Patent Application
20240038915
The present application relates to the field of photovoltaic (PV) cells, also called solar cells and more particularly that of their assembly and of their interconnection.
It relates to an assembly of solar cells provided with a particular interconnection structure, to the creation of such an assembly as well as to a photovoltaic module including such an assembly.
A conventional technique for interconnection of solar cells is based on the use of an electrically conductive metal band which ensures the electric connection between a cell and the following cell.
Such a type of interconnection is illustrated in
According to one alternative, illustrated in
In this case, the cells are generally disposed next to each other and this results in a surface 5 which is lost between the cells, which increases the bulk of the assembly and which is consequently called a “dead zone”.
Another assembly technique called “Shingle” allows to limit the bulk and involves superimposing the edges of cells 11, 12 over a small surface. The interconnection between a conductive zone 7 at the front face 2A of a cell 11 and a conductive zone 8 at the rear face 2B of another cell 12 is thus carried out via a conductive material 9, of the type braze material added at a zone of overlap between the cells or conductive glue of the ECA (for Electrically Conductive Adhesive) type containing acrylate or epoxy. This interconnection structure has the advantage of not creating a dead zone between cells 11, 12. However, it results in a rigid mechanical structure that can be fragile when it undergoes significant thermomechanical stresses.
The document “Materials Challenge for shingled cells interconnection” by Beaucarne et al., 6th workshop on metallization and interconnection for crystalline silicon solar cells, 2016, proposes an assembly of the Shingle type by using a glue of the ECA (for Electrically Conductive Adhesive) type with a silicone base (more mechanically flexible than acrylate or epoxy) in order to make the final assembly more flexible. Such a structure allows, however, little deformation in the plane of the cells.
The problem arises of finding a new interconnection technique improved with respect to the disadvantages mentioned above.
According to the invention, an assembly of solar cells is created comprising:
Such a structure allows to carry out a mechanical decoupling between the cells and to confer onto the assembly an increased flexibility which makes it more resistant to thermomechanical stresses.
Preferably the assembly of said one or more second conductive blocks is offset with respect to the assembly of said one or more first conductive blocks, which allows better deformation in a plane parallel to the cells and contributes to making the assembly more flexible and thus resistant to certain thermomechanical stresses.
Advantageously, one or more or each of said one or more first conductive blocks can be facing an empty space and/or a zone of insulating material disposed between said second region of said oblong conductive portion and said second peripheral zone.
Advantageously, one or more second conductive blocks or each of the second conductive blocks can be arranged facing an empty space and/or a zone of insulating material disposed between said first region of said oblong conductive portion and said first peripheral zone.
According to one possible embodiment this insulating material can be a polymer material. Such a type of material has the advantage of having a low Young's modulus which favours the flexibility of the assembly.
According to a specific embodiment, at least one of said one or more first conductive blocks can be surrounded by a passivation insulating zone arranged between said first region of an oblong conductive portion and said first peripheral zone of the first cell.
According to a specific embodiment, at least one of said one or more second conductive blocks can be surrounded by a passivation insulating zone arranged between said second region of said oblong conductive portion and said first peripheral zone of the first cell.
The oblong conductive portion can be advantageously in the form of at least one conductive wire, or several distinct juxtaposed conductive wires or even a conductive strip, in particular flat.
One specific embodiment provides said conductive blocks in the form of spots of conductive glue, in particular a glue made of polymer material loaded with conductive particles, such as a glue of the ECA type. In this case, the flexibility of the assembly can be favoured.
In this case, a connection structure having a lower electric contact resistance can be obtained.
According to a specific embodiment said conductive blocks have a substantially rectangular or substantially parallelepipedic shape with rounded corners. Such a shape of the conductive blocks can also allow to obtain an increased flexibility of the structure.
The invention relates to a method for creating a solar module provided with an assembly as defined above.
