[0001] This application is a complete specification of and claims priority to Indian provisional patent application No. 201841022289 dated June 14, 2018.
FIELD OF THE INVENTION
[0002] The present invention relates generally to system for cleaning or maintenance and in particular to a system for cleaning solar panels.
DESCRIPTION OF THE RELATED ART
[0003] Solar panels are essential components of large scale solar photovoltaic (PV) power plants. These panels convert sunlight falling on their surface into electricity. Many of such panels are mounted in long arrays at commercial solar PV power plants. The power output produced gets affected if the sunlight falling on the surface gets masked by the presence of dust and dirt settled on the panels. Since solar power plants are erected at remote dry places, such performance degradation happens very frequently. The large numbers of solar panels pose big challenge in manually cleaning the surfaces to get rid of dust and dirt. Also, most manual cleaning methods require large quantity of water. Hence, there is a need to automate the cleaning so as to handle such large number of panels, with efficient use of water.
[0004] Prior art systems for cleaning the solar panel have to be moved or deployed over the entire panel surface through secondary means. Conventional cleaning systems are mounted dedicatedly for each array of solar panel, also called 'mounted systems'. Mounted systems need to be permanently fixed to each array. Hence if there are one hundred arrays of panels in a large power plant, equal number of systems have to be procured and deployed, resulting in very heavy investment. Also, this requires

disturbing/strengthening of support structure for the panels to bear the weight of the cleaning system.
[0005] Further, state of the art systems may use self-propelled and self-guided robot-like machines or 'robotic systems' that move over the surface of multiple panels to clean. Robotic systems have difficulty in maneuvering or navigating over steeply inclined surfaces (which are typically present in far-off locations from equator) due to wheel slippage on smooth surfaces and dust accumulation. Each system has to be very compact and has to be equipped with complex sensors and controls as well as software algorithms. Also, they need to have captive battery pack within the available space and hence, have weight constraints to power the unit over the entire duty cycle time. All these make the robotic systems expensive to procure and complex to manage.
[0006] A robot cleaning system for cleaning the solar panels and a method of controlling the robot are disclosed in the patent application US20110137458A1. A system and a method for cleaning a row of solar panels are disclosed in the patent US8771432B2. Apparatuses, systems and methods for cleaning photovoltaic devices are disclosed in PCT application WO2013017960. Chinese patent application CN105119565A discloses a cleaning device for photovoltaic power plant. The present invention discloses an improved solar panel cleaning system that overcomes some of the drawbacks of the existing systems.

[0007] In various embodiments provided herein is a solar panel cleaning system for cleaning an array of solar panels. The array includes a top edge, a bottom edge, a left edge and a right edge. The system includes a primary frame configured to move in a horizontal plane. Further, the primary frame is configured to align with the top edge of the array. In various embodiments, the system further includes a secondary frame. The secondary frame includes at least one motorized cleaning head configured to clean the solar panels. Further, the secondary frame is configured to move towards or away from the primary frame towards the bottom edge of the array for cleaning each of the solar panels.
[0008] In various embodiments, the system further includes a winch mechanism for connecting and moving the secondary frame with reference to the primary frame. In some embodiments, the primary frame includes at least two lateral wheels configured to align the frame along the top edge of the array. Further, the primary frame includes a plurality of wheels configured to move the primary frame horizontally to varying locations along the top edge to effect cleaning.
[0009] In various embodiments, the secondary frame includes a set of wheels and at least one cleaning head rotatable about a horizontal axis. In some embodiments, the secondary frame is configured to move along a length of a solar panel. In one embodiment, the cleaning head includes bristles, fabric elements or cleaning pads.
[0010] In various embodiments, the secondary frame is configured to move under the primary frame to clean up to the top edge of the solar panel array and to dock with the primary frame in that position. The entire system is movable in a horizontal direction over the array for cleaning an adjacent area. In some embodiments, the primary frame, the secondary frame and the cleaning head are powered by electric motors. In one

embodiment, the system includes at least one rechargeable battery for powering the motors.
[0011] In various embodiments, the winch mechanism is mounted on the primary frame. In one embodiment, the mechanism includes at least two cables and two winch drums operated by at least one winch motor. In some embodiments, the system is configured to be portable from one array to another to effect cleaning.
[0012] In various embodiments, the system includes a controller configured to control movement of the primary frame, the secondary frame or the cleaning head, or actuation of the water spray mechanism for effectively cleaning the area of the solar panel array. In some embodiments, the system includes a plurality of sensors positioned on the primary or the secondary frame and configured to determine an edge of the array and to provide input to the controller to limit travel of the primary or the secondary frame to within the boundaries of the array. The sensors may be selected from one or more of an optical camera, an infrared sensor, or an ultrasonic sensor. In some embodiments the system may further comprise a water spray mechanism and the controller may be configured to provide control inputs to the mechanism for cleaning a stain on the array surface.

