Wave energy converter

Abstract

A float structure for a wave energy converter comprises a substantially toroidal float element 15 with a central aperture. A frame comprises a plurality of strut members 19 connected between the toroi

Description

[0001] This disclosure relates to a wave energy converter for converting energy from waves on a body of water into other useful forms of energy. BACKGROUND

[0002] It is known to generate power from renewable sources in a number of ways. For example, wind turbines can convert kinetic energy of wind energy into electrical energy by way of using the wind to cause rotation of a rotor provided with several rotor blades, and 10 by using the rotation of the rotor to drive an electricity generator. It is also known to convert the kinetic energy in tidal movements of water to drive rotors so as to generate electricity, or to convert the kinetic energy in waves on a body of water into electricity by allowing the waves to impart movement to parts of a wave energy converter that can then impart this movement to an electrical generator. 15

[0003] Instead of converting kinetic energy directly into electrical energy, it is also known to convert kinetic energy into potential energy, for example by using motion caused by movement of air or water to pressurise a storage container with fluid. The pressurised fluid can then be released at a subsequent time to flow through a turbine or the like in order to drive an electrical generator. 20

[0004] In most renewable energy converters, it is necessary to transfer kinetic energy from a moving body of fluid (whether air or water) to kinetic energy of a moving piece of machinery, and then to convert the kinetic energy of the moving piece of machinery into another form of energy, such as electrical energy or potential energy. This is typically achieved by way of a power take off device, which may comprise for example an electrical 25 generator or a hydraulic or pneumatic pump.

[0005] US2010 / 0126164 discloses a wave energy converter comprising a float structure having a tapered underside to reduce the impact due to wave slam and bending moments while providing little reduction in the surface area responding to the wave surface in order to maintain a supposed beneficial power generating capability of a flat float. The float 30 structure has a toroidal shape with a central aperture. The float is moveably mounted on a central shaft or spar that is anchored in or tethered to the seabed, the central shaft or spar passing through the aperture of the toroidal float structure. Because the float structure is less dense than water, it will move up and down the central shaft or spar due to passage of waves past the wave energy converter, with the central shaft or spar remaining relatively 35 stationary. In this way, kinetic energy in moving waves can be converted into kinetic energy in the moving float structure, and this can in turn be converted into electrical or potential energy by way of a power take off device.

[0006] A similar type of wave energy converter is known from CN102536615, where a float structure is configured to move up and down a relatively stationary anchored shaft, 5 and wherein a ratchet mechanism in the float structure is used to drive a rotor of an electrical generator.

[0007] Both of these known wave energy converters employ relatively monolithic float structures that can be subject to large forces in rough sea conditions, and these can apply unduly large forces between the float structure and the central spar or shaft, giving rise to 10 significant wear on the power take off device and the coupling between the float structure and the central spar or shaft. BRIEF SUMMARY OF THE DISCLOSURE

[0008] Viewed from a first aspect, there is provided a float structure for a wave energy 15 converter, the float structure comprising: C\l a substantially toroidal float element with a central aperture, the toroidal float LO element disposed generally in a horizontal plane; and a frame, the frame comprising a plurality of strut members connected at a first end QQ to the substantially toroidal float element and connected at a second end to a substantially 20 cylindrical central collar member configured slidably to receive an elongate shaft extending generally perpendicular to the plane of the substantially toroidal float element through the central aperture of the toroidal float element; wherein the float element comprises a hollow body; wherein the hollow body is configured to be adjustably ballasted; and 25 wherein the float structure further comprises an active ballasting mechanism to add or remove water from the hollow body in response to a detected magnitude of acceleration of the float structure as it moves on the surface of the water.

[0009] The second end of each strut member may be connected to an outer part of the collar member. The second end of each strut member may be connected to a lower part 30 of the collar member.

[0010] The first end of each strut member may be connected to an inner external part of the toroidal float element. The first end of each strut member may be connected to an upper external part of the toroidal float element.

[0011] The plurality of strut members are advantageously angled such that the collar 35 member is held above a plane of the toroidal float element. In this way, the collar member may be held away from the water surface when the float structure is floating on a body of water.

[0012] The plurality of strut members may define a generally pyramidal frame structure between the collar member and the float element, with the collar member disposed 5 generally at an apex of the pyramidal frame structure.

[0013] The plurality of strut members may comprise a number N of strut members, where N is an integer greater than 1, preferably greater than 2. N may be less than or equal to 10. N may be less than or equal to 8. N may be less than or equal to 6.

[0014] The first ends of the strut members may be connected to the toroidal float element 10 by way of pivotal connections. The second ends of the strut members may be connected to the collar member by way of pivotable connections. The pivotable connections may be universal joints. The pivotable connections may permit a degree of pivotal movement between the toroidal float element, the strut members and the collar member. This can help to absorb forces generated when the float structure is subject to movement due to 15 waves on the surface of a body of water.

[0015] The strut members may be of substantially equal lengths. The struct members may each have a length greater than a radius of the central aperture of the toroidal float element and be configured to define a substantially or generally pyramidal frame structure above the plane of the toroidal float element. 20

[0016] The strut members may be made of metal, for example aluminium or alloys thereof, or other materials that are resistant to seawater.

[0017] Also disclosed, but not claimed, is a float structure for a wave energy converter, the float structure comprising: a pyramidal frame having an apex and a base with N base vertices, where N is an 25 integer greater than two; and at least one float element; wherein the at least one float element is distributed around the base of the pyramidal frame so that the float structure floats on or in a body of water with the apex uppermost. 30

[0018] Advantageously, the pyramidal frame structure has a right pyramidal configuration, with the apex located substantially directly above a centre of the base. A right pyramidal configuration may provide improved stability of the float structure when floating on or in the body of water with the apex uppermost.

[0019] The pyramidal frame structure may have a regular pyramidal configuration. In other words, all of the side faces of the pyramidal frame structure other than the base are substantially congruent triangles.

