CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based on and claims priority from Korean Patent Application No. 10-2012-0101422, filed on Sep. 13, 2012 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a solar tracker for photovoltaic power generation. More particularly, the present invention relates to a solar tracker for photovoltaic power generation, which tracks an orientation movement of the sun in a day and a change of solar altitude that is the height of the sun depending on seasons using a direct cylinder to heighten power generation efficiency through forming of a solar cell plate at right angles to the sun to correspond to the movement (trace) of the sun. 
         [0004]    2. Description of the Prior Art 
         [0005]    In order to make a solar cell plate positioned at right angles to the sun, a solar tracker must drive at least two axes, that is, an X axis for tracking an azimuth angle with respect to diurnal movement of the sun and a Y axis for tracking an altitude angle with respect to seasonal movement of the sun, and various types of mechanical configurations may be adopted to achieve this.  FIG. 1  is a perspective view of a solar tracker  1  in the related art that is devised to rotate about the X axis to track an east-west azimuth angle and to rotate about the Y axis to aim at the altitude of the sun. 
         [0006]    According to the solar tracker  1  in the related art, in order to track the azimuth angle and the altitude angle of the sun, it is required to continuously drive both an azimuth angle tracking device and an altitude angle tracking device to continuously track the azimuth angle and the altitude angle of the sun. Accordingly, the solar tracker in the related art has the problems that complicated mathematical calculations through a computer are required, or precise control and frequent driving of the tracking devices are required to cause the tracking devices to frequently get out of order. 
         [0007]    Further, as the solar cell plate becomes large-sized to obtain a larger quantity of electric power, structure design is required to achieve rigidity to sufficiently endure against deformation or shaking of the panel due to external actions such as strong wind and the like, separately from the mechanical performance thereof, and to prevent overturn of the overall structure. Accordingly, the structure becomes complicated with heavy weight, and the manufacturing and constructing costs are increased. 
       SUMMARY OF THE INVENTION 
       [0008]    Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the related art while advantages achieved by the related art are maintained intact. 
         [0009]    An embodiment of the present invention is related to providing of a solar tracker including a driving device which has a simple structure with rigidity and endurance to sufficiently endure against wind pressure, and can accurately control an altitude angle and an azimuth angle through a simple mechanical operation. 
         [0010]    In one aspect of the present invention, there is provided a solar tracker which includes a solar cell plate including one or more solar cell panels; an upper structure including supporting the solar cell plate; a main post and a base bottom portion supporting the upper structure; an altitude angle adjustment direct cylinder adjusting an altitude angle of the solar cell plate to correspond to an altitude of the sun that is seasonally changed; and an azimuth angle adjustment direct cylinder adjusting an azimuth angle according to time to correspond to a diurnal movement of the sun if the altitude angle is fixed by the altitude angle adjustment direct cylinder. 
         [0011]    In this case, an upper surface of the base bottom portion is fixed to one end portion of the main post, is connected to one end portion of the altitude angle adjustment direct cylinder through a hinge having a single degree of freedom, and is connected to one end portion of the azimuth angle adjustment direct cylinder through a locking type crisscross connector having two degrees of freedom. A bottom surface of the upper structure is connected to the other end portions of the main post, the altitude angle adjustment direct cylinder, and the azimuth angle adjustment direct cylinder through locking type crisscross connectors, respectively. 
         [0012]    Since the locking type crisscross connectors are vulnerable to breakdown due to an external effort force acting on the side surfaces thereof in the case where they are used on the structure, rotation locking portions for restricting rotational movement with two degrees of freedom are provided to restrict relative movement of the locking type crisscross connectors that are connected to the altitude angle adjustment direct cylinder and the azimuth angle adjustment direct cylinder after the altitude angle adjustment direct cylinder and the azimuth angle adjustment direct cylinder complete the angle adjustment operations so that the overall structure can be structurally stabilized as a rigid body. 
