Abstract:
System and method for cleaning rows of solar panels. Each solar row has an upper edge elevated above ground level and a lower edge to provide an inclination of the solar row. A cleaning assembly cleans the solar panel surfaces. A support frame supports the cleaning assembly and enables upward and downward motion in the width and length directions of the solar row. Operation and movement of the cleaning assembly is controlled so as to clean a surface of the solar panels during downward movement. The cleaning assembly is preferably not operative during upward movement. During downward movement, the cleaning assembly removes dirt, debris and dust from the surface of the solar panels and generates an air stream to blow off the dirt, debris, and dust. The system further includes a guide system for moving the cleaning assembly to align with successive solar panel rows.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation-in-part of prior U.S. application Ser. No. 13/751,903, filed Jan. 28, 2013, which claims priority of U.S. Provisional Patent Application Ser. No. 61/647,010 filed May 15, 2012, 61/663,827 filed Jun. 25, 2012 and 61/725,280 filed Nov. 12, 2012, and also claims the priority of U.S. Provisional Patent Application Ser. No. 61/819,107 filed May 3, 2013. The entire contents of all of the foregoing prior applications are incorporated by reference herein. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The challenges of global climate change and energy security demands have made the development of renewable energy alternatives vital for the future of mankind. The use of direct sun radiation on solar panels can potentially produce more than enough energy to meet the energy needs of the entire planet. As the price of solar power decreases and that of conventional fuels rises, the solar business has entered a new era of worldwide growth. 
         [0003]    In order to bring technologies to exploit solar energy one step closer to par with petroleum, efficiency rates of solar systems must improve. 
         [0004]    Solar panel surfaces are typically made of high quality glass and the efficiency of the renewable energy they generate depends, among other things, on the cleanliness of the glass surfaces. Due to dust and other type of dirt and/or debris on the surfaces of the solar panels, energy losses, in some cases, can reach over forty percent (40%). 
         [0005]    As most solar parks or other installations and concentrations of solar panels are located in desert areas where the sun&#39;s radiation is intensive and exposure to dusty conditions is high, cleaning the solar panels becomes essential. 
         [0006]    Currently, existing cleaning processes of solar panels are costly, labor intensive and consume high volumes of water. Due to shortage of water in desert areas, solar panel cleaning using water, or wet cleaning, is a major obstacle for the solar industry. 
       OBJECTS AND SUMMARY OF THE INVENTION 
       [0007]    An object of the present invention (hereinafter will be referred to as “the invention”) is to provide a system and a method that will make solar panel cleaning simple, efficient, and which could be water free. 
         [0008]    Another object of the invention is to provide a system and a method that will make the solar panel cleaning process automatic and economical. 
         [0009]    Yet another object of the invention is to provide such a system for the cleaning process that will require minimal maintenance and supervision with low construction cost. 
         [0010]    Still another object of the invention is to provide such a system and a method that will achieve high quality cleaning along with a high level of reliability in all weather and topographic conditions. The system and method should be adaptable to existing as well as to newly built solar parks. 
         [0011]    Another object is to provide a system for cleaning a plurality of rows of solar panels. 
         [0012]    According to the present invention, a solar panel cleaning system and method is provided for cleaning solar panels of a plurality of solar row. The solar rows each have a length and a width, and the solar rows are inclined and have an upper end and a lower end in the width direction of the solar row, the upper end being elevated to a position higher than the lower end. The cleaning system comprises a cleaning apparatus that is selectively operative to clean a solar panel surface of a solar row; a support frame that supports said cleaning apparatus, said support frame being configured to selectively move said cleaning apparatus in both said width direction and said length direction over a surface of the solar row; and a controller coupled to said cleaning apparatus and to said support frame to selectively move said cleaning apparatus in said length direction of the solar row, and to selectively move said cleaning apparatus up and down in said width direction of the solar row, between said upper and lower ends, and to cause said cleaning apparatus to clean a solar panel surface of the solar row during a downward movement of said cleaning apparatus in said width direction of the solar row. The system further includes a guide system for moving the cleaning assembly to align with successive solar panel rows. 
         [0013]    In a specific embodiment, the cleaning apparatus is caused to clean the solar surface during a downward movement of the cleaning apparatus in the width direction of the solar row. 
         [0014]    More specifically, a control system controls operation of the cleaning assembly and movement of the cleaning assembly to effect a cleaning cycle during the downward movement of the cleaning assembly. The control system then causes movement of the cleaning assembly along the solar row, to a new position at which the control system effects a new cleaning cycle. The process continues over the length of the solar row. Thereafter, the cleaning assembly may be brought to a storage or rest position. 
         [0015]    A combined motion along both the width and length directions of the solar row can be implemented, especially at the last stage of the downward motion of the cleaning assembly. This creates a diagonal downward path of the cleaning assembly. 
