Abstract:
Embodiments of solar panel cleaning apparatuses, solar panel cleaning systems, and solar panel cleaning methods are disclosed. In certain embodiments, the disclosed solar panel cleaning apparatuses, systems and methods do may not require any water or other cleaning liquids in the whole cleaning process, which makes them prominent well suited in for water-deficit environments such as deserts. In one embodiment, the solar panel cleaning apparatus comprises one or more rotatable brushes each having a rotational axis and a drive configured to move each of the one or more rotatable brushes in a direction that is not perpendicular to the rotational axis. The solar panel cleaning apparatus is may be configured such that the angle of the rotational axis of at least one of the one or more rotatable brushes is adjustable relative to the direction of travel.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Application No. 61/515,177 filed Aug. 4, 2011, the entire contents of which is specifically incorporated herein by reference without disclaimer. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to cleaning systems for photovoltaic installations, more particularly, apparatuses, systems, and methods for cleaning photovoltaic devices. 
         [0004]    2. Description of the Related Art 
         [0005]    The efficiency of a solar panel is measured by the ratio of the amount of sunlight it receives to the amount of electricity it generates. After a solar panel is installed, dust and other debris typically begins to accumulate on the solar panel surfaces. Dust accumulated on a solar panel often reduces the number of photons that the solar panel can convert to electric energy during a unit of time, and therefore may significantly reduce the efficiency of the solar panel. As such, many systems comprise a solar panel cleaning system to improve the efficiency of solar panels. Typically, most solar panel cleaning systems use liquid cleaning solutions or water for cleaning the solar panels. 
         [0006]    Dust and other debris may also become moist from rain, dew, and other condensation on the panels. The moistened dust and debris may become sticky and adhere to the surfaces of the solar panel. This typically complicates the cleaning process, and is one reason that most cleaning systems use liquid cleaning solutions in the cleaning process. 
         [0007]    In the field of solar panel cleaning systems, one common practice is water-rich solutions, which use a large amount of water to wash away dusts on a solar panel. This water-rich solution, however, is high cost and impractical in water-deficient environments such as deserts. Another common practice in the field of solar panel cleaning systems is to use dust-repelling coating, which does not involve intensive water use. Unfortunately, dust-repelling coating cannot effectively remove all dust on a solar panel, but even a very low percentage of dust retention on a solar panel will cause a reduction in the solar panel efficiency. Furthermore, any moisture from humidity condensation or sporadic rain will cause the dust to turn into mud and stick to the solar panels, making dust-repelling coatings ineffective. 
       SUMMARY OF THE INVENTION 
       [0008]    Embodiments of solar panel cleaning apparatuses, solar panel cleaning systems, and solar panel cleaning methods are disclosed. The disclosed solar panel cleaning apparatuses, systems and methods can efficiently clean dust and debris from a surface of a solar panel. In certain embodiments, the disclosed solar panel cleaning apparatuses, systems and methods may not require water or other cleaning liquids in the cleaning process, which makes them well suited for water-deficit environments such as deserts. 
         [0009]    Embodiments of a solar panel cleaning apparatus are disclosed. In one embodiment, the solar panel cleaning apparatus comprises one or more rotatable brushes each having a rotational axis and a drive configured to translate each of the one or more rotatable brushes in a direction that is not perpendicular to the rotational axis. The solar panel cleaning apparatus may be configured such that the angle of the rotational axis of at least one of the one or more rotatable brushes is adjustable relative to the direction of translation 
         [0010]    In one embodiment, the solar panel cleaning apparatus may further comprise a rotation drive coupled to the one or more rotatable brushes and configured to rotate the one or more rotatable brushes. The solar panel cleaning apparatus may also comprise a track coupled to the one or more rotatable brushes via a support assembly, and the track may be configured to guide the one or more rotatable brushes along a path, where the path is in a direction that is not perpendicular to the rotational axis. The solar panel cleaning apparatus may also comprise a support assembly configured to support the one or more brushes. 
         [0011]    In one embodiment, the solar panel cleaning apparatus may comprise a first drive mechanism to support and drive the rotatable brushes. The solar panel cleaning apparatus may further comprise a second drive mechanism configured to assist maintaining uniform brush contact and pressure along the length of a solar panel face, increase operating stability and reduce vibration. 
         [0012]    In one embodiment, the drive of the solar panel cleaning apparatus comprises one or more motors. The one or more motors may be configured to operate the one or more rotatable brushes. Each of the one or more rotatable brushes of the solar panel cleaning apparatus may comprise a shaft extending along the rotational axis and a sweeping member coupled to the shaft and configured to be rotatable about the rotational axis. The shaft and the sweeping member may be further configured to be pivotable about an axis perpendicular to a plane of the solar panel array. 
