Patent Application
20200127153
Disclosed embodiments are related to wire interconnections for solar cells.
Traditionally, solar cells are interconnected with wires extending between electrical contacts on opposite sides of the cells. To mitigate the strain within each solar cell, conventional buswires utilize multiwire technologies which include the use of 10 to 20 thin round wires for the solar cell interconnection. Multiwires have shown promising results such as smaller solar cell stresses, reduced sensitivity to solar cell cracking, reduced silver paste usage, and higher efficiencies through higher current and fill factors.
In some embodiments, a solar cell module includes a first solar cell and a second solar cell, where the first solar cell and the second solar cell both include an upper surface, a lower surface opposing the upper surface, at least one electrical contact located on the upper surface, and at least one electrical contact located on the lower surface. The solar cell module also includes at least one first interconnection wire that is disposed on and extends across at least a portion of the upper surface of the first solar cell, at least one second interconnection wire that is disposed on and extends across at least a portion of the lower surface of the second solar cell, and at least one cross-connect wire disposed between the first solar cell and the second solar cell. The at least one first interconnection wire is in electrical contact with the at least one electrical contact on the upper surface of the first solar cell and the at least one second interconnection wire is in electrical contact with the at least one electrical contact on the lower surface of the second solar cell. The at least one cross-connect wire is in electrical contact with the at least one first interconnection wire and the at least one second interconnection wire.
In some embodiments, a method for interconnecting solar cells includes positioning a first solar cell proximate to a second solar cell, where the first solar cell and the second solar cell both include an upper surface, a lower surface opposing the upper surface, at least one electrical contact located on the upper surface, and at least one electrical contact located on the lower surface. The method also includes electrically connecting at least one first interconnection wire to the at least one electrical contact on the upper surface of both the first solar cell and second solar cell, electrically connecting at least one second interconnection wire to the at least one electrical contact on the lower surface of both the first solar cell and second solar cell, and electrically connecting a cross-connect wire to the at least one first interconnection wire and the at least one second interconnection wire, wherein the cross-connect wire is disposed between the first solar cell and the second solar cell.
In some embodiments, a solar cell module includes a first solar cell and a second solar cell, wherein the first solar cell and the second solar cell both include an upper surface, a lower surface opposing the upper surface, at least one electrical contact located on the upper surface, and at least one electrical contact located on the lower surface. The solar cell module also includes at least one first interconnection wire that is disposed on and extends across at least a portion of the upper surface of both the first solar cell and the second solar cell, at least one second interconnection wire that is disposed on and extends across at least a portion of the lower surface of both the first solar cell and the second solar cell, and at least one cross-connect wire disposed between the first solar cell and the second solar cell. The at least one first interconnection wire is in electrical contact with the at least one electrical contact on the upper surface of both the first solar cell and the second solar cell and the at least one second interconnection wire is in electrical contact with the at least one electrical contact on the lower surface of both the first solar cell and the second solar cell. The at least one cross-connect wire is in electrical contact with the at least one first interconnection wire and the at least one second interconnection wire.
In some embodiments, a mechanical wire cutter includes a first outer blade, a second outer blade, and an inner blade slidably disposed between the first outer blade and the second outer blade. The inner blade includes an indentation sized and shaped to receive a wire when the inner blade is in a first extended position with the indentation extended beyond the first outer blade and the second outer blade. The wire is cut by the first outer blade and the second outer blade when the inner blade is moved from the first extended position to a second retracted position with the indentation located between the first outer blade and the second outer blade.
In some embodiments, a method for cutting an interconnection wire of a solar cell includes moving an inner blade slidably disposed between a first outer blade and a second outer blade to a first extended position, moving the inner blade from a first lateral position to a second lateral position to capture a wire in an indentation formed in the inner blade, and moving the inner blade to a second retracted position with the indentation located between the first outer blade and the second outer blade to cut the captured wire with the first outer blade and the second outer blade.
It should be appreciated that the foregoing concepts, and additional concepts discussed below, may be arranged in any suitable combination, as the present disclosure is not limited in this respect. Further, other advantages and novel features of the present disclosure will become apparent from the following detailed description of various non-limiting embodiments when considered in conjunction with the accompanying figures.
The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures may be represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing. In the drawings:
Despite the benefits of multiwire technology, the implementation of multiwires in solar cells remains complex due to the inclusion of additional manufacturing steps. These manufacturing steps may include laminating wires into sheets to obtain acceptable alignment or the use of expensive equipment to snake the wires between cells. These complex steps are used due in part to the conventional buswire tabbing (i.e., stringing) method of snaking buswires between positive and negative contact areas (e.g., fingers, sheets, and strips) which forms an “S”-style interconnection. Another challenge with the “S”-style interconnection includes mitigating the effect of stresses this configuration imparts onto adjacent cell side surfaces during thermal cycling, which may increase cell breakage and negatively affect cell yield. For example, during solar panel operation, several degradation and failure modes are associated with the fluctuation of operating temperature. For example, the operating temperatures of a system may reach extremes between −40° C. and 85° C. which causes corresponding expansions and contractions of the many different materials within the solar panel. Due to mismatched coefficients of thermal expansion between silicon, solder, wire, encapsulant, glass superstrate, other glass, and/or any other cell materials, these temperature changes can also cause the cells, and therefore the gap between the cells (i.e., side surface to side surface cell spacing), to change during thermal cycling as well which causes thermal cycling of the associated interconnections. As a result, typical solar cell assemblies including multiwire connections may have relatively large spacings between adjacent solar cells to accommodate these spacing changes between cells during usage.
