Patent Publication Number: US-2011067692-A1

Title: Solid core structure parabolic trough solar energy collection system

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     This application claims the benefit of priority to U.S. App. Ser. No. 61/274,046 filed Aug. 11, 2009 and entitled “Solid Core Structure Parabolic Trough Solar Energy Collection System,” inventors Kip H. Dopp and Darren T. Kimura, which application is incorporated by reference in its entirety. 
     This application also incorporates by reference the following patent applications, some of which are referred to elsewhere in the text, in their entirety as if put forth in full below: U.S. application Ser. No. 11/811,329 (filed Jun. 8, 2007) “Mirror Assemblies for Concentrating Solar Energy”; U.S. application Ser. No. 11/811,109 (filed Jun. 8, 2007) “Use of Brackets and Rails in Concentrating Solar Energy Collectors”; U.S. application Ser. No. 11/811,027 (filed Jun. 8, 2007) “Protecting Solar Energy Collectors from Inclement Weather”; U.S. application Ser. No. 11/811,073 (filed Jun. 8, 2007) “Use of Identical Components in Solar Energy Collectors”; U.S. application Ser. No. 11/811,153 (filed Jun. 8, 2007) “Support of Heat Collectors in Solar Energy Collectors”; PCT App. No. PCT/US2007/013618 (filed Jun. 8, 2007) “Apparatus and Methods for Concentrating Solar Power”; PCT App. No. PCT/US2009/041171 (filed Apr. 20, 2009) “Parabolic Trough Solar Energy Collection System”; PCT App. No. PCT/US2008/007115 (filed Jun. 6, 2008) “Parking Solar Energy Collectors”; and the PCT Application filed concurrently with this application on Aug. 11, 2010 and entitled “Solid Core Structure Parabolic Trough Solar Energy Collection System,” inventors Kip H. Dopp and Darren T. Kimura. 
    
    
     The present invention relates to the structural improvement of a concentrating parabolic trough collector through the use of non-conventional core materials that enable the reduction in metal frame structures, weight, and fasteners and that may increase the collector&#39;s durability and integrity. 
     BACKGROUND AND SUMMARY OF THE INVENTION 
     Solar energy is an environmentally friendly source of renewable and sustainable energy that does not necessarily rely on the use of fossil fuels and reduces the release of green house gases that are attributed to global warming and related environmental problems. In many cases, solar energy can be captured and used locally, thereby reducing requirements for transportation or importation of fuels such as petroleum. Concentrating solar power (CSP) systems are one of several technologies that may be used to harness solar energy form the sun. 
     Solar heaters, such as concentrating troughs, focus sunlight from mirrors and/or lenses onto a central receiver which can be a tube through which a heat transfer fluid flows. The trough collector may be positioned to track the sun so the reflected solar energy is concentrated onto the tube. The heated tube warms the fluid, and high quality heat from the heated fluid can be used to generate electricity, create air conditioning, drinking water from sea water or as steam. Trough solar energy collectors have been designed and manufactured to numerous specifications. The Micro Concentrated Solar Power (MicroCSP™) collectors, for instance, may provide a modular and scalable approach to solar technology suitable for electricity generation, process heat or other energy use. 
     Various MicroCSP™ collectors have been described in the prior patent applications referenced above. Provided herein is a frame assembly that may be used to construct solar energy collection and conversion systems using a suitable rigid material such as expanded polystyrene or extruded polystyrene, polyurethane, fiberglass, or recyclable materials for example, to support the reflective surface. Preferably, a foam material such as expanded polystyrene or extruded polystyrene may be used as the support surface in lieu of ribs or complex metal frames previously described in patent applications incorporated by reference above, may provide increased solar energy collection efficiency, reduced manufacturing costs, lighter in weight, provides for easy assembly, prolonged life, improved durability, larger or smaller collector apertures, and a modular structure suitable for ground, rooftop or trellis application. 
     Also provided herein is a method of achieving the desired panel shape by hot wire cutting the foam material with a CNC machine, a laser cutting machine or other device, or by molding or extruding the foam like material into the parabolic form. The collectors are formed into partial parabolic shapes whereby two or more pieces are used to form a complete parabolic trough collector. This design allows for efficient nesting of the pieces thereby minimizing shipping costs and reducing manufacturing costs. Once the panel is cut or molded to shape, a reflective element may then be applied. The reflective elements may also be applied to the foam material prior or during the creation of the parabolic form. 
     Further, provided herein are various methods of applying the reflective element to the panel, which may include attachment, adhesion or integration with the surface. Once applied to the formed foam material, the reflective element may be reinforced with cowlings or other fastening devices on each side of the parabola piece(s) in order to provide rigidity, reflective stability and to hold the reflector in place. End caps or other fastening components may also be applied at each end of the panel to further lock the reflective element in place, to provide additional structural strength to the panel design, and to provide a point of attachment for the arm, tracking system or for cosmetic treatment. 
     In addition to the foam material being formed into an appropriate shape giving the collector its parabolic functional characteristics, a method of maintaining the reflector&#39;s parabolic shape with the formed foam material may include the use of embedded inserts to secure the end caps and cowlings. An interconnect piece may be used to tie the parabolic shapes together and provide a support for a stanchion to hold the receiver tube and glass envelope in position. A method of connecting multiple panel rows together may comprise using connectors to tie the panels together. The connecting piece may serve to improve multiple collector row strength, may be decorative, and may be used for torsion control. 
     Thus, in one instance, disclosed is a trough solar energy collector having a rotational axis comprising
         a collector tube,   a first reflective panel and a second reflective panel,
           each of said first and second reflective panels comprising
               a polymeric core having an arc-shaped surface   a reflector on the arc-shaped surface of the polymeric core   cowling along a longitudinal edge extending along the polymeric core and   extending parallel to the rotational axis of the solar collector   
               the first reflective panel being positioned to illuminate a first side of the collector tube,   
           the second reflective panel being positioned to illuminate a second side of the collector tube.       

