NL2006170C2

NL2006170C2 - A method of manufacturing a solar panel.

Info

Publication number: NL2006170C2
Application number: NL2006170A
Authority: NL
Inventors: Patrick Willem Hubert Heuts; Klaas Heres
Original assignee: Tsc Solar B V
Priority date: 2011-02-09
Filing date: 2011-02-09
Publication date: 2012-08-10

Description

A method of manufacturing a solar panel

FIELD OF THE INVENTION

The invention relates to a method of manufacturing a 5 solar panel with a front side and a rear side and comprising an assembly of solar cells, contacts of the solar cells being coupled to terminals of the solar panel through conductors in a layer stack on the rear side of the solar panel, which method comprises the steps of providing foils 10 on a carrier device to form the layer stack, assembling the solar panels on top of the layer stack, providing a top foil and laminating the foils of the layer stack, the top foil and the solar panel

The invention further relates to a resulting solar panel, 15 and to equipment for use in the method.

BACKGROUND OF THE INVENTION

Solar panels are considered as a primary energy sustainable energy source for houses and other buildings.

20 The adoption of solar panels economically depends on the effective cost thereof relative to conventional energy sources. The efficiency of a solar panel is therefore a very important parameter for determining its quality. Generally, research and development efforts focus on an improved 25 conversion of solar energy into electrical energy in the solar cells. Major improvements have been reached in relation thereto. However, it is known that quite some energy is lost again within the assembly making up the solar panel. Such losses result for instance from resistive losses 30 in interconnects and conductors, and/or due to contact resistances .

A relevant reduction in resistive losses was achieved in the creation of back contacted solar cells, such that all 2 contacts are present on the rear side. This reduces the length and complexity of interconnects. The back contacts are enabled through the provision of through silicon vias.

An example of such a solar panel is known from US5,972,732.

5 This patent proposes the provision of electrical conductors on a backsheet according to a placement configuration, so as to result in a suitable electrical circuit together with the solar cells. The conductors are prepatterned, based on the electrical requirements to be manufactured and in part 10 dictated by the dimensions of the solar cells to be used in the solar panel.

A disadvantage of said proposal from US5,972,732 is the problematic positioning of each of the conductors. Adequate positioning requires a correct position of a reference point 15 on the conductor and a correct rotation of the object around such reference point. Doing this for each prepatterned conductor individually will lead to large processing times. Furthermore, a certain tolerance in positioning precision is to be accepted, which likely results in higher resistances 20 and/or lower resolution.

An alternative implementation is known from W02009/134939. Here, a backsheet with a patterned metallization is used. A further conductor is thereon inserted, either by preassembly on the backsheet, or via a 25 pick-and-place robot during the assembly and adhered to the metalized backsheet via conductive adhesive. A Multilevel metallization on the backsheet could be used as an alternative to the application of separate conductors. The resulting backsheet with multiple metallization levels is 30 also known per se as a printed or flexible circuit. The chosen pattern is preferably in the form of a serpentine circuit layout.

3 A disadvantage of the use of printed or flexible backsheets for solar cells resides in thermal cycling. As is known to a person skilled in the art of assembly of electronic components, printed circuits and silicon have 5 quite different coefficients of thermal expansion. Due to temperature changes in production, but particularly during use, the printed circuit and the silicon material will expand or contract. The expansion and contraction of the printed circuit will be higher than that of the silicon, and 10 may deviate from the silicon in phase (e.g. timing).

Stresses therefore occur that constitute a threat to the operation of the product. Particularly, the connections between printed circuit and silicon are vulnerable to cracking and failure. Such failure is not merely relevant 15 for miniature components such as integrated circuits, but also to solar panels. First of all, the solar cells are larger such that the lateral differences in expansion are larger. Secondly, solar panels are used at outside locations with major differences in temperature, both between 20 individual locations (e.g. a desert or a city in Europe) over time (heating up in the sun, cooling down due to wind and cold at other locations), and differentially (exposed front side, i.e. outside temperature, rear side coupled to a house that is typically provided with heating).

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SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide an improved method of manufacturing a solar panel.

It is a further object of the invention to provide a solar 30 panel thus made.

This object is achieved in a method of manufacturing a solar panel with a front side and a rear side and comprising an assembly of solar cells, contacts of the solar cells 4 being coupled to terminals of the solar panel through conductors in a layer stack on the rear side of the solar panel, which method comprises the steps of providing foils on a carrier device to form the layer stack, assembling the 5 solar cell on top of the layer stack, providing a top foil and laminating the foils of the layer stack, the top foil and the solar cell, wherein the conductors are provided by: applying an electrically conductive foil on a positioning member 10 - patterning the electrically conductive foil according to a predefined pattern with at least one patterning device, and transferring the patterned electrically conductive foil from the positioning member to the carrier device.

