Reflecting photonic concentrator
A linearly reflecting trough concentrator that receives spectral energy, preferably visible and near-infrared solar energy spectra, and linearly reflects that energy onto a smaller area on one side of the device, thereby concentrating the energy. The linearly reflecting trough concentrator has the geometry of a single slope-relief interval in a Fresnel lens, and in preferred embodiment comprises an array of heliostatic facets connected continuously to form the base of the trough, a non-imaging focal point where a photonic receiver is located, and a relief surface to connect the heliostatic array to the receiver location. When spectral energy enters the trough at an angle normal to the array's horizontal reference, the concentrator linearly reflects energy to one side of the device where an energy receiver is mounted. The concentrator comprises an array of heliostats oriented according to the negative profile of two interleaved linear Fresnel lens, where the slope of one is the relief of the other. The concentrator reflects energy above and to each side of the device. Optionally using a reflecting projector on one side of the device, energy is then doubly concentrated to the other side. The device offers higher concentration ratios with an equivalent trough depth than prior art reflective trough concentrators. The device requires less depth and offers a lower-profile than prior art reflecting concentrators with the same degree of concentration.
The present invention relates generally to solar energy concentration, optics, and power systems, and more specifically to a reflecting photonic concentrator system using a heliostatic array.
BACKGROUND OF THE INVENTIONCapturing solar radiation energy for conversion to heat and electricity has become a significant alternate energy source. However, although safe and clean, such systems typically are not very efficient and therefore often require significant time before investment in such technologies is returned. Attempts have been made to concentrate solar radiation energy to improve the efficiency of solar energy systems. Prior art linear trough concentrators that track the light source, especially the sun, are mostly parabolic in cross-section and require significant depths to realize higher degrees of concentration.
For solar thermal applications where a fluid is superheated in a pipe, the width of the pipe does not require a significant depth to achieve reasonable concentration levels. For photovoltaic (PV) applications however, the width of a horizontally oriented photovoltaic cell requires significant depth but still achieves geometric concentration of less than three (3×), the theoretical maximum for the aperture width of a parabolic trough over the PV width, because the tangent of the reflectively incident angle on the PV approaches infinity using this geometry.
One attempt to improve the efficiency of conventional PV panels is described in U.S. Pat. No. 4,023,368 issued 17 May 1977 to Kelly, which relates to the use of side reflectors to reflect incident sunlight onto conventional solar cells that have been placed obliquely to the sun's normal rays. U.S. Pat. No. 5,899,199 issued 4 May 1999 and U.S. Pat. No. 6,131,565 issued 17 Oct. 2000, both to Mills, relate to a solar energy collector system employing at least one group of rotatable arrays of reflectors and at least two spaced-apart target receiver systems associated with the or each group of reflectors. These patents require rotation of the arrayed reflectors and do not provide for the use of stationary reflectors. U.S. Pat. No. 6,612,705 issued 2 Sep. 2003 to Davidson et al. relates to a multiple reflecting optical system for projecting reflected solar energy onto a conversion surface perpendicular to the original rays's direction by means of reflective balls. However, this reference does not provide for the concentration of incident solar energy. U.S. Pat. Appl. 20010045212 filed 29 Nov. 2001 by Frazier relates to a solar collection system that requires double reflection of incident light off two reflective surfaces. None of these systems, however, create the desired multiplier effect necessary to attain optimal device efficiency.
What is needed is a system for solar radiation collection, concentration, and conversion into thermal and electric energy that is cost-competitive with conventional energy sources. The ideal system should achieve concentration multiplier effects sufficient to attain optimal device efficiency. The ideal system would present a low architectural profile, yet be capable of tracking the sun both as it proceeds across the sky throughout the day and throughout the seasons. Finally, the ideal system would comprise a static unit and not require the use of complicated internal adjustments in order to maximize energy concentration.
