WO2021219185A1

WO2021219185A1 - A wind turbine blade installation method

Info

Publication number: WO2021219185A1
Application number: PCT/DK2021/050131
Authority: WO
Inventors: Adrian Botwright
Original assignee: Vestas Offshore Wind A/S
Priority date: 2020-04-28
Filing date: 2021-04-28
Publication date: 2021-11-04
Also published as: EP4143436A1

Abstract

The invention provides a method for horizontal installation of a blade (11) of a horizontal axis wind turbine (1), wherein the blade (11) extends longitudinally between a blade root (111) and a blade tip (112), the method comprising providing a nacelle (15) for the wind turbine, and a rotor hub (18) mounted to the nacelle, providing a first blade guide device (41) so as to be fixed in relation to the hub (18), the first blade guide device comprising a first engagement device (416), providing a second blade guide device (42) so as to be fixed in relation to the blade (11), the second blade guide device comprising a second engagement device (426), moving the blade (11) towards the hub (18) by means of lifting means (3), providing, while the blade (11) is supported by the lifting means (3), an engagement movement of the first engagement device and/or of the second engagement device, which leads the first engagement device, and/or the second engagement device, to an engagement position in which the first and second engagement devices, and thereby the first and second blade guide devices (41, 42), are engaged to each other, and providing a mounting movement of the blade, with the first and second blade guide devices (41, 42) engaged to each other, towards a mounting position in which it is fastened to the hub (18), wherein the engagement movement is substantially parallel to, or has a component in, a longitudinal direction of the blade.

Description

A WIND TURBINE BLADE INSTALLATION METHOD

TECHNICAL FIELD

The present invention relates to a method for installation of a blade of a horizontal axis wind turbine, and a method for planning and executing an installation of one or more blades of a horizontal axis wind turbine.

BACKGROUND

A horizontal axis wind turbine typically comprises a tower supporting a nacelle to which a rotor is mounted. The rotor comprises one or more wind turbine blades which extend radially from a central hub.

There are different known ways of installing blades to a horizontal axis wind turbine. Blades may be installed in an installation process of a wind turbine, or a wind turbine farm. One or more blades may also be installed in a service process of a wind turbine. For example, a blade of a wind turbine may be removed, and replaced by another blade, or the blade may be reinstalled after service or repair.

In some methods, the blades are mounted to the hub on the ground, and the assembled rotor, with the hub and the blades, is lifted with a crane to the nacelle, at the top of the tower of the wind turbine, and mounted to it. In other methods, the blades are lifted individually one after the other with a crane to the hub which is mounted to the nacelle at the top of the tower of the wind turbine. In such individual blade mounting methods the hub may be rotated between each blade installation so as to accommodate for the mounting of the next blade. For example, on three bladed wind turbines, the hub is rotated 120 degrees between each blade installation.

For individual mounting of blades, one of two fundamentally different methods are typically used. The first one is vertical blade installation, where the blade is oriented in a vertical direction when it is brought into a mating position with the hub. The second individual blade installation method is horizontal blade installation. In horizontal blade installation, the blade is oriented substantially horizontally when it is brought towards a mounting position in which it is fastened to the hub. With the present trend towards increasing sizes of wind turbines and their blades, it is becoming more important to control the orientation of the blade while it is moved towards the hub. The ability to control the blade is dependent on the wind speed. For orientation control it is known to use, besides a lifting wire to the crane, control wires or tag lines. Nevertheless, the need for a safe installation process prevents installation when wind speeds, or wind gust speeds, are above a certain limit.

Further, where the wind turbine is an offshore turbine, wave induced tower oscillations may cause the hub to oscillate in relation to the blade to be installed. Such oscillations may make blade installation difficult.

EP2927478A1 discloses a stabilisation beam being attached to a blade holder, attached to a crane and holding a blade. The stabilisation extends from the blade holder towards the blade root, in parallel with the blade longitudinal direction. An elongated guiding element is attached to a forward end of the wind turbine rotor hub, so as to be aligned with the rotational axis of the rotor hub. While the blade is held by the crane, a distal end of the stabilisation beam, extending transversely to the rotor hub rotational axis, is positioned forward, along the hub rotational axis, of a distal end of the guiding element. The distal end of the stabilisation beam then has to be moved laterally to the blade longitudinal direction, to be coupled to the distal end of the elongated guiding element. The guiding element and the stabilization beam are then coupled to each other. Then, the blade is attached to the rotor hub.

The coupling in said document of the guiding element and the stabilisation beam is quite complicated. Thereby, there is a risk of unintentional movements of parts involved. Thereby, there is a risk of damage to parts involved. For example, there is a risk that the stabilisation beam comes into contact with the rotor hub. Therefore there is a desire for a safer blade installation method.

Thus, it would be beneficial with a blade installation method which further improves the control of the blade. This may allow blades to be installed in higher wind speeds than those in which known installation methods are allowed. SUMMARY

It is an object of the invention to provide one or more of an increase the tolerance of blade installation methods to weather conditions; an improved control of the blade during blade installation, for example of the orientation of the blade; and a blade installation method, with an improved control of the blade, while maintaining a high degree of safety during the installation.

The object is reached with a method according to claim 1. Thus, the invention provides a method for horizontal installation of a blade of a horizontal axis wind turbine, wherein the blade extends longitudinally between a blade root and a blade tip. The method comprises providing a nacelle for the wind turbine, and a rotor hub mounted to the nacelle. The method comprises providing a first blade guide device in fixed relation to the hub, the first blade guide device comprising a first engagement device. The method comprises providing a second blade guide device in fixed relation to the blade, the second blade guide device comprising a second engagement device. The method comprises moving the blade towards the hub by means of lifting means. The method comprises providing, while the blade is supported by the lifting means, an engagement movement of the first engagement device and/or of the second engagement device, which leads the first engagement device, and/or the second engagement device, to an engagement position in which the first and second engagement devices, and thereby the first and second blade guide devices, are engaged to each other. The method comprises providing a mounting movement of the blade, with the first and second blade guide devices engaged to each other, towards a mounting position in which the blade is fastened to the hub. According to the invention, the engagement movement is substantially parallel to, or has a component in, a longitudinal direction of the blade.

Thus, the engagement movement, which leads to the engagement position in which the first and second engagement devices are engaged to each other, may be substantially parallel to the blade longitudinal direction. As exemplified below, at least a part of the engagement movement may have a component in the blade longitudinal direction and another component in the transverse direction of the blade. The transverse component may be provided by an engagement guiding arrangement, as exemplified below. Thus, the engagement movement may be at least partly parallel to the blade longitudinal direction. The engagement movement may start where the blade is at a distance from the hub. Thereby, the blade may be oriented as it will be oriented in the mounting position. Preferably, the engagement movement leads the first and/or second engagement device all the way to the engagement position.

As exemplified below, the blade may be guided, in the mounting movement, by the engaged first and second blade guide devices. The engaged first and second blade guide devices may secure that any movement of the hub is followed by the blade, and vice versa. This may make the blade installation less dependent on the weather. For example, the blade control may be improved, and the wind speed tolerance may be increased. Further, the blade installation may be allowed despite a risk of tower oscillations due to conditions at the site of the wind turbine. As suggested, tower oscillations may be wave induced tower oscillations in an offshore wind turbine.

