WO2017184893A1

WO2017184893A1 - Mirror collector for parabolic solar trough

Info

Publication number: WO2017184893A1
Application number: PCT/US2017/028684
Authority: WO
Inventors: Oliver J. BRAMBLES; Emil CASHIN; Troy O. Mcbride; Joel STETTENHEIM; Nicholas T. KATTAMIS; Sheldon D. STOKES; Richard W. KASZETA; Patrick J. MAGARI; Scott Snyder; Leif Johnson; Daniel Iliescu
Original assignee: Norwich Technologies, Inc.
Priority date: 2016-04-20
Filing date: 2017-04-20
Publication date: 2017-10-26

Abstract

A concentrated solar power system that is actuated to track a solar light source. A plurality of curved mirrors for a solar energy collector each having a mirrored surface, a curvature, and a support system that maintains the desired curvature under gravitational and wind loading conditions. In various configurations, the mirror is supported by support structures constructed with support masts and cable arrangements. The support structures are designed to be less expensive than conventional support structures by use of less material and by employing simplified manufacturing methods. The plurality of curved mirrors can track the solar light source individually or in multiple numbers (e.g., synchronously).

Description

MIRROR COLLECTOR FOR PARABOLIC SOLAR TROUGH

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to and the benefit of co-pending U.S.

provisional patent application Serial No. 62/325,202 filed April 20, 2016, which application is incorporated herein by reference in its entirety.

STATEMENT REGARDING FEDERALLY FUNDED RESEARCH OR DEVELOPMENT

[0002] This invention was made with government support under DE-EE0006687 awarded by the Department of Energy. The government has certain rights in the invention.

FIELD OF THE INVENTION

[0003] The invention relates to concentrating solar power in general and particularly to a system that employs reflective panels to focus solar radiation upon a linear receiver.

BACKGROUND OF THE INVENTION

[0004] Solar parabolic troughs, which focus sunlight on tubes carrying a fluid that conveys heat for steam generation (e.g. to a steam-driven electric generator, for industrial process heat, or for the generation of process steam) or to a body of material for energy storage, are a proven, reliable, and relatively low-cost technology for collecting energy. They are the most widely deployed form of concentrating solar power (CSP) at this time. The tubes upon which the light is focused in such systems are typically termed "receiver tubes," "receivers," or "heat collection elements." At a typical electric generation plant employing solar parabolic troughs, many receivers (for example, in one embodiment, thousands) are arrayed with reflective troughs in parallel rows to form a "solar field" that can collect sufficient energy for a generating system of economical size.

[0005] Both Fresnel and mirror systems have been used to focus sunlight upon linear fluid-conducting receivers, but parabolic trough mirrors are the most commonly deployed technology. In a typical mirror system (herein also termed a "collector assembly") comprising reflective surfaces and supporting members that hold mirrors in place and prevent unacceptable deformation of mirrors due to wind loadings and other forces, a truss comprising abundant rigid frame members (e.g., struts) upholds the mirror and enables the mirror to maintain its parabolic shape with sufficient accuracy in spite of wind forces and other deforming forces. The efficiency with which the receiver can absorb energy from the sunlight depends in part upon the accuracy with which a mirror focuses sunlight upon a receiver. A truss or similar structure that supports a mirror (also known as a "collector") also typically supports struts that hold a receiver approximately at the linear focus of the mirror.

[0006] In a typical receiver constructed according to the prior art, a central liquid- carrying tube with an outer optical absorption coating is surrounded by a vacuum held within a transparent concentric envelope. Light focused on the receiver by a mirror passes through the transparent concentric envelope and through the vacuum and impinges on the central liquid-carrying tube. The coating on the central tube absorbs most (preferably all, although this cannot be realized in practice) of the energy incident upon it and is thus heated. This heat is transmitted by conduction through the wall of the central tube and thence to the tube's liquid contents. The heated liquid is pumped through the receiver and, in general, through additional receivers, being thus raised to a high temperature before being pumped to a boiler, or energy storage device such as a reservoir of hot fluid). The function of the vacuum between the inner, fluid-carrying tube and the outer, transparent envelope is to prevent loss of heat from the receiver by convection and conduction to the outer envelope and thence, by radiation and conduction, to the environment.

[0007] A receiver design that offers advantages over the standard, vacuum-containing receivers of the state of the art has been disclosed and discussed in U. S. patent application Serial Number 13/831 ,632, issued on March 17, 2015 as U. S. Patent No. 8,978,642 hereinafter the Stettenheim patent, the disclosure of which is incorporated herein by reference in its entirety. In particular, the Stettenheim patent discloses an advanced cavity receiver comprising a fluid-carrying receiver tube of whose solar-absorbing surface a lengthwise portion is exposed within an air-filled cavity to light focused thereon by a parabolic trough mirror (and in some embodiments secondarily by appropriate shaped reflecting cavity walls), and the remainder of whose surface is embedded in insulation to reduce thermal losses. In the Stettenheim patent, the term "tube" refers to any elongated, two-ended, hollow body whose cross-sectional form is a simple closed figure (for example, in one embodiment, a circle, a rectangle, or a rectangle with rounded comers). However, only cylindrical and rounded-rectangular tubes surrounded by insulation are specifically described in the

Stettenheim patent. [0008] The mirrors employed in trough CSP systems constructed according to the prior art are a large portion of system mass and cost, and the accuracy with which they concentrate sunlight upon the receivers directly impacts system efficiency and, ultimately, per-unit cost of energy delivered. Mirrors per se, according to prior art, account for approximately 12% of trough CSP solar field capital cost, and supporting steel structure— whose bulk and cost are partly dependent on the weight of components to be supported and held rigidly in position, including mirrors— an approximate additional 24% of trough CSP capital cost. Moreover, ease of manufacture and optical performance (accuracy of focusing of solar radiation upon the receiver) are also suboptimal in CSP trough systems constructed according to the prior art. Finally, cavity receivers having nonstandard tube-and-shell geometries, such as those disclosed by the Stettenheim patent, will benefit from integration with mirror systems (herein also termed "collector assemblies") that depart from the prior art.

[0009] There is thus a need for CSP collector assemblies that are lower in weight than collector assemblies constructed according to the prior art while maintaining or improving optical accuracy.

SUMMARY OF THE INVENTION

[0010] The invention relates to CSP collector assemblies that are lower in weight than collector assemblies constructed according to the prior art while maintaining or improving optical accuracy and, in some embodiments, performing optimally in conjunction with cavity receivers such as those disclosed by the Stettenheim patent.

