Abstract:
The present invention relates to a simplified and lower cost two-axes tracker for solar PV (photovoltaic) or CPV (concentrated photovoltaic) solar panel, as well as heliostat solar reflectors and solar Stirling engine. In particular, the disclosure addresses a simplified and gravity centered tracker structure with low cost single or dual linear actuators mounted on the side of ground post which is easier for replacement and maintenance at lower cost.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based on and claims benefit of U.S. Provisional Application Ser. No. 61/274,927, filed on Aug. 24, 2009. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a simplified and lower cost two-axes tracker for solar PV (photovoltaic) or CPV (concentrated photovoltaic) solar panel, as well as heliostat solar reflectors and solar Stirling engine. In particular, the disclosure addresses a simplified and gravity centered tracker structure with low cost single or dual linear actuators mounted on the side of ground post which is easier for replacement and maintenance at lower cost. 
         [0004]    2. Description of the Prior Art 
         [0005]    Photovoltaic solar panels are gradually becoming a fixture on roof tops in residential street. The sun exposure to fix panel on the roof is proportional to sine of sun elevation angle to the panel. In other words, solar collection on horizontal flat panel at sunrise and sunset are near zero at lowest elevation angle. At 34 degree latitude location, solar panel could collect 49% more power if mounted on a two-axes solar tracker relative to a horizontal fixed panel. The PV panels commonly seen on residential roof are not practical to have a solar tracker. In a solar farm, mounting photovoltaic solar panels on a tracker is feasible if the tracker cost is not predominant. In CPV (Concentrated Photovoltaic) systems, the solar panels must face the sun directly to concentrate solar beam with optical accessory. The cost of traditional two-axes tracker constitute a major cost item for PV and CPV systems. In PV systems, if the solar tracker cost more than half of the solar panels cost, it might be as well ignore the solar tracker since the improvement does not worth the investment. In addition, moving parts of solar tracker has lower reliability than fixed parts. However, it is mandatory for CPV systems to collect sun rays perpendicular to the panel to function properly. 
         [0006]    In concentrated solar thermo power (CSP) applications, solar trackers are also used to reflect and concentrate sun rays to a center chamber. A great number of solar reflectors are attached to two-axes trackers in a large field to collect the solar energy focusing on a centralized heating chamber of water or molten salt for turbo engine electricity generation. Such large solar plant is commonly called “heliostat”. The cost of solar trackers constitutes a major portion of total cost for heliostat farm. In yet another field of application, the solar thermo Stirling engine also needs two-axes sun tracking to collect concentrated solar rays to heat up the Stirling engine in order to generate electricity. This disclosure will benefit the solar thermo concentration with its simplified installation, lower parts cost, lower maintenance and longer durability for a large solar farm. 
         [0007]    A typical two-axes solar tracker consists of a ground post secured to the ground structure with concrete base. A better ecological ground post uses a helical pile post drilling directly into the ground without concrete base. On top of the ground post, a slewing drive is mounted to support the weight of solar panel and azimuth rotation at the same time. On top of the slewing drive, a linear actuator is attached between the slewing drive and solar panel structure for the lifting of solar panel in the elevation direction. Two axes of motions in azimuth and elevation will drive the solar panel to face the sun directly. 
         [0008]    However, there are a few drawbacks with a traditional tracker. 1) The slewing drive not only has to support the entire weight of the panel, but also has to bear the lateral force and torque caused by constant tilting and the wind load on the solar panel. 2) The weight of solar panel and torque caused by the lateral force makes the size of slewing drive highly dependant on the size and weight of solar panel. The components of worm drive and the rotating gear must be packaged together with the ball bearings which support the entire weight and torque applied to the slewing drive, which makes the slewing drive very bulky. 3) If any fault occurred in the slewing drive, the entire solar panel has to be dismantled in order to repair or replace the slewing drive. 4) With the lifting mechanism of a single solar panel by the linear actuator, the center of gravity of solar panel with respect to the pivoting point of slewing drive is constantly changing which mandate the slewing drive to carry the maximum torque possible. Therefore, the slewing drive and the linear actuator must be designed for the maximum torque and lateral force of the tilted panel, which makes a traditional two-axes tracker very bulky and costly. This disclosure proposes a simplified solar tracker at a very low cost, light weight and low maintenance for the benefit of coming solar energy revolution. 
