Abstract:
A solar photovoltaic module containing a housing that supports an array of photovoltaic cells and corresponding light guides. The housing includes a base member having a generally planar support surface and two side walls projecting from the support surface. Two side panels detachably connect to the side walls, and a top panel detachably connects to the side panels. The top panel includes a plurality of concentrating lenses that focus incident solar radiation into the inside of the housing towards the light guide. The light guides are disposed between the corresponding concentrating lenses and photovoltaic cells such that the concentrating lenses and light guides work together to direct light onto the photovoltaic cells. At least one retaining member interfaces to the light guides and applies a downward force that biases the respective light guides toward the corresponding photovoltaic cells.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates generally to the field of photovoltaic systems. More particularly, this invention relates to concentrated solar photovoltaic systems and parts thereof. 
         [0003]    2. State of the Art 
         [0004]    Terrestrial solar photovoltaic systems convert solar insolation into electrical energy using photovoltaic cells. The amount of electrical energy that a photovoltaic cell produces is proportional to the intensity of the insolation it receives and the surface area of the cell. Photovoltaic cells are typically made from various semiconductor materials such as, but not limited to, silicon or gallium arsenide. Single junction photovoltaic cells, which are typically realized by silicon material, are less efficient at converting solar isolation to electrical energy, and thus require a larger size and a greater number of cells to provide a required amount of electrical output. Multiple junction (MJC) photovoltaic cells, which are typically realized by gallium arsenide material, by contrast, are more efficient, and require less size and a smaller number of cells to provide a required amount electrical output. 
         [0005]    Concentrating the insolation received by a photovoltaic cell can effectively decrease costs by increasing the electrical output of the photovoltaic cell. One form of concentration is realized by a concentrator lens and a light guide that cooperate to channel insolation to the photovoltaic cell. These components must be manufactured and assembled with tight tolerances in order to properly channel sunlight to the photovoltaic cell. In addition, the photovoltaic cell heats up as it receives insolation. This heat limits the photovoltaic cell&#39;s efficiency. A number of housings and mounting devices have been disclosed in the art that support photovoltaic cells and associated concentration mechanisms. Among these are U.S. Pat. No. 6,399,874; PCT Pub. No. WO 2006/114457 A1; and U.S. Pat. No. 6,483,093. These photovoltaic cell systems presently rely on an adhesive bond between the light guide and the photovoltaic cell to mechanically support the secondary optical device in place above the photovoltaic cell. The adhesive bond thus takes on a mechanical load due to the weight of the light guide and the lateral and/or sheering forces that arise from the transportation, positioning, or movement of the system. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention is directed to a solar photovoltaic module to be used for the generation of power suitable for terrestrial applications, including power grid fields, rooftop systems, private or public utilities, and commercial and residential building applications. The solar photovoltaic module includes a housing having a base member, two side panels detachably connected to the base member, a top panel detachably connected to the side panels, and two end panels detachably connected to the base member and/or the side panels. The top panel contains an integral array of concentrating lenses that focus solar energy through the interior of the housing to an array of photovoltaic cells via corresponding light guides mounted within the housing. The base member of the housing mechanically supports the array of photovoltaic cells and corresponding light guides. The concentrating lenses, light guides, and photovoltaic cells cooperate to convert solar radiation incident on the concentrating lens to electrical energy for output. 
         [0007]    In the preferred embodiment, the base member includes a generally planar support surface having one or more recesses that receive the photovoltaic cells of the module. A plurality of cooling fins extend downward opposite the support surface and run along the length of the base member. The cooling fins dissipate heat away from the photovoltaic cells. The base member also has two side walls that angularly extend from opposite edges of the support surface, and two shoulders extending from the bottom of the side walls to further assist with supporting the side panels. The side walls project upward from opposite edges of the support surface at obtuse angles, preferably in a range between sixty to seventy-five degrees, and most preferably, between sixty-three to seventy degrees. The shoulders preferably attach at right angles to the side walls, which creates a support surface perpendicular to the bottom of the side panels as the side panels are mounted parallel to an exterior surface of the side wall. The side panels are mounted to the side walls by a plurality of self tapping screws or other fasteners that pass through holes or slots in the side panels and fasten the side panels to the side walls. The side walls preferably include a rib which defines a channel accessible for receiving the set screws or other fasteners. 
