Patent Publication Number: US-2013247960-A1

Title: Solar-light concentration apparatus

Description:
CROSS-REFERENCE 
     This application is a continuation of U.S. patent application Ser. No. 13/053,184, filed Mar. 21, 2011 which claims the benefit of priority of U.S. Provisional Patent Application No. 61/315,744 filed Mar. 19, 2010; this application is a continuation-in-part of U.S. patent application Ser. No. 13/028,957, filed Feb. 16, 2011. Through the &#39;957 Application, the present application is a continuation of U.S. patent application Ser. No. 13/007,910, filed Jan. 17, 2011, now U.S. Pat. No. 7,991,261. Through the &#39;910 Application, the present application is a continuation of U.S. patent application Ser. No. 12/113,705, filed May 1, 2008, now U.S. Pat. No. 7,873,257. Through the &#39;705 Application, the present application claims the benefit of priority of U.S. Provisional Patent Application No. 60/915,207 filed May 1, 2007; U.S. Provisional Patent Application No. 60/942,745 filed Jun. 8, 2007; and U.S. Provisional Patent Application No. 60/951,775 filed Jul. 25, 2007. Each of the foregoing applications is incorporated herein by reference in their entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to apparatuses for collecting, concentrating and harvesting solar-light by total internal reflection. 
     DESCRIPTION OF THE RELATED ART 
     Concentrating Photovoltaic (CPV) solar panels are known and they are used to generate electricity for industrial and personal use. 
     Optical concentrators for photovoltaic (PV) solar applications are well known and they use reflective, refractive, diffractive, TIR waveguides, luminescence optics or combinations of these optical elements. 
     Optical concentrators using planar or slab waveguides in conjunction with collecting and focusing refractive optical elements have been used to improve the solar energy concentration onto reduced size PV cells to reduce the cost of the PV cell and to minimize the height of the solar panels. 
     There is a need to further optimize the design, the manufacturing and the assembling operations related to concentrating photovoltaic (CPV) solar panels based on planar or slab waveguides that use total internal reflection and the corresponding optical focusing elements. Both the optical efficiency and the overall efficiency that depends on the efficiency of the PV cells needs further refinements. The design of the optical components needs to be done also by considering the current and the future advances in the PV cells designs and manufacturing coupled to the waveguide optics. 
     SUMMARY OF THE INVENTION 
     This invention discloses an optical solar concentrator having a focusing layer including focusing optical elements that concentrate sunlight onto the corresponding deflectors of a waveguide. The deflectors are located in the lower surface of the waveguide and in the focal plane of the focusing elements. The deflectors redirect the light inside the waveguide under total internal reflection conditions in order to collect the focused light and couple the sunlight to a photovoltaic cell. The sun light exiting from the waveguide is first redirected and further concentrated by a secondary optic that couple the light to the PV cell. The focusing optical elements and the deflectors are either longitudinal or annular and the PV cell is in several embodiments a multi-junction PV cell. The multi-junction cells have are designed for a spectral response that matches the spectrum of the light reaching the PV cell through the combined focusing elements, the waveguide and the secondary optical element. 
     The invention discloses several embodiments of the concentrators where the annular focusing elements and the annular deflectors have both circular and polygonal outer surfaces. The polygonal ouster surfaces allow for the better clustering of the optics to increase the active surface of the solar panels. 
     The invention also discloses a tray that that protects the optics and locates the PV cells relative to the optics. In some embodiments the material of the tray is similar to the material of the waveguide to allow the two parts to expand and shrink at the same rate during manufacturing and in the field and in the day and night conditions. 
