ASTM E905-87(2021)
(Test Method)Standard Test Method for Determining Thermal Performance of Tracking Concentrating Solar Collectors
Standard Test Method for Determining Thermal Performance of Tracking Concentrating Solar Collectors
SIGNIFICANCE AND USE
5.1 This test method is intended to provide test data essential to the prediction of the thermal performance of a collector in a specific system application in a specific location. In addition to the collector test data, such prediction requires validated collector and system performance simulation models that are not provided by this test method. The results of this test method therefore do not by themselves constitute a rating of the collector under test. Furthermore, it is not the intent of this test method to determine collector efficiency for comparison purposes since efficiency should be determined for particular applications.
5.2 This test method relates collector thermal performance to the direct solar irradiance as measured with a pyrheliometer with an angular field of view between 5 and 6°. The preponderance of existing solar radiation data was collected with instruments of this type, and therefore is directly applicable to prediction of collector and system performance.
5.3 This test method provides experimental procedures and calculation procedures to determine the following clear sky, quasi-steady state values for the solar collector:
5.3.1 Response time,
5.3.2 Incident angle modifiers,
5.3.3 Near-normal incidence angular range, and
5.3.4 Rate of heat gain at near-normal incidence angles.
Note 4: Not all of these values are determined for all collectors. Table 1 outlines the tests required for each collector type and tracking arrangement.
× = Required.
⊗ = Required but method may not be practicable for point focus collectors—Safety precautions and technical precautions must be followed because of potential damage to equipment and subsequent damage to personnel due to high levels of solar irradiance on the receiver support structure.
** = Optional test that may provide useful information on the effect of the accuracy of the manufacturer's tracking equipment on thermal performance.
5.4 This test method may be used to evaluate...
SCOPE
1.1 This test method covers the determination of thermal performance of tracking concentrating solar collectors that heat fluids for use in thermal systems.
1.2 This test method applies to one- or two-axis tracking reflecting concentrating collectors in which the fluid enters the collector through a single inlet and leaves the collector through a single outlet, and to those collectors where a single inlet and outlet can be effectively provided, such as into parallel inlets and outlets of multiple collector modules.
1.3 This test method is intended for those collectors whose design is such that the effects of diffuse irradiance on performance is negligible and whose performance can be characterized in terms of direct irradiance.
Note 1: For purposes of clarification, this method shall apply to collectors with a geometric concentration ratio of seven or greater.
1.4 The collector may be tested either as a thermal collection subsystem where the effects of tracking errors have been essentially removed from the thermal performance, or as a system with the manufacturer-supplied tracking mechanism.
1.4.1 The tests appear as follows:
Section
Linear Single-Axis Tracking Collectors Tested as
Thermal Collection Subsystems
11–13
System Testing of Linear Single-Axis Tracking Collectors
14–16
Linear Two-Axis Tracking and Point Focus Collectors
Tested as Thermal Collection Subsystems
17–19
System Testing of Point Focus and Linear Two-Axis
Tracking Collectors
20–22
1.5 This test method is not intended for and may not be applicable to phase-change or thermosyphon collectors, to any collector under operating conditions where phase-change occurs, to fixed mirror-tracking receiver collectors, or to central receivers.
1.6 This test method is for outdoor testing only, under clear sky, quasi-steady state conditions.
1.7 Selection and preparation of the collector (sampling m...
General Information
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Standards Content (Sample)
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.
Designation: E905 − 87 (Reapproved 2021)
Standard Test Method for
Determining Thermal Performance of Tracking
Concentrating Solar Collectors
This standard is issued under the fixed designation E905; 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 1.7 Selection and preparation of the collector (sampling
method, preconditioning, mounting, alignment, etc.), calcula-
1.1 This test method covers the determination of thermal
tion of efficiency, and manipulation of the data generated
performanceoftrackingconcentratingsolarcollectorsthatheat
through use of this standard for rating purposes are beyond the
fluids for use in thermal systems.
scope of this test method, and are expected to be covered
1.2 This test method applies to one- or two-axis tracking
elsewhere.
