WO2020085902A1

WO2020085902A1 - Installation of a wind turbine blade on a hub of a wind turbine

Info

Publication number: WO2020085902A1
Application number: PCT/NL2019/050695
Authority: WO
Inventors: Hendrikus Jacobus Weterings
Original assignee: Itrec B.V.
Priority date: 2018-10-23
Filing date: 2019-10-22
Publication date: 2020-04-30
Also published as: NL2021862B1

Abstract

Method for six-o'clock installation of a wind turbine blade on a horizontal axis rotational hub that is arranged on top of a tower of a wind turbine, wherein the wind turbine blade has a root end and a tip end. By means of a lifting device mounted on a land based vehicle or on a vessel, a wind turbine blade is brought into a pre-installation position, wherein the wind turbine blade is in a generally vertical orientation and underneath the blade mounting structure in said six-o'clock position. The lifting device is provided with a boom and with a wind turbine blade root end spatial orienting and support device that comprises a base mounted to said boom,and a multiple degrees of freedom movable blade root end retainer that is supported on said base via multiple actuators allowing multiple degrees of freedom of the movable blade root end retainer relative to the base.

Description

INSTALLATION OF A WIND TURBINE BLADE ON A HUB OF A WIND TURBINE

The present invention relates to the installation of a wind turbine blade on a horizontal axis rotational hub that is arranged on top of a tower of a wind turbine. In particular, at sea the installation of a blade is challenging, taking into account that nowadays wind turbine blades having a length of about 60 meters have become prominent. The challenge is further increased when the wind turbine is installed using a vessel in floating condition, so subject to sea-induced motion during the installation.

Onshore wind turbine towers generally are mounted on a soil-bound foundation and are as a result relatively still at the level of the hub during installation of a wind turbine blade. Offshore wind turbine towers are in majority also mounted on a soil-bound foundation, e.g. on a monopile foundation, a jacket type foundation, etc. Installation of the blade, and potentially also of other components of the wind turbine, can be done from a vessel in floating condition or from a so-called jack-up type vessel. Floating foundations of offshore wind turbines are also envisaged, e.g. in deeper water, where the installation vessel will be floating as the depth is too much for a jack-up type vessel. In a floating foundation situation, the tower may be significantly more affected by the sea state during blade installation, e.g. depending on the actual design of the foundation.

A horizontal axis rotational hub of a sizable wind turbine, e.g. one or several megawatts wind turbine, commonly has three blade mounting structures. Each blade mounting structure commonly includes a bearing allowing for variation of the pitch angle of the blade. The bearing commonly has a ring, e.g. an outer ring, attached to the hub body and a ring, e.g. an inner ring, to be attached to the root end of the rotor blade. In the industry a bolted connection between the root end of the blade and the blade mounting structure, e.g. the inner ring of the bearing, is the common standard. Nowadays T-bolt fastening arrangement is often employed. The bolted connection commonly involves a circular array of longitudinal bolts extending from a stern face of the root end of the blade, with the blade mounting structure having a corresponding array of bolt holes in which the longitudinal bolts are to be received. A nut is then commonly tightened on each bolt. Introducing the multitude of bolts simultaneously into the bolt holes requires an accurate alignment of the wind turbine blade relative to the blade mounting structure, which is already challenging due to the size and weight of the rotor blade, wind effects, etc. In addition, as explained, motions may result from the vessel and/or the tower being affected by the sea state. In the industry, especially offshore but also on land, there nowadays is the desire to reduce the number of wind turbine blades that need to be installed onto the hub that is arranged on top of a tower. Often two blades are already installed onto the hub prior to the hub with the two blades, or the nacelle including the hub and the two blades, being lifted to the top of the tower. This is generally known as the bunny ears approach. Commonly only one, a third, additional wind turbine blade is then to be installed onto the hub once the hub is mounted on top of the tower. The bunny ears approach is a challenge in itself due to the extreme size of this pre-assembly, e.g. in view of transportation and/or lifting, wind effects on the pre assembly, etc.

In one installation approach the horizontal axis rotational hub is oriented so that the blade mounting structure of the hub is arranged in a three-o'clock or nine -o'clock position or thereabout, so generally facing sideways. A wind turbine blade is then lifted and brought in horizontal general alignment with the sideways facing blade mounting structure. Lifting is commonly done by one or more cranes, with a gripper assembly engaging the shell of the wind turbine blade near its center of gravity, and/or with the use of one or more slings that have been slung around the wind turbine blade.

Another known approach is the six-o'clock installation of the wind turbine blade. Herein the horizontal axis rotational hub is oriented so that the blade mounting structure of the hub is arranged in downwards direction, called the six-o'clock position. A wind turbine blade is then lifted and brought in vertical general alignment with the downwards facing blade mounting structure. Lifting is commonly done by one or more cranes, with a gripper assembly engaging the shell of the wind turbine blade near its center of gravity, and/or with the use of one or more slings that have been slung around the wind turbine blade.

The present invention aims to provide measures that allow for improved installation of a wind turbine blade on the horizontal axis rotational hub that is arranged on top of a tower of a wind turbine, in particular at sea but possibly also on land. The improvement may reside in the efficiency of the blade installation, e.g. the installation requiring less time and/or effort, and/or being possible within an enlarged weather window (e.g. in stronger winds and/or less advantageous sea state).

According to a first aspect thereof the invention provides a method for six-o'clock installation of a wind turbine blade on a horizontal axis rotational hub that is arranged on top of a tower of a wind turbine, wherein the wind turbine blade has a root end and a tip end, wherein the method comprises:

- positioning a blade mounting structure of a horizontal axis rotational hub that is arranged on top of a tower of a wind turbine in a six-o'clock position,

- bringing, by means of a lifting device mounted on a land based vehicle or on a vessel, a wind turbine blade into a pre-installation position, wherein the wind turbine blade is in a generally vertical orientation and underneath the blade mounting structure in said six-o'clock position, wherein the lifting device is provided with a boom and with a wind turbine blade root end spatial orienting and support device, wherein said wind turbine blade root end spatial orienting and support device comprises:

- a base mounted to said boom,

- a multiple degrees of freedom, preferably six degrees of freedom, movable blade root end retainer that is supported on said base via multiple actuators allowing multiple degrees of freedom of the movable blade root end retainer relative to the base, wherein, e.g. provided on the movable blade root end retainer, are used to fix the root end of the wind turbine blade relative to the blade root end retainer, wherein the method comprises, after said bringing of the wind turbine blade in said pre installation position, operating the actuators of the wind turbine blade root end spatial orienting and support device in order to align the root end of the wind turbine blade with the blade mounting structure in said six-o'clock position, wherein the method comprises lifting the aligned root end of the turbine blade into a fastening position relative to the blade mounting structure of the hub in said six-o'clock position, followed by fastening the root end to the blade mounting structure and by disengaging the blade root end retainer from the wind turbine blade root end.

