NL2012555B1

NL2012555B1 - Photovoltaic module with interconnection wrap around cells.

Info

Publication number: NL2012555B1
Application number: NL2012555A
Authority: NL
Inventors: Adrianus Maria Van Roosmalen Johannes
Original assignee: Stichting Energieonderzoek Centrum Nederland
Priority date: 2014-04-02
Filing date: 2014-04-02
Publication date: 2016-02-15
Also published as: NL2012555A

Description

Photovoltaic module with interconnection wrap around cells Field of the invention

The present invention relates to a photovoltaic module comprising a back side connection substrate and a plurality of cells, each having a front side metallization and a back side metallization.

Prior art

When using H-pattern technology photovoltaic cells for assembling photovoltaic modules, a process called tabbing-stringing is utilized. Conductors on the front side of the cells are connected to conductors on the rear of an adjacent cell by tabbing and are connected into strings prior to lamination. By making use of tabbing, significant power is lost because of the electrical resistivity of the tabs, in the order of 3% of the produced power. Solutions to lower the losses in the tabs by increasing the width are not useful, because this causes and increase in shadow loss of the cell. Solutions to lower the losses in the tabs by increasing the thickness are not useful, because this causes too high mechanical stress.

To circumvent the power losses in the tabs Metal Wrap Through type of cells are known using via’s to create conductors for both contacts on the rear of the cells, so an electrical connection is made from the front metallization to a conductor (contact pad) on the rear of the same cell prior to interconnection to an adjacent cell. Connections between the cells can then be made at the rear, where the issue of shadow loss does not apply. A know method to connect back contact cells is the conductive back sheet technology.

In known metal wrap around solar cells, the front cell metallization is wrapped around the cell edge to a contact pad on the rear, also providing conductors for both contacts on the rear, see eg. the article ‘ACE Designs: The beauty of rear contact solar cells’ by A. Schönecker et al, presented at the 29th IEEE Photovoltaic Specialists Conference, 20-24 May 2002, USA.

American patent publication US-A-4610077 discloses a wrap around solar cell, in which slits are made in the solar cell to make smaller pieces after processing. It is noted that still the cell metallization is used to contact pads on the rear of the same cell.

Summary of the invention

The present invention seeks to provide an improved and easy to assemble photovoltaic module.

According to the present invention, a photovoltaic module according to the preamble defined above is provided, wherein electrical connections are provided between a first cell and a second, adjacent, cell of the plurality of cells, each of the electrical connections comprising a busbar in contact with the back side metallization of the first cell, and extending over the back side connection substrate into a space between the first cell and second cell, and a contacting part connecting the busbar to the front side metallization of the second cell via an edge of the second cell. By not providing a cell with all contacts on its own back side, but providing an electrical connection between two adjacent cells during assembly of the photovoltaic module, the assembly thereof can be made more efficiently.

Short description of drawings

The present invention will be discussed in more detail below, using a number of exemplary embodiments, with reference to the attached drawings, in which

Fig. 1 shows a perspective view of a part of a photovoltaic module according to an embodiment of the present invention;

Fig. 2 shows a perspective view of a part of a photovoltaic module according to a further embodiment of the present invention;

Fig. 3 shows a top view of a photovoltaic module according to an even further embodiment of the present invention; and

Fig. 4 shows a top view of four different types of cells usable in a photovoltaic module according to the present invention.

Detailed description of exemplary embodiments

The present invention embodiments aim to provide more efficient and cost-effective manufacturing of photovoltaic modules such as solar panels, etc. This is achieved with the embodiments of the present invention as described below. A perspective view of a first embodiment of the present invention is shown in Fig. 1. Two cells 10, 10’, with a thickness t, are shown positioned on a back side connection substrate 1, each cell 10, 10’ having a front side metallization 4 and a back side metallization 3. The first cell 10 (on the right in Fig. 1) is shown semi-transparent, to be able to show the back side metallization 3. The back side metallization 3 and front side metallization 4 may be provided with associated connecting pads 5, 6. In an embodiment, the electrical connection comprises a connecting pad 5 near the edge of the second cell 10’, and can be an integral part of the front side metallization 4. . In the embodiment shown in Fig. 1, the electrical connection also comprises a connecting pad 6 near the edge of the first cell 10. Such a positioning of the pad 6 near the edge can be advantageous in the case of bi-facial cells 10, 10’, or in implementations where the conductor on the back side is not optimal (e.g. in the case of (cold) sprayed Cu on a substrate, the conductance may be less than the case of a Cu foil).

In an alternative embodiment, a connecting pad 6 is provided for the back side metallization 3 in a center part of the first cell 10. The conductance on cell level will then be optimal.

