FIELD OF THE INVENTION The present invention relates to the use of unmanned aerial vehicles (UAV) or drones for the positioning of wind turbine components, for example during assembly and maintenance.

BACKGROUND OF THE INVENTION

Wind turbines are large structures which comprise many large and heavy

components such as generating equipment, tower segments, wind turbine blades and so on. Wind turbine components may need to be transported. Additionally, the components may need to be positioned more precisely on site. For example the component may need to be lifted, translated and oriented relative to other components during assembly of the wind turbine and/or disassembly for maintenance. This presents several challenges, particularly in harsh environments such as offshore wind systems.

Existing systems for positioning wind turbine components involve the use of cranes or similar heavy lift plant equipment and with bulky support structures. Such equipment may need to be sized greater than the height of the wind turbine tower in order to position the components onto the tower. Furthermore, these systems may require highly skilled manual control. These methods can be inefficient and potentially dangerous for the technicians involved.

It is against this background that the embodiments of the invention have been devised to provide improved, more efficient, safe, and cost effective approaches for positioning wind turbine components for the purposes of assembly and

maintenance. SUMMARY

According to an aspect of the invention there is provided a power supply system for at least one unmanned aerial vehicle. The system comprises a remote power supply and a tethering system. The tethering system comprises at least one umbilical cable having a first end connectable to an unmanned aerial vehicle and a second end operably connected to the remote power supply for providing power to said unmanned aerial vehicle via the umbilical cable and a support arrangement for supporting the second end of the umbilical cable at a predetermined height above the ground.

The at least one umbilical cable may have a length equal to or larger than the predetermined height at which it is supported. In embodiments, the predetermined height may be above 10 metres for example above 20 or 40 metres.

The support arrangement may comprise a mast. For example, the mast may be a telescopic mast configured to vary the height at which it supports the second end of said at least one umbilical cable. Additionally or alternatively the support

arrangement may vary the height by other means, for example using inflatable, concertina or bellows structures.

The support arrangement may be mounted to a land based or marine based vehicle.

In some embodiments, the support arrangement comprises a tower of a wind turbine.

Additionally or alternatively the support arrangement may comprise an auxiliary unmanned aerial vehicle. For example, the auxiliary unmanned aerial vehicle may carry the second end of the umbilical cable. The auxiliary unmanned aerial vehicle may comprise a rotorcraft or a balloon for example. In further embodiments, the support arrangement may comprise multiple auxiliary unmanned aerial vehicles.

The tethering system may be configured such that the auxiliary unmanned aerial vehicle can draw power from the remote power supply for its own propulsion. The auxiliary unmanned aerial vehicle may comprise a power connector for each umbilical cable and the power connector may be configured for receiving the second end of said at least one umbilical cable.

The system may further comprise a power outlet cable for providing power from the remote power supply to the auxiliary aerial vehicle and one or more umbilical cables. The auxiliary unmanned aerial vehicle may be configured to receive power from the remote power supply via the power outlet cable and distribute the power to the unmanned aerial vehicle via the one or more umbilical cables.

The system may further comprise a plurality of unmanned aerial vehicles each comprising a power connector for receiving the one or more umbilicals such that each unmanned aerial vehicle receives power form the remote power supply via the auxiliary aerial vehicle.

The tethering system may further comprise a tethering dispenser configured to dispense or retract the umbilical cable and/or power outlet cable. The power supply may be an electrical power supply and the umbilical cable comprises electrical power cables. For example, the power supply may be ground based generator or battery.

In some embodiments, the at least one unmanned aerial vehicle may comprise a combustion engine and the umbilical cable comprises a duct for transporting fuel to the engine.

The remote power supply may be configured to provide said at least one unmanned aerial vehicle with at least 200kW of power, for example at least 1 MW, at least 2MW or between 5 and 8 MW of power.

The at least one unmanned aerial vehicle may be a rotorcraft, such as a multirotor. According to a further aspect, a method of supplying power to an unmanned aerial vehicle comprises connecting the unmanned aerial vehicle to a remote power supply by a tethering system. The tethering system comprises at least one umbilical cable having a first end connectable to an unmanned aerial vehicle and a second end operably connected to the remote power supply for providing power to said unmanned aerial vehicle via the umbilical cable. The method further comprises supporting the second end of the umbilical cable at a predetermined height above the ground using a support arrangement. The unmanned aerial vehicle and tethering system may have any of the features described in relation to the embodiments above.

