Abstract:
A photovoltaic structure, or a photovoltaic structure for a roadway suitable for circulation of pedestrians and vehicles, including: at least one photovoltaic cell; and a non-opaque coating covering at least a front face of the photovoltaic cell and having an outer surface which is macrotextured and microtextured irregularly, with a mean texture depth MTD, measured according to the norm NF EN 13036-1, of between 0.2 mm and 3 mm, and a polishing resistance value PRV, according to the norm NF EN 13043, of at least PRV 44 , or PRV 50 , or PRV 53 .

Description:
[0001]    The present invention relates to photovoltaic structures, intended in particular to form a roadway suitable for pedestrian and vehicular traffic and having in particular an outer surface that reproduces the texture of a trafficable road surface dressing. 
       PRIOR ART 
       [0002]    There is a need to use roads as a means of producing energy during the day, whether this is to supply buildings located in the vicinity (businesses, eco-districts, single-family houses, etc.) or to supply the power grid or traffic control devices. 
         [0003]    Owing to the extent of the surface area of the road network, this could make it possible to avoid fields of solar modules that use arable land for energy production or to increase the surfaces that are currently usable such as roofs. 
         [0004]    US 2005/0199282 A1 discloses a roadway that incorporates a photovoltaic structure, comprising solar cells covered by a non-opaque surfacing that must withstand the weight of vehicles and provide a sufficient coefficient of friction to allow the latter to travel without skidding. 
         [0005]    As examples of surfacings, mention is made of materials such as transparent plastics surface-coated with an abrasion-resistant layer, tempered or annealed glass, a complex formed of 5 mm glass beads bonded by an epoxy resin onto annealed glass, with a preference for a complex formed of polycarbonate-backed acrylic. 
         [0006]    The structure may have frictional elements at the surface that are intended to increase the coefficient of friction. These frictional elements may be arranged in patterns such as long or short straight or curved lines, circles or other geometrical figures. 
         [0007]    The frictional elements may be formed by bars or spikes or by grooves cut into the surface of the surfacing. The frictional elements, when they are added, may be made of stainless steel or of polycarbonate. 
         [0008]    There is a need to further improve the photovoltaic structures intended for pedestrian or vehicular traffic. 
       SUMMARY 
       [0009]    One subject of the invention is, according to a first of its aspects, a photovoltaic structure (also referred to as complex) in particular for a roadway suitable for pedestrian and vehicular traffic, comprising:
       at least one photovoltaic cell,   a non-opaque surfacing, covering at least the front face of said photovoltaic cell and having an irregularly macrotextured and microtextured outer surface with a mean texture depth MTD measured according to the NF EN 13036-1 standard of between 0.2 mm and 3 mm and a PSV (polished stone value) value according to the NF EN 13043 standard of at least PSV 44 , better still PSV 50 , even better still PSV 53 .       
 
         [0012]    The term “irregularly” is understood to mean the fact that the reliefs giving the macrotexture and the microtexture do not all have the same shape or the same size. These reliefs may be obtained from texturing elements that do not have the same shape or the same size, being non-calibrated. The nature, the mean size, the mean aspect ratio and the mean surface density of the texturing elements are specifically chosen so as to obtain the desired MTD and PSV values. 
         [0013]    Unlike the uniformly textured structure presented in patent application US 2005/0199282, a structure according to present invention has, at the surface, an irregular, preferably random, dispersion of non-opaque relief elements, of irregular and preferably random shape themselves, which approaches the surface appearance of a well-known surface dressing of the road industry. Furthermore it has both macroscopic-scale (macrotexture) and microscopic-scale (microtexture) topographies favorable to grip. Therefore, the particular surface characteristics of the present invention are selected to have favorable levels of macrotexture and of microtexture that meet specifications in terms of MTD and PSV making the surfacing suitable for traffic. 
         [0014]    Moreover, the present invention is preferably carried out using texturing elements such as glass grains which 1) replicate the texture of a road and provide measured grip properties that conform to the specifications (BO [Official Bulletin] 2002-10: circular 2002-39 of 16 May 2002 relating to the grip of new treads and the control of the macrotexture) and 2) can be applied, if this is desired, to construction sites using public works machinery and techniques. 
