WO2010078940A2

WO2010078940A2 - Apparatus for extracting energy from wave motion

Info

Publication number: WO2010078940A2
Application number: PCT/EP2009/009137
Authority: WO
Inventors: Alan Wilson
Original assignee: Alan Wilson
Priority date: 2008-12-18
Filing date: 2009-12-18
Publication date: 2010-07-15
Also published as: GB0822987D0; WO2010078940A3

Abstract

An apparatus for extracting useful energy from wave motion, said apparatus comprising spaced apart first and second buoys arranged to float on or adjacent the surface of the water, each of said first and second buoys being connected to a submerged reaction mass by means of a respective linkage, whereby relative motion between each of the first and second buoys with respect to the reaction mass due to the action of waves is converted into useful energy.

Description

Apparatus for Extracting Energy from Wave Motion

This invention relates to an apparatus for extracting useful energy from wave motion.

According to the present invention there is provided an apparatus for extracting useful energy from wave motion, said apparatus comprising spaced apart first and second buoys arranged to float on or adjacent the surface of the water, each of said first and second buoys being connected to a submerged reaction mass by means of a respective linkage, whereby relative motion between each of the first and second buoys with respect to the reaction mass due to the action of waves is converted into useful energy.

In one embodiment the first and second buoys are preferably arranged to capture the differential energy between a wave peak and a wave trough, the first and second buoys being connected to the reaction mass by said linkages such that the first and second buoys can be moved up and down by the waves, out of phase with each other, causing reciprocating motion of at least part of each linkage with respect to the reaction mass.

In an alternative embodiment the first and second buoys are connected to the reaction mass by said linkages such that the buoys may move independently or in phase with one another whereby relative motion of the first and second buoys and the reaction mass under the action of wave motion may be converted into useful energy. In this embodiment the reaction mass may be arranged to be closer to the surface to enable it to also react with wave action at varying wavelengths.

Preferably said linkages are operatively coupled to at least one pump, compressor or other energy conversion mechanism provided on the reaction mass for converting wave motion into useful energy or work.

In one embodiment said linkages comprise an elongate flexible linkage extending between said first and second buoys via the reaction mass.

Preferably said flexible linkage is maintained under tension by the action of said reaction mass upon said flexible linkage and the forces acting on the ends of the flexible linkage due to the buoyancy of the first and second buoys. The movement of the buoys and/or the reaction mass due to wave motion causes reciprocal movement of the flexible linkage with respect to the reaction mass, enabling the efficient extraction of energy from the waves.

The flexible linkage is preferably connected to the reaction mass by means of one or more pulley wheels or guides provided on the reaction mass, preferably at the lower side regions or corners of the reaction mass or upon a jib extension mounted thereon.

The flexible linkage may comprise a cable, rope or other elongate flexible member, formed from a suitable material, such as steel or a polymeric material, and may be supported on one or more pulley wheels or guides provided on the reaction mass, preferably provided at each bottom corner of the reaction mass.

In an alternative embodiment each linkage comprises an elongate member and a crank arrangement connected to the reaction mass whereby relative motion between each of the first and second buoys and the reaction mass is transmitted into a rotating or reciprocating motion of a part of a pump or an energy conversion device. Each linkage may comprise a rigid member or beam or may comprise a flexible member, such as a cable. Preferably the crank arrangements are interconnected whereby the buoys are linked via the respective linkages such that the first and second buoys members move with respect to the reaction mass out of phase with one another. Each crank arrangement may incorporate gearing.

In one embodiment each crank arrangement may comprise an elongate member pivotally mounted on the reaction mass, or on a jib extension mounted thereon for pivotal motion about a fulcrum, a respective buoy being connected to a first end of the respective elongate member, the opposite ends of the elongate members being linked by a rigid or flexible linkage, said linkage cooperating with the energy conversion device to extract energy from relative movement of the buoys with respect to the reaction mass due to wave action.