15 In a further embodiment, a positioning apparatus for use in the inventive method is provided, comprising a positioning member, means for attachment of the foil onto the positioning member and cutting means.

Use of a positioning member separately from the carrier 20 device allows the use of foils and separate conductors and still ensures positional accuracy. It is based on the insight that the positioning member may be accurately positioned to the carrier device, and that transfer of the foil can be achieved without loss in positional accuracy.

25 The resulting device does not have the risk of failure in thermal cycling, since the individual conductors laminated within the layer stack allows more freedom with respect to differential expansion and contraction.

Suitably, the foil is retained on the positioning 30 member during patterning by means of vacuum. The term 'vacuum' herein as refers to any reduced pressure compared to atmospheric pressure. The vacuum is suitably created in that the positioning member comprises vacuum means. This is 5 for instance achieved with a vacuum chamber in the positioning member with holes between said vacuum chamber and an adhesion location for the foil. By reducing the pressure in the vacuum chamber, the foil will be adhered to 5 the positioning member. Most suitably, such adhesion locations are present merely locally. This allows that other locations are not exposed to the vacuum or reduced pressure and that the foil may be removed there without counterforce. In a preferred embodiment, the positioning member is 10 provided with a plurality of localized vacuum means that can be individually driven. This allows optimum combination of retaining the foil on the positioning member and patterning the foil. Furthermore, this allows the transfer of the patterned foil in a wave-like movement. Both a radially 15 extending wave (from the center ) and a transversal wave may be applied.

In a further embodiment, the positioning member and/or the carrier device is provided with an alignment reference. This alignment reference is detected in the transferring 20 step, so as to ensure that the created pattern is not misaligned with respect to the carrier device. Furthermore the alignment is to be appropriate over the complete surface area of the carrier device in at least two directions.

In a first implementation of such alignment reference, 25 either the carrier device or the positioning member or both comprise an optical sensor of irradiation suitable for detection of the optically detectable alignment reference. Typically, the sensor will be present below a foil, that is suitable transparent for any radiation used for the 30 alignment reference.

One implementation of an alignment reference is a local source of irradiation present in either the carrier device or the positioning member. The local source preferably emits 6 radiation in a direction substantially normal to its main surface. Suitable examples of sources of irradiation include laser diodes and light emitting diodes. The local source of irradiation may be further used to measure a distance 5 between the positioning member and the carrier device during the transfer step. The intensity of the detected radiation is a function of the distance. A calibration step will enable a correct interpretation of the distance on the basis of the detected intensity. Suitable a plurality of local 10 sources is present, so that the distance across the carrier device can be measured during the transfer step. An alternative implementation of an alignment reference is a reflector or diffuser. An optical sensor, suitably provided with a local light source can thus detect the amount of 15 reflected radiation. Such an alignment reference could be embodied as the locally present through-holes defining the vacuum in the positioning member.

It will be understood that in case of local alignment references as specified above, it is preferable that a 20 plurality of alignment references is present across the surface of the positioning member of the carrier device.

In one preferred embodiment, the alignment reference is defined in the carrier device, particularly in the embodiment of using a local source of irradiation as the 25 alignment reference. The carrier device will typically be provided with a sequence of foils in a sequence of process steps. When present within the carrier device, it will be increasingly difficult to specifically detect any radiation through the growing sequence of foils on top of the carrier 30 device. However, adequate detection of a light source through a plurality of foils is feasible even when the light intensity decreases.

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The patterning is suitably carried out with mechanical means, e.g. with cutting, punching or the like. Optical patterning, and particularly maskless optical patterning constitutes an alternative implementation.

5 In a further embodiment, the patterning process comprises a first step of low resolution patterning and a second step of high resolution patterning. The low resolution patterning is suitably implemented mechanically, whereas the high resolution patterning is preferably an 10 optical patterning step. Such multi step process allows a combination of sufficient speed and sufficiently high resolution at relevant locations.

In one implementation, the high resolution patterning is applied after transferring the conductive foil. This high 15 resolution patterning is particularly envisaged to remove certain bridges in the pattern. The bridges could provide some continuity in the foil that support an adequate transfer. With the subsequent removal, short-circuits are prevented. In a further embodiment thereof, undesired 20 portions of the transferred pattern are thereafter removed mechanically.

Alternatively and/or additionally, the further, high resolution patterning step is used for correction of mistakes in the cutting process.

25 In an even further embodiment, the high resolution patterning step is used to disconnect certain test pads after testing the circuit. Such testing is particularly beneficial when embedding functionality into the solar panel. The removal could be carried from the rear side, for 30 instance through a window in any carrier foil (also referred to as backsheet) if present.

