Patent Publication Number: US-9425732-B2

Title: Solar panel rack

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of International Patent Application PCT/US2014/042296 titled “Solar Panel Rack” and filed Jun. 13, 2014, which claims benefit of priority to U.S. Provisional Patent Application No. 61/842,516 titled “Solar Panel Rack” and filed Jul. 3, 2013, each of which is incorporated by reference herein in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The invention relates generally to the collection of solar energy, and more particularly to solar panel mounting racks and their components. 
     BACKGROUND 
     Ground-mounted photovoltaic solar panels are conventionally supported on solar panel mounting racks. Commercially available solar panel racks are typically produced using aluminum extruded sections or steel roll formed sections in order to provide the structural strength required to withstand loads associated with outside conditions such as wind and snow. 
     SUMMARY 
     Solar panel racks, their components, and related methods by which the solar panel racks may be manufactured, assembled, and used are disclosed. 
     In one aspect, a solar panel rack comprises one or more sheet metal brackets and an underlying support structure to which the sheet metal brackets are attached. Each sheet metal bracket comprises one or more upwardly pointing clinching tabs and one or more upwardly pointing protrusions. The clinching tabs are configured to be clinched to features on a solar panel or solar panel assembly to attach the solar panel or solar panel assembly to the solar panel rack in a desired location in a plane defined by the solar panel rack. The protrusions are configured to facilitate electrical contact between the brackets and the solar panel or solar panel assembly when the features on the solar panel or solar panel assembly are clinched by the clinching tabs. 
     The features on the solar panel or solar panel assembly may be sandwiched between the protrusions and the clinching tabs when the clinching tabs are clinched, for example. 
     The upwardly pointing protrusions may be configured to pierce an insulating coating on the features on the solar panel or solar panel assembly when the features are clinched by the clinching tabs. Accordingly, the upwardly pointing protrusions may comprise sharp edges, sharp points, or a combination of sharp edges and sharp points. The upwardly pointing protrusions may have a conical volcano shape, for example. 
     Each sheet metal bracket may comprise one or more upwardly pointing positioning tabs configured to contact features on the solar panel or solar panel assembly to position the solar panel or solar panel assembly in the desired location. The positioning tabs of each sheet metal bracket may be located, for example, in a square or rectangular arrangement in a central portion of a top panel of the sheet metal bracket and extend upward from the top panel. Each sheet metal bracket may be configured to position and attach adjacent corners of, for example, four solar panels or solar panel assemblies to the solar panel rack. 
     The electrical contact facilitated by the upwardly pointing protrusions may form part of an electrical path from the solar panel or solar panel assemblies through the one or more sheet metal brackets and the underlying support structure to ground. 
     The underlying support structure may comprise, for example, two or more hollow sheet metal beams arranged side by side and in parallel with each other to define a plane. The beams may be supported in any suitable manner as described herein, for example. Each sheet metal bracket may have an inner cross-sectional shape substantially conforming to the outer cross-sectional shape of a corresponding hollow sheet metal beam to which it is attached. 
     Each sheet metal bracket may comprise one or more tabs configured to engage corresponding slots or other openings in the underlying support structure to attach the sheet metal bracket to the underlying support structure, and one or more downwardly pointing protrusions configured to flex a portion of the underlying support structure to provide an elastic restoring force securing the tabs in the slots or other openings. If the underlying support structure comprises hollow sheet metal beams to which the sheet metal brackets are attached, the one or more downwardly pointing protrusions on each sheet metal bracket may be configured to flex an upper panel of the hollow sheet metal beam to provide the restoring force securing the tabs in the slots or other openings. 
     Each sheet metal bracket may be formed by bending a sheet metal blank along bend lines predefined in the sheet metal blank by bend-inducing features. 
     In another aspect, a solar panel rack comprises one or more sheet metal brackets and an underlying support structure to which the brackets are attached. Each sheet metal bracket comprises one or more upwardly pointing clinching tabs configured to be clinched to features on a solar panel or solar panel assembly to attach the solar panel or solar panel assembly to the solar panel rack in a desired location in a plane defined by the solar panel rack, one or more tabs configured to engage corresponding slots or other openings in the underlying support structure to attach the bracket to the underlying support structure, and one or more downwardly pointing protrusions configured to flex a portion of the underlying support structure to provide an elastic restoring force securing the tabs in the slots or other openings. 
     The underlying support structure may comprise, for example, two or more hollow sheet metal beams arranged side by side and in parallel with each other to define a plane, with each sheet metal bracket attached to a corresponding one of the hollow sheet metal beams. The beams may be supported in any suitable manner as described herein, for example. The one or more downwardly pointing protrusions on each sheet metal bracket may be configured to flex an upper panel of the hollow sheet metal beam to provide the restoring force securing the tabs in the slots or other openings. 
     Each sheet metal bracket may comprise one or more upwardly pointing positioning tabs configured to contact features on the solar panel or solar panel assembly to position the solar panel or solar panel assembly in the desired location. The positioning tabs of each sheet metal bracket may be located, for example, in a square or rectangular arrangement in a central portion of a top panel of the sheet metal bracket and extend upward from the top panel. Each sheet metal bracket may be configured to position and attach adjacent corners of, for example, four solar panels or solar panel assemblies to the solar panel rack. 
     If the underlying support structure comprises hollow sheet metal beams to which the sheet metal brackets are attached, each sheet metal bracket may have an inner cross-sectional shape substantially conforming to the outer cross-sectional shape of the hollow sheet metal beam to which it is attached. 
     Each sheet metal bracket may be formed by bending a sheet metal blank along bend lines predefined in the sheet metal blank by bend-inducing features. 
     Solar panel racks, their components, and related manufacturing and assembly methods disclosed herein may advantageously reduce material, manufacturing and installation costs for solar panel systems. This may result from a reduced amount of material used in the solar panel rack design, the use of cost-effective manufacturing methods, reduced shipping costs of solar panel rack components, which may be shipped to an installation site as substantially flat sheet metal blanks prior to bending to form the components, reduced storage space required for the components, and reduced labor requirements for installing the solar racks and/or an increased rate of installation. 
     These and other embodiments, features and advantages of the present invention will become more apparent to those skilled in the art when taken with reference to the following more detailed description of the invention in conjunction with the accompanying drawings that are first briefly described. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A-1C  show several views of a portion of an example solar panel rack with solar panels mounted on the rack ( FIGS. 1A, 1B ) and without solar panels mounted on the rack ( FIG. 1C ). 
         FIGS. 2A-2B  show a transverse support in an example solar panel rack ( FIG. 2A ) and an expanded view ( FIG. 2B ) of a notch in the transverse support configured to receive and attach to a beam bracket that is configured to attach a longitudinal beam to the transverse support. 
