Abstract:
A segment of a solar collector including a top side, a bottom side and a circumferential end face having at least one longitudinal side, wherein the longitudinal side forms a top edge with the top side and forms a bottom edge with the bottom side, and comprises a core structure having at least one core made of foamed material. The segment of a solar collector further includes a shell made of one or a plurality of layers of a fiber material, wherein the shell at least partially covers the top side, the bottom side and at least the longitudinal side of the circumferential end face, wherein at least one layer of the shell extends about the top edge and at least one layer of the shell extends about the bottom edge, and a reflection layer disposed on the top side.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation application of U.S. patent application Ser. No. 13/383,926 filed on Jun. 14, 2010 which is the United States national phase of International Application No. PCT/EP2010/058284 filed Jun. 14, 2010, and claims priority to German Patent Application No. 10 2009 033 490.4 filed Jul. 15, 2009, the disclosures of which are hereby incorporated in their entirety by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to the design of solar collectors and the design of segments of a solar collector. Solar collectors are often used in the form of parabolic-trough concentrators in power plants, or for recovery of process heat. 
         [0004]    2. Description of Related Art 
         [0005]    Such large-scale plants can largely consist of a plurality of serially arranged solar collectors with trough-shaped reflectors which will direct the sunlight onto a tubular absorber. For orienting the solar collectors corresponding to the sunlight, it is known to rotate the trough-shaped reflectors about their longitudinal axis. In order to reduce the apparatus-related expenditure when using this approach, it is mostly provided that, with the aid of a drive unit, a plurality of serially arranged reflectors are rotated simultaneously. 
         [0006]    Since, in this manner, constructions having a length of up to 120 m are to be rotated, the trough-shaped reflectors must have a high torsional stiffness so that the deviation of the rotational angle during rotation of the reflectors cannot exceed a mere minimum. 
         [0007]    In the past, for this reason, solar collectors were often built from steel constructions with mirrors mounted thereon, however at the penalty of a massive weight of the solar collectors. Further, complex support structures were required, and the weight resulted in high costs for transportation. Frequently, the reflectors had to be built in situ from individual components, thus causing considerable assembly work at the installation site. 
         [0008]    Solar collectors of lightweight construction often have the disadvantage that their structure has insufficient self-supporting properties, with the consequence that a large number of supports are required and or that the solar collectors can be only quite small in size. 
         [0009]    Thus, it is an object of the present invention to provide a segment of a solar collector which allows for a solar collector with light-weighted design, high torsional stiffness and self-supporting structure, while also the assembly work in situ is to be kept small. 
         [0010]    Further, it is an object of the present invention to provide a solar collector having a light-weighted design and a self-supporting structure. 
       SUMMARY OF THE INVENTION 
       [0011]    According to the invention, it is provided that a segment of a solar collector comprises a top side, a bottom side and a circumferential end face having at least one longitudinal side, wherein the longitudinal side forms a top edge with the top side and forms a bottom edge with the bottom side. The segment further comprises a core structure having at least one core made of foamed material. Arranged on the core structure is a shell made of one or a plurality of layers of a fiber material, wherein the shell at least partially covers the top side, the bottom side and at least the longitudinal side of the circumferential end face, and wherein at least one layer of the shell extends about the top edge and at least one layer of the shell extends about the bottom edge. The segment further comprises a reflection layer disposed on the top side. 
         [0012]    The use of a core structure comprising at least one core of foamed material makes it possible to accomplish a particularly light-weighted design of the segment and thus of a solar collector. The shell comprising one or a plurality of layers of a fiber material has the effect that the segment is given sufficient stability. 
         [0013]    With the aid of the longitudinal side, two adjacent segments can be connected to each other, wherein the shell of a segment that extends about the top edge and the bottom edge in combination with the shell of an adjacent segment that extends about the top edge and the bottom edge, forms a kind of profile carrier shaped as a double T. 
         [0014]    In this manner, there is obtained a considerably high structural strength of a solar collector consisting of the segments according to the invention. Particularly, this effect is intensified if two adjacent segments are bonded to each other since, in this manner, the two likewise bonded shells of the adjacent segments will be connected to each other by substance-to-substance bonding and thus will form a particularly firm structure. By using a fiber material for the shell, the bonding of the adjacent segments will establish a support structure of the fiber material that can be considered as forming virtually one integral piece, which is the case because the fiber material can be soaked by the adhesive. Thus, the segments according to the invention can be assembled into solar collectors having a self-supporting structure, so that the solar collectors can have a large length without the need for additional support elements. 
