Patent Publication Number: US-2022216826-A1

Title: Photovoltaic Panel Cleaning System

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. patent application Ser. No. 17/124,107 filed on Dec. 16, 2020, which is incorporated by reference herein. 
     FIELD 
     The present disclosure relates to a photovoltaic (PV) panel cleaning system and more particularly to a modular system for cleaning one or more PV panels. 
     BACKGROUND AND SUMMARY 
     Photovoltaic solar panels use sunlight as a source of energy to generate electricity. Such panels are prone to soling because of ambient conditions and airborne foreign objects. For example, soiling may be caused by dust, ashes from wildfires, snow, leaves, rain, pollen and other objects or liquids that obstruct sunrays on the panels thereby significantly reducing electrical energy generated by the panels. Such reduction of energy generated can be detrimental to the economics of owning and operating solar panels. Periodic cleaning of the panels is required in order to reduce the energy production loss caused by soiling. Some cleaning approaches include employing robots that use liquids such as detergent or water to clean the panels. Other cleaning approaches include manually cleaning the panels. Exemplary conventional cleaning devices are disclosed in U.S. Patent Publication No. 2019/0353406 entitled “Device and Method for Automatically Dry Cleaning Reflective Panels” which published to Simonette on Nov. 21, 2019, and PCT Patent Publication No. WO2019/215756 entitled “Automated System for Cleaning of Solar Photovoltaic Panels in Solar Array and Method thereof” which published to Bagalkote on Nov. 14, 2019; both of which are incorporated by reference herein. These traditional approaches are energy intensive, inefficient, detrimental to the environment, and/or labor intensive. 
     In accordance with the present invention, a PV panel cleaning system is provided. In one aspect, the panel cleaning system includes a storage tank containing pressurized air, first and second linear actuators, and a panel-cleaning device wherein the pressurized air contained in the storage tank operates the first and second actuators and the panel-cleaning device to clean PV panels. In another aspect, the panel cleaning system includes a storage tank, first and second linear actuators, and a panel-cleaning device wherein the panel-cleaning device includes one or more nozzles and a wiper blade to clean PV panels. A further aspect includes sensors associated with the first and second actuators and panel-cleaning device and configured to scan and detect fluid and debris on the PV panels to be removed. Another aspect provides sensors associated with a panel cleaning system and a programmable controller or processor configured to execute instructions stored in a nontransitory computer-readable medium. A method of using a panel cleaning system is also provided. 
     The panel cleaning system according to the present disclosure is advantageous over conventional panel cleaning systems. For example, the panel cleaning system includes no rotating parts and consumes no net energy. That is, cleaning PV panels using the panel cleaning system allows the PV panels to generate additional electrical energy. A portion of the additional electrical energy generated by the PV panels is used to operate system. In this way, there is a net energy gain when using the panel cleaning system to clean the PV panels. Another benefit of the panel cleaning system is that it is a low maintenance system without the need of human involvement for operations. The panel cleaning system is advantageously modular so that it can be used for a single PV panel or arrays of multiple PV panels. The present system advantageously does not use liquids such as water (which can undesirably freeze and break components) to clean the PV panels thereby not voiding roof or panel warranties. 
     Additional advantages and features of the present invention can be ascertained from the following description and claims taken in conjunction with the appended drawings. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
         FIG. 1  is a schematic representation of a panel cleaning system according to the principles of the present disclosure; 
         FIG. 2  is a perspective view of first and second actuators and a panel-cleaning device of the panel cleaning system shown in  FIG. 1  located on a roof of a building; 
         FIG. 3  is a perspective view of the first actuator shown in  FIG. 2 ; 
         FIG. 4  is a perspective view of the second actuator shown in  FIG. 2 ; 
         FIG. 5 a    is a schematic representation of the first actuator; 
         FIG. 5 b    is a schematic representation of the second actuator; 
         FIG. 6  is a back view of the first and second actuators and the panel-cleaning system; 
         FIG. 7 a    is a front view of the panel-cleaning device; 
         FIG. 7 b    is a back view of the panel-cleaning device; 
         FIG. 8 a    is a side view of the panel-cleaning system with a wiper blade deflated; 
         FIG. 8 b    is a side view of the panel-cleaning system with the wiper blade inflated; 
         FIG. 8 c    is an enlarged view of the wiper blade indicated as area  8   c  in  FIG. 8   b;    
         FIG. 9  is a functional block diagram showing components of an exemplary panel cleaning system shown in  FIG. 1 ; 
         FIG. 10  is a flowchart showing control logic employed in the panel cleaning system; 
         FIG. 11  is a schematic representation of another panel cleaning system; 
         FIG. 12  is a functional block diagram showing components of an exemplary panel cleaning system shown in  FIG. 11 ; 
         FIG. 13  is a schematic representation of another panel cleaning system; 
         FIG. 14  is a schematic representation of an actuator of a panel-cleaning device of the panel cleaning system of  FIG. 13 ; and 
         FIG. 15  is a functional block diagram showing components of an exemplary panel cleaning system shown in  FIG. 13 . 
