A method for handling a wind turbine rotor blade

Abstract

The invention provides a method for handling a wind turbine rotor blade (11) of a horizontal axis wind turbine (1), which wind turbine comprises a tower (14) supported by and fixed to a foundation (17), a nacelle (15) on the tower, and a rotor hub (18) rotatably mounted to the nacelle, the method comprising - fixedly mounting a blade supporting device (21a, 21b) to the foundation and / or to the wind turbine, - lifting the blade to the hub, or lowering the blade from the hub, and - positioning the blade on the blade supporting device (21a, 21b) so as to be supported by the blade supporting device, before the blade is lifted to the hub, or upon lowering the blade from the hub.

Description

[0001] A METHOD FOR HANDLING A WIND TURBINE ROTOR BLADE

[0002] TECHNICAL FIELD

[0003] The present invention relates to a method for handling a wind turbine rotor blade of a horizontal axis wind turbine.

[0004] BACKGROUND

[0005] A horizontal axis wind turbine is known to have an electric generator in a nacelle on top of a tower, where a rotor, with one or more blades, with a substantially horizontal axis, is mounted to the nacelle and arranged to drive the generator.

[0006] Due to large blade sizes of modern wind turbines, challenges are created for the installation and service of the wind turbines. For example, when installing or replacing one or more blades of a wind turbine, the weight and size of the blades, and weather conditions, require careful consideration and planning. The challenges may be augmented when the wind turbine is placed offshore. Even more considerations may be needed when an offshore wind turbine is placed on a floating foundation, which may move in relation to the seabed during an installation or service procedure.

[0007] SUMMARY OF THE INVENTION

[0008] The present invention aims to facilitate blade installation and service operations on a wind turbine, in particular a wind turbine supported by an offshore floating foundation.

[0009] This object of the invention is reached with a method according to claim 1. Thus, the invention provides a method for handling a wind turbine rotor blade of a horizontal axis wind turbine, which wind turbine comprises a tower supported by and fixed to a foundation, a nacelle on the tower, and a rotor hub rotatably mounted to the nacelle, the method comprising fixedly mounting a blade supporting device to the foundation and / or to the wind turbine, lifting the blade to the hub, or lowering the blade from the hub, and positioning the blade on the blade supporting device so as to be supported by the blade supporting device, before the blade is lifted to the hub, or upon lowering the blade from the hub.

[0010] It is understood that the blade supporting device is not the hub. Neither is the blade supporting device a part of the hub, nor is the hub a part of the blade supporting device.

[0011] The blade may be supported by a lifting yoke. Thereby, positioning the blade on the blade supporting device may comprise positioning the yoke, supporting the blade, on the blade supporting device.

[0012] It is also understood that the blade supporting device may be fixedly mounted to the wind turbine. By the wind turbine being fixed to the foundation, relative movements between the wind turbine and the foundation are prevented. By the blade supporting device being fixed to the foundation and / or to the wind turbine, relative movements between, on one hand the blade supporting device and on the other hand the foundation and / or to the wind turbine, are prevented. If the blade supporting device is fixedly mounted to the foundation, since the tower, and thereby the wind turbine, is fixed to the foundation, the blade supporting device is fixed in relation to the wind turbine.

[0013] The method may be used to mount the blade to the hub. The blade may be elongated and extend from a blade root to a blade tip. For mounting the blade to the hub, one of the blade root and the hub may comprise a plurality of protruding engagement devices, and the other of the blade root and the hub may form a plurality of engagement apertures, each arranged to receive a respective of the engagement devices. Thereby, upon lifting the blade to the hub, the blade may be mounted to the hub.

[0014] The method may also be used to remove the blade from the hub. Thereby, the blade may be lowered from the hub.

[0015] The foundation may be a floating foundation. Since the blade supporting device is fixed in relation to the wind turbine, relative movement between the blade supporting device and the hub is prevented. This facilitates the operation of lifting the blade from the blade supporting device and mounting it to the hub, and also the operation of demounting the blade from the hub and lowering it to the blade supporting device.

[0016] In some embodiments, the blade supporting device, or a part of the blade supporting device, is demounted after the step of lifting the blade to the hub. Thereby, the blade supporting device, or a part thereof, may be temporarily installed for the blade lifting or lowering steps.

