EP4267854A1

EP4267854A1 - Undersea cabling arrangement for floating wind turbine array

Info

Publication number: EP4267854A1
Application number: EP21848307.1A
Authority: EP
Inventors: Christophe BEKHOUCHE; Jan Ole DUNSERUD; Cliff ZIMSEN
Original assignee: Aker Offshore Wind AS
Current assignee: Aker Offshore Wind AS
Priority date: 2020-12-28
Filing date: 2021-12-27
Publication date: 2023-11-01
Also published as: WO2022146143A1

Abstract

The disclosure relates to an array of floating wind turbine assemblies (212), comprising at least two floating wind turbine assemblies (212). Each of the at least two floating wind turbine assemblies (212) comprise an ingoing and an outgoing electrical connection (242, 244), a first electrical cable (226) extending from the ingoing connection (242) on one lateral side of a first of the at least two floating wind turbine assemblies (212), and a second electrical cable (228) extending from the outgoing connection (244) on the same lateral side of the first of the at least two floating wind turbine assemblies (212). The second electrical cable (228) is connected to the ingoing electrical connection (244) of a second of the at least two floating wind turbine assemblies (212).

Description

UNDERSEA CABLING ARRANGEMENT FOR FLOATING WIND TURBINE ARRAY

Technical field

The present disclosure relates to arrays of floating wind turbine assemblies and a method for electrical connection of an array of floating power plants, as well as to a method for installation of an array of wind turbine assemblies, and a lifting apparatus and method.

Background

In recent decades, there has been an increasing desire to produce energy by sustainable means, as opposed to relying on the Earth's finite supply of fossil fuels. The goal of sustainable energy production may be achieved in many ways, and today one of the most popular is through the deployment of renewable energy devices, such as wind turbines.

Advancements in technology have enabled renewable energy devices such as wind turbines to be located offshore, where they may be able to be larger and better positioned to harness wind, solar, tidal, wave power etc. than their onshore counterparts. The operation of locating a power plant such as a wind turbine or solar panel offshore involves the transport and subsequent installation of the power plant at the offshore location, which can be a complex and expensive operation. Very often, offshore power plants are installed in arrays comprising multiple power plants (e.g. multiple wind turbines, multiple solar panels), which can be installed and maintained as a group of wind turbines, which may assist to improve the cost-efficiency of the whole process.

The installation of an array of power plants (e.g. an array of wind turbines) may require each power plant to be connected in an electrical network. In the case of an array of wind turbines, the more wind turbines in the array, the more complex this network may become, which may increase the cost of materials required to establish the network, as well as the complexity of the network itself which may lead to complications in cases where a wind turbine is required to be disconnected from the array (e.g. when a turbine is to be repaired or maintained). Such complications are undesirable as they may greatly increase the time and cost associated with operations on such an array.

Additionally, installation of power plants must be done within weather windows, when the weather is mild enough to enable the power plants to be installed without risk to personnel or equipment. Summary

It is an object of the present disclosure to mitigate, alleviate or eliminate one or more of the above-identified deficiencies and disadvantages in the prior art and solve at least the above mentioned problem.

According to a first aspect there is provided an array of floating wind turbine assemblies, comprising: at least two floating wind turbine assemblies; each of the at least two floating wind turbine assemblies comprising an ingoing and an outgoing electrical connection; a first electrical cable extending from the ingoing connection on one lateral side of a first of the at least two floating wind turbine assemblies; a second electrical cable extending from the outgoing connection on the same lateral side of the first of the at least two floating wind turbine assemblies, the second electrical cable connecting to the ingoing electrical connection of a second of the at least two floating wind turbine assemblies.

According to a second aspect there is a method for electrical connection of an array of floating wind turbine assemblies, comprising: providing at least two floating wind turbine assemblies at an offshore location, each of the at least two floating wind turbine assemblies comprising an ingoing and an outgoing electrical connection; connecting a first electrical cable to a first of the at least two floating wind turbine assemblies at the ingoing electrical connection thereof, and connecting a second electrical cable to a second of the at least two floating wind turbine assemblies at the outgoing electrical connection thereof, and extending the first and second electrical cable both from the same lateral side of the first of the at least two floating wind turbine assemblies; connecting the second electrical cable to a second of the at least two floating wind turbine assemblies at the ingoing electrical connection thereof. According to a third aspect there is provided an array of offshore wind turbine assemblies, comprising: at least two wind turbine assemblies; a common array cable configurable to be secured to a subsea location; each of the at least two wind turbine assemblies being electrically connected to the common array cable by a connection cable.

A fourth aspect relates to a method for installation of an array of wind turbine assemblies, comprising: providing at least two wind turbine assemblies at an offshore location; connecting a connection cable to each of the at least two wind turbine assemblies; providing a common array cable at an offshore location; securing the connection cable at a subsea location; electrically connecting each of the at least two wind turbine assemblies to the common array cable via the connected connection cable.

According to a fifth aspect there is provided a lifting apparatus for use in the construction of an offshore wind turbine, comprising; a lifting arrangement for engaging and lifting an object; a mounting arrangement for mounting the lifting apparatus to a wind turbine tower of the offshore wind turbine; an anchoring arrangement for anchoring the lifting apparatus to a buoyant structure of the offshore wind turbine.

A sixth aspect relates to a lifting method for use in construction of a floating offshore wind turbine, comprising: providing a buoyant structure with a turbine tower mounted thereon; mounting a lifting arrangement on the turbine tower via a mounting arrangement; anchoring the lifting arrangement to the buoyant structure; lifting an object relative to the turbine tower using the lifting apparatus.

Hence, it is to be understood that the herein disclosed disclosure is not limited to the particular component parts of the device described or steps of the methods described since such device and method may vary. It is also to be understood that the terminology used herein is for purpose of describing particular embodiments only, and is not intended to be limiting. It should be noted that, as used in the specification and the appended claim, the articles "a", "an", "the", and "said" are intended to mean that there are one or more of the elements unless the context explicitly dictates otherwise. Thus, for example, reference to "a unit" or "the unit" may include several devices, and the like. Furthermore, the words "comprising", "including", "containing" and similar wordings does not exclude other elements or steps.

The present disclosure will become apparent from the detailed description given below. The detailed description and specific examples disclose preferred embodiments of the disclosure by way of illustration only. Those skilled in the art understand from guidance in the detailed description that changes and modifications may be made within the scope of the disclosure.

Brief descriptions of the drawings

The above objects, as well as additional objects, features and advantages of the present disclosure, will be more fully appreciated by reference to the following illustrative and non-limiting detailed description of example embodiments of the present disclosure, when taken in conjunction with the accompanying drawings.

Figure 1 is a schematic illustration of an array of offshore wind turbine assemblies.

Figure 2 is an illustration of an electrical connection to a buoyant structure of a wind turbine assembly.

Figure 3 is an illustration of cables extending from a buoyant structure of a wind turbine assembly.

Figure 4A illustrates an array of wind turbine assemblies in a standard configuration. Figure 4B is a side view of one of the wind turbine assemblies of Figure 4A.

Figure 5 is a schematic illustration of an example of an array of wind turbine assemblies.

Figures 6 to 9 illustrate steps involved in a method for installing wind turbine assemblies.

Figure 10 is a schematic illustration of a partially constructed wind turbine.

Figure 11 is a plan view of the partially constructed wind turbine of Figure 10. Figure 12 is an illustration of a repositioning arrangement.

