SECONDARY SOLAR CONCENTRATOR
An external concentrator is provided for use with heat collection elements (HCE's of a solar parabolic trough power plant. In one arrangement, the concentrator includes a plurality of ribs that are adapted to extend radially outward from the outside surface of an HCE and along the linear length of the HCE to help redirect stray/spilled light into the absorber tube of the HCE. In another arrangement, the concentrator includes a shield placed on or near a surface of the HCE opposite of the parabolic reflective trough. The reflective shield includes ribs or brims that are disposed adjacent to one or both lateral edges of a reflective shield applied to the outside surface of a HCE tube to increase the collection of stray light reflected by the reflective trough.
The present application claims the benefit of the filing date of U.S. Provisional Application No. 62/346,020 having a filing date of Jun. 6, 2016, the entire contents of which are incorporated herein by reference.
FIELDThe present disclosure is directed to improving the performance of parabolic trough solar collectors. More specifically, the present disclosure is directed to a secondary solar concentrator that improves concentration of beam radiation onto tubular receivers or heat collection elements (HCE's) of parabolic trough solar collectors.
BACKGROUNDA parabolic trough power plant generates electricity using concentrated sunlight as the heat source for its power cycle. Most commonly rows of single-axis-tracking, linear parabolic mirrors form a solar field that concentrate beam radiation onto tubular receivers which are also known as heat collection elements (HCE's). See, e.g.,
Aspects of the presented inventions are based on the recognition by the inventor that the focal point of linear parabolic reflectors/mirrors is often not exact. That is, the consistency of the actual foci of the parabolic mirrors as it focuses light onto the HCE's is somewhat loose in tolerance. Along these lines, a portion of the beam radiation reflected by the mirrors may not contact the heat collection elements mounted along the foci of the linear parabolic reflectors. Stated otherwise, some of the reflected beam radiation is lost via spillage. The reflected beam radiation which never contacts an HCE is lost energy, which could be utilized to further heat the heat-transfer fluid and further improve overall efficiency of the system. To reduce such spillage, the presented inventions are directed to a secondary solar concentrator that may be affixed about an external surface of an existing HCE to capture and redirect reflected beam radiation that would otherwise bypass the HCE.
In one aspect, an external concentrator includes a plurality of ribs that are adapted to extend radially outward from the outside surface of an HCE and along the linear length of the HCE to help redirect stray/spilled light into the absorber tube of the HCE. The number and spacing of the ribs may be varied. In any arrangement, the ribs form a reflective surface that allows for redirecting stray light into the HCE.
In a further arrangement, the external concentrator includes two sets of ribs that are disposed on different radial sections of the outside surface of the HCE. In such an arrangement, the different sets of ribs may be separated by a reflective shield that covers a portion of the HCE tube. Most commonly, when applied to an HCE tube, the reflective shield is disposed outside of the tube opposite of the vertex of a parabolic reflector that focuses light onto the tube.
In another arrangement, the external concentrator includes two sets of ribs that are disposed on different radial sections of the outside surface of the HCE. In such an arrangement, individual ribs may be disposed in non-radial orientations relative to the surface of the HCE, and different orientations relative to other ribs.
In yet another arrangement, the external concentrator may include ribs or brims that are disposed adjacent to one or both lateral edges of a reflective shield applied to the outside surface of a HCE tube. In such an arrangement the ribs/brims may connect to the reflective shield at a pivot point and be disposed in various angular orientations relative to the surface of the HCE. Such ribs/brims may extend above and outward from the surface of the HCE to collect additional stray light. Certain embodiments also contemplate spacing the reflective shield and/or the ribs at a distance from the surface of the HCE.
In another aspect, a method is provided for retrofitting existing parabolic trough power plants to increase efficiency.
Reference will now be made to the accompanying drawings, which assist in illustrating the various pertinent features of the presented inventions. The following description is presented for purposes of illustration and description and is not intended to limit the inventions to the forms disclosed herein. Consequently, variations and modifications commensurate with the following teachings, and skill and knowledge of the relevant art, are within the scope of the presented inventions. The embodiments described herein are further intended to explain the best modes known of practicing the inventions and to enable others skilled in the art to utilize the inventions in such, or other embodiments and with various modifications required by the particular application(s) or use(s) of the presented inventions.