[0011] According to one aspect, the invention features a concentrated solar power system , comprising a mirror collector system having a plurality of curved panels, at least one of said curved panels having a parabolic cross-section, an upper mirrored surface, and a structural sub-substructure, said structural substructure having a first value of a designed material characteristic along a first axis and having a second value of said designed material characteristic along a second axis, said first and second axes being perpendicular and said first and said second values are different; a plurality of linear heat collecting receivers located at each located at a respective focal point of said plurality of curved panels; a plurality of tensioned structural elements connected to said plurality of curved panels and said plurality of linear heat collecting receivers, said plurality of tensioned structural elements configured to provide at least a portion of a structure configured to maintain said plurality of tensioned structural elements in a fixed relation to said plurality of curved panels; and a torsional element configured to provide torsional rigidity along a linear axis of said plurality of said curved panels; said plurality of curved panels configured to track a solar light source by at least one heliostat-controlled motor operationally connected to at least one of said plurality of curved panels.

[0012] In one embodiment, at least one of said curved panels comprises a parabolic trough.

[0013] In another embodiment, at least one of said plurality of curved panels is mounted on a truss based support structure.

[0014] In yet another embodiment, at least one of said plurality of curved panels is shaped and supported by a suspension cable structure mounted on a truss-based structure.

[0015] In still another embodiment, at least one of said plurality of curved panels is supported by a truss-based structure mounted directly on a rotating shaft connected to one of said at least one heliostat-controlled motor.

[0016] In a further embodiment, at least one of said plurality of curved panels is configured to be actuated in synchronicity with another of said plurality of curved panels.

[0017] In yet another embodiment, at least one of said plurality of curved panels is configured to be actuated without regard to the actuation of another of said plurality of curved panels.

[0018] According to one aspect, the invention features an improved mirror support system useful in a solar power application. According to the prior art, a truss comprising a multiplicity of rigid members (e.g., struts, ribs) in compression uphold a mirror; in contrast, the invention comprises suspension support structures that employ members in both tension and compression. Members in tension can comprise cables, wires or thin rods, which can bear heavy loads relative to their weight and which produce minimal optical occlusion of the system, where they are located above the mirror. Also in various embodiments, the invention comprises relatively stiff solar reflector panels consisting essentially of layered composite materials. Relatively stiff solar reflector panels reduce the amount of force (and thus the amount of a given material) needed to stabilize the solar reflector's overall shape against wind loading and other loading.

[0019] Suspension collector support systems according to embodiments of the invention can provide advantages compared to the prior art, including lower weight, superior maintenance of optical accuracy under wind loading and other loadings, and other advantages that shall be made clear hereinbelow. [0020] According to one aspect, the invention features a mirror collector system for concentrating solar power along a line in a parabolic trough solar power plant, comprising a plurality of curved panels, the curved panels having a parabolic cross-section, an upper mirrored surface, and a structural sub-substructure, the structural substructure having a first value of a designed material characteristic along a first axis and having a second value of the designed material characteristic along a second axis, the first and second axes being perpendicular and the first and the second values are different; a plurality of linear heat collecting receivers located at each located at a respective focal point of the plurality of curved panels; a plurality of tensioned structural elements connected to the plurality of curved panels and the plurality of linear heat collecting receivers, the plurality of tensioned structural elements configured to provide at least a portion of a structure configured to maintain the plurality of tensioned structural elements in a fixed relation to the plurality of curved panels; and a torsional element configured to provide torsional rigidity along a linear axis of the plurality of the curved panels.

[0021] In one embodiment, the upper mirrored surface comprises a mirrored film.

[0022] In another embodiment, the upper mirrored surface comprises a glass mirror.

[0023] In yet another embodiment, the designed material characteristic comprises an elastic modulus.

[0024] In still another embodiment, the torsional element comprises a tubular structure.

[0025] In a further embodiment, the torsional element comprises a space frame structure.

[0026] In yet another embodiment, the designed material characteristic is a moment of inertia.

[0027] In a further embodiment, the designed material characteristic is a flexural rigidity.

[0028] In an additional embodiment, the plurality of curved panels are configured to be formed using a roll forming technique.

[0029] In another embodiment, the plurality of curved panels are configured to be formed using metal stamping.

[0030] In an additional embodiment, the first and the second values of the designed material characteristic comprise a structural strength. In a further embodiment, the structural strength exceeds a structural strength for a glass mirror panel lacking the structural sub- substructure.

[0031] As used herein, the term "mirror" refers to elements that reflect

electromagnetic radiation. The term "solar reflector" is used interchangeably herein with the term "mirror." In various embodiments, a solar reflector may be single-layered or multi- layered; solid or hollow; comprise liquid, solid, and gaseous components; be rigid or deformable; comprise a single continuous part or of a multiplicity of parts, joined or unjoined, acting in harmony; and may otherwise vary in form and detail. Solar reflectors are often referred to as "parabolic" herein, but this term is illustrative, not restrictive: it is intended throughout that solar reflectors may be planar, parabolic, hyperbolic, mosaic, or of other forms, including complex and time-varying forms not corresponding to simple curves of classic geometry.

[0032] As used herein, the term "receiver" refers to elements that absorb some portion of electromagnetic energy concentrated thereon by a collector assembly and that convert this absorbed energy to other forms (e.g., heat, electricity, phase or chemical change of a substance). Typically in a trough CSP system, a receiver is linear or tubular in overall form. Typically also, a receiver's hollow interior conveys a fluid that absorbs heat while passing through the receiver and gives up some of this heat in another portion of the CSP system in order that the heat may be stored, used directly (e.g., for industrial processes, desalination, or the like), or used in the making of electricity. A receiver may, alternatively or additionally, comprise a photovoltaic capability for the direct conversion of focused solar energy to electricity. Also, in some forms of CSP, alteration of a fluid (e.g., chemical breakdown of waste) may occur inside a receiver by heating, or by direct effects of concentrated radiation, or by both.

[0033] As used herein, the term "cable" refers to a multiplicity of potential structural elements used in tension including but not limited to a single filament of wire, multiple filaments of wire wound into a flexible cable assembly, or thin rods. Furthermore, a "cable" is not limited to metallic construction, but instead encompasses a variety of other non- metallic materials including but not limited to man-made polymers, elastomers, carbon fiber, and fiberglass constructions.

