WO2003080939A1

WO2003080939A1 - Foundation structure

Info

Publication number: WO2003080939A1
Application number: PCT/GB2003/001159
Authority: WO
Inventors: James Ingram; Stuart Mcintyre
Original assignee: Boreas Consultants Limited
Priority date: 2002-03-20
Filing date: 2003-03-19
Publication date: 2003-10-02
Also published as: GB2402695A; GB0206569D0; GB0422928D0; AU2003226495A1

Abstract

A foundation structure which is self supporting and can be installed on the seabed without the need for support cranes or vessels is generally depicted at 1, and comprises an elongate body 3 which is adapted to hold a wind turbine tower 18, nacelle 19 and one or more rotor blades 4. The installation structure can be manoeuvred to its offshore position using a vessel 2 and buoyancy means 7. Once in position, the structure is lowered to the seabed and a pumping mechanism 12 is used to sink the structure into the seabed. The structure can then be anchored using support braces 6.

Description

Foundation Structure

The present invention relates to a foundation structure for use in the offshore wind farm industry.

As resources of fossil fuels, such as coal, oil or natural gas are depleted, an increasing amount of interest is taken in the possibility of obtaining energy from natural resources. It is also widely accepted that the world' s dependence on fossil fuels for energy has resulted in a large number of environmental problems, including global warming, air quality deterioration, oil spills and acid rain, and thus the search for alternative energy resources has gathered speed. Much of the research has focused on utilising resources such as the sun, sea and wind.

Wind energy is recognised worldwide as a proven technology which can be utilised to meet the world's increasing electricity demands in a sustainable, economical and, most importantly, an environmentally friendly manner. In particular, wind power can be used to generate electricity without air emissions, water pollution or waste products, and can greatly reduce the pollution which is currently generated by fossil fuels.

Today wind energy is the fastest growing source of electricity in the world and capable of competing with the well established forms of power generation. However, the use of wind energy is not without its problems.

Whilst most people would agree that the concept of using a natural renewable resource to generate energy in a clean and environmentally friendly manner is a good idea, the erection of on-shore wind turbines, comprised of a tower, a nacelle containing a generator, and a rotor assembly comprised of blades and a hub, is often controversial. Largely, this is due to the visual impact of the large and often cumbersome apparatus, which is required. For example, near populated areas, the construction of wind turbines may be opposed by residents who regard them as unsightly, noisy or that their presence will reduce property values. In addition, a variety of restrictions have effect on the construction of these wind farms, including planning constraints and restrictions on the visual impact and sound emissions from the turbines.

The idea of taking the wind industry offshore has developed as a result of these issues. The idea of offshore wind farms was in fact raised more than 20 years ago, and has been particularly used in lowland countries such as The Netherlands and Denmark who realised they could take advantage of the less turbulent but higher winds which occurred offshore.

Offshore wind farms have minimal environmental effects, and do not encounter the same planning restrictions or difficulties with nearby residents that have arisen with the development of on-shore wind farms. As a consequence, the size and sound emissions of the farms do not have to be strictly regulated and, as a consequence, much larger multi-megawatt machines can be used offshore. In addition, the size of the offshore resource is huge, even when restrictions such as shipping lanes, areas of limited sea depth and known dumping grounds are taken into account.

Today the vast potential of the offshore industry is a key area of research and development in the field of renewable energy resources . Nevertheless, the disadvantage of offshore development lies in the fact that it is much more expensive than on-shore farms. It is estimated that capital costs are in the region of 30% to 50% higher offshore due to the larger machine size, maintenance and operational costs, including the cost of transporting and installing turbines at sea. It will be appreciated that the construction of turbines, delivery to site and assembly of the large machines require specialist equipment and this greatly increases the costs in running an offshore farm. At present, a common method of constructing offshore wind turbines utilises a floating or jacked up crane vessel construction. Typically a specially adapted ship is piloted to the area where the turbine is to be constructed. Generally, as a result of the size of the crane and structure they must carry, these vessels are large in size and thus relatively expensive to use. Once the vessel has reached the area where the turbine is to be positioned, a mono-pile foundation or concrete gravity base foundation is placed onto the seabed onto which the offshore wind turbine can be mounted. A gravity base foundation settles on the seabed and rises above the sea surface. If necessary the foundation is further stabilised using sand, rock, or alternatively water. A pylon-like turbine tower can then be fitted onto the concrete foundation, the turbine tower carrying the nacelle and the blades which spin upwind of the tower itself. However, this process incurs significant costs, as it is necessary for the crane carrying vessel to remain in the area in order to support the wind turbine.

