GB2594095A

GB2594095A - Wave energy device

Info

Publication number: GB2594095A
Application number: GB2005635.4A
Authority: GB
Inventors: Dawson Topher
Original assignee: Individual
Current assignee: Individual
Priority date: 2020-04-17
Filing date: 2020-04-17
Publication date: 2021-10-20
Anticipated expiration: 2040-04-17
Also published as: GB2594095B; GB202005635D0

Abstract

Disclosed is a wave energy extraction device comprising a plurality of bags (12) of a flexible material which is impervious to water, each bag being connected by a tether (13) to a ballast item and a baffle (14) which in use is at least partly horizontal, each bag is also connected to a turbine module (20), each flexible bag in use contains sufficient gas, when only partly inflated, to provide buoyancy sufficient to support the ballast item and the baffle (14) immersed in calm water with the flexible bag floating in the calm water, partly being above the surface. The bags and turbine may be connected by two tubes, where each tube has one flow valves to ensure a singular direction of flow from the bags through the turbine and back to the bags.

Description

Wave Energy Device The present invention relates to a wave energy device, that is to say a device for obtaining energy, in particular electrical energy, from waves on water, for example on the sea.

Wave energy devices have been proposed for many decades. By way of example GB 1 580 805 (M.J.French) describes a wave energy device with an elongated flexible enclosure, divided into compartments along its length, and attached to a rigid beam. A problem with this device is the risk of abrasion and wear at the attachment between the flexible material and the rigid beam. As another example, GB 2 498 826 (S.D.Lewis) describes a device with floating flexible bags linked by tubes to a turbine/generator or pump, and with the tubes staked to the sea bed. However, staking the tubes to the seabed makes it difficult for the device to cope with tidal depth variations.

According to the present invention there is provided a wave energy device comprising a plurality of flexible bags formed of a flexible impervious material, each bag being connected to a ballast item and to a baffle which in use extends at least partly horizontally, and each bag being provided with a tube communicating with a turbine module, each flexible bag in use containing sufficient gas, when only partly inflated, to provide buoyancy sufficient to support the ballast item and the baffle plate immersed in calm water with the flexible bag floating in the calm water, partly being above the surface.

The flexible bags might be called bladders, as they are sealed enclosures apart from connection to the tube. The device would typically be installed in an area of sea, lake or reservoir in which suitable waves are expected, and secured in position by one or more moorings. As waves pass by the device, the baffles inhibit vertical motion of the bags, so there are changes in pressure in the bags. As long as the phase of the wave is different for different bags, air will flow from one bag to another, through the turbine module. The turbine module contains a turbine which is caused to turn by the flow of air, so the turbine can be used to provide energy for example by connecting it to a generator.

Each bag may be connected to the corresponding ballast item and the corresponding baffle by at least one tether comprising a strap or cable, or a rigid rod, as long as the connection is such that the inclination of the baffle from the horizontal or the inclination of the tether from the vertical can freely vary. The length of the tether affects how deep the baffle is below the surface, and It is beneficial if the tether is of such a length that the baffle is deep enough to be in water which is substantially still even when there are waves on the surface. On the other hand the tether should not be too long, as this would imply longer tubes to carry gas between the bags and the turbine module, leading to increased gas friction losses. The tubes are led downwards and join the turbine module low down in order that the connections have the least strain due to wave motion. In one embodiment the tethers should be of length between 1 m and 10 m, more preferably between 2 m and 6 m, where energy is to be obtained from waves of wavelength up to about 20 m; the tethers should be longer if longer wavelengths are to be made use of.

In the presence of waves, the baffles typically rotate about a horizontal axis to only a small extent, usually no more than 10°, but the bags may move quite a lot in the horizontal direction when waves hit them, so the orientation of the tether relative to the baffle, where they are connected, will vary by a greater amount, for example +/-200. The freedom of the bags to move when hit by waves is expected to enable the bags to survive when fabric bags attached to rigid structures would fail.

