GB2597329A

GB2597329A - Construction of wind turbine towers for heavy maintenance lifting operations

Info

Publication number: GB2597329A
Application number: GB2011203.3A
Authority: GB
Inventors: Hylland Pål; Yttervik Rune; Karsten Lyngvær Bernt; Axel Munkebye Aarnes Knut
Original assignee: Equinor Energy AS
Current assignee: Equinor Energy AS
Priority date: 2020-07-20
Filing date: 2020-07-20
Publication date: 2022-01-26
Also published as: GB202011203D0; WO2022019771A1

Abstract

A wind turbine having a foundation (6, fig.1), a tower 10, a nacelle, a rotor and a number of blades; the tower has a longitudinal central axis C, an outer face 50 and an inner face 48 which defines a longitudinally extending void for at least a portion of the length of the tower; the tower is provided with one or more of at least one load shelf 38, at least one tower wall thickening (52, fig.12), at least one tower internal reinforcement element 62, and at least one specified material selection. Preferably the load shelf is separately made, attached by welding, adhesive, threaded fixings, or rivets, and supported by ribbed triangular stiffening plates or stiffening flanges 44. There may also be a pressure transmitting plastic or settable liquid filler between the load shelf and the tower. Materials used may be composites of two or more metals, fibre composite, carbon composite, aramid fibre composite.

Description

CONSTRUCTION OF WIND TURBINE TOWERS FOR HEAVY MAINTENANCE LIFTING OPERATIONS

This invention relates to the construction and maintenance of wind turbines, and in particular, the design, construction and / or modification of wind turbine towers to accommodate increased sizes and weights of components of wind turbines.

Over recent decades, wind turbines have become an increasingly important source of renewable energy. A typical wind turbine comprises a tower having a nacelle at its upper end. The nacelle at least typically houses bearings, gearing, an electrical generator, and control systems. Connected to the gearing is a rotor that carries a plurality of rotor blades (typically three). The nacelle is able to rotate relative to the tower so that the blades are directed towards the wind (i.e. so that the plane in which they rotate is perpendicular to the wind direction).

The tower is typically hollow and has a longitudinal axis extending between the base of the tower to the top of the tower. In a plane substantially perpendicular to the longitudinal axis of the tower, the cross-section of the tower is typically substantially circular. The tower may have a constantly dimensioned cross-section along its length or may taper from a larger dimensioned cross-section at the base of the tower to a smaller dimensioned cross-section at the top of the tower. In such circumstances the tower is a truncated cone.

The tower is typically constructed from a number of pre-fabricated units which, when joined end to end, form the tower.

Once the tower has been constructed the nacelle is attached to the top of the tower and the elements of the wind turbine housed in the nacelle installed therein. The rotor and the blades of the turbine are then attached.

The most common method of performing the construction and / or maintenance of wind turbines is to use large mobile cranes transported by trucks or boats. These cranes have as disadvantages their high cost and the difficulty of accessing remote sites. A further disadvantage is that as wind turbines become taller, the height to which a mobile crane must reach becomes larger.

Wind turbines may be located on land or offshore. Over recent years there has been increasing interest in offshore wind turbines. These have significant advantages over land-based turbines. Generally the wind is stronger and more reliable offshore (in this regard it is relevant that the power obtainable is -2 -proportional to the cube of the wind speed), there may be fewer environmental and aesthetic objections (particularly when they are located some distance offshore), and the scale of the wind turbines may be larger. However, locating wind turbines offshore provides additional challenges in relation to construction and maintenance, and these challenges further increase with scaling of larger wind turbines.

Historically, most offshore wind turbines have been similar to onshore wind turbines in that they comprised towers that have foundations in the seabed and a lower portion of the tower is below the surface of the sea. However, in recent years floating offshore wind turbines have been developed. These can be located in deep water and hence further out to sea where the wind is stronger, and where they may be entirely out of sight from land.

Offshore wind turbines, whether floating or anchored, pose additional difficulties in construction and maintenance because any floating structures are mobile to some extent on their moorings.

According to a first aspect of the present invention there is provided a wind turbine comprising a foundation, a tower, a nacelle, a rotor and a number of blades in which the tower has a longitudinal central axis, a base, and a top, in which the base is closer to the surface of the earth than the top when the wind turbine is in use, the tower has an outer face and an inner face, the inner face defines a longitudinally extending void for at least a portion of its length, the wind turbine tower is adapted to support one or more items of construction or maintenance equipment on the tower, and the tower is provided with of one or more of at least one load shelf, at least one tower wall thickening, at least one tower internal reinforcement element, and at least one specified material selection.

The one or more of at least one load shelf, at least one tower wall thickening, at least one tower internal reinforcement element, and at least one specified material selection are collectively referred to hereafter as "the strengthening means".

The use of the strengthening means in the structure of the wind turbine tower has the benefit that the fabric of the tower is adapted so that anticipated or measured localised zones of stress or strain are strengthened by the strengthening means so that the maximum stresses or strains that can be safely experienced by those zones is increased to exceed the anticipated or measured forces. This has the benefit that stresses or strains at magnitudes which could cause damage to the towers of known wind turbines can be safely experienced by wind turbines -3 -according to the present invention. As a result of the present invention the tower of a wind turbine is able to safely support construction or maintenance equipment, for example lifting equipment, and loads generated by the operation of that equipment, for example the loading of the equipment and whatever that equipment is lifting, without damage to the tower. As such that equipment may be for lifting heavy items such as the nacelle, gearbox, generator, rotor or the blades for the wind turbine from adjacent the base of the tower into position.

The ability to lift such heavy items using a lifting means supported on the tower of the wind turbine has the significant advantage that it is no longer necessary to use stand-alone cranes with ability to lift the necessary loads the height of the tower whenever heavy construction or maintenance work needs to occur in connection with a wind turbine. It also has the advantage that as wind turbines, and in particular offshore wind turbines increase in size, in particular tower height, it is not necessary to develop ever taller cranes.

The tower may be of a substantially circular cross-section in a plane perpendicular to the longitudinal central axis. In other embodiments of the present invention the tower may have alternative cross-sections. The tower may have the shape of a truncated hollow cone or other truncated hollow frustum with a diameter or other dimension that is greater at the base of the tower than at the top of the tower.

