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BACKGROUND OF THE INVENTION
The present invention is directed toward the art of support structures for
parabolic reflectors, and more particularly concerns a support structure
for a large parabolic reflector which is intended primarily for use as a
solar reflector and which is comprised of a large number of small
reflecting sections arranged into a paraboloid.
Large dimension parabolic reflectors, on the order of twenty feet in
diameter and larger, have historically been proposed for use in a variety
of applications, including use in a solar collection system. However,
large dimension parabolic reflectors have always been difficult and
expensive to manufacture and hence are presently considered impractical,
except perhaps in special purpose applications, such as large telescopes.
In addition to the cost involved in producing such a parabolic reflector
per se, the support structure for such reflectors also is complicated and
expensive. Additionally, the support structure must be designed for the
particular reflector application, and a support structure suitable for one
application would not necessarily be suitable for any other reflector
applications.
For instance, those support structures which have been developed for
parabolic reflector telescopes are not suitable for solar collector
applications, wherein the reflective surface must be as open as possible
to the sun, and wherein the support structure must be capable of
withstanding harsh weather environments, including high winds and hail,
without damage to either the support structure or the reflector.
Other large-dimension curved structures besides parabolas have been
constructed using a plurality of relatively small size plane sections of
various forms. An example of using relatively small sections to construct
a spherical structure is shown in U.S. Pat. No. 2,978,704, titled: Random
Structural Devices. As suggested herein, large dimension parabolic
reflectors can also be constructed with small-size sections, at
considerable cost savings over a single surface reflector.
Although such a construction technique may significantly reduce the cost of
producing a parabolic reflector per se, the problems of adequately
supporting and protecting that structure, especially under extreme weather
conditions, remain. To the best of the inventor's knowledge, there is very
little information available concerning support structures for
large-dimension parabolic reflectors intended for outdoor use, especially
where the reflector comprises a plurality of relatively small sections and
is intended for use as a solar collector.
Necessarily, such a support structure must have the proper strength in
order to support the plurality of reflecting sections without breakage
during normal operation, and must be capable of protecting the reflecting
sections in weather extremes. It must further interfere only minimally, if
at all, with the amount of sun reaching the reflecting surfaces of the
individual sections.
Additionally, such a support structure should be relatively inexpensive, so
that the combined support structure-parabolic reflector may be
economically practical as a solar collector. Further, the support
structure should be relatively simple and inexpensive to install on site,
and must be capable of accurately tracking the sun in its movement across
the sky.
Accordingly, it is a general object of the present invention to provide a
support structure for a parabolic reflector which overcomes one or more of
the disadvantages of the prior art noted above.
It is another object of the present invention to provide such an apparatus
which is relatively simple to install on site.
It is a further object of the present invention to provide such an
apparatus which is capable of withstanding the stresses of weather
extremes.
It is another object of the present invention to provide such an apparatus
which is capable of supporting a parabolic reflector without
counterweights.
It is an additional object of the present invention to provide such an
apparatus which is capable of supporting a large-dimension parabolic
reflector comprised of a plurality of relatively small-size reflecting
sections.
It is yet another object of the present invention to provide such an
apparatus which is capable of supporting a multiple-section parabolic
reflector over an extended period of time without damaging the individual
sections.
It is a still further object of the present invention to provide such an
apparatus which permits the individual sections comprising the parabolic
reflector to be separately focused.
It is another object of the present invention to provide such an apparatus
which is capable of tracking the sun with the parabolic reflector.
SUMMARY OF THE INVENTION
Accordingly, there is provided with a special-purpose support structure for
supporting large-dimension reflectors which exhibit a curved surface, such
as a parabolic reflector. The support structure includes a first rigid
support matrix which comprises a plurality of strut-like members which are
joined together at matrix joints in such a manner that the first rigid
support matrix approximates the curved shape of the large-dimension
reflector which it is to support. A plurality of standoff elements are
provided in the support structure, with the standoff elements being
connected to the matrix joints and extending away therefrom. Additionally,
there are securing member mounted on each of the standoff elements for
securing the curved reflector in position away from the first rigid
support matrix.
DESCRIPTION OF THE DRAWINGS
A more thorough understanding of the invention may be obtained by a study
of the following detailed description taken in connection with the
accompanying drawings in which:
FIG. 1 is a diagram showing the principal components of a solar collection
system, including the support apparatus of the present invention.
