Patent Publication Number: US-2022224283-A1

Title: Staged stowage of solar trackers and method thereof

Description:
BACKGROUND 
     Technical Field 
     The present disclosure relates to solar power generation systems, and more particularly, to solar tracker actuating systems for adjusting the orientation of the solar power generation components to track the location of the sun. 
     Background of Related Art 
     Solar cells and solar panels are most efficient in sunny conditions when oriented towards the sun at a certain angle. Many solar panel systems are designed in combination with solar trackers, which follow the sun&#39;s trajectory across the sky from east to west in order to maximize the electrical generation capabilities of the systems. The relatively low energy produced by a single solar cell requires the use of thousands of solar cells, arranged in an array, to generate energy in sufficient magnitude to be usable, for example as part of an energy grid. As a result, solar trackers have been developed that are quite large, spanning hundreds of feet in length. 
     Adjusting massive solar trackers requires power to drive the solar array as it follows the sun. As will be appreciated, the greater the load, the greater the amount of power necessary to drive the solar tracker. An additional design constraint of such systems is the rigidity required to accommodate the weight of the solar arrays and at times significant wind loading. 
     Further, the torsional excitation caused by wind loading exerts significant force upon the structure for supporting and the mechanisms for articulating the solar tracker. As such, increases in the size and number of components to reduce torsional excitation are required at varying locations along the length of the solar tracker. The present disclosure seeks to address the shortcomings of prior tracker systems. 
     SUMMARY 
     The present disclosure is directed to a method of managing dynamic response to wind in a solar tracker system are provided. The method includes determining a wind speed, comparing the wind speed to a predetermined threshold value to determine if the wind speed equals or exceeds the predetermined threshold, positioning a windward most solar tracker to a predetermined angle based on the comparing, and positioning a leeward most solar tracker to the predetermined angle based on the comparing. The solar trackers are positioned at the predetermined angle at a predetermined interval starting at the windward most solar tracker and the remaining solar trackers remain in a normal operating condition. 
     In aspects, the determining includes a gradated series of wind speeds. In other aspects the predetermined angle includes a gradated series of angles. 
     In certain aspects the predetermined threshold value includes a gradated series of thresholds. In other aspects, the predetermined interval is every fourth solar tracker. 
     According to another aspect of the present disclosure a method of managing dynamic response to wind in a solar tracker. The method includes determining a wind speed, comparing the wind speed to a predetermined threshold value to determine if the wind speed equals or exceeds the predetermined threshold, and positioning a first and a second solar tracker to a first predetermined angle and a second predetermined angle based on the comparing. 
     In aspects, the second predetermined angle is rotated in the opposing angle of the first predetermined angle. 
     In other aspects, the method further includes determining a position of the first solar tracker, determining a position of the second solar tracker; determining a shading of the first and second solar tracker, communicating the position of the first and second solar tracker, positioning at least one of the first and second solar tracker based on the determined position of adjacent solar trackers to reduce the shading. 
     In certain aspects, the communication includes wireless communication. 
     According to another aspects of the present disclosure a solar tracker system includes a solar tracker including a plurality of solar modules, each of the solar modules being spatially configured to face in a normal manner in an on sun position in an incident direction of electromagnetic radiation derived from the sun. The solar modules include a tracker controller. The tracker controller includes a processor, a memory with instructions stored thereon, a power supply configured to provide power to the tracker controller, and a motor controller. The tracker controller is configured track the sun position. The tracker controller is configured to determine the wind speed. The processor compares the wind speed to a predetermined threshold value to determine if the wind speed equals or exceeds the predetermined threshold and positioned a windward most solar tracker to a predetermined angle based on the comparing. Solar trackers are positioned at the predetermined angle at a predetermined interval starting at the windward most solar tracker. The processor positioned a leeward most solar tracker to the predetermined angle based on the comparing. The remaining solar trackers remain in a normal operating condition. 
     In aspects, the determining includes a gradated series of wind speeds. 
     In other aspects, the predetermined angle includes a gradated series of angles. 
     In certain aspects, the predetermined threshold value includes a gradated series of thresholds. 