         [0016]    A guide system extending substantially perpendicular to the solar rows is provided for moving the cleaning assembly to successive solar rows to clean the plurality of successive solar rows. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The invention, together with further objects and advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawings, wherein like reference numerals identify like elements, and wherein: 
           [0018]      FIG. 1  is a top view of a first embodiment of a solar panel cleaning system in accordance with the invention; 
           [0019]      FIG. 2  is a sectional view taken along the line  2 - 2  in  FIG. 1 , showing the solar panel cleaning system in a downward motion cleaning the solar panel; 
           [0020]      FIG. 3  is a sectional view taken along the line  3 - 3  in  FIG. 1 ; 
           [0021]      FIG. 4  is a detailed cross-sectional view of the rotating cleaning assembly; 
           [0022]      FIG. 5  is a sectional view taken along the line  5 - 5  in  FIG. 1 ; 
           [0023]      FIG. 6  is a cross-sectional view of a second embodiment of a solar panel cleaning system in accordance with the invention; and 
           [0024]      FIG. 7  is a side view of an embodiment of the invention for cleaning multiple solar panel rows. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]    Referring to the accompanying drawings wherein the same reference characters refer to the same or similar elements,  FIG. 1  is a top view of an exemplifying embodiment of a solar panel cleaning system in accordance with the invention, some details of which are omitted for the sake of simplicity and clarity. 
         [0026]    The solar panel cleaning system is shown in combination with a row of solar panel assemblies  111  (hereinafter referred to as “the solar row”). The solar row  111  comprises a plurality of solar panels of most any type and construction known to those skilled in the art. For example, a single solar panel typically would have a face area less than about one square meter. A length of the solar row  111  can vary between about a few meters to about a few kilometers. A width of the solar row  111  ranges from about one meter to about several meters. 
         [0027]    The surface of each solar panel in the solar row  111  is preferably made of transparent material such as glass. The solar panel surface may be coated with a repellent coating that makes the cleaning process of the surface easier. 
         [0028]    As shown in  FIG. 2 , the solar row  111  is constructed in an angular or inclined position toward the sun, which creates a lower edge (the rightward edge) and a higher edge (the leftward edge) of the solar row  111 . 
         [0029]    A pair of parallel rails  112 ,  113  are connected to the upper edge and the lower edge of the solar row  111 , respectively. Rails  112  and  113  may be made from steel, fiberglass or other metallic or non-metallic materials. In some embodiments of the invention, rails  112  and  113  can be used as electricity conductors, i.e., electrical cables may be arranged in an interior of the rails  112 ,  113  or along an outer surface of the rails  112 ,  113 , or the rails  112 ,  113  may be made of electrically conducting material and can be used as electrical conductors for the system. 
         [0030]    The cleaning system includes a support frame that enables bi-directional movement of a cleaning assembly, described below. This bi-directional movement enables the cleaning assembly to move along the solar row in two directions—along the length of the solar row  111  (left-right in  FIG. 1 ) and in the width direction of the solar row  111 . The support frame includes a main frame  114  that is configured to be movable along the length of the solar row  111 . Main frame  114  is preferably made from aluminum constructive profiles but other materials such as steel or fiberglass can be used. Supporting elements  115  are connected to the main frame  114  for support, four of which are shown in  FIG. 1 . 
         [0031]    Several wheels having different functions are connected to the main frame  114 , there being a total of six such wheels in the illustrated embodiment although the number, function and position of the wheels may vary. These wheels enable the main frame  114  to move along the solar row  111  in the length direction of the solar row. Of these wheels, three wheels  126  support the main frame  114  in a perpendicular direction relative to the surface of the solar panels in the solar row  111  (see  FIG. 1 ). Two other wheels  133  support the main frame  114  in a parallel direction relative to the surface of the solar panels in the solar row  111 . Instead of two wheels  133 , other amounts of wheels may be used, such as four. 
         [0032]    A drive wheel  132  is arranged in the same orientation as wheels  126 , i.e., in a perpendicular direction relative to the surface of the solar panels in the solar row  111 , and is driven by a drive system  117 , such as a motor, in forward and reverse directions. Drive wheel  132  functions to drive the main frame  114  along the solar row in the length direction of the solar row. The motor in drive system  117  may be any type of motor or other system capable of generating a motive force, such as a DC motor. When a motor is present in drive system  117 , an encoder is connected to the motor and reads the angular position of the motor. The angular position is converted by a processor into a determination of the location of the cleaning system along the solar row  111 . Drive wheel  132  can drive the frame  114  along the solar row in two directions. 
         [0033]    A movement limiting sensing device  116 , e.g., a limit switch or a sensor, is located on the upper edge of the main frame  114  (see  FIG. 1 ). 
         [0034]    A secondary frame  136  is configured to be movable along the main frame  114 . When the main frame has a longitudinal axis as shown, the secondary frame  136  may be considered to move longitudinal or in the longitudinal or length direction along the main frame  114 . Secondary frame  136  is preferably made from aluminum profiles, although other materials may be used. 
         [0035]    Secondary frame  136  supports at least one and preferably a plurality of cleaning apparatus, such as rotational cleaning units or rotational cleaning apparatus  124  (hereinafter referred to as an “RCA”). As shown in  FIGS. 1 and 2 , the secondary frame  136  supports two RCAs  124 . Each RCA  124  is connected to the secondary frame  136  through a respective central shaft  324  and bearings (not shown) to enable the RCAs  124  to rotate on the secondary frame  136 . The rotational axis of each RCA is shown in broken lines  325  in  FIG. 1 . 