         FIGS. 3A-3C  show beam brackets attached to and positioned in notches in a transverse support ( FIG. 3A ), an expanded view of a beam bracket positioned in a notch with its upper flanges open to receive a longitudinal beam ( FIG. 3C ), and an expanded view of a bracket positioned in a notch with the bracket&#39;s upper flanges closed ( FIG. 3B ). 
         FIGS. 4A-4C  show longitudinal beams positioned in beam brackets attached to a transverse support, with the upper flanges of the beam brackets open ( FIG. 4A ) and closed ( FIG. 4B, 4C ) to secure the longitudinal beams to the transverse support. 
         FIGS. 5A-5D  show several views of a beam bracket configured to attach longitudinal beams to transverse support structures in the example solar panel rack. 
         FIG. 6A  shows a sheet metal blank that may be folded to form a hollow longitudinal beam for the example solar panel rack,  FIG. 6B  shows an expanded view of a portion of the blank of  6 A,  FIGS. 6C-6H  show several views of the longitudinal beam at different stages of folding,  FIG. 6I  shows an expanded view of a sheet metal blank as in  6 A comprising bend-inducing features formed with a lance, and  FIG. 6J  shows an expanded view of a sheet metal blank as in  6 A comprising bend-inducing features formed by laser-cutting. 
         FIGS. 7A-7G  show several views of a collapsible and expandable internal splice and its use in coupling two hollow beam sections together to form a longer hollow beam. 
         FIGS. 8A and 8B  show a longitudinal beam end cap ( FIG. 8B ) and three such end caps at the ends of longitudinal beams in a portion of a solar panel rack ( FIG. 8A ). 
         FIGS. 9A and 9B  show perspective and side views, respectively, of a panel bracket configured to attach the corners of four neighboring solar panels to a longitudinal beam in the example solar panel rack,  FIG. 9C  shows a panel bracket attached to a longitudinal beam, and  FIGS. 9D-9G  show successive stages of attaching four neighboring solar panels to the example solar panel rack using the panel brackets. 
         FIGS. 10A-10C  illustrate a clinching process by which two neighboring solar panels may be simultaneously secured to the example solar panel rack by the panel bracket of  FIGS. 9A-9G . 
         FIGS. 11A and 11B  show perspective and side views, respectively, of another variation of a panel bracket configured to attach the corners of four neighboring solar panels to a longitudinal beam in the example solar rack. 
         FIGS. 12A and 12B  show close up views of the panel bracket of  FIGS. 11A and 11B , illustrating two variations of a protrusion that may be formed on a panel bracket to facilitate electrical contact between the panel bracket and a solar panel. 
         FIGS. 13A and 13B  show two perspective views illustrating frame portions of solar panels in place on the panel bracket of  FIGS. 11A and 11B  with the panel bracket clinching tabs not clinched,  FIG. 13C  shows a corresponding side view of the solar panels in place on the panel bracket with the clinching tabs not clinched, and  FIG. 13D  shows the same side view as  FIG. 13C  but with the panel bracket clinching tabs clinched to secure the solar panel frame portions. 
         FIG. 14A  shows a top perspective view of solar panels in place on the panel bracket of  FIGS. 11A and 11B  with the panel bracket clinching tabs clinched to secure the solar panel frame portions,  FIG. 14B  shows a cross-sectional view identified in  FIG. 14A  and a close-up of that cross-sectional view, and  FIG. 14C  shows a related close-up view of another cross-section of the same assembly of solar panels on a panel bracket. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description should be read with reference to the drawings, in which identical reference numbers refer to like elements throughout the different figures. The drawings, which are not necessarily to scale, depict selective embodiments and are not intended to limit the scope of the invention. The detailed description illustrates by way of example, not by way of limitation, the principles of the invention. This description will clearly enable one skilled in the art to make and use the invention, and describes several embodiments, adaptations, variations, alternatives and uses of the invention, including what is presently believed to be the best mode of carrying out the invention. 
     As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly indicates otherwise. Also, the term “parallel” is intended to mean “parallel or substantially parallel” and to encompass minor deviations from parallel geometries rather than to require that any parallel arrangements described herein be exactly parallel. Similarly, the term “perpendicular” is intended to mean “perpendicular or substantially perpendicular” and to encompass minor deviations from perpendicular geometries rather than to require that any perpendicular arrangements described herein be exactly perpendicular. 
     This specification discloses solar panel mounting racks, their components, and related methods by which the solar panel racks may be manufactured, assembled, and used. As illustrated in the various figures, the disclosed solar panel racks may be used, for example, in a ground-mounted configuration to support photovoltaic panels in fixed positions to collect and convert solar radiation to electricity. Other configurations and applications for the disclosed solar racks will also be described below. 
     Various components of the disclosed solar panel racks including, for example, the hollow beams, beam brackets, internal expandable beam splices, and solar panel brackets further described below, may be advantageously used in other structures unrelated to solar panels or to the collection of solar energy. The discussion of these components in relation to their roles in the disclosed solar panel rack is not intended to limit the scope of their potential use. 
     Referring now to  FIGS. 1A-1C , an example solar panel rack  100  comprises a vertical support  105 , a transverse support  110  attached to an upper portion of the vertical support, and three hollow beams  115  supported by transverse support  110 . Hollow beams  115  are arranged in parallel orientations, with their upper surfaces defining a plane in which solar panels are to be supported. In the illustrated example, hollow beams  115  are secured in notches  117  ( FIG. 2A ) in transverse support  110  by beam brackets  120 . Panel brackets  125 , attached to hollow beams  115 , are configured to attach solar panels  130  to the upper surfaces of beams  115 . 
     Although the illustrated solar panel rack comprises three parallel hollow beams, more generally the solar panel rack comprises two or more parallel hollow beams arranged to define a plane in which solar panels are to be supported. Transverse support  110  and hollow beams  115  may be configured so that the plane in which the solar panels are supported is tilted with respect to vertical, rather than oriented horizontally. The tilt angle may be selected to allow the solar panels to better collect solar energy. (In this specification, “vertical” indicates the direction opposite to the force of the Earth&#39;s gravity). For example, and as illustrated, vertically oriented substantially identical notches  117  in the upper edge of transverse support  110  may be located to secure the beams  115  at progressively varying heights so that the beams can define a plane having a desired tilt angle. Further, beams  115  may have non-rectangular cross-sections ( FIG. 6D ) such that flat upper surfaces of the hollow beams are angled with respect to the vertical to define the desired tilted plane. The upper edge of transverse support  110  may be angled substantially parallel to the intended plane of the solar panels, as illustrated, to provide clearance for the solar panels. 
