WO2008084262A2

WO2008084262A2 - Power generation means

Info

Publication number: WO2008084262A2
Application number: PCT/GB2008/050020
Authority: WO
Inventors: Michael Andrew Woodward
Original assignee: Michael Andrew Woodward
Priority date: 2007-01-09
Filing date: 2008-01-09
Publication date: 2008-07-17
Also published as: GB0700347D0; GB2448669A; WO2008084262A3

Abstract

A power generation means comprises at least one barrier (1) defined a retained body of water (7), the barrier (1) being located between the retained body of water (7) and a body of water (5), wherein the height of the barrier (1) is dependant upon the level of water in the retained body of water. Preferably having buoyancy means (6) associated therewith. The barrier (1) can be hinged to a base (4) and floats at an inclined angle on the retained body of water (7). Because the barrier (1) floats on the retained body of water (7), it can be maintained at approximately the level of the retained body of water (7). This, in combination with the inclination of the barrier (1), enables the tide or waves on the body of water (5) to climb the barrier (1), overtop it and flow into the retained body of water (7). When an adequate head of water is achieved between the retained body of water (7) and the body of water (5), the stored potential energy may be harnessed by at least one turbine (18, Figure 5b) driving a generator, for the generation of electricity. This process may be enhanced by locating a concentrating means (44, Figure 13) in front of the barrier in order to direct a broad wave front onto a relatively small barrier (1).

Description

Power Generation Means

This invention relates to a power generation means comprising a barrier. In particular, it relates to a power generation means comprising a barrier capable of extracting both tidal and wave energy through the collection of water in a retained body of water. There is preferably provided a means for concentrating wave and/or tidal energy on the barrier.

There are several known prior art arrangements in which wave energy drives water to an elevated storage means for discharge through turbines back down to sea level.

One such arrangement is "Bott's Mauritius reef wall and lagoon", wherein a sea wall is provided that forms an impounded lagoon. This arrangement requires specific geographical features and may have a detrimental effect on the local ecosystem.

The Norwegian "Tapchan" (tapered channel) provides a converging inclined channel that leads to a raised lagoon. The arrangement again requires specific geographical features: a limited tidal range and deep water with low-lying land adjacent thereto.

The device known as "Wave Dragon" rises and falls with the tide and features a floating reservoir with an inclined plane leading up to it. Whilst this arrangement does not require specific geographical features, the device is only capable of extracting wave energy.

The present invention arose in an attempt to provide an improved means for harnessing both tidal and wave energy that does not require a specific geography.

According to a first aspect of the present invention, there is provided a power generation means comprising at least one barrier for retaining a body of water, the barrier being hingeably mounted to a floor of the retained body of water, wherein the height of the barrier is at least partially dependant on the height of the retained body of water, wherein the barrier is located between a body of water and the retained body of water, and wherein the dimensions of the barrier are selected such that in use the barrier is maintained at an inclined angle to permit waves to overtop the barrier and flow into the retained body of water. In this arrangement, the barrier is to be maintained at a level only slightly above that of the retained body of water, maximising the quantity of water entering the retained body of water due to waves incident on the barrier, and automatically raising the barrier as the level of water rises in the retained body of water. This has the advantage that if the waves are relatively large, a significant difference may be achieved between the level of the retained body of water compared to the body of water, which will typically be the open sea. The inclination of the panel can be set to maximise the energy harnessed, having regard to the quantity of water entering the retained body of water and the head of water in the retained body of water relative to the mean level of the body of water.

The hinge may not be mounted directly to the floor provided it is mounted to an extension of the floor such that is seals with the floor.

The term "retained body of water" as used throughout the specification, including the claims, refers to a body of water retained by the power generation means. This may be a closed body of water contained on all sides, but is to include any body of water retained by the power generation means, including non-closed bodies of water such as estuaries, river banks or the open sea when retained by the barrier.

Preferably, the barrier has buoyancy means associated therewith arranged to float at a level dependant on the level of water in the retained body of water, for this will automatically maintain the barrier at an optimum height.

Advantageously, at least one barrier comprises a base portion and a panel hinged to the base portion, the panel having buoyancy means thereon such that the top of the panel floats slightly above the level of the retained body of water.

Preferably, the barrier is mounted to a floor of the body of water and typically the barrier would be an off-shore retained body of water formed by several such barriers, or one barrier and fixed side barriers forming a retained body of water with the shore. Advantageously, there is a seal provided between the floor and the barrier, and the side structure and barrier, to minimise the escape of water from the retained body of water.