[0020] The pyramidal frame structure may be a tetrahedral frame structure, and N=3. 5 This is simple in manufacture and has excellent structural rigidity due to each side being triangular. The tetrahedral frame structure may be a regular tetrahedral frame structure having six edges of substantially equal length. Alternatively, the tetrahedral frame structure may have a base with three edges of substantially equal length, but with the remaining three edges of the tetrahedral frame structure (extending from the base vertices 10 to the apex) being either shorter than or longer than the base edges.

[0021] Alternatively, the pyramidal frame structure may be square, rhombic or rectangular pyramidal, with a substantially square, rhombic or rectangular base, and four triangular side faces that meet at the apex. In this case, N=4. The four triangular side faces may be substantially equilateral or may be isosceles. In examples where the base is 15 substantially square, the four side faces may comprise substantially congruent triangles.

[0022] Alternatively, the pyramidal frame structure may be a pentagonal pyramid, with a pentagonal base, and five triangular side faces that meet at the apex. In this case, N=5. The five triangular side faces may be substantially equilateral or may be isosceles.

[0023] Alternatively, the pyramidal frame structure may be a hexagonal pyramid, with a 20 hexagonal base, and six triangular side faces that meet at the apex. In this case, N=6. The six triangular side faces may be substantially isosceles.

[0024] It will be appreciated that this may be generalised for larger values of N.

[0025] N may be less than or equal to 10. N may be less than or equal to 8. N may be less than or equal to 6. 25

[0026] In some examples, the base of the pyramidal frame structure may have a star shaped configuration, and the pyramidal frame structure may be a right star pyramid.

[0027] The pyramidal frame structure may comprise an assembly of poles or tubes. For example, where the pyramidal frame structure is a tetrahedral frame structure, it may comprise six poles or tubes in a tetrahedral arrangement, connected to each other where 30 the poles or tubes meet at the apex and at the base vertices.

[0028] The poles or tubes may be made of metal, for example aluminium or alloys thereof, or other materials that are resistant to seawater.

[0029] In the context of the present disclosure, the expression “distributed around the base of the pyramidal frame” is intended to mean that the at least one float element is arranged on or around the base of the pyramidal frame in such a way that the float structure can float stably on or in a body of water with the apex uppermost.

[0030] For example, the at least one float element may comprise a substantially toroidal float element that is connected to the pyramidal frame at each of the N base vertices. 5

[0031] Alternatively, the at least one float element may comprise N similar or identical float elements, one float element attached at each of the N base vertices.

[0032] Alternatively, the at least one float element may comprise N similar or identical float elements, one float element attached at each edge of the base of the pyramidal frame. 10

[0033] Where the at least one float element comprises N float elements, the float elements may be connected to each other by way of a ring structure beneath the base of the pyramidal frame. The float elements may be connected to the ring structure, and the ring structure may be connected to the base of the pyramidal frame. Alternatively, the float elements may be connected directly to the base of the pyramidal frame, and the ring 15 structure may be connected to the float elements. Alternatively, the float elements and the ring structure can be connected to each other and to the base of the pyramidal frame.

[0034] The at least one float element may be fixedly connected to the base of the pyramidal frame.

[0035] Alternatively, the at least one float element may be pivotably fixed to the base of 20 the pyramidal frame so as to allow relative movement between the at least one float element and the pyramidal frame. The pivotable connection may comprise at least one universal joint.

[0036] One float element may be provided at each base vertex of the pyramidal frame.

[0037] The at least one float element may comprise N float elements in combination with 25 a ring-shaped float element.

[0038] Viewed from a second aspect, there is provided a float structure for a wave energy converter, the float structure comprising: a substantially toroidal float element of radius R1; a substantially cylindrical central collar member of outer radius R2 <R1 and inner 30 radius R3 <R2; a plurality of N strut members connected between the toroidal float element and the collar member, where N is an integer greater than two; wherein the strut members are of substantially equal lengths, each strut member having a length L >(R1-R2); wherein each strut member is connected at a first end to the toroidal float element by way of a pivotable connection; wherein each strut member is connected at a second end to the collar member by way of a pivotable connection; 5 wherein the float element comprises a hollow body; wherein the hollow body is configured to be adjustably ballasted; and wherein the float structure further comprises an active ballasting mechanism to add or remove water from the hollow body in response to a detected magnitude of acceleration of the float structure as it moves on the surface of the water. 10

[0039] The second end of each strut member may be connected to an outer part of the collar member. The second end of each strut member may be connected to a lower part of the collar member.

[0040] The first end of each strut member may be connected to an inner external part of the toroidal float element. The first end of each strut member may be connected to an 15 upper external part of the toroidal float element.

[0041] The plurality of N strut members are advantageously angled such that the collar member is held above a plane of the toroidal float element. In this way, the collar member may be held away from the water surface when the float structure is floating on a body of water. 20

[0042] The plurality of N strut members may define a generally pyramidal frame structure between the collar member and the float element, with the collar member disposed generally at an apex of the pyramidal frame structure.

[0043] N may be less than or equal to 10. N may be less than or equal to 8. N may be less than or equal to 6. 25

[0044] The pivotal connections may be universal joints. The pivotable connections may permit a degree of pivotal movement between the toroidal float element, the strut members and the collar member. This can help to absorb forces generated when the float structure is subject to movement due to waves on the surface of a body of water.

[0045] Viewed from a third aspect, there is provided a float structure for a wave energy 30 converter, the float structure comprising: a substantially toroidal float element of radius R1; a substantially cylindrical central collar member of outer radius R2 <R1 and inner radius R3 <R2; a first plurality of N strut members connected between the toroidal float element and the collar member, where N is an integer greater than two, and wherein the first plurality of strut members are of substantially equal lengths; a second plurality of M strut members connected between the toroidal float 5 member and an apex above the collar member, where M is an integer greater than two, and wherein the second plurality of strut members are of substantially equal lengths; wherein each strut member of the first and second pluralities of strut members is connected at a first end to the toroidal float element by way of a pivotable connection; wherein each strut member of the first plurality of strut members is connected at a 10 second end to the collar member by way of a pivotable connection; wherein the float element comprises a hollow body; wherein the hollow body is configured to be adjustably ballasted; and wherein the float structure further comprises an active ballasting mechanism to add or remove water from the hollow body in response to a detected magnitude of acceleration of 15 the float structure as it moves on the surface of the water.

