Abstract:
In a reflector dish, a small quantity of elongate mirror-surfaced reflector panels are structurally integrated with a support framework that is configured to enable convenient shipping and on-site assembly and erection of a reflector dish assembly with an effective reflecting surface that closely approximates a desired parabolic dish shape with short focal length, synthesized from combination of the reflector panels originally procured as flat rectangular sheet metal panels and formed to provide the desired dish curvature. The panels can be conveniently shipped to location along with a corresponding quantity of reinforced crescent-shaped support frames to which the panels are made to attach as structural elements, by novel attachment hardware, for erection at the operational site.

Description:
FIELD OF THE INVENTION 
     The present invention relates to the field of dish reflectors and more particularly to the structure of a rectangular reflector dish for a solar heat concentrator. The dish is readily assembled from a small quantity of cost-effective curve-shaped elongate panels. 
     BACKGROUND OF THE INVENTION 
     Typically, reflector dishes are circular with polar cross-sectional shape that is parabolic and made to be symmetrical about a central axis. Solar concentrators have been formed as arrays of elongated horizontal troughs with a vertical cross-sectional shape that extends uniformly to a designated full horizontal length; the vertical cross sectional shape is typically parabolic and symmetrical about the horizontal axis. Circular dishes have been manufactured from small, curved, typically square or hexagonal tiles. 
     It is known to fabricate such reflectors from strips, panels or segments for purposes of facilitating the handling and shipping of large reflector assemblies. In addition to the requirement for a suitable reflective surface, design considerations include parametric options such as segment size, inversely-related segment quantity and sophistication of segment curvature which can be zero (flat) or curved in one axis or two axes, in addition to mechanical mounting and environmental wind/weather considerations. NOTE: for purposes of the present descriptions, the terms X-axis and Y-axis refer to a dish that is shaped symmetrically about a Z axis, and the terms horizontal and vertical refer to the X-axis and Y-axis respectively in the case where the Z axis is horizontal, i.e. the dish on earth aimed at the horizon. 
     DISCUSSION OF KNOWN ART 
     U.S. Pat. No. 6,485,152 B2 to Wood discloses a MATRIX SOLAR DISH with fixed slender glass mirrors patterned from orthogonal planes parallel to the axis of symmetry of a paraboloid and intersecting the paraboloid, making the all parabolic trusses uniform. 
     U.S. Pat. No. 5,640,950 to Cordy, Jr., discloses a SIMPLIFIED CRADLE AND DISH FOR A SOLAR-POWERED HIGH-PRESSURE STEAM GENERATOR with a cradle that permits a concentrator dish to rotate around the declination axis to follow the sun through its seasonal motions. 
     U.S. Pat. No. 5,374,317 to Lamb et al discloses a MULTIPLE REFLECTOR CONCENTRATOR SOLAR ELECTRIC POWER SYSTEM that uses multiple reflectors to concentrate sun light onto a panel of photo-voltaic (PV) cells. 
     U.S. Pat. No. 4,784,700 to Stem et al discloses a POINT FOCUS SOLAR CONCENTRATOR USING REFLECTOR STRIPS OF VARIOUS GEOMETRIES TO FORM PRIMARY AND SECONDARY REFLECTORS, i.e. “cylindrical reflector strips some of which are tilted to simulate a point focus by overlaying the line focii of each segment at a coincident point”. 
     OBJECTS OF THE INVENTION 
     It is an object to provide a structural solution for a reflector dish suitable for concentrating sun rays for purposes of energy recovery power generation that will prove to be practical, cost-effective, highly efficient, easy to manufacture, transport, and assemble on site from a reasonably small number of component parts, and that will perform reliably under normal to extreme weather-related variations including temperature, humidity, precipitation, and wind conditions. 
     SUMMARY OF THE INVENTION 
     These and other objects and advantages have been realized in a reflector structure that integrates the reflector elements with their support structure and that enables site erection of a reflecting surface that closely approximates a desired dish contour curve with parabolic radian shape about an axis of symmetry. The reflecting surface is synthesized from a small quantity N of mirror-surfaced panels originally procured as flat rectangular metal panels and shaped in a novel forming process to have the desired curvature: concave on the reflective side. The panels are shipped along with a corresponding small quantity N+1 of support frames to which the panels are attachable by novel attachment hardware for erection at the operational site. 
