Patent Publication Number: US-2012042869-A1

Title: Methods and systems for a heliostat mirror and solar tracker assembly

Description:
RELATED APPLICATIONS 
     This application claims priority to and the benefit of U.S. Provisional Patent Application Ser. No. 61/374,970, filed 18 Aug. 2010, and entitled “Methods and systems for a heliostat mirror assembly and solar tracker.” 
    
    
     NOTICE OF COPYRIGHT 
     A portion of the disclosure of this patent document may contain material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the interconnect as it appears in the Patent and Trademark Office Patent file or records, but otherwise reserves all copyright rights whatsoever. 
     BACKGROUND 
     Various solar trackers are known. For example, some known solar trackers include:
         Panels in a plane on a fixed monopost or the like, with a single central support,   Panels in a plane on a lower non-rolling rotating frame, and   Panels in multiple planes with multiple horizontal axes on an inclined structure (stands) with a lower rolling platform.       

     Some solar trackers may roll on a running surface or track. Accordingly, they can require a perfect horizontal surface as a running surface or track. Due to high rigidity in some systems, if the surface or track were not perfectly horizontal, the passage of a wheel on a lower point thereof would cause the wheel to be suspended without touching the surface. A wheel losing contact with the support surface or track can make the rotation of the assembly difficult. 
     Other examples include two-axle solar trackers that include a moving supporting system for solar panels formed by a vertical axle and a horizontal axle in relation to which the system rotates in order to track the sun&#39;s path. 
     SUMMARY 
     Various apparatus and methods are described for a cable-pulley driven ring-shaped heliostat tracker assembly. The ring-shaped heliostat tracker assembly includes at least a ring-shaped rail track, one or more cables, a heliostat mirror, two or more wheels joined to a structure housing the heliostat mirror, a fixed center axis of rotation of the cable-pulley driven ring-shaped heliostat tracker assembly, one or more position encoders to indicate a position of the heliostat mirror on the ring-shaped rail track, and one or more cables attached to any combination of 1) the wheels, 2) the structure or 3) both, as well as attached to a cable winder spool and a cable unwinder spool. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The multiple drawings included in the attached APPENDIX refer to the embodiments of the invention. 
         FIG. 1  illustrates a top down diagram of an embodiment of cable-pulley driven ring-shaped heliostat tracker assembly. 
         FIG. 2  illustrates a diagram of an embodiment of the heliostat mirror being held in a desired position on the ring-shaped rail track and at a desired rate vector by maintaining equal tension on the one or more cables in both directions around the ring shaped rail track with two or more spools. 
         FIG. 3  illustrates a diagram of an embodiment of a drive control circuit directing the two spools to exactly follow the same torque amount and at a same rate but maintain the rate in the opposite magnitude in order to keep tension in the cables and correspondingly maintain a desired position on the ring shaped rail track and a desired shape of the heliostat mirror. 
         FIG. 4  illustrates a front on view of an embodiment of a ring shaped rail guide and containment method, where the ring shaped rail of the heliostat tracker anchors and captures the route and position of the wheel rollers of the heliostat mirror within a known radial track. 
         FIG. 5  illustrates a side view of the same ring shaped rail guide and containment method and apparatus shown in  FIG. 4 . 
         FIG. 6  illustrates a diagram of an embodiment of a ring-shaped rail constructed of an I-beam and attached to a post, where the ring shaped rail houses the wheels, which structurally join to the structure housing the heliostat mirror to create a centered axis of rotation for the ring-shaped rail. 
         FIG. 7A  illustrates a diagram of an embodiment of a heliostat mirror constructed with multiple facets being multiple individual optical elements making up a structure of the heliostat mirror, where brackets and fixed shim kits are pre-configured and fabricated to set a canting adjustment for each particular optical element location within the multiple faceted heliostat mirror. 
         FIG. 7B  illustrates an expanded view of embodiment of an individual optical element in the heliostat mirror shown in  FIG. 7A . 
         FIG. 8  illustrates a diagram of an embodiment of an individual optical element connecting to a structure of the heliostat mirror with brackets and fixed shims to set the cant of that optical element. 