[0046] N may be equal to M. N may be different to M. N may be less than or equal to 10. N may be less than or equal to 8. N may be less than or equal to 6. M may be less than or equal to 10. M may be less than or equal to 8. M may be less than or equal to 6.

[0047] Ends of the second plurality of M strut members may be joined to each other at 20 the apex.

[0048] The first plurality of N strut members may each have a length L where L is approximately equal to R1-R2. In other words, the first plurality of N strut members may each have a length L such that the collar member is disposed generally within a central aperture of the toroidal float element, optionally in substantially the same horizontal plane 25 as the toroidal float element.

[0049] The pivotable connections may be universal joints. The pivotable connections may permit a degree of pivotal movement between the toroidal float element, the strut members and the collar member. This can help to absorb forces generated when the float structure is subject to movement due to waves on the surface of a body of water. 30

[0050] The second plurality of M strut members may define a generally pyramidal frame structure between the collar member and the apex.

[0051] In all of the aforementioned aspects, the at least one float element or the toroidal float element may be made of a solid material that is less dense than water. If the wave energy converter is used in a marine environment, the solid material must be less dense 35 than sea water.

[0052] Alternatively, the at least one float element or the toroidal float element comprises a hollow body. The hollow body may be entirely filled with air or another gas that is less dense than water. The hollow body may be entirely hollow. Alternatively, the hollow body may incorporate a sponge or foam or honeycomb structure. The sponge or foam or 5 honeycomb structure may be an open cell structure or a closed cell structure.

[0053] The at least one float element or the toroidal float element comprises a hollow body that is configured to be adjustably ballasted. The hollow body may, for example, be partially filled with water to provide a ballast. Incorporating an open cell sponge or foam or honeycomb structure may be particularly advantageous so as to constrain movement of 10 ballast water within the float element and thus reduce unwanted stress and strain forces on the pyramidal frame as the float structure moves on the surface of the body of water.

[0054] The active ballasting mechanism is configured to add or remove water from the hollow body in response to a detected magnitude of acceleration of the float structure as it moves on the surface of the water. The active ballasting mechanism may comprise an 15 accelerometer. The active ballasting mechanism may comprise a pump to add or remove water from the hollow body of the float element. The active ballasting mechanism may <N comprise a processor to control the pump in response to acceleration measurements LO obtained by the accelerometer. In this way, the buoyancy of the at least one float element or the toroidal float element can be adjusted for changing wave and weather conditions. QQ 20 For example, in conditions of high wind and large waves, it may be advantageous to increase the ballasting of the at least one float element or the toroidal float element. For example, in conditions of low wind and small waves, it may be advantageous to decrease the ballasting of the at least one float element or the toroidal float element.

[0055] The float structure may further comprise a power take off device. 25

[0056] In the float structure of some aspects, the power take off device may be suspended from the apex of the pyramidal frame. The power take off device may be suspended from the apex of the pyramidal frame by a rigid suspension member. The power take off device may be suspended from the apex of the pyramidal frame by a non-rigid suspension member. The power take off device may be mounted at the apex of the 30 pyramidal frame. The power take off device may be fixedly mounted at the apex of the pyramidal frame. The power take off device may be pivotably mounted at the apex of the pyramidal frame. The power take off device may be disposed within the pyramidal frame.

[0057] In embodiments where the power take off device is suspended from the apex of the pyramidal frame, the power take off device may be considered to be pendulum 35 mounted. The power take off device in these embodiments can move within to the pyramidal frame. The power take off device may be provided with at least one damping mechanism to damp movement of the power take off device relative to the pyramidal frame. The at least one damping mechanism may comprise a spring member. The at least one damping mechanism may comprise an elastomeric member. The at least one damping mechanism may comprise at least one tether. 5

[0058] In the float structure of some aspects, the power take off device may be connected to the collar member. The power take off device may be mounted above the collar member. This may be advantageous in order to distance the power take off device from the surface of the body of water. Alternatively, the power take off device may be mounted under the collar member. Alternatively, the power take off device may be 10 incorporated in the collar member.

[0059] In the float structure of some aspects, the power take off device may be suspended from the apex by a plurality of power take off device strut members. The power take off device strut members may be connected to the power take off device by pivotable connections, for example universal joints. The power take off device strut 15 members may be connected to a top of the power take off device by pivotable connections, for example universal joints. The power take off device strut members may <N be connected to the apex by pivotable connections, for example universal joints. The LO power take off device strut members may be angled more vertically that the plurality of M strut members. CO 20

[0060] The power take off device may comprise an electrical generator. The power take off device may comprise a hydraulic pump. The power take off device may comprise a pneumatic pump.

[0061] The power take off device may comprise at least one gear mechanism.

[0062] The float structure in combination with a power take off device may be considered 25 to form a wave energy converter.

[0063] The wave energy converter of the present invention is configured for use in combination with an elongate shaft configured to engage with the gear mechanism of the power take off device. The elongate shaft has an upper end that engages with the power take off device of the float structure, and a lower end. 30

[0064] In some aspects, the substantially cylindrical central collar member is configured slidably to receive the elongate shaft. The substantially cylindrical central collar member may additionally be configured rotatably to receive the elongate shaft.

[0065] In some aspects, the power take off device is configured slidably to receive the elongate shaft. The substantially cylindrical central collar member may additionally be 35 configured rotatably to receive the elongate shaft.

[0066] The elongate shaft may be a pole or tube made of metal, for example aluminium or alloys thereof, or other materials that are resistant to seawater.

