Patent Publication Number: US-2013240025-A1

Title: Buoyant solar panel, and solar power plant consisting of an assembly of said panels

Description:
The invention relates to the field of solar panels and in particular solar panel power plants in an aquatic environment. By “solar panel” is meant generally in the following text a panel having conventional dimensions of the order of 1 to 3 m 2 , that can be easily handled and transported, and capable of providing an output of the order of 1.3 kW/m 2    
     Despite the current development of solar power, tight budgets for land (cost per m 2 ) and technical requirements (construction, fixing etc.) place a severe restriction on development in some regions or some urban environments. Land-based power plants are not compatible with other uses of the land, for example agriculture. Moreover, solar power plants are sometimes criticized for their appearance, which can affect the aesthetics of a landscape or the external finish of a building supporting the panels. 
     The aquatic environment offers a very promising possibility for such solar panel installations, both in a marine environment and on lakes or rivers: the surface area cost is small and there is little or no human habitation. The concept of solar panels installed in an aquatic environment is already known. The existing devices use for example an artificial island several tens or even hundreds of metres wide or a buoyant support typically having sides or a diameter of several metres on which a large number of conventional solar panels are placed. This type of power plant is heavy, inconvenient to install and forms a screen that is detrimental to photosynthesis on the sea bed. Moreover, this type of power plant has a surface that is very exposed to birds alighting on the panels and to their faeces, which cause rapid deterioration and/or costly maintenance. Inasmuch as the power plant is less accessible than on land, the upkeep and maintenance are correspondingly more expensive. 
     The purpose of the present invention is to overcome all or some of the aforementioned drawbacks of the known solar panels and the corresponding power plants. 
     To this end, a subject of the invention is a solar panel comprising solar power collecting means, such as solar collectors or photovoltaic cells, an upper face, characterized by comprising a unitary buoyant structure on which the solar power collecting means are mounted, the latter being incorporated into a solar module arranged, in particular flat, on the buoyant structure, the panel having, in a direction perpendicular to the upper face, a substantially constant thickness at least in a peripheral region of the panel. 
     The solar panels are therefore buoyant independently of one another. Their buoyant structure is so named because it supports and carries the collecting means (it is in this sense “structural”). The compact design of the panels according to the invention makes them robust and easy to transport. The distribution of the buoyancy means below the upper face allows for excellent support and maximum stability of the panel when afloat. Moreover, they can withstand the weight of one or two persons to provide for maintenance operations. 
     According to further advantageous features of the invention, the solar power collecting means are constituted by photovoltaic cells. 
     According to yet further advantageous features of the invention, the buoyant structure is shaped to position the upper face substantially horizontally. The panel provides minimum windage and is less subject to overturning or destabilization resulting from a heavy swell. The stability of the panel on the surface of the water is significantly improved. 
     According to yet further advantageous features of the invention, the buoyant structure is adapted to position the upper face substantially flush with the level of the surrounding liquid, in particular seawater or fresh water. In this embodiment, the upper face of the panel is constantly wetted under the activity of the swell. Birds that do not like to have wet feet will not alight, or rarely, on the upper face of the panel, thus avoiding bird faeces and providing the panel with a long life time and minimum cleaning. The costs of cleaning and maintenance are considerably reduced, optimizing the economic operating conditions of such panels. 
     According to yet further advantageous features of the invention, viewed from above the solar panel has the general shape of a parallelogram, for example a rectangle or square. Its surface area is preferably less than 4 m 2 , for example between 1 and 2 m 2 . The panel typically, but non-limitatively, has dimensions of the order of 1.50 m-1.60 m by 0.90 m-1 m. Such a panel is very compact owing to its external dimensions. Its dimensions are similar to the conventional dimensions of a panel used on land, on the ground or mounted on a roof. Such panel can be transported easily and allows for easy installation. Moreover, in the event of malfunction, it can be replaced independently and singly, without affecting the other surrounding panels that are operating correctly. 
     According to yet further advantageous features of the invention, the buoyancy means are uniformly distributed below the upper face. 
     According to yet further advantageous features of the invention, the buoyancy means are distributed on the periphery of the upper face. 
     According to yet further advantageous features of the invention, the buoyant structure comprises a chassis in which are stacked, from bottom to top, at least one support plate, in particular made of fibreglass, at least one buoyant slab, in particular made of polymer, and a layer of solar power collecting means. 
