Patent Publication Number: US-2023141720-A1

Title: Systems, methods, and machines for driving multiple foundation components at once

Description:
CROSS-REFERENCE TO RELATED APPICATIONS 
     This is a continuation of U.S. Pat. Application No. 16/735,694 titled “Systems, methods and machines for driving screw anchors,” filed on Jan. 6, 2020 which claims priority to U.S. Provisional Pat. Application Nos. 62/793,331, filed on Jan. 16, 2019, titled “Mandrels and machines for driving foundation piles and related systems and methods,” and 62/788,715 filed on Jan. 4, 2019, titled Solar pile driving machines and attachments and related methods of use, the disclosures of which are hereby incorporated by reference in their entirety. 
    
    
     BACKGROUND 
     Solar energy is one of Earth’s largest potential sources of energy. Above the atmosphere, solar irradiance per unit area is 1.361 kilowatts per square meter. At sea level, the usable energy density is reduced to 250 watts per square meter. Using a two-dimensional model to approximate the Earth, 250 watts/square meter ∗ π ∗ 6,371,000 meters 2  yields about 32,000 terra (trillion) watts of energy that continuously strikes Earth’s surface. Assuming the sun continues to burn and emit photons for a billion more years, the survival of human life ultimately depends on harnessing this essentially unlimited, source of clean energy. 
     The main impediment to widescale solar adoption thus far has been cost. Unlike other energy sources, solar energy costs are frontloaded while the operating costs are comparatively low. Fossil fuel-based energy sources require up-front costs as well as pay-as-you-go costs from consuming fuel. Unfortunately, not all the ongoing costs are reflected in the price of energy generated from fossil-fuel sources. These “dirty” energy sources have significant external costs stemming from CO 2  emissions that, in the absence of a carbon tax, are not reflected in the cost. In addition, entrenched utilities and fossil fuel producers have lobbied effectively to stymie the progress of solar, even in states with the greatest solar potential. 
     Notwithstanding these headwinds, the cost of solar has now dropped low enough that even when coupled with energy storage, it is equivalent to or less expensive than coal, oil and even natural gas. In the context of the electricity market, the relative cost difference between competing sources is quantified in terms of the cost per unit, typically a kilowatt hour (kWh). Large scale solar arrays, so called “utility-scale” arrays, may have tens to hundreds of megawatts of power generating capacity, putting them on the same scale as small coal and natural gas-fueled power plants. These arrays usually generate power that is fed into the grid and sold at wholesale prices on the order of a few cents per kWh. The development of utility-scale solar projects is funded with so-called power purchase agreements (PPAs). With a PPA, an off taker (e.g., utility, grid operator, etc.) agrees to purchase all the power generated by the system at a fixed rate for the operational life of the array (e.g., 30 years). This enables a bank or other investor to accurately value the predicted future stream and to loan money against it to finance construction of the array. 
     Utility-scale solar power plants are predominantly configured as fixed-tilt ground mounted arrays or single-axis trackers. Fixed-tilt arrays are arranged in East-West oriented rows of panels tilted South at an angle dictated by the latitude of the array site -the further away from the equator, the steeper the tilt angle. By contrast, single-axis trackers are installed in North-South rows with the solar panels attached to a rotating axis called a torque tube that move the panels from an East-facing orientation to a West-facing orientation throughout the course of each day, following the sun’s progression through the sky. For purposes of this disclosure, both fixed-tilt and single-axis trackers are referred to collectively as axial solar arrays. 
     Excluding land acquisitions costs, overall project costs for utility-scale arrays may include site preparation (road building, leveling, grid and water connections etc.), foundations, tracker or fixed-tilt hardware, solar panels, inverters and electrical connections (conduit, wiring, trenching, grid interface, etc.). Many of these costs have come down over the past few years due to ongoing innovation and economies of scale, however, one area that has been largely ignored is foundations. Foundations provide a uniform structural interface that couples the system to the ground. When installing a conventional single-axis tracker, after the site has been prepared, plumb monopiles are usually driven into the ground at regular intervals dictated by the tracker manufacturer and site plan; the tracker system components are subsequently attached to the head of those piles. Most often, the piles used to support the tracker have an H-shaped profile, but they may also be C-shaped or even box-shaped. In conventional, large-scale single-axis tracker arrays, the procurement and construction of the foundations may represent up to 5-10 percent of the total system cost. Despite this relatively small share of the total cost, any savings in steel and labor associated with foundations will amount to a significant amount of money over a large portfolio of solar projects. Also, tracker development deals are often locked-in a year or more before the installation costs are actually incurred, so any post-deal foundation savings that can be realized will be on top of the profits already factored in to calculations that supported the construction of the project. 
