WO2024261676A1 - Plastic photovoltaic module with improved resistance to stresses and conversion efficiency - Google Patents

Abstract

A photovoltaic module (10) including: a frontsheet (13) that receives light rays; a backsheet (16) of plastic material; an encapsulant region (14) arranged between the frontsheet and the backsheet. The photovoltaic module also includes a plurality of photovoltaic cells (20) arranged in rows and columns inside the encapsulant region (14). The photovoltaic cells of each pair of adjacent columns are separated by a corresponding inter-cell portion (18); the photovoltaic cells of each pair of adjacent rows are separated by a corresponding inter-string portion (19) of the encapsulant region (14). The backsheet forms a plurality of ribs (30a), which extend parallel to a first direction (Y) which is alternately parallel to the columns or the rows, and form interface regions (30a) arranged respectively below corresponding inter-cell portions or corresponding inter-string portions. Each interface region is at least partly exposed to the air and redirects towards at least one photovoltaic cell, by means of total internal reflection, at least part of the light rays that traversed the overlying corresponding inter-string or inter-cell portion.

Description

PLASTIC PHOTOVOLTAIC MODULE WITH IMPROVED RESISTANCE TO

STRESSES AND CONVERSION EFFICIENCY

Cross-Reference to Related Applications

This Patent Application claims priority from Italian Patent Application No . 102023000012810 filed on June 21 , 2023 , the entire disclosure of which is incorporated herein by reference .

Technical Field

The present invention relates to a plastic photovoltaic module with improved resistance to stresses and conversion ef ficiency .

Background

Renewable energy generation technologies are becoming increasingly important in a society attentive to the cost of energy production and the relative polluting ef fects . Among the technologies which have been developed in the field of renewable energies , that which exploits solar radiation is one of the most widespread .

The basic element capable of converting solar energy into electrical energy, in the form of direct current ( DC ) , is represented by what is called "photovoltaic cell" ( or simply "cell" ) . A photovoltaic cell typically comprises at least one j unction of regions in semiconductor material with opposite dopings ( P and N) . Furthermore , the photovoltaic cell exploits the photoelectric ef fect , i . e . , the phenomenon of the creation of electron-hole pairs as a result of the absorption, by the semiconductor material , of photons suf ficiently energetic to allow the charge carriers ( electrons and holes ) to overcome the j unction ' s intrinsic potential barrier .

The semiconductor material typically used in photovoltaic cells is silicon (Si) , in particular, crystalline silicon (c-Si) , and more specifically, monocrystalline silicon (mono-Si) . The energy conversion efficiencies typically achievable by single- j unction monocrystalline silicon cells can be in the range of 20-25%.

Accordingly, a "photovoltaic module" (or simply "module") is generally referred to as a device housing a plurality of photovoltaic cells connected so as to obtain, in output to the module, predetermined electrical characteristics. Electrical connections of cells, typically in mixed series-parallel diagrams, are implemented so as to obtain a maximum supply voltage and a maximum current which can be supplied to an external load, coupled to the module. The connections between cells can be made by means of "ribbon" connections of conductive material, typically copper, connecting opposite faces of consecutive cells.

Figure 1 shows the typical internal structure of a module 1 containing a plurality of cells 2. In order to provide an adequate protection of the cells 2 and their connections against atmospheric agents and UV rays, the module 1 has a multilayer laminated structure, i.e., obtained as a result of lamination processes. In particular, the module 1 comprises five layers, overlaying each other: a first layer 3, referred to as frontsheet; a second and a fourth layer 4', 4" approximately identical to each other and generally referred to as first and second encapsulant layer 4', 4"; a third layer 5, which is also known as silicon layer, is incorporated between the first and the second encapsulant layers 4', 4" and comprises a plurality of cells 2; and a fifth layer 6, referred to as backsheet. The terms "front" and "rear" refer to the overlapping of layers as shown in Figure 1, therefore meaning that the frontsheet 3 represents the face of the module 1 facing the solar radiation and that the face of the cell 2 absorbing the radiation is the one facing the frontsheet 3 . However, in the case of what are called "bi facial" photovoltaic cells , scattered radiation from the ground or other surfaces in proximity to the module can also be converted, being absorbed by the face of the cell facing the relative backsheet .

The module 1 is also provided with a frame structure 7 , which is necessary for the installation of the module 1 in typical contexts for photovoltaic systems and plants .

In more detail , the first and the second encapsulant layer 4 ' , 4" form an encapsulant region, within which the cells 2 are embedded . In particular, the first and the second encapsulant layers 4 ' , 4" are typically formed by a plastic material , such as ethylene vinyl acetate (EVA) copolymer .