       BRIEF SUMMARY OF THE INVENTION 
       [0009]    With the above mentioned deficiencies, the subject disclosure may resolve some or all of the issues related to a traditional two-axes tracker. In the first aspect of the invention, the disclosed two-axes tracker is designed to keep the solar panel weight and lateral force away from the azimuth and elevation drives. The weight of the solar panel will sit on top of rotating head, which is looping directly on top of the ground post with upper and lower bearings fitting in-between. The rotating head and bearings not only carry the entire panel weight in the vertical direction, but also leveraged on the torque caused by the wind load of solar panel in the lateral direction. In addition, the upper and lower bearings are selectively using low cost, maintenance free bushing materials for long term usage. Therefore, the azimuth drive, which is attached to the side between the lower post and upper rotating head, is free from both the vertical (gravitational weight) and lateral torque of the solar panel. Hence, the azimuth drive demands very little force for turning the entire solar panel. 
         [0010]    In another aspect of the disclosure, the solar tracker will be divided into two sections of equal weight carried by a horizontal beam (tubing) with center of gravity on top of the cylindrical rotating head. Each section of the solar panels are also balanced on the horizontal beam, enabling rotation of two solar panel sections around the center line of gravity on the horizontal beam freely. Therefore, the elevation drive of the solar panel also demands very little force for rotation similar to the azimuth drive. 
         [0011]    In another aspect of the disclosure, the azimuth and elevation drivers can be mounted as an accessory to the side of the ground post and rotating head with nuts and bolts, which can be easily installed, removed, replaced in routine maintenance by a single person. This is the major difference from the traditional tracker, where the slewing drive is located at the center between the ground post and solar panel. If anything happen to the slewing drive, the entire solar panel has to be removed or dismantled. By attaching the azimuth drive on the side proposed by this disclosure, it can extend the life of solar tracker by routine maintenance or replacement of low cost linear actuator. 
         [0012]    In yet another aspect of the disclosure, the two-axes solar tracker is designed with a wind lock device which can be activated whenever a strong wind exceeds a threshold. The wind lock device uses electromagnetic force to lock up the solar tracker in wind neutral position firmly on the ground post using two electromagnetic activated locks. This will bear the vibration and pounding of solar tracker exercised on the linear actuators during strong wind. Furthermore, in windy areas with constant blowing wind, this wind lock device can be used in a stepwise wind lock to protect the linear actuators between activations. This will greatly prolong the life span of linear actuator and the solar tracker from wind abuse. 
         [0013]    These and other features, aspects and advantages of the present disclosure will become understood with reference to the following description, appended claims and accompanying figures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is the general view of the two-axes tracker with rotating cylindrical rotating head before the attachment of linear actuators. 
           [0015]      FIG. 2  is a sectional view of single linear actuator attachment to the ground post and rotating head for azimuth rotation. 
           [0016]      FIGS. 3A-3C  illustrate three top views of upper rotating head rotation versus ground post by linear actuator extension. 
           [0017]      FIG. 4  is a side view of tracker azimuth and elevation rotation by two linear actuators. 
           [0018]      FIGS. 5A-5C  show an alternative solar tracker frame mounting with rotation around fixed horizontal beam. 
           [0019]      FIG. 6  is a sectional view of double linear actuators for azimuth rotation. 
           [0020]      FIGS. 7A-7C  illustrate three top views of double linear actuators azimuth rotation. 
           [0021]      FIG. 8  is a sectional view of stepping motor and gear attachment to the ground post and rotating head for azimuth rotation. 
           [0022]      FIG. 9  is a sectional view of wind lock devices for azimuth and elevation lock. 
           [0023]      FIG. 10  is a modified 2-axes tracker for light pole mount. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0024]    Spatially relative terms, such as “beneath”, “below”, “lower”, “above”, “upper” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. 