Preferably the lifting the aligned root end of the turbine blade into said fastening position is performed by operating the actuators of the wind turbine blade root end spatial orienting and support device. This allows to make optimal use of the accurate motion control afforded by said spatial orienting and support device, with said control being active at the very height of the root end of the blade to be installed. In an alternative approach the lifting into the fastening position is done by, for example, moving the base of the wind turbine blade root end spatial orienting and support device relative to the boom, e.g. the base being movable up and down along the boom, or by, for example, telescoping the boom or otherwise moving the boom with the wind turbine blade root end spatial orienting and support device thereon.

The first aspect of the invention is in particular advantageous in embodiments wherein the movable blade root end retainer of the wind turbine blade root end spatial orienting and support device has six degrees of freedom relative to the base. This is known for example as a Stewart platform system. For example, there are six actuable legs, e.g. linearly extendable and retractable legs, arranged between the base and the movable blade root end retainer. In six degrees of freedom, of 6 DoF design, there is mobility in X, Y, and Z- direction, as well as pitch, yaw, and roll.

For example, there are six hydraulic cylinder type legs between the base and the movable blade root end retainer.

For example, each of the actuable legs, e.g. linearly extendable and retractable legs, has a stroke length of at least 1 meter.

As preferred, the movable blade root end retainer is located above the base, thereby making it possible to avoid interference between the base on the one hand and the hub and/or nacelle and/or already installed blades of the wind turbine on the other hand.

Preferably the method is performed without any physical and/or load transferring contact between the lifting device with the spatial orienting and support device on the one hand and the tower with the hub, and commonly also a nacelle, on the other hand during the installation of the wind turbine blade. Preferably also there is no physical and/or load transferring contact between the wind turbine blade to be installed on the one hand and the and the tower with the hub, and commonly also a nacelle, on the other hand during the installation of the wind turbine blade. So, most preferred, is an embodiment wherein the wind turbine blade is solely supported by the lifting device, e.g. the weight of the wind turbine blade when in its vertical orientation being primarily or solely carried by the spatial orienting and support device. The use of any hoisting cables between the tower with the hub on the one hand and the wind turbine blade, e.g. as illustrated in EP 2 224 126, is preferably avoided for installation of the blade. In an embodiment the root end of the wind turbine blade is provided with a bearing ahead of the installation of the blade onto the hub, so that the bearing is to be secured to the blade mounting structure of the hub in the installation process.

As preferred the movable blade root end retainer is provided with one or more turbine blade root end engagement members, e.g. mobile engagement members, that are configured to fix the root end of the wind turbine blade relative to the blade root end retainer so that the position of the root end relative to the retainer is defined and maintained. Examples of engagement members are described herein, for example pins that are introducible into cross-holes in the root end of the blade. In another embodiment, the engagement members comprise friction clamps that are pressed onto the root end.

In an embodiment the boom and the wind turbine blade root end spatial orienting and support device mounted thereon are embodied to support, without additional support of the weight of the blade by other arrangements, the entire weight of the wind turbine blade, e.g. at least when the blade is in said pre-installation position. This, for example in embodiments, allows to avoid the need for any load being borne by the tower, nacelle, and/or hub during the installation of the blade, or even, for example in embodiments, to avoid the need for any physical, e.g. load transmitting, contact between the lifting device and the tower, nacelle, and/or hub during the installation of the blade.

In an embodiment, the base is mounted, e.g. fixed, to a top end of the boom. In another embodiment the base is mounted to be displaceable along at least a section of the boom, e.g. over a height over at least one, e.g. between one and 10 meters, e.g. in order to adjust the location of the base relative to the boom and/or in view of a heave motion compensation by means of the base when the lifting device is mounted on a vessel that installs the blade while being in floating condition.

In an embodiment the boom is pivotal at a lower end thereof about a substantially horizontal boom pivot axis.

In an embodiment the boom is telescopic, e.g. the boom having a lower boom section and an upper boom section telescoping relative to the lower boom section. In an embodiment a heave motion compensating drive is provided to periodically extend and retract the boom so as to afford heave motion compensation for the wind turbine blade root end spatial orienting and support device mounted thereon. For example For example the boom, e.g. in extended state of a telescopic boom, has a length of at least 40 meters, e.g. of at least 60 meters, e.g. measured from a substantially horizontal boom pivot axis.

For example the boom has a latticed upper section, e.g. with a square or rectangular cross- section measuring at least 2 x 2 meters, e.g. 4 x 4 meters.

In an embodiment the boom is embodied to provide a heave motion compensation for the wind turbine blade root end spatial orienting and support device, e.g. providing an effective stroke in longitudinal direction of the boom, of at least 2 meters, e.g. of between 6 and 10 meters, e.g. about 8 meters.

In an embodiment the wind turbine blade root end spatial orienting and support device is also configured and operated to provide a heave motion compensation, so in combination with the boom providing a heave motion compensation for the wind turbine blade root end spatial orienting and support device. For example a majority of this motion is provided by the boom and the remainder by the spatial orienting and support device. For example when sea state is calm all heave motion compensation is provided by the spatial orienting and support device.

In an embodiment a spatial location sensor system is provided, which is configured and operated to sense the relative position and/or motion in directions of said multiple degrees of freedom of the movable blade root end retainer relative to the hub, e.g. the blade mounting structure thereof, said sensed positions and/or motions being used to control at least the operation of the actuators of the spatial orienting and support device. For example laser distance sensors are arranged to provide data representing the actual spatial location and orientation and/or speed of the root end relative to the blade mounting structure. One or more reference markers may be provided on the hub, e.g. on the blade mounting structure, as part of the sensor system.

In an embodiment the boom is pivotal and n the method comprises:

- bringing the pivotal boom of the lifting device in a substantially horizontal pick-up orientation,

- arranging, possibly pre-arranging, the wind turbine blade to be installed in a substantially horizontal pick-up position, generally parallel to the pivotal boom in said substantially horizontal pick-up orientation thereof, preferably on an upward facing loading side of said pivotal boom,

- whilst both the boom of the lifting device and the wind turbine blade to be installed are in said substantially horizontal pick-up orientation, using one or more turbine blade root end engagement members, e.g. provided on the blade root end retainer, to fix the root end of the wind turbine blade relative to the blade root end retainer,

- moving, by means of the pivotal boom, said wind turbine blade from said horizontal pick-up position into a pre-installation position, wherein the wind turbine blade is in a generally vertical orientation and underneath the blade mounting structure in said six-o'clock position.