         FIG. 9  illustrates a diagram of an embodiment of the heliostat mirror constructed with multiple facets being multiple individual optical elements making up a structure of the heliostat mirror, where the multiple individual optical elements are individually moveable mirrors that make up a hyperbola shaped for the heliostat mirror. 
         FIG. 10  illustrates a diagram of an embodiment of an individual optical element facet optical element that couples to its own drive mechanism to move to change the shape of the heliostat mirror. 
     
    
    
     While the invention is subject to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and will herein be described in detail. The invention should be understood to not be limited to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention. 
     DETAILED DISCUSSION 
     In the following description, numerous specific details are set forth, such as examples of specific heliostats, named components, connections, etc., in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without these specific details. In other instances, well known components or methods have not been described in detail but rather in a block diagram in order to avoid unnecessarily obscuring the present invention. Thus, the specific details set forth are merely exemplary. The specific details may be varied from and still be contemplated to be within the spirit and scope of the present invention. 
     In general, example processes of and apparatuses to provide various heliostat designs and features including an example heliostat mirror and solar tracker assembly is described. One or more cables are attached to the ring-shaped heliostat tracker assembly to control a position of the heliostat mirror on the ring shaped heliostat tracker assembly by winding the one or more cables with a cable winder spool and a cable unwinder spool. The ring-shaped rail track couples to two or more wheels joined to a structure housing a heliostat mirror. One or more position encoders track the heliostat mirror to indicate a position of the heliostat mirror on the ring-shaped rail track. 
     The heliostat mirror and solar tracker assembly includes features such as:
         1) a cable-pulley driven ring-shaped heliostat tracker assembly;   2) a ring shaped rail guide and containment method, where the ring shaped rail of the heliostat tracker anchors and captures the route and position of the wheel rollers of the heliostat mirror within a known radial track;   3) a ring shaped rail attachment method;   4) An intra heliostat concept, where the heliostat mirror is constructed with multiple facets with multiple individual optical elements making up a structure of a heliostat mirror;   5) multiple individually moveable mirror facets make up the shape of the heliostat mirror of the heliostat tracker assembly; as well as   6) many more features.       

       FIG. 1  illustrates a top down diagram of an embodiment of cable-pulley driven ring-shaped heliostat tracker assembly. The cable-pulley driven ring-shaped heliostat tracker assembly  100  includes at least a ring-shaped rail track  102 , one or more cables  104 , a heliostat mirror, two or more wheels  106  joined to the structure housing the heliostat mirror, a fixed center axis of rotation  108 , wheel rail guide attachment, a cable follower  110 , one or more position encoders to indicate the position of the heliostat mirror on the ring-shaped rail track, and one or more cables attached to any combination of 1) the wheels  106 , 2) the structure or 3) both, as well as attached to a cable winder spool  112  and a cable unwinder spool  114 . 
     Some embodiments provide the high-reflectivity mirror on a mount that allows rotation about a vertical axis relative to the earth&#39;s surface by being mounted on a ring-shaped rail track. The ring-shaped rail track includes an elevated ring that is mounted above the ground and the structure also rotates about a vertical axis, normal to the earth&#39;s surface. 
     The ring-shaped rail track may be circular or oval in shape. Multiple wheels physically join with a structure attached to and housing the heliostat mirror. The multiple wheels may couple and attach to the ring-shaped track. The structure attaches to the cable and which then gives the structure on the multiple wheels a fixed center axis of rotation. One or more radial position encoders placed at fixed point(s) give a mechanism to accurately track a current position of the heliostat mirror on the fixed ring-shaped rail track. 
     The wheels or similar movement mechanism provides an easy way to have the heliostat mirror follow and track the pulling of the cable. 
     In one embodiment, movement of the mount about the azimuth and elevation axes can be driven by cables attached to mounts that ride on pulleys positioned around the circumference of the ring and about the structure of the heliostat in the azimuth plane, or similar mechanical pulley apparatus in the elevation plane. 
     The ring-shaped rail track can be an elevated ring that is mounted above the ground. Additionally, the rail may be constructed of round tubing or other pre-shaped structural materials such as I-beams, angle iron, T-beams, for example. The rail can be mounted above the ground on pile-driven posts, which can eliminate the need for leveling the ground underneath the ring. The ring mounted to the posts can be leveled relative to the posts via an internal jack screw mechanism, pile driven to all have a same height, or leveled and secured by other means, and the excess post material can be removed and recycled appropriately, if required. 
