Abstract:
A solar concentration system includes an optically clear shell member having an outer surface and an inner surface, with the inner surface defining a hollow interior portion, a liquid contained within the hollow interior portion of the optically clear shell, and a solar collection system contained within the hollow interior portion of the optically clear shell. The solar collection system includes a tracking system configured and disposed to selectively shift within the hollow interior portion, a reflector member mounted to the tracking system, and a solar receiver mounted to the tracking system. The tracking system being configured and disposed orient the reflector member and the solar receiver to follow a path of the sun enhancing the collection of solar energy.

Description:
BACKGROUND 
     The present invention relates to solar concentrators and, more particularly, to a solar concentrator including an optical tracking system. 
     Solar power systems fall generally into two categories: fixed position flat panels and tracking concentrator systems. Fixed position flat panel systems employ one or more stationary panels that are arranged in an area having an unobstructed view of the sun. As the earth rotates, the sun&#39;s rays move over the stationary panel(s) with varying degrees of intensity depending upon geographic location, the time of day and the time of the year. In contrast, solar concentrator systems collect, and focus the sun&#39;s rays onto one or more solar cells. Certain solar concentration systems employ tracking systems that follow the sun&#39;s path in order to enhance energy collection. Simply put, fixed position flat panels represent a passive solar collection system, while solar concentrator systems represent a more active energy collection system. 
     Solar concentrator systems utilizing photovoltaic cells typically operate at or below about 500 suns concentration. Operating at higher sun concentration levels creates cooling challenges. In order to address the cooling challenges, certain solar concentration systems employ liquid cooling systems such as found in U.S. Pat. No. 4,081,289. In the &#39;289 patent, a sphere contains a liquid medium and a plurality of fixed solar panels. The sphere acts as a lens and the liquid as a focal and cooling medium. The liquid is circulated within the sphere to carry away heat generated by solar rays impacting the fixed solar cells. In addition to serving as a heat exchange medium, the liquid, in combination with the sphere, focuses the sun&#39;s rays toward the fixed solar cells. While effective as a cooling medium, the use of the sphere and liquid to focus light imparts significant limitations on energy collection. That is, the actual focal point of the light passing through the sphere and the liquid is outside of the sphere itself. 
     Solar concentrator systems allow the use of fewer semiconductor elements to produce a given amount of electric power. However, the use of fewer semiconductor elements results in a need for optics and a system for tracking the sun. At present, the additional cost associated with the necessary optics and tracking systems does not exceed the cost benefit of a reduced number of solar cells. 
     SUMMARY 
     According to one exemplary embodiment, a solar concentration system includes an optically clear shell member having an outer surface and an inner surface, with the inner surface defining a hollow interior portion, a liquid contained within the hollow interior portion of the optically clear shell, and a solar collection system contained within the hollow interior portion of the optically clear shell. The solar collection system includes a tracking system configured and disposed to selectively shift within the hollow interior portion, a reflector member mounted to the tracking system, and a solar receiver mounted to the tracking system. The tracking system being configured and disposed to orient the reflector member and the solar receiver to follow a path of the sun enhancing the collection of solar energy. 
     According to another exemplary embodiment, a method of concentrating solar energy includes receiving solar energy through a surface of an optically clear shell, guiding the solar energy through a liquid contained in the optically clear shell, folding the solar energy back through the liquid toward a solar receiver, and shifting the solar receiver within the optically clear shell to track the sun, wherein the solar energy collected by the solar receiver is converted into electrical energy. 
     Additional features and advantages are realized through the techniques of the present invention. Other embodiments and aspects of the invention are described in detail herein and are considered a part of the claimed invention. For a better understanding of the invention with the advantages and the features, refer to the description and to the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The forgoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is an elevational view of a solar concentrator including a solar collection system in accordance with an exemplary embodiment; 
         FIG. 2  is the solar concentrator showing the solar collection system shifting to track the sun; 
         FIG. 3  is an elevational view of a solar receiver portion of the solar collection system in accordance with an exemplary embodiment; and 
         FIG. 4  is a schematic view of the solar concentrator showing the solar collection system focusing solar rays onto the solar receiver in accordance with an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     With reference now to  FIGS. 1 and 2 , a solar concentration system constructed in accordance with an exemplary embodiment, is indicated generally at  2 . Solar concentration system  2  includes a base member  4  that supports an optically clear shell  10 . Optically clear shell  10  includes an outer surface  12  having an anti reflective and/or anti-fouling coating such as polydimethylsiloxane (PDMS). Optically clear shell  10  includes an inner surface  14  that defines a hollow interior portion  18 . In accordance with an exemplary embodiment, hollow interior portion  14  is filled with a liquid  20  such as water. Of course other liquids such as glycol, alcohol, and the like can also be employed to prevent freezing or to adjust an optical index. Solar concentration system  2  is further shown to include a solar collection system  30  arranged within hollow interior portion  18 . 
