Patent Publication Number: US-2021175841-A1

Title: Solar tracker stow system and method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 15/955,519, filed Apr. 17, 2018, entitled “SOLAR TRACKER CONTROL SYSTEM AND METHOD” having attorney docket number 0105935-005US0, which is a non-provisional of and claims priority to U.S. Provisional Applications entitled “PNEUMATIC ACTUATOR SYSTEM AND METHOD” and “PNEUMATIC ACTUATION CIRCUIT SYSTEM AND METHOD” and “SOLAR TRACKER CONTROL SYSTEM AND METHOD” respectively and having attorney docket numbers 0105935-003PR0 and 0105935-004PR0 and 0105935-005PR0 and respectively having application Nos. 62/486,335, 62/486,377 and 62/486,369. These applications are hereby incorporated herein by reference in their entirety and for all purposes. 
    
    
     STATEMENT REGARDING FEDERALLY-SPONSORED RESEARCH 
     This invention was made with Government support under contract number DE-AR0000330 awarded by DOE, Office of ARPA-E. The Government has certain rights in this invention. 
    
    
     This application is related to U.S. Non-Provisional application Ser. No. 15/955,044 and 15/955,506, filed Apr. 17, 2018 entitled “PNEUMATIC ACTUATOR SYSTEM AND METHOD” and “PNEUMATIC ACTUATION CIRCUIT SYSTEM AND METHOD” respectively, and having attorney docket numbers 0105935-003US0 and 0105935-004US0. These applications are hereby incorporated herein by reference in their entirety and for all purposes. 
     This application is also related to U.S. application Ser. No. 15/012,715, filed Feb. 1, 2016, which claims the benefit of U.S. provisional patent application 62/110,275 filed Jan. 30, 2015. These applications are hereby incorporated herein by reference in their entirety and for all purposes. 
     This application is also related to U.S. application Ser. Nos. 14/064,070 and 14/064,072, both filed Oct. 25, 2013, which claim the benefit of U.S. Provisional Application Nos. 61/719,313 and 61/719,314, both filed Oct. 26, 2012. All of these applications are hereby incorporated herein by reference in their entirety and for all purposes. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1 a  and 1 b    illustrate a respective top perspective and bottom perspective view of a solar tracker in accordance with various embodiments. 
         FIG. 2  illustrates a side view of a solar tracker. 
         FIG. 3  illustrates a side view of an actuator in accordance with one embodiment, which comprises a V-shaped bottom plate, a planar top-plate, and a set of bellows that are disposed between the top and bottom plates and surrounded by a set of washers. 
         FIG. 4  illustrates an example of a solar tracking system that includes a row controller that controls a plurality of rows of solar trackers. 
         FIG. 5  is an exemplary illustration of a set of rows, including a first tracker and second tracker, with each tracker comprising a plurality of actuators disposed along a common axis and with each actuator comprising a first and second bellows. 
         FIG. 6  is a block diagram of elements of a solar tracking system that includes a row controller and a first and second solar tracker. 
         FIG. 7  illustrates an example of a tracker tracking the position of sun throughout the day as the sun moves through the sky. 
         FIG. 8 a    illustrates an example of a tracker being in a non-ideal position relative to the sun and  FIG. 8 b    illustrates moving the tracker to an ideal position with the tracker axis being coincident with the center of the sun. 
         FIG. 9  illustrates an example method of controlling one or more solar trackers to match the angle or position of the sun. 
         FIG. 10  illustrates a state diagram associated with controlling one or more solar trackers. 
         FIG. 11  illustrates a tracking window that can be used by the when controlling one or more solar trackers. 
         FIG. 12  illustrates a method of identifying a stow event and generating a stow in one or more tracker. 
         FIG. 13  illustrates a method  1300  of level-calibrating a solar tracker in accordance with an embodiment. 
         FIG. 14  is a block diagram of elements of a solar tracking system that includes an array controller, a first and second row controller and four solar trackers. 
         FIG. 15  illustrates an example embodiment of a row controller featuring a “stow on power loss” function. 
     
    
    
     It should be noted that the figures are not drawn to scale and that elements of similar structures or functions are generally represented by like reference numerals for illustrative purposes throughout the figures. It also should be noted that the figures are only intended to facilitate the description of the preferred embodiments. The figures do not illustrate every aspect of the described embodiments and do not limit the scope of the present disclosure. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIGS. 1 a  and 1 b    illustrate respective top perspective and bottom perspective views of a solar tracker  100  in accordance with various embodiments.  FIG. 2  illustrates a side view of the solar tracker  100 . As shown in  FIGS. 1 a , 1 b    and  2 , the solar tracker  100  can comprise a plurality of photovoltaic cells  103  disposed along a length having axis X 1  and a plurality of pneumatic actuators  101  configured to collectively move the array of photovoltaic cells  103 . As shown in  FIG. 1 b   , the photovoltaic cells  103  are coupled to rails  102  that extend along parallel axes X 2 , which are parallel to axis X 1 . Each of the plurality of actuators  101  extend between and are coupled to the rails  102 , with the actuators  101  being coupled to respective posts  104 . As shown in  FIG. 2 , the posts  104  can extend along an axis Z, which can be perpendicular to axes X 1  and X 2  in various embodiments. 
     As shown in  FIG. 2 , and discussed in more detail herein, the actuators  101  can be configured to collectively tilt the array of photovoltaic cells  103  based on an angle or position of the sun, which can be desirable for maximizing light exposure to the photovoltaic cells  103  and thereby maximizing electrical output of the photovoltaic cells  103 . In various embodiments, the actuators  101  can be configured to move the photovoltaic cells  103  between a plurality of configurations as shown in  FIG. 2 , including a neutral configuration N where the photovoltaic cells  103  are disposed along axis Y that is perpendicular to axis Z. From the neutral configuration N, the actuators  101  can be configured to move the photovoltaic cells  103  to a first maximum tilt position A, to a second maximum tilt position B, or any position therebetween. In various embodiments, the angle between the neutral configuration N and the maximum tilt positions A, B can be any suitable angle, and in some embodiments, can be the same angle. Such movement can be used to position the photovoltaic cells  103  toward the sun, relative to an angle of the sun, to reflect light toward a desired position, or the like. 
     In one preferred embodiment as shown in  FIGS. 1 a  and 1 b   , a solar tracker  100  can comprise a plurality of photovoltaic cells  103  that are collectively actuated by four actuators  101  disposed along a common axis. However, in further embodiments, a solar tracker  100  can comprise any suitable number of actuators  101  including one, two, three, four, five, six, seven, eight, nine, ten, fifteen, twenty, fifty, one hundred, or the like. Similarly, any suitable number of photovoltaic cells  103  can be associated with a solar tracker  100  in further embodiments. Additionally, while photovoltaic cells  103  are shown in example embodiments herein, in further embodiments, actuators  101  can be used to move various other objects or structures, including mirrors, reflectors, imaging devices, communications devices, and the like. 
       FIG. 3  illustrates a side view of an actuator  101  in accordance with one embodiment. As shown in the example of  FIG. 3 , the actuator  101  comprises a V-shaped bottom plate  310 , a planar top-plate  330 , and a set of bellows  300  that are disposed between the top and bottom plates  330 ,  310  and surrounded by a set of washers  350 . The washers  350  are coupled to a hub assembly  370  that extends between the bottom and top plates  310 ,  330 , with the hub assembly  370  defined by a plurality of stacked hub units  373 . 
     The example embodiment of  FIG. 3  illustrates the actuator  101  in a neutral configuration N (see  FIG. 2 ), where the top plate  330  extends along axis Y, which is perpendicular to axis Z in the neutral configuration N. However, as discussed herein, the top plate  330  can be configured to tilt to the left and right (or east and west as discussed herein) based on selective inflation and/or deflation of the bellows  300 . Components of an actuator  101  can comprise various suitable materials, including metal (e.g., steel, aluminum, iron, titanium, or the like), plastic or the like. In various embodiments, metal parts can be coated for corrosion prevention (e.g., hot dip galvanized, pre galvanized, or the like). 
     A row controller  380  can be operably coupled with bellows  300  of the actuator via pneumatic lines  390 . More specifically, an east bellows  300 E can be coupled to a pneumatic circuit  382  of the row controller  380  via an east pneumatic line  390 E. A west bellows  300 W can be coupled to the pneumatic circuit  382  of the row controller  380  via a west pneumatic line  390 W. A pneumatic control unit  384  can be operably coupled to the pneumatic circuit  382 , which can control the pneumatic circuit  382  to selectively inflate and/or deflate the bellows  300  to move the top plate  330  of the actuator  101  to tilt photovoltaic cells  103  coupled to the top plate  330 . 
     For example, as described herein, bellows  300  of an actuator  101  can be inflated and/or deflated which can cause the bellows  300  to expand and/or contract along a length of the bellows  300  and cause movement of washers  350  surrounding the bellows  300 . Such movement of the washers  350  can in turn cause rotation, movement or pivoting of the hub units  373  of the hub assembly  370 . Such pivoting of hub units  373  of the hub assembly  370  can be generated when a solar tracker  100  is moving between a neutral position N and the maximum tilt positions A, B as shown in  FIG. 2 . 
     As shown in  FIG. 3 , a bellows  300  can comprise a convoluted body defined by repeating alternating valleys  302  and peaks  304  extending between a first and second end of the bellows  300 . In various embodiments, a bellows  300  can be generally cylindrical about a central axis along which the bellows  300  extend. In various embodiments, the bellows  300  and portions thereof can have one or more axes of symmetry about a central axis. For example, in various embodiments, the convolutions of the bellows  300  can have circular radial symmetry and/or axial symmetry about a central axis between the first and second ends or at least a portion thereof. However, as shown in  FIG. 3 , the bellows  300  can be held within an actuator  101  in a curved configuration such that the portion of the bellows  300  proximate to the hub assembly  370  is compressed compared to the portion of the bellows that is distal from the hub assembly  370 . 
     In various embodiments, the bellows  300  can be configured to expand along the length of the bellows  300  when fluid is introduced into the hollow bellows  300  or when the bellows  300  are otherwise inflated. Accordingly, the bellows  300  can be configured to contract along the length of the bellows  300  when fluid is removed from the hollow bellows  300  or when the bellows  300  are otherwise deflated. 
     Where bellows  300  are configured to expand lengthwise based on increased pressure, fluid or inflation and configured to contract lengthwise based on decreased pressure, fluid or inflation, movement of the photovoltaic cells  103  via one or more actuators  101  can be achieved in various ways. For example, referring to the example of  FIG. 3 , rotating the photovoltaic cells  103  west (i.e., to the right in this example) can be achieved via one or more of the following: 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Examples of Actions to Rotate Actuator 101 West 
               
