FIELD

The invention relates to a method for installation of a wind turbine blade to a nacelle installed on an offshore wind turbine tower. The invention also relates to: a combination of a blade installer unit and a blade gripping device for use on a vessel or barge in such a method; a vessel or barge provided with such a combination; and a combination of such a vessel or barge and one or more wind turbine blades. The invention also relates to a method of removal of a wind turbine blade from a nacelle of an offshore wind turbine, for example for maintenance of the removed blade, wherein the same or a different blade may then subsequently be reinstalled to the nacelle.

BACKGROUND

Offshore wind turbines are typically installed by first installing a wind turbine tower on a base structure such as a monopile or other foundation supported on the sea floor, then installing a nacelle on top of the tower, and then installing wind turbine blades to the nacelle. In a known installation method, the blades are lifted to the level of the nacelle by a large crane, wherein the blade is suspended from the crane by a rope with the blade in a horizontal orientation to be mounted to a lateral side of the nacelle. This known method is associated with various challenges. Firstly, adverse weather conditions such as heavy winds affect control of the blade as it is suspended from the crane, rendering blade installation not only inefficient but also dangerous, in particular since the suspended blade needs to closely approach the nacelle. Moreover, in view of a trend towards increasingly larger, in particular taller, wind turbines, providing a sufficient number of suitably large cranes at relevant offshore locations becomes impractical and expensive. Therefore, there is a need for improvements in the area of offshore wind turbine blade installation. In any case, in view of increasing demand for clean energy, there is an ongoing desire to make installation and maintenance of offshore wind turbines more efficient.

SUMMARY

An object of the invention is to provide a method for offshore wind turbine blade installation which is less sensitive to weather conditions and/or more suitable for larger turbine sizes. An object is to make offshore wind turbine blade installation more efficient, safer, faster and/or easier. An object is to at least provide an alternative installation method.

To that end, an aspect of the invention provides a method for installation of a wind turbine blade to a nacelle installed on an offshore wind turbine tower. The method comprises, at the offshore wind turbine tower, providing a vessel or barge with one or more wind turbine blades and a blade installer unit. The blade installer unit comprises a boom and a cart movable along the boom. The boom has a lower end and an upper end, and is preferably a truss-like boom. The cart has a cart base engaged with the boom and a coupling unit movably coupled to the cart base.

The method comprises bringing the boom towards the offshore wind turbine tower, in particular with respect to the vessel, in particular by adjusting the boom angle of the boom.

The method comprises actuating a tower gripping device arranged on the boom, preferably at an upper end of the boom, to cause the tower gripping device to engage the tower.

The method comprises gripping a blade of the one or more wind turbine blades by a blade gripping device while said blade gripping device is disengaged from the cart and the boom. The blade gripping device may be realized in various ways, for example in the form of a blade gripping device known as such, and preferably provides a soft but firm grip of the blade so as to releasably fixate the position of the blade with respect to the blade gripping device, without damaging the surface of the blade. For example, the blade may be gripped at positions corresponding to internal stiffening structures of the blade, so as to prevent deformation of the blade from the gripping.

The method comprises engaging the blade gripping device with the coupling unit of the cart while the blade continues to be gripped by the blade gripping device, to thereby receive the blade on the cart, wherein the blade is oriented predominantly horizontally, at least upon receipt on the cart. It shall be appreciated that in the present context, the expression “receive the blade on the cart” is not limited to the blade being received on top of the cart, or being received from above with respect to the cart. Thus, when the blade is “on” the cart, the blade could for example be to a side of the cart and/or below the cart.

The method comprises moving the cart with the blade gripping device and the blade along the boom towards, e.g. to, the upper end of the boom. Thereto, rails can be provided along the boom for transportation of the cart thereon. Alternatively, the cart could move over chords of the boom, e.g. with rollers or hooks.

The method comprises rotating the coupling unit with respect to the cart base to rotate the blade gripping device with the blade to orient the blade predominantly vertically. Such rotating may be performed e.g. during and/or after the moving of the cart towards the upper end of the boom.

The method comprises, using the blade installer unit, aligning the blade with the nacelle for mounting of the blade to the nacelle. As will be explained further herein, such aligning may be realized in various way, and may include, and/or be part of, the moving of the cart along the boom and/or the rotating of the coupling unit with respect to the cart base.

