Improved solar cell strings for photovoltaic modules

Abstract

The invention relates to a solar cell string (1) for a photovoltaic module, comprising (i) a string of solar cells (2a, 2b, 2c) facing each other with opposite polarities and being shingled in the direction of the string with or without partial overlap of the solar cells (2a, 2b, 2c); and (ii) at least one elongated and electrically conductive interconnect (3a, 3b) extending in the direction of the string from one side of a solar cell to the opposite side of the next solar cell (2a, 2b, 2c) to mechanically and electrically connect the shingled solar cells (2a, 2b, 2c) in the direction of the string on alternating top and bottom sides of the solar cells. ) of positive and negative electrodes; and (iii) at least two adhesives, optionally thermal adhesive foils (4a, 4b), covering at least one elongated interconnect (3a, 3b) and at least a portion of the top or bottom side of each solar cell, wherein the solar cells include the elongated interconnects, provided that (a) there are no horizontal gaps between the shingled solar cells; (b) the adhesives (4a, 4b) do not contact each other and do not extend beyond one solar cell, do not extend into the optional partial overlap of the solar cells (2a, 2b, 2c), and at least partially cover and mechanically fix at least one interconnect (3a, 3b) to the solar cell (2a, 2b, 2c).

Description

[0001] The invention relates to a solar cell string (1) for a photovoltaic module, comprising (i) a string of solar cells (2a, 2b, 2c) facing each other with opposite polarities and being shingled in the direction of the string with or without partial overlap of the solar cells (2a, 2b, 2c); and (ii) at least one elongated and electrically conductive interconnect (3a, 3b) extending in the direction of the string from one side of a solar cell to the opposite side of the next solar cell (2a, 2b, 2c) to mechanically and electrically connect the shingled solar cells (2a, 2b, 2c) in the direction of the string on alternating top and bottom sides of the solar cells. ) of positive and negative electrodes; and (iii) at least two adhesives, optionally thermal adhesive foils (4a, 4b), covering at least one elongated interconnect (3a, 3b) and at least a portion of the top or bottom side of each solar cell, wherein the solar cells include the elongated interconnects, provided that (a) there are no horizontal gaps between the shingled solar cells; (b) the adhesives (4a, 4b) do not contact each other and do not extend beyond one solar cell, do not extend into the optional partial overlap of the solar cells (2a, 2b, 2c), and at least partially cover and mechanically fix at least one interconnect (3a, 3b) to the solar cell (2a, 2b, 2c).

[0002] Typically, photovoltaic modules are assembled from many strings of solar cells (i.e., solar panels) that are produced and shipped separately, and these strings are arranged side by side to form a large flat body. The solar cells of the string are electrically interconnected by wires or ribbons that connect the electrode side of one cell to the electrode side of an adjacent cell, allowing current to flow in the direction of the string. Solar strings with solar cells arranged in parallel often feature a front-front configuration, in which all the front sides of the cells have the same electrode charge, and wires or ribbons connect the front electrode of one cell to the oppositely charged back electrode of an adjacent cell.

[0003] The most common interconnect scheme features a gap between adjacent cells so that the interconnect can be guided from the top side of one cell to the bottom side of the connected cell.

[0004] In another approach, solar cells can be connected with a slight overlap, allowing direct conductive contact of adjacent cells.

[0005] Overlapping and shingled strings of solar cells do not require conventional wire or ribbon interconnects because the oppositely charged cell electrodes are in close proximity. Mechanical and conductive contact is typically achieved by adding a low resistance conductive interconnect material such as a conductive bonding alloy. The metallized interconnects are typically thicker to enhance current flow. Since gaps between front-to-front arranged solar cells for electrical insulation are no longer required, the size of shingled front-to-back arranged solar cells and solar cell strings can be designed to be smaller, providing the opportunity to achieve higher module efficiencies.

[0006] However, mechanical stresses on the interconnections in the overlap of shingled solar cells have the potential for (micro) cracks, which can lead to a reduction in the current or even electronic short circuits due to thermomechanical stresses. Another disadvantage of shingling solar cells in the overlap region with direct contact is the relatively large overlap, which is necessary to ensure good contact, so that the overlap is no longer available for current formation.

