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ASTM E781-86(2009)

(Practice)

Standard Practice for Evaluating Absorptive Solar Receiver Materials When Exposed to Conditions Simulating Stagnation in Solar Collectors With Cover Plates

Standard Practice for Evaluating Absorptive Solar Receiver Materials When Exposed to Conditions Simulating Stagnation in Solar Collectors With Cover Plates

SIGNIFICANCE AND USE
Although this practice is intended for evaluating solar absorber materials and coatings used in flat-plate collectors, no single procedure can duplicate the wide range of temperatures and environmental conditions to which these materials may be exposed during in-service conditions.
This practice is intended as a screening test for absorber materials and coatings. All conditions are chosen to be representative of those encountered in solar collectors with single cover plates and with no added means of limiting the temperature during stagnation conditions.
This practice uses exposure in a simulated collector with a single cover plate. Although collectors with additional cover plates will produce higher temperatures at stagnation, this procedure is considered to provide adequate thermal testing for most applications.
Note 1—Mathematical modelling has shown that a selective absorber, single glazed flat-plate solar collector can attain absorber plate stagnation temperatures as high as 226°C (437°F) with an ambient temperature of 37.8°C (100°F) and zero wind velocity; and a double glazed one as high as 245°C (482°F) under these conditions. The same configuration solar collector with a nonselective absorber can attain absorber stagnation temperatures as high as 146°C (284°F), if single glazed, and 185°C (360°F), if double glazed, with the same environmental conditions, (see “Performance Criteria for Solar Heating and Cooling Systems in Commercial Buildings,” NBS Technical Note 1187 ).
This practice evaluates the thermal stability of absorber materials. It does not evaluate the moisture stability of absorber materials used in actual solar collectors exposed outdoors. Moisture intrusion into solar collectors is a frequent occurrence in addition to condensation caused by diurnal breathing.
This practice differentiates between the testing of spectrally selective absorbers and nonselective absorbers.
Testing Spectrally Selective Absorber Coatings and Materials—Spec...
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1.1 This practice covers a test procedure for evaluating absorptive solar receiver materials and coatings when exposed to sunlight under cover plate(s) for long durations. This practice is intended to evaluate the exposure resistance of absorber materials and coatings used in flat-plate collectors where maximum nonoperational stagnation temperatures will be approximately 200°C (392°F).
1.2 This practice shall not apply to receiver materials used in solar collectors without covers (unglazed) or in evacuated collectors, that is, those that use a vacuum to suppress convective and conductive thermal losses.
1.3 The values stated in SI units are to be regarded as the standard.
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 appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

General Information

Status
Historical
Publication Date
31-Mar-2009
ICS
27.160 - Solar energy engineering
Technical Committee
E44 - Solar, Geothermal and Other Alternative Energy Sources
Current Stage
Ref Project

Relations

Replaces
ASTM E781-86(2003) - Standard Practice for Evaluating Absorptive Solar Receiver Materials When Exposed to Conditions Simulating Stagnation in Solar Collectors With Cover Plates
Effective Date
01-Apr-2009
Referred By
ASTM E744-07(2022) - Standard Practice for Evaluating Solar Absorptive Materials for Thermal Applications
Effective Date
01-Apr-2009
Referred By
ASTM E782-95(2022) - Standard Practice for Exposure of Cover Materials for Solar Collectors to Natural Weathering Under Conditions Simulating Operational Mode
Effective Date
01-Apr-2009