     In some embodiments the tray is made of a polycarbonate that includes a carbon fiber filler to dissipate the heat from the PV cell. One such a material is Raheama made by Tejin Limited of Japan. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding of the present invention, as well as other aspects and further features thereof, reference is made to the following description which is to be used in conjunction with the accompanying drawings, where: 
         FIG. 1  is a perspective exploded view of a solar-light concentration apparatus according to an embodiment of the invention; 
         FIG. 2  is a cross-sectional view of a photovoltaic solar-light concentration apparatus according to an embodiment of the invention with solar-light schematically shown by solid lines; 
         FIG. 3  is detail A of  FIG. 2   
         FIG. 4  is a perspective view of the photovoltaic solar-light concentration apparatus of FIGS.  1 , 2 , 3  and  12  with the sun schematically shown and a trajectory of the sun during the course of a day shown in dotted lines; 
         FIG. 5  is a close-up view of the photovoltaic solar-light concentration apparatus of  FIG. 2  shown having a focusing layer positioned off-set with respect to a waveguide; 
         FIG. 6  is a perspective view of a photovoltaic solar-light concentration apparatus according to another embodiment of the invention; 
         FIG. 7   a  is a cross-sectional view of the photovoltaic solar-light concentration apparatus of  FIG. 6 ; 
         FIG. 7   b  is a cross-sectional view of another embodiment of a photovoltaic solar-light concentration apparatus having a cladding layer; 
         FIG. 8   a  is a perspective view of another embodiment of the photovoltaic solar-light concentration apparatus; 
         FIG. 8   b  is a cross section view of the secondary optic show in  FIGS. 7   a - b  and  FIG. 8   a;    
         FIG. 9  a series of solar concentrators as shown in  FIG. 8   a , arranged in a string and also as a panel composed of strings; 
         FIG. 10  illustrates another embodiment of the invention showing of a string of photovoltaic concentrators; 
         FIG. 11  illustrates another embodiment of the invention showing a series of photovoltaic panels mounted on a dual axis; 
         FIG. 12  is a general view of a photovoltaic solar concentrator as shown in more details is FIGS.  2 - 3 - 4 . 
         FIGS. 13   a - b - c - d - e - f - g  illustrate another embodiment of the invention showing a hexagonal shaped photovoltaic solar concentrator with a secondary optic. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIGS. 1 to 5 , an embodiment of a photovoltaic solar-light concentration apparatus  10  will be described. 
     The photovoltaic solar-light concentration apparatus  10  is generally rectangular in shape. It is contemplated the focusing layer  20  and the waveguide  30  could be generally square. A second embodiment of a photovoltaic solar-light concentration apparatus  10 ′ having a generally circular shape will be described in greater detail below with reference to  FIGS. 6 and 7 . 
     The photovoltaic solar-light apparatus  10  comprises a focusing layer  20  and a waveguide  30  separated by an air gap  40 . The focusing layer  20  and the waveguide  30  are generally rectangular. The focusing layer  20  and the waveguide  30  are parallel to each other. 
     The focusing layer  20  comprises a plurality of longitudinal focusing elements  22  disposed an abutting side-by-side position. The plurality of longitudinal focusing elements  22  forms a plurality of stripes, wherein each stripe is a cylindrical lens. It is contemplated that the focusing elements  22  could be more elaborate and consists of various optical active facets of various shapes. Each focusing element  22  (i.e. stripe) collects concentrates (by focusing) solar-light  1  (shown in  FIGS. 2 and 3 ) into a solar-light beam. The solar-light beam is narrower than a span of the solar-light  1  impacting the focusing element  22 . The band of solar-light  1  exits the focusing layer  20  through a focussing side  24  of the focusing layer  20 . 