In an embodiment at least one storage rack is arranged, e.g. on a deck of the vessel, that is adapted for storage therein of one or more, preferably multiple, wind turbine blades in horizontal orientation thereof, said storage rack having a longitudinal side, wherein the pivotal boom of the lifting device is movable into said substantially horizontal pick-up orientation, parallel and adjacent to said longitudinal side of the storage rack, and wherein, possibly, an auxiliary crane is used to retrieve a wind turbine blade from the storage rack and to bring said wind turbine blade in said substantially horizontal pick-up position.

In an embodiment use is made of a vessel on which the lifting device is mounted, the vessel being in floating condition during installation of the wind turbine blade.

In an embodiment use is made of a vessel on which the lifting device is mounted, the vessel being in floating condition during installation of the wind turbine blade, wherein the vessel has a hull with a bow, a stern, and a longitudinal hull axis, e.g. a monohull or a catamaran type hull, e.g. a SWATH type hull, preferably the method being performed with the bow heading into oncoming waves and the stern being directed towards the tower, the hull having a deck with a storage area for storage of multiple wind turbine blades in horizontal orientation thereof, e.g. in at least one storage rack that is arranged on said deck, said storage area or storage rack having a longitudinal side parallel to the longitudinal hull axis, wherein the lifting device is mounted on said hull in proximity of the stern, said lifting device comprising a pedestal fixed to the hull and extending above the deck, said pedestal having a pedestal top, wherein said lifting device further comprises a vessel roll motion compensating boom support member, which boom support member is pivotally connected to the pedestal top so as to be pivotal about a horizontal longitudinal axis that is parallel to the longitudinal hull axis in order to compensate for roll motion of the vessel, wherein said lifting device further comprises a pivotal boom having a lower end which is connected to the vessel roll motion compensating boom support member via a transverse axis, perpendicular to the horizontal longitudinal axis, wherein the method comprises moving the pivotal boom between a substantially horizontal pick-up orientation, parallel and adjacent to said longitudinal side of the storage area or storage rack, and said pre-installation position, wherein the wind turbine blade is in a generally vertical orientation and underneath a blade mounting structure in a six-o'clock position of said horizontal axis rotational hub that is arranged on top of a tower of an offshore wind turbine.

In an embodiment the root end of the wind turbine blade is provided with a T-bolt fastening arrangement comprising:

- multiple cross holes extending across a thickness of a wall of the root end of the wind turbine blade,

- multiple longitudinal holes extending longitudinally within the thickness of the wall of the root end of the wind turbine blade and each intersecting a cross hole at an inner end of the longitudinal hole, wherein the outer end of each longitudinal hole is located in a stern face of the root end, so that a plurality of cross bolts each having a hole therein is locatable in said multiple cross holes and a plurality of longitudinal bolts is arrangable in said longitudinal holes so that an inner end of each longitudinal bolt is attachable in a hole of a cross bolt, wherein the method comprises securing a wind turbine blade support device of a wind turbine blade lifting device to the root end of the wind turbine blade by means of:

- turbine blade root engagement pins, e.g. actuator driven pins, of said wind turbine blade support device, which pins are each introduced into a cross hole, for example a cross hole devoid of cross bolt therein, and/or

- extended cross bolts, each having a cross bolt engagement section that extends outward or inward of the thickness of the wall of the root end, said wind turbine blade support device engaging on said cross bolt engagement section, e.g. said cross bolt engagement section being releasably coupled to said cross bolt.

A second aspect of the invention relates to a method for six-o'clock installation of a wind turbine blade on a horizontal axis rotational hub that is arranged on top of a tower of a wind turbine, wherein the wind turbine blade has a root end and a tip end, wherein use is made of a land based vehicle or of a vessel on which a lifting device is mounted, said lifting device being provided with a pivotal boom and with a wind turbine blade root end support device, wherein said wind turbine blade root end support device comprises:

- a base mounted to said pivotal boom, e.g. at a top end of the boom,

- a blade root end retainer that is supported on said base, wherein the method comprises:

- arranging, possibly pre-arranging, the wind turbine blade to be installed in a substantially horizontal pick-up position, generally parallel to the pivotal boom in said substantially horizontal pick-up orientation thereof, preferably above an upward facing loading side of said pivotal boom,

- moving, by means of the pivotal boom of the land based vehicle or of the vessel, said wind turbine blade from said horizontal pick-up position into a pre-installation position, wherein the wind turbine blade is in a generally vertical orientation and underneath the blade mounting structure in said six-o'clock position, - aligning the root end of the wind turbine blade with the blade mounting structure in said six- o'clock position, and

- lifting the root end of the turbine blade into a fastening position relative to the blade mounting structure of the hub in said six-o'clock position, followed by fastening the root end to the blade mounting structure and by disengaging the blade root end retainer from the wind turbine blade root end.

In this second aspect of the invention the wind turbine blade root end support device may not have the spatial orientation functionality as discussed herein with reference to the first aspect of the invention. For example the boom is mounted with the lower end thereof on a Stewart platform to provide the spatial orientation functionality.

However, in a preferred embodiment of the second aspect of the invention the wind turbine blade root end support device is further enhanced with a spatial orientation functionality, for instance the lifting device being provided with a wind turbine blade root end spatial orienting and support device comprises:

- a base mounted to the boom, e.g. at the top end thereof, e.g. the boom being telescopic,

- a multiple degrees of freedom, preferably six degrees of freedom, movable blade root end retainer that is supported on said base via multiple actuators allowing multiple degrees of freedom of the movable blade root end retainer relative to the base.

In an embodiment of the second aspect of the invention at least one storage rack is arranged, e.g. on a deck of the vessel, that is adapted for storage therein of one or more, preferably multiple, wind turbine blades in horizontal orientation thereof, said storage rack having a longitudinal side, wherein the pivotal boom of the lifting device is movable into said substantially horizontal pick-up orientation, parallel and adjacent to said longitudinal side of the storage rack, and wherein, possibly, an auxiliary crane is used to retrieve a wind turbine blade from the storage rack and to bring said wind turbine blade in said substantially horizontal pick-up position. A third aspect of the invention relates to a vessel that is adapted for six-o'clock installation of a wind turbine blade on a horizontal axis rotational hub that is arranged on top of a tower of an offshore wind turbine, wherein the wind turbine blade has a root end and a tip end, wherein the vessel has a hull with a deck on which at least one storage rack is arranged that is adapted for storage therein of multiple wind turbine blades in horizontal orientation thereof, said storage rack having a longitudinal side, wherein a lifting device is on said hull, said lifting device being provided with a pivotal boom and with a wind turbine blade support device, for example a wind turbine blade root end support device, for example a wind turbine blade root end spatial orienting and support device, wherein the pivotal boom of the lifting device is movable into a substantially horizontal pick up orientation, parallel and adjacent to said longitudinal side of the storage rack, and wherein the vessel comprises at least one auxiliary crane that is adapted to retrieve a wind turbine blade from the storage rack and to bring said wind turbine blade in a

substantially horizontal pick-up position, generally parallel to the pivotal boom in said substantially horizontal pick-up orientation thereof, preferably on top of said pivotal boom, and wherein the boom is provided with a wind turbine blade support device that is adapted to retain and support the wind turbine blade relative to the boom, wherein the lifting device is adapted to pivot the boom and the wind turbine blade retained and supported thereon by the wind turbine blade support device from said horizontal pick-up position into a pre-installation position, wherein the wind turbine blade is in a generally vertical orientation and underneath a blade mounting structure in a six-o'clock position of said horizontal axis rotational hub that is arranged on top of a tower of an offshore wind turbine.