The back side connection substrate 1 provides for interconnection of all of a plurality of cells 10, 10’ in a photovoltaic module. The back side connection substrate 1 may be a sheet, foil or (glass) plate, (e.g. a rear encapsulant of the photovoltaic module) and may be provided with conductive areas, which are local (making the electrical connections between cells 10, 10’ with dedicated tracks) or may be spanning the entire surface (Cu foil). Also other conductive elements may be used, such as an aluminum foil with a Cu top layer, or an aluminum foil with local (cold sprayed) Cu contact pads.

Electrical connections are provided between a first cell 10 and a second, adjacent, cell 10’of the plurality of cells, allowing to provide strings of cells in the photovoltaic module. Each of the electrical connections comprises a busbar 7 in contact with the back side metallization 3 of the first cell 10, as shown in the embodiment of Fig. 1 via a contact pad 5. The busbar 7 extends over the back side connection substrate 1 into a space between the first cell 10 and second cell 10’, and a contacting part 8 is provided which connects the busbar 7 to the front side metallization 4 of the second cell 10’ via an edge of the second cell 10’. It is noted that the front side metallization 4 is not connected to any back side contact of the same cell 10’, as in various prior art types of photovoltaic cells. A direct contact with the ‘adjacent’ cell 10’ can be made as opposed to prior art arrangements, where a front side collector is brought to the actual back side of the cell itself, prior to making contact to an adjacent cell. In general, in the present invention embodiments, the position where the busbar 7 contacts the back side metallization 3 is indifferent, it can be anywhere on the back side of the first cell 10, and can even span the entire back side of the first cell 10.

Furthermore, it is noted that the busbar 7 extend under the first cell 10, but not under the second cell 10’. The busbar 7 may also be embodied as a tab of the first cell 10, having a thickness in the space between the adjacent cells 10, 10’ which is similar to the thickness t of the cells 10, 10’, as a result of which the contacting part 8 only needs to span a short distance. In general, the contacting part 8 spans the height difference between the busbar 7 and front surface of the second cell 10’, i.e. the wafer thickness minus the Cu thickness.

The present invention embodiments can also be indicated as I-rap, which stands for Interconnection Wrap Around. The connections of the front side cell metallization 4 to the interconnection metal (busbar 7) that is organized as conductive back sheet or plate (back side connection substrate 1) are realized by means of an interconnection material at the edge(s) of the cells 10, 10’.

The back side connection substrate 1 may be implemented as a conductive back sheet. Conductive back sheets are known, however in implementations where the conductive back sheet works together with solar cells that have all contacts on the rear. Not all types of solar cells have contacts on the rear and special measures may need to be taken to get all contacts on the rear, e.g. by metal wrap through (MWT) or back contact (IBC) technology. At present, most solar cells still use a so-called H-pattem technology with contacts on both sides of the cell. Conductive back sheet offers advantages with respect to a higher module power output and improved module making with respect to H-pattern technology. By dividing H-pattern cells in smaller pieces and connecting them to a conductive back sheet through connections at the edge of the cells 10, 10’as in the present invention embodiments, the advantages of H-pattern cells and conductive back sheet technology can be combined.

In the embodiment as shown in Fig. 1, cells 10, 10’are used having a thickness of less than 200pm, e.g. 180pm, allowing to easily provide the contacting parts 8 over the edge of the second cell 10’.

The contacting part 8 may be provided in several manner, e.g. using a solder, or even a low-temperature solder. Alternatively, a conductive adhesive is used and applied from the front side of the photovoltaic module being assembled. Also, a conductive ink may be used, or a wire bonding technique. As a further alternative, plating may be used to locally provide the contacting part, e.g. using Cu plating.

As mentioned, the busbar 7 may comprise copper (Cu) for providing a sufficiently low resistivity internal in the photovoltaic module. In further embodiments, also further elements of the electrical connection between adjacent cells 10, 10’ may be made of copper or a copper alloy, such as the contacting part 8, connecting pads 5, 6, or even (parts of) the front and/or back side metallizations 3, 4.

In order to prevent any possible negative influence of the (conducting) contacting part on the second cell 10’, the second cell 10’may be provided with an isolating layer directly on the surface of the edge of the second cell 10’. The isolating layer may be provided only directly below the contacting part 8, or may extend over a wider surface area on or around the edge of the second cell 10’.

The cells 10, 10’as shown in Fig. 1 have an elongated pattern of fingers forming the front and back side metallization 3, 4 of the cells 10, 10’, wherein the front and back side metallization 3, 4 are rotated over 180°. This allows to easily make series connected strings of cells 10, 10’using only the small electrical connection with the busbar 7 and the contacting part 8. Also when using different front and/or back side metallizations 3, 4 for the adjacent cells 10, 10’, series configurations of strings can be easily implemented, as shown in the perspective view of Fig. 2, where the front side metallization 4 comprises an elongate collecting bar 4b, and multiple fingers 4a extending perpendicular to the elongate collecting bar 4b. In general terms, the front and/or back side metallization 3, 4 of the plurality of cells 10, 10’ comprise finger type conductors extending away from the contacting part 8 in the embodiments shown in Fig. 1 and 2.

