Field of the invention

The present invention relates to a back side connection layer (in the form of a foil or substrate) for connecting positive and negative back side contacts of a plurality of photovoltaic (PV) cells for forming a photo-voltaic module.

Prior art

International patent publication WO2013/182955 discloses a back-sheet for photovoltaic modules comprising back-contact solar cells. A conductive back-sheet is provided formed as a connecting circuit to electrodes of the solar cells of the module.

International patent publication WO2012/026806 discloses a photovoltaic device and module having an improved passivation of surfaces. It comprises a circumferential outer wall and/or an aperture wall intended for a back contact metal wrap-through photovoltaic device. A pn-junction is provided between a first and second semiconductor layer.

International patent publication WO2011/160161 discloses a photovoltaic module coupled on a back side to an electrically conducting or conductive and structured layer for conducting electrical energy generated in the solar cell. In one embodiment an electrical component can be embedded in the conductive structured layer for a solar cell.

Summary of the invention

The present invention seeks to provide an improved back side contact layer for a photovoltaic module allowing incorporation of a by-pass circuit.

According to the present invention in a first aspect, a back side contact layer according to the preamble defined above is provided, wherein a by-pass diode connection path having a predetermined minimal width (w) is formed in the back side connection layer along an edge direction of two adjacent cells, the two adjacent cells being positioned at an inter-cell distance (s) from each other, wherein outer contacts on each of the adjacent cells are displaced to a distance (d) from an edge of the respective adjacent cell, wherein the distance d is larger than 0, such that the total distance between a row of outer contacts (2d+s) is larger than or equal to the sum of the predetermined minimal width (w) and the width (2i) of two scribe lanes adjacent to the by-pass diode connection path (or in mathematical terms 2d+s>w+2i).

In a second aspect, a back side contact layer according to the preamble defined above is provided, wherein a by-pass diode connection path having a predetermined minimal width (w) is formed in the back side connection layer along an edge direction of two adjacent cells, the two adjacent cells being positioned at an inter-cell distance (s) from each other, with a meandering pattern around outer contacts positioned near edges of the two adjacent cells. In similar mathematic terms as in the first aspect, this would relate as 2d+s<w+2i.

Both aspect of the present invention, and the further embodiments as described in the further dependent claims, allow a more efficient lay-out of the back side contact layer and a by-pass diode conductor of a more suitable width.

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 detail view of a back side contact layer part overlying two adjacent PV cells with a strip conductor for a by-pass diode connection according to a prior art embodiment;

Fig. 2 shows a detail view of a back side contact layer part overlying two adjacent PV cells with a strip conductor for a by-pass diode connection according to an embodiment of the present invention;

Fig. 3 shows a schematic view of two adjacent PV cells having edge contacts and a conducting strip according the embodiment of Fig. 2;

Fig. 4 shows a schematic view of two adjacent PV cells having edge contacts and a conducting strip according to a further embodiment of the present invention;

Fig. 5 shows a schematic view of an embodiment of the present invention where an edge contact is indented.

Detailed description of exemplary embodiments

The present invention embodiments relate to an improved lay-out and placement of a back side connecting sheet in a photovoltaic module having a plurality of photovoltaic cells 1 utilizing by-pass diodes and associated circuitry to improve performance of the PV module when e.g. partially shaded.

Fig. 1 shows a detail view of a part of back side contact layer 3 overlying two adjacent PV cells (of which only the edges 7 are indicated). The back side contact layer 3 includes a strip conductor 6 for a by-pass diode connection, which is positioned in between two contact layer parts 3, separated by two scribe lanes 8. In a typical set-up of a PV module, two PV cells are positioned adjacent to each other with a spacing of 1.25mm (nominal, between the solid line edges 7) which may even be further apart as indicated by the small dash line 7a (1.75 mm apart). The adjacent cells are provided with back side contacts at their outer edge, or outer contacts 4, 5, of which one is shown for each of the adjacent cells in Fig. 1. In order to fit a by-pass diode conductor 6 in the available space in the back side contact layer 3, the by-pass diode conductor 6 has a typical width of only 0.75mm (as 1mm wide scribe lanes 8 are needed to provide sufficient isolation).