reflecting concentrating collectors in which the fluid enters the
1.8 This test method does not provide a means of determin-
collectorthroughasingleinletandleavesthecollectorthrough
ing the durability or the reliability of any collector or compo-
a single outlet, and to those collectors where a single inlet and
nent.
outlet can be effectively provided, such as into parallel inlets
and outlets of multiple collector modules. 1.9 The values stated in SI units are to be regarded as
standard. The values given in parentheses after SI units are
1.3 This test method is intended for those collectors whose
provided for information only and are not considered standard.
design is such that the effects of diffuse irradiance on perfor-
1.10 This standard does not purport to address all of the
mance is negligible and whose performance can be character-
safety concerns, if any, associated with its use. It is the
ized in terms of direct irradiance.
responsibility of the user of this standard to establish appro-
NOTE 1—For purposes of clarification, this method shall apply to
priate safety, health, and environmental practices and deter-
collectors with a geometric concentration ratio of seven or greater.
mine the applicability of regulatory limitations prior to use.
1.4 The collector may be tested either as a thermal collec-
1.11 This international standard was developed in accor-
tion subsystem where the effects of tracking errors have been
dance with internationally recognized principles on standard-
essentially removed from the thermal performance, or as a
ization established in the Decision on Principles for the
system with the manufacturer-supplied tracking mechanism.
Development of International Standards, Guides and Recom-
1.4.1 The tests appear as follows:
mendations issued by the World Trade Organization Technical
Section
Barriers to Trade (TBT) Committee.
Linear Single-Axis Tracking Collectors Tested as
Thermal Collection Subsystems 11–13
System Testing of Linear Single-Axis Tracking Collectors 14–16 2. Referenced Documents
Linear Two-Axis Tracking and Point Focus Collectors
2.1 ASTM Standards:
Tested as Thermal Collection Subsystems 17–19
System Testing of Point Focus and Linear Two-Axis
E772Terminology of Solar Energy Conversion
Tracking Collectors 20–22
2.2 Other Standard:
1.5 This test method is not intended for and may not be
ASHRAE 93-86,Methods of Testing to Determine the
applicable to phase-change or thermosyphon collectors, to any
Thermal Performance of Solar Collectors
collector under operating conditions where phase-change
occurs, to fixed mirror-tracking receiver collectors, or to NOTE 2—Where conflicts exist between the content of these references
and this test method, this test method takes precedence.
central receivers.
NOTE3—Thedefinitionsanddescriptionsoftermsbelowsupersedeany
1.6 This test method is for outdoor testing only, under clear
conflicting definitions included in Terminology E772.
sky, quasi-steady state conditions.
1 2
This test method is under the jurisdiction of ASTM Committee E44 on Solar, For referenced ASTM standards, visit the ASTM website, www.astm.org, or
GeothermalandOtherAlternativeEnergySourcesandisthedirectresponsibilityof contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Subcommittee E44.20 on Optical Materials for Solar Applications. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved Jan. 1, 2021. Published January 2021. Originally the ASTM website.
approved in 1982. Last previous edition approved in 2013 as E905 – 87 (2013). Available from the American Society of Heating, Refrigerating, and Air
DOI: 10.1520/E0905-87R21. Conditioning Engineers, Inc., 1791 Tullie Circle, N.E. Atlanta, GA 30329.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E905 − 87 (2021)
3. Terminology 3.2.8 rate of heat gain, n—the rate at which incident solar
energy is absorbed by the heat transfer fluid, defined math-
3.1 Definitions:
ematically by:
3.1.1 area, absorber, n—total uninsulated heat transfer sur-
˙
face area of the absorber, including unilluminated as well as Q 5 m˙C ∆t (1)
p a
illuminated portions. (E772)
3.2.9 response time, n—time required for ∆ t to decline to
a
10%ofitsinitialvalueafterthecollectoriscompletelyshaded
3.1.2 collector, point focus, n—concentrating collector that
from the sun’s rays; or the time required for ∆t to increase to
concentrates the solar flux to a point. (E772) a
90% of its value under quasi-steady state conditions after the
3.1.3 collector, tracking, n—solar collector that moves so as
shaded collector at equilibrium is exposed to irradiation.
to follow the apparent motion of the sun during the day,
3.2.10 quasi-steady state, n—refers to that state of the
rotating about one axis or two orthogonal axes. (E772)
collector when the flow rate and inlet fluid temperature are
3.1.4 concentration ratio, geometric, n—ratio of the collec-
constant but the exit temperature changes “gradually” due to
tor aperture area to the absorber area. (E772)
the normal change in solar irradiance that occurs with time for
clear sky conditions.