     In yet another aspect, the predetermined interval is every fourth solar tracker. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various aspects of the present disclosure are described herein below with reference to the drawings, which are incorporated in and constitute a part of this specification, wherein: 
         FIG. 1  is a top, perspective view of a solar tracking system provided in accordance with the present disclosure that is configured to articulate the angle of a solar array to track the location of the sun; 
         FIG. 2  is a bottom, perspective view of the solar tracking system of  FIG. 1 ; 
         FIG. 3  is an end view of the solar tracking system of  FIG. 1  shown with a solar array of the solar tracking system in a horizontal orientation; 
         FIG. 4  is an side view of the solar tracking system of  FIG. 1  shown with a solar array of the solar tracking system in an articulated orientation; 
         FIG. 5  is a side view of a field of the solar tracking systems of  FIG. 1  shown with solar arrays of the solar tracking system in a staged stow arrangement; 
         FIG. 6  is a side view of a field of the solar tracking systems of  FIG. 1  shown with solar arrays of the solar tracking system in a “W” stow arrangement; and 
         FIG. 7  depicts a logic flow for a control algorithm in accordance with the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure is directed to solar tracking systems and methods for articulating a solar tracking system to compensate for the impacts of wind and wind loading of solar tracker systems. In general a solar tracking system includes a solar array that is supported by a plurality of support beams. The plurality of support beams, in turn, is supported by a plurality of torque tubes. The plurality of torque tubes are coupled to an articulation system, which in turn, is supported by a plurality of bases that is configured to be anchored in the ground or to a stationary structure 
     With reference to  FIGS. 1-5 , a solar tracking system capable of tracking the location of the sun provided in accordance with the present disclosure is illustrated and generally identified by reference numeral  10 . The solar tracking system  10  includes a solar array  20 , a plurality of support beams  30  ( FIG. 3 ) that are configured to support the solar array  20 , a plurality of torque tubes  40  ( FIG. 2 ) that are configured to support the plurality of support beams  30 ), a plurality of bases  50  that is configured to rotatably support the plurality of torque tubes  40 , and an articulation system  100  ( FIG. 1 ) that is configured to rotate the plurality of torque tubes  40 , and therefore the solar array  20 , relative to the base  50 . 
     In one embodiment, as illustrated in  FIG. 1 , the solar array  20  is broken up into a first portion  20   a  and a second portion  20   b , where the first and second portions  20   a ,  20   b  are spaced apart from one another along the length thereof defining a gap  20   c  there between. Each portion of the first and second portions  20   a ,  20   b  is substantially similar, thus, only the first portion  20   a  will be described in detail herein below in the interest of brevity. The first portion  20   a  of the solar array  20  includes a plurality of photovoltaic modules  22 , each of which is mechanically and electrically coupled to one another, although it is contemplated that each (or a group of) photovoltaic module  22  may be mechanically and/or electrically insulated from one another. In embodiments, the photovoltaic modules  22  may be any suitable photovoltaic module capable of generating electrical energy from sunlight, such as monocrystalline silicon, polycrystalline silicon, thin-film, etc. The photovoltaic modules  22  define an upper surface  22   a  and an opposite, bottom surface  22   b . As can be appreciated, the upper surface  22   a  of the photovoltaic modules  22  includes the photovoltaic cells (not shown) while the bottom surface  22   b  includes any suitable means for fixedly or selectively coupling the photovoltaic modules  22  to the plurality of support beams  30 , such as mechanical fasteners (e.g., bolts, nuts, etc.), adhesives, welding, etc. In embodiments, the photovoltaic cells may be disposed within a suitable frame  22   c  ( FIG. 3 ) which includes suitable means for fastening the photovoltaic modules  22  to the plurality of support beams  30 . In this manner, the frame  22   c  may include fastening means on a bottom surface thereof, or clamps or other suitable fasteners (e.g., Z-brackets, C-clamps, angle brackets, etc.) may be utilized to about a portion of the frame  22   c  and selectively or fixedly couple the frame  22   c  to the plurality of support beams  30 . Although generally illustrated as having a generally U-shaped profile, it is contemplated that the support beam  30  may include any suitable profile, such as square, rectangular, oval, etc. It is envisioned that the support beam  30  may be selectively or fixedly coupled to the torque tube  40  and/or frames  22   c  of the photovoltaic modules  22  using any suitable means, such as mechanical fasteners (e.g., bolts, clamps, etc.), adhesives, welding, etc. In one non-limiting embodiment, the support beam  30  is coupled to the torque tube using a U-bolt or other similar fastener. 
       FIG. 3  depicts a typical stowed position for a solar tracker. In this position or the 0° position the photovoltaic modules  22  are essentially parallel to the ground. This has been the position that most solar tracker manufacturers recommend and specify that the solar tracker return to when the wind speeds observed at about three meters above the ground reach approximately 30 miles-per-hour (MPH). 