[0067] The elongate shaft may be anchored to the seabed. The lower end of the elongate shaft may be anchored to the seabed. The lower end of the shaft may be sunk 5 directly into the seabed. Alternatively, the lower end of the shaft may be connected to a foundation. The foundation may be a gravity foundation. The foundation may be a monopile foundation. The foundation may be a tripod foundation. The foundation may be a jacket foundation. The foundation in these examples comprises a heavy block, for example of concrete, that may rest on the seabed (gravity foundation) or may be sunk into 10 the seabed, for example by way of piling or by way of a borehole. The lower end of the elongate shaft may be fixedly connected to the foundation. The lower end of the elongate shaft may be moveably connected to the foundation, for example through a universal joint. This can allow the elongate shaft to move to some extent with the body of water, and may reduce unwanted bending moments on the elongate shaft. 15

[0068] Alternatively, the lower end of the elongate shaft may be tethered to the seabed by way of one or more tethers. The at least one tether may comprise a cable, for example <N made of steel or other appropriate materials. The at least one tether may be connected to LO at least one foundation as described above. The use of tethers can also help to reduce bending moments by allowing the elongate shaft to move with the body of water. CO 20

[0069] The upper end of the elongate shaft may be provided with a toothed rack. The gear mechanism of the power take off device may be configured to engage with the toothed rack. Accordingly, when the float structure and power take off device move up and down due to the passage of waves on the surface of the body of water, the power take off device will move up and down relative to the upper end of the elongate shaft, and the gear 25 mechanism of the power take off device will be driven through engagement with the toothed rack on the upper end of the elongate shaft.

[0070] The power take off device may be configured with an aperture through which the upper end of the elongate shaft is received, with the gear mechanism of the power take off device engaged with the toothed rack. In this way, the power take off device is securely 30 held on the upper end of the elongate shaft, being permitted to move up and down the upper end of the elongate shaft but without significant play in other directions.

[0071] An upper end stop may be provided at or close to the top of the upper end of the elongate shaft so as to prevent the power take off device from being lifted off the upper end of the elongate shaft after installation, for example due to large waves.

[0072] The toothed rack need not extend the entire length of the elongate shaft, but only to a predetermined depth below which it is unlikely that the power take off device will fall. This may be, for example, 1 m less than the all-time low water mark for the location where the float structure is deployed. 5

[0073] The gear mechanism of the power take off device may comprise a toothed wheel that engages with the toothed rack at the upper end of the elongate shaft. The toothed wheel may drive a crankshaft that in turn drives an electrical generator, or hydraulic pump, or pneumatic pump.

[0074] The power take off device may comprise a standard wind turbine power take off 10 device, subject to minor modifications for fitting to the float structure and around the upper end of the elongate shaft.

[0075] A substantially constant stroke length of the gear mechanism of the power take off device relative to the toothed rack on the upper end of the elongate shaft may be maintained by one or more of the following adjustments. 15

[0076] Firstly, in embodiments where the power take off device is suspended from the apex of the pyramidal frame, the distance between the power take off device and the apex of the pyramidal frame may be adjusted.

[0077] Secondly, since the float elements are configured to be adjustably ballasted, water may be added or removed from the interiors of the float structures so as to adjust a 20 floating height of the float structure and hence of the power take off device relative to the upper end of the elongate shaft.

[0078] Thirdly, where the lower end of the elongate shaft is moveably connected to at least one foundation, for example by way of one or more tethers or by way of an adjustable universal joint, the position of the upper end of the elongate shaft and the toothed rack 25 relative to the surface of the body of water can be adjusted.

[0079] By adjusting one or more of these parameters, it may be possible to maintain a substantially constant stroke length regardless of changing wave conditions, such as changing wave heights.

[0080] Adjusting one or more of these parameters may also take into account changes in 30 heave, wave periodicity and / or wave length.

[0081] It will be appreciated that the primary motion of the float structure and power take off device that is useful for energy conversion is heave. Heave is defined as an up and down movement of a floating object due to waves on the surface of a body of water. Embodiments of the present disclosure make use of heave motion to drive the power take off device.

[0082] In some embodiments, rotational movement of the float structure and power take off device relative to the elongate shaft may be useful for energy conversion. 5

[0083] In some embodiments, pitch and / or roll movement of the float structure and power take off device relative to the elongate shaft may be useful for energy conversion.

[0084] The frame structure with the power take off device connected thereto may permit a degree of pitch, roll and / or yaw movement. By permitting a degree of pitch, roll and / or yaw, it may be possible to reduce excess stress and / or strain on the components of the 10 system due to wave movements.

[0085] The provision of a flexible anchoring mechanism for the elongate shaft, for example by way of a universal joint or tethering, also permits a degree of sway and / or surge movement, likewise helping to reduce excess stress and / or strain on the components of the system due to wave movements. 15

[0086] Viewed from a fourth aspect, there is provided a wave energy converter C\l comprising the float structure of the first, second or third aspect and a power take off LO device having a gear mechanism, the power take off device connected to the float structure. CO

[0087] Viewed from a fifth aspect, there is provided a wave energy converter system 20 comprising the wave energy converter of the fourth aspect in combination with an elongate shaft that is anchored to the seabed, wherein the gear mechanism of the power take off device engages with the elongate shaft.

[0088] Embodiments of the present disclosure may be particularly suited for installation in existing offshore wind farms comprising a plurality of wind turbines. The elongate shafts 25 may be anchored to the seabed as hereinbefore described, or may be anchored by connection to existing wind turbine foundations or towers. The connection may be rigid. The connection may be by way of one or more tethers. The float structures and power take off devices may thus be located between adjacent wind turbine structures in an offshore wind farm, and may make use of existing foundation structures. This can reduce 30 the cost of installation.

[0089] Moreover, it has surprisingly been found that there is often a phase difference between wind power generation and wave power generation in a given area, for example at a given offshore wind farm. During periods of relatively stable wind at wind speeds appropriate for driving wind turbines at high efficiency, it has been found that wave motion 35 at the surface of the sea can be unsuited for driving wave energy converters at high efficiency. Conversely, during periods of good wave propagation across the surface of the sea, during which wave energy converters can be driven at high efficiency, the accompanying wind (or lack of wind) can be unsuited for driving wind turbines at high efficiency. Accordingly, it has surprisingly been found that a combination of wind turbines 5 and wave energy converters at an offshore location can facilitate a more sustainable and more continuous generation of power.

