Solar module having reflector between cells

• US 5,994,641 A
• Filed: 04/24/1998
• Issued: 11/30/1999
• Est. Priority Date: 04/24/1998
• Status: Expired due to Term

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: ASE Americas Incorporated (Carl-Zeiss-Stiftung)
• Inventors: Kardauskas, Michael J.
• Primary Examiner(s): CHAPMAN, MARK A
• Application Number:
  US09/066,157
• Time in Patent Office: 585 Days
• Field of Search: 136/246, 438/71, 438/72
• US Class Current: 136/246
• CPC Class Codes: H01L 31/048 Encapsulation of modules
• 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: H01L 31/056 the light-reflecting means being of the back surface reflector [BSR] type
• CPC Class Codes: Y02E 10/52 PV systems with concentrators

Abstract

A photovoltaic module comprising an array of electrically interconnected photovoltaic cells disposed in a planar and mutually spaced relationship between a light-transparent front cover member in sheet form and a back sheet structure is provided with a novel light-reflecting means disposed between adjacent cells for reflecting light falling in the areas between cells back toward said transparent cover member for further internal reflection onto the solar cells. The light-reflecting comprises a flexible plastic film that has been embossed so as to have a plurality of small V-shaped grooves in its front surface, and a thin light-reflecting coating on said front surface, the portions of said coating along the sides of said grooves forming light-reflecting facets, said grooves being formed so that said facets will reflect light impinging thereon back into said transparent cover sheet with an angle of incidence greater than the critical angle, whereby substantially all of the reflected light will be internally reflected from said cover sheet back to said solar modules, thereby increasing the current output of the module.

Claims

1. A solar cell module comprising:

a support structure having a planar surface adapted to support an array of solar cells;

a plurality of solar cells overlying said planar surface, said cells having front and back surfaces with said back surfaces facing said planar surface, said cells being spaced from one another in an array of rows and columns, whereby predetermined areas of said planar surface are free of solar cells;

a transparent cover member overlying and spaced from all of said solar cells;

a light-reflecting medium overlying said predetermined areas of said planar surface, said light-reflecting medium comprising a flexible laminated sheet material in the form of a flexible plastic film coated with a light-reflecting coating, said laminated sheet material having a thickness less than the thickness of said cells, said plastic film being textured by embossing so that said laminated sheet material has a plurality of light-reflecting facets each having a predetermined angular relationship with respect to said cover member and said planar surface, whereby light impinging on said facets is reflected back to said transparent cover member at an angle relative to said cover member which is greater than the critical angle, whereby said reflected light is internally reflected by said cover member back toward said solar cells.

2. The module of claim 1 wherein said laminated sheet material has a plurality of parallel V-shaped grooves with said facets constituting the sides of said grooves.

3. The module of claim 2 wherein said grooves have a depth less than the thickness of said plastic film.

4. The module of claim 2 wherein each facet extends at an angle between 25 and 35 degrees relative to the plane of said cover member.

5. The module of claim 2 wherein said plastic film has a thickness in the range of 0.004 inch to 0.010 inch, and said grooves have a depth of approximately 0.002 inch.

6. The module of claim 5 wherein said grooves have a repeat spacing of about 0.007 inch.

7. The module of claim 2 wherein said plastic film has a thickness in the range of 0.004 inch to 0.010 inch and said grooves have a repeat spacing of about 0.007 inch.

8. The module of claim 2 wherein said light-reflecting medium comprises several pieces of said laminated sheet material disposed so that said grooves extend in a first direction between adjacent rows of cells and a second direction between adjacent columns of cells.

9. The module of claim 2 wherein said flexible laminated sheet material has a first plurality of grooves extending parallel to one another and a second plurality of grooves extending parallel to one another but at an angle to said first plurality of grooves.

10. The module of claim 9 wherein said solar cells have a rectangular shape, and said first and second pluralities of grooves are arranged to define a plurality of rectangular open areas sized to accommodate said solar cells, and said laminated sheet material is disposed so that each of said open areas is covered by a solar cell and said grooves are located in spaces between solar cells.

11. The module of claim 2 wherein said grooves have a depth of approximately 0.002 inch.

12. The module of claim 1 wherein said light-reflecting medium comprises a film of a flexible thermoplastic organic polymer and said coating is made of aluminum or silver.

13. The module of claim 12 wherein said organic polymer is a polyethylene terephthalate material.

14. The module of claim 12 wherein said coating is made of aluminum or silver.

15. The module of claim 12 wherein said coating is made of silver.

16. The module of claim 12 wherein said coating is made of aluminum.

17. The module of claim 1 wherein said cells and said light-reflecting medium are encapsulated in a light transmitting polymer material that extends to and is bonded to said cover member and said planar surface of said support structure, with said light transmitting polymer being engaged with and bonded to said light-reflecting medium.