[0007] WO2019 / 016118A1 discloses a solar cell string, which includes (i) a string of solar cells, which are shingled in the direction of the string, resulting in overlapping positive and negative electrodes; (ii) interconnects, which are used to electrically connect the positive and negative electrodes of the shingled solar cells; and (iii) an adhesive foil, which spans at least a portion of the string and is positioned as follows: (a) on the top side (sun-facing side) of at least two shingled solar cells, and / or (b) on the bottom side (far side) of two shingled solar cells, or (c) on the top side of one solar cell and on the bottom side of the overlapping solar cells, in which case the adhesive foil includes the interconnects and connects the overlap, thereby mechanically connecting and positioning the shingled solar cells.

[0008] U.S. Patent 7432438B2 relates to an electrode for contacting a conductive surface of a photovoltaic element, the electrode comprising an electrically insulating optically transparent film, an adhesive layer disposed on a planar surface of the film, and a plurality of substantially parallel conductive wires embedded in the adhesive layer, wherein the wires are located on the planar surface of the film and the thickness of the adhesive layer is less than the thickness of the wires embedded therein, wherein a portion of the surface of the wire protrudes from the adhesive layer and at least a portion of the surface is covered by a coating composed of an alloy having a low melting point to facilitate welding the wires to the conductive surface and a first terminal strip.

[0009] The object of the present invention is to provide an electrically conductive, efficient and mechanically stable solar cell string for assembling a photovoltaic module, in particular an electrically conductive, efficient and mechanically stable shingled solar cell string.

[0010] In a first aspect of the invention, this object is achieved by a solar cell string (1) for a photovoltaic module, said solar cell string comprising:

[0011] (i) a string of at least two solar cells (2a, 2b, 2c) facing each other with opposite polarity and shingled in the direction of the string with or without partial overlap of the solar cells (2a, 2b, 2c);

[0012] (ii) at least one elongated and electrically conductive interconnect (3a, 3b), optionally a wire, ribbon or bus bar, extending in the direction of the string from one side of one solar cell to the opposite side of the next solar cell (2a, 2b, 2c) to mechanically and electrically connect the positive and negative electrodes of the shingled solar cells (2a, 2b, 2c) in the direction of the string on alternating top and bottom sides of the solar cells, and

[0013] (iii) at least two adhesives (4a, 4b), optionally thermal adhesive foils, covering at least one elongated interconnect (3a, 3b) and at least a portion of the top or bottom side of each solar cell comprising the elongated interconnect;

[0014] The prerequisite is that (a) there are no horizontal gaps between the shingled solar cells; (b) the adhesive (4a, 4b) does not touch each other, does not extend beyond one solar cell, does not extend into the optional partial overlap of the solar cells (2a, 2b, 2c), and at least partially covers and mechanically fixes at least one interconnect (3a, 3b) to the solar cell (2a, 2b, 2c).

[0015] The term "solar cell string" as defined herein includes all mechanical and conductive arrangements of more than one solar cell that generate and transmit photovoltaically generated current along adjacently positioned solar cells in the direction of the string, i.e., in the direction of current flow from the solar cell at one end to the solar cell at the opposite end.

[0016] The solar cell string of the present invention is used in a photovoltaic module, i.e., for assembly and forming part of a functional photovoltaic module. Optionally, the solar cell used in the present invention is conventional, e.g., having a semiconductor material, e.g., anode and cathode material, i.e., positive and negative electrodes, located between the top and bottom surfaces, which can be formed, e.g., by metallization or a transparent conductive coating (e.g., a transparent film coating).

[0017] The term "shingled in the string direction" as used herein means that consecutive, i.e. adjacent solar cells are vertically offset in the string direction. In a string of solar cells arranged according to the invention, the solar cells are shingled in an overlapping or non-overlapping manner, which means that consecutive solar cells partially cover each other, i.e. an upper cell partially shades a vertically offset lower solar cell, or, alternatively, consecutive solar cells are vertically offset but do not form a horizontal gap.

[0018] The overlapping edge area of ​​the vertically offset lower solar cells is optionally minimized to avoid loss of photovoltaic activity due to shading in the resulting solar cell module.

[0019] The solar cell string of the present invention comprises at least one elongated and electrically conductive interconnect (3a, 3b), optionally a wire or a bus bar, which extends in the direction of the string from one side of a solar cell to the opposite side of the next solar cell (2a, 2b, 2c) to mechanically and electrically connect the positive and negative electrodes of the shingled solar cells (2a, 2b, 2c) on the alternating top and bottom sides of the solar cells along the direction of the string.

