WIND TURBINE & METHOD FOR INSTALLING A WIND TURBINE

Abstract

A wind turbine for deployment offshore. The wind turbine including: a tower-float assembly having a tower (3) for supporting a nacelle (13a) and a rotor (13b), and a float (5) arranged to maintain at least part of the tower above a surface of a body of water; a keel assembly (7) including at least one keel module (25) and at least one rod (9) connecting the keel module to the tower-float assembly, wherein the at least one rod is arranged to move relative to the tower-float assembly to deploy the keel module, and the keel module is movable relative to the tower-float assembly, in response to movement of the at least one rod, between a non-deployed position proximal the tower-float assembly and a deployed position which is distal from the tower-float assembly in a downwardly direction, thereby increasing an effective length of the wind turbine; and the at least one rod is arranged to transfer bending moments to the tower-float assembly.

Claims

1.-40. (canceled)

41. A wind turbine for deployment offshore, including: a tower-float assembly having a tower for supporting a nacelle and a rotor, and a float arranged to maintain at least part of the tower above a surface of a body of water; a keel assembly including at least one keel module and at least one rod connecting the keel module to the tower-float assembly, wherein the at least one rod is arranged to move relative to the tower-float assembly to deploy the keel module, and the keel module is movable relative to the tower-float assembly, in response to movement of the at least one rod, between a non-deployed position proximal the tower-float assembly and a deployed position which is distal from the tower-float assembly in a downwardly direction, thereby increasing an effective length of the wind turbine; wherein the at least one rod is pivotally attached to the tower-float assembly and is arranged for pivoting movement relative to the tower-float assembly such that the keel module is moveable from the nondeployed position to the deployed position along a curved path; and the at least one rod is arranged to transfer bending moments between the keel module and the tower-float assembly in a deployed condition.

42. A wind turbine according to claim 41, wherein the at least one rod is arranged to transmit at least one of compressive forces and shear forces between the keel module and the tower-float assembly in the deployed condition.

43. A wind turbine according to claim 41, wherein the at least one rod is arranged to pivot through an angle of approximately 90 degrees from a non-deployed condition to the deployed condition.

44. A wind turbine according to claim 41, wherein the at least one rod is arranged generally horizontally when the keel module is in the non-deployed position and the at least one rod is arranged generally vertically when the keel module is in the deployed position.

45. A wind turbine according to claim 41, further including a plurality of rods connecting the keel module to tower-float assembly.

46. A wind turbine according to claim 41, further including a plurality of keel modules.

47. A wind turbine according to claim 46, wherein the at least one rod comprises a first rod connecting the keel member to the tower-float assembly, the first rod is pivotally attached to the tower float assembly at a first pivot axis; and including a second rod connecting a second keel member to the tower-float assembly, the second rod is pivotally attached to the tower float assembly at a second pivot axis, wherein the second rod is arranged to overlap the first rod when the keel module and second keel module are each in their respective non-deployed positions.

48. A wind turbine according to claim 41, wherein at least one rod is tubular.

49. A wind turbine according to claim 45, wherein the plurality of rods are connected together by bracing members.

50. A wind turbine according to claim 41, wherein at least one keel module includes a housing.

51. A wind turbine according to claim 50, wherein the housing has a hollow interior and the hollow interior is arranged to be filled with ballast.

52. A wind turbine according to claim 41, wherein the at least one rod has a length that is greater than or equal to 30 m.

53. A wind turbine according to claim 41, wherein there is a rigid connection between the at least one rod and the keel module.

54. A wind turbine according to claim 41, wherein at least one rod has a fixed length.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[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 first prior art floating wind turbine in a first operating condition;

[0106] FIG. 2 shows the wind turbine of FIG. 1 in a second operating condition;

[0107] FIG. 3 shows a second prior art floating wind turbine in a first operating condition;

[0108] FIG. 4 shows the wind turbine of FIG. 3 in a second operating condition;

[0109] FIG. 5 is an isometric view of a wind turbine according to a first embodiment of the invention, which includes a tower, a float, and a keel that is movable with respect to the float;

[0110] FIG. 6 is an enlarged isometric view of a lower part of the wind turbine of FIG. 5;

[0111] FIGS. 7a to 7c show a drive system that is use to deploy the keel;

[0112] FIGS. 8 to 15 illustrate a wind turbine installation process;

[0113] FIG. 16 shows a drive system for use in a second embodiment of the invention;