SUMMARY OF THE INVENTIONAccordingly, it is an object of the present invention to provide a reflecting concentrator assembly that is cost-competitive with conventional energy sources. It is another object of the present invention to provide a reflecting concentrator assembly that achieves concentration multiplier effects sufficient to attain optimal device efficiency.
It is a further object of the present invention to provide a reflecting concentrator assembly that presents a low architectural profile, yet be capable of tracking the sun both as it proceeds across the sky throughout the day and throughout the seasons.
It is yet another object of the present invention to provide a reflecting concentrator assembly that does not require the use of complicated internal adjustments in order to maximize energy concentration.
The present invention is a linearly reflecting trough concentrator with asymmetrical geometry that realizes 7× geometric concentration with trough depth comparable to prior art parabolic trough concentrators. The concentrator assembly of the present invention requires less depth to provide a lower profile device that more readily integrates with building applications and that is more compact for space applications, e.g. satellite solar power. The concentrator assembly evenly distributes reflected energy to avoid the creation of “hot spots” on the target concentration areas that are oriented in a vertical or near vertical plane. Also, the assembly may be scaled to allow greater degrees of concentration by increasing the width of the concentration area without significantly increasing the depth.
BRIEF DESCRIPTION OF THE DRAWINGS
In a linearly reflecting trough concentrator of the present invention and being formed from a heliostatic array, photonic energy, especially in the form of light waves in the visible and infrared spectra, strikes a set of reflective surfaces at an incident angle of 90 degrees. Each of the individual reflective surfaces describe a separate heliostat. The light is then reflected to a target plane in such a way that it is evenly reflected to avoid hot spots. A second set of reflective surfaces similarly reflect light arriving at an incident angle of 90 degrees toward an opposing target plane in the same manner.
When the individual heliostatic reflective surfaces are joined together along their lateral edges, a parabolic curve is formed, thereby creating a single heliostat. In the same manner, when the second set of reflective surfaces are likewise joined together, a separate parabolic curve is formed representing a second heliostat. According to the principle of a Fresnel lens, the depth required to maintain one larger curve may be reduced by dividing the curve into segments and then flattening the curved segments onto the same plane. The segment's curvature is the slope, and the interval segment necessary to join each slope is the relief.
In a first embodiment, the present invention provides a reflective concentrator assembly that uses the Fresnel lens principle to describe the negative, inside profile of two refractive lenses that are superimposed, or interleaved, over one another. Where the first set of reflective surfaces are slopes having their own reflective target, the second set of reflective surfaces are reliefs that allow the first three slopes to be formed contiguously by a reflective material or substrate. Further, the relief surfaces do not interfere with the reflective pathway of photonic energy toward the target area when that photonic energy strikes the heliostatic array at an incident angle of 90 degrees. Because one embodiment of the concentrator assembly is symmetrical, the inverse is true where the second set of reflective surfaces are slopes having their own target, and the first set of reflective surfaces are reliefs.
A heliostatic array may be formed from a single piece of bright aluminum or from reflective material applied to a molded or extruded plastic. Four times (4×) the energy concentration is realized when the device reflects light striking a 12.8 inches wide heliostatic array onto a 3.2 inch target using a reflecting projector. In an embodiment with 6 heliostats, light striking three of the heliostats reflects directly onto the target area, while light striking the other three heliostats reflects toward the projector and is reflected a second time toward the target area. The number of heliostats, i.e. slopes and reliefs, may be increased to allow a flatter profile while ensuring that any particular slope/relief surface does not interfere with the reflective path of another surface toward its target area.
Without the reflecting projector, 2× concentration is realized when light striking the 12.8 wide heliostatic array is reflected toward two 3.2 inch targets above and on each side of the heliostatic array.
In a third embodiment of the present invention, shown in
In a Fresnel lens, the convex thickness of a lens may be reduced by dividing the arc of the lens into segments and then flattening the top of each curved segments onto the same plane. The segment's curvature is the slope, and the interval segment necessary to eliminate thickness and join each slope is the relief. The preferred embodiment of the disclosed invention is derived from embodiments having multiple negative (concave) Fresnel slope-relief intervals.
