WO2013107724A2

WO2013107724A2 - Tidal energy system

Info

Publication number: WO2013107724A2
Application number: PCT/EP2013/050641
Authority: WO
Inventors: Gareth Elphinstone
Original assignee: E&H Building Contractors Ltd
Priority date: 2012-01-17
Filing date: 2013-01-15
Publication date: 2013-07-25
Also published as: GB2499705A; GB201300694D0; WO2013107724A3; GB201200748D0; GB2499705B

Abstract

A system for the capture of tidal energy has an off-shore docking component with multiple docking stations anchored or tethered not to drift with the tide, and moored to the docking stations multiple buoyant energy capture components having at least two hulls and disposed therebetween a submerged or submergible energy capture mechanism such as a vertical axis rotor, which energy capture components can drift relative the docking station according to the direction of tidal flow. The system can efficiently capture the fastest tidal flow near the surface, can be deployed in deep offshore and in inshore waters, is adaptable as to the form of energy produced and is not visually intrusive.

Description

Tidal Energy System

FIELD OF THE INVENTION

This invention relates to the field of energy capture. More particularly, the device relates to a system, device and method for the capture of energy from a fluid stream such as tidal flow.

BACKGROUND OF THE INVENTION

Tidal energy is recognised as a highly regular and predictable source of energy or power which is under-utilised and could represent a significant proportion of energy need of coastal countries.

Numerous tidal energy devices and systems for the capture of tidal energy and river flow energy have been contemplated. Many tidal energy devices are large scale industrial systems, which require substantial onshore and offshore infrastructure and are often visually intrusive. In efforts to increase the theoretical efficiency of tidal energy devices, many innovators have sought to increase the size of the device to maximise the capture diameter of a rotor, to minimise operational losses and capital costs associated with each machine and to maximise the throughput of power associated with each machine.

WO-A-2009/ 126995 describes a central axis tidal flow turbine, which comprises a turbine body having a central axis and mounted thereon a rotor having a hub and a plurality of blades extending from a blade root mounted on the hub to a blade tip, and a housing surrounding the rotor and adapted to direct water flow towards the blades, the blades being splayed rearward from the blade root to tip by an angle of 1 to 20 degrees. The turbine housing is preferably secured to an underwater surface, such as the seabed, via a mounting structure aligned with the tidal flow direction.

The Atlantis Resources (www.atlantisresourcescorporation.com) planned AKIOOO tidal turbine installed at the European Marine Energy Centre tidal test site off Orkney is a central horizontal axis double rotor three-bladed seabed mounted tidal turbine (see www.emec.org.uk/site_activity.asp) standing 22.5 m tall, weighing 1,300 tonnes and having an 18 m rotor diameter. The device is designed to generate up to 1 MW of power.

WO-A-2005/080789 describes a variant horizontal axis tidal flow turbine for use in high head applications, which comprises a central aperture in the tidal rotor to allow marine mammals to safely pass (and to reduce debris blockage). This device finds potential application in dams but also in open water. The further developed version described in WO-A-2009/098057 refers to a stator housing a shaftless rotor of a hydroelectric turbine which is permitted to undergo

hypocycloidal motion within the stator. The developed version provides the housing for the rotor, which housing forms the outer ring and is configured such that the rotor is received in a channel shaped to allow hypocycloidal motion.

Several disadvantages are inherent in large seabed mounted systems and include, for example, the challenges of installing large scale devices in strong tidal streams and the need for provision of substantial seabed foundations for seabed mounted devices.

The present inventor has recognised that in seeking to enhance operational efficiency by producing large devices, installation costs have significantly increased, maintenance costs are substantial and taking a machine out of commission for maintenance leads to total loss in power generating capability. Furthermore, large scale devices do not make maximum utility of the highest tidal flow in the water column, closest to the surface.

A number of array devices for wave and tidal energy capture have been proposed which utilise an array of interconnected devices or modules.

For example, US-A-2008/0093859 describes an array of tidal and river energy capture devices. Each device comprises a horizontal central axis rotor supported by strut submerged beneath a flotation hull. The rotor is provided on an air compressor, the tidal or river stream producing compressed air that is fed ashore through a compressed air line. A plurality of devices are provided successively along a steel cable and anchored to the shore at right angles to the prevailing tide. Each device feeds its compressed air line into a single high pressure line leading to an onshore turbine connected to the local power grid. Several tidal energy devices utilising vertical axis turbines or Darrieus-type turbines have been proposed. In US-A-2006/0008531 , a system comprising a side-by- side series of Darrieus-type turbines arranged with the axis horizontal to provide a paddle type arrangement provided with funnels to channel tidal flow through the turbines in a barrage arrangement is proposed for use in shallow waters. The turbines, according to US-A-2006/0008531 should be mounted on the seabed with the funnels directed along the direction of prevailing tidal flow. The Darrieus turbines are positioned such that the axis is horizontal and perpendicular to the prevailing tidal flow, a single axis leading to a seabed mounted 90 degree gearbox. A vertical axis output shaft emanating from this gearbox is driven by the barrage of Darrieus rotors allowing location of the turbine generator and auxiliary systems above water level. In US-A-2002/197148, there is described an installation for harvesting tidal energy in deep waters using a Darrieus-type turbine arrangement. A semi-submersible platform provides a support for a turbine comprising three sets of two-bladed Darrieus rotors arranged vertically on top of one another, with blades off-set by 30 degrees to enable self- starting, to produce a turbine of about 20 meters in height. Funnels may be installed to direct additional volume of water through the turbine. The semi-submersible platform provides a platform above the surface for housing the electric power generator assembly.

The prior art thus suffers from disadvantages mentioned, which typically include substantial infrastructure requirement, both onshore and offshore, substantial deployment and maintenance requirement, deep water sites, difficulty in undertaking maintenance and visual intrusiveness, which can cause difficulties in obtaining planning permissions.

The present inventor has found that a new approach to the capture of tidal energy overcomes many of the above problems.

PROBLEM TO BE SOLVED BY THE INVENTION

There remains a need for improvements in tidal energy capture systems and devices which address one or more of the aforementioned problems. It is an object of this invention to provide a system for the capture of tidal energy which is deployable in remote locations with minimal fixed onshore and offshore infrastructure requirements.

It is an object of this invention to provide a device for the capture of tidal energy which is readily transportable and enables ready maintenance access.