[0114] FIG. 17 shows a wind turbine according to a third embodiment of the invention having an arrangement of buoyancy collars temporarily attached to a float to improve the buoyancy of the float;

[0115] FIG. 18 shows a float and keel structure of a wind turbine in accordance with a fourth embodiment of the invention, the keel structure being in a deployed condition;

[0116] FIG. 19 shows a detailed upper end of a part of the float structure shown in FIG. 18, together with a drive system, when the keel structure is in a non-deployed condition;

[0117] FIG. 20 shows a detailed lower end of a part of the float structure shown in FIG. 18, when the keel structure is in a deployed condition; and

[0118] FIG. 21 shows a float and keel structure of a wind turbine in accordance with a fifth embodiment of the invention, with the keel structure being in a non-deployed condition; and

[0119] FIG. 22 shows the float and keel structure of FIG. 21, with the keel structure being in a deployed condition.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0120] FIGS. 5 to 7c show a wind turbine 1 in accordance with a first embodiment of the invention. The wind turbine 1 includes a tower 3, a float 5, a keel 7, connector members 9, and a drive system 11 for moving the keel 7. The wind turbine also includes a nacelle 13a and a rotor 13b mounted on the tower 3.

[0121] The tower 3 and float 5 together are referred to as the tower-float assembly. The keel 7 and connector members 9 together are referred to as the keel assembly.

[0122] The purpose of the float 5 is to maintain the tower 3 above the surface of the sea 10, in its correct orientation (substantially vertical) to ensure that the rotor 13b and nacelle 13a can operate properly. The float 5 effectively provides a floating hull for the tower 3, nacelle 13a and rotor 13b. The float 5 comprises a plurality of buoyancy aids, preferably in the form of buoyancy tanks 15. Each buoyancy tank 15 comprises a cylindrical drum that is closed at each end. Each buoyancy tank 15 can be made from steel, and/or other materials such as concrete, carbon fibre, and glass reinforced plastic (GRP). Each buoyancy tank 15 has a central longitudinal axis Z-Z. Each buoyancy tank 15 is oriented such that the central longitudinal axis is arranged substantially vertically, and therefore the tanks are arranged as floating columns. In the arrangement shown in FIG. 5 there are three outer buoyancy tanks 15. Each outer buoyancy tank 15 is arranged at the apex of a triangle, and preferably an equilateral triangle, when viewed in plan. A central buoyancy tank 15b is located centrally between the three outer buoyancy tanks 15. The central buoyancy tank 15b has a central longitudinal axis Y-Y, which is arranged parallel with the longitudinal axes of the outer buoyancy tanks 15. Each outer buoyancy tank 15 is connected to the central buoyancy tank 15 by upper and lower bracing members such as braces 17,19. The upper and lower braces 17,19 protrude radially outwards from upper and lower parts of the central buoyancy tank 15 respectively. The upper and lower braces 17,19 connect to upper and lower parts respectively of the outer buoyancy tanks 15. The braces 17,19 fix the outer buoyancy tanks 15 to the central buoyancy tank 15b.

[0123] Optionally, a heave plate 21 can be attached to a lower end of the central buoyancy tank 15b. The heave plate 21 is arranged transversely to the longitudinal axis Y-Y of the central buoyancy tank 15b. Bracing members 23 can be used to further support the heave plate 21. The heave plate 21 has a larger width (or diameter) than an underside of the central buoyancy tank 15b. As shown in FIG. 5, the heave plate 21 can have a hexagonal shape, when viewed in plan.

[0124] The tower 3 is mounted on top of the central buoyancy tank 15. The tower 3 has a central longitudinal axis X-X that is arranged co-axially with the central longitudinal axis Y-Y of the central buoyancy tank 15b.

[0125] The keel 7 provides resistance to heave motion, and helps to stabilize the wind turbine. The keel 7 is movably attached to the float-tower assembly and is arranged to move from a non-deployed position adjacent to the lower parts of the buoyancy tanks 15,15b to a deployed position, which is distal from the lower parts of the buoyancy tanks 15,15b. That is, the keel 7 is moveable from a non-deployed position that is relatively shallow in the water to a deployed position which is located deeper in the water. The keel 7 is moved vertically upwards and downwards. Adjusting the position of the keel 7 adjusts the positon of a centre of mass of the wind turbine. Deploying the keel 7 effectively increases the length of the wind turbine, which has the effect of moving the centre of mass downwards. Having a lower centre of mass provides a more stable wind turbine.

