METHOD FOR ASSEMBLING A WIND TURBINE AND A WIND TURBINE SYSTEM

Abstract

A method for assembling a wind turbine, including: attaching an elevator carriage (27) to a nacelle (9) to form a carriage-nacelle assembly (27,9); and mounting the carriage-nacelle assembly (27,9) on to a tower (3) as a unit.

Claims

1-20. (canceled)

21. A vessel including a platform system for transferring a carriage-nacelle assembly or a carriage-rotor-nacelle assembly from the vessel to the side of an offshore wind turbine tower, the platform system comprising a movable platform, a platform control system, at least one actuator and at least one sensor, wherein the platform control system is arranged to control operation of the at least one actuator to adjust an orientation of the movable platform in response to signals received from the at least one sensor to account for movement of the vessel caused by wind and waves while transferring a load to a receiving structure.

22. The vessel according to claim 21, wherein the platform control system is configured to maintain the movable platform substantially motionless relative to the wind turbine tower while transferring the carriage-nacelle assembly or carriage-rotor-nacelle assembly from the vessel to the wind turbine tower.

23. The vessel according to claim 21, wherein the platform control system is configured to maintain the movable platform in a substantially horizontal orientation.

24. The vessel according to claim 21, wherein the movable platform comprises platform rails for transporting the carriage-nacelle assembly or carriage-rotor-nacelle assembly to the wind turbine tower.

25. A wind turbine system comprising the vessel according to claim 21 and the carriage-nacelle assembly or carriage-rotor-nacelle assembly, wherein the carriage-nacelle assembly or carriage-rotor-nacelle assembly comprises an elevator carriage.

26. A wind turbine system comprising the vessel according to claim 25, wherein the elevator carriage comprises at least one carriage support formation for engaging with at least one tower support formation on the wind turbine tower to support the weight of the carriage-nacelle assembly or carriage-rotor-nacelle assembly on the side of the wind turbine tower, the elevator carriage has a rail attachment system for releasably attaching to at least one elevator rail on the wind turbine tower, and the elevator carriage has a drive system for elevating the carriage-rotor-nacelle assembly to the top of the wind turbine tower along the at least one elevator rail on the wind turbine tower.

27. A method of transferring a carriage-nacelle assembly or a carriage-rotor-nacelle assembly from a vessel to an offshore wind turbine tower, the vessel including a platform system comprising a movable platform, a platform control system, at least one actuator and at least one sensor, the method comprising: transporting the carriage-nacelle assembly or carriage-rotor-nacelle assembly to the wind turbine tower with the vessel; manoeuvring the vessel to position the movable platform adjacent a base of the wind turbine tower; supporting the carriage-nacelle assembly or carriage-rotor-nacelle assembly on the movable platform, controlling operation of the at least one actuator with the platform control system to adjust an orientation of the movable platform in response to signals received from the at least one sensor to account for movement of the vessel caused by wind and waves while transferring a load to a receiving structure; and transferring and mounting the carriage-nacelle assembly or carriage-rotor-nacelle assembly to the side of the wind turbine tower.

28. The method of transferring of claim 27, comprising maintaining the movable platform substantially motionless relative to the wind turbine tower while transferring the carriage-nacelle assembly or carriage-rotor-nacelle assembly from the vessel to the wind turbine tower.

29. The method of transferring of claim 27, comprising maintaining the movable platform in a substantially horizontal orientation.

30. The method of transferring of claim 27, comprising transporting the carriage-nacelle assembly or carriage-rotor-nacelle assembly to the wind turbine tower along platform rails on the movable platform.

31. The method of transferring of claim 27, wherein the carriage-rotor-nacelle assembly comprises a rotor having a rotor hub and the method comprises mounting carriage-rotor-nacelle assembly onto the wind turbine tower with the rotor hub orientated generally downwards.

32. The method of transferring of claim 31, wherein the rotor has rotor blades and the method comprises supporting tips of the rotor blades with tensioned straps connected to the nacelle.

33. The method of transferring of claim 27, wherein the carriage-nacelle assembly is adapted to receive a rotor having a rotor hub and the method comprises mounting the carriage-nacelle assembly onto the wind turbine tower orientated to receive a rotor hub that is orientated generally downwards.