BRIEF DESCRIPTION OF THE DRAWINGS [0034] The objects and features of the invention can be better understood with reference to the drawings described below, and the claims. The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. In the drawings, like numerals are used to indicate like parts throughout the various views.

[0035] FIG. 1 is a diagram of a typical prior art structural frame for a parabolic trough concentrating solar power system in which abundant frame members provide structural rigidity.

[0036] FIG. 2 is an example of a suspension cable structure, shown here for a parabolic trough system.

[0037] FIG. 3 is a schematic cross section of a cable system connected to

compression elements above and below the set of solar reflector elements, which are represented as a parabolic trough.

[0038] FIG. 4 is a schematic longitudinal elevation of a portion of a cable system connected to compression elements above and below the set of solar reflector elements.

[0039] FIG. 5 is a partial schematic plan (top view) of a suspension system showing a central compression element supporting a distribution of tension elements, which in turn support a set of solar reflector elements at multiple points.

[0040] FIG. 6 is a diagram of pre-fabricated sub-assemblies which can be rapidly combined on site to reduce the installation time that would otherwise be required to construct the full assembly from its individual components.

[0041] FIG. 7A is a schematic cross section of a solar reflector element consisting of a structural composite panel assembly comprising a top layer that has a mirrored surface and one or more backing layers laminated by adhesive or other mechanical means to provide structural rigidity.

[0042] FIG. 7B is a table of mechanical properties of illustrative three-ply reflector panel composites.

[0043] FIG. 8 is an exploded schematic view of multiple layers that may constitute a structural composite reflector panel.

[0044] FIG. 9 is a diagram of schematic receiver support or mast cross sections.

[0045] FIG. 10 is a schematic diagram of a trussed mast structure.

[0046] FIG. 11 comprises two schematic diagrams in different views of suspension cable systems using rigid compression frame structures. [0047] FIG. 12 shows three views of a first suspension cable system using a compression ring structure.

[0048] FIG. 13 shows three views of a second suspension cable system using a compression ring structure.

[0049] FIG. 14 depicts deformations of a two-mast mirror suspension system under three conditions of tilt.

[0050] FIG. 15 depicts calculated slope error for the tilt configurations of FIG. 14.

[0051] FIG. 16 tabulates mirror-suspension system characteristics for 6 conditions of tilt and wind loading.

[0052] FIG. 17 is a schematic showing a plurality of light-weight array parabolic troughs actuated by motors interspaced with the troughs. The parabolic troughs (1701) connected to a drive (1702) can have individual support grounded structures (1703), can be connected directly to the motor drive without a ground supporting structure (1704), or a common grounded support structure (1705).

[0053] FIG. 18 is an example of a light-weight grounded structural frame for a parabolic trough (1801) which comprises a full truss-based ground structure (1802) and a full truss-based support for the trough (1803).

[0054] FIG. 19 is an example of a light-weight grounded structural frame for a parabolic trough (1901) which comprises a suspension cable structure (1903) for the support and shaping of the parabolic trough (1901) mounted on a truss-based ground structure (1902).

[0055] FIG. 20 is an example of parabolic troughs (2001) shaped and supported by a truss-based rigid structure (2002) mounted directly on the rotating shafts of the motor (2003).

DETAILED DESCRIPTION OF THE DRAWINGS

[0056] We describe an array of cost-effective parabolic troughs for concentrated solar power (CSP) applications, with reduced-length individual solar reflector elements actively oriented by a series of distributed drives. The distributed dives in conjunction with the lighter support structure will reduce the misalignment of each reflector and the misalignment of the overall array due to the smaller torsional loads and the shorter distance over which they act while adjusting the reflector's orientation.

[0057] We describe improved collector assemblies for concentrating solar power applications, including parabolic-trough reflectors that optimize the performance of nonstandard receiver tube and shell geometries under a range of real-world physical and cost constraints and that feature improved optical efficiency and thermal efficiency while reducing the weight of structural material. By reducing material costs and conferring other advantages, these improved collector assemblies lower the cost of a CSP trough system.

[0058] The invention encompasses solar collector assembly designs that provide advantages over the prior art. The collector assembly designs described herein can reduce the initial capital cost of solar thermal systems by reducing the material weight of the assembly. The suspension structures detailed in this invention take advantage of high tensile strength to weight ratio cables or wires, configured on both sides of the solar reflectors to more efficiently balance the forces and to more evenly distribute material. The cables and wires can be relatively narrow in diameter relative to their lengths, and thereby cast very small shadows across the collector and receiver elements, minimizing optical losses. The thin diameter to axial length aspect ratio of cables or wires has even greater advantages as the focal length of concentrators increases, as the trend in collector systems progresses to larger aperture widths in order to capitalize on economies of scale. For the same reason, suspension systems particularly benefit nonstandard collector systems that have higher focal length to aperture aspect ratios relative to the typical state of the art.

[0059] Suspension structures have been applied to heliostat-type solar reflectors that concentrate sunlight to a point receiver. Unlike those applications, this invention provides suspension systems that are suitable for solar concentrators using linear receivers, as distinguished by the following key differences: (1) asymmetric reflector profiles require asymmetric structural configurations; (2) a linear receiver element induces additional loads which preferably should be supported, either separately from or integrally with the support of the rest of the suspension structure; (3) alignment of a collector along the linear receiver requires additional resistance to both bending along and rotation about the longitudinal axis; (4) curvature of reflector elements limits the number of joints between reflector panels along the curved profile, in contrast to joints between planar reflector panels, which can more directly transfer axial stresses in the plane of the panels.

[0060] In some aspects of the invention, such as parabolic trough applications, the above differences lead to the following consequences: (1) suspension cables preferably should be sized and arranged differently above and below the reflector surface; (2) masts or other receiver supports may need to be provided; (3) a torque tube or other rotationally rigid longitudinal spanning structure preferably should be provided; (4) reflector panel elements comprise single panels, in terms of a structural unit, extending either the full length or the half-length (about the plane of symmetry) of the curved profile.

[0061] FIG. 1 is a schematic transverse cross-sectional diagram of a typical prior-art structural frame for a parabolic trough CSP system in which abundant frame members provide structural rigidity. Assembly 100 comprises a linear receiver element 102, receiver supports 104, reflector panels 106, and structural support framing elements 108. In some instances, the framing elements 108 connect to a torque-resisting, longitudinal spanning element 110 which may be in the form of a beam or structural tube, or alternately in the form of a space frame, which itself may be integrated into the support framing 108.