In view of the above, the inventors have recognized the numerous benefits of a solar cell interconnection that replaces “S”-style wires with a cross-connect wire disposed between adjacent solar cells that is electrically connected to one or more interconnection wires located on the corresponding faces of the solar cells. Such an arrangement avoids the snaking of wires between positive and negative contact areas of adjacent solar cells which has numerous benefits. The interconnection may simplify tabbing (i.e., stringing) equipment used to assembly solar cell modules, mitigate stresses encountered by the interconnect or cell caused by external factors, allow for suitable interconnection wire alignment and multiplicity without the use of a wire carrier, provide wire strain relief for cell spacing changes due to thermal cycling or mechanical cycling, allow denser arrangement of solar cells (i.e., closer cell spacing), and/or allow the use of optimized and different interconnection wire or cross-connect wire cross sections and coatings for minimal shading losses and improved electrical and mechanical contacts.
In view of the above, in one embodiment of the present disclosure, a method for interconnecting solar cells includes positioning a first solar cell proximate to a second solar cell. Each of the solar cells includes an upper surface, a lower surface opposite the upper surface, and at least one side surface extending between the upper and lower surfaces. A first interconnection wire is positioned on and extends across at least a portion of the upper surfaces of the first and second solar cells. The first interconnection wire is then electrically connected to at least one electrical contact disposed on the upper surface of the first solar cell and at least one electrical contact disposed on the upper surface of the second solar cell. A second interconnection wire is positioned across at least a portion of the lower surfaces of the first and second solar cells. The second interconnection wire is then electrically connected to at least one electrical contact disposed on the lower surface of the first solar cell and at least one electrical contact disposed on the lower surface of the second solar cell. A cross-connect wire is positioned between the first and second solar cells and electrically connected to the first interconnection wire and second interconnection wire at a location between the first and second solar cells. A portion of the first interconnection wire is removed such that the electrical contacts positioned on the upper surfaces of the first and second solar cells are electrically isolated from each other. Similarly, a portion of the second interconnection wire is removed such that the electrical contacts positioned on the lower surfaces of the first and second solar cells are electrically isolated from each other. Instead, the at least one electrical contact on the upper surface of the first solar cell may be electrically connected to the at least one electrical contact located on the lower surface of the second solar cell through the cross-connect wire placing the solar cells in series with one another. Thus, the solar cells may be interconnected to form a solar cell module without snaking or bending “S”-style interconnection wires between the adjacent solar cells.
In some embodiments, the amount of wire removed from a first interconnection wire and/or a second interconnection wire may be sufficient to prevent electrical shorting due to disturbances of the ends of the wire as might occur in the case of thermal expansion and/or other forces being applied to the interconnected solar cells. A portion of wire from a first interconnection wire and/or a second interconnection wire may be removed using any suitable arrangement including, but not limited to, mechanical cutters and laser cutters. In some embodiments, the amount of wire removed may be approximately equal to a diameter of an interconnection wire. In some embodiments, an amount of interconnection wire removed may be greater than or equal to approximately 75 μm, 100 μm, 150 μm, 200 μm, 250 μm, 300 μm, 350 μm, or any other suitable length. Correspondingly, an amount of interconnection wire removed may be less than or approximately equal to 400 μm, 325 μm, 275 μm, 225 μm, 175 μm, 125 μm, 90 μm, or any other suitable length. Combinations of the above noted ranges are contemplated including, for example, an amount of interconnection wire removed may be between or equal to 75 μm 125 μm, 100 μm 225 μm, 100 μm and 400 μm, as well as 75 μm 325 μm. Of course, any suitable amount of interconnection wire may be removed, including amounts both greater than and less than those noted above, as the present disclosure is not so limited.
In some embodiments, the amount of wire removed from a first interconnection wire and/or a second interconnection wire may be greater than 0.25 wire diameters, 0.5 wire diameters, 0.75 wire diameters, 1 wire diameter, 1.5 wire diameters, or any other suitable diameter. Correspondingly, an amount of interconnection wire removed may be less than 2 wire diameters, 1.25 wire diameters, 1 wire diameter, 0.75 wire diameters, 0.5 wire diameters, or any other suitable diameter. Combinations of the above noted ranges are contemplated including, for example, an amount of interconnection wire removed may be between or equal to 0.25 wire diameters and 1.5 wire diameters, 0.5 wire diameters and 1.25 wire diameters, as well as 0.25 wire diameters. Of course, any suitable amount of wire may be removed from the first interconnection wire and the second interconnection wire, including amounts both greater than and less than those noted above, as the present disclosure is not so limited.
While the above embodiment is directed to forming a series connection between two solar cells, embodiments in which the disclosed methods and systems may be modified to create modules with a plurality of solar cells that are connected in series and/or parallel with one another using an arrangement of a plurality of interconnection and a corresponding plurality of cross-connect wires are also contemplated as the present disclosure is not so limited.
