Method for retrofitting a wind turbine foundation and wind turbine foundation

Abstract

A method for retrofitting a wind turbine foundation is provided. The foundation includes a first substantially elongate pile (31) in the ground. The method further includes: arranging a lower end of an elongate channel (41) of a second substantially elongate pile (40) around the first pile (31), wherein the elongate channel (41) extends substantially along a longitudinal direction of the second pile (40), and wherein the channel (41) is configured to receive at least a portion of the first pile. The method further includes lowering the second pile (40) such that the elongate channel (41) surrounds at least a portion of the first pile (31). Finally, the second pile (40) is driven into the ground (35).

Description

Technical Field

[0001] The present disclosure relates to methods for retrofitting a wind turbine foundation. The present disclosure also discloses a foundation for a wind turbine and a wind turbine including such a foundation. Background Art

[0002] Wind turbines are generally regarded as an environmentally safe and desirable renewable energy source. In general, wind turbines harness the kinetic energy of the wind and convert this kinetic energy into electrical energy. To maximize power generation efficiency and simplify the connection to the power grid, several wind turbines are often positioned close to each other at locations commonly referred to as "wind farms". In particular, these wind farms can be located in areas with relatively strong winds (such as, for example, at an offshore location).

[0003] Offshore foundations can be fixed or floating. In a floating wind turbine, the wind turbine is mounted on a floating structure that is anchored to the seabed by a plurality of cables. A cylindrical buoy or a tension leg platform wind turbine can be an example of a floating wind turbine. In a fixed foundation, the wind turbine foundation is connected to the ground. Examples of fixed foundations can be a jacket or a monopile. A jacket is a truss-like grid structure of steel profiles. These steel profiles can be welded or bolted together. Thus, the manufacture of a jacket can be time-consuming.

[0004] A monopile is a foundation structure for a wind turbine located at an offshore location and includes a single pile. The pile can generally have a long cylindrical caisson or tube that is driven into the seabed. The pile is fixed to the seabed by friction between the pile and the seabed along the portion of the pile that is buried in the seabed. The pile can be formed by assembling different sections at an onshore location. Subsequently, the pile can be driven to the required penetration depth at the offshore location of the turbine. Using a pile as a foundation structure can be advantageous because the same heavy lifting equipment can be used for both pile driving and the installation of the wind turbine, thus facilitating an assembly line type of operation involving relatively few and standardized operations. Monopile foundations can also be used in onshore locations.

[0005] The pile can be provided with a transition piece attached to the top of the pile for mounting the wind turbine. Methods for mounting the transition piece on the pile can include grouting, forging, or field welding. In general, the transition piece provides a mating surface to which the lower portion of the wind turbine tower can be attached (e.g., bolted).

[0006] Selecting a suitable wind turbine site is crucial for the economic and technical success of any wind turbine project. For example, it is important to consider a wind turbine location with suitable wind class and relatively low amounts of wind shear, among other things. However, typically the best offshore or onshore wind turbine sites have already been utilized. In offshore locations, such wind farms may include "old" wind turbines, i.e., wind turbines that have in most cases been phased out and which have a relatively low nominal power, for example, in the range of 1.5 - 3 MW. These old wind turbines may have reached the end of their service life. When a wind turbine needs to be decommissioned, the wind turbine is removed from its foundation, and the foundation may also need to be removed from the seabed. This can be an expensive process.

[0007] In addition, modern wind turbines are configured to generate a greater amount of electrical power than older wind turbines. However, modern wind turbines with higher nominal power require higher wind speeds to achieve this higher nominal power.

[0008] Accordingly, the present disclosure provides methods and systems for reusing a wind farm site, i.e., an offshore or onshore wind turbine site. Summary of the Invention

[0009] According to one aspect, there is provided a method for retrofitting a wind turbine foundation. The wind turbine foundation includes a first substantially elongated pile in the ground. The method includes disposing a lower end of an elongated channel of a second substantially elongated pile around the first pile, wherein the elongated channel extends substantially along a longitudinal direction of the second pile, and wherein the elongated channel is configured to receive at least a portion of the first pile. The method further includes: lowering the second pile such that the elongated channel surrounds at least a portion of the first pile; and driving the second pile into the ground.

[0010] According to this first aspect, the second pile can be lowered such that the elongated channel surrounds at least a portion of the first pile (forming part of a previously installed wind turbine foundation). Then, the second pile is driven into the ground. In this regard, the second hollow pile can be adapted to support a relatively new and relatively large - power wind turbine configured to generate a large amount of electrical power (compared to a less - efficient wind turbine that may have been previously installed on the first pile).

[0011] In addition, the second pile (and thus the corresponding wind turbine supported by the second pile) is installed at the location where the wind turbine was previously used, i.e., at the location corresponding to the first pile, which may, for example, have the best wind and soil conditions. Also, by installing the second pile in the previously installed foundation, part of the existing facilities, access roads, geotechnical studies, expropriation, permits, etc. can be at least partially reused, reducing the required investment and thus reducing the economic investment for installing a more - powerful wind turbine.

[0012] In addition, since the second pile is arranged around the previously installed first pile, the cost of demolishing the previously installed pile can be avoided.