     The waveguide  30  is a planar slab of acrylic glass. The waveguide  30  is injection molded. It is contemplated that the waveguide  30  could be thermoformed or injection molded from one or more moldable materials. For example, the waveguide  30  could be molded from optical grade polycarbonate, such as CALIBRE™, IUPILON™, LEXAN™, MAKROLIFE™ MAKROLON™, PANLITE™, TARFLON™ or LBE™. The waveguide  30  could also thermoformed or injection molded from polymethyl methacrylate (Plastic Materials) such as any of POLICRIL™, PLEXIGLAS™, GAVRIELI™, VITROFLEX™, LIMACRYL™, R-CAST™, PER-CLAX™, PERSPEX™, PLAZCRYL™, ACRYLEX™, ACRYLITE™, ACRYLPLAST™, ALTUGLAS™, POLYCAST™, OROGLASS™, OPTIX™, LUCITE™ and ACRYLIC™. The focusing layer  20  is made of the same materials and using the same manufacturing methods as the waveguide  30 . Materials for the focusing layer  20  and the waveguide  30  are selected from same or different materials selected from the materials listed before. 
     The waveguide  30  is optically coupled to the focusing layer  20 . The waveguide  30  has an entry surface  32  disposed facing the focussing side  24  of the focusing layer  20 , a reflecting surface  34  opposite to the entry surface, and an exit surface  36  at an end of the entry surface  32  and the reflecting surface  34 . 
     A plurality of longitudinal deflectors  50  is disposed on the reflecting surface  34 . The plurality of longitudinal deflectors  50  is integrally formed with the waveguide  30  by injection molding. It is contemplated that the plurality of longitudinal deflectors  50  could be formed by injection compression molding. The longitudinal deflectors  50  are parallel to each other and parallel to the exit surface  36 . The plurality of longitudinal deflectors  50  consists in a plurality of adjacent spaced apart stripes. It is contemplated that the deflectors  50  can be equally spaced or can be spaced at variable distances one relative to the other or in clusters. It is also contemplated that the stripes could not be spaced apart. Each longitudinal deflector  50  (i.e. stripe) has a shape of a wedge. It is contemplated that the longitudinal deflectors  50  could have more elaborate shapes than a single wedge. 
     The plurality of deflectors  50  is arranged in a one-to-one optical relationship with respect to the plurality of focusing elements  22 . The plurality of deflectors  50  is positioned in the focal plane of the focusing elements  22  so that each deflector  50  receives the solar-light  1  coming from a single corresponding one focusing element  22 . It is contemplated that, the plurality of deflectors  50  could not be positioned in the focal plane of the focusing elements  22 . The deflectors  50  have a deflecting surface  52  positioned at an angle with respect to the incoming solar-light  1  beam so as to redirect the solar-light  1  into the waveguide  30  at an angle that ensures total internal reflection. It is contemplated that the deflecting surface  52  could be flat, segmented, multi-faceted or curved. It is also contemplated that the deflecting surface  52  could be mirror-coated or uncoated. It is also contemplated that the deflecting surface  52  could be sized and positioned with respect to the focusing elements  22  to always capture and deflect the entire solar-light beam  1  so that no focused light passes by the deflecting surface  52 . This prevents direct focused light  1  not intercepted by surface  52  from escaping from the waveguide  30 . It is contemplated that the waveguide  30  and thus the deflecting surface  52  could be slightly closer to the focusing element  22  (short focus) or a little further from the focusing element  22  (far focus) for as long as no light escapes the deflecting surface  52 . Starting with this first reflection at the deflecting surface  52 , the solar-light  1  is reflected between the entry surface  32  and the reflecting surface  34  at angles that exceed the critical angle (hence ensuring total internal reflection). The solar-light  1  is therefore trapped into the waveguide  30 , and the total internal reflections direct unidirectionally the solar-light  1  toward the exit surface  36  of the waveguide. This combination of a longitudinal focusing element  22  and a longitudinal deflecting element  50  that together generate a band or stripe shaped solar beams  1  advancing via total internal reflection in the waveguide  30  allows for the optimum concentration since no solar light  1  will be directed towards the lateral walls/surface of the waveguide  30  to lower the amount of solar light  1  advancing towards the exit surface  36 , that happens in some other known planar waveguides  30  for light concentration. 
