HELIOSTATS

PRIOIRTY

[0001] The present non-provisional Application claims the benefit of commonly owned provisional Application having serial number 62/613,570, filed on January 4, 2018, which provisional Application is incorporated herein by reference in its entirety for all purposes

FIELD OF THE INVENTION

[0002] The present invention is an improved mirror panel assembly used for reflecting light to a target. More specifically, this mirror panel approach is intended for use in applications related to the field of Concentrated Solar Power (CSP), such as for heliostats and solar troughs, among others. The mirror panels are coupled to underlying support structures using pivotable (canting) hardware modules that allow the mirror panels to be pivoted and optionally laterally moveable relative to the support structure during installation and set-up.

BACKGROUND OF THE INVENTION

[0003] Solar power plants or other systems that collect and concentrate solar energy onto one or more centralized targets are well known in the art. The concentrated solar energy often is used to directly or indirectly produce electricity and/or heat. Direct conversion, often referred to as concentrating photovoltaics (CPV) occurs in some modes of practice when photovoltaic cells (also known as solar cells) serve as the target(s) to convert incident, concentrated solar energy into electricity using photovoltaic effects. Indirect conversion, often referred to as Concentrating Solar Power (CSP) occurs when thermal energy of the concentrated solar energy is used in some modes of practice to heat a working fluid, or sequence of working fluids. The working fluid or fluids in turn drive machinery such as a turbine system to generate electric power. Working fluids include steam, oil, molten salt, or the like.

[0004] U.S. Pat. Nos. 8,833,076; 8,697,271; 7,726,127; 7,299,633; and U.S. Pat. Pub. No. 2013/0081394 A1 describe systems in which solar energy heats molten salt to store the thermal energy. The molten salt can store the heat for extended periods of time for later use on demand. The molten salt thus functions as a thermal battery that is charged by the sun. The thermal energy stored in the molten salt is used in illustrative modes of practice to heat steam that drives a turbine to generate electricity. After heating the steam, the molten salt cools down but is readily heated again, or re-charged, with solar energy, by heating again using concentrated solar energy. Molten salt can be heated, used, and recharged this way many times without being consumed to any significant degree. Facilities that use molten salt in this fashion are projected to have lifespans extending for decades.

[0005] CSP systems typically rely on a field of reflecting devices that track, reflect, and collectively concentrate incident sunlight onto a solar receiver. Many types of reflecting devices are known. Examples include heliostats, parabolic dishes, trough concentrators, and the like. A CSP system often may use hundreds or even thousands of reflecting devices to concentrate solar energy.

[0006] Mirrors in most instances are a fundamental element of the reflecting devices used in CSP plants. The primary function of the mirrors is to reflect sunlight onto a target where the resultant concentrated sunlight can then be converted into other forms of useful energy, such as electricity or heat. Mirrors may have a variety of shapes, and many shapes are suitable to redirect sunlight onto a desired target. As examples of shapes, mirrors may be flat, curved in two dimensions, curved in three dimensions, faceted, and the like.

[0007] The mirrors often are supported by a suitable support structure so that the mirrors substantially maintain their shape without undue sagging, thermal deformation, or shape deformation as the mirrors articulate and are impacted by wind, moisture, age, temperature changes, and other surrounding factors. A mirror panel is a component of many different types of reflector devices. A heliostat is one type of reflector device. A heliostat is a term in the art that refers to an assembly comprising one or more mirror panel assemblies, one or more drive mechanisms attached to the mirror panel to articulate the mirror panel to track the sun, and a base structure mounted to the drive mechanism to attach the heliostat to the ground, a frame, or other fixed or moveable mounting site. Trough reflectors are another type of reflecting device.

[0008] Larger heliostats may include an array of mirror panel assemblies or facets. Each individual mirror panel assembly forms a facet of the overall, resultant reflecting surface. The facets in some instances may be spaced apart by a suitable gap so that adjacent mirror panels do not touch or overlap other mirror panels. Forming large heliostats from such facets allows the overall shape of the reflecting function to be optimally shaped and aimed to reflect and concentrate sunlight onto the desired target.

[0009] Connecting mirror panel assemblies to a support structure poses many technical challenges. As one, it is desirable to provide a connection that poses little if any risk of twisting or otherwise distorting the mirror panels. Further, the connection strategy should allow the mirror panel assembly to be easily canted to properly contribute to the overall shape of the desired reflecting surface without undue complexity. Further, installation and canting should be easy to accomplish without requiring large crews or long periods of time.

SUMMARY OF THE INVENTION

[00010] The present invention provides improved strategies for incorporating mirror panel assemblies into heliostats. Preferred embodiments of the invention allow a three-point, planar attachment of mirror panel assemblies to an underlying support structure to minimize the risk that attachment will twist or otherwise distort panels. The attachment strategy allows each mirror panel assembly to be canted in any direction to achieve a desired array shape. Through a suitable range of motion, the connection strategy mimics a more expensive ball joint connection while being more stable. Installation is easy and quick. In some modes of practice, a single person can quickly adjust a mirror panel assembly to a desired canting deployment from a single side of the assembly.

[00011] In one aspect, the present invention relates to a heliostat, comprising:

a) a base;

b) a rotatable and tiltable support structure coupled to the base such that the rotatable and tiltable support structure can be rotated around an azimuth axis and tilted with respect to a pivot axis; and

c) a pivotable and cantable mirror panel assembly coupled to the rotatable and tiltable support structure, wherein:

(i) a first end of the pivotable and cantable mirror panel assembly is pivotably coupled to the rotatable and tiltable support structure at a first attachment site to allow the pivotable and cantable mirror panel assembly to pivot relative to the rotatable and tiltable support structure, and wherein said coupling at the first attachment site further allows the mirror panel assembly to spherically rotate and axially shift relative the rotatable and tiltable support structure; and

(ii) a second end of the pivotable and cantable mirror panel assembly is coupled to the rotatable and tiltable support structure at second and third attachment sites such that the pivotable and cantable mirror panel assembly can be independently raised and lowered at the second and third attachment sites relative to the rotatable and tiltable support structure to cant the mirror panel assembly.