         [0013]    Further, the solar cell plate may include a plurality of solar cell panels arranged with a predetermined size, and may be used in a photovoltaic power generation device that performs large-scale power generation. In order to solve the problems that such a large-scale solar cell plate is vulnerable to wind pressure, a rotary shaft is provided in each solar cell panel, a worm gear is installed at one end of the rotary shaft, and a worm gear device is attached so that a motorized or air pressure type motor is engaged with the worm gear provided at the one end of the rotary shaft to enable the solar cell panel to be opened or closed. An opening/closing adjustment portion may be provided to mitigate the wind pressure that acts on the structure through opening of the solar cell panel when the wind pressure reaches a predetermined strength. 
         [0014]    Further, in order to drive the upper structure that includes the solar cell plate to match the altitude angle and the azimuth angle of the sun, the direct cylinder may include a complex multistage direct cylinder having a heavy weight and a long stroke distance, which can be obtained by coupling a plurality of single direct cylinders in parallel and coupling the coupled signal direct cylinders as a plurality of stages. 
         [0015]    As illustrated in  FIG. 2 , the altitude angle of the sun, which is repeatedly changed according to seasons of the year in the range of the winter solstice having the lowest altitude angle and the summer solstice having the highest altitude angle, has an extremely small diurnal change, whereas the azimuth angle of the sun is repeatedly changed in one direction, that is, from sunup to sundown, in a day. The solar tracker according to the present invention fixes the altitude angle until the altitude of the sun secedes from a predetermined range after matching the altitude through once driving of one shaft that tracks the altitude angle, and drives only the other shaft that tracks the east-west azimuth angle in daily repetition. Accordingly, the consumption of firm power of the driving unit for tracking the sun can be minimized, and the operating and management costs of the device can be reduced. 
         [0016]    According to the solar tracker according to the present invention, since the direct cylinder that is a driving device for adjusting the angle of the solar cell plate also serves as the base structure of the device, the structure of the driving device can be remarkably simplified to unlimitedly lengthen the size and capacity of the photovoltaic power generator per unit device, the manufacturing and constructing costs can be greatly reduced, and the endurance can be heightened. 
         [0017]    Since the solar tracker according to the present invention can open and close the plurality of solar cell panels, the wind pressure that acts on the while solar cell plate is mitigated by opening a part of or all the solar cell panels when the wind pressure reaches the predetermined strength, and thus the safety and the endurance of the overall structure of the solar tracker can be secured. 
         [0018]    Further, according to the solar tracker according to the present invention that uses the locking type crisscross connectors and the direct cylinders, the weight of the large-capacity structure and the external effort force such as wind pressure can be appropriately dispersed to and supported by the main post and the direct cylinders, and the solar tracker can be installed with a high height from the ground. Accordingly, the utilization of the space below the solar tracker becomes natural and the damage of the green space can be minimized. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    The above and other objects, features and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: 
           [0020]      FIG. 1  is a perspective view illustrating an example of a solar tracker in the related art; 
           [0021]      FIG. 2  is a view explaining an altitude angle and an azimuth angle of the sun which are changed according to a change of seasons and days; 
           [0022]      FIG. 3  is a perspective view of a solar tracker for photovoltaic power generation according to an embodiment of the present invention; 
           [0023]      FIG. 4  is a view illustrating an arrangement of locking type crisscross connectors according to an embodiment of the present invention; 
           [0024]      FIGS. 5A and 5B  are side views explaining adjustment of an altitude angle of a solar tracker for photovoltaic power generation according to an embodiment of the present invention; 
           [0025]      FIG. 6  is a perspective view explaining adjustment of an altitude angle and an azimuth angle of a solar tracker for photovoltaic power generation according to an embodiment of the present invention; 
           [0026]      FIG. 7  is a view illustrating an assembling state of an azimuth angle adjustment direct cylinder according to an embodiment of the present invention; 
           [0027]      FIG. 8  is a cross-section view illustrating an assembling state of an azimuth angle adjustment direct cylinder according to an embodiment of the present invention; 
