GB2341645A

GB2341645A - A water wave energy harnessing device

Info

Publication number: GB2341645A
Application number: GB9920714A
Authority: GB
Inventors: Alexander George Southcombe
Original assignee: Individual
Current assignee: Individual
Priority date: 1998-09-17
Filing date: 1999-09-03
Publication date: 2000-03-22
Anticipated expiration: 2019-09-03
Also published as: AU5640899A; GB2341645B; WO2000017518A1; GB9920714D0

Abstract

An apparatus for harnessing energy from water waves comprises a first reservoir 1 having at least one non-return valve 2 for admitting water from under a wave peak, a second reservoir 3 having at least one non-return valve 4 for releasing water at a wave trough, a power generating device 7, 8, 9 disposed between the first and second reservoirs 1, 3 that operates in response to the pressure difference of the water in the reservoirs 1, 3 where the second reservoir adjoins the first reservoir and is separated therefrom by a dividing wall. The apparatus is submerged under the surface of the water. Preferably the generating device may be a water wheel 7 that drives a water pump 9 and a plurality of the apparatuses may be provided in a horizontal and or vertical array (figures 2, 3) such that the pump 9 from each apparatus feeds a common conduit 11 which is connected to a high level reservoir and a turbine generator (figure 3). The reservoirs may be received in a floating cradle (figures 4, 5).

Description

2341645 APPARATUS FOR HARNESSING WAVE ENERGY The present invention relates

to an apparatus for harnessing the energy of water waves.

A device for extracting energy from water waves is described in US Patent No. 4141670. The device is mounted at the surface of the water and comprises high-level and low-level reservoirs each having non-return valves for permitting water from wave crests to enter the high level reservoir and water from the low-level reservoir to escape as a wave trough passes. Water is allowed to pass from the high-level to the lowlevel reservoir via a vertical axis turbine thereby generating useful power related to the difference in heads of pressure of the water in the two reservoirs that results from their vertical separation.

The above device has restricted application as it must be disposed at the surface of the water and the energy derived is dependent on the vertical separation distance between the two reservoirs.

A further device for extracting energy from water waves is described in British Patent Application GB-A-2036189. This device is also mounted at the surface of the water and comprises high and low pressure vessels each connected to gas tanks. An air cushion is maintained in the pressure vessels above the water level, with compressors connecting the air cushions to the gas tanks to allow air to flow between the air cushions and their respective gas tanks. The movement of air between the air cushions and the gas tanks alters the pressure in the pressure vessels, causing entry and exit valves provided in the high and low pressure vessels respectively to open and close at relevant times allowing ingress of water to the high pressure vessel and egress of water from the low pressure vessel. This causes water to flow from the highpressure vessel to the low-pressure vessel through a generator.

The device is bulky in that it comprises two reservoirs that are separate and interconnected by an elongate pipeline. This increases drag and thus reduces the power output. It is, in addition, mechanically complicated, requiring gas compressors, ballast systems, stabilisers and the like, which increases the cost of the device.

2 It is an object of the present invention to obviate or mitigate the aforesaid disadvantages.

According to the present invention there is provided apparatus for harnessing water wave energy, the apparatus comprising a first reservoir having at least one nonreturn valve for admitting water from under the peak of a wave, the water having a pressure that is in excess of the pressure of water already in the reservoir, the captured water in the first reservoir having a first pressure, a second reservoir adjoined to the first reservoir and separated therefrom by a dividing wall, the second reservoir having at least one non-return valve for releasing water to the surroundings when the water pressure in the second reservoir exceeds that of the surrounding water under a wave trough to leave water in the second reservoir that is at a second pressure lower than said first pressure, and a power generating device disposed between the reservoirs such that the water flows from the first reservoir to the second reservoir via the power generating device, the power generating device generating power in response to the difference between the first and second water pressures.

