WO2017186244A1

WO2017186244A1 - A method for erecting a multirotor wind turbine with elevated hub height

Info

Publication number: WO2017186244A1
Application number: PCT/DK2017/050125
Authority: WO
Inventors: Jesper Lykkegaard NEUBAUER
Original assignee: Vestas Wind Systems A/S
Priority date: 2016-04-29
Filing date: 2017-04-27
Publication date: 2017-11-02

Abstract

A method for erecting a multirotor wind turbine (1), the multirotor wind turbine (1) comprising a tower structure (2) and at least two load carrying structures (3) is disclosed. Each load carrying structure (3) carries at least one energy generating unit (8). A first end (4) of each of the load carrying structures (3) is mounted on the tower structure (2) at or near the top of the tower structure (2). Each of the load carrying structures (3) is pivoted in such a manner that a second end (5) of each load carrying structure (3) is elevated to a position above the top of the tower structure (2). The load carrying structures (3) are fixed in the elevated position. The hub height of the energy generating units (8) can be elevated without requiring a crane with increased lifting capability.

Description

A METHOD FOR ERECTING A MULTI ROTOR WIND TURBINE WITH ELEVATED HUB HEIGHT FIELD OF THE INVENTION

The present invention relates to a method for erecting a multirotor wind turbine. The method according to the invention allows the hub height of at least one rotor to be arranged at an elevated level with respect to a top of a tower structure.

BACKGROUND OF THE INVENTION

Wind turbines normally comprise one or more energy generating units, each energy generating unit comprising a rotor comprising a hub carrying one or more wind turbine blades. The wind acts on the wind turbine blades, thereby causing the hub to rotate. The rotational movements of the hub are transferred to a generator, either via a gear

arrangement or directly, in the case that the wind turbine is of a so-called direct drive type. In the generator, electrical energy is generated, which may be supplied to a power grid.

Some wind turbines are provided with two or more energy generating units in order to increase the total power produced by the wind turbine, without having to provide the wind turbine with one very large, and therefore heavy, energy generating unit. Such wind turbines are sometimes referred to as 'multirotor wind turbines'.

In multirotor wind turbines the energy generating units may be carried by one or more load carrying structures which are, in turn, connected to a tower structure. Thereby at least some of the energy generating units are not mounted directly on the tower structure, and they may have a centre of gravity which is displaced with respect to a longitudinal axis defined by the tower structure.

It is an advantage to arrange the rotor(s) of a wind turbine at as high a level as possible, because this increases the power which it is possible to extract from the wind. This is, e.g., the case at sites with a positive wind shear, i.e. at sites where the wind speed increases as a function of altitude. In these cases arranging the rotor(s) at as high a level as possible ensures that the rotor(s) is/are arranged in a region with as high wind speed as possible. However, there is normally a limit on the lifting capability of available cranes, and this imposes a limit on the possible hub height of wind turbines.

DE 10 2012 020 052 B3 discloses a multirotor wind turbine comprising a foundation, a tower and at least two nacelles with rotors on the tower. Two arms are mounted on the tower via a bearing, and each arm carries a nacelle. Adjusting means are provided between the arms and the tower in order to allow the arms to be pivoted, in order to lower the nacelles towards the ground level.

GB 2 443 886 A discloses a multirotor wind turbine arrangement comprising a tower and at least two arms projecting outwards therefrom. A wind turbine is attached to an end of each arm. The arms may be mounted pivotally on the tower in order to selectively lower each turbine towards the base of the tower. The turbines can not be elevated to a position above the top of the tower.

DESCRIPTION OF THE INVENTION

It is an object of embodiment of the invention to provide a method for erecting a multirotor wind turbine, in which the hub height of at least one energy generating unit can be elevated above a maximum lifting height of available cranes.

It is a further object of embodiments of the invention to provide a method for erecting a multirotor wind turbine, in which the total power production of the resulting wind turbine is increased. The invention provides a method for erecting a multirotor wind turbine, the multirotor wind turbine comprising a tower structure and at least two load carrying structures, each load carrying structure being arranged for carrying at least one energy generating unit and for being connected to the tower structure at or near a top of the tower structure, the method comprising the steps of: - mounting a first end of each of the load carrying structures on the tower structure at or near the top of the tower structure, in such a manner that a second end of each load carrying structure arranged opposite to the first end of the load carrying structure, is arranged at the same vertical level as the first end or lower, pivoting each of the load carrying structures in such a manner that the second end of each load carrying structure is elevated to a position above the top of the tower structure, and

- fixing the load carrying structures in the elevated position.