         [0015]    In one of its embodiments, the structure according to the present invention is a trafficable encapsulated photovoltaic unit. 
         [0016]    The surfacing of a structure according to the invention makes it possible, owing to the texture of its outer surface, to exhibit the grip suitable for vehicular or pedestrian traffic, while effectively protecting the photovoltaic cells positioned beneath this surfacing. 
         [0017]    The invention makes it possible to not replace existing roadways; the structure according to the invention may be compatible with most of these roadways without requiring excavations or the laying of thick and rigid photovoltaic blocks. 
         [0018]    Furthermore, the invention makes it possible to use the know-how and the customary equipment that is used for manufacturing and maintaining road surfacings (finishing machines, spreading of binder and gravel, etc.). 
         [0019]    Thus, the invention allows easy implantation of the photovoltaic structure and, from an economic viewpoint, makes it possible to significantly reduce the laying and integration costs. 
         [0020]    The grip characteristics of the surfacing according to the invention are preferably close to those of conventional bituminous road surfacings and the optical characteristics are compatible with obtaining a satisfactory conversion efficiency of the solar energy into electrical energy. 
         [0021]    The photovoltaic structure according to the invention may be produced according to two methods of implementation in particular. 
         [0022]    According to a first method of implementation, the photovoltaic cells are present within one or more modules covered by the non-opaque and textured surfacing, the module(s) being inserted between this surfacing and the underlying road. In particular, the surfacing may, according to this first method of implementation, also extend to the portion of the road bearing the photovoltaic modules but not covered thereby, or else be limited to just the surface of the modules. The latter may be attached to the roadway by a tie layer. 
         [0023]    According to a second method of implementation, the photovoltaic cells are encapsulated in the non-opaque and textured surfacing, the surfacing then extending preferably both on top of and underneath the photovoltaic cells. The surfacing may extend in contact with a tie layer deposited on the road or directly in contact therewith. In particular, according to this second method of implementation, the surfacing may be preassembled with one or more photovoltaic modules, containing the photovoltaic cells, preferably using a mold. 
         [0024]    Another subject of the invention is, according to another of its aspects, independently of or in combination with the aforegoing, a photovoltaic structure suitable for pedestrian and vehicular traffic, comprising at least one photovoltaic cell encapsulated in a non-opaque surfacing, having an irregular, textured, outer surface that is suitable for pedestrian and vehicular traffic. 
         [0025]    Another subject of the invention is, according to another of its aspects, independently of or in combination with the aforegoing, a photovoltaic structure suitable for pedestrian and vehicular traffic, comprising at least one photovoltaic cell covered by a surfacing that has an outer surface textured with an irregular relief, characterized by aggregates of irregular shape and/or by an imprint of aggregates of irregular shape. 
         [0026]    Another subject of the invention is, according to another of its aspects, independently of or in combination with the aforegoing, a photovoltaic structure suitable for pedestrian and vehicular traffic, comprising a surfacing that covers at least one photovoltaic cell, this surfacing comprising a bituminous binder, a clear road binder of synthetic or plant origin, resins, adhesives or polymers, such as epoxy or polyurethane, and optionally texturing elements such as aggregates or grains made of glass, that provide surface texturing. 
         [0027]    Another subject of the invention is, according to another of its aspects, independently of or in combination with the aforegoing, a photovoltaic structure that makes it possible to produce a roadway, in the form of a rolled-up flexible sheet, to be rolled out in order to form the wearing surface, comprising photovoltaic cells and a surfacing that covers them, this surfacing having a textured outer surface. 
         [0028]    According to all these subjects of the invention, the surfacing may be as defined subsequently, in the same way as the texturing elements used. 
         [0029]    Another subject of the invention is a process for manufacturing a photovoltaic structure, in particular according to the first aspect as defined above, comprising the steps consisting in:
       positioning texturing elements, preferably aggregates of irregular, in particular random, shape, in the bottom of a mold, the texturing elements preferably being arranged in a single layer,   positioning one or more photovoltaic cells in the mold,   injecting or casting a non-opaque material in the fluid state into or in the mold in order to cover the photovoltaic cell(s), and retain the texturing elements. Preferably, the texturing elements are positioned with a given surface density.       
