WO2018071969A1

WO2018071969A1 - A solar concentrator and a method for concentrating solar power

Info

Publication number: WO2018071969A1
Application number: PCT/AU2017/051128
Authority: WO
Inventors: Richard Mark Pashley; Charles Evan MILLWARD
Original assignee: Richard Mark Pashley; Millward Charles Evan
Priority date: 2016-10-18
Filing date: 2017-10-18
Publication date: 2018-04-26

Abstract

A solar concentrator for a concentrated solar power generator (1) including a cavity (2) formed in the Earth (3). The cavity has a generally rectangular peripheral edge (4) for defining a correspondingly rectangular opening (5). Generator (1) includes a solar concentrator having a mounting member, in the form of a generally rectangular fiberglass support dish (6), which extends along a generally rectangular paraboloidal manifold, and which is located wholly within cavity (2). A concave reflective surface (7) is fixedly supported by and extends across the entire upper surface of dish (6) for concentrating solar radiation. Surface 7 has a peripheral edge (8) with four generally parabolic portions for collectively defining a second opening (9) that, in use, is disposed relative to opening (5) for receiving solar radiation that has passed through opening (6). A collector, in the form of a thermal receiver (10), is disposed opposite surface (7) for absorbing at least a portion of the solar radiation concentrated by surface (7).

Description

A SOLAR CONCENTRATOR AND A METHOD FOR CONCENTRATING SOLAR

POWER

FIELD OF THE INVENTION

[0001] The present invention relates to a solar concentrator and a method for concentrating solar power.

[0002] Embodiments of the invention have been particularly developed for a concentrated solar power generator that produces steam and will be described hereinafter with reference to that application. However, it will be appreciated that the invention is not limited to such a field of use and is applicable to other concentrated solar power generators, including without limitation, those that store collected heat in molten salts or other storage media, those that focus the solar energy into an optical receiver for transmission by a fibre optic cable, and others.

BACKGROUND

[0003] Any discussion of the background art throughout the specification should in no way be considered as an admission that such art is widely known or forms part of common general knowledge in the field.

[0004] As energy storage solutions become increasingly economically viable for small- scale to utility-scale installations, it is becoming possible to provide grid-level load matching and peak matching while relying upon of a greater number of non-dispatchable electrical generation sources such as PV arrays and wind generation. The wider adoption of these sustainable technologies should, over time, reduce the reliance on the consumption of fossils fuels, and alleviate the pollution and other deleterious environmental impacts that arise from such consumption.

[0005] A popular form of non-dispatchable generation for small-scale installations is provided by flat plate, solid state direct photovoltaic systems that do not need to concentrate the sun's power. However, at a utility-scale, this technology is still relatively expensive to install and the investment payback times are long.

[0006] Two other known technologies for electric generation on a utility-scale include wind turbine electricity generation and solar heating collection. The basic science of these technologies, while known, continues to be explored in an attempt to develop practical applications of the technologies. The widespread adoption of these more sustainable technologies depends critically on the associated capital and running costs, which are both typically significant and often prohibitive to the widespread application of the technologies. For the solar heating collection technologies the generally high capital cost and operational costs arise from, amongst other things:

• The nature and type of the structures used to form the large solar collectors and the associated supporting structures. These collectors, to have a high efficiency, are typically parabolic dishes often having a surface area of 500 m² or more and which weigh 20 tonnes or more. Additionally, the collectors are usually movably mounted to a motorised support structure allow for tracking of the sun during the day. (Solar concentrators are often favoured as they typically provide higher efficiencies than, for example, parabolic troughs and tower heliostat configurations).

• The quality and quantity of materials needed to be included in the structures, collectors and other elements to gain the required function and efficiencies.

• The precision engineering required in the construction and maintenance of the structures.

• The amount of land area required for the structures.

• The location of the structures, which is often remote.

• The environmental conditions to which those structures are exposed.

[0007] Accordingly, there is a need in the art for an improved solar concentrator and a concentrated solar power generator.

SUMMARY OF THE INVENTION

[0008] It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.

[0009] According to a first aspect of the invention there is provided a method for placing a dish reflector for concentrating solar power, the method including the steps of: excavating an open cavity below ground level that defines a generally parabolic or spherical support surface for receiving the dish reflector; and

placing the dish reflector within the cavity.

[0010] In an embodiment the dish reflector reflects solar radiation entering the open cavity.

[0011] According to a second aspect of the invention there is provided a solar concentrator including:

a concave reflective surface for concentrating solar radiation;

a support surface that is substantially coextensive with the reflective surface for directly and complementarity engaging with a substrate; and a support structure extending between the reflective surface and the support surface.

[0012] In an embodiment the reflective surface extends across substantially all of the concave surface.

[0013] In an embodiment the solar concentrator includes a collector for absorbing at least a portion of the solar radiation concentrated by the reflective surface.

[0014] In an embodiment the support structure is located in a cavity and is movable for tracking the sun.

[0015] In an embodiment the support structure is located in a cavity and includes a thin film light reflective mirror or reflective coating for defining the reflective surface.

[0016] In an embodiment the cavity is formed in the Earth.

[0017] In an embodiment the reflective surface has a span of between 20 m to 200 m.

[0018] In an embodiment the support structure is movable and includes one or more wheels, bearings and/or rollers.

[0019] In an embodiment at least one of the wheels, rollers and/or bearings are spring loaded to accommodate minor positional variations of the reflective surface.

[0020] In an embodiment the support structure is located in a cavity and a water drainage collector is situated at the bottom of the cavity to collect rainwater and/or to facilitate washing of the reflective surface.

[0021] In an embodiment: the support structure is located in a cavity; the reflective surface includes a point of maximum focus; and the concentrator includes a solar receiver disposed at the point of maximum focus.

