Patent Application
20240274738
The present invention is directed to solar cell string assemblies with strings of solar cells with electrically conducting interconnect(s) in string direction, and with a flat adhesive(s), optionally a foil, for adhesively attaching the interconnect(s) to the solar wafers positioned adjacent or shingled in string direction, wherein the adhesive extends to at least one solar cell or adhesive of solar cell of at least one parallel solar cell string for mechanically bridging and connecting parallel solar cell strings, wherein the substantially flat adhesive does not extend adhesively from one solar cell (2a) to an adjacent solar cell in string direction, wherein the solar cells in parallel connected solar cell strings do not have electrically conductive contact. The invention further pertains to photovoltaic modules comprising these parallel solar cell string assemblies.
Typically, a photovoltaic module is assembled from a number of individually produced and separately transported solar cell strings, i.e. solar panels, and the strings are arranged side by side to form one large flat body. The solar cells of the string are electrically interconnected by wires or ribbons that connect the electrode side of one cell with the electrode side of the adjacent cell, thus allowing for current flow in string direction. Solar cell strings with solar cells arranged in parallel regularly feature a front-front configuration, where all front sides of the cells have the same electrode charge and the wire or ribbon will connect the front electrode of one cell with the rear electrode of opposite charge of the adjacent cell for serial connectivity. Alternatively, solar cells arranged in parallel may also feature a front-back configuration, where adjacent cells along the string direction have top and bottom sides facing each other in opposite polarity and the wire or ribbon establishes serial connectivity. A further option for solar strings is a front-front configuration with back contact energy conversion, e.g. “interdigitated back contact” (IBC) solar cells, where the entire front of the solar cell absorbs sunlight without shading from wires or ribbons. Most common interconnection schemes feature a certain gap between neighboring cells to enable the guidance of an interconnector from one side (one polarity) of one cell to the other side (opposite polarity) of the connected cell.
In an alternative way the solar cells can be connected by a slight overlap and thus allowing direct conductive contact of adjacent cells.
Overlapping shingled solar cell strings do not need conventional wire or ribbon intercon-nectors because of the close proximity of oppositely charges cell electrodes. Mechanical and conductive contact is routinely achieved by adding low resistance electrically conductive interconnect materials such as conductive adhesive alloys. The metallization interconnect is often rather thick to improve current flow. Since the gap for electrical insulation between front-front-arranged solar cells is no longer required, the shingled front-rear-arranged solar cells and the solar cell string can be dimensioned smaller giving the opportunity to achieve higher module efficiencies
However, mechanical stress on the interconnect in the overlap of shingled solar cells has the potential for (micro)cracks, possibly leading to reduced current flow or even short-circuiting of the electrons due to thermo-mechanical stress. A further disadvantage of solar cell shingling with direct contact in the overlapping zone is the relatively large overlap, necessary to guarantee a good contact and hence that the overlap part is no longer available for current formation.
WO2019/016118A1 discloses solar cell strings comprising (i) a string of solar cells shingled in string direction resulting in positive and negative electrode overlap, (ii) an interconnect for electrically connecting the positive and negative electrodes of the shingled solar cells, and (iii) an adhesive foil spanning at least part of the string and positioned on (a) the top (sun facing) sides of the at least two shingled solar cells, and/or (b) the bottom (far) sides of the at least two shingled solar cells, or on (c) the top side of one solar cell and on the bottom side of the overlapping solar cell, in which case the adhesive foil comprises the interconnect and connects the overlap in order to mechanically connect and position the shingled solar cells.
U.S. Pat. No. 7,432,438 B2 relates to an electrode for contacting an electrically conductive surface of a photovoltaic element, the electrode comprising an electrically insulating optically transparent film, an adhesive layer provided on a planar surface of the film, and a plurality of substantially parallel, electrically conductive wires embedded into the adhesive layer, wherein the wires lie over the planar surface of the film, and the adhesive layer has a thickness less than the thickness of the wires embedded therein, wherein part of the surfaces of the wires protrudes from the adhesive layer and at least part of the surfaces are covered by a coating consisting of an alloy having a low melting point, to facilitate soldering the wires to the electrically conductive surface and to a first terminal bar.
