The invention relates to a method and a device for attaching an elongated conductor to a solar element.
According to a previously known method, crystalline solar cells are contacted on the front side with conductive strips. According to patent disclosure DE 10 2006 006 715 A1, grippers are used to grip a conductive strip and place it on the solar cells in controlled manner. The conductive strip then has applied to it a longitudinal tensile stress before it is fastened onto the solar cells. Before the conductive strip is cut through, and before it is fastened onto the solar cells, the conductive strip is clamped onto the solar cells by means of a hold-down system. In this example, fastening of the conductive strip is effected by means of an adhesive substance.
However, this approach is not suitable for thin-film solar cells or for solar elements that have greater dimensions than the crystalline solar cells. With greater dimensions, the requirements for accuracy when placing the conductive strip are significantly higher. Furthermore, with greater dimensions that are characteristic of longer conductive strips, the curvature and any ripples of the conductive strips assume an increasingly important role. Moreover, it is important to ensure that despite their greater length the conductive strips have a contact resistance relative to the solar element that is as constant as possible. Any false alignments cause power losses.
If the conductive strip is stretched, hardening of the conductive strip can result. This hardening can cause damage to the crystals of a crystalline solar cell. Thin-film solar cells can also be damaged by the conductive strip if it is not applied with sufficient care. Stretching of the conductive strip can also cause brittleness which can result in micro-cracks which are undesirable.
The task therefore presents itself of developing a method for contacting solar elements with an elongated conductor which avoids the disadvantages stated above. The method shall function reliably and reproducibly and shall be particularly suitable for the application of conductors that are longer than 300 mm.
A further objective of the invention is to provide a corresponding device that enables the method to be executed automatically.
It is regarded as an advantage of the invention that through the special method and the correspondingly designed device, homogeneous, low-resistance contactings are possible also over greater lengths.
Further advantages are the wrinkle- or crease-free application of long conductive strips, the high accuracy and outstanding reproducibility, as well as the assurance of a uniform transition resistance between the elongated conductor and the solar element.
The above, as well as other advantages of the present invention, will become readily apparent to those skilled in the art from the following detailed description of a preferred embodiment when considered in the light of the accompanying drawings in which:
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.
The present invention is concerned with a partial aspect of the manufacturing of solar elements. The term “solar element” is used here as generic term for solar cells, solar modules, and solar systems. The invention is independent of whether the solar elements are crystalline, polycrystalline, or amorphous. The invention can also be applied with particular advantage to thin-film solar elements. Application of the invention is not restricted to silicon solar cells. It can also be applied to other types of solar cells (e.g. organic solar cells).
Typically, at least some of the manufacturing steps are executed in an automated processing system 100. A corresponding processing system 100 according to a first embodiment of the invention is shown in
The first station 110 is designed to apply via a dispenser 111 a special adhesive substance to the solar elements 1 in one, two, or more parallel lines. The number of the adhesive-substance lines is adapted to the number of parallel elongated conductors that should be applied to the solar elements 1. Shown in
The special adhesive substance is designed in such manner that it is electrically conductive either already before hardening or only after hardening. The special adhesive substance is preferably pasty so that it can be applied from the dispenser 111 to the solar elements 1 in precisely dispensed quantities. Particularly suitable is a special adhesive substance that contains electrically conductive metal particles. Preferable is a conventional silver-conductive adhesive. Depending on the number of the desired parallel lines of adhesive substance, the dispenser 111 can have one, two, or more adhesive substance nozzles. Alternatively, a slit nozzle can be employed that has a corresponding number of outlet openings. In
The term “elongated conductor 2” is used here for conductive strips, conductive tapes, and conductive tracks. The cross section of the elongated conductor 2 can be circular (round wire) or semicircular, oval, square, rectangular, hexagonal, or octagonal. Preferably, a flat conductive strip with rectangular cross section is used as the elongated conductor 2.
Preferably, copper is used as material. Aluminum, silver, gold, platinum and titanium are also suitable. The metal alloys that are commonly used in semiconductor technology can also be used as conductor. Particularly preferable is a tinned copper conductor.
If a copper conductor is used, it should have a tensile strength with a value below Rm=250 N/mm2. At values above 250 N/mm2 there is a danger when straining of embrittlement and formation of micro-cracks. Designated as yield point with Re is that tensile stress at which flow begins without the tensile stress being further increased. The term “strain” is used here as a synonym for the words stretch, extend, elongate, tauten.
Straining is performed so that the conductor 2 has applied to it a predefined tensile stress in the longitudinal direction. Through straining of the conductor 2 particularly advantageous conductor surfaces are created.
