Patent Application
20180090635
The disclosed technology relates to the field of photovoltaic cells, for example, to methods for electrically contacting a photovoltaic cell, e.g., to interconnect a plurality of such photovoltaic cells. More particularly, certain aspects of the disclosed technology relate to methods for electrically contacting a photovoltaic cell, such as a busbar-free photovoltaic cell, and to methods for electrically interconnecting such photovoltaic cells, e.g., busbar-free photovoltaic cells.
In typical commercially available photovoltaic cells, an electrical current generated under illumination is collected at metal fingers that are electrically connected to a few, e.g., typically three, wide busbars. Tinned copper strips or ribbons, which may also be referred to as connectors or interconnectors, may be soldered to the busbars to electrically connect photovoltaic cells within a module in a photovoltaic cell system known in the art, e.g., to connect photovoltaic cells in series or in parallel. The size of the interconnectors is preferably limited to avoid excessive shadowing on the illuminated surface of the cells.
Furthermore, methods are known in the art for contacting and interconnecting busbar-free photovoltaic cells. In such methods, the metal fingers of the busbar-free photovoltaic cells are contacted and connected by means of multiple electrically conductive wires. These electrically conductive wires may thus replace the busbars and the interconnectors. It is a feature of such methods that a lower cost of photovoltaic modules can be achieved, e.g., due to a reduced silver consumption for the metallization and/or due to an increased module efficiency resulting from a lower series resistance and improved light harvesting.
The wires for contacting the busbar-free photovoltaic cells may, for example, be solder-coated copper wires. The wires may furthermore be soldered onto the cells before encapsulation, e.g., as described in “Multi-wire interconnection of busbar-free solar cells”, Johann Walter et al, Energy Procedia 55(2014) 380-388. In this approach, the wires may be preferably soldered to solder pads provided on the metal fingers of the cell. However, such prior-art methods may have the disadvantages of requiring a carefully controlled wire expansion during the soldering process, a risk of wire displacement from the solder pads during soldering and a need for a high positioning accuracy.
In EP1547158, a method is described in which busbar-free photovoltaic cells are contacted and interconnected by means of an electrode comprising an electrically insulating optically transparent film, an adhesive layer on one surface of the film and a plurality of substantially parallel, electrically conductive wires embedded into the adhesive layer, a part of the surfaces of the wires protruding from the adhesive layer. The electrically conductive wires are covered by a coating consisting of an alloy with a low melting point. The technology is based on applying the foil directly onto the metallized cell and performing a pressing and heating process, thereby bonding the wires to the metal fingers of the photovoltaic cell and providing an electrical contact between the wires and the metal fingers. The temperature during the connection process can be kept low, resulting in a reduced stress on the cells. However, a disadvantage of this approach is that the wires attached to the film are only contactable at one side of the film. Therefore a terminal bar needs to be provided at the end of the wires to enable interconnection of cells. Another disadvantage is that differences in thermal expansion between the cells and the wires may generate mechanical stress in the system.
One objective of the disclosed technology is to provide good and efficient electrical contacts and interconnections in photovoltaic cell systems, e.g., for busbar-free photovoltaic cells, such as silicon photovoltaic cells.
The above objective may be accomplished by a method and device according to the disclosed technology.
An aspect of embodiments of the disclosed technology is that a high contacting flexibility may be provided in a photovoltaic cell system, e.g., a higher contacting flexibility as compared to known methods.
One feature of embodiments of the disclosed technology that photovoltaic cells, e.g., busbar-free photovoltaic cells, such as silicon photovoltaic cells, can be interconnected without the need for providing terminal bars or end ribbons.
Another feature of embodiments of the disclosed technology is that electrical contacts and/or interconnections for photovoltaic cells are provided while simultaneously providing a good encapsulation of the photovoltaic cells in an easy and efficient manner
A further feature of embodiments of the disclosed technology that differences in thermal expansion between the photovoltaic cells and interconnecting wires are relieved.
One or more aspects of the disclosed technology relate to a method for electrically contacting photovoltaic cells, e.g., busbar-free photovoltaic cells. One exemplary method of the present disclosure comprises providing a woven fabric that includes a plurality of electrically conductive wires, the electrically conductive wires being provided in a single one of a warp direction and a weft direction. The woven fabric further includes a plurality of polymer yarns, the polymer yarns being provided in at least the other one of the warp direction and the weft direction. For example, the electrically conductive wires may be provided in the weft direction and the polymer yarns may be provided in the warp direction. For example, the electrically conductive wires may be provided in the warp direction and the polymer yarns may be provided in the weft direction. For example, the electrically conductive wires may be provided in either one of the weft direction and the warp direction and the polymer yarns may be provided in both the weft direction and the warp direction.