US2019/0296172 A1 discloses a solar panel comprising first and second cover members, i.e. foils, that completely cover the solar cells of the panel together with their electrical interconnects, i.e. wires, on top and bottom and further seal these on the sides, similar to laminating a document on both sides. The sealing members block moisture and oxygen and chemically connect elements on the solar panel. The sealing member can be adhesive, e.g. be made from polymers like EVA and resins.
It is the objective of the present invention to provide conductively efficient and mechanically stable, optionally flexible solar cell string assemblies for use in the production of photovoltaic modules, in particular conductively efficient and mechanically stable shingled and non-shingled solar cell strings and solar cell string assemblies of these.
In a first aspect of the invention the objective is solved by a solar cell string assembly comprising at least two parallel solar cell strings (1), optionally in front-front or front-back solar cell configuration with electrically conducting interconnect(s) (3) and serial interconnection in string direction (5), and with a flat adhesive(s) (4), optionally a foil, for adhesively attaching the interconnect(s) (3) to the solar cell wafers (2a) positioned adjacent or shingled in string direction (5), wherein this adhesive (4) extends to at least one solar cell (2) of at least one parallel solar cell string (1), but does not extend from one solar cell (2a) to an adjacent solar cell in string direction (5) for mechanically bridging and connecting parallel solar cell strings (1) in a solar cell string assembly, wherein the solar cells (2a) in parallel connected solar cell strings (1) do not have electrically conductive contact.
This arrangement of parallel linked solar cell strings in the solar cell string assembly has the advantage that the flat adhesive(s) already being functional for attaching the interconnect(s) to the solar cell wafer(s) of one string further spans at least partially the solar cell(s) (2a) in a parallel solar cell string, thus providing a highly economical, environmentally protective and mechanically stabilizing means that links the structural stability of one string with that of a parallel string in the string assembly for use in the production of a photovoltaic module. Moreover, the adhesive does not span adjacent solar cells in string direction, thus providing more flexibility for the individual strings but at the same time providing further mechanical stability to each solar cell in a string to due to its mechanically connecting solar cells in parallel strings.
The term solar cell string assembly, as used herein, is meant to encompass any at least two solar cell strings arranged adjacent and in parallel in string direction with or without a gap or overlap, i.e. negative gap, between strings and with or without vertical offset of the parallel solar cell strings, wherein the parallel solar cell strings are mechanically connected by at least one flat adhesive for fixing the interconnect(s) on one solar cell wafer of one string to a solar cell wafer in the parallel solar cell string. The term solar cell assembly is understood to refer to an arrangement, layout, array, system, formation, set-up and/or configuration of solar cell strings as described herein. As used herein, the term solar cell is intended to designate a solar cell wafer unit together with its functionally essential components such as interconnects and optionally adhesives as well as further optional components. The term solar cell wafer, as used herein, is meant to include semiconductor contacts and metallic contact structures like fingers, busbars or pads.
In one embodiment, the invention relates to a solar cell string assembly for use in a photovoltaic module comprising at least two parallel solar cell strings (1) of at least two solar cells (2a), the solar cells (2a) comprising
The term “substantially flat adhesive”, as used herein, is meant to be understood to relate to a continuous adhesive having a flat and planar profile as in a sheet, layer or foil, i.e. the adhesive forms a two-dimensional layer with a height much lower than the width and length of the layer, e.g. a height less than 1/10, 1/50, 1/100, 1/1000th of the width and length of the layer. Typical and exemplary heights of substantially flat adhesives for practicing the present invention and for fixing electrically conductive interconnects, e.g. wires, to solar cells are 50 to 300 micrometer. The flat adhesive can be applied to the interconnects and the solar cell wafers as a sheet, layer or foil or, alternatively as a spray coat, subsequently forming a sheet, layer or foil with sufficient structural integrity to remain mechanically intact over the whole area covered in the string assembly of the present invention, thereby connecting parallel solar cells and solar cell strings in the solar cell string assembly of the present invention. It is noted that the terms sheet, layer and foil are used interchangeably to indicate the planar character of the substantially flat adhesive.