The present invention relates to a method for erecting a multirotor wind turbine. In the present context the term 'multirotor wind turbine' should be interpreted to mean a wind turbine which comprises two or more energy generating units, each energy generating unit comprising a rotor.

The multirotor wind turbine comprises a tower structure and at least two load carrying structures. The tower structure is preferably a substantially vertical structure which is anchored, at a lower part, to a foundation structure. Accordingly, the tower structure resembles a traditional wind turbine tower for a single rotor wind turbine.

Each load carrying structure is arranged for carrying one or more energy generating units and for being connected to the tower structure. Accordingly, a given load carrying structure forms a connection between the one or more energy generating units, carried by the load carrying structure, and the tower structure, and is capable of handling the loads involved with carrying the energy generating units. Furthermore, the load carrying structure may transfer loads from the energy generating unit(s) to the tower structure. Each load carrying structure is connected to the tower structure at or near a top of the tower structure, i.e. at or near the highest point of the tower structure. In the present context the term 'energy generating unit' should be interpreted to mean a part of the wind turbine which actually transforms the energy of the wind into electrical energy. Each energy generating unit thereby typically comprises a rotor, carrying a set of wind turbine blades, and a generator. The energy generating unit may further comprise a gear arrangement interconnecting the rotor and the generator. The generator, and possibly the gear arrangement, may be arranged inside a nacelle.

According to the method of the invention, a first end of each of the load carrying structures is initially mounted on the tower structure at or near the top of the tower structure.

Accordingly, a given load carrying structure is connected to the tower structure via its first end. Each load carrying structure further comprises a second end being arranged opposite to the first end. Accordingly, a given load carrying structure is an elongated structure, e.g. in the form of an arm, a beam or the like, with the first and second ends forming the extremes of the elongated structure. The second end of each load carrying structure is arranged at the same vertical level as the first end or lower. In the case that the second end of a given load carrying structure is arranged at the same level as the first end, the load carrying structure is arranged substantially horizontally in the sense that it extends away from the tower structure along a substantially horizontal direction. In the case that the second end is arranged at a lower level than the first end, the load carrying structure extends away from the tower structure along a downwardly inclined direction. In any event, the first end of a given load carrying structure, forming the connection point between the load carrying structure and the tower structure, defines the highest level at which the load carrying structure is arranged. Furthermore, this level is arranged at or near the top of the tower structure.

Next, each of the load carrying structures is pivoted in such a manner that the second end of each load carrying structure is elevated to a position above the top of the tower structure. Finally, the load carrying structures are fixed in the elevated position, i.e. once the wind turbine starts operating, the load carrying structures are in the elevated position, i.e. the second ends of the load carrying structures are arranged at a level above the top of the tower structure. Since the first ends of the load carrying structures are mounted on the tower structure at or near the top of the tower structure, the second ends of the load carrying structures are also arranged above the first ends of the load carrying structures when the pivoting of the load carrying structures has been completed, i.e. when the second ends are in their elevated position. Thus, when the load carrying structures are in this position, they extend from the tower structure along a direction which is upwardly inclined and away from the tower structure. The load carrying structures may be pivoted substantially simultaneously, or they may be pivoted one at a time. However, when the pivoting has been completed, the second ends of all of the load carrying structures are arranged in the elevated position, i.e. at a level above the top of the tower structure.

Assuming that the top of the tower structure corresponds to a maximum lifting capacity of an available crane, then the tower structure can be erected and the first ends of the load carrying structures can be mounted on the tower structure by utilising the full lifting capacity of the crane. In the case that the energy generating units should also be mounted on the load carrying structures by means of the crane, this height would also define the maximum possible hub height for the energy generating units. However, since the second ends of the load carrying structures are elevated to a position above the top of the tower structure, the levels of the second ends exceed the level defined by the maximum lifting capacity of the crane. Thereby it is possible to mount the energy generating units at a higher level than the level defined by the maximum lifting capacity of the crane, i.e. the hub heights of the energy generating units are elevated. Accordingly, the total power production of the wind turbine can be increased, due to the elevated hub heights.

