Patent Description:
Offshore wind turbines require various items of on-board equipment to supply electrical power from a generator of the turbine to the grid. Such equipment may comprise several components and functional units required for operation of the wind turbine, such as switchgear, frequency converters, transformers and/or a controller, in addition to connections for cables that run between the seabed and the nacelle atop the mast or tower of the turbine.

At least part of the electrical equipment required by an offshore wind turbine may be pre-installed inside a foundation of the turbine, such as a monopile. Part of that equipment may also be located in the tower mounted atop the foundation. For example, <CIT> discloses equipment floors or platforms within a segment or section of a wind turbine tower.

In principle, much of the necessary equipment could be pre-installed in foundation or tower components of a wind turbine and transported within those components to an installation site. However, such equipment could be damaged by vibration, impact or moisture while the components are being transported and installed and so may require repair or replacement. This is a particular problem with monopile foundations, which are designed to be driven into the seabed under repeated impacts from a piledriver.

One approach to address this problem is to install a short, minimal foundation underwater and then to place an entire supporting structure with pre-installed electrical equipment and connections onto the foundation. This approach is appropriate for jackets or tripod supporting structures but not for monopiles.

<CIT> discloses a wind turbine whose tower is attached to an offshore support structure comprising a transition piece to connect the tower to a foundation, such as a jacket foundation, a gravity foundation or a monopile. The transition piece is attached to the foundation above the water level. The transition piece, which may be made of reinforced concrete, comprises a floor, walls and a roof defining an internal space that can house electrical equipment and that can be used by personnel to access the equipment and the interior of the tower. The transition piece supports, and is surmounted by, the tower. However, the use of a transition piece requires alignment with, and between, the mast and the monopile.

More generally, conventional transition pieces perform several functions, such as to provide: a work platform, which may comprise a service crane; a way of accessing the work platform, such as a ladder extending from a boat landing facility; an attachment interface, such as a flange, for mounting the tower; internal platforms for equipment; and a gas-tight deck for fixing cables.

In <CIT>, a transition piece is a cylindrical extension of a monopile that contains pre-installed electrical equipment. Being bolted to a flange at the top of the monopile, it complicates the installation process.

Alternatively, electrical connection may be done only after installation of the monopile, for example by pulling cables with dedicated winches. In <CIT>, electrical equipment is lifted inside the mast after installation. A power control module is placed on a temporary support device and a tower section is placed around the power control module. After connecting the power control module to the tower section, the connected power control module and tower section are removed from the temporary support device. The power control module hangs suspended in the tower section.

Monolithic wind turbines, with a monopile as long as possible, are preferred to reduce the size of the tower. There is a requirement for quick and easy manufacture and installation of electrical and electronic equipment and for that equipment to perform reliably over years of service offshore.

In this respect, the invention contemplates various improvements to the teaching of <CIT>, which discloses a method of installing an electrical platform unit inside a monopile without recourse to a transition piece. The monopile of <CIT> comprises three interfaces, namely a flange for connecting a tower on top of the monopile, an internal support for the electrical platform unit, and another support for a work platform that surrounds the top of the monopile.

The electrical platform unit of <CIT> is challenging to lower into the monopile and to align correctly with the monopile. Structures protruding from the top of the electrical platform unit also hinder convenient lifting arrangements.

After installation of the electrical platform unit, <CIT> teaches that a protective cap has to be installed over the open top of the monopile to protect the electrical platform unit and its on-board equipment from the weather. Installing and removing the cap before mounting a tower to the monopile adds further procedural steps; also, when installed, the cap complicates access to the interior of the monopile.

<CIT> also contemplates that the work platform and the electrical platform unit must be installed in separate, successive steps before the tower is mounted on the monopile. The invention proposes other sequences and arrangements, not disclosed in <CIT>, that simplify the procedure and the structure and that provide better support to the work platform and the electrical platform unit without complicating or compromising how the tower is mounted on the monopile.

Other known examples of components installed within a wind turbine are described in <CIT>, <CIT>, <CIT>, <CIT> and <CIT>. Additionally, an example of a method of mounting an offshore tower onto a pile is described in <CIT>.