The reduced dependence on the weather makes the timing of the blade installation more predictable. This provides an important advantage, since equipment for blade installation, such as a crane, may generate costs which are proportional to the duration in which it is present at the installation site. Therefore, since the invention allows a reduction of the risk of waiting for the weather conditions to improve, installation costs may be reduced.

The blade mounting movement towards the hub mounting position may be parallel with the blade longitudinal direction. Where the mounting movement is parallel with the blade longitudinal direction, the engagement movement may thus be substantially parallel with the mounting movement. Thereby, the engaging and mounting movements may be performed without any substantial changes in the movement direction of any part involved. Thereby, embodiments of the method may provide a simplicity in the blade installation procedure. This decreases the risk of unintentional movements of any part involved. Thereby, safety is increased.

The blade root may have a circular cross-section. Thereby, the blade root may be substantially cylindrical. The blade root may have an end face which is perpendicular to a central axis of a cylinder formed by the blade root. Threaded pins may be distributed along a periphery of the blade root end face. The pins may be arranged to enter respective holes in the rotor hub. The pins may protrude from the blade root end face. The pins may extend in parallel with the blade root cylinder axis. The mounting movement may start where the blade is at a distance from the hub. In the mounting position, the blade may be mounted to a circular mounting flange of the hub. Thereby, the threaded pins may enter respective holes in the mounting flange. For aligning the pins and the holes circumferentially, a blade pitch system of the wind turbine may be used. Thereby, the blade pitch system may be used to move the holes circumferentially.

The blade longitudinal direction of the blade may be defined by the blade root cylinder axis. The blade longitudinal direction of the blade may be defined by a straight line from a centre of the blade root to the blade tip. Such a line may be substantially parallel with the blade root cylinder axis. In some cases, e.g. where the blade has a so called pre-bend, a straight line from a centre of the blade root, to the blade tip, may be slightly non-parallel with the blade root cylinder axis. Thereby, the engagement movement may be substantially parallel to, or have a component along, the blade root cylinder axis.

The method is easily adapted to installation processes for new wind turbines, as well as service processes on wind turbines. Thus, in some embodiments, the blade installation is done while the wind turbine is shut down after having operated to produce power to a grid.

Thereby, the blade installation may be done in a service operation on the wind turbine.

The engagement movement may be provided while the blade is supported by the lifting means. The lifting means may comprise a crane. The lifting means may lift the blade towards the hub. The lifting means may be separate from the wind turbine. However, in some embodiments, the lifting means could be mounted on or in the wind turbine. The support of the blade by the lifting means may be done by means of a holding device of the lifting means. The holding device may be in any suitable form, e.g. a blade gripping device. The holding device may engage the blade in a region between the blade root and the blade tip. For example, the holding device may engage the blade at a shoulder of the blade. The blade may be suspended from a crane boom of the lifting means with one or more wires between the boom and the blade holding device. The vertical position of the blade may be adjusted by feeding the wire in or out. The position of the blade may be also adjusted by adjusting the angle of the crane boom. The crane boom may be arranged to rotate around a vertical axis. Such a rotation may be referred to as a slewing action of the crane. Preferably, the engagement movement involves moving the blade. The blade may undergo the engagement movement. Thereby, the second engagement device may move with the blade. The engagement movement may involve moving the blade towards the hub. Thereby, the blade may be supported by the lifting means. The engagement movement of the blade may be substantially parallel to the longitudinal direction of the blade.

This engagement movement of the blade may considerably simplify the blade installation procedure compared to what is described in said prior art EP2927478A1. The blade may be oriented substantially horizontally during the engagement movement. The blade may be suspended from a crane boom. The crane boom may extend, as seen from above, substantially perpendicularly to the blade longitudinal direction. The crane boom may extend, as seen along the longitudinal axis of the blade, in an angle between a horizontal direction and a vertical direction. Since in said prior art, as mentioned, the distal end of the stabilisation beam has to be moved laterally to the blade longitudinal direction, to be coupled to the distal end of the elongated guiding element, the crane operation may require a coordination of a boom angle adjustment, and a feeding action of the wire by which the blade is suspended from the boom. This may be a complicated operation, with a risk of unintentional movements of the stabilisation beam.

Instead, where, according to embodiments of the invention, the engagement movement of the blade is substantially parallel to the longitudinal direction of the blade, the engagement movement may be provided simply by a slewing action of the crane. Thereby, the second engagement device may be stabbed into the first engagement device with the crane slewing action. This simplifies the engagement operation, thereby reducing the risk of unintentional movements. Thereby, safety is increased during the installation procedure.

As suggested below, the second engagement device may be arranged to be moved in relation to the blade. This relative movement may be substantially parallel to the blade longitudinal direction. Thereby, the engagement movement may involve a movement of the second engagement device in relation to the blade. Thereby, the blade may be stationary. If the engagement movement of the second engagement device shifts the centre of gravity of the combination of the blade and the holding device, then it is preferred that this shift of centre of gravity is countered by movement of a weight arranged on the holding device or by shifting the engagement points of the lifting means on the holding device. In some embodiments, the engagement movement involves moving the first engagement device along the blade longitudinal direction. For this, the first blade guide device may comprise an actuator for the first engagement device movement, as exemplified below. Thereby, the blade may be stationary.

The first blade guide device is preferably not a part of the wind turbine. The first blade guide device may be temporarily provided in fixed relation to the hub. Providing the first blade guide device may comprise mounting the first blade guide device to the nacelle, or to the hub.

As exemplified below, the second blade guide device may be mounted to the blade or to the holding device of the lifting means. The second blade guide device may be mounted permanently or temporarily to the holding device. The second blade guide device may be mounted temporarily to the blade. The second blade guide device is preferably not a part of the wind turbine.

As, suggested, the blade may be guided, in the mounting movement, by the engaged first and second blade guide devices. Thereby, merely a slewing action of a crane supporting the blade may be necessary to execute the mounting movement.

In the engagement movement, the first or the second engagement device may move towards the other of the first and second blade guide devices. In the engagement position, the first or the second engagement device may be prevented from moving further in relation to the other of the first and second blade guide devices. In the engagement position, relative movements between the first and second engagement devices in a transverse direction of the blade, may be prevented. As exemplified below, in the engagement position one of the first and second engagement devices may be biased towards the other of the first and second engagement devices, in the longitudinal direction of the blade.

Preferably, the engagement prevents relative movements between the first and second blade guide devices in a longitudinal direction of the blade. The engagement movement may be a coupling movement of the first engagement device and/or of the second engagement device. The engagement position may be a coupling position. The engagement movement may lead the first engagement device, and/or the second engagement device, to the coupling position in which the first and second engagement devices, and thereby the first and second blade guide devices, are coupled to each other. The coupling may comprise securing the first blade guide device to the second blade guide device. The first and second engagement devices may form a locking arrangement. The first and/or second engagement device may be arranged to be actuated for the coupling by a remote control device. In some embodiments, the engagement may be performed mechanically, without any active control action. For example, the first and second engagement devices may comprise a barb and/or a cam cleat. The cam cleat may be similar to cam cleats that are used on sailing yachts. The first and second engagement devices may be arranged to be released from each other by an actuation controlled by a remote control device.