     According to yet further advantageous features of the invention, the chassis comprises a frame the fibreglass sides of which are connected at the corners of the frame via brackets, in particular made from stainless metal. 
     According to yet further advantageous features of the invention, the chassis comprises a stainless metal structure having the general form of a frame. 
     According to yet further advantageous features of the invention, the solar panel comprises shock absorbing fenders situated on the periphery of the panel, these fenders being in particular buoyant and made from polyurethane. 
     According to yet further advantageous features of the invention, the solar panel comprises attachment means allowing several solar panels of the same type to be secured together. 
     According to yet further advantageous features of the invention, the solar panel comprises at least one watertight electrical connector allowing the photovoltaic cells to be electrically connected. Said connector is accessible and provides a high level of safety in use. 
     A subject of the invention is also a solar power plant comprising an assembly of several solar panels having all or some of the aforementioned features, the individually buoyant panels being juxtaposed forming a net, having in particular the general shape of a square or rectangle. Other shapes can of course be envisaged, for example circular or polygonal shapes. Although assembled together, each panel is independently buoyant in water. The power plant offers very easy installation and maintenance. As the panels as a whole are flush with the surface of the water, there is a low visual impact on the marine and coastal environment. The independent panels are able to move in relation to each other (by deformation of the cables, cords, straps or rigid rods connecting them together): the panels are able to adopt a more or less tilted position in relation to each other so as to be fully adapted to swell phenomena. The costs are optimized and offer a genuine alternative both to conventional power plants on land and to the known more complex or rigid marine power plants. 
     According to further advantageous features of the invention, the panels of the power plant are secured directly to each other by means of a system of cords, cables or straps connecting their chassis or their support plate or their shock absorbing fenders. 
     According to yet further advantageous features of the invention, the panels are secured on a common net of cables, cords or straps, by means of their chassis or support plate or their shock absorbing fenders. 
     According to yet further advantageous features of the invention, the power plant comprises peripheral retaining means situated around the set of solar panels so as to immobilize it with a substantially flat arrangement of the juxtaposed panels. 
     According to yet further advantageous features of the invention, the peripheral retaining means are constituted by several flotation buoys immobilized by a system of submerged weights, in particular four flotation buoys situated at the four corners of a set of solar panels having a generally square or rectangular shape. 
     According to yet further advantageous features of the invention, at least one peripheral retaining means incorporates in a particular embodiment a static converter for processing the electricity originating from the solar panels of the photovoltaic type by suitable conducting means, said converter conveying the electricity to an electricity network remote from the solar power plant. 
    
    
     
       The invention will be better understood on reading the following description of a non-limitative embodiment of the invention and in the light of the attached drawings, in which: 
         FIG. 1  represents a solar panel according to a first embodiment of the invention, 
         FIG. 2  represents an exploded perspective view of the solar panel in  FIG. 1 , 
         FIG. 3  is a perspective view of a detail of the construction of the panel in  FIG. 1  showing the position of a watertight electrical connector, 
         FIG. 4  is a perspective view of a solar panel according to a further embodiment of the invention, 
         FIG. 5  shows a detail of the construction of the panel in  FIG. 4 , representing attachment means of the panel, 
         FIG. 6  represents a solar panel according to yet a further embodiment of the invention, 
         FIG. 7  is an exploded perspective view of the solar panel in  FIG. 6 . 
         FIG. 8  represents a solar panel according to yet a further embodiment of the invention, in which concentration means are provided, contributing in particular to the structural stability and stiffness of the panel, 
         FIG. 9  represents an exploded perspective view of the solar panel in  FIG. 8 , 
         FIG. 10  represents yet a further embodiment of the solar panel according to the invention, 
         FIGS. 11 and 12  show two variant embodiments of the solar panel in  FIG. 10 , in which an inflatable structure is load-bearing or not, 
         FIGS. 13 and 14  represent two perspective views, top and bottom, of a solar panel according to a further embodiment of the invention, in which the buoyancy means are constituted by a peripheral inflatable sponson, 
         FIG. 15  represents yet a further embodiment of the invention in which the buoyancy means are constituted in this example by two superimposed layers of bamboo canes, 
         FIG. 16  represents in a top view, an example of a solar panel power plant according to the invention, 
         FIG. 17  shows an enlarged view of a detail of the assembly of solar panels according to the invention, in which the panels are directly connected to each other, 
         FIG. 18  shows retaining means situated on the periphery of the solar panel power plant according to the invention, said means typically being a flotation buoy, 
         FIG. 19  is an enlarged view of the buoy in  FIG. 18 , showing the mechanical connection means and the electrically conducting means reaching the buoy, into which a static converter is incorporated, 
         FIG. 20  is an enlarged view of the assembly of solar panels according to the invention, in which the panels are secured to a net of cables, cords or straps, 
         FIGS. 21 and 22  are enlarged views of the mechanical connection means of the assembly in  FIG. 20  and the electrically conducting means connecting the panels to the buoy containing a static converter, and 
         FIG. 23  is a perspective view of peripheral retaining means of the power plant, typically a retaining buoy, showing a system of submerged weights to which the retaining means are connected. 
