WO2012024738A1 - Panneaux de miroir pour concentrateurs solaires de grande superficie - Google Patents

Panneaux de miroir pour concentrateurs solaires de grande superficie Download PDF

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Publication number
WO2012024738A1
WO2012024738A1 PCT/AU2011/001104 AU2011001104W WO2012024738A1 WO 2012024738 A1 WO2012024738 A1 WO 2012024738A1 AU 2011001104 W AU2011001104 W AU 2011001104W WO 2012024738 A1 WO2012024738 A1 WO 2012024738A1
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WO
WIPO (PCT)
Prior art keywords
panel
components
mirror
metal
metal skin
Prior art date
Application number
PCT/AU2011/001104
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English (en)
Inventor
Keith Lovegrove
Glen Harvey Johnston
Gregory John Burgess
Original Assignee
The Australian National University
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Filing date
Publication date
Priority claimed from AU2010903835A external-priority patent/AU2010903835A0/en
Application filed by The Australian National University filed Critical The Australian National University
Publication of WO2012024738A1 publication Critical patent/WO2012024738A1/fr

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Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/08—Mirrors
    • G02B5/0808—Mirrors having a single reflecting layer
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24S—SOLAR HEAT COLLECTORS; SOLAR HEAT SYSTEMS
    • F24S23/00—Arrangements for concentrating solar-rays for solar heat collectors
    • F24S23/70—Arrangements for concentrating solar-rays for solar heat collectors with reflectors
    • F24S23/82—Arrangements for concentrating solar-rays for solar heat collectors with reflectors characterised by the material or the construction of the reflector
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24S—SOLAR HEAT COLLECTORS; SOLAR HEAT SYSTEMS
    • F24S23/00—Arrangements for concentrating solar-rays for solar heat collectors
    • F24S23/70—Arrangements for concentrating solar-rays for solar heat collectors with reflectors
    • F24S2023/83—Other shapes
    • F24S2023/832—Other shapes curved
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24S—SOLAR HEAT COLLECTORS; SOLAR HEAT SYSTEMS
    • F24S25/00—Arrangement of stationary mountings or supports for solar heat collector modules
    • F24S25/60—Fixation means, e.g. fasteners, specially adapted for supporting solar heat collector modules
    • F24S2025/601—Fixation means, e.g. fasteners, specially adapted for supporting solar heat collector modules by bonding, e.g. by using adhesives
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/40—Solar thermal energy, e.g. solar towers