[00012] In another aspect, the present invention relates to a the present invention heliostat, comprising:

a) a base;

b) a pivotable support structure supported by the base, wherein the pivotable support structure is pivotable with respect to at least a first axis;

c) a drive system that actuates the pivotable support structure to pivot with respect to the first axis;

d) a mirror panel system attached to the pivotable support structure, wherein the mirror panel system comprises at least one mirror panel assembly; and e) an attachment system that couples the at least one mirror panel assembly to the pivotable support structure, said attachment system comprising:

i. a first attachment connecting the mirror panel assembly to the

pivotable support structure in a manner that allows the mirror panel assembly to move with at least one degree of freedom comprising at least one of pivoting relative to a mirror axis, spherically rotating with respect to the pivotable support structure, and laterally shifting relative to the pivotable support structure;

ii. a second attachment that adjustably connects the mirror panel

assembly to the pivotable support structure, wherein adjusting the second adjustable attachment raises and lowers the mirror panel assembly relative to the pivotable support structure, wherein the first attachment allows the mirror panel assembly to move with at least one degree of freedom to accommodate adjustment of the second adjustable attachment; and

iii. a third attachment that adjustably connects the mirror panel assembly to the pivotable support structure, wherein adjusting the third adjustable attachment raises and lowers the mirror panel assembly relative to the pivotable support structure, wherein the first attachment allows the mirror panel assembly to move with at least one degree of freedom to accommodate adjustment of the third adjustable attachment.

[00013] In another aspect, the present invention relates to a heliostat, comprising: a) a base;

b) a rotatable and tiltable support structure coupled to the base;

c) pivotable mirror panel assembly coupled to the pivotable and tiltable support structure, wherein the mirror panel assembly is cantable and pivotable relative to the rotatable and tiltable support structure; and

d) a hinged drive system, wherein the hinged drive system is rotatably coupled to the base such that the drive system is rotatable about an azimuth axis to cause rotation of the rotatable and tiltable support structure and the mirror panel assembly about the azimuth axis relative to the base, and wherein the hinged drive system is coupled to the rotatable and tiltable support structure such that such that hinging actuation of the drive system tilts the rotatable and tiltable support structure and the mirror panel assembly through a range of motion such that the rotatable and tiltable support structure and the mirror panel assembly are tiltable relative to a pivot axis.

[00014] In another aspect, the present invention relates to a heliostat, comprising: a) a base;

b) a pivotable support structure supported by the base, wherein the pivotable support structure is pivotable relative to at least a first axis;

c) a drive system that actuates the pivotable support structure to pivot relative to the first axis;

d) a mirror panel system, wherein the mirror panel system comprises:

i. a first mirror panel assembly attached to the pivotable support

structure, wherein the mirror panel assembly;

ii. a second mirror panel assembly attached to the pivotable support structure adjacent to the first mirror panel assembly along a common boundary; and

wherein:

a first end of each of the first and second pivotable and cantable mirror panel assemblies is pivotably coupled to the rotatable and tiltable support structure at a common, first attachment site to allow each of the pivotable and cantable mirror panel assemblies to pivot relative to the rotatable and tiltable support structure, and wherein said coupling at the first attachment site further allows each of the mirror panel assemblies to spherically rotate and axially shift relative the rotatable and tiltable support structure; and (ii) a second end of each pivotable and cantable mirror panel assembly is coupled to the rotatable and tiltable support structure at corresponding second and third attachment sites such that each pivotable and cantable mirror panel assembly can be independently raised and lowered at the corresponding second and third attachment sites relative to the rotatable and tiltable support structure to cant the mirror panel assembly.

[00015] In another aspect, the present invention relates to a heliostat, comprising: a) a base;

b) a pivotable support structure supported by the base, wherein the pivotable i support structure is pivotable around at least a first axis of rotation;

c) a drive system that actuates the pivotable support structure to rotate around at least the first axis of rotation;

d) a mirror panel system, wherein the mirror panel system comprises at least one mirror panel assembly attached to the pivotable support structure, wherein the at least one mirror panel assembly comprises a perimeter, a light reflecting side, and an oppositely facing side, wherein the mirror panel assembly comprises a post projecting laterally outward from the perimeter proximal to a first end of the mirror panel assembly, and first and second threaded studs projecting outward from the oppositely facing side of the mirror panel assembly distal from the first end of the mirror panel assembly; and e) an attachment system that couples the mirror panel assembly to the pivotable support structure, said attachment system comprising:

i. a first bracket that is attached to the pivotable support structure and that is connected to the post of the mirror panel assembly in a manner effective to provide a connection with at least one degree of freedom;

ii. a second bracket attached to the pivotable support structure and comprising a first canting hardware module, wherein the first canting hardware module threadably engages the first threaded stud such that actuation of the first canting hardware module causes relative axial movement between the first canting module and the first threaded stud, and wherein the connection between the first bracket and the post allows the mirror panel assembly to move with at least one degree of freedom to accommodate adjustment of the first canting module; and

iii. a third bracket attached to the pivotable support structure and comprising a second canting hardware module, wherein the second canting hardware module threadably engages the second threaded stud such that actuation of the second canting hardware module causes relative axial movement between the second canting module and the second threaded stud, and wherein the connection between the first bracket and the post allows the mirror panel assembly to move with at least one degree of freedom to accommodate adjustment of the second canting module.