In one embodiment each linkage may be associated with an energy conversion device, such an as electrical generator, for extracting energy from said wave motion. In an alternative embodiment each linkage may be associated with a pump or compressor for pumping or compressing a fluid or a gas. The energy conversion device or pump may incorporate or comprise a reciprocating pump, the or each linkage preferably being drivingly connected to a piston of said pump. Alternatively said energy conversion device or pump may incorporate or comprise a rotary device. In the first mentioned embodiment having a single flexible linkage between the first and second buoys the rotary device may comprise one or more pulleys or wheels around which said flexible linkage passes such that reciprocating motion of the flexible linkage leads to rotary motion of the one or more pulleys. In said second embodiment, wherein said linkages comprise rigid members, said rotary device may be operatively connected to said crank arrangement of each linkage. The rotary device may comprise a pump, a compressor, or an electricity generator.

In one embodiment reciprocating motion of the or each linkage may be converted into a rotary motion by a rack and pinion arrangement, preferably wherein a pinion is rotatably mounted on the reaction mass for driving an energy conversion device or pump and a rack is operatively connected to the or each linkage for reciprocating motion with respect to the pinion. Further, the reciprocating motion may serve to operate a hydraulic ram mechanism and accumulator or storage vessel to enable steady power take off between strokes

The sides of the reaction mass may diverge outwardly towards a base region of the reaction. In one embodiment said tank may be in the form of a hollow truncated pyramid. Alternative geometries may also be used.

The buoyancy and geometry of the reaction mass may be such that its downward forces and inertia in the water act as a relatively stable fulcrum for the first and second buoys to act about.

The inclined side walls of the reaction mass may also assist in utilizing a component of the downward force exerted by the underwater portion of a wave. Such force component will push the leading face of the reaction mass down and away from the leading buoy (that has been raised by the portion of the wave above the water) - therefore enabling the leading buoy to be pulled even further from the reaction mass thus creating additional energy. As a wave arrives the leading buoy will rise up the wave front toward the top of the wave. As the buoy rises up to the peak of the wave, the wider underwater base of the same wave will act on a forward face of the reaction mass and will push the reaction mass down and away from the leading buoy. This action will increase the relative distance travelled by the buoy and therefore increase the energy created. As the wave continues over the reaction mass it may loose a little energy and height having just exchanged energy with the leading buoy and then the reaction mass. The waves downward pressure on the reaction mass will continue to push it downward relative to the buoys and due to the mass tanks relative inertia in the water it will be slow to 'recover' to its buoyant position.

In the second embodiment, the buoys may work in tandem as described above, however where the buoys are connected to the reaction mass by a respective crank arrangement, such offers the opportunity for each buoy to operate and create power independently. Here each buoy would recover to its stroke start position by virtue of the gravitational force acting upon the buoy/linkage /crank/linkage and by ensuring that the return stroke would have minimal resistance from an energy conversion device or pump in a return direction thereof, e.g. by a ratchet mechanism or a return valve in a hydraulic ram assembly.

Preferably the reaction mass is tethered to a fixed structure, which may be provided on (or may comprise) the sea bed. Said fixed structure may a fixed object, such as an offshore platform, wind farm offshore towers or any other substantially stationary and suitably massive anchor point. The reaction mass may be tethered to said fixed structure by one or more elongate members. A power take off means may be associated with said one or more members to extract and/or utilise useful energy from relative movement between the reaction mass and said fixed structure due to wave motion and/or tidal effects.

Preferably the apparatus is slack tethered from an anchor point on the reaction mass, preferably located adjacent to at least one bottom corner of the reaction mass, or jib extension mounted thereon, to a fixed anchor point provided, for example, on the sea-bed. Such anchoring will enable the complete apparatus to be maintained normal to wave and tide direction and facilitate drift and extreme weather conditions.

