Patent Publication Number: US-2015083112-A1

Title: Heliostat drive-structure mechanical interface

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     The present application claims priority to and the benefit of U.S. Provisional Patent Application No. 61/880,739, filed on Sep. 20, 2013, the entire disclosure of which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     This disclosure relates generally to heliostats having reflectors configured to redirect sun light to a target or receiver, and in particular to the mechanical interface between a heliostat drive assembly configured to orient the reflector and the structure upon which the drive is mounted. 
     In Concentrating Solar Power (CSP) plants, arrangements of heliostats reflect sunlight toward a receiver mounted atop a tower containing a working fluid. One type of receiver transfers incident radiant energy to the working fluid to produce high-pressure, high-temperature steam through the means of a heat exchanger or a phase change of the working fluid itself. The working fluid can be water, air, or a salt material heated to a molten state. The output steam can facilitate a variety of applications, such as electrical power generation, enhanced oil recovery, and desalination. Heliostats are generally mounted on the ground in an area facing or surrounding the receiver tower. Each heliostat has a reflector: a rigid reflective surface, such as a mirror, that tracks the sun through the actuation of a heliostat drive mechanism about at least one axis. Sun-tracking involves orienting the reflector throughout the day so as to optimally redirect sunlight from the sun toward the receiver and maintain the desired temperature of the working fluid. 
     One approach to constructing a heliostat field is to utilize a small amount of comparatively large heliostats (e.g., greater than between 50 and 150 m 2 ). In such a power plant, having a fewer number of heliostats may necessitate the manufacture of very precise, and thus very expensive, components for the positioning of the reflective surfaces. Another approach, however, is to use a large amount of comparatively small heliostats (e.g., between 1 and 10 m 2 ), such as with reflective surfaces that measure between 1 and 3 m on each side. Such an approach may be more efficient at redirecting sun light because there are more individually adjustable reflective surfaces. In addition, smaller heliostats may be cheaper to produce and easier to assemble, decreasing installation time and operations costs. However, a plant comprising more heliostats will necessarily require the same amount of additional drive assemblies, increasing the number of repeated steps during installation. Accordingly, there is a need for heliostat assemblies that are both economical to manufacture and efficient to install. 
     A major cost driver in CSP plants is the cost of manufacturing, installing, and maintaining the components of the heliostat fields. Heliostat fields are typically deployed by installing ballast foundations into the ground and mounting the heliostats and reflectors thereto. Installing these ballast features may require significant ground preparation and heavy machinery, for example to dig holes of a suitable depth for structure posts. Deploying a plurality of heliostats may also be very time consuming if separate ballasts must be installed for each heliostat assembly, and the requisite labor can be a major contributor to operations and maintenance costs. If the interface between the heliostat and the ballast or structure to which it is mounted is complex, this can increase the time it takes to remove or replace heliostats in need of repair. Additionally, heliostats require power and data distribution means for actuation and control. Power and data is typically distributed to a heliostat drive via power and data distribution cables that may be routed through conduit, the ballast, or elements of the mounting structure. Feeding wires and cables through ballasts or structures may require additional setup time whenever a heliostat is installed or removed. This additional setup time becomes compounded during the installation or maintenance of a field comprising a plurality of heliostats, impacting labor costs. Accordingly, there is a need for heliostats having a drive assembly and mounting structure that are designed to minimize installation and replacement times. 
     SUMMARY OF THE INVENTION 
     Improved heliostat assemblies are described herein, wherein the assemblies are configured to facilitate rapid and repeatable installation (or removal) of heliostat drives onto (or from) heliostat structures. The improved heliostat assemblies thereby reduce construction and maintenance costs by reducing labor time and the mean time to repair a heliostat. To provide these advantages, the heliostat structures and drives may comprise compatible mechanical interface features that facilitate the installation of heliostat drives onto heliostat structures in one of a plurality of optional orientations utilizing a minimum of fasteners. In addition, the heliostat structures and drives may comprise cable management features for routing heliostat power and data cable connectors for convenient access to field power and data distribution cables. The heliostat assemblies of the present invention thereby obviate the need to route power and data distribution cables through heliostat ballasts or ground-mounted structures, reducing the time to install and remove units. 