     Also disclosed is an end arm in assembled or disassembled form comprising
         a hub fitting having an opening,   a plurality of top fittings configured to engage with top portions of respective ones of a first reflective panel and a second reflective panel,   a bottom fitting configured to engage with bottom portions of each of the first reflective panel and the second reflective panel, and   a plurality of fitting couplers securing the plurality of top fittings and the bottom fitting to the hub fitting.       

     In addition, disclosed is a method comprising 
     simultaneously slicing a plurality of arcuate reflector cores from a polymer blank, 
     placing reflective surfaces on concave portions of the arcuate reflector cores, 
     affixing cowling along edges of the arcuate reflector cores to form arc-shaped reflectors. 
     Further, disclosed is a method comprising
         using a first set of sliced polymeric cores to form a first plurality of arc-shaped reflectors;   using a second set of sliced polymeric cores to form a second plurality of arc-shaped reflectors;   affixing a first and second reflector selected from said first plurality of arc-shaped reflectors and said second plurality of arc-shaped reflectors along an adjacent edge of each of said first and second arc-shaped reflectors at a mid-point between a larger arc formed by the first and second arc-shaped reflectors and distant from ends of the first and second arc-shaped reflectors.       

     These and other aspects of the inventions are discussed further below in the text as well as the claims, which are hereby incorporated by reference into the text herein. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIGS. 1 and 2  depict a support structure comprised of a foam material, end arms, and end caps. 
         FIG. 3  illustrates hot wire cutting with a CNC machine. 
         FIG. 4  depicts an outer coating. 
         FIG. 5  illustrates two panels forming the wings, which may fit together using an H-clip that also attaches a stanchion. 
         FIG. 6  illustrates reflective panels on a foam material. 
         FIG. 7  illustrates a foam material with end caps, cowlings and inserts for a support structure. 
         FIG. 8  shows decorative end caps for a support structure. 
         FIG. 9  depicts an end arm assembly. 
         FIG. 10  shows a corner end panel interconnect. 
         FIG. 11  illustrates inserts in an end cap. 
         FIG. 12  shows an H-clip. 
         FIG. 13  illustrates a receiver tube. 
         FIG. 14  illustrates a stanchion that is used to hold a receiver tube. 
         FIGS. 15-18  depict a U-bolt assembly with a receiver tube bearing, a receiver tube bearing attachment, a receiver tube bearing attachment screw, and a stanchion bracket. 
         FIG. 19  shows a silicone foam gasket. 
         FIG. 20  depicts a glass envelope. 
         FIG. 21  shows inner and outer reflective covers with an insulating material. 
         FIG. 22  shows a locator tube. 
         FIG. 23  depicts a locator tube collar. 
         FIG. 24  illustrates a stand for a support structure. 
         FIG. 25  depicts torsion cables to adjust tension on a support structure. 
         FIG. 26  illustrates multiple cores, one bare ( 2603 ), one  2601  with reflector panel  2602 , and one  2601  with a backing panel  2604  applied. 
         FIG. 27  likewise shows two cores, one with a backing panel. 
         FIG. 28-30  provide various views of partially-assembled collectors ganged together ( FIGS. 28 and 29 ) and alone. 
         FIG. 31-32  illustrate inserts into cores that can be used in conjunction with screws or bolts to secure cowling, end caps, clips, backing, or other components to reflector cores. 
         FIG. 33  illustrates two end arms, each attached to a locator tube collar in a bearing assembly in a stand. 
         FIG. 34  illustrates some details of a panel-joining fitting. 
         FIG. 35  illustrates two arc-shaped reflective panels joined to one another by a clip  3504  as well as a stanchion  3501  supporting the collector tube. 
         FIG. 36  illustrates telescoping glass tubes (with one tube withdrawn) concentric with the collector tube. 
         FIGS. 37A and 37B  depict cross sectional views of two clips. 
     
    
    
     DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS 
     Various aspects of the inventions disclosed herein may be understood better by reference to the following discussion in conjunction with the figures, which form a part of this specification and are incorporated by reference. The discussion of particular examples does not limit the scope of the invention, and the discussion is provided only to aid in understanding various aspects of the inventions disclosed herein. The claims are to be afforded a broad interpretation consistent with the principles, as well as the general and specific description herein. 
     By way of introduction to various parts and combinations of parts,  FIG. 28-30  illustrate a partially-assembled solar energy trough collector which may include a collector tube  2801 , a plurality of arc-shaped reflectors  2802  connected by at least one fastener  2803  at a midpoint of the larger arc formed by joining the arc-shaped reflectors, and end arms  2806 . An arc-shaped reflector may have a core, a reflective portion  2807 , cowlings  2805 , and optional end caps  2804  as described more fully below. A support structure is a trough collector as discussed above that does not have a reflective portion. 
       FIG. 1  illustrates how one particular collector may be formed using a core such as a foam material  201 , a plurality of end arms  102 , and a plurality of end caps  103 . Each of these pieces is discussed below in further detail. 
     1. Core 
     A core may be a polymer, a polymeric foam material, or a honeycomb material such as a composite honeycomb sheet (e.g. aluminum honeycomb core with rigid sheets sandwiching the honeycomb and/or rigid polymer filling the interstices). A core is preferably rigid, so that a concave arcuate surface on the core may have a reflective surface applied that conforms in shape to that of the concave arcuate surface. 
     The concave arcuate surface may be parabolic, cylindrical, or other concave arc on one side of the core. The opposite side of the core may be of convex curvature that is a mirror image of the curvature of a second core, as explained later. The opposite side may therefore be of convex curvature or may have no curvature. 
     A core that is flexible may be used if it retains accurate concave curvature when other pieces such as cowling, end caps, reflective element, backing, and/or end arms are applied. 
