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
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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.
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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 E7
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