           [0028]      FIG. 9  is a perspective view illustrating a locking type crisscross connector of a solar tracker for photovoltaic power generation according to an embodiment of the present invention; 
           [0029]      FIG. 10  is a cross-sectional view illustrating a locking type crisscross connector of a solar tracker for photovoltaic power generation according to an embodiment of the present invention; 
           [0030]      FIG. 11  is a cross-sectional view illustrating a locking state of a locking type crisscross connector of a solar tracker for photovoltaic power generation through an operation of a clamp bolt according to an embodiment of the present invention; 
           [0031]      FIG. 12  is a cross-sectional view illustrating a locking release state of a locking type crisscross connector of a solar tracker for photovoltaic power generation through an operation of a clamp bolt according to an embodiment of the present invention; 
           [0032]      FIG. 13  is a cross-sectional view illustrating a locking type crisscross connector of a solar tracker for photovoltaic power generation, in which a locking nut and an electromagnet are installed, according to an embodiment of the present invention; 
           [0033]      FIG. 14  is a perspective view illustrating an open state of solar cell panels in a solar tracker for photovoltaic power generation according to an embodiment of the present invention; 
           [0034]      FIG. 15  is a perspective view explaining a method for opening solar cell panels in a solar tracker for photovoltaic power generation according to an embodiment of the present invention; 
           [0035]      FIGS. 16A and 16B  are plan views explaining opening of solar cell panels in a solar tracker for photovoltaic power generation according to an embodiment of the present invention, as seen from “A” in  FIG. 15 ; 
           [0036]      FIGS. 17A and 17B  are cross-sectional views explaining opening and closing state of solar cell panels in a solar tracker for photovoltaic power generation according to an embodiment of the present invention; 
           [0037]      FIG. 18  is a perspective view explaining simultaneous opening of plural solar cell panels which are connected in series by one motor according to another embodiment of the present invention; 
           [0038]      FIG. 19  is a perspective view of a direct cylinder that can be used according to another embodiment of the present invention; and 
           [0039]      FIG. 20  is a side view of a solar tracker for photovoltaic power generation according to another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0040]    Hereinafter, a solar tracker according to preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
         [0041]      FIG. 3  is a perspective view of a solar tracker for photovoltaic power generation according to an embodiment of the present invention. 
         [0042]    As illustrated in  FIG. 3 , a solar tracker  100  that is driven to trace solar light depending on the change of solar altitude and azimuth includes a solar cell plate  20  including one or more solar cell panels  10 , an upper structure  30  on which the solar cell plate  20  is mounted, and a main post  40  and a base bottom portion  50  supporting the load of the solar tracker  100  for supporting the upper structure  30 . 
         [0043]    At this time, it is preferable that the base bottom portion  50  may be formed of a concrete or steel structure to sufficiently endure the turnover or tilting of the solar tracker  100  or strong wind pressure. 
         [0044]    Further, the solar tracker includes an altitude angle adjustment direct cylinder  60  adjusting an altitude angle of the solar cell plate to correspond to an altitude of the sun that is seasonally changed, and an azimuth angle adjustment direct cylinder  70  adjusting an azimuth angle that is at right angles to the altitude angle according to time to correspond to a diurnal movement of the sun if the altitude angle is fixed by the altitude angle adjustment direct cylinder  60 . If an operation command of a signal or current is received from a control device (not illustrated), the altitude angle adjustment direct cylinder  60  and the azimuth angle adjustment direct cylinder  70  extend or contract to perform a straight movement upward and downward, and an azimuth angle rotary shaft and an altitude angle rotary shaft are rotated so that the upper structure  30  tracks the sun to face the sun in a vertical direction. 
         [0045]    At this time, an upper surface of the base bottom portion  50  is fixed to one end portion of the main post  40 , is connected to one end portion of the altitude angle adjustment direct cylinder  60  through a hinge  61  having a single degree of freedom, and is connected to one end portion of the azimuth angle adjustment direct cylinder  70  through a locking type crisscross connector  80   a  having two degrees of freedom. A bottom surface of the upper structure  30  is connected to the other end portions of the main post  40 , the altitude angle adjustment direct cylinder  60 , and the azimuth angle adjustment direct cylinder  70  through the locking type crisscross connectors  80   b,    80   c,  and  80   d,  respectively. 