It is an object of this invention to provide a tidal energy system and device for the capture of tidal energy which is visually appealing and/or

unobtrusive. SUMMARY OF THE INVENTION

In accordance with a first aspect of the invention, there is provided a system for the capture of tidal energy, the system comprising an off-shore docking component which is anchored or tethered or otherwise positioned not to drift with the tide and which comprises at least one docking station; and at least one energy capture component, which is buoyant and which comprises a support structure and having at least two hulls having disposed therebetween a submerged or submergible energy capture mechanism, the at least one energy capture component being moored to the off-shore docking component via the at least one docking station and capable of drifting relative the docking station according to the direction of tidal flow.

In a second aspect of the invention, there is provided an energy capture device for capturing tidal or river- flow energy, the device being buoyant and comprising a support structure having at least two hulls having disposed therebetween a submerged or submergible energy capture mechanism, which when deployed, moored to a point stationary relative the tidal flow, the device is capable of drifting to relative alignment with the direction of tidal flow.

In a third aspect of the invention, there is provided an off-shore docking component for use with a tidal energy capture system as defined above, said docking component comprising a means for anchoring, tethering or fixing the docking component such as to prevent drift of the component with the tide and which comprises at least one docking station. In a fourth aspect of the invention, there is provided an array of energy capture devices as defined above, the energy capture devices arranged such that each is capable of drifting to relative alignment with the direction of tidal flow. ADVANTAGES OF THE INVENTION

The system and device of the present invention provide particular advantages in tidal energy capture in that they efficiently capture the fastest tidal flow near the surface, can be deployed in deep offshore and in inshore waters, are adaptable as to the form of energy produced, readily maintainable without disrupting energy generation and are not visually intrusive.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a diagrammatic representation of one embodiment of a tidal energy capture system in perspective view according to one aspect of the invention;

Figure 2 shows a plan view of the tidal energy capture system of

Figure 1;

Figure 3 shows a side view of the tidal energy capture system of Figure 1 in situ;

Figure 4 is a plan image providing a representation of downstream effects in a tidal energy capture system according to one embodiment;

Figure 5 shows a diagrammatic representation of another embodiment of a tidal energy capture system in perspective view according to one aspect of the invention;

Figure 6 shows a sub-surface side-view of the system of Figure 5;

Figure 7 shows a perspective view of the system of Figure 5 illustrating only the components on or above the surface, in situ;

Figure 8 shows a side aspect of one embodiment a tidal energy capture device of the present invention;

Figure 9 shows a front aspect of the device of Figure 7;

Figure 10 shows a rear aspect of the device of Figure 7; Figure 11 shows a rear perspective view of the device of Figure 7;

Figure 12 shows a perspective view of the lower portion of the device of Figure 7 when cut at the waterplane;

Figure 13 shows a lower portion of the device of Figure 7 in cross- section at the waterplane;

Figure 14 shows a front sub-surface perspective view of a device according to another embodiment; and

Figure 15 is a schematic illustration of a horizontal cross-section of the shape of a duct according to one embodiment of the energy capture device of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention provides for an improved tidal energy capture device and a tidal energy capture system incorporating said device as a tidal energy capture component.

The energy capture system of the invention comprises an off-shore docking component and at least one energy capture component moored to the offshore docking component via the at least one docking station and capable of drifting relative the docking station according to the direction of tidal flow.

An off-shore docking component for use with an energy capture system of the invention provides a further aspect of the invention. The off-shore docking component is typically anchored or tethered or otherwise positioned not to drift with the tide. It comprises at least one docking station and preferably an array of docking stations numbering from say 3 to 9 or more. The or each docking station may be adapted for receipt of a mooring from an energy capture

component, typically the energy capture component being a buoyant device having an energy capture mechanism suspended therefrom or mounted thereunder for capturing energy, which buoyant energy capture component is configured to drift into alignment with the flow of the tide. The off-shore docking component should, therefore, be configured with docking stations in an arrangement that allows the energy capture component to drift unencumbered into alignment with the tidal flow direction and preferably in a configuration whereby the tidal flow on any in situ energy capture component is not significantly disrupted by any other energy capture component.

The docking component, which comprises one or more docking stations, may comprise a frame portion having one or a plurality of docking stations formed thereon, preferably in the form of posts protruding, typically upward, from the frame portion. In situ, the docking component is typically semi- submerged, whereby the frame portion is submerged and each docking post is partially submerged such that at least a distal end of the post (relative to the frame) is close to or protrudes above the surface of the water (thereby enabling an energy capture component to be docked or secured thereto).

The frame portion may rest or be fixedly secured to the seabed (e.g. with posts or piles) and the docking posts protruding therefrom may be telescopic buoyant devices of sufficient telescopic extent to enable them to protrude from the surface of variable depth of water in which the frame portion is situated or the docking posts may be buoyant post elements tethered to the frame element.

Preferably, however, the frame portion is at least partially buoyant, or is provided with buoyancy from securely attached docking posts protruding therefrom or dedicated buoyancy posts and, optionally, is controllably or variably buoyant. (Preferably, the docking component is tethered to the seabed or seashore). Thus it is preferred that when deployed, the frame element is submerged to a predetermined depth below the surface with the docking posts protruding above the surface. This is obtainable by providing the docking component with buoyancy that partially offsets the weight of the docking component. The docking component should preferably, therefore have an average specific gravity of about or marginally less than that of the fluid in which it is disposed, so, in the case of seawater, about or marginally less than about 1.02 (e.g. between 1 and 1.02). The frame, portions of the frame, buoyancy posts or elements protruding from the frame and/or the posts or other components of the docking component may be provided with buoyancy, e.g. by providing such components in the form of hollow sections of pipe or tubing, optionally partially filled with fluid to achieve the desired average specific gravity or buoyancy.

The frame should be capable of being submerged, in use, to a distance below the surface to allow clearance between the energy capture devices moored to the docking component and the frame of the docking component and preferably to minimize tidal flow disturbance by the frame on the flow entering the energy capture components. For example, the frame element, or a portion thereof as required, preferably is submerged or submergible in use by an amount to allow sufficient clearance thereabove for the buoyant energy capture components tethered to the docking component to move relative to the docking component for alignment with a change in tidal flow direction and is thus more preferably submerged or submergible by an amount greater than the depth of a submerged portion of the energy capture component(s) tethered to the docking component, preferably at least 1.5 times the depth of a submerged portion of the energy capture component(s) and still more preferably at least 2 times the depth. The submerged portion of the energy capture component(s) is typically the hull (or at least a major portion of the hull) and thus the depth of the submerged portion of the energy capture component may be (or may be substitutable by and equally applicably be) the depth of the hull of the energy capture component. In one embodiment of the invention, the frame element or at least a portion of the frame element is configured to be submerged to a clearance depth in the range of 1.5 to 10 m, more preferably 2 to 5 m and still more preferably 3 to 5 m.