     
    
    
     Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION 
     Example embodiments will now be described more fully with reference to the accompanying drawings. 
     With reference to  FIGS. 1, 2 and 9 , a photovoltaic (PV) panel cleaning system  10  is provided for cleaning a solar panel array  11  ( FIG. 2 ) located on a roof  14  of a building  16 . Solar panel array  11  includes PV panels  12 . Cleaning system  10  includes a compressor  18 , a storage tank  20 , a first actuator  22 , a second actuator  24 , a panel-cleaning device or panel-cleaner  26 , and a programmable controller or processor  28  configured to execute instructions stored in a nontransitory computer-readable medium ( FIG. 9 ). Cleaning PV panels  12  using system  10  allows PV panels  12  to generate additional electrical energy. A portion of the additional electrical energy generated by panels  12  is used to operate system  10 . In this way, there is a net energy gain when using system  10  to clean panels  12 . 
     As shown in  FIG. 1 , the compressed air from compressor  18  is discharged to storage tank  20  (via passageway  30 ) where it is stored for use. Compressor  18  may be an electric compressor, for example. Compressor  18  and storage tank  20  are located remotely from roof  14  of building  16 . That is, compressor  18  and storage tank  20  may be housed within a shed or other housing structure, for example, located remotely from roof  14  of building  16 . Storage tank  20  includes an inlet  32 , a first outlet  33 , and a second outlet  34 . Inlet  32  is in fluid communication with compressor  18  via passageway  30  so that compressed air discharged from compressor  18  flows to inlet  32  of storage tank  20 . 
     First actuator  22  may be located on roof  14  at a first side of panel array  11  and may be a rodless pneumatic linear actuator. With reference to  FIGS. 1-3, 5   a , and  6 , first actuator  22  includes a housing  36 , a piston or drive member  40  ( FIG. 5 a   ), and a carriage  42 . Piston  40  is movably disposed within a cavity  44  of housing  36  and separates cavity  44  into a first region  46  and a second region  48 . Carriage  42  is mechanically connected to piston  40  through a slot  50  formed in housing  36  so that carriage  42  and piston  40  move relative to housing  36 . Slot  50  extends substantially a length of housing  36 . In some configurations, carriage  42  may be magnetically connected to piston  40  disposed within housing  36  so that carriage  42  and piston  40  move relative to housing  36 . 
     As shown in  FIG. 3 , one or more sensors  49  are coupled to carriage  42  and are configured to continuously or intermittingly scan PV panels  12  to detect fluid or debris located on PV panels  12  as carriage  42  moves along PV panels  12 . Sensors  49  may be optical sensors, for example, and may be passive or active optical sensors. This data is communicated to controller  28  and used at least in part to determine the cleaning cycle of system  10 . Stated differently, movement of piston  40  (and carriage  42 ) may be based at least in part on the data provided by sensors  49 . For example, sensors  49  are able to scan and detect the debris size and type located on PV panels  12 . In this way, piston  40  is operated to slow down or stop at a particular location so that compressed air discharged from panel-cleaning device  26  is directed at the debris until it is removed from PV panels  12 . 
     Second actuator  24  is located on roof  14  at a second side of panel array  11  and may be a rodless pneumatic linear actuator. With reference to  FIGS. 1, 2, 4, 5   b , and  6 , second actuator  24  includes a housing  52 , a piston or drive member  54  ( FIG. 5 b   ), and a carriage  56 . Piston  54  is movably disposed within a cavity  58  of housing  52  and separates cavity  58  into a first region  60  and a second region  62 . Carriage  56  is mechanically connected to piston  54  through a slot  63  formed in housing  52  so that carriage  56  and piston  54  move relative to housing  52 . Slot  63  extends substantially a length of housing  52 . In some configurations, carriage  56  may be magnetically connected to piston  54  disposed within housing  52  so that carriage  56  and piston  54  move relative to housing  52 . 
     As shown in  FIG. 4 , one or more sensors  59  are coupled to carriage  56  and are configured to continuously or intermittingly scan PV panels  12  to detect fluid or debris located on PV panels  12  as carriage  56  moves along PV panels  12 . Sensors  59  may be optical sensors, for example, and may be passive or active optical sensors. This data is communicated to controller  28  and used at least in part to determine the cleaning cycle of system  10 . Stated differently, movement of piston  54  (and carriage  56 ) may be based at least in part on the data provided by sensors  59 . For example, sensors  59  are able to scan and detect the debris size and type located on PV panels  12 . In this way, piston  54  is operated to slow down or stop at a particular location so that compressed air discharged from panel-cleaning device  26  is directed at the debris until it is removed from PV panels  12 . 