The method comprises mounting the aligned blade to the nacelle, for example using bolts or otherwise. It shall be appreciated that where the present disclosure refers to a blade being aligned and/or mounted to a nacelle, more specifically the blade is aligned and/or mounted to a wind turbine rotor at the nacelle, even more specifically to a structure, e.g. interface and/or opening and/or flange, on the rotor which structure is configured and intended for connection with a proximal end of a wind turbine blade.

After the blade has thus been mounted to the nacelle, the gripping of the blade by the blade gripping device may be released, so that the cart with the blade gripping device may be returned along the boom, and so that the nacelle with the installed blade may be rotated about the nacelle’s axis.

The blade gripping device thus remains engaged with the blade and it is the blade gripping device that is being coupled by the coupling unit of the blade installer unit. This reduces the hand-overs of the blade during installation, there is only a hand-over of the blade gripping device to the coupling unit, not of the, more vulnerable, blade itself. The blade gripping device only releases the blade after the blade has been installed to the nacelle.

A further aspect provides a combination of a blade installer unit and a blade gripping device for use on a vessel or barge in a method as described herein. The blade installer unit comprises the boom, the cart and the tower gripping device. The blade gripping device is configured to grip a wind turbine blade and is engageable with and disengageable from the coupling unit of the cart.

A further aspect provides a vessel or barge provided with a combination of a blade installer unit and a blade gripping device as described herein. The vessel or barge can be any type of vessel used in offshore installation, such as a vessel using dynamic positioning, or a jackup vessel, or a self-propelled or towed barge, etc. A jack-up vessel is preferred for particularly stable positioning of the vessel during installation. A further aspect provides a combination of a vessel or barge as described herein and one or more wind turbine blades for an offshore wind turbine.

Advantageously, such a method, and similarly such a vessel or barge and such combinations, obviate the need for a large crane to reach up to or beyond the level of the installed nacelle. Rather, the blade installer unit can be relatively compact yet still enable the blade to be aligned with the nacelle for coupling, namely from below in a predominantly vertical orientation of the blade. Moreover, compared to the traditional crane-based method as described in the background section, the positioning of the blade with respect to the nacelle can be particularly well controlled, in particular by the combination of the boom, the cart and the blade gripping device. The positioning of the boom can be well controlled with respect to the tower on which the nacelle is arranged, wherein in particular the tower gripping device can stabilize and/or secure the boom with respect to the tower and thus with respect to the nacelle. In turn, the cart can be configured to be moved stably and precisely along the boom to raise the blade towards the nacelle, while the blade gripping device can be stably engaged by the cart.

The cart enables controlled rotation of the blade gripping device with respect to the boom by rotation of the coupling unit with respect to the cart base, so that the blade can be received on the cart at a low level in a predominantly horizontal orientation and can subsequently be mounted to the nacelle from below in a predominantly vertical orientation. Thus, the blade can be well controlled throughout the installation, while the level of the blade, and thereby effects of wind on the blade, can be relatively low throughout the installation. Specifically, at the start of the installation, the blade can be in a predominantly horizontal orientation so that all of the blade can be at a low level, e.g. at or somewhat above the deck of the vessel; at the end of the installation, only the end of the blade that is to be connected to the nacelle is at the level of the nacelle, while the rest of the blade can remain as low as possible due to the predominantly vertical orientation.

As used herein, the expression ‘predominantly horizontal orientation’ can be generally understood as an orientation in which the respective object, here the blade, extends further along the horizontal plane than along the vertical direction. Similarly, in a ‘predominantly vertical orientation’ the blade extends further along the vertical direction than along the horizontal plane. Thus, a ‘predominantly horizontal orientation’ deviates less than 45 degrees from an exactly horizontal orientation, and a ‘predominantly vertical orientation’ deviates less than 45 degrees from an exactly vertical orientation. In embodiments, the terms can be understood more narrowly, for example as deviating less than 40, 30, 20 or 10 degrees from an exactly horizontal, respectively vertical, orientation. Orientations closer to exactly horizontal, respectively vertical, are generally preferred as they strengthen the advantages of keeping the level of the blade relatively low, in particular reducing the effect of wind.

By engaging the blade gripping device with the coupling unit of the cart while the blade is already gripped by the blade gripping device, the initial gripping of the blade can be performed in a stable manner at a convenient location, such as where the blade is initially stored on a deck of the vessel.