[0017] Lifting or lowering the blade may be done by means of a lifting yoke holding the blade. The yoke may be suspended from a crane boom. Preferably, the yoke is engaged with and guided by two elongated, parallel guide elements when the blade is lifted or lowered.

[0018] The crane boom may be mounted in or on the nacelle. Thereby, the crane boom may reach over and in front of hub. For example, where the hub is adapted to carry three blades extending radially outwardly from to hub, the hub may be parked so that two of the blades are directed partly upwards and partly sideways, in a so called bunny ear position. Thereby, the crane boom may be mounted to the nacelle, and arranged to reach over the hub and between the blades in the bunny ear position. The yoke may be suspended in a wire, cable, or rope extending between the crane boom and the yoke. Thereby the wire, cable, or rope may extend vertically past the hub, on a side of the hub which is opposite to the nacelle. The guide elements are preferably provided in addition to the wire, cable, or rope extending between the crane boom and the yoke.

[0019] The guide elements may extend from the crane boom to the blade supporting device or to the foundation. The guide elements may be flexible. For example, they may be formed by two wires, cables, or ropes. In some embodiments however, the guide elements may be rigid, e.g. in the form of beams or poles. The guide elements may be separated so as to extend in parallel at a distance from each other. The yoke may comprise guide element engagement devices for the engagement with the guide elements. The engagement devices may comprise respective wheel arrangements or borings for the engagements. Thereby, the yoke can move along the guide elements, while the guide elements restrict lateral movements of the yoke while allowing the yoke to move along the guide elements.

[0020] Thereby, the guide elements serve to reduce or disallow swinging of the yoke in a horizontal plane, e.g. turning of the yoke with the blade around a vertical axis. Thereby, the blade held by the yoke can be kept in a desired orientation. The guide elements may be particularly advantageous where the foundation is a floating foundation. Since the foundation, and thereby the wind turbine, may move, it can be a challenge moving the blade safely between the hub and the blade supporting device. Further, it may be challenging to control exactly where the blade lands when moved downwards from the hub. In addition, with a moving floating foundation it may be challenging to control the mating of the blade to the hub when the blade is moved towards the hub. The guide elements will reduce or eliminate these problems. The guide elements will reduce relative movements between on one hand the blade and on the other hand the blade supporting device and the hub. Thereby, a lower safety factor on the crane design may be allowed.

[0021] A tension adjustment arrangement may be provided, e.g. on the crane boom or at bottom ends of the guide elements, for adjusting the tension in the guide elements.

[0022] In some embodiments, one or more taglines are provided to prevent swinging movements of the blade, e.g. turning of the blade around a vertical axis. The taglines could extend from the foundation to the blade. For example, a tagline may be connected to the blade, at a distance from a lifting wire, lifting cable, or lifting rope for the blade, and also connected to the foundation.

[0023] The method may comprise providing a crane boom which is mounted to the nacelle and reaches over the hub. Thereby, the following steps may be conducted before the yoke is engaged with a blade that is mounted to the hub, e.g. to remove the blade from the hub. In one of the steps, the hub is turned so that the blade, when mounted to the hub, moves to a position which is not in a six o’clock position. This movement may be from a six o’clock position, or from another position which is not a six o’clock position. A six o’clock position can be regarded as a position in which the blade points straight downwards when the wind turbine is viewed from the front, i.e. from where the wind approaches during normal operation of the wind turbine. Subsequently, while the blade is not in the six o’clock position, a lifting yoke is lifted towards the hub while the lifting yoke is suspended from the crane boom. Thereby, the lifting yoke is suspended in front of the hub. I.e. a lifting wire, a lifting cable, or a lifting rope may extend in front of the hub. Subsequently the rotor is turned so that the blade moves to the six o’clock position. Thereby, the yoke is preferably lifted high enough to avoid interference with the blade. Thereby, where the blade is, e.g. due to a rotor tilt and / or a blade prebend, in the path of the yoke, interference can be avoided when the yoke is lifted to subsequently engage the blade. For such an engagement, the blade may be moved downwards.