At least one load shelf may be located on the outside face of the tower. At least one load shelf may comprise at least one load surface which is adapted to transmit a load force applied to the load surface into the structure or fabric of the tower at or in the region of the longitudinal position on the tower of the load shelf.

The load force may be the weight of the construction or maintenance equipment supported by the load shelf. Alternatively, the load force can be the combined weight of the construction or maintenance equipment and, for example, a load being lifted by that construction or maintenance equipment.

The at least one load surface may extend around the whole perimeter of the tower.

Alternatively, the at least one load surface may extend around only a portion of the perimeter of the tower. That portion of the perimeter may be a continuous portion or a discontinuous portion made up of a number of sub-portions In some examples of the present invention where the at least one load surface extends around only a portion of the tower, the at least one load surface -4 -comprises a plurality of load sub-surfaces all of which are located at substantially the same longitudinal position on the tower and which are spaced from each other around at least a portion of the perimeter of the tower. The load sub-surfaces may be evenly distributed around the perimeter or a portion of the perimeter of the tower.

Where the load surface or a plurality of load sub-surfaces extends around the whole perimeter of the tower, albeit that the sub-surfaces are separated by portions of the perimeter where there is no subsurface, this has the advantage that the lifting means or other equipment supported on the load surface can be supported anywhere around the tower's perimeter, and as a result may operate anywhere around the tower's perimeter.

In the embodiments of the present invention where there are a plurality of load sub-surfaces the gaps between the load sub-surfaces may be used to index the position of the lifting means or other equipment and / or hold the lifting means or other equipment in a fixed position on the perimeter of the tower.

The included angle between the central axis of the tower and the at least one load surface in the radial direction from the central axis of the tower may be around 90 degrees. This has the effect that when the wind turbine is in use, or once the tower has been erected in the process of readying the wind turbine for use, the load surface is substantially horizontal. The load surface may, in such circumstances, face away from the tower base / upwards.

The included angle between the central axis of the tower and at least one load surface in the radial direction from the central axis of the tower may be one of between 10 and 90 degrees, between 20 and 90 degrees, between 30 and 90 degrees, between 40 and 90 degrees, between 50 and 90 degrees, between 60 and 90 degrees, between 70 and 90 degrees, between 80 and 90 degrees, and between 85 and 90 degrees. The load surface may face away from the tower base / upwards (when the wind turbine is in use, or once the tower has been erected in the process of readying the wind turbine for use).

At least one load shelf may comprise at least one second face. In some examples of the present invention, each second face is associated with a load surface, each second face is substantially parallel to the load surface with which it is associated, and each second face is closer to the base of the tower than the load surface with which it is associated. In some alternative examples, each second face is associated with a load surface, each second face is not parallel to the load -5 -surface with which it is associated, and each second face is closer to the base of the tower than the load surface with which it is associated.

At least one load shelf may further comprise one or more stiffening plates, each stiffening plate may extend between a second face of the load shelf and the outside face of the tower, and each stiffening plate may extend longitudinally along a portion of the outside face of the tower. This configuration of the load shelf is advantageous because the flanges help to prevent the deformation of the load shelf when under load. In particular, they support the load face and transmit the load forces into the structure of the tower.

At least one load shelf may have a cross-section in a radial direction from the central axis of the tower that has an outer perimeter which is substantially triangular in shape. Again, this configuration of the load shelf is advantageous because the flanges help to prevent the deformation of the load shelf when under load. In particular, they support the load face and transmit the load forces into the structure of the tower.

At least one load shelf may be fabricated separately from the walls of the tower and subsequently fixed to the tower.

At least one load shelf may also include at least one base plate. Each base plate may have a first and a second face with the first face of each base plate being configured and contoured to overlie a portion of the outside face of the tower, and the load surface may extend from the second face of the base plate. The first face of the base plate may closely overlie a portion of the outer face of the tower. In this context, it is to be understood that closely overlying means that the whole or at least 80% of the whole of the first face is in contact with the outside face of the tower.

At least one load shelf may further comprise a base plate where the base plate is configured to surround and be in contact with a longitudinally extending portion of the outside face of the tower. The base plate may be dimensioned so that it surrounds and is in contact with a longitudinally extending portion of the outside face of the tower at a predetermined longitudinal position on the tower. That is the base plate has the form of a sleeve with the first face of the base plate defining the same shape (in a plane perpendicular to the central axis of the tower) as the cross section of the tower for the longitudinal portion of the tower overlaid by the sleeve.

The sleeve may have a number of reinforcement straps, ribs or other reinforcing structures attached to the second face of the base plate to decrease the likelihood of the base plate deforming. Those straps, ribs or other reinforcing -6 -structures may be substantially parallel to the surface of the tower radially inwardly of the straps, ribs or other reinforcing structures.

The base plate may have the same dimensions in the longitudinal direction of the tower as the load shelf.

Alternatively, the base plate may have a greater dimension in the longitudinal direction of the tower than the load shelf. In some instances, the edge of the base plate nearest the top of the tower may be substantially the same distance from the top of the tower as the distance between the top of the tower and the intersection of the load surface and the base plate. The load shelf having a base plate has the advantage that forces transmitted from the load shelf into the tower are spread out over the area of the base plate rather than a smaller area of contact by load shelfs that do not include a base plate. This results in a lower force per unit area and thus lower stresses and strains in the fabric of the tower.

In some wind turbines according to the present invention the tower decreases in external dimensions in the plane perpendicular to the central axis from a larger dimension at the base of the tower to a smaller dimension at the top of the tower. In such wind turbines at least one load shelf is configured to surround and be in contact with a longitudinally extending portion of the outside face of the tower, the base plate is dimensioned so that it surrounds and is in contact with that longitudinally extending portion of the outside face of the tower at a predetermined longitudinal position on the tower. This configuration has the effect that the load shelf cannot move towards the base of the tower from fits predetermined position because the tower between the load shelf and the bas will not fit between the faces of the load shelf that are in contact with the outside face of the tower.