 
         [0033]    Another subject of the invention is a process for manufacturing a photovoltaic structure, in particular according to the first aspect as defined above, comprising the steps consisting in:
       positioning one or more photovoltaic cells in a mold,   injecting or casting a non-opaque material in the fluid state into or in the mold,   before curing said material, embedding texturing elements, preferably aggregates of irregular, in particular random, shape, in its surface, the texturing elements preferably being arranged in a single layer.       
 
         [0037]    Another subject of the invention is a process for manufacturing a photovoltaic structure, in particular according to the first aspect as defined above, comprising the steps consisting in:
       positioning one or more photovoltaic cells in a mold, the bottom of which is textured, preferably with a relief that reproduces the imprint of aggregates of irregular, in particular random, shape, and   injecting or casting a non-opaque material in the fluid state, which is intended to cure, into or in the mold. Preferably, the reliefs that reproduce the imprint of the texturing elements are distributed with a given surface density.       
 
         [0040]    Another subject of the invention is a process for manufacturing a photovoltaic structure, in particular according to the first aspect as defined above, comprising the steps consisting in:
       positioning one or more photovoltaic cells in a mold,   depositing a transparent polymer film of given thickness on the photovoltaic cell(s),   depositing texturing elements, preferably aggregates of irregular, in particular random, shape, on its surface, the texturing elements preferably being arranged in a single layer,   subjecting the assembly to a hot pressurized laminator, the heat ensuring the softening of the film and enabling the aggregates to be embedded therein. Preferably, the texturing elements are positioned with a given surface density.       
 
         [0045]    In all the processes involving texturing elements, the latter are preferably trapped between one quarter and three quarters of their height, preferably at around mid-height. The production of a single layer is preferable for reasons of photovoltaic performance. 
         [0046]    Thus, in a first embodiment, texturing elements such as transparent aggregates are spread to saturation, and ideally as a single layer, on the bottom of a mold. Once the transparent material which will have been injected or molded therein attains its final mechanical properties, the aggregates will be set in the material and will provide surface texturing. 
         [0047]    In a second embodiment, transparent aggregates are inserted in the surface of the molded photovoltaic complex, ideally before the injected or molded transparent material has completely cured. 
         [0048]    In a third embodiment, one face of the casting or injection mold advantageously reproduces the imprint of a texture valid for a road application, in particular having the desired MTD and PSV values, defined above. The cast or injected transparent material then reproduces said texture. 
         [0049]    Surfacing 
         [0050]    The surfacing according to the invention is advantageously produced so as to have technical characteristics suitable both for pedestrian and vehicular traffic but that also enable its use in the photovoltaic field. In particular, these characteristics relate to the transparency and the surface texturing of said surfacing. 
         [0051]    Transparency 
         [0052]    In order to guarantee the desired photovoltaic performance, the surfacing is non-opaque. It advantageously has a degree of transparency of between 50% and 95%. 
         [0053]    In order to characterize the degree of transparency, a spectrophotometer equipped with an integrating sphere is used. This device makes it possible to quantify the light which passes directly through the sample and that which is scattered by the sample, for a range of wavelength values, in steps of 5 nm for example, this range preferably lying around the peak of efficiency of the photovoltaic cells, plus or minus 100 nm. 
         [0054]    The degree of transparency is measured for the thickness of surfacing passed through by the light incident upon the wearing surface, before reaching the photovoltaic cells. 
         [0055]    The surfacing to be characterized is used on a glass plate. This plate is first characterized in terms of transparency by using the same spectrophotometer. The measurement is carried out in accordance with the protocol described above and the transparency values obtained are subtracted from those of the glass plate. 
         [0056]    In order to have a characterization of the optical efficiency of the structure according to the invention, the transmission values are weighted by the spectral response (sensitivity depending on the wavelengths) of the photovoltaic cells, the sensitivities of which in the blue (450-520 nm) and in the violet (380-450) may be different depending on the type of technology used. Since the maximum efficiency of the current technologies is in the green around 600 nm, the surfacing is preferably produced so that in the range 500 to 700 nm, its degree of transparency is greater than 50%. 