[0024] Thus, subsequently to turning the hub so that the blade moves to the six o’clock position, the lifting yoke may be engaged with the blade, the blade may be decoupled from the hub, and the step of lowering the blade may be performed.

[0025] The turn of the hub to move the blade away from the six o’clock position may be e.g. at least 5 or 10 degrees, e.g. around 15 degrees. The yoke may be lifted from the blade supporting device. The embodiment with the turn of the blade away from the six o’clock position may be particularly advantageous where the crane boom is not tumable around a vertical axis.

[0026] In some embodiments, the method comprises,

[0027] - while the blade is held by a lifting yoke which is suspended from a crane boom during any one of the steps of lifting the blade to the hub or lowering the blade from the hub,

[0028] - turning the blade by means of the yoke, from a first position to a second position wherein the blade is closer to a horizontal position on one of the first and second positions than in the other of the first and second positions.

[0029] Thus, the yoke may be arranged to turn the blade from a substantially horizontal position to a substantially vertical position, or vice versa. Thereby, where the blade is vertically oriented when being mounted or dismounted to the hub, and horizontal when supported by the blade supporting device, the blade orientation may be changed as needed when transported between the hub and the blade supporting device. Thereby, said arrangement where the yoke is engaged with and guided by two elongated, parallel guide elements, is particularly useful to ensure that the turning of the blade from the first to the second position is done in a controlled manner.

[0030] Preferably, where lifting or lowering the blade is done by means of a blade crane comprising a crane boom which is fixed to the nacelle. Thereby, the crane boom may be fixed so that it cannot be turned around a vertical axis. This allows the crane being provided in a simpler form, since no slewing bearing is needed. Also, an easy installation of the crane is allowed, since the crane may have less parts and be relatively light. Preferably, the crane boom is telescopic. Thereby, the crane boom may comprise a plurality of telescope parts. The telescopic parts may be arranged as concentric tubular sections adapted to slide into one another.

[0031] Preferably, where the crane boom is telescopic, and where the method comprises installing the blade crane in or on the nacelle, the blade crane installation comprises lifting, by means of a service crane which is permanently installed in or on the nacelle, the telescope parts separately. Thereby, a simple and effective crane installation is provided with the service crane.

[0032] Preferably, the crane boom reaches, when the blade is lifted or lowered, over the hub and in front of the hub. As suggested above, the hub may be parked so that two of three blades on the rotor are directed partly upwards and partly sideways, in a bunny ear position. Thereby the third blade points downwards or at least with a downwards component. Thereby, the crane boom may reach between the blades forming the “bunny ears”. As suggested above, before the yoke is engaged with the third blade, the hub may be turned so that the third blade moves to a position which is not in a six o’clock position. Thereby, the turning of the hub is preferably limited so that none of the blades forming the bunny ears interfere with the crane boom.

[0033] The object is also reached with a method for handling a wind turbine rotor blade of a wind turbine, which wind turbine comprises a tower, a nacelle on the tower, and a rotor hub rotatably mounted to the nacelle, the method comprising lifting the blade to the hub, or lowering the blade from the hub, by means of a blade crane comprising a crane boom which is fixed to the nacelle. The crane boom may be telescopic. Thereby, the crane boom may comprise a plurality of telescope parts, and the method may comprise, for installing the blade crane in or on the nacelle, lifting, by means of a service crane which is permanently installed in or on the nacelle, the telescope parts separately. Upon the installation, the crane boom may reach, when the blade is lifted or lowered, over the hub and in front of the hub.

[0034] The object is also reached with a blade supporting device adapted to be fixedly mounted to a wind turbine and / or a foundation supporting the wind turbine, the blade supporting device being adapted to support a blade for a rotor of the wind turbine. It is understood that the blade supporting device is not a hub of a rotor of the wind turbine. As suggested above, where the foundation is a floating foundation, by fixing the blade supporting device in relation to the wind turbine, relative movement between the blade supporting device and the hub is prevented. As also suggested above, this facilitates lifting and lowering the blade towards and away from the hub. It should be noted that the blade supporting device is preferably also adapted to support a lifting yoke adapted to engage the blade for the lifting or lowering of the blade.

[0035] The object is also reached with a power generating assembly according to claim 15.

