Glossary of Solar Radiation Resource Terms

Other relevant glossaries


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Electromagnetic Radiation - the energy produced by an oscillating electrical (and magnetic) field, transmitted by photons. See Electromagnetic Spectrum.


Electromagnetic Spectrum - the entire energy range of electromagnetic radiation specified by frequency, wavelength, or photon energy. The low end of the spectrum is infrared radiation (heat), and passes through the colors of visual light from red through violet, through ultraviolet radiation, x-rays, and gamma rays. Radio and television are transmitted on specific electromagnetic frequencies.


Emissivity - the ratio of the actual amount of electromagnetic radiation emitted by an object to the amount emitted by an ideal blackbody at the same temperature.


Energy - the ability to do work. Some units of energy, such as foot-pounds, measure the ability to lift a weight a certain height, units, such as calorie, indicate the ability to increase temperature, while units of radiation are usually the frequencies or wavelengths of photons.


Environment Canada - Environment Canada is the federal coordinating agency for all environmental issues pertaining to Canada.


EPRI - the Electric Power Research Institute, a research consortium of electric power companies in the United States.


Equation of Time - the annual East-West swing of the location of the Sun which can be detected by noting the position of the Sun at the same time (such as noon) each day. This motion is caused by the libration (wobble) of the Earth and can be estimated by (Spencer, J. W. (1971). Fourier series representation of the position of the Sun. Search 2 (5), 172 ) :

  ET = 229.18 x ( 0.000075 + 0.001868 cos D - 0.032077 sin D -

      0.014615 cos 2D - 0.040849 sin 2D )

where

  D = nD ( 360° / 365 )

and nD is the number of the day (e.g., Feb. 1 makes nD = 32).

NREL uses solar position algorithms that do not require the equation of time (Michalsky, J. J. (1988). The Astronomical Almanac's algorithm for approximate solar position (1950-2050). Solar Energy 40 (3), 227-235 ) .


Equinox - literally "equal night", a day when the number of hours of daylight equals the number of hours of night. The vernal equinox, usually March 21, signals the onset of Spring, while the autumnal equinox, usually September 21, signals the onset of Autumn.


Erg - a metric unit of energy (dyne-cm). A joule is 10,000,000 ergs.


ERSATZ - literally "inferior substitute", the 222 measurement sites in the 1952-1975 SOLMET/ERSATZ solar & meteorological hourly network that did not measure solar radiation. The solar radiation for these sites was modeled from cloud cover data and other information. The SOLMET/ERSATZ network has been replaced by the 1961-1990 National Solar Radiation Data Base.


ETR - extraterrestrial radiation, also known as "top-of-atmosphere" (TOA) irradiance, is the amount of global horizontal radiation that a location on Earth would receive if there was no atmosphere or clouds (i.e., in outer space). This number is used as the reference amount against which actual solar energy measurements are compared.


Evaporation - the process of converting a substance (such as water) from its liquid phase to its gaseous phase.


Extraterrestrial Radiation - abbreviated ETR, also known as "top-of-atmosphere" (TOA) irradiance, is the amount of global horizontal radiation that a location on Earth would receive if there was no atmosphere or clouds (i.e., in outer space). This number is used as the reference amount against which actual solar energy measurements are compared.


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