If the baffle is just deep enough to be still in the wave regime for which the wave energy device is optimised, then in much bigger waves which may damage the device the baffles will to some extent rise and fall with the bigger wave, and thus stress the device less.

The baffle connected to a bag may be a rigid element, such as a steel plate or a concrete plate, and so may be referred to as a baffle plate, or it may comprise a number of substantially rigid elements linked together, arranged to remain substantially in a plane and to inhibit vertical movement. Alternatively the baffle may comprise a rigid frame, for example a square, triangular or hexagonal frame, covered by fabric; the fabric may define a pyramidal shape above the frame leading to the connection to the bag; and may define a pyramidal shape below the frame to carry loose ballest such as sand or gravel. The baffle may comprise such a fabric-covered rigid frame of circular shape if there is no requirement to link adjacent straight edges of adjacent baffles.

Each bag may be of a substantially inextensible but flexible sheet material, for example a woven fabric laminated to one or more thin plastic layers. The sheet material used to make inflatable dinghies or ribs would for example be suitable, as it is not affected by immersion in water. It may for example be of polyurethane fabric, polyvinyl chloride (PVC) fabric, or a sheet of chlorosolfonated polyethylene (CSPE), which is a type of synthetic rubber (CSPE), such as that sold under the brand (Hypalon Trade mark).

The shape of the bag is not critical, although a suitable shape has a hemispherical or similarly curved top part, and a lower part which tapers conically down to connections to the tube and to to the ballast item and the baffle. Such a shape, which resembles that of a hot air balloon, produces the least stress and weight of material for the enclosed volume. Alternatively the bags might be of generally cylindrical form, with rounded or conical ends, or of generally rectangular form, like a lifting bag.

The turbine module may be arranged to float. It may define a flow duct and a turbine mounted to rotate within the flow duct, the flow duct communicating at opposite ends with an inlet chamber and an outlet chamber. Each tube may be in communication with the inlet chamber and with the outlet chamber through respective one-way valves that are oriented in opposite directions, such that gas can flow from the tube into the inlet chamber through one valve and can flow from the outlet chamber to the tube through the other valve. This ensures that the gas flows in a consistent direction through the turbine, flowing out from a bag that is at higher pressure and into a bag that is at lower pressure.

The ballast item and the baffle that are connected to a bag may be separate, or may be a single component that serves both purposes. For example a plate of reinforced concrete, if of suitable dimensions, may act as the ballast item and also as the baffle.

In one embodiment the device includes a multiplicity of bags and baffles arranged as a line, or as an array, adjacent baffles in the line or the array being flexibly linked to each other. For example all the baffles in an array may be square, or all the baffles may be of equilateral triangle shape, and in either case adjacent straight edges of adjacent baffles may be linked to each other for example by a hinge mechanism or by rope loops, so the inclination from the horizontal of adjacent baffles may differ. Where the baffles and the bags are arranged as an array, the gaps between adjacent baffles are desirably of width less than 10% of the width of the baffle; and no more than 150 mm. The flexible linkages between adjacent baffles preferably provide no bending moment; the linkages may for example be provided by ropes or plastc snap-rings passing through holes near the edges of the baffles, or by rods fitting through eye-bolts that project from the edges of the baffles, to form a hinge. The purpose of the flexible linkages is (a) so that individual baffle plates may be small enough to manufacture, handle and transport easily; (b) to enable modular assembly and disassembly of arrays onsite; and (c) to limit the bending moments which large waves would impose in the plane of the baffles.