In another embodiment, a second patterned electrically conductive foil is provided in addition to the - first 8 patterned electrically conductive foil. In addition to enabling the provision of a multilevel interconnect system (with conductors mutually crossing each other), this allows the provision of the (electrically) conductive foils in a 5 size format different from that of the carrier device and any backsheet. The transfer of conductive foils with smaller size in at least one dimension may well have practical advantages .

In a most suitable embodiment, the first and the second 10 (electrically conductive) foils could be patterned with a repetitive pattern. Such provision of repetitive patterns on separate foils offers the benefit of scalability, such that solar panels of different size may be more easily assembled in a single assembly line.

15 In order to mutually attach such a first and a second conductive foil a mutual overlap area is suitably included. The overlap areas thereafter suitably form an electrically conductive connection with any intermediate layer of conductive adhesive, solder or the like as known to the 20 skilled person.

BRIEF DESCRIPTION OF THE FIGURES

These and other aspects of the invention will be further elucidated with reference to the Figures, in which 25 Fig. la-c show in a diagrammatical top view a sequence of steps of the method in which a conductive foil is patterned on a positioning device

Fig. 2 shows in a diagrammatical top view a conductor pattern on top of a carrier device; and 30 Fig. 3 shows in a diagrammatical cross-sectional view a further stage in the assembly of the method of the present invention 9

DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT

The Figures are not drawn and purely diagrammatical. Equal reference numerals in different Figures refer to same or like elements.

5 Fig.la-c show a sequence of steps in the patterning of a conductive foil to specific conductors. Fig. la herein shows a positioning device 20. The positioning device 20 is effectively a table onto which a foil can be provided and positioned. The dimensions of the present positioning device 10 are suitably in the order of 1 x 2 meters, but this is not essential. The foil typically is provided therein in similar dimension or in smaller dimensions, according to different embodiments of the present invention. The positioning device 20 is provided with means for attachment of the foil. Such 15 means may be clamping means as known to the skilled person, but are preferably vacuum means, in particularly means with which the foil is attracted to the table by underpressure. The positioning device 20 of this embodiment specifically is provided with a plurality of holes 22, which are coupled to 20 a plurality of vacuum chambers within the positioning table. Most suitably, substantially each hole is coupled to a separate vacuum chamber. However, the invention will also work with less spatial resolution of the vacuum means. In this case, a plurality of holes will be coupled to a single 25 vacuum chamber. Each vacuum chamber is again provided with means to switch on or switch off the vacuum, e.g. varying the pressure in the vacuum chamber so as to attract a foil by underpressure, not attract with atmospheric pressure, or blow a foil away by more than atmospheric pressure. The 30 positioning device 20 is further provided with means for positioning a foil, particularly a reference. Suitably, this means are embodied as a set of protrusions on the table.

Such protrusions are sufficiently low so that the foil can ΙΟ be easily rolled out on top thereof. However, they are sufficiently high so that the protrusions may be visible or sensible through the conductor foil. Particularly, due to the protrusions reflection behavior of the conductive and 5 typically metallic foil may be modified, which can be optically detected. Moreover, such protrusions are not so sharp as to give a risk of cracking the foil. Other positioning means may be used alternatively.

Fig. lb shows a portion of a conductor foil 30 (e.g. on 10 top of the positioning device). It is shown as being cut in accordance with a specific pattern, so as to be divided into a first areas 32 of conductors to be transferred into the assembly of the solar panel, and second areas 33 not to be transferred and thus to be disposed as waste. The pattern 15 shown here comprises finger-shaped elements. This turns out suitable for the connection of the distributed contacts. Cutting is suitably carried out with known mechanical means, that are preferably automatically driven, e.g. as a robot. The robot may determine its position with respect to the 20 positioning device based on optical inspection so as to identify the one or more optically detectable references. Alternatively or additionally, the robot may identify edges and corners of the positioning device itself and thereof define its position. Suitably, the robot is integrated in an 25 apparatus with the positioning table, so that its positioning is simplified by design.

Fig. lc shows the positioning device 20 with a portion of the conductor foil, after transfer of the first areas 32. Left behind on the positioning device 20 are the second 30 areas 33. Where the first areas 31 were present, the holes 22 giving access to the vacuum chambers are visible again. Thus, in this embodiment, the conductor foil is merely partially transferred, and the second areas 33 remain 11 attached to the positioning device. This has the advantage that these second areas 33 cannot by accident fall onto the carrier device or cause trouble otherwise. This results in an efficient production process. It will be understood that 5 in order to ensure that the second areas 33 remain on the positioning device 20, the resolution of the vacuum chambers needs to be sufficient.

