TROUGH SHAPED FRESNEL REFLECTOR SOLAR CONCENTRATOR

Abstract

The present invention is a solar concentrator composed of a generally V-shaped trough of reflective Fresnel steps. The Fresnel reflective steps concentrate the sunlight entering the mouth of the V-shaped trough and parallel to its central axis into a central focal area. By disposing a solar energy receiving element at the central focal area of sunlight concentration a preferred embodiment as a concentrating solar energy collector is realized. Various types of solar energy receiving structures are shown that serve to convert the concentrated sunlight into other forms of useful energy to realize the preferred embodiment as a concentrating solar energy collector.

Claims

1. A solar concentrator comprising: a. a V-shaped support structure having a first side and a second side that oppose, and are mirror images of, one another, wherein a slope extending from a lowermost edge to an uppermost edge of the first side and the second side, respectively, is constant; b. a solar tracking device; c. a plurality of support members extending from the support structure, said support members being disposed parallel to a central axis of the concentrator, wherein the solar tracking device directs movement of the concentrator such that incoming solar radiation is always parallel to each of the support members; and d. a plurality of plane reflectors, wherein each reflector is connected to at least one support member, wherein the reflectors are collectively arranged in a stepped architecture along the support structure, wherein the reflectors reflect and concentrate the incoming solar radiation to a central focal area disposed upon the central axis of the concentrator.

2. The solar concentrator of claim 1, further comprising a solar energy receiving element disposed at the central focal area, wherein each reflector illuminates an entire width of the receiving element, wherein the receiving element converts the concentrated solar radiation to another form of energy.

3. The solar concentrator of claim 2, wherein, when the support structure is in an upright position, the receiving element is positioned lower than the uppermost edge of the support structure.

4. The solar concentrator of claim 2, wherein, when the support structure is in an upright position, the receiving element is positioned higher than the uppermost edge of the support structure.

5. The solar concentrator of claim 2, wherein, when the support structure is in an upright position, the receiving element is positioned at the same height as the uppermost edge of the support structure.

6. The solar concentrator of claim 2, wherein the receiving element has a circular cross-section.

7. The solar concentrator of claim 2, wherein the receiving element has a rectangular cross-section.

8. The solar concentrator of claim 2, wherein the receiving element has a triangular cross-section.

9. The solar concentrator of claim 2, wherein the receiving element comprises a fluid, wherein the fluid is circulated through the receiving element, wherein the concentrated solar radiation is absorbed by the receiving element and converted to heat energy that is transferred to the fluid circulating through the receiving element.

10. The solar concentrator of claim 2, wherein the receiving element comprises photovoltaic cells positioned along the width of the receiving element, wherein the photovoltaic cells convert the concentrated solar radiation into electrical energy.

11. The solar concentrator of claim 10, wherein the receiving element comprises a fluid, wherein the fluid is circulated through the receiving element to cool the photovoltaic cells and harvest thermal energy.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] For a more complete understanding of the present invention, the objects and advantages thereof, reference is now made to the ensuing descriptions taken in connection with the accompanying drawings briefly described as follows.

[0008] FIGS. 1a and 1b are cross-sectional drawings illustrating the theoretical concept of the present invention;

[0009] FIG. 2 shows a cross-sectional representation of the present invention with a higher concentration ratio and two different fabrication methods for the trough sides, Fresnel reflectors;

[0010] FIG. 3 shows a cross-section of the present invention with an alternate solar energy receiving element;

[0011] FIG. 4 shows a representation of the present invention as a solar collector with a glazing over the trough;

[0012] FIGS. 5a-5d show alternate embodiments of the solar energy receiving element;

[0013] FIG. 6 is a perspective view of the present invention; and

[0014] FIG. 7 is a cross-sectional representation of one possible tracking mechanism for the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0015] Preferred embodiments of the present invention and their advantages may be understood by referring to FIGS. 1a-7 wherein like reference numerals refer to like elements.

[0016] FIGS. 1a and 1b are cross-sectional representations of the basic concept of the present invention designed to illustrate the theory and operation of the invention.

