阅读说明：本技术 包含散热材料的聚光子模块的制造 (Fabrication of concentrator submodules comprising heat sink material ) 是由 A·巴博 Y·鲁约尔 C·赛拉内 C·魏克 于 2018-11-29 设计创作，主要内容包括：一种用于制造聚光光伏太阳能子模块的方法,所述聚光光伏太阳能子模块具有预定义的凹形几何形状的反射表面,其特征在于,所述方法包括在单个步骤中对多层组件进行层压,并且,在层压步骤过程中,结构元件的反射表面通过与反模的凸表面进行接触而成型。(A method for manufacturing a concentrated photovoltaic solar sub-module having a reflective surface of a predefined concave geometry, characterized in that it comprises laminating the multilayer assembly in a single step and in that, during the lamination step, the reflective surface of the structural element is shaped by contact with a convex surface of a counter-mold.)

1. A method for manufacturing a concentrated photovoltaic solar sub-module having a reflective surface of a predefined concave geometry, characterized in that it comprises laminating, in a single step, a multilayer assembly comprising in sequence:

-a structural element having a reflective first surface and a second surface opposite to the first surface;

-a layer of a material having a good thermal conductivity, the thermal conductivity of which is higher than the thermal conductivity of the material constituting the structural element, said layer being located on the second surface of the structural element;

-a layer of sealant or adhesive;

-a photovoltaic receiver, the layer of encapsulant or adhesive being located between the layer of material having good thermal conductivity and the photovoltaic receiver;

-a layer made of a transparent sealing material covering at least the entire surface of the photovoltaic receiver; and

-a transparent protective layer covering the layer made of transparent sealing material;

and, during the lamination process, the reflective surface of the structural element is shaped by contact with the convex surface of the counter mold, so as to obtain a reflective surface of predefined concave geometry.

2. Method for manufacturing a concentrated photovoltaic solar sub-module according to the previous claim, wherein the predefined concave geometry of the reflecting surface is a paraboloid.

3. The method for manufacturing a concentrated photovoltaic solar sub-module according to any of the preceding claims, wherein the structural elements are made of composite material.

4. The method for manufacturing a concentrated photovoltaic solar sub-module according to any of the previous claims, wherein the material with good thermal conductivity is graphite.

5. Method for manufacturing a concentrated photovoltaic solar sub-module according to the previous claim, wherein the thickness of the graphite sheets is comprised between 50 and 500 μ η ι.

6. The method for manufacturing a concentrated photovoltaic solar sub-module according to any of claims 1 to 3, wherein the material with good thermal conductivity is graphene.

7. The method for manufacturing a concentrated photovoltaic solar sub-module according to any of the previous claims, wherein the transparent sealing material and the transparent protective layer cover the entire surface of the material with good thermal conductivity, protecting it.

8. Method for manufacturing a concentrated photovoltaic solar sub-module according to any of the previous claims, wherein said material with good thermal conductivity covers the entire surface of the second surface of the structural element.

9. A concentrated photovoltaic solar sub-module having a reflective surface of a predefined concave geometry, characterized in that it comprises:

-a structural element having a reflective first surface forming a reflective surface of the sub-module and a second surface opposite to said first surface;

-a layer of a material with good thermal conductivity placed directly on the second surface of the structural element;

-a layer of sealant or adhesive;

-a photovoltaic receiver, the layer of encapsulant or adhesive being located between the layer of material having good thermal conductivity and the photovoltaic receiver;

-a layer made of a transparent sealing material covering at least the entire surface of the photovoltaic receiver; and

-a transparent protective layer forming a second surface of the submodule, said second surface being opposite to said reflective surface, said transparent protective layer covering said layer made of transparent sealing material.

Technical Field

The present invention relates to the manufacture of elements for concentrated photovoltaic modules, and more particularly to the manufacture of elements for concentrated photovoltaic modules based on reflective linear parabolic concentrators (or mirrors). The element is referred to as a concentrated photovoltaic sub-module.

Background

Each of said submodules comprises an optical device for concentrating the light (this optical device is commonly referred to as a mirror or a concentrator) and a photovoltaic cell forming a photovoltaic receiver and located on the back of the mirror or concentrator opposite to the reflecting surface.