[0022] In an embodiment the solar receiver is movable relative to the support structure for tracking the point of maximum focus.

[0023] In an embodiment the reflective surface includes a range of points of maximum focus and the solar receiver is fixed relative to the support structure and disposed along the range of points of maximum focus.

[0024] According to a third aspect of the invention there is provided a method of concentrating solar radiation including the steps of:

providing a concave reflective surface for concentrating solar radiation;

providing a support surface that is substantially coextensive with the reflective surface for directly and complementarily engaging with a substrate; and

having a support structure extend between the reflective surface and the support surface.

[0025] According to a fourth aspect of the invention there is provided a solar concentrator including: a reflective surface for concentrating solar radiation; and

a support member for supporting the reflective surface, the support member being secured to a substrate such that, in use, wind loads on the reflective surface and the support member bias the support member toward the substrate.

[0026] In an embodiment the substrate is one or more sidewalls of a cavity.

[0027] In an embodiment the support member is contained within the cavity.

[0028] In an embodiment the support member is wholly contained within the cavity.

[0029] In an embodiment the cavity is formed in the Earth.

[0030] In an embodiment the support member is movably secured to the substrate.

[0031] In an embodiment the solar concentrator includes a collector for absorbing at least a portion of the solar radiation concentrated by the reflective surface.

[0032] In an embodiment the support member is a support dish that is located in a cavity and which is movable for tracking the sun.

[0033] In an embodiment the support member includes a thin film light reflective mirror or reflective coating for defining the reflective surface.

[0034] In an embodiment the support member includes a support dish which is movable and has one or more wheels, bearings and/or rollers.

[0035] According to a fifth aspect of the invention there is provided a method for concentrating solar radiation including the steps of:

providing a reflective surface for concentrating solar radiation; and

supporting the reflective surface with a support member;

securing the support member to a substrate such that, in use, wind loads on the reflective surface and the support member bias the support member toward the substrate.

[0036] According to a sixth aspect of the invention there is provided a solar concentrator including:

a mounting member for locating in a cavity, wherein the cavity has a first peripheral edge for defining a first opening; and

a concave reflective surface that is supported by the mounting member for concentrating the solar radiation, wherein the reflective surface has a second peripheral edge for a defining a second opening that, in use, is disposed relative to the first opening for receiving solar radiation that has passed through the first opening.

[0037] In an embodiment the mounting member lies substantially within the cavity.

[0038] In an embodiment the mounting member lies wholly within the cavity. [0039] In an embodiment the mounting member, in use, does not pass through the first opening.

[0040] In an embodiment the reflective surface, in use, does not pass through the first opening.

[0041] In an embodiment the cavity is defined by at least one sidewall and the mounting member is connected to the at least one sidewall.

[0042] In an embodiment the at least one sidewall is defined by one or more of: a surface of the Earth; and a building or another fixed manmade structure.

[0043] In an embodiment:

a. the at least one sidewall includes a curved sidewall surface that terminates at the first peripheral edge; and

b. the mounting member includes: a first surface that is engaged with the

sidewall surface; and a second surface that supports the reflective surface.

[0044] In an embodiment the second surface defines, at least in part, the reflective surface.

[0045] In an embodiment the at least one sidewall includes a non-curved sidewall surface.

[0046] In an embodiment the reflective surface extends along a generally parabolic path.

[0047] In an embodiment the reflective surface extends along a plurality of generally parabolic paths.

[0048] In an embodiment the reflective surface extends along two intersecting generally parabolic paths.

[0049] In an embodiment the generally parabolic paths intersect normally.

[0050] In an embodiment the reflective surface extends along more than two generally parabolic paths and wherein at least two of the more than two generally parabolic paths have respective vertices that are offset from each other.

[0051] In an embodiment the reflective surface extends along a generally spherical path.

[0052] In an embodiment the reflective surface extends along a plurality of intersecting generally spherical paths.

[0053] In an embodiment the intersecting generally spherical paths have offset centres.

[0054] In an embodiment the reflective surface extends along a single generally spherical path.

[0055] In an embodiment the first and the second openings substantially overlie each other. [0056] In an embodiment, in use, the first and the second openings do not intersect with each other.

[0057] In an embodiment the mounting member is fixedly located in the cavity.

[0058] In an embodiment the reflective surface is fixedly supported by the mounting member.

[0059] In an embodiment the reflective surface is movably supported by the mounting member.

[0060] In an embodiment the reflective surface is integrally formed with the mounting member.

[0061] In an embodiment the reflective surface is coated on the mounting member.

[0062] In an embodiment the reflective surface is formed with the mounting member as a laminate.

[0063] In an embodiment the reflective surface is a surface treatment on the mounting member.

[0064] In an embodiment the reflective surface is defined by a thin film light reflective mirror.

[0065] In an embodiment the reflective surface is defined by a reflective coating.

[0066] In an embodiment the support member includes a support layer for lining the cavity.

[0067] In an embodiment the reflective surface is a reflective coating on the support layer.

[0068] In an embodiment the support member includes a support frame for supporting the reflective surface, and wherein the support frame is movably mounted to the support layer.

[0069] In an embodiment the support layer includes one or more of: a base frame; a concrete slab; a settable material; and other structural layers.

[0070] In an embodiment the support frame includes one or more of at least one wheel and at least one roller for movably connecting with the support layer.

[0071] In an embodiment the support layer includes one or more of at least one wheel and at least one roller for movably connecting with the support frame.

[0072] In an embodiment the support frame includes one or more of: metal members; composite members; and plastics members.

[0073] In an embodiment the reflective surface is continuous.

[0074] In an embodiment the reflective surface is segmented.

[0075] In an embodiment the reflective surface is movably supported by the support member. [0076] In an embodiment the reflective surface is movably supported by the support member for allowing tracking of the solar radiation passing through the first opening.