[00016] In another aspect, the present invention relates to a method of providing a heliostat, comprising the steps of:

a) providing a base;

b) providing a support structure pivotably coupled to the base; and

c) providing a mirror panel assembly that is attached to the support structure,

comprising the steps of:

i. causing the mirror panel assembly to be connected to the support structure at a first attachment site such that mirror panel assembly can move with at least one degree of freedom at the first adjustment site to accommodate canting adjustment of the mirror panel assembly;

ii. causing the mirror panel assembly to be adjustably connected to the support structure at a second attachment site such that adjustment of the second attachment site cants the mirror panel assembly on demand and such that the connection at the first attachment site is able to move with at least one degree of freedom to accommodate the adjustment of the second attachment site; and

iii. causing the mirror panel assembly to be adjustably connected to the support structure at a third attachment site such that adjustment of the third attachment site cants the mirror panel assembly on demand and such that the connection at the first attachment site is able to move with at least one degree of freedom to accommodate the adjustment of the third attachment site. BRIEF DESCRIPTION OF THE DRAWINGS

[00017] Fig. 1 schematically shows a concentrating power system including a central tower and a field of heliostats that concentrates incident sunlight onto the tower.

[00018] Fig. 2 is a front view of a heliostat of the present invention used in the system of Fig. 1.

[00019] Fig. 3 is a rear perspective view of the heliostat of Fig. 2.

[00020] Fig. 4 is an exploded perspective view of the heliostat of Fig. 2

[00021] Fig. 5 is an exploded perspective view of the heliostat similar to that of Fig. 4 except that the cross braces and trusses are assembled to form a pivotable support structure.

[00022] Fig. 6 is a perspective view of the pivotable support structure of Fig. 5 mounted to the torque tube used in the heliostat of Fig. 2.

[00023] Fig. 7 is a close up perspective view of the heliostat of Fig. 2 showing the hinged drive that connects the torque tube to the base.

[00024] Fig. 8A is a top plan view of a mirror panel assembly of the heliostat of Fig.2.

[00025] Fig. 8B is an exploded perspective view of a mirror panel assembly of Fig.

8A.

[00026] Fig. 9 is a perspective view of a long truss used in the pivotable support structure of the heliostat of Fig. 2, which further shows how brackets of an attachment system are mounted onto the top chord of the truss.

[00027] Fig. 10 is a perspective view of a short truss used in the pivotable support structure of the heliostat of Fig. 2, which further shows how brackets of an attachment system are mounted onto the top chord of the truss.

[00028] Fig. 11 is a front perspective view of a bracket used in the heliostat of Fig. 2 that provides a pivotable connection between a pair of adjacent mirror panel assemblies and a short truss.

[00029] Fig. 12 is a side perspective view of the bracket of Fig. 11.

[00030] Fig. 13 is a top perspective view of a bracket used in the heliostat of Fig. 2 that connects the mirror panel assembly to a long truss, wherein during set-up the bracket allows pivoting and axial up and down adjustment of the mirror panel assembly relative to the underlying support structure.

[00031] Fig. 14 is a bottom perspective view of the bracket of Fig. 13.

[00032] Fig. 15 is a top perspective view of a bracket identical to that of Fig. 13 that cooperates with the bracket of Fig. 13 to help connect the mirror panel assembly to the long truss. [00033] Fig. 16 is a bottom perspective view of the bracket of Fig. 15.

[00034] Fig. 17 is a perspective view of a cross-brace used in the heliostat of Fig. 2.

[00035] Fig. 18 is a close-up perspective view of a portion of the heliostat of Fig. 2 showing how a long truss and an adjacent short trust are mounted to an end of the torque tube.

[00036] Fig. 19 is a bottom plan view of a portion of the heliostat of Fig. 2 showing how a pair of adjacent mirror panel frames of two mirror panel assemblies is mounted to the pivotable support structure, wherein the frames are adjacent along a common boundary.

[00037] iFig. 20 is a close-up perspective view of a portion of the heliostat of Fig. 2 showing how a cross brace is connected to an outermost long truss (i.e., a long truss mounted proximal to an end of the torque tube of Fig. 2).

[00038] Fig. 21 is a close-up perspective view of a portion of the heliostat of Fig. 2 showing how cross braces are connected to an inner long truss (i.e., a long truss mounted inwardly distal from an end of the torque tube of Fig. 2).

[00039] Fig. 22 is a close-up perspective view of a portion of the heliostat of Fig. 2 showing how cross braces are connected to a short truss.

[00040] Fig. 23 is a close-up perspective view of a portion of the heliostat of Fig. 2 showing how a stud on a mirror panel is attached to a long truss.

[00041] Fig. 24 is a close-up perspective view of a portion of the heliostat of Fig. 2 showing how a post on a mirror panel is attached to a short truss.

[00042] Fig. 25 is a side view showing a truss being installed onto the torque tube used in the heliostat of Fig. 2, wherein the torque tube is fitted through the enlarged portion of the key way region of the truss to allow the truss to be easily moved over the tube to a desired mounting location.

[00043] Fig. 26 is a side view of the truss of Fig. 25 being shifted downward to a desired mounting position on the tube adjacent corresponding mating flanges on the tube.

[00044] Fig. 27 shows the truss of Fig. 26 bolted to the mating flanges on the tube.

DETAILED DESCRIPTION OF PRESENTLY PREFERRED EMBODIMENTS

[00045] The present invention will now be further described with reference to the following illustrative embodiments. The embodiments of the present invention described below are not intended to be exhaustive or to limit the invention to the precise forms disclosed in the following detailed description. Rather a purpose of the embodiments chosen and described is so that the appreciation and understanding by others skilled in the art of the principles and practices of the present invention can be facilitated.