       FIG. 2  illustrates a diagram of an embodiment of the heliostat mirror being held in a desired position on the ring-shaped rail track and at a desired rate vector by maintaining equal tension on the one or more cables in both directions around the ring shaped rail track with two or more spools. 
     The structure housing the heliostat mirror  218 , cable winder spool  212 , cable unwinder spool  214 , a tension cable  206 , master winder motor  224 , and a slave unwinder motor  220 . 
     The heliostat mirror may be held in a desired position on the ring-shaped rail track and at a desired rate vector by maintaining equal tension on the one or more cables in both directions around the ring shaped rail track, and is moved about the axis of rotation by winding the cable onto the cable winder spool from one direction and unwinding the cable from the cable unwinder spool in the opposite direction. The tracker assembly has a master winder motor and a slave unwinder motor. Each cable drive either winds or unwinds its corresponding spool reel. 
     In some embodiments, the primary control method may use a “master winding spool/reel” known as the “position and rate master” reel. Following a time based position generated by an astronomical table for a particular heliostat, the master reel can pull the cable on the movement side of the heliostat. For example, the tension can be based on the position and velocity commanded by the position requirement driven from the astronomical table and correlated with an astronomical clock for time accuracy. 
     The “unwinding spool” also known as the “follower slave spool/reel” may exactly follow the same torque required by the “master winding” reel, which can be the rate master and may be a slave torque follower to maintain equal and opposite tension in the cables if desired. The rate of the slave reel may follow the torque requirement as defined appropriately to maintain the desired shape in the heliostat structure. Should additional shape forming or correction of the heliostat be required based on wind loading, mechanical beam sagging, or desired optical figure correction based on the mechanical shape, a torque offset can be made between the master winder and slave un-winder reels to impart any required or desired deformation of the heliostat structure. 
     The cable pulley system attaches to the top and bottom of the heliostat mirror to stabilize both the top and bottom of mirror of the heliostat tracker, which makes the heliostat tracker more better in withstanding deflection of the position of the heliostat tracker due to wind gusts and as well maintain accuracy of position. A similar cable control method can be deployed in both the elevation axis (vertical) and the horizontal axis. In an embodiment, the tension cable(s) attaches to wheel rail guide on the bottom of the structure and then also to top of the structure. 
     The cable may be made of a durable substance such as braided stainless, braided Kevlar® or some other high-tension cable with predictable material properties and/or low elasticity. If elasticity is required in the system, it can be built into the motion controls system based on known or calibrated and measured behaviors of the cables used. Additionally, in some systems, the elasticity or lack of elasticity must be repeatable over time. Accordingly, some embodiments may add compensating leading or lagging components to the cables system&#39;s control loops. These components can provide for a system that will be predictable and repeatable. Additionally, some embodiments may be able to be compensated for with minimal calibration of the measured elasticity based on variations over time. 
     Note, with the cable pulley system, no centralized gear box exists to drive the horizontal and vertical positioning of the mirror of the heliostat, rather the cable driven system controls these axes of the mirror. 
     This cable pulley control method can be applicable to both the azimuth axis and elevation axis, and can impart both a desired shape and control in both axes individually. Additionally, the control method for the azimuth and elevation axis may be coordinated together. For example, with both axes working in an interpolated torque control, a hyperbolic shape of the heliostat is possible based in the desired performance, shape and output characteristics of the mirrors of the heliostat. 
       FIG. 3  illustrates a diagram of an embodiment of a drive control circuit directing the two spools to exactly follow the same torque amount and at a same rate but maintain the rate in the opposite magnitude in order to keep tension in the cables and correspondingly maintain a desired position on the ring shaped rail track and a desired shape of the heliostat mirror. 
     As discussed, the heliostat may be held in the desired position and at desired rate vectors by maintaining equal tension on the cables in both directions around the ring, and is moved about the axis of rotation by winding cable onto a reel from one direction and unwinding cable from another reel in the opposite direction. 