One type of foundation currently used, the so called "gravity base" relies on its own weight to support the turbine and the tower and to prevent the tower from overturning due to the pressure exerted by the wind acting on the tower and rotor blades. However these foundations are large and heavy and require crane carrying vessels for construction. They are also limited to shallow waters because of the high hydrodynamic forces they attract.

It is therefore an object of the present invention to provide a more economical design of installation foundation structure for use in the offshore wind energy industry.

It is a further object of the present invention to provide a foundation structure which eliminates the need for a floating crane vessel during installation, and thus can be installed and decommissioned in a more cost efficient manner, than conventional foundation structures. It is an object of the present invention to provide a foundation structure for use in the offshore wind energy industry, which can be installed without the need for heavy lifting vessels, and which is simple to recover for decommissioning or reinstallation at a different location. According to a first aspect of the present invention, there is provided a self supporting foundation structure for use in the offshore wind farm industry which can be installed on the seabed without the need for support cranes, wherein the foundation structure comprises an elongate body having a personnel landing platform and a plurality of support braces.

Preferably the foundation structure is provided with buoyant means such that it is self supporting on the surface of a body of water. Advantageously this facilitates towing of the foundation structure from a first location to a second location where the structure is lowered to the seabed.

Preferably the buoyant means has adjustment means adapted to increase the draught and decrease the freeboard of the structure until the structure is installed on the seabed.

Preferably the buoyant means has release means, for removal of the buoyant from an operable position, thereby to facilitate lowering of the installation structure to the seabed.

Preferably the buoyant means is re-usable. Advantageously the buoyant means may include sections of the turbine tower that need transporting to site in any event.

Preferably, the elongate body is substantially annular.

The foundation structure is used to hold or secure a turbine tower, nacelle and rotor blades. The tower, nacelle and rotor blades may be mounted on the foundation structure once the structure has been anchored in position on the seabed. Alternatively the tower, nacelle and rotor blades may be attached to or loaded onto the foundation structure and held in an inoperable position prior to towing to the offshore location and during anchoring of the structure on the seabed.

The turbine tower, nacelle and one or more rotor blades are mounted on the elongate body. Preferably the foundation structure has a base portion which is adapted to be driven, sunk or pushed into the seabed. The base portion will typically have a skirting means and may be manufactured from metal.

Preferably the base portion of the foundation structure comprises a plurality of fronds or frond mattresses to inhibit seabed scour .

The support braces may be connected to the elongate body of the installation structure. Alternatively the support braces may be connected to the personnel landing platform.

The personnel platform is adapted to receive personnel landed from marine vehicles or certain types of aircraft.

Typically the personnel landing platform will have monitoring means to monitor the integrity and stability of the foundation structure, as well as drilling and maintenance tools. The personnel landing platform may have a series of walkways to allow access to the monitoring means, drilling and maintenance tools.

Advantageously the foundation structure can support itself until it is anchored in position. Once the s^tructure is anchored in position it is capable of supporting the wind turbine tower, nacelle and rotor assembly.

Most preferably the elongate body has a pumping mechanism which takes up loose material such as sand, silt or mud from the seabed and passes it in a substantially upward direction through the elongate body or alternatively through temporary pipe work. The pumping mechanism may include one or more one way valves. Preferably the elongate body also comprises means for evacuating the loose material from the elongate body such that it is deposited on the upper surface of the base portion. Thus on operation the pumping mechanism is used to secure the base into the seabed and also to inhibit scouring around the base of the structure.

