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Glossary of Solar Radiation Resource Terms |
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Other relevant glossaries
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Gigawatt -
1,000,000,000 (or 109) Watts. This unit
rose to public prominence in the 1985 motion picture Back to the Future in which
1.21 gigawatts of power were required for the time-travelling vehicle.
Global Horizontal Radiation -
also called Global Horizontal Irradiance; total
solar radiation; the sum of
Direct Normal Irradiance (DNI),
Diffuse Horizontal Irradiance (DHI), and
ground-reflected radiation;
however, because ground reflected radiation is usually insignificant compared to direct
and diffuse, for all practical purposes global radiation is said to be the sum of direct
and diffuse radiation only:
GHI = DHI + DNI * cos (Z)
where
Z is the solar
zenith angle.
Click Shining On (Figure 3) to see solar components
Greenhouse Effect -
the warming of the Earth by the atmosphere because of water vapor and gases such as
carbon dioxide, which absorb and emit
infrared radiation, or heat. Thus, the
high-energy photons such as light and
ultraviolet radiation
are passed through the atmosphere to the Earth, which tends to absorb them and
emit lower-energy photons which are then captured in the atmosphere and partially sent
back to Earth. As the presence of infrared absorbers rises in the atmosphere, the more
solar energy is retained at heat in the atmosphere and on the surface of the Earth.
Because glass also passes light and tends to absorb and reflect heat, this effect is
compared to that of a greenhouse.
Ground-Reflected Radiation -
the radiation from the sun which is reflected back into the atmosphere after
striking the Earth.
Click Shining On (Figure 3) to see solar components
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