         [0013]    In one embodiment, the pivot angle between the one or more brushes and the direction of travel of the solar panel cleaning apparatus is between zero (0) and ninety (90) degrees. In certain embodiments, the rotation drive of the solar panel cleaning apparatus comprises a worm drive. The solar panel cleaning apparatus may further comprise a bevel gear reduction gearbox. The bevel gear reduction gearbox allows a single motor to simultaneously actuate the rotation and pivoting of the rotatable brushes as well as the lateral translation of the solar panel cleaning apparatus. In an another embodiment, the rotation drive of the solar panel cleaning apparatus comprises one or more sprockets or gears configured to translate rotation of the shaft into mechanical power for moving the rotational brushes along the path. In certain embodiments, the support assembly of the solar panel cleaning apparatus comprises one or more thrust slide bearings. 
         [0014]    A solar panel cleaning system is also disclosed. In one embodiment, the solar panel cleaning system comprises a solar panel power system comprising one or more solar panels, and a solar panel cleaning apparatus coupled to the one or more solar panels. The solar panel cleaning apparatus may comprise one or more rotatable brushes each having a rotational axis and a drive configured to move each of the one or more rotatable brushes in a direction that is not perpendicular to the rotational axis. 
         [0015]    In one embodiment, the solar panel cleaning system may further comprise a rotation drive coupled to the one or more rotatable brushes and configured to rotate the one or more rotatable brushes. The solar panel cleaning system may further comprise a track coupled to the one or more rotatable brushes and configured to guide the one or more rotatable brushes along a path, where the path is in a direction that is not perpendicular to the rotational axis. In a further embodiment, the solar panel cleaning system comprises a support assembly configured to support the one or more brushes. 
         [0016]    In one embodiment, the drive of the solar panel cleaning system comprises one or more motors. The one or more motors are configured to operate the one or more rotatable brushes. In a further embodiment, each of the one or more rotatable brushes of the solar panel cleaning system comprises a shaft extending along the rotational axis and a sweeping member coupled to the shaft and configured to be rotatable about the rotational axis. 
         [0017]    In one embodiment, the angle between the one or more brushes and the direction of travel of the solar panel cleaning system is between zero (0) and ninety (90) degrees. In certain embodiments, the rotation drive of the solar panel cleaning system comprises a worm drive. In certain embodiments, the support assembly of the solar panel cleaning system comprises one or more thrust slide bearings. 
         [0018]    A method for cleaning solar panels is also disclosed. In one embodiment, the method comprises rotating one or more rotatable brushes around a rotational axis such that the one or more rotatable brushes contact the solar panel, and moving the one or more rotatable brushes in a direction that is not perpendicular to the rotational axis. In one embodiment, the one or more rotatable bushes of the solar panel cleaning method are adjustable such that the one or more rotatable brushes are not perpendicular to the direction of travel. 
         [0019]    In a further embodiment, the method may comprise guiding the one or more rotatable brushes along a path with a track, where the path is in a direction that is not perpendicular to the rotational axis. The method may also comprise supporting, with a support assembly, the one or more rotatable brushes, such that the one or more rotatable bushes are in contact with a surface of the one or more solar panels. Additionally, the method may comprise operating the one or more rotatable brushes with one or more motors, adjusting the one or more rotatable brushes such that the angle between the one or more rotatable brushes and the direction of travel is between zero (0) and ninety (90) degrees, and resting the one or more rotatable brushes in a dock after the cleaning process. 
         [0020]    The term “coupled” is defined as connected, although not necessarily directly, and not necessarily mechanically. 
         [0021]    The terms “a” and “an” are defined as one or more unless this disclosure explicitly requires otherwise. 
         [0022]    The term “substantially” and its variations are defined as being largely but not necessarily wholly what is specified as understood by one of ordinary skill in the art, and in one non-limiting embodiment “substantially” refers to ranges within 10%, preferably within 5%, more preferably within 1%, and most preferably within 0.5% of what is specified. 
         [0023]    The terms “comprise” (and any form of comprise, such as “comprises” and “comprising”), “have” (and any form of have, such as “has” and “having”), “include” (and any form of include, such as “includes” and “including”) and “contain” (and any form of contain, such as “contains” and “containing”) are open-ended linking verbs. As a result, a method or device that “comprises,” “has,” “includes” or “contains” one or more steps or elements possesses those one or more steps or elements, but is not limited to possessing only those one or more elements. Likewise, a step of a method or an element of a device that “comprises,” “has,” “includes” or “contains” one or more features possesses those one or more features, but is not limited to possessing only those one or more features. Furthermore, a device or structure that is configured in a certain way is configured in at least that way, but may also be configured in ways that are not listed. 