     A photovoltaic (PV) cell  60  is optically coupled to the waveguide and is disposed at the exit surface  36  of the waveguide  30  and collects the solar-light  1  trapped in the waveguide  30 . The photovoltaic cell  60  in  FIGS. 1-2  is a single junction cell. It is contemplated that the photovoltaic cell  60  could be made of mono-crystalline or poly-crystalline Si, can be a multi-junction cell as shown in FIGS.  7 - 8 - 10  or a thin film. It is contemplated that the photovoltaic cell  60 ′ could be any multi-junction cell. It is contemplated that a secondary optic element  80 ′, as shown in  FIGS. 7-8  could be optically coupled to waveguide  30 ′ to either change the direction of the solar beam exiting the waveguide  30 ′ or provide thermal insulation or additional focus/concentration of the solar beam  1  exiting the waveguide  30 ′ and reaching the photovoltaic cell  60 ′. The secondary optic  80 ′ can be a surface of the waveguide  30 ′ that is flat or curved and is angled to changes the direction of the solar beam travelling in the waveguide  30 ′ to reach the photovoltaic cell  60 ′ that is not co-linear with the solar beam traveling inside the waveguide  30 ′. The secondary optic can be also a separate element made of different optical material than the waveguide  30 ′ for higher concentration that increases the temperature of the waveguide towards to exit surface  36 ′, and can made of glass. The secondary optic  80 ′ being separated from the waveguide  30 ′ acts as a thermal buffer or barrier between the waveguide  30 ′ and the photovoltaic cell  60 ′ to also increase the efficiency of the photovoltaic cell  60 ′. 
     As best seen in  FIG. 4 , the solar-light concentration apparatus  10  can be positioned so as to track the solar-light  1  over the course of a year. This can be done by positioning the photovoltaic solar-light concentration apparatus  10  at different angles depending on the position of the sun  5  at noon-time over the year. Alternatively, as seen in  FIG. 5 , the focusing layer  20  can be positioned off-set of the waveguide  30 . The shifting of position of the focusing layer  20  is adjusted during the year depending on the sun&#39;s  5  positions. Another way of accommodating the change in sun&#39;s  5  noon-time position is by introducing a prism in the air gap  40  for deflecting the solar-light  1  before the solar-light  1  enters the waveguide  30 . The prism influences an angle of impact of the solar-light  1  onto the deflectors  50 . 
     Referring now to  FIGS. 6 to 8 , the second embodiment of photovoltaic solar-light concentration apparatus  10 ′ will now be described. The photovoltaic solar-light concentration apparatus  10 ′ is similar in construction to the photovoltaic solar-light concentration apparatus  10 , but differs in shape. Elements of the photovoltaic solar-light concentration apparatus  10 ′ common to the photovoltaic solar-light concentration apparatus  10  will be given the same reference numeral with a ′, and details of the common elements will not be repeated. 
     The photovoltaic solar-light concentration apparatus  10 ′ has a focusing layer  20 ′ and a waveguide  30 ′ separated by an air gap  40 ′. It is completed that the air gap  40 ′ could be replaced by a cladding layer  70 ′ (see  FIG. 7B ). The cladding layer  70 ′ can have a refractive index lower that the refractive index of the upper focusing layer and lower than that of the waveguide. The advantage of having such cladding layer  70 ′ is that it can protect the integrity of the concentrator in the field. The cladding layer  70 ′ can be made of any suitable material such as, for example, fluorinated ethylene propylene. The thickness of the cladding layer  70 ′can be relatively thin and still be effective. The focusing layer  20 ′ is disk-shaped, and comprises a plurality of focusing elements  22 ′ concentrically disposed in an abutting side-by-side relationship. The focusing elements  22 ′ are cylindrical lenses having an annular shape. A central portion  21 ′ of the focusing layer  20 ′ is deprived of focusing elements  22 ′. 
