PHOTOVOLTAIC MODULE COMPRISING AN ENCAPSULATION STRUCTURE BASED ON AT LEAST ONE POLYMER MATERIAL AND LOCALLY SOFTENED

Abstract

The invention relates to a photovoltaic module including a photovoltaic unit having a plurality of photovoltaic cells electrically connected in series and spaced apart from one another, the adjacent photovoltaic cells being electrically connected pairwise by a metal interconnector which extends at least in part into an interconnection space separating said adjacent photovoltaic cells, an encapsulation structure made of a polymer-based encapsulation material, which sandwiches the opposite sides of the photovoltaic cells, defining a region of cell coverage, and the interconnector in the interconnection space, defining a region of interconnector coverage, and a spacer incorporated into the encapsulation structure and partially superposed on the interconnector in the region of interconnector coverage, the spacer being made of a material having, at least at a temperature of 40 C., a modulus of elasticity lower than the modulus of elasticity of the encapsulation material.

Claims

1. A photovoltaic module comprising: a photovoltaic unit comprising a plurality of photovoltaic cells electrically connected in series and spaced apart from one another, the adjacent photovoltaic cells being electrically connected pairwise by a metal interconnector which extends at least in part into an interconnection space separating said adjacent photovoltaic cells, an encapsulation structure based on at least one polymer encapsulation material, which sandwiches the opposite sides of the photovoltaic cells, defining a region of cell coverage, and the interconnector in the interconnection space, defining a region of interconnector coverage, and a spacer incorporated into the encapsulation structure and partially superposed on the interconnector in the region of interconnector coverage, the spacer being made of a material having at least, at a temperature of 40 C., a modulus of elasticity lower than the modulus of elasticity of the polymer encapsulation material.

2. The photovoltaic module according to claim 1, wherein the material of the spacer has a modulus of elasticity more than 2 times, preferably more than 5 times, or even more than 10 times, lower than the modulus of elasticity of the polymer encapsulation material at a temperature of 40 C.

3. The photovoltaic module according to claim 1, wherein the material of the spacer has a modulus of elasticity lower than the modulus of elasticity of the encapsulation material at a temperature of 20 C., and preferably at any temperature between 40 C. and 20 C.

4. The photovoltaic module according to claim 1, wherein the material of the spacer has a modulus of elasticity, measured at 40 C., between 0.1 MPa and 300 MPa, and preferably between 1 MPa and 10 MPa.

5. The photovoltaic module according to claim 1, wherein the material of the spacer is an elastomer, in particular chosen from silicone elastomers, rubbers, fluoroelastomers, thermoplastic elastomers and blends thereof.

6. The photovoltaic module according to claim 1, wherein the spacer has a thickness between 100 m and 1500 m and/or a width between 100 m and 1500 m.

7. The photovoltaic module according to claim 1, wherein the spacer takes the form of a strip, in particular of rectangular or square cross section.

8. The photovoltaic module according to claim 1, wherein the spacer extends from one end to the other, i.e. the entire length, of the interconnection space between the adjacent photovoltaic cells, said length being measured parallel to the facing lateral sides of said adjacent cells.

9. The photovoltaic module according to claim 1, wherein the photovoltaic module comprises a plurality of spacers at least partially covering the interconnector in the region of interconnector coverage.

10. The photovoltaic module according to claim 1, wherein, in the thickness of the PV module, at least two spacers are arranged on either side of the interconnector.

11. The photovoltaic module according to claim 1, wherein more than 70% by weight, preferably more than 80% by weight, preferably more than 90% by weight, preferably more than 95% by weight, and preferably 100% by weight of the encapsulation material is a polymer material.

12. The photovoltaic module according to claim 1, wherein the polymer material is selected from ethylene vinyl acetate, ethylene methyl acrylate copolymer, low-density polyethylene terephthalate, nylon 11, polycarbonate, polyethylene terephthalate glycol, polymethyl methacrylate, polypropylene, polypropylene copolymer, polypropylene homopolymer, polytetrafluoroethylene, styrene-acrylonitrile copolymer, thermoplastic polyurethane, acrylonitrile butadiene styrene, polyethylene and blends thereof.