Against this background, the invention resides in a wind turbine equipment canister for supporting and enclosing electrical equipment or instrumentation of a wind turbine. The canister comprises: a housing defining or containing at least one internal platform for supporting the equipment; a lifting interface on a top of the housing; and at least one support formation positioned on or projecting laterally beyond a side wall of the housing, the support formation being capable of supporting the weight of the canister suspended therefrom when the canister is installed within a monopile foundation for a wind turbine.

To aid alignment and support, at least a portion of the side wall tapers in diameter downwardly toward a base of the housing. For example, the side wall may comprise a cylindrical upper portion and a frusto-conical lower portion that tapers downwardly from the upper portion. The downwardly-tapering portion of the side wall can serve as a support formation. At least one vertically-oriented alignment formation may also be provided on the side wall to aid angular alignment of the canister.

For weatherproofing, at least the top of the housing may be substantially closed or may be penetrated by at least one opening that is closable by a hatch.

The support formation may be substantially level with the top of the housing, for example as a lateral extension of the top of the housing. Alternatively, the support formation could be at a level beneath the top of the housing.

The lifting interface suitably comprises posts upstanding from the top of the housing, the posts having a quick-release mechanism for engagement with a lifting frame.

The canister may be attached to a work platform that extends laterally beyond a diameter of the housing. For example, the canister could hang beneath or extend through the work platform.

The inventive concept also embraces a monopile foundation for a wind turbine, containing at least part of a canister of the invention. The housing of the canister, for example around a cylindrical upper portion, may conveniently be a sliding fit for longitudinal movement within an open top of the foundation.

The foundation may further comprise an internal support formation that is positioned to engage the support formation of the canister. Such an internal support formation may project inwardly from a surrounding wall of the foundation. An internal support formation of the foundation may define a support surface that is inclined inwardly and downwardly, for example to complement a downwardly-tapering portion of the canister.

For angular orientation, the foundation may comprise at least one internal guide formation that is configured for engagement with an abovementioned alignment formation of the canister. Such a guide formation may, for example, comprise downwardly-converging rails.

The canister could be recessed fully beneath a top end of the foundation. Alternatively, the support formation of the canister can rest upon a top interface of the foundation, such as a top flange, that is configured for mounting a tower upon the foundation. In that case, the support formation of the canister may be disposed inboard of an outer portion of the top interface, which outer portion is configured for mounting the tower upon the foundation.

The support formation of the canister could overlie an upper hang-off formation of an intermediate support structure, sleeve or insert that embraces the canister. For example, a lower part of the support structure may comprise an inwardly-facing support formation that complements the shape of the housing of the canister.

The inventive concept further embraces a wind turbine that comprises a tower mounted on a foundation of the invention, enclosing a canister of the invention.

Conveniently, the support formation of the canister can be sandwiched between mutually-opposed ends of the foundation and the tower. In that case, fastenings that join the tower to the foundation may extend through holes in the support formation of the canister.

The wind turbine may further comprise an external work platform, which may be supported by legs that are disposed externally around the foundation. Where the tower and the foundation are in mutual abutment, the tower and/or the foundation may extend through a wider opening that penetrates the work platform. Alternatively, the work platform may be sandwiched between mutually-opposed ends of the foundation and the tower. In that case, the work platform may be penetrated by an opening that is narrower than the mutually-opposed ends of the foundation and the tower. Fastenings, such as bolts, that join the tower to the foundation can extend through holes or bores in the work platform.

In some embodiments, the support formation of the canister may rest on a bottom interface of the tower, such as a bottom flange that is configured to mount the tower to the foundation.

The inventive concept extends to a wind turbine that comprises a monopile foundation and a tower mounted atop the foundation. The wind turbine further comprises: a canister disposed at least partially within the foundation and supporting and enclosing electrical equipment of the wind turbine; and optionally an external work platform extending outside the foundation or the tower. A side wall of a housing of the canister has at least a portion that tapers in diameter downwardly toward a base of the housing. A part of the canister and/or a part of the work platform is sandwiched between mutually-opposed ends of the foundation and the tower. Conveniently, fastenings that join the tower to the foundation may extend through holes in the sandwiched part of the canister and/or the work platform.