         [0008]    The top panel is attached to and supported by the side panels, and is mounted substantially parallel to the support surface such that the concentrating lenses are parallel with the support surface. End panels are mounted to respective ends of the base member, perpendicular to the direction of the array of photovoltaic cells. The array of photovoltaic cells and light guides are thus enclosed by the base member, side panels, top panel, and end panels. Sealing adhesives are applied to the enclosed housing to keep out water, dust, or other particles. The housing also preferably contains a valve that regulates air pressure inside the housing in accordance with the atmospheric pressure, which varies as the ambient temperature changes. This valve adjusts the pressure without allowing water, dust, or other contaminants inside the housing. 
         [0009]    Inside the module, a light guide is secured and aligned between a respective photovoltaic cell and concentrating lens, preferably by an adhesive bond between the bottom surface of the light guide and the top surface of the photovoltaic cells and by a retaining member that is mechanically attached to interior surfaces of the sidewalls. In the preferred embodiment, the sidewalls contain a plurality of teeth protruding from the interior surface that grip the retaining member in an interference or snap fit. The retaining member has side edges that snap into place under the teeth as the retaining member is pushed in a downward direction over the top of the light guide. The retaining member includes a cut-out that is preferably shaped to correspond to a top portion of the light guide such that the top portion passes through the cut-out as the retaining member is lowered and snapped into place. The cut-out also defines a plurality of metal fingers in the corners of the cut-out. As the retaining member is pushed in a downward direction, its side edges are snapped into place under the teeth of the sidewalls, and its metal fingers are pushed upward by the corners of the top portion of the light guide. In the assembled configuration, the metal fingers act as springs and excerpt a downward retaining force on the light guide. 
         [0010]    The concentrating lenses in the top panel are preferably Fresnel lenses, but not limited thereto, that receive solar radiation over a large surface area and channel it to the respective light guides. The light guide directs incident light onto the corresponding photovoltaic cell. In the preferred embodiment, the light guide operates to collimate, homogenize, and mix the incident light for output to the corresponding photovoltaic cell. The Fresnel lenses are designed to channel insolation at predetermined angles over a set distance, which, in conjunction with the light guides, focus insolation onto the photovoltaic cells&#39; smaller surface areas at a much greater intensity. The light guide is preferably realized by a prism having the shape of an inverted pyramid with an entry aperture greater than that of the photovoltaic cell, whereby the incident light is directed to the photovoltaic cell by refraction at the sidewalls of the prism. A reflective coating can also be applied to the sidewalls of the prism in order to limit optical loss. 
         [0011]    The photovoltaic module is assembled by bonding the array of photovoltaic cells to the base member, electronically coupling the photovoltaic cells in a desired configuration to an electrical output, and assembling the housing. The photovoltaic module provides a new mounting structure that helps to support the light guides of the module, as well as to maintain alignment with the corresponding photovoltaic cells. The mounting structure also counteracts the loading normally placed on the adhesive bonds between the array of light guides and the array of photovoltaic cells when the photovoltaic module is transported, moved, or rotated. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a partial-broken front perspective view of the concentrated solar photovoltaic module of the present invention. 
           [0013]      FIG. 1A  is a broken-exploded front perspective view of the bottom portion of the concentrated solar photovoltaic module of  FIG. 1  with an end panel that is secured thereto. 
           [0014]      FIG. 2  is a front sectional view of the base member of the concentrated solar photovoltaic module of  FIG. 1 . 
           [0015]      FIG. 3  is a top planar view of the retaining member of the concentrated solar photovoltaic module of  FIG. 1 . 