When these concentrating photovoltaic sub-modules are used, they can form a concentrating photovoltaic module, the focal line of the concentrator of a sub-module being located on the back of the concentrator of the adjacent sub-module. The photovoltaic receivers of adjacent sub-modules are located at the focal line. Thus, each mirror functions as a carrier for the photovoltaic receiver in addition to functioning as a concentrator. Thus, a concentrated photovoltaic module is an assembly of a plurality of substantially identical elements (called sub-modules).

The concentrators or mirrors of these concentrating solar submodules have a reflecting surface consisting of a mirror, and a back surface to which one or a group of photovoltaic cells is fixed (see document US 1993/5180441). The parabolic shape of the module enables the rays to be concentrated. Light striking the first sub-module is reflected by the reflective surface of the first sub-module, thereby concentrating the light onto the photovoltaic cells of a second sub-module located adjacent to the first module.

It is also possible to manufacture a concentrated photovoltaic submodule of parabolic shape (see document US 2007/0256726) in which the light is not concentrated at the focal point of a mirror, but at the focal point of a composite solid element consisting of a plurality of mirrors. In this document, the photovoltaic cell is located on the front side of the concentrator. To avoid the formation of air bubbles between the various components of the sub-module, multiple vacuum lamination is performed to integrate the optics, photovoltaic cells and wiring. Vacuum lamination may thus use little or no adhesive to ensure better attachment of the optics, cells, or wires to their respective carriers. Since these different laminations form a planar composite structure, there is another manufacturing step in which the reflector is affixed to a convex or concave surface to create a parabolic shape that is used to focus the light onto the focal point of the solid optical element.

Document US 2004/0118395 proposes a solar concentrator of parabolic shape comprising a honeycomb structure surrounded by two skins. Such a honeycomb structure enables a lightweight concentrator to be obtained, which is able to support a thin mirror or a thin reflective surface and which has good mechanical strength. However, the element does not comprise a photovoltaic cell, since the element is intended to heat a fluid. In addition, the element is manufactured in a plurality of steps, specifically: the reflective surface is cold deformed, the mirror is secured to one of the two skin layers with an adhesive, and the surfaces of the skin layers and mirror are treated.

The reflecting surface may be composed of a metal layer having high reflectivity covered with a protective film, or a metal layer adhered to a substrate including an organic composite material (see document US 1994/5344496). A mesh of high thermal conductivity material may also be added to the back of the reflective surface to improve heat dissipation from the sub-module. The manufacture of the sub-modules is very complicated because many steps are required, for example, forming and polishing the reflective surface or treating the surface. It is also desirable to provide a step of bonding the photovoltaic cell to the mirror.

The use of composite materials in concentrating solar submodules makes it possible to obtain lightweight and rigid submodules, but these materials have a thermal conductivity lower than that of certain metals, in particular aluminium. However, raising the temperature of the submodules has the undesirable effect of reducing the efficiency of the photovoltaic cell and reducing its lifetime.

To improve the heat dissipation of planar photovoltaic modules used, for example, on the roof of a building, large heat sinks composed of graphite (see document US 2010/0186806) or of graphite sheets (see document WO2012/044017) may be used. A heat sink or graphite sheet is located on the back of the photovoltaic module and below the photovoltaic cells to limit their temperature rise. However, these solutions require additional steps in the manufacturing process of the module or do not allow the manufacture of lightweight and rigid concentrator solar modules.

Disclosure of Invention

The present invention aims to remedy the above-mentioned drawbacks of the prior art; more specifically, the present invention aims to provide a method for manufacturing a concentrated photovoltaic sub-module comprising a heat sink material comprising only a single step.

One subject of the present invention is therefore a method for manufacturing a concentrated photovoltaic solar sub-module having a reflective surface with a predefined concave geometry, characterized in that it comprises the lamination, in a single step, of a multilayer assembly comprising, in succession: a structural element having a reflective first surface and a second surface opposite the first surface; a layer of a material having a good thermal conductivity, the thermal conductivity of which is higher than the thermal conductivity of the material constituting the structural element, said layer being located on the second surface of the structural element; a layer of sealant or adhesive; a photovoltaic receiver, the layer of encapsulant or adhesive being located between the layer of material having good thermal conductivity and the photovoltaic receiver; a layer made of a transparent sealing material covering at least the entire surface of the photovoltaic receiver; and a transparent protective layer covering the layer made of transparent sealing material, and wherein, during the lamination process, the reflective surface of the structural element is shaped by contact with the convex surface of the counter-mould, so as to obtain a reflective surface of predefined concave geometry.