[0090] Additionally, adding wave energy converters of aspects of the present disclosure to an existing offshore wind turbine installation allows the existing electrical infrastructure to be used to collect the generated electrical power. The electrical power may be brought 10 onshore by way of subsea electrical cables. Because of the phase difference between wind power generation and wave power generation, the electrical infrastructure may be less prone to overloading, and may be less subject to peaks and troughs of electrical current.

[0091] Advantageously, embodiments of the present disclosure may be combined with at 15 least one energy storage device. Examples of suitable energy storage devices include mechanical, hydraulic, pneumatic, electrical or chemical energy storage devices. For example, electrical energy generated from kinetic energy by a wave energy converter system of the present disclosure may be used to charge a battery device or to charge a capacitor device. For example, electrical energy generated from kinetic energy by a wave 20 energy converter system of the present disclosure may be used to pressurise a pneumatic or hydraulic pressure container by way of an electric pump. For example, electrical energy generated from kinetic energy by a wave energy converter system of the present disclosure may be used to pump water or another fluid from a lower level to a higher level, and the water or fluid may subsequently be allowed to flow from the higher level to the 25 lower level through a turbine or the like in order to generate electrical power when required. Other energy storage devices may be employed as appropriate. BRIEF DESCRIPTION OF THE DRAWINGS

[0092] Embodiments of the invention are further described hereinafter with reference to 30 the accompanying drawings, in which: Figure 1 is a schematic side elevation of a first embodiment of a wave energy converter; Figure 2 is a schematic plan view of the first embodiment of Figure 1; Figure 3 is a schematic side elevation of an elongate shaft for use with the first 35 embodiment; Figure 4 shows a power take off device with a gear mechanism engaging a toothed rack on the elongate shaft of Figure 3; Figure 5 shows a schematic side elevation of a second embodiment of a wave energy converter; 5 Figure 6 shows a schematic perspective view of the second embodiment of Figure 5; Figure 7 shows a schematic side elevation of a third embodiment of a wave energy converter; Figure 8 shows a schematic perspective view of the third embodiment of Figure 7. 10 DETAILED DESCRIPTION

[0093] Figures 1 and 2 show a schematic view of a first embodiment, comprising a float structure 1 for a wave energy converter indicated generally at 100. The float structure 1 xt CM O CO comprises a pyramidal frame 10, here shown as a substantially rigid tetrahedral frame. 15 The pyramidal frame 10 has an apex 11 and a base 12, with three base vertices 13. A lumped float element 14, for example in the form of a buoy, is attached to each base vertex 13 of the pyramidal frame, for example by way of a universal joint 17 to allow pivoting movement between each float element 14 and its respective base vertex 13. The float elements 14 are mounted beneath the base 12 of the pyramidal frame 10 so as to 20 help keep the pyramidal frame 10 above the water surface 50. There is also provided a toroidal or annular float element 15 in combination with the lumped float elements 14. The toroidal or annular float element 15 helps to provide additional flotation stability. The toroidal or annular float element 15 may be connected to the lumped float elements 14 and / or to the base vertices 13 of the pyramidal frame 10. 25

[0094] The pyramidal frame 10 is made of strut members that define edges of the pyramidal frame 10. The strut members may be aluminium or aluminium alloy tubes connected to each other at the apex 11 and the base vertices 13.

[0095] The float structure 1 shown in Figures 1 and 2 further comprises a submersible pump 16 configured to pump water into or out of the float elements 14 and / or the toroidal 30 or annular float element 15. The float elements 14 and / or 15 are hollow or comprise an open-cell sponge or foam or honeycomb structure so as to allow the float elements 14 and / or 15 to be adjustably ballasted by water. The pump 16 is provided as part of an active ballasting mechanism to add or remove water from the float elements 14 and / or 15 in response to a detected magnitude of acceleration of the float structure 1 as it moves on the water surface 50. The active ballasting mechanism may comprise an accelerometer. The active ballasting mechanism may comprise a processor to control the pump 16 in response to acceleration measurements obtained by the accelerometer. In this way, the buoyancy of the at least float elements 14 and / or 15 can be adjusted for changing wave 5 and weather conditions. For example, in conditions of high wind and large waves, it may be advantageous to increase the ballasting of the float elements 14 and / or 15. For example, in conditions of low wind and small waves, it may be advantageous to decrease the ballasting of the float elements 14 and / or 15. 10 15 20

[0096] The float structure 1 of Figures 1 and 2 further comprises a power take off device 20. The power take off device 20 may be suspended from the apex 11 of the pyramidal frame 10. The power take off device 20 may be suspended from the apex 11 of the pyramidal frame 10 by a rigid or a non-rigid suspension member 22. Alternatively, the power take off device 20 may be mounted at the apex 11 of the pyramidal frame 10. The power take off device 20 may be fixedly or pivotably mounted at the apex 11 of the pyramidal frame 10. The power take off device 20 may be disposed within the pyramidal frame 10.

[0097] In embodiments, such as shown in Figures 1 and 2, where the power take off device 20 is suspended from the apex 11 of the pyramidal frame 10, the power take off device 20 may be considered to be pendulum mounted. The power take off device 20 in these embodiments can move within to the pyramidal frame 10. The power take off device 20 may be provided with at least one damping mechanism 21 to damp movement of the power take off device 20 relative to the pyramidal frame 10. The at least one damping mechanism 21 may comprise a spring member, an elastomeric member and / or at least one tether. 25

[0098] The wave energy converter 100 is configured for use in combination with an elongate shaft 200 configured to engage with a gear mechanism of the power take off device 20. The elongate shaft 200 is shown in schematic form in Figure 3. The elongate shaft 200 has an upper end 201 that engages with the power take off device 20 of the float structure 1, and a lower end 202. 30

[0099] The power take off device 20 is configured slidably to receive the elongate shaft 200.

[00100] The elongate shaft 200 may be a pole or tube made of metal, for example aluminium or alloys thereof, or other materials that are resistant to seawater.