Preferably, the frame element has a substantially planar portion which includes a portion over which, in situ, clearance is required.

The frame may be made up of a component or components of any suitable profile. For example, the frame may be made up of components of square, rectangular, circular or other profile. Preferably, the frame (or at least a planar portion of the frame) is made up of components having an oval or elliptical profile wherein the ellipse is formed substantially in the plane of the frame whereby it causes minimal disturbance to tidal flow. Docking stations, to which energy capture components (or devices) of the system may be fixed or moored, are preferably in the form of docking posts protruding from the frame, preferably a planar frame portion, of the docking component. The docking stations should preferably, in situ, protrude a suitable amount above the surface of the water, e.g. from 30 cm to 1 m. Since the docking stations are typically directly upstream of the energy capture components, there is potential for an effect on the tidal flow reaching the energy capture components, thus it is preferable that the profile of the docking station or post is such as to minimize wake effects, especially in the upper portion of the water column. As such, it is preferred that the profile of the docking station or docking post is small and it is preferable that the docking station or docking post is configured for hydrodynamic low turbulence or non-turbulent flow. Ideally, the docking station or docking post has a surface and subsurface elliptical profile or teardrop profile to enhance flow characteristics past the docking station, the elliptical profile or teardrop profile arranged to be orientated into the oncoming tidal flow. Still more preferably, since the tidal flow direction may vary slightly it is preferable that the elliptical profile of the docking stations or docking posts may be adjusted in orientation in order to minimize flow disturbance by the docking station or docking post. Such adjustment in orientation of the docking station or docking post may be achieved, for example, by allowing some directionality and rotation by the docking component itself, so that it adjusts its rotational orientation according to the direction of tidal flow to some degree and thus would adjust the direction of orientation of the profile of the docking stations or docking posts, or, for example, by providing that the docking posts may rotate about their longitudinal axes or providing the docking posts with an outer casing providing the elliptical or teardrop or other hydrodynamic profile shape which may rotate about the docking post so as to be orientated in a most streamlined fashion. The docking station and docking post preferably have a width (being the maximum width normal to the direction of tidal flow at any particular time) of up to 20 cm, preferably up to 15 cm, still more preferably up to 10 cm, yet more preferably from about 1.5 cm to about 5 cm and most preferably 3 cm or less. Optionally, the frame has a sub-surface shape that may provide, at least some limited directionality to the frame, such as fins provided to adjust the frame to an optimal direction relative the tidal flow. Tidal flows in ebb and flood can vary in direction (e.g. vary from 180 degrees difference) especially when closely located to the shore or to a headland or suchlike. Thus it is a preferred embodiment that the tethering of the docking component allows a certain degree of freedom in rotational movement of the docking component to enable directional features to have effect. The directional features are preferably fins protruding forward and/or backward and/or upward and/or downward from the body of the frame.

Still further, the docking component, and in particular the submerged frame of the docking component may be configured to positively direct tidal fluid flow toward the energy capture components tethered thereto, so as to enhance the efficiency of the system, thus acting, in part, as tidal flow

concentrators. In particular, the docking component may optionally provide a ducting or funneling function toward the upper portion of the water column and to within the 'harbour' defined by the frame of the docking component. For example, a frame may be provided with peripheral vanes (sloping upward from external to the docking component toward the frame) such as to encourage tidal flow in the upper portion of the water column, above the submerged frame and optional peripheral buoyancy posts (which provide stability for the docking component) may be configured with vanes shaped to draw fluid into the area or harbour defined by the docking component. Thus the shaped vanes or channels may improve relative fluid flow velocity in the vicinity of the energy capture components.

Preferably, however, the docking component is configured to have minimal effect on tidal flow characteristics, and thus is provided with hydrodynamically shaped components which allow energy from the tidal flow to be captured by the energy capture components.

The size of the docking component depends on several factors, including the number, size and length of tether of energy capture components. However, typically the docking component may have in situ proportions (length and width) of 5 m up to say 50 m, and preferably 10 to 25 m, e.g. 12 m width and 20 m length. The optionally planar frame portion upon which docking stations may be mounted is preferably in the region of 5 m to about 25 m, e.g. 10 to 20 m, such as 12 to 15 m. The depth of the docking component is preferably the depth of clearance required, discussed above, plus the vertical thickness of the frame, thereby enabling use of the system in relatively shallow waters.

The docking component may be of any suitable shape that is capable of achieving, through docking stations thereon, a desired arrangement of docking stations and thus a desired arrangement in the form of an array of energy capture components or devices. Preferably, the docking component should comprise a submerged frame having at least a circular or polygonal portion, e.g. a circular, triangular, quadrangular (e.g. square or rectangular), pentagonal, heptagonal or octagonal portion. More preferably, the submerged frame has a circular, quadrangular (e.g. square or rectangular) or pentagonal portion.

Typically, the shape of the docking component and more particularly the portion of the submerged or submergible frame providing sufficient clearance for energy capture components determines the possible arrangement of energy capture components by the options for arrangement thereon of docking stations, which may be distributed about a circular submerged frame, or where shaped along frame edge or at the apices thereof. Thus the shape and configuration of the frame limits how and where the docking stations may be distributed thereon and to some extent the shape of an array of energy capture components.

Optionally, an array comprises multiple array units, e.g. located side by side. An array unit may be taken to be an array of devices (energy capture components) that may be formed in a repeatable shape or unit and is typically an array of such devices that are provided on a single docking component or frame thereof. Multiple docking components may be provided in a multiple array unit arrangement.

An array of energy capture components or devices (and thus also, typically, the arrangement of posts) may be provided in any suitable arrangement depending upon the number of energy capture devices deployed or deployable. Preferably, where the array comprises more than two devices, the array is nonlinear.

Any number of devices may be deployed in an array. Optionally, the array comprises at least three and may comprise any number, preferably from 3 to 15, more preferably 3 to 9, still more preferably 5 or 7. Preferably, the configuration of an array is selected to minimize wake effects from one energy capture component on another. Thus, regular (or near regular) pentagonal or heptagonal arrangement is beneficial since at least one tidal flow direction results in no or minimal wake effects and, if the tidal flow direction is off-centre, the wake effect consequences are minimized. However, by providing that the docking component (and thus frame) may have some freedom of rotation and some directionality, any wake effects from devices in the array can be mitigated by always providing the array in a preferred configuration relative to the tidal flow direction, even where the tidal flow direction varies. Thus, preferably, the array is configured such that in a pre-determined tidal flow direction, wake effects are minimized by ensuring that each energy capture component has a clear

unencumbered tidal flow path.