[0013] Generally speaking, installing a second hollow pile around the first pile that forms part of the previously installed foundation can provide a cost-effective, efficient, and relatively easy-to-implement solution for installing an updated and more powerful wind turbine at the optimal offshore wind turbine location.

[0014] According to another aspect, there is provided a wind turbine foundation for a wind turbine. The wind turbine foundation includes a first elongate pile and a second elongate pile, and the bottom ends of the first elongate pile and the second elongate pile are arranged in the seabed. The second elongate pile surrounds the first elongate pile.

[0015] According to this aspect, there is provided a wind turbine foundation that includes a second pile surrounding the first pile, on which a relatively high-power wind turbine can be installed. In addition, the second pile can be installed in an existing area where the use of wind has been approved, that is, at the location corresponding to the first pile.

[0016] In yet another aspect, there is provided a method for repowering an offshore wind farm. The offshore wind farm includes a plurality of first wind turbines installed on a first offshore wind turbine foundation. The first offshore wind turbine includes a first substantially elongate pile driven into the seabed. The method includes selecting one or more first offshore wind turbine foundations and removing the first offshore wind turbines installed on the selected first offshore wind turbine foundations. The method further includes: arranging one or more second piles around at least a portion of the first pile of the selected first offshore wind turbine foundation; lowering the second piles to receive at least a portion of the first pile of the selected first offshore wind turbine foundation and driving the second piles into the seabed. In addition, a second offshore wind turbine is installed on the second piles. The second wind turbine has a higher nominal power than the first wind turbine.

[0017] According to this aspect, the nominal power of the wind farm can be increased, thereby reducing the installation cost.

[0018] Technical solution 1. A method for retrofitting a wind turbine foundation, the wind turbine foundation including a first substantially elongate pile (31) in the ground, the method comprising:

[0019] Arranging (200) the lower end of an elongate passage (41) of a second substantially elongate pile (40) around the first pile (31), wherein the elongate passage (41) extends substantially along the longitudinal direction of the second pile (40), and wherein the passage (41) is configured to receive at least a portion of the first pile (31);

[0020] Lower the second pile (40) such that the elongated channel (41) surrounds at least a portion of the first pile (31).

[0021] Drive the second pile (40) into the ground (35).

[0022] Technical solution 2. The method according to technical solution 1, characterized in that the lower end of the elongated channel of the second pile arranged around the first pile includes:

[0023] Attach a retainer to the second pile (40) to hold the second pile;

[0024] Connect a lifting device to the retainer to lift the retainer;

[0025] Lift the retainer attached to the second pile (40) to a substantially vertical position; and

[0026] Position the lower end (441) of the second pile (40) at or near the upper end (312) of the first pile (31).

[0027] Technical solution 3. The method according to any one of technical solutions 1 to 2, characterized in that the lower end of the elongated channel of the second pile (40) arranged around the first pile (31) includes centering the elongated channel of the second pile relative to the first pile (31).

[0028] Technical solution 4. The method according to any one of technical solutions 1 to 3, characterized in that the second pile (40) has a cylindrical or conical shape.

[0029] Technical solution 5. The method according to any one of technical solutions 1 to 4, characterized in that the first pile (31) extends from an upper end (312) to a lower end (311), defining a first length, and the second pile (40) extends from an upper end (442) to a lower end (441), defining a second length, wherein the second length is longer than the first length.

[0030] Technical solution 6. The method according to any one of technical solutions 1 to 5, characterized in that it further includes:

[0031] Position the bottom portion of the wind turbine tower (2) on the second pile (40).

[0032] Aspect 7. The method according to Aspect 6, characterized in that arranging the bottom part of the wind turbine tower on the second pile includes connecting a transition piece (95) to the second pile (40) and connecting the transition piece (95) to the bottom part of the wind turbine tower (2).

[0033] Aspect 8. The method according to Aspect 7, characterized in that connecting the transition piece (95) to the second pile (40) includes positioning the lower part of the transition piece (95) in the space formed between the inner side wall (80) of the elongated channel (41) and the outer side wall (81) of the first pile (31).

[0034] Aspect 9. The method according to Aspect 8, characterized in that connecting the transition piece (95) to the second pile (40) includes filling at least a part of the space formed between the inner side wall (80) of the elongated channel of the second pile and the outer side wall (81) of the first pile (31) with grout to connect the second pile to the transition piece.

[0035] Aspect 10. The method according to any one of Aspects 1 to 9, characterized in that it further includes attaching the second pile to the first pile.

[0036] Aspect 11. The method according to any one of Aspects 1 to 10, characterized in that it further includes removing an old transition piece (33) connected to the first pile (31) before arranging the second pile around the first pile.

[0037] Aspect 12. The method according to any one of Aspects 1 to 11, characterized in that the wind turbine is an offshore wind turbine and the ground (35) is the seabed.

[0038] Aspect 13. A method for power retrofitting an offshore wind farm including a plurality of first wind turbines installed on a first offshore wind turbine foundation, wherein the first offshore wind turbine foundation includes a first substantially elongated pile (31) driven into the seabed (35); the method includes:

[0039] selecting one or more first offshore wind turbine foundations,

[0040] removing the first offshore wind turbines installed on the selected first offshore wind turbine foundations;

[0041] retrofitting the selected offshore wind turbine foundations according to Aspect 12; and

[0042] Install a second offshore wind turbine (41) on the modified offshore wind turbine foundation, wherein the second wind turbine has a higher nominal power than the first wind turbine, and wherein.