Definitions

  • the present invention relates generally to solar thermal power stations and, in particular, to solar concentrators for such power stations.
  • a sandwich panel comprising a relatively light weight core sandwiched between two or more metal skins.
  • the sandwich panel exhibits the desired rigidity by virtue of the fact that if the panel is flexed in one direction, one metal skin experiences a tensile force and the other metal skin experiences a counteracting compressive force, these countervailing forces acting against each other in a roughly equal and opposite manner to impose rigidity on the panel. Flexing the panel in the other direction causes the metal skins to exchange the aforementioned roles, still however imposing rigidity on the panel. Selection of suitable core filler material results in light weight construction which, together with the aforementioned rigidity, provides lightweight stable reflective panels.
  • a mirror panel comprising a lightweight rigid core, a thin metal skin on opposite sides of the core, to provide structural rigidity, and a reflective mirror surface formed on the anterior side of one of the metal skins.
  • a solar mirror sandwich panel comprising: a reflective lamina component having a reflective surface that has an average slope error of less than or equal to about 6 milliradians and preferably less than 2 milliradians; two metal skin components for stiffening the solar panel, and a core filler component disposed between the metal skin components; wherein said components are bonded together using adhesive and are arranged in a curved configuration to provide a curved solar panel.
  • a method of making a solar mirror panel comprising the steps of: providing an assembly comprising a reflective lamina component having a reflective surface, two metal skin components, a core filler component located between the metal skin components, and adhesive materials disposed between said components; conforming the components to a mould having an at least partially curved surface in contact with said components, and controllably heating at least part of at least one surface of the mirror panel to heat the adhesive material disposed between the core filler component and each of the reflective lamina component and the metal skin components, without heating the bulk mass of the core filler component.
  • Mirror panels manufactured in this way can be of any perimeter shape, including but not limited to triangles, trapeziums and squares.
  • Fig. 1 depicts a cross section of sheet metal + EPS sandwich panel (not to scale);
  • Fig. 2 shows an example of a process 200 for fabricating a solar panel using transient thermal bonding of EPS foam cored panels
  • Fig. 3 shows a plot of areal cost vs. tensile stiffness for a range of possible skin materials
  • Fig. 4 shows a plot of areal cost vs. E.t2 ( a measure of flexural rigidity) for a range of possible filler materials
  • Fig. 5 depicts a cross-section through double sheet metal skinned, polystyrene foam filled panel
  • Fig. 6 depicts an equilateral triangular mirror panel constructed of 3 identical short isosceles triangles
  • Fig. 7 depicts an equilateral triangular mirror panel constructed of 3 identical trapezoids
  • Fig. 8 depicts an equilateral triangular mirror panel constructed of 3 identical trapeziums
  • Fig. 9 shows deflection tests for a 1.2 m x 1.2 m dual skin, foam core panel;
  • Fig. 10 shows a comparative view of a hand-made trapezoidal sub-panel;
  • Fig. 11 shows a contour plot of a flux distribution
  • Fig. 12 depicts a foam-filled dual metal skin trapezoidal mirror panel with out- of-phase trapezoidal metal substrates
  • Fig. 13 depicts a lay-up of a foam-filled metal skinned panel, showing front and rear metal skins, foam core and mirrored glass laminated onto the front metal skin;
  • Fig. 14 shows a front view of a foam-filled mirror panel triangular prototype
  • Fig. 15 shows a rear view of the foam-filled mirror panel of Fig. 14;
  • Fig. 16 shows an edge view of a foam-filled mirror panel, showing mirrored glass, folded sheet-metal edges and foam core;
  • Fig. 17 depicts predicted surface deflection characteristics for the foam-filled mirror panel
  • Fig. 18 depicts a layout of approximately 1200 data points used for photogrammetric analysis of the foam mirror panel surface quality
  • Fig. 19 shows a contour plot of the foam mirror panel (of Fig. 14) surface shape determined from the photogrammetric analysis
  • Fig. 20 shows a plot showing the relative depth coordinate deviations between the measured paraboidal data and an ideal paraboloid based on data in Fig. 19;
  • Fig. 21 shows a layout of flux mapping equipment and measurement components
  • Fig. 22 shows a plot of variation of flux image Gaussian standard deviation as a function of mirror panel-to-target distance for the foam mirror panel flux image
  • Fig. 23 shows X and Y cross sections through flux intensity distribution for foam filled mirror flux image
  • Fig. 24 shows a plot of Percent-Power-In-Radius (PR) for the flux
  • Fig. 25 shows a Hot-laminated glass-on-metal-laminate (GOML) foam-core mirror panel on a mounting frame;
  • GOML Hot-laminated glass-on-metal-laminate
  • Fig. 26 shows a Spherical fibre-glass mould in an oven with a trapezoidal mirror facet and vacuum bag
  • Fig. 27 depicts a surface plot of the triangular mirror panel of Fig. 25;
  • Fig. 29 shows a frequency distribution of surface slope errors across the mirror panel of Fig. 25;
  • Fig. 30 shows X- and Y-cross-sections through a measured flux distribution
  • Fig. 31 shows a Percent power-in-radius (PIR) plot for the flux distribution of
  • Fig. 32 depicts deflections at 3 locations on the surface of the mirror panel of Fig 25 as a function of equivalent hydraulic loading pressure
  • Figs. 33A and 33B show a possible flow chart for a process for fabricating mirror panels
  • Fig. 34 depicts a mirror cleaning tunnel
  • Fig. 35 depicts a radiant heat oven for laminating glass-on-metal-laminate elements
  • Fig. 36 depicts a heated clamshell mould for panel fabrication
  • APPENDIX A sets out attributes of various skin materials
  • APPENDIX B sets out attributes of various core filler materials
  • APPENDD C sets out salient qualities of a range of panel designs based on different combinations of materials and construction techniques
  • APPENDIX D shows a spread sheet calculation of the costs associated with trapezoidal sub-panels.
  • a solar mirror sandwich panel comprising a reflective lamina component having a reflective surface that has an average slope error of less than or equal to about 6 milliradians and preferably less than 2 milliradians, two metal skin components for stiffening the solar panel, and a core filler component disposed between the metal skin components, wherein said components are bonded together using adhesive and are arranged in a curved configuration to provide a curved solar mirror panel.
  • a solar mirror sandwich panel comprising a reflective lamina component having a reflective surface formed on side of said reflective lamina component, two metal skin components for stiffening the solar panel, and a core filler component disposed between the metal skin components, said core filler component being material selected from the group consisting of expanded polystyrene, paper honeycomb, fibreboard, and cardboard, wherein said components are bonded together using adhesive and are arranged in a curved configuration to provide a curved solar mirror panel.
  • the core filler component may comprise at least one of a polymer, paper honeycomb, plastics, and cardboard.
  • the reflective lamina component may comprise a glass sheet with a mirror backing.
  • the glass sheet may have a thickness of less than about 2 mm.
  • a thickness of said core filler component may be between about 5 millimetres and about 100 millimetres.
  • the metal skin components may comprise a steel sheet having a thickness between about 0.2 mm and 1.0 mm.
  • the metal skin components may comprise the same materials.