In a preferred embodiment, the docking component is a semi- submergible component for anchoring to the seabed and having a rectangular or pentagonal planar frame portion providing clearance of 3 to 5 m for an array of 3 to 9, preferably 5 to 7 buoyant energy capture components thereabove.

In one particular embodiment, the docking component comprises a frame providing the required clearance, which has an arrangement formed with two mooring crossbars (e.g. parallel crossbars) in a plane substantially parallel with the water surface from which a plurality (e.g. three to seven, preferably five) docking stations may protrude up through the water surface. At each end of the two mooring crossbars may be provided a more substantial end bar adjoining the ends of the two mooring crossbars and of a length extending in both directions beyond the ends of the two mooring crossbars. Each of said end bars may be provided with additional buoyancy elements, protruding upward, which optionally protrude through the water's surface defining floating pods located at the peripheries of the frame. This arrangement provides stability and buoyancy.

The docking component or parts therefore may be manufactured from any suitable material, such as steel, composite materials (such as fibre- reinforced polymer resin composites) or plastics.

Preferably, the energy capture system of the present invention further comprises a converted or stored energy transfer system. The energy capture system may be provided according to the form of energy produced by the energy capture component and intended to transfer. For example, typically the energy capture component will generate electrical, e.g. dc, power from the captured mechanical energy of the tidal current and the converted energy (electrical power) may be transferred by an energy transfer system. In such a case, the energy transfer system may be in the form of a cable arrangement capable of connecting with the power generation or storage system of the energy capture component and transporting power to a power destination, e.g. a central bank of batteries for storage, or a shore-based substation and interconnector for supply of power to a power grid. Alternatively, the energy transfer system may transfer energy in the formed of stored energy, e.g. as a compressed fluid such as air or as hydrogen produced from an electrolyser (powered on board by tidal powered electricity), in which the energy transfer system comprises a fluid interconnection with a supply outlet from the energy capture component and a fluid transport conduit or network of conduits, which supply fluid to a energy destination (e.g. storage tank onshore or offshore).

The converted or stored energy transfer system is typically co- located with the docking component, e.g. by cables tied to or running through the frame of the docking component, and preferably provide energy transfer interconnection with the energy capture components at the respective docking stations.

An energy capture device, which may be an energy capture component of the system of the invention, forms a further aspect of the invention. According to this aspect, an energy capture device is buoyant and comprises a support structure having at least two hulls and disposed therebetween a submerged or submergible energy capture mechanism. The support structure is preferably capable of supporting the energy capture mechanism in some manner and, optionally, ancillary workings associated with the energy capture mechanism or energy conversion or transfer. The support structure preferably comprises a floating platform. By floating platform, it is meant that there is a platform that is in situ located on or above the water, by virtue of the buoyancy of the device as a whole, but which platform may though need not be in contact with the surface of the water between the hulls. The device is suitable for being moored to a fixed, moveable or anchored point (such as a docking station) which is stationary relative to a flow (of river or tide) in which it is located. In situ, the device is typically capable of drifting into alignment with tidal flow direction.

The energy capture mechanism may be a rotor, but various possible energy capture mechanisms for capturing energy from a throughf ow of fluid may be envisaged and utilised in the device of the invention. For example, the energy capture mechanism may be drag or lift driven and may be have a single rotational axis that may be horizontal longitudinal (e.g. a conventional three bladed upstream or downstream mounted rotor), horizontal transverse (e.g. a paddle wheel type rotor, partially dispose din the water) or a vertical axis rotor. An example of a horizontal transverse rotor associated with a duct, which may be adapted for the present device is illustrated in WO-A-2010/146612. Alternatively, the energy capture mechanism may comprise a elliptical conveyor mechanism, which is drag driven whereby a elliptical conveyor carries paddle elements along a path through a channel defined by the hulls which elements optionally take a flattened

configuration for the return portion upstream along the elliptical conveyor mechanism. As a further alternative, the energy capture mechanism may comprise a plurality of transverse and/or vertical elements (e.g. cylinders) forming bluff bodies disposed between the hulls of the device and supported in receiving structures (e.g. in the respective hulls) which elements are configured to move (within the receiving structures) in at least one plane normal to their longitudinal axes in response to vortices, wherein the receiving structures are provided with means for capturing or converting the energy of movement, e.g. by a magnet and coil arrangement, which energy capture mechanism may be adapted from the disclosure in WO-A-2006/055393.

The energy capture mechanism is preferably a rotor which is driven to rotate by through flowing tidal energy and which energy of rotation is captured by the device and used/converted to a useable or intermediate energy form. The rotor may be a conventional horizontal axis rotor (such as that used as a propeller or as a rotor in conventional wind turbines), but is preferably a vertical axis rotor. Vertical axis rotors have the benefit that they rotate irrespective of the direction of fluid flow and that any ancillary workings of the rotor (e.g. gear or turbine) may be located out of the water (e.g. supported by the platform). Optionally, the vertical axis rotor is a Darrieus rotor, a Savonius rotor or, preferably, a helical bladed rotor. Preferably, the rotor is a Gorlov type helical rotor, such as that described in WO-A-96/38667 (the disclosure of which is incorporated herein by reference).

Preferably, the energy capture mechanism (e.g. vertical axis helical rotor) is supported by and suspended beneath the support structure or platform thereof and thus between the two hulls.

Preferably, the hulls have a small waterplane area (i.e. the device is a SWATH device, that is small waterplane area twin hulled device) whereby the disturbance of fluid flow and drag at the upper part of the water column where the energy capture mechanism (e.g. rotor) is located is minimized. Buoyancy (via displacement, typically, but optionally aided) is provided by larger volume buoyancy elements at the lower (or distal, relative to the platform) portions of the hulls. The any number of buoyancy elements may be provided distributed along the hulls or, for example, one buoyancy element may be provided at the extreme fore and aft of each hull. Preferably, the hull buoyancy elements provided are longitudinally extending along the lower portion of each hull, for example of cylindrical or torpedo shape. Utilising submerged buoyancy elements at the lower portions of the hulls results in enhanced stability of the device on the water and thus less movement of the rotor (or other energy capture device) into and out of the water and more consistent alignment of the moored device with the tidal flow direction. Submerged buoyancy elements and small waterplane area hulls also have a particular advantage that there is a reduced effect (and drag) on the fast flowing surface water as the buoyancy elements are submerged.

The hulls between which the energy capture mechanism is disposed may define a channel or duct through which tidal flow may pass.