       Tracker Supporting Structure  
       [0025]    As shown in  FIG. 1 , one aspect of the disclosed two-axes tracker generally designated as  10 , includes a fixed cylindrical ground post  20 , with a cylindrical rotating head  30  looped on top of the ground post  20 . The rotating head  30  is made of a cylindrical tube with top end sealed (welded) by a top square plate  36 , or other shape such a U-shaped pipe holder, etc. Preferred embodiment of the ground post  20  and rotating head  30  are made of rust-proof steel material which attract magnet. Inside the rotating head, the lower end is a cylindrical bushing  34  tightly fits between the gap of the ground post and the cylindrical rotating head. The lower bushing  34  not only facilitates coaxial rotation of the rotating head versus the ground post, but also leverages on the lateral torque exercised on the solar panel by the wind load. Inside the top end of rotating head  30 , a cylindrical flanged bushing  22  (which could be closed at the flange top) is tightly fitted between the rotating head and the ground post. In other words, the top flange of bushing  22  fits the inner wall of rotating head  30  and bottom cylinder of  22  fits inside the inner wall of ground post  20 . Therefore, the top flanged bushing  22  supports the entire weight of tracker frame and solar panel in the vertical direction and provides pivot point of lateral wind load torque leveraged by the lower bushing  34 . Preferred embodiment is putting another thrust washer bushing on top of flanged bushing for easier rotation. However, commercial flanged bushing may not fit exactly the inner diameter of outer rotating head and inner diameter of ground post. Therefore, the flanged bushing can be replaced by top disk bushing  16  or washer busing  17  as depicted at the right hand side of flanged bushing in  FIG. 1 ; where the disk diameter can be smaller than the inner diameter of rotating head. It is even better to use double layers of disk or washer bushings with lubricant sides face each other to facilitate smooth frictionless rotation of the rotating head. The lubricant could be either liquid or solid lubricant with no refill needed throughout the life time of tracker. Additional side wall bushing identical to  34  inside the rotating head at top and bottom ends are needed to maintain coaxial rotation and lateral support whenever top disk or washer bushings are used. Preferred embodiment of rotating bushings is made of metal alloy materials with embedded solid lubricant. 
         [0026]    Alternative to flanged bushing  22  is using a single piece tapered roller bearing  19 , or using a combination of thrust roller bearing  18  on the top and a cylindrical bushing identical to  34  at the side wall. However, the top end of ground post needs to be welded with a cylindrical neck to fit into the center hole of a tapered roller bearing or a thrust roller bearing. The advantage of using thrust roller bearing is that its diameter does not have to fit exactly the inner diameter of rotating head; since identical cylindrical bushings  34  are used at top and bottom ends to facilitate rotating head coaxial rotating and bear the lateral force. Alternative to cylindrical bushing  34  is a cylindrical roller bearing, or specifically a needle bearing to narrow the gap between the rotating head and the ground post. Using roller bearing, the rotating head can be rotated faster with less friction. However, solar tracker azimuth rotation of 180 degrees in 12 hours daylight is a very slow rotation which enables the usage of lower cost bushings. In addition, the force needed for rotation is mainly to counter the wind load on solar panel with a small proportion used for rotating head. 
         [0027]    Flanged bushing, disk or washer bushings seem to provide the best combination of lower cost and maintenance free for long term usage under rough weather conditions. In addition, the cylindrical bushing, circular flanged bushing and disk or washer bushing designed for industrial heavy machinery are commercially available in many sizes. The bushings are made of porous alloy, brass, bronze or synthetic materials. It also provides low friction rotation and low maintenance with one time solid lubricant for long term usage under extreme weather conditions. 
         [0028]    On top of the rotating head, an elongated cylindrical horizontal beam (tubing)  50  is secured with U-clamps  44  to the top plate  36  with a cylindrical bushing looped in between as illustrated in  FIG. 1 . The top cylindrical bushing is made of similar material as the bushing inside the rotating head. The horizontal beam  50  is preferably seamless galvanized steel tubing for better rotation. On both sides of horizontal beam  50 , two symmetrical tracker frame  521  and solar panel  52  are attached. The horizontal beam  50  is balanced with center of gravity on the cylindrical bushing  40 . Furthermore, the tracker frames  52  at both sides of rotating head  30  are further balanced on the horizontal beam  50  as center line of gravity. Therefore, two sides of solar panels  52  on the tracker not only balanced on the center cylindrical bushing  40 , but also balanced on the beam  50 . The balanced weight on both axes requires two symmetrical solar panels  52  being mounted on the beam  50 . An alternative mounting of tracker frame with non-rotating beam  50  will be discussed in later section. This tracker mounting is quite different from traditional solar panel mounting with one big panel pivoted at the slewing drive and lifted instead of rotated by a linear actuator. Two sided panels mounting also has the advantage of allowing near zero degree elevation to catch the sunrise and sunset on the horizon. In addition, it is easier to dispose dust and water in vertical panel position at night.  FIG. 1  only illustrates the solar tracker without azimuth and elevation actuators. It demonstrates that the tracker can be rotated in azimuth and elevation with minimal force before any electro-mechanical driver is attached. This is the key difference from the traditional tracker and advantage of this disclosure. 