     
    
    
     In the figures, the fine dash-dotted lines represent arbitrary limits of representation, although in reality the elements continue beyond said lines. 
       FIG. 1  represents a solar panel  1  according to the invention. The panel shown is typically a solar panel with photovoltaic cells  2  arranged on an upper face of the panel  1 . The upper face denotes more specifically a face of the panel which is turned upwards and is exposed to solar radiation. In the example shown, said upper face comprises 60 solar cells of standard sizes 156 mm×156 mm, giving it dimensions of the order of 0.93 m×1.56 m. The solar panel of said example has a surface area of the order of 1.45 m 2 , on the understanding that panels having other dimensions and a different number of cells are also included within the scope of the invention. It will be understood more generally that such a panel has a surface area of less than 4 m 2 , in particular a cell surface area comprised between 1 and 2 m 2 , the criterion being that such a panel should have standard dimensions and be sufficiently compact to allow easy transportation and installation by one or two persons. Conventionally, a solar panel with photovoltaic cells has an output comprised between 0.1 and 0.15 kW/m 2 , for example 0.13 kW/m 2 . A panel having the dimensions of the preceding example of 1.45 m 2  therefore provides an output of approximately 0.19 kW. 
     In order to protect the photovoltaic cells  2 , the latter are typically grouped in a solar module  3  constituted by an upper protective layer made of perfectly transparent tempered glass that may be treated against mosses. The glass can moreover optionally be polarizing, as known to a person skilled in the art of solar photovoltaic modules. The module is also constituted by a lower layer covered with a special film. The photovoltaic cells  2  are inserted by encapsulation between the two layers in a watertight body 
     that is transparent and UV-resistant. The solar module is very resistant to mechanical stresses and to impacts. Within the scope of the invention, the solar module, which is referred to more simply and more generally as “photovoltaic cells”, is mounted in a watertight manner on a unitary buoyant carrying structure. The photovoltaic cells are arranged on an upper face, exposed to solar radiation, of the solar panel  1 . 
     The buoyant structure is called “unitary” in the sense that it is constituted by elements assembled rigidly together in a compact manner, i.e. with no element or portion thereof projecting with respect to the general shape of the panel. As its name indicates, the panel has a generally flattened shape which in a top view is that of a quadrilateral, typically a rectangle having the aforementioned dimensions. 
     Remarkably, the panel  1  according to the invention has a substantially constant thickness in at least one peripheral region. 
     With reference to the embodiment in  FIG. 2 , the panel  1  comprises a chassis  4  having the general shape of a rectangular frame. The sides of the chassis  4  are arranged on the periphery of the panel  1 . The height of the chassis  4  substantially determines the height of the panel. The chassis  4  comprises four corners  5  or metal brackets. These corners  5  are connected in twos by profiles  6  typically made of fibreglass, in order to form the short and long sides of the frame. The profiles have a lower rim  7  turned towards the centre of the panel  1 , said rim constituting a retaining surface of the elements inserted in the chassis  4 . Moving from bottom to top in  FIG. 2 , the stack within the chassis  4  consists of:
         a support plate  8  forming a stiff base of the panel  1 , for example made of fibreglass,   buoyancy means  9  constituted in this example by a buoyant slab for example made of polymer, the function of which is on the one hand to ensure the buoyancy of the panel on the surface of the water, but also to constitute a structural element contributing a high degree of stiffness to the panel (in particular opposing bending and twisting or warping of the panel).   a layer of photovoltaic cells  2  in the form of a solar module  3  as explained previously.       