Subsequently, since the blade gripping device and the blade can travel together while the blade gripping device provides a stable releasable coupling of the blade to the cart, no releasing or adjusting of the gripping or additional gripping of the blade is necessary until the blade has been mounted to the nacelle. Instability and possible damage to the blade surface due to so-called hand-over of the blade can thus be avoided.

Thus, preferably, a load bearing gripping of the blade occurs only for one uninterrupted period during installation, namely by the blade gripping device. Nevertheless, it shall be appreciated that intermediate releasing or adjusting of the gripping of the blade by the blade gripping device is not necessarily excluded in the present method, and may in some cases be beneficial e.g. with respect to load distribution adjustment.

The engaging of the blade gripping device with the coupling unit of the cart may be considered as a form of docking, in the sense that the gripped blade can thereby be coupled to the cart, in particular stably and releasably, wherein the cart can thereby support the blade via the boom which in turn is supported by the vessel and stabilized to the tower by the tower gripping device.

Preferably, the gripping of the blade by the blade gripping device while the blade gripping device is disengaged from the cart is performed while the blade gripping device is engaged with a manipulator such as a crane, in particular a manipulator mounted on the vessel or barge, such as a deck crane or a leg-mounted crane.

In this way, such a crane or other manipulator can move the blade gripped by the blade gripping device from an initial position, such as a storage position on a deck of the vessel. Using a separate manipulator such as a crane in this way advantageously provides versatility, in particular regarding the initial or storage position, so that multiple blades can be subsequently installed from mutually different initial or storage positions on the vessel.

Preferably, the engaging of the blade gripping device with the coupling unit of the cart comprises moving the blade gripping device with the gripped blade to the cart using the crane or other manipulator with which the blade gripping device is then engaged. In the following, where the present disclosure refers to a crane, it shall be appreciated that alternatively or additionally a different type of lifting manipulator could be used, for example comprising an A-frame.

Thus, the blade gripping device with the gripped blade can be handed over to the cart from the crane which can be used to allow the blade gripping device to grip the blade at its initial or storage position, so that versatility regarding the initial or storage position can be combined with the options and advantages of the blade installer unit as described herein. The used crane can be relatively compact, since it does not need to move the blade to a very high level such as to the nacelle, but merely to the level of the cart, which can be positioned at a relatively low level along the boom.

Preferably, the blade gripping device is disengaged from the crane after the blade gripping device is engaged with the coupling unit of the cart, and preferably before the cart with the blade gripping device and the blade is moved along the boom.

Thereby, a stable and secure handover to the cart of the blade installer unit can be realized, while thereafter the crane does not hamper the operation of the blade installer unit.

Preferably, the engagement between the blade gripping device and the crane comprises suspension of the blade gripping device from the crane, preferably using a yoke, so that the suspended blade gripping device can grip the blade from above.

In this way, blades can be stored relatively closely together on a relatively low level on the vessel, while at least the top most blade or blades can still be gripped by the blade gripping device. The use of a yoke, which may also be denoted as a spreader bar, can advantageously help to control the position of the blade and blade gripping device while suspended when moving from the initial or storage position to the cart.

Preferably, the blade gripping device is returned from the coupling unit of the cart to the crane after the blade has been mounted to the nacelle for installation of a further blade of the one or more wind turbine blades to the same or a different nacelle.

The blade gripping device can thus be repeatedly exchanged between the crane and the coupling unit of the cart for Preferably, the engaging of the blade gripping device with the coupling unit of the cart releasably fixates the blade gripping device with respect to the coupling unit of the cart.

Thereby the position of the blade can be controlled by controlling the position of the coupling unit, in particular by controlling the rotation of the coupling unit with respect to the cart base, the position of the car base along the boom, and the position of the boom with respect to the tower and nacelle.

Preferably, the rotating of the coupling unit with respect to the cart base is about a predominantly horizontal rotation axis extending at an angle, in particular transverse, to a hinging axis about which the boom is hingeable with respect to the vessel or barge to adjust the boom angle of the boom. Reference is made to the detailed description for further explanation of the possible relation between the rotation axis and the hinging axis. It shall be appreciated that the rotation axis mentioned here may be one of several rotation axes available in the cart, wherein another one of such rotation axes may e.g. be used for detailed alignment of the blade to the nacelle.

