Abstract:
Optics are provided for use in solar concentrators, the optics having a light guide, a redirecting layer including a plurality of lenses, and a plurality of reflector elements. Sunlight is received by the redirecting lenses, which focus the sunlight onto reflective surfaces of the reflector elements. The reflective surface of each reflector element redirects the light into the light guide, which guides the light toward a solar energy collector, such as a photovoltaic cell. The light from the light guide may be directed onto the solar energy collector by a light conditioning element.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to optics. 
       BACKGROUND 
       [0002]    Optics can be used in solar concentrators (such as those in concentrated photovoltaic systems) to concentrate sunlight onto solar energy collectors, such as photovoltaic cells. 
         [0003]    Solar concentrators employ optics to concentrate sunlight received over a relatively larger area onto a relatively smaller area where a photovoltaic cell (or some other means of harvesting solar energy) can be placed. In concentrated photovoltaic systems, the combination of the concentrating optical elements and the smaller photovoltaic cell would, in theory, be less expensive than would be an equivalent larger photovoltaic cell required to capture the same amount of sunlight. The first generations of solar concentrators were, however, quite complex and bulky, and suffered from many other drawbacks known in the art. Thus solar concentrators such as concentrated photovoltaic solar energy concentrators have not seen widespread general commercial acceptance. 
         [0004]    Therefore, as is a slim-profile optic that concentrates light in a highly efficient manner for use in a solar concentrator. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]    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: 
           [0006]      FIG. 1  is a cross-sectional view of an embodiment of a solar concentrator device; 
           [0007]      FIG. 2  is a cross-sectional view of another embodiment of a solar concentrator device having an alternative light conditioning element; 
           [0008]      FIG. 3  is a cross-sectional view of an embodiment of a solar concentrator device similar to that of  FIG. 1 , but having a different redirecting layer; 
           [0009]      FIG. 4  is a cross-sectional view of an embodiment of a solar concentrator device similar to that of  FIG. 3  except with spaced-apart lenses; 
           [0010]      FIG. 5  is a cross-sectional view of an embodiment of a solar concentrator device having a protective coating; 
           [0011]      FIG. 6  is a cross-sectional view of an embodiment of a solar concentrator device having an optical coupling layer between the light guide and the redirecting layer; 
           [0012]      FIG. 7  is a cross-sectional view of an embodiment of a solar concentrator device having optical coupling layers between the light guide and the redirecting layer, and the light guide and the reflector elements; 
           [0013]      FIG. 8  is a partial cross-sectional view of an embodiment of a solar concentrator device having a low refractive index film on step portions of the second surface of the light guide; 
           [0014]      FIG. 9  is a cross-sectional view of an embodiment of a solar concentrator device having protrusions extending from the second surface of the light guide into the reflector elements; 
           [0015]      FIG. 10  is a partial cross-sectional view of another embodiment of a solar concentrator device having protrusions extending from the second surface of the light guide into the reflector elements; 
           [0016]      FIG. 11  is a cross-sectional view of an embodiment of a solar concentrator device that is sloped; 
           [0017]      FIG. 12  is a cross-sectional view of another embodiment of a solar concentrator device that is sloped; 
           [0018]      FIG. 13  is a cross-sectional view of an embodiment of a solar concentrator device that has a substantially flat light guide; 
           [0019]      FIG. 14  is a cross-sectional view of an embodiment of a solar concentrator device that has reflector elements integrally formed with the light guide; 
           [0020]      FIG. 15  is a perspective view of an embodiment of a solar concentrator device having the general shape of a circular disk; 
           [0021]      FIG. 16  is a perspective view of an embodiment of a cropped solar concentrator device; 
           [0022]      FIG. 17  is a perspective view of an embodiment of a solar concentrator device having the general shape of a planar cuboid with symmetry about a central plane; 
           [0023]      FIG. 18  is a perspective view of an embodiment of a solar concentrator device having the general shape of a planar cuboid with a solar energy collector along an edge of the light guide; 
           [0024]      FIG. 19A  is a plan view of an embodiment of a solar concentrator device that have an array of lens-reflector element pairs; 
           [0025]      FIG. 19B  is a cross-sectional view of the solar concentrator device of  FIG. 19A  taken along line  19 B- 19 B; 
           [0026]      FIG. 19C  is a partial cross-sectional view of the solar concentrator device having reflector elements that have reflective surface with a convex portion; 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    Referring to  FIG. 1 , there is shown a cross section of a solar concentrator  100  including a light guide  104 , a plurality of reflector elements  106  and a redirecting layer  108 . The light guide  104  is made of a light transmissive material such as glass, polycarbonate or injection molded poly(methyl methacrylate) (PMMA). Other non-limiting examples of light transmissive materials that may be used include injection molded polymethyl methacrylimide (PMMI), Cyclo Olefin Polymers (COP), Cyclo Olefin Copolymers (COC), silicones and other light transmissive polymeric materials. The light guide  104  is wedge-shaped in cross section and includes a first surface  112  and a second surface  114 . The second surface  114  includes a plurality of step portions  120  adjacent to a plurality of inter-step portions  122 . 