     The portion of the example solar panel rack illustrated in  FIGS. 1A-1C  may be repeated as a unit to form a linearly extending, modular, solar panel rack of desired length. In such linearly extending solar panel racks, corresponding hollow beams in adjacent repeating units may be arranged collinearly and spliced together with internal expandable splices  135  as further described below. Two or more such linearly extending solar panel racks may be arranged in parallel and side-by-side to support two or more corresponding spaced-apart rows of solar panels in an array of solar panels. 
     Individual solar panels to be supported by solar panel rack  100  may have, for example, a width of about 0.9 meters to about 1.3 meters and a length of about 1.5 meters to about 2.5 meters. More generally, such solar panels may have any suitable dimensions. The width of the solar panel rack may be selected, for example, to be approximately equal to an integer multiple of the solar panel width or length, or to a sum of integer multiples of the solar panel width and the solar panel length. As illustrated, for example, the solar panel rack may have a width approximately equal to twice the length of a solar panel. More generally, solar panel rack  100  may have any suitable width. Solar panels may be grouped into assemblies of solar panels prior to being installed on solar panel rack  100 . Such a solar panel assembly may be handled and installed similarly to as described herein for an individual solar panel. 
     Beams  115  may have lengths of, for example, about 3 meters to about 8 meters. The beam lengths may be selected, for example, to be approximately equal to an integer multiple of the solar panel width or length, or to a sum of integer multiples of the solar panel width and the solar panel length. Two or more beams  115  may be spliced together as noted above to form part of a solar panel rack having an overall length of, for example, about 24 meters to about 96 meters supported by multiple transverse supports  110  and corresponding vertical supports  105 . Though  FIGS. 1A-1C  show a single transverse support used to support one beam-length of solar panel, in other variations two or more transverse supports  110 , with corresponding vertical supports  105 , may be spaced along a beam-length of the solar panel. For example, in linearly extending solar panel racks comprising beams collinearly spliced together to lengthen the rack, there may be one, two, or more than two transverse supports spaced along the solar panel rack between beam splices or between the end of the solar panel rack and a beam splice. 
     Although the example solar panel rack of  FIGS. 1A-1C  is shown comprising a vertical support, a transverse support, hollow beams, brackets for attaching the hollow beams to the transverse support, and brackets for attaching the solar panels to the hollow beams, variations of the solar panel rack may lack any one of these components, or lack any combination of these components, and may comprise additional components not shown. 
     Transverse supports, hollow beams, and brackets used in the solar panel racks disclosed in this specification may advantageously be formed by bending sheet metal blanks into the desired shape. Flat sheet metal blanks from which these components are formed may be patterned, for example, with slits, grooves, score lines, obround holes, or similar bend-inducing features that define predetermined bend lines along which the sheet metal blanks may be bent to form the desired structures. 
     Such bend-inducing features may include, for example, slits, grooves, displacements, and related bend-inducing features as disclosed in U.S. Pat. No. 6,877,349, U.S. Pat. No. 7,152,449, U.S. Pat. No. 7,152,450, U.S. Pat. No. 7,350,390, and US Patent Application Publication No. 2010/0122,563, all of which references are incorporated herein by reference in their entirety. A “displacement” as disclosed in these references is a bend-inducing feature comprising a tongue of material defined in a sheet metal blank by a cut or sheared edge located on or adjacent the bend line, with the tongue displaced at least partially out of the plane of the sheet metal blank before the sheet metal blank is bent along that bend line. The use of bend-inducing features, particularly those disclosed in these references, may increase the precision with which the sheet metal blanks may be bent into the desired components and reduce the force necessary to bend the blanks. The bend-inducing features disclosed in the cited references may exhibit edge-to-face engagement, as described in the references, upon bending. Such edge-to-face engagement may contribute to the precision with which bending may be accomplished and to the stiffness and strength of the resulting component. 
     Example flat sheet metal blanks from which hollow beams  115  may be formed in some variations are illustrated in  FIGS. 6A-6J  and described below. For other components of solar panel rack  100  for which no corresponding flat sheet metal blank with bend-inducing features is illustrated, the predetermined bend lines defined by bend inducing features in such sheet metal blanks should be understood to be located at positions corresponding to the bends evident in the finished structures shown in the drawings. 
     In some variations, transverse supports, hollow beams, and/or brackets used in the solar panel may be formed from sheet metal blanks without the use of bend-inducing features to predefine the bend lines. In such variations, the sheet metal blanks may be bent into the desired shape using, for example, conventional press-brake, stamping press, or roll-forming technology. 
     Sheet metal blanks for the components of solar panel rack  100 , including bend-inducing features if used, may be formed using laser cutting, computer numerical controlled (CNC) metal punching, and/or metal stamping, for example. Such techniques allow for low cost manufacturing of the components. 
     The use of sheet metal components in solar panel rack  100  allows such components to be attached to each other using sheet metal screws or other sheet metal fasteners, rather than with double sided bolt/washer/nut fastener assemblies which can be difficult and slow to install. The single sided installation process of driving a sheet metal screw using, for example, a magnetic electric drive attachment may be advantageous for both the reduced cost of the fasteners and the increased ease and speed of installation. The use of sheet metal components as described herein may also reduce the overall amount and weight of material used in the solar panel racks while maintaining desired stiffness and strength. Nevertheless, as suitable, one or more components not formed from bent sheet metal, such as cast, extruded, or machined components, for example, may be substituted for the sheet metal components otherwise described in this specification. 
     The individual components of the example solar panel rack  100  of  FIGS. 1A-1C  are next described in further detail with respect to additional drawings. 
     Referring again to  FIGS. 1A-1C , vertical support  105  may be, for example, any conventional pile or post suitable for supporting solar panel rack  100  and may be formed from any suitable material. Vertical support  105  may have a Σ (sigma) cross section, for example. Although  FIGS. 1A-1C  show only one vertical support  105  attached to transverse support  110 , other variations of the solar panel rack may use two or more such vertical supports spaced apart and attached to transverse support  110 . For ground-mounted configurations, vertical support  105  may be, for example, driven into the ground, ballasted with respect to the ground, screwed into the ground, or affixed to or upon the ground by any other suitable means. 
     As illustrated in the various figures, transverse support  110  has a saddle shape selected to reduce the amount of material necessary to provide sufficient strength and stiffness to support beams  115  and solar panels  130 . As noted above, notches  117  in the upper edge of transverse support  110  are configured to receive brackets  120  and beams  115 . Any other suitable shape or configuration for transverse support  110  may also be used. 
     Transverse support  110  may be attached to vertical support  105  using bolt/washer/nut assemblies or any other suitable fasteners or method. Attachment may be accomplished, for example, with suitable fasteners passing through vertical slots in vertical support  105  and through horizontal slots in transverse support  110 . Alternatively, attachment may be accomplished, for example, with suitable fasteners passing through horizontal slots in vertical support  105  and through vertical slots in transverse support  110 . Such arrangements of vertical and horizontal slots provide an adjustment that may be used to compensate for imprecision in the placement of vertical support  105  with respect to other vertical supports in the solar panel rack. 