In this way, the cart can adjust the orientation of the blade from predominantly horizontal to predominantly vertical in a particularly stable manner, with a well-balanced load of the blade on the boom, the vessel and the tower.

Preferably, prior to installation, the wind turbine blades are stored on a deck of the vessel or barge in a storage position in which they extend substantially parallel to the predominantly horizontal orientation of the blade upon receipt on the cart.

Thereby, the orientation of the blade may be kept substantially the same while moving the blade from the storage position to the cart, simplifying operations and reducing space requirements. Preferably, the boom is at least partly aligned with the wind turbine tower, preferably prior to causing the tower gripping device to engage the tower.

Such alignment between boom and tower can advantageously facilitate alignment between the blade and the nacelle, and moreover can promote a stable engagement of the boom with the tower via the tower gripping device.

Preferably, the at least partly aligning of the boom comprises moving the boom with respect to a deck of the vessel or barge, in particular using a skid, such as an XY-skid, by which the boom may be mounted to the deck.

Thereby, the positioning of the vessel or barge itself with respect to the tower need not be very precise. Precise positioning of the vessel or barge at sea can be challenging and time-consuming, in particular in adverse weather and/or sea conditions. The use of a skid can provide one or more controllable degrees of freedom in the position of the boom with respect to the deck. For example, an XY-skid provides at least two mutually orthogonal translational degrees of freedom along the surface of the deck, for example longitudinal and transverse movement along the deck. Alternatively or additionally, a skid or other adjustable mounting structure may provide one or more other degrees of freedom, possibly including one or more rotational degrees of freedom. Apart from the aligning, such a skid may additionally or alternatively be used to bring the boom towards the tower, e.g. during and/or after the aligning.

In any case, as alluded to elsewhere herein, the boom angle of the boom is preferably adjustable. This concerns in particular adjustability between a boom angle in which the boom extends outside a perimeter of the vessel or barge towards the tower, and a boom angle in which the boom extends less or not outside said parameter, e.g. when the vessel or barge is sailing. Preferably, the boom is provided on a cantilever, which cantilever is movable with respect to a deck of the vessel or barge, and can, at least in an extended position, reach beyond the deck. The movability of the cantilever may be provided by the described optional skid, or a similar skid, which may then be arranged between the cantilever and the deck. Alternatively or additionally, such a skid could be provided between the cantilever and the boom.

Such a cantilever advantageously enables the boom to extend from the vessel towards the nacelle in a relatively upright orientation, so that load are transferred mainly to the vessel and less or not to the tower, while the vessel need to approach the tower very closely. Once the vessel is stably positioned at the tower, the cantilever with the boom can be extended towards the tower. After installation and before setting sail, the cantilever can be retracted again.

Thus, in one or more of various possible ways, the boom may thus be brought towards the tower while the vessel or barge remains at a fixed position, e.g. in case of a jack-up vessel at a raised position with its legs supported on the sea floor. The various possible ways include using a skid, adjusting the boom angle, and by moving a cantilever with respect to the deck, as described herein.

Preferably, the alignment of the blade with the nacelle comprises adjusting the cart base and/or the coupling unit and/or the blade gripping device with respect to the boom, additional to the upwards movement of the cart along the boom and the rotating of the coupling unit with respect to the cart base. For example, the coupling unit may be adjusted with respect to the cart base by translation and/or by additional rotation, e.g. about one or more different rotation axes. Preferably, the coupling unit is adjustable with respect to the cart base along six degrees of freedom, i.e. three translation directions and three rotation axes. Alternatively or additionally, the cart base may be adjusted with respect to the boom by sideways and/or front-to back translation, and/or by rotation. Alternatively or additionally, the blade gripping device may be translated and/or rotated with respect to the coupling unit of the cart. Thus, various adjustments may be possible, each of which is preferably well controlled so as to provide versatile yet stable alignment of the blade. Still, in some embodiments, alignment of the blade with the nacelle could be realized by the aligning of the boom with respect to the tower, the initial gripping of the blade, the moving of the cart along the boom, and the rotating of the coupling unit with respect to the cart.

Preferably, the engagement of the tower by the tower gripping device synchronizes a movement of the upper end of the boom with a movement of the tower, in particular a movement of a part of the tower with which the upper end of the boom is engaged.