18. The module of claim 1 wherein said flexible laminated sheet material is interposed between said cells and said planar surface of said support structure, and further wherein said cells and said laminated sheet material are encapsulated in a light transmitting polymer material that extends to and is bonded to said cover member and said planar surface of said support structure.

19. The module of claim 18 wherein said plastic film has a plurality of parallel V-shaped grooves with said facets constituting the sides of said grooves, and further wherein said grooves have a depth of approximately 0.002 inch.

20. In a solar cell module having a plurality of electrically interconnected solar cells arrayed in rows and columns on a planar surface of a support structure with at least some of said cells being spaced from one another so that selected areas of said planar surface are not covered by said cells, a light-transparent cover member overlying and spaced from said cells, and a light-transparent solid medium overlying and encapsulating said cells, said light-transparent solid medium being bonded to said cover member, the improvement comprising:

a flexible laminated light-reflecting medium overlying said planar surface in said selected areas and encapsulated by said light-transparent solid medium, said light-reflecting medium comprising a flexible plastic film that has a front surface facing said cover member and a rear surface and which has been embossed at said front surface so that said front surface defines a plurality of V-shaped grooves each having an included angle between 110° and

130°

, and a reflective film covering and bonded to said front surface, said reflective film conforming to the shape of and being coextensive with said grooves whereby portions of said reflective film covering the sides of said grooves form a plurality of light reflective facets that are bonded to said light-transparent solid medium, each of said facets extending at an angle to said cover member such that light impinging on said facets will be reflected upwardly through said light-transparent solid material into said transparent cover member and then downwardly through said light-transparent sold material toward said cells.

21. The improvement of claim 20 wherein said grooves each have a depth of approximately 0.002 inch.

22. The improvement of claim 20 wherein the geometry of said grooves is such that incident light normal to the solar cell module which impinges on said light-reflecting medium will be reflected by said reflective facets back through said light-transparent solid medium to said cover member at an angle to said cover member which is greater than the critical angle.

23. The improvement of claim 20 wherein said film has a thickness in the range of 0.004 inch to 0.010 inch.

24. The improvement of claim 20 wherein said grooves have a repeat spacing of approximately 0.007 inch.

25. A solar cell module comprising:

a structure adapted for supporting an array of solar cells;

a plurality of solar cells arrayed on said support structure so that selected areas of said support structure are exposed;

a light-reflecting medium disposed in said selected areas so as to extend into proximity with each adjacent cell bordering said areas;

a light-transparent cover member overlying and spaced from said solar cells, said cover member being parallel to said support structure and the planes of said solar cells, said cover member having an index of refraction between 1.3 and 3.0; and

a light-transparent optical medium covering said cells and said light-reflecting medium, said light transparent optical medium extending to and being bonded to said cover sheet;

said light-reflecting medium comprising a flexible laminated sheet material in the form of a flexible plastic film with a thickness between 0.004" and 0.010" that has front and rear surfaces and has been embossed so that said front surface is characterized by a plurality of V-shaped grooves, and a light-reflecting metallic coating covering said front surface of said plastic film, portions of said metallic coating on the areas of said front surface that define said plurality of grooves forming light-reflecting facets, said grooves having a geometry such that light passing through said light transparent optical medium and impinging on said light-reflecting facets will be reflected upwardly through said optical medium to said cover member and thereafter internally reflected downwardly from said cover member through said light transparent optical medium to said solar cells.

26. A module according to claim 25 wherein said cells have a rectangular shape and are arranged in rows and columns, and further wherein said light-reflecting medium comprises strips of said flexible laminated sheet material disposed between adjacent rows of cells and also between adjacent rows of cells.

27. A method of increasing the output current of a given solar cell module having a back sheet, a transparent front cover sheet, and a plurality of solar cells arrayed on said back sheet between said back sheet and said cover sheet, said array of cells defining land areas therebetween, said method comprising:

(1) placing in said land areas a flexible light-reflecting laminated sheet material comprising a flexible plastic film having front and rear surfaces and a thin reflective coating on said front surface facing said cover sheet, said plastic film having a plurality of V-shaped grooves embossed in said front surface, portions of said reflective coating along said grooves forming flat light-reflecting facets with said facets oriented as an angle of between 25 and 35 degrees to said cover sheet; and

(2) reflecting solar radiation impinging on said facets via said transparent cover sheet back into said transparent cover sheet so that said reflected solar radiation will be reflected internally from said cover member downwardly toward said solar cells, whereby light impinging on said facets is directed onto said solar cells and thereby increases the output current of said solar cell module.