     Referring now to  FIGS. 2A and 2B , in the illustrated example transverse support  110  is formed from a flat sheet metal blank that is bent along predefined bend lines to form panel section  110   a , upper flange  110   b , and lower flanges  110   c . Upper flange  110   b  and lower flanges  110   c  are bent perpendicular to panel  110   a  to impart stiffness to panel  110   a . The sheet metal blank for transverse support  110  is also bent along predefined bend lines to form flanges  110   d , which are oriented perpendicular to panel  110   a  to form side walls to notches  117 . Panel  110   a  includes one or more tabs  140  projecting into each notch  117 . Variations including two or more tabs per notch, for example, may have one or more tabs projecting into the notch from either side of the notch. In variations having only one projecting tab per notch, the tabs on the outer notches may preferably be located on the sides of the notches interior to the solar panel rack, away from the edges of the solar panel rack. Tabs  140  may be defined in the sheet metal blank by sheared or cut edges, and remain in the plane of panel  110   a , or at least substantially parallel to the plane of panel  110   a , when flanges  110   d  are bent perpendicular to panel  110   a . As described below, tabs  140  may be inserted into slots or other openings in brackets  120  to temporarily secure brackets  120  in notches  117  without the use of fasteners. Although two tabs  140  are used for each notch  117  in the illustrated example, any other suitable number of tabs  140  may be used per notch. Alternatively, flanges  110   d  may comprise one or more preformed slots or other openings into which one or more tabs on brackets  120  may be inserted to temporarily secure brackets  120  in notches  117 . In the illustrated example, the dimensions and cross-sectional shape of notches  117  in transverse support  110  are selected to conform to the shape of brackets  120  and to provide a friction fit for brackets  120 . 
     The predefined bend lines in the sheet metal blank for transverse support  110  may comprise any suitable bend-inducing features as described herein, known in the art, or later developed. The sheet metal blank for transverse support  110  may be formed, for example, from galvanized steel sheet having a thickness, for example, of about 1.9 millimeters. Any other suitable material and thickness may also be used. 
     Referring now to  FIGS. 3A-3C, 4A-4C, 5A, and 5B , in the illustrated example bracket  120  is formed from a flat sheet metal blank that is bent along predefined bend lines to form bottom panel  120   a , side panels  120   b , and upper flanges  120   c . Side panels  120   b  are bent with respect to bottom panel  120   a  to form a bracket shape conforming to the shape of notch  117  (Figure B) and to the cross-sectional shape of beams  115  ( FIG. 6D ). Upper flanges  120   c  may be bent to close ( FIG. 3B ) and to open ( FIG. 3C ) the upper end of bracket  120 . Side panels  120   b  comprise slots  120   d  configured and positioned to engage with corresponding tabs  140  on flanges  110   d  of transverse support  110  when brackets  120  are properly positioned in notches  117  in transverse support  110 . 
     The predefined bend lines in the sheet metal blank for bracket  120  may comprise any suitable bend-inducing features as described herein, known in the art, or later developed. The sheet metal blank for bracket  120  may be formed, for example, from galvanized steel sheet having a thickness, for example, of about 1.9 millimeters. Any other suitable material and thickness may also be used. 
     Once bent into shape, brackets  120  are inserted into notches  117  and temporarily secured in place by engaging tabs  140  on transverse support  110  with slots  120   d  on brackets  120 . Beams  115  are positioned in place in brackets  120  ( FIG. 4A ), and then upper flanges  120   c  of brackets  120  are bent into their closed positions ( FIGS. 4B, 4C ) to capture beams  115  within brackets  120 . Sheet metal fasteners may then be driven through preformed holes  110   e  in flanges  110   d  of transverse support  110  and through correspondingly aligned preformed holes  120   e  in bracket  120  into beams  115  to secure the brackets  120  and the beams  115  to transverse support  110 . Additional sheet metal fasteners may be driven through preformed holes  120   f  in upper flanges  120   c  of brackets  120  into beams  115  to further secure beams  115  to brackets  120 . The sheet metal fasteners attaching transverse support  110  and brackets  120  to beams  115  may preferably be self-drilling fasteners that drill into and engage beams  115 . The use of such self-drilling fasteners allows the position of transverse supports  110  and vertical supports  105  along beams  115  to be selected at the installation site to adapt to local circumstances, such as to rocks or other objects that might interfere with or constrain the positioning of vertical supports  105 . Alternatively, the sheet metal fasteners attaching transverse support  110  and brackets  120  to beams  115  may engage preformed holes in beams  115 . (Preformed holes referred to here and elsewhere in the specification are formed in corresponding sheet metal blanks prior to bending of the sheet metal blanks to form the desired components). 
     The ability to temporarily position brackets  120  in transverse support  110  without the use of fasteners, by means of the tab and slot arrangement just described, allows beams  115  to be positioned in the solar panel rack prior to final attachment of the brackets using sheet metal screws. A benefit of this arrangement is that installers need not handle multiple components at one time, nor are fasteners handled at that same time as well. De-coupling complex installation steps may facilitate faster installation as well as lower the labor costs and skill required. 
     The inventors have recognized that hollow sheet metal beams such as beams  115  may buckle under load if they are supported by hard narrow edges that concentrate the reaction force from the supporting structure onto a narrow region of the hollow beam. Brackets  120  increase the load capacity of beams  115  by distributing the force from the load on beams  115  along the length of the brackets. This helps to prevent buckling that might otherwise occur if the force from the load on beams  115  were concentrated at the hard upper edge of transverse support  110 . Further, each bracket  120  may be shaped so that its stiffness progressively and gradually decreases with distance in both directions away from transverse support  110  along its beam  115 . (The stiffest portion of a bracket  120  is the central region of the bracket that is in contact with and supported by transverse support  110 ). Because of this progressive decrease in stiffness, the ends of brackets  120  away from transverse support  110  displace significantly downward under load and consequently do not themselves present hard edges that promote buckling of beams  115 . 
     Referring now to  FIGS. 5A-5D , in the illustrated example brackets  120  have stiffness that progressively decreases with distance from transverse support  110  because bottom panels  120   a , side panels  120   b , and upper flanges  120   c  all have widths that progressively decrease from a wide central portion to narrower portions at the panel&#39;s outer edges, farthest from transverse support  110 . That is, material has been removed from central regions of the panels away from the transverse support  110 , with the regions from which material has been removed having widths that increase with distance from transverse support  110 . This configuration enhances load capacity in all four primary load directions—vertically upward, downward, and in both lateral directions. Any other suitable shape or configuration of brackets  120  may also be used to provide the progressive decrease in stiffness just described. For example, the progressive decrease in stiffness of the bracket may alternatively be provided by progressive changes in width of only some of its panels, although such a configuration may not enhance load capacity in directions perpendicular to the panels that do not exhibit progressively reduced stiffness. Further, although the illustrated brackets  120  are symmetric about transverse support  110  and about hollow beams  115 , neither of these symmetries is required. 