In some embodiments, during an intermediate step, a solar cell module may include a first solar cell and a second solar cell. The first and second solar cells may include an upper surface, a lower surface opposite the upper surface, and at least one side surface extending between the upper surface and lower surface. The solar cell module may also include a first interconnection wire that is disposed on and extends across at least a portion of the upper surfaces of the first and second solar cells. The first interconnection wire may be electrically connected to at least one electrical contact disposed on the upper surface of the first solar cell and at least one electrical contact disposed on the upper surface of the second solar cell. The solar module may also include a second interconnection wire that is disposed on and extends across at least a portion of the lower surfaces of the first and second solar cells. The second interconnection wire may be electrically connected to at least one electrical contact disposed on the lower surface of the first solar cell and at least one electrical contact disposed on the lower surface of the second solar cell. The first interconnection wire and second interconnection wire may be electrically connected to a cross-connect wire disposed between the first solar cell and the second solar cell such that the first and second interconnection wires are electrically connected to one another through the cross-connect wire. This intermediate assembly may then be subjected to additional processing and manufacturing steps to provide the desired interconnected module.
In some embodiments, a solar cell module includes a plurality of first interconnection wires disposed on and extending across the upper surfaces of a corresponding plurality of solar cells and a plurality of second interconnection wires disposed on and extending across the lower surfaces of the plurality of solar cells. The upper surface and lower surface interconnection wires may also be independently connected to the corresponding electrical contacts formed on the upper and lower surfaces of the solar cells. At least one cross-connect wire may be electrically connected with the plurality of first and second interconnection wires such that the solar cells are interconnected with one another according to the methods and arrangements noted above. Thus, in one embodiment, the cross-connect wire may electrically connect the plurality of first interconnection wires to the plurality of second interconnection wires. In certain embodiments, the plurality of first interconnection wires may be offset from the plurality of second interconnection wires so that they are not aligned in the same planes oriented normal to the opposing top and bottom surfaces of the solar cells. According to this embodiment, the plurality of first interconnection wires and the plurality of second interconnection wires may be substantially parallel to each other such that they extend in a first direction and are offset from each other in a direction that is perpendicular to that first direction. In other words, the planes normal to the opposing top and bottom surfaces of the solar cells the interconnection wires are located within may be offset from one another. Further, the plurality of first interconnection wires and the plurality of second interconnection wires may contact the cross-connect wire at different locations along the length of a cross-connect wire that extends between adjacent solar cells.
Without wishing to be bound by theory, and as elaborated on below, it is believed that offsetting the first and second sets of interconnection wires from one another may reduce the resulting stresses in an electrical connection by providing strain relief and/or an increased ability of the interconnection wires to buckle during cyclic changes in solar cell spacing occur as might occur during thermal cycling. In some embodiments, the plurality of first and second interconnection wires may be offset regularly, in a repeating pattern. However, embodiments in which the spacing of the first and second interconnection wires is irregular are also contemplated. Further, in some embodiments, interconnection wires located on one side of a solar cell or module may be located within some predetermined distance of a midpoint between the corresponding interconnection wires located on the opposing side of the solar cell or module. For example, an interconnection wire may be located within a distance from the midpoint of the two opposing interconnection wires that is between or equal to 0% and 25% of the overall distance between the two interconnection wires. Thus, an interconnection wire may be located in a number of different positions between two interconnection wires located on an opposing side of a solar cell or module. In one specific example, an interconnection wire may be located at the midpoint between the two interconnection wires located on the opposing side of the solar cell or module. However, it should be understood that the current disclosure is not limited to any particular pattern and/or spacing of the interconnection wires relative to each other.
In some embodiments, a mechanical wire cutter for cutting wire may include a first outer blade, a second outer blade, and an inner blade. The inner blade may be slidably disposed between the first outer blade and the second outer blade in at least one direction relative to the first outer blade in the second outer blade. The inner blade may include an indentation sized and shaped to receive a wire. In particular, the indentation may be sized and shaped to receive, hold, and apply force to an interconnection wire. The indentation may be arranged to accommodate a wire oriented in a direction that is angled and/or substantially perpendicular relative to the first outer blade and the second outer blade. For example, the indentation may be extend through the inner blade in a direction that is angled, and in some embodiments substantially perpendicular, to an interface of the inner blade with the first and/or second outer blade. The inner blade may be moveable between a first extended position and a second retracted position. In a first extended position, the indentation is positioned distally outward from an associated edge of the first outer blade and the second outer blade. In the first extended position, the indentation may also receive a wire to be cut by the wire cutter. After a wire is received in the indentation, the inner blade may be moved to the second retracted position where the indentation is located between the first outer blade and the second outer blade. Accordingly, a portion of wire held within the indentation may be cut by the first outer blade and the second outer blade as the inner blade is moved toward the second retracted position. Thus, the wire may be cut at two opposing ends of the portion of the wire held within the indentation with the ends of the cut portion corresponding to the locations of the interfaces of the inner blade with the first and second outer blades. Additionally, such an arrangement may beneficially allow a portion of the wire to be removed without significantly stressing the remaining portions of the wire.