     The controls strategy in the drive control circuit  300  maintains the tension with the cables, spools and drives. Not only does this allow for repeatable and precise control with a low cost electro-mechanical system, it can also have the capability to measure the deflection in the entire structure, and correct for wind loading and structural deformations which other system&#39;s do not do today. The drive control circuit  300  controls both torque compensation and position/rate command. In the diagram, “A”=rate and position control of the master winder; “Pe”=external encoder feedback of the heliostats current position to the drive circuit, vector “Ap”=position and velocity of the master winder; vector “Bp” position and velocity of the slave unwinder; and “B” is maintained as a slave follower drive to the master drive (A). 
     The slave unwinder should provide a vector of torque opposite in direction but approximately equal to in amount the torque vector provided from the master winder. The slave unwinder “B” follows the master “A”, to impart torque, cable tension, maintain structural shape, or intentionally impart deflection based on the commanded magnitude difference between torque vector “A” and torque vector “B.” 
     This cable control method with encoder feedback can measure the location and position of the heliostat structure relative to the axis of rotation. Likewise, additional instrumentation, such as accelerometers, load cells, or strain gauges, may measure the mirror&#39;s location in the heliostat system similar to an encoder and its position relative to the structure and the desired tracking location. The same set or another set of instrumentation, such as an accelerometer, load cells, or strain gauges, may also measure deflection of the mirror structure and its structural shape. For example, the application of the accelerometer with the cables can measure and then change the deflection of the structure as desired. This cable control method with the instrumentation feedback can measure structural deflection to maintain desired shape or deflection. The instrumentation of the load cells, strain gauges and/or accelerometers to measure the deflection of the structure and structural shape provides a direct and/or secondary cascade control feedback to the primary feedback of the winder wheels with the cables in order to correct and alter the mirror&#39;s structural shape. The instrumentation of the load cells, strain gauges and/or accelerometers are strategically placed throughout the structure and measure the mirror&#39;s and structural characteristics throughout multiple spots within the system and structure. Closed loop compensation can be made for beam sagging or external forces such as wind loading with this method. 
     For the control method described, the encoder may be centrally placed in the axes for precise measurement of the rate of the other entire structure or the appropriate axis. By monitoring the central encoder and the rates of the winder and un-winder reels, it may also be possible to measure the imparted deflection of the heliostat structure and the vector movements of the heliostat structure based on the attachment points of the cables to the structure. The deflection of the structure can be imparted as desired depending on the placement of the cable attachment points to the structure as well as the vectors of movement at those attachment points. In addition, by using known predictive behavior of the structure in regards to the point of cable attachment relative to the geometry of the structure these responses can be accurately imparted and measured. 
     In some embodiments, a method of heliostat control may use the centrally located encoder that feeds back about the center of the azimuth and elevation axes. Control of the axes can be by cables or similar systems. An example control system including cables may utilize position, rate, and torque control of the cables about a winding reel or similar apparatus. Precise positioning of the heliostat may be possible in addition to accurate measurement of the heliostat mechanical shape. Additionally, in some systems, the cables may impart a desired heliostat shape. The desired shape may be based on desired optical and mechanical performance of the heliostat structure. 
       FIG. 4  illustrates a front on view of an embodiment of a ring shaped rail guide and containment method, where the ring shaped rail of the heliostat tracker anchors and captures the route and position of the wheel rollers of the heliostat mirror within a known radial track.  FIG. 5  illustrates a side view of the same ring shaped rail guide and containment method and apparatus shown in  FIG. 4 . 
     Multiple layers of wheel rollers  406  may sandwich on top and below the ring shaped rail  402  (as shown). Alternatively multiple layers of rail  402 , such as an I-beam or rail tubes, may sandwich on top and below the wheel  406 . 
     The ring shaped rail track  402  is mounted on multiple pile driven posts or multiple concrete caissons such as a first post  430 . 
     In one embodiment, the pair of wheels  406  is drawn against the rail from top and bottom. The wheels  406  can be convex (as shown), flat, concave, or another appropriate mating surface to a round, flat, or otherwise shaped rail. The wheels&#39; shape conforms to rotationally match the shape of the ring shaped rail  402 . Each wheel  406  has a bearing axis. 
     In some embodiments, the mount will rotate around the circular rail on circular wheels. If the rail is constructed of round tubing, the wheels can have convex surfaces that contact the rail and maintain contact with the wheel in both the vertical and horizontal directions (azimuth and elevation). The pairs of wheels ride above and below the rail. 
