Floating wind turbine and a method for the installation of such floating wind turbine

1. A floating wind turbine comprising a hull, a wind turbine mounted on top of the hull and a counterweight suspended below the hull by a counterweight suspension means, wherein

the counterweight comprises one or more counterweight buoyancy tanks;

the one or more counterweight buoyancy tanks have dimensions such that when the internal volume is filled with air or another gas, the total buoyancy of the counterweight is substantially equal to or greater than its weight, making it capable of floating in a towing/maintenance position with substantially no additional support in the vertical direction;

when the one or more counterweight buoyancy tanks are partly or completely flooded with water, the counterweight will sink to an installed position at a level determined by the counterweight suspension means;

the counterweight suspension means is separately or jointly capable of transferring both forces and moments to the hull, thereby enabling the counterweight to stabilize the hull when the counterweight is in its installed position;

wherein the counterweight is shaped as a polygon comprising a set of the one or more counterweight buoyancy tanks located at each corner of the polygon, and

wherein each corner is connected to at least two separate attachment points on the hull by respective counterweight suspension means.

2. The floating wind turbine according to claim 1 , wherein after installation the hull is functionally a spar buoy.

3. The floating wind turbine according to claim 1 , wherein after installation the hull is functionally a semisubmersible.

4. The floating wind turbine according to claim 1 , wherein after installation the hull is functionally a tension leg platform.

5. The floating wind turbine according to claim 1 , wherein the counterweight suspension means comprises telescopic tubes.

6. The floating wind turbine according to claim 1 , wherein the counterweight suspension means is supplemented with or replaced by a telescopic center tube.

7. The floating wind turbine according to claim 1 , wherein an attachment of the counterweight suspension means to the polygonal counterweight is separated from the center of gravity of the polygonal counterweight by a distance which is equal to or larger than half of the distance from the center of gravity of the hull to an attachment of the counterweight suspension means to the hull.

8. The floating wind turbine according to claim 1 , wherein the counterweight is attached to the hull during towing.

9. The floating wind turbine according to claim 1 , wherein a static and dynamic response of the floating foundation can be adjusted before installation through a combination of adjustment of i) ballasting of the counterweight buoyancy tanks, ii) ballasting of the hull, and/or iii) adjustment of the installed depth of the counterweight.

10. The floating wind turbine according to claim 1 , wherein a static and dynamic response of the floating foundation can be adjusted after installation through a combination of adjustment of i) ballasting of the counterweight buoyancy tanks, and ii) ballasting of the hull.

11. The floating wind turbine according to claim 1 , wherein after installation the counterweight rests on the seabed.

12. The floating wind turbine according to claim 1 , wherein the hull has a hull bottom arrangement comprising lateral braces connecting lateral nodes comprising hull buoyancy tanks; and wherein each lateral node is connected via respective counterweight suspension means to at least two separate attachment points on the counterweight.

13. The floating wind turbine according to claim 12 , wherein the counterweight is shaped as a triangle with a respective set of the one or more counterweight buoyancy tanks in each counterweight corner, and the hull bottom arrangement is formed as a hull triangle with the hull buoyancy tanks at each hull lateral node, wherein each counterweight corner is connected via respective counterweight suspension means with at least two lateral nodes in the hull bottom arrangement; and wherein each lateral node is connected via respective counterweight suspension means with at least two counterweight corners.

14. The floating wind turbine according to claim 13 , wherein the hull bottom arrangement is the triangle opposite the apex of a tetrahedron, and wherein a wind turbine tower is connected to the apex; wherein the projection of the triangle opposite the apex is rotated relative to the projection of the triangle of the counterweight.

15. The floating wind turbine according to claim 1 , wherein respective sets of the one or more counterweight buoyancy tanks are connected by braces to form the polygon.

16. The floating wind turbine according to claim 1 , wherein the respective counterweight suspension means connecting each corner to the at least two separate attachment points on the hull extend from the respective corner to a lateral node on the hull and do not cross a center line of the polygon.

