ASTM G173-03(2008)
(Guide)Standard Tables for Reference Solar Spectral Irradiances: Direct Normal and Hemispherical on 37° Tilted Surface
Standard Tables for Reference Solar Spectral Irradiances: Direct Normal and Hemispherical on 37° Tilted Surface
SIGNIFICANCE AND USE
Absorptance, reflectance, and transmittance of solar energy are important factors in material degradation studies, solar thermal system performance, solar photovoltaic system performance, biological studies, and solar simulation activities. These optical properties are normally functions of wavelength, which require the spectral distribution of the solar flux be known before the solar-weighted property can be calculated. To compare the relative performance of competitive products, or to compare the performance of products before and after being subjected to weathering or other exposure conditions, a reference standard solar spectral distribution is desirable.
These tables provide appropriate standard spectral irradiance distributions for determining the relative optical performance of materials, solar thermal, solar photovoltaic, and other systems. The tables may be used to evaluate components and materials for the purpose of solar simulation where either the direct or the hemispherical (that is, direct beam plus diffuse sky) spectral solar irradiance is desired. However, these tables are not intended to be used as a benchmark for ultraviolet radiation used in indoor exposure testing of materials using manufactured light sources.
The total integrated irradiances for the direct and hemispherical tilted spectra are 900.1 W·m-2 and 1000.4 W·m-2, respectively. Note that, in PV applications, no amplitude adjustments are required to match standard reporting condition irradiances of 1000 W·m-2 for hemispherical irradiance.
Previously defined global hemispherical reference spectrum (G159) for a sun-facing 37°-tilted surface served well to meet the needs of the flat plate photovoltaic research, development, and industrial community. Investigation of prevailing conditions and measured spectra shows that this global hemispherical reference spectrum can be attained in practice under a variety of conditions, and that these conditions can be interpreted as representative fo...
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 nanometer (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 ) 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 atmospheric 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 depending on time of day, geographical location, and changing atmospheric conditions. The availability of the SMARTS model (as an adjunct (ADJG173CD )to this standard) used to generate the standard spectra a...
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Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: G173 − 03 (Reapproved2008)
Standard Tables for
Reference Solar Spectral Irradiances: Direct Normal and
Hemispherical on 37° Tilted Surface
This standard is issued under the fixed designation G173; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
A wide variety of solar spectral energy distributions occur in the natural environment and are
simulatedbyartificialsourcesduringproduct,material,orcomponenttesting.Tocomparetherelative
optical performance of spectrally sensitive products a reference standard solar spectral distribution is
required. These tables replace ASTM standard G159, which has been withdrawn. The solar spectral
energydistributionpresentedinthisstandardarenotintendedasabenchmarkforultravioletradiation
in weathering exposure testing of materials. The spectra are based on version 2.9.2 of the Simple
Model of theAtmospheric RadiativeTransfer of Sunshine (SMARTS) atmospheric transmission code
(1,2). SMARTS uses empirical parameterizations of version 4.0 of the Air Force Geophysical
Laboratory (AFGL) Moderate Resolution Transmission model, MODTRAN (3,4) for some gaseous
absorption processes, and recent spectroscopic data for others. An extraterrestrial spectrum differing
onlyslightlyfromtheextraterrestrialspectruminTablesE490isusedtocalculatetheresultantspectra
(5).The hemispherical tilted spectrum is similar to the hemispherical spectrum in use since 1987, but
differs from it because: (1) the wavelength range for the current spectrum has been extended deeper
into the ultraviolet; (2) uniform wavelength intervals are now used; (3) more representative
atmospheric conditions are represented,; and (4) SMARTS Version 2.9.2 has been used as the
generating model. For the same reasons, and particularly the adoption of a remarkably less turbid
atmospherethanbefore,significantdifferencesexistinthereferencedirectnormalspectrumcompared
to previous versions of this standard.The input parameters used in conjunction with SMARTS for the
selected atmospheric conditions are tabulated. The SMARTS model and documentation are available
as an adjunct (ADJG173CD ) to this standard.