Detailed description

The present description provides an improved array of floating wind turbine assemblies and method for electrical connection of array of floating wind turbine assemblies. According to an example embodiment there is provided an array of floating wind turbine assemblies, comprising: at least two floating wind turbine assemblies; each of the at least two floating wind turbine assemblies comprising an ingoing and an outgoing electrical connection; a first electrical cable extending from the ingoing connection on one lateral side of a first of the at least two floating wind turbine assemblies; a second electrical cable extending from the outgoing connection on the same lateral side of the first of the at least two floating wind turbine assemblies, the second electrical cable connecting to the ingoing electrical connection of a second of the at least two floating wind turbine assemblies.

Figure 1 illustrates an illustration of an array of offshore wind turbine assemblies 212, which in this case refers to a wind turbine 215 mounted upon a floating platform 214. Here, three wind turbine assemblies 212 are illustrated, although it should be noted that other examples containing more or fewer wind turbine assemblies 212 are also possible. Further, in this example, each of the offshore wind turbine assemblies 212 are identical, however in other examples there may be differences between each of the wind turbine assemblies 212. For example, the wind turbines 215 may be of different energy-generation capacities, may have more or fewer blades, or be otherwise differently configured.

Although not illustrated in detail, the wind turbine assemblies 212 are located in an offshore location. The offshore location may be in a sea or an ocean, or may be in a lake or similar body of water. As stated, each of the wind turbine assemblies 212 comprises a buoyant structure in the form of a floating platform 214 with a wind turbine 215 mounted thereon. The floating platform 214 supports the weight of each of the wind turbines 215 and permits the wind turbine assemblies 212 to float on the surface of a body of water, in a configuration that is conducive to the production of electricity. Each of the floating platforms 214 is anchored in position by an anchoring means 220, which in this example comprises three anchoring members 220a-c. In this case, anchoring means 220 comprises three anchoring members that may be cables or chains. However, in other examples, a different anchoring means 220 may be used, for example a fixed structure. Further, more or fewer than three anchoring means 220a-c may be used. The anchoring means is configured to hold the respective floating platform 214 in an offshore location, although may permit the floating platform 214 some degree of movement, for example some degree of vertical movement which may be necessary if the floating platform 214 is in a location affected by tides, and/or some degree of horizontal movement, which may be necessary where the floating platform 214 is affected by wind or tidal motion with a force acting in horizontal direction.

Each of the wind turbine assemblies 212 comprises two electrical cables connected thereto. In Figure 1, the leftmost wind turbine assembly 212 comprises a first electrical cable 226 and a second electrical cable 228 connected thereto. Although described as electrical cables, both may additionally comprise other means of transmission, such as fibre optic cables that permit the transmission of data (e.g. for operation of some feature on the wind turbine assembly). In some examples, the electrical cables 226, 228 may be used for both power and data transmission. The electrical cables 226, 228 may permit an electrical current to flow to and from the wind turbine assemblies 212. In this example, the first electrical cable 226 may be considered to be an ingoing electrical cable (e.g. a cable that permits flow of an electrical current to the wind turbine assembly 212), while the second electrical cable 228 may be considered to be an outgoing electrical cable (e.g. a cable that permits flow of an electrical current from the wind turbine assembly).

As illustrated in Figure 1, each of the floating wind turbine assemblies comprises a central vertical axis 240. The first and second electrical cables 226, 228 are configured such that both the first and second electrical cables 226, 228 extend from one lateral side of the wind turbine assembly 212. Each of the first and second electrical cables 226, 228 may be considered to extend in a radial direction relative to the central vertical axis 240, and may be offset from each other by a relatively small angle (e.g. they may have a relatively small circumferential offset relative to the central vertical axis 240). For example, the circumferential offset between the first and second electrical cables 226, 228 may be fewer than 90 degrees (e.g. an acute angle), fewer than 45 degrees, fewer than 20 degrees, or the like.

Each of the first and second cables 226, 228 may be configured to extend from the wind turbine assembly 212 and towards the seabed, lakebed or other surface located below the wind turbine assembly 212 in a wave configuration, as is illustrated in Figure 1. As such, at least a part of each of the first and second cables 226, 228 may comprise a buoyant member, or buoyant members connected thereto so as to provide at least a part of each of the first and second electrical cables 226, 228 with some buoyancy, thereby assisting to permit each to remain buoyantly suspended in a subsea location. Having such a wave configuration may permit the wind turbine assembly 212 some degree of vertical and/or horizontal motion without the either of the cables 226, 228 being held in tension, which may cause damage to the cables. As the first and second electrical cables 226, 228 are permitted some degree of movement, each cable may be considered to be a dynamic cable, which is some degree of free movement and may be able to move with surrounding water, e.g. as a result of wave or tidal motion, which may assist to prevent damage to the cable as a result of offshore weather conditions. A portion of each of the cables 226, 228 rests on a surface below each of the wind turbine assemblies 212 (e.g. the seabed or lakebed), and each cable 226, 228 has, in this example, a circumferential offset such that there is no overlap between each of the cables. This may avoid the cables becoming tangled or damaged as a result of contact or interference therebetween. In addition, each of the first and second cables 226, 228 may extend from the wind turbine assemblies 212 so as to position each cable 226, 228 away from the anchoring means 220, for example as far as is possible from the anchoring means 220, so as to minimise interference therebetween, and remove any risk of damage to the cables 226, 228. In this example, the first and second cables 226, 228 extend radially from the wind turbine assembly 212 between the second and the third anchoring members 220b, 220c.

Here, the second electrical cable 228 extends from a first wind turbine assembly 212 (here, the leftmost wind turbine assembly) and towards a second wind turbine assembly 212 (in Figure 1, the central wind turbine assembly). The second electrical cable 228 may be an outgoing cable for a first of the wind turbine assemblies 212, and an ingoing cable for a second of the wind turbine assemblies 212. As such, the second electrical cable 228 of the first wind turbine assembly may be considered to function as the first electrical cable 228 of the second of the assemblies 212. As is illustrated in Figure 1, the cables 226, 228 extend along the lower subsea surface (e.g. the seabed, lakebed, etc.) initially in a direction radially away from the central axis 240 of the wind turbine assembly 212, before then extending in the direction of the next wind turbine assembly 212 in the array (e.g. the cable extends from the first to the second wind turbine assembly 212). In this example, the wind turbine assemblies 212 are in the form of a linear array, and as such, the cable comprises a bend of approximately 90 degrees. However, it should be noted that in other array configurations, the angle may differ. In this example, the cable 226, 228 extends along the lower surface (e.g. seabed, lakebed etc.) in a U-shape or an approximate U-shape. However, it should be noted that other shapes may be envisaged, for example a V-shape. The cable 226, 228 may comprise additional winding sections, where there are illustrated straight sections in Figure 1. For example, the cable may have a winding and/or undulating configuration on the seabed, lakebed, etc. as the cable 226, 228 transitions between each wind turbine assembly 212 in the array, and/or the cable may comprise straight sections as illustrated in Figure 1. Having the cables configured in such a shape may minimise interference between the cables 226, 228 and the anchoring means 220, while at the same time allowing both cables to extend from the wind turbines 212 both on the same lateral side of the wind turbines 212, and while optionally providing enough cable slack at a desired location to permit for some movement of the cable 226, 228 on the seabed, lakebed, etc..

Having the cables both extend laterally from the wind turbine assemblies may permit a user to more easily remove a wind turbine assembly from the array. For example, a wind turbine assembly may be disconnected from the array, and then each of the first and second cables 226, 228 connected to a junction box, thereby allowing continued operation of the array, in a single operation. As such, the configuration may enable better functioning of an array compared to known configurations.

