WO2010120186A1

WO2010120186A1 - Floating windmill and method of installation, intervention or decommissioning

Info

Publication number: WO2010120186A1
Application number: PCT/NO2010/000138
Authority: WO
Inventors: Ove Tobia Gudmestad; John GRØNLI; Helge Arne Gudmestad
Original assignee: Universitetet I Stavanger
Priority date: 2009-04-16
Filing date: 2010-04-15
Publication date: 2010-10-21
Also published as: NO330525B1; NO20091484L

Abstract

The present invention relates to a floating windmill, comprising a generator house (12) with a generator and a plurality of rotor blades (13) at an upper part of an upright shaft (11), and a flotation system (1) at a lower part of said shaft (11), characterized by said floatation system (1) comprising a ballast system (6) for ballasting and de-ballasting of said windmill and thus altering the height of the windmill above water level, and further comprising a pivotal connection (14) of the blades (13) between a substantially vertical and a substantially horizontal position. The invention also relates to a method of installation, intervention or decommissioning of said windmill.

Description

Floating windmill and method of installation, intervention or decommissioning

The present invention relates to a floating windmill and method of installation, intervention or decommissioning of said windmill, according to the preamble of claims 1 and 10, respectively.

At present the costs of installation, intervention and decommissioning of offshore wind concepts are unreasonably high when using state of the art conventional technology, such as jackups or offshore crane vessels. There is thus a need for new thinking to develop safe but less costly technology and procedures for said operations.

For deepwater offshore wind concepts state of the art is to use crane vessels for said operations, however, this might not be attractive in view of the costs of employing sufficiently size vessels that can operate under most weather conditions. It should in this respect be noted that smaller crane vessels might have movement characteristics that will make such operations difficult or impossible large periods of the year, thus the need for large and costly cranes.

The prior art design of floating windmills requires the use of larger cranes for installation of generator house/ turbine as well as the blades of the windmill. The investment costs of the windmills are thus larger than necessary and heavy maintenance is particularly difficult, requiring the use of large crane vessels.

The present invention aims at solving or at least mitigating the above or other drawbacks or deficiencies by providing a floating windmill and method of installation, intervention or decommissioning of said windmill, according to the characterizing clause of claims 1 and 10, respectively.

Advantageous embodiments of the invention are set forth in the dependent claims.

In view of the above, the inventors of the present invention have developed new technology for installation, intervention and decommissioning of offshore wind concepts. The inventors will in particular suggest the use of ballast procedures combined with use of offshore service vessels to perform said operations safely. The technology development suggested includes new modules that can be handled by work procedures used by the offshore service industry. In particular, this involves for the following phases: • Installation: Tow to field of the base wind energy concept combined with new technology components that can be handled offshore with the use of service vessels. With the present invention, installation of generator house/ wind turbines as well as the blades of the windmill should be substantially reduced.

• Interventions: Use of ballast procedures combined with maintenance directly from service vessels.

• Decommissioning: Reverse installation.

Throughout these operations procedures for ballast control and technology for mooring as developed for the offshore drilling industry will become central elements.

hi the following, non-limiting embodiments of the present invention are described in more detail with reference to the accompanying drawings, wherein:

Figure 1 is a side view of a first embodiment of a floating windmill according to the present invention, having free hanging counterweights, during normal operation,

Figure 2 is a partial view of the windmill of Fig. 1, in an installation position,

Figure 3 is a partial view of a second embodiment of a floating windmill according to the invention, having integrated counterweights, during normal operation,

Figure 4 is a partial view of the embodiment shown in Fig. 3, in an installation position, and

Figure 5 is a side view of a third embodiment of two windmills according to the invention, having towers of different lengths and provided on the same foundation.

A floating windmill for deep waters, e.g. offshore, comprises flotation elements 1 that ensure buoyancy, stability and the required motion characteristics of the windmill. In the present invention, the basic flotation elements below water are designed according to characteristics developed for optimization of motion and stability of a floating offshore windmill. In addition to the general outline of the below water part of the windmill, a mooring system 2 should be in place. This mooring system 2 could consist of pre-installed anchors 3, for example suction anchors installed by the use of support vessels suitable for said installation operations, and in addition there should be mooring lines 4 that are to be connected to the below water flotation elements after the windmill has been installed. The mooring lines could be made of different materials, wire made of steel or polyester is foreseen, possibly in combination with chains. It should be noted that polyester wire might be favored as the weight of steel wire or chains is high, necessitating additional ballast from below the water flotation elements 1. The mooring lines might be attached to fairleads 5 mounted on the flotation element 1 and typically tightened above the water.