  • the metal skin components may have the same thickness.
  • the components may be bonded using one or more adhesives.
  • the components may be bonded using fusible film.
  • the components may be bonded using hot melt adhesive.
  • the components may be bonded with a fusible film of Ethyl Vinyl Acetate having a fusing temperature of approximately 100 Degrees C.
  • the metal skin components may comprise a steel sheet having a thickness between about 0.2 mm and 1.0 mm and which has a corrosion protection coating based in part on a zinc and aluminium formulation.
  • the components may be bonded using a fusible Ethyl Vinyl Acetate film having a fusing temperature of approximately 100 Degrees Centigrade.
  • Also disclosed is a method of making a solar mirror panel comprising the steps of providing an assembly comprising a reflective lamina component having a reflective surface, two metal skin components, a core filler component located between the metal skin components, and adhesive materials disposed between said components, conforming the components to a mould having an at least partially curved surface in contact with said components, and controllably heating at least part of at least one surface of the mirror panel to heat the adhesive material disposed between the core filler component and each of the reflective lamina component and the metal skin components, without heating the bulk mass of the core filler component.
  • the step of controllably heating at least part of at least one surface of the mirror panel may comprise applying heat using a heated body in contact with said metal skin component to set the adhesive between said metal skin components and core filler components.
  • the step of controllably heating at least part of at least one surface of the mirror panel may comprise applying heat using a heated body in contact with said reflective lamina component to set the adhesive between said reflective lamina and core filler components.
  • a thickness of said core filler component may between about 5 millimetres and about 100 millimetres.
  • a single adhesive may be used between adjacent components. Two or more adhesives may be used.
  • the adhesive material may comprise fusible film.
  • the adhesive material may comprise a hot melt adhesive.
  • Said heated body may comprise a metal sheet.
  • Said core filler component may comprise expanded polystyrene (EPS).
  • EPS expanded polystyrene
  • the step of controllably heating at least part of at least one surface of the mirror panel may comprise applying heat using a radiant heat lamps directed at said reflective lamina and metal skin components to set the adhesive between said reflective lamina and skin and core filler components.
  • the step of controllably heating at least part of at least one surface of the mirror panel may comprise applying heat using a hot oven with forced convection to transfer heat to said reflective lamina and metal skin components to set the adhesive between said reflective lamina and skin and core filler components.
  • the rate of heating and amount of heat applied to said reflective lamina and metal skin components to set the adhesive between said reflective lamina and skin and core filler components may be optimised so that the process is completed before the core material has become hotter than its own softening point.
  • Fig. 2 shows an example of a process 200 for fabricating a solar panel using transient thermal bonding of EPS foam cored panels.
  • a first step 201 panel components are cut to size.
  • the process follows an arrow 202 to a step 203 in which panel components are assembled as shown in Fig 1.
  • the core material is Expanded Polystyrene (EPS).
  • the adhesive / bonding layers are fusible films with a fusing temperature close to or slightly in excess of the softening temperature of the EPS core.
  • the assembly may include edge strips.
  • the process follows an arrow 204 to a step 205 in which a decision is made as to whether to elect option 1 or option 2, these representing alternate fabricating sub-processes.
  • the process follows an arrow 206 to a step 207 in which heat and pressure are rapidly applied to the top and bottom of the laid up components by means of curved heated plates.
  • the heat is conducted through the metal and glass layers and causes the film layers to melt.
  • the pressure applied by the plates causes the components to bond in the desired curved shape.
  • the amount of heat which is transferred and the pressure applied are such that the EPS foam does not suffer significant shrinkage or collapse. Either the thermal mass and initial temperature of the heated plates or else the initial temperature and duration of contact of the heated plates are optimised to achieve this.
  • the heat and pressure may however be sufficient to permanently deform the EPS into a curved shape (this is desirable at it improves the optical quality of the panel and avoids creep in the panel shape).
  • the EPS may be pre-formed to the desired curved shape (again using moderate heat and pressure) before being assembled with the other components.
  • the process then follows an arrow 208 to a step 209.
  • step 20S if option 2 is elected, the process follows an arrow 212 to a step 213 in which, as an alternative to application of pre-heated plates, pressure is applied using curved plates, and in a following step 215, heat is rapidly applied by some other means (e.g. by heat lamps, inductive heating, oil filled tubes etc) in order to melt the film without causing the EPS to collapse.
  • the process may then optionally follow a dashed arrow 216 to a step 217, in which cooling is applied to the plates to avoid excess heating of the EPS, the cooling being applied by passing cooled liquid through channels in the plates.
  • the process then follows a dashed arrow 218 to the step 209. If the cooling step 217 is not to be performed, then the process is directed from the step 215 directly to the step 209 without performing the optional step 217.
  • the step 209 allows the adhesive to cure, after which the process follows an arrow 210 to a step 211 in which the fabricated panel is removed from the fabrication equipment.
  • the disclosed invention relates to mass produceable mirror panels (also referred to as MPMPs in this specification) suitable for solar thermal power stations comprised of large dish concentrators or other types of solar concentrators, and a die/tooling system for mirror panel mass production.
  • MPMPs mass produceable mirror panels
  • the criteria in regard to which the performance of the MPMPs may be judged may include:
  • the disclosed MPMPs show an approximate surface slope error (measure of optical accuracy) of 1 to 6.0 miHiradian.
  • the surface slope error should be less than 6.0 milliradian, and preferably less than 2.0 milliradian.
  • MPMP samples have been subjected to 960 hours of exposure in a temperature and humidity cycling oven, and did not display significant distortion or destruction of the component parts of the panel. At least 2 full mirror panels have been exposed to outdoor weather conditions for more than 12 months, without showing signs of degradation or distortion.
  • the MPMPs exhibit an areal weight of approximately 13 kg m-2.
  • Durable MPMP samples have withstood both 960 hours of humidity and temperature cycling, and more than 12 months exposure to the elements at a test facilities at the Australian National University.
  • the reflective element of the panel which utilises thin glass-on-metal-laminate (GOML) technology, demonstrates very satisfactory corrosion resistance.
  • the MPMP embodiments have been developed and implemented in a staged manner that can be characterised by the following Milestones.
  • Solid-body panel having its own inherent stiffness, such that it forms both a mirror-mountable substrate and a structurally self-supporting member
  • the two construction types identified were: (i) "Cored” mirror panels, whereby the GOML mirror surface formed one skin of a dual-skin construction, bonded either side of a core material having significantly greater thickness than the skins.
