WO2008092194A1

WO2008092194A1 - Solar energy collector heliostat

Info

Publication number: WO2008092194A1
Application number: PCT/AU2008/000095
Authority: WO
Inventors: Philipp Schramek; Andrew Tanner; Peter Le Lievre
Original assignee: Solar Heat And Power Pty Ltd
Priority date: 2007-01-29
Filing date: 2008-01-29
Publication date: 2008-08-07

Abstract

Disclosed herein are variations of heliostats that may be used in solar energy collector systems, and related methods. A reflector structure of the heliostat may be rotated about a first fixed horizontal rotational axis. The reflector structure may be rotated about a second rotational axis that is substantially orthogonal to the first rotational axis. First and second actuators may be employed to effect rotation about the first and second axes, respectively. The reflector structure's motion may be confined to a three-dimensional volume that allows for closer side-to-side packing of the heliostats in a heliostat field.

Description

SOLAR ENERGY COLLECTOR HELIOSTAT

FIELD OF THE INVENTION

This invention relates to a heliostat for use in a solar energy collector field. The term "heliostat" in the context of this specification is to be understood as meaning a device that is arranged to be driven to follow relative diurnal movement of the sun during the course of a solar year while reflecting incident solar radiation along a substantially constant path angle to a receiver.

BACKGROUND OF THE INVENTION

Solar energy collector fields have been proposed and constructed for reflecting incident radiation toward at least one, e.g., tower-mounted, receiver or absorber. An example of one such field arrangement is provided in U.S. Patent No. 4,117,682. Also, various field arrangements have been developed for minimizing mutual blocking and shading of heliostats in order to maximize reflection and hence, concentration of incident solar radiation. One example of such an arrangement involves multi-tower receivers and the selective redirection of reflected radiation from one receiver to another, and in this context, reference is made to U.S. Patent No. 5,899,199.

In collector fields that employ a plurality of separate heliostats for concentrating radiation on a receiver, each heliostat conventionally has a reflector structure that pivots about a fixed vertical axis for azimuthal tracking and about a horizontal axis (that is itself rotated about the vertical fixed axis) for tracking in elevation. Examples of such heliostats are disclosed in U.S. Patent Publication No. 2005/279953 (Gerst, published December 22, 2005) and International Patent Publication No. WO2005/098327 (Yutaka et al., published October 20, 2005). Another example of a heliostat arrangement is disclosed in U.S. Patent Publication No. 2004/074490 (Mills et al., published April 22,

2004, now abandoned), and in this case, a reflector element (for example, a hexagonally shaped reflector element) is pivotally supported by a carrier that is pivotal about an axis that is, as described, disposed parallel to the ground plane, with the axis of the reflector element being not parallel to the pivot axis of the carrier. To increase the collection efficiency of a solar energy collector system employing heliostats, it is desired that the heliostats be close packed together. However, it is desired to move the reflector element of a heliostat to track diurnal motion of the sun, to direct incident solar radiation to a selected target receiver, and/or to stow or park the reflector element. Such positioning of reflector elements can lead to increased risk of collision between adjacent ones of the heliostats. Improved heliostats are desired, e.g., heliostats that allow close packing without substantially increasing the risk of collision between reflector elements.

SUMMARY OF THE INVENTION

Described here are heliostats that may be used in a variety of solar energy collector arrays. Some variations of the heliostats described here may be configured to allow relatively close side-to-side packing in a solar energy collector array, e.g., a multi-tower solar array. Related methods are also disclosed.

In general, the heliostats are configured to confine movement of their reflector elements to a three-dimensional space that may allow close packing of adjacent heliostats. For example, the reflector movement of some variations of the heliostats having a fixed horizontal rotational axis may be confined to a three-dimensional space that has two relatively planar, opposing side surfaces, hi these variations, heliostats may be placed side-to-side (e.g., within a row in a solar array) to within about 6 inches, to within about 4 inches, to within about 3 inches, to within about 2 inches, to within about 1 inch, or even less. Further, such heliostat packing may be achieved without substantially increasing the risk of collisions, and may reduce the risk of collisions, between adjacent ones of the heliostats (e.g., heliostats within a row).

The heliostats comprise a reflector structure, a vertically extending support member, and a linkage coupling the reflector structure to the vertically extending support member. The reflector structures comprise a reflector element that is arranged in use to reflect incident solar radiation to a receiver, e.g., a tower-mounted receiver. The linkage is configured to confine rotation of the reflector structure to a volume described by at least a portion of a central slice of a sphere that is substantially aligned with the vertically extending support member. In these heliostats, the reflector element may be any suitable reflector element, e.g., a reflector element comprising a flat reflective surface or a curved reflective surface, such as a reflective surface having a cylindrical curvature or a spherical curvature.

In some variations of these heliostats, the linkage may comprise a first rotational element coupled to the vertically extending support member, where the first rotational element is configured to rotate a reflector structure about a first fixed horizontal rotational axis. The linkage may further comprise a second rotational element that is configured to rotate the reflector structure about a second rotational axis that is substantially orthogonal to the first rotational axis. The first rotational element may be configured to pivotally couple a carrier-mounting member to the vertically extending support member. In those variations, the second rotational element may be configured to pivotally couple a carrier configured to support the reflector element to the carrier- mounting member. In some cases, the heliostats may comprise a first actuator arranged when actuated along a first actuator axis to effect pivotal movement of the reflector structure about the first rotational axis, and/or a second actuator arranged when actuated along a second actuator axis to effect pivotal movement of the reflector structure about the second rotational axis. If present, the first and/or second actuators may be a linear actuator.