3.1.5 quasi-steady state, n—solar collector test conditions
3.2.10.1 Discussion—It is defined by a set of test conditions
when the flow rate, fluid inlet temperature, collector
described in 10.1.
temperature, solar irradiance, and the ambient environment
have stabilized to such an extent that these conditions may be
3.2.11 solar irradiance, direct, in the aperture plane,
considered essentially constant (see Section 8).
n—direct solar irradiance incident on a surface parallel to the
collector aperture plane.
3.1.6 Discussion—The exit fluid temperature will, under
these conditions, also be essentially constant (see ASHRAE 3.2.12 solar irradiance, total, n—total solar radiant energy
incident upon a unit surface area (in this standard, the aperture
93-86).
of the collector) per unit time, including the direct solar
3.2 Definitions of Terms Specific to This Standard:
irradiance, diffuse sky irradiance, and the solar radiant energy
3.2.1 altazimuthal tracking, n—continual automatic posi-
reflected from the foreground.
tioningofthecollectornormaltothesun’sraysinbothaltitude
3.2.13 thermal performance, n—rate of heat flow into the
and azimuth.
absorber fluid relative to the incident solar power on the plane
3.2.2 area, aperture (of a concentrating collector),
of the aperture for the specified test conditions.
n—maximum projected area of a solar collector module
3.3 Symbols:
through which the unconcentrated solar radiant energy is
2 2
A =collector aperture area, m (ft ).
a
admitted,includinganyareaofthereflectororrefractorshaded
2 2
A =absorber area, m (ft ).
abs
by the receiver and its supports and including gaps between
2 2
A =ineffective aperture area, m (ft ).
reflector segments within a module. (E772) 1
C=geometric concentration ratio A /A , dimensionless.
a abs
3.2.3 clear-sky conditions, n—refer to a minimum level of −1 −1
C =specific heat of the heat transfer fluid,J·kg ·° C
p
−2 −2
direct normal solar irradiance of 630 W · m (200 Btu · ft · −1 −1
(Btu · lb ·°F ).
−1
h ) and a variation in both the direct and total irradiance of
E =diffuse solar irradiance incident on the collector
s,d
less than 64% during the specified times before and during −2 −1 −2
aperture, W · m (Btu · h ·ft ).
each test.
E =direct solar irradiance in the plane of the collector
s,D
−2 −1 −2
3.2.4 end effects, n—inlinearsingle-axistrackingcollectors, aperture, W · m (Btu · h ·ft ).
the loss of collected energy at the ends of the linear absorber E =directsolarirradianceintheplanenormaltothesun,
s,DN
−2 −1 −2
when the direct solar rays incident on the collector make a W·m (Btu · h ·ft ).
non-zeroanglewithrespecttoaplaneperpendiculartotheaxis E =globalsolarirradianceincidentonahorizontalplane,
s,2π
2 −1 −2
of the collector. W·m (Btu · h ·ft ).
E =totalsolarirradianceincidentonthecollectoraperture,
s,t
3.2.5 fluid loop, n—assembly of piping, thermal control,
−2 −1 −2
W·m (Btu · h ·ft ).
pumping equipment and instrumentation used for conditioning
f=focal length, m (ft).
the heat transfer fluid and circulating it through the collector
g=spacing between the effective absorbing surfaces of
during the thermal performance tests.
adjacent modules, m (ft).
3.2.6 module, n—the smallest unit that would function as a
K=incident angle modifier, dimensionless.
solar energy collection device.
L=length of reflector segment, m (ft).
l =length of receiver that is unilluminated, m (ft).
3.2.7 near-normal incidence, n—angular range from exact
r
−1
m =mass flow rate of the heat transfer fluid, kg · s (lbm ·
normal incidence within which the deviations in thermal
−1
h ).
performance measured at ambient temperature do not exceed
−1
˙
Q =net rate of energy gain in the absorber, W (Btu · h ).
