METHOD FOR PRODUCING A PHOTOVOLTAIC MODULE TO BE APPLIED TO A SURFACE HAVING BIAXIAL CURVATURE

Abstract

A method for manufacturing a flexible photovoltaic panel to be fixed to a double curvature support surface is provided. The method includes generating a numerical model of a flat structure that is curved to conform to the double curvature support structure, identifying, in the flat structure, compression zones subject to formation of creases or lifting as a result of a curvature imposed by the double curvature support surface, determining a pattern of photovoltaic cells to be arranged on the flat structure, producing a flat photovoltaic panel on the basis of the pattern of photovoltaic cells, and forming cut-outs in the compression zones, the cut-outs being configured to close as a result of the curvature imposed by the double curvature support surface.

Claims

1. A method for manufacturing a flexible photovoltaic panel to be fixed to a double curvature support surface, said method comprising: generating a numerical model of a flat structure that is curved to conform to the double curvature support surface, identifying, in said flat structure, compression zones subject to formation of creases or lifting as a result of a curvature imposed by the double curvature support surface, determining a pattern of photovoltaic cells to be arranged on said flat structure, said pattern comprising a plurality of blocks of photovoltaic cells separated from each other by said compression zones, wherein neighboring photovoltaic cells of a single block of photovoltaic cells have smaller mutual distances than neighboring photovoltaic cells separated by one of said compression zones, producing a flat photovoltaic panel on the basis of said pattern of photovoltaic cells, wherein said flat photovoltaic panel comprises: a plurality of photovoltaic cells arranged according to said pattern of photovoltaic cells, an encapsulating layer configured to contain said plurality of photovoltaic cells, and at least one front layer made of flexible plastics material, the at least one front layer being joined to the encapsulating layer and overlapping said encapsulating layer on a first surface thereof, said at least one front layer being exposed in use to sunlight, and forming cut-outs in said compression zones, wherein said cut-outs are configured to close as a result of the curvature imposed by the double curvature support surface.

2. The method of claim 1, wherein said flat photovoltaic panel further comprises at least one back layer made of flexible material, the at least one back layer being joined to the encapsulating layer and overlapping said encapsulating layer on a second surface thereof that is opposite said first surface, and wherein said cut-outs also pass through said at least one back layer.

3. A flexible photovoltaic panel to be fixed to a double curvature support surface, wherein said flexible photovoltaic panel comprises: a plurality of photovoltaic cells arranged according to a pattern of photovoltaic cells, said pattern comprising a plurality of blocks of photovoltaic cells separated from each other by compression zones, wherein neighboring photovoltaic cells of a single block of photovoltaic cells have smaller mutual distances than neighboring photovoltaic cells separated by one of said compression zones, an encapsulating layer configured to contain said plurality of photovoltaic cells, at least one front layer made of flexible plastics material, the at least one front layer being joined to the encapsulating layer and overlapping said encapsulating layer on a first surface thereof, said at least one front layer being exposed in use to sunlight, and wherein cut-outs passing through said encapsulating layer and said at least one front layer are formed in said compression zones, said cut-outs being configured to close as a result of a curvature imposed by the double curvature support surface.

4. The flexible photovoltaic panel of claim 3, further comprising at least one back layer made of flexible material, the at least one back layer being joined to the encapsulating layer and overlapping said encapsulating layer on a second surface thereof that is opposite said first surface, wherein said cut-outs also pass through said at least one back layer.

5. The flexible photovoltaic panel of claim 4, wherein said at least one back layer comprises a conductive backsheet.

6. The flexible photovoltaic panel of claim 4, wherein said at least one back layer comprises magnetic material.

7. The flexible photovoltaic panel of claim 3, wherein electrical contacts are formed on a back side of the photovoltaic cells.

8. The flexible photovoltaic panel of claim 3, further comprising adhesive seals arranged in said cut-outs and configured to mechanically fix the flexible photovoltaic panel to the double curvature support surface.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0026] The present invention will be better described by some preferred embodiments, which are provided by way of non-limiting example and with reference to the accompanying drawings, in which:

[0027] FIG. 1 is a schematic cross-sectional view of a portion of a photovoltaic panel according to the present invention;

[0028] FIG. 2 is a schematic cross-sectional view of a variant of the photovoltaic panel in FIG. 1;

[0029] FIG. 3 is a block diagram which shows the main steps of a method for producing a photovoltaic panel according to the present invention;

[0030] FIG. 4 shows a flat structure model showing the complete shape of a photovoltaic panel;

[0031] FIG. 5 shows the model of FIG. 4 to which an arrangement of photovoltaic cells is applied; and

[0032] FIGS. 6 and 7 show a portion of the photovoltaic panel at a cut-out, respectively with the photovoltaic panel in a flat configuration and applied to a double curvature support surface.