As suggested below, in some embodiments, the engagement position may be maintained merely by the second engagement device being biased to the first engagement device, or vice versa.

In some embodiments, the mounting movement is at least partly accomplished by an actuation of the first blade guide device and/or the second blade guide device. The actuation may be in the longitudinal direction of the blade. The actuation may shorten an extension, in the longitudinal direction of the blade, of a combination of the first and second blade guide devices. The actuation may include driving, by means of the first and/or the second blade guide device, the blade towards the hub. For example, the first and/or the second blade guide device may comprise a telescopic pole. The telescopic pole may be arranged to be actuated so as to expand and retract. Such an actuation may be controlled by a remote control device. During the mounting movement, the telescopic pole may extend substantially parallel to the blade longitudinal direction.

In the engagement position, the first and second engagement devices may be located transversally externally of the blade root. In the engagement position, the first and second engagement devices may be located at a distance from the blade root.

In some embodiments, where the blade comprises a blade root with a circular cross-section, the engaged first and second engagement devices are located straight above an imaginary straight line extending perpendicularly to the blade root cross-section, and through a centre of the cross-section. Thereby, a centre of gravity of the blade, or of a combination of the blade and the blade holding device of the lifting means, may be located along a blade longitudinal axis. The blade longitudinal axis may extend through the centre of the blade root cross- section. Thereby, the engaged first and second engagement devices may be located in a vertical plane coinciding with the longitudinal axis. The vertical plane may include the centre of gravity of the blade, or of the combination of the blade and the blade holding device of the lifting means. Thereby, if a portion of the blade weight is supported by the engaged first and second engagement devices, the blade will not tend to rotate around a longitudinal axis. Thereby, gravity can stabilize the blade when the first and second engagement devices are engaged to each other.

As suggested, in the mounting position, the blade may be mounted to a circular mounting flange of the hub. As exemplified below, the first blade guide device may be mounted on the nacelle. Thereby, the first blade guide device may extend from the nacelle so that the engagement devices are located straight above an imaginary straight line extending perpendicularly to a plane of the hub mounting flange, and through a centre of the mounting flange.

The method may comprise, after engaging the first and second blade guide devices to each other, supporting the weight of the blade by the lifting means and the first and second blade guide devices. Thereby, a portion of the blade weight may be supported by the first and second blade guide devices. The portion of the blade weight supported by the first and second blade guide devices, may be 1-10%, preferably 2-5%, of the blade weight.

The support by the first and second blade guide devices may be provided by lowering, when the first and second engagement devices have been engaged to each other, the holding device of the lifting means. Thereby, the blade may change from a horizontal position to a position where the blade tip is lower than the blade root. Alternatively, the tip may be higher than the blade root before the first and second engagement devices are engaged to each other. Thereby, lowering, when the first and second engagement devices have been engaged to each other, the holding device of the lifting means, will put a portion of the blade weight on the first and second engagement devices. The lowering of the holding device is preferably to a level where the blade is horizontal. As suggested, the support of the blade by the lifting means may be done by means of a holding device of the lifting means. The holding device may engage the blade in a region between the blade root and the blade tip. The holding device may be, compared to the engaged first and second engagement devices, closer to the blade tip. The holding device may be suspended in one or more wires of the lifting means. A combination of the blade and the holding device may present a centre of gravity. Thereby, the method may further comprise providing a relative movement, between said centre of gravity and a connection between the holding device and the one or more wires, so that the centre of gravity becomes, compared to the wire to holding device connection, closer to the blade root. Thereby, a portion of the blade weight may be put on the engaged first and second engagement devices.

In some embodiments, said relative movement may be provided by moving said connection between the holding device and the one or more wires, in a direction away from the blade root. This may be done before or after the first and second engagement devices have been engaged to each other. In some embodiments, said relative movement may be provided by moving a weight on the holding device towards the blade root. This movement may be accomplished by one or more actuators. The actuators may be controlled by a remote control device.

Preferably, providing the first blade guide device comprises mounting the first blade guide device on the nacelle. The first blade guide device may be mounted e.g. on a roof of the nacelle. In some embodiments, one or more nacelle lifting points, used for lifting the nacelle for mounting the nacelle on top of a tower of the wind turbine, are used for mounting the first blade guide device.

Optionally, mounting the first blade guide device on the nacelle is done before mounting the nacelle on top of a tower of the wind turbine. This may be particularly advantageous at an installation process of a new wind turbine. The blade guide device may be provided mounted onto the nacelle when the nacelle is mounted lifted and mounted on top of the tower. It might be easier to mount the blade guide device to the nacelle before the latter is mounted onto the tower, than after the nacelle is mounted onto the tower. For an offshore wind turbine installation, the first blade guide device may be mounted to the nacelle, on a deck on a marine vessel used for the installation. However, in some embodiments, mounting the first blade guide device on the nacelle is done after mounting the nacelle on top of a tower of the wind turbine. Thereby, the method can be used not only for installation processes of new wind turbines, but also for service of wind turbines. Moving the first blade guide device up to the nacelle may be done by hoisting means. Thereby, the first blade guide device may be moved up outside of the wind turbine tower. The hoisting means may be provided in or on the nacelle. The hoisting means comprise be a winch or a crane in or on the nacelle. The hoisting means may be temporarily or permanently installed in or on the nacelle.

For an offshore wind turbine, the first blade guide device may be hoisted from a platform at a foundation of the wind turbine.

In alternative embodiments, the method may comprise moving the first blade guide device up to the nacelle by means of hoisting means provided separately from the wind turbine. Thereby the hoisting means may be, e.g. a sea vessel crane in the case of an offshore wind turbine, or a mobile crane in the case of an onshore wind turbine.

The method may comprise, after fastening the blade to the hub, dismounting the first blade guide device from the nacelle, and moving the first blade guide device down from the nacelle by means of hoisting means. The hoisting means may be provided in or on the nacelle. Thereby, the blade guide device may be moved down outside of the wind turbine tower. In one embodiment, the engagement between the first and the second engagement devices is maintained while the first blade guide device is dismounted from the nacelle and the first blade guide device is hoisted from the nacelle together with the second blade guide device. This prevents the need for a separate hoisting operation to remove the first blade guide device from the nacelle.

As suggested, moving the blade towards the hub by means of lifting means may comprise supporting the blade by means of a holding device of the lifting means. Thereby, providing the second blade guide device may comprise providing the second blade guide device mounted to the holding device. Thereby, the second blade guide device may be retracted after mounting the blade to the hub. Thereby, the holding device may be easier to handle and store when not used for holding a blade. This may be particularly beneficial in case of an offshore wind turbine. Thereby, the holding device may be moved to and from a deck of a marine vessel. The space on the deck may be limited.

In some embodiments, the first and/or the second blade guide device comprises a pole. The pole may be telescoping. Where the first blade guide device comprises a telescoping pole, the first engagement device may be mounted to a distal end of the pole. Where the second blade guide device comprises a telescoping pole, the second engagement device may be mounted to a distal end of the pole. The pole may extend substantially in the longitudinal direction of the blade. By the telescoping pole, a controlled way of reducing the distance between the hub and the blade may be provided during the mounting movement of the blade.

