Abstract:
The invention relates to an absorber ( 40 ) for a solar panel, provided for containing a heat transfer fluid ( 42 ), including first ( 44 ) and second ( 46 ) plates arranged opposite each other and attached to each other via a plurality of connection points ( 58, 60 ), first and second matrices having protruding geometrical shapes ( 50, 52 ) formed on the outer surfaces of the first and second plates, respectively, the matrices being offset relative to each other so as to provide a flow path for the heat transfer fluid in the absorber, an inlet ( 54 ) and an outlet ( 56 ) for the heat transfer fluid arranged at both ends of the heat transfer fluid flow path, respectively, characterized in that at least some of the geometrical shapes have a generally protruding shape with a recess at the center thereof so as to form a cavity ( 64, 66 ), and in that at least some of said non-through connection points are provided in at least some of said recesses.

Description:
REFERENCE TO RELATED APPLICATIONS 
     This application is the U.S. nationalization of PCT/EP2009/050119, filed 7 Jan. 2009, which is hereby incorporated by reference. This application claims priority from Patent Application No. EP 08106014.7, filed 18 Dec. 2008, which is hereby incorporated by reference. 
     TECHNICAL FIELD 
     The present invention relates in general to a thermal solar panel consisting of converting light into heat. More particularly, the present invention relates to an absorber for such a solar panel provided to contain liquid or heat-bearing fluid. 
     TECHNOLOGICAL BACKGROUND 
     The prior art discloses numerous types of thermal solar panels comprising an absorber containing heat-bearing fluid which may be water for example, water mixed with an antigel or even just air. 
     According to a first category of thermal solar panels illustrated in  FIG. 1 , these panels  1  comprise an absorber  2  formed by tubes  3  fitted with fins in which heat-bearing fluid circulates in closed circuit. The tubes are heated conventionally by solar radiation and transmit heat to the heat-bearing fluid which circulates inside these tubes. For a higher yield, the absorber is placed in a glazed insulating box, not illustrated here, to get a greenhouse effect. A reflector is usually arranged under the tubes to further boost heat recovery. 
     Another existing type of absorber comprises a metal plate arranged under the glass panel, and under which are arranged fine metal conduits containing heat-bearing fluid and winding over the entire length of the panel. 
     Such thermal solar panels have a number of drawbacks, including more especially the mechanical complexity and fragility of the absorber as well as a relatively low yield due to the low volume of heat-bearing fluid for a determined glazed surface of the solar panel. 
     According to a second category of thermal solar panels, known especially from document CH 624 753, the solar sensor  1 , shown in  FIG. 2 , comprises two metallic plates  2 , between which heat-bearing fluid circulates. Pads in the form of bosses  4  are foamed at regular intervals on the metal plates  2 . The bosses of one metal plate are offset by a semi-boss relative to those of the other plate. The two metal plates  2  are welded together by means of welding beads  6  made by a roller and arranged so that a turbulent flow of the heat-bearing fluid circulating between the plates is generated. With such a solar sensor, a higher yield can be attained independently of the position of the sun. Also, the turbulent flow brings good heat exchange between the plates metal and heat-bearing fluid. Such a solar sensor can be made at less cost and be easily mounted on the exterior of a roof. 
     Even though the solar sensor presented within the scope of document CH 624 753 has a higher yield and is mechanically simpler than those comprising tubes, it still has some drawbacks, in particular resistance to pressure exerted by heat-bearing fluid on the metal plates of the sensor. In fact, it has been noted within the scope of the present invention that in normal usage conditions dilation of heat-bearing fluid contained in the sensor causes pressure on the plates, inducing the welding beads located between the bosses to give way. 
