WO2009022186A2

WO2009022186A2 - Wave energy converter

Info

Publication number: WO2009022186A2
Application number: PCT/GB2008/050715
Authority: WO
Inventors: Bruce Palmer
Original assignee: Worldwavepower Limited
Priority date: 2007-08-16
Filing date: 2008-08-15
Publication date: 2009-02-19
Also published as: GB0715961D0; WO2009022186A3; GB2451879A

Abstract

A wave energy converter comprises a contai ner for containing a volume of fluid, the container having first and second ends, buoyancy means disposed proximate the first end of the container, a fluid receptacle arranged such that fluid may flow from the container to the receptacle, a fluid outlet channel connected to the receptacle, a turbine disposed in the outlet channel, resistance means disposed proximate the second end of the container, and means for compressing the container in response to relative movement of the buoyancy means and resistance means.

Description

Wave Energy Converter

The present invention relates to a wave energy converter.

The depletion of the earth's natural resources, coupled with the need to cut carbon dioxide emissions, has led to a great deal of research into renewable energy sources, such as wind, wave and solar energy. Ocean waves represent a considerable renewable energy resource. Waves are generated by the wind as it blows across the surface of oceans and they can travel great distances without significant energy loss. The majority of the energy of a wave is contained near the surface of the water.

There have been many attempts to harness the vast amounts of energy provided by waves and many countries have set targets for renewable energy resources. However, the main problem presented by harnessing wave power is one of economics. Systems for converting wave power into usable forms of energy must be able to do so at competitive prices. However, existing wave energy converters tend to be expensive. Furthermore, the systems need to be able to withstand the extreme conditions presented in coastal waters.

It is the object of the present invention to overcome some of the problems of the prior art systems, or at least to provide an alternative to them. The solution provides a system for converting energy from waves.

According to the present invention there is provided a wave energy converter as set out in the accompanying claims.

In use of the wave energy converter according to a preferred embodiment, the buoyancy means will float on the surface of a body of water, which may conveniently be a sea or ocean, and the container will extend downwards below the surface of the water. The buoyancy means will stay at or proximate the surface of the water and will rise and fall according to the motion of the waves. When a wave causes the buoyancy means to rise, the resistance means is prevented by drag from rising at the same rate. This causes relative movement, i.e. separation of the buoyancy means and resistance means which in turn actuates the means for compressing the container, so that the container is compressed and a volume of liquid located within the container is forced into the receptacle. The water then exits the receptacle through the outlet channel, rotating the turbine as it does so. The exit through the channel is driven by gravity / hydrostatic pressure. The turbine is preferably configured to convert the energy of the waves into electrical energy.

As the wave passes the buoyancy means will begin to return to its original position and the separation between it and the resistance means will reduce.

The resistance means may comprise a plate member disposed perpendicular to the longitudinal axis of the container. The size of the plate member may be chosen to suit the requirements of the energy converter. Typically, the plate may be a circular plate extending radially from a central point of the container. The plate member is preferably weighted to provide additional resistance.

In an alternative embodiment, the resistance means comprises an anchor. The anchor may conveniently be attached to any suitable structure, such as, but not limited to, the sea-bed. The resistance means may alternatively be weighted.

In any event, it is preferred that the wave energy converter is provided with some form of mooring means to ensure that it remains in a specified location. It is well understood that certain areas have particularly high wave energy and in this manner the wave energy converter may be positioned for best results. Furthermore, it will be necessary to ensure that the wave energy converter does not interfere with other activities, in particular, fishing.

The wave energy converter is preferably configured to convert wave energy into electrical energy. In particular, the wave energy converter is preferably configured to convert horizontally propagating wave energy into rotational torque. The rotation of the turbine is used to generate electrical energy. The wave energy converter may be connected to an electricity grid. The wave energy converter may conveniently be moored in the region of an underwater hub designed to connect to the electricity grid. The compression means may conveniently comprise a hydraulic system including hydraulic rams arranged to compress the container in response to separation of the resistance means and buoyancy means. In such a system, at least one longitudinal hydraulic ram may be connected between the resistance means and the buoyancy means, such that during separation the rams also extend. This longitudinal ram is hydraulically connected to at least one compression ram, so that extension of the longitudinal ram causes the compression ram to extend and thus compress the container, which in turn causes liquid in the container to flow up into the receptacle.

