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Publication numberUS20080168981 A1
Publication typeApplication
Application numberUS 11/844,877
Publication dateJul 17, 2008
Filing dateAug 24, 2007
Priority dateAug 25, 2006
Publication number11844877, 844877, US 2008/0168981 A1, US 2008/168981 A1, US 20080168981 A1, US 20080168981A1, US 2008168981 A1, US 2008168981A1, US-A1-20080168981, US-A1-2008168981, US2008/0168981A1, US2008/168981A1, US20080168981 A1, US20080168981A1, US2008168981 A1, US2008168981A1
InventorsEric Bryant Cummings, Kirsten Kaye Pace, Jacques Jean Belanger
Original AssigneeCoolearth Solar
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Rigging system for supporting and pointing solar concentrator arrays
US 20080168981 A1
Abstract
Embodiments in accordance with the present invention relate to the design of inexpensive mounting and pointing apparatuses for linear arrays of solar energy collectors and converters. Particular embodiments in accordance with the present invention disclose a rigging system comprising at least one, and preferably a plurality of, tensile cables onto which a plurality of solar modules are fastened. Such an arrangement provides a way of suspending solar modules over land, vegetation, bodies of water, and other geographic features without substantial perturbation of the underlying terrain. Certain embodiments comprise additional tensile cables fastened to the solar modules, such that differential axial motion of the cables produces a rotational motion component of the individual solar modules of the array. This rotational motion component effects an orientation control along one rotational axis.
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Claims(24)
1. A method of fastening solar modules to at least one cable under tension, at least one of the cables connected to a damping element.
2. A method according to claim 1 providing for axial motion of the arrays of solar modules by applying a common axial translation to cables connected to the modules
3. A method according to claim 1 providing for motion of the arrays of solar modules normal to the cable axis by applying a common translation of the cables normal to the cable axes.
4. A method according to claim 1 providing for rotation of the solar modules by applying a relative axial motion between at least one cable and at least two other cables.
5. A method according to claim 1 providing for rotation of the solar modules by applying a relative motion to cables normal to the axial direction.
6. A method according to claim 5 in which said actuation is accomplished via a tensioned cable.
7. A method according to claim 1 in which at least one cable comprises a cable having one or more of the functions selected from mechanical connection, electrical connection, fluid connection, heat exchanger, optical connection, networking connection.
8. A method according to claim 1 wherein flutter of the tensioned cable is suppressed by the use of partially filled rigid liquid conduits.
9. A method according to claim 1 wherein flutter of the tensioned cable is suppressed by the use of partially filled or substantially full flexible liquid conduits.
10. An assembly comprising a solar concentrator supported by a tensile truss.
11. An assembly according to claim 10 wherein the tensile truss comprises at least two tensioned cables connected by a transverse element.
12. An assembly according to claim 11 wherein the tensile truss is configured to exhibit a first order restoring force in resistance to displacement normal to an axis of the truss along the tensioned cables
13. An assembly according to claim 11 wherein the tensile truss further comprises a third tensioned cable connected to the transverse element between the first tensioned cable and second tensioned cable.
14. An assembly according to claim 13 wherein the tensile truss is configured to exhibit a first order restoring force at a connection between the transverse element and third tensioned cable in resistance to displacement in any direction along a plane defined by the transverse element and the third tensioned cable.
15. An assembly according to 14 further comprising a second tensile truss according to 11 oriented to in a different plane than the first tensile truss.
16. A ground anchor comprising:
a tube having a first end configured to contact the ground, and an open end opposite to the first end;
a tapered collet having a flared portion disposed within the tube and a narrow, threaded end protruding from the tube; and
a nut configured to engage the threaded end and rotatable to clamp a cable disposed within the collet.
17. A method of transferring tensile forces from a truss structure to the ground, the method comprising:
in a first stage, drawing together a plurality of tensile cables to a group at a pivot; and
in a second stage transferring tensile forces in the cables from the pivot to the ground.
18. The method of claim 17 further comprising a third stage wherein tensile forces in the cables are transferred to the pivot after first drawing a plurality of cables together to a second group.
19. The method of claim 17 wherein the group is created forming a cable bundle, mechanically mating the cables to a common rigid part, or mechanically mating the cables to a secondary cable.
20. The method of claim 17 wherein the tensile forces are transferred from the pivot to the ground by bringing one or more cables or tensile elements to ground anchors or footings, or by compressive elements or bending forces.
21. A method of rotating a truss, the method comprising:
providing a truss having a first end and a second end and a contact point, the truss configured to rotate about a pivot point;
providing a driving mechanism;
connecting a first end of a first cable to a first end of the truss, and connecting a second end of the first cable to the driving mechanism;
connecting a first end of a second cable to a second end of the truss, and connecting a second end of the second cable to the driving mechanism; and
causing the driving mechanism to pull on the first cable at a first rate and pull on the second cable at a second rate, such that the truss rotates and the contact point engages the first cable or the second cable, thereby imparting additional rotational moment to pivoting of the truss.
22. The method of claim 21 wherein the driving mechanism comprises a rotating drum.
23. The method of claim 22 wherein the first rate is imparted by a first radius of the drum in contact with the first cable, and the second rate is imparted by a second radius of the drum in contact with the second cable.
24. The method of claim 21 wherein the driving mechanism comprises:
a first rotating drum in contact with the first cable and configured to rotate at a first speed; and
a second rotating drum in contact with the second cable and configured to rotate at a second speed.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS

The instant nonprovisional patent application claims priority to U.S. Provisional Patent Application No. 60/840,110, filed Aug. 25, 2006 and incorporated by reference in its entirety herein for all purposes. The instant nonprovisional patent application is also related to the following provisional patent applications, the disclosures of which are incorporated by reference in their entireties herein: U.S. Provisional Patent Application No. 60/839,841 filed Aug. 23, 2006; U.S. Provisional Patent Application No. 60/839,855 filed Aug. 23, 2006; and U.S. Provisional Patent Application No. 60/840,156 filed Aug. 25, 2006.

BACKGROUND OF THE INVENTION

Solar radiation is the most abundant energy source on earth. However, attempts to harness solar power on large scales have so far failed to be economically competitive with most fossil-fuel energy sources.

One reason for the lack of adoption of solar energy sources on a large scale is that fossil-fuel energy sources have the advantage of economic externalities, such as low-cost or cost-free pollution and emission. Political solutions have long been sought to right these imbalances.

Another reason for the lack of adoption of solar energy sources on a large scale is that the solar flux is not intense enough for direct conversion at one solar flux to be cost effective. Solar energy concentrator technology has sought to address this issue.

Specifically, solar radiation is one of the most easy energy forms to manipulate and concentrate. It can be refracted, diffracted, or reflected, to many thousands of times the initial flux, utilizing only modest materials.

With so many possible approaches, there have been a multitude of previous attempts to implement low cost solar energy concentrators. So far, however, solar concentrator systems cost too much to compete unsubsidized with fossil fuels, in part because of excessive material and installation costs in the mechanical supports and solar tracking apparatus for the collectors. While many solar collectors utilize support trusses, their architectures lead to excessive material usage, and complicated and time consuming assembly and installation, rendering them unsuitable for large-scale solar farming.

In addition, conventional concentrator support systems require extensive grounds preparation, often making the land unsuitable for other uses and destroying natural habitats.

Accordingly, there is a need in the art for designs that efficiently and effectively support and align solar concentrators without an excessive installation burden.

BRIEF SUMMARY OF THE INVENTION

Embodiments in accordance with the present invention relate to the design of inexpensive mounting and pointing apparatuses for linear arrays of solar energy collectors and converters. Particular embodiments in accordance with the present invention disclose a rigging system comprising at least one, and preferably a plurality of, tensile cables onto which a plurality of solar modules are fastened. Such an arrangement provides a way of suspending solar modules over land, vegetation, bodies of water, and other geographic features without substantial perturbation of the underlying terrain. Certain embodiments comprise additional tensile cables fastened to the solar modules, such that differential axial motion of the cables produces a rotational motion component of the individual solar modules of the array. This rotational motion component effects an orientation control along one rotational axis.

One embodiment in accordance with the present invention further comprises a plurality of supports that provide for motion of at least one cable normal to its axis. This produces a rotational motion component of the individual solar modules of the array to effect an orientation control along a second rotational axis.

Certain embodiments provide for the common translation of a plurality of cables connected to the modules. This allows the array of modules to be translated normal to the axis. Another embodiment provides for the common axial translation of cables such that the modules can be translated in an axial direction.

Particular embodiments of the present invention may utilize a rotary actuator in concert with at least one winch drum having a variable cross section designed to feed and draw control cables attached to structures of the present invention, at appropriate and generally unmatched rates to effect a controlled motion of the structures.

Particular embodiments of the present invention may additionally comprise vibration dampers to reduce motion under wind loading, etc. Particular embodiments can employ one or more cable-based actuation systems to adjust orientation along rotational axes.

