WO2006079823A1

WO2006079823A1 - Wave energy converter

Info

Publication number: WO2006079823A1
Application number: PCT/GB2006/000278
Authority: WO
Inventors: Bruce William Palmer
Original assignee: Bruce William Palmer
Priority date: 2005-01-29
Filing date: 2006-01-27
Publication date: 2006-08-03
Also published as: GB0501873D0

Abstract

A wave energy converter (2) comprising: a first container (4) for containing a volume of fluid, the container (4) having a first end (4a) and a second end (4b); a second container (6) in fluid connection with said first end (4a) of said first container (4); a turbine (7) disposed in said first container (4); resistance means (8) disposed at the second end (4b) of said first container (4); and means for compressing (22) said first container (4) in response to elongation of said first container (4).

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.

According to the present invention there is provided a wave energy converter comprising: a first container for containing a volume of fluid, the container having a first end and a second end; buoyancy means disposed at the first end of said first container; a turbine disposed in said first container; resistance means disposed adjacent the second end of said first container; and means for compressing said first container in response to separation of the buoyancy means and the resistance means.

The buoyancy means is preferably a second container in fluid communication with the first end of said first container. The wave energy converter provides a passive system for converting energy from waves. The first container is preferably an elongate, cylindrical structure and it preferably depends from the second container, which acts as the buoyancy means. In use of the wave energy converter the second container will float on the surface of a body of water, which may conveniently be a sea or ocean, and the first container will extend downwards below the surface of the water: The second container will stay on the surface of the water and will rise and fall according to the motion of the waves. When a wave causes the second container to rise the resistance means, which is disposed adjacent the second end of the first container, is unable to rise at the same rate. The separation of the buoyancy means and the resistance means actuates the means for compressing the first container, which duly compresses the first container and forces a volume of liquid, which is located within the first container, to pass through the turbine and into the second container. Other than the opening which connects it to the first container, the second container is preferably closed. When the liquid enters the second container the air which was located in the second container is pressurised. Pressurisation of the air cavity has the combined effects of driving the liquid back into the first container for the "return stroke" and promoting resonant motion of the system as energy is transferred to and from the air pocket. The turbine is preferably configured to convert the energy of the waves into electrical energy.

Preferably, the second end of the first container is closed and more preferably the first container and second container define a closed system. In use, the wave energy converter may conveniently be filled with a predefined volume of fluid. The fluid may conveniently be fresh water and it may be sufficient to fill the first container. The ratio of the volume of the first container to the volume of the second container is preferably at least 1 : 1.5, more preferably at least 1 :2 and most preferably at least 1 :3.

The second container preferably contains a volume of a compressible fluid, such as air. When the fluid from the first container is forced into the second container it compresses the fluid which is already present. This pressurisation helps to return the fluid to the first container on the "return stroke". The second container may be filled with any suitable compressible fluid. For example, a gas such as helium may be used. As the wave passes the buoyancy means will return to its original position. When this happens the volume of water which passed through the turbine in the first step will now pass back through the turbine in the opposite direction. The air in the second container, which is pressurised when the liquid is forced into the second container, helps to drive the liquid back through the turbine and into the first container. The turbine is preferably configured to operate in both directions such that energy is generated on both the "up stroke" and the "return stroke".

The resistance means preferably comprises a plate member disposed perpendicular to the longitudinal axis of said first 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 about a central axis of the first container. The plate member is preferably weighted to provide additional resistance.

In an alternative embodiment, it is preferred that 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.

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 is preferably 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 plurality of compression plates arranged to compress the first container in response to the separation of the buoyancy means and the resistance means. The compression plates are preferably arranged in pairs, with the plates being disposed on opposite sides of the first container. The compression plates are preferably mounted on a support frame and follow the movement of the second container. The compression plates are preferably connected to the resistance means via a suitable gear mechanism, which converts the relative downward movement of the resistance means into a compression force perpendicular to the direction of separation. It is preferred that a plurality of such pairs of compression plates are provided along the length of the first container.

The term "relative downward movement" is used, but it is actually the second container and the support frame which are moving upwards. Vertical rack members are attached to the resistance means and extend upwards towards the second container. When the second container moves upwards on a wave the rack members appear to move downwards with respect to the compression plates. The gear mechanism converts the linear vertical motion into linear horizontal motion in order to exert a compression force.

The turbine is disposed at the first end of said first container, adjacent the buoyancy means. When the first container is compressed the water is forced through the turbine and, if present, into the second container. This in turn makes the second container heavier and, therefore, less buoyant. At a pre-determined point the increased weight of the second container will overcome its buoyancy and the second container will stall to sink. At this point the first container will begin to contract and water will pass back through the turbine in the opposite direction. If the second container is a sealed system then the pressurised air in the container will assist in forcing the water back through the turbine. The turbine is configured to operate in both directions in order to maximise the efficiency of the wave energy converter.