Such method(s) may further include bringing the woven fabric into physical contact with a surface of a photovoltaic cell including a plurality of metal contacts, and performing a heating process, thereby establishing an electrical connection between the respective metal contacts and at least one electrically conductive wire and thereby liquefying, e.g., melting, the plurality of polymer yarns such as to transform the plurality of polymer yarns into an encapsulation layer.
In a method in accordance with embodiments of the disclosed technology, the plurality of metal contacts may for example include, e.g., a plurality of parallel metal lines, such as metal fingers, having a longitudinal direction. In such embodiments, bringing the woven fabric into physical contact with the surface of the photovoltaic cell may include orienting the woven fabric such that the electrically conductive wires are in a direction other than the longitudinal direction of the parallel metal lines, e.g., substantially orthogonal to the longitudinal direction of the parallel metal lines.
In a method in accordance with embodiments of the disclosed technology, the plurality of metal contacts may for example include, e.g., be composed of, metal features extending in different non-parallel, i.e., intersecting, directions. It is a feature of such embodiments that any orientation of the woven fabric with respect to the photovoltaic cell may be used.
In a method in accordance with embodiments of the disclosed technology, the woven fabric may include a twill weave fabric. It is a feature of using a twill weave fabric that the plurality of electrically conductive wires is exposed at the surfaces of the fabric over a length, also referred to as ‘float’, between two consecutive intersections with the fabric that bridges several polymer yarns. The float can be made sufficiently large to allow a good and reliable electrical connection of the metal wires to the metal contacts of the photovoltaic cell.
In a method in accordance with embodiments of the disclosed technology, the provided polymer yarns may include, or consist of, polymer ribbons.
In a method in accordance with embodiments of the disclosed technology, the polymer ribbons may be provided in the warp direction, e.g., exclusively in the warp direction, and the electrically conductive wires may be provided in the weft direction, e.g., exclusively in the weft direction.
In a method in accordance with embodiments of the disclosed technology, performing the heating process may include performing a first heating step at a first temperature and afterwards performing a second heating step at a second temperature, the second temperature being higher than the first temperature. The first temperature may be selected to enable soldering of the plurality of metal wires to the metal contacts of the photovoltaic cell. The second temperature may be selected to enable melting of the polymer yarns. For example, the first temperature may be in the range between 120° C. and 240° C. and the second temperature may be 10° C. to 50° C. higher than the first temperature, although all embodiments of the disclosed technology are not limited thereto. It is a feature of using a two-step heating process that the first heating step corresponding to the soldering may be performed at a first temperature that is lower than the melting temperature of the polymer wires. Therefore, during soldering, the polymer material is not yet liquefied, such that the risk of penetration of polymer material between the metal contacts and the metal wires, which would lead to bad contacts, can be avoided.
In accordance with embodiments of the disclosed technology, the polymer yarns forming the encapsulation layer may be preferably made of a material that is transparent to light, such as for example a polyolefin material. The material of the polymer yarns may have a transparency higher than 95%, or higher than 98%, or at least 99% in some embodiments, e.g., for light in the wavelength range between 350 nm and 1000 nm, or for light in the wavelength range between 240 nm and 1200 nm, in certain implementations.
In accordance with embodiments of the disclosed technology, the electrically conductive wires may be preferably metal wires coated with a solder material, e.g., a solder alloy. The electrically conductive wires may also be spread, e.g., substantially evenly spread, over the woven fabric, e.g., at least in an area of physical contact between the woven fabric and the surface of the photovoltaic cell.
In accordance with embodiments of the disclosed technology, the solder material may have preferably a melting temperature that is lower than the melting temperature of the plurality of polymer yarns.
The disclosed technology further relates to a method for electrically connecting photovoltaic cells, e.g., silicon photovoltaic cells, and to a method for fabricating photovoltaic modules.
An exemplary method for electrically connecting a first photovoltaic cell with a second photovoltaic cell in accordance with embodiments of the disclosed technology may comprise providing a woven fabric including a plurality of electrically conductive wires, the electrically conductive wires being provided in a single one of a warp direction and a weft direction, the woven fabric further including a plurality of polymer yarns, the polymer yarns being provided in at least the other one of the warp direction and the weft direction. This method further include bringing a first part of the woven fabric into physical contact with a surface of the first photovoltaic cell including first metal contacts, and bringing a second part of the woven fabric into physical contact with a surface of the second photovoltaic cell including second metal contacts. Such method(s) may also include performing a heating process, thereby establishing an electrical connection between the respective first metal contacts and at least one electrically conductive wire and between the respective second metal contacts and at least one electrically conductive wire, at least one electrically conductive wire being electrically connected to both a first metal contact and a second metal contact, and thereby liquefying the plurality of polymer yarns and transforming them into an encapsulation layer.