As the first and second reservoirs are adjoined to one another, the flow of water between the reservoirs can be made as direct as possible. This enables a high volume of water flow to pass through the device, enabling energy to be collected from the small pressure differences in the water under the wave peak and trough. The water entering the first reservoir under a wave peak may be evacuated from the second reservoir half a wavelength later from the second reservoir. The apparatus may thus be situated underneath the water surface, where it is subjected to less damage from the waves than if it was situated at the surface. The apparatus may be also made compact and streamlined, reducing drag so that it is more efficient than known designs.

t:l zD The first and second reservoirs are preferably elongate chambers which are designed to be of a length at least equal to the expected wavelength of the water waves. The chambers are preferably attached to one another along an elongate side of each reservoir. Preferably the first reservoir is located above the second reservoir in use. The power generating device may be disposed adjacent the first and second reservoirs at an end of the apparatus, or may be disposed between the first and second 3 reservoirs, for example along the elongate sides thereof that are attached to one another. A plurality of power generating devices may be provided between the reservoirs.

The power generating device may be a water wheel or turbine that drives a water pump, or may be a turbine capable of generating electrical energy.

Preferably there is provided a plurality of said non-return valves in said first and second reservoirs and a plurality of such devices in a horizontal and/or vertical array feeding a common output conduit.

The output conduit may be connected to a high level reservoir and a turbine generator.

The apparatus may include a floating cradle in which the reservoirs are supported such that, in use, they are disposed just beneath the surface of the water. Preferably a vertical and horizontal array of reservoirs are supported by the floating cradle such that at least some of the reservoirs are disposed in use just beneath the surface of the water.

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

Figure I is a diagrammatic representation of a first embodiment of apparatus according to the present invention; Figure 2 is a diagrammatic representation of a non-return valve used in the apparatus of Figure I in plan and side views; Figure.3 is a diagrammatic representation of a system employing a plurality of apparatuses in accordance with the present invention; Figure 4 is a diagrammatic representation of the system of figure 3' showing a high level reservoir and a turbine generator; Figure 5 is a diagrammatic side view of a system housed in a floating cradle; Figure 6 is an end view of the system of figure 5; Figure 7 is a top plan view of the system of figure 5; and Figure 8 is a diagrammatic representation of a second embodiment of apparatus according to the present invention.

I 4 Referring now to figure I of the drawings, a single wave energy harnessing device of the present invention has an elongate high-pressure reservoir I with a plurality of non-return valves 2 and an adjacent elongate low-pressure reservoir 3 with a plurality of non-return valves 4. The reservoirs are attached one to another along an adjoining elongate wall. The device is disposed below the surface of the sea and is designed to be as long as the greatest expected wavelength.

The non-retum valves 2 of the high-pressure reservoir I are arranged along one side of the reservoir 1. The non-return valves 4 of the low- pressure reservoir 3 are similarly arranged along a side of the reservoir 3. The valves 2, 4 may be simple flap valves made of a flexible plastics material, as illustrated in figure 2 of the drawings. The aperture in the vessel wall is provided with a grid or mesh to prevent the valve flap being sucked through the aperture.

Each of the non-return valves 2 in the high-pressure reservoir is opened when the external water pressure is greater than that inside the reservoir 1. The non-retum valves 4 in the low-pressure reservoir are opened when the pressure of the water inside the reservoir exceeds that of the external water.

An output of the high-pressure reservoir I is connected by a conduit 5 to an input 6 of the low-pressure reservoir 3 via a water wheel 7, the output 8 of which drives a pump 9 that draws in water from the surroundings and expels it through a non-return valve 10 at high-pressure to a high-pressure conduit 11. From there the water is delivered to a turbine or other power-generating device.

The operation of the device is cyclical as each wave peak and trough passes over the reservoirs. When a wave peak P approaches the highpressure reservoir 1, the water pressure increases from X-R to a maximum pressure X directly under the peak P (R being the reduction of water pressure in the high-pressure reservoir from the previous cycle, as described below). When the external water pressure reaches X-R the valves 2 below the wave peak P open so as to allow relatively high-pressure water n to enter the high-pressure reservoir 1. This continues while the external water pressure rises to X and stops when it drops below the pressure of the collected water in the high-pressure reservoir I whereupon the valves 2 close. This process is repeated for all the non-retum valves 2 along the length of the reservoir as the wave peak P moves over them and the maximum pressure in the high-pressure reservoir I thus tends to X. Since the reservoir is as long as the greatest expected wavelength, at least one nonreturn valve 2 will be open at any point in time in the cycle.