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ASTM E781-86(2009) - Standard Practice for Evaluating Absorptive Solar Receiver Materials When Exposed to Conditions Simulating Stagnation in Solar Collectors With Cover PlatesASTM E781-86(2009) - Standard Practice for Evaluating Absorptive Solar Receiver Materials When Exposed to Conditions Simulating Stagnation in Solar Collectors With Cover Plates
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ASTM E781-86(2009) - Standard Practice for Evaluating Absorptive Solar Receiver Materials When Exposed to Conditions Simulating Stagnation in Solar Collectors With Cover Plates
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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: E781 − 86(Reapproved 2009)
Standard Practice for
Evaluating Absorptive Solar Receiver Materials When
Exposed to Conditions Simulating Stagnation in Solar
Collectors With Cover Plates
This standard is issued under the fixed designation E781; 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.
1. Scope Hemispherical Emittance Using Solar Simulation
E772Terminology of Solar Energy Conversion
1.1 This practice covers a test procedure for evaluating
E903Test Method for Solar Absorptance, Reflectance, and
absorptive solar receiver materials and coatings when exposed
Transmittance of Materials Using Integrating Spheres
to sunlight under cover plate(s) for long durations. This
E962
practice is intended to evaluate the exposure resistance of
absorber materials and coatings used in flat-plate collectors
3. Terminology
where maximum nonoperational stagnation temperatures will
3.1 Definitions:
be approximately 200°C (392°F).
3.1.1 See Terminology E772 for definitions.
1.2 This practice shall not apply to receiver materials used
4. Significance and Use
in solar collectors without covers (unglazed) or in evacuated
collectors, that is, those that use a vacuum to suppress
4.1 Although this practice is intended for evaluating solar
convective and conductive thermal losses.
absorbermaterialsandcoatingsusedinflat-platecollectors,no
single procedure can duplicate the wide range of temperatures
1.3 The values stated in SI units are to be regarded as the
and environmental conditions to which these materials may be
standard.
exposed during in-service conditions.
1.4 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the 4.2 This practice is intended as a screening test for absorber
materials and coatings. All conditions are chosen to be repre-
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica- sentative of those encountered in solar collectors with single
bility of regulatory limitations prior to use. cover plates and with no added means of limiting the tempera-
ture during stagnation conditions.
2. Referenced Documents
4.3 Thispracticeusesexposureinasimulatedcollectorwith
2.1 ASTM Standards:
a single cover plate.Although collectors with additional cover
B537Practice for Rating of Electroplated Panels Subjected
plates will produce higher temperatures at stagnation, this
to Atmospheric Exposure
procedureisconsideredtoprovideadequatethermaltestingfor
D1898Practice for Sampling of Plastics (Withdrawn 1998)
most applications.
E408Test Methods for Total Normal Emittance of Surfaces
NOTE 1—Mathematical modelling has shown that a selective absorber,
Using Inspection-Meter Techniques
single glazed flat-plate solar collector can attain absorber plate stagnation
E434Test Method for Calorimetric Determination of Hemi-
temperatures as high as 226°C (437°F) with an ambient temperature of
spherical Emittance and the Ratio of SolarAbsorptance to
37.8°C (100°F) and zero wind velocity; and a double glazed one as high
as 245°C (482°F) under these conditions. The same configuration solar
collector with a nonselective absorber can attain absorber stagnation
This practice is under the jurisdiction of ASTM Committee E44 on Solar,
temperatures as high as 146°C (284°F), if single glazed, and 185°C
GeothermalandOtherAlternativeEnergySourcesandisthedirectresponsibilityof
(360°F), if double glazed, with the same environmental conditions, (see
Subcommittee E44.05 on Solar Heating and Cooling Systems and Materials.
“Performance Criteria for Solar Heating and Cooling Systems in Com-
Current edition approved April 1, 2009. Published June 2009. Originally 4
mercial Buildings,” NBS Technical Note 1187 ).
approved in 1981. Last previous edition approved in 2003 as E781–86(2003). DOI:
4.4 This practice evaluates the thermal stability of absorber
10.1520/E0781-86R09.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
materials.Itdoesnotevaluatethemoisturestabilityofabsorber
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. AvailablefromU.S.GovernmentPrintingOfficeSuperintendentofDocuments,