In some embodiments, more than one electrically conductive wire may be electrically connected to both a first metal contact and a second contact. A plurality of electrically conductive wires may be electrically connected to both a first metal contact and a second contact, for example each electrically conductive wire may be electrically connected to both a first metal contact and a second metal contact.
The surface of the first photovoltaic cell that includes first metal contacts may for example be a front surface of the first cell, and the surface of the second photovoltaic cell that includes second metal contacts may for example be a rear surface of the second cell. In such method according to embodiments of the disclosed technology, an electrical series connection may be established between the first photovoltaic cell and the second photovoltaic cell.
In a method in accordance with embodiments of the disclosed technology, the first part may be brought into contact with this first photovoltaic cell on a first side of the woven fabric, the second part may be brought into contact with the second photovoltaic cell on a second side of the woven fabric, in which the first and second side are opposite sides of the woven fabric.
In a method in accordance with embodiments of the disclosed technology, the single woven fabric may be a twill weave fabric. The first part may include an uneven warp-face twill weave, and the second part may include an uneven weft-face twill weave.
A method in accordance with embodiments of the disclosed technology may further include providing at least one diode in a border region of the woven fabric. One terminal of the at least one diode may be connected to the electrically conductive wires, e.g., to at least one of the electrically conductive wires, to all of the electrically conductive wires, etc. Another terminal of the at least one diode may be adapted for connecting to at least one further photovoltaic cell.
In a method in accordance with embodiments of the disclosed technology, the first photovoltaic cell and the second photovoltaic cell may be connected such as to form at least a part of a first cell string.
In a method in accordance with embodiments of the disclosed technology, the at least one further photovoltaic cell may form at least a part of a second cell string, and the at least one diode may be a bypass diode for connecting the first cell string to said the second cell string.
A method for fabricating a photovoltaic module in accordance with embodiments of the disclosed technology may include electrically connecting a plurality of photovoltaic cells using a method as described hereinabove.
In a further aspect, embodiments of the disclosed technology relate to a photovoltaic module including at least two photovoltaic cells, e.g., a plurality of photovoltaic cells, the at least two photovoltaic cells, e.g., the plurality of photovoltaic cells, being electrically contacted and electrically connected by means of a plurality of electrically conductive wires, wherein the photovoltaic module is free of terminal bars and free of end ribbons.
The at least two photovoltaic cells, e.g., the plurality of photovoltaic cells, may be busbar-free photovoltaic cells. The at least two photovoltaic cells may for example be electrically connected in series, although all embodiments of the disclosed technology are not limited thereto.
It is a feature of methods according to embodiments of the disclosed technology that the electrically conductive wires may be exposed at both opposite sides or opposite surfaces of the woven fabric. Therefore the woven fabric can be electrically contacted at both surfaces of the fabric. This offers a high flexibility of contacting and interconnection of photovoltaic cells, such as for example series connection of photovoltaic cells.
It is another feature of methods according to embodiments of the disclosed technology that the woven fabric includes an encapsulation material. Therefore process steps for contacting and interconnecting the photovoltaic cells and process steps for encapsulating the photovoltaic cells or the photovoltaic module may be combined in a single process.
It is yet another feature of methods according to embodiments of the disclosed technology that the electrically conductive wires used for contacting and interconnecting the photovoltaic cells are provided in a ‘wave’ pattern, e.g., as a consequence of the electrically conductive wires being woven into the woven fabric. When the contacted and/or interconnected photovoltaic cells are subject to changes in temperature, such wave pattern can offer a stress relief.
It is still another feature of methods according to embodiments of the disclosed technology that photovoltaic cells and/or photovoltaic modules may be provided with an improved optical yield. Such improved optical yield may result from light reflection at the electrically conductive wires towards the photovoltaic cells. Due to the wave pattern of the electrically conductive wires, the wires can be locally spaced apart from the cell surface, resulting in a reduced shadowing effect.
It is an aspect of methods in accordance with embodiments of the disclosed technology that bifacial photovoltaic cells can be interconnected by such method.
It is another aspect of methods according to embodiments of the disclosed technology that there is no need for providing a terminal bar at the end of the wires to enable interconnection of cells. A method of the present disclosure can therefore be used for fabricating transparent photovoltaic modules, i.e., photovoltaic modules with a spacing between the interconnected cells, such as for example for building integrated applications. Using a method according to embodiments of the disclosed technology, the areas between the interconnected cells can be made transparent, without terminal bars between the cells.
It is yet another aspect of methods in accordance with embodiments of the disclosed technology that the woven fabric can have a uniform thickness, e.g., the presence of the electrically conductive wires does not add a topography to the fabric. Therefore the amount of encapsulation material, e.g., including or corresponding to the polymer wires in a method according to embodiments of the disclosed technology, may be reduced as compared to known methods, e.g., because there is no need for levelling off a variation in topography or a thickness or height difference.