The inventive concept also extends to methods of assembling a wind turbine on a pre-installed monopile foundation. One such method comprises: lowering a canister into an open top of the foundation, the canister supporting and enclosing electrical equipment of the wind turbine; sliding the canister down within the foundation, and mounting a tower on the foundation, sandwiching part of the canister between mutually-opposed ends of the foundation and the tower.

Another such method comprises: lowering an external work platform onto an open top of the foundation; and mounting a tower on the foundation, sandwiching part of the work platform between mutually-opposed ends of the foundation and the tower. That method further comprises: preliminarily, lowering a canister into an open top of the foundation, the canister supporting and enclosing electrical equipment of the wind turbine; supporting the external work platform on the canister; and enclosing the canister when mounting the tower on the foundation. For example, the work platform and the canister could be lowered onto the foundation when they are already conjoined, or the work platform could be joined to the canister after the canister has been lowered into the foundation.

Another such method comprises: lowering a canister into an open top of the foundation, the canister supporting and enclosing electrical equipment of the wind turbine; and suspending at least part of the canister from a support formation of the foundation. That method may further comprise mounting a tower on the foundation in mutual end-to-end abutment, enclosing the canister. For example, the canister may be suspended from an inboard side of the support formation and the tower may be mounted on an outboard side of the support formation.

When being lowered, the canister may be slid down within the foundation. The canister may be oriented about horizontal and/or vertical axes in consequence of downward movement of the canister relative to the foundation. The canister could be seated into a support structure that is suspended from the support formation.

Another method is described which comprises: mounting at least a lower part of a tower on the foundation; and lowering a canister into the foundation through the tower, or the part of the tower, that is mounted on the foundation, the canister supporting and enclosing electrical equipment of the wind turbine. At least part of the canister may be suspended from a support formation of the tower, such as a bottom interface formation that is used for mounting the tower on the foundation.

In summary, monopiles without transition pieces are gaining acceptance as a low-cost solution for offshore wind turbine foundations. However, in view of pile-driving vibration especially, secondary structures attached to the pile, along with any mechanical or electrical outfitting, need to be retrofitted offshore. The key to successfully designing such foundations is to enable offshore retrofitting to be performed cost-effectively.

Embodiments of the invention envisage a substantially fully-enclosed canister that can be lifted into a monopile offshore and that provides a permanent housing for the electrical equipment and cable hang-offs that are required inside the monopile. Beneficially, the canister can be completed onshore in a factory set-up, including integration and commissioning of the equipment onboard, before being transported offshore.

It is envisaged that at least an outer shell of the canister could be made from a material such as fibre-reinforced plastics (FRP) or glass-reinforced plastics (GRP), although the shell could instead be made predominantly from steel or aluminium. FRP or GRP is lightweight, relatively low cost and weather-resistant. Also, FRP or GRP is suitable for series production using formwork, enabling the canister of the invention to be built locally in or near any of the countries that are active in the offshore wind industry globally.

In the embodiments to be described, the design of the canister provides an optimised shape to enable production-line fabrication techniques to be applied to the use of reinforced plastics or metals or combinations thereof, using moulds or jigs as appropriate. The optimised shape of the canister also enables self-guiding and location stability for loadout and installation, while ensuring that the canister is stable and self-supporting once lowered into a monopile.

The shell of the canister provides weather-resistant containment for the electrical equipment within, during: installation of the equipment in a manufacturing facility; transportation to site; installation; and in-place service.

The canister provides for hang-off of cables required for a wind turbine array, with sufficient space within the shell for efficient cable pull-in and connection to switchgear.

A simple seal arrangement can be provided at the top of the canister and monopile, with thermal isolation from cold-bridging to the monopile structure to minimise condensation.

Simplified configuration of rigging and installation avoids the need for large and complex installation aids.