         [0046]    It is preferable that the center of gravity of the upper structure  30  is positioned between points where the locking type crisscross connectors  80   b,    80   c,  and  80   d  are connected to the bottom surface of the upper structure  30  to provide a stable structure. 
         [0047]    The locking type crisscross connectors  80   b,    80   c,  and  80   d  for connecting the altitude angle adjustment direct cylinder  60 , the azimuth angle adjustment direct cylinder  70 , and the main post  40  with the upper structure  30  and the base bottom portion  50  have crisscross mechanical shafts  93  with two degrees of freedom, and thus the respective mechanical shafts can form any angle between them. 
         [0048]    As illustrated in  FIG. 4 , in order to prevent distortion of the solar tracker  100  due to the rotating force and to achieve mechanically stable driving, it is necessary to make the locking type crisscross connector  80   b  that connects the bottom surface of the upper structure  30  with one end portion of the main post  40  in a state where the upper structure  30  is horizontally maintained and the locking type crisscross connector  80   d  that connects the altitude angle adjustment direct cylinder  70  with the bottom surface of the upper structure  30  concentrically coincide with each other to configure any one shaft of the crisscross mechanical shafts of the locking type crisscross connectors  80   b  and  80   d  as the altitude angle rotary shaft (Y axis) of the solar tracker  100 . Further, it is necessary to make the locking type crisscross connector  80   b  that connects the bottom surface of the upper structure  30  with one end portion of the main post  40  and the locking type crisscross connector  80   c  that connects the altitude angle adjustment direct cylinder  60  with the bottom surface of the upper structure  30  concentrically coincide with each other to configure one remaining shaft of the crisscross mechanical shafts of the locking type crisscross connector  80   b  as the altitude angle rotary shaft (X axis) of the solar tracker  100 . Further, it is preferable that the crisscross connectors  80   b,    80   c,  and  80   d  that connect the main post  40 , the azimuth angle adjustment direct cylinder  70 , and the altitude angle adjustment direct cylinder  60  with the bottom surface of the upper structure  30  are installed to be arranged in the same direction so that the upper structure  30  can smoothly be rotated. 
         [0049]    Referring to  FIG. 5A , according to the solar tracker  100  as configured above, if the solar altitude is lowered, the altitude angle adjustment direct cylinder  60  is lengthened according to a command of a control device (not illustrated) and the upper structure  30  is rotated about the altitude angle rotary shaft to lower the altitude thereof along the sun, while if the solar altitude is heightened as shown in  FIG. 5B , the altitude angle adjustment direct cylinder  60  is shortened according to the command of the control device and the upper structure  30  is reversely rotated about the altitude angle rotary shaft to heighten the altitude thereof along the sun. 
         [0050]    In an example as illustrated in  FIG. 6 , the upper structure  30  is rotated at a certain angle as the azimuth angle adjustment direct cylinder  70  operates to be lengthened or shortened in a state where the upper structure  30  is rotated about the altitude angle rotary shaft to maintain a certain altitude angle as the altitude angle adjustment direct cylinder  60  is lengthened. If the altitude angle adjustment direct cylinder  60  that moves the altitude angle rotary shaft is stopped, the altitude angle is maintained, and if the azimuth angle adjustment direct cylinder  70  that moves the azimuth angle rotary shaft is lengthened or shortened in this state, the solar tracker  100  repeats the azimuth angle tracking at the maintained altitude angle. That is, after the altitude is set through once driving of the altitude angle rotary shaft that tracks the altitude angle, the altitude angle is fixed until the altitude of the sun secedes from the predetermined range, and thereafter, only the azimuth angle adjustment direct cylinder  70  that tracks the east-west azimuth angle is driven to simplify the operation of the solar tracker  100 . 