At least one load shelf may further comprise a pressure transmitting filler between the base plate and the portion of the tower. The filler will maximise the contact between the load shelf and the outside face of the tower and thus the area over which forces transmitted from the load shelf into the tower. The filler will also accommodate any irregularities in the surface of the tower. Such irregularities may be the result of the method of construction of the tower, for example the heads of fixing means such a rivets, bolts or other fixing means including a helical thread, or damage to the tower. The filler may be put in place as a paste or highly viscous fluid and subsequently allowed to harden. The filler may also have adhesive properties. -7 -

The load shelf may be fixed to the tower by one or more of welding, an adhesive, a number of fixings comprising a helical thread, or a number of rivets.

The tower of the wind turbine of the present invention may comprise one or more tower walls each with an outside and an inside face. At least one tower wall thickening may comprise at least one thickening plate. Each thickening plate may be configured to conform to the surface contours of the tower at a location where the wall of the tower is to be thickened, and each thickening plate is fixed to a tower wall. The fixing of thickening plates to a tower wall has the benefit that the portion of the wall to which the or each plate is fixed will have greater resistance to damage as a result of stresses and strains experienced by that portion of wall relative to unthickened portions of tower wall.

The use of thickening plates rather than simply using uniformly thicker walls during the construction of the tower is advantageous because it means that only those portions of the tower wall that need increased resistance to damage are thickened with the result that less material is used in the construction of the tower.

This is economically and environmentally beneficial.

At least one thickening plate may be fixed to an outside face of the tower. Alternatively or additionally, at least one thickening plate may be fixed to an inside face of the tower.

At least one thickening plate may have a first and second face. The first face may be adapted to overlie a portion of a face of the tower, the second face may be adapted to face away from the overlaid face of the tower. The first face of the plate may be smooth, and the second face of the plate may be smooth or may comprise a number of ribs or other stiffening features. The ribs or other stiffening features will increase the stiffness of the thickening plates. There may be more than one rib or other stiffening features, and at least two of the ribs or other stiffening features may be linear. At least two of the linear ribs or other stiffening features may extend in different directions.

At least one thickening plate may define a number of apertures, and those apertures may extend through the plate from one face to the other. Such a plate may provide the required level of increase in resistance to stress and strain in a tower wall to which it is attached whilst, at the same time, minimising the mass of the thickening plates.

At least one thickening plate may be fixed to a face of the tower at approximately the same longitudinal position on the tower as a load shelf of the -8 -present invention. Alternatively or additionally at least one thickening plate may be fixed to a face of the tower at a position longitudinally adjacent to a load shelf.

At least one thickening plate may further comprise a pressure transmitting filler between the base plate and the portion of the tower. The filler will maximise the contact between the thickening plate and the face of the tower and thus the transmission of force between the structure of the tower and the thickening plate. The filler will also accommodate any irregularities in the surface of the tower. Such irregularities may be the result of the method of construction of the tower, for example the heads of fixing means such a rivets, bolts or other fixing means including a helical thread, or damage to the tower. The filler may be put in place as a paste or highly viscous fluid and subsequently allowed to harden. The filler may also have adhesive properties.

At least one tower internal reinforcement element may comprise one or more stiffening elements. At least one stiffening element may be a plate, and the plate may be fixed to the inner face of one or more of the walls of the tower along at least one edge of the plate. The fixing of a plate to the inside face of one or more of the walls of the tower with the plate extending between a plurality of positions on the inside face of one or more walls has the benefit of increasing the stiffness of the tower and increasing the resistance to damage to the fabric of the tower as a result of high levels of stress or strain in the fabric of the tower close to the plate.

Alternatively or additionally, at least one stiffening element may be a rib, and the rib may be fixed to the inner face of one or more of the walls of the tower.

Alternatively or additionally at least one stiffening element may be a rod or a beam. The rod or beam may have a first and second end, and the first and second ends may be directly or indirectly fixed to the inner face of a tower wall at first and second positions respectively. Optionally, at least one tower internal reinforcement element may be comprised of two or more stiffening elements, each stiffening element may be a rod or a beam, and each rod or beam may form part of a lattice of rods and / or beams. The rods and the beams in the lattice may be fixed to each other to increase the rigidity of the lattice. In some embodiments not all of the rods or beams in the lattice are fixed to a tower wall.

The lattice may, again, increase the stiffness of the tower in the region of the lattice giving the same benefits as previously discussed for increasing the stiffness of the tower. -9 -

At least one stiffening element may be fixed to the tower at a longitudinal position on the tower at approximately the same longitudinal position on the tower as a load shelf. Alternatively or additionally, at least one stiffening element may be fixed to a surface of the tower at a position longitudinally adjacent to a load shelf.

One or more of at least a portion of the tower, at least one load shelf, at least one tower wall thickening, and at least one tower internal reinforcement element may comprise a material selected to provide a resistance to loading that exceeds the resistance to loading of the material or materials from which the tower or the rest of the tower is comprised. The selected material may be a composite material. The composite material may be a composite of two or more metals, a fibre composite, a carbon and or aramid fibre composite, or another known composite with appropriate structural characteristics.

The wind turbine of the present invention may be an offshore wind turbine.

The foundation of an offshore wind turbine is, for the purposes of the present invention the portion of the wind turbine that is below the water.

According to a second aspect of the present invention there is provided a method of constructing a wind turbine according to the first aspect of the present invention in which the method comprises the steps of (a) constructing a foundation and a tower and erecting same, (b) lifting a nacelle to the top of the tower, (c) attaching the nacelle to the top of the tower, (d) mounting at least a rotor and electricity generating equipment in or adjacent to the nacelle, and (e) lifting each blade and attaching it to the rotor, in which the lifting of the nacelle, at least a rotor and electricity generating equipment, and blades into position is performed by at least one lifting means supported on the tower, and the one or more of at least one load shelf, at least one tower wall thickening, at least one tower internal reinforcement, and at least one specified material selection are so located that they transfer loading forces generated by the lifting means into the structure of the tower or assist in diffusing the transferred loading forces within the structure of the tower to prevent the accumulation of stresses or strains of sufficient magnitude within the structure of the tower to damage the tower.

The method may include a tower which comprises at least one load shelf, and the load shelf supports a lifting means.

