NO20191414A1

NO20191414A1 - Floating windmill installation

Info

Publication number: NO20191414A1
Application number: NO20191414A
Authority: NO
Inventors: Kåre Olav Krogenes; Lars Helge Helvig; Lars Henning Helvig
Original assignee: Blue Wind As
Priority date: 2019-11-28
Filing date: 2019-11-28
Publication date: 2021-05-31
Also published as: NO346371B1

Description

Field of the invention

The invention relates to a floating windmill installation and methods for use of a floating windmill installation.

Background of the invention

Floating offshore windmills are desirable because it makes it possible to utilize offshore wind resources on deeper water. However, there are some challenges, assembly of the windmill and maintenence is two of them.

When installing and assembling a floating windmill today a lot of the preparations need to be done prior to moving the windmill structure out to the location of the windfarm. This is in a large part due to the need for calm sea and weather conditions for performing marine operations such as lifting of heavy components. Due to the need of deep water for the assembly and preparations, these operations might need to be done at several locations to get access to deep enough water and get access to docks for performing such operation. Due to this the windmill structure might need to be moved between several sites during the building/assembly process. This increases the cost of setting up windfarm with floating windmills.

It is similar for maintenance. Today the common approach to preform maintenance is to tow the windmill structure from the location offshore and into a fjord with calmer water. The fjord should preferably be deep enough for vertically immerse the windmill to gain access for maintenance. This is a time consuming and expensive operation. To perform maintenance offshore on location is challenging due to different heave for the windmill and for a maintenance/service vessel. Performing maintenance offshore will also requires long periods with calm weather, which is not common on offshore wind locations.

For maintenance that requires disassembly of heavy parts that are located high up the cost of using external lifting vessels are high. Due the weight of components and the height of the windmills, only the largest lifting vessels are capable of performing such operations.

It is need for equipment, systems and methods for simplifying and reducing the cost of maintenance on offshore floating windmills. Especially the cost related to assembly and disassembly. One such cost is the cost for using external lifting vessels.

Disclosure of the state of art

US2013078109 (A1) describes structures and methods for elevating and retracting offshore wind turbine assemblies. Structures and methods are presented for elevating and retracting offshore wind turbine assemblies mounted on a tower in order to facilitate both service of the assemblies at any time, as well as preservation of the assemblies through storms or other high-wind weather events. Among the structures presented are folding wind turbine blades that may be folded into compact clusters and secured to braces in order to minimize damage during storms or other high-wind events.

Objects of the present invention

One object of the invention is to provide a method for performing maintenance offshore on a floating windmill.

Another object is to provide a structure for supporting a windmill offshore.

Yet another objective is to provide a floating windmill installation that can store windmill blades.

A further object is to provide a method for disassembly of a windmill fan without the need for an external lifting vessel.

One particular object is to provide a method and a floating installation where a windmill can be raised and lowered to be able to set down windmill blades inside the hull of the floating installation.

One particular object is to provide a method for disassemble and assemble a windmill where the three degrees of freedom of a windmill are used together with the ability to raise and lower the tower of the windmill.

Summary of the invention

In one aspect the invention relates to a floating windmill installation. The floating windmill installation comprises a windmill comprising an tower, a floating installation comprising a aperture, said aperture penetrating the floating installation from a top deck to a bottom, for accommodating the tower, and means for raising and lowering the tower up and down through the aperture.

The means for raising and lowering the tower can comprise one or several ballast tanks in the tower adapted to receive and hold fluid.

The floating installation can comprise one or several ballast tanks adapted to receive and hold fluid to be used as ballast to lower and raise the floating installation in the water.

The floating windmill installation can comprise a pressurized air or gas system for displacing fluid out of one or more of the ballast tanks.

The floating windmill installation can comprise a number of pumps for pumping water from the surrounding water into one or more of the ballast tanks.

The means for raising or lowering the tower can comprise pitch racks along the tower and gears and motor for providing movement.

The floating installation can comprise storage space for storing a number of blades.

The storage space can be adapted for storing blades in an vertical orientation.