     Additionally, each pair of wheels can be held securely to the rail by a mechanism that draws the wheels against the rail. This mechanism  432  can be a force spring loaded mechanism, or make use of an inverse gas shock or vacuum piston/cylinder vacuum of inverse pressure that provides the containment force between wheels for tube to draw the wheels against the rail or similar means and increases tracking precision. 
     Additionally, another guide  434  may provide a containment force for the other side of wheel so the wheel rotates without contacting the post/caisson. 
     In some embodiments, the mount will have multiple contact points and surfaces with the rail, with each contact consisting of a pair of wheels. Additionally, the mount may have the capability to maintain the balance of the mass of the structure in the negative elevation (normal to the surface), relative to the load requirements in the positive elevation direction. 
     The mass of the heliostat structure may be spread across multiple contact points. For example, in one embodiment, the mount can have three or four contact points with the rail, with each contact point consisting of a pair of wheels. 
     Note, a shot pin attachment bracket  436  permanently installs the ring shaped rail  402  to the posts  430  anchoring and elevating the ring shaped rail above the ground  438 . The posts are cut to length. During horizontal alignment of the ring shaped rail, temporary brackets with compression screw fittings or similar holds the rail in place for leveling, and then shot pins are inserted for final permanent assembly. 
       FIG. 6  illustrates a diagram of an embodiment of a ring-shaped rail constructed of an I-beam and attached to a post, where the ring shaped rail houses the wheels, which structurally join to the structure housing the heliostat mirror to create a centered axis of rotation for the ring-shaped rail. 
     The ring shaped rail  602  is mounted on multiple pile driven posts or multiple concrete caissons such as a first post  630 . 
     A shot pin attachment bracket permanently  636  installs the ring shaped rail  602  to the posts  630  anchoring and elevating the ring shaped rail  602 . The posts are cut to length. During horizontal alignment of the ring shaped rail  602 , temporary brackets with compression screw fittings or similar holds the rail  602  in place for leveling, and then shot pins are inserted for final permanent assembly. 
     As discussed, the ring-shaped rail  602  may be constructed of an I-beam shaped rail, a tubular shaped rail, or other shaped rail. An outside rail structure of the ring shaped rail houses the two or more wheels  606 , which structurally join to the structure housing the heliostat mirror to create the centered axis of rotation for the ring-shaped rail. 
     In this embodiment, the steel I-beams, tubular or similar tracking surface form the rail  602  that contains the wheels  606 . The dimensional tolerance between wheel and track or bearing method can be cost/accuracy optimized based on type, material selection and lubrication method. 
     Additionally, some systems may use form a low cost tubular ring using commercially available standard piping instead of a rail or concrete ring. By containing the circular ring with convex wheels sandwiched around the ring and potentially “tensioned” to the ring, this gives additional vertical and horizontal repeatability and precision of the structure. Additionally, this might be accomplished at a lower cost than rails or a flat concrete ring. A single convex wheel in an I-beam may provide the same stability as two wheels on a tubular rail in the horizontal and vertical direction, with less moving parts. Additional repeatability and cleaning benefits may be gained. For example, a circular shape may be more repeatable along the ring surface. Additionally, gravity may make it difficult for particulates and foreign materials to collect on the ring. In some embodiments, little or no ground preparation is needed with driven posts that are attached to the ring, as the ring can be leveled and then the excess post material cut off to match any ground surface contour that exists. 
     Some embodiments may also potentially provide lowered installation costs and material costs. For example, some systems may use a pipe ring structure and driven posts. In such a system it can be that little or no concrete or ground preparation is required. The elevated ring may also reduce the environmental impact to the installation site by using minimal ground or surface preparation and allowing indigenous wildlife and plant material room underneath the heliostat structure. For example, a raised ring that allows indigenous life to continue to inhabit the site minimizes environmental impact, which can be a deal breaker. 
     An environmental seal  640  maintains the surface of the rail  602  that the wheels  606  rotate on from the weather and solar elements. The multiple point ring attachment and elevation minimizes ground surface preparation, environmental disturbance and wildlife disturbance. 