For a better understanding of the present invention reference will now be made to the accompanying drawing showing, solely by way of example, an embodiment of the invention and, in which: Figure 1 shows a sectional view of a wave energy converter.

Fig. 1 shows a wave energy converter 2 comprising a first container 4 for containing a volume of fluid and buoyancy means, in the form of a second container 6. The first container 4 has a first end 4a, which is in fluid communication with the second container 6, and a second end 4b. Resistance means, in the form of a plate member 8, is disposed adjacent the second end 4b of the first container. A turbine 7 is provided at the first end 4a of the first container 4.

The first container 4 is an elongate, tubular structure, approximately 20m in length and with a diameter of approximately 3m.The volume of the first container is approximately 140m³. The first container 4 is made of a flexible, elastic plastics material. The first container 4 is closed at its bottom end 4b by a base member 5 and it is in fluid connection with the second container 6 at its top end 4a.

The second container 6 is a buoyant, spherical structure which is designed such that, in use of the wave energy converter 2, it floats on the surface of a body of water with the first container 4 depending downwards below the surface of the water. The second container 6 is made of a lightweight, durable material such as aluminum or composites and has a diameter of approximately 8m. The volume of the second container is approximately 270m³. The second container 6 is provided with a double layer outer surface. The second container 6 has an inlet port 10, which is connected to the top end 4a of the first container 4, and an inspection hatch 12, which is provided on an upper surface of the second container 6 directly opposite the inlet port 10. The first container 4 and second container 6 define a closed system in which a predetermined volume of fluid, such as, but not limited to, fresh water, is housed. In a typical embodiment of the wave energy converter 2 the volume of fluid may be sufficient such that it fills the first container 4. The volume of the second container 6 must be at least equal to the volume of the first container 4. The ratio of the volume of the first container to the volume of the second container is preferably at least 1 :1.5 and more preferably 1 :2.

In an alternative embodiment of the invention the base member 5 may be omitted such that the bottom end 4b of the first container 4 is open to allow water to enter. In use the second container 6 is intended to float on the surface of a body of water. With the bottom end 4b of the first container 4 open this will mean that the water will fill the first container 4.

A support frame 14 is attached to the second container 6 and extends parallel to, and on opposite sides of, the first container 4. The resistance means, in the form of the plate member 8, is attached to the bottom end 14b of the support frame 14, adjacent the base member 5 of the first container 4. The plate member 8 is connected to the support frame 14 by means of vertical rack members 16, 17 which extend along the length of the support frame 14. Also attached to the support frame 14 are a plurality of gear mechanisms 18, 19. The vertical rack members 16, 17 are provided with teeth (not shown) which engage with corresponding teeth (not shown) on the gear mechanisms 18, 19 respectively. Each of the gear mechanisms 18, 19 is provided with an associated compression member 20, 21 respectively. Each of the compression members 20, 21 comprises a compression plate 22, which is arranged parallel to the longitudinal axis of the first container 4, and a horizontal rack member 24, which extends perpendicularly to the compression member 22 and is provided with a plurality of teeth (not shown) which engage with corresponding teeth (not shown) on the associated gear mechanism 18, 19. The combination of the vertical rack members 16, 17, horizontal rack members 24 and gear mechanisms 18, 19 form rack and pinion mechanisms which convert the vertical linear motion of the vertical rack members 16, 17 into rotary motion of the gear mechanisms 18, 19 and on into horizontal linear motion of the horizontal rack members 24, as will be described in more detail below. The wave energy converter 2 is provided with four pairs of compression members 20, 21 but the actual number may vary depending on the length of the first container 4. Although the compression members 22 are shown on either side of the first container 4, they may actually be disposed around the circumference of the first container 4. This serves to ensure that the first container 4 is efficiently squeezed during operation. Adjacent compression plates 22 are connected to one another by means of resilient biassing means, in the form of compression springs 26, which permit the structure to extend and contract along with the first container.

The turbine 7 is mounted at the first end 4a of the first container 4, adjacent the inlet port 10 of the second container 6. The turbine 7 is configured to operate when it is rotated in both directions, such that it will generate power when water passes through it in both directions, as will be described in more detail below. The turbine 7 is set up to convert mechanical energy into electrical energy. The turbine 7 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. It is envisaged that the wave energy converter 2 may form part of a larger system comprising a plurality of similar wave energy converters. The wave energy converters 2 may conveniently be grouped together, for example secured together in a single line or in a bunch. The wave energy converters 2 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 2 may conveniently be provided with mooring means (not shown) to prevent them from being carried away by the waves.