     In accordance with an exemplary embodiment, solar collection system  30  includes a tracking system  34  having a base element  36  that is configured and disposed to rotate about an axis  37 . Tracking system  34  is further shown to include a support arm  39  that is operatively connected to base element  36  in a manner that will be detailed more fully below. Support arm  39  includes a first end  42  that extends to a second end  43  through an arcuate intermediate portion  44 . Intermediate portion  44  is provided with a plurality of gear teeth  46  that are configured and disposed to cooperate with a corresponding gear element (not shown) provided within base element  36 . In this manner, support arm  39  shifts between first end  42  and second end  43  relative to base element  36 . That is, tracking system  34  includes at least one of an alt/azimuth and an elevation drive system that aims solar collection system  30  toward the sun&#39;s position in the sky at a given time and in a particular geographic area such as shown in  FIG. 2 . More specifically, tracking system  34  rotates about axis  37  and shifts support arm  39  between first and second ends  42  and  43  to position reflector member  56  relative to the sun. 
     In accordance with an exemplary embodiment, reflector member  56  is mounted to first end  42  of support arm  39 . Reflector member  56  includes a plurality of reflector surfaces  58 - 60  that are arranged in a stepped configuration. In accordance with one exemplary embodiment, reflective surfaces  58 - 60  are flat to reduce cost. Reflective surfaces  58 - 60  fold the optical path such that the focus is within optically clear shell  10 . The use of multiple reflective surfaces aids in correcting spherical aberration, however, it should be understood that reflector member  56  could also include a single reflector that is formed, for example, to have a flat circular construction. Of course, it should be understood that reflector  56  can take on a variety of forms. That is, reflector member  56  could include one or more planer mirrors, convex mirrors, and/or concave mirrors depending upon the level of solar concentration desired. In any event, solar rays passing through optically clear shell  10  impact reflector member  56 . Reflector member  56  folds the rays back towards a solar receiver system  70  mounted at second end  43  of support arm  39 . 
     As best shown in  FIG. 3 , solar receiver system  70  includes a heat sink  74  having a plurality of fins  76 . A solar receiver  78  is mounted to heat sink  74  and is encapsulated by a clear shell  84 . Clear shell  84  provides a seal that protects solar receiver from liquid  20 . In accordance with one aspect of an exemplary embodiment, clear shell  84  is formed from a plastic encapsulant such as or epoxy. In accordance with another aspect of an exemplary embodiment, clear shell  84  is formed having multiple layers formed from materials such as glass, acrylic, silicone and plastic. Solar receiver  78  takes the form of a photovoltaic cell that is configured and disposed to convert light energy to electrical energy. With this arrangement, the solar rays folded back from reflector member  56  impinge upon solar receiver  78 . More specifically, the distortion produced by passing light through a sphere would locate the focal point of the solar energy at a point outside hollow interior portion  18 . Reflector member  56  corrects for the distortion by folding the light back to a focal point within hollow interior portion  18 , i.e., upon solar receiver  78  as shown in  FIG. 4 . Solar receiver  78  in turn produces an electrical output. In accordance with an exemplary embodiment, reflector member  56  concentrates the solar energy passing though shell  10  to a level of about 2000 suns (200 watts/cm 2 ) or more of incident light. This level of solar concentration produces a significant amount of heat that must be dissipated. Towards that end, the heat developed by the concentrated solar rays impinging upon solar receiver  78  is dissipated by heat sink  74 . Heat sink  74  initiates a convective cooling effect through liquid  20  to lower temperatures at solar receiver  78 . 
     As further shown in  FIG. 1 , solar receiver  70  includes a light cup  94 , or reflective optic, that is positioned across solar receiver  78 . Light cup  94  collects any stray solar rays that are folded back from reflector member  56  towards solar receiver  78  in order to achieve even higher energy conversion efficiencies. In place of light cup  94 , a light pipe, or refractive optic, (not shown) having a substantially cylindrical cross-section is employed to gather stray light. The use of light cup  94  (reflective optic) or a light pipe (not shown) (refractive optic) improves collection efficiency in the presence of optical distortions and tracking errors (improved acceptance angle). In addition to improving collection efficiency, light cup  94  and/or the light pipe homogenize the gathered light with respect to solar receiver  74 . 
     The low cost per watt is further enhanced by tracking system  34 . That is, tracking system  34  represents a near zero mass within liquid  20  which decreasing costs associated with moving the various optical components. In addition, liquid  20  serves as a dampener. More specifically, liquid  20  acts to dampen the motion of tracking system  34  thereby limiting oscillations of the collection components, e.g., reflector member  56  and solar receiver  78 . By minimizing oscillations of the collection components, the need for complicated correction algorithms is avoided. The stepped configuration of reflector member  56  further aids in damping. Finally, the use of a passive, convective, cooling system eliminates the need to complicated and costly fluid circulation systems. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, element components, and/or groups thereof. 
     The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiment was chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated 
     While the preferred embodiment to the invention has been described, it will be understood that those skilled in the art, both now and in the future, may make various improvements and enhancements which fall within the scope of the claims which follow. These claims should be construed to maintain the proper protection for the invention first described.