The vessel may, for example, be employed in the method of the first or second aspect of the invention.

In an embodiment of the vessel two wind turbine blade storage racks are arranged on the deck of the vessel, parallel to one another, possibly parallel to a longitudinal axis of the vessel between the bow and the stern of the vessel, and with a pathway in between the storage racks, wherein the pivotal boom of the lifting device is movable into said substantially horizontal pick-up orientation located in said pathway between the storage racks, parallel and adjacent to said longitudinal sides of the storage racks.

The third aspect of the invention also relates to a method for six-o'clock installation of a wind turbine blade on a horizontal axis rotational hub that is arranged on top of a tower of an offshore wind turbine, wherein use is made of the vessel.

A fourth aspect of the invention relates to a method for six-o'clock installation of a wind turbine blade on a horizontal axis rotational hub that is arranged on top of a tower of a wind turbine, wherein the wind turbine blade has a root end and a tip end, wherein the method comprises:

- bringing a wind turbine blade into a pre-installation position, wherein the wind turbine blade is in a generally vertical orientation and underneath the blade mounting structure in said six- o'clock position,

- providing a wind turbine blade root end spatial orienting and support device, wherein said wind turbine blade root end spatial orienting and support device comprises:

- a base mounted to said boom,

- a multiple degrees of freedom, preferably six degrees of freedom, movable blade root end retainer that is supported on said base via multiple actuators allowing multiple degrees of freedom of the movable blade root end retainer relative to the base,

- using one or more turbine blade root end engagement members, e.g. provided on the movable blade root end retainer, to fix the root end of the wind turbine blade relative to the blade root end retainer, wherein the method comprises, after said bringing of the wind turbine blade in said pre installation position, operating the actuators of the wind turbine blade root end spatial orienting and support device in order to align the root end of the wind turbine blade with the blade mounting structure in said six-o'clock position, wherein the aligned root end of the turbine blade is lifted into a fastening position relative to the blade mounting structure of the hub in said six-o‘clock position, preferably said lift being performed with the spatial orienting and support device, followed by fastening the root end to the blade mounting structure and by disengaging the blade root end retainer from the wind turbine blade root end.

A fifth aspect of the invention relates to a system for six-o'clock installation of a wind turbine blade on a horizontal axis rotational hub that is arranged on top of a tower of an offshore wind turbine, wherein the wind turbine blade has a root end and a tip end, wherein the system comprises:

- a wind turbine blade root end spatial orienting and support device comprising:

- a base mountable to a boom of a lifting device, e.g. a pivotal boom,

- one or more turbine blade root end engagement members, e.g. provided on the movable blade root end retainer, adapted to fix the root end of the wind turbine blade relative to the blade root end retainer.

The fifth aspect of the invention also relates to a method for six-o'clock installation of a wind turbine blade on a horizontal axis rotational hub that is arranged on top of a tower of an offshore wind turbine, wherein the wind turbine blade has a root end and a tip end, wherein use is made of the system and wherein the root end of the wind turbine blade is fixed or fixated relative to the blade root end retainer by said one or more turbine blade root end engagement members, e.g. provided on the movable blade root end retainer.

In an embodiment the one or more turbine blade root end engagement members comprise:

- turbine blade root engagement pins, e.g. actuator driven pins, of said wind turbine blade support device, which pins are each introducible into a cross hole in the root end of the wind turbine blade, e.g. a cross hole of a T-bolt connection arrangement for the wind turbine blade, for example a cross hole devoid of cross bolt therein,

- extended cross bolts of a T-bolt connection arrangement for the wind turbine blade, each having a cross bolt engagement section that extends outward or inward of the thickness of the wall of the root end, said wind turbine blade support device engaging on said cross bolt engagement section, e.g. said cross bolt engagement section being releasably coupled to said cross bolt.

It will be appreciated that the system of the fifth aspect of the invention may further comprise a lifting device having a boom, e.g. in the embodiments described herein.

A sixth aspect of the invention relates to a method for installation, e.g. six-o'clock installation, of a wind turbine blade on a horizontal axis rotational hub that is arranged on top of a tower of an offshore wind turbine, wherein the wind turbine blade has a root end and a tip end, wherein the root end is provided with a T-bolt fastening arrangement comprising:

- multiple longitudinal holes extending longitudinally within the thickness of the wall of the root end of the wind turbine blade and each intersecting a cross hole at an inner end of the longitudinal hole, wherein the outer end of each longitudinal hole is located in a stern face of the root end, so that a plurality of cross bolts each having a hole therein is beatable in said multiple cross holes and a plurality of longitudinal bolts is arrangable in said longitudinal holes so that an inner end of each longitudinal bolt is attachable in a hole of a cross bolt, wherein the method comprises securing a wind turbine blade support device of a wind turbine blade lifting device to the root end of the wind turbine blade by means of:

- turbine blade root engagement pins, e.g. actuator driven pins, of said wind turbine blade support device, which pins are each introduced into a cross hole, for example a cross hole devoid of cross bolt therein,

The sixth aspect of the invention also relates to a wind turbine blade support device for use during installation of a wind turbine blade to a blade mounting structure of a horizontal axis hub on a tower of a wind turbine, for example in a six-o’clock installation method but possibly also for three- or nine o’clock installation, wherein the support device is provided with turbine blade root engagement members, e.g. pins, e.g. actuator driven pins, which pins can each be introduced into a cross hole, for example of a T-bolt connection arrangement, for example a cross hole that is temporarily devoid of cross bolt therein. A seventh aspect of the invention relates to a land based vehicle or a vessel configured for six-o'clock installation of a wind turbine blade on a horizontal axis rotational hub that is arranged on top of a tower of a wind turbine, wherein the wind turbine blade has a root end and a tip end, wherein the vehicle or vessel is provided with a lifting device mounted thereon, wherein the lifting device is provided with a boom, e.g. a pivotal boom, and with a wind turbine blade root end spatial orienting and support device, wherein said wind turbine blade root end spatial orienting and support device comprises:

- a base mounted to said boom,

- a multiple degrees of freedom, preferably six degrees of freedom, movable blade root end retainer that is supported on said base via multiple actuators allowing multiple degrees of freedom of the movable blade root end retainer relative to the base, wherein the root end of the wind turbine blade is fixable relative to the blade root end retainer by means of one or more turbine blade root end engagement members, e.g. provided on the movable blade root end retainer, wherein the lifting device is adapted to bring a wind turbine blade into a pre-installation position, wherein the wind turbine blade is in a generally vertical orientation and underneath a blade mounting structure of the hub in a six-o'clock position of the blade mounting structure, and wherein wind turbine blade root end spatial orienting and support device is configured to, after said bringing of the wind turbine blade in said pre-installation position, operating the actuators of the wind turbine blade root end spatial orienting and support device in order to:

- align the root end of the wind turbine blade with the blade mounting structure in said six- o'clock position, and, optionally,

- to lift the root end of the turbine blade into a fastening position relative to the blade mounting structure of the hub in said six-o'clock position, so as to allow for a following fastening of the root end to the blade mounting structure.