1. Scope 1705 to 4000 nm). The data tables represent reasonable
cloudless atmospheric conditions favorable for photovoltaic
1.1 These tables contain terrestrial solar spectral irradiance
(PV) energy production, as well as weathering and durability
distributions for use in terrestrial applications that require a
exposure applications.
standard reference spectral irradiance for hemispherical solar
irradiance (consisting of both direct and diffuse components)
1.2 The 37° slope of the sun-facing tilted surface was
incidentonasun-facing,37°tiltedsurfaceorthedirectnormal
chosen to represent the average latitude of the 48 contiguous
spectral irradiance. The data contained in these tables reflect
United States. A wide variety of orientations is possible for
reference spectra with uniform wavelength interval (0.5 nano-
exposed surfaces. The availability of the SMARTS model (as
meter(nm)below400nm,1nmbetween400and1700nm,an
an adjunct, ADJG173CD ) to this standard) used to generate
intermediate wavelength at 1702 nm, and 5 nm intervals from
the standard spectra allows users to evaluate differences
relative to the surface specified here.
ThesetablesareunderthejurisdictionofASTMCommitteeG03onWeathering
1.3 The air mass and atmospheric extinction parameters are
and Durability and is the direct responsibility of Subcommittee G03.09 on
chosen to provide (1) historical continuity with respect to
Radiometry.
previous standard spectra, (2) reasonable cloudless atmo-
Current edition approved June 1, 2008. Published October 2008. Originally
´1
spheric conditions favorable for photovoltaic (PV) energy
approved in 2003. Last previous edition approved in 2003 as G173–03 . DOI:
10.1520/G0173-03R08.
production or weathering and durability exposure, based upon
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
modern broadband solar radiation data, atmospheric profiles,
this standard.
and improved knowledge of aerosol optical depth profiles. In
Available from ASTM International Headquarters. Order Adjunct No.
ADJG173CD. Original adjunct produced in 2005. nature,anextremelylargerangeofatmosphericconditionscan
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
G173 − 03 (2008)
be encountered even under cloudless skies. Considerable and the foreground included in the plane’s field of view,
departure from the reference spectra may be observed depend- including both diffuse and direct solar radiation.
ing on time of day, geographical location, and changing
3.3.4.1 Discussion—For the special condition of a horizon-
atmospheric conditions. The availability of the SMARTS tal plane the hemispherical solar irradiance is properly termed
model (as an adjunct (ADJG173CD )to this standard) used to
global solar irradiance, E . Incorrectly, global tilted, or total
G
generate the standard spectra allows users to evaluate spectral global irradiance is often used to indicate hemispherical
differences relative to the spectra specified here. irradiance for a tilted plane. In case of a sun-tracking receiver,
this hemispherical irradiance is commonly called global nor-
2. Referenced Documents
mal irradiance. The adjective global should refer only to
hemispherical solar radiation on a horizontal, not a tilted,
2.1 ASTM Standards:
surface.
E490Standard Solar Constant and Zero Air Mass Solar
Spectral Irradiance Tables
3.3.5 solar irradiance, spectral E —solar irradiance E per
λ
E772Terminology of Solar Energy Conversion
unit wavelength interval at a given wavelength λ (unit: Watts
-2 -1
2.2 ASTM Adjunct: per square meter per nanometer, W·m ·nm ):
ADJG173CDSimple Model for Atmospheric Transmission
dE
E 5 (2)
of Sunshine
λ
dλ
3.3.6 spectral interval—the distance in wavelength units
3. Terminology
between adjacent spectral irradiance data points.