According to a particular embodiment of the invention:

the predefined concave geometry of the reflecting surface may be a paraboloid;

the structural element may be made of composite material;

the material with good thermal conductivity may be graphite, more particularly a graphite sheet whose thickness is comprised between 50 μm and 500 μm;

the material with good thermal conductivity may be graphene;

the transparent sealing material and the transparent protective layer may cover the entire surface of the material with good thermal conductivity, thereby protecting the material with good thermal conductivity; and is

The material with good thermal conductivity may cover the entire surface of the second surface of the structural element.

Another subject of the invention is a concentrated photovoltaic solar submodule having a reflective surface with a predefined concave geometry, comprising: a structural element having a reflective first surface forming a reflective surface of the sub-module and a second surface opposite the first surface; a layer of a material having good thermal conductivity placed directly on the second surface of the structural element; a layer of sealant or adhesive; a photovoltaic receiver, the layer of encapsulant or adhesive being located between the layer of material having good thermal conductivity and the photovoltaic receiver; a layer made of a transparent sealing material covering at least the entire surface of the photovoltaic receiver; and a transparent protective layer forming a second surface of the sub-module, the second surface being opposite the reflective surface, the transparent protective layer covering the layer of transparent sealing material.

Drawings

Other features, details and advantages of the invention will become apparent from a reading of the description provided with reference to the accompanying drawings, which are given by way of example and respectively show:

fig. 1a shows a cross-sectional view of a module consisting of two sub-modules, illustrating the operation of a concentrated photovoltaic module;

FIG. 1b shows the characteristic dimensions of a concentrated photovoltaic module;

FIG. 2 shows a schematic diagram of a method for manufacturing a concentrated photovoltaic sub-module;

FIG. 3 shows a schematic diagram of a process for manufacturing a concentrated photovoltaic sub-module according to an embodiment of the invention;

FIG. 4 shows a graph of temperature along an operating concentrated photovoltaic sub-module, according to an embodiment of the invention;

FIG. 5 shows a graph of current and power as a function of voltage for three concentrating photovoltaic sub-modules.

The elements shown in the figures are not drawn to scale and so the scale does not represent reality.

Detailed Description

Lamination is the step of applying pressure to two or more layers of hot material to bond and compress them. The pressure and temperature of this step depend on the materials used. The lamination here allows the concentrator to be shaped by applying a reverse mold.

Fig. 1a shows a cross-sectional view of two concentrating photovoltaic sub-modules, illustrating the operation of the concentrating photovoltaic module. Although only two sub-modules M1 and M2 are shown, the operations described below may be applied to multiple sub-modules. The light ray RL illuminates the first reflective surface FR of the first submodule M1. The reflecting surface FR is typically constituted by a parabolic cylindrical mirror. The parabolic shape of the mirror of sub-module M1 enables ray RL to converge at the focal point of the mirror, the location of which is precisely calculated to enable the photovoltaic receiver R to be located at the focal point. This position also corresponds to a certain point on the second surface FA of the second submodule M2. The parabolic mirror has thermal, structural and optical functions. In particular, in addition to concentrating light to one point, the parabolic mirror is also able to dissipate heat so that the receiver R is at the highest temperature T_maxAnd the lowest temperature T is at the lower part of the sub-module_minThe receiver R is located at the upper part of the sub-module. The heat dissipation is indicated by arrows T in the figure_maxIs connected to T_minThe arrows of (A) indicate the temperature gradient along the submodule (US 1993/5180441). To be able to manufacture a system comprising a plurality of submodules, the second surface FA of submodule M1 may also carry a photovoltaic receiver, and the surface FR of submodule M2 may be reflective.

FIG. 1b shows a concentrated photovoltaic moduleThe characteristic dimension of (2). The sub-module is given a shape of a section of a paraboloid with a focal length f. The width of the development of the paraboloid of the section is L_mir. The distance between two sub-modules is L_ouv. The length of the sub-module is l_mirThickness of the condenser is e_mirThe thickness of the submodule is e.

FIG. 2 shows a schematic diagram of a method for manufacturing a concentrated photovoltaic sub-module. The transparent layer FAV covers a transparent seal E covering the photovoltaic receiver R, the structural elements being located on a counter-mold CF in the lower chamber CI of a laminator, more particularly a laminator such as used in the field of manufacturing conventional planar photovoltaic modules.