Particular embodiments may use ground mounted rigid posts to anchor the system and transmit compressive and other loads to the ground. Particular embodiments may further employ a system of guy cables and ground anchors to distribute loads to the ground and reduce bending forces in ground mounting posts. Particular embodiments of these ground anchors provide for adjustment of the relative guy cable position by means of a collet whose clamping force increases with guy-cable load. Particular embodiments of these ground anchors further provide for tightening of these collets via mechanical preloads provided by threaded elements. Particular embodiments of the ground anchors provide mounting and indexing features to support the use of a removable hydraulic cable tensioner tool which works in concert with the means of mechanical preloading to allow convenient and reliable cable-tension adjustment under high tensile loads. Particular embodiments of ground anchors further contain mechanical features to allow installation in the ground via a rotating tool that may further provide an axial compression or motion that may be coordinated with the rotation to drive the ground anchor into the ground. Particular embodiments of this tool and anchor may further provide for drilling a pilot hole for the anchor prior to or simultaneous with the driving operation.

An embodiment of a method in accordance with the present invention comprises fastening solar modules to at least one cable under tension, at least one of the cables connected to a damping element.

An embodiment of an assembly in accordance with the present invention comprises a solar concentrator supported by a tensile truss.

An embodiment of a ground anchor according to the present invention comprises a tube having a first end configured to contact the ground, and an open end opposite to the first end. A tapered collet having a flared portion is disposed within the tube and a narrow, threaded end protruding from the tube. A nut is configured to engage the threaded end and rotatable to clamp a cable disposed within the collet.

An embodiment of a method in accordance with the present invention of transferring tensile forces from a truss structure to the ground, comprises, in a first stage, drawing together a plurality of tensile cables to a group at a pivot, and in a second stage transferring tensile forces in the cables from the pivot to the ground.

An embodiment of a method in accordance with the present invention of rotating a truss, comprises, providing a truss having a first end and a second end and a contact point, the truss configured to rotate about a pivot point, and providing a driving mechanism. A first end of a first cable is connected to a first end of the truss, and connecting a second end of the first cable to the driving mechanism. A first end of a second cable is connected to a second end of the truss, and connecting a second end of the second cable to the driving mechanism. The driving mechanism is caused to pull on the first cable at a first rate and pull on the second cable at a second rate, such that the truss rotates and the contact point engages the first cable or the second cable, thereby imparting additional rotational moment to pivoting of the truss.

These and other embodiments of the present invention, as well as its features and some potential advantages are described in more detail in conjunction with the text below and attached figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a drawing of a high-concentration-factor two-angle tracking solar collector system that utilizes rigging, damping, actuation, and ground tackle according to one embodiment of the present invention. FIG. 1A shows details of an internal segment of the solar collector system in FIG. 1.

FIG. 2 shows a perspective view of a one-angle tracking solar collector system that employs rigging, damping actuation, and ground tackle according to an embodiment of the present invention. FIG. 2A shows an enlarged view of the system of FIG. 2.

FIG. 3 shows a simplified perspective view of a two-angle tracking solar collector system that illustrates rigging and actuation according to an embodiment of the present invention.

FIG. 4A shows a simplified schematic diagram illustrating one embodiment in accordance with the present invention. The embodiment of FIG. 4 a shows a three-cable rigging assembly of solar modules according to the present invention, wherein the assembly is controlled only at the termini.

FIG. 4B shows a simplified schematic view of a rigging assembly that is controlled at the termini and an internal point. Additional internal control points could be used to maintain control authority over large distances.

FIG. 5A shows a simplified schematic view of an embodiment in accordance with the present invention wherein common axial motion of the control cables translates modules axially. Such an embodiment would allow an operator to mitigate shading between rows of modules, for example.

FIG. 5B shows a simplified schematic view of an embodiment wherein common motion of the control cables normal to their axis translates modules accordingly. Such an embodiment would allow an operator to lower the modules for servicing, for example.

FIG. 5C shows a simplified schematic view of another embodiment in accordance with the present invention involving a three-cable rigging assembly of solar modules. In accordance with the embodiment of FIG. 5C, cable 3 moves axially with respect to cables 1 and 2 to rotate solar modules simultaneously.

FIG. 5D shows a simplified schematic view of another embodiment in accordance with the present invention involving a four-cable rigging assembly of solar modules. In accordance with the embodiment of FIG. 5D, cables 3 and 4 move axially with respect to cables 1 and 2 to rotate solar modules simultaneously. The use of one redundant cable prevents wind forces from producing large torques on the solar modules.

FIG. 5E shows a simplified schematic view of another embodiment in accordance with the present invention. In accordance with the embodiment of FIG. 5E, relative motion of the control cables normal to their axes produces rotational motion of the modules about the cable axis.

FIG. 6 shows a drawing of a truss element actuated via a circular pulley.

FIG. 7 shows a drawing of a truss element actuated via a material efficient drive scheme according to a component of an embodiment of the present invention.

FIGS. 8A-B shows views of a single drum roller according to a component of embodiments of the present invention that can actuate the truss element shown in FIG. 7.

FIG. 9 shows a double counter-rotating drum mechanism according to a component of embodiments of the present invention that can actuate the truss element shown in FIG. 7.

FIG. 10 shows a double co-rotating drum mechanism according to a component of embodiments of the present invention that can actuate the truss element shown in FIG. 7.

FIG. 11 shows a tensile truss utilized in the embodiment of the present invention in FIGS. 1 and 1A.

FIG. 12 shows a tensile truss that conveys a tensile load to other apparatus utilized in the embodiment of the present invention in FIGS. 1 and 1A.

FIGS. 13A-B shows two alternate three-dimensional tensile truss components of embodiments of the present invention.

FIG. 14 shows a compressive truss component of embodiments of the present invention for supporting tensile structures.

FIG. 15 shows a compressive truss component that provides for reduced solar collector shading and actuation using a material efficient scheme according to a component of embodiments of the present invention.

FIGS. 16A-D show views of a compressive truss having increased out-of-plane stiffness utilized in the embodiment of the present invention shown in FIGS. 1 and 1A.

FIG. 17 shows a detail of the out-of-plane stiffener.

FIGS. 18A-B show an embodiment of an end termination of an array in accordance with the present invention in which tensile cables are brought together in one stage and their tensile load transferred to a pivot axis in another stage and then to ground tackle in a third phase.

FIGS. 19A-C show embodiments of an end termination of an array in accordance with the present invention in which the outer sets of tensile cables are brought together in on stage, then the entire set of cables or the tensile loads of the cables are brought together to a pivot axis in another stage and then to ground tackle in a third phase.

FIGS. 20A-D show embodiments of posts and ground tackle for interior supports within the array.

FIGS. 21-21A show perspective and detailed views, respectively, of a ground anchor component of the embodiments of the present invention shown in FIGS. 1, 1A, and 2.

FIG. 22 shows a detail of cable-coupler plate that is a component of the embodiments of the present invention shown in FIGS. 1 and 1A.

FIGS. 23A-B show details of cable mounts employed by the embodiment of the invention in FIG. 1.

FIG. 24 shows a plan view of a 1 MW farm comprising sequential and side-by-side arrays of rigged solar modules.

FIG. 25A shows a sketch of a tensile truss according to an embodiment of the present invention constructed from a metal sheet.

FIG. 25B shows a sketch of part of a chain of tensile truss units constructed from a long metal sheet, roll, or continuous rolling operation.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments in accordance with the present invention relate to the design of inexpensive and minimum-material mounting and pointing apparatus for linear arrays of solar energy collectors and converters. Particular embodiments in accordance with the present invention disclose the design of a rigging system comprising at least one tensile cable onto which a plurality of solar modules are fastened, thus providing a means of suspending solar modules over land, vegetation, bodies of water, and other geographic features without preparation of perturbation of the underlying terrain. One such embodiment 100 is shown in FIG. 1. FIG. 1A shows details for a typical interior segment of the array in FIG. 1 for clarity.

Elements 102 in FIGS. 1 and 1A are two-dimensional solar concentrators that require accurate pointing and tracking of the sun along two rotational axes. In this embodiment, the diameter of these concentrators is 2.5 m and the distance between vertical posts is 20 m. The side-by-side arrangement of these concentrators provides cost advantages in the ability to share equipment, minimize the length of support conduits and cabling, etc.

One rotational axis, 104, coincides with the long axis of the rigging system. Each concentrator individually pivots about a second rotational axis 106 along a diameter that is perpendicular to the first axis.

Elements 108 are trusses comprised of elements under tension to provide stiffness in the plane normal to the second rotational axis of the concentrators. Elements 110 are tensile trusses that provide stiffness along the secondary axis and further provide a tension force along the diameter of the concentrators that assists with maintaining the relative position of elements within the concentrators and facilitates servicing of the concentrators. Elements 112 are pivoting compressive trusses that support the tensile trusses at positions in the interior of the array. Elements 114 are pivoting compressive trusses that support the tensile trusses at terminal ends of the array.

Element 116 is a multiple-element cable that includes a thermal management system that damps vibrations. Embodiments of such multi-element cables are described at length in U.S. Provisional Patent Application No. 60/839,855, filed Aug. 23, 2006 and incorporated by reference herein for all purposes. Elements 118 are liquid-air heat exchangers that provide additional vibration damping.