[00046] Fig. 1 schematically illustrates a concentrating solar energy system 10 that incorporates principles of the present invention. System 10 includes a central tower 12 including a mast 14 and a target region 16 at the top of the mast. A field of heliostats 18 is deployed around central tower 12. The heliostats 18 redirect and concentrate incident sunlight onto target region 16. If system 10 embodies a photovoltaic solar power system (also known as concentrating photovoltaics, or CPV), target region 16 generally would include solar cells that absorb the concentrated light and generate electricity that could then be stored for later use or distributed to one or more users or a power grid or the like. If system 10 embodies a concentrating solar power (CSP) system, used to convert solar energy into electricity, heat, or mechanical energy, then the thermal energy generated on target region 16 may be used to heat a working fluid. The thermal energy in the heated fluid may then be used directly or indirectly to generate electricity, heat, or pressure. A CSP embodiment of system 10 is particularly useful in molten salt-based power systems such as those described in U.S. Pat. Nos. 8,833,076; 8,697,271 ; 7,726,127; 7,299,633; and U.S. Pat. Pub. No. 2013/0081394 Al .

[00047] Figs. 2 through 27 illustrate an exemplary embodiment of heliostat 18 used in system 10 of Fig. 1. Referring first mainly to Figs. 2 through 7, heliostat 18 includes a base in the form of pedestal 20 attaching heliostat 18 to the ground 22 or other supporting surface. Pivotable support structure 60 interconnects mirror panel system 138 to pedestal 20.

Pivotable support structure 60 includes torque tube 62, long trusses 72, short trusses 98, and cross-braces 128 and 129. Mirror panel system 138 is attached to pivotable support structure 60 using attachment system 182 (discussed further below as including brackets 184, 198, and 216). Pivotable support structure 60 is coupled to pedestal 20 by drive system 34. Mirror panel system 138 can be actuated to rotate or pivot relative to two independent axes (also referred to as first and second degrees of actuation) 26 and 48. This allows mirror panel system 138 to be aimed in a manner effective to track the sun and redirect incident sunlight onto a desired target such as target region 16 in Fig. 1. Heliostat 18 includes features to provide such first and second degrees of actuation.

[00048] For example, to provide a first degree of actuation, a rotatable vertical shaft (not shown) is rotatably housed inside pedestal 20. Such a shaft rotates about a vertical, or azimuth, axis 26. A motor 27 is incorporated into drive system 34 in order to rotate the drive shaft. An access port (not shown) may be provided at one or more locations on pedestal 20 to provide access to service, maintain, install, repair, or replace components inside pedestal 20. Drive system 34 is fixedly attached to the vertical shaft housed inside pedestal 20. Mirror panel system 138, in turn, is coupled to the drive system 34 through the pivotable support structure 60. Thus, rotation of the shaft inside pedestal 20 causes mirror panel system 138 to rotate about the vertical, azimuth axis 26 as well.

[00049] Drive system 34 (shown best in Figs. 4, 5, and 7) provides a second degree of actuation to tilt mirror panel system 138 about horizontal pivot, or elevation axis 48. Drive system 34 is in the form of a hinge 36 (Fig. 4) that includes a lower body 38 having a central region that is attached to the rotatable shaft (not shown) inside pedestal 20. An upper body in the form of lever armature 46 includes lever arms 50 and cross beam 52. Lever arms 50 are pivotably coupled to lower body 38 at pivot axis 48.

[00050] Actuation rod 54 includes bottom tube 55 and upper rod 57 that can be actuated to telescope into and out of bottom tube 55. Upper rod 57 is pivotably connected to cross beam 52 by bracket 56. Bottom tube 55 is pivotably connected to lower body 38 by bracket 58. Actuation rod 54 can be actuated by motor 30 (Fig. 5) to open and close hinge 36. Based on corresponding actuation of actuation rod 54, pivot, or elevation, axis 48 serves as a fulcrum to raise and lower lever armature 46 relative to the lower body 38. Thus, such actuation tilts upper armature 46 up or down as desired. Because mirror panel system 138 is connected to the upper, lever armature 46, tilting of lever armature 46 about pivot or elevation axis 48 causes corresponding tilting of mirror panel system 138 as well. A controller (not shown) may be coupled to motors 27 (Fig. 7) and 30 (Fig. 5) to help control actuation of the rotatable shaft inside pedestal 20 or actuation rod 54.

[00051] The hinge functionality incorporated into drive system 34 provides a range of motion from a fully closed configuration to a fully open configuration. Drive system 34 can be actuated to maintain any desired configuration within the operational range. For example, drive system 34 may be deployed in a closed configuration. In this configuration, pivotable support structure 60, and hence mirror panel system 138, are supported in a generally horizontal configuration with respect to the ground 22 or other supporting surface.

Alternatively, drive system 34 may be deployed in a partially open configuration. In this configuration, pivotable support structure 60, and hence mirror panel system 138, are supported at any desired angle with respect to the ground 22 within a suitable range of motion, such as from greater than 0 degrees (where 0 degrees corresponds to a horizontal orientation with respect to ground 22) to 90 degrees (where 90 degrees corresponds to a vertical orientation with respect to ground 22). In an illustrative mode of practice, a suitable range of motion spans a total angular range of 100 degrees from 10 degrees below horizontal when actuated in one direction to 90 degrees (vertical) when actuated in the other direction.

[00052] For purposes of illustration, as seen best in Fig. 2, mirror panel system 138 includes a 4 x 6 array of mirror panel assemblies 140. Many other array sizes may be used. For example, exemplary arrays include m x n arrays where m is 1 to 20 or more and n is 1 to 20 or more.

[00053] Now referring to Figs. 3 through 6, 9, 10, 18, and 25 through 27, pivotable support structure 60 includes elevation tube 62 (also referred to as a torque tube), long trusses 72, short trusses 98, cross braces 128, and attachment system 182. Elevation tube 62 includes tubular body 63 extending from first end 65 to second end 67. Attachment flanges 66 extend outward from tubular body 63. Flanges 66 provide features that allow tube 62 to be connected to other heliostat components using any suitable attachment technique. For example, flanges 66 may include apertures that allow tube 62 to be bolted, pinned, or screwed to other components of heliostat 18. In the illustrated embodiment, attachment flanges 66 allow tube 62 to be bolted to trusses 72 and 98. Central flanges 69 allow tube 62 to be bolted to lever armature 46 of drive system 34.