Certain variations of heliostats described here comprise a vertically extending support member and a carrier-mounting member pivotally mounted to the vertically extending support member about a fixed horizontal first axis that is located adjacent an upper region of the support member. A carrier is pivotally mounted to the carrier- mounting member about a second axis that is substantially orthogonal to the first axis. A reflector element is carried by the carrier and arranged in use to reflect incident solar radiation to a target receiver, e.g., a tower-mounted receiver. A first actuator is arranged when actuated to effect pivotal movement of the carrier-mounting member about the first axis, and a second actuator is arranged when actuated to effect pivotal movement of the carrier about the second axis. These variations of heliostats may incorporate a reflector element comprising a flat or curved reflective surface, .e.g., a reflective surface having a cylindrical or spherical curvature. For example, in some variations, the reflective surface of a reflector element may be concave to focus or enhance concentration of reflected radiation at the target receiver. Some of these heliostats may be configured to map out a volume defined by at least a portion of a vertically oriented central slice of a sphere when the first and second actuators are actuated to effect pivotal movement of the carrier-mounting member and the carrier, respectively.

When the heliostats are tracking diurnal (relative) movement of the sun, first and second actuators may be actuated in a manner that is controlled to provide for a substantially constant path angle of reflection from the heliostat with changes in azimuthal and elevation angle of the sun. Also, if the carrier-mounting member is pivotal (relative to the vertically extending support member) about a fixed horizontal axis, adjacent heliostats may be positioned side-by-side in closely spaced relationship with reduced or minimal risk of collision occurring between the reflector elements of adjacent heliostats during relative orientation of the reflector elements.

Methods for positioning reflector element to direct incident solar radiation to a target receiver are provided. These methods comprise providing a heliostat comprising a reflector structure that, in turn, comprises a reflector element arranged in use to reflect incident solar radiation to a receiver. The heliostat used in the methods comprises a vertically extending support member, and a linkage coupling the reflector structure to the vertically extending support member. The linkage is configured to confine rotation of the reflector structure to a volume defined by at least a portion of a central slice of a sphere that is substantially aligned with the vertically extending support member. The methods comprise applying force along a first actuator axis to cause the reflector element to pivot about a first rotational axis, and applying force along a second actuator axis to cause the reflector element to pivot about a second rotational axis that is substantially orthogonal to the first rotational axis.

Any of the heliostats described here may be configured for use in a solar energy collector array. For example, some solar energy collector arrays comprise two or more heliostats described here, wherein a first heliostat is confined in movement to a first volume and a second heliostat is confined in movement to a second volume. The first heliostat is arranged adjacent to the second heliostat such that a planar vertical surface of the first volume is aligned with and adjacent to a planar vertical surface of the second volume. Multiple heliostats in an array may be analogously close-packed, e.g., to form a row of heliostats.

Some variations of solar energy collector arrays described here comprise two or more heliostats, where at least some adjacent heliostats may be packed essentially continuously, e.g., along a row. These arrays may comprise two or more heliostats, in which a first heliostat having a first width is arranged adjacent to a second heliostat having a second width, hi these arrays, a center-to-center spacing between the first and second heliostats may be substantially equal to the sum of one half the first width and one half the second width. Thus, if the first and second heliostats in the arrays have the same width, then the first and second heliostats may be arranged adjacent to each other so that their center-to-center spacing is substantially equal to the width of the first and second heliostats. Multiple heliostats in an array may be similarly close-packed, e.g., where several adjacent heliostats have center-to-center spacings substantially equal to the sum of half their respective widths.

The following description provides illustrative examples of heliostats and related methods, and the description is provided with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a rear perspective view of a variation of a heliostat with a tilted reflector structure.

FIG. 2 illustrates a side view of the variation of the heliostat shown in FIG. 1.

FIG. 3 shows a side view of the variation of the heliostat shown in FIG. 1, with a reflector structure tilted in a generally forward, upward-facing direction. FIG. 4 illustrates a side view of the variation of a heliostat shown in FIG. 1, with a reflector structure tilted in a generally forward-facing direction.

FIG. 5 illustrates a rear view of the variation of the heliostat shown in FIG. 1.

FIG. 6 shows on an enlarged scale relative to FIG. 1 a carrier-mounting member of the heliostat.

FIGS. 7 A to 7D illustrate multiple views of another variation of a heliostat.

FIGS. 8 A to 8E provide multiple views of a variation of vertically extending support member that may be used with the heliostats described here.

FIGS. 9 A to 9C provide multiple views of a variation of a carrier-mounting member that may be used with the heliostats described here.

FIG. 10 illustrates another variation of a linkage between a vertically extending support member and a reflector structure that may be used with the heliostats described here.

FIG. 11 illustrates an example of a vertically oriented central slice of a generally spherical volume traced out by rotation of a heliostat reflector structure about the first and second rotational axes.

FIG. 12 shows a front, perspective view of a variation of a reflector structure with a reflector element partially cut away to reveal a carrier.

FIGS. 13 A and 13B illustrate one variation of a method for securing a reflector element to a carrier. FIG. 13B is a view along axis "A" shown in FIG. 13 A.