Figure 2 illustrates an electrical connection to a buoyant structure 214 of a wind turbine assembly 212. Here, both the first and second electrical cables 226, 228 are connected to the buoyant structure 214. In this case, the first electrical cable 226 is connected to an ingoing electrical connection 242, while the second electrical cable 228 is connected to an outgoing electrical connection 244. Both the ingoing and outgoing electrical connections 242, 244 are adjacently located, and hang off the buoyant structure 214. Although not illustrated in detail, the first and second electrical cables 226, 228 may extend from the buoyant structure 214 via a bending stiffener, so as to ensure that the cables 226, 228 are not damaged as a result of bending under their own weight at the point of connection to the buoyant structure 214. As both the first and the second electrical cables 226, 228 extend laterally from the same side of the buoyant structure 214, a single bending stiffener may be used, thereby saving cost relative to known methods, which may have cables extending in vastly differing directions, thereby requiring the use of multiple bending stiffeners. In addition, in known methods, an I- tube may be required in order to wrap around and support an electrical cable connecting to a wind turbine assembly. However, in this example, no l-tube may be necessary.

In the illustration of Figure 2, the buoyant structure 214 is in the form of three columns, connected together to form a buoyant triangular structure. However, the skilled reader will understand that other configurations of buoyant structure may be possible. In this case, a wind turbine is mounted on the buoyant structure 214, which provides power. Figure 3 further illustrates the first and second cables 226, 228 as connected to the buoyant structure 214. In this Figure, the wave formation of each of the cables 226, 228 and the circumferential offset can be clearly seen. In this example, as well as those previous, the cables may be able to be installed (e.g. attached to the buoyant structure 214 and laid on the seabed or lakebed) by a vessel, which may comprise a crane or other installation apparatus for such a purpose.

Various further inventive aspects and embodiments according to the present disclosure will now be outlined in the following numbered clauses:

CLAUSE 1. An array of floating wind turbine assemblies, comprising: at least two floating wind turbine assemblies; each of the at least two floating wind turbine assemblies comprising an ingoing and an outgoing electrical connection; a first electrical cable extending from the ingoing connection on one lateral side of a first of the at least two floating wind turbine assemblies; a second electrical cable extending from the outgoing connection on the same lateral side of the first of the at least two floating wind turbine assemblies, the second electrical cable connecting to the ingoing electrical connection of a second of the at least two floating wind turbine assemblies.

CLAUSE 2. The array of clause 1, wherein the second electrical cable is positioned on the seabed in a U-shape between the first and the second of the at least two floating wind turbine assemblies.

CLAUSE 3. The array of clause 1 or 2, wherein the second electrical cable is positioned on the seabed in a V-shape between the first and the second of the at least two floating wind turbine assemblies.

CLAUSE 4. The array of any preceding clause, wherein each of the floating wind turbine assemblies comprises a vertical axis, and the first electrical cable extends from the first of the floating wind turbine assemblies at an angle that is circumferentially offset by 90 degrees or fewer from the second electrical cable extending from the first of the floating wind turbine assemblies, relative to the vertical axis of the first of the floating wind turbine assemblies.

CLAUSE 5. The array of clause 4, wherein the first electrical cable extends from the first of the floating wind turbine assemblies at an angle that is circumferentially offset by 45 degrees or fewer from the second cable extending from the first of the floating wind turbine assemblies, relative to the vertical axis of the first of the floating wind turbine assemblies.

CLAUSE 6. The array of any preceding clause, wherein the ingoing and outgoing electrical connections are adjacent.

CLAUSE 7. The array of any preceding clause, wherein the first and second electrical cables are supported on a first of the at least two wind turbine assemblies by a single bending stiffener adjacent the ingoing and outgoing electrical connection to the floating wind turbine assembly.

CLAUSE 8. The array of any preceding clause, wherein the floating wind turbine assembly comprises a buoyant structure, and the ingoing and outgoing electrical cables are mounted on the buoyant structure.

CLAUSE 9. The array of any preceding clause, wherein each of the floating wind turbine assemblies are floating wind turbine assemblies. CLAUSE 10. A method for electrical connection of an array of floating wind turbine assemblies, comprising: providing at least two floating wind turbine assemblies at an offshore location; connecting an ingoing and an outgoing electrical cable to a first of the at least two floating wind turbine assemblies, and extending the ingoing and outgoing electrical cable both from the same lateral side of the first of the at least two floating wind turbine assemblies; connecting an ingoing and an outgoing electrical cable to a second of the at least two floating wind turbine assemblies, the outgoing cable of the first of the wind turbine assemblies being the same as the ingoing cable of the second of the wind turbine assemblies, and extending the ingoing and outgoing electrical cable both from the same lateral side of the second of the at least two floating wind turbine assemblies.

CLAUSE 11. The method of clause 10, comprising positioning the electrical cable between two of the at least two floating wind turbine assemblies in a U-shape.

CLAUSE 12. The method of clause 10 or 11, comprising disconnecting the ingoing and outgoing cable from at least one of the at least two floating wind turbine assemblies, and connecting the ingoing and outgoing cable to a junction box.

Moving to the description of Figures 4 to 9, there provided an improved array of offshore wind turbine assemblies and method for installation of array of floating wind turbine assemblies. According to an example embodiment there is provided an array of floating wind turbine assemblies, comprising: at least two floating wind turbine assemblies; a common array cable configurable to be secured to a subsea location; each of the at least two floating wind turbine assemblies being electrically connected to the common array cable by a connection cable.

Figure 4A is a schematically illustrated array 10 of wind turbine assemblies 12, according to a known array structure, while Figure 4B illustrates an individual wind turbine assembly 12 shown from a side view in order to further illustrate the configuration of the associated cabling. In this example, four wind turbine assemblies 12 are illustrated, each being substantially identical. Each of the wind turbine assemblies 12 comprises a wind turbine 15 located on a floating platform 14 in an offshore location. The offshore location of the wind turbine assemblies 12 is indicated in Figure 4B by waterline 16. The floating platforms 14 of each wind turbine assembly 12 are held in place by an anchoring means 20. In this case, the anchoring means is in the form of three anchor members 20a-c, which may be chains or cables. Each wind turbine assembly 12 comprises one anchoring means 20, which connects the wind turbine assembly 12 to the seabed 22. Although not illustrated in Figures 4A or 4B, there may be a connection point on the seabed corresponding to each of the securing members 20a-c.

Here, each wind turbine assembly 12 is connected to the array 10 via an array cable 18. The array cable 18 is connected towards the base of each wind turbine assembly 12 in the array 10, and in use all (or substantially all) of the array cable 18 is located below the waterline 16. In this example, there are four wind turbine assemblies 12 that form the array 10, although the skilled reader will understand that an array can have more or fewer wind turbine assemblies 12 than those illustrated.

Here, the wind turbine assemblies 12 are illustrated as being daisy chained together, meaning that a first wind turbine assembly 12a is connected to a second wind turbine assembly 12b, which in turn is connected to a third wind turbine assembly 12c, as is illustrated. The power generated by each wind turbine assembly 12 may therefore be relayed to a desired location 22 via the array cable 18, with the power from wind turbine assemblies 12 being located further from the desired location 22 being routed through those wind turbine assemblies being located closer to the desired location 22.