[0043] Technical solution 14. A wind turbine foundation for a wind turbine, comprising:

[0044] A first slender pile (31) and a second slender pile (32),

[0045] The bottom end (311) of the first slender pile (31) driven into the ground (35) and the bottom end (441) of the second slender pile (41),

[0046] wherein the second slender pile (41) is arranged to surround the first slender pile (31).

[0047] Technical solution 15. The wind turbine foundation according to technical solution 14, characterized in that the bottom end (311) of the second pile (31) is arranged deeper in the seabed than the bottom end (411) of the first pile (31). Description of the drawings

[0048] The following will describe non-limiting examples of the present disclosure with reference to the drawings, in which:

[0049] Figure 1 A perspective view of a wind turbine according to an example is shown;

[0050] Figure 2 A detailed internal view of the nacelle of a wind turbine according to an example is shown;

[0051] Figures 3 to 7 Schematically shows a series of situations that may occur during the execution of a method for modifying the foundation of a previously installed offshore wind turbine according to an example;

[0052] Figure 8 Schematically shows an example of a wind farm layout, where the wind farm has not been modified;

[0053] Figure 9 Schematically shows after the wind farm has been modified Figure 8 Another layout of the wind farm;

[0054] Figure 10 Is an illustration of a block diagram describing an example of a method for modifying a wind turbine foundation, the wind turbine foundation including a first substantially slender pile in the seabed;

[0055] Figure 11A diagrammatic illustration of an example of a method for retrofitting an offshore wind farm that includes a plurality of first wind turbines mounted on a first offshore wind turbine foundation. Detailed Description

[0056] In these figures, the same reference numerals have been used to denote matching elements.

[0057] In the present disclosure, expressions such as up, down, vertical, horizontal, etc. are given with reference to the expected positions of the reference pile and the transition piece during installation.

[0058] Throughout the present disclosure, the term "ground" encompasses the term "seabed". Throughout the present disclosure, the term "seabed" refers to the bottom of the sea or ocean in which an offshore wind turbine foundation can be installed.

[0059] Figure 1 A perspective view showing an example of a wind turbine 1. As shown, the wind turbine 1 includes a tower 2 extending from a support surface 3, a nacelle 4 mounted on the tower 2, and a rotor 5 coupled to the nacelle 4. The rotor 5 includes a rotatable hub 6 and at least one rotor blade 7 that is coupled to the hub 6 and extends outwardly from the hub 6. For example, in the example shown, the rotor 5 includes three rotor blades 7. However, in alternative embodiments, the rotor 5 may include more or fewer than three rotor blades 7. Each rotor blade 7 may be spaced apart from the hub 6 to facilitate rotation of the rotor 5 so that kinetic energy can be converted from wind energy into useful mechanical energy and subsequently into electrical energy. For example, the hub 6 may be rotatably coupled to a generator 10 ( Figure 2 ) positioned within the nacelle 4 or forming part of the nacelle to permit the generation of electrical power. In this example, the wind turbine is an onshore wind turbine, and in other examples, it may be an offshore wind turbine.

[0060] Figure 2 Shows Figure 1 A simplified internal view of an example of the nacelle 4 of the wind turbine 1. As shown, the generator 10 may be disposed within the nacelle 4. Generally, the generator 10 may be coupled to the rotor 5 of the wind turbine 1 for generating electrical power from the rotational energy generated by the rotor 5. For example, the rotor 5 may include a main rotor shaft 8 coupled to the hub 6 to rotate therewith. The generator 10 may then be coupled to the rotor shaft 8 such that rotation of the rotor shaft 8 drives the generator 10. For example, in the embodiment shown, the generator 10 includes a generator shaft 11 that is rotatably coupled to the rotor shaft 8 via a gearbox 9. In other examples, the generator may be directly coupled to the rotor hub.

[0061] It should be understood that the rotor shaft 8, the gearbox 164, and the generator 10 may be generally supported within the nacelle 4 by a support frame or base plate 12 positioned at the top of the wind turbine tower 2.

[0062] The nacelle 4 is rotatably coupled to the tower 2 via a yaw system 20. The yaw system includes a yaw bearing (not visible in Figure 2 ), which has two bearing members configured to rotate relative to each other. The tower 2 is coupled to one of the bearing members, and the bottom plate or support frame 12 of the nacelle 4 is coupled to the other bearing member. The yaw system 20 includes a ring gear 21 and a plurality of yaw drives 22, which have a motor, a gearbox, and a pinion that engages with the ring gear to rotate one of the bearing members relative to the other.

