Field of the Invention

The present invention relates to an installation arrangement for installation of a floating wind turbine, and a method of installing a floating wind turbine.

Background of the Invention

Different configurations of floating wind turbines utilize different types of floatation systems, including semi-submersible, barge, and spar types. The spar type is known to be more resistant to wave action and can support a heavy upper structure. However, the depth needed to accommodate a floating wind turbine with a spar type floatation system typically requires the spar type floatation system (the lower part) and the upper part of the wind turbine to be transported separately from the quay to a location with a sufficient water depth, where upending of the lower part and final assembly of the wind turbine can take place.

According to one approach described in US 2017/0197690, the upper part and the lower part are loaded from the quay on a specially designed carrier vessel and transported to a location with a sufficient water depth. At that location, the lower part is lifted into the water by a crane and initially floats horizontally in the water. The upper end of the lower part is attached to the crane via a crane line, and the lower part is then brought into a vertical state by loading ballast into the lower part. Thereafter, the upper part is moved to a pair of arm-shaped structures directly above the lower part. The lower part is lifted by the crane and/or the vessel is lowered, so that the lower part and the upper part meet each other and are then joined by welding or bolting, etc.

In particular the final steps of uniting and joining the lower part and the upper part described in US 2017/0197690 appear to be sensitive to relative movement between the lower part and the upper part, which is fixed to the vessel. It seems that heaving of the vessel and/or leaning of the lower part due to underwater currents would make it very difficult to safely join the lower part and the upper part.

It would therefore be desirable to provide for improved installation of a floating wind turbine, in particular installation that is less sensitive to the local environment at a deep sea location, such as weather and underwater currents.

Summary

In view of the above-mentioned and other drawbacks of the prior art, it is an object of the present invention to provide for improved installation of a floating wind turbine, in particular installation that is less sensitive to the local environment at a deep sea location, such as wind, waves, and underwater currents.

According to a first aspect of the present invention, it is therefore provided an installation arrangement for installation of a floating wind turbine including an elongated lower part with a bottom portion and a top portion, and an upper part with at least one blade attached thereto, to be joined to the top portion of the lower part during installation of the floating wind turbine, the installation arrangement comprising an elongated first floating structure having a first winch and a second winch spaced apart in a longitudinal direction of the first floating structure; an elongated second floating structure having a first winch and a second winch spaced apart in a longitudinal direction of the second floating structure; a joining structure attached to the first floating structure and the second floating structure, and holding the first floating structure and the second floating structure with an elongated open space therebetween; and the lower part of the wind turbine to be installed arranged in the elongated open space between the first floating structure and the second floating structure, wherein the bottom portion of the lower part of the wind turbine is releasably joined to each of the first winch and the second winch of the first floating structure and the first winch and the second winch of the second floating structure by respective winch lines. The present invention is based on the realization that coupling the bottom portion of the lower part of the wind turbine to winch lines enables controlled upending of the lower part, and also provides a stable coupling between the lower part of the wind turbine and the first and second floating structures. As compared to the situation in US 2017/0197690, without wires coupling the bottom portion of the lower part of the wind turbine to the vessel holding the upper part, the heaving of the vessel can be considerably reduced and the bending torque acting on the structure holding the upper portion of the lower part of the wind turbine in place to enable joining of the lower part and the upper part of the wind turbine can be considerably reduced. As a consequence, embodiments of the installation arrangement according to the present invention allow wind turbine installation in weather and/or current conditions that are not feasible using currently available installation arrangements and techniques. This, in turn, provides for increased utilization of costly equipment and vessels, and improved ramp up of installed offshore wind power.

According to a second aspect of the present invention, it is provided a method of installing a floating wind turbine, comprising the steps of: providing an installation vessel including: an elongated first floating structure having a first winch and a second winch spaced apart in a longitudinal direction of the first floating structure; an elongated second floating structure having a first winch and a second winch spaced apart in a longitudinal direction of the second floating structure; and a joining structure attached to the first floating structure and the second floating structure, and holding the first floating structure and the second floating structure with an elongated open space therebetween; arranging an elongated lower part of the wind turbine substantially horizontally in the open space between the first floating structure and the second floating structure of the installation vessel, a bottom portion of the lower part of the wind turbine being releasably joined to each of the first winch and the second winch of the first floating structure and the first winch and the second winch of the second floating structure by respective winch lines; arranging an upper part of the wind turbine, having at least one blade attached thereto, on the installation vessel over the open space between the first floating structure and the second floating structure of the installation vessel; controlling, at an installation location, each of the first winch and the second winch of the first floating structure and the first winch and the second winch of the second floating structure, of the installation vessel, to allow the lower part of the wind turbine to sink until the lower part of the wind turbine is substantially vertically arranged in the open space between the first floating structure and the second floating structure of the installation vessel; joining the upper part of the wind turbine to the lower part of the wind turbine; and releasing the winch lines from bottom portion of the lower part of the wind turbine.