[0062] FIG. 2 is a schematic drawing (axonometric view) of portions of an illustrative

CSP trough system 200 according to one embodiment of the invention. The system 200 comprises a suspension cable structure and a solar reflector 202, the latter shown here as approximately parabolic in cross-section. The solar reflector 202 may comprise stiff (structural composite) mirror panels that are supported primarily by a suspension cable system. The employment of a structural (load-bearing) stiff solar reflector 202 is discussed further with reference to FIG. 6 and FIG. 7A. A central torque tube 204 or similar structure is used to span between foundation pylons 206 and to provide torsional rigidity and rigid attachment points for suspension masts (e.g., mast 208). Torsion forces may be applied to the system by tracking motors, asymmetric weight loads, unevenly distributed wind loading, and/or other asymmetric torque-producing loads. The portion of the system 200 supported by the pylons 206 may be rotated around the axis defined by the torque tubes 204 for sun tracking. Masts comprise hollow sections or trusses that extend above and below the torque tube 204 to provide attachment points for cables represented in Fig. 2 by cables 210, 212. Suspension cables 210 run from the masts 208 to various points on the surface of the reflector 202. Opposing, pre-tensioned cables, e.g., cable 210 and cable 212, provide restoring force to resist deformation of the reflector 202 by changing loads, e.g., by wind loading and changing gravitational loading as the trough sweeps through its angular range, and by other loading. Precisely made cables enable accurate assembly of the mirror structure in a parabolic shape. A receiver 214 is held accurately in position by the upper support masts (e.g., mast 208) and by cables (e.g., cable 210).

[0063] FIG. 3 is a schematic transverse cross-sectional view of an illustrative solar collector module 300 according to an embodiment of the invention. Module 300 utilizes a multiplicity of cables 302 connected to an upper mast 304 and a lower mast 306. The upper mast 304 is so called because it is above the solar reflector panels 308, and the lower mast 306 is so called because it is below the solar reflector panels 308. In this embodiment, each module 300 comprises a single upper mast 304 that is located halfway along the longitudinal dimension of the module 300, and a single lower mast 306 that is similarly located. The upper mast 304 and lower mast 306 form an opposed pair. In various other embodiments, two or more such mast pairs may be located at various points along the longitudinal dimension of a module similar to module 300.

[0064] In FIG. 3, the solar reflector panels 308 are represented as constituting a parabolic trough reflector. In the embodiment shown in illustrative module 300, the trough reflector as a whole comprises eight solar reflector panels (as is shown in more detail in FIG. 5). The masts 304 and 306 are attached to a relatively rigid longitudinal spanning element 310, also herein termed a "torque tube," which (a) resists twisting and bending and (b) transfers both dead and live loads to pylons or other bearing structures (not shown in FIG. 3) located at the ends of each collector module 300. The torque tube may or may not be strictly tubular: any extended structure (e.g., tube, truss, other) capable of bearing the requisite loads is contemplated and within the scope of the invention. In the embodiment depicted, suspension cables 302 extending from reflector panels 306 connect directly to the base of the upper mast 304, the upper end of which provides an attachment point for cables 302 and a rigid support for the receiver 312. The upper mast 304 also bears in compression forces exerted thereon by the cables 302. Similarly, the lower mast 306 bears in compression forces exerted in tension by cables 302 (i.e., those cables attached to the underside of the reflector panels308). The forces exerted and borne by the cables 302 and masts 304, 306 are in net balance at all times except during brief intervals of time when dynamic loads are being taken up by slight deformations of various components of the system. In other variations, support masts may be provided for the cables 302 separately from receiver supports. In essence, the solar reflector panels 308 are suspended between the masts 304 and 306.

[0065] In the system 300, the reflector panels 308 are layered composite structures that are formed precisely in a parabolic shape and that provide rigidity between attachment points. The nature of the layered composite panels comprised by the embodiment of FIG. 3 and by various other embodiments is further described and is illustrated in FIG. 7A and FIG. 8. Reflector panels 308 are connected to the torque tube 310 in the center of the trough, then supported by cables 302 attached to the reflector panels 308 at the trough lip 314 and at second point 316 approximate midway between centerline and lip. We have used computer structural studies to provide bounding values for the stiffness of the mirror panels and cables and enable specification of requisite cable pretensions to prevent cables from going slack.

[0066] In the system 300, with the aperture shape of the parabola supported entirely by cables 302 and the mirror panels 308 themselves, the collector framework can be reduced to a central spine, illustrated as the torque tube 310, that provides rigidity in bending and torsion. In order for the cable array to keep the collector aligned, the masts preferably should be rigidly coupled to this central spine. Simulation studies on mast stiffness have identified torque tube stiffness as a limiting factor; for example, a 12 in² hollow steel torque square tube with 0.25 in wall thickness is a sufficient baseline member to avoid excessive displacement error in the masts under realistic gravitational and wind loadings. Other studies of this illustrative scenario have examined the twist of the torque tube 310 along a long run of modules 300 (multiple spans) under a constant wind moment per unit length, as well as the bending stiffness of the tube 310 between pylons. These studies concluded that torsional rigidity of the 12 in² torque tube 310 was sufficient only for module strings extending -24 m (assuming 12 m spans between pylons) beyond the tracking drive. Various other forms of torque tube or frame may achieve similar or improved torsional and bending stiffness with less material usage: the design details of the torque tube 310 of any given embodiment will depend complexly on the materials used and all dimensions of other components (e.g., parabola curvature, aperture width, module length, string length, receiver linear density).

[0067] When deployed as components of a typical solar field, modules similar to module 300 are typically coupled end to end to form strings or runs, and multiple strings are built in parallel, separated by sufficient space to prevent mutual shading during prime operating hours.

[0068] In FIG. 3, module 300 is depicted as oriented vertically. However, in typical operation, one or more tracking motors (not shown) that are coupled to the torque tube 310 either directly or via the torque tubes of additional modules (not shown), and can exert torque on each module string, changing the axial orientation of the string in order to track sun motion. Distributed tracking drives (e.g., those manufactured by Inter Control), as opposed to conventional motors located at the ends of module strings or runs, may in various embodiments reduce the need for torsional stiffness. For example, in some embodiments, a drive may be located every -48 m (four 12-meter module spans) and would be sufficient. Computer modeling of a distributed drive system as a series of torsionally fixed points on a long shaft shows that for a given allowable collector twist, the number of spans between two drives (torsionally fixed boundary conditions) is twice the number of spans from a single drive to a free end, as in typical trough systems.

