Abstract:
A solar concentrator including a housing having a receiving wall, a reflecting wall and at least two end walls, the receiving, reflecting and end walls defining a three-dimensional volume having an inlet, wherein a vertical axis of the housing is generally perpendicular to the inlet, a receiver mounted on the receiving wall of the housing, the receiver including at least one photovoltaic cell, wherein a vertical axis of the receiver is disposed at a non-zero angle relative to the vertical axis of the housing, at least one clip disposed on the reflecting wall, an optical element received within the three-dimensional volume, the optical element including at least one tab, the tab being engaged by the clip to align the optical element with the receiver, and a window received over the inlet to enclose the housing.

Description:
PRIORITY 
       [0001]    The present patent application claims priority from U.S. Ser. No. 61/175,136 filed on May 4, 2009, the entire contents of which are incorporated herein by reference. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
       [0002]    The invention(s) disclosed herein was/were made with the support of the government of the United States pursuant to contract number DE-FC36-07G017052 awarded by the Department of Energy. Therefore, the government of the United States may have certain rights in the disclosed invention(s). 
     
    
     FIELD 
       [0003]    The present patent application relates to concentrating solar power systems and, more particularly, to solar concentrators having a fully enclosed housing, wherein the housing supports a solar cell array in an off-axis configuration. 
       BACKGROUND 
       [0004]    Photovoltaic solar concentrators typically are used to generate electrical power by concentrating sunlight onto photovoltaic devices, thereby collecting sunlight from a large area and concentrating it on a relatively small area of solar cells. Therefore, high efficiency solar cells, such as gallium arsenide-based (“GaAs”) solar cells, may be used in place of less efficient (and less expensive) silicon solar cells, thereby producing more energy per unit area at a reduced cost. 
         [0005]    Solar concentrators may be configured in various ways and typically include refracting optics, reflecting optics or various combinations thereof. Regardless of the concentrating optics used, excess heat must be removed and the solar cells must be protected from the environment. Therefore, the design process generally requires a compromise between the thermal and/or protective features. For example, prior art systems that utilize Fresnel lenses (refracting optics) require placing the solar cells in the back of an enclosure, which makes it difficult to remove excess heat, requiring a larger heat sink. 
         [0006]    Furthermore, efficient operation of solar concentrators requires precise alignment of the optical elements with the solar cells. Indeed, a more precise alignment enables a higher degree of optical concentration, thereby reducing the aggregate solar cell cost. However, prior art solar concentrator designs typically require costly manufacturing steps to achieve precise alignment, while others sacrifice precision, and therefore efficiency, to reduce manufacturing costs. 
         [0007]    Accordingly, there is a need for a solar concentrator that quickly and easily aligns the optical elements with the solar cells in an off-axis configuration, while providing the solar cells with the requisite thermal and environmental protections. 
       SUMMARY 
       [0008]    In one aspect, the disclosed solar concentrator may include a housing having a receiving wall, a reflecting wall and at least two end walls, the receiving, reflecting and end walls defining a three-dimensional volume having an inlet, wherein a vertical axis of the housing is generally perpendicular to the inlet, a receiver mounted on the receiving wall of the housing, the receiver including at least one photovoltaic cell, wherein a vertical axis of the receiver is disposed at a non-zero angle relative to the vertical axis of the housing, at least one clip disposed on the reflecting wall, an optical element received within the three-dimensional volume and engaged by the clip to align the optical element with the receiver, and a window received over the inlet to enclose the housing. 
         [0009]    In another aspect, the disclosed solar concentrator may include a housing including a receiving wall, a reflecting wall, a lower wall and at least two end walls, the receiving, reflecting, lower and end walls defining a three-dimensional volume having an inlet, wherein a vertical axis of the housing is generally perpendicular to a plane defined by the inlet, a plurality of receivers mounted on the receiving wall of the housing, each receiver defining a vertical axis and including at least one photovoltaic cell, a lens focused on the photovoltaic cell, and a heat sink connected to the photovoltaic cell, wherein the photovoltaic cell and the lens are disposed within the three-dimensional volume and the heat sink is external of the three-dimensional volume, wherein the vertical axis of the receiver is disposed at a non-zero angle relative to the vertical axis of the housing, a plurality of optical elements received within the three-dimensional volume, each optical element including a front tab and a rear tab, a plurality of front clips disposed on the lower wall of the housing, each front clip engaging an associated one of the front tabs, a plurality of rear clips disposed on the reflecting wall of the housing, each rear clip engaging an associated one of the rear tabs, and a window connected to the inlet of the housing to form an enclosed three-dimensional volume. 