     In this example, the panel is placed flat, substantially horizontally (theoretical position on the surface of calm water, in the absence of swell). 
     According to a particularly beneficial aspect of the invention, the buoyancy means  9  are included within the thickness of the panel, considered in a direction perpendicular to the upper face of the panel. In the example in  FIGS. 1 and 2 , these buoyancy means even represent almost the thickness of the panel  1 , or at least more than 75% thereof. The buoyancy means are moreover in this example uniformly distributed in the form of a slab below the upper face of the panel  1 . As will be stated subsequently, it is noted that an at least peripheral distribution of the buoyancy means in a peripheral region ensures suitable stability on the surface of the water. 
     The buoyant structure is adapted to position the upper face of the panel  1  in a manner that is substantially flush with the water level (theoretical position in calm water). To this end, the buoyancy properties of the buoyancy means  9  must be adapted to the overall weight of the solar panel  1 , so as to compensate for the effect of gravity on the panel  1  by buoyancy and thus to place its upper face at the required level. This is particularly true in the first embodiment. It will become apparent subsequently that the panel  1  can be kept afloat by other means or with the assistance of other means, in which case this criterion may be less important. 
     In a variant embodiment (not shown) of the buoyancy means, the latter can be constituted by a cellular structure, for example in a honeycomb. 
     The solar panel in  FIGS. 1 to 3  moreover comprises attachment means  10 , constituted in the case in point by a stainless metal ring firmly fixed to each of the corners  5 . These attachment means  10  make it possible to secure together several panels  1  of the same type or to make them fast 
     on a fixed point by means of a system of cables, cords or straps or even rigid rods/link rods. 
     The solar panel of the invention comprises moreover a watertight electrical connector  11  allowing the panel to be electrically connected to a static converter external to the panel as explained hereinafter. Such a watertight connector has for example an IP68 level of protection according to international classification. In the example shown, the watertight connector  11  emerges onto a short side of the chassis  4 , typically in the centre, within the thickness of the edge of the panel  1 . In a variant, the connector can also emerge onto a long side of the panel. In yet another variant, it can be incorporated into the securing mechanism of the panel. 
     Further embodiments are described hereinafter only insofar as they differ from the preceding embodiment. Means that are similar in their structure or function to those previously described have numerical references that are identical or increased by one hundred with respect to the preceding disclosure. 
       FIG. 4  represents a further embodiment of a panel  101  according to the invention, in which the buoyant structure comprises a chassis  104  having the general shape of a rectangular frame in a top view. The chassis  104  is constituted by four quarter-circle or quarter-cylinder corners  105  connected in twos by profiles  106  having a U-shaped transverse cross-section, the opening of the U being turned towards the centre of the panel  101  while the central portion joining the two arms of the U is turned towards the outside of the panel  101 . Preferably, the central portion of the U turned outwards has a rounded shape or at least rounded corners having a smooth appearance, similar to the rounded quarter-circle or quarter-cylinder corners  105 . 
     The chassis  104  in  FIG. 4  comprises an inner rim (not shown) or a retaining peripheral support surface for the stacked elements similar to those previously described (support plate, buoyancy means having the form of a buoyant slab, solar module  103 ). The 
     chassis constitutes a structural element replacing in this instance the chassis  4  of the panel in  FIGS. 1 to 3 . 
     The chassis  104  constitutes moreover a peripheral shock absorbing fender allowing the contact between panels or with any foreign object to be damped. It thus protects the photovoltaic cell module  103  from any damage. It is noted that the peripheral fender can be formed over the entire periphery of the panel. In a variant embodiment, the fender can be localized in some peripheral areas only, for example at the outer corners of the panel. 
     Optionally, such a chassis  104  can additionally provide a buoyancy function, capable of use instead of, or as well as, the buoyancy means situated below the upper face of the panel  101 . To this end, the chassis  104  can be constituted by hermetically sealed profiles  106  (on the open side of the U) or covered with a buoyant material (not shown). The buoyant structure as a whole is adapted, as previously, to float with the upper face of the panel flush with the water level (theoretical position in calm water). 
     The panel  101  is here also equipped with an IP68-level watertight connector  111  emerging onto the outside of the chassis  104 . 
