Method and a system for installing at least parts of a wind turbine on a floating foundation

Abstract

Method for installing at least parts of a wind turbine on a floating foundation comprising the steps of positioning the floating foundation at an anchoring system, b) attaching a mooring system to the positioned floating foundation, c) moving the floating foundation vertically in relation to water level, wherein the amount of movement is such that the foundation is still floating at least partially within water, installing at least parts of the wind turbine on the vertically moved foundation, detaching the mooring system from the floating foundation.

Description

[0001] Method and a System for Installing at least Parts of a Wind Turbine on a Floating Foundation

[0002] The subject matter relates to a method and a system for installing at least parts of a wind turbine on a floating foundation.

[0003] The need for wind energy exploitation in deep water increases due to the limited availability of shallow water off-shore installation sites near shore. Such deep water installations require floating foundations, which, when towed / transported to their final destination, are moored with catenary or taut spread mooring lines and potentials anchors in sea bed or suction caissons or the like.

[0004] However, installing the wind turbine on such floating foundations is still challenging. The wind turbine, comprising at least the tower, the nacelle, the hub and the blades, could be installed on the foundation at a harbour installation site. Usually, the foundation itself can be assembled onshore or in a dry dock. Then, the foundation is lifted into water and towed by tug boats to an installation site along a quayside. The foundation will then be moored. After that, installation of the parts of the wind turbine is possible from shore, using heavy lift cranes for the lifting operation. The problem arises from the constant movement of the platform due to waves in the harbour or dock. When installing the wind turbine onto a floating foundation any relative movement between the foundation and the turbine while the turbine is held by a crane can damage the turbine, crane or foundation. Hence it is necessary to minimise relative motion.

[0005] One possible approach to this is to perform the installation at port, with the crane on shore. However, even small waves present in ports may result in too large relative motion. It is thus necessary to, as far as practical, stop the foundation from moving. At current, it has been proposed to install the wind turbine only in benign weather conditions. During these times, the waves are very small. However, in harbours and basins, small waves and wakes cannot be excluded at all times. Thus, even when installing during benign weather conditions, even accepting the significant reduction in available installation time, the problem of movement is still not resolved completely.

[0006] Another approach lies in full grounding of the foundation, which means that the foundation will be completely submerged to sea-bed, which requires expensive seabed preparation. This could be done by ballasting the foundation such that it sits on the sea-bed.

[0007] Another option, which to the inventor’s knowledge has not been tested, lies in affixing the foundation to the quay wall. However, this will create extreme loads to both the foundation and the quay.

[0008] To exclude the risk of movement completely, the whole foundation including the wind turbine parts could be assembled on-shore or in a dry dock. This would cause significant cost and launching the complete installation into water is not yet understood no tested and bears enormous risks.

[0009] Further, the lifting crane could be provided with a dynamic positioning system. Such a system would compensate for vertical and horizontal movement of the foundation due to the waves. However, this system cannot compensate for pitch and roll. Hence it is not a full solution.

[0010] Based on the above problems with installing wind turbines on floating foundations, the subject-matter was based on the object of reducing the risk of damaging the foundation during the installation operation of the wind turbine. This object is solved by the subject matter with a method according to claim 1 and a system according to claim 21.

[0011] The subject-matter is based on the concept of moving the foundation out if its floating equilibrium position. This movement causes the foundation to be less- or insusceptible to smaller waves. Since the installation takes place in sheltered environments like harbour basins or ports, the conditions are expected to be benign and only small waves, for instance at maximum 20cm to 30cm are expected. This results in only very limited movements required to provide stable conditions for the installation of the parts of the wind turbine.

[0012] For preparation purposes, dredging, quay reinforcements, etc. may be necessary. Such preparation work is usual for any wind turbine installation and would also be undertaken for other installation method.

[0013] According to the subject matter, it is proposed to position the floating foundation at an installation position. Such an installation position may be close to shore, at a waterside of a quay, a harbour, a jack-up barge at some sheltered location or the like. The floating foundation can be towed to this location. This may involve the use tug boats for manoeuvring the foundation. It may be possible that the foundation has been fabricated / assembled on-shore and was lifted / launched into the water thereafter by a crane or other means. As will be described later, such a crane may also be used for the turbine installation. It may be possible to use the same crane for launching and installation. An installation position may also, for example, be a sheltered position, a sheltered bay position, a sheltered bay position using a jack-up barge to provide the crane rather than an onshore crane.