[0063] The blade 7 is coupled to the hub 6 by means of a pitch bearing 100 between the blade 7 and the hub 6. The pitch bearing 100 includes an inner ring and an outer ring. The wind turbine blade can be attached to either the inner bearing ring or the outer bearing ring, while the hub is connected to the other bearing ring. When the pitch system 101 is actuated, the blade 6 can perform a relative rotational movement with respect to the hub 5. Accordingly, the inner bearing ring can perform a rotational movement with respect to the outer bearing ring. Figure 2 The pitch system 101 of

[0064] Figures 3 to 7 Schematically shows a series of situations that may occur during the execution of a method for retrofitting an offshore wind turbine foundation according to an example, the foundation including a first substantially elongated pile in the seabed. The method is described below with reference to the series of situations shown by Figures 3 to 7 .

[0065] In this example, the wind turbine foundation is an offshore wind turbine foundation and the ground is the seabed. However, in some other examples, the foundation may correspond to an onshore wind turbine foundation.

[0066] In the present disclosure, the term "retrofitting a wind turbine foundation" refers to reusing at least a part of an already installed wind turbine foundation. Retrofitting a wind turbine foundation may include power retrofitting of the wind turbine foundation, i.e., retrofitting an existing wind turbine foundation to accommodate a wind turbine with a higher nominal power. Retrofitting may also include correcting an incomplete or failed monopile installation on the ground. An installation may be considered incomplete or failed when the expected bearing capacity of the installed monopile is not achieved. This may occur when a rocky ground is found to cause the monopile to not be driven to the expected depth.

[0067] In Figure 3In this case, a foundation 30 is provided. The foundation 30 includes a first substantially elongated pile 31. The first elongated pile is a single pile. As used herein, a pile is an elongated connecting member, for example made of steel. The pile is driven several meters into a surface such as a seabed in the case of an offshore wind turbine, or several meters into the ground in the case of an onshore wind turbine. The pile may be cylindrical in shape. However, the pile may also be conical, or they may have any other suitable shape.

[0068] The first pile 31 (e.g., a single pile) extends longitudinally from a lower end 311 to an upper end 312 (see also Figure 4 ). The upper end 312 of the pile 31 in this figure extends above the water surface 32. Thus, the length of the first pile 31 is defined between the two ends. The width and depth of the first pile or single pile can be determined by engineering analysis, taking into account the applied loads (e.g., lateral shear forces), seabed conditions, and other factors. For example, the first pile can withstand the wind turbine loads of a first type of wind turbine.

[0069] An offshore support structure, such as a transition piece 33, may also be provided. The transition piece 33 may be attached to the upper end 312 of the first pile 31. As shown in the figure, the lower part of the transition piece is located below the water surface 32. In particular, in order to install the transition piece 33 onto the first pile 31, the transition piece 33 may be lifted onto the first pile 31 and positioned on the upper end of the first pile 31. The transition piece 33 may include a retainer (not shown) that engages the upper end (invisible) of the first pile 31 and attaches the transition piece 33 to the first pile 31. This fixes the transition piece 33 relative to the first pile 31.

[0070] The transition piece 33 may also include adjustment elements (not shown) in the form of, for example, jacks, which can be used to adjust the vertical orientation of the transition piece 33 relative to the first pile 31. For example, once the first pile 31 has been drilled / driven into the seabed 35, it may not be strictly vertical, and these jacks can thus enable the transition piece 33 to be adjusted to provide a horizontal flat surface for installing the wind turbine tower.

[0071] A grouting chamber for receiving grout may be provided between the inner surface 331 of the transition piece 33 and the outer surface 332 of the first pile 31. The inner surface 331 of the transition piece is also shown in Figure 4 . The grouting chamber may be provided with an adhesive or grout. In this way, the transition piece 33 can be properly attached to the first pile 31.

[0072] The wind turbine tower 2 may be connected to the transition piece 33. The transition piece 33 may also include an upper flange (invisible). The wind turbine tower 2 may include a flange at its lowest part. This flange may be bolted to the upper flange of the transition piece.

[0073] Before placing the transition piece 33 on the pile 31, such a transition piece 33 can be prefabricated, and it can include prefabricated auxiliary elements and facilities. For example, the transition piece 33 can be provided with an outer pipe, a ladder, a platform, an access device, and a vessel landing device. Prefabrication of such devices and equipment can be very beneficial in terms of both time and cost.

[0074] An offshore wind farm or wind power plant requires cables to transmit the electricity generated by the wind turbines to an onshore power conversion center. Additionally, the offshore wind turbines may require additional cables that can connect the offshore wind turbines to other offshore wind turbines or an offshore power conversion center. The cables for such offshore facilities can pass through the outer pipe that forms part of the transition piece 33.

[0075] Figure 3 An initial situation showing a method for retrofitting a wind turbine foundation is presented. In this initial situation, a first pile 31 is shown driven into the seabed 35. Additionally, as described above, a transition piece 33 is installed on the first pile 31, and an old wind turbine tower is fixed to the transition piece 31. The wind turbine can be configured to provide, for example, 2 MW of electrical power.

[0076] In Figure 4 the transition piece is removed from the first pile 31. A retainer can be attached to the transition piece 33. Lifting equipment (such as a crane) can be attached to the retainer through a lifting equipment attachment. The lifting equipment can thus lift the retainer and the transition piece simultaneously. The lifting equipment can be provided with a steering mechanism. The steering mechanism can allow the transition piece to be installed and removed at different angles. In this way, the transition piece 33 can be lifted and removed from the pile 31 in the direction of the arrow (arrow A). However, as described above, the pile 31 can remain driven in the seabed 35.

