WIND TURBINE WITH FLOATING FOUNDATION

Abstract

A wind turbine, having a floating foundation (1), a support structure (2) and a generator (3). The generator (3) is an up-wind generator. The floating foundation (1) is assembled from tubular steel sections (5, 6, 7, 8) of uniform diameter, forming a frame with a mooring turret (4) at one corner. The support structure (2) hays at least two beams (11, 12) extending substantially transverse to the floating foundation (1). The beams are connected at a first end to a respective opposite side of said foundation frame and at a second end to said nacelle (17). The support structure (2) and the floating foundation (1) form a triangle with the nacelle (17) fixedly mounted at the apex. The support structure (2) comprises tensioned backstays (13, 14, 15, 16) supporting the beams (11, 12) and ensuring that they are substantially subjected to compression forces only.

Claims

1-12. (canceled)

13. A wind turbine comprising: a floating foundation; a support structure; a generator; the generator including a nacelle and a rotor and being an up-wind generator; wherein the floating foundation is assembled from tubular steel sections of uniform diameter, the tubular sections forming a generally A-shaped frame with a mooring turret at an apex of the frame and two legs extending from the turret, the frame being generally situated in one plane; the support structure having at least two beams extending substantially transverse to the plane of the floating foundation, the beams being connected at a first end to a respective opposite leg of the two legs of the A-shaped foundation frame and at a second end to the nacelle; the beams being attached close to each end of a transverse section extending between the two legs of the A-shaped foundation frame or alternatively the beams having a transverse section extending between the at least two beams at a distance from the floating foundation; and the support structure together with the floating foundation forming a triangle with the nacelle fixedly mounted at an apex of the support structure, the rotor facing the apex of the frame.

14. The wind turbine of claim 13, wherein the support structure comprises tensioned backstays supporting the beams and ensuring that the beams are substantially subjected to compression forces only.

15. The wind turbine of claim 13, wherein the support structure beams being assembled from truss work sections.

16. The wind turbine of claim 13, wherein the support structure beams being assembled from pipe sections.

17. The wind turbine of claim 13, wherein the floating foundation comprises straight tubular sections that are connected to each other by bolted connections.

18. The wind turbine of claim 13, wherein the floating foundation comprises straight tubular sections that are connected to each other by welding.

19. The wind turbine of claim 17, wherein the connections comprise connection pieces made from the same type of tubular steel as the tubular sections.

20. The wind turbine of claim 13, wherein each of the tubular sections has at least one airtight compartment providing buoyancy.

21. The wind turbine of claim 15, wherein the truss beams are assembled from identical truss sections manufactured by robot welding and which are connected to each other by bolted connections.

22. The wind turbine of claim 13, wherein the turret has a sufficient height to protrude through the water plane while the rest of the foundation is below the water surface.

23. The wind turbine of claim 14, wherein the support structure leans at an angle towards the apex of the A-shaped foundation frame.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0025] FIG. 1 shows the floating wind turbine of the present invention in isometric view,

[0026] FIG. 2 shows the wind turbine of FIG. 1 in a side elevation view,

[0027] FIG. 3 shows the wind turbine of FIG. 1 floating in a body of water,

[0028] FIG. 4 shows the base part of the foundation in exploded view,

[0029] FIG. 5 shows a truss structure of the turbine during manufacture, and

[0030] FIG. 6 shows an alternative embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0031] FIG. 1 shows an exemplary embodiment of the wind turbine of the invention in isometric view. The turbine comprises a floating foundation 1, a support structure 2 and a generator 3. The foundation 1 in general comprises rolled tubular steel sections that form a general A-shape with a turret 4 at its apex, two first sections 5, 6 extending from the turret with an angular separation of about 45, two further sections 7, 8 extending in parallel from the free end of each of the first sections 5, 6 and a transverse tubular section 9 connecting the two further sections 7, 8.

[0032] The foundation 1 is airtight and will have sufficient buoyancy to support the support structure 2 and generator 3. The interior of the foundation 1 may be divided into a multiple of compartments to allow for adjustment of the buoyancy.

[0033] The turret 4 accommodates a swivel (not shown) to which mooring lines 10 are to be attached. The mooring lines 10 are at the opposite ends attached to anchors (not shown). The anchors may be of any type suitable for long time mooring, such as suction anchors, piles, drag anchors, mushroom anchors, augers or dead-weights. The lines 10 extends in a catenary fashion between the anchor and the turret 4. This allows for the foundation to move to somewhat relative to the seabed, both in horizontal and vertical directions. The mooring forces in this type of mooring will be lower than a tensioned mooring.