         [0010]    In another aspect, a method for aligning an optical element with a receiver including at least one photovoltaic cell may include the steps of (1) providing a housing including a receiving wall, a reflecting wall and at least two end walls, the receiving, reflecting and end walls defining a three-dimensional volume having an inlet, wherein a vertical axis of the housing is generally perpendicular to the inlet, (2) positioning at least one clip on the reflecting wall of the housing, (3) mounting the receiver on the receiving wall of the housing, wherein a vertical axis of the receiver is disposed at a non-zero angle relative to the vertical axis of the housing, (4) positioning the optical element within the three-dimensional volume such that the optical element is engaged by the clip and (5) positioning a window over the inlet to enclose the housing. 
         [0011]    Other aspects of the disclosed solar concentrator will become apparent from the following description, the accompanying drawings and the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a front perspective view, partially exploded, of one aspect of the disclosed solar concentrator; 
           [0013]      FIG. 2  is a top plan view of the solar concentrator of  FIG. 1 ; 
           [0014]      FIG. 3  is a side elevational view, in section, of the solar concentrator of  FIG. 2 ; 
           [0015]      FIG. 4  is side elevational view, in section, of a detailed portion of the solar concentrator of  FIG. 3 ; 
           [0016]      FIG. 5  is a side elevational view, in section, of another aspect of the disclosed solar concentrator; and 
           [0017]      FIG. 6  is a side perspective view of an optical element of the solar concentrator shown in  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    As shown in  FIG. 1 , one aspect of the disclosed solar concentrator, generally designated  10 , may include a housing  12 , a window  14 , an array of receivers  16 ,  18 ,  20 ,  22 ,  24 ,  26  and an array of optical elements  28 ,  30 ,  32 ,  34 ,  36 ,  38 . In one aspect, the number of optical elements  28 ,  30 ,  32 ,  34 ,  36 ,  38  may correspond to the number of receivers  16 ,  18 ,  20 ,  22 ,  24 ,  26 . While six optical elements  28 ,  30 ,  32 ,  34 ,  36 ,  38  and six receivers  16 ,  18 ,  20 ,  22 ,  24 ,  26  are shown in the solar concentrator  10 , those skilled in the art will appreciate that solar concentrators may be constructed with various numbers of receivers and optical elements without departing from the scope of the present disclosure. 
         [0019]    Optionally, the solar concentrator  10  may include brackets  40 ,  42  or like devices connected to the housing  12  such that the solar concentrator  10  may be mounted to a solar tracker (not shown). The solar tracker may be configured to rotate the solar concentrator  10  such that the vertical axis A ( FIG. 3 ) of the solar concentrator  10  is aligned with the sun as the sun moves across the sky. 
         [0020]    The optical elements  28 ,  30 ,  32 ,  34 ,  36 ,  38  may be mirrors or like devices, such as parabolic mirrors, and may be sized and shaped to receive incoming sunlight and focus the incoming sunlight onto the receivers  16 ,  18 ,  20 ,  22 ,  24 ,  26 . Those skilled in the art will appreciate that the overall size, shape and geometry of the optical elements  28 ,  30 ,  32 ,  34 ,  36 ,  38  may depend upon the size and shape of the housing  12 , as well as the positioning of the receivers  16 ,  18 ,  20 ,  22 ,  24 ,  26  within the housing  12 , among other things. 
         [0021]    In one particular aspect, one or more of the optical elements  28 ,  30 ,  32 ,  34 ,  36 ,  38  may be optical concentrators disclosed in U.S. Patent Pub. No. 2008/0223443 titled “Optical Concentrator, Especially for Solar Photovoltaics” filed by Benitez et al. on Mar. 14, 2008, the entire contents of which are incorporated herein by reference. 
         [0022]    Referring to  FIG. 3 , each optical element  28 ,  30 ,  32 ,  34 ,  36 ,  38  may include a front tab  44  and a rear tab  46 . The front and rear tabs  44 ,  46  may be integral with the optical elements  28 ,  30 ,  32 ,  34 ,  36 ,  38 , or may be connected to the optical elements  28 ,  30 ,  32 ,  34 ,  36 ,  38  by, for example, fasteners, adhesives or the like. 
         [0023]    Each receiver  16 ,  18 ,  20 ,  22 ,  24 ,  26  may include one or more photovoltaic cells for converting harvested light into electrical energy. Referring to  FIG. 3 , in one particular aspect, each receiver  16 ,  18 ,  20 ,  22 ,  24 ,  26  may include one or more photovoltaic cells  48 , a lens  50  and a heat sink  52 . The photovoltaic cells  48  may be any cells capable of converting light into electrical energy, such as silicon solar cells, GaAs solar cells or the like. The lens  50  may focus harvested light, particularly light directed to the receivers  16 ,  18 ,  20 ,  22 ,  24 ,  26  by the optical elements  28 ,  30 ,  32 ,  34 ,  36 ,  38 , onto the photovoltaic cells  48 . The heat sink  52  may be any device capable of dissipating heat from the photovoltaic cells  48 , such as a fanned heat sink, a heat pipe or the like. 