Typically the plurality of support braces are constructed of tubulars or piping through which drilling or piling apparatus can be passed. In order to anchor the installation structure to the seabed a drill shoe or the like can be passed through the support braces in order to lay tension anchoring means which hold the structure in position. The anchoring process and drilling or piling of the support braces can be operated from the personnel landing platform or from a remote location.

Preferably the tension anchoring or piling means is used to maintain the stability of the foundation structure and prevent movement or tipping of the structure.

Advantageously the foundation structure is self supporting and thus can be installed in an offshore position without the requirement of a vessel carrying support cranes remaining in the area.

According to a second aspect of the present invention there is provided a method of installing a structure for use in the offshore wind farm industry, the structure comprising an elongate body which has a pumping mechanism for taking up loose material from the seabed and an evacuation means, and also a plurality of support braces which are constructed of tubulars or piping through which drilling apparatus can be passed, wherein the structure also comprises a personnel landing platform, the method comprising the steps:

(a) manoeuvring the structure by towing or other means to an offshore position using a vessel; (b) lowering, sinking or placing the structure to the seabed; (c) pumping loose material from the seabed in a substantially upward direction through the elongate body using the pumping mechanism; (d) evacuating the loose seabed material such that it is deposited on the upper surface of the base portion; (e) passing drilling or piling means through the support braces in order to lay tension anchoring or piling means to anchor the structure to the seabed.

Preferably buoyant means are provided on the structure such that it is self supporting on the surface of a body of water in the step where the structure is manoeuvred to the offshore location. In the step where the structure is lowered, sunk or placed on the seabed the buoyant means may be released, removed or altered.

Optionally the step of drilling or piling through the support braces in order to lay the tension anchoring or piling means can be operated from the personnel landing platform.

Alternatively the step of drilling or piling through the support braces in order to lay the tension anchoring or piling means can be operated from a remote location.

Advantageously the steps for installing the structure can be carried out without the need for support cranes to be present. This eliminates the need for a vessel carrying the support crane to remain next to the structure as it is being installed.

Optionally, the tower, nacelle and rotor blades may be mounted on the foundation structure after the step where the drilling or piling means is passed through the support braces in order to lay tension anchoring or piling means. Alternatively the tower, nacelle and rotor blades may be attached to or loaded onto the installation structure before the step where the structure is towed to the offshore location.

According to a third aspect of the present invention there is provided a method of installing a wind turbine for use in the offshore wind farm industry, using a foundation structure, the structure comprising an elongate body which has a pumping mechanism for taking up loose material from the seabed and an evacuation means, and also a plurality of support braces which are constructed of tubulars or piping through which drilling or piling apparatus can be passed, wherein the structure also cθ4-nprises a personnel landing platform, the method comprising the steps:

a) manoeuvring a self-supporting foundation structure by towing or other means to an offshore location using a vessel; b) dropping, lowering, sinking or placing the self-supporting foundation structure on the seabed; c) anchoring or piling the structure to the seabed. 3

Optionally the transportation vessel may be removed prior to the step of anchoring or piling the structure to the seabed.

Preferably in the step where the structure is manoeuvred to the offshore location, buoyant means are provided on the structure such that it is self supporting on the surface of a body of water.

In the step where the structure is lowered, sunk or placed on the seabed the buoyant means may be released, removed or altered.

Optionally, the tower, nacelle and rotor blades may be mounted on the foundation structure after the step where the structure is anchored to the seabed. Alternatively the tower, nacelle and rotor blades may be attached to or loaded onto the installation structure before the step where the structure is towed to the offshore location.

Following the step where the foundation structure is dropped, lowered, sunk or placed on the seabed the pumping mechanism on the elongate body takes up loose material such as sand, silt or mud from the seabed and passes it in a substantially upward direction through the elongate body. The loose material is then evacuated from the elongate body such that it is deposited on the upper surface of the base portion to secure the base into the seabed and also to prevent scouring at the base portion.

Typically the step where the structure is anchored to the seabed can be operated from a remote source or by machinery and tools located on the personnel landing platform.