In Fig. 3 a simplified view is shown of a string of cells 10, interconnected according to the present invention, where the connections between adjacent cells 10 are provide at 90° angles, allowing to provide a more meandering pattern of cells 10. This may be accomplished using a properly designed front and back side metallization 3, 4. Every time, the back side metallization 3 of a cell 10 is connected via a busbar 7 (on the back side connection substrate 1) and a connecting part 8, to the front side metallization 4 of an adjacent cell 10’.

The combination of H-pattern technology having contacts on both sides of the cell (known as such) with a conductive back sheet technology (including the pick-and- place processing instead of the tabbing-stringing of prior art assembly of photovoltaic panels) of the present invention embodiments provides advantages over prior art assembly methods. The feature that the contact from front to the conductive back sheet is made with an interconnection material on module level (the contact of the rear to the conductive back sheet is done in a standard way) provides for an easy and efficient assembly of photovoltaic modules.

For standard 156x156 mm cells, the resistive losses across the cell may be too high if contacts on the edge only are used. There, the invention seems particularly suited for concepts that employ smaller cells, e.g. half cells, a high voltage concept with a plurality of series connected small cells, etc. Thus, in a further embodiment, the plurality of cells 10, 10’ comprise cells having a front surface of less than 200 cm2. These smaller cells 10, 10’ may be cut from a single wafer. If the processing and lay out of the wafer is executed properly, no printing (e.g. of the collecting fingers of the front side metallization 4) is needed right up to the edge of the wafer.

In further embodiments, especially suitable for applications where the cells 10, 10’are provided between two large substrates (e.g. two glass plates), the precise shape of each cell 10, 10’may be adapted to provide space for the entire electrical connection, including the busbar 7 and contacting part 8. This may e.g. be accomplished by (locally) providing an indentation in the second cell 10’(for the contacting part 8), and optionally also at the underside of the first cell 10 an indentation or recession is made to provide space for the busbar 7. This is particularly useful when space is limited, e.g. when using two glass plates. Each cell 10 may have an indentation, e.g. at the position of the front contact 6.

In Fig. 4 a series connection of four cells 10 is shown, each cell 10 showing a different front side metallization 4. The top left cell 10 is provided with a plurality of diagonal oriented collecting fingers, comprising extending fingers 4c and four collecting fingers 4d. This provides for four local contact possibilities for the front side metallization 4, and in the embodiment shown, the one on the right edge of the cell 10 is used, to connect to the back side metallization 3 of the adjacent cell with a busbar 7 similar shown to the embodiments described above. In this case, an electrical connection is provided locally over the edge of the second cell 10’.

The top right cell 10 is provided with a rectangular patterned collecting grid 4e (thin lines in a pattern). To allow proper collection of the solar cell current, in this case, a combined busbar 7’ is provided at multiple locations along the edge of the second cell 10’ contacting each finger of the patterned collecting grid 4e. A similar arrangement can be applied when using a front side metallization having a plurality of parallel diagonal fingers 4f, as shown for the lower right cell 10 in Fig. 4, allowing to use a continuous configuration of busbar 7”. In the lower left cell, the front side metallization 4 comprises a honeycomb structure 4g, also allowing a continuous busbar 7’”. The advantage of using these types of cells 10, 10’is that the orientation in the photovoltaic module is (completely or partially) indifferent.

The embodiments of the present invention may also be formulated in the following manner:

Embodiment 1. A photovoltaic module comprising a back side connection substrate 1 and a plurality of cells 10, 10’, each having a front side metallization 4 and a back side metallization 3, wherein electrical connections are provided between a first 10 and a second 10’, adjacent, cell of the plurality of cells, each of the electrical connections comprising a busbar 7 in contact with the back side metallization 3 of the first cell 10, and extending over the back side connection substrate 1 into a space between the first cell 10 and second cell 10’, and a contacting part 8 connecting the busbar 7 to the front side metallization 4 of the second cell 10’ via an edge of the second cell 10’.

Embodiment 2. Photovoltaic module according to embodiment 1, wherein the electrical connection comprises a connecting pad 5 near the edge of the second cell 10’. Embodiment 3. Photovoltaic module according to embodiment 1 or 2, wherein the electrical connection comprises a connecting pad 6 near the edge of the first cell 10. Embodiment 4. Photovoltaic module according to embodiment 1 or 2, wherein a connecting pad 6 is provided for the back side metallization 3 in a center part of the first cell 10.

Embodiment 5. Photovoltaic module according to any one of embodiments 1-4, wherein the contacting part 8 is provided locally over the edge of the second cell 10’.