Certain objectives, features and/or advantages of various inventive aspects have been described herein above. Of course, it is to be understood that not necessarily all such objects, features or aspects may be achieved in accordance with any particular embodiment of the disclosed technology. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one objective/feature/aspect or group of objectives/features/aspects as taught herein without necessarily achieving other objectives, features, aspects and/or advantages as may be taught or suggested herein.
Particular and innovative aspects of the disclosed technology are set out in the accompanying independent and dependent claims. Features from the dependent claims may be combined with features of the independent claims and with features of other dependent claims as appropriate and not merely as explicitly set out in the claims.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter.
Any reference signs in the claims of any priority applications shall not be construed as limiting the scope of any inventions claimed herein.
In the different drawings, the same reference signs refer to the same or analogous elements.
The drawings are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. The dimensions and the relative dimensions do not necessarily correspond to actual reductions to practice of the invention.
The disclosed technology will be described with respect to particular embodiments and with reference to certain drawings though innovations herein are not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting.
Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequence, either temporally, spatially, in ranking or in any other manner. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the disclosed technology can operate in other sequences than described or illustrated herein.
Moreover, the terms top, bottom, over, under and the like in the description and the claims are used for descriptive purposes and not necessarily for describing relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other orientations than described or illustrated herein.
The term “comprising”, used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It needs to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression “a device comprising components A and B” should not be limited to devices consisting only of components A and B.
Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the disclosed technology. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments.
Similarly it should be appreciated that in the description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this invention.
Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination.
In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention and how it may be practiced in particular embodiments. However, it will be understood that embodiments of the disclosed technology may be practiced without these specific details. In other instances, well-known methods, procedures and techniques have not been described in detail, so as not to obscure an understanding of the present description.
In the context of embodiments of the disclosed technology, the front surface or front side of a photovoltaic cell or of a photovoltaic module refers to the surface or side adapted for being oriented towards a light source and thus for receiving illumination. However, in case of bifacial photovoltaic cells or modules, both surfaces are adapted to receive impinging light. In such case, the front surface or front side is the surface or side adapted for receiving the largest fraction of the light or illumination. The back surface, rear surface, back side or rear side of a photovoltaic cell or a photovoltaic module is the surface or side opposite to the front surface or side.
In the context of embodiments of the disclosed technology, a busbar refers to an electrically conductive strip for collecting an electrical current, e.g., a current generated under illumination, from a plurality of metal contacts provided on a surface of a photovoltaic cell. A busbar is provided for direct electrical connection with an external electrical lead. A busbar typically collects the current from finer or narrower metal contacts, also called metal fingers, on the cell. These finer or narrower metal contacts collect current from the cell and deliver the current to the busbars; they are typically not provided for direct electrical connection to an external electrical lead.
In the context of embodiments of the disclosed technology, a busbar-free photovoltaic cell is a photovoltaic cell not having busbars. A busbar-free photovoltaic cell may typically include a plurality of metal contacts on a surface of the cell, but it does not include an electrically conductive element for collecting current from the plurality of metal contacts.
In the context of embodiments of the disclosed technology, a twill fabric or a twill weave is a weave wherein one or more weft yarns (or warp yarns) alternately pass over and under two or more warp yarns (or weft yarns respectively) in a regular repeated manner, with a step or offset between rows. Twill weave is a basic weave characterized by pronounced diagonal ridges, called twill lines. Where is referred to yarns in the context of embodiments of the disclosed technology, reference is made to elongate elements suitable for forming a woven fabric by weaving. A yarn may have a homogeneous structure, e.g., obtained by extrusion, or a composite structure, e.g., by combining component filaments into a thread or strand. A yarn may be composed of a single material or a combination of materials. Particularly, a yarn may refer to a thread, a wire, a filament, a strand, a ribbon, a strip, a tubular structure or a similar elongate element suitable for being woven into a woven fabric.
The disclosed technology relates to methods for electrically contacting a photovoltaic cell and/or for electrically interconnecting photovoltaic cells, e.g., busbar-free photovoltaic cells. Such methods according to embodiments of the disclosed technology are generally based on the usage of a woven fabric, preferably a twill fabric, such as a fabric made of an optically transparent polymer material, with electrically conductive wires provided in, e.g., woven into, the fabric in a single direction, e.g., such that the electrically conductive wires are provided substantially parallel to each other. The fabric is brought into physical contact with a surface of a photovoltaic cell, for example, a busbar-free photovoltaic cell, to which a contact is to be made and a heating process is performed. By performing the heating process, an electrical contact and/or electrical connection is established between the electrically conductive wires of the fabric and metal contacts of the photovoltaic cell. Furthermore, the polymer material is molten and transformed into an encapsulation layer of the photovoltaic cells by this heating process, such that the encapsulation layer embeds the electrically conductive wires.
