Photovoltaic system

Abstract

A flexible composite strip is described comprising a flexible printed circuit (2) comprising at least a first and a second conductive track (5, 6), and a plurality of groups (4) of photovoltaic cells (3) that are connected in parallel to said first and second tracks (5, 6) to power them; the composite strip comprises a plurality of solder pads (12) in which the first and second conductive track (5, 6) are accessible; the flexible composite strip is configured to be cut at the solder pads (12).

Description

Photovoltaic system Technical field The present invention relates to a photovoltaic module designed, in particular, for windows or French windows. Background of the technique Luminescent solar concentrators (LSCs) are devices based on a sheet or film coated with dye molecules capable of capturing a portion of the incident solar radiation and re-emitting it. Some of the radiation emitted by the dye molecules is trapped inside the film or sheet due to the phenomenon of total internal reflection. If the sheet or film has a sufficiently smooth interface with the air, the part of the fluorescent light trapped inside undergoes a multiple reflection process from one interface to another and reaches the perimeter of the sheet. On the lateral surface of the film or sheet are photovoltaic cells arranged in modules, called "arrays," which convert the fraction of light radiation trapped within the film or sheet into electrical current. This electrical current can be used advantageously to power external devices, such as lights, charging systems, shading systems, or integrated lighting, etc., or it can be stored in local storage systems or fed into the electrical grid. The photovoltaic cells located on the edge of the luminescent sheet are usually connected in series with each other in order to add up the potential difference generated by each cell, thus minimizing ohmic losses due to the interconnections between one cell and another. The current flowing through the photovoltaic cell string is limited by the current supplied by the least illuminated cell. Unfortunately, any local shading of the luminescent film results in uneven illumination of the photovoltaic cell array and, in the case of a series connection, a loss of overall efficiency related to the current limitation induced by the least illuminated cell. This problem can be overcome by connecting the photovoltaic cells in parallel. In this case, the current generated by the array is the sum of the current generated by each individual photovoltaic device, while the potential difference remains almost constant, regardless of the cells' illumination level. In the case of solar photovoltaic concentrators, the current density generated by the photovoltaic devices can be several tens of mA / cm², and parallel connection can result in arrays that supply a total current of several amperes. The greater the current flowing through the circuit, the greater the ohmic losses due to the electrical resistance of the interconnections and contacts. The option typically adopted in the manufacture of photovoltaic arrays for solar photovoltaic concentrators is the creation of series-parallel circuits, in which the cells are soldered onto a printed circuit board that provides the electrical connection for the individual photovoltaic devices and also acts as a mechanical support. If the cells are arranged in sets, the potential difference generated by the cells connected in series is greater than that of a single photovoltaic device, and the current is less than that which would be obtained in the case of a parallel connection of all the photovoltaic devices. Typically, the arrays used in solar photovoltaic concentrators consist of 20 to 30 photovoltaic devices connected in series. These arrays are then connected in parallel. The printed circuit board of the photovoltaic arrays is usually between 10 cm and 30 cm long and slightly wider than the thickness of the photovoltaic film (6-15 mm). Thanks to the mixed series and parallel connection, possible local variations in the illumination of the luminescent sheet do not limit the total current supplied by the entire module, but only that supplied by each individual set. Each photovoltaic array is connected to the next by means of plate-to-plate connectors, essentially known in the art, which allow the assembly of arrays of arbitrary length, even several meters. The longer each array, the fewer interconnections are needed for a given total length and, consequently, the lower the cost of the interconnecting components. On the other hand, the longer each array, the greater the module's sensitivity to any unavoidable local variations in illumination, with the resulting loss of efficiency already described. A drawback of prior art solutions stems from the fact that the printed circuit board to which the photovoltaic cells are connected—that is, the cell array—has a predetermined length. In the case of sheets larger or longer than a single module, several arrays must be connected using appropriate connectors, which raises the overall cost of the multi-module system to often unacceptable levels. Furthermore, the fixed length of the individual module may not be suitable for fully utilizing the sheet's dimensions, even when joining several arrays, since continuous glass sheets, glass covers, and windows rarely have standard dimensions. The industry recognizes the need for greater versatility in the production of photovoltaic cell arrays and, consequently, in the manufacture of LSC devices with arbitrary dimensions, also to facilitate the implementation of this technology in the residential and general construction sectors. This need must be combined with the constraint of minimizing both the number of connectors present and the current flowing within the photovoltaic array, in order to also reduce ohmic losses, the cross-section of the conductors, and, consequently, their cost. In this context, the objective is to provide a photovoltaic module for luminescent solar concentrators that is capable of overcoming at least some of the drawbacks of the previous technique and of satisfying the need mentioned above. The related prior art is described in patent publications US 2020 / 143995 A1 (specifically, Figure 3) and US 9526132 B2 (Figures 3 and 4). Description of the invention In particular, the objective of the invention is to provide a photovoltaic module for photovoltaic concentrators that is easy and practical to use, versatile and relatively inexpensive. This objective is achieved by means of a photovoltaic module comprising the technical characteristics described in one or more of the appended claims. The dependent claims correspond to possible different embodiments of the invention. According to a first aspect, the invention relates to a composite material strip comprising a flexible printed circuit including at least a first and a second conductive track and several groups of photovoltaic cells connected in series, wherein the cell groups power the conductive tracks. The flexible printed circuit board preferably has a thickness of between 0.2 and 2 mm and is manufactured, for example, on a Kapton® substrate. The cell groups are placed one after the other along the strip, and there are contact pads between consecutive groups. The conductive tracks can be accessed through the contact pads. The strip is configured to be cut at the height of the contact pads. Preferably, the flexible composite strip comprises a pair of tracks not electrically connected to the tracks connected to the photovoltaic cells. Preferably, the flexible composite strip comprises a graphical indication, for example a dashed line, to identify the corresponding cutting lines that respect the electrical connections of the photovoltaic cells and photovoltaic cell groups. Preferably, the flexible composite material strip comprises an adhesive, for example in the form of double-sided adhesive tape, for attaching it to an edge of a corresponding luminescent sheet. Preferably, the flexible composite material strip comprises at least one electronic component to protect the photovoltaic cells. The electronic protection component is preferably mounted on the flexible printed circuit board on the side opposite the photovoltaic cells. According to one aspect, the invention relates to a photovoltaic module comprising a piece of a flexible composite material strip as described above. The photovoltaic module comprises a conversion circuit soldered to said piece. The conversion circuit has an input connected to the tracks powered by the photovoltaic cells and an output at a predetermined voltage. The conversion circuit is configured to convert the input voltage into the predetermined output voltage, said predetermined output voltage being the output voltage of said photovoltaic module. Preferably, the flexible composite material strip comprises a pair of tracks not electrically connected to the tracks powered by the photovoltaic devices, and the output of the conversion circuit is connected to said tracks. Other features and advantages of the aspects mentioned above and of other aspects become more evident in the non-restrictive description below, relating to a preferred embodiment of a photovoltaic module for a luminescent solar concentrator. Brief description of the drawings The following description is set forth with reference to the accompanying drawings, which are provided for illustrative purposes only and do not restrict the scope of the invention, and in which: Figure 1 is a schematic side view of a luminescent solar concentrator comprising a photovoltaic module according to the invention; Figure 2 is a schematic side view of a luminescent solar concentrator comprising a photovoltaic module according to the invention; Figure 3 is a schematic plan view of a photovoltaic module according to the invention; Figure 4 is a schematic plan view of a photovoltaic module according to the invention; Figure 5 is a schematic plan view of a composite material strip according to the invention; Figure 6 is a schematic perspective view of a luminescent solar concentrator comprising a photovoltaic module according to the invention; Figure 7 is a schematic perspective view of a luminescent solar concentrator comprising a photovoltaic module according to the invention. Detailed description of the preferred embodiments of the invention With reference to the attached drawings, number 100 indicates a luminescent solar concentrator. According to one embodiment, illustrated for example in Figure 1, the concentrator 100 comprises a sheet 101 of fluorescent material, i.e., within which are dispersed dyes not illustrated. These dyes emit light or fluorescent radiation FL that propagates isotropically when, during use, the sheet is stimulated by solar radiation SR. Part of the fluorescent radiation FL is trapped by total internal reflection inside sheet 101 and is transmitted to an edge 102 of sheet 101. According to the invention, the concentrator 100 comprises a photovoltaic module, designated in its entirety with the number 1. Photovoltaic module 1 is applied to sheet 101 at edge 102 and along its length. According to one embodiment, illustrated for example in Figure 2, the concentrator 100 comprises a glass sheet 103, a glass sheet 104 and a film 105 interposed between the glass sheets 103 and 104 to form a layered sheet 106. In film 105, several dyes are dispersed, making it luminescent. Part of the fluorescent radiation FL is trapped by total internal reflection in film 105 and is transmitted towards an edge 107 of sheet 106. Concentrator 100 comprises the photovoltaic module 1 applied to sheet 101 at edge 107 and along the same. The sheet 101 and / or the plate 106 can be coated with a reflective material 108, preferably on the respective edges 102, 107, in order to minimize optical losses near module 1. Photovoltaic module 1 defines a photovoltaic receiver for concentrator 100. Module 1 comprises a flexible printed circuit board 2. The flexible printed circuit board 2 preferably has a thickness between 0.2 and 2 mm. For example, the flexible printed circuit board 2 is manufactured on a Kapton® substrate. Module 1 comprises several photovoltaic or solar cells 3 soldered onto the printed circuit board 2. According to one embodiment, the cells 3, illustrated schematically in the accompanying drawings as, for example, a diode representing the equivalent circuit, are divided into groups 4 formed, for example, by five cells 3 connected in series. According to other embodiments, the groups 4 comprise four cells 3, six cells, or any other number depending on the desired output. The groups 4 of module 1 are identical to each other, connected in parallel, and provide a predetermined output voltage determined by the number and type of the corresponding cells 3. The photovoltaic module 1 comprises several groups 4 of photovoltaic cells 3 connected in series with each other. The groups 4 of cells are connected in parallel in such a way that they provide a voltage equal to that of a single group, which increases the current. Preferably, each solar cell 3 has dimensions less than or equal to 20 x 20 mm and, preferably, less than or equal to 10 x 10 mm. The groups of 4 cells 3 preferably have a length less than or equal to 10 cm and, more preferably still, less than or equal to 5 cm. Preferably, the photovoltaic module 1 comprises electronic components to protect the photovoltaic cells 3, mounted on the printed circuit board 2 on the opposite side from the cells 3. The protection components may include, for example, bypass diodes or varistors. For example, Figures 3, 4, and 5 illustrate bypass diodes, labeled with the number 15, each connected in antiparallel to a corresponding group 4 of photovoltaic cells 3. Printed circuit board 2 comprises a first and a second track 5, 6 for connecting groups 4 in parallel. Groups 4 are connected in parallel to tracks 5, 6. Tracks 5 and 6 define a DC output, depending on the number of groups 4 connected in parallel, powered by the groups 4 themselves. According to one embodiment, the printed circuit board 2 comprises a third and a fourth track 8 and 9 that are not directly connected to the photovoltaic cells 3, as described in more detail below. With regard to module 1, the printed circuit board 2, together with the groups 4 of photovoltaic cells 3 connected in parallel to tracks 5 and 6 and, if necessary, the protection devices, preferably constitute a single piece 20 of a strip of flexible composite material 200 comprising the flexible printed circuit board 2, in the form of a strip, comprising tracks 5, 6, 8 and 9 (if any), to which a succession of groups 4 is soldered. The strip 200 is called a 'composite' strip since it comprises several components. As described in more detail below, piece 20 is preferably cut from strip 200. Groups 4 feed, both in strip 200 and in piece 20, tracks 5 and 6 which define a direct current output supplied by groups 4. Preferably, the dimensions of cells 3 are small enough to allow strip 200, and therefore module 1, to have a longitudinal bending radius of less than 10 cm and, more preferably, less than 5 cm. Module 1 comprises a conversion circuit 7 configured to convert the input voltage into an output voltage having a predetermined value, i.e., a predetermined voltage, for example, 18 V. According to one embodiment, circuit 7 has an input connected to tracks 5 and 6 and an output connected to tracks 8 and 9. According to one embodiment, the output of circuit 7 is used directly or can be used to power other devices. According to one embodiment, the output of circuit 7 can be used directly or can be used to power other devices and is connected to tracks 8 and 9 to carry the predetermined voltage also to an opposite end of module 1. In this way, the output of photovoltaic module 1 presents a standard electrical characteristic regardless of the length of module 1, i.e., the length of piece 20. In general, the DC-DC output of conversion circuit 7 has an output voltage equal to the predetermined voltage mentioned above. In practice, the conversion circuit 7 is powered through tracks 5 and 6 and provides as its output the predetermined voltage, for example, 18 volts, which can be used directly or via tracks 8 and 9. According to one embodiment, the conversion circuit 7 is manufactured on a flexible printed circuit board. The conversion circuit 7 comprises, for example, a DC-DC boost converter 7a, of essentially known type, which increases the potential difference supplied by the 4 cell groups 3 of piece 20. According to one embodiment, the flexible conversion circuit 7 is configured to perform maximum power point tracking, i.e., it is configured to modify the operating point of the photovoltaic devices present in piece 20 in order to optimize the electrical performance of module 1. According to one embodiment, module 1 comprises the two tracks 8, 9 connected to the output of the conversion circuit 7, i.e., supplied at the predetermined voltage. According to a simpler embodiment, module 1, i.e., the flexible printed circuit on which it is manufactured, does not have the two tracks 8, 9 and the predetermined output voltage is available in the conversion circuit 7. Hereafter in this document, reference is made to four tracks without limiting the scope of the invention. As illustrated in Figure 7, according to one embodiment, module 1 comprises a pair of conductors 10, 11, soldered to tracks 8, 9, to which, for example, connectors for photovoltaic systems could be connected if necessary. In practice, the traces or conductors 5, 6 carry the current supplied by each group 4 of cells 3 to the DC-DC conversion circuit, which raises the voltage supplied by each group 4 of cells 3 to a value that allows its connection to external DC-AC converters or to low-voltage consumers (<50 V). Essentially, at the ends of each group 4 along strip 200, strip 200 comprises contact pads 12 to which the conversion circuit 7 can be soldered to the printed circuit board. In practice, tracks 5, 6, 8 and 9 are accessible on contact pads 12. Advantageously, the 200 strip can be cut to the desired length on one of the 12 pads to obtain the 20 piece. Next, the conversion circuit 7 can be soldered to tracks 5, 6, 8 and 9 on one of the pads 12 of piece 20, preferably at one of its ends. The conversion circuit is connected to the pads directly connected to the photovoltaic device groups, and to two other pads, electrically connected to a bus that allows a constant and optimized voltage line for the entire length of photovoltaic module 1. This solution allows the positive and negative poles of module 1 to be obtained at either end of module 1. According to one embodiment, it is possible to keep the positive pole at one end and the negative pole at the opposite end, depending on the interconnection requirements. According to one embodiment, tracks 5, 6, 8 and 9 are thinned at the height of pads 12, to facilitate cutting of strip 200. Preferably, on pads 12, i.e., between the groups 4 of cells 3 along strip 200, strip 200 has a graphic indication 13, for example, a dashed line, to identify where to cut strip 200 in order to obtain piece 20 respecting the series and parallel connections of cells 3 and groups 4. Each group 4 is separated from the next group 4 along the printed circuit of strip 200 by a parting line that allows strip 200 to be cut without adversely affecting the electrical functionality of module 1. According to one embodiment, strip 200 comprises an adhesive 14, for example, in the form of double-sided adhesive tape, applied to strip 200 on the side of cells 3 to facilitate the attachment of module 1 to a corresponding sheet, for example, sheets 101 and 106. Adhesive 14 is transparent and allows optical coupling of photovoltaic devices with the sheet material. Edges 102 and 107 can be advantageously coated with reflective material 108 in order to minimize optical losses resulting from the use of the adhesive 14 employed to make the photovoltaic cells 3 adhere to the sheets 101 and 106. The solution described offers significant advantages, particularly in the production of luminescent solar concentrators. The 200 strip with cells 3 and tracks 5, 6, 8 and 9 can be manufactured in an indefinite length and packaged, for example, in convenient rolls. Depending on the dimensions of the sheet to which module 1 is to be applied, it is possible to cut a piece 20 from strip 200 of the appropriate length, at the height of pads 12 and / or dashed lines 13. Next, the conversion circuit 7 is soldered to piece 20, specifically to tracks 5, 6, 8 and 9. The module 1 obtained in this way can be applied, for example, by means of adhesive 14, to the corresponding edge of the sheet. In practice, the conversion circuit transforms the direct current supplied by each of the groups into direct current with a higher voltage independent of the length of module 1. The conversion circuit maintains a constant output voltage from the luminescent solar concentrator, regardless of the size of the luminescent sheet. In general, once the photovoltaic module is fixed to the sheet, the assembly can be subjected to other processes, for example, sealing with silicone and / or encapsulating the edges in specific profiles or other processes, which are not the subject of this description, in order to manufacture the luminescent solar concentrator. The proposed solution allows the formation of a flexible photovoltaic receiver of arbitrary length, with a constant output voltage suitable for optical coupling to solar concentrators of different sizes. The absence of connecting elements makes the strip extremely thin and flexible, allowing it to be supplied in the form of long coils that can be cut as needed. In general, LSC devices offer numerous and significant advantages compared to traditional flat-plate concentrating photovoltaic systems. The main advantages are as follows: a) a significant reduction in the amount of semiconductor material used; b) capture of the direct and diffuse components of solar radiation, which is converted with the same efficiency regardless of the orientation of the panel, with the consequent possibility of its use both on facades exposed directly to the sun and on facades exposed only to the diffuse component, regardless of the inclination of the collection surface; c) Good heat dissipation thanks to the large area of ​​the collector panel in contact with the external environment. This allows photovoltaic devices coupled to the edges of the sheet to operate under reduced temperature conditions, giving them high conversion efficiency (in fact, the efficiency of commercial semiconductors decreases as the temperature increases); d) absence of solar tracking systems: this feature, which makes LSC photovoltaic panels unique compared to conventional CPV panels, significantly increases the architectural integration of the devices and considerably reduces the cost, weight and maintenance tasks; e) The possibility of identifying dyes that allow a good degree of overlap between the emission spectrum of the dye itself and the spectral response curve of the photovoltaic cells. This allows the cells to operate by maximizing conversion efficiency and minimizing overheating and any damage.

Claims

1. A strip of flexible composite material comprising a flexible printed circuit (2) including at least a first and a second conductive track (5, 6), said strip of flexible composite material comprising several groups (4) of photovoltaic cells (3), said groups (4) being connected in parallel to said first and second tracks (5, 6) to power said first and second tracks (5, 6) and successively placed along said flexible printed circuit (2), each group (4) of photovoltaic cells (3) comprising several photovoltaic cells (3) connected in series, said strip of flexible composite material being characterized in that it comprises several contact pads (12) in which said first and second conductive tracks (5, 6) are accessible, each contact pad (12) being interposed, along said flexible printed circuit (2), between a first and a second consecutive group (4) of photovoltaic cells (3),and said strip of flexible composite material being configured to be cut at the height of the contact pads (12).

2. The strip of flexible composite material according to claim 1, comprising a third conductive track (8) and a fourth conductive track (9) not electrically connected to said first and second conductive tracks (5, 6).

3. The strip of flexible composite material according to claim 1 or 2, comprising a graphic indication (13), for example, a dashed line, on said contact pads (12) to identify the corresponding cutting lines while respecting the electrical connections of said photovoltaic cells (3) and of said groups (4) of photovoltaic cells (3).

4. The strip of flexible composite material according to any one of claims 1 to 3, comprising an adhesive (14), for example, in the form of double-sided adhesive tape,applied to the flexible printed circuit board (2) above said photovoltaic cells (3) to bond said flexible composite strip to an edge (102, 107) of a corresponding luminescent sheet (101, 106).

5. The flexible composite strip according to claim 4, wherein said adhesive (14) is transparent.

6. The flexible composite strip according to any one of the preceding claims, wherein said photovoltaic cells (3) have dimensions less than or equal to 20 × 20 mm and, preferably, less than or equal to 10 × 10 mm.

7. The flexible composite strip according to any one of the preceding claims, wherein said groups (4) of photovoltaic cells have a length less than or equal to 10 cm, preferably less than or equal to 5 cm.measured along said flexible printed circuit board (2).

8. The flexible composite strip according to any one of the preceding claims, comprising at least one electronic component for protecting said photovoltaic cells (3), said electronic protection component being mounted on said flexible printed circuit board on the side opposite the photovoltaic cells (3) with respect to the flexible printed circuit board.

9. The flexible composite strip according to any one of the preceding claims, wherein said flexible printed circuit board (2) has a thickness between 0.2 and 2 mm.

10. A photovoltaic module comprising a piece (20) of a flexible composite strip (20) according to any one of the preceding claims, said piece (20) comprising the printed circuit board (2) and the groups (4) of photovoltaic cells (3) connected in parallel to said first and second tracks (5, 6),the photovoltaic module further comprising at least one conversion circuit (7) soldered to said piece (20), said conversion circuit (7) having an input connected to said first and second tracks (5, 6) and an output at a predetermined voltage, said conversion circuit (7) being configured to convert a voltage at said input into said predetermined output voltage, said predetermined output voltage being the output voltage of said photovoltaic module.

11. The photovoltaic module according to claim 10, wherein said strip of flexible composite material (200) comprises a third conductive track (8) and a fourth conductive track (9) not electrically connected to said first and second conductive tracks (5, 6), said output at a predetermined voltage being connected to said third and fourth tracks (8, 9).

12. The photovoltaic module according to claim 10 or 11,wherein said conversion circuit (7) is soldered to said piece (20) on a first contact pad (12) located at one end of said piece (20).

13. The photovoltaic module according to any one of claims 10 to 12, wherein said conversion circuit (7) is manufactured on a second flexible printed circuit board.

14. The photovoltaic module according to any one of claims 10 to 13, wherein said conversion circuit (7) is configured to modify the operating point of the photovoltaic cells (3) present in said piece (20) in order to optimize the electrical performance of said photovoltaic module.

15. A kit for manufacturing at least one photovoltaic module (1) according to any one of claims 10 to 14.The kit comprises a flexible composite strip (200) according to any one of claims 1 to 9 and at least one conversion circuit (7) that can be soldered to or to a portion (20) of the flexible composite strip (200), the conversion circuit (7) having an input that can be connected to the first and second tracks (5, 6) and an output at a predetermined voltage, the conversion circuit (7) being configured to convert a voltage at the input into the predetermined output voltage, the predetermined output voltage being the output voltage of the photovoltaic module (1).

16. The kit according to claim 15, wherein the flexible composite strip (200) comprises a third conductive track (8) and a fourth conductive track (9) that are not electrically connected to the first and second conductive tracks (5, 6),said output being able to be connected to a predetermined voltage of said conversion circuit (7) to said third and fourth tracks (8, 9) .,

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