     The use of brackets  120  exhibiting progressive decreases in stiffness as described in this specification may advantageously increase the capacity of a solar panel rack to handle high loads caused by wind or snow, for example. Brackets  120  are not required to exhibit such progressive decreases in stiffness, however. For example, the bottom panels, side panels, and upper flanges of bracket  120  may be formed as complete panels without material removed from central regions as described above, and thus fully wrap the bottom and side panels of a beam  115  for the length of the bracket  120 . In such variations, the bracket  120  may have a length of, for example, about 1/10 of the beam length to about ⅓ of the beam length. Brackets of sufficient length, for example greater than or equal to about ⅓ of the beam length, may advantageously spread the load on the beam along the beam to significantly reduce a stress spike that may otherwise occur in the beam. Also in such variations, the bracket  120  may have a length of, for example, about 2 times the beam height (or about 2 times the largest cross-sectional dimension perpendicular to the beam length) to about 7 times the beam height (or about 7 times the largest cross-sectional dimension perpendicular to the beam length). Brackets of sufficient length, for example greater than or equal to about 5 times the beam height (or about 5 times the largest cross-sectional dimension perpendicular to the beam length), may advantageously spread the load on the beam along the beam to significantly reduce a stress spike that may otherwise occur in the beam. In such variations (in which the bottom panels, side panels, and upper flanges of bracket  120  may be formed as complete panels without material removed from central regions), bracket  120  may be formed, for example, from galvanized steel sheet having a thickness of, for example, about 1.5 millimeters. Any other suitable material and thickness may also be used. 
     Referring now to  FIGS. 6A-6J , in the illustrated example each beam  115  is formed from a flat sheet metal blank  145  ( FIGS. 6A-6C, 6I, 6J ) that is bent along predefined bend lines to form a beam  115  having a quadrilateral cross-section comprising bottom panel  150   a , side panel  150   b , top panel  150   c , side panel  150   d , and closure flanges  150   e  and  150   f  ( FIGS. 6D-6H ). Upon bending of sheet metal blank  145  into the desired cross-sectional shape, flange  150   e  and bottom panel  150   a  overlap, and flange  150   f  and side panel  150   d  overlap. Flanges  150   e  and  150   f  may then be fastened to the panels with which they overlap using sheet metal fasteners passing through preformed holes, for example, or by any other suitable method, to secure beam  115  in its closed configuration. 
     In the illustrated example, beam  115  is secured in its closed configuration using tabs and slots preformed in sheet metal blank  145 . As illustrated, flange  150   f  comprises a repeating pattern of tabs  155  and flange  150   e  comprises a corresponding repeating pattern of slots  160  formed along the bend line between flange  150   e  and side panel  150   d . When sheet metal blank  145  is bent to form the desired cross-sectional shape, tabs  155  remain in the plane of bottom panel  150   a , or at least substantially parallel to the plane of bottom panel  150   a , and thus protrude from flange  150   f . These protruding tabs  155  may be inserted through corresponding slots  160  ( FIGS. 6E, 6G ) and then bent to lie flat alongside panel  150   d  ( FIGS. 6F, 6H ) to secure bottom panel  150   a  to side panel  150   d.    
     Preformed tabs  155  may be formed as tongues of material defined by a cut or sheared edge, with the tongues displaced at least partially out of, but still substantially parallel to, the plane of sheet metal blank  145  prior to bending ( FIGS. 6B, 6C, 6I ). This may be accomplished using sheet metal lancing methods, for example. Alternatively, preformed tabs  155  may be formed as tongues of material defined by a laser-cut edge, with the tongues remaining within the plane of sheet metal blank  145  prior to bending of the blank ( FIG. 6J ). 
     The use of integrated tabs  155  and slots  160  as just described allows sheet metal blank  145  to be bent into shape and joined to itself to form a beam  115  without the use of welding, fasteners, or other means of joinery. Such other means of joinery may be used in addition to such tabs and slots if desired, however. 
     As noted above, beams  115  as illustrated have quadrilateral cross-sectional shapes. Such quadrilateral cross-sectional shapes may allow beams  115  to provide optimal load capacity in all four primary load directions—vertically upward, downward, and in both lateral directions. (Lateral loads may be caused by wind, for example). Other cross-sectional beam shapes may also be used, however, if suitable. 
     Sheet metal blank  145  may comprise preformed holes or slots into which tabs on panel brackets  125  are to be inserted, as further described below. Alternatively, sheet metal blank  145  may comprise predefined features that, upon folding of the blank, form tabs on beam  115  that may be inserted into preformed holes or slots on panel brackets  125 . Such tab and slot arrangements predefine the locations of panel brackets  125 , and thus of solar panels  130 , with respect to the beams in solar panel rack  100 . This promotes installation speed and prevents errors that might otherwise occur in positioning panel brackets  125  and solar panels  130  on solar panel rack  100 . 
     The predefined bend lines in sheet metal blank  145  may comprise any suitable bend-inducing features as described herein, known in the art, or later developed. Sheet metal blank  145  may be formed, for example, from galvanized steel sheet having a thickness, for example, of about 0.9 millimeters or about 1.2 millimeters. Any other suitable material and thickness may also be used. 
     The inventors have determined that the resistance of beams  115  to buckling under stress may be promoted by particular configurations of bend-inducing features used to define the bend lines in sheet metal blank  145 . The inventors have recognized that a beam&#39;s resistance to buckling increases as the length of the individual bend-inducing features defining the bend lines is shortened. As further explained below, the inventors have also recognized that there is typically a practical lower limit to the length of a bend-inducing feature, with that lower limit related to the composition and the thickness of the sheet of material. These opposing trends result in optimal ranges for the lengths of bend-inducing features used to define bend lines in sheet metal blanks to be formed into hollow beams such as beams  115 . 
     Referring now to  FIG. 6I , bend lines in sheet metal blank  145  may be defined by rows of spaced-apart displacements  165 , each of which has a length along the bend line identified as “A” in the drawing. Each displacement  165  comprises a cut or sheared edge  165   a  of a tongue of material  165   b . Severed edge  165   a  is at least partially curved, and typically has ends that diverge away from the bend line. Tongue  165   b  is displaced at least partially out of the plane of sheet metal blank  145  at the time displacement  165  is formed, prior to bending of the blank, but remains attached to and substantially parallel to the blank. Lateral ends of the severed edge  165   a , and thus of tongue  165   b , have a radius of curvature R (not shown). 
