ASTM_G_173_-_03_2012.pdf

Designation:G17303(Reapproved 2012)Standard Tables forReference Solar Spectral Irradiances:Direct Normal andHemispherical on 37 Tilted Surface1This standard is issued under the fixed designation G173;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.INTRODUCTIONA wide variety of solar spectral energy distributions occur in the natural environment and aresimulated by artificial sources during product,material,or component testing.To compare the relativeoptical performance of spectrally sensitive products a reference standard solar spectral distribution isrequired.These tables replace ASTM standard G159,which has been withdrawn.The solar spectralenergy distribution presented in this standard are not intended as a benchmark for ultraviolet radiationin weathering exposure testing of materials.The spectra are based on version 2.9.2 of the SimpleModel of the Atmospheric Radiative Transfer of Sunshine(SMARTS)atmospheric transmission code(1,2).2SMARTS uses empirical parameterizations of version 4.0 of the Air Force GeophysicalLaboratory(AFGL)Moderate Resolution Transmission model,MODTRAN(3,4)for some gaseousabsorption processes,and recent spectroscopic data for others.An extraterrestrial spectrum differingonly slightly from the extraterrestrial spectrum in Tables E490 is used to calculate the resultant spectra(5).The hemispherical tilted spectrum is similar to the hemispherical spectrum in use since 1987,butdiffers from it because:(1)the wavelength range for the current spectrum has been extended deeperinto the ultraviolet;(2)uniform wavelength intervals are now used;(3)more representativeatmospheric conditions are represented,;and(4)SMARTS Version 2.9.2 has been used as thegenerating model.For the same reasons,and particularly the adoption of a remarkably less turbidatmosphere than before,significant differences exist in the reference direct normal spectrum comparedto previous versions of this standard.The input parameters used in conjunction with SMARTS for theselected atmospheric conditions are tabulated.The SMARTS model and documentation are availableas an adjunct(ADJG173CD3)to this standard.1.Scope1.1 These tables contain terrestrial solar spectral irradiancedistributions for use in terrestrial applications that require astandard reference spectral irradiance for hemispherical solarirradiance(consisting of both direct and diffuse components)incident on a sun-facing,37 tilted surface or the direct normalspectral irradiance.The data contained in these tables reflectreference spectra with uniform wavelength interval(0.5 nano-meter(nm)below 400 nm,1 nm between 400 and 1700 nm,anintermediate wavelength at 1702 nm,and 5 nm intervals from1705 to 4000 nm).The data tables represent reasonablecloudless atmospheric conditions favorable for photovoltaic(PV)energy production,as well as weathering and durabilityexposure applications.1.2 The 37 slope of the sun-facing tilted surface waschosen to represent the average latitude of the 48 contiguousUnited States.A wide variety of orientations is possible forexposed surfaces.The availability of the SMARTS model(asan adjunct,ADJG173CD3)to this standard)used to generatethe standard spectra allows users to evaluate differencesrelative to the surface specified here.1.3 The air mass and atmospheric extinction parameters arechosen to provide(1)historical continuity with respect toprevious standard spectra,(2)reasonable cloudless atmo-spheric conditions favorable for photovoltaic(PV)energyproduction or weathering and durability exposure,based uponmodern broadband solar radiation data,atmospheric profiles,and improved knowledge of aerosol optical depth profiles.Innature,an extremely large range of atmospheric conditions can1These tables are under the jurisdiction ofASTM Committee G03 on Weatheringand Durability and is the direct responsibility of Subcommittee G03.09 onRadiometry.Current edition approved Nov.1,2012.Published November 2012.Originallyapproved in 2003.Last previous edition approved in 2008 as G17303(2008).DOI:10.1520/G0173-03R12.2The boldface numbers in parentheses refer to the list of references at the end ofthis standard.3Available from ASTM International Headquarters.Order Adjunct No.ADJG173CD.Original adjunct produced in 2005.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 be encountered even under cloudless skies.Considerabledeparture from the reference spectra may be observed depend-ing on time of day,geographical location,and changingatmospheric conditions.The availability of the SMARTSmodel(as an adjunct(ADJG173CD3)to this standard)used togenerate the standard spectra allows users to evaluate spectraldifferences relative to the spectra specified here.2.Referenced Doc