         [0024]    Other features and associated advantages will become apparent with reference to the following detailed description of specific embodiments in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]      FIGS. 1A-1C  are diagrams illustrating various views of one embodiment of a solar panel cleaning system. 
           [0026]      FIG. 2  is a schematic diagram illustrating a perspective view of one embodiment of a rotatable brush. 
           [0027]      FIGS. 3A-3D  are diagrams illustrating various views of one embodiment of a support structure for a solar panel cleaning system. 
           [0028]      FIGS. 4A-4D  are diagrams illustrating various views one embodiment of a drive mechanism for a solar panel cleaning system. 
           [0029]      FIG. 5  is a schematic flow chart diagram illustrating one embodiment of a method for cleaning solar panels. 
           [0030]      FIG. 6  is a schematic flow chart diagram illustrating one embodiment of a method for cleaning solar panels. 
           [0031]      FIG. 7  is a schematic diagram illustrating one embodiment of a solar panel cleaning system with only one motor. 
           [0032]      FIGS. 8A-8D  illustrate one embodiment of a solar panel cleaning system with only one motor. 
           [0033]      FIGS. 9A-9E  illustrate various parts of one embodiment of a solar panel cleaning system. 
       
    
    
     DETAILED DESCRIPTION 
       [0034]    Various features and advantageous details are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known starting materials, processing techniques, components, and equipment are omitted so as not to unnecessarily obscure the invention in detail. It should be understood, however, that the detailed description and the specific examples, while indicating embodiments of the invention, are given by way of illustration only, and not by way of limitation. Various substitutions, modifications, additions, and/or rearrangements within the spirit and/or scope of the underlying inventive concept will become apparent to those skilled in the art from this disclosure. 
         [0035]      FIG. 1A  illustrates one embodiment of a solar panel cleaning system  100 . The solar panel cleaning system  100  may comprise one or more solar panels  102 . Additionally, the solar panel cleaning system  100  may comprise one or more rotatable brushes  104 . Rotatable brushes  104  may be configured to be rotatable along a rotational axis  106 . For example, rotatable brushes  104  may rotation in direction  122  or the opposite direction of  122 . Details about the structure of the rotatable brushes  104  are depicted in  FIG. 2 . 
         [0036]    In one embodiment, the solar panel cleaning system  100  may also comprise a support assembly  114 . The system  100  may also comprise one or more motors  110 . Motors  110  may be configured to rotate or pivot rotatable brushes  104 , and/or move rotatable brushes  104  along direction  108  or the opposite direction of  108 . In a further embodiment, the system  100  may comprise a support structure  112  configured to support rotatable brushes  104 . Support structure  112  may be coupled to the motors  110 . In one embodiment, the system  100  may comprise a first drive assembly  116 . The first drive assembly  116  may further comprise a drive transmission  118 . In a further embodiment, the system  100  may comprise a dock  120 . As illustrated in  FIG. 1A , the dock  120  may be attached on one side of the one or more solar panels  102 . 
         [0037]    In one embodiment, the support assembly  114  may comprise a frame or support structure coupled to the solar panel. In another embodiment, the support assembly  114  may comprise an drive track  406  as shown in  FIGS. 4A-4C  and a guide track  302  as shown in FIGS.  3 A- 3 C. In still a further embodiment, the support assembly  114  may comprise both the frame and tracks  302 ,  406 . 
         [0038]    In one embodiment, the one or more motors  110  are configured to operate the one or more rotatable brushes  104 . As used herein, the term “operate” means rotating the brushes  104  along the rotational axis  106 . The term “operate” may further mean moving the brushes  104  along the direction  108  or the opposite direction of  108 . Also, the term “operate” may mean pivoting (e.g. in direction  124  or the opposite) the rotatable brushes  104  to a position where the rotational axis  106  is not perpendicular to the direction  108 . Additionally, “operate” may mean lowering the brushes  104  such that the brushes are in contact with a surface of the solar panels  102 . 
         [0039]    In one embodiment, the system  100  may comprise only one motor  110 . In this specific embodiment, the one or more rotatable brushes  104  may be configured to rotate together in the same direction along the rotational axis  106 . In an another embodiment, the system  100  may comprise two or more motors  110 . In this embodiment, the one or more rotatable brushes  104  may be configured to rotate in different directions along the rotational axis  106 . The system  100  may further comprise a pivot  111  coupled to each of the rotatable brushes  104  and configured to rotate the rotatable brushes  104 . 
