Patent Application
20140060615
The invention concerns a method and a device for connecting solar cells to form a solar cell string. Further, the invention concerns a solar cell string. The invention is particularly suited for connecting so-called back surface solar cells, which are distinguished in that the plus and minus poles are located on the same side.
Solar cells take advantage of the photo effect in order to produce an electrical current from radiant energy. They normally consist of silicon (or another semiconductor) and have a p-n junction, in order to separate the charge carriers. In conventional solar cells, the p-doped zone and the n-doped zone are located above one another. In order to interconnect (“string”) an array of solar cells in series, using conductors made of copper, for example, the surface facing the sun (in short, “sunny side”) of one cell must always be electrically connected to the back surface of the next cell A disadvantage of solar strings of this type is that shading of the sunny side by the electrical conductors (typically, coated copper ribbons) cannot be avoided, thus having a negative effect on the efficiency. For some time, back surface solar cells (also known as back surface contact solar cells, primarily known by their English name, “Back Contact Cells”) have been known, which, in comparison with conventional solar cells, are enjoying an increasing popularity. Because the poles (+, −) are located on the back surface with back surface solar cells (i.e. on the surface opposite the surface facing the sun), there is the advantage, compared to conventional solar cells, that on the front, not active, surface there are no, (e.g. with IBC solar cells, “Interdigitated Back Contact Cells”), or only very limited (e.g. with MWT solar cells, “Metal Wrap Through” technology), shadings. This results in a greater efficiency. In addition, the conductors on the back surface can be made to nearly any arbitrary size, without causing shading. A disadvantage is that in the production of the contacts (by means of soldering, for example) for the back surface solar cells—due to the asymmetrical assembly (silicon-copper)—there are stronger sags than with conventionally strung cells. The reason for this bimetal effect is due to the different expansion coefficients of silicon and copper, and the supply of heat necessary for the electrical connection.
It is therefore an objective of the invention to create a method and a device for connecting solar cells, with which solar cell strings can be easily and inexpensively produced. In particular, the method and the device should be suitable for connecting back surface solar cells. Furthermore, it should be possible to operate the device reliably, and the device should be distinguished by a high level of productivity. The solar strings produced in this manner should experience no, or only slight sagging as a result of the thermal load, e.g. resulting from the soldering procedure.
These objectives are attained according to the invention with a method for connecting solar cells disposed behind one another along a longitudinal axis, and in particular, back surface solar cells, to form a solar cell string, wherein the method exhibits the following steps: attachment of at least one insulating strip to the solar cell, extending at least in sections in the longitudinal axis, wherein the insulating strip applied thereto preferably exhibits or provides some free space for creating the electrical contact to the solar cells; and positioning electrical conductors, extending in the longitudinal axis, on the at least one insulating strip, for connecting two respective neighboring solar cells, wherein the conductors can be connected to the solar cells via the free space mentioned above. The insulating strip can be designed to be continuous, and can extend over the entire length of the solar cell string. This also has the advantage that no additional element is necessary for the frequently desired coating of the electrical conductors between the solar cells. Alternatively, the respective insulating strip can also be partitioned into insulating sections, wherein each insulating section can be allocated to one solar cell of the solar cell string. It is advantageous that the insulating strip is comparatively narrow in relation to the width of the solar cells, as a result of which, the expenditure in terms of material can be significantly reduced. Insulating strips of this type are inexpensive and can be obtained in different widths, thicknesses and compositions, or can be readily produced, and can be optimally adapted to the respective use.
The insulating strip substantially consists of a material that is not, or is only slightly, electrically conductive, and is preferably made of a flexible plastic material.
In a first embodiment, the insulating strip is designed as a double-sided adhesive strip, which is attached to the solar cells by means of pressure. The attachment is preferably on the back surface of the solar cell thereby (i.e. the surface facing away from the surface facing the sun). An insulting strip of this type can be particularly easily applied to the solar cell, in a single production step, A prior application of adhesive is clearly not necessary. A particular advantage is that the conductor can, at least provisionally, be attached to the insulting strip simply by pressing it in place, preferably such that it cannot detach therefrom, and attached to the solar cells provided with insulating strips, more or less automatically, and in a reliable manner. Commercially available double sided adhesive strips with insulating properties may be used, which can be obtained, for example, in rolls, thus also having cost-saving benefits. The base material for these strips may consist of plastic (e.g. PP, PE, PET, PTFE), coated on both sides with an acrylic adhesive, for example.
Furthermore, it may be advantageous if the at least one insulating strip is provided with openings or holes, in order to create the free space for establishing an electrical contact to the solar cells, wherein the providing with holes preferably occurs during the feeding of the insulating strip to the solar cells. A design of this type ensures that different sizes and types of solar cells can be readily processed, using the same starting insulating strip material. It is, of course, also conceivable to use pre-manufactured insulating strips, which already contain holes. The free spaces could alternatively be formed by interruptions between individual, short insulting strip sections, disposed successively in the longitudinal axis.