It shall be appreciated that the top of the tower may move somewhat with respect to the base of the tower due to flexing of the tower, e.g. by wind. If the tower gripping device grips the tower relatively firmly at a relatively high level, e.g. about 20 m or less from the top of the tower, while some movement is allowed in the boom and/or between the boom and the vessel, the movement of the upper end of the boom can be substantially synchronized with the movement of the top of the tower, where the nacelle is. Advantageously, alignment of the blade to the nacelle can thus be less or not affected by such tower flexing. Special motion compensation mechanisms can be obviated thereby, although such mechanisms may nevertheless be used.

Preferably, the method comprises extending an extendable boom portion of the boom from a base boom portion of the boom to thereby upwardly extend the boom, preferably prior to actuating the tower gripping device. Each of the extendable boom portion and the base boom portion may be truss-like boom portions.

In this way, the boom can be relatively compact when the vessel or barge is sailing, yet reach relatively high up to accommodate relatively tall wind turbine towers. It shall be appreciated that such upward extension of the boom raises the level of the upper end of the boom, in particular further towards, but not necessarily up to, the nacelle at the top of the tower. Preferably, the upper end of the boom remains at a distance from the top of the tower, wherein the remaining distance to the nacelle can be bridged by the blade when the blade is in a predominantly vertical orientation at or near the upper end of the boom. To that end, the blade gripping device preferably grips the blade at a distance from the nacelle facing end of the blade. Preferably, the blade gripping device grips the blade at a center of mass of the blade, so that the blade can be well balanced, in particular in various orientations.

The one or more wind turbine blades are preferably arranged parallel to a longitudinal axis of the vessel or barge, in particular while such blades are stored on the vessel or barge prior to their installation.

Space on the vessel or barge can thereby be used efficiently, while the blades can remain largely or fully within the perimeter of the vessel or barge while stored.

Preferably, the blade installer unit is arranged spaced apart from a bow and stern of the vessel or barge, in particular at a port or starboard side of the vessel or barge.

Thereby, the blades need not change orientation when moving from their storage position to the cart, at least when the blades are stored parallel to the longitudinal axis of the vessel or barge. Meanwhile, the blade installer unit can thus be brought close to the tower without occupying a large deck area of the vessel or barge.

The boom is preferably positioned at a side of the tower corresponding to a front side of the nacelle, i.e. a side from which the rotor of the nacelle extends outside the stator of the nacelle. In this way, the part of the rotor to which the blade is to be mounted can be directly above the boom, facilitating a stable positioning of the blade at the nacelle by the blade installer unit, and thus promoting a particularly well controlled installation.

During some or all of the installation process, the blade installer unit and/or the blade gripping device and/or the crane may be controlled partly or fully automatically and/or remotely, e.g. by an electronic controller in wired and/or wirelessly communication with respective actuators. To facilitate feedback based control, various sensors such a position sensors and/or force sensors may be provided in communication with such a controller. In some cases, also the vessel itself may be partly or fully controlled automatically and/or remotely. The mounting of the blade to the nacelle may also be controlled automatically and/or remotely, although it shall be appreciated that manual mounting is not excluded.

DETAILED DESCRIPTION

In the following, the invention will be explained further using example of embodiments and drawings. The drawings are schematic and merely show examples. In the drawings, corresponding elements have been provided with corresponding reference signs. In the drawings:

Figs. 1 to 20 show perspective views of a vessel provided with wind turbine blades and a blade installer unit at an offshore wind turbine tower on which a nacelle has been installed, wherein subsequent figures show subsequent moments during installation of wind turbine blades to the nacelle;

Figs. 21A-B show side views of a blade gripping device disengaged from (Fig. 21A) and engaged with (Fig. 2 IB) a coupling unit of a cart of a blade installer unit according to a first embodiment;

Figs. 22A-B show side views of a blade gripping device disengaged from (Fig. 22A) and engaged with (Fig. 22B) a coupling unit of a cart of a blade installer unit according to a second embodiment; and Figs. 23A-B show side views of a blade gripping device disengaged from (Fig. 23A) and engaged with (Fig. 23B) a coupling unit of a cart of a blade installer unit according to a third embodiment.

Figures 1 to 20 show subsequent moments during an example of a performance of a method for installation of a wind turbine blade 1 to a nacelle 2 installed on an offshore wind turbine tower 3.