         [0057]    Surface Texturing: 
         [0058]    In order to guarantee the desired grip performance, the surfacing according to the invention is advantageously produced so as to have an outer surface which is both macrotextured and microtextured. 
         [0059]    Macrotexture 
         [0060]    The macrotexture of the surfacing characterizes the surface irregularities in the range 0.5 to 50 mm horizontally (according to the NF EN ISO 13473-1 standard); the macrotexture facilitates the drainage of the water at the surface of the structure according to the invention and makes it possible to avoid loss of tire/roadway grip in rainy weather. 
         [0061]    A macrotexture has a texture wavelength ranging from 50 mm to 0.5 mm and a microtexture has a texture wavelength of less than 0.5 mm. 
         [0062]    The macrotexture preferably has an irregular relief, which is advantageously obtained owing to a well-defined choice of texturing elements, with a size and a surface density that are specifically chosen, of irregular, in particular random, shape, such as aggregates, or being the imprint of texturing elements of irregular shape, inspired by the surface topography of road surface dressings. 
         [0063]    Furthermore, the outer surface of the coating has a macrotexture depth preferably such that the mean texture depth MTD measured according to the NF EN 13036-1 standard is at least 0.20 mm, and preferably 0.30 mm, and ideally 0.60 mm or more, preferably being between 0.2 mm and 3 mm. 
         [0064]    Microtexture 
         [0065]    The surface of the surfacing also has a microtexture, in order to ensure good grip of the tires. 
         [0066]    The microtexture characterizes the surface irregularities, the characteristic horizontal size of which is less than 0.5 mm, according to the NF EN ISO 13473-1 standard. 
         [0067]    The grip of the surfacing of the invention with respect to traffic, which conveys the quality of the microtexture, must remain after polishing, and may be expressed:
       in terms of coefficient of friction μ WS , measured with a Wehner and Schulze machine. Such a machine firstly carries out up to 180 000 polishing cycles on the surface to be measured (disk with a diameter of 225 mm), obtained by three cones under a mixture of water and silica. Secondly, the device accelerates a head bearing three rubber-based pads having a size of 30 mm×14.5 mm each up to 3000 rpm, which corresponds to a tangential speed of 100 km/h. Water at 10° C. is sprayed onto the surface to be characterized until a theoretical water film thickness of 0.5 mm is formed. At that moment, the pads are applied to the surface to be measured with a pressure of 0.2 N.mm −2 , equivalent to a tire pressure of 2 bar. The coefficient of friction μ WS  is calculated at the speed of 60 km/h, and may be given in terms of polished stone value PSV;   in terms of Polished Stone Value (PSV), using a friction pad as described in the NF EN 1097-8 standard. The surfacing according to the invention advantageously has a PSV value according to the NF EN 13043 standard of at least PSV 44 , preferably PSV 50 , and ideally PSV 53 .       
 
         [0070]    Irregular Nature of the Texture 
         [0071]    The coating according to the invention has an irregularly macrotextured and also irregularly microtextured outer surface. 
         [0072]    It should be understood that the relief of the macrotexture or of the microtexture is not reproduced in an identical manner, due to the use of texturing elements that do not have the same shape or the same size, and that are not calibrated. The relief may have a random nature, both in its macrotexture and its microtexture. The texturing elements are for example shards or grains of glass, as specified below. 
     
    
     
       DETAILED DESCRIPTION 
         [0073]    The invention will be better understood on reading the following description, of exemplary embodiments that are not limiting thereto, and on examining the appended drawing, in which: 
           [0074]      FIG. 1  schematically represents, in cross section taken through the thickness, an example of a roadway equipped with a photovoltaic structure according to the invention, 
           [0075]      FIGS. 2 and 3  are views similar to  FIG. 1 , of the embodiment variants of the photovoltaic structure, 
           [0076]      FIGS. 4A to 4E  illustrate the production of a structure and the use thereof according to one exemplary embodiment of the invention, and 
           [0077]      FIGS. 5A to 5E  and  6 A to  6 D are views similar to  FIGS. 4A to 4E , of embodiment variants of the invention. 
       
    
    
       [0078]    In the drawing, the relative proportions of the various constituent elements have not always been respected, for the sake of clarity. Likewise, the texturing elements have been represented very schematically, in a reduced number, in order to simplify the drawing. The conventional electrical connection elements have not been represented. 