The conductors can be conductor elements in the shape of strips, designed as flexible components for creating stress relief structures, made of highly conductive metal (e.g. copper). Copper bands can be used, for example, which are plated with tin (coated with lead) or silver. Other materials (such as aluminum) are also conceivable, however. These stress relief structures prevent an undesired, thermally effected sagging of the solar cells in a subsequent contacting procedure, by means of soldering, for example, or welding. As relief structures, the conductors may be curved, or exhibit springs, which compensate for expansions caused by heat. The specified conductor elements, designed as flexible components, are preferably made of narrow metal bands, which are plastically deformed by means of shaping procedures. The metal bands, and therefore, the conductor elements can, for conventional solar cells, be between 0.01 mm and 1 mm thick, and 0.5 mm to about 50 mm wide. These consist of copper bands, which are normally tin-plated (coated with lead), or in some cases, are silver-plated.
If the electrical conductors for the electrical connection of the solar cells are strip-shaped conductor elements (“conductor ribbons”), it may be advantageous if the conductor elements are drawn, preferably from a metal strip roll, and subsequently cut to length and shaped to create the stress relief structures. For this, the cutting and shaping procedures, preferably using a shaping unit, containing bending punches and bending dies, can preferably occur simultaneously. The simultaneous cutting and creating of the stress relief structures using the shaping unit may also be advantageous without the use of the aforementioned insulating strip.
The device according to the invention for the electrical connection of solar cells and in particular of back surface solar cells, to form a solar cell string exhibits an application unit for applying at least one insulating strip to the solar cells disposed behind one another along a longitudinal axis, wherein the applied insulting strip preferably exhibits or provides free spaces for creating the electrical contact to the solar cells. Furthermore, the device exhibits an assembly unit for positioning electrical conductors, used to connect two adjacent solar cells to one another, on the at least one insulating strip, wherein the conductors can preferably be connected to the solar cells via the aforementioned free spaces.
If the at least one insulating strip is designed as a double sided adhesive strip, it may be advantageous that the application unit exhibits a means for pressing the insulating strip onto the solar cells. The pressure means can be a relatively immobile component having a sliding surface, on which the insulating strip can be fed, and which, at least in sections, presses against the back surface of the solar cells with a means for obtaining a preload force, for example. It is to be understood that the pressure means can also be designed differently. It would be conceivable, for example, to use a freely rotating deflection roller for the insulating strip, which can unwind over the back surface of the solar cell.
The device can exhibit a hole making station for providing the openings in the insulating strip. The hole making station can be disposed thereby, advantageously, between an insulating strip roll, mounted so as to be freely rotating at a right angle to the longitudinal axis, and the application unit. The hole making station can exhibit means for punching or cutting openings in the insulating strip.
The solar cells can exhibit two or three rows of contact zones disposed next to one another, which are oriented basically parallel to one another in the longitudinal axis. Each row of contact zones can have a plus or minus pole allocated to it thereby. In this case, it may be advantageous if the device exhibits one application unit for each row of contact zones, and if applicable, a hole making station, wherein the application units can be disposed in a row next to each other, or offset to one another, in relation to the longitudinal axis. It can be particularly advantageous if the application units are disposed offset to one another such that the respective application units are each allocated to one of three solar cells disposed behind one another.
In another embodiment, the device can exhibit at least one supply roll or reel for providing material for producing the conductor, from which conductor material can be drawn by means of a drawing unit.
The drawing unit can exhibit at least one gripper, for grabbing, in a clamping manner, the free end of the conductor material from the supply roll.
Furthermore, it may be advantageous if the device exhibits a shaping unit for creating the stress relief structures for the conductor elements. Using the shaping unit, flat attachment sections and contact sections of the conductor element can be produced in a simple manner, preferably lying in a common plane. The conductor elements can be produced from a narrow copper band. A shaping unit of this type can also be used in other devices for connecting solar cells. A device of this type could, for example, exhibit an application unit for coating the solar cells with an insulating material. This shaping unit could even be advantageous for conventional stringers, in which a surface facing the sun is connected to a back surface in each case. In this case, the device for the electrical connection of solar cells would comprise an assembly unit for positioning electrical conductors on the solar cells in order to connect two neighboring solar cells, and a shaping unit for creating the stress relief structures of the conductor elements.
The shaping unit can contain a bending die and a bending punch, wherein at least the bending die has a two-part design, and wherein the two bending die parts can be displaced in relation to one another, in order to adjust the lengths of the conductor elements in the longitudinal axis. With a configuration of this type, an efficient operation and broad field of use is ensured, and an exchange of the shaping tool for refitting for different solar cell sizes is not necessary.
Furthermore, it may be advantageous if the shaping unit contains a bending die and a bending punch, wherein the bending die and the bending punch each have a two-part design. The bending die parts and the associated punch parts can be displaceable in relation to one another at a right angle to the longitudinal axis, in pairs, for forming a deformation of the conductor element in the transversal direction. This can be useful for preventing any possible turning of the solar cells in relation to the orientation of the row of contact zones having the same polarization.