[0013] The invention has other advantages and features which will be more readily apparent from the following detailed description of the invention and the appended claims, when taken in conjunction with the accompanying drawings, in which:
[0014] FIG. 1A shows solar panel cleaning system illustrating primary and secondary
frames.
[0015] FIG. IB illustrates primary and secondary frames of solar panel cleaning system
in docked position.
[0016] FIG. 1C shows secondary frame of solar panel cleaning system in deployed
position.
[0017] FIG. ID shows side view of the cleaning system.
[0018] FIG. IE shows top view of cleaning system showing electrical connectivity to the
secondary frame.
[0019] FIG. IF frontal view of cleaning system.
[0020] Throughout the views like numbers are used to indicate like parts.

[0021] While the invention has been disclosed with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the invention. In addition, many modifications may be made to adapt to a particular situation or material to the teachings of the invention without departing from its scope.
[0022] Throughout the specification and claims, the following terms take the meanings explicitly associated herein unless the context clearly dictates otherwise. The meaning of "a", "an", and "the" include plural references. The meaning of "in" includes "in" and "on." Referring to the drawings, like numbers indicate like parts throughout the views. Additionally, a reference to the singular includes a reference to the plural unless otherwise stated or inconsistent with the disclosure herein.
[0023] The invention in its various embodiments proposes a system for cleaning an array of solar panels in large solar PV power plants. The system includes a compact assembly of a primary frame and a secondary frame operating together to waterlessly clean an array of solar panels.
[0024] In various embodiments, the system 100 as shown in FIG. 1A for cleaning an array of solar panels S is movably installed thereon. In some embodiments, the array may be square or rectangular array. In various embodiments, the solar panels are arranged in a linear fashion along a common plane. In one embodiment, the array S includes a top edge, a bottom edge, a left edge and a right edge. The system 100 includes a primary frame 101 and a secondary frame 102 connected by a winch mechanism 115. In some embodiments, the primary frame 101 is configured to align with the top edge of the array. In various embodiments, the primary frame 101 is configured to move horizontally along the top edge of the solar panels S, while secondary frame 102 is configured to move in a transverse direction along the slope of

the panels to effect cleaning, as shown in FIG. 1A. In one embodiment, the secondary frame is configured to move along a length of a solar panel. In some embodiments, the secondary frame 102 is configured to move under the primary frame 101 to clean up to the top edge of the solar panel array and to dock with the primary frame 101 in that position. Further, the entire system 100 is configured to move in a horizontal direction to clean an adjacent panel, as illustrated in FIG. IB. In one embodiment, the secondary frame 102 is deployable along the slope of the panel as shown in FIG. 1C.
[0025] In various embodiments, the primary frame 101 includes a plurality of wheels as shown in FIG. ID to facilitate movement along the top of the panels to varying locations to effect cleaning. In one embodiment, the primary frame 101 includes at least two lateral wheels 110 configured to align the frame 101 along the top edge of the array. In various embodiments, the primary frame 101 is configured to move in a horizontal plane. In some embodiments, the primary frame 101 is provided with six rubberized wheels that support the primary frame over the panels S. In one embodiment, the primary frame is provided with four wheels 108 on the top surface of the panel S, while two wheels 110 are provided at the edge of the panels. The arrangement of wheels is configured to provide robust and stable positioning and movement of the primary frame 101 without any additional support or fixtures on the solar panel array. In one embodiment, the wheels 108 or 110 are provided powered movement via electric motors 112 mounted on the body 104 of the primary frame.
[0026] In various embodiments, the secondary frame 102 includes wheels 120 to facilitate movement of the secondary frame 102 smoothly over the panel surface without scratching or damaging. In some embodiments, the secondary frame 102 includes a motorized cleaning head 116. In one embodiment, as illustrated in FIG. IE, the cleaning head 116 includes a motorized cylindrical brush. In some embodiments, the cleaning head 116 includes bristles, fabric elements or cleaning pads. In one embodiment, the cleaning head 116 is rotatable about a horizontal axis.