     Document WO 01/14080 in particular also discloses a heat exchanger  23 , illustrated in  FIGS. 3   a  and  3   b , comprising two walls  13 ,  15  connected specifically by compression and forming into a plurality of points  11  then sealed at their edge  25 . Although this type of alternative solution enables a stronger join of the two walls  13  and  15 , it also means some drawbacks and in particular needs a relatively large flat space  19  around each connection point  11 . The need for such space  19  makes it difficult to implement on a solar sensor structure such as presented in document CH 624 753. In fact, if the space between the bosses is increased, all the more reducing the communication surfaces between the bosses of the two plates and resulting in making the path of the heat-bearing fluid less efficient, then this space is kept as such and in this case the risk of perforation of a boss is considerably higher and the tightness of the sensor is threatened. 
     SUMMARY OF THE INVENTION 
     The aim of the present invention is to respond to the above-mentioned drawbacks, at the same time retaining advantages associated with the second category, by providing an efficacious absorber, that is, having optimised heat yield, but also simple, robust and tight, that is, able to reliably support the pressure of heat-bearing fluid which it contains. 
     To this end and according to a first aspect, the present invention relates to an absorber for a solar panel, provided to contain heat-bearing fluid, comprising first and second plates arranged opposite one another and fixed to one another by means of a plurality of connection points, first and second matrices of geometric shapes protruding, formed on the outer faces respectively of the first and second plates, the matrices being offset relative to one another so as to trace a circulation path for heat-bearing fluid in the absorber, inlet means and outlet means of heat-bearing fluid arranged respectively at one end and at the other end of the circulation path of the heat-bearing fluid, wherein at least part of the geometric shapes has a general protruding form, hollow in its centre so as to define a cavity, and in that at least some of said connection points, non-traversing, are arranged in at least some of said cavities. 
     In this way, it is possible to keep joined together the two plates by using a limited number of connection points without diminishing the communication surfaces between the protuberances of the two plates and without risk for tightness of the absorber to the extent where the cavities ensure sufficient space to make an efficacious connection point. The resulting absorber is remarkable in that it combines obtaining good heat yield with a fixing system via non-traversing connection ensuring excellent hold and perfect tightness between the plates. 
     According to an advantageous variant embodiment, the hollow geometric shapes have a general annular protruding form. Such a form has the advantage of being simple and therefore easily swageable while ensuring an optimised communication surface between the annular forms of a plate with the offset forms of the other plate. Also, it has been shown within the scope of the present invention that the path of the resulting heat-bearing fluid both maximises the sinuous character of the path travelled by the heat-bearing liquid, ensuring optimised heat yield, and also avoiding losses of heat-bearing fluid via the absorber on the possible angles of the geometric shapes of the matrix able to cause unwanted excessive dilation for reasons of mechanical resistance of the absorber. 
     According to another advantageous variant embodiment, the non-traversing connection points located in cavities are made by mechanical deformation of the two plates so as to join them together. The non-traversing connection points preferably located in cavities are points for clinching the two plates together. It is evident in this respect that the clinching is a mechanical assembly technique of plates, whereof the principle consists of connecting the two plates by stamping between a punch and a matrix without extra material. Even though such a solution requires a considerable space around the clinching point, it proves particularly robust while being rapid, and perfectly adequate due to the cavities in which these connection points are made. Alternatively, the non-traversing connection points located in cavities are rivets swaging the two plates together without perforating any of them. 
     According to another advantageous variant embodiment, a continuous connection at the periphery of the plates is obtained by ultrasonic welding or laser fusion or welding of the two plates together. The major advantage of using welding by ultrasound or laser fusion or welding is fixing the two plates tightly together, without leaving shavings from plates or other waste material between the plates. Also, this type of continuous welding proves to be faster than traditional welding techniques, this advantage being amplified by the continuous character of the welding. Advantageously, at least one ultrasonic welding or laser fusion or welding line of the two plates is added between the geometric shapes. Adding such welding lines while retaining the advantages of this type of welding without waste reinforces holding the plates together. 