Embodiment 6. Photovoltaic module according to any one of embodiments 1-5, wherein the contacting part 8 is provided at multiple locations along the edge of the second cell 10’.

Embodiment 7. Photovoltaic module according to any one of embodiments 1-6, wherein the contacting part 8 is provided using solder, low temperature solder, conductive adhesive, conductive ink, wire bonding, plating, or Cu plating.

Embodiment 8. Photovoltaic module according to any one of embodiments 1-7, wherein the plurality of cells 10, 10’ comprise cells having a front surface of less than 200 cm2.

Embodiment 9. Photovoltaic module according to any one of embodiments 1-8, wherein each of the plurality of cells 10, 10’ has a thickness of less than 200 pm, e g. 180pm.

Embodiment 10. Photovoltaic module according to any one of embodiments 1-8, wherein an indentation is provided in the second cell 10’ to allow provision of the contacting part 8.

Embodiment 11. Photovoltaic module according to any one of embodiments 1-9, wherein the edge of the second cell 10’ is provided with an isolating layer. Embodiment 12. Photovoltaic module according to any one of embodiments 1-10, wherein the busbar 7 comprises copper.

Embodiment 13. Photovoltaic module according to embodiment 12, wherein further elements 5, 6, 8 of the electrical connection comprise copper.

Embodiment 14. Photovoltaic module according to any one of embodiments 1-13, wherein the front and/or back side metallization 3, 4 of the plurality of cells 10, 10’ comprise finger type conductors extending away from the contacting part 8. Embodiment 15. Photovoltaic module according to any one of embodiments 1-14, wherein the front and/or back side metallization 3, 4 of the plurality of cells 10, 10’ comprise one or more of the group of: - collecting fingers 4c, 4d with a multiple diagonal orientation; - collecting fingers 4f with a single diagonal orientation; - a rectangular patterned collecting grid 4e; - a honeycomb patterned collecting grid 4g.

The present invention embodiments have been described above with reference to a number of exemplary embodiments as shown in the drawings. Modifications and alternative implementations of some parts or elements are possible, and are included in the scope of protection as defined in the appended claims.

Claims

A photovoltaic module comprising a back side connection substrate (1) and a plurality of cells (10, 10 '), each having a front side metallization (4) and a back side metallization (3), wherein electrical connections are provided between a first (10) and a second (10 '), adjacent, cell of the plurality of cells, and each of the electrical connections includes a conductor (7) which is in contact with the rear side metallization (3) of the first cell (10) and extends over the rear side connection substrate (1) in a space between the first cell (10) and second cell (10 '), and a contact part (8) connecting the conductor (7) to the front side metallization (4) of the second cell (10') via an edge of the second cell (10 ').

The photovoltaic module according to claim 1, wherein the electrical connection comprises a connection area (5) at the edge of the second cell (10 ').

The photovoltaic module according to claim 1 or 2, wherein the electrical connection comprises a connection area (6) at the edge of the first cell (10).

The photovoltaic module according to claim 1 or 2, wherein a connection area (6) is provided for the rear side metallization (3) in a middle part of the first cell (10).

The photovoltaic module according to any one of claims 1-4, wherein the contact part (8) is present locally over the edge of the second cell (10 ").

The photovoltaic module according to any of claims 1-5, wherein the contact part (8) is present at a plurality of locations along the edge of the second cell (10 ").

The photovoltaic module according to any of claims 1-6, wherein the contact part (8) is provided using solder, low-temperature solder, conductive glue, conductive ink, wire connection, plating, or Cu plating.

The photovoltaic module according to any of claims 1-7, wherein the plurality of cells (10, 10 ') comprises cells with a face surface area of less than 200 cm 2.

The photovoltaic module according to any of claims 1-8, wherein each of the plurality of cells (10, 10 ') has a thickness of less than 200 µm, e.g. 180 µm.

The photovoltaic module according to any one of claims 1-8, wherein a recess is provided in the second cell (10 ') to enable provision of the contact part (8).

The photovoltaic module according to any of claims 1-9, wherein the edge of the second cell (10 ') is provided with an insulating layer.

The photovoltaic module according to any of claims 1-10, wherein the conductor (7) comprises copper.

The photovoltaic module according to claim 12, wherein further elements (5, 6, 8) of the electrical connection comprise copper.

A photovoltaic module according to any one of claims 1-13, wherein the front and / or back side metal 1 comprises ring (3, 4) of the plurality of cells (10, 10 ') as finger-shaped conductors extending from the contact part (8).

The photovoltaic module according to any of claims 1-14, wherein the front and / or back demetallization (3, 4) of the plurality of cells (10, 10 ') comprises one or more of the group of: - collection fingers ( 4c, 4d) with a multiple diagonal orientation; - collective fingers (4f) with a single diagonal orientation; - a collection grid (4e) provided with a rectangular pattern; - a collection grid (4g) with a honeycomb pattern.