In some embodiments, the first and or the second engagement device may be arranged on a guide unit, e.g. in the form of a rail. The guide unit may be formed by a pole of the first or the second blade guide device. Thereby, the engaged first and second engagement devices may move along the pole. Thereby, an alternative controlled way of reducing the distance between the hub and the blade may be provided during the mounting movement of the blade.

In some embodiments, providing the second blade guide device comprises providing the second blade guide device mounted to the blade. Optionally, the second blade guide device may be mounted close to an end surface of the blade root, such as within 2 metres, preferably within 1 metre from the blade root end surface. Thereby, the second engagement device of the second blade guide device may be fastened to the blade in any suitable manner. For example, the second engagement device may be fastened to the blade with a strap of a flexible belt. Thereby, the first blade guide device may comprise a pole, e.g. a telescoping pole, with the first engagement device mounted at a distal end of the pole. Thereby, when the blade has been mounted to the hub, the second blade guide device may be released from the blade, while still engaged to the first blade guide device. Such a release may be done my releasing the strap or the belt. This release action may be controlled by a remote control device.

When the second blade guide device has been released from the blade, it may still be engaged to the first blade guide device. The second blade guide device may subsequently be released from the first blade guide device. Thereby, the second blade guide device may be retrieved from the nacelle. For example, the second blade guide device may be retrieved by a crane in or on the nacelle, or by pivoting the first blade guide device over the nacelle before releasing the second blade guide device .

As exemplified below, after the blade has been mounted to the hub and the second blade guide device has been released from the blade, the first engagement device may be moved away from the hub, while the first blade guide device is mounted to the nacelle. Thereby, where the second blade guide device is still engaged to the first blade guide device, the second blade guide device may be de-coupled from the first blade guide device while the first engagement device has been moved away from the hub. Thereby, the second blade guide device may be retrieved on or in the nacelle, e.g. on a roof of the nacelle.

In some embodiments, the second blade guide device comprises a pole, e.g. a telescopic pole, mounted to the blade, e.g. with a strap of a flexible belt.

Preferably, the method comprises, for the engaging of the first and second blade guide devices to each other, guiding, by means of an engagement guiding arrangement of the first and/or the second blade guide device, one of the blade guide devices into the engagement position. The engagement guiding arrangement may guide one of the blade guide devices into engagement with the other of blade guide devices.

The engagement guiding arrangement could be provided in any suitable manner. It may adjust a transverse misalignment of the first and second engagement devices. Thereby, at least a part of the engagement movement leading the first engagement device, and/or the second engagement device, to the engagement position may have a component in a transverse direction of the blade. Thus, the engagement movement of the first engagement device, and/or the second engagement device, may have a component in a transverse direction of the blade. Nevertheless, preferably, the engagement movement leading the first engagement device, and/or the second engagement device, to the engagement position has a component in the longitudinal direction of the blade. Thus, any part of the engagement movement may be substantially parallel to the blade longitudinal direction, or it may present an angle to the blade longitudinal direction which is non-zero, and less than ninety degrees.

Where the engagement movement involves moving the blade, the engagement movement of the blade may be substantially parallel to the longitudinal direction of the blade. Thereby, a part of the engagement movement of the second engagement device may have a component in the transverse direction of the blade. This transverse engagement movement component of the second engagement device may be provided by the engagement guiding arrangement.

Thereby, a connection, e.g. in the form of a pole, between the second engagement device and the blade may flex.

For example, the engagement guiding arrangement may comprise a funnel. The funnel may be oriented so that an axis of rotation symmetry thereof is substantially parallel to the blade longitudinal direction. Thereby, one of the first and second engagement devices may be fixed to the funnel, e.g. at a narrow end of the funnel. A wide end of the funnel may be arranged to receive the other of the first and second engagement devices. Thereby, the engagement device received by the funnel may enter the funnel and, as it is moved into the funnel, it may become transversely aligned with the engagement device fixed to the funnel. Thereby, the step of engaging the first and second blade guide devices to each other may be facilitated.

As suggested, one of the blade guide devices may comprise a pole. The pole may be telescopic. A distal end of the pole may be arranged to enter the engagement guiding arrangement, e.g. in the form of a funnel. One of the blade guide devices may comprise an elongated object, adapted to be inserted into the funnel. The elongated object may be formed by an end of a pole of one of the blade guide devices.

Alternatively, the engagement guiding arrangement may be fixed to a distal end of the pole of one of the blade guide devices. Thereby an elongated object of the other blade guide device may be adapted to be inserted into the funnel. The pole may be telescopic.

One of the engagement devices may comprise a stopping device. Thereby, the other of the engagement devices may be stopped in the engagement movement by the stopping device.

The engagement device with the stopping device may be provided fixed to an engagement guiding arrangement, e.g. in the form of a funnel. The other of the engagement devices may be provided at a distal end of an elongated object. The elongated object may bottom out in the funnel by the distal end of the elongated object coming into contact with the stopping device. In some embodiments, the stopping device may be provided where there is no engagement guiding arrangement. The engagement position may be provided by the second engagement device being biased to the first engagement device, e.g. by a slewing action of the lifting means, in the form of a crane, supporting the blade. Where an elongated object bottoms out in a funnel by a distal end of the elongated object coming into contact with a stopping device, a crane supporting the blade may be controlled to keep the elongated object bottomed out in the funnel.

In some embodiments, the first and/or second blade guide devices has a shock absorption capacity. Thereby, the engagement movement, of the first engagement device and/or of the blade, may be dampened as the engagement position is reached.

Alternatively, or in addition to the engagement guiding arrangement, the method may involve further measures to lead the first engagement device, and/or the second engagement device, to the engagement position. For example, the first and/or the second engagement device may be moved transversely to the blade longitudinal direction. For example, the vertical position of the second engagement device may be adjusted by control of the lifting means supporting the blade. For example, a wire of the lifting means, in the form of a crane, in which the blade is suspended, may be fed in or out, for adjusting the vertical position of the blade, and thereby the vertical position of the second engagement device. The horizontal position of the second engagement device may be adjusted, e.g. by control of taglines. The taglines may be arranged to control the position of the blade around a vertical axis.

In some embodiments, the first blade guide device may be arranged to that the first engagement device makes one or more transversal movements which may be horizontal and/or vertical. Thereby, for the engagement movement, the first and second engagement devices may be aligned for their engagement. Further, for the mounting movement, the blade root may be aligned with the hub by one or more transversal movements of the first engagement device, while the first engagement device is engaged to the second engagement device.

As exemplified below, in some embodiments the first engagement device may be arranged to move with three degrees of freedom, along the longitudinal extension of the blade, along a vertical transverse direction and along a horizontal transverse direction. In some embodiments, the method may involve the use of one or more sensors for determining the position of the second engagement device in relation to the position of the first engagement device. For example, an imaging sensor may be fixed in relation to the first or the second engagement device. The imaging sensor may be a camera. Images from the imaging sensor may be displayed to an operator. Based on images from the imaging sensor, the lifting means, e.g. including taglines thereof for control of the blade, may be controlled, so as to control the position of the second engagement device in relation to the position of the first engagement device.