     According to another advantageous variant embodiment, the inlet means and outlet means of the heat-bearing fluid are arranged diagonally opposite on the external face of one of the two plates. These inlet and outlet means ensure circulation through the absorber and are localised on the external face of the lower plate, once mounted in a panel, such that the joints used are protected from direct exposure to light radiation, which could alter their tightness while retaining maximal surface exposure on the external face of the upper plate of the absorber as well as protection of the glass plate of the panel intended to cover the absorber. Advantageously, these inlet means and outlet means are end fittings arranged on a flat portion of the lower plate opposite to a geometric form of the upper plate to reduce the total thickness of the absorber. 
     According to a second aspect, the present invention relates to a thermal solar panel comprising an absorber ( 30 ) arranged in a frame ( 31 ) and covered by a glass plate ( 32 ), in which is mounted an absorber as claimed in any one of the variants according to the first aspect and provided to contain the heat-bearing fluid. 
     According to an advantageous variant embodiment, the lower plate of the absorber is supported by inner rims of the panel. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       Other characteristics and advantages of the present invention will emerge from the detailed following description of embodiments of the invention given by way of non-limiting examples. 
         FIG. 1 , already described, illustrates a first type of absorber for thermal solar panel according to the prior art; 
         FIG. 2 , already described, illustrates a second type of absorber for thermal solar panel according to the prior art; 
         FIGS. 3   a  and  3   b , already described, illustrate a third type of absorber for thermal solar panel according to the prior art; 
         FIG. 4  illustrates a plan view of an absorber for thermal solar panel according to a preferred embodiment of the present invention; 
         FIG. 5  is an enlargement of portion of the absorber according to the preceding figure; 
         FIGS. 6   a ,  6   b ,  6   c  and  6   d  illustrate sectional views respectively according to the axes I-I, II-II, III-III and IV-IV, of  FIG. 5 ; 
         FIGS. 7   a ,  7   b ,  7   c ,  7   d ,  7   e , and  7   f  illustrate different stages for executing a manufacturing process of an absorber according to an embodiment; 
         FIG. 8  schematically illustrates an example of a thermal solar panel incorporating an absorber. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention will be described hereinbelow solely by way of example in relation to  FIGS. 4 to 8 . Reference is made initially to the  FIG. 4  which illustrates a plan view of an absorber for a solar panel according to a preferred embodiment of the present invention. The absorber  40  for solar panel is provided to contain heat-bearing fluid  42 . The absorber is mainly made by means of two metal plates superposed and fixed together tightly. In this figure, only the upper plate  44  is visible, the lower plate ( 46 ,  FIG. 6   a ) being located underneath. 
     A continuous connection  48  obtained by ultrasonic welding or laser fusion continue of the two plates ensemble is advantageously provided for tight fixing on the periphery of the plates. This first solution proves the simplest and the fastest to carry out, at the same time ensuring proper peripheral tightness. An alternative solution, though less interesting due to being more complex to execute, consists of folding the edges of one of the two plates then sliding the other plate into the gap left between the folded plate and the fold and finally welding the two plates now attached. Another possible solution, equally less interesting c due to being more complex to execute, consists of folding the edges of the two swaged plates at least once onto one another, preferably twice, and wedging them between two flat rods providing a sandwich effect, then applying thereto a rivet at regular intervals to pinch them without passing through the now folded rim and making them tight. Preferably, a 3M adhesive called ‘sealskin’ is added in between the plates to fully guarantee tightness. This latter solution based on a mechanical crimping system, even though not as easy to implement, proves more solid than the second solution based on welding attached plates, and gives the absorber a rim which is firmer and more rigid for easier handling and placing in the solar panel. It is also noted that the rods, for example made of brass or steel, are cut out at angles of the plates so that they do not overlap, while the tight fit of the corners can be ensured by welding. 