The invention relates more specifically to a method for carrying out an assembly of solar cells, said assembly comprising a first cell connected to a second cell, said second cell being arranged so that a peripheral zone of a rear face of the first cell called “first peripheral zone” overlaps with a peripheral zone of the front face of the second cell called “second peripheral zone”,
the method comprising steps of:
The present invention will be better understood upon reading the description of exemplary embodiments given, for purely information and in no way limiting purposes, while referring to the appended drawings in which:
Identical, similar or equivalent parts of the various drawings carry the same numerical references so as to facilitate the passage from one drawing to another.
The various parts shown in the drawings are not necessarily shown on a uniform scale, to make the drawings more readable.
Moreover, in the following description, terms that depend on the orientation of the structure such as “front”, “upper”, “rear”, “lower”, “lateral”, “central”, “peripheral” apply while considering that the structure is oriented in the manner illustrated in the drawings.
Reference is now made to
The solar cells 101, 102 are formed from a semiconductor substrate, which can be poly or monocrystalline and in particular contain polycrystalline or monocrystalline silicon. Each of the cells 101, 102 is provided with at least one face 2A called “front face”, receiving light and which is intended to be exposed to solar radiation, and a face 2B called “rear face”, opposite to the front face 2A. The rear face 2B can optionally also be intended to be exposed to solar radiation. In this particular case, the cell is called “bifacial”.
At least one first solar cell 101 of this assembly is provided with contacts distributed over the rear face 2B, including one or more contacts (not shown) with respectively one or more zones with n-type doping (in other words having a doping producing an excess of electrons) and one or more contacts (not shown in this drawing) with respectively one or more zones with p-type doping (in other words according to a doping involving producing a deficit of electrons), the n-type zone(s) associated with the p-type zone(s) forming at least one junction.
The assembly is such that a peripheral zone 23B located on the rear face 2B of the first cell 101 is disposed facing a peripheral zone 22A of the front face 2A of a second cell 102.
The solar cells 101, 102 are thus assembled here according to an assembly of the type called “shingle”, in other words so as to partly overlap, which allows in particular to create a compact assembly. The overlap can be provided over a distance typically of at least 0.2 mm and which can be between for example 0.5 mm and several millimetres.
Besides the assembly, the connection of the cells 101, 102 to each other is carried out here using a specific connection structure 40 that is arranged between the cells 101, 102, and is preferably confined at a region in which they overlap.
This connection structure 40 is formed by an oblong conductive portion 41 which, in the specific exemplary embodiment illustrated in 3, is in the form of a conductive strip. On and in contact with the outer surface of this oblong conductive portion 41, protruding conductive blocks 42, 43 are provided to be respectively placed in contact with the solar cells 101, 102 and allow to ensure an electric connection from one cell to another.
The conductive blocks 42, 43 are distributed alternatingly over a first region 41A of said conductive portion 41 placed facing the peripheral zone 23B of the first cell 101 and over a second region 41B, opposite to the first region, of said conductive portion 41, the second region being disposed facing the peripheral zone 22A of the second cell 102. In the case in which the oblong conductive portion 41 is in the form of a conductive strip having a flat shape, the first region 41A and the second region 41B are respectively a first face 41A and a second face 41B opposite to the first face 41A.
The connection structure 40 thus includes one or more first conductive blocks 42 on the first face 41A and one or more second conductive blocks 43 on the face 41B opposite to the first face 41A.
Confining the connection structure 40 and the conductive blocks 42, 43 at the region of overlap of the cells 101, 102 allows to not obstruct parts, including of the rear face 2B, that it could be desired to expose to solar radiation.
In order to confer flexibility onto the assembly, the blocks 42, 43 are distributed here along an axis AA′, alternatingly on the first face 41A and on the second face 41B, with, preferably, an offset provided from one conductive block 42 to the other 43 along this axis AA′. The assembly of the block(s) 42 formed on the first face 41A is thus offset from the assembly of the block(s) 43 located on the second face 41B.
Thus, in the succession of conductive blocks 42, 43, along the axis AA′ each conductive block 43 is offset from the following block 42.