FIG. 2 is a perspective view of one embodiment of the present invention,
with a single support structure.
FIG. 3 is an exploded view of one portion of the embodiment of FIG. 2.
FIG. 4 is a partial perspective view of another embodiment of the present
invention, with a double support structure.
FIG. 5 is an exploded view of a portion of the embodiment of FIG. 4.
FIG. 6 is a perspective view of a standoff element, a connecting hub, and a
securing member which connect the two support structures and the
reflecting sections of the embodiment of FIG. 4.
FIG. 7 is a perspective view showing the axis structure between the support
structure for the parabolic reflector and apparatus for tracking the sun.
FIG. 8 is a perspective view showing the structure for securing the
individual reflecting sections in place to form a parabolic reflector.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to FIG. 1, the reflector support structure of the present
invention is shown in the context of a complete solar energy collection
system. A parabolic reflector is shown generally at 10, and is comprised
of a plurality of triangular sections 11--11 of conventional mirrored
glass. Triangular sections 11--11 may be plane or slightly curved or
dished. Triangular sections 11--11 are arranged and positioned such that
their respective apex points lie on the surface of a true parabola.
Reflector 10 thus is substantially parabolic.
In the embodiment shown in FIG. 1, a first reflector support matrix, also
of generally parabolic configuration, shown generally at 12, is provided
inside parabolic reflector 10. Reflector support matrix 12 comprises a
plurality of elongated rod-like elements 13--13 which are joined together
at their ends, at joints 14--14, to form a plurality of intersecting open
triangles in a generally parabolic arrangement. The joints 14--14, in the
configuration shown, lie substantially on the surface of a true imaginary
parabola.
Extending outwardly from each joint 14, and fixedly connected thereto, is
an elongated standoff element 15 which has located therealong positioning
elements (not shown in FIG. 1) which may be moved longitudinally along
standoff elements 15, and which hold triangular sections 11--11 at their
apexes in a parabolic arrangement 10.
In FIG. 1, four triangular sections 11--11 are shown for each triangular
portion of support matrix. This is shown most clearly in FIG. 3. In an
even more simple embodiment, the triangular sections 11--11 could be the
same size as the triangular support matrix portions. A more complicated
embodiment, using two support matrixes, wherein 16 triangular sections
11--11 are used for each triangular portion of the first support matrix is
shown in FIGS. 4 and 5.
A boiler 16 of conventional design and of a size which is commensurate with
parabolic reflector 10, is located substantially at the focal point of
parabolic reflector 10 and parabolic support matrix 12. An elongated
support element 18 connects boiler 16 and the back center of the parabolic
support matrix 12, and supports boiler 16 at the focal point thereof. The
boiler 16 may take various configurations, and may be a mercury heat
exchanger. An example of a boiler which may be useful is described in U.S.
Pat. No. 4,019,868, issued to Sebacher, et al, on Apr. 26, 1977 and
titled: Solar Hydrogen Generator.
Encircling parabolic reflector 10 and parabolic support matrix 12 is a
terrain support apparatus which includes first and second support rings 20
and 22. The first support ring 20 is stationary and is supported off the
ground at a selected angular orientation to the terrain by a plurality of
upright posts 24--24. The second support ring 22, which is of
substantially the same configuration and size as the first support ring
20, is positioned on top of the first support ring and rotates relative to
the first support ring by means of rollers or similar conventional devices
26 through a motor 31.
Parabolic reflector 10 and parabolic support matrix 12 are secured to an
axis structure 27 which is in turn rotatably connected to second support
ring 22 through conventional means, such as a motor-driven gear
arrangement 29. This arrangement permits parabolic reflector 10 to be
rotated within support rings 20 and 22.
In operation, second support ring 22 is rotated relative to first support
ring 20 at specified time intervals to maintain the correct reflector
azimuth for the parabolic reflector 10, while parabolic reflector 10
itself is periodically rotated, through axis structure 27, to maintain a
correct reflector altitude. Hence, parabolic reflector 10 follows the path
of the sun as it moves from horizon to horizon.