         [0036]    A drive system  125  is provided to drive the RCAs  124 . Drive system  125  may comprise a DC motor, or another type of motor or motive power source may be used. A power transfer system is provided to convey the motive power from the drive system  125  to the RCAs  124  and convert the motive power into rotational force to rotate the RCAs  124 . For example, a pulley  128  may be connected to the drive system  125  and belts  127  wound around the pulley  128  and the RCAs  124 . There may be one belt  127  wound around each RCA  124  and the pulley  128 . The drive system  125  causes the pulley  128  to rotate and the rotation of the pulley  128  causes the belts  127  to move, which in turn causes a shaft of each RCA  124  to rotate. The belts  127  may be made of polyurethane and be round, but other types of belt shapes, such as V belts or timing belts, and other materials may be used. 
         [0037]    In a preferred embodiment of the invention there are two RCAs  124 , but the cleaning system in accordance with the invention is equally usable with only a single RCA  124  or with three or more RCAs  124 . 
         [0038]    Also, in a preferred embodiment of the invention, the RCAs  124  have roughly octagonal shapes as shown in  FIG. 4 , but other shapes such as cylindrical, square, hexagonal and any other flat or polygon shapes may be used without deviating from the scope and spirit of the invention. 
         [0039]    Referring still to  FIG. 4 , on the outer surface of each RCA  124 , one or more flexible fins  140  are connected via a connection technique to a retaining member of the RCA  124 . For example, the fins  140  may be structured to provide a quick connector between the fins  140  and the recesses in the outer surface of the retaining member of the RCA  124 . Using a quick connector, of which various types are known to those skilled in the art, periodic cleaning of the fins  140  can be easily implemented by removing them from engagement with the RCA  124 , cleaning them and then reconnecting them with the RCA  124 . Additional details about the fins  140  and their connection to the RCA  124  are set forth below. 
         [0040]    Referring back to  FIG. 1 , a winch cylinder  130  has one or more cables or ropes (hereinafter referred to as cables for ease of description)  131  attached thereto and partly wound thereon. Rotation of the winch cylinder  130  controls winding or unwinding of the cables  131 . This controlled winding and unwinding drives the secondary frame  136  upward along the angular slope of the main frame  114 , i.e., longitudinally along the main frame  114 . As illustrated, winding of the cables  131  by the winch cylinder  130  causes the upward movement of the secondary frame  136  along the solar panels in the solar row  111 , while unwinding of the cables  131  by the winch cylinder  130  causes the downward movement of the secondary frame  136  along the solar panels in the solar row  111  (which is aided by gravitational pull of the secondary frame  136  downward). Winch cylinder  130  is driven by a drive system  118 , which may include a DC motor. 
         [0041]    The cables  131  are preferably made of a composite material such as KEVLAR® as an outer sleeve, and flexible isolated conductive wire as the inner core inside the sleeve. An outer diameter of each cable  131 , i.e., the outer diameter of the outer sleeve, may be about 7 mm. and the diameter of the inner core may be about 4 mm. Other materials, constructions and diameters can be utilized for the cables  131 . Additional details about the drive system  118  and the connection of the cables  131  are set forth below. 
         [0042]    A power source  119  is provided to power the cleaning system, e.g., one or more batteries that may be rechargeable, replaceable, etc. For example, the power source  119  may provide power to a programmable control unit  120  that controls the operation of the cleaning system, including the operation and movement of the cleaning assembly via the various motors. The power source  119  may itself include a set of solar panels  171  attached to the main frame  114 . Solar panels  171  are designed to charge any batteries of the power source  119  during daylight hours and when the solar rays are received by the solar panels  171 . The power source  119  and solar panels  171  are attached to the main frame  114  to be movable therewith and thereby allow the cleaning system to operate independently without connection to any other source of electricity (other than that provided by the solar panels  171  and on-board power source  119 ). 
         [0043]    Several sensing devices or sensors are provided in the cleaning system. For example, sensor  129  is positioned on the rail  112  (proximate the left edge in the construction shown in  FIG. 1 ) to detect a maximum leftward movement of the main frame  114  on the rails  112 ,  113 . Similarly, sensor  135  is positioned on the rail  112  (proximate the right edge in the construction shown in  FIG. 1 ) to detect a maximum rightward movement of the main frame  114  on the rails  112 ,  113 . Sensor  129  and/or sensor  135  may alternatively be placed on the rail  113 . Sensor  116  is positioned on the main frame  114  (proximate an upper edge in the construction shown in  FIG. 1 ) to detect a maximum upward movement of the secondary frame  136  on the main frame  114 . Similarly, sensor  134  is positioned on the main frame  114  (proximate a lower edge in the construction shown in  FIG. 1 ) to detect a maximum downward movement of the secondary frame  136  on the main frame  114 . 