[0077] Therefore, the old transition piece connected to the first pile can be removed. In an example, removing the old transition piece can include attaching a retainer for holding the old transition piece to the old transition piece, and using lifting equipment to lift the old transition piece so that the transition piece is removed from the first pile.

[0078] In Figure 5 a second substantially elongated pile 40 or monopile can be provided. The second pile (and the remaining part of the wind turbine to be installed, including the transition piece and the wind turbine tower) can be placed on the main deck of, for example, a vessel and transported to the desired offshore location, i.e., the offshore location corresponding to the first pile 31.

[0079] The second pile can be arranged to receive at least a part of the first pile. Thus, the second pile can surround the first pile.

[0080] The second pile 40 extends longitudinally from a lower end 441 to an upper end 442, thereby defining a length. The material of the pile can be substantially the same as that described above for the first pile, such as steel. The outer diameter of the second pile 40 can be greater than the outer diameter of the first pile 31. The first pile extends from an upper end to a lower end, defining a first length, and the second pile extends from an upper end to a lower end, defining a second length.

[0081] In some examples, the length of the second pile can be longer than the length of the first pile. In some of these examples, an upper portion of the second pile can stand above an upper portion of the first pile. Alternatively or additionally, the portion of the second pile driven into the ground can be longer than the portion of the first pile driven into the ground.

[0082] In some examples, the length of the second pile and the length of the first pile can be substantially the same. The upper portions of the first and second portions can be substantially at the same height.

[0083] In some examples, the length of the second pile can be shorter than the length of the first pile. In some of these examples, the portion of the first pile driven into the ground can be longer than the portion of the first pile above the ground. This shorter portion driven into the ground can be compensated for by a larger second pile diameter. Accordingly, the contact area between the second pile and the ground can be greater than the contact area between the first pile and the ground.

[0084] In particular, the second pile 40 can include an elongate channel 41 along at least a portion of the longitudinal length of the second pile 40. The elongate channel can extend from the lower end 441. In Figure 5 the example, the elongate channel can extend from the lower end 441 to the upper end 442. Accordingly, a through hole can be formed in the second pile 40. In some examples, the elongate channel can extend from the lower end 441 to a section below the upper portion. Accordingly, a blind hole can be formed in the second pile 40.

[0085] In some examples, the channel 41 can have the same diameter at the upper end 442 of the second pile 40 and at the lower end 441 of the second pile 40. In any case, the channel 41 can be specifically shaped and sized to receive the first pile 31. To this end, the inner diameter defined by the inner sidewall of the channel 41 can be greater than the outer diameter of the first pile 31.

[0086] According to this example, a retainer (not shown) for holding the pile can be provided. As explained above, a lifting device can also be provided. The retainer can be attached to the second pile 40, for example, located on the deck of a vessel. The retainer can be, for example, a device for clamping the pile or a lifting beam having one or more controllable slings around the pile. The lifting device can also be connected to the retainer. The retainer (and thus the second pile 41) can be lifted and displaced towards the previously installed first pile 31.

[0087] Using a lifting device, the second pile 40 can be in a substantially vertical position. The passage 41 of the second pile 40 can be aligned with the upper end of the first pile 31. Thus, the elongated passage can be centered relative to the first pile. At this point, the second pile 40 can be displaced in the direction of the arrow (arrow B) using a lifting device. Thus, the second pile can be lowered to at least partially shield or cover the first pile. Thus, the first pile 31 can be received in the lower end of the second pile 40. Thus, the second pile is moved relative to the first pile until the second pile 40 is at least partially inserted into the seabed 35.

[0088] The pile 40 can be appropriately driven into the seabed by a hammer (such as a hydraulic hammer). The upper end 442 of the pile 40 can have a diameter exceeding the diameter of the hammer, and it can function to evenly distribute the impact of the "blow" of the hammer to the pile. In the present disclosure, the term "blow" is defined as the load transfer from the hammer to the pile 40. During the "blow", the hammer can be lifted by the pressure of the hydraulic fluid supplied to the hammer by a power unit (not shown). When the fluid pressure is removed, the hammer (not shown) descends and generates a downward stroke on the upper end 442 of the pile 40.

[0089] As shown in this figure, the inner sidewall 80 of the second pile 40 (specifically, the inner sidewall 80 of the elongated passage) surrounds the outer sidewall 81 of the first pile 30.

[0090] In an example, the pile 40 can be driven into the seabed by a vibration drive and a drilling device.

[0091] Obviously, additional piles can be installed in a substantially similar manner around the installed first and second piles.

[0092] In some examples, the lower end of the elongated passage of the second pile arranged around the first pile can include: attaching a retainer for holding the pile to the second pile and connecting a lifting device for lifting the retainer to the retainer; lifting the retainer having the second pile to a substantially vertical position; and arranging the lower end of the second pile at or near the upper end of the first pile.

[0093] In an example, the lower end of the elongated passage of the second pile arranged around the first pile includes centering the elongated passage relative to the first pile. For example, the distance between the inner sidewall 80 of the elongated passage and the outer sidewall 81 of the first pile can be between 0.5 meters and 10 meters, specifically between 0.5 meters and 5 meters.

