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.
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.
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:
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As seen in the cross-sectional view of
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As seen in
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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
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.
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Similarly,
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The collector assembly 88 further includes a secondary optic 90. As shown in more detail in magnified view
For example,
The secondary optic 90 of
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
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.
This application is a continuation-in-part of U.S. Ser. No. 11/535,373, filed on Sep. 26, 2006, by the same inventor.
Number | Date | Country | |
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Parent | 11535373 | Sep 2006 | US |
Child | 12046749 | US |