[0020] In an alternative embodiment of the invention, the solar cell string (1) of the invention is one in which the shingled solar cells at least partially overlap and the interconnection (3a, 3b) is not fixed to at least one or both solar cells in the overlapping region. This alternative has the advantage that the shingled solar cell string retains some additional mechanical flexibility in the overlapping region.

[0021] In another alternative embodiment, the shingled solar cells do not overlap in a solar cell string.

[0022] In the string of the present invention, the interconnects used to mechanically and electrically connect the electrodes of the shingled solar cells can be any material used for the described functions. For example, at least one elongated interconnect (3a, 3b), optionally a wire, ribbon or bus bar, which can further connect all the contact structures, optionally to the contact fingers of each solar cell.

[0023] In an optional embodiment, the solar cell string (1) of the present invention is one in which the height or diameter of at least one elongated interconnect (3a, 3b) determines the minimum vertical offset (5), optionally the gap (5), of adjacent solar cells in the solar cell string (1). In other words, consecutive and adjacent solar cells are only vertically separated and mechanically connected by the interconnect, and the mechanical flexibility of the interconnect substantially determines the flexibility of the solar cell string.

[0024] For example, at least one interconnect (3a, 3b) is selected from the group consisting of: a busbar, a ribbon, and a metal wire, optionally the metal wire is coated with a solderable material, optionally coated with a solder comprising Ag-, Cu-, Bi-, In-, Pb-, Sn-, and combinations thereof, optionally a solder comprising SnBi- or In-. In a non-limiting embodiment, the interconnect (3a, 3b) may be in mechanical and electrical contact with the conductive layer of the solar cell.

[0025] The solar cell string of the invention comprises at least two adhesives (4a, 4b), optionally thermal adhesive foils, covering at least one elongated interconnect (3a, 3b) and at least a portion of the top or bottom side of each solar cell comprising the elongated interconnect.

[0026] It is well known that adhesives used on the top side of a solar cell, i.e. the adhesive facing the sun, must be transparent to sunlight in order to start and continue the photovoltaic process in the solar cell. The adhesive may not be transparent if it does not substantially prevent sunlight from reaching the photovoltaically active top side, or if the adhesive is located on the bottom, i.e. the shadowed side, of the solar cell.

[0027] Adhesive (4a, 4b), for example, adhesive foil, optionally thermal adhesive foil is a polymer foil or includes a polymer foil, optionally selected from the group including: composite thermosetting plastics (duroplasts), optionally EVAs (ethylene vinyl acetate), TPSEs (thermoplastic silicone elastomers), TPUs (thermoplastic polyurethanes), PETs (polyethylene terephthalates), TPOs (thermoplastic polyolefin elastomers), ionomers; thermoplastic plastics, optionally PVBs (polyvinyl butyral), silicone, polyolefins (PO), PPs (polypropylene), ionomers; and a combination of thermal composite thermosetting plastics (thermoduoplasts), optionally a polymer foil thermal adhesive, whose temperature range is 50°C to 250°C, optionally 60°C to 200°C, optionally 75°C to 175°C.

[0028] The solar cell string of the present invention is unique in that: (a) there is no horizontal gap between the shingled solar cells, i.e. the solar cells partially overlap, or the horizontal distance between adjacent cells, i.e. the gap (5) is zero; (b) the adhesive (4a, 4b) does not contact each other and does not extend beyond one solar cell, does not extend into the optional partial overlap of the solar cells (2a, 2b, 2c), and at least partially covers and mechanically fixes at least one interconnect (3a, 3b) to the solar cell (2a, 2b, 2c).

[0029] The solar cell string and embodiments thereof as described herein have many advantages. For example, the adhesive, in particular the adhesive foil, only fixes the interconnection / wire to each solar cell and does not extend to the next solar cell. Therefore, mechanical stability, limited flexibility and connectivity are essentially provided only by the solar cell connection interconnections, and these interconnections do not span any horizontal gaps between consecutive solar cells, thus avoiding mechanical stress when excessively bending the interconnections between solar cells, but allowing some limited mechanical flexibility, which of course depends on the flexibility of the interconnection material used and its size and shape, such as wire or ribbon.