            
           
           
               
               
               
            
               
                 East Bellows 300E 
                 West Bellows 300W 
                 Result 
               
               
                   
               
               
                 Increase Pressure 
                 Maintain Pressure 
                 Rotate West 
               
               
                 Increase Pressure 
                 Reduce Pressure 
                 Rotate West 
               
               
                 Maintain Pressure 
                 Reduce Pressure 
                 Rotate West 
               
               
                 Decrease Pressure 
                 Decrease Pressure More Than 
                 Rotate West 
               
               
                   
                 East Bellows 300E 
                   
               
               
                 Increase Pressure 
                 Increase Pressure Less Than 
                 Rotate West 
               
               
                   
                 East Bellows 300E 
               
               
                   
               
            
           
         
       
     
     Referring again to the example of  FIG. 3 , rotating the photovoltaic cells  103  east (i.e., to the left in this example) can be achieved via one or more of the following: 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Examples of Actions to Rotate Actuator 101 East 
               
            
           
           
               
               
               
            
               
                 East Bellows 300E 
                 West Bellows 300W 
                 Result 
               
               
                   
               
               
                 Maintain Pressure 
                 Increase Pressure 
                 Rotate East 
               
               
                 Reduce Pressure 
                 Increase Pressure 
                 Rotate East 
               
               
                 Reduce Pressure 
                 Maintain Pressure 
                 Rotate East 
               
               
                 Decrease Pressure More Than 
                 Decrease Pressure 
                 Rotate East 
               
               
                 West Bellows 300W 
                   
                   
               
               
                 Increase Pressure Less Than 
                 Increase Pressure 
                 Rotate East 
               
               
                 West Bellows 300W 
               
               
                   
               
            
           
         
       
     