     It has been previously reported that the position of the solar tracker  10  in  FIG. 3  represents the most beneficial position to prevent damage to the solar tracker  10  by the wind. Further, it is common for solar tracker arrangements, where there are multiple trackers  10  arranged in parallel north-south lines, to be mechanically coupled to one another such that all of the solar trackers  10  move in unison as they track the path of the sun from east to west. As a result, for most solar tracker facilities, upon observation of a wind speed in excess of some threshold (e.g., 30 MPH) the entire field of trackers  10  moves to a 0° position. Even for some solar tracker  10  facilities where the solar trackers are not mechanically coupled, the 0° position stow strategy remains the industry standard. The immediate result is that that in windy conditions, the energy production from the solar tracker  10  is significantly reduced, as the tracker is prevented from following the sun. But another result, is that in this position the solar trackers experience turbulence, oscillations, and in fact incredible stresses. Indeed, applications have determined that because of the alternating stresses applied to the tracker  10  as wind flows both over and under the photovoltaic modules  22  in the 0° position, this is in fact one of the worst wind stowage positions for a solar tracker. 
     One aspect of the present disclosure is directed to an alternative slow position. This alternative stow position is depicted in  FIG. 4 . As seen in  FIG. 4 , rather than the 0° position, the solar tracker  10 , and therewith the photovoltaic modules  22 , are arranged at about a 30° down angle facing the wind. That is the edge of the photovoltaic module  22  closest to the direction of the wind, is angled below horizontal, about 30°. The result is that the forces acting on the tracker. Though described herein as about 30°, the present disclosure is not so limited, any down angle will result in some benefit in the experienced wind loading, however, a greater than 30° down angle has resulted in consistently greater benefits. The contemplated ranges of down angle are 10-15, 15-20, 20-25, 25-30, 30-35, 35-40, 40-45, 45-50, 50-55, and 55-60. However, contemplated ranges are not intended to be limiting. 
     Even though the flow of air over the trackers results in a more stable flow causing less turbulence and oscillation, if as is common, the solar trackers  10  are mechanically linked, the resulting position will still result in considerable decrease in energy production. Indeed, this is particularly heightened in instances where it is an east wind that causes the movement of the solar trackers  10  in that direction, and it is afternoon, where the sun is west of its zenith. In such a scenario, the solar trackers  10  would generate even less power than those at the 0° position. 
     With reference to  FIG. 5 , a further aspect of the present disclosure is directed to a staged stow arrangement is shown. In an exemplary staged stow arrangement, the windward most (e.g., either the east most or west most) solar tracker  10  of a solar power plant  60  is placed in the stowed position 30° down angle at a first detected wind speed (e.g., 30 MPH). This allows the windward most solar tracker  10  to serve as a temporary wind fence for the subsequent rows of solar trackers  10  and normalize wind vectors. In addition to the east most solar tracker  10 , every successive fourth tracker  10  of the solar power plant  60 , is also placed in the stowed position (e.g., 30° down angle). Finally, the leeward most tracker  10  may also be placed in the stowed position. As will be appreciated, this can only be employ if each tracker  10  is independently movable relative to the other trackers  10 . Such an arrangement and the mechanisms for action are described in greater detail in the commonly assigned U.S. Pat. No. 9,905,717 entitled Horizontal Balanced Solar Tracker filed Dec. 9, 2012, and incorporated herein by reference. 
     With each tracker  10  being independently driven, and capable of the staged stow arrangement described above, a significant portion of all of the trackers  10  of the solar power plant  60  remain in normal operation tracking the sun across the sky and only a portion of the solar trackers  10  experience a reduction in energy production. A further aspect of the present disclosure is that rather than have a single wind speed threshold for stowing the solar trackers  10 , a gradated series of wind speeds can be used to move trackers into the stowed position. In this scenario, a first portion of the solar trackers  10  can be placed in the stowed position at a predetermined wind speed (e.g., 30 MPH) and a second portion can be placed in a stowed position at a second predetermined wind speed (e.g., 40 MPH) and all of the solar trackers  10  may be placed in the stowed position at a third wind speed (e.g., 50 MPH). The number of stages, the parameters, and which rows of trackers  10  stow can be adjusted depending on site specific information (e.g., prevailing wind direction, peak wind speeds, etc.). 