While permitting the connection of each of the wind turbine assemblies 12 to an array 10, the illustrated configuration may have drawbacks, particularly when considering the disconnection of one of the turbines, such as the case may be when maintenance or repairs are required. In this instance, the disconnection of a single wind turbine assembly 12 may have an effect on the ability of all of the other turbine assemblies 12 in the array 10 to produce power, as it may disrupt the array network while the turbine assembly is being removed. This is therefore detrimental to the operation of the array, as it creates a period of downtime in which no electrical power is being produced.

Figure 5 illustrates an example of an array 110 of wind turbine assemblies 112 according to the present disclosure. As in the previous Figures 4A and 4B, this array 110 of wind turbine assemblies 112 comprises four wind turbine assemblies 112. Again, the array 110 may comprise more or fewer wind turbine assemblies 112 than those illustrated in this example. Each of the wind turbine assemblies 112 comprises a wind turbine 115 mounted on a floating platform 114, which supports the wind turbine 115 located thereon on the surface of a body of water, such as the sea, ocean, a lake or the like. The floating platform is, in turn, secured in place by an anchoring means 120. The anchoring means 120 of this example is comprised of three anchor members 120a-c. The securing members may be cables, chains, or the like, and each of the securing members 120a-c may be secured to a fixed point. The fixed point may be on the floor of the sea, ocean, lake, or the like, in which the array 110 of wind turbine assemblies 112 is located. A fixed point may be an anchor which is installed in place, for example by being physically fastened to the floor of the sea, ocean, lake or the like, or an anchor which may be sufficiently heavy so as to not be affected by movement of the wind turbine assembly, for example as a result of waves or tidal motion.

In this example, a common array cable 124 forms part of the array 110. The common array cable 124 is electrically connected to each of the wind turbine assemblies 112 of the array 110 by a connection cable 126. An individual connection cable 126 connects each of the wind turbine assemblies 112 of the array to the common array cable 124. Therefore, in this example, as there are illustrated four wind turbine assemblies 112 forming part of the array 110, then there are four connection cables 126, each corresponding to a respective wind turbine assembly 112. As illustrated, each of the connection cables 126 is positioned in a wave formation, which may assist to provide slack in the cable such that movement of the wind turbine assembly 112 relative to the common array cable 124 does not induce a high tension load in the connection cable 126, and does not result in large forces acting on the common array cable 124, which may cause damage to either cable 124, 126, or to the electrical connection therebetween. The wave formation may be achieved by attaching buoyancy members (not illustrated) to the connection cables 126, by providing a buoyant sheath around all or part of the buoyant connection cables 126 (e.g. whereby the buoyant sheath may have variable buoyancy therealong), to induce a buoyancy of the connection cable 126 relative to the surrounding fluid (e.g. fresh water or seawater), by fabricating all or part of the connection cable 126 from a buoyant material, or the like, or any combination thereof. In such examples, the connection cable 126 may be considered to be a buoyant connection cable 126. The buoyancy of the connection cable 126 may therefore be such that the connection cable 126 (or at least a portion thereof) is buoyantly suspended in the surrounding fluid, e.g. the seawater. The buoyancy of the connection cable 126 may therefore be such that it naturally assumes a wave formation when submerged, for example when electrically connected to both the wind turbine assembly 112 and the common array cable 124, as is illustrated in Figure 5.

A similar wave formation may be seen in Figures 4A and 4B. In line with the disclosure of this example, the array cable 18 of Figures 4A and 4B may be made buoyant by the attachment of buoyancy members thereto. It should be noted that, in the example of Figures 4A and 4B, the array 10 comprises wind turbine assemblies 12 each being connected to an array cable 18 having two wave formations therein. In contrast, the wind turbine assemblies 112 of Figure 5 require connection to one single cable having a wave formation (in this case, the buoyant connection cable 126). As such, in the example of Figure 5, a reduced number of buoyancy members are required as compared to that of Figures 4A and 4B, thereby saving the cost of the buoyancy equipment (e.g. buoyancy members, sheaths, or the like) and their installation. In the case of wind turbine assemblies 112 that must be transported offshore, this additionally reduces the complexity involved with having to transport both cables and buoyancy equipment to the offshore location.

Although in the example illustrated, the connection cable 126 is buoyant and extends from the wind turbine assembly 112 (e.g. the floating platform 114 of the wind turbine assembly 112) to the seabed, in other examples there may be a different configuration. For example, where the wind turbine assembly 112 is not a floating wind turbine assembly, but rather is fixed to the seabed (for example by a support structure such as a pile or a jacket structure) the connection cable may extend along the length of the support structure to the seabed. In such cases, the connection cable 126 may not require to be buoyant, and may have a negative buoyancy, for example. In examples where the wind turbine assembly 112 is fixed to the seabed, lakebed or the like, the connection cable 126 may be fastened to the support structure by any appropriate means, such as ties or clamps. As such, in this case, the connection cable 126 may not have a wave shape.

Illustrated in Detail A of Figure 5 is a securing arrangement 128. In this example, the securing arrangement 128 assists to secure a portion of the connection cable 126 relative to the common array cable 124, such that movement of the connection cable 126 is prevented or restricted. The securing arrangement 128 may be used to secure the connection cable 126 to a subsea securing point, which may be on the seabed, lakebed, or the like. The remainder of the connection cable 126 may have some degree of freedom of movement (relative to the secured portion held by the securing arrangement 128), and at least some of the remainder of the connection cable 126 may be buoyantly suspended, as is illustrated in Figure 5. The connection cable 126 may be considered to be a dynamic cable, or at least the potion of the buoyant that has some degree of freedom of movement may be considered to be a portion of dynamic cable, as relative movement of the cable is permissible. Having a dynamic cable may permit movement of the cable in response to forces from the surrounding water, thereby assisting to prevent damage to the cables as a result of offshore weather conditions. The portion of the connection cable 126 that is secured by the securing arrangement 128 may be located closer to the common array cable 124 than the wind turbine assembly 112, and may be located adjacent the common array cable 124. The secured portion of the connection cable 126 may extend from a point in the subsea location to the connection with the common array cable 124, or as illustrated, there may be further non-secured section of the connection cable 126 (e.g. a portion of the connection cable 126 that is not secured by the securing arrangement 128) located between the securing arrangement 128 and the connection between the common array cable 124 and the connection cable 126.

The securing arrangement may be any suitable arrangement that restricts movement of the connection cable 126. For example, the securing arrangement 128 may simply be a bag of weighted material (e.g. sand) that is placed over the connection cable 126, or bags of a weighted material, in order to restrict movement thereof. Alternatively or additionally, the securing arrangement 128 may be an anchor point that is installed on the seabed, and to which the connection cable 126 is connected (e.g. coupled or fastened via a cable or coupling). Having a securing arrangement while the array 110 is in use may assist to reduce or remove forces incident on the junction between the common array cable 128 and the connection cable 126 as a result of movement of the connection cable 126, for example due to wave or tidal motion, subsea or underwater currents, movement of the wind turbine assembly 112, or the like.

The electrical connection between the connection cable 126 and the common array cable 124 may be a direct electrical connection, as is schematically illustrated in Figure 5, or the connection may alternatively be via at least one additional component, such as a further section of spooled or spare cable, a further electrical component, or the like.

Illustrated in Detail B is further detail surrounding the connection between the connection cable 126 and the common array cable 124. As illustrated in Detail B, the connection is a branched connection in the form of a Y-type connection, or a Y-type connector. Having a Y-connector or branched connector may permit a simpler connection of each wind turbine assembly 112 to the common array cable 124, by permitting the connection cable 126 to be connected to the common array cable 124 at one point. In addition, having a Y-connector or branched connector in combination with a common array cable may permit a simpler configuration of the array 110. For example, rather than having to have an ingoing and an outgoing array cable to connect each wind turbine assembly to adjacent wind turbine assemblies, having a Y-connector or Y-connection arrangement permits each wind turbine assembly 112 in the array 110 to be connected to the common array cable 124 at a one point (e.g. a single point) and may permit each to share the common array cable 124.