     The waveguide  30 ′ is disk-shaped and has the same size as the focusing layer  20 ′. The waveguide  30 ′ has an exit surface  36 ′ centrally located. The exit surface  36 ′ is positioned underneath the central portion  21 ′ of the focusing layer  20 ′ and has a radius of the central portion  21 ′. 
     The waveguide  30 ′ has a plurality of deflectors  50 ′ disposed on a reflecting surface  34 ′ of the waveguide  30 ′. The plurality of deflectors  50 ′ consists in annular wedges disposed concentrically. The deflectors  50 ′ are isolated with respect to each other. The plurality of deflectors  50 ′ is disposed in the waveguide  30 ′ so as to create a one-to-one relationship with the plurality of focusing elements  22 ′. Similarly to the solar-light concentration apparatus  10 , the solar-light  1  is trapped into the waveguide  30 ′ and is directed unidirectional by total internal reflection toward the exit surface  36 ′. 
     A secondary optic  80 ′ is disposed at the exit surface  36 ′. The secondary optic  80 ′ is disk-shaped. The secondary optic  80 ′ directs and concentration the solar-light  1  coming radially from the exit surface  36 ′ into a spot. It is contemplated that the secondary optic  80 ′ could be omitted. 
     A photovoltaic cell  60 ′ is disposed underneath a center of the secondary optic  80 ′. The photovoltaic cell  60 ′ has a square shaped active area. It contemplated that photovoltaic cell  60 ′ could be circular. 
       FIGS. 8   a  and  8   b  show a photovoltaic concentrator ( 800 ′) having a focusing layer ( 820 ′) with annular and concentric focusing elements ( 822 ′) and a planar slab waveguide ( 830 ′) having deflecting elements ( 850 ′) not shown but similar to item ( 50 ′) of  FIG. 7   a , concentrator ( 800 ′) having a square or rectangular shape (top view) that is useful for assembling a string ( 900 ′) of concentrators to make a PV solar concentration panel ( 990 ′) both shown in  FIG. 9 . This concentrator  800 ′ is square or rectangular shaped (four faces polygon) having lateral surfaces ( 828 ′) and having in the center a disc shaped secondary optic ( 880 ′) element to redirect and further concentrate the light onto a multi-junction PV cell ( 860 ′) show in  FIG. 8   b.    
       FIG. 10  shows a blown up detail of an assembly ( 1000 ′) of four concentrators ( 800 ′) including a top layer ( 1021 ′) made of four coplanar focusing layer elements ( 820 ′), a middle layer made of four coplanar waveguide elements ( 830 ′) and a base layer or a tray ( 1062 ′) wherein the tray holds and aligns four multi-junction PV cells ( 1060 ′) onto which the concentrators ( 800 ′) direct the light. 
       FIG. 11  shows a series ( 1100 ′) of solar panels ( 990 ′) on a dual axis solar tracker. 
       FIG. 12  is a general view of solar concentrator ( 10 ) as shown in more details is FIGS.  2 - 3 - 4 . Solar concentrator ( 10 ) includes a focusing layer ( 20 ) and a waveguide ( 30 ) that collect, focus and direct the sunlight ( 1 ) through an exit surface ( 36 ) towards a PV cell ( 60 ). 
     Referring back to  FIGS. 1-13  they show several embodiments of solar-light concentration apparatus several embodiments of solar-light concentration apparatus according to this invention. 
     Referring to  FIGS. 1-5  they show some of the several embodiments of solar-light concentration apparatus ( 10 ) having a focusing layer ( 20 ) with longitudinal focusing elements ( 22 ) and a waveguide ( 30 ) having longitudinal deflectors ( 50 ) and a multi-junction PV cell ( 60 ). 
     Referring to  FIGS. 5-13  they show some of the several embodiments of a revolved solar-light concentration apparatus ( 10 ′/ 800 ′/ 1300 ′) having a focusing layer ( 20 ′/ 820 ′/ 1320 ′) with annular focusing elements ( 22 ′/ 822 ′/ 1322 ′) and a waveguide ( 30 ′/ 830 ′/ 1330 ′) having annular deflectors similar to ( 50 ′) shown  7   a,  a secondary optic ( 80 ′/ 880 ′/ 1380 ′) and a multi-junction PV cell ( 60 ′/ 860 ′/ 1360 ′). 
     General comparison of concentrations for revolved and linear geometries for the concentrator of the current invention. 
     The formula for geometrical concentration is: 
     