[0014] The floating foundation may, according to embodiments, be a buoy foundation, a sparbuoy foundation, a semi-submersible platform foundation, a tension leg platform (TLP) foundation or any foundation being buoyant and floating. It should be noted that in the following the terms foundation and floating foundation, as well as platform, may be used as synonyms.

[0015] The positioning of the foundation at the installation position may be such that the foundation is positioned at its neutral buoyancy position (i.e. its floating equilibrium position). This position may be a free floating position where the buoyancy of the foundation is sufficient to keep the foundation floating on water.

[0016] After the foundation has been positioned free floating at its installation position, a mooring system may be attached to the foundation. A mooring system may be understood as a system that keeps the foundation at a certain position. The mooring system may also be understood as tendon, tendon system, tensioning system, fixing system or the like. The mooring system may comprise tendons, ropes, lines, cables, catenae, chains, ropes or the like, all of which are termed “lines” in the following. The terms tendons, ropes, lines, cables, catenae, chains can be used as synonyms. The lines may be spread, in particular equally spread, to steady the foundation in its position. The lines may be attached around the foundation at positions. The lines may be attached around the foundation such that, when vertically moved, the tension forces apply essentially equally on all lines.

[0017] The vertical movement of the foundation may also be understood as applying a net vertical force to the foundation. A net vertical downward force can, for example, be applied to the foundation by tension in the moorings, either by tensioning the mooring lines, or by ballasting the foundation. A net vertical upward force can, for example, be applied to the foundation by removing slack from the moorings and de-ballasting the foundation.

[0018] It may be possible that the mooring system has been installed at the installation site prior to the positioning of the foundation. The mooring system may be attached to the positioned floating foundation. This may comprise affixing the lines to attachment points of the foundation. These attachment points may be mooring attachment points on the foundation, which are used for mooring the foundation at the final destination, after assembly and transport to the final destination in deep sea. However, it may also be possible that additional attachment point in addition to the mooring attachment points are provided. It may be possible that the additional attachment points have less mechanical strength than the mooring attachment points, since the additional attachment points are only used for installation purposes and are subject to less mechanical stress than the mooring attachment points. The attachment points may be positioned around the foundation such that, when the foundation is vertically moved, the tension forces apply essentially equally on all attachment points.

[0019] After the foundation has been positioned and secured in place, it is proposed that the mooring system is vertically moved.

[0020] The vertical movement can be obtained by tensioning the mooring system. Tensioning may be understood as exerting tensile forces onto the lines of the mooring system. The tensioning may be such that the foundation is moved vertically out of its neutral buoyancy position. The tensioning may be such that the foundation is moved vertically relative to the water level. The tensioning may be such that the movement is a vertical movement. The vertical movement can be either upward or downward, as explained below.

[0021] It is important to note that the movement is such that the foundation is neither moved vertically down to such an extent that the foundation rests on the sea-bed nor moved vertically up to such an extent that the foundation is lifted out of the water.

[0022] The amount of movement preferably is only a fraction of the flotation depth of the foundation in its neutral buoyancy position. The fraction is preferably less than 25%, more preferably less than 10%, in particular less than 5%, however, more than 0,5%. As has been said, the movement is such that the foundation is still floating at least partially within water.

[0023] After the foundation has been moved vertically, it is proposed that at least parts of the wind turbine are installed on the vertically moved foundation. The installation may include lifting the parts of the wind turbine onto the foundation and securing the parts of the wind turbine at the foundation. In particular, parts of the wind turbine may be installed one by one, which means that for instance at first a tower is installed, thereafter, the nacelle is mounted to the tower and thereafter the blades. It should be noted that this is a mere example and that more or less parts than the named ones can be installed.

[0024] It is also proposed, according to embodiments, that the tension in the lines is reduced prior to step e] gradually. Thus, the foundation is vertically moved into its buoyant neutral position over a timespan, i.e. several minutes. By this, damages to the lines and the attachments can be prevented. The foundation is not subject to increased mechanical stress. Waves induced by the vertical movement of the foundation are reduced in size, when the movement is gradual, i.e. slow.

[0025] It may be possible to not only install parts of the wind turbine in the manner as explained, but also further structures of the foundation may be attached to the foundation while being in the vertically moved position. These structures may include stability modules that may be required during towing the foundation. Such stability modules may be required at least of TLPs.