In an embodiment of the invention, a method of positioning a wind turbine

component comprises attaching a system according to any of the embodiments described above to the component, powering the unmanned aerial vehicle from the remote power supply via the tether system, generating a command signal to move the unmanned aerial vehicle and positioning the component with the unmanned aerial vehicle.

According to a further aspect, a method of positioning a wind turbine component comprises connecting an unmanned aerial vehicle to a remote power supply via a tethering system, connecting the component to the unmanned aerial vehicle and positioning the component with the unmanned aerial vehicle. The unmanned aerial vehicle and tethering system may have any of the features described in relation to the embodiments above.

Positioning of a wind turbine component may include lifting the component, moving to another geographical location, orienting the component, positioning the

component for assembly or dismantling the wind turbine. The wind turbine component may comprise a load of greater than 100kg, for example, greater than 200kg, 400kg or 600kg and may be one of a wind turbine blade, rotor hub, gear box, tower component. According to a further aspect, a system for positioning a wind turbine component comprises an unmanned aerial vehicle, an attachment means for attaching the wind turbine component to the unmanned aerial vehicle, a remote power supply for supplying power to the unmanned aerial vehicle to lift the component and

a tether system comprising an umbilical cable connecting the unmanned aerial vehicle to the remote power supply. The remote power supply provides power to the unmanned aerial vehicle via the tether system.

A further aspect of the invention relates to the use of a power supply system for at least one unmanned aerial vehicle during positioning of a wind turbine component. The system comprises a remote power supply and a tethering system comprising at least one umbilical cable having a first end connectable to an unmanned aerial vehicle and a second end operably connected to the remote power supply for providing power to said unmanned aerial vehicle via the umbilical cable and a support arrangement for supporting the second end of the umbilical cable at a predetermined height above the ground.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows a tethered drone positioning a wind turbine blade according to an embodiment of the present invention;

Figure 2 is a block diagram representing a control system associated with a drone; Figure 3 shows an example ground station for control of a drone;

Figure 4 shows a system positioning a component and including a tether support; Figures 5a-c show the system of Figure 4 at varying stages of deployment;

Figures 6 and 7 show example guidance systems for positioning a wind turbine blade relative to a nacelle;

Figures 8-1 1 show alternative tether supports; Figures 12a and 12b show a further embodiment in which two UAVs are used to position a wind turbine blade; Figure 13 shows a further embodiment in which a swarm of drones is used to position a wind turbine blade;

Figure 14 shows a yet further embodiment in which a swarm of drones is used to position a wind turbine blade.

DETAILED DESCRIPTION

In general, the present invention relates to the use of one or more tethered unmanned aerial vehicles (UAV), also referred to as drones, for the positioning of wind turbine components. Although the embodiments described below relate to positioning of a wind turbine blade, it will be appreciated that the described systems could also be used to move other large and heavy components such as wind turbine generating equipment, tower segments, gear boxes and the like. For brevity, this discussion will refer to a 'drone' as any type of unmanned air vehicle, be it a relatively small-scale rotorcraft such as a multirotor, for example a tricopter, quadcopter, pentacopter, hexacopter, octocopter or a larger-scale unmanned helicopter. Figure 1 shows an embodiment of the invention in which a tethered drone 10 is used to move a wind turbine rotor blade 12. As shown in Figure 1 , the drone 10 is coupled to the blade 12 via an attachment means 14 such that upward movement of the drone 10, in the direction indicated by the arrow 16, lifts the blade 12 upwards with it. Likewise, horizontal movement of the drone 10 results in corresponding horizontal movement of the blade 12. In the illustrated embodiment, the attachment means 14 comprises a clamp 18 which engages the outer surface 20 of the blade12. The clamp 18 includes a frame 22 which applies a clamping force to a plurality of pads 24 which contact the blade surface 20 to prevent slippage of the blade 12 relative to the frame 22 during flight. The attachment means 14 further comprises a plurality of tension elements 26. Each tension element 26 extends from the frame 22 to the drone 10 in order to transfer the load of the blade 12 to the drone 10. The tension elements 26 may be heavy-duty ropes, belts, rods or chains. It will be appreciated that other forms of attachment means may be used to couple the drone 10 to a component that is to be positioned depending on the weight and dimensions of the component.