         [0029]    At this point, those skilled in the art may vary the rotating head attachment to the horizontal beam in many ways. For example, a square or rectangle beam may replace the cylindrical beam as long as the section atop the rotating head is cylindrical; such as a square beam can fit inside cylindrical tube in the middle section. A square or rectangle beam may be more convenient for solar panel frame mounting. 
         [0000]    Azimuth Rotation with Single Linear Actuator 
         [0030]      FIG. 2  illustrates the sectional view of azimuth rotation with a single linear actuator attached to the side between the rotating head and ground post. An L-shaped bracket  38  is attached onto the upper rotating head  30  with open end linked to the jack head  27  of linear actuator via a horizontal hinge  25  (a bolt fits on two holes). The body of linear actuator  28  is attached to the ground post  20  via a rotating arm  26  which is hinged on  24 . Hinge  24  is built like a door hinge fixed on the ground post  20  with an extended bar. Preferred embodiment of the rotating arm  26  is to twist the end ninety degrees in order to clamp on the linear actuator  28  horizontally. It is more logical to attach L-bracket  38  to the upper rotating head  30  since it has larger diameter than ground post  20 ; and therefore shorter L-bracket  38  is needed. The main body of linear actuator  28  is clamped by the rotating arm  26 . Preferred embodiment is clamping on top end of linear actuator body perpendicular to the arm. Reverse attachment of linear actuator and jack head on rotating head and ground post is possible, but it is less preferred. 
         [0031]    In  FIGS. 3A-3C , the rotating mechanism of the upper rotating head  30  versus the lower ground post  20  is illustrated from the bottom (or top) view. The smaller solid circle is the ground post  20 , while the larger dotted circle  30  is the cylindrical rotating head. The initial position of the tracker is shown in  FIG. 3C  when L-bracket  38  and hinge  24  are aligned. The L-bracket  38 , arm  26  and jack head  27  form a right triangle with arm  26  and jack head  27  as two legs. This is the position of the tracker when the solar panel normally facing the east in the morning. As the linear actuator jack head extends as illustrated in  FIG. 3B , the jack head will push the long arm  38  together with the rotating head  30  to rotate clockwise versus ground post  20 . (The actuator  28  will not be pushed back since in geometry theory with one leg  26  of right triangle fixed and the other leg  27  extends, the “hypotenuse” line between hinges  24  and  25  must increase in length as depicted in the upper right triangle of  FIG. 3B . Therefore, rotating head  30  must be rotated clockwise to increase the hypotenuse which results in the entire tracker frame rotating clockwise). The solar panel will be pushed to face south (assuming the tracker is located at northern hemisphere) in  FIG. 3B . In southern hemisphere, the linear actuator would be attached to opposite side. When the linear actuator is near fully extended at  FIG. 3A , the bracket  38  and rotating head  30  is pushed near 180° opposite the hinge  24 . Therefore, the solar panel is rotated to face the sunset. A little more then 180° rotation is possible providing the L-bracket  38  and rotating arm  26  is made longer. This is needed if the tracker latitude location is just under the tropics. If the tracker is located at latitude higher then the tropics, the actuator attachment needs not be changed throughout all seasons of the year. If the tracker is located between the two tropics, especially near the equator, dual hinges  24 ,  74  can be installed on opposite side of ground post  20  as illustrated at  FIG. 3C . On the day when the sun orbit is crossing the zenith point in the summer, rotating arm  26  and linear actuator can be hinged to opposite side hinge  74  and the rotating head L-bracket  38  will be rotated 180° to rotate in opposite plane facing the sun orbit. 
         [0032]    Those skilled in the art can easily change the configuration of the linear actuator attachment with different length and different angle of attachment between the ground post, rotating head, and it is not necessary to form a right triangle in the initial position. By changing this attachment, it may make azimuth rotation to a greater angle. But it does not change the essence of the disclosure of using linear actuator to do the azimuth rotation. 