The conductor 2 is preferably strained so that slight plastic deformation occurs to eliminate any curvature of the conductor 2. In other words, straining takes place so that the yield point Re is minimally exceeded.
Preferably, straining of the conductor 2 is controlled by the straining being defined as a percentage of the pull-out length before straining and the processing unit 100 being correspondingly set. The parameter for straining is preferably between 1 and 17% of the pulled-out length before straining. Particularly preferable is a parameter that has a value between 1 and 5%.
Stretching of the elongated conductor 2 is monitored to prevent exceeding of a tensile limit K. The tensile limit K can be defined in various different ways. In the present case, the said parameter serves as tensile limit K. Instead of defining the tensile limit K as a percentage extension of the pull-out length, the tensile limit K can also be defined as, for example, a maximum tensile stress. The maximum tensile stress is defined in such manner that straining of the conductor 2 lies within the specified range of the parameter. The tensile limit K can also, for example, be expressed as a percentage yield point Re. In this case, the tensile limit K is between 100 and 117% of the yield point Re. Preferably, the tensile limit K is between 100 and 105% of the yield point Re. In other words, the tensile limit K is slightly above the yield point Re.
In the second station 120 the desired number of elongated conductors 2 is applied to the solar elements 1. Shown in
In the example shown, the third and fourth stations 130, 140 are identically embodied and serve to harden the special adhesive substance by means of the heat generated by infrared radiators 131, 141. Instead of the infrared radiators 131, 141, other heat sources such as, for example, induction coils or resistance heating elements can also be used.
The said elements of the second station 120 are described in more detail below. The following explanation is given only in relation to the visible elements that are arranged on the right side of the solar elements 1 (viewed in the x direction) and can be transferred 1:1 to the elements that are situated on the left side of the second station 120.
To make the elongated conductor 2 available in sufficient length, a strip feeder 11 is provided. As shown in more detail in
Preferably, four sensors are arranged along the vertical path of the compensator 16.1 to regulate the drum motor 122 of the drum 15.
The use of a drum motor 122 assures that when pulling out the elongated conductor 2, the tensile stress in the conductor 2 is not excessively high.
Overall, the strip feeder 11 allows a continuous and certain feeding of the required conductor 2.
A further element that is used is a cutting/clamping unit 17, which can be seen more clearly in
The cutting/clamping unit 17 in its entirety is movable in the x direction with a pneumatic carriage 21. Preferably, in the x direction two positions of the cutting/clamping unit 17 are prespecified. Held by guiding parts, the elongated conductor 2 passes under and through a clamping plate 18 to a cutting blade 23. The clamping plate 18 is pressed upwards by compression springs 20.3 or, if the elongated conductor 2 should be clamped, pressed downwards onto the elongated conductor 2 by a pneumatic clamping cylinder 37.1 through a piston rod 37.2, a fork 19.1, and an eccentric shaft 25.1.
The cutting blade 23 is actuated by the pneumatic cutting cylinder 38 via a link 24. Clamping unit 17.2 and cutting head 17.1 are movably borne on a linear guide 22, the clamping unit 17.2 of a first compression spring 20.1 and the cutting head 17.1 of a second compression spring 20.2 being supported relative to the pneumatic carriage 21. An optional proximity sensor 26 detects the position of the cutting/clamping unit 17 and can be used for crack monitoring of the elongated conductor 2 when straining (this step is explained later).
In a lateral cross section view in
The cutting/clamping unit 17 also serves for temporary one-sided holding-fast of the elongated conductor 2. Furthermore, the cutting/clamping unit 17 can cut the elongated conductor 2, which takes place through a movement of the cutting blade 23. The movement of the cutting blade 23 is generated by the pneumatic cutting cylinder 38 (see
Provided in addition to the cutting/clamping unit 17 are a so-called pull-out carriage 14 and a so-called roll-on carriage 13 (see
The pull-out carriage 14 is shown in
The vertical pneumatic carriage 28.1 is in turn movable in the x direction by a horizontal pneumatic carriage 28.2. The gripper 29 is similar to the clamping unit 17.2 of the cutting/clamping unit 17, with a clamping plate 30 which is movable about a swivel axle 31 acting from below.
The gripper 29 of the pull-out carriage 14 has a pneumatic cylinder 29.1 which by means of a piston rod (not visible) converts a translatory movement into a tipping movement of a fork 19.2. The tipping movement is converted into a turning movement of an eccentric shaft 25.2. By means of the eccentric movement of the eccentric shaft 25.2, the clamping plate 30 is moved upwards. Springs 39 press the clamping plate 30 downwards.