     Heliostat assemblies according to an embodiment of the present invention may comprise: a drive chassis comprising a drive post having a groove, and a structure comprising a structure post having an alignment feature, wherein the drive post is inserted into the structure post and is aligned via the alignment feature. The alignment feature of the structure post may comprise a first tube end having a plurality of grooves, wherein the grooves are spaced equidistant from each other by an offset angle and define multiple heliostat drive orientations relative to the structure post. The drive post may further comprise a second tube end having a groove. The drive post attaches to the structure post via a plurality of fasteners that fit into the grooves of the alignment feature. The plurality of fasteners are spaced equidistant from each other by an offset angle such that the drive chassis can be installed in any of the multiple heliostat drive orientations as defined by the grooves of the alignment feature. The structure post may further comprise a contacting region having a smaller diameter than the first tube end, wherein the drive post makes contact with the contacting region. 
     The heliostat assembly may further comprise a capsule inserted into the drive post, wherein the capsule contains cable-mounting components and electronics components. The cable-mounting components may comprise cable connectors that egress from the capsule. The capsule may comprise a cable-positioning feature having a protrusion that orients the cable-mounting components at an acute angle relative to the capsule. The protrusion may be positioned within the groove of the drive post and within a groove of the alignment feature. The protrusion is further positioned between at least two of said plurality of fasteners and is spaced equidistant from said fasteners by an offset angle. 
     These and other features and advantages of the present invention are discussed or apparent in the following detailed description of the invention in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a perspective view of a heliostat drive assembly and a heliostat structure; 
         FIG. 1B  is a perspective view of the heliostat drive assembly before it is inserted into a post of the heliostat structure; 
         FIG. 1C  is a perspective view of the heliostat drive assembly after it has been inserted a post of the heliostat structure; 
         FIG. 2A  is a side view of a structure post without a drive assembly installed; 
         FIG. 2B  is a side view of the drive assembly comprising an electronics capsule installed in the structure post of  FIG. 2A ; 
         FIG. 2C  is a bottom cut-away view of a heliostat drive assembly installed in the structure post of  FIG. 2A ; 
         FIGS. 3A-3F  are top cut-away views of a heliostat drive assembly installed in the structure post of  FIG. 2A  in six different orientations; 
         FIG. 4A  is a side view of the mechanical interface between the heliostat drive assembly and the heliostat structure; 
         FIG. 4B  is a side view of the heliostat drive assembly installed in the structure post; 
         FIG. 4C  is a side view of a contacting feature inside the structure post; 
         FIG. 5A  is a perspective view of the drive post with the electronics capsule inserted therein; and 
         FIG. 5B  is a perspective view of the electronics capsule of  FIG. 2B . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An improved heliostat assembly is described herein, with reference to  FIGS. 1-5 . The exemplary heliostat assembly is advantageously configured to provide for a mechanical interface between a heliostat drive and a mounting structure that is quick to install and provides convenient access to cable-mounting components. 
     A heliostat assembly according to an embodiment of the present invention may comprise at least one heliostat drive installed onto a heliostat structure, as illustrated in  FIGS. 1A-1C . A heliostat structure  101  may comprise structure posts  110  connected by cross members  111 , wherein each of the structure posts may be connected to one another by at least one cross member. A heliostat drive  130  may be installed in each structure post  110 . The heliostat drives are configured to rotate a reflector (not shown) about at least one axis, the reflector being mounted to the drive via a reflector channel  114 . The structure may be rooted to the ground via a ground interface feature  112 . The ground interface feature  112  may comprise stakes embedded in the ground or in a foundation, or may comprise weights or a ballast material. The structure may be formed from a suitably rigid and corrosion-resistant material, such as a steel alloy. The drive may be mounted to the structure by physically inserting the drive post  160  into the structure post  110 . The structure post may comprise an alignment feature  113 , such that the drive post  160  can only be installed in an orientation selected from a plurality of orientations defined by the alignment feature.  FIG. 1B  illustrates the drive prior to installation in the structure post and  FIG. 1C  illustrates the heliostat assembly post-installation. 