-10 -The method may include a tower which comprises at least two load shelfs, further comprises the steps of (i) a first lifting means lifting a second lifting means onto a load shelf which is between the first lifting means and the top of the tower and the second lifting means is supported on that load shelf, (ii) the second lifting means lifting the first lifting means onto a load shelf which is between the second lifting means and the top of the tower and the first lifting means is supported on that load shelf, (Hi) steps (i) and (h) are repeated until the lifting means closest to the top of the tower is sufficiently close to the top of the tower that that lifting means can perform the lifting for steps (b) to (e) of the second aspect of the present invention. Alternatively, the method may include a tower which may comprise at least two load shelfs, further comprising the steps of (i) a first lifting means lifting a second lifting means onto a load shelf which is between the first lifting means and the top of the tower and the second lifting means is supported on that load shelf, (ii) the second lifting means lifting the first lifting means onto a load shelf which is between the second lifting means and the top of the tower and the first lifting means is supported on that load shelf, (H) steps (i) and (h) are repeated until the lifting means closest to the top of the tower is sufficiently close to the top of the tower that that it may lift a third lifting means from the base of the tower onto an uppermost load shelf, and (iv) the third lifting means performs the lifting for steps (b) to (e) of the second aspect of the present invention.

In the above methods, each of the first and second lifting means may have a maximum lifting height, and the load shelves are longitudinally spaced along the tower at a distance equal to or less than maximum lifting height of the first and second lifting means.

According to a third aspect of the present invention there is provided a method of maintaining a wind turbine according to the first aspect of the present invention comprising the step of locating a lifting means in a position at or near the top of the tower from which the lifting means can perform the lifting necessary to perform the maintenance, in which the one or more of at least one load shelf, at least one tower wall thickening, at least one tower internal reinforcement element, and at least one specified material selection are so located that they transfer loading forces generated by the lifting means into the structure of the tower and / or assist in diffusing the transferred loading forces within the structure of the tower to avoid the concentration of stresses or strains within the structure of the tower of sufficient magnitude to damage the tower.

The present invention will be further described and explained by way of example and with reference to the accompanying drawings in which Figure 1 shows a schematic view of an offshore floating wind turbine; Figure 2 shows a schematic view of an onshore wind turbine; Figure 3 shows a perspective view of a first embodiment of a load shelf of the present invention when viewed from the side and above; Figure 4 shows a sectional view AA of the load shelf of Figure 3; Figure 5 shows a perspective view of the load shelf of Figure 3 when viewed from the side and below; Figure 6 shows a perspective view of a second embodiment of a load shelf of the present invention when viewed from the side and above; Figure 7 shows a sectional view AA of the load shelf of Figure 6; Figure 8 shows a perspective view of the load shelf of Figure 6 when viewed from the side and below; Figure 9 shows a perspective view of a third embodiment of a load shelf of the present invention when viewed from the side and above; Figure 10 shows a sectional view AA of the load shelf of Figure 9; Figure 11 shows a perspective view of the load shelf of Figure 9 when viewed from the side and below; Figure 12 shows a sectional view of a first embodiment of a tower wall thickening according to the present invention; Figure 13 shows a second embodiment of a tower wall thickening according to the present invention; and Figure 14 shows an embodiment of a tower internal reinforcement according to the present invention.

In the following examples, like elements in different embodiments are labelled with the same reference numerals.

With reference to Figure 1 an offshore wind turbine 2 floats in water 4 with a buoyant foundation 6 beneath the surface 8 of the water, and a tower 10 above the -12 -surface of the water. The buoyant foundation 6 is anchored to the seabed or earth 14 by known anchor means (not shown).

The interface between the buoyant foundation 6 and the tower 10 may be referenced as the base of the tower 10. The tower 10 has a top which is, when the wind turbine 2 is in use, the vertically uppermost part of the tower.

The tower 10 is substantially circular in cross-section for all or at least a portion of its length. The tower 10 also tapers from a larger circumference at its base or a position between the base and the top of the tower 10 to a smaller circumference at the top of the tower 10.

Attached to the top of the tower 10 is a nacelle 12 which houses at least an electrical generator (not shown) and, optionally, a gearbox (not shown). Extending from the nacelle 12 is a rotor 16 to which three blades 18 (only two blades are visible in Figure 1). The rotor 16 may be connected the mechanical input of the gearbox where a gearbox is present, and the mechanical output of the gearbox is connected to the electrical generator with the result that rotation of the rotor 16 as a result of wind acting on the blades 18 causes the generation of electricity. Alternatively, the rotor 16 is connected to the electrical generator with the same result.

With reference to Figure 2, an onshore wind turbine 20 has a foundation 22 beneath the surface of the earth 14, and a tower 10 above the surface of the earth 14. The interface between the foundation 22 and the tower 10 may be referenced as the base of the tower 10. The tower 10 has a top which is, when the wind turbine 20 is in use, the vertically uppermost part of the tower.

The tower 10 is substantially circular in cross-section for all or at least a portion of its length. The tower 10 also tapers from a larger circumference at the base of the tower 10 or a position between the base and the top of the tower 10 to a smaller circumference at the top of the tower 10.

Attached to the top of the tower 10 is a nacelle 12 which houses at least an electrical generator (not shown) and, optionally, a gearbox (not shown). Extending from the nacelle 12 is a rotor 16 to which three blades 18 (only two blades are visible in Figure 1). The rotor 16 may be connected the mechanical input of the gearbox and the mechanical output of the gearbox is connected to the electrical generator with the result that rotation of the rotor 16 as a result of wind acting on the blades 18 causes the generation of electricity. Alternatively, the rotor 16 is connected to the electrical generator with the same result.

-13 -With reference to Figures 3 to 5, a load shelf 24 comprises an annular disc with an inner face defining a diameter 26, a load surface 28 and a second surface 30. The load shelf extends fully around the tower 10 at a predetermined longitudinal position along the length of the tower. The determined position of the load shelf 24 can be referenced relative to the top or base of the tower 10.