[00054] As seen best in Figs. 25 through 27, flanges 66 are shaped to allow easy insertion onto tube 62, shifting into final position, and then attachment to the long trusses 72 and the short trusses 98. Each of flanges 66 and flange apertures 68 includes an arcuate perimeter 70 that is wider at the bottom and narrows toward the top.

[00055] Still referring collectively to Figs. 3 through 6, 9, 10, 18, and 25 through 27, long trusses 72 and short trusses 98 are bolted to flanges 66 of elevation tube 62. In the illustrative embodiment shown in the Figures, attachment system 182 (including brackets 184, 198, and 216) connects each mirror panel assembly 140 to a long truss 72 at two or more, preferably two, attachment sites and to a short truss 98 at a one or more, preferably one, attachment site. Each mirror panel assembly 140 is attached to a long truss 72 by attachment components (brackets 198 and 216 described further below) that allow each assembly 140 first to be canted and optionally laterally adjusted to a desired orientation. In the meantime, each mirror panel assembly 140 is attached to a short truss 98 by attachment components (bracket 184 described further) below that allow the assembly 140 to pivot, rotate, and shift axially to accommodate the canting adjustment at the long truss 72. When the desired orientation is achieved, the attachment components at the long truss 72 are tightened to secure the assembly 140. Tightening the pivoting connection at the short truss 72 is optional, but not required as the two connections at the long truss 72 are sufficient to lock the mirror panel assembly 140 into the desired orientation.

[00056] Two canting attachment sites on the long truss 72 per mirror panel assembly 140 are preferred for simple, fast canting set up of the corresponding mirror panel assembly 140. A single, pivoting attachment site on the short truss 98 per mirror panel assembly 140 is preferred for simple, fast canting set up of the corresponding mirror panel assembly 140. A single pivoting attachment in cooperation with two canting attachments 182 also provides a three-point attachment strategy to help ensure that a mirror panel remains flat during canting set up and then fixation without undue distortion of the mirror panel that could result more easily if more than three attachment points are used. Mirror panel assemblies 140 are arranged in pairs along common boundaries 142 so that each pair shares a common attachment site on the short trusses 98 proximal to the common boundary 142.

[00057] Each long truss 72 includes a top chord 74 and bottom chord 76. Chords 74 and 76 may be formed from one or more segments joined together to form the completed chord. For purposes of illustration, each of top chord 74 and bottom chord 76 is formed from two segments joined at center splices 78. Vertical struts 80 and diagonal struts 82 provide an internal web that structurally supports the chords 74 and 76. Vertical struts 80 and diagonal struts 82 are configured so that long truss 72 tapers from a relatively wide central region 84 to relatively narrow ends 77. As an option, either long truss 72 and/or short truss 98 (described below) may have a non-tapered configuration. In such a layout, the top and bottom cords would be substantially parallel to each other, thus maintaining substantially the same chord height from the central region out to the ends.

[00058] Central region 84 includes a central flange 86 supported by a frame provided by flange frame segments 88, top chord 74, diagonal struts 82, and bottom chord 76. Central flange 86 includes a large aperture in the form of key way 92 having relatively large lower region 94 that tapers to provide relatively smaller upper region 96.

[00059] Each short truss 98 includes a top chord 100 and bottom chord 102. Chords 100 and 102 may be formed from one or more segments joined together to form the completed chord. For purposes of illustration, each of top chord 100 and bottom chord 102 is formed from two segments joined at center splices 104. Vertical struts 106 and diagonal struts 108 provide an internal web that structurally supports the chords 100 and 102. Vertical struts 106 and diagonal struts 108 are configured so that short truss 98 tapers from a relatively wide central region 110 to relatively narrow ends 111. [00060] Central region 110 includes a central flange 112 supported by a frame provided by flange frame segments 114, top chord 100, diagonal struts 108, and bottom chord 102. Central flange 112 includes a large aperture in the form of keyway 118 having relatively large lower region 120 that tapers to provide relatively smaller upper region 122.

[00061] Keyway 92 of each long truss 72, or key way 118 of each short truss 98, as the case may be, allows easy installation and then attachment of each long truss 72 or short truss 98, respectively, to the elevation tube 62 as shown by the sequence in Figs. 25 through 27.

For purposes of illustration, the attachment strategy will be described with respect to a long truss 72. However, the attachment strategy for each long truss 72 and each short truss 98 is the same, as the cooperating attachment structures on torque tube 62 are the same in the illustrative embodiment shown in the Figures. In a first stage of attachment, elevation tube 62 is aligned with the relatively large, lower region 94 in the keyway 92 of long truss 72. Lower region 94 is large enough that truss 72 and/or tube 62 are easily positioned in a desired position with flange 86 of truss 72 adjacent to a corresponding flange 66 of tube 62. In a second stage, truss 72 and tube 62 are then shifted relative to each other in order to seat the tube 62 into the smaller upper region 96 with flanges 86 and 66 adjacent and aligned for securement to each other. In a third stage, the flanges 86 and 66 are attached to each other by a suitable fastening strategy to securely fix truss 72 to tube 62. For purposes of illustration, apertures 68 on flange 66 of tube 62 align with corresponding apertures on flange 86 to allow the components to be secured to each other with bolt assemblies.

[00062] A similar attachment strategy is used with respect to each short truss 98. In a first stage of attachment, elevation tube 62 is aligned with the relatively large region 120 of short truss 98. Lower region 120 is large enough that truss 98 and/or tube 62 are easily positioned in a desired position with flange 112 of truss 98 adjacent to a corresponding flange 66 of tube 62. In a second stage, truss 98 and tube 62 are then shifted relative to each other in order to seat the tube 62 into the smaller upper region 122 with flanges 112 and 66 adjacent and aligned for securement to each other. In a third stage, the flanges 112 and 66 are attached to each other by a suitable fastening strategy to securely fix truss 98 to tube 62. For purposes of illustration, apertures 68 on flange 66 of tube 62 align with corresponding apertures on flange 112 to allow the components to be secured to each other with bolt assemblies.