Where an optimisation is requested in terms of the weight of the module 1 , plastic materials with suitable thermo-mechanical and weatherability characteristics can be used to form the frontsheet 3 ; an example plastic material is polymethylmethacrylate ( PMMA) . Furthermore , the backsheet 6 can also be formed by one or more plastic materials ; for example , the backsheet 6 can itsel f be formed by a multilayer structure including at least one polyethylene terephthalate ( PET ) layer .

Accordingly, various techniques have been implemented to increase the conversion ef ficiency of photovoltaic modules . In particular, ef ficiency recovery is mainly achieved by using structures which exploit the reflection and refraction phenomena of solar radiation to direct light rays towards the cells , rather than towards regions in which the cells are absent . Such structures comprise , for example : beam concentrators ( focusers ) , such as lenses or reflective surfaces with parabolic sections typically positioned in the frontsheet of the module ; or beam redirectors , configured to cause multiple reflections at the interfaces between the layers inside the module .

The above-mentioned recovery structures have the disadvantage of being complex to make , generating an increase in the number of steps required in the lamination process and a consequent increase in costs . In addition, particular techniques for increasing conversion ef ficiency may not be easy to implement ( or may even sometimes be unfeasible ) depending on the material used to manufacture the module , and/or may cause mechanical stresses such as to compromise the robustness and reliability of the module over time .

It is therefore the aim of the present invention to provide a solution which at least partially overcomes the drawbacks of the prior art .

Summary

According to the present invention, a plastic photovoltaic module is provided as defined in the appended claims .

Brief Description of the Figures

For a better understanding of the present invention, preferred embodiments thereof will now be presented, for merely illustrative and non-limiting purposes , with reference to the enclosed drawings , in which :

Figure 1 schematically shows an exploded perspective view of a photovoltaic module according to the state of the art ;

Figure 2 schematically shows an exploded perspective view of a photovoltaic module according to an embodiment of the present invention;

Figure 3 schematically shows a top view of a portion of the photovoltaic module of Figure 2 ;

Figure 4 shows an electric diagram related to the photovoltaic module of Figure 2 ;

Figure 5 schematically shows a perspective view with portions removed of a part of the photovoltaic module of Figure 2 ;

Figure 6 schematically shows a perspective bottom view of a portion of the photovoltaic module of Figure 2 ;

Figure 7 schematically shows an enlarged bottom view of a portion of the photovoltaic module of Figure 2 ;

Figure 8 schematically shows a cross-section of a portion of the photovoltaic module of Figure 2 ;

Figure 9 schematically shows an exploded perspective view of a photovoltaic module according to a di f ferent embodiment ;

Figures 10 and 11 schematically show cross-sections of portions of the photovoltaic module of Figure 9 ;

Figure 12 schematically shows a cross-section of a further portion of the photovoltaic module of Figure 9 ; and Figure 13 shows a block diagram of a photovoltaic system comprising the present photovoltaic module .

Description of Embodiments

With reference to Figure 2 , a photovoltaic module ( or simply "module" ) according to an embodiment of the present invention is indicated as a whole with the number 10 and comprises a structure of layers , overlaying each other along a direction paral lel to an axis Z of an orthogonal reference system XYZ , the axis Z being perpendicular to the layers .

In detail , the module 10 comprises : a first layer 13 , referred to as frontsheet 13 ; a second and a fourth layer 14 ' , 14" , identical to each other and referred to as first and second encapsulant layers 14 ' , 14" ; a third layer 15 , hereafter referred to as the conversion layer 15, embedded between the first and second encapsulant layers 14', 14" and comprising a plurality of photovoltaic cells 20 (or simply "cells") separated from each other; and a fifth layer 16, referred to as backsheet 16.

In more detail, the frontsheet 13, the first and second encapsulant layers 14', 14", the conversion layer 15 and the backsheet 16 have planar shapes parallel to the plane XY and are stacked according to the following order (from top to bottom) : frontsheet 13; first encapsulant layer 14', arranged below the frontsheet 13, in direct contact; conversion layer 15, arranged below the first encapsulant layer 14', in direct contact; second encapsulant layer 14", arranged below the conversion layer 15, in direct contact; and backsheet 16, arranged below the second encapsulant layer 14", in direct contact. Furthermore, the terms "front" and "rear" refer to the overlapping of layers as shown in Figure 2; consequently, the frontsheet 13 represents the face of the module 10 facing the Sun, in use, and thus the face on which the light rays from the Sun hit. Consequently, the faces of the cells 20 which absorb direct solar radiation are those facing the frontsheet 13. However, as will become clearer in the following, the cells 20 are of bifacial type, i.e., they are photovoltaic cells capable of absorbing the radiation hitting the relative rear faces, i.e., the faces facing the backsheet 16.