Preferably, restraint means is provided that controls the angular displacement of the panel which prevents the panel exceeding a maximum angle even when the level of the water in the retained body of water exceeds the level of the body of water. In this way, in the case of a tidal barrier, at low tide the water level in the retained body of water cannot "flip" the panel over. Similarly, in the case of a wave energy system, high seas cannot cause the retained body of water level to raise to such an extent as to cause the panel to "flip" over.

Preferably, the panel comprises a first portion hinged to the base and an extension portion hinged to the top of a first portion of the panel and restraint means for controlling the angular displacement of the extension portion such that the incline of the extension portion can not exceed a maximum angle even when the level of the water in the retained body of water exceeds the level of the body of water, the extension portion being arranged to float on the water in the retained body of water. This permits the extension portion of the panel to be restrained at a desired inclination to maximise the energy received by water entering the retained body of water but permits the panel height to then be increased whilst maintaining the same inclination.

Advantageously, the panel comprises one or more further extension panels each hinged to the top of the preceding extension panel and each restrained such that the incline of the extension portion can not exceed a maximum angle even when the level of the water in the retained body of water exceeds the level of the body of water, each extension portion being arranged to float on the water in the retained body of water enabling the barrier to retain the same inclination for a large range of retained body of water levels.

Where the body of water is tidal the barrier preferably comprises at least one buoyancy tank that may be vented to lower the barrier as the tide floods, so that the level of water in the retained body of water may be maximised. The buoyancy tank is filled with air and the the barrier is raised before the high tide.

The system preferably comprises at least one turbine, coupled to a generator for the generation of electricity, the turbine being connected such that an adequate difference in the water level between the retained body of water and the body of water can be harnessed to drive the turbine. The turbine may be located in a base of the barrier.

The barrier system may be arranged to float on the body of water instead of the retained body of water.

The power generation means may comprise concentrating means for concentrating a wave arriving at the barrier or as it approaches the barrier.

Preferably, the concentrating means comprises a plate maintained at a predetermined level below the surface of the body of water and hinged vanes connected to the plate that may be rotated in the plane of the plate, beyond the plan of the plate to effectively alter the size and/or profile of the plate. More preferably, the level of the plate and hinged vanes below the surface of the body of water is adjustable. Such an arrangement allows waves to be directed/controlled using refraction in order to optimise wave energy incident upon the barrier of the power generation means.

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

Figure Ia schematically illustrates in perspective view a barrier system that may be used in a power generation means according to the present invention;

Figure Ib schematically illustrates in side elevation the barrier system of Figure 1 ;

Figure 2a, 2b and 2c illustrate the top portion of a barrier system comprising a plurality of extension members that may be used in a power generation means according to the present invention;

Figure 3 illustrates a barrier system comprising restraint means that can be used in a power generation means according to the present invention;

Figure 4 illustrates rigid restraints that can be used on a barrier used on the extension members of a power generation means according to the present invention;

Figures 5a and 5b illustrate a first embodiment of the present invention; Figure 6 is a side elevation of a barrier system comprising a turbine, which can be used in a power generation means according to the present invention;

Figure 7 is a plan view of a second embodiment of the present invention;

Figure 8 is a side elevation of a third embodiment of the present invention; Figures 9a and 9b illustrate, in plan view, respectively fourth and fifth embodiments of the present invention;

Figure 10 is a side elevation of a sixth embodiment of the present invention, which includes a wave attenuating device and a motion damping device;

Figure 11 illustrates a wave concentrating means on a front face of a barrier for use in a power generation means according to the present invention;

Figures 12a, 12b and 12c illustrate a segment of a wave concentrating means, located in the body of water in front of a barrier system, for use in a power generation means according to the present invention;

Figure 13 illustrates a seventh embodiment of the present invention, comprising a wave focussing device;

Figure 14 illustrates the barrier system (collector) used in the power generation means of Figures 13 and 15, in plan view.

Figure 15 illustrates an eighth embodiment of the present invention, comprising an array of wave focussing devices in front of an array of collectors; Figure 16 illustrates a support pillar and float of a concentrating means for use in a power generation means according to the present invention; and

Figure 17 illustrates an alternative mooring system for a wave concentrating means, located in the body of water in front of a barrier system, for use in a power generation means according to the present invention. Figure 18 illustrates an alternative wave concentrating means, located in the body of water in front of a barrier system, for use in a power generation means according to the present invention.