DETAILED DESCRIPTION

[0033] FIG. 1 shows a diagram of the layers that make up a flexible photovoltaic panel according to the present invention. According to the diagram of layers, the flexible photovoltaic module, which is denoted as a whole by reference sign 1, comprises:

[0034] a plurality of photovoltaic cells 2 arranged side by side, in particular cells made of mono- or poly-crystalline silicon. According to a preferred embodiment, the photovoltaic cells 2 are “back-contact” cells in which all of the electrical contacts (not shown) are formed on the back of the cell;

[0035] at least one encapsulating layer 3 made of thermoplastic material and configured to contain the photovoltaic cells 2, the encapsulating layer being formed by a first layer and a second layer 3a, 3b which are arranged on opposite sides of the photovoltaic cells 2 and fused around the photovoltaic cells;

[0036] at least one front layer 4 joined to the encapsulating layer 3 and overlapping the encapsulating layer 3 on a first surface thereof, the at least one front layer 4 being exposed in use to sunlight, the at least one front layer 4 being made of flexible plastics material; and

[0037] at least one back layer 6 made of flexible material, the at least one back layer being joined to the encapsulating layer 3 and overlapping the encapsulating layer 3 on a second surface thereof that is opposite the first surface.

[0038] According to an embodiment which is not shown, the back layer 6 may be absent.

[0039] In the present description, the terms “front” and “back” refer to the use condition of the photovoltaic panel. A “front” layer is oriented toward the sunlight, and is located between the light source and the encapsulating layer containing the photovoltaic cells. A “back” layer is located on the opposite side of the encapsulating layer containing the cells.

[0040] This flexible photovoltaic module is produced according to conventional production techniques, i.e. by the following steps:

[0041] selecting the photovoltaic cells on the basis of electrical parameters;

[0042] welding the photovoltaic cells to each other, so as to form rows of electrically connected cells which are known as strings. Welding takes place using tinned copper metal parts, which ensure good electrical conductivity;

[0043] assembling the strings in regular shapes, typically rectangles, in order to form a photovoltaic module having the desired dimensions, and simultaneously forming the electrical contacts through which the generated current is extracted from the finished module;

[0044] overlapping the various layers according to the arrangement shown in FIG. 1; and

[0045] laminating in a flat vacuum laminating machine, in accordance with a temperature cycle that depends on the materials used.

[0046] Lamination requires a typical cycle time of 10-20 minutes, and is currently the most reliable, fast and economic process for producing photovoltaic modules based on poly- or mono-crystalline silicon cells.

[0047] FIG. 2 shows a variant of the layering shown in FIG. 1, in which the back layer 6 comprises a conductive backsheet 7, i.e. a metal film which is contained inside the back layer(s) 6 and shaped so as to create an electrical circuit to which the photovoltaic cells 2 are connected. With the variant shown in FIG. 2, the production process does not include the creation of the strings of welded cells, since the single cells are directly connected to the conductive backsheet 7 which creates the complete electrical contact of the photovoltaic module. The other steps of the process described above remain the same. The variant shown in FIG. 2 makes it possible to more easily obtain freer arrangements of the photovoltaic cells, in which the linear geometry of the rows (strings) is replaced by a greater freedom of arrangement. The use of back-contact cells makes this easier to achieve.

[0048] With reference to FIGS. 3-7, a method is described for manufacturing the flexible photovoltaic panel 1 that may be fixed to a double curvature support surface, such as the roof of a car. The support surface is denoted by reference sign R in FIG. 7. The support surface may be convex, as shown in the example. However, the present invention also encompasses concave or saddle-shaped support surfaces. The photovoltaic panel 1 is made to adhere to the support surface R by means of the back layer 6 thereof or, if the back layer is absent, by means of the encapsulating layer 3.

[0049] Firstly, a numerical model of a flat structure which is curved to conform to the support surface is generated (step 10 in FIG. 3). The modelled flat structure is shown schematically in FIG. 4 and denoted by reference sign 101.