A woven fabric provided in a method in accordance with embodiments of the disclosed technology includes a plurality of electrically conductive wires, the electrically conductive wires being provided in a single one of a warp direction and a weft direction. The woven fabric further includes a plurality of polymer yarns, the polymer yarns being provided in at least the other one of the warp direction and the weft direction. For example, the electrically conductive wires may be provided in the weft direction and the polymer yarns may be provided in the warp direction. For example, the electrically conductive wires may be provided in the warp direction and the polymer yarns may be provided in the weft direction. For example, the electrically conductive wires may be provided in either one of the weft direction and the warp direction and the polymer yarns may be provided in both the weft direction and the warp direction.
A woven fabric provided in a method in accordance with embodiments of the disclosed technology may thus include a plurality of polymer yarns provided in a warp direction and/or in a weft direction. The woven fabric further includes a plurality of electrically conductive wires that are provided in a single one of the warp direction and the weft direction. The polymer yarns may be preferably made of a material that is optically transparent in a wavelength range that is absorbed by the photovoltaic cell, e.g., silicon photovoltaic cell. For example, the polymer material may have an optical transparency higher than 95%, or higher than 98%, or at least 99% in some embodiments, for light in the wavelength range between 350 nm and 1000 nm, or for light in the wavelength range between 240 nm and 1200 nm, the present disclosure not being limited thereto. The material of the polymer yarns furthermore may have preferably a good UV stability, e.g., it may show no degradation or no substantial degradation under UV illumination, e.g., a very limited or negligible degradation under UV illumination. For example, the polymer yarns may include, or may be composed of, a polyolefin material, a thermoplastic polyurethane (TPU) or a polyvinyl butyral (PVB), embodiments of the disclosed technology not being limited thereto.
In embodiments according to the disclosed technology, the polymer yarns may include, or be, polymer wires. In embodiments according to the disclosed technology, the polymer yarns may include, or be, polymer ribbons. For example, such polymer ribbons may be obtained by cutting or slitting a polymer foil into ribbons, e.g., to obtain strips of the polymer foil. It is a feature of such polymer ribbons that an easy, fast and efficient weaving can be performed, e.g., such that the weaving process can be carried out in a cost-effective manner For example, a densely woven fabric can be provided in accordance with embodiments of the disclosed technology, e.g., having a relatively high encapsulant mass per unit of fabric area for a relatively low ribbon count per unit of fabric length in the weft direction. For example, the width of such ribbons may be optimized to the photovoltaic cell to be electrically contacted, e.g., to the intended interconnection pattern for such cells.
The electrically conductive wires may for example be made of a metal, such as copper or another suitable metal having a high electrical conductivity, and they may be covered by a solder coating, such as for example by a coating (e.g., an alloy) including Sn, Bi, In, Cu and/or Ag, although embodiments of the disclosed technology are not limited thereto.
In a method in accordance with embodiments of the disclosed technology, twill weave may be a preferred weave for providing the polymer yarns, e.g., polyolefin encapsulation yarns, and the electrically conductive wires, e.g., solder coated copper wires. The high density of wires per unit area of a twill weave allows the integration of a sufficiently large volume of polymer yarns, so that after the heating process a good encapsulation of the photovoltaic cells is obtained. It is a feature that there may be no need for providing additional encapsulation material when using a method of the present disclosure. However, the skilled person will understand that additional encapsulation may be provided in accordance with embodiments of the disclosed technology to even further improve the insulation of the cells, e.g., if a particular application requires a particularly high quality of encapsulation, e.g., to protect the cells from a harsh environment.
In a twill fabric as used in a method in accordance with embodiments of the disclosed technology, the electrically conductive wires, e.g., each electrically conductive wire, may alternately pass over a first number of polymer yarns and under a second number of polymer yarns. In a method in accordance with embodiments of the disclosed technology, the polymer yarns may be provided in a balanced twill fabric, in which this first number of polymer yarns equals this second number of polymer yarns. Thus, in embodiments of the disclosed technology, a balanced twill fabric may be used, but embodiments of the disclosed technology are not limited thereto. For example, as further described in more detail, in a method in accordance with embodiments of the disclosed technology, an uneven twill fabric may be used, wherein the first number of polymer yarns over which an electrically conductive wire passes is different from the second number of polymer yarns under which the electrically conductive wire passes. Thus, in embodiments of the disclosed technology, an uneven twill fabric may be used. In a twill fabric as used in a method in accordance with embodiments of the disclosed technology, the electrically conductive wires, e.g., each electrically conductive wire, may be alternately exposed at a first surface of the fabric and at a second, opposite, surface of the fabric. It is a feature that the electrically conductive wires in the fabric can thus be electrically contacted from either side of the fabric, e.g., the fabric is double-side contactable. By selecting the number of polymer weft yarns (or warp yarns) over and under which the electrically conductive wires alternately pass, e.g., by selecting the first number of polymer yarns and the second number of polymer yarns as described hereinabove, a length (also called ‘float’) of the electrically conductive wires on a surface of the fabric between two consecutive intersections with the fabric may be determined. In case of a balanced twill, the length of the exposed parts of the conductive wires may be substantially equal at both sides, i.e., at both surfaces, of the fabric. In case of an uneven twill fabric, the electrically conductive wires may protrude more prominently on one side of the fabric than on the other side of the fabric, such that the length of the exposed parts of the conductive wires may be different between both sides, i.e., between both surfaces, of the fabric.