     One reason monopiles continue to dominate the market for single-axis tracker foundations is simplicity. It is relatively easy to drive monopiles into the ground along a straight line with existing technology, however, the design is inherently wasteful. The physics of a monopile mandates that it be oversized because single structural members are not good at resisting bending forces. When used to support a single-axis tracker, the largest forces on the foundation are not from the weight of the components, but rather the combined lateral force of wind striking the solar panels. This lateral force gets translated into the foundation as a bending moment. The magnitude of this force is much greater than the static loading attributable to the weight of the panels and tracker components. It acts like a lever arm trying to bend the pile, and the longer the lever arm, the greater the magnitude of the force. Many tracker companies specify a minimum foundation height of 40-inches or more. Therefore, in the context of single-axis trackers, monopile foundations must be oversized and driven deeply into the ground to withstand lateral loads. 
     The applicant of this disclosure has proposed a replacement to H-pile foundations that uses a pair of angled legs to form an A-frame-shaped truss foundation. Known commercially as EARTH TRUSS, each leg consists of a screw anchor driven substantially into the ground, and upper leg joined to the end of the screw anchor and an adapter or TRUSS CAP that joins the free end of each upper leg to unitize the structure. This configuration has the advantage of converting lateral loads into axial forces of tension and compression in the legs, rather than putting the foundation into bending. As a result of the more efficient distribution of lateral loads, the foundation may be constructed with less steel and driven to shallower depths than an equivalent H-pile foundation. However, in order to maximize its competitiveness relative to H-piles, EARTH TRUSS must similarly fast and easy to install. To that end, it is an object of this disclosure to provide machines and related systems and methods for installing screw anchors efficiently and consistently under a variety of soil and geologic conditions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1 A  is an exploded view of a foundation system installed with equipment according to various embodiments of the invention; 
         FIG.  1 B  is a front view of the foundation system shown in  FIG.  1 A  after assembly; 
         FIG.  2 A  is a front view of a machine for driving a pair of screw anchors at substantially the same time according to various embodiments of the invention; 
         FIG.  2 B  is a side view of the machine of  FIG.  2 A ; 
         FIG.  2 C  is a top view of a portion of the machine of  FIGS.  2 A and  2 B ; 
         FIG.  3 A  is a front view of the machine of  FIG.  2 A  after a pair of screw anchors have been loaded onto the respective drivers; 
         FIG.  3 B  is a front view of the machine of  FIG.  3 A  at an intermediate driving stage; 
         FIG.  3 C  is a front view of the machine of  FIG.  3 A  after a pair of adjacent screw anchors have been driven and the drive assemblies have been withdrawn; 
         FIG.  4    is a flow chart detailing the steps of a method for driving a pair of adjacent screw anchors with the machine shown in  FIGS.  2 A-C and  3 A-C  according to various embodiments of the invention; 
         FIG.  5 A  is a front view of another screw anchor driving machine according to various other embodiments of the invention; 
         FIG.  5 B  is a front view of the machine of  FIG.  5 A  while driving a pair of adjacent screw anchors into the ground; 
         FIG.  6    is a flow chart detailing the steps of a method for driving a pair of adjacent screw anchors with the machine shown in  FIGS.  5 A-B  according to various embodiments of the invention; 
         FIG.  7 A  is a front view of yet another screw anchor driving machine according to various additional embodiments of the invention; 
         FIG.  7 B  is a front view of the machine of  FIG.  7 A , engaged and a screw anchor driving operation; and 
         FIG.  8    is a flow chart detailing the steps of a method for driving a pair of adjacent screw anchors with the machine shown in  FIGS.  2 A-C  according to various embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is intended to convey a thorough understanding of the embodiments described by providing a number of specific embodiments and details involving A-frame foundations used to support single-axis solar trackers. It should be appreciated, however, that the present invention is not limited to these specific embodiments and details, which are exemplary only. It is further understood that one possessing ordinary skill in the art in light of known systems and methods, would appreciate the use of the invention for its intended purpose. 
     Turning now to the drawing figures, where like numerals are used to refer to like structures,  FIG.  1 A  is an exploded view of a multi-piece truss foundation according to various embodiments of the invention. As discussed in the background above, truss foundation  100  is meant to replace conventional H-piles as a foundation to support single-axis solar trackers and other structures. The system includes a pair of truss legs, each composed of a screw anchor  105  joined to an upper leg  110 . Screw anchors  105  are elongated hollow members with an external thread form  106  beginning at the below-ground end and a driving coupler  107  at the above-ground terminal end. In various embodiments, driving coupler  107  is selectively coupled to the chuck of a rotary driver to enable anchor  105  to be driven into supporting ground. Driving coupler  107  also provides a mechanism for joining upper legs  110  to their respective screw anchors. As shown, the portion of driving coupler  107  that extends upward is received into the open end of one of the upper legs. Similarly, coupling portions  123  projecting below TRUSS CAP or adapter  120  are received into the opposing end of each upper leg  110  to complete the A-frame-shaped truss structure. In various embodiments, a crimping device is used to secure the overlap connections between adapter  120  and upper legs  110  and between upper legs  110  and their respective screw anchors  105 . It should be appreciated, however, that other methods of joining these structures may also be used, including set screws, bolts, threads or other suitable methods. 