Alternatively, the apparatus may be rigidly tethered to a fixed structure via an energy conversion device, to facilitate the extraction of energy due to the motion of the apparatus with respect to the fixed structure. Said fixed structure may a fixed object, such as an offshore platform, wind farm offshore towers or any other substantially stationary and suitably massive anchor point. The reaction mass and/or the first and second buoys may be profiled / shaped and/or provided with control surfaces, such as keels or fins, to ensure that they can be maintained normal to wave and wind direction and further to take advantage of wind to orientate to whole assembly normal to maximum wave, swell and wind direction in order to also maximise power output.

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

Figure 1 is a schematic illustration of an apparatus for extracting useful energy from wave motion according to a first embodiment of the present invention;

Figure 2 is a schematic illustration of a wave energy extraction apparatus according to a second embodiment of the present invention

As shown in Figure 1, an apparatus for extracting useful energy from wave motion according to a first embodiment of the present invention comprises first and second buoys 10,20 arranged to float on the surface of the water, said buoys 10,20 being interconnected by means of a cable 30, said cable 30 passing over guide pulleys 42,44 provided on jib extensions on the lower corners of a submerged reaction mass 40 in the form of a truncated pyramidal tank.

A power take off module (PTO) 50 will be attached to the base of the reaction mass 40 and may comprise a combination of hydraulic rams in a sealed casing connected to a hydraulic accumulator, generator and control systems within the power module via high pressure lines for converting motion of the buoys and reaction mass due to wave motion into useful energy. The power take off module may be combined into a single module that can be visualized as a long vertical dual skinned box that would drop into a hole of similar clearance fit dimensions in the centre of the reaction mass. The reaction mass 40 therefore may act as a platform for accommodating a 'power module'. This will have the majority of the sensitive components in a water tight removable module attached to the top of the reaction mass for ease of maintenance and replacement. Alternatively the cable 30 may be operatively connected to a pump unit or compressor unit mounted on the reaction mass whereby the motion of the buoys and reaction mass due to wave motion may be utilised to pump or compress a fluid or a gas, thus avoiding the need for an external power source.

The reaction mass assembly, comprising the reaction mass 40 and its associated components (buoys 10,20, linkages/cable 30, and power take off module 50 or pump or compressor unit), may be 'slack anchored' from an anchor point 62 on the apparatus adjacent to a bottom corner of the reaction mass or jib extension mounted thereon to the sea bed or fixed object by a mooring line 70 connected to the reaction mass, preferably adjacent one side of the reaction mass.

To counter any tendency for the reaction mass assembly to be pulled from its optimal vertical axis and to assist its ability to be normal to the direction of the waves, the reaction mass assembly may have a substantially central anchor point. Alternatively, as shown in the drawings, the reaction mass may comprise a rectangular truncated pyramid. This shape provides greater resistance / reaction to the buoy turning moments and more naturally aligns the reaction mass normal to wave direction due to 'offset' mooring via an ellipse shaped anchor points 62, 64 located on the bottom corner of the reaction mass or the jib extensions thereon adjacent the guide pulleys 42,44 of the cable 30.

A sliding ring on the anchor line may be provided for taking up a position on the ellipse relative to the angle of the line, therefore allowing the reaction mass to remain at its correct orientation. The orientation of the ellipse shaped anchor point may be such that it will enable the whole apparatus to take up a 'drift orientation' normal to wave action - in turn ensuring that the first and second buoys are respectively located at the wave peak and wave trough positions for maximum power transfer.

In an alternative embodiment, a portion 90 of the reaction mass assembly may be hard anchored to a fixed anchor point 120, possibly provided on the sea bed 130, via a fixed beam 110 attached to an energy conversion device, pump or compressor, such as a dual acting hydraulic ram assembly 100 fixed to the base 90 of the reaction mass assembly, to extract and/or utilise energy from the movement of the reaction mass assembly with respect to said fixed anchor point due to wave, tide and swell motion. The reaction mass remains substantially fixed with respect to the differential movement of the buoys due to wave height displacement. The fixed beam 110 and hydraulic ram assembly 100 will have an overall length such that at high tide and maximum wave height, the linkage will be as vertical as anchoring constraints allow with respect to its anchor point in order to capture the maximum component of mass displacement. At low tide the reaction mass will adopt a position governed by the length of the fixed beam and hydraulic ram assembly depending upon wind and sea current directions and adopt a lesser angle giving a reduced power mass displacement component.