FIGS. 14A and 14B illustrate another variation of a method for securing a reflective element to a carrier. FIG. 14B is a view along axis "B" as shown in FIG. 14A. FIG. 15 shows a diagrammatic representation of a variation of a heliostat field and an associated tower-mounted target receiver.

FIG. 16 shows a diagrammatic representation of an example of a control system that may be used with a heliostat field.

DETAILED DESCRIPTION OF THE INVENTION

Described here are variations of heliostats that may be used in any combination in a solar energy collector array, e.g., a multi-tower solar array. Related methods are also described.

In general, the heliostats are configured to confine movement of their reflector elements to a three-dimensional space that can allow close packing of adjacent heliostats while maintaining or reducing the risk of collisions between reflectors of adjacent heliostats in a solar array. In some variations of the heliostats configured with a fixed horizontal rotational axis, reflector element movement may be confined to a three-dimensional space that has two relatively planar, opposing side surfaces. Adjacent ones of the heliostats can then be relatively precisely packed (e.g., into rows) using these planar surfaces. Such heliostat packing may be achieved without substantially increasing the risk of collisions, and may reduce the risk of collisions, between adjacent ones of the heliostats (e.g., heliostats within a row).

As used herein the phrases parallel, aligned, "substantially parallel," and

"substantially aligned" and the like are all meant to encompass minor deviations from parallel or aligned geometries, rather than to require an exactly parallel or aligned geometry. Similarly, the phrases orthogonal, normal, "substantially normal," and "substantially orthogonal" are meant to encompass minor deviations from orthogonal geometries, rather than to require an exactly orthogonal geometry.

In general, the heliostats described here comprise a reflector structure mounted on a vertically extending support member, where the reflector structure may be positioned to track diurnal motion of the sun, to direct incident solar radiation to a target receiver, e.g., a tower-mounted receiver, and/or to a stow or parked position.

The reflector structure of a heliostat comprises a reflective element that may be curved (e.g., cylindrical or spherical) to focus and concentrate the solar radiation, e.g., at a target receiver, or may be planar. The reflector structure is coupled to the vertically extending support member via a linkage that is configured to support the reflector structure and to allow rotation around a first rotational axis, and rotation around a second rotational axis that is substantially orthogonal to the first rotational axis. The heliostats may comprise a first actuator configured to effect rotation around the first rotational axis, and/or a second actuator configured to effect rotation around the second rotational axis. At least one of the first and second actuators may be a linear actuator, hi some variations, both the first and second actuators are linear actuators.

The heliostats described here may be configured as fixed horizontal axis heliostats, where the reflector structure of each heliostat may be continuously positioned over at least a portion of a substantially vertical central slice of a generally spherical space. As used herein "central slice" is meant to encompass any interior slice of a sphere and is not limited to slices that are centered on or incorporate the center of the sphere. Hence, for fixed horizontal axis heliostats, an inter-heliostat collision sphere mapped about by the motion of the reflector structure is effectively truncated at two opposing sides of the heliostats, allowing for relatively close side-to-side packing of heliostats. In these variations, heliostats may be placed side-to-side (e.g., within a row in a solar array) so that a spacing between outer edges of adjacent heliostats is less than about 20%, less than about 15%, less than about 10%, less than about 5%, less than about 2%, less than about 1%, less than about 0.5% or an even smaller percentage of a transverse dimension of a heliostat (e.g., a width), or less than about 6 inches, less than about 4 inches, less than about 3 inches, less than about 2 inches, less than about 1 inch, or even less. The heliostat's ability to confine the position of the reflector structure within this slice of sphere may allow for enhanced positioning capabilities for tracking diurnal motion of the sun, and for directing the reflected solar radiation to a selected receiver, e.g. one or more tower-mounted receivers, with reduced risk of inter-heliostat collisions.

The reflector structure of the heliostats described here may be coupled to an upper (distal) end of a vertically extending structure via the linkage to allow for rotation about the first and second rotational axes. In some variations, the linkage may comprise two rotational elements, where a first rotational element allows the reflector structure to be pivoted around the first rotational axis, and a second rotational element allows the reflector structure to be pivoted around the second rotational axis. The first and second rotational elements may have any suitable structure. For example, at least one of the first and second rotational elements may comprise one or more bearings, axles, gears, pivots, wheels, or combinations thereof. The first and second rotational elements may in some variations be separate elements, e.g., the first rotational element may comprise a first bearing or first set of bearings, and the second rotational element may comprise a second bearing or a second set of bearings. In certain variations, the first and second rotational elements may be part of a unitary element, e.g., a joint configured to allow rotation about two orthogonal axes.

In some variations of the heliostats, the linkage between the reflector structure and the vertically extending support member may comprise one or more arms or other structural members that couple the reflector structure to a rotational element that is coupled to the vertically extending structure. For example, the linkage may comprise a carrier-mounting member, where the carrier-mounting member is coupled to the vertically extending support member via a first rotational element that allows rotation about a fixed horizontal axis. The carrier member may then be coupled to a carrier that is configured to support a reflector element via a second rotational element.