The canister may be made in standardised shapes and sizes to enable use in monopiles of various designs and diameters across multiple projects.

A significant cost saving of the arrangement proposed by the invention is the elimination of a separate gas-tight deck that is conventionally required inside a monopile.

Thus, the invention provides electrical and instrumentation canisters for monopiles used in the offshore wind industry, and methods for their installation. The lightweight canister of the invention is easy to transport and install and could form a permanent housing for the mechanical and electrical outfitting required within a wind turbine monopile foundation. The canister has very low maintenance requirements. Thus, the invention enables low-cost installation and protection of the mechanical and electrical outfitting inside the monopile. In these and other ways, the invention improves existing monopile and transition piece designs known in the offshore wind industry.

Embodiments of the invention provide a canister for carrying equipment, such as electrical equipment, for a wind turbine. The canister comprises a housing that may be arranged to slide longitudinally within a monopile foundation and/or a tower of the wind turbine. The housing has at least one internal platform and a lifting interface. The top of the housing may be substantially closed.

The housing may have an upper section and a lower section. The upper section may be substantially cylindrical whereas the lower section may be frusto-conical or otherwise downwardly-tapering.

At least one of the top, the upper section and the lower section of the housing suitably comprises an interface for the canister to be supported by a complementary formation that is directly or indirectly connected to the monopile. For example, a transition between the upper and lower sections of the canister may serve as an interface or support formation.

The canister may comprise two or more floors or platforms connected by ladders, stairways and/or lift shafts, and may comprise chambers for electrical equipment within. The top of the housing may, for example, comprise a horizontal roof with at least one access hatch. More generally, the canister may further comprise at least one hatch for controlling access to the floors, platforms, ladders, stairways, lift shafts and/or chambers, and for sealing openings in the shell of the canister for weatherproofing. At least one such opening may be provided for electrical cables to enter or exit the canister.

A lifting interface may be mounted on the top of the canister, for example comprising padeyes or a mechanical quick-connector system such as that supplied under the registered trade mark 'Balltec LiftLOK'.

There is also described a method for installing at least one platform for electrical equipment inside a wind turbine. The method comprises: lifting a unit comprising the at least one platform, wherein the unit also comprises a support interface and a lifting interface, and may be a substantially closed container; installing the unit at least partially inside a monopile and/or a tower of the wind turbine; and optionally installing an external work platform around the monopile, for example around the top of the monopile.

Where an external work platform is installed around the top of the monopile, it may be installed before, during or after installing the unit. Thus, those steps may be reversed or combined. The method may further comprise mounting a tower on the monopile either directly or via the work platform, for example by bolting together flanges.

Distinct interfaces may be provided on the monopile for the unit, the work platform and the tower. Alternatively, the work platform may be connected to the top of the canister, before or after installing the canister, thus requiring interfaces on the monopile only for the tower and either the canister or the platform.

The work platform may be fixed to the monopile or the flange, for example by being sandwiched between the monopile and the tower and/or by being fixed to mounting formations on the outside or inside of the monopile.

The canister may be suspended from the work platform or the work platform may be supported via the canister.

The canister may be suspended from an interface situated at the top of the monopile, not necessarily recessed beneath the top of the monopile. In that case, an upper section of the canister may extend above the top of the monopile.

A support formation such as a flange on the monopile for mounting the tower may be adapted or extended also to support the canister.

An interface piece at the top of the monopile such as a support structure may provide support to the canister.

The canister could be supported by an interface inside the tower. Such an interface could be at or close to the bottom of the tower. For example, the interface could be defined by the top of a flange at the bottom of the tower that is also used to mount the tower to the monopile.

Referring firstly to <FIG> of the drawings, a wind turbine equipment canister <NUM> of the invention comprises a hollow, substantially closed housing or shell whose side wall is rotationally symmetrical about a vertical central longitudinal axis <NUM>. The side wall of the shell comprises a cylindrical upper portion <NUM> of substantially constant circular cross-section and a frusto-conical lower portion <NUM> that tapers downwardly from the diameter of the upper portion <NUM>.