         [0051]    As illustrated in  FIGS. 7 and 8 , in order for the azimuth angle adjustment direct cylinder  70 , which is connected to the locking type crisscross connector  80   d  that has two degrees of freedom on the bottom surface of the upper structure  30 , to remove the twist of the azimuth angle adjustment direct cylinder  70  that occurs due to the driving of the altitude angle adjustment direct cylinder  60  and the azimuth angle adjustment direct cylinder  70  as the upper structure  30  is rotated to achieve a smooth operation and stable structure, it is preferable that a thrust bearing  71  is inserted between the locking type crisscross connector  80   d  and the azimuth angle adjustment direct cylinder  70  and a bearing holder  72  is fixed thereto when the locking type crisscross connector  80   d  and the azimuth angle adjustment direct cylinder  70  are connected with each other so that the azimuth angle adjustment direct cylinder  70  can be freely rotated about the shaft in the direction of the length of the azimuth angle adjustment direct cylinder  70 . 
         [0052]    Further, in another embodiment of the present invention, the solar tracker  100  uses only one direct cylinder and the remaining direct cylinder may be fixed to the main post. In this case, one-shaft type tracker that has a strong structure and reduces the mechanical operation portion can be configured. 
         [0053]    According to an embodiment of the present invention, the solar tracker  100  includes one fixed main post  40 , the auxiliary altitude angel adjustment direct cylinder  60 , and the auxiliary azimuth angle adjustment direct cylinder  70 , and thus the overall structure of the tracker  100  has three posts to sufficiently resist against the vertical effort force including the vertical load. However, since both ends of the altitude angle adjustment direct cylinder  60  and the azimuth angle adjustment direct cylinder  70  are connected through the hinge  61  or the locking type crisscross connector  80  having the crisscross mechanical shaft  93  that can be freely rotated, the connection portions are vulnerable to vibration or shaking that acts on the side surface due to the wind pressure or the like. Accordingly, after the driving of the solar tracker  100  is completed, the relative rotational movement of the locking type crisscross connector  80  is restricted according to the command or signal from the control device (not illustrated) to enable the overall structure to function as a rigid body. 
         [0054]    The locking type crisscross connector  80  includes a crisscross mechanical shaft  93  provided therein to perform rotational movement with two degrees of freedom.  FIG. 9  illustrates the locking type crisscross connector  80  that can restrict the relative rotational movement. For this, the locking type crisscross connector  80  may include a clamp bolt  91 , a locking nut  92 , and a cylinder  94 . As illustrated in  FIG. 10 , in order to suppress the rotational movement of a shaft arm  89  of the locking type crisscross connector  80  and the crisscross mechanical shaft  93 , a cut portion is formed by cutting a lower end of the shaft arm  89  that supports both end portions of the crisscross mechanical shaft  93  in the locking type crisscross connector  80 , a through-hole is formed in the cut portion to tighten and loosen the cut portion, and the clamp bolt  91  included in the locking type crisscross connector is provided in the through-hole of the cut portion. Further, one end of a clamp rod  95  that enables the clamp bolt  91  to tighten and loosen the cut portion is connected with the clamp bolt  91  in the cut portion. The other end of the clamp rod  95  is connected with a rod of the cylinder  94 , and the cylinder  94  is fixed to an outer surface of the shaft arm  89  of the locking type connector. 
         [0055]    As illustrated in  FIG. 11 , if the cylinder rod of the cylinder  94  is lengthened by electricity or fluid power, it lowers the clamp rod  95  connected thereto downward, and the clamp rod  95  rotates the clamp bolt  91 . Accordingly, the cut portion of the shaft arm  89  of the cut crisscross connector is pulled to restrict the rotational movement of the shaft arm  89  of the locking type crisscross connector and the crisscross mechanical shaft  93 . 