Compression forces are required to maintain tensile forces in the cable. The posts 120 and compressive trusses 112 and 114 support a portion of the compressive load, but the primary compressive backbone of the tensile truss is the ground on which the system is mounted via the ground tackle 122. Architectures according to embodiments of the present invention utilize the ground as the primary compressive structural element and thereby externalizes a significant amount of the structural material cost.

Elements 124 are features of the compressive trusses that facilitate actuation along the primary axis of the system. Elements 126 are cables that are drawn and fed from a specialized drum winch 128 to rotate the compressive trusses along the primary axis, thereby rotating the entire tensile truss system and concentrators. A similar actuation scheme is used on the secondary axes of the concentrators. The resulting relative motion of tensile cables pivot each concentrator.

Solar energy modules provide electricity, heat, or other conversion product approximately in proportion to the collection area of the module. To obtain high total collection area, there are several advantages to arraying multiple distinct solar modules rather than a single large solar module, e.g., for ease of distribution, installation, and service, to provide for more practical solar tracking, etc. One minimum material implementation of a solar collector is an inflated concentrator or “balloon” as shown in FIGS. 1 and 1A. As used herein, the term “balloon” refers to this specific type of concentrator but is intended to refer more generally to any type of solar energy collector, e.g., one-sun solar cells and modules, rigid concentrator mirrors, Fresnel lenses, etc.

The conventional approach to mounting solar modules is to use an extended truss made of beams and extrusions that support compressive loads and consequently require a significant amount of material to resist bucking and distortion under wind loading, or completely separate mounts, each individually tied to a solid surface, e.g., ground via concrete pads. Such conventional mounts may offer disadvantages in that they:

    • may require excessive material to support tensile loads and prevent deflection;
    • may require redundant mounting and pointing apparatus; and/or;
    • may require excessive preparation of or access to the terrain below the modules, impacting the use of land below the modules and potentially increasing the environmental impact of solar installations.

Moreover rigid structures must be designed not to buckle or fail in bending or shear under the heaviest design loads, which are generally far more severe than loads at the maximum operating loads. For example, a solar installation may be designed to survive a wind storm of 125 mph, but may be designed to operate efficiently only at a wind speed of 25 mph or lower. In this case, wind generated forces on the structure at the survival condition are 25 times larger than those encountered in the most severe operating conditions.

The use of flexible cables allows one to exploit the large difference between operating and surviving regimes. For example, cables can be pretensioned such that they always remain in tension under operating conditions but may become slack (under compression) under survival conditions. Because cables generally do not fail in bending or buckling, stress considerations require cables only to be designed to withstand maximum tensile loads under survival conditions.

Because pointing stability may be important in many applications, stiffness considerations typically drive the size of truss elements according to the present invention. Under tension, the axial stiffness and mechanical behavior of cables is not substantially different from that of a rigid cylindrical extrusion having the same material per unit axial length. For a given span and material use, elongational stiffness is typically far greater than bending or torsional stiffness. Embodiments according to the present invention are architected to rely substantially on axial stiffness, potentially driving a far lower material use per unit collector area than conventional collector mounts.

Possible disadvantages of minimum materials structures is their tendency to exhibit vibrational resonances. The deflection of such structures can be much larger for dynamic forcing than static forcing, particularly dynamic forcing having a spectral component near or at a vibrational resonant frequency.

Accordingly, approaches to mitigating dynamic deflections can include one or more various combinations of

    • increasing the cross-sectional area of structural elements to make them stiffer;
    • adjusting cable tension to drive resonances away from dominant excitation frequencies;
    • adding at least one node to at least one truss at periodic (repeating), aperiodic (non-repeating), or quasi-aperiodic (occasionally repeating) intervals;
    • adding at least one mass to at least one truss at periodic (repeating), aperiodic (non-repeating), or quasi-aperiodic (occasionally repeating) intervals, including unequal masses;
    • adding at least one spring to at least one truss at periodic (repeating), aperiodic (non-repeating), or quasi-aperiodic (occasionally repeating) intervals, including unequal springs;
    • constructing at least one truss at least in part from materials that intrinsically damp vibration;
    • constructing at least one truss at least in part from assemblies of materials or patterned materials that exhibit enhanced vibration damping over that of the component material or materials;
    • adding at least one vibration damper not directly associated with the truss assembly, e.g., liquid-filled bladders, straight and serpentine arrangements of tubes with or without gas pockets, multiple-element flexible cables, dash-pots, skids, elements that rub under vibration, and the like;

Certain embodiments incorporating these approaches to reduce dynamic deflections employ judicious material selection or operation (e.g., choosing a vibration damping cable material or an appropriate cable tension); provide secondary functions (e.g., using liquid-filled or gas/liquid channels that also facilitate thermal management). Other embodiments include features that can be installed conveniently in the field in response to observed vibration problems (e.g., liquid-filled or liquid-gas filled dampers that serve no other purpose, masses, or dashpots between truss elements or between cables and fixed objects).

Embodiments of the present invention accordingly employ a plurality of solid, i.e. able to resist static stresses, high-aspect-ratio tensile members. Alternative embodiments in accordance with the present invention may employ a plurality of non-solid members.

As used herein, the term “cable” may comprise at least one wire, extrusion, wire rope, natural or synthetic rope, weaves, fiber-reinforced composites, fiber-reinforced ropes, cable assemblies, and the like. In a particular embodiment, a flexible metal tape or strip that is able to buckle under compression without damage may be used. As used herein, the term “cable” may also refer to any structural member that is not required to support substantial bending loads or axial compression in normal operation, regardless of whether the actual member itself is able to support bending or compression. Thus, embodiments of the present invention provide for the use of one or more conventional compressive truss elements (such as angle extrusions, I-extrusions, C-extrusions, rods, tubes, or rectangular bars) in place of wire ropes or the like.

As used herein, the term “fastened” means at least partly constrained from relative translation in at least one direction or partly constrained from relative rotation in at least one direction over at least a finite range of motion. A further element of this invention is a method of fastening the balloon to the cables. The fasteners must attach the balloon firmly to the cable, and allow for smooth rotation during tracking. These fasteners may comprise of a swaged ball, sleeve, double sleeve, eye, cable tie, clamp, and the like. A preferred embodiment of the fastener is a loop of flexible material such as rope or wire that tightens around the cable and attaches to the balloon. Because the balloon is held by a single strand or cable, it is free to rotate around the axis of the strand or cable, while staying firmly attached. This replacement of bearings and sliding joints with cables that undergo elastic torsion is an element of other embodiments of this invention, including replacing a thrust bearing at the end termination of the arrays, etc.

One simple embodiment in accordance with the present invention comprises a single tensioned cable onto which multiple solar modules are fastened. However, such an arrangement may provide little rotational stability for the modules. Accordingly, another embodiment in accordance with the present invention comprises a plurality of tensioned cables spaced so that modules are fastened at two separate points, and are thus constrained in their rotation about the axis bisecting the cables than for a single cable. In accordance with a specific embodiment, the cables may be oriented substantially parallel to each other.

FIGS. 2-2A show perspective and enlarged views, respectively, of internal segments of one-dimensional tracking solar collector 200 according to an embodiment of the present invention that employs two such tensile cables. Elements 202 are tensile cables; elements 204 are compressive trusses; elements 206 are compressive posts; and elements 208 are solar collectors, e.g., solar panels. Elements 210 are optional vibration damper to reduce cyclical stresses.

Elements 204 are designed to support actuation using drawn and fed cables 212 in concert with a specialized drum 214. However, a wide range of alternative actuation schemes are possible, including but not limited to gear motors, ratcheting motors, motor driven pulleys or chains, rotary hydraulic or pneumatic actuators, linear electrical, hydraulic, or pneumatic actuators, etc. Alternatively, a fixed or manual adjustment is possible.

The expense and complexity of a more sophisticated cable truss like those in FIGS. 1 and 1A may not be justified for collectors having a cosine dependence of power on pointing angle error. However, considerations such as vibrational resonances and cyclical loading under large-scale vibrations may justify the use of stiffer designs. Such a non-tracking or one-dimensionally tracking collector array may be mounted substantially in an East-West orientation.

FIG. 3 shows a drawing of internal segments of a two-dimensional tracking solar collector 300 according to an embodiment of the present invention. Like in FIGS. 1-2A, the entire array pivots about one axis 302. In addition, each collector pivots about individual secondary axes 304 similarly to the embodiment in FIGS. 1-1A.

In the embodiment of FIG. 3, this rotation results from motion 306 of a control cable 308 with respect to another control cable 310 that doubles in this embodiment as a structural support cable. Pivoting tether points 312 convert the relative cable motion to rotary motion of the solar collector.

In this embodiment 300, the truss comprises a side of the collector, a compressive element 314 and a tensile element 316. Such a two-dimensional collector array may be mounted substantially in a North-South orientation, such that self-shading effects near dawn and dusk can be reduced by spacing parallel rows of these arrays further apart in the East-West direction, making less efficient use of land area, but more efficient use of the solar collector area.

In this embodiment 300, a damper 320 is connected to the truss through an element 318. Damper 320, may be a hollow member partially filled with liquid or a solid, functions to limit vibration or flutter of the truss in response to external forces such as wind.