In a further embodiment, the fixed anchoring point 120 may comprise an existing wind turbine tower or oil or gas or desalination tower or other offshore structure, and include a boss on a guide ring that can rotate near the base of the tower or upon which an anchor can slide, allowing the whole apparatus to 'rotate' to a position governed by wave, wind, tide and swell. The fixed beam and hydraulic ram assembly length may be arranged be such that, at high tide, the assembly will not come into physical contact with the tower, avoiding the risk of damage to either assembly due to such physical contact. The ring guide may have locating points and locking points pre-fabricated into the base of the tower such that the ring guide, together with rotating ring and boss, can be either fitted pre installation or 'dropped' over the tower top during scheduled maintenance / replacement of components mounted on the tower, such as a wind turbine assembly.

A further variation of this embodiment will enable the whole reaction mass assembly to be up wave and up wind of a wind turbine or other tower such that the reaction mass assembly will additionally protect the tower from normal and potentially harmful resonant components of wave and wind by dissipating much of the energy of said components into the reaction mass assembly and therefore away from the upper reaches of the wind tower where such components have the largest moment with respect to the towers anchor point.

A further variation again will allow the whole reaction mass assembly due to its inherent stability to be engineered to enable it as a floating base for a wind tower or other similar offshore structure.

The submersion depth of the reaction mass 40, determined by its buoyancy, may be governed by the ratio of sea water to air contained within the reaction mass (like a submarine). During manufacture, and up to the point of deployment, the reaction mass will only have air inside, or may have a predetermined amount of ballast, such as concrete, whereby the reaction mass can float to a location where it is desired to be deployed. During a setting to work phase of the deployment process, once the first and second buoys have been attached to the reaction mass, the reaction mass tank will be filled with enough water or other relatively dense material, such as concrete, to just about submerge it. The depth submerged will govern the tension maintained between the first and second buoys and the tension should be such that all buoys are just held in tension. The depth to which the reaction mass is submerged and the length of the cable 30 used to connect the buoys 10,20 to the reaction mass and to each other may be selected to suit the prevailing wave conditions.

The submersion level of the reaction mass 40 may be governed by either filling with more water or other relatively dense material to make it sink more or by pumping air into the tank to force water out. An inflatable air bag may be provided on or within the reaction mass, whereby said bag may be filled with air to adjust the buoyancy of the reaction mass by forcing out the 'more dense' water and therefore decrease depth. This technique may be used to 'trim' the assembly when setting to work, subsequent 'in situ' maintenance and recovery for base workshop repairs etc. The tank may be initially at least partially filled with a dense material, such as concrete, to provide ballast for the reaction mass.

The tether length between the first and second buoys 10,20, governed by the length of the cable 30, may be set prior to the reaction mass 40 being filled to an appropriate level with water. As the reaction mass is filled, it will take up the slack of the cable 30 until the buoys 10,20 are 'just' held in tension. This arrangement is self-governing with respect to sea level and tidal action.

The semi-submerged reaction mass 40 will continually seek to return to its nominal depth about a median position dictated by the ratio of water to air. Exact ratios will depend to a small degree upon local water density and changes in atmospheric pressure

The geometry of the reaction mass 40 may be such that it will maintain vertical stability and be resistive to upward movement. The reaction mass 40 preferably comprises a tank having a truncated pyramid shape. Such shape gives the reaction mass greater mass towards its base. The shape also enables a greater mass of surrounding water to be above the sloping faces therefore aiding resistance to turning moments generated by the 'pull' of the first and second buoys. Any residual buoyancy within the reaction mass will be maximized at its narrower top also helping to maintain vertical stability. The mass of the tank will enable stability of position relative to the forces generated by the buoys 10,20. Alternatively, the reaction mass 40 may comprise a rectangular truncated pyramid. This shape provides greater resistance / reaction to the buoy turning moments and more naturally aligns the reaction mass normal to wave direction due to 'offset' mooring via an ellipse shaped anchor point.