           [0016]      FIG. 4  is a top perspective view of the retaining member and prism of the concentrated solar photovoltaic module of  FIG. 1 . 
           [0017]      FIG. 5  is a front view of the assembled photovoltaic module of  FIG. 1  without the end panel. 
           [0018]      FIG. 6  is a schematic of an electrical power sink electronically coupled to a plurality of the photovoltaic modules of  FIG. 1  arranged in parallel. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0019]    Referring to  FIGS. 1 ,  1 A,  2 , and  5 , shown is a concentrated solar photovoltaic module  10  of the present invention.  FIG. 1  shows a front perspective view of the invention.  FIG. 1A  shows an enlarged view of a bottom portion of  FIG. 1  with an end panel  44  shown in an exploded view.  FIG. 2  shows an enlarged section view of a base member  12 , photovoltaic cell  18 , light guide  32 , and retaining member  34  of  FIG. 1 .  FIG. 5  shows a front section view of  FIG. 2  with side panels  24  and a top panel  40  attached to the base member  12 . 
         [0020]    The base member  12  has a generally planar support surface  14 . The support surface  14  contains one or more recesses  16  shaped to receive an array of photovoltaic cells  18  that are mounted therein preferably by double-sided thermally conductive tape. The photovoltaic cell  18  is a device that converts light energy into electrical energy. The photovoltaic cell  18  is typically realized by a photovoltaic integrated circuit together with a bypass diode and electrical interconnections mounted on a substrate. Other configurations can be used. The electrical outputs of the photovoltaic cells  18  are electronically connected to each other in a desired configuration (typically in a series or parallel configuration) by conductors supported by the base member  12 . A plurality of cooling fins  20  extend down from the base member  12  opposite the support surface  14  along the length of the photovoltaic module  10 . The cooling fins  20  are open to the atmosphere, and heat is therefore dissipated via convection. The cooling fins are preferably integrally formed with the base member  12 , but may also be separately attached. Various types of photovoltaic cells  18 , which convert solar insolation (sunlight) into electrical energy, can be employed, such as gallium arsenide photovoltaic cells, silicon photovoltaic cells, amorphous silicon photovoltaic cells, polycrystalline photovoltaic cells, micro-crystalline photovoltaic cells, photoelectrochemical cells, nanocrystal photovolatic cells, and others. The base member  12  is preferably made by the extrusion of a thermally conductive material such as aluminum, but is not limited to thermally conductive materials. 
         [0021]    The base member  12  also includes two side walls  22  that angularly extend from opposite edges of the support surface  14  for mechanically supporting a plurality of side panels  24  ( FIGS. 1 ,  1 A,  5 ). The side panels  24  mount parallel to the side walls  22 . Two shoulders  26 , are integrally formed and extend from the bottom of the side walls  22  to further assist with supporting the side panels  24 . In one embodiment, the side walls  22  project upward from opposite edges of the support surface  14  at obtuse angles, preferably in a range between sixty and ninety degrees, and most preferably between sixty-three and seventy degrees. The shoulders  26  preferably project from the side walls  22  at right angles, which provides a support area  26   a  perpendicular to the bottom of the side panel  24  as it is mounted parallel to the side wall  22  ( FIGS. 1A ,  2 ). 
         [0022]    The side panels  24  may be mounted to the side walls  22  at different heights depending on the distance desired between the top panel  40  and the support surface  14 . At the lowest height allowed, the bottom of the side panels  24  would be supported by the support area  26   a  of the shoulders  26 . In the preferred embodiment ( FIG. 1 ), the side walls  22  include a rib  28  defining a channel  30  accessible for receiving self tapping screws or other fasteners for mounting the side panels  24  parallel to the side walls. The assembly of the side panels  24  is further discussed below with reference to  FIG. 5 . 