In a known manner, the cells 20 are embedded in an encapsulant region 14 formed by the first and second encapsulant layers 14', 14"; furthermore, the cells 20 may be, for example, single- j unction monocrystalline silicon photovoltaic cells, but it is understood that the use of other types of semiconductor materials is equivalent for the purposes of the present invention.

Without any loss of generality, as shown in Figure 3, there are one hundred and twenty cells 20, they have a rectangular shape when viewed on the plane XY, and have dimensions for example equal to 105x210 mm along the axis X and the axis Y, respectively. In particular, the cells 20 are divided into a first and a second group Gl, G2, which are equal to each other and arranged symmetrically relative to an axis H parallel to the axis Y.

For example, referring to the first group Gl, the relative cells 20 are arranged in rows (parallel to the axis X) and columns (parallel to the axis Y) . Without any loss of generality, there are ten rows and six columns. In the following, reference is made to the six cells 20 of each row as a corresponding string 22.

In practice, the conversion layer 15, and thus also the module 10, has a rectangular shape, here for example with a shape factor of approximately 0.6, with the longest side parallel to the axis Y and with a length of approximately 2.2 metres. Although not shown, variations are still possible in which the cells 20 are arranged so that the respective longest sides are parallel to the shortest side of the module 10; however, the arrangement shown in Figure 3 allows to reduce the thermo-mechanical stresses to which the module 10 is subjected in use.

Accordingly, although not visible in Figures 2 and 3, the conversion layer 15 comprises, in addition to the cells 20, the relative electrical connections, which are of a known type and are shown schematically in Figure 4. For example, the connection between the cells 20 is made by means of "ribbon" connections (not shown) of conductive material

(e . g. , copper) . In particular, for each string 22, the ribbon connections connect opposite faces (i.e., faces facing the frontsheet 13 and faces facing the backsheet 16) of consecutive cells 20 to each other, so that each string 22 has a first and a second terminal. Furthermore, the electrical connections between the cells 20 are such that, assuming an index k and an index j to denote the rows, i.e., strings 22, it is verified that the second terminal of the k-th string is connected to the second terminal of the k+l-th string (with k = 1, 3, 5, 7, 9) , and furthermore the first terminal of the j-th string is connected to the first terminal of the j+l-th string (with j = 2, 4, 6, 8) . The first terminal of the first string and the first terminal of the tenth string form, respectively, a first and a second terminal 100, 200 of the module 10. Furthermore, the first terminals of the pairs of corresponding strings of the first and second group Gl, G2 are connected to each other.

As can be seen in Figures 3 and 4, the module 10 can also comprise diodes 300, which are used to manage partial shading situations of circuit sections of the module 10, by means of electrical isolation from the remaining sections, in order to maximise energy production. In particular, there are five diodes 300; moreover, the n-th diode 300 (with n = 1, ..., 5) has cathode and anode connected to the first terminal of the [ 1+ (n-1 ) *2 ] -th string and to the first terminal of the (2*n)-th string, respectively.

For the purpose of assembly in typical contexts of photovoltaic systems and installations, the module 10 also provides a frame structure 17, which can comprise a minimum of 2 sides and a maximum of 4 sides. The frame 17 can have a known shape and can have a composite structure, comprising plastic materials, such as polyethylene terephthalate (PET) , and glass fibres. Furthermore, the frame structure 17 mechanically couples to the frontsheet 13, the first and second encapsulant layers 14', 14", the conversion layer 15 and the backsheet 16 in a known manner .

In more detail, the module 10 is a plastic-type photovoltaic module. In fact, the frontsheet 13 and the backsheet 16 can be formed, for example, by high-temperature resistant polyethylene terephthalate (HT PET) ; the first and second encapsulant layers 14', 14" can be formed by thermoplastic olefins (TPO) adapted to protect and seal the cells 20 with respect to the external environment.

As can be seen in Figures 2 and 3 and in Figure 5, and referring for the sake of brevity to the first group G1 of cells 20 (but the same considerations also apply to the second group G2 of cells 20) , pairs of adjacent strings 22 are separated by corresponding portions (denoted by 19) of the encapsulant region 14, which are referred to in the following as inter-string regions 19; each inter-string region 19 extends parallel to the axis X. Furthermore, adjacent pairs of cells 20 of the same string 22 are separated by corresponding portions (denoted by 18) of the encapsulant region 14, which extend parallel to the axis Y, and which are referred to in the following as inter-cell regions 18. Each inter-string region 19 extends through the first and second group Gl, G2 ; each inter-cell region 18 extends through the group thereof. In a known manner, although not shown, the inter-cell regions 18 can accommodate electrical connections between the cells 20.