Referring to Figure Ia and Ib, there is shown a barrier system for use in a power generation means according to the present invention, which comprises a barrier 1 which consists of two parts. The first part is a panel 2, which has either internal chambers or an external chamber 6 (as shown). By filling these chambers with air the panel may be made to float. The second part is a base unit 4, which is located on a sea or estuary bed. These two parts are connected by a hinge 3 and together they form a unit section of a barrier 1. A line made up of these units, abutted together, form barrier 1.

The barrier 1 forms the front face, i.e. the face facing the prevailing waves, of a retained body of water 7 located in the sea. The other walls of the retained body of water may also be floating walls, or they may be formed by the coast, or masonry walls or other. The front faces of the base and the floating panel, form an inlet ramp to the retained body of water 7.

A wave, on arriving at the barrier, rises and flows over the top of the panel 2 into the retained body of water 7. Since the panel floats on the water in the retained body of water it will float higher as the water in the retained body of water rises, moving from the position shown in broken line to the position shown in solid line. This will trap the overtopping water in the retained body of water. The height of the water in the retained body of water will rise above sea level and therefore some of the energy of the wave has been captured as water with potential energy in the retained body of water.

Energy may also be collected from the tides by using a similar device in a tidal barrage design. Here the flood tide over tops the panel 2, which floats up and traps it in the retained body of water, so that the ebb tide does not drain it away. The floating wall acts as an automatic sluice gate. This over topping process may be enhanced by venting the buoyancy tank 6 in the panel 2 and allowing it to sink onto the base. The flood tide will now flow into the retained body of water 7 with little hindrance. When the tide turns buoyancy tanks 6 are refilled with air and the panel 2 will float up, trapping the flood tide.

In either a wave or tidal device, the collected water in the retained body of water is discharged through a turbine back down to sea level, or other. The turbine drives a generator, which supplies electricity.

Essential to the performance of the invention is that the dimensions and location of the wall are such that the panel remains at an inclination to the sea, or body of open water 5, even when the retained body of water is full, so that waves incident on the barrier 1 may flow up the panel 2. However, individual designs will depend on whether the device is primarily a wave power, tidal power or hybrid (Le. extracting energy from both waves and tidal action) device and this may vary still further depending on the wave climate and the secondary applications.

This is a large marine structure and the economical materials for these are reinforced concrete or steel. Either would be satisfactory for the panel and the base with a preference for reinforced concrete because of its longevity and low maintenance, in a marine environment. The base 4 is filled with the cheapest available material, e.g. dredged material or mine waste or other, as ballast.

Further material requirements are for seals and hinges. Rubber if kept out of sunlight and cold will survive 25 years in sea water. This or other marine resistant, flexible material would be suitable for the seals between adjacent ramps or structures. The hinges may be also made partly of rubber, as only a few degrees of rotation are required. The higher hinges rotate through perhaps 40 to 50 degrees, due in part to being submerged by a wave breaking on them or flowing over them and forcing them under the surface of the retained body of water. Alternatively, a piano type hinge may be used and various marine resistant metals (e.g. brass, stainless steel, phosphor bronze, nylon or such) may be used with or without seals as appropriate.

There will be an optimum rise angle of the floating wall that collects the greatest volume of water at the chosen elevation. The minimum elevation is the minimum working head of the turbines. The optimum angle will be the elevation that collects the most recoverable energy from the waves. The top portion of the ramp may be made steeper in order to reduce the tendency for waves to break on the ramp.

Referring to Figures 2a, 2b and 2c, in order to cope with variations in wave energy and/or in sea level due to the tides and still maintain the optimum angle, the top of the panel 2 may comprise a series of buoyant extension panels 8 each hinged to a preceding panel.

As the level of water in the retained body of water rises, the buoyant panels progressively rise. They are constrained mechanically, (not shown), by employing either the restraint means illustrated in Figures 3 or 4 or any suitable alternative restraint means. By this means the desired (most preferably optimum) angle may be achieved at the top of the inlet ramp.

Once there is water in the retained body of water, at a higher elevation than that of the body of water, then the pressure of this water will tend to push the floating panel 2 over.