While in Detail B the Y-connector illustrates each cable having a stepped configuration so as to merge into one single cable, it may be the case that one of the cables 124 runs straight, while the other of the cables 126 connects at a right or oblique angle relative thereto.

The common array cable 124 may be secured in place by any appropriate means. For example, the common array cable 124 may be secured in place by a weighted arrangement, for example which may be positioned in contact (e.g. above, or on top of) the common array cable 124 to assist to hold it in place, and which may be a simple and effective method for securing the cable 124 in place. An example of a weighted arrangement (e.g. an anchor arrangement) may be a bag of sand or stones, or a non-buoyant block of material. Alternatively or additionally, the common array cable 124 may simply be secured under its own weight in cases where the common array cable 124 has a negative buoyancy. Providing the common array cable 124 with a negative buoyancy may have the advantage of permitting the common array cable to be installed more simply and quickly than in other examples. Alternatively or additionally, the common array cable 124 may be affixed to a subsea structure, thereby holding it in place. For example, existing equipment that is located in a subsea location, such as pipework, or equipment that is installed with the specific intention of securing the cable 124, such as anchor points.

In some examples, a trench or structure may be installed or located on the seabed, lakebed, or the like, for positioning of the common array cable 124 therein. This may assist to prevent the array cable from moving from its subsea location without having to provide or install equipment or structures, which may pose logistical and cost challenges.

As illustrated, the connection cable 126 connects each wind turbine assembly 112 to the common array cable 124. The connection cable 126 may connect to the base of the respective wind turbine assembly 112 to permit transfer of power and, in some examples, electrical signalling between an external location (e.g. an onshore location) and the wind turbine assembly 112. The connection cable 126 may be connected to each wind turbine assembly 112 to maximise the distance between the connection cable 126 and the anchoring means 120. For example, where the anchoring means comprises three anchor members 120a- c, the connection cable 126 may be located between two of the anchor members 120a-c. For example, the connection cable 126 may run outwardly from the wind turbine assembly between two of the anchor members 120a-c, also running outwardly from the wind turbine assembly (a illustrated in Figure 5). The connection cable 126 may run outwardly equidistant from two of the anchor members 120a-c. The connection cable 126 may be located approximately angularly centrally between two of the anchor members 120a-c. The location of the connection cable 126 may be selected to minimise interference between the connection cable 126 and the anchor members 120a-c. In addition, in this example, having only a single connection member 126 extending from each turbine, as opposed to two in previous examples, may minimise the likelihood of any interference between each connection member 126 and the anchor members 120a-c.

In Figures 6 to 9, steps in the installation process of the array of wind turbine assemblies is described. In Figure 6, it can be seen that the wind turbine assemblies 112 have been positioned in a desired location for the array 110. Each of the wind turbines 112 is provided on a floating platform 114. In some examples, the floating platform 114 may be first towed to the desired location, for example by a tow vessel. Each wind turbine 112 may be provided and installed on the floating platform thereafter. Once the floating platform 114 has been provided at the desired location, the floating platform 114 may then be secured in the desired location. As previously described, and as illustrated in this example, this may be by the anchoring means 120. Once the floating platform 114 has been secured in place by the anchoring means 120 as previously described, it may be desirable at this stage to install a wind turbine 112 on each floating platform 114.

With the wind turbine assembly 112 in place, the connection cable 126 may be connected thereto. In some examples, the connection cable 126 may be installed entirely after the installation of the wind turbine assembly 112. The connection cable 126 having buoyancy members attached thereto may automatically provide the connection cable 126 with the desired wave formation when installed. In some other examples, adjustment of the buoyancy members on the connection cable 126 may be possible after installation, either by adjusting the buoyancy members in a subsea location, or by bringing at least a portion of the connection cable 126 to the surface, to adjust the buoyancy members at a surface location (e.g. on a vessel).

In order to assist in the installation of the connection cable 126, the securing arrangement 128 may be positioned towards a distal end of the connection cable 126 (relative to the wind turbine 112 and floating platform 114). The securing arrangement 128 secures a portion of the connection cable 126, in this case, to the seabed, lakebed, or the like. The securing arrangement 128 therefore assists in the installation process of the array 110 as it reduces the effect of subsea motion of the connection cable 126 on the installation process, by providing a restriction to such movement.

In Figure 7, there the process of connecting the connection cable 126 to the common array cable 124 is illustrated. In this case, a vessel 130 is used to carry the common array cable 124, and install it in the desired position. As can be more clearly seen in Detail C of Figure 7, a Y-connector 132 is located on the vessel 130 to which both the common array cable 124 and the connection cable 126 are attached. As is illustrated, securing arrangement 128 holds the connection cable 126 in position while the connection cable 126 extends from the securing arrangement 128 (e.g. located on the seabed or lakebed) and to the vessel 130. In having a securing arrangement 128 then it is ensured that the weight of the connection cable 126 located between the securing arrangement 128 and the wind turbine assembly 112 is not being supported by the vessel, which may be damaging to the vessel 130, or in particular to the Y-connector 132 on the vessel, which may otherwise be required to bear a significant weight. Instead, the securing arrangement 128 ensures that the weight of the connection cable 126 is distributed between the wind turbine assembly 112, and the seabed.

In Figure 8, there is a progression of the installation process shown. Here, the common array cable 124 and the connection cable 126 have been connected at the Y-connector 132, also illustrated in Detail D. The vessel 130 has then proceeded to lower the Y-connector from the vessel 130 and towards the seabed or lakebed. In this case, the Y-connector is taking the weight of the length of common array cable 124 and the length of connection cable 126 that is not positioned on the seabed or lakebed. It is desirable to minimise this weight to reduce the stresses on the Y-connector, which may not be designed to withstand very high stresses. The securing arrangement 128 is therefore of increased importance at this stage, as it serves to minimise the length of connection cable 126 that is not resting on the seabed, and the weight thereof that must be supported by the Y-connector 132.

Further progression of the method is illustrated in Figure 9. Here, the connection of one turbine 112 to the array 110 has been completed, and the vessel 130 is then able to continue towards a second wind turbine assembly 112 that is awaiting connection to the array 110. As the vessel 130 moves towards the second wind turbine assembly 112, it continues to lay a length of common array cable 124 on the seabed or lakebed. In addition, the Y-connector 132 that connects the first wind turbine assembly 112 to the array 110 is now positioned on the seabed.

Once the vessel reaches the second wind turbine assembly 112, the buoyant connection cable is retrieved and taken on board the vessel, and the steps of attaching both the common array cable 124 and the connection cable 126 via a Y-connector are repeated, as before. These steps may be continued several times depending on the desired number of wind turbine assemblies to be in the array 110.

As is illustrated in both Figures 5 and 9, each of the wind turbine assemblies 112 is attached via the connection cable 126 to the common array cable 124 at different axial locations. Each Y-connector 132 may be spaced along the common array cable at any appropriate distance, for example 100m, 200m, 300m or more. It should also be understood that, if required, it may be possible to electrically connect a first and second wind turbine assembly 112 to the common array cable 124 with a relatively short axial separation, for example lm, 5m, 10m or the like. Any two Y-connectors 132 may be connected to, or form part of, the common array cable 124 with a degree of axial separation.