In some embodiments, a mechanical wire cutter includes one or more actuators arranged to selectively translate the first outer blade, second outer blade, and/or inner blade relative to one another. This relative translation of the blades may be done either independently or through a combination of movements of the various blades. For example, the wire cutter may include a first actuator operatively coupled to the first outer blade and the second outer blade such that the actuator is constructed and arranged to move the first and second outer blades relative to a stationary inner blade. Alternatively, a first actuator may be operatively coupled to the inner blade of a mechanical wire cutter such that the actuator is constructed and arranged to move the inner blade relative to stationary first and second outer blades. The first actuator may be any suitable actuator including, but not limited to, an electric motor drive linear actuator, an electrical solenoid actuator, a linear hydraulic actuator, a linear pneumatic actuator, and/or any other appropriate type of actuator capable of providing relative motion in a desired direction between the inner and outer blades of a mechanical wire cutter. While embodiments in which one of the inner or outer blades is movable are described above, embodiments in which both the inner and outer blades of a wire cutter are displaced during an actuation cycle are also contemplated. Additionally, in some embodiments, it may be desirable to translate a mechanical wire cutter between two or more positions for cutting wires at these separate positions. For example, a wire cutter may also include one or more second actuators connected to a chassis of the wire cutter which may be arranged to translate the wire cutter in one or more directions between the two or more positions.
In some embodiments, a method of cutting an interconnection wire includes moving an inner blade disposed between a first outer blade and a second outer blade to a first extended position so that an indentation formed in the inner blade is extended beyond the distal edges of the first and second outer blades. The inner blade may be moved from a first lateral position to a second lateral position to capture a wire inside of the indentation. The indentation may be sized and shaped to appropriately capture and hold a wire therein. In combination with the first and second outer blades, the indentation may also be constructed to apply a force to the wire when the inner blade is retracted relative to the outer blades to cut and remove a portion of the wire. Specifically, the inner blade may be moved from the first extended position to a second retracted position to move the indentation between the first outer blade and the second outer blade to shear the captured wire against the outer edges of the first and second outer blades. In some embodiments, the captured wire may be cut simultaneously by the first and second outer blades to prevent excess stress on the wire.
In some embodiments, it may be desirable for a wire cutter to be positioned closely or in contact with a wire to be cut. That is, cutting blades such as a first outer blade and a second outer blade may be placed in contact with the wire to be cut prior to the actual cutting of the wire. Such an arrangement may reduce the amount of deformation and stress added to the wire during a cutting process. In some embodiments, a wire cutter may include a contact sensor arranged to determine the position of the first and second outer blades relative to a wire. The contact sensor may include a voltage generator which applies a non-zero voltage across the first and second outer blades. According to this embodiment, when the first and second outer blades are placed into contact with a conductive wire, a circuit will be completed between the first and second outer blades which may cause a detectable decrease in voltage and/or a flow of current between the first and second outer blades using an appropriate voltage and/or current sensor. Such a voltage decrease and/or flow of current may be indicative of contact of the first and second outer blades with the wire to be cut. In an alternative embodiment, the contact sensor may include an optical sensor which may receive optical information from the wire cutter and/or wire to be cut so that the relative position of the inner and outer blades relative to a wire to be cut may be determined. Such an arrangement may be useful for feedback control of the various blades of the wire cutter. While two possible contact sensing arrangements are described above, it should be understood that the current disclosure is not limited to only these embodiments. Instead, any appropriate method and/or system capable of detecting contact and/or the close proximity of the one or more outer blades of a mechanical wire cutter to a wire to be cut may be used as the disclosure is not limited in this fashion.
In some embodiments, a plurality of wire cutters may be arranged in an array so that multiple wires at regular or irregularly spaced intervals may be cut simultaneously. According to this embodiment, the wires to be cut may be parallel to one another so that multiple wire cutters may be rigidly mounted to one another and operated simultaneously to remove portions of one or more associated wires. In one embodiment, the wire cutters may be linearly arranged such that an outer blade of a first wire cutter may be adjacent to an outer blade of a second wire cutter. However, embodiments in which one or more intervening structures are included and/or the mechanical wire cutters are spaced from one another are also contemplated. According to this embodiment, indentations on an inner blade of each of the wire cutters may be parallel to one another with openings facing in the same direction. In some embodiments, multiple wire cutter arrays may be used to remove portions of wire attached to different regions of the solar cell simultaneously. For example, multiple arrays of wire cutters may be used to remove portions of interconnection wire disposed on and extending across both the upper surface of a solar cell and a lower surface of the solar cell. In this example, the arrays of wire cutters may be disposed opposite one another so that one array may remove portions of wire from the upper surface of the solar cell and a second array may remove portions of wire from the lower surface of the solar cell. Of course, it should be understood that one or more arrays of wire cutters may be positioned in any suitable location relative to a first and second solar cell to effectively remove portions of interconnection wire as the present disclosure is not so limited.
For the sake of clarity, the embodiments described below are discussed relative to interconnection wires positioned on the upper surfaces and lower surfaces of the related solar cells. However, it should be understood that the described surfaces may be generalized to any appropriate upper and lower surfaces and are not limited to any particular orientation. Therefore, in certain embodiments, an upper surface of a solar cell may correspond to the sunny side (i.e., photovoltaic side) of a solar cell and a lower surface of the solar cell may correspond to the back side (i.e., non-photovoltaic side) of a solar cell. In other embodiments, an upper surface of a solar cell may correspond to the back side and a lower surface of the solar cell may correspond to the sunny side. Of course, the upper and lower sides of the solar cell may be any suitable combination of opposing surfaces of a solar cell that allow for interconnection of one or more electrical contacts of adjacent solar cells as the present disclosure is not so limited.