The sevenths aspect of the invention also relates to a method for six-o'clock installation of a wind turbine blade on a horizontal axis rotational hub that is arranged on top of a tower of an offshore wind turbine wherein use is made of the land based vehicle or the vessel, e.g. the vessel remaining in floating condition during the installation of the wind turbine blade

An eights aspect of the invention relates to a land based vehicle or a vessel configured for six-o'clock installation of a wind turbine blade on a horizontal axis rotational hub that is arranged on top of a tower of a wind turbine, wherein the wind turbine blade has a root end and a tip end, wherein the vehicle or vessel is provided with a lifting device mounted thereon, wherein the lifting device is provided with a pivotal boom having a lower end and a top end, wherein the lower end is pivotal relative to the vehicle or vessel about a generally horizontal pivot axis, so that the pivotal boom is movable between a substantially horizontal pick-up orientation and a pre-installation position, wherein a loading side of the pivotal boom is facing upwards when said pivotal boom is in said substantially horizontal pick-up orientation, wherein top end of the pivotal boom is provided with a wind turbine blade root end support device, wherein said wind turbine blade root end support device comprises:

- a base mounted to the top end of said boom,

- a blade root end retainer that is supported on said base, wherein, in use, a wind turbine blade is to be arranged in horizontal orientation thereof above the loading side of the pivotal boom in said substantially horizontal pick-up orientation, e.g. by means of an auxiliary crane, and then the root end of the wind turbine blade is fixable relative to the blade root end retainer by means of one or more turbine blade root end engagement members, e.g. provided on the blade root end retainer, wherein the lifting device is adapted to pivot the pivotal boom and the wind turbine blade retained and supported thereon by the wind turbine blade support device from said horizontal pick-up position into said pre-installation position wherein the wind turbine blade is in a generally vertical orientation and underneath a blade mounting structure in a six-o'clock position of said horizontal axis rotational hub that is arranged on top of a tower of an offshore wind turbine. The eights aspect of the invention also relates to a method for six-o'clock installation of a wind turbine blade on a horizontal axis rotational hub that is arranged on top of a tower of an offshore wind turbine wherein use is made of the land based vehicle or the vessel, e.g. the vessel remaining in floating condition during the installation of the wind turbine blade.

A ninth aspect of the invention relates to a vessel, e.g. a monohull or catamaran type vessel, configured for six-o'clock installation of a wind turbine blade on a horizontal axis rotational hub that is arranged on top of a tower of an offshore wind turbine with the vessel remaining in floating condition, wherein the vessel has a hull with a bow, a stern, and a longitudinal hull axis, the hull having a deck with a storage area for storage of multiple wind turbine blades in horizontal orientation thereof, e.g. in at least one storage rack that is arranged on said deck, said storage area or storage rack having a longitudinal side parallel to the longitudinal hull axis, wherein a lifting device is mounted on said hull in proximity of the stern, said lifting device comprising a pedestal fixed to the hull and extending above the deck, said pedestal having a pedestal top, wherein said lifting device further comprises a vessel roll motion compensating boom support member, which boom support member is pivotally connected to the pedestal top so as to be pivotal about a horizontal longitudinal axis that is parallel to the longitudinal hull axis in order to compensate for roll motion of the vessel, wherein said lifting device further comprises a pivotal boom having a lower end which is connected to the vessel roll motion compensating boom support member via a transverse axis, perpendicular to the horizontal longitudinal axis so as to allow motion of the pivotal boom between a substantially horizontal pick-up orientation, parallel and adjacent to said longitudinal side of the storage area or storage rack, and a pre-installation position, wherein the wind turbine blade is in a generally vertical orientation and underneath a blade mounting structure in a six-o'clock position of said horizontal axis rotational hub that is arranged on top of a tower of an offshore wind turbine.

The ninth aspect of the invention also relates to a method for six-o'clock installation of a wind turbine blade on a horizontal axis rotational hub that is arranged on top of a tower of an offshore wind turbine wherein use is made of the vessel remaining in floating condition. Preferably the vessel is arranged with the stern directed towards the tower, preferably the bow heading into oncoming waves, so that roll is reduced.

It will be appreciated that one or more features, e.g. structural features or features of a method discussed herein with reference to one aspect of the invention, either as essential within the context of an aspect of the invention and/or as an optional, e.g. as a preferred, feature, can be readily combined or integrated in any another aspect of the invention.

The invention and aspects thereof will now be explained in more detail with reference to the drawings. In the drawings:

- Fig. 1 shows a wind turbine tower and an example of a vessel equipped with storage racks for horizontal storage of wind turbine blades and equipped with a lifting device provided with a pivotal boom and with a wind turbine blade root end spatial orienting and support device,

- Fig. 2 shows a part of figure 1 on a larger scale,

- Fig. 3 shows the stern of the vessel of figures 1 and 2, with the pedestal and the roll motion compensating arrangement of the pivotal and telescopic boom,

- Fig. 4 shows the view of figure 1 near the top of the wind turbine on a larger scale,

- Fig. 5a, 5b respectively illustrate the lifting device on the vessel in an extended state of the boom and in a retracted state of the boom,

- Fig. 6a illustrates an example of a wind turbine blade root end spatial orienting and support device in closed condition,

- Fig. 6b illustrates the device of figure 6a in opened condition,

- Fig. 7a illustrates another example of a wind turbine blade root end spatial orienting and support device in closed condition,

- Fig.7b illustrates the device of figure 7a in opened condition.

In the figures a vessel 1 is shown that is adapted for six-o'clock installation of a wind turbine blade 20 on a horizontal axis rotational hub 85 that is arranged on top of a tower 81 of an offshore wind turbine 80. In more detail the tower 81 is placed on a soil-based foundation, e.g. a monopile, which is not shown. On top of the tower 81 there is a nacelle 82 wherein an electrical generator is housed. At the front end of the nacelle 82 there is the hub 85, which is commonly connected to the generator via a gearbox located in the nacelle. As an alternative direct drive generators are known, so that the gearbox is dispensed with.

