ASTM E772-87(2001)
(Terminology)Standard Terminology Relating to Solar Energy Conversion
Standard Terminology Relating to Solar Energy Conversion
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Designation:E772–87 (Reapproved 2001)
Standard Terminology Relating to
Solar Energy Conversion
This standard is issued under the fixed designation E772; 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 (e) indicates an editorial change since the last revision or reapproval.
absorber—that part of a solar collector whose primary func- may be the aperture plane, the collector, or any other plane
tion is to absorb radiant energy and transform it into another of interest.)
form of energy. angle of reflection—the angle between the direction of propa-
gation of a reflected ray and the normal to the surface at the
NOTE 1—Athermal absorber usually possesses a solid surface through
point of reflection.
which energy is transmitted by thermal conduction to the transfer fluid;
angle of refraction—the angle between the direction of
however, the transfer fluid itself can be the absorber in the case of an
optically transparent container and a “black liquid”. A photovoltaic propagationofarefractedrayandthenormaltotheinterface
absorber converts part of the incident solar flux into electrical energy, and
at the point of refraction.
part to thermal energy.
aperture area—see area, aperture.
apparent solar time, apt—the hours of the day as computed
absorptance, a—theratiooftheabsorbedradiantorluminous
from the position of the sun using the equation of time. (See
flux to the incident flux. (Practice E491, for Solar Simula-
2 ASHRAE Handbook of Applications, 1982, Chapter 57.)
tion for Thermal Balance Testing of Spacecraft ). See
area, absorber—the total uninsulated heat transfer surface
radiometric properties and quantities.
area of the absorber, including unirradiated as well as
absorption—the process by which incident radiant energy is
irradiated portions.
transformed into another form of energy by interaction with
area, aperture— of a flat plate collector, (1) the maximum
matter.
projected area of a solar collector through which the uncon-
air handling unit—a device used for distributing conditioned
centrated solar radiant energy may be admitted to the
air supply to a room, space, or area.
absorber. (2) effective aperture area—the area as defined
air mass, AM—the ratio of the mass of atmosphere in the
above projected normal to the sun’s rays and corrected for
actual observer-sun path to the mass that would exist if the
2 2
any shading. Units: square metres (m ) [square feet (ft )].
observer was at sea level, at standard barometric pressure,
area, collector panel—the total area of the panel assembly
and the sun was directly overhead.
(with its containing box, if present), projected on the
NOTE 2—(Sometimes called air mass ratio.) Air mass varies with the
aperture plane.
zenith angle of the sun and the local barometric pressure, which changes
area, gross aperture— of a concentrating collector, the
with altitude. For sun zenith angle, Z, of 62° or less and local atmospheric
maximum projected area through which the unconcentrated
pressure, P, where P is standard atmospheric pressure, AM . sec Z
o
solar radiant energy is admitted, including any area of the
(P/P ).
o
reflector or refractor shaded by the receiver and its supports,
albedo—the use of the term albedo is discouraged in favor of
and including gaps between reflector segments within a
the preferred term, reflectance.
collector module.
altazimuthal mount—a supporting device that facilitates
area, gross collector—the maximum area of the complete
tracking of the sun and allows rotation about horizontal and
collector module, including integral mounting means, pro-
vertical axes. It can be used to aim equipment such as
jected on the aperture plane.
heliostats, concentrating collectors, exposure specimens, or
area, net aperture—of a concentrating collector, the maxi-
radiometers.
mum projected area through which the unconcentrated solar
angle of incidence—theanglebetweenarayandthenormalto
radiant energy is admitted, excluding any area of the
the plane on which it is incident. (The plane of incidence
reflector or refractor shaded by the receiver and its supports,
and excluding gaps between reflector segments within a
collector module.
auxiliary energy subsystem—in solar energy applications,
These definitions are under the jurisdiction ofASTM Committee E44 on Solar,
Geothermal, and OtherAlternative Energy Sources and are the direct responsibility
equipment using nonsolar energy sources to supplement or
of Subcommittee E44.09 on Photovoltaic Electric Power Conversion.
backup the output provided by a solar energy system.
Current edition approved Feb. 27, 1987. Published April 1987. Originally
beam, radiant energy—a collection of rays confined to a
published as E772–80. Last previous edition E772–84.