[0027] In various embodiments, the winch mechanism 115 is configured for connecting and moving the secondary frame 102 with reference to the primary frame 101. In some embodiments, the mechanism 115 includes at least two cables and two winch drums 114 as shown in FIG. IF operated by at least one winch motor. In one embodiment, the winch mechanism 115 is powered by electric motor 130. In some embodiments, the winch mechanism 115 is mounted on the primary frame.
[0028] In various embodiments, the secondary frame 102 is connected to the primary frame 101 through two ropes 122 as shown in FIG. IE. In some embodiments, the secondary frame 102 is configured to move towards or away from the primary frame 101 towards the bottom edge of the array for cleaning each of the solar panels using the mechanism 115. The winding and unwinding of these ropes 122 makes the secondary frame 102 to move up or down over the inclined panel surface. In one embodiment, the two ropes 122 may be insulated electrical conductors, and configured to carry power or sensor inputs between the primary frame 101 and secondary frame 102. In one embodiment, a set of slip-rings 128 and carbon brush 126 arrangement mounted on the primary frame 101, are configured to ensure electrical supply to the secondary frame 102 through the rotating winch drums 114. In alternative embodiments, ropes 122 are configured to carry only mechanical load, and are used for up and down movement of the secondary frame 102, and electrical supply is provided by one or more of an on¬board battery, on-board solar panel, or another set of electrical conductors connecting the primary 101 and secondary frame 102. In such embodiments a wireless protocol such as Bluetooth, Zigbee, Ultra Wideband, infrared or WiFi may be employed for transmitting sensory information between the primary and secondary frames.
[0029] In various embodiments, the system 100 further includes a main embedded control system 132 as shown in FIG. ID placed in the primary frame 101, for operation and control of the cleaning system 100. Further, the primary frame 101 is provided with the required battery pack 134 with capacity to provide operation of the system 100 for a

predetermined cycle time. The battery pack 134 is configured to power all motors 112, 118, 130 and controls 132.
[0030] In various embodiments, the controller 132 is configured to cause an upward or downward movement of the secondary frame 102 and a rotation of the brush 116. The entire panel is cleaned by the action of rotating brush 116. In one embodiment, motor 118 mounted on the brush axis is configured to drive the brush 116. One cycle of down and up movement of the secondary frame 102, thus, cleans the solar panel array for the length of the brush 116. Further, the secondary frame 102 is configured to dock with the primary frame 101, and the system 100 is moved by a predetermined distance to a location where the panel is yet to be cleaned, and the cycle is repeated. This way, the entire area of the solar panel array is cleaned.
[0031] In some embodiments, the primary frame 101, the secondary frame 102 and the cleaning head 116 are powered by electric motors. In one embodiment, the system includes at least one rechargeable battery for powering the motors. In some embodiments, the system may be powered directly by the solar panel power bus. In some embodiments the system may include provision to connect to the solar panel power bus to recharge the battery pack.
[0032] In various embodiments, the system 100 further includes a plurality of sensors positioned on the primary 101 or the secondary frame 102 and configured to determine an edge of the array. Further, the sensors are configured to provide input to the controller 132 to limit travel of the primary 101 or the secondary frame 102 to within the boundaries of the array.
[0033] In some embodiments, the sensors mounted on the primary frame 101 are configured to detect its position with respect to the start and end of the array. In one embodiment, the position sensors may be placed on the body 104 of the primary frame 101 so as to detect the longitudinal edges of the solar panel S. In some embodiments, the

plurality of sensors mounted on the secondary frame 102 are configured to detect the bottom edge of the solar panel S. In various embodiments, the sensors may be placed on the body 106 of the secondary frame 102 so as to detect the bottom edge of the solar panel.
[0034] In various embodiments the controller 132 is configured to control movement of the primary frame 101, the secondary frame 102 or operation of the cleaning head 116 for effectively cleaning the area of the solar panel array. The controller is configured to clean the entire area of a solar panel array by moving the primary frame 101 horizontally to various adjacent locations on the array S and the secondary frame 102 down the length of each solar panel to cover the area of the array. The control actions by the controller 132 may be based on inputs from the sensors.
[0035] In various embodiments, the sensors placed on the body of the primary frame 101 or the secondary frame 102 may include an optical sensor such as a camera, an infrared sensor or an ultrasonic sensor. In some embodiments, the controller 132 is configured to cause reversing of a direction of travel or stop the drive motor based on the inputs from the sensors on the primary frame 101. In one embodiment, the inputs from the sensors on the secondary frame 102 are configured to ensure stopping of downward movement or switch off or /reversing of the winch motor by the controller 132 as required.
[0036] In various embodiments, the system 100 is configured to be portable from one array to another to effect cleaning. In one embodiment, the lateral wheels 108 and 110 are configured to disengage the system 100 from a position in the array and engage the system to a new position in the array. In some embodiments, the controller 132 is configured to cause the cleaning system 100 to move horizontally to position the cleaning head 116 at various locations to clean the entire surface of the solar panel array. The system 100 is configured to clean dust and dirt by the action of one or more cleaning arrangements such as brushes rotating continuously and moving over the panel surfaces.