         [0040]    In some embodiments, motors  110  may be attached to a top edge of rotatable brushes  104 , or a bottom edge of rotatable brushes  104 , or a location between the top and bottom edge of rotatable brushes  104 . In some embodiments, motors may be configured to move with rotatable brushes  104  along direction  108  or the opposite direction. In some embodiments, motor  110  may be configured to pivot with rotatable brushes  104  clockwise or counter-clockwise in the plane of the one or more solar panels  102 . In some embodiments, motors  110  do not move with rotatable brushes  104 . 
         [0041]    In one embodiment, the rotatable brushes  104  may move in a direction opposite to direction  108 . In this specific embodiment, when in a run position, the angle between the rotational axis  106  and the direction  108  may be between ninety (90) and one hundred and eighty (180) degrees. When the brushes  104  are in rest position, the rotational axis  106  may be perpendicular to the direction  108 . In this specific embodiment, the rotatable brushes  104  may be rotated counter-clockwise from a rest position until the support structure  112  contacts the guide track  302  or a lower edge of the one or more solar panels  102  to reach a run position. 
         [0042]    In one embodiment, the rotatable brushes  104  are configured to move in a direction  108  that is not perpendicular to the rotational axis  106  while rotating along the rotational axis  106 . In one embodiment, the rotatable brushes  104  are configured to engage a surface of the one or more solar panels  102  when the brushes  104  are in motion. In one embodiment, the rotatable brushes  104  rests in the dock  120  after the cleaning process. 
         [0043]    In some embodiments, rotatable brushes  104  may be further configured to pivot in the plane of the one or more solar panels  102 . For example, rotatable brushes  104  may be configure to pivot in direction  124  or the opposite direction of  124 . Rotatable brushes  104  may be in either a rest position  130  or a run position  140 , as illustrated in  FIG. 1B . When in a rest position  130 , rotatable brushes  104  may be substantially perpendicular to direction  108 . When in a run position  140 , the angle between the rotational axis  106  and the direction  108  may be an angle between zero (0) and ninety (90) degrees. 
         [0044]    In one embodiment, one or more rotatable brushes  104  are pivoted clockwise (direction  124 ) from a rest position until the support structure  112  contacts the guide track  302  or a lower edge of the one or more solar panels  102  to reach a run position. Alternatively, the rotatable brushes  104  may be pivoted counter-clockwise (the opposite of direction  124 ) to reach a run position. In one embodiment, the one or more rotatable brushes  104  may be configured to be in parallel to each other while either in a rest position or in a run position. 
         [0045]    In some embodiments, only the one or more rotatable brushes  104  pivots clockwise or counter-clockwise. In some embodiments, support structure  112  and/or first drive assembly  116  pivot together with rotatable brushes  104 , as illustrated in  FIG. 1B . 
         [0046]    In some embodiments, system  100  may comprise a support member  126  for each of the one or more rotatable brushes  104  configured to support the rotatable brushes, as illustrated in  FIGS. 1A and 1C . In some embodiments, support member  126  may be configured to move with rotatable brushes  104  along direction  108  or the opposite of direction  108 . Support member  126  may be further configured to pivot with rotatable brushes  104  clockwise or counter-clockwise, as illustrated in  FIG. 1C . 
         [0047]      FIG. 2  illustrates one embodiment of a rotatable brush  104 . In one embodiment, the rotatable brush  104  may comprise a shaft  204  and a sweeping member  204 . The shaft  204  may be coupled to a drive transmission  202  and the shaft  204  may be configured to be rotatable along axis  106 . In one embodiment, the sweeping member  206  may comprise bristles. In an alternative embodiment, the sweeping member  206  may comprise foam. In an alternative embodiment, the sweeping member  206  may comprise a sponge. One of ordinary skill in the art of solar panel cleaning system may recognize other alternatives for the sweeping member  206 . 
         [0048]      FIG. 3A  illustrates a top view of one embodiment of the support structure  112  as shown in  FIG. 1 . In one embodiment, the support structure  112  may comprise one or more guide rollers  304  for each of the one or more rotatable brushes  104 . The support structure  112  may also comprise one or more pivots  306  for each of the one or more rotatable brushes  104 . The support structure  112  may further comprise a support structure  308  configured to hold the support structure  112  assembly together. 
         [0049]    In one embodiment, the guide rollers  304  may be configured to engage a guide track  302 . While in motion, the guide rollers  304  may be configured to hold tight with the guide track  302  such that the guide rollers  304  would move in a path defined by the guide track  302 . In one embodiment, the pivots  306  may be configured to pivot clockwise or counter-clockwise. In various embodiments, guide track  302  is shown at the lower end of the system for illustrative purposes. This is not intended to be limiting. For example, one of ordinary skill in the art will recognize that the guide track  302  need not necessarily be positioned at a lower end. Rather, the track  302  may alternatively be positioned at the top or at the sides of the any particular system, depending upon the system configuration. 