The means for raising and lowering the tower up and down through the aperture can be remotely controlled.

In another aspect the invention relates to a method to raise or lower a windmill, on a floating windmill installation, relative to a floating installation. The method comprises the following steps: accommodate a tower of a windmill in a aperture in the floating installation, and move the tower up or down inside the aperture of the floating installation to raise or lower the windmill.

The method can be used to disassemble a blade from a two blade windmill and can comprise the following steps: position a service vessel with a frame to a position for receiving a blade from the windmill, move a windmill blade to a position above the frame, lower the tower until the blade is resting in the frame of the service vessel 30, and disconnect the blade from the windmill.

The method can include the step to motion compensate the frame.

The step to lower the tower can include to adjust the buoyancy of the tower.

The method can be used to disassemble a blade from a windmill and storing said blade inside the floating installation. The method can comprise the following steps: position the blade above a desired vertical storage space inside a floating installation, using azimuth, yaw and pitch rotation of the windmill, lower the tower until the downward pointing blade is fully or partly contained inside the floating installation, hang of the blade inside the floating installation and disconnect it from the windmill.

The method can be used to disassemble a blade from a windmill and can comprise the following steps: position a service vessel with a frame to a position for receiving a blade from the windmill, raise the frame up to a position below the blade, angel the frame, rotate a fan until the blade and the frame are parallel to each other, lower the tower until the blade rests in the frame, and disconnect the blade from the windmill.

The method can include the step to motion compensate the frame.

The step to lower the tower can include to adjust the buoyancy of the tower.

In a third aspect the invention relates to the use of a number of floating windmill installation according to any of the claims 1-9 in a windfarm to optimize the power output of a windfarm by adjusting the height of individual windmills to reduce blockage and wake effect in the windfarm as a whole.

Description of the figures

Figure 1 shows a floating windmill installation with a service vessel next to it Figure 2a - 2i shows the disassembly of the fan on a floating windmill installation Figure 3a – 3o shows the disassembly of a fan on a floating windmill installation where the floating installation comprises storage space for one or more blades. Figure 4a – 4k shows the installation of a floating windmill installation comprising a two blade windmill

Reference numbers

1 Floating windmill installation

2 Water surface

4 Sea floor

6 Surrounding water

10 Windmill

11 Nacelle

12 Hub

13 Blade

13a Tip

13b Hub interface

12, 13 Fan

14 Tower

15 Ballast tank tower

16 Liquid level inside tower

16a Liquid inside tower

20 Floating installation

20` Floating installation adapted for storing blades

21 Hull

22 Aperture

23 Top Deck

24 Bottom

25 Ballast tank floating installation

26 Liquid level inside floating installation

26a Liquid inside floating installation

27 Mooring lines

30 Service vessel

31 Stern of service vessel

32 Frame for blades

33 Lifting and motion compensation system

Description of preferred embodiments of the invention

Fig 1 shows a floating windmill installation 1. The floating windmill installation comprises a windmill 10 and a floating installation 20.

The windmill 10 comprises, a nacelle 11, a hub 12, a number of blades 13 and a tower 14. For the purpose of simplifying, the hub 12 together with the blades 13 is defined as a fan 12, 13. The blade 13 is defined with two ends, a tip 13a and a hub interface 13b. The hub interface 13b is the end that connects to the hub 12.

The floating installation 20 is in this embodiment what can be described as a spare buoy floating in a body of water 6. The floating installation 20 comprises a hull 21, an aperture 22, a top deck 23, a bottom 24, a number of ballast tanks 25, and mooring lines 27 for anchoring the floating installation 20 to a sea floor 4.

For the general windmill 10 there are usually three degrees off freedom; azimuth, yaw and pitch. Azimuth is the rotation of the fan 12, 13 that generate torque for power generation. Yaw is the rotation of the nacelle 11 around the longitudinal axis of the tower 11. Yaw is usually used to adjust the windmill in regards to the wind direction to get the fan 12, 13 more or less perpendicular to the direction of the wind. Pitch is the rotation of the blades 13 around there longitudinal axis. In addition to the three degrees of freedom of an general windmill, the windmill 10 has the ability to be raised and lowered relative to the floating installation 20. The three degrees of freedom and the ability to raise and lower the windmill will in some section of the description for short be referred to as the ability to move the windmill 10.