Another aspect in accordance with embodiments of the present invention is the mechanism to provide common axial motion of cables fastened to the modules to effect axial motion of the modules as shown in the embodiment of FIG. 5A. Such motion is useful for example to minimize shadowing effects between adjacent rows of solar modules disposed on different cable systems at different times of day and different days of the year. This common axial displacement can be fixed at install time, manually adjusted, or actuated.

A further element of embodiments in accordance with this invention is a mechanism that provides for the common translation of at least the cables fastened to the concentrator in a direction having a component normal to the axes of the cables. This allows the modules to have a similar translation, as shown in the embodiment of FIG. 5B. This motion for example could be used to raise and lower an assembly of modules, for example for ease of installation or service, to mitigate wind loading, to minimize dust deposition, or to reduce shadowing effects.

A further element of embodiments in accordance with this invention is a mechanism that provides for the tension in the cables to be raised or lowered. For example, such a mechanism could slacken cables to facilitate lowering the array e.g., for maintenance, to avoid wind stresses, etc. This mechanism can be accomplished by any combination of the following: winch, block, cleat, pulley system, power winch, chock, clamp, and the like.

Another element in accordance with an embodiment of the present invention comprises a third control cable that is fastened to the module such that the relative axial motion of one or more cables produces a rotational motion component of the module. This third control cable thus provides for angular positioning of the module in one direction as shown in the embodiment of FIG. 5C.

In general, the number of cables in the tensile truss will be larger than the number of control cables. The number of control cables cited in these embodiments refers to structures having the kinematic effect of a control cable, i.e., the kinematic control cable could be an assembly of cables and compressive elements that could logically be replaced by a single cable to perform a kinematic operation.

Another embodiment comprises arranging the fastening points on the solar collector module such that the axis of rotation is substantially normal to the axis of the cables. Another embodiment in accordance with this invention, as shown in FIG. 3, comprises a fourth cable attached to the module. The fourth cable is used in conjunction with the third cable, such that the differential axial motion of the third and fourth cable with respect to the first and second cable produces a rotational motion of the module as shown in FIG. 5D. The fourth cable is kinematically redundant, but can reduce the stress or moment associated with rotation or wind loads on the solar collector module.

Another embodiment of the present invention comprises an arrangement of six cables disposed such that relative motion of three substantially parallel pairs of cables effect substantially the same rotation to two concentrators arranged side-by-side. Such a configuration is employed by the embodiment shown in FIGS. 1 and 1A. Such an arrangement uses a rigid connection between the concentrators to obviate one pair of control cables.

Another embodiment of the present invention comprises an arrangement of seven cables having the same structure as the six-cable system, but providing an extra control cable at the center. Such a configuration can reduce torsional loads or stresses in the connection between the concentrators.

Another embodiment of the present invention comprises an arrangement of eight cables to service two side-by-side concentrators. In such an arrangement, the connection between concentrators, if any, does not necessarily bear any pointing-related loads.

A further element in accordance with an embodiment of the present invention comprises a mechanism for rapidly rotating the solar modules, e.g., in response to a serious fault such as critical overheating. A rotation mechanism in accordance with an embodiment of the present invention may comprise a manual or automatic release mechanism. Such a release mechanism could be automatically or manually restored to an operating position.

A further element in accordance with one embodiment of the present invention comprises a mechanism that provides for motion having a component normal to the cable axis of at least one cable relative to other cables such that the solar modules experience a motion having a rotational component.

A further element in accordance with one embodiment of the present invention comprises a mechanism that provides for motion of all cables fastened to the solar modules in the trajectory of a substantially rigid-body rotational motion about some axis. Such cable motion produces a rotational motion of the solar modules having a component in the axial direction of the cable, as shown in FIG. 5E and the embodiments in FIGS. 1-3. It is preferred that the axis of rotation coincide with a point on the mechanism that is substantially free of moments from the cable tension and can rotate about a pivot that is substantially under tension.

Actuation

Because the cables only support tensile loads substantially, a coordinated motion of such mechanisms could occur at least near the two ends of the cables, as shown in FIG. 4A and possibly also at points in between, as shown in FIG. 4B and the embodiments in FIGS. 1-3. This coordinated motion can be accommodated by the use of a wide variety of mechanisms or schemes, including rigid mechanical linkages, slaved servo motors, rotary electrical, pneumatic, or hydraulic actuators or motors or linear electrical, pneumatic, or hydraulic actuators, etc. The motion of the actuators could be coupled to the truss through one or more gears, pulleys, chains, timing belts, etc.

Any of the above arrangements could support embodiments in accordance with the present invention. However, a preferred implementation may employ one or more additional cables in tension whose axial motion produces a common actuation of all mechanisms.

Such a cable or cables could turn a pulley, preferably designed to index to features on the cable in the manner of a timing belt, which drives a rotational element such as a gear, gear train, a wheel or wheel segment or the like to actuate coordinated motion. The actuation cable may contain cable splices or shunt connections, e.g., via swages or clamps to facilitate actuation of a mechanism or mechanisms that lied between the cable terminal. Alternatively the actuation cable itself can be used directly or via a pulley or other force-direction-changing element to actuate mechanisms by applying tensile forces.

In certain embodiments, the tensile forces may be resisted by a combination of spring forces, or tensile forces from a complementary cable. In accordance with one embodiment, the complementary cable is an extension of the same cable moving in substantially the opposite direction, e.g., through the action of a 180 degree, direction changing pulley. Another preferred embodiment employs the complementary axial motion of two splices on complementary sides of the same cable.

Such actuation cables may not be sufficiently stiff to actuate over long runs. In some embodiments according to the present invention, actuation mechanisms can be placed at shorter intervals than an entire array to increase stiffness and provide for better wind-load handling.

FIG. 6 shows an illustration of a pulley system 600 for actuating the rotation of a support truss 602 relative to a smaller pulley 612 from the frame of reference of the truss. In this frame, the smaller pulley moves in an arc 614 about the pivot point of the truss. Cable 608 and 610 are simultaneously drawn and fed to produce this motion. Possible advantages of using a circular pulley or arc segment B for this rotary actuation may the same rates of feeding, and drawing 608 and 610 are identical, and that the rotation rate at a given feed rate is constant. A possible disadvantage of using a circular-arc pulley is the need for significant material simply to maintain the circular shape of the pulley.

In the illustrated material efficient pulley 604, the region between spokes is subject to bending under belt tension. Such bending can reduce the stiffness of the actuation and reduce tracking accuracy under wind, gravity, and inertial loading. An amount of material may be needed to make a sufficiently stiff pulley to maintain rigidity. Moreover the rotation forces can only be transmitted to the truss frame at points such as 606 where the pulley is near the truss elements. If these connection points lie in the interior of a truss element, the strength and stiffness of the actuation further relies on the bending strength and stiffness of the truss elements.

Other embodiments in accordance with the present invention alternatively use a minimum material cabling scheme that substantially eliminates bending. This alternative approach may utilize existing elements of compressive truss assemblies.

FIG. 7 shows an embodiment 700 of such an actuation method, taking the frame of reference of the truss. The compressive truss 702 is rotated about its pivot point 720 by drawing and feeding cables 708 and 710 using mechanism 712. Driving mechanism 712 can alternatively be mounted on the truss to be actuated and the cables 708 and 710 pull on points and over pivots that lie in another frame of reference, e.g., that of the ground or of another truss element. The cables 708 and 710, which can be portions of the same cable or two distinct cables, pull directly on the truss at points 716.

Over some angular range, 708 and 710 lay across a contact point 718 that is held in place by the truss members 704. This contact point prevents the lever arm between the cables 708 and 710 and the pivot from varying too greatly with the rotation of the truss. The contact point 718 and the two points 716 can be viewed as a triangular approximation of a circular arc. The use of additional pivot points can provide a better arc approximation, if warranted. As the truss rotates around its pivot, the driving mechanism 712 moves relative to the truss along an arc 714.

A possible advantage of this arrangement is material efficiency for a given actuator stiffness: the actuator stiffness is primarily derived from the axial stiffness of truss elements. Moreover truss elements that support a pivot can confer other advantages.

For example, in the embodiment of a truss in FIG. 7, the pivot support elements 704 redistribute compressive stresses in the truss in such a way that less material can be used in other elements. The only truss part required specifically for actuation is the end of the member forming the contact point 718, which is compact and simple compared to the extra wheel in FIG. 6 (604).

The approach shown in FIG. 7 could offer a disadvantage in the need to draw and feed cables at different rates and at rates that vary with the position of the truss. However, this could be overcome by operating a coordinated pair of motors driving, e.g., conventional drum winches to feed and draw cables separately.

Alternatively, a mechanical ratching device could be produced that exploits the finite elasticity of the control cables and structure to allow a single motor feed and draw cables alternately while not detensioning the cables. This arrangement has the advantage of being able to regulate the cable tension by adjusting the relative amounts of drawing and releasing from their kinematically matched ideal. However, it has the disadvantage of mechanical complexity, the need for ratchets and pawls to be operated frequently under load and the need for the complex mechanisms to withstand loads at full rated wind speed, unless a separate braking mechanism is employed.