The inner diameter 26 of the load shelf 24 is such that the inner face is in close contact with the outer surface of the tower 10 at the predetermined position. The inner face may define a truncated conical surface dimensioned to mirror the taper of the tower at the predetermined longitudinal position. The inner face is, in some examples, sufficiently accurately formed that the load shelf 24 cannot move any further towards the base of the tower 10 than the predetermined position because the inner face interferes with the surface of the tower 10. In other examples, a plastic or liquid filler that will set to a non-plastic solid can be introduced between the inner face and the tower 10 to fix the longitudinal position of the load shelf 24 relative to the tower 10 and to ensure continuous contact between the inner face and the tower 10.

The load surface 28 is flat, extends in a plane that is approximately perpendicular to the central axis C of the tower 10, and faces towards the top of the tower 10. The load surface may be adapted to have construction or maintenance equipment such as a lifting means mounted onto or resting on that load surface. In alternative embodiments, not illustrated, the load surface 28 can be at other angles to the central axis C of the tower 10.

The second surface 30 of the load shelf 24 is flat and substantially parallel to the load surface 28. In alternative, unillustrated, embodiments of the load shelf the load surface 28 and second surface 30 can be non-parallel. In some embodiments, the distance between the load surface 28 and second surface 30 is greatest adjacent the tower 10 and decreases as the distance from the tower 10 increases.

With reference to Figures 6 to 8, a load shelf 32 comprises an annular disc 34 and a number of stiffening flanges 36. The annular disc 34 has an inner face defining a diameter 26, a load surface 28 and a second surface 30. The annular disc 34 extends fully around the tower 10 at a predetermined longitudinal position along the length of the tower. The determined position of the annular disc 34 can be referenced relative to the top or base of the tower 10.

-14 -The inner face of the annular disc 34 is so dimensioned that the inner face is in close contact with the outer surface of the tower 10 at the predetermined position. The inner face may define a truncated conical surface to mirror the taper of the tower at the predetermined longitudinal position. The inner face is, in some examples, sufficiently accurately formed that the load shelf 32 cannot move any further towards the base of the tower 10 than the predetermined position because the inner face interferes with the tower 10.

The load surface 28 is flat, extends in a plane that is approximately perpendicular to the central axis C of the tower 10, and faces towards the top of the tower 10. The load surface may be adapted to have a lifting means or other apparatus mounted onto or resting on that surface. In alternative embodiments, not illustrated, the load surface 28 can be at other angles to the central axis C of the tower 10.

The second surface 30 of the load shelf 24 is flat and substantially parallel to the first load surface 28. In alternative, unillustrated, embodiments, the first load surface 28 and second surface 30 can be non-parallel. In some embodiments, the distance between the first load surface 28 and second surface 30 is greatest adjacent the tower 10 and decreases as the distance from the tower 10 increases.

Extending between the second surface 30 and the face of the tower 10 are a number of stiffening flanges 36. There are four stiffening flanges 36 in the embodiment illustrated in Figures 6 to 8 (one is not visible behind the tower 10), other embodiments may have different numbers of stiffening flanges 36.

The stiffening flanges 36 increase the stiffness of the annular disc 34 and help spread any forces applied to the annular disc 34 over a larger surface area of the tower 10 than the load shelf 24 of Figures 3 to 5. This has the result of reducing the risk that those forces will cause damage to the tower 10.

The inner face of the annular disc and the portion of the stiffening flanges 36 that are adjacent to the tower 10 may be in direct contact with the surface of the tower 10 or a plastic or liquid filler that will set to a non-plastic solid can be introduced between stiffening flanges 36 and the tower 10 to fix the position of the load shelf 32 relative to the tower 10 and to ensure continuous contact between the surface of the inner face of the annular disc and the stiffening flanges 36 closest to the tower and the tower. The filler may also be an adhesive.

With reference to Figures 9 to 11, a load shelf 38 comprises an annular disc 40, a base plate 42, and a number of stiffening flanges 44. The base plate 42 has -15 -the form of a cylindrical or hollow truncated sleeve with an inner face that defines a diameter 26 at the portion of the base plate 42 closest to the base of the tower 10 or, in alternative embodiments, for the longitudinal extent of the base plate in the direction of central axis C. Where the sleeve is a hollow truncated cone the end of the sleeve closest to the top of the tower will define a diameter that is smaller than the diameter 26.

The annular disc 40 extends from the face of the base plate 42 facing away from the tower 10, and has a load surface 28 and a second surface 30. The annular disc 40 extends fully around the tower 10 at a predetermined longitudinal position along the length of the tower. The determined position of the annular disc 40 can be referenced relative to the top or base of the tower 10.

The inner face of the base plate 42 is such that the inner face is in close contact with the outer surface of the tower 10 at the predetermined position. The inner face of the base plate is, in some examples, sufficiently accurately formed that the load shelf 38 cannot move any further towards the base of the tower 10 than the predetermined position because the inner face of the base plate interferes with the wall of the tower 10. In other examples, a plastic or liquid filler that will set to a non-plastic solid can be introduced between the base plate 42 and the tower 10 to fix the position of the load shelf 38 relative to the tower 10 and to ensure continuous contact between the surface that defines the inner diameter 26 and the tower 10.

The filler may also be an adhesive.

The second surface 30 of the annular disc 40 is flat and substantially parallel to the load surface 28. In alternative, unillustrated, embodiments, the first load surface 28 and second surface 30 can be non-parallel. In some embodiments, the distance between the load surface 28 and second surface 30 is greatest adjacent the tower 10 and decreases as the distance from the tower 10 increases.

Extending between the second surface 30 and the face of the base plate 42 facing away from the tower 10 are a number of stiffening flanges 44. There are four stiffening flanges 44 in the embodiment illustrated in Figures 9 to 11 (one is not -16 -visible behind the tower 10), other embodiments may have different numbers of stiffening flanges 44.

The stiffening flanges 44 increase the stiffness of the annular disc 34 and help spread any forces applied to the annular disc 40 to the base plate 42. The base plate 42 spreads those forces over a larger surface area of the tower 10 than the load shelfs 24 or 32 of Figures 3 to 5 and 6 to 8. This has the result of reducing the risk that those forces will cause damage to the tower 10.

The decision as to which of the load shelfs 24, 32 or 38 is appropriate to use on any given wind turbine 2 or 20 will depend in part on the anticipated magnitude of the forces that will be transmitted to the tower 10 from the load shelf 24, 32 or 38.