       
         
           
             C 
             = 
             
               
                 A 
                 c 
               
               
                 A 
                 a 
               
             
           
         
       
     
     here C is the geometrical concentration factor of the revolved geometry, A c  is the sun collection area and A a  is the energy absorber area. 
     For the revolved and linear geometries, the collection area is the same. What differs is the area of the absorber. 
     For the linear geometry, the area of the absorber is equal to 
     
       
      
       A 
       a 
       =h·l  
      
     
     where l is the length of the linear focusing elements. 
     For the revolved geometry, the area of the absorber is equal to 
       A a =2πr centre h
 
     where r centre  is the radius of hole at the centre of the optics and h is the height of the waveguide. 
     For the case where r centre =20 mm, h=4 mm and l=200 mm, the revolved geometry has a concentration factor which is approximately 1.6 times the concentration of the linear geometry. 
     With numbers: 
     Therefore, for a collection area of approximately A c =314 cm 2 , and the parameters as specified above, we have the following: 
     Revolved Geometry 
     The concentration factor of the revolved geometry is 62.5 for the above scenario. Further concentration can be added by using a secondary optic with an additional concentration factor of 1.5. This increases the total concentration for the revolved optic to 93.75. With this concentration, a multi-junction pv cell at 40% efficiency can be used which has an area of 3.3 cm 2 . 
     Linear Geometry 
     The concentration factor of the linear geometry is approximately 39.3 for the above scenario. Since the absorber area of the linear geometry is very large (8 cm 2  in this scenario), a PV cell with efficiency of 8% will have to be used, since multi-junction cells are too expensive to used to cover that much area. 
     The increased concentration of the revolved geometry in combination with the secondary optic and the possibility to use a multi-junction cell makes the revolved geometry a much more attractive design than the linear geometry. Also the fact that the deflection elements and the focusing elements can be diamond turned more efficiently makes the revolved geometry more attractive for higher concentration in many applications. 
     In particular,  FIG. 8   a  and  FIG. 13  show the solar-light concentration apparatus ( 800 ′/ 1300 ′) having a planar focusing layer ( 820 ′/ 1320 ′) with a regular polygonal entry surface facing impinging sunlight ( 1 ) and including a plurality of annular focusing elements ( 822 ′/ 1322 ′) disposed along concentric circles. The solar-light exiting each of the plurality of annular focusing elements ( 822 ′/ 1322 ′) is an annular band of solar-light. The focusing layer ( 820 ′/ 1320 ′) is injection molded of poly-methyl methacrylate or other thermoplastic materials and forms a planar slab of a certain thickness. 
     The spectrum of the sunlight entering the focusing layer is partially absorbed by the poly-methyl methacrylate (or other materials) therefore altering the spectrum of the exiting light and this impacts the performance of the system since it requires a customized multi-junction PV cell. A planar waveguide ( ) slab is optically coupled to the focusing layer having a regular polygonal shape and an optically smooth flat upper surface ( ) and an opposed lower flat surface having a corresponding regular polygonal shape. The lower surface ( ) is parallel to the upper surface ( ) to create a waveguide of a constant thickness. Both surfaces are bare, that is they don&#39;t have any type of mirror coating to reduce the cost and the damage that can be caused in operation due to sun exposure or the humidity that will lower the reflections inside the waveguide. 
     The waveguide ( ) is separated from the focusing layer ( ) by a material having a lower index of refraction than the waveguide ( ). In this embodiment the waveguide has an annular-exit surface ( ) and a plurality of annular deflecting elements ( ) each located in the focal plane of a corresponding focusing element and along concentric circles on the lower surface of the waveguide. By placing the deflecting elements on the lower surface of the waveguide the optical coupling with the focusing elements is improved and less light escape through the waveguide. The annular deflecting elements are disposed to deflect the focused solar at an angle that causes total internal reflection of the solar-light inside the waveguide, the solar-light being conveyed toward the exit surface of the waveguide by multiple total internal reflections between the parallel upper and lower surfaces of the waveguide that are not mirror coated. The waveguide layer is molded of poly-methyl methacrylate or other moldable material. The spectrum of the sunlight entering the waveguide ( ) is partially absorbed by the poly-methyl methacrylate (or other materials) therefore further altering the spectrum of the light exiting the waveguide and this impacts the performance of the concentrating system since it requires a customized multi-junction PV cell responsive to this changed solar spectrum. 