     (i) Polymeric Core 
     A core may be a polymer such as a rigid or semi-rigid polymer. The core may be solid or a foam that has cells (either open or closed). Preferably, a closed cell foam material is used because of its moisture resistant characteristics. The polymer may have sufficient rigidity and surface strength such that the curved surface deforms little when a reflective material is applied to the surface. The core&#39;s curved surface therefore accurately imparts its curvature to an applied material. 
     As shown in  FIGS. 1 ,  2 , and  26 , a core formed from a foam material  201 ,  2601  such as expanded polystyrene (EPS), extruded polystyrene (XPS), or expanded extruded polystyrene (XEPS) may be used to form the arc-shaped reflectors  101  of the collector. Other suitable materials like polyurethane, fiberglass or epoxy may alternatively be used to form the panels. XPS, for instance, has good moisture resistant characteristics. Different densities of foam may be used, and density may be around two or three pounds per cubic foot, for instance. 
     Foam is inexpensive to manufacture and may be locally produced, shaped, and modified. Using foam may reduce the number of parts required because tooling is not required to achieve the collector shape. The foam allows for single piece manufacturing (e.g. a core may be formed as a single piece in a mold or cut from a block of foam) and is easy to handle, thereby reducing assembly time and easing field assembly. The foam material  201 ,  2601  is also lightweight while maintaining sufficient strength to bear wind loads, significant advantages for roof-mount applications. The formed foam material may easily be shaped and sized to various apertures. For instance, a wider aperture increases the amount of reflective surface per panel, thereby allowing higher temperatures to be reached and therefore providing greater power conversion efficiencies. 
     In addition, the foam core  201 ,  2601  may provide a better substrate for the reflective element  601  ( FIG. 6) and 2602  ( FIG. 26 ) because, when adhered to a reflective element such as polished metal, the composite is a significantly stronger and a more accurately formed structure. One reason for this is that the reflective element  601 ,  2602  is supported by a solid substance, the foam material  201 ,  2601  rather than spanning a set of ribs, as described in prior patent applications incorporated by reference above. The formed foam material  201 ,  2601  may provide structural integrity and resistance to forces that may flex or twist the support structure. Thus, the foam core  201 ,  2601  provides better support as well as a protective backing to the arcuate reflective surface. 
     Any core may have other materials applied to it or incorporated into it, such as moisture barrier layer or layers, adhesive, UV blocker or absorbent, and strengthening layer or layers. Thus, various protective layers of material may be applied to any or all surfaces of the core (e.g. convex and/or concave arcuate surfaces), or anchors may be incorporated into a core, for instance. 
     (i) Honeycomb Core 
     As mentioned, a honeycomb core may be e.g. an aluminum honeycomb sheet. The sheet may be made rigid by applying rigid or semi-rigid layers to one or more surfaces of the core or by solidifying a material such as a polymer in the interstices of the honeycomb. These layers may include any of the rigid or semi-rigid polymers such as polycarbonate, polyurethane, and polystyrene. 
     Any core will have a concave arcuate surface on which a reflective layer is placed and optionally a convex arcuate surface as well on which a backing material or materials may be placed. 
     2. Method to Achieve the Desired Collector Panel Shape 
     As shown in  FIG. 3 , the foam material  201  ( FIG. 2 ),  2601  ( FIG. 26 ) may be shaped into its desired panel shape by hot wire cutting one or more foam blanks  302  such as one or more blocks of foam using a CNC machine  301 , or by using a laser cutting machine or other device. In the system depicted in  FIG. 3 , a plurality of cores are formed simultaneously by using hot wires  303  to cut one or a plurality of foam blanks. Multiple cores are therefore formed simultaneously from polymer blanks. The foam blank may be molded and cut into one or more cores  201  close to the location of any given project site thereby reducing shipping costs. 
     Use of a CNC hot wire  301  cutting machine to cut the foam material  201  may reduce overall tooling costs as compared to the tooling costs of stamping out ribs, described in prior patent applications incorporated by reference above. The collectors may be shaped to form parabolically shaped wings  501  ( FIG. 5 ) whereby two pieces are positioned together along their longitudinal ends to form a complete parabolic trough collector  501  having a larger arc-length than either of the pieces. This design allows for efficient nesting of the pieces during fabrication and shipment to reduce material drop when cutting and also minimizes shipping costs. The foam sections  201 ,  2601  may be cut with areas of greater or lesser thicknesses to provide features like reflector stops that stand above the overall surface and help hold a reflector panel in place, height adjustment to accommodate parts that interface with the core, and areas of increased strength where needed (e.g. in the vicinity of fasteners and/or cowling). 
     A bottom or convex face of a core may be identical in curvature to a top or concave face of another core if desired, especially if the cores are both sliced simultaneously from the same polymer blank. 
     It is thought that a polymeric core may be uniform in tension and compression throughout the polymer of the core, especially where the core or multiple cores are formed by slicing a foam blank (such as a block) into the desired shape without further heating and bending of the bulk foam material. While a core may also be made by extruding the foam or by molding it, it is theorized that heating and bending foam that has already polymerized introduces compression and tension into the foam (especially into closed-cell foam), as may polymerizing a polymer in an arcuately-shaped mold. 
     Further, slicing a foam blank provides cores than are “skinless” as compared to a core that is formed in a mold. A core cut from a polymeric blank has little to no skin. Any skin formed by slicing a foam blank using hot wires or laser cutting is typically quite thin and/or discontinuous and is believed to be thinner overall than skin formed during polymerization in a mold. A core formed in a mold typically has a skin with physical properties much different from the bulk foam beneath the skin. When a core is sliced from a foam blank, the surface of the core is very much like the bulk foam beneath the surface. The core sliced from a blank is therefore expected to be more uniform than a core formed in a mold. Methods of slicing a core from a blank therefore provide a skinless core as distinguished from a polymeric core formed in a mold. 