[0036] BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Below examples of the invention will be described in detail with reference to the drawings, in which:

[0038] - fig. 1 is a perspective view of a wind turbine on a floating foundation,

[0039] - fig. 2A is a perspective view of a wind turbine rotor blade,

[0040] - fig. 2B is a perspective view of a root of the blade in fig. 2A,

[0041] - fig. 3 is a sideview of a portion of the wind turbine in fig. 1,

[0042] - fig. 4 is a flow diagram depicting steps in an embodiment of a method according to the invention,

[0043] - fig. 5 is a perspective view of a part of a blade supporting device used in the method depicted in fig. 4,

[0044] - fig. 6 is an exploded view of a crane used in the method depicted in fig. 4,

[0045] - fig. 7 and fig. 8 are perspective views of the crane in fig. 6 during assembly thereof,

[0046] - fig. 9 is a perspective view of a part of the wind turbine in fig. 1 with the crane in fig.

[0047] 6,

[0048] - fig. 10 is a front view of a part of a rotor of the wind turbine in fig. 1,

[0049] - fig. 11 is a perspective view of a part of the wind turbine and foundation in fig. 1, and a yoke placed on a blade supporting device fixed to the foundation,

[0050] - fig. 12 - fig. 14 are perspective views of respective portions of the wind turbine in fig.

[0051] 1, at respective steps of the method depicted in fig. 4,

[0052] - fig. 15 - fig. 16 are perspective views of the wind turbine and foundation in fig. 1, at respective steps of the method depicted in fig. 4, - fig. 17 is a perspective view of a portion of a wind turbine and a foundation, with a blade supporting device according to an alternative embodiment of the invention.

[0053] DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0054] Fig. 1 shows a horizontal axis wind turbine 1. In this example, the wind turbine is an offshore wind turbine. However, the invention is equally applicable to an onshore wind turbine.

[0055] The wind turbine is supported by a floating foundation 17. The foundation 17 is arranged to float in a body of water, such as a sea or a lake. The foundation 17 is arranged to be partially submerged in the body of water. An anchoring assembly (not shown) is arranged to anchor the floating foundation to the bottom of the body of water. The anchoring assembly may comprise a plurality of anchoring lines.

[0056] The floating foundation 17 comprises four floating bodies 1701, 1702. The floating bodies may be shaped as cylinders with substantially vertical centre axes. The floating bodies comprise three corner bodies 1701 which are located at respective comers of a virtual triangle formed in a top view of the foundation. The floating bodies further comprise a centre body 1702, which is located at the centre of said virtual triangle. Structural elements 1703 connect the corner bodies 1701 with the centre body 1702. The structural elements may form trusses. The wind turbine is located of the centre body 1702.

[0057] Alternatively, the foundation does not have a centre body. Thereby the wind turbine could be located on one of the comer bodies 1701, which are connected with each other by structural elements.

[0058] The wind turbine 1 comprises a tower 14 supporting a nacelle 15. A rotor 16 is mounted to the nacelle. The tower is supported by the foundation 17. The nacelle 15 can be turned, or yawed, in relation to the tower 14, around a vertical axis.

[0059] The rotor 16 comprises a plurality of wind turbine blades 11, 12, 13 that extend radially from a central hub 18. In this example, the rotor 16 comprises three blades 11, 12, 13. The hub 18 is mounted to the nacelle 15. Fig. 2A is a view of one of the blades 11 of the wind turbine 1. The blade 11 extends from a root end 111 to a tip end 112 in a longitudinal 'spanwise' direction. The blade may be of any suitable length, e.g. in the interval 30-160 metres. The blade 11 may transition from a circular profile to an airfoil profile moving from the root end 111 of the blade 11 towards a shoulder 113 of the blade 11. The shoulder 113 may be the widest part of the blade 11. The blade 11 may have its maximum chord at the shoulder 113. The blade 11 extends between a leading edge 114 and a trailing edge 115 in a transverse 'chordwise' direction. The blade presents a pressure surface 116 on a pressure side of the blade 11 and a suction surface 117 on a suction side of the blade 11. The blade 11 comprises a shell 118. The shell may be formed primarily of fibre-reinforced composite FRC. The blade may comprise an internal structure. The internal structure may comprise two spar caps and one or more webs.