The illustrated drone 10 is a rotorcraft, having a plurality of rotors 28 for generating lift. For example the drone 10 may comprise two or more counter-rotating rotors 28 such as four, five, six or eight rotors 28. In the embodiment of Figure 1 , for example, the drone 10 is an eight rotor multirotor, also known as an octocopter. Variation in the speed of each rotor 28 of the drone 10 controls the speed and direction of flight. In alternative embodiments, the drone 10 may include one or more fixed wings and/or one or more rotary blades or rotors. Any suitable drone structure may be used, ducted fan drones may be particularly suited to lifting applications, for example. The drone 10 is desirably capable of vertical take-off and landing (VTOL) or, at least, point take-off and landing (PTOL) to facilitate accurate positioning of the component. The drone 10 is associated with a flight control system to control movement of the drone. Such systems are known in the art and one such system is shown

schematically in Figure 2.

Figure 2 illustrates a system diagram of a typical drone system 10 which may be used in any of the described embodiments. The drone system 10 includes a control system 32, one or more propulsion units 34, a power system 52, a communication system 38, a sensor suite 40, a mission planning system 42 and a navigation system 44. The drone system 10 may be operated in conjunction with a ground-or base- station computer system 46, hereinafter referred to as the 'ground-station', which will be described in more detail later with reference to Figure 3.

Movement of the drone 10 may be controlled according to a variety of inputs relating to current state of the drone 10 and desired state of drone 10. The control system 32 receives data from various inputs and processes the data to produce a command signal to the rotors 28. The control system 32 may be autonomous or may require some level of operator control.

The control system 32 is the main computing unit that controls the flight of the drone 10 by controlling the propulsion units 34 based on inputs from the sensor suite 40 and navigation system 44. The control system 32 may implement remote control flight based on received control inputs from a ground based controller, autonomous flight, based on its internal mission planning algorithms, or semi-autonomous flight, in which a blend of on-board mission planning and ground based direction are used. The main responsibility of the control system 32 is as a lower layer controller which is responsible for positional control of the drone 10 (altitude and lateral position), attitude control (pitch, roll and yaw), and velocity control (horizontal and vertical speed) based on remote control actions or based on self-generated flight directions. The control system 32 comprises a suitable processing environment having a processor and a memory with associated on-board communications functionality, such as a data bus, so it is able to communicate with other on-board systems.

The control system 32 controls movement of the drone 10 by distributing power between propulsion units 34 of the drone 10. Figure 2 shows four propulsion units 34 as would be present in a quadcopter, for example. However it will be appreciated that the teaching could be applied to other propulsion configurations as discussed above. In embodiments, the propulsion units 34 may include electric motors each driving a respective rotor 28. Alternatively, the propulsion units 34 may be engines such as turbine engines or internal combustion engines which produce thrust using rotors, jets or any other means known in the art.

The communication system 38 provides the means to send and receive data to and from systems that are external to the drone 10. For example, the drone 10 may send telemetry data to the ground station 46, and may send positional, attitude and velocity data to other drones operating in the area, either as part of a drone swarm or operated independently. The communication system 38 may also receive data from external systems, and in this context it may receive remote control commands from the ground station 46 if the drone 10 is operated in remote control flight mode.

Alternatively it may upload mission data from the ground station 46. The communication system 38 also permits incoming and outgoing communication with other drones so that flight paths and mission objectives can be coordinated with them to achieve a collective goal. The sensor suite 40 is operably connected to the control system 32 and provides appropriate sensor data to assist with the operation of the drone. For example, the sensor suite may comprise proximity detectors, a global navigation satellite system/global positioning system (GNSS/GPS) unit for positioning control, optical still and video cameras for carrying out inspection and guidance tasks, inertial navigation systems to name a few examples. Typically such a sensor suite 40 would be adaptable to carry more or fewer sensors as required for a particular task. Note that in this context the GPS unit 48 may receive signals directly from satellites in order to fix the position of the drone, although another option would be to implement a differential GPS system (known in the art) which receives signals from a ground- based differential GPS beacon in order to provide a higher positional accuracy compared to direct GPS. Note that a GPS unit 48 is shown here as integral with the navigation system.