Reaction plates 46,48 may be suspended beneath the reaction mass 40, preferably adjacent the pulleys 42,44, to provide a drag force in opposition to the vertical motion of the respective buoy. Each reaction plate comprises a substantially flat horizontal plate or elongate member mounted on a vertical support pole to be connected to the reaction mass. Such reaction plates 46,48 may only be required in certain sea states or for certain wave conditions.

The apparatus is highly scalable in size and therefore power output is only limited by the sea state and the mechanical strength of materials and components used. Useful energy can be generated and/or wave energy can be utilised despite rough conditions due to the buoyancy forces of the buoys causing them rise in opposition to the reaction mass. Further energy can be captured and/or utilised by capturing the motion of the reaction mass relative to the sea bed

The submersion level of the reaction mass is self governing in all tide conditions as the buoys' upward buoyancy forces are in opposition to the reaction mass's downward force and inertia. This enables the whole apparatus to have relative stability and facilitates slack mooring. Slack mooring assists the apparatus to withstand ' 100 year' storm conditions. Slack mooring further facilitates the reaction mass to be 'normal' to wave direction therefore maximizing energy capture.

In the case of fixed beam mooring, the length is such that in 'maximum' conditions - the mooring beam length is adequate to cope. However in 100 year sea conditions the overall system strength will enable total submersion and still generate useful power due to the differential buoyancies and relative movement of the whole assembly WRT fixed anchor point (where applicable).

The buoys 10,20 may be positioned at up to average half-wave pitch distance apart to maximize energy capture, said positioning being determined by the dimensions of the reaction mass 40 and the location of the pulleys 42,44 thereon. Alternatively, the optimal pitch of the buoys 10,20 with respect to the reaction mass 40 may need to be tuned in line with the relative sizes of the buoys, reaction mass and wave conditions

The reaction mass 40 can behave as a float / buoy until it is commissioned therefore easing manufacture and deployment.

The mass of the reaction mass 40 may primarily comprise of water. This is readily available and therefore the mass of the reaction mass can be initially set by filling the reaction mass with the requisite volume of water to maintain the buoys in tension. As the reaction mass sinks it will brings the buoys 10,20 into tension via the linkages, 30 thereby bringing the overall system into equilibrium - such that wave and tidal action displacing the buoys will cause reciprocation of the linkages thereby generating useful power.

The volume of the reaction mass (after trials) can be rapidly set by e.g. inserting a polystyrene (or other buoyant material) body into the tank of the volume required to enable just enough water to enter the tank for optimal float / sink depth.

The buoyancy of the reaction mass 40 can be reduced by filling with more water. The buoyancy of the reaction mass can be increased by pumping air into the reaction mass itself or into an air bag provided therein or thereon. The buoyancy of the reaction mass 40 is preferably adjusted to allow the reaction mass 40 to sink to a sufficient depth that the reaction mass is not affected by the waves at the surface to which the buoys 10,20 are exposed.

The cable 30, tether or other linkages connecting the buoys to the reaction mass can be pre- connected prior to final deployment (submersion of the reaction mass) simplifying the set to work process. In the embodiment shown in Figure 1 , the twin connected buoys ensure reciprocation and that each buoy can use the other as a 'return' mechanism for the next upward 'power' stroke.

A further embodiment of the present invention is illustrated in Figure 2. In such embodiment, each of the first and second buoys 10,20 is connected to the reaction mass 40 via respective flexible or rigid linkage 200,202 connected to an end of a respective crank arm 204,206 pivotally mounted on a corner of the reaction mass or a jib connected thereon for pivotal movement about a substantially central fulcrum. Second ends of each crank arm

204,206 are linked by a respective further flexible or rigid linkage 208, 210, said further linkages cooperating with a power take off module or pump or compressor unit 50 mounted on the base of the reaction mass 40. The apparatus is otherwise similar to the embodiment shown in Figure 1.