Various embodiments of the present application may include solar cell interconnection constructions and methods for manufacturing those interconnections. More specifically, in one embodiment, the disclosed interconnections may avoid snaking interconnection wires from the back side of a first solar cell to the sunny side of a second solar cell by using two independent sets of interconnection wire and a cross-connect wire. A first set of interconnection wires are attached to the lower surface of the first solar cell while another set of interconnection wires are attached to the upper surface of the second solar cell. A cross-connect wire may be inserted in between and perpendicular to these two sets of interconnection wires. Electrical contact may be made between the interconnection wires and solar cells and between the interconnection wires and cross-connect (i.e., interconnection) wire using any suitable technique, including, but not limited to, soldering, applying conductive adhesives, and welding (e.g., spot welding). At this stage, the cells are shorted. Removal of small portions of the upper surface interconnection wires and lower surface interconnection wires may be done to create an electrical pathway from the negative contact area on the first solar cell to the positive contact area on the second solar cell, thereby completing the cell interconnection. For example, a portion of each of the first and second interconnection wires may be removed to electrically isolate the upper surfaces from the lower surfaces of each solar cell while retaining an electrical connection between the upper surface of one cell with the lower surface of the adjoining solar cell through the cross-connect wire. Using the proposed method of cell interconnection, interconnection wire technologies are suitable for use with any thin or free-standing cells with thicknesses in the range of about 50 μm to 200 μm. The proposed interconnection technique may replace traditional interconnection wire “S”-style interconnects so that the interconnection of solar cells may be simplified and resistance to thermal cycling of the solar cell may also be improved.
Without wishing to be bound by theory, a minimum cell spacing with the disclosed interconnect systems and methods disclosed herein may be determined by a transverse dimension (e.g., a diameter) of the cross-connect wire and the ability to remove small portions of interconnection wire on either side of the cross-connect wire to provide the desired electrical interconnection. Thus, a spacing of the adjacent solar panels may be between or equal to, 2 and 10 times, 2 and 5 times, and/or any other appropriate multiple of a transverse dimension of the cross-connect wire, though other spacing are also contemplated as the disclosure is not so limited. In a related embodiment, a thickness of the cross-connect wire may be less than or equal to 3 times a thickness of the solar cells. In either case, the cell spacing may be reduced in comparison to typical systems, thereby improving solar cell density within a solar module.
In some embodiments, appropriate solar cell spacing for use with a cross-connect wire and interconnection wires may be greater than or equal to approximately 0.3 mm, 0.5 mm, 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, or any other suitable spacing. Correspondingly, a solar cell spacing may be less than or equal to approximately 3.5 mm, 3 mm, 2.5 mm, 2 mm, 1.5 mm, 1 mm, 0.5 mm, or any other suitable spacing. Combinations of the above noted ranges are contemplated including, for example, solar cell spacing between or equal to 0.3 mm and 1.5 mm, 0.5 mm and 2 mm, 1 mm and 3 mm, as well as 0.5 mm 2.5 mm. Of course, any suitable cell spacing for a given interconnection wire thickness and corresponding wire removal lengths may be used including spacing both greater than and less than those noted above as the present disclosure is not so limited.
In some embodiments, appropriate solar cell thicknesses for use with a cross-connect wire and interconnection wires may be greater than or equal to approximately 50 μm, 75 μm, 100 μm, 150 μm, 250 μm, 350 μm, 450 μm, 500 μm, or any other suitable thickness. Correspondingly, a solar cell thickness may be less than or equal to approximately 550 μm, 475 μm, 375 μm, 275 μm, 175 μm, 125 μm, 100 μm, or any other suitable thickness. Combinations of the above noted ranges are contemplated including, for example, solar cell thickness between or equal to 75 μm and 275 μm, 100 μm and 475 μm, 150 μm and 475 μm, as well as 50 μm and 550 μm. Of course, any suitable cell thickness may be used including thicknesses both greater than and less than those noted above as the present disclosure is not so limited.
In some embodiments, it may be desirable for a cross-connect wire to have a diameter, or any other appropriate transverse dimension, corresponding to an associated solar cell thickness. For example, the cross-connect wire may have a diameter approximately equal to that of the solar cell thickness so that interconnection wires disposed on and extending across an upper surface and a lower surface of a solar cell can remain substantially straight and not deformed. However, in other embodiments, it may be desirable for the cross-connect wire to have a diameter larger than that of a solar cell thickness so that the cross-connect wire may reduce the amount of electrical resistance between interconnected solar cells. In some embodiments a cross-connect wire may have a diameter greater than or equal to approximately 0.5 times a solar cell thickness, 1 times solar a cell thickness, 1.25 times a solar cell thickness, 1.5 times a solar cell thickness, 2 times a solar cell thickness, or any other suitable. Correspondingly, a cross-connect wire may have a diameter less than or equal to approximately 5 times a solar cell thickness, 3 times a solar cell thickness, 2 times a solar cell thickness, 1.5 times a solar cell thickness, 1.25 times a solar cell thickness, 1 times a solar cell thickness, or any other suitable multiple of an associated solar cell thickness. Combinations of the above noted ranges are contemplated including, for example, cross-connect wire diameters between or equal to 0.5 and 5 times a solar cell thickness, 0.5 and 2 times a solar cell thickness, 1 and 1.5 times a solar cell thickness, 1 and 3 times a solar cell thickness, as well as 0.5 and 1.5 times a solar cell thickness. Of course, any suitable diameter may be used for the cross-connect wire, including amounts both greater than and less than those noted above as the present disclosure is not so limited.
