28-11-2012, 01:46 PM
SOLAR RADIATION
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Solar radiation
One of the basic processes behind the photovoltaic effect, on which the operation of
solar cells is based, is generation of the electron-hole pairs due to absorption of visible or
other electromagnetic radiation by a semiconductor material. Today we accept that
electromagnetic radiation can be described in terms of waves, which are characterized by
wavelength (λ ) and frequency (ν ), or in terms of discrete particles, photons, which are
characterized by energy ( hν ) expressed in electron volts. The following formulas show the
relations between these quantities.
The sun
Many people on the Earth are fascinated by the existence of the sun. There are several
examples in human history that the sun became an object of worship and people believed that
it possessed divine powers. No wonder, the sun is the source of all life on the Earth. The sun
is an intensely hot, self-luminous body of gases (mainly hydrogen and helium) at the centre of
the solar system. Figure 2.2 shows a photograph of the sun. The sun is a medium-size mainsequence
star. Here are some basic technical facts about the sun1.