With reference to Figure 12, the tower 10 comprises a tower wall 46 with an inside face 48 and an outside face 50. The tower wall 46 has the form of a hollow truncated cone with the greater diameter of the cone being greatest at the base of the tower 10. Fixed to the inside face 48 of the tower wall 46 is a thickening plate 52. The thickening plate 52 has the form of a truncated cone and is coaxial with the longitudinal axis C (not shown in Figure 12) of the tower 10.

The thickening plate 52 is so dimensioned that the outside diameter of the thickening plate 52 matches the diameter of the inside face 48 at the longitudinal position along the tower 10 to which it is desired to attach or fix the thickening plate 52.

The thickening plate 52 is fixed to the inside face 48 of the tower wall 46 by a known force transmitting /fixing means. A non-exhaustive list of possible fixing means includes welding, an adhesive, a number of nuts and bolts, or a number of rivets In alternative embodiments, there may be a difference in dimension between the outside diameter of the plate 52 and the diameter of the inside face 48 that is sufficient to allow a plastic or liquid filler that will set to a non-plastic solid to be introduced to fix the position of the thickening plate 52 relative to the tower 10, and to ensure continuous contact between the thickening plate 52 and the tower 10.

The filler may also be an adhesive.

The diametrically inside face of the thickening plate 52 may be smooth or incorporate one or more ridges or other features that enhance the stiffness of the thickening plate 52.

The thickening plate 52 is longitudinally positioned on the tower 10 at a position that corresponds to the longitudinal position of a load shelf 24. As a result, -17 -the thickening plate 52 helps spread any forces applied to the tower wall 46 by the load shelf 24 over a larger surface area than the contact area between the load shelf 24 and the tower 10.

More than one thickening plate 52 may be fixed to the tower 10 and each thickening plate 52 may be fixed to the tower 10 at the same longitudinal position as a load shelf 24 (as shown in Figure 12), or alternatively in a position longitudinally adjacent to a load shelf 24, or spaced from a load shelf 24.

Load shelves 32 or 38 could be substituted for load shelf 24 and the same benefits would be achieved.

With reference to Figure 13, the tower 10 comprises a tower wall 46 with an inside face 48 and an outside face 50. The tower wall 46 has the form of a hollow truncated cone with the greater diameter of the cone being greatest at the base of the tower 10. Fixed to the outside face 48 of the tower wall 46 is a thickening plate 54. The thickening plate 54 has the form of a truncated cone and is coaxial with the longitudinal axis C (not shown in Figure 13) of the tower 10.

The thickening plate 54 is dimensioned such that the inside diameter of the thickening plate 54 matches the diameter of the outside face 50 at the longitudinal position along the tower 10 to which it is desired to attach or fix the thickening plate 54.

The thickening plate 54 is fixed to the outside face 50 of the tower wall 46 by a known force transmitting / fixing means. A non-exhaustive list of possible fixing means includes welding, an adhesive, a number of nuts and bolts, or a number of rivets.

In alternative embodiments, there may be a difference in dimension between the inside diameter of the plate 54 and the diameter of the outside face 50 that is sufficient to allow a plastic or liquid filler that will set to a non-plastic solid to be introduced to fix the position of the thickening plate 54 relative to the tower 10, and to ensure continuous contact between the thickening plate 54 and the tower 10. The filler may be an adhesive.

The diametrically outside face of the thickening plate 54 may be smooth or incorporate one or more ridges or other features that enhance the stiffness of the thickening plate 54. Such ridges or other features may be present on all or only a portion of the diametrically outside face of the thickening plate 54.

The thickening plate 54 is longitudinally positioned on the tower 10 at a position that corresponds to the longitudinal position of a load shelf 24 (shown in -18 -dashed lines in Figure 13 for clarity) and the load shelf 24 is fixed to the diametrically outside face of the thickening plate 54. As a result, the thickening plate 54 helps spread any forces applied to the thickening plate 54 from the load shelf 24 before those forces are transmitted to the tower wall 46 by the thickening plate 54.

More than one thickening plate 54 may be fixed to the tower 10 and each thickening plate 54 may be fixed to the tower 10 at the same longitudinal position as a load shelf 24 (as shown in Figure 13), or alternatively in a position longitudinally adjacent to a load shelf 24, or spaced from a load shelf 24.

With reference to Figure 14, the tower 10 comprises a tower wall 46 with an inside face 48 and an outside face 50. The tower wall 46 has the form of a hollow truncated cone with the internal diameter of the hollow cone being greatest at the base of the tower 10. Extending between four positions on the inside face 48 of the tower 10 is a tower internal reinforcement element 62. The tower internal reinforcement element 62 comprises four beams 56, four ties 58, and four mount elements 60. Each beam 56 extends between two mount elements 60 and each end of each beam is fixed to a mount element 60, Two beams 56 are fixed to each mount element 60. The mount elements 60 are fixed to the inside face 48 of the tower wall 46 and are circumferentially spaced from each other by around 90 degrees.

Fixed to the approximate middle of each beam 56 is a tie 58. Each tie extends between the beam 56 to which it is fixed and the inside face of the wall 48. The ties are fixed to the inside wall 48 of the tower wall 46 at a position circumferentially spaced by about 45 degrees from the two mount elements 60 which are fixed to the beam 56 to which the tie is fixed. This has the result that the tower internal reinforcement element 62 is fixed to the inside face 48 of the tower wall 46 circumferentially every 45 degrees. This increases the stiffness of the tower wall 46 in the region of the tower internal reinforcement element 62. The tower internal reinforcement element 62 does not, however, prevent passage up and down the tower by human operatives because the tower internal reinforcement element creates a clear space between the beams 56.

More than one tower internal reinforcement element 62 may be fixed to the tower 10 and each tower internal reinforcement element 62 may be fixed to the tower 10 at the same longitudinal position as a load shelf 24 (not shown in Figure -19 - 14), in a position longitudinally adjacent to a load shelf 24, or spaced from a load shelf 24.