As described above, the first and second actuators, if present, are configured to rotate the reflector about the first and second rotational axes, respectively. The first actuator is configured to apply force along a first actuator axis to rotate the reflector structure about the first rotational axis, and the second actuator is configured to apply force along a second actuator axis to rotate the reflector structure about the second rotational axis. In some variations, neither the first nor the second actuator axes is parallel to the first or the second rotational axis.

Any suitable type of actuator may be used in the heliostats described here. For example, geared drives, stepper motors, linear actuators, such as electrically energized or pneumatically or hydraulically activated actuators, or any combination thereof may be used, hi some variations, a series of electrical pulses may be applied to an actuator comprising a stepper motor to effect extension and retraction of the actuator. The first and second actuators in a single heliostat may be identical or different.

Further, any suitable type of reflector element may be used in the heliostats described here. For example, reflector elements in some variations may comprise a glass mirror that is coupled to the carrier (e.g., adhered to the carrier). Reflector elements may comprise a reflective surface (e.g., a mirror surface) that is flat, or curved. Reflector elements may have any suitable shape, e.g., rectangular, elongated, polyhedral, and the like.

Variations of heliostats that may be used in solar energy collector arrays, e.g., multi-tower solar arrays, are illustrated in the Figures. Referring first to FIGS. 1 to 6, heliostat 1 comprises a reflector structure 11 that is supported by a ground-mounted or ground-anchored vertically extending support member 10. The vertically extending support members referred to herein may have any suitable construction or structure, e.g., they may comprise one or more hollow or solid posts or pedestals, hi some variations, vertically extending support members may comprise a tubular or generally cylindrical post or pedestal, hi certain variations, a vertically extending support member may comprise multiple posts or pedestals. For example, some vertically extending support members may comprise two, three or more angled struts. The vertically extending support member may have any suitable dimensions, e.g., about Im to about 5m, e.g., about 3m or about 2m, e.g., about 1.75m.

Reflector structure 11, in turn, comprises a reflector element 18 and a carrier 17 that is configured to support the reflector element 18. The reflector structure 11 is coupled to the vertically extending support member 10 so that the reflector structure 11 (and hence the reflector element 18) can be rotated about a first rotational axis, and independently about a second axis that is substantially orthogonal to the first axis, to reflect incident solar radiation to at least one receiver (not shown). In the variation of the heliostat shown in FIGS. 1 to 6, the first rotational axis 14 is located near an upper (distal) end 110 of the vertically extending support member 10. The second rotational axis 28 may be generally parallel to a longitudinal axis 147 of the reflector structure 11. The first rotational axis may be "fixed" relative to the (stationary) support member 10 and, thus, the reflector structure 11 is precluded from rotating about a vertical axis of the vertically extending support member. In the variation shown in FIGS. 1 to 6, the first rotational axis is a fixed horizontal axis.

As stated above, the heliostats described here comprise a linkage between the vertically extending support member and the reflector structure. The linkage may comprise a first rotational element configured for rotation about the first rotational axis, and a second rotational element configured for rotation about the second rotational axis. Referring again to FIGS. 1 to 6, heliostat 1 comprises a linkage 148 that comprises a first rotational element 144 that is configured to allow rotation of reflector structure 11 around the first rotational axis 14, which in this case is a fixed horizontal axis. In some variations of the heliostats, the distal end 110 of vertically extending support member 10 may comprise a platform 12 configured to support the first rotational element 144. As described above, the first rotational element 144 may have any suitable structure, e.g., one or more pivots, bearings, axles, gears, wheels, or the like. For example, as illustrated by example in FIGS. 1 to 6, the first rotational element 144 may comprise one or more bearings 13 (e.g., two or more spaced-apart self-aligning bearings 13, where the first (horizontal) rotational axis 14 extends through the spaced-apart bearings). Platform 12, if present, may extend at least partially across the upper end of vertically extending support member 10, and in some variations platform 12 may cap or close an open upper end of vertically extending support member 10.

Still referring to FIGS. 1 to 6, the linkage 148 comprises a second rotational element 145. The second rotational element 145 may have any suitable structure that allows rotation of the reflector structure about the second rotational axis 28 that is substantially orthogonal to the first (horizontal) rotational axis 14. For the variation of the heliostat illustrated in FIGS. 1 to 6, the second rotational element 145 comprises a pivotal connector 21. hi general, the second rotational element may have any suitable structure, e.g., a bearing, a gear, a wheel, an axel, or the like.

In the particular heliostat variation illustrated in FIGS. 1 to 6, the linkage 148 comprises a carrier-mounting member 15 that is coupled to the vertically extending support member 10 via stub axles 16 that are journalled in the bearings 13. Thus, the carrier mounting member 15 is pivotally mounted about the first (horizontal) rotational axis 14. The carrier mounting member 15 supports a carrier 17 that, in turn, carriers a reflector element 18, which may be rectangular.

As illustrated in detail in FIG. 6, the carrier-mounting member 15 may comprise a pivotal arm 19 (e.g., a channel-shaped pivotal arm) and two spaced-apart downwardly projecting limbs 20 that carry the stub axles 16. The second rotational element 145 that, in this case, comprises pivotal connector 21 is provided adjacent one end of the pivotal arm 19. The pivotal connector 21 is connected to an extensible shaft portion 22 of a first actuator 23. The first actuator 23 may comprise an electrically energized (telescopic) linear actuator that has a fixed body portion 24 connected to the vertically extending support member 10 by way of a clamp or other structure 25 that is pivotally connected to a distal portion 110 of the vertically extending support member 10. When energized (e.g., positively and negatively, such as with positive and negative electrical pulses) the first actuator 23 extends and retracts along a first actuator axis 50 to impart counterclockwise and clockwise pivotal movement to the carrier-mounting member 15 relative to the vertically extending support member 10 and about the first (fixed horizontal) axis 14. As illustrated in this variation, the first actuator axis may extend in a direction that is not aligned with either of the first and second rotational axes.