The structural element has a reflective surface and in particular comprises a core layer RD, also referred to as reinforcement, which is surrounded by two skin layers P, one of which is covered by a reflective film F.

The transparent layer FAV and the seal E cover at least the entire surface of the receiver R, which is located between the structural element and the seal E.

The area of the structural elements and the reflective film R is the same as the area of the desired sub-module.

The lower chamber CI and the upper chamber CS of the laminator are evacuated by a vacuum pump PV.

Denoted (FAV, E, R, P, RD, P, F), the assembly consisting of transparent layer FAV, transparent encapsulant E, photovoltaic receiver R, skin layer P, core layer RD and reflective film F is planar and is preferably hot laminated under vacuum and shaped using reverse mold CF.

In the lamination step, the counter-mould CF enables to define a concave parabolic shape of the reflective surface of the sub-module. The inverse CF thus has a surface that will be in direct contact with the reflective surface of the structural element during the lamination step. The surface has a predefined geometrical shape corresponding to the shape that the reflective surface of the structural element is intended to obtain. The reverse mould CF may be made of metal or composite material and covered with a non-stick layer (made of teflon for example). The material of the reverse-mode CF is selected to be a thermal conductor and to have high mechanical strength at the lamination temperature.

The temperature, pressure conditions and duration of the lamination step are selected by the skilled person depending on the materials to be laminated. For example, the lamination step may last for at least 15 minutes, the temperature of lamination advantageously being comprised between 120 ℃ and 170 ℃, and the lamination pressure may be about 1000mbar (10)⁵Pa)。

The thickness of the assembly is preferably less than 10mm in order to maintain and ensure an optimal parabolic shape of the assembly. The thickness may also be limited by the effective height of the laminator and the counter mold CF. During the lamination process, the counter-mold CF and the components (FAV, E, R, P, RD, P, F) are for example placed on a hot plate PC and a uniform vertical load is gradually applied from above by means of the film M that fully conforms to its shape. During lamination, it is necessary to cross-link seal E sufficiently and to bake correctly the various elements making up the module, which are located further away or closer to the hot plate PC. For this purpose, the thermal lamination procedure is optimized in terms of temperature, pressure and duration, depending on the materials used.

The skin layer P may be made of a pre-impregnated polymer/fibre material which enables adhesion of the reflective film F to the core layer RD to be obtained. The thickness of the prepreg is less than 200 μm and the percentage of resin is comprised between 40% and 55%. The polymer is selected from polyester, epoxy or acrylic and the fibres are selected from glass, carbon or aramid.

The core layer RD of the composite material MC may be a honeycomb structure made of aramid, polypropylene, polycarbonate or aluminium of the Nomex type.

The core layer RD may also be a foam made of PET (polyethylene terephthalate), PU (polyurethane), PVC (polyvinyl chloride), PEI (polyetherimide) or PMI (polymethylene imine).

The transparent sealing member E may have a thickness of less than 500 μm and may be made of a crosslinked elastomer such as EVA (ethyl vinyl acetate), or a thermoplastic elastomer or an IONOMER thermoplastic copolymer (IONOMER). In the case of thermoplastic elastomers, the seal E is more particularly made of polyolefin, silicone, thermoplastic PU, polyvinyl butyral or functional polyolefin.

The transparent layer FAV may have a thickness of less than 200 μm and may be made of ECTFE (or HALAR, ethylene chlorotrifluoroethylene copolymer), FEP (fluorinated ethylene propylene), PMMA (polymethyl methacrylate), PC (polycarbonate), ETFE (ethylene tetrafluoroethylene), PVDF (polyvinylidene fluoride), PET, thin glass, or CPI (transparent polyimide).

The reflective film F may be a polymer film with aluminum deposition or with silver deposition. Ideally, the thickness of the reflective film F should be thick enough so that the optional 3D cellular reinforcement RD is not visible through the reflective surface of the module, thereby not disrupting light collection while ensuring that the total weight of the sub-module remains low. The thickness of the film is advantageously comprised between 200 μm and 250 μm.

The photovoltaic receiver R consists of photovoltaic cells which are interconnected by wires (wire bonding) and mounted on an SMI-PCB (insulated metal substrate-printed circuit board) receiver by soldering or gluing using, for example, a conductive silver adhesive. The cells may also be interconnected by straps, which enables the use of SMI-PCB receivers to be avoided. The cell may be a silicon cell, or a multijunction cell made of a III-V or II-VI semiconductor, or a multijunction cell made of a material having a silicon-based perovskite structure.