[0069] FIG. 4 is a schematic longitudinal (side) view 400 of the solar collector module of FIG. 3, which utilizes a system of cables 302 connected to an upper mast 402 above and a lower mast 306 below the solar reflector panels 308. The longitudinal spanning member 310 is also depicted in FIG. 4. FIG. 4 illustrates that a plurality (in this case, 4) of reflector panels may be comprised by a single module 300. FIG. 4 also illustrates that the orientations of cables 302 are not confined to the plane of FIG. 3 or any other single plane: rather, they form a three-dimensional structure designed to optimally bear and match loads throughout the module 300. The cables used to support a typical truss radio mast would be an apt comparison. Moreover, in addition to supporting reflector panels 304, the cables 302, in some embodiments of the invention, can also stabilize the supports (e.g., mast 304) for the receiver 306. The number and spacing of masts 304, 306 and/or receiver supports may differ in various embodiments, and each reflector panel 308 may be supported by cables 302 attached to one or multiple masts 304, 306.

[0070] FIG. 5 is a schematic longitudinal (overhead) view 500 of the solar collector module of FIG. 3, which utilizes a system of cables 302 connected to an upper mast 402 above. The lower mast 306 of FIG. 3 and FIG. 4 is not depicted in FIG. 5. The axis of the receiver 306 (which for clarity is not shown) is above and parallel to the axis 502 of the longitudinal spanning element 310.

[0071] In various embodiments not explicitly depicted herein, a structure other than a parabolic mirror trough is supported by a suspension system. For example, linear planar arrays of photovoltaic (PV) panels, either fixed or operated in a single-axis tracking manner, are in various embodiments supported and, if appropriate, rotated for sun-tracking purposes by essentially the same methods described herein for the support, stabilization, and rotation of solar reflector assemblies. Of note, constraints on shape stabilization would be relaxed for a PV panel assembly as compared to constraints for a solar reflector assembly of roughly comparable dimensions: a PV array need not be positioned with millirad-scale accuracy in order to fully realize its efficiency potential. Thus, suspension system costs are likely lower when a PV assembly is incorporated into a suspension system rather than a mirror assembly.

[0072] FIG. 6 is a schematic diagram of illustrative pre-fabricated sub-assemblies which, according to an embodiment of the invention, can be rapidly combined on-site in order to reduce installation time for a module (e.g., module 300 of FIG. 3) compared to that required to construct the full assembly of a solar collector module 600 from its individual components. In one embodiment of the invention, these sub-assemblies comprise a primary structure 602, composite mirror panel sections 604a, 604b, secondary structure (lower masts) 606a, 606b, and a set of cables (not shown). The primary structure 602, in one embodiment of the invention, comprises a torque tube (longitudinal spanning element) 608, a receiver element 610, and receiver supports and/or masts 612a, 612b. Connections between subassembly components may be keyed or tabbed to facilitate high-precision alignment of every component.

[0073] FIG. 7A is a schematic cross section of an illustrative solar reflector subassembly 700 according to an embodiment of the invention. The sub-assembly 700 comprises one or more structural composite panels 702 comprising a top layer 704 that has a mirrored surface 706 and one or more backing layer 708, laminated to the top layer by 704 adhesive or other mechanical means to provide structural rigidity. The backing layer 708 may have an outer sealant coating or layer 710. The laminated sub-assembly 700 is a structural reflector, that is, it not only focuses sunlight that impinges on its reflective upper surface 706 but in addition is mechanically rigid and strong enough to contribute significantly to the support of incident loads, including its own weight and forces transmitted to the subassembly 700 from its edges. The obj ective of the backing layer 706 and in some embodiments of the top layer 704 as well is to provide stiffness at the lowest possible material density. This may be achieved in various embodiments of the invention by incorporating materials that are hollow, porous, punched, or perforated, honeycomb composites, foams, ribbed, corrugated, roll-formed, woven, or subject to other fabrication or processing techniques to achieve low mass density and high stiffness. In various other embodiments, the sub-assembly 700 comprises two or more backing layers, each laminated to its neighbors by adhesive layers or other means. A multi-layer reflector assembly is depicted in FIG. 8.

[0074] In various embodiments of the invention that incorporate nonstandard receivers, e.g., receivers as described in the Stettenheim patent, a relatively low panel curvature may be utilized, that is, the panel may be flatter than an otherwise comparable parabolic reflector constructed according to the prior art. The curvature of such a prior-art reflector is indicated by the dashed line 712. Lower reflector curvature is advantageous in the construction of a structural, laminated reflector because it enables a simpler laminate structure and therefore is less costly to manufacture. For example, feedstock for backing layer manufacture may comprise a 1-in thick rigid honeycomb sheet. Such sheets may in various embodiments be of polymer materials, metal, paper, foam, or other materials capable of formation into honeycomb or low-density sheets with appropriate mechanical properties (e.g., flexural rigidity). Such sheets can be deformed to yield parabolic curved layers, but the thicker the sheet, the less curvature can be accommodated without cracking or breakage. Thus, for a lower-curvature mirror, fewer (in some embodiments, only one) honeycomb sheet plies may be required for manufacture, while for a higher-curvature mirror, multiple, thinner honeycomb sheet plies may be required to achieve comparable mechanical strength, with correspondingly greater numbers of adhesive layers and manufacturing complexity. It is, in short, less costly to manufacture structurally rigid lower-curvature mirrors than to manufacture comparable higher-curvature mirrors.

[0075] FIG. 7B presents a table 712 showing selected mechanical properties (i.e., thickness, areal density (kg/m²)) of candidate materials for seven illustrative three-ply reflector panel composites. Each row of the table 712 corresponds to a single illustrative three-ply composite comprising an upper sheet, lower sheet, and honeycomb sheet between the upper and lower sheets. Properties of adhesive layers comprised by these illustrative panel structures are omitted from the table 712 of FIG. 7B. The flexural rigidity ("EI") or bending stiffness of each composite is given in the far-right column of the table 712. In FIG. 7B, "G10 phenolic" refers to G-10 grade phenolic sheeting (e.g., that manufactured by the United States Plastic Corp.) and "Nomex" is the trade name of a flame-resistant meta-aramid material manufactured by E. I. du Pont de Nemours and Company. G10 phenolic has an eightfold higher elastic modulus than polycarbonate and only a 50% higher density, enabling lower overall mass density for the seventh (bottom row) composite material in the table 712, as compared to other composites in the table 712, while retaining high EI.