With particular reference to Figs. 1 and 2, the method comprises, at the offshore wind turbine tower 3, providing a vessel 4 or barge with one or more wind turbine blades 1 and a blade installer unit 5. In the shown example, the blade installer unit 5 is arranged spaced apart from a bow and stern of the vessel 4, here at a starboard side of the vessel 4. Alternatively, the blade installer unit 5 could be arranged at the port side. Further alternative arrangements are possible, for example wherein the blade installer unit is arranged centrally on the deck, and the blades to be installed are stored on a separate transport vessel.

The blade installer unit 5 comprises a boom 6 and a cart 7 movable along the boom 6. The boom 6 has a lower end and an upper end. The cart 7 has a cart base 8 engaged with the boom 6 and a coupling unit 9 movably coupled to the cart base 8. The cart 7, in particular the cart base 8, may be a trolley. The boom 6 may form a chute along which the cart base 8 can move.

Figures 1 to 20 also show an example of a vessel 4, here a jack-up vessel, provided with an example of a combination of the blade installer unit 5 and a blade gripping device 10 for use in a blade installation method as described and shown herein. The blade gripping device 10 is configured to grip a wind turbine blade 3 and is engageable with and disengageable from the coupling unit 9 of the cart 7.

The vessel 4 is shown in combination with wind turbine blades 1 for an offshore wind turbine 11, wherein the wind turbine blades 1 are arranged parallel to a longitudinal axis of the vessel 4. In Figs. 1 to 5, the shown vessel 4 is provided with twelve such blades 1, of which only one has been provided with a reference sign for clarity of the drawings. Figs. 6 to 13 show one of the twelve blades 1 being installed, and Figs. 18 to 20 show two more of the blades 1 being installed, so that in Fig. 20 a wind turbine 11 is provided with three of the blades 1 installed to its nacelle 2, with nine of the blades remaining on the vessel 4 for installation at further wind turbine towers.

With particular reference to Figs. 2 and 3, the method comprises bringing the boom 6 towards the offshore wind turbine tower 3, in particular with respect to the vessel 4, in particular by adjusting the boom angle of the boom 6 and/or using an optional skid described elsewhere herein.

In the shown example, the boom 6 is at least partly aligned with the wind turbine tower 3, prior to causing a tower gripping device 12 to engage the tower 3.

The at least partly aligning of the boom 6 may comprise moving the boom 6 with respect to a deck 13 of the vessel 4, in particular using a skid by which the boom 6 may be mounted to the deck 13.

In the shown example, the boom 6 is provided on a cantilever 14, which cantilever 14 is movable with respect to a deck 13 of the vessel 4, for example using the aforementioned skid. The cantilever 14 can, at least in an extended position, reach beyond the deck 13.

In the shown example, with particular reference to Figs. 3 and 4, the method comprises extending an extendable boom portion 6b of the boom 6 from a base boom portion 6a of the boom 6 to thereby upwardly extend the boom 6, preferably prior to actuating a tower gripping device 12. In the shown example, each of the boom portions 6a and 6b is a truss-like boom portion. Although a frame-like or plate-like structure is here visible at the upper end of the extendable boom portion 6b, such a structure may be omitted so that also the upper end of the extendable boom portion 6b is truss-like, in particular similar to and continuing from the other parts of the extendable boom portion 6b as shown here.

With particular reference to Fig. 4, the method comprises actuating a tower gripping device 12 arranged on the boom 6, here at an upper end of the boom 6, to cause the tower gripping device 12 to engage the tower 3.

In the shown example, the tower gripping device 12 can be extended, in particular folded out, from a back side of the boom for engagement of the tower 3, wherein the tower gripping device 12 can otherwise be retracted, e.g. folded in, for more compact transport.

In the shown example, the engagement of the tower 3 by the tower gripping device 12 synchronizes a movement of the upper end of the boom 6 with a movement of the tower 3. The synchronization is at least with a part of the tower to which the tower gripping device 12 is engaged, but may at least to some extend also be with other parts of the tower, including the top of the tower, mainly depending on the tower’s stiffness between the other part and the gripped part.

With particular reference to Figs. 5 and 6, the method comprises gripping a blade 1 of the one or more wind turbine blades 1 by the blade gripping device 10 while said blade gripping device 10 is disengaged from the cart 7 and the boom 6.