The shaping unit can be a component of a punching station, by means of which the conductor element, aside for the shaping procedure, can be cut to the desired length. The cutting means can be integrated thereby in the bending die or the bending punch by means of a corresponding shaping. Of course, the punching station could also exhibit a separate blade, which can be operated independently of the shaping unit, for cutting the conductor elements to length.
Furthermore, the device can exhibit a conveyor device for conveying the solar cells, disposed behind one another, in the longitudinal direction. For this, the application unit can be disposed above or below the conveyor device, such that the at least one insulating strip is attached to the solar cells during the conveyance procedure.
The shaping unit and, if applicable, the punching station, can be disposed, in relation to the longitudinal axis, next to the conveyor device. The conductor elements can be removed from the punching station by means of an assembly unit functioning according to a pick-and-place procedure, and deposited on the at least one insulating strip.
Another aspect of the invention concerns a solar cell string, which is preferably produced according to the method described above and/or using the device described above. The solar cell string exhibits solar cells disposed successively along a longitudinal axis. Preferably, this concerns back surface solar cells thereby. The solar cell string exhibits at least one insulating strip disposed on the solar cells, extending in the longitudinal axis, and electrical conductors extending in the longitudinal axis, attached to the insulating strip, which each electrically connect two adjacent solar cells to one another. The insulating strip can exhibit openings or other free spaces, by means of which the electrical conductors are each applied to a contact location on the back surfaces of the solar cells, for creating an electrical contact. The insulating strip can be continuous over all of the cells in a string, and thus cover the electrical conductor, such that are not visible when the solar module is fully assembled.
The conductors can each be strip shaped conductor elements, which are designed as curved components in order to create stress relief structures. The conductor elements can each exhibit at least one flat attachment section, which lies on the insulating strip, as well as, if applicable, flat contact sections, which lie on the solar cells in the regions of the contact locations.
Further individual characteristics and advantages of the invention can be derived from the following description of embodiment examples, and from the drawings. They show:
a shows an application unit according to an alternative embodiment example to that in shown in
The following detailed description and appended drawings describe and illustrate various exemplary embodiments of the invention. The description and drawings serve to enable one skilled in the art to make and use the invention, and are not intended to limit the scope of the invention in any manner. In respect of the methods disclosed, the steps presented are exemplary in nature, and thus, the order of the steps is not necessary or critical.
Back surface solar cells are processed using the illustrated device. The solar cells are placed on the conveyor belt 38 thereby in the embodiment example according to
The device 1 furthermore comprises a punching station, indicated by the numeral “40,” which is disposed next to the conveyor device 9. Conductive material containing strip-shaped copper, for example, (e.g. tin-plated copper bands) is processed in the punching station 40 to form conductor elements. The copper bands are between 0.01 mm and 1 mm thick, and have a width of 0.5 mm to up to 50 mm. Details regarding the design of the punching station can be derived from the following
Details of the application station can be discerned in
The insulating strips 11, separated into single sections, are designed as double-sided adhesive strips, which can be attached to the solar cells simply by pressing. The insulating strips 11 consist, for example, of an insulating plastic (e.g. PP, PE, PET, PTFE), which is coated on both sides with an acrylic adhesive, for example. The insulating strip is guided along a sliding surface 44 of a pressing element 14, and redirected. The pressing force, indicated by an arrow P in
The insulating strip material rolled onto the supply role need not necessarily be prepared in advance, and already exhibit separation locations. The insulating strip material can, for example, be cut into single strip sections during the feed process. A structural solution in this regard is shown in
The two-piece design of the shaping unit 17 enables the production of conductor elements of different lengths, without it being absolutely necessary to cut off parts of the conductor material. It should be noted that the first and the last conductor elements of a solar cell string are normally shorter than the strips between them, because the latter each connect two solar cells to one another. The starting and end conductor elements are preferably each produced at the same time. For this, an offset (cf. the following
It can be seen from
It is clear, once again, from
The device described above also enables a continuous connecting (“stringing”) of back surface solar cells, wherein, in each case, a string can be formed having the plus pole in one direction and the minus pole in the other direction. The next string is then produced such that its polarity is the reverse thereof. This corresponds to the configuration in a solar module, and enables a higher throughput during the lay-up, because the string no longer needs to be rotated for the lay-up, but instead, needs only to be displaced. In order to produce this positive characteristic, the first cell of the new string must be applied in the same manner as the last solar cell in the previous string. The polarity can be determined by rotating the solar cells 180° by means of robots 36 (
The completion stations and units of the device described above, and shown in the figures can also be spatially separate from one another, in order to be able to carry out the individual procedures in parallel, thus generating the highest possible throughput.
It is clear that with the device it is also possible to create a solar cell string in which the solar cells, disposed behind one another, or in rows next to one another, respectively, have the same orientation.
The solar cell string shown in
In accordance with the provisions of the patent statutes, the present invention has been described in what is considered to represent its preferred embodiment. However, it should be noted that the invention can be practiced otherwise than as specifically illustrated and described without departing from its spirit or scope.
| Number | Date | Country | Kind |
|---|---|---|---|
| 12182323.1 | Aug 2012 | EP | regional |