[0037] In various embodiments, the system 100 may be used to clean any type of plate-like installation such as solar PV arrays, solar hot water systems with flat plate collectors etc. that have glass covered frontage.
[0038] In some embodiments a water container and spray mechanism may be integrated into the cleaning head to selectively apply water for any stains such as caused by bird droppings that may block solar radiation and adversely affect performance of the solar array. In some embodiments the controller 132 may receive inputs from a camera sensor to identify locations where a stain is present on the array and to actuate the water spray mechanism at the location of the stain for effective cleaning.
[0039] Advantages of the system disclosed over the existing are manifold. The invention permits deployment of one single unit over multiple arrays, as well as does not need additional strengthening or fixtures on existing solar panel arrays, because of the light weight and mechanically robust design. Compared to robotic systems, the present invention comfortably moves over any steep inclination as it does not depend on wheel friction for traction. Further, the disclosed system operates through very simple mechanism and logic, thereby keeping the overall cost of manufacture and maintenance very low. As the primary frame needs to move only in the horizontal direction, there is no big weight constraint unlike the robotic system that has to move upward on a steep slope. This enables housing a battery pack of sufficient size for the required duty cycle, without difficulty. Further, the system is simple and compact. The system is configured to cover vast areas in quick time, and also, by use of suitable bristle/pad/fabric as the medium engaging on the panel surface, reduces or even eliminates the need for water.
[0040] While the above is a complete description of the embodiments of the invention, various alternatives, modifications, and equivalents may be used. Therefore, the above description and the examples should not be taken as limiting the scope of the invention which is defined by the appended claims.

We claim:
1. A solar panel cleaning system for cleaning an array of solar panels, the array
having a top edge, a bottom edge, a left edge and a right edge, the system
comprising:
a primary frame configured to move in a horizontal plane, wherein the
primary frame is configured to align with the top edge of the array;
a secondary frame comprising at least one motorized cleaning head
configured to clean the solar panels, wherein the secondary frame is
configured to move towards or away from the primary frame towards the
bottom edge of the array for cleaning each of the solar panels; and
a winch mechanism for connecting and moving the secondary frame with
reference to the primary frame.
2. The system of claim 1, wherein the primary frame comprises at least two lateral wheels configured to align the frame along the top edge of the array and a plurality of wheels configured to move the primary frame horizontally to varying locations along the top edge to effect cleaning.
3. The system of claim 1, wherein the secondary frame comprises a set of wheels and at least one cleaning head rotatable about a horizontal axis, wherein the frame is configured to move along a length of a solar panel.
4. The system of claim 1, wherein the cleaning head comprises bristles, fabric elements or cleaning pads.
5. The system of claim 1, wherein the secondary frame is configured to move under the primary frame to clean up to the top edge of the solar panel array and to dock with

the primary frame in that position, and wherein the entire system is movable in a horizontal direction over the array for cleaning an adjacent area.
6. The system of claim 1, wherein the primary frame, the secondary frame and the cleaning head are powered by electric motors.
7. The system of claim 6, comprising at least one rechargeable battery for powering the motors.
8. The system of claim 1, wherein the winch mechanism is mounted on the primary frame, the mechanism comprising at least two cables and two winch drums operated by at least one winch motor.
9. The system of claim 1, wherein the system is configured to be portable from one array to another to effect cleaning.
10. The system of claim 1, comprising a controller configured to control movement of the primary frame, the secondary frame or the cleaning head for effectively cleaning the area of the solar panel array.
11. The system of claim 1, comprising a plurality of sensors positioned on the primary or the secondary frame and configured to determine an edge of the array and to provide input to the controller to limit travel of the primary or the secondary frame to within the boundaries of the array.
12. The system of claim 11, wherein the sensors are selected from one or more of an optical camera, an infrared sensor, or an ultrasonic sensor.

13. The system of claim 1, further comprising a water spray mechanism and wherein the controller is configured to provide control inputs to the mechanism for cleaning a stain on the array surface.