The floating installation 20 has several functions, such as providing buoyancy, stability, means for anchoring and providing a platform to be used when performing maintenance on the windmill 10 or on the floating installation 20 itself.

The floating installation 20 is designed with the aperture 22 penetrating the floating installation 20 from the top deck 23 to the bottom 24. This aperture 22 is a channel running through the entire floating installation 20 from top to bottom and can be a moon pool. This aperture 22 is designed to accommodate the tower 14. The tower 14 is often longer than the vertical length of the floating installation 20. To be able to lower the nacelle 14 down towards the top deck 22a on the floating installation 20 the tower 14 need to extend out of the aperture 22 and down in the water 6 below the floating installation.

To be able to raise and lower the tower 14 inside the aperture 22 the floating windmill installation 1 need to be equipped with suitable means for lowering and raising of the tower 14.

For fully being able to exploit the possibilities raising from the ability to raise and lower the tower 14 it can be an advantage to enable remote control over the means for raising and lowering the tower 14.

The ability to lowering and raise the tower 14 of a floating windmill 10, will reduce or eliminate the need for large and expansive lifting vessels when assembling, disassembling or performing maintenance on blades 13, the nacelle 11 or other heavy components.

In one possible embodiment the tower 14 can be raised and lowered inside the aperture 22 by adjusting the buoyancy of the tower 14. The tower 14 then needs to float freely inside the aperture 22 of the floating installation 20. To enable this the tower 14 can be equipped with ballast tanks 15. The ballast tanks 15, can simply be one or several compartments in the inner volume of the tower 14, that can receive and hold fluid to be used as ballast.

To regulate the buoyancy i.e. the height of the tower over water there are several possible solutions. In one possible embodiment pressurized air or gas is used to displace water out of the tower through an opening near the bottom end to raise the tower 12. By bleeding of said air or gas from the tower 14 water can flow back in through an opening near the bottom end, lowering the tower 14. In another possible embodiment pumps and valves are used to pump water inn and out of the tower 14 and to contain the water in the tower 14.

A mechanism for locking the position of the tower 14 relative to the floating installation 20 can be included in the floating windmill installation 1. The possibility of locking the tower 14 to the floating installation 20 can be beneficial in several situation for instance while transporting the floating windmill installation 1, or when personnel is onboard the floating windmill installation 20.

An alternative way of moving the tower 14 up and down relative to the floating installation 20 can be pitch racks along the tower 14 and gears and motor for providing movement.

The floating windmill installation 1 can also be equipped to raise and lower the floating installation 20 relative to a the sea surface 2. This can be done by moving water inn and out of the floating installation to adjust the buoyancy. To be able to do this the floating installation 20 needs to be equipped with ballast tanks 25. The ballast tanks 25 of the floating installation can simply be one or several compartments inside the hull 21 of the floating installation adapted to receive and hold fluid to be used as ballast. A associated system for moving water inn and out of the hull 21 of the floating installation 20 is also needed. The system for adjusting the buoyancy of the floating installation 20 can be similar to the solution described for the tower 14 i.e valves and pumps, pressurized air system or a combination.

In addition to buoyancy adjusting liquid ballast 16a, 26a both the tower 14 and the floating installation 20 can be equipped with solid ballast for safely maintaining an orientation in the water 6.

The ability to adjust the buoyancy (raise or lower it in the water 6) of the floating installation 20 simplifies operations such as entering the floating installation 20, adjusting the height of the top deck 23 when a service vessel 30 is approaching to interact with the floating windmill installation 1 etc.

When the floating windmill installation 1 is operational the tower 14 and the floating installation 20 can float independent of each other. The floating installation 20 is maintaining the orientation of the tower 14 and the position in the horizontal plane. Since the two floating bodies (floating installation 20 and windmill 10) are floating independently of each other one will get an heave reducing effect on the windmill 10.