Annual Book of ASTM Standards, Vol 15.03. specific path.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E772
blackbody—ahypothetical“body”thatcompletelyabsorbsall Test Methods D93, for Flash Point by the Pensky-Martens
incident radiant energy, independent of wavelength and Closed Tester.
direction;thatis,onewhichneitherreflectsnortransmitsany concentrating collector— see collector, concentrating.
of the incident radiant energy. It is the emitter of electro- concentration ratio, geometric—the ratio of the collector
magnetic radiant energy which, at a given temperature, aperture area to the absorber area.
presentsthemaximumspectraldensityofradiantexitanceor concentrator—an optical device (lenses or mirrors) that, as
radiance at all wavelengths. part of a solar collector, receives the unconcentrated solar
irradiance and redirects (concentrates) it to a smaller area
NOTE 3—Norealmaterialisablackbody.Acompletelyenclosedcavity
(the receiver).
with opaque walls at a uniform temperature contains blackbody radiation.
conical, v— over a solid angle larger than an infinitesimal
Ablackbodyradiatorcanbeapproximatedinthelaboratorytoanydesired
element of solid angle and less than a hemisphere. The
degree of approximation by a furnace containing a cavity with opaque
walls at a uniform temperature, that contains an aperture through which geometryofthesolidanglemustbedescribedinthetext.For
theblackbodyradiationisobserved.Thedegreeofapproximationtoatrue
incident beams it is assumed that the radiance is constant
blackbody radiator is inversely related to the ratio of the area of the
over the entire solid angle. (See Radiometric properties
aperture to the area of the interior wall of the cavity.
and quantities)
containment material—in a solar energy system, a material
blackbody radiant energy— see radiant energy, blackbody.
that encloses the heat-transfer fluid or is in contact with the
building heat loss factor—a measure of the heat loss rate of
heat transfer or heat storage material, or both.
a building expressed in joules per degree day (or Btu per
convection—the transport of heat by fluid flow.
degree day). This factor is multiplied by the number of
convection, forced—convection caused by mechanical forces
degreedaysinagivenperiodtoestimatetheenergyrequired
such as fans and injectors.
to heat the building during that period.
convection, natural—convectionwithinafluid,duetodensity
charge capacity—see thermal capacity.
differences caused by temperature differences.
cloud cover—that portion of the sky which is covered by
cover plate, collector—a sheet of transparent (or translucent)
clouds, usually expressed in tenths of sky covered.
glazing placed above the absorber in a solar collector, to
collector, concentrating—asolarcollectorthatusesreflectors, provide thermal and environmental protection.
lenses, or other optical elements to redirect and concentrate degree day—see degree day, heating and degree day, cool-
the solar irradiance on the collector aperture onto an ab- ing.
sorber of which the surface area is smaller than the collector degree-day, cooling, (DDC or DDF, Celsius or Fahrenheit
aperture area. respectively)—one cooling degree-day is counted for each
degree that the daily mean temperature is higher than a base
collector effıciency— see efficiency, collector.
temperature; used to estimate energy requirements for air
collector, evacuated tube—a solar collector made from trans-
conditioning or refrigeration.
parent tubing (usually glass) with an evacuated space be-
degree-day, heating, (DDC or DDF, Celsius or Fahrenheit
tweenthetubeandtheabsorber.Theabsorbermayconsistof
respectively)—one heating degree-day is counted for each
an inner tube or another shape, with means for removal of
degree that the daily mean temperature is lower than a base
thermal energy and may be specially coated.
temperature; used to estimate energy requirements for heat-
collector, flat plate—a nonconcentrating solar collector in
ing.
which the absorbing surface is essentially planar.
design life—the period of time during which a system or
collector, line-focus—a concentrating solar collector that con-
component is expected to perform its intended function,
centrates the solar flux in one dimension only.
without significant degradation of performance and without
collector, point focus—a concentrating collector that focuses
requiring major maintenance or replacement.
the solar flux to a point.
diffuse, adj—referring to radiometric quantities, indicates that
collector, solar thermal—a device designed to absorb solar the flux propagates in many directions, as opposed to direct
irradiance and to transfer the thermal energy to a fluid beam which refers to collimated flux. When referring to
passing through it.
solar irradiance, it is the global irradiance less the direct
beam irradiance. When referring to reflectance, it is the
collector subsystem—that portion of the solar system which
directionalhemisphericalreflectancelessthespecularreflec-
includes the solar collectors and related piping or ducts.