[0026] Eventually, in particular when all parts of the wind turbine are installed, in particular when all part of the wind turbine are installed which require crane lifting from shore, in particular which require crane support while affixing to the foundation, the mooring system is detached from the floating foundation. The then assembled foundation may be further assembled with part of the wind turbine which do not require support of a lifting crane during their installation. The foundation may be towed to the final off-shore destination, for instance in a wind farm, or to a wet storage site.

[0027] It has been found that only a relatively small displacement of the foundation out of its buoyant neutral position is required. Since the installation takes place in benign environments, such as a port, a harbour, a quay, a port basin or the like, the wave expected are small, i.e. less than 50cm in wave range.

[0028] According to embodiments, it is proposed that step c] comprises moving the floating foundation vertically down. It has been found that by moving the foundation down, the foundation is stabilized against vertical movement induced by waves. The vertical movement is preferably larger than the foundation would be dipped into water due to the weight of the part(s) to be installed. This results in the lines being under tensile force even after placing the part to be installed onto the foundation. The lines will be pulled by a pulling force. The force applied to the lines equals the buoyancy force caused by the displacement of the foundation under water. Any waves smaller than the distance the foundation has been pulled down will not result in motion in the foundation.

[0029] It should be noted that the vertical downward movement can be, for instance, be obtained by tensioning the mooring lines, which are attached to ground lower than the foundation. This tensioning results in pulling the foundation down. Due to tensioning, the foundation is moved vertically out of its neutral buoyancy position.

[0030] Vertical downward movement can be, for instance, also be obtained by ballasting the foundation, thus pushing the foundation down. Due to the ballasting, the foundation is moved vertically out of its neutral buoyancy position. The tensioning may be such that the foundation is moved vertically relative to the water level. It may then be possible to reel-in any slack on the mooring lines, and then de-ballast the foundation. This approach does not require a high-tension reeling system. According to embodiments, it is proposed that step c] comprises pulling the floating foundation vertically up. Besides pulling the foundation under water, it may also be possible to lift the foundation out of its buoyant neutral position. Again, small waves lower than the amount of lifting the foundation will not result in motion in the foundation. Pulling the foundation up may, for instance, be obtained by tensioning the mooring lines, which are attached to ground or a crane higher than the foundation. This tensioning results in pulling the foundation up. Due to tensioning, the foundation is moved vertically out of its neutral buoyancy position.

[0031] Pulling the foundation up may, for instance, be obtained by de-ballasting the foundation. Slack of mooring lines, which are attached to ground or a crane higher than the foundation can be reeled-in. Then, the foundation may be ballasted again. The foundation is moved vertically out of its neutral buoyancy position.

[0032] According to embodiments, it is proposed that the mooring system comprises lines and the floating foundation is moved vertically by means of the lines. Mooring lines can be made from syntetic material or steel ropes or chains. As explained above, the mooring lines can also be termed lines, tendors, tension lines, chains, ropes, catenae and the like. The term line or mooring line will be used as synonym for all of these. It is proposed that temporary mooring lines are attached to the foundation. Moreover, in case of pulling the foundation down, anchors may be provided as will be described later. The mooring lines may be attached to these anchors as well. It may be possible to attach the mooring lines to these anchors prior or after the foundation is towed into the installation position. The lines may be secured above or at water level for ease of installation. The lines may be attached to the quay. The lines may be equipped with floating aids, to allow the lines to float while not being installed / attached to a foundation. Floating aids can be buoys.

[0033] According to embodiments, it is proposed that the mooring system comprises a tensioning system attached to the lines for hauling the lines. The tensioning system may be installed on the foundation, on the anchors or separated from either. The tensioning system is configured to apply tension forces onto the lines, while these are affixed to the foundation. The tensioning system may apply tensioning forces on each of a plurality of lines. It is proposed that the foundation is held by more than one line. The lines may be spread around the foundation. The tensioning system may be configured to apply essentially similar tension forces to each of the lines. This allows the foundation to be stabilized in the moved position. The tensioning system may also be used for reeling in slack of the lines when ballasting / de-ballasting is applied as explained above.

[0034] It may also be possible to provide a ballasting / de-ballasting system. By such a system, temporal ballasting loads may be applied to the foundation. By such a system, loads may be temporally de-ballasted from the foundation.

[0035] According to embodiments, the anchors for holding the lines are configured to resist a vertical load. By using the anchors and the tensioning system, the foundation can be pulled down into the water.