62%, such that the errors caused by testing at angles other
−1
˙
than exact normal incidence cannot be distinguished from Q =rate of energy loss, W (Btu · h ).
L
errors caused by other inaccuracies (that is, instrumentation r=overhang of the receiver past the end of the reflectors, m
errors, etc.). (ft).
E905 − 87 (2021)
R(θ)=ratio of the rate of heat gain to the solar power collector aperture due to decreased projected area (cosine
incident on the aperture, dimensionless. response) and other optical losses. The first effect is accounted
s=angle which the collector aperture is tilted from the for primarily in terms of the data generated for near-normal
horizontal to the equator, and is measured in a vertical N-S incidence thermal performance for a given collector. The
plane, degrees. cosineresponseportionofthesecondeffectisaccountedforby
t =ambient air temperature, °C (°F). the determination of the solar power incident on the plane of
amb
t =temperature difference across the absorber, inlet to the aperture. The departure of the optical response of the
∆ a
outlet, °C (°F). collector from the cosine response is determined by obtaining
t =temperature difference across the absorber inlet to the incident angle modifier data.The incident angle modifier is
∆ a,i
outlet at the time of initial quasi-steady state conditions, °C important in predicting such collector characteristics as all-day
(°F). thermal performance.
t =temperature difference across the absorber inlet to
∆ a,f
outlet at the time final quasi-steady state conditions are
5. Significance and Use
reached, °C (°F).
5.1 This test method is intended to provide test data essen-
t =temperature difference across the absorber inlet to
∆ a,T
tial to the prediction of the thermal performance of a collector
outlet at time T, °C (°F).
in a specific system application in a specific location. In
t =temperature of the heat transfer fluid at the inlet to the
f,i
addition to the collector test data, such prediction requires
collector, °C (°F).
validated collector and system performance simulation models
w=width of reflector segment, m (ft).
thatarenotprovidedbythistestmethod.Theresultsofthistest
β=solar altitude angle, degrees.
method therefore do not by themselves constitute a rating of
Γ(θ )=end effect factor, dimensionless.
||
the collector under test. Furthermore, it is not the intent of this
δ=solar declination, degrees.
test method to determine collector efficiency for comparison
θ=angle of incidence between the direct solar rays and the
purposes since efficiency should be determined for particular
normal to the collector aperture, degrees.
applications.
θ , θ = angles of incidence in planes parallel and
|| '
5.2 This test method relates collector thermal performance
perpendicular, respectively, to the longitudinal axis of the
to the direct solar irradiance as measured with a pyrheliometer
collector, degrees.
with an angular field of view between 5 and 6°. The prepon-
θ =maximum angle of incidence at which all rays incident
ι
derance of existing solar radiation data was collected with
on the aperture are redirected onto the receiver of the same
instruments of this type, and therefore is directly applicable to
module, degrees.
prediction of collector and system performance.
θ' =minimum angle of incidence at which radiation re-
c
flected from one module’s aperture is intercepted by the
5.3 This test method provides experimental procedures and
receiver of an adjacent module, degrees.
calculation procedures to determine the following clear sky,
φ=solar azimuth angle measured from the south, degrees.
quasi-steady state values for the solar collector:
5.3.1 Response time,
4. Summary of Test Method
5.3.2 Incident angle modifiers,
4.1 Thermal performance is the rate of heat gain of a
5.3.3 Near-normal incidence angular range, and
collectorrelativetothesolarpowerincidentontheplaneofthe
5.3.4 Rate of heat gain at near-normal incidence angles.
collector aperture. This test method contains procedures to
NOTE 4—Not all of these values are determined for all collectors. Table
measure the thermal performance of a collector for certain
1 outlines the tests required for each collector type and tracking arrange-
well-defined test conditions. The procedures determine the
ment.
opticalresponseofthecollectorforvariousanglesofincidence
5.4 This test method may be used to evaluate the thermal
ofsolarradiation,andthethermalperformanceofthecollector
performance of either (1) a complete system, including the
at various operating temperatures for the condition of maxi-
tracking subsystems and the thermal collection subsystem, or
mum optical response. The test m
...
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