       FIG.  1 B  shows a completed truss foundation  100  of  FIG.  1 A . Upper legs  110  have been sleeved over driving couplers  107  as well as over connecting portions  123  of adapter or truss cap  120  and the overlapping areas crimped. When installing a foundation for a single-axis tracker, dozens of such foundations  100  are installed along an intended North-South oriented tracker row with the truss legs straddling the row. In various embodiments, recessed portion  122  will be elevated directly above the North-South line of the row. This portion  122  may act as a rest for the torque tube while bearings and drive motors are attached to their respective foundations. A single row may span more than  300  feet and include more than a dozen such foundations as well as one or more tracker motor foundations. 
       FIG.  1 A  and B show but one type of foundation that may be installed with the various machines shown and discussed in the context of this disclosure. It should be appreciated that foundation components driven with the various machines disclosed herein may take on other forms as well. As used herein, the term “screw anchor” is used generally to refer to a foundation component that is rotated into the ground with a combination of torque and downforce, with or without the assistance of a tool, drill or other assisting mechanism through its open center. 
     The remaining figures show various different screw anchor driving machines as well as flow charts of related methods of operating such machines to effect a screw anchor driving operation according to various embodiments of the invention. Starting with  FIG.  2 A  and B, these figures are front and side views respectively of screw anchor driving machine  200  for installing a pair of adjacent screw anchors according to various exemplary embodiments of the invention. In order to form a truss foundation, the truss legs must be oriented at angles relative to one another rather than driven plumb. To that end, various embodiments of the invention provide a machine adapted to drive two adjacent screw anchors at the same time or in overlapping time at angles relative to one another. As discussed above in the context of  FIG.  1 A  and B, in various embodiments, each adjacent leg will consist of a two or more sections - a threaded or partially threaded screw anchor driven until only a portion remains above ground, and an upper leg coupled to the screw anchor. The focus of this disclosure is limited to machines and methods for installing screw anchors of each adjacent foundation pair. The anchors shown herein are exemplary only and should not be construed as limiting on the various embodiments of the invention. 
     Exemplary machine  200  is a tracked vehicle powered by a gasoline or diesel engine similar to various other tracked vehicles known in the art including general-purpose equipment such as backhoes and excavators, as well as purpose-built pile driving rigs, drill-rigs and the like. Such vehicles are typically made for off-road use only and therefore are geared for power rather than speed, and ride on metal or rubberized tracks such as tracks  212 . Tracks provide greater traction and much larger contact surfaces with the supporting ground relative to tires. Chassis  214  rides on tracks  212  and supports main body  216 . Main body  216  includes the motor, a controllable connection to an accessory mast, and a set of physical controls as well as one or more electronic control interfaces such as to a separate remote control. In  FIG.  2 B , hydraulic control interface is shown. In various embodiments, this may enable an operator to walk beside the machine while staying out of the way of the moving tracks. In other embodiments, the machine may include a touch screen or other tactile human interface instead of or in addition to the hydraulic control interface and may operate in partial or fully autonomous mode. For example, though not shown, the machine may include a GPS-based positioning system that drives the machine to the appropriate location. 
     In various embodiments, main body  216  is operable to rotate about chassis  214  while the chassis remains stationary to work 360-degrees around the machine without moving it. In exemplary machine  200 , at least one hydraulic accessory movement assembly  218  includes at least one hydraulic articulating arm  218 A that enables machine  200  to pitch accessory mast  220  forward and backward. Assembly  218  may also include a second lifting and telescoping arm  218 B that enables the machine to move the accessory mast  220  vertically (in Z) and horizontally (in X). Though not shown, assembly  218  may also include a trunnion subassembly that allows machine  200  to adjust accessory mast  220  in yaw with respect to the machine. 
     Machine  200  and hydraulic accessory movement assembly  218  provide motive power and movement respectively to driving components located on accessory mast  220 . As shown, mast  220  includes parallel frame members  221  that serve as a scaffold to support the driving assemblies  230 A/B and driving arms  231 A/B. Frame members  221  may also enable entire accessory attachment  220  to be disconnected from machine  220 , if necessary, such as for repair, servicing, replacement, and/or for transport. This type of modular configuration is often used with general purpose equipment such as excavators, tractors and backhoes so that they can receive attachments to perform specific tasks. 