     Accordingly, in various embodiments, by selectively increasing and/or decreasing the amount of fluid within bellows  300 E,  300 W, the top plate  330  and photovoltaic cells  103  can be actuated to track the location or angle of the sun. 
     While various embodiments of an actuator  101  can include two bellows  300 E,  300 W, further embodiments can comprise a single bellows  300  or any suitable plurality of bellows  300 . In various embodiments, actuators  101  include orifices which equalize the flow among many actuators  101 , and/or limit the rate of motion as discussed herein. 
     Turning to  FIG. 4 , in various embodiments, a plurality of solar trackers  100  can be actuated by a row controller  380  in a solar tracking system  400 . In this example, four solar trackers  100 A,  100 B,  100 C,  100 D can be controlled by a single row controller  380 , which is shown being operably coupled thereto. As described in more detail herein, in some examples, a plurality of trackers  100  or a subset of trackers  100  can be controlled in unison. However, in further embodiments, one or more trackers  100  of a plurality of trackers  100  can be controlled differently than one or more other trackers  100 . 
     While various examples shown and described herein illustrate a solar tracking system  400  having various pluralities of rows of trackers  100 , these should not be construed to be limiting on the wide variety of configurations of photovoltaic panels  103  and pneumatic actuators  101  that are within the scope and spirit of the present disclosure. For example, some embodiments can include a single row or any suitable plurality of rows, including one, two, three, four, five, six, seven, eight, nine, ten, eleven, twelve, fifteen, twenty, twenty five, fifty, one hundred, and the like. 
     Additionally, a given row can include any suitable number of actuators  101  and photovoltaic panels  103 , including one, two, three, four, five, six, seven, eight, nine, ten, eleven, twelve, fifteen, twenty, twenty five, fifty, one hundred, two hundred, five hundred, and the like. Rows can be defined by a plurality of physically discrete tracker units. For example, a tracker unit  100  can comprise one or more actuators  101  coupled to one or more photovoltaic panels  103 . 
     In some preferred embodiments, the axis of a plurality of solar trackers  100  can extend in parallel in a north-south orientation, with the actuators  101  of the rows configured to rotate the photovoltaic panels about an east-west axis. However, in further embodiments, the axis of trackers  100  can be disposed in any suitable arrangement and in any suitable orientation. For example, in further embodiments, some or all rows may not be parallel or extend north-south. Additionally, in further embodiments, rows can be non-linear, including being disposed in an arc, circle, or the like. Accordingly, the specific examples herein (e.g., indicating “east” and “west”) should not be construed to be limiting. 
     Also the rows of trackers  100  can be coupled to the ground, over water, or the like, in various suitable ways including via a plurality of posts. Additionally, while various embodiments described herein describe a solar tracking system  400  configured to track a position of the sun or move to a position that provides maximum light exposure, further examples can be configured to reflect light to a desired location (e.g., a solar collector), and the like. 
       FIG. 5  is an exemplary illustration of a set of rows, including a first tracker  100 A and second tracker  100 B, with each tracker  100  comprising a plurality of actuators  101  disposed along a common axis (e.g., as shown in  FIGS. 1 a , 1 b    and  4 ) with each actuator  101  comprising a first and second bellows  300 . More specifically,  FIG. 5  illustrates a first solar tracker  100 A that comprises a first actuator  101 AA and a second actuator  101 AB on which a first set of photovoltaic cells  103 A are disposed. The first actuator  101 AA of the first tracker  100 A comprises east and west bellows  300 AE 1 ,  300 AW 1  and the second actuator  100 B of the first tracker  100 AB comprises east and west bellows  300 AE 2 ,  300 AW 2 . 
     A second solar tracker  100 B comprises a first actuator  101 BA and a second actuator  101 BB on which a second set of photovoltaic cells  103 B are disposed. The first actuator  101 BA of the second tracker  100 B comprises east and west bellows  300 BE 1 ,  300 BW 1  and the second actuator  100 BB of the second tracker  100 B comprises east and west bellows  300 BE 2 ,  300 BW 2 . 
     A row controller  380  is shown comprising a pneumatic control unit  384  that is operably connected to a pneumatic circuit  382  that drives the bellows  300  of the first and second trackers  101 A,  101 B via respective pneumatic lines  390  that are configured to introduce and/or remove fluid from the bellows  300  (e.g., via respective bellows branches  392  that extend from the pneumatic lines  390 ). More specifically, a first east pneumatic line  390 E 1  is shown being operably connected to the first and second east bellows  300 AE 1 ,  300 AE 2  of the first tracker  100 A. Accordingly, because the first and second east bellows  300 AE 1 ,  300 AE 2  of the first tracker  100 A share a common pneumatic line  390 E 1 , pneumatic circuit  382  can drive, introduce fluid to, remove fluid from, and/or otherwise control the first and second east bellows  300 AE 1 ,  300 AE 2  in unison via the common pneumatic line  390 E 1 . 
     Similarly, a first west pneumatic line  390 W 1  is shown being operably connected to the first and second west bellows  300 AW 1 ,  300 AW 2  of the first tracker  100 A. Accordingly, because the first and second west bellows  300 AW 1 ,  300 AW 2  of the first tracker  100 A share a common pneumatic line  390 W 1 , pneumatic circuit  382  can drive, introduce fluid to, remove fluid from, and/or otherwise control the first and second west bellows  300 AW 1 ,  300 AW 2  in unison via the common pneumatic line  390 W 1 . 
     Accordingly, with the first and second east bellows  300 AE 1 ,  300 AE 2  and the first and second west bellows  300 AW 1 ,  300 AW 2  being respectively configured to be driven in unison, the first and second actuators  101 AA,  101 AB of the first solar tracker  100 A can be driven in unison, which allows for the set of photovoltaic cells  103 A coupled to the first and second actuators  101 AA,  101 AB to be rotated laterally about a common axis that extends through the first and second actuators  101 AA,  101 AB. 
     While this example of  FIG. 5  illustrates the first tracker  100 A comprising a first and second actuator  101 AA,  101 AB, it should be clear that a plurality of actuators  101  can be driven or controlled in a similar manner, including trackers  100  having four actuators  101  as illustrated in  FIGS. 1 a , 1 b    and  4 . 
     The second tracker  100 B is shown having a similar configuration. More specifically, a second east pneumatic line  390 E 2  is shown being operably connected to the first and second east bellows  300 BE 1 ,  300 BE 2  of the second tracker  100 B. Accordingly, because the first and second east bellows  300 BE 1 ,  300 BE 2  of the second tracker  100 B share a common pneumatic line  390 E 2 , pneumatic circuit  382  can drive, introduce fluid to, remove fluid from, and/or otherwise control the first and second east bellows  300 BE 1 ,  300 BE 2  in unison via the common pneumatic line  390 E 2 . 
     Similarly, a second west pneumatic line  390 W 2  is shown being operably connected to the first and second west bellows  300 BW 1 ,  300 BW 2  of the second tracker  100 B. Accordingly, because the first and second west bellows  300 BW 1 ,  300 BW 2  of the second tracker  100 B share a common pneumatic line  390 W 2 , pneumatic circuit  382  can drive, introduce fluid to, remove fluid from, and/or otherwise control the first and second west bellows  300 BW 1 ,  300 BW 2  in unison via the common pneumatic line  390 W 2 . 
     As discussed herein, pneumatics can introduce and/or remove fluid from bellows  300  of one or more actuators  101 . For example, pneumatics can actuate a plurality of actuators  101  associated with a solar tracker  100 . In further examples, pneumatics can actuate a plurality of solar trackers  100  disposed in one or more rows. In various embodiments, a pneumatics system (e.g., including the pneumatic circuit  382 , pneumatic lines  290 , and the like) can comprise a plenum structure for a CADS harness, which in some embodiments can include a high flow capacity main line with flow restrictions  391  on bellows branches  392  to maintain main line pressure on long rows. In some embodiments, pneumatic routing can be disposed on the north side of all actuators of a tracking system  400 . In further embodiments, pneumatic routing can be disposed exclusively on the south side of all actuators of the tracking system  400  or on both the north and south sides. 
     In some embodiments, (e.g., as shown in  FIG. 5 ) flow restrictions  391  on some or all bellows branches  392  can be desirable for equalizing flow (and therefore motion rate) of some or all actuators  101  in a tracker  100 , a row of trackers  100  or across rows of differing lengths and differing pneumatic impedance. The flow restrictions  391  can be tuned to equalize flow within a desired percentage range in accordance with various embodiments. Such configurations can equalize motion rate for some or all of the actuators (keeps panels matched) and can allow for more arbitrary field layout of pneumatic lines  390 . Various embodiments can include a hermetic connector-to-bellow polymer-weld. Further embodiments can comprise air brake tubing and fittings for a solar application. In some embodiments, the pneumatic circuit  382 , using low pressure, can pump between CADS channels rather than using a source/exhaust system. For example, the system can comprise a row controller  380  that pumps between CADS channels. 
     Some embodiments can comprise a replenish-leaks-on-power-loss function. For example, an additional low pressure regulator can be added to a row controller  380  or other portion of the solar tracking system  400 , with a normally-open valve connecting it to a manifold cross-over. The valve can be held closed when the system is powered. When power is lost, the valve opens, replenishing any leaks from an attached high-pressure air tank. This can allow the solar tracking system  400  to maintain a stow position for an extended period of power-loss, even with leaks in the system. For example, FIGS. 8 and 15 of U.S. patent application Ser. No. 15/955,506 referenced above and incorporated by reference herein illustrate example embodiments of row controllers featuring a “replenish-leaks-on-power-loss” function. 
     In further embodiments the solar tracking system  400  can comprise a wind flutter damper-compressor. For example, some configurations can use the fluttering motion of a tracker  100  induced by wind to operate a compressor to augment air supply. One or more pistons (or bellows  300 ) distributed throughout the tracker  100  can generate additional makeup air to reduce energy consumption while also limiting the magnitude of any fluttering behavior preventing resonance. Additionally, some embodiments can comprise a double 5/2 valve arrangement, which can include a source or exhaust connected to east-output or west-output. 