         [0044]    An encoder of the motor of the drive system  117 , when present, transmits limits and position signals to the programmable control unit  120 , which allows an effective operation of the system. In some cases, an encoder can replace sensors  129  and  135  by feeding a position of the cleaning assembly corresponding to the positions of sensors  129  and  135 . Programmable control units  120  are very well known in the industry and will not be described in detail herein. 
         [0045]      FIG. 2  shows details of the secondary frame  136  that is movable downward and upward along the main frame  114 , in the width direction of the solar row  111 . To provide the solar row  111  with its angularity relative to ground level  150 , an angular construction  139  supports the solar row and has a longer vertical riser construction proximate the upper edge of the solar row  111  and a shorter vertical riser construction proximate the lower edge of the solar row  111 . 
         [0046]    The secondary frame  136  has mounted thereon a plurality of wheels  137 , e.g., four wheels, that rotate perpendicularly to the solar panel surface, i.e., their axis of rotation is perpendicular to the normal of the surface of the solar panels in the solar row  111 . One or more additional wheels  138 , e.g., four wheels, are mounted on the secondary frame  136  to rotate parallel to the solar panel surface, i.e., their axis of rotation is parallel to the normal of the surface of the solar panels in the solar row  111 . 
         [0047]    Wheels  137 ,  138  are connected through bearings (not shown) to the secondary frame  136  and roll against the surface of the profiles that make up the main frame  114 . Wheels  137  and  138  therefore enable the secondary frame  136  to move upward and downward along the main frame  114 . This movement of the secondary frame  136  relative to the main frame  114  and solar row  111  is independent of the movement of the mainframe  114  along the length of the solar row  111 . 
         [0048]    In the situation shown in  FIG. 2 , the RCAs  124  rotate in the same direction, counterclockwise as indicated by arrow  141 . This direction of rotation preferably occurs as the secondary frame  136  moves downward along the main frame  114 . The RCAs  124  are driven by the drive system  125  through the pulley  128  and the belts  127 . The belts  127  drive the two RCAs  124  through two additional pulleys (not shown) that are attached to each RCA  124 . 
         [0049]    Each RCA  124  in  FIG. 2  includes four fins  140  that, through a control scheme originated at the drive system  125 , rotate at approximately  170  rpm, although other rotational speed are feasible. While the fins  140  rotate and the secondary frame  136  moves downward, an outer part of the fins  140  touch, sweep and wipe the surface of the solar panels in the solar row  111 . Rotation of the fins  140  creates an air blowing effect which helps to push the dirt, debris and the dust on the surface of the solar panels downward as a result of the slope of the solar row  111 . 
         [0050]      FIG. 2  also shows a connection between the cable  131  that winds and unwinds about the shaft coupled to the winch  130  (see  FIG. 1 ), and an upper edge of the secondary frame  136 , close to a center region of an upper profile that is part of the secondary frame  136 . Each cable  131  may be similarly connected to the shaft and secondary frame  136 . When the winch cylinder  130  rotates in one direction, the length of the cables  131  between the shaft of the winch cylinder  130  and the secondary frame  136  becomes shorter, and the secondary frame  136  is moved upward. When the winch cylinder  130  rotates in the opposite direction, the length of the cables  131  between the shaft of the winch cylinder  130  and the secondary frame  136  becomes longer and the frame  136  moves downward. An angular condition should be set between a long axis of the winch cylinder  130  and the cables  131 , which angle will ensure an orderly winding arrangement of the cables  131  on the winch cylinder  130 . 
         [0051]    As an alternative, the cables  131  may be connected to the center of the winch cylinder  130  and to two opposite sides of the upper profile of the secondary frame. Preferably, the cables  131  in this configuration would also create an angle between them that allows orderly rolling of the cables  131  on and off the winch cylinder  130 . 
         [0052]    Instead of the foregoing structure that imparts movement to the secondary frame  136  relative to the main frame  114 , other movement systems that enable the secondary frame  136  to move along the main frame  114  are contemplated to be within the scope of the invention. For example, one such alternative includes a system with a timing belt path and a timing pulley that is driven by a gear motor. 
         [0053]      FIG. 3  shows the upper rail  112  and supporting element  115  each having a substantially square cross-section, although other shapes are possible. Wheel  126  is mounted on the supporting element  115  to rotate against an upper surface of the rail  112 . The axis of rotation of wheel  126  is perpendicular to the normal to the surface of the solar panels in the solar row  111 . Wheel  133  is also mounted on the supporting element  115  to rotate against a side surface of the rail  112 . The axis of rotation of wheel  126  is parallel to the normal to the surface of the solar panels in the solar row  111 . An assembly is formed by the supporting element  115 , wheels  126  mounted thereto and wheel  133  mounted thereto. There are three such assemblies, as shown in  FIG. 1 . Another assembly includes one of the supporting elements  115 , one of the wheels  132  and the drive system  117 . These four assemblies enable mobility of the cleaning assembly along the solar row  111  in two directions. 
         [0054]      FIG. 4  shows the RCA  124  and the fins  140  connected thereto. As shown in FIG. 
         [0055]      4 , the RCA  124  preferably has an octagonal shape with eight cavities  143 , although, as mentioned before, other polygonal shapes, flat and cylindrical shapes can be provided for the RCA  124 . 
