Cementitious Solar Collector

Abstract

A solar collector including a reflective surface formed along an axis and a structure composed of at least one cementitious material that is coupled to and supports the reflective surface. The optic structure is made strong and light by the addition of a filler material within the cement. One or more bearings, photovoltaics, and secondary optics make the solar collector useful in a wide variety of applications and environmental conditions.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates in general to solar energy collection, and, more particularly, to cementitious structures that collect radiant energy from the sun and methods for making such structures.

2. Description of the Related Art

Photovoltaic (PV) cells have been used to convert solar radiant energy into electricity for many years now. However, despite substantial investment, they have not been widely adopted by the energy industry to generate electricity. There are a couple of reasons for this circumstance.

PV cells are very expensive to create per unit area. Their high cost has made the energy they produce too expensive to compete with conventional sources of energy, such as natural gas and coal.

One way to reduce the area of PV cells needed to produce electricity is to concentrate sunlight onto the cells. If a collector can concentrate sunlight by a factor of 500, then 500 times less area of PV cells is needed to produce the same amount of electricity. Hence, the cost of the energy produced should be vastly reduced.

The idea of concentrating sunlight onto PV cells is not a new one, but the cost and problems associated with building a collector, known in the industry as a solar concentrator, more than offset the cost savings in the reduced number of PV cells. This has prevented PV cells adoption for large-scale electrical energy production.

Many solar concentrators fall into three primary design categories. The first design category is the parabolic dish. This design uses a single parabolic mirror that is similar in shape to a large satellite dish. The mirror collects sunlight and focuses it to a focal point. At this focal point can be PV cells or a heat engine such as a sterling engine.

The second design category is the “power tower.” This design uses many heliostats (small mirrors that track the sun) and points them all to a common focal point. At this focal point can be PV cells or a sterling engine.

The third design is commonly used (albeit in small numbers) in commercial power plant applications and is known in the industry as a solar trough. This design utilizes a single mirror that is parabolic along only one axis that looks something like a trough. This mirror collects sunlight and then focuses this sunlight into a line. At the focus can be a pipe that contains a working substance to be heated, or PV cells. This design has the advantage of a mirror that is easy to manufacture in small size sheets since it is curved in only one direction and it is relatively easy to apply a reflective coating or a glass mirror. Another advantage is the light in the focal plane can form a rectangular shape, important for focusing light onto rectangular PV cells or a continuous pipe structure. The primary drawback to this design is that since sunlight is concentrated only along one axis, a very large mirror is required to achieve high concentrations. Constructing, supporting, and controlling such large mirrors turns out to be a costly endeavor, in fact, too costly to offset the savings produced by needing fewer PV cells.

Because the dish, heliostat, and trough structures above establish and maintain optical alignment of the mirror or mirror sections, they must be capable of withstanding wind and of securely supporting other solar collector substructures without significantly distorting the mirror shape. Thus, steel trusses anchoring in a concrete foundation is a common collector structure design. However, this and other currently used designs are relatively expensive (i.e., they can represent up to 40% of the total solar collector cost), heavy, and cause concerns over longevity and ability to keep mirrors in alignment during periods of high winds.

In view of the problems experienced with the construction and operation of cost-effective solar collectors/concentrators, a need continues to exist for solar concentrator structures that have a minimum of components and have the potential to be less costly to manufacture and maintain while providing a strong supporting structure that better ensures efficient performance of the light-collecting surface.

SUMMARY OF THE INVENTION

The invention relates in general to a solar collector that includes a reflective surface formed along a parabolic, circular, or flat surface of a new and improved support structure. More particularly, the invention involves a structure that supports a reflective surface and includes at least one cementitious material. Preferably, the structure further includes a filler material at least partially encased by the cementitious material.

The filler material preferably is chosen from the group consisting of a chopped natural or a synthetic fiber. Thus, in one embodiment of the invention, the filler material is a straw or straw-like material. The filler provides support for the cementitious material, while lessening the overall weight of the solar collector structure.

In another embodiment of the invention, the structure further includes a sheeting material disposed upon over the filler material. The sheeting material preferably comprises a plastic or plastic-like film such that it aids the flowability of the cementitious material during the casting or forming process.