     Each of the plates  44 ,  46  is swaged so that its outer face, that is, the face not in contact with the other plate, is covered by a matrix of geometric shapes. The upper plate  44  is therefore covered by a first matrix of geometric shapes  50  protruding on its external face, while the lower plate  46  is covered by a second matrix of geometric shapes  52  equally protruding on its external face. 
     The two matrices are therefore both inverted relative to one another such that the protuberances of the geometric shapes are oriented to the exterior of the absorber and also relative to one another to the exterior of the absorber and also relative to one another to form a circulation path for heat-bearing fluid  42  in the absorber between the inlet  54  and the outlet  56  of the heat-bearing fluid. The inlet and the outlet are preferably made in the form of admission and evacuation end fittings arranged respectively at one end and at the other end of the circulation path for heat-bearing fluid. So for example the inlet end fitting  54  is used to introduce non-heated heat-bearing fluid into the absorber  40 . Next, the heat-bearing fluid  42  passes through the entire absorber by winding through the two matrices to exit heated via the outlet means end fitting  56 . 
     To ensure that the plates are held together firmly, and are capable of resisting pressure exerted by the heat-bearing fluid  42 , the plates  44  and  46  are fixed to one another by means of a plurality of connection points  58 ,  60  non-traversing, distributed over the surface of the absorber. The detail of the arrangement of these connection points relative to forms geometric shapes will be explained in detail hereinbelow in conjunction with  FIG. 5 . With a view to reinforcing the plates being held together, one or more ultrasonic welding lines  62  or laser fusion lines of the two plates can also be provided. These welding lines  62  are distributed over the surface of the absorber and arranged between the geometric shapes  50 ,  52 . 
     It is evident that the geometric shapes  50 ,  52  have been illustrated as identical in  FIG. 4 . But, it is evident that it is perfectly feasible to provide geometric shapes of different shapes to the extent where communication surfaces are provided between the forms  50  of the upper plate and the forms  52  of the lower plate. 
       FIG. 5  is an enlargement of a portion of the absorber of  FIG. 4  illustrating in detail the geometric shapes according to a preferred embodiment of the invention. The geometric shapes  50 ,  52  advantageously have a general annular protruding form. But, it is understood that other forms could also be used, such as for example an open annular form or again a polygonal band form. More generally, it is provided that at least some geometric shapes, and preferably all, are hollow in their centre and define a cavity  64 ,  66 , preferably flat, and that connection points  58 ,  60 , non-traversing, are arranged in at least some of the cavities, preferably all. 
     It is also evident from  FIG. 5  that using an annular form both for the forms swaged on the upper plate and those swaged on the lower plate has the advantage of providing communication surfaces  68  optimised for the path of heat-bearing fluid. According to a preferred variant, the rings of the two surfaces are the same size and offset such that the centre of one ring A located on a surface is far from the centre of each of the adjacent rings B, C, D and E located on the other surface by a length equal to an external radius of a ring plus an inner radius of a ring. Such overlapping of rings gives the best compromise between the size of the communication surface  68  to the extent where the entire bandwidth of a ring covers at a maximum the entire bandwidth of the adjacent ring on the other surface, and the size of the cavity in which the connection point is made, which corresponds to the internal disc of a ring and is therefore maximal. 
     The non-traversing connection points  58 ,  60  located in the cavities  64 , respectively  66  are made by mechanical deformation of the two plates in the cavity so as to join them together. An advantageous solution consists of making clinching points. These clinching points can be obtained simply by stamping between a punch and a matrix of the cavity to be clinched. Finished examples of clinching points are given in document WO 01/14080. Alternatively, rivets fitting the two plates together can be used without perforating them. The rivets are preferably cylindrical and advantageously have an empty space for fitting plates without perforation of the latter, the material being deformed inside this recess. The interior of the rivets can be soaked in adhesive to reinforce the hold of the fitted plates. Another alternative comprising ultrasonic welding or laser fusion at the level of the cavities could be equally feasible even if it does not fully offer the same guarantee of stability to pressure of the entire absorber. 