  • Milestone 3 also signalled significant investment into Finite Element Modelling software and techniques to assess the mechanical performance of the different designs developed.
  • EPS expanded polystyrene
  • Milestone 4 undertook the process of constructing prototypes of the two most promising mirror panel designs proposed in Milestone 3. These were:
  • Milestone 4 described an attempt to incorporate both of these designs into one unit, whereby trapezoidal sub-panels - which had been identified for use with sheet-metal shell designs - were fabricated as a foam core construction, and the three trapezoidal elements fastened together to form the desired triangular mirror panel.
  • a foam cored mirror panel consisting of a GOML front skin and a thin sheet- metal rear skin bonded either side of an expanded polystyrene (EPS) core, was constructed.
  • EPS expanded polystyrene
  • a wet-adhesive bonding system was used, for this prototype.
  • the foam- cored system showed superior structural rigidity over the GOMOGL construction, but required a more complex fabrication process.
  • a glass-on-metal-on-glass GOMOGL mirror panel consisting of thin glass mirror bonded on the anterior side of a sheet-metal substrate, and a thin, clear glass sheet bonded to the posterior side, was fabricated using a hot-laminating system. Although the GOMOGL panel showed lower structural rigidity, it also demonstrated a high level of resistance to thermal deformation due to the symmetric force pairs that are created either side of the sheet-metal substrate.
  • Strand 7 FEM software was used to predict the structural deformations expected for the mirror panel prototypes. Physical measurements were also undertaken to confirm the predicted deformations. Physical measurement using 150 Pa (equivalent to a 60 km hr-1 wind load) distributed load on the foam-cored panel showed deflections in the order of 1.35 mm, with corresponding surface slope errors of approximately 1 milliradian. Similar loading on the GOMOGL panel showed deformations of 1.8 mm, and corresponding slope error of approximately 1.9 milliradian.
  • the foam-cored mirror panel showed a focal flux distribution that enabled 90% light capture in a circular aperture having 0.28 m radius.
  • the GOMOGL mirror panel prototype showed approximately 80% capture at the same aperture radius.
  • a second, foam-cored mirror panel prototype was constructed using the hot- laminated GOML mirror facets, and both photogrammetric surface deformation studies and videographic flux-map studies showed the panel to perform with a similar, , performance compared to the first foam-cored mirror panel constructed using wet- bonding methods reported in regard to Milestone 5.
  • Milestone 7 reported the results of a design study for a feasible manufacturing process for producing the foam-cored mirror panel.
  • one production unit would be expected to produce approximately 1 mirror panel per hour. Multiple production units would scale this rate up proportionately.
  • the foam-cored mirror panel has an areal weight of approximately 13 kg m-2.
  • Solid-body panel having its own inherent stiffness, such that it forms both a mirror- mountable substrate and a structurally self-supporting member
  • type 1 structures are thick foam/fibreglass shell structures and the ArmacelTM range of products (consisting of thick, low-density core material wrapped in vacuum heat-shrunk plastic film).
  • Type 2 structures use thin substrate material (eg. polymer or sheet metal) upon which a mirror can be mounted, and several (generally 3 to 6) supporting ribs beneath the substrate that provide rigidity and shape control.
  • substrate material eg. polymer or sheet metal
  • Type 3 structures are similar to Type 2 devices, but use a more dense supporting structure under the substrate that constitutes a 3-D framework with multiple contact points between the substrate and the framework.
  • a panel comprised of an expanded polystyrene (EPS) foam filler bonded between two sheet metal skins, with the entire structure formed at the time of bonding (by conformance to a mould) to take up a spherical shape, as shown in Fig. 1.
  • the thin back-silvered glass mirror would be bonded onto the concave metal skin.
  • a panel having a pressed sheet-metal skin, with curved, folded returns pressed into its perimeter and curved, pressed-metal ribs mounted beneath the central regions of the panel.
  • Fig. 3 shows a plot of cost per unit area as a function of the tensile stiffness (given by the tensile modulus times thickness) for the different skin materials. Preliminary criteria for assessment of the skins was lowest areal cost for a given tensile stiffness. From the results shown in Fig. 3, it appears that sheet steel is the most cost-effective skin material, unless a skin with relatively low stifmess is required. Judged in the light of the other 9 criteria listed in section 0, sheet steel does appear to have a high probability of satisfying these as well.
  • a symmetric sandwich panel made up of two identical skins of thickness t, and Young's modulus E s and a core of thickness tc and Young's modulus E c has an apparent Young's modulus in flexure given by -
  • Eflex E s - (l - 2t ⁇ ) 3 (E s - Ec) (1)
  • h 2 ts + tc is the total thickness of the panel.
  • the flexural rigidity, D, of a panel is given by -
  • Fig. 4 shows a plot of cost per square metre against E c tc 2 for a range of different foam core materials. Examination of Fig. 4 indicates that expanded polystyrene (EPS) and extruded
  • polystyrene (Styrofoam) are the most cost-effective filler materials for consideration - i.e. they have the lowest ratio of cost per square metre to Et 2 .
  • Paper honeycomb and cardboard are not shown on the graph but should also be considered, as they are both rigid and relatively inexpensive. However, judged by the other criteria paper honeycomb has two major drawbacks, in that it,
  • Corrugated fibreboard also suffers from defect (i) above and is also not readily deformable to a spherical profile.
  • Fig. 4 shows that Styrofoam has a comparable cost / Et 2 ratio to EPS. However it is less suited to the present application as it can only be obtained in flat sheets, which must be hot wire cut or machined to the desired shape. It is also not readily available in sheets of the required width.
  • Table 1 presents the results of cost versus rigidity calculations for tetrahedral space- frame, pressed/formed ' Weldmesh' wire grid, and pressed metal ribs. These three structures are taken (for comparison purposes) as supporting a laminate made up of a lmm thick mirror bonded to 0.8mm thick sheet steel.
  • the tetrahedral frame and pressed Weldmesh supports could possibly be of interest where the main panel has an intermediate rigidity, requiring a lesser degree of support than a glass on metal laminate.
  • the various fibreglass panels and an Armacel panel see Table C.l.
  • the fibreglass panels are already more expensive than other options, even without the addition of a frame.
  • extra rigidity can be obtained more cheaply by increasing the core thickness than by adding a frame; and the mounting of a frame to an Armacel panel would require the bonding of the frame to the film surface at a number ( ⁇ 10) of points.
  • Appendix C describes the salient qualities of a range of panel designs based on different combinations of materials and construction techniques. Where appropriate the structural components in the different designs were adjusted to meet the specification criteria of 1 mm deflection in the centre of the panel. Costing estimates were then made of the different aspects of the designs, i.e. materials, construction, tooling. From these estimates, an overall areal cost for the different designs was arrived at.
  • Table C.l in Appendix C shows the weight, costs and structural properties of a range of panel designs. Three different designs are seen to be in the desired range:
  • thermoplastic skins typically have a much higher coefficient of thermal expansion than that of glass. In the case of Luran S 797 S film the difference is so large as to result in significant distortion of a panel under the anticipated environmental temperature range. Although films of lower coefficient of thermal expansion are available, they are generally expensive.
  • Sheet steel appropriately coated for corrosion protection is the skin material that best meets the selection criteria.
  • the coating must be compatible with the bonding methods applied including the bonding of mirror to the outer surface. Good results have been obtained using a commercial product (Colorbond) consisting of a steel sheet with a Zinc / Aluminium (Zincalume) coating under a paint coating.
  • the sheet metal surface should not suffer from significant outgassing after bonding to the mirror.
  • Colorbond skin (0.8 mm) pressed to have folded, curved edges, with central area rib support on the underside of the panel.
  • Thin (1.0 mm) mirrored glass will be bonded onto the front (concave) side of the panel after panel manufacture.
  • the triangular panel shape has also been modified such that it is composed of 3 sub- panels. This strategy has been dictated by the availability of commercial sheet metal coming in maximum widths of 1500 mm (a complete triangular mirror panel 2200 to 2400 mm on a side has a vertical height of 1900 to 2100 mm, also requiring extra width around its periphery for the folded edges).
  • Three sub-panel shapes have been considered, consisting of
  • the short isosceles triangle and trapezoid sub-shapes represent approximately equal, optimal (minimum wastage) use of sheet metal, while the trapezium shape, due to its non- parallel edge nature, does not make optimum use of sheet metal area, and was thus discarded from further consideration.
  • Fig. 10 shows one of the two trapezoidal sub-panels.
  • the trapezoidal sub-panel was fabricated using two 0.35 mm colorbond skins with curved, folded edge returns, bonded either side of a 30 mm thick expanded polystyrene (EPS) sheet, as shown schematically in Fig. 5.
  • EPS expanded polystyrene
  • the mirrored glass was bonded onto the sub-panel while pressed between the metal/foam panel and a spherical mould surface, such that the glass/front surface of the panel continued to hold the spherical shape after the adhesive had set and the sub-panel was removed from the mould.
  • Structural deflection tests were performed on square, dual skin, foam core test panel, having dimensions 1.2 m x 1.2 m x 30 mm (EPS thickness) x 2x0.35 mm (colorbond sheets), by supporting it at its four vertices, applying a distributed load (water bags) over a l m x l m central area, and measuring the deflection at its centroid.
  • Fig. 9 shows the results of these deflection tests.
  • a hydraulic pressure loading of 150 Pa corresponds to an equivalent wind speed of
  • Fig. 9 indicates that a deflection between approximately 0.5 mm and 0.9 mm occurs at this loading. These deflection figures indicate a slope error of between
  • the mirror sub-panel focal distribution was tested in a preliminary manner by pointing it at the sun and focusing its focal region onto a white screen. Focal area minimisation appeared to occur at a distance of approximately 14 m to 16 m from the sub-panel,.
  • Fig. 11 shows a contour plot of a flux distribution, and a crude analysis indicates that an estimated 90% of the flux distribution falls within an approximate diameter of 500 mm.
  • the ANU 400 m 2 Dish receiver has an entrance aperture diameter of 700 mm, and if similar sub-panels as the present hand-made unit were used to cover the surface of the dish, it could be anticipated that 100% of the reflected flux would be captured, as compared to less than 85% with the existing mirror panels.
  • Appendix D shows a spread sheet calculation of the costs of component materials and operations deemed necessary to undertake a production run of trapezoidal sub-panels sufficient to provide the reflecting surfaces for 200 x 400 m 2 solar concentrators.
  • Milestone 4 detailed the design, construction and preliminary performance characteristics of a prototype trapezoidal, foam-filled mirror sub-panel. That stage of the project combined the two panel designs put forward in Milestone 3, into one panel. Work has progressed further under the present Milestone to produce working, full-size prototypes of two panels, with the introduction of a new glass-on-metal-laminate (GOML) design that has been designated GOMOGL - glass-on-metal-on-glass-laminate. The two panels are thus constructed as:
  • Efforts were then directed to the construction of a heavy metal- frame mould, having a short isosceles triangle (SIT) aperture that could be used to apply curved, folded edges to the perimeter of sheet-metal substrates, with the intent of measuring the degree of deflection that occurred in substrates made with the mould after they were laminated with glass in the laminating oven.
  • SIT short isosceles triangle
  • Fig. 12 shows the overall layout of the panel
  • Fig. 13 shows a cross-section (not to scale) through the main structural elements of the panel. Note that while Fig. 13 appears to show a flat profile across the panel, in actual fact the panel is curved to a spherical profile having an approximate radius of curvature of 28 m.
  • the present foam-filled panel consists of three trapezoidal glass mirrors bonded onto three similar trapezoidal sheet metal substrates on the anterior face, which in turn are bonded onto a foam core, with a final posterior metal skin bonded to the foam.
  • the anterior trapezoidal sheet metal substrates are butted together at the trapezoid joints to form a completely flat surface onto which the mirror trapezoids can be bonded. This means that the panel is truly contiguous across the trapezoids, with no separation and consequential fixing between trapezoidal sub-panels.
  • the mirror trapezoids and front sheet-metal substrate trapezoids are aligned in- phase, so that the mirrors do not bridge across the substrate joints, but the rear metal trapezoidal skin are aligned out-of-phase with the joins on the front faces. This may assist cross-sub-panel rigidity. Out-of-phase layering of the front glass and metal skin will also be tested, and is attractive in that it further enhances the cross-sub-panel rigidity.
  • this design also means that the glass is providing some component of the overall structural rigidity of the overall panel. This may have adverse ramifications on rigidity if fractures in the glass along the underlying substrate butt-joints occur.
  • the folded edges around the perimeter of the panel are comparatively small, having a 12mm depth.
  • This feature has allowed the dual advantages to be achieved that (i) the folds can be applied to the sheet-metal with a normal, straight-edge metal folder, but (ii) the fold depth is such that it is large enough to provide significant edge rigidity, but is small enough to let the edges be elastically deformed to a curved profile upon fabrication. While this design has allowed successful fabrication of the panel, it does incur some residual stress in both the metal edges and the foam core, as these are stressed against their natural shapes.
  • the prototype shows a number of improvements compared to the foam-filled- panel constructed for Milestone 4, which consisted of three individually fabricated segments which were subsequently joined together.
  • the design is more rigid, has an increased glass area (due to the smaller margins between trapezoidal mirror segments), is quicker to manufacture, and does not require curves on deep folded edges
  • Figs. 14, 15 and 16 show front, back and side views of the foam-filled mirror panel, respectively.
  • the glass-on-metal-on-glass-laminate (GOMOGL) consists of a panel of sheet-metal, bonded on either side with a sheet of glass (actually one side is mirrored glass, while the other is clear glass, to minimise cost - mirrored glass is almost twice as expensive as clear glass).