[0034] The support structure 2 comprises two truss beams 11, 12. Each beam 11, 12 is attached to further sections 7, 8 of the foundation 1 close to where the transverse section 9 is attached. The truss beams 11, 12 extends to the generator 3, which is fixedly attached to the beams 11, 12. The beams 11, 12 may be attached to one another at their upper ends but may also be coupled via the generator 3.

[0035] It is also conceivable within the ambit of the invention to use pipe sections instead of truss beams. As will be explained below, the support structure will substantially be subjected to compression forces only. Consequently, the pipe sections for the support structure 2 need not have the same diameter and wall thickness as the tubular sections of the floating foundation 1.

[0036] The support structure 2 can also comprise a set of backstays, such as four backstays 13, 14, 15, 16. The backstays 13, 14, 15, 16 extend from close to the upper end of the truss beams 11, 12 to each end of the further tubular sections 7, 8.

[0037] In order for the generator rotor not to interfere with the backstays 13, 14, 15, 16, the truss beams 11, 12 are leaning towards the turret 4 at an angle.

[0038] The generator 3 comprises a nacelle 17 that is fixedly attached to the upper ends of the beams 11, 12. A rotor 18, preferably with three blades is rotatably attached to the nacelle. Both the nacelle and the rotor are standard mass-produced units.

[0039] FIG. 2 shows the turbine in a side elevation view. As can be seen in this view, the up-wind backstays 13, 16 extend practically in a vertical plane and the rotor 18 is also arranged in a vertical plane, while the truss beams 11, 12 form an angle of about 15 with the vertical plane. The down-wind backstays 14, 15 form an angle of about 25 with the vertical plane. The foundation 1 is designed to float substantially horizontally.

[0040] FIG. 3 shows the turbine floating at sea and subjected to waves. Waves are allowed to wash over the tubular sections of the foundation 1. Due to the relatively small diameter of the tube sections, it is expected that the forces from wave and current will be small. This reduces the mooring forces.

[0041] The truss beams may be of the same design as used for crane booms. These are known to be light weight but have a great strength.

[0042] FIG. 4 shows the substantial part of the foundation 1 in an exploded view. The turret 4 basically comprises a cylindrical part 19 with short tubular connection pieces 20, 21 welded to the side thereof. The cylindrical part is open at the lower end (not shown) to receive the swivel (not shown) and closed at its upper end. The cylindrical part 19 may have a larger diameter than the connection pieces 20, 21, but is preferably made from the same tube as the remaining tubular parts of the foundation 1.

[0043] The first sections 5, 6 and the further section 7, 8 are uniform rolled steel tubes having the same diameter. Consequently, these sections can be formed from a continuous length of tube that is cut into proper length.

[0044] To connect the first sections 5, 6 with the further sections 7, 8 connection pieces 22, 23 have each been formed by two short tubular pieces that are cut at an angle and welded together to extend from one another at the angle intended for the joining of the first sections 5, 6 and the further sections 7, 8.

[0045] The sections 5, 6, 7, 8 is preferably connected to the connection pieces by bolts. This facilitates transport of the parts to an assembly site where the foundation 1 can be assembled using simple tools. It is however also possible to weld the parts together or use a combination of welds and bolts.

[0046] The transverse section 9 is not shown in FIG. 4. This section is an option, which may be omitted if it is not proven necessary. The transverse section 9 will enhance the stiffness and buoyancy of the foundation 1. Short connecting pieces may be welded to the further sections 7, 8 to allow for a bolted connection of the transverse section 9 to the further sections 7,8.

[0047] The tube sections are preferably made airtight, e.g., by welding a bulkhead (not shown) inside the sections, close to each end thereof. If it is desired to divide a section into further compartments, further bulkheads may be welded into the tubes. If it is desired to be able to adjust the buoyancy, holes (not shown) for valves can be made at appropriate places on the tube sections to allow for flowing air or/and water into or out of compartments in the tube sections.

[0048] The tube sections 5-8 should be pressure tested before assembly.

[0049] FIG. 5 shows a part of a truss beam 11, 12. These beams preferably have a uniform cross section along their length so that they can be manufactured from identical truss sections. Each truss section is preferably welded by welding robots in a line production operation. The truss sections are preferably connected to complete beams by bolts. As stated above, it is possible to use pipe sections instead of truss sections.

[0050] Although, a square cross-section with four corner rods 24 that are interconnected by a plurality of inclined rods 25 are shown for the truss beams, they may have any suitable cross section, such as triangular.

[0051] The truss beams are preferably bolted to the foundation, to one another and to the nacelle.

[0052] The assembly of the turbine can be done as follows:

[0053] The tube sections and truss sections are made short enough to facilitate transport by conventional ships and lorries, preferably in ISO containers.

[0054] At the assembly site, which conveniently is a port where the wind turbine can be transferred to an installation ship or barge, the parts are assembled by bolting the tube sections together. The swivel is installed in the turret cylinder part 19. The assembly may be done on shore and the complete wind turbine subsequently lifted onto a ship or barge, or the assembly may be done on the deck of a ship or barge. In the latter case, the assembly may at least partly be done while the ship or barge is sailing to the installation site.

[0055] When the tube sections 5-8 have been bolted together, the truss sections 11, 12 are assembled and connected to the foundation 1.

[0056] The wires 13-16 are then connected at their lower ends to the foundation and at their upper ends to (or close to) the upper ends of the truss beams. The wires may alternatively be connected to the nacelle. The wires are tightened to a predetermined tension. The wires ensure that the truss beams are always kept in compression, as the wires will take up substantially all moments.

[0057] Mounting of the nacelle and the rotor may also take place while the foundation is afloat.

[0058] Cables for power and signal will be connected to the nacelle 17 and fed through the truss beams 11, 12. A coupling for the electric cables may conveniently be installed at the lower end of one of the truss beams 11, 12, so that a power line, that may have already been installed at the installation site, may easily be connected to the wind turbine upon installation.

[0059] The mooring lines, which have already been deployed, are coupled to the turret 4 upon installation.

[0060] The wind turbine is deployed either by lifting it from the deck and into the water or by de-ballasting a barge, upon which the wind turbine is situated, until the wind turbine is afloat.

[0061] When deployed, the wind turbine functions are tested, and the wind turbine is left to produce electric power.

[0062] The steel tube sections and truss beams are made of a selected steel grade that has been known for many years to endure harsh conditions and salt water in the offshore oil and gas industry. When the time for supervision and maintenance of these structures is reached, the wind turbine may be brought onto the deck of a vessel and either maintained on the deck or brought to the shore. It may also be towed to the shore.

[0063] Maintenance of the nacelle can be done by climbing a ladder (not shown) within the truss beams 11, 12. An elevator may also be installed inside the truss beams 11, 12 to bring people and parts up to the nacelle.

[0064] When the rotor blades need to be changed, this can either be done by lifting the blades from the wind turbine while it is floating (as is common practice with most sea based wind turbines today) or by bringing the turbine onto the deck of a vessel.

[0065] FIG. 6 shows an alternative embodiment of the invention. This embodiment is very similar to the embodiment of FIGS. 1-5, but a few changes have been made.

[0066] Instead of the foundation 1 having five tubular sections, it has only two sections 5 and 6, extending at an angular separation from the turret 4. The support structure 2 is also made up of tubular sections instead of truss beams. Tubular sections 11 and 12 extend from a respective side of the foundation 1 to the generator 3. Instead of the section 9 forming a part of the foundation shown in FIG. 9, the embodiment of FIG. 6 has a transverse section 9 extending between the support structure sections 11 and 12 at a location distant from the foundation 1. Two inclined tubular struts 30, 31 extend from the tubular sections 11 and 12, respectively, to the transverse section 9.

[0067] Next the height of the turret 4 has been elongated. This enables the foundation to be ballasted to a lower position with respect to the water surface. As shown in FIG. 6, the foundation sections 5 and 6 are situated completely below the water, while the turret 4 protrudes through the surface. This gives a very small water plane area, which is made up of the cross-sectional area of the turret and the support structure sections 11 and 12. A small water plane area results in an improved stability and makes the floating structure less influenced by wave actions.

[0068] It is indeed possible to combine features of the embodiment of FIGS. 1-5 and 6, such as using truss beams in the embodiment of FIG. 6, or elongating the turret 4 of FIGS. 1-5 to enable the foundation to be ballasted to a position below the water surface.

[0069] With the above described designs, it is possible to manufacture a wind turbine by using standard components or at least components that are within the ambit of standardized production. The number of parts is also reduced. This lowers fabrication costs and time considerably.

[0070] The amount of material (steel weight), which is a significant part of costs, is also reduced compared to known designs. This also reduces the environmental impact.

[0071] The production can be done almost everywhere where these is an engineering industry. This facilitates production close to the deployment site, which has significance for the overall environmental impact.

[0072] The wind turbine design is scalable and only limited by the sizes of nacelle and rotor available.

[0073] Due to the turret, the foundation 1 will turn with the current and waves so that the turret will be facing the oncoming current and waves. As the currents, waves and wind generally comes from approximately the same direction, the wind will almost always be approximately up-wind of the rotor. In some situations, the wind direction may be slightly different form the direction of the current and waves, but the difference is seldom more than a few degrees. This has in total very little significance on the overall performance. Consequently, a yaw mechanism or any other active means to keep the rotor against the wind has been dispensed with.