As is more or less standard the hub 85 is equipped for mounting three blades 20, each on an associated blade mounting structure 86 of the hub 85. As is known in the art, the blade mounting structure may be formed of or comprise a bearing, often called blade pitch bearing, which allows the pitch of blade to be varied by a pitch variation mechanism of the wind turbine.

In the example depicted in figures 1 and 2, which is generally to scale, the blades 20 have a length of about 60 meters each. So the wind turbine has a rotor diameter of about 125 meters.

The wind turbine blade 20 has a root end 21 and a tip end 22. Generally the blade 20 has a hollow reinforced shell body as is known in the art. The root end 21 may be embodied as a hollow cylindrical portion of the blade 20. The blade 20, in particular also the root end thereof, may be of a composite material structure.

The vessel 1 has a hull, here a monohull 2, with a deck 3 on which at least one storage rack 4, 5, 6 is arranged. Each rack 4, 5, 6 is adapted for storage therein of multiple wind turbine blades 20 in horizontal orientation thereof.

Here, as preferred, two wind turbine blade storage racks 4, 5 are arranged on the deck 3 of the vessel, here near the stern, parallel to one another, and here parallel to a longitudinal axis of the vessel between the bow 7 and the stern 8 of the vessel 1.

A pathway is present between these two storage racks 4,5.

Each of the storage racks 4, 5 has a longitudinal side along the pathway.

At the bow 7 of the vessel 1 a bridge and crew accommodation structure 10 is arranged on the hull 2. The deck 3 is aft of the structure 10 and extend to the stern 8 of the vessel. As preferred the length of the deck 3 is such that at least two storage racks can be placed along the length. Here at the stern side two parallel racks 4, 5 with the pathway in between, generally the pathway located on the longitudinal axis of the monohull 2. And here with at least one further rack, here a broader rack 6, between the structure 10 and the racks 4, 5.

One or more, here two, auxiliary cranes 15, 16 having an operative reach covering the one or more storage racks 4,5, 6, are provided that are adapted to handle the blades 20 in horizontal orientation thereof, in particular for storage of the blades 20 in the racks 4,5,6 and retrieval of the blades 20 from the racks. A lifting device 40 is mounted on the hull 2, here as preferred on the stern end of the hull, in proximity of the stern, and on the longitudinal axis of this monohull.

The lifting device 40 comprises a pedestal 41 that is fixed, e.g. by welding, bolts, etc., to the hull, here on the deck 3. The pedestal 41 extends above the deck 3. The pedestal has a pedestal top. Preferably the pedestal is rigid, e.g. a welded steel pedestal structure, so that the top thereof is immobile relative to the deck 3 of the vessel on which the pedestal is mounted. In another embodiment the pedestal may comprise a slew bearing allowing to slew the top of the pedestal relative to a foot of the pedestal that is fixed to the hull. A slew drive is then provided to perform the slew motion.

The lifting device 40 further comprises a vessel roll motion compensating boom support member 44, which boom support member 44 is pivotally connected to the pedestal top so as to be pivotal about a horizontal longitudinal axis 45 that is parallel to the longitudinal hull axis in order to compensate for roll motion of the vessel 1.

Between the pedestal 41 and the member 44 one or more actuators 46, e.g. hydraulic cylinders 46, are arranged, that allow to control the orientation and/or motion of the member 44 relative to the pedestal 41. For example hydraulic cylinders 46 on each side of the pedestal 41 are provided, symmetrical relative to the axis 45. The actuators 46 may provide for controlled damping when the functionality is used to compensate for roll motion of the vessel 1.

The lifting device further comprises a pivotal as well as telescopic boom 50 having a lower end 51 which is connected to the vessel roll motion compensating boom support member 44 via a transverse and generally horizontal axis 52, perpendicular to the horizontal longitudinal axis 45.

The boom 50 is telescopic, here the boom has a lower boom section 55 and an upper boom section 56 telescoping relative to the lower boom section 55.

As illustrated in figure 5a a heave motion compensating drive 60 is provided and operated to periodically extend and retract the boom 50 so as to afford a heave motion compensation for the wind turbine blade root end spatial orienting and support device mounted thereon as will be explained below. Here a winch 60 is mounted to a cantilevered foot portion 55a at the lower end of the boom section 55. A winch driven cable 61 extends over a sheave 62 at an elevated location on the lower boom section 55 to the lower end of the upper boom section 65. This allows to raise and lower the upper boom section 56 and thus to adjust the length of the boom. When operated as a heave compensating winch 60, the winch 60 provides heave compensation as will be explained herein. For example the boom 50 and drive 60, 61 are embodied and operated to provide a heave motion compensation for the wind turbine blade root end spatial orienting and support device, e.g. providing an effective stroke in longitudinal direction of the boom of at least 2 meters, e.g. of between 6 and 10 meters, e.g. about 8 meters.

One or more actuators 42 are mounted between the member 44 and the lower end of the boom 50, here the lower boom section 55, so as to allow for controlled pivoting of the boom 50 about the axis 52. For example hydraulic cylinders 42 on each side of the pedestal 41 are provided, symmetrical relative to the axis 45.

As preferred, the boom 50 is counterbalanced with one or more counterweights arranged below the axis 52, so generally opposite the boom 55. Here, as preferred, two

counterbalance arms 57a, b extend generally downwards from the cantilevered foot portion 55a, each having a counterweight 58a, b at the lower or free end thereof. This allows for the counterweights 58a, b to swing past the pedestal 41 as will be explained below.

The arrangement is such that the boom 50 is pivotal into a non-depicted substantially horizontal pick-up orientation, wherein the boom 50 moves into the pathway between the storage racks 4, 5. In this position the boom 50 is parallel and adjacent to the adjacent longitudinal sides of the storage racks 4,5.

The boom 50 is also pivotal into a pre-installation position, depicted in figures 1 , 2, 4, wherein the wind turbine blade 20 is in a generally vertical orientation and underneath a blade mounting structure, e.g. the respective pitch bearing for the blade, in a six-o'clock position of the horizontal axis rotational hub 85.

The auxiliary crane 31 here, as preferred, is adapted to retrieve a wind turbine blade 20 from any of the racks 4, 5, and to bring said wind turbine blade 20 in a substantially horizontal pick-up position, generally parallel to the pivotal boom 50 in the above mentioned

substantially horizontal pick-up orientation thereof. As preferred the blade 20 is then positioned above an upward facing loading side 54 of the boom 50.

On top of the boom 50, here on top of the telescoping upper boom section 56, a wind turbine blade root end spatial orienting and support device 60 is mounted. The device 60 comprises a base 61 that is mounted, here rigidly affixed, to the boom 50. As preferred the base 61 is cantilevered from the boom 50 at the loading side 54 of the boom, so extends outward and away from the boom itself.