The last approved version of this historical standard is referenced on 732 N. Capitol St., NW, Mail Stop: SDE, Washington, DC 20401, http://
www.astm.org. www.access.gpo.gov.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E781 − 86 (2009)
materials used in actual solar collectors exposed outdoors. 5.2.1.1 Type I—Tempered low-iron glass with spectral char-
Moistureintrusionintosolarcollectorsisafrequentoccurrence acteristics approximating those shown in Fig. 2.
in addition to condensation caused by diurnal breathing. 5.2.1.2 Type II—Alternativetypesofsolartransmittingglass
or plastic materials might be used for the cover plate if the
4.5 This practice differentiates between the testing of spec-
absorber is to be used under that material.
trally selective absorbers and nonselective absorbers.
5.2.2 The solar-weighted transmittance values of the cover
4.5.1 Testing Spectrally Selective Absorber Coatings and
plate test patches (5.2.3 and 5.2.4) shall remain above the
Materials—Spectrally selective solar absorptive coatings and
indicated percentage of their initial values in the following
materials require testing in a covered enclosure that contains a
wavelength regions:
selectively coated sample mounting plate, such that the enclo-
300 to 400 nm−90%
sureandmountingplatesimulatethetemperatureconditionsof
400 to 2100 nm−95%
a selective flat-plate collector exposed under stagnation condi-
5.2.3 An easily removable test patch of the cover material
tions.
measuring 50 by 50 mm (2 by 2 in.) shall be fastened onto the
4.5.2 Testing Nonselective Coatings and Materials—
innersurfaceofthetransparentcoverplateinornearonelower
Spectrally nonselective solar absorptive coatings and materials
corner.Byperiodicallymeasuringthetransmittanceofthistest
require testing in a covered enclosure that contains a nonse-
patch, an indication of the effect of any condensable effluents
lective coated sample mounting plate, such that the enclosure
on the cover material can be monitored.
and mounting plate simulate the temperature conditions of a
5.2.4 An easily removable specimen of the cover plate
covered, nonselective flat-plate collector exposed under stag-
material measuring 50 by 50 mm (2 by 2 in.) should also be
nation conditions.
mounteddirectlyonanexterioruppercornerofthecoverplate
to monitor the effects of atmospheric contamination and
5. Test Apparatus
ultravioletdegradation.Theseeffectsaregenerallymoresevere
5.1 Test Enclosure—(Fig. 1), consisting of a box that ap-
for plastic materials than for glass.
proximatesthedimensionsofatypicalflat-platesolarcollector
5.3 Seals—A seal that does not outgas at the stagnation
and shall have minimum dimensions of 0.75 by 1.5 by 0.1 m
temperature should be used to make the box weather-resistant.
(29 by 60 by 4 in.) deep. The box should be constructed of
materials that are impervious to moisture. Wood should not be
5.4 Insulation—The bottom and sides of the enclosure shall
usedforconstructionofthebox.Careshallbetakentoprevent
be insulated to have a thermal conductance of less than 0.515
2 2
water leakage at joints, seams, and seals.
W/(m ·K)(0.091 Btu/(h·ft ·°F)), that is, an R value of 11 or
5.1.1 Pre-Exposure of Test Box—Prior to use, the test
greater with materials that do not outgas at the stagnation
apparatus shall be placed in an operational environment where
temperature.
all components are allowed to equilibrate at the stagnation
5.5 Sample Mounting Plate—A metallic mounting plate
temperature for a sufficient length of time to allow for
with lateral dimensions approximately the same as the internal
outgassing of the components. This procedure may aid in
enclosure dimensions (less the thickness of the insulation on
eliminating contamination of the cover plate and the samples
the sides of the box) shall be mounted approximately 10 mm
during actual testing periods and is especially important where
(0.4 in.) above the bottom insulation by a thermally insulating
coatings employing organic components are used. If the cover
material.
plate is in place during this outgassing procedure, it shall be
5.5.1 The mounting plate used to support selective speci-
cleaned before the box is put into service in order to restore its
mens shall have a selective surface. The solar absorptance (α)
original transmittance.
oftheselectivecoatingshallbegreaterthan0.90,andtheroom
5.2 Cover Plate—The box shall have a single cover plate temperature emittance (ε) shall be less than 0.15 at all times.
that is glazed and hinged to provide access.
5.5.2 The mounting plate used to support nonselective
5.2.1 Two types of cover plate materials may be used: specimens shall be coated with any nonselective black coating
FIG. 1 Typical Cross Section of Exposure Test Apparatus
E781 − 86 (2009)
FIG. 2 Transmittance of Low-Iron Glass
that is the
...