This heave reducing effect is a result that originates from several factors. One of them is the slim structure of the tower 14 compare to a typical floating structure for a windmill. The buoyancy of a body with a lower volume in the waterline will be less affected by the fluctuating water level (waves). So by decoupling the movement of the tower 14 from the movement of the floating installation 20 one achieves less heave for the tower 14 ie. the windmill 10. Since the windmill 10 do not gain any buoyancy from the floating installation 20 the length of the tower 14 below water needs to be adapted to this to get sufficient buoyancy.

This heave reducing effect is important for enabling maintenance and other operations that includes lifting of heavy components to and from the windmill 10. Reducing or eliminating the heave of the windmill 10 will expand the weather window i.e more days in a typical year will be open to perform operations of such character.

To illustrate the use of liquid ballast to adjust the buoyancy of the tower 14 and the floating windmill 20 the figures shows the tower 14 and the floating installation 20 in section. This is make it clear how the liquid level 16 of the ballast tank 15 of the tower 14 and the liquid level 26 of the ballast tank 25 of the floating installation changes with the draught of the tower 14 and the draught of the floating installation 20.

Three alternative embodiments of the floating windmill installation 10 will be described together with the related operations to disassemble or assemble the fan 12, 13 of such embodiments. These operations are described as examples of operations that are enabled by the inventive features that enables raising and lowering the tower 12 and the floating installation 20 in the water 6.

Other operations are also enabled by the floating windmill installation 1 and the related service vessels, such as replacing one or more blades 13 or replacing other heavy components on the floating windmill installation 1.

The three embodiments can in short be described as:

- a floating windmill installation 1 with a three blade windmill,

- a floating windmill installation 1` with a floating installation 20` adapted for storing blades 13,

- a floating windmill installation 1`` with a two blade windmill 10`.

All the three alternative embodiments can be combined with the inventive feature of raising and lowering the tower 14 for instance by such means as adjusting the buoyancy of the tower 14.

The floating windmill installation 1 with a three blade windmill poses a challenge with regards to lowering the tower 14 to perform maintenance and/or connect/disconnects blades 13. At one point when lowering the tower 14 the tip 13a of one or two blades 13 will reach the water surface 2. It is not desirable to immerse blades into the water 6 surrounding the floating installation 20. To overcome this problem a service vessel 30 with a lifting and motion compensation system 33 for lifting and motion compensating a frame 32 is developed.

As seen in fig 2a-2c the operational sequence can be as follows:

- approach the floating windmill installation 1 with a stern 31 of the service vessel 30, - lift and angel the liftable frame 32 by using a lifting and motion compensation system 33, and

- use the three degrees of freedom of the windmill 10 together with the ability to raise and lower the tower 14 of the windmill 10 to position the blade 13 in the frame 32, - disconnect the blade 13.

The liftable frame 32 is compensated for heave, role and pitch by the use of the motion compensation system 33. In combination with the maneuvering of the service vessel 30 the motion compensation system 33 maintains the frame 32 in a stable position. The windmill 10 is kept in a stable position due to the heave reducing design in combination with the mooring lines 27 of the floating installation 20. As both the blade 13 and the liftable frame 32 is stable the blade 13 can be placed in the liftable frame 32 by using the ability to move the windmill in combination with maneuvering the liftable frame 32 in position.

As seen in fig.2d-2i the operation can continue. With one blade disconnected from the windmill 10 a second service vessel 30 with two horizontal frames 32 can take the place of the first service vessel 30.

- position the second service vessel 30,

- use the ability to move the windmill 10 to place a second blade 13 in the first frame 32 on the second service vessel 30,

- disconnect the blade 13 from the hub 12,

- position the second frame 32 for receiving the next blade 13,

- use the ability to move the windmill 10 to place the blade 13 in the frame 32, - disconnect the blade 13 from the hub 12.

As an optional feature the frame 32 can be skidded a distance out from the stern 31 of the service vessel 30 while performing the operation to be able to keep a safe distance between the service vessel 30 and the floating windmill installation 1.