         [0079]    A first example of a photovoltaic structure  10  according to the invention is represented in  FIG. 1 . The structure  10  comprises one or more modules  11  containing photovoltaic cells and a transparent surfacing  12  that covers this or these modules  11 . 
         [0080]    The surfacing  12  mechanically protects the photovoltaic cells while allowing pedestrian and vehicular traffic and its transparency enables production of electrical energy by the modules  11 . 
         [0081]    The structure  10  has an irregular, granular, outer surface  13 , preferably having a random relief. 
         [0082]    The surfacing  12  is for example formed, as illustrated, from a binder  14 , also referred to as a matrix, embedded in which are transparent texturing elements  16 , such as aggregates formed from glass shards or glass grains, giving the outer surface  13  its granular appearance. The texture of the surfacing may also be produced by structuring of the surface, without inclusion of aggregates in the binder. 
         [0083]    The terms “transparent”, “translucent” and “non-opaque” are considered to be synonyms within the context of the present invention. 
         [0084]    The texture of the surfacing  12  guarantees a road holding similar to “conventional” roads, preferably with MTD and PSV values as defined above. 
         [0085]    The photovoltaic modules  11  may be flexible or semi-rigid, or even rigid. 
         [0086]    A tie layer  17  may ensure the attachment of the module(s)  11  to the road R, which may be new or existing. 
         [0087]    The example from  FIG. 1  corresponds to the first method of implementation of the invention, defined above, according to which the surfacing  12  extends on top of the photovoltaic module(s)  11  and is not inserted between the latter and the underlying road. Other variants will be described below. 
         [0088]    Irrespective of the embodiments, the binder used preferably has a degree of transparency ranging from 80% to 100%. 
         [0089]    Preferably, the material of the surfacing is selected so that the latter remains transparent over time, which can be verified via aging tests in a climatic chamber, by following for example the NFT 30-049 standard. The surfacing will lose no more than 20% after 5 days of aging in the WOM (Weather O Meter) according to the NFT 30-049 standard and preferably no more than 10% of its initial transparency. 
         [0090]    The structure illustrated in  FIG. 1  may be produced by spreading the binder in the fluid state over the surface of the photovoltaic modules  11 , and before the binder cures, the texturing elements  16  (preferably in the form of transparent aggregates of irregular shape) may be spread to saturation over the surface. 
         [0091]    The amount of binder may be realized according to the traditional road know-how in order to trap the inclusions formed by the texturing elements, preferably at around mid-height. 
       Exemplary Embodiments of the Surfacing 
       [0092]    According to a first exemplary embodiment of the surfacing, the binder is of bituminous type as defined in the NF EN 12591 standard, clear, i.e. unpigmented, the penetration classes of which determined according to the EN 1426 method may be, without limitation, 160/220, 100/150, 70/100, 50/70, 40/60, 35/50, 30/45 or 20/30 (in tenths of a millimeter). Mention will be made, for example, of the Bituclair binder sold by Colas. 
         [0093]    According to a second exemplary embodiment of the surfacing, the binder is a clear road binder of synthetic or plant origin, the penetration classes of which determined according to the EN 1426 method may be, without limitation, 160/220, 100/150, 70/100, 50/70, 40/60, 35/50, 30/45 or 20/30 (in tenths of a millimeter). Mention will be made, for example, of the Végécol or Végéclair binders sold by Colas. 
         [0094]    According to a third exemplary embodiment of the surfacing, the binder is of purely synthetic or plant origin nature, the binder preferably being of organic nature, preferably of polymeric nature. Mention will be made, by way of example and without limitation, of an acrylic, epoxy or polyurethane resin, such as the epoxide varnishes referred to as Vernis D sold by Résipoly, or else a Sovermol polyurethane sold by BASF. 
         [0095]    The binders used in the invention may comprise initiators or catalysts, in particular for accelerating the curing. They may also comprise additives, thickeners, fluxes or others to facilitate the spreading and the obtaining of a film-forming surface of controlled thickness. 