Both the inter-cell regions 18 and the inter-string regions 19 are filled with the same material as the first and second encapsulant layer 14', 14"; in fact, in the intercell regions 18 and in the inter-string regions 19, the first and second encapsulant layer 14 ' , 14" are in direct contact .

The backsheet 16 of the module 10 is delimited by an upper face 16a and a lower face 16b opposite each other . As can be seen in Figures 5-7 , the lower face 16b of the backsheet 16 is machined so as to form a lattice 30 of first and second ribs 30a, 30b, which, in use , are exposed to air . In particular, in the following reference is made to the first ribs 30a as the longitudinal ribs 30a, since they extend parallel to the axis H, which represents a longitudinal axis of the module 10 . Furthermore , reference is made to the second ribs 30b as the transverse ribs 30b, since they extend parallel to the axis X .

With reference to the plane XY, the longitudinal ribs 30a and the transverse ribs 30b are arranged laterally of fset relative to the overlying cells 20 , so that each longitudinal rib 30a extends below a corresponding inter-cell region 18 and each transverse rib 30b extends below a corresponding inter-string region 19 . The lattice 30 of ribs gives structural rigidity to the module 10 , increasing the flexural strength thereof .

As can be seen in Figures 6- 8 , the longitudinal ribs 30a and the transverse ribs 30b have an elongated shape , which, in each cross-section taken in a plane perpendicular to the direction of elongation, is approximately pointed . Furthermore , the longitudinal ribs 30a are equal to each other ; the transverse ribs 30b are equal to each other . By way of example , and without any loss of generality, it is also assumed that the cross-sections of the longitudinal ribs 30a and the cross-sections of the transverse ribs 30b have the same shape .

In detail , as shown in Figure 8 ( in which an inter-cell region 18 is visible ) with reference to the longitudinal ribs 30a, part of the backsheet 16 is delimited below by a rear flat surface SBO , parallel to the plane XY; each longitudinal rib 30a extends downwards from the rear flat surface SBO with a thickness Sz, along the axis Z, and a width Dx, along the axis X.

Again with reference to Figure 8, the inter-cell region 18 extends, as previously explained, between two adjacent cells 20 and has a width DRX, along the axis X.

In more detail, each longitudinal rib 30a has a symmetrical structure relative to a plane of symmetry 98 parallel to the plane YZ and is delimited below by a lower edge 99 lying in the symmetry plane 98; without any loss of generality, the two cells 20 delimiting the corresponding inter-cell region 18 are also arranged symmetrically with respect to the plane of symmetry 98 and are spaced by the aforementioned width DRX. Furthermore, the longitudinal rib 30a is delimited by a pair of first walls 32, which are flat and symmetrical to each other, and by a pair of second walls 34, which are flat, symmetrical to each other and arranged below the first walls 32. Each second wall 34 contacts the corresponding overlying first wall 32; furthermore, the second walls 34 contact each other along the lower edge 99. The first walls 32 and the second walls 34 are inclined with respect to the plane of symmetry 98, the second walls 34 being more inclined than the first walls 32. In particular, the direction of inclination of the first walls 32 can form an angle with the plane of symmetry 98 comprised between 3° and 10°, with a value for example equal to 7°, while the direction of inclination of the second walls 34 is such that, along the lower edge 99, the second walls 34 form an angle a comprised for example between 100° and 110° (e.g., equal to 105, 75° ) . In even greater detail, the aforementioned thickness Sz is equal to the distance of the lower edge 99 from the rear flat surface SBOT, it is comprised for example in the range 1mm - 15mm and is for example equal to 12mm. The aforementioned width Dx is equal to the distance between the upper edges (denoted by 101) of the first wall 32; the width Dx can be comprised in the range 2mm - 20mm and is for example equal to 12mm.

In the example shown in Figure 8, the width DRX is less than the width Dx, so that a projection along the axis Z of the inter-cell region 18 falls entirely within the longitudinal rib 30a. For example, the width DRX is comprised in the range 0.7mm - 4mm and is for example equal to 2mm.

Although not shown, what is shown in Figure 8 with reference to the longitudinal ribs 30a also applies to the transverse ribs 30b and the inter-string regions 19, with the difference that the transverse ribs 30b and the interstring regions 19 have a width Dy and a width DRY, respectively, along the axis Y. The width DRY can differ from the width DRX; for example, the width DRY is comprised in the range 1mm - 6mm and is for example equal to 4mm.