     Some embodiments may use a method of circular heliostat rail guidance that includes a structure to reduce run out along the azimuth axis travel. Some embodiments may also reduce the impacts of a circular rail guided system on the repeatability and positioning of the elevation axis. This might be achieved by containing the wheel driven mechanisms in a geometric structure that reduces mechanical run out and backlash in both the elevation and azimuth directions normal and vertical to the earth&#39;s surface. 
       FIG. 7A  illustrates a diagram of an embodiment of a heliostat mirror constructed with multiple facets being multiple individual optical elements making up a structure of the heliostat mirror, where brackets and fixed shim kits are pre-configured and fabricated to set a canting adjustment for each particular optical element location within the multiple faceted heliostat mirror.  FIG. 7B  illustrates an expanded view of embodiment of an individual optical element in the heliostat mirror shown in  FIG. 7A . 
     The heliostat mirror may be a multiple faceted construction with multiple individual optical elements, such as optical elements 1,1, 1,2, . . . 4,3, 4,4, making up the structure of a heliostat mirror. The example optical element  742  is positioned at location 4,1, on the mechanical structure  718  housing the heliostat. The individual optical elements mount to the mechanical structure  718  housing the heliostat. Thus, smaller mirrors are used to form a larger mirror structure. 
     The optical elements can be pre-canted based on a shim attachment method. In some embodiments, when implemented with an array of mirrors on each mount, the individual mirrors can be canted to accommodate specific focal length requirements of the combined array. The shim canting can be imparted based on the final assembly datums between the optical surface of each optical element relative to the heliostat mechanical structure and the relative datum offsets when assembled together. 
     Shim kits and attachment kits are pre-fabricated and configured for each optical element location 1,1; 1,2; 3,3; etc. in the mirror. The number of different canting configurations is optimized for production cost and optical performance within each optical assembly, multiple assemblies or structures of assemblies. 
     This embodiment uses smaller mirrors inside a larger structure. For example, when implemented with an array of mirrors on the major axes of each mount, each individual mirror in the array can have a dual-axis tracking mechanism along the minor axes. Individual mirror control can allow for two different kinds of canting adjustments:
         1) adjustment of individual mirrors to optimize the shape of the array (focal length) based on location in the heliostat field, time of day, and day of year; and   2) continuous movement of the individual mirrors in the array to improve the resolution of the heliostat tracking between incremental moves of the major axes, since major axes only move periodically in order to reduce the peak electrical demand of the entire heliostat field.       

     The major axes changes occur when the entire heliostat mirror structure is moved by for example the cable pulley drive system. The array of optical elements within the heliostat mirror are all on a common structure mount that allows rotation about a vertical axis relative to the earth&#39;s surface by being mounted on the ring shaped rail. The common structure mount also rotates about a horizontal axis, normal to the earth&#39;s surface. The minor axes changes occur when individual mirror elements are moved by that mirror element&#39;s own drive mechanism. 
     In some embodiments an “intra heliostat optical element” takes the benefits of the larger ring structure&#39;s stability and low cost, but offer smaller mirrors. Using that cost savings to put more control on the smaller mirrors. Smaller mirrors can have significant advantages over larger mirror structures in deflection and focusing ability. The controls resolution required to control smaller mirrors can also be less than larger mirrors due to the physics of the smaller structure and decreased deformations. Accordingly, lower resolution encoders and less precise motor systems can be used. Smaller mirrors also can have an advantage in robustness, if one 1 m̂2 heliostat fails, this represents a much smaller percentage of the total field than one 100 m̂2 heliostat. A disadvantage of the smaller mirrors and smaller heliostats can be cost. For example, such a system may include more foundations, more mirrors, more controls, more wires and more terminations. This can increase costs for the additional items, as well as labor costs. Using the large ring structure may lower other costs, which can be invested in smaller mirrors to provide a potentially higher performing heliostat system. Such a system may have fewer foundations and may yield a higher value offering. 
       FIG. 8  illustrates a diagram of an embodiment of an individual optical element connecting to a structure of the heliostat mirror with brackets and fixed shims to set the cant of that optical element. 
     Individual optical elements, such as a first optical element  842 , mounts via the mounting bracket and shims  844  to the mechanical structure  818 . 
