 W rcf2 at 480 nm, but secondary General, which is called the solar constant, 1367 W m-2, according to Iqbal's (1983). Orbit of the earth around the sun is an ellipse and the land is slightly closer to the sun in January than in July. Therefore solar radiation has a maximum value 1413 W m-2 in January and minimum 1332 W m-2 in July.
Just about 1025 W РїР“2 reaches the surface of the earth, when the sun is directly above his head in a cloudless sky. This figure, about 945 W m-2 for radiation coming directly from the sun, the rest of the solar radiation received indirectly from the sky.
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