The sensor suite 40 may provide information to the control system 32 relating to the current state e.g. position and orientation of the drone 10. The sensor suite 40 comprises a plurality of sensors 50 which may detect absolute position, orientation, relative position etc. of the drone 10. The sensors 50 may include optical sensors, radar, radio frequency sensors or the like. The sensors 50 may also be used to detect properties of the drone payload during flight, for example sensors 50 may measure the position and orientation of the component during flight. For example, where the component to be positioned is a rotor blade which needs to be mounted onto a wind turbine nacelle, the sensor suite may include one or more optical sensors for detecting the position of the root of the blade relative to the hub of the nacelle into which it is to be installed. The optical sensors may be mounted to the drone, blade and/or hub as will be described in more detail in relation to Figures 6 and 7 below. The mission planning system 42 provides a link to the ground station 46 to store missions that have been generated thereon and to which the drone 10 follows in use. The mission planning system 42 may include suitable memory storage and

algorithms to store, provide and generate on the fly appropriate mission objectives, waypoints, operational envelopes and so on.

The navigation system 44 provides control inputs to the control system 32 regarding path following based on input from the GPS 48 and/or the sensor suite 40. In embodiments where the drone flight is automated, the navigation system 44 may execute a predetermined map of flight. Alternatively, the navigation system 44 may be controlled remotely and may require user input such as steering commands. In embodiments, the system also includes GPS 48 to provide positioning information to the navigation system 44. The control system 32 distributes power provided by a remote power supply

52. The power supply 52 used depends on power requirements of the propulsion units 34. In embodiments where the propulsion units 34 are electric motors, the power supply 52 may supply electrical power, for example by a battery or electrical generator. In embodiments, the power supply 52 may supply electrical power via high voltage cables. Accordingly, the drone may include a voltage reducing transformer and cooling apparatus. In embodiments where the propulsion units 34 are turbine engines or fuel cells, the power supply may be a fuel source supplying fuel power via fuel conduits. The power supply 52 is positioned remotely from the drone 10. More particularly, the power supply 52, which supplies the majority of power for lifting the component 12, is not stored on the body of the drone 10. In embodiments the power supply 52 is at a fixed position in the ground station 46. The power supply 52 may be mounted to a land-based or marine based vehicle. In the illustrated embodiment, the power supply 52 is mounted on a flatbed lorry. In embodiments, the drone 10 may comprise one or more onboard batteries or auxiliary power units for emergency use, for example if power from the remote power supply 52 is lost via damage to cables or generating equipment. In embodiments, the power supply 52 may form part of the ground station 46. The ground station 46 also provides a ground-based control hub for the one or more drones and is suitable equipped with a computing platform 56 having an appropriate processing module 58 and memory storage 60. The computing platform 56 implements a suitable ground station software package 62 to provide appropriate ground station facilities for controlling and coordinating the one or more drones 10. A user interface 64 is provided to enable to a user/operator to view data relating to the drone system and to input control and parameter data into the ground station 46. The user interface 64 may comprise of a display screen and audio output, and a user input means such as a keyboard, joystick, mouse, on-screen buttons or a

combination of these. The ground station 46 also has a communications system 66 in order to send data to and receive data from the drone 10.

Referring back to Figure 1 , the drone 10 is connected to the remote power supply (not shown) via a tether system 70. The tether system 70 comprises an umbilical 72 that is configured to transmit power to the drone 10 such that it can reposition the component 12 for example by lifting and translating the component 12. The umbilical 72 is in the form of an elongate flexible member that allows a range of motion of the drone 10 relative to the power supply.

In embodiments where the power supply is an electrical power supply the umbilical comprises electrical power cables capable of delivering sufficient power from the electrical power supply to the drone 10 to power flight of the drone 10 and

associated payload. The electrical power cables may be insulated by any means known in the art.

The system is capable of lifting a component of a wind turbine, such as a

blade. Wind turbine components may have a mass in excess of 100kg, for example. As such, in embodiments the one or more drones of the system are provided with sufficient power to lift and manoeuvre loads in excess of 100kg. In embodiments, the power is sufficient to manoeuvre 200kg, 400kg, 600kg or in excess of 1 tonne, for example from 6 to 10 tonnes. The power requirements for lifting such components may be in the order of several hundred kilowatts, for example in excess of 200kW, 400kW, 600kW. In particular embodiments the power requirements for the one or more drones may be in excess of 1 MW, for example up to 5 MW to 8 MW.