     The alignment feature  113  may comprise a plurality of grooves  200  that allow for mounting of the heliostat drive, as illustrated in  FIG. 2A . In the illustrated embodiment the structure post has six grooves, although it may have more or less grooves depending on system requirements. The structure post grooves  200  define a plurality of possible heliostat drive orientations, each orientation being offset by an angle of rotation. The alignment feature may have a first tube end, wherein the grooves  200  are set equidistant from each other around the circumference of the first tube end. In the illustrated embodiment the six adjacent grooves  200  are separated from each other by an angle of sixty degrees. The first tube end may be either made integral with the structure post, or it may be a separate part that is placed on top of the structure post. The alignment feature  113  may also comprise an intermediate tapered segment  115  between the first tube end and the remainder of the structure post  110 . The tapered segment  116  has smaller diameter than the remainder of the structure post and serves to increase the stability of the structure when subjected to transverse loads. 
     A capsule  150  may be inserted into the drive post  160 , and the drive post may be inserted into the structure post  113 , as illustrated in  FIG. 2B . The capsule may comprise cable-mounting components  170  for connecting to power and data transmission cables. The cable-mounting components may egress from the capsule  150  and may be routed through one of the plurality of grooves  200 . The drive post  160  is fixedly attached to the structure post  113  via a plurality of fasteners  210 . The fasteners may comprise bolts, screws, or other suitable means of attachment. In the illustrated embodiment, the drive post is fixedly mounted within the structure post  113  by tightening three bolts  210 . 
     A cable-positioning feature  320  may be made integral with the capsule  150  to allow cable-mounting components  170  to exit the structure post  113 , as illustrated in  FIG. 2C . The cable-positioning feature fits within a groove  200  not occupied by any of the fasteners  210 . Nuts  250  may be included in the capsule  150  to provide for mounting of the drive post  230  to the structure post  110  by tightening the bolts  210 . The nuts may be of a square shape to limit slippage or loosening within the drive post. The fasteners may be offset from each other by an equidistant angle. In the illustrated embodiment, for example, the three fasteners are each offset by 120 degrees. The cable-positioning feature may be set between at least two of said fasteners and may be spaced equidistant from said fasteners by an offset angle, such as 60 degrees. 
     The locations of the grooves  200  define multiple orientations of the heliostat drive when mounted on the structure, as illustrated in  FIGS. 3A ,  3 B,  3 C,  3 D,  3 E, and  3 F, each depicting a different installation orientation. For example, having six grooves positioned around the circumference of the alignment feature allows for the heliostat drives to be orientated in any of six positions.  FIGS. 3A-3F  show how the heliostat can be set to different orientations to face in different initial directions, as indicated by the arrow. As described above, fasteners  210 , such as bolts, may be used to hold the drive tube in place when inserted into a structure post  110 . In the depicted embodiment, the threaded portions of the bolts  210  fit within the grooves  200  of the alignment feature and the bolt heads grip the alignment feature when tightened, fixedly attaching the drive post to the structure post. The present embodiment allows for heliostats to be repeatedly installed onto structures using basic hand tools within minutes. Because the heliostats can be installed in different orientations and then be actuated to a desired facing, the present invention eliminates the need to orientate all newly installed drives with respect to a certain direction, which can reduce installation time. 
     The drive post  160  of the drive assembly  130  may further comprise a second tube end and a groove  170 , as illustrated in  FIG. 4A . The groove  170  may extend from the second tube end of the drive post up towards the drive chassis  180 . The groove may be sized to be wider than the positioning feature  320  of the capsule  150  (see  FIGS. 2B and 2C ). When installed, the drive post groove  170  may align with one of the alignment feature grooves  200 , as illustrated in  FIG. 4B . 
     The structure post may further comprise a contacting feature  270  at the boundary between the alignment feature  113  and the tapered segment  115 , as illustrated in  FIG. 4C . The contacting feature  270  may comprise an indented segment of the structure post that contacts the side of the second tube end when it is installed, or it may comprise a ledge internal to the tube that contacts the bottom of the second tube end when it is inserted into the first tube end of the structure post. Alternatively, the structure post may have two or more diameters or wall thicknesses such that the internal diameter of the structure post at the cable-positioning feature is smaller than the internal diameter of the structure post at the alignment feature or at the base of the structure post. In this way the contacting feature creates contact between the second tube end of the drive post  160  and the inside of the structure post  110 . The drive post  160  may rest on the contacting feature  270  such that the fasteners  210  do not make contact with the bottom of the grooves  200 . This design thereby facilitates the quick alignment of fasteners  210  in the grooves  200  and allows for easy tightening of any bolts being utilized. The sizes of the contacting feature, the drive post, and the structure post can be configured to increase the stiffness of the system. 