     Driving assemblies  230 A/B are attached to frame members  221  via mounting plate  225  and are configured in an upside-down V shape separated by an adjustable angle via rotating plates  233 A/B. In various embodiments, plate  225  may be moved up and down along frame members  221  to set an initial driving height of the mast. In various embodiments, plate  225  may be adjusted vertically until common hinge point  228  is aligned with the intended work point height of the truss, that is the height above ground of the intersection of imaginary straight lines through the center of each leg. In various embodiments, in order to drive a pair of screw anchors to achieve a consistent work point height, accessory mast  220  is leveled or adjusted to an orientation normal to the intended position of the torque tube, and is also adjusted in pitch, roll and yaw with respect to the machine, if necessary to be properly aligned along the intended North-South row of the tracker with other foundations in the same row. Then, driving arms  231 A/B are rotated to their respective driving angles and assemblies  230 A/B are lowered along arms  231 A/B until they reach the ground. In this example, after the anchors are loaded, each mandrel  243 A/B will extend out of the open end, lower end of its corresponding anchor by a few inches. In various embodiments, mandrels  243 A/B and anchors  105  will maintain this spatial relationship during driving to allow the mandrel tip to function like a screw tip and/or a drill helping to keep the anchor on-axis, increasing soil pressure around the thread form, and even drilling through rocks and cementitious soils, if necessary. In various embodiments, the tip of each mandrel  243 A/B may be removable, even after a screw anchor is attached, to allow different tips to be used for different soil conditions, and/or to allow the tip to be replaced or serviced. 
     It should be appreciated that  FIG.  2 A  could depict either a front or rear view of the machine depending on where accessory attachment  220  is positioned with respect to the machine’s orientation. Frame members  221  shown here are joined together with orthogonal members to make a ladder-like frame member. In some embodiments, frame  221  may be fixed and only moved by the actuating hydraulic accessory movement assembly  218  connecting attachment  220  to the machine. In other embodiments, part or all of frame members  221  may move independent of assembly  218 , such as, for example, sliding up or down vertically and/or sliding left or right (in the Y-direction), or even rotating about the one or more articulating arms (in roll) to compensate for uneven ground under the machine. 
     As shown in the figures, frame members  221  support a pair of independent driving assemblies  230 A and  230 B via mounting plate  225 . As discussed above, both assemblies  230 A/B may travel together up and down frame members  221  to orient them to the correct work point height. In various embodiments, they may also move independent of one another along their respective driving arms  231  to enable a pair of screw anchors to be driven into the ground at angles to each other and at independent rates of feed and speed. 
       FIG.  2 C  is a close-up showing details of the components of drive assemblies  230 A/B. As drawn, assembly  230 B is essentially the same as assembly  230 A, however, in various embodiments they do not need to be exactly the same. In the example of the figures, rotational adjustment of each assembly  230 A/B in-plane is about common hinge point  228 . In various embodiments, each assembly  230 A/B may swing through a range of angles about common hinge point  228 . Common hinge point  228  may unite each assembly  230 A/B onto shared mounting plate  225 , with hinge brackets  233 A/B to enable them to rotate with respect to frame members  221 . In some embodiments, common mounting plate may be fixed to the frame so that it does not move independent of the frame, however, in other embodiments, it may move in-plane, up and down frame members  221 . In such embodiments, hinge brackets  233 A/B swing through respective arcs corresponding to a range of possible driving angles. As shown, pins on the back side of each hinge bracket  233 A/B engage respective channels formed in shared mounting plate  225 . In other embodiments, plate  225  may also move about hinge pin  226  via its own channel and a boss pin connected to the frame. This may be particularly useful when driving on sloped ground to recalibrate frame members  221  to a vertical orientation before moving hinge brackets  233 A/B to the desired driving angle(s). 
     In various embodiments, the angle between the driving axes defined by the two hinge brackets may vary in a range from as little as 35-degrees to as much as 70-degrees, corresponding to anchors driven in the ground at angles in a range of ±55 degrees to ±72.5 degrees. In other embodiments, the angle between the two hinge brackets may be limited to a range of 40 degrees to 60 degrees, corresponding to anchors driven in the ground at angles in a range of ±60 degrees to ±70 degrees. 
     Continuing with  FIG.  2 C , in this example, each driving assembly  230 A/B consists of three independent motors  232 A/B,  234 A/B and  236 A/B. It should be appreciated that although three motors are shown, in various embodiments fewer or more motors may be used. Also, one or more of the motors may be positioned elsewhere, such as at the base of each driving arm  231 A/B. For example, the motors used to move respective assemblies  230 A/B may be fixed at or near the distal end of each arm  231 A/B and used chain to move assemblies  230 A/B along their respective arms. 