Preferably the duct is defined further by a duct floor disposed along a length (preferably the full length) of the channel or duct between the two hulls.

Optionally the duct floor and/or the duct-wall forming portion of the hulls are provided with throughflow means, such as aperture or channels linking the duct volume with the exterior of the device to enable pressure equalizing or flow rate enhancement during operation of the device. Such apertures or channels in the duct floor may be formed between a series of longitudinal or transverse elements making up the duct floor and, in the hulls, may be formed between a series of longitudinal elements or a series of vertical elements or sections separated by gaps. The elements or sections follow a curve or may be offset relative to one another. Optionally, vertical elements or sections forming at least a portion of the duct-wall forming part of the hulls may be section members having an aerofoil cross-section, whereby the trailing or edge portion of one aerofoil section member is adjacent the leading portion or edge of the immediately adjacent trailing aerofoil section member, where 'aerofoil section member' includes any wing-like body, between which members a gap or slot may be provided so that high energy flow from outside the duct may be introduced into the duct between the aerofoil section members. Optionally, such duct-wall forming vertical sections or members providing inlet slots are provided only in a diffuser portion of a duct of a device of the invention, the diffuser portion substantially being downstream of the energy capture element.

Such a duct floor (provided with throughflow means) may, optionally, for example be composed, or partially composed, of a series of transverse elements (e.g. cylinders or bars), the ends of which are supported by a receiving structure associated with each of the two hulls, which optionally are configured so that the transverse elements are moveable within the receiving structure in at least one, optionally two, planes normal to their longitudinal axes. The elements may be moveable relative and within the receiving structure in response to fluid motion by vortex induced motion, galloping motion or combination thereof. The receiving structure may optionally be provided with an energy conversion means for converting the energy of the element motion into a usable form of energy, such as electrical power, an example of such system is described in WO-A-2006/055393 (the disclosure of which is incorporated herein by reference). For example, the energy conversion means may comprise a magnet adjacent to one or a pair of coiled wires moveable normal to the plane of the magnet (or relative to the magnet) in response to movement of the transverse elements, whereby a current is induced in the coils by such movement relative to the magnet. The coils may be connected to a power conversion system whereby the induced current may be captured. The presence of the leading edge of the duct floor in the form of a bluff body may induce turbulence and vortices along the inner and outer surfaces of the duct floor by fluid flowing past the body and through the duct. By providing means for capturing such vortices by vortex induced motion of the elements making up the duct floor, such turbulence may be dissipated and reduced risk of damage of a downstream energy capture element, for example. In addition, low flow energy may be captured by such means. Similarly, such vortex induced motion energy capture means may be incorporated into the side walls of the duct by providing vertical elements (e.g. cylinders) to make up at least a portion of the duct walls and supported in receiving structures and configured for vortex-induced movement (and capture of energy of such movement) in at least one plane normal to their longitudinal axes. Optionally, such vortex induced motion energy capture means may be provided in the walls and/or floor of the duct adjacent to and/or upstream from and/or downstream from the energy capture means.

Preferably, however, the hulls (i.e. the duct walls) are solid along a substantial length of the duct. The floor may optionally be solid, or may be provided with hydrodynamic channels or longitudinal throughflow channels in order to reduce drag from the floor of the duct. In a preferred embodiment in which the two hulls define a duct along with, preferably, a duct floor, the duct may be configured to have any suitable shape, which shape may depend on several factors including the type and position of the energy capture element. For example, the duct may be configured to have a straight walled constant profile (square or rectangular) planar channel duct, or may be a diverging or converging duct, or may be a variable profile duct.

In a preferred embodiments of the invention in which the energy capture mechanism comprises a rotor disposed in a duct, the duct may be defined as having: an inlet portion, being upstream of the location of the rotor; a rotor portion, being that part of the duct in which or laterally adjacent which the rotor is disposed; and an outlet portion, being that part of the duct downstream of the rotor. The upstream extremity of the inlet portion of the duct may be or may define the inlet (or inlet plane), whilst the downstream extremity of the outlet portion may be or may define the outlet (or the outlet plane). Preferably, in a downstream direction of use or intended use, the inlet leads to the inlet portion which leads adjacently to the rotor portion where the rotor is disposed which leads to the outlet portion ending in the outlet. The duct from inlet to outlet may take any desired or effective configuration, such as a straight walled convergent or divergent duct, or where the walls define curves from inlet to outlet of varying radius in which the inlet is larger than the outlet or vice versa.

Preferably, however, the duct according to this embodiment comprises an inlet portion which has convex curved walls (defined by the internal surface of the hulls) that are generally converging from the inlet of the inlet portion to the downstream end of the inlet portion, whereby the cross-sectional area of the duct (being a cross-section across the longitudinal axis of the duct) or width of the duct at the downstream end of the inlet portion is smaller than at the inlet, a constricted rotor portion, defining a neck, which is preferably substantially constant in cross sectional area (e.g. constant in cross section along its length or varying by no more than 10% in width) or duct width, and a diffuser shaped outlet portion having convex curved walls (defined by the internal surface of the hulls) that are generally diverging from the upstream end of the outlet portion to the outlet, whereby the cross-sectional area of the duct (being a cross-section across the longitudinal axis of the duct) or width of the duct at the upstream end of the outlet portion is smaller than at the outlet. Variation in the cross-sectional area along the length of the duct is preferably contributed to by variation in distance between the walls (the internal surfaces of the hulls), i.e. the width of the duct, along the length of the duct and, optionally, by varying the 'slope' of the duct floor and the depth of the duct.

The cross-sectional area of the duct may be defined depending upon whether or not nominal duct ceiling or a physical duct ceiling is provided.

Optionally, the duct is open at the upper end whereby there is no physical duct ceiling in contact with the water. In that case, the nominal duct ceiling, for the purpose of determining cross-sectional area may be taken to be at the water level inside the duct when the device is at rest in the water with no tidal flow (resting surface water level). Optionally a physical ceiling may be provided, which may be positioned between the hulls whereby it is at or below the resting surface water level or a physical ceiling may be provided that is positioned between the hulls whereby it is above the resting surface water level, but may be effective in containing the maximum depth of fluid flowing through the duct at high flow rates. Where a physical ceiling is provided in the duct, it may take any desirable configuration, for example it may be sloped downward (relative to the resting surface water level) from the inlet to the downstream end of the inlet portion or it may slope upward or it may be substantially parallel with the resting surface; and similarly for the outlet portion, whilst at the rotor portion, it may preferably be substantially parallel with the resting surface water level.

