Abstract:
A sun tracking solar power generation system can include drive members for driving a plurality of parallel sun tracking assemblies. The drive components of the drive system can be arranged in a recess or trench created in the ground. This arrangement can reduce the material and labor costs for constructing a solar power system.

Description:
BACKGROUND OF THE INVENTIONS 
       [0001]    1. Field of the Inventions 
         [0002]    The present application is directed to sun tracking systems, such as sun tracking photovoltaic installations in which a plurality of parallel rows of photovoltaic modules are driven with a single drive unit so as to pivot about parallel pivot axes. 
         [0003]    2. Background 
         [0004]    Some known sun tracking photovoltaic solar power systems such as utility-scale, photovoltaic installations, are designed to pivot a large number of solar modules so as to track the movement of the sun using the fewest possible number of driver motors. For example, some known systems include parallel rows of photovoltaic modules supported on torque tubes. The torque tubes can comprise a number of long shafts connected together in an end to end fashion. The torque tubes are supported in an orientation parallel to each other such that their pivot axes are parallel. These shafts are sufficiently long that they must be supported by many vertical columns, known as “piles”. 
         [0005]    In some systems, each drive unit includes an electric motor and a controller and is connected to each of the parallel torque tubes with a series of drive struts which are connected in an end to end fashion, in a direction extending transverse to the torque tubes. Each of the torque tubes include a torque arm extending from the torque tube to the drive strut. The electric motor drives the drive strut in an oscillating motion so as to pivot the torque tubes to provide the desired sun tracking movement. 
       BRIEF SUMMARY 
       [0006]    An aspect of at least one of the inventions disclosed herein includes the realization that large cost savings can be achieved by altering the ground at the site at which a large solar sun tracking photovoltaic system is constructed. During construction of some known systems, the ground at the installation site was altered as little as possible for environmental impact reasons and to reduce construction costs. Thus, in the known systems, the height of the piles was determined by variance required for drive struts to cycle through the sun tracking movement without colliding with the ground. 
         [0007]    Using this criteria for the minimum height of the piles creates a significant impact on the design of the entire system. For example, the solar power installations must be designed to withstand expected wind forces that are predetermined for the installation site. When wind blows in a direction transverse to the torque tube, the greatest torques are applied to the piles. The magnitude of the torque is directly affected by the height of the pile. Thus, the higher the pile, the larger the torque. 
         [0008]    An aspect of at least one of the inventions disclosed herein includes the realization that by altering the ground so as to create trenches directly below the drive struts, shorter piles can be used. With shorter piles, the torque applied to the piles is less under the loads created by the same wind speeds noted above. On a large solar installation, this can result in a large savings in material costs for the piles, as well as the required depth for driving the piles, the amount of cement or concrete needed to construct sufficient foundations for the piles, as well as the associated labor, and other costs. 
         [0009]    Thus, in accordance with an embodiment, a solar array can comprise a pile configured to support a shaft, the pile having a lower end fixed to a ground. At least a first shaft can be supported by the pile such that the shaft can pivot relative to the pile, about a pivot axis, the shaft supporting at least one solar module. At least a first arm having a first and second ends can have its first end connected to the first shaft, the first arm extending from the first end along a substantially radial direction relative to the pivot axis such that the second end of the first arm moves through an arcuate path as the first shaft pivots about the pivot axis. A trench can be formed in the upper surface of the ground wherein the upper surface of the ground surrounding the trench is generally planar, the trench being sized such as the second end moves from at least a first position above the generally planar upper surface of the ground to a second position within the trench and below the upper surface of the ground. 