As shown in
The tape guide 33 of the roll-on carriage 13 can be moved with a vertical pneumatic carriage 32.1 (acting in the z direction) and the horizontal pneumatic carriage 32.2 acting in the y direction under the pulled-out elongated conductor 2. When this is done, first the tape guide 33 is lowered by a movement in the negative z direction and then the tape guide 33 is pushed under the elongated conductor 2 by a horizontal movement in the negative y direction.
Preferably, the first and second stations 110, 120 can be moved ±10 mm in the y direction, for example with micrometer screws, so as to perform, for example, a fine adjustment. Preferably, the pressure rollers 27.1, 27.2 can additionally be moved in the y direction relative to the gripper 29 and the tape guide 33.
Now that the basic elements of the second station 120 have been described, the method according to the invention will be described in individual steps. The following description and the representation in the
In a second step, which is shown in
The gripper 29 of the pull-out carriage 14 now grasps the free end of the elongated conductor 2. This takes place through the pneumatic cylinder 29.1 initiating a turning movement of the eccentric shaft 25.2 as described. By means of the eccentric movement of the eccentric shaft 25.2, the clamping plate 30 is moved in such manner that the elongated conductor 2 is clamped, as shown in
In a next step, which is shown in
Instead of pulling out or unwinding the elongated conductor by a translatory movement of the pull-out carriage 14, in another embodiment this step can also be executed by the cutting/clamping unit 17 through the latter moving in the negative x direction. Handing over of the free end of the conductor 2 can then take place at the end of this movement of the cutting/clamping unit 17. Readying of the elongated conductor 2 can also take place through a combination of movements of the cutting/clamping unit 17 and the pull-out carriage 14.
In a next step, which is shown in
In a next step, which is not shown, the pull-out carriage 14 travels back (i.e. the travel distance that was covered for straining is retraced) until the proximity sensor 26 detects the cutting/clamping unit 17 in the starting position again. By means of these intermediate steps the elongated conductor 2 was stretched in controlled manner.
In a next step, which is shown in
In a next step, which is shown in
Now, as shown in
The press-on carriage 13 then travels back as far as the cutting/clamping unit 17, as shown in
The press-on roller 27.1 of the pull-out carriage 14 then travels back and the gripper 29 is opened to release the end of the elongated conductor 2. The elongated conductor 2 can now be cut off with the cutting blade 23. Now, or at another suitable point in time, the cutting/clamping unit 17 can be moved back into the starting position as indicated in
Thereafter, if necessary, the end-pieces of the elongated conductor 2 are rolled-on with the press-on rollers 27.1, 27.2, as indicated in
Thereafter the press-on rollers 27.1, 27.2 are raised and the individual elements moved into the starting position. Preferably, the cutting/clamping unit 17 travels in advance and the pull-out and roll-on carriages 14, 13 follow into their respective starting positions.
The pull-out carriage 4 according to the invention fulfills the following conditions:
Furthermore, the pull-out carriage 14 can preferably engage in mechanical interaction with the cutting/clamping unit 17 to expose an end of the conductor 2 and be able to grip this free end with the gripper 29.
The roll-on carriage 13 according to the invention has at least one press-on roller 27.2 to roll-on the elongated conductor 2. The roll-on carriage 13 preferably has a tape guide 33. The employment of such a roll-on carriage 13 is optional. The rolling-on can also take place completely with the pull-out carriage 14, this variant being suitable for relatively short rolling-on lengths since otherwise the guiding function of the roll-on carriage 13 is absent.
The cutting/clamping unit 17 serves to hold fast the elongated conductor 2 as well as having means to cut off the conductor 2. Preferably the cutting/clamping unit 17 has one or more sensors (e.g. the proximity sensor 26) to monitor the straining of the elongated conductor 2.
In a preferred embodiment a sensor (preferably a strain gauge) is employed on the cutting/clamping unit 17 or on the pull-out carriage 14 to determine the tensile stress on the elongated conductor 2.
The processing system 100 is so designed that the elongated conductor 2 can be placed onto and rolled onto the special line of adhesive substance with absolute accuracy. Finally, an optional cover strip can be rolled out over the conductor 2. The cover strip is so applied as to ensure that there is no trapped air underneath the cover strip.
Shown in
Shown in
The invention can be used for front-side as well as back-side contacting of solar elements 1.
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 |
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08164185.4 | Sep 2008 | EP | regional |