An embodiment of the actuation motor employs a specially designed drum that, by construction, feeds and draws cables when rotated at substantially the kinematically matched rates required of the truss as shown in FIGS. 8A-B. The drum can further be designed such that the rotation rate of the truss is constantly proportional to the rotation rate of the drum regardless of angle.

The design of such drums is straight-forward, but may require iteration. A first step is to analyze the trajectory of the cable mounting and pivot points, truss pivot points, and the position of the drum or drums. In a first iteration, the drum can be approximated as having a fixed cable diameter. The required feed and drawing rates for all truss angles could be calculated.

The instantaneous drum radius should be approximately equal to the respective feed or drawing rate required. The drum radius vs. angle curve can then be iteratively refined taking into account the actual cable angles, out-of-plane motion, and cable stretch.

The cable stretch calculation may take into account static loads on the actuator cables, e.g., from the system weight as well as cable pretension. A highly refined drum design may result in less tension variation in actuator cables and improved absolute angular accuracy, etc. Because of the finite rigidity of all the elements of the actuator system, however, an approximate drum design may suffice. It is possible to accommodate drum inaccuracy by the addition of a compliant support, however this lowers the stiffness of the actuator. Not all arrangements of drum, pivots, and attachment points can be accommodated by a drum e.g., since cables will not follow a local indentation in the drum radius but will skip from one tangent surface, over the indentation, to the next tangent surface. Such ill-conditioned drums are typically encountered with ill-conditioned geometries, e.g., sharp pivot points.

To avoid such trouble, cable pivots may be tailored curves or simple arcs designed such that cables engage and disengage with the pivots at a point that where the surface is substantially tangent to the disengaged cable path. If cable pivots are made too large, they may reduce stiffness by producing off-element-axis loads that contribute to element bending.

Because the truss and its angular rotation range is symmetrical, the drum in FIGS. 8A-B can be decomposed into a pair of identical drums placed back to back. In some embodiments according to the present invention, these drums can be separated and mounted such that they counter rotate at the same rate, as shown in FIG. 9 or co-rotate as shown in FIG. 10. Both co-rotating and counter-rotating arrangements provide for convenient driving from a single rotary actuator (e.g., motor, crank, etc.)

In some embodiments of the present invention, the relatively large diameter of the drum relative to common motor shaft diameters can be exploited to provide a significant effective gear ratio, e.g., by the use of a small spur, worm, or helical gear on the motor shaft and a circumferential spur or helical gear mounted, cast, or machined onto one or more drums. Such an arrangement can obviate or mitigate any additional gearing requirements on the rotary actuator that turns the drums. Multiple drums could also be actuated by drawing a cable, pulley, or timing belt, as described earlier to reduce the number of actuator drives. In the co-rotating arrangement in FIG. 10, both cables lie in substantially the same plane perpendicular to their axes of rotation. It is also possible to coordinate an axial motion of one or drums with rotation such that the out-of-plane motion of the cables is substantially suppressed.

In some embodiments of the present invention, a braking device or mechanical latch can be deployed to lock the position of the array, for example, in preparation for a severe windstorm. Such a latch may be deployed in positions throughout the angular range of travel or at one or more specific “home” positions.

Oscillation Damping and Suppression

If all cables have a similar catenary shape under loading of the modules and the cables are parallel to each other, no module rotation arises from the lowest order modes of oscillation of excited cables (e.g., by wind forcing). This feature is useful for solar modules that employ solar concentration at high concentration factors, since unintended rotation produces angular misalignments that seriously reduce the module efficiency.

However, higher-order oscillation modes can produce angular misalignments. An element of embodiments in accordance with this invention is to deploy oscillation damping elements on the cables to reduce high-order oscillations, including damping elements that cross from one cable to another and elements that propagate along one cable. Such damping elements could include rigid or flexible conduits partly filled with liquid, (e.g., water), gels, pastes, emulsions, thixotropic materials, colloidal suspensions, fibers, or granular materials (e.g., dirt, sand, sawdust, and the like), or flexible conduits that are substantially filled with liquid and possibly suspended particles, such that sloshing of the liquid under forcing from the cable oscillation damps the oscillation energy, as shown in the embodiments in FIGS. 1-2.

A particular embodiment in accordance with the present invention could employ such conduits further as heat exchange components for the solar modules, using a coolant as the liquid. Alternatively, aerodynamic flutter dampers could be employed similar to those used on power cables in windy areas.

Low-order relative oscillations of the cables toward and away from each other can produce compressive and tensile stresses on the solar modules that could affect their function or lifespan. One or more linkages that support compression and/or tension fastened between cables substantially normal to the axis of the cables can reduce such damage or degradation. These could be inserted where needed. Relative axial motion of cables produced by flutter could be suppressed by an arrangement of such linkages inclined at an angle with respect to the normal of the cable axis. Such linkages can kinematically support any relative cable motion that is desired to point the solar modules.

Tensile Trusses

The simplest tensile truss is a tensioned cable. Such a truss generally has considerably larger stiffness in the axial direction than directions perpendicular to this axis. A tensioned cable resists axial deflection with a force that is initially linear with the ratio of the displacement to the cable length, whereas the resistive force to perpendicular deflections is initially of third order in the ratio of the displacement to the cable length and therefore is much less stiff to forces perpendicular to the cable.

Some applications, such as unconcentrated or low-concentration-factor solar collectors may tolerate large perpendicular deflections. Other applications require greater stiffness and the use of a more complicated tensile truss structure.

The stiffness of cable systems according to the present invention can be increased by the use of tensile truss structures such as that shown in FIG. 11. This tensile truss 1100 is part of the embodiment shown in FIGS. 1-1A.

The primary cables 1102 are tensioned sufficiently that the transverse elements (here vertical cables) 1106 are substantially under tension in normal operation. A third cable 1104 can provide stiffness along its axis. An axial deflection of a transverse element is resisted by axial stiffness of cable 1106 and of the cables 1102. That is, vertical motion of an element requires a first-order axial displacement of cable 1102. Without such a tensile truss, the resistance of a cable to deflection perpendicular to its axis builds up far more slowly, initially as the cube of the displacement. However, this stiffness advantage can be lost depending on how cables 1102 are supported.

Some embodiments of the present invention utilize compressive trusses to constrain cables 1102 substantially against motion perpendicular to their axes. Such embodiments rely on substantially spatially uniform wind loading within the interior of a series of tensile trusses to suppress differential axial displacements by symmetry.

Other embodiments utilize additional compressive trusswork at various positions, e.g., periodic, aperiodic, or quasi-aperiodic, within a series of tensile trusses to stiffen the truss against differential axial displacement of cables 1106. Other embodiments utilize modest bending stresses and beam flexure to resist or mitigate these unwanted displacement. In situations where differential axial motion of cables 1102 is produced by wind loading, these displacements are likely to be cyclical or vibrational. In some embodiments of this invention, such cyclical displacements are mitigated by the use of dampers, as previously discussed.

Alternative tensile truss architectures according to embodiments of the present invention include designs such that additional tensile cables and stretch from points on compressive trusses or some or all of the vertical cables 1106 are eliminated by stretching cables directly to the proximity of mounted apparatus.

FIG. 12 depicts another element of the embodiment shown in FIGS. 1-1A. In particular, FIG. 12 shows a split tensile truss 1200 in which the elements 1206 may comprise apparatus related to the concentrator.

Minimum material and robust concentrator designs may benefit from the application of tensile forces. For example, in the embodiment shown in FIGS. 1-1A, the tension in element 130 is used to reduce material in the mount of a solar receiver module and provide a convenient method for mounting and dismounting concentrators with access only to the outer edge of the truss e.g. location 132. Like the truss in FIG. 11, this tensile truss also stiffens the system.

FIGS. 13A-B show two embodiments of tensile trusses according to the present invention that comprise a three-dimensional frame. Such frames are useful for providing stiffness or tensile forces in multiple directions.

The frame 1300 being comprised of a folded tensile truss 1302 is a simple way to produce tensile forces 1304. However, displacement between a center of load 1308 and the primary tensioning cables can produce a moment that rotationally deflects the array, as indicated by 1306. This folded-truss frame may thus be less useful for high-precision-pointing applications.

In contrast, the more complicated frame 1350, a part of the embodiment shown in FIGS. 1-1A, substantially avoids such moments and their resulting rotational displacements.

Compressive Trusses

The architecture of embodiments according to the present invention utilizes the ground as a primary compressive element, but it is generally impossible to eliminate additional compressive elements in any non-trivial design. As used herein, a compressive truss is an assembly of at least one structural element such that at least one structural element in the assembly experiences compressive loads during normal operation.

A design goal of compressive elements according to the present invention is to minimize the overall structural material costs for a given mounting rigidity. The simplest compressive “truss” is a single element that constrains the motion of at least one cable.

For example fixed-angle collectors according to an embodiment of this invention could be mounted on a tensile truss strung between at least one post and terminated by at least one ground-mounted cable. In this embodiment, the compressive truss is simply the post.

Many embodiments of the present invention utilize at least one post as a compressive element, generally but not universally in concert with additional ground tackle such as cables and ground anchors. Such posts can employ their resistance to bending to stiffen the rigging system in addition to or alternative to their compressive stiffness. If bending resistance is required, including to resist loads that directly produce bending or to prevent buckling, preferred embodiments of such posts are those having a large product of elastic modulus and second moment of inertia in relation to their unit mass cost.