[0126] The keel 7 has a modular construction, which comprises a plurality of keel modules 25. In the arrangement shown in FIG. 5, the keel 7 includes three keel modules 25. Each keel module 25 comprises a housing. Each housing is filled with ballast to weigh the keel 7. Typically solid ballast is used. For some applications each housing can be filled with a slurry. Each housing typically has a plate-like overall structure, that is, the housing can have an overall structure that is relatively flat, like a disk. The housing can comprise upper 32 and lower planar walls, vertical side walls 34 and a hollow interior (see FIG. 8). The hollow interior comprises a grillage, which gives a cellular structure 36. Each keel module 25 can have a hexagonal shape when viewed in plan. The housing structure can include beams, such as steel. The beams can comprise beam sections, such as I, H and channel sections. The beams can be used for external vertical walls 34 and/or internal vertical walls of the housing. Plates, such as steel plates, can be provided for upper 32 and lower walls of the housing. The housing can be made from steel reinforced concrete.

[0127] Typically, each keel module 25 is associated with a respective outer buoyancy tank 15 and is arranged to move with respect to its buoyancy tank 15. Each keel module 25 is positioned below its respective outer buoyance tank 15, and is arranged to move in a direction that is substantially co-axial with the longitudinal axis Z-Z of the respective buoyancy tank.

[0128] As shown in FIG. 5, a preferred arrangement of the keel 7 is that the keel modules 25 are located in a plane, and each keel module 25 acts as a heave plate. The plane is transverse to the longitudinal axes Z-Z of the outer buoyancy tanks 15. Each keel module 25 is located within the plane at the apex of a triangle, and preferably an equilateral triangle, when viewed in plan. Each keel module 25 is preferably connected to at least one other keel module 25 by way of a bracing member 27, and preferably is connected to a plurality of other keel modules 25. The bracing members 27 provide the keel 7 with a rigid structure, and help to prevent the rods 9 from flexing. Optionally, the bracing members 27 can be of the type that can be adjusted. For example, the length of the bracing members 27 can be adjusted to tension the keel structure after installation. The keel 7 moves as a unit with respect to the tower-float assembly during deployment and retraction of the keel 7. The position of the keel 7 is fixed with respect to the float 5 when the keel 7 is in the deployed position. An aperture 29 is formed by the keel modules 25 and bracing members 27. The aperture 29 is located centrally. The aperture 29 is aligned with the heave plate 21.

[0129] The connector members are in the form of rods 9. The rods 9 connect the keel 7 to the tower-float assembly. The keel 7 is moveably connected to the tower-float assembly. Each rod 9 has a fixed length, and is preferably tubular. At least one rod 9, and preferably a plurality of rods 9, connects the keel 7 to each of the outer buoyancy tanks 15. In FIG. 5, a set of three rods 9 is provided per keel module-buoyancy tank pair. Respective rods 9 in each set protrude perpendicularly upwards from an upper surface 32 of the respective keel module 25. Additionally, or alternatively, the rods 9 can be connected to an interior surface of the keel module 25. Lower (distal) ends of the rods 9 are fixed to their respective keel module 25. Upper (proximal) ends of the rods 9 are fixed together by bracing members 33. The rods 9 in each set of rods are arranged substantially parallel with one another. The rods 9 in each set of rods are distributed evenly around the outer surface of the respective buoyancy tank 15. This provides a well-balanced arrangement. The rods 9 are movably connected to the outer buoyancy tanks 15 by at least one guide 31. A plurality of guides 31 is provided for each rod 9. Four guides 31 per rod are shown in FIG. 5. The number of guides 31 is in part determined by the height of the outer buoyancy tank 15. The guides 31 are arranged to enable each rod 9 to slide along a rectilinear path. For example, the guides 31 can be mounted on an outer surface of the buoyancy tank 15 in sets, and preferably on a curved outer surface. Each set of guides 31 is associated with one of the rods 9. The guides 31 in a set of guides are arranged along a line on the outer surface, and spaced apart along the length of buoyancy tank 15. Thus each rod 9 is constrained to move along a single axis. Thus each keel module 25 is constrained to move vertically upwards and downwards. This enables the keel 7 to be moved vertically downwards when deployed.