[0077] In an embodiment the solar concentrator includes a substantially transparent cover for extending over at least a portion of the second opening.

[0078] In an embodiment the cover includes predetermined optical properties.

[0079] In an embodiment the solar concentrator includes a substantially transparent cover for extending over at least a portion of the first opening.

[0080] In an embodiment the second opening has an area of at least 300 m².

[0081] In an embodiment the second opening has an area of at least 10,000 m².

[0082] In an embodiment the second opening has an area of at least 30,000 m².

[0083] In an embodiment the second opening has a span in a first direction of at least

20 m.

[0084] In an embodiment the second opening has a span in the first direction of between 20 m and 200 m.

[0085] In an embodiment the reflective surface redirects at least a portion of the solar radiation toward a solar collector.

[0086] In an embodiment the solar collector is fixed relative to the reflective surface.

[0087] In an embodiment the solar collector moves relative to the reflective surface.

[0088] In an embodiment the solar collector includes a thermal collector.

[0089] In an embodiment the solar collector includes a further reflective surface for further redirecting the solar radiation.

[0090] In an embodiment the solar concentrator includes a drainage opening for allowing liquid to drain from the reflective surface.

[0091] According to a seventh aspect of the invention there is provided a method for concentrating solar radiation including the steps of:

locating a mounting member in a cavity, wherein the cavity has a first peripheral edge for defining a first opening; and

supporting a concave reflective surface with the mounting member for

concentrating the solar radiation, wherein the reflective surface has a second peripheral edge for a defining a second opening that, in use, is disposed relative to the first opening for receiving solar radiation that has passed through the first opening.

[0092] According to an eighth aspect of the invention there is provided a concentrated solar power generator including:

a cavity having a first peripheral edge for defining a first opening;

a mounting member for locating in the cavity; a concave reflective surface that is supported by the mounting member for concentrating solar radiation, wherein the reflective surface has a second peripheral edge for a defining a second opening that, in use, is disposed relative to the first opening for receiving solar radiation that has passed through the first opening;

a collector that is disposed opposite the reflective surface for absorbing at least a portion of the solar radiation concentrated by the reflective surface.

[0093] According to a ninth aspect of the invention there is provided a method for generating concentrated solar power, the method including the steps of:

providing a cavity having a first peripheral edge for defining a first opening;

locating a mounting member in the cavity;

supporting a concave reflective surface with the mounting member for

concentrating solar radiation, wherein the reflective surface has a second peripheral edge for a defining a second opening that, in use, is disposed relative to the first opening for receiving solar radiation that has passed through the first opening;

disposing a collector opposite the reflective surface for absorbing at least a portion of the solar radiation concentrated by the reflective surface.

[0094] In an embodiment the step of forming the cavity includes forming a first peripheral edge for the sidewall to define an opening through which solar radiation is able to enter the cavity.

[0095] According to a tenth aspect of the invention there is provided a method for mounting a solar concentrator, wherein the solar concentrator includes a support dish having a concave surface and a convex surface for respectively defining a reflective surface and a support surface and the method includes the steps of:

forming a cavity in a substrate to define at least one sidewall; and

mounting the support dish in the cavity such that the support surface engages with one or more of the at least one sidewall.

[0096] In an embodiment the step of mounting the support dish includes locating the support dish wholly within the cavity.

[0097] According to an eleventh aspect of the invention there is provided a concentrated solar power generator including a plurality of the solar concentrators, each concentrator being in accordance with at least one of the second, fourth or sixth aspects of the invention.

[0098] In an embodiment each concentrator is adjacent to at least one other of the concentrators and adjacent concentrators have different orientations. [0099] In an embodiment the adjacent concentrators are fixed and the different orientations provide those concentrators with peak collection capacity at different times.

[00100] In an embodiment the plurality of concentrators includes three like concentrators that are fixed adjacent each other and which have different orientations.

[00101] According to a twelfth aspect of the invention there is provided a method for generating concentrated solar power including the step of providing a plurality of the solar concentrators, wherein each concentrator is in accordance with at least one of the second, fourth or sixth aspects of the invention.

[00102] Reference throughout this specification to "one embodiment", "some embodiments" or "an embodiment" means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases "in one embodiment", "in some embodiments" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments.

[00103] As used herein, and unless otherwise specified, the use of the ordinal adjectives "first", "second", "third", etc., to describe a common objects, merely indicate that different instances of like objects are being referred to, and are not intended to imply that the objects so described must be in a given sequence temporally, of importance, spatially, in ranking, or in any other manner.

[00104] In the claims below and the description herein, any one of the terms "including", "includes" or "which includes" or the like is an open term that means "including at least the elements/features that follow, but not excluding others" unless the context clearly requires otherwise. Thus, the term "including", when used in the claims, should not be interpreted as being limitative to the means or elements or steps listed thereafter. For example, the scope of the expression "a device including A and B" should not be limited to devices consisting only of elements A and B.

[00105] As used herein, the term "exemplary" is used in the sense of providing examples, as opposed to indicating quality. That is, an "exemplary embodiment" is an embodiment provided as an example, as opposed to necessarily being an embodiment of exemplary quality or status. BRIEF DESCRIPTION OF THE DRAWINGS

[00106] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 illustrates a concentrated solar power generator according to an embodiment of the invention, where the elements are illustrative and not to scale;

Figure 2 is a section taken along section line 2-2 of Figure 1 ;

Figure 3 is a schematic diagram of a parabolic substrate over which a support member with a parabolic reflective surface is able to move;

Figure 4 is a schematic diagram of a parabolic substrate over which a support member with a spherical reflective surface is able to move;

Figure 5 is a schematic diagram of a deeper parabolic substrate over which a support member with a spherical reflective surface is able to move;

Figure 6 is a schematic cross-sectional view of a segmented dish according to another embodiment of the invention; and

Figure 7 is a perspective view of an alternative paraboliodal manifold used in other embodiments of the invention.