[0030] Optionally, an adhesive, such as a thermal adhesive foil, does not extend into the overlapping areas of consecutive solar cells.

[0031] In another embodiment of the invention, interconnections in overlapping regions of consecutive solar cells in a string are not electrically or mechanically connected (eg soldered) to the solar cells, thus saving expensive connection materials, such as solder paste, such as silver containing solder paste.

[0032] And, for the alternative of not having an adhesive (e.g. thermal adhesive foil) extending to the partially overlapping area of ​​two consecutive solar cells in a string, there will be less stress during adhesive lamination, resulting in improved process yield, and the lack of adhesive foil will reduce the bending stress of the interconnector after lamination.

[0033] The solar cell strings of the invention are generally more flexible, but also resistant to mechanical stresses (e.g. during transport, weather influences, etc.), and they can be easily and economically produced, since, for example, the interconnects (e.g. wires) can first be positioned and fixed to the adhesive (e.g. foil), and then the solar cells can be positioned and fixed in a shingled arrangement. Alternatively, the interconnects (e.g. wires) can first be positioned and fixed to consecutive solar cells, and then the adhesive foil can be positioned and fixed.

[0034] Further aspects of the invention relate to a method for producing a solar cell string as described herein, and to a photovoltaic module comprising the solar cell string.

[0035] In the following, the present invention will be illustrated by means of representative examples and drawings, neither of which should be construed as limiting the scope of the present invention beyond the appended claims.

[0036] Reference numerals list

[0037] (1) Solar cell string

[0038] (2) (2a, 2b, 2c) Solar cell

[0039] (3a, 3b) Conductive interconnection

[0040] (4a, 4b) Adhesive (optionally thermal adhesive foil)

[0041] (5) Vertical offset (gap) between adjacent solar cells in a solar cell string

[0042] Instruction Manual

[0043] FIG. 1 schematically shows a shingled solar cell string 1 for assembling a photovoltaic module according to the present invention, which has three continuous solar cells 2a, 2b, 2c and which have a partial overlap at the end. Interconnections 3a, 3b can be implemented, for example, as busbars, ribbons and metal wires, optionally metal wires coated with weldable materials, such as described herein. The dotted line indicates that the structure is located below the solar cell. For example, the interconnection 3a is located at the top of the solar cell 2a (direct sunlight) and continues to be an interconnection 3b when located below the solar cell 2b (shadow). The adhesive foil 4a is transparent, while the adhesive foil 4b may optionally not be transparent because it is shielded in any case in operational use. The adhesive foil 4a attaches the interconnection 3a to the top side of the solar cell 2a and hardly extends into the partial overlap 5 of the solar cell 2a and the solar cell 2b. Therefore, the adhesive foil 4a contributes to the minimum vertical offset together with the height or diameter of the interconnection 3a. In an alternative embodiment, the adhesive 4a does not extend into the overlap 5, and the vertical offset is determined only by the height or diameter of the interconnection 3a. The adhesive foil 4b attaches (i.e. fixes) the interconnect 3b to the bottom side of the solar cell 2b and may or may not optionally extend into the partial overlap 5 of the solar cell 2a and the solar cell 2b. Optionally, the interconnects 3a, 3b may not be attached (i.e. fixed) to the solar cells 2a, 2b in the overlap region 5 and limited mechanical flexibility, such as bending, may be allowed, depending on the shape, material properties and flexibility of the interconnects 3a, 3b.

[0044] 2 is a side view of an embodiment of the solar cell string of FIG. 1 , wherein adhesive 4 a, 4 b (e.g., thermal adhesive foil) attaches interconnects 3 a, 3 b to solar cells 2 but does not extend into the overlap region, and wherein the vertical offset of the solar cells is substantially determined by the height or diameter of the interconnects 3 a, 3 b.

[0045] 3 is a side view of the solar cell string of FIG. 2 with the option of linear interconnects 3a, 3b, wherein the vertical offset of the solar cells 2 is substantially determined by the diameter of the interconnects 3a, 3b and the adhesive foils 4a, 4b do not extend into the overlapping area of ​​the solar cells 2.

