An off-shore wind turbine system is assembled using a platform or jack-up vessel, and a first base anchored to the seafloor at a blade assembly off-shore location. A buoyant tower is attached to the first base. A crane provided on the platform or jack-up vessel is used to lift blades and blades, which are then coupled to a turbine held in a nacelle provided at the top of the buoyant tower. The buoyant tower, the nacelle, and the blades are detached from the first base. The buoyant tower, the nacelle, and the blades are towed to a wind farm and connected to a second base provided in the wind farm. The buoyant tower, the nacelle, and the blades are further stabilized using mooring lines spanning between the buoyant towers and other bases provided in the wind farm. The first base and/or the second base include anti-rotation features.

The invention relates to a floating foundation for wind turbine generators and a method for installing a wind turbine generator on top of and performing maintenance on said foundation. The floating foundation includes a tower and two support legs pivotally connected to the tower, forming a tripod-like structure. The floating foundation may include hydrodynamic damping elements and a single point mooring system leaving the foundation free to weathervane. The invention also relates to a method for using the structure as a crane, lowering and raising the turbine platform against and from e.g. a service barge during maintenance or assembly.

A vibration device for inserting a foundation element into the ground includes a base frame having an inner space, and one or more vibration elements that are connected to the base frame. During use, the base frame extends at least partly around a side wall of the foundation element to at least partially enclose said foundation element in the inner space. A vibration system, a vibration assembly and a method for inserting a foundation element into the ground.

Method for installing a wind turbine blade to a nacelle of an offshore wind turbine, comprising the steps of: providing a vessel or barge with wind turbine blades and a blade installer unit comprising a blade receiving cart; at the offshore wind turbine, bringing a boom of the blade installer unit towards a wind turbine tower of the wind turbine; actuating a tower gripping device unit until the tower gripping device unit engages the tower; inserting a blade into the blade receiving cart, wherein the blade is in approximately horizontal position in the cart; moving the blade receiving cart up towards the upper end of the boom of the blade installer unit; rotating the blade until the blade is in approximately vertical position; moving the blade with respect to the cart until the blade engages the nacelle for coupling to the nacelle.

Installation vessel for installation of a monopile to support an offshore wind turbine. The vessel has a pile holding device with a pile holder and a support assembly which is configured to move the pile holder in a horizontal plane relative to the hull. A monitoring system is configured to, in a gripping phase wherein the monopile is suspended from a crane and is to be gripped by the pile holder, monitor the suspended monopile in the horizontal plane relative to the pile holder. The system provides signals representative of the position and movement of the monopile relative to the pile holder to the motion control unit of the support assembly.

A method of mounting a wind turbine rotor blade to a partial assembly is provided, the partial assembly including a number of rotor blades mounted to a hub which in turn is connected to a rotor shaft of a wind turbine, the method including the steps of A) effecting a rotation of the rotor shaft to turn the partial assembly from its starting position through an initial arc (.sub.0); B1) allowing the partial assembly to swing through a free swing arc in the opposite direction; B2) effecting a rotation of the rotor shaft to extend the free swing arc () by a further arc (); and C) repeating steps B1 and B2 until the partial assembly has reached a final position at an angular displacement of 120 to the initial position.

A method for installation of a transition piece on a monopile foundation of an offshore wind turbine along a common axis extending in a longitudinal direction is performed from a floating installation vessel. Buffer elements are arranged around an inner circumference of the transition piece and/or the monopile structure. The transition piece is lifted and lowered onto the monopile structure by use of a crane, and landed onto the monopile structure through the use of the buffer elements. A number of hydraulic cylinder jacks for circumferential alignment of bolt holes are provided in the transition piece and monopile, and alignment tools are used for alignment of the flanges provided on each of the transition piece and the monopile. The transition piece is lifted and the buffer elements are removed after which the transition piece is lowered onto the monopile, and bolts are tensioned fix the transition piece to the monopile.

A crane, in particular an offshore leg encircling crane for use on a jack up-vessel, includes a revolving superstructure with a crane housing to which a boom is connected. The crane includes a hoisting system and a luffing device for pivoting a boom up to an upright position and down. The luffing device includes first left-hand and right-hand luffing cable sheave sets provided at opposite sides at a top of a luffing frame structure, and second left-hand and right-hand luffing cable sheave sets provided at opposite sides of a head structure of the boom. A variable length luffing system extends from the luffing winch via the first left-hand and right-hand luffing cable sheave sets to extend in a luffing direction to the second left-hand and right-hand luffing cable sheave sets.

An integrated vessel with wave compensation capability for transportation of completed offshore wind turbines includes a wind turbine conveyor system, a dynamic positioning propeller system, and a six-degree-of-freedom parallel manipulator system, as well as a foundation monopile of a fixed wind turbine arranged in the hull; the completed offshore wind turbines are fixed on the wind turbine conveyor system by multiple wind turbine stabilizing blocks, and a clamping system is equipped in the six-degree-of-freedom parallel manipulator system. The invention uses the conveyor system to transfer and the clamping system to clamp the completed wind turbine, as well as the six-degree-of-freedom parallel manipulator system to transport, which reduces the difficulty of the operation, improves the automation of the installation process, and reduces the labor cost of the wind turbine installation; the invention reduces the difficulty of the installation process, and improves the efficiency of the wind turbine installation.

There is provided a control system for controlling power transmission associated with a first wind turbine. The control system is configured to: monitor an alternating current, AC, phase angle associated with the first wind turbine and/or monitor a rate of change of the AC phase angle associated with the first wind turbine; determine whether there is a change in the AC phase angle which is above a first threshold value and/or determine whether the rate of change of the AC phase angle is above a second threshold value; and in response to determining that there is a change in the AC phase angle which is above the first threshold value and/or the rate of change of the AC phase angle is above the second threshold value, cause the first wind turbine to operate its dynamic braking system, DBS, to reduce an instantaneous power output of the first wind turbine.