As shown, each of the ribs is an elongated element that is substantially rectangular in cross-section having two ends/edges and two opposing side surfaces. However, it will be appreciated that in further embodiments the ribs 50 may be shaped (e.g., curved, parabolic, cusp etc.). In any arrangement, the ribs will typically each have an end/edge surface that may be disposed along the length of the HCE 20. However, in various embodiments the ribs may be spaced above the surface of the HCE 20. The cross-sectional height of each rib, extending radially outward from the surface of the HCE 20, permit gathering of stray and misaligned reflected light rays while allowing properly directed light rays to pass into the HCE. In this regard, one or both side surfaces of each of the ribs 50 forms a reflector that allows for capturing stray and misaligned reflected light rays, which may then be re-directed onto the absorber tube 22 within the evacuated glass envelope 24. To redirect the stray reflected light rays, one or both side surfaces of the ribs is a partially reflective surface, which may be formed of, for example, reflective polished aluminum or specially coated reflective metal. Alternatively, a reflective film may be applied to the ribs 50.
The redirection of the stray and misaligned light rays by the ribs 50 is at least partially illustrated in
While the ribs 50 provide the ability to capture some additional light rays which would otherwise spill past the HCE 20, it is been recognized that additional spilled light rays may be recaptured by the use of the external reflective shield 60. The illustrated embodiment of the reflective shield 60 is a corrugated element that is adapted for disposition on a radial outside portion of the HCE 20. More specifically, the reflective shield is disposed on the outside surface of the glass envelope 24 on the side of the glass envelope that is opposite of the vertex of the parabolic reflector. Referring again to
As noted above, the disclosed embodiment of the external concentrator 40 utilizes a pair of rib sets 50 that are separated by a reflective shield 60. The size and orientation of each of these elements may be varied. For instance, the number of the rib reflectors of each rib set may be varied based on physical parameters of the system with which they are used. Commonly, a height of the ribs in the radial direction will be between about ½ cm and about 3 cm. However, other sizes are possible and considered within the scope of the presented inventions. For instance, the height of the ribs will vary based on the diameter of the HCE. Along these lines, the height of the ribs may be between about 1% and 40% of the diameter of the HCE. Further, it will be appreciated that the axial length of the ribs may be varied based on, for example, the length of an HCE on which the ribs will be placed. Likewise, the number and placement of the radial ribs about the outside surface of the HCE 20 may likewise be varied. Currently, it is believed that the location of the reflectors should extend from approximately 30° (i.e., 0) on either side of a reference line between the vertex of the parabolic receiver and a central axis of the HCE 20 to about 90° (i.e., φ) on either side of the reference line. However, these angles may be increased plus or minus 30°. See
To correctly position the ribs and reflective shield, the present embodiment of the external concentrator 40 utilizes wire cables 62 that are spaced along the length of the concentrator 40. See
Accordingly, each rib 50 may have a rib axis 32 that intersects the center line 30 of the HCE 20 at the same point, wherein this point is located at some distance from the central axis of the HCE 20. In other embodiments, individual ribs 50 within a rib set, located on one side of the collector may be oriented a different angles relative to each other. For example a first rib 50a or subset of ribs located on one side of the HCE 20 may have a rib axis 32a that intersects center line 30 at a first location 100a, and a second rib 50b or subset of ribs located on the same side of the HCE 20 may have a rib axis 32b that intersects center line 30 at a second location 100b. Further, ribs 50 located on opposite sides of the HCE 20 may be oriented independently of each other. In such an embodiment (not shown) a first rib 50 located on a first side of the HCE may have rib axis 32 that intersects a center line 30 at a first point, and a corresponding second rib 50 located on the opposite side of the HCE may have a rib axis 32 that intersects the center line 30 at a second point.
In addition to varying the orientation of the ribs 50 in relation to the HCE 20,
To further increase the amount of radiation received by the HCE 20, the brims 150 illustrated in
As shown, the reflective shield 60 in
The foregoing description has been presented for purposes of illustration and description. Furthermore, the description is not intended to limit the inventions and/or aspects of the inventions to the forms disclosed herein. Consequently, variations and modifications commensurate with the above teachings, and skill and knowledge of the relevant art, are within the scope of the presented inventions. Along these lines, different aspects of the inventions shown in different figures may be utilized in various combinations including combinations not explicitly shown. The embodiments described hereinabove are further intended to explain best modes known of practicing the inventions and to enable others skilled in the art to utilize the inventions in such, or other embodiments and with various modifications required by the particular application(s) or use(s) of the presented inventions. It is intended that the appended claims be construed to include alternative embodiments to the extent permitted by the prior art.