Referring to Figure 3 this pressure may be opposed by a restraint mechanism 9. The restraint mechanism 9 preferably comprises a hinged tie but may comprise any suitable mechanism. The solid line shows the panel 2, extensions 8 and hinged tie 9 in the fully elevated position. The dashed line shows them in the lowered position. The heel of the panel 2 may also abut the base 4 in the fully elevated position and this will also inhibit any further rotation of the panel. Such a feature may be taken in isolation of the restraint mechanism 9.

When the water level reaches the extension panels 8 these too will tend to be pushed over. Figure 4 illustrates a restraint mechanism that consists of a foot 14 that is part of an extension panel that catches on a stirrup 15 that is part of the preceeding extension panel. As the water level in the retained body of water rises, the buoyant extensions will tend to float higher. The hinge will convert this to a rotary motion and the foot and stirrup will limit this rotation to give the desired angle at the top of the inlet ramp. There may be a spring provided (not shown) that resists the foot settling in the stirrup. This will stop a low water head pushing an extension fully up and reducing the collection efficiency of the barrier.

Referring again to Figure 3, the bases 4 are located on the seabed and they include a moulded front face 10 which forms the bottom section of the inlet panel 2, a body which may be filled with ballast 11, a means of supporting the bottom hinge and a toe 12. The base 4 stretches the length of the outer retained body of water front face and is made in sections, (coincident with the buoyant panel sections), that are structurally linked together. The toe stops cross currents undermining the front of the base. The front face 10 is preferably kinked, as shown, to reduce the size of the base and save costs. The floor 13 of the base is preferably stepped, as shown, to reduce the amount of sea bed preparation required. It is important that the height of the bottom hinge 3 is the same everywhere along the wall as this permits the simplest design of seal between sections. Again for ease of seal design the wall should run in a straight line. There may be a fortuitous situation where the base 4 be formed from the seabed itself such as the edge of a coral reef.

Referring now to Figure 5a there is depicted, in plan view, a first embodiment of a power generation means according to the present invention. In this embodiment the power generation means is a stand alone device comprising a single barrier 1, side walls 16 and a back wall 17 which includes at least one turbine 18. The barrier 1, side walls 16 and back wall 17 together provide a retained body of water. Here the barrier 1 is aligned orthogonally to the direction of the prevailing waves 19. The device is located off shore and a power cable 20 conducts the electricity to the shore 21, either over or under the water. Figure 5b illustrates this arrangement in cross section. Whilst the back wall 17 is shown as a wall, it may alternatively consist of a panel 1 mounted on top of a base 4 which houses a turbine 18. Further, where a side wall 16 of the retained body of water 7 is exposed to waves from the body of water 5 then the side wall 16 may consist of a barrier 1 in order that any obliquely incident waves are collected in the retained body of water 7.

As depicted in Figure 6, the base 4 of a barrier arrangement may be modified to accommodate at least one turbine 18.

Referring now to Figure 7, a second embodiment of the invention is shown.

This embodiment constitutes the simplest form of the invention and comprises a single barrier 1 with the shore 21 forming a retained body of water 7. The barrage here is made up of two types of barrier 1. The section in the deep part of the estuary is formed by using a panel over, a base with turbine design, as in Figure 6. The rest of the barrage may be formed using a barrier as depicted in Figure 1. With this arrangement, the flood tide flows over the barrier and is trapped in the retained body of water 7. This process may be enhanced by venting the buoyancy tanks of the panels 2, on the rising tide and re-filling them as high tide approaches, thereby maximising the volume of water overtopping the barrier. Further this design does not require locks for the passage of ships as during the latter part of every flood tide the panels 2 are lowered and ships may pass safely overhead.

Referring now to Figure 8 a third embodiment of the invention is illustrated in cross section. In this arrangement there is provided a front wall 22, a back wall 23 and two sides walls (not shown) which enclose a retained body of water 24. The front wall

22 is shown to house at least one turbine, this may however be omitted. The back wall

23 consists of a panel 2, (which may comprise extensions), which is mounted on a base 4. As shown, the panel 2 preferably at least partially floats on the body of water 5.

With this arrangement, as the tide ebbs, the panel 2 will lower and any water in the retained body of water 24 that is at a higher elevation than the panel 2 will flow over the panel and into the body of water 5. However, as the tide floods, the panel 2 will rise and no water will flow into the retained body of water 24 and hence the height of the retained body of water 24 will be that of the low tide. It is preferable that the panel 2 is sheltered from waves, and may face either into an estuary or towards the shore or other in order to achieve this. This avoids damage to the panel and also avoids any water spilling over the panel 2 into the retained body of water 24.