[00063] The attachment strategy for the long and short trusses 72 and 98 allows for simple attachment of the trusses 72 and 98 to the tube 62. Each truss 72 and 98 can be slid over the tube 62 starting from one end or the other, as appropriate, and then shifted down the length of the tube 62 into the desired position. The enlarged lower regions 94 and 120 in trusses 72 and 98 are large enough provide sufficient clearance for this deployment. Once in the desired position, each truss 72 or 98 can be shifted when adjacent a corresponding flange 66 on tube 62 so that the upper regions 96 and 122 of trusses 72 and 98 now have a closer fit with tube 62. The complementary flanges on the trusses 72 and 98 and the tube 62 can then be fastened together by any suitable fastening technique. Examples of fastening techniques included bolting, welding, brazing, screwing, pinning, riveting, gluing, clamping, crimping, combinations of these, and the like.

[00064] Referring now to Figs. 2 through 7, and 17 through 27, horizontal cross braces 128 and diagonal cross braces 129 help to structurally strengthen pivotable support structure 60 overall and help to hold long trusses 72 and short trusses 98 in proper position. Cross- braces 128 and 129 are connected to trusses 72 and 98 via attachment system 182, which also is used to connect mirror panel system 138 to the pivotable support structure 60. In this embodiment, each cross brace 128 and 129 is the same as the other cross braces 128 and 129, except that the diagonally deployed cross braces 129 are longer than the horizontal cross braces 128 to achieve a desired spacing among the trusses 72 and 98. As seen best in Fig. 17, each cross brace 128 (cross braces 129 are identical except for being longer) includes body 132 extending between ends 130. Each end 130 includes an aperture 134 to attach ends 130 to the attachment system 182.

[00065] As seen best in Figs. 2 through 5, 8A and 8B, and 19 mirror panel system 138 includes an array of mirror panel assemblies 140. The mirror panel assemblies 140 are deployed in pairs 162, wherein each pair 162 includes a common boundary 142 proximal to a common, shared attachment site relative to the underlying pivotable support structure 60. As seen best in Figs. 8 A and 8B, each mirror panel assembly 140 includes a mirror panel 160 and a frame 170. Each mirror panel assembly includes a perimeter 144 including first end 146 and opposing second end 148, and third end 150 and opposing fourth end 152. A light redirecting side 154 of mirror panel 160 redirects incident sunlight toward a desired target. Opposite facing side 156 of mirror panel 160 is coupled to the underlying frame 170 using adhesive 172. Other suitable attachment techniques could be used.

[00066] Each mirror panel assembly 140 includes coupling structures that are cooperative with features of attachment system 182 to help attach the mirror panel assembly 140 to the underlying pivotable support structure 60. In the illustrative embodiment, as shown best in Figs. 8A and 8B, coupling structures include post 176 and studs 178 and 180. Post 176 along with complementary coupling structure of attachment system 182 helps to provide a pivoting attachment connecting the mirror panel assembly to the pivotable support structure 60 that allows the mirror panel assembly to pivot around a mirror axis 158. In addition, there is a slip-fit clearance between the post 176 and the upper aperture 194 in the first bracket 184 (described further below), that further allows relative rotational motion between the mirror axis 158 and an axis 195 defined by the upper aperture 194. The rotational freedom allows this interface to provide slight spherical motion within a range of motion sufficient to allow canting adjustment of mirror panel 140 at the attachment sites on the corresponding long truss 72. Additionally, the post 176 is free to move axially along mirror axis 158. Thus, this connection provides a combination of pivoting, rotational, and axial degrees of freedom.

[00067] Stud 178 cooperates with complementary coupling structure of attachment system 182 to provide a first adjustable attachment (described further below with respect to brackets 198 and 216) that helps to connect the mirror panel assembly 140 to the pivotable support structure 60. Adjusting the first adjustable attachment raises and lowers the mirror panel assembly 140 relative to the pivotable support structure 60 to cant the mirror panel assembly 140 to a desired orientation, wherein the pivoting attachment provided in part by post 176 helps to allow the mirror panel assembly 140 to pivot, rotate, and move axially to accommodate adjustment of the first adjustable attachment. Similarly, Stud 180 cooperates with complementary coupling structure of attachment system 182 to provide a second adjustable attachment that helps to connect the mirror panel assembly 140 to the pivotable support structure 60. Adjusting the second adjustable attachment raises and lowers the mirror panel assembly 140 relative to the pivotable support structure 60 to cant the mirror panel assembly 140 to a desired orientation, wherein the pivoting attachment provided in part by post 176 helps to allow the mirror panel assembly 140 to pivot, rotate, or move axially to accommodate adjustment of the second adjustable attachment.

[00068] As shown best in Figs. 6, and 9 through 24, attachment system 182 is used to attach mirror panel assemblies 140 to the pivotable support structure 60. Attachment system 182 includes first bracket 184, second bracket 198, and third bracket 216. In the illustrative embodiment in the Figures, each mirror panel assembly 140 is attached to the pivotable support structure 60 by a single first bracket 184 proximal to an end of the mirror panel assembly 140. Mirror panel assemblies 140 are grouped in pairs 162 along common boundaries 142 to allow both mirror panel assemblies 140 of such a pair to share a common first bracket 184. Each first bracket 184 is mounted to the top chord 100 of a short truss 98 of pivotable support structure 60 and pivotably connects to the post 176 of the mirror panel assembly 140 to the pivotable support structure 60 in a manner that allows the mirror panel assembly 140 to pivot around a mirror axis 158, to rotate to provide a suitable spherical range of motion at the connection, and to axially shift to allow lateral motion relative to pivotable support structure 60.