Embodiments of the present invention will now be described by way of example only, with reference to the following Figures in which:

Figure 1 is a schematic view of the foundation structure being manoeuvred by a towing vessel to its offshore position, according to a preferred embodiment of the present invention;

Figure 2 is a schematic view of the foundation structure at the offshore area where it is to be installed, when released from the vessel; Figure 3 is a schematic view of the foundation structure when submerged into the seabed;

Figures 4 to 6 are a schematic view depicting the process by the which the foundation structure is secured in position;

Figures 7 and 8 are schematic views of the foundation structure in position where the base is submerged in the seabed;

Figure 9 is a schematic view of the foundation structure when anchored in position in the seabed;

Figure 10 is a schematic drawing of the foundation structure when installed and anchored or piled on the seabed, and when the turbine has been installed to its working position; and

Figures 11 and 12 illustrate the foundation structure when anchored in position on the seabed and in use.

Referring firstly to Figure 1, a preferred embodiment of the foundation structure of the present invention is generally illustrated at 1. It can be seen that the foundation structure can be manoeuvred to its offshore position using a vessel adapted for towing 2.

The foundation structure comprises an elongate body 3 which is of a substantially annular/tubular shape. The foundation structure is adapted to hold a turbine tower 18, a nacelle 19 and one or more rotor blades 4. In one embodiment the turbine tower 18, nacelle 19 and rotor blades may be mounted on the installation structure once the structure has been anchored in position as shown in Figure 9. In an alternative embodiment the turbine tower 18, nacelle 19 and rotor blades may be attached to or loaded onto the installation structure before towing to the offshore location. If the turbine tower 18, nacelle 19, and rotor blades 4 are held in an inoperable position during anchoring of the structure they are transferred to an operable position once the structure is securely anchored to the seabed.

The advantage of the present invention lies in the fact that the foundation structure can support itself until it is securely anchored in position on the seabed. As a result it is not necessary to maintain a support crane at the site and thus, the vessel which manoeuvres the foundation structure to its position does not need to remain next to the structure as it is being installed. Once the structure is anchored or piled in position it is capable of supporting the turbine tower, nacelle and rotor blades in operable positions.

The installation structure also comprises a number of support braces 6. These may be connected to the elongate body 3 and may act to maintain it in a substantially upright and vertical position. Alternatively the support braces may be connected to the personnel landing platform 8. The structure aLso comprises buoyancy means 7 to aid transportation, and a personnel landing platform 8 which takes the form of a raised level surface. The lower end of the installation structure, which is eventually submerged in the seabed 9 comprises a base 10 which is typically made of metal and has skirting means 11 which can be sunk into the seabed 9.

To install the structure, the vessel 2 releases the structure, once it has been manoeuvred to a suitable offshore position, allowing the lower sections of the structure to submerge down to the seabed 9, as illustrated in Figures 2 and 3. To facilitate submersion the buoyancy means may be released, removed or altered in order to allow the lower half of the structure to sink below the water line.

It will be appreciated that it is important that the installation structure is firmly established in position and securely anchored to the seabed prior to erecting or commencing operation of the turbine tower 18, nacelle 19 and rotor blades 4.

Whilst the design of the installation structure of the present invention is such that it can support itself in position on the seabed, the apparatus is specially adapted to allow the base 10 of the structure to be sunk into the seabed 9 if necessary. This is achieved using a pumping mechanism as illustrated at 12 in Figure 4, where loose material such as sand, silt or mud is pumped into the elongate body 3 and evacuated through a pipe, tubular, pump or alternative evacuation mean 13 which in one embodiment is located on the personnel landing platform 8. It will be appreciated that the evacuating means may also be located on the elongate body itself. Using this process, loose material 14 from the seabed 9 is taken from the lower surface of the base 10 and pumped onto the upper surface of the base 15. This may be achieved using one or more one-way valves along the system.