In any case, the duct floor may be of any suitable or desirable configuration, e.g. sloping upward (relative to the resting surface water level) from the inlet to the downstream end of the inlet portion or substantially parallel with the resting surface; substantially parallel with the resting surface water level at the rotor portion; and for the outlet portion it may preferably be sloping downward from the rotor end to the outlet or be substantially parallel with the resting surface water level. Optionally, the duct floor may follow the general profile of preferred longitudinally extending buoyancy elements provided at the lower portion of the hulls. Preferably, the duct floor is substantially parallel with the resting surface water level throughout, optionally with an inlet lip which slopes upward from the inlet and optionally with an outlet lip, which diffuses downward toward the outlet, which lips represent a minor length of the respective inlet and outlet portions.

In the preferred embodiment, where the duct floor is substantially level throughout, and where there may or may not be a physical duct ceiling, the width of the duct may be the defining feature thereof, whereby the width of the duct at the downstream end of the inlet portion is smaller than at the inlet, the width of the constricted rotor portion is substantially constant (e.g. the width being constant along the length of the rotor portion or varying along its length or varying by no more than 10%) and the width of the diffuser shaped outlet portion at the upstream end of the outlet portion is smaller than at the outlet.

In accordance with this preferred embodiment, the width of the duct at the inlet (Wi) is greater than the width of the rotor portion (W_R), which is less than the width of the duct at the outlet (Wo). More preferably, W₀>Wi.

Preferably the ratio Wi: W_R is within the range 5: 1 to 1 : 1, more preferably 2:1 to 1.1 : 1, still more preferably 1.5:1 to 1.25: 1 and yet more preferably 1.4: 1 to 1.3:1. Preferably the ratio Wo:Wi is within the range 1 : 1 to 5: 1 (e.g. up to 3 : 1), more preferably 1.2: 1 to 2: 1 , still more preferably 1.3:1 to 1.7: 1, for example about 1.5: 1.

Preferably, the total duct length (L_T) may be defined relative to the width of the rotor portion, W_R (which may be taken as the width of the rotor portion at the axis of the rotor, where the width along the rotor portion is not constant), which width W_R is preferably substantially equal to the length of the rotor portion, L_R, which in the case of a vertical axis rotor is effectively the same as the effective diameter of the rotor (and thus 2x the radius of the rotor r_R) and in any case W_R is preferably no more than 1.2x L_R; more preferably no more than 1. lx L_R and still more preferably no more than 1.05x L_R. W_R, for any kind of rotor, is preferably approximately the effective diameter of the rotor, so that the rotor is a relatively snug fit into the rotor portion of the duct. Accordingly, it is preferable that L_T is in the range 1 .5 to 5 x WR, more preferably 2 to 4 x WR, still more preferably 2.3 to 3.5 x W_R and still more preferably 2.5 to 3 x W_R (e.g. about 2.7 to 2.8 W_R).

More particularly, the length of the inlet portion according to the preferred embodiment, Li may be defined relative to the width of the rotor portion and is preferably in the range 0.1 to 1 WR, more preferably 0.2 to 0.75 WR, still more preferably 0.3 to 0.5 W_R and most preferably about 0.4 W_R.

The diffuser shaped outlet portion of the duct preferably has an outlet width W₀ that is defined relative to WR, whereby the ratio W₀:W_R is in the range 5 : 1 to 1 : 1 , more preferably 4: 1 to 1 .5 : 1 , still more preferably 3 : 1 to 1 .75 : 1 and yet more preferably 2.5 : 1 to 1 .8 : 1 . The outlet portion length, L₀, may preferably also be defined relative to W_R and is preferably in the range 0.5 to 4 WR, more preferably 1 to 3 WR, still more preferably 1 .25 to 2 WR and most preferably about 1 .33 WR.

In a particularly preferred embodiment, the rotor is a vertical axis rotor, more preferably helically bladed, and WR and L_R are each in the range 10 cm to 20 m, more preferably 50 cm to 10 m, still more preferably 1 m to 8 m, still more preferably 2 m to 5 m, e.g. 2.5 m to 4 m, such as about 3 m and are preferably substantially the same (e.g. the same or differing by no more than say 10%).

Preferably, the depth of the duct, which may be defined by the depth of the duct floor relative the resting surface water level or may be defined by the vertical extension of the rotor, e.g. vertical axis rotor. The depth of the duct may be the same, more or less than the width of the rotor portion of the duct, preferably the depth of the duct (and the depth of the rotor) is less than WR, more preferably in the range 0.25 to 0.8 WR, still more preferably 0.5 to 0.75 WR.

Preferably, in one particular embodiment, the rotor has a depth of 1 to 3 m, more preferably 1.5 to 2.5 m.

The support structure, e.g. the platform, may be used to support the ancillary workings, e.g. turbine, of the energy capture mechanism (e.g. rotor).

Preferably, where the energy capture mechanism is a rotor, e.g. a turbine rotor, the support structure (or platform) may support the ancillary workings, preferably in a housing (or nacelle) formed on the support structure (or platform). Thereby the ancillary workings may be held out of the water, in use, requiring less in the way of sealing, and may be accessed without removing the turbine from the water.

Optionally, the rotor may be raised from the water to allow maintenance, in situ. Preferably, the device, and in particular the housing on the support, are configured and shaped to resemble a boat, for example in a small boat harbor, such as a motor boat or such like. A footboard may be provided for access along the edges of the device, either side of the housing. Preferably, the support structure (e.g. the platform) of the device comprises a housing that tapers toward the upstream end of the housing (relative the tidal flow when in situ) and more preferably the housing is shaped to provide an aerodynamic profile from a plurality of directions. In particular, it is preferred that the housing is so shaped that wind in a direction different (e.g. opposing, or perpendicular) to the tidal flow at any particular time does not produce such drag as to substantially affect the direction of orientation of the device relative to the tidal flow. In particular, it is preferred that the housing has no outer surface that is slopes away from a centre position of the housing, more preferably, the housing comprises a curved casing that is preferably oval shaped in plan with an curved upper profile. More preferably, the housing is curved such that in windy conditions, a balanced pressure and optionally a slight downward pressure (i.e. counter lift) results. Preferably, in use, the housing protrudes upwards to a distance no more than 3 m from the surface of the water, still more preferably no more than 2 m and most preferably no more than 1.5 m.

The ancillary workings may be, for example, a turbine or electrical generator or a fluid compression pump.

The device of the invention may be used for various applications. For example, an array of devices may be used to generate electricity which may be taken ashore for feeding to an electricity grid or to feed a local demand.