In some embodiments, it may be desirable for a vertical height change between a cross-connect wire and an adjacent electrical contact disposed on a surface of an associated solar cell to correspond to the associated solar cell thickness. Without wishing to be bound by theory, an interconnection wire may remain straight and substantially unreformed due to a small or zero change in vertical height between a connection with the cross-connect wire and adjacent electrical contacts of an associated solar cell. Accordingly, in some embodiments, a change in the vertical height between the cross-connect wire and the adjacent electrical contacts of the solar cells may be greater than or equal to approximately 0.5 times a solar cell thickness, 0.75 times a solar cell thickness, 1 times a solar cell thickness, 1.25 times a solar cell thickness, or any other suitable multiple of an associated solar cell thickness. Correspondingly, a change in vertical height between the cross-connect wire and the adjacent electrical contacts of the solar cells may be less than or equal to approximately 1.5 times a solar cell thickness, 1.25 times a solar cell thickness, 1 times a solar cell thickness, 0.75 times a solar cell thickness, or any other suitable multiple of an associated solar cell thickness. Combinations of the above noted ranges are contemplated including, for example, vertical height changes between or equal to 0.5 and 1.25 times solar cell thickness, 1 and 1.25 times solar cell thickness, 0.5 and 0.75 times solar cell thickness, as well as 0.75 and 1.25 times solar cell thickness. Of course, any suitable vertical height change between the cross-connect wire and adjacent electrical contacts may be employed, including amounts both greater than and less than those noted above, as the present disclosure is not so limited.
The length of unsupported interconnection wire on either side of the cross-connect wire may be approximately equal to the distance from the cross-connect to the electrical connection at the electrical contact on an associate solar cell. For example, there may be approximately 1.4 mm of unsupported interconnection wire when there is an approximately 1 mm cell gap, approximately 1 mm cell side surface to cross-connect wire electrical connection, and a 100 μm cross-connect wire radius. Without wishing to be bound by theory, if the cells have only one degree of freedom, cell displacements may have one of two effects: the sunny side or back side interconnection wires may buckle or the cross-connect wire may be bent (i.e., deformed). Without wishing to be bound by theory, the larger the unsupported length of interconnection wire the more deflection the interconnection wire may undergo for a given force applied to the interconnection wire. Accordingly, it may be desirable to minimize the unsupported length of wire for a given cell spacing and electrical contact position. In some embodiments, the amount of unsupported interconnection wire may be greater than or approximately equal to 0.75 mm, 1 mm, 1.5 mm, 2 mm, 2.5 mm, and or any other suitable length. Correspondingly, the amount of unsupported interconnection wire may be less than or approximately equal to 3 mm, 2.25 mm, 1.75 mm, 1.25 mm, 0.8 mm, and/or any other suitable length. Combinations of the above noted ranges are contemplated including unsupported links of wire between 1 mm and 2.5 mm, 1 mm and 3 mm, 2 mm and 2.5 mm, as well as 0.75 and 3 mm. Of course, any suitable length of unsupported wire may be employed including links greater than and less than those noted above, as the present disclosure is not so limited.
In some embodiments, an interconnection wire and/or a cross-connect wire may have a particular cross-section to improve solar cell efficiency. Without wishing to be bound by theory, light may reflect off of the interconnection wires and/or cross-connect wires. When a solar cell is covered in encapsulant and/or a glass layer, the solar cell may exhibit a critical angle for total internal reflection of light at an interface between the exterior glass layer and the air in the surrounding ambient environment. Accordingly, in some embodiments, it may be desirable to control an angle of light reflected from the interconnection wires and/or cross-connect wires to reflect light at an angle that is less than this critical angle. For example, unlike a circular cross section which may reflect light in a number of different directions, in some embodiments, an interconnection wire and/or a cross-connect wire may have a polygonal cross-section such as a triangle or pentagon which may include top surfaces oriented outward from an underlying surface of a solar cell such that incident light on these surfaces may be reflected off of the surfaces at a desired angle. According to this embodiment, these surfaces of the cross-connect wire may be angled by a predetermined amount relative to an upper or lower surface of solar cell such that incident light may either be reflected towards a photosensitive surface of the solar cells and/or at a shallow angle that is less than the critical angle to promote total internal reflection of the incident light. In some embodiments, polygonal cross-sections may be combined with rounded cross-sections in order to provide additional total internal reflection of light. For example, an approximately triangular cross section may include rounded or semicircular edges adjacent a surface of a solar cell the wire is disposed on. As another example, an approximately pentagonal cross section may have a pointed top and rounded sides. To further promote total internal reflection of the reflected light, in some embodiments, an encapsulant of a system may be optically matched an associated glass layer such that an index of refraction of the encapsulated is substantially the same as a corresponding index of refraction of the glass layer to further promote the reflection of light rays back into the photovoltaic.