         [0010]    In accordance with another embodiment, a solar array can comprise a pile configured to support a shaft, the pile having a lower end fixed to a ground. At least a first shaft can be supported by the pile such that the shaft can pivot relative to the pile, about a pivot axis, the shaft supporting at least one solar module. At least a first arm having a first and second ends can have its first end connected to the first shaft, the first arm extending from the first end along a substantially radial direction relative to the pivot axis such that the second end of the first arm moves through an arcuate path as the first shaft pivots about the pivot axis. Additionally, the array can include means for allowing the second end to move from at least a first position above the generally planar upper surface of the ground to a second position below the upper surface of the ground without touching a surface of the ground. 
         [0011]    In accordance with yet another embodiment, a method of constructing a solar array can be provided. The method can include fixing a pile to a ground and supporting at least a first shaft with the pile such that the shaft can pivot relative to the pile, about a pivot axis, the shaft supporting at least one solar module. The method can also include connecting at least a first arm to the first shaft such that the first arm extends along a substantially radial direction relative to the pivot axis such that the second end of the first arm moves through an arcuate path as the first shaft pivots about the pivot axis. Additionally, the method can include forming a trench in the upper surface of the ground wherein the upper surface of the ground surrounding the trench is generally planar, the trench being sized such as the second end moves from at least a first position above the generally planar upper surface of the ground to a second position within the trench and below the upper surface of the ground. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a schematic diagram of a prior art sun tracking photovoltaic system, with which the present inventions can be used. 
           [0013]      FIG. 2  is a schematic diagram of an electrical system for the photovoltaic system of  FIG. 1 . 
           [0014]      FIG. 3  is a perspective view of the solar collection system of  FIG. 1 , illustrating a plurality of piles mounted to the ground and supporting a plurality of torque tubes with a sun-tracking drive in accordance with an embodiment; 
           [0015]      FIG. 4  is an end view of one of the rows of solar modules of  FIG. 3 , with the solar module in a maximum tilted position. 
           [0016]      FIG. 5  is a perspective view of a sun tracking photovoltaic system in accordance with an embodiment, with all but one of the associated solar modules removed. 
           [0017]      FIG. 6  is an end view of one of the rows to solar modules showing the location of a drive system and drive struts positioned within a trench. 
           [0018]      FIG. 7  is an end view of one of the rows of solar modules of  FIGS. 5 and 6 , showing the solar module in a maximum tilted position (in dashed line) and in a “noon” position (in solid line). 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    The following detailed description is merely illustrative in nature and is not intended to limit the embodiments of the subject matter or the application and uses of such embodiments. As used herein, the word “exemplary” means “serving as an example, instance, or illustration.” Any implementation described herein as exemplary is not necessarily to be construed as preferred or advantageous over other implementations. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the proceeding technical field, background, brief summary, or the following detailed description. 
         [0020]    Certain terminology may be used in the following description for the purpose of reference only, and thus are not intended to be limiting. For example, terms such as “upper”, “lower”, “above”, and “below” refer to directions in the drawings to which reference is made. Terms such as “front”, “back”, “rear”, and “side” describe the orientation and/or location of portions of the component within a consistent but arbitrary frame of reference which is made clear by reference to the text and the associated drawings describing the component under discussion. Such terminology may include the words specifically mentioned above, derivatives thereof, and words of similar import. Similarly, the terms “first”, “second”, and other such numerical terms referring to structures do not imply a sequence or order unless clearly indicated by the context. 
         [0021]    The inventions disclosed herein are described in the context of non-concentrated and concentrated photovoltaic arrays and modules. However, these inventions can be used in other contexts as well, such as concentrated thermal solar systems, etc. 
         [0022]    In the description set forth below, an example of a prior art a solar energy collection system  10  is described in the context of being formed by a plurality of solar collection modules, supported so as to be pivotally adjustable for sun-tracking purposes. The inventions described below, with reference to  FIGS. 5 and 6 , can be used with the solar collection system  10  described in  FIGS. 1-4 , as well as the variations and equivalents thereof. The system  10  can include a support member supporting a plurality of solar collection devices as well as wiring for connecting the various solar collection devices to each other and to other modules. The collection system  10  or the modules included in such a system, can be pivoted by a sun-tracking drive. 