[0060] Reference is made to fig. 2B and fig. 3. The blade root 111 comprises a root shell 115 forming a tubular shape of the blade root. The root shell 115 has at the root end a circular cross-sectional shape. The blade root end 111 is defined by an end surface 113 of the root shell. The end surface 113 is oriented substantially perpendicularly to a longitudinal direction of the blade. A plurality of protruding engagement devices 119 extend from the blade root end. The engagement devices extend substantially in parallel with the blade longitudinal axis. The engagement devices are in this example in the form of pins or studs. Preferably the studs are threaded. As illustrated in fig. 3, in a respective blade mounting flange 182 for each blade, the hub 18 forms a plurality of engagement apertures 181 each arranged to receive a respective of the engagement devices 119. The blade mounting flange may form, or be fixed to, a bearing ring of a pitch bearing for adjusting the pitch angle of the blade while the wind turbine is in operation. Each blade is mounted the hub by the studs 119 entering the apertures 181, so as to extend through the holes. When the end surface 113 of the blade abuts the mounting flange 182 of the hub, end portions of the studs extend into the interior of the hub, and nuts are threaded on the stud end portions to secure the blade to the blade mounting flange. In alternative embodiments, the hub comprises protruding engagement devices. Thereby, the blade may form a plurality of engagement apertures each arranged to receive a respective of the engagement devices.

[0061] Embodiments of the invention provides a method for handling a wind turbine rotor blade of a horizontal axis wind turbine. The blade installation may be done while the wind turbine is shut down after having operated to produce power to a grid. Thereby the blade installation may be a part of a service operation. Alternatively, the blade installation may be a part of an installation process of a new wind turbine.

[0062] Below such an embodiment of the method will be described with reference to fig. 4 and further figures. The embodiment comprises removing one of the blades 11 from the hub 18.

[0063] The method comprises fixedly mounting SI a blade supporting device 21a, 21b to the foundation and / or to the wind turbine. The blade supporting device, or a part thereof, may be permanently installed. Thereby, the blade supporting device, or a part thereof, is mounted to the foundation and / or to the wind turbine at an installation process of the foundation and the wind turbine. In some embodiments, the blade supporting device, or a part thereof, is temporarily installed.

[0064] In the example in fig. 1, a part 21a of the blade supporting device is permanently installed to the foundation, where the tower 14 is supported. This is shown in more detail in fig. 11. In addition to a method for handling a wind turbine rotor blade, the permanently installed blade supporting device part 21a may serve as a working platform for other processes. A further part 21b of the blade supporting device is temporarily mounted to the permanently installed blade supporting device part 21a. Thereby, the temporarily installed blade supporting device part 21b forms an extension of the permanently installed blade supporting device part 21a.

[0065] As exemplified in fig. 5, the temporarily installed blade supporting device part 21b comprises lower attachment devices 241 for guide elements described below. More generally, such attachment devices may be mounted to the blade supporting device 21a, 21b, or to the foundation 17 (fig. 1).

[0066] As exemplified in fig. 1, the method comprises rotating the hub 18, so that one of the blades is in a six o’clock position, and the other two blades 12, 13 are in a bunny ear position.

[0067] Reference is made to fig. 6 - fig. 9. The method further comprises installing S2 a blade crane 2, depicted in an exploded view in fig. 6. As can be seen in fig. 9 blade crane comprises a crane boom 23 which is mounted to the nacelle 15 and reaches over the hub 18. The crane boom 23 is telescopic. As can be seen in fig 6, the crane boom 23 comprises a plurality of telescope parts 231. The crane 2 further comprises a hoist 201 with drums for a lifting wire, cable, or rope. The crane further comprises a stand 202 for supporting the crane boom 23.

[0068] Upper attachment devices 241 for the guide elements described below are mounted to one of the telescope parts 231, which part is intended to form a distal end of the boom 23.

[0069] The method further comprises lifting the stand 202 of the crane 2 from the foundation 17 (fig. 1) to the nacelle, using a service crane. The service crane may be permanently installed in the nacelle. Further, the stand 202 is mounted to the nacelle. For the crane installation, a top cover of the nacelle may be removed, e.g. as illustrated in fig. 9.