         [0056]    By contrast, as illustrated in  FIG. 12 , if the cylinder rod of the cylinder  94  is shortened by the electricity or fluid power, it pulls the clamp rod  95  upward, and the clamp rod  95  rotates the clamp bolt  91  in reverse direction. Accordingly, in the case of a right-handed screw, a gap of the cut portion of the shaft arm  89  of the locking type crisscross connector widens to be loosened, and thus the rotational movement of the shaft art  89  of the locking type crisscross connector and the crisscross mechanical shaft  93 . 
         [0057]    Further, as shown in  FIG. 13 , the locking type crisscross connector  80  is configured in a manner that an electromagnet  96   a  is inserted in the crisscross mechanical shaft  93 , screw threads are formed on an outside of a portion in which the electromagnet  96   a  that is inserted into the crisscross mechanical shaft  93  is positioned to be engaged with the locking nut  92  that is a female screw, and an electromagnet  96   b  is built in the locking nut  92 . If DC current flows to the electromagnets  96   a  and  96   b,  the electromagnets  96   a  and  96   b  are polarized to produce attraction and repulsion power and thus the locking nut  92  is rotated at a predetermined angle to cause the occurrence of a fastening force of the screw. 
         [0058]    In order to further secure the fastening force, as illustrated in  FIG. 10 , the locking type crisscross connector  80  is configured in a manner that an electric, air pressure type, or hydraulic motor  97  is installed in empty space of the locking type crisscross connector  80 , gears processed on side surface portions of the locking nut  92  are engaged with each other through a driving gear  98  connected to the motor and a driven gear  99  engaged with the driving gear  98 , and the locking nut  92  is rotated by the rotation of the motor  97  to additionally restrict the rotational movement of the shaft arm  89  of the locking type crisscross connector and the crisscross mechanical shaft  93 . In this case, the locking nut  92  is rotated by the magnetic force of the electromagnets  96   a  and  96   b,  and thus the shaft arm  89  of the locking type crisscross connector is tightened to restrict the rotational movement. In this case, even if the locking nut  92  is unable to show complete fastening force in some reasons, additional rotating force is compulsorily added to the locking nut  92  through the engaged gears by the driving force of the motor  97 , and thus more complete locking can be achieved. 
         [0059]    The above-described methods for preventing the relative rotational movement of the locking type crisscross connector  80  may be applied to both sides of the crisscross mechanical shaft  93  to restrict the both sides or may be applied to only one side of the crisscross mechanical shaft  93  of the locking type crisscross connector  80  to restrict the only one side. It is preferable to selectively apply the methods depending on the size and the weight of the solar tracker. 
         [0060]    Further, the solar cell plate  20  includes a plurality of solar cell panels  10  arranged with a predetermined size, and may be used in a photovoltaic power generation device that performs large-scale power generation. In order to solve the problems that such a large-scale solar cell plate is vulnerable to the wind pressure, a rotary shaft  111  is provided in the solar cell panel  10 , stoppers  116   a  and  116   b  are mounted on the outline of the solar cell panel  10 , a motorized or air pressure type motor  113 , a worm  114 , and a worm gear  115  are installed to open and close the solar cell panel  10  as a rotary door. A panel opening/closing adjustment portion  110  may be provided to mitigate the wind pressure that acts on the structure through opening of the solar cell panel so that the strong wind passes through the open solar cell panel  10  when the wind pressure reaches a predetermined strength. 