[0076] In general, composites with high EI and low areal density are preferred.

Higher EI enables a structural reflector panel of given size and shape to bear greater loads without breakage or unacceptable deformation, which tends to allow reductions in number and mass of other structural components of a CSP system without compromising

performance. Lower areal density decreases gravity loads on both the structural reflector panel and other structural components of a CSP system, again tending to allow reductions in number and/or mass of structural components without compromising performance.

[0077] In various other embodiments not depicted herein, structural panels comprise structural materials other than honeycomb materials. These alternative materials include but are not limited reflector panel materials created by roll forming, such as the structural reflector material manufactured by Insolare Inc. Roll forming is a procedure where continuous bending operations are applied to a material, e.g., sheet metal or strips of metal, to plastically deform the material along a linear axis. Roll stations shape the material in tandem sets of rolls through progressive stages until the required configuration is achieved. Virtually any material that can be formed through sheet forming techniques can be roll formed. A structural trough reflector manufactured by Insolare comprises a ribbed metal sheet that is roll-formed into a structural parabolic unit. Another illustrative material for structural reflector panels is the punched-metal structure manufactured by Gossamer Innovations Inc., a form of expanded metal sheeting in which a multiplicity of bent tabs are punched from a sheet of metal (e.g., aluminum), said tabs remaining attached to the sheet while being bent into a position that enables the tabs to act as spacers or supports for a second sheet of material. All low-density, high-strength materials capable of acting as a structural sheet layer in a solar reflector are contemplated and within the scope of the invention.

[0078] FIG. 8 is an exploded schematic view of a portion of an illustrative multi-ply structural composite solar reflector subassembly 800. The top layer 802 has a highly reflective mirrored surface (not separately depicted) that may incorporate a film or coating that enhances the reflectivity and provide environmental protection. In one embodiment of the invention, the backing layers 806a, 806b comprise relatively stiff but lightweight honeycomb interlayer fastened mechanically or by use of adhesive layers 808a, 808b, 808c. A backing layer 810 completes the composite panel and adds further rigidity. In various other embodiments, the number of honeycomb backing layers may be one or any greater number.

[0079] FIG. 9 depicts four illustrative schematic cross sections that may describe any or all of receiver supports and/or mast elements (of, e.g., the system 300 of FIG. 3) to support tension members and/or torque-resisting longitudinal spanning elements (torque tubes).

Section 900 is a hollow structural tube or pipe that may be straight or tapered along its length. Section 902 shows a triangular arrangement of three axial members connected and stabilized by trussed elements. Section 904 shows a rectangular arrangement of three axial members connected and stabilized by trussed elements. Section 906 makes a hexagonal arrangement of six struts or axial members connected and stabilized by trussed elements at the perimeter of the section. In some configurations, additional structural stability may be provided by connecting tension elements (e.g., cables, as indicated by lines 908, only one of which is labeled) across the interior space between outer struts. In any of the cross sections 902, 904, 906, or other configurations incorporating multiple framing elements, some or all of the connecting elements may be either rigid members or cables or wires. The geometries shown in FIG. 9 are exemplary, and are not exhaustive.

[0080] FIG. 10 is an illustrative schematic diagram of an illustrative space frame or trussed mast structure 1000 according to an embodiment of the invention. In this embodiment, which uses the four-sided geometry similar to that of Section 904 in FIG. 9, four rigid axial members 1002 (only one of which is explicitly labeled) are arranged in a rectangular configuration and linked on each side by tensioned crisscrossed cables 1004 (only one of which is explicitly labeled). The use of cables in place of rigid members in upper (above mirror) masts can reduce shadowing of the receiver and thereby can increase the optical efficiency. The box arrangement of the axial members 1002 is prevented from collapsing under the pull of the cables 1004 by appropriately spaced arrangements of spacer struts 1006 (only one of which is explicitly labeled).

[0081] In various CSP module embodiments where the structure 1000 is employed as combined receiver support and mirror cable attachment, mirror cables 1008 (only three of which are depicted, and only one of which is explicitly labeled) are attached at or just below the uppermost arrangement of spacer struts 1006. Above this point, the structure 1000 supports only the load of the receiver's weight and therefore need not be as strong: thus, the portion 1010 of the rigid axial members 1002 that is above uppermost spacer struts 1006 may be weaker (e.g., thinner).

[0082] The structure 1000 is illustrative of a class of mast structures that may vary endlessly in detail, as for example in cross section (e.g., per the cross-sectional variations of FIG. 9). All such structures are contemplated and within the scope of the invention.

[0083] FIG. 11 depicts two schematic views of an illustrative cable-suspension suspension system 1 100 comprising rigid compression frame structures according to an embodiment of the invention. A triangular suspension frame 1102 is centered on axis of symmetry 1104 of the parabolic trough mirror 1106. Suspension elements (e.g., cables), e.g. cables 1 108a, 1108b, connect the mirror 1106 to the frame 1102. For clarity, suspension elements are omitted from the right-hand side of both views. The frame 1 102 need not be triangular in various other embodiments, but may take on a variety of forms. The receiver 1108 is shown located at the focal line of the parabolic trough mirror 1106. The parabolic trough mirror 1 106 comprises structural composite subassemblies similar to those depicted in FIG. 7A and FIG. 8. System 1100 is advantageous because the mechanical support functions of the upper mast 304, lower mast 3046 and torque tube 310 in FIG. 3 are all performed by a single structure, namely the suspension frame 1102. However, the system 1100 preferably should be rotated if sun-track is to be achieved, and although possible such rotation is not straightforward with a triangular structure. This drawback is addressed by the illustrative frame designs shown in FIG. 12 and FIG. 13.