Again with reference to Figure 8, it shows how the frontsheet 13 has a thickness S3, while the encapsulant region 14 has a thickness S4; the backsheet 16 has a thickness S5, understood as the distance between the upper face 16a and the rear flat surface SBOT. The thickness S3 can be comprised in the range 0.3mm - 2mm, with a value for example equal to 1mm; the thickness S4 can be comprised in the range 0.3mm - 1.5mm, with a value for example equal to 0.9mm; the thickness S5 can be comprised in the range 0.3mm - 2mm, with a value for example equal to 1mm. The conversion layer 15 has a thickness Se, which is in a first approximation negligible relative to the thicknesses S3, S4 and S5 and is mainly determined by the photovoltaic cell technology employed . For example , the thickness Se can be equal to 0 . 16 mm .

As can be seen in Figures 6 and 7 , wherein the lower edge of the transverse ribs 30b is indicated with 199 , the lattice 30 also has periodic intersections 40 between the longitudinal ribs 30a and the transverse ribs 30b .

For practical purposes , in addition to structurally reinforcing the module 10 , the longitudinal ribs 30a and the transverse ribs 30b also carry out a function of redirecting light rays towards the cells 20 , i . e . , a function of collecting and recovering those light rays which, passing through the inter-cell regions 18 or the inter-string regions 19 , would not contribute to the energy conversion of the module 10 since not absorbed by any of the cells 20 .

For example , referring for the sake of simplicity to the inter-string region 18 shown in Figure 8 (but the same considerations al so apply to any inter-string region 19 ) , a light ray C penetrating the module 10 by filtering through the inter-cell region 18 can be redirected towards the lower face of a cell 20 in the following manner .

In detail , the light ray C undergoes , at a first interface between a second wall 34 and the air surrounding the longitudinal rib 30a, a first total internal reflection ( TIR) , followed by a second TIR reflection at a second interface between a first wall 32 and the air surrounding the longitudinal rib 30a, finally striking the lower face of a cell 20 , where it can be absorbed . The total internal reflection is made possible by the refractive index di f ference existing between the plastic material forming the backsheet 16 ( and thus the longitudinal ribs 30a and the transverse ribs 30b ) , which has a value comprised in the range [ 1 . 54- 1 . 55 ] , and the air surrounding the longitudinal ribs 30a and the transverse ribs 30b . The necessary condition for a TIR reflection to occur at the first walls 32 and the second walls 34 is that whereby, with reference to the optical diagram of Figure 8 , the angles 0i and 02 formed by the light ray C with the normal s , respectively, to the aforementioned second wall 34 and the aforementioned first wall 32 are greater than the relative limit angle defined by the refractive index di f ference .

The path of the light ray C can also be dif ferent from that schematically shown in Figure 8 . For example , the light ray C can first intercept a first wall 32 and/or be redirected towards the cells 20 after having experienced only one TIR reflection on a second wall 34 or, again, following more than two reflections .

In practice , disregarding any re fractions within the module 10 , the optical path followed by the light ray C within the longitudinal rib 30a and the cell 20 on which the light ray C finally hits depend on the angle at which the light ray C hits the module 10 , the width DRX and the inclination of the first and second walls 32 , 34 , which represent corresponding design parameters , which can be designed as a function, for example , of an expected angle representing the angle at which the light rays are expected to hit the module 10 .

The conversion performance of the module 10 is thus overall improved, with an average increase in ef ficiency estimated at around 5% relative to a plastic photovoltaic module that does not adopt sunlight recovery solutions in regions where photovoltaic cells are absent .

The Applicant has also veri fied that the photovoltaic module according to the embodiment described, in addition to being able to be made by using plastic materials (recycled and/or recyclable) , exhibits adequate performance in terms of resistance to thermo-mechanical stresses, preventing possible breakage of the photovoltaic cells and their internal connections during the average life of the module. Furthermore, the present module can be manufactured economically; in fact, the backsheet and the relative longitudinal and transverse ribs can be manufactured by means of extrusion.

Figure 9 shows a photovoltaic module 110 according to a different embodiment, which is referred to in the following as module 110. Elements already present in the module 10 are indicated with the same reference marks, except where otherwise indicated; moreover, the module 110 is now described with reference to the differences relative to the module 10.

As shown in Figure 10, the lower face (indicated with 116b) of the backsheet (indicated with 116) is machined so as to form ribs 130, which are equal to each other and extend parallel to the axis Y. The ribs 130 are thus arranged periodically along the axis X, with a period P; pairs of adjacent ribs delimit above and laterally a corresponding cavity 146, which is open downwards.

In detail, the backsheet 116 comprises a top portion 150, which is planar in shape and extends below the second encapsulant layer 14", in direct contact. The ribs 130 extend downwards from the top portion 150.