Claims

1. A solar cell string (1) for a photovoltaic module, wherein include: (i) a string of at least two solar cells (2a, 2b, 2c) facing each other with opposite polarity and shingled in the direction of the string with or without partial overlap of the solar cells (2a, 2b, 2c); (ii) at least one elongated and electrically conductive interconnect (3a, 3b), the at least one elongated and electrically conductive interconnect (3a, 3b) being a wire, ribbon or bus bar extending in the direction of the string from one side of one solar cell to the opposite side of the next solar cell (2a, 2b, 2c) to mechanically and electrically connect the positive and negative electrodes of the shingled solar cells (2a, 2b, 2c) in the direction of the string on alternating top and bottom sides of the solar cells; as well as (iii) at least two adhesives (4a, 4b), the at least two adhesives (4a, 4b) being thermal adhesive foils covering at least one elongated and electrically conductive interconnect (3a, 3b) and at least a portion of the top side or bottom side of each solar cell, the solar cell comprising the elongated and electrically conductive interconnect; The prerequisite is that (a) there is no horizontal gap between the shingled solar cells; (b) the adhesive (4a, 4b) does not touch each other and does not extend beyond one solar cell, and when there is a partial overlap between at least two shingled solar cells (2a, 2b, 2c), the adhesive (4a, 4b) does not extend into the partial overlap of the solar cells (2a, 2b, 2c); and (c) the adhesive (4a, 4b) at least partially covers and mechanically fixes at least one elongated and electrically conductive interconnect (3a, 3b) to at least two solar cells (2a, 2b, 2c).

2. The solar cell string (1) according to claim 1, in, The shingled solar cells at least partially overlap, and at least one elongated and electrically conductive interconnect (3a, 3b) is not secured to at least one or both solar cells in the overlapping region.

3. The solar cell string (1) according to claim 1, in, Shingled solar cells do not overlap.

4. The solar cell string (1) according to any one of claims 1 to 3, in, At least one elongated and electrically conductive interconnect (3a, 3b) is further connected to all contact structures.

5. The solar cell string (1) according to any one of claims 1 to 3, in, At least one elongated and electrically conductive interconnect (3a, 3b) is further connected to the contact fingers of each solar cell.

6. The solar cell string (1) according to any one of claims 1 to 3, in, The height or diameter of at least one elongated and electrically conductive interconnect (3a, 3b) determines the minimum vertical offset of adjacent solar cells in the solar cell string (1).

7. The solar cell string (1) according to any one of claims 1 to 3, in, The height or diameter of at least one elongated and electrically conductive interconnect (3a, 3b) determines the gap (5) between adjacent solar cells in the solar cell string (1).

8. The solar cell string (1) according to any one of claims 1 to 3, in, At least one elongated and electrically conductive interconnect (3a, 3b) is selected from the group consisting of: a bus bar, a ribbon and a metal wire.

9. The solar cell string (1) according to claim 8, in, The metal wire is coated with a solderable material.

10. The solar cell string (1) according to claim 9, in, The solderable material is a solder containing Ag-, Cu-, Bi-, In-, Pb-, Sn- and combinations thereof.

11. The solar cell string (1) according to claim 10, in, The solder is a SnBi- or In-containing solder.

12. The solar cell string (1) according to any one of claims 1 to 3, in, At least one elongated and electrically conductive interconnect (3a, 3b) is in mechanical and electrical contact with the conductive layer of the solar cell.

13. The solar cell string (1) according to any one of claims 1 to 3, in, The heat-bonding foil is or comprises a polymer foil selected from the group consisting of composite thermosets, thermoplastics or thermoplastic elastomers.

14. The solar cell string (1) according to claim 13, in, The thermoplastic elastomer is ethylene vinyl acetate, thermoplastic silicone elastomer, thermoplastic polyolefin elastomer or ionomer.

15. The solar cell string (1) according to claim 13, in, The thermoplastic plastic is polyvinyl butyral, polyurethane, polyethylene terephthalate, polyolefin, polyethylene or polypropylene.

16. The solar cell string (1) according to any one of claims 1 to 3, in, The thermal adhesive foil is or comprises a polymer foil, the polymer foil being a polymer foil thermal adhesive having a temperature range of 50°C to 250°C.

17. The solar cell string (1) according to claim 16, in, The polymer foil thermal adhesive has a temperature range of 60°C to 200°C.

18. The solar cell string (1) according to claim 17, in, The polymer foil thermal adhesive has a temperature range of 75°C to 175°C.

19. A photovoltaic module comprising a solar cell string (1) according to any one of claims 1 to 18.

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