[00069] Each second bracket 198 and third bracket 216 is mounted to the top chord 74 of a long truss 72 of pivotable support structure 60 in a manner such that a pair comprising a second bracket 198 and a third bracket 216 connects corresponding studs 178 and 180, respectively, to the pivotable support structure 60. Such connection is made in a manner such that adjusting the second, adjustable bracket 198 or the third bracket 216, as the case may be, raises and lowers the corresponding mirror panel assembly 140 relative to the pivotable support structure 60 for an adjustment such as to cant the mirror panel assembly 140 to a desirable orientation. As such adjustment is made at the second and third brackets 198 and 216, the connection provided by the corresponding first bracket 184 allows the mirror panel assembly 140 to pivot and move laterally to accommodate the adjustments. Each of the second and third brackets 198 and 216 are independently adjustable so that only one or both of the attachments at the brackets is adjusted to set a desired orientation of the corresponding mirror panel assembly 140.

[00070] Figs. 11, 12 18, 22, and 24 show the first bracket 184 in more detail. First bracket 184 includes base 186 and walls 188 and 190 projecting from base 186. Each wall 188 includes a lower aperture 192 that allows an egress so that ends 130 of cross brace 129 can reach and be mounted to the threaded studs 196. As illustrated, a first pair of cross braces 129 is able to reach through aperture 192 of wall 188 from one side of first bracket 184, while a second pair of cross braces 129 is able to reach through aperture 192 of the other wall 190 from the other direction. Each of walls 188 and 190 includes an upper aperture 194 that pivotably supports the post 176 of a corresponding mirror panel assembly. The upper apertures 194 of walls 188 and 190 are offset from each other such that each aperture 194 can support a corresponding post 176 without interference from a post 176 supported by the other wall. However, the layout could be modified to allow both apertures 194 to be in alignment, but the offset configuration allows posts 176 on adjacent mirror panel assemblies 140 to be longer without having to further increase the spacing between a pair of mirror panel assembles 140 at their common boundary 142. Longer posts 176 may be desirable in installations in which more axial shifting at the connection might be expected, such as if the mirror panel assembly 140 will be canted significantly to achieve a desired facet deployment within array 138. Longer posts 176 also make assembly easier. Thus, each bracket 184 is able to support two, adjacent mirror panel assemblies 140. Each bracket 184 comprises dual functionality, therefore, in terms of providing attachment sites for adjacent mirror panel assemblies 140 as well as providing attachment sites for cross braces 128 approaching bracket 184 from each side.

[00071] Figs. 13, 14, 18, 20, 21, and 23 show the adjustable second bracket 198 in more detail. Second bracket 198 includes a base plate 200. Canting hardware stack 204 is mounted within a relatively large aperture in base plate 200 to allow canting hardware stack

204 to shift laterally if desired. Canting hardware stack 204 includes sleeve 205 having top flange 206, threaded bore 212, and faceted end 208. Sleeve 205 is pivotably clamped to base plate 200 by hardware components 210. Sleeve 205 can be pivoted and rotated relative to base plate 200. In brief, stud 178 of a corresponding mirror panel assembly 140 threadably engages threaded bore 212 of hardware stack 204. Sleeve end 208 can be gripped by a suitable tool in order to rotate sleeve 205. Due to the threadable engagement between sleeve

205 and stud 178, such rotation raises or lowers stud 178, and hence mirror panel assembly 140, depending on which way sleeve 205 is rotated. As this raising and lowering occurs, sleeve 205 is able to pivot to accommodate the resultant adjustment. As hardware stack 204 is adjusted, the post end of the mirror panel assembly 140 proximal to post 176 is free to rotate, move spherically, and/or shift axially relative to bracket 198 as needed to

accommodate the movement of the studs 178 and 180 relative to the canting hardware stacks. Once the hardware stacks are securely tightened, the mirror orientation is fixed. Further details and the operation of canting hardware stack 204 are further described in Assignee’s co-pending PCT Patent Application No. PCT/US 17/50262, filed September 6, 2017, titled Heliostat Mirror Panels with Pivotable Hardware Modules, and being in the names of Gregory and Cobeaga.

[00072] Adjustable second bracket 198 also includes threaded studs 214. Studs 214 provide attachment sites for ends 130 of corresponding cross braces 129. Thus, each second bracket 198 has dual functionality in the sense of providing attachment sites for cross braces 128 and a corresponding mirror panel assembly 140.

[00073] Figs. 15 and 16 show the adjustable third bracket 216 in more detail. The structure and function of third bracket 216 is identical to that of second bracket 198 in the illustrative embodiment. In a manner similar to adjustable second bracket 198, adjustable third bracket 216 includes a base plate 218 having aperture 220. Canting hardware stack 222 is mounted to base plate 218 via aperture 220. Stack 222 includes sleeve 223 having top flange 224, threaded bore 230 and faceted end 226. Hardware components 228 pivotably secures sleeve 223 to the base plate 218. Because aperture 220 is relatively large compared to the size of sleeve 223, hardware components 228 can be loosened and then retightened to laterally shift stack 222 to a different position if desired. Adjustable third bracket 216 also includes threaded studs 232. Studs 232 provide attachment sites for ends 130 of first and second cross braces 128. Thus, each second bracket 216 has dual functionality in the sense of providing attachment sites for cross braces 128 and a corresponding mirror panel assembly 140.