Claims
1. A solar concentrator configured for attachment to a generally cylindrical outside surface of a heat collection element (HCE) positioned along a focal line of a parabolic reflector, comprising:
- at least first and second elongated ribs each having, in cross-section, an edge surface adapted for disposition along a length of the HCE and at least one reflective side surface extending outward from the outside surface of the HCE, wherein said elongated ribs are radially spaced about the outside surface of the HCE.
2. The solar concentrator of claim 1, wherein said first and second elongated ribs comprise a first set of elongated ribs and a second set of elongated ribs, respectively.
3. The solar concentrator of claim 1, wherein each rib of each set of ribs is spaced from at least one adjacent rib when attached to the outside surface of the HCE.
4. The solar concentrator of claim 3, further comprising:
- a reflective shield having a reflective surface disposed toward the outside surface of the HCE.
5. The solar concentrator of claim 4, wherein said reflective shield covers between about 15° (i.e., ˜0.25 rad) and about 120° (i.e., ˜2.1 rad) of the outside surface of the HCE.
6. The solar concentrator of claim 5, wherein said reflective shield is disposed on the outside surface of the HCE between said first and second elongated ribs.
7. The solar concentrator of claim 4, wherein said reflective shield is corrugated.
8. The solar concentrator of claim 4, further comprising:
- first and second brims attached to lateral edges of said reflective shield at first and second attachment points.
9. The solar concentrator of claim 8, wherein said brims are, in cross-section, disposes at an angle +/−90° (β) on either side of a radial line extending through a centerline axis of the HCE.
10. The solar concentrator of claim 9, wherein said brims, in cross-section, are:
- rectangular,
- parabolic; or
- curved.
11. The solar concentrator of claim 2, wherein said first and second sets of elongated ribs are disposed on opposite sides of a reference line extending between a vertex of the parabolic reflector and a centerline of the HCE.
12. The solar concentrator of claim 11, wherein each set of elongated ribs are radially spaced over about 15° (i.e., ˜0.25 rad) and about 120° (i.e., ˜2.1 rad) of the outside surface of the HCE.
13. The solar concentrator of claim 1, wherein a height of said ribs, in cross section, is between about 1% and about 40% of a diameter of said generally cylindrical heat collection element (HCE).
14. A solar concentrator configured for attachment to a generally cylindrical outside surface of a heat collection element (HCE) positioned along a focal line of a parabolic reflector, comprising:
- a reflective shield extending over an outside surface of the HCE, having a reflective surface disposed toward the outside surface of the HCE;
- at least first and second elongated brims extending from lateral edges of the reflective shield each having at least one reflective side surface extending outward from the outside surface of the HCE, wherein the elongated brims are connected to the reflective shield at first and second attachment points.
15. The solar concentrator of claim 14, wherein the first and second elongated brims, in cross-section, extend from the HCE a length between 1-40% of the HCE diameter.
16. The solar concentrator of claim of claim 15, wherein the brims, in cross-section, are:
- rectangular;
- parabolic; or
- curved.
17. The solar concentrator of claim 16, wherein the first and second elongated brims are oriented at an angle relative to first and second cross-sectional radial lines, respectively, wherein the first and second cross-sectional radial lines extend from a central axis of the HCE through the first and second attachment points, respectively.
18. The solar concentrator of claim 17, wherein the first and second elongated brims are oriented at an angle between 0-90° in either direction of the first and second cross-sectional radial lines, respectively.
19. The solar concentrator of claim 14, wherein the reflective shield forms a corrugated surface comprising a plurality of alternating ridges and grooves.
20. The solar concentrator of claim 19, wherein the corrugated surface, in cross-section, is formed from one of alternating:
- rectangular sections;
- parabolic sections; or
- curved sections.
Type: Application
Filed: Jun 6, 2017
Publication Date: Dec 7, 2017
Inventors: Ryan S. Wood (Broomfield, CO), Adam Calihman (Boulder, CO)
Application Number: 15/615,187