         [0028]    In the embodiment shown in  FIG. 1 , the redirecting layer  108  has an input surface  118 , a plurality of plano-convex lenses  116  that are adjacent to one another, and a planar surface  148  for coupling light to the light guide  104 . Alternatively, other types of positive lenses, whether simple or complex, may be used. The redirecting layer  108  can be overmolded onto the first surface  112  of the light guide  104  or alternatively bonded thereto with an optical adhesive or by laser welding. 
         [0029]    The plurality of reflector elements  106  can include flat, parabolic, analytical or free-form (e.g. non-uniform rational B-spline (NURBS)) reflective surfaces  103 , or a combination thereof to redirect light  132  received from the lenses  116  to the light guide  104  via the inter-step portions  122 . For example, each reflector element  106  may comprise, in cross-section, a first portion  105  and a second portion  107 . In cross-section the first portion  105  may be flat or slightly curved (convex or concave) and the second portion  107  may be an elongated curve. The first portion  105  and the second portion  107  are designed to cooperate in such a manner that light received from the corresponding lens  116  is reflected by the first portion  105  to the second portion  107 , and light reflected by the second portion  107  is transmitted via the inter-step portion  122  to the light guide  104 . Some light  131  reflected by the first portion  105  may be transmitted directly to the light guide  104  through the inter-step portion  122 . 
         [0030]    The plurality of reflector elements  106  can be overmolded onto the second surface  114  or alternatively bonded thereto, for example with an optical adhesive or by laser welding. The redirecting layer  108  and the plurality of reflector elements  106  are made of light transmissive materials, such as a silicone of lower refractive index than the material of the light guide  104 . The solar concentrator device  100  can be flexible where flexible materials are used, e.g., where the light guide  104  is made of, a high refractive index, deformable silicone. 
         [0031]    The light guide  104  may be coupled, at least in part, by means of a light conditioning element  110  to a solar energy collector. Some of the light  130  from the light guide  104  may enter the solar energy collector directly. The light conditioning element  110  may have the shape of a dome and have a reflective coating  128 . The light conditioning element  110  can be made of metal or any other suitable material manufactured in the shape of a dome, attachable to the light guide  104 , and coated on the concave side of the dome with a reflective material. In one embodiment, the light conditioning element  110  can be an optically transmissive element integrally formed (such as by injection molding as a single piece) with the light guide  104  and coated on the convex side of the dome with a reflective material. The reflective coating  128  can be made of a dielectric, or metals such as aluminum or silver. The solar energy collector  102  can be the terminus of an optical fibre  102  which transmits light to a remote, solar energy collector  102 . In other embodiments the solar energy collector  102  can be a photovoltaic cell or other type of suitable light-collector. 
         [0032]    Light  131  from the light guide  104  passes through a light coupling surface  124  and is coupled to the solar energy collector  102  either directly (e.g., where the light to the solar energy collector need not be reflected by the light conditioning element  110 ), or after having been reflected by the light conditioning element  110 . Where the light conditioning element  110  and the light guide  104  are integrally formed, the light conditioning element  110  can have a cavity into which the solar energy collector can be inserted. Where the light conditioning element  110  and the light guide  104  are two separate pieces, the solar energy collector can be held in place by means of a clamp or a tray (not shown). 