     Attachment means  110 , constituted in the case in point by pins inserted in each of the corners  105  of the panel  101 , allow several panels  101  of the same type to be secured together or anchored on a fixed point by means of a system similar to the one mentioned previously (cables, cords, straps, rigid rods/link rods). 
     According to a further embodiment shown in  FIGS. 6 and 7 , the buoyant structure of the panel  201  comprises a chassis  204  having an outer form similar to the chassis  104  in  FIG. 4 , and is reinforced by an inner frame  204 ′ comparable to the frame  6  in  FIGS. 1 to 3 . The mechanical strength is provided both by the inner frame  204 ′ and by the chassis  204 . Stacked elements are inserted in the buoyant structure ( FIG. 7 ), from bottom to top: a support plate  208 , buoyancy means  209  also contributing to the rigidity of the panel, a photovoltaic cell module  3 . 
     The stacked elements are held by a lower rim or bearing surface  207  provided at the base of the inner frame  204 ′ or at the base of the chassis  204 , the rim in this instance projecting towards the inside of the panel  201  below the inner frame  204 ′ (non shown). 
     The chassis  204  comprises a peripheral fender similar to  104  in  FIGS. 4 and 5 , extending over the entire periphery of the panel or situated in localized areas only. 
     The panel  201  is also equipped with an IP68-level watertight connector (not shown) emerging onto the outside of the chassis  204 . 
     The panel  201  also comprises attachment means  210 , which can be similar to those already mentioned, or in a variant as shown in  FIGS. 6 and 7 , elements protruding with respect to the upper face of the panel  201 . In this example, each element has the form of a horizontal bar connected to the upper face of the chassis and held at a distance therefrom by means of one or two vertical pins. There are four of said protruding elements, substantially situated at the four corners of the chassis  204 . They allow several panels  201  of the same type to be secured together or made fast on a fixed point by means of a system of cables or cords. 
     A further embodiment is also shown in  FIGS. 8 and 9 . The panel  301  comprises a buoyant structure similar to the panel in  FIGS. 1 to 3 . Unlike in the previous instance, the solar module  303  is here provided with a solar concentrator or is arranged so as to optimize the output of the photovoltaic cells  302 . In a non-exhaustive example of the arrangement of the photovoltaic cells inside a solar module, the cells  302  can be covered with polarizing means (not shown) or be arranged for example non-horizontally (for example vertically). In the latter instance, solar radiation reflection means  312 , constituted by concave reflective surfaces, are arranged in the solar module  303 . These concave surfaces can be for example shaped semi-cylindrically, juxtaposed in 
     a generally planar form. The concave portions receiving the cells  302  are turned upwards. A transparent wall  313  covers the reflection means  312 . End plates also close the ends of the semi-cylinders so as to form with the reflection means  312  a hermetically sealed watertight housing. The end plates are for example formed of the short sides or the long sides of the chassis  304  in the form of a frame (short sides in the example shown). Provision can be made for the panel  301  to be constituted by the following stacked elements: support plate, buoyancy means, solar module (from bottom to top). In a variant, provision can be made for the solar module  303  itself to provide the buoyancy of the panel as a result of the volume of air that it encloses in a watertight manner. In the latter instance, the support plate and/or the buoyancy means can be dispensed with. The element  314  within which the reflection means  312  are formed is in this instance structural and contributes to the stiffness of the buoyant structure when combined with the chassis  304  in the form of a frame. The hollow and protruding forms act in a similar manner to stiffening ribs and oppose in particular the bending and twisting of the panel. 
     The panel  301  is here also equipped with an IP68-level watertight connector  311  emerging onto the outside of the chassis  304 . 
     Attachment means  310 , constituted by rings connected to each of the corners of the panel  301 , allow several panels  301  of the same type to be secured together or made fast to a fixed point by means of a system similar to the one mentioned previously (cables, cords, straps, rigid rods/link rods). The buoyant structure constituted is adapted for the panel to float such that the upper face of the panel  301  is flush with the water level (theoretical position in calm water). 