13. The photovoltaic module according to claim 1, wherein the encapsulation material is able to have a modulus of elasticity between 10 MPa and 10 GPa, at a temperature of 40 C.

14. Process for manufacturing a photovoltaic module according to any of the preceding claims, the process comprising: providing a multilayer stack comprising a photovoltaic unit comprising photovoltaic cells electrically connected in series and spaced apart from one another, adjacent photovoltaic cells being electrically connected pairwise by an interconnector which extends at least in part into an interconnection space separating said adjacent photovoltaic cells, a spacer which is at least partially superposed on the interconnector in the interconnection space, and at least two encapsulation layers sandwiching the photovoltaic unit and thermoforming the multilayer stack until the photovoltaic module is obtained.

15. The process according to claim 14. wherein the thermoforming is achieved via lamination of the multilayer stack between a heated bottom lamination plate and a membrane to which a fluid pressure is applied.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0072] FIG. 1 and FIG. 2 are photographs of prior-art photovoltaic modules,

[0073] FIG. 3 is an optical micrograph of a broken interconnector of a prior-art photovoltaic module,

[0074] FIG. 4 are electroluminescence images of prior-art photovoltaic modules acquired, from left to right, after lamination, after 30 thermal cycles, and after 60 thermal cycles,

[0075] FIG. 5 schematically shows a top, front and side view of one example of a photovoltaic module according to the invention,

[0076] FIG. 6 is a schematic view of the photovoltaic module in cross section through a region of interconnector coverage,

[0077] FIG. 7 schematically illustrates one example of a process for manufacturing by lamination the photovoltaic module according to the invention,

[0078] FIG. 8 is a view of a finite-element mesh of part of a module according to the invention such as illustrated in FIG. 6, in the region of interconnector coverage,

[0079] FIG. 9 are images of the von Mises stress distribution in a reference mesh and in the mesh of FIG. 6 after a numerical thermomechanical simulation of a thermal cycle,

[0080] FIG. 10 is a graph illustrating the variation in the von Mises stress along the path illustrated in FIG. 6,

[0081] FIG. 11 is a graph illustrating, for various meshes, the variation in the maximum stress in the interconnector as a function of the modulus of elasticity of the material of the spacer and the decrease, expressed in percent, of said stress with respect to the reference mesh without spacer,

[0082] FIG. 12 is a graph illustrating, for various meshes, the variation in the maximum stress in the interconnector as a function of the width of the spacer and the decrease, expressed in percent, of said stress with respect to the reference mesh without spacer, and

[0083] FIG. 13 is a graph illustrating, for various meshes, the variation in the maximum stress in the interconnector as a function of the thickness of the spacer and the decrease, expressed in percent, of said stress with respect to the reference mesh without spacer.

DETAILED DESCRIPTION

[0084] FIGS. 1 to 4 were described above.

[0085] FIG. 5 illustrates one example of a photovoltaic module 1 according to the invention. The photovoltaic module comprises two photovoltaic units 6, which each comprise spaced apart from one another four photovoltaic cells 3 in wafer form.

[0086] Each photovoltaic cell is separated from the photovoltaic cell which is adjacent to it by an interconnection space 2.

[0087] This number of photovoltaic units 6 and of photovoltaic cells 3 is non-limiting and other arrangements may be envisaged.

[0088] The photovoltaic module further comprises connection terminals 7 taking the form of metal bands, between which the photovoltaic units are arranged in parallel and are electrically connected, in order to collect the generated current.

[0089] Within each photovoltaic unit 6, the adjacent photovoltaic cells 3 are connected pairwise in series by metal, copper for example, interconnectors 4 which extend, in the Y direction, from one end to the other between the electrical terminals 7.