Still referring to FIGS. 1 to 6, two lugs 26 are located at opposite ends of the pivotal arm 19 and provide bearings 27 through which the second rotational axis 28 extends. The second rotational axis 28 is orthogonal to and independently pivotable about the first rotational axis 14. The bearings 27 may carry short axles 29 by which the carrier 17 is pivotally mounted about the second axis 28 to the carrier-mounting member 15. A downwardly projecting limb 30 is located at one end of the pivotal arm 19 and may optionally carry a pivotal connection 31 for a clamp or other structure 32. The clamp or structure 32 functions to provide a pivotal connection between the carrier- mounting member 15 and a second actuator 33. The second actuator 33 may be similar to the first actuator 23. For example, the second actuator may comprise an electrically energized (telescopic) linear actuator that, with positive and negative energization, e.g., positive and negative electrical pulses, extends and retracts along a second actuator axis 51 to impart counterclockwise and clockwise pivotal movement to the carrier 17 about the second axis 28. The second actuator axis may extend in a direction that is not aligned with either the first or second rotational axes, or with the first actuator axis. It should be pointed out that the first and second actuators employed in the heliostats may be any suitable type of actuators (e.g., electrically driven, hydraulically driven, pneumatically driven, or linear or nonlinear), and the first and second actuators may be identical or different.

Other variations of heliostats are contemplated in which one or more of the features described above may be varied. Referring now to FIGS. 7 A to 7D, another variation of a heliostat is illustrated. FIGS. 7 A to 7D provide rear perspective, front, side, and top views, respectively, of the heliostat 700. The heliostat 700 comprises vertically extending support member 710, a reflector structure 711 that comprises a carrier 717 that is configured to support a reflector element 718, and a linkage 748 coupling the reflector structure 711 to the vertically extending support member 710. The linkage 748 comprises a first rotational element 744 that is configured to allow rotation of reflector structure 711 about a first rotational (fixed horizontal) axis 714.

Linkage 748 comprises a second rotational element 745 that is configured to rotate reflector structure 711 about a second rotational axis 728. In this variation, rotational element 745 comprises pivotal connectors disposed on opposite ends of a carrier- mounting element 715. A first actuator 723 provides force along a first actuator axis 750 to effect clockwise and counterclockwise rotations about the first rotational axis

714, and a second actuator 733 provides force along a second actuator axis 751 to effect clockwise and counterclockwise rotations about the second rotational axis 728. In this variation, the first actuator 723 is mounted to vertically extending support member 710, e.g., with a clamp or pivot tab 752, and is coupled at its distal end 755 to the carrier-mounting member 715 at position 753 to rotate the reflector structure 711 about axis 714 as the actuator 723 is extended and retracted. The second actuator 733 is pivotally mounted to the carrier-mounting member 715, e.g., with a clamp or pivot tab 754, and is coupled to the carrier 717 at position 757 to rotate the reflector structure 711 about axis 728 as the actuator 733 is extended and retracted. Thus, as first rotational axis 714 is a fixed horizontal axis in this variation, actuator 723 can rotate the reflector structure 711 to follow elevational (zenith) changes in sun position, and actuator 733 can rotate the reflector structure 711 to track azimuthal changes in sun position. As shown, actuator 733 may alternatively be coupled to the carrier at position 758. In this variation, neither actuator axis is aligned with the first or second rotational axis.

FIGS. 8 A to 8E illustrate a variation of a vertically extending support member that may be used with any of the heliostats described here. FIG. 8B is rotated 90° relative to FIG. 8 A, FIG. 8C provides an enlarged view of the encircled region A, FIG. 8D provides a top view, and FIG. 8E provides an enlarged view of the encircled region B. Vertically extending support member 810 comprises a post section 808 and a platform 812 disposed on the distal end 840 of member 810. Platform 812 supports a first rotational element 844. hi this variation, the first rotational element comprises two collinear stub axles that define a first rotational (fixed horizontal) axis 814. Mounted to vertically extending support member 810 is pivot tab 852, to which an actuator may be coupled. Many other variations of vertically extending support members may be used with the heliostats described here, e.g., vertical support members comprising multiple posts or pedestals. For example, some vertically extending support members may comprise two, three or more angled struts.

FIGS. 9A to 9D illustrate a variation of a carrier-mounting member that may be used with any of the fixed horizontal axis heliostats described here. FIG. 9 A is a perspective view, FIG. 9B is a side view, FIG. 9C is a top view, and FIG. 9D is an end view of a carrier-mounting member 915. In this variation, carrier-mounting member 915 comprises a pivotal arm 919 and two spaced-apart limbs 920 extending normal from the pivotal arm 919. The limbs 920 each comprise an orifice 960 through which an axle or a pair of stub axles (not shown) may extend to define a first rotational axis 914. Bearings 927 are provided on each of two lugs 926 disposed on opposite ends of pivotal arm 919. A second rotational axis 928 extends through bearing 927. A projecting limb 930 is disposed on one end 962 of the pivotal arm 919, and extends normal from the pivotal arm 919. An actuator (not shown) configured for providing azimuthal motion of a reflector structure (not shown) may be pivotally coupled to an end 961 of the limb 930. An actuator mount 963 is disposed on an opposite end 964 of arm 919 and may be configured to be coupled (e.g., pivotally coupled) to an actuator (not shown) configured for providing elevational motion of a reflector structure (not shown).