[0094] In Figure 6In [description], the first pile 31 has been received into the passage of the second pile, and the second pile 40 has been driven into the seabed 35. As shown in the figure, the inner wall 80 of the second pile 40 (specifically, the inner wall 80 of the elongated passage) surrounds the outer wall 81 of the first pile 30. In particular, the side wall 80 of the second pile is arranged radially outward relative to the side wall 81 of the first pile. The side wall 80 of the second pile can be arranged at a distance between 0.5 meters and 10 meters relative to the side wall 81 of the first pile.

[0095] In some examples, the second pile can substantially surround the first pile along its length. In other examples, the second pile can only surround a part of the first pile.

[0096] In some examples, after removing the wind turbine and the transition piece, a part of the first pile can be cut and removed from the remaining part of the first pile. The length of the remaining part of the first pile can be shorter than the length of the first pile that holds the wind turbine. In these examples, the remaining part of the first pile can guide the second pile.

[0097] In an example, the lower end of the second pile is arranged deeper in the seabed than the bottom end of the first pile. However, in some other examples, the lower end of the second pile can be arranged at a shallower position in the seabed relative to the lower end of the first pile. The lower end of the second pile can also be at a depth substantially similar to the bottom end of the first pile.

[0098] A second pile 40 can be provided, which can be adapted to support a more modern and more powerful wind turbine relative to the wind turbine previously installed on the first pile (see Figure 3 ). As a result, the new wind turbine (which is more modern and more powerful compared to the wind turbine previously installed on the first pile) utilizes the optimal wind conditions at the offshore location corresponding to the wind turbine previously installed on the first pile. In addition, further geotechnical studies for positioning the new second pile are avoided. Additionally, due to the previously installed first pile, the seabed is harder, and thus the stability of the foundation is improved.

[0099] Once the second pile is fully driven around the first pile, the second pile can be connected to the first pile. Grout can be inserted into at least a part of the space between the inner wall of the elongated passage and the outer wall of the first pile. Thus, the first pile and the second pile can cooperate to bear the wind turbine load. Attaching the second pile to the first pile can help reduce the size of the second pile and thus reduce the cost of the retrofitted foundation.

[0100] In Figure 7 , a second transition piece 95 can be provided. The second transition piece 95 can be the same as or similar to the above-mentioned transition piece.

[0101] The second transition member 95 can be attached to the lifting device using a retainer as described above. The retainer with the second transition member 95 can be lifted to a substantially vertical position to install the second transition member 95 onto the second pile 40. In this regard, the lower portion 98 of the second transition member 95 can be aligned and displaced in the direction of the arrow (arrow C) towards the gap 97 formed between the outer wall of the first pile and the inner wall of the second pile. In this example, the bottom end of the transition member is disposed between the first and second elongated piles. However, in other examples, the transition member can partially surround the second pile.

[0102] The transition member can also include brackets for temporarily supporting the transition member before grouting. The brackets can be attached to the outer surface of the transition member, and they can support the weight of the transition member 95, for example, on the upper end of the second pile. These brackets can be supported by the lifting device or can be temporarily connected to the second pile.

[0103] Once the second transition member 95 is installed on the brackets, an annular space is formed between the lower portion 98 of the second transition member 95 and the inner portion of the side wall of the second pile. This annular space can be grouted to form a grouting chamber. The grouting chamber of the wind turbine foundation is adapted to receive grout. As used herein, the term grout includes any cement-based curable material or mixture of curable materials. The grout is used to support this wind turbine foundation.

[0104] The grout is thus introduced into the gap between the transition member and the inner side wall of the second pile. As a result, the second transition member 95 can be properly attached to the second pile 40. Subsequently, a new wind turbine tower (not shown) (and the corresponding wind turbine) can be installed on the second transition member 95.

[0105] Alternatively, a new wind turbine tower (not shown) (and the corresponding wind turbine) can be directly installed onto the flange of the second monopile, i.e., without a transition member.

[0106] Generally speaking, the bottom portion of the wind turbine tower can be disposed on the second pile. In particular, by connecting the transition member to the second pile and connecting the transition member to the bottom portion of the wind turbine tower, the bottom portion of the wind turbine tower can be disposed on the second pile. In an example, connecting the transition member to the second pile includes positioning the lower portion of the transition member in the space formed between the inner side wall of the elongated channel and the outer side wall of the first pile. In a further example, connecting the transition member to the second pile includes filling at least a portion of the space formed between the inner side wall of the elongated channel and the outer side wall of the first pile with grout for connecting the second pile to the transition member.

[0107] In an example, a wind farm can thus be provided that includes a plurality of wind turbines installed on the foundation as described above.

[0108] Figure 8Schematically shows the layout of a wind farm 90 including a plurality of foundations supporting wind turbines. These wind turbines may be relatively old. Compared with state-of-the-art wind turbines, these old wind turbines may have a relatively low nominal power. Each foundation (and its corresponding tower and wind turbine) may be the same as or similar to Figure 3 shown. The layout shown in this figure includes seventy "old" and / or "less powerful" wind turbines (each black dot 89 represents a wind turbine, tower, and its corresponding foundation). As described above, each of these less powerful wind turbines 89 may be configured to generate, for example, 2 MW. As a result, the electric power provided for such a wind farm may be around 140 MW.

