Solar Radiation Terminology |
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In meteorology, the radiation occuring between 0.29 µm and 4 µm is referred to as solar radiation. Radiation in the spectral range longer than µm is defined as terrestrial radiation.
Irradiance / Irradiation: Recommended Symbols and Conversion
Irradiation is the energy received per area. It is expressed in J m-2 (joule per square meter). The International Solar Energy Society recommends the symbol H. Other units are J cm-2 (joule per square centimeter) and Wh m-2 (watt-hour per square meter) though the latter should not be used as it does not belong to the standard unit system (S.I., International System). See conversion factors.
Irradiance is defined as a power received per area. It is expressed in W m-2 (watt per square meter). The S.I. (International System) recommends the symbol E.
Irradiance and irradiation values stand for area densities, i.e. no subscripts are used to indicate the surface area. All symbols refer to horizontal planes; for a tilted plane, the slope β (beta) and the plane azimuth α (alpha) are added in brackets.
Subscript 0 stands for extraterrestrial or astronomical.
Subscript h stands for hourly and subcript d for daily.
The conversion from irradiation (energy) into irradiance (power) is performed by dividing irradiation by the duration of the measurement. Reciprocally, irradiance is converted into irradiation by multiplying by a time duration.
| To convert from | Into | Divide by |
| Hourly irradiation in J/m2 (including time averaged values, e.g., monthly means, yearly means etc.) | irradiance in W/m2 | 3600 (number of seconds in an hour) |
| Hourly irradiation in Wh/m2 (including time averaged values, e.g., monthly means, yearly means etc.) | irradiance in W/m2 | 1 |
| Daily irradiation in J/m2 (including time averaged values, e.g., monthly means, yearly means etc.) | irradiance in W/m2 | 86400 = 24 * 3600 (number of seconds in a day) |
| Daily irradiation in Wh/m2 (including time averaged values, e.g., monthly means, yearly means etc.) | irradiance in W/m2 | 24 (number of hours in a day) |
To convert 10-days sums of irradiation, or monthly sums or yearly sums or similar quantities, into irradiance, convert them first to averaged values by dividing them by the duration of the observation (e.g., 10 days, 28 or 30 or 31 days, 365 or 366 days). Then use the table above.
Bibliography and copyright
Dogniaux R., Grueter J. W., Kasten F., Page J. K., Perrin de Brichambaut C., Treble F. C., Palz W., 1984. Solar Meteorology (Units and Symbols). International Journal of Solar Energy, 2, 249-255.
European Solar Radiation Atlas, 2000, includ. CD-ROM. Edited by J. Greif, K. Scharmer. Scientific advisors: R. Dogniaux, J. K. Page. Authors : L. Wald, M. Albuisson, G. Czeplak, B. Bourges, R. Aguiar, H. Lund, A. Joukoff, U. Terzenbach, H. G. Beyer, E. P. Borisenko. Published for the Commission of the European Communities by Presses de l'Ecole, Ecole des Mines de Paris, France.
13-12-2008 - Copyright L. Wald, Mines ParisTech - Armines
Last update: 2/23/12 5:20 PM