One or more of a portion of the tower wall 46, the load shelves 24, 32, 38, thickening plates 52, 54, and tower internal reinforcement element 62 may be comprised of a material or a combination of materials that alone or in combination are selected to provide a resistance to loading that exceeds the resistance to loading of the material or materials from which the tower wall or the rest of the tower wall is comprised. The selected material may be a composite material. The composite material may be a composite of two or more metals, a fibre composite, a carbon and or aramid fibre composite, or another known composite with appropriate structural characteristics.

The above description is meant to be exemplary only, and one skilled in the art will recognize that changes may be made to the embodiments described without departing from the scope of the invention disclosed. Still other modifications which fall within the scope of the present invention will be apparent to those skilled in the art, in light of a review of this disclosure.

Various aspects of the wind turbines disclosed in this description, the drawings and the claims may be used alone, in combination, or in a variety of arrangements not specifically discussed in the description, drawings and claims. This disclosure is therefore not limited in its application to the details and arrangement of components set forth in the foregoing description or illustrated in the drawings. For example, aspects described in one embodiment may be combined in any manner with aspects described in other embodiments. Although particular embodiments have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from this invention in its broader aspects. The scope of the following claims should not be limited by the embodiments set forth in the examples, but should be given the broadest reasonable interpretation consistent with the description as a whole.