Depending on the particular embodiment, an interconnection wire and/or a cross-connect wire may include one or more flat surfaces that are angled relative to an underlying surface a solar cell in order to promote total internal reflection of incident light within the a solar module. For example, as noted above, the one or more flat angled surfaces may be angled to a suitable angle so as to cause light to reflect at a shallow angle to cause total internal reflection. In some embodiments, the angle of the flat angled surface relative to an upper or lower surface of a solar cell may be greater than or equal to approximately 20°, 22°, 25°, 28°, 30°, 35°, and/or any other suitable angle. Correspondingly, the angle of the flat angled surface relative to the solar cell may be less than or equal to approximately 40°, 32°, 29°, 27°, 24°, 21°, and/or any other suitable angle. Combinations of the above noted ranges are contemplated including, for example, angles between 20° and 40°, 22° and 32°, 22° and 27°, as well as 25° and 32°. Of course, any suitable angle may be used including angles greater than and less than those noted above as the present disclosure is not so limited.
Conventional solar cells include a wide variety of materials and structural arrangements. For example, typical solar cells may be covered in an encapsulant with a glass superstrate layer on the upper or sunny surface of the solar cells and an opaque layer on the lower or dark surface of the solar cells. In such an embodiment, the solar cells may include electrical contacts in the form of a plurality of relatively thin conductive fingers on the upper surfaces of the solar cells and conductive sheets on the bottom surfaces of the solar cells. In another embodiment, the one or more solar cells may be bifacial solar cells. In such an embodiment, interconnected bifacial solar cells may be placed in an encapsulant between two opposing glass layers associated with the upper and lower surfaces of the solar cells. Such an arrangement may permit the solar cells to absorb light incident on either side of the solar cell assembly. In such an embodiment, the electrical contacts on both the top and bottom surfaces of the cells may include a plurality of conductive fingers.
For the sake of clarity, the current embodiments described in the application describe electrical connections between the various electrical contacts and/or fingers of the solar cells. However, it should be understood that the current disclosure is not limited to connection with any particular type of electrical contact of a solar cell. Suitable electrical contacts for use with a solar cell may include conductive fingers, strips, solid sheets, combinations of the forgoing, and/or any other appropriate form or electrical contact suitable for use with a solar cell. Therefore, it should be understood that any suitable type and number of electrical contacts may be used on a solar cell.
In some embodiments, a solar cell may be arranged with a particular number of electrical contacts to which interconnection wires may be connected. For example, in some embodiments, an upper surface of a solar cell may include a plurality of fingers or other electrical contacts which may be interconnected using an interconnection wire. The plurality of fingers may be disposed at regular or irregular intervals in a pattern. On the lower surface of a solar cell, the solar cell may include a single electrical sheet contact (i.e. a conductive sheet), or a plurality of fingers or metal strips which may be disposed at regular or irregular intervals. In some embodiments, an equal number of interconnection wires may be used on each of the upper and lower surfaces of a solar cell to electrically connect electrical contact(s) on the upper surface and electrical contact(s) on the lower surface. In some embodiments, a different number of interconnection wires may be used on each of the upper surface and the lower surface of a solar cell. For example, 15 interconnection wires may be used to electrically connect electrical contact(s) on the upper surface and 14 interconnection wires may be used to electrically connect electrical contact(s) on the lower surface of a solar cell. Of course, any suitable number of contacts may be used on each of the upper surface and the lower surface of the solar cell along with any suitable number of interconnection wires.
The interconnection and cross-connect wires described herein may have any appropriate construction suitable for use in electrically connecting the electrical contacts of two or more solar cells. For example, appropriate wires may include, but are not limited to braided wires, solid wires, stranded wires, and/or any other appropriate form of wire. In some embodiments, a wire may also be formed of a plurality of smaller wires. For example, a wire may include 10 to 20 smaller wires though any other appropriate number of smaller wires may be used as well. Such an arrangement may help to reduce the physical strain on any one wire. Additionally, while the use of wires may be advantageous due to their flexibility and ease of use during manufacture, the current disclosure is not limited in this fashion. Accordingly, the embodiments described herein may use any appropriately sized and shaped conductor capable of being positioned and oriented in the described manners to electrically connect the various electrical contacts of two adjacent solar cells as the disclosure is not so limited.
Changes in solar cell spacing may occur as a result of many factors, including, but not limited to, mechanical loading and/or thermal cycling. As the solar cell spacing changes during a displacement cycle, forces on the interconnection may cause deformation of the cross-connect wire as opposed to imparting stress into cell surfaces and points of electrical connection which may occur with a standard “S”-style interconnect. During operation, solar cells may be cycled between various extreme temperatures due to changes in environmental temperature as well as temperature changes due to cyclic exposure to sun light. These cyclic temperature changes may also result in cyclic strains and stresses being applied to the various components of interconnected solar cells due to mismatches in thermal expansion of these components. For example, in some embodiments, extreme temperatures a solar module may be subjected to may include temperatures in the range between −40° C. and 85° C. In some cases, a 24-hour period could see one or multiple temperatures cycles over a range of about −20° C. and 43° C. Assuming there is at least one thermal cycle per day, over 20 years a system may undergo a total of about 7,300 thermal cycles. For a period over 40, years, a system may undergo about 14,600 thermal cycles. Without wishing to be bound by theory, the disclosed cross-connect wires may experience less fatigue from the cyclical temperature loading due to better strain relief than traditional “S-style” interconnects.