FIG. 10 provides another variation of a linkage between a vertically extending support member and a reflector structure that may be used with any of the fixed horizontal axis heliostats described here. The vertically extending support member 1010 comprises a top plate 1012 that supports a pair of lugs 1070, each comprising a bearing 1071. In this variation, the linkage comprises a first rotational element 1044 that comprises coaxial bearings 1071 with an axle 1072 extending through the bearings to define a first rotational (fixed horizontal) axis 1014. The reflector structure 1011 is then structurally linked to rotational element 1044 via carrier-mounting member 1015 that is similar to carrier-mounting member 15 depicted in FIGS. 1 to 6, and carrier- mounting member 915 depicted in FIGS. 9 A to 9D.

FIG. 11 illustrates an example of a three-dimensional collision space traced out by the rotation of a reflector structure of one variation of heliostat disclosed herein about its first and second rotational axes, where the first rotational axis is a fixed horizontal axis. The relative placement of adjacent heliostats may be determined by their three-dimensional collision spaces, or collision volumes. As described above and shown in FIG. 11 , when a first rotational axis of a heliostat is a fixed horizontal axis, the heliostat when rotated may be confined to a vertically-oriented central slice of a spherical volume. In the example of FIG. 11, the collision volume shown corresponds to possible rotation of the reflector structure in a 180 degree arc about the fixed horizontal rotational axis. In variations in which the reflector structure rotates by less than 180 degrees (e.g., by about 90 degrees, about 120 degrees, or about 150 degrees) about the fixed horizontal axis, the collision volume is a correspondingly truncated portion of that shown in FIG. 11.

In FIG. 11, heliostat 1200 comprises reflector structure 1211 that is coupled to vertically extending support member 1210 via linkage 1248. Linkage 1248 is configured to allow rotation about a first fixed horizontal axis 1214, and independent rotation about a second axis 1228 that is substantially orthogonal to the first horizontal axis 1214. The linkage 1248 comprises a carrier-mounting member 1215 that supports carrier 1217 of reflector structure 1211. Carrier 1217 supports a reflector element (not shown). The first actuator 1223 applies force along a first actuator axis 1250 to rotate the reflector structure 1211 about first horizontal axis 1214, and the second actuator 1233 applies force along a second actuator axis 1251 to rotate the reflector structure

1211 about second rotational axis 1228. In this variation, the first actuator axis 1250 is not aligned with the first or second rotational axes, and the second actuator axis is not aligned with the first or second rotational axes. By rotating the reflector structure 1211 about the first fixed horizontal axis 1214 and about the second rotational axis 1228, a collision space 1252 in the shape of at least a portion of a vertically oriented central slice of a sphere is mapped out. Because the collision space 1252 is truncated along the sides 1253 to form relatively planar vertical sides, close adjacent packing (e.g., within a row) of these heliostats is possible, e.g., where a spacing between outer edges of adjacent heliostats is less than about 20%, less than about 15%, less than about 10%, less than about 5%, less than about 2%, less than about 1%, less than about 0.5% or an even smaller percentage of a transverse dimension of a heliostat (e.g., a width), or less than about 6 inches, less than about 5 inches, less than about 4 inches, less than about 3 inches, less than about 2 inches, less than about 1 inch, or even closer. There may still be collisions possible between rows of such fixed horizontal axis heliostats.

Heliostats similar to heliostats 1200 may be employed in multi-tower solar arrays. Multi-tower solar arrays may comprise target receivers located at opposite ends of a heliostat field. The heliostat variations illustrated in FIGS. 11 may configured to be rotated over a range of angles corresponding for example, to about a 90° arc, about a 120° arc, or about a 150° arc of the collision space to track diurnal motion of the sun, and to direct incident radiation to a target receiver. In some cases, one or more heliostats in an area may be configured to change the target receiver to which it is directing incident radiation.

Solar energy collector arrays are described here in which at least some of the heliostats may be essentially continuously packed side-to-side, e.g., within a row. Each heliostat may have a transverse dimension (a width) that represents a transverse end-to- end distance that defines a width of the central slice of sphere that indicates the collision volume for that heliostat. For example, referring back to the exemplary heliostat illustrated in FIGS. 1 to 6, dimension 250 is a width extending from one outer edge to an opposite outer edge of the reflector structure 11. The variation of the heliostat illustrated in FIGS. 7A-7D has a similar end-to-end transverse width 790 that extends from one outer edge to an opposite outer edge of reflector structure 711. Thus, in some variations of arrays described here, two adjacent heliostats may be arranged such that a center-to-center distance is substantially equal to the sum of half the width of the first heliostat and half the width of the second heliostat. If two adjacent heliostats have substantially the same width, then the center-to-center spacing between those heliostats may be substantially equal to the width of those heliostats. For example, for an array with a first heliostat similar to heliostat 1 in FIGS. 1 to 6 adjacent to a second heliostat similar to heliostat 700 in FIGS. 7A-7D, the center-to-center distance between those two heliostats in the array may be substantially equal to Vz (dimension 250) + ¹A (dimension 790). By "substantially equal", it is meant here that the center-to-center distance is equal to the sum of half the widths of each heliostat plus or minus minor deviations. For example, in some cases, heliostats may be arranged adjacent to each other such that a spacing between outer edges of the adjacent heliostats is less than about 20%, less than about 15%, less than about 10%, less than about 5%, less than about 2%, less than about 1%, less than about 0.5%, or an even smaller percentage of a width of either heliostat, or less than about 6 inches, or less than about 5 inches, or less than about 4 inches or less than about 3 inches, or less than about 2 inches, or less than about 1 inches, or even smaller.