The flat adhesive(s) extending from one or more solar cell(s) in one string to one or more solar cell(s) in a parallel string may cover and adhere to part of the solar cells covered or it may cover most if not all of at least one of the solar cells involved.
In one embodiment, the at least one substantially flat adhesive (4), optionally thermoadhesive foil(s), extends to an adhesive of a solar cell (2a) of at least one parallel solar cell string (1) for mechanically bridging and connecting parallel solar cell strings (1) in the solar cell string.
In one embodiment, the solar cell string assembly of the present invention is one, wherein the at least one adhesive (4) covers completely one side of at least one solar cell (2a), and extends to and adhesively connects to the adhesive of at least one solar cell (2a) of at least one parallel solar cell string (1).
In the solar cell string assembly of the present invention the solar cells (2a) in string direction are optionally positioned on the same level with or without a gap between adjacent solar cells (2a), or alternatively, the solar cells (2a) are vertically offset in string direction with or without partial overlap of solar cells (2a).
In one embodiment of the solar cell string assembly of the invention the solar cells are optionally shingled and overlap at least partially in string direction and the at least one interconnect (3) is not fixated to at least one or both of the solar cell wafers (2) in the overlap region.
In a further embodiment of the solar cell string assembly of the invention the height or diameter of the at least one elongated interconnect (3) determines the minimum vertical offset, optionally gap (5) of adjacent solar cells (2a) in a solar cell string (1).
In one alternative embodiment, the solar cell strings for use in a solar cell string assembly of the present invention may comprise at least one adhesive, optionally thermoadhesive foil(s), that covers at least the full width of a solar cell wafer as measured perpendicular to the string direction.
In another alternative embodiment the solar cell string for use in the present invention may comprise at least one adhesive (4), optionally thermoadhesive foil(s), that covers at least the full length of a solar cell wafer as measured parallel to the string direction.
The term “solar cell string”, as defined herein, encompasses all mechanical and conductive arrangements of more than one solar cell that generates and transports a photovoltaically ge-nerated current along adjacently positioned solar cells in string direction, i.e. in the direction of current flow from the solar cell on one end to the solar cell on the opposite end.
The solar cell string assemblies of the present invention are for use in a photovoltaic module, i.e. for assembling and forming part of a functional photovoltaic module. Optionally, the solar cells for use in the present invention are conventional, e.g. with a semiconductor material positioned between top and bottom surfaces, e.g. anode and cathode materials, i.e. positive and negative electrodes, that may, for example, be formed by metallization or a transparent conductive coating, e.g. a transparent film coating.
It is understood that solar cells in the solar cell strings of the string assembly of the present invention may optionally have front-front or front-back configuration, i.e. top and bottom sides may face each other in the same or opposite polarity, and that the planar sides of two adjacent solar cells in a solar cell string or the assembly are substantially parallel and may optionally overlap partially or not at all, optionally featuring a gap between adjacent solar cells in horizontal or vertical direction. The interconnect(s) is configured in any way that allows for serial connectivity in the strings.
In one embodiment of the solar cell string assembly of the invention, the solar cells and their wafers in the string are positioned on the same level with a gap between adjacent solar cells, or the solar cells and their wafers in the string are shingled in string direction with or without partial overlap of solar cells.
The term ,,shingled in string direction”, as used herein, is meant to indicate that consecutive, i.e. neighboring solar cells and their wafers are vertically offset in string direction. In a string the solar cells may be shingled with or without overlap, meaning that consecutive solar cells partially cover each other, i.e. the upper cell partially shades the vertically offset lower solar cell, or alternatively, the consecutive solar cells are offset vertically but do not form a horizontal gap.
The overlapped edge region of the vertically offset lower solar cell may be optionally mini-mized to avoid loss of photovoltaic activity due to shading in the resulting solar module.