In some embodiments, where providing the first blade guide device comprises mounting the first blade guide device on the nacelle, the method comprises, after fastening the blade to the hub, moving, while the first blade guide device is mounted to the nacelle, the first engagement device away from the hub. Thereby, the first engagement device may be moved out of a volume which would be swept by the hub while the hub rotates. Where more than one blade is to be mounted to the hub, moving the first engagement device away from said swept volume allows the hub to be rotated after the blade has been installed, to put the hub in a position for receiving a further blade.

Preferably, the method comprises, after fastening the blade to the hub, dismounting the first blade guide device from the nacelle, and moving the first blade guide device down from the nacelle by means of hoisting means provided in or on the nacelle. Thereby, the first blade guide device may be moved down outside of the wind turbine tower. The hoisting means may comprise a winch or a crane in or on the nacelle. The hoisting means may be temporarily or permanently installed in or on the nacelle. Nevertheless, in alternative embodiments, the method may comprise, after fastening the blade to the hub, dismounting the first blade guide device from the nacelle, and moving the blade guide device down from the nacelle by means of hoisting means provided separately from the wind turbine. Thereby the hoisting means may be, e.g. a sea vessel crane in the case of an offshore wind turbine, or a mobile crane in the case of an onshore wind turbine.

As suggested, the wind turbine may be an offshore wind turbine. Thereby, a particular benefit of the invention may be taken advantage of. The engagement of the first and second blade guide devices may as suggested reduce relative movements between the hub and the blade. As suggested, such relative movement may for offshore wind turbines be caused by wave induced oscillations of the tower and/or of the crane likely in combination with wind induced oscillations.

The object is also reached with a method for planning and executing an installation of one or more blades of a horizontal axis wind turbine. The method may comprise the step of assessing installation conditions, comprising one or more of wind conditions, sea wave and current conditions. The installation conditions may alternatively, or in addition, comprise air temperature, and/or the time of day. The method may further comprise determining if at least one installation condition is above a threshold value. If at least one threshold value is above then install the one or more blades with the method according any embodiment thereof, e.g. according to the first aspect of the invention. If not installation condition is above the threshold value, then install the one or more blades without use of the method according to the present invention. If the method according to the invention, then it was found to be highly advantageous that the first blade guide device is installed on the nacelle before installation of the nacelle as this method saves time compared to installing the nacelle before installing the first blade guide device.

Based on the assessment, it may be determined whether the blade guide devices should be used. The use of the blade guide devices may be done selectively depending on the installation conditions, e.g. the weather conditions. Thereby, the blade guide devices may be used as a backup solution for certain weather conditions. During such weather conditions, blade installation without the blade guide devices may not be feasible or may involve additional risk to personnel or equipment, or risk of unacceptable delays. However, the use of the blade guide devices may be omitted, if the weather conditions allow this. Thereby, the time and cost of the blade installation may be reduced.

For example, in the case of an installation of a new wind turbine, it may be decided based on the assessment, whether to install the first blade guide device to the nacelle, before the nacelle is mounted on top of the tower.

The objects are also reached with a blade guide arrangement for horizontally mounting a blade, of a horizontal axis wind turbine, to a rotor hub mounted to a nacelle of the wind turbine, the arrangement comprising a first blade guide device adapted to be mounted so as to be fixed in relation to the hub, the first blade guide device comprising a first engagement device, and a second blade guide device adapted to be mounted so as to be fixed in relation to the blade, the second blade guide device comprising a second engagement device, wherein the first and second engagement devices are arranged to be coupled to each other in a coupling position, wherein the first blade guide device or the second blade guide device comprises an engagement guiding arrangement arranged to guide, during an engagement movement of the first and/or the second engagement device, the first and/or the second engagement device to the coupling position.

As suggested above, the engagement guiding arrangement may comprise a funnel. The engagement guiding arrangement may be fixed to one of the first and second engagement devices.

BRIEF DESCRIPTION OF THE DRAWINGS

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

Fig. 1 is a view of a wind turbine,

Fig. 2 is a perspective view of a wind turbine rotor blade,

Fig. 3 and fig. 4 are side views of a nacelle of the wind turbine in fig. 1, at a blade installation method according to an embodiment of the invention,

Fig. 5 shows a step in the blade installation method, with the wind turbine and a jack up sea vessel,

Fig. 6 and fig. 7 show front views of the nacelle in fig. 3 and fig. 4, and a part of a blade for the wind turbine,

Fig. 6b shows a top view of the nacelle in fig. 3 and fig. 4, and a part of a blade for the wind turbine,

Fig. 7b shows a longitudinal cross-section of a part of a blade guide arrangement for the blade in fig. 7,

Fig. 8 and fig. 9a show perspective views of a first blade guide device,

Fig. 9b shows a front view of the nacelle in fig. 3 and fig. 4, Fig. 10 shows a front view of a nacelle and a part of a blade, in an alternative embodiment of the invention, and

Fig. 11 is a flow diagram showing steps in a method according to an embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

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.

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 a foundation 17. In this example the foundation is a monopile foundation. In other embodiments, the foundation may be of another type, e.g. a jacket foundation, or an onshore foundation. 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. 2 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 root end may be generally circular. The blade may be of any suitable length, e.g. in the interval 30-120 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.

It should be noted that the proportions of the blade are provided for easy of understanding, and not necessarily representative of the shape of a wind turbine blade in practice.

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. Embodiments of the invention provides a method for installation of a 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. The method could be performed offshore. Alternatively, the method may be used for an onshore wind turbine.

Reference is made to fig. 3. The method may comprise mounting a first blade guide device 41 to the nacelle 15. Thereby, the first blade guide device 41 may be fixed in relation to the hub 18. For this, the first blade guide device 41 may be moved up to the nacelle by means of hoisting means 151 provided in or on the nacelle. In the example in fig. 3, the hoisting means is a service crane permanently installed in the nacelle. The crane is arranged to reach outside of the nacelle through an opening in a cover of the nacelle, for example in the roof of the nacelle. The opening may be arranged to be covered by one or more hatches (not shown). More generally, the hoisting means 151 may be a crane or a winch, which is permanently or temporarily installed in or on the nacelle.

The first blade guide device 41 may be lifted from a platform at the offshore foundation of the wind turbine, from a floating sea vessel, or from a seabed secured jack-up vessel. In case of an onshore wind turbine, the blade guide may be lifted from the ground, or from a vehicle.

After use, the first blade guide device 41 may be lowered from the nacelle with the same hoisting means 151.

As suggested above, in some embodiments, the first blade guide device 41 may be mounted to the nacelle 15 before mounting the nacelle on top of the tower 14 of the wind turbine 1. The first blade guide device may comprise one or more mounting elements 404.

As exemplified in fig 4, the first blade guide device 41 may be mounted on a roof of the nacelle 15. One or more nacelle lifting points, used for lifting the nacelle for mounting the nacelle on top of a tower of the wind turbine, may be used for mounting the first blade guide device. The first blade guide device may be mounted to the nacelle by fastening the one or more mounting elements of the first blade guide device to the nacelle. This simplifies the mounting procedure of the first blade guide device. Thereby, access for staff, working with the first blade guide device mounting, is required only to the nacelle roof.

A mounting arrangement for fastening the blade to the hub may comprise threaded pins along the periphery of the blade root, adapted to engage holes 181 along a mounting flange 182 of the hub. For mounting the blade, the hub may be positioned around the rotor axis, so that the mounting flange 182 is oriented vertically.