       FIGS. 6   a  and  6   d  illustrate sectional views respectively according to the axes I-I, II-II, III-III and IV-IV, of  FIG. 5 , distinguishing the connection points made by clinching, as well as the communication surfaces between geometric shapes defining the path of the heat-bearing fluid. 
     Section I-I, illustrated in  FIG. 6   a , has been selected such that the geometric shapes  50  of the upper plate  44  and the corresponding connection points  58  are visible. The annular form of at least some geometric shapes, such as forms  50   a  and  50   b , defines a central cavity  64   a , respectively  64   b , in which a connection point  58   a , respectively  58   b  is provided, preferably by clinching together of the two plates  44  and  46 . 
     The section II-II, illustrated in  FIG. 6   b , has been selected such that the geometric shapes  52  of the lower plate  46  and the corresponding connection points  60  are visible. The annular form of the form  52   a , respectively  52   b , defines a central cavity  66   a , respectively  66   b , in which connection point,  60   a , respectively  60   b  is provided, preferably by clinching together of the two plates  44  and  46 . 
     The section III-Ill, illustrated in  FIG. 6   c , has been selected such that the geometric shapes  50  and  52  of the two plates  44  and  46  as well as the corresponding connection points  58  and  60  are visible. In this figure the communication zones  68   a  and  68   b  optimised between the first ring  50   a  of the upper plate and the ring  52  of the lower plate and respectively between this ring  52  and the second ring  50   b  of the upper plate are initially evident. It is then evident that it is possible to make the connection points  64  from one and/or from the other side of the absorber. The example illustrated in this figure consists of making the connection points located in the cavities of the rings of the upper plate from the side of the lower plate and inversely. It is understood that other side of the lower plate and inversely. It is understood that other alternatives are feasible. 
     Finally, section IV-IV, illustrated in  FIG. 6   d , has been selected so as to make visible the communication between the geometric shapes of the two surfaces without the connection points between the plates being visible. In this figure, the resulting path of the heat-bearing fluid through the absorber is easily identified. In fact, from the viewpoint of the start at the level of the ring  50   a  located on the upper plate, it is obvious that the liquid it contains will spread in the ring  52   a  located on the lower plate, which in turn will spread the liquid which has circled the ring  52   a , to the ring  50   b  located on the upper plate, which will similarly spread the liquid to the ring  52   b , which spreads it to the ring  52   c  and so on until it reaches the end outlet means of the absorber. This is how, as planned, winding circulation of heat-bearing fluid through the absorber is achieved. 
       FIGS. 7   a  to  7   f  illustrate the different stages for carrying out a manufacturing process of an absorber according to an embodiment. First,  FIG. 7   a  illustrates a roller, for example made of copper, aluminium, stainless steel or thermoplastic material, serving as primary material for the plates. Since the material used for the upper plate, specifically that subjected to solar radiation, and the lower plate can be different, a roller is preferably used for each type of plate, lower or upper. So for example the material used could be copper for the lower plates, while for the upper plates the copper will be chromed in advance and rolled separately. This chroming can for example be done by copper-plating a substrate by depositing an initial layer of nickel and a final layer of black chrome. According to the preferred size of the absorber, and therefore of the solar panel, a first stage comprises severing first and second plates from the roller or rollers used. Next, as shown in  FIG. 5   b  and using a press having a matrix of preferred forms, a second stage comprises swaging the first plate to cut out a first matrix of corresponding geometric shapes then swaging the second plate with offset using a press to cut out a second matrix of geometric shapes offset relative to the first matrix of the first plate. It is noted that advantageously the matrix of geometric shapes of the press is asymmetrical and that the swaging steps are simply completed by introducing the first, respectively the second (illustrated in dotted lines), plate at one end, respectively at the other end, of the press. It is also evident that the press also comprises at two of its ends arranged diagonally to the removable peaks for perforating at preferred points two holes on the lower plate on which will be mounted the end fittings of the inlet and outlet means of the heat-bearing fluid, the peaks being removed when the upper plates exit the absorber.  