         [0050]    In one embodiment, there may be only one motor  110 . In such an embodiment, the one or more pivots  306  may be powered by the same motor. As such, the one or more pivots  306  may be configured to pivot in the same direction synchronously. In an another embodiment, there may be two or more motors  110 . In such an embodiment, the one or more pivots  306  may be powered by different motors. As such, the one or more pivots  306  may be configured to pivot in the same direction asynchronously. 
         [0051]      FIG. 3B  is a side view of one embodiment of the support structure  112 . In the depicted embodiment, the support structure  112  may comprise one or more guide rollers  304 . The guide rollers  304  may be configured to engage the guide track  302 . The support structure  112  may also comprise one or more pivots  306 . In one embodiment, the support structure  112  may further comprise a joint bar  314 . 
         [0052]    In one embodiment, each of the one or more pivots  306  may be coupled to each of the one or more rotatable shafts  204 . In one embodiment, each of the one or more pivots  306  and each of the one or more rotatable shafts  204  may be connected by a drive  307 . In such an embodiment, the rotation of the rotatable shaft  204  can be transferred through the drive  307  to pivot the pivots  306  clockwise or counter-clockwise. In one embodiment, the motor  110  may be coupled to the shaft  204  providing a rotation force on the brushes  104 . In particular, one or more motors  110  may be coupled directly to the shaft  204 . In such an embodiment, the drive  307  may translate rotation of the shaft  204  into rotation of the guide rollers  304 . Alternatively, the one or more motors  110  may be coupled directly to the guide rollers  304  or an axel coupled to the guide rollers  304 . In such an embodiment, the drive  307  may translate rotation of the guide rollers into a rotation force on the shaft  204  causing the rotatable brushes  104  to rotate or pivot. One of ordinary skill in the art will recognize alternative arrangements of the motors  110 , drive  307 , rotatable brushes  104  and guide rollers  304  that may be suitable for use with the present embodiments. 
         [0053]    In certain embodiments, the drive  307  connecting each of the one or more pivots  306  and each of the one or more rotatable shafts  204  may be a worm drive  307 . In an alternative embodiment, the drive  307  connecting the pivot  306  and the rotatable shaft  204  may be a sprocket drive  307 . One of ordinary skill in the art of solar panel cleaning system may recognize other alternatives for the drive  307  connecting the pivot  306  and the rotatable shaft  204 . 
         [0054]    In one embodiment, the joint bar  312  may be configured to hold the pivots  306  together as shown in  FIG. 3B . The joint bar  312  may also be configured to separate the one or more pivots  306 . In one embodiment, joint bar  312  may be configured to keep the distance between the one or more pivots  306  constant. The joint bar  312  may also be configured to move together with the one or more pivots  306  when the pivots  306  rotates clockwise or counter-clockwise. 
         [0055]      FIG. 3C  is another side view of one embodiment of the support structure  112  revealing more details about one part of the support structure  112 . In the depicted embodiment, the support structure  112  may comprise a plurality of springs  310  coupled to the support structure  308  around the pivot  306 . The springs  310  may be configured to hold the pivot  306  in position such that each of the pivot  306  will not hit the guide roller  304  on one side and the support structure  308  on the other side when the pivot  306  rotates clockwise or counter-clockwise. 
         [0056]    In one embodiment, the guide roller  302  may be configured to be in contact the guide track  302 . In certain embodiments, the guild roller  302  may be in pie-shaped as shown in  FIG. 3B . The thickness of the guide roller  302  may be larger than the diameter of the guide track  302 . In certain embodiments, the guide roller  302  may also have a curved-in edge  314 . The curved-in edge  314  may be wider than the diameter of the guide track  302 . In such an embodiment, the curved-in edge  314  may be configured to embrace and contact the guide track  302 . 
         [0057]    In some embodiments, support structure  112  may comprise a cable  320  (or belt) that runs the length of the one or more solar panels  102 , as illustrated in  FIG. 3D . The cable  320  (or belt) may be driven by one or more statically mounted motors  110  attached to an end of one or more solar panels  102 . The cable  320  (or belt) can also be used to drive rotatable brushes  104  using relative lateral motion of the cable. In some embodiments, cable  320  (or belt) may be powered by one or more pulleys that are powered by one or more motors  110  attached to the solar panel structure. 