34. The method of transferring of claim 27, wherein the carriage-nacelle assembly or carriage-rotor-nacelle assembly comprises an elevator carriage and a nacelle, and the nacelle is releasably pivotally attached to the elevator carriage, and the method comprises changing the orientation of the elevator carriage from a substantially horizontal orientation to a substantially vertical orientation.

35. The method of transferring of claim 27, wherein the carriage-nacelle assembly or carriage-rotor-nacelle assembly comprises an elevator carriage, the method comprising the platform control system using control signals and status information from sensors on the elevator carriage to align the elevator carriage onto the wind turbine tower.

36. The method of transferring of claim 27, wherein the wind turbine tower comprises at least one tower support formation, and the carriage-nacelle assembly or carriage-rotor-nacelle assembly comprises an elevator carriage with at least one carriage support formation, and the method comprises engaging the at least one carriage support formation with the at least one tower support formation to support the weight of the carriage-nacelle assembly or carriage-rotor-nacelle assembly on the side of the wind turbine tower.

37. The method of transferring of claim 27, wherein the carriage-nacelle assembly or carriage-rotor-nacelle assembly comprises an elevator carriage having a rail attachment system, and the method comprises releasably attaching the rail attachment system to at least one elevator rail on the wind turbine tower.

38. The method of transferring of claim 37, comprising elevating the carriage-rotor-nacelle assembly to the top of the wind turbine tower along the at least one elevator rail and mounting the rotor-nacelle assembly onto the top of the wind turbine tower.

39. The method of transferring of claim 27, wherein the carriage-nacelle assembly or carriage-rotor-nacelle assembly comprises an elevator carriage having an umbilical cable for connecting the elevator carriage to at least one of a power source and a control system, the method comprising transferring connection of the umbilical cable from a control system located on the vessel to the wind turbine tower, during transferring and mounting the carriage-nacelle assembly or carriage-rotor-nacelle assembly to the side of the wind turbine tower.

Description

[0104] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which:

[0105] FIG. 1 shows a wind turbine system according to the invention;

[0106] FIG. 2 is an isometric view of an underside of a carriage and rail system from the wind turbine system of FIG. 1;

[0107] FIG. 3 is a plan view of the underside of the carriage and rail system of FIG. 2;

[0108] FIG. 4a is an isometric view from one end of the carriage and rail system of FIG. 2;

[0109] FIG. 4b is an end view from one end of the carriage and rail system of FIG. 2;

[0110] FIG. 5 is a side view of the carriage and rail system of FIG. 2;

[0111] FIGS. 6 to 13 show steps in a wind turbine assembly method according to the invention;

[0112] FIG. 14a is an isometric view of a carriage and rail system including a platform for maintenance work;

[0113] FIGS. 14b and 14c show alternative maintenance platforms, each including a crane;

[0114] FIG. 15 illustrates transferring a carriage-a rotor-nacelle assembly to a ship by means of the carriage;

[0115] FIG. 16 shows a variant of the ship design wherein a movable platform is located at one side of the ship; and

[0116] FIG. 17 shows a variant of the carriage, wherein drive units are mounted to a carriage frame in a manner that enables the positions of the drive units to be adjusted.

[0117] FIG. 1 shows a wind turbine system 1 according to the invention. The wind turbine system 1 includes a tower 3, a nacelle 9, a rotor 11 (the combined rotor 11 and nacelle 9 are hereinafter referred to as the rotor-nacelle assembly 11,9) and an elevator system 7 for elevating the rotor-nacelle assembly 11,9 up the tower 3. The rotor 11 comprises a hub 13 and a plurality of blades 15, typically two or three blades 15.

[0118] The tower 3 is an offshore tower. Preferably the tower 3 has a single tubular structure. However other arrangements are possible. For example, the tower 3 can have a plurality of tubular structures, typically three, connected by steel latticework. The tower 3 has a base 17 and a top 19. The tower 3 includes a plurality of support formations 20 mounted on to an outer surface of the tower. The support formations 20 are in the form of hooks, though other formations can be used.