The sun's rays, when they strike the inside reflecting surface of parabolic
reflector 10, are focussed by the individual triangular sections 11--11 to
the boiler 16. The boiling medium in boiler 16 is raised to a temperature
between 600.degree. F. and 1000.degree. F. when plane triangular sections
are used, and between 3000.degree. F. and 6000.degree. F., when curved
triangular sections are used, resulting in superheated steam which can
then be utilized to drive conventional steam generators or similar means.
FIG. 2 shows in more detail the parabolic reflector 10 and parabolic
support matrix 12 shown in FIG. 1. Parabolic support matrix 12 comprises a
plurality of elongated struts or rods 13 joined together at their ends, at
joints 14, in such an arrangement as to form the parabolic support matrix
shown in FIG. 2.
The arrangement of struts 13--13 form a plurality of open triangles, with
each strut 13, except for those in the top row, forming one side of 2
adjacent triangles. The specific arrangement of the triangles and their
relative sizes can be obtained in a number of ways, but in the instant
case was achieved by projecting the lower half of a subdivided isohedron
onto a true parabolic surface.
Each of the joints 14--14 lies substantially on the surface of a true
parabola, while struts 13--13 extend in a straight line between joints
14--14. The upper row of struts 13--13 all lie in the same plane and form
rim 30 of the support matrix, as shown in FIG. 2, while the remainder of
support matrix 12 extends downward therefrom in a parabolic configuration.
The individual struts 13--13 are of varying length, depending upon their
location in the support matrix.
In the embodiment shown, struts 13--13 are lengths of 11/2" galvanized
pipe, since galvanized pipe offers relatively high strength at a low cost.
Other materials, however, such as aluminum tubing, can be effectively
used.
Stabilizing rim 30 are a plurality of guide wires 34 (shown in FIG. 2 but
not FIG. 1) which run cross-ways of rim 30 from each joint 14 on the rim
to an opposing joint on the opposite side of the rim. Hence, each joint 14
or rim 30 is connected by stiff wire, or small-diameter tubing, to an
opposing joint on the rim. Guide wires 34 provide necessary support
structure rigidity.
The structure of the joints 14--14 is shown more clearly in FIG. 6. The
construction of each joint 14 will vary depending upon its location, and
whether there is more than one support matrix provided. Each joint will
include a full hub or collar element which is shown generally at 35, a
triangular section securing element, shown generally at 42, and a standoff
element 15. When two support matrixes are used a modified hub 36 is
included at each joint. A full hub 35 is used wherever the struts forming
either the first or second matrixes are joined. A modified hub 36 is used
for attaching a standoff element 15 to a strut 13 intermediate of its
ends.
Joint 14 shown in FIG. 6 is the joint structure shown as 38 in FIG. 4. It
includes a tubular T shaped modified hub 36, having a cross member 36a
which is secured to a single strut 13 in the first support structure, and
a base member 36b, into which one end of standoff element 15 is inserted.
The modified hub 36 is positioned intermediate of the strut 13 and is used
both on the first and second support structures to permit subdivision of
each structural support portion.
Midway along standoff element 15 in FIG. 6 is a full hub 35 which receives
the ends of various numbers of struts 13, depending upon location, in a
second support matrix. Hub 35 includes a central ring 35a, through the
center of which standoff element 15 extends, and a plurality of fins
35b--35b which extend radially outward from central ring 35a and which
receive the ends of struts 13.
Standoff element 15 in FIG. 6 is a rod-like strut which extends
perpendicularly from modified hub 36 and through full hub 35 so that it
hence extends perpendicularly from a plane which is tangent to an
imaginary parabolic surface connecting each joint of the parabolic support
matrix.
The length of standoff element 15 depends upon the number of parabolic
support matrixes used. In the embodiment of FIG. 2, for instance, only one
support matrix is shown, and the length of standoff element 15 is
approximately 2 inches. In the embodiment of FIG. 4, standoff element 15
might be approximately 4 inches.