         [0023]    Continuing with  FIGS. 1 &amp; 2 , the base member  12  supports a light guide  32  that is mounted atop a corresponding photovoltaic cell  18  via an adhesive bond  32   b . The light guide  32  directs incident light received from a plurality of concentrating lenses  42  onto the corresponding photovoltaic cell  18 . In the preferred embodiment, the light guide  32  operates to collimate, homogenize, and mix the incident light received at its top portion  32   a  for output to the corresponding photovoltaic cell  18 . The light guide  32  is preferably realized by a prism having the shape of an inverted pyramid with an entry aperture roughly four times that of the photovoltaic cell  18 , whereby the incident light is directed to the photovoltaic cell  18  by refraction at the sidewalls of the prism. A reflective coating can also be applied to the sidewalls of the prism in order to limit optical loss. The prism is durable, thermally stable, and easily manufactured to yield low tolerances. The light guide  32  is also secured and aligned with a retaining member  34  placed over the top of the light guide  32 . The retaining member  34  is preferably mechanically attached to the side walls  22  of the base  12  via a snap fit, interference fit, or other mechanical means. 
         [0024]    Turning to  FIG. 3 , shown is a top planar view of an exemplary embodiment of the retaining member  34 , which is realized by a thin plate of metal having a plurality of sides  35  and a centrally located cut-out  36 . The cut-out  36  is shaped to receive the top portion  32   a  of the light guide  32  such that the top surface  32   a  will pass through the cut-out  36  as the retaining member  34  is placed over the light guide  32 . While the light guide is preferably a prism in the shape of an inverted pyramid, other shapes could be used, and the cut-out  36  could be shaped accordingly. The cut-out  36  is also shaped to define a plurality of slots  36   a  that define a plurality of metal fingers  36   b  at the corner edges of the cut-out  36 . These metal fingers  36   b  interface a plurality of corners  32   b  of the light guide  32  as the top portion  32   a  of the light guide  32  passes through the cut-out  36  ( FIG. 3 ). 
         [0025]    Turning to  FIG. 4 , shown is a top perspective view of the retaining member  34  and light guide  32  of the concentrated solar photovoltaic module  10  of the present invention. The corners  32   b  of the light guide  32  contact the metal fingers  36   b  of the retaining member  34  as the retaining member  34  is pushed over the top of the light guide  32 . The metal fingers  36   b  are pushed in an upward direction by the corners  32   b  such that when the retaining member  34  is fully in position, the metal fingers  36   b  are elevated with respect to the generally planar surface of the retaining member  34  but still contact the corners  32   b.    
         [0026]    Turning back to  FIG. 2 , the retaining member  34  is mechanically attached to the interior sides  22   a  of the side walls  22  of the base member  12 . The side walls  22  contain a plurality of teeth  23  projecting from the interior sides  22   a . These teeth  23  interface the sides  35  of the retaining member  34 . As the retaining member  34  is pushed down onto the light guide  32 , the sides  35  are snapped into place under the teeth  23 . 
         [0027]    In the preferred embodiment, the retaining member  34  is formed with slightly larger dimensions than the distance between opposing teeth  23  on respective opposing opposite side walls  22 . As the retaining member  34  is pushed downward, it bends into a convex shape relative to the support surface  14  as its sides  35  curve in an upward direction underneath the opposing teeth  23 . The teeth  23  project in a downward direction such that the opposing sides  35  of the retaining member  34  snap into gaps defined by adjacent teeth on the opposing side walls  22 . The downward angle of the teeth  23  resists deflection of the retaining member  34  to a concave shape and thus aids in fixing the retaining member  34  in the desired convex shape. In the convex shape, the metal fingers  36   b  of the retaining member  34  contact the corners  32   b  of the light guide  32  and apply a biasing force downward toward the support surface  14  and the photovoltaic cells supported thereon ( FIG. 3 ). In this manner, the light guide  32  is mechanically supported between the retaining member  34  and the corresponding photovoltaic cell. Such retaining forces mitigate or possibly eliminate the need for the adhesive bond between the photovoltaic cells  18  and the light guide  32 . In addition, the cut-out  36  is preferably shaped such its edges touch or are in close proximity to the sides of the light guide  32  when placed into its concave configuration as described above. This configuration ensures alignment of the light guides  32  and also provides lateral stability to the light guides  32 . 