     As shown in  FIG. 1 , a first fluid passageway  64  extends from first outlet  33  of storage tank  20  to an inlet  66  of a 3-way valve  67 . A second fluid passageway  68  extends from a first outlet  70  of 3-way valve  67  to a first inlet  69  of housing  36  of first actuator  22 . A first sensor  65  is disposed along second fluid passageway  68  upstream of first inlet  69  of the housing  36  and is configured to measure an operating parameter indicative of a pressure of the compressed air flowing through second fluid passageway  68 . This data is communicated to controller  28  and used at least in part to determine the cleaning cycle of system  10 . First sensor  65  may be a pressure sensor such as a pressure gauge or pressure transducer, for example. A third fluid passageway  72  extends from a second outlet  73  of 3-way valve  67  to a second inlet  74  of housing  36  of first actuator  22 . A second sensor  71  is disposed along third fluid passageway  72  upstream of second inlet  74  of the housing  36  and is configured to measure an operating parameter indicative of a pressure of the compressed air flowing through third fluid passageway  72 . This data is communicated to controller  28  and used at least in part to determine the cleaning cycle of system  10 . Second sensor  71  may be a pressure sensor such as a pressure gauge or pressure transducer, for example. 
     As shown in  FIG. 5 a   , a first valve  76  is associated with first inlet  69  of housing  36  and is movable between an open position in which compressed air flowing through second fluid passageway  68  is allowed to flow to first region  46  of housing  36 , and a closed position in which compressed air flowing through second fluid passageway  68  is prevented from flowing to first region  46 . First valve  76  may be disposed within first inlet  69 . Similarly, a second valve  78  is associated with second inlet  74  of housing  36  and may be movable between an open position in which compressed air flowing through third fluid passageway  72  is allowed to flow to second region  48  of housing  36 , and a closed position in which compressed air flowing through third fluid passageway  72  is prevented from flowing to second region  48 . Second valve  78  may be disposed within second inlet  74 . It will be appreciated that first and second valves  76 ,  78  could be electromagnetic, solenoid-activated valves, for example. 
     As shown in  FIG. 1 , a first fluid line  80  extends from second fluid passageway  68  at a location between 3-way valve  67  and first valve  76  to a first inlet  82  of housing  52  of second actuator  24 . A third sensor  81  is disposed along first fluid line  80  upstream of first inlet  82  of the housing  52  and is configured to measure an operating parameter indicative of a pressure of the compressed air flowing through first fluid line  80 . This data is communicated to controller  28  and used at least in part to determine the cleaning cycle of system  10 . Third sensor  81  may be a pressure sensor such as a pressure gauge or pressure transducer, for example. A second fluid line  84  extends from third fluid passageway  72  at a location between 3-way valve  67  and second valve  78  to a second inlet  85  of housing  52 . A fourth sensor  83  is disposed along second fluid line  84  upstream of second inlet  85  of housing  52  and is configured to measure an operating parameter indicative of a pressure of the compressed air flowing through second fluid line  84 . This data is communicated to controller  28  and used at least in part to determine the cleaning cycle of system  10 . Fourth sensor  83  may be a pressure sensor such as a pressure gauge or pressure transducer, for example. 
     As shown in  FIG. 5 b   , a third valve  86  is associated with first inlet  82  of housing  52  and is movable between an open position in which compressed air flowing through first fluid line  80  is allowed to flow to first region  60  of housing  52 , and a closed position in which compressed air flowing through first fluid line  80  is prevented from flowing to first region  60 . Third valve  86  may be disposed within first inlet  82 . Similarly, a fourth valve  88  is associated with second inlet  85  of housing  52  and may be movable between an open position in which compressed air flowing through second fluid line  84  is allowed to flow to second region  62  of housing  52 , and a closed position in which compressed air flowing through second fluid line  84  is prevented from flowing to second region  62 . Fourth valve  88  may be disposed within second inlet  85 . It will be appreciated that third and fourth valves  86 ,  88  could be solenoid valves, for example. 