     Because of the increased demand for high solar efficiency for a reduced foot print this invention shows the coupling of the waveguide optics to multi-junction cells that are not only smaller in size to increase the optical concentration but also they are more efficient and more flexible to be made for a specific and more customized input solar spectrum affected by the absorption caused by the focusing elements and the waveguide that are made of moldable plastic resins. Also the lengthy travel of the light trough the waveguide contributes to a larger spectrum absorption in the waveguide than in the focusing layer. A multi junction photovoltaic cell is disposed to receive the solar light emerging from the waveguide and the multi-junction PV cell is designed to provide an optimum electronic efficiency for the sunlight spectrum exiting the waveguide. 
     In some embodiments of the invention a disc shaped secondary optical element ( ) having an annular entry surface ( ) and a reflecting surface ( ) is located between the waveguide and the multi-junction PV cell as shown in  FIG. 13 . The secondary optical element is disposed to couple the solar light from the waveguide onto the photovoltaic cell by deflection from the reflecting surface ( ). The secondary optical element ( ) is made of glass, preferably a high refractive index optical glass. The spectrum of the sunlight exiting the secondary optical element is also changed by any absorption in the secondary optical element. 
     As shown in  FIG. 13   c  a tray is used under the waveguide to retain the waveguide and the focusing layer and to further position the secondary optic and/or the PV cell. The tray is molded of a material that ideally has the same thermal expansion as the waveguide and or the focusing layer. In higher concentration applications the tray is made of a conductive polymer such as for example Raheama made by Teiji Japan. 
     Raheama consists of 50-200 micrometer fibers cut from a cylindrical graphite fiber stock measuring about 8 micrometers in diameter. It disperses well in plastic, allowing manufacturers to produce heat-radiation components of almost any shape. Raheama&#39;s thermal expansion coefficient is as low as that of ceramics, so compacts created with the material have exceptional dimensional stability. Raheama also offers high electrical conductivity, making it suitable for the prevention of static and shielding from radio waves. 
     Raheama has two standard specifications, R-A201 and R-A301, each boasting its own set of special features. R-A201 offers superior moldability and dispersion as a filler in plastic or rubber. It also combines with other fillers. R-A301 provides superior heat radiation, ranging from high levels of thermal conductivity using just small amounts of filler to extra-high levels as more filler is added. 
     Table with some of the item numbers. 
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                 Item # 
                 Item 
               
               
                   
                   
               
             
            
               
                   
                   1 
                 Solar light 
               
               
                   
                   5 
                 The sun 
               
               
                   
                  10 
                 Photovoltaic solar light concentraion apparatus 
               
               
                   
                  20 
                 Focusing layer 
               
               
                   
                  22 
                 Longitudinal focusing elements 
               
               
                   
                  24 
                 Focusing surface of the focusing layer 
               
               
                   
                  30 
                 Waveguide with longitudinal deflectors 
               
               
                   
                  32 
                 Entry surface of the waveguide 
               
               
                   
                  34 
                 Reflecting surface of the waveguide 
               
               
                   