If two cells 1 , 2 (see also Fig. 3 and 4) are adjacent and both cells 1 , 2 have contacts on the back side of the solar cell and are positioned along the edges, then in between the cells 1 , 2 there is hardly any room for a Cu-strip (by-pass diode conductor 6) that is extending towards the junction box, as is clear from Fig. 1 and the description above. The room between the contacts 4, 5 of two neighboring cells 1 , 2 is small.

Moreover to manufacture the strip 6, isolation scribes 8 of typically 1 mm are needed, which also 'eats' away conductive material in between the contacts 4, 5. This then would lead to a very small strip 6 that should be able to carry a current of typically 9A and would therefore lead to a high power dissipation, which can be detrimental to the device and has an adverse effect of module operation under shade conditions.

As an example thereof the following calculations can be made for a small Cu track for a by-pass diode. The properties of a typical foil used for the bypass diode conductor 6 are a length 1=0.5m; a thickness ί=35μιη, a width w=0.75mm and a resistivity p=17.10 ^"9 Qm, resulting in a resistance R = ^≡ ^/-^ Ω - In a conducting state the by-pass diode typically carries a current of 8 A, which implies a power dissipation of P=R I ² ≥ 21 W. Since a typical PV module power rating is about 200W, this would result in a loss of more than 10%, which is not acceptable.

This problem may be solved in a first aspect of the present invention by a group of embodiments wherein a by-pass diode connection path 6 having a predetermined minimal width (w) is formed in the back side connection layer 3 along an edge direction of two adjacent cells 1, 2, the two adjacent cells being positioned at an inter- cell distance (s) from each other, wherein outer contacts 4, 5 on each of the adjacent cells are displaced to a distance (d) from an edge of the respective adjacent cell such that the total distance between a row of outer contacts 2d+s is larger than the sum of the predetermined minimal width (w) and the width (2i) of two scribe lanes adjacent to the by-pass diode connection path 6. In mathematical terms, the distance (d) of outer contact 4, 5 of two neighboring the cells 1, 2 is chosen to meet the formula 2d+s>w+2i. The resulting by-pass diode connection path 6 may in this group of embodiments even be implemented as a straight metallization path.

In Fig. 2, a further solution for this problem is provided, in the sense that a bypass diode connection path 6 having a predetermined minimal width (w) is formed in the back side connection layer 3 along an edge direction of two adjacent cells 1, 2, the two adjacent cells being positioned at an inter-cell distance (s) from each other, with a meandering pattern around outer contacts 4, 5 positioned near edges of the two adjacent cells 1, 2. Note that in this group of embodiments the distance d can even be equal to zero, i.e. the outer contact are arranged directly on an edge of the cell 1, 2. This has a more optimal current path on the cell 1 , 2 as a consequence and results in less metal usage on the cell (often this is Ag and therefore costly).

More generically, the plurality of cells 1 , 2 comprise cells having a symmetric pattern of the positive and negative back side contacts 11, 12, wherein a subset 4, 5 of positive or negative back side contacts are arranged along the edge direction of neighboring cells 1, 2. Examples of such cells 1, 2 are Interdigitated Back Contact (IBC) cells or Emitter Wrap Through (EWT) cells ,

In a further embodiment, the two adjacent cells 1, 2 are oriented with respect to each other such that the outer contacts 4, 5 are interspersed along the edge direction. . E.g. in the case of a PV cell 1, 2 having a length / along the edge direction of the two adjacent cells 1, 2, a number of n contacts are positioned equidistantly at one edge with an offset 0, and with an offset of l/2n at the opposite edge. This is shown more clearly in the schematic view of Fig. 3, where n=4. The back side contacts 11, 12 of the used PV cells 1 , 2 are indicated using open rounds and solid rounds, as in back side contact PV cells both the positive and negative contacts are provided in a pattern adjacent to each other. It is noted that in the PV module, PV cells 1, 2 as described above are invariant for 180 degrees rotation, allowing an easy PV cell placement for PV module manufacturing.