         [0024]    Referring back to  FIG. 1 , the window  14  may be a generally planar sheet of transparent or partially transparent material. In one aspect, the window  14  may be formed from glass. In another aspect, the window  14  may be formed from a polymeric material, such as polycarbonate or acrylic. The transparency, flexibility and weatherability of the material (or materials) used to form the window  14  may be selected based upon design considerations. 
         [0025]    The housing  12  may be a generally rigid, elongated, trough-like structure that houses the receivers  16 ,  18 ,  20 ,  22 ,  24 ,  26  and the optical elements  28 ,  30 ,  32 ,  34 ,  36 ,  38  therein. However, as shown in  FIGS. 1-3 , portions of the receivers  16 ,  18 ,  20 ,  22 ,  24 ,  26 , particularly the heat sink  52 , may be external of the housing  12 . The housing  12  may be formed as a single piece or as an assembly of multiple pieces. Appropriate materials for forming the housing  12  include steel and moldable fiberglass, though various materials, including combinations of materials, capable of withstanding exposure to the elements may be used. 
         [0026]    Referring to  FIGS. 1 and 3 , the housing  12  may include a first end wall  54 , a second end wall  56 , a receiving wall  58 , a reflecting wall  60  and a lower wall  62 . The first end wall  54 , the second end wall  56 , the receiving wall  58  and the reflecting wall  60  may define an upper lip  64  of the housing  12  that may form an inlet  65  for receiving light into the housing  12 . As shown in  FIG. 3 , the inlet  65  may be generally planar and the vertical axis A of the housing  12  may be generally perpendicular to the plane defined by the inlet  65 . The upper lip  64  of the housing  12  may be sized and shaped to closely correspond with the size and shape of the window  14 . 
         [0027]    Thus, the window  14  may be received over the lip  64  of the housing  12  to fully enclose the housing  12 . The window  14  may be secured to the lip  64  of the housing  12  by adhesives, tape (e.g., double-sided tape) or mechanical fasteners. Optionally, a gasket (not shown) may be positioned between the window  14  and the lip  64  to ensure a water-tight seal therebetween. 
         [0028]    As shown in  FIG. 1 , the receivers  16 ,  18 ,  20 ,  22 ,  24 ,  26  may be positioned along the receiving wall  58  of the housing  12  such that they are offset from the center of the housing  12 . Furthermore, as shown in  FIG. 3 , the receiving wall  58  may be configured to position the receivers  16 ,  18 ,  20 ,  22 ,  24 ,  26  such that a vertical axis D (i.e., an axis parallel with a surface normal) of the receivers  16 ,  18 ,  20 ,  22 ,  24 ,  26  is at a non-zero angle relative to the vertical axis A of the housing  12 . Therefore, the receivers  16 ,  18 ,  20 ,  22 ,  24 ,  26  may not obstruct light (arrow B) entering the housing  12 . 
         [0029]    In one aspect, the non-zero angle between the vertical axis D of the receivers  16 ,  18 ,  20 ,  22 ,  24 ,  26  and the vertical axis A of the housing  12  may be about 20 to about 80 degrees. In another aspect, the non-zero angle between the vertical axis D of the receivers  16 ,  18 ,  20 ,  22 ,  24 ,  26  and the vertical axis A of the housing  12  may be about 40 to about 70 degrees. In yet another aspect, the non-zero angle between the vertical axis D of the receivers  16 ,  18 ,  20 ,  22 ,  24 ,  26  and the vertical axis A of the housing  12  may be about 50 to about 60 degrees. In yet another aspect, the non-zero angle between the vertical axis D of the receivers  16 ,  18 ,  20 ,  22 ,  24 ,  26  and the vertical axis A of the housing  12  may be about 55 degrees. 
         [0030]    Still referring to  FIG. 3 , the optical elements  28 ,  30 ,  32 ,  34 ,  36 ,  38  may be positioned along the reflecting wall  60  of the housing  12 . Therefore, the optical elements  28 ,  30 ,  32 ,  34 ,  36 ,  38  may be positioned to direct incoming light (arrow B) toward the receivers  16 ,  18 ,  20 ,  22 ,  24 ,  26  in an off-axis direction, as shown by arrow C. 