The steps of the methods according to various embodiments of the present invention need not necessarily be performed in any particular order, except where this is technically required. For instance, the upper part of the wind turbine may be arranged on the installation vessel before or after the lower part of the wind turbine is arranged in the elongated open space, etc.

In summary, the present invention thus relates to an installation arrangement comprising an elongated first floating structure having a first winch and a second winch spaced apart in a longitudinal direction; an elongated second floating structure having a first winch and a second winch spaced apart in the longitudinal direction; a joining structure attached to the first floating structure and the second floating structure, and holding the first floating structure and the second floating structure with an elongated open space therebetween; and the lower part of the wind turbine to be installed arranged in the elongated open space between the first floating structure and the second floating structure, wherein the bottom portion of the lower part of the wind turbine is releasably joined to each of the first winch and the second winch of the first floating structure and the first winch and the second winch of the second floating structure by respective winch lines. Brief Description of the Drawings

These and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing an example embodiment of the invention, wherein:

Fig 1 is an illustration of an example of floating wind turbines that may suitably be installed using embodiments of the installation arrangement and method according to the present invention; and

Figs 2-11 schematically illustrate different steps of an installation method according to an example embodiment of the present invention, using an installation arrangement according to an example embodiment of the present invention.

Detailed Description of Example Embodiments

Fig 1 schematically shows an offshore wind farm 1 including a plurality of wind turbines 3, here in the form of vertical axle wind turbines (VAWTs) floating in the sea 5. These floating wind turbines 3 are illustrative examples of floating structures that can advantageously be installed using embodiments of the installation arrangement and method according to the present invention. It should, however, be noted that the installation arrangement and method according to the present invention is not limited to installation of VAWT, but is also suitable for installation of horizontal axle wind turbines (HAWTs) with spar type floatation systems.

An example embodiment of the installation method according to the present invention, and the installation arrangement according to an example embodiment of the present invention, will now be described with reference to the illustrations in figs 2-11 .

Referring first to fig 2, an elongated lower part 7 of a wind turbine 3 (in fig 1 ) is lowered from the quay 9 into the water by cranes 11 a-b. The elongated lower part 7 may have been manufactured in the vicinity of the quay 9, for example by welding steel sections together.

When the lower part 7 of the wind turbine is floating generally horizontally in the water, it is combined with an installation vessel 13 to form an installation arrangement according to an example embodiment of the present invention. This will be described with reference to the illustrations in fig 3 and figs 4a-b.

As is schematically shown in fig 3, the installation vessel 13 comprises an elongated first floating structure 15, an elongated second floating structure 17, and a joining structure 19. The first floating structure 15, here in the form of a first barge, has a first winch 21 and a second winch 23 spaced apart in a longitudinal direction of the first floating structure 15. Similarly, the second floating structure 17, here in the form of a second barge, has a first winch 25 and a second winch 27 spaced apart in a longitudinal direction of the second floating structure 17. The joining structure 19 is attached to the first floating structure 15 and the second floating structure 17, and holds the first floating structure 15 and the second floating structure 17 with an elongated open space 29 therebetween, here in a catamaran configuration.

The first winch 21 of the first floating structure 15 is opposite the first winch 25 of the second floating structure 17 in respect of the open space 29 between the first 15 and second 17 floating structures, and the second winch 23 of the first floating structure 15 is opposite the second winch 27 of the second floating structure 17 in respect of the open space 29 between the first 15 and second 17 floating structures.

In fig 3, the winches are indicated as all being arranged adjacent to the open space 29, which may simplify the routing of the winch lines 35a-d. It may, however, be beneficial to arrange at least a pair of the winches, such as the second winch 23 of the first floating structure 15 and the second winch 27 of the second floating structure 17 further away from the open space 29, to provide a longer lever for the torque resulting from, for example, deep sea currents that may be acting on the lower part 7 during and after upending. For example, the second winch 23 of the first floating structure 15 may be arranged at the long side of the first floating structure 15 facing away from the open space 29, and the second winch 27 of the second floating structure 17 may be arranged at the long side of the second floating structure 17 facing away from the open space 29. A pulley arrangement may be provided on the first 15 and second 17 floating structures to ensure that the front winch lines 35b, 35d can run freely between the bottom portion 33 of the lower part 7 and their respective winches 23, 27.