There are several ways in which the flotation elements can be designed, but in accordance with preferred embodiments of the invention a ballast system 6, designed as an integral part of the flotation element 1, is provided. This ballast system 6 comprises water ballast tanks that can be filled up or emptied to ensure that the windmill during installation and heavy maintenance can be lowered (ballasted down) to a required depth. The ballast system 6 should comprise the required number of ballast tanks 7 and pumps 8 to ensure that the necessary (predetermined) ballast operations can be carried out. It should also be noted that it is assumed that heavy ballast is placed near the bottom of the flotation elements 1 to ensure proper stability of the windmill. To avoid large motions (e. g. pitch motions) of the windmill, gyros 9 could be installed inside the flotation element 1 to compensate for the movements in waves or strong winds.

Note that it might be necessary to tighten the mooring system 2 when the windmill is lowered into the maintenance draft specified by the service vessel (not shown) attending the maintenance operation.

During operation of the windmill, the present above the water parts of the design comprises above-the-water shaft 11, generator house 12 with gearbox and turbines and blades 13 of the windmill. During normal operation, the differences between the present invention and a traditional floating windmill may not be visible, see Figure 1 for reference.

As described above in the introduction and the prior art description, however, the installation and in particular the maintenance of the blades of the windmill will require use of a large crane, of which the day-rate for hiring might be very large. Furthermore, cranes that behave stable in waves (even in waves that are expected to occur most of the year) will have to be of the semi submersible design that is particularly costly to hire.

With the present invention, however, all lifting of the blades 13 of the windmill can be performed while the blades 13 are in horizontal position. This will be ensured by mounting a strong hinge 14 between the generator house 12 and the shaft 11. The hinge 14 could in practice be designed such that the generator house 12 is installed vertically on the top of hinge 14 (or together with the hinge 14) that is located on top of the shaft 11. This installation can be carried out inshore in sheltered waters by service vessels or the generator house 12 can be floated over the above-the-water shaft 11 on two barges (not shown) and transferred to the shaft 11 by de-ballasting said shaft 11.

Thereafter the blades 13 are lifted in position and installed horizontally on the top of the generator house 12 by the cranes of a service vessel at a height determined by the reach of the cranes and the ballast system 6 of the flotation elements 1. Figure 4 shows how the installation of the generator house 12 and the blades are carried out. Alternatively, the installation can be carried out by float-over technology where the equipment is placed between barges that are hauled in place over the generator house 12. The transfer of the blades 13 is thereafter carried out by de-ballasting the shaft 11.

Following the installation of the windmill blades 13, the windmill is de-ballasted such that the blades 13 reach a height where the hinge 14 with the generator house 12 on top can be turned 90 degrees to ensure that the windmill blades 13 get in the standard traditional vertical position for efficient generation of electricity. Through this operation the generator house 12 will get in the traditional horizontal position. As part of this operation, it could be possible to slide the generator house back by engaging a rail system mounted on the underside of the generator house. Hereby the hinge 14 will act as a counterweight until the windmill blades 13 can be engaged to ensure that the generator house 12 be placed in a balanced position on top of the shaft 11. Figure 3 shows the generator house 12, the hingel4 and the blades 13 in operational position, and with the arrow indicating one direction of sliding movement of said generator house.

As a less complex alternative, the generator house 12 can be designed with at least one free hanging counterweight 17 hanging outside the shaft 11 of the windmill and below the hinge 14 during installation in order to balance the weight of the generator house 12 and the blades 13. Said counterweight 17 preferably has an aerodynamic shape, e.g. a tail wing shape assisting the positioning of the rotor blades 13 against the wind and as shown in the figures. Alternative designs of the hinge could be considered as well, as designed by a person skilled in the art.

As soon as the hinge 14 is fixed and secured, the windmill can be de-ballasted to required position to be ready for use. The hinge 14 could also be designed such that it can rotate e. g. on a joint 18 to ensure that the blades are in optimum position with respect to the wind direction to produce as much electricity as possible.

Details of the hinge 14 are shown in Figure 2. It should be noted that it in principle also could be considered a design according to the principles described above whereby the blades 13 rotate in the horizontal plane on top of the generator house 12 and shaft 11.