After the crest of the wave has passed, the buoyancy means will lower relative to the resistance means. At this point the container will begin to expand and water will be drawn into the container from the outside water mass, through the inlet valve. The longitudinal ram is caused to extend, which in turn retracts the compression ram, drawing liquid up into the container from the surrounding region.

For a better understanding of the present invention reference will now be made to the accompanying drawings showing, solely by way of example, various embodiments of the invention and, in which:

Figure 1 shows a sectional view of a wave energy converter in accordance with a first embodiment of the present invention;

Figure 2 shows a sectional view of a wave energy converter in accordance with a further embodiment of the present invention;

Figure 3 shows a sectional view of a wave energy converter in accordance with a yet further embodiment of the present invention; and

Figure 4 shows a sectional view of a wave energy converter in accordance with another embodiment of the present invention.

Fig. 1 shows a wave energy converter 1 comprising a substantially cylindrical container 2 for containing a volume of fluid and buoyancy means 3. Buoyancy means 3 contains within it a receptacle or header tank 4, which may for example be supported by struts or braces (not shown) connected to an interior wall of the buoyancy means 3. The container 2 has a first end 2a, which is in fluid communication with the receptacle 4 via fluid a pathway 5, which runs between the receptacle 4 and an internal wall of buoyancy means 3. Resistance means, in the form of a plate member 6, is disposed at the base of the converter, proximate a second end 2b of the container 2. A fluid outlet channel 7 allows liquid to pass from the receptacle 4 to the exterior of the converter 1. A turbine 8 is provided within and proximate the lower end of the outlet channel 7. The turbine 8 is arranged for driving an electrical generator 9 disposed within the buoyancy means 3. The turbine 8 only needs to operate when it is rotated in a single direction, that caused by the action of downward flowing liquid through the outlet channel 7. The turbine 8 is set up to convert mechanical energy into electrical energy. The turbine 8 may conveniently be connected to an electricity grid, which may be used to supplement energy generated by other means, such a from the burning of fossil fuels, or it may be the sole source of energy.

The container 2 is an elongate structure of substantially lenticular or "pillow-shaped" cross- section, approximately 20m in length and with a major diameter of approximately 9m and a minor diameter of approximately 6m. The volume of the container is approximately 660m³.

The container 2 is made of a flexible, elastic plastics material, for example a composite plastics bonded material, which is capable of elongating along its longitudinal axis. A flap inlet valve 10 is provided at the end 2b to allow fluid to enter the container 2 from the surrounding body of water but prevent its exit from the container 2. Fluid communication between the top end 2a of container 2 and the pathway 5 is regulated by a spring valve 11 depending from the buoyancy means. This valve 11 acts to permit liquid to flow from container 2 into pathway 5 but prevent its return. A further flap valve 12 is provided within plate member 6 proximate end 2b of container 2, arranged to enable liquid to flow upwardly through plate member 6, but prevent downward flow. This valve aids intake of water into the container 2 during a wave trough phase as described below, but maintains maximum water resistance of the plate member 6 during a swell phase.

Buoyancy means 3 is a buoyant, spheroid structure which is designed such that, in use of the wave energy converter 1, it floats on the surface of a body of water with the container 2 depending downwards below the surface of the water. The buoyancy means 3 is made of a lightweight, durable material such as aluminium and has a diameter of approximately 30m. To aid buoyancy, a chamber 13 provided in the region underneath the receptacle 4 may be pressurised, filled with air or other buoyant material.

The buoyancy means structure includes a support frame 14 attached to its underside which extends parallel to, and on opposite sides of, the container 2, and is attached to the container 2 at its lower end. The support frame carries hydraulic compression rams 15 arranged so as to be extendable in the horizontal direction. The compression ram outputs are connected to a compression plate 16. As shown, five compression rams 15 are positioned on each side of container 2, with each group of five rams connected to a respective compression plate 16. The support frame 14 also supports at least one longitudinal hydraulic ram 17, in this case two such rams are shown. The distal ends of the longitudinal rams carry the resistance plate member 6. Hydraulic chambers within the longitudinal rams 17 are linked to those of the compression rams 15 to form a closed-loop hydraulic system, such that extension of the longitudinal rams 17 causes extension of the compression rams 15.

The operation of the wave energy converter 1 will now be described by way of an illustrative example. The wave energy converter 1 is positioned in a body of water, such as a sea, which is known to experience waves of a sufficient magnitude. The buoyancy means 3 floats on the surface of the water with the container 2 depending downwards below the surface of the water.