     Further, a foam core sliced from a blank may have already been formed at a higher temperature than foam formed in a mold. Foam typically has low thermal conductivity, and it is anticipated that a large blank of foam during polymerization experiences a higher temperature within much of the foam because of the large size of the blank and/or a high temperature for a much greater period of time than does a core formed in a mold. The much smaller quantity of foam in a mold for a core can cool more quickly, providing a lower temperature at which polymerization occurs in most or all of the foam and/or a much faster cool-down time. It is therefore believed that a foam core sliced from a blank will have already been subjected to a higher temperature and/or a higher temperature for a longer period of time than a molded core experiences, a sort of “pretreatment” of the foam that may lead to longer service life for a core formed from a polymer blank. 
     3. Outer Coating 
     As shown in  FIG. 4  and  FIG. 27 , the outer surface  2701  of the formed foam material  201  may be coated with a suitable outer coating  401 ,  2702  such as an epoxy, paint, vinyl or other UV inhibitor to (1) protect the foam from UV rays, (2) seal the foam from moisture, and/or (3) provide additional structural support. The coating  401 ,  2702  may be a material such as plastic or other polymer such as polyvinylchloride, metal such as aluminum, fiberglass, canvas or other material that is fused, or otherwise externally affixed to the formed foam material  201 ,  2601 , or that may be fabric layered, thereby providing impact resistance to harsh weather. The coating may be applied by spraying, troweling, dipping, fusing or pouring the desired material onto the foam or alternatively, the plastic material may be modified to allow for the appropriate protective outer coating to be included in, or combined with, the foam material itself. 
     4. Arc-Shaped Reflector (Wing) 
     As shown in  FIG. 5  and  FIG. 28-30 , there may be two or more symmetrical arc-shaped reflectors or wings  501 ,  2802 . These wings  501 ,  2802  may be attached at the bottom of the parabolic arc with a fastener such as a clip, e.g. an H- or other shaped-clip  502 ,  2803  and  3701  and  3702  of  FIGS. 37A and 37B  described in further detail below. The clip  502 ,  2803 ,  3701 ,  3702  may optionally have a provision for attaching a stanchion  503 ,  2808  described in further detail below, which supports the receiver tube  1301 ,  2801  also described in further detail below. 
     The wings  501 ,  2802  may also be independently rotated so they may close in upon each other in a clamshell like configuration  504  which allows for the protection or storage of the collector. Specifically, the wings may be attached pivotably to allow each wing to pivot and rotate on top of the other  504 . This protects the inside of the panel and reduces the wind load profile. The wing is driven by a sprocket assembly that when reaching a certain point, engages the second half of the panel and drives it synchronously. The wings, also or instead may be decorative. 
     5. Reflective Panels 
     As shown in  FIG. 6  and  FIG. 26 , the core supports reflective element panels or panel segments  601 ,  2602  that are placed onto the formed foam surface  602 ,  2603 . One or more reflective panels  601 ,  2602  may form the reflective surface upon the support structure. The reflective element may be a flexible material such as polished aluminum, aluminum laminated with reflective Mylar, or other suitable material such as epoxy sputtered with silver or a glass mirror. Preferably, a flexible aluminum panel polished to a mirror finish is used as the reflective element. The reflective element may be flexible so that a flat sheet of the reflective element can be bent into the desired shape at room temperature and pressure, or the reflective element may be rigid at room temperature and pressure but capable of being deformed into the desired shape using heat and optionally pressure or vacuum. 
     One or more flat but flexible reflective panels  601 ,  2602  may be retained onto the formed foam surface  602 ,  2603  mechanically through the use of cowlings  702  ( FIG. 7) and 2805  ( FIG. 28-30 ) and end caps  703 ,  2804  discussed in further detail below, or through the use of adhesion using an adhesive such as 3M adhesive, or both. The formed foam material  602 ,  2601  beneath the reflective element provides the desired panel shape (such as parabolic shape, flat, or partially parabolic shape that a wing may take). 
     6. Top and Bottom Longitudinal Cowlings 
     As shown in FIGS.  7  and  28 - 30 , the formed foam material  701  and the reflective element  2807  may be mechanically held together using reinforcing cowlings  702 ,  2805  on each longitudinal edge of the parabola pieces. The cowlings  702 ,  2805  mechanically hold the reflective element in place and provide rigidity. The end caps  703 ,  2804  discussed in further detail below, may also serve to mechanically hold down the reflective element to the core  701 . 
     The top and bottom cowlings  702 ,  2805  may be made of aluminum (polished or unpolished) or other metal such as stainless steel that has high rigidity or a plastic. The cowlings  702 ,  2805  may be applied by positioning inserts  704  or  3101  or  3201  of  FIGS. 31 and 32 , discussed in further detail below, to allow fasteners to be placed into the core foam material  701 ,  3102 ,  3202 . An alternative may include using glue to bond the cowlings  702 ,  2805  to the foam material  701 ,  3102 ,  3202  or using a band or cable to join the upper and lower cowlings  702 ,  2805  to prevent deflection under load. 
     The top and bottom cowlings  702 ,  2805  may also accommodate a variety of thicknesses of the combination of core, reflective element, and/or backing through the use of laterally opposed interlocking notches  706  to provide a cowling with variable opening size. This assembly  705  allows for the adjustability of the opening of the cowling assembly to accommodate varying thicknesses of the combination of the formed foam material, outer coating, and the reflective element. The adjustability of the opening may also accommodate the need to add, change, or remove the reflective material. This cowling assembly  705  also serves to lock the adjusted width in place because the cowlings legs rotate in towards the center as the width is adjusted, thereby providing increased holding pressure on the combination of the formed foam material, outer coating, and the reflective element. This may provide a significantly stronger and more secure attachment of the reflective material. Lastly, the top and bottom cowlings  702  are secured longitudinally with inserts  704  through the center to engage the edge of the panels and force the reflective material to form and maintain a parabolic shape. 