FIG. 5   c  illustrates a stage comprising placing the end fittings at pierced points provided for this purpose, either by screwing or welding or by any other adequate method ensuring proper tightness.  FIG. 5   d  illustrates the stage comprising arranging the two plates so that the matrices of forms have the preferred offset and tightly fixing the rims of the two plates together. The lower plate is illustrated in this figure under the upper plate. This tight fixing stage is advantageously completed by continuous ultrasonic welding of the rims. Other alternatives for tightly fixing the rims of the plates together have been described earlier. The additional welding lines between the geometric shapes will be made preferably at this time, in the event where they are provided. It is also noted that this fixing stage can be carried out after that explained above.  FIG. 5   e  illustrates an important stage comprising connecting the two plates together without traversing them. The example illustrated in this figure refers to the solution for connection points obtained by riveting. It is clear that connection via clinching of the two plates between a matrix and a punch at preferred points could be done in the same way. Advantageously, tightness tests are conducted on the resulting absorber, as illustrated for example in  FIG. 5   f . The opening of one of the two end fittings is blocked by a stopper, whereas the other opening is connected to a tube putting the absorber under pressure. In this way, any deficiency in the tight connection of the two plates is located and can be repaired. It is clear that in the event where the upper plate is chromed, it is preferably covered by a plastic protective film from the outset of the process, and is removed only at the last moment during installation of the absorber in the frame of the solar panel. Finally, the absorber obtained according to this type of manufacturing process is similar to that illustrated in  FIG. 4 , and is intended to be incorporated in a thermal solar panel. 
       FIG. 8  illustrates schematically an example of a thermal solar panel incorporating an absorber. In this figure, the geometric shapes have been illustrated schematically in the form of a disc for simplification. The absorber  40  is arranged in a frame  72  and covered on the top by a glass plate  70  giving a greenhouse effect between the latter and the preferably blackened upper plate of the absorber. The thermal solar panel also comprises a mechanism ensuring circulation of heat-bearing fluid in the absorber between the first inlet end fitting of the liquid and second outlet end fitting means for evacuating heat-bearing fluid, once heated, through the absorber. As this mechanism is not directly associated with the principle of the present invention, it has not been shown here. According to an advantageous variant embodiment, the lower plate of the absorber is supported by inner rims of the panel. 
     By way of remarks, it is clear that using copper as metal for the upper plate has the advantage of being a good conductor having good heat yield. Also, copper can be more easily fitted, which makes geometric shapes with greater relief, thus increasing the volume of heat-bearing fluid. The lower metal plate could be aluminium, which is more resistant and stiffens the whole absorber while reducing its thickness. This also ensures proper support on the inner rims of the solar panel incorporating the absorber. 
     It is evident also that using non-traversing connection points ensures not only tightness of the interior of the absorber, without waste, but also excellent holding together of the plates, as opposed to traditional fixing by welding the plates together and risking being detached during dilation of the heat-bearing fluid contained by the absorber. The total tightness of the absorber is obtained by tightly fixing the rims of the two plates together. 
     It is clear that various modifications and/or improvements evident to the expert can be made to the abovedescribed present invention without departing from the scope of the invention as defined by the attached claims. In particular, it is clear that the geometric shapes are not necessarily all the same. For example, some forms can be annular and others forms can be circular. There could also be the possibility of having annular forms on a plate and disc forms (i.e. dome) on the other plate. Also, it is clear that connection points are not necessarily present in each hollow form. Finally, it should be noted that the hollow forms intended to receive a connection point in their cavity can have different forms, including an annular, circular or annular elliptical form, open or closed, a hollow polygonal form, for example rectangular or diamond-shaped, or any other hollow form leaving a central cavity sufficiently large to make a connection point.