The following are examples of manufacturing photovoltaic sub-modules:

the transparent layer FAV consists of a thickness of 25 μm and a weight per unit area of 54g/m²HAAR (ECTFE) or FEP;

the transparent seal E consists of a thickness of 50 μm and a weight per unit area of 45g/m²(ii) an ionomer of (a);

the photovoltaic receiver R is made up of a triple junction solar cell with a width of 10mm and a length of 10mm and a SMI-PCB receiver with a thickness of 75 μm;

the core layer RD is formed by a layer having a thickness of 3mm and a weight per unit area of 78g/m²Is surrounded by two skin layers P consisting of a weight per unit area of 110g/m²The carbon/epoxy prepreg of (a);

reflecting film F reflecting film made of PET, aluminum-containing sinkThe thickness of the reflective film F was 71 μm, and the weight per unit area was 105g/m²。

The assembly was placed on a parabolic shaped aluminum counter mold CF of height 28mm in the lower chamber CI (effective height 35mm) of the laminator. The temperature of the hot plate was 150 ℃. Lower chamber CI degased for 300 seconds: the lower chamber CI and the upper chamber CS are pumped out by a vacuum pump PV. Next, in a second phase of duration 600 seconds, a uniform vertical load (with film M) was gradually applied at a rate of 1400mbar/min on top of the counter-mold CF on the hotplate PC until a stable segment of 1000 mbar.

Spread width L of submodule_mirIs 180mm, length l_mir1m, and the cell width is 10 mm. The focal length f of the sub-modules is 75mm and the distance between two sub-modules is L_ouv＝150mm。

The structural element may comprise a mirror made of aluminium having a thickness of less than 0.5 mm. The assembly consisting of transparent layer FAV, seal E, photovoltaic receiver R and aluminum mirror is laminated in a single step on counter-mold CF in the same way as described above. In this case, the total weight of the sub-modules would be slightly larger (30%). The mechanical strength of the sub-modules is low and therefore additional supports will be needed: in particular, three supports are required for a sub-module of length 1m, whereas two supports are required for a sub-module of the same size made of composite material. However, since the degradation of the reflective part is lower than that of the organic layer, the lifetime of the sub-module is longer.

Fig. 3 shows a schematic diagram of a method for manufacturing a concentrated photovoltaic sub-module according to an embodiment of the invention. A layer C of adhesive or encapsulant is added between the structural element and the photovoltaic receiver R, and a layer FG of a material with good thermal conductivity (called heat sink layer). The heat dissipation layer FG is located on the surface of the structural element, and a layer C of adhesive or sealant enables the receiver R to be held in place on the heat dissipation layer FG. The thermal conductivity of the material from which the heat dissipation layer FG is made is higher than the thermal conductivity of the material from which the structural element is made, so as to be able to follow the submodule (in particular, in the photovoltaic reception sector)At R) to efficiently dissipate heat. Advantageously, such a material has a thermal conductivity close to that of aluminium (i.e. higher than 100W/(m.k)) and a low density, thereby enabling a lightweight sub-module capable of dissipating heat as efficiently as a sub-module comprising an aluminium mirror. The material may be, for example, graphite. Specifically, the density of graphite is 1.35g/cm³The thermal conductivity in the x and y directions is 140W/(m.K), the thermal conductivity in the z direction is 8W/(m.K), and the thermal conductivity of aluminum is 237W/(m.K), the density is 2.7g/cm³。

According to another embodiment of the present invention, the transparent layer FAV and the sealing member E may cover the entire surface of the heat dissipation layer so as to protect it. The heat dissipation layer FG may cover the entire surface of the structural element or only a part thereof. In the latter case, the thickness of the heat dissipation layer FG is greater than it would be if it covered the entire surface of the structural element. However, the heat dissipation layer FG covers at least the area of the structural element under the photovoltaic receiver R, since it is important to be able to dissipate the heat accumulated in the receiver R, which makes it possible to avoid a drop in the efficiency of the receiver R and to prolong its lifetime.

According to one embodiment, the material with good thermal conductivity making up the heat dissipation layer FG is graphite or graphene. More specifically, the heat dissipation layer FG is made of graphite with a thickness comprised between 50 μm and 500 μm to ensure good heat dissipation, while maintaining softness and lightness.