[00101] The lower end 202 of the elongate shaft 200 may be anchored to the seabed 203. 35 The lower end 202 of the shaft 200 may be sunk directly into the seabed 203, or may be connected to a foundation 204. The foundation 204 may comprise a heavy block, for example of concrete, that may rest on the seabed 203 (gravity foundation) or may be sunk into the seabed 203, for example by way of piling or by way of a borehole. The lower end 202 of the elongate shaft 200 may be fixedly connected to the foundation 204, or may be 5 moveably connected to the foundation 204, for example through a universal joint 205. This can allow the elongate shaft 200 to move to some extent with the body of water, and may reduce unwanted bending moments on the elongate shaft 200.

[00102] Alternatively (not shown in Figure 3), the lower end 202 of the elongate shaft 200 may be tethered to the seabed 203 by way of one or more tethers. The at least one tether 10 may comprise a cable, for example made of steel or other appropriate materials. The at least one tether may be connected to at least one foundation as described above. The use of tethers can also help to reduce bending moments by allowing the elongate shaft 200 to move with the body of water.

[00103] The upper end 201 of the elongate shaft may be provided with a toothed rack 15 206. A gear mechanism of the power take off device 20 is configured to engage with the toothed rack 206. Accordingly, when the float structure 1 and power take off device 20 move up and down due to the passage of waves on the surface 50 of the body of water, the power take off device 20 will move up and down relative to the upper end 201 of the elongate shaft 200, and the gear mechanism of the power take off device 20 will be driven 20 through engagement with the toothed rack 206 on the upper end 201 of the elongate shaft 200.

[00104] The power take off device 20 may be configured with an aperture through which the upper end 201 of the elongate shaft 200 is received, with the gear mechanism of the power take off device 20 engaged with the toothed rack 206. In this way, the power take 25 off device 20 is securely held on the upper end 201 of the elongate shaft 200, being permitted to move up and down the upper end 201 of the elongate shaft 200 but without significant play in other directions.

[00105] An upper end stop 207 may be provided at or close to the top of the upper end 201 of the elongate shaft 200 so as to prevent the power take off device 20 from being 30 lifted off the upper end 201 of the elongate shaft 200 after installation, for example due to large waves.

[00106] Figure 4 shows, in schematic form, a power take off device 20 comprising a gear mechanism 26 that engages with the toothed rack 206 at the upper end 201 of the elongate shaft 200. Up and down movement of the power take off device 20 relative to the 35 elongate shaft 200 will cause the gear mechanism 26 to rotate due to engagement with the toothed rack 206. Rotational movement of the gear mechanism 26 can be used to drive an electrical generator in the power take off device 20, or to drive a pneumatic or hydraulic pump.

[00107] Figure 5 shows a schematic side elevation of a second embodiment of a wave energy converter 10, and Figure 6 shows a schematic perspective view of the embodiment 5 of Figure 5.

[00108] The float structure 1 for a wave energy converter 100 of the second embodiment comprises a substantially toroidal float element 15 of radius R1. In the illustrated example, the radius R1 is an inner radius of the toroidal float element 15, which is shown with a central aperture 17. The float structure 1 further comprises a substantially cylindrical 10 central collar member or gimbal 18 of outer radius R2 <R1 and inner radius R3 <R2. A plurality of N strut members 19 are connected between the toroidal float element 15 and the collar member 18, where N is an integer greater than two (in the illustrated example, N=6). The strut members 19 are of substantially equal lengths, and each strut member 19 has a length L >(R1-R2). Each strut member 19 is connected at a first end to the toroidal 15 float element 15 by way of a pivotable connection. Each strut member 19 is connected at a second end to the collar member 18 by way of a pivotable connection. C\J

[00109] The second end of each strut member 19 may be connected to an outer part of the collar member 18, and / or to a lower part of the collar member 18 as shown.

[00110] The first end of each strut member 19 may be connected to an inner external part 20 of the toroidal float element 15, as shown. Alternatively, the first end of each strut member 19 may be connected to an upper external part of the toroidal float element 15.

[00111] The plurality of strut members 19 are angled such that the collar member 18 is held above a plane of the toroidal float element 15. In this way, the collar member 18 may be held away from the water surface 50 when the float structure 1 is floating on a body of 25 water. The plurality of strut members 19 define a generally pyramidal frame structure between the collar member 18 and the float element 1, with the collar member 18 disposed generally at an apex of the pyramidal frame structure.

[00112] The pivotal connections may be universal joints. The pivotable connections may permit a degree of pivotal movement between the toroidal float element 15, the strut 30 members 19 and the collar member 18. This can help to absorb forces generated when the float structure is subject to movement due to waves on the surface 50 of a body of water.

[00113] A power take off device 20 is connected to the collar member 18. In the illustrated embodiment, the power take off device 20 is mounted above the collar member 18. However, the power take off device 20 may be mounted beneath the collar member 18 or may be incorporated in the collar member 18.

[00114] An elongate shaft 200, which may be anchored or tethered to the seabed, is also shown in Figures 5 and 6. The elongate shaft 200 may be similar to the rectangular cross-5 section elongate shaft 200 shown in Figures 3 and 4, or may have a circular cross-section as shown in Figures 5 and 6. Although not shown in Figures 5 and 6, the upper end 201 of the elongate shaft 200 is provided with a toothed rack.

[00115] The collar member 18 and the power take off device 20 are each configured with a central aperture sized and shaped slidably to receive the upper end 201 of the elongate 10 shaft 200 and the toothed rack. Where the upper end 201 of the elongate shaft 200 has a circular cross-section, the float structure 1 may rotate around the elongate shaft 200 as indicated in Figure 6. Moreover, due to the pivotable connections between the strut members 19, the toroidal float element 15 and the collar member 18, the float structure 1 may also pitch and / or roll relative to the elongate shaft 200 as indicated in Figure 5. 15

[00116] As with the embodiments of Figures 1 to 4, the embodiment of Figures 5 and 6 is configured to convert kinetic energy from heave motion of the float structure 1 relative to the elongate shaft 200 due to waves into electrical or potential energy by way of the power take off device 20. In some variants, rotational kinetic energy from rotation of the float structure 1 about the elongate shaft 200 may also be converted into electrical or potential 20 energy.

[00117] Figure 7 shows a schematic side elevation of a third embodiment of a wave energy converter 10, and Figure 8 shows a schematic perspective view of the embodiment of Figure 7.