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FIG. 1 Hot Spot Effect  
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FIG. 2 Bypass Diode Effect  
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ASTM E781-86(2023)(Practice)
Standard Practice for Evaluating Absorptive Solar Receiver Materials When Exposed to Conditions Simulating Stagnation in Solar Collectors with Cover Plates

SIGNIFICANCE AND USE
4.1 Although this practice is intended for evaluating solar absorber materials and coatings used in flat-plate collectors, no single procedure can duplicate the wide range of temperatures and environmental conditions to which these materials may be exposed during in-service conditions.  
4.2 This practice is intended as a screening test for absorber materials and coatings. All conditions are chosen to be representative of those encountered in solar collectors with single cover plates and with no added means of limiting the temperature during stagnation conditions.  
4.3 This practice uses exposure in a simulated collector with a single cover plate. Although collectors with additional cover plates will produce higher temperatures at stagnation, this procedure is considered to provide adequate thermal testing for most applications.
Note 1: Mathematical modeling has shown that a selective absorber, single glazed flat-plate solar collector can attain absorber plate stagnation temperatures as high as 226 °C (437 °F) with an ambient temperature of 37.8 °C (100 °F) and zero wind velocity, and a double glazed one as high as 245 °C (482 °F) under these conditions. The same configuration solar collector with a nonselective absorber can attain absorber stagnation temperatures as high as 146 °C (284 °F) if single glazed, and 185 °C (360 °F) if double glazed, with the same environmental conditions (see “Performance Criteria for Solar Heating and Cooling Systems in Commercial Buildings,” NBS Technical Note 1187).4  
4.4 This practice evaluates the thermal stability of absorber materials. It does not evaluate the moisture stability of absorber materials used in actual solar collectors exposed outdoors. Moisture intrusion into solar collectors is a frequent occurrence in addition to condensation caused by diurnal breathing.  
4.5 This practice differentiates between the testing of spectrally selective absorbers and nonselective absorbers.  
4.5.1 Testing Spectrally Selective...
SCOPE
1.1 This practice covers a test procedure for evaluating absorptive solar receiver materials and coatings when exposed to sunlight under cover plate(s) for long durations. This practice is intended to evaluate the exposure resistance of absorber materials and coatings used in flat-plate collectors where maximum non-operational stagnation temperatures will be approximately 200 °C (392 °F).  
1.2 This practice shall not apply to receiver materials used in solar collectors without covers (unglazed) or in evacuated collectors, that is, those that use a vacuum to suppress convective and conductive thermal losses.  
1.3 The values stated in SI units are to be regarded as the standard.  
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 appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

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ASTM
ASTM E822-92(2023)(Practice)
Standard Practice for Determining Resistance of Solar Collector Covers to Hail by Impact with Propelled Ice Balls

SIGNIFICANCE AND USE
2.1 In many geographic areas there is concern about the effect of falling hail upon solar collector covers. This practice may be used to determine the ability of flat-plate solar collector covers to withstand the impact forces of hailstones. In this practice, the ability of a solar collector cover plate to withstand hail impact is related to its tested ability to withstand impact from ice balls. The effects of the impact on the material are highly variable and dependent upon the material.  
2.2 This practice describes a standard procedure for mounting the test specimen, conducting the impact test, and reporting the effects.  
2.2.1 The procedures for mounting cover plate materials and collectors are provided to ensure that they are tested in a configuration that relates to their use in a solar collector.  
2.2.2 The corner locations of the four impacts are chosen to represent vulnerable sites on the cover plate. Impacts near corner supports are more critical than impacts elsewhere. Only a single impact is specified at each of the impact locations. For test control purposes, multiple impacts in a single location are not permitted because a subcritical impact may still cause damage that would alter the response to subsequent impacts.  
2.2.3 Resultant velocity is used to simulate the velocity that may be reached by hail accompanied by wind. The resultant velocity used in this practice is determined by vector addition of a 20 m/s (45 mph) horizontal velocity to the vertical terminal velocity.  
2.2.4 Ice balls are used in this practice to simulate hailstones because natural hailstones are not readily available to use, and ice balls closely approximate hailstones. However, no direct relationship has been established between the effect of impact of ice balls and hailstones. Hailstones are highly variable in properties such as shape, density, and frangibility.2 These properties affect factors such as the kinetic energy delivered to the cover plate, the period during ...
SCOPE
1.1 This practice covers a procedure for determining the ability of cover plates for flat-plate solar collectors to withstand impact forces of falling hail. Propelled ice balls are used to simulate falling hailstones. This practice is not intended to apply to photovoltaic cells or arrays.  
1.2 This practice defines two types of test specimens, describes methods for mounting specimens, specifies impact locations on each test specimen, provides an equation for determining the velocity of any size ice ball, provides a method for impacting the test specimens with ice balls, and specifies parameters that must be recorded and reported.  
1.3 This practice does not establish pass or fail levels. The determination of acceptable or unacceptable levels of ice-ball impact resistance is beyond the scope of this practice.  
1.4 The size of ice ball to be used in conducting this test is not specified in this practice. This practice can be used with various sizes of ice balls.  
1.5 The categories of solar collector cover plate materials to which this practice may be applied cover the range of:  
1.5.1 Brittle sheet, such as glass,  
1.5.2 Semirigid sheet, such as plastic, and  
1.5.3 Flexible membrane, such as plastic film.  
1.6 Solar collector cover materials should be tested as:  
1.6.1 Part of an assembled collector (Type 1 specimen), or  
1.6.2 Mounted on a separate test frame cover plate holder (Type 2 specimen).  
1.7 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.  
1.8 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 appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.9 This international standard was developed in accordance with internatio...