At the same time as the high-pressure reservoir I is being filled a wave trough T approaches the device and the external water pressure decreases from Y+S (S being the increase in pressure of the water in the lowpressure from the last cycle, as described below) to a minimum pressure Y directly under the trough T. When the external water pressure reaches Y+S the underlying non-return valves 4 are forced open and the water inside the low-pressure reservoir 3 is thus discharged to the surroundings. This continues while the pressure of the surrounding water drops to Y and stops when it rises above the pressure of the water in the low-pressure reservoir 3, whereupon the valves 4 close. This process is repeated for all the non-retum valves 4 along the length of the reservoir resulting in the pressure of the water in the lowpressure reservoir 3 tending towards Y. Again, since the device is as long as the wavelength at least one nonreturn valve 4 is always open.

The presence of high-pressure water in the high-pressure reservoir I and lowpressure water in the low-pressure reservoir 3 means that the highpressure water passes from the high to the low-pressure reservoirs, thereby driving the water wheel 7. During this process, the pressure of the water in the high-pressure reservoir I drops by R and the water pressure in the low-pressure reservoir 3 increases by S. The used water is then released to the surroundings as the wave trough T passes.

After the wave peak P has passed the non-return valves 2 in the highpressure reservoir I they remain closed until the next peak approaches and the pressure of the surrounding water reaches X-R again. Similarly, after the wave trough T has passed the non-return valves 4 in the low- pressure reservoir 3 they remain closed until the next trough T approaches and the pressure drops to Y+S again.

The working pressure for the water wheel 7 is the difference between the water pressure in the high-pressure reservoir I and that in the lower pressure reservoir 3) and is dependent on the height between the peaks and troughs of the passing waves.

6 The amount of water passing through the water wheel will depend on its size, design, the height of and the differential pressure between wave peaks and troughs. The power output of the wheel will thus vary with wave activity. The pump is designed to absorb this variation and supply a proportionate amount of water to the conduit 11.

Figures 3 and 4 show a plurality of devices in vertical and horizontal array below the surface of the sea. The output of each pump 9 is connected to a common vertical high-pressure conduit 11 to produce an adequate supply to a high level reservoir 12 disposed above sea level as shown in figure 4. The high level reservoir 12 (or equivalent) continuously supplies a turbinelgenerator unit 13 that provides useful power output. This arrangement balances out variations in the wave pattern so that a continuous supply of energy is available.

It will be understood that by operating under the surface of the water, where the conditions are more favourable than at the surface, the device is more efficient than known designs.

The closer the device is to the surface of the water the more efficient it will be. This is because the efficiency of flow of the water between the reservoirs is dependent on the ratio C+D: D where C is the increase in water pressure as a result of the wave peak and D is the water pressure provided by the column of water and atmospheric pressure that is always above the device.

In order to exploit the increased efficiency immediately below the water surface the device can be seated in a floating cradle as shown in figures 5, 6 and 7. The reservoirs 1, 3 are received in a cradle 15 to which is attached four floats 16. Location maintaining drives 17 and swivel drives 18 are also provided on the cradle. The floating cradle 15 enables the device to be positioned more easily and to be moved using the drives 17 and 18. The cradle may thus be held on station by reference to a GPS system (not shown), and may be swivelled to keep the device in optimum alignment with the prevailing wave direction. The floating cradle 15 may be tethered to the seabed b,,. suitable mechanical means such as anchor cables (not shown) that may be alterable in length. The depth at which the cradle holds the basic 7 units may be controlled so that the outlet valves may be held very near to the surface under a wave trough by means of electronically controlled flotation devices. For example, compressed air tanks may be used to fill or empty the floats 16 to a desired amount.

Each reservoir unit may be provided with buoyancy bags or tanks (not shown) so that they can easily be floated to the surface and removed from the cradle for repair and maintenance without the use of undersea divers.