     If the radius of curvature R of the ends of the displacements is too small, the sheet metal blank may crack at the ends of the displacements upon folding of the blank. The inventors have determined that the radius of curvature R of the ends of the displacement  165  in sheet metal blank  145  should be selected to be R min , or larger than but approximately R min , where R min  is the minimum radius of curvature that may be used without initiating cracking at the ends of the displacements upon folding the sheet metal blank to form the beam. The practical lower limit to the length of a displacement  165  is approximately 2R min . Typically, larger sheet thicknesses require a larger radius of curvature R to prevent cracking. More brittle materials also require a larger radius of curvature. The inventors have also found that resistance to beam buckling decreases with increasing displacement length “A”, and that resistance to beam buckling has typically decreased significantly for displacements having a length “A” greater than approximately 6R min . Thus inventors have determined that bend inducing displacements to be used in forming a hollow sheet metal beam  115  preferably have a length “A” that satisfies the relationship A≦˜6R min , or more preferably satisfies the relationship ˜2R min ≦A≦˜6R min . 
     Referring now to  FIG. 6J , bend lines in sheet metal blank  145  may alternatively be defined by rows of spaced-apart “smile shaped” slits  170 , with adjacent slits on alternating sides of the bend line. Slits  170 , which penetrate through sheet metal blank  145 , define tongues  170   a  that remain in the plane of sheet metal blank  145  prior to bending. As illustrated, lateral ends of the slits  170  diverge away from the bend line. Each of slits  170  has a length along the bend line identified as “A” in the drawing. The inventors have determined that such bend-inducing smile-shaped slits to be used in forming a hollow sheet metal beam  115  preferably have a length “A” that falls within the same range as that for the use of displacements as discussed above. That is, the length A of the smile shaped slits should satisfies the relationship A≦˜6R min , or more preferably satisfies the relationship ˜2R min ≦A≦˜6R min , where R min  is the minimum radius of curvature that may be used for displacements (as discussed above) without initiating cracking at the ends of the displacements upon folding the sheet metal blank to form the beam. 
     Beams  115  may be formed, for example, from galvanized steel sheets having a thickness of about 0.9 millimeters or about 1.2 millimeters and bend lines defined by displacements or smile-shaped slits, as described above, having lengths of about 9 millimeters or less. 
     As noted above, two beams  115  may be arranged collinearly in a solar panel rack  100  and spliced together using internal splices  135 . Referring now to  FIGS. 7A-7G , in the illustrated example a splice  135  may be formed from a sheet metal blank that is bent along predefined bend lines to form a short hollow beam section having a quadrilateral cross-section comprising bottom panel  175   a , side panel  175   b , top panel  175   c , side panel  175   d , and closure flange  175   e . Panels  175   a ,  175   b ,  175   c , and  175   d  correspond in position, shape, and orientation to panels in beam  115 . Closure flange  175   e  may be bent into contact with and optionally fastened to side wall  175   b . Outer cross-sectional dimensions of splice  135  approximately match the internal cross-sectional dimensions of beams  115 , to allow a tight fit between the splice and a beam as further described below. Splices  135  may have a length, for example, of about 0.25 meters to about 1.0 meters. 
     Splice  135 , and the sheet metal blank from which it is formed, also comprise two or more additional predefined bend lines which may be bent with low force to partially collapse splice  135 . In the illustrated example, splice  135  comprises predefined low-force bend lines  180  and  185  running parallel to the long axis of the splice in side panels  175   b  and  175   d , respectively, which are positioned on opposite sides of splice  135 . These low force bend lines allow splice  135  to be partially collapsed ( FIG. 7C ), and then inserted into an end of a hollow beam  115  ( FIGS. 7D and 7E ). Typically, splice  135  is inserted into beam  115  to a depth of about one half the length of splice  135 , as shown in  FIG. 7A , for example. A second hollow beam  115  may then be slid over the remaining exposed half length of splice  135 . 
     Splice  135 , in its collapsed configuration, may thus be positioned entirely within two adjacent and collinear hollow beams  115 . Sheet metal fasteners may then be inserted through preformed clearance holes  190  ( FIG. 7E ) in each of the two hollow beams  115  to engage preformed holes in side panels  175   b  and  175   d  of splice  135  to pull splice  135  into its expanded configuration ( FIGS. 7F, 7G ). The two hollow beams  115  are thereby coupled to each other through their attachment to splice  135 . (Note that in order to show a perspective view of an expanded splice  135  in position inside a hollow beam  115 ,  FIG. 7G  shows only one of the two hollow beams  115  typically coupled to such a splice). 
     Further, because the outer cross-sectional dimensions of splice  135  approximately match the internal cross-sectional dimensions of beams  115 , when splice  135  is expanded within beams  115  the splice&#39;s top, bottom, and side panels fit tightly against the corresponding panels of the beams  115 . This provides strength and stiffness that allows splice  135  and its attached beams  115  to handle multidirectional loads. In addition, splice  135  does not interfere with the positions of other components of solar rack  100  that are attached to beams  115 , such as panel brackets  125  for example, because splice  135  in its final configuration is located within beams  115 . 
     Hollow beams  115  may optionally comprise preformed holes  195  ( FIG. 7E ) through which a screwdriver or other object may be temporarily inserted as a stop to control the depth to which a splice  135  is inserted into a hollow beam  115 . 
     The predefined bend lines in the sheet metal blank for splice  135  may comprise any suitable bend-inducing features as described herein, known in the art, or later developed. The sheet metal blank for splice  135  may be formed, for example, from galvanized steel sheet having a thickness, for example, of about 0.9 millimeters to about 1.2 millimeters. Any other suitable material and thickness may also be used. 
     Referring now to  FIGS. 8A and 8B , solar panel rack  100  may also comprise end caps  200  inserted into and closing the ends of hollow beams  115  at the ends of solar panel rack  100 . An end cap  200  may be formed from a sheet metal blank bent along predefined bend lines to form end panel  205   a  and side flanges  205   b . End panel  205   a  may be inserted into the end of a hollow beam  115 , with tabs  205   c  on end panel  205   a  engaging corresponding preformed slots in the hollow beam  115  to retain the end cap in the hollow beam. Alternatively, hollow beam  115  may comprise tabs that are inserted into preformed slots in side flanges  205   b  to retain the end cap in the hollow beam. In either case, side flanges  205   b  may extend outward from and collinearly with hollow beam  115  to support an overhanging portion of a panel bracket  125  positioned at the end of hollow beam  115  ( FIG. 8A ). 