Figures 9a and 9b illustrate, in plan view, respectively fourth and fifth embodiments of the invention. The fourth and fifth embodiments represent compound arrangements combining the power generation means of the first and third embodiments. For ease of explanation, the arrangement of the first embodiment will be referred to as type A and the arrangement of the third embodiment as type B.

Referring to Figure 9a, a type A power generation means 26 is located adjacent to a type B power generation means 25. The back wall of the type A arrangement is the front wall of the type B arrangement. The method of working is for the high tide and/or waves to fill the type A 26 arrangement in the normal way (as described above). When the tide has ebbed by an adequate amount, water will be discharged through turbines 27 to the body of water 5. As the tide passes through low tide the type B arrangement is drained to the level of low tide. The returning flood tide will rise to a level such that the height difference between the retained body of water 7 and the body of water 5 is inadequate to drive the turbines 27 and these will be stopped. At this point further turbines 28, acting between the retained body of water 7 and the second retained body of water 24 will start operating. They will continue operating until the tide has ebbed to the point where the original turbines 27 can be restarted. The cycle can then be repeated and this means power may be generated continuously.

Referring to Figure 9b, a type A arrangement 26 is separated from a type B arrangement 25 by a third retained body of water 29. The body of water 29 is enclosed by the back wall of the Type A arrangement, the front wall of the type B arrangement and two side walls 30 which are preferably of the same design as the back wall 23 in Figure 8. The front wall of the Type B arrangement contains sluice gates 31. Here the body of water 29 will drain away any time that its level is higher than the body of water 5, by flowing over the panels 2 in the side walls. However if the body of water 5 is higher than that of the body of water 29 the panels will rise and stop any water flowing from the body of water 5 into the body of water 29. These side walls are preferably sheltered from any waves.

Here the method of working is for the high tide and or waves to fill the type A arrangement in the normal way. Also the low tide will drain the type B arrangement as previously described. The water from the body of water 7 will discharge through the turbine 28 into the body of water 29. From here at the lower period of the tide it will flow over the side walls 30 into the body of water 5. At the higher periods of the tide, the sluice gates 31 will be opened, and the water, from the body of water29, will flow through them into the body of water 24. The sheltered side walls will inhibit any water from flowing from the body of water 5 into the body of water 29. This again will enable continuous power generation. The advantage of this arrangement is that only one set of turbines are required.

In both compound arrangements the other walls may be barrier walls, reverse barrier walls, masonry walls or other. Where it is environmentally acceptable the side walls may be formed by the shore.

In any of the above power generation systems the performance may be enhanced by pumped storage, i.e. pumped higher at high tide for type A retained body of water systems or pumped lower at low tide for type B retained body of water systems.

Referring now to Figure 10 a sixth embodiment of the invention is shown. This embodiment comprises a wave attenuating device and a motion damping device. Either of which may be used alone or in combination in any of the alternative embodiments. Waves over topping the panel 2 will produce waves in the body of water 7. These waves may have a destructive effect on the back and side walls. The mushroom attenuator 32 is intended to dissipate the energy of the wave in the body of water before it reaches these walls. The elliptically shaped chamber is attached to a base which consists of a perforated plate 33. This assembly floats in the retained body of water and is moored across the wave's path. A wave arriving at the float will try to lift it. This will be opposed by the perforated plate which will dissipate some energy as turbulence in the water. Some of the wave will be forced to over top the float and this will also be dissipated as turbulence in the water on the far side of the float. There may be more than one line of floats.

A similar arrangement of perforated plate 35 is attached to the final extension of the back wall panel 34. Should a wave reach the back wall it will attempt to raise it. The perforated float will resist this and the wave will be forced to overtop the extension and flow back into the body of water 5.

To increase the energy collection efficiency of the system there may be provided means for concentrating waves. Waves may be concentrated by refraction. The concentrating means may be at the barrier or in front of it in the body of water.

The concentrating means may be adjustable. By concentrating a wave, more of it may be made to flow into an elevated body of water, than a wave that has not been concentrated and might not even reach the top of the barrier.