In a preferred method embodiment of the invention, constructing a solar collector includes the steps of providing a parabolic-, dish- or flat-shaped mold, providing a filler material within the parabolic mold, at least partially encasing the filler material with a cementitious material, and coupling a reflective element to a surface of the cementitious material.

The mirrors or reflective surfaces of the collector can be made of any plastic that can be directly applied or thermoformed, such as Acrylic or Polycarbonate, and coated with a reflective MYLAR film that can be protected from UV radiation via a poly-vinyl substrate. Since the curve on each of the mirrors used in the present invention is not a compound curve, a flat sheet of Acrylic can be easily thermoformed to the desired curve using a thermoforming technique that is inexpensive to implement. A mosaic of glass strips can also be employed.

Each mirror or reflective surface rests on a support that help each mirror keep its optical shape. The cementitious structure plays an important role in the present invention since plastics and glass in general are not dimensionally stable. The structure must be coupled to the mirror or reflective surface in a manner that does not distort its figure.

Moreover, a solar collector structure ideally should be rotatable and/or tiltable to maximize exposure to light given certain environmental, topographical, or solar tracking conditions. Hence, some embodiments include bearing means, such as rotary bearings or slew bearings, coupled with a bottom of the structure.

Additional features and advantages of the invention will be forthcoming from the following detailed description of certain specific embodiments when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the advantages of the invention will be readily understood, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments that are illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the invention and are not therefore to be considered to be limiting of its scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings, in which:

FIG. 1 illustrates a front elevational view of a solar collector of the invention.

FIG. 2 illustrates a cross-sectional view taken along line 2-2 in FIG. 1.

FIG. 3 illustrates a fragmentary magnified view taken from phantom line 3 in FIG. 2.

FIG. 4 is an elevational side view of a second embodiment of the invention.

FIG. 5A is a side view of a third embodiment of the invention.

FIG. 5B is an enlarged cross-sectional view of the embodiment of FIG. 5A.

FIG. 6 is a flow diagram of a method of the invention.

FIG. 7 is an elevational side view of a fourth embodiment of the invention.

FIG. 8 is a perspective view of a fifth embodiment of the invention.

FIGS. 9A and 9B are perspective views of a sixth embodiment of the invention and a magnified portion of that embodiment, respectively.

FIGS. 10 and 11 illustrate a circular or dish embodiment of a photovoltaic receiver of the invention.

FIGS. 12 and 12A show a side view and cross-sectional view, respectively, of a spherical optic of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Turning to FIG. 1, a solar trough 4 of the invention is shown. In this embodiment, a reflective surface 6 is formed parabolic along an axis 8 and is a supported by a parabolic trough structure 10 composed of at least one cementitious material.

As seen in the cross-sectional view of FIG. 2, the trough structure 10 preferably further includes a filler material 12 that is at least partially encased by a cementitious material 14. Preferably, the cementitious material is polymer concrete. However, other cement compositions may be used instead of, or in addition to, polymer concrete. In order to keep the trough structure 10 strong and rigid, yet lessen the weight of the structure, the filler material preferably is a chopped natural or synthetic fiber. Straw or straw-like grass material is especially preferred, given its abundance and relatively low cost.

Turning to the magnified fragmentary view of FIG. 3, the trough structure 10 preferably further includes a sheeting material 16 disposed upon the filler material 12. The sheeting material 16 preferably is a plastic or plastic-like film. By at least partially covering or encasing the filler material 12 with the sheeting material 16, the cementitious material 14 better flows around the filler material.

As seen in FIG. 4, a second embodiment of a solar collector 20 of the invention includes a parabolic trough 22 having a reflective surface 24 and a support scaffold 26. The trough 22 is made from cementitious material and includes three bales of straw 28 or other filler material disposed within the trough interior (as shown, the bales are laid end-to-end; however, they also could be arranged otherwise, e.g., side-to-side). Preferably, the bales 28 have rounded (e.g., 45 degree) corners 30 such that gussets are formed, thereby adding strength and rigidity to the trough 22.

Turning to FIGS. 5A and 5B, a third embodiment is depicted in side view and in cross-section. Trough 40 has a parabolic top surface 42 and a flat bottom surface 44. So that different sections of troughs can be arrayed together with clamps or other fasteners, rods 48 may be transversely disposed through the trough structure during casting. The rods may be rebar, steel pipe, or other material suitable for joining different troughs together to form an array. Using a hollow rod, such a pipe, also allows for the trough 40 to be pivoted through, for example, mounting a bearing within the pipe (not shown). Furthermore, the pipe can be a conduit for electricity or fluids.