[0036] According to embodiments, it is proposed that the tensioning system comprises at least one of a) a winch, b] a pulley system, and / or a crane. It is proposed that a winch is preferably temporarily installed on the foundation. For instance, one winch can be installed on the foundation for one mooring line each. The winches can be installed only for the duration of the installation of the wind turbine. Besides a winch, it may also be possible to use a pulley system. The lines may be affixed to an anchor and the foundation as well as a pulley system. Tug boats or an onshore winch may be attached to the pulley system to apply the tension force onto the lines. It may also be possible to use a crane. In this case, it may be possible to use a reverse roller at the anchor. One end of the line may be attached to the crane and the other end may be attached to the foundation. The reverse roller may be attached to the anchor.

[0037] According to embodiments, it is proposed that the tensioning system is installed on the floating foundation or the anchor. As explained above, the installation on the foundation may be temporal. An on-shore anchor may also be used. In this case, the tensioning system may be installed on the on-shore anchor, in particular as a permanent installation.

[0038] An anchor may be installed on-shore, for instance close to the installation position, e.g. the quay, or on the sea-bed. In the latter case, the anchor may be founded in the seabed, for instance using piles, columns, masts or the like, which are grounded, in particular pile founded (hammered), into the sea-bed. The structures may be made from steel and / or steel reinforced concrete. It may also be possible to use caisson anchors or gravity anchors. Gravity anchors may be such that their weight is sufficient to hold down the foundation, i.e. that their weight is higher than the buoyant force exerted by the pulled down foundation. Gravity anchors may rely on their mass to hold down the foundation. These anchors are preferably concrete structures holding heavy rocks.

[0039] According to embodiments, it is proposed that the floating foundation is moved vertically in relation to water level by an amount such that parts of the foundation are above water level. It is important to note that the method according to embodiments pertains to such pulling operations, during which the foundation is still within water. The foundation is neither pulled up such that it is fully out of the water nor pulled down that it is completely drowned into the water.

[0040] According to embodiments, it is proposed that the floating foundation is vertically moved down by an amount that depends on a weight of the to be installed part(s) of the wind turbine.

[0041] According to embodiments, it is proposed that the floating foundation is vertically moved down such that the sum of tension forces of all the mooring lines depends on a weight of the to be installed part(s) of the wind turbine, in particular that the sum of tension forces of all the lines is equal or greater than the weight of the to be installed part(s) of the wind turbine. In order to install the part(s) of the wind turbine, these part(s) are lifted by a heavy duty crane onto the foundation after it has been moved vertically. In order to dimension the amount of movement, it is proposed to obtain the weight (mass) of the part(s) to be installed. The weight of the part(s) (component(s)) to be installed can be calculated in advance. Based on the weight, the amount of vertical movement, by which the foundation will be “moved down” may be such that the sum of all tension forces in all lines is equal to or higher than the weight of the to be installed part(s).

[0042] According to embodiments, it is proposed that the floating foundation is moved vertically in relation to water level by an amount such that the movement comprises a safety margin. The safety margin may be such that the amount of tension forces applied depending on the weight of the part(s) to be installed is increased by at least 0,5%, preferably 1% or 2%, preferably less than 10%. The safety margin may be such that the amount of vertical movement is increased by at least 0,5%, preferably 1% or 2%, preferably less than 10% compared to the movement without safety margin. Once the parts are placed onto the foundation, the tension in the mooring lines will only be the safety margin.

[0043] According to embodiments, it is proposed that the floating foundation is vertically moved down by an amount such that the buoyancy induced by the movement is equal or greater than a weight of the to be installed part of the wind turbine. It is to be understood that when the part(s) of the wind turbine are placed onto the foundation, the weight of the part(s) works against the buoyant force of the foundation. The tensile force in the lines, which move / hold the foundation down is thus reduced. In order to keep the foundation stable, even when the full weight of the part(s) to be installed is applied onto the foundation, the pre-loaded tensile forces of all lines should be higher than the weight of the part(s) to be installed. In that case, the foundation remains stable, since it will not be pushed further down due to the extra weight applied. According to embodiments, it is proposed that the floating foundation is vertically moved down depending on the weight of only one part of the to be installed parts of the wind turbine and steps c] and d] are repeated at least twice. It is possible to apply a first tensile force onto the lines which depends on a first part to be installed. After this first part has been installed, the tensile force in the lines is reduced by the weight of the part which was installed. If then a further part is to be installed, the lines may be tensioned again by a force depending on the weight of the further part to be installed. Thus, the foundation is moved down step by step. This results in less tensile stress applied to the lines, since the tensile force applied depends only on the weight of one or a plurality of parts to be installed. Before tensioning, it may be possible to apply a ballast to the foundation to move it down by the ballast, then reel in slack of the lines and after that remove the ballast. The lines are then also tensioned and apply a tension force onto the foundation.