In a further embodiment the positive and negative back side contacts 11, 12 are arranged in a plurality of rows, and an outer one of the plurality of rows comprising the outer contacts 4, 5 has less contacts than the other of the plurality of rows 11, 12. This will allow a more smooth meandering of the conductive lead for the bypass diode (bypass diode conductor 6) and thus provides advantages for the manufacturing of the back side connection layer, more particular for providing the isolation lanes 8 therein, e.g. by scribing.

By realizing a meandering conductive track 6 and by positioning the edge contacts 4, 5 of two adjacent cells 1, 2 in an interspersed fashion as shown in Fig. 3 the conductive lead for the bypass diode (by-pass diode conductor 6) can be realized having a greater width than in the prior art embodiment, e.g. having a width of at least 2mm or even 5 mm. This can be combined with a further embodiment, wherein the inter-cell distance (s) between two adjacent cells is less than 2 mm. These solutions also allows modules with more than three bypass diodes in a single PV module. More generally, the present invention also relates to a photovoltaic module comprising a plurality of photovoltaic cells and a back side connection layer according to any one of the embodiments described herein.

The present invention in general relates to a configuration of back contacted cells 1, 2 with contacts 4, 5 along the edges attached to a PCB-like Cu-foil (back side connection layer 3) that comprises small strips 6 of Cu-foil that meanders in between the edge contacts 4, 5 of adjacent cells 1, 2. The by-pass diode connection path 6 extends to a junction box connection part of the back side connection layer 3 in a further embodiment. The by-pass connection path 6 can then stretch out towards the junction box where they are connected to bypass diodes and where they form a bypass circuit in a usual fashion for PV modules. The contacts 4, 5 of two adjacent cells 1, 2 are interspersed, allowing a meandering path 6 in between the edge contacts 4, 5 of either cells 1 , 2 that can in an alternating way be under the first cell and the second, neighboring, cells 1, 2.

In a further embodiment, which is shown schematically in Fig. 4, the meandering conductive path 6 is provided for the purpose of bypass diode connection, in a metal foil 3 in combination with back-contacted cells (IBCs, EWTs) with multiple current collection points 11, 12, on their back side of which a subset (outer contacts 4', 5') is positioned close by the edges of the cell 1, 2. Or in other words, the outer contacts 4', 5' of two adjacent cells 1, 2 are indented toward a center of the respective cell 1, i.e. away from the edge of the cell 1, 2. This can e.g. be implemented using an indented busbar configuration, e.g. using an 'elbow' type or 90 degree configuration, as shown schematically in the embodiment depicted in Fig. 5 In this drawing, the current collecting lines 15, 18 are shown, together with the collection busbars 14, 17. On one side of this PV cell, a contact 12 is provided, whereas on the other side, the contact 4 is displaced over the distance d, using a further conductor 16.

Or, in respect to regular PV cells 1, 2 having edge contacts, the outer back contacts 4', 5' on an edge of a cell 1, 2 are moved towards the center of the cell 1, 2, away from the edge (cf. the outer contacts 4, 5 in Fig. 4 in comparison to the embodiment of Fig. 3). In this embodiment, a more smoothly meandering pattern may be used for the by-pass diode conductor 6, having an even larger width than the embodiment described with reference to Fig. 3.

The present invention embodiments allow application of a foil technology for back-contacted cells 1, 2 with contacts 4, 5 positioned along the edges of the cell 1, 2 (which is required by cell symmetry), and allows realizing a metal foil-based PV module with back contacted cells including but not limited to IBC cells and EWT cells, wherein standard bypass circuit can be integrated.

In a further embodiment, the back side connection layer further comprises a bypass diode directly connected to the by-pass diode connection path 6, i.e. as part of the contacting foil 3, which allows protection of the by-pass diodes as well by an encapsulating layer of the PV module.

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.