     These and other objects and advantages of the present invention will become apparent from the following more detailed description, taken in conjunction with the accompanying drawings which illustrate the invention, by way of example. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a solar reflector installation utilizing a reflector dish structure in accordance with a preferred embodiment of the present invention. 
         FIG. 2  is a front elevation of the reflector dish structure of  FIG. 1 , removed from the base support and receptor assembly. 
         FIG. 3  is a top view of the reflector dish structure of  FIG. 2   
         FIG. 4  is a rear elevation of the reflector dish structure of  FIGS. 1-3 . 
         FIG. 5  is an enlarged front elevation of the reflector dish structure of  FIGS. 1-4  showing a typical attachment plate. 
         FIG. 6  is a cross-section taken at  6 - 6  of  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a perspective view of a solar reflector installation  10  utilizing a parabolic reflector dish structure  12  in accordance with a preferred embodiment of the present invention. A ground support post  14  supports the reflector dish structure  12  along with a receptor support frame  16  which is rigidly attached to the reflector dish structure  12  and supports a receptor  18  with its thermal element located at the focal point of dish structure  12 . 
     The reflector dish structure  12  includes a rear dish support framework  20  to which receptor  18  is attached by support frame  16 , forming an integral movable structural, unit that is attached to the stationary ground support post  14  in a swivel manner. A motor drive mechanism enables the structural unit to be rotated for azimuth angle and tilted for inclination angle under computer control so as to track the reflective surface with the movement of the sun, keeping the sun&#39;s rays reflected to the focal point on receptor  18  as indicated by the broken lines. Clearance for such movement of the movable structural unit is provided by portions cut away from panels  12 C′ and  12 C″ and rear support framework  20  to form clearance slot  12 D. 
     For purposes of the present descriptions, unless indicated otherwise, the dish structure is presumed to be oriented with its central axis, i.e. X-axis oriented horizontal and its Y-axis oriented vertical, the reflective side of the mirror dish being referred to as the front side. 
     In the embodiment shown, the reflector surface of dish structure  12  is made up from six generally rectangular side-by-side panels:  12 A (two places),  12 B (two places),  12 C′ and  12 C″, each shaped with curvature to closely approximate a desired parabolic surface shape and finished to have an efficient reflective surface. 
     The panels  12 A- 12 C″ forming the reflector surface are assembled on-site by attachment to the structural framework  20  which includes vertical arches  20 A, reinforcing trusses  20 B and horizontal stringers  20 C all attached together structurally with the panels  12 A- 12 C″ as part of an integral structure that can be readily assembled on-site from panels and sub-assemblies of support structure that can all be readily transported to the site. 
       FIG. 2  is a front view of dish structure  12  of  FIG. 1 , showing six panels located side-by-side: two panels  12 A, two panels  12 B, panel  12 C′ and panel  12 C″. These panels are originally fabricated from substantially rectangular flat sheet metal stock, which are then formed in a process to have the desired parabolic curvature in both X and Y axes. Panels  12 A are identical and panels  12 B are identical: in each pair one is inverted relative to the other, to form mirror images of each other. Panels  12 C′ and  12 C″ may be identical originally, each with a cutout portion to form opening  12 D, then, with one reversed relative to the other, they become mirror-images of each other; they are then formed to the parabolic shape as shown. Once the panels have been formed to final shape, their reflective surface can be applied in a suitable manner, e.g.: the surface of the metal itself can be polished and sealed with a coating that resists oxidizing or an appropriate specialized reflective coating such as a silvered mirror or silicon oxide glass coating may be applied. 
     The rear support framework  20  seen at the left and right side of  FIG. 2  is attached to the rear side of the six panels  12 A- 12 C″ in such a manner that the six panels themselves become part of the structural entity. Clearance slot  12 D is seen in the lower central region. Fastening plates  22  arranged in an array as shown are each backed by a similar attachment plate on the rear as shown in  FIGS. 4 ,  5  and  6 . 
       FIG. 3  is a top view of the dish structure  12  of  FIG. 2  showing support structure  20  with seven Y-axis spacer struts  20 A stabilized by attachment to horizontal rear stringer struts  20 C. 