[0130] The length of the rods 9, and hence the deployment depth of the keel 7, is selected in accordance with the size of the wind turbine and the environmental conditions. The rods 9 have a sufficient length to enable the keel 7 to be deployed to the deployment position. Consequently, the rods 9 tend to have a much larger length than the height of the buoyancy tanks 15. It will be appreciated that some wind turbines may require a deeper or shallower deployment. The deployment position is determined according to the design of the wind turbine.

[0131] At least some of the rods 9, and preferably each rod 9, include a set of drive formations 35, for interacting with the drive system 11. Each drive formation 35, can be for example a tooth-like sheer plate that protrudes radially outwards from the rod 9. In a preferred arrangement, the drive formations 35 are spaced apart along at least part of the length of the rod and are arranged in at least one line. Preferably at least some drive formations 35 protrude outwardly in a first radial direction. Preferably at least some drive formations 35 protrude radially outwardly in a second direction. Typically the second direction is opposite to the first direction. One of the first and second directions can be towards the respective buoyancy tank 15.

[0132] The drive system 11 is arranged to deploy the keel 7 by lowering it deeper into the sea. The drive system 11 is also arranged to retract the keel 7 by raising it to a shallower depth. The drive system 11 achieves this by interacting with drive formations 35 to move the rods 9 upwards or downwards as required, which drives movement of the keel 7. At least part of the drive system 11 is removable from the tower-float assembly, which allows the drive system 11 to be reused. Allowing for delays and repairs, six drive systems 11 can be cycled during a typical windfarm installation campaign. This reduces the cost of the installation. Also, after the installation has been completed, the drive system 11 can be returned to shore. The drive system 11 can be reinstalled on a wind turbine for maintenance or decommissioning. The drive system 11 can be stored and maintained onshore for use in future field developments. In one arrangement, the drive system 11 includes a set of drive units, for example in the form of hydraulic cylinders 37. The drive system 11 preferably includes a rigid frame 39. Typically, at least one hydraulic cylinder 37 is provided for each rod 9. Each hydraulic cylinder 37 is releasably attachable to its respective buoyancy tank 15 adjacent its respective rod 9, for example each cylinder 37 can be bolted to the tank 15 or can make use of a quick release mechanism such as clamps or toggles. Having hydraulic cylinders 37 that are releasably attachable to the buoyancy tanks 15 enables the cylinders 37 to be removed from the tower-float assembly after the keel 7 has been deployed. This enables the hydraulic cylinders 37 to be used on other wind turbines in the installation, thus fewer drive systems 11 are required than the total number of wind turbines in an installation.

[0133] The hydraulic cylinders 37 on each buoyancy tank 15 are connected together by the frame 39. The frame 39 includes engagement formations 41 that are arranged to engage and release the drive formations 35. The frame 39 is driven by the cylinders 37. The frame is able to move upwards or downwards according to the direction of action of the cylinders 37. The frame 39 lowers and lifts the keel 7 by selectively interacting with the drive formations 35. This is achieved by the engagement formations 41 selectively engaging and disengaging the drive formations 35. Thus the drive system 11 is able to selectively drive the rods 9 in upwardly and downwardly directions. Operation of the hydraulic cylinders 37 is synchronised to ensure that the keel is deployed evenly. For example a suitable control system can be provided to control operation of the hydraulic cylinders 37. When deploying the keel 7, the hydraulic cylinders 37 are synchronized to drain fluid at the same time thereby maintaining the frame 39 in a substantially horizontal orientation. When the hydraulic cylinders 37 reach the end of their stroke, stops 43 mounted to the buoyancy tank 15 temporarily fix the positions of the rods 9, for example by each stop 43 engaging one of the drive formations 35, which relieves the load on the hydraulic cylinders 37. The engagement formations 41 release their respective drive formations and the hydraulic cylinders 37 are then extended upwards to elevate the frame 39 to an upper position, wherein the engagement formations 41 engage a new drive formation 35 further up the rod 9. The stops 43 disengage the rods 9, and the cycle repeats until the keel 7 reaches the deployed position.

[0134] The deployed position for the keel 7 is achieved when the permanent shear stops 45, which are located towards upper ends of each rod 9 contacts an upper surface 46 of its respective buoyancy tank 15 (see FIG. 7b). The hydraulic cylinders 37 are fully closed and the rigid frame 39 rests on top of the support columns 47. The hydraulic cylinders 37 are not required for the normal operation of the wind turbine and so may be detached and removed from site and reused on subsequent floating foundations. FIG. 7c shows the top of the outer buoyancy tank 15 after removal of the drive units 37.