         [0056]    In a preferred embodiment of the invention, the fins  140  fold around solid center elements  142 . The center elements  142  can either be connected to the fins  140  or stand as separate elements. Each fin  140 , after being folded around a respective one of the center elements  142 , slides into a respective cavity  143  in the RCA  124  and are locked in the cavities  143  by an appropriate locking mechanism. For example, the locking mechanism may comprise at least one flexible side O-ring (not shown). 
         [0057]    When the RCA  124  rotates, the fins  140  with their locking elements  142  are pushed toward projections of the cavities  143  by centrifugal force and are locked and rotate along with the RCA  124 . Although  FIG. 4  shows four fins for the RCA  124 , any other number of fins can be used, from one to eight when the octagonal shaped RCA  124  has eight cavities  143 . 
         [0058]    In a preferred dry cleaning system and method, the fins  140  may be made of fabric. A preferred fabric is microfiber fabrics which are known by professionals for their cleaning and durability qualities. Microfiber fabrics are also very soft and they will not harm the surface of the solar panels. Other fabrics and/or materials are also viable. For a wet cleaning system and method, the fins  140  should be made from different materials and/or fabrics. 
         [0059]    Regardless of the type of cleaning system, the fabrics may be coated with silicon, neoprene or other rubber-like materials. In some conditions, combinations of different types of fins can be used. The quick connection capability between the fins  140  and RCA  124 , described above, facilitates easy and quick replacement of the fins  140  to enable them to be washed periodically. The preferred quick connection described above is only one manner for connecting the fins  140  to the RCA  124  and additional types of quick connection between the fins  140  and the RCA  124  are also considered part of the invention, such as Velcro strips, zippers and the like. 
         [0060]    A length of the RCA  124  and the length of the fins  140  can vary. Preferred sizes of the fins  140  are between about 400 mm, and a preferred length of the RCA  124  is about 1400 mm. 
         [0061]      FIG. 5  shows an assembly  80  of the winch that includes the winch cylinder  130 , and the ropes or cables  131  that wind about the winch cylinder  130  and connect the winch cylinder  130  to the secondary frame  136 . As explained above, each cable  131  has conductive inner core and KEVLAR® as an outer sleeve, with other constructions and materials for cables  131  being contemplated by the inventors. 
         [0062]    Drive system  118  drives and rotate the winch cylinder  130  through a pulley  160  that receives the motive output of the drive system  118 , a belt  161  that passes around the pulley  160  and another pulley  162  that is connected to the winch cylinder  130 . Drive system  118  may include a DC motor that can rotate in two directions, i.e., cause clockwise and counterclockwise rotation of the pulley  160 . Rotational force can thus be transferred from the drive system  118  to the winch cylinder  130  through a belt or gear reduction. The rotational speed of the winch assembly  80  can be around 100 rpm, although other rotational speeds can be used. 
         [0063]    The winch assembly  80  also includes two conductive shafts  163  mounted on respective bearings  164 , which in turn are housed partly in and supported by respective two bearing housings  165 . Bearing housings  165  are connected to the main frame  114 , and more specifically to an upper profile from which the main frame  114  is formed (see  FIG. 1 ). One conductive shaft  163  at one end of the winch cylinder  130  passes through the pulley  162  and the other conductive shaft at the opposite end of the winch cylinder  130  passes through an end disc  168 . 
         [0064]    Electrically conductive brushes  166  are situated in each of the bearing housings  165  and transmits electricity to the two cables  131  through connectors  167  while the winch cylinder  130  is rotating. Two electrical wires  169  connect the electrically conductive brushes  166  to an electrical power supply through the control unit  120  (see  FIG. 1 ). 
         [0065]    In one embodiment, two drive systems  118  are provided. In this case, the end disc  168  is replaced by another pulley, like pulley  162 . 
         [0066]    A locking mechanism  170  is optionally provided to lock the secondary frame in position. Locking mechanism  170  utilizes a solenoid which when energized, locks the secondary frame  136  in, for example, the upper position while the cleaning system is in a rest mode. 
         [0067]    When the control unit  120  gives a command that connects the drive system  118  of the winch assembly  80  to the electricity power supply at a certain polarity, the winch cylinder  130  rotates in a predetermined direction, the cables  131  become shorter and the secondary frame  136  moves upward in the width direction of the solar row. Once the secondary frame  136  reaches the upper end of the main frame  114 , the sensor  116  provides a signal to the control unit  120 . At this stage, control unit  120  provides the drive system  118  with signals or electrical conditions that causes the secondary frame  136  to move downward, preferably at a predetermined speed, in the width direction of the solar row. These electrical conditions depend on, for example, one or more of the following: an angular position of the solar panel row  111 , weight of the secondary frame  136  and the specifications of the RCA  124 . The electrical conditions can be one or more of the following: the voltage and the polarity supply to the drive system  118 , the operation of a motor of the drive system  118  as a braking generator under short circuit condition, and the operation of the motor of the drive system  118  as a braking generator on specific loads such as power resistor or diodes in any possible configuration. While other arrangements are feasible, two possible configurations include Zener-type diodes or diodes in serial connection. 