         [0058]    In some embodiments, cable  320  (or belt) may be looped around the rotating axis  106  of rotatable brushes  104 , causing brush rotation as the structure moves laterally, thus using a single motor for rotation and lateral movement (e.g. in direction  108 ) of rotatable brushes  104 . 
         [0059]    In some embodiments, support structure  112  may comprise a caster wheel to allow the rotatable brushes  104  move easily in direction  108  or the opposite direction. 
         [0060]      FIG. 4A  is a top view of the first drive assembly  116  shown in  FIG. 1 . In one embodiment, the first drive assembly  116  may comprise one or more drive transmissions  402 . For illustrative purpose, the drive transmission  402  on the left side of  FIG. 4A  is shown in rest position, and the drive transmission  402  on the right side of  FIG. 4A  is shown in run position. In one embodiment, the first drive assembly  116  may comprise one or more drive wheels  404 . The first drive assembly  116  may also comprise one or more engagement member  408 . In one embodiment, the first drive assembly  116  may further comprise a joint bar  410 . 
         [0061]    In one embodiment, the drive transmission  402  may be coupled to the one or more rotatable shafts  204 . The drive transmission  402  may also be configured to engage the drive track  406 . In one embodiment, the drive transmission  402  may be configured to transform the torque from the rotatable shafts  202  into the rotation of the drive wheel  404 . In certain embodiment, the drive transmission  402  may be a worm drive. In an alternative embodiment, the drive transmission  402  may be a sprocket drive. One of ordinary skill in the art of solar panel cleaning system may recognize other alternatives for the drive transmission  402 . 
         [0062]    In one embodiment, the drive wheel  404  and the engagement member  408  may be placed on the opposite sides of the drive track  406 . In one embodiment, drive wheel  404  may be positioned on the side of the drive track  402  that is distal to the rotatable shaft  204 . In such an embodiment, the engagement member  408  may be place on the side of the drive track  406  that is proximal to the rotatable shaft  204 . The engagement member  408  may be configured to contact the drive track  406 . 
         [0063]    In one embodiment, the engagement member  408  may be a runner wheel. In an alternative embodiment, the engagement member  408  may be a slide bearing. One of ordinary skill in the art of solar panel cleaning system may recognize other alternatives for the engagement member  408 , such as a nylon slide member, a metal guide hook, or the like. 
         [0064]    In one embodiment, the joint bar  410  may be configured to hold the one or more drive transmissions  402  together. The joint bar  410  may also be configured to separate the one or more drive transmission  402 . In one embodiment, joint bar  410  may be configured to keep the distance between the one or more drive transmissions  402  constant. The joint bar  410  may also be configured to move together with the one or more drive transmissions  402  when the rotatable shafts  204  rotates clockwise or counter-clockwise. In one embodiment, the joint bar  306  as shown in  FIG. 3B  and the joint bar  410  as shown in  FIG. 4A  may be configured to hold the one or more rotatable shafts  204  in parallel to each other. 
         [0065]      FIG. 4B  is a side view of the drive transmission  116 . In the depicted embodiment, the drive transmission  116  may be supported by a support member  412 . The support member  412  may form a rectangular shape that frames the drive track  406  inside. The one or more drive transmissions  402  may be coupled to the support member  412 . 
         [0066]      FIG. 4C  illustrates a side view of the drive transmission  116  looking from the left hand side of  FIG. 1 . In the depicted embodiment, the drive transmission  116  may comprise a mounting point  414 . In one embodiment, the mounting point  414  may be configured to engage a surface of the solar panel on one side. In such an embodiment, the mounting point  414  may be also configured to engage the drive track  406  on the other side. Although it is not shown in  FIG. 3 , the guide track  302  may also comprise a mounting point  414 . In various embodiments, the mounting point  414  may be integral with the solar panel  102  and/or the tracks  302 ,  406 . 
         [0067]    In one embodiment, the solar panel  102  may be configured to engage the one or more brushes  104  as shown in  FIG. 1  on the top side of the solar panel  102 . In such an embodiment, the solar panel  102  may also be configured to engage the mounting point  414  on the bottom side of the solar panel  102 . 
         [0068]    In one embodiment, the drive wheel  404  may be pie-shaped as shown in  FIG. 4A . In one embodiment, the edge of the runner wheel  404  may be configured to be thicker than the diameter of the drive track  406 . The runner wheel  404  may also have a concave edge. In such an embodiment, the concave edge of the runner wheel  404  may be configured to embrace and contact the drive track  406 . 
         [0069]    In one embodiment, the edge of the engagement member  408  may be configured to be thicker than the diameter of the drive track  406 . The engagement member  408  may also have a concave edge. In such an embodiment, the concave edge of the engagement member  408  may be configured to embrace and contact the drive track  406 . In one embodiment, the concave edges of the drive wheel  404  and the engagement member  408  may be configured to contact and embrace the drive wheel  306  on the opposite sides. 