Alternatively, the array may be used to provide a desalination station to provide fresh water in remote locations (e.g. for collection by boats and ships). An array may be utilized to produce hydrogen from the energy (e.g. via one or a plurality of electro lysers), which hydrogen may be stored in a common storage vessel associated with the array, for use as a hydrogen fuel station.

The invention will now be described in more detail, without limitation, with reference to the accompanying Figures.

In Figure 1, a tidal energy capture system 101 is shown which comprise a docking component 103, which in use is partially buoyant and comprises a frame 105, which in use is submerged and the plane of which is substantially parallel with the water surface, and in this case six posts 107 protruding (in use, upwardly out above the water surface) from respective apices of the frame 105 and providing docking stations for six energy capture components 109 moored to the docking stations 107 via tethers 111. The energy capture components 109 are designed to give the appearance of a collection of moored boats, to fit in with a typical local marine environment. The energy capture components 109 are buoyant having a floating platform 113 having two hulls 115 of SWATH (small waterplane area twin-hull) configuration, the two hulls 115 defining a submerged duct 117 through which a portion of the tidal flow may pass and, disposed within the duct 117 between the two hulls a vertical axis rotor 119, typically of a Gorlov design, for converting the energy of tidal flow into rotational energy (and ultimately to another form of energy, such as electrical). The energy capture components 109, in use, rotate about the docking stations 107 to trail the docking stations 107 and face the oncoming tidal flow. The frame 105 is sufficiently submerged to allow the energy capture components 109 to pass over the frame 105 and has the further benefit of not significantly disrupting the upper part of the water column which has the highest tidal flow. By providing a partially buoyant docking component 103 to which the energy capture components 109 are moored, the energy capture components 109 will always be able to capture the uppermost part of the water column, when the tide is high and low. The relatively small energy capture components 109 enable their use in in- shore waters whilst multiple independent components allows servicing and any problems to only have minimal impact. Figure 2 illustrates the system of Figure 1 in plan view in which the frame 205 of the docking component 203 has moored thereto six energy capture components 209.

As can be seen in Figure 3, which shows a side view, the system 301 may be loosely secured to the seabed 321, to prevent the docking component 303 drifting with the tide, by an anchor 323 and anchor tether 325. The docking component 303 is sufficiently buoyant that docking stations 307 protrude above the water level 327 whilst being sufficiently submerged that there is enough clearance between the frame 305 and the energy capture components 309 for the latter to pass over the frame 305 when they rotate about the docking stations 307 to face the direction of tidal flow, shown here with tidal flow indicators 329.

Figure 4 shows a plan view of an alternative array of energy capture components 409 illustrating the wake 431 in blue shading downstream of each energy capture component or device 409. In this Figure, the tidal flow is from right to left. The array of energy capture components in Figure 4 is pentagonal. In this arrangement, it is possible that the wake 431 from each energy capture component 409 does not disturb any of the other energy capture components 409 of the array. Even if the tidal flow were such that the wake 431 from one energy capture component 409 affected another, the arrangement is such that only one would be fully affected, thus pentagonal is a preferred arrangement.

In Figure 5, a yet further arrangement of the system 501 is shown in which a docking component 503 has a frame 505 has two parallel mooring crossbars 533 in a plane substantially parallel with the water surface, in use, from which five docking stations 507 protrude from the water surface. At each end of the two mooring crossbars 533 is provided a more substantial end bar 535 adjoining the ends of the two mooring crossbars 533 and of a length extending in both directions beyond the ends of the two mooring crossbars 533. Protruding upward and through the water's surface from each end of the two end bars 535 are four supports 537 for four floating pods 539 having additional buoyancy and located at the peripheries of the frame 505 to provide additional buoyancy and stability to the docking component 503. The parallel crossbars 533 of the frame 505 are arranged to be substantially normal to the prevailing tidal flow directions. The docking stations 507 are elliptical in shape in order to minimise the wake felt by the energy capture components 509 as the tidal flow passes the docking stations 507.

In Figure 6, which shows a side view of a system from Figure 5, from a sub-surface perspective, the elliptical shape of the docking stations 607 mounted on the mooring crossbar 633 is apparent. By providing additional buoyancy and stability at the periphery of the docking component 603 by way of the supports 637 and floating pods 639, the docking stations 607 need display less (or no) intrinsic buoyancy and thus can be slim- lined.

This system is shown from an aerial perspective in Figure 7, where it can be seen that the floating pods 739 define peripheral points of the docking component and the boundaries of a 'harbour', within which the energy capture components 709 operate.

Figure 8 illustrates in side aspect one embodiment of an energy capture component 809 for use in the present invention. A floating platform 813 has formed thereon a housing 839, which may be shaped and configured to resemble a boat's pilothouse or wheelhouse or bridge, which may house the electrical and electromechanical workings of a turbine (e.g. a vertical axis turbine) thereby maintaining those components above the surface of the water and allowing access for maintenance and repair in situ. The floating platform may sit on the water or, optionally, may be disposed above the surface of the water supported by the buoyant hulls, thereby avoiding additional drag. Beneath the floating platform 813 is one of two hulls 815 which together define a duct (not shown) through which tidal flow may pass, a portion of the energy of which may be captured by means of a vertical axis rotor. Each hull 815 comprises a slim profile upper portion 841, which provides the small waterplane (of the SWATH design) and a buoyant lower element 843. The energy capture component 809 may be tethered, e.g. to a docking component (not shown) via a tether 811, whereby the energy capture component may move to face the oncoming tidal flow. In Figure 9, which is a front view of the energy capture component of Figure 8, the energy capture component 909 has a floating platform 913, supporting a housing 939 for containing a turbine or workings therefor (e.g. drive train, generator, gear box if required). A helical rotor 919 is disposed beneath the floating platform in a duct 917 defined by the space between the two hulls 915. A duct floor 945 is formed between lower parts of the two hulls. The duct 917 is of varying width between the two hulls 915, which are preferably mirror images of one another. The slim profile upper portions 941 of each hull 915 may be shaped to give the duct 917 a narrow neck 951 having the highest fluid flow (where the rotor 919 may be located) fed by a wider inlet leading to a broader diffuser outlet, in the tidal flow direction. The slim profile upper portions 941 of each hull have an internal duct surface 947 which defines the duct shape which duct shape typically varies along the flow direction of the duct 917, but is preferably constant in a vertical direction at any particular point along the flow direction. As can be seen from Figure 9, along the flow direction the duct inlet 949 of the internal duct surface 947 defining the duct 917 narrows to a neck 951 at which point in the duct the rotor 919 may be located.