         [0061]      FIG. 14  is a perspective view illustrating an example of the solar tracker  100  having a large-scale solar cell plate  20  with the panel opening/closing adjustment portion  110 .  FIG. 14  shows a state where two columns of solar cell panels  10  are simultaneously opened to reduce the wind pressure that acts on the whole solar cell panels  10 . In the panel opening/closing adjustment portion  110 , as shown in  FIG. 15 , a rotary shaft  111  is installed inside the center of the solar cell panel  10  so that the solar cell panel  10  can be rotated, a worm gear  115  is mounted at one end of the rotary shaft  111 , and a bearing holder  35  is connected to the other end of the rotary shaft  111  to be rotatable. Further, a frame  33  that constitutes the upper structure  30  is installed on the outside of the solar cell panel  10 , the rotary shaft  111  is positioned on an upper surface of the frame  33  by a rotary shaft holder  35 , and a first stopper  116   a  and a second stopper  116   b  are mounted on the left and right of the rotary shaft  111  of the frame  33  that corresponds to a portion on which the solar cell panel  10  is opened or closed as being rotated about the rotary shaft  111 . The worm  114  that is engaged with the worm gear  115  provided at one end of the rotary shaft and a motor  113  that has a built-in speed reducer to rotate the worm  114  are connected to each other and are mounted on the upper surface of the frame  33 . 
         [0062]    Further, a pair of a first lock lever unit  117   a  and a second lock lever unit  117   b  are vertically and horizontally provided on the frame  33  in a direction that is at right angles to the direction in which the rotary shaft  111  of the solar cell panel  10  is installed, and locking grooves  119  are formed on left and right surfaces of the solar cell panel  10  which correspond to the first lock lever unit  117   a  and the second lock lever unit  117   b.  A first limit switch  118   a  and a second limit switch  118   b  are installed inside the locking groove  119  on one of the left and right surfaces, a bracket  34  is installed on a lower portion of the frame  33 , and a third limit switch  118   c  is mounted at an end of the bracket  34  so that the limit switch  118   c  becomes in contact with the solar cell panel at a point where the solar cell panel is opened at a specified angle. 
         [0063]      FIGS. 16A and 16B  are plan views explaining opening of the solar cell panel  10  as seen from “A” in  FIG. 15 .  FIG. 16A  illustrates a case where the solar cell panel  10  is closed, and  FIG. 16B  illustrates a case where the solar cell panel  10  is opened. The solar cell panel  10  may be rotated by the operation of the motor  113  within a predetermined angle range which is set by the third limit switch  118   c  provided on the bracket  34  that is positioned at a specified opening angle, and may not be rotated in the reverse direction by the first stopper  116   a  and the second stopper  116   b.    
         [0064]      FIGS. 17A and 17B  are cross-sectional views explaining opening and closing state of the solar cell panel  10 . In the state where the solar cell panel  10  is closed as shown in  FIG. 17A , the first limit switch  118   a  and the second limit switch  118   b,  which are provided in line in the locking groove  119  on the side surfaces of the solar cell panel  10  to correspond to the first lock lever unit  117   a,  are simultaneously pressed by the lock lever of the first lock lever unit  117   a  to be in a turned-off state, and thus the motor  113  that rotates the solar cell panel  10  can operate in neither a forward direction nor a backward direction. 
         [0065]    In the case of opening the solar cell panel  10 , it is required that a panel opening switch (not illustrated) of the panel opening/closing adjustment portion  110  operates. When the panel opening switch becomes in a turned-on state, a panel closing switch (not illustrated) of the panel opening/closing adjustment portion  110  is released to be in a turned-off state, and a panel closing circuit is unable to operate. In this case, as illustrated in  FIG. 17B , since single solenoids built in the first lock lever unit  117   a  and the second lock lever unit  117   b  operate to move backward, the solar cell panel  10  is in an openable state, and the first limit switch  118   a  and the second limit switch  118   b  are released from their pressed state to make the motor  113  start its operation. At this time, even if the second limit switch  118   b  that controls the motor  113  to be rotated in reverse direction is released from the pressed state, the panel closing circuit remains in a turned-off state and does not operate. 
         [0066]    As illustrated in  FIG. 16B , since the worm  114  is rotated through the speed reducer (not illustrated) by the operation of the motor  113  and the worm gear  115  that is engaged with the worm  114  is rotated, the solar cell panel  10  is opened slowly, and if the solar cell panel  10  reaches a specified opening angle, it presses the third limit switch  118   c  that is at an appropriate position. At this time, the third limit switch  118   c  is released to stop the operation of the motor  113 , and the single solenoids of the first lock lever unit  117   a  and the second lock lever unit  117   b  are released to move forward to make the lock levers return to their original positions by spring forces, respectively. 