The further embodiment shown in Figure 2 may be arranged such that the buoys 10,20 are connected to the power take off unit 50 to be constrained to move out of phase with one another, as with the first embodiment shown in Figure 1. Alternatively the buoys 10,20 may be connected to the power take off unit 50, via the respective linkage and crank arm assemblies, to allow the buoys 10,20 to move independently. Such arrangement enables movement of the reaction mass 40 due to waves, as well as the movement of the buoys 10,20, to be converted into useful energy or work. For example, the reaction mass 40 may be arrange to located in the trough of a wave while the buoys 10,20 are located in respective wave crests such that the reaction mass 40 and buoys 10,20 move out of phase with each other. In such embodiment, the reaction mass would be submerged to the shallower depth than with the previous embodiments and the reaction plates 46,48 would be omitted.

The apparatus according to the preferred embodiments of the present invention may be used to convert wave energy into useful energy, such as electricity, which may be utilised locally or remote from the apparatus or may be stored for later use. Alternatively the apparatus may be used to pump or compress a fluid or a gas using wave energy as a power source. For example, the apparatus may be used as an offshore pump or compressor in the requistration of carbon dioxide into emptied or depicted oil and/or gas fields.

The invention is not limited to the embodiment(s) described herein but can be amended or modified without departing from the scope of the present invention.

Claims

1. An apparatus for extracting useful energy from wave motion, said apparatus comprising spaced apart first and second buoys arranged to float on or adjacent the surface of the water, each of said first and second buoys being connected to a submerged reaction mass by means of a respective linkage, whereby relative motion between each of the first and second buoys with respect to the reaction mass due to the action of waves is converted into useful energy.

2. An apparatus as claimed in claim 1, wherein the first and second buoys are arranged to capture the differential energy between a wave peak and a wave trough, the first and second buoys being connected to the reaction mass by said linkages such that the first and second buoys can be moved up and down by the waves, out of phase with each other, causing reciprocating motion of at least part of each linkage with respect to the reaction mass or, alternatively, wherein the first and second buoys are connected to the reaction mass by said linkages such that the buoys may move independently or in phase with one another whereby relative motion of the first and second buoys and the reaction mass under the action of wave motion may be converted into useful energy.

3. An apparatus as claimed in claim 2 wherein said linkages are operatively coupled to at least one pump, compressor or other energy conversion mechanism provided on the reaction mass for converting wave motion into useful energy or work.

4. An apparatus as claimed in any preceding claim, wherein said linkages comprise an elongate flexible linkage extending between said first and second buoys via the reaction mass.

5. An apparatus as claimed in claim 4, wherein said flexible linkage is maintained under tension by the action of said reaction mass upon said flexible linkage and the forces acting on the ends of the flexible linkage due to the buoyancy of the first and second buoys.

6. An apparatus as claimed in claim 5, wherein the flexible linkage is mounted on the reaction mass by means of one or more pulley wheels or guides provided on the reaction mass.

7. An apparatus as claimed in claim 6, wherein said guide means are provided at the lower side regions or corners of the reaction mass or upon a jib extension mounted thereon.

5 8. An apparatus as claimed in any of claims 4 to 7, wherein said flexible linkage comprises a cable, rope or other elongate flexible member, formed from a suitable material, such as steel or a polymeric material.

9. An apparatus as claimed in any of claims 1 to 3, wherein each linkage comprises an 10 elongate member and a crank arrangement pivotally mounted on the reaction mass.

10. An apparatus as claimed in claim 9, wherein each elongate member comprises a rigid member or beam.

15 11. An apparatus as claimed in claim 9, wherein each elongate members comprises a flexible member, such as a cable.