The device 60 further has a multiple degrees of freedom, here as preferred six degrees of freedom, movable blade root end retainer 62 that is supported on the base 61 via multiple actuators, here six hydraulic cylinders 63, thereby allowing multiple, here six, degrees of freedom of the movable blade root end retainer 62 relative to the base 61. The skilled person will appreciate that the device 60 is similar to what is known as a Stewart platform. The arrangement of actuators may vary, depending on requirements, e.g. an alternating V shaped arranged as depicted here or, for example, pairs of actuators being more or less parallel to one another in the pair, the pairs being arranged in a triangular setting.

An example of a device 60 is illustrated in figures 6a, b. Here it can be seen that the base 61 preferably is forked, e.g. U or V-shaped in top view, so as to have a central passage therein wherein the root end of the blade 20 can be introduced sideways. The retainer 62 is embodied, as preferred, as an openable annular retainer 62, e.g. with two mobile retainer member parts 62a, b, that are for example hinged at hinges 64a, b to a third part, or alternatively directly to one another, and are lockable to one another by means of locking arrangement 65. This allows for the retainer 62 to have a closed condition, fig. 6a, and an opened condition, fig. 6b, allowing sideways introduction of the root end 21 into the retainer 62 and, of course, disengagement of the retainer 62 from the root end 21 once the root end has been fastened to the hub.

It is envisaged that one or more turbine blade root end engagement members, e.g. provided on the movable blade root end retainer 62, are used to fix the root end 21 of the wind turbine blade 20 relative to the blade root end retainer 62, preferably so that the retainer 62 is in full control of the spatial orientation and motions of the root end 22 relative to the base 63, with the actuators 63 effectively governing said spatial orientation and motions.

The figures 7a, b illustrate an embodiment of the device 60 that is adapted to interacts in a affixing and load bearing manner with the root end 22 of the wind turbine blade 20 by interaction with a T-bolt fastening arrangement of the root end of the blade 20.

In general, as known in the art, e.g. as shown in EP 2 558 716, a T-bolt fastening

arrangement comprises: - multiple cross holes extending across a thickness of a wall of the root end of the wind turbine blade,

- multiple longitudinal holes extending longitudinally within the thickness of the wall of the root end of the wind turbine blade and each intersecting a cross hole at an inner end of the longitudinal hole, wherein the outer end of each longitudinal hole is located in a stern face of the root end, so that a plurality of cross bolts each having a hole therein is locatable in said multiple cross holes and a plurality of longitudinal bolts is arrangable in said longitudinal holes so that an inner end of each longitudinal bolt is attachable in a hole of a cross bolt.

In the figures 7a, b it is illustrated that the retainer may be equipped with mobile turbine blade root engagement pins 66, e.g. actuator driven pins, which pins are each introduced into a cross hole, for example a cross hole devoid of cross bolt therein.

One can also envisage that instead of common cross bolts, which normally do not project outward from the root end, some of the cross bolts are embodied as extended cross bolts, each having a cross bolt engagement section that extends outwards of the thickness of the wall of the root end. The retainer 62 can then engage on the cross bolt engagement section, e.g. said section being embodied as a hook, eye, trunnion, etc.

One can also envisage that actuable wedge clamping members are arranged on the retainer 62, so that - when the annular body of the retainer is closed about the root end - the wedge clamping members are made to engage on the exterior of the root end to grip the root end 21. Other actual clamping members, e.g. with clamps mobile transverse to the root end, e.g. like a friction clamp in pipelaying, are also possible.

One can also envisage that the root end 21 of the blade 20 is provided with a engagement collar, e.g. one or more circumferential ribs on the exterior, with the retainer 62 having complementary engagement members, e.g. radially mobile engagement members.

Also the one or more turbine blade root end engagement members can be separated components that are mounted releasable between the retainer 62 and the root end 21.

As explained herein it is envisaged that a blade 20 is loaded onto the boom 50, preferably said boom being horizontal at said loading stage, and then engaged at the root end 21 thereof by the device 60 which is brought from its opened condition into its closed condition.

If desired one or more additional supports can be arranged between the boom 50 and the blade 20 to provide support at one or more locations remote from the root end. For example one or more mobile auxiliary blade support members are mounted on the loading side of the boom 50 for this purpose. They primarily function as long as the boom is horizontal and during the first stage of upward pivoting motion. The blade 20 may simple rest on said one or more auxiliary blade support members.

The boom 50 and the wind turbine blade root end spatial orienting and support device 60 mounted thereon are embodied to support, without additional support of the weight of the blade by other arrangements, the entire weight of the wind turbine blade, e.g. at least when the blade is in the pre-installation position.

In operation the blade 20 is loaded onto the boom 50 and then the boom 50 is pivoted upwards, here towards the stern of the vessel that is directed towards and relatively closely spaced from the tower 81. In this manner the blade 20 is brought into a pre-installation position. Possibly the boom 50 is varied in length, e.g. extended, in this process to achieve a desired pre-installation position. If desired, once this position is reached, the heave compensation drive 60, 61 of the telescopic boom 50 can be activated so that the root end 21 is compensated for heave motion, at least to some, e.g. to a major, degree.

Then the actuators 63 of the wind turbine blade root end spatial orienting and support device 60 are operated, preferably by a computerized control system linked to said actuators 63, in order to align the root end 21 of the wind turbine blade with the blade mounting structure in said six-o'clock position. As explained this may involve accurately aligning longitudinal bolts pre-assembled on the root end 21 with corresponding holes in the blade mounting structure which requires a significant accuracy in all directions and angles. A six-degree freedom device 60 is capable to provide such accuracy, even taking into account that sea state induced motion of the vessel, and thereby of the boom, continuously impairs said alignment.

Once alignment has been achieved it is envisaged that the aligned root end of the turbine blade is lifted by means of the lifting device into a fastening position relative to the blade mounting structure of the hub in said six-o'clock position. As preferred this lifting stage of the aligned root end is also performed by the device 60, so without making use of any other lifting motion developed by the boom 50. This is done in view of the controllability and accuracy of the motion of the retainer 62 governed by the actuators 63. It is noted that, when present, the boom 50 may be operated in heave compensation mode, so with the telescopic boom continuously retracting and extending, e.g. governed by active heave compensation winch 60. Once the fastening position relative to the blade mounting structure of the hub is reached, e.g. the stern face of the root end 21 contacting a corresponding face of the blade mounting structure, e.g. of a ring of a bearing, the root end is fastened to the blade mounting structure. For example nuts are applied onto the ends of the longitudinal bolts now protruding through respective holes in the blade mounting structure. Once fastening, at least preliminary, has been achieved the retainer 62 is opened and the device 60 is disengaged from the blade root end 21.