         [0000]    Elevation Rotation with Linear Actuator 
         [0033]      FIG. 4  illustrates the attachment of the linear actuator for the rotation of the solar panel in elevation direction. An upper V-shaped bar  51  is attached to both sides of the horizontal beam  50  with hinge  54  at open end. A lower fixed bar  49  is attached to the rotating head  30  horizontally with hinge  56  at open end. The hinges  54  and  56  are attached to the jack head and body of the linear actuator  58  respectively. Alternative to V-shaped bars, the hinge  54  can be attached directly on the tracker frame. As the jack head of linear actuator  58  extends, the V-shaped bar  51  will rotate the horizontal beam  50  and tracker frame toward lower elevation angle (perpendicular line to the panel versus horizon). Since both solar panels are balanced on the beam  50 , the rotation of solar panel demands little rotational torque. Normally, the maximum required elevation rotation of solar panel is from zero degree (vertical position) to 90 degree (flat position). If more than 90 degrees rotation is needed, it can be accomplished by simply attaching the horizontal bar  49  to a lower position. 
         [0034]    As one can observe in  FIG. 4 , the rotation of azimuth linear actuator  28  shall not be interfered by elevation linear actuator  58 . Therefore, the V-shaped bar  51  and fixed horizontal bar  49  must keep clearance of the azimuth actuator  28 . The actuator  58  can be shorter length with shorter horizontal bar  49  and V-shaped bar  51 , or the rotating head  30  can be made longer. Alternatively, one shall design the length of azimuth actuator  28  just long enough to rotate the rotating head  30  to 180 degree while keeping the horizontal bar  49  long. 
         [0035]    To those skilled in the art, the V-shaped bar and horizontal bar can be changed in shape and attachment mechanism, such as changing of V-shaped bar  51  into U-shaped and changing single bar  49  into parallel bars to hinge linear actuator from both sides. 
         [0000]    Alternative Elevation Rotation with Non Rotating Beam 
         [0036]      FIGS. 5A-5C  illustrate an alternative of rotating the tracker frame with horizontal beam fixed directly on the top plate  36  of rotating head. The horizontal beam is secured and fixed to the rotating head plate with simple U-bolts type of device  44  without bushing  40 . The horizontal beam is not rotated versus the rotating head, but rather the tracker frame is rotated with respect to the horizontal beam. Multiple bushings  59  are secured between the tracker frame crossing beams and the horizontal beam with clamps or U-bolts. Preferred embodiment will be a pillow block clamp  62  securing the cylindrical bushing  59  on the crossing beam  54 . The pillow block clamp  62  and cylindrical bushing  59  is depicted at  FIG. 5C . 
         [0037]    If flat photovoltaic solar panels are mounted on the tracker, the crossing beam may be a reversed T-beam with the height of T matching the solar panel depth. Preferred embodiment of the T-beam is made from bended metal strip with a center reversed U-shaped T-post as depicted in  FIG. 5A . The solar panel  52  can be further secured on the U-shaped T-post from the top edge of panel with clamping brackets  60  and screw  61  drilled into the bottom of T-post. With cylindrical bushings, the crossing T-beams  54  of the tracker frame can be rotated around the fixed horizontal beam  50  by the linear actuator  58 . To complete the tracker frame, L-beams  55  can be connected to both end of crossing T-beams to make a rectangular tracker frame. Furthermore, four triangular plates  53  can be attached to four corners joining the L-beam and T-beam for rectangular tracker frame support. The length and spacing of T-beams shall accommodate the dimension of solar panels  52  to be mounted. One difference from previous rotating horizontal beam is that the V-shaped bar  51  must be attached to the tracker frame rather than on the fixed horizontal beam. 
         [0038]    The alternative installation using rotation of T-beam rather than rotation of horizontal beam can accommodate larger tracker frame for larger solar panel output. Comparing to previous embodiment with one bushing carrying the entire tracker load, the tracker frame rotation on horizontal beam distributes the larger tracker load on multiple bushings. Furthermore, non-rotating of the horizontal beam put less stress on the elevation linear actuator. The alternative installation is preferred on larger tracker. 