In more detail, each rib 130 is symmetrical relative to a corresponding plane of symmetry 198 (one shown in Figure 10) parallel to the plane YZ and comprises a respective upper portion 152 and a respective lower portion 154. The sectional shape of each rib 130 is invariant for translations along the axis Y . Furthermore , in section, the upper portion 152 has a trapezoidal shape and is delimited laterally by a respective pair of flat walls 132 ; in particular, in section, the upper portion 152 has the shape of an isosceles trapezoid, in which the respective walls 132 define the oblique sides of the trapezoid, the maj or base of the trapezoid being integral with the top portion 150 , the minor base facing downwards . The lower portion 154 has , in section, a convex curvilinear profile , with convexity facing downwards . The upper portion 152 and the lower portion 154 contact each other and the upper portion 152 extends above the lower portion 154 . The walls 132 of the upper portions 152 of the ribs 130 and the lower portions 154 form the lower face 116b .

The periodicity of the ribs 130 is such that adj acent upper portions 152 contact each other along top edges 299 . In particular, with reference to a first and a second rib 130 ' , 130" adj acent to each other, and with reference to the first and second wall 132a, 132b to indicate the wall of the first rib 130 ' facing the second rib 130" and the wall of the second rib 130" facing the first rib 130 ' , respectively, the first and the second wall 132a, 132b contact along a top edge 299 , parallel to the axis Y . In practice , the first and the second wall 132a, 132b define a dihedral-shaped groove 138 , which lies on the top edge 299 ; the groove 138 delimits above and laterally an upper portion of the corresponding cavity 146 , the lower portion of which is delimited laterally by the corresponding lower portions 154 . In particular, the first and the second wall 132a, 132b define an angle p having a value for example equal to 100 ° . Without any loss of generality, the ribs 130 have a thickness SMAX , which is for example equal to 2.5 mm, while the top portion 150 has a thickness SMIN, which is for example equal to 1 mm. Each top edge 299 lies at a distance from the second encapsulant layer 14" equal to the thickness SMIN. The edges 299 are therefore parallel and coplanar to each other.

Each inter-cell region 18 overlies, at a distance, the top edge 299 of a corresponding groove 138. Furthermore, in the example shown in Figure 10, each cell 20 overlies a plurality of corresponding ribs 130. For example, the period P can be equal to 4 mm; furthermore, as mentioned above, the width DRX of each inter-cell region 18 is for example equal to 2 mm.

As shown in Figure 9, the module 110 has a plurality of support bars 140 below the backsheet 116, which are equal to each other and extend parallel to the axis X; the support bars 140 are arranged periodically along the axis Y. In particular, each support bar 140 is arranged below a corresponding inter-string region 19.

As can be seen in Figure 11, the support bars 140 can for example have a substantially triangular cross-section, with an upper side 140a parallel to the plane XY and facing the backsheet 116 and oblique sides 140b. Furthermore, the vertical projection of each inter-string region 19 falls within the upper side 140a of the corresponding support bar 140.

The support bars 140 can have a composite structure, formed by materials such as polyethylene terephthalate (PET) and glass fibres (e.g., in percentages respectively equal to 70% and 30%) , and may have been treated during processing with additives such as to make them substantially white, so as to increase the ability of the support bars 140 to reflect sunlight. Furthermore, the support bars 140 can have a hollow structure , with an inner perimeter conformal with the outer one ; the hollow structure allows the overall weight of the module 110 to be reduced .

As can be seen in Figure 11 , each support bar 140 has a width DB , understood as the width ( along the axis Y) of the respective upper side 140a . The width DB can be comprised in the range 8mm - 20mm, with a value for example equal to 16mm . Furthermore , the support bars 140 extend vertically with a thickness SB for example comprised in the range 16mm - 28mm, with a value for example equal to 22mm .

The Applicant has veri fied that the use of the ribs 130 and support bars 140 confers improved structural rigidity to the module 110 .

A detail of the coupling between the ribs 130 and the support bars 140 is shown in Figure 12 . In particular, it can be noted how each support bar 140 is fixed to the backsheet 116 by means of gluing regions 145 formed by a bonding material , for example a mono-component hygro- hardening adhesive ; the gluing regions 145 may also have been treated during processing with additives such as to make them substantially white , so as to increase the ability to reflect sunlight ( e . g . , with a light rays reflection percentage in the visible range at least equal to 89% ) .

In more detail , parts of the lower portions 154 of the ribs 130 contact the upper sides 140a of the support bars 140 . Furthermore , for each support bar 140 , corresponding gluing regions 145 fill the portions of the cavities 146 overlying the respective upper side 140a . In practice , each groove 138 is partly exposed to air and partly filled by corresponding gluing regions 145 .