In the cross-sectional view of this embodiment, the filler material (straw bale 50 with rounded corners 51) is surrounded by a mesh member 52 and incased in cement 54. The mesh member 52 preferably is used to hold the bale 50 in place during casting and to provide additional structural support. Suitable materials for mesh member 52 include, but are not limited to, steel chain link fence panels and wire mesh panels.

As shown in FIG. 6, a method for constructing a solar trough according to the invention involves the steps of: (a) providing a mold or form; (b) providing a filler material within the mold or form; (c) at least partially encasing the filler material with a cementitious material; and (d) coupling a reflective element to a surface of the cementitious material. Furthermore, methods of the invention may include the step of coupling a bearing means to a side opposite of the reflective element (e.g., the bottom side of the cementitious structure if the reflective element is coupled to the top side of the cementitious structure).

Preferably, the reflective element is attached directly to the cementitious material, thereby forming a parabolic, circular, or flat optical axis and taking advantage of the rigidity of cement. Also preferably, the filler material is at least partially enveloped with a sheeting material prior to step (c). If different troughs are to be joined together, at least one rod is cast into each trough such that the rod of one trough can be coupled to the rod of another to form an array.

Turning to FIG. 7, a trough structure 60 supported by a rotary bearing 62 is shown. The rotary bearing 62 preferably is made of steel such that it would support the weight of trough structure 60 upon surface S and may be of the trust bearing type. Hence, rotary bearing 62 provides for rotation (as shown by arrow R) of the trough structure around axis A₁.

Similarly, FIG. 8 depicts a trough structure 70 having a light reflecting surface 72 disposed on a top surface and a pair of bearing means 74 and 76 coupled to a bottom side of the trough. Bearing 74 is a slew bearing having rollers 78 (partially shown in phantom line) that allow trough structure 70 to be tilted off of axis A₂ as indicated by arrows T. Bearing 76 is a rotary bearing that provides for rotation about axis A₂. Thus, the trough structure 70 can be rotated and/or tilted without a truss or other support structure, thereby reducing weight and cost. In addition, mounting the trough structure on a bearing places the trough closer to the ground, with decreases wind and load exposure.

Turning to FIG. 9A, a trough structure 80 is show that is composed of a first trough 81 and a second trough 83 disposed in a pair-arrangement. The trough structure 80 has a hydraulic means 82 coupled with the trough to provide tilting force. The hydraulic means further includes a bearing 84 within which arm 86 is set such that trough 80 may be rotated. Near the top of trough 80 is a collector assembly 88 disposed at a focal point. Furthermore, as can be seen in the figure, the collector assembly 88 preferably is disposed between the first trough 81 and the second trough 83.

The collector assembly 88 further includes a secondary optic 90. As shown in more detail in magnified view FIG. 9B, the secondary optic 90 includes a spherical optic 92 nested in a cylindrical photovoltaic receiver 94, which is supported by steel tube 96 (within which electrical and heat can be exchanged and/or components are routed). The spherical optic 92 and cylindrical photovoltaic receiver 94 may assume a variety of embodiments.

For example, FIGS. 10 and 11 illustrate a first embodiment of a photovoltaic receiver 100. On the interior surface of support structure 102 are photovoltaic cells 104 and triangular prisms 106. The triangular prisms 106 preferably are bonded to the top of photovoltaic cells such that an incident light ray (R₁) may be refracted (R₂) onto the photovoltaics.

The secondary optic 90 of FIG. 9B also may take the form of the embodiment illustrated in FIGS. 12 and 12A. FIG. 12 shows a side view of a spherical optic 110 that includes a glass tube 112 (preferably borosilicate) having reflective (e.g., metal) support ends 114 and an interior photovoltaic receiver area 116. As shown in the cross-sectional view of FIG. 12A, the photovoltaic receiver 116 further includes a plurality of heat exchange pipes 120 coupled to the back side of a photovoltaic material 122 and a trapezoidal prism 124 optically coupled to the front side of photovoltaic 122 (also shown in a magnified detail 12D for clarity). The heat exchange pipes 120 convey coolant to and from the photovoltaic 122, while trapezoidal prism 124 augments the efficiency of incoming light collection.