         [0068]    Another important load arrangement that can control the downward speed of the secondary frame  136  is the connection of the drive system  118 , while it operates as a generator, to a special electronic circuit that converts the generating power of the drive system  118  into a sufficiently high voltage that can charge the batteries in the power source  119 , to which it is connected in an electrical circuit. This arrangement can reduce the required energy to operate the cleaning system. All of these electrical conditions are designed to control the downward speed of the secondary frame  136  and they are part of the present invention. 
         [0069]    When the secondary frame  136  starts its downward motion, the control unit  120  connects the cables  131  to the power supply in a certain polarity that causes the RCAs  124  to rotate at a pre-determined speed and in a desired direction, and thereby clean the surface of the solar panels of the solar row  111 . 
         [0070]    With respect to more particular details about an exemplifying operation and control of the cleaning system, in any of the embodiments described above, during the vast majority of the time, the system remains in its stationary position with power source  119  connected to and charged by the solar panels  171  (hereinafter this position is referred to as “the home station”). The control unit  120  can trigger a command that will start the system&#39;s cleaning process. This command can come from either a preprogrammed schedule or from a command initiated by a control center of the solar panel installation. The solar panel installation may include several solar rows and thus, one cleaning system for each solar row. The solar installation will therefore have several cleaning systems. Optionally, each cleaning system has its own address and location code. 
         [0071]    The triggering command is system independent and each system can be autonomous. The control center of the solar panel installation can optionally continuously monitor the output power of the solar row(s)  111  in the installation, the location of each cleaning system and can optionally detect technical problems of any system. 
         [0072]    Optionally, the cleaning process can be controlled by a control unit that receives and factors in dynamic information, such as local weather conditions (present and forecast), sand storms and other factors that negatively impact the output power of the solar panels in the solar row  111 . These factors can be taken into account in order to trigger the cleaning process, or a schedule for cleaning the solar panels. Such information is typically provided by suitable feeds from various servers connected to the control unit, which are omitted from the description for the sake of simplicity. One skilled in the art would readily understand from the disclosure herein how the control unit would receive and process information of value in determining a cleaning regime for the solar panels in the solar installation and how to implement this regime using the cleaning system described herein, 
         [0073]    Since the monitoring process can calculate the power output for any given solar row  111 , the control unit can be configured by appropriate analysis techniques to detect any broken or stolen solar panel. 
         [0074]    When the cleaning system is in its home station, the secondary frame  136  is preferably at the uppermost end of the main frame  114 , the main frame  114  at the rightmost position relative to the solar row  111 , and the locking mechanism  170  is in a lock position which requires no power. None of the drive systems  117 ,  118 ,  125 , or motors operate. 
         [0075]    Once the cleaning system receives an initiation or start command, the drive system  118  activates the winch cylinder  130 , the locking mechanism  170  releases the drive system  118  and the secondary frame  136  starts to move downward. The downward speed of the secondary frame  136  is controlled as explained above. The drive system  125  also starts to rotate and causes rotation of any RCAs  124  coupled thereto, e.g., two in the illustrated embodiment. Rotation of the RCAs  124  causes the fins  140  to rotate to clean the surface of the solar panels in the solar row  111  by pushing the dust, debris and dirt downward. Rotation of the fins  140  also creates an air blowing effect which helps to push and clean the dust, debris and dirt downward along the slope of the solar panels. 
         [0076]    When the secondary frame  136  reaches the lower edge of main frame  114 , the sensor  134  transmits a signal to the control unit  120  which is configured to direct, in response to the signal from sensor  134 , the drive system  117  starts to rotate initiating motion of the main frame  114  along the length of the solar row in a leftward direction (in the embodiment of  FIG. 6 ). The encoder of a motor in drive system  117  generates pulses during the operation of the motor. After a preset number of pulses, the motor stops by command from the control unit  120 . The number of encoder pulses can be correlated to a preset distance along the length of the solar row  111 . This preset distance may be equal to the width of the RCAs  124  less a few centimeters to ensure minimal overlap between the cleaning cycles. 
         [0077]    During the operation of the drive system  117  and the movement of the main frame  114  along the solar row  111 , the drive system preferably continues its operation and RCAs  124  with the fins  140  rotate and perform self-cleaning. When the main frame  114  reaches the preset travel distance, drive systems  117  and  125  stop, and drive system  118  starts rotating the winch cylinder  130  in an upward motion mode and the system starts a new cleaning cycle. 
         [0078]    Once the system reaches the end of the length of the solar row, sensor  129  provides a signal and drive systems  117  and  125  stop and the last cycle in this direction starts. Once the last cycle is complete, the system optionally starts a repeating cleaning process in the opposite direction until the system reaches its home station. This repeating cleaning process is optional. 
         [0079]    Control unit  120  may be configured to provide any number of different cleaning cycles, with different directions of movement of the secondary frame  136  and main frame  114 . It is even possible to implement a control scheme at the control unit  120  wherein there is only a unidirectional cleaning process such that at the end of this process, the system will travel continuously to the home station. Another control scheme is that the cleaning cycle will repeat more than one time. 