For practical purposes , the ribs 130 and the support bars 140 perform both a mechanical reinforcing function and an optical function of redirecting sunlight at the intercell regions 18 and at the inter-string regions 19.

For example, as can be seen in Figure 10, a light ray C which penetrates the module 110, filtering through the inter-cell region 18, can be redirected towards the rear face of a cell 20 by following a path like the one shown. In detail, the light ray C undergoes, at an interface between a wall 132 and the air surrounding the ribs 130, a TIR reflection which causes a redirection thereof towards the rear face of a cell 20, where it can be absorbed. The TIR reflection is made possible by the difference in refractive index between the plastic material from the backsheet 116, and thus of the ribs 130, and the air surrounding the ribs 130. For a TIR reflection to occur at the walls 132, the light rays C must intercept the walls 132 at angles, with respect to the normals to the walls 132, greater than the relative limit angle defined by the refractive index difference .

Alternatively, as can be seen in Figure 12, the light ray C can penetrate the module 110 by filtering through an inter-cell region 18 overlying a coupling region between the ribs 130 and the support bars 140. Also in this case, the ray C can be redirected towards the rear face of a cell 20 and be absorbed, following a path like the one shown. In detail, the ray C undergoes a reflection at an interface between a wall 132 and a corresponding gluing region 145, since the bonding material of the gluing regions 145 is of the reflective type.

With reference to Figure 11, i.e., with regard to the support bar 140, a light ray C which penetrates the module 110 by filtering through the inter-string region 19 can be redirected towards the cells 20, following a path such as the one diagrammed . In detail , the light ray C ' undergoes a reflection when it hits the upper side 140a of the support bar 140 . In fact , the support bar 140 , thanks to the reflective treatment of the plastic materials forming it , ef fectively directs the l ight ray C ' towards the cells 20 , where it can be absorbed . In general , the upper side 140a of the support bar 140 reflects any l ight ray hitting thereon, regardless of the angle of incidence .

The support bars 140 can also carry out the function of redirecting any scattered radiation from the ground or other surfaces arranged near the module 110 towards the cells 20 . For example , as can be seen in Figure 11 , light rays A can undergo reflections at the interface between the air surrounding the support bar 140 and the oblique sides 140b, being directed towards the cells 20 .

It can therefore be concluded that , similarly to the photovoltaic module of the embodiment of Figure 2 , the module 110 also has advantages in terms of greater resistance to thermo-mechanical stresses and higher energy conversion ef ficiency .

As shown in Figure 13 , each embodiment of the present module can be used, for example , in a photovoltaic system (hereinafter referred to as a system for brevity) 500 . The module ( indicated generically as 400 ) can, for example , be installed on a solar radiation tracker device of known type (not shown) .

The system 500 further comprises a storage system 501 and an inverter circuit 502 . In more detail , the inlet of the storage system 501 is connected to the outlet of the module 400 , in order to store the energy produced by the latter ; the outlet of the storage system 501 , in direct current , is connected to a first inlet of the inverter circuit 502 , which also has a second inlet , which is connected to the outlet of the photovoltaic module 400 . The outlet of the inverter circuit 502 can be connected to a first load 503 operating in alternate current , which is generated by the inverter circuit 502 based on the energy supplied by the module 400 and/or by the storage system 501 . Furthermore , the outlets of the storage system 501 and the photovoltaic module 400 are connected to a second load 504 , which operates in direct current and can be supplied directly by the energy produced by the module 400 and/or by the storage system 501 .

Finally, it is clear that modi fications and variations may be made to what has been described and illustrated herein without thereby departing from the scope of the present invention, as defined in the attached claims .

For example , the alignment of the longitudinal ribs 30a and the transverse ribs 30b with respect to the corresponding inter-cell regions 18 and the corresponding inter-string regions 19 , respectively, can di f fer from that described . Furthermore , the longitudinal ribs 30a and the transverse ribs 30b can have di f ferent shapes relative to what is described and/or be di f ferent from each other . In addition, only the longitudinal ribs 30a or only the transverse ribs 30b may be present .

The frontsheet 13 can be coated with a UV- , moisture- and scratch-resistant layer and/or an anti-reflective layer . More in general , the module can comprise additional layers , interposed between the previously mentioned layers . Furthermore , the plastic materials forming the frontsheet 13 and the backsheet 16 , 116 can be di f ferent from each other .

The backsheet 16 , 116 can also comprise additional ribs , which are arranged, in view from above , outside the perimeter of the conversion layer 15.

In a variant (not shown) of the embodiment shown in Figures 9-12, the ribs and the support bars can be rotated by 90° relative to what is shown. Furthermore, each support bar is arranged below a corresponding inter-cell region. However, in general the support bars can be absent.