[0044] It is also possible to only move the foundation down by a fractional amount of the required amount prior to the installation. Then, during installation, i.e. while the weight of the part is placed onto the foundation, the tension forces may be incremented. This will reduce the total tension forces required, however, it will increase the complexity and risk of the installation operation.

[0045] According to embodiments, it is proposed that the floating foundation is vertically moved down depending on the weight of all to be installed parts of the wind turbine and steps c] and d] are performed only once. In this embodiment, the installation time is reduced, since only once the foundation is moved down. The tensile stress is higher than in the embodiment above, however, only one step of applying the tensile forces is necessary. In this embodiment, it is possible to move down the foundation by an amount sufficient for all parts to be installed in one go rather than only moving down for the next part to be installed. This requires greater forces and tensions.

[0046] According to embodiments, it is proposed that after step d] and prior to step e), the tensioning of the mooring system is released after all parts of the wind turbine are installed on the floating foundation. The remaining amount of vertical movement, after the installation of the part(s) is finished, is the safety margin. It is proposed to release the tensioning prior to step e). By releasing the tensioning, the foundation will be put in free floating state.

[0047] According to embodiments, it is proposed that the at least one anchor is installed at least on one of on-shore, for instance at the quay, underwater at the quay, underwater on the seabed. As explained above, for moving the foundation down, an anchor is necessary. It is proposed that each line is attached to an anchor. Thus, a plurality of anchors can be necessary. The anchors can be installed at least in parts on-shore. However, then the foundation can only be moved vertically by the vertical distance between the attachment point and the anchor. An anchor may also be installed under water, for instance at the quay. This allows affixing the anchor at the quay wall. Another option is to install the anchor in sea-bed, as explained above.

[0048] According to embodiments, it is proposed that the anchor is at least one of a caisson, a gravity anchor, a pile founded in sea-bed and a bollard.

[0049] According to embodiments, it is proposed that the floating foundation is vertically moved up such that a majority of the floating foundation is still under water. This vertical movement results in lifting the foundation in parts out of the water. In this case, it is preferred that a secondary crane system is installed to lift the foundation in addition to the crane required to lift the parts to be installed. The amount of movement may be less than in the embodiment above, since it may only account for the maximum height of waves to be expected.

[0050] The vertical upward movement may be obtained by applying a lifting or pulling force onto the foundation, e.g. by a lifting crane and tension lines. After the lifting operation, the lines apply a tension force onto the foundation to keep it in the moved position. It may also be possible to de-ballast the foundation to have it moving up, then reel in any slack in the tension lines, ballast the foundation again by which the lines keep the foundation in the lifted position.

[0051] After the foundation is positioned, the lines are attached to the foundation, and the foundation is moved up by only a “safety margin” required to negate the impact of the waves. Then, the part(s) to be installed are placed onto the foundation, adding weight to the foundation. The lines need to carry both the weight of the foundation (less its remaining buoyancy) and the weight of the part(s) to be installed.

[0052] According to embodiments, it is proposed that the floating foundation is vertically moved up by a fraction of the height of the floating foundation. The amount can be less then 10% and more than 0,5%, 1% or 2% of the height of the foundation.

[0053] According to embodiments, it is proposed that the floating foundation is vertically moved up such that the tension forces of all the lines is a fraction of the weight of the floating foundation. The sum of the tensile forces may be equal or higher (i.e. a safety margin) than the buoyancy of the foundation caused by the highest expected wave.

[0054] According to embodiments, it is proposed that when the floating foundation is vertically moved up, in step d) only a part of the to be installed parts of the wind turbine are installed, and prior to step e), the floating foundation is vertically moved down to reduce tensioning of the mooring system, wherein the floating foundation is still pulled up relative to water level and steps d) is repeated. After a first part is installed, the foundation may be lowered and the thus added buoyancy may reduce the tension force in the lines until the tension force is returned to only the safety margin. This is preferred not to exceed the maximum tensile strength of the lines. These steps can be repeated until all parts are installed.