The buoyancy means 3 will stay on the surface of the water and will rise and fall according to the motion of the waves. When a wave swell causes the buoyancy means 3 to rise, the plate member 6 acts as a resistance means by virtue of its high drag coefficient. The motion of plate member 6 will therefore be much less than that of buoyancy means 3. This causes the longitudinal hydraulic rams 17 to elongate to compensate for the motion difference. The extension of longitudinal rams 17 causes corresponding extension of compression rams 15. This extension causes the compression plates 16 to be brought together, squeezing the container 2. Liquid contained with container 2 is therefore forced up through valve 11 into pathway 5. Inlet valve 10 prevents liquid exit through the bottom of container 2. The liquid is forced through pathway 15 and flows into receptacle 4, acting as a header tank. Liquid within receptacle 4 drains away through outlet channel 7, causing rotation of turbine 8 as it does so. This rotation is converted into electrical energy by generator 9. The rotation of the turbine 8 is aided by the head built up in the liquid by virtue of the header tank receptacle 4, ensuring a strong flow through the outlet channel 7.

As the wave passes, the buoyancy means 3 begins to lower due to the trough, and the converter 1 experiences a net downward thrust due to gravity. Again, the movement of the buoyancy means 3 is greater than that of the resistance plate member 6. This relative movement retracts longitudinal rams 17, which in turn retract compression rams 15. As compression plates 16 move apart, a region of low pressure is created in container 2, which causes liquid to be drawn into the container 2. This effect is aided by the elasticity of the container 2 urging it to return to its original position. Liquid is drawn into container 2 through inlet valve 10 at its base, with valve 11 blocking inward flow at the top end. Valve 12 in plate member 6 also permits liquid from the surrounding region to be drawn toward and into container 2.

The operation of the wave energy converter 1 is passive and it will simply move with the motion of the waves and generate energy accordingly.

Fig. 2 shows another embodiment of the wave energy converter 1 ^Λ in accordance with the present invention. Many features of this embodiment are similar to those of the first embodiment, and these retain the original reference numerals. The changed features will be denoted by the suffix "^Λ". In Fig. 2, the converter V is shown in which container 2 is in its expanded state, i.e. compression plates 16 have been caused to move apart due to relative movement between the buoyancy means 3^Λ and resistance means 6\

In this embodiment, the buoyancy means 3^Λ is of a slightly different form to that shown in Fig. 1, though its operation remains unchanged. Pathway 5^Λ for leading water from container 2 into receptacle or header tank 4 is located vertically above container 2, which simplifies the construction of the receptacle 4 within the buoyancy means 3'. Two outlet channels 7 are provided leading from the receptacle 4 to the exterior of the converter V, with respective turbines 8 and electrical generators 9 provided for each channel 7. Resistance means 6^Λ is of simplified construction, with valve 12 being omitted. This does not adversely affect the operation of the converter 1\

In the above-described embodiment, compression of the container 2 is produced due to separation of the buoyancy means and resistance means, i.e. during passage of a wave peak.

However, it can be seen that by changing the connections between rams 15 and 17, compression of the container 2 could be effected during the opposite phase of the wave cycle, by a reduction in distance between the buoyancy means and resistance means, i.e. during passage of a wave trough.

A further embodiment is schematically shown in Fig. 3, in which various features are similar to those of the embodiment of Fig. 2, and as far as possible the original reference numerals have been retained. The changed features will be denoted by the suffix """. In this case, a single buoyancy means 3" includes a plurality of respective frame 14 and container 2 subassemblies. In Fig. 3, two such subassemblies are shown, although more may be provided.

As shown, the subassemblies are linearly arranged. This aids stability of the converter, as the sub-assemblies act as a keel.

The two subassemblies shown in Fig. 3 are of the same phase, i.e. both subassemblies act to compress the respective containers 2 due to separation of the buoyancy means 3" and resistance means 6", i.e. during passage of a wave peak. As shown, each container 2 is expanded by respective compression plates 16, implying that the wave cycle is at a trough.

Alternatively, the subassemblies could have opposite phases, i.e. the first subassembly acts to compress the container 2 due to separation of the buoyancy means 3" and resistance means 6", i.e. during passage of a wave peak, while in contrast, the second subassembly acts to compress container 2 during a reduction in distance between the buoyancy means 3" and resistance means 6", i.e. during passage of a wave trough. This is achieved by changing the connections between rams 15 and 17 of the second subassembly, as outlined previously. Using this configuration, energy is produced during both phases of the wave cycle.