[0090] Each metal interconnector 4 comprises portions 4a making contact with one side of a photovoltaic cell, which portions are connected together by portions 4b which each extend into the interconnection space provided between the photovoltaic cells 3. The metal interconnector 4 consecutively makes contact with one side of one photovoltaic cell and then with an opposite side of the adjacent photovoltaic cell. Thus, when observed in the cross-sectional plane (x,z) illustrated in FIG. 6, the interconnector winds from one connection terminal to the other, between the photovoltaic cells 3.

[0091] The photovoltaic module further comprises an encapsulation structure 8 based on at least one polymer material, within which encapsulation structure the photovoltaic units 6 are completely immersed.

[0092] The encapsulation structure 8 wholly covers the opposite sides 9a, 9b of the photovoltaic cells 3, thus defining, with each photovoltaic cell 3, a region of cell coverage 10.

[0093] Moreover, the encapsulation structure 8 covers the interconnectors in the various interconnection spaces 2 between the adjacent photovoltaic cells, thus defining, with the interconnector 4, a region of interconnector coverage 11. In the example illustrated in FIG. 6, spacers 12 have been incorporated into the bulk of the encapsulation structure 8. They are arranged on either side of the interconnector in each interconnection space 2 between the bottom side 13i and the top side 13s of said incorporation structure 8 and the interconnector 4.

[0094] Within each interconnection space 2, the spacers 12 may extend from one end to the other, i.e. the entire length, of the facing sides of the adjacent photovoltaic cells, and parallel to said sides. They may further be superposed on each other or offset with respect to each other along the y-axis, as illustrated in FIG. 6.

[0095] The spacers are moreover superposed on the interconnector 4 in each interconnection space 2, in the region of interconnector coverage, as may be seen in the cross section in a (y,z) plane in FIG. 6.

[0096] The spacers are for example an elastomeric strip the modulus of elasticity of which is between 0.1 MPa and 300 MPa.

[0097] In order to manufacture the photovoltaic module illustrated in FIG. 5, a multilayer stack 20 may be prepared in the following manner. The photovoltaic units 6, the connection bands 7 and the spacers 12 are arranged between bottom and top sheets 21i, 21s made of a soft polymer material, of a low modulus of elasticity, between 10 MPa and 10 GPa at 40 C. for example. The sheets 21i,s thus entirely cover the photovoltaic units 6, the connection bands 7 and the spacers 12. The assembly thus formed may optionally be arranged between bottom and top external sheets 22i, 22s made of another rigid other polymer material, of a high modulus of elasticity, between 1 GPa and 100 GPa at 40 C. for example, in order to form the multilayer stack 20. After lamination between a bottom lamination plate 24i and a membrane 25, a photovoltaic module 1 is thus obtained, the photovoltaic module having a multilayer encapsulation structure comprising a flexible internal encapsulation layer in which the photovoltaic units are immersed, the flexible internal encapsulation layer optionally being sandwiched between top and bottom rigid external encapsulation layers.

[0098] The lamination of the multilayer stack 20 is conventionally carried out by heating the multilayer stack to a temperature suitable for making the polymer materials flow and with a pressure applied to the membrane 25 in order to heat seal the various sheets 21i,s and optionally 22i,s and the photovoltaic units 6 together, then by cooling until the photovoltaic module is obtained.

[0099] The effect of the spacer in the interconnection space is illustrated below.

[0100] A 2D finite-element mesh 30 of a portion of the photovoltaic module including the interconnection space 2 was generated, as illustrated in FIG. 8. Quadrangular finite elements were chosen such that the thickness e.sub.i of the interconnector was discretised with at least 4 finite elements.

[0101] The encapsulation structure 8 modelled thus comprises bottom and top polyamide layers 11, the modulus of elasticity of which at 40 C. is equal to 1620 MPa and the CTE of which is equal to 10.sup.4 K.sup.1. The thickness of each of the bottom and top layers is 400 m.

[0102] The internal layer 15, of 1200 m thickness, is made of thermoplastic polyolefin, the modulus of elasticity of which at 40 C. is 590 MPa and the CTE of which is equal to 510.sup.4 K.sup.1.

[0103] The photovoltaic cell 3, of thickness equal to 150 m, is made of silicon, the modulus of elasticity of which is equal to 166 GPa and the CTE of which is equal to 2.610.sup.6 K.sup.1.