         [0023]      FIG. 1  illustrates the solar collection system  10 , which can be considered an electricity farm. The solar collection system  10  includes a solar collector array  11  which includes a plurality of solar collection modules  12 . Each of the solar collection modules  12  can include one or a plurality of solar collecting devices  14  supported by a drive shaft or torque tube  16 . Each of the torque tubes  16  are supported above the ground by a support assembly  18 . Each of the support assemblies  18  can include a pile and a bearing assembly  20 . 
         [0024]    With continued reference to  FIG. 1 , the system  10  can also include a tracking drive  30  connected to the torque tube  16  and configured to pivot the torque tube  16  so as to cause the collector devices  14  to track the movement of the sun. In the illustrated embodiment, the torque tubes  16  are arranged generally horizontally and the modules  12  are connected to each other, as more fully described in U.S. patent application Ser. No. 13/176,276, filed Jul. 5, 2011, the entire contents of which is hereby expressly incorporated by reference. However, inventions disclosed herein can be used in the context of other types of arrangements. For example, the system  10  can include a plurality of modules  12  that are arranged such that the torque tube  16  is inclined relative to horizontal, wherein the torque tubes  16  are not connected in an end to end fashion, such as the arrangement illustrated and disclosed in U.S. Patent Publication No. 2008/0245360. The entire contents of the 2008/0245360 patent publication is hereby expressly incorporated by reference. Further, the inventions disclosed herein can be used in conjunction with the systems that provide for controlled tilting about two axes, although not illustrated herein. 
         [0025]    The solar collection devices  14  can be in the form of photovoltaic panels, thermal solar collection devices, concentrated photovoltaic devices, or concentrated thermal solar collection devices. In the illustrated embodiment, the solar collection devices  14  are in the form of non-concentrated, photovoltaic modules. 
         [0026]    With reference to  FIG. 2 , solar collection system  10  can further include an electrical system  40  connected to the array  11 . For example, the electrical system  40  can include the array  11  as a power source connected to a remote connection device  42  with power lines  44 . The electrical system  40  can also include a utility power source, a meter, an electrical panel with a main disconnect, a junction, electrical loads, and/or an inverter with the utility power source monitor. The electrical system  40  can be configured and can operate in accordance with the descriptions set forth in U.S. Patent Publication No. 2010/0071744, the entire contents of which is hereby expressly incorporated by reference. 
         [0027]      FIG. 3  illustrates the array  11  with all but one of the solar collection devices  14  removed. As shown in  FIG. 3 , each of the support assemblies  18  includes the bearing  20  supported at the upper end of a pile  22 . The torque tube  16  can be of any length and can be formed in one or more pieces. The spacing of the piles  22  relative to one another, can be determined based on the desired limits on deflection of the torque tubes  16  between the support structures  18 , wind loads, and other factors. 
         [0028]    The tilt drive  30  can include a drive strut  32  coupled with the torque tube  16  in a way that pivots the torque tube  16  as the drive strut  32  is moved axially along its length. The drive strut  32  can be connected with the torque tube  16  with torque arm assemblies  34 . In the illustrated embodiment, the torque arm assemblies  34  disposed at an end of each of the torque tube  16 . The length of the torque arm assemblies  34  is determined to provide the desired leverage for visiting the torque tube  16  because the length of the torque arm assemblies  34  has a direct relationship on the amount of force that must be applied to the drive strut  32  in order to pivot the torque tube  16 . Shorter torque arm assemblies  34  would require a higher force to be applied to the drive strut  32 . 