In this embodiment, the first blade guide device comprises an engagement guiding arrangement 415, described further below. Further, in this embodiment, the first blade guide device 41 extends from the nacelle 15 so that the engagement guiding arrangement 415 is located on an imaginary straight line extending perpendicularly to a plane of the hub mounting flange, above the hub mounting flange and passing through a point vertically above the centre of the mounting flange, CMF. This allows for a blade which weight is being supported partially by the first and second blade guide devices 41, 42 after engaging the first and second blade guide devices to each other to be automatically centred horizontally in the plane of the hub mounting flange through gravity. This was found to be a major advantage in speeding up the alignment of the blade root to the hub mounting flange. The first blade guide device may also comprise a first engagement device, described closer below.

Reference is made also to fig. 5. The method may comprise supporting the weight of a blade 11 with lifting means 3. The lifting means 3 may be a crane. The lifting means may be provided on a marine vessel. The vessel could be a jack-up ship 2, as exemplified in fig. 5. The support of the blade by the lifting means 3 may be done by means of a holding device 301 of the lifting means. The holding device may be suspended in one or more wires 302 from a crane boom 304. The holding device 301 may be a device arranged to grip the blade. The holding device may engage the blade in a region between the blade root and the blade tip, e.g. at the shoulder of the blade. For attachment of the blade root to the nacelle hub 18, the blade 11 is held aloft with its spanwise axis extending horizontally. In this context, the term horizontal may be understood as substantially horizontal. In particular, a blade 11 extends in a lateral direction during the attachment step to a blade pitch-bearing at a hub 18. The proposed method and apparatus will guide the blade 11 during the attachment phase. It will prevent the blade from slewing about the axis of a bearing wire 302 from which it is suspended. Slewing of a blade 11 during attachment may tend to occur due to crosswinds. When subject to cross winds, a suspended, horizontally extending blade 11 may tend to slew like compass needle, which would be undesirable.

The vertical position of the blade may be adjusted by feeding the wire in or out, as depicted by the double arrow WF. The position of the blade may be also adjusted by adjusting the angle BA of the crane boom. The crane boom may be arranged to rotate around a vertical axis. Such a rotation may be referred to as a slewing action SA of the crane.

The method may comprise moving the blade 11 towards the hub 18 by means of the lifting means 3, while the weight of the blade is supported by the lifting means. The method may comprise the lifting means 3 moving the blade 11 from a deck 21 of the vessel to towards the hub 18 by means of the lifting means 3. In some embodiments, the lifting means may be a mobile crane for installing the blade in an onshore wind turbine.

Reference is made also to fig. 6. The method may comprise providing a second blade guide device 42 so as to be fixed in relation to the blade 11. In this embodiment, the blade guide device is mounted to the blade holding device 301. In this embodiment, the second blade guide device comprises a telescoping pole 423. The telescoping pole may extend from the holding device 301. The pole may be substantially parallel to the blade longitudinal direction.

The method may comprise providing, while the blade 11 is supported by the lifting means 3, an engagement movement of the blade, so as to engage the first and second blade guide devices 41, 42 to each other. The engagement movement is preferably substantially parallel to a longitudinal direction of the blade. The engagement movement may be provided by a slewing action SA of the lifting means, (fig. 5).

In some embodiments, the engagement movement may involve a movement of a second engagement device 426 in relation to the blade. Thereby, the blade may be stationary. The second engagement device 426 may be fixed to a distal end of the telescopic pole 423. The engagement movement may be provided by an extension of the telescopic pole 423. Thereby, the telescopic pole 423 may form an actuator for the second engagement device movement.

For aligning the first and second blade guide devices 41, 42 vertically, the vertical position of the blade may be adjusted by feeding the lifting means wire 302 in or out, as depicted by the double arrow WF. The lateral position of the blade may also be adjusted by adjusting the angle BA of the crane boom, (fig. 5).

Reference is made also to fig. 6b. For aligning the first and second blade guide devices 41, 42 horizontally, taglines 305 of the lifting means may be used. The taglines may extend from the crane boom 304 to the holding device 301, or to the blade 11. The taglines may be arranged to control the position of the blade around a vertical axis. The vertical axis may coincide with the wire 302. Thereby, the horizontal position of the second engagement device 426, located at a distance from the wire 302, may be adjusted. As suggested, second engagement device 426 may be provided at a distal end of the pole 423.

Reference is made also to fig. 7 and fig. 7b. The method may comprise, for the engaging of the first and second blade guide devices 41, 42 to each other, guiding, by means of the engagement guiding arrangement 415 of the first blade guide device, the second blade guide device 42 into engagement with the first blade guide device 41. In this embodiment, the engagement guiding arrangement comprises a funnel 415. The funnel may be oriented so that an axis of rotation symmetry thereof is substantially parallel to the blade longitudinal direction. A wide end of the funnel may be arranged to receive the second engagement device 426. The second engagement device 426 may be provided at a distal end of an elongated object 428. The elongated object may be formed by a distal part of the pole 423. The elongated object may be adapted to be inserted into the funnel 415. Thereby, the second engagement device 426 may enter the funnel and, as it is moved into the funnel, it may become transversely aligned with the first engagement device 416. Thereby, the step of engaging the first and second blade guide devices to each other may be facilitated.

As exemplified in fig. 7b, the first engagement device 416 is fixed to the funnel 415, e.g. at a narrow end of the funnel. The first engagement device 416 may comprise a stopping device 4162. The stopping device may be arranged to stop the engagement movement of the second blade guide device. Thereby, the elongated object 428 may bottom out in the funnel by a distal end of the elongated object coming into contact with the stopping device. Thereby, the method may comprise stabbing the pole 423 into the funnel 415.

As exemplified in fig. 7b, the first engagement device 416 may comprise a cam cleat 4161. The second engagement device 426 may comprise a transversely widened part. The widened part may form a barb. The barb and the cam cleat may prevent the barb from exiting the funnel 415. Thus, the engagement devices 416, 426 may lock the blade guide devices to each other in the longitudinal direction of the blade. In addition, the engagement devices may prevent relative transverse movements between the engagement devices. Thus, the engagement movement leads the second engagement device 426 to an engagement position in which the first and second engagement devices are engaged to each other. Thereby, relative movements between the blade 11 and the hub 18 may be prevented.

As understood from fig. 6b, the engaged first and second engagement devices are, when engaged, located vertically above an imaginary straight line extending perpendicularly to a cross-section of the blade root 111, and through a centre of the cross-section.

As exemplified in fig. 6, the method may involve the use of an imaging sensor 427. The imaging sensor may be fixed in relation to the second engagement device 426. The imaging sensor may be a camera 427. Images from the imaging sensor may be displayed to an operator. Based on images from the imaging sensor, the lifting means may be controlled, so as to control the position of the second engagement device in relation to the position of the first engagement device.

Reference is made again to fig. 7. The method may comprise, after engaging the first and second blade guide devices 41, 42 to each other, supporting the weight of the blade 11 by the lifting means 3 and the first and second blade guide devices 41, 42. A combination of the blade 11 and the holding device 301 may present a centre of gravity. The method may comprise providing a relative movement, between said centre of gravity and a connection 303 between the holding device and the one or more wires 302. Thereby, the centre of gravity may become, compared to the wire to holding device connection 303, closer to the blade root 111.

