Field of the Invention

The present invention relates to a floating wind power plant, comprising a support structure resting on a sea surface and wind turbine units mounted on said support structure, wherein said support structure comprises two or more elongated floating elements, which floating elements are substantially parallel and being interconnected through a connecting structure, and wherein each of said wind turbine units comprises a tower, a nacelle fixed non-rotatably on top of said tower, rotor blades arranged on a hub rotatably mounted on said nacelle, and wherein the support structure is connected through connecting wires or chains to a anchored floating element allowing the sup port structure to freely rotate in the wind around said anchored floating element, wherein the anchored floating element is located in a position between the elongated floating elements at a windward side of the floating wind power plant, when said wind turbine is in use, wherein the connection wires or chains are connected at intermediate positions along the length of the elongated floating elements.

Background of the Invention

From the state of the art are known floating wind power plants with a support struc ture extending vertically underneath the wind turbine unit, which support structure comprises a keel weight for keeping the tower of the wind turbine unit in a vertical orientation. These floating wind power plants have a number of drawbacks. One drawback is the use of a keel weight. The use of a keel weight means a high amount of material is necessary to construct the floating wind power plant, both for the keel weight itself and for the structure creating the buoyancy force necessary to counteract the keel weight. From DE 197 27 330 A1 is known a floating wind power plant according to the intro duction, where two elongated floating elements support a platform on which wind turbine units are mounted. This floating wind power plant has a number of drawbacks described in the following.

One drawback is that the floating wind power plant comprises a platform with a flat face on which the wind turbine units are placed. This requires a large amount of mate rial to construct and is heavy. In turn, the size of the elongated floating elements providing the buoyancy for the floating wind power plant have to be increased as well, which further increases material consumption and weight. Another drawback is that there is no mechanism to keep the anchored floating element from colliding with the support structure. Thus no protection against damage of the support structure or the anchored floating element is provided. Collision can in the worst case lead to sinking of the floating wind power plant. A further drawback is that the floating wind power plant is cumbersome and expen sive to produce, install and maintain.

A further drawback is that the largest wind turbine units at the time of writing of DE 197 27 330 A1 where 1 MW. The construction is thus not intended for the large wind turbine units of up to 14 MW available today.

Thus, there exists a need for providing a floating wind power plant without a keel weight. There exists a need for providing a floating wind power plant which can be construct ed using less material to reduce costs and increase environmental sustainability.

There exists a need for providing a floating wind power plant where the anchored floating element and the support structure cannot collide.

There exists a need for providing a floating wind power plant which is efficiently pro duced, installed and maintained. Object of the Invention

It is an object of the invention to provide a floating wind power platform addressing the above mentioned drawbacks and needs. It is an object of the invention to provide a floating wind power plant which can be constructed using less material to reduce costs and increase environmental sustainabil ity.

It is an object of the invention to provide a floating wind power plant where the an- chored floating element and the support structure cannot collide.

It is an object of the invention to provide a floating wind power plant which is effi ciently produced, installed and maintained.

Description of the Invention

This is achieved with a floating wind power plant according to the introduction and as described in the preamble of claim 1, which is peculiar in that the connection wires or chains have lengths ensuring that the anchored floating element is maintained in the position between the elongated floating elements, and

that the connecting structure comprises a lattice structure in which the towers are used as lattice member and comprises lattice members extending obliquely in direction along the elongated floating elements and transversal to the direction of the elongated floating elements. Herewith is achieved a lower weight of the floating wind power plant. More specifi cally, an optimal combination of weight, buoyancy and stability is achieved. Thus, high stability is achieved while at the same time the amount of material is minimised. This minimises the draught of the floating wind power plant, and reduces the amount of material necessary for construction of the floating wind power plant. This reduces the cost of production of the floating wind power plant. Finally, using less material is also more sustainable for the environment. By using the tower as a lattice member, the tower is reinforced. Lattice members con necting to the tower support the tower. Thus the tower is supported against vibrations in the nacelle.

Typically, the material of the floating wind power plant will be steel.

The elongated floating elements typically have a length between one to three times a height of the tower of the wind turbine unit.

The exact length is determined by multiple factors such as the weight of the wind tur bine units, wave pattern and wind distribution in an area where the floating wind pow er plant is used.

A distance between the elongated floating elements is determined by a length of the rotor blades and a necessary distance between the rotor blades of the wind turbine units.

By elongated floating elements being substantially parallel it is understood that a di verging angle between the elongated floating elements is between -5 to 5 degrees, preferably -2 to 2 degrees.

The elongated floating elements are oriented horizontally. By that is understood that the elongated direction of the elongated floating elements is in a plane with the sea surface.

The wind turbine units convert kinetic energy of the wind into electrical energy.

The floating wind power plant is primarily intended for large wind turbine units of 6 megawatts and larger, preferably 8 megawatts.

By fixed nacelle it is understood that the nacelle cannot rotate around a vertical axis with respect to the tower to adjust for the wind direction. In other words, the nacelle does not comprise a yaw adjustment mechanism. The floating wind power plant can comprise lattice members forming a cross in a hor izontal plane between the elongated floating elements. The cross connects the elongat ed floating elements.

By windward side of the floating wind power plant is understood a side on which the anchored floating element is located when the wind blows and the floating wind pow er plant is in use.

By leeward side of the floating wind power plant is understood a side opposite of where the anchored floating element is located when the wind blows and the floating wind power plant is in use.

The floating wind power plant comprises two tension wires or chains which each con nect the anchored floating element to one of the elongated floating elements.

The purpose of the two tension wires or chains is to transfer a main part of the force between the anchored floating element and the support structure and thereby holding the floating wind power plant in place.

Preferably, the tension wires are arranged such that the anchored floating element cannot collide with the support structure.

The floating wind power plant can comprise two support wires or chains which each connect the anchored floating element to an elongated floating element. A length of the support wires or chains is smaller than a distance between the elongated floating elements to which the wires are connected.

Preferably, the length of the support wires or chains is smaller than 80%, even more preferably smaller than 70%, and most preferable smaller than 60% of the distance between the elongated floating elements to which the wires are connected.

Herewith it is achieved that the anchored floating element cannot collide with the sup port structure. Thus, the floating wind power plant is more reliable, especially in the harsh weather conditions encountered offshore. The floating wind power plant can provide a stable positioning of the wind turbine units without the use of any dedicated keel weight. Herewith, the amount of material necessary for construction of the floating wind power plant is reduced. Thus, produc tion costs are reduced and environmental sustainability is improved.

A floating wind power plant with elongated floating elements can be constructed us ing only approximately 50% of the material of a conventional floating design compris ing a support structure with vertical extension further into the seawater using a keel weight.

The draught is typically around 4 to 5 meters for a floating wind power plant with 8 megawatt (MW) wind turbine units.

The low draught allows a simple construction, installation and maintenance. The float- ing wind power plant can be constructed land based in a dock. Thus, costly water- based cranes are not necessary. After construction the floating wind power plant can be towed to its operating area by tugboats. Maintenance likewise can be performed in a dock at land. Furthermore is achieved a more stable orientation of the floating wind power plant, as swaying of the support structure is reduced. A better force distribution between the wires relative to the wind direction is achieved. Thus, a more stable alignment in the direction of the wind is achieved. The floating wind power plant comprises a bottom anchor located at the bottom of a seabed.

The floating wind power plant comprises an electrical connection. The electrical con nection connects the floating wind power plant with the power grid. More specifically, the electrical connection connects the wind turbine units with the power grid. The power grid can be on-shore. The anchored floating element is arranged to provide a buoyancy equal to the maxi mum pull force the support structure exerts on the anchored floating element when the floating wind power plant is in use.

The anchor chain or wire and the electrical connection can be arranged rotatably at the anchored floating element. Thus, the support structure can rotate freely around the anchored floating element.

In a further embodiment of the floating wind power plant according to the invention, the floating wind power plant is peculiar in that the tower of each wind turbine unit is located on top of one of the elongated floating elements.

The floating wind power plant can comprise two elongated floating elements, where a wind turbine unit is placed on top of each elongated floating element.

The floating wind power plant can comprise three elongated floating elements. On top of each of the outer elongated floating elements, a wind turbine unit can be placed. The inner elongated floating element can be shorter than the outer elongated floating elements.

Transversal lattice members connecting the elongated floating elements can comprise a sub-lattice for reinforcement. The sub-lattice structure can be triangles, pyramidal or tetrahedral.

The connecting structure can comprise lattice members forming pyramids. Each pyr amid connects two adjacent, elongated floating elements.

In a further embodiment of the floating wind power plant according to the invention, the floating wind power plant is peculiar in that it comprises a reinforcing structure in which the towers are used as lattice member and comprises lattice members extending in a plane of the elongated floating element and the tower placed on top of said elon gated floating element. The technical effect achieved herewith is an increased strength of the floating wind power plant. The lattice structure reinforces the structure. This is achieved in a way which reduces the total amount of material necessary for the floating wind power plant. Using the tower as a lattice member in the structure, both reinforces the tower and reduces the weight of the tower. Lattice members connecting the tower and the elongated floating element reinforce the tower. Thus the tower itself can be produced with less material without compromising the strength of the construction.

In a further embodiment of the floating wind power plant according to the invention, the floating wind power plant is peculiar in that the towers are arranged at a central position along the length of the elongated floating elements.

Hereby several technical effects are achieved. Firstly, the towers are arranged at a po sition where the buoyancy forces of the support structure are largest. Thus, the best balanced buoyancy is achieved. Secondly, the movements of the towers are smallest in the central position. Thus, the movement of the towers and therewith the motion- induced mechanical load on the wind turbine units are minimised. A lifetime of the wind turbine units is increased and less material can be used in the construction of the wind turbine unit.

In a further embodiment of the floating wind power plant according to the invention, the floating wind power plant is peculiar in that the support structure comprises a wind rudder. In a further embodiment of the floating wind power plant according to the invention, the floating wind power plant is peculiar in that connection points between the con necting wires or chains and the elongated floating elements are arranged at a wind ward side of the support structure and the wind rudder is arranged at a leeward side of the support structure, preferably at an end of the leeward side.

The wind rudder can be a flat face oriented vertically and along the direction of the elongated floating elements. The technical effect achieved is that the floating wind power plant adjusts itself to the direction of the wind. By adjusting itself to the direction of the wind it is understood that after adjustment, the wind direction is parallel to the elongated floating elements and that the wind blows from the side of the floating wind power plant where the an chored floating element is located.

This maximises the electrical energy produced by the floating wind power plant as it is always adjusted to the wind and the wind turbine units can extract the most energy from the wind.

In a further embodiment of the floating wind power plant according to the invention, the floating wind power plant is peculiar in that a rotor plane for the rotor blades is orientated transversally to the direction of the elongated floating elements.

The technical effect achieved is that the rotor plane in use always is transversal to the wind direction, which maximises the energy conversion of the wind turbine units.

In a further embodiment of the floating wind power plant according to the invention, the floating wind power plant is peculiar in that the elongated floating elements are pipes.

By pipe is understood a tubular section or hollow cylinder. The material of the pipes is usually steel.

The pipes can be filled with gas such as air. Alternatively, the pipes may be filled with other gases such as carbon dioxide or nitrogen, which prevent rusting.

As a further alternative, the pipes can be filled with a foam material. This prevents sinking in case of leakage of a pipe.

As a further alternative, the pipes can be divided into watertight sections by watertight bulkheads. There can be doors between the sections for accessing each section. Herewith is achieved a compartmentalisation, which prevents sinking of the floating wind power plant in case of leakage of an elongated floating element.

In a further embodiment of the floating wind power plant according to the invention, the floating wind power plant is peculiar in that each of the elongated floating ele ments comprises two or more parallel elongated pipes, which parallel elongated pipes are interconnected by a floating element lattice structure.

The elongated floating element can comprise three parallel elongated pipes. The three parallel elongated pipes can form the edges of a triangle. The floating element lattice structure can comprise members which form triangles with the parallel elongated pipes. Alternatively, the floating element lattice structure can be pyramidal or tetrahe dral. The technical effect achieved is an increased strength and structural stability of the elongated floating elements. The floating element lattice structure reinforces the elon gated floating element and makes it stiffer. A higher strength per weight than with a single pipe is achieved. In a further embodiment of the floating wind power plant according to the invention, the floating wind power plant is peculiar in that it comprises a bottom anchor located at the bottom of a seabed. The bottom anchor is connected to an anchor chain or wire. On the anchor chain or wire there is arranged a buoyancy device exerting an upward- directed buoyancy force on the anchor chain or wire, preventing the anchor chain or wire from falling to the seabed. The buoyancy device in use is located in an upper sea layer below the sea surface.

By upper sea layer it is understood a sea layer in a depth from the sea surface between 15 meters and 60 meters, preferably 20 to 45 meters, and most preferably 25 to 35 meters.

Hereby, it is achieved that the anchor chain or wire, and/or an electrical wire fastened to the anchor chain or wire are prevented from falling to the seabed. Thus, damage through interaction with the seabed is avoided. This is advantageous at high sea depths. With high sea depths are understood sea- depths larger than 300 meters, preferably 400 meters, most preferably 500 meters.

In a further embodiment of the floating wind power plant according to the invention, the floating wind power plant is peculiar in that the support structure comprises pro pellers for manoeuvring of the floating wind power plant, which propellers are placed below the sea surface.

Preferably, the floating wind power plant comprises four propellers. Two propellers are placed on opposing ends of the elongating floating element.

The propellers can be oriented transversal to the direction of the elongated floating elements.

The floating wind power plant can comprise a control system. The control system can control the propellers based on instructions from a control station on land.

The control system can also control the propellers automatically. The automatic con trol of the propellers can be based on input such as for example sea currents, wind direction and wave direction and/or height. The inputs can be obtained by sensors on the floating wind power plant. Alternatively, the inputs can be obtained from external data sources.

The technical effect achieved is that a yaw adjustment mechanism can be implement ed using the propellers. Thus the support structure and the wind turbine units can be placed optimally with respect to the wind direction.

Furthermore, the propellers can be used for manoeuvring in a dock or when bringing the floating wind power plant to its destination area.

In a further embodiment of the floating wind power plant according to the invention, the floating wind power plant is peculiar in that it comprises a wind shaper, which wind shaper shapes the incoming air, leading it to the lower rotor blade of the wind turbine units. Thereby, the wind speed at the lower rotor blade of the wind turbine units is increased. The wind shaper can be an oblique face. The oblique face can be fastened to lattice members connecting the tower with the elongated floating element. Alternatively, the wind shaper can be partially duct-formed.

The wind shaper is located at a windward side of the wind turbine units.

The floating wind power plant can comprise solar cells. The solar cells convert light into electricity. The solar cells can be located on the wind shaper. The solar cells can be located on a second oblique face. The second oblique face is located on a leeward side of the wind turbine units.

Description of the Drawing

Fig. 1 shows an embodiment of a floating wind power plant according to the inven tion in a perspective view,

Fig. 2 shows the floating wind power plant shown in Fig. 1 from a side,

Fig. 3 shows the floating wind power plant shown in Figs. 1-2 from the windward side,

Fig. 4 shows the floating wind power plant shown in Figs. 1-3 from above,

Fig. 5 shows the floating wind power plant shown in Figs. 1-4 connected to a bot tom anchor,

Fig. 6 shows another embodiment of a floating wind power plant with a wind shap er in a perspective view,

Fig. 7 shows another embodiment of a floating wind power plant in a perspective view,

Fig. 8 shows the floating wind power plant shown in Fig. 7 from a side,

Fig. 9 shows the floating wind power plant shown in Figs. 7-8 from the windward side,

Fig. 10 shows the floating wind power plant shown in Fig. 9 from above,

Fig. 11 shows another embodiment of a floating wind power plant according to the invention in a perspective view,

Fig. 12 shows the floating wind power plant shown in Fig. 11 from a side, Fig. 13 shows the floating wind power plant shown in Figs. 11-12 from the wind ward side,

Fig. 14 shows the floating wind power plant shown in Figs. 11-13 from above,

Fig. 15 shows the floating wind power plant shown in Figs. 11-14 from below,

Fig. 16 shows a part of the connecting structure of the floating wind power plant shown in Figs. 11-15,

Fig. 17 shows another part of the connecting structure of the floating wind power plant shown in Figs. 11-15,

Fig. 18 shows a zoom of an elongated floating element of the floating wind power plant shown in Figs. 11-15,

Fig. 19 shows an example of an offshore wind park comprising floating wind power plants according to the invention,

Fig. 20 shows an embodiment of a floating wind power plant comprising propellers from a side,

Fig. 21 shows an embodiment of a floating wind power plant comprising a buoyancy device when the wind is not blowing,

Fig. 22 shows an embodiment of a floating wind power plant comprising a buoyancy device when the wind is blowing, and

Figs. 23a-b shows a anchored floating element according to the invention.

Detailed Description of the Invention

In the following text the figures will be described one by one, and the different parts and positions seen in the figures will be numbered with the same numbers in the dif ferent figures. Not all parts and positions indicated in a specific figure will necessarily be discussed together with that figure.

List of reference numerals

I Floating wind power plant

3 Support structure

5 Sea surface

7 Wind turbine unit

9 Elongated floating elements

I I Pipes 13 Tower

15 Nacelle

17 Rotor blades

19 Hub

21 Anchored floating element

23 Connecting wires or chains 25 Windward side

27 Leeward side

29 Tension wires or chains 31 Support wires

33 Wind direction

35 Lattice structure

37 Lattice members

39 Central position

41 Connecting structure

43 Windward end

44 Wind shaper

45 Oblique face

46 Solar cells

47 Second oblique face

48 Reinforcing structure

49 Wind rudder

51 Connection points

53 End of leeward side

55 Rotor plane

57 Bottom anchor

59 Seabed

61 Anchor chain or wire

63 Buoyancy device

65 Upper sea-layer

67 Floating element lattice structure

69 Buoyancy pipe

71 Reinforcement pipe

73 Sub-lattice 75 Lattice members forming pyramids

77 Outer elongated floating element

79 Inner elongated floating element

81 Propellers

85 Control system

86 Buoyancy container

87 Vertical connector

89 Vertical axis

91 Bearing

92 Electrical connection

93 Commutator

95 Junction box

97 Electrical wire

99 First part, electrical wire

101 Second part, electrical wire

Figures 1-5 show an embodiment of a floating wind power plant according to the in- vention.

Fig. 1 shows the floating wind power plant in a perspective view, Fig. 2 shows the floating wind power plant from a side, Fig. 3 shows the floating wind power plant from the windward side, Fig. 4 shows the floating wind power plant from above, Fig. 5 shows the floating wind power plant shown in Figs. 1-4 connected to a bottom an chor.

The floating wind power plant 1 comprises a support structure 3. The support structure rests on a sea surface 5.

Wind turbine units 7 are mounted on the support structure 3. The support structure 3 comprises two elongated floating elements 9. The elongated floating elements 9 are parallel. The elongated floating elements 9 are connected with a connecting structure 41.

The elongated floating elements 9 are pipes 11.

On each elongated floating element 9, a wind turbine unit 7 is mounted. The wind turbine units 7 comprise towers 13. On top of each tower, a nacelle 15 is mounted. The nacelle 15 is fixed non-rotatably on top of the tower 13. By this it is understood that the wind turbine unit 7 does not comprise a yaw adjustment mechanism. Rotor blades 17 are arranged on a hub 19. The rotor blades 17 and the hub 19 are arranged rotatably to said nacelle 15. The wind turbine units convert kinetic energy of the wind into electrical energy through a generator (not shown).

The tower 13 of each wind turbine unit 7 is located on top of one of the elongated floating elements 9.

The towers 13 are inclined towards the windward side 25. The tower can be inclined in an angle of 0 to 10 degrees, preferably 5 to 7 degrees, most preferably 6 degrees.

The support structure 3 is connected to a anchored floating element 21 through con necting wires or chains 23. The support structure can freely rotate in the wind around the anchored floating element 21.

The anchored floating element 21 is located in a position between the elongated float ing elements 9. The anchored floating element 21 is located at a windward side 25 of the floating wind power plant 1, when said wind turbine units are in use.

The connecting wires or chains 23 have lengths ensuring that the anchored floating element 21 is maintained in the position between the elongated floating elements 9.

The floating wind power plant 1 comprises two tension wires or chains 29. The ten sion wires or chains 29 connect the support structure 3 to the anchored floating ele- ment 21. The tension wires or chains 29 are connected to the support structure 3 at an intermediate position along the direction of the elongated floating elements 9.

The tension wires 29 transfer the main part of the force between the anchored floating element 21 and the support structure 3.

The floating wind power plant 1 further comprises two support wires or chains 31. The support wires or chains 31 are connecting the anchored floating element with the support structure 3. The support wires or chains 31 connect to the support structure 3 at a windward side of the tension wires or chains 29. Preferably, the support wires or chains 31 connect to the support structure 3 at a windward end 43 of the support struc ture.

The connecting structure 41 comprises a lattice structure 35 in which the towers 13 are used as lattice members 37.

The lattice structure 35 comprises lattice members 37 which extend obliquely in direc tion along the elongated floating elements 9. The lattice structure 35 also comprises lattice members 37 which are transversal to the direction of the elongated floating elements 9.

Furthermore, the lattice structure 35 comprises lattice members 37 which extend obliquely between the elongated floating elements 9.

Fig. 5 shows the floating wind power plant comprising a bottom anchor 57 located at the bottom of a seabed 59. The bottom anchor 57 is connected to an anchor chain or wire 61.

Figs. 6 shows another embodiment of a floating wind power plant with a wind shaper in a perspective view.

The floating wind power plant 1 comprises a wind shaper 44. The wind shaper 44 shapes the incoming air leading it to the lower rotor blade of the wind turbine units 7. Thereby the wind speed at the lower rotor blade of wind turbine units 7 is increased. The wind shaper 44 can be an oblique face 45. The oblique face 45 can be fastened to lattice members 37 connecting the tower 13 with the elongated floating element 9.

Alternatively, the wind shaper 44 can be partially duct-formed.

The wind shaper 44 is located at a windward side of the wind turbine units 7.

The wind shaper 44 comprises solar cells 46. The solar cells 46 generate electricity when the sun is shining.

Solar cells 46 are mounted on a second oblique face 47. The second oblique face 47 is located on a leeward side of the wind turbine units 7.

Figs. 7-10 show another embodiment of a floating wind power plant.

Fig. 7 shows the floating wind power plant in a perspective view, Fig. 8 shows the floating wind power plant from a side, Fig. 9 shows the floating wind power plant from the windward side, Fig. 10 shows the floating wind power plant from above.

The floating wind power plant 1 comprises a reinforcing structure 48 in which the towers 13 are used as lattice members 37 and comprises lattice members 37 extending in a plane of the elongated floating element 9 and the tower 13 placed on top of said elongated floating element.

The towers 13 are arranged at a central position along the length of the elongated floating elements 9.

This ensures an optimal weight distribution, where the weight of the wind turbine units 7 is placed, where the buoyancy of the elongated floating elements is largest.

Additionally, a lever is maximised for counteracting rotational weight forces occur ring due to the weight of the wind turbine units 7 during inclination of the support structure 3 in rough sea. The support structure 3 comprises a wind rudder 49.

Connection points 51 between the connecting wires or chains 23 and the elongated floating elements 9 are arranged at a windward side 25 of the support structure 3 and the wind rudder 49 is arranged at a leeward side 27 of the support structure 3, prefera bly at an end 53 of the leeward side.

A rotor plane 55 for the rotor blades 17 is orientated transversally to the direction of the elongated floating elements 9.

Figs. 11-18 show another embodiment of a floating wind power plant according to the invention.

Fig. 11 shows the floating wind power plant 1 in a perspective view, Fig. 12 shows the floating wind power plant from a side, Fig. 13 shows the floating wind power plant from the windward side, Fig. 14 shows the floating wind power plant from above, Fig. 15 shows the floating wind power plant from below, Fig. 16 shows a part of the con necting structure of the floating wind power plant, Fig. 17 shows another part of the connecting structure of the floating wind power plant shown in Figs. 11-15, Fig. 18 shows a zoom of an elongated floating element of the floating wind power plant shown in Figs. 11-15,

This floating wind power plant 1 is capable of supporting 14 MW (megawatt) wind turbine units 7.

Each of the elongated floating elements 9 comprises three parallel elongated pipes 11.

The parallel elongated pipes are interconnected by a floating element lattice structure 67.

Two elongated buoyancy pipes 69 are located in a horizontal plane and deliver buoy ancy to the support structure 3. On top and between said buoyancy pipes a reinforce ment pipe 71 is placed. The three parallel elongated pipes form the edges of a triangle.

The floating element lattice structure 67 comprises members which form triangles with the parallel elongated pipes. Alternatively, the floating element lattice structure can be pyramidal or tetrahedral.

The floating element lattice structure 67 increases strength and structural stability of the elongated floating elements 9. The floating element lattice structure 67 reinforces the elongated floating element and makes it stiffer. A higher strength per weight than with a single pipe is achieved.

The floating wind power plant 1 comprises three elongated floating elements 9. On top of each of the outer elongated floating elements 77 a wind turbine unit 7 is placed. The inner elongated floating element 79 is shorter than the outer elongated floating elements 9.

Transversal lattice members connecting the elongated floating elements can comprise a sub-lattice for reinforcement. The sub-lattice structure can be triangular, pyramidal or tetrahedral.

The connecting structure can comprise lattice members forming pyramids. Each pyr amid connects two adjacent elongated floating elements.

The connecting structure comprises lattice members forming pyramids 75. The top of two adjacent pyramids are connected with a lattice member. A lattice member in each pyramid extends beyond the top of the pyramid connecting to an upper end of a tower 13 of a wind turbine unit 7.

Fig. 19 shows an example of an offshore wind park comprising floating wind power plants according to the invention.

The distance between the bottom anchor 57 and the support structure 3 is approxi mately 500 meters. Thus, in an offshore wind park with 32 square kilometres, 32 sepa rate floating wind power plants 1 can be placed. In this case the offshore wind park is arranged in a 4 by 8 grid.

Fig. 20 shows a section cut of an embodiment of a floating wind power plant com prising propellers. The elongated floating element 9 is shown from a side.

The elongated floating elements 9 comprise propellers 81 for manoeuvring of the floating wind power plant 1. The propellers are placed below the sea surface.

The floating wind power plant 1 comprises four propellers 81. A propeller is placed at each end of an elongating floating element 9.

The propellers are oriented transversally to direction of the elongated floating ele ments.

The floating wind power plant comprises a control system 85. The control system 85 can control the propellers 81 based on instructions from a control station (not shown) on land.

The control system 85 can also control the propellers 81 automatically. The automatic control of the propellers 81 can be based on input such as for example sea currents, wind direction and wave direction and/or height. The inputs can be obtained by sen sors on the floating wind power plant. Alternatively, the inputs can be obtained from external data sources.

The technical effect achieved is that a yaw adjustment mechanism can be implement ed using the propellers. Thus the support structure and the wind turbine units can be placed optimally with respect to the wind direction.

Furthermore, the propellers can be used for manoeuvring in a dock or when bringing the floating wind power plant to its destination area.

Fig. 21 shows an embodiment of a floating wind power plant comprising a buoyancy device when the wind is not blowing, and Fig. 22 shows an embodiment of a floating wind power plant comprising a buoyancy device when the wind is blowing.

The floating wind power plant 1 comprises a bottom anchor 57 located at the bottom of a seabed 59. The bottom anchor can be a single element as shown in Fig. 22. Al ternatively, the bottom anchor can comprise multiple elements such as shown in Fig. 21.

The bottom anchor 57 is connected to an anchor chain or wire 61. On the anchor chain or wire 61 there is arranged a buoyancy device 63. The buoyancy device 63 exerts an upward-directed buoyancy force on the anchor chain or wire 61, preventing the anchor chain or wire from falling to the seabed. The buoyancy device 63 is in use located in an upper sea layer 65 below the sea surface 5.

The buoyancy force of the buoyancy device 63 is adjusted to the weight of the anchor chain or wire 61. Thus, for larger sea depths and larger anchor chains or wires, a greater buoyancy force of the buoyancy device 63 is necessary.

Fig. 23 a and Fig. 23 b show a anchored floating element according to the invention. The anchored floating element comprises a buoyancy container 86.

The anchored floating element 21 is arranged to provide a buoyancy equal to the max imum pull force the support structure 3 exerts on the anchored floating element 21 when the floating wind power plant 1 is in use.

The anchored floating element 21 comprises a vertical connector 87. The vertical con nector 87 is connected to the bottom anchor 57 with the anchor chain or wire 61. The vertical connector is rotatable around a vertical axis 89. The vertical connector 87 is mounted with a bearing 91.

The floating wind power plant 1 comprises an electrical connection 92. The electrical connection connects the floating wind power plant 1 with the power grid. More specif ically, the electrical connection 92 connects the wind turbine units 7 with the power grid. The power grid can be on-shore. The electrical connection 92 can comprise an electrical wire 97. A first part 99 of the electrical wire either runs along the anchor wire or chain 61 or is integrated with the anchor wire or chain 61.

The electrical connection 92 connects to the anchored floating elements 21 vertical connector 87 via a commutator 93. The electrical connection 92 leads to a junction box 95. The junction box 95 can be on top of the anchored floating element. A second part 101 of the electrical wire 97 connects the junction box 95 to the wind turbine units on the support structure to the electrical connection 92 of the anchored floating element with an on-shore power grid. The junction box 95 is waterproof.

The connecting wires or chains 23, 29, 31 connecting the anchored floating element with the support structure 3 are connected in close proximity to each other. With close proximity is understood a distance less than half the maximum diameter of the an chored floating element, preferably less than 30% of the maximum diameter of the anchored floating element.

The anchor chain or wire 61 connecting the bottom anchor with the anchored floating element, optionally via the buoyancy device 63, connects to anchored floating element via the vertical connector 87. The second part 101 of the electrical wire 97 connects the vertical connector 87 of to the anchored floating element 21 to the power grid.

The vertical connector 87 is mounted rotatably with a bearing 91 at the anchored float ing element. The second part 101 of the electrical wire 97 and the anchor chain or wire 61 are connected to the vertical connector 87. The connecting wires or chains 23, 29, 31 and the second part 101 of the electrical wire 97 are not connected to the an chored floating element 21 via the vertical connector 87. Thus, the support structure 3 can rotate freely around the anchored floating element 21 without entangling or dam aging the anchor chain or wire 61 or the electrical connection 92.