  • a GOMOGL SIT sub-panels may be constructed by first laying the mirror segments, then the flat sheet-metal substrate (with 12 mm straight-folded edges) then the anterior clear glass segments onto a convex (male) mould. Two part epoxy can be used to bond the layers, with compression applied using a vacuum bag to constrain the layers to take the shape of the mould while the epoxy cured.
  • the full-size panel can be completed by fixing the GOMOGL SITs to profile-cut ribs using screws. In a production situation, an automated fastening system can replace the screws.
  • Fig. 17 shows the surface deflections predicted by Strand 7 for the foam-filled mirror panel subject to a uniform normal load of ISO Pa.
  • the model has the same constraints as the test conditions for the prototype panel - i.e. the bottom of the corner brackets are only fixed in the direction normal to the plane of the panel.
  • the average (vertical) deflection is 0.31 mm and the average surface slope error is 0.29 milliradian.
  • the figure indicates that a deflection of 0.40 mm can be expected at the centre of the panel, while a deflection of 0.37 mm can be expected at the centre of one of the trapezoidal sub-panels.
  • Photogrammetry is the technique of extracting 3 -dimensional object coordinates for signalised, or unique, data points placed across the object surface.
  • the technique uses image data from many photographs (24 photos were used in the present photogrammetric study) taken from many different viewing positions around the object to be measured. High coordinate precisions are possible with this analysis technique (relative precisions of 1: 80,000 were achieved in the present study).
  • absolute data point coordinate precisions of approximately 10-15 micron were obtained. This makes possible surface characterisations that highlight features that influence the optical performance of a surface.
  • Fig. 18 shows a layout plot of the data points arrayed across the triangular aperture of the panel
  • Fig. 19 shows a contour plot of the 3D data extracted from the photogrammetric analysis of the foam-filled panel.
  • the plot shows a subtraction of the ideal depth coordinates from the measured depth coordinates for approximately 1200 data points across the panel surface.
  • the ideal surface against which the measured data points are compared is a spherical surface having a 28 m radius of curvature (ROC), or 14 m focal length. This surface corresponds to the ROC of the mould on which the panel was made. It should be noted that if the measured data conformed exactly to an ideal surface, then the subtraction between the measured and ideal coordinates should leave a surface plot that is flat through the origin in the x-y plane - i.e. all deviations are zero.
  • the panel surface is significantly 'flatter' than the mould (i.e. the overall deviation is negative, which indicates that the panel depth coordinates are less (lower) than the mould coordinates. This is illustrated in Fig. 20 below.
  • Flux mapping has been used to characterise the actual focal region light distributions for the mirror panels. This technique involves reflecting light from the sun from the mirror panel onto a diffuse, white target, and photographing the resulting flux distribution on the target. Fig. 21 illustrates this process.
  • the mirror panel-flux target vector should be paraxial with the mirror panel-sun vector.
  • the layout shown in Fig. 21 shows a non-paraxial alignment. This arose because no facilities are available to mount the mirror panel and flux target at the large focal distances required from each other (approximately 13 - 20 m) and have them track the sun with a fixed alignment.
  • the non-paraxial alignment means that the flux image captured in the present study will show some skewing, or coma.
  • these effects are small enough to still allow representative assessments of the focal light distributions, and put a 'worst-case' bound on the data extracted from the flux maps.
  • Post processing of the flux image yields information about the energy content, spatial distribution and radiant intensities of the focal spot.
  • absolute insolation measurements were not available at the time of the flux maps. Absolute values of integrated power, peak intensity and percent power within radius thus cannot be presented for the measured flux maps.
  • an intrinsic calibration procedure was applied to some flux maps that displayed appropriate characteristics amenable to this procedure, and this leads to flux map parameters that will be within approximately 15% to 20% of their true values.
  • a determination of the optimal focal point of the mirror panels This is achieved by fitting a 2-dimensional gaussian distribution to the flux images (taken at different panel-to-target distances), and extracting the standard deviation (SD) of the fitted distribution. Plotting this value against the panel-to-target distances shows where the SD is a minimum, which in turn defines the 'tightest' flux distribution, and the focal point for the mirror panel.
  • SD standard deviation
  • Fig. 23 indicates that under insolation conditions of 1000 W m '2 a peak flux intensity of approximately 1.6 x 10 4 W m "2 , or a concentration ratio of 16 suns, can be expected.
  • the expected peak concentration ratio for 216 such mirror panels (constituting the 400 m 2 surface area of the Generation I ANU Big Dish design) is then approximately 3,460 suns.
  • the existing mirror surfaces on the ANU Dish produced a peak concentration ratio of approximately 1,200 suns when first installed. This indicates that the foam-filled mirror panel has a surface quality approximately 3 times better than the current mirror panels.
  • the percent-power-in-radius (PIR) plot shown in Fig. 24 indicates that 90% of the flux power would be captured within a 0.29 m radius from the flux centroid.
  • the receiver on the ANU Dish has an aperture with a 0.35 m radius.
  • Fig. 24 indicates that approximately 97% of the incident flux radiation would be captured in this aperture.
  • Panel sizes and shapes are limited to the short-isosceles-triangle (SIT) sub-panel shape and dimensions. This cannot be extended beyond 2.2 m on its longest side before structural rigidity becomes compromised. It can be noted that even with a 2.2 m side dimension the GOMOGL panel is significantly less rigid than the foam filled panel.
  • SIT short-isosceles-triangle
  • the team's assessment of the relative merits of the two panel types is that the foam-filled mirror panel offers more attractive characteristics than those of the GOMOGL panel. Dominant of these are the ability to make large area mirror panels (significantly larger than the 2.2 m equilateral triangular panel prototype), having almost any desired aperture shape and 'tailored' structural rigidity (by the use of suitable thickness foam core material).
  • Part of the finalisation process in step 2 has been the development and fabrication of a suitable mould for fabricating hot-laminated GOML mirror panels.
  • Fig. 25 shows the hot-laminated GOML foam-core mirror panel.
  • the panel is shown mounted on a triangular support frame.
  • Fig. 26 shows the fibreglass mould mounted in the bonding oven, with a trapezoidal mirror panel shown under a vacuum bag prior to lamination.
  • ROC radius of curvature
  • Fig. 27 shows the measured surface of the mirror panel.
  • the panel has been oriented to fall on a regular coordinate system (x,y transverse displacements, z-depth displacement, origin at central vertex of the panel).
  • Performing a least-squares linear fit on the measured depth (z) coordinates versus their radial displacement from the origin allows an estimation of the optimal focal length for the panel. Performing this analysis yields a best-fit ROC of 35.28 m.
  • a depth subtraction between the measured and ideal z-coordinates for a sphere having this best-fit ROC (35.28 m) is undertaken. Positive deviations on the surface indicate displacements of the measured surface above the ideal surface.
  • Fig. 28 shows a plot of depth-deviations versus x-displacement. The figure indicates that worst case deviations are in the order of +lmm to -2.5mm.