         [0031]    In one particular aspect, the lower wall  62  of the housing  12  may include front clips  66  for receiving the front tabs  44  of the optical elements  28 ,  30 ,  32 ,  34 ,  36 ,  38  and the reflecting wall  60  of the housing  12  may include rear clips  68  for receiving the rear tabs  46  of the optical elements  28 ,  30 ,  32 ,  34 ,  36 ,  38 . Additional clips may be used to secure the optical elements  28 ,  30 ,  32 ,  34 ,  36 ,  38  relative to the housing  12 . 
         [0032]    Furthermore, while the use of clips and tabs is shown and described, those skilled in the art will appreciate that various mechanical devices (e.g., hooks, straps or belts) or features (e.g., notches or ribs), as well as adhesives, may also be used to engage and secure the optical elements  28 ,  30 ,  32 ,  34 ,  36 ,  38  relative to the housing  12  without departing from the scope of the present disclosure. Still furthermore, while the clips  66 ,  68  shown in  FIG. 3  are associated with the housing  12 , those skilled in the art will appreciate that the clips  66 ,  68  may be mounted on the optical elements  28 ,  30 ,  32 ,  34 ,  36 ,  38  for engaging the housing  12 , particularly a rib, flange, notch or like feature on the housing  12 . 
         [0033]    In one particular aspect, the front and rear clips  66 ,  68  may be integral with the housing  12 . For example, the front and rear clips  66 ,  68  may be formed by roll forming or break forming during construction of the housing  12 . In another aspect, the front and rear clips  66 ,  68  may be separate components that have been connected to the housing  12 . For example, the front and rear clips  66 ,  68  may be mechanical clips that have been secured to the housing  12  with fasteners (e.g., screws or rivets). 
         [0034]    Accordingly, the front and rear clips  66 ,  68  positioned within the housing  12  may facilitate precise alignment of the optical elements  28 ,  30 ,  32 ,  34 ,  36 ,  38  relative to the receivers  16 ,  18 ,  20 ,  22 ,  24 ,  26  in an off-axis configuration, thereby simplifying the installation process. Furthermore, when the window  14  is secured to the housing  12 , the housing  12  and window  14  may form an enclosure that protects the optical elements  28 ,  30 ,  32 ,  34 ,  36 ,  38  and the delicate components of the receivers  16 ,  18 ,  20 ,  22 ,  24 ,  26  from exposure to the environment. 
         [0035]    Front clip  66  may restrain the position of optical elements  28 ,  30 ,  32 ,  34 ,  36 ,  38  at the front location of the optical element in all three directions. However, as shown in  FIG. 4 , the optical elements  28 ,  30 ,  32 ,  34 ,  36 ,  38  may have a foot  70  or like feature, which may be long and slender, that attach to the rear clips  68 , which prevent movement in the direction parallel to the sun&#39;s rays, but which allow movement in the other two directions normal to the direction parallel to the sun&#39;s rays. This advantageous arrangement allows the optical elements  28 ,  30 ,  32 ,  34 ,  35 ,  38  to move slightly with respect to the housing  12  due to different coefficients of thermal expansion, while maintaining precise location in the direction which is critical to the optical performance of the system, which is the direction parallel to the sun&#39;s rays. 
         [0036]    Referring to  FIG. 6 , in one alternative aspect, an optical element  28 ′ may include an optical surface  80  having a forward end  82  and a rear end  84 . A protruding portion  86 , which may be non-optical, may extend distally from the forward end  82  and may include a front tab  88 . Therefore, in one aspect, the front tab  88  may be displaced by a distance X from the forward end  82  of the optical surface  80 . In another aspect, the front tab  88  may also be centered relative to the optical surface  80  along the protruding portion  86 . Additional front tabs (not shown) may be included along the protruding portion  86  without departing from the scope of the present disclosure. 
         [0037]    Referring to  FIG. 5 , the optical element  28 ′ may be received within the housing  12  such that the front tab  88  is received in a corresponding clip  90  secured to the housing  12 , thereby precisely aligning the optical surface  80  of the optical element  28 ′ with the receiver  16  in an off-axis configuration. Additional tabs  92  extending from the rear end  84  of the optical element  28 ′ may engage corresponding clips  94  secured to the housing  12  to further secure the optical element  28 ′ relative to the housing  12 . In one particular aspect, the additional tabs  92  may be spring-loaded to absorb stresses between the optical element  28 ′ and the housing  12 . 
         [0038]    Although various aspects of the disclosed solar concentrator have been shown and described, modifications may occur to those skilled in the art upon reading the specification. The present application includes such modifications and is limited only by the scope of the claims.