3.1 Definitions—Definitions of most terms used in this
3.3.7 spectral passband—the effective wavelength interval
specification may be found in Terminology E772.
within which spectral irradiance is allowed to pass, as through
3.2 Definitions:The following definition differs from that in
a filter or monochromator. The convolution integral of the
Terminology E772, representing information current as of this
spectral passband (normalized to unity at maximum) and the
revision.
incident spectral irradiance produces the effective transmitted
3.2.1 solar constant—the total solar irradiance at normal
irradiance.
incidence on a surface in free space at the earth’s mean
3.3.7.1 Discussion—Spectral passband may also be referred
distance from the sun. (1 astronomical unit, or AU = 1.496 ×
toasthespectralbandwidthofafilterordevice.Passbandsare
10 m).
usually specified as the interval between wavelengths at which
3.2.1.1 Discussion—The solar constant is now known
one half of the maximum transmission of the filter or device
-2
within about 61.5 W·m . Its current accepted values are
occurs, or as full-width at half-maximum, FWHM.
-2 -2
1366.1 W·m (Tables E490) or 1367.0 W·m (World Meteo-
3.3.8 spectral resolution—the minimum wavelength differ-
rologicalOrganization,WMO),andaresubjecttochange.Due
ence between two wavelengths that can be identified unam-
totheeccentricityoftheearth’sorbit,theactualextraterrestrial
biguously.
solar irradiance varies by 63.4% about the solar constant as
3.3.8.1 Discussion—In the context of this standard, the
the earth-sun distance varies through the year.Throughout this
-2
spectral resolution is simply the interval, ∆λ, between spectral
standard the solar constant is defined as 1367.0 W·m .
data points, or the spectral interval.
3.3 Definitions of Terms Specific to This Standard:
3.3.9 total ozone—the depth of a column of pure ozone
3.3.1 aerosol optical depth (AOD)—the wavelength-
equivalent to the total of the ozone in a vertical column from
dependent total extinction (scattering and absorption) by aero-
the ground to the top of the atmosphere (unit: atmosphere-cm
sols in the atmosphere. This optical depth (also called “optical
or atm-cm).
thickness”) is defined here at 500 nm.
3.3.1.1 Discussion—See Appendix X1. 3.3.10 total precipitable water—the depth of a column of
water (with a section of 1 cm ) equivalent to the condensed
3.3.2 air mass zero (AM0)—describes solar radiation quan-
water vapor in a vertical column from the ground to the top of
tities outside the Earth’s atmosphere at the mean Earth-Sun
the atmosphere (unit: cm or g/cm ).
distance (1 Astronomical Unit). See Tables E490.
3.3.11 wavenumber—a unit of frequency, ν, in units of
3.3.3 integrated irradiance E —spectral irradiance inte-
λ1-λ2
-1
reciprocal centimeters (symbol cm ) commonly used in place
grated over a specific wavelength interval from λ to λ ,
1 2
-2
of wavelength, λ (units of length, typically nanometers). To
measured in W·m ; mathematically:
7 -1
convert wavenumber to nanometers, λnm=1·10 / ν cm .
λ2
E 5 E dλ (1)
* See X1.2.
λ12λ2 λ
λ1
3.3.4 solar irradiance, hemispherical E —onagivenplane,
H
4. Significance and Use
the solar radiant flux received from within the 2π steradian
field of view of a tilted plane from the portion of the sky dome
4.1 Absorptance, reflectance, and transmittance of solar
energy are important factors in material degradation studies,
solar thermal system performance, solar photovoltaic system
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
performance,biologicalstudies,andsolarsimulationactivities.
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
These optical properties are normally functions of wavelength,
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. which require the spectral distribution of the solar flux be
G173 − 03 (2008)
known before the solar-weighted property can be calculated. spheric parameters. Earlier global hemispherical reference
To compare the relative performance of competitive products, spectrum may be closely, but not exactly, reproduced with
or to compare the performance of products before and after improvedspectralwavelengthrange,uniformspectralinterval,
being subjected to weathering or other exposure conditions, a andspectralresolutionequivalenttothespectralinterval,using
reference standard solar spectral distribution is desirable. inputs in X1.4.