Due to the high power requirements of the drone 10, the umbilical 72 may include heavy electrical cables. The weight of the cables may be minimised by use of high voltage (low current) cables however in such embodiments the drone 10 may further require a voltage reducing transformer and associated cooling apparatus may be required in order to provide the motors with suitable electrical power. Furthermore, in embodiments the umbilical 72 may also include data communications cables such as electrical or fibre optic cables forming part of the communication system.

Wind turbine components, such as blades, may need to be positioned at high altitudes. For example, a wind turbine nacelle upon which some components may need to be mounted may be over 80m above ground level, in some cases wind turbine towers may be up to 180m above ground level. As such the length of the umbilical 72 that is required to connect the drone 10 to a ground based power supply could be substantial and may need to be in excess of the height of the tower to allow manoeuvrability of the drone 10 relative to it. The lengthy and heavy cables may therefore exert considerable additional load on the drone 10. As such, the system further comprises a tether support for supporting the umbilical 72 at a predetermined position above the ground thereby reducing the free length of cables and thereby reducing the load the umbilical 72 exerts on the drone 10.

Figure 4 shows an example tether support 80. The system of Figure 4 is

substantially the same as that described in relation to Figure 1. The system includes a drone 10 having an attachment means 14 and a remote power supply 52. A tether system 70 comprising an umbilical 72 connects the drone 10 to the power supply.

The tether system further comprises a support for supporting the umbilical 72 at a position between the drone 10 and power supply. In this embodiment, the power supply and tether support are mounted to a flatbed lorry 74. The drone 10 is also positioned on the lorry 74 prior to attachment to a component and subsequent deployment. The tether support 80 is in the form of a mast that supports the umbilical 72 at a predetermined height hi above the ground. More particularly, the umbilical 72 includes a first end 82 connected to the drone 10 and a second end 84 operably connected to the remote power supply 52. The mast 80 supports the second end 84 of the umbilical 72 at a predetermined height hi above the ground. In embodiments the mast 80 supports the second end 84 at a position of greater than 30 metres above ground level, for example the support may hold the second end at a position of greater than 40 or 50 metres above ground level. In the illustrated embodiment the mast 80 includes a base 86 attached to the flat-bed lorry 74 at approximately ground level and a support end 88 distal from the base 86 at a predetermined height hi . The mast 80 has an adjustable height such that the distance between the base 86 and support end 88 can be varied as required. The mast 80 is in the form of a telescopic mast with a plurality of mast sections 90 that can move relative to each other. In the illustrated embodiment, the mast sections 90 includes a plurality of telescoping tubes each having a circular cross-section and arranged concentrically with each other, although it will be appreciated that tubes having alternative geometry such as tubes having polygonal cross-sections could also be used.

The mast sections 90 are axially moveable relative to one another in order to extend the length of the mast 80 and thereby increase the height hi of the support above the ground. The mast 80 further comprises one or more actuators (not shown) for moving the plurality of mast sections 90 in an axial direction shown by the arrow 92 in order to extend the mast 80. The one or more actuators may be a hydraulic actuator or a ball screw actuator, for example.

Figures 5a-c show the variable height mast 80 of Figure 4 during various stages of deployment. More particularly, Figure 5a shows the mast 80 in an unextended initial condition wherein the mast sections 90 are all nested within each other such that the height h2 of the mast and therefore the height of the support end 88 is equal to the height of the outer section. The mast 90 may be more easily transported between wind turbine sites in the unextended position. Figure 5b shows the mast 80 in an extended condition wherein the inner mast sections 90 are displaced in an axial direction indicated by the arrows 92. In the extended condition, the height hi of the mast 80, and therefore the height of the support 88, is greater than the height h2 of the mast in its unextended condition. In embodiments, the height hi of the mast 80 in the extended condition is at least 10 times the height h2 of the mast 80 in the unextended condition. For example, the height hi of the mast 80 in the extended condition may be at least 15 or 20 times the height h2 of the mast 80 in the unextended condition. Figure 5c shows the system of Figures 5a and 5b during positioning of a wind turbine component 12 relative to a wind turbine. A component 12, in this example a wind turbine blade shown schematically, is attached to the drone 10 and is being lifted to a desired height h3 above ground and then precisely positioned relative to a wind turbine 100 for installation. More particularly the drone 10 is lifting the blade to a height h3 substantially equal to the height of the hub 102 within the nacelle 104 of the wind turbine 100 so that the blade root (not shown) can be attached to the hub 102.