Figure 11 shows a plan view of an arrangement where the concentrating means is at the barrier 1. In such an arrangement the front face of the base 4 and panel 2 are not flat surfaces but are moulded into a centrally domed ridge or alternative suitable arrangement. Figure 11 illustrates this by drawing the contour lines 36 of such an arrangement. Further it illustrates the path of waves (wave ray) 37 incident on the barrier. This arrangement will concentrate waves to an area around the top of the panel

2_

Figures 12a, 12b and 12c illustrate a segment of a wave concentrating means, that may be located in the body of water in front of a barrier system of any of the embodiments of the present invention. In an arrangement where the concentrating means is mounted in the body of water 5 in front of the barrier 1 the concentrating means may comprise a plurality of segments 38.

Figure 12a illustrates a plan view of such a segment. It consists of a flat plate

39, hinge mounted vanes 40, which may have further support (not shown), side floats 41 and plate support legs 42. A cross section along A-A is illustrated in Figure 12b. The plate support pillars 42 are adjustable so that the depth of the plate below the surface of the body of water 5 may be varied. They may be multi-telescopic extension legs, a scissor type arrangement or any other suitable arrangement.

The whole assembly, i.e. the floats 41, the plate support pillars 42, the plate 39 and the hinged vanes 40, is at least marginally buoyant. This gives the plate a reference to the surface level of the body of water 5. The plate 39, vanes 40, and support pillars 42 are preferably individually marginally negatively buoyant in order to allow the floats 41 to be as small as possible, so that the floats afford the minimum resistance to waves. The plate and vanes inhibit any vertical motion.

The vanes on each segment are individually adjustable. Segments are attached to adjacent segments and together form the equivalent of an optical lens. Anchors (not shown) are preferably provided to maintain the position and/or orientation of the concentrating means in the body of water 5.

The plate assembly, i.e. the plate 39 and extended vanes 40, effectively reduces the depth of the water that the wave sees. Since the velocity of waves depends on the depth of water they are travelling in they will slow down at the plate assembly and be refracted. Similarly as the wave exits from the plate it will re-enter deeper water, speed up and again be refracted. Figure 12c illustrates the passage of a wave ray 37 across a segment 38 where a pair of hinged vanes 40, have been rotated outwards. It is refracted, according to Snell's law, as it slows down at the front face of the plate assembly and again at the rear face as it speeds up on re-entering deeper water. The angle of rotation of the vanes may be set manually or it may be set automatically by any suitable control/actuation means. The angle of rotation will be set according to the direction of the waves, for each individual vane 40. An advantage of this design is that, should the waves be too energetic, the segments may be de-focused progressively, so as to avoid damage to the barrier system.

The velocity of a wave is also a function of its wavelength. In order to achieve the required refractive index for waves of different wavelength the depth of the plate assembly is preferably adjustable. Such adjustment is preferably achieved by adjusting the length of the support pillars 42.

Figure 13 illustrates, in plan view, a seventh embodiment of the present invention. Here the concentrating means 44 is composed of three pairs of segments 38 that are symmetrically disposed around the optical axis. Whilst three pairs of segments are illustrated any suitable number of segments may be implemented. The concentrating means is located in front of a barrier arrangement (a collector) by moorings 46 (four shown). Also shown is the path that an off axis wave front (as shown by wave rays 37) takes as it approaches the concentrating means, is refracted twice at the concentrating means, and then travels towards the collector 45.

If the position of the concentrating means 44 can be maintained to a high degree, it is possible to replace the back petals of the segments with an appropriate angle to the back of the plate.

The segments break the wave front up into individual portions which may be called crestlets. The crestlets from the outer segments have further to travel to the collector than those close to the optical axes and thus arrive later. The concentrating means in effect is a pseudo-frequency converter and this improves the energy collection efficiency of the collector 45. The line of the segments will generally be orthogonal to the prevailing waves though geography or other considerations may change this. Whatever orientation is chosen waves will arrive at the segments from various angles other than normal incidence, by the nature of the sea. In this case the appropriate petals will be rotated to a position that gives the required degree of refraction. With a single segment and collector arrangement, the front vane will be set to an angle such that the refracted wave runs parallel to the optical axes. The back vane will be set to refract the wave towards the collector.

The efficiency of the concentrating means in this arrangement decreases as the angle the incident waves make to the optical axes increases. To accommodate this it is possible that the concentrating means is winched around so that it lies directly between the incoming waves and the collector. In this position the concentrating means will be at its maximum efficiency.