     As shown, motors  232 A/B,  234 A/B and  236 A/B are oriented to extend away from the driving axes to prevent mechanical interference between the two assemblies near common hinge point  228  while driving. After driving begins, the motors of each assembly  230 A/B will move away from each other as they travel down their respective drive arms  231 A/B. For a given driving angle, the maximum screw anchor length will in part be dictated by the intended work point of the truss foundation. When the truss is complete, the work point will be the apex of the triangle created by the legs of the A-frame. On the machine, the work point may will coincide with common hinge point  228  since each driving arm  231 A/B will always point at it. When simultaneously driving adjacent screw anchors with the machine of  FIGS.  2 A-C , neither assembly may pass through hinge point  228  but both should start as close to it as possible to maximize the length of anchor that can be used for a given work point height. 
     The first motor of each assembly  230 A/B is rotary drive motor  232 A/B. In various embodiments, rotary driver motors  232 A/B impart torque to the head of each screw anchor. As shown, the output of each rotary drive motor  232 A/B engages a gear that in turn causes rotary drivers  235 A/B to impart torque to attached screw anchors. Motors  232 A/B may be powered by a hydraulic fluid, as is known in the art, or alternatively, by electric current, coming from machine  200 . As seen in 2C, the top of each screw anchor is received within the driving collars  235 A/B of rotary drivers  232 A/B. One or more recesses formed in collars  235 A/B may engage protruding features in the screw anchor heads to enable them to be driven in either direction (e.g., clockwise or counter clockwise). Alternatively, pins, bolts or other fasteners may be used to temporarily couple each screw anchor to its respective collars  235 A/B. The specific method of engagement with the upper end of each screw anchor is not critical to the various embodiments of the invention. 
     In various embodiments, screw anchors are loaded onto the respective assemblies  230 A/B by sleeving the upper end of each anchor over the tip of mandrels  243 A/B and sliding them up the respective shafts until they reach rotary drivers  235 A/B. The tip of each mandrel  243 A/B may protrude slightly out of the bottom end of each anchor once the anchor is loaded. In various embodiments, a second drive motor  234 A/B on each assembly  230 A/B is used to drive mandrels  243 A/B or other tools. As shown, the output shaft of these second motors  234 A/B engages the upper or top gear assembly which in turn rotates a fitting that rotates and/or moves mandrels  243 A/B. In various embodiments, this fitting passes through the center of rotary drivers  235 A/B so that mandrels  243 A/B extend along the same axis as screw anchors  105  but can move independent of them through their respective centers. It should be appreciated that in other embodiments, instead of using a gear assembly to rotate the mandrel, compressed air or hydraulics may be used to reciprocate the mandrel within the shaft of the screw anchor in addition to rotation to clear a path ahead of it and even to break up small rocks or other impediments encountered while driving. For example, a drill bit may be located at the tip of each mandrel  243 A/B. Having separate motors  234 A/B to the mandrels allows them to be actuated at different rotational speeds than screw anchors. 
     The third pair of motors shown in assemblies  230 A/B are axial drive motors  236 A/B. In various embodiments, these motors control movement of assemblies  230 A/B in the axial direction, that is up and down drive arms  231 A/B. In various embodiments, the rate of travel provided by these motors will be synchronized to the effective rate of travel of rotary driver motors  232 A/B so that screw anchors are pushed into the ground at the same rate that their thread pitch and rotational speed will allow them to travel to prevent augering of the bore hole. As shown, these motors  236 A/B have a geared output shaft that communicates with respective rack gears  241 A/B extending along each arm  231 A/B. As discussed above, in alternative embodiments, axial drive motors  236 A/B may be fixed at the lower end of each arm  231 A/B. In such embodiments, a driven chain may be connected to an output gear of each drive motor  236 A/B to pull assemblies  230 A/B up or down respective drive arms  231 A/B. When screw anchors are driven to their target depth, drive motors  236 A/B enable assemblies  230 A/B to be retracted up and away from the driven anchors so that another pair of anchors may be loaded. 
       FIGS.  3 A-C  show front views of exemplary screw anchor driving machine  200  of  FIGS.  2 A-C  engaged in different stages of a screw anchor driving process according to various embodiments of the invention. Starting with 3A, in this figure, machine  200  has been loaded with a pair of screw anchors  105 . In various embodiments, the diameter of mandrels  243 A/B is small enough to enable them to fit inside rotary drivers  235 A/B while leaving sufficient clearance for hollow screw anchors to fit in the space between the outside diameter of the mandrel and the inside diameter of the rotary driver. 
       FIG.  3 B  shows exemplary machine  200  of 3A, after a simultaneous screw anchor driving operation has begun. Motors  232 A/B are actuated to move assemblies  230 A/B down their respective arms to put down force on the head of the screw anchors and mandrel while motors  234 A/B impart torque to the head of each anchor. The combined rotation of the rotary driver, sympathetic action of the mandrel driver, and downward force of the axial driver on the entire assembly cause the screw anchors to steadily penetrate into the ground. In various embodiments, the force of these three components is maintained until each anchor reaches its target depth. 