         [0000]    Azimuth Rotation with Dual Linear Actuators 
         [0039]    Yet another aspect of the disclosure is the use of two linear actuators for azimuth rotation as illustrated in  FIG. 6 . Two linear actuators  29 ,  39  are attached to the ground post  20  and rotating head  30  on L-brackets  25  and  35 , respectively. Both attachments on the L-brackets  25  and  35  are via horizontal rotating hinges. In between the upper and lower linear actuators, a rotating ring  21  encircles and attached to the ground post  20  via a cylindrical bushing or needle bearing. A horizontal arm  23  is fixed to the rotating ring  21  at one end, and attached with a cylindrical hinge  27  on the open end. Cylindrical hinge  27  is a simple tubing with both ends bolted with washer bushings on the jack head rings of two linear actuators at the top and the bottom, respectively. 
         [0040]    The rotating mechanism of dual linear actuators is illustrated in  FIGS. 7A-7C . On  FIG. 7C  is the closed position of two linear actuators; where the linear actuator  39  is on top of linear actuator  29  with rotating ring  21  and hinge  27  in between. When the lower actuator  29  extends, the upper actuator  39  and rotating head  30  will be pushed to turn clockwise, together with the rotating ring  21 , arm  23  and hinge  27 . In  FIG. 7B , the position of rotating head  30  is turned about 120° when the lower actuator  29  is fully extended while the actuator  39  is still in the initial position. When the upper actuator  39  is fully extended, the rotating head  30  attached to actuator  39  is further rotated about 120 more degrees at  FIG. 7A . In the second rotation, the center ring  21 , horizontal arm  23  and rotating hinge  27  stay in the same position. Therefore, the upper rotating head  30  can be rotated about 240 degrees with respect to the lower ground post  20 . 
         [0041]    The advantages of using two linear actuators are twofold; 1) the rotating head  30  can be rotated more than 180 degrees to around 240 degrees, 2) two shorter linear actuators are used instead of a single long actuator. By rotating 240 degrees, the area of the world between two Tropics zones can benefit without moving the actuators whenever the Sun orbit is crossing the Zenith point. These tropical zones of the world enjoy the most sunshine days throughout the year. The disadvantage of dual linear actuator is that the actuators must be very short to make clearance for the solar panels in low elevation angle. However, if traditional lifting of solar panel for elevation rather than rotating for elevation is used, the dual linear actuators may not have the problem of clearance. 
         [0000]    Azimuth Rotation with Stepping Motor and Geared Drive 
         [0042]    Yet another aspect of the disclosure is the use of direct stepping motor drive with gear ring looped on either the rotating head or the ground post as illustrated in  FIG. 8 . For illustration, the gear ring  31  is fixed on the rotating head  30 . The direct drive stepping motor  33  is then attached to the ground post  20  with matching rotor gear  32 . Reduction gear may be used for the stepping motor to get finer rotation resolution. Alternatively, the stepping motor and gear ring can be changed in positions. It is a custom designed fitting to mate the rotor gear  32  and gear ring  31  for desired resolution in azimuth rotation. If the gear ring has  720  teeth, then 180° rotation will take 360 steps of geared rotation. If each stepping of motor makes one tooth step without gear reduction, it results in half degree of azimuth rotation. Finer resolution requires either increase the teeth number of gear ring or gear reduction in stepping motor. It is noticed that a circular gear ring  31  is hard to replace after the tracker is installed in place. Instead, a half circle gear ring  311  depicted at the left of  FIG. 8 . is used for half circle or more rotation. Half circle gear ring  311  has the advantage of retrofitting onto the rotating head if the original ring wore out or rusted after long term usage. The half circle can be more than 180 degrees which can be looped up from the smaller ground post while installation. 
         [0043]    Another alternative of geared ring with stepping motor is using a horizontal worm drive gear  32  mating with a slanted gear ring  41  as depicted in the lower right corner of  FIG. 8 . A stepping motor  43  is coupled with the worm drive  42  as illustrated. The worm drive  42  is used mostly in existing two-axes tracker slewing drive packed together with the azimuth rotating ball bearing ring. Using worm drive with slanted gear ring together with motor gear reduction can achieve desired rotation resolution without changing the gear ring teeth number. It also has smoother rotation with slanted gear teeth. 