As mentioned above, the baffle connected to a single bag may be a rigid baffle plate, or may comprise a number of substantially rigid elements linked together, arranged to remain substantially in a plane and to inhibit vertical movement. Similarly, where the device includes a multiplicity of bags arranged as a line or as an array, with the baffles linked flexibly to each other to form a baffle layer, that entire layer may be made of multiple substantially rigid elements linked together. For example the baffle layer may be formed of multiple tyres that are interlinked by ropes, and with a fabric sheet covering the layer of tyres. Such a baffle layer may include concrete blocks cast onto parts of the ropes, to The turbine module may float within the array, and may also be provided with a baffle that is flexibly linked to adjacent baffles in the array. The turbine module in this case may be at the centre of the array. For example a square array may consist of a three-by-three array of square baffle plates, with a turbine module connected to the baffle plate at the centre of the array, and with eight flexible bags, one bag connected to each of the other baffle plates of the array. The flexible linkage of the baffle plates to each other ensures that although any one bag can move up and down to some extent with the waves, vertical movement of the array of baffle plates as a whole is minimal. By way of example if each baffle plate, in plan view, is 2 m square and is on average 3 m below the surface, then the weight of water above one baffle plate is about 12 tonnes, so the weight of water over the array is about 108 tonnes.

A wave power system may comprise several such arrays arranged next to each other, with the baffles of one array being flexibly linked to the baffles of an adjacent array.

So a large-scale system might consist of 50, 100 or 200 arrays linked to each other in this way. The entire system may be provided with anchors or other mooring devices at positions around its periphery.

Where a device comprises a multiplicity of bags and baffles arranged as a line or in an array, each bag may instead be connected by a linkage to a respective junction member, and the junction members being interlinked by struts to form a framework. This underwater framework holds the bags into position relative to one another, which may avoid the need to interlink the baffles. In this context each linkage may comprise a tube, and each junction member comprise a tube junction, and at least some of the interlinking struts comprise gas tubes. Hence the gas flows to and from the turbine module flow through at least some of the struts of the framework. In some cases the tube junction may comprise one-way valves Most wave power devices are designed to obtain energy from waves of a particular range of sizes, to suit an area of sea where they are intended to be used. As a general rule areas exposed to waves from open ocean will experience waves of greater height and wavelength than areas that are less exposed. In the Atlantic ocean near South Uist for example there is significant energy available from waves of a period between 6 and 14 s. The corresponding wavelengths can be estimated as (g/2n)T2= 1.5612, and so these periods correspond to wavelengths about 56 m to 305 m. In contrast in a more sheltered area the waves may have a period in the range 1 s to 5 s and so a wavelength between about 1.6 m and 40 m. The bags of a line or an array must be spaced apart enough that there is a significant phase difference between the bags. Hence the length of a line or the width of an array should ideally be approximately equal to the largest wavelength that is expected, or at any rate equal to the wavelength of the waves for which the device is designed. In a device to efficiently absorb energy from waves of wavelength less than say 10 or 20 m the invidual bags of an array may be interlinked by interlinking the edges of baffles. For a device to efficiently absorb energy from longer wavelengths the individual bags may be interlinked by tubes that carry the gas flows, and these tubes may for example form a framework. Such a framework may be hexagonal, formed of equilateral triangles.

The baffle is desirably deep enough to be substantially unaffected by the wave regime for which the wave energy device is optimised. As a wave passes, the water at different depths below the surface moves in circular paths, the amplitude of this movement decreasing exponentially with depth, as the amplitude at depth d for a wave of wavelength A is exp(-2nd/ A) times the suface amplitude. So to get down to 10% of the surface amplitude the depth must be about a third of the wavelength.

The invention will now be further and more particularly described, by way of example only, and with reference to the accompanying drawings, in which: Figure 1 shows a perspective view of a wave power device of the invention; Figure 2 shows a schematic view of the turbine module of the device of figure 1; Figure 3 shows a plan view of an alternative wave power device of the invention; Figure 4 shows a perspective view of a part of the device of figure 3, including a valve box; Figure 5a shows a schematic sectional view of the valve box of figure 4; and Figure 5b shows a perspective view of an internal diaphragm of the valve box shown in figure 5a.