[00118] The float structure 1 for a wave energy converter 100 of the third embodiment 25 comprises a substantially toroidal float element 15 of radius R. In the illustrated example, the radius R1 is an inner radius of the toroidal float element 15, which is shown with a central aperture 17. The float structure 1 further comprises a substantially cylindrical central collar member or gimbal 18 of outer radius R2 <R1 and inner radius R3 <R2.

[00119] A first plurality of N strut members 19 are connected between the toroidal float 30 element 15 and the collar member or gimbal 18. The first plurality of strut members 19 are of substantially equal lengths.

[00120] A second plurality of M strut members 30 are connected between the toroidal float member 15 and an apex 11 above the collar member 18, where M is an integer greater than two, and wherein the second plurality of strut members 30 are of substantially equal 35 lengths.

[00121] Each strut member of the first and second pluralities of strut members 19, 30 is connected at a first end to the toroidal float element 15 by way of a pivotable connection. Each strut member of the first plurality of strut members 19 is connected at a second end to the collar member 18 by way of a pivotable connection. 5

[00122] The first plurality of N strut members 19 may each have a length L where L is approximately equal to R1-R2. In other words, the first plurality of N strut members 19 may each have a length L such that the collar member 18 is disposed generally within a central aperture 17 of the toroidal float element 15, for example in substantially the same horizontal plane as the toroidal float element 15. 10

[00123] The second plurality of M strut members 30 may define a generally pyramidal frame structure between the collar member 18 and the apex 11.

[00124] The pivotal connections may be universal joints. The pivotable connections may permit a degree of pivotal movement between the toroidal float element 15, the strut members 19, 30 and the collar member 18. This can help to absorb forces generated 15 when the float structure 1 is subject to movement due to waves on the surface 50 of a body of water.

[00125] A power take off device 20 is connected to the apex 11 by a plurality of power take off device strut members 31. The power take off device strut members 31 may be connected to the power take off device 20 by pivotable connections such as universal 20 joints. The power take off device strut members 31 may be connected to the apex 11 by pivotable connections, for example universal joints. The power take off device strut members 31 may be angled more vertically that the plurality of M strut members 30.

[00126] An elongate shaft 200, which may be anchored or tethered to the seabed, is also shown in Figures 7 and 8. The elongate shaft 200 may be similar to the rectangular cross-25 section elongate shaft 200 shown in Figures 3 and 4, or may have a circular cross-section as shown in Figures 7 and 8. Although not shown in Figures 7 and 8, the upper end 201 of the elongate shaft 200 is provided with a toothed rack.

[00127] The collar member 18 and the power take off device 20 are each configured with a central aperture sized and shaped slidably to receive the upper end 201 of the elongate 30 shaft 200 and the toothed rack. Where the upper end 201 of the elongate shaft 200 has a circular cross-section, the float structure 1 may rotate around the elongate shaft 200 as indicated in Figure 8. Moreover, due to the pivotable connections between the strut members 19, 30, 31, the toroidal float element 15, the collar member 18 and the power take off device 20, the float structure 1 may also pitch and / or roll relative to the elongate 35 shaft 200 as indicated in Figure 7.

[00128] As with the embodiments of Figures 1 to 4, the embodiment of Figures 7 and 8 is configured to convert kinetic energy from heave motion of the float structure 1 relative to the elongate shaft 200 due to waves into electrical or potential energy by way of the power take off device 20. In some variants, rotational kinetic energy from rotation of the float 5 structure 1 about the elongate shaft 200 may also be converted into electrical or potential energy.

[00129] Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of them mean “including but not limited to”, and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. 10 Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

[00130] Features, integers, characteristics, compounds, chemical moieties or groups 15 described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and / or all of the steps of any method or process so disclosed, may be combined in any combination, 20 except combinations where at least some of such features and / or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so 25 disclosed.

[00131] The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

Claims

1. A float structure for a wave energy converter, the float structure comprising:a substantially toroidal float element with a central aperture, the toroidal float5 element disposed generally in a horizontal plane; anda frame, the frame comprising a plurality of strut members connected at a first end to the substantially toroidal float element and connected at a second end to a substantially cylindrical central collar member configured slidably to receive an elongate shaft extending generally perpendicular to the plane of the substantially toroidal float element through the10 central aperture of the toroidal float element;wherein the float element comprises a hollow body;wherein the hollow body is configured to be adjustably ballasted; andwherein the float structure further comprises an active ballasting mechanism to add or remove water from the hollow body in response to a detected magnitude of acceleration15 of the float structure as it moves on the surface of the water.

2. A float structure for a wave energy converter, the float structure comprising:a substantially toroidal float element of radius R1;a substantially cylindrical central collar member of outer radius R2 <R1 and inner 20 radius R3 <R2;a plurality of N strut members connected between the toroidal float element and the collar member, where N is an integer greater than two;wherein the strut members are of substantially equal lengths, each strut member having a length L >(R1-R2);25 wherein each strut member is connected at a first end to the toroidal float elementby way of a pivotable connection;wherein each strut member is connected at a second end to the collar member by way of a pivotable connection;wherein the float element comprises a hollow body;30 wherein the hollow body is configured to be adjustably ballasted; andwherein the float structure further comprises an active ballasting mechanism to add or remove water from the hollow body in response to a detected magnitude of acceleration of the float structure as it moves on the surface of the water.35 3. The float structure as claimed in claim 1 or 2, wherein the second end of each strutmember is connected to an outer part of the collar member.

4. The float structure as claimed in any preceding claim, wherein the first end of each strut member is connected to an inner external part of the toroidal float element, or wherein the first end of each strut member is connected to an upper external part of the toroidal float element.

5. The float structure as claimed in any preceding claim, wherein the plurality of strut members are angled such that the collar member is held above a plane of the toroidal float element.10 6. The float structure as claimed in claim 2 or any one of claims 3 to 5 depending fromclaim 2, wherein N is less than or equal to 10, or wherein N is less than or equal to 8, or wherein N is less than or equal to 6.