[0109] Figure 9 Shows a repowered wind farm 99 that has been retrofitted with new and more powerful wind turbines using the method described above. Figure 8 The wind farm 90 has been power retrofitted into a repowered wind farm 99. In this figure, reference numeral 91 (a black dot surrounded by a circle) represents a previously installed foundation that has been retrofitted, where a more powerful and efficient wind turbine has been installed. Reference numeral 92 represents the location of a previously installed wind turbine that has been removed. In this example, no wind turbine is installed at location 92.

[0110] In some examples, all previously installed foundations 89 may be retrofitted to obtain retrofitted wind turbine foundations to support more powerful and heavier wind turbines.

[0111] In some examples, a plurality of previously installed foundations may be retrofitted to support new wind turbines, and a plurality of installed foundations may still support old wind turbines. The wind farm may thus include a plurality of new wind turbines installed on retrofitted wind turbine foundations, i.e., including a second pile surrounding a first pile, and a plurality of old wind turbines installed on the first pile.

[0112] The wind turbines installed on the retrofitted wind turbine foundations 91 utilize the favorable wind conditions and / or good soil conditions of the offshore location where, for example, "old" wind turbines were installed. For example, the retrofitted wind farm may include forty "new" wind turbines 91, each wind turbine configured to generate 12 - 20 MW. As a result, a wind farm 99 with 40 wind turbines can deliver 480 MW - 800 MW of electricity. Therefore, it is clear that compared with Figure 8 the less efficient wind farm shown in Figure 9 the retrofitted wind farm shown in is configured to generate more electric power, and all of this is achieved with fewer wind turbines that form part of the retrofitted wind farm.

[0113] Note that a wind turbine may require a cable that can connect an offshore wind turbine to other offshore wind turbines or a control center or an offshore conversion center. In this regard, once a new wind turbine is installed on a previously installed foundation, a first cable section of an "old" wind turbine connected to the wind farm can be replaced by a second cable section of a second wind turbine connected to the wind farm. In the example, only a part of the first cable section is replaced.

[0114] In the example, a method for power retrofitting an offshore wind farm is provided, the offshore wind farm including a plurality of first wind turbines installed on a first offshore wind turbine foundation. The method includes: selecting a part of the first offshore wind turbine foundation including a first elongate pile in the seabed; installing a second wind turbine on the selected first offshore wind turbine foundation, wherein the second wind turbine has a higher nominal power than the first wind turbine; and installing the second wind turbine as described above.

[0115] ​ is a diagrammatic illustration of an example of a method for retrofitting a wind turbine foundation, the wind turbine foundation including a first substantially elongate pile in the ground.

[0116] Block 200 represents the lower end of an elongate channel that surrounds the first pile with a second substantially elongate pile. The elongate channel extends substantially along the longitudinal direction of the second pile. The channel is configured to receive at least a part of the first pile. The second pile can be the same as described above.

[0117] Block 201 represents lowering the second pile such that the elongate channel surrounds at least a part of the first pile. Thus, the second pile can surround the first pile.

[0118] At block 202, the second pile can be driven into the ground (such as the seabed). The second pile can be drilled into the ground or the seabed as described above.

[0119] In some examples, according to any of the examples described herein, ​ the method can include additional operations, such as attaching the first pile to the second pile.

[0120] With this arrangement, a second pile can be provided that is configured to support a relatively modern and efficient wind turbine. Additionally, this new wind turbine can be installed at the same location as the previously installed first pile, i.e., at a location that may be optimal in terms of soil or wind conditions.

[0121] ​ is a diagrammatic illustration of an example of a method for power retrofitting an offshore wind farm, the offshore wind farm including a plurality of first wind turbines installed on a first offshore wind turbine foundation. The first offshore wind turbine includes a first substantially elongate pile or monopile driven into the seabed.

[0122] Block 300 represents the selection of one or more first offshore wind turbine foundations.

[0123] At block 301, provision is made for removing the first offshore wind turbine installed on the selected first offshore wind turbine foundation. In some examples, removing the first offshore wind turbine installed on the selected first offshore wind turbine foundation may include removing the first transition piece of the first pile attached to the selected first offshore wind turbine foundation.

[0124] In some examples, a portion of the selected first pile may be cut and removed from the remaining portion of the selected first pile. Thus, the remaining portion may still be driven into the seabed.

[0125] Block 302 represents arranging one or more second piles around the first pile of the selected first offshore wind turbine foundation.

[0126] In some examples, arranging the second pile around the first pile of the selected first offshore wind turbine foundation may include positioning the lower end of the elongated channel of the second pile to surround the upper end of the first pile, the elongated channel extending substantially along the longitudinal direction of the second pile to receive at least a portion of the first pile.

[0127] At block 303, the second pile is lowered to receive the first pile of the selected first offshore wind turbine foundation. The first pile may be inserted into the channel extending through at least a portion of the second pile.

[0128] At block 304, the second pile is driven into the seabed. In some examples, the second pile may be attached to the first pile. The bearing capacity of the foundation may thus be increased.