       FIG.  3 C  shows machine  200  after each anchor has been driven and drive assemblies  230 A/B are retracted along their respective drive arms  231 A/B. In various embodiments, assemblies  230 A/B are retracted up their respective arms  231 A/B until mandrels have emerged from the open, above-ground end of each driven screw anchor  105 . Once the end of each mandrel  243 A/B clears its screw anchor, attachment  220  may be elevated to up and away so that the machine  200  can be moved to the next foundation location. As shown in this example, a portion of each screw remains above ground after driving. In various embodiments, the screw anchors are long enough to achieve the desired embedment depth as well as to provide several additional inches of above-ground length to facilitate attachment to above-ground truss components. In various embodiments, retraction of the driving assemblies occurs by engaging the drive motors to move each assembly along its drive axis in the opposite direction from driving. In other embodiments, this may also be accomplished in part by telescoping a portion of each mandrel into itself to provide clearance. 
     Turning now to  FIG.  4   , this figure is a flow chart detailing the steps of an exemplary method for simultaneously driving screw anchors with a machine according to the various embodiments of the invention. The method begins in step  250  with loading the machine with a pair of screw anchors. In various embodiments and as discussed and shown herein, this may consist of loading a pair of elongated, open-ended screw anchors onto respective mandrels of a dual screw anchor driving machine or attachment. The attachment or mast of the machine may be oriented to a loading geometry to provide easy access to the mandrels. In various embodiments, this may be done by a human operator or, alternatively, by a semi or fully autonomous loader. Once the screw anchors are sleeved over their respective mandrels, they are coupled to their respective rotary drivers. This may be done with one or more pins or features that allow the anchors to be rotated into a locked position with the rotary driver and to be unlocked by reversing the driver. As discussed herein, in various embodiments, when the anchors are loaded, the mandrel tip may protrude some distance out of the open, threaded end of each anchor. 
     Next, in step  255 , the individual assemblies are adjusted to their respective desired driving angles. In various embodiments, this is accomplished by rotating a hinge bracket about a fixed rotation point as shown and discussed above. If the machine is on relatively flat ground, each assembly may be oriented to a reciprocal angle (e.g., ± 70 degrees with respect to grade). Otherwise, if the ground slopes in the East-West direction, the degree of slope may be added or subtracted from the driving angle to achieve alignment with other anchors in the current row. Alternatively, the shared hinge or mounting plate may first be rotated to provide a plumb reference for the individual assemblies before the individual assemblies are rotated to their respective driving angles. In various embodiments, the driving assemblies are oriented with respect to each other in a common plane so that an imaginary line extending along each driving axis will intersect in free space. Co-planarity may be important to ensure that loading forces applied to the A-frame are non-bending (i.e., tensile and compressive only). In various embodiments, the point of intersection coincides with the hinge point rotationally interconnecting the hinge plate and hinge brackets. 
     After the driving assemblies have been oriented to the desired driving angle, in step  260 , each anchor is driven to depth. As discussed herein, driving an anchor to depth may consist of several simultaneous actions. In some embodiments, this may occur at the same time. In other embodiments, the first assembly may drive until sufficient clearance is achieved and the second assembly may then begin driving. In various embodiments, each rotary driver may be actuated to begin rotating the screw anchors in the driving direction (e.g., clockwise or counter clockwise) dictated by the orientation of the threads or partial thread form. In various embodiments, at substantially the same time, the mandrel drivers are actuated to begin rotating the mandrels or in some cases hammering or vibrating them within the shaft of and ahead of each anchor. In addition, the axial drive motors will be actuated to apply downward pressure to the rotary driver and mandrel driver assemblies to motivate the anchors and mandrels into the ground in straight lines and along the driving axes dictated by the orientation of the drive arms. In various embodiments the action of all three will be synchronized in real-time to achieve the desired feed and speed for the current anchors. In various embodiments, this simultaneous action will continue until each anchor reaches the target depth. Because they are being driven independently, one may reach its target depth before the other. In some embodiments, the mandrel may pause operation or retract along its axis while the rotary driver continues to drive the anchor through any void created by the mandrel tip. 
     Once the target depth is reached, the process of withdrawal begins in step  265 . In various embodiments, this may consist of a combination of reversing the axial drive motor to move each assembly along its drive arm away from the driven anchors combined with counter rotation of the rotary drivers to decouple them from the driving collars. It may also be necessary to remove any pins used to couple each anchor to its rotary driver before actuating the drive motor to move the assembly away from the anchor. Once the driving assembly, including the mandrels have cleared the above-ground ends of each anchor, the machine may be moved along the North-South installation line of the tracker assembly to the next driving location in step  270 . In various embodiments, one or more known GPS-based systems may be used to move the machine to a precise location along the North-South line so that the next pair of anchors can be installed at the location specified in the site plan. 