Claims

-20 -CLAIMS1. A wind turbine comprising a foundation, a tower, a nacelle, a rotor and a number of blades in which the tower has a longitudinal central axis, a base, and a top, in which the base is closer to the surface of the earth than the top when the wind turbine is in use, the tower has an outer face and an inner face, the inner face defines a longitudinally extending void for at least a portion of the length of the tower, the wind turbine is adapted to support one or more items of construction or maintenance equipment on the tower, and the tower is provided with one or more of at least one load shelf, at least one tower wall thickening, at least one tower internal reinforcement element, and at least one specified material selection.
2. A wind turbine according to claim 1 in which the tower has a substantially circular cross section in a plane perpendicular to the longitudinal central axis.
3. A wind turbine according to claim 1 or 2 in which at least one load shelf is located on an outside face of the tower and comprises at least one load surface adapted to transmit a load force applied to the load surface into the structure of the tower at or in the region of the longitudinal position on the tower of the load shelf.
4. A wind turbine according to claim 3 in which each load surface extends around the perimeter of the tower.
5. A wind turbine according to claim 3 in which the each load surface extends only around a portion of the perimeter of the tower.
6. A wind turbine according to claim 3 in which each load surface comprises a plurality of load sub-surfaces located at substantially the same longitudinal position on the tower, and the load sub-surfaces are spaced from each other around at least a portion of the perimeter of the tower.
7. A wind turbine according to claim 6 in which the load sub-surfaces are evenly distributed around the perimeter of the tower.
-21 - 8. A wind turbine according to any of claims 3 to 7 in which the included angle between the central axis of the tower and at least one load surface in the radial direction from the central axis of the tower is around 90 degrees.
9. A wind turbine according to any of claims 3 to 7 in which the included angle between the central axis of the tower and at least one load surface in the radial direction from the central axis of the tower is between 10 and 90 degrees, between 20 and 90 degrees, between 30 and 90 degrees, between 40 and 90 degrees, between 50 and 90 degrees, between 60 and 90 degrees, between 70 and 90 degrees, between 80 and 90 degrees, or between 85 and 90 degrees.
10. A wind turbine according to any of claims 3 to 9 in which at least one load shelf comprises at least one second face, each second face is associated with a load surface, each second face is substantially parallel to the load surface with which it is associated, and each second face is closer to the base of the tower than the load surface with which it is associated.
11. A wind turbine according to any of claims 3 to 9 in which at least one load shelf comprises at least one second face, each second face is associated with a load surface, each second face is not parallel to the load surface with which it is associated, and each second face is closer to the base of the tower than the load surface with which it is associated.
12. A wind turbine according to claim 10 or 11 in which the load shelf further comprises one or more stiffening plates, each stiffening plate extends between a second face of the load shelf and the outside face of the tower, and each stiffening plate extends longitudinally along a portion of the outside face of the tower.
13. A wind turbine according to any of claims 3 to 9, 11 or 12 in which at least one load shelf has a cross section in a radial direction from the central axis of the tower that has an outer perimeter that is substantially triangular.
14. A wind turbine according to any of claims 1 to 13 in which at least one load shelf is fabricated separately from the tower and subsequently fixed to the tower.
-22 - 15. A wind turbine according to claim 14 in which at least one load shelf further comprises at least one base plate, each base plate has a first and a second face, the first face of each base plate is configured and contoured to overlie a portion of the outer face of the tower, and the load surface extends from the second face.
16. A wind turbine according to claim 14 or 15 in which the base plate has the same dimensions in the longitudinal direction of the tower as the load shelf.
17. A wind turbine according to claim 14 or 15 in which the base plate has a greater dimension in the longitudinal direction of the tower than the load shelf.
18. A wind turbine according to claim 17 in which the edge of the base plate nearest the top of the tower is substantially the same distance from the top of the tower as the distance between the intersection of the load surface and the base plate and the top of the tower.
19. A wind turbine according to any of claims 1 to 18 in which the tower decreases in external dimensions in the plane perpendicular to the central axis from a larger dimension at the base of the tower to a smaller dimension at the top of the tower, at least one load shelf is configured to surround and be in contact with a longitudinally extending portion of the outside face of the tower, the base plate is dimensioned so that it surrounds and is in contact with a longitudinally extending portion of the outside face of the tower at a predetermined longitudinal position on the tower.
20. A wind turbine according to any of claims 1 to 19 in which at least one load shelf further comprises a pressure transmitting filler between the load shelf and the outside face of the tower.
21. A wind turbine according to any of claims 1 to 20 in which the load shelf is fixed to the tower by one or more of welding, an adhesive, a number of fixings comprising a helical thread, or a number of rivets.
22. A wind turbine according to any of claims 1 to 21 in which the at least one tower wall thickening comprises at least one thickening plate, each thickening plate -23 -is configured to conform to the surface contours of the tower at a location where the wall is to be thickened, and each thickening plate is fixed to the tower.
23. A wind turbine according to claim 22 in which at least one thickening plate is fixed to an outside surface of the tower.
24. A wind turbine according to claim 22 or 23 in which at least one thickening plate is fixed to an inside surface of the tower.
25. A wind turbine according to any of claims 22 to 24 in which at least one thickening plate has a first and second face, the first face is adapted to overlie a surface of the tower, and the second face is adapted to face away from the overlaid surface of the tower, the first face of the plate is smooth, and the second face of the plate comprises a number of ribs or other stiffening features.
26. A wind turbine according to claim 25 in which there are more than one ribs or other stiffening features, and at least two of the ribs or other stiffening features are linear.
27. A wind turbine according to claim 26 in which at least two of the linear ribs or other stiffening features extend in different directions.
28. A wind turbine according to any of claims 22 to 27 in which at least one thickening plate defines a number of apertures, and those apertures extend through the plate from one face to the other.
29. A wind turbine according to any of claims 22 to 28 when dependent on any of claims 3 to 21 in which at least one thickening plate is fixed to a surface of the tower at approximately the same longitudinal position on the tower as a load shelf.
30. A wind turbine according to any of claims 22 to 29 when dependent on any of claims 3 to 21 in which at least one thickening plate is fixed to a surface of the tower at a position longitudinally adjacent to a load shelf.
-24 - 31. A wind turbine according to any of claims 1 to 30 in which at least one tower internal reinforcement element comprises one or more stiffening elements, at least one stiffening element is a plate, and the plate is fixed to the inner face of one or more of the walls of the tower along at least one edge of the plate.
32. A wind turbine according to any of claims 1 to Si in which at least one tower internal reinforcement element comprises one or more stiffening elements, at least one stiffening element is a rib, and the rib is fixed to the inner face of one or more of the walls of the tower.
33. A wind turbine according to any of claims 1 to 32 in which at least one tower internal reinforcement element is comprised of one or more stiffening elements, at least one stiffening element is a rod or a beam, the rod or beam has a first and second end, the first and second ends are fixed directly or indirectly to the inner face of a tower wall at a first and second position.
34. A wind turbine according to any of claims 1 to 33 in which at least one tower internal reinforcement element is comprised of two or more stiffening elements, each stiffening element is a rod or a beam, and each rod or beam forms part of a three dimensional lattice of rods and / or beams.
35. A wind turbine according to any of claims 31 to 34 when dependent on any of claims 3 to 21 in which at least one stiffening element is fixed to the tower at a longitudinal position on the tower at approximately the same longitudinal position on the tower as a load shelf.
36. A wind turbine according to any of claims 31 to 35 when dependent on any of claims 3 to 21 in which at least one stiffening element is fixed to a surface of the tower at a position longitudinally adjacent to a load shelf.
37. A wind turbine according to any of claims 1 to 36 in which one or more of at least a portion of the tower, at least one load shelf, at least one tower wall thickening, and at least one tower internal reinforcement comprises a material selected to provide a resistance to loading that exceeds the resistance to loading of the material or materials from which the tower or the rest of the tower is comprised.
-25 - 38. A wind turbine according to claim 37 in which the selected material is a composite material.
39. A wind turbine according to any of claims 1 to 38 in which the wind turbine is an offshore wind turbine, and the foundation of the wind turbine is the portion of the wind turbine that is below the water.
40. A wind turbine according to any of claims 1 to 39 in which the item of construction or maintenance equipment comprises a lifting device.
41. A method of constructing a wind turbine according to any of claims 1 to 39 comprising the steps of (a) constructing a foundation and a tower and erecting same, (b) lifting a nacelle to the top of the tower, (c) attaching the nacelle to the top of the tower, (d) mounting at least a rotor and electricity generating equipment in or adjacent to the nacelle, and (e) lifting each blade and attaching it to the rotor, in which the lifting of the nacelle, at least the rotor and electricity generating equipment, and blades into position is performed by at least one lifting means supported on the tower, and the one or more of at least one load shelf, at least one tower wall thickening, at least one tower internal reinforcement, and at least one specified material selection are so located that they transfer loading forces generated by the lifting means into the structure of the tower or assist in diffusing the transferred loading forces within the structure of the tower to avoid the accumulation of stresses or strains of sufficient magnitude within the structure of the tower to damage the tower.
42. A method according to claim 41 in which the tower comprises at least one load shelf, and the load shelf supports a lifting means.
43. A method according to claim 42 in which the tower comprises at least two load shelfs, and further comprises the steps of -26 - (i) a first lifting means lifting a second lifting means onto a load shelf which is between the first lifting means and the top of the tower and the second lifting means is supported on that load shelf, (ii) the second lifting means lifting the first lifting means onto a load shelf which is between the second lifting means and the top of the tower and the first lifting means is supported on that load shelf, (iii) steps (I) and (ii) are repeated until the lifting means closest to the top of the tower is sufficiently close to the top of the tower that that lifting means can perform the lifting for steps (b) to (e) of claim 41.
44. A method according to claim 42 in which the tower comprises at least two load shelfs, further comprising the steps of (i) a first lifting means lifting a second lifting means onto a load shelf which is between the first lifting means and the top of the tower and the second lifting means is supported on that load shelf, (ii) the second lifting means lifting the first lifting means onto a load shelf which is between the second lifting means and the top of the tower and the first lifting means is supported on that load shelf, (iii) steps (i) and (ii) are repeated until the lifting means closest to the top of the tower is sufficiently close that that it may lift a third lifting means from the base of the tower onto an uppermost load shelf, and (iv) the third lifting means performs the lifting for steps (b) to (e) of claim 41.
45. A method according to claim 43 or 44 in which each of the first and second lifting means has a maximum lifting height, and the load shelves are longitudinally spaced along the tower at a distance equal to or less than maximum lifting height of the first and second lifting means.
46. A method of maintaining a wind turbine according to any of claims 1 to 39 comprising the step of locating a lifting means in a position at or near the top of the tower from which the lifting means can perform the lifting necessary to perform the maintenance, in which the one or more of at least one load shelf, at least one tower wall thickening, at least one tower internal reinforcement element, and at least one specified material selection are so located that they transfer loading forces -27 -generated by the lifting means into the structure of the tower or assist in diffusing the transferred loading forces within the structure of the tower to avoid the concentration of stresses or strains within the structure of the tower at sufficient magnitude to damage the tower.