The advantage of pumping the loose seabed material 14 onto the upper surface 15 of the base 10 is two-fold. Firstly, the loose material acts to secure the base 10 into the seabed, thus anchoring the installation structure by exerting weight onto the upper surface 15. In addition, the pumping of loose material 14 onto the upper surface 15 of the base 10 also helps to prevent scouring of the bottom of the structure. Scouring is often seen in underwater structures which are positioned on or near the seabed and occurs as a result of the turbulence of the water on the seabed. Typically sand, silt or mud is washed away and the area of seabed near the structure is eroded away. It will be appreciated that this would be detrimental to the functioning of a wind turbine, as it would affect the stability of the apparatus. However, by pumping the loose material 14 through the pipe 13 onto the upper surface 15 of the base 10, the effects of scouring are eliminated.

The base may also comprise a plurality of fronds or preferably a concrete frond mattress. Mattresses of this type are known in the art and comprise a plurality of plastic or metal sections which act to maintain the loose material around the base, and thus prevent erosion.

It can be seen from Figures 5 and 6 that the process of removing loose material from the seabed and pumping it onto the upper surface of the base acts to sink the base 15 into the seabed 9, securing the installation structure in position. Once this process is complete, operators and crew can be landed onto the personnel landing platform 8 from vessel 2, as shown in Figures 7 and 8. Crew can be landed from marine vehicles or alternatively certain types of aircraft.

Typically the personnel landing platform will comprise a series of walkways (not shown) which allow access onto the apparatus for the next stage in the installation procedure. At this stage in the installation procedure, the installation structure is stabilised in the seabed and can adequately support itself in position. However, in order to support the extra weight once the wind turbine is constructed and functioning, the method described herein also comprises an anchoring process which can be seen in Figure 9.

In addition to providing access to operators and personnel, the personnel landing platform 8 will be fitted with monitors and drilling and maintenance tools which allow the foundation structure to be anchored or piled into the seabed, as shown in Figure 9.

To anchor the structure in position the support braces 6 which support the elongate body 3 in a substantially upright position can be drilled or piled through, in order to position pre-stressed tension anchoring or piling means 16 into the seabed. This is possible as the braces will typically be constructed from piping or tubulars, which allow passage of a drill shoe or other drilling or piling apparatus (not shown) . The tension anchoring or piling means 16 can be used to both stabilise and anchor the installation structure in place, and also to maintain it within this position.

For example if erosion of the seabed, due to scouring or general wear and tear begins to occur, tension monitors on the platform 8 will notify personnel and re-tensioning can be performed as necessary.

Once the installation structure is secure, the wind turbine generally depicted at 17 in Figures 10, 11 and 12 and comprising turbine tower 18, nacelle 19 and rotor blades 4 can be installed, or moved to an operable position. Operation of the turbine can thereafter be commenced. As the installation structure is securely anchored in place, no external supporting means such as a crane or vessel is required.

An important aspect and advantage of the present invention lies in the fact that the installation structure does not require support cranes when being installed on the seabed. This greatly improves the ease by which a wind turbine can be constructed, by facilitating the manner in which the structure can be installed, thus reducing the cost involved in installing wind turbines offshore. Most importantly, the structure is constructed to be able to support itself in its offshore position on the seabed, without the requirement of a support mast or crane, until it has been securely anchored in place.

Various modifications may be made to the invention herein described without departing from the scope thereof.

Claims

1. A self supporting foundation structure for use in the offshore wind farm industry which can be installed on the seabed without the need for support cranes, wherein the foundation structure comprises an elongate body having a personnel landing platform and a plurality of support braces.

2. A foundation structure as claimed in Claim 1, which is used to hold or secure a turbine tower, nacelle and rotor blades.

3. A foundation structure as claimed in Claims 1 to 2, having buoyant means such that it is self supporting on the surface of a body of water.

4. A foundation structure as claimed in Claim 3, wherein the buoyant means incudes adjustment means so as to increase the draught and decrease the freeboard of the structure until t is installed on the seabed.

5. A foundation structure as claimed m Claims 3 to , wherein the buoyant means includes release meansto facilitate lowering of the foundation structure to the seabed.

6. A foundation structure as claimed in any one of the preceding Claims, wherein the elongate body is substantially annular.

7. A foundation structure as claimed in Claim 2, wherein the tower, nacelle and rotor blades are mounted on the foundation structure once the structure has been anchored in position on the seabed.