7. A float structure for a wave energy converter, the float structure comprising:15 a substantially toroidal float element of radius R1;a substantially cylindrical central collar member of outer radius R2 <R1 and inner radius R3 <R2;a first plurality of N strut members connected between the toroidal float element and the collar member, where N is an integer greater than two, and wherein the first 20 plurality of strut members are of substantially equal lengths;a second plurality of M strut members connected between the toroidal float member and an apex above the collar member, where M is an integer greater than two, and wherein the second plurality of strut members are of substantially equal lengths;wherein each strut member of the first and second pluralities of strut members is 25 connected at a first end to the toroidal float element by way of a pivotable connection;wherein each strut member of the first plurality of strut members is connected at a second end to the collar member by way of a pivotable connection;wherein the float element comprises a hollow body;wherein the hollow body is configured to be adjustably ballasted; and30 wherein the float structure further comprises an active ballasting mechanism to addor remove water from the hollow body in response to a detected magnitude of acceleration of the float structure as it moves on the surface of the water.

8. The float structure as claimed in claim 7, wherein N is equal to M, optionally 35 wherein N and M are less than or equal to 10, or wherein N and M are less than or equal to 8, or wherein N and M are less than or equal to 6.

9. The float structure as claimed in claim 7, wherein N is different to M, optionally wherein N is less than or equal to 10, or wherein N is less than or equal to 8, or wherein N is less than or equal to 6, or wherein M is less than or equal to 10, or wherein M is less than or equal to 8, or wherein M is less than or equal to 6.

510. The float structure as claimed in any one of claims 7 to 9, wherein ends of the second plurality of M strut members are joined to each other at the apex.

11. The float structure as claimed in any one of claims 7 to 10, wherein the first plurality 10 of N strut members each have a length L where L is approximately equal to R1-R2.

12. The float structure as claimed in any one of claims 1 to 11, wherein the hollow body is entirely hollow.15 13. The float structure as claimed in any one of claims 1 to 11, wherein the hollow bodyincorporates a sponge or foam or honeycomb structure.

14. The float structure as claimed in any one of claims 1 to 13, wherein the active ballasting mechanism comprises an accelerometer.2015. The float structure as claimed in any one of claims 1 to 14, wherein the active ballasting mechanism comprises a pump to add or remove water from the hollow body of the float element.25 16. The float structure as claimed in claim 15 depending from claim 14, wherein theactive ballasting mechanism comprises a processor to control the pump in response to acceleration measurements obtained by the accelerometer.

17. The float structure as claimed in any preceding claim, further comprising a power 30 take off device.

18. The float structure as claimed in clam 17, wherein the power take off device is connected to the collar member.35 19. The float structure are claimed in claim 18, wherein the power take off device ismounted above the collar member.

20. The float structure are claimed in claim 18, wherein the power take off device is mounted below the collar member.

21. The float structure are claimed in claim 18, wherein the power take off device is 5 incorporated in the collar member.

22. The float structure as claimed in clam 17 depending from any one of claims 7 to 11 or from any one of claims 12 to 16 depending from any one of claims 7 to 11, wherein the power take off device is suspended from the apex by a plurality of power take off device 10 strut members.

23. The float structure as claimed in any one of claims 17 to 22, wherein the powertake off device comprises an electrical generator.15 24. The float structure as claimed in any one of claims 17 to 22, wherein the powertake off device comprises a hydraulic or pneumatic pump.

25. The float structure as claimed in any one of claims 17 to 24, wherein the power take off device comprises at least one gear mechanism.2026. The float structure as claimed in claim 25, wherein the power take off device is configured to receive an upper end of an elongate shaft, and wherein the gear mechanism is configured to engage with the upper end of the elongate shaft so that the gear mechanism is driven when the power take off device moves up or down the upper end of 25 the elongate shaft.

27. The float structure as claimed in claim 26, wherein the power take off device is configured with an aperture through which the upper end of the elongate shaft is received.30 28. The float structure as claimed in claim 26 or 27 depending ultimately from claim 2or 7, wherein the collar member is configured slidably, and optionally rotatably, to receive the elongate shaft.

29. A wave energy converter system comprising the float structure of any one of claims 35 17 to 28, in combination with an elongate shaft that is anchored to the seabed, wherein thegear mechanism of the power take off device engages with the elongate shaft.

30. The wave energy converter system as claimed in claim 29, wherein the elongate shaft is a pole or tube made of metal, for example aluminium or alloys thereof, or other materials that are resistant to seawater.5 31. The wave energy converter system as claimed in claim 29 or 30, wherein theelongate shaft has an upper end that engages with the power take off device of the float structure, and a lower end.

32. The wave energy converter system as claimed in claim 31, wherein the lower end 10 of the elongate shaft is anchored to the seabed.

33. The wave energy converter system as claimed in claim 31 or 32, wherein the lower end of the shaft is sunk directly into the seabed.15 34. The wave energy converter system as claimed in claim 31 or 32, wherein the lowerend of the shaft is connected to a foundation.

35. The wave energy converter system as claimed in claim 34, wherein the lower end of the elongate shaft is fixedly connected to the foundation.2036. The wave energy converter system as claimed in claim 34, wherein the lower end of the elongate shaft is moveably connected to the foundation.

37. The wave energy converter system as claimed in claim 31 or 32, wherein the lower25 end of the elongate shaft is tethered to the seabed by way of at least one tether.

38. The wave energy converter system as claimed in claim 37, wherein the at least onetether is connected to at least one foundation on the seabed.30 39. The wave energy converter system as claimed in any one of claims 31 to 38,wherein the upper end of the elongate shaft comprises a toothed rack.

40. The wave energy converter system as claimed in claim 39, wherein the gear mechanism of the power take off device is configured to engage with the toothed rack.35xt CMLO41. The wave energy converter system as claimed in claim 40, wherein the gear mechanism of the power take off device comprises a toothed wheel that engages with the toothed rack at the upper end of the elongate shaft.5 42. The wave energy converter system as claimed in claim 41, wherein the toothedwheel drives a crankshaft that in turn drives an electrical generator, or hydraulic pump, or pneumatic pump.

43. The wave energy converter system as claimed in any one of claims 29 to 42, in 10 combination with at least one energy storage device.

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