[0055] A further aspect relates to an installation system according to claim 21. The subject matter will be explained in more detail with reference to the following figures. In the figures show:

[0056] Fig. la a first installation system for pulling the foundation downward in untensioned state according to embodiments;

[0057] Fig. lb the installation system of Fig. 1 in tensioned state;

[0058] Fig. 2a an on-shore lifting of the installation according to embodiments;;

[0059] Fig. 2b an off-shore lifting of the installation according to embodiments;

[0060] Fig. 3 a second installation system for moving the foundation upward according to embodiments;

[0061] Fig. 4a-c different tensioning systems according to embodiments;

[0062] Fig. 5a-c a first installation system for moving the foundation downward by ballasting according to embodiments

[0063] Fig. 6a a mooring system with tension lines according to embodiments;

[0064] Fig. 6b the mooring system of Fig. 3a with tensioned lines

[0065] Fig. 7 a flowchart of a method according to embodiments;

[0066] Fig. la schematically illustrates a first possible installation system. Illustrated is a floating foundation 2, which is free floating on sea level 16. The foundation 2 is positioned at an installation site near a quay 4. Underwater, on the sea-bed 14, anchors 12 are installed. The anchors 12 may be grounded in the sea-bed 12, for instance pile founded, or gravity type anchors, or caisson anchors or the like. The anchors 12 may be made from concrete, in particular steel reinforced concrete.

[0067] Attached to the anchors 12 are lines 8. As can be seen, the lines 8 are not tensioned. The lines 6 are attached to attachment points 6 at the foundation 2.

[0068] At the attachment points 6, a tensioning system may be installed. This may be a winch.

[0069] Once the foundation 2 is attached to the lines 8 by means of the attachment points 6, the tensioning system may be put into operation. By means of the tensioning system, the lines 8 are hauled such that they exert a pull down force onto the foundation 2. The foundation 2 is pulled vertically down.

[0070] Depending on the sum of all tension forces of all lines 8, the foundation 2 is pulled vertically down by a certain amount. In Fig. lb such a situation is illustrated.

[0071] As can be seen, the lines 8 are fully tensioned. The foundation 2 is pulled vertically down compared to Fig. la. The buoyant force of the foundation 2 is increased due to the pulling down. The increased buoyant force is compensated by the sum of all tension forces of all lines 8. It should be noted that the vertical component of the tension force needs to be taken into account.

[0072] In the pulled down position, a crane 18a lifts parts of a wind turbine 18a onto the foundation 2. The crane 18a is in Fig. 2a installed at an on-shore installation site. In contrast to that, Fig. 2b shows an installation site in shallow waters, however, off. Shore. The crane 18b an be installed on jack-up barge 5. As can be seen, it is not necessary that the installation site is immediately within a harbour basin or at a quayside.

[0073] When lowering the wind turbine 18b onto the foundation 2, the weight of the turbine 18b works on the foundation 2, and works against the buoyant force of the foundation 2. The foundation 2 is pulled down to such an extent that the resulting additional buoyant force is at least equal, preferably slightly higher than the weight of the turbine 18b to be placed onto the foundation 2. Thus, when the turbine 18b is fully placed onto foundation 2, the lines 2 are still tensioned, but to a lesser degree. This remaining tensioning may be such that even smaller waves do not cause the foundation to move vertically.

[0074] After the turbine 18b has been placed onto foundation 2, further part of the turbine 18b can be placed onto the foundation2, wherein then the lines 8 are tensioned anew. For the sake of brevity, in Figs 2a, b a turbine 18b with tower, nacelle and blades is depicted, these structures may however be installed one by one.

[0075] Fig. 3 illustrates a further embodiment. Therein, the foundation 2 is not pulled down, but lifted up. A secondary crane 20, in addition to crane 18a may be provided. The lines are attached to the attachment points 6 and the crane 20. The crane 20 or winches at crane 20 or attachment points 6 apply tension forces onto lines 8, such that they lift the foundation up. The amount by which the foundation is lifted may depend on the highest expected waves. Thus, for instance, the foundation is lifted 20cm or 30cm only.