DETAILED DESCRIPTION

[00107] Described herein are solar concentrators and concentrated solar power generators.

[00108] Referring to Figure 1 and Figure 2 there is illustrated a concentrated solar power generator 1 including a cavity 2 formed in the Earth 3. The cavity has a generally rectangular peripheral edge 4 for defining a correspondingly rectangular opening 5. Generator 1 includes a solar concentrator having a mounting member, in the form of a generally rectangular fiberglass support dish 6, which extends along a generally rectangular paraboloidal manifold, and which is located wholly within cavity 2. That is, dish 6 is disposed below edge 4 and does not extend through opening 5. A concave reflective surface 7 is fixedly supported by and extends across the entire upper surface of dish 6 for concentrating solar radiation. Surface 7 has a peripheral edge 8 with four generally parabolic portions for collectively defining a second opening 9 that, in use, is disposed relative to opening 5 for receiving solar radiation that has passed through opening 6. A collector, in the form of a thermal receiver 10, is disposed opposite surface 7 for absorbing at least a portion of the solar radiation concentrated by surface 7. [00109] Generator 1 is intended for use in the Southern Hemisphere of the Earth. Accordingly, dish 6, and hence surface 7, is inclined on its east-west axis to the north such that surface 7 is inclined to the north. For a fixed dish, the quantum of the inclination will be dependent upon the location of generator 1. In this embodiment dish 6, and hence surface 7, is movably located in cavity 2 and the inclination to the north is varied with time to increase the solar radiation that is redirected relative to the same static dish. In further embodiments, and to the same end, the inclination of dish 6 is also variable along its north-south axis instead of or in addition to any variation that is available along the east- west axis.

[001 10] In other embodiments, dish 6 includes a single thin fibreglass curved sidewall that defines on one face surface 7 and which includes on the other face a plurality of reinforcing elements. In other embodiments, dish 6 is constructed from other materials, including other classes of materials and combinations of materials. For example, in some embodiments dish 6 includes a very thin curved sidewall - which is able to be rigid, semirigid or pliant - and a lightweight metal frame that is generally rectangular, although complementarily curved to engagement continuously and directly with the underside of the sidewall. In other embodiments use is made of a hub and a plurality of radially diverging struts extending outward from the hub. A circumferential peripheral rim is supported by the struts and a flexible plastics or other sheet material is supported by and extends across the frame to define surface 7.

[001 11] Cavity 2 includes a lower sidewall that is defined by a thin reinforced concrete slab 1 1 that defines a substrate for supporting dish 6. That is, slab 11 is shaped to complementarily movably receive dish 6 and extend along the same generally paraboloidal manifold. Furthermore, dish 6 includes a plurality of spaced apart like rollers 12 (only one of which is numbered) for facilitating that movement. Cavity 2 also includes a generally vertical upper sidewall 13 for defining edge 4 and for providing an additional wind shield for dish 6.

[001 12] In other embodiments, cavity 2 includes a lower sidewall that is covered with a different material or combination of materials. For example, in some embodiments, use is made of a lining such as plastics sheeting or sprayed concrete. However, in other embodiments use is made of concrete footings and a frame extending between the footings. In other embodiments, cavity 2 is lined with a further fibreglass or other dish. In still further embodiments, the lower sidewall is a surface of the Earth and dish 6 is located directly upon, or supported directly upon, that surface of the Earth.

[001 13] It will be appreciated that the lower sidewall referred to above is intended to support a substrate. However, in other embodiments - for example, if the support member is mounted directly to the Earth - the lower sidewall defines, at least in part, the substrate. This substrate is preferentially shaped to substantially complementarily receive the support member. In some embodiments the support member has a base which is generally flat and, hence, the substrate will also be flat. (In such embodiments the support member will typically have an upper face that is generally parabolic or paraboloidal). In other embodiments the support member has a base which is generally parabolic or paraboloidal, and opposed surface of the substrate is complementarily shaped to receive the support member.

[001 14] In the Figure 1 embodiment, dish 6 is mounted for rotational movement along the east-west axis with the use of rollers 12. The movement is actuated by a controller (not shown) which controls an electric motor (not shown) that drives a mechanical linkage with dish 6. In other embodiments, use is made of a manually driven linkage such as a hand crank and ratchet system. This allows dish 6 to be adjusted for the declination of the sun in the north-south direction by rotating the entire dish on the east-west axis.

[001 15] This form of manual adjustment, or adjustment using simple linkages and small electric motors, which is simply implausible for prior art systems, is made feasible due to the light weight nature of the preferred embodiments of the invention combined with those embodiments making use of off-angle reflections. As presently envisaged by the inventors, sufficient performance is available from dish 6 while making incremental movements every week or so to cater for seasonally dependent declinations of the sun. Where even greater conversion efficiencies are required it is possible to move dish 6 more regularly and with smaller increments.

[001 16] In other embodiments rollers are not used, and dish 6 includes, for example, a frame that is slidably mounted to a substrate.

[001 17] In further embodiments, dish 6 includes neither a roller nor a frame and is moved manually and held in place due to the frictional engagement between the large opposed and abutted surfaces areas of the support member (that is, the surface area of the underside of the dish) and the substrate.

[001 18] It will be appreciated that the design of the preferred embodiments is such that wind forces will typically always increase the frictional engagement between the support surface and the substrate and hence more securely retain the reflective surface and the support member within cavity 2. For moveably dishes disposed in particularly windy locations, where there is a desire for a greater safety factor, use is made of restraining rods or straps (typically on the underside of the support surface or the reflective surface) to allow for the desired movement of surface 7 while preventing unintended removal of dish 6 from cavity 2. [001 19] In other embodiments, cavity 2 is inclined to the north along the east-west axis. That is, peripheral edge 4 need not extend only along a horizontal plane. Furthermore, in some embodiments not all of edge 4 lies on the same plane. For example, in some embodiments edge 4 lies upon two or more intersecting planes. In other embodiments, edge 4 extends horizontally and vertically and includes one or more portions that are curved.