In yet another embodiment, each heliostat in the array may be separate yet connected to adjacent heliostatic reflectors so that the entire array is initially collapsed and is expanded in place. This embodiment is particularly well suited for deployment into outer space and other applications that may benefit from transportation of a smaller, collapsed apparatus followed by expanded deployment of the apparatus once disposed at the point of use. It is further understood that concentrators of the present invention may be mounted on means capable of tracking the motion of the sun both as it proceeds across the sky throughout the day and throughout the seasons in order to maximize the amount of spectral energy captured.
It will now be apparent to those skilled in the art that other embodiments, improvements, modifications, details, variations, and uses can be made consistent with the letter and spirit of the foregoing disclosure and within the scope of this patent, which is limited only by the following claims, construed in accordance with the patent law, including the doctrine of equivalents.
Claims
1. A reflective photonic concentrator having a plurality of heliostats formed according to the concave side of two linear Fresnel lens, such that the heliostats are interleaved so that an arc that is the slope for one of the interleaved reflectors is a relief to the other interleaved reflector.
2. The reflective photonic concentrator of claim 1 having two symmetrical and opposed heliostats that reflect toward opposite targets.
3. The reflective photonic concentrator of claim 1 further being capable of mechanically alternating between a collapsed position and an expanded, operation position.
4. The reflective photonic concentrator of claim 1 further focused to concentrate photonic energy in infinite-infinite, infinite-finite, finite-finite, and finite-infinite conjugates toward vertical or near-vertical planes above and on each side of the reflective concentrator.
5. The reflective photonic concentrator of claim 1 further having a reflective, diffusing projector to redirect photonic energy striking one vertical or near vertical plane across the reflective concentrator to the opposite vertical or near vertical plane.
6. A reflective linear trough concentrator having an asymmetrical geometry for reflectively concentrating spectral energy with the invention comprising:
- a) a reflective surface area for linear concentration of energy onto an energy receiver;
- b) a vertically oriented sidewall with inward tilt where an energy receiver is located to receive concentrated energy; and
- c) a relief plane that connects the bottom of the reflective surface area to the bottom of the sidewall where the energy receiver is located.
7. The reflective surface area of the reflective concentrator of claim 6 where a single heliostat, formed from a plurality of smaller non-imaging heliostatic facets, and a single relief are arranged according to the geometry of the inside profile (the concave side) of a single Fresnel slope-relief lens interval.
8. The reflective surface area of the reflective concentrator of claim 6 using a single paraboloid and imaging heliostat in infinite-infinite or infinite-finite conjugates, and having a relief such that the profile appears as the geometry of a single Fresnel slope-relief lens interval.
9. The vertical orientation of the reflective concentrator of the sidewall of claim 6, the sidewall being between 30 degrees inward to the trough and 90 degrees normal to the horizontal plane of the invention.
10. The relief plane of the reflective concentrator of claim 6 that connects the bottom of the reflective surface area to the bottom of the sidewall where the energy receiver is located such that the shadow of the top edge of an inwardly tilted sidewall strikes the angle where the relief plane meets the reflective surface area.
11. The asymmetrical geometry of the reflective concentrator of claim 6 where the energy is redirected across the line of symmetry.
12. The rotational axis of the reflective concentrator of claim 6 where the axis is orthogonal to the reflective plane and parallel to the linear extension of the reflective surface.
13. The symmetrical assemblage of two asymmetrical reflective concentrators of claim 6 where the back of one concentrator's sidewall is oriented to the back of the other concentrator's sidewall.
14. The rotational axis of the symmetrical assemblage of claim 8 where the axis is orthogonal to the reflective plane and parallel to the linear extension of the reflective surface.
Type: Application
Filed: May 6, 2005
Publication Date: Nov 9, 2006
Inventor: Christopher Straka (Owl's Head, ME)
Application Number: 11/124,615
International Classification: F24J 2/38 (20060101);