     With reference to  FIG. 1, 7, 8   a ,  8   b , panel-cleaning device  26  includes a carriage  90 , one or more nozzles or outlet slots  91  ( FIG. 1 ), and an optional wiper blade  92  ( FIGS. 7 a , 8 a , and 8 b   ). Panel-cleaning device  26  may be an air knife which generates high intensity airflow to blow off liquid and debris from the PV panels  12 . Carriage  90  has a first end  93   a  that is mechanically coupled to sliding carriage  42  of first actuator  22 , which engages a C-shaped track of housing  36  and a second end  93   b  that is mechanically coupled to sliding carriage  56  of second actuator  24 , which engages a C-shaped track of housing  52 . That is, first end  93   a  is positioned on and supported by a top surface of carriage  42  and is coupled to carriage  42  via fasteners (e.g., screws, bolts, and/or rivets) extending through a lower surface of first end  93   a  and the top surface of carriage  42 . Similarly, second end  93   b  is positioned on and supported by a top surface of carriage  56  and is coupled to carriage  56  via fasteners (e.g., screws, bolts, and/or rivets) extending through a lower surface of second end  93   b  and the top surface of carriage  56  ( FIG. 6 ). In this way, movement of pistons  40 ,  54  of actuators  22 ,  24 , respectively, also moves carriage  90  along panel array  11 . In some configurations, first end  93   a  is magnetically coupled to carriage  42  and second end  93   b  is magnetically coupled to carriage  56 . That is, a first magnet is coupled to the lower surface of first end  93   a  and a second magnet is coupled to the top surface of carriage  42 . In this way, the first magnet produces a magnetic force urging the second magnet towards it thereby coupling first end  93   a  and carriage  42  to each other. Similarly, a third magnet is coupled to the lower surface of second end  93   b  and a fourth magnet is coupled to the top surface of carriage  56 . In this way, the third magnet produces a magnetic force urging the fourth magnet towards it thereby coupling second end  93   b  and carriage  56  to each other. Alternatively, a first magnet can be located at the top surface of carriage  42  and magnetic material at the bottom surface of the end  93   a , and a second magnet can be located at the top surface of carriage  56  and magnetic material at the lower surface of the end  93   b.    
     One or more sensors  97  are coupled to carriage  90  and are configured to continuously or intermittingly scan PV panels  12  to detect fluid or debris located on PV panels  12  as carriage  90  moves along PV panels  12 . Sensors  97  may be optical sensors, for example, disposed along a length of carriage  90 , and may be passive or active optical sensors. This data is communicated to controller  28  and used at least in part to determine the cleaning cycle of system  10 . Stated differently, movement of pistons  40 ,  54  may be based at least in part on the data provided by sensors  97 . For example, sensors  97  are able to scan and detect the debris size and type located on PV panels  12 . In this way, pistons  40 ,  54  are operated to slow down or stop at a particular location, so that compressed air discharged from nozzles  91  is directed at the debris until it is removed from PV panels  12 . 
     As shown in  FIG. 1 , a manifold  96  is associated with the carriage  90  and includes an inlet  98  and a plurality of outlets  100 . That is, manifold  96  can be disposed within carriage  90 , for example. A fluid passageway  102  extends from second outlet  34  of storage tank  20  to inlet  98  of manifold  96 . A valve  104  is disposed along fluid passageway  102  and is movable between an open position in which compressed air flowing through fluid passageway  102  is allowed to flow to manifold  96 , and a closed position in which compressed air flowing through fluid passageway  102  is prevented from flowing to manifold  96 . 
     Each nozzle  91  is in fluid communication with a respective outlet  100  of manifold  96 . Each nozzle  91  is also configured to entrain surrounding compressed air and direct the compressed air to the panel array  11  to clean the PV panels  12 . Each nozzle  91  is designed and positioned such that nozzles  91  clean fluid or debris such as dirt, pollen, or dust, for example, located on panels  12  without touching panels  12 . That is, each nozzle  91  is spaced apart from panels  12  approximately 1-5 millimeters (mm). As shown in  FIG. 7 b   , nozzles  91  generate a uniform sheet of laminar airflow to blow off liquid and debris from the PV panels  12 . The uniform sheet of laminar airflow discharged from nozzles  91  attaches to a surface of the PV panels  12  using the Coand{hacek over (a)} effect. 
     The pressure of compressed air discharged from each nozzle  91  is lower than the pressure of compressed air stored in storage tank  20 . The pressure and flow rate of compressed air discharged from each nozzle  91  are controlled so that maximum cleaning efficiency of the panels  12  is achieved for a particular location. That is, the pressure and flow rate of compressed air discharged from each nozzle  91  are controlled based in part on the debris size and type and ambient conditions (e.g., ambient temperature and humidity). In some configurations, a heating element may be located along fluid passageway  102  to heat compressed air flowing therethrough. In this way, the compressed air discharged from each nozzle  91  is able to melt ice or snow that has accumulated on panels  12 . 