To provide a long lever also in the longitudinal direction of the first 15 and second 17 floating structures for the torque resulting from, for example, deep sea currents that may be acting on the lower part 7 during and after upending, the first and second winches of each floating structure may advantageously also distanced from each other in the longitudinal direction. Advantageously, the first winch 21 and the second winch 23 of the first floating structure 15 may be spaced apart in the longitudinal direction of the first floating structure 15 a distance corresponding to at least 50% of a total length of the first floating structure 15; and the first winch 25 and the second winch 27 of the second floating structure 17 may be spaced apart in the longitudinal direction of the second floating structure 17 a distance corresponding to at least 50% of a total length of the second floating structure 17. For further improved stability, the winches may be arranged even further apart in the longitudinal direction, such as at least 80% of the total length of the respective floating structures.

As is indicated by the block arrows in fig 3, the installation vessel 13 may be moved in relation to the floating lower part 7 of the wind turbine 3 to arrange the lower part 7 substantially horizontally in the open space 29 between the first floating structure 15 and the second floating structure 17 of the installation vessel 13.

Fig 4a and fig 4b are schematic top and bottom views, respectively, of an exemplary installation arrangement 31 according to the present invention. As is indicated in fig 4a and fig 4b, the installation arrangement 31 has been formed by arranging the lower part 7 of the wind turbine 3 in the open space 29 (fig 3) between the first floating structure 15 and the second floating structure 17 and releasably joining a bottom portion 33 of the lower part 7 to the first winch 21 and the second winch 23 of the first floating structure 15 and to the first winch 25 and the second winch 27 of the second floating structure 17 by respective winch lines 35a-d of the winches. In the example in figs 4a-b, the installation arrangement 31 comprises a winch line coupling arrangement 37 coupled to the respective winch lines 35a-d of the first winch 21 and the second winch 23 of the first floating structure 15 and the first winch 25 and the second winch 27 of the second floating structure 17. The winch line coupling arrangement 37 is here exemplified as a “bucket”, that is releasably coupled to the bottom portion 33 of the lower part 7 of the wind turbine 3. For example, there may be play between the “bucket” and the bottom portion 33 of the lower part 7, so that the “bucket” can be released from the bottom portion 33 by lowering the “bucket” further down when the lower part 7 is upended and floating. It should be understood that the winch line coupling arrangement 37 can be realized in many different ways. For example, a “plug” may extend axially with play into a corresponding axial cavity at the bottom portion 33 of the lower part 7, or a rigid or flexible net or grid may be user instead of the “bucket” shown in figs 4a-b, for surrounding the bottom portion 33 of the lower part 7, including a bottom end of the lower part 7. As an alternative to using a winch line coupling arrangement 37, the winch lines 35a-d may be releasably attached directly to the bottom portion 33 of the lower part 7, and remote control may be used for releasing the winch lines 35a-d from to bottom portion 33 of the lower part 7, when this is desired. Such remote control may, for example, be achieved using one or more remotely operated vessels (ROVs) as is well known to the skilled person.

When the installation arrangement 31 has been formed as described above, solid ballast 39 may be added to the bottom portion 33 of the lower part 7. In fig 5, it is schematically indicated that a suitable solid ballast 39, such as iron ore, is moved from the quay 9 to the interior of the lower part 7 through an opening 41 , which is later closed. As is also shown in fig 5, a top portion 43 of the wind turbine 3 may be lifted from the quay 9 to the installation vessel 13. The top portion 43 may advantageously be arranged on the joining structure 19 of the installation vessel 13, over the open space 29 where the lower part 7 is now shown as being arranged. Alternatively, the top portion 43 may be arranged at another position on the installation vessel 13, and more than one top portion 43 may be arranged on the installation vessel 13. Although not shown in the figures, the installation vessel 13 may be provided with a crane for moving a top portion 43 to the joining structure 19.

When the solid ballast 39 has been added and the top portion 43 of the wind turbine 3 has been arranged on the installation vessel 13, the installation arrangement 31 may be towed, as is indicated in fig 6, to a predefined installation location, which may be the final location of the wind farm 1 in fig 1 , or an intermediate location with a sufficient water depth to allow upending.

As an alternative to the procedure described above with reference to figs 2-6, one or more lower parts 7 may be towed or otherwise transported to the installation location, and the procedure described above with reference to figs 3-6 may take place at the installation location instead of at the quay 9.