The operation of the wave energy converter 2 will now be described by way of an illustrative example. The first container 4 is filled with a supply of fluid, such as, but not limited to, fresh water. The wave energy generator 2 is then positioned in a body of water, such as a sea, which is known to experience waves of a sufficient magnitude.

The wave energy converter 2 provides a passive system for converting energy from waves. The second container 6 is buoyant and floats on the surface of the water with the first container 4 depending downwards below the surface of the water.

The second container 6 will stay on the surface of the water and will rise and fall according to the motion of the waves. When a wave causes the second container 6 to rise the plate member 8 experiences increased resistance and is prevented from rising at the same rate. The plate member 8 is attached to rack members 16, 17. The displacement of the second container 6 from the plate member 8 causes the vertical rack members 16, 17 to move downwards relative to the first container 4 in a linear motion. The teeth on the vertical rack members 16, 17 are engaged with the gear mechanisms 18, 19 and the linear motion of the vertical rack members 16, 17 is converted into rotary motion. This rotary motion is, in turn, converted into horizontal linear motion by way of the interaction between further teeth on the gear mechanism 18, 19 and corresponding teeth on the horizontal rack members 24. The horizontal linear motion of the horizontal rack members 24 causes the compression plates 22 to exert a compression force on the first container 4.

The compression force exerted on the first container 4 by the compression plates 22 forces the water from the first container 4 into the second container 6. In passing from the first container 4 to the second container 6 the water passes through the turbine 7 causing it to rotate and generate energy. The volume of the second container 6 is at least as large as the volume of the first container 4 such that, even in the most extreme cases, all of the water form the first container 4 may pass from the first container 4 into the second container 6.

As the wave passes the second container 6 will begin to return to its original position. When this happens the volume of water which passed through the turbine 7 in the first step will now pass back through the turbine 7 in the opposite direction. As mentioned above, the turbine' 7 is configured to operate in both directions in order to maximise output from the wave energy converter 2. The operation of the wave energy converter 2 is passive and it will simply move with the motion of the waves and generate energy accordingly.

Initial studies show that a system with a cylindrical lower chamber of 140m³ and an upper chamber of 210-28Om³ has a generating potential in excess of IMW. It is reasonable to consider that generation may be greater than IMW, with sensible assumptions producing generating potential in the order of 3MW.

Claims

1. A wave energy converter comprising:

a first container for containing a volume of fluid, the container having a first end and a second end;

buoyancy means disposed at the first end of said first container;

a turbine disposed in said first container;

resistance means disposed adjacent the second end of said first container; and

means for compressing said first container in response to separation of the buoyancy means and the resistance means.

2. A wave energy converter according to claim 1, wherein the buoyancy means comprises a second container in fluid connection with said first end of said first container.

3. A wave energy converter according to claim 2, wherein the volume of the second container is larger than the volume of the first container.

4. A wave energy converter according to claim 3, wherein the ratio of the volume of the^' first container to the volume of the second container is at least 1:1.5.

5. A wave energy converter according to claim 4, wherein the ratio of the volume of the first container to the volume of the second container is at least 1 :2.

6. A wave energy converter according to claim 5, wherein the ratio of the volume of the first container to the volume of the second container is at least 1 :3.

7. A wave energy converter according to any preceding claim, wherein the first container is an elongate, cylindrical structure.

8. A wave energy converter according to any preceding claim, wherein the second end of the first container is closed.

9. A wave energy converter according to claim 8, as dependent on any one of claims 2-7, wherein the first container and second container define a closed system.

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

11. A wave energy converter according to claim 10, wherein the plate member is weighted.

12. A wave energy converter according to any one of claims 1 -9, wherein the resistance means comprises an anchor.

13. A wave energy converter according to any preceding claim, wherein the compression means comprises a plurality of compression plates.

14. A wave energy converter according to claim 13, wherein the compression plates are connected to the resistance means by a gearing mechanism.

15. A wave energy converter according to claim 14, wherein the gearing mechanism converts vertical displacement of the buoyancy means and the resistance means into a horizontal compression force.

16. A wave energy converter according to any one of claims 13-15, wherein the compression plates are arranged in pairs, with the plates being disposed on opposite sides of the first container.

17. A wave energy converter according to any one of claims 13-16, wherein the compression plates are disposed around the first container.

18. A wave energy converter according to any preceding claim, wherein the turbine is disposed at the first end of said first container.

19. A wave energy converter according to any preceding claim, wherein the turbine operates in both directions.