Referring now to Figure 1, a wave energy device 10 comprises eight flexible buoyant bags 12 (only seven are visible), each connected by a rope tether 13 to a square baffle plate 14 made of reinforced concrete, each tether 13 being attached to the centre of the square baffle plate 14, so each baffle plate 14 is in a substantially horizontal plane. The bags 12 are of a flexible and substantially inextensible fabric such as PVC fabric or Hypalon, with a rounded top and tapering downward to the point of attachment of the tether 13. Each bag is about half filled with air, the dimensions being such that the bag 12 provides enough buoyancy to support the baffle plate 14; each bag 12 projects slightly above the water surface 16 which is shown schematically as having waves. In each case the weight of the baffle plate 14 is sufficient to ensure the tether 13 remains taut; the baffle plate 14 itself is heavy enough to act as the required ballast item.

The device 10 includes nine baffle plates 14, arranged as a three-by-three array, and adjacent straight edges of adjacent baffle plates 14 are flexibly linked together by rope ties 18 (four are shown schematically), so there are narrow gaps between the adjacent edges. In practice ropes may be cast into the concrete that forms a baffle plate 14, protruding from the centre of a plate edge to be tied to the rope protruding from an adjacent baffle plate 14.

A cylindrical turbine module 20 is connected by a tether 21 above the central baffle plate 14 of the array, floating upright, so the bags 12 surround the turbine module 20. There are eight ports 22 (only one is shown in Figure 2) around the lower end of the turbine module 20, and each bag 12 communicates through a flexible hose or tube 24 to a corresponding one of the ports 22. At least in calm water the top of the turbine module 20 is above the surface; this may enable access to the module 20 for maintenance.

Referring now to Figure 2, the turbine module 20 comprises an outer tubular casing 25 which is sealed at both ends, and a concentric inner tube 26 which is shorter and open at both ends, the bottom end of the inner tube 26 being supported by and sealed to an annular bulkhead 27 about an eighth of the length of the outer casing 25 above the bottom of the outer casing 25; and the top end of the inner tube 26 is spaced clear of the top end of the outer casing 25. A turbine 30 is mounted near the top of the inner tube 26, so there is minimal clearance between the wall of the inner tube 26 and the blades of the turbine 30, and directly drives a generator 31. A power output cable 32, in this case, extends from the generator 31 and emerges from the bottom of the outer casing 25.

There are eight ports 22 around the bottom of the turbine module 20, but only one is shown for clarity. Each port 22 is connected to a hose or tube 24 as mentioned above, and the port 22 is a short branched tube that connects via a one-way valve 33a with the chamber 34 below the bulkhead 27, and connects via a one-way valve 33b with the annular space or chamber 36 surrounding the inner tube 26, above the annular bulkhead 27. These one-way valves 33a and 33b are in opposite orientations. Hence If the air pressure in any of the bags 12 is above the pressure in the chamber 34, then air can flow from those bags into the chamber 34, so feeding air upstream of the turbine 30; while if the pressure in any of the bags 12 is below the pressure in the annular chamber 36, then air can flow from the annular space 36 downstream of the turbine 30 into those bags 12. Thus as waves pass the device 10, air is caused to flow from the higher-pressure bags 12 to the lower-pressure bags 12.

It will therefore be appreciated that the device 10 will function in this way only if, within the array of bags 12, different bags 12 are subjected to different phases of the wave.

So, for example, if waves of a wavelength 5 m are to be taken advantage of, then the width of the array should be of a size similar to 5 m; for example with baffle plates 14 that are about 1.5 m or 2 m square; while to extract energy from a wave of wavelength 10 m would suggest a larger device 12, for example with baffle plates 14 that are for example 3.5 m or 4.0 m square.