     Turning to  FIG. 6 , a block diagram of a set of elements  600  of one example embodiment of a solar tracking system  400  is illustrated, which includes a row controller  380  and a first and second solar tracker  100 A,  100 B. The row controller  380  is shown comprising a control device  651 , a fluid source  652 , a fluid source pressure sensor  653 , a temperature sensor  654 , a wind sensor  655 , a sun sensor  656  and a clock  657 .  FIG. 14  is a block diagram that illustrates another example embodiment of a solar tracking system  400  that comprises an array controller  1400  a first and second row controller  380  and a first, second, third, fourth solar tracker  100 A,  100 B,  100 C,  100 D. 
     The embodiments of  FIGS. 6 and 14  are merely examples and should not be construed to be limiting on the wide variety of architectures of a solar tracking system  400  that are within the scope and spirit of the present disclosure. For example, some embodiments can include an array controller  1400  that controls one or more row controller  380 , which in turn control one or more solar trackers  100 . In some embodiments, one or both of the array controller  1400  and/or row controllers  380  can be absent, with one or more remaining elements performing sensing and/or control functions. 
     Additionally, while the array controller  1400 , row controller  380  and solar tracker  100  are shown having a plurality of control and sensing elements, in some examples any shown elements can be absent or additional control and/or sensing elements can be present. In other words, in further examples, any of the array controllers  1400 , row controller  380  and solar tracker  100  can be more or less complex and can have more or fewer elements compared to the examples of  FIGS. 6 and 14 . 
     For example, in some embodiments east/west bellows pressure sensors  601 E,  601 W can be disposed at one or more row controller  380  and/or array controller  1400  and not the solar trackers  100 . In further embodiments, east/west bellows pressure sensors  601 E,  601 W can be disposed at one or more solar tracker  100 , which in some embodiments can include east/west bellows pressure sensors  601 E,  601 W associated with one or more actuators  101  of such trackers  100 . Still further embodiments can include east/west bellows pressure sensors  601 E,  601 W on every row of trackers  100 , on every couple of rows of trackers  100 , and the like. 
     Accordingly, in some examples, bellows sensors  601  can be co-located at one or more bellows  300  or can be associated with pneumatic lines associated with one or more bellows  300 . For example, in some embodiments, bellows pressure sensors  601  can be respectively configured to sense the pressure of a single bellows  300  or the pressure of a group of bellows  300  including a plurality of east bellows  300 E, a plurality of west bellows  300 W, one or more bellows  300  from a plurality of trackers  100 , and the like. 
     Also, any of the functions or methods described herein can be performed exclusively at one of an array controller  1400 , row controller  380  and solar tracker  100  in some embodiments, or can be performed collectively by two or more of an array controller  1400 , row controller  380  and solar tracker  100 . For example, it should be appreciated that embodiments illustrating functions or method being performed by a row controller should be construed to be performed alternatively and/or additionally by one or both of an array controller  1400  and row controller. 
     In various embodiments, the control device  651  can be any suitable computing device, which can include a processor, memory, power source, networking hardware, and the like. The control device  651  can store computer readable instructions (e.g., software, firmware and the like) on one or more computer readable medium, which can control one or more pneumatic circuits  382 , which can in turn drive or control one or more solar trackers  100  as described in more detail herein. In various embodiments, a pneumatic control unit  384  can comprise the control device  651  or vice versa. In some embodiments, the control device  651  can comprise a specialized embedded system or can comprise devices such as a smartphone, laptop computer, tablet computer or the like. 
     Some embodiments can comprise solar electrical string powered controls with no battery backup. For example, the array can be used to power controls. In one configuration, a large array  400  can have significant available energy even early in the morning before inverters start. A 50 kW array (e.g., including eight trackers  100 ) with 10 W/m{circumflex over ( )}2 irradiance can generate 500 W which can be sufficient to power control systems. Even cloudy days can have more than enough power to run a compressor. Such embodiments can be employed with or without battery backup. Additionally, the control system can be configured to move one or more trackers  100  of an array  400  away from vulnerable positions before energy is lost for the day. In such examples, a stow-on-power-loss function can be desirable. 
     While backup power can be provided via a battery, further embodiments can comprise a wind turbine to provide backup power (or backup air supply) during wind events combined with power outages. Risks to a solar array structure can be greatest during extreme wind events, and using wind to provide energy can help guarantee that energy is available when needed. 
     While some embodiments include the control device  651  being located onsite and proximate to one or more solar trackers  100  being controlled, further embodiments can include the control device  651  or portions thereof being located in a disparate location from the solar trackers  100 . For example, in some embodiments, control device  651  or portions thereof can be embodied in one or more physical or virtual computing devices located away from the solar trackers  100  and control data and sensing data can be communicated to and from such a disparate location via various suitable networks, including a cellular network, satellite network, the Internet, a Wi-Fi network, microware network, a laser network, a serial communications system, or the like. 
     The fluid source  652  can comprise any suitable container for storing fluid. For example, in embodiments where air is used as a fluid for controlling bellows  300  of one or more solar trackers  100 , the fluid source  652  can comprise one or more air tank and/or air compressor of any suitable size and shape. While some embodiments include a fluid source  652  at the row controller  380 , further embodiments can include one or more fluid sources  652  proximate to one or more solar trackers  100 . For example, where a plurality of solar trackers  100  are disposed in a row, a fluid source can be disposed at an end of a row. Additionally, where other fluids (e.g., oxygen, nitrogen, water, oil, or the like) are used, a fluid source  652  can be configured to store such fluids. 
     A fluid source pressure sensor  653  can be associated with a fluid source  652  and can be configured to sense a pressure associated with the fluid source  652 . Additionally in further embodiments, the pressure sensor  653  or other sensors can be configured to sense a volume of fluid present within the fluid source  652 . Data associated with a pressure, volume or the like, of a fluid source can be used as discussed in more detail herein. 
     The row controller  380  and/or array controller  1400  can comprise various additional sensors, including a temperature sensor  654 , a wind sensor  655 , a sun sensor  656 , and the like. As discussed herein, a temperature sensor  654  can be configured to sense a temperature associated with, and can be configured to determine a fluid volume, or the like, within various portions of a solar tracking system  400 , including the fluid source  652 , pneumatic lines  370 , pneumatic circuit  382 , or the like. A wind sensor  655  can be used to determine wind speed or velocity near the row controller  380 , which as discussed herein can be used to determine whether one or more solar trackers  100  should be moved to a stowed position to prevent wind damage to the solar trackers  100 , whether rigidity of one or more actuators  101  should be increased or decreased, or whether an alert should be sent to a user regarding wind conditions. 
     As discussed herein, a solar tracking system  400  can be configured to move one or more solar trackers  100  to track the position or angle of the sun, which can be desirable for maximizing electrical energy generated by photovoltaic cells  103  of the system  400 . In some embodiments, the sun sensor  656  can be used to determine an angle or position of the sun, which can be used to determine how the solar trackers  100  should be driven as discussed herein. However, in further embodiments, a sun sensor  656  can be absent and an angle or position of the sun can be determined in other ways. 
     In various embodiments, a clock  657  can be used to determine an angle or position of the sun. For example, where the location of the solar tracking system  400  and/or components thereof are known (e.g., via GPS or a defined location indicator), astrological charts can be consulted which can identify a position or angle of the sun at the location at a time defined by the clock  657 . Accordingly, in various embodiments, the row controller  380  can store or otherwise have access to astrological charts that identify what the angle and/or position of the sun will be at various times in the future relative to one or more locations. 
     A row controller  380  is shown being operably connected to first and second solar trackers  100 A,  100 B in  FIG. 6 . An array controller  1400  is shown as being operably connected to a first and second row controller  380  in  FIG. 14 . Such an operable connection can include a fluidic and/or data communication connection with the solar trackers  100  and/or row controller  380  in the case of array controller  1400 . For example, a fluidic connection can include fluidic lines  390  (see  FIGS. 3 and 5 ) that allow fluid to travel from the array controller  1400  and/or row controller  380  to the one or more solar trackers  100  and/or vice versa. However, in some embodiments, where a fluid source  652  is absent at the row controller  380  and/or array controller  1400 , such a fluidic connection can be absent. For example, where one or more fluid sources  652  are located at one or more trackers  100 , an operable connection between the row controller  380  and the one or more trackers  100  can include only a data communication connection. In another example, one or more trackers  100  can be self-powered with distributed air compressors or pumps. 
     In various embodiments, a data communication connection can include any suitable wired and/or wireless communication channel that allows data to pass from the array controller  1400  to one or more row controller  380 , from one or more row controllers  380  to the one or more solar trackers  100  and/or vice versa. For example, in some embodiments, sensing data from the one or more solar trackers  100  can be communicated to the one or more row controllers  380  and/or array controller  1400  as discussed herein, which can inform control of the one or more solar trackers  100  by a row controller  380  and/or array controller  1400 . Additionally or alternatively, control data, or other suitable data (e.g., sensing data) can be communicated to the one or more solar trackers  100  from the row controller  380  and/or array controller  1400 . For example, where valves or other components are present at the one or more trackers  100 , such valves or components can be controlled via data sent to the one or more trackers  100  from a row controller  380  and/or an array controller  1400  that controls a plurality of row controllers  380 . 