In addition to the possibility of moving or skidding the frame 32 it can, similar to the liftable frame 32, be motion compensated so that it is not affected by the movements of the second service vessel 30.

The second embodiment is a floating windmill installation 1` with a three-blade windmill and with a floating installation 20` adapted for storing blades 13. With reference to figure 3a-3o the disassembly of the fan 12, 13 will be described.

To avoid immersing one or two blades in the water surrounding the floating installation 20` when lowering the tower, the floating installation 20` is designed and equipped to receive and store one or more blades vertically. To disassemble the fan 12, 13 of the windmill 10 the possibility to move the tower 14 up and down is used in combination with the tree degrees of freedom (azimuth, yaw and pitch) to maneuver the first blade 13 down into the storage space inside the floating installation 20.

As seen in fig 3a-3c the operational sequence can be as follows:

- rotate the fan 12, 13 (azimuth) (if needed) until the tip 13a of one of the blades 13 points down towards the floating installation 1,

- rotate the nacelle 11 (yaw) (if needed) until the tip 13a is above the storage space (this can also be done before the azimuth rotation),

- lower the tower 14 so the blade 13 slides down into the hull 21 of the floating installation 20 and adjust the pitch of the blade 13 if needed,

- secure the blade inside the hull 21, and disconnect the blade 13 from the hub 12.

After the first blade is disconnected and stored inside the floating installation 20 the two remaining blades can be laid down on a service vessel 30 with three skiddable frames 32. As seen in figure 3d -3h.

The first blade 13 is now stored in the floating installation 20 and if it is to be placed onto the service vessel 30 it can be connected to the hub 12 of the windmill 10 again, and the windmill 10 can lift the blade 13 onto a third skiddable frame 32 onboard the service vessel 30. As seen in figure 3i – 3o.

The third embodiment is a floating windmill installation 1`` with a two blade windmill 10`. By using a two blade windmill instead of a three blade windmill the nacelle can be lowered down all the way to the top deck 23 of the floating installation 20 without immersing any blades 13 into the water 6. The blades 13 can due to this be laid directly down on, or picked up from a service vessel 30, using the possibility to move the tower 14 up and down in combination with the windmills three degrees of freedom (azimuth, yaw and pitch). The sequence of installing a floating windmill installation 1`` with a two blade windmill 10` at sea and assemble the nacelle 11 and fan 12,13 is showed in figure 4a – 4k.

Using a number of floating windmill installation 1 that is adapted for raising and lowering the windmill 10 in a windfarm opens up for new possibilities when it comes to optimizing the power output from the windfarm. By adjusting the height of individual windmills in the windfarm one can reduce the blockage, and wake effects. The blockage effect arises from wind slowing down as it approaches wind turbines. There is an individual blockage effect for every turbine and a global effect for the whole windfarm, which is larger than the sum of the individual effects. There is a wake after each wind turbine where the wind slows down. This effects, with wind turbines shielding and impacting each other can be reduced by optimizing the relative position of each windmill fan 12, 13.

Another possibility that is enabled by the possibility to lower and raise the tower is that the windmill can be lowered during storms and rough weather. This can be done to avoid damage during extreme weather conditions.

The installation and assembly process that is showed for a two blade windmill 10` in figure 4a – 4k can be used for all embodiments of the invention. To enable such an method for a three blade windmill an service vessel 30 with a lifting and motion compensation system 33 that lifts the frame 32 (as seen in figure 2c) need to be used in addition. This second service vessel 30 is needed to mount the last blade 13.

A floating installation 20` without a windmill can be used as a support vessel for a floating windmill park. The floating installation for such an application need to comprise a lifting installation for lifting heavy windmill components such as blades and internal storage space for storing a number of blades. An floating installation for such an application do not necessary need to comprise an aperture.

Claims

1. Floating windmill installation (1), characterized in that the floating windmill installation (1) comprises:

-a windmill (10) comprising a tower (14),

-a floating installation (20) comprising a aperture (22), said aperture (22) penetrating the floating installation (20) from a top deck (23) to a bottom (24), for accommodating the tower (14), and

- means for raising and lowering the tower (14) up and down through the aperture (22).