     The predefined bend lines in the sheet metal blank for end cap  200  may comprise any suitable bend-inducing features as described herein, known in the art, or later developed. The sheet metal blank for end cap  200  may be formed, for example, from galvanized steel sheet having a thickness, for example, of about 0.5 millimeters to about 1.2 millimeters. Any other suitable material and thickness may also be used. 
     Referring now to  FIGS. 9A-9G , in the illustrated example a panel bracket  125  is formed from a sheet metal blank that is bent along predefined bend lines to form a top panel  210   a , side panels  210   b  bent downward from top panel  210   a  so that top panel  210   a  and side panels  210   b  together conform to the cross-sectional shape of a hollow beam  115 , four positioning tabs  210   c  located in a square or rectangular arrangement in a central portion of top panel  210   a  and extending upward from panel  210   a , four solar panel clinching tabs  210   d  extending upward from panel  210   a  and each positioned adjacent to a positioning tab  210   c , and flanges  210   e  bent perpendicularly outward from side panels  210   b  to stiffen side panels  210   b.    
     Side panels  210   b  of panel brackets  125  comprise tabs  210   f  that may be inserted into preformed slots in a hollow beam  115  to position the panel brackets at desired locations on the hollow beam ( FIGS. 9B, 9C ). As further described below, panel brackets  125  are configured to properly position and attach the corners of up to four solar panels  130  to a hollow beam  115 . This arrangement allows the preformed slots in hollow beams  115  to predefine the positions of solar panels  130  on solar panel rack  100 . 
     To position and attach solar panels  130  to solar panel rack  100 , panel brackets  125  are first positioned on hollow beams  115  using the tab and slot arrangement described above. Panel brackets  125  may then be further secured to the beams with sheet metal fasteners driven through preformed holes  215  in side panels  210   b  into preformed holes in hollow beams  115 . Solar panels  130  are then guided into position by contact between outer edges of solar panels  130  and positioning tabs  210   c , as well as by contact between solar panels  130  and clinching tabs  210   d  ( FIGS. 9D-9G ). 
     Clinching tabs  210   d  are configured to be clinched around industry-standard features  220  on solar panels  130  to attach the solar panels to panel brackets  125  and thus to hollow beams  115  ( FIGS. 10A, 10C ). In the illustrated example, a pair of clinching tabs  210   d  located on the same side of a hollow beam  115  may be simultaneously clinched around features  220  on adjacent solar panels  130  using a conventional clinching tool shown in  FIG. 10B  in its open  225 A and clinched  225 B configurations. This simultaneous clinching method increases the speed of installation. Optionally, solar panels  130  may be further secured to panel brackets  125  with fasteners passing through preformed holes in panel bracket  125 . Features  220  may be flanges on an outer frame of solar panel  130 , for example. 
       FIGS. 11A-14C  show another variation of panel bracket  125 . This variation of the panel bracket is also configured to properly position and attach the corners of up to four solar panels  130  to a hollow beam  115 , with slots in hollow beams  115  predefining the positions of solar panels  130  on solar panel rack  100 . Referring now to  FIGS. 11A and 11B , the illustrated panel bracket  125  is formed from a sheet that is bent along predefined bend lines to form a top panel  230   a , end panels  230   b  bent downward from top panel  230   a , side panels  230   c  also bent downward from top panel  230   a , top beam attachment panels  230   d  bent outward from side panels  230   c  into an orientation parallel to top panel  230   a , and side beam attachment panels  230   e  bent downward from top beam panels  230   d  so that a top beam panel  230   d  and its side beam panels  230   e  together conform to the cross-sectional shape of a hollow beam  115 . End panels  230   b  may be bent into position prior to side panels  230   c , provide a hard stop defining the final orientation of side panels  230   c , and brace side panels  230   c  in their final position. Side beam attachment panels  230   e  comprises (e.g., hook-like) tabs  230   h  that may be inserted into preformed slots in a hollow beam  115  to position the panel brackets at desired locations on the hollow beam. 
     The sheet from which panel bracket  125  is formed is also bent along predefined bend lines to form six positioning tabs  230   f  located in a square or rectangular arrangement in a central portion of top panel  230   a  and extending upward from panel  230   a , and four solar panel clinching tabs  230   g  also extending upward from panel  230   a . As further explained below, these positioning and clinching tabs function similarly to positioning tabs  210   c  and clinching tabs  210   d  of the panel bracket of  FIGS. 9A-9G . 
     In addition to the features just described, panel brackets  125  of  FIGS. 11A-14C  include upward pointing protrusions  235 , which are configured to facilitate electrical contact between the panel bracket and a metal frame or other conducting feature of a solar panel attached to the solar panel rack by the panel bracket. The electrical contact facilitated by protrusions  235  may form part of an electrical path from the solar panel, through the solar panel rack, to electrical ground. Such a ground path may run, for example, from a metal frame of the solar panel through panel bracket  125  to a beam  115 , and then from the beam  115  through a beam bracket  120  to saddle  110 , and then from saddle  110  through vertical support  105  to ground. 
     The metal frame or other conducting component of the solar panels intended to form part of such a ground path may have an insulating or partially insulating coating that reduces its conductivity. For example, anodized aluminum solar panel frames and galvanized steel solar panel frames will likely have such insulating or partially insulating coatings. Protrusions  235  may be configured to pierce such a coating to increase the conductivity of the contact between the panel bracket  125  and the solar panel. This may be accomplished, for example, with a protrusion geometry that provides strength under compression in combination with one or more sharp edges positioned to pierce the insulating coating when clinching tabs  230   g  are clinched around the solar panel frame and squeeze the panel frame between protrusions  235  and clinching tabs  230   g.    
     Any suitable geometry for protrusions  235  may be used. Referring to  FIGS. 11A and 12A , protrusions  235  may have, for example, the shape of a conical volcano with a sharp and substantially continuous rim  235   a . In an alternative example shown in  FIG. 12B , protrusions  235  have the shape of a conical volcano with a ruptured rim exhibiting sharp points  235   b.    
     Protrusions  235  may be formed integrally with panel bracket  125 . For example, the protrusions illustrated in  FIGS. 12A and 12B  may be formed in the panel bracket sheet metal blank with a punch and a die. Alternatively, protrusions  235  may be formed separately from panel bracket  125  and then attached to panel bracket  125  by any suitable method. 
     Referring now to  FIGS. 13A-13C , to attach one or more solar panels  130  to a solar panel rack  100  using panel brackets  125  of  FIGS. 11A and 11B , the panel brackets  125  are first positioned on hollow beams  115  using the tab and slot arrangement described above. Panel brackets  125  may then be further secured to the beams with sheet metal fasteners driven through preformed holes  237  in side beam attachment panels  230   e . One, two, three, or four solar panels  130  are then guided into position by contact between outer edges of solar panels  130  (e.g., solar panel frames) and positioning tabs  230   f , as well as by contact between solar panels  130  and clinching tabs  230   g.    