  • the panel shows positive deviations at its centre and negative deviations around its perimeter, with high positive deviations at two of its vertices.
  • Fig. 12 of Milestone 5 shows a similar surface deviation plot for the previous foam-cored mirror panel (bonded together with wet adhesive). That is, it appears a common distortion mode for panels of this type to deflect upwards in their centres and at their vertices.
  • the magnitude of deviations on the previous, wet-bonded, panel appear to be lower (approximately ⁇ 1 mm) than those exhibited in the present (hot-laminated GOML) panel.
  • Fig. 29 shows the frequency distribution of surface slope errors calculated for the panel.
  • the mode of the distribution indicates the standard deviation of the equivalent bi-variate Gaussian distribution of slope errors for the panel.
  • the figure indicates a primary mode of approximately 3.5 milliradian, although a secondary mode is also indicated at approximately 6.5 milliradian.
  • This type of bi-modal distribution makes it difficult to characterise a surface with a single figure of merit (ie. slope error standard deviation), and it is clear that a simple bi-variate Gaussian distribution of surface slope errors is not a very applicable model with which to identify this surface.
  • Peak concentrations in the order of 12,000 to 14,000 W m '2 (12-14 suns) can be expected from the panel.
  • peak concentrations in the order of 10 to 12 suns could be expected.
  • Interpretation of the performance of the focal flux distribution is best undertaken using a percent power-in- radius (PR) plot of the power distribution in the flux region.
  • PR percent power-in- radius
  • Fig. 30 shows that the flux image saturated the camera CCD array slightly, such that the peak of the distribution is slightly truncated. Taking this into account, indicates that a peak intensity of some 10,000 W m "2 occurred in the distribution. This is comparable to the figure of 10,000 to 12,000 W m '2 predicted in the ray-trace model for the panel.
  • Fig. 31 shows a PIR plot for the distribution. Slight extrapolation from the graph indicates a 90% capture radius of 0.36 m. This figure also shows a good correlation with the figure of 0.356 m predicted in the ray-trace study.
  • Fig. 32 shows the results of structural deflection tests that have been performed on the panel.
  • the panel (Fig. 25) was loaded uniformly across its surface to simulate wind loads up to 40 km hr "1 (equivalent hydraulic loading of 150 Pa).
  • deflections of approximately 1.5 mm were observed at the three test positions. This compares favourably with the same figure of 1.5 mm for the previous foam-cored mirror panel (reported in Milestone 5).
  • the prototype hot-laminated GOML mirror panel is showing acceptable performance for use in high-level concentration (approximately 500-1000 suns peak concentration ratio) applications on large-area devices such as the ANU Big Dish. Somewhat better performance appears possible using wet-laminated fabrication techniques, although this is not a preferred method of construction.
  • Milestone 7 The specified objective for Milestone 7 was to 'Design machinery for manufacture of mirror panels'.
  • Figs. 33A and 33B show that there are six main components utilised in the mirror panel manufacture process:
  • the thin glass mirrors will also be supplied cut to the required sizes and shapes.
  • the glass typically comes with light paper between the glass sheets, and a form of talc powder is resident on the painted rear surfaces of the glass. This powder must be thoroughly removed before using the glass.
  • the EPS will come supplied as a flat sheet, cut to the required size and shape. No further processing is required for this component.
  • Metal edge strips approximately 35mm wide, may be used for protecting the edges of the mirror panel, and for structural support, will come supplied from the manufacturer with both edges pre-cut to the required curved profile that accommodates the curvature on the panel.
  • These sheet-metal components also typically come with a plastic protective film that requires removal before making use of the edge strips.
  • the fusible film will be supplied on a roll, and must be cut to the required size and shape when laid-up between the sheet-metal substrate and the thin mirror.
  • the wet adhesive which may be used to bond the metal skins either side of the EPS core typically comes in drums, and must be applied, most likely with an industrial spray application system.
  • a heated "clamshell” type mould that bonds the GOML and metal skins to the EPS core material, while maintaining the surface profile on the final mirror panel unit.
  • Fig. 34 shows a schematic of the functional elements of a continuous feed cleaning tunnel for the mirror elements.
  • mirror blanks are fed into the tunnel from the input handling table, flexible entrance and exit flaps contain the working fluids within the confines of the cleaning tunnel, and a conveyor transport system moves the mirrors through a water jet cleaning section, an air drying jet system and finally a radiant heat drying section before exiting to the output handling table. Wash water is scavenged in a suitable tank, and reused after filtering to supply the cleaning liquid.
  • Fig. 35 shows a diagram of the radiant heat oven used to bond the mirrored glass onto the sheet-metal substrates.
  • the oven consists of an insulated box, containing arrays of heat lamps placed above and below a sheet-metal mould, having the required curvature to impart a pre-curvature into the mirror panel elements during fabrication.
  • the mirror panel elements (glass/fusible film/sheet-metal) are vacuumed onto the surface of the metal mould prior to heating.
  • a alternative implementation has heating elements supported with fans for enhanced convective heat transfer to the mirror panel elements.
  • Fig. 36 shows the clamshell mould for shaping and bonding the finished mirror panel.
  • the mould can be made from either fibreglass or an egg-crate sub-structure and sheet- metal surface type structure.
  • the clamshell design uses hinged male and female halves to clamp either side of the mirror panel. This design both holds the mirror panel to the required shape, and applies heat to accelerate the cure time of the adhesive used to bond together the sheet-metal and GOML elements either side of the EPS core material. Alternatively it can be used to bond the complete panel assembly using exclusively fusible film adhesives in a single process.
  • the “Max deflection” values are those predicted for a total load (normal to the panel) of 150 Pa. They are obtained using a flat plate model of the panel - The deflection is reduced by approximately 25% if a shell model is used, in the case of an homogenous panel (effect on a panel with a frame or ribs not yet determined).
  • the modelling of the panels was done using the Strand7 finite elemnt modelling package.
  • the plate surface was divided into ⁇ 300 elements unless otherwise specified.
  • a choice is available between various different types of plate elements - the simplest is a "Tri3" (i.e. a triangular element defined by 3 points), which requires the least computational time.
  • Tri3 i.e. a triangular element defined by 3 points
  • the model with a composite material the program does not allow for coupling effects.
  • all modelling was done using Tri6 elements. Note that in some cases the panel on its own was modelled using Tri3, but the panel with mirror (value in square brackets) using Tri6.
  • the “mean abs rot” column refers to the mean absolute rotation of all nodes on the plate (i.e. nodes on folds and frames are not included), which is closely corrlated with the mean slope error.
  • Values for the steel + EPS sandwich do not (except) for the weight include the effect of the mirror stiffness. Values for the various GOML combinations do include the stiffness of the mirror.
  • Rigidity, deflection and rotation values in the table are for the Armacel panel on its own.