       FIG. 6  is a side view of a field of the solar tracking systems of  FIG. 1  shown with solar arrays of the solar tracking system in a “W” stow arrangement, in accordance with the present disclosure. A further aspect of the present disclosure is directed to a W-stow arrangement of the solar trackers  10 . In the W-arrangement, every other tracker  10  rotates in opposing directions. As a result. If the windward most tracker rotates 30° down angle, the next tracker  10  would rotate 30° up angle. The resulting turbulence of the multiple ridges in this W arrangement across the solar power plant results in reduced force impacting all of the solar trackers  10 . Various eddies and counter flows induced by this arrangement affect not just the flow of air over trackers  10  deep within the solar power plant, but also those trackers  10  on the windward most side of the solar power plant  60 . Moreover, the resulting turbulence helps to reduce oscillations and prevent any single tracker from approaching any of its harmonics, which could be very detrimental to the trackers  10  and the power plant as a whole. Though described in connection with a 30° down and up angles, other angles are contemplated within the scope of the present disclosure. 
     In practice, upon observing a threshold wind speed, the individually movable trackers  10  can be driven in the appropriate direction to form the W-shape. That is, each tracker  10  is driven in the opposite direction of the trackers  10  on either side. As will be appreciated, there is some risk of shading of a neighboring tracker  10  as a result of the W-stow position. Accordingly, those of skill in the art will appreciate that one or more of the trackers may be driven to a greater or lesser angle than its neighbors in order to avoid this shading, which can dramatically reduce energy production. 
     With reference to  FIG. 7  the flow diagram includes various blocks described in an ordered sequence, in accordance with the present disclosure. However, those skilled in the art will appreciate that one or more blocks of the flow diagram may be performed in a different order, repeated, and/or omitted without departing from the scope of the present disclosure. Further, the below description of the flow diagram refers to various actions or tasks performed by one or more controllers, but those skilled in the art will appreciate that in some instances, the controllers perform the actions or tasks via one or more software applications, such as the application which could be firmware, executing on the controllers. 
       FIG. 7  depicts a logic flow for a control algorithm  700  in accordance with the present disclosure. Initially, at block  702  the controller determines the wind speed at the solar power plant  60 . The wind speed may be determined, for example, by a wind speed sensor, or by receiving this information over a network. The network may be wireless or wired. In an embodiment the controller is configured to wirelessly (e.g., Zigbee, Wi-fi, Bluetooth®, etc.) communicate the wind speed to a wireless device, or to the Cloud for monitoring. It is contemplated that the signal could be communicated to a device with a display or dashboard for monitoring multiple solar trackers  10 . The wind speed sensor may be integrated or remote. At block  704 , the controller determines whether the wind speed equals or exceeds a predetermined threshold. The predetermined threshold may be for example 40 miles per hour. If the wind speed does not exceed this predetermined threshold (“No” at block  704 ) then the controller continues to monitor the wind speed. If the wind speed does exceed the predetermined threshold (“Yes” at block  704 ), then at block  706  the controller positions the windward most solar tracker  10  to a predetermined angle based on this wind speed. For example, the predetermined angle may be 30 degrees down angle. 
     At block  708  the leeward most solar tracker  10  is positioned at the predetermined angle based. At block  710 , solar trackers  10  at a predetermined interval are positioned at the predetermined angle. For example, the predetermined interval may be every fourth solar tracker  10  starting from the most windward solar tracker. For example, by getting every fourth row to a high angle, like 30 degrees, the remaining rows are shielded, thus creating a “wind fence” intermittently throughout the row. At block  712 , the remaining solar trackers  10  remain in a normal operating condition. For example, this would allow the remaining solar trackers  10  to maximize energy production. For example, the two exterior rows and every fourth interior row are positioned into stow at the predetermined 30 degrees down angle, and the remaining interior rows can either operate normally or stow horizontally. 
     In another embodiment, two sets of parameters are used for the stow logic. A set of primary parameters, which use a first stow trigger speed on the most windward and leeward solar tracker  10  rows, as well as rows at a predetermined interval. A set of secondary parameters, which use a second set of stow trigger speeds, which are higher than the first stow trigger speed. For example, the primary parameters may be stow at 30 mph, dwell for 15 minutes, and unstow at 20 mph. Whereas the secondary parameters may be stow at 33 mph, dwell for 15 minutes, and unstow at 23 mph. Thus allowing for an increase in the allowable tracking speed on interior rows and a decrease in stow hours. 
     In another embodiment, the risk associated with higher secondary parameters may be monitored. For example this can be calculated by analyzing motor current, flutter amplitude, and tracker performance during wind events at the site. 
     While several embodiments of the disclosure have been shown in the drawings, it is not intended that the disclosure be limited thereto, as it is intended that the disclosure be as broad in scope as the art will allow and that the specification be read likewise. Any combination of the above embodiments is also envisioned and is within the scope of the appended claims. Therefore, the above description should not be construed as limiting, but merely as exemplifications of particular embodiments. Those skilled in the art will envision other modifications within the scope of the claims appended hereto.