Located near the end of standoff element 15 is securing element 42, which
holds one apex of several triangular reflecting sections 11--11 firmly in
place. Positioning element 42 of FIG. 6 comprises two relatively thin
members 44a, 44b of a flexible but stiff material, such as a stiff rubber
or Teflon, which, when moved close together, hold the apexes of several
triangular reflecting sections 11--11 in place to form the parabolic
reflector 10. When stiff members 44 and 46 are held close enough together
by plate 46 and by nut and washer arrangement 45, several triangular
reflecting sections 11--11 may be held firmly in position, as shown in
FIGS. 6 and 8. Members 44a and 44b are sufficiently flexible, however, to
permit a slight movement of reflecting sections 11--11 to take up a
certain amount of environmental stresses, particularly changes in
temperature, without breakage.
At no time will securing element 42, and hence reflecting sections 11--11,
come into contact with the parabolic support matrix 12, and hence, no
stress will be placed on reflecting sections 11--11 by the parabolic
reflector structure itself.
A further key structural advantage to securing element 42 is that it may be
moved a ways longitudinally along standoff element 15, permitting
individual focusing of each reflecting sections 11--11 onto boiler 16. In
this manner, the parabolic reflector 10 may be tuned to maximum
effectiveness.
Reflecting sections 11--11 may be comprised of a number of different
materials, among them being glass and polished metal, such as aluminum. It
has been found, however, that the conventional double-sided mirror,
silvered on the backside, is the best when both cost and reflective
quality are considered. The support structure of the present invention
permits the use of this relatively inexpensive material.
The reflecting sections 11--11 may be plane, which is a relatively easy and
inexpensive shape to manufacture, or they may be slightly curved. If
reflecting sections 11--11 are curved, the total reflecting quality of the
complete parabolic reflector 10 will be better than with plane reflecting
sections, and the solar collector operation will improve. The National
Aeronautics and Space Administration has developed a method of fabricating
curved silvered glass which is suitable for use with the present
invention. It is available on microfilm under the number
NTIS-N75-32894/8ST in engineering libraries of several universities, under
the title "Light Weight Reflector Assembly and Method." It should be
understood, however, that the present invention is capable of functioning
efficiently with plane reflecting sections.
In the embodiment shown in FIG. 2, the support matrix 12 is provided inside
the reflector 10. This configuration has been found to reduce the amount
of reflected sunlight to the boiler by approximately 15%, which is
acceptable in view of the cost savings produced in construction of large
parabolic reflectors by use of the support structures disclosed herein.
Referring again to FIG. 1, the combination of parabolic reflector 10 and
parabolic support matrix 12 is encircled by first and second support rings
20 and 22. Support ring 22 rides on top of support ring 20, by means of
conventional rollers 26 or similar devices. Support rings 20 and 22 are
substantially circular in configuration, and have diameters slightly
greater than the diameter of parabolic reflector 10. In the case of a 30
foot diameter parabolic reflector, for instance, the diameter of support
rings 20 and 22 is approximately 31.82 feet.
First and second support rings 20, 22 may be constructed of a variety of
materials, but in the embodiment shown are aluminum tubing, approximately
4 inches thick and 9 inches wide. It should be understood, however, that
rings 20 and 22 may take various configurations. They may be square or
rectangular in cross-section or they may be two non-girders formed into
circles.
Support ring 20 is supported off the terrain by means of a plurality of
posts 24, at an angle 52 from the vertical which is equal to the latitude
of the particular terrain location of the collector. Hence, the angle 52
of the support rings will vary, depending upon the latitude of the
location of the apparatus.
Hence, first support ring 20 is fixedly supported by means of a plurality
of support posts 24, while second support ring 22 is rotatably connected
to support ring 20 by means of rollers or the like, driven by means of
motor-driven gearing 31.
FIG. 7 shows in more detail the axis structure 27 by which the combination
of parabolic reflector 10 and parabolic support matrix 12 is rotatably
connected to support ring 22. A series of struts 60 are connected between
(1) the ends of a number of standoff elements which extend from hubs 35,
and (2) a common joint 62, which in turn extends into a short axle and
gear arrangement 64, which controls rotation of the combination relative
to first and second support rings 20 and 22. Axis structure 27 extends
through reflector 10 and support matrix 12 at approximately their combined
center of gravity, and hence, no counterweights are needed to stabilize
the reflector during rotation.