The shell is completed and closed at its bottom end by a flat circular base <NUM> and at its top end by a generally flat circular roof <NUM>. The base <NUM> and the roof <NUM> lie in respective horizontal planes. The roof <NUM> is surmounted by a lifting interface that, in this example, comprises hollow vertical posts <NUM> equiangularly spaced about the central longitudinal axis <NUM>. The canister <NUM> is stable when free-standing on its base <NUM>.

A male hang-off formation projects outwardly in a horizontal direction from the upper portion of the side wall. In this example, the hang-off formation takes the form of a circumferential flange <NUM> surrounding the shell in alignment with the upper portion <NUM>. The flange <NUM> is shown here at the level of the roof <NUM>, for example as a horizontal extension of the roof <NUM>.

The flange <NUM> need not be continuous as shown here but could be interrupted by one or more circumferential gaps. In other examples, a flange or other hang-off formation could be at a different vertical level along the canister <NUM>, for example at the level of the lower portion <NUM> or at the interface between the upper and lower portions <NUM>, <NUM>. It would also be possible to support the canister <NUM> other than by a hang-off arrangement.

Elongate alignment formations <NUM> mounted externally on the side wall of the shell lie in respective vertical planes that also contain the central longitudinal axis <NUM>. Those planes, and hence the alignment formations <NUM>, are also equiangularly spaced about the central longitudinal axis <NUM>.

On its upper side within the shell, the base <NUM> defines a lower equipment platform or deck of the canister <NUM>. A parallel upper equipment platform or deck <NUM> extends across the canister <NUM> at the junction between the upper and lower portions <NUM>, <NUM> of the shell. The base <NUM> and the upper equipment deck <NUM> support items of equipment (not shown) that are required for operation of the wind turbine, such as switchgear, a transformer, a converter and/or control equipment. When the canister <NUM> is installed in a wind turbine, cables from outside the canister <NUM> can be connected to that equipment to convey power and data signals within, into and out of the wind turbine as required. The roof <NUM> may, of course, also serve as an equipment deck after the canister <NUM> has been installed.

The roof <NUM> is penetrated by a central opening <NUM> that communicates with the interior of the shell. The opening <NUM> can be closed by a hatch <NUM> shown here beside the opening, hence weatherproofing the roof <NUM> and substantially sealing the shell of the canister <NUM>. When the hatch is open as shown, a frame <NUM> within the shell may extend upwardly from the base <NUM> and through the upper equipment deck <NUM> to protrude above the roof <NUM> through the central opening <NUM>. The frame <NUM> may, for example, support cables that extend into the tower of the completed wind turbine structure and/or may serve as the base of a lift shaft also extending into the tower. At its lower end, the frame <NUM> may extend to cable hang-off provisions mounted on the base <NUM> for supporting cables that, in use, hang down toward the seabed into the foundation beneath the canister <NUM>.

An internal ladder <NUM> provides alternative access between the base <NUM>, the upper equipment deck <NUM> and the roof <NUM> of the canister <NUM>. Again, a hatch <NUM> may close the opening that accommodates the ladder <NUM>.

Moving on now to <FIG>, <FIG> and <FIG>, these drawings shows the canister <NUM> in its context of use, in which the canister <NUM> is supported above sea level in the monopile foundation of a wind turbine.

In the exploded view of <FIG>, the canister <NUM> is shown in coaxial alignment with the open top of a pre-installed foundation in the form of a tubular monopile <NUM> that receives the canister <NUM> telescopically as the canister <NUM> is lowered by a crane. In effect, the canister <NUM> is installed as a cartridge into a socket within the open top of the monopile <NUM>. <FIG> also shows the canister <NUM> when lowered into position within the monopile <NUM>.

For the purpose of lifting and lowering the canister <NUM>, <FIG> and <FIG> show a lifting frame <NUM> that can be engaged from above with the lifting interface of the canister <NUM>. Specifically, the lifting frame <NUM> comprises vertical pins <NUM> that are positioned to engage within respective ones of the upstanding tubular posts <NUM> on the roof <NUM> of the canister <NUM>. A mechanical quick-connector system such as the aforementioned Balltech LiftLOK may act between the pins <NUM> and the posts <NUM> to engage and disengage the lifting frame <NUM>. <FIG> also shows a load orientation system <NUM> that may be interposed between the lifting frame <NUM> and the hook <NUM> of a crane to control the orientation of the canister <NUM> about a vertical axis.