[0119] The elevator system 7 includes a pair of rails 21 mounted to an outer surface of the tower 3. The rails 21a,21b extend along at least a substantial part of the length of the tower, typically from a position adjacent the base 17 to a position adjacent the top 19 of the tower. Each rail 21a,21b has a substantially T-shaped cross-section, which is best seen in FIGS. 4a and 4b. Each rail 21 includes internal and external teeth 23a,23b,25a,25b running along the length of the rail.

[0120] The elevator system 7 includes a carriage 27. The carriage 27 comprises a chassis 29, a rail attachment system 31 for attaching the carriage to the rails 21a,21b and a drive system 33 for moving the carriage 27 along the rails 21a,21b. The carriage 27 also includes a connector assembly 35 for pivotally attaching the carriage 27 to the nacelle 9 and a driver 37 for pivoting the nacelle 9 with respect to the chassis 29.

[0121] The rail attachment system 31 includes four sets of rollers bearings 41 for engaging the rails 21. Two sets of the roller bearings 41 engage a first rail 21a and two sets of the roller bearings 41 engage a second rail 21b. The roller bearings 41 are located on an underside 43 of the chassis, that is, a side that faces towards the tower 3 when the carriage 27 is attached to the tower. The roller bearings 41 engage an outermost surface 45 of the rails. The rail attachment system 31 includes four sets of adjustable roller bearings 47 for selectively engaging the rails 21. Two sets of the adjustable roller bearings 47 selectively engage the first rail 21a and two sets of the adjustable roller bearings 47 selectively engage the second rail 21b. The adjustable roller bearings 47 are located on the underside 43 of the chassis. Each adjustable roller bearing 47 comprises a pair of curved arms 51. Each arm 51 is pivotally attached to the chassis 29 towards one end. Sets of rollers 53 are located towards a free end of each arm 51. Actuators adjust the position of the arms 51 in response to control signals received from a controller. The controller is arranged to selectively move the sets of rollers 53 into and out of engagement with their respective rails 21a,21b. The rollers 53 are arranged to engage rail surfaces 49 that face towards the tower. When the carriage 27 is mounted on to the tower, the bearings 47 are in an open, disengaged, position. The controller actuates the actuators to move the rollers 53 in to engagement with their respective rails 21a,21b. This firmly attaches the carriage 27 to the rails 21a,21b, and the carriage 27 is ready to move along the rails.

[0122] The drive system 33 includes at least one drive source 55, such as an electric motor, and an arrangement of gears for engaging the internal and external teeth 23a,25a on the rails. A first drive unit 56 including a set of six gears is arranged to engage the teeth on the first rail 21a:

[0123] an inner set of three gears 57 engage the internal teeth 23a and an outer set of three gears 59 engage the outer teeth 25a. A second drive unit 56 including a set of six gears is arranged to engage the teeth on the second rail 21b: an inner set of three gears 57 engage the internal teeth 23b and an outer set of three gears 59 engage the outer teeth 25b. The drive source 55 is arranged to rotate the gears 57 either directly or via a transmission. As the gears 57,59 rotate the carriage 27 moves along the rails 21a,21b. The drive system 33 includes a ratchet arrangement to prevent the carriage 27 from falling down the tower 3, for example in the event of a power failure. The ratchet is releasable to enable the carriage 27 to move down the tower. In preferred arrangements, the drive system 33 is arranged to selectively engage the rails 21a,21b. For example, the drive system 33 can include a controller and actuators for controlling operation of the first and second drive units 56. The actuators are arranged to move the gears 57,59 into and out of engagement with their respective teeth 23a,25a,23b,25b, in response to control signals from the controller. Thus the gears 57,59 can be in a disengaged position as the carriage 27 is mounted onto the tower 3 and can be moved into an engaged position to drive the carriage along the rails 21a,21b.

[0124] The carriage 27 includes carriage support formations 39. The carriage support formations 39 are arranged to engage with the support formations 20 on the tower 3, when the carriage-turbine assembly is initially attached to the tower 3. The tower support formations 20 are arranged to support the weight of the carriage-rotor-nacelle assembly 27,9,11 until the rail attachment system 31 engages the rails and the drive system 33 is engaged.