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Abstract

L'invention décrit un panneau sandwich de miroir solaire (2000), comprenant un composant de laminé réfléchissant (2002) possédant une surface réfléchissante qui présente une erreur de pente moyenne inférieure ou égale à environ 6 milliradians, deux composants de revêtement métallique (2004, 2005) destinés à renforcer le panneau solaire, et un composant d'agent de remplissage central (2003) disposé entre les composants de revêtement métallique (2004, 2005). Lesdits composants sont liés ensemble à l'aide d'un adhésif (2001) et sont agencés selon une configuration incurvée pour créer un panneau solaire incurvé.
PCT/AU2011/001104 2010-08-26 2011-08-26 Panneaux de miroir pour concentrateurs solaires de grande superficie WO2012024738A1 (fr)

Applications Claiming Priority (2)

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AU2010903835 2010-08-26
AU2010903835A AU2010903835A0 (en) 2010-08-26 Mirror panels for large area solar concentrators

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WO2012024738A1 true WO2012024738A1 (fr) 2012-03-01

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US9494340B1 (en) 2013-03-15 2016-11-15 Andrew O'Neill Solar module positioning system
US10078197B2 (en) 2016-09-21 2018-09-18 The United States Of America As Represented By Secretary Of The Navy Foam sandwich reflector

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4124277A (en) * 1977-02-16 1978-11-07 Martin Marietta Corporation Parabolic mirror construction
US4465734A (en) * 1981-08-21 1984-08-14 Glaverbel Composite mirror panels
US7077532B1 (en) * 2000-04-05 2006-07-18 Sandia Corporation Solar reflection panels
WO2010115237A1 (fr) * 2009-04-06 2010-10-14 Wizard Power Pty Ltd Panneaux miroirs solaires et fabrication de ceux-ci

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4124277A (en) * 1977-02-16 1978-11-07 Martin Marietta Corporation Parabolic mirror construction
US4465734A (en) * 1981-08-21 1984-08-14 Glaverbel Composite mirror panels
US7077532B1 (en) * 2000-04-05 2006-07-18 Sandia Corporation Solar reflection panels
WO2010115237A1 (fr) * 2009-04-06 2010-10-14 Wizard Power Pty Ltd Panneaux miroirs solaires et fabrication de ceux-ci

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US9494340B1 (en) 2013-03-15 2016-11-15 Andrew O'Neill Solar module positioning system
US10190804B2 (en) 2013-03-15 2019-01-29 Andrew O'Neill Solar module positioning system
US10078197B2 (en) 2016-09-21 2018-09-18 The United States Of America As Represented By Secretary Of The Navy Foam sandwich reflector

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