[0076] Then, the turbine 18a is placed onto foundation 2, as explained above. Because a part of the turbine 18a has been placed onto foundation 2, the foundation moves slightly down. This movement is compensated for by again lifting foundation 2 up by the same amount prior to placing a further part of the turbine 18a onto the foundation 2.

[0077] Fig. 4a illustrates a tensioning system using a winch 7a. At least one line 8, preferably selected or all lines 8, in particular evenly distributed lines 8 are installed at a winch 7a, for instance either individually or on one single winch 7a. The winch 7a is installed on the foundation. The lines 8 are routed via deflection rolls 7b to the anchors 12. By winching the lines 8, the foundation is moved vertically down. Fig. 4b illustrates another tensioning system using a tug boat 9. At least one line 8, preferably selected or all lines 8, in particular evenly distributed lines 8 are installed at tug boat 9. On the tug boat, a winch 7a may optionally be installed. The lines 8 are routed via the attachment points 6 to the anchors 12. By moving the tug boat away from the foundation 2 or winching by winch 7 the lines 8, the foundation is moved vertically down.

[0078] Fig. 4c illustrates another tensioning system, which is on-shore. At least one line 8, preferably selected or all lines 8, in particular evenly distributed lines 8 are installed at a winch 7a, for instance either individually or on one single winch 7a. The winch 7a is installed on-shore at quay 4. The lines 8 are routed via deflection rolls 7b to the anchors 12. By winching the lines 8, the foundation is moved vertically down.

[0079] Figs. 5a-c illustrate another tensioning system using ballasting. A shown in Fig. 5a, the foundation is installed with mooring lines 8 at an installation position. The lines 8 are untensioned.

[0080] The, as shown in Fig. 5b, the foundation 2 maybe ballasted. In the illustrated example, the ballasting can be water 13. The water 13 is pumped into hollow structures of the foundation 2. The weight of the water 13 forces the foundation 2 down. While being ballasted, the lines 8 are tensioned or at least reeled in such that they are not loose.

[0081] Then, as shown in Fig. 5c, the ballast can be removed, e.g. by pumping the water 13 out of the foundation 2. The buoyant force of the foundation works against the tension of the lines 8, which hold the foundation 2 down.

[0082] Fig. 6a illustrated possible installations of anchors 12 and tensioning systems 6. The variants depicted may be combined or used alone. A first variant of an anchor 12 is on sea-bed 12. Another variant of an anchor 12 is at the quay wall 4. Another variant is to arrange the anchor 12 on shore near the quay wall 4. A tensioning system may be installed either at the attachment points 6, or the onshore anchor 12. As can be seen in Fig. 6a, the lines are not tensioned yet. The level meter 15 indicates the foundation 2 being in its floating equilibrium position.

[0083] Fig. 6b illustrated the system, after the lines 8 have be put under tension force. The foundation is thus vertically pulled down. The level meter 15 indicates the foundation 2 being in pulled down.

[0084] Fig 7 illustrates a flow chart of a method according to embodiments.

[0085] In a first step 40, a foundation is assembled on-shore or in a dry dock and the lowered into water.

[0086] In parallel, an installation site can be constructed in step 42. The construction can include dredging, reinforcement of the quay, installation of at least a first crane 18a, potentially a secondary crane 20, anchors 12. At the anchors 12, mooring line 8 may be attached and secured at the quay 4 or provided with floating aids.

[0087] In step 44, the foundation 2 is towed to an installation site and put into position. The towing can be done by tug boats.

[0088] Within installation position, the foundation 2 moored in step 46. The mooring lines 8 are attached to the attachment point 6. The mooring lines can be arranged around foundation 2 at various attachment points 6. The positioning of the attachment points 6 can be such that vertical forces applied onto the foundation are essentially equally distributed.

[0089] Then, in step 48, a tensioning system is activated and the lines 8 are hauled to exert a vertical force onto the foundation 2. In this embodiment, the pulling down will be described. The lines 8 are tensioned such that the foundation is pulled down. In step 50, parts of a turbine 18b are installed on the foundation 2 using crane 18a.

[0090] Steps 48 and 50 can be repeated until all parts are installed. Then, the lines 8 are released from the tensioning force, the lines 8 are detached from the attachment points 6 and the foundation 2 can be towed away.