[0125] The connector assembly 35 includes arms 58 that protrude upwards from the chassis 29. The arms 58 are inclined to the plane of the chassis. The arms 59 protrude beyond a leading edge 61 of the chassis. A pivot pin 63 connects arms 58 with receiving formations 65 on the nacelle casing, or on a separate adaptor plate (not shown), which can be secured between a yaw bearing and a tower top flange. Thus the rotor-nacelle assembly 11,9 is pivotally attached to the carriage chassis 29. Preferably the receiving formations 65 are located at approximately the centre of gravity of the rotor-nacelle assembly 11,9. This reduces the force required in order to pivot the rotor-nacelle assembly 11,9 with respect to the chassis 27. The driver 37 preferably comprises a linear driver, for example a hydraulic ram. The length of the linear driver 37 is adjustable, and is typically telescopically adjustable. A controller is provided to controllably adjust the length of the linear driver, for example a hydraulic controller. The driver 37 is pivotally attached to the chassis 27 towards a first end 67 of the linear driver. The second end 69 of the linear driver is arranged to engage with the nacelle 9 or hub 13 in order to pivot the rotor-nacelle assembly 11,9 with respect to the chassis 27. This is achieved by adjusting the length of the linear driver 37 at the appropriate time.

[0126] The carriage 27 is attached to the rotor-nacelle assembly 11,9 prior to mounting the assembly 11,9 on to a side of the tower 3. This enables a fast assembly time, which is particularly important for offshore wind farms where changeable weather can provide limited windows of opportunity for assembling the wind turbines. In particular, the carriage 27 is releasably attached to the nacelle 9 by means of the pivot pin 63. By removing the pivot pin 63, either manually or by means of an actuator, the carriage 27 is separable from the rotor-nacelle assembly 11,9 when the nacelle 9 is located at the top 19 of the tower. This enables the carriage 27 to return to the bottom of the tower for reuse.

[0127] The carriage 27 also includes alignment sensors to assist with mounting the carriage-rotor-nacelle assembly 27,11,9 on to the tower 3.

[0128] For offshore wind farms, the carriage-rotor-nacelle assembly 27,11,9 is transported to the tower 3 by ship 71. The ship 71 is essentially a conventional ship that has been modified to transport at least one, and typically two or three, carriage-rotor-nacelle assemblies 27,11,9. That is, according to the invention, the ship does not have to be a crane vessel type ship that is capable of raising its hull out of the water or a semi-submersible crane vessel.

[0129] Each carriage-rotor-nacelle assembly 27,11,9 is mounted on an individual movable support 73 on the deck of the ship. The carriage-rotor-nacelle assembly 27,11,9 is supported by the movable support 73 in a manner such that the rotor hub 13 faces generally downwards towards the ship deck and the rotors 11 are arranged substantially horizontally. The movable support 73 supports the hub 13. The nacelle 9 protrudes upwardly from the hub 13. The movable support 73 is mounted on rails 75. The movable support 73, and hence the carriage-rotor-nacelle assembly 27,11,9 mounted thereon, is movable along the rails 75. The rails 75 guide the movable support 73 and the carriage-rotor-nacelle assembly 27,11,9 to a transfer site.

[0130] The movable support 73 includes a wheeled undercarriage 74. The wheeled undercarriage includes rails 76 on an upper surface. The movable support 73 includes a slidable uppercarriage 78. The slidable uppercarriage 78 is mounted on the undercarriage 74 and is arranged to slide along the rails 76. The uppercarriage 78 includes a base 80 and support arms 82 that are arranged to engage and support the rotor hub 13.

[0131] The ship 71 includes a platform system 77 for transferring the carriage-rotor-nacelle assembly 27,11,9 from the ship 71 to the tower 3. The platform system 77 includes a movable platform 79, a control system, actuators 83 such as hydraulic rams, and sensors. The control system is arranged to automatically control operation of the actuators 83 to adjust the orientation of the movable platform 79 in response to signals received from the sensors to account for movement of the ship caused by wind and waves while transferring the carriage-rotor-nacelle assembly 27,11,9 from the ship 71 to the tower 3. The control system adjusts the orientation of the movable platform 79 seeking to maintain the platform 79 in a substantially horizontal orientation, irrespective of the orientation of the ship's deck. The movable platform control system controls positioning of the platform such that the platform is held substantially motionless relative to the tower irrespective of the motion of the vessel to which it is attached. This accounts for motion of the vessel during a transfer. Typically the system includes 3 to 6 actuators 83.