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ASTM
ASTM E881-92(2022)(Practice)
Standard Practice for Exposure of Solar Collector Cover Materials to Natural Weathering Under Conditions Simulating Stagnation Mode

SIGNIFICANCE AND USE
4.1 This practice describes a weathering box test fixture and establishes limits for the heat loss coefficients. Uniform exposure guidelines are provided to minimize the variables encountered during outdoor exposure testing.  
4.2 Since the combination of elevated temperature and solar radiation may cause some solar collector cover materials to degrade more rapidly than either exposure alone, a weathering box that elevates the temperature of the cover materials is used.  
4.3 This practice may be used to assist in the evaluation of solar collector cover materials in the stagnation mode. No single temperature or procedure can duplicate the range of temperatures and environmental conditions to which cover materials may be exposed during stagnation conditions. To assist in evaluation of solar collector cover materials in the operational mode, Practice E782 should be used. Insufficient data exist to obtain exact correlation between the behavior of materials exposed in accordance with this practice and actual in-service performance.  
4.4 This practice may also be useful in comparing the performance of different materials at one site or the performance of the same material at different sites, or both.  
4.5 Means of evaluating the effects of weathering are provided in Practice E765, and in other ASTM test methods that evaluate material properties.  
4.6 Exposures of the type described in this practice may be used to evaluate the stability of solar collector cover materials when exposed outdoors to the varied influences that comprise weather. Exposure conditions are complex and changeable. Important factors are material temperature, climate, time of year, presence of industrial pollution, etc. Generally, because it is difficult to define or measure precisely the factors influencing degradation due to weathering, results of outdoor exposure tests must be taken as indicative only. Repeated exposure testing at different seasons over a period of more than one year is req...
SCOPE
1.1 This practice covers a procedure for the exposure of solar collector cover materials to the natural weather environment at elevated temperatures that approximate stagnation conditions in solar collectors having a combined back and edge loss coefficient of less than 1.5 W/(m2·°C).  
1.2 This practice is suitable for exposure of both glass and plastic solar collector cover materials. Provisions are made for exposure of single and double cover assemblies to accommodate the need for exposure of both inner and outer solar collector cover materials.  
1.3 This practice does not apply to cover materials for evacuated collectors, photovoltaic cells, flat-plate collectors having a combined back and edge loss coefficient greater than 1.5 W/(m2·°C), or flat-plate collectors whose design incorporates means for limiting temperatures during stagnation.  
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 appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

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ASTM E782-95(2022)(Practice)
Standard Practice for Exposure of Cover Materials for Solar Collectors to Natural Weathering Under Conditions Simulating Operational Mode

SIGNIFICANCE AND USE
3.1 This practice describes a weathering box test fixture and provides uniform exposure guidelines to minimize the variables encountered during outdoor exposure testing.  
3.2 This practice may be useful in comparing the performance of different materials at one site or the performance of the same material at different sites, or both.  
3.3 Since the combination of elevated temperature and solar radiation may cause some solar collector cover materials to degrade more rapidly than either alone, a weathering box that elevates the temperature of the cover materials is used.  
3.4 This practice is intended to assist in the evaluation of solar collector cover materials in the operational, not stagnation mode. Insufficient data exist to obtain exact correlation between the behavior of materials exposed according to this practice and actual in-service performance.  
3.5 Means of evaluation of effects of weathering are provided in Practice E781, and in other ASTM test methods that evaluate material properties.  
3.6 Tests of the type described in this practice may be used to evaluate the stability of solar collector cover materials when exposed outdoors to the varied influences which comprise weather. Exposure conditions are complex and changeable. Important factors are solar radiation, temperature, moisture, time of year, presence of pollutants, etc. These factors vary from site to site and should be considered in selecting locations for exposure. Control samples must always be used in weathering tests for comparative analysis. Outdoor exposure for at least two years is required to make evident changes, such as surface degradation without the use of sophisticated analytical equipment.  
3.7 Temperature conditions attained with this box may not exactly duplicate those that occur under operational conditions with fluid flow. Dependent on environmental exposure conditions, the cover plate temperatures obtained with this box may be higher or lower than those obtained und...
SCOPE
1.1 This practice provides a procedure for the exposure of cover materials for flat-plate solar collectors to the natural weather environment at temperatures that are elevated to approximate operating conditions.  
1.2 This practice is suitable for exposure of both glass and plastic solar collector cover materials. Provisions are made for exposure of single and double cover assemblies to accommodate the need for exposure of both inner and outer solar collector cover materials.  
1.3 This practice does not apply to cover materials for evacuated collectors or photovoltaics.  
1.4 The values stated in SI units are to be regarded as the standard.  
1.5 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 appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.6 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

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