Thus, as shown by
This arrangement means that the electric connection between the two cells 101 and 102 is not established according to a vertical (axis parallel to the vector z of the orthogonal reference frame [O;x;y;z]) conduction path, but according to an S-shaped path. Such an arrangement allows to favour a mechanical decoupling between the cells 101, 102 and allows a deformation of the cells 101, 102 after a thermomechanical stress or after a manipulation of the assembly of cells 101, 102.
The oblong conductive portion 41, when it is in the form of a strip, can be provided with a width W (smaller dimension measured in a plane parallel to the cells and to the plane [O;x;y]) for example between 0.1 and several millimetres, and advantageously between 0.2 mm and 1 mm. Typically, the width W of the strip corresponds to the width of overlap between the cells 101, 102, for example approximately 1 mm. The strip can also be provided with a thickness e (dimension measured parallel to the axis z) for example between 10 μm and 500 μm, for example approximately 50 μm. The strip can optionally extend over the entire length of a cell.
As for the conductive blocks 42, 43, they can be provided with a thickness for example between 5 μm and 200 μm, for example approximately 50 μm. This thickness is adapted in particular according to the number of blocks, their surface and their rate of distribution on the oblong conductive portion 41.
With regard to the composition of the structure, the oblong conductive portion 41 can be formed by one or more metal material(s) for example such as copper or silver or tinned copper. A specific embodiment provides a conductive portion 41 formed by a core made of conductive material, in particular a metal material such as copper or silver, coated with zone of insulating material forming a discontinuous insulating sheath around the conductive blocks. The insulating material can be a polymer, for example a polyimide such as Kapton™.
The conductive blocks 42, 43 are typically made of a material different than that of the oblong conductive portion 41 and can be in particular added onto this oblong conductive portion 41 typically in the form of spots of conductive glue or zones of braze material.
For example, when the conductive blocks 42, 43 are brazing zones, they can be formed from a metal alloy of the tin-silver-copper type (SnAgCu, also known by the name SAC) which is an alloy without lead. An alloy of the “SAC305” type composed of more than 95% tin, approximately 3.0% silver and approximately 0.5% copper can in particular be used.
When the conductive blocks 42, 43 are spots of conductive glue, an ECA (for Electrically Conductive Adhesive) glue can be used. Such a glue is formed by a polymer matrix, typically of the epoxide, acrylate or silicone type, loaded with conductive particles. For example a silver epoxy glue of the type EPO-TEK® H20E, Loctite® 8282 or Loctite® 8311 can in particular be used.
Thus, with such a connection structure 40, the conductive blocks 42, 43 ensure both the mechanical and electric contact on the cells 101, 102, while the oblong portion 41 allows to ensure the mechanical decoupling between the cells and the assembly to resist thermal and/or mechanical stresses.
As shown in
In the exemplary embodiment illustrated in
Digital simulations of stressing via the Ansys® tool were carried out to allow to compare a connection structure as described above with respect to a conventional connection structure implementing a simple conductive band between two overlapping cells. Results of such a simulation are given by the graph of
For the conventional structure, the interconnection consists of a continuous bead of glue of the ECA type 50 μm thick and 156 mm long, corresponding to an M2 format of solar cells. The material of the glue is considered to have a Young's modulus at 1 GPa.
A connection structure as implemented according to the invention is considered at the same time, with at least three conductive blocks (two on one face, one on another face) on a conductive strip made of copper 156 mm long with a Young's modulus for the copper of 124 GPa.
The number of conductive blocks varies from 3 to 50 to evaluate the change in the deformation capacities of the structure according to the invention.
For each of the established models of simulations, an arbitrary deformation of 1 μm is applied.
Since the geometries and the materials simulated are not identical between the two structures, levels of mechanical stress are not compared. The output piece of data chosen to establish the comparison here is an average density of accumulated elastic energy in the complete interconnection after a deformation of 1 μm. This piece of data can be equated with the inverse of the mechanical flexibility. The results are shown by the curve C40 normalised with respect to the conventional interconnection (Cconv).
