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Description  |
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BACKGROUND OF THE PRESENT INVENTION
The collector system of the present invention, basically includes a
semi-cylindrical or other optical concentrating means which can take any
of a wide variety of cross sectional shapes such as parabolas, hyperbolas,
catenaries, semi-ellipses, higher order curves or composite surfaces made
up of segments of simple curves, including planes. Such shapes can be used
in semi-cylindrical reflectors of any required length or to form circular
mirrors or mirrors of any desired shape.
The collector elements are made of metal, and coated with a good radiation
absorber, preferably black, by any known process, the simplest of which
consists of a black coated metal strip in intimate thermal contact with a
pipe, tube duct or other channel through which the heat-transfer fluid
flows. These range in complexity of manufacture from simple lengths of
pipe or tubing, soldered or otherwise fastened to the black metal strips
or plates, either flat or curved to conform to the shape of the pipe,
thereby improving the thermal contact, to laminate strips with internal
fluid channels between the laminae, or extrusions combining the fluid
channels and collector plates in one piece.
Various designs exist for improving the collection efficiency and/or
concentration of the radiation by proper orientation of the system of the
present invention. Instead of continuous orientation, with the requisite
sensors, controls and motor-drive mechanism, the necessary performance may
be achievable by means of a monthly, for example, change in the collector
angle and the proper design and construction of the collector elements.
Therefore, one of the principal objects of the present invention is to
provide a solar energy collector device comprising an elongated optical
concentrating member, generally semi-cylindrical in cross section and
having a reflective inner surface, and a multipartite collector that
sequentially heats the heat-transfer fluid carried in pipes, tubes or
ducts associated with the multipartite collector in a manner so as to
improve the instantaneous and/or average energy collection efficiency of
the device relative to a single-element collector.
A further object of this invention is to provide a bank of said solar
energy collector devices in assembly.
Yet another object of this invention is to provide a solar energy collector
device in which the energy is concentrated, permitting the attainment of
somewhat higher temperatures than in a conventional flat-plate collector.
Another object of this invention is to provide a solar energy collector
device which results in lower energy losses and provides for insulation
more effectively than in a flat-plate collector while permitting higher
temperatures.
A still further object of the present invention is to provide a solar
energy collector device which operates efficiently with no required
adjustment of tilt angle, as in most focusing collectors.
BRIEF DESCRIPTION OF THE DRAWINGS:
FIG. 1 is a semi-schematic plan view of a bank of solar energy collector
devices, in assembly, in accordance with the present invention;
FIG. 2 is a transverse sectional view through a single solar energy
collector assembly angled away from vertical, the angle being
approximately equal to the latitude;
FIG. 3 is a transverse sectional view through a single solar energy device
and indicating a typical angle of light incidence;
FIG. 4 is a schematic illustration of a collector bank on a roof of
non-optimum pitch;
FIGS. 5A, B and C schematically illustrate some of the cross sectional
configurations of the reflector members, possible in accordance with the
present invention;
FIG. 6 is a cross sectional view of a modified form of multipartite
collector of the present invention;
FIG. 7 is an enlarged cross sectional view of a further modification of a
collector segment as applied to the form of the invention illustrated in
FIG. 6; and
FIG. 8 is an enlarged cross sectional view of a modified form of a single
collector plate which may be integrally molded or otherwise formed with
one or a plurality of conduits.
DETAILED DESCRIPTION OF THE DRAWINGS:
With reference to the drawings in which like reference characters designate
like or corresponding parts throughout the various views, and with
particular reference to FIG. 1, a typical bank of solar energy collector
devices is illustrated at 10 in any appropriate type of fixed frame 12,
illustrated in broken lines. Three of the devices 14, 16 and 18 are
illustrated; however, in practice any required number thereof may be
included in said bank 10.