     The solar trackers  100 A,  100 B can include a respective one or more east bellows  300 AE,  300 BE that are associated with one or more respective east bellows pressure sensors  601 AE,  601 BE. Solar trackers  100 A,  100 B can further include a respective one or more west bellows  300 AW,  300 BW that are associated with one or more respective west bellows pressure sensors  601 AW,  601 BW. For example, as discussed and shown herein (e.g., in  FIGS. 1 a , 1 b   ,  4  and  5 ), a solar tracker  100  can comprise one or more actuators  101  that each comprise a pair of bellows  300 . 
     In various embodiments, a bellows pressure can be used to determine an inflation/deflation state of the bellows  300 , a volume of fluid present in the bellows, and the like, which can be desirable for monitoring and controlling the bellows  300  of a solar tracking system  400 . Some embodiments can include one or more pressure sensor  601  associated with a given bellows  300 , whereas further embodiments can include pressure sensors associated with only a subset of bellows  300 . Pressure sensors can be disposed proximate to, within or on a bellows  300  or can be operably coupled to a fluidic line  390  or branch  392  associated with one or more bellows  300 . Bellows pressure data obtained from one or more pressure sensors  601  can be used as discussed in more detail herein. 
     Additionally, the solar trackers  100 A,  100 B can comprise various additional sensors, including respective inclinometers  603 A,  603 B, temperature sensors  605 A,  605 B, wind sensors  607 A,  607 B, and the like. In various embodiments, an inclinometer  603  can measure an angle of slope or tilt of the photovoltaic cells  103  associated with a tracker  100 . For example, an inclinometer  603  can measure an angle of slope or tilt associated with a tracker  100  being in a neutral configuration N, maximum tilts A, B, or any other configurations therebetween, as shown in  FIG. 2 . Such an identified angle of slope or tilt associated with photovoltaic cells  103  can be used to determine the position of the photovoltaic cells  103  of the tracker  100  relative to a position or angle of the sun as discussed in more detail herein. 
     In some embodiments, a tracker  100  can comprise one or more inclinometers  603  that can be coupled with or associated with various portions of a tracker  100 , including a top plate  330 , actuator  101 , photovoltaic cells  103 , or the like. Additionally, in further embodiments, inclinometers  603  can be absent and/or other suitable sensors can be used to determine an angle of slope or tilt associated with photovoltaic cells  103 . 
     As discussed herein, temperature sensors  605 A,  605 B can be configured to determine a temperature associated with, and configured to determine a fluid volume, or the like, within various portions of a solar tracking system  400 , including the bellows  300 , pneumatic lines  370  or the like. The wind sensors  607 A,  607 B can be used to determine wind speed or velocity near solar trackers  100 A,  100 B, which as discussed herein can be used to determine whether one or more solar trackers  100  should be moved to a stowed position to prevent wind damage to the solar trackers  100 , whether rigidity of one or more actuators  101  should be increased or decreased, or whether an alert should be sent to a user regarding wind conditions. 
     In further embodiments, control of a solar tracking system  400  can comprise temperature and humidity abatement via pneumatic venting, which can include opening both fill and vent valves in a row controller  380  or other suitable location and/or using an orificed connection for a row controller  380 . Further control system embodiments can comprise modifying/controlling Voc (open circuit voltage), which can be desirable for reducing design constraints (e.g., string length) and improve cost of inverters, combiner boxes, wiring, and the like. Some embodiments can include modifying/controlling Isc (short circuit current), which can reduce design constraints (e.g., current) and can improve the cost of inverters, combiner boxes, wiring, and the like. Still further embodiments can comprise modulating the tracker position to increase convection and therefore increase operating voltage and energy output. 
     In some instances, it can be desirable to reduce the range of motion of one or more tracker  100 , including by limiting the range of motion of one or more actuator  101 , bellows  300 , or other suitable portion of a tracker  100 . For example, limiting the range of motion of one or more tracker  100  can be performed in response to environmental or system conditions, including elevated wind events, high temperature events, low temperature events, and the like. Limiting the range of motion of the tracker  100  can include limiting the range of motion of a tracker  100  to a smaller range of motion compared to a standard range of motion of the tracker  100 , with some examples including immobilizing the tracker  100 . In some examples, generating a stow of a tracker  100  can include limiting the range of motion of the tracker  100  in response to a stow event. 
     Some embodiments can comprise off-angle tracking for electrical current health inspection. For example, off-angle tracking during high irradiance hours can provide an indication of string level health or health of a row controller&#39;s worth of panels. In some embodiments, such a determination can comprise measuring a dip in current output when portions of an array&#39;s tracker are pointed away from the sun. Where actuators  101  or other portions of a tracker  100  are broken, wiring is wrong, or the like, less of a dip would be observed, which could indicate an issue with the system in that portion. On the other hand, where actuators  101  or other portions of a tracker  100  are healthy, larger dips during off-sun tracking would be observed, which could indicate that portion of the system being healthy. Further embodiments can comprise a pressure/position check to monitor bellows for material degradation or other defects. 
     Some embodiments can use pulse width modulation (PWM) or proportional voltage or current control to control valves instead of calculated open-time in order to optimally utilize valve cycle life and minimize tracker twist due to long valve open times. Further embodiments can be configured to monitor pressures/angles of one or more actuators  101  to determine a leak location. For example, leaks can be predicted if pressures/angles in a particular row or tracker  101  are changing differently than other rows/trackers, or differently than expected based on temperature variations and other factors. This can allow leaks to be located on the row-level or tracker-level. Leaks can be located even more precisely, in still further embodiments, with more sensors and/or by learning the system response to leaks as a function of leak location, and adapting control code to recognize patterns that are characteristic of specific leak locations. 
     While  FIG. 6  and the examples discussed herein illustrate specific example embodiments of a solar tracking system  400 , these examples should not be construed to be limiting on the wide variety of suitable configurations of a solar tracking system  400 . For example, any of the elements can be absent in some embodiments, or can be present in a plurality in some embodiments. Additionally, various sensors or elements shown located at the row controller  380  can alternatively, or additionally, be located at the solar trackers  100 , or vice versa. Also, it should be clear that the example sensors or elements shown in  FIG. 4  can be replaced or augmented by suitable equivalents or other sensors or elements that provide for similar functionalities. 
       FIG. 7  illustrates an example of a tracker  100  tracking the position of sun  700  throughout the day as the sun  700  moves through the sky. As shown in this example, one or more photovoltaic cells  103  disposed on the tracker  100  are oriented facing the sun  700  such that tracker axis  750 , which is perpendicular to the planar face of the photovoltaic cells  103 , is coincident with the sun  700 . Accordingly, as shown in this example, the tracker  100  can pivot the photovoltaic cells  103  throughout the day (e.g., via actuators  101 ) to match the angle or location of the sun  700  such that the photovoltaic cells  103  receive maximum sun exposure, which can maximize generation of electrical current by the photovoltaic cells  103 . 
     However, in further embodiments, a tracker  100  can track the changing position or angle of the sun  700  in various suitable ways. For example, while the example of  FIG. 7  illustrates tracking such that tracker axis  750  is coincident with the center of the sun  700 , in further embodiments, it can be desirable to track the sun  700  with tracker axis  750  not being coincident with the center of the sun  700 . 
     For example, in some embodiments, photovoltaic cells  103  can be configured with an optimal exposure angle that is not directly perpendicular to the planar face of the photovoltaic cells  103 . In further examples, heat generated at the photovoltaic cells  103  via exposure with tracker axis  750  being coincident with the center of the sun  700  can reduce electrical output, so pointing the tracker  700  off-center of the sun can be desirable in some embodiments. Additionally, variables like angle or position of the sun in the sky, weather conditions, or the like can also affect an optimal exposure angle of the photovoltaic cells  103 . Accordingly, the examples herein should not be construed as limiting. 
     Turning to  FIGS. 8 a  and 8 b   , an example of a tracker  100  being in a non-ideal position relative to the sun  700  is shown in  FIG. 8 a    and moving the tracker  100  to an ideal position with tracker axis  750  being coincident with the center of the sun  700  is shown in  FIG. 8 b   . As discussed herein, it can be desirable for solar trackers  100  to track the position or angle of the sun  700  to maximize electrical current output by photovoltaic cells  103  on the tracker  100 . For example, where it is determined that the current angle of the photovoltaic cells  103  of the tracker  100  is not within a desirable range of an optimal exposure angle of the photovoltaic cells  103 , then the tracker  100  can be tilted so that the photovoltaic cells  103  are positioned within a desirable range of an optimal exposure angle of the photovoltaic cells  103 . Using the examples of  FIGS. 8 a  and 8 b   , in  FIG. 8 a   , it can be determined that the tracker  100  is in a non-ideal configuration and can be moved to, or within a range of an ideal configuration, for example, by rotating the photovoltaic cells  103  to the right as shown in  FIG. 8   b.    
       FIG. 9  illustrates an example method  900  of controlling one or more solar trackers  100  to match the angle or position of the sun. For example, in various embodiments a pneumatic control unit  384  ( FIGS. 3 and 5 ) or control device  651  ( FIG. 6 ) can be configured to perform the method  900  of  FIG. 9 , or the like. 
     The method  900  begins at  910 , where a current angle or position of the sun is determined. For example, in some embodiments a current angle of the sun can be determined based on a determined time (e.g., via a clock  657  in  FIG. 6 ), a determined or defined position of a tracker  100  or solar tracking system  400 , and based on astrological sun charts that indicate sun position based on time and location. In further embodiments, a current angle or position of the sun can be determined based on a sun sensor  656  ( FIG. 6 ) or other suitable method or device. 