In Figure 10, which shows a rear aspect of the energy capture component 1009 from a downstream direction, internal duct surfaces 1047 separate from the neck 1051 in the flow direction to provide a diffuse outlet 1053 which is wider than the neck 1051 and the inlet (shown at 949). The total width of the device may be 5 m and a total height of 3.95 m.

Figure 11 shows a rear perspective view of the energy capture component 1109 having a floating platform 1013 supporting a housing 1039 and having therebeneath a duct 1117 defined by the internal ducting surface 1147 of the slim profile upper portions 1141 of the hulls 1115 and by the duct floor 1145.

Figure 12 illustrates the duct 1217 of an embodiment of an energy capture element 1209 cut at the water plane level. Here the shape of the internal ducting surface 1247 is illustrated as it ducts from an inlet 1249 to a narrow neck 1251 to create a venturi duct where the rotor 1219 may be located and then tapers to form a wider diffuse outlet 1253, thus the highest flow rate will pass where the rotor 1219 is located and the diffuse outlet 1253 will allow enable pressure downstream fluid flow.

Figure 13 shows a plan of the energy capture element 1309, such as that shown in Figure 12, in cross-section at the water plane. As can be seen, the internal ducting surfaces 1347 are shaped to narrow the duct 1317 from its inlet 1349 of 3.98 m to a neck 1351 providing a close fit for a 3 m diameter vertical axis rotor 1319 and then widens to a diffuse outlet 1353 of 4.83 m.

Figure 14 shows a sub-surface front perspective of a energy capture element 1409 according to another embodiment in which the duct 1417 is defined by slim profile upper portions 1441 of two hulls 1415 and a duct floor 1445, which slim profile upper portions are provided as a series (in tidal flow direction) of vertical slat elements 1455 aligned along a pre-determined curve defining the profile of the duct 1417. The slat elements 1455 allow, between the gaps, water to flow in and out of the duct 1417 in order to maintain fluid flow rate.

Figure 15 illustrates in horizontal cross section the shape of a duct

1517 according to a preferred embodiment, in which the opposing internal duct surfaces 1547 define a duct of length L_T 1557 composed of an inlet portion 1559 of length Li, rotor portion 1561 of length L_R and outlet portion 1563 of length L₀. Typically, the inlet 1549 has a width Wi of greater than the rotor portion width 1565 , W_R, and less than the outlet 1553 width W₀.

The invention has been described with reference to a preferred embodiment. However, it will be appreciated that variations and modifications can be effected by a person of ordinary skill in the art without departing from the scope of the invention.

Claims

CLAIMS:

1. A system for the capture of tidal energy, the system comprising

an off-shore docking component which is anchored or tethered or otherwise positioned to inhibit drift with the tide and which comprises at least one docking station; and

at least one energy capture component, which is buoyant and which comprises a support structure and having at least two hulls having disposed therebetween submerged or submergible a tidal energy capture mechanism,

the at least one energy capture component being moored to the off-shore docking component via the at least one docking station and capable of drifting relative the docking station according to the direction of tidal flow.

2. A system as claimed in claim 1 , wherein there is accommodated on the support structure of the at least one energy capture component an energy conversion or storage component.

3. A system as claimed in claim 1 or claim 2, which further comprises a converted or stored energy transfer system.

4. A system as claimed in any one of the preceding claims, wherein the two hulls of the energy capture component are provided with buoyancy elements at their lower portions.

5. A system as claimed in any one of the preceding claims, wherein the energy capture component is of a small waterplane area twin hull (SWATH) design.

6. A system as claimed in any one of the preceding claims, wherein the offshore docking component is semi-submergible and comprises a planar frame portion configured to be disposed below the surface of the water and protruding from one side thereof the at least one docking station, whereby there is sufficient clearance over the planar frame portion for the at least one energy capture component to drift relative the docking station according to the direction of tidal flow.

7. A system as claimed in any one of the preceding claims, wherein the docking component comprises a plurality of docking stations whereby the system comprises an array of energy capture components.

8. A system as claimed in any one of the preceding claims, wherein the or each energy capture component is provided with a housing on the support structure thereof to house ancillary workings associated with a tidal energy capture mechanism.

9. A system as claimed in any one of the preceding claims, wherein the tidal energy capture mechanism is a rotor.

10. A system as claimed in any one of the preceding claims, wherein the rotor is disposed in a duct defined by the two hulls and a duct floor linking the lower portions of the two hulls.

11. An energy capture device for capturing tidal or river- flow energy, the device being buoyant and comprising a support structure and having at least two hulls having disposed therebetween a submerged or submergible energy capture mechanism, which when deployed, moored to a point stationary relative the tidal flow, the device is capable of drifting to relative alignment with the direction of tidal flow.

12. A device as claimed in claim 11 , wherein the energy capture mechanism is an energy capture rotor.

13. A device as claimed in claim 12, wherein the rotor is a vertical axis rotor.

14. A device as claimed in claim 13, wherein the vertical axis rotor is a helical rotor.

15. A device as claimed in any one of claims 11 to 14, which comprises two hulls of a small waterplane area twin hull (SWATH) design.

16. A device as claimed in any one of claims 11 to 15, wherein two hulls define therebetween a channel having an entrance at an end of the device to be moored and an exit at an end of the device to be free from mooring, wherein the width of the channel decreases along at least a portion of the channel from the entrance thereby creating a venturi or funneling effect.

17. A device as claimed in claim 16, wherein the rotor is positioned at or immediately downstream from a portion of the channel with minimum width.

18. A device as claimed in any one of claims 11 to 17, wherein the rotor is adapted for connection with a power generation system, which is preferably mounted on the support structure.

19. An off-shore docking component for use with a tidal energy capture system as claimed in claim 1 , said docking component comprising a means for anchoring, tethering or fixing the docking component such as to prevent drift of the component with the tide and which comprises at least one docking station.

20. An energy capture device for capturing tidal or river- flow energy, the device being buoyant and comprising a support structure (e.g. a floating platform) having at least two hulls having disposed therebetween a submerged or submergible energy capture mechanism, characterized in that each hull is provided with a buoyancy element at a distal portion to the support structure (e.g. platform) providing the buoyancy to the device.

21. An energy capture device as claimed in claim 20, which has a small waterplane area twin hull design.

22. An energy capture device as claimed in claim 20 or claim 21 , which comprises a channel or duct defined by the two hulls together with a duct floor linking the two hulls at portions thereof distal to the support structure (e.g. platform).

23. A system, off-shore docking component or energy capture device as defined herein with reference to the drawings.