With reference to FIG. 2, the collector system comprises a semi-cylindrical
member 20 having a mirror inner surface 22. A split collector plate means
24 and 26, thermally insulated from each other by an air space
therebetween, bisects the area within the semi-cylindrical member 20. The
collector plates 24 and 26 are designed to heat a fluid such as water,
oil, air, or some fluid used in a refrigeration cycle, more efficiently
than can be done with a flat plate collector, and much more simply than is
ordinarily possible with a focusing collector. A fluid conduit 28 is fixed
in any conventional manner, as by soldering 30, to the lower collector
plate 24, and a similar conduit 32 is similarly fixed at 34 to the upper
plate 26. Conduits 28 and 32 are interconnected at 35.
The bank 10 of FIG. 1 is longitudinally mounted in an East, West
disposition and the angle 36 approximately equals the latitude of the
installation. The angle 38 of FIG. 3 designates a typical angle of
incidence of light rays. The angle of incidence 38 will change with the
time of day. A calculatable fraction of the light incident on the left
half of the mirror surface 22 will be collected on surface a of collector
plate 24 and the balance of surface c, and similarly for the right half of
mirror surface 22 on surfaces b and d. For clear days at noon, the annular
angular excursion of the sun is plus or minus 23.5 degrees, and the system
will produce an average concentration of 70 percent of the radiation on
the a-b surface combination, for East-West alignment of the mirror axis at
the elevation angle 36, equal to the latitude. But because of the mirror
surface properties, for angles of incidence up to 45 degrees, there is
more radiant energy concentrated on plate 24 than on plate 26. Thus, if
the heat exchange fluid passes through the system twice, first down pipe
32, FIGS. 1, 2 and 3, and then back through pipe 28, it is heated more
effectively than is possible with a flat plate collector, and higher
conversion efficiencies are possible. Lenses, Fresnel lenses, and
combinations of these with mirrors may also be used to concentrate the
radiation.
As illustrated in FIGS. 2 and 3, the open top of the semi-cylindrical
member 20 is sealed by a transparent cover 40, of glass or of any
appropriate synthetic material.
FIG. 4 illustrates the orientation of a bank of solar energy collector
devices of the present invention, oriented to a non-optimum roof pitch.
Numeral 50 designates the roof pitch, 52 the basic reflector member, 54 a
supplementary plane reflector, 56 the split collector plate, and 58 the
correct collector angle.
FIGS. 5A, B and C are schematic illustrations of just some of the
alternative cross sectional configurations of reflector members that may
be used in place of the semi-circular members of FIGS. 2 and 3. FIG. 5A
illustrates the use of plane mirrors 60, FIG. 5B illustrates segments of
simple curves 62, and FIG. 5C illustrates the use of a thin film reflector
64 suspended between two supporting bars 66 and 68.
Calculations shown in Table I are useful in assessing the performance of
the system. At an angle of incidence 38, as shown in FIG. 3, a calculable
fraction of the light incident on the left half of the mirror aperture
will be collected on surface a, and the rest on surface c. Similarly for
the right half, with surface b and d. Table I shows the energy
distribution for a range of incidence angles, and the last two columns
show the distribution averaged over both surfaces of each collector plate.
TABLE I
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Fraction of energy collected by surface Average for each
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plate
a c b d (a+b)/2
(c+d)/2
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0<.theta.<7.5.degree.
.96 .04 .65 .35 .805 .195
7.5.degree.<.theta.<15.degree.
.90 .10 .54 .46 72 .28
15.degree.<.theta.<22.5.degree.
.82 .18 .49 .51 .655 .345
22.5.degree.<.theta.<30.degree.
.75 .25 .45 .55 .60 .40
30.degree.<.theta.<37.5.degree.
.67 .33 .40 .60 .535 .465
37.degree..5 .degree.<.theta.<45.degree.
.575 .425 .34 .66 .46 .54
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A more effective, but somewhat more troublesome and expensive, way to use
the system is to collect on the four surfaces separately, running the
fluid sequentially through cdba, with c and d, a and b separated by a thin
insulator. The final pass along a would usually have an effective
concentration of about 85%, or a concentration ratio of .85/.5 = 1.7. This
is enough to yield satisfactory temperatures for solar air-conditioning
systems to operate with acceptable efficiency.