Generally, other favorable factors include good vibration damping ability. Favorable materials are wooden beams and poles, e.g., utility poles, “railroad ties,” pressure-treated, creosoted, or otherwise environmentally protected lumber, redwood, pine, spruce, etc., straight and tapered steel and aluminum extrusions, and the like as is well known in the art. Other favorable materials include concrete-, sand-, dirt-, foam-, or gravel-, and water-filled hollow materials, etc.

In embodiments that require one- or two-angle tracking of the sun, at least one additional compressive truss element is needed. This element can be as simple as a single element that supports more than one tensile element supporting collectors and is actuated by rotating the element through moments applied to the element. Alternatively, a single compressive element could be actuated by one or more elements. These elements could be compressive, e.g., a thrust rod from a linear actuator, or tensile, e.g., a cable connecting with an actuator.

Additional elements to the compressive truss may be added for a variety of purposes. Examples of such purposes include but are not limited to, increasing static or dynamic stiffness per weight or cost, avoiding or minimizing shading of collectors, supporting actuation, and supporting ancillary hardware such as interconnections and heat exchangers, etc.

FIG. 14 shows an example of a tensile truss designed to support tandem collectors according to an embodiment of the present invention. This truss 1400 is designed to support rotation about the pivot point 1402. The compressive arms 1404 typically are designed to avoid buckling under stress loads. The circular tube geometry shown has a large specific second moment of inertia per unit material, but alternative cross sections, e.g., I-beams, C-channels, square or rectangular extrusions, substantially solid wood, may be more favorable given application-specific loading and vibration damping requirements, etc.

Element 1406 supports a tensile truss as in FIG. 12. Elements 1408 and 1410 support a tensile truss as in FIG. 11. The combination of these trusses has the geometry of FIG. 13B (1310 and 1312). Element 1412 is a feature to provide for passages of cables, e.g., FIG. 11 (1104).

By design, this truss can be constructed from a minimal number of different components or differently designed parts. However, it contains no means for actuation and requires different-thickness cables for the tensile truss in 1410 and 1408 to equate displacement under load since the cable connected to 1410 may be loaded with more force (for example twice the force) than the cable connected to 1408, due for example to the forces of wind and/or gravity.

FIG. 15 shows another embodiment of a truss design. The truss 1500 pivots about 1502. Elements 1504 support a tensile truss cable a 1506. Their tension preloads element 1508 with a tensile force that offsets the compression developed by constraining the other tensile truss at points 1510.

A difference between this truss design and others, is the incorporation of the element 1518 used with cables 1520 and pivot 1522 to support rotary actuation as described previously. A pretension in 1520 redistributes loads such that the elements 1514 are always under tension in operation. For this reason, in this design, 1514 can take the form of a cable or a low-profile rigid member such as a rod or slender bar, which is fortuitous because it is in a position to shade concentrators at certain times of the day and year.

One issue with both of the substantially planar designs shown in FIGS. 14 and 15, is their reliance on shear, torsion, and/or bending to resist out-of-plane twisting. Such twisting could result from unbalanced or dynamic wind forces.

FIGS. 16A-D show different views of an alternate design taken from the embodiment shown in FIGS. 1-1A, that employs an out-of-plane truss structure to stiffen the compressive truss against out-of-plane deflection. In addition to the element in FIG. 15, the design 1600 in FIGS. 16A-D contains tensile elements 1602 and compressive elements 1604, which act in concert to produce a linear axial displacement of one or more elements to out-of-plane deflections (except for rigid-body rotations of the entire assembly). The benefit of such out-of-plane stiffness depends on the nature of wind loading (uniform vs. non-uniform) and the ability of the structure to dampen vibrations. In some embodiments of the present invention, such out-of-plane stiffening may be deployed only where needed, at periodic, a-periodic, or quasi-periodic intervals.

The cost in installation time and complexity of such out-of-plane stiffeners may be an important consideration. FIG. 17 shows details of the interior compressive truss design 1700 of the embodiment in FIGS. 1-1A. Element 1702 is a screw adjustment that can extend or shorten compressive element 1704. Extending element 1702 flexes and/or rotates element 1706 such that the cables or cable 1708 that cross at the intersection of 1704 and 1706 can be tensioned. Such an adjustment feature is favorable because it can eliminate costly hardware like turnbuckles, etc. Moreover, provision for such elements can inexpensively be built in to a system and only actually installed if the conditions warrant.

End Terminations

The ends of rows of cables may require special treatment, owing to a need to transfer tensile forces from the tensile trusses to the firmament. One treatment could be to anchor one or more cables to one or more rigid posts fixed in the firmament, with or without reinforcements to relieve bending stresses and limit deflection of the posts. These reinforcements could be cables or compressive truss elements as known in the art.

A more complex termination scheme may be needed if the system tracks the sun through one or two angles. For example, one or more cables could be anchored to a rigid bar which can pivot on a rigid structure that is fixed in the firmament. In such arrangements, elements of the termination are operated in bending, and therefore may require excessive amounts of materials, particularly for structures that are more than 5 meters across as the embodiment in FIG. 1. In accordance with the architectural methodology in accordance with the present invention, certain embodiments of end terminations rely substantially on axial forces on elements and make maximal use of tensile elements to reduce material cost.

A tensile collector support structure according to certain embodiments of the present invention typically contains more than one cable spaced apart. In order to allow such cables to pivot about an axis, these cables or the tensile forces they bear, may be combined to a relatively small region disposed about a pivoting axis, and to transfer the loads from a relatively small region disposed about this pivoting axis to the ground.

In some embodiments, the transfer of tensile stresses to the ground involves two stages. The first stage is a simultaneous drawing together of cables or the tensile forces to a pivot, e.g., by forming a cable bundle, mechanically mating cables to a common rigid part or secondary cable, etc. The second stage is the transfer of those forces from the pivot to the firmament, e.g., by bringing one or more cables or tensile elements to ground anchors or footings or by (less materially efficiently) by compressive elements or bending forces.

The ability of cables to twist substantially without fatigue provides an opportunity to obviate a separate pivot means, e.g., shaft in a bearing or bushing. A cable segment that is one hundred to preferably 1000 times its strand diameter or more in length can repeatedly twist 180 degrees with minimal degradation. Such cable segments can comprise an inexpensive pivot according to the present invention.

In many embodiments of the present invention, it is desirable to distribute the load to multiple ground anchors or footings. In some embodiments, it is cost effective to form a bundle from tensile support cables, use the bundle itself as a pivot or pass the bundle through a separate pivot structure, then split more than one of the cables from the bundle to go to separate ground locations.

In some embodiments, such as that in FIG. 1, the tensile structural cables are displaced asymmetrically about the pivot point. This displacement is often necessary to provide for a full angular pivot range and to provide for side reinforcement of interior posts, etc. In such cases, a component of the force in the tensile structural cables is transmitted to the elements, pivot, and post of the adjacent compressive truss when the cables are brought in line with the axis. This additional loading may require significant changes to the design of the compressive truss and ground tackle near the termination. Alternatively, or in conjunction, stages can be added to the transfer of the tensile forces from the truss structure to the ground.

FIGS. 18A and B show views of a termination having three such transfer stages. (FIG. 18A is an end view in which only one of the posts is visible) In the first stage, the tensile cables 1802 are brought together in a group to a cable plate assembly 1804 that is at an axis that mitigates the unusual loading profile on the last compressive truss (indicated by the dashed lines). A compressive element 1806 takes a substantial amount of the unbalanced load from transferring the tensile forces to the pivot axis in the second stages and transfers these loads to the firmament. The remainder of the tensile loads are transferred to the firmament in the third stage.

In order to retain the rigidity of the tensile truss system, the angular position of the cable plate may be rigidly controlled, e.g., via a minimum material actuation means 1808, or a wide range of alternative techniques as previously disclosed. Moreover, it may be advantageous to add a truss 1810 to stiffen the termination system.

The termination embodiment in FIGS. 18A-B produces a large internal compressive force on the last compression truss. FIGS. 19A-B show an alternative embodiment of a three-stage termination design in which the cables are grouped or their forces brought to a compact location at the location of the pivot 1908 after a plurality of cables, e.g., the outer set of cables 1904, are combined to a second group, e.g., are bundled, or their carried forces otherwise brought to a compact location 1906. The reaction force needed to support this redirection of forces is provided by the truss system 1910, which may further serve as a component in a minimum materials actuation system.

FIG. 19C shows an alternative embodiment that comprises a tetrahedral truss mounted with one edge along the pivot axis. This tetrahedral truss utilizes at least two compressive elements 1918. The other four elements, e.g, 1920, 1922, and 1924 may be purely tensile. In the embodiment shown, this tetrahedral truss derives sufficient torsional stiffness with respect to the last interior compression truss 1902 from the arrangement of cables, compressive elements, posts, and ground tackle to obviate a separate rotation actuator. In other embodiments this tetrahedral truss may be actuated to further stiffen the system.