       FIG. 4  is a rear view of the dish structure  12  of  FIG. 2  showing the rear side of the six reflector panels  12 A- 12 C″ along with the support structure consisting of seven arched Y-axis members  20 A attached at their ends to the top and bottom panel edges and braced by a framework of typically smaller diameter straight tubes  20 B attached to the panel by rectangular rear attachment plates  22 , typically welded to tubes  20 B and attached to the reflector panels  12 A- 12 C″ by fasteners such as screws, nuts and bolts, eyelets or rivets, spanning and overlapping the small gaps between adjacent reflector panels caused by their curvature, which due to their uniform width, causes adjacent panels to contact and abut each other only at top and bottom, as shown. 
       FIG. 5  is an enlarged front elevation of a portion of the reflector dish structure of  FIGS. 1-4  showing a typical front attachment plate  22 , spanning and overlapping the gap between two adjacent reflector panels, e.g. panels  12 A′ and  12 B′ as shown, fastened by a plurality of machine screws  24  traversing panels  12 A′ and  12 B′. For location on the reflective side of the mirror dish panels  12 A′ and  12 B′ as shown, it is preferable for the exposed surface of attachment plate  22  to be made reflective, similar to the reflecting surfaces of the panels. As an alternative to the rectangular shape shown, plate  22  could be made and utilized effectively in a variety of other shapes such as square or other polygonal shape, elliptical, round etc, 
       FIG. 6  is a cross-section taken at  6 - 6  of  FIG. 5  showing a typical front attachment plate  22  on the upper side and a second similar rear attachment plate  22  on the lower side as a reinforcement, with the machine screws  24  engaging corresponding nuts  26  tightened against the rear attachment plate  22 , which serves as an attachment tie point that is typically welded to one or more tubular support structure members such as spacer tube  20 B shown. 
     Assuming the rear support structure consists of seven generally Y-axis arched Y-axis members  20 A numbered consecutively 1-7, there are three identical pairs (1,7; 2,6; 3,5) and a central member (4) specially shaped with a bifurcated cutaway region to provide the clearance slot  12 D seen in the lower central region, as in  FIG. 3 . The seven Y-axis sub-assemblies can be pre-assembled each with arched Y-axis members  20 A and its associated bracing framework  20 B, forming a set of crescent-shaped support sub-assemblies that are convenient in size for shipment to the site. 
     Each of the six crescent-shaped Y-axis support sub-assemblies flanking the central Y-axis support sub-assembly, as best seen at the left and right sides in  FIGS. 1 and 3 , includes in its support framework five spacer struts that are generally oriented in the X-axis and spaced approximately equidistantly apart, and four diagonal reinforcing struts extending between opposite ends of adjacent spacer pillars. 
     The overall reflector assembly and its framework are mirror-image symmetric about the central Y-axis axis, and apart from the region of the clearance slot  12 D, mirror-image symmetric about the central horizontal axis. 
     On-site, the crescent-shaped support sub-assemblies are attached to the reflector panels  12 A- 12 C″ and then finally stabilized by the additional fastening at all intersections of five generally horizontal arched stringers  20 C, of tubing typically larger in diameter than the arched Y-axis members  20 A: an identical stringer pair top and bottom, the upper mid stringer (full length) and the lower mid co-linear pair of short length stringers, spaced apart at clearance slot  12 D. 
     Generally all of the support structure members are of thin-wall tubing, preferably stainless or other metal such as aluminum, and secured together with suitable releasable fastenings such as machine screws and nuts that allow future maintenance, replacement or disassembly into sizes convenient for transporting in the event of relocation. 
     The overall size of the reflector dish structure  12  can be made generally within a range from 12 to 50 feet on a side. The structure shown as the preferred embodiment can be shaped to provide parabolic curvature that enables the focal point to be located at a distance from the center of the dish equal to about half the width or height of the reflector, i.e. substantially shorter focal length than found in conventional solar reflector dishes of known art. 
     Although it is considered preferable and most economical of material to make the reflector dish structure  12  approximately square, i.e. with an aspect ratio close to 1:1, as shown and described, the structural principles of the invention could be practiced to produce viable reflector dish structures with aspect ratios at least as high as 2:1 elongated in either the X-axis or the Y-axis. 
     The quantities of reflector panels and the quantities and arrangement of support structure members shown are considered optimal and exemplary, however the principles of the invention could be practiced successfully with quantities and arrangements other than as shown, as a matter of design choice. 
     The invention may be embodied and practiced in other specific forms without departing from the spirit and essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description; and all variations, substitutions and changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.