Such an arrangement permits support matrix 12 and hence, parabolic
reflector 10 as well, to follow the path of the sun as it moves across the
sky. It also permits reflector support matrix 12 and reflector 10 to be
rotated so that they face the terrain. Typically, a fairly rigid
lightweight protective covering (not shown) may be provided over the
exterior of the reflector 10 so that when the support matrix 12 and
reflector 10 are rotated upside down, the protective covering is exposed
to the weather. The protective covering serves to protect the reflector
during extreme weather conditions, in particular, hail, dust storms, and
high winds.
Referring now to FIGS. 4 and 5, there is shown another embodiment of the
present invention which is somewhat more complicated than the embodiment
of FIGS. 2 and 3. In the embodiment of FIGS. 4 and 5, an intermediate
parabolic support matrix 70 is provided between a base parabolic support
matrix 72 and a parabolic reflector 74. A substantial portion of the
complete structure is shown in FIG. 4.
The arrangement of this embodiment is shown most clearly in FIG. 5, wherein
the relationship between a single portion of the base parabolic support
matrix is shown with its corresponding intermediate support matrix and
corresponding reflector structure. As with the embodiment of FIGS. 2 and
3, the more complex embodiment includes a first set of standoff elements
76 located at each joint 78 of each triangular portion 80 of the base
parabolic support structure, and a second set of standoff elements 82
intermediate of each pair of joints 78--78. Hubs (not shown) such as hubs
35 in FIG. 6, are located at each joint 78 while modified hubs (not
shown), such as hubs 36 in FIG. 6, are used intermediate of joints 78.
The intermediate parabolic support matrix 70 comprises a plurality of
struts 86 which are approximately half as long as the struts comprising
base parabolic support matrix 68. Each strut 86 is connected between hubs
(not shown) which are similar to hubs 35 in FIG. 6, which are positioned
on standoff elements 76 and 82, as shown in FIG. 5. This results in a four
triangle section of intermediate support matrix for each portion 80 of
base support matrix. Struts 86 may be lighter in weight than those struts
comprising the base parabolic support matrix. For example, struts having a
diameter of 1/2 inch and a wall thickness of 1/16th inch have been found
to be useful for a 30 foot diameter reflector. In addition to standoff
elements 78 and 82 which extend through the hubs which support struts 86,
further standoff elements 92 are provided, located intermediate each strut
86 and connected thereto by a modified hub (not shown) similar to hub 36
shown in FIG. 6.
At the end of standoff elements 78, 82 and 92, a securing element (not
shown) similar to element 42 in FIG. 6 is provided to hold the reflecting
sections which fit together to comprise the parabolic reflector 10.
Because standoff elements 78, 82 and 92 all support individual reflecting
sections 94--94, there are four reflecting sections for each intermediate
support matrix section, and hence sixteen reflecting sections for each
portion 80 of the base support matrix 72. This arrangement is shown most
clearly in FIG. 5. In the embodiment of FIG. 4, which was developed by
projecting a subdivided isohedron onto a parabolic surface, there are 40
triangular shaped portions which comprise the base parabolic support
matrix. Hence, a total of 640 reflecting sections will comprise the
parabolic reflector 10.
The support structure described above is advantageous, as it has sufficient
strength to support the reflecting sections, and to take up environmental
stress, so as to minimize possible damage to the reflecting sections. In
addition, such a structure permits the reflecting sections to be
individually focused on to a boiler, increasing the potential efficiency
of the reflector. In the arrangement shown above, each reflecting section
reflects substantially the same amount of light to the boiler when the
reflector is properly oriented with respect to the sun.
The above-described support structure permits, in practical terms, the use
of plane triangles to construct a large-dimension parabolic reflector.
Such a complete structure can be used advantageously in solar collection
systems. The support structure is relatively inexpensive, as it can be
made from commercially available, relatively inexpensive, materials, and
can be assembled quickly and easily on site. It has extremely high
strength, and can protect the reflector structure against weather
extremes, particularly high winds and hail, without blocking a substantial
amount of light from the reflector.
Although a preferred embodiment of the invention has been disclosed for
purposes of explanation, it should be understood that various changes, and
modifications can be made to the embodiment shown without departing from
the spirit of the invention. It should be understood, for instance, that
although the support matrix is shown as being interior of the reflecting
sections, the same principles could be used to provide an exterior support
matrix. Additionally, it should be understood that the particular hub
configuration shown is not critical. Various configurations may be
successfully used. The invention is defined by the claims, which follow.
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