While not intending to limit the invention, the following example is disclosed to further illustrate the invention method.

A parabolic-shaped form is constructed of wood and secured to the top of a parabolic-shaped mold having a non-adhesive film disposed over the top of the mold. If desired, holes may be provided in the form such that pipes (used to link different troughs together as described above) may be inset laterally through the form.

In order to better hold filler materials (to be added) in place, chain link fence sections are form-fitted to the entire interior of the assembled mold. Next, cement is poured into the mold such that the fence section on the bottom surface of the mold is covered (typically a depth of 2-3 inches) and allowed to set. Plastic-wrapped straw bales now are placed in the mold on top of the cement and arranged such that each bale is about 1-2 inches from the mold sides and 1 inch or less from each other. Another panel of chain link fence is disposed over the top of the bales to better secure them in place.

Next, cement is poured over the bales such that they and the fence panel are encased. The top surface of the cement is smoothed and the entire trough is allow to set before the form on the sides of the mold is removed. The trough is then lifted from the mold, and further processing takes place to add a reflective surface and, if desired, additional structures, such as one or more bearing means as depicted in FIGS. 7 and 8.

While embodiments of the present invention have been illustrated in detail, the skilled artisan will appreciate that modifications and adaptations to those embodiments may be made without departing from the scope of the present invention as set forth in the following claims.

Claims

1. A solar optic, comprising: a structure composed of at least one cementitious material and having a face;a filler material at least partially encased by the cementitious material; anda reflective surface adhered to said face of the structure.

2. The optic of claim 1, wherein said face is a parabolic, circular, or flat face.

3. The optic of claim 1, wherein said structure further includes a sheeting material disposed upon said filler material.

4. The optic of claim 1, wherein said filler material is selected from the group consisting of chopped natural or synthetic fibers.

5. The optic of claim 3, wherein said sheeting material comprises a plastic film.

6. The optic of claim 4, wherein said filler material is a straw or straw-like material.

7. The optic of claim 6, wherein said bale has at least one rounded corner forming a gusset.

8. The optic of claim 1, further including a rod extending from a side of said structure, said rod being adapted for coupling said structure to a second rod of a second solar optic structure.

9. The optic of claim 8, wherein said rod is hollow, thereby providing a conduit.

10. The optic of claim 1, wherein said filler material is at least partially surrounded by a mesh member.

11. The optic of claim 1, further including a bearing means coupled with a bottom side of said structure.

12. The optic of claim 11, wherein said bearing means supports substantially all of said structure's weight.

13. The optic of claim 11, wherein said bearing means is adapted to allow said structure to be tilted.

14. The optic of claim 11, wherein said bearing means is adapted to allow said structure to both rotate along an axis and be titled off said axis.

15. The optic of claim 1, further including a photovoltaic collector assembly disposed at a focal point.

16. The optic of claim 1, including a first trough and a second trough disposed in pair-wise arrangement and a photovoltaic collector assembly disposed between the said first trough and the second trough.

17. The optic of claim 15, wherein said photovoltaic collector assembly further includes a secondary optic.

18. The optic of claim 15, wherein said photovoltaic collector assembly further includes a prism in optical contact with a photovoltaic cell.

19. The optic of claim 15, wherein said collector assembly further includes both a secondary optic and a photovoltaic element.

20. The optic of claim 18, wherein said prism is a trapezoidal prism.

21. A method for constructing a solar optic, comprising the steps of: (a) providing a mold or form;(b) providing a filler material within said mold or form;(c) at least partially encasing said filler material with a cementitious material; and(d) adhering a reflective element to a surface of said cementitious material.

22. The method of claim 21, further including the step of coupling a bearing means to a side opposite of said reflective element.

23. The method of claim 22, comprising coupling at least one rotary bearing and slewing bearing.

24. The method of claim 21, wherein said reflective element is attached directly to said cementitious material.

25. The method of claim 21, wherein step (b) further includes at least partially enveloping said filler material with a sheeting material prior to step (c).

26. The method of claim 21, further including the step of placing a rod transversely through the mold or form prior to step (c).