[0017] Referring in detail to FIG. 1a, the V shape of the underlying support structure is illustrated by the flat planar surfaces 15. Because this support structure is flat & planar it will be able to be sourced from various off-the-shelf materials which will allow for reduction of costs compared to other trough designs that require a support structure adapted to accommodate curved mirrors or a curved underlying geometry. In the present invention Fresnel reflectors 3 are also flat which are cheaper to source or manufacture than the curved reflectors of other trough designs. Supports 16 for each individual Fresnel reflector 3 are also flat linear structures. They are oriented parallel to the central axis of the trough and the solar light rays and do not need to be reflective.

[0018] The structure with sides 14 which are also reflective would serve to add to the stability of the trough structure but is not necessary as part of the total Fresnel reflector of this design as the reflective surfaces of structure 14 could be replaced by stepped reflectors like the other ones shown in the illustrations of the invention.

[0019] By putting a solar energy receiving element 2 in the focal area along the length of the trough one preferred embodiment of the present invention a Fresnel trough solar collector is achieved. The solar energy receiving element is a structural element that is designed to receive and absorb solar energy and convert it to another type of energy. In FIG. 1a the solar energy receiving element 2 is a pipe or tube having a dark or black surface through which a fluid such as water or oil is circulated. The black surface of the pipe absorbs the solar energy and converts it to heat which is then transferred to the fluid circulating thru the pipe.

[0020] FIG. 1a shows the path of the light rays 4, shown with vector arrows, that enter the mouth of the concentrator and how they are reflected off the Fresnel steps 3 onto the receiver 2. Some of these light rays strike the receiver 2 directly from above. Further consideration of FIG. 1a shows that the angle of inclination of each reflective Fresnel step must be constructed such that the light striking it is reflected onto the receiver. The solar rays 4 and the Fresnel steps, off which they are shown reflected, illustrate that in the present invention each Fresnel reflector is at least wide enough to fully illuminate the width, profile, of the receiver 2. This feature of the present invention insures maximum efficiency and minimum cost of the Fresnel reflectors.

[0021] It is obvious from an examination of FIG. 1 that only direct solar radiation that is parallel to the trough's central axis is reflected onto the receiver and thus this concentrator, like most other trough solar concentrators, must track the sun's image across the sky in at least one direction; either in elevation, North/South, or azimuth, East/West. This illustration and all the present illustrations show the angle between the trough walls as 90 degrees but, in fact, the angle may be any angle.

[0022] FIG. 1b shows the present invention with the receiver 2 at a different position in the trough structure. This illustrates that the receiver in this invention is not restricted to any one position. In fact, the receiver may be positioned anywhere along a line representing a central axis of the trough, equal distance from the trough sides. The receiver may be positioned at the aperture opening of the trough, down inside the trough as shown in this drawing or even above the aperture opening.

[0023] FIG. 2 shows the solar collector of this invention in a higher concentration ratio with a wider trough opening, aperture, and more reflective Fresnel steps 3. Here it can be seen that the angle of inclination of each Fresnel reflector step varies depending on its position on the trough side. When designing troughs of the present invention the angle and width of each reflector must be determined based on the trough concentration ratio, aperture width, the width of the receiver and the individual position of the reflector on the trough side.

[0024] The bracketed section 17 shows an alternative construction of the Fresnel trough reflector that lacks the underlying planar support wall. This embodiment could be achieved by stamping it from a highly reflective material of sufficient gauge. Here again, it can seen that solar radiation strikes the receiver from the reflective Fresnel steps 3 and from direct solar radiation. Also, it can be seen that the reflected radiation from each Fresnel step fully illuminates the width, profile, of the receiver.

[0025] FIG. 3 shows the present invention in its preferred embodiment as a solar collector with a receiver having an alternative shape. The receiver illustrated here 2 has the cross-section of an equilateral triangle. This receiver 2 may be a triangular shaped tube or pipe with a black outer surface that carries a circulating fluid to be heated or it may be a triangular shaped tube that has photovoltaic solar cells 6 attached to the two underside surfaces or to all three of its outer surfaces. If configured with solar cells on the surfaces of the triangular receiver, the sunlight on the lower two surfaces facing the Fresnel reflector is concentrated by the factor of the concentration ratio of the Fresnel reflector on each side while the sunlight falling on the upper surface is direct sunlight with a concentration ratio of 1.