         [0033]    In the light guide  104 , at least some of the light  131  is totally internally reflected by the first surface  112  and the step portions  120  of the second surface  114 , and travels towards the central edge  124  of the light guide  104 . This light  131  originates at an inter-step portion  122  of the second surface  114  and travels from a reflector element  106 . Light  131  that exits the reflector element  106  from the inter-step portion  122  is reflected by the surfaces of the reflector element  106  via total internal reflection (TIR) or, where the reflective surface  107  of the reflector element  106  is coated with a reflective material, by specular reflection. The refracted light  132  is redirected towards the reflector element  106  from a corresponding lens  116  in the redirecting layer  108 . The lens  116  may receive collimated light  133 , such as from the sun. In embodiments of the solar concentrator device where the input light  133  is not collimated, a redirecting layer  108  may not be required. 
         [0034]    In one embodiment, the solar concentrator device  100  can be generally in the shape of a circular disk (i.e., is discoid), being revolved around a central axis  136  such that in plan view, the optically active elements (reflector elements  106 , step portions  120 , inter-step portions  122 , and lenses  116 ) follow concentric circles of increasing diameter from the central axis  136  to the peripheral edge  126  (an example of which is shown in  FIG. 15 ). In another embodiment, the solar concentrator device  100  can be generally in the shape of a planar cuboid, being linearly symmetrical about a central plane  137 , such that when viewed from above, the optically active elements (reflector elements  106 , step portions  120 , inter-step portions  122 , and lenses  116 ) follow straight, parallel lines (examples of which are shown in  FIGS. 5 &amp; 6 ). In yet another embodiment, the solar concentrator device  100  can be a more complex, free-form shape. Examples of more complex solar concentrator device shapes are described in further detail below. 
         [0035]    In a similar embodiment of a solar concentrator device  200 , shown in  FIG. 2 , the first surface  112  of the light guide  104  can be sloped with respect to the input surface  118  such that the redirecting layer  108  is wedge-shaped in cross section and the thickness of the solar concentrator device  200  is substantially constant. The substantially uniform thickness of the solar concentrator device  200  facilitates alignment of the focal point of each lens  116  with the same portion of each of the corresponding reflector elements  106 . A light conditioning element  210  reflects at least some of the light  130  from the light guide  104  through a light coupling area  224  towards the solar energy collector. 
         [0036]    In the illustrated embodiment, the light conditioning element  210  has a plurality of curved reflecting surfaces  218 ,  219  that reflect light  130  from the light guide  104 . In other embodiments the light conditioning element  210  can have more or fewer reflecting surfaces  218 ,  219  and the reflecting surfaces  218 ,  219  can have any shape that couples light  130  from the light guide  104  to the solar energy collector. As shown in  FIG. 2 , the light conditioning element  210  can be integrally formed (e.g., by injection molding as a single piece) with and of the same material as the light guide  104 . Alternatively, the light conditioning element  210  may be formed as a separate piece. 
         [0037]    Where the light conditioning element  210  is formed of a light transmissive material having a high index of refraction, the reflective surfaces  218 ,  219  can be made to reflect light  130  by TIR. Where the reflective surfaces  218 ,  219  are made to reflect light  130  by TIR and the light conditioning element  210  is formed as a separate piece from the light guide  104 , the light conditioning element  210  is coupled to the light guide  104  by means of an optical adhesive or any other suitable bonding material or method. The optically transmissive material of which the light conditioning element  210  is made can have thermally insulating properties. An example of such a thermally insulating, optically transmissive material is glass. 
         [0038]    Alternatively, the reflective surfaces  218 ,  219  can comprise mirrors. For example, a reflective coating comprising a dielectric, or metals such as aluminum or silver can be applied to reflective surfaces  218 ,  219  of the optically transmissive material. The light conditioning element  210  can also be made of metal or any other suitable material, attachable to the light guide  104 , and may be coated with a reflective material. 
         [0039]    Turning to  FIG. 3 , there is shown a cross-section of a solar concentrator device  300 , differing from the embodiment of  FIG. 1  only in that the overall thickness of the redirecting layer  308  is equal to the center thickness of the lenses and the solar energy collector  102  is a photovoltaic cell  302 . In this embodiment the overall thickness of the solar concentrator device  300  decreases as one moves outward from the central axis  136  or central plane  137  to the peripheral edge  126 . Each of the reflector elements  106  can be the same size and shape (as shown in  FIG. 3 ), however in an alternative embodiment, the reflector elements  106  can vary in shape moving from the central axis  136  or central plane  137  to the peripheral edge  126 . The reflector elements  106  reflect the light  131  from a corresponding lens  316 . 