         [0015]    According to a preferred embodiment, it is provided that the shell consists of at least one first shell member made of a fiber material that is arranged on the top side and covers the core structure on the top side, and of a second shell member made of a fiber material that is arranged on the bottom side and covers the core structure on the bottom side. 
         [0016]    In this manner, the shell of the core structure can be produced in a simple manner. 
         [0017]    In the above arrangement, it can be provided that the first shell member extends around the top edge and/or the second shell member extends around the bottom edge. In a segment according to the invention which comprises two or more longitudinal sides of the surrounding end face, via which the segment can be connected to other segments, it can be provided that the shell member extends around the top edges of all longitudinal sides while the second shell member extends around the bottom edges of all longitudinal sides. By the provision of a first and a second shell member, the inventive shell of the core structure can be produced in a simple manner, while at the same time advantageously safeguarding the desired extension of the shell around the top edge and around the bottom edge. 
         [0018]    Additionally or alternatively thereof, it can be provided that the shell comprises a third shell member made of a fiber material that is arranged on the at least one longitudinal side and covers the core structure on the longitudinal side, said third shell member extending around the top edge and/or the bottom edge. The first, the second and/or the third shell member can respectively consist of at least one layer of fiber material, preferably of at least two layers of fiber material and with particular preference of three layers of fiber material. Particularly, it is provided that the layers of the shell are made of glass-fiber or carbon-fiber material and comprise unidirectional or multi-axial fibers. 
         [0019]    Thereby, the desired strengthening effect of the shell can be achieved in an advantageous manner. By use of said layers of unidirectional or multi-axial fibers, the segments can be given high resistance to rupture and high torsional stiffness while, at the same time, a solar collector composed of the segments according to the invention can have a particularly advantageous self-supporting structure. This can be accomplished particularly by selecting, for different layers of the shell, materials with different fiber directions, since the fiber direction can be selected corresponding to the respective stress direction of the segments. 
         [0020]    According to a preferred embodiment, it is provided that reinforcement strips of fiber material are arranged around the top edge, the bottom edge and/or around the further edges formed between the surrounding end faces and the top side and the bottom side, so as to reinforce the top edge, the bottom edge and the further edge of the core structure. 
         [0021]    According to a particularly preferred embodiment, it is provided that the core structure comprises at least one rib of a fiber material, preferably of wood, said rib being preferably arranged parallel to the at least one longitudinal side. Such a rib is effective to increase the stability of the core structure. 
         [0022]    In the above arrangement, it can be provided that the core structure consists of two cores of foamed material and of three ribs of fiber material, said ribs and said cores of foamed material being arranged alternately. In other words: The core structure consists of two cores of foamed material, which cores are enclosed by two ribs, with a further rib being arranged between the cores of foamed material. The two outer ribs herein are arranged respectively on one of the longitudinal sides. Such a configuration has proven to be particularly advantageous. 
         [0023]    It can be provided that each rib comprises a cover made of a fiber material, thus allowing for a very high stability of the ribs. 
         [0024]    According to one embodiment of the invention, it is provided that, adjacent to the longitudinal side, a flange is arranged for attachment of the segment to an opposite segment. When assembling a solar collector from segments according to the invention, flanges arranged on the segments for mutual attachment of opposite segments have been found to be of particular advantage. In this manner, a plurality of segments serially fastened via the longitudinal sides of the segments can be connected, with the aid of the flanges, to a further row of flanges. In this regard, it can be provided that the flanges are a part of the overall structure of the segment and thus are formed by the core structure and the shell. 
         [0025]    The top side of the core structure can have a curvature so that the reflection layer on which there is arranged the part of the shell covering the top side of the core layer, is also curved. In this manner, the segments according to the invention can be assembled to parabolic-trough-shaped or parabolic solar collectors. 