[00120] It will be appreciated that for installations of the embodiments in the Northern Hemisphere of the Earth that the north-south orientations will be typically a mirror image for the same latitudes in the Southern Hemisphere.

[00121] Dish 6 spans about 30 m along the north-south axis, and about 30 m along the east-west axis. In other embodiments dish 6 has different dimensions and spans. Furthermore, due to the advantageous features of the embodiments of the invention, it is possible to achieve spans of many tens of meters. Conversely, in other embodiments, use is made of one or more dishes having a span of less than 10 m.

[00122] Although dish 6 remains wholly within cavity 2, in other embodiments either or both of the support member or the reflective surface extend beyond opening 5. For example, for some such embodiments a portion of a support member or a reflective surface extends beyond opening 5 when the reflective surface is at an extreme of the range of available movement. In other such embodiments, edge 8 extends beyond edge 4, although preferentially only minimally.

[00123] In further embodiments, use is made of a wind deflector such as a skirt that extends along all, or substantially all, of edge 4 and inwardly toward edge 8. In other embodiments the deflector extends inwardly beyond edge 8. For example, in some embodiments the skirt is an inwardly extending fixed lip of sidewall 13, while in other embodiments it is a flexible member that is attached on its outer periphery to sidewall 13 and which has an inner periphery that rests over edge 8. It will be appreciated by those skilled in the art, given the benefit of the teaching herein, that other wind deflectors are available.

[00124] Dish 6, and also surface 7, extends along two normal paraboloidal paths to define the manifold. These two paths respectively extend along the east-west axis and the north-south axis of dish 6 with the vertices of the paths being coincident. In other embodiments, the vertices are offset. For example, in one specific embodiment, the vertices are offset along the north-south axis.

[00125] In further embodiments, dish 6 is a segmented dish, in that surface 7 follows a plurality of paraboliodal paths having offset vertices. A schematic cross-sectional view along the east-west axis of such a segmented dish 20 is illustrated in Figure 6. This dish includes three segments, being a central segment 21 and two mirror image outer segments 22 and 23 that extend outwardly from segment 21. Segment 21 follows a paraboloidal manifold along two normally intersecting parabolas having coincident vertices 24, the tangents of which are parallel to the immediately underlying substrate. In this embodiment, the substrate underlying the coincident vertices is substantially horizontal. However, in other embodiments the substrate at that point is other than horizontal. Segments 22 and 23 extend along the east-west axis outwardly in opposite directions from the periphery of segment 21. Segments 22 and 23 follow respective paraboloidal manifolds defined in the east-west direction by half parabolas 25 and 26. Those half-parabolas have respective vertices 27 and 28 that are offset by the span of segment 21. The tangents of the vertices 27 and 28 are also angularly offset from the tangent of vertex 24 by 22.5°, although in opposite directions.

[00126] Extending between segments 22 and 23 are two further outer segments (not shown). Those further segments extend outwardly from segment 21 and follow a paraboloidal manifold that extends along the north-south axis. This manifold includes a continuation of the north-south extending parabola of segment 21.

[00127] Segment 21 is similar to that defined by dish 6 and provides maximum reflective effectiveness during the middle hours of the day. Segment 23 and 22 provide maximum reflective effectiveness respectively during the early and the later hours of the day. In this way, the overall contribution by the compound dish, for a given total span, is made more consistent during the normal daylight hours. That is, while the peak energy reflected will be less (relative to a non-compound dish of the same span), the total energy reflected over the day will be similar. This has the advantage of:

• Reducing the risk of large energy losses due to intermittent cloud cover.

• Facilitates the use of the embodiments to generate a pseudo base load.

• Offers design flexibility to reduce reliance on energy storage.

[00128] In other embodiments, the dish includes more than three segments. Moreover, in further embodiments, the tangents of the vertices of the outer segments are inclined at more or less than 22.5^s relative to the vertex for the centre segment.

[00129] In the Figure 6 embodiment the segments define a single continuous and segmented reflective surface. In other embodiments the segmented reflective surface includes adjacent segments that are spaced apart. In further embodiments - for example, those used in higher latitudes - one or more of the outer segments are releasably or removably fixed to the centre segment. This allows use of all segments during the longer days of the year when the sun traverses through a larger arc, and only the centre segment during the shorter days of the year. [00130] It has been found by the inventors for the embodiment of Figure 1 that, if reflective surface 7 has a focal length below 10, the reflections typically become too scattered as the sun moves off-angle. Conversely, for focal lengths of greater than 16, the engineering for the receiver typically becomes too cumbersome and expensive. Accordingly, in the embodiment of Figure 1 , both paraboloidal paths have a focal length of about 13. In other embodiments, however, where different design optimisations are required, different focal lengths are used, including focal lengths that lie outside the above range. When use is made of segmented dishes, such as exemplified in Figure 6, use is made of focal lengths selected from a larger range.

[00131] In other embodiments use is made of a paraboloidal manifold such as that illustrated in Figure 7. It will be appreciated that other such manifolds are also applicable.

[00132] In one embodiment, receiver 10 includes an array of pipes (not shown) each having a plurality of s-bends connected in series. The array extends along the east-west span of dish 6, while straight portions of the s-bends, which are about 1 m in length, extend along the north-south axis. In use, water is pumped into both ends of the array. The s-bends include computer controlled values to allow selective extraction of the steam from the s-bends as the water is superheated by the concentrator defined by dish 6.