tance.
collector, tracking—a solar collector that moves so as to
follow the apparent motion of the sun during the day,
NOTE 4—Diffuse has been used in the past to refer to hemispherical
rotating about one axis or two orthogonal axes. collection (including the specular component) or irradiation, with equal
radiance for all directions over a hemisphere. This use is deprecated in
collector, trickle—a flat plate solar collector in which unpres-
favor of the more precise term hemispherical.
surized liquid flows or “trickles” over the absorber.
directional—over an infinitesimal element of solid angle in a
collector cover (glazings)— see cover plate, collector.
given direction. For properties, a solid angle small enough
combustible liquid—a liquid having a flash point at or above
37.8°C(100°F).Theflashpointofaliquidhavingaviscosity
less than 45 SUS at 37.8°C (100°F) and a flash point below
93.4°C (200°F) shall be determined in accordance with the Annual Book of ASTM Standards, Vol 05.01.
E772
thatthepropertydoesnotvarywithinthesolidanglemaybe that hold specimens at an inclination angle equal to the
considered an element of solid angle. Indicated by the latitude of the rack location, facing south.
symbols u, F, where u is the angle between the given
flammable liquid—a liquid having a flash point below 37.8°C
direction and the normal to the sample surface, and;uf is the
(100°F) and having a vapor pressure not exceeding 40 psi
azimuth angle of the direction measured counter-clockwise
(absolute) at 37.8°C and shall be known as a Class I liquid.
from a reference mark on the sample. See radiometric
flash point—of a liquid, the minimum temperature at which it
properties and quantities.
gives off vapor in sufficient concentration to form an
discharge capacity, thermal—the amount of heat that can be
ignitable mixture with air near the surface of the liquid
removed from a storage device during a period of time and
within the vessel as specified by appropriate test procedure
for a specific set of values for the initial and final tempera-
and apparatus.
tures of the storage device, the temperature of the entering
flux, radiant—see radiant flux.
fluid, and the mass flow rate of fluid through the storage
forced convection— see convection, forced.
system.
free convection—see convection, natural.
discharge test time—the duration of a single transient test in
Fresnel lens, circular—a sheet of transparent material into
which energy is removed from the storage device.
whichconcentricgrooveshavebeenformedinsuchapattern
distribution subsystem—thatportionofthesolarsystemfrom
thatlightwillbefocusedaswithalens.(Focusingmirrorsof
the storage device to the point of ultimate use.
similar design are also available.)
drainback solar energy system—see solar energy system,
Fresnel lens, linear—a sheet of transparent material into
drainback.
which parallel grooves have been formed in such a pattern
draindown solar energy system—see solar energy system,
that light will be focused as by a cylindrical lens. (Focusing
draindown.
mirrors of similar design are also available.)
efficiency, collector—of a solar thermal collector, the ratio of
Fresnel-reflector system—flat mirrors arranged in an array
the amount of energy removed by the heat transfer fluid to
such that they reflect onto a target, the illuminated area of
the solar energy incident on the collector.
which simulates the shape and size of the flat mirror. (Such
NOTE 5—Forflat-platecollectors,thevalueoftheincidentsolarenergy
anarraysimulatestheray-tracingofaparabolictroughofthe
used is usually based on gross collector area; for concentrating collectors
same aperture angle.)
the value is usually based on the aperture area.
full radiator—see blackbody.
efficiency, instantaneous collector—ratio of the amount of
gross collector area— see area, gross collector.
energy removed by the heat transfer fluid of a solar collector
heat-actuated cooling—the use of thermal energy to initiate a
overaspecifiedtimeperiod(usually5or15min)tothesolar
thermodynamic cycle which results in a local decrease in
energy incident on the collector area in the same period,
temperature.
under steady-state or quasi-steady state.
heat capacity—see thermal capacity.
heat loss rate—the rate at which heat is lost from a system or
NOTE 6—For flat plate collectors, the area used is usually the gross
collector area; for concentrating collectors the area used is usually the
component of a system, per degree temperature difference
gross aperture area.
between its average temperature and the average ambient air
temperature.
efficiency, period system—ratio of the useful energy supplied
heat transfer fluid—( 1) in solar energy systems, a liquid or
by the solar energy system over a period of time to the
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