[0070] The telescope parts 231 (fig. 6) are lifted separately to the nacelle by means of the service crane. Thereby, the upper attachment devices 241 (fig. 6) for the guide elements described below may be mounted to one of the telescope parts. Further, the guide elements described below may be lifted to the nacelle with the service crane.

[0071] As exemplified in fig. 7, using the service crane 151, one of the telescope parts 231 is attached to the stand 202. The attachment comprises an articulated joint. Thereby, the telescope part attached to the stand 202 is oriented vertically. Using the service crane 151, further telescope parts 231 are successively introduced into respective previously installed telescope parts 231, as exemplified in fig. 7. Further, as exemplified in fig. 8, the hoist 201 is installed on the crane boom using the service crane 151.

[0072] Thereafter, the crane boom 23 is folded to be substantially horizontal. For this a suitable actuator or tool (not shown) may be used. Further, the crane boom is telescopically extended. For the extension, a suitable tool or actuator (not shown) may be provided, for example a hydraulic actuator. Thereby, the crane boom 23 reaches between the blades 12, 13 in the bunny ear position, over the hub 18, and in front of the hub, as exemplified in fig. 9. As exemplified in fig. 9, a platform may be provided for access around the crane during installation and use. The method further comprises yawing the nacelle so that the blade to be removed is located above the blade supporting device 21a, 21b (fig. 1).

[0073] Reference is made to fig. 10. The method further comprises turning S3 the hub 18 so that the blade 11 to be removed moves to a position which is not in a six o’clock position. In this example, the blade 11 is positioned to that it extends in an angle VT, e.g. 15 degrees, from the six o’clock position. Since the rotor is tilted, as is common on horizontal axis wind turbines, a blade will, in the six o’clock position, extend with a forward component, away from the tower. Moving the blade away from the six o’clock position will allow moving a lifting yoke, as described below, up towards the hub, without interfering with the blade.

[0074] As exemplified in fig. I l a lifting yoke 22 is moved S4 to the blade supporting device 21a, 21b. The yoke 22 is adapted to engage and support a blade. Thus, it is understood in addition to being adapted to support a blade, the blade supporting device 21a, 21b is adapted to support a blade lifting yoke 22. The yoke may be transferred from a vessel (not shown). The vessel may be docked to the foundation 17 (fig. 1). The transferral of the yoke from the vessel to the blade supporting device may be done by a crane onboard the vessel, or by a crane on the foundation. In onshore embodiments, the yoke may be transferred from the ground or from a vehicle which is parked next to the wind turbine, wherein the transferral of the yoke from the ground or the vehicle to the blade supporting device may be done by a crane on the ground, or by a crane onboard the vehicle. The blade supporting device 21a, 21b may be provided with suitable guide devices for a desired position and orientation of the yoke in relation to the wind turbine.

[0075] The yoke 22 may comprise two clamps for engaging the blade, which clamps are intended to be distributed along the longitudinal axis of the blade. The yoke preferably has a tilt function, whereby a hook lifting point of the yoke can be moved in relation to the clamps, so that, as exemplified below, when the yoke is suspended, the orientation of clamps, and thereby the orientation of the longitudinal axis of a blade held by the yoke, can be changed.

[0076] The method further comprises installing S5 the guide elements 24 so as to extend between the lower attachment devices 241 and the upper attachment devices 242 (fig. 9). The guide elements 24 may be wires, cables, or ropes. The guide elements may be lowered from the crane 2 (fig. 9). The guide elements 24 are further arranged to extend through guide element engagement devices on the yoke. A tension adjustment arrangement, e.g. in the form of the crane hoist 201 (fig. 9), may be provided for adjusting the tension in the guide elements 24.

[0077] While the blade is not in the six o’clock position, the lifting wire of the crane 2 is lowered and a yoke engagement device, e.g. a hook or similar, on the lifting wire is engaged with the yoke 22. As exemplified in fig. 12, subsequently the yoke 22 is lifted S6 by means of the crane 2 towards the hub. The yoke is lifted far enough so as for the blade 11 to be turned to the six o’clock position without interfering with the yoke. Subsequently the hub 18 is turned S7 so that the blade 11 moves to the six o’clock position, as exemplified with the arrow AM in fig. 12. Preferably, before the hub is turned S7, one of the guide elements is loosened or detached, to avoid interference with the blade 11 when the blade moves to the six o’clock position. When the blade has moved to the six o’clock position, the guide element can be tightened or attached.

