Abstract:
A nontracking solar concentrator, called the wedge, is given the ability to collect overhead light. This is made possible by a new prism, having the cross section of a cornucopia, that delivers an abundance of bright light into the wedge to create a higher intensity focus.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates to the collection of sunlight, specifically to a new panel that delivers overhead light into a solar concentrating wedge. 
         [0002]    The two most practical nontracking solar thermal concentrators are the well known compound parabolic concentrator (CPC) and the lesser known optical wedge. Both collectors use a reflective geometry, instead of sun-tracking machinery, to focus light onto a heat pipe. 
         [0003]    The low profile wedge is scalable. When filled with inexpensive water, the wedge can be built with a very large collection area and take advantage of the economies of scale that are necessary to become cost effective. The water-filled wedge can also transport any absorbed energy by flowing to the focus. In the past, however, each potential advantage was cancelled by the fact that a low profile wedge could only collect light from low in the sky. 
       SUMMARY OF THE INVENTION 
       [0004]    The primary object of this invention is to allow the wedge to collect overhead sunlight. 
         [0005]    Accordingly, the primary object is accomplished in the following manner: a wedge-shaped tank is filled with water and a panel is placed on top. Inside the panel is a new prismatic guiding plate that takes powerful overhead light and folds it into angled beams that are acceptable to the wedge. The result is a scalable nontracking solar concentrator with a very hot focus. 
         [0006]    Another object is to greatly reduce the cosine losses associated with the low profile wedge. Other objects and advantages will become apparent from the following detailed description and accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is an end view of a prior art water-filled wedge. 
           [0008]      FIG. 2  is an end view of a water-filled wedge with new panel. 
           [0009]      FIG. 3  is a partial view of the optics in the new panel. 
           [0010]      FIG. 4  is an exploded view of the new panel. 
           [0011]      FIG. 5  is a perspective view of a water-filled wedge with panels. 
           [0012]      FIG. 6  is a partial view of the panel optics collecting solstice rays. 
           [0013]      FIG. 7  is a partial view of the panel optics collecting equinox rays. 
           [0014]      FIG. 8  is an end view of a water-filled wedge, panel and stacked-pipe absorber. 
           [0015]      FIG. 9  is an end view of a water-filled wedge, panel and CPC secondary. 
           [0016]      FIG. 10  is an end view of a 8° water-filled wedge and panel. 
       
    
    
     DESCRIPTION OF THE INVENTION 
       [0017]    In  FIG. 1 , a prior art water-filled wedge  2  is shown collecting sunlight. Rays  4  and  6  outline the angular field of view of the nontracking solar concentrator. Ray  6  is the maximum elevation ray that the wedge can collect. After entering water  8  and reflecting from the bottom, ray  6  approaches water surface  10  at greater than the critical angle and is totally internally reflected  12  back into the water toward the focus. Whereas, if high ray  14  enters the water, it will reflect and exit the water as lost energy  16 . Only the light between rays  4  and  6  can be collected. 
         [0018]    A major problem for the prior art wedge is that before arriving at the collector the low-angled light passes through an extra thick air mass which absorbs much of the radiant energy. 
         [0019]    The horizontal wedge also suffers a cosine loss. The light approaches water surface  10  at an oblique angle, causing a further decrease in the energy density of the light. For example, 60° incident light has an energy density half of what it could be because the cosine of 60 is 0.50. 
         [0020]    The prior art wedge is limited to collecting low intensity light from low in the sky. 
         [0021]    In  FIG. 2 , new water-filled wedge  18  collects powerful overhead light between rays  20  and  22  during the brightest part of the year. At the same time, high overhead light greatly reduces the cosine loss. Both improvements are made possible by panel  24  of the present invention. 
         [0022]      FIG. 3 . Inside of panel  24 , there is a guiding plate  26  that has many rows of cornucopia-shaped prisms  28 . Overhead rays  20  and  22  enter the plate and emerge diagonally toward bottom glass  30 . All rays approaching the glass within angle range  32  (45° through 90°) can be accepted by the water-filled wedge and reflected to the focus. 
         [0023]      FIG. 4 . Panel  24  is a watertight housing constructed of a frame  34 , tempered low-iron bottom glass  30  and top glass  36 . Plate  26  is manufactured in clear plastic by the injection molding process. Essential reflector  38  can be a polished aluminum strip or extrusion. 