         [0070]    In one embodiment, the support member  412  may be configured to hold the drive wheel  404  and the engagement member  408  together. The support member  412  may also be configured to keep the drive wheel  404  and the engagement member  408  in a distance such that both the drive wheel  404  and the engagement member  408  contact the drive track  406 . In certain embodiments, the support member  412  may be a tension member. In such an embodiment, the tension member may be configured to adjust the distance between the drive wheel  404  and the engagement member  408  so that the drive wheel  404  and the engagement member  408  may pinch tightly to the drive track  406 . 
         [0071]    In some embodiment, system  100  may further comprise a self-cleaning assembly  430 , as illustrated in  FIG. 4D , configured to automatically clean the one or more rotatable brushes  104 . In some embodiments, self-cleaning assembly  430  may comprise a cover  432  on top of each of the one or more rotatable brushes  104 . Cover  432  may be rectangular, cylindrical, or of other shapes. 
         [0072]    During operation, rotatable brushes  104  pivot clockwise or counter-clockwise, and the cover  432  pivots on a single centered axis  434 . While pivoting with the rotatable brushes  104 , cover  432  hinges downward, a surface of the cover  432  engages rotatable brushes  104 , and cleans the rotatable brushes  104 . When rotatable brushes  104  are in rest position, the clearance  438  disappears as the brushes move to a vertical position. This is because the center distance  436  between the brushes is increased as they approach a vertical position. When rotatable brushes  104  are in rest position, the rotatable brushes  104  can be rotated while in contact with a cleaning edge on the inside of the cover  432 , and the rotatable brushes  104  may be cleaned. 
         [0073]    In some embodiments, system  100  may further comprise one or more sensor configured to be able to communicate with other systems through a wireless link. For example, system  100  may be connected with multiple systems and/or devices to form a network. Sensors in system  100  may be configured to monitor the operation and condition of system  100  and send corresponding information to a control center. The control center may be configured to receive information from system  100 , and/or sending instructions to system  100  to monitor, control, and/or operate system  100 . For example, sensors attached to system  100  may be configured to detect and identify malfunctions of system  100 , maintenance requirements, whether conditions, and/or other information, and send the information (e.g. an error code or other codes to identify types of malfunctions, types of maintenance required, level of whether condition, etc.) to a control center through a wireless network. Upon receiving information from system  100 , control center may analyze the information and send instructions to system  100  according to result of analysis. 
         [0074]    In some embodiments, sensors attached to system  100  may be configured to monitor climatic condition which system  100  is in, such as temperature, humility, solar panel surface moisture, and the like. Based the climatic information, system  100  may optimize the frequency of cleaning the solar panels  102 , and/or the rotatable brushes  104 , or select a mode of operation for system  100 . In some embodiments, system  100  may be configured to receive climatic and/or other information from a control center through one or more sensors connected to a network. Based on the received climatic and/or other information, system  100  may optimize the frequency of cleaning the solar panels  102 , and/or the rotatable brushes  104 , or select a mode of operation. 
         [0075]    In some embodiments, rotatable brushes  104  may be configured to move along a direction  108  or the opposite direction without rotating along axis  106 . In some embodiments, system  100  may be configured to provide water or other kinds of cleaning fluid to rotatable brushes  104  for cleaning of solar panels  102 . For example, rotatable brushes  104  may be configured to spay water or other kinds cleaning fluid on solar panels  102  while moving along direction  108  or the opposite direction. 
         [0076]      FIG. 5  illustrates one embodiment of a method  500  for cleaning one or more solar panels  102 . In one embodiment, the method  500  may comprise rotating  502  the one or more rotatable brushes  104  along the rotational axis  106  such that the one or more brushes  104  contact the one or more solar panels  102 . Additionally, the method  500  may comprise moving  504  the one or more rotatable brushes  104  in the direction of travel  108  that is not perpendicular to the rotational axis  106 . 
         [0077]      FIG. 6  illustrates another embodiment of a method  600  for cleaning one or more solar panels  102 . In one embodiment, the method  600  may comprise supporting  602 , with a support assembly  114 , the one or more rotatable brushes  104  such that the one or more rotatable brushes  104  are on top of the one or more solar panels  102 . Additionally, the method  600  may comprise aligning  604  the one or more rotatable brushes  104  to a position where the angle between the one or more rotatable brushes  104  and the direction of travel  108  may be between zero (0) and ninety (90) degrees. Specifically, aligning  604  the one or more rotatable brushes  104  may comprise keeping the drive wheels  404  in contact with the edge of the solar panels  102  and rotating the rotatable brushes  104  clockwise or counter-clockwise until the support structure  112  is in contact with the guide track  302  or the lower edge of the one or more solar panels  102 . 