     A capsule  150  may be inserted inside the drive post  160  as illustrated in  FIGS. 5A and 5B , wherein the capsule may be used to house electronics and facilitate the egress of power and data distribution cables  170 . The capsule may be designed to fit inside the drive post and may be removed for maintenance or replacement. The electronics may supply control, instrumentation, health monitoring, and calibration functions to the heliostat. A capsule  150  as shown in  FIG. 5B  may comprise cable-mounting components, attachment nuts  310 , and electronics for heliostat control, such as a motor controller board (not shown). The capsule may further comprise a cable-positioning feature  320  that provides strain relief to emergent cable-mounting components and reduces the likelihood of cable damage from cable movement. The cable-positioning feature may comprise a protrusion sized to fit within the groove  170  of the drive post and within any of the grooves  200  of the alignment feature. The heliostat may therefore be positioned in any configuration that allows for simultaneous mating of the fasteners with the structure grooves and the protrusion with a structure groove not mated with a fastener. The protrusion may be set at an angle to provide protection from rain and washing; this angle may be an acute angle relative to the capsule. 
     The capsule  150  may further comprise recessed portions into which the nuts  310  are embedded. The nuts may be threaded to interface with the fasteners of the drive post. In this way the same fasteners are used to stabilize the capsule within the drive post and fixedly mount the drive post to the structure post. 
     The cable-mounting feature  170  may comprise two cable ends, for example a female cable end  190  and a female cable end  195 . The cable ends egress from the capsule and are guided by way of the cable-positioning feature  320  through the groove  170  of the drive post and a groove  200  of the alignment feature  113  at the end of the structure post. The cable ends may be of different lengths for easy identification; for example the female cable end may be longer than the male cable end. The cable positioning feature may also orient the cable ends  190  and  195  at an angle relative to the capsule via a protrusion. 
     Each heliostat assembly may additionally comprise a data and power connection for directing the drive to a desired orientation. The power connection may supply an energy path to a motor controller board of the heliostat drive. The motor controller board may transmit power to the electrical components of the drive assembly, such as motors that drive at least one transmission. The data connection may provide communication and control pathways to the heliostat drive control boards from a central or distributed controller or network. The power and data connections may comprise, for example, cables or wires that connect to the control board housed within the capsule. 
     Two inter-drive cables (not shown) may be connected to the cable- mounting components that egress from the capsule through the drive post groove and an alignment feature groove. The inter-drive cables may be used to connect the heliostat to other heliostats in the field, in this way power and/or data can be transmitted to heliostats connected in series. The inter-drive cables may be pre-wired to the cable management components, or they may be installed on site. One method of configuring the inter-drive cables is to provide one long cable and one short cable for each heliostat drive. The long cable may be configured to have sufficient length to reach the short cable of an adjacent heliostat drive on the same or neighboring structure. The inter-drive cables and cable-mounting components may be coated with material to enhance their lifetime when exposed to environmental conditions, such as a UV coating, plastics, metals, or other materials that can delay or prevent cable degradation. 
     Inter-drive cables may be attached to the structure with the use of one or more fastening devices. Potential fastening devices may include twist ties, clamps, clips, wires, adhesives, or another suitable method of attaching the cables to the structure. These fastening devices may help to minimize the movement of the cable in wind, and also act as strain relief by keeping the cables affixed to the structure. 
     When connecting inter-drive cables between heliostats, the cable may be left to hang between structure posts, or it may be held off the ground by a supporting feature. Examples of supporting features may include a wire, a rigid member, a flexible member, a slot, or an enclosed tube. The supporting feature be made integral with the structure or installed thereon. A supporting feature may be used to provide strain relief when a cable is run from one heliostat structure to another and may be made of a variety of materials, including but not limited to: metal, plastic, composites, or string. Alternatively, cables may be routed along the cross members between structure posts. 
     Various combinations and/or sub-combinations of the specific features and aspects of the above embodiments may be made and still fall within the scope of the invention. Accordingly, it should be understood that various features and aspects of the disclosed embodiments may be combined with or substituted for one another in order to form varying modes of the disclosed invention. Further it is intended that the scope of the present invention herein disclosed by way of examples should not be limited by the particular disclosed embodiments described above.