The wind turbine is preferably a horizontal axis wind turbine (HAWT), i.e. the rotating axis of each rotor is preferably arranged along a substantially horizontal direction.

The step of pivoting each of the load carrying structures may comprise pulling at least two load carrying structures towards each other by means of a wire. The wire could, e.g. interconnect the second ends of the two load carrying structures. In this case, the second ends of the load carrying structures may be pulled towards each other and upwards by shortening the part of the wire which is arranged between the second ends of the load carrying structures. The wire may, e.g., be pulled by means of one or more winches. According to this embodiment, the step of fixing the load carrying structures in the elevated position may comprise fixing the wire.

As an alternative, the load carrying structures may be pivoted by means of a motor mechanism, a hydraulic mechanism, a winch mechanism, or in any other suitable way.

Alternatively or additionally, each load carrying structure may comprise a secondary structure extending from the first end of the load carrying structure in an upwards direction, and the step of pivoting each of the load carrying structures may comprise pulling the secondary structures of at least two load carrying structures towards each other, and the step of fixing the load carrying structures in the elevated position may comprise fixing at least two secondary structures to each other. The secondary structures could, e.g., be in the form of additional arms, beams or trusses, extending from the first ends of the load carrying structures along a direction which differs from the direction defined by the first end and the second end of the respective load carrying structures. The secondary structures may, e.g., be pulled towards each other by means of a wire interconnecting the secondary structures, by means of a motor mechanism or by means of a hydraulic mechanism. Finally, the load carrying structures are fixed in the elevated position by fixing the secondary structures to each other. For instance, the secondary structures may be brought to a position in which they are arranged adjacent to each other during the step of pulling the secondary structure towards each other. In this case the secondary structures can easily be fixed to each other, thereby fixing the load carrying structures in the elevated position.

The step of fixing at least two secondary structures to each other may comprise bolting the secondary structures to each other. Alternatively, the secondary structures may be fixed to each other by other means, such as by means of robes, wires, clamps, etc.

The method may further comprise the step of hoisting each of the load carrying structures to the mounting position by means of a hoisting mechanism arranged on the tower structure. According to this embodiment, the load carrying structures can be mounted on the tower structure without the need for an external crane. Accordingly, an external crane is only required for erecting the tower structure. This reduces the costs of erecting the wind turbine. The load carrying structures may be hoisted substantially simultaneously or one at a time. In the case that the load carrying structures are hoisted one at a time, less space is required on the ground, and the hoisting is easier and less complex to handle. For instance, a hinge may be installed near the top of the tower structure before the load carrying structure is hoisted. When the hoisting has been completed, the first end of the load carrying structure may be attached to the hinge, and the load carrying structure is then ready to be pivoted as described above.

In the case that the load carrying structures are provided with secondary structures, the secondary structures may be mounted on the tower structure before the load carrying structures are hoisted to their mounting positions. The first end of each load carrying structure may then be joined to a respective secondary structure.

The method may further comprise the step of mounting an energy generating unit at the second end of each load carrying structure. According to this embodiment, the energy generating unit is eventually mounted at the load carrying structure at a level which is above the top of the tower structure, since the second end of the load carrying structure has been pivoted to arrange the second end at the elevated level, as described above. Accordingly, the hub height of the energy generating unit is elevated above a level defined by a maximum lifting capacity of an available crane.

The step of mounting an energy generating unit at the second end of each load carrying structure may be performed either before or after the load carrying structure is hoisted to the mounting position. In the case that the energy generating unit is mounted before the load carrying structure is hoisted, then the energy generating unit may be mounted on the load carrying structure while the load carrying structure is still on the ground, and the load carrying structure may subsequently be hoisted to the mounting position along with the energy generating unit. Furthermore, the step of mounting an energy unit may be performed either before or after the step of pivoting the load carrying structures.

The step of mounting an energy generating unit may comprise hoisting the energy generating unit to a mounting position at the second end of the load carrying structure by means of at least one hoisting mechanism arranged at the load carrying structure. According to this embodiment, the energy generating units can be mounted on the load carrying structure without the need for an external crane. Accordingly, the hub height of a given energy generating unit is not limited by a maximum lifting capacity of an available crane.