In the shown example, the gripping of the blade 1 by the blade gripping device 10 while the blade gripping device 10 is disengaged from the cart 7 is performed while the blade gripping device 10 is engaged with a crane 15, here a deck crane 15 mounted on the vessel 4.

In the shown example, the engagement between the blade gripping device 10 and the crane 15 comprises suspension of the blade gripping device 10 from the crane 15, preferably using a yoke 16, so that the suspended blade gripping device 10 can grip the blade 1 from above.

With particular reference to Figs. 7-9, the method comprises engaging the blade gripping device 10 with the coupling unit 9 of the cart 7 while the blade 1 continues to be gripped by the blade gripping device 10, to thereby receive the blade 1 on the cart 7, wherein the blade 1 is oriented predominantly horizontally, at least upon receipt on the cart 7.

In the shown example, prior to installation, the wind turbine blades 1 are stored on a deck 13 of the vessel 4 in a storage position S in which they extend substantially parallel to the predominantly horizontal orientation of the blade 1 upon receipt on the cart 7, see e.g. Fig. 9.

In the shown example, the engaging of the blade gripping device 10 with the coupling unit 9 of the cart 7 comprises moving the blade gripping device 10 with the gripped blade 1 to the cart 7 using the crane 15 with which the blade gripping device 10 is then engaged.

In the shown example, the engaging of the blade gripping device 10 with the coupling unit 9 of the cart 7 releasably fixates the blade gripping device 10 with respect to the coupling unit 9 of the cart 7.

The engaging of the blade gripping device 10 with respect to the coupling unit of the cart 7 can be realized in various ways, including but not limited to a first, second and third possible way as explained below with reference to Figs. 21A-B, 22A-B and 23A-B, in which the blade, the yoke and the crane are not shown, merely for clarity of the drawings. The A-figures show a moment before engagement, while the B-figures show the blade gripping device 10 engaged with the coupling unit 9.

In a first possible way, shown in Figs. 21A-B and corresponding to what is shown in Figs. 7-9, the blade gripping device 10 approaches the coupling unit 9 at least partly from below, thereafter being coupled to the coupling unit 9 at a top side, e.g. by pens, and supporting against the coupling unit 9 at a back side.

In a second possible way, shown in Figs. 22A-B, the blade gripping device 10 approaches the coupling unit 9 at least partly from above, thereafter supporting on the coupling unit 9 at a bottom side as well as against a back side, and coupled to the coupling unit 9 at a top end of the back side.

In a third possible way, shown in Figs. 23A-B, the blade gripping device 10 approaches the coupling unit 9 to be hooked into engagement with the coupling unit 9 centrally at the back side, as well as being coupled at a top end of the back side.

Returning to Fig. 9, in the shown example, the blade gripping device 10 is disengaged from the crane 15, in particular from the yoke 16, after the blade gripping device 10 is engaged with the coupling unit 9 of the cart 7.

With particular reference to Figs. 10-12, the method comprises moving the cart 7 with the blade gripping device 10 and the blade 1 along the boom 6 towards, here to, the upper end of the boom 6.

In the shown example, the cart 7 with the blade gripping device 10 and the blade 1 is moved along the boom 6 only after the blade gripping device 10 is disengaged from the crane 15.

It shall be appreciated that, while moving along the boom 6, the cart 7 may transition from the base boom portion 6a to the extendable boom portion 6b, e.g. in a conventional manner, wherein in particular a possible difference such as a difference in width between the boom portions 6a and 6b may be overcome. For example, an adapter unit (not shown) may be provided movable along the extendable boom portion 6b and configured to receive the cart 7 thereon so that the cart 7 can move along the extendable boom portion 6b together with the adapter unit. Alternatively, the cart 7 could be provided with multiple sets of wheels, each set being adapted to a different one of the boom portions 6a and 6b, among various other options.

With particular reference to Figs. 11 and 12, the method comprises rotating the coupling unit 9 with respect to the cart base 8 to rotate the blade gripping device 10 with the blade 1 to orient the blade 1 predominantly vertically, as shown in Fig. 12. In the shown example, with particular reference to Fig. 10, the rotating of the coupling unit 9 with respect to the cart base 8 is about a predominantly horizontal rotation axis R extending at an angle, in particular transverse, to a hinging axis H about which the boom is hingeable with respect to the vessel 4 to adjust the boom angle of the boom 6. In Fig. 10, the rotation axis R can be seen to extend predominantly horizontally, mainly in a transverse direction of the vessel 4, while the hinging axis H extends mainly in a longitudinal direction of the vessel 4, so that the rotation axis R extends mainly transverse to the hinging axis H. It shall be appreciated that the rotation axis R is here predominantly horizontal but need not be exactly horizontal, in particular also in view of the boom angle which is here predominantly vertical but not exactly vertical, namely slightly leaning towards the tower 3.