In the design in FIG. 19, this actuation system could employ the same apparatus and drum used by interior actuators. One aspect of this particular design, however, is that the arms 1912 of the truss 1910 are long and may be heavily loaded, possibly requiring excessive material to avoid bucking. In accordance with an alternative embodiment of the present invention, the truss can be designed such that cables combine more closely to the pivot point to reduce forces and compressive element length.

A wide range of alternative staging architectures according to the present invention may be designed by one skilled in the art. Possible architectures include those that minimize material, reuse components used elsewhere, minimize footprint, etc. Some embodiments of a termination in accordance with the present invention provide for substantial open area between ground elements, e.g., 1914 and 1916, such that maintenance vehicles or traffic can pass through this region at least part of the day. Particular embodiments in accordance with the present invention are envisioned to have access and service roads routed among and through terminations.

The mechanism that tensions the ends of the cables should be able to support the cable tension along with any lateral forces or increased tensile forces produced by the wind. One embodiment of such a mechanism is a truss which uses the cables as tensile elements and a minimum number of compressive elements to perform its function, since that arrangement should provide for minimizing the number of cable attachments and the truss material, and therefore minimizing cost.

An embodiment of a linkage between the terminal mechanisms and a mounting firmament is a pole placed or recessed in the firmament and guyed such that the pole substantially bears a compressive stress and the guys bear a tensile stress that is communicated to the mounting firmament via mechanical connectors, stakes, concrete pads or the like. As used herein the term “firmament” means a load supporting structure such as a roof-top, wall, paved surface, ground, bedrock, lake bed, ocean floor, etc.

Embodiments in accordance with the present invention may comprise additional tensile cables fastened to the solar modules. In accordance with such embodiments, differential axial motion of cables produces a rotational motion component of the individual solar modules of the array to effect an orientation control along one rotational axis.

An embodiment in accordance with the present invention may further comprise a plurality of supports. Such supports provide for motion of at least one cable normal to its axis to produce a rotational motion component of the individual solar modules of the array to effect an orientation control along a second rotational axis.

An embodiment in accordance with the present invention may further provide for the common translation of cables connected to the modules, such that the array of modules can be translated normal to the axis. Other embodiments in accordance with the present invention provide for the common axial translation of cables such that the modules can be translated in an axial direction.

FIGS. 20A through D show several embodiments of mounting systems used to transfer loads to the firmament. These examples show the use of a post 2002 mounted in the ground whose surface is indicated by 2004.

Element 2006 is a ground anchor, footing, or other mounting element. Element 2008 is a cable arrangement, gusset plate, truss, or other optional reinforcement that relieves the post of bending stresses while providing room for cables crossing from the collectors and collector supports.

FIG. 20B shows a detail of the top region of the mount shown in FIG. 20A. In this embodiment, the reinforcement 2010 is arranged to provide a pivot for a compressive truss that is clear of cables. For example, the cable 2010 could pass through a hole in a hollow shaft 2012 or be mounted to 2012. In this embodiment, 2012 endures cantilever loads and bending from tension in 2010. Because of the relatively compact geometry, the element 2012 can be designed to handle such loads without excessive bending, stress, or cost.

FIG. 20C shows an alternate mounting system in which mounts are guyed on one side only, leaving the other side clear of cables. The dots 2013 indicate the cooperation of other structural elements not shown. In such an embodiment, it is preferable to alternate or vary the side that is guyed.

FIG. 20D shows an alternate arrangement in which a single anchor is shared between two posts to prevent axial motion. This arrangement may have advantages in material efficiency and convenience of installation, however, the ground tackle must be designed to resist side loads.

The mechanism that tensions the ends of the cables should be able to support the cable tension along with any lateral forces or increased tensile forces produced by the wind. One embodiment of such a mechanism is a truss which uses the cables as tensile elements and a minimum number of compressive elements to perform its function, since that arrangement should provide for minimizing the number of cable attachments and the truss material, and therefore minimizing cost.

An embodiment of a linkage between the terminal mechanisms and a mounting firmament is a pole placed or recessed in the firmament and guyed such that the pole substantially bears a compressive stress and the guys bear a tensile stress that is communicated to the mounting firmament via mechanical connectors, stakes, concrete pads or the like. As used herein the term “firmament” means a load supporting structure such as a roof-top, wall, paved surface, ground, bedrock, lake bed, ocean floor, etc.

Embodiments in accordance with the present invention may comprise additional tensile cables fastened to the solar modules. In accordance with such embodiments, differential axial motion of cables produces a rotational motion component of the individual solar modules of the array to effect an orientation control along one rotational axis.

An embodiment in accordance with the present invention may further comprise a plurality of supports. Such supports provide for motion of at least one cable normal to its axis to produce a rotational motion component of the individual solar modules of the array to effect an orientation control along a second rotational axis.

An embodiment in accordance with the present invention may further provide for the common translation of cables connected to the modules, such that the array of modules can be translated normal to the axis. Other embodiments in accordance with the present invention provide for the common axial translation of cables such that the modules can be translated in an axial direction.

Ground Tackle

An element of embodiments according to the present invention is to externalize the cost of the primary compressive backbone of a solar collector system. Interfaces of the system to the ground is of interest for such installations.

Ground anchor solutions are well known in the art. A particular embodiment of a ground anchor 2100 for use in accordance with embodiments of the present invention is shown in FIGS. 21-21A. In FIG. 21A a high-torsional-strength structure, e.g., a square or circular tube or pipe is connected to a broad helical feature 2104, as is known in the art of ground anchors.

The end of the tube 2102 may optionally contain a feature 2106, e.g., a chamfer that sharpens the edge, serrations, which assist with cutting and displacing soil, clay, or rocks, etc. Toward the top of the body 2102, is a feature 2108 that provides for engaging with a rotary tool to drive the ground anchor. Such a rotary tool may further provide an axial force or preferably displacement coordinated with rotary motion such that the helix 2104 drives smoothly into the firmament.

The length of 2102 and the dimensions of 2104 should be sufficient to hold required loads for a given firmament. The size and material thickness of 2102 should be coordinated with its length and the dimensions of 2104 such that the torsional or compressive strength is at least often not exceeded while driving the anchor into the firmament.

Element 2110 is a collet that holds at least one cable in its bore 2112. A taper of the collet 2114 and anchor cap 2116 ensures that when the collet is loaded, e.g., through the action of a nut 2118 on a thread, the assembly firmly clamps a cable or cables passing through 2112. This taper further ensures that tension in the cable acts to increase the clamping load on the cable.

The tapers can work several ways. In one embodiment, the tapers of the collet and cap are substantially matched. In the embodiment shown, the tapers of the collet and cap are different such that compressive forces on the cable are concentrated further down the collet. Such a mismatch in taper may provide for enhanced “binding” of the collet and the cap and lower long-term reliance on continued cable tension or the pretension from 2118.

The feature 2120 on the anchor is designed to mate with a hydraulic cable tensioner. Such a tensioner can clamp or threat on such a feature, clamp to the cable held by the anchor and make adjustments of the cable length to achieve a desired tension or displacement.

Connected to the feature 2120, the hydraulic tensioner apparatus can further “unbind” or unclamp the collet 2110 e.g., by turning a nut 2118, then pressing 2118 toward the cap 2108 or by otherwise releasing a pretensioner 2118, including cases in which the pretension is manually released, e.g., by manually turning a nut. Such a device could further provide for automatic or manual pretensioning following the adjustment, e.g., by a reversal of the steps to release the cable from the clamp.

In several positions of the embodiment shown in FIGS. 1-1A, one or more tensioned cables are preferably coupled to one or more other cables. For example, FIG. 22 shows a cable plate 2202 that provides linkage between eight highly tensioned cables 2204 that comprise the main tensile structure of the truss and 2206, a cable that communicates the combined tensile forces to the end terminations of the apparatus. An alternate embodiment of this plate couples these cables with multiple cables to the end terminations.

One method of combining cables known in the art is the use of various crimps and clamps. The advantage of using a cable plate as in FIG. 22 is that individual cables can be more easily tensioned.

As with the ground anchor in FIGS. 21-21A, the cable plate employs collets, tapered holes, and pretensioning nuts to clamp cables. Also like the ground anchor in FIGS. 21-21A, the clamping structure contains a mounting feature for a hydraulic tensioner apparatus.

An aspect of certain embodiments of the present invention is the ability to flex, bend, or roll at least some of the tensile structure when not under tension. This can provide for prefabrication of dimensionally accurate assemblies, convenient distribution, and convenient and accurate assembly in the field. For example, complete sections or multiple-section runs of these cable assemblies could be manufactured using automated apparatus and distributed on spools, rollers, or other convenient distribution aides. Accordingly, any element connected to the cables in such embodiments may be sufficiently flexible or compact and strong to avoid damage when assemblies are flexed.

FIGS. 23A and B show designs of cable connections that illustrate features of such cable connectors. The design in FIG. 23A provides for attaching two substantially orthogonal cables 2306 and 2308 via sandwiching them between two compact rigid stamped sheet metal plates 2302 and 2304. This connector can be used to facilitate pivoting of concentrators about their secondary axis.

In other embodiments, cables could be held in a single or multiple piece assembly made via an array of techniques known in the art, e.g., injection-molding, casting, including zinc alloy casting, extrusion, etc. In other embodiments, such articles could be attached to cables via fasteners, e.g., 2314, via clamps, swages, crimps, adhesives, solders, brazes, welds, etc.