The step of hoisting the energy generating unit to the mounting position may be performed by means of a first hoisting mechanism arranged at the first end of the load carrying structure and a second hoisting mechanism arranged at the second end of the load carrying structure.

In this case, the step of hoisting the energy generating unit to the mounting position may comprise moving the energy generating unit from a position near a base of the tower structure to the mounting position by controlling the first hosting mechanism and the second hoisting mechanism in dependence of each other.

According to this embodiment, only a relatively small area around the base of the tower structure needs to be suitable for positioning an energy generating unit to be mounted on the wind turbine. In the case that the wind turbine is an offshore wind turbine, the energy generating unit could, e.g., be arranged on an access platform mounted on the tower structure near the sea level. In the case that the wind turbine is an onshore wind turbine, only a small area around the wind turbine needs to be prepared for receiving an energy generating unit. For instance, in order to be suitable for having an energy generating unit positioned thereon, the ground must be stabilized and possible trees must be cut down. Furthermore, the landscape must be suitable for the purpose, e.g. not containing steep slopes, etc. It is an advantage that only a small area around the tower structure of the wind turbine needs to fulfil these requirements.

In order to obtain that the energy generating unit is moved from the position near the base of the tower structure to the mounting position, the energy generating unit may initially be moved along a substantially vertical direction by primarily operating the first hoisting mechanism. Subsequently, a pull provided by the first hoisting mechanism may be gradually decreased while a pull provided by the second hoisting mechanism is gradually increased. Thereby the energy generating unit follows a path which is increasingly along a substantially horizontal direction. BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in further detail with reference to the accompanying drawings in which

Figs. 1-6 illustrate a multirotor wind turbine during various steps of a method for erecting the wind turbine according to an embodiment of the invention. DETAILED DESCRIPTION OF THE DRAWINGS

Fig. 1 is a front view of a multirotor wind turbine 1 during erection of the multirotor wind turbine 1. The multirotor wind turbine 1 comprises a tower structure 2 and two load carrying structures 3. A first end 4 of each load carrying structure 3 is mounted on the tower structure 2, near the top of the tower structure 2.

In Fig. 1, each of the load carrying structures 3 extend away from the tower structure 2 along a downwardly inclined direction, i.e. in such a manner that a second end 5 of each load carrying structure 3 is arranged at a distance from the tower structure 2, and at a lower vertical level than the first end 4. Each load carrying structure 3 comprises a secondary structure 6, extending from the first end 4 of the load carrying structure 3 in an upwards direction. A wire 7 interconnects the secondary structure 6 of each load carrying structure 3 to the second end 5 of the load carrying structure 3.

Thus, in Fig. 1 the tower structure 2 has been erected, and the load carrying structures 3 have been mounted on the tower structure 2, via their first ends 4, at a position near the top of the tower structure 2.

In Fig. 2, the two secondary structures 6 of the load carrying structures 3 have been pulled towards each other. Thereby the load carrying structures 3 have been pivoted about a point at or close to the first ends 4 of the load carrying structures 3. Accordingly, the second ends 5 of the load carrying structures 3 have been elevated to a position above the top of the tower structure 2. Furthermore, the two secondary structures 6 have been fixed to each other, e.g. by means of bolts, thereby fixing the load carrying structures 3 in the elevated position shown in Fig. 2.

In Fig. 3 an energy generating unit 8 has been positioned on the ground, near the base of the tower structure 2. The energy generating unit 8 comprises a nacelle 9, carrying a rotor 10. Two wind turbine blades 11 have been mounted on the rotor 10, the wind turbine blades 11 pointing in an upwards direction. This is sometimes referred to as a 'bunny ear configuration'.

The energy generating unit 8 is connected to a first hoisting mechanism (not shown) arranged near the first end 4 of one of the load carrying structures 3, via a first wire 12. The energy generating unit 8 is further connected to a second hoisting mechanism (not shown) arranged near the second end 5 of the load carrying structure 3, via a second wire 13. Thereby the energy generating unit 8 can be hoisted from the position illustrated in Fig. 3 to a mounting position on the load carrying structure 3, near the second end 5, by appropriately operating the first and second hoisting mechanisms.