         [0026]    The layers of the shell, the at least one core of foamed material, the ribs of the core structure, the shell of the ribs, and/or the reinforcing strips can be bonded to each other, preferably by means of an epoxy resin adhesive or another resin-based adhesive such as e.g. polyester or polyvinyl resin. The mutual bonding of the individual component parts of a segment according to the invention advantageously allows for a particularly tight connection between the individual component parts. The use of an epoxy resin adhesive has the benefit that this adhesive will become connected in an advantageous manner to the layers of the shell consisting of fiber material, and to the ribs made of fiber material, particularly if the fiber material ribs consist of wood. In this manner, it is advantageously rendered possible for the adhesive to become anchored to the respective material. When using glass-fiber or carbon-fiber material for the layers of the shell, the material will advantageously be soaked by the epoxy adhesive, thus generating a structure of epoxy resin and glass fibers or carbon fibers which has a high stability. When bonding different layers of the shell of a segment or of adjacent segments, the use of the epoxy adhesive makes it possible to bond the layers to each other in such a manner that they can nearly be regarded as being one integral piece. 
         [0027]    The object forming the basis of the invention is further achieved by a solar collector comprising a plurality of segments according to the invention. 
         [0028]    In this regard, it is preferably provided that, in the solar collector, two adjacent segments are bonded to each other via the longitudinal sides and that a row of mutually bonded segments can be connected, with the aid of the flanges, to a further row of opposite segments. 
         [0029]    Such a solar collector can be conveniently produced and be transported to its installation site in that a row of adjacent segments are bonded to each other already at the production site and in situ merely have to be connected to a further row of segments according to the invention. 
         [0030]    The solar collectors composed of the segments according to the invention are very light-weighted and thus transportable in a convenient manner. Further, the solar collectors have a high torsional stiffness and comprise a self-supporting structure. 
         [0031]    According to a particularly preferred embodiment, it is provided that two rows of adjacent segments are connected to each other via said flanges, there further being provided a U-profile enclosing the flanges. Said U-profile can consist e.g. of a plurality of layers of fiber material which are bonded to each other preferably by an epoxy resin adhesive. It has been found that the use of a U-profile makes it possible to achieve a particularly high torsional stiffness of the solar collector. The solar collector according to the invention can consist of e.g. 24 segments according to the invention. 
         [0032]    According to one embodiment of the invention, it is provided that a framework construction is arranged on the surface formed by the bottom side of the segments so as to increase the torsional stiffness, said framework construction being attached to the bottom side of the solar collector preferably via fastening means bonded between two adjacent segments. 
         [0033]    The framework construction can be connected e.g. to a support structure of an absorber. Another option resides in that the framework construction of the solar collector is preferably connected to an attachment metal plate of a solar collector support. In this manner, it can be safeguarded that a very high stability of the framework construction is achievable. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0034]    The invention will be explained in greater detail hereunder with reference to the accompanying Figures. In the Figures, the following is shown: 
           [0035]      FIG. 1  is a schematic representation of an inventive segment of a solar collector, 
           [0036]      FIG. 2  is a schematic sectional view of the segment shown in  FIG. 1 , 
           [0037]      FIG. 3  is an enlarged schematic sectional view of an inventive segment, 
           [0038]      FIG. 4  is a schematic sectional view of two adjacent inventive segments, 
           [0039]      FIG. 5  is a schematic sectional view of an inventive solar collector, and 
           [0040]      FIG. 6  is a schematic perspective view of an inventive solar collector. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0041]    In  FIG. 1 , an inventive segment  1  of a solar collector is schematically illustrated. Said segment  1  comprises a top side  2 , a bottom side  4  and a surrounding end face  6  having two longitudinal sides  8 . The longitudinal sides  8  together with the top side  2  form a respective top edge  10  and, together with the bottom side  4 , a respective bottom edge  12 . At least the top side  2  of the segment is curved, wherein the upper surface is provided with a reflective layer  14  adapted to reflect incident sunlight. 
         [0042]    Via said longitudinal sides  8 , a plurality of segments  1  according to the invention can be connected to each other to form a row of segments  1 , e.g. by mutual bonding of the segments on the longitudinal sides  8 . 
         [0043]    Adjacent to the longitudinal sides  8 , the segment  1  according to the invention comprises a flange  16  by which the inventive segment  1  can be connected to an opposite segment of identical design. 
         [0044]    In  FIG. 2 , the segment according to  FIG. 1  is schematically shown in sectional view. Segment  1  comprises a core structure  20  enclosed by a shell  22 . 