An electrical generator may be placed on top of the floating cradle, which means that power generation may be carried out at sea, which is useful for some offshore installations, or may be used to provide power for a floating warning light or buoy.

Alternatively, a generator may be placed out of the water, for example on a sea-going platforrn or on land, being powered from the high-pressure water conduit 11. It therefore requires less protection against waves than if it was placed in the water, making the device more economical. Maintenance of the power generating device is also easier if the device is placed in dry conditions.

Referring now to figure 8, an alternative embodiment of reservoir unit is C> described. The same reference numerals have been used as for the embodiment shown in figures I to 7.

A plurality of water wheels 7 are provided along the adjoining wall between the reservoirs 1, 3. The water wheels may be located along the same axle (not shown), one end of which drives the pump 9.

By providing a plurality of water wheels between the two reservoirs, the flow of water between the two reservoirs is made as direct as possible, thus allowing a large flow of water. This is achieved by the water entering the high-pressure reservoir I at, for example, point Q and exiting the lower pressure reservoir 3 at point Z half a wavelength along the reservoirs. The points Q and Z move down the length of the reservoirs sequentially as the waves travel over the device.

It will be appreciated that numerous modifications to the above described design may be made without departing from the scope of the invention as defined in 8 the appended claims. For example, the water wheel or wheels may be replaced by any suitable mechanical device for generating power such as, for example, a turbine. The electricity generated by such a turbine could either be used on site, or transmitted to the land by any suitable means. One method for transmission of the energy would be to use the electricity generated by the device to generate hydrogen gas by electrolysis, which could then be shipped or pumped to land for use as a fuel.

The non-retum valves need not necessarily be arranged along the sides of the high-pressure and low-pressure reservoirs respectively but, rather, at any suitable location where they will be acted upon by the changes in pressure created by the wave peaks and troughs.

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Claims

An apparatus for harnessing water wave energy, the apparatus comprising a first reservoir having at least one non-return valve for admitting water from under the peak of a wave, the water having a pressure that is in excess of the pressure of water already in the reservoir, the captured water in the first reservoir having a first pressure, a second reservoir adjoined to the first C) reservoir and separated therefrom by a dividing wall, the second reservoir having at least one non-retum valve for releasing water to the surroundings when the water pressure in the second reservoir exceeds that of the surrounding water under a wave trough to leave water in the second reservoir that is at a second pressure lower than said first pressure, and a power generating device disposed between the reservoirs such that the water flows from the first reservoir to the second reservoir via the power generating device, the power generating device generating power in response to the difference between the first and second water pressures.
2. An apparatus according to claim 1, wherein the first and second reservoirs are elongate chambers.
3. An apparatus according to claim 2, wherein the chambers are attached to one another along an elongate side of each reservoir.

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4. An apparatus according to any preceding claim, wherein the power generating device is disposed adjacent the first and second reservoirs at an end of the apparatus.
5. An apparatus according to any of claims 1 to 3, wherein the power generating device is disposed in the dividing wall between the first and second reservoirs.

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6. An apparatus according to claim 5, wherein a plurality of power generating devices are provided between the reservoirs.
7. An apparatus according to any preceding claim, wherein the power generating device is a water wheel or turbine that drives a water pump.
8. An apparatus according to any of claims I to 6, wherein the power generating device is a turbine capable of generating electrical energy.
9. An apparatus according to any preceding claim, wherein a plurality of said non-return valves are provided in said first and second reservoirs and a plurality of such devices in a horizontal and/or vertical array feeding a common output conduit.
10. An apparatus according to any preceding claim, including a floating cradle in which the reservoirs are supported such that, in use, they are disposed just beneath the surface of the water.
11. An apparatus according to claim 10, wherein a vertical and horizontal array of reservoirs are supported by the floating cradle such that at least some of the reservoirs are disposed in use just beneath the surface of the water.
12. An apparatus substantially as hereinbefore described with reference to figures I to 7 or figure 8 of the accompanying drawings.

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