In Fig. 4, the hoisting mechanisms are being operated, and the energy generating unit 8 is in the process of being hoisted from the position illustrated in Fig. 3 towards a mounting position on the load carrying structure 3.

In Fig. 5, the hoisting of the energy generating unit 8 has been completed, and it has been mounted at the operating position near the second end 5 of the load carrying structure 3. Furthermore, an additional energy generating unit 8 has been mounted on the other load carrying structure 3, essentially as described above and illustrated in Figs. 3 and 4. It should be noted that the energy generating units 8 could be hoisted substantially simultaneously, thereby balancing the loads introduced in the load carrying structures 3 and the tower structure 2 during hoisting of the energy generating units 8.

In Fig. 6 a third wind turbine blade 11 has further been mounted on the rotors 10 of each of the energy generating units 8. Accordingly, the erection of the multirotor wind turbine 1 has been completed, and the multirotor wind turbine 1 is ready for use.

It is clear from Fig. 6, that the hub height of the rotors 10 of each of the energy generating units 8 is arranged at a vertical level which is above the top of the tower structure 2.

Furthermore, the energy generating units 8 have been positioned at this level without requiring a crane with a lifting capacity matching this level. This is due to the fact that the load carrying structures 3 are pivoted after they have been mounted on the tower structure 2 with their first ends 4 at or near the top of the tower structure 2, in such a manner that their second ends 5 are elevated to a level above the top of the tower structure 2. As described above, increasing the hub height increases the amount of power which the wind turbine 1 may extract from the wind, and it is therefore an advantage to increase the hub height.

Claims

1. A method for erecting a multirotor wind turbine (1), the multirotor wind turbine (1) comprising a tower structure (2) and at least two load carrying structures (3), each load carrying structure (3) being arranged for carrying at least one energy generating unit (8) and for being connected to the tower structure (2) at or near a top of the tower structure (2), the method comprising the steps of:

- mounting a first end (4) of each of the load carrying structures (3) on the tower

structure (2) at or near the top of the tower structure (2), in such a manner that a second end (5) of each load carrying structure (3) arranged opposite to the first end (4) of the load carrying structure (3), is arranged at the same vertical level as the first end (4) or lower,

- pivoting each of the load carrying structures (3) in such a manner that the second end (5) of each load carrying structure (3) is elevated to a position above the top of the tower structure (2), and - fixing the load carrying structures (3) in the elevated position.

2. A method according to claim 1, wherein the step of pivoting each of the load carrying structures (3) comprises pulling at least two load carrying structures (3) towards each other by means of a wire.

3. A method according to claim 1 or 2, wherein each load carrying structure (3) comprises a secondary structure (6) extending from the first end (4) of the load carrying structure (3) in an upwards direction, wherein the step of pivoting each of the load carrying structures (3) comprises pulling the secondary structures (6) of at least two load carrying structures (3) towards each other, and wherein the step of fixing the load carrying structures (3) in the elevated position comprises fixing at least two secondary structures (6) to each other.

4. A method according to claim 3, wherein the step of fixing at least two secondary structures (6) to each other comprises bolting the secondary structures (6) to each other.

5. A method according to any of the preceding claims, further comprising the step of hoisting each of the load carrying structures (3) to the mounting position by means of a hoisting mechanism arranged on the tower structure (2).

6. A method according to any of the preceding claims, further comprising the step of mounting an energy generating unit (8) at the second end (5) of each load carrying structure (3).

7. A method according to claim 6, wherein the step of mounting an energy generating unit (8) comprises hoisting the energy generating unit (8) to a mounting position at the second end (5) of the load carrying structure (3) by means of at least one hoisting mechanism arranged at the load carrying structure (3).

8. A method according to claim 7, wherein the step of hoisting the energy generating unit (8) to the mounting position is performed by means of a first hoisting mechanism arranged at the first end (4) of the load carrying structure (3) and a second hoisting mechanism arranged at the second end (5) of the load carrying structure (3).

9. A method according to claim 8, wherein the step of hoisting the energy generating unit (8) to the mounting position comprises moving the energy generating unit (8) from a position near a base of the tower structure (2) to the mounting position by controlling the first hosting mechanism and the second hoisting mechanism in dependence of each other.