         [0040]      FIG. 4  shows a cross-sectional view of a solar concentrator device  1900  differing from the solar concentrator device  300  illustrated in  FIG. 3  only in that the lenses  1916  are spaced-apart from one another, such that the redirecting layer  1908  is discontinuous. As the lenses  1916  may be smaller in this embodiment, a conservation of materials may be realized. 
         [0041]    As shown in  FIG. 5 , in some embodiments, the exposed surface of the lenses  816  may be covered by a protective coating  840 . Such a protective coating  840  may be especially beneficial where the lenses are made of an elastomeric or deformable material such as a soft silicone. As an example, the protective coating  840  can be a hydrophobic coating or mica applied to the exposed surface of the lenses  816 . The lenses  816  may alternatively include water/dirt-resistant nanostructures  842 , such as lotus leaf nanostructures, on their exposed surfaces. These water/dirt-resistant nanostructures  842  can be molded or applied directly onto the surface of the lenses  816  during manufacturing. The surface of the lenses  816  may also have anti-reflective textures thereon, such as moth eye or cone textures. The anti-reflective textures may be applied to the surface of the lenses  816  or may be integrally formed thereon. It is also possible to affix a planar sheet of glass to the edges  826  of the solar concentrator device  800 , such that the glass sheet is suspended over the lenses  816  to protect the solar concentrator device  800 . 
         [0042]    As shown in  FIG. 6 , a solar concentrator device  900  may include an optical coupling layer  946  between the redirecting layer  908  and the light guide  904 . The optical coupling layer  946  can be made of a deformable, optically transmissive material such as a silicone have a durometer less than 40 Shore A, which is deformable under an applied pressure, and can be overmolded or otherwise bonded (such as with an optically transmissive adhesive) to either the planar first surface  112  of the light guide  904  and/or to the planar surface  148  of the redirecting layer  908 . The deformable, optically transmissive material may also be elastomeric. Alternatively, the optical coupling layer  946  may be made of a heat-deformable, optically transmissive material such as PMMA (e.g., Evonik™ PLEXIGLAS™ or ACRYLITE™ 8N) films having a pencil hardness in the range of 6 B to 3 H, hybrid PMMA-silica films having a pencil hardness in the range of 6 B to 9 H, or optical adhesives such as methyl methacrylate (MMA)-based optical adhesives. The optical coupling layer  946  may be formed separately from the redirecting layer  908  and the light guide  904 . 
         [0043]    The solar concentrator device  900  may be assembled by clamping the redirecting layer  908  and the light guide  904  together with the optical coupling layer  946  disposed therebetween such that the optical coupling layer  946  is deformed by the pressure applied thereto. Alternatively, where the optical coupling layer  946  is made of a PMMA or hybrid PMMA-silica film, the solar concentrator device  900  optic may be thermoformed or molded at high temperatures, which may cause the layers (redirecting layer  908 , light coupling element  946  and light guide  904 ) to become fused together to create a monolithic optic. An optical bond between the redirecting layer  908 , the optical coupling layer  946  and the light guide  908  can thus be created to facilitate the transmission of light  132  to the light guide  904  through the optical coupling layer  946  from the redirecting layer  908 . 
         [0044]    In this embodiment, the light guide  904 , the redirecting layer  908  and the reflector elements  106  can be made of the same or different light transmissive materials, such as glass or an injection molded polymer. The light coupling element  946  may be made of a deformable, low refractive index material such as a silicone sandwiched between a light guide  904  made of a high refractive index material such as glass or an injection molded polymer and a redirecting layer  908  made of a high refractive index material such as glass or an injection molded polymer to form the optic of the solar concentrator device  900 . 
         [0045]    As shown in  FIG. 7 , the solar concentrator device  2300  may additionally or alternatively include an optical coupling layer  2378  between the light guide  2304  and the reflector elements  2306 . The optical coupling layer  2378  can be made of the same materials as optical coupling layer  946  and can similarly be overmolded or otherwise bonded to the light guide  2304  and/or the reflector elements  2306 . 