     Individual mirrors can be pre-canted to allow quick change-out during service periods. The mounting bracket is aligned and has connections to incorporate a quick change out feature to replace broken elements without a manual canting adjustment. Instead, mounting bracket and fixed shim kits are pre-configured and fabricated to set a canting adjustment for each particular optical element location within the multiple faceted heliostat mirror structure, and also adapted for each individual heliostat array within multiple heliostat array structures and the geographic location and orientation of each structure within a field of array structures. Additionally, shims might be used instead of jackscrews to cant the individual mirrors in order to minimize heliostat assembly time. Thus, shims might be designed specifically for individual mirrors, mirror facets, specific to a particular heliostat or mirror location on the heliostat. 
       FIG. 9  illustrates a diagram of an embodiment of the heliostat mirror constructed with multiple facets being multiple individual optical elements making up a structure of the heliostat mirror, where the multiple individual optical elements are individually moveable mirrors that make up a hyperbola shaped for the heliostat mirror. The major and minor axes of the individual optical elements making up the heliostat mirror will follow a heliostat tracking path relative to the angle of the Sun in the sky. Near to the ideal tracking path can be maintained through major axes changes and minor axes changes. 
     Multiple individually moveable mirror facets make up the hyperbola shaped heliostat mirror assembly of the heliostat tracker, including a first optical mirror element  942 . These optical elements are individually controlled optical facets inside the main heliostat structure. Each mirror facet may move to change the shape of the mirror in real time to better match the angle of the sun throughout the day as well as throughout the year due to the angle of the sun in the sky relative to the heliostat on the ground changing both during the day and during the different seasons making up a year. Thus, minor axis adjustments in the azimuth and elevation axes can be made inside the major axis adjustments of the main structure to optimize overall heliostat shape and optical characteristics based on position, geographic location, time of day, time of year, etc. The minor axes adjustments can also be used to compensate for mount deflection due to wind loading, using feedback from accelerometers and position encoders on the heliostat structure to provide the desired feedback and locations of feedback. The minor axis corrections for each optical element may be smaller steps and in magnitude than the major axis changes. The minor axis corrections for each optical element may also occur individually or in staged groups to limit peak power demand of entire field during “major axis” movements. 
       FIG. 10  illustrates a diagram of an embodiment of an individual optical element facet optical element that couples to its own drive mechanism to move to change the shape of the heliostat mirror. An example first optical element  1042  couples to a drive mechanism  1050  that attaches to the heliostat mechanical substructure  1018 . This gives individual axis and control of each facet in the heliostat mirror assembly. 
     In some embodiments, the minor axes can be driven with a dual-axis mechanism controlled by a rotary motor, a set of gears attached to a motor, an electrical linear actuator, and/or a hydraulic actuator, and appropriately chosen encoders based on the resolution requirements. For example, if the use of hydraulics was implemented in linear actuators, it may be very precise based on the nature of the fluids used. For example, some fluids can allow for use of an air filled bladder accumulator in the fluid system to provide the stored energy and making continuous corrections while minimizing peak power demand. Because the bladder only needs to be recharged periodically, it can serve as a mechanical or fluid battery to allow continuous motion of the minor axis in between moves of the major axis and reduce peak heliostat field power requirements. In the case of an electric motor or actuator, an electrical battery method may be employed to yield the same advantage in peak heliostat field power demand and used to control the minor axes in between major axis moves, and power distribution requirements. 
     The drive for each individual optical element may use energy storage concepts. 
     In the case of electric motors, batteries and/or photovoltaic modules can be deployed to allow for continuous movement of minor axes in between major axis moves while still limiting peak power demand of all systems at an installation together. 
     In the case of cylinder driven movements by fluid or pneumatic means, charged cylinders or nitrogen filled bladders can store energy by means of intermittent use of pumps for individual systems or shared between several systems as required to recharge cylinders or bladders at a frequency to limit peak power demand of the entire installation. The system can recharge cylinders or bladders at a frequency to limit peak power demand of the entire installation. 
     In some embodiment, major axis moves can also make use of the stored energy for more frequent or continuous movement as dictated by economic and engineering optimizations. The minor axis moves can be made continuously or at greater frequencies than major axis moves by deploying energy storage strategies. 
