Beam Integration For Concentrating Solar Collector

• US 20070251568A1
• Filed: 04/26/2006
• Published: 11/01/2007
• Est. Priority Date: 04/26/2006
• Status: Active Grant

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Palo Alto Research Center, Inc. (Xerox Holdings Corp.)
• Inventors: Maeda, Patrick
• Granted Patent: US 7,855,335 B2
• Time in Patent Office: Days
• US Class Current: 136/246
• CPC Class Codes: F24S 23/30 with lenses
• CPC Class Codes: F24S 23/71 with parabolic reflective surfaces with cylindro-parabolic reflective surfaces F24S23/74
• CPC Class Codes: F24S 23/79 with spaced and opposed interacting reflective surfaces
• CPC Class Codes: G02B 19/0028 refractive and reflective surfaces, e.g. non-imaging catadioptric systems
• CPC Class Codes: G02B 19/0042 for use with direct solar radiation
• CPC Class Codes: H01L 31/0543 comprising light concentrating means of the refractive type, e.g. lenses
• CPC Class Codes: H01L 31/0547 comprising light concentrating means of the reflecting type, e.g. parabolic mirrors, concentrators using total internal reflection
• CPC Class Codes: Y02E 10/52 PV systems with concentrators

Abstract

A concentrating solar collector that utilizes a solar collector optical system to concentrate solar light onto a PV cell (image plane), wherein the solar collector optical system includes an array of first optical elements that divide the solar light into separate beams, and a secondary optical system that integrates (superimposes) the separate beams in a defocused state at the image plane, thereby forming a uniform light distribution pattern on the PV cell. The secondary optical system is positioned at a distance from the aperture plane, whereby the rays of each separate beam leaving the secondary optical element are parallel. The image plane (PV cell) is located at the back focal point of the second image element, whereby all of the separate beams are superimposed on the PV cell in a defocused state. Optional intervening third optical elements are used to increase the acceptance angle.

Claims

1. A concentrating solar collector apparatus including a photovoltaic (PV) cell defining an image plane and a solar collector optical system for concentrating solar light onto the PV cell, wherein the solar collector optical system comprises:

a plurality of first optical elements for dividing the solar light into a plurality of separate beams; and

a secondary optical system for integrating the plurality of separate beams such that the plurality of separate beams are superimposed on the PV cell in a defocused state.

2. The concentrating solar collector according to claim 1, wherein the plurality of first optical elements comprises an array of lenslets disposed in an aperture plane.

3. The concentrating solar collector apparatus according to claim 2,

wherein each of the plurality of first optical elements defines a focal length,

wherein the secondary optical system comprises a secondary optical element disposed at a distance equal to twice said focal length from the aperture plane, whereby the rays of each said separate beam are parallel between the second optical element and the image plane.

4. The concentrating solar collector apparatus according to claim 3, wherein the PV cell is disposed at a distance equal to said focal length from the second optical element.

5. The concentrating solar collector apparatus according to claim 3, further comprises a plurality of third optical elements, each third optical element being disposed at a distance equal to said focal length from both the second optical element and a corresponding first optical element.

6. The concentrating solar collector apparatus according to claim 1, wherein the plurality of first optical elements comprises a curved surface that is truncated by four straight peripheral edges.

7. The concentrating solar collector apparatus according to claim 2, wherein each lenslet comprises a curved upper surface that is truncated by four straight peripheral edges, thereby forming a square lenslet aperture.

8. The concentrating solar collector apparatus according to claim 2, wherein each lenslet comprises one of a hexagonal and a keystone-shaped lenslet aperture.

9. The concentrating solar collector apparatus according to claim 2, wherein the secondary optical system comprises a concave primary mirror and a convex secondary mirror that define a central optical axis [X₀] and a primary focal point located on the central optical axis and a first region of the image plane.