Each subassembly is connected to an individual respective resistance means 6", or, in the case where each subassembly is of the same phase, may be connected to a common, shared resistance means.

A further embodiment of the present invention is shown in Fig. 4. Here, a wave energy converter generally similar to that of Fig. 2 is shown, but in this embodiment the buoyancy means 3^Λ additionally comprises a buoyancy frame 20 attached to the frame 14. A number of mooring buoys 22, which may be standard 'off the shelf deep water mooring buoys, are attached to the frame 20 to further aid buoyancy.

It is envisaged that wave energy converters in accordance with the present invention may form part of a larger system comprising a plurality of similar wave energy converters. The wave energy converters may conveniently be grouped together, for example secured together in a single line or in a bunch. The wave energy converters do not require to be spaced apart as they are able to operate passively as they rise and fall on the waves. The wave energy converters may conveniently be provided with mooring means (not shown) to prevent them from being carried away by the waves.

Initial studies show that a system with a cylindrical container of about 660m³ and a receptacle of about 525m³ has a generating potential in excess of IMW, with reasonable assumptions suggesting an average output of around 2.5MW. The output will of course be dependent on the prevalent sea-state, although the converter will be usefully operable throughout a range of wave-heights, for example from about 0.5m to about 6m. In addition, the converter is robust enough to withstand harsh conditions such as storms.

The above-described embodiments are exemplary only, and various alternatives or modifications within the scope of the claims will be apparent to the skilled person. For example, form some deployments, the resistance means may be anchored, e.g. to the sea-bed. The resistance means may also be weighted to increase the drag effect. Although compression is achieved using compression plates in the above-described embodiments, compression may alternatively be achieved by the use of bellows, a hydraulic ram or the like, as would be apparent to those skilled in the art. Additionally, compression means other than a hydraulic system may be employed, for example a mechanical linkage may be used.

The buoyancy means may take a variety of forms. The top of the converter may be open, so that liquid incident thereon, e.g. rain or spray would land in the receptacle and increase the output flow.

Claims

1. A wave energy converter comprising: a container for containing a volume of fluid, the container having first and second ends, buoyancy means disposed proximate the first end of the container, a fluid receptacle arranged such that fluid may flow from the container to the receptacle, a fluid outlet channel connected to the receptacle, a turbine disposed in the outlet channel, resistance means disposed proximate the second end of the container, and means for compressing the container in response to relative movement of the buoyancy means and resistance means.

2. A wave energy converter according to Claim 1, comprising at least one additional container disposed proximate the buoyancy means, and respective means for compressing said at least one additional container.

3. A wave energy converter according to either of Claims 1 and 2, comprising an outlet valve located between the or each container and the receptacle, arranged to permit fluid flow from the respective container to the receptacle but prevent fluid flow from the receptacle into the respective container.

4. A wave energy converter according to any preceding claim, comprising an inlet valve in fluid communication with the or each container, arranged to permit fluid flow into the respective container, but prevent fluid flow from the respective container.

5. A wave energy converter according to any preceding claim, wherein the means for compressing the container does so in response to separation of the buoyancy means and resistance means.

6. A wave energy converter according to any of Claims 1 to 4, wherein the means for compressing the container does so in response to a reduction in distance between the buoyancy means and resistance means.

7. A wave energy converter according to any preceding claim, wherein the means for compressing the or each container comprises a hydraulic system connected between the resistance means and buoyancy means.

8. A wave energy converter according to Claim 7, wherein the hydraulic system comprises a plurality of hydraulic rams.

9. A wave energy converter according to Claim 8, wherein the hydraulic system comprises a compression plate linked to a hydraulic ram output to effect compression of the respective container.

10. A wave energy converter according to any preceding claim, wherein the receptacle comprises a header tank.

11. A wave energy converter according to Claim 10, wherein the tank is located within the buoyancy means.

12. A wave energy converter according to Claim 11, wherein a fluid pathway is located within the buoyancy means in fluid communication with the or each container and the tank.

13. A wave energy converter according to any preceding claim, wherein the or each container is an elongate, cylindrical structure.

14. A wave energy converter according to any preceding claim, wherein the resistance means comprises a plate member disposed perpendicular to the longitudinal axis of the or each container.

15. A wave energy converter according to Claim 14, wherein the plate member is weighted.

16. A wave energy converter according to any one of Claims 1-13, wherein the resistance means comprises an anchor.