     The cowlings may be made of flat sheet stock that is bent into a shape to conform with the longitudinal edges of the core, or the cowlings may be rigid channels or conformal material that, alone or together with the core material, provide rigidity to the arc-shaped reflector formed from the core, reflector material, longitudinal cowlings, and optional end caps. The cowlings may themselves be polymeric (e.g. polycarbonate, solid rigid polystyrene), metallic (e.g. aluminum, stainless steel, or other material), ceramic, or other material that aids in protecting the core as well as providing additional rigidity. 
     7. Transverse End Caps 
     As shown in  FIG. 8  and  FIG. 28-30 , a support structure may also have transverse end caps  801 ,  2804  which provide further rigidity to the assembly and resistance to flexure and/or torsion. The end caps  801 ,  2804  located at either end of the collector are identical and may be attached to an end arm  901  ( FIG. 9 ),  2806  ( FIG. 28-30 ) described below. The end caps  801 ,  2804  may be made of any suitable rigid material, preferably aluminum (polished or unpolished) or another metal, such as stainless steel, that has high rigidity. The end caps  801 ,  2804  may be used at both ends of the panels to further lock the reflective element in place, transfer load, retain the parabolic shape and provide additional structural strength to the panel design. 
     The end caps  801 ,  2804  may be a single piece of metal stamped, or otherwise cut, from a sheet and having a surface that has a shape which is generally parabolic or substantially arc-shaped to fit the profile of the formed foam material and provide a structural frame. The end caps  801 ,  2804  preferably may have a tab such as an outer perimeter tab to encase the edge of the formed foam material and to allow for points of attachment. The tab may therefore be configured to overlap the reflector and/or cowling, and the tab may be configured to allow the core to insert within the tabbed portion of the end cap so that the assembled pieces may be secured. The tab may protect the edge of the panel, hold the reflective element in place, add a dimension to the end cap  801 ,  2804  for rigidity, and provide a finished look to the support structure. 
     One or more ribs may be used in place of or in addition to end caps. Ribs attach directly to the end arms and form arc-shaped members that make the end-arm a more rigid structure independently of whether reflector panels or wings are attached to the core and end-arms. A rib is therefore separate from a reflector panel or wing and end cap as discussed above. 
     8. End Arms 
     End arms help to support Mirrored panels and transmit movement induced by a motor to the panels to track the sun&#39;s apparent movement. An end arm may be configured in a number of ways. 
     As shown in  FIG. 9  and  FIG. 33 , the end arms  901 ,  3301  may be similar to the end arms described in prior patent applications incorporated by reference herein. The support structure may have transverse end arms  901 ,  3301  which provide further rigidity to the support structure and resistance to flexure and/or torsion. The end arms  901 ,  3301  located at either end of the collector, are identical and may be attached to a stand. Additionally, the end arm  901 ,  3301  may rotate as one unit about the longitudinal axis. 
     An end arm  505  as illustrated in  FIG. 5  may be formed by stamping or otherwise cutting the end arm from sheet-metal. An end arm can be a single piece of material such as metal stamped from sheet-stock, so that the end arm depicted in  FIG. 5  has a generally “T”- or “Y”-shaped structure. Alternatively, an end arm may be formed using two pieces as shown in  FIG. 5  that each have a generally “L”-shaped structure. In this instance, the two stampings may be identical and positioned together during assembly to provide a generally “T- or “Y”-shaped structure when the support structure is viewed from the side. An end arm  505  may also be formed by superimposing two or more end pieces having a “T,” “Y,” or “L” shape and attaching them to one another directly or with or without a cowling. An end arm need not be “T”- or “Y” shaped. It may be solid or perforated to which parts are attached, for instance. 
     An end arm  901  may be formed from individual fittings such as welded, die cast, or molded fittings that are formed to accept tubing, rods, or other fitting couplers and attach to the wings. As depicted in  FIGS. 33 and 34 , the fittings may comprise a bottom fitting  3302  that engages with bottom cowling of adjacent arc-shaped reflectors, an end fitting  3303  that engages with an arc-shaped reflector  3305  (two of which are shown stacked awaiting assembly to the end arms), and a hub fitting  3304 . 
     A bottom fitting  3302  may have a collar or shape  3308  that engages another depression or opening  3309  of the same or an adjacent panel. A bottom fitting may be formed in one piece as shown so that the piece engages both of the reflective panels of adjacent panels to form a larger arc from the two panels. A bottom fitting may instead be formed in two or more pieces that are secured to one another. A bottom fitting may have one or more collar portions  3313  that overlie an edge of the reflective layer or element and/or the cowling  3314  as well as the core. The collar portion  3313  may also or instead overlap a backing material  3315  applied to the core. The bottom fitting may also have holes that allow e.g. a bolt or screw to engage with a fastener or anchor in the core. A bottom fitting may also have one or a plurality of holes  3316  that receive fitting couplers  3317  that engage with the hub fitting. 
     An end fitting  3303  may have a collar or shape  3306  that engages a recess or opening  3307  in the arcuate reflector panel  3305 . Screws or bolts may be inserted through holes  3310 ,  3311  in the end and bottom fittings to secure an arc-shaped reflector to fittings in the core by screwing into anchors in the foam or honeycomb beneath the optional end-caps. An end fitting may have one or more collar portions  3318  that overlie an edge of the reflective layer and/or the cowling as well as the core. The collar portion may also or instead overlap a backing material applied to the core. An end fitting may also have one or a plurality of holes  3319  that receive fitting couplers  3320  that engage with the hub fitting. An end fitting may also optionally have a flat rectangularly-shaped surface  3322  along an edge of the end-fitting so that e.g. a flat bar  2901  ( FIG. 29 ) can be attached upon the edge of adjacent collectors to gang the collectors together and therefore move multiple collectors simultaneously using a single motor and drive sprocket. 