         [0078]    In one embodiment, the method  600  may further rotating  608  the one or more rotatable brushes  104  along the rotational axis  106 . The method  600  may also comprise moving  610  the one or more rotatable brushes along the direction of travel  108 . The direction of travel  108  may not be perpendicular to the rotational axis  106 . In one embodiment, the method  600  may comprise guiding  612  the one or more brushes along a path. The path may be not perpendicular to the rotational axis  106 . In addition, the path may be defined by the guide track  302  and the drive track  406 . 
         [0079]    In one embodiment, the solar panel cleaning method  600  may comprise stopping  614  the rotatable brushes  104  from rotating and moving along the direction of travel  108  after a solar panel cleaning process. Additionally, the method  600  may comprise adjusting  616  the one or more rotatable brushes  104  such that the rotatable axis  106  is perpendicular to the direction of travel  108 . In some embodiments, method  600  may comprise cleaning  618  the rotatable brushes  104  (e.g. with a self-cleaning assembly). In certain embodiments, the method  600  may further comprise resting  620  the one or more rotatable brushes  104  in a dock  120 . 
         [0080]      FIG. 7  illustrates one embodiment of a solar panel cleaning system  700  with only one motor  110 . The system  700  may comprise a solar panel bank  102 . The system  700  may also comprise a main rotatable brush  704  coupled to the motor  110 . The main brush  700  may be configured to be rotatable along the rotational axis  106 . The system  700  may further comprise one or more drive transmissions  402 . Each of the drive transmission  402  may be coupled to a rotatable brush  104  or  704 . In one embodiment, the system  700  may also comprise one or more gear sets  702  coupled to each of the rotatable brushes  104  or  704 . The system  700  may also comprise one or more drive links  706  coupled to the drive transmissions  402 . 
         [0081]    In one embodiment, the drive transmission  402  may be coupled to the gear set  702  and the rotatable brushes  104  or  704 . The drive transmission  402  may also be configured to transfer the rotation of the rotatable brushes  104  or  704 . In one embodiment, the drive transmission may be a sprocket drive. In an another embodiment, the drive transmission  402  may be a pulley drive. 
         [0082]    In one embodiment, the motor  110  may be coupled to a main rotatable brush  704  and configured to operate the main brush  704 . The rotation of the main brush along the rotational axis  106  may be transferred, through the gear set  702 , the drive transmission  402  and the drive link  706 , to one or more additional rotatable brushes  104  and operate the additional brushes  104 . In one embodiment, the drive link  704  may be a chain. In an alternative embodiment, the drive link  706  may be a belt. 
         [0083]      FIG. 8A  shows one embodiment of a solar panel cleaning system  800  with one motor  110 . In one embodiment, a solar panel bank  102 . The system  800  may comprise a first drive assembly  116  coupled to an edge of the solar panel bank  102 . In such an embodiment, the system  800  may also comprise a support structure  112  coupled to an edge of the solar panel system  800 . The first drive assembly  116  and the support structure  112  may be configured to coupled to two parallel edges of the solar panel bank  102 . In one embodiment, the system  800  may comprise one or more rotatable brushes  104 . In the depicted embodiment, the rotatable brushes  104  are in rest position. In certain embodiment, the system  800  may also comprise one or more bevel gearboxes  802 . 
         [0084]      FIG. 8B  shows the solar panel cleaning system  800  with the rotatable brushes in a run position.  FIG. 8C  shows a side view of the solar panel cleaning system  800 . One embodiment of the bevel gearbox  802  is shown in  FIG. 8D . 
         [0085]      FIG. 9  illustrates one embodiment of the solar panel cleaning system. The rotatable brushes  104  are shown in a rest position (A) and run position (B). The first drive assembly  116  is shown to be rotating the rotatable brushes  104  clockwise (C) and counter-clockwise (D). An embodiment of the support structure  112  is also illustrated. 
         [0086]    All of the methods disclosed and claimed herein can be made and executed without undue experimentation in light of the present disclosure. While the apparatus and methods of this invention have been described in terms of preferred embodiments, it will be apparent to those of skill in the art that variations may be applied to the methods and in the steps or in the sequence of steps of the method described herein without departing from the concept, spirit and scope of the invention. In addition, modifications may be made to the disclosed apparatus and components may be eliminated or substituted for the components described herein where the same or similar results would be achieved. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope, and concept of the invention as defined by the appended claims.