     A fluid line  105  extends from fluid passageway  102  to an inlet  106  of wiper blade  92 . In some configurations, fluid line  105  extends from storage tank  20  to wiper blade  92 . A valve  108  is associated with inlet  106  of wiper blade  92  and is movable between an open position in which compressed air flowing through fluid line  105  is allowed to flow to wiper blade  92 , and a closed position in which compressed air flowing through fluid line  105  is prevented from flowing to wiper blade  92 . Valve  108  can be disposed within inlet  106 , for example. 
     With reference to  FIGS. 7 a , 7 b , 8 a , and 8 b   , wiper blade  92  is removably coupled to and supported by a leading edge  107  of carriage  90  and extends substantially a length of carriage  90 . In some configurations, wiper blade  92  can be removably coupled to carriage  90  via fasteners. In other configurations, wiper blade  92  can be removably coupled to carriage  90  via adhesive attachment means. Wiper blade  92  is also made of an inflatable material. In some configurations, wiper blade  92  is made of polyvinyl chloride (PVC), urethane, textile reinforced urethane plastic, rubber, thermoplastic or polyurethane, for example. Wiper blade  92  is operable between a first state (inflated state) in which compressed air flows to a cavity  109  of wiper blade  92  to inflate wiper blade  92 , and a second state (deflated state) in which compressed air is purged from wiper blade  92 . When wiper blade  92  is in the first state, an outer surface  110  of wiper blade  92  contacts PV panels  12 . In this way, wiper blade  92  is able to remove debris located on the PV panels  12  as carriage  90  moves along PV panels  12 . When wiper blade  92  is in the second state, valve  108  purges compressed air within cavity  109  to ambient surroundings thereby causing wiper blade  92  to deflate and become spaced apart from PV panels  12   
     Outer surface  110  of hollow wiper blade  92  is coated with micro fabrics  111  to provide for a soft and flexible contact between wiper blade  92  and PV panels  12 . In some configurations, only a portion of hollow wiper blade  92  that comes in contact with PV panels  12  is coated with micro fabrics  111 . Micro fabrics  111  can be made of compositions of polyester and polyamide. For example, micro fabrics  111  can be 80% polyester and 20% polyamide, 50% polyester and 50% polyamide, or 90% polyester and 10% polyamide. Micro fabrics  111  have a thickness in the range of 1-20 mm, more preferably 2-5 mm, deposited on outer surface  110  of wiper blade  92 . Micro fabrics  111  are glued (laminated with glue and heat) on wiper blade  92 . Optionally, micro fabrics  111  can be attached with clips or other fastening mechanisms on wiper blade  92 . 
     As shown in  FIG. 9 , controller  28  is in communication with compressor  18 , actuators  22 ,  24 , panel-cleaning device  26 , valves  67 ,  76 ,  78 ,  86 ,  88 ,  104 ,  108 , sensors  49 ,  59 ,  65 ,  71 ,  81 ,  83 ,  97 , and an inverter  113 . Controller  28  can control operation of compressor  18 , actuators  22 ,  24  and device  26 , and can open and close valves  67 ,  76 ,  78 ,  86 ,  88 ,  104 ,  108 . 
     A mobile device  114  (e.g., a tablet, a smartphone, a laptop, or other similar device) includes a processor that is configured to execute instructions stored in a nontransitory computer-readable medium, such as a read-only memory (ROM) and/or random-access memory (RAM). Mobile device  114  includes a software application  116 . The functions of the software application  116  is accessed using, for example, native application editions of the software and/or web applications of the software. Mobile device  114  and controller  28  are configured to, using the software application  116 , communicate via wireless communication protocol, which includes an internet, Wi-Fi, Bluetooth®, or cellular connection or any other wireless communication protocol, for example. In this way, a user may control operations of system  10  using mobile device  114 . 
     With reference to  FIG. 10 , a flowchart illustrating exemplary software control logic  200  is shown. Control logic  200  begins at  204  when the system  10  is activated. The system  10  may be activated, for example, in response to 1) inverter  113  indicating a predetermined threshold decrease in electricity generation, 2) an operator sending a cleaning command to controller  28  via mobile device  114 , 3) one or more sensors  49 ,  59 ,  65 ,  71 ,  81 ,  83 ,  97  detecting fluid or debris on panel array  11 , or 4) a preset schedule to clean panel array  11 . 
