A solar collector is a device for extracting the energy of the sun
directly into a more usable or storable form. The energy in sunlight is in the
form of electromagnetic radiation from the infrared (long) to the ultraviolet (short) wavelengths.
The solar energy striking the earth's surface at any one time depends on weather
conditions, as well as location and orientation of the surface, but overall, it
averages about 1000 watts per square meter on a clear day with the surface
directly perpendicular to the sun's rays.

Solar radiation is radiant energy emitted by the sun from a nuclear fusion reaction that creates
electromagnetic energy. The spectrum
of solar radiation is close to that of a black body with a temperature of about 5800 K. About
half of the radiation is in the visible
short-wave part of the electromagnetic spectrum. The other
half is mostly in the near-infrared
part, with some in the ultraviolet part of the spectrum. ^[1] When
ultraviolet radiation is not absorbed by the atmosphere or other protective
coating, it can cause a change in the skin color of humans.