Various further inventive aspects and embodiments according to the present disclosure will now be outlined in the following numbered A clauses:

CLAUSE Al. An array (110) of offshore wind turbine assemblies (112), comprising: at least two wind turbine assemblies (112); a common array cable (124) configurable to be secured to a subsea location; each of the at least two wind turbine assemblies (112) being electrically connected to the common array cable (124) by a connection cable (126). CLAUSE A2. The array (110) of clause Al, wherein the connection cable (126) connects each of the at least two wind turbine assemblies (112) to the common array cable (124) at an axially separated location.

CLAUSE A3. The array (110) of clause Al or A2, wherein the connection between the common array cable (124) and the connection cable (126) is in the form of a branch connection from the common array cable (124).

CLAUSE A4. The array (110) of any preceding A clause, wherein the common array cable (124) is connected to the connection cable (126) via a branched connector.

CLAUSE A5. The array (110) of any preceding A clause, comprising a securing arrangement (128) to secure a portion of each of the connection cables (126) of the array at a subsea location.

CLAUSE A6. The array (110) of clause A5, wherein the securing arrangement (128) comprises an anchor in the form of a weighted component.

CLAUSE A7. The array (110) of clause A5 or A6, comprising a connection point at the subsea securing location for securing one of the connection cables (126) thereto.

CLAUSE A8. The array (110) of any preceding A clause, wherein at least a portion of the connection cable (126) is buoyant.

CLAUSE A9. The array (110) of any preceding A clause, wherein the connection cable (126) comprises at least one buoyancy member mounted thereon.

CLAUSE A10. The array (110) of any preceding A clause, wherein at least a portion of each of the connection cables (126) is suspended in a subsea location at a position below a water level.

CLAUSE All. The array (110) of clause A10, wherein at least a portion of each of the connection cables (126) is suspended in a wave formation.

CLAUSE A12. The array (110) of any preceding A clause, wherein each of the at least two wind turbine assemblies (112) are connected to the common array cable (124) by a single connection cable (126) for each one of the at least two wind turbine assemblies (112). CLAUSE A13. The array (110) of any preceding A clause, wherein the common array cable (124) has a negative buoyancy.

CLAUSE A14. The array (110) of any preceding A clause, wherein the at least two wind turbine assemblies (112) are directly electrically connected to the common array cable (124).

CLAUSE A15. The array (110) of any preceding A clause, wherein the at least two wind turbine assemblies (112) are coupled to the common array cable (124), each by a separate connection cable (126).

CLAUSE A16. The array (110) of any preceding A clause, wherein the subsea location is the sea bed.

CLAUSE A17. The array (110) of clause A16, wherein the common array cable (124) is secured to the sea bed.

CLAUSE A18. The array (110) of any preceding A clause, wherein the common array cable (124) is connected to a second common array cable of a second array of wind turbine assemblies (112).

CLAUSE A19. A method for installation of an array (110) of offshore wind turbine assemblies (112), comprising: providing at least two wind turbine assemblies (112) at an offshore location; connecting a connection cable (124) to each of the at least two wind turbine assemblies (112); providing a common array cable (124) at an offshore location; securing the connection cable (126) at a subsea location; electrically connecting each of the at least two wind turbine assemblies (112) to the common array cable (124) via the connected connection cable (126).

CLAUSE A20. The method of clause A19, comprising securing the at least two wind turbine assemblies (112) to the seabed at an offshore location via an anchor arrangement. CLAUSE A21. The method of clause A19 or A20, comprising electrically connecting each of the at least two wind turbine assemblies (112) to the common array cable (124) via a floating vessel (130).

CLAUSE A22. The method of any of clauses A19 to A21, comprising electrically connecting each of the at least two wind turbine assemblies (112) to the common array cable (124) and securing the connection cable (126) to the subsea location in a single operation.

The person skilled in the art will realise that the present disclosure is not limited to the preferred embodiments described above. The person skilled in the art further realises that modifications and variations are possible within the scope of the appended claims. For example, there may be many different possibilities to the described securing and anchoring arrangements, to the number of wind turbine assemblies in the array, to the layout of the described array, or the like. Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed disclosure, from a study of the drawings, the disclosure, and the appended claims.

Further aspect: A lifting apparatus and lifting method

With the installation of offshore wind farms, in particular floating offshore wind farms, becoming more commonplace, there is an increasing requirement to develop a process for installation that is both cost effective and time-efficient.

For reasons of safety, the installation of wind turbines in a wind farm can only be undertaken when weather conditions are sufficiently mild to permit installation while exposing the personnel installing the wind farms to minimum risk. In many locations (e.g. locations in the North Sea) the weather can be notorious for changing very quickly, meaning therefore that acceptable time windows for installing wind turbines can be brief.

To install each wind turbine in a wind farm, there is a need to install some means for anchoring each wind turbine in place, as well as a need to construct the wind turbine in the offshore location, which may be provided in several parts. In addition, sufficient equipment and machinery needs to be provided. The more equipment that is required for the construction, then the longer and more expensive the construction may be. There is therefore a need for equipment and a corresponding method for installation of a wind turbine that is both time and cost efficient.

According to this further aspect, there is provided an improved lifting apparatus for use in the construction of offshore wind turbine and lifting method for use in construction of floating offshore wind turbine. According to one example there is provided a lifting apparatus for use in the construction of an offshore wind turbine, comprising: a lifting arrangement for engaging and lifting an object; a mounting arrangement for mounting the lifting apparatus to a wind turbine tower of the offshore wind turbine; an anchoring arrangement for anchoring the lifting apparatus to a buoyant structure of the offshore wind turbine.

In use, the lifting arrangement may be mounted on a wind turbine tower and anchored to the buoyant structure on which the wind turbine tower floats. The anchoring of the lifting arrangement to the buoyant structure may provide stability to the lifting apparatus, for example as a counterweight when being used to lift an object. This may avoid the need to have additional equipment located offshore, in order to ensure stability of a wind turbine tower when mounting a wind turbine tower thereon, thereby reducing the complexity and cost of the operation.

Figures 10 and 11 illustrate an example of a lifting apparatus 310 (represented in a boxed outline in this illustration) mounted upon a wind turbine tower 312, and anchored to a buoyant structure 314 via an anchoring arrangement 316. The lifting apparatus 310 may be considered to be a lifting device. Here, the buoyant structure is in the form of three columns 318 that are connected together by connectors 320, which are in the form of a truss structure in this example (see also Figure 11). The wind turbine tower 312 represents a partially constructed wind turbine, which may not yet comprise a nacelle and/or turbine blades, which may be expected to be present on an offshore wind turbine. In this example, the wind turbine tower 312 is mounted on a column 318 of the buoyant structure 314, although other mounting locations may be possible. For example, the wind turbine tower 312 may be mounted on a central surface, e.g. a platform, of the buoyant structure 314. The portion of the buoyant structure 314 (e.g. the column 318) on which the turbine tower 312, and in the immediate vicinity thereof, is mounted upon may be referred to as the proximal portion, whereas the portion of the buoyant structure that is located further from the mounting location of the wind turbine tower 312 may be referred to as the distal portion.

The anchoring arrangement 316 comprises, in this example, two anchor cables 316a, 316b which are connect the lifting apparatus 310 to the buoyant structure 314. The anchor cables 316a, 316b may be held in tension and may offer support to the lifting apparatus 310 against forces that act to pull the lifting apparatus 310 in an opposing direction. The anchoring arrangement 316 (e.g. the two cables thereof 316a, 316b) may connect the lifting apparatus to the distal portion of the buoyant structure 314. For example, the anchoring arrangement 316 may connect the lifting apparatus to or along an apex of the buoyant structure 314, or to or along a plurality of apexes on the buoyant structure, at the distal portion of the buoyant structure 314.