12 An apparatus as claimed in any of claims 9 to 11, wherein the crank arrangements are interconnected whereby the buoys are linked via the respective linkages such that the 0 first and second buoys members are constrained to move with respect to the reaction mass out of phase with one another.

13. An apparatus as claimed in any of claims 9 to 11, wherein each crank arrangement is independently pivotally mounted on the reaction mass to enable independent movement of 5 each buoy with respect to the reaction mass.

14. An apparatus as claimed in any of claims 9 to 13, wherein each crank arrangement comprises an elongate member pivotally mounted on the reaction mass, or on a jib extension mounted thereon for pivotal motion about a fulcrum, a respective buoy being connected to a 0 first end of the respective elongate member, the opposite ends of the elongate members being linked by a rigid or flexible linkage, said linkage cooperating with at least one pump, compressor or other energy conversion mechanism provided on the reaction mass for converting wave motion into useful energy.

15. An apparatus as claimed in claim 14, wherein each crank arrangement is coupled to said at least one pump, compressor or other energy conversion mechanism by means of gearing.

5 16. An apparatus as claimed in any preceding claim, wherein said linkages are operatively coupled to one or more energy conversion devices, such as an electrical generator, for extracting energy from said wave motion.

17. An apparatus as claimed in any of claims 1 to 15, wherein said linkages are 10 operatively coupled at least one pump or a compressor for pumping or compressing a fluid or a gas.

18. An apparatus as claimed in any preceding claim, wherein the reaction mass comprises a tank defining a closed chamber.

15

19. An apparatus as claimed in claim 18, wherein the reaction mass is at least partially filled with concrete, or other dense material.

20. An apparatus as claimed in claim 18 or claim 19, wherein filling means are provided 20 to enable the chamber of the reaction mass to be at least partially filled with seawater, as required, to enable adjustment of the buoyancy of the tank.

21. An apparatus as claimed in any of claims 18 to 20, wherein the reaction mass incorporates or comprises an inflatable air bag for adjusting the buoyancy of the tank and/or

25 for recovering the reaction mass.

22. An apparatus as claimed in claim 20, wherein said inflatable bag is mounted within the reaction mass.

30 23. An apparatus as claimed in claim 22, wherein the sides of the reaction mass diverge outwardly towards a base region of the reaction.

24. An apparatus as claimed in claim 23, wherein said tank is in the form of a hollow truncated pyramid.

25. An apparatus as claimed in any preceding claim, wherein the reaction mass is tethered to a fixed structure.

5 26. An apparatus as claimed in claim 26, wherein said fixed structure is mounted on or located on the seabed.

27. An apparatus as claimed in claim 26, wherein said fixed structure comprises a relatively massive floating structure.

10

28. An apparatus as claimed in any of claims 25 to 27, wherein said fixed structure comprises a fixed object, such as an offshore platform, wind farm offshore towers or any other substantially stationary and suitably massive anchor point.

15 29. An apparatus as claimed in any of claims 25 to 28, wherein the reaction mass is tethered to said fixed structure by one or more elongate members, a power take off means being associated with said one or more members to extract and/or utilise useful energy from relative movement between the reaction mass and said fixed structure due to wave motion and/or tidal effects. 0

30. An apparatus as claimed in any preceding claim, wherein the reaction mass and/or the first and second buoys are profiled / shaped and/or provided with control surfaces, such as keels or fins, to ensure that they can be maintained normal to wave and wind direction and further to take advantage of wind to orientate to whole assembly normal to maximum 5 wave, swell and wind direction in order to also maximise power output.

31. An apparatus as claimed in any preceding claim, wherein at least one reaction body, such as a substantially horizontal reaction plates, is suspended beneath the reaction mass to enhance the stability of the reaction mass and resist vertical movement of the reaction mass 0 within the water.

32. An apparatus as claimed in claim 31, wherein a plurality of said reaction bodies are suspended beneath the reaction mass, preferably at least one reaction body being provided to be directly beneath each one of said buoys to provide a drag force in opposition to the vertical motion of the respective buoy.