         [0024]      FIG. 5 . Now that the wedge is capable of collecting high intensity light, it will make good economic sense to scale up. A larger collection area will make it necessary for panel  24  to be built in sections that are arrayed side by side. Each panel  24  is plane parallel to water surface  40  and may be placed on, above, or below the water surface. Plate  26  and the reflectors are oriented east to west. 
         [0025]    Wedge  18  is shown in the northern hemisphere at the 34 th  parallel (Los Angeles, Calif. for example) where light is collected from the southern sky and guided by total internal reflection to exit glass  42 . High noon rays  20  and  22  define a 23.5° elevation field of view that allows solar collection three months before and three months after summer solstice. Azimuth field of view (not shown) changes over the six month collection period and is greatest around summer solstice. 
         [0026]    The wedge&#39;s long axis is east to west, while overall length is determined by the temperature rise and flow rate requirements of a particular jobsite. 
         [0027]    The work of the collector is to make fresh water and generate electricity without air pollution. The collector can make it&#39;s own demineralized water for use in the wedge tank. 
         [0028]    In  FIG. 6 , ten solstice rays are shown entering plate  26 . Ray  22 a impinges tilted first surface  44  and refracts into the clear plastic according to Snell&#39;s Law. Shaped reflector  38 , adjacent to the second plastic surface, directs ray  22   a  up to point  46  where it internally reflects toward exit surface  48  and into the air, then traversing glass  30  and into the water. Ray  22   a  is the most steeply inclined of the rays, exiting wedge bottom glass  50  into air-gap  52  and reflecting at metallic mirror  54 . All subsequent reflections at the wedge bottom are total internal reflections. Ray  22   a  approaches the glass/air interface at greater than the critical angle and is internally reflected  56  back into the water toward the focus downstream. 
         [0029]    Ray  22   b  internally reflects from a different bottom facet of plate  26  and propagates into the water. Ray  22   c  internally reflects from an exit surface, refracts out the bottom facet to a “scoop” section of reflector  38  and into the water. 
         [0030]    First surface facet  58  causes two of the rays to be lost, suggesting a plate  26  gross throughput of 80% for solstice rays. 
         [0031]    In  FIG. 7 , equinox rays  20  enter, are guided and exit plate  26 . The underside of reflector  38  directs some of the rays. Rays travel down through glass  30  and back up to glass  30  for a total internal reflection. If a anti-reflection film is deposited on the air side of glass  30 , light transmission will be improved and total internal reflection will not be affected. 
         [0032]      FIG. 8 . Collected light  60  approaches exit glass  42  in a range of rays having a maximum half angle of 38°. The rays refract into air (55° half angle) and hit a stacked-pipe absorber  62 , heating the working fluid inside. A geometric concentration ratio of 5:1 is found by dividing the panel  24  aperture by the maximum water height. 
         [0033]    In  FIG. 9 , a CPC secondary reflector  64 , designed to accept a 55° half angle, takes the 5× concentrated light and multiplies it 2.5 times resulting in a concentration ratio of 12.5:1. An additional benefit is that the concentrated light is distributed on both sides of absorber  66 . 
         [0034]      FIG. 10 . Panel  24  allows the wedge to work at higher latitudes where the summer solstice sun appears lower in the sky. At the 40 th  parallel for example, the lower solstice ray will be collected by 8° wedge  68 . The smaller wedge angle produces a wider collector for a given height and a total geometric concentration ratio of 16:1.  FIGS. 8 ,  9  and  10  have identical heights and all pipes are the same diameter. The trade-off is a smaller 12.5° field of view that equates to a collection period of 3.2 months (1.6 months before and after summer solstice). 
         [0035]    Some of the collected light is absorbed by the water, raising the water temperature. This energy is not lost because warm water  70  flows under panel  24  toward the focus as preheated feed water for the pipes. Panel  24  insulates the warm water during the slow journey. 
       SUMMARY 
       [0036]    The reader has been shown a completely new optic that delivers the brightest light available into the water-filled solar concentrating wedge. The intense light will accelerate heat transfer operations in the collector for the first time. 
         [0037]    There has always been a need for a cost effective solar concentrator. Now, the purely optical wedge has the power to be that technology.