The tether support 80 provides a rigid, structural support for the umbilical 72 at a predetermined height hi above the ground. In the illustrated embodiment the umbilical 72 is supported at a predetermined height hi that is greater than 50% of the desired positioning height h3, in this example the height of the nacelle 104. In embodiments, the umbilical 72 is supported at a height hi that is greater than 20% or 30% of the maximum vertical extent of the drone 10 during flight.

Figure 5c also shows, in phantom, the free length of an umbilical 106 that would be required if the tether support 80 was not present. It will be appreciated that the longer umbilical 106 required would add considerable load to the drone 10 compared to the shorter, supported umbilical 72. The length of the umbilical is preferably equal to or larger than the height hi of the support 80 such that the drone is able to land while the support 80 is in an extended condition.

Once the component 12 has substantially reached the desired vertical height h3, more precise positioning of the component 12 may be achieved using a guidance system including optical sensors, for example optical markers may be placed on either of the hub or blade root and optical sensors may be positioned on the other of the hub or blade root to facilitate precise positioning of the blade root within the hub. It will be appreciated that other types of sensor known in the art may be used additionally or alternatively.

Figures 6 and 7 show example guidance systems according to particular

embodiments. Referring to Figure 6, in one embodiment the guidance system 200 may include a radar transceiver 202. The radar transceiver 202 may be attached to the blade and oriented to point towards the hub 102 of the nacelle 104 so that it views the circular blade root socket on the hub as a target 204. The guidance system 200 will have an appropriate knowledge database to recognise the shape of the hub and provide flight path information to the drone 10 and/or the ground station 46 so that the drone 10 is able to position itself appropriately. Instead of radar, a lidar (Light Detection and Ranging) based guidance system is also considered to be

appropriate.

As an alternative to the above approach, the radar transceiver 202 may instead be positioned in the hub 102 such that the root of the wind turbine blade 12 is the target 104. The guidance system 200 will transmit guide path information to the drone 10 either directly or via the ground station 46, in order to guide the wind turbine component 12 into position.

Figure 7 shows a further alternative embodiment in which the guidance system 300 includes an optical camera 302. The optical camera 302 may be positioned on the blade 12 or in the hub 102 and may be configured to view an appropriate optical target 304. The guidance system 80 therefore is able to recognise the optical target 304 and derive information about the relative distance and orientation of the target 304 in order to provide the drone 10 and/or the ground station 46 with suitable guide path information so that the drone 10 is able to guide the wind turbine component 12 into the desired position.

Although the embodiments above, show a telescopic mast for adjusting the height of the support, it will be appreciated that the height of the support could be adjusted by other means known in the art. For example, the tether support may comprise a plurality of structural members connected to one another via articulated joints in a concertina fashion such motion of the joints causes upward extension of the support in a manner similar to known mobile elevated work platforms or cherry pickers.

Additionally or alternatively the variable support may comprise an inflatable member wherein inflation caused the support to extend upwardly or a bellows member.

Figures 8-1 1 shows alternative tether supports for use alternatively or in addition to the tether support described in the embodiments above.

Figure 8 shows an alternative embodiment of the invention in which a drone 10 is carrying and positioning a wind turbine component 12. The drone 10 is connected to a remote power supply 52 via an umbilical 72 in much the same way as described in relation to the embodiments above. The remote power supply 52 is a ground-based power supply. A tower 106 is positioned between the drone 10 and remote power supply and supports the tether at a height above the ground. The umbilical 72 may extend along the length of the tower 106 for example; the umbilical may be contained within the tower 106 or may extend over an outside surface of it. In the embodiment of Figure 8 the tower 106 has a fixed height hi . The fixed height tower 106 may be formed from any structural material known in the art. For example, the tower 106 may be formed from steel or concrete and may have a similar form to electricity pylons, for example. The tower 106 could be part of an existing structure or building. In embodiments, the tower 106 could be a wind turbine tower. For example, the tower 106 could be a wind turbine tower to which the component is to be mounted or a neighbouring wind turbine tower within the same wind farm.