[0026] FIG. 4 shows the present invention as a solar collector with a glazing 5 covering the mouth of the trough structure thus enhancing the properties of one preferred embodiment of the present invention as a solar thermal collector designed to convert solar energy into heat in a fluid. The glazing 5 is a structural element that will increase the efficiency of energy conversion by providing thermal insulation retarding the convective loss of heat from the hot receiving element and by trapping the loss of energy by infrared emission from the hot receiver. The glazing 5 may be made of glass or a transparent plastic material. Alternatively, the receiver 2 could be an evacuated tube receiver thus eliminating the need for a glazing.

[0027] FIGS. 5a-5d show alternative shapes and orientations for the receiver element in the preferred embodiment as a solar collector. These alternative receiver shapes may have a heat collecting fluid circulated thru them or they may have photovoltaic solar cells attached to their outer surfaces 6. It is to be noted here that in the event solar cells are attached to these alternative receiver tubes a cooling liquid or air may be circulated thru them to cool the cells.

[0028] FIG. 5a shows a receiver tube whose cross section is an equilateral triangle.

[0029] FIG. 5b shows a receiver tube whose cross section is a right triangle. This right triangle receiver tube is especially suited to match the 90-degree angle of the underlying V trough Fresnel reflector structure of the embodiments shown in this document. However, it is again to be mentioned here that the present invention is not limited to the having an underlying V trough angle of 90 degrees and that, indeed, the present invention can be made with other underlying V angles.

[0030] FIG. 5c shows a receiver tube whose cross section is an equilateral triangle and on whose sides 6 are mounted solar cells. Inside and concentric with the triangular tube is a round tube 7. The round tube 7 is thermally bonded to the triangular tube by a heat transfer material 8 so that a cooling fluid can be circulated thru the round tube 7 to keep the solar cells from overheating.

[0031] FIG. 5d shows a square tube on whose sides are mounted solar cells 6. In the present invention this receiver would be mounted with its axis from diagonally opposite corners along the trough central axis. The square tube has an economic advantage over triangular tubes in that square tubes are more easily sourced off-the-shelf.

[0032] FIG. 6 shows a perspective view of the present invention in its preferred embodiment as a concentrating solar collector showing both round and triangular tube receivers 2 and showing the reflective steps 3 of the Fresnel reflector. This preferred embodiment is shown in a housing 9 with a glazing 5 covering it.

[0033] FIG. 7 shows a simple and inexpensive tracking mechanism that may be used with the present invention in its' preferred embodiment as a solar collector. The tracking mechanism consists of a hinge 10 to which the collector housing 9 is mounted and on which it pivots allowing the collector to track the suns motion across the sky in the vertical, North/South, direction. The hinge 10 is also mounted to a base 13 allowing for the needed angle of rotation for the desired hours of solar energy collection. The rotation of the collector is accomplished by a linear actuator 12 which extends and retracts to pivot the collector on the hinge 10. Pivots 11 where the linear actuator attaches to the collector housing 9 and the base 13 allow for the pivoting motion of the collector and the angular motion of the linear actuator that is required to accomplish the tracking of the collector.

[0034] The linear actuator in this tracking mechanism must be controlled by a solar aiming device, not here shown, that tracks the vertical motion of the sun across the sky and provides a signal to the linear actuator telling it in which direction to move the collector and how far, thus keeping the axis of the Fresnel concentrator of the present invention pointed at the sun. Solar aiming devices of this type are readily available off-the-shelf devices.

[0035] The tracking mechanism herein described is presented for illustrative purposes only and is not the subject of this invention. Other tracking mechanisms commonly known to the state of the art may be used with the present invention.

[0036] While the foregoing written description of the invention enables one of ordinary skill to make and use what is considered presently to be the best mode thereof, those of ordinary skill will understand and appreciate the existence of variations, combinations, and equivalents of the specific embodiment, method, and examples herein. The invention should therefore not be limited by the above described embodiment, method, and examples, but by all embodiments and methods within the scope and spirit of the invention.