[0135] To lift the keel 7, for example for decommissioning or maintenance purposes, the hydraulic cylinders 37 are reinstalled on to the tower-float assembly and the above process is performed in reverse. For example, the engagement formations 41 drivingly engage the drive formations 35 at a low part of the cylinder 37 stroke, drive the rods 9 upwards, and then release the drive formations 35 at an upper part of the cylinder stroke.

[0136] The wind turbine is held in position using mooring lines 49, which connect to cable/chain tensioning units 51 at deck level via sheaves 53 mounted lower down the float 5. Additionally, or alternatively, tensioning units fitted as an integral part of the mooring line 49 and operated underwater may be used. The wind turbine floats with an operational water line at approximately below the height of the upper braces 17.

[0137] Since the rods 9 are rigid, the keel 7 reacts to dynamic transverse, pitch and roll loads by transmitting bending moments to the tower-float assembly. This makes the float 5 more responsive to motion of the keel 7 and the keel 7 more responsive to motion of the float 5. Thus the float 5, rods 9 and keel 7 behave as a single body, which makes the behaviour of the wind turbine more predictable. If cables rather than rigid rods 9 were to support the keel 7 from the float 5, the cables typically would not transmit bending moments from keel 7 to tower-float assembly nor from tower float assembly to keel 7. Motion of the float 5 would not be as responsive to motion of the keel 7. Likewise, motion of the keel 7 would not be as responsive to motion of the float 5. Typically a cable connection would allow the float 5 and keel 7 to move more independently as two separate bodies. In particular, the mass moment of inertia of a single body system is greater than for a two body system. The rigid rod system thus presents a larger resistance to dynamic loading in rotation and improved wind turbine generation performance.

[0138] Having an adjustable keel 7 helps to ensure that the centre of mass of the wind turbine is located below the centre of buoyancy when the keel 7 is deployed. This allows reduction of the footprint of the final assembly. Hence, less space is required at the assembly site and a barge assembly technique becomes feasible. When the geometry of the wind turbine and its mass distribution is such that its centre of mass is below its centre of buoyancy in operation, then the single body behaves in operation as a spar foundation. The required water plane area to achieve stability is less than if the single body behaved as a semi-submersible foundation in which the centre of mass is above the centre of buoyancy.

[0139] Furthermore the single body retains sufficient static stability with the keel 7 retracted for assembly, transportation and launch phases.

[0140] In addition to the lower ends of the buoyancy tanks 15,15b, the keel 7 geometry has a planar top surface and a planer bottom surface, which are orientated transversely to the direction of heave. This generates added mass and damping effects which reduces heave motion of the wind turbine. The tower-float assembly's response to the wave spectrum at any given geographic location may thus be engineered by a suitable selection of the keel's surface area, mass and depth to achieve an optimum added mass, damping coefficient and mass moment of inertia.

[0141] A method for installing a wind turbine will now be described with reference to FIGS. 8 to 15.

[0142] Component parts of the keel assembly and tower-float assembly are fabricated and gathered together adjacent an assembly quay. Typically the components are of a weight defined by the capacity of an available shore side crane.

[0143] A submersible installation barge 55 moors alongside the assembly quay. The barge 55 has a deck 57 that is fitted with buoyancy tanks 59 to enable controlled sinking of the cargo barge.

[0144] The fabricated component parts are loaded onto barge 55 sequentially and assembled in a sequence that minimizes assembly time.

[0145] The keel modules 25 are laid flat on the deck 57 (see FIG. 8). If required, the keel modules 25 are connected together by bracing members 27. The keel modules 25 include internal cells 36 that are filled with solid ballast either prior to lifting onto the barge 55 or after mounting on the deck 57. The solid ballast is preferably crushed mineral ore, and is preferably supplied to the keel modules 25 in the form of a slurry. For example, the slurry can be pumped from a cargo vessel preferably via a water pumped slurry system. The cargo vessel may moor alongside the barge 55 and fill the empty cells 36 of each keel module 27 with the slurry. Water drains through holes formed in keel module walls leaving solid ballast material filling the cells 36.

[0146] The central buoyancy tank 15b is mounted centrally, optionally with the heave plate 21 pre-attached to the lower end of the tank (see FIG. 9). The central buoyancy tank 15b is positioned ready for connection to the outer buoyancy tanks 15, for example by welding or a mechanical connection. Temporary access platforms 61 and plant 63 may be installed on top of the central buoyancy tank 15 to support the works, if applicable.

[0147] A first outer buoyancy tank 15 is placed on top of one of the keel modules 25 (see FIG. 10). Preferably the rods 9 are pre-attached to the first outer buoyancy tank via guides 31. The upper brace 17 comprises a first portion 17a that protrudes outwardly from the central tank 15b and a second portion 17b that protrudes outwardly from the outer tank 15. The first and second parts 17a,17b are abutted end to end and connected together, for example by welding or other mechanical connection means. The lower brace 19 comprises a first portion 19a that protrudes outwardly from the central tank 15b and a second portion 19b that protrudes outwardly from the outer tank 15. The first and second parts 19a,19b are abutted end to end and connected together, for example by welding or other mechanical connection means. The lower end of each rod 9 is secured to its respective keel module 25 either by welding, pin and clevis arrangement, or other suitable means of connection.

[0148] Preferably, the drive system 11 is pre-installed on the tower-float assembly, typically on an upper surface of the outer buoyancy tank 15, prior to mounting the buoyancy tank 15 on to the barge 55. At least part of the drive system 11, which typically includes a hydraulic drive or an electric motor, is releasably attached to the tower-float assembly, for example using bolts, clamps and/or toggles.

[0149] Each of the remaining outer buoyancy tanks 15 is then installed in a similar manner to the first outer buoyancy tank (see FIG. 11).

[0150] The tower 3, nacelle 13a and rotor 13b are mounted on to the central buoyancy tank 15b, typically on an upper surface thereof (see FIG. 12). This completes the assembly of the wind turbine.

[0151] The wind turbine 1 is tested and commissioned as fully as possible on the barge 55 before departure to the field.

[0152] The barge 55, with the wind turbine mounted thereon, is towed out to the launch location, or travels under its own motion if powered. As the barge 55 clears the quay, an optional second barge may moor alongside the quay to start the assembly process for another wind turbine. It will be apparent that the keel 7 is in the non-deployed position at this stage.

[0153] When at the launch location, ballast tanks in the hull of the barge 55 are flooded in a controlled sequence. The barge 55 submerges and the buoyancy tanks 59 maintain a water plane area and hence intact stability (see FIG. 13). As the barge 55 submerges, the wind turbine 1 becomes self-buoyant and detaches from the barge deck 57. The barge 55 and wind turbine 1 separate from one another. The wind turbine 1 is towed clear of the barge 55 and is taken to its target installation position. FIG. 14 shows the submerged barge moved clear of the wind turbine 1.

[0154] The barge 55 resurfaces (see FIG. 15) and returns to port to repeat the assembly and load out operation.

[0155] The keel modules 25 are lowered by the drive system 11 to the deployed position. The deployed position is at a greater depth than the non-deployed position. The drive system 11 lowers the rods 9 downwards, thereby increasing the depth at which the keel modules 25 are located. The drive system 11 drives the rods 9. Movement of the rods 9 is constrained by the guides 31. Each rod 9, and hence the keel module 25, is constrained to move along an axis. Each axis is substantially vertical in calm seas. The deployed position is typically achieved when the rods 9 have completed the maximum extent of their stroke.

[0156] The mooring lines 49 are attached to the sea bed to fix the location of the wind turbine 1.

[0157] The installation method has the following, advantages: [0158] Since assembly of the wind turbine 1 takes place on the deck 57 of the barge 55 the area of the quayside required during the assembly process is minimized. [0159] Using a barge 55 for the assembly process minimizes the time the floating turbine assembly spends in port by enabling movement of the barge 55 as in a production line to separate work stations each, optimized for either float assembly or turbine assembly. This avoids concentration of material, tooling and personnel at a single work station and allows separate assembly work to take place simultaneously. [0160] A continuous assembly process can be set up that uses three separate barges each following the other between: a float assembly workstation; a turbine assembly workstation; and the installation site location to maintain a continuous installation process. [0161] Having barges available enables installed wind turbines to be moved, should that be necessary. For example, a wind turbine can be moved from the installation site using one of the available barges to a new installation site, or to a marine port for maintenance or decommissioning as a dry hull.

[0162] Part of a wind turbine in accordance with a second embodiment of the invention is shown in FIG. 16. The wind turbine in accordance with the second embodiment is similar to the first embodiment except that the drive system 111 has a different arrangement from the drive system 11.

[0163] In the second embodiment, a pair of drive units, preferably in the form of a pair of hydraulic cylinders 137 is provided for each rod 109. The drive units 137 are mounted on an outer buoyancy tank 115. Each cylinder includes a drive device 141 for selectively engaging the drive formations 135 formed on the rods 109. This provides a more compact rigid design.

[0164] A wind turbine 201 in accordance with a third embodiment is shown in FIG. 17. The wind turbine according to the third embodiment is similar to the first embodiment, or second embodiment, except that the float 205 can include buoyancy collars 200 fitted to the outer buoyancy aids (see FIG. 17), such as outer buoyancy tanks 215, The buoyancy collars 200 provide additional buoyancy to the float 205 during the installation process. Preferably the buoyancy collars 200 are releasably attached to the outer buoyancy tanks 215. The buoyancy collars are typically removed prior to normal operation of the wind turbine. The buoyancy collars 200 can include apertures and/or recesses to enable the rods 209 to move relative to the buoyancy collars 200. For example, the buoyancy collars 200 may be fitted temporarily to the outer buoyancy tanks 215 during the assembly phase. The collars provide additional buoyancy and stability to the float 205 prior to the keel 207 being at least partially deployed. The buoyancy collars are typically removed after the wind turbine has floated off the barge 255 and after the keel modules 225 have been lowered to a sufficient depth to ensure static stability of the wind turbine without the need for the buoyancy collars. This allows for a more compact float 205 configuration.

[0165] FIG. 18 shows buoyancy tanks 315 and a keel 307 of a wind turbine 301 in accordance with a fourth embodiment of the invention. The keel 307 comprises a plurality of keel modules 325. The embodiment can be arranged similar to the first, second or third embodiments, except that the drive system 311 used to move the keel 307 from the non-deployed to the deployed conditions is different. In the fourth embodiment the drive system 311 includes an arrangement of strand jacks 312 to move the keel 307 from the non-deployed to the deployed conditions. As shown in FIGS. 18 and 19, a plurality of strand jacks 312 are mounted on upper ends 316 of each buoyancy tank 315. Typically a strand jack 312 is provided for each rod 309 (six are shown in FIGS. 18 and 19). Each strand jack 312 includes a feedable drive element 312a, which are sometimes referred to as steel cable strands, that is used to drive its respective rod 309 in an axial direction. The rods 309 are each constrained to move along a respective rectilinear path in a generally vertical direction. This drives the respective keel module 325 along a rectilinear path in a generally vertical direction. A strand jack is an established technology that is suitable for the purpose of deploying the rods 309.

[0166] The rods 309 that are associated with a particular buoyancy tank 315, and a particular keel module 325, are connected together by an annular member 314. The annular member 314 is located towards the upper ends of the rods 309.

[0167] FIG. 20 shows a lower end 318 of a buoyancy tank 315, when the keel 307 is the deployed condition. Brackets 320 are located towards the lower end 318 of each buoyancy tank. The brackets 320 limit movement of the rods 309, and therefore define the deployed position of the keel 307. The annular member 314 engages the brackets 320 and arrests movement of the rods 309.

[0168] After the keel 307 has been deployed, the strand jacks 312 can be removed from each buoyancy tank 315, for example can be used on another wind turbine.

[0169] In this embodiment the keel 307 comprises a plurality of keel modules 325, one keel module per buoyancy tank. Each keel module 325 is rigidly attached to its respective rods 309, for example the rods 309 can fit into sockets located in the keel module housing. The keel modules 325 are connected together. The drive system 312 can be arranged to move the keel modules 325 simultaneously, for example by synchronising operation of the strand jacks 312. In some arrangements, the keel modules 325 are not connected together and the drive system 312 can be arranged to move the keel modules 325 independently of each other.

[0170] FIG. 21 shows buoyancy tanks 415 and a keel 407 of a wind turbine 401 in accordance with a fifth embodiment of the invention. This embodiment differs from the preceding embodiments in that the rods 409 are pivotally attached to their respective buoyancy tanks 415 by pivot pins 420. In FIG. 21 pairs of rods 9 are pivotally attached to their respective buoyancy tank 415, typically towards the lower end of the buoyancy tank. The rods 409 are located on opposite sides of the respective buoyancy tank 415, and are typically diametrically opposite to one another.