The monopile <NUM> has a female hang-off formation that forms part of a first interface of the monopile <NUM>, namely that between the monopile <NUM> and the canister <NUM>. The female hang-off formation is exemplified here by an inner circumferential flange <NUM> that is cooperable with the corresponding flange <NUM> of the canister <NUM> to support the weight of the canister <NUM>. The inner flange <NUM> lies in a horizontal plane that is spaced sufficiently beneath the top of the monopile <NUM> as to recess the top of the canister <NUM> at a level beneath the horizontal plane of the upper end of the monopile <NUM>.

Conveniently, cooperation between the flange <NUM> of the canister <NUM> and the flange <NUM> of the monopile <NUM> effects or enables a seal. That seal protects the interior of the monopile <NUM> and the portion of the canister <NUM> beneath the flange <NUM> from the weather once the canister <NUM> has been installed. The roof <NUM> of the canister <NUM> may also be weatherproofed, for example with hatches <NUM>, <NUM> as noted above. This means that a temporary cap over the open top of the monopile <NUM> is not essential to protect the equipment within the canister <NUM> from the weather, hence simplifying the wind turbine installation process.

<FIG> shows downwardly-converging Y-shaped alignment rails <NUM> that are angularly spaced around the interior of the monopile <NUM>. Each of the alignment rails <NUM> serves as a guide formation, being positioned to receive a respective one of the alignment formations <NUM> of the canister <NUM> and to guide the canister <NUM> into correct angular alignment with the monopile <NUM> as the canister <NUM> is lowered into the open top of the monopile <NUM>. Once seated into the monopile <NUM> in the correct angular alignment, the canister <NUM> may be held down by anti-lift fixings acting between the cooperating circumferential flanges <NUM>, <NUM> of the canister <NUM> and the monopile <NUM>.

Externally, the monopile <NUM> is encircled by an angularly-spaced array of outwardly-projecting studs <NUM> that lie in a horizontal plane spaced beneath the top of the monopile <NUM>. The studs <NUM> align with, and support, respective legs <NUM> of a work platform <NUM> that is also shown in <FIG>, <FIG>, <FIG>. Thus, the studs <NUM> and the legs <NUM> together define a second interface of the monopile <NUM>, namely that between the monopile <NUM> and the work platform <NUM>. Specifically, the legs <NUM> hang from the work platform <NUM> and lie against the exterior of the monopile <NUM> to engage the studs <NUM>. That engagement between the legs <NUM> and the studs <NUM> fixes the work platform <NUM> relative to the monopile <NUM> as shown in <FIG> before a tubular tower <NUM> is mounted on the monopile <NUM> as shown in <FIG> and <FIG>.

<FIG> also shows a ladder arrangement <NUM> beneath and connecting to the work platform <NUM> that provides for docking a service vessel to the wind turbine and for access of personnel to the wind turbine via the work platform <NUM>.

<FIG> shows that a circular opening <NUM> penetrates the work platform <NUM> in coaxial alignment with the top of the monopile <NUM>. In this example, the work platform <NUM> is asymmetric in plan view, having a major portion laterally offset to one side of the opening <NUM>.

In this example, the opening <NUM> in the work platform <NUM> has an inner diameter that is slightly smaller than the outer diameter of the top of the monopile <NUM>. The opening <NUM> is surrounded by a circular array of holes <NUM> that together receive a corresponding array of pins or bolts <NUM> projecting vertically from a flange <NUM> at the top of the monopile <NUM> and into a complementary flange <NUM> at the bottom of the tower <NUM> as shown in <FIG>.