10. The concentrating solar collector apparatus according to claim 9, each lenslet of the array of lenslets defines an associated optical axis that is parallel to the central optical axis and intersects the concave primary mirror.

11. The concentrating solar collector apparatus according to claim 9, further comprising a solid, light-transparent optical structure having a first side including a relatively large convex surface, a second side including a substantially flat first aperture surface defining the aperture plane, and a relatively small curved surface defined in a central portion of the aperture surface,

wherein the primary mirror is disposed on the convex surface, and

wherein the secondary mirror is disposed on the curved surface.

12. The concentrating solar collector apparatus according to claim 11, wherein the plurality of first optical elements comprises a plurality of lenslets disposed on the first aperture surface of the optical structure.

13. The solar collector according to claim 12, wherein the plurality of lenslets are integrally molded with the optical structure such that the plurality of lenslets protrude from the aperture surface.

14. The concentrating solar collector apparatus according to claim 11, wherein the optical structure comprises one of glass and plastic.

15. The concentrating solar collector apparatus according to claim 11, wherein each of the plurality of first optical elements comprises one of a spherical, conic, aspherical, cylindrical, toroidal, on-axis or off-axis sectioning, concave and convex surface shape.

16. The concentrating solar collector apparatus according to claim 11, wherein the primary mirror and secondary mirror comprise a first and second films of a reflective mirror material that is deposited onto the convex surface and the curved surface, respectively.

17. The concentrating solar collector apparatus according to claim 9, wherein each of the lenslets comprises a curved upper surface defining a secondary optical axis that is parallel to the central optical axis, wherein the curved upper surface is truncated by four straight peripheral edges, thereby forming a square lenslet aperture.

18. The concentrating solar collector apparatus according to claim 17, wherein the lenslets are arranged such that at least one said straight peripheral edge of each lenslet is shared with at least one adjacent lenslet.

19. The concentrating solar collector apparatus according to claim 18, further comprising a solid, light-transparent optical structure having a first side including a relatively large convex surface, a second side including a substantially flat first aperture surface defining the aperture plane, and a relatively small curved surface defined in a central portion of the aperture surface,

wherein the primary mirror is disposed on the convex surface, and

wherein the secondary mirror is disposed on the curved surface.

20. The concentrating solar collector apparatus according to claim 19, wherein the lenslets are integrally molded with the optical element such that the lenslets are disposed over an entirety of the first aperture surface.

21. The concentrating solar collector apparatus according to claim 2, further comprising a solid, light-transparent optical structure having a first side including a relatively large convex surface surrounding a rear aperture surface, a second side including a front aperture surface defining the aperture plane, and a relatively small curved surface defined in a central portion of the front aperture surface,

wherein the secondary optical system comprises at least one of a concave primary mirror disposed on the convex surface and a convex secondary mirror disposed on the curved surface.

22. The concentrating solar collector apparatus according to claim 21, wherein the plurality of first optical elements comprises an array of lenslets disposed on the front aperture plane.

23. The concentrating solar collector apparatus according to claim 21,

wherein the convex surface of the optical structure defines a plurality of protrusions, and

wherein the concentrating solar collector apparatus further comprises a plurality of curved mirrors, each curved mirror being disposed on an associated said protrusion.

24. The concentrating solar collector apparatus according to claim 21,

wherein the curved surface of the optical structure defines a plurality of indentations, and

wherein the concentrating solar collector apparatus further comprises a plurality of curved mirrors, each curved mirror being disposed on an associated said indentation.

25. The concentrating solar collector apparatus according to claim 21, wherein the rear aperture surface comprises an array of lenslets.

26. A Cassegrain-type concentrating solar collector comprising:

a photovoltaic (PV) cell defining an image plane;

a concave primary mirror and a convex secondary mirror that collectively define a central optical axis and a primary focal point located on the central optical axis and a first region of the image plane; and

an array of lenslets, each optical element defining a focal point that coincides with a corresponding surface portion of the concave primary mirror.