FIG. 12 illustrates a variation of a reflector structure 1411 that may be used in any of the heliostats described here. There, the carrier 1417 comprises a skeletal frame, which may be rectangular, having longitudinally extending frame portions 1434 and transverse ribs 1435. Typically, the carrier 1417 has dimensions between about Im and about 3m, e.g., about 2m x about 2m, , about 2m x about 3m, about Im x about 2m, about 1.5m x about 2.5m, or about 1.8m x about 2.4m. The carrier 1417 supports the reflector element 1418. As illustrated in an exaggerated way in FIG. 12, the longitudinally extending frame portions and the ribs may be curved. Although FIG. 12 illustrates a variation of a reflector structure in which the longitudinal frame portions and ribs are curved orthogonally to each other, e.g., to form a spherical reflector element or mirror, other reflector structures may be used with the heliostats described here. For example, cylindrical reflector elements, or flat (planar) reflector elements may be used. If curved reflector elements are used (e.g., spherical or cylindrical), a radius of curvature within the range of for example about 40m to about 80m may be used. The actual or approximate radius of a reflector element in any given situation may be dependent upon the distance that the heliostat is to be located from a target receiver.

Reflector elements (e.g., reflector element 1418 in FIG. 12) used in reflector structures may comprise any suitable material. For example, reflector elements may comprise polished metal, or a glass mirror having a rear silvered surface. If present, a silvered surface may be coated or otherwise treated with a protective layer to reduce possible weathering effects. Glass mirrors, when employed, may typically have a thickness of about 0.001m to about 0.005m, e.g., on the order of about 0.003m.

The reflector elements may be bonded to a carrier to form a reflector structure for use in the heliostats described here. Any suitable method may be used to bond reflector elements to carriers. For example, a reflector element may be secured to a carrier by bonding the rear face of a reflector element to the skeletal members of the carrier with an adhesive, e.g., a urethane adhesive, and the reflector element may be formed with a concavity that conforms with the curvatures (e.g., orthogonal or cylindrical) of the carrier by loading the reflector element against the carrier during the time that the adhesive takes to set and cure. Some variations of methods are illustrated in FIGS. 13A and 13B and 14A and 14B.

Referring first to FIGS. 13A and 13B, a reflector element 1518 maybe pressed against a former 1573 having a curved molding surface 1574. The curvature of the molding surface 1574 may be selected to mirror the desired curvature of the reflector element 1518. For example, if the desired reflector element is a cylindrical concave reflector having a radius of curvature such that the reflector ends are offset -2.5mm from a center of the reflector element, former 1573 can be made (e.g., machined) to have a curved convex molding surface 1573 with ends offset +2.5mm from a center to be aligned with the reflector element's center. After the appropriate former is prepared, a mirror (e.g., a glass panel) may be placed face down on the former molding surface, as indicated in FIG. 13B, and pressed to follow the contour of the curved surface of the former. A flat carrier 1517 (which may be a steel carrier) may have adhesive 1577 placed on a surface to be bonded to the mirror. Any suitable type and application of adhesive may be used, e.g., polyurethane adhesive may be applied as beads to the bonding surface of the carrier. The adhesive-applied surface of the carrier 1517 may be placed over the mirror 1518 pressed against the former 1573. Pins 1575 coupled to a support frame 1576 (e.g., a steel support frame) may be used to align the mirror with the former, and to fix the height of the carrier above the mirror so that the adhesive when cured fixes the gap between the mirror and the carrier to set the desired curvature of the mirror.

An alternative method for imparting curvature to a reflector element is illustrated in FIGS. 14A and 14B. hi this variation, a carrier 1617 is manufactured to have a predetermined radius of curvature, e.g., a spherical concave radius or a cylindrical concave radius. The curved carrier 1617 may be supported from beneath, e.g., with adjustable support stands 1678. As shown in FIG. 14B, a mirror 1618 may be pressed face up against the curved carrier 1617 with an adhesive (e.g., a urethane-based adhesive) interspersed between the mirror and the carrier. Force may be applied directly to the mirror (e.g., with weights such as sand bags) to press the mirror against the curved carrier. Alternatively, an interface board 1679, e.g., a caul board, may be placed over the mirror 1618, and weights or force (indicated by arrows 1680) may be placed against the interface board to force the mirror against the curved carrier. The interface board, e.g., caul board, may function to distribute applied force over a surface area of the mirror. For example an interface board may be used that distributes applied force over a majority of the surface area of the mirror, e.g., greater than about 60%, or greater than about 80% of the mirror's surface area. After the adhesive has cured, the curvature of the carrier may be retained by the reflector element.