It will be appreciated that the lifting of the aligned root end of the turbine blade into the fastening position may also be done by telescoping the boom, yet this harder to control and thus only within a limited weather window and/or only in calm seas.

Claims

C L A I M S

1. Method for six-o'clock installation of a wind turbine blade on a horizontal axis rotational hub that is arranged on top of a tower of a wind turbine, wherein the wind turbine blade has a root end and a tip end, wherein the method comprises:

- a base mounted to said boom,

- a multiple degrees of freedom, preferably six degrees of freedom, movable blade root end retainer that is supported on said base via multiple actuators allowing multiple degrees of freedom of the movable blade root end retainer relative to the base, wherein one or more turbine blade root end engagement members, e.g. provided on the movable blade root end retainer, are used to fix the root end of the wind turbine blade relative to the blade root end retainer, wherein the method comprises, after said bringing of the wind turbine blade in said pre installation position, operating the actuators of the wind turbine blade root end spatial orienting and support device in order to align the root end of the wind turbine blade with the blade mounting structure in said six-o'clock position, wherein the method comprises lifting the aligned root end of the turbine blade into a fastening position relative to the blade mounting structure of the hub in said six-o'clock position, followed by fastening the root end to the blade mounting structure and by disengaging the blade root end retainer from the wind turbine blade root end.

2. Method according to claim 1 , wherein the lifting the aligned root end of the turbine blade into said fastening position is performed by operating the actuators of the wind turbine blade root end spatial orienting and support device.

3. Method according to claim 1 or 2, wherein the movable blade root end retainer of the wind turbine blade root end spatial orienting and support device has six degrees of freedom relative to the base, for example wherein there are six actuable legs, e.g. linearly extendable and retractable legs, arranged between the base and the movable blade root end retainer, for example each of the actuable legs, e.g. linearly extendable and retractable legs, has a stroke length of at least 1 meter.

4. Method according to any of claims 1 - 3, wherein the movable blade root end retainer is located above the base.

5. Method according to any of claims 1 - 4, wherein the method is performed without any physical and/or load transferring contact between the lifting device with the spatial orienting and support device on the one hand and the tower with the hub, and commonly also a nacelle, on the other hand during the installation of the wind turbine blade.

6. Method according to any of claims 1 - 5, wherein the movable blade root end retainer is provided with one or more turbine blade root end engagement members, e.g. mobile engagement members, that are configured to fix the root end of the wind turbine blade relative to the blade root end retainer so that the position of the root end relative to the retainer is defined and maintained.

7. Method according to any of claims 1 - 6, wherein the boom and the wind turbine blade root end spatial orienting and support device mounted thereon support, without additional support of the weight of the blade by other arrangements, the entire weight of the wind turbine blade, e.g. at least when the blade is in said pre-installation position.

8. Method according to any of claims 1 - 7, wherein the base is mounted, e.g. fixed, to a top end of the boom.

9. Method according to any of claims 1 - 8, wherein the boom is pivotal at a lower end thereof about a substantially horizontal boom pivot axis.

10. Method according to any of claims 1 - 9, wherein the boom is telescopic, e.g. the boom having a lower boom section and an upper boom section telescoping relative to the lower boom section.

11. Method according to any of claims 1 - 10, wherein a heave motion compensating drive is provided and operated to periodically extend and retract the boom so as to afford heave motion compensation for the wind turbine blade root end spatial orienting and support device mounted thereon, e.g. the boom and drive being embodied and operated to provide a heave motion compensation for the wind turbine blade root end spatial orienting and support device, e.g. providing an effective stroke in longitudinal direction of the boom of at least 2 meters, e.g. of between 6 and 10 meters, e.g. about 8 meters.

12. Method according to any of claims 1 - 11 , wherein the wind turbine blade root end spatial orienting and support device is configured and operated to provide a heave motion compensation, preferably in combination with the boom providing a heave motion compensation for the wind turbine blade root end spatial orienting and support device.

13. Method according to any of claims 1 - 12, wherein a spatial position sensor system is provided, which is configured and operated to sense the relative position and/or motion in directions of said multiple degrees of freedom of the movable blade root end retainer relative to the hub, e.g. the blade mounting structure thereof, said sensed positions and/or motions being used to control at least the operation of the actuators of the spatial orienting and support device.

14. Method according to any of claims 1 - 13, wherein the boom is pivotal and wherein the method comprises:

15. Method according to claim 14, wherein at least one storage rack is arranged that is adapted for storage therein of one or more, preferably multiple, wind turbine blades in horizontal orientation thereof, said storage rack having a longitudinal side, wherein the pivotal boom of the lifting device is movable into said substantially horizontal pick-up orientation, parallel and adjacent to said longitudinal side of the storage rack, and wherein, possibly, an auxiliary crane is used to retrieve a wind turbine blade from the storage rack and to bring said wind turbine blade in said substantially horizontal pick-up position.

16. Method according to any of claims 1 - 15, wherein use is made of a vessel on which the lifting device is mounted, the vessel being in floating condition during installation of the wind turbine blade.

17. Method according to any of claims 1 - 16, wherein use is made of a vessel on which the lifting device is mounted, the vessel being in floating condition during installation of the wind turbine blade, wherein the vessel has a hull with a bow, a stern, and a longitudinal hull axis, e.g. a monohull or a catamaran type hull, e.g. a SWATH type hull, preferably the method being performed with the bow heading into oncoming waves and the stern being directed towards the tower, the hull having a deck with a storage area for storage of multiple wind turbine blades in horizontal orientation thereof, e.g. in at least one storage rack that is arranged on said deck, said storage area or storage rack having a longitudinal side parallel to the longitudinal hull axis, wherein the lifting device is mounted on said hull in proximity of the stern, said lifting device comprising a pedestal fixed to the hull and extending above the deck, said pedestal having a pedestal top, wherein said lifting device further comprises a vessel roll motion compensating boom support member, which boom support member is pivotally connected to the pedestal top so as to be pivotal about a horizontal longitudinal axis that is parallel to the longitudinal hull axis in order to compensate for roll motion of the vessel, wherein said lifting device further comprises a pivotal boom having a lower end which is connected to the vessel roll motion compensating boom support member via a transverse axis, perpendicular to the horizontal longitudinal axis, wherein the method comprises moving the pivotal boom between a substantially horizontal pick-up orientation, parallel and adjacent to said longitudinal side of the storage area or storage rack, and said pre-installation position, wherein the wind turbine blade is in a generally vertical orientation and underneath a blade mounting structure in a six-o'clock position of said horizontal axis rotational hub that is arranged on top of a tower of an offshore wind turbine.

18. Method according to any of claims 1 - 17, wherein the root end of the wind turbine blade is provided with a T-bolt fastening arrangement comprising: