WO2021173002A1

WO2021173002A1 - Rotateable foundation for an offshore wind turbine

Info

Publication number: WO2021173002A1
Application number: PCT/NO2021/050051
Authority: WO
Inventors: Bjarte Nordvik
Original assignee: Bjarte Nordvik
Priority date: 2020-02-26
Filing date: 2021-02-26
Publication date: 2021-09-02
Also published as: NO20200232A1

Abstract

The document describes a floating foundation for an offshore wind turbine, the foundation comprising a transition piece for carrying the wind turbine, and a stabilizing part for stabilizing the transition piece with or without the wind turbine, the stabilizing part comprising a horizontal part and a vertical part which are both correctively joined to the transition piece, the vertical part comprising a corrective leg which projects downwards in a water mass when the foundation is in an operational position, the horizontal part comprising an anchor attachment and a corrective arm, the foundation being formed with the anchor attachment attached to the corrective arm at a distance from the transition piece, so that in an operational position, when the foundation is anchored, the transition piece can rotate around the anchor attachment under the influence of elemental forces, and an apparatus which includes the foundation, a method for stabilizing a foundation, and related aspects of the invention.

Description

NIPO

WO 2021/173002 PCT/N02021/050051

ROTATEABLE FOUNDATION FOR AN OFFSHORE WIND TURBINE

The description relates to an invention in the technical field of offshore wind energy. A rotatable foundation for an offshore wind turbine, an apparatus for extracting energy from wind which comprises the rotatable foundation, and more are described. To reduce pollution and limit global warming it is desirable to develop technology that can make renewable energy more competitive.

Offshore wind is a particularly interesting resource related to renewable energy ex traction. There is a great potential in utilizing sea areas and the wind over such areas to extract electrical energy. A challenge related to the extraction of energy from off- shore wind is the cost. For offshore wind to be a competitive energy source, it is cru cial that the costs related to the production, installation and operation and mainte nance of offshore wind turbines are reduced. To reach this goal, developing new cost- effective technology is important.

A great number of technical solutions have been developed for producing wind energy offshore. Some of these are related to fixed foundations, whereas others are related to floating foundations. The floating foundations are advantageous in many cases, espe cially for use at great sea depths, typically of over 50 metres.

At sea, an offshore wind turbine and its foundation are subjected to strong forces from wind, waves and currents. Particularly critical are the wind forces. Calculations have shown that the tilting forces acting on a wind turbine at sea will typically be 15 times as strong in the primary direction of the wind relative to a direction at 90 degrees thereto. To prevent a wind turbine from tilting too much under tough weather condi tions at sea, it is important that the foundation is constructed to counteract tilt caused by said forces, and then especially tilt in the wind direction. Stability against tilt is a challenge and a cost-driver in floating foundations, especially for floating foundations that are going to be used in areas with a potential for harsh NIPO

WO 2021/173002 ² PCT/N02021/050051 wind and wave conditions. Existing solutions for ensuring stability in areas like that are generally large, heavy and expensive. An example of such a solution is known as the "Hywind".

The offshore-wind solution "Hywind" includes an example of a foundation for an off shore wind turbine, the foundation being a floating vertical spar buoy. To counteract tilting forces, the spar buoy reaches deep into the ocean in an operational position, and it is generally very heavy. The weight is, to a great extent, due to the need of the spar-buoy solution for corrective ballast. Its size makes it costly to produce and to transport to a destination offshore, and it makes "Hywind" unusable in sea areas with limited depths.

In this document, several solutions related to the stability of an offshore wind turbine are described, each of the solutions together or separately solving one or more chal lenges of extracting energy from offshore wind.

Another challenge in extracting offshore wind energy is related to the installation, re moval and maintenance of equipment. A wind turbine has several heavy, large parts placed on or at the top of a wind-turbine tower. For example, a nacelle may weigh several hundred tonnes, and it is possibly to be installed at over 100 metres above the sea surface. Lifting equipment like that to or from the top of the tower is a complex and risk-filled task, especially offshore and especially when the lifting is carried out from a vessel which, in the waves offshore, is moving relative to a floating wind- turbine foundation.

Further in this document, several solutions related to the production, installation, re moval and/or maintenance of equipment are described.

In a first aspect of the description, a ballast element for adding ballast to a floating foundation for a wind turbine and for supplying a corrective force to the foundation when the foundation is tilted is described, the ballast element being formed with a hole for receiving a corrective leg belonging to the foundation, and the ballast element comprising connecting means in order to be movably suspended from a bottom side of the foundation.

The ballast element may be torus-shaped or cylinder-shaped, for example. The ballast element may typically be suspended via, for example, a chain or some form of wire. The connecting means may comprise, for example, one or more chains or wires or the like for suspending the ballast element from the foundation. As the ballast element is freely suspended, and not rigidly attached to the foundation, it can move relative to NIPO

WO 2021/173002 ³ PCT/N02021/050051 the structure of the foundation, including the corrective leg of the foundation. By a tilt beyond a certain degree, the movement of the ballast element relative to the struc ture may be large enough for the ballast element to come into contact with the correc tive leg, and at least some of the gravitational forces acting on the ballast element may then act on the corrective leg so that it counteracts the tilt and thereby has a corrective and stabilizing effect on the foundation.

In a second aspect of the description, a tower for a wind turbine for a floating founda tion is described, the tower having an inner cavity and an opening to the sea to re ceive water from a water mass into the inner cavity. The water mass may be part of a sea, and the water mass may have waves. Such a design of the tower may reduce buoyancy resulting from water being displaced by the tower when the tower is in an operational position and the lower part of the tower penetrates a sea surface, and may reduce an effect of waves on the tower and the stability thereof.

The lower part of the tower may be connected to a transition piece belonging to the foundation, the transition piece being formed with an opening to the sea which leads to an opening to the opening of the tower to allow water to move up through the tran sition piece into the tower. The lower part of the tower may function as a corrective leg / a corrective keel (in this connection, called a keel hereinbelow) for the founda tion, or be in direct connection to a vertical, stabilizing part belonging to the founda tion. The vertical, stabilizing part may be formed with an opening to the sea through out its length, an opening which may lead to the opening in the tower. The tower may be welded or bolted to the transition piece.

Such an opening to the sea may allow waves to move freely into and within the cavity and take approximately the same height as the waves on the outside of the cavity when the foundation with the tower is in an operational position, so that wave move ments will have less effect on the foundation and reduce their influence on the tower.

The tower and/or the vertical, stabilizing part may comprise a ventilation means to provide for air to enter the cavity when the amount of water in the cavity decreases and to evacuate air when the amount of water in the cavity increases. The ventilation means may also be included as part of the floating apparatus for cooling down a gen erator.

In a third aspect of the description, a rotor for a wind turbine is described, the rotor comprising a connecting means for connecting the rotor and thereby an upper part of the wind turbine to one or more tension rods or one or more wires. NIPO

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A non-rotating part of the rotor may be constructed to absorb forces to relieve a bend ing moment on the tower.

In one embodiment, the rotor may have a central hole through the rotor to be pene trated by a connecting means which may be connected to an inner structure in a na celle or a tower carrying the rotor. The connecting means may be used to join an up per part of a wind turbine to a first end of a tension rod which, at a second end, may be attached to an external attachment point, for example an attachment point on an outer portion of a foundation for the wind turbine. By means of this tension rod and the connecting means, forces may be absorbed to reduce a bending moment on the tower or a wind-turbine foundation, for example. By absorbing bending moments by the use of tension rods, junctures between a vertical part of the foundation and a hor izontal part of the foundation, for example, may be protected from forces that could potentially be critical and that might result in fractures. A rigid connection between the horizontal, stabilizing part and a transition piece, for example, may be protected in this way. The solution may, for example, allow a higher wind-turbine tower on the foundation.

In one embodiment, the rotor may comprise a swivel rotatably attached to an outer surface of the rotor, the swivel comprising the connecting means for joining the rotor, and thereby an upper part of the wind turbine, to a tension rod.

In a fourth aspect of the description, a nacelle for a wind turbine is described, the na celle comprising a front part and a rear part, the front and rear parts being releasably lockable to each other to form the nacelle, the front part of the nacelle comprising a connecting means for connecting the nacelle to a rotor.

The rear part or the front part may comprise a generator, among other things. The front and rear parts of the nacelle may be mounted on an underlying surface which may, in turn, be part of a tower pipe which may be penetrated by a tower for a wind turbine. Then the nacelle may be moved in its entirety up and down along the tower on the tower pipe. The tower pipe is attached to the tower.

The front part and/or the rear part may be adapted for being attached to a hoisting means for the part or parts to be hoisted to or towards the top of the wind turbine.

The nacelle may comprise one or more further parts that can releasably be locked to the front part and/or the rear part of the nacelle. The front and rear parts of the na celle may be releasably locked to each other via a tower for a wind turbine, by the front and rear parts both being lockable to the tower and thereby being locked to each NIPO

WO 2021/173002 ⁵ PCT/N02021/050051 other, and/or the front and rear parts may be releasably lockable to each other.

The nacelle may be formed in such a way that it may be penetrated in its entirety by a windmill tower. The nacelle may be formed with an opening for receiving the windmill tower. The opening may be a substantially, for example, cylinder-shaped or cone- shaped hole through the nacelle, from a lower surface of the nacelle to an upper sur face of the nacelle.

A divisible nacelle may simplify operations for installation, removal, maintenance and the like.

In a fifth aspect of the description, an upper adapter piece for a wind turbine is de scribed, the adapter piece comprising an upper nacelle carrier and a lower nacelle car rier, a hinge and a tilting mechanism, the upper and lower nacelle carriers being tilt- ably attached to each other by the hinge, and the tilting mechanism being connected to the upper and lower nacelle carriers to tilt the two nacelle carriers relative to each other.

A nacelle may typically be attached to a wind-turbine tower via the upper adapter piece. The upper adapter piece may further comprise a bearing to allow rotation of the nacelle relative to the wind-turbine tower. The upper adapter piece may further com prise a rotary means for rotating the nacelle relative to the tower.

One or both of the nacelle carriers may be vertically divisible into, for example, two parts, for example in such a way that each part may be shaped like a crescent.

The tilting mechanism may comprise, for example, a hydraulic cylinder or an electric motor for supplying a force for tilting the upper part relative to the tower.

The lower nacelle carrier may typically have a lower connection to the tower and also an upper connection to the upper nacelle carrier. The lower nacelle carrier may com prise the bearing and be connected to the tower via the bearing, to allow rotation of the nacelle carrier on the tower. Further, the lower nacelle carrier may be connected to the upper nacelle carrier via the tilting mechanism. In addition to having a lower connection to the lower nacelle carrier, the upper nacelle carrier may have an upper connection to a nacelle. The connection to the nacelle may be a connection via a bear ing which allows rotation of the nacelle on the upper nacelle carrier. In a typical em bodiment, the lower nacelle carrier or the upper nacelle carrier will comprise a bearing to allow rotation of the nacelle carrier on the tower or of the nacelle on the nacelle carrier, but it is also possible to have a nacelle carrier without such a bearing and to NIPO

WO 2021/173002 ⁶ PCT/N02021/050051 have a nacelle carrier with both a bearing on the lower nacelle carrier and a bearing on the upper nacelle carrier.

The rotary mechanism may be a mechanism for rotating the nacelle carrier relative to the tower or for rotating the nacelle relative to the nacelle carrier.

In a sixth aspect of the description, an angle stabilizer for stabilizing the force direc tion of a force from an anchor line acting on a floating foundation for a wind turbine is described, the angle stabilizer comprising a rigid angle-stabilizer structure and a weight connected to the rigid angle-stabilizer structure, and the angle stabilizer being arranged to connect the anchor line to the anchor point of the foundation via the rigid angle-stabilizer structure.

The angle-stabilizer structure may comprise, for example, three rigid rods joined to each other in such a way that they form a rigid triangular structure. The angle stabi lizer may comprise a lengthening element in the form of a rigid stay, a chain or a wire or the like which may be connected to the angle-stabilizer structure. The weight may be connected to the angle-stabilizer structure via the lengthening element.

Several angle stabilizers may be connected to a foundation. For example, one angle stabilizer may be connected to a foundation for each of three anchor lines. A plurality of the weights of the several stabilizers may each be connected to at least one other of the weights of the several angle stabilizers by using, for example, a stay, a wire or a chain or the like.

The foundation may be attached to a first corner of the angle-stabilizer structure. The weight is typically connected, for example via a stay or a wire, to a lower part of the angle-stabilizer structure, and the anchor line is typically connected to a second corner of the angle-stabilizer structure. The anchor line may have a typical cock's-foot con figuration so that two parts, each one in a respective anchor line, can share a corner of the triangle. Naturally, other configurations of the angle-stabilizer structure are possible; it does not have to be shaped like a triangle. Other variants of connecting the anchor line to the angle stabilizer or the angle stabilizer to the foundation, for ex ample, are also possible.

In a seventh aspect of the description and in a first aspect of the invention, a floating foundation for an offshore wind turbine is described, the foundation comprising a tran sition piece for carrying the wind turbine, and a stabilizing part for stabilizing the tran sition piece with or without the wind turbine, the stabilizing part comprising a horizontal part and a vertical part which are both cor- NIPO

WO 2021/173002 ⁷ PCT/N02021/050051 rectively joined to the transition piece, the vertical part comprising a corrective leg for projecting downwards in a water mass in an operational position, the horizontal part comprising a corrective arm and, connected to the corrective arm, at a distance from the transition piece, an anchor attachment, so that, in an operational position, when the foundation is anchored, the transition piece can rotate around the anchor attachment under the influence of elemental forc es, like forces from wind, waves and/or currents.

The foundation may be anchored to a seabed via an anchor line connected to the an chor attachment. The foundation may be free of direct anchoring of the transition piece, which may be anchored only via the corrective arm and the anchor attachment and an anchor line. The foundation may comprise an anchor and an anchor line. The foundation may be anchored via the anchor attachment in such a way that the transi tion piece can rotate around the anchor attachment when affected by elemental forces like waves, wind and/or currents. The water mass is a water mass for carrying the foundation, a water mass on which the foundation can float.

The foundation is constructed for being anchored at the anchor attachment, not at the transition piece, so that, in an operational position, the transition piece and thereby also a wind turbine installed on the foundation can rotate around the anchor attach ment under the influence of elemental forces like forces from waves, currents and/or wind. In that way, the foundation may work self-orientingly and turn itself and the wind turbine into an advantageous position in relation to stability and in relation to efficient production of energy. This advantageous position will typically be with the transition piece substantially downwind of the anchor attachment.

The anchor attachment may be a device comprising several parts. For example, the anchor attachment may comprise a vertical structure, which may be attached to the corrective arm and, in an operational position, may be directed some distance into a water mass, and one or more connecting means for connecting an anchor line to the anchor attachment.

The term "corrective" refers to an effect in relation to the stability of the foundation, typically a tilt-counteracting effect. The corrective parts are generally rigidly attached to the transition piece, directly or via other parts of the foundation, so that if a force acts on one of the parts, it will act on and be counteracted by the others as well. The corrective parts may, for example, be rigidly attached to the transition piece, directly or via some other corrective structure, for example by being welded or bolted to the NIPO

WO 2021/173002 ⁸ PCT/N02021/050051 transition piece, or one or more of the corrective parts may be connected to the tran sition piece via, for example, a hinge allowing movement at least in one plane. The corrective arm may, in the further text, be referred to as "the arm", "the corrective arm" or, as it is part of the horizontal part of the foundation and/or because, in some embodiments, it is substantially horizontal when the foundation is in an operational position on calm water, as "the horizontal arm". The corrective leg may, in the further text, be referred to as "the leg", "the corrective leg" or, as it is part of the vertical part of the foundation and/or because, in some embodiments, it is substantially vertical when the foundation is in an operational position on calm water, as "the vertical leg". The stabilizing part of the foundation comprises a rigid structure which comprises at least part of the transition piece, the horizontal part and the vertical part.

The terms "leg" and "arm" are not to be regarded as restrictive to form or design. The leg and the arm may both have any form that in some way may be practical or advan tageous. The leg may stand vertically into the water mass in an operational position, or for example downwards at an angle. The leg may be split in, for example, two or three or more than three elements projecting downwards, which may each be di rected, for example, directly vertically downwards or downwards at an angle. They may, for example, extend downwards in a mutually diverging manner. The arm may do the same.

In a typical embodiment, the anchor attachment may be attached to a first end of the arm, whereas the transition piece is attached to a second end of the arm, so that the arm, in its longitudinal direction, extends from the anchor attachment to the transition piece. In an alternative embodiment, the arm may extend from the transition piece to the anchor attachment, and further through and beyond the anchor attachment. In a further embodiment, the arm may extend from the anchor attachment to the transi tion piece and further through and beyond the transition piece. In a further embodi ment, the arm may extend through and beyond both the transition piece and the an chor attachment. In all embodiments of the foundation in accordance with the first aspect of the invention, the anchor attachment will be at a distance from the transition piece, wherein the distance may be, for example, more than 10 metres, more than 20 metres, more than 30 metres, more than 50 metres, more than 70 metres, more than 100 metres, or more than 150 metres.

The terms "vertical" / "substantially vertical" and "horizontal" / "substantially horizon tal" typically refer to a position or a form of an object when the foundation is in an operational position under normal conditions in relation to wind and waves. NIPO

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The vertical part of the foundation is a part of the foundation which, in an operational position, will substantially be an underwater part, as, in an operational position, it will extend downwards in a water mass from the transition piece or from the horizontal part of the foundation. The vertical part may work as a keel, and/or as ballast, to sta bilize the foundation against tilt. The vertical part may typically project more than 20 metres, more than 30 metres, more than 50 metres, more than 70 metres, more than 100 metres or more than 150 metres into the water mass from the surface of the wa ter mass. The primary purpose of the vertical part may typically be to counteract a sideways tilt, even if it may also have a stabilizing effect against a tilt in the longitudi nal direction.

The longitudinal direction of the foundation may be said to be the direction from the anchor attachment to the transition piece and vice versa. A sideways tilt may then be, for example, a tilt perpendicular to the longitudinal direction of the foundation.

The horizontal part of the foundation is a part of the foundation that, in an operational position, will project substantially horizontally from the transition piece. It may be an gled upwards or downwards by some degrees relative to a horizontal plane, for exam ple 5, 10 or 15 degrees upwards or downwards relative to the horizontal plane. The horizontal part may primarily work against a tilt in the longitudinal direction of the foundation.

The transition piece is a part of the foundation on which or connected to which a wind turbine may stand. Beyond said function, the term is not to be read as restrictive to the form or design of the part. This transition piece is joined to the corrective arm and to the corrective leg. The leg may be directly joined to the transition piece, or it may be joined to the transition piece via, for example, the arm. The leg may be attached to the front part of the corrective arm. The leg may, for example, be included as part of the anchor attachment, so that the foundation may rotate freely around the leg. This embodiment of the foundation has considerable advantages in that there is less area to be moved through the water if the wind changes direction. This may be advanta geous in relation to sideways stability, for example. The leg may project directly downwards, straight downwards, or downwards at an angle, from a position where it is joined to another rigid structure belonging to the foundation, for example from a position on the corrective arm, from a position on the transition piece, or from the anchor attachment. The leg may, for example, project downwards from a position on the arm equal to or less than 25 % of the length of the arm from the transition piece, equal to or less than 50 % of the length of the arm from the transition piece, equal to NIPO

WO 2021/173002 ^{1 0} PCT/N02021/050051 or less than 75 % of the length of the arm from the transition piece, equal to or less than 90 % of the length of the arm from the transition piece, or more than 90 % of the length of the arm from the transition piece.

To stabilize the foundation in relation to sideways tilt, it may be an advantage to re duce friction that will arise between the structure of the foundation and a water mass by rotation of the foundation. By placing the leg at, in connection to, or having the leg as part of the anchor attachment rather than having the leg directly under the transi tion piece, this friction will be reduced, as a distance through which the leg will have to move through the water mass by rotation will be smaller at the anchor attachment than at the transition piece. Thereby the friction will also be reduced, and the stability is improved.

Such a positioning of the leg may further be favourable in relation to the effect of an oceanic current on the position of the transition piece in the water, and it may give a more even distribution of weight on the corrective arm. Further, it may be beneficial to avoiding collisions with underwater structures, for example.

A foundation in accordance with the first aspect of the invention can offer better sta bility for a wind turbine, against forces from wind, waves and currents in combination, relative to its vertical size and its mass, compared to the prior art, such as "Hywind", by it having a design more suitable for the purpose.

The corrective arm may be rigidly attached to the anchor attachment and to the tran sition piece and may form a rigid connection between the anchor attachment and the transition piece.

The foundation will typically be formed in such a way that, in an operational position, it will follow the wind so that the transition piece will normally be staying substantially downstream of the anchor attachment in a wind acting on the foundation. That is to say, if the wind is blowing directly from the north to the south, then the foundation will typically rotate with the wind so that the transition piece will be standing south of the anchor attachment. The wind forces will then primarily act on the wind turbine in the longitudinal direction of the corrective arm. Depending on the lengths, weights and designs of the anchor attachment and the arm, the arm may then provide the founda tion with very good stability properties against tilt caused by wind forces. By the foun dation corrective with forces acting on it, sideways tilt may be prevented, which will have a great effect on its stability. Oceanic currents and waves may also affect the position of the transition piece relative to the anchor attachment, but, under typical NIPO

WO 2021/173002 ^{1 1} PCT/N02021/050051 conditions, the wind direction will typically have the greatest effect on the position.

Some embodiments of the invention may have more than one corrective arm. In em bodiments with more than one corrective arm, the corrective arm that connects the anchor attachment to the transition piece may be called the primary corrective arm, and other corrective arms may be called secondary corrective arms. In embodiments with one or more other corrective arms, that one or they will typically not be parallel to the primary corrective arm. Such a secondary corrective arm may then have a cor rective effect against a tilt that deviates from the longitudinal direction of the primary corrective arm. In most embodiments, the corrective arm will be substantially horizon tal, but may, in some embodiments, be angled, for example, somewhat downwards or upwards relative to a horizontal plane, for example between the anchor attachment and the transition piece.

The foundation and a wind turbine installed on the foundation are further subjected to tilting forces from the rotation of the blades of the wind turbine and from waves, which will have a direction against which the corrective arm is not very effective. The corrective leg will have a stabilizing effect against these forces.

The corrective arm that forms a link between the anchor attachment and the transition piece may be formed like an elongated pipe. The length of the arm will, in part, de termine the tilt of the tower in the wind direction when the transition piece is pushed down as a result of the force of the wind against the turbine. The arm will typically be fully submersible during normal operation, or it may be semisubmersible. The anchor attachment may be attached to a first end of the corrective arm, and the transition piece to a second end.

The corrective arm may have one or more chambers which can selectively be filled with or emptied of ballast. In embodiments in which a corrective arm has several chambers, the centre of buoyancy and/or the centre of gravity of the foundation may be adjusted by adjusting the contents of the chambers. In this way, by adjusting the contents of the chambers, the centre of buoyancy and/or the centre of gravity of the foundation may be adjusted horizontally and/or vertically. This may be advantageous for stabilizing the foundation in relation to forces from the anchor attachment and ac cording to wind and/or wave conditions.

Please note that when the stability of the foundation, and its centre of gravity and centre of buoyancy and the like are described, this may apply to the foundation with a wind turbine installed on the transition piece of the wind turbine. NIPO

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It may further be advantageous to have the centre of buoyancy of the foundation as near a surface of a water mass as possible. The foundation in accordance with the first aspect of the invention allows the centre of buoyancy to be lifted by means of the hor izontal part - in that the corrective arm may have considerable buoyancy.

Typically, when the foundation is in an operational position, the weight of the arm will be balanced in such a way that the arm is fully submersible to limit the influence of the power of the waves and also have better control of the buoyancy of the device. Depending on what is desirable, the amount of ballast and/or the positioning of ballast in the corrective arm may be changed, for example, so that, for example, it has posi tive buoyancy at the end attached to the transition piece in order to carry at least part of the weight of the transition piece, or at the end towards the leg if the leg stands at the opposite end of the arm relative to the transition piece. It is normally desirable to have a distribution of ballast in the arm that makes downward bending of the arm be avoided, to avoid strong bending forces on one or more parts of the arm or some oth er structure rigidly attached to the arm.

The anchor attachment may comprise a column, further described as an anchor tower. The foundation may be configured in such a way that at least part of the anchor tower projects above a water surface in an operational position, and in such a way that it may be pulled down in the water when the anchor attachment is pulled downwards by downward forces imposed on the anchor attachment via an anchor line. In that way, the buoyancy of the foundation at the anchor attachment may be increased to com pensate for downward forces by the anchor tower displacing a larger volume of water when being pulled downwards.

Inside, the anchor attachment or anchor tower may hold some or all the parts belong ing to one or more control systems and/or one or more transformers for power pro duction and/or power transmission from a wind turbine, and/or a passage of a cable for transmitting power to shore.

The top of the anchor tower may be arranged as a landing platform for a helicopter.

The anchor tower may be attached in a rotationally loose manner to the anchor at tachment, and thus not be an integrated part of the corrective arm. The anchor tower may be an extension of the corrective leg. In one embodiment, the anchor tower may be at the centre in relation to the anchor lines, which will be advantageous in embod iments in which the anchor tower has a passage of a cable for transmitting power to shore. NIPO

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The anchor attachment may comprise an anchor ring. The anchor ring may be rotata bly attached to a vertically directed structure belonging to the anchor attachment. The vertically directed structure may be the corrective leg of the foundation, the anchor tower, or some other vertically directed structure. The anchor ring may be shaped like a ring. The anchor ring may be penetrated by, for example, the vertically directed structure or another part of the anchor attachment, or the anchor ring may penetrate the vertically directed structure. The anchor ring may comprise one or more connect ing means for connecting the anchor ring to one or more anchor lines. The anchor at tachment may comprise one or more angle stabilizers for stabilizing the direction of the force that acts on the anchor attachment from the anchor line. These one or more angle stabilizers may be connected to the anchor ring. The anchor ring may be any type of anchor for anchoring the foundation. The anchor line may be any type of an chor line. The foundation may comprise more than one anchor and at least one anchor line for each of the more than one anchors. In some embodiments, the foundation may comprise more than one anchor attachment. When anchoring offshore, it may be advantageous, and even necessary, in many cases to have anchor lines of a material of a low specific weight. Such anchor lines are usually expensive relative to heavier alternatives. Embodiments of the foundation in accordance with the invention may have anchor lines that are of a greater specific weight, like an anchor chain in steel, for example. A heavy anchor line may be advantageous for the foundation as the weight of the anchor line may add weight to the anchor attachment, which may be utilized to contribute to the stabilization of the foundation.

When strong wind forces act on a wind turbine standing on the foundation, they will blow the wind turbine and the foundation rearwards from the anchor attachment. The anchor attachment will then pull at the anchor line, which will exert a counterforce on the anchor attachment. This counterforce will, at least partially, work vertically and exert a downward force relative to the anchor attachment. This will have a further stabilizing, corrective effect on the foundation and the wind turbine.

As the anchor attachment is pulled downwards, the angle from the anchor line to the anchor attachment may change, and thereby also the direction of the force that is ex erted on the foundation from the anchor line. The anchor attachment may therefore comprise an angle stabilizer to keep the direction of the force exerted on the anchor attachment from the anchor line more stable. The angle stabilizer may comprise a rigid structure which comprises a weight, and which is arranged to be connected to the anchor attachment and to the anchor line. NIPO

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The corrective leg is a structure primarily for stabilizing the wind-turbine foundation against tilt in other directions than the wind direction prevalent at any time. A purpose of the leg is to have a corrective effect against sideways load. The leg with its weight may further be used to even out the loads in the longitudinal direction of the transition piece. The positioning of the leg relative to the tower and the anchor attachment af fects the distribution of the centres of buoyancy and gravity of the foundation and loads, for example from gravitational force on the structure of the foundation. The foundation may, with advantage, be designed in such a way that the leg is placed in an advantageous position with a view to the centre of buoyancy, the centre of gravity and/or structural loads.

To maintain sideways stability, it may be beneficial to add weight in a lower part of the leg and/or lengthen the leg downwards. The leg may be formed with a surface that ensures great damping against sideways tilt. For example, the leg may be formed like a column, a pipe, or a cone, but it may also, with advantage, have a flatter form in the vertical plane. The leg may function as and/or be formed like a keel, or like a buoy.

The leg may be formed with one or more chambers that can be filled with ballast ma terial. The leg may be without chambers for receiving ballast, and the body of the leg may constitute a ballast in itself.

As the corrective leg is not a primary stabilizer against wind forces, but against minor, sideways forces, its mass and/or length may be limited compared with, for example, the spar buoy that is used in the "Hywind" solution. This may be very advantageous, for example in relation to the transport of foundations over sea areas with relatively shallow water, and makes it possible for the floating foundation in accordance with the first aspect of the invention to be installed also in sea areas with relatively shallow water.

In some embodiments, the leg will be placed directly under a platform for a wind- turbine tower on the transition piece, then usually, but not necessarily, as a vertical extension of a tower. The leg may alternatively be placed at a horizontal distance from the platform and at a horizontal distance from the transition piece, for example in the direction from or towards the anchor attachment. The leg may be part of or joined directly to the tower for a wind turbine which is to be carried by the wind-turbine foundation.

The leg may, for example, be formed like an open pipe and allow ingress of water. An open bottom may minimize the water displacement by the leg in an operational posi- NIPO

WO 2021/173002 ^{1 5} PCT/N02021/050051 tion, thereby reducing a buoyancy of the leg and/or the effect of the leg on the foun dation. The leg may typically be rigidly attached to the transition piece, directly or indirectly, for example via the arm.

The foundation may have more than one leg. In one embodiment, one of several legs, for example, may be a lower part of the tower for a wind turbine, whereas another leg is independent of the tower and rigidly attached to a bottom side of the foundation at a distance from the tower. Several legs may be advantageous because then it is pos sible, with several legs of less mass and/or smaller lengths, to achieve the same sta bility as or better stability than that achievable with one leg.

The corrective leg may be rigidly attached to the transition piece, either directly or via the arm. In embodiments of the foundation, the leg may be raised and lowered verti cally. A raisable and lowerable leg may, for example, be advantageous in cases in which the foundation is to be towed at sea across areas with sea depths smaller than the depth of the leg in an operational position.

The foundation may further comprise one or more water brakes. The one or more wa ter brakes may be suspended from one or more lower parts of the structure of the foundation and may be advantageous in that they may brake vertical movement of the foundation. They may be formed and suspended in such a way that, by vertical movement of the foundation, they will push a considerable water mass, which will en sure that they subject the foundation to a force against the direction of the move ment. They may be formed in such a way that they primarily brake by vertical move ment in one direction, for example upwards.

The foundation may comprise a motorized rotary means for controlled rotation of the foundation. In advantageous embodiments, the rotary means may be connected to a control system so that the foundation may be rotated back into a starting position. For example, it may have been set in such a way that if the device has rotated through more than two revolutions around the anchor point, the rotary means will rotate the foundation two revolutions back. This may be advantageous, for example for avoiding undesired twisting of an electrical cable between the device and the seabed.

The rotary means may comprise a thruster, for example. The rotary means will typi cally be placed in connection to the foundation with a distance to the anchor attach ment, towards the transition piece. In embodiments, the rotary means may be rigidly attached to the transition piece of the foundation or be of an embodiment in which it may rotate to control the direction of force. NIPO

WO 2021/173002 ^{1 6} PCT/N02021/050051

The foundation may further comprise a rudder. The rudder may, for example, be at tached to the corrective leg, but may also be attached to the transition piece or to the corrective arm independently of the leg. The rudder may be rotatable through 360 degrees. The rudder may be used to influence rotation of the foundation, for example by being turnable in such way that it affects the rotation against an oceanic-current direction, for example to improve the stability of the foundation and/or to improve the orientation of a wind turbine mounted on the foundation relative to a wind direction so that the wind turbine may more effectively extract energy from the wind.

The corrective leg of the foundation may be rotatable or comprise a rotatable part and be formed in such a way that it may function as a rudder. In one embodiment, the foundation may have both a rotatable corrective leg and a rudder. In such an embod iment, the corrective leg may, for example, be rotatable through a smaller angle than the rudder, and the rudder may be the primary means for adjusting the influence of an oceanic current on the position of the transition piece of the foundation relative to the anchor attachment, and the corrective leg may be a secondary means for the same.

Most known offshore wind turbines have a nacelle with blades mounted on it, the na celle being rotatable to angle the blades in a way that makes them utilize a wind ef fective for extracting electrical energy - typically at 90 degrees to the wind direction. With a foundation that is rotatable, it is not equally important for the nacelle to be rotatable through 360 degrees. It is then conceivable that the nacelle may be rota- tionally rigid on the tower, or have a minor freedom of rotation, for example +-10 de grees, +-20 degrees, or +-45 degrees.

The corrective leg may be placed at or near the anchor attachment. To stabilize a foundation in relation to sideways tilt, it may be beneficial to minimize friction be tween the structure of the foundation and a water mass arising by rotation of the foundation. This friction may be reduced by limiting the distance over which the leg has to be moved by rotation of the foundation. It may thus be advantageous for the stability of the foundation if the leg is placed at or near the centre of rotation to limit said distance, to reduce the friction.

In an eighth aspect of the description, a floating foundation for a wind turbine is de scribed, the foundation comprising:

- a transition piece and a corrective leg, the corrective leg projecting downwards in a water mass when the foundation is in an operational position;

- a rigid structure, which comprises and joins together at least part of the transition NIPO

WO 2021/173002 ^{1 7} PCT/N02021/050051 piece and at least part of the corrective leg; and

- a ballast element formed with a hole for receiving the corrective leg, the ballast element being movably suspended from the rigid structure, so that the cor rective leg penetrates the ballast element and so that the ballast element will come into contact with and have a corrective effect on the corrective leg and thereby also have a corrective effect on the foundation when the foundation is tilted beyond a cer tain degree.

The ballast element may be the ballast element in accordance with the first aspect of the description.

The foundation in accordance with the eighth aspect of the description may have any one of the features mentioned in connection with the foundation in accordance with the seventh aspect of the description.

In a nineth aspect of the description, a floating foundation for an offshore wind turbine is described, the foundation comprising:

- a transition piece for supporting the wind turbine;

- a first corrective arm and a second corrective arm, the first arm and the second arm being attached to and projecting from the transition piece, and the first arm comprising a hinge and being articulatedly joined to the tran sition piece via the hinge to allow movement of the first arm in the horizontal plane.

The floating foundation in accordance with the nineth aspect of the description may have the first and second arms attached to the transition piece with an angle between them of less than 120 degrees, of less than 110 degrees, of less than 100 degrees, or, typically, of about 90 degrees. The angle between the two arms may be smaller than 90 degrees or more than 120 degrees. The movement of the first arm allowed by the hinge may be a movement that changes the angle between the two arms. The floating foundation may have more than two substantially horizontal, corrective arms.

An outer part of the first arm and an outer part of the second arm of the latter founda tion may be attached to each other with a fastening means, such as a wire or a chain or the like.

An outer part of the first arm and/or an outer part of the second arm may each have an anchor attachment for joining the arm to an anchor.

In a typical embodiment, the first arm may be attached to a first anchor, which lies on a substantially opposite side of the first arm relative to the second arm, via an anchor NIPO

WO 2021/173002 ^{1 8} PCT/N02021/050051 line extending from the anchor attachment of the first arm to the first anchor. The second arm may typically be attached to a second anchor, which lies on a substantially opposite side of the second arm relative to the first arm, via an anchor line that ex tends from the anchor attachment of the second arm to the second anchor.

The first arm and the second arm may be floating arms, semisubmersible arms or fully submersible arms.

The first arm may have cavities which may selectively be holding ballast or be empty of ballast. In that way, the centres of buoyancy and gravity of the arm, and thereby also the centres of buoyancy and gravity of the foundation, can be adjusted. The arm may have several cavities distributed over its longitudinal axis. The second arm may have such cavities.

As in connection with aspects of the description described earlier, descriptions like "substantially horizontal" and " movement of the first arm in the horizontal plane" re fer to a position and movement in an operational position of the foundation under normal, calm conditions at sea. This also applies in the further description and further aspects of the description.

The foundation in accordance with the nineth aspect of the description may be a foun dation to be anchored in a way that does not allow the foundation to rotate, or it may be a foundation to be anchored in a way that allows rotation. The foundation may be anchored as mentioned above, wherein the first and second arms are both anchored to an anchor each. It may alternatively be anchored only from one arm, so that the foundation may rotate around the anchor attachment of that one arm.

The foundation in accordance with the nineth aspect may comprise any one of the fea tures mentioned in connection with the foundations in accordance with the seventh and/or the eighth aspect of the description.

Any one of the foundations in accordance with the seventh, the eighth or the nineth aspect of the description may comprise one or more of the ballast element in accord ance with the first aspect of the description or the angle stabilizer in accordance with the sixth aspect of the description, and/or any one of the features of one of the other foundations.

In a tenth aspect of the description, a wind turbine for an apparatus for extracting energy from wind is described, the wind turbine having an upper part and a lower part, the upper part being tiltably attached to the lower part at a hinge, and the wind NIPO

WO 2021/173002 ^{1 9} PCT/N02021/050051 turbine comprising a tilting mechanism to enable tilting of the upper part relative to the lower part to allow the upper part to be kept stable when the wind turbine is tilted.

The tower of the wind turbine may further comprise a control unit connected to the tilting mechanism to automatically control the cylinder in order to keep the upper part correctly angled relative to a horizontal plane. The upper part may comprise a nacelle with a rotor and blades. The upper part may further comprise a tower extension - a structure similar to an upper part of a typical tower for a wind turbine - to which the nacelle is attached. The upper part of the wind turbine may be part of a tower for a wind turbine, and the lower part may be a tower or part of a tower for a wind turbine.

In this connection, "to keep the upper part stable" may mean to keep an angle be tween the upper part and a horizontal plane stable. This may then happen by chang ing an angle between the upper part and the lower part, when the wind turbine is tilt ed. The upper part may also be referred to as an "upper end".

As mentioned earlier, a floating wind turbine could tilt under the influence of strong forces from wind and/or from waves. Such a tilt may change the position of the blades of the wind turbine in a way that makes the ability of the wind turbine to extract ener gy from the wind be reduced. By having a tiltable upper part, the blades of the wind turbine may be kept more stably in a position that allows efficient energy extraction. A wind turbine with a tiltable upper part may be advantageous for several types of float ing foundations but may be particularly advantageous for a foundation that can be rotated like the foundation in accordance with the first aspect of the invention or in accordance with the eighth aspect of the description.

The wind turbine may comprise an upper adapter piece. The nacelle may be connected to the tower via the upper adapter piece. The upper adapter piece may be rotatably attached to the tower, and/or the nacelle may be rotatably attached to the tower, so that the nacelle can be rotated relative to the tower around the longitudinal axis of the tower.

The upper adapter piece may comprise a tower pipe, an upper nacelle carrier and a lower nacelle carrier, the hinge, the tilting mechanism.

In an eleventh aspect of the description, a wind turbine for a floating apparatus for extracting energy from wind is described, the wind turbine comprising a lifting beam mounted on an upper part of the tower of the wind turbine, above a position for a na celle on the tower. NIPO

WO 2021/173002 ^{2 0} PCT/N02021/050051

The lifting beam may comprise one or more sheaves, and/or other lifting means, and can be used for raising and/or lowering a nacelle to or from an upper part of the tow er. The lifting beam may be placed at the top of the tower of the wind turbine, for ex ample.

The wind turbine may be part of a floating apparatus for extracting energy from wind, wherein the apparatus may further comprise any one of the floating foundations in accordance with the seventh, the eighth or the nineth aspect of the description. The wind turbine may comprise one or more of the tower in accordance with the second aspect of the description, the rotor in accordance with the third aspect of the descrip tion, the nacelle in accordance with the fourth aspect of the description and/or the adapter piece in accordance with the fifth aspect of the description. In embodiments in which the wind turbine comprises the tower in accordance with the second aspect of the description, the foundation of the wind turbine may be adapted for such a tower by the foundation having an opening for the tower to the sea.

The wind turbine in accordance with the tenth aspect of the description may comprise the adapter piece in accordance with the fifth aspect, the nacelle in accordance with the fourth aspect, the rotor in accordance with the third aspect or the tower in accord ance with the second aspect of the description and/or any one of the features men tioned in connection with the wind turbine in accordance with the eleventh aspect of the description. The wind turbine in accordance with the eleventh aspect of the de scription may comprise the adapter piece in accordance with the fifth aspect, the na celle in accordance with the fourth aspect, the rotor in accordance with the third as pect or the tower in accordance with the second aspect of the description and/or any one of the features mentioned in connection with the wind turbine in accordance with the eleventh aspect of the description.

In a second aspect of the invention and a twelfth aspect of the description, a floating apparatus for extracting energy from wind is described, the apparatus comprising a wind turbine and the foundation in accordance with the seventh aspect of the descrip tion, the foundation being anchored to a seabed via an anchor line which connects the anchor attachment of the foundation to an anchor. A floating apparatus for extracting energy from wind is described as well, the apparatus comprising a wind turbine and the foundation in accordance with the eighth or the nineth aspect of the description, the foundation being anchored to a seabed via an anchor line which connects the an chor attachment of the foundation to an anchor.

The foundation may be anchored via several anchor lines, each leading to one or more NIPO

WO 2021/173002 ^{2 1} PCT/N02021/050051 anchors. The anchor lines may be connected to an anchor ring, which may be part of the anchor attachment, and which may be rotatably attached to a vertically projecting structure belonging to the anchor attachment. The anchor ring may typically be rotat able relative to the vertical structure of the anchor attachment. The vertical structure may project upwards, downwards, or both upwards and downwards in a water mass relative to the corrective arm, generally from an outer part of the corrective arm. The vertical structure may penetrate the surface of the water mass. The anchor lines may be connected to the anchor attachment / anchor ring via angle stabilizers. A plurality of anchor lines and anchors may be beneficial for stabilizing the position of the foun dation in a water mass in an operational position.

The wind turbine comprises a tower. The tower may have a cavity with an opening for receiving water, and the foundation may have an opening for allowing water to reach the opening of the tower, so that water may enter the tower in situations in which the tower penetrates a surface of a water mass. The opening may comprise an open lower end of the tower. An opening for allowing water to enter the tower may be an ad vantage, to reduce buoyancy resulting from water pressure and reduce the vertical influence of waves on the foundation and tower.

The tower, or part of the tower, may be formed like a pipe, with an inner, axial cavity. Such a form may reduce the mass of the tower relative to the circumference and height of the tower seen in relation to a tower which does not have such an inner cavi ty. Reduced mass may be advantageous for reducing the weight that the wind-turbine foundation will have to carry per metre of tower. A lower mass of the tower entails a reduction in the need for mass in the keel to stabilize the foundation. The inner cavity may be of any shape. The inner cavity may extend from a lower end of the tower and in the longitudinal direction of the tower towards the upper end of the tower. The in ner cavity may extend through the entire length of the tower, along a major part of the length of the tower or along a minor part of the length of the tower. The cavity may extend through 70 % of the length of the tower, 30 % of the length of the tower, 50 % of the length of the tower, or any percentage of the length of the tower over 0 % of the length of the tower and up to 100 % of the length of the tower.

With a tower that is formed like a pipe with an opening at the bottom and an inner cavity, which allows water inflow into the cavity, the diameter of the tower may be increased without any significant change in the displaced amount of liquid. A larger tower diameter may, for example, open to the use of a generator with a larger diame ter, if the generator sits in the tower. NIPO

WO 2021/173002 ²² PCT/N02021/050051

The foundation may have an opening in the transition piece, through which the tower of a wind turbine can be moved vertically. The method for stabilizing the foundation may comprise lowering the tower into a water mass. This may give increased stability in that the tower may function as a keel, in that the centre of gravity of the tower, and the foundation with the tower, is moved downwards, and/or in that the forces to which a wind turbine on the foundation may be subjected are thereby reduced.

The apparatus may have a hoisting means for hoisting the tower up or down. The hoisting means may, for example, comprise a winch, which may, for example, sit on the transition piece of the foundation, and one or more sheaves and wires connecting the winch to the tower.

The apparatus may have locking means for locking the tower in a position, to prevent undesired vertical movement of the tower relative to the foundation. The locking means may be locking means for locking the tower in a small number of different posi tions, such as an uppermost position, a middle position and a lowermost position. In some embodiments, the locking means may lock the tower in further positions, such as an upper middle position and a lower middle position.

The apparatus may have braking means to allow vertical movement of the tower and simultaneously brake the movement so that it will not be too fast. Such braking means may reduce the load on parts of the apparatus, such as the transition piece, nacelle and/or rotor.

The tower may have one or more inner chambers for receiving ballast to change the mass of the tower. The tower may be attached to the foundation in a way that allows vertical movement of the tower. The vertical position of the tower may then be ad justed by adjusting the mass of the tower, as it may have an effect on how far the tower will sink into a water mass. The tower may, for example, comprise one or more chambers which may selectively be filled with or emptied of water or air and means for filling or emptying the one or more chambers.

The apparatus may comprise a lifting means, for example a winch or a toothed rack, to lift equipment or parts belonging to the wind turbine to or towards the top of the tower of the wind turbine and/or to lift equipment down from the top of the tower. The lifting means may be a hoisting means for hoisting a nacelle or parts for a nacelle, for example, to the top of the tower. The lifting means may also be used for lifting equipment down from the tower.

When lifting operations are carried out by using lifting means belonging to vessels that NIPO

WO 2021/173002 ^{2 3} PCT/N02021/050051 are moving relative to a wind turbine on a floating foundation, the relative motion will complicate the lifting operation. Such relative motion is avoided if lifting means that belong to the wind turbine itself are used. The lifting operation is thereby simplified.

The lifting means may be a lifting means for moving equipment, for example a nacelle, a rotor or blades, some distance to or from the top of a nacelle. For example, a vessel may be used to lift a nacelle 30 metres, or 50 metres, or 70 metres, or more than 70 metres or less than 30 metres, and the lifting means belonging to the wind tur bine is used to lift the remaining metres to or from the top of a tower. The lifting means may otherwise be a lifting means for lifting equipment from a transition piece belonging to the foundation for the wind turbine to the top of the tower.

The apparatus may comprise one or more further lifting means for lifting equipment from a vessel to the transition piece of the foundation.

The tower may be rotationally rigidly attached to the foundation, typically to the tran sition piece. The nacelle may be rotationally rigidly attached to the tower. Rotationally rigidly secured connections may be, for example, welded and/or bolted connections, and may be less complicated and more robust than more advanced connections allow ing rotation. Such rotationally rigid connections may be used on a wind turbine that stands on a rotatable foundation, like the foundation in accordance with the first as pect of the invention, like an apparatus in accordance with the second aspect of the invention, as the foundation itself may then be oriented to set the blades of the wind turbine correctly relative to the wind direction.

With the nacelle rotationally rigidly attached to the tower, the generator, among other things, may be moved from the top of the tower and down into the structure. The wind turbine may comprise a generator placed in the transition piece or in the tower near the transition piece. "Near the transition piece" may mean, for example, less than 10 metres from the transition piece, vertically in the tower, less than 5 metres from the transition piece, less than 3 metres from the transition piece, or less than 1 metre from the transition piece. In that way, access to the generator for maintenance or repair may be simpler, and the weight of the generator will be moved from the top of the tower, from the nacelle where the generator normally is, to or towards a lower end of the tower. Moving weight downwards will have a considerable effect for the stability of the apparatus, and it may reduce the need for stabilizing weight and/or length of the vertical, stabilizing part and/or the horizontal, stabilizing part of the foundation. Moving the generator down to or towards the transition piece may be ad vantageous for, thus, being able to use a type of generator that requires more space NIPO

WO 2021/173002 ^{2 4} PCT/N02021/050051 and/or is heavier. For example, a so-called "direct drive" generator may be used - a generator with a relatively large diameter compared with a conventional generator, but not requiring a gearbox.

The wind turbine may have a lower adapter piece between the tower and the transi tion piece. The tower may be connected to the transition piece via the lower adapter piece. In some embodiments, the tower may be releasably attached to the lower adapter piece, and the lower adapter piece may be releasably attached to the transi tion piece. The generator may be placed in the lower adapter piece.

In embodiments of the floating apparatus, the floating apparatus hay have a ballast element which is suspended with adjustable depth. In such embodiments, the appa ratus may comprise lifting means for adjusting the depth to the ballast element. This may be particularly advantageous in embodiments of the apparatus that have a tower that can be moved vertically, for compensating for a changed centre of gravity and/or centre of buoyancy when the tower is moved vertically.

In a thirteenth aspect of the description, a floating apparatus for extracting energy from wind is described, the floating apparatus comprising a plurality of wind turbines erected from one floating foundation.

The foundation may be any foundation for an offshore wind turbine, for example any one of the foundations in accordance with the seventh, eighth or nineth aspect of the description.

Each of the several wind turbines may comprise a plurality of blades, a nacelle, a rotor and a tower, for example. The plurality of wind turbines may be two wind turbines, three wind turbines, four wind turbines, five wind turbines, or more than five wind turbines. In alternative embodiments, two or more wind turbines, for example, may share one tower, but each have a nacelle, a rotor and blades. Several wind turbines may be interconnected in other ways than just by standing on the same foundation. They may also be interconnected by means of a structure, such as a rod, a stay, a beam, a tower or the like.

In a possible embodiment, two or more wind turbines may be attached to a horizontal tower stay which is, in turn, attached to a common vertical tower. The horizontal tow er stay may be removably attached to the vertical tower, so that the horizontal tower stay can be loosened from the tower and be hoisted down for maintenance or repair, for example. Alternatively, the horizontal tower stay may be permanently, not remov ably, attached to the tower, and the tower may be attached in a vertically movable NIPO

WO 2021/173002 ^{2 5} PCT/N02021/050051 manner to the foundation so that the tower may be run vertically up or down relative to the foundation and thus be lowerable for maintenance or repairs on one or more of the wind turbines.

The foundations described above may be so advantageous in relation to the prior art that their carrying capacity relative to their size, weight and horizontal and/or vertical extent(s) may facilitate carrying larger, more extensive structures than single wind turbines.

The size of a wind turbine is limited by the fact that the energy utilization may gradu ally, with increasing size of the wind turbine, become ineffective and have challenges connected to a so-called "circumferential speed" of the blades. Then it may be more effective to utilize the carrying capacity of the foundations by erecting several wind turbines from a foundation, rather than increasing the size of one wind turbine erected on the foundation. In a typical wind farm, it is possible to have better energy utiliza tion of an area by placing several wind turbines on the same foundation.

One or more of a plurality of wind turbines on a common foundation may have any one or more of the features mentioned regarding the wind turbines earlier in this doc ument.

With several wind turbines on one foundation, they may be configured in such a way that at least two of them do not rotate in the same direction, so that forces from the rotation of the wind turbines at least partially balance each other out.

In a fourteenth aspect of the description, a floating apparatus for extracting energy from wind is described, the floating apparatus comprising a wind turbine and a foun dation, the tower of the wind turbine comprising a hinge and being divided into an upper part and a lower part, the upper part of the tower and the lower part of the tower being attached to each other through the hinge in a way that allows the upper part of the tower to be tilted between a raised position and a lowered position, and the tower comprising a locking means for releasably locking the tower in the raised posi tion to prevent undesired tilting from the raised position.

In a fifteenth aspect of the description, a floating apparatus for extracting energy from wind is described, the floating apparatus comprising a wind turbine and a foundation and a hinge, the tower of the wind turbine being hinged against the foundation through the hinge in a way that allows the tower to be tilted between a lying position and a raised position, and the tower comprising a locking means for releasably locking the tower in the raised position to prevent undesired tilting from the raised position. NIPO

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In a sixteenth aspect of the description, a floating apparatus for extracting energy from wind is described, the floating apparatus comprising a foundation with a transi tion piece, two wind-turbine towers and a lifting tower, the lifting tower standing in a central position on the transition piece with one wind- turbine tower on either side of it and comprising lifting means for lifting the towers between a lying position and a standing position, the wind-turbine towers each com prising a hinge which makes the tower movable around the hinge between said lying and standing positions.

The hinges may connect the wind-turbine towers to a transition piece belonging to the foundation, or they may connect upper parts of the wind-turbine towers to lower parts of the wind-turbine towers. The hinges may make it possible for the entire wind tur bine towers or part or parts thereof to be laid down, for example in such a way that they are lying substantially horizontally. The wind turbine towers may also comprise locking means for locking the wind-turbine towers in a position, for example in a lying position and/or in a standing position.

In an advantageous embodiment, the lifting means and the hinges may be adapted in such a way that the towers, when being laid down, are laid down to separate sides, in a symmetrical manner, so that balance is achieved. The towers may, for example, be laid down at an angle to each other of substantially 180 degrees and each at a sub stantially 90-degree angle to a horizontal part of the foundation. Alternatively, the towers may be laid down at an angle of less than 180 degrees to each other and of less than 90 degrees to the horizontal part of the foundation.

Such a symmetrical solution may be advantageous to, for example, assembling and dismantling towers on floating structures, where maintaining stability may be crucial for a safe and feasible operation.

In a seventeenth aspect of the description, a floating apparatus for extracting energy from wind is described, the apparatus comprising:

- a wind turbine and a foundation for carrying the wind turbine, the wind turbine com prising a tower, and the foundation comprising a substantially vertical, stabilizing part and a substantially horizontal, stabilizing part; and

- an upper tension rod and a lower tension rod and a connecting means,

- the connecting means being permanently attached to an upper part of the tower;

- the upper tension rod extending from an outer portion of the horizontal, stabilizing part to the connecting means; and

- the lower tension rod extending from the outer portion of the horizontal, stabilizing NIPO

WO 2021/173002 ^{2 7} PCT/N02021/050051 part to a lower part of the vertical, stabilizing part, so that the tension rods can absorb bending moments to reduce potentially destructive forces acting on parts of the structure of the floating apparatus.

Any one of the floating apparatuses in accordance with the twelfth, thirteenth, four teenth, fifteenth, sixteenth or seventeenth aspect of the invention may comprise one or more of the ballast element in accordance with the first aspect of the description, the tower in accordance with the second aspect of the description, the rotor in accord ance with the third aspect of the description, the nacelle in accordance with the fourth aspect of the description, the adapter piece in accordance with the fifth aspect of the description, the angle stabilizer in accordance with the sixth aspect of the description, any one of the foundations in accordance with the seventh, eighth or nineth aspect of the description, any one of the wind turbines in accordance with the tenth or eleventh aspect of the description, and/or any one of the features mentioned in connection with one of the other floating apparatuses.

In an eighteenth aspect of the description and a third aspect of the invention, a meth od for stabilizing a foundation for a wind turbine is described, the method comprising the steps of:

- providing a foundation having a transition piece, an anchor attachment and a correc tive arm, the transition piece and the anchor attachment being rigidly connected to each other via the corrective arm;

- anchoring the foundation via the anchor attachment in such a way that the transition piece can rotate around the anchor attachment to orient itself into a favourable posi tion; and

- letting the foundation orient itself, as a result of influence from elemental forces, until the transition piece of the foundation is substantially downstream of the anchor attachment in a wind that affects the foundation, so that the corrective arm stabilizes the transition piece against elemental forces in the direction of the wind.

The foundation may, for example, be any one of the foundations in accordance with the seventh, eighth or nineth aspect of the description.

The method for stabilizing the foundation may further comprise controlling the orien tation of the foundation at least partially, for a more accurate positioning of the transi tion piece in the desired position relative to the anchor attachment. The rotation may, for example, be controlled by means of a rudder or by means of a rotary means, such as a propeller. It may be very advantageous to control the orientation at leas partially, for the transition piece to be placed accurately in the desired position, as a more accu- NIPO

WO 2021/173002 ^{2 8} PCT/N02021/050051 rate positioning of the transition piece relative to the anchor attachment may affect the stabilizing effect that the arm may have against the forces applied to the founda tion and turbine by wind and waves.

In a nineteenth aspect of the description, a method for stabilizing a floating foundation for a wind turbine is described, the wind turbine comprising a rigid structure compris ing a corrective leg, the method comprising the steps of:

- providing a ballast element in accordance with the first aspect of the description; and

- suspending the ballast element from a bottom side of the rigid structure belonging to the foundation, with the leg of the foundation through the hole of the ballast element, in a way that allows movement of the ballast element relative to the rigid structure and that will make the ballast element come into contact with and exert a stabilizing force on the structure when the foundation is tilted beyond a certain degree.

The leg of the foundation may be an extension of a tower for a wind turbine standing on the foundation. The foundation may, for example, be any one of the foundations in accordance with the seventh, eighth or nineth aspect of the description.

The method in accordance with the third aspect of the invention may comprise the step of:

- suspending the ballast element in accordance with the first aspect of the description from a bottom side of the foundation, with the leg of the foundation through the hole of the ballast element, in a way that allows movement of the ballast element relative to the rigid structure and that will make the ballast element come into contact with and exert a stabilizing force on the structure when the foundation is tilted beyond a certain degree.

In a twentieth aspect of the description, a method for reducing bending forces on a connection between a vertical part and a horizontal part of a floating foundation for a wind turbine is described, the method comprising the step of:

- extending a tension rod between an outer portion of the foundation and a connecting means that is in contact with an upper portion of a tower for a wind turbine that stands on the floating foundation and/or extending a tension rod between an outer portion of the foundation and a lower portion of a vertical part of the foundation.

The outer portion may be a substantially horizontal outer portion, for example an out er portion of the horizontal part of the foundation.

The connecting means may be, for example, a rod extending from the tower, or from a rotationally rigid part of the rotor, or extending through a central hole in the rotor, NIPO

WO 2021/173002 ^{2 9} PCT/N02021/050051 or a swivel on an outer, rotatable surface of the rotor.

The foundation may be, for example, any one of the foundations in accordance with the seventh, eighth or nineth aspect of the description.

In a twenty-first aspect of the description, a method for installing a nacelle on a tower for a wind turbine is described, the method comprising the steps of:

- providing a nacelle in accordance with the fourth aspect of the description;

- lifting the front and rear parts of the nacelle to a position of installation for the na celle on the tower;

- releasably locking the front part of the nacelle to the rear part of the nacelle after lifting to the position of installation, to combine the two parts.

In some embodiments of the nacelle, it may become complete by combining the front and rear parts. In other embodiments, the nacelle may have further parts that must be connected to the front and/or rear part(s) to make it complete.

The method may comprise lifting one or more further parts belonging to the nacelle to the position of installation on the tower. The method may further comprise releasably locking one or more further parts to the front and/or rear part(s) of the nacelle, to combine the parts in order to form a complete nacelle.

In a twenty-second aspect of the description, a method for uninstalling a nacelle in accordance with the fourth aspect of the description from a tower belonging to a wind turbine is described, the method comprising the steps of:

- releasing a releasable locking between a front part and a rear part of the nacelle, and releasing the parts of the nacelle from the tower;

- lifting the front and rear parts off the tower.

The method may comprise releasing the further parts of the nacelle and lifting the further parts of the nacelle down from the tower.

The lifting may be carried out by, for example, using lifting means belonging to the tower or belonging to a foundation on which the tower is erected, or belonging to a vessel. The foundation may, for example, be any one of the foundations in accordance with the seventh, eighth or nineth aspect of the invention. The nacelle may be the nacelle in accordance with the fourth aspect of the description, for example.

A wind-turbine tower may comprise a guiding means for guiding the nacelle parts when the nacelle parts are being lifted. For example, the tower may comprise a tower NIPO

WO 2021/173002 ^{3 0} PCT/N02021/050051 pipe with an inner diameter larger than the outer diameter of the tower, to which the parts of the nacelle can be attached, which can guide the parts during lifting.

The steps comprising lifting the parts of the nacelle may comprise guiding the parts of the nacelle by means of the guiding means during lifting of the parts of the nacelle.

The guiding means may comprise a tower pipe.

The method for installing the nacelle may comprise one or more of the steps of:

- connecting the front part of the nacelle to the tower pipe;

- connecting the rear part of the nacelle to the tower pipe;

- hoisting the tower pipe to the nacelle position;

- disconnecting the front part of the nacelle from the tower pipe and installing the front part of the nacelle on the tower;

- disconnecting the rear part of the nacelle from the tower pipe and installing the rear part of the nacelle on the tower; and/or

- removing the tower pipe from the tower.

The method for uninstalling the nacelle may comprise one or more of the steps of:

- hoisting a tower pipe up to or towards the nacelle on the tower;

- uninstalling the front part of the nacelle from the tower;

- uninstalling the rear part of the nacelle from the tower;

- connecting the front part of the nacelle to the tower pipe;

- connecting the rear part of the nacelle to the tower pipe;

- hoisting the tower pipe down;

- disconnecting the front part of the nacelle from the tower pipe and lifting the front part of the nacelle away from the tower;

- disconnecting the rear part of the nacelle from the tower pipe and lifting the rear part of the nacelle away from the tower;

- removing the tower pipe from the tower.

In one embodiment of the method, the front and rear parts of the nacelle may be screwed to one and the same tower pipe. The front part of the nacelle may be at tached to a front part of the tower pipe, and the rear part of the nacelle may be at tached to a rear part of the tower pipe. The tower pipe may be permanently but mov- ably attached to the tower, or it may be detachably attached to the tower. The tower pipe may, for example, be disconnected and removed from the tower after the instal lation of the nacelle on the top of the tower, or it may be disconnected from the tower NIPO

WO 2021/173002 ^{3 1} PCT/N02021/050051 after the nacelle has been lowered and removed from the tower when the nacelle is being removed from the tower. The tower may comprise the tower pipe.

The front part of the nacelle may be connected to the rear part of the nacelle through part of the tower. For example, a drive line may run from the rotor attached to the front part of the nacelle to a generator in the rear part of the nacelle. The tower may have a hole, through which part of the drive line may join the front part of the nacelle to the rear part of the nacelle.

The hoisting device for hoisting the nacelle up and down may typically be a winch with a wire or a toothed rack in the longitudinal direction of the tower, but is not restricted to being one of the two examples mentioned.

In one embodiment, the tower may have several tower pipes, and each part of the nacelle may be connected to a separate tower pipe. To avoid unintended rotation by a tower pipe around the axis of the tower during the hoisting operation, the tower may have a guide rail along the longitudinal direction of the tower, to which the tower pipe, for example, may be connected.

In embodiments in which the wind turbine has a rotatable nacelle, the tower may typi cally have two tower pipes, one outside the other, arranged in such a way that they can be rotated mechanically relative to each other, the inner tower pipe being at tached to the tower and the outer one being attached to a nacelle or part of a nacelle.

A tower pipe can normally be placed, for example, above a position for a nacelle on the tower, below a position for a nacelle. A tower may have a tower pipe above and a tower pipe below the position of a nacelle on the tower. The position of the nacelle may be a position for the installation of a nacelle that is not installed on the tower, or a position in which a nacelle is installed on the tower.

The tower may have a horizontal opening for connecting a nacelle part to another na celle part, for example a front part of the nacelle to a rear part of the nacelle.

In embodiments of the invention, the nacelle may be lifted up above the tower and lowered onto the tower, so that the tower penetrates the nacelle. The nacelle may then be attached to a tower pipe, and then the tower pipe may be lowered over the tower, so that the tower penetrates the tower pipe. The nacelle and/or the tower pipe may then have a funnel-like shape, which can be used for guiding the nacelle and/or the tower pipe down over the tower. This may, for example, be a relevant solution in embodiments in which the tower can be lowered, in which the tower has a limited NIPO

WO 2021/173002 ³² PCT/N02021/050051 height, or in which sufficiently dimensioned lifting equipment for hoisting the nacelle and/or the tower pipe over a tall tower is available.

If the foundation for a floating apparatus for extracting energy from wind comprises the lifting means, this may simplify the operations further. Challenges connected to such operations, when carried out on a typical nacelle, are the considerable weight of the nacelle and relative movements between the tower of a wind turbine and a vessel with lifting means.

In a twenty-third aspect, a floating apparatus for extracting energy from wind is de scribed, the apparatus comprising a foundation and two wind turbines, the two wind turbines and their associated towers being erected from the foundation of the appa ratus and interconnected by at least one tension rod.

The two wind turbines may comprise a first wind turbine and a second wind turbine. The tension rod may join an upper part of the tower of the first wind turbine to a lower part of the tower of the second wind turbine. Several tension rods may connect the towers of the two wind turbines. For example, a first tension rod may join an upper part of the tower of the first wind turbine to an upper part of the tower of the second wind turbine, a second tension rod may join an upper part of the tower of the first wind turbine to a lower part of the tower of the second wind turbine, and a third ten sion rod may join a lower part of the tower of the first wind turbine to an upper part of the tower of the second wind turbine.

The two towers may each comprise a hinge, by which hinges the towers may change between a raised position and a lying position. The towers may be arranged in such a way that they can be laid/raised symmetrically relative to each other and a horizontal axis that runs parallel to a horizontal part of the foundation of the apparatus. The foundation of the apparatus may be any foundation in accordance with the sev enth, eighth or nineth aspect of the description, or another type of foundation. The wind turbines of the apparatus may be joined to each other and/or to a section, typi cally an outer section, of a horizontal part of the foundation through a plurality of ten sion rods to absorb bending moments. The towers of the two wind turbines may stand at an upward slope from the founda tion in the erected position, so that the towers extend away from each other from the bottoms of the towers towards the tops of the towers. This will allow the towers to stand close to each other on the foundation, whereas there is ample space for the blades of the wind turbines to rotate without any risk of colliding at the upper ends of NIPO

WO 2021/173002 ³³ PCT/N02021/050051 the towers.

The towers may be attached to each other and to the foundation via a solid supporting structure to absorb bending moments. The apparatus may have both a supporting structure like that and the tension rods mentioned earlier.

Any one of the apparatuses for extracting energy from wind, may comprise a control system. The control system may, for example, be adapted for controlling a rotor brake, angles of rotor blades, the resistance of a generator, the rotation of a founda tion, and/or the rotation of a nacelle and/or a rotor. The control system may comprise one or more sensors, for example for obtaining information on wind speed, wind direc tion, wave height, oceanic-current strength and oceanic-current direction, the pitch of the rotor blades, the rotary speed of the rotor, the position of the wind turbine and/or the orientation of the wind turbine. The information may be used in connection with the control through the control system, and/or the information may be gathered and transmitted to a receiver for other use, such as gathering meteorological data and/or data for use in, for example, the further developing of designs of apparatuses for ex tracting energy from wind.

A control system like that may be particularly advantageous for apparatuses with sev eral wind turbines, for reasons related to stability, among other things. The floating apparatus, with a rotatable foundation, can rotate in consequence of elemental forces, which include wind, oceanic currents and waves, in a direction that will normally place the transition piece and the wind turbine downstream of the anchor attachment in re lation to the direction of the wind.

In an apparatus that has a rotatable foundation and two or more wind turbines, the wind turbines of the apparatus may be affected by a wind in such a way that the ap paratus rotates in the horizontal plane until there is balance between the force im posed on the wind turbines by the wind in relation to the anchor attachment. The force from the wind on the wind turbines may also result in a downward force. Varying force on the wind turbines from the wind may result in different downward forces im posed on the apparatus and its foundation from the two or more wind turbines. This difference may, in turn, lead to a sideways tilt of the apparatus and its foundation.

The control system may comprise sensors for obtaining information from several wind turbines. The control system may further comprise a program for using information relating to, for example, forces affecting the apparatus, the orientation of the appa ratus, the position of the apparatus, the pitch of the rotor blades and the rotational NIPO

WO 2021/173002 ³⁴ PCT/N02021/050051 speed of the rotor to calculate the stability of the apparatus and whether control has to be carried out to improve the stability. The control may comprise increased or re duced braking of a rotor, changed resistance in a generator, changed pitch of rotor blades, rotation of a nacelle, rotation of a rotor, rotation of a wind-turbine tower, or rotation of the foundation, or other things.

The control system may also be used for controlling the foundation to improve or op timize the energy production of the apparatus in relation to the prevailing elemental forces, including forces from wind, oceanic currents and waves.

A control system like that can contribute to the stability of the apparatus so that the dimensions of the foundation can be limited. For example, the length and/or weight of the vertical part of the foundation may be reduced for an apparatus with such a con trol system relative to an apparatus without such a control system.

Any one of the floating apparatuses for extracting energy from wind in accordance with the twelfth aspect to the seventeenth aspect of the description and the twenty- third aspect of the description may comprise any feature of a part for a floating appa ratus for extracting energy from wind mentioned in connection with the methods. Any one of the wind turbines in accordance with the tenth or the eleventh aspect of the description may comprise any one of the features mentioned in connection with parts for a wind turbine mention in connection with the methods. Any one of the foundations in accordance with the seventh to the nineth aspect of the description may comprise any one of the features for a foundation mentioned in connection with the methods.

The term "tilt" recurs in the document. This term refers to a change in the position of an object relative to an axis or a plane or another object. For example, a tilt of the foundation is described. In that connection, "tilt" typically indicates a changed angle of a vertical part of the foundation relative to a horizontal plane, for example a horizontal plane given by a sea surface by calm sea. A "tiltable" upper end of a wind-turbine tower is an upper end whose position/angle may be changed relative to another part of the wind-turbine tower.

When a tension rod between an upper part of a wind turbine and a part of a founda tion is described, this tension rod may be attached to a connecting means on a front side of the rotor of the wind turbine and the blades of the wind turbine, what may be referred to as upstream of the blades in the wind when the wind is acting directly on the blades of the wind turbine. Other tension rods, for example tension rods that join together two towers, may be attached to the towers downstream of the blades. NIPO

WO 2021/173002 35 PCT/N02021/050051

A "tension rod" may be a wire, a chain, a fibre strap, or some other type of line or a form of rod which is suitable for connecting and absorbing forces from, for example, a tower and a horizontal part of a foundation for a wind turbine or two wind-turbine towers. In what follows, examples of preferred embodiments are described, which are visual ized in the accompanying drawings, in which:

Figure 1 illustrates a cross section of a floating apparatus for extracting wind en ergy, with the foundation in accordance with the first aspect of the in vention, and with a wind turbine standing on the foundation; Figure 2 shows an alternative embodiment of the apparatus with two wind tur bines, seen from the front;

Figure 3 shows an alternative embodiment of the apparatus with two wind tur bines, seen from above;

Figure 4 shows an alternative embodiment of the apparatus with one wind tur- bine, seen from above;

Figure 5 shows an alternative embodiment of the apparatus with a wind turbine, seen from the front;

Figure 6 shows a cross section of an alternative embodiment of the apparatus with a natural division into a foundation, an adapter piece and a tower; Figure 7 shows a cross section of a further alternative embodiment of the foun dation and the wind turbine, the wind turbine having a divisible nacelle and the apparatus comprising lifting means for lifting the parts of the nacelle towards or from the top of the tower;

Figure 8 shows a cross section of an embodiment of an upper adapter piece; Figure 9 shows a divisible nacelle which is mounted on an upper adapter piece which is penetrated by the tower;

Figure 10 shows a divisible nacelle which is mounted on an upper adapter piece, the nacelle being attached to a hoisting boom placed in the upper part of the tower; NIPO

WO 2021/173002 36 PCT/N02021/050051

Figure 11 shows an upper adapter piece in a lower position, the front and rear parts of the nacelle having been loosened from the upper adapter piece and being shown hoisted away from the tower;

Figure 12 shows a section of a further alternative embodiment of the apparatus, where a lift/lower tower is shown in its upper position with freely sus pended ballast hung off in the foundation;

Figure 13 shows a section of a further alternative embodiment of the apparatus, where a raise/lower tower is shown in its lower position, with freely sus pended ballast hung off in the foundation; Figure 14 shows a section of a further alternative embodiment of the apparatus, where a raise/lower tower is shown in its upper position, the nacelle having been tilted upwards to compensate for the tilt of the device;

Figure 15 shows an alternative foundation for a floating apparatus for extracting wind energy, seen from above, the foundation having a plurality of cor- rective arms, two of which being articulated on the transition piece, and the arms being connected to an anchor each;

Figure 16 shows an alternative foundation for a floating apparatus for extracting wind energy, seen from above, the foundation having three arms joined to a transition piece, one arm of which being non-articulatedly connect ed to the transition piece, the apparatus being anchored via an anchor attachment on an outer part of the non-articulated arm;

Figure 17 shows an alternative foundation for a floating apparatus for extracting wind energy, seen from above, the apparatus having three wind tur bines and three arms; Figure 18 shows a section of an anchor attachment belonging to a foundation for a floating apparatus for extracting wind energy, the anchor attachment comprising angle stabilizers.

Figure 19 shows an alternative embodiment of an apparatus with two wind tur bines, seen from the front, the apparatus having a hoisting tower in the middle, and the wind-turbine towers having a hinge each, and an upper part of the wind-turbine towers having been tilted into a lower position around the hinge; NIPO

WO 2021/173002 37 PCT/N02021/050051

Figure 20 shows the embodiment shown in figure 19, seen from the front, here with each of the towers raised into an upper position around the hinge;

Figure 21 shows an alternative embodiment of the apparatus with two wind tur bines, seen from the front, the apparatus having a hoisting tower in the middle, which, in an extension, also comprises a vertical leg, the upper parts of two wind-turbine towers being hinged to the hoisting tower and having been tilted into a lower position around the hinge;

Figure 22 shows the embodiment of the apparatus shown in figure 21, seen from the front, here with the hoisting tower raised and the wind turbines raised;

Figure 23 shows the embodiment of the apparatus shown in figure 21 and figure 22, seen from the front, with a hoisting tower in the middle which, in an extension, also comprises a vertical leg lowered into an operational posi tion, both wind-turbine towers having been raised into an upper position around the hinge;

Figure 24 shows an alternative embodiment of the apparatus with two wind tur bines, seen from the front, with a hoisting tower in the middle which, in an extension, also comprises a vertical leg, the tower being in a lower position with horizontal tower stays mounted on it, to which the nacelles are attached;

Figure 25 shows the embodiment shown in figure 24, seen from the front, the hoisting tower being in the upper position with horizontal tower stays mounted on it, to which the nacelles are attached;

Figure 26 shows an alternative embodiment of the apparatus with two wind tur bines, seen from the front, with a hoisting tower in the middle which, in an extension, also comprises a vertical leg, the upper part of the tower being connected to a hoisting mechanism having, as shown here, low ered horizontal tower stays, on which the nacelles are mounted, into a lower position; and

Figure 27 shows an alternative embodiment of the apparatus with four wind tur bines, seen from the front, in an operational position.

Please note that the figures are meant to illustrate the invention(s) described in the NIPO

WO 2021/173002 ^{3 8} PCT/N02021/050051 document, not necessarily to render the details of the illustrated objects accurately. The figures are not drawn to scale.

Figure 1 shows an embodiment of the foundation 1 in accordance with the first aspect of the invention in an operational position in a sea 900 with a sea surface 901, the foundation 1 having an anchor attachment 11, a transition piece 12, a vertical, correc tive leg 13 and a horizontal, corrective arm 14 connecting the anchor attachment 11 to the transition piece 12.

In the embodiment, the leg 13 and the arm 14 are cylinder-shaped, both having a plurality of chambers 16 which can selectively be filled with water 162 or other ballast heavier than water, or with air 161 or some other substance lighter than water, to adjust the weight and/or the centre of buoyancy of the foundation. Normally, the con tents of the chambers 16 will be of such a mass that the arm 14 is sufficiently heavy to lie below the sea surface, but in some cases, it may be relevant to change the con tents of the chambers 16 so that the arm 14 may be semisubmersible. In the embodiment in figure 1, the leg 13 is connected to the arm 14 at a first end of the arm 14, whereas the transition piece 12 is connected to the arm 14 at a second, opposite end of the arm 14.

On the transition piece 12, there stands a wind turbine 2. The wind turbine has a tow er 21, a nacelle 22, a rotor 23 and blades 24. Together with the foundation 1, the wind turbine 2 constitutes a floating apparatus 100 for extracting energy from wind.

Here, the horizontal, corrective arm 14 is shown with air 161 in three chambers 16 nearest to the transition piece 12, and one chamber nearest to the leg 13 for absorb ing a considerable part of the weight of the transition piece 12 and the leg 13. Further, the horizontal, corrective arm 14 has water 162 in the remaining other chambers 16. The number of chambers 16 and the distribution of air 161 and water 162 in them are shown only to illustrate that it is possible to have a selective distribution of weight and buoyancy in the chambers 16, it is not necessarily representative of what the distribu tion will look like in a stable operational embodiment.

In the embodiment shown, the vertical, corrective leg 13 has a lowermost section 15 with a material of a very high specific weight.

The foundation 1 is anchored by means of anchors that are connected to the anchor attachment 11 of the foundation 1 via anchor lines 31. The anchor attachment 11 in cludes an anchor tower 70 projecting up from the arm 14 and above the sea surface NIPO

WO 2021/173002 ^J ^ PCT/N02021/050051

901. This anchor tower 70 may counteract forces to which the foundation 1 is subject ed from an anchor line 31, by the anchor tower 70, by being pulled downwards, dis placing water and thereby providing increased buoyancy.

By the foundation 1 being anchored at the anchor attachment 11 having a horizontal distance to and being rigidly connected to the transition piece 12, the transition piece 12 may rotate around the anchor attachment 11. The foundation 1 is built and an chored in such a way that it will be rotating naturally in consequence of forces from wind, currents and/or waves. The embodiment of the foundation 1 includes a motor ized propeller 17, which may be used for controlled rotation of the foundation 1. The propeller 17 may, for example, be used for rotating the foundation back into a starting position if, for example, the foundation has rotated more than 1 rotation from the starting position. This may be advantageous, for example, in order to avoid twisting of any cables and/or lines and/or the like connected to the apparatus 100. In most cases, the foundation 1 will rotate naturally in such a way that the main wind direction will be identical to the direction from the anchor attachment 11 to the transition piece 12, so that the transition piece 12 will stay substantially downstream of the anchor attach ment 11 in a wind that acts on the foundation. Therefore, the wind turbines 2 are mounted in the way shown in figure 1, with the front of the wind turbine with the rotor 23 and blades 24 facing the anchor attachment 11, so that the blades 24 are allowed to stand substantially in an optimum position, at 90 degrees to the wind direction.

To reduce a bending moment between the corrective arm 14 and the tower 21, the apparatus 100 further includes a first tension rod 43 which extends from the first end of the arm, at the anchor tower 70, to a front portion of the nacelle 22 at the rotor 23. To reduce a bending moment between the corrective arm 14 and the corrective leg 13, the apparatus 100 further includes a second tension rod 44 which extends from a lower part of the corrective leg 13 to the corrective arm 14 near the transition piece 12.

In the embodiment, the transition piece 12 of the foundation 1 has a vertical adapter- part section 121 and a horizontal adapter-part section 122. The wind turbine 2 stands on the vertical section 121, and the horizontal, corrective arm 14 is rigidly attached to the horizontal section 122. By tough conditions, for example by high waves and strong wind, the foundation 1 may be subjected to strong bending moments and/or shear forces between the vertical part 121 and the horizontal part 122. Therefore, the foun dation 1 is also provided with a structural element 123 for absorbing such forces. In the embodiment, the transition piece 12 further has an open lower end 125. The NIPO

WO 2021/173002 ^{4 0} PCT/N02021/050051 open solution allows water to move in the lower end 125, which reduces the lift direct ly below the wind turbine 2 and will be stabilizing, especially vertically, as, because of the design, waves will have less effect on the vertical position of the wind turbine 2 as the waves can freely enter the transition piece 12 and the tower 21.

Figure 2 shows an embodiment of a floating apparatus 100 for extracting energy from wind, seen from the front in an operational position, with the foundation 1 with two wind turbines 2. Each wind turbine 2 has a tower 21 which is articulated into an upper tower part 211 and a lower tower part 212. The two upper tower parts 211 are con nected with a wire 73 and the two lower tower parts with a stay 74. The foundation has a vertical, corrective leg 13 and a horizontal, corrective arm 14 which are both joined to a transition piece 12.

Figure 3 shows an embodiment of a floating apparatus 100 for extracting energy from wind, seen from above in an operational position, the apparatus 100 having two wind turbines 2 erected from a foundation 1. The two wind turbines 2 have a tower 21 each. The towers 21 are connected via a wire 73. The foundation 1 has a corrective, horizontal arm 14, and an anchor point 11 connected to a first end of the arm 14 and a transition piece 12 for carrying the wind turbines 2 connected to a second, opposite end of the arm 14. The apparatus 10 further has one tension rod 43 extended from the rotor 23 of each wind turbine 2 to the anchor point 11.

Figure 4 shows an embodiment of the floating apparatus 100 seen from above in an operational position, the apparatus comprising a wind turbine 2 and a foundation 1, the wind turbine 2 being erected on a transition piece 12 belonging to the foundation 1. This apparatus 100, too, has a tension rod 43 extended between an anchoring point 11 belonging to the foundation 1 and the rotor 23 of the wind turbine 2 to absorb bending forces.

Figure 5 shows an embodiment of the apparatus 100 from the front in an operational position, the apparatus having a wind turbine 2 erected on a foundation 1 for a wind turbine 2. The apparatus further comprises a ballast element 45 which is movably suspended from the foundation 1, for stabilizing the foundation 1. The ballast element 45 has a centre hole which is penetrated by a vertical, corrective leg 13 belonging to the foundation 1. When the foundation 1 is tilted, the ballast element 45 will come into contact with the corrective leg 13 and subject the corrective leg 13 to a force that will have a corrective effect on the foundation 1.

Figure 6 illustrates a lower adapter piece 75, housing a generator 25, for connecting a NIPO

WO 2021/173002 PCT/N02021/050051 tower 21 to a transition piece 12. In the figure it is illustrated that the lower adapter piece 75 is a separate part in relation to the tower 21 and the transition piece 12. The generator 25 can be turned so that it stands on edge in the lower adapter piece 75 in order to be retrieved from the lower adapter piece 75, for example for repair or for the generator 25 to be changed. The lower adapter piece 75 may be attached to the tran sition piece 12 and to the tower 21, for example by being welded or bolted thereto.

Figure 6 further shows an embodiment in which the nacelle 22 of the wind turbine is permanently rotationally rigidly attached to the tower 21 by, in this embodiment, be ing bolted to it. In other embodiments, the nacelle 22 may, for example, be welded to it. In alternative embodiments, the nacelle 22 may be movably attached to the tower 21 but with limited movability. A rotationally rigid connection potentially increases the structural strength of the connection between the tower 21 and the nacelle 22, seen in relation to typical rotationally non-rigid connections.

The wind turbine 2 has an angular gear 230, and a drive line 26 that runs from the rotor 23 to the generator 25 to transmit rotational forces to the generator 25 for the extraction of electrical energy. The nacelle 22 is further shown penetrated by the tow er 21, with the angular gear 230 placed in a cavity in the tower 21 with a shaft in to the rotor 23.

The rotationally rigid connection between the tower 21 and the nacelle 22 allows the generator 25 to be placed in the lower adapter piece 75 at a distance from the nacelle 22. In this embodiment, the generator 25 is advantageously placed right down at the transition piece 12 of the foundation 1. Such a positioning makes the generator 25 be more easily accessible for maintenance and/or repair. Another very important ad vantage by the generator 25 being moved down into the lower adapter piece 75, be low the tower 21, is that the diameter of the transition piece 12 may be utilized. Fur ther, by the weight of the generator 25 being moved closer to the sea surface, the potential tilting forces that must be taken into consideration with a view to the stabil ity of the foundation will be considerably reduced. Thereby the foundation 1 may have sufficient stability with a shorter and/or lighter, horizontal, corrective arm 14 and/or a vertical, corrective leg 13, seen in relation to a foundation for an apparatus 100 with the generator 25 placed in the nacelle of the wind turbine 2.

The foundation 1 shown in figure 6 further has a ballast tank 141 placed on an oppo site side of the transition piece 12 relative to the anchor attachment 11 of the founda tion 1, which may selectively be filled or emptied of ballast, the ballast being, for ex ample, sea water. This ballast tank 141 can typically be filled with water under normal NIPO

WO 2021/173002 ⁴² PCT/N02021/050051 conditions but be emptied of water to ensure buoyancy to the rear of the wind turbine 2 by strong wind to counteract tilt.

Figure 7 further shows an alternative embodiment of the apparatus 100, and of the foundation 1 and the wind turbine 2, the nacelle 22 having been lowered into a lower position. In this embodiment, the wind turbine has a divisible nacelle 22 which is pen etrated by the tower 21. The nacelle 22 has a front part 221 and a rear part 222 which are mounted on an upper nacelle carrier 92. The apparatus 100 comprises lifting means 27 which include a winch with sheaves and wires, which can be used to carry out lifting of the parts 221, 222 of the nacelle 22.

Figure 7 further shows that the angular gear 230 is in the rear nacelle part 222 and disengaged from the drive shaft 261. The front nacelle part 221 and the rear nacelle part 222 can then be released from the upper nacelle carrier 92.

Figure 8a shows an upper adapter piece 90. The adapter piece comprises a tower pipe 91 which can be placed around part of a tower 21 to carry a nacelle 22 on the tower 21. The tower pipe 91 is shown here with an outward cone for simplifying the position ing of the tower pipe 91 around the tower 21. The tower pipe 91 may be attached to the tower 21 to carry a load of the nacelle 22. The tower pipe comprises an upper na celle carrier 92 and a lower nacelle carrier 93 and also a tilting mechanism 80 which, here, includes a hydraulic cylinder 81 and a hinge 82 to allow tilting of the upper na celle carrier 92 relative to the lower nacelle carrier 93, and also an upper rotary means 96 and an upper bearing 94 for rotating the upper nacelle carrier 92 relative to the lower nacelle carrier 93, and a lower rotary means 97 and a lower bearing 95 for rotating the lower nacelle carrier 93 on the tower pipe 91 and relative to the tower 21. By having both the upper rotary means 96 and the lower rotary means 97, the tower pipe has a redundant rotary mechanism.

Figure 8b shows another embodiment of an upper adapter piece 90, the upper adapter piece comprising a tower pipe 91 which can be placed around part of a tower 21. The tower pipe 91 can be attached to a tower for a wind turbine and can carry the load of a nacelle 22. The tower pipe 91 comprises an upper nacelle carrier 92 and also an up per bearing 94 for rotating the upper nacelle carrier 92 around the tower pipe 91 by means of an upper rotary means 96.

Figure 9 shows an embodiment of a divisible nacelle 22 in the upper position thereof, mounted on an upper adapter piece 90 which is penetrated by a tower 21. The rear part 222 and the front part 221 of the nacelle 22 are permanently mounted on an up- NIPO

WO 2021/173002 ^{4 3} PCT/N02021/050051 per nacelle carrier 92 belonging to the adapter piece 90, and the tower pipe 91 is permanently mounted to the tower 21. The tower 21 comprises a lifting means 27 mounted on an upper end of the tower 21. Figure 9 further shows a rotor 23 attached to the front part 221 of the nacelle 22, and a rigid attachment structure 231 mechani cally attached to a stationary part of the rotor 23. The attachment structure 231 con nects a tension rod to the stationary part of the rotor and thereby to the nacelle 22 and the upper part of the tower 21. The tension rod 43 is further attached to a device 251 which is designed to take wind forces acting on the nacelle 22.

Figure 10 illustrates a nacelle 22 in a middle position mounted on an upper adapter piece 90 which is penetrated by a tower 21. The adapter piece 90 comprises a tower pipe 91 and an upper nacelle carrier 92. The nacelle 22 is permanently mounted on the nacelle carrier 92. The tower pipe 91 has been loosened from the tower 21 and may thus be moved up and down. The tower 21 comprises a lifting means 27 which comprises sheaves and a hoisting line. The hoisting line 27 is attached to the nacelle 22 and carries the weight of the nacelle 22. This alternative embodiment shows what is usually called a "direct drive configuration" in which the generator 25 constitutes the principal weight. Figure 10 further shows an attachment structure 231, which is me chanically attached to the tower 21, and a tension rod 43 attached to the attachment structure 231. Here, the tension rod 43 is shown resting against a stationary part of a rotor 23 belonging to the nacelle 22. The attachment structure 231 is attached to the tension rod 43 which is designed to take wind forces that act on the nacelle 22.

Figure 11 shows a tower pipe 91 with a nacelle 22 in a lower position, the tower pipe 91 being penetrated by a tower 21. The tower pipe 91 rests against a lower part of the tower 21. The nacelle 22 has a front part 221 and a rear part 222 which, in the figure, have been loosened from the upper nacelle carrier 92 and which are each hanging on a respective hoisting line 26. Figure 11 further shows a rotor 23 with a rotating part 232 and a swivel 233 rotatably attached to the rotating part 232 of the rotor 23 so that the swivel 233 can rotate relative to the rotating part 232 of the rotor 23. The swivel 233 functions as an attachment structure 231 for joining a tension rod 43 to the tower 21 via the nacelle 22 via the rotor 23.

Figure 12 further shows an alternative embodiment of the foundation 1 and the wind turbine 2. In this embodiment, the transition piece 12 has an opening to allow vertical movement of the wind turbine 2, which allows the tower 21 to be lowered into a water mass 900. The foundation 1 has a ballast element 45 which is movably suspended on a wire from the transition piece 12 of the foundation 1. The ballast element 45 is not NIPO

WO 2021/173002 PCT/N02021/050051 rigidly attached to the foundation 1 but is penetrated by a corrective leg 13 belonging to the foundation 1. The ballast element 45 will therefore have a corrective effect on the foundation 1 in that it will exert a force on the corrective leg 13 of the foundation 1, which, in this embodiment, is an extension of the tower 21, when the foundation 1 is tilted.

A lower part of the tower 21 may then, when submerged, function as a second, cor rective, vertical leg 13. The tower 21 also has a pressure-tight chamber 126 which can selectively be filled with, for example, air or water.

The foundation also has a lifting means 27 in a winch for moving the wind turbine 2 vertically, and a locking ring 41 for locking the tower 21 in a vertical position.

In this embodiment, the wind turbine 2 has a nacelle 22 which can be divided into a front part 221 and a rear part 222, with a generator 25 in the rear part 222 of the nacelle 22. The wind turbine 2 further has drive line 26 extending from the rotor 23, through the front part 221 of the nacelle 22 and the tower 21 to the generator 25. The front part 221 of the nacelle and the rear part 222 of the nacelle each have a coupling 223 for connecting the nacelle part 221, 222 to the tower 21.

The drive line has three parts: a front drive-line part 261 in the front nacelle part 221, a middle drive-line part 262 in the tower 21, and a rear drive-line part 263 in the rear nacelle part 222. These three drive-line parts 261, 262, 263 are connected to each other when the front nacelle part 221 and the rear nacelle part 222 are connected to the tower 21.

If the nacelle 22 is to be lowered to a lower level, the middle drive-line part 262 must be disconnected from the front drive-line part 261 and the rear drive-line part 263. Then the nacelle 22 can be lowered to the transition piece 12.

The wind turbine 2 may be lowered for, for example, equipment to be removed or in stalled, or for equipment, such as the nacelle 22, the rotor 23 or other equipment, to be maintained, or it may be lowered to improve the stability, by moving the tower 21 further down. As the lower part of the tower 21 functions as the corrective leg 13 of the foundation 1, a lowering of the tower will result in a lengthening, into the water mass, of the corrective leg 13.

Figure 13 shows the same embodiment of the wind turbine 2 and foundation 1 as fig ure 12, but with the wind turbine 2 considerably lowered so that it is in a lower posi tion. The tower 21 in figure 13, which is in a lower position than that shown in figure NIPO

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12, with a larger part of the tower 21 submerged in water, holds water in a greater portion of the chamber 126 than the tower 21 shown in figure 12. The wind turbine 2 can be lowered for, for example, equipment to be removed or installed, or for equip ment, such as the nacelle 22, the rotor 23 or something else, to be maintained, or it may be lowered to improve the stability.

Figure 14 shows an alternative embodiment of the apparatus 100, with a foundation 1 and a wind turbine 2. The wind turbine has a penetrable nacelle 22, which is penetrat ed by the tower 21 of the wind turbine. The nacelle 22 is further tiltably mounted on the tower 21, so that the nacelle 22 and thereby also blades mounted on the nacelle 22 can be held more stably vertically when the foundation 1 is tilted, and so that the nacelle 22 may, for example, be tilted to create a larger distance between the blades 24 and the tower 21 by strong wind.

In this embodiment, the foundation 1 further has an anchor attachment 11, a first tension rod 43 extending from the anchor attachment 11 of the foundation 1 to a front portion of the nacelle 22 and a second tension rod 44 that extends from the anchor attachment 11 of the foundation 1 to a ballast element 45 hanging on a wire from the transition piece 12 of the foundation 1. The ballast element 45 is not rigidly attached to the foundation 1 but will have a corrective effect on the foundation in that it will exert a force on the corrective leg 13 of the foundation 1, which, in this embodiment, is an extension of the tower 21, when the foundation 1 is tilted.

Figure 15 shows an alternative embodiment of the apparatus 100, including an alter native embodiment of a foundation 1, in which the foundation 1 does not have a cor rective leg but, instead, has a first substantially horizontal, corrective arm 51, a sec ond substantially horizontal, corrective arm 52 and a third substantially horizontal, corrective arm 53. The second arm 52 and the third arm 53 are each connected to a transition piece 12 via a respective hinge 54. The hinge 54 allows some movement of said arms 52, 53 relative to the first arm 51 and relative to the transition piece 12 of the foundation 1 in the horizontal plane. The transition piece 12 carries a wind turbine 2. Please note that when "movement in the horizontal plane" is described, then this ap plies when the foundation is lying flat, in a normal position, on calm water. When the foundation 1 is tilted, the plane will be tilted correspondingly.

Each of the substantially horizontal, corrective arms 51, 52, 53 are mounted on an anchor tower 70 in connection to the anchor attachment 11, and are anchored via the NIPO

WO 2021/173002 ^{4 6} PCT/N02021/050051 anchor attachment 11 and an anchor line 31 connected to an anchor 3. The arms 51, 52, 53 are further interconnected via hawsers 55. The hawsers 55 restrict movement of the arms 51, 52, 53 relative to each other. In combination with the hinges, the hawsers make the arms able to move somewhat but the movement be limited. Alter native embodiments without hawsers, with or without other movement-restricting means, such as spring-based movement-restricting means, are conceivable.

Figure 16 shows an alternative foundation 1 with a first horizontal, corrective arm 51, a second horizontal, corrective arm 52 and a third horizontal, corrective arm 53. The second arm 52 and the third arm 53 are each connected to a transition piece 12 with a respective hinge 54. The hinges 54 allow some movement of said arms 52, 53 relative to the transition piece 12 in the horizontal plane. The corrective arm 51 is rigidly at tached to the transition piece 12 carrying a wind turbine 2.

The first arm 51 has an anchor attachment 11 and is anchored via the anchor attach ment 11 and an anchor line 31 connected to an anchor 3 so that the foundation 1 can rotate around the anchor attachment 11 on the corrective arm 51. The arms 51, 52,

53 each have a first end and a second end. The arms are connected to each other at their second ends, via hawsers 55, and are connected to the foundation 1 at their first ends. The hawsers 55 restrict movement of the arms 51, 52, 53 relative to each other.

Figure 17 shows an alternative embodiment of the apparatus 100, which includes an alternative foundation 1 and three wind turbines 2. The foundation 1 does not have a corrective leg, but has a first substantially horizontal, corrective arm 51, a second substantially horizontal, corrective arm 52 and a third substantially horizontal, correc tive arm 53. The second and third arms 52, 53 are each connected to the first correc tive arm 51 via a respective hinge 54. The hinges 54 allow some movement of the second arm 52 and third arm 53 relative to the first corrective arm 51 in the horizon tal plane. Each of the horizontally corrective arms 51, 52, 53 are connected to a tran sition piece 12.

The first corrective arm 51 has a first end an opposite second end, the first end having an anchor attachment 11, and the second end being connected to the transition piece 12 of the foundation 1. The foundation 1 is anchored via the anchor attachment 11, connected to an anchor line 31 connected to the anchor 3. In that way the foundation 1 can rotate around the anchor attachment 11.

The second arm 52 and the third arm 53 are connected to the first arm 51 and to the transition piece 12 by the use of hawsers. The hawsers 55 restrict movement of the NIPO

WO 2021/173002 ^{4 7} PCT/N02021/050051 arms 51, 52, 53 relative to each other.

One of the wind turbines 2 is erected on the transition piece of the foundation 1, one is erected on an outer part of the second arm 52, and one is erected on an outer part of the third arm 53. Each of the second arm 52 and the third arm 53 has a transition piece 12 for carrying their respective wind turbines 2.

Figure 18 shows an embodiment of an anchor attachment 11 belonging to a founda tion 1 for a floating apparatus 100 for extracting energy from wind. The anchor at tachment 11 includes an angle stabilizer 32, the purpose of which is to stabilize an angle of attack B from the anchor line 32 to the floating apparatus 100, an anchor ring 34 and an anchor-attachment column 35. The angle stabilizer 32 consists of an upper anchor point 36, a lower anchor point 37, a rigid, corrective stabilizer arm 38 and a weight 33. The upper anchor point 36 is connected to the anchor ring 34. The anchor ring 34 is rotatably attached to the anchor-attachment column 35 which is, in turn, attached to a corrective arm 14 belonging to the foundation 1. It may be advanta geous to have a plurality of anchors 3 with associated anchor lines 31 connected to angle stabilizers 32, to stabilize the direction of force from the anchor line 31 on the anchor attachment 11 and to keep the position of the foundation 1 stable. In figure 18, two anchors 3 are shown, but it may be advantageous to have more than two, for example three or four or five anchors 3. The angle of attack B may be designed at 0 to 180 degrees and will typically be project-specific based on depth conditions, among other things. A typical angle B under normal conditions will be in the interval of 20 to 45 degrees.

The angle stabilizers 32 comprise a rigid structure 39. In the embodiment shown, the rigid structure 39 is shaped like a rectangular triangle. A first corner of the rigid struc ture 39 is connected to the anchor ring 34, a second corner of the rigid structure 39 is connected to a weight 33, and a third corner of the rigid structure 39 is connected to an anchor line 31. The weights 33, in turn, are connected to each other. The weights 33 are connected to each other and to the rigid structure 39 of the angle stabilizer via rigid, stabilizing stays 38. Alternatively, the weights 33 may be connected to each other and/or to the rigid structure 39 via wires or chains, for example.

Figure 19 shows an embodiment of a floating apparatus 100 for extracting energy from wind, in which two wind turbines 2 are placed on one foundation 1. The wind turbines 2 each have a tower 21 with an upper part 211 and a lower part 212 which are hinged together through a hinge 72. The lower part of the lower tower 21 is at tached to the transition piece 12. The towers are attached to each other at the tops of NIPO

WO 2021/173002 ^{4 8} PCT/N02021/050051 their lower parts 212 through a brace 78. The apparatus 100 further has a hoisting tower 79 which is temporarily attached to the transition piece 12 and to the lower towers 21. In the embodiment, the hoisting tower 79 advantageously stands in the centre between the two towers and perpendicularly to the hinges 72. The hoisting tower 70 has a hoisting device 77, which can pull at two hoisting lines 76. The hoisting lines extend from the hoisting device 77, over respective upper sheaves and on to respective towers 21, at the upper parts 211 thereof, where they are attached. In the division between the upper part 211 and the lower part 212 of the tower 21, there is a flange on each side (not shown). When the hoisting device 77 pulls at the two hoisting lines 76, the two upper tower parts 211 will be tilted in parallel around their respective hinges 72 towards upper operational positions. The hinges 72 will position the two flanges in positions in which they are optimally arranged for being screwed or welded together when the towers 21 have reached their operational, raised positions. The hoisting device 77 may pull at the two hoisting lines 76 individually to maintain stabil ity.

Figure 20 shows the same as figure 19 but now with the two towers 21 raised into an upper position, in which the upper tower part 211 and the lower tower part 212 can be joined together, and the two towers can be attached to each other with the wire 73. The hoisting tower 79 will typically be removed when the towers 21 have been raised into operational positions.

Figures 21, 22 and 23 show an embodiment of a floating apparatus 100 for extracting energy from wind, in which two wind turbines 2 are placed on a foundation 1 that comprises, among other things, a ballast element 45 which can be raised and lowered. The ballast element 45 is shown in an upper position, hung off in the transition piece 12 in figures 21 and 22. The same apparatus 100 is also shown in figure 23. The ap paratus 100 has two wind-turbine towers 21, and a central, supporting tower 215. The central tower 215 can be raised and lowered vertically. A lower part of the central tower 215 functions as a vertical, corrective leg 13 for the foundation 1. The founda tion 1 includes a transition piece 12 for carrying the wind turbines. The transition piece 12 has an opening which is penetrated by the central tower 215. The central tower 215 also penetrates the ballast element 45, which, like the transition piece, has an opening for such penetration. In figure 23, the central tower 215 has been lowered into a low operational position, like the ballast 45.

The two wind-turbine towers 21 of the apparatus 100 are hingedly joined to the cen tral tower 215 and can, through the hinges 72, be laid down or raised by means of NIPO

WO 2021/173002 ^{4 9} PCT/N02021/050051 lifting means that include lifting wires 28 connected to an upper part of the central tower 215 and an upper part of each of the two wind-turbine towers 21.

Figure 23 shows the apparatus 100 in an operational position, in which the central tower 212, like the ballast element 45, has been lowered into a low position. The rais ing and lowering of the central tower 215 are done by moving water out of or into one or more chambers in the central tower 215, primarily in a lower part of the central tower 215, by using means suitable for the purpose. This may be, for example, means that include a pump (not shown). In the raised positions, the wind-turbine towers 21 can be joined to each other by the use of one or a plurality of lifting wire(s) 28 or, for example, by the use of stays.

Figures 24 and 25 show two alternative embodiments of a floating apparatus 100 for extracting energy from wind, in which two wind turbines 2 are placed on one founda tion 1. The two wind turbines are connected to each other and to a common, central tower 215 via a horizontal tower stay 213 each and a connecting unit 214. Figure 25 shows the apparatus 100 in an operational position, whereas figure 24 shows the ap paratus 100 with lowered wind turbines 2. The raising and lowering of the central tow er 215 can typically be done by, respectively, evacuating water from and filling water into the legs 13 in order thus to change the buoyancy of the central tower 215. The two tower stays 213 are connected, in outer parts, to an upper part of the central tower 215, and, in figure 25, to a transition piece 12 belonging to the foundation 1.

Figure 26 shows an alternative embodiment of a floating apparatus 100 for extracting energy from wind, in which two wind turbines 2 are placed on one foundation 1. The two wind turbines are connected to each other and to a common, central tower 215 via a horizontal tower stay 213 each and a connecting unit 214. The apparatus has a hoisting device / lifting means 77 which is connected to two wires 76 which are at tached, via two sheaves at the top of the central tower 215, to a wind turbine 2 each, at the nacelle (not shown) of the wind turbine. The hoisting device 77 may raise and lower horizontal tower stays 213 from a lower service position into an upper opera tional position.

Figure 27 shows further embodiments of the floating apparatus 100 for extracting en ergy from wind in one of several possible configurations in which more than two wind turbines 2 are placed on one foundation 1.

It should be noted that all the above-mentioned embodiments illustrate the invention, but do not limit it, and persons skilled in the art may construct many alternative em- NIPO

WO 2021/173002 ° ^u PCT/N02021/050051 bodiments without departing from the scope of the attached claims. In the claims, reference numbers in brackets are not to be regarded as restrictive.

The use of the verb "to comprise" and its different forms does not exclude the pres ence of elements or steps that are not mentioned in the claims. The indefinite article "a" or "an" before an element does not exclude the presence of several such elements.

The fact that some features are indicated in mutually different dependent claims does not indicate that a combination of these features cannot be used with advantage.

Claims

NIPO WO 2021/173002 51 PCT/N02021/050051 C l a i m s

1. A floating foundation for an offshore wind turbine, wherein the foundation comprises a transition piece for carrying the wind turbine, and a stabilizing part for stabilizing the transition piece with or without the wind turbine, the stabilizing part comprising an equal to or approximately horizontal part and an equal to or approximately vertical part which are both correctively joined to the transition piece, the vertical part comprising a corrective leg for projecting downwards in a water mass when the foundation is in an operational position, the horizontal part comprising an anchor attachment and a corrective arm, the foundation being formed with the anchor attachment attached to the corrective arm at a distance from the transition piece, so that, in an opera tional position, when the foundation is anchored, the transition piece can ro tate around the anchor attachment when influenced by elemental forces like forces from wind, waves and/or currents.

2. The floating foundation in accordance with claim 1, wherein the vertical part and/or the horizontal part are rigidly and permanently attached to the tran sition piece, directly or via another rigid structure.

3. The floating foundation in accordance with claim 1, wherein the horizontal part is attached to the transition piece via a hinge.

4. The floating foundation in accordance with claim 1, claim 2 or claim 3, wherein the anchor attachment and the transition piece are each attached to a respective end of the arm.

5. The foundation in accordance with any one of claims 1 to 4, wherein the an chor attachment comprises parts of or all of the vertically stabilizing part.

6. The foundation in accordance with any one of claims 1 to 5, wherein the an chor attachment comprises the leg, and wherein the leg therefore is at a horizontal distance from the transition piece.

7. The foundation in accordance with any one of claims 1 to 6, wherein the foundation has an opening in the transition piece to allow water from a wa ter mass, on which the foundation is meant to float, to enter through the opening and/or to allow a wind-turbine tower to be raised and lowered through the opening. NIPO

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8. The foundation in accordance with any one of claims 1 to 7, wherein the arm and/or leg of the foundation may comprise one or more chambers which can selectively be willed with or emptied of ballast so that the centres of buoy ancy and gravity can be adjusted.

9. The foundation in accordance with any one of claims 1 to 8, wherein the an chor attachment comprises an anchor tower, the anchor tower being perma nently attached to the corrective arm so that, in an operational position, an upper part of the anchor tower is normally above a surface of a water mass and, in an operational position, a lower part of the anchor tower is normally below the surface of the water mass.

10. The foundation in accordance with claim 9, wherein the anchor tower has a cavity for accommodating control systems and transformers for power pro duction for a wind turbine.

11. The foundation in accordance with claim 10, wherein the cavity accommo dates one or more control systems and/or one or more transformers for power production for a wind turbine and/or the power production of a wind farm.

12. The foundation in accordance with any one of claims 9 to 11, wherein the anchor tower comprises a landing place for a flying device, such as a drone or a helicopter.

13. The foundation in accordance with any one of claims 1 to 12, wherein the foundation comprises a rudder for manipulating the influence of a current on a rotation of the foundation.

14. The foundation in accordance with any one of claims 1 to 13, wherein the foundation comprises one or more water brakes for braking vertical move ment of the foundation.

15. A ballast element for adding ballast to a foundation for a wind turbine and corrective force on the foundation when the foundation is tilted, wherein the ballast element is formed with a hole for receiving a corrective leg belonging to the foundation, and the ballast element comprises connecting means in order to be movably suspended from a bottom side of the foundation. NIPO

WO 2021/173002 ⁵³ PCT/N02021/050051

16. An angle stabilizer for a foundation for a floating apparatus for extracting energy from wind, for stabilizing the force direction of a force from an an chor line acting on the foundation, wherein the angle stabilizer comprises a rigid angle-stabilizer structure and a weight connected to the rigid angle- stabilizer structure, the angle-stabilizer structure being arranged to be mov- ably connected to the foundation, and the angle-stabilizer being arranged to be connected to the anchor line.

17. The foundation in accordance with any one of claims 1 to 14, wherein the foundation comprises the ballast element in accordance with claim 15, the ballast element being movably joined to a rigid structure belonging to the foundation, with the leg penetrating the hole of the ballast element in a way that will make the ballast element come into contact with and have a correc tive effect on the leg and thereby also have a corrective effect on the foun dation when the foundation is tilted beyond a certain degree.

18. The floating foundation in accordance with any one of claims 1 to 14 or 17, wherein the foundation further comprises a second corrective arm, at least one of the two corrective arms comprising a hinge and being articulatedly joined to the transition piece via the hinge to allow movement of the at least one of the two corrective arms in the horizontal plane.

19. The floating foundation in accordance with claim 18, wherein the foundation further comprises at least one further corrective arm.

20. The floating foundation in accordance with claim 19, wherein at least one of the at least one further corrective arms comprises a hinge and is articulated ly joined to the transition piece via the hinge to allow movement of the at least one of the at least one further corrective arms in the horizontal plane.

21. The floating foundation in accordance with any one of claims 1 to 14, or 17 to 20, wherein the foundation comprises the angle stabilizer in accordance with claim 16, the angle stabilizer being movably suspended from or at the anchor attachment.

22. The floating foundation in accordance with any one of claims 1 to 14 or 17 to 21, wherein the leg is joined to the corrective arm at a horizontal distance from the transition piece. NIPO

WO 2021/173002 ⁵⁴ PCT/N02021/050051

23. The floating foundation in accordance with claim 22, wherein the leg is joined to an outer end of the corrective arm, at or in connection to the an chor attachment.

24. A floating apparatus for extracting energy from wind, the apparatus com prising a foundation in accordance with any one of claims 1 to 14 or 17 to 23 and a wind turbine.

25. The floating apparatus in accordance with claim 24, wherein the apparatus further comprises a tension rod extended between an upper part of the wind turbine and an outer part of the horizontal part of the foundation to absorb a bending moment acting on the structure of the apparatus.

26. The floating apparatus in accordance with claim 24 or 25, wherein the appa ratus further comprises a tension rod extended between a lower part of the vertical part of the foundation and an outer part of the horizontal part of the foundation to absorb a bending moment acting on the structure of the appa ratus.

27. A method for stabilizing a foundation for a wind turbine, wherein the method comprises the steps of:

- providing a foundation in accordance with any one of claims 1 to 14 or 17 to 23;

- anchoring the foundation via the anchor attachment in such a way that the transition piece can rotate around the anchor attachment defining a centre of the rotation, to orient itself in a favourable position; and

- letting the foundation orient itself, as a result of influence from elemental forces, until the transition piece of the foundation is downwind of the anchor attachment, so that the corrective arm stabilizes the transition piece against elemental forces in the direction of the wind.

28. A tower for a wind turbine for a floating foundation, wherein the tower has an inner cavity and an opening to the sea to receive water from a water mass into the inner cavity.

29. A rotor for a wind turbine, wherein the rotor comprises a connecting means for connecting the rotor, and thereby an upper part of the wind turbine, to one or more tension rods or one or more wires or the like. NIPO

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30. The rotor in accordance with claim 29, wherein the rotor comprises a swivel rotatably attached to an outer surface of the rotor, the swivel comprising the connecting means.

31. The rotor in accordance with claim 30, wherein the rotor has a central hole through the rotor and a connecting means for penetrating the rotor through the hole, the connecting means being suitable for attaching to a nacelle to connect a tension rod or a wire or the like via the connecting means to the nacelle and thereby to the upper part of the wind turbine.

32. A nacelle for a wind turbine, wherein the nacelle comprises the rotor in ac cordance with any one of claims 29 to 31.

33. A nacelle for a wind turbine, wherein the nacelle comprises a front part and a rear part, the front and rear parts being releasably lockable to each other to form a complete nacelle, the front part of the nacelle comprising a con necting means for connecting the nacelle to a rotor.

34. The nacelle in accordance with claim 33, wherein the nacelle comprises the rotor in accordance with any one of claims 29 to 31.

35. A nacelle for a wind turbine, wherein the nacelle has a through opening ver tically through the nacelle, so that the nacelle can be mounted on a wind- turbine tower by receiving the tower through the opening.

36. The nacelle in accordance with claim 32, 33 or 34, wherein the nacelle has a through opening vertically through the nacelle, so that the nacelle can be mounted on a wind-turbine tower by receiving the tower through the open ing.

37. An upper adapter piece for a wind turbine, wherein the adapter piece com prises an upper nacelle carrier and a lower nacelle carrier for carrying a na celle, a hinge and a tilting mechanism, the upper and lower nacelle carriers being tiltably attached to each other through the hinge, and the tilting mechanism being connected to the upper and lower nacelle carriers to tilt the two nacelle carriers relative to each other.

38. The upper adapter piece in accordance with claim 37, wherein the upper adapter piece comprises a bearing and a rotary means to allow rotation of a nacelle carried by the nacelle carrier relative to a wind-turbine tower. NIPO

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39. The upper adapter piece in accordance with claim 37 or 38, wherein the up per adapter piece has a vertical through opening so that the upper adapter piece can be mounted on the wind-turbine tower by receiving the tower through the opening.

40. A tower for a wind turbine, wherein the tower has an upper part and a lower part, the upper part of the tower and the lower part of the tower being joined to each other via a hinge for an angle between the upper part and the lower part to be changeable to allow the upper part of the tower to be laid down or raised.

41. The tower in accordance with claim 40, wherein the tower further comprises a locking means for locking the tower in a raised, operational position.

42. The tower in accordance with any one of claim 40 or 41, wherein the tower has an inner cavity and an opening to the sea to receive water from a water mass into the cavity.

43. A floating foundation for a wind turbine, wherein the foundation comprises:

- a transition piece and a corrective leg, the corrective leg projecting down wards in a water mass when the foundation is in an operational position;

- a rigid structure, comprising and joining together at least part of the tran sition piece and at least part of the corrective leg; and

- the ballast element in accordance with claim 15, the ballast element being movably suspended from the rigid structure in such a way that the corrective leg penetrates the ballast element and in such a way that the ballast element will come into contact with and have a corrective effect on the corrective leg and thereby also have a corrective ef fect on the foundation when the foundation is tilted beyond a certain de gree.

44. A floating foundation for an offshore wind turbine, wherein the foundation comprises:

- a transition piece for carrying the wind turbine;

- a substantially horizontal, stabilizing part, which comprises a first correc tive arm and a second corrective arm, the first arm and the second arm being attached to and projecting from the transition piece, and the first arm comprising a hinge and being articulatedly NIPO

WO 2021/173002 PCT/N02021/050051 joined to the transition piece via the hinge to allow movement of the first arm in the horizontal plane.

45. A wind turbine for an apparatus for extracting energy from wind, wherein the wind turbine has an upper part and a lower part, the upper part being tiltably attached to the lower part through a hinge, and the wind turbine comprising a tilting mechanism for tilting the upper part relative to the lower part, in order to keep the upper part stable when the turbine is tilted.

46. The wind turbine in accordance with claim 45, wherein the tilting mechanism comprises a hydraulic cylinder connected to the upper and lower parts for tilting the upper part relative to the lower part.

47. The wind turbine in accordance with claim 45 or 46, wherein the tilting mechanism further comprises a control unit connected to the hydraulic cyl inder for automatically controlling the cylinder to keep the upper part cor rectly angled in relation to optimizing the energy extraction of the wind tur bine.

48. A wind turbine for extracting energy from wind, wherein the wind turbine comprises:

- the upper adapter piece in accordance with any one of claims 37 to 39; and/or

- the rotor in accordance with any one of claims 29 to 31; and/or

- the nacelle in accordance with any one of claims 32 to 36; and/or

- the tower in accordance with any one of claims 28 or 40 to 42; and/or

- a lifting beam mounted on an upper part of the wind turbine for lifting equipment or parts for the wind turbine towards or from the upper part of the wind turbine.

49. The wind turbine in accordance with any one of claims 45 to 47, wherein the wind turbine comprises:

- the upper adapter piece in accordance with any one of claims 12 to 14; and/or

- the rotor in accordance with any one of claims 3 to 5; and/or

- the nacelle in accordance with any one of claims 6 to 10; and/or

- the tower in accordance with any one of claims 2 or 15 to 17; and/or

- a lifting beam mounted on an upper part of the wind turbine for lifting NIPO

WO 2021/173002 ⁵⁸ PCT/N02021/050051 equipment or parts for the wind turbine towards or from the upper part of the wind turbine.

50. A floating apparatus for extracting energy from wind, wherein the apparatus comprises a foundation in accordance with any one of claims 1 to 14 or 17 to 23 and/or a wind turbine in accordance with any one of claims 45 to 49.

51. A floating apparatus for extracting energy from wind, wherein the apparatus comprises:

- a wind turbine and a foundation for carrying the wind turbine, the wind turbine comprising a tower, and the foundation comprising a substantially vertical, stabilizing part and a substantially horizontal, stabilizing part; and

- an upper tension rod and a lower tension rod and a connecting means, wherein

- the connecting means is permanently attached to an upper part of the tower;

- the upper tension rod extends from the outer portion of the horizontal, stabilizing part to the connecting means; and

- the lower tension rod extends from the outer portion of the horizontal, sta bilizing part to a lower part of the vertical, stabilizing part, so that the tension rods can absorb bending moments to reduce potentially destructive forces acting on parts of the structure of the floating apparatus.

52. The floating apparatus in accordance with claim 51, wherein the foundation of the apparatus is a foundation in accordance with any one of claims 1 to 14 or 17 to 23.

53. The floating apparatus in accordance with any one of claims 50 to 52, wherein the wind turbine of the apparatus is a wind turbine in accordance with any one of claims 45 to 49.

54. The floating apparatus in accordance with any one of claims 24 to 26 or 50 to 53, wherein the apparatus is anchored to a seabed via an anchor on the seabed and an anchor line connecting the anchor to the anchor attachment of the foundation.

55. The floating apparatus in accordance with any one of claims 24 to 26 or 50 to 54, wherein the tower of the wind turbine has one or more inner cham bers which can selectively be filled with or emptied of ballast to adjust the mass of the tower. NIPO

WO 2021/173002 ⁵⁹ PCT/N02021/050051

56. The floating apparatus in accordance with any one of claims 24 to 26 or 50 to 55, wherein the apparatus comprises a lifting means for lifting equipment or parts of the wind turbine to or towards the top of the tower of the wind turbine.

57. The floating apparatus in accordance with any one of claims 24 to 26 or 50 to 56, wherein the tower of the wind turbine is rotationally rigidly attached to the foundation, and wherein the nacelle of the wind turbine is rotationally rigidly attached to the tower.

58. The floating apparatus in accordance with any one of claims 24 to 26 or 50 to 57, wherein the wind turbine comprises a generator, a drive line, a rotor and a lower adapter piece, the lower adapter piece functioning as a link be tween the tower of the wind turbine and the transition piece of the founda tion and comprising the generator of the wind turbine, the drive line of the wind turbine joining the rotor of the wind turbine to the generator.

59. The floating apparatus in accordance with any one of claims 24 to 26 or 50 to 58, wherein the wind turbine comprises a generator, a drive line and a ro tor, the generator of the wind turbine being integrated in the transition piece of the apparatus, and the drive line of the wind turbine joining the rotor of the wind turbine to the generator.

60. A floating apparatus in accordance with any one of claims 24 to 26 or 50 to 59, wherein the apparatus comprises a hoisting tower comprising lifting means for raising a wind-turbine tower.

61. The floating apparatus in accordance with claim 60, wherein the apparatus further comprises at least two towers that each comprise a hinge, the hinge of each tower making it possible for the tower to be laid down or raised around the hinge.

62. The floating apparatus in accordance with claim 61, wherein the lifting means are connectable to the towers so that the lifting means can raise or lower the towers around the hinges of the towers, and wherein the towers are arranged in such a way on the transition piece of the apparatus that they can be raised or lowered symmetrically to preserve a weight balance for maintaining stability. NIPO

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63. A method for stabilizing a floating foundation for a wind turbine, wherein the wind turbine comprises a rigid structure and a corrective leg, the corrective leg projecting downwards in a water mass when the foundation is in a op erational position, the method comprising the steps of:

- providing a ballast element in accordance with claim 15; and

- suspending the ballast element from a bottom side of the rigid structure belonging to the foundation, with the leg of the foundation through the hole of the ballast element, in a way that allows movement of the ballast element relative to the rigid structure and that will make the ballast element come into contact with and exert a stabilizing force on the leg and thereby the rig id structure when the foundation is tilted beyond a certain degree.

64. The method in accordance with claim 27, wherein the method further com prises the steps of:

- providing a ballast element in accordance with claim 15; and

- suspending the ballast element from a bottom side of a rigid structure be longing to the foundation, with the leg of the foundation through the hole of the ballast element, in a way that allows movement of the ballast element relative to the rigid structure and that will make the ballast element come into contact with and exert a stabilizing force on the structure when the foundation is tilted beyond a certain degree.

65. The method in accordance with claim 27, 63 or 64, wherein the foundation comprises a rotary means and the method further comprises the step of:

- controlling the rotation of the foundation by using the rotary means to place the transition piece of the foundation in an advantageous position rela tive to the anchor attachment of the foundation.

66. The method in accordance with claim 27, 63, 64 or 65, wherein the founda tion comprises a rotary means and the method further comprises the step of:

- controlling the rotation of the foundation to run the transition piece back into a starting position to avoid twisting of a cable or the like, by using the rotary means.

67. A method for reducing bending forces on a connection between a vertical part and a horizontal part of a floating foundation for a wind turbine, where in the method comprises the step of:

- extending a tension rod between an outer portion of the horizontal part of NIPO

WO 2021/173002 ⁶¹ PCT/N02021/050051 the foundation and a connecting means which is in contact with an upper portion of a tower for a wind turbine standing on the floating foundation and/or extending a tension rod between an outer portion of the horizontal part of the foundation and a lower portion of a vertical part of the founda tion.

68. A method for installing a nacelle on a tower for a wind turbine, wherein the method comprises the steps of:

- providing a nacelle comprising a front part and a rear part, the front and rear parts being releasably lockable to each other to form a complete na celle;

- lifting the front part of the nacelle and the rear part of the nacelle into a position of installation for the nacelle on the tower;

- releasably locking the front part of the nacelle to the rear part of the na celle after lifting to the position of installation, to combine the two parts to install the nacelle on the wind-turbine tower.

69. A method for uninstalling a nacelle from a tower for a wind turbine, wherein the nacelle comprises a front part and a rear part, the front and rear parts being releasably lockable to each other to form a complete nacelle, the method comprising the steps of:

- lifting the front and rear parts away from the tower.

70. The method in accordance with claim 68 or 60, wherein the wind turbine is part of an apparatus which further comprises a foundation for the wind tur bine and a lifting means, the lifting being carried out by using the lifting means of the apparatus.

71. The method in accordance with any one of claims 68 to 70, wherein the ap paratus further comprises a guiding means for guiding the nacelle parts dur ing lifting of the nacelle parts, the method comprising one or more of the steps of:

- connecting the front part of the nacelle to the tower pipe;

- connecting the rear part of the nacelle to the tower pipe;

- hoisting the tower pipe to an installation position for the nacelle;

- disconnecting the front part of the nacelle from the tower pipe and in stalling the front part of the nacelle on the tower; and NIPO

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- disconnecting the rear part of the nacelle from the tower pipe and installing the rear part of the nacelle on the tower.

72. A method for erecting a tower belonging to an apparatus for extracting en ergy from wind, the apparatus comprising a foundation with a hoisting tower and at least two wind-turbine towers joined to the foundation, the hoisting tower comprising a lifting means connected to the two wind-turbine towers, wherein the method comprises the step of:

- using the lifting means to raise the wind-turbine towers.

73. The method in accordance with claim 72, wherein the step of "using the lift ing means to raise the wind-turbine towers" includes lifting the towers sym metrically towards or from a raised position so that a weight load on the foundation from the towers is equal on two sides of a horizontal axis to maintain the stability of the foundation while the lifting is being done.

74. The floating apparatus in accordance with any one of claims 24 to 26 or 50 to 62, wherein the foundation of the apparatus is a foundation for carrying a plurality of wind turbines and wherein the apparatus comprises a plurality of wind turbines.

75. The floating apparatus in accordance with claim 74, wherein the floating ap paratus has two wind turbines, the two wind turbines standing on the transi tion piece of the foundation, the two wind turbines having a tower each and the towers being connected by one or more structures, such as one or more tension rods, and the two towers, in the raised position, standing at opposite angles relative to a vertical axis from the transition piece of the foundation, so that they are sloping away from each other form the positions of the tow ers on the transition piece of the foundation to their upper ends.

76. The floating apparatus in accordance with claim 75, wherein, at the rotors of the wind turbines, the two wind turbines are connected via tension rods to a section, for example an outer section, of the horizontal part of the founda tion, and/or wherein, at the upper ends, the two wind turbines are connect ed to each other via tension rods.

77. The floating apparatus in accordance with any one of claims 24 to 26, 50 to 62 or 74 to 76, wherein the apparatus comprises a control system for con trolling one or more parts of the apparatus to improve the stability of the NIPO

WO 2021/173002 ^{O J} PCT/N02021/050051 apparatus or to improve the ability of the apparatus to extract energy from the wind.

78. The floating apparatus in accordance with claim 77, wherein the control sys tem comprises one or more sensors for obtaining information which can be used to control the one or more parts of the apparatus and a program for using the information to determine an advantageous adjustment of at least one of the one or more parts of the apparatus that can be controlled to im prove the stability of the apparatus or to improve the ability of the apparatus to extract energy from the wind.

79. The apparatus in accordance with claim 78, wherein the apparatus compris es two wind turbines, and wherein the control system comprises one or more sensors for obtaining information related to how forces from the wind turbines affect the stability of the apparatus and wherein the control system is connected to one or more parts of the apparatus that can be adjusted to influence the stability of the apparatus.

80. A method for stabilizing an apparatus for extracting energy from wind, wherein the apparatus is an apparatus in accordance with claim 79, the method comprising the steps of:

1. using the one or more sensors to obtain information on how forces from the wind turbines affect the stability of the apparatus;

2. using the program of the control system to determine an advantageous adjustment of at least one of the one or more parts of the apparatus that can be adjusted in order to influence the stability of the apparatus; and

3. letting the control system automatically adjust one or more of the one or more parts of the apparatus that can be adjusted in order to influence the stability of the apparatus based on what was determined by the program in point 2.