Figure 9 shows a variation on the embodiment of Figure 8 in which the remote power supply 52 is positioned at the top of the tower 108 and therefore closer to the drone 10 when deployed. Mounting the power supply 52 closer to the drone 10 may require less cabling, thereby reducing material costs and potentially providing a more efficient system. Figure 10 shows an alternative embodiment in which the support comprises a further auxiliary drone 1 10. The system comprises a primary or lifting drone 10 attached to a wind turbine component 12 for positioning it. As in the previous embodiments, the primary drone 10 is connected to a remote power supply 52 via a tether system. An auxiliary drone 1 10 is positioned along the umbilical 72 to support its weight. The auxiliary drone 1 10 comprises a support means 1 12 for engaging and supporting the umbilical 72. In embodiments the support means 1 12 could be a sling in which the umbilical could be held or could be a clamp for engaging the outer surface umbilical 72.

The auxiliary drone 1 10 may comprise an on-board power supply or may also draw power from remote power 52 supply directly or via the tether. In embodiments, the auxiliary drone 1 10 may comprise a plug that co-operates with a socket in the tether or vice versa.

Figures 1 1 show an alternative embodiment comprising two supports for the umbilical 72. This embodiment uses a combination of the supports of Figures 9 and 10. The remote power supply 52 is positioned on the tower of a wind turbine 100 and an auxiliary drone 1 10 further supports the umbilical 72 between the tower 100 and the drone 10 positioning the wind turbine component. In embodiments where the support 108 is a wind turbine tower, existing wind turbine power equipment could be additionally used to power the drone 10. For example, existing voltage switching apparatus could be used. In embodiments, more than one drone may be used to move a wind turbine component. Figures 12a and 12b show a particular configuration wherein two drones 10a, 10b are used to lift a wind turbine blade. More particularly, the system comprises a first drone 10a and a second drone 10b. The first and second drones 10a, 10b are each attached to the wind turbine blade 12 via respective attachment means 14a, 14b. The attachment means 14a, 14b are each in the form of a rope sling that surrounds the blade 12 at respective axial positions. A ground-based remote power supply 52 supplies sufficient power to both the first and second drones 10a, 10b so that they can together lift and manoeuvre the blade 12. The first and second drones 10a, 10b are each connected to the remote power supply via first and second umbilicals 172 a, 172b respectively.

A tether support, in the form of a tower 106, supports both the first and second umbilicals 172a, 172b at a predetermined location hi above the ground to lessen the length of freely moveable cable required.

Figure 13 illustrates an alternative configuration in which a wind turbine blade 12, is being lifted towards the nacelle 104 by a plurality of drones10a-e. In order to connect the drones 10a-e with a remote power supply 52, a tether system 70 is provided. The tether system 70 is configured principally to provide power to the drones but may also convey data to and from the drones if appropriate.

The power supply 52 is supported in an elevated position on the wind turbine nacelle in the same manner as in the embodiments of Figures 9 and 1 1 . As such the mass of the umbilical that needs to be carried by the drone connected to it can be reduced, which increases the payload capacity of the drone. The wind turbine could be replaced by a tower as shown in the embodiment in Figure 8. In the Figure 13 embodiment, the first drone 10a that is connected to the power supply 52 via a first umbilical 272a is configured to provide power to another drone 10b by way of a second umbilical 272b which is connected to a power plug on the drone 10a. The same configuration is used to 'daisy chain' umbilicals 272c, 272d between neighbouring drones 10b-d in the flight formation. The use of multiple drones 10a-d in this way not only distributes the weight of the blade 12 but also distributes the weight of the power cables 272a-d between the drones 10a-d.

Figure 14 shows a further embodiment, in which the first drone 10a (i.e. the drone closest to the power supply) may provide a plurality of power connections for the other drones 10b-d and thereby acts as a power hub. The first drone or 'power hub' drone 10a is preferably not used for lifting the blade 12 rather its sole purpose is to provide a further elevated power plug for powering the 'lifting' drones 10b-d. The 'lifting' drones 10b-d each being coupled with the component 12. As the power is being divided up from the first drone 10a, the current in each umbilical 372b-d extending from the power hub drone 10a to the lifting drones 10b-d is not as high as in the power outlet cable 372a between the power source 52 and first drone 10a. Accordingly the umbilicals 372b-d need not be as heavy-duty and may be lighter than the power outlet cable 372a. In this embodiment the length of the power outlet cable is preferable greater than or equal to the height at which the power supply 52 is supported such that the first drone or 'power hub' drone may land while connected.

In embodiments, multiple power hub drones 10a may be provided to increase the number of lifting drones that may be supplied with power.

In any of the embodiments described above, the umbilical may be provided on a spool or drum to dispense out or retract back in, in dependence on the flight of the drone to further minimize the free length of cabling.