     The method  900  continues at  920  where an ideal angle of the photovoltaic panels  103  to match the current angle of the sun is determined. For example, as discussed herein, such an ideal angle of the photovoltaic panels  103  can be an angle where the tracker axis  750  is coincident with the center of the sun  700  (see e.g.,  FIGS. 7 and 8   b ) or other suitable angle, which can include an angle that maximizes the electrical output of the photovoltaic cells  103 . 
     At  930 , a current angle of the photovoltaic cells  103  is determined, and at  940  a difference between the current angle of the photovoltaic cells  103  and the ideal angle of the photovoltaic cells  103  is determined. For example, as discussed herein, in some embodiments, one or more inclinometer  603 A,  603 B of a respective solar tracker  100  can be used to identify a current angle of the photovoltaic cells  103 . 
     The method  900  continues at  950  where a determination is made whether the difference between the current angle of the photovoltaic cells  103  and the ideal angle of the photovoltaic cells  103  is within a defined range. For example, in various embodiments, a tolerance range about an ideal angle of the photovoltaic cells  103  can be desirable to allow for movements of the photovoltaic cells  103  in the wind; to conserve energy by not requiring constant movement of the photovoltaic cells  103  to maintain an exact ideal angle, and the like. For example, such a tolerance range can be +/−0.5°, +/−1.0°, +/−2.0°, +/−3.0°, +/−5.0°, +/−10.0° +/−15.0° and the like. Additionally, such a tolerance range can be symmetrical about an ideal angle as shown in the examples above or can be asymmetrical. Additionally, such a tolerance range can be static or dynamic based on various factors, including the current angle of the sun, weather conditions, or the like. 
     If a determination is made at  950  that the difference between the current angle of the photovoltaic cells  103  and the ideal angle of the photovoltaic cells  103  is not within a defined range, then the method  900  continues to  960  where bellows  300  of one or more actuators  101  of one or more trackers  100  are inflated and/or deflated to change the angle of the photovoltaic panels  103  toward the determined ideal angle for the photovoltaic panels  103 . However, if at  950  a determination is made that the difference between the current angle of the photovoltaic cells  103  and the ideal angle of the photovoltaic cells  103  is within the defined range, then the method  900  cycles back to  910 . 
     Accordingly, in various embodiments, the position of one or more trackers  100  can be monitored to determine whether the angle of the trackers  100  is within a tolerance range of an ideal angle, and if not, the trackers  100  can be actuated to be within the tolerance range. In various embodiments, such monitoring and control can be applied to all trackers  100  within a solar tracking system  400  or one or more subsets of trackers  100  can be monitored and controlled separately. For example, in some embodiments, it can be desirable to control trackers  100  individually based on individual current angles of the trackers  100  and/or individual locations of the trackers  100 . Also, such monitoring and control can be performed continuously or can be performed periodically. For example, the method  900  can be performed on a time delay every second, five seconds, ten seconds, sixty seconds, five minutes, fifteen minutes, thirty minutes, or the like. 
     In various embodiments, solar trackers  100  can enable tweaking of photovoltaic system performance characteristics to capture additional value. For example, open circuit voltage of photovoltaic cells  103  can increase as temperature decreases. Overall system design of some embodiments can be dictated by a maximum voltage that occurs very infrequently (e.g., on the coldest mornings of the coldest days of the year). Intelligent tracking can ameliorate this worst case scenario and can improve project design economics. 
     To avoid this scenario, controls of some embodiments can leverage another principle of photovoltaic cells  103 ; namely that cell voltage can also be related to incident light. By pointing the trackers  100  somewhere other than directly at the sun, resulting in fewer photons striking the photovoltaic cells  103 , system voltage is reduced. When photovoltaic cell  103  temperature rises from a combination of ambient temperature and direct solar heating of the photovoltaic cells  103 , system voltage can be reduced further, and the trackers  100  can then return to a position with maximum incident light on the photovoltaic cells  103 . 
     This application can include a combination of design features such as detecting photovoltaic cells string voltage (e.g., directly or through query of some other system device such as an inverter), sensing of ambient temperature or photovoltaic cells&#39; temperature, measurement of direct or indirect solar irradiance, and the like. 
     One benefit of being able to relax the constraint of minimum design temperature in some embodiments can be the potential for more photovoltaic cells  103  (and system power) per infrastructure investment. For example, wiring can be done per string, combiner boxes accept a maximum number of strings, and the like. If the number of photovoltaic cells  103  per string increases by 5%, the same amount of power can be generated with 5% fewer strings, and the infrastructure investment associated with those eliminated strings can be avoided. There is also potential for reduction in installation labor, as wiring of additional strings is much more involved than additional photovoltaic cells  103 . 
     Additionally, higher system voltage can drive additional system efficiency by reducing the string current at a fixed power output. This can be directly valued in additional energy production, or can enable other system savings through reduction of conductors or the like. Further embodiments can comprise moving photovoltaic cells  103  using intelligent algorithms to improve performance or system design. 
     Turning to  FIGS. 10 and 11 , a state diagram  1000  is shown in  FIG. 10  with reference to a tracking window  1100  illustrated in  FIG. 11 . As shown in  FIG. 11 , the tracking window  1100  can comprise a negative east tracking window portion  1101  and a positive west tracking window portion  1102  that have equal size on opposing sides of a current angle of the sun  1103 . A negative east tracking window half  1105  separates an east invalid region (EIR) and an east semi-valid region (ESVR). A positive west tracking window half  1105  separates a west semi-valid region (WSVR) and a west invalid region (WIR). An east out of bound region (EOB) and west out of bounds region (WOB) are on distal ends of the tracking window  1100 . An east valid region (EVR) and west valid region (WVR) are separated by the current angle of the sun  1103 . 
     As discussed herein, control determinations can be made for one or more trackers  100  based at least in part on a determination of where a current angle of the tracker  100  is within the tracking window  1100  compared to the current angle of the sun or an ideal tracker target angle. Turning to  FIG. 10 , where a tracker  100  is in a locked position  1001 , if at  1004  the tracker  100  is determined to be in the east semi-valid region (ESVR) or in the east invalid region (EIR) and the current destination angle is moving west CAD-MW, then the tracker  100  is actuated to move west  1006 . Additionally, where the tracker  100  is in a locked position  1001  and the tracker  100  is determined at  1004  to be in the east out of bounds region (EOB), then the tracker  100  can be actuated to move west  1006 . 
     For example, a locked position for the tracker  100  can include various configurations, including a stopped configuration where the tracker  100  is not being actuated by fluid being introduced and/or removed from the bellows  300  such that the actuators  101  are in a state of equilibrium. Such a locked configuration may or may not include a mechanical locking mechanism in addition to an equilibrium state between bellows  300  of one or more actuators  101 . In some embodiments, a locked state can comprise valves associated with the bellows  300  being in a closed configuration. 
     Also, equilibrium between bellows  300  of an actuator  101  can include a range of pressures. For example, where bellows pressures of X:X generate equilibrium of an actuator  101  such that the actuator  101  does not move, bellows pressures of 2×:2×, 5×:5×, 10×:10× and the like, can also generate equilibrium of an actuator  101 . In various embodiments, higher pressures of equilibrium can generate more stiffness in the actuator  101 , which can be desirable for resisting external forces (e.g., wind) that may cause rotation of the photovoltaic cells  103 . However, higher pressures in the bellows  300  can require more fluid and energy, which may undesirably consume more energy than necessary and/or cause more wear on bellows  300  or other components of a tracker  100 . Accordingly, in some embodiments, it can be desirable to keep relative pressure between bellows  300  as low as possible to maintain appropriate function of the tracker  100 . 
     Returning to the state diagram  1000  of  FIG. 10 , if the tracker  100  is moving west  1006  and it is determined at  1008  that the bellows  300  with most pressure (BMP) has a pressure that is less than a max pressure high (MPH) and where bellows  300  with most pressure (BMP) also has a greater pressure than a max pressure low (MPL), then at  1010 , the west bellows  300 W of the tracker  100  will vent and the east bellows  300 E will fill. 
     For example, as discussed above, high fluid pressure in bellows  300  can cause undesirable wear on the bellows  300  and can even cause failure of the bellows  300  or related components. Accordingly, a max pressure high (MPH) can be defined for the bellows  300 , which can be based on a maximum bellows operating pressure that limits undesirable wear on the bellows  300  and is below a pressure that would cause failure of the bellows  300 . 
     Similarly, while low bellows operating pressures can be desirable for consuming less energy and limiting wear on the bellows  300  and other components, low bellows operating pressures below a certain threshold can be inadequate for desirable operation of the actuators  101  of a tracker  100 . Accordingly, a max pressure low (MPL) can be defined for a lowest desirable operating pressure of bellows  300  of a tracker  100 . 
     Some embodiments can comprise variable max pressure high (MPH) and/or a max pressure low (MPL). In one example, material creep reduction can include adjusting a control method to have a max bellow pressure dependent on external loads (e.g., reduce pressure when wind speed is low and increase pressure as wind speed increases). The reduced average pressure over time can limit material creep. In another example, a constant bellows stress function can include increasing pressure at a flat configuration (e.g., parallel to the ground) to provide more stiffness in stow, which can also provide better accuracy and decrease material fatigue. Bellows stress can be inversely proportional to angle, and proportional to pressure. High pressure at low angle in some embodiments can allow for roughly constant bellows material stress throughout the range of motion of the actuator  101 . Additionally, changing peak pressures can be desirable for controlling the resonant modes and stiffness of a tracker and portions thereof. For example, changing peak pressures can be desirable for withstanding force generated by winds as discussed herein. 