     A hub fitting  3304  may have the locator tube collar mentioned previously, an end of which is depicted as  3312  in  FIG. 33  and the collar end of which is seen as  2809  in  FIG. 28 . As shown in these figures and in  FIG. 23 , a locator tube collar  2301 ,  2809  of the hub fitting  3304  may be used to connect the end arms  901  perpendicular to the locator tube  2201 . The hub fitting may have means for mounting a drive sprocket  3001  as seen in  FIG. 30 . Such means include holes  2810  ( FIG. 28 ) such as threaded holes for bolts, a keyway and corresponding key (either as a separate piece or formed integrally with the hub fitting), screws, rivets, welding, adhesive, and any other known fastening arrangement for securing one piece to another. A hub fitting  3304  also may have holes  3321  extending radially from the hub and into which couplers  3317 ,  3320  insert to couple a plurality of end fittings and one or a plurality of bottom fittings. The locator tube  2201  ( FIG. 22 ) inserts through the locator tube collar  2301 ,  2809  of the hub fitting and engages with a bearing. The bearings may be roller, ball, plastic, or graphite bearings that are retained in the stand by screws in the stand and from a cap that mates with the stand. The hub fitting, made of any suitable rigid material, preferably aluminum (polished or unpolished) or another metal such as stainless steel that has high rigidity, slides onto the locator tube  2201  and may be secured with bolts and/or a keyway  2202 . The keyway may allow for accurate positioning of the locator tube collar  2301 ,  2809  on the locator tube  2201 . The collar  2301  may consist of one or more elements that allow each end arm  901 ,  3301  to rotate independently of the other so the wings may rotate together in a clamshell configuration as mentioned earlier. 
     Couplers  3317  and  3320  may run radially from the hub fitting  3304  on a locator tube collar and to the end  3303  and bottom  3302  fittings, thereby forming generally two “L” shapes or a “Y” shape. Various lengths of couplers may be used to adjust the shape and length of the end arm  901 ,  3301  to allow forming collectors of varying aperture widths mentioned earlier. The fittings may be rods such as solid or tubular metal rods (e.g. aluminum), and the rods may be e.g. cylindrical, square, rectangular, regular, or irregular in cross-section. 
     The fittings and/or couplers may be formed of polymer (such as a rigid non-foamed polymer as discussed herein), metal such as aluminum, ceramic, or other suitable material. 
     9. Corner End Panel Interconnect 
     As shown in  FIG. 10 , there may be a corner end panel interconnect  1001  that serves to tie the end caps  1102  to the cowlings  702  structurally, providing for extra strength and support. The corner end panel interconnect  1001  may be made of any suitable rigid material, preferably aluminum (polished or unpolished) or a metal such as stainless steel that has high rigidity. It is either die cast or metal stamped into its desired shape. 
     The corner element  1001  may bridge one panel to another to maintain alignment and transfer torque to the next row of collectors. Potentially, multiple corner end panel interconnect  1001  pieces may be used to tie the bottom cowlings together to form an I-beam type structural member. This member may also be a one piece extruded shape. 
     An interconnect may also be a section of flat bar  2901  ( FIG. 29 ), for instance. And end fitting may have a flat rectangularly-shaped surface  3322  along an edge of the end-fitting so that e.g. flat bar  2901  can be attached to the edge of adjacent collectors to gang the collectors together and therefore move multiple collectors simultaneously using a single motor and drive sprocket. 
     10. Inserts/Anchors 
     As shown in  FIGS. 11 ,  31 , and  32 , inserts  1101 ,  3101  or embedded anchors  3201  may be used to attach the cowlings (e.g.  FIG. 7   702 ,  FIG. 28-30   2805 ) to the formed foam material  701 ,  3102 ,  3202 . One insert or anchor  1101 ,  3101 ,  3201  may be used every few feet. The inserts or embedded anchors may also be used to secure the end caps  1102  that maintain the parabolic shape and engage with the end arms  901 ,  2806  as a means of support. 
     An insert may be glued into foam or other polymer of a core, as shown in  FIG. 31 . The foam may be melted, and an insert may be anchored into the foam by heating and embedding it and allowing the polymer to resolidify around the anchor. As shown in  FIG. 32 , a small hole may be formed in a surface of the foam by melting the surface, and the insert, may be glued into the hole. 
     11. Fastener (e.g. Clip) 
     As shown in the figures, a clip ( 502  ( FIG. 5 ),  1201  ( FIG. 12 ),  2803  ( FIG. 28-30 )) such as an H-clip may be used to attach two arc-shaped reflectors  501 ,  2802  together at the bottom of a parabola by connecting the cowling of one arc-shaped reflector to the cowling of the opposite reflector. A clip such as an H-clip may therefore have two sets of arms, one set that engages one arc-shaped reflector and one set that engages the other arc-shaped reflector. 
     A clip  502 ,  1201 , 2803  may also optionally have a provision for attaching a stanchion  1401 ,  2808  to support the receiver tube  1301  and glass envelope  2001 . The stanchion  1401 ,  2808  may be positioned on top of the H-clip  1201  in the center of collector. This allows the stanchion  1401  to remain stationary and ensures the receiver tube  1301  is always centered at the focal point of the collector. 
     A clip as used in the collector depicted in  FIG. 28-30  may not have the exact shape of an “H” as the H-clip of  FIG. 12  has. A clip  3701 ,  3702  in this instance may have a cross-section similar to that depicted in  FIG. 37A  or  37 B and be generally H-shaped. 
     The fastener need not be a clip. For instance, the fastener may be a screw that joins flat tabs from adjoining cowling together or a latch and receiving portion on adjacent panels, for instance. 