The density of the conductive wires in the fabric, e.g., the average number of conductive wires per unit of length of fabric in a direction, in the plane of the fabric, that is perpendicular to the longitudinal orientation of the conductive wires, or the lateral distance between neighboring conductive wires in the fabric, and the twill line slope may be optimized and adapted to the metal contact pattern on the surface of the photovoltaic cell. The density of the conductive wires and the twill line slope have an influence on the length of the current path in the metal contacts of the cell towards the metal wires in the fabric and thus on resistive losses. Further, the density of the conductive wires, and their diameter, has an influence on shadowing losses. For example, in case the metal contact pattern of the photovoltaic cell consists of a plurality of parallel metal fingers, the density of conductive wires in the fabric may be optimized taking into account the finger spacing and finger resistance at one hand and shadowing losses at the other hand.
The twill fabric 10 shown in
However, in some methods in accordance with embodiments of the disclosed technology, the twill fabric 10 may also be an uneven twill fabric. In a twill fabric having an uneven twill weave, warp (and/or weft) yarns may protrude more prominently on one side of the fabric than on the other side of the fabric. For example,
In a method in accordance with embodiments of the disclosed technology, the polymer yarns may include polymer ribbons. It is a feature of such embodiments that easier processing and a faster and more cost-effective weaving may be provided as compared to weaving of polymer wires, e.g., extruded polymer wires. A dense weave may thus be provided, with a low ribbon count per cm, e.g., enabling a fast and cost-effective weaving, and a high polymer mass per unit area of the fabric.
In a method in accordance with embodiments of the disclosed technology, the polymer ribbons may be preferably provided in the warp direction y, e.g., exclusively in the warp direction y, and the electrically conductive wires 12 may be preferably provided in the weft direction x, e.g., exclusively in the weft direction x, as shown in
In a method in accordance with embodiments of the disclosed technology, a fabric 10, e.g., as shown in
In embodiments of the disclosed technology, the plurality of metal contacts 21 of the photovoltaic cell 20 may have a configuration different from a finger configuration, e.g., different from a configuration consisting of a plurality of substantially parallel metal lines. An example of an alternative metal contact pattern that may be used is shown in
In a method for electrically contacting a photovoltaic cell 20 according to the present disclosure, a woven fabric 10 including polymer yarns 11, e.g., polymer wires 11, and electrically conductive wires 12, as described hereinabove, is brought into physical contact with a surface of the photovoltaic cell 20 to which an electrical connection is to be made. This is schematically illustrated in
In
Next, e.g., after the step of bringing the fabric 10 into contact with a surface of the cell 20, a heating process is performed. The heating process may form part of a lamination or encapsulation process of the photovoltaic cell or photovoltaic module. This process may be done in a standard laminator as used in known methods for encapsulating photovoltaic modules. During heating, a pressure may be applied, for example a pressure in the range between 0.8 bar and 1 bar, embodiments of the disclosed technology not being limited thereto.
The heating process may include a first heating step at a first temperature and a second heating step at a second temperature. The first temperature, e.g., the temperature to which the structure is heated during the first heating step, may be selected based on the melting temperature of the solder material, e.g., the solder coating of the plurality of electrically conductive wires. The first temperature may, for example, be in the range between 45° C. and 400° C., or in the range between 120° C. and 240° C. During this first heating step, the solder coating on the electrically conductive wires may melt such that solder joints are created with the metal contacts of the cell. In other words, the electrically conductive wires may be soldered to the metal contacts at the locations where the electrically conductive wires are in contact with the metal contacts, e.g., at locations 17 such as indicated by circles in the example shown in
After soldering, in a first step of the heating process, the temperature may be raised to a second temperature in a second step of the heating process. The second temperature may be selected based on the melting temperature of the material of the polymer yarns. Preferably the polymer yarns may have a melting temperature that is higher, such as for example 10° C. to 50° C. higher, than a soldering temperature of the electrically conductive wires 12, e.g., than a melting temperature of a solder alloy coating of the electrically conductive wires 12. As a result of this second heating step, the plurality of polymer wires or yarns may liquefy, e.g., may melt, such as to transform the plurality of polymer yarns into a smooth cell encapsulation layer.