     At  208 , control logic  200  determines, using controller  28 , whether wiper blade  92  needs to be inflated. For example, wiper blade  92  may need to be inflated to remove certain fluid or debris detected by sensors  49 ,  59 ,  97 . In another example, the operator may select an option to inflate wiper blade  92  when sending the cleaning command to controller  28  via mobile device  114 . If so, control logic  200  proceeds to  212 ; otherwise, control logic  200  proceeds to  216 . At  212 , control logic  200  provides, using controller  28 , compressed air from storage tank  20  to wiper blade  92 . That is, controller  28  moves valve  108  from the closed position to the open position. In this way, compressed air from storage tank  20  flows to wiper blade  92  so that wiper blade  92  is inflated. 
     At  216 , control logic  200  provides, using controller  28 , compressed air from storage tank  20  to actuators  22 ,  24 . For example, to clean an upper portion of panel array  11 , valves  67 ,  78 ,  88  are each moved from the closed position to the open position and valves  76 ,  86  are each moved from the open position to the closed position, so that compressed air from storage tank  20  flows to regions  48 ,  62  of actuators  22 ,  24 , respectively, thereby exerting a force on pistons  40 ,  54  to cause pistons  40 ,  54  and panel-cleaning device  26  to move in a second direction Y 2  along panel array  11 . Compressed air contained in regions  46 ,  60  of actuators  22 ,  24  are purged to ambient surroundings. It is understood that valves  67 ,  76 ,  78 ,  86 ,  88  may be moved simultaneously or in a sequence (e.g., moving valves  76 ,  86  to the closed position, then moving valve  67  to the open position, and finally moving valves  78 ,  88  to the open position). 
     To clean a lower portion of panel array  11 , valves  67 ,  76 ,  86  are each moved from the closed position to the open position and valves  78 ,  88  are each moved from the open position to the closed position, so that compressed air from storage tank  20  flows to regions  46 ,  60  of actuators  22 ,  24 , respectively, thereby exerting a force on pistons  40 ,  54  to cause pistons  40 ,  54  and panel-cleaning device  26  to move in a first direction Y 1  along panel array  11 . Compressed air contained in regions  48 ,  62  of actuators  22 ,  24  are purged to ambient surroundings. It is understood that valves  67 ,  76 ,  78 ,  86 ,  88  may be moved simultaneously or in a sequence (e.g., moving valves  78 ,  88  to the closed position, then moving valve  67  to the open position, and finally moving valves  76 ,  86  to the open position). 
     At  220 , control logic  200  determines, using controller  28 , whether the speed of panel-cleaning device  26  needs to be adjusted. For example, data obtained via one or more sensors  49 ,  59 ,  65 ,  71 ,  81 ,  83 ,  97  is communicated to controller  28  so that controller  28  can increase or decrease speed of panel-cleaning device  26 . That is, if sensors  49 ,  59 ,  97  detect heavy debris on panels  12  then the speed of panel-cleaning device  26  may be decreased. If sensors  49 ,  59 ,  97  detect little or no debris on panels  12  then the speed of panel-cleaning device  26  may be increased. If so, control logic  200  proceeds to  224 ; otherwise, control logic  200  proceeds to  228 . 
     At  224 , control logic  200  adjust, using controller  28 , the position of valves  78 ,  88  to increase or decrease the speed of panel-cleaning device  26  in a second direction Y 2  along panel array  11 , or the position of valves  76 ,  86  to increase or decrease the speed of panel-cleaning device  26  in a first direction Y 1  along panel array  11 . At  228 , control logic  200  provides, using controller  28 , compressed air from storage tank  20  to nozzles  91 . That is, controller  28  moves valve  104  from the closed position to the open position, so that compressed air from the storage tank  20  flows to nozzles  91  where it is directed to the PV panels  12  to clean the PV panels  12 . The control logic  200  then proceeds to  236  and ends. The system  10  ends when, for example, a stop command is generated from controller  28 . The stop command may be generated based on data from sensors  49 ,  59 ,  65 ,  71 ,  81 ,  83 ,  97 , or based on the ending of the predetermined cleaning cycle. In some configurations, the stop command may be generated based on a system fault detection being activated, or an operator manually stopping the cleaning cycle. 
     System  10  of the present disclosure provides the benefit of cleaning PV panels  12  without using rotating parts or liquids such as water. Another benefit of panel cleaning system  10  is that it is a low maintenance system without the need of human involvement for operations. 
     With reference to  FIGS. 11 and 12 , another system  310  is provided. The structure and function of system  310  may be similar or identical to system  10  described above, apart from any exception noted below. 
     As shown in  FIG. 11 , system  310  includes a compressor  318 , a storage tank  320 , a first actuator  322 , a second actuator  324 , a panel-cleaning device  326 , and a programmable controller or processor  328  ( FIG. 12 ) configured to execute instructions stored in a nontransitory computer-readable medium. The structure and function of compressor  318 , storage tank  320 , first actuator  322 , second actuator  324 , and panel-cleaning device  326  may be similar or identical to that of compressor  18 , storage tank  20 , first actuator  22 , second actuator  24 , and panel-cleaning device  26  respectively, described above, and therefore, will not be described again in detail. 