[0104] The interconnector 4, of thickness equal to 200 m, is made of copper and has a modulus of elasticity equal to 130 GPa and a CTE equal to 1.410.sup.5 K.sup.1.

[0105] The thickness e.sub.spacer and width l.sub.spacer of the spacers 12 and the modulus of elasticity of the material from which they are made are parameters that were modified during simulation.

[0106] The simulations were carried out assuming a plane deformation state, with models of thermoelastic material behaviour, and using the ABAQUS simulation tool. Each finite element was considered to be in a stress-free state at 25 C., then cooling of the photovoltaic module to a temperature of 40 C. was simulated, this temperature being that of the thermal cycling specified in standard IEC6215.

[0107] A reference mesh, such as that illustrated in FIG. 8, was generated without any spacer present.

[0108] A comparative mesh was also generated, in which the modulus of elasticity of the material of the spacer was 100 GPa, i.e. more than 160 times greater than that of the encapsulation material of the layer 15 and of the encapsulation material of the layers 14i and 14s. The width l.sub.spacer was 1 mm and the thickness e.sub.spacer was equal to 200 m.

[0109] A mesh of a PV module according to the invention was generated, the latter being identical to the comparative mesh except that the modulus of elasticity at 40 C. of the material of the spacer was 1 MPa.

[0110] FIG. 9 illustrates the effect of thermal expansion between 20 C. and 40 C., which induces von Mises stresses that are higher in the interconnector in the absence of a spacer (mesh 35). The spacer, which is less rigid than the encapsulation material, increases the flexibility of the region of interconnector coverage, the von Mises stresses being lower locally in the interconnector (mesh 36).

[0111] This observation is confirmed by FIG. 10, which shows the variation in the von Mises stresses , expressed in MPa, as a function of the y-coordinate S (in mm) along the path 37 illustrated in FIG. 8 for the reference mesh 35 (without spacer) (curve 40), for the comparative mesh (curve 41) and for the mesh according to the invention (curve 42). The presence of a spacer having too high a rigidity, greater than the rigidity of the encapsulation materials, increases the concentration of stresses in the central part of the interconnector. The maximum von Mises stress is 39% higher than in the reference mesh without spacer. In contrast, a spacer softer than the encapsulation materials makes it possible to limit this stress concentration, the maximum value of the von Mises stress in the interconnector being decreased by 52%.

[0112] FIG. 11 is a graph showing the maximum value of the von Mises stress along the path 37 for meshes in which the spacers all have a square cross section (same width l.sub.spacer of 200 m and same thickness e.sub.spacer of 200 m), the modulus of elasticity varying from 0.1 MPa to 330 MPa. A general increase in von Mises stress is observed with increasing modulus of elasticity.

[0113] FIG. 12 illustrates the variation in the maximum value of the von Mises stress in the interconnector, for meshes in which the modulus of elasticity at 40 C. of the material of the spacer is 1 MPa, the thickness e.sub.spacer is 200 m and the width l.sub.spacer varies from 200 m to 1000 m (the case l.sub.spacer=0 (corresponds to the reference case without spacer). It may be seen that an increase in the width of the spacer induces a decrease of up to more than 50% in the maximum value of the von Mises stress in the interconnector, compared with the reference case.

[0114] FIG. 13 illustrates the variation in the maximum value of the von Mises stress in the interconnector, for meshes in which the modulus of elasticity at 40 C. of the material of the spacer is 1 MPa, the width l.sub.spacer is 1000 m and the thickness e.sub.spacer varies from 100 m to 400 m (the case e.sub.spacer=0 corresponds to the reference case without spacer). It may be seen that an increase in the thickness of the spacer induces a decrease of up to more than 80% in the maximum value of the von Mises stress in the interconnector, compared with the reference case.

[0115] As should be clear on having read the present description, the invention therefore decreases the risk of rupture of the interconnector during thermal cycling.

[0116] The expression between A and B is understood to be strictly equivalent to the expression greater than or equal to A and less than or equal to B.