It is a feature of using such a two-step heating process as described hereinabove that the first heating step, corresponding to the soldering, can be performed at a first temperature that is lower than the melting temperature of the polymer wires. Therefore, during soldering, the polymer material is not yet liquefied and thus the risk of penetration of polymer material between the metal contacts and the metal wires, which could lead to connections with a high electrical resistance, is avoided.
Thus, the heating process may include a first heating step at a first temperature to establish the electrical connections and a second heating step at a second temperature, higher than the first temperature, to liquefy the polymer wires, e.g., the polymer yarns, and to form the encapsulation layer.
After having performed the heating process, an encapsulated and contacted photovoltaic cell is obtained, the metal contacts 21 of the cell being electrically connected by electrically conductive wires 12. In operation, an electrical current generated by the photovoltaic cell can be collected at the metal contacts 21 of the cell and it can then be further collected by the electrically conductive wires 12. The electrically conductive wires 12 may thus replace the busbars of photovoltaic cells as known in the art. The electrically conductive wires 12 can be connected to an external lead, e.g., by soldering, for example during the lamination process.
The present disclosure further provides a method for electrically connecting photovoltaic cells, e.g., busbar-free photovoltaic cells, for example as part of a method for fabricating a photovoltaic module.
A method for electrically connecting a first photovoltaic cell 201 with a second photovoltaic cell 202 according to embodiments of the disclosed technology is schematically illustrated in
The method may include providing a woven fabric 10 as described above, e.g., providing a woven fabric as for example illustrated in
In a method of the present disclosure for electrically connecting a first photovoltaic cell 201 with a second photovoltaic cell 202, a first part 1 of the woven fabric 10 is brought into physical contact with a surface of the first photovoltaic cell 201 including first metal contacts and a second, e.g., remaining, part 2 of the woven fabric 10 is brought into physical contact with a surface of the second photovoltaic cell 202 including second metal contacts. In the example shown in
It is a feature of a method in accordance with embodiments of the disclosed technology that a series connection of photovoltaic cells can be made without the need for providing a terminal bar as is the case in some prior art solutions. This is because the woven fabric 10 used in a method in accordance with embodiments of the disclosed technology can have metal wires exposed at both opposite surfaces of the fabric, thus enabling electrical connections at both surfaces, i.e., both sides, as illustrated in the example of
Instead of providing a series connection of cells, the first photovoltaic cell 201 and the second photovoltaic cell 202 may for example be electrically connected in parallel. For realizing a parallel connection, a first woven fabric may be brought into contact with the front surface of the first photovoltaic cell and with the front surface of the second photovoltaic cell. A second woven fabric may be brought into contact with the rear side of the first photovoltaic cell and with the rear side of the second photovoltaic cell. This is followed by a heating process as described above.
Furthermore, as for example illustrated in
Furthermore, in the first part 1 of the wave fabric 10, a number of polymer yarns 11 over which an electrically conductive wire 12 passes may be larger than the number of yarns 19 under which the electrically conductive wire 12 passes on the first side of the woven fabric, e.g., such as to expose segments of the electrically conductive wire 12 on the first side in the first part of the woven fabric that are longer than segments of the electrically conductive wire 12 covered by the polymer yarns 11, e.g., by polymer ribbons, on the first side in the first part of the woven fabric. Since, in this example, the first side is contacting the first photovoltaic cell 201 in the first part 1 of the fabric, a good area of contact can be provided between the conductive wires 12 and the cell 201.
Likewise, in the second part 2 of the wave fabric 10, a number of polymer yarns 11 over which an electrically conductive wire 12 passes may be larger than the number of yarns 19 under which the electrically conductive wire 12 passes on the second side of the woven fabric, e.g., such as to expose segments of the electrically conductive wire 12 on the second side in the second part of the woven fabric that are longer than segments of the electrically conductive wire 12 covered by the polymer yarns 11, e.g., by polymer ribbons, on the second side in the second part of the woven fabric. Since, in this example, the second side is contacting the second photovoltaic cell 202 in the second part 2 of the fabric, a good (e.g. sizeable) area of contact can be provided between the conductive wires 12 and the cell 201.