[00133] In other embodiments the pipes are in a sawtooth or wave-shaped configuration.

[00134] In other embodiments use is made of different collectors/receivers. An example of a further track free collector is provided in US patent application 2016/0048008, {Wang et at), the disclosure of which is incorporated herein by way of cross reference. This collector uses an optical capture system to support a tracking-free SC which, when applied to embodiments of the invention, offers scope to further reduce the capital costs associated with those embodiments.

[00135] It will be appreciated that the above embodiment makes use of both on-angle and off-angle parabolic reflections.

[00136] In further embodiments the reflector includes a fibre optic system for transmitting the solar radiation (via a fibre optic cable) to a remote device that subsequently consumes or stores the energy.

[00137] In other embodiments, the receiver is a conventional receiver, such as is used in a conventional paraboloidal dish concentrator, and which tracks the sun continually. Typically, such a conventional receiver is about 0.5 m in diameter. If the embodiment of the invention concerned includes a movable dish, the conventional receiver is attached to the dish at the focal point such that the reflected radiation is focused on a receiver. If the embodiment of the invention concerned includes a fixed dish, the receiver is able to be mounted for mechanical movement above the dish to continually coincide with the point of maximum focus.

[00138] In other embodiments use is made of a dish with a different form factor. For example, in some embodiments use is made of generally circular dishes, while in other embodiments generally square or generally oval dishes are used. In the preferred embodiments, however, use is made of generally rectangular dishes to increase the land utilisation, particularly for those sites where multiple solar concentrators are placed adjacent to each other. Moreover, it has been found that if excavation of cavity 2 is required, that excavation is most simplified when for rectangular dishes.

[00139] The preferred embodiments take advantage of the fact that the concentration of the sun's power is in principle a simple process. Moreover, the potential solar concentrating power of large parabolic reflecting dishes is high. When considering two- axis tracking it is noted that the concentrating power is well over 1 ,000 times, which is much higher than for other configurations such as: single-axis tracking; the use of a linear Fresnel prism; or the use of trough systems (which offer about 80 times concentration). With the average Earth's solar radiation of 800 W/m², a large single dish of 500 m² is able to produce very high temperatures - in some cases up to 1 ,700 ⁹C at the focal point in the collector/receiver - and produce a thermal power output of up to, on average, about 400 kW. Recently developed collectors are able to achieve thermal energy absorption rates of up to 97%. However, conventional wisdom dictates that concentrated solar power generators should have the form more typically of radio telescopes. Accordingly, known devices have a large area dish (for example, up to 500 m²), the weight of which can be 20 tonnes. Moreover, the support structure for the dish can easily be a further 7 tonnes. This high level of structural overhead is required as the dish, which has a high surface area, is fully exposed to all wind forces and requires considerable structure to prevent the dish from the large wind shear impacts.

[00140] In recognition of the limitations of the existing art, preferred embodiments of the invention provide a parabolic or spherical reflector for concentrating solar power, based upon:

• The excavation of an open cavity below effective ground level

• Locating with the cavity either a fixed parabolic or spherical reflector surface or a mobile parabolic or spherical reflector. If the latter, then the preference is for the reflector surface to be free to move into any position or orientation on the parabolic or spherical surface that has been constructed below effective ground level.

[00141] This below effective ground level construction allows an even distribution of the weight of the reflecting object (dish, frame or other structure) over the excavated curved surface. This in turn greatly increases the range of spans of the reflective object that are available for use. Even so, it is presently envisaged by the inventors that the overall economic factors will result in the span of the embodiments most likely implemented to be in the range of 20 m to 200 m. By comparison, the presently available dishes are limited in size, typically by the economics of having to build structures that can withstand the environmental rigours of strong winds. These considerations are greatly ameliorated, if not practically completely removed, by the design principles of the present embodiments.

[00142] In other embodiments spans are available outside of the range mentioned above.

[00143] The basic principles of the embodiments are widely applicable to differently configured solar concentrators and concentrated power generators. To illustrate the range of applications there are provided below several non-limiting examples.

[00144] Example 1 : This example is similar to the embodiment in Figure 1 , where the support member and the reflective surface are fixed. More particularly, a parabolic cavity is formed in the ground with a span of 20 m such that the focal point is at a similar height above ground level to the depth of the parabolic cavity. The orientation of the parabolic cavity is selected to give optimum solar light collection at the latitude where the cavity is located. Typically, the side walls of the parabolic cavity should reach a maximum slope of about 45° to the horizontal. Increasing the cavity depth to produce higher slopes, see for example in Figure 5, gives little further improvement in solar collection. The surface of the inside of the cavity - that is, the curved sidewall - is pre-coated with a layer of cement to form the mounting member before reflective sheets are fixed over the entire parabolic surface to define the reflective surface. In other embodiments use is made of thin plastic sheeting instead of or in addition to the layer of cement. A drain hole through all the layers is positioned at the lowest point and this is attached to a pipe and pressure activated pump to remove and collect rain water and/or to facilitate regular washing of the reflective surface. A suitable solar thermal collector (for example, a superheated steam generator) (not shown) is positioned at the focus of the parabola. It will be appreciated that in this example the thermal collector is fixed. However, in other embodiments the thermal collector is movable.

[00145] In this embodiment the solar concentrator includes:

a concave reflective surface for concentrating solar radiation, which is defined by the generally upwardly facing reflective surface of the thin plastics sheet;

a support surface in the form of the underside of the thin plastics sheet that is coextensive with the reflective surface and which directly and complementarity engages with a substrate in the form of the layer of cement; and a support structure, being the thin plastics sheet, for extending between the reflective surface and the support surface.

[00146] In other embodiments the layer of cement is omitted and the substrate is the underlying upwardly facing surface of the Earth. That is, in such embodiments, the support surface is directly engaged with the Earth.