The bolts <NUM> and flanges <NUM>, <NUM> form part of a third interface of the monopile <NUM>, namely that between the monopile <NUM> and the tower <NUM> that surmounts the monopile <NUM>. It will be apparent that the peripheral region of the work platform <NUM> immediately surrounding the opening <NUM> is sandwiched and indeed clamped between the monopile <NUM> and the tower <NUM>, thereby further locating the work platform <NUM> relative to the monopile <NUM>.

<FIG> show further provisions for defining the first interface between the monopile <NUM> and the canister <NUM>. These provisions may be additional to, or instead of, the cooperating flanges <NUM>, <NUM> at or near the top of the canister <NUM>. They comprise additional cooperating flanges <NUM> at a lower position on the upper portion <NUM> of the side wall, and wedge-faced supports <NUM> extending inwardly from the side wall of the monopile <NUM> in opposition to the lower portion <NUM> of the side wall. The wedge faces of the supports <NUM> engage, and complement the inclination and curvature of, the frusto-conical lower portion <NUM> of the side wall. The supports <NUM> could be discrete structures angularly-spaced around the central longitudinal axis <NUM> of the canister <NUM> or could be parts of a circumferentially-continuous ring that encircles the interior of the monopile <NUM>.

The flanges <NUM>, <NUM>, the additional flanges <NUM> and the supports <NUM> may be used individually or in any combination. In the remaining drawings, the flanges <NUM> are omitted for simplicity but the supports <NUM> are retained or replaced with equivalent features.

<FIG> show various other arrangements and methods of the invention for assembling a wind turbine that incorporates a canister <NUM> of the invention. Like numerals are used for like features.

The arrangement and method steps shown in <FIG> correspond to those of <FIG> except that the circular opening <NUM> in the work platform <NUM> is wider than the outer diameter of both the monopile <NUM> and the tower <NUM>. Consequently, the monopile <NUM> and/or the tower <NUM> can extend through opening <NUM> and hence through the work platform <NUM> to abut directly at their mutual interface, where the bolts <NUM> extend through the abutting flanges <NUM>, <NUM>. In this arrangement, unlike that of <FIG>, the work platform <NUM> is not clamped between monopile <NUM> and the tower <NUM> but instead relies upon engagement of the legs <NUM> under the work platform <NUM> with the studs <NUM> on the exterior of the monopile <NUM>.

<FIG> show a variant of the invention in which the work platform <NUM> is attached directly to the canister <NUM> before or after the canister <NUM> is installed in the monopile <NUM>. In the former case, the work platform <NUM> and the canister <NUM> are installed together on the monopile <NUM>, being lifted together as an assembly by a lifting frame <NUM> as shown in <FIG>. For example, the canister <NUM> could be pre-inserted into the opening <NUM> in the work platform.

In the example shown in <FIG>, the work platform <NUM> is clamped between the monopile <NUM> and the tower <NUM> in a manner similar to that shown in <FIG>. In other words, the bolts <NUM> extend through the flanges <NUM>, <NUM> and through the platform <NUM> sandwiched between the flanges <NUM>, <NUM>. In view of this, and as the work platform <NUM> can also rely upon its attachment to the canister <NUM> for support, legs <NUM> under the work platform <NUM> engaging with studs <NUM> on the monopile <NUM> are optional and have been omitted from these drawings. However, a second interface such as that defined by the studs <NUM> and the legs <NUM> could be provided, for example in an alternative arrangement in which the opening <NUM> of the work platform <NUM> is wide enough for the monopile <NUM> and the tower <NUM> to abut directly at their mutual interface in a manner akin to that shown in <FIG>.

<FIG> show an arrangement of the invention in which the top of the canister <NUM> is not recessed below the top of the monopile <NUM> but instead projects above the top of the monopile <NUM>. In this example, the flange <NUM> of the canister <NUM> lies on an inwardly-projecting flange <NUM> that is positioned at or near to the top of the monopile <NUM>.

The arrangement is such that at least part of the canister <NUM>, in this case the posts <NUM> of the lifting interface, extends above the top of the monopile <NUM>. Thus, this upwardly-projecting part of the canister <NUM> lies within the base of the tower <NUM> as shown in <FIG>.