[0084] FIG. 12 shows three schematic views of an illustrative suspension cable system 1200 using a compression ring structure (compression frame) according to an embodiment of the invention. In this embodiment, a circular frame 1202 is employed, rather than a triangular frame as in FIG. 11. Cables (e.g., cable 1204) are attached to a limited number of attachment points on the frame 1202 and exert tension on the parabolic mirror trough 1206 from above and below. A circular suspension frame offers several advantages over triangular or other suspension frames. First, the inherent mechanical strength of a circular structure allows equivalent bearing strength with less material usage than any other structure (assuming roughly symmetrical interior loads, as in a bicycle wheel). Second, a circular structure is easily rotated, e.g., by mounting the structure on powered bearing rollers, or by mounting the structure on passive bearing rollers and pulling on one or more points of the structure perimeter (e.g., by winching in a cable attached to the perimeter), or by other means. Thus, a circular suspension frame such as that of system 1200 realizes advantages addition to those of other embodiments described herein, and in particular is advantageous over the prior art in that powerful, axially mounted motors are not required for sun-tracking rotation of the system 1200; a number of alternative, lower-cost schemes for sun-tracking rotation may be applied. All such schemes are contemplated and within the scope of the invention.

[0085] FIG. 13 shows three schematic views of an illustrative suspension cable system 1300 using a compression ring structure according to an embodiment of the invention. In this embodiment, a circular frame 1302 is employed, as in FIG. 12. Cables (e.g., cable 1304) are attached to a limited number of attachment points on the frame 1302 and exert tension on the parabolic mirror trough 1306 from above and below. System 1300 is similar to system 1200 except that the cables 1304 issue from distributed attachment points from the frame 1302. Such an arrangement, by distributing stresses more evenly on the frame 1302, may allow the use of even less material for an otherwise equivalent system. [0086] Reference is now made to FIG. 14. Structural finite-element (FEA) computational models have been used to analyze various embodiments under gravity and wind load; these structural models capture the mirror surface, cable system, torque tube, and receiver supports. FIG. 14 schematically depicts the behavior of a model employed to study deformation of a two-mast embodiment resembling system 300 of FIG. 3 under three conditions of tilt (gravity loading), i.e., 0° (left), 45° (middle) and 90° (right) pitch angles. Gravity loads tend to dominate mirror surface deformation; wind loads up to 25 mph are relatively benign with regard to the mirror surface. For these analyses, wind loadings (net force and moment coefficients, as well as extreme-case pressure distributions on the mirror surface) have been adapted from National Renewable Energy Laboratory wind-tunnel data given in Hosoya et al. 2008, "Wind Tunnel Tests of Parabolic Trough Solar Collectors, "NREL/SR-550-32282 on conventional troughs with 80° rim angle. It is expected that wind pressure distributions and governing loads will differ somewhat for a flatter collector profile (e.g., 55° rim angle as in the analysis here discussed), but wind tunnel studies, e.g., Peterka et al. 1980, "Mean Wind Forces on Parabolic-Trough Solar Collectors," SAND80-7023, Sandia National Laboratory, have found that peak loads are neither strongly nor consistently associated with rim angle.

[0087] For initial analysis, 6 different cases were considered where the pitch angle of the collector and the wind loading were varied: 0°, 45°, 90°, 30°, 30° with 5 m/s wind and 30° with 1 1 m/s wind. For this analysis, 0° indicates the collector facing vertically upwards and 90° represents a collector aimed at the horizon. 30° was chosen for the wind loading cases as this configuration represented a maximum wind loading configuration (Sun et al.,"A review of wind loads on heliostats and trough collectors," Renewable and Sustainable Energy Reviews, 32(2014): 206-221). Deformation of the mirror and receiver support were calculated and used as inputs to optical ray tracing models. FIG. 14 schematically depicts the deformation of the mast and mirror under three illustrative conditions of gravitational loading.

[0088] FIG. 14 schematically depicts portions of an illustrative CSP system 1400 whose upper mast 1402, lower mast 1404, and mirror undergo various degrees and types of deformation under various conditions of gravitational loading. In a hypothetical condition of no gravitational loading, depicted in all three of the tilt conditions in FIG. 14, the mirror curve is described by a dotted line 1406 and the upper mast 1402 and lower mast 1404 are undeformed. In a condition of gravitational loading with 0° tilt (condition depicted at left) the mirror sags symmetrically and its curve is described by a first solid line 1408. Also under this tilt condition, the upper mast 1402, upon which a number of cables (e.g., cable 1408) pull, deforms outward in the vicinity of the cable anchor points, as indicated by broadened mast outlines 1412. In FIG. 14, for clarity, cables are depicted only for the deformed state of each tilt position.

[0089] In a condition of gravitational loading with 45° tilt (depicted in center of FIG.

14), the mirror sags asymmetrically and its curve is described by a second solid line 1414. The upper mast 1402 also deflects, as indicated by shifted outline 1416 and indicated end deflection 1418. The lower mast 1404 deflects in a manner similar to that of the upper mast 1402 (deflection not explicitly labeled in FIG. 14).

[0090] In a condition of gravitational loading with 90° tilt (depicted at right of FIG.

14), the mirror sags asymmetrically and its curve is described by a third solid line 1420. The upper mast 1402 and lower mast 1404 deflect in a manner generally similar to that of the 45° case, only more pronounced (mast deflections are not explicitly labeled in FIG. 14). In sum, warping and deflection of components is asymmetrical with nonzero tilt or otherwise unbalanced force loading and increases in magnitude with increasing tilt and other unbalanced loads. The precise form and degree of deformation depends on the flexibility of all components involved, including mirror panels and cables, as well as on location and number of cables, pretensioned forces in cables, reflector panel rigidity, mast rigidity, and other factors. In general, mirror deflection varies along mirror profile as well as with tilt angle. Loading by wind, snow, and other factors will in general complicate the gravity deformations schematically depicted in FIG. 14.

[0091] Reference is now made to FIG. 15. Ray -tracing codes and capabilities have been developed that enable rapid analysis of the optical effects of structural deformations of various embodiments. The codes take as input a deflected mirror profile and/or receiver position from mechanical FEA modeling, and output optical flux distribution and geometric optical efficiency. This structural-optical model connection enables the definition of adequate structural stiffness values for key collector elements of various embodiments, including cables, cable masts, torque tube, mirror panels, and receiver supports.

[0092] The slope error of the mirror (units of millirads, mrad) is determined using ray tracing to calculate the deviation of the reflected light beam from the focal line owing to the deformation of the mirror at discrete locations on the mirror surface. The equivalent slope error at each discrete (or local) position is then calculated using the equation fd = (2^■ sdx)^■ d

where fd is the local focal deviation calculated using the ray tracing, sdx is the local slope deviation, and d is the distance between the local mirror surface and the focal point, as described in Meiser et al., "Analysis of parabolic trough concentrator mirror shape accuracy in different measurement setups," Energy Procedia 49 (2014) 2135-2144. The root mean square (RMS) slope error for each mirror configuration (tilt condition) is then calculated. This slope error contains errors due to both mirror position and gradient. FIG. 15 shows the calculated slope error for the three mirror configurations of FIG. 14 as a function of position (units of meters) along the linear collector aperture.