Thus the bags 12, about half-filled with air, float with their middle at about the wave mid height, being weighed down by the weight of the baffle plates14; the baffle plates 14, by virtue of their shape and horizontal orientation, also restrain the bags 12 vertically so they do not move up and down significantly with passing waves. Groups of eight such bags 12 are moored in a wave field far enough apart to receive different phases of a wave. Each bag 12 is connected by the tube 24 to the turbine module 20 at the centre of the array, connecting at a port 22 to two valves 33a and 33h. One valve 33a feeds high pressure air into a high-pressure chamber 34 that feeds air to the turbine 30. Hence the pulses of elevated-pressure air from bags 12 being squeezed by a wave crest are rectified and smoothed to flow through the turbine 30. Lower-pressure air that has passed through the turbine 30 exits through the other valve 33b, to fill any bags 12 that are at a trough of the wave. So the air is recycled between high pressure bags 12 and low pressure bags 12 as waves pass. Any heat generated by the turbine 30 or the generator 31 is carried away by the air flow and dissipated to the surrounding water.

The baffle plates 14, as they are flexibly linked to each other, form a continuous horizontal plane in still water, which engages such a large mass of water that even when there are waves it moves vertically very little. The baffle plates may be moored by one or more mooring warps to an anchor on the seabed. Such an array is desirably moored at one point only, so it can swing to align with the waves; but if multiple arrays are joined together to form a large system, it is preferable to provide multiple moorings, so the system doesn't swing.

In heavy weather the waves may impose a significant horizontal force on the device 10, but that increases the tension in the mooring, and the downward component of that mooring tension may be arranged to overcome the buoyancy of the bags, so they partially or completely submerge. This can assist survival of the device 10 in the event of a storm.

The device 10 may include means to adjust the buoyancy of the device during operation, by pumping air in or out of the air circuit. The high pressure chamber 34 may include a blow-off valve which is set at a pressure the bags 12 can stand, so that if there is excess pressure due to a large wave, the excess pressure is vented to the low-pressure side, downstream of the turbine 30, so that the generator 31 is protected from overspeed. Under normal operation the field of the generator 31 may be varied to match the load to the resource.

It will be appreciated that baffle plates 14 may differ in their details, depending on the material of which they are made, and their size. For example a thin baffle plate of steel may be combined with a block of lead to act as a ballast item; as another option baffle plates that are 3.0 or 3.5 m square may be of reinforced concrete, comprising a flat base plate of that size, with reinforcing ribs on the top and/or bottom face that extend from the middle to each corner, and with a lifting eye at the middle, to which the tether 13 would be connected, and the thickness of the concrete, and so its weight, may be sufficient that no separate ballast item is needed. And as another alternative, in place of an array of baffle plates 14, there may be a mesh of ropes interlinking multiple tyres and concrete blocks, and covered with a shet of fabric. The tethers 13 must be strong enough to support the baffle and ballast during operation, and so may be steel cables or steel chains, where large baffle plates are used. However, in many cases the tethers 13 may by of a suitably strong rope of a synthetic material. For example a HDPE (Dyneema) rope only mm diameter has a strain of 127 tonnes, and synthetic rope is commercially available up to breaking loads of over 500 tonnes.

Referring now to Figure 3, this shows an alternative wave energy device 40 in plan view; the bags 12 (only one is indicated, schematically), may be the same as those described above. Referring also to Figure 4, below each bag 12 a pipe 42 extends down to a valve box 44. The pipe 42 tethers the bag 12 to the valve box 44. From the underside of the valve box 44 is suspended a baffle 45 (described below). There are eighteen bags 12 arranged in a hexagonal array with a turbine module 46 at the centre. The corresponding eighteen valve boxes 44 and the turbine module 46 are interconnected by gas pipes 48, so that the valve boxes 44 and the gas pipes 48 form a generally horizontal framework around and connected to the turbine module. This framework of equilateral triangles holds the bags 12 and the baffles 45 in their relative positions, while allowing them to move with the waves; it is substantially rigid in the plane of the array but there is some compliance orthogonal to that plane. Some of the gas pipes 48 (shown in solid lines) are supply pipes arranged to carry higher-pressure gas away from the periphery of the array and towards the turbine module 46, while the other gas pipes 48 (shown in broken lines) are return pipes arranged to carry lower-pressure gas from the turbine module 46 outward towards the periphery of the array. The six gas pipes 48 that connect directly to the turbine module 46 may be of a larger diameter than the other gas pipes 48, as they typically carry larger gas flows.