         [0096]    The binders used have a good UV resistance (both in terms of transparency and mechanical properties), water resistance, heat resistance, cold resistance and frost resistance, which can be verified in a climatic chamber, by following for example the NFT 30-049 standard, and also good adhesion to the texturing elements  16  and the surface of the photovoltaic modules  11 . Furthermore, these binders advantageously have a flexibility similar to the complex formed by the wearing surface of the existing road and photovoltaic modules, namely ideally an elastic modulus of between 0.1 and 10 GPa. 
         [0097]    The examples of surfacings given above apply for all structures according to the invention. 
       Examples of Texturing Elements 
       [0098]    The production of a single layer of texturing elements  16  is preferable for reasons of photovoltaic performance, since the optical transmission drops with the thickness of material. 
         [0099]    The choice of the nature, particle size, shape factor and surface density of the texturing elements aims to obtain:
       a good angularity, allowing good grip between the tires and the roadway, under dry or wet conditions: the macrotexture thus obtained enables the drainage of water under the tire, whereas the microtexture contributes to the grip; a random texture characterized by texturing elements of random shape or that reproduces the relief of texturing elements of random shape is advantageous from this point of view;   an abrasion resistance in order to retain over time the desired road-holding quality; the use of mineral materials of great hardness, as texturing elements, is advantageous from this point of view;   a good surface finish in order to ensure correct adhesion to the binder; the use of aggregates of irregular, in particular random, shape may contribute to the good attachment of these aggregates to the matrix;   a good transparency, in order to retain the photovoltaic performance.       
 
         [0104]    The texturing elements are advantageously transparent materials (glass, polycarbonate, etc.), preferably made of glass, shards or grains, preferably grains of glass (crushed recycled or new glass). 
         [0105]    The size of these elements, differentiated using a screen, may be monodisperse or polydisperse, and range from 0.1 to 10 mm, better still from 0.4 to 4 mm, and more preferably have a size ranging from 0.9 to 1.4 mm. 
         [0106]    In order to obtain the desired level of macrotexture, the surface density of these texturing elements at the surface of the surfacing is preferably between 0.1 and 5 kg/m 2 , and advantageously between 0.7 and 1.5 kg/m 2 . 
         [0107]    The shape factor of these structuring elements, that is to say the ratio for one element between its greater length and its smaller width, is preferably less than or equal to  8  and preferably between  1  and  3 . 
         [0108]    The mean texture depth MTD of such elements preferably is close to 0.8 mm and corresponds to the ideal threshold of 0.6 mm, whereas in terms of grip and resistance to polishing, after 180 000 polishing cycles in the Wehner and Schultze machine, the texturing elements preferably have a coefficient of friction μ WS  of 0.4, exceeding the μ WS =0.30 threshold of a Polished Stone Value 50. 
         [0109]    The examples of texturing elements above apply for all the embodiments. 
         [0110]    The photovoltaic modules  11  may be thin, flexible or semi-rigid (for example photovoltaic modules of the Unisolar brand) and may be adhesively bonded directly to the surface of a road made of bituminous mixes or made of cement concrete. The rear face of the modules  11  is preferably sufficiently rigid and solid to protect the photovoltaic cells from any puncturing by the surface asperities of the existing road (for example by the tops of aggregates), while following the change in the surface topography of the roads (for example following the formation of ruts or a crack). For example, the rear face of the modules  11  is characterized by a fluorinated resin such as ethylene-tetrafluoroethylene, for example that sold under the name Tefzel by DuPont, preferably having a thickness of 0.2 to 5 mm. 
         [0111]    The roadway may be new or existing, preferably being produced from bituminous mix formulations that are not very prone to rutting, so that the topography of the surface of the road only changes slightly as vehicles pass over it. 
         [0112]    The adhesive bonding of the modules  11  to the surface of the road R is carried out with the tie layer  17 , which may be formed of special industrial adhesives, or else of a bituminous binder, optionally reinforced by an addition of a polymer such as SBS, hot or as an emulsion. 
         [0113]    In a first embodiment, the adhesive or the bituminous binder forming the tie layer  17  is directly spread on the surface of the road R, spread out as a thin layer, then the photovoltaic modules  11  are deposited thereon while the adhesive has not cured or while the bituminous binder is still viscous and tacky. 
