WO2005021960A1

WO2005021960A1 - Method and apparatus for generating electricity

Info

Publication number: WO2005021960A1
Application number: PCT/GB2004/050005
Authority: WO
Inventors: James Summersell
Original assignee: Individual
Current assignee: Individual
Priority date: 2003-08-28
Filing date: 2004-08-25
Publication date: 2005-03-10
Anticipated expiration: 2006-02-28
Also published as: GB2388631A; GB2388631B; GB0320091D0

Abstract

A method is disclosed of generating electricity ftom a change in the vertical level of at least two bodies of water (33A, 3313). For each body of water (33A, 33B), an object (32A, 32B) is floated on the water. The resulting vertical motion of the objects (32A, 32B) is employed to operate means for pumping fluid (36). The pumped fluid is employed to generate electricity at an electricity generating station. The vertical level of each body of water (33A, 33B) changes in a cyclical manner, with the water rising during at least one part of a cycle and falling during at least one other part of that cycle. The respective cycles associated with the at least two bodies of water (33A, 33B) are arranged to be out of phase.

Description

METHOD AND APPARATUS FOR GENERATING ELECTRICITY

The present invention relates to a method and apparatus for generating electricity from changes in the vertical level of a body of water.

A large amount of potential energy is stored in the vast body of ocean water that is made to rise and fall on a daily basis by the operation of ocean tides. The movement of this huge mass of water can be harnessed to generate electricity, and several schemes have been previously proposed.

The ocean tides, being the daily rise and fall of ocean levels relative to coastlines, are a result of the gravitational force of the moon and the sun as well as the rotation of the earth. Both the moon and the sun exert a gravitational force on the ocean water, with the moon exerting a larger gravitational force because, although it is smaller in mass, it is far closer to the earth than the sun. The gravitational force causes the ocean water, which makes up 71% of the earth's surface, to bulge along an axis pointing towards the moon, and the tides are produced by the rotation of the earth beneath this bulge of water. This is known as the Lunar Tide. The smaller gravitational effect of the sun results in the same effect of bulging along an axis pointing towards the sun on facing and opposing sides of the earth. This is known as the Solar Tide. The actual tides result from a superposition of the Lunar and Solar Tides.

Figure 1A of the accompanying drawings is a schematic diagram illustrating the relative positions of the earth 2, moon 4 and sun 6 during a Neap Tide in which the Lunar Tide 8 is aligned orthogonally to the Solar Tide 10. Figure IB of the accompanying drawings illustrates the relative positions of the earth 2, moon 4 and sun 6 during a Spring Tide in which the Lunar Tide 8 is aligned with the Solar Tide 10, resulting in the maximum tidal range.

Several schemes have been proposed to harness the power of the tides to generate electricity. One of these is illustrated schematically in Figure 2 of the accompanying drawings, comprising a barrage 12 placed across an estuary 13. A passageway 14 for water is disposed through a lower portion of the barrage 12, with a turbine 16 located within the passageway 14. As the tide rises, with the level of the water 17 rising on the ocean side of the barrage 12, two sluice gates 15 are lifted to allow water to enter through the passageway 14, thus turning the turbine 16 to generate electricity.

When the water 18 on the estuary side of the barrage 12 has risen to its maximum level, the sluice gates 15 are lowered to hold the water 18 and prevent it from flowing back through the passageway 14. When the water 17 on the ocean side of the barrage 12 is at the low-tide point, the sluice gates 15 are raised to allow the hydrostatic head created by the body of water 18 to force water back through the passageway 14; this movement of water turns the turbine 16 and generates electricity.

The above process is repeated as the tide rises and falls. As there are two high and two low tides each day, electricity generation from tidal power plants such as that shown in Figure 2 is characterised by periods of maximum generation, with little or no electricity generation in between. Alternatively, the turbine 16 can be used as a pump to pump extra water into the basin 18 behind the barrage 12 during periods of low electricity demand. This water can then be released when demand on the system is at its greatest, thus allowing the tidal plant to function with some of the characteristics of a "pumped storage" hydroelectric facility.

Other schemes have been proposed that do not rely directly on the tidal movements of the ocean, but rather the disturbances on the surface of the ocean in the form of waves. Figures 3 A and 3B of the accompanying drawings shows just one example of such a scheme, which is used in Wavegen's Limpet and Osprey modules (see wavegen.co.uk). The wave energy collectors are in the form of a partially submerged shell 20 into which sea water is free to enter and leave. As the water enters, with a rising wavecrest 22, the level of water in the chamber 20 rises in sympathy. A column of air, contained above the water level, is compressed by this movement to generate a stream of high velocity air 24 in an exit blowhole. This is illustrated in Figure 3A of the accompanying drawings. The reverse situation is shown in Figure 3B in which a falling wavecrest 28 causes a column of air above the water level in the chamber 20 to be decompressed thereby generating a stream of high velocity air 30 entering into the blowhole. The air stream is allowed to flow via a pneumatic turbine, thus extracting energy on the system and generating electricity.

Although the movement of ocean water, and therefore its potential for generating electricity, varies throughout the day, ocean tides are a valuable renewable energy source because of their reliability, predictability and dependability. Tidal electricity can be used to displace electricity which would otherwise be generated by fossil fuel fired power plants, thus reducing emissions of greenhouse and acid gasses. Because of this valuable, renewable energy resource, alternative ways of harnessing the power of the ocean tides are always sought.

According to a first aspect of the present invention, there is provided a method of generating electricity from a change in the vertical level of at least two bodies of water by, for each body of water, floating an object on the water, employing the resulting vertical motion of the object to operate means for pumping fluid, and employing the pumped fluid to generate electricity at an electricity generating station, wherein the vertical level of each body of water changes in a cyclical manner, with the water rising during at least one part of a cycle and falling during at least one other part of that cycle, and wherein the respective cycles associated with the at least two bodies of water are arranged to be out of phase.

Electricity may be generated from the pressure of the pumped fluid at the electricity generating station, or equivalently the kinetic energy of the pumped fluid.

The pumped fluid may comprise a gas.

The pumped fluid may comprise water.

The pumping means may cause water to be pumped from the body of water itself.

The cycles may not repeat exactly. The vertical level of each body of water may change in a predetermined manner, for example with the ocean tides. The pumping means may be operable to cause water to be pumped directly to the electricity generating station for the generation of electricity. In this respect, a cycle may comprise at least one active period in which the vertical motion of the object is sufficient to operate the pumping means to deliver water with a sufficient pressure to the electricity generating station