[00147] Example 2: A parabolic cavity is formed in the ground as described in Example 1 above, with an additional plastic parabolic or spherical reflector positioned within the cavity. This parabolic reflector is illustrated in Figure 3, and is controlled to move across the parabolic surface using wheels, bearings and/or rollers to track the sun. The plastic moveable parabolic reflector is coated with a thin layer of a reflective material such as: silvered glass, (spherically) curved mirror panels, mirrored plastic sheeting (made from, for example, PVC or acrylic), plexiglass, or thin aluminium mirror sheet or foil.

[00148] Example 3: The reflector is also able to be made spherical (that is, circular in section), rather than parabolic depending upon the application. As can be seen in Figure 4, a spherical reflector approximates to a parabolic reflector when the radius of the curvature of the reflective surface is shallow.

[00149] Example 4: A support member having a curved frame that extends along one or more of the parabolic or spherical paths is able to be fitted into the parabolic cavity and controlled for movement. The frame is able to include wheels, rollers and/or bearings. However, in other embodiments the support member includes wheels, rollers and/or bearings that are mounted to the lower sidewall and which are selectively directly physically engaged with the underside of the frame to allow for the controlled movement. In this way, the reflective surface is able to be moved to track the sun. In this embodiment the reflective surface is fixedly attached to the frame and includes an array of curved glass mirror panels. In other embodiments different materials are used, such as plastic or aluminium mirror sheeting.

[00150] Example 5: A parabolic cavity is excavated in the ground and has a span of about 200 m. As the weight of the solar concentrator (that is, the support member and the reflective surface) are distributed evenly over the underlying ground surface of the excavated cavity such a large span is able to be accommodated.

[00151] It will be appreciated by those skilled in the art, with the benefit of the teaching herein, that the optimum span for a given reflective surface will depend on local conditions such as soil properties and the maximum operating temperature of the collector device. The latter will also be dependent upon the collection area available and sun intensity. Concentrators having these large spans are applicable for collecting thermal energy for use in high temperature processes such as, by way of example, metal smelting and carbon fibre production.

[00152] Example 6: An array of parabolic reflectors and corresponding coated cavities are produced with each having a different orientation to average out or moderate the sum of the collector output from each reflector in the array. The cavity orientations are determined by the precise geographical location and the extent of the moderation sought. This system would obviate or remove the need for solar tracking. This moderation/averaging of the output is particularly advantageous for those applications where the energy captured is being used to provide a consistent base-load power and/or to minimise energy storage requirements for the associated concentrated solar generator.

[00153] The use of the above examples provides greater scope for the use of parabolic reflectors for concentrating solar power, particularly for large dishes. In practice, there is a need to use dishes with a radius of at least 10 m to produce sufficiently high temperatures (typically about 400 °C to 1 ,000 °C) at the focal point collector. Otherwise the transport and storage of the collected heat becomes uneconomical. To do this, the heat is often collected as superheated steam. This, in turn, has many uses, including electricity generation.

[00154] As discussed above, the limiting factor of the prior art resides with the high cost of production of the two axis parabolic dish and support structure in the conventional above ground, radio telescope-like, format. The cost arises from the above ground design, which means the structure has to be rigid and yet moveable. Additionally, accurate parabolas, reflector efficiency and collector alignment become crucial in such systems because of the high production and running costs. Each of these concerns are either greatly ameliorated or eliminated by the design principles used in the embodiments described above. That is, the substrate and/or the support member is formed by a suitably shaped open cavity or shielded cavity, often excavated in the earth, such that the dish is mostly or entirely below ground level or at least substantially shielded from wind forces. In this way, the reflecting parabolic or spherical surface is able to be, if movable, readily and cheaply supported by rollers, bearings and/or wheels. If fixed, then the reflective surface and/or support member are able to be mounted directly to the substrate (which is defined by the sidewall or sidewalls of the cavity). This change in configuration removes the need for a heavy support frame, and is highly resistant to the effects of wind shear. In addition, the reflective surface is able to be configured to move in almost any direction, within the cavity, and even rotated, to encompass all seasonal variations. That is, at least some embodiments are not limited to one or two axis movement of the reflective surface. [00155] In one of the simplest embodiments, a parabolic cavity is created in the ground and a reflecting material, such as mirrored plastic film or even aluminium mirror sheeting, is used to completely cover the curved surface of the cavity. The collector is positioned at the focal point using either cables or a rigid structural support. This configuration does not produce optimum sun concentration, due to a lack of solar tracking, but it is inexpensive to install and operate. Not only does this embodiment do away with the prior art structural issues, it also need not be constructed with the same level of engineering precision as use is made of both on-angle and off-angle reflections.

[00156] Another embodiment includes a support member which is a parabolic or spherical metal frame that is located within a cavity. The cavity is able to be defined wholly or in part by an excavation in the Earth, or by another man made structure. In other embodiments, the frame is of a plastic composite such as fibreglass. The frame has rollers, wheels and/or bearings. For those embodiments making use of a plastic frame, the wheels or rollers are fixed to the sidewall of the cavity. In this way the movement of the parabolic (or spherical) frame and the plastic parabola (or sphere) within the cavity is able to be controlled while retaining the reflective surface within the cavity. Accordingly, insofar as the reflective surface, and the associated support member, is subject to wind forces, those forces will result in an increased locating bias for those elements with the substrate. That is, the wind forces will result in a more secure support of the reflective surface and/or the support member to the substrate.

[00157] The substantially reduced cost of constructing, commissioning and operating the embodiment of the invention allows other losses - for example, a lower collection efficiency due to the use of lower cost reflective materials - to be more easily tolerated. These low costs also allow reduced angles of tracking to become economically viable in more situations, further reducing capital and running costs. Further, the more even distribution of weight afforded by the design principles, allows very large reflectors to be used with spans of over 100 m.