         [0067]    By contrast, in the case of closing the solar cell panel  10 , it is required to operate the panel closing switch of the panel opening/closing adjustment portion  110 . At a moment where the panel closing switch becomes in a turned-on state, the panel opening switch is released to be in a turned-off state, and thus a panel opening circuit is unable to operate. On the other hand, the motor  113  starts its operation in reverse direction due to the change of the polarity of current, and the worm gear  115  is rotated through the worm  114  to close the solar cell panel  10 . At this time, although the third limit switch  118   c  that has been pressed to be in a turned-off state is recovered to the turned-on state, the solar cell panel opening circuit is released to be in the turned-off state and thus does not operate. Further, if the solar cell panel  10  is closed to reach the first lock lever unit  117   a  and the second lock lever unit  117   b  and the side surface of the solar cell panel  10  pushes a tilted surface of the lock lever, the lock lever is pushed backward, and at a moment where the lock lever is pushed over a predetermined distance, the first limit switch  118   a  and the second limit switch  118   b,  which are built in the locking groove  119  on the side surface of the solar cell panel, are pressed by the lock lever that is pushed by a spring force to be in the turned-off state (to be released). Simultaneously with this, the motor  113  stops its operation, and the solar cell panel  10  is not opened in any direction (is fixed) by the first and second stoppers  116   a  and  116   b  and the first and second lock lever units  117   a  and  117   b.    
         [0068]    As illustrated in  FIG. 18 , the panel opening/closing adjustment portion of the solar cell panel  10  according to another embodiment of the present invention may be configured in a manner that respective worm gears included in a plurality of solar cell panels  10  are connected in a line to one worm gear driving shaft  36  that is positioned on the upper surface of the frame, and by operating one motor  113  connected to one end of the worm gear driving shaft, the plurality of solar cell panels connected in series are simultaneously opened or closed. 
         [0069]    According to the present invention, large-capacity and large-scale solar tracker  100  using the locking type crisscross connector and the direct cylinder can be obtained due to its simple construction. Since the main post, which shoulders a burden with large part of the load of the structure and the external effort force, is formed of a steel structure or a concrete structure, the scale of the main post may be increased. In order to cope with the large scale of the solar tracker  100 , as illustrated in  FIG. 19 , a complex multistage direct cylinder  120  that has a large capacity and a long stroke distance can be obtained by connecting a plurality of direct cylinders  121  in parallel and connecting a holder  122  to the plurality of direct cylinders  121 . 
         [0070]      FIG. 20  illustrates a large-scale solar tracker according to another embodiment of the present invention. The large-scale and large-capacity solar tracker  100  may be configured by the complex multistage direct cylinder  120 , and in the inside of the main post  30  that is formed of the steel structure or the concrete structure, rainwater storage facilities  31  storing rainwater for the purpose of cooling of the photovoltaic power generation module, resident space for board and lodging and for business, elevating facilitates for moving persons and goods, and a management office for controlling and managing power generation equipment may be provided. 
         [0071]    Although preferred embodiments of the present invention have been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. Accordingly, it can be understood that the present invention is not limited to the embodiments as disclosed herein, but is only defined within the scope of the appended claims.
A solar tracker is provided to fix an altitude angle until the altitude of the sun secedes from a predetermined range after matching the altitude through once driving of one shaft that tracks the altitude angle and to drive only the other shaft that tracks an east-west azimuth angle in daily repetition in a state where the altitude angle of the sun, which is repeatedly changed according to seasons of the year in the range of the winter solstice having the lowest altitude angle and the summer solstice having the highest altitude angle, has an extremely small diurnal change, whereas the azimuth angle of the sun is repeatedly changed in one direction, that is, from sunup to sundown, in a day. Accordingly, consumption of firm power of a driving unit for tracking the sun can be minimized, and the operating and management costs of the device can be reduced.