Embodiments of the interconnection arrangements disclosed herein may operate without breakage for any appropriate number of displacement cycles which may occur during the operational lifetime of an assembly from sources such as thermal cycling, vibration, mechanical loading, and/or any other appropriate source of displacement. In some embodiments, the number of operational cycles a solar cell interconnection may withstand may be greater than 50,000 cycles, 75,000 cycles, 100,000 cycles, and/or any other suitable number of cycles. Correspondingly, a number of operational cycles a solar cell interconnection may withstand may be less than 150,000 cycles, 100,000 cycles, 75,000 cycles, and/or any other suitable number cycles. Combinations of the above noted ranges are contemplated including numbers of cycles withstood between or equal to 50,000 cycles and 150,000 cycles, 50,000 cycles and 75,000 cycles, 75,000 cycles and 150,000 cycles, as well as 50,000 cycles and 75,000 cycles. Of course, any suitable number displacement cycles may be withstood including numbers of cycles greater than or less than those noted above, as the present disclosure is not so limited.
Turning now to the figures, several non-limiting embodiments are described in further detail. It should be understood that the various components, systems, and methods described in relation to the figures may be used either individually and/or in combination as the disclosure is not limited to only the specifically depicted embodiments.
As shown in
In some embodiments, the method for interconnecting solar cells shown in
In some embodiments, the process of
In addition to the above, it should also be noted that while
In
In the embodiment shown in
After contacting an interconnection wire 200 to be cut with the mechanical wire cutter 501 as shown in
In the embodiment of
After positioning a wire in an indentation of a mechanical wire cutter, as shown in
As shown in
As shown in
P
cr=(π2EI)/(KL)2
where Pcr is Euler's critical load at which buckling will occur, E is the modulus of elasticity of the column, I is the moment of inertia of the column, L is the unsupported length, and K is the effective length factor.
In order to determine if the sunny side interconnection wire or back side interconnection wire will buckle, the forces on the cross-connect wire were modeled. As illustrated in
According to the model depicted in
To further validate the hypothesis that the disclosed interconnection redirects displacements into the cross-connect wire, additional FEA results are shown in
In some embodiments, to find the bending mode of the cross-connect wire when the cells and interconnect are encapsulated, the cross-connect wire was assumed to bend as if it were a cylindrical beam with pinned boundary conditions. Without wishing to be bound by theory, such a model may include most parameters from the previously discussed model. That is, the dimensions of the interconnection wire and cross-connect wire are the same, the unsupported length of cross-connect wire is the same, the interconnection wire at the center simulated as a point load, and the pinned boundary conditions where the cross-connect wire can rotate but not translate is the same. However, in contrast to the previously discussed models, additional loads were distributed along the length of the cross-connect wire from the encapsulant.
In some embodiments, at equilibrium the cross-connect wire may be straight and parallel to the interconnected solar cell side surfaces. The encapsulant (e.g., ethylene vinyl acetate) may surround this equilibrium state. Accordingly, if adjacent cells displace towards or away from each other, the encapsulant adds resistance which is modeled as a distributed load on the cross-connect wire. Without wishing to be bound by theory, the load is not evenly distributed, but rather the portions of wire which move the most will encounter the highest resistance which results in a different bending profile as shown in
FEA was performed to assess the accuracy of the bending that will occur at this interconnect including encapsulation, the results of which are shown in
In both embodiments of analytical and FEA models including encapsulant as described above, the maximum stress was found to be at the interconnection wire and cross-connect wire joint. According to the results shown in
It should be understood that while particular modeling and physical experiments are described above where relatively high strains and stresses are developed in the interconnection and/or cross connect wires, these examples are meant to demonstrate that it is possible to move these strains and stresses from the connections between the interconnect wires and the surfaces of the solar cells to another location where it can be more easily managed. For example, bending and deformation of the cross-connect wires is described above. However, in addition to this benefit, it should be understood that the various interconnect and cross-connect wires may be appropriately constructed to handle the applied deformations and/or stresses. For example, the disclosed solar modules may include one or more of the following to address the applied stresses and/or deformations: the interconnect and/or cross connect wires may be formed from a conductive hardenable alloy such as a beryllium copper; the interconnect and/or cross connect wires may be formed from a soft annealed conductive material such as annealed copper to permit the wires to undergo plastic deformation when stressed; and/or a softer encapsulant may be used to help mitigate the developed stresses and strains. Of course it should also be understood that the presented examples and constructions are only exemplary and that a solar module may be appropriately designed to provide any desired combination of developed stresses and/or deformations for a desired application.
While the present teachings have been described in conjunction with various embodiments and examples, it is not intended that the present teachings be limited to such embodiments or examples. On the contrary, the present teachings encompass various alternatives, modifications, and equivalents, as will be appreciated by those of skill in the art. Accordingly, the foregoing description and drawings are by way of example only.
This application is a national stage filing under 35 U.S.C. § 371 of International Patent Application No. PCT/US2018/039437, filed Jun. 26, 2018, which claims the benefit under 35 U.S.C. § 119(e) to U.S. Provisional Application No. 62/524,809, filed Jun. 26, 2017, and also claims the benefit under 35 U.S.C. § 119(e) to U.S. Provisional Application No. 62/628,893, filed Feb. 9, 2018, which are herein incorporated by reference in their entirety.
This invention was made with Government support under Grant No. DE-EE0007535 awarded by the Department of Energy. The Government has certain rights in the invention.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2018/039437 | 6/26/2018 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62628893 | Feb 2018 | US | |
| 62524809 | Jun 2017 | US |