     A clip may span some or all of the distance from one end cap to the other end cap. Since a clip need only provide an attachment point to improve rigidity of the assembly, a clip may be relatively short, being less than about 1/10 of the length of the cowling with which it engages. If further rigidity is desired, the clip can be made longer. The clip may be positioned at a midpoint along the longitudinally extending cowling for instance, or multiple clips may be positioned approximately equidistantly along the longitudinally extending cowling. 
     12. Longitudinal Collector Tube 
     As shown in  FIG. 13  and  FIG. 28-29 , a longitudinal collector tube  1301 ,  2801  similar to that described in prior patent applications incorporated by reference above, may be positioned with the parabola to receive light and solar thermal energy reflected by a parabolically-shaped reflective panel of a solar energy collector. 
     The collector or receiver tube  1301 ,  2801  may have a working fluid, preferably an oil, Freon or water, working through the interior of the pipe. The receiver tube  1301  may connect to a joint or pass through a locator tube collar  2301  ( FIG. 23 ) ( 3312  of hub  3304  in  FIG. 33 ) and locator tube  2201  ( FIG. 22 ) joined to a stand  2401  ( FIG. 24 ) that supports the support structure. Each support structure may have its own receiver tube  1301 ,  2801  that joins to adjacent receiver tubes through joints, hoses, or other types of connectors typically used in joining tubes that will undergo thermal expansion and contraction. Alternatively, a single receiver tube  1301 ,  2801  may be used for ganged support structures or for two or three adjacent support structures. A support structure may have one or more stanchions  1401 ,  2808  to support the receiver tube, as explained in further detail below. The receiver tube may be painted with black paint or coated with a coating that absorbs solar energy and transmits the resultant heat to the tube wall. If the trough solar energy collector has an axis of rotation coaxial with the collector tube, the collector tube may be configured to rotate with the trough solar energy collector, or the collector tube may be fixed in position so that the trough collector rotates about the stationary collector tube. If the axis of the collector tube does not coincide with the rotational axis of the trough solar energy collector, the collector tube may revolve about the axis of rotation of the trough solar energy collector. 
     13. Stanchion 
     As shown in  FIG. 14  and  FIG. 35 , one or more stanchions  1401 , 3501  similar to those described in prior patent applications incorporated by reference above, may be used to support a longitudinal receiver tube  1301  by means of a bearing ( FIG. 15   1501 ,  FIG. 35   3502 ) and bearing attachment ( FIG. 17   1702 ,  FIG. 35   3503 ) as explained in further detail below, as well as to support the glass envelope  2001  described below. One or more two-leg stanchions and/or single-leg stanchions  1401  are positioned between transverse end arms  901  and may attach to the arc-shaped reflector panel. The stanchion  1401 ,  3501  may be positioned on top of or formed as part of a clip  1201 ,  3504  in the center of the collector to keep it stationary and ensure the receiver tube  1301  is always centered at the focal point. A stanchion  1401 ,  3501  may be made of any suitable rigid material. preferably aluminum, stainless steel, or the like, may have adjustment screws  1503  or bolts or plastic screws, explained below, which can be adjusted to provide better reflective focus across the collector. 
     Collector tube height can be adjusted by moving the plate  3506  on which the bearing rests up or down and then tightening the bearing attachment  3503  to secure the collector tube  3507  and bearing  3502  in place. An additional cap (not shown for sake of clarity) engages with bolt-holes  3508  onto the stanchion to retain an insulating glass envelope (discussed below). 
     14. U-Bolt Assembly 
     As shown in  FIGS. 15-18 , a U-bolt assembly may be used to fasten the receiver tube bearing  1501 , described below, to the stanchion  1401 . thereby allowing for adjustability of the receiver tube  1301 . The U-bolt assembly shown in  FIGS. 15-1   8 , which is secured by nuts, extends in a “U” shape through the bottom of the stanchion  1401 , around the receiver tube bearing  1501 , and back through the other side of the stanchion. Additionally, there may be a bolt extending through the bottom of a bracket where the “U” bolt is attached. This allows for height adjustments of the receiver tube bearing  1501  centering the receiver tube  1301 . 
     15. Receiver Bearing Adjustment Screw 
     As shown in  FIGS. 15 and 16 , stanchions may have adjustment screws  1503  and  1601  or bolts or plastic screws that can be adjusted to provide better reflective focus across the collector. Adjustment screws  1503  and  1601  may adjust the height of the receiver tube bearing  1602  to provide optimal reflective focus across the length of the collector, thereby increasing collector efficiency. 
     16. Receiver Tube Bearing Attachment 
     As shown in  FIG. 17 , a receiver tube bearing attachment  1701  may be used to accommodate the thermal expansion and contraction of the receiver tube  1301 . The bearing attachment  1701  permits the panels to rotate around the receiver tube  1301  and position the receiver tube  1301  to ensure maximum reflective focus and collector efficiency. This allows the receiver tube  1301  to slide longitudinally as the receiver tube  1301  expands and contracts. 
     17. Stanchion Bracket 
     As shown in  FIGS. 18 and 33 , stanchion brackets  1801 ,  3303 ,  3305  may be used to support the glass envelope  2001 , described below. The brackets  1801 ,  3303 ,  3305  may be made of any suitable rigid material, preferably aluminum, stainless steel, or otherwise, clamp together to compress against the glass and provide support across the length of the glass envelope  2001 . An additional cap (not shown for sake of clarity) engages with bolt-holes  3508  on the stanchion bracket  3505  to retain an insulating glass envelope. 
     18. Gaskets 
     As shown in  FIG. 19 , silicone  1901 , preferably, or another resilient polymer, organic or inorganic gel, ceramic or metals able to withstand high temperatures as described in prior patent applications incorporated by reference above, may be used to support the glass envelope  2001  and serve as an end seal. The silicone foam gaskets  1901  are placed at the ends of the glass envelope  2001  between the receiver tube  1301  and the glass and are clamped down by a bracket secured with bolts. 