         [0028]    The teeth  23  may be located at different heights along the side walls  22  relative to the support surface  14  such that the retaining member  34  may be snapped into place at different heights depending on its length. As the sidewalls  22  angle downward towards the support surface  14 , a retaining member  34  of a given length will experience a tighter and tighter fit as it is pushed downward on top of the light guide  32  because the distance between the sidewalls  22  decreases in that direction. This allows for greater manufacturing tolerances of the retaining member  34 . The retaining member  34  can be manufactured at different lengths if the teeth  23  are formed to accommodate it at different heights and the fingers  36   b  are formed long enough such that they still interface the top corners of the light guide  32 , even if a significant portion of it passes through the cavity  36 . 
         [0029]    Turning to  FIG. 5 , the side panels  24  are mounted to an exterior surface  22   b  of the side walls  22  and parallel to the side walls  22 . A plurality of self tapping screws  38  or other fasteners pass through holes or slots  24   a  ( FIG. 1A ) in the side panels  24  and into the channels  30 . Alternatively, holes may be drilled directly into the side walls  22  and set screws may be used to secure the side panels  24 . The self tapping screws  38  may be loosened or removed, the side panels  24  slid along the length of the side walls  22 , and the self tapping screws  38  reinserted through the holes of the side panels  24  and into the side walls  22 . A top panel  40  containing an integral array of concentrating lenses  42  is attached and mounted to the side panels  24 . The top panel  40  can be formed by bonding or mechanically fastening a number of lenses  42  together or by molding the lenses  42  together with as an integral lens array. The lens assembly is then secured by a support assembly (e.g., two side supports and two end supports) and sealed with a compound to provide both mechanical fastening and water tight sealing. The top panel  40  is then fastened to the side panels  24  with a plurality of self tapping screws or other fasteners, which are inserted through slots or holes in the top panel  40 . 
         [0030]    The fixation of the side panels  24  to the side walls  22  of the base member  12  through the use of the slots  24   a , self tapping screws, or other equivalent means allows the height of the side panels  24 , and thus the top panel  40 , to be adjusted relative to the base member  12 . The distance between the concentrating lenses  42  in the top panel  40  and the light guide  32  and photovoltaic cells  18  may therefore be varied as desired, and the focal point of the concentrating lens(es)  42  may be moved to ensure that the concentrating lenses  42  are focused to a desired part of the light guide  32 . 
         [0031]    The preferred configuration arranges the concentrating lenses  42  parallel to the corresponding array of photovoltaic cells  18 . The concentrating lenses  42  are preferably Fresnel lenses, but can include other lenses known in the art that concentrate light (insolation) and focus it on a smaller surface area. The concentrating lenses  42  cooperate with the light guides  32  and photovoltaic cells  18  to convert insolation incident on the concentrating lenses  42  to electrical energy for output. The concentrating lenses  42  receive the insolation over a large surface area and channel it onto a smaller area at the top of the light guide  32 . In the preferred embodiment, the array of light guides  32  collimate, homogenize, and mix the light received from the concentrating lenses  42  and focus it onto the corresponding photovoltaic cells&#39;  18  smaller surface area at a much greater intensity. 
         [0032]    Two end panels  44  are attached to the base member  12  at opposite ends. Two of the cooling fins  20  are formed to together define a channel  20   a  for receiving a self tapping screw. The end panels  44  are mounted perpendicular to the longitudinal axis  46  of the photovoltaic module  10  ( FIG. 1 ). The end panels  44  are mounted to the module  10  at the base  12  by self tapping screws passing through the end panels  44  and into the channel  20   a . The array of photovoltaic cells  18  and light guides  32  are thus enclosed by the base member  12 , side panels  24 , top panel  40 , and end panels  44 . Sealing adhesives are applied to the enclosed housing to keep out water, dust, or other particles. The housing also contains a valve (not shown) that regulates air pressure inside the housing in accordance with the atmospheric pressure, which varies as the ambient temperature changes. This valve adjusts the pressure without allowing water, dust, or other contaminants inside the housing. 