         [0114]    In a second embodiment, the binder intended to form the tie layer  17  is deposited in the factory on the lower face of the photovoltaic modules  11 , which face may be untreated or may have undergone a plasma or corona treatment in order to promote a better adhesion to the binder; the complex thus obtained is then adhesively bonded to the road R by a slight reheating of the binder on the back of the modules  11 . The complex corresponding to this second embodiment may be laid on a new or existing road. 
         [0115]    With reference to  FIG. 2 , a photovoltaic structure  10  according to the second method of implementation of the invention defined above will now be described, in which the photovoltaic cell(s)  11  are encapsulated in the surfacing  12 . The latter may also be attached to the road R by a tie layer  17 , in the manner of the examples described previously with reference to  FIG. 1 . 
         [0116]    The encapsulation ensures the (mechanical, hygrometric, leaktightness, etc.) protection of the photovoltaic cells. 
         [0117]    The encapsulation is preferably produced by pre-positioning the photovoltaic cell(s)  11  within a mold as illustrated in  FIGS. 4A ,  5 A or  6 A, and described in detail below. Next, the structure  10  is removed from the mold and may be attached to the existing road R owing to the tie layer  17 . 
         [0118]    In order to produce the surface texture of the surfacing, in a first embodiment, illustrated in  FIGS. 4A to 4E , texturing elements  16  such as transparent aggregates are spread to saturation over the bottom of a mold, preferably in the form of a single layer, in what will then be the wearing surface of the structure. A transparent binder  14  is then injected or poured into the mold. Once this material has attained its final hardness and mechanical properties, the aggregates are firmly attached to the contents of the mold and provide the desired surface texturing. 
         [0119]    In a second embodiment, illustrated in  FIGS. 5A to 5E , the transparent binder  14  is firstly injected or poured into the mold ( FIG. 5B ), then the texturing elements such as transparent aggregates are spread over the free surface of the mold ( FIG. 5C ), while the injected or poured material has not attained its final properties and still behaves as a viscous fluid. The texturing elements may be sunk in the binder via a mechanical stress or sink by means of their own weight; it is also possible to heat the texturing elements in order to melt the binder in the immediate vicinity thereof. Once the binder  14  has attained its final hardness and mechanical properties, the aggregates are firmly attached to the contents of the mold and provide the desired surface texturing ( FIG. 5D ). 
         [0120]    These first two embodiments use texturing elements  16  added to the binder  14  in order to give the surfacing  12  the desired texture, preferably in the form of a single layer. 
         [0121]    In a third embodiment, illustrated in  FIG. 3  and in  FIGS. 6A to 6D , the lower face  45  of the mold M is textured and the desired texture is given by the shape of this lower face. This face of the mold may reproduce an imprint of random, irregular road texture, for example that of a surface dressing having good grip to tires. After removal from the mold, a wearing surface is obtained with relief elements  36  that give the desired macrotexture and microtexture. 
         [0122]    In a fourth embodiment:
       a transparent polymer film, of given thickness, is deposited on the photovoltaic cell(s),   texturing elements, in particular aggregates of irregular, better still random, shape, are deposited on its surface, the texturing elements preferably being arranged in a single layer, and these elements are subjected to a hot pressurized laminator. The heat ensures the softening of the film and enables the aggregates to be embedded therein.       
 
         [0125]    As encapsulant can be used for carrying out the invention according to the second method of implementation, use may be made of any transparent material (degree of transparency between 80% and 100%) capable of being poured or injected into a mold, in which photovoltaic cells have been pre-positioned. 
         [0126]    The role of the binder is to mechanically protect the photovoltaic cells, to hold the optional texturing elements that will give the surface its texture, and therefore to enable the desired roadholding, while being and remaining transparent over time (by satisfying the climatic chamber aging test according to the NFT 30-049 standard for example). 
         [0127]    The binder may be the same as according to the first method of implementation of the invention (see the section “Exemplary embodiments of the surfacing” above) and have the same characteristics. 
         [0128]    Thus, according to a first example, the binder is of bituminous type as defined in the NF EN 12591 standard, clear (unpigmented), the penetration classes of which determined according to the EN 1426 method may be, without limitation, 160/220, 100/150, 70/100, 50/70, 40/60, 35/50, 30/45 or 20/30 (in tenths of a millimeter). Mention will be made, for example, of the Bituclair binder sold by Colas. 
         [0129]    According to a second example, the binder is a clear road binder of synthetic or plant origin, the penetration classes of which determined according to the EN 1426 method may be, without limitation, 160/220, 100/150, 70/100, 50/70, 40/60, 35/50, 30/45 or 20/30 (in tenths of a millimeter). Use may be made of the Végécol or Végéclair binders sold by Colas. 
         [0130]    According to a third example, the binder is of purely synthetic or plant origin nature, preferably of organic nature, preferably of polymeric nature. Mention will be made, by way of example and without limitation, of an acrylic, epoxy or polyurethane resin, such as the epoxide varnishes referred to as Vernis D sold by Résipoly, or else a Sovermol polyurethane sold by BASF. 
         [0131]    The texturing elements may be the same as those listed in the section “Examples of texturing elements”. The choice of the nature and of the particle size of these inclusions corresponds to the same criteria as those defined above. By way of example, glass aggregates, having a size of between 0.9 and 1.4 mm, may be used as texturing elements in combination with polyurethane of Sovermol type as binder. The degree of transparency of such a surfacing is between 60% and 95% at 600 nm and ideally 95%. The PSV values are preferably at least PSV 44 , better still PSV 50 , even better still PSV 53 , and the mean texture depth MTD is preferably between 0.2 and 3 mm. 
         [0132]    As a function of the transparency and mechanical protection objectives, the thickness of the photovoltaic structure  10  according to the invention ranges for example from 0.5 to 30 mm, ideally from 0.6 to 12 mm. It is not necessary for the thicknesses of binder on top of and underneath the photovoltaic modules or cells  11  to be identical. 
         [0133]    The adhesive bonding of the photovoltaic structure according to this second method of implementation of the invention to the surface of the road may be carried out with special industrial adhesives, or else with a bituminous binder, optionally reinforced by an addition of a polymer such as SBS, hot or as an emulsion. 
         [0134]    In a first embodiment, the binder is directly spread on the surface of the road, spread out as a thin layer, then the prefabricated photovoltaic structure is deposited thereon while the adhesive has not cured or while the bituminous binder is still viscous and tacky. 
         [0135]    In a second embodiment, the binder is deposited in the factory on the lower face of the prefabricated photovoltaic structure, which face may be untreated or may have been treated by plasma or corona effect in order to promote a better adhesion to the binder; the photovoltaic structure is then adhesively bonded to the road by a slight reheating of the binder on the back thereof. 
         [0136]    The front face may be produced during the manufacture of the photovoltaic structure in the factory. 
         [0137]    The wearing surface may also be produced on the road construction site, after having spread the photovoltaic modules or cells over the first bituminous layers. 
         [0138]    A photovoltaic structure according to the invention may also be proposed in the form of a textured complex that can be rolled out having a large radius of curvature, whether the upper face (after rolling out) is already pretextured or whether a layer based on a transparent binder bearing texturing elements such as transparent aggregates is added thereto. The complex may include flexible electrical paths and connectors. Construction site machinery may be used to roll out the complex on an existing road. 
         [0139]    In a third embodiment, the surfacing is advantageously produced by impregnation using a roller. The photovoltaic structure is positioned on the road to be covered, and a roller preimpregnated with binder, in particular with resin, is passed over the structure in the style of an application of paint. 
         [0140]    Roadway 
         [0141]    Generally, the roadway may be new or existing, but preferably produced from bituminous mix formulations that are not very prone to rutting, so that the topography of the surface of the road only changes slightly as vehicles pass over it. The roadway may be a road, a freeway, a sidewalk. 
         [0142]    Use of the Electrical Energy Produced 
         [0143]    The electrical energy produced by a photovoltaic structure according to the invention may be used in various ways, for example in eco-districts, solar farms, powering public lighting, road signaling or recharging electrical vehicles, this list not being limiting. 
         [0144]    The invention may also be used for any type of application where the concept of grip is important or for esthetic reasons. 
         [0145]    The expression “comprising a” should be understood as being synonymous with “comprising at least one”.