[00158] Accordingly, it will be appreciated that, in other embodiments, a solar concentrator includes:

a reflective surface for concentrating solar radiation; and

[00159] The support member is in some embodiments fixedly secured to the substrate, while in other embodiments the support member is movably secured to the substrate.

Moreover, in some embodiments the support member fixedly supports the reflective surface while in other embodiments the support member movably supports the reflective member. The latter applies typically for those embodiments where movement is required and the support member is fixedly secured to the substrate.

[00160] In some embodiments the support member is integral with the substrate, and in other embodiments the support member is integral with the reflective surface.

[00161] In some embodiments the reflective surface is continuous, while in other embodiments the reflective surface is segmented.

[00162] In other embodiments, the solar concentrator includes:

[00163] In some embodiments the concave surface is a compound concave surface. That is, the surface follows a plurality of concave surfaces. Preferentially the compound concave surface is continuous, in that the individual compound surfaces co-terminate at opposed edges. In other embodiments, the compound surface is segmented.

[00164] The major advantages of the preferred embodiments of the invention include:

• The ability to use relatively cheap construction materials and methods because the ultimate structure does not have to withstand high wind loads.

• The ability to seal the unit, for example, by covering the cavity or dish with glass or another translucent material to reduce risk of damage and to reduce cleaning costs.

• The low cost of the construction allows multiple dish configurations to be contemplated including: arrays of dishes having varying orientations to concentrate solar energy at different times of the day; a single dish structure with segmented reflective surfaces having different orientations targeting maximum concentration at particular times of the day.

• The low cost of construction allows for solar energy to be used economically in processes like desalination where a simple "boil and condense" methodology is applicable. • Making those associated systems and technologies that rely upon solar technologies more attractive. For example, embodiments of the invention are able to be designed for generating heat via steam, or the storage of heat economically in molten salts, and the like.

• The ability to economically construct large concentrators to generate much higher solar thermal intensities which could be used for many applications, such as in metal smelting, carbon fibre production and ceramics production.

Conclusions and Interpretation

[00165] It will be appreciated that the disclosure above provides various significant solar concentrators and concentrated solar power generators as well as enabling further associated technologies and processes making use of such concentrators and generators.

[00166] It should be appreciated that in the above description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, Figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the Detailed Description are hereby expressly incorporated into this Detailed Description, with each claim standing on its own as a separate embodiment of this invention.

[00167] Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those skilled in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination.

[00168] In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.

[00169] Similarly, it is to be noted that the term "connected", when used in the claims, should not be interpreted as being limited to direct connections only. Thus, the scope of the expression "a device A connected to a device B" should not be limited to devices or systems wherein an output of device A is directly connected to an input of device B. It means that there exists a path between an output of A and an input of B, which may be a path including other devices or means. "Connected" may mean that two or more elements are either: in direct physical contact, or electrical contact, or communicative contact with each other; or not in direct physical contact, or electrical contact, or communicative contact with each other but yet still co-operate or interact with each other.

[00170] Thus, while there has been described what are believed to be the preferred embodiments of the invention, those skilled in the art will recognize that other and further modifications may be made thereto without departing from the spirit of the invention, and it is intended to claim all such changes and modifications as falling within the scope of the invention. Functionality may be added or deleted from the block diagrams and operations may be interchanged among functional blocks. Steps may be added or deleted to methods described within the scope of the present invention.

Claims

1. A method for placing a dish reflector for concentrating solar power, the method

including the steps of:

excavating an open cavity below ground level that defines a generally parabolic or spherical support surface for receiving the dish reflector; and

placing the dish reflector within the cavity.

2. A method according to claim 1 wherein the dish reflector reflects solar radiation entering the open cavity.

3. A solar concentrator including:

a concave reflective surface for concentrating solar radiation;

a support surface that is substantially coextensive with the reflective surface for directly and complementarily engaging with a substrate; and

a support structure extending between the reflective surface and the support surface.

4. A solar concentrator according to claim 3 wherein the reflective surface extends across substantially all of the concave surface.

5. A solar concentrator according to claim 3 or claim 4 including a collector for

absorbing at least a portion of the solar radiation concentrated by the reflective surface.

6. A solar concentrator according to any one of claims 3 to 5 wherein the support structure is located in a cavity and is movable for tracking the sun.

7. A solar concentrator according to any one of claims 3 to 5 wherein the support structure is located in a cavity and includes a thin film light reflective mirror or reflective coating for defining the reflective surface.

8. A solar concentrator according to any one of claims 6 to 7 wherein the cavity is formed in the Earth.

9. A solar concentrator according to any one of claims 3 to 8 wherein the reflective surface has a span of between 20 m to 200 m.

10. A solar concentrator according to any one of claims 3 to 9 wherein the support structure is movable and includes one or more wheels, bearings and/or rollers.

1 1. A solar concentrator according to claim 10 wherein at least one of the wheels, rollers and/or bearings are spring loaded to accommodate minor positional variations of the reflective surface.

12. A solar concentrator according to any one of claims 3 to 6 wherein the support structure is located in a cavity and a water drainage collector is situated at the bottom of the cavity to collect rainwater and/or to facilitate washing of the reflective surface.

13. A solar concentrator according to claim 3 wherein: the support structure is located in a cavity; the reflective surface includes a point of maximum focus; and the concentrator includes a solar receiver disposed at the point of maximum focus.

14. A solar concentrator according to claim 13 wherein the solar receiver is movable relative to the support structure for tracking the point of maximum focus.

15. A solar concentrator according to claim 13 wherein the reflective surface includes a range of points of maximum focus and the solar receiver is fixed relative to the support structure and disposed along the range of points of maximum focus.