The lifting apparatus 310 is mounted (e.g. connected such as by a securing member) to the wind turbine tower 312 by a mounting arrangement 322, and may be considered to comprise the mounting arrangement 322. In this example, the mounting arrangement 322 comprises a securing ring 324 located around the wind turbine tower 312 and a plurality of elongate members 326 which connect the securing ring 324 to the lifting apparatus 310. Optionally, the mounting arrangement may be provided with a removable platform, which may be mounted on or around the wind turbine tower 312 to assist to stabilise the lifting apparatus 310. The elongate members 326 may be in the form of rigid rods, or may be in the form of flexible cables held in tension. The mounting arrangement 322 effectively holds the lifting apparatus 310 on the wind turbine tower 312, and may provide a simple means for mounting and dismounting the lifting apparatus 310 on the wind turbine tower 312 by simply attaching the securing ring 324 and elongate members 326 as illustrated. In addition, where the securing ring 324 may enable the lifting apparatus 310 to be mounted on a wind turbine towers 312 having a different diameters, for example as it may be able to be simply resized. The skilled reader will understand that other forms of mounting arrangement would be possible. For example, the wind turbine tower 312 may comprise a platform to which the lifting apparatus 310 may be affixed, such as bolted thereto.

Although the lifting apparatus 310 is illustrated as being located on the top of the wind turbine tower 312, in other examples, the lifting apparatus may be mounted part way up the wind turbine tower 312 (e.g. at a midpoint of the wind turbine tower). In such examples, the lifting apparatus 310 may be mounted on the tower using a mounting arrangement 322 as described, optionally with a platform for positioning of the lifting apparatus 310 thereon.

As described, the wind turbine tower 312, with the lifting apparatus 310 mounted thereon, is mounted on a column 318 of the buoyant structure 314, at the proximal portion of the buoyant structure 314. In this case, the buoyant structure 314 has a triangular prism shape, which may assist to provide a buoyant and stable platform onto which the turbine tower 312 is mounted. A column 318 is located along each apex of the buoyant structure 314. As the wind turbine tower 312 is mounted on one of the columns 318, then it may be considered to be mounted on or adjacent an apex, and therefore an extremity, of the buoyant structure 314. This location may provide ease of access for construction of the wind turbine.

The lifting apparatus 310 comprises a lifting arrangement 328 which itself may comprise an elongate member such as a cable, chain, etc., and a hoisting mechanism, such as a strand jack or winch arrangement. The hoisting mechanism may permit the incremental or steady lifting of an object. As the turbine tower, and the lifting apparatus 310 mounted thereto, is located on an extremity of the buoyant structure 314, the lifting arrangement 328 may be able to be positioned such that at least a part thereof has a vertical position that is away from the buoyant structure 314. That is, at least a part of the lifting arrangement 328 may be located such that the location directly vertically below is separate from the buoyant structure 314. Such a positioning of the lifting arrangement 328 may facilitate construction of the wind turbine by permitting objects (such as an object 330 as illustrated in Figures 1 and 2) to be brought into proximity of the lifting apparatus 310 without hindrance from the buoyant structure 314, and be engaged by the lifting arrangement 328 to be lifted. Engagement may be by any appropriate means, such as by a tie, basket, hook, or the like. Here, the lifting arrangement 328 comprises a cable 332, which is able to be connected to the object 330 to be lifted. A strand jack, winch etc. which is connected to the other end of the cable 332 and which is comprised by the lifting apparatus 310 may then be operated to lift the object 330. As illustrated, the object 330 is able to be attached simply, by bringing said object 330 simply into the proximity of the buoyant structure 314.

The attachment of an object 330 to the cable 332 of the lifting arrangement 328 results in a bending moment acting on the lifting apparatus 310, as a result of the weight of the object 330. In order to ensure the stability of the lifting apparatus 310 mounted on the wind turbine tower 312, a countering moment is required. Often, this may be acquired by attaching a weight, which may be slidably disposed on an arm or rail. The weight may then be slid along the rail in order to vary the magnitude of the counter moment. However, such a solution requires a weight to be sourced and, in this case, brought to an offshore location and installed with the lifting apparatus onto the wind turbine tower 312, which may be a complex and/or expensive operation.

In this case, the object may be a nacelle for a wind turbine, or may be a wind turbine blade or component of a blade of the wind turbine, which may be required to be located at the top of the wind turbine tower 312 (shown partially constructed in this example). However, it should be noted that the lifting apparatus 310 is not restricted to lifting any one object in particular.

In this example, the lifting apparatus 310 is anchored to the buoyant structure 314 (e.g. the distal portion of the buoyant structure 314). In doing so, a counter moment acts on the lifting apparatus 312 that is opposite to that exerted as a result of the weight of the object 330 to be lifted, thereby stably balancing the lifting apparatus 310 on the wind turbine tower 312. Using this solution, there is no requirement for a counterweight. In some examples, where the use of an additional counterweight is desired, the magnitude of the counterweight may be greatly reduced, thereby resulting in cost and time savings of transporting and installing such a counterweight in the illustrated system of Figures 10 and 11. Having the lifting apparatus 310 being anchored to the distal portion may increase the stability of the lifting apparatus 310 while keeping the tension in the cables 316a, 316b to a minimum. While, in this example, the anchoring arrangement 316 comprises two cables 316a, 316b to anchor the lifting apparatus 310 to the buoyant structure 314, in other examples a single cable 316 may be present. In further examples, the anchoring arrangement 316 may be anchored to a connector 320 (e.g. a midpoint on a connector), rather than being anchored to a column 318.

In this example, the cables 316a, 316b are anchored to either lateral side of a rear portion the lifting apparatus 310, although in other examples, the cables 316a, 316b may be mounted to an upper location of the lifting apparatus 310 or may be mounted to the centre of the rear portion of the lifting apparatus 310.

As can be most clearly seen in Figure 10, the lifting apparatus 310 enables an object to be lifted while the buoyant structure is floating on the surface of a body of water 334, while the object to be lifted 330 may be provided on a vessel (not illustrated), for example.

Once the object 330 has been lifted to the desired height, it may be moved into an appropriate location. This is illustrated in Figure 10 as the object being shown in an initial position at 330a, and a final position at 330b. The initial position 330a may be the position of the object 330 when it is first raised to the desired location, while the final location 330b may be the position that is desired by a user. In order to move (e.g. slide) the object to the final position 330b, a repositioning arrangement 338 (e.g. a gantry) may be used. The repositioning arrangement 338 may comprise two leg supports 340, 342 (see Figure 12) and an overhead portion 344, and may be positioned such that the leg supports 340, 342 straddle the wind turbine tower 310. The gantry may additionally comprise a repositioning arrangement in order to reposition the object 330 and slide it to the required position on the wind turbine tower 312. The repositioning arrangement may comprise gripping means and/or moving means in order to move the object 330 on the wind turbine tower 312.

The second aspect of this disclosure shows a lifting method for use in construction of a floating offshore wind turbine, comprising: providing a buoyant structure with a turbine tower mounted thereon; mounting a lifting arrangement on the turbine tower via a mounting arrangement; anchoring the lifting arrangement to the buoyant structure; lifting an object relative to the turbine tower using the lifting apparatus.