[0091] Reference signs

[0092] 2 foundation

[0093] 4 quay 6 attachment points

[0094] 7a winch

[0095] 7b deflection roll

[0096] 8 lines

[0097] 9 tug boat 12 anchor

[0098] 13 water

[0099] 14 sea bed

[0100] 15 level meter

[0101] 16 water level 18a crane

[0102] 18b turbine part(s)

[0103] 20 secondary crane

[0104] 40-50 steps

Claims

C l a i m s1. Method for installing at least parts of a wind turbine on a floating foundation comprising the steps of: a] positioning the floating foundation at an anchoring system, b] attaching a mooring system to the positioned floating foundation, c] moving the floating foundation vertically in relation to water level, wherein the amount of movement is such that the foundation is still floating at least partially within water, d] installing at least parts of the wind turbine on the vertically moved foundation, e] detaching the mooring system from the floating foundation.

2. Method according to claim 1, characterized in that step c] comprises either a) Moving the floating foundation such that there is a net-downards force applied by the moorings or b] Moving the floating foundation such that there is a net upwards force.

3. Method according to claim 1 or 2, characterized in that the mooring system comprises lines and the floating foundation is moved vertically by means of the lines, in particular that the lines are taut mooring lines or tension lines.

4. Method according to claim 3, characterized in thatthe mooring system comprises a tensioning system attached to the lines for hauling the lines.

5. Method according to claim 4, characterized in that the tensioning system comprises at least one of a] a winch, b] a pulley system, c] a crane.

6. Method according to any one of claims 3 to 5, characterized in that the tensioning system is installed on the floating foundation or an anchor.

7. Method according to any one of the preceding claims, characterized in that the floating foundation is moved vertically in relation to water level by an amount such that at least parts of the foundation are above water level.

8. Method according to any one of the preceding claims, characterized in that the floating foundation is moved vertically in relation to water level by an amount such that the movement comprises a safety margin.

9. Method according to any one of the preceding claims, characterized in that the floating foundation is vertically pulled down by an amount that depends on a weight of the to be installed part of the wind turbine.

10. Method according to any one of the preceding claims, characterized in thatthe floating foundation is vertically pulled down such that the sum of tension forces of all the lines depends on a weight of the to be installed part of the wind turbine, in particular that the sum of tension forces of all the lines is equal or greater than the weight of the to be installed part of the wind turbine.

11. Method according to any one of the preceding claims, characterized in that the floating foundation is vertically pulled down such that the buoyancy induced by the movement is equal or greater than a weight of the to be installed part of the wind turbine.

12. Method according to any one of the preceding claims, characterized in that the that the floating foundation is vertically pulled down depending on the weight of only a part of the to be installed parts of the wind turbine and steps c] and d] are repeated at least twice.

13. Method according to any one of the preceding claims, characterized in that the that the floating foundation is vertically pulled down depending on the weight of all to be installed parts of the wind turbine and steps c] and d] are performed only once.

14. Method according to any one of the preceding claims, characterized in that after step d] and prior to step e), the tensioning of the lines is released after all parts of the wind turbine are installed on the floating foundation.

15. Method according to any one of the preceding claims, characterized in that the at least one anchor is installed at least on one of:a] on-shore at the quay, b] underwater at the quay, c] underwater on the seabed.

16. Method according to any one of the preceding claims, characterized in that the anchor is at least one of a] a caisson b] a gravity anchor c] a pile founded in sea-bed d] a bollard.

17. Method according to any one of the preceding claims, characterized in that the floating foundation is vertically pulled up such that a majority of the floating foundation is still under water.

18. Method according to any one of the preceding claims, characterized in that the floating foundation is vertically pulled up by a fraction of the height of the floating foundation.

19. Method according to any one of the preceding claims, characterized in that the floating foundation is vertically pulled up such that the tension forces of all the lines is a fraction of the weight of the floating foundation.

20. Method according to any one of the preceding claims, characterized in that when the floating foundation is vertically pulled up, in step d] only a part of the to be installed parts of the wind turbine are installed, and prior to step e), thefloating foundation is vertically move down to reduce tensioning of the mooring system, wherein the floating foundation is still pulled up relative to water level and step d] is repeated.

21. Installation system configured to install at least parts of a wind turbine on a floating foundation according to one of the preceding steps comprising: a mooring system configured to be attached to a floating foundation positioned at a waterside of a quay, a tensioning system configured to apply tension to the mooring system such that the floating foundation is moved vertically in relation to water level, wherein the amount of movement is such that the foundation is still floating at least partially within water, and an installation system configured to install at least parts of the wind turbine on the vertically moved foundation.

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