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.

A windmill construction (10), comprising a rotor-nacelle assembly (12) with blades (14), a tower (16), a substructure (20) and a foundation (22). The substructure (20) comprises a first guide collar (24) and a second guide collar (26) for support of the tower (16), said first guide collar (24) being located in a lower part of the substructure (20) and said second guide collar (26) being located in an upper part of the substructure (20). The substructure (20) comprises a jack-up assembly (30) for receipt of modular tower segments (18), said tower segments (18) are arranged to be assembled in the substructure (20) and erectable by the jack-up assembly (30) to produce an assembled tower (16). The invention is also directed to a method for assembly of a windmill construction.

A connecting device for a tower-like structure is provided, and includes a plurality of connecting elements which are arranged between an upper component and a lower component of the structure in order to produce a slip joint, and for the purpose of load transfer between the upper component of the structure and the lower component of the structure, are to be positioned next to one another in the peripheral direction about the longitudinal axis and/or in the longitudinal direction thereof with respect to a central longitudinal axis of the structure. With respect to the longitudinal axis, the connecting device has a greater thickness in the centre thereof than at its upper and/or lower end.

A windmill construction (10), comprising a rotor-nacelle assembly (12) with blades (14), a tower (16), a substructure (20) and a foundation (22). The substructure (20) comprises a first guide collar (24) and a second guide collar (26) for support of the tower (16), said first guide collar (24) being located in a lower part of the substructure (20) and said second guide collar (26) being located in an upper part of the substructure (20). The substructure (20) comprises a jack-up assembly (30) for receipt of modular tower segments (18), said tower segments (18) are arranged to be assembled in the substructure (20) and erectable by the jack-up assembly (30) to produce an assembled tower (16). The invention is also directed to a method for assembly of a windmill construction.

For installing a blade on a horizontal axis rotational hub of an offshore wind turbine, use is made of a blade installation device that is temporarily installed on the offshore wind turbine. A mounting part is mounted on the foundation of the offshore wind turbine and/or on a lower portion of the wind turbine mast. A crane mast is erected vertically and is supported by the mounting part. The crane mast has a track. A blade manipulator assembly includes a trolley moving over the track and one or more blade root engagement members that engage a root end of the blade. The blade installation device includes a hoist system with a crane boom that is mounted to a top end of the crane mast, a winch, and a winch driven cable. In the method, the trolley is brought in a lower position thereof and the blade root engagement members engage on the root end of the blade that is in the lower receiving position thereof. The cable of the hoist system is attached to the blade at a distance remote from the root end, preferably at a center of gravity of the blade. The method includes the lifting of the blade to the blade installation position by operating the winch of the hoist system and simultaneously moving the trolley along the track by the trolley drive.

A cable head ring for use in connecting a wind turbine tower to a concrete foundation. The cable head ring includes an annular plate for connecting to the upper end of the concrete foundation, an inner tubular web extending axially from the annular plate and an outer tubular web extending axially from the annular plate. An annular gap is formed between the inner and outer tubular webs for receiving a tubular wind turbine component. The annular plate has a plurality of passages extending axially therethrough for receiving tensioning tendons of the concrete foundation. The inner and outer tubular webs include holes extending radially therethrough. The positions of the holes in the inner tubular web correspond to the positions of the holes in the outer tubular web such that a fastener can extend radially through a hole in the inner tubular web and a hole in the outer tubular web.

A method for installing a wind turbine tower is provided, wherein the tower includes a tower fastening portion and a tower through hole in the tower fastening portion, including: providing a vessel with a vessel fastening portion and a vessel through hole in the vessel fastening portion, landing the tower onto the vessel with the tower through hole at the vessel through hole, positioning a stud in the tower through hole and the vessel through hole, wherein the stud includes an upper portion protruding from the tower through hole in an upward direction and a lower portion protruding from the vessel through hole in a downward direction, fastening the tower fastening portion to the vessel fastening portion by a lower fastening element attached to the lower portion and an upper fastening element attached to the upper portion, wherein the lower fastening element and the upper fastening element are both detachable from the stud in a non-destructive way.