[0078] As exemplified in fig. 13, subsequently the lifting yoke 22 is engaged S8 with the blade 11. For this, the yoke would be lowered. In addition, the degree of extension of the telescoping crane boom 23 could be adjusted to control the position of the yoke. The position of the guide element engagement devices on the yoke could be adjusted in order to keep the guide elements 24 straight.

[0079] The yoke 22 is preferably attached at the centre of gravity of the blade 11. More specifically, the clamps of the yoke are distributed along the longitudinal axis of the blade, on opposite sides of the blade centre of gravity. The yoke could comprise a movable lifting point to adapt the position of the lifting point to the position of the combined centre of gravity for the yoke and the blade.

[0080] Subsequently, as exemplified in fig. 14, the blade 11 is decoupled S9 from the hub 18. Thereby, the yoke 22 which is suspended from a crane boom 23 holds the blade 11. For this a hoist system may be attached to the crane boom 23. By means of the yoke tilt function, the blade is turned from the tilted orientation caused by the rotor tilt, to a vertical orientation. More specifically, by turning the yoke lifting point in relation to the blade 11, as indicated by the arrow AY in fig. 14, the blade is turned to vertical as indicated by the arrow AB. Subsequently the blade is lowered S10, while the yoke is engaged with and guided by the two elongated, parallel guide elements 24.

[0081] As exemplified in fig. 15 with the arrow AB2, before the blade and the yoke has reached the blade supporting device 21a, 21b, the blade is turned SI 1 by means of the yoke tilt function, from vertical position to a horizontal position. Thereby, the guide elements 24 serve to control the positions of the blade 11 and the yoke 22, by counteracting tendencies of translatory motions of the blade and yoke.

[0082] As exemplified in fig. 15, one or more tag lines 25, extending from the blade 11 to the foundation 17, may be arranged to prevent rotation of blade around a vertical axis. The tension in the one or more taglines may be controlled by respective hoists, which may be controlled remotely.

[0083] As exemplified in fig. 16, upon lowering the blade from the hub, the yoke with the blade 11 is positioned S12 on the blade supporting device 21a, 21b. Thereupon, the yoke is detached from guide elements 24 and crane lifting wire. Thereafter, the yoke may be attached to a crane to be lifted away S13 with the blade. Thereby, the yoke and the blade may be transferred to a vessel (not shown). The vessel may have a positioning system so that it can be held in a fixed position in the relation to the foundation 17 at a distance from the foundation. In other embodiments, the vessel may be docked to the foundation 17. Thereby, the crane may be on board the vessel, or on the foundation. In some embodiments, the blade is transferred to another yoke before being lifted away to the vessel. Thereby, a lighter yoke may be used for the lift to the vessel. In onshore embodiments, the yoke with the blade may be transferred to the ground, or to a vehicle. The vehicle may be parked next to the wind turbine. Thereby, the crane may be on the ground or on the vehicle. In some embodiments, the yoke is used as transport cradle for the blade, as the blade is transported away from the wind turbine. In other embodiments, the blade is transferred to a cradle before being transported away from the wind turbine.

[0084] Understood that for mounting a blade to the hub, the steps described above are done substantially in the reverse order. For example, a yoke, with the blade, is positioned on the blade supporting device 21a, 21b, before the blade is lifted to the hub. Thereby, the blade supporting device 21a, 21b, or a part thereof, could be demounted after the step of lifting the blade to the hub.

[0085] It should be noted that where one or both of the remaining blades are to be dismounted from the hub, the crane boom 23 (fig. 9) may be telescopically retracted, so that the hub can be turned so as for one of the remaining blades to be positioned for being dismounted.

[0086] Thereafter, the boom 23 may again be extended.

[0087] As suggested above, in some embodiments, the blade supporting device may be mounted on the wind turbine, rather than on the foundation. Fig. 17 shows an example where the blade supporting device 21a, 21b is mounted on the tower 14 of the wind turbine.