         [0080]    In some cases, the control unit  120  can cause downward movement of the secondary frame  136  during movement of the main frame  114  along the length direction of the solar row, thereby creating a diagonal cleaning path for the RCAs  124  which are mounted on the secondary frame  136 . This diagonal movement is especially advantageous at the last stage of the downward movement of the secondary frame  136  during a cleaning process. 
         [0081]    There are also cleaning operations where the end of the cleaning process is initiated by the accumulated distances from the home station and not by the sensor  129 . Another possible cleaning operation is to have two cleaning systems at each end of the solar row  111  and a sensor in a middle region of the solar row  111 . Each cleaning system can clean part of the solar row  111  and therefore reduce the cleaning duration of a solar row  111  (in half). 
         [0082]    Control of the system by the control unit  120 , the sensors and the encoder are very well known by professionals in the electronic industry and therefore their description is omitted for the sake of simplicity. 
         [0083]      FIG. 6  is a partial cross-sectional, side view of another embodiment of a cleaning system in accordance with the invention. In this embodiment, the secondary frame  136  described above is not present and instead, the cleaning system includes a conveyor belt  224  that has a plurality of fins  240  on its outer surface. The conveyor belt  224  is installed along the main frame  114  and driven by a motorized driving cylinder  228  arranged in a loop of the conveyor belt  224  and at a lower section of the main frame  114 . 
         [0084]    A tension cylinder  230  is also arranged in the loop of the conveyor belt  224  and at an upper section of the main frame  114 . Tension cylinder  230  provides necessary tension to the conveyor belt  224  to enable its movement. Conveyor belt  224  is driven so that its upper section moves upward over the solar panel row  111  in the width direction of the solar row without touching the surface of the solar panels in the solar row  111 , while the lower section of the conveyor belt  224  moves downward over the solar panel row  111  and the fins  240  along this lower section touch, sweep, wipe and clean the surface of the solar panel in the solar row  111 . 
         [0085]    Supporting cylinders  229  are arranged in the loop of the conveyor belt  224  to support the movement of the conveyor belt  224  and the upper section of the conveyor belt  22 , i.e., prevent the upper section from coming into contact with the lower section and adversely affecting the operation of the fins  240  along the lower section. 
         [0086]    The width of the conveyor belt  224  and the length of its fins  240  can vary. A preferred length of each fin  240  is about 400 mm. A preferred width of the conveyor belt is about 1,200 mm. The fabric and/or the material of the fins  240  is/are identical to those of the fins  140  described above. The fins  240  are connected preferably to the conveyor belt  224  in a quick release connection, similar to that used above to connect fins  140  to the RCAs  124 . 
         [0087]    Operation of the cleaning system in accordance with this embodiment is similar to that described with reference to the embodiment shown in  FIGS. 1-5 . Thus, for the vast majority of the time, the cleaning system is in its home station. When a start command is triggered, the driving cylinder  228  is rotated and in turn starts causing the conveyor belt  224  to move. The fins  240  on the lower section of the conveyor belt  224  touch, sweep, wipe and clean the surface of the solar panels in the solar row  111 . After a preset travel distance of the conveyor belt  224 , which preset travel distance  224  can be determined by data from an encoder attached to the driving cylinder  228 , the driving cylinder  228  stops rotating and the main frame  114  travels along the length of the solar row for a preset distance. Then, a new cleaning cycle begins. In all other aspects, the operation and the control of this embodiment of the system are substantially identical to the description provided above with respect to the embodiment illustrated in  FIGS. 1-5 . 
         [0088]    With respect to the power supply for any of the embodiments of the cleaning system described above, the system includes at least one rechargeable battery, preferably a lead, sealed-type battery, although other types of batteries may be used. Regardless of which battery is used, the battery provides the required power supply to the system&#39;s drive systems  117 ,  118 ,  125 , motors thereof and control unit  120  and electronic element. 
         [0089]    During daylight while the system is at stationary position, the battery can be recharged by the solar panels  171 . These panels  171  can be located in various locations along the system and can be cleaned either by the cleaning system itself, i.e., RCAs  124  or manually. It is essential to emphasize that there are other ways to provide the cleaning system with the necessary power supply. For example, the battery can be charged from an external source such as an existing power grid or the output of the solar farm or solar installation at which the cleaning system is used. 
         [0090]    Electricity can also be supplied without the battery. In one such embodiment, electricity can be transferred to the cleaning system through conductive rails and movable connectors similar to the ones used in the train (railroad) industry. All such power supply arrangements are part of the invention. 
         [0091]      FIG. 7  is a side view of an embodiment of the present invention to clean multiple solar panel rows in a given solar park, and two partial side views of solar row A and solar row B of the solar park. Solar rows A and B are each substantially the same as or similar to solar row  111  of  FIG. 1 . Each solar row includes rails  112 ,  113  (referred to as rails or profiles  112   a  and  112   b  in  FIG. 7 ). Only rail or profile  112   a  and  112   b  are shown in  FIG. 7 . Rails or profiles  113   a  and  113   b , corresponding to rail  113  in  FIG. 1 , are not shown in  FIG. 7 .  FIG. 7  illustrates in detail an apparatus to clean multiple solar panel rows combined with elements that were already described with reference to  FIGS. 1-6 . Therefore, not all elements from the basic system of  FIGS. 1-6  will be described or mentioned. 