For said relative movement, the method may comprise moving the connection 303, in a direction away from the blade root 111. This may be done before or after the blade guide devices 41, 42 have been engaged to each other. At the connection 303 a hook of the lifting means may be engaged with a bracket of the holding device 301. The holding device 301 may comprise an actuator for moving the connection 303 along the longitudinal extension of the blade 11. In some examples, the connection 303 is moved away from the blade root 111 before the blade guide devices 41, 42 have been engaged to each other. After bringing the blade guide devices 41, 42 have been engaged to each other, the holding device 301 may be lowered. Alternatively, the connection 303 is moved away from the blade root 111 upon engaging the blade guide devices 41, 42 to each other. Thereby, a part of the blade weight may be supported by the first and second blade guide devices 41, 42.

In some embodiments, said relative movement may be provided by moving a weight on the holding device towards the blade root. This movement may be accomplished by one or more actuators.

The method may comprise providing a mounting movement of the blade, while the first and second blade guide devices 41, 42 are engaged to each other, towards a mounting position in which it is fastened to the hub 18. Thereby, the blade may be guided, in the mounting movement, by the engaged first and second blade guide devices. Said threaded pins 119 may be distributed along a periphery of an end face of the blade root 111. In the mounting movement, the threaded pins may enter the respective holes in the hub mounting flange 182.

The mounting movement may at least partly be accomplished by an actuation of the first blade guide device 41 and/or the second blade guide device 42. For example, the mounting movement may be accomplished by a retraction of the telescoping pole 423 of one of the blade guide devices, in this example the second blade guide device 42. The actuation may include driving, by means of the first and/or the second blade guide device 41, 42, the blade 11 towards the hub 18 in the longitudinal direction of the blade.

In some embodiments, the mounting movement may at least partly be accomplished by a slewing action SA (fig. 5) of the lifting means. Alternatively, the crane boom may be stationary during the movement. The may result in the one or more wires 302 of the lifting means presenting an angle to the vertical direction.

In some embodiments, the first and second engagement devices are biased against each other in the longitudinal direction of the blade. Such biasing may be accomplished by a slewing action SA of the lifting means. Thereby, the locking to prevent separation of the first and second engagement devices may be omitted. In some embodiments, the first blade guide device may comprise two first engagement devices. Thereby, the second blade guide device may comprise two second engagement devices. The engagement devices may be positioned so that one set of engaged engagement devices is located above the hub, and another set of engaged engagement devices is located below the hub. Thereby, a rotation of the blade around its longitudinal axis may be prevented.

Reference is also made to fig. 8, showing a perspective view of an example of the first blade guide device 41. The mounting movement may comprise moving, preferably with motion providing means, the first engagement device 416 towards the hub 18. As exemplified in fig.

8 with the double arrow B, the first engagement device 416 may be moved in relation to a stationary part 418 of the first blade guide device 41, towards and away from the hub. This movement may be provided by motion providing means, e.g. comprising an electric motor or a hydraulic actuator. In some embodiment, the first blade contact device 41 may comprise a trolley arranged to move the first engagement device 416.

The first engagement device 416 may be moved transversely to the blade longitudinal direction. Thereby the blade may be accurately aligned with the hub. As exemplified in fig. 8 with the double arrow C, the first engagement device 416 may be moved vertically in relation to the stationary part 418 of the first blade guide device 41.

As exemplified in fig. 8 with the double arrow D, the first engagement device 416 may be moved horizontally and transversely to the blade longitudinal direction. This movement may be relative to the stationary part 418 of the first blade guide device 41. This may be accomplished for example by a telescopic movement of a horizontal connection element 419 of the first blade guide device 41. The connection element 419 may connect the first engagement device 416 with the nacelle 15, or with one or more further elements connected to the nacelle, such as the stationary part 418 of the first blade guide device 41.

Thus, in some embodiments the first engagement device 416 may be arranged to move with three degrees of freedom, along the longitudinal extension of the blade, along a vertical transverse direction and along a horizontal transverse direction. However, in some embodiments, the first engagement device 416 may be arranged to move only along transverse directions of the blade. After fastening the blade 11 to the hub 18, the first and second engagement devices 416, 426 may be released from each other by an actuation controlled by a remote control device. Preferably, the second blade guide device 42 is retracted after mounting the blade to the hub. The retraction may be done by retracting the telescopic pole 423 of the second blade guide device 42.

Reference is made also to fig 9a and fig. 9b. The method may comprise, after fastening the blade 11 to the hub 18, moving, while the first blade guide device 41 is mounted to the nacelle 15, the first engagement device 416 away from the hub. The first blade guide device 41 may comprise moving means 411 for moving the first engagement device 416, from a receiving position to a retracted position, exemplified in fig. 9a. Thereby, the first blade guide device may be moved away from the hub 18. As exemplified in fig. 9b, in the receiving position, the first engagement device 416 is at least partly located within a volume V which would be swept by the hub 18 while the hub rotates. As exemplified in fig. 9a, in the retracted position, the first engagement device 416 is moved away from the swept volume V. The moving means may comprise an actuator 411. The actuator may be a hydraulic actuator or an electric motor. In this example, the first engagement device 416 is moved by a swing motion, e.g. of about 90 or 180 degrees, around a vertical axis. The movement from the receiving position to the retracted position may be accomplished in a variety of manners, e.g. by a telescoping member, and/or by a swing motion in any suitable direction, e.g. downwards.

When the blade is installed, the hub may be rotated to install a further blade. When use of the first blade guide device 41 is completed, the first blade guide device may be removed from the nacelle 15. Thereby, hoisting means 151, such as the hoisting means described with reference to fig. 3, may be used for moving the first blade guide device down from the nacelle. As stated, more generally, the hoisting means 151 may be a crane or a winch, which is permanently or temporarily installed in or on the nacelle. In alternative embodiments, the lifting means 3 may be used to move the blade guiding device down from the nacelle.

13.

Reference is made to fig. 10, illustrating an alternative embodiment of the invention. The method may comprise providing the second blade guide device 42 mounted to the blade 11. The second blade guide device may be mounted close to an end surface of the blade root, such as within 2 metres, preferably within 1 metre from the blade root end surface. The second engagement device 426 may be provided at a distal end of an elongated object 428. The elongated object may be adapted to be inserted into the funnel 415 of the first blade guide device 41. The funnel may be mounted to a distal end of a telescopic pole 413 of the first blade guide device 41.

The engagement movement may be provided by a slewing action SA (fig. 5) of the lifting means. In some embodiments, the engagement movement may involve a movement of the first engagement device 416. Thereby, the blade may be stationary. The engagement movement may be provided by an extension of the telescopic pole 413. Thereby, the telescopic pole 413 may form an actuator for the first engagement device movement.

In this embodiment, the second engagement device 42 is fastened to the blade 11 with a flexible belt 429. The belt may circumvent the blade root 111. In the mounting movement, the telescopic pole 413 may be retracted to guide the blade to the hub.

When the blade has been mounted to the hub, the second blade guide device 42 may be released from the blade, while still engaged to the first blade guide device 41. Such a release may be done by releasing the belt 429. This release action may be controlled by a remote control device.