In one alternative embodiment of the present invention the solar cell strings in the string assembly of the present invention comprise shingled solar cells that overlap at least partially in string direction and the at least one interconnect is not fixated to at least one or both of the solar cell wafers in the overlap region. This alternative has the advantage that the shingled solar cell string maintains some additional mechanical flexibility in the overlap region.
In another alternative embodiment the shingled solar cells do not overlap in the solar cell string. The solar cell string in the string assembly of the invention comprises at least one elongated electrically conducting interconnect, optionally a wire or busbar, extending in string direction for mechanically and electrically connecting the positive and negative electrodes of the shingled or non-shingled solar cells in string direction
In the string assembly of the present invention the at least one interconnect for mechanically and electrically connecting the electrodes of the solar cell wafers may be any material serving said function. For example, the at least one elongated interconnect, optionally a wire, ribbon or bus bar, may further connect all contact structures, optionally contact fingers on each solar cell.
In one optional embodiment the solar cell string in the string assembly of the present invention may be one, wherein the height or diameter of the at least one elongated interconnect determines the minimum vertical offset, optionally gap of adjacent solar cells in the solar cell string. In other words, the consecutive neighboring solar cells are vertically separated and mechanically connected only by the interconnect and the mechanical flexibility of the interconnect essentially determines the flexibility of the solar cell string.
For example, the at least one interconnect is selected from the group consisting of bus bars, ribbons and metal wires, optionally metal wires coated with solderable material, optionally with Ag—, Cu—, Bi—, In—, Pb—, Sn— and combinations thereof—comprising solder, optionally SnBi— or In-comprising solder. In one non-limiting embodiment, the interconnect mechanically and electrically may contact a conductive layer on the solar cell.
The solar cell string in the solar cell string assembly of the present invention comprises at least one substantially flat adhesive, optionally at least two substantially flat adhesives, optionally thermoadhesive foils, positioned on and adhesive to, thus covering, the at least one elongated interconnect and at the same time at least part of the top or bottom side(s) of each solar cell wafer that comprises the elongated interconnect(s).
It is common general understanding that adhesives on the side(s) of a solar cell, directed towards the sun must be transparent for the sun light to initiate and continue the photovoltaic pro-cess in the solar cell.
The substantially flat adhesive(s), for example, adhesive layers or foils, optionally thermoadhesive foils, are made from or comprise a polymer material, optionally selected from the group consisting of duroplasts, optionally EVAs (ethylene vinyl acetates), TPSEs (thermoplastic silicone elastomers), TPUs (thermoplastic polyurethanes), PETs (polyethylene terephthalates), TPOs (thermoplastic polyolefin elastomers), ionomers, thermoplasts; optionally PVBs (polyvinylbutyrals), silicones, polyolefins (PO), PPs (polypropylenes), ionomers; and combinations of thermoduoplasts, optionally a polymer foil thermoadhesive at temperatures in the range of 50 to 250° C., optionally in the range of 60 to 200° C., optionally in the range of 75 to 175° C.
Further aspects of the present invention relate to a photovoltaic module comprising a solar cell string assembly of the present invention as described herein.
In one embodiment, the photovoltaic module of the present invention comprises at least two parallel positioned solar cell strings, the parallel solar cell strings positioned on the same level or shingled perpendicular to the string direction, without electrically conductive contact between parallel solar cells in the parallel strings, optionally having a gap or electrically insulating material between parallel solar cells.
Another aspect encompasses the use of a solar cell string assemblies of the invention as described herein for producing a photovoltaic module.
Further aspects of the present invention relate to a method for producing the solar cell string assemblies as described herein, and to a photovoltaic module comprising the solar cell string assemblies.
In the following the present invention will be illustrated by representative examples and figures, none of which are to be interpreted as limiting the scope of the present invention beyond the appended claims.
(3) electrically conducting interconnect (e.g. wire, busbar, etc.)
| Number | Date | Country | Kind |
|---|---|---|---|
| 21178533.2 | Jun 2021 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/065585 | 6/8/2022 | WO |