Thus, the electrical contact between cell and weave can be optimized by combining an uneven warp- and weft-face twill in one weave of the fabric 10, e.g., having a warp-face in the first part 1 and a weft-face in the second part 2. For example, the probability to contact the metal fingers of a photovoltaic cell, e.g., a bifacial solar cell, may improve when the warp-face part of the combined twill weave is covering the top side the cell, whereas the weft-face part of the same weave covers the bottom side of an adjacent photovoltaic cell, e.g., an adjacent bifacial solar cell. For example, the denominator and numerator designating the twill weave, as known in the art to identify twill weaves and described further hereinabove, in the first part may correspond respectively to the numerator and the denominator designating the twill weave in the second part, or, otherwise said, the denominator and numerator may be exchanged, e.g., switched over, between the first part and the second part. For example, as illustrated in
A method in accordance with embodiments of the disclosed technology may be used for fabricating a photovoltaic module including a plurality of photovoltaic cells. This is schematically illustrated in
In a method for fabricating a photovoltaic module in accordance with embodiments of the disclosed technology, the photovoltaic cells and the woven fabric may be preferably assembled on a rigid carrier or on a flexible carrier supported by a rigid structure, e.g. on a vacuum chuck. In some embodiments, a transparent carrier such as a glass plate may be used. It is a feature or benefit that such transparent carrier may function as a superstrate in the photovoltaic module. In such embodiments the process of electrically connecting the photovoltaic cells, the process of encapsulation of the cells and the process of providing a superstrate may be combined.
In the example shown in
In a next step, illustrated in
The first row 41 of photovoltaic cells may be further connected to another, second row of photovoltaic cells. This may be done as for example illustrated in
The process can be repeated to connect additional rows of photovoltaic cells, e.g., until a complete module is obtained. Next a heating process is performed, as described hereinabove. During the heating process, electrical connections are established between metal contacts of the photovoltaic cells and electrically conductive wires of the fabrics, and the polymer yarns liquefy and form an encapsulation layer. In embodiments wherein an encapsulation layer is provided on the carrier, e.g., glass carrier, before providing the cells and fabrics, the polymer yarns may liquefy and dissolve in the encapsulation layer, which, in some embodiments, may include the same or a similar material. In embodiments wherein a carrier, e.g., glass carrier, without a layer of encapsulation material is used, a sufficient amount of polymer material may preferably be provided in the fabric to fully encapsulate the cells and to avoid the need for providing additional encapsulation material.
Furthermore, the method may include providing a diode 25 at an interconnection between two photovoltaic cells, e.g., between a last photovoltaic cell of a row, e.g., the first row 41, and a first photovoltaic cell of the following row, e.g., the second row 42. Thus, a diode may be provided on and/or in a border region of a woven fabric, e.g., at or near an edge of the woven fabric. For example, a diode may be provided in an overlap region where two edges of respectively two adjacent woven fabrics overlap. The diode may thus be provided to connect two adjacent photovoltaic cell strings.
For example, the diode may include a silicon n-p junction diode. The diode may have a length equal to the length of photovoltaic cell, e.g., about equal to the width of a photovoltaic cell in the direction along which a single row, or each row, is laid out. The diode may have a width that allows integration of the diode in a space between two adjacent photovoltaic cells, e.g., between two adjacent cell string rows 47, 48 in a module, as shown in
It is a feature of a method for fabricating a photovoltaic module according to embodiments of the disclosed technology that there is no need for providing an end ribbon at the end of a row or string of photovoltaic cells.
In some embodiments, a good transparency of the woven fabric can for example be used to provide double-glass building integrated photovoltaic modules with large spacing between neighboring cells. A transparent nature of the insulating yarns may also allow the use of bifacial cells.
In a further aspect, the disclosed technology also relates to a photovoltaic module including at least two photovoltaic cells, in which the at least two photovoltaic cells are electrically contacted and electrically connected by means of a plurality of electrically conductive wires. The photovoltaic module may be free of terminal bars and free of end ribbons. The photovoltaic module may be fabricated by a method in accordance with embodiments of the disclosed technology. The at least two photovoltaic cells may be busbar-free photovoltaic cells. The at least two photovoltaic cells may be electrically connected in series. Further features of a photovoltaic module in accordance with embodiments of the disclosed technology will be clearly understood by the skilled person from the description provided hereinabove relating to methods in accordance with embodiments of the disclosed technology.
The foregoing description details certain embodiments of the disclosure. It will be appreciated, however, that no matter how detailed the foregoing appears in text, the invention may be practiced in many ways. It should be noted that the use of particular terminology when describing certain features or aspects of the invention should not be taken to imply that the terminology is being re-defined herein to be restricted to including any specific characteristics of the features or aspects of the invention with which that terminology is associated.
While the above detailed description has shown, described, and pointed out novel features of the invention as applied to various embodiments, it will be understood that various omissions, substitutions, and changes in the form and details of the device or process illustrated may be made by those skilled in the technology without departing from the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 15161636.4 | Mar 2015 | EP | regional |
This application is a (bypass) continuation of International application No. PCT/EP2016/056739, filed 25 Mar. 2016, published as WO2016/156276, which claims priority to EP application No. 15161636.4, filed 30 Mar. 2015. The contents of each are incorporated by reference herein in entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2016/056739 | Mar 2016 | US |
| Child | 15719411 | US |