         [0045]    Said core structure  20  consists of two cores  24  made of foamed material, and of ribs  26  made of a fiber material. Said ribs  26  can be produced e.g. of wood or a wood-like material. Preferably, the ribs  26  are made of Australian pine since this type of wood has a particularly high stiffness. 
         [0046]    The ribs  26  are each provided with a cover  28  made of a fiber material. Two of the ribs  26  are arranged on the longitudinal sides  8  of segment  1  so that the ribs enclose the cores  24  of foamed material. The third rib  26  with cover  28  is arranged between the cores  24  of foamed material. 
         [0047]    Said cover  28  made of fiber material increases the stability of the ribs  26 . 
         [0048]    Said shell  22  enclosing the core structure  20  can consist of one or a plurality of layers of fiber material. 
         [0049]    In the embodiment depicted in  FIG. 2 , shell  22  consists of a first shell member  30  and a second shell member  32 , each of them made of a layer of fiber material. The first shell member  30  is arranged on the top side  2  and covers the core structure  20  on the top side  2 , while the second shell member  32  is arranged on the bottom side  4  and covers the core structure  20  on the bottom side  4 . In this arrangement, the first shell member  30  extends around the top edges  10  formed between the longitudinal sides  8  and the top side  2 , while the second shell member  32  extends around the bottom edges  12  formed between the longitudinal sides  8  and the bottom side  4 . The first shell member  30  and the second shell member  32  can consist of one or a plurality of layers of a fiber material. 
         [0050]    Since the first shell member  30  and the second shell member  32  extend around the top edge  10  and the bottom edge  12 , the bonding connection of the inventive segment  1  to a further inventive segment  1  via the respective longitudinal sides  8  will generate a stable structure from the respective shells  22  of the inventive segments  1 . In this manner, there can be formed solar collectors which have a self-supporting structure and further have a high torsional stiffness and breakage resistance. 
         [0051]    On the top side  2  of the inventive segment  1 , a refection layer is arranged, not shown in  FIG. 2 . 
         [0052]    In  FIG. 3 , the region around the longitudinal sides  8  of an inventive segment  1  is schematically shown in enlarged sectional view. 
         [0053]    The embodiment shown in  FIG. 3  substantially has the same structure as the embodiment of an inventive segment  1  shown in  FIG. 2 . The essential difference resides in that the first shell member  30  consists of three layers  30   a - 30   c  while the second shell member  32  consists of three layers  32   a - 32   c.  The layers  30   a - 30   c  and respectively  32   a - 32   c  each consist of a fiber material, e.g. a glass fiber material. These can be applied in the form of glass fiber mats. In this regard, it can be provided e.g. that the layers  30   c  and  32   c  facing toward core structure  20  consist of a glass fiber material comprising multi-axially oriented fibers, whereas the outer layers  30   a , 30   b , 32   a , 32   b  consist of a glass fiber material comprising unidirectional fibers. Further, reinforcement strips  34  are provided which are arranged on the top edge  10  and the bottom edge  12  and reinforce the edges of the core structure  20 . Also said reinforcement strips  34  can consist of a fiber material. 
         [0054]    When producing the inventive segment  1 , the ribs  26  will first be bonded to the shell  28  with the aid of an adhesive, preferably an epoxy resin adhesive. The individual layers of the second shell member  32  will also be bonded with the aid of an adhesive, preferably an epoxy resin adhesive, and the core structure  20  will be arranged on the second shell member  32 . In case it is intended to use reinforcement strips  34 , these can be inserted and also bonded prior or subsequent to the placement of the core structure  20 . Then, the individual layers of the first shell member  30  will be applied and bonded. By the use of a fiber material for the individual layers of the shell members  30  and  32 , the shell members, if an epoxy resin adhesive is used, will be advantageously soaked by the epoxy resin adhesive, so that a very good connection will be effected between the individual layers. The substance-to-substance bond between the individual layers is of such a good quality that the shell consisting of the individual layers can be considered as forming one integral piece. 
         [0055]    Uneven spots or free spaces as caused e.g. by the reinforcement strips  34  can be compensated for, or filled, by the adhesive material. 
         [0056]    In  FIG. 4 , two mutually bonded inventive segments  1  are schematically illustrated in sectional view. 