Fig. 2 shows a top view of the first areas 32 that have been transferred to a carrier device 10. Fig. 3 shows a 10 diagrammatical cross-sectional view substantially corresponding to the situation shown in Fig. 2. The foil has been provided onto a first insulating layer 35, that is again attached to the carrier device, for instance with clamping means or by materials interaction, such as adhesion 15 by gentle heating or a minor amount of any adhesive in a reversible manner. The foil comprises a plurality of fingers 71 coupled to major conductors 61, 62. In operation, the conductors 61, 62 will be coupled to the different contacts 51, 52 of the solar cell (e.g. in and out) and thus carry a 20 different voltage. Several conductors 61, 62 may be connected together in a circuit as desired. In one important embodiment, this circuit is a combination of serial and parallel connections so as to arrive at an output voltage and output current that are corresponding to requirements as 25 well as minimal resistive losses. Use is suitably made of a DC coupler which makes the circuit variable. In this example, the size of one solar cell 100 is indicated with respect to the shown assembly. The solar cell is most suitably a solar cell with rear side contacts that are 30 embodied as dot-shaped, mutually isolated contacts. Mutual coupling occurs merely on the level of the conductor foil. The location of the contacts of the solar cells is indicated in Fig 2. First contacts 51 coupled to p-type regions 31 in 12 the solar cell 100 are assembled to finger-shaped conductors connected to conductors 61. Second contacts 52 coupled to n-type regions 33 in the solar cell 100 - in a silicon solar cell with an n-type doped substrate 10 located at the rear 5 side 12 - are assembled to finger-shaped conductors 71 connected to conductors 62. The number and extension of finger-shaped conductors 71 is herein merely indicative. It may well be that the number of first contacts 51 is lower than the number of second contacts 52 or vice versa. The 10 solar cell 100 is furthermore provided with a passivation layer 32 both on the front side 11 and the rear side 12. Further details such as through-holes, contacts on the front side, etc are present as known to the skilled person in the art.

15 While merely a portion of the conductor foil is shown, it will be clear that the conductor pattern is based on a regular distribution of contacts 51, 52 and is therewith itself also regular. It may well be made repetitive. This allows the transfer of certain standard repetitive conductor 20 patterns on the basis of which a circuit layout is defined on the carrier device 80. Adjacent foils may be coupled together by overlapping conductors 65. The effective electrical connection is typically established in a lamination process for the solar panel. Conductive adhesive 25 may be applied between the foils as required.

Claims

Method for manufacturing a solar panel with a front side and a rear side and comprising an assembly of solar cells, wherein contacts of the solar cells are coupled to conductors in a stack of layers at the rear of the solar panel, which method comprises the steps of providing films on a carrier body to form the stack of layers; the assembly of the solar cells on top of the stack of layers; applying an upper film over the solar cells and laminating the films of the stack of layers, the upper film and the solar cells, in which the conductors are provided by:

15. Applying an electrically conductive film to a positioning body; Patterning the electrically conductive film according to a predetermined pattern with at least one patterning device, 2. and; Transferring the patterned electrically conductive film from the positioning body to the carrier body.

A method according to claim 1, wherein the film is retained on the positioning body during vacuuming.

3. Method as claimed in claim 1 or 2, wherein a further patterning step is carried out after transferring the patterned electrically conductive foil.

Method according to claim 3, wherein the further patterning step is performed with an optical means, for example with a laser.

The method of claim 1, wherein a carrier film is applied to the carrier body prior to transferring the patterned electrically conductive film.

The method of claim 1 or 5, wherein a second patterned electrically conductive film is transferred from a positioning body to the carrier body in addition to the - first - patterned electrically conductive film. 15

7. Method as claimed in claim 6, wherein a first conductor on the first patterned, electrically conductive foil is connected to a second conductor on the second patterned, electrically conductive foil.

8. Method as claimed in claim 7, wherein the second conductor is connected to the first conductor in that the first and the second patterned electrically conductive foil each have an overlap surface and are positioned such that the overlap surfaces overlap when viewed in a perpendicular projection from the first to the second film.

9. Method as claimed in claim 1, wherein the carrier body and the positioning body are provided with positioning means for checking the mutual positioning.

10. The method of claim 1, wherein a carrier film is applied to the patterned electrically conductive film to form a stack prior to transferring said stack to the carrier body.

11. Solar panel with a front side and a rear side and comprising assembled solar cells, contacts of which 10 solar cells are connected to conductors in a stack of layers at the rear of the solar panel, the stack of layers, the solar cells connected thereto and an upper foil being laminated together and wherein the conductors are provided by patterning a conductor film according to any of claims 1 to 10 in situ.

12. Positioning device for a film comprising a positioning body, means for holding the film of the positioning body and cutting means.

A positioning device according to claim 12, wherein the means for holding comprises means for applying a vacuum. 25

14. Positioning apparatus as claimed in claim 13, wherein the means for applying a vacuum comprise a number of vacuum chambers which are independently controlled such that first parts of a foil can be detached from the positioning body after cutting, while second parts are retained on the positioning body.