[0088] As will be understood by those skilled in the present field of art, numerous changes and modifications may be made to the above described and other embodiments of the present invention, without departing from its scope as defined in the appending claims.

Claims

CLAIMS1. A method for handling a wind turbine rotor blade (11) of a horizontal axis wind turbine (1), which wind turbine comprises a tower (14) supported by and fixed to a foundation (17), a nacelle (15) on the tower, and a rotor hub (18) rotatably mounted to the nacelle, the method comprising fixedly mounting a blade supporting device (21a, 21b) to the foundation and / or to the wind turbine, lifting the blade to the hub, or lowering the blade from the hub, and positioning the blade on the blade supporting device (21a, 21b) so as to be supported by the blade supporting device, before the blade is lifted to the hub, or upon lowering the blade from the hub.

2. A method according to claim 1, wherein the foundation (17) is a floating foundation.

3. A method according to any one of the preceding claims, wherein the blade supporting device (21a, 21b), or a part of the blade supporting device, is demounted after the step of lifting the blade to the hub.

4. A method according to any one of the preceding claims, wherein lifting or lowering the blade is done by means of a lifting yoke (22) holding the blade, which yoke is suspended from a crane boom (23), wherein the yoke is engaged with and guided by two elongated, parallel guide elements (24) when the blade is lifted or lowered.

5. A method according to claim 4, wherein the guide elements (24) extend from the crane boom (23) to the blade supporting device (21a, 21b) or to the foundation.

6. A method according to any one of the preceding claims, comprising providing a crane boom (23) which is mounted to the nacelle (15) and reaches over the hub (18), turning the hub (18) so that the blade (11), when mounted to the hub, moves to a position which is not in a six o’clock position, subsequently, while the blade is not in the six o’clock position, lifting a lifting yoke (22) towards the hub while the lifting yoke issuspended, in front of the hub, from the crane boom, and subsequently turning the rotor so that the blade moves to the six o’clock position.

7. A method according to claim 6, comprising, subsequently to turning the hub (18) so that the blade (11) moves to the six o’clock position, engaging the lifting yoke (22) with the blade, decoupling the blade from the hub, and performing the step of lowering the blade.

8. A method according to any one of the preceding claims, comprising,- while the blade (11) is held by a lifting yoke (22) which is suspended from a crane boom (23) during any one of the steps of lifting the blade to the hub (18) or lowering the blade from the hub,- turning the blade by means of the yoke, from a first position to a second position wherein the blade is closer to a horizontal position on one of the first and second positions than in the other of the first and second positions.

9. A method according to any one of the preceding claims, wherein lifting or lowering the blade (11) is done by means of a blade crane (2) comprising a crane boom (23) which is fixed to the nacelle (15).

10. A method for handling a wind turbine rotor blade (11) of a wind turbine, which wind turbine comprises a tower (14), a nacelle (15) on the tower, and a rotor hub (18) rotatably mounted to the nacelle, the method comprising lifting the blade to the hub, or lowering the blade from the hub, by means of a blade crane (2) comprising a crane boom (23) which is fixed to the nacelle.

11. A method according to any one of claims 9-10, wherein the crane boom (23) is telescopic.

12. A method according to claim 11, comprising installing the blade crane (2) in or on the nacelle, wherein the crane boom (23) comprises a plurality of telescope parts, wherein the blade crane installation comprises lifting, by means of a service crane which is permanently installed in or on the nacelle, the telescope parts separately.

13. A method according to any one of claims 9-12, wherein the crane boom (23) reaches, when the blade (11) is lifted or lowered, over the hub (18) and in front of the hub.

14. A blade supporting device (21a, 21b) adapted to be fixedly mounted to a wind turbine (1) and / or a foundation (17) supporting and fixed to the wind turbine, the blade supporting device being adapted to support a blade (11) for a rotor (16) of the wind turbine.

15. A power generating assembly comprising a wind turbine (1), a foundation (17) supporting the wind turbine, and a blade supporting device (21a, 21b) according to claim 14 which is fixedly mounted to the wind turbine and / or the foundation, wherein the foundation is a floating foundation.

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