                  36 
                 Exit surface of the waveguide 
               
               
                   
                  40 
                 Air gap 
               
               
                   
                  50 
                 Longitudinal deflectors 
               
               
                   
                  52 
                 Deflecting surface of the deflector 
               
               
                   
                  60 
                 Multi-junction photovoltaic cell 
               
               
                   
                  10′ 
                 Second embodiment of photovoltaic solar-light 
               
               
                   
                   
                 concentration apparatus 
               
               
                   
                  20′ 
                 Focusing layer 
               
               
                   
                  21′ 
                 Central portion of the focusing layer 
               
               
                   
                  22′ 
                 Annular Focusing elements 
               
               
                   
                  30′ 
                 Waveguide with annular deflectors 
               
               
                   
                  34′ 
                 Reflecting surface of the waveguide 
               
               
                   
                  36′ 
                 Exit surface of waveguide 
               
               
                   
                  40′ 
                 Air gap 
               
               
                   
                  41′ 
                 Cladding 
               
               
                   
                  50′ 
                 Deflectors of waveguide 
               
               
                   
                  60′ 
                 Multi-junction photovoltaic cell 
               
               
                   
                  70′ 
                 Cladding layer to replace air gap 
               
               
                   
                  80′ 
                 Secondary optic 
               
               
                   
                  800′ 
                 Solar concentration apparatus 
               
               
                   
                  820′ 
                 Focusing layer 
               
               
                   
                  822′ 
                 Annular Focusing element 
               
               
                   
                  824′ 
                 Lateral Surface 
               
               
                   
                  830′ 
                 Waveguide with annular deflectors 
               
               
                   
                  860′ 
                 Multi-junction photovoltaic cell 
               
               
                   
                  662′ 
                 Bypass diode 
               
               
                   
                  880′ 
                 Secondary optic 
               
               
                   
                  881′ 
                 Reflecting surface 
               
               
                   
                  882′ 
                 Top surface of secondary optic 
               
               
                   
                  883′ 
                 Entry surface of the secondary optic 
               
               
                   
                  884′  
                 Lower surface of the secondary optic 
               
               
                   
                  886′  
                 Exit surface of the secondary optic 
               
               
                   
                  900′  
                 String of concentrators 
               
               
                   
                  990′  
                 Solar Panel 
               
               
                   
                 1000′ 
                 Matrix of concentrators 
               
               
                   
                 1010′ 
                 String of concentrators 
               
               
                   
                 1021′ 
                 Focusing layer 
               
               
                   
                 1031′ 
                 Waveguide 
               
               
                   
                 1060′ 
                 Multi-junction photovoltaic cell 
               
               
                   
                 1062′ 
                 Concentrator tray 
               
               
                   
                 1300′ 
                 Solar concentration apparatus 
               
               
                   
                 1320′ 
                 Focusing layer 
               
               
                   
                 1322′ 
                 Annular Focusing Element 
               
               
                   
                 1326′ 
                 Tray 
               
               
                   
                 1328′ 
                 Lateral Surface 
               
               
                   
                 1330′ 
                 Waveguide with annular deflectors 
               
               
                   
                 1360′ 
                 Multijunction photovoltaic cell 
               
               
                   
                 1380′ 
                 Secondary Optic 
               
               
                   
                 1381′ 
                 Reflecting surface 
               
               
                   
                 1382′ 
                 Top surface of secondary optic 
               
               
                   
                 1383′ 
                 Entry surface of secondary optic 
               
               
                   
                 1384′ 
                 Lower surface of secondary optic 
               
               
                   
                 1386′ 
                 Exit surface of the secondary optic 
               
               
                   
                   
               
            
           
         
       
     
     Modifications and improvements to the above-described embodiments of the present invention may become apparent to those skilled in the art. The foregoing description is intended to be exemplary rather than limiting. The scope of the present invention is therefore intended to be limited solely by the scope of the appended claims.