4.2 These tables provide appropriate standard spectral irra- 4.5 Reference spectra generated by the SMARTS Version
diance distributions for determining the relative optical perfor- 2.9.2 model for the indicated conditions are shown in Fig. 1.
manceofmaterials,solarthermal,solarphotovoltaic,andother Theexactinputfilestructurerequiredtogeneratethereference
systems. The tables may be used to evaluate components and spectra is shown in Table 1.
materials for the purpose of solar simulation where either the
4.6 The availability of the adjunct (ADJG173CD ) standard
direct or the hemispherical (that is, direct beam plus diffuse
computer software for SMARTS allows one to (1) reproduce
sky) spectral solar irradiance is desired. However, these tables
the reference spectra, using the above input parameters; (2)
are not intended to be used as a benchmark for ultraviolet
compute test spectra to attempt to match measured data at a
radiation used in indoor exposure testing of materials using
specifiedFWHM,andevaluateatmosphericconditions;and(3)
manufactured light sources.
computetestspectrarepresentingspecificconditionsforanaly-
4.3 The total integrated irradiances for the direct and hemi- sis vis-à-vis any one or all of the reference spectra.
-2 -2
spherical tilted spectra are 900.1 W·m and 1000.4 W·m ,
4.7 Differences from the previous standard spectra (G159)
respectively. Note that, in PV applications, no amplitude
can be summarized as follows:
adjustments are required to match standard reporting condition
4.7.1 Extended spectral interval in the ultraviolet (down to
-2
irradiances of 1000 W·m for hemispherical irradiance.
280 nm, rather than 305 nm),
4.4 Previously defined global hemispherical reference spec- 4.7.2 Better resolution (2002 wavelengths, as compared to
trum (G159) for a sun-facing 37°-tilted surface served well to 120),
meet the needs of the flat plate photovoltaic research, 4.7.3 Constant intervals (0.5 nm below 400 nm, 1 nm
development, and industrial community. Investigation of pre- between 400 and 1700 nm, and 5 nm above),
vailing conditions and measured spectra shows that this global 4.7.4 Better definition of atmospheric scattering and gas-
hemispherical reference spectrum can be attained in practice eous absorption, with more species considered,
under a variety of conditions, and that these conditions can be 4.7.5 Better defined extraterrestrial spectrum,
interpreted as representative for many combinations of atmo- 4.7.6 More realistic spectral ground reflectance, and
FIG. 1 Plot of Direct Normal Spectral Irradiance (Solid Line) and Hemispherical Spectral Irradiance on 37° Tilted Sun-Facing Surface
(Dotted Line) Computed Using Smarts Version 2.9.2 Model With Input File in Table 1
G173 − 03 (2008)
TABLE 1 SMARTS Version 2.9.2 Input File to Generate the Reference Spectra
Card ID Value Parameter/Description/Variable Name
1 ’ASTM_G 173_Std_Spectra’ Header
2 1 Pressure input mode (1 = pressure and altitude): ISPR
2a 1013.25 0. Station Pressure (mb) and altitude (km): SPR, ALT
3 1 Standard Atmosphere Profile Selection (1 = use default atmosphere): IATM1
3a ’USSA’ Default Standard Atmosphere Profile: ATM
4 1 Water Vapor Input (1 = default from Atmospheric Profile): IH2O
5 1 Ozone Calculation (1 = default from Atmospheric Profile): IO3
6 1 Pollution level mode (1 = standard conditions/no pollution): IGAS (see X1.3)
7 370 Carbon Dioxide volume mixing ratio (ppm): qCO2 (see X1.3)
7a 1 Extraterrestrial Spectrum (1 = SMARTS/Gueymard): ISPCTR
8 ’S&F_RURAL’ Aerosol Profile to Use: AEROS
9 0 Specification for aerosol optical depth/turbidity input (0 = AOD at 500 nm): ITURB
9a 0.084 Aerosol Optical Depth at 500 nm: TAU5
10 38 Far field Spectral Albedo file to use (38= Light Sandy Soil): IALBDX
10b 1 Specify tilt calculation (1 = yes): ITILT
10c 38 37 180 Albedo and Tilt variables-Albedo file to use for near field, Tilt, and Azimuth: IALBDG,
TILT, WAZIM
11 280 4000 1.0 1367.0 Wavelength Range-start, stop, mean rad
...
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