         [0057]    The two inventive segments  1  are bonded to each other via the longitudinal side  8 . The segments  1  substantially have the structure shown in  FIGS. 2 and 3 . The shell  22  of the segments  1  can consist of a plurality of layers of fiber material. By the bonding of the segments  1  on the longitudinal side  8 , the fiber material of shell  22  is soaked by the adhesive, preferably an epoxy resin adhesive, thus generating a very good connection between the shells  22  of the individual segments. 
         [0058]    The substance-to-substance connection obtained by the bonding is excellent enough for allowing the two shells of the two segments  1  to be considered as one integral piece, as indicated by the interrupted line in  FIG. 4 . In this manner, the shells  22  of the mutually bonded segments  1  are combined to a support structure shaped as double T. Achieved thereby is a particularly high stability of a solar collector composed of a plurality of segments  1 , while the solar collector is given an advantageous self-supporting structure as a result of the bonded shell  22 . 
         [0059]    Due to the materials used for the inventive segments, it is made possible to assemble the inventive segments into a solar collector of low weight and high stability. 
         [0060]    The inventive segments can be reinforced by further layers of fiber material which are located in regions of elevated mechanical stress. For instance, the flange can be reinforced by added layers. 
         [0061]    In  FIG. 5 , a solar collector  100  according to the invention is schematically depicted in sectional view, while the interior structure of the sectioned segments  1  is not shown. In  FIG. 6 , a solar collector  100  according to the invention is schematically depicted in perspective view. In the view of  FIG. 6 , the solar collector  100  is presented in a strongly pivoted position. 
         [0062]    The solar collector  100  consists of a plurality of interconnected segments  1 , wherein adjacent segments  1  are connected via the longitudinal sides  8  to thus form a row of segments  1 . With the aid of the flanges  16  of the segments  1 , two rows of segments  1  are assembled into a parabolic trough. As evident from  FIG. 6 , a solar collector can consist of 24 segments  1 . 
         [0063]    The flanges  16  are enclosed by an elongated U-profile  36  whereby the size of the flanges  16  can be kept small and the torsional stiffness of the solar collector  100  can be improved. Said U-profile  36  can consist of a plurality of mutually bonded fiber material layers. The two rows of segments  1  and the U-profile  36  can be bolted or bonded to each other. 
         [0064]    Arranged at the respective ends of solar collector  100  are solar collector supports  38  on which the solar collector is rotatably suspended via attachment metal plates  40 . In this arrangement, it can be provided that a plurality of solar collectors  100  are arranged behind each other in a row and connected to each other, so that a plurality of solar collectors  100  can be rotated by a common drive unit for adjusting the solar collectors to the altitude of the sun. 
         [0065]    In the focus of the parabolic troughs formed by the segments  1 , a tubular absorber  42  is arranged, which is supported by a support structure  44 . In operation, the medium to be heated will flow through absorber  42 . 
         [0066]    On the bottom side of solar collector  100  formed by the bottom sides  4  of the segments  1 , a framework construction  46  is arranged for improving the torsional stiffness of solar collector  100 . With the aid of fastening means, not shown in  FIGS. 5 and 6 , said framework construction  46  can be attached to the surface formed by the bottom sides  4  of the segments  1 , wherein said fastening means can e.g. be bonded between two adjacent segments and/or be bolted to the ribs—not shown in FIGS.  5  and  6 —of segments. The framework construction is further connected to U-profile  36  and said attachment metal plate  40 . Further still, the framework construction  46  is connected to the support structure  44  of absorber  42 . Obtained in this manner is a very high stability and torsional stiffness of the solar collector  100  of the invention. The torsional stiffness herein is so high that, in a row of a plurality of solar collectors  100  of a length of 120 mm, a rotary movement will cause a rotary deviation of the solar collectors of merely 5 millirad. 
         [0067]    The framework construction  46  is preferably made of a stable material, e.g. steel. 
         [0068]    The inventive segments advantageously allow for the production of very light-weighted solar collectors having a self-supporting structure and also a very high torsional stiffness. Already at the factory site, a plurality of inventive segments can be bonded to form a row of segments so that, at the installation site, these segments merely have to be connected to a further row of segments via the flanges. In this regard, it has been observed segments of a width of up to 12 can be bonded together at the factory site without entailing transport problems. 
         [0069]    The solar collectors of the invention can have a length of up to 12 m and an aperture of 4.60 m.