AU2006244561A1

AU2006244561A1 - Reflecting photonic concentrator

Info

Publication number: AU2006244561A1
Application number: AU2006244561A
Authority: AU
Inventors: Christopher W. Straka
Original assignee: STRAKA CHRISTOPHER
Current assignee: STRAKA CHRISTOPHER
Priority date: 2005-05-06
Filing date: 2006-05-02
Publication date: 2006-11-16
Also published as: WO2006121686A3; EP1886073A4; US20060249143A1; WO2006121686A2; EP1886073A2

Description

WO 2006/121686 PCT/US2006/016682 Reflecting Photonic Concentrator Technical Field [001] 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 Invention [002] Capturing 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. [003] 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 (3x), 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. [004] 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. Nos. 5,899,199 issued 4 May 1999 and 6,131,565 issued 17 October 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

I

WO 2006/121686 PCT/US2006/016682 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 September 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. Apple. 20010045212 filed 29 November 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. [005] 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 Invention [006] Accordingly, 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. [007] 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. [008] 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. 2 WO 2006/121686 PCT/US2006/016682 [009] The present invention is a linearly reflecting trough concentrator with asymmetrical geometry that realizes 7x 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 [010] Figure 1 shows the reflection path of light from a heliostatic array of the present invention onto two opposing target areas. [011] Figure 2 shows a reflection path of light from a heliostatic array and reflecting projector of the present invention onto one target area. [012] Figure 3 shows a side view and ray-trace diagram of reflective concentrator with faceted, non-imaging heliostat. [013] Figure 4 shows a side view and ray-trace diagram for parabolic imaging heliostat. [014] Figure 5 shows an isometric projection of reflective concentrator. [015] Figure 6 shows a symmetrical assemblage of two reflective concentrators. Detailed Description of the Preferred Embodiments [016] 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 3 WO 2006/121686 PCT/US2006/016682 light arriving at an incident angle of 90 degrees toward an opposing target plane in the same manner. [017] 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. [018] 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. [019] Figure 1 shows the concentrator assembly of the present invention and depicts the reflective pathway of energy striking the heliostatic array at incident angle of 90 degrees and being reflected toward the two target areas. It is contemplated that these two target areas may comprise photonic transducers or receiving devices. In a second embodiment, a reflective projector may be used in conjunction with the heliostatic array. The reflective surface of the projector is designed to receive photonic energy arriving at a plurality of incident angles from the second set of reflective surfaces of the concentrator, and to evenly reflect and distribute that energy to the first target area described above. 4 WO 2006/121686 PCT/US2006/016682 [020] Figure 2 represents the concentrator assembly with the reflective projector attached to the right side of the heliostatic array and depicts the path of photonic energy striking the heliostatic array at incident angle of 90 degrees. While a first set of light rays strike the first set of reflective surfaces and are reflected toward the first target area directly, a second set of light rays reflect from the second set of reflective surfaces onto the projector surface, which in turn reflects these rays again toward the first target area. The projector substitutes the second target area described above so that photonic energy striking the projector surface is redirected to the first target area. It is contemplated that this target area may comprise a photonic transducer or receiving device. [021] 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 (4x) 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. [022] Without the reflecting projector, 2x 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. [023] In a third embodiment of the present invention, shown in Figure 3, concentrating reflector 10 comprises reflective surface area 20, relief plane 30, and vertically oriented sidewall 40 for mounting solar receiver 50. In a preferred embodiment, wherein reflective surface 20 is faceted and non-imaging, a parabolic shape is described having a curve formed of large intervals to form the single heliostat. When the profile of the single reflective surface 20 is joined to relief plane 30, the negative profile, i.e., the concave inside edge, is described for a single convex slope relief Fresnel lens interval. 5 WO 2006/121686 PCT/US2006/016682 [024] 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. [025] Figure 3 also shows a ray-trace diagram that depicts the reflection path of Spectral energy 60 that strikes reflective surface area 20 to be concentrated onto solar receiver 50. Spectral energy 60 enters the aperture of the concentrating reflector 10 at an incident angle of ninety (90) degrees to the horizontal plane of the invention. In a preferred embodiment, the horizontal plane is depicted by transparent glazing surface 11 that bridges the left and right top edges of the concentrating reflector's side view. In a preferred embodiment of seven heliostatic facets 21 through 27 that are connected contiguously to form a non-imaging reflective array, spectral energy 60 is redirected onto solar receiver 50. This embodiment describes a geometric concentration ratio of seven (7x) where seven facets 21 through 27 concentrate spectral energy 60 entering an aperture area that is seven times wider than the width of solar receiver 50. At each point where the heliostatic facets join one another, two reflected rays 61 and 62 emerge from one spectral ray 60 that enters the aperture of concentrating reflector 10. Reflected ray 61 optimally strikes at or near the top edge of solar receiver 50 as a result of reflection calculated from the angle of each facet at its top most end. Reflected ray 62 optimally strikes at or near the bottom edge of solar receiver 50 as a result of reflection calculated from the angle of each facet at its bottom-most end. [026] Figure 4 shows a side view of imaging reflective concentrator 110 having an imaging focus of concentrated spectral energy. In this embodiment different from that shown in Figure 1, reflective surface 120 is a continuous paraboloid with no discernable facets. Incident spectral rays 160 enter aperture 111 to be concentrated onto solar receiver 150. Relief plane 130 joins the reflective surface area to sidewall 140, which may optionally be used to mount solar receiver 150. [027] Figure 5 shows an isometric projection of concentrating reflector 10. Concentrating reflector end 13 is beveled inwardly from the top aperture area where 6 WO 2006/121686 PCT/US2006/016682 glazing 11 sits to the bottom of reflector 12 where relief slope 30 joins reflective surface area 20. In one embodiment, lip 14 is provided to describe a seating area for glazing 11. The dimension of rotational axis 80 runs lengthwise through any point of concentrating reflector 10. Rotation about this single axis enables linear concentration for an energy source, ideally the sun, relative to a static orientation of the concentrating reflector. [028] Figure 6 shows an end view of an assemblage of two asymmetrical concentrating reflectors 210 and 210' oriented back-to-back to form a single symmetrical reflecting concentrator 200 that rotates linearly about a single axis 280. Rotation about this single axis enables linear concentration for an energy source, ideally the sun, relative to a stationary orientation of the assemblage. [029] 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. [030] 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. 7

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. 8 WO 2006/121686 PCT/US2006/016682

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. 9 WO 2006/121686 PCT/US2006/016682

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. 10