A heliostat field that may incorporate any of the heliostats described herein is shown diagrammatically in FIG. 15. There a plurality of heliostats 36Q), where j may vary from 1 to n, are installed in a solar energy collector field 37. Each of the heliostats 36(1), . . . 36(n) is, at a selected point t] in time, oriented to reflect incident solar radiation 3 to a shared target receiver 38, which may be a tower-mounted receiver. FIG. 16 illustrates a control system 1982 that may be used to control a heliostat such as those described here, or to control multiple heliostats, e.g., a group of heliostats 1936(k), where k may vary from 1 to n, similar to the group of heliostats 36(j) in FIG. 15. For each heliostat 1936(k) controlled by the control system 1982, first and second actuators 1923(k) and 1933(k) may be actuated when required in a manner that is controlled by a computer-driven processor 1939. For a single heliostat field, one or many processors may be used to control the heliostats. The actuators of the individual heliostats may be controlled to track diurnal movement of the sun, to adjust the illumination of one or more target receivers, and/or to stow or park a reflector element.

In some variations, the control systems may be used to cause one or more heliostats to change the target receiver at which the heliostat is directing solar radiation.

This disclosure is illustrative and not limiting. Further modifications will be apparent to one skilled in the art in light of this disclosure and are intended to fall within the scope of the appended claims.

Claims

CLAIMSWhat is claimed is:

1. A heliostat comprising: a vertically extending support member; a carrier-mounting member pivotally mounted to the vertically extending support member about a fixed horizontal first axis that is located adjacent an upper region of the support member; a carrier pivotally mounted to the carrier-mounting member about a second axis that is substantially orthogonal to the first axis; a reflector element carried by the carrier and arranged in use to reflect incident solar radiation to a target receiver; a first actuator arranged when actuated to effect pivotal movement of the carrier- mounting member about the first axis; and a second actuator arranged when actuated to effect pivotal movement of the carrier about the second axis.

2. The heliostat of claim 1, wherein the reflector element comprises a reflective surface having a cylindrical curvature or a spherical curvature.

3. The heliostat of claim 1, configured to be confined to a volume defined by at least a portion of a vertically oriented central slice of a sphere when the first and second actuators are actuated to effect pivotal movement of the carrier-mounting member and the carrier, respectively.

4. A heliostat comprising: a reflector structure comprising a reflector element arranged in use to reflect incident solar radiation to a receiver; a vertically extending support member; and a linkage coupling the reflector structure to the vertically extending support member, wherein the linkage is configured to confine rotation of the reflector structure to a volume defined by at least a portion of a central slice of a sphere that is substantially aligned with the vertically extending support member.

5. The heliostat of claim 4, wherein the linkage comprises a first rotational element coupled to the vertically extending support member, the first rotational element configured to rotate a reflector structure about a first horizontal rotational axis.

6. The heliostat of claim 5, wherein the linkage comprises a second rotational element configured to rotate the reflector structure about a second rotational axis that is substantially orthogonal to the first rotational axis.

7. The heliostat of claim 5, further comprising a first actuator arranged when actuated along a first actuator axis to effect pivotal movement of the reflector structure about the first rotational axis.

8. The heliostat of claim 6, further comprising a second actuator arranged when actuated along a second actuator axis to effect pivotal movement of the reflector structure about the second rotational axis.

9. The heliostat of claim 6, further comprising a first actuator arranged when actuated along a first actuator axis to effect pivotal movement of the reflector structure about the first rotational axis and a second actuator arranged when actuated along a second actuator axis to effect pivotal movement of the reflector structure about the second rotational axis.

10. The heliostat of claim 9, wherein at least one of the first and second actuators is a linear actuator.

11. The heliostat of claim 5, wherein the first rotational element is configured to pivotally couple a carrier-mounting member to the vertically extending support member.

12. The heliostat of claim 6, wherein the second rotational element is configured to pivotally couple a carrier configured to support the reflector element to the carrier- mounting member.

13. The heliostat of claim 4, wherein the reflector element comprises a reflective surface having a cylindrical curvature or a spherical curvature.

14. The heliostats of claims 1 or 4, configured for use in a solar energy collector array.

15. A solar energy collector array comprising two or more heliostats of claims 1 or 4, wherein a first heliostat confined in movement to a first volume is arranged adjacent to a second heliostat confined in movement to a second volume such that a planar vertical surface of the first volume is aligned with and adjacent to a planar vertical surface of the second volume.

16. A method for positioning a reflector element to direct incident solar radiation to a target receiver, the method comprising: providing a heliostat of claim 4; applying force along a first actuator axis to cause the reflector element to pivot about a first rotational axis; and applying force along a second actuator axis to cause the reflector element to pivot about a second rotational axis that is substantially orthogonal to the first rotational axis.

17. A solar energy collector array comprising two or more heliostats, wherein: a first heliostat having a first width is arranged adjacent to a second heliostat having a second width; and a center-to-center spacing between the first and second heliostats is substantially equal to the sum of one half the first width plus one half the second width.

18. The solar energy collector array of claim 17, wherein the first and second widths are substantially the same, and the center-to-center spacing between the first and second heliostats is substantially equal to the width of the first and second heliostats.