Figure 14 illustrates a detailed plan view of the collector 45. The collector is in essence a retained body of water 7 bounded by walls as described previously. However, here the front walls form a funnel shape, the sides of which are on a line that goes slightly wide of their respective ends of the concentrating means.

The back walls 17 and/or side walls 48 may contain turbines. The funnel walls are barrier walls 1. The length of the base wall of the funnel is preferably of the order of the width of a segment 38 of the concentrating means. The barrier walls are joined by corner units 47 which are hollow caisson structures with a face sloping back away from the waves at approximately the same height and angle as the panel 2. Their sides are at right angles to the adjacent panels 2. They are preferably part filled with dredged material or other as per the base 4. They reach at least to a height that is the maximum height of the barrier 2. A seal is provided between the barrier 1 and corner units 47 so as to avoid leakage from the retained body of water into the body of water 5 (not shown).

These corner units may also be used to separate sections of a straight barrier wall. In this configuration the corner units would itself have a straight line profile. They may be used where the depth of the seabed varies or for reasons of maintenance or other.

If the wave collector is located in a region of high tidal range then it may be possible to build a type B arrangement immediately behind the back wall. This would enhance the energy output of the collector. If there are no environmental objections, the walls of the type B arrangement may include the shore.

Referring now to Figure 15, an eighth embodiment of the present invention is shown, which comprises an array of collectors 45 (three of which are illustrated) positioned behind an extended line of segments 38. Here, there are five pairs of segments, symmetrically positioned either side of the optical axis of a collector. Any desired number of segments/collectors may however be implemented. The outermost segments abut to the segments of the adjacent collector (for clarity neither the floats 41 nor the mooring system 46 are illustrated).

For incident waves running parallel to the optical axis each individual collector and its segments work as detailed for the seventh embodiment. However, for off axis waves, segments that lie closer to the line of the waves (see A-B, Figure 15) heading directly to the collector 45 are co-opted from adjacent collectors. The wave rays 37 illustrate this situation. The advantage of this arrangement is that it increases the efficiency of the concentrating means. A further advantage of this design is that only vanes on the back face of the segments are required thus reducing cost and complexity.

Referring now to Figure 16 there is illustrated a support pillar 42 and float 41a of the concentrating means. As depicted, the floats 41 may be split into individual floats 41a, attached to the top of each support pillar. The support pillars may be braced in order to support them. These floats 41a, may be hydro-dynamically shaped and also free to rotate around the pillar 42 on bearings 43. They may be adapted to self align to the water currents and this will reduce drag.

Referring to Figure 17, there is illustrated an alternative mooring method, for an adjustable concentrating means. In this arrangement the concentrating means is positively buoyant and is restrained from floating to the surface by the anchor ropes 50 (two illustrated). There are preferably four or more anchor ropes 50 provided. The anchor ropes are attached to anchors 51 located on the bed of the body of water 5. The height of the concentrating means in the water may be adjusted by winches 49, which shorten or lengthen the anchor ropes, as required. The height selected depends on the state of the tide and the wavelength of the swell.

Referring now to Figure 18, an alternative adjustable concentrating means is shown that features a segment with a downwards sloping extension 52 provided at the front of plate 39. The downwards sloping extension 52 allows for the collection of wave energy that would otherwise pass under the segment. A downwards sloping extension 52 may be used with any segment that does not feature front mounted vanes. The downwards sloping extension 52 will result in greater forces being exerted on the segment and therefore such a segment may be made to have greater buoyancy and stronger anchor lines.

Alternatively, the energy passing under the plate 39 may be collected by downward suspended vanes mounted underneath the plate 39. These would preferably be adjustably oriented so as to reflect the wave towards the wave collector.

The wave concentrating means, as hereinbefore described, may be taken in isolation and used with other wave power devices, e.g. a modified wave dragon device. Here, since the wave dragon is relatively easily moved, a simpler form of fixed lens may be used and the wave collector, i.e. wave dragon, moved to the area of concentration of the waves (focal point). It may also be used with Tapchan to increase the wave front collected and the efficiency of collection.

The wave concentrating means concentrates waves, which may result in a net displacement of water, and therefore produce water currents. These currents may be used to modify the physical structure of the coast, or other, by adding or removing material.

Claims

1. A power generation means comprising at least one barrier for retaining a body of water, the barrier being hingeably mounted to a floor of the retained body of water, wherein the height of the barrier is at least partially dependant on the height of the retained body of water, wherein the barrier is located between a body of water and the retained body of water, and wherein the dimensions of the barrier are selected such that in use the barrier is maintained at an inclined angle to permit waves to overtop the barrier and flow into the retained body of water.