     Panel-cleaning device  326  includes a carriage  390  and a plurality of nozzles or slots  391 . Carriage  390  has a first end  393   a  that is mechanically coupled to first actuator  322  and a second end  393   b  that is mechanically coupled to second actuator  324 . In this way, movement of pistons of actuators  322 ,  324 , also moves carriage  390  along panel array. 
     Each nozzle  391  is coupled to and supported by carriage  390 . Each nozzle  391  is designed and positioned such that nozzles  391  clean fluid or debris such as dirt, pollen, or dust, for example, located on the panel array without touching the panel array. That is, each nozzle  391  is spaced apart from the panel array. 
     A first fluid passageway  340  extends from an outlet  342  of storage tank  320  to a first nozzle  391   a  of nozzles  391 . A first valve  343  is disposed along first fluid passageway  340  and is movable between an open position in which compressed air flowing through first fluid passageway  340  is allowed to flow to first nozzle  391   a , and a closed position in which compressed air flowing through first fluid passageway  340  is prevented from flowing to first nozzle  391   a . A second fluid passageway  346  extends from first fluid passageway  340  at a location between outlet  342  and first valve  343  to a second nozzle  391   b  of nozzles  391 . A second valve  348  is disposed along second fluid passageway  346  and is movable between an open position in which compressed air flowing through second fluid passageway  346  is allowed to flow to second nozzle  391   b , and a closed position in which compressed air flowing through second fluid passageway  346  is prevented from flowing to second nozzle  391   b.    
     A third fluid passageway  350  extends from first fluid passageway  340  at a location between outlet  342  and first valve  343  to a third nozzle  391   c  of nozzles  391 . A third valve  352  is disposed along third fluid passageway  350  and is movable between an open position in which compressed air flowing through third fluid passageway  350  is allowed to flow to third nozzle  391   c , and a closed position in which compressed air flowing through third fluid passageway  350  is prevented from flowing to third nozzle  391   c . As shown in  FIG. 12 , controller  328  is in communication with compressor  318 , actuators  322 ,  324 , panel-cleaning device  326 , and valves  348 ,  343 ,  352 . Controller  328  can control operation of compressor  318 , actuators  322 ,  324  and device  326 , and can open and close valves  348 ,  343 ,  352 . 
     System  310  provides the benefit of allowing the compressed air directed from one of nozzles  391   a ,  391   b ,  391   c  to be controlled independently of the other nozzles  391   a ,  391   b ,  391   c . In this way, compressed air is allowed to be focused on a smaller area of panel array that needs cleaning. 
     With reference to  FIGS. 13-15 , another system  410  is provided. The structure and function of system  410  may be similar or identical to systems  10 ,  310  described above, apart from any exception noted below. 
     As shown in  FIG. 13 , system  410  includes a compressor  418 , a storage tank  420 , a first actuator  422 , a second actuator  424 , a panel-cleaning device  426 , and a programmable controller or processor  428  configured to execute instructions stored in a nontransitory computer-readable medium ( FIG. 15 ). The structure and function of compressor  418 , storage tank  420 , first actuator  422 , and second actuator  424 , may be similar or identical to that of compressor  18 , storage tank  20 , first actuator  22 , and second actuator  24 , respectively, described above, and therefore, will not be described again in detail. 
     Panel-cleaning device  426  includes an actuator  460  and a nozzle  462 . With reference to  FIGS. 13 and 14 , actuator  460  is a rodless pneumatic linear actuator and includes a housing  463 , a piston  464  ( FIG. 14 ), and a carriage  466  ( FIG. 13 ). Housing  463  includes a first end  468  mechanically coupled to a carriage of first linear actuator  422  and a second end  470  mechanically coupled to a carriage of second linear actuator  424 . In some configurations, first end  468  may be magnetically coupled to the carriage of first linear actuator  422  and second end  470  may be magnetically coupled to the carriage of second linear actuator  424 . Piston  464  is movably disposed within a cavity  472  of housing  463  and separates cavity  472  into a first region  474  and a second region  476 . Carriage  466  is mechanically or magnetically connected to piston  464  so that carriage  466  and piston  464  move relative to housing  463 . 