The installation operations as described can be very efficiently carried out in a deep fjord with the use of service vessels under controlled conditions where there are virtually no waves present.

For heavy maintenance, the windmill can be ballasted to required depth, the hinge 14 can be activated and the blades 13 can be moved into horizontal position and continued to be ballasted down to a depth where the cranes of (not shown) service vessels can perform operations on the blades 13 and the generator house 12.

The windmill preferably includes a joint 18 at the upper part of the shaft 11, said joint enabling rotation of the generator house 12 about the longitudinal axis the shaft 11. It is thus secured that the blades 13 are in optimum position with respect to the current wind direction.

From reasons of cost two or more windmills provided on one single foundation 20 comprising flotation and mooring systems as described above are feasible within the scope of the invention, as indicated in Figure 5. The same methods as described above can then be applied, provided that the shafts 21, 22 of the windmills are of different lengths in such a way that it is possible to arrange the blades 13 at different heights. Further the length of the blades 13 should be such that they do not interfere with the shafts 21, 22 of the adjacent or neighboring windmill(s) when the blades 13 are arranged in a horizontal position. For one of the windmills, principally the windmill with the lowest shaft 21, 22 the blades 13 can thereafter be rearranged into a vertical position, until all the blades of all the windmills are rearranged into a vertical position. In this respect the height difference is an important design parameter, in order to avoid submerging of the lowest windmill and its generator house 12 when service is performed on a higher windmill, said height difference should be kept within certain limits.

According to the invention there is thus also disclosed a method of installation, intervention or decommissioning of a windmill as described above, comprising the steps of; ballasting or de-ballasting said windmill to a required height above sea level, arranging the rotor blades 13 in a substantially horizontal position, or parts for connection with the rotor blades 13, e.g. generator, rotor shaft, etc., in a position for substantially horizontal mounting of the rotor blades 13, and conducting or continuing installation, intervention or decommissioning operations.

The use of the wording "floating" windmill in the description and claims should not be construed as only encompassing said windmill in its deployed floating state, but to encompass the windmill in any state, e.g. stored onshore or onboard a vessel before deployment, or at factory during or after its production.

Further it should be noted that the use of directional terms such as "upright",

"horizontal", "vertical", etc. relates to the windmill in its operational position deployed at sea.

Claims

C l a i m s

1.

A floating windmill, comprising a generator house (12) with a generator and a plurality 5 of rotor blades (13) at an upper part of an upright shaft (11), and a flotation system (1) at a lower part of said shaft (11), characterized by said floatation system (1) comprising a ballast system (6) for ballasting and de-ballasting of said windmill and thus altering the height of the windmill above water level, and further comprising a pivotal connection (14) of the blades (13) between a substantially vertical and a substantiallyo horizontal position.

2.

The windmill according to claim 1, characterized in that said ballast system (6) comprises at least one ballast tank (7) and at least one pump (8) connected to saids ballast tank (7) for pumping and ballasting or de-ballasting of seawater.

3.

The windmill according to claim 1 or 2, characterized in that said pivotal connection

(14) is a hinge. 0

4.

The windmill according to any of the preceding claims, characterized by at least one counterweight (17) mounted externally to the generator house (12). S 5.

The windmill according to any of claims 1 to 3, characterized by comprising a rail system connected to the generator house (12) for sliding movement of the generator house (12) relative to a longitudinal axis of the shaft (11). 0 6.

The windmill according to claims 4 or 5, characterized by comprising a joint (18) at upper part of the shaft, said joint enabling rotation of the generator house (12) about the longitudinal axis the shaft (11). S 7.

The windmill according to any of the preceding claims, characterized by comprising a mooring system (2) having mooring lines (4). The windmill according to any of the preceding claims, characterized by comprising a plurality of windmills having shafts (21, 22) of different heights mounted on one single foundation (20).

9.

The windmill according to any of the preceding claims, characterized by comprising a gyro (9) to compensate for movements in waves and strong winds.

10.

A method of installation, intervention or decommissioning of a windmill according to any of the preceding claims, characterized by comprising the steps of; ballasting or de-ballasting said windmill to a required height above sea level, and arranging the rotor blades (13) in a substantially horizontal position, or parts for connection with the rotor blades (13) in a position for substantially horizontal mounting of the rotor blades (13), and conducting or continuing installation, intervention or decommissioning operations.

1 1.

The method according to claim 10, characterized by the further step of using one or several cranes of a service vessel or float-over technology in said installation, intervention or decommissioning operations.