In <FIG>, the work platform <NUM> is supported, optionally, by legs <NUM> under the work platform <NUM> engaged with studs <NUM> on the monopile <NUM>. Also, the opening <NUM> of the work platform <NUM> is wide enough for the monopile <NUM> and the tower <NUM> to abut directly at their mutual interface in a manner akin to that shown in <FIG>. However, with a narrower opening <NUM>, it would instead be possible for the work platform <NUM> to be clamped between the monopile <NUM> and the tower <NUM> like the arrangement of <FIG> and <FIG>. In either case, the flange <NUM> of the canister <NUM> could be clamped between the flanges <NUM>, <NUM> of the monopile <NUM> and the tower <NUM>, or between one of the flanges <NUM>, <NUM> and the work platform <NUM>. Also, the bolts <NUM> that extend through the flanges <NUM>, <NUM> of the monopile <NUM> and the tower <NUM> could, in principle, also extend through the flange <NUM> of the canister <NUM>.

The arrangement of the invention shown in <FIG> corresponds to that shown in <FIG> except that an intermediate support structure <NUM> hangs from the inwardly-projecting flange <NUM> of the monopile <NUM>. The support structure <NUM> has a hang-off flange <NUM> at its upper end that lies on the flange <NUM> of the monopile <NUM>. The flange <NUM> of the canister <NUM> lies on the hang-off flange <NUM> of the support structure <NUM> and so is also supported by the underlying flange <NUM> of the monopile <NUM>.

The support structure <NUM> also an inwardly-facing frusto-conical surface <NUM> at its lower end that complements, receives and supports the lower portion <NUM> of the side wall of the canister <NUM>. That frusto-conical surface <NUM> replaces the supports <NUM> of the preceding embodiments, which are therefore omitted from <FIG>.

The variants mentioned in relation to the arrangement of <FIG> could also be applied to the arrangement of <FIG>. Analogously, the hang-off flange <NUM> of the support structure <NUM> could be clamped directly or indirectly between the flanges <NUM>, <NUM> of the monopile <NUM> and the tower <NUM>. Similarly, the bolts <NUM> that extend through those flanges <NUM>, <NUM> of the monopile <NUM> and the tower <NUM> could extend through the hang-off flange <NUM>. However, in the arrangement shown in <FIG>, the hang-off flange <NUM> is inboard of the inwardly-projecting flange <NUM> at the base of the tower <NUM>.

The complementary flange <NUM> at the top of the monopile <NUM> is extended in a radially inward direction to accommodate the combined width of the concentric flanges <NUM>, <NUM>.

Turning finally to <FIG>, these drawings show a further arrangement of the invention in which the canister <NUM> is lowered into the monopile <NUM> only after mounting the tower <NUM> to the monopile <NUM> as shown in <FIG>. This arrangement is apt to be used where the tower <NUM> comprises stacked sections affixed end-to-end, meaning that the canister <NUM> does not have to be lifted to and lowered from the full height of the tower <NUM> but only to and from the height of its lowest section.

In the example shown in <FIG>, the flange <NUM> of the canister <NUM> rests upon an inwardly-projecting flange <NUM> within the tower <NUM>, for example at the base of the tower <NUM> as shown. The major portion of the canister <NUM> beneath the flange <NUM> hangs into the open top of the monopile <NUM>, where optional supports <NUM> cradle the lower portion <NUM> of the side wall of the canister <NUM>.

Claim 1:
A wind turbine equipment canister (<NUM>) for supporting and enclosing electrical equipment of a wind turbine, the canister comprising:
a housing defining or containing at least one internal platform (<NUM>, <NUM>) for supporting the equipment;
a lifting interface (<NUM>) on a top of the housing; and
at least one support formation (<NUM>) positioned on or projecting laterally beyond a side wall of the housing, the side wall having at least a portion (<NUM>) that tapers in diameter downwardly toward a base of the housing (<NUM>), and the support formation being capable of supporting the weight of the canister suspended therefrom when the canister is installed within a monopile foundation (<NUM>) for a wind turbine.