         [0092]    The main frame  311  of the system of  FIG. 7  is mounted on four wheels  312  (various numbers of wheels can be used) which roll on two rails  313  (only one rail is shown in  FIG. 7 ) that are directed perpendicularly to the solar rows of the solar park. Two rails  313  are the preferred number of rails, but any number of rails can be used, or other types of paths such as concrete paths or the like can be used. Main frame  311  carries a cleaning apparatus as described in  FIGS. 1-6 . A driving mechanism  320  drives the main frame  311  two directions along the rails  313 . Supporting frames  314 ,  315  are mounted on main frame  311  and an electrical piston  316  is connected to supporting frames  314  and  315 . Changing the position (i.e., extension) of piston  316  will change the height of the axle point  322 . Piston  316  can be a hydraulic piston or a cable winch. The upper frame  318  is connected through an axle  322  to the supporting frames  314  and  315 . The axle point  322  allows the upper frame  318  to change its angle relative to the main frame  311 . Another electrical piston  317  changes the angular position of upper frame  318  relative to main frame  311 . Piston  317  can be a hydraulic piston or a cable winch.  2112  and  2113  are two profiles that can be aligned with the profiles  112  and  113  of the solar rows, respectively. 
         [0093]    A control unit  319  controls the position of the system in three dimensions relative to the solar rows A and B. The input data to control unit  319  can be provided by sensors and encoders that are well known in the industry and are not described here. An electrical power supply such as batteries or an external electricity power supply is not described here.  111   a,    112   a  and  111   b,    112   b  are profiles or rails of the solar rows A and B, respectively, of the solar park, and correspond respectively to rails  112 ,  113  of  FIG. 1 . 
         [0094]    At the starting position, the cleaning system of the present invention is stationed on the profiles  2112  and  2113  of the system of  FIG. 7 . The profiles  2112  and  2113  are in line with the profiles  112   a  and  113   a  (i.e., rails  112 ,  113  of  FIG. 1 ) of the solar row A. Upon receiving a start cleaning command, the cleaning system moves from profiles  2112  and  2113  toward profiles  112   a  and  113   a , respectively, to engage the profiles (rails)  112   a  and  113   a  (rails  112  and  113 ), and the cleaning cycle of solar row A starts. This cleaning cycle has been described herein with reference to  FIGS. 1-6 . Once the cleaning cycle is completed, the system of  FIGS. 1-6  moves backward from profiles  112   a  and  113   a  toward profiles  2112  and  2113  of the  FIG. 7  system, until the whole cleaning apparatus is stationed back on profiles  2112  and  2113 . 
         [0095]    At this stage, the control unit  319  provides a command to the driving mechanism  320  and the system of  FIG. 7  moves on the rails  313  from solar row A toward solar row B. When the system of  FIG. 7  arrives close to solar row B, the sensors and the encoders of the  FIG. 7  system transfer to the control unit  319  accurate data regarding the relative position between the  FIG. 7  system and the solar row B. The control unit  319  processes the data and provides operating commands to driving mechanism  320 , and to pistons  316  and  317 . The  FIG. 7  system changes its horizontal, height and angular positions until the profiles  2112  and  2113  are aligned with  112   b  and  113   b , respectively (i.e., rials  112  and  113  of solar row B). The start cleaning command is then given and the cleaning system moves from profiles  2112  and  2113  toward profiles  112   b  and  113   b , and the cleaning cycle of solar row B starts, as described herein with reference to  FIGS. 1-6 . The above-described process can be repeated for any number of solar rows. 
         [0096]    The main advantage of the system and method of  FIG. 7  is that a single cleaning system can clean multiple solar rows and, in turn, significantly reduce the cleaning cost per row. Additionally, as the system is not stationary in a given location, it can provide more flexibility as far as the real estate space next to the rows is concerned. 
         [0097]    The embodiments of the invention described above provide several advantages. Among others, one or more of the embodiments provide a system and a method that will make solar panel cleaning simple, efficient, and which could optionally not use water. Also, a system and method are disclosed that will make the solar panel cleaning process automatic and economical. Even further, a system for cleaning solar panels is provided that requires minimal maintenance and supervision with low construction cost. The invention also provides a solar panel cleaning system and method that could achieve high quality cleaning along with a high level of reliability in all weather and topographic conditions. The system is even adaptable to existing as well as newly built solar parks and solar installations. 
         [0098]    It is to be understood that the present invention is not limited to the embodiments described above, but includes any and all embodiments within the scope of the following claims. While the invention has been described above with respect to specific apparatus and specific implementations, it should be clear that various modifications and alterations can be made, and various features of one embodiment can be included in other embodiments, within the scope of the present invention. It is to be understood that the present invention is not limited to the embodiments illustrated and described herein.