2. Floating windmill installation (1) according to claim 1, characterized in that the means for raising and lowering the tower (14) comprises one or several ballast tanks (15) in the tower (14) adapted to receive and hold fluid.

3. Floating windmill installation (1) according to claim 1, characterized in that the floating installation (20) comprises one or several ballast tanks (25) adapted to receive and hold fluid to be used as ballast to lower and raise the floating installation (20) in the water (6).

4. Floating windmill installation (1) according to claim 2 or 3, characterized in that the floating windmill installation (1) comprises a pressurized air or gas system for displacing fluid out of one or more of the ballast tanks (15, 25).

5. Floating windmill installation (1) according to claim 2 or 3, characterized in that the floating windmill installation (1) comprises a number of pumps for pumping water from the surrounding water (6) into one or more of the ballast tanks (15, 25).

6. Floating windmill installation (1) according to claim 1, characterized in that the means for raising or lowering the tower (14) comprises pitch racks along the tower (14) and gears and motor for providing movement.

7. Floating windmill installation (1) according to claim 1, characterized in that the floating installation (20) comprises storage space for storing a number of blades (13).

8. Floating windmill installation (1) according to claim 7, characterized in that the storage space is adapted for storing blades (13) in an vertical orientation.

9. Floating windmill installation (1) according to claim 1, characterized in that the means for raising and lowering the tower (14) up and down through the aperture (22) can be remotely controlled.

10. Method to raise or lower a windmill (10, 10`), characterized in that the windmill is part of a floating windmill installation (1), and that the windmill is raised or lowered relative to a floating installation (20), and that the method comprises the following steps:

- accommodate a tower (12) of a windmill (10, 10`) in a aperture (22) in the floating installation 20, and

- move the tower (14) up or down inside the aperture (22) of the floating installation (20) to raise or lower the windmill (10, 10`).

11. Method according to claim 10, characterized in that the method is used to disassemble a blade (13) from a two blade windmill (10`) and comprises the following steps:

- position a service vessel (30) with a frame (32) to a position for receiving a blade (13) from the windmill (10`),

- move a windmill blade (13) to a position above the frame (32),

- lower the tower (14) until the blade (13) is resting in the frame (32) of the service vessel 30, and

- disconnect the blade (13) from the windmill (10`).

12. Method according to claim 11, characterized in that the method includes the step to motion compensate the frame (32).

13. Method according to claim 10 or 11, characterized in that, the step to lower the tower (14) includes to adjust the buoyancy of the tower (14).

14. Method according to claim 10, characterized in that the method is used to disassemble a blade (13) from a windmill (10) and storing said blade (13) inside the floating installation (20`), the method comprises the following steps:

- position the blade (13) above a desired vertical storage space inside a floating installation (20`), using azimuth, yaw and pitch rotation of the windmill (10), - lower the tower (14) until the downward pointing blade (13) is fully or partly contained inside the floating installation (20`),

- hang of the blade (13) inside the floating installation (20`), and - disconnect the blade (13) from the windmill (10).

15. Method according to claim 10, characterized in that the method is used to disassemble a blade (13) from a windmill (10) and comprises the following steps:

- position a service vessel (30) with a frame (32) to a position for receiving a blade (13) from the windmill (10),

- raise the frame (32) up to a position below the blade (13),

- angel the frame (32),

- rotate a fan (12,13) until the blade (13) and the frame (32) are parallel to each other,

- lower the tower (14) until the blade (13) rests in the frame (32), and

- disconnect the blade (13) from the windmill (10).

16. Method according to claim 15, characterized in that the method includes the step to motion compensate the frame (32).

17. Method according to claim 10 or 15, characterized in that, the step to lower the tower(14) includes to adjust the buoyancy of the tower (14).

18. Use of a number of floating windmill installation (1) according to any of the claims 1-9 in a windfarm to optimize the power output of a windfarm by adjusting the height of individual windmills (10) to reduce blockage and wake effect in the windfarm as a whole.