Lastly, the photovoltaic cells can be in different numbers and be arranged in different row and column arrangements than described. Furthermore, cells can be formed by a semiconductor material other than silicon.

1. A photovoltaic module (10; 110) comprising:

- a frontsheet (13) configured to receive light rays;

- a backsheet (16; 116) of a first plastic material; an encapsulant region (14) arranged between the frontsheet and the backsheet; and

- a plurality of photovoltaic cells (20) arranged in rows and columns inside the encapsulant region (14) , the photovoltaic cells of each pair of adjacent columns being separated by a corresponding inter-cell portion (18) of the encapsulant region (14) , the photovoltaic cells of each pair of adjacent rows being separated by a corresponding interstring portion (19) of the encapsulant region (14) , the interstring portions and the inter-cell portions being configured to be traversed by a part of the light rays received from the f rontsheet ; wherein the backsheet forms a plurality of first ribs (30a; 130) , which extend parallel to a first direction (Y) , which is alternatively parallel to the columns or the rows, and are laterally offset in a second direction (X) , said first ribs forming interface regions (30a; 138) arranged respectively below corresponding inter-cell portions (18) if the first direction is parallel to the columns, or below corresponding inter-string portions (19) if the first direction is parallel to the rows; said interface regions are at least partly exposed so that, when the photovoltaic module is arranged in air, the interface regions are at least partly exposed to the air, each interface region being furthermore configured to redirect towards at least one photovoltaic cell, by means of total internal reflection, at least part of the light rays that have traversed the overlying corresponding inter-string portion or inter-cell portion.

Claims

2. The photovoltaic module (10) according to claim 1, wherein each interface region (30a) is formed of a corresponding first rib (30a) which extends below the overlying corresponding inter-cell portion (18) if the first direction (Y) is parallel to the columns, or below the overlying corresponding inter-string portion (19) if the first direction (Y) is parallel to the rows.

3. The photovoltaic module (10) according to claim 2, wherein each first rib (30a) has a pointed shape.

4. The photovoltaic module (10) according to claim 3, wherein each pointed shape is symmetrical relative to a corresponding plane of symmetry (98) and is laterally delimited by a pair of first upper flat walls (32) , which are symmetrical to each other and have a first inclination relative to the plane of symmetry, and by a pair of second lower flat walls (34) , which are symmetrical to each other, are arranged below the upper flat walls, with which they are respectively in contact, and have a second inclination relative to the plane of symmetry, the second inclination being greater than the first inclination, said lower flat walls coming into contact with each other along an edge (99) , which is parallel to the first direction (Y) .

5. The photovoltaic module (10) according to any one of the claims from 2 to 4, wherein the first direction (Y) is parallel to the columns and wherein the second direction (X) is parallel to the rows; and wherein the backsheet (16) forms, furthermore, a plurality of second ribs (30b) which extend parallel to the second direction (X) and are laterally offset in the first direction (Y) .

6. The photovoltaic module (10) according to claim 5, wherein the first and the second ribs (30a, 30b) form a lattice .

7. The photovoltaic module (110) according to claim 1, wherein each pair of first adjacent ribs (130) delimits a corresponding groove (138) ; and wherein each interface region (138) comprises a corresponding groove which is arranged below the corresponding inter-cell portion (18) if the first direction (Y) is parallel to the columns, or below the corresponding inter-string portion (19) if the first direction (Y) is parallel to the rows.

8. The photovoltaic module (110) according to claim 7, wherein each groove (138) has a dihedral shape.

9. The photovoltaic module (110) according to claim 7 or 8, further comprising:

- a plurality of support structures (140) , which are arranged below the first ribs (130) and extend transversally to the first ribs; for each support structure, corresponding gluing regions (145) , which are interposed between the support structure and corresponding portions of the first ribs, so as to fill the corresponding grooves (138) and fix the support structure to the first ribs.

10. The photovoltaic module (110) according to claim 9, wherein each support structure (140) comprises a respective face (140a) facing the first ribs (130) and configured to reflect light rays.

11. The photovoltaic module (10; 110) according to any one of the preceding claims, wherein the first ribs (30a; 130) and the encapsulant region (14) are arranged on opposite sides of the backsheet (16; 116) .

12. The photovoltaic module (10; 110) according to any one of the preceding claims, wherein the frontsheet (13) is made of a second plastic material.

13. A photovoltaic system (500) comprising at least a photovoltaic module (10; 110) according to any one of the preceding claims and at least one of a storage system (501) and an inverter circuit (502) electrically coupled to the photovoltaic module.