[0129] Finally, at block 305, a second offshore wind turbine is installed on the second pile. The second wind turbine has a higher nominal power than the first wind turbine.

[0130] Thus, the wind farm can be retrofitted for power. The total power generation can thus be increased.

[0131] This written description uses examples to disclose the invention, including preferred embodiments, and also enables any person skilled in the art to practice the invention, including making and using any device or system and performing any combined method. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. If such other examples have structural elements that are not different from the literal language of the claims, or if they include equivalent structural elements that have insubstantial differences from the literal language of the claims, then such other examples are intended to be within the scope of the claims. Those of ordinary skill in the art may mix and match aspects of the various described embodiments and other known equivalents of each such aspect to construct additional embodiments and techniques in accordance with the principles of this application. If reference numerals associated with the drawings are placed in parentheses in the claims, they are merely for the purpose of attempting to increase the intelligibility of the claims and should not be construed as limiting the scope of the claims.

Claims

1. A method for retrofitting a wind turbine foundation, the wind turbine foundation comprising a first substantially elongate pile (31) in the ground, the method comprising: Arranging (200) a lower end of an elongate passage (41) of a second substantially elongate pile (40) around the first substantially elongate pile (31), wherein the elongate passage (41) extends substantially along a longitudinal direction of the second substantially elongate pile (40), and wherein the passage (41) is configured to receive at least a portion of the first substantially elongate pile (31); Lowering (201) the second substantially elongate pile (40) such that the elongate passage (41) surrounds at least a portion of the first substantially elongate pile (31); Driving (202) the second substantially elongate pile (40) into the ground (35); Connecting a transition piece (95) to the second substantially elongate pile (40) and connecting the transition piece (95) to a bottom portion of a wind turbine tower (2).

2. The method according to claim 1, wherein Arranging the lower end of the elongate passage of the second substantially elongate pile around the first substantially elongate pile comprises: Attaching a retainer to the second substantially elongate pile (40) to hold the second substantially elongate pile; Connecting a lifting device to the retainer to lift the retainer; Lifting the retainer attached to the second substantially elongate pile (40) to a substantially vertical position; and Arranging the lower end (441) of the second substantially elongate pile (40) at or near an upper end (312) of the first substantially elongate pile (31).

3. The method according to claim 1, characterized in that, Arranging the lower end of the elongate passage of the second substantially elongate pile (40) around the first substantially elongate pile (31) includes centering the elongate passage (41) of the second substantially elongate pile relative to the first substantially elongate pile (31).

4. The method according to any one of claims 1 to 3, characterized in that, The second substantially elongate pile (40) has a cylindrical or conical shape.

5. The method according to any one of claims 1 to 3, characterized in that, The first substantially elongate pile (31) extends from an upper end (312) to a lower end (311), defining a first length, and the second substantially elongate pile (40) extends from an upper end (442) to a lower end (441), defining a second length, wherein the second length is longer than the first length.

6. The method according to claim 1, wherein Connecting the transition piece (95) to the second substantially elongate pile (40) includes positioning a lower portion of the transition piece (95) in a space formed between an inner sidewall (80) of the elongate passage (41) and an outer sidewall (81) of the first substantially elongate pile (31).

7. The method according to claim 6, wherein Connecting the transition piece (95) to the second substantially elongate pile (40) includes filling at least a portion of the space formed between the inner sidewall (80) of the elongate passage of the second substantially elongate pile and the outer sidewall (81) of the first substantially elongate pile (31) with grout to connect the second substantially elongate pile to the transition piece.

8. The method according to any one of claims 1 to 3, characterized in that, It further includes attaching the second substantially elongated pile to the first substantially elongated pile.

9. The method according to any one of claims 1 to 3, characterized in that, It further includes removing an old transition piece (33) connected to the first substantially elongated pile (31) before arranging the second substantially elongated pile around the first substantially elongated pile.

10. The method according to any one of claims 1 to 3, characterized in that The wind turbine is an offshore wind turbine, and the ground (35) is a seabed.

11. A method for power retrofitting an offshore wind farm including a plurality of first offshore wind turbines installed on a first offshore wind turbine foundation, wherein, The first offshore wind turbine foundation includes a first substantially elongated pile (31) driven into the seabed (35); the method includes: selecting one or more first offshore wind turbine foundations, removing the first offshore wind turbine installed on the selected first offshore wind turbine foundation; retrofitting the selected offshore wind turbine foundation according to the method of claim 10; and installing a second offshore wind turbine on the retrofitted offshore wind turbine foundation, wherein the second offshore wind turbine has a higher nominal power than the first offshore wind turbine.

12. A wind turbine foundation for a wind turbine, comprising: a first substantially elongated pile (31) and a second substantially elongated pile (40), lower ends (311) of the first substantially elongated pile (31) and lower ends (441) of the second substantially elongated pile (40) driven into the ground (35), wherein the second substantially elongated pile (40) is arranged to surround the first substantially elongated pile (31); wherein a transition piece (95) is connected to the second substantially elongated pile (40) and to a bottom portion of the wind turbine tower (z).

13. The wind turbine foundation according to claim 12, characterized in that, The lower end (441) of the second substantially elongated pile (40) is arranged deeper in the seabed than the lower end (311) of the first substantially elongated pile (31).

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