     Returning to the state diagram  1000  of  FIG. 10 , where the tracker  100  is moving west  1006  and it is alternatively determined at  1008  that the tracker  100  is in the east invalid region (EIR) or is in the east out of bounds region (EOB), then at  1010 , the west bellows  300 W of the tracker  100  will vent and the east bellows  300 E will fill. Where, at  1010 , the west bellows  300 W of the tracker  100  are venting and the east bellows  300 E are filling, if it is determined at  1012  that the tracker  100  is in the west invalid region (WIR) or is in the west out of bounds region (WOB), then the tracker  100  assumes a locked position  1001 . 
     However, where the tracker  100  is moving west  1006  and it is alternatively determined at  1014  that the bellows with most pressure (BMP) has a pressure that is greater than the max pressure high (MPH), then the west bellows  300 W of tracker  100  vent at  1016 . Where the west bellows  300 W of the tracker  100  are venting west at  1016  and it is determined at  1018  that the tracker  100  is in the west invalid region (WIR) or is in the west out of bounds region (WOB), then the tracker  100  assumes a locked position  1001 . Alternatively, if it is determined at  1020  that the tracker  100  is in the east invalid region (EIR) or is in the east out of bounds region (EOB), then at  1010 , the west bellows  300 W of the tracker  100  will vent and the east bellows  300 E will fill. 
     However, where the tracker  100  is moving west  1006  and it is alternatively determined at  1022  that the bellows with most pressure (BMP) has a pressure that is less than the max pressure high (MPH), then the east bellows  300 E of tracker  100  fill at  1024 . Where the east bellows  300 E of the tracker  100  are filling at  1024  and it is determined at  1026  that the tracker  100  is in the west invalid region (WIR) or is in the west out of bounds region (WOB), then the tracker  100  assumes a locked position  1001 . Alternatively, if it is determined at  1028  that the tracker  100  is in the east invalid region (EIR) or is in the east out of bounds region (EOB), then at  1010 , the west bellows  300 W of the tracker  100  will vent and the east bellows  300 E will fill. 
     Similar actions can occur on the left half of the state diagram  1000  of  FIG. 10 . For example, where a tracker  100  is in a locked position  1001 , if at  1054  the tracker  100  is determined to be in the west semi-valid region (WSVR) or in the west invalid region (WIR) and the current destination angle is moving east (CAD-ME), then the tracker  100  is actuated to move east  1056 . Additionally, where the tracker  100  is in a locked position  1001  and the tracker  100  is determined at  1054  to be in the west out of bounds region (WOB), then the tracker  100  can be actuated to move east  1056 . 
     If the tracker  100  is moving east  1056  and it is determined at  1058  that the bellows  300  with most pressure (BMP) has a pressure that is less than a max pressure high (MPH) and where bellows  300  with most pressure (BMP) also has a greater pressure than a max pressure low (MPL), then at  1060 , the east bellows  300 E of the tracker  100  will vent and the west bellows  300 W will fill. 
     Where the tracker  100  is moving east  1056  and it is alternatively determined at  1058  that the tracker  100  is in the west invalid region (WIR) or is in the west out of bounds region (WOB), then at  6010 , the east bellows  300 E of the tracker  100  will vent and the west bellows  300 W will fill. Where, at  1060 , the east bellows  300 E of the tracker  100  are venting and the west bellows  300 W are filling, if it is determined at  1062  that the tracker  100  is in the east invalid region (EIR) or is in the east out of bounds region (EOB), then the tracker  100  assumes a locked position  1001 . 
     However, where the tracker  100  is moving east  1056  and it is alternatively determined at  1064  that the bellows with most pressure (BMP) has a pressure that is greater than the max pressure high (MPH), then the east bellows  300 E of tracker  100  vent at  1066 . Where the east bellows  300 E of the tracker  100  are venting at  1066  and it is determined at  1068  that the tracker  100  is in the east invalid region (EIR) or is in the east out of bounds region (EOB), then the tracker  100  assumes a locked position  1001 . Alternatively, if it is determined at  1070  that the tracker  100  is in the west invalid region (WIR) or is in the west out of bounds region (WOB), then at  1060 , the east bellows  300 E of the tracker  100  will vent and the west bellows  300 W will fill. 
     However, where the tracker  100  is moving east  1056  and it is alternatively determined at  1072  that the bellows with most pressure (BMP) has a pressure that is less than the max pressure high (MPH), then the west bellows  300 W of tracker  100  fill at  1074 . Where the west bellows  300 W of the tracker  100  are filling at  1074  and it is determined at  1076  that the tracker  100  is in the east invalid region (EIR) or is in the east out of bounds region (EOB), then the tracker  100  assumes a locked position  1001 . Alternatively, if it is determined at  1078  that the tracker  100  is in the west invalid region (WIR) or is in the west out of bounds region (WOB), then at  1060 , the east bellows  300 E of the tracker  100  will vent and the west bellows  300 W will fill. 
     For the east filling at  1024  and  1010  and for the west filling at  1074  and  1060 , the fill routine can have various duty cycles (e.g., 80% on and 20% off), with a total period that can be based on the number of actuators  101  in a tracker  100 . In various embodiments, a pressure measurement can be taken at the end of each off period, and if it is determined that a bellows  300  is over pressure (e.g., greater than max pressure high (MPH)), then the off period can be maintained and pressure measurements can be maintained until no bellows  300  is over pressure. 
     As discussed herein, in various embodiments a tracking window  1100  can be used to control one or more actuators  101  of a solar tracker  100 . Referring to the tracking window  1100 , in another embodiment, if the tracker  100  is in a valid region (e.g., east or west valid regions (EVR) (WVR)) and the tracker  100  is in a locked position, then valves associated with the bellows  300  of the actuators  101  of the tracker  100  can be in a closed configuration. However, if the tracker  100  enters a semi-valid region (e.g., east or west semi-valid regions (ESVR) (WSVR)), and the position of the tracker  100  is locked, then the tracker position can be unlocked, which can include opening one or more valves associated with the bellows  300  of the actuators  101  of the tracker  100 . For example, at least one valve can open to introduce or remove fluid from one or more bellows  300  to drive the tracker  100  toward the sun. 
     However, in some embodiments, where the tracker  100  is determined to be in an out of bounds region (e.g., east or west out of bounds (EOB)(WOB)), then two or more valves can be opened to drive the tracker  100  towards the sun. For example, where the tracker  100  crosses into an out-of-bounds region from an invalid region, then a determination can be made as to what valve is already on and one or more additional valves can be enabled based on the identity of the first enabled valve. 
     Additionally, where the tracker  100  is driving towards the sun, then the enabled valves can be disengaged or disabled when the tracker  100  reaches an opposite tracking window boundary, which can include the current angle of the sun boundary  1103 , the boundary between a valid and semi-valid region, or the like. 
     For introducing fluid to bellows  300 , in various embodiments, fluid will only be added to the bellows of maximum pressure (BMP) if such bellows  300  has a pressure that is below the bellows max pressure high (MPH) and the identified pressure of the BMP is considered valid. In various embodiments, it can be desirable to not increase the pressure of the BMP more than the MPH, which in various embodiments can be defined as half of a maximum PSI window. 
     In various embodiments, movement of actuators  101  by removing or releasing fluid from bellows  300  can be the implemented method of actuation unless the pressure identified for the relevant pneumatic circuit is valid and the BMP has a pressure that is less than the max pressure low (MPL), which can be defined as half of a maximum PSI window. Additionally or alternatively, movement of actuators  101  by removing or releasing fluid from bellows  300  can be the implemented method of actuation unless the pressure identified for the relevant pneumatic circuit is valid and the tracker  100  is determined to be in an out-of-bounds region (e.g., east or west out of bounds (EOB) (WOB)). 
     Turning to  FIG. 12 , a method  1200  of identifying a stow event and generating a stow in one or more tracker  100  is illustrated. The method  1200  begins at  1205 , where one or more trackers  100  are tracking the position of the sun (e.g., as shown in  FIG. 7, 8   a ,  8   b  or  9 ) and at  1210 , sensing data from one or more row controller sensors and/or one or more solar tracker sensors. At  1215 , the received sensing data is processed to determine whether a stow event is present, and at  1220  a determination is made whether a stow event is present. 
     For example, in some embodiments, data regarding wind speed or velocity can be obtained from wind sensors  655  at a row controller and/or wind sensors  607 A,  607 B of one or more solar trackers  100 A,  100 B. Such wind data can be evaluated to determine whether it indicates wind conditions that pose a threat to one or more trackers  100 . In other words, where the solar trackers  100  comprise large planar photovoltaic panels  103 , wind force can have a strong and undesirable impact on the panels  103 , which can potentially cause damage to the photovoltaic panels  103 . Accordingly, where wind data identifies wind conditions above a certain threshold and for a certain time period, it can be determined that a stow event is present (i.e., an event that warrants stow of one or more trackers  100 ). 
     Additionally or alternatively, wind data can indicate that actuator stiffness should be increased to make the actuators  101  of one or more trackers more rigid to oppose wind force. For example, as discussed herein, opposing bellows  300 E,  300 W of an actuator can be at equilibrium or generate movement at various opposing pressures, with equilibrium at greater pressures generating more rigidity in the bellows  300 E,  300 W and therefore more rigidity in the actuators  101 . However, maintaining the lowest operating pressures possible can be desirable to reduce wear on the bellows  300  and actuators  101  and also to reduce fluid and power consumption. Accordingly, it can be desirable to have actuators  101  operate at a minimum operating pressure when no wind is present and to dynamically increase pressure, stiffness or rigidity of the actuators  101  in response to increasing wind velocity or speed. However, at a certain threshold, it can be desirable to put the trackers  100  into a stow configuration to protect the trackers  100  from damage. 