2. A power generation means as claimed in claim 1, wherein the barrier at least partially floats on the retained body of water and the barrier comprises restraining means to prevent the barrier rotating about the hingeable mountings by more than a predetermined amount.

3. A power generation means as claimed in claim 1 or 2, wherein the barrier has variable buoyancy means associated therewith arranged to float at a level dependant on the level of water, or other, in the retained body of water.

4. A power generation means as claimed in any preceding claim wherein there is a seal provided between the barrier and surfaces adjacent to the barrier.

5. A power generation means as claimed in any preceding claim, wherein said body of water is the sea.

6. A power generation means as claimed in any preceding claim, wherein at least one barrier comprises a base portion and a panel hinged to the base portion, the panel having buoyancy means thereon such that the top of the panel floats slightly above the level of the retained body of water.

7. A power generation means as claimed in claim 6, wherein restraint means are provided to control the angular displacement of the panel such that the incline of the panel cannot exceed a maximum angle even when the level of the water in the retained body of water exceeds the level of the body of water.

8. A power generation means as claimed in claim 6 or 7, wherein the panel comprises a first portion hinged to the base and an extension portion hinged to the top of a first portion of the panel and restraint means for controlling the angular displacement of the extension portion such that the incline of the extension portion can not exceed a maximum angle even when the level of the water in the retained body of water exceeds the level of the body of water, the extension portion being arranged to float on the water in the retained body of water.

9. A power generation means as claimed in any one of Claims 6 to 8, wherein the panel comprises one or more further extension panels each hinged to the top of the preceding extension panel and each restrained such that the incline of the extension portion can not exceed a maximum angle even when the level of the water in the retained body of water exceeds the level of the body of water, each extension portion being arranged to float on the water in the retained body of water.

10. A power generation means as claimed in any preceding claim, wherein the barrier has a profiled surface for concentrating a wave incident thereon.

11. A power generation means as claimed in any preceding claim, comprising concentrating means located in the body of water for concentrating a wave prior to the arrival of the wave at the barrier.

12. A power generation means as claimed in claim 11, wherein the concentrating means comprises at least one device located in the body of water that is at least partially buoyant and comprises portions which may be manually or automatically extended or retracted to alter the speed and/or direction of waves incident upon the concentrating means.

13. A power generation means as claimed in claim 11 or 12, wherein the concentrating means comprises a plate maintained at a predetermined level below the surface of the body of water and hinged vanes connected to the plate that may be rotated in the plane of the plate, beyond the plan of the plate, to effectively alter the size and/or profile of the plate.

14. A power generation means as claimed in claim 13, wherein the depth of the plate below the surface of the body of water is adjustable.

15. A power generation means as claimed in any one of claims 11 to 14, wherein the profile of a front and/or a back face of the concentrating means, is adjustable.

16. A power generation means as claimed in any preceding claim, wherein the body of water is tidal and the barrier comprises at least one buoyancy tank that may be vented to lower the barrier on the flood tide so that water may flow over the barrier to the retained body of water.

17. A power generation means as claimed in any preceding claim, comprising at least one turbine that drives a generator for the generation of electricity, the turbine being connected such that a difference in the water level between the retained body of water and the body of water can be harnessed to drive the turbine.

18. A power generation means as claimed in any preceding claim, comprising a second barrier, and a second retained body of water, wherein the second barrier is located between the body of water and the second retained body of water and is in a position at least partially sheltered from waves on the body of water.

19. A power generation means as claimed in any preceding claim, comprising a second barrier, and a second retained body of water, wherein the barrier floats on the body of water and is at least partially sheltered from waves on the body of water.

20. A power generation means as claimed in claim 18 or 19, wherein turbine discharge from the first retained body of water may be discharged into either the body of water or the second retained body of water.

21. A power generation means as claimed in any of claims 18 to 20 comprising a third retained body of water located between the retained body of water and the second retained body of water, wherein turbine discharge from the retained body of water discharges into the third retained body of water, and the third retained body of water may drain into either the body of water or the second retained body of water.

22. A wave power system comprising a power generation means as claimed in any preceding claim.

23. A tidal power system comprising a power generation means as claimed in any preceding claim.

24. A power generation means as hereinbefore described with reference to one or more of the accompanying drawings.