28. A method of increasing the output current of a given solar cell module having a back sheet, a transparent front cover sheet, and a plurality of solar cells arrayed on said back sheet between said back sheet and said cover sheet, said array of cells defining land areas therebetween, said method comprising:

providing an extended length web of a flexible plastic film having flat front and back surfaces and a thickness in the range of 0.004 to 0.010 inch;

embossing said front surface of said plastic film so as to form parallel V-shaped grooves therein each having a depth of approximately 0.002 inch and an included angle in the range of 110°

to 130°

;

coating said embossed front surface of said plastic film with a reflective coating having a thickness of about 1000 Angstroms or less so as to form a laminated film material comprising said plastic film and said coating, with portions of said coating along said grooves forming light-reflecting facets;

severing at least one selected length of said laminated film material from said web and placing said at least one selected length in said land areas between said back sheet and said front cover sheet so that the widest portions of said grooves face said cover sheet; and

reflecting solar radiation impinging on said facets via said transparent cover sheet back into said transparent cover sheet so that said reflected solar radiation will be reflected internally from said cover member downwardly toward said solar cells, whereby light impinging on said facets is directed onto said solar cells and thereby increases the output current of said solar cell module.

29. The method of claim 28 wherein said cells are rectangular in shape and are arranged in rows and columns, and further wherein several lengths of said laminated film material severed from said web are placed in said land areas so that between said rows said grooves run parallel to said rows and between said columns said grooves run parallel to said columns.

30. A method of manufacturing a solar cell module comprising the following steps:

providing an extended length web of a flexible plastic film having flat front and back surfaces and a thickness in the range of 0.004 to 0.010 inch;

embossing said front surface of said plastic film so as to form contiguous parallel V-shaped grooves therein, with each groove having an included angle in cross section in the range of 110 to 130 degrees;

coating said embossed front surface of said plastic film with a reflective coating having a thickness of about 1000 Angstroms or less so as to form a laminated film material comprising said plastic film and said reflective coating, with portions of said reflective coating along said grooves forming light-reflecting facets;

severing at least one selected length of said laminated film material from said web;

providing a back sheet, a transparent front cover sheet, and a plurality of solar cells arrayed on said back sheet with land areas between said cells;

placing said at least one selected length of said laminated film material in said land areas in overlying relation with said back sheet, with the widest portions of said grooves facing away from said back sheet; and

sealing said cells and said laminated film material to said cover sheet and said back sheet with a polymeric light-transmitting medium that is interposed between and bonded to said cover sheet and said back sheet and encapsulates said cells and said at least one selected length of said laminated film material, whereby to form a sealed solar module.

31. The method of claim 30 wherein said reflective coating is a metal film or comprises a plurality of dielectric films.

32. The method of claim 30 wherein said grooves have a depth of approximately 0.002 inch.

33. A method of manufacturing a solar cell module comprising the following steps:

providing an extended length web of a laminated film material that comprises (a) a flexible plastic film having flat front and back surfaces and a thickness in the range of 0.004 to 0.010 inch, with said front surface of said plastic film embossed so as to form contiguous parallel V-shaped grooves therein with each groove having in cross-section an included angle in the range of 110 to 130 degrees, and (b) a reflective coating on said front surface having a thickness of about 1000 Angstroms or less, with portions of said reflective coating along said grooves forming light-reflecting facets;

severing at least one selected length of said laminated film material from said web;

providing a back sheet, a transparent front cover sheet, and a plurality of solar cells arrayed on said back sheet with land areas between said cells;

placing said at least one selected length of said laminated film material in said land areas in overlying relation with said back sheet, with the widest portions of said grooves facing away from said back sheet; and

sealing said cells and said laminated film material to said cover sheet and said back sheet with a polymeric light-transmitting medium that is interposed between and bonded to said cover sheet and said back sheet and encapsulates said cells and said at least one selected length of said laminated film material, whereby to form a sealed solar module.

34. A solar cell module comprising:

a support structure having a planar surface adapted to support an array of solar cells;

a plurality of solar cells arrayed on said planar surface, said cells having front and back surfaces with said back surfaces facing said planar surface, said cells being spaced from one another in an array of rows and columns, whereby predetermined areas of said planar surface are free of solar cells;

a transparent cover member overlying and spaced from all of said solar cells;

a light-reflecting medium overlying said predetermined areas of said planar surface, said light-reflecting medium comprising a flexible laminated sheet material in the form of a flexible plastic film having a thickness in the range of 0.004 inch to 0.010 inch and coated with a light-reflecting coating having a thickness substantially less than the thickness of said plastic film, said plastic film being textured by embossing so that said laminated sheet material has a plurality of V-shaped grooves each having an included angle in the range of 110°

to 130°

with the sides of said grooves functioning as light-reflecting facets, whereby light impinging on said facets is reflected back to said transparent cover member at an angle relative to said cover member which is greater than the critical angle, whereby said reflected light is internally reflected by said cover member back toward said solar cells; and

a light-transmitting polymer material disposed between and bonded to said cover member and said support structure in encapsulating relation with said solar cells and said light-reflecting medium.

35. A solar cell module according to claim 34 wherein said light-transmitting polymer material is EVA or an ionomer.

36. A solar cell according to claim 35 wherein said plastic film is a polyester or a polyolefin.