[0132] The movable platform 79 can be located towards one end of the ship 71, and preferably towards the stern of the ship. The movable platform 79 is arranged as a gang plank such that it overhangs an edge of the ship.

[0133] Preferably the movable platform 79 includes rails 84, and the uppercarriage 78 is arranged to slide on to the platform along rails 84. Thus the movable support 73, and hence the carriage-rotor-nacelle assembly 27,11,9 is movable from a storage position on to the movable platform 79. From here, the carriage-rotor-nacelle assembly 27,11,9 can be transferred to the tower 3. Preferably the ship includes a ramp 85 for raising the carriage-rotor-nacelle assembly 27,11,9 to the height of the movable platform 79. The rails 75 extend up the ramp 85.

[0134] A method of assembling an offshore wind turbine will now be described with reference to FIGS. 1 and 6 to 13.

[0135] A tower 3 is erected at an offshore windfarm site. The tower 3 includes elevator rails 21a,21b.

[0136] A carriage-rotor-nacelle assembly 27,11,9 is assembled by attaching the rotor 11 to the nacelle 9, and pivotally connecting the carriage 27 to the nacelle 9. This typically takes place at a dockside. Supporting straps 40 can be used to connect the tips of the rotor blades 15 to the nacelle 9 for additional support. The rotor blades 15 are very flexible and gravity loading tends to bend them downwards during transit, and they will vibrate with large amplitudes if not constrained. The straps 40 prevent the rotor blades 15 from flexing during transit and increase the clearance between the rotor blade tips and the water. The straps 40 are removably attached to the rotor blades 15. The carriage 27 is typically locked in a horizontal orientation for transportation (see FIGS. 1 and 6). Each carriage-rotor-nacelle assembly 27,11,9 is loaded on to the ship 71. Each carriage-rotor-nacelle assembly 27,11,9 is mounted on to a movable support 73, such that the rotor hub 13 faces generally downwards towards the ship's deck and the rotors 11 are arranged substantially horizontally (see FIG. 1).

[0137] The ship 71 travels to the tower 3. The ship 71 is manoeuvred into position such that the movable platform 79 is adjacent the base 17 of the tower. The carriage-rotor-nacelle assembly 27,11,9 is transported on to the movable platform 79.

[0138] An umbilical cable is connected to the carriage 27. The umbilical cable provides power to the carriage 27. The umbilical cable facilitates transmission of control signals and status information between the carriage 27 and a control system located on the ship 71. A remote-control console is connected to the umbilical cable. The remote-control console is arranged to send control signals to the carriage 27. The remote-control console enables control signals to be sent to the carriage 27 by manual intervention, for example to control the attachment system 31, the drive system 33 to adjust the position of the carriage 27 on the rails 21a,21b, control the linear driver 37 to adjust the orientation of the rotor-nacelle assembly 11,9 and/or to operate an actuator to disconnect the pivot pin 63.

[0139] The orientation of the carriage 27 is changed from a substantially horizontal orientation to a substantially vertical orientation in readiness to engage the tower rails 21a,21b.

[0140] The carriage-rotor-nacelle assembly 27,11,9 is transferred across to the tower 3 by adjusting the position and of the movable platform 79. The carriage support formations 39 are brought into engagement with the tower support formations 20. The transfer is conducted at minimal speed and substantially zero acceleration to avoid damage to the tower and carriage-rotor-nacelle assembly 27,11,9. During the transfer of the carriage-rotor-nacelle assembly 27,11,9 to the tower 3 the umbilical cable is attached at the control system on the ship and control signals and status information from sensors on the carriage 27 are used by the platform control system 81 to correctly align the carriage 27 to the tower rails 21a,21b. At this stage, the carriage-rotor-nacelle assembly 27,11,9 is attached to a lower side of the tower. The weight of the carriage-rotor-nacelle assembly 27,11,9 is supported by the tower support formations 20.

[0141] Carriage actuators are then operated to engage the rails 21a,21b with the adjustable roller bearings 47, and the internal and external teeth 23a,23b,25a,25b with the gears 57,57,59,59.

[0142] At this stage, the weight of the carriage-rotor-nacelle assembly 27,11,9 is supported by the tower support formations 20, the bearings 41,47 and the drive system 33, and the carriage-rotor-nacelle assembly 27,11,9 is ready to be elevated to the top 19 of the tower. When the carriage-rotor-nacelle assembly 27,11,9 is secured to the rails 21a,21b the umbilical cable connection is transferred to the tower 3 and the ship 71 moves away from the tower.

[0143] The drive system 33 is activated and the carriage-rotor-nacelle assembly 27,11,9 is driven up the tower 3. When the assembly reaches the top 19 of the tower, the drive system 33 locks the position of the carriage-rotor-nacelle assembly 27,11,9 against further movement.

[0144] The linear driver 37 is actuated to rotate the rotor-nacelle assembly 11,9. The nacelle 9 is pivoted from a substantially vertical orientation to a substantially horizontal orientation. The rotor 11 is pivoted from a substantially horizontal orientation of the blades 15 to a substantially vertical orientation. At this stage, mating faces of a nacelle yaw bearing 87 and a tower top flange 89 are substantially parallel but are not contacting.

[0145] Holes for a bolted connection between tower top flange 89 and the nacelle yaw bearing 87 are aligned and guide bolts inserted.

[0146] The drive system 33 unlocks its drive motors and gradually lowers the rotor-nacelle assembly 11,9 vertically downwards so that the yaw bearing 87 engages the top flange 89. Once sufficient bolts are fitted to secure the rotor-nacelle assembly 11,9, the actuator 37 is disconnected at the hub end and the pivot pin 63 is removed, allowing the carriage 27 to return to the base of the tower.

[0147] The drive system 33 is actuated to drive the carriage 27 down the tower towards the base. When received at the base of the tower 3, the adjustable bearings 47 and drive gears 57,59 are disengaged from the rails 21a,21b, and the ship 71 returns to pick up the carriage 27, which can be reused.

[0148] Control of the carriage's 27 functions during elevation, rotation, disconnection and return of the carriage 27 is a combination of automatic control and manual intervention control via the remote-control console connected to the carriage 27 via the umbilical cable.

[0149] Optionally, the carriage 27 can be adapted to include a maintenance platform 91 (see FIG. 14). This enables maintenance work to be carried out on the wind turbine post installation, using the carriage 27 as an elevator for the platform 91. The platform 91 can include an aperture 93 that is arranged to receive a rotor blade 15. The rotor 11 can be locked in place to prevent rotation of the blades 15. One of the blades 15 can be oriented to depend substantially vertically downwardly (as shown in FIG. 14a). As the carriage 27 moves up the rails 21a,21b the blade 15 enters into the aperture 93. The carriage 27 can be locked off at the appropriate height along the rails to enable maintenance workers to inspect the rotor. The platform can be used to provide personnel access to the nacelle and for the transport of equipment and spare parts. With a suitable arrangement of the nacelle this could be used as a working platform to replace major components. Preferably the platform includes a safety rail 98.

[0150] The platform can include maintenance equipment such as a crane 94 (see FIGS. 14b and 14c). Carriage supports 96 are provided to hold the platform in place. The platform includes a safety rail 98.

[0151] The advantages of the invention, for a typical windfarm installation are: [0152] Reduced installation cost: the invention described is estimated to be competitive with current installation methods and will be considerably cheaper when installing wind turbines in deep water offshore sites or onshore wind turbines with high towers because it requires smaller, less expensive and more available installation equipment and will achieve a faster rate of installation. [0153] Faster and less weather dependent installation: the invention described makes productive use of available weather windows, reducing the time period for installation and commissioning of a typical project and minimising downtime during major repairs on operational wind turbines. [0154] Improved turbine availability: in the event of a major failure or planned re-fit the complete rotor nacelle assembly is quickly removed and replaced in one operation, allowing repairs to the failed unit to be carried out onshore and reducing downtime compared to in situ repair operations. This will lower risk and costs over the operational lifetime of a typical project. [0155] Improved safety: reduced number of complex lifting operations and simplifies operations and maintenance on major components.

[0156] Overall, these factors combine to result in a substantial saving in the Levelised Cost of Energy (LCoE) for a typical offshore wind farm, as well as a more efficient and safer installation and maintenance operations.

[0157] Although the present invention has been described in connection with specific preferred embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. Furthermore, it will be apparent to the skilled person that modifications can be made to the above embodiment that fall within the scope of the invention.

[0158] For example, the carriage 27 can be used to transfer the rotor-nacelle assembly 11,9 on to the ship 71 (see FIG. 15).

[0159] The ship 71 can include an elevator 95 for lifting the carriage-rotor-nacelle assembly 27,11,9 to the level of the movable platform 79 (see FIGS. 15 and 16). The elevator 95 can be used in addition, or as an alternative, to the ramp 85.

[0160] The movable platform 79 can be mounted at the side of the ship, for example to a port or starboard side of the ship (see FIG. 16).

[0161] The rails 21a,21b on the tower can be arranged and fixed to the tower wall in various ways to optimise manufacturing and to have minimum effect on the dynamics and long-term operation of the tower. For example, the pair of rails 21a,21b can be replaced with a single rail. The single rail can have a T-shaped cross-section. The carriage 27 can include stabilizers for maintaining the orientation of the carriage-rotor-nacelle assembly 27,11,9 with respect to the tower 3.

[0162] A tripod lattice tower can be used rather than the more conventional tubular tower. T-shaped rails can be fixed onto each leg of the tower and the three ‘faces’ of the tower provide increased flexibility for the vessel to offload the carriage-rotor-nacelle assembly 27,11,9 depending upon weather conditions.

[0163] For some towers the distance between the first and second rails 21a,21b is not constant. For example, the distance between the rails 21a,21b may decrease close to the top 19 of the tower. To allow for the varying distance between the tower rails, the drive units 101 on the carriage 27 can be supported on sliding bearings 103 (see FIG. 17), so that the distance between the drive units 101 is adjustable while the carriage moves along the rails. For example, the distance between drive gears 105 associated with the first rail 21a and drive gears 105 associated with the second rail 21b is adjustable. The distance can be adjusted automatically by an actuator while the carriage moves along the rails. The carriage 27 can include an arrangement of rods 107. The rods 107 are arranged transversely to the direction of motion of the carriage. The drive units 101 include the sliding bearings 103. The sliding bearings 103 are mounted on to the rods 107. The position of the drive units 101 with respect to the rods is adjustable.

[0164] The drive system 33 shown is one of many alternative arrangements for a geared linear drive. The drive motors can be hydraulic or electric, transmitting drive torque to the pinion gears either directly or via a step-down transmission system.

[0165] Other types of driver 37 can be used. For example, the driver 37 for rotating the rotor-nacelle assembly 11,9 can include at least one electric linear actuator.

[0166] The bearings 41,47 that allow linear movement of the carriage 27 along the tower rails 21a,21b under load can be sliding bearings, for example PTFE pads.

[0167] For onshore wind turbine assembly, the main components of the rotor-nacelle assembly 11,9 (nacelle 9, hub 13, and blades 15) are generally transported to a site as separate components.

[0168] The carriage 27 can also be transported to site separately.

[0169] A carriage-nacelle assembly 27,9 can be assembled on site, by attaching the carriage 27 to the nacelle 9. The carriage-nacelle assembly 27,9 can be mounted onto the tower 3 with or without the rotor 11 being attached to the nacelle 9. In the latter case, the rotor 11 is attached to the nacelle 9 while the carriage-nacelle assembly 27,9 is mounted on the tower to produce a carriage-rotor-nacelle assembly 27,11,9. The carriage-rotor-nacelle assembly 27,11,9 is then elevated to the top of the tower.

[0170] Rails 21a,21b having a different cross-section can be used instead of a T-shaped cross-section.

[0171] A different number of elevator rails 21a,21b can be used. For example the tower can use a single elevator rail, three or four rails. Any practicable number of rails can be used.