         [0044]    The advantage of this approach is the stepping motor and geared ring takes little space on the rotating head and ground post to avoid interference with elevation actuator. Also, the rotating head can be rotated 360 degrees potentially. It could be lower cost if mass production of identical geared motor is needed in a large scale solar farm. However, the disadvantages of this approach are: 1) The gear ring and stepping motor are exposed to adverse weather condition which need to be covered and sealed to protect the gear and motor, 2) The gear ring and rotor gear has to be custom made for every size of rotating head, 3) The mating between gear ring and stepping motor must be tightly fitted which may become a problem after wind load damage and long term vibration, 4) Replace the wear out gear ring must remove the rotating head or two piece gear ring being designed. 
         [0000]    Azimuth Rotation with Stepping Motor and Magnetic Rotor 
         [0045]    Yet another aspect of the disclosure is the use of direct stepping motor drive without a geared ring on the rotating head. Instead, a permanent or electromagnetic magnetic rotor  321  is used for the rotor of the stepping motor with or without reduction gear as depicted at the lower left corner of  FIG. 8 . The rotating head  30  must be made of steel material attractable by the magnetic rotor. It is equivalent to a gearless friction rotor  321  versus the rotating head  30 . However, the magnetic attraction by the rotor ensures non-slipping in the friction drive between the rotor  321  and the rotating head  30 . The rotating force or rotating friction is proportional to the size of magnetic rotor  321 . Therefore, the larger the size and the heavier the weight of the tracker frame load, the stronger the magnetic force needed. However, since the larger tracker requires larger ground post  20  and rotating head  30 , the magnetic rotor  321  can be larger as well. Furthermore, if electromagnetic rotor is used, the attraction force is proportional to the solenoid current and number of rings of winding wire. The rotor can be smaller diameter with much stronger force than the permanent magnet. 
         [0046]    The advantage of magnetic rotor is the simplicity and lower cost of the azimuth drive. Without the gear ring and geared rotor, it removes the problem of corrosion, rain and dust cover, maintenance and lubrication. The ratio of the diameter of rotating head  30  divided by the diameter of magnetic rotor  321 ; multiplied by the steps per revolution of stepping motor will be the azimuth resolution in one revolution. A resolution of one to two degrees is adequate for a photovoltaic solar panel. Higher degree of resolution needs reduction gear in the rotor for higher precision systems such as CPV or Heliostat tracker. 
       Wind Lock Devices for Azimuth and Elevation Rotations 
       [0047]    It is shown in  FIG. 3A-3C  that the installed solar panel  52  is best to be aligned with L-bracket  38  to avoid interference with the linear actuator  28 . As depicted at  FIG. 3C , the jack head  27  force vectors is largest since the jack head is near perpendicular to the L-bracket  38  and the solar panel  52  in  FIG. 3A , the force vector is smallest with slanted angle between the jack head  27  and L-bracket  38 . This position is not good for the wind load pushing on the linear actuator at a small slanted angle. For elevation rotation shown in  FIG. 4 , the problem becomes even worse when fully extended jack head of linear actuator  58  with smallest slanted angle. It must stand up against maximum side blowing wind on near vertical solar panel. 
         [0048]    A proposed solution to the above problem is using an electromagnetic wind lock devices  65  as depicted in  FIG. 9 . Since both rotating head  30  in azimuth rotation and horizontal beam  50  in elevation rotation is cylindrical shaped, an electromagnetic lock shaped like an old style automobile drum brake is used. The difference is that the drum brake uses friction force for braking while the wind lock uses the electromagnetic attraction force for locking In  FIG. 9 , the rod  63  of an electromagnetic lock device  65  is drum shaped matching cylindrical tubing with a solenoid activation coil  64  surrounding the rod at back. When solenoid  64  is activated by DC current, the rod  63  will be magnetized to attract to the rotating head  30  or the horizontal beam  50  both made of steel for wind locking However, in the design when horizontal beam is fixed with rotating tracker frame, the electromagnetic rod head has to be designed to attract the tracker frame. The wind lock device  65  is attached to the ground post  20  and top plate  36  with securing brackets  66  for the azimuth and elevation wind lock devices  65 , respectively. The wind lock devices  65  are useful devices to protect the linear actuator in the flat solar tracker position to counter strong wind exceeding designed threshold. 