[00074] Attachment system 182 makes it simple to mount a mirror panel assembly 140 to the pivotable support structure 60. The post 176 of a mirror panel assembly 140 is slid into the aperture 194 of a corresponding first bracket 184. Threaded studs 178 and 180 then can be inserted into the threaded bores 212 and 230 of corresponding second and third brackets 198 and 216. The sleeves 205 and 223 of the canting hardware stacks 204 and 222 can then be independently actuated to lower and/or raise the mirror panel assembly to achieve the desired orientation. This adjustment causes relative axial movement between the studs 178 and 180 and the corresponding sleeves 205 and 223 to cant the mirror to a desired orientation Sleeves 205 and 223 are able to pivot during such axial adjustment, wherein the axial adjustment generally is along axes that are orthogonal to the base plates 200 and 218, respectively. Additionally, the pivoting connection between post 176 and first bracket 184 allows mirror panel assembly 140 to pivot, to spherically rotate, and to shift axially with respect to a mirror axis 158 that is axially aligned with the longitudinal axis of post 176.

Such mirror axis 158 generally is orthogonal to the wall 188 or 190, as the case may be, that pivotably supports post 176. In many embodiments, the longitudinal axis of post 176 can be aligned such that it passes through or substantially coincides with, the center of gravity of mirror panel assembly 140. The result is that the assembly 140 is quite stable with respect to gravity since the lever arm length over which the gravity load acts to exert a twisting moment on the on the assembly 140 is very small or even substantially zero. The assembly 140 has much less tendency to deflect or otherwise distort under its own weight as a result. This is a signifipant advantage, because twisting of assembly 140 due to gravity loads, and corresponding distortion of the optical shape, can be minimized or even substantially avoided.

[00075] In contrast, many conventional mirror facet designs (including 3-point and 4- point attachment strategies) use mounting features that attach mirror panel assemblies to other components via connections that are all perpendicular to the glass surface. For a 3- point attachment, this is particularly problematic when the assembly is vertically oriented, because the gravity loads acting relative to the center of gravity tend to generate a significant gravity moment. This moment tends to bend or twist the face assembly, distorting the light reflecting surface to cause slope errors or other performance issues. Making a frame stiffer can mitigate this problem, but this adds more cost and more weight, which could worsen the problem. Advantageously, preferred embodiments of the present invention significantly reduce these risks through a combination of beneficial features. By moving the pivoting connection so that the pivoting action acts with respect to an axis that is substantially parallel to the reflecting surface and that substantially passes through the center of gravity, the gravity moment can be dramatically reduced or avoided. This also eliminates a need for a third canting attachment site, which reduces hardware costs and simplifies the canting process as there are only two adjustment points rather than three or more. As an additional preferred feature, the axial shifting of studs 178 and 180 during canting adjustment occurs at two attachment sites in preferred embodiments on axes that are perpendicular to the mirror axis 158 about which assembly 140 pivots at the bracket 184.

[00076] The benefits of the three point pointing strategy are most important on the one side of a 3 -point mount facet with the single attachment point. If a single attachment stud perpendicular to the mirror surface (similar to the two studs that mate with the canting stacks) were to be used, instead of the post 176 whose axis passes through the facet center of gravity (CG), the offset CG could cause the stud to bend. Also, the reflective surface of the facet could twist. Such degradation can greatly affect how much sunlight gets reflected to the target. The orientation of post 176 helps reduce the risks of such bending and twisting.

[00077] In contrast, the opposite side of a three-point-mount facet with two threaded studs spaced relatively far apart creates much less of an issue. This is because, although the two studs could bend, the structure will have more of a parallelogram-motion, resulting in mostly in-plane motion of the reflective surface. In-plane motion of the reflective surface has very little effect on whether the sunlight reaches the target.

[00078] In summary, a three-point mount is particularly advantageous because this mounting strategy does not over-constrain the facet. However, the strategy does pose design challenges in terms of limiting slope error on the single-mount side due to gravity moments (and wind loads). The present invention provides innovative technical solutions to these design challenges. In order to address these issues, the present invention (1) moved the attachment point in alignment with the facet CG, which effectively eliminates twisting due to gravity loads and (2) increased the inherent torsional stiffness of the frame 170, which would also partially helps with gravity loads, and which helps resist slope errors caused by wind loading. [00079] Principles of the present invention can be practiced in order to provide heliostats such as heliostat 18 shown in the Figures. The result is that a heliostat comprising pedestal 20 is provided. Pivotable support structure 60 is coupled to pedestal 20. At least one mirror panel assembly 140 is attached to the support structure 60 by an attachment strategy comprising three attachment sites. At a first attachment site, the mirror panel assembly 140 is pivotably connected via post 176 to the support structure 60 at a first attachment site provided by bracket 184 such that mirror panel assembly 140 can pivot, rotate and move axially at the first adjustment site to accommodate adjustment of the second and third attachment sites. Next, studs 178 and 180 engage brackets 198 and 216 at second and third attachment sites such that adjustment of the second and third attachment site raises and lowers the mirror panel assembly 140 on demand. While this adjustment is occurring, the connection at the first attachment site at bracket 184 is able to pivot, to spherically rotate, and/or laterally shift to accommodate the adjustment of the second and third attachment sites.

[00080] This three-point connection provides a planar support attachment with a reduced tendency to twist or otherwise distort mirror panel assembly 140 as compared to attachment strategies using four or more attachment sites. Optical characteristics of a light reflecting surface can be impaired by the process of securing a facet at four or more sites, as doing this increases the risk of imparting twist. A four point or higher attachment scheme also increases the risk of optical distortions if the underlying support structure were to deflect due to external loads such as wind, gravity, or the like. The collective features of the three- point connection also mimic a ball joint connection that allows the mirror panel assembly 140 to be easily tilted with respect to multiple axes to cant in any direction during heliostat set-up through a range of motion sufficient to encompass many angles of canting deployment. The three point connection is an extremely economic way to mimic a more expensive ball joint connection within such range of motion.

[00081] All patents, patent applications, and publications cited herein are incorporated by reference in their respective entireties for all purposes. The foregoing detailed description has been given for clarity of understanding only. No unnecessary limitations are to be understood therefrom. The invention is not limited to the exact details shown and described, for variations obvious to one skilled in the art will be included within the invention defined by the claims.