8. A foundation structure as claimed in Claim 2, wherein the tower, nacelle and rotor blade are attached to or loaded onto the foundation structure and held in an inoperable position prior to manoeuvring to the offshore location and during anchorage of the structure on the seabed

9. A foundation structure as claimed in any one of the preceding Claims, having a base portion which is adapted to be driven, sunk or pushed into the seabed.

10. A foundation structure as claimed in Claim 9, wherein the base portion has a skirting means.

11. A foundation structure as claimed in Claims 9 to 10, wherein the base portion is manufactured from metal.

12. A foundation structure as claimed in any one of Claims 9 to 11, wherein the base portion comprises a plurality of fronds or a frond mattress.

13. A foundation structure as claimed in any one of the preceding Claims, wherein the support braces are connected to the elongate body.

14. A foundation structure as claime*-! in any one of Claims 1 to 12, wherein the support braces are connected to the personnel landing platform.

15. A foundation structure as claimed in any one of the preceding Claims, wherein the personnel platform is adapted to receive personnel landed from marine vehicles and certain types of aircraft.

16. A foundation structure as claimed in any one of the preceding Claims, wherein the personnel landing platform has monitoring means to monitor the integrity and stability of the foundation structure.

17. A foundation structure as claimed in any one of the preceding Claims, wherein the personnel landing platform has drilling or piling and maintenance tools.

18. A foundation structure as claimed in any one of the preceding Claims, which is adapted to be self supporting until it is anchored or piled into position.

19. A foundation structure as claimed in any one of the preceding Claims, wherein the elongate body has a pumping mechanism which takes up loose material such as sand, silt or mud from the seabed and passes it in a substantially upward direction through the elongate body.

20. A foundation structure as claimed in Claim 19, wherein the pumping mechanism includes one or more one way valves .

21. A foundation structure as claimed in Claims 19 to 20, wherein the elongate body comprises means for evacuating the loose material, such that it is deposited on the upper surface of the base portion, and acts to secure the base onto the seabed and prevent scouring at the base portion.

22. A foundation structure as claimed in any one of the preceding Claims, wherein the plurality of support braces are constructed of tubulars or piping through which drilling or piling apparatus can be passed.

23. A foundation structure as claimed in Claim 22, wherein drilling apparatus can be passed through the support braces in order to lay tension anchoring means to hold the structure in position.

24. A foundation structure as claimed in Claim 22, wherein piling apparatus can be passed through the support braces in order to drive pile anchoring means to hold the structure in position.

25. A foundation structure as claimed in Claims 22 to 24, wherein the entire anchoring process is operable from the personnel landing platform.

26. A foundation structure as claimed in Claims 22 to 24, wherein the entire anchoring process is operated from a remote location.

27. A foundation structure as claimed in Claims 23 to 26, wherein the tension anchoring means are used to maintain the stability and prevent movement or tipping of the foundation structure.

28. A foundation structure as claimed in Claims 23 to 26, wherein the pile anchoring means are used to maintain the stability and prevent movement or tipping of the foundation structure.

29. A foundation structure as claimed in any one of the preceding Claims, which can be installed in an offshore position without the requirement of a vessel carrying support cranes remaining in the area.

30. A method of installing a structure for use in the offshore wind farm industry, the method comprising the steps of:

(a) manoeuvring the structure by towing or other means to an offshore position using a vessel; (b) lowering, sinking or placing the structure to the seabed; (c) depositing loose material from the seabed on an upper surface of a base portion of the structure; and (d) anchoring the structure to the seabed.

31. A method of installing a structure for use in the offshore wind farm industry as claimed in Claim 30, wherein buoyant means are provided on the structure, such that it is self supporting on the surface of a body of water in the step where the structure is manoeuvred to the offshore location.

32. A method of installing a structure for use in the offshore wind farm industry as claimed in Claim 31, wherein in the step where the structure is lowered, sunk or placed on the seabed, the buoyant means are released, removed or altered.

33. A method of installing a structure for use in the offshore wind farm industry as claimed in any one of Claims 30 to 32, wherein the anchoring of the structure to the seabed is performed by drilling through support braces in the structure in order to lay tension anchoring means.