         [0029]    Additionally, the array  11  can include an electrical wire tray  60  supported by one or more of the piles  22 , or by other means. The tray  60  can be used to support any of the wires that may be used for the operation of the system  10 . For example, although not illustrated in  FIG. 3 , each of the solar collection devices  14  includes a power output device (not shown). Such power output devices can be in the form of direct current (DC), electrodes, or alternating current (AC) electrodes. Photovoltaic devices are typically designed to output a direct current. However, the modules  12  can include dedicated inverters (not shown) such that each module  12  outputs an alternating current. Further, a selected subset of the modules  12  can include inverters, combining the direct current of several modules  12  with one inverter. The outputs from each of these inverters can then be combined. 
         [0030]    Thus, whether or not the modules  12  output DC or AC current, the modules  12  each have one or more wires extending from the module, to adjacent modules  12 , and eventually to the tray  60 , then eventually to the remote connection device  42 , or other electrical equipment. The tray  60  is typically mounted above the ground at a distance of about 9-12 inches. 
         [0031]      FIG. 4  illustrates, in an end view, the tray  60  supported by the pile  22 , a clearance  100  which, as noted above, can be about 9-12 inches. 
         [0032]      FIG. 4  also illustrates an optional maximum tilt angle for the module  14 . The maximum tilt angle of the module  14  can be determined based on a number of factors, depending on the characteristics and performance of the system  10 . For example, the maximum tilt angle of the module  14  can be chosen based on the position of the sun when the module  14  is first exposed to sunlight each day, or the angle at which the module  14  stops being exposed to light at the end of the day. Optionally, the maximum tilt angle can be chosen to provide a “safety” position designed to minimize the loads created during extreme weather, such as high winds. The maximum tilt angle of the module  14  can also be determined based on other factors. With the maximum tilt angle determined, the tilt drive  30  can be configured to drive the torque tubes  16  through the desired tilting motion and including the maximum tilt angles. 
         [0033]    The piles  22 , accordingly, are sized such that the modules  12  do not collide with the tray  60 . Thus, the piles  22  are typically sized such that the edges of the solar modules  12  do not collide with the tray  60  when the modules  12  are at their maximum tilt positions. 
         [0034]    With the final height of the pier  22  determined as such, the maximum wind loads for the site of installation of the system  10  can be determined, which provides the information sufficient to determine the appropriate strength of the piers  22 . For example, one overriding calculation is the maximum torque applied to the piers  22  under a maximum wind load condition. The maximum torque applied to the piers  22  is directly proportional to the height  102  of the axis of rotation  104  of the torque tubes  16  above the ground  106 . For example, the maximum torque applied to the piers  22  is the product of the height  102  times the maximum wind force created by the predetermined maximum wind speed and the aerodynamics of the modules  12  and torque tubes  16 . 
         [0035]    With the maximum torque calculated as such, the appropriate dimensions, i.e., thickness, cross-sectional shape, and depth of the pier  22  below the surface of the ground  106 , as well as the magnitude of required cement or concrete  108  beneath the surface of the ground  106 , will be required. At some sites, it may be necessary to pile drive the piers  22  to a required depth, as well as provide concrete foundations, wherein the piers  22  extend below the concrete  108 . These techniques are well-known in the art. 
         [0036]    With reference to  FIGS. 5 and 6 , as noted above, an aspect of at least one of the inventions disclosed herein includes the realization that significant cost savings can be achieved by modifying the ground surface existing at an installation site of a system  10 , so as to provide clearance for drive struts  32  and torque arms  34 , such that those components can, in at least one position during operation, extend below the surface of the surrounding ground. As such, the height of the piers  22  can be reduced, thereby reducing the calculated maximum torque applied to the piers  22 , and thereby reducing the required material thicknesses, pile-driving depths, and required concrete foundations. In some installations, this reduction of pile height and installation requirements can produce cost savings that significantly outweigh the cost of altering the ground under the drive struts  32  and torque arms  34 . 
         [0037]    With reference to  FIG. 5 , an embodiment of the solar system in accordance with the present embodiment is illustrated therein, and is identified with the reference numeral  10 A. The components of the system  10 A can be similar or the same as the components of the system  10  illustrated in  FIGS. 1-4 , except as noted below. Thus, the components of the system  10 A are identified using the same reference numerals of the system  10 , except a letter “A” has been added thereto. 
         [0038]    With continued reference to  FIG. 5 , the system  10 A differs from the system  10  in that the tray  60  has been removed, with the associated wires being buried beneath the surface of the ground  106 . Additionally, the system  10 A is installed such that the drive struts  32  and/or portions of the torque arms  34  are positioned below the surface of the ground  106 , in a trench  110 , in at least one orientation during operation. 
         [0039]    The trench  110  can have any configuration. In the illustrated embodiment, the trench  110  is in the shape of a trough-shaped trench. Other configurations can also be used. 
         [0040]    In some embodiments, with reference to  FIG. 6 , the trench  110  can be formed by digging a straight-sided channel  112  into the ground  106 , and backfilling with material so as to form a trough-shaped trench  110 . The backfill can be any desired material appropriate for providing stable slopes to the trench  110 , including but without limitation, cement, concrete, rocks, etc. 
         [0041]    As shown in  FIG. 6 , the lower end of the torque arms  34  and the drive struts  32 , in some orientations, are positioned lower than the upper surface  114  of the ground  106  adjacent to the torque arms  34  and the drive struts  32 , during operation. In some embodiments, the trench  110  can have a sufficient depth  116  such that as the drive struts  32  are driven through their reciprocal sun tracking motion, the struts  32  rise above the upper surface of the ground  114 . 
         [0042]    Thus, for example, as shown in  FIG. 7 , at a maximum tilt position (shown in dashed line), the drive strut  32  and lower end of the torque arm  34  can be above the upper surface of the ground  114 . However, during other orientations, such as when the modules  12  are horizontal and the torque arms  34  are proximally vertical (referred to as the “noon position”, shown in solid line in  FIG. 7 ), the lower end of the torque arms  34  and the drive struts  32  are below the surface of the ground  114 . However, in some embodiments, the trench  110  can be sufficiently deep such that the lower ends of the torque arms  34  the drive struts  32  are below the surface of the ground  114  during all orientations during operation. 
         [0043]    In either of the configurations disclosed above, the height of the piers  22 A can be shorter than the height of the piers  22  illustrated in  FIG. 4 . Thus, when the system  10 A is constructed at the same site as the system  10  of  FIGS. 1-4 , a significant cost savings can be achieved based on the ability to use shorter, and potentially thinner, piles  22 A and other reduced installation and strength requirements associated with the shorter piles  22 A. More specifically, the height  102 A of the distance from the upper surface of the ground  114  to the rotational axis  104  of the torque tubes  16  is smaller than the height  102  of  FIG. 4 . Thus, the maximum torque applied to the piers  22 A during a maximum wind speed event at the site, results in a lower maximum torque, thereby lowering the minimum strength requirements for the piers  22 A and the associated installation requirements. 
         [0044]    As noted above, the system  10 A does not include the tray  60  used for the system  10 . Thus, in the embodiment illustrated in  FIGS. 5 and 6 , wires  120  used for connecting the modules  12  together and to the remote connection device  42 , are buried beneath the upper surface  114  of the ground. In some embodiments, the wires  120  can be buried below the trench  110 . In some embodiments, a separate trench  122  can be dug beneath the trench  112 . The wires  120 , along with other direct current feeders  124 , can be buried in the trench  122  and backfilled with the appropriate material. As such, the system  10 A further avoids the limitations associated with the tray  60  illustrated in  FIG. 3 . Of course, the wires  120 ,  124  can be arranged in other configurations, including a trench separate from the trench  110 , or other configurations. 
         [0045]    While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or embodiments described herein are not intended to limit the scope, applicability, or configuration of the claimed subject matter in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing the described embodiment or embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the scope defined by the claims, which includes known equivalents and foreseeable equivalents at the time of filing this patent application.