     The heliostats can be used to power a utility-scale solar powered chemical plant. A field of sun-tracking mirrors (heliostats) reflects sunlight onto a receiver on the top of a tower. The resulting heat that is collected may be used to heat absorbent-particles. These absorbent-particles can drive one or more chemical reactions without a catalyst. The chemical plant may generate syngas from the reactions and supply the syngas to a liquid fuel synthesis plant, such as a gasoline synthesis plant. Likewise, improved PV performance occurs due to the better control and the maintained optimal angles of incidence between the Sun and the mirror structure, as well the maintained structural shape of the heliostat mirror. This technology then allows the individual modules to each be optimized for their angle incident with respect to the Sun. Thus, both the overall structure and each of the modules location and angle of incidence to the Sun can be optimized. 
     Some embodiments provide for high flux requirements and high temperatures that are beyond all the existing solutions. For example, steam and molten salt to steam technologies for electrical power generation plants that exist today actually have trouble staying below 600° C. Accordingly, some embodiments can provide for systems that may get to 1300° C., or higher. Heliostats today generally do not meet this requirement. The following discussion will focus on a variety of design configurations of the heliostat structure. In other words, various mechanisms which support and move the mirror to reflect sunlight from the sun to the receiver. 
     In some embodiments, a higher performing heliostat will be able to generate higher fluxes. Additionally, some systems may use fewer heliostats than other systems to generate the same flux needed. This will potentially yield benefits in capital expenditures with fewer heliostats and higher flux yield per square meter of heliostat and with a higher performing plant. Accordingly, the revenue generation potential may be higher as the utilization of the “solar power system” heliostats will be greater. 
     Some embodiments may provide a lower cost or higher value solar thermal power system, where value is generally described as performance divided by cost of capital expenditures for higher system yields. 
     Some heliostats may be categorized into two basic groups. One group is azimuth-elevation, with one axis of rotation that is vertical. Another type of and the other is horizontal and tilt-tilt, with a starting position (when mirror is horizontal) and both rotation axes are horizontal and 90 degrees apart. One axis remains horizontal at all times, with the other rotation axis rotating about the first. Within these two categories, the method for actuating rotation of the mirror pan around each axis, as well as the physical location of the actuators can vary. The possible combinations are numerous but the following discussion will be kept limited to those approaches that seem to hold more promise. 
     In one embodiment, the software used to facilitate the feature associated with the heliostats described above can be embodied onto a machine-readable medium. A machine-readable medium includes any mechanism that provides (e.g., stores and/or transmits) information in a form readable by a machine (e.g., a computer). For example, a machine-readable medium includes read only memory (ROM); random access memory (RAM); magnetic disk storage media; optical storage media; flash memory devices; DVD&#39;s, electrical, optical, acoustical or other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, EPROMs, EEPROMs, FLASH, magnetic or optical cards, or any type of media suitable for storing electronic instructions. The information representing the apparatuses and/or methods stored on the machine-readable medium may be used in the process of creating the apparatuses and/or methods described herein. 
     Some portions of the detailed descriptions above are presented in terms of algorithms and symbolic representations of operations on data bits within a computer memory. These algorithmic descriptions and representations are the means used by those skilled in the data processing arts to most effectively convey the substance of their work to others skilled in the art. An algorithm is here, and generally, conceived to be a self-consistent sequence of steps leading to a desired result. The steps are those requiring physical manipulations of physical quantities. Usually, though not necessarily, these quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated. It has proven convenient at times, principally for reasons of common usage, to refer to these signals as bits, values, elements, symbols, characters, terms, numbers, or the like. These routines, algorithms, etc. may be written in a number of different programming languages. In addition, an algorithm may be implemented with lines of code in software, configured logic gates in software, or a combination of both. 
     It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise as apparent from the above discussions, it is appreciated that throughout the description, discussions utilizing terms such as “processing” or “computing” or “calculating” or “determining” or “displaying” or the like, refer to the action and processes of a computer system, or similar electronic computing device, that manipulates and transforms data represented as physical (electronic) quantities within the computer system&#39;s registers and memories into other data similarly represented as physical quantities within the computer system memories or registers, or other such information storage, transmission or display devices. 
     While some specific embodiments of the invention have been shown, the invention is not to be limited to these embodiments. Circuits may be implemented in hardware, software or any combination of both. The invention is to be understood as not limited by the specific embodiments described herein, but only by scope of the appended claims.