The second blade guide device 42 may subsequently be released from the first blade guide device 41. Thereby, the second blade guide device may be retrieved from the nacelle. For example, the second blade guide device may be retrieved while the first engagement device 416 is moved away from the hub, e.g. as illustrated in fig. 9a.

In some embodiments, where the first or the second blade guide device 41, 42 comprises a pole 413, 423, a portion of the pole including a distal end of the pole, may be arranged to flex. Thereby, a misalignment between the blade and the hub may be provided during the engagement of the engagement devices 416, 426. Thereby, the pole portion may flex to avoid large bending moments in the pole.

Reference is made to fig. 11 depicting steps in a method according to an embodiment of the invention, e.g. as exemplified above. The method comprises providing SI a first blade guide device 41 so as to be fixed in relation to a hub 18 fixed to a wind turbine nacelle 15. The first blade guide device comprises a first engagement device 416. The method comprises providing S2 a second blade guide device 42 so as to be fixed in relation to a blade 11 of the wind turbine. The second blade guide device 42 comprises a second engagement device 426. The method further comprises moving S3 the blade 11 towards the hub 18 by means of lifting means 3. The method further comprises providing S4, while the blade 11 is supported by the lifting means 3, an engagement movement of the first engagement device and/or of the blade. The engagement movement is substantially parallel to, or has a component in, a longitudinal direction of the blade. The engagement movement leads the first engagement device, and/or the second engagement device, to an engagement position in which the first and second engagement devices, and thereby the first and second blade guide devices 41, 42, are engaged to each other. The method further comprises providing S5 a mounting movement of the blade, with the first and second blade guide devices 41, 42 engaged to each other, towards a mounting position in which it is fastened to the hub 18.

Many alternatives to the examples described are possible and will occur to those skilled in the art without departing from the scope of the invention which is defined by the claims.

Claims

1. A method for horizontal installation of a blade (11) of a horizontal axis wind turbine (1), wherein the blade (11) extends longitudinally between a blade root (111) and a blade tip (112), the method comprising providing a nacelle (15) for the wind turbine, and a rotor hub (18) mounted to the nacelle, providing a first blade guide device (41) in fixed relation to the hub (18), the first blade guide device comprising a first engagement device (416), providing a second blade guide device (42) in fixed relation to the blade (11), the second blade guide device comprising a second engagement device (426), moving the blade (11) towards the hub (18) by means of lifting means (3), providing, while the blade (11) is supported by the lifting means (3), an engagement movement of the first engagement device and/or of the second engagement device, which leads the first engagement device, and/or the second engagement device, to an engagement position in which the first and second engagement devices, and thereby the first and second blade guide devices (41, 42), are engaged to each other, and providing a mounting movement of the blade, with the first and second blade guide devices (41, 42) engaged to each other, towards a mounting position in which the blade is fastened to the hub (18), characterised in that the engagement movement is substantially parallel to, or has a component in, a longitudinal direction of the blade.

2. The method according to claim 1, wherein the engagement movement involves moving the blade.

3. The method according to any one of the preceding claims, wherein the blade is guided, in the mounting movement, by the engaged first and second blade guide devices.

4. The method according to any one of the preceding claims, wherein the engagement prevents relative movements between the first and second blade guide devices (41, 42) in a longitudinal direction of the blade.

5. The method according to any one of the preceding claims, wherein the mounting movement is at least partly accomplished by an actuation of the first blade guide device (41) and/or the second blade guide device (42), preferably the actuation includes driving, by means of the first and/or the second blade guide device (41, 42), the blade (11) towards the hub (18) in the longitudinal direction of the blade.

6. The method according to any one of the preceding claims, wherein the blade comprises a blade root (111) with a circular cross-section, wherein the engaged first and second engagement devices are located straight above an imaginary straight line extending perpendicularly to the blade root cross-section, and through a centre of the cross-section.

7. The method according to any one of the preceding claims, comprising, after engaging the first and second blade guide devices (41, 42) to each other, supporting the weight of the blade (11) by the lifting means (3) and the first and second blade guide devices (41, 42).

8. The method according to claim 7, wherein the support of the blade by the lifting means (3) is done by means of a holding device (301) of the lifting means, the holding device engaging the blade in a region between the blade root and the blade tip, wherein the holding device is, compared to the engaged first and second engagement devices (416, 426), closer to the blade tip, preferablythe holding device (301) is suspended in one or more wires (302) of the lifting means (3), wherein a combination of the blade and the holding device presents a centre of gravity, the method further comprising providing a relative movement, between said centre of gravity and a connection (303) between the holding device and the one or more wires, so that the centre of gravity becomes, compared to the wire to holding device connection (303), closer to the blade root (111).

9. The method according to any one of the preceding claims, wherein providing the first blade guide device (41) comprises mounting the first blade guide device on the nacelle (15), optionally before mounting the nacelle on top of a tower of the wind turbine.

10. The method according to any one of the preceding claims, wherein moving the blade (11) towards the hub (18) by means of lifting means (3) comprises supporting the blade by means of a holding device (301) of the lifting means, wherein providing the second blade guide device (42) comprises providing the second blade guide device mounted to the holding device, preferably the method further comprising retracting the second blade guide device (42) after mounting the blade to the hub.

11. The method according to any one of the preceding claims, wherein the first and/or the second blade guide device comprises a telescoping pole (413, 423).

12. The method according to any one of the preceding claims, wherein providing the second blade guide device (42) comprises providing the second blade guide device mounted to the blade (11), optionally close to an end surface of the blade root, such as within 2 metres, preferably within 1 metre from the blade root end surface.

13. The method according to any one of the preceding claims, comprising, for the engaging of the first and second blade guide devices (41, 42) to each other, guiding, by means of an engagement guiding arrangement (415) of the first and/or the second blade guide device, one of the blade guide devices into the engagement position.

14. The method according to any one of the preceding claims, wherein providing the first blade guide device (41) comprises mounting the first blade guide device on the nacelle (15), the method comprising, after fastening the blade (11) to the hub (18), moving, while the first blade guide device (41) is mounted to the nacelle (15), the first engagement device (416) away from the hub.

15. The method according to any one of the preceding claims, wherein the wind turbine (1) is an offshore wind turbine.

16. The method for planning and executing an installation of one or more blades (11) of a horizontal axis wind turbine (1), comprising the step of assessing installation conditions, comprising one or more of wind conditions, sea wave and current conditions, if at least one installation condition is above a threshold value, then install the one or more blades with the method according to any one of the preceding claims, and if no installation condition is above the threshold value, then install the one or more blades without use of the method according to one of the preceding claims.

17. A blade guide arrangement for horizontally mounting a blade (11), of a horizontal axis wind turbine (1), to a rotor hub (18) mounted to a nacelle (15) of the wind turbine, the arrangement comprising a first blade guide device (41) adapted to be mounted in fixed relation to the hub (18), the first blade guide device comprising a first engagement device (416), and a second blade guide device (42) adapted to be mounted in fixed relation to the blade (11), the second blade guide device comprising a second engagement device (426), wherein the first and second engagement devices are arranged to be coupled to each other in a coupling position, characterised in that the first blade guide device or the second blade guide device comprises an engagement guiding arrangement (415) arranged to guide, during an engagement movement of the first and/or the second engagement device, the first and/or the second engagement device to the coupling position.