During thermal lamination, the sub-module comprising the heat dissipation layer FG and the layer C of adhesive or sealant is preferably assembled under vacuum and shaped with a reverse mold CF.

As mentioned above, in the lamination step, the counter-mould CF enables to define the concave parabolic shape of the reflective surface of the sub-module and to optimize the thermal lamination procedure in terms of temperature, pressure and duration, depending on the materials used.

According to another embodiment of the invention, the layer C of sealant or adhesive is made of EVA, polyolefin, silicone, thermoplastic polyurethane, polyvinyl butyral, functional polyolefin or ionomer. Typically, the same material is used for layer C of adhesive or sealant and seal E.

Although the material from which the sub-modules are made must be able to obtain a parabolic shape that ensures good light concentration, so that the conditions of the environment of the module (earth, stratosphere or space) are met, so that the required heat dissipation can be achieved, the choice of said material depends on the weight of the target sub-module.

Although the material from which the sub-modules are made must be able to obtain a parabolic shape that ensures good light concentration, so that the conditions of the environment of the module (earth, stratosphere or space) are met, so that the required heat dissipation can be achieved, the choice of said material depends on the weight of the target sub-module. Therefore, the weight per unit area is 80g/m²To 300g/m²In between, and in combination with an aluminium honeycomb of 3mm thickness of the structural element, a lightweight, much smaller (30% difference) robust sub-module can be produced without a heat-spreading layer than conventional assemblies. If a heat dissipating graphite layer is added, the weight of the sub-module will be the same as the weight of a conventional module, but will still be stronger than a conventional sub-module.

The following is an example of the fabrication of a photovoltaic sub-module according to one embodiment of the invention:

the transparent layer FAV consists of a thickness of 25 μm and a weight per unit area of 54g/m²HAAR (ECTFE) or FEP;

the transparent seal E and the layer C of adhesive or sealant are formed with a thickness of 50 μm and a weight per unit area of 45g/m²(ii) an ionomer of (a);

the photovoltaic receiver R is made up of a triple junction solar cell with a width of 10mm and a length of 10mm and a SMI-PCB receiver with a thickness of 75 μm;

the heat dissipation layer FG is a graphite sheet with a thickness of 130 μm;

the core layer RD is formed by a layer having a thickness of 3mm and a weight per unit area of 78g/m²Is surrounded by two skin layers P consisting of a weight per unit area of 110g/m²The carbon/epoxy prepreg of (a);

the reflective film F consists of a reflective film made of PET, an aluminum-containing deposit and a protective varnish, the thickness of the reflective film F being 71 μm perThe weight per unit area was 105g/m²。

The assembly is laminated on a counter mould CF, which lamination and counter mould have the same features as described above for the manufacture of embodiments of photovoltaic sub-modules not comprising a heat sink layer FG.

Figure 4 compares the temperature along two concentrating photovoltaic sub-modules in operation, as a function of distance from the top of the mirror. On the x-axis, a distance of 2.5cm corresponds to the position of the focal point and thus of the photovoltaic receivers R on the two submodules. Therefore, the photovoltaic module made according to the above manufacturing example, comprising 130 μm graphite sheets, has almost the same heat dissipation as the sub-module, the structural element of which is a mirror made of aluminum, having a thickness of 0.2mm and not comprising graphite sheets.

FIG. 5 compares the current and power values of three sub-modules according to the voltage variation, and the external illumination is 735W/m². Of the three submodules compared, the structural element of one of the submodules was a mirror made of aluminum with a thickness of 200 μm, the structural elements of the other two submodules comprised a core layer surrounded by two skin layers, one of the two submodules also comprising a heat-dissipating graphite layer with a thickness of 130 μm. The continuous illumination of the sub-module under study was 735W/m²This leads to a temperature increase, the magnitude of which depends on the material used. However, the temperature rise directly results in a voltage drop, resulting in a decrease in the maximum power point. The power of a submodule comprising a core layer surrounded by two skin layers and without a heat sink layer is then reduced by 10% compared to a submodule comprising a mirror made of aluminium. The addition of a heat-dissipating graphite layer over the entire surface of the structural element makes it possible to correct this effect and to obtain an efficiency equivalent to that of a submodule comprising mirrors made of aluminum and a higher mechanical strength.