With particular reference to Fig. 13, the method comprises, using the blade installer unit 5, aligning the blade 1 with the nacelle 2 for mounting of the blade 1 to the nacelle 2; and mounting the aligned blade 1 to the nacelle 2.

The alignment of the blade 1 with the nacelle 2 may comprise adjusting the cart base 8 and/or the coupling unit 9 and/or the blade gripping device 10 (e.g. one via another one) with respect to the boom 6 additional to the upwards movement of the cart 7 along the boom 6 and the rotating of the coupling unit 9 with respect to the cart base 8.

In the shown example, a load bearing gripping of the blade 1 occurs only for one uninterrupted period during installation, namely by one and the same blade gripping device 10, in the shown example starting in Fig. 5 and continuing to Fig. 13, whereafter the blade 1 is released from the blade gripping device 10.

In the shown example, with particular reference to Figs. 15-20, the blade gripping device 10 is returned from the coupling unit 9 of the cart 7 to the crane 15 after the blade 1 has been mounted to the nacelle 2 for installation of a further blade 1, here to the same nacelle 2. The rotor of the nacelle 2 may be rotated after each blade installation to allow installation of a subsequent blade 1 from below, until blade installation to the nacelle 2 has been completed, as shown in Fig. 20. Thereafter, the vessel 4 may sail to a next offshore wind turbine tower with nacelle for blade installation there.

A blade installer unit and blade gripping device as described herein, in particular in combination with a vessel or barge, may also be used for maintenance and/or removal of blades. In case of blade removal, the method can essentially be inversed compared to the installation method described herein, as shall be appreciated by the skilled person having the benefit of the present disclosure. Maintenance can be performed on a removed blade, for subsequent reinstallation using the method described herein. In some cases, the blade may not need to be removed from the cart to perform maintenance, e.g. maintenance may be performed while the blade is held by the blade gripping device on the cart in a predominantly horizontal orientation at a low level along the boom. Alternatively, the removed blade could be replaced by a different blade, e.g. a new blade, wherein the old blade may e.g. be refurbished at a suitable location, e.g. on shore.

More broadly, the present disclosure also relates to a method for handling a wind turbine blade for an offshore wind turbine, for example as part of the installation method described herein. The method for handling comprises: gripping the blade by a blade gripping device while said blade gripping device is engaged with a first manipulator, e.g. the manipulator of as described herein, or another crane or other lifting device, and disengaged from a second manipulator, e.g. the blade installer unit as described herein, or another crane or lifting device; engaging the blade gripping device with the second manipulator while the blade continues to be gripped by the blade gripping device; and disengaging the blade gripping device from the first manipulator while the blade gripping device is engaged with the second manipulator and the blade continues to be gripped by the blade gripping device.

Advantageously, such a method of handling a wind turbine blade can be applied in a broad range of blade handling scenarios, including for installation, maintenance and/or removal of wind turbine blades as described herein, but also in other scenarios, e.g. not involving the described blade installer unit. The handling method reduces the risk of damage to the blade during the handling due to the continued gripping by the same gripping device, while versatile handling of the blade is still possible by the transferring or handing over of the blade gripping device.

Although the invention has been explained herein using examples of embodiments and drawings, these do not limit the scope of the invention as defined by the claims. Many variations, combinations and extension are possible, as will be appreciated by the skilled person having the benefit of the present disclosure. All such variants are included within the scope of the invention as defined by the claims.

LIST OF REFERENCE SIGNS

1. Blade

2. Nacelle

3. Tower

4. Vessel

5. Blade installer unit

6. Boom

6a. Base boom portion

6b. Extendable boom portion

7. Cart

8. Cart base

9. Coupling unit

10. Blade gripping device

11. Wind turbine

12. Tower gripping device

13. Deck

14. Cantilever

15. Crane

16. Yoke

H. Hinging axis of boom with respect to vessel

R. Rotation axis between cart base and coupling unit

S. Storage position