[0171] The keel 407 comprises a plurality of keel modules 425, typically one for each buoyancy tank 415. Each keel module 425 is connected to one of the pairs of rods 409. Preferably the keel module is cylindrical, with the longitudinal axis of the cylinder being arranged perpendicular to the longitudinal axes of the rods 409. This means that the keel module 425 can be used as a float during transportation. The keel module 425 is typically attached to the distal ends of the respective pair of rods 409.

[0172] Each pair of rods 409 is arranged to pivot through an angle of approximately 90 degrees, moving its respective keel module 425 from a non-deployed position to a deployed position. Each pair of rods 409 is arranged to pivot from a generally horizontal orientation, in the non-deployed condition, to a generally vertical orientation in the deployed condition. The pairs of rods 409 are arranged to fold inwards. The arrangement is such that, when each pair of rods 409 is in a generally horizontal orientation, at least one pair of rods 409 overlies at least one other pair of rods 409 (see FIG. 21, which shows a folded arrangement). To facilitate this, the pivot axes of each pair of rods 409 are vertically offset from one another, to allow nestling of the pairs of rods 409 in the non-deployed condition.

[0173] The pairs of rods 409 can be limited to pivot through 90 degrees by means of appropriate blocking members or a suitable mechanism. Typically, the blocking members are arranged to prevent the pairs of rods 409 pivoting beyond the vertical direction.

[0174] The system includes a locking mechanism that is arranged to lock the orientation of respective pairs of rods with respect to their buoyancy tank 415. For example, the locking mechanism can be arranged to lock respective pairs of rods in the deployed orientation, i.e. in a generally vertically orientation. The locking mechanism ensures that the rods 409 are locked to their buoyancy tanks 415 so that the overall arrangement acts as a single body.

[0175] In this embodiment a drive system is not needed to move the keel modules 425 from the non-deployed positions to the deployed positions. During transit, the keel modules 425 can be filled with air. Due to the reduced displacement of the assembly's launch and transit condition, the wind turbine may be launched in the shallow waters of a port facility rather than requiring a submersible barge to assist launch into deeper costal waters. When located at the site of use, each keel module 425 can be filled with ballast. A preferred ballast is a solid ore, such as iron ore, that can be provided by a dredge pumping ship. This removes the ballasting operation off the critical path during on-shore assembly of the wind turbine 401. The weight of ballast in the keel modules 425 causes the keel modules 425 to sink under the action of gravity thereby rotating respective pairs of rods 409 about their respective pivot axes until the keel module 425 reaches its deployment position. Thus a drive system is not required to deploy the keel modules 425.

[0176] Of course, a drive system can be used to assist with the controlled deployment of the keel modules 425 if desired.

[0177] 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.

[0178] For example, the drive system can include at least one drive unit in the form of an electric motor and a suitable drive mechanism for driving each rod 9. A suitable drive mechanism may comprise a rack and pinion drive gear system or other drive mechanism suited to the environment and mode of operation. One drive motor and rack and drive mechanism can be provided per rod 9. In another arrangement one drive motor and drive mechanism can be provided per keel module 25.

[0179] More than one type of drive system 11 can be included in a wind turbine. For example, some buoyancy tanks 15 may include a drive system 11 according to the first embodiment, while other buoyancy tanks may include a drive system 11 according to the second embodiment.

[0180] A different number of buoyancy aids can be used.

[0181] A different number of keel modules 25 can be used. The number of keel modules 25 typically matches the number of outer buoyancy tanks.

[0182] The keel 7 can have a different arrangement from that shown. For example, the keel 7 does not have to have a triangular arrangement. The keel modules 25 can have different shapes from hexagonal.

[0183] The keel modules 25 can comprise open concrete boxes.

[0184] The drive devices 41,141 be in the form of hydraulic clamps.

[0185] In some embodiments at least one rod can comprise first and second tubular members concentrically arranged. This is to help provide a sufficient tensile capacity to take dynamic loading and fatigue margin for the life of the rod. The second tubular member can be located within the first tubular member. The second tubular member can be fixed to the first tubular member.

[0186] The central buoyancy tank can be arranged to include some ballast water at the start of operations. This ballast water may be used to assist with tensioning the mooring system during installation. Further ballast water may be gradually discharged over time to offset the increase in marine growth weight on the submerged buoyancy tanks. The central buoyancy tank can include a system for controlling the influx of water into the tank, and expulsion of water from the tank, in order to adjust the amount of water ballast contained therein.

[0187] The buoyancy collars 200 can comprise solid buoyancy blocks or inflatable buoyancy units.