     Additionally, in various embodiments, the bellows  300  and pressures experienced by the bellows  300  can be used to identify whether wind is present and whether the wind conditions are such that the tracker  100  should be put into a stow configuration for protection against the wind or whether increasing the pressure of the bellows  300  to prevent wobble would be desirable. For example, where a pressure sensor associated with a bellows  300  senses a series of pressure spikes and dips, this can be an indication of wind affecting the position of the photovoltaic cells  103  of the tracker  100 . If such a sensed condition reaches one or more thresholds (e.g., a maximum or minimum pressure outside of a median pressure; number of pressure spikes and/or dips of a certain magnitude, and the like), then the tracker  100  can be put into a stow configuration or the pressure of the bellows  300  can be increased to combat wobble. Although such sensing can be performed by wind and/or pressure sensors, in further examples such sensing can be performed by one or more of inclinometers, changes in power output of photovoltaic cells, or any combination of pressure sensors, inclinometers, photovoltaic power output, and the like. 
     In various embodiments, it can be desirable for actuators  101  to be configured to stow on power loss. In other words, where the pneumatics system loses power, one or more actuators  101  of the system  400  will default to a desired safe stow position. For example, using a cross-over valve, the valve can “normally open” with a spring-return. It is held closed when the system is powered. When power is lost the cross-over valve opens. This can create a “stow on power loss” function for the system. In some examples, a cross-over valve can connect the east and west control air tubes or east and west valve circuits. Air from higher pressure bellows can flow to lower pressure bellows. The cross-over valve can reduce total system air use by up to 50%, in various embodiments. 
     For example,  FIG. 15  illustrates an example embodiment of a row controller  380  featuring a “stow on power loss” function. Pressurized air can be input to a set of solenoid valves  1510  arranged into “east” and “west” valve circuits. The solenoid valves  1510  can be arranged such that they can provide the following functions to the row controller  380 : fill east, dump east, fill west, and dump west. In some embodiments of an operating scenario, an electronic control unit  384  can determine a need to rotate a solar panel  103  or similar object about an axis of rotation. For example, the electronic control unit  384  can determine a need to rotate one or more solar panels  103  about an axis of rotation such that the top surface of each solar panel  103  stays substantially perpendicular to the direction of incoming solar rays as the sun moves across the sky from east to west, requiring a rotation of the solar panel  103  toward the west. The electronic control unit  384  can therefore command a solenoid valve  310  to open such that pressurized air flows into the “east” control lines  390 , causing one or more “east” bellows  300  to inflate and expand, tilting the solar panel toward the “west” direction. The electronic control unit  384  can also determine that pressure in the “west” bellows  300  should be released to allow the “west” bellows  300  to deflate and collapse, further allowing a rotation toward the “west.” 
     The “east” valve circuits can be independent from control of the “west” valve circuits. This can allows for the simultaneous inflation or deflation of both the “east” and “west” bellows  300 , such that the overall tension in the mounting system can be controlled. For example, in the event of a wind storm, it can be desirable to inflate both “east” and “west” bellows  300  without causing a change in angle of the solar panel in order to increase the rigidity or tension in the system to handle the increased turbulence from the storm. Similarly, it can be desirable to reduce the overall pressure in both “east” and “west” bellows  300  at the same time. 
     A fifth solenoid valve  1510 V can be a “cross-over” valve which connects the “east” and “west” valve circuits. In some embodiments, the cross-over valve  1510 V can be a “normally-open” two-way valve, three-way valve, or the like. A “normally-open” solenoid valve can be a valve which defaults to an open position (such that fluid is allowed to pass through the valve) upon the removal of power. During a normal operation of row controller  380 , cross-over valve  1510 V can be energized such that it closes, stopping fluid flow through the valve to allow independent operation of the “east” and “west” valve circuits. However, in the event of the removal of power, cross-over valve  1510 V can default to its “normally open” configuration, allowing the pressure in the “east” and “west” valve circuits to equalize, which in turn allows the solar panels to return to a “zero” position. This configuration of row controller  380  can enable a fail-safe mode where some or all controlled tracker rows  100  can move to a flat position if the power being supplied to energize valve  1510 V is lost. This configuration can be called “stow on power loss.” 
     Accordingly, a stow event can be present based upon various detected failures in a solar tracking system  400 , including power loss, failure of pneumatic elements (e.g., bellows  300 , pneumatic lines  390 , a pneumatic circuit  382 , fluid source  652 , valves, or the like), failure of one or more sensors (e.g., pressure sensors  653 ,  601 , temperature sensors  654 ,  605 , wind sensors  655 ,  607 , sun sensors  656 , clock  657 , inclinometer  603 , and the like), or failure of control systems (e.g., the control device  651 , pneumatic control unit  384 , and the like). In various embodiments, control systems can execute a stow event or a stow event can occur automatically upon such a failure. For example, power or pressure loss can automatically result in fluid valves causing a stow of the trackers  100  as described herein. 
     Returning to the method  1200  of  FIG. 12 , if at  1220  it is determined that a stow event is not present, then the method  1200  cycles back to  1205  where tracking based on the position of the sun continues. However, if at  1220  it is determined that a stow event is present, at  1225  the bellows  300  of one or more trackers  100  are inflated and/or deflated to generate a stowed configuration for the one or more trackers  100 . 
     In various embodiments, a stow configuration of a tracker  100  can include various suitable configurations. For example, in some embodiments, a stow position for an actuator can be a flat or neutral position N, or maximum tilt positions A, B (see  FIG. 2 ). In some embodiments, a stow at maximum tilt positions A, B can include pressurizing the tracker against a stop to rigidly fix the tracker  100  at one of the maximum tilt positions A, B. In other words, a bellows  300  opposing the stop can be inflated to force the actuator  101  or other portion of the tracker  100  against the stop. The non-opposing bellows  300  can be fully deflated in some embodiments to allow for the opposing bellows  300  to provide maximum force against the stop. 
     In further embodiments, the bellows  300  of one or more actuators  101  can be inflated to an equilibrium to rigidly fix the bellows  300  in a desired configuration. For example, in some embodiments, inflation of both bellows  300 E,  300 W of an actuator to a maximum fill pressure can generate a flat stow or a stow in the neutral configuration N (see  FIG. 2 ). 
     Returning to the method  1200  of  FIG. 12 , at  1230  sensing data is obtained from one or more row controller sensors and/or one or more solar tracker sensors, and at  1235 , the sensing data is processed to determine whether a stow event is still present. If at  1240  a determination is made that a stow event is still present, then at  1245 , tracker stow is maintained and the method  1200  cycles back to  1230  where further sensing data is received and the state of the solar tracking system  400  is monitored. However, if at  1240  a determination is made that a stow event is not still present, then at  1250 , stow is removed and tracking based on position of the sun is resumed. The method  1200  then cycles back to  1210  where monitoring for a further stow event occurs. 
       FIG. 13  illustrates a method  1300  of level-calibrating a solar tracker  100  in accordance with an embodiment. For example, when a solar tracker  100  is at the factory or set in place via posts  104  (See  FIGS. 1 a , 1 b    and  2 ) or other suitable structures, it can be desirable to calibrate or “zero” the system by determining an output of inclinometers  603  (See  FIG. 6 ) of one or more trackers  100  that should be defined as where the tracker  100  is level. The method begins at  1310  where a leveling device is coupled with the tracker  100  at a position that is parallel to the plane of the photovoltaic panels  103 . For example, in some embodiments, a leveling device can be coupled to a top plate  330  of an actuator  101  or other suitable structure that is parallel to the plane of the photovoltaic panels  103 . 
     Additionally, a leveling device can comprise any suitable device that can sense and/or present a level status, including a bubble level, a digital level, plumb bob, or the like. In some embodiments, a body of a leveling device can comprise opposing faces disposed at a right angle (e.g. an angle bracket), which can be desirable for coupling to squared portions of an actuator  101 , tracker  100 , or the like. In further embodiments, the leveling device can comprise a magnet, which can be desirable for coupling to metal portions of an actuator  101 , tracker  100 , or the like. 
     Returning to the method  1300 , at  1320  one or more bellows  300  of one or more actuators  101  are inflated and/or deflated to move the photovoltaic cells  103  toward a level position, and if it is determined at  1330  that a level state has not yet been attained the one or more bellows  300  of one or more actuators  101  are further inflated and/or deflated to further move the photovoltaic cells  103  toward a level position. However, where it is determined at  1330  that a level status has been obtained, then the current inclinometer reading is defined or set as being level for the photovoltaic cells  103  of the tracker  100 . 
     For example, setting a current inclinometer reading as being level for the photovoltaic cells  103  of the tracker  100  can include a manual input to a device at a row controller  380 . Additionally, in some embodiments, a wired or wireless connection with a row controller  380  can communicate a level status or otherwise facilitate calibration of the level status of a tracker  100 . 
     The described embodiments are susceptible to various modifications and alternative forms, and specific examples thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the described embodiments are not to be limited to the particular forms or methods disclosed, but to the contrary, the present disclosure is to cover all modifications, equivalents, and alternatives. 
     In some embodiments, the bellows  300  can be in the form of an elastic vessel which can expand with the introduction of a pressurized fluid, and which can collapse or shrink when the pressurized fluid is released. The term ‘bellows’ as used herein should not be construed to be limiting in any way. For example the term ‘bellows’ as used herein should not be construed to require elements such as convolutions or other such features (although convoluted bellows  300  can be present in some embodiments). As discussed herein, bellows  300  can take on various suitable shapes, sizes, proportions and the like. 
     It should be noted that the figures are not drawn to scale and that elements of similar structures or functions are generally represented by like reference numerals for illustrative purposes throughout the figures. It also should be noted that the figures are only intended to facilitate the description of the preferred embodiments. The figures do not illustrate every aspect of the described embodiments and do not limit the scope of the present disclosure.