         [0049]    In this disclosure, we propose an even more useful application of the wind lock device. In windy places such as costal areas when the solar panel is under constant wind assault, the linear actuators will be under perpetual wind abuse and prone to failure. An innovative idea is adopting a stepwise wind lock to counter constant blowing wind using the same wind lock device. The procedure of stepwise wind lock is described as follows: 1) The wind locking period down-counter reaches zero at the tracker controller, 2) The electromagnetic solenoid  64  is commanded by the controller to release rod  63  to unlock position, 3) The linear actuator  28  or  58  is commanded by controller to rotate one step in azimuth or elevation direction, 4) The wind lock rod  63  is activated to lock up the tracker in current position and the tracker controller restart the locking period down counter. 
         [0050]    It is a very slow motion for the tracker rotation in a day. The most azimuth rotation is 180 degrees, while the most elevation rotation is only 90 degrees. If the rotation is happened at equinox day with 12 hours of day light, each degree of azimuth rotation takes 4 minutes while elevation rotation takes 8 minutes. On the other hand, each step of linear actuator activation may take only fraction of second. Therefore, the solar tracker is in the locking state for majority of time. The wind locking between consecutive activations will alleviate the linear actuator from constant wind load vibration and pounding. This will prolong the life of linear actuators and therefore increase the life of solar tracker in windy areas. 
       Mounting Two-Axes Solar Tracker on Light Pole 
       [0051]      FIG. 10  illustrates subject two-axes tracker modified to be mounted on a light pole. Since the light pole is not uniformly cylindrical shaped with the base larger than the top, an inner uniform cylindrical tubing  20  is looped and secured on the light pole at the top and bottom ends. The cylindrical tubing substitute the ground post  20  in  FIG. 1 . But there is an extruded flange ring  36  attached on the bottom part of tubing  20  to serve similar function of holding and supporting the rotating head  30 . The rotating head  30  is build like a flanged bushing with the bottom flange sitting on top of extruded flange  36  of inner tubing  20 . An optional thrust washer  17  is inserted between the flange ring  36  and flange bushing  30  facilitating easier rotation. Also, there are optional upper and lower bushings  34  inserted fittingly between the inner tubing  20  and outer rotating head  30  facilitating easier rotation and bear the lateral torque and force. However, if the outer lining of tubing  20  and inner lining of rotating head  30  are made of porous bushing material and fit nicely, the bushings  34  are not necessary. 
         [0052]    The horizontal beam  50  is held on by the flange of the rotating head  30  and secured with U-bolts to the body of rotating head  30  horizontally. Multiple cylindrical bushings  56  are looped on the horizontal beam for the elevation rotation of solar panels  52 . It is identical to the elevation rotation with non-rotating beam discussed previously. In addition, a rechargeable battery and controller box  45  is attached at convenient location of the light pole for night time lighting. 
         [0053]    The attachment of azimuth rotation with single or dual linear actuators is similar to those described in  FIGS. 2 and 6 . The elevation rotating is similar to that described in  FIG. 4  except the elevation actuator is mounted on one side of the rotating head and tracker frame rather than the center as depicted in  FIG. 4 . 
         [0054]    The construction of inner tubing  20  and outer rotating head  30  will depend on whether the tubing can be looped on the pole from the top. It will be easier with a complete rotating assembly built and looped from the top before the light fixture is installed. However, retrofitting on existing light pole will be a challenging engineering problem. It will require inner tubing, outer tubing and thrust washer to be built in half cylinders or rings and mated to make full cylindrical inner and outer tubing. Furthermore, the mating seams of each cylinder and each washer ring are preferred to be interleaved while mounting to provide better security for the mating seams. 
         [0055]    Although various aspects of the disclosed two-axes tracker have been shown and described, modification may occur to those skilled in the art upon reading the specification. Furthermore, many aspects of the disclosed two-axes tracker is not limited to photovoltaic panel tracking application, but can be applied to much broader aspect of solar tracking, or satellite tracking For example, the disclosed two-axes tracker can be used for a concentrated photovoltaic panel; a dish concentrator for Stirling engine, a heliostat solar reflector, a linear trough solar concentrator, a solar thermo concentrator or a satellite dish antenna. The present application includes such applications or modifications and limited only by the scope of the claims.