     One or more sensors  478  are associated with housing  463  and are configured to continuously or intermittingly scan a panel array to detect fluid or debris located on the panel array. Sensors  478  may be optical sensors, for example, and may be passive or active optical sensors. This data is communicated to controller  428  and used at least in part to determine the cleaning cycle of system  410 . Stated differently, movement of piston  464  (and carriage  466 ) may be based at least in part on the data provided by sensors  478 . For example, sensors  478  are able to scan and detect the debris size and type located on the panel array. In this way, piston  464  is operated to slow down or stop at a particular location so that compressed air discharged from nozzle  462  is directed at the debris until it is removed from the panel array. 
     A first fluid passageway  430  extends from a first outlet  431  of storage tank  420  to a first inlet  432  of housing  463  of actuator  460 . A second fluid passageway  434  extends from first fluid passageway  430  to a second inlet  438  of housing  463  of actuator  460 . A first valve  440  is associated with first inlet  432  of housing  463  and is movable between an open position in which compressed air flowing through first fluid passageway  430  is allowed to flow to region  476  of housing  463 , and a closed position in which compressed air flowing through first fluid passageway  430  is prevented from flowing to region  476 . First valve  440  may be disposed within first inlet  432 . Similarly, a second valve  444  is associated with second inlet  438  of housing  463  and may be movable between an open position in which compressed air flowing through second fluid passageway  434  is allowed to flow to region  474  of housing  463 , and a closed position in which compressed air flowing through second fluid passageway  434  is prevented from flowing to region  474 . Second valve  444  may be disposed within second inlet  438 . 
     A third valve  448  is disposed along first fluid passageway  430  and is movable between an open position in which compressed air is allowed to flow through first fluid passageway  430 , and a closed position in which compressed air is prevented from flowing through first fluid passageway  430 . A fourth valve  456  is disposed along second fluid passageway  434  and is movable between an open position in which compressed air is allowed to flow through second fluid passageway  434 , and a closed position in which compressed air is prevented from flowing through second fluid passageway  434 . 
     Nozzle  462  is coupled to and supported by carriage  466 . Nozzle  462  is designed and positioned such that nozzle  462  cleans fluid or debris such as dirt, pollen, or dust, for example, located on the panel array without touching the panel array. That is, nozzle  462  is spaced apart from the panel array and directs compressed air to the panel array to clean the panel array. A third fluid passageway  452  extends from a second outlet  454  of storage tank  420  to nozzle  462 . A fifth valve  450  is disposed along third fluid passageway  452  and is movable between an open position in which compressed air flowing through third fluid passageway  452  is allowed to flow to nozzle  462 , and a closed position in which compressed air flowing through third fluid passageway  452  is prevented from flowing to nozzle  462 . 
     Controller  428  is in communication with compressor  418 , actuators  422 ,  424 ,  460 , valves  440 ,  444 ,  448 ,  450 ,  456 , and sensor  478 . Controller  428  can control operation of compressor  418 , actuators  422 ,  424 ,  460 , and can open and close valves  440 ,  444 ,  448 ,  450 ,  456 . 
     Valves  440 ,  448  are each moved from the closed position to the open position so that compressed air from storage tank  420  flows to region  476  of actuator  460  thereby exerting a force on piston  464  to cause piston  464  and carriage  466  to move in a first lateral direction X 1  along the panel array. Compressed air contained in region  474  of actuator  460  is purged to ambient surroundings. Similarly, valves  444 ,  456  are each moved from the closed position to the open position so that compressed air from storage tank  420  flows to region  474  of actuator  460  thereby exerting a force on piston  464  to cause piston  464  and carriage  466  to move in a second lateral direction X 2  along the panel array. Compressed air contained in region  476  of actuator  460  is purged to ambient surroundings. 
     System  410  provides the benefit of allowing nozzle  462  to move laterally along the panel array. In this way, compressed air is allowed to be focused on a smaller area of the panel array that needs cleaning. 
     While various embodiments have been disclosed, other variations are envisioned. For example, linear actuators  22 ,  24  may be single acting actuators as opposed to double acting actuators. Furthermore, actuator  22  may be replaced with a rail and sliding guide member and the sliding guide member may be attached to panel-cleaning device  26 . In this way, the sliding guide member may slide along the rail when actuator  24  moves the panel-cleaning device  26  along panel array  11 . It is also envisioned that the PV panels may be supported within frames which have posts mounted to the ground, or which are mounted on top of a vehicle parking roof or the like, or floating on water instead of the roof mounting illustrated, such that the present cleaning apparatus is mounted to such a frame or associated peripherally located structure. Furthermore, a blower can be used to run the nozzles for cleaning the PV panels instead of compressed air from the storage tank. Furthermore, features from one embodiment can be interchanged with features of another embodiment disclosed hereinabove, and the claims can be multiply dependent on each other in any combination. Variations are not to be regarded as a departure from the present disclosure, and all such modifications are intended to be included within the scope and spirit of the present invention.