         [0046]    As shown in  FIG. 8  the solar concentrator device  2400  may include a low refractive index film  2480  between each reflector element  106  and the light guide  104  to facilitate TIR at the interface between the low refractive index film  2480  and the reflector element  106 . Light  133  from the redirecting layer  308  passes through the low refractive index film  2480  at an angle of incidence that is less than the critical angle so it passes through to the reflective element  106 . The light is reflected by the first portion  105  of the reflective surface  103  can undergo TIR at the interface between the low refractive index film  2480  and the reflector element  106  and does not escape from the reflector element  106  until it is reflected by a second portion  107  of the reflective surface  103  of the reflector element and can pass through the corresponding inter-step portion  122  and into the light guide  104 . 
         [0047]      FIG. 9  shows a cross-section of an solar concentrator device  700  that differs from the half cross-section of the solar concentrator device  200  of  FIG. 2  only in that the second surface  714  is not stepped, but rather is substantially flat with protrusions  722  extending therefrom, and the light conditioning element  710  is positioned along a light output edge  670  or a light output corner  1164  (described in further detail below). The light conditioning element  710  has a light conditioning surface  774  that reflects light exiting the light guide  704 . An optical aperture through which light enters the light guide  704  is formed between each of the protrusions  722  and its corresponding reflector element  706  (similar to that formed between the inter-step portions  122  and the reflector elements  106 ). Each protrusion  722  is encapsulated (as shown in  FIG. 9 ) by or otherwise optically coupled to a reflector element  706 . 
         [0048]      FIG. 10  shows a partial cross-section of a solar concentrator device  1000  that includes a redirecting layer  1008  that has a plurality of concavo-convex lenses  1016 , a stepped light guide  1004 , and a reflector layer  1054  that has a plurality of reflector elements  1006 . The planar surface  1048  of the redirecting layer  1008  has a plurality of concavities  1050  being the concave portions of each concavo-convex lens  1016 . Separating the concavities  1050  of the redirecting layer  1008 , may be a plurality of planar segments  1052 . The redirecting layer  1008  can be overmolded onto the first surface  112  of the light guide  1004  or alternatively bonded thereto with an adhesive or by laser welding, such that the planar segments  1052  are bonded to the planar first surface  112  of the light guide  1004 . The gaps  1056  remaining between the first surface  112  of the light guide  1004  and the concavities  1050  of the redirecting layer  1008  can be filled with air or any suitable light transmissive material that has a lower refractive index than the redirecting layer  1008 . 
         [0049]    The step portions  1020  of the second surface  114  of the light guide  1004  need not be parallel to the first surface  112  of the light guide  1004  as shown in the figures described above, but rather can be sloped as shown in  FIG. 10 . The light guide  1004  can also have protrusions  1060  similar to those of  FIG. 9  extending from the second surface  114 . 
         [0050]    In this embodiment, the plurality of reflector elements  1006  are provided in a reflector layer  1054  which may be overmolded onto the second surface  114  of the light guide  1004  or alternatively bonded thereto with an optical adhesive or by laser welding. The reflector layer  1054  thereby includes a plurality of reflector elements  1006  and a plurality of secondary reflector sections  1058  joining the reflector elements  1006 . The redirecting layer  1008  and the reflector layer  1054  can be made of a silicone of lower refractive index than the material of the light guide  1004 . As with other similar embodiments, the solar concentrator device  1000  can be flexible where flexible materials are used, e.g., a high refractive index silicone is used for the light guide  1004 . 
         [0051]    In this embodiment, light received by a solar energy collector is coupled into the light guide  1004  where it is totally internally reflected towards the central edge by the first surface  112  of the light guide  1004 , by the step portions  1020  of the light guide  1004 , and/or by the secondary reflector sections  1058  of the reflector layer  1054 . Total internal reflection can occur on the first surface  112  of the light guide  1004  both where it interfaces with a gap  1056 , and where it interfaces with a planar segment  1052  of the redirecting layer  1008 . Each inter-step portion  1022 , formed at least in part on a surface of a protrusion  1060 , allow a wider range of angles of light to exit through the aperture that is formed between the inter-step portions  1022  and the reflector elements  1006  than would be possible without the protrusion  1060 . Light exiting the reflector element  1006  is reflected by the surfaces of the reflector elements  1006  such that beams of substantially collimated light are transmitted from the concave portions (cavities)  1050  of the redirecting layer  1008 . Light converges to the cavities  1050  by the convex portion  1062  of the lenses  1016  from the collimated input light  133   
         [0052]      FIG. 11  shows a cross-section of a solar concentrator device  2000  that has a sloped orientation with respect to the direction of the input light  133 . If the solar concentrator device  2000  is oriented to emit input light  133  in a downward direction as shown in  FIG. 11 , then the solar concentrator device  2000  can be said to have a downward slope to the solar energy collector  102  from the peripheral edge  2026 . 
