ASTM G173-03(R2020) pdf free download

ASTM G173-03(R2020) pdf free download.Standard Tables for Reference Solar Spectral Irradiances: Direct Normal and Hemispherical on 37° Tilted Surface
1. Scope
1.1 These tables contain terrestrial solar spectral irradiance distributions for use in terrestrial applications that require a standard reference spectral irradiance for hemispherical solar irradiance (consisting of both direct and diffuse components) incident on a sun-facing, 37° tilted surface or the direct normal spectral irradiance. The data contained in these tables reflect reference spectra with uniform wavelength interval (0.5 nano- meter (nm) below 400 nm, 1 nm between 400 and 1700 nm, an intermediate wavelength at 1702 nm, and 5 nm intervals from 1705 to 4000 nm). The data tables represent reasonable cloudless atmospheric conditions favorable for photovoltaic (PV) energy production, as well as weathering and durability exposure applications. 1.2 The 37° slope of the sun-facing tilted surface was chosen to represent the average latitude of the 48 contiguous United States. A wide variety of orientations is possible for exposed surfaces. The availability of the SMARTS model (as an adjunct, ADJG173CD 3 ) to this standard) used to generate the standard spectra allows users to evaluate differences relative to the surface specified here. 1.3 The air mass and atmospheric extinction parameters are chosen to provide (1) historical continuity with respect to previous standard spectra, (2) reasonable cloudless atmo- spheric conditions favorable for photovoltaic (PV) energy production or weathering and durability exposure, based upon modern broadband solar radiation data, atmospheric profiles, and improved knowledge of aerosol optical depth profiles. In nature, an extremely large range of atmospheric conditions can be encountered even under cloudless skies. Considerable departure from the reference spectra may be observed depend- ing on time of day, geographical location, and changing atmospheric conditions. The availability of the SMARTS model (as an adjunct (ADJG173CD 3 )to this standard) used to generate the standard spectra allows users to evaluate spectral differences relative to the spectra specified here. 1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appro- priate safety, health, and environmental practices and deter- mine the applicability ofregulatory limitations prior to use. 1.5 This international standard was developed in accor- dance with internationally recognized principles on standard- ization established in the Decision on Principles for the Development of International Standards, Guides and Recom- mendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
3. Terminology
3.1 Definitions—Definitions of most terms used in this specification may be found in Terminology E772. 3.2 Definitions:The following definition differs from that in Terminology E772, representing information current as of this revision. 3.2.1 solar constant—the total solar irradiance at normal incidence on a surface in free space at the earth’s mean distance from the sun. (1 astronomical unit, or AU = 1.496 × 10 11 m). 3.2.1.1 Discussion—The solar constant is now known within about 61.5 W·m -2 . Its current accepted values are 1366.1 W·m -2 (Tables E490) or 1367.0 W·m -2 (World Meteo- rological Organization, WMO), and are subject to change. Due to the eccentricity ofthe earth’s orbit, the actual extraterrestrial solar irradiance varies by 63.4 % about the solar constant as the earth-sun distance varies through the year. Throughout this standard the solar constant is defined as 1367.0 W·m -2 . 3.3 Definitions ofTerms Specific to This Standard: 3.3.1 aerosol optical depth (AOD)—the wavelength- dependent total extinction (scattering and absorption) by aero- sols in the atmosphere. This optical depth (also called “optical thickness”) is defined here at 500 nm. 3.3.1.1 Discussion—See Appendix X1.3.3.4 solar irradiance, hemispherical E H —on a given plane, the solar radiant flux received from within the 2π steradian field of view of a tilted plane from the portion of the sky dome and the foreground included in the plane’s field of view, including both diffuse and direct solar radiation. 3.3.4.1 Discussion—For the special condition of a horizon- tal plane the hemispherical solar irradiance is properly termed global solar irradiance, E G . Incorrectly, global tilted, or total global irradiance is often used to indicate hemispherical irradiance for a tilted plane. In case of a sun-tracking receiver, this hemispherical irradiance is commonly called global nor- mal irradiance. The adjective global should refer only to hemispherical solar radiation on a horizontal, not a tilted, surface.