On route to the installation location, or when the installation arrangement 31 has arrived at the installation location (or when the installation arrangement 31 has been formed at the installation location), the procedure of upending the lower part 7 can commence. Due to the solid ballast (39 in fig 5) added to the bottom portion 33 of the lower part 7, the lower part 7 strives to stand up. An intermediate state of the upending procedure is shown in fig 7, where the first 21 and second 23 winches of the first floating structure 15 and the first 25 and second 27 winches of the second floating structure 17 of the installation arrangement 31 are controlled by a winch control system 45 that is coupled to each of the winches. The installation arrangement 31 may be controlled to this intermediate state before arriving at the installation location, in order to stabilize the installation arrangement by the keel formed by the lower part 7. In fig 7, the winch control system 45 is schematically represented by a simple box, and the coupling to the respective winches by lines representing functional connection. It should be understood that the control system may be distributed and that the couplings may be wired or wireless. The winch control system 45 is configured to acquire signals indicative of tensions in the winch lines 35a-d, and individually control operation of the winches based on the acquired signals. In particular, the winch control system 45 may be configured to control the first 21 and second 23 winch of the first floating structure 15 and the first 25 and second 27 winch of the second floating structure 17 in such a way that tension is maintained in all of the winch lines 45a-d during the upending procedure. This is to provide for a continuous and stable mechanical coupling between the lower part 7 of the wind turbine 3 and the installation vessel 13, so that the lower part 7 and the installation vessel 13 move together, as one unit, in response to external factors, including wind, waves and currents.

The goal of the procedure of upending the lower part 7 is to position the lower part 7 in line with the upper part 43 that is arranged on (and temporarily coupled to) the joining structure 19 of the installation vessel 13 and at a suitable vertical position for joining a top portion 47 of the lower part 7 to the upper part 43 of the wind turbine 3, while maintaining the abovedescribed mechanical coupling between the lower part 7 and the installation vessel 13. To that end, the lower part 7 may be provided with at least one ballast tank (not shown) and the installation arrangement 31 may include a pump (not shown) for pumping sea water into or out of the at least one ballast tank, to control the level of the lower part 7. Advantageously, adjustable sea water ballasting and control of the winches by the winch control system 45 (fig 7) may be used to sink the lower part 7 to a configuration where the lower part 7 is in line with the upper part 43, straight under the upper part 43 (arranged on the joining structure 19), and with maintained non-zero tension in the wires 35a-d. From that configuration, the lower part 7 may be raised by controlling the winches, possibly in combination with reducing the controllable ballast, until the lower part 7 of the wind turbine 3 comes into contact with the upper part 43 of the wind turbine 3. The upper part 43 can then be joined to the lower part 7 of the wind turbine 3, for example by bolting corresponding flanges together. In particular, the configuration of the installation arrangement 31 according to embodiments of the present invention allows this joining to take place under more difficult environmental conditions than was previously possible, because of the stable mechanical coupling, via the wires 35a-d, between the installation vessel 13 and the lower part 7 of the wind turbine 3.

Following the joining, the winch lines 35a-d are released from the bottom portion 33 of the lower part 7. One example of such a release of the winch lines 35a-d is schematically shown in fig 9, where the release is achieved by controlling the winches (possibly in combination with the optional ballast pump) to allow the “bucket” (or other structure) to go free underneath the bottom portion 33 of the lower part 7 of the now assembled wind turbine 3. Alternatively, as was described further above, the winch lines 35a-d may be released using an ROV, or by other means for remote control.

When the winch lines 35a-d have been released, the wind turbine 3 may be decoupled from the installation vessel 13. As is schematically indicated in fig 10, the decoupling may be achieved by first moving the winch lines 35a-d (and any winch line coupling arrangement 37) out of the way by operating the winches, and releasing the wind turbine 3 from the joining structure 19. In fig 10, it is schematically indicated that the joining structure 19 comprises a hinged part 49 that can be pivoted out of the way to provide an open path along the open space 29 between the first floating structure 15 and the second floating structure 17. Alternatively, the joining structure 19 may be permanently open in one longitudinal direction, in analogy with the so-called “fifth wheel” of a trailer coupling (but in a completely different scale). Finally, the installation vessel 13 may be moved away from the assembled wind turbine 3, and be used for installation of the next wind turbine. The assembled wind turbine 3 may moored using, perse, known mooring techniques, possibly after towing to its final destination.

The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims.

In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.