         [0053]    The redirecting layer  2008  generally increases in thickness from the edge closest to the solar energy collector  102  to the peripheral edge  2026  and can have a sloped planar surface  2048 . In order to maintain the orientation of the lenses  2016 , the lenses  2016  can be stepped as shown in  FIG. 11 . 
         [0054]    The first surface  2012  of the light guide  2004  may also be sloped to complement the planar surface  2048  of the redirecting layer  2008 . The step portions  2020  of the second surface  2014  of the light guide  2004  may be parallel to the planar surface  2048  and may therefore also be sloped. 
         [0055]    In some embodiments, due to the sloped configuration of the solar concentrator device  2000 , light emitted by the reflector elements  2006  via the inter-step portions  2022  may only reflect from the first portion  2005  of the reflective surface  2003 , in which case only the first portion  2005  needs to be reflective. The sloped configuration of the solar concentrator device  2000  may also facilitate the optimization of the design of the light conditioning element  2010  for efficient transmission of light to the solar energy collector  102  from the light guide  2004 . 
         [0056]      FIG. 12  shows a cross-section of an solar concentrator device  2100  that differs from the solar concentrator device  2000  of  FIG. 11  only in that the lenses  2116 , their corresponding reflector elements  2106  and the distance between a lens  2116  and its corresponding reflector element  2106  are scaled in inverse proportion with their distance from the solar energy collector  102  and has an optical coupling layer  2146  similar to that of the solar concentrator device  900  of  FIG. 6 . The plane of the input surface  2118  can therefore be made perpendicular to the direction of the input light. Such scaling of the optical elements may help when the input light  133  is more uniform in intensity and collimated across the input surface  2118 . 
         [0057]      FIG. 13  is a cross-section of a solar concentrator device  2200  that is similar to the solar concentrator device  100  of  FIG. 1 , except that the light guide  2204  of the solar concentrator device  2200  comprises a substantially flat sheet of light transmissive material. The light transmissive material of the redirecting layer  2208  can have an index of refraction that is higher than the surrounding environment of the solar concentrator device  2200  (typically a gas such as air) but lower than the light transmissive material of the reflector elements  2206  and the light guide  2204 . Light  131  can therefore be guided within the light guide  2204  by total internal reflections on the first surface  2212  of the light guide  2204  and portions of the second surface  2214  exposed to the surrounding environment. However, light  131  travelling within the light guide  2204  that originating from a portion of the second surface  2214  to which an reflector element  2206  is optically bonded can be transmitted from the reflector element  2206  and reflected by the reflecting surface  2207  from the corresponding lens  2216  (without undergoing TIR at the interface between the planar surface  2248  of the redirecting layer  2208  and the first surface  2212  of the light guide  2204 ). 
         [0058]      FIG. 14  shows a cross-section of an solar concentrator device  2700  that differs from the solar concentrator device  2200  of  FIG. 13  only in that the reflector elements  2706  are integrally formed with the light guide  2704  and there is an optical coupling layer  2788  similar to the optical coupling layer  946  of  FIG. 6 . The optical coupling layer  2788  is made of a light transmissive material that has an index of refraction that is lower than the index of refraction of the light guide  2704  such that light  131  can be guided within the light guide  2704  by total internal reflection even if the index of refraction of the redirecting layer  2708  is not lower than that of the light guide  2704 . Manufacture of this solar concentrator device  2700  may be simpler than other solar concentrator devices because it comprises only two separate parts—the redirecting layer  2708  and the light guide  2704  with integrally formed reflector elements  2706 . The two parts can be assembled into a solar concentrator device  2700  using an optical adhesive as the optical coupling layer  2788 . 