The angle of incidence, 38, in FIG. 3 is as shown for the results in Table
I. But for a collector of fixed tilt, the angle 38 at noon normally
changes from one side to the other with season, and during the summer,
angle 38 changes sides twice each day. Therefore, the hottest surface will
sometimes be a and sometimes b, and the flow sequence cdba is changed
sometimes to dcab.
In practice the direction and sequential flow of the heat transfer fluid
through successively hotter parts of the conduit means is coordinated with
the angle of tilt of the collector system and the angle of incidence of
the radiant energy from the sun on the collector so as to permit optimum
energy collection.
For large scale industrial utilization of solar energy a focusing collector
system is normally required and an expensive, complicated aiming system is
normally necessary. However, a large diameter solar collector system, as
illustrated in FIG. 6, will accomplish this purpose. It comprises a
semi-cylindrical mirror reflector 70, a transparent cover 72, a plurality
of pairs of collector plates 74 and 76, separated by insulator plates 78,
fluid conduits 80 and 82 fixed relative to each pair of collector plates
74 and 76, and tubular convection shield 84 enclosing each pair of plates
74 and 76, their associated insulator plate 78 and fluid tubes 80 and 82.
As illustrated in FIG. 7, laminar collector plates 85 and 86, similar to
plates 74 and 76, may be formed to provide channels 88 and 90 for passage
of the heat-transfer fluid on the respective sides of the insulator plate
92. As in the above described forms of the invention, the collector plates
are coated with black surfaces and the insulator plate 92 therebetween
permits the heat absorption of the opposed collector plates 84 and 86 to
be used independently. The above described assembly is enclosed in a
tubular convection shield 94 which is preferably evacuated and sealed, to
eliminate convective heat losses, said tube being formed of clear glass or
of an appropriate clear synthetic material. A plurality of the above
described assemblies may be substituted for the similarly shielded
assemblies of FIG. 6. The transparent cover plate 72 may be omitted.
However, a plastic cover formed of a material marketed by DuPont under the
trade name of Tedlar, or a similar material, may be utilized just for
protection of the mirror surfaces.
Appropriate insulation materials may be utilized wherever needed such as
between the collector assembly and the fixed frame to eliminate conduction
and convection heat losses.
Laminar collector plates and insulator plates in combination with the fluid
conduits of FIGS. 6 and 7 may be substituted for the split plates and
fluid conduits of FIGS. 2 and 3.
For small, virtually maintenance-free installations, the collector array
and optical system should be sealed in an insulated box with a clear glass
cover. The collector array can consist of two or more fluid channels
attached to metal collector strips, as shown in FIGS. 2, 3, 6, 7 and 8,
with the fluid circulated through the channels in order of increasing
energy input. As seen in FIG. 8, a collector plate 96 and one or a
plurality of conduits 98 may be integrally extruded or otherwise formed.
Modular kits for do-it-yourself home installations could be marketed with
enough design variations available to allow each to have unique and
distinctive features. These modules can be connected in series in whatever
shape of array is best suited to the user's situation. Such kits could
also be made in somewhat more complicated form for use by professional
installers.
For most installations, it is most convenient to store the heated fluid in
an insulated tank at ground level, rather than at the usual roof-top level
of the solar collector system. Therefore it becomes necessary and
convenient to use a sensor-controlled fluid pump to circulate the
heat-exchange fluid appropriately. Many standard, simple circuits exist
for comparing the fluid temperatures in the tank and collector, and
causing the pump to act only when it is beneficial for it to do so.
Particular advantages of this program are evident for the retrofitting of
a solar water heater to an existing hot water system. Here it saves the
price of a new hot-water tank, and it permits the use of the existing gas
or electric system as backup without extensive modification. The ability
of the sensor-controlled pump, combined with the present multipartite
collector system to produce and store hotter water than that available
from a simple flat-plate collector, permits the continued use of a smaller
hot water storage tank than is normally recommended for a solar hot-water
system.
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