     Depending on the desired work point height for the truss foundation, it may not be possible to drive two screw anchors at the same time with the machine shown in  FIGS.  2 A-B . In particular, lower work point heights will make clearance between the driving assemblies more difficult. Soil properties may also make simultaneous driving difficult because unstructured soils may require longer screw anchors and correspondingly deeper driving depths to achieve the required resistance to forces of tension and compression without raising the work point height. In response to this problem, various embodiments of the invention provide a machine that can simultaneously drive two standard length anchors, or alternatively, a single extended length anchor at a first angle, and then a second adjacent extended length anchor at a second angle. Such a machine is shown, for example, in  FIG.  5 A  and B. 
     Machine  300  of  FIG.  5 A  and B is similar to machine  200  of the previous figures but instead of having two symmetric driving arms, one of the arms  331 A is extended in length. This allows machine  300  to be used in a simultaneous driving mode where two standard length screw anchors are driven at substantially the same time, or alternatively, in a serial mode where a first extend length anchor is driven and then the extend driving arm is rotated to a second angle so that a second extend length anchor may be driven. In exemplary machine  300 , extended length drive arm  331 A passes through common hinge point  338 . This asymmetric configuration allows extended length anchors to be loaded and driven in a serial driving mode. When driving serially, the extended length anchor is loaded onto extended mandrel  343 A of extended driving  331 A assembly and the assembly is rotated about hinge point  338  to the desired angle (e.g., 70-degrees with respect to horizontal). Screw anchors driven to depth in the same manner, (i.e., by a combination of the action rotary driver, the mandrel and the axial drive motor) until the target depth is reached. The rotary driver is then decoupled from the anchor and the driver and mandrel are backed away in the axial direction along arm  331 A until the tip of extended mandrel  343 A clears the driven anchor. A second anchor must be loaded onto the mandrel while machine  300  remains at the same location. This may be done before rotating the extended driving assembly  330 A to the desired angle for the second anchor or after. In either case, once the extended assembly  330 A is oriented at the desired angle, the extended driving assembly once again travels along extended drive arm  331 A while driving the extended length anchor to target depth. If the additional length provided by the extended driving assembly is not needed, simultaneous driving may be performed by both assemblies  330 A/ 330 B in a manner consistent with that discussed in the context of the previous figures. Both drive assemblies are supported by mast  320 . 
       FIG.  6    is a flow chart detailing the steps of a method for driving single, extended-length screw anchors with the extended anchor driving assembly of  FIG.  5 A  and B. The method begins in step  350  by loading a screw anchor onto the extending assembly. In various embodiments, this may consist of moving the drive assembly up the rail until sufficient clearance is achieved. The anchor may then be manually sleeved over the mandrel until the top of it engages the rotary driver. In other embodiments, this may consist of placing the anchor into a holder attached to the extended driving assembly arm so that as the moving assembly slides down the rail, the mandrel enters the top, open end of the anchor and travels through the shaft until the top of the anchor engages the rotary driver. In other embodiments, an automated or robotic loader could pick and place anchors from a supply and load them onto the rail. After the anchor is loaded, in step  355  the machine may rotate the driving assemblies about the hinge point until the extended driving assembly’s drive axis is oriented at the desired drive angle for the first screw anchor. Then, in step  360 , the first screw anchor is driven to the target depth. As discussed herein, in various embodiments, this is accomplished by engaging an axial drive motor to move the driving assembly down the mast, a rotary driver to impart torque to the head of the anchor and a tool driver to actuate a mandrel or drill through screw anchor. Once the first screw anchor has been driven to target depth is reached, in step  365  the mandrel and driving assembly automatically retract by traveling back up the driving arm until the top of the driven anchor is cleared. In step  370 , an operator or automated loading mechanism must load the assembly with a second anchor. Once loaded, in step  375  the driving assemblies rotate within the same plane until the extended assembly is oriented at the second driving angle. Because the extended assembly passes through the work point, it can drive anchors in either direction (East or West). In step  380  the extended driving assembly is actuated again to drive the second anchor of the pair at the second angle until it reaches the target depth. The machine is then moved along the North-South line of the tracker row or onto the next row where the process of driving the anchor pair starts again. 
     Depending on how frequently the extended driving assembly must be used relative to both assemblies at the same time on a given job site, it may be desirable and/or necessary to go faster than the serialized process described in the context of the machine shown in  FIGS.  5 A-B  when longer screw anchors are needed most or all the time. To that end,  FIGS.  7 A- 7 C  show another exemplary machine  400  for driving two anchors of regular or extended length in rapid succession according to various embodiments of the invention. The advantage of this exemplary machine  400  over that of  FIG.  6 A  and B is that it can install two anchors serially without needing to reload between successive drives and both may be extended length. Because the drive arms  440 A/B of this exemplary machine are oriented parallel to one other, they never intersect (e.g., occupy the same space at the same time). This eliminates the spatial constraints discussed in the context of other embodiments of two drive assemblies needing to occupy the same space. 