The turbine module 46 may be substantially equivalent to the turbine module 20 described above with reference to figure 2, except that the one-way valves 33a and 33b are not provided. Instead the supply gas pipes 48 communicate directly to the chamber 34 upstream of the turbine 30, while the lower-pressure return pipes 48 communicate directly to the annular space 36 downstream of the turbine 30.

Referring to Figure 4, the baffle 45 in this embodiment comprises a circular ring SO of plastic pipe covered above and below with circular fabric sheets 52 which are sewn together or bonded around their periphery; a strut 53 of plastic tube with rounded end-caps extends between the centres of the two fabric sheets 52 so they are taut and conical. An eyebolt 55 attached to the top of the strut 53 projects through the centre of the top sheet 52, to which a tether 56 is attached. The other end of the tether 56 is attached to the underside of the valve box 44. The lower fabric sheet 52 is partly filled by a layer of ballast material 58, such as shingle or sand, By way of example the diameter of this baffle 45, that is to say the outer diameter of the ring SO of plastic tube, may for example be 10 m, 20 m or 30 m. In contrast the bags 12 would be significantly smaller, for example of half that diameter or less.

Referring now to Figures 5a and 5b, the valve box 44 is a cylindrical box divided into two chambers 60 and 61 by a generally horizontal diaphragm 62. The diaphragm 62 is flat except at positions where one of the gas pipes 48 communicates with the valve box 44, where it is distorted up or down as a half cone. The supply pipes 48 are arranged to communicate with the lower chamber 60 by an upward-deformed half-cone, whereas the return pipes 48 are arranged to communicate with the upper chamber 62 by a downward-deformed half-cone. As shown in figure Sa, the pipe 42 coming down from the bag 12 extends through to the underside of the diaphragm 62 into the lower chamber 60. At the bottom end of the tube 42 is a one-way valve 66 allowing flow down into the lower chamber 60. A short curved pipe 64 leads from the upper chamber 61 ito the pipe 42, with a one-way valve 66 allowing flow from the pipe 64 into the pipe 42; this forms part of the return gas circuit. There is a one-way valve 66 at the end of each gas pipe 48, where it communicates wuth the lower chamber 60 or the upper chamber 61, so gas can flow along a supply pipe 48 only in the direction towards the turbine module 46, and so that gas can flow along a seturn pipe 48 only in the direction away from the turbine module 46 and towards the periphery of the array.

The wave power device 40 operates in substantailly the same way as the device 10 described above. As long as there are waves, and a sufficient phase difference between a wave at the positions of different bags 12 in the array, gas will flow from bags 12 at higher pressure through the turbine 30 to bags 12 at lower pressure. The gas pipes 48 may for example be of length 20 m, 50 m or even longer, so this device 40 is suitable for use with long wavelength waves. As indicated in figure 3, a system may comprise a number of these devices 40, each separately moored, but connected by cables 70 (indicated by lines of dots) to one another, to form a higher-power system.

It will also be appreciated that the device 40 may be modified for example to use a baffle plate 14 as described in relation to the device 10. The bags 12 may be provided with a rope or cable tether to the valve box 44, in addition to the pipe 42. The dimensions may differ from those mentioned above; and the length of the tethers 13 or 56 should be selected in relation to the wavelengths of the waves for which the device is optimised, to ensure the baffles are deep enough to be in water substantially unaffected by the waves; for example the tethers may be a third the length of the design wavelength.