It is observed on the one hand that the average density of accumulated elastic energy in the connection structure according to the invention always has a value smaller than the reference structure. With regard to the influence of the number of conductive protrusions, even when considering 50 protrusions (which in the present case is equal to an electric connection point every 1.5 mm) the accumulated level of energy is 5 times smaller than that present in the case of a conventional connection structure.
In a second case (
The geometric optimum of the connection structure and in particular the number, the size and the density of the conductive blocks 42, 43 depends on a compromise between a necessary mechanical flexibility while guaranteeing sufficient electric performance of the interconnection.
The first connection structure according to the invention (curve C1) is formed here by a band of copper having thickness*length*width dimensions of 0.05*156*1 mm and conductive blocks protruding on the band and formed by a braze material of the SAC305 type. The brazing zones have dimensions of 0.05*1*1 mm (thickness*length*width).
The series resistance of a second interconnection as implemented according to the invention with spots of glue of the ECA type is also illustrated (curve C2).
The comparison is carried out using an analytical calculation (R=(Rho*L)/S), with R the electric resistance of the material, Rho the resistivity of the material, L the length and S its cross-section, while considering resistivities for the copper of 17e-9 ohm·m, for the SAC305 braze: 1.3e-6 ohm·m, for the ECA glue 4e-2 ohm·m.
The results are presented in the form of curves C1, C2 according to the number n of spots of glue or of brazing zones along the zone of overlap between cells.
The structure according to the invention allows to use a material of the braze type for the connections on the cells. Indeed, it is observed that the interconnection proposed in this invention always has a theoretical electric resistance lower than that of a conventional structure.
Another example of a structure for interconnection between cells 101, 102 is given in
The conductive blocks 42, 43 (not shown in
The passivation zones 54, 55 can be in the form of a film or of a layer of insulating material for example a polymer material such as Kapton™, and transparent in the case in which the film is wider than the zone of overlap of the cells, and added onto the conductive wires 81, 91.
As visible in
An alternative embodiment with this time a single conductive wire 81 to carry out the connection between conductive blocks 42 connected to the cell 101 and conductive blocks 42 connected to the cell 101 is given in the transverse cross-sectional views of
The conductive wire 81 has in the example illustrated a parallelepipedic shape. A wire having a cylindrical shape can also be used.
With regard to its manufacturing, a connection structure 40 as described above can be made in several ways.
A first possibility involves functionalising the oblong portion 41 then carrying out the assembly with the cells. Thus, the conductive blocks 42, 43 are formed on the oblong portion 41, for example on an upper face and on a lower face of a conductive strip, then the interconnection structure is disposed in such a way that it is interposed in the zone of overlap between the cells 101, 102. Then the assembly is carried out.
One can start for example from a conductive strip on which one or more conductive blocks are made, for example in the form of spots of conductive glue on a first face. The conductive blocks can be made for example by screen printing by using a mask, optionally temporary, arranged on the front face and including one or more openings exposing the first face of the conductive strip.
Then, one or more conductive blocks are formed on a second face for example spots of conductive glue on a second face opposite to the first face. Likewise, conductive blocks can be made on the second face, for example by screen printing, by using for example the same mask or another mask, optionally temporary, arranged on the second face and including one or more openings exposing the second face of the conductive strip.
According to an alternative illustrated in
Alternatively to this step, other conductive blocks can be added in the form of spots of glue or brazing zones onto the conductive wires 81, 91 and then the assembly with the other cell is carried out.
According to another alternative illustrated in
Then (
Such an alternative is adapted in particular when the blocks are in the form of drops of braze (brazing paste).
According to another alternative, it is also possible to create one or more conductive blocks on each cell then add each cell provided with the conductive blocks onto one of the faces of the conductive strip.
According to a specific embodiment, a distribution of the material of the conductive blocks is carried out simultaneously in several points of the conductive strip, for example via a plurality of distribution needles delivering drops of glue, in particular an ECA glue.
| Number | Date | Country | Kind |
|---|---|---|---|
| FR2007989 | Jul 2020 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FR2021/051393 | 7/26/2021 | WO |