Welds and high temperature operations may unfavorably affect the strength of cables. Alternatively, lower temperature mating techniques, such as molten zinc or soldering could be utilized, including casting parts directly on cables.

The design in FIG. 23 provides clearance from cables in the region 2310 indicated by the dashed line, allowing apparatus mounted to the location 2312 to be pivoted over a wider angle than otherwise possible. This design keeps vertical loads on the axis of the cable 2306 and therefore provides for enhanced vertical stiffness. Such accommodation is similarly possible for cable 2308.

In some embodiments, such connectors are required at the intersection of three cables. The use of one or more compact rigid pieces at cable intersections can compensate for the finite size of cables or other apparatus to allow loads to be placed substantially along the axes of one or more cables. Such crossing connectors may further provide for cables to pivot during operation or to move with constraints such that a cable assembly can be rolled without damage, but is rigid when cables rotate into their operating position.

FIG. 23B shows an embodiment of a cable-mounted pivot according to the present invention. The cable 2316 is clamped in this instance via forces from a mechanical fastener 2322, but in other embodiments this connector could be crimped, swaged, or otherwise mated with the cable as previously discussed. Because loads from 2318 are off the axis of the cable, the element that mates with 2318 should be designed to prevent the action of these generated couples from bending or twisting cable 2316 where rigidity is important.

Connections between cables can be made a number of ways. One favorable technique is to pass a cable through the center of another cable by separating its strands. The cables can then be fastened via the use of one or more crimps or swages alone or in combination with a full or partial sleeve. Cables could alternatively be secured by soldering, zinc or zinc alloy casting, or zinc or molten zinc gluing, etc.

FIG. 24 shows a plan view of a solar farm according to an embodiment of the present invention. Collector arrays are most efficiently placed in elongated rows. If these arrays track the sun in two dimensions, then these rows may be most favorably placed in a substantially North-South orientation, as disclosed previously. This orientation allows collectors to be packed as tightly as possible along the primary axis while avoiding self-shading, which provides for the minimum material usage. If multiple rows of concentrators are used, the spacing of these rows should be wide enough that self shading at the beginning or end of the day is acceptable.

The distance between adjacent rows should at least be wide enough to provide for convenient servicing. The spacing between rows in some embodiments may be influenced by other factors, e.g., the space needed to support parking underneath the array, the space needed for planting and harvesting, etc.

A slight Western slope to the land is generally desirable because it biases the operation window toward the end of the day, when energy demand is strong. If tracking along one or more axis is manual, it may be favorable to orient arrays East-West so one axis need be adjusted only for seasonal variations. Such an orientation limits the productivity of the system so this tradeoff is not anticipated to be justified frequently.

In some embodiments of the present invention, it is convenient and effective to fabricate one or more elements of the tensile truss structure from sheets or strips of material, e.g., sheet metal, fiberglass, extruded plastic, composites, fabrics, weaves, and the like. FIG. 25A shows a tensile truss 2502 similar in operation to that in FIG. 11, but constructed from sheets rather than ropes, possibly from a single sheet or possibly a plurality of sheets fastened, welded, sewn, bonded, or otherwise connected together. The truss supports concentrators at points 2504.

Like in FIG. 11, the truss is pulled as indicated by the arrows and the resulting tensile forces are redistributed by a series of openings 2506 and links 2508 such that tensile forces resist motion in the plane of the truss. In this embodiment, the links 2508 fit the description of “cables” as used herein.

As with the truss in FIG. 11, a sufficient tension should be applied such that the local forces on links never becomes compressive in normal operation. This method of making a truss may be less tolerant of compressive forces in severe loadings than a cable truss, since it is possible for links to buckle tightly enough to deform plastically. An advantage of the cutouts 2506 is a reduction in wind loading, material usage, and mass.

The thickness of the sheet or sheets and dimensions of the openings and links should be designed in concert to provide for a desired wind loading, load bearing, stiffness, and out-of-plane flexibility. Out of plane flexibility can obviate damage from buckling and can also allow such trusses to be manufactured and delivered on rolls.

FIG. 25B shows a portion of a chain of such trusses 2510 assembled from a long sheet, strip, or roll of material. Alternatively, the body 2510 could be constructed in a continuous process. Such a process may include hot or cold rolling of a sheet of metal including steel, aluminum, stainless steel, etc., possibly providing spatial patterning to avoid excessive cutting waste; stamping, punching, plasma-cutting, laser-cutting, water-jet cutting, etc. of one or more openings; recycling or remelting of cutout material; heat-treating; annealing; surface treatment, e.g., hardening, anti-corrosion, priming, pickling, painting, scale removal, metal coating such as galvanization; embossing or stamping of stiffening or strengthening features; the incorporation of mounting elements and features; spooling into rolls; cutting at determined lengths; and the like.

The truss may further provide heat dissipation surface area in a distributed coolant-air heat exchanger. The truss may also provide damping directly by judicious design of laminated, corrugated, and energy-absorbing sheet materials or provide for mounting of other dampers.

Having thus described exemplary embodiments of the present invention, it should be noted by those skilled in the art that the within disclosures are exemplary only and that various other alternatives, adaptations, and modifications may be made within the scope of the present invention. Accordingly, the present invention is not limited to the specific embodiments as illustrated herein, but is only limited by the following claims.

Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US7687706Sep 17, 2007Mar 30, 2010Steven CongerSolar array support methods and systems
US7900401 *Nov 1, 2004Mar 8, 2011Airlight Limited (Ag)Pneumatic two-dimensional structure
US7954296 *Mar 20, 2009Jun 7, 2011Dennis John NewlandRadial tetrahedral modular structures
US8212140Oct 21, 2008Jul 3, 2012P4P, LlcSolar array support methods and systems
US8278547Jun 20, 2008Oct 2, 2012P4P Holdings LlcSolar array support methods and systems
US8322332 *Nov 8, 2010Dec 4, 2012Rogers William ESelf-erecting gimbal mounted solar radiation collectors
US8381464May 14, 2009Feb 26, 2013P4P Holdings LlcSolar array support methods and systems
US8429861Oct 15, 2009Apr 30, 2013P4P Holdings LlcSolar array support methods and systems
US8448390 *Mar 8, 2012May 28, 2013Olympic Energy Systems, Inc.Catenary cable solar panel suspension system
US8479724Mar 16, 2011Jul 9, 2013The United States Of America As Represented By The Secretary Of The NavyPassive cooling system for lightweight solar collector assembly and array
US8519257Feb 4, 2010Aug 27, 2013P4P Holdings, LLCSolar array support methods and systems
US8522772Feb 16, 2011Sep 3, 2013The United States Of America As Represented By The Secretary Of The NavyTracking system for lightweight solar collector assembly and array
US8530757Feb 3, 2012Sep 10, 2013Thomas & Betts International, Inc.Water-resistant while-in-use electrical box
US8657454Dec 28, 2011Feb 25, 2014The United States Of America As Represented By The Secretary Of The NavyVacuum formed reflector for solar energy
US8763321Jan 17, 2013Jul 1, 2014Olympic Energy Systems, Inc.Universal non-penetrating roof solar panel mounting system
US8806814 *Aug 24, 2012Aug 19, 2014Au Optronics CorporationPhotovoltaic array system, photovoltaic device thereof, and frame element of photovoltaic device thereof
US20100313500 *Jun 8, 2010Dec 16, 2010Adensis GmbhSupporting structure for an open-space photovoltaic system
US20110056484 *Nov 8, 2010Mar 10, 2011Rogers William ESelf-erecting gimbal mounted solar radiation collectors
US20130174891 *Aug 24, 2012Jul 11, 2013Au Optronics CorporationPhotovoltaic array system, photovoltaic device thereof, and frame element of photovoltaic device thereof
EP2518420A1 *Apr 27, 2011Oct 31, 2012NV Bekaert SAPhotovoltaic energy harvesting system with flexible support
WO2010022280A1 *Aug 20, 2009Feb 25, 2010Skyfuel, Inc.Hydraulic-based rotational system for solar concentrators that resists high wind loads without a mechanical lock
WO2011029758A1 *Sep 1, 2010Mar 17, 2011Hans Guenter CzalounPhotovoltaic system formed by a plurality of photovoltaic modules
Classifications
U.S. Classification126/600, 29/428, 52/690, 405/259.1, 52/146
International ClassificationF24J2/00, E04C3/02, E21D21/00, B21D39/00, E04H12/20
Cooperative ClassificationH01L31/0422, H01L31/0522, Y02E10/52, F24J2002/5458, Y02E10/47, F24J2/54, F24J2/5241
European ClassificationF24J2/52A10, H01L31/042B, H01L31/052B, F24J2/54
Legal Events
DateCodeEventDescription
Dec 20, 2007ASAssignment
Owner name: COOLEARTH SOLAR, CALIFORNIA
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:CUMMINGS, ERIC BRYANT;PACE, KIRSTEN KAYE;BELANGER, JACQUES JEAN;REEL/FRAME:020329/0764;SIGNING DATES FROM 20071101 TO 20071106