The method may comprise subsequent repositioning of the object 330, which may involve gripping of the object 330 on the wind turbine tower 312. The gripping and repositioning of the object 330 may be performed by a repositioning arrangement, which may be in the form of a gantry. The method may comprise repositioning the object from an initial position to a final position on the wind turbine tower 312. The repositioning arrangement may be provided on a vessel, and the vessel may be separate from the buoyant structure 314.

The method may comprise providing the buoyant structure and turbine tower in an offshore location. The method may comprise providing the repositioning arrangement in an offshore location.

The person skilled in the art realises that the present disclosure is not limited to the preferred examples described above. For example, there may be many different possibilities to the described lifting appratuses, from the type of mounting arrangement used, to the configuration of the anchoring arrangement, or the like. Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed disclosure, from a study of the drawings, the disclosure, and the appended claims.

Various further inventive aspects and embodiments according to the present disclosure will now be outlined in the following numbered B clauses:

CLAUSE Bl. A lifting apparatus (310) for use in the construction of an offshore wind turbine, comprising; a lifting arrangement (328) for engaging and lifting an object (330); a mounting arrangement (322) for mounting the lifting apparatus (310) to a wind turbine tower (312) for an offshore wind turbine; an anchoring arrangement (316) for anchoring the lifting apparatus (310) to a buoyant structure (314) of an offshore wind turbine. CLAUSE B2. The lifting apparatus (310) of clause Bl, wherein the mounting arrangement (328) is for mounting the lifting apparatus (310) on a wind turbine tower of a partially-constructed wind turbine (312).

CLAUSE B3. The lifting apparatus (310) of any preceding B clause, wherein the lifting arrangement (328) comprises a cable (332) for attaching an object (330) to be lifted thereto.

CLAUSE B4. The lifting apparatus (310) of any preceding B clause, wherein the lifting arrangement (328) comprises a strand jack mechanism for incrementally lifting an object (330).

CLAUSE B5. The lifting apparatus (310) of any preceding B clause, wherein the mounting arrangement (322) is coupled to a wind turbine tower (312).

CLAUSE B6. The lifting apparatus (310) of any preceding B clause, wherein the anchoring arrangement (316) comprises an anchor cable configurable to connect the lifting arrangement (328) and the buoyant structure (314).

CLAUSE B7. The lifting apparatus (310) of clause B6, wherein the mounting arrangement (328) is coupled to a wind turbine tower (312), and the wind turbine tower (312) is mounted upon a buoyant structure (314) at a mounting location, the buoyant structure (314) comprising a proximate turbine portion located adjacent the mounting location of the turbine tower, and a distal portion, the anchor cable being connected to the distal portion.

CLAUSE B8. The lifting apparatus (310) of clause B7, wherein the buoyant structure (314) is a triangular prism shape.

CLAUSE B9. The lifting apparatus of clause B8, wherein the anchor cable is connected to along an apex of the buoyant structure (314) at the distal portion.

CLAUSE BIO. The lifting apparatus (310) of clause B8 or B9, wherein the buoyant structure (314) comprises a truss structure.

CLAUSE Bll. A lifting method for use in construction of a floating offshore wind turbine, comprising: providing a buoyant structure (314) with a turbine tower (312) mounted thereon; mounting a lifting arrangement (328) on the turbine tower (312) via a mounting arrangement (322); anchoring the lifting arrangement (328) to the buoyant structure (314); lifting an object (330) relative to the turbine tower (312) using the lifting arrangement (328).

CLAUSE B12. The lifting method of clause Bll, comprising mounting a lifted object (330) onto the turbine tower (312). CLAUSE B13. The lifting method of clause B12, comprising repositioning a lifted object (330) relative to the turbine tower (312) subsequent to mounting the lifted object thereon, using a repositioning arrangement (338).

Claims

1. An array of floating wind turbine assemblies (212), comprising: at least two floating wind turbine assemblies (212); each of the at least two floating wind turbine assemblies (212) comprising an ingoing and an outgoing electrical connection (242, 244); a first electrical cable (226) extending from the ingoing connection (242) on one lateral side of a first of the at least two floating wind turbine assemblies (212); a second electrical cable (228) extending from the outgoing connection (244) on the same lateral side of the first of the at least two floating wind turbine assemblies (212), the second electrical cable (228) connecting to the ingoing electrical connection (244) of a second of the at least two floating wind turbine assemblies (212).

2. The array of claim 1, wherein the second electrical cable (228) is positioned on the seabed in a U-shape between the first and the second of the at least two floating wind turbine assemblies (212).

3. The array of claim 1 or 2, wherein the second electrical cable (228) is positioned on the seabed in a V-shape between the first and the second of the at least two floating wind turbine assemblies (212).

4. The array of any preceding claim, wherein each of the floating wind turbine assemblies comprises a vertical axis (240), and the first electrical cable (226) extends from the first of the floating wind turbine assemblies (212) at an angle that is circumferentially offset by 90 degrees or fewer from the second electrical cable (228) extending from the first of the floating wind turbine assemblies (212), relative to the vertical axis (240) of the first of the floating wind turbine assemblies (212).

5. The array of claim 4, wherein the first electrical cable (226) extends from the first of the floating wind turbine assemblies (212) at an angle that is circumferentially offset by 45 degrees or fewer from the second cable (228) extending from the first of the floating wind turbine assemblies (212), relative to the vertical axis (240) of the first of the floating wind turbine assemblies (212).

6. The array of any preceding claim, wherein the ingoing and outgoing electrical connections (242, 244) are adjacent.

7. The array of any preceding claim, wherein the ingoing and outgoing electrical connections are (242, 244) are located on the same lateral side of each wind turbine assembly (212) of the at least two wind turbine assemblies (212).

8. The array of any preceding claim, wherein the first and second electrical cables (226, 228) are supported on a first of the at least two wind turbine assemblies (212) by a single bending stiffener adjacent the ingoing and outgoing electrical connection (242, 244) to the floating wind turbine assembly (212).

9. The array of any preceding claim, wherein the floating wind turbine assembly (212) comprises a buoyant structure (214), and the first and second electrical cables (226, 228) are mounted on the buoyant structure (214).

10. A method for electrical connection of an array of floating wind turbine assemblies (212), comprising: providing at least two floating wind turbine assemblies (212) at an offshore location, each of the at least two floating wind turbine assemblies (212) comprising an ingoing and an outgoing electrical connection (242, 244); connecting a first electrical cable (226) to a first of the at least two floating wind turbine assemblies (212) at the ingoing electrical connection thereof (242), and connecting a second electrical cable (228) to a second of the at least two floating wind turbine assemblies (212) at the outgoing electrical connection thereof (244), and extending the first and second electrical cable (226, 228) both from the same lateral side of the first of the at least two floating wind turbine assemblies (212); connecting the second electrical cable (226, 228) to a second of the at least two floating wind turbine assemblies (212) at the ingoing electrical connection thereof (242).

11. The method of claim 10, comprising positioning the second electrical cable (228) between the first and second of the at least two floating wind turbine assemblies (212) in a U-shape.

12. The method of claim 10 or 11, comprising disconnecting the first and second cable (226, 228) from at least one of the at least two floating wind turbine assemblies (212), and connecting the first and second cable (226, 228) to a junction box.

13. The method of any of claims 10 to 12, comprising connecting a third electrical cable to the second of the at least two wind turbine assemblies (212) at an outgoing electrical connection (244) thereof and to a third wind turbine assembly at an ingoing electrical connection (242) thereof.