     The seal created contains the ambient atmosphere within the chamber of the glass envelope  2001  when a cover, described below, is placed on or in the opening of the glass envelope  2001  housing. The silicone end seals  1901  may be pliable and movable to allow thermal expansion without undue stress being created on the ends of the glass envelope  2001  or the receiver tube  1301 . 
     19. Glass Envelope 
     As shown in  FIG. 20 , the glass envelope  2001 , a transparent tubular housing similar to those described in prior patent applications incorporated by reference above, may be used to enclose the receiver tube  1301  to provide an insulating layer and reduce heat loss. The glass envelope  2001  may vary in thickness, preferably around 2 millimeters thick and may have a chamber that is sufficiently large to contain the receiver tube  1301  positioned within the glass chamber. The glass envelope  2001  may be transparent to UV, visible, and/or infrared light. Preferably, the glass envelope  2001  is transparent to at least the sun&#39;s visible and infrared radiation. The envelope  2001  may be formed from borosilicate glass such as Pyrex. Alternatively, the envelope  2001  may be formed of an acrylic polymer such as polymethacrylate, a butyrate, a polycarbonate, or other polymer that admits at least 70% of the sunlight  14  incident upon it. The glass envelope  2001  may contain air, other gases, or be evacuated or partially evacuated in some variations. 
     Additionally, the glass envelope  2001  may be sliced to shape leaving at least one opening to allow easy access to the chamber, so the envelope  2001  may be placed over the receiver tube  1301  without having to slide it on and risk breakage. This opening allows for convenient and easy installation, assembly, replacement, and cleaning. The one or more openings may run the entire length of the glass envelope  2001  and may be as wide as or wider than the receiver tube  1301  that is to reside within the chamber of the envelope  2001 . Once placed over the receiver tube  1301 , the glass envelope  2001  opening may be filled with an inner and outer reflective cover  2101  described below, and an insulating material  2102 , all of which are sealed by the silicone foam gaskets  1901 . 
     A glass envelope may be a telescoping envelope as illustrated in  FIG. 36 . One glass tube  3601  nests within a second glass tube  3602  around a collector tube  3603 . During collector assembly, the nested tubes are placed over the collector tube, and subsequently the outer glass tube is slid along the inner glass tube so that one of the tubes can be secured to a side of the stanchion and the other of the glass tubes can be secured to or in the vicinity of the locator tube collar  3312  of the hub  3304  of  FIG. 33 . 
     20. Inner and Outer Reflective Cover 
     As shown in  FIG. 21 , a cover assembly, similar to that described in prior patent applications incorporated by reference above, may be placed on or in the glass envelope  2001  opening, and may or may not be retractable. The cover assembly may consist of an inner and outer cover  2101 , as well as insulating material  2102 . The cover assembly may be attached in a manner to allow the cover be retractable for venting and cleaning of the glass envelope  2001 . 
     The inner and outer covers  2101  are often movable and may fit within or upon the one or more openings of the glass envelope  2001 . The inner and outer covers  2101  may be made of any suitable rigid material, preferably aluminum (polished or unpolished), may be formed of a metal such as stainless steel that has high rigidity, or may be silvered to make a reflective surface. The outer cover  2104  may provide a protective backing for the glass envelope  2001 . The inner cover  2103  acts as a lens to better direct solar radiation onto the receiver tube  1301 . The inner cover  2103  focuses solar energy upon the receiver tube  1301  when it is seated in the glass envelope  2001  and reflects any solar radiation that is not reflected directly onto the receiver tube  1301 . The inner cover&#39;s  2103  surface may reflect at least 50% of the radiation incident upon it, and preferably the surface reflects greater than 80% or 90% of the radiation incident upon it. Inserted in between the inner and outer cover  2101  is a thermally insulating material  2102  able to withstand high temperatures, preferably a rigid polymer like polycarbonate, polyamide, or polyimide that may have a mirrored coating to reflect light. The insulating material  2102  and the inner and outer covers  2101  may be clamped together by a bolt, screw, rivet, or any other suitable fastener. 
     21. Locator Tube 
     As shown in  FIG. 22 , a locator tube  2201 , similar to that described in prior patent applications incorporated by reference above, may be used to support a solar collector, as well as to join two solar collectors together. The tube  2201 , which extends through an end arm  901 , may be made of any suitable rigid material, preferably aluminum (polished or unpolished) or a metal such as stainless steel that has high rigidity. In addition, the locator tube  2201  rests on a stand  2401 , described below, allowing it to rotate around the receiver tube  1301 . The locator tube  2201  may also contain a keyway or a key which allows it to drive the locator tube collar  2301  described below. 
     The locator tube  2201  and locator tube collar  2301  may each have holes through which bolts or adjusting screws, for example, extend. The bolts or screws secure the locator tube collar  2301  and locator tube  2201  so that they rotate in unison. Additionally, the bolts or screws may extend through the holes to support the receiver tube  1301  and the locator tube may be used as a race for the bearing to allow the receiver tube  1301  to pass through. 
     22. Stand 
     As shown in  FIG. 24 , a support structure is typically secured to stands  2401  containing bearings, similar to those described in prior patent applications incorporated by reference above, to allow the support structure to pivot along an axis defined by the bearings. The stand  2401  may be made of aluminum (polished or unpolished) or a metal such as stainless steel that has high rigidity. The stand  2401  may have a locator tube  2201  extending through the bearing at either or both ends of the bearing and extending into a locator tube collar  2301  of the support structure, thereby providing a more rigid structure. 
     23. Torsion Cables 
     As shown in  FIG. 25 , the support structure  2502  may have optional torsion cables  2501 , similar to those described in prior patent applications incorporated by reference above, that may extend diagonally from one end arm to the opposite end arm of the support structure  2502 . The torsion cables  2501  may therefore cross in an “X”-shaped configuration, for instance. The torsion cables  2501  help provide a rigid structure that resists torsion without adding significant weight to the support structure or shading to the solar panels or reflective element.