         [0059]    While a full cross-sections of solar concentrator devices having symmetry about a central axis  136  or plane  137  are not shown for all embodiments of the solar concentrator devices  800 ,  900 ,  2300 ,  700 ,  2000 ,  2100 ,  2200 ,  2700  described above, a person skilled in the art will appreciate that the cross-sections shown can be reflected through a central axis  136  or plane  137  and a suitable light conditioning element  110 ,  210  employed to produce symmetric solar concentrator devices. 
         [0060]    As described above,  FIG. 15  is a perspective view of a solar concentrator device  400  having the general shape of a circular disk and having circular symmetry about a central axis  136 . This embodiment can have a cross-sectional profile similar to any of the embodiments described above. In this embodiment, the redirecting layer  408  is discoid and comprises a plurality of lenses  416  concentrically disposed. The lenses  416  may be cylindrical lenses forming concentric rings about the central axis  136  of the solar concentrator device  400 . The light guide  404  is also disk-shaped and has substantially the same diameter as the redirecting layer  408 . The light guide  404  has a centrally located light coupling surface  424 , which may, for example, have the shape of a truncated cone, or a cylinder. The plurality of reflector elements (not shown) is concentrically disposed. The disk-shaped solar concentrator device  400  can be cropped to make the solar concentrator device  400  a tileable shape, such as square or hexagonal, while conserving its revolved geometry. Where the solar concentrator device  400  has a revolved geometry, the light conditioning element  410  also has a revolved geometry, whether it is a light conditioning element that guides light by TIR or specular reflections. 
         [0061]    The solar energy collector  102  is a point destination. As shown in  FIG. 15 , the solar energy collector  102  can be the terminus of an optical fibre  402  which transmits light to a remote, solar energy collector. 
         [0062]    In an alternate embodiment shown in  FIG. 16 , the solar concentrator device  400  may be cropped to make an solar concentrator device  1100  rectangular in shape with the axis of rotational symmetry  1162  at one corner  1164  of the solar concentrator device  1100 , as shown in  FIG. 16 . The redirecting layer  1108  is generally in the shape of a planar cuboid and comprises a plurality of lenses  1116  coaxially disposed. The lenses  1116  can be cylindrical lenses forming concentric circular arcs centred on the axis of symmetry  1162 . The light guide  1104  also has the shape of a planar cuboid and has substantially the same width and length as the redirecting layer  1108 . The light guide  1104  has a light coupling surface  1124  located in the vicinity of the axis of symmetry  1162 . The light coupling surface  1124  can have the shape of a truncated cone, or a cylinder. The solar energy collector  1102  is disposed along the central axis  1162 , and is optically and mechanically bonded to the light coupling surface  1124 , for example by means of an optical adhesive. The plurality of reflector elements  1106  is likewise coaxially disposed. In this embodiment, light propagates in the light guide towards the outer edges  1166 . 
         [0063]    With reference to  FIG. 17 , there is shown a perspective view of a solar concentrator device  500  having the general shape of a planar cuboid with height Z, relatively small as compared to its width X and length Y. In this embodiment, the optically active elements (reflector elements  506 , step portions  520 , inter-step portions  522 , and lenses  516 ) lie along straight and parallel lines, parallel to the central plane  137 . The solar concentrator device  500  can have a longitudinal section along width X similar to any of the figures described above showing cross-sections of solar concentrator devices. The solar concentrator device  500  has two redirecting layers  508 , and two light guides  504 , each disposed on either side of the central plane  137 . The solar concentrator device  500  can be symmetric about the central plane  137  as shown in  FIG. 17 , but need not be symmetric. Each light guide  504  has a light coupling surface  524  in the vicinity of the central plane  137  to transmit light to the solar energy collector  502 . In the illustrated embodiment, the light coupling surfaces  524  complement the shape of the profile of the solar energy collector  502 , such that the solar energy collector  502  can be held in place by the light coupling surfaces  524 . The solar energy collector  502 , which can be photovoltaic cells, or a longitudinal light conditioning element optically coupled to a point collector such as the terminus of an optical fibre, or any other type of longitudinal solar energy collector, is disposed lengthwise along the central plane  137 . In one embodiment, the solar concentrator device  500  can be manufactured as a single piece with a cavity located longitudinally along the central plane  137  for insertion of the solar energy collector  502 . In another embodiment, each side of the solar concentrator device  500  (comprising a redirecting layer  508 , a light guide  504  and a plurality of collecting elements  506 ) can be manufactured separately and then bonded together by means of an optical adhesive or any other suitable material or method, including clamping. 
