UO Solar Radiation Monitoring Laboratory

Home page button

Sponsors button

Site map button

Search button

Contact us button

Educational material button

SRML Glossary — "E"

Special thanks to NREL

We'd like to thank the National Renewable Energy Laboratory for making available to us their glossary, which is the basis of ours. We've edited and reformatted it, and linked it to our Web pages, and we'll continue to add our own specialized terms, illustrations, and examples. Please note that the Solar Radiation Monitoring Laboratory takes full responsibility for any inaccuracies that may occur.

Links to other glossary sections:

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z


Earth Sun Distance Factor     The distance between the earth and the sun changes by +/-1.5% from average as the earth orbits the sun. The aphelion of the orbit occurs approximately July 5 and the perihelion occurs about January 3-5. The intensity of radiation falls off by the inverse square of the distance from the source. The earth-sun distance factor is the amount that the extraterrestrial irradiance changes as the earth orbits the sun

 

 

 

Electro-
magnetic Radiation
 
  The energy produced by an oscillating electrical (and magnetic) field, transmitted by photons. See Electromagnetic Spectrum.
Electro-
magnetic 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 * ( 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 100,000 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.
   
Links to other glossary sections:

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Image map links to top of page and home page
Link to top of page Link to home page
© 2000, UO Solar Radiation Monitoring Laboratory.
Last revised: December 11, 2000.


Top of page
Site map
Educational material
Home page
Search
Sponsors
Contact us

Home page URL: solardat.uoregon.edu