As another modification a wave power device may consist of a turbine module 20 with only six bags 12, each bag 12 being connected by a pipe 42 to a box provided with a baffle, as in figure 4. The six boxes and the turbine module 20 can be interconnected by a hexagonal framework of gas pipes 48, forming equilateral triangles, like that shown in figure 3, but in this case the flow paths may be equivalent to those in the device 10, with only the six radial tubes 48 carrying gas, and the six tubes 48 that link adjacent boxes around the hexagon being blanked off. This simpler array does not require valves in the boxes, as the one-way valves 33a and 33b are provided in the turbine module 20; but the framework of equilateral triangles formed by the gas pipes 48 holds the bags 12 in their positions relative to one another in the array. In this example each gas tube 48 might be of length 10 m, 20 m or 50 m, so the device may be designed to suit waves of an expected wavelength.

Claims

Claims 1. A wave energy device comprising a plurality of flexible bags formed of a flexible impervious material, each bag being connected to a ballast item and to a baffle which in use is at least partly horizontal, and each bag being provided with a tube communicating with a turbine module, each flexible bag in use containing sufficient gas, when only partly inflated, to provide buoyancy sufficient to support the ballast item and the baffle immersed in calm water with the flexible bag floating in the calm water, partly being above the surface.
2. A wave energy device as claimed in claim 1 wherein the connection between the bag and the baffle is provided by a tether arranged such that the inclination of the baffle from the horizontal and of the tether from the vertical can freely vary.
3. A wave energy device as claimed in claim 1 or claim 2 wherein each bag is of a substantially inextensible but flexible sheet material, selected from a woven fabric laminated to one or more thin plastic layers, or polyurethane fabric, polyvinyl chloride (PVC) fabric, or a sheet of chlorosuifortated polyethylene (CSPE).
4. A wave energy device as claimed in any one of the previous claims wherein the turbine module is arranged to float.
5. A wave energy device as claimed in any one of the previous claims wherein the turbine module defines a flow duct and a turbine mounted to rotate within the flow duct, the opposite ends of the flow duct communicating with an inlet chamber and an outlet chamber.
6. A wave energy device as claimed in claim 5 wherein each tube is in communication with the inlet chamber and with the outlet chamber through respective one-way valves that are oriented in opposite directions, such that gas can flow from the tube into the inlet chamber through one valve and can flow from the outlet chamber to the tube through the other valve.
7. A wave energy device as claimed in any one of the previous claims wherein the ballast item and the baffle that are connected to a bag are a single component that serves both purposes.
8. A wave energy device as claimed in any one of the previous claims wherein the device includes a multiplicity of bags and baffles arranged as a line or in an array, adjacent baffles in the line or the array being flexibly linked to each other.
9. A wave energy device as claimed in claim 8 wherein the baffles are arranged in an array, all the baffles in the array are of the same size and shape with straight edges, and adjacent straight edges of adjacent baffles are flexibly linked to each other.
10. A wave energy device as claimed in claim 8 or claim 9 wherein the baffles are arranged as an array and the turbine module floats within the array, and is provided with a baffle that is flexibly linked to adjacent baffles in the array.
11. A wave energy device as claimed in claim 8, claim 9 or claim 10, wherein the baffles are moored by one or more mooring warps to an anchor on the seabed, being moored at one point only, so it can swing to align with the waves.
12. A wave power system that comprises several wave energy devices as claimed in claim 8, claim 9 or claim 10 arranged next to each other, with the baffles of one line or array being flexibly linked to the baffles of an adjacent line or array.
13. A wave power system as claimed in claim 12, also comprising multiple mooring devices at positions around its periphery, to prevent the system from swinging around.
14. A wave energy device as claimed in any one of claims 1 to 7 wherein the device includes a multiplicity of bags and baffles arranged as a line or in an array, each bag being connected by a linkage to a respective junction member, and the junction members being interlinked by struts to form a framework.
15. A wave energy device as claimed in claim 14 wherein each linkage comprises a tube, each junction member comprises a tube junction, and at least some of the interlinking struts comprise gas tubes.
16. A wave energy device as claimed in claim 15 wherein each junction member comprises at least one one-way valve.