17. A method for the installation of a floating wind turbine comprising:

providing a hull, a wind turbine mounted on top of the hull and a counterweight suspended below the hull by a counterweight suspension means, wherein the counterweight comprises one or more counterweight buoyancy tanks; the one or more counterweight buoyancy tanks have dimensions such that when the internal volume is filled with air or another gas, the total buoyancy of the counterweight is substantially equal to or greater than its weight, making it capable of floating in a towing/maintenance position with substantially no additional support in the vertical direction; when the one or more counterweight buoyancy tanks are partly or completely flooded with water, the counterweight will sink to an installed position at a level determined by the counterweight suspension means; the counterweight suspension means is separately or jointly capable of transferring both forces and moments to the hull, thereby enabling the counterweight to stabilize the hull when the counterweight is in its installed position; the counterweight is shaped as a polygon comprising a set of the one or more counterweight buoyancy tanks located at each corner of the polygon wherein each corner is connected to at least two separate attachment points on the hull by respective suspension means;

filling the one or more counterweight buoyancy tanks of the counterweight partly or completely with air or another gas;

attaching the counterweight to the hull prior to towing;

towing the counterweight with the hull to a desired offshore position;

flooding the one or more counterweight buoyancy tanks partly or completely with water when a desired offshore position has been reached,

permitting the counterweight to sink to an installed position at a level determined by the counterweight suspension means; and

transferring forces and moments to the hull by the counterweight suspension means which are separately or jointly capable of transferring both forces and moments to the hull, thereby enabling the counterweight to stabilize the hull when the counterweight is in its installed position.

18. A method for the installation of a floating wind turbine comprising:

providing a hull, a wind turbine mounted on top of the hull and a counterweight suspended below the hull by a counterweight suspension means, wherein the counterweight comprises one or more counterweight buoyancy tanks; the one or more counterweight buoyancy tanks have dimensions such that when the internal volume is filled with air or another gas, the total buoyancy of the counterweight is substantially equal to or greater than its weight, making it capable of floating in a towing/maintenance position with substantially no additional support in the vertical direction; when the one or more counterweight buoyancy tanks are partly or completely flooded with water, the counterweight will sink to an installed position at a level determined by the counterweight suspension means; the counterweight suspension means is separately or jointly capable of transferring both forces and moments to the hull, thereby enabling the counterweight to stabilize the hull when the counterweight is in its installed position; the counterweight is shaped as a polygon comprising a set of the one or more counterweight buoyancy tanks located at each corner of the polygon wherein each corner is connected to at least two separate attachment points on the hull by respective suspension means;

filling the one or more counterweight buoyancy tanks of the counterweight partly or completely with air or another gas before launch and towing;

towing the hull and the counterweight to a desired offshore position;

attaching the counterweight to the hull when a desired offshore position has been reached;

flooding the one or more counterweight buoyancy tanks partly or completely with water,

permitting the counterweight to sink to an installed position at a level determined by the counterweight suspension means; and

transferring forces and moments to the hull by the counterweight suspension means which are separately or jointly capable of transferring both forces and moments to the hull, thereby enabling the counterweight to stabilize the hull when the counterweight is in its installed position.

19. A method for the maintenance of a floating wind turbine comprising:

providing a hull, a wind turbine mounted on top of the hull and a counterweight suspended below the hull by counterweight suspension means, wherein the counterweight comprises one or more counterweight buoyancy tanks; the one or more counterweight buoyancy tanks have dimensions such that when the internal volume is filled with air or another gas, the total buoyancy of the counterweight is substantially equal to or greater than its weight, making it capable of floating in a towing/maintenance position with substantially no additional support in the vertical direction;

when the one or more counterweight buoyancy tanks are partly or completely flooded with water, the counterweight will sink to an installed position at a level determined by the counterweight suspension means; the counterweight suspension means is separately or jointly capable of transferring both forces and moments to the hull, thereby enabling the counterweight to stabilize the hull when the counterweight is in its installed position; the counterweight is shaped as a polygon comprising a set of the one or more counterweight buoyancy tanks located at each corner of the polygon wherein each corner is connected to at least two separate attachment points on the hull by respective counterweight suspension means;

raising the hull from an installed position to a maintenance position by partly or completely filling the one or more buoyancy tanks of the counterweight with air or another gas;

carrying out maintenance; and

flooding the one or more counterweight buoyancy tanks partly or completely to lower the hull to an installed position.