       FIGS. 10 and 11  show a further embodiment of the solar panel  401  according to the invention, in which the solar module  403  is incorporated into a buoyant structure arranged above the photovoltaic cells  402  or entirely covering them. The buoyant structure comprises a flexible or rigid pneumatic envelope  415  closed on itself in a watertight manner. The latter is for example made of 
     polymer. The envelope has a generally rectangular shape in top view, the peripheral edges coinciding substantially with those of the solar module  403  comprising the photovoltaic cells  402 . The envelope  415  comprises an upper wall  416  that is transparent or translucent or at least permeable to solar radiation. The side walls  417  can also be permeable to solar radiation. The envelope has an upper portion having at the centre a slightly domed or substantially planar shape, the peripheral portions also being rounded around the peripheral edges of the solar module  403 . The buoyant structure is structural in this instance and provides the stiffness of the assembly. The solar power collecting means, in the case in point the photovoltaic cells, are situated inside and at the base of the envelope  415 . As shown in this example, the upper face on which the photovoltaic cells are arranged is not necessarily a face situated at the top of the panel, but a face turned upwards. 
       FIG. 12  shows a further embodiment of a panel  501  according to the invention. The latter comprises a buoyant structure constituted by a pneumatic envelope  515  as in the previous instance. The structure comprises moreover a support plate  518  on which the solar module  503  is arranged, the cells being situated on an upper face, i.e. turned upwards. The envelope can be closed on itself in a watertight manner, or can be connected in a watertight manner to a peripheral area of the support plate  518 , around the solar module  503 . The support plate  518  contributes to the stiffness of the assembly (opposing bending, bending or warping). 
     The panel  411  is also equipped with an IP68-level sealed connector  411  emerging onto the outside of the carrying structure, for example below the solar module  403  or the support plate  518 . 
     In the examples in  FIGS. 10 to 12 , attachment means  410  for example constituted by securing rings can be provided at the four corners of the panel  401  in order to connect together several panels of the same type or to connect them to a fixed point, by means of a system similar to that previously mentioned (cables, cords, straps, rigid rods/link rods). 
     The buoyant structure constituted is adapted for the panel to float such that the upper wall  416 ,  516  of the envelope  415 ,  515  is flush with the water level (theoretical position in calm water). 
       FIGS. 13 and 14  represent yet a further embodiment of a panel  601  according to the invention. The panel comprises a buoyant structure constituted by a pneumatic sponson (or float)  615  having the general shape of a rectangular frame. Its arms have for example a substantially circular transverse cross-section. The sponson  615  is situated on the periphery of the panel  601 . The solar module  603  incorporating the cells  602  is mounted on a support plate  618  having a generally rectangular shape corresponding substantially to the shape of the solar module. The support plate  618  is mounted and fixed on its periphery on an upper area of the pneumatic sponson  615 . 
     The buoyant structure constituted by the adjacent support plate  618  and the pneumatic sponson  615  is stiff and resistant to the effects of bending, twisting or warping. 
     The panel  601  is equipped with an IP68-level sealed connector  611  emerging onto the outside of the buoyant structure, for example below the support plate  618 . 
     Attachment means  610  constituted by securing rings are provided at the four corners of the panel  601  in order to connect together several panels of the same type or to connect them to a fixed point, by means of a system similar to that previously mentioned (cables, cords, straps, rigid rods/link rods). 
     The buoyant structure is adapted for the panel  601  to float such that the upper face is flush with the water level (theoretical position in calm water). 
       FIG. 15  represents yet a further embodiment of the panel  701  according to the invention, wherein the buoyant structure is constituted by a solar module  703  having photovoltaic cells  702  and a support plate  718  of the same type as those in  FIGS. 13 and 14 . 
     The solar module  703  is here mounted on “natural” buoyancy means  715  of the bamboo cane or wood log type or other equivalent elements having a low environmental impact, such as recycled plastic bottles. In the example shown in  FIG. 15 , the structure is constituted by two superimposed layers of bamboo rods or logs juxtaposed in parallel in each layer, the bamboo canes of the two adjacent layers being perpendicular to each other. It is understood that any configuration comprising at least two layers of bamboo rods or logs falls within the scope of the invention. It is perfectly possible to envisage an arrangement of three layers or even more. As in the embodiments previously described, the panel  701  is equipped with an IP68-level watertight connector  711  emerging onto the periphery of the buoyant structure, for example below the support plate  718 . 
     Attachment means  710  constituted by securing rings are provided at the four corners of the panel  701  to connect together several panels of the same type or to connect them to a fixed point, by means of a similar system to the one previously described (cables, cords, straps, rigid rods/link rods). 
     The buoyant structure is adapted for the panel  701  to float such that the upper face is flush with the water level (theoretical position in calm water). 
     Each panel  1 - 701  of the invention previously described constitutes a basic component of a larger power plant that is also a subject of the present invention. This power plant constitutes a “field” or “set” of solar panels  1 - 701  such as those previously described, which are individually buoyant when installed, the panels being juxtaposed and secured together by systems of cables or cords to form a net. This net can have a generally rectangular or square shape in top view, as shown in  FIG. 16 . 
     Without exceeding the scope of the invention, the net can have other geometrical shapes in top view, for example circular, hexagonal or other. 
       FIG. 16  represents in top view an example of such a power plant comprising a net having the appearance of a matrix: in fact 
     in this example the solar panels  1 - 701  are aligned with each other in rows and columns. 
     The example represents 240 solar panels  1 - 701  aligned in 20 columns each of 12 panels. In this example it is assumed that the rectangular panels  1 - 701  have dimensions of 1.56 m×0.93 m, and that a gap d of the order of 0.30 m is made between each panel (in this instance, between two adjacent rows and between two adjacent columns). Other panel dimensions can be envisaged. The connection and said gap between the panels are provided by a system of cords or cables. It is noted that such a gap between the panels advantageously provides for the passage of light between the panels, allowing good conditions for photosynthesis on the sea bed to be maintained and avoiding disturbance to the environment for flora and/or fauna. In some situations, it is appropriate to avoid the power plant forming a screen with large dimensions which would be harmful to the environment. The net of panels  1 - 701  is held on the periphery and/or subjected to outward peripheral traction, under the effect of peripheral retaining means  20 ,  21 . These include buoys  20  situated around the net of panels  1 - 701 . In the example described, four buoys  20  situated at the four corners of a rectangle or square are connected together in twos by four linkages  21  constituted by substantially tensioned cables or cords or straps. In a variant embodiment, said linkages can be constituted by rigid rods which moreover can contain the electrical connection or pneumatic elements or connecting links with the panels. The linkages  21  produce a rectangular or square form of the power plant. The buoys are immobilized as will become apparent hereinafter. The distance D between each panel situated on the outside of the net and the adjacent linkage is approximately 1.5 m (non-limitatively, by way of illustration only). The set of panels connected to each other is attached on the periphery to the linkages  21  by means of cords or cables or straps or rigid peripheral link rods  22 . Given the aforementioned dimensions, in this example, a field (or net) of solar panels  1 - 701  is obtained having dimensions of the order of 30.31 m by 28 m (L×H), i.e. roughly square in shape. 
     According to a particular embodiment of a power plant according to the invention, the panels  1 - 107  are secured directly to each other by means of a system of cords or cables or straps  23  connecting their chassis or their fenders. The structure of each panel by itself provides for the take-up of stresses, essentially tensile forces in the general plane of the set of panels  1 - 107 .  FIG. 17  represents an example of this type of power plant, the panel  107  shown being of a particular type previously described, on the understanding that other types of panels falling within the scope of the invention can be also used, in particular panels referenced  1 ,  201 - 701 . In this example, four panels  107  arranged in a square are connected diagonally in twos by a set of two cords  23  crossing at their centre. The cords  23  can be free or joined at their crossing point. 
     On the periphery, the panels are also connected to the linkages by cords or cables or connecting straps  22 . 
     Moreover, conducting cables  24  electrically connect the panels  1 - 107  to an external static converter. To this end, the panels  1 - 107  can be connected to an external cable or to a common network by means of their single connector  11 - 711  or by means of two connectors provided on each panel, the panels being in the latter instance provided with integrated electrically conducting means and capable of being arranged in series (which limits the routing of the electricity cables on the outside of the panels and thus ensures better protection of said cables). 
     With reference to  FIG. 18 , one corner of the solar panel power plant  101  is shown. As is apparent in this example, inner linkages  25  can be provided to supplement the linkages  21  connecting the buoys situated at the corners of the power plant. These inner linkages are for example situated between each column and each row or line of solar panels  101 , so as to also form a net or a matrix. The panels  101  are connected or secured to said net or to said common matrix of cables or cords or straps by means of their buoyant structure, in particular their chassis or by means of their fenders. Said inner linkages  25  provide the mechanical strength of the power plant assembly, by withstanding all or some of the tensile stresses 
     applied to the panels towards the outside of the power plant (through the retaining means and also by the effect of the swell). The mechanical stresses applied to the panels  101  are thus considerably reduced, making it possible to have only the necessary dimensions and therefore a reduced cost of the panels. 
     It is noted with reference to  FIGS. 18 and 19  that the conducting cables electrically connected to the solar panels  101  are also connected to a static converter (not shown) advantageously housed in one of the buoys  20  of the power plant. The buoy is thus equipped with a watertight opening system (not shown) and comprises a fully watertight enclosure protected from external attack. In a variant of the invention (not shown), the static converter can be situated in another enclosure close to the power plant or remotely. An electrical connection is also provided between the convertor and a power plant or a remote electricity network. 
       FIGS. 20 to 22  represent in perspective view and at different angles a further embodiment of the power plant of panels  101  according to the invention. 
     This embodiment is very close to that in  FIG. 18 , with the only difference being that floats  26  are provided on the net or matrix of cords, cables or straps (inner linkages  25 ), as well as on the outer linkages  21  of the retaining means. 
     The floats  26  are distributed over the entire length of the linkages  21 ,  25  and are spaced apart in twos by approximately 0.5 m to 1 m (other arrangements are possible). Thus the net (or matrix) is itself buoyant. The buoyancy means incorporated into the panels can be retained as explained in the examples previously described or can optionally be made lighter or reduced or even dispensed with in order to simplify the structure of the panels and reduce their production cost. 
     In this example,  FIGS. 21 and 22  represent the electrical connection between the different panels and the static converter, provided by conducting cables  27  routed along the inner linkages  25 . 
     The buoys  20  are immobilized by a system of submerged weights  28  (dead weights) situated approximately 15 to 30 m, for example 20m, below the buoy  20  and resting on the bed  29  of the body of water. The invention is thus applicable in particular to marine environments or other aquatic environments having a water depth of approximately 15-30 m. Further embodiments can also be envisaged within the scope of the invention. The connection between the buoys  20  and the weights can be provided by a chain  30 , a cable or any other equivalent means. In the non-limitative example in  FIG. 23  three weights  28  of 5 tonnes each are provided. 
     In the event of installation in a marine environment, compensation means for the height h of the set of panels  1 - 107  with respect to the sea bed  29  are provided in order to adapt continuously and automatically to the tides (for example an adequate length of chain connecting each buoy  20  to the submerged weights  28 ). 
     Solar panels having photovoltaic cells have been described above. The invention can be applied similarly to solar thermal panels (heat exchanger/heat pump; this embodiment is not shown). Such a panel according to the invention comprises means of heat exchange combined with a buoyant structure. The panel thus constituted can be made fast to further panels in a manner comparable to that described for solar photovoltaic panels. Ducts can be tilted in order to ensure satisfactory operation of the device. Pipes connect the panels to an external device using or treating the water heated by the solar panels. 
     In a variant, the power plant can be constituted by of a mix of solar photovoltaic panels and solar thermal panels. 
     In the event of moving the solar power plant on the surface of the water, the linkages can be provided, optionally in a temporary and detachable manner, with means that are rigid under tension/compression, for example rigid rods or braces (connecting the buoys), ensuring that the power plant retains its general shape and that the panels do not knock together, releasing the anchoring of the buoys. 
     In a variant embodiment of the invention, rigid buoys having longitudinal shapes can be provided and installed on the sides of the polygon, for example on the four sides of the rectangle formed by the solar panel power plant. These rigid buoys are connected in twos at their ends and keep the general shape of the peripheral part of the power plant. They also facilitate the operations of moving the power plant. 
     It has also been stated that each solar panel according to the invention has a substantially constant thickness in a direction perpendicular to the upper face of the panel. This configuration can be permanent using a non-modifiable or convertible panel. On the other hand, in a variant embodiment (not shown) of the invention, the solar panel according to the invention is capable of being converted between a first configuration in which the panel effectively has a substantially constant thickness in a direction perpendicular to the upper face of the panel, and a second configuration in which the thickness is not constant, the upper face of the panel being in the latter instance inclined with respect to the horizontal, for example for increased exposure to light or to solar radiation. 
     Of course, the invention is not limited to the means that have just been described and comprises all the technical equivalents.