         [0064]    Cuboid shaped solar concentrator devices  500  may be cropped to make the solar concentrator device any desirable overall shape, such as hexagonal or circular discs, keeping the optically active elements straight and parallel. In some embodiments, the solar concentrator device  500  may include a secondary optical element to aid in coupling light to the solar energy collector  502  from the light guides  504 . 
         [0065]    With reference to  FIG. 18 , a solar concentrator device  600  may include one redirecting layer  508 , one light guide  504 , and one set of reflector elements  506 , such that the solar energy collector  602 , runs along light coupling surface  624  of the solar concentrator device  600 , as shown in  FIG. 18 . In this embodiment the exposed surface of the solar energy collector  602  can be coated with a reflective material  672  such that some, preferably most or most preferably, all, light is reflected from the light guide  504 . Alternatively, a tubular cavity or other means for retaining the solar energy collector  602  along the light coupling surface  624  can be provided with a reflective peripheral surface for reflecting light from the light guide  504 . In another embodiment, a light conditioning element optically coupled to a point destination may extend longitudinally across the light output edge  670  such that the light from the light guide  504  is coupled to the solar energy collector through the light coupling surface  624 . In some embodiments, such as that shown in  FIG. 18 , the solar energy collector  602  can cover the entire light coupling surface  724 . 
         [0066]    The solar concentrator device  2500  shown in  FIG. 19A  has an array of lens-reflector element pairs. In this embodiment, the redirecting layer  2508  includes a substrate sheet  2586  made of light transmissive material and the array of lenses  2516  extending from the first surface  2587  of the substrate sheet  2586 . The lenses  2516  may be integrally formed with the substrate sheet  2586 , may be 3D printed or overmolded onto the substrate sheet  2586 , or may be otherwise optically bonded to the first surface  2587  (e.g., using an optical adhesive, by laser welding or any other means known in the art). The lenses may, for example, be spherical caps or quarter-spherical caps (not shown). 
         [0067]    Similar to the light guide  2204  of  FIG. 13 , the light guide  2504  can comprise a substantially flat sheet of light transmissive material. A light conditioning element  2510  may also be provided to receive light from all directions within the light guide  2504  and thereby receive more of the light from the reflector elements  2506  at any given distance from the solar energy collector  102 . In the illustrated embodiment, the solar energy collector  102  is the terminus of an optical fibre. The light conditioning element  2510  may be integrally formed with the light guide  2504 , may be 3D printed or overmolded onto the light guide  2504 , or may be otherwise optically bonded to the second surface  2514  of the light guide  2504  (e.g., using an optical adhesive, by laser welding or any other means known in the art). Alternatively, a cavity may be provided in the light guide  2504  and the light conditioning element  2510  may be inserted into the cavity. 
         [0068]    The array of reflector elements  2506  may be integrally formed with the light guide  2504 , may be 3D printed or overmolded onto the light guide  2504 , or may be otherwise optically bonded to the second surface  2514  of the light guide  2504  (e.g., using an optical adhesive, by laser welding or any other means known in the art). The reflector elements  2506  can be nubs and can each have a reflective surface  2503  having a first portion  2505  that is, for example, a concave reflector  2505   a  (as shown in  FIG. 19B ) or convex reflector (as shown in  FIG. 19C ). The reflector elements  2506  may be non-uniform in shape, size and/or orientation so that each reflector element  2506  reflects approximately the same amount of light from its corresponding lens  2516 . 
         [0069]    The solar concentrator device  2500  may include an optical coupling layer  2589  between the second surface  2588  of the substrate sheet  2586  and the first surface  2512  of the light guide  2504  similar to the optical coupling layer  946  of the solar concentrator device  900  of  FIG. 6 . The optical coupling layer  2589  has an index of refraction that is lower than that of the light guide  2504  such that light  131  is reflected at the first surface  2512  of the light guide  2504  by TIR. 
         [0070]    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.