     Referring now to  FIGS. 13D-14C , clinching tabs  230   g  are configured to be clinched around industry-standard features (e.g., frames) on solar panels  130  to attach the solar panels to panel brackets  125  and thus to hollow beams  115 . In the illustrated example, a pair of clinching tabs  230   g  located on the same side of a hollow beam  115  may be simultaneously clinched around features on adjacent solar panels  130  using a conventional clinching tool (e.g., as shown in  FIG. 10B  in its open  225 A and clinched  225 B configurations). Optionally, solar panels  130  may be further secured to panel brackets  125  with fasteners passing through preformed holes in panel bracket  125 . 
     The close-up cross-sectional view in  FIG. 14B , taken along line A-A of  FIG. 14A , shows a flange on the frame of a solar panel  130  sandwiched between a protrusion  235  and a clinching tab  230   g , thus facilitating electrical contact between the panel bracket  125  and the solar panel  130  through protrusion  235  as described above.  FIG. 14C  shows a related cross-sectional view, taken parallel to line A-A of  FIG. 14A  but further along the panel bracket and away from protrusions  235 . As the latter figure shows, away from protrusions  235  the flange of the solar panel frame is bent downward past protrusions  235  to make direct contact with panel bracket top panel  230   a  and be sandwiched between top panel  230   a  and clinching tab  230   g . Bent in this manner, the flange on the solar panel frame typically exhibits a restoring force toward its original flat configuration that tends to pull the flange tightly against protrusion  235 , further enhancing electrical contact between the solar panel and the panel bracket. 
     Referring again to  FIGS. 11A and 11B , in these examples the beam attachment top panels  230   d  include downward pointing protrusions  240 . These protrusions are configured to elastically flex a top panel of the hollow beam to which the panel bracket is attached, so that the beam exerts a restoring force tending to pull tabs  230   h  on beam attachment side panels  230   e  toward the top of the beam, thereby tightly securing the tabs in position in the slots that they engage in the beam. In the illustrated examples, protrusions  240  are downward pointing dimples integrally formed in the sheet metal blank for panel bracket  125 . Any other suitable geometry for protrusions  240  may be used. Rather than integral with panel bracket  125 , protrusions  240  may be separately formed and then attached to beam attachment top panels  230   d.    
     In variations including protrusions  240 , a tight fit between beam attachment panels  230   d  and  230   e  and the beam and/or contact between tabs  230   h  and the beam may provide acceptable electrical contact between the panel bracket and the beam for a desired ground path. Alternatively, or in addition, suitable electrical contact may be provided by fasteners engaging the beam through preformed holes  237  in panels  230   e , or in any other suitable manner. 
     Protrusions  235  and protrusions  240  may be advantageous but are not required. Further, protrusions  235  may be used without protrusions  240 , and protrusions  240  may be used without protrusions  235 . Either or both protrusions  235  and protrusions  240  may be used in variations of the panel brackets illustrated in  FIGS. 9A-9G , on panel  210   a  for example. 
     In addition to positioning solar panels  130  and attaching them to beams  115 , panel brackets  125  as described herein also better distribute the load from solar panels  130  along beams  115  than would be the case if the solar panels were attached directly to beams  115 . The ability of a single panel bracket  125  to position and attach corners of up to four solar panels to solar panel rack  100  may reduce part counts and labor, and thus cost. 
     Although panel brackets  125  are shown has having particular numbers of positioning and clinching tabs, any suitable number of such tabs may be used. 
     The predefined bend lines in the sheet metal blank for panel bracket  125  may comprise any suitable bend-inducing features as described herein, known in the art, or later developed. The sheet metal blank for panel bracket  125  may be formed, for example, from galvanized steel sheet having a thickness, for example, of about 1.5 millimeters. Any other suitable material and thickness may also be used. Bend lines between top panel  210   a  and side panels  210   b  may preferably be predefined, for example, by bend-inducing features disclosed in US Patent Application Publication No. 2010/0122563. 
     Although the illustrated examples of solar panel rack  100  are described above as configured for ground mounting, solar panel rack  100  may alternatively be mounted on roof-tops. Variations of solar panel rack  100  to be roof-top mounted may use vertical supports  105  as described above, or substitute any suitable vertical support. Any suitable method of attaching solar panel rack  100  to a roof-top may be used. 
     As illustrated, transverse support  110  in solar panel rack  100  is statically mounted to vertical supports  105  so that solar panel rack  100  maintains a fixed orientation. In other variations, transverse support  110  may be pivotably mounted to vertical supports  105 , by any suitable pivot mechanism, to rotate around an axis extending parallel to the long axes of hollow beams  115 . This arrangement allows transverse support  110  and beams  115  to be rotated so that solar panels  130  track motion of the sun across the sky during, for example, the course of a day or the course of a year. Any suitable rotation drive may be used to rotate the upper portion of such a solar panel rack  100  in this manner. 
     Although solar panel rack  100  is described above as supporting photovoltaic solar panels, in other variations the solar panel racks described herein may be used to support solar water heating panels rather than, or in addition to, photovoltaic solar panels. Any suitable modification may be made to the solar panel racks described herein to accommodate mounting such solar water heating panels. 
     Further, although the rack structures disclosed herein have been described as supporting solar panels, they may instead be used to support reflectors such as mirrors, for example, used to direct solar radiation to a solar energy receiver, for example. Such rack structures supporting reflectors may be statically mounted, or pivotably mounted as described above so that the reflectors may be rotated about an axis to track motion of the sun. 
     The hollow beams, beam brackets, and hollow beam splices described above are not restricted to use in solar panel racks but may instead be used individually or in any combination with each other in any structure for which they are suitable. Further, the cross-sectional shapes of hollow beams, beam brackets, and splices as disclosed herein are not restricted to the particular quadrilateral cross-sectional shapes shown in the drawings, but instead may take any shape suitable for the purpose for which the beams, beam brackets, or splices are employed. The hollow beam splices described herein are not restricted to use in coupling hollow beams formed from folded sheet metal, but may instead be used to couple hollow beams, tubes, or pipes formed by any method including cast, extruded, or machined hollow beams. Generally, the cross-sectional shape of the splice in its expanded form should conform to and tightly fit an inner cross-sectional shape of the hollow beams, pipes, or tubes to be coupled. Similarly, the cross-sectional shape of a beam bracket should conform to and tightly fit an outer cross-sectional shape of the hollow beam that it is supporting. 
     This disclosure is illustrative and not limiting. Further modifications will be apparent to one skilled in the art in light of this disclosure and are intended to fall within the scope of the appended claims.