34. A method of installing a structure for use in the offshore wind farm industry as claimed in Claim 33, wherein the step of drilling through the support braces in order to lay the tension anchoring means is operated from a remote location.

35. A method of installing a structure for use in the offshore wind farm industry as claimed in any one of Claims 30 to 32, wherein the anchoring of the structure to the seabed is performed by driving piles through support braces in the structure in order to provide piled anchoring means .

36. A method of installing a structure for use in the offshore wind farm industry as claimed in Claims 30 to 35, which can be carried out without the need for support cranes to be present.

37. A method of installing a structure for use in the offshore wind farm industry as claimed in any one of Claims 30 to 36, wherein a tower, nacelle and rotor blades are mounted on the foundation structure after the step where the drilling means is passed through the support braces in order to lay tension anchoring means.

38. A method of installing a structure for use in the offshore wind farm industry as claimed in any one of Claims 30 to 36, wherein a tower, nacelle and rotor blades are mounted on the foundation structure after the step where the piling means is passed through the support braces in order to provide pile anchoring means .

39. A method of installing a structure for use in the offshore wind farm industry as claimed in any one of Claims 30 to 36, wherein a tower, nacelle and rotor blades are attached to or loaded onto the foundation structure before the step where the structure is manoeuvred to the offshore location.

40. A method of installing a wind turbine for use in the offshore wind farm industry, the method comprising the steps:

(a) manoeuvring a self-supporting installation structure by towing or other means to an offshore location using a vessel; (b) dropping, lowering, sinking or placing the self- supporting installation structure on the seabed (c) anchoring the structure to the seabed; and (d) erecting a wind turbine on the foundation structure.

41. A method of installing a wind turbine for use in the offshore wind farm industry as claimed in Claim 40, wherein the transportation vessel is removed prior to the step of anchoring or piling the structure to the seabed.

42. A method of installing a wind turbine for use in the offshore wind farm industry as claimed in Claim 41, wherein buoyant means are provided on the structure such that it is self supporting on the surface of a body of water in the step where the structure is manoeuvred to the offshore location.

43. A method of installing a wind turbine for use in the offshore wind farm industry as claimed in Claim 42, wherein the buoyant means are released, removed or altered in the step where the structure is lowered, sunk or placed on the seabed.

44. A method of installing a wind turbine for use in the offshore wind farm industry as claimed in any one of Claims 40 to 43, wherein a tower, nacelle and rotor blades are mounted on the foundation structure after the s;ep where the structure is anchored to the seabed.

45. A method of installing a wind turbine for use in the offshore wind farm industry as claimed in any one of Claims 40 to 43, wherein a tower, nacelle and rotor blades are attached to or loaded onto the installation structure before the step where the structure is manoeuvred to the offshore location.

46. A method of installing a wind turbine for use in the offshore wind farm industry as claimed in Claims 40 to 45, wherein following the step where the foundation structure is dropped, lowered, sunk or placed on the seabed, a pumping mechanism takes up loose material from the seabed and passes it in a substantially upward direction through and evacuated from an elongate body in the structure such that it is deposited on the upper surface of a base portion of the structure to secure the base portion to the seabed.

47. A method of installing a wind turbine for use in the offshore wind farm industry as claimed in any one of Claims 40 to 46, wherein the anchoring of the structure to the seabed is performed by drilling through support braces in the structure in order to lay tension anchoring means.

48. A method of installing a wind turbine for use in the offshore wind farm industry as claimed in any one of Claims 40 to 47, wherein the anchoring of the structure to the seabed is performed by piling through support braces in the structure in order to provide pile anchoring means.

49. A method of installing a wind turbine for use in the offshore wind farm industry as claimed in any one of Claims 40 to 48, wherein the step where the structure is anchored to the seabed is operated from a remote source.

50. A method of installing a wind turbine for use in the offshore wind farm industry as claimed in any one of Claims 40 to 49, wherein the step where the structure is anchored to the seabed is operated from a personnel landing platform located on the structure.