         [0033]    The photovoltaic module  10  is assembled by first bonding the array of photovoltaic cells  18  to the support surface  14  of the base member  12 . The photovoltaic cells  18  are then electronically connected in a desired configuration (for example, preferably in parallel or in series with each other as shown in  FIG. 6 ). The array of light guides  32  is then mounted to the base member  12  atop the array of photovoltaic cells  18  via a plurality of adhesive bonds  32   c . The retaining member  34  is then lowered over the top surface  32   a  of the light guide  32  such that the top surface  32   a  passes through the cut-out  36  of the retaining member  34 . The retaining member  34  is snapped into place by pushing down on the sides  35  until they snap under the teeth  23  on the interior surface  22   a  of the sidewall  22 . The side panels  24 , top panels  40  and end panels  44  are then installed as discussed above, and the module  10  is sealed to keep out water, dust, and other contaminants. 
         [0034]    The structure of the photovoltaic module  10  supports and properly aligns the array of light guides  32  with the corresponding array of photovoltaic cells  18 . The retaining members  34  provide lateral stability to the light guide  32  and will absorb some of the lateral forces present when the photovoltaic module is transported, moved, or rotated. The retaining members  34  also restrict the assembly tolerances of the light guide  32  relative to the photovoltaic cells  18  during installation, which allows for more accurate alignment in the field. 
         [0035]    Turning to  FIG. 6 , shown is an array of photovoltaic modules  10  whose electrical outputs are coupled in parallel with each other and to an electrical power sink  46 . The electrical power sink  46  can be a DC/AC inverter and possibly a battery bank for energy storage. The DC/AC inverter converts the electrical energy outputted by the photovoltaic module  10  (in the form of DC current) into AC current for energy supply applications. The battery bank stores the electrical energy outputted by the photovoltaic modules  10  for energy supply applications. Note that the electrical outputs of the photovoltaic modules  10  can be arranged in different configurations, such as a series configuration or hybrid parallel-series configuration as desired. 
         [0036]    There have been described and illustrated herein several embodiments of a photovoltaic system, a module for housing and securing a plurality of photovoltaic cells and reflector assemblies, and methods of assembling a photovoltaic system. While particular embodiments of the invention have been described, it is not intended that the invention be limited thereto, as it is intended that the invention be as broad in scope as the art will allow and that the specification be read likewise. Thus, while particular materials, dimensions, fasteners, reflectors, lenses, etc. have been disclosed, it will be appreciated that other suitable substitutes can be used as well. While the embodiment of the present invention discloses a light guide mounted directly on a corresponding photovoltaic cell with an adhesive bond, it will be appreciated by those skilled in the art that the light guide could be mounted above the photovoltaic cell without any adhesive bonds. In addition, while a retaining member mounted to the side walls of the base has been disclosed, it will be appreciated that the retaining member could be mounted to the side panels instead. Further, while the preferred embodiment discloses a single top panel containing concentrating lenses as part of the photovoltaic module, it will be appreciated that a plurality of top panels, each containing one or more concentrating lenses, may be integrated together as part of the photovoltaic module. It will also be appreciated that a tube containing a thermally conductive fluid may be secured to or integrated into the base member in order to scavenge the heat production of the photovoltaic cells for use as a source of heat for additional applications. In addition, while the preferred embodiment discloses a prism in the shape of an inverted pyramid with a corresponding retaining member having a cut-out shaped to receive it, it will be appreciated by those skilled in the art that other shapes and elements may be used for the light guides and the corresponding retaining members and parts thereof. It will be appreciated by those skilled in the art that these and other modifications could be made to the provided invention without deviating from its spirit and scope as claimed.