[0050] Considering the double curvature surface R along which the photovoltaic module 1 is intended to be curved, it is necessary to study the deformations required to adapt the module 1 to the surface R. This may be done theoretically, using three-dimensional modelling systems such as the Rhinoceros® software developed by Robert McNeel & Associates, which makes it possible to study the compression and expansion zones of a flat structure which is curved in order to adhere to a surface having a bidimensional curvature.

[0051] Then, in the modelled flat structure 101, compression zones are identified that are subject to formation of creases or lifting as a result of the curvature imposed by the support surface R (step 20 in FIG. 3). The compression zones are shown approximately using dashed lines and denoted by reference signs 102 and 103 in FIG. 4. It is therefore possible to shape the edge of the photovoltaic module so as to remove the excess parts of the surface, i.e. those parts which, after curving, would form folds or other deformations, as will be described below.

[0052] A pattern of photovoltaic cells to be arranged on the flat structure 101 is then determined. The pattern comprises a plurality of blocks of photovoltaic cells (numbered 111 to 118 in FIG. 5) which are separated from each other by the compression zones 102, 103 determined in the preceding step, wherein neighboring cells of a single block of cells (for example in the single block 111 or 112) have smaller mutual distances than neighboring cells separated by one of the compression zones 102, 103 (for example neighboring cells of the block 111 and of the block 112 which are separated by the compression zone to the top left in FIGS. 4 and 5, which compression zone is denoted by reference sign 102 in FIG. 4).

[0053] The photovoltaic panel is then produced according to the lamination process described above, with the photovoltaic cells 2 arranged on the basis of the pattern of photovoltaic cells determined in step 30 (step 40 in FIG. 3).

[0054] Cut-outs 104, 105 are then formed in the compression zones 102, 103 in order to remove the excess material as stated above (step 50 in FIG. 3). In so doing, it is possible to optimize the initial shape of the photovoltaic module by creating empty spaces (the cut-outs 104, 105; see also FIG. 6) which tend to close once the double curvature starts (see FIG. 7). This makes it possible to obtain the maximum coverage of the final surface R, even though starting from a flat photovoltaic module. In fact, the original photovoltaic module has a greater surface area than the curved surface to be covered. It is noted that the cut-outs 104, 105 are formed starting from the edge of the photovoltaic panel 1, and are oriented in mutually orthogonal directions.

[0055] The freedom to shape the edge of the photovoltaic module clearly depends on the presence or absence of cells that have the correct shape and that cannot be recut. To this end, it is necessary to start by finding a compromise between the arrangement of the cells and the requirements for shaping that depend on the particular curvature to be obtained. It is therefore understood how the described method for producing photovoltaic modules according to the variant in FIG. 2 may be more suitable for the purposes of the present invention.

[0056] The photovoltaic panel 1 described above may be fixed to the support surface R in a manner known per se, for example using mechanical means or adhesive materials, such that the back layer 6 or, if the back layer is absent, the encapsulating layer 3 adheres to the support surface R. According to one embodiment, the back layer 6 may comprise a magnetic material, in particular a permanent magnet, in order to facilitate the application of the photovoltaic panel 1 to a support surface R made of iron, or more generally a ferromagnetic support surface.

[0057] The advantage of the present invention for the purposes of industrial production is clear. There is no longer any need to create molds for each type of surface, for the purpose of using hot-forming or injection-molding methods. The best shaping of the photovoltaic module may be studied numerically, and it is possible to produce the photovoltaic module using the efficient, fast and economic method described hereinabove, in order to then shape the edges thereof simply by using a numerically-controlled cutter. Last but not least, the present invention makes it possible to create photovoltaic modules that may be applied to cars that are already in circulation, by making the module adhere to existing roofs.

[0058] A further development is that of using the cut-outs 104, 105 to apply adhesive seals for sealing off the cuts from the upper side which is exposed to the hydrodynamic friction of air, and at the same time may be used to mechanically fix the module to the roof of the car if intended for the aftermarket. These seals may be pre-formed so as to have the shape of the cut or may be created at the time using adhesive resins.

[0059] The application of the photovoltaic module may be facilitated by using vacuum techniques, i.e. by applying a vacuum bag above the module so as to compress it and make it adhere homogenously to the double curvature surface. In this process, heat may also be applied (for example by radiating lamps) such that, if thermosetting resins are used, the adhesion of the module to the surface is facilitated.