     Machine  400  shown in  FIGS.  7 A-B . This machine is similar to those shown in conjunction with the various other embodiments, including a tracked chassis, hydraulic system, and one or more articulating arm that supports mast  420  of a driver attachment. The attachment shown here consists of a pair of parallel frame members  440 A/B that moves as an entire assembly relative to base machine  400 . Chassis  414  rides on tracks  412  and supports main body portion  416 . In various embodiments the connection between mast  420  and main body portion  416  allows the entire attachment assembly to tilt forward and backward (move in pitch) and to telescope towards and away from the chassis (move in yaw), as well as to move rotate about common hinge point  448  (move in roll). Mast  420  may also include a telescoping feature to raise or lower the driving assemblies relative to the ground while remaining in the same plane. Drive assemblies  430 A/B travel along their respective frame members  440 A/B to allow regular or extended length anchors to be loaded at the same time and then driven serially into the ground. Frame members  440 A/B are fixed together at a uniform distance so that they remain parallel regardless of the angular orientation of the attachment and/or frame. 
     Screw anchors may be loaded onto machine  400  of  FIGS.  7 A-B  in the same manner as in other embodiments. That is, they may be manually slid over respective mandrels  443 A/B, attached to the rotary driver of drive assemblies  430 AB, or alternatively, loaded with auto loading mechanism that grab an anchor from a cache of anchors and move it into the path of the one of the mandrels so that the mandrel can pass through it until the top of the anchor engage the rotary driver. The exemplary robotic auto loaders  418  shown in  FIGS.  8 A-C  are single-plane loaders that rotate about respective Z-axes. Each loader has a rotating arm that swings outward until it is adjacent to the next available foundation anchor from a supply of available anchors carried by the machine. A claw at the end of the arm closes to grab the shaft of an available screw anchor. The arm rotates back towards its respective driving assembly to transfer the anchor to the driving assembly. In either case, once each drive assembly is loaded, mast  420  is rotated to the first driving so that the first driving assembly  430 A can begin driving the first screw anchor into the ground. Once that anchor is driven to the target depth, drive assembly  430 A is retracted up frame member  440 A, and the mast is rotated until assembly  430 B is oriented at the second driving angle. Drive assembly  430 B is actuated along frame member  440 B to drive the second screw anchor into the ground at the second angle until the target depth is again reached. Assembly  430 B is then withdrawn so that the machine can be reloaded and moved to the next installation site along the tracker row or at the beginning of the next row. 
       FIG.  8    is a flow chart detailing the steps of a method for installing a pair of adjacent screw anchors with machine  400  shown in  FIGS.  7 A/B . The method begins in step  450  where a pair of screw anchors are loaded onto the respective rotary drivers on the mast of the machine. As discussed above, this may consist of manually sleeving the anchors past the tip of each mandrel until it engages the driving head of one of the rotary drivers. Alternatively an autoloading mechanism may grab an available screw anchor from a supply carried on the machine and move it into position so that the mandrel can be automatically actuated to travel down its frame member, passing through the screw anchor until the top of the anchor engages the driving head of the rotary driver. Then, in step  455 , the mast and/or frame members are moved until the first drive assembly is oriented along the intended drive access. In some embodiments, this may simply involve rotating the pair of frame members about a common hinge point, such as point  448  in  FIG.  7 B . In other embodiments, the machine may move the entire mast in several directions at once to achieve alignment with the desired drive axis. In step  460 , the first screw anchor is driven to depth by engaging the axial drive motor, rotary driver and, if necessary, the tool driver to rotate the screw anchor into the supporting ground to the desired depth. In step  465  the first drive assembly is retracted back up its frame member until it clears the driven anchor and the mast and/or frame members are rotated to the second drive angle. In step  470 , the second anchor is driven to depth by repeating substantially the same process with the second drive assembly. Once complete, in step  475  the second assembly is withdrawn from the driven anchor so that the machine may be reloaded and positioned at the next foundation location point on the array. 
     The embodiments of the present invention are not to be limited in scope by the specific embodiments described herein. Indeed, various modifications of the embodiments of the present inventions, in addition to those described herein, will be apparent to those of ordinary skill in the art from the foregoing description and accompanying drawings. Thus, such modifications are intended to fall within the scope of the following appended claims. Further, although some of the embodiments of the present invention have been described herein in the context of a particular implementation in a particular environment for a particular purpose, those of ordinary skill in the art will recognize that its usefulness is not limited thereto and that the embodiments of the present inventions can be beneficially implemented in any number of environments for any number of purposes. Accordingly, the claims set forth below should be construed in view of the full breath and spirit of the embodiments of the present inventions as disclosed herein.