[0093] The results for each of the 6 test cases discussed above with reference to FIG.

15 are tabulated in FIG. 16. The RMS errors determined from the FEA and ray tracing models represent the slope error in the panels owing to deformation from the support structure under loading but neglect any slope error than is inherently present in the panel. The panels developed by Gossamer Space Frames have an RMS slope error of approximately 1.1 mrad and therefore the slope error of the system can be assumed to be

1 2 2

System ⁼ I Support + ^σραηβΙ

where <J_support is the slope error due to deformation of the panel from the support structure under loading and <J_panel is the slope error inherent in the panel. This system error represents the error due to mirror structure owing to gravitational loading and wind deflections and compare favorably to the system slope error of 2.3 mrad calculated for a Gossamer Space Frame, Inc. system, as described in Chen et al, "Next Generation Parabolic Trough Solar Collectors for CSP ," Proceedings of the 6th International Conference on Energy Sustainability, 2012. This combination of errors excludes errors due to (for example) torsion, receiver alignment, and tracking. These errors will contribute towards the optical error budget. Under all examined load conditions to date, these system errors are lower than 4 mrad.

[0094] The optical efficiency of the mirror-receiver pair has been calculated for each configuration using an optimized cavity receiver resembling those disclosed in the

Stettenheim patent. Under real-world conditions, receiver alignment, sun tracking and torsional errors will be present. Therefore, for purposes of calculating the optical efficiency it is useful to estimate these errors. A ray -tracing model has been used to calculate the optical performance of the cavity receiver. For each configuration, the rays were traced using the deformed mirror surface and displaced receiver location from ANSYS models. An additional Gaussian scatter was imposed on the reflected ray to represent the additional errors. The combination of these errors can be estimated as

where a_panel is the slope error inherent in the panel (-1.1 mrad), c_t0rsion is the ^error due to torsion (~1 mrad), ^alignment is the error due to receiver alignment (-1.5 mrad), and <J_trac]i is the error due to sun tracking (-1.5 mrad). These errors combine to give an additional scatter of 3.2 mrad to be applied to reflected ray.

[0095] The table in FIG. 16 shows the optical efficiency of the mirror-receiver pair discussed above with reference to FIG. 14 and FIG. 15 for each mirror loading configuration using the assumptions defined above for reflectivity, transmittance, and absorptivity for additional errors of 3.2 mrad. The optical efficiency for each mirror loading configuration is above 78%.

INCORPORATION BY REFERENCE

[0096] Any patent, patent application, patent application publication, journal article, book, published paper, or other publicly available material identified in the specification is hereby incorporated by reference herein in its entirety. Any material, or portion thereof, that is said to be incorporated by reference herein, but which conflicts with existing definitions, statements, or other disclosure material explicitly set forth herein is only incorporated to the extent that no conflict arises between that incorporated material and the present disclosure material. In the event of a conflict, the conflict is to be resolved in favor of the present disclosure as the preferred disclosure.

[0097] While the present invention has been particularly shown and described with reference to the preferred mode as illustrated in the drawing, it will be understood by one skilled in the art that various changes in detail may be affected therein without departing from the spirit and scope of the invention as defined by the claims.

What is claimed is:

Claims

1. A concentrated solar power system , comprising :

a mirror collector system having:

a plurality of curved panels, at least one of said curved panels having a parabolic cross-section, an upper mirrored surface, and a structural sub-substructure, said structural substructure having a first value of a designed material characteristic along a first axis and having a second value of said designed material characteristic along a second axis, said first and second axes being perpendicular and said first and said second values are different;

a plurality of linear heat collecting receivers located at each located at a

respective focal point of said plurality of curved panels;

a plurality of tensioned structural elements connected to said plurality of curved panels and said plurality of linear heat collecting receivers, said plurality of tensioned structural elements configured to provide at least a portion of a structure configured to maintain said plurality of tensioned structural elements in a fixed relation to said plurality of curved panels; and a torsional element configured to provide torsional rigidity along a linear axis of said plurality of said curved panels;

said plurality of curved panels configured to track a solar light source by at least one heliostat-controlled motor operationally connected to at least one of said plurality of curved panels.

2. The concentrated solar power system according to claim 1 wherein at least one of said curved panels comprises a parabolic trough.

3. The concentrated solar power system according to claim 1 wherein at least one of said plurality of curved panels is mounted on a truss based support structure.

4. The concentrated solar power system according to claim 1 wherein at least one of said plurality of curved panels is shaped and supported by a suspension cable structure mounted on a truss-based structure.

5. The concentrated solar power system according to claim 1 wherein at least one of said plurality of curved panels is supported by a truss-based structure mounted directly on a rotating shaft connected to one of said at least one heliostat-controlled motor.

6. The concentrated solar power system according to claim 1 wherein at least one of said plurality of curved panels is configured to be actuated in synchronicity with another of said plurality of curved panels.

7. The concentrated solar power system according to claim 1 wherein at least one of said plurality of curved panels is configured to be actuated without regard to the actuation of another of said plurality of curved panels.

8. The concentrated solar power system according to claim 1 wherein said upper mirrored surface comprises a mirrored film.

9. The concentrated solar power system according to claim 1 wherein said upper mirrored surface comprises a glass mirror.

10. The concentrated solar power system according to claim 1 wherein said designed material characteristic comprises an elastic modulus.

11. The concentrated solar power system according to claim 1 wherein said torsional element comprises a tubular structure.

12. The concentrated solar power system according to claim 1 wherein said torsional element comprises a space frame structure.

13. The concentrated solar power system according to claim 1 wherein said designed material characteristic is a moment of inertia.

14. The concentrated solar power system according to claim 1 wherein said designed material characteristic is a flexural rigidity.

15. The concentrated solar power system according to claim 1 wherein said plurality of curved panels are configured to be formed using a roll forming technique.

16. The concentrated solar power system according to claim 1 wherein said plurality of curved panels configured to be formed using metal stamping.

17. The concentrated solar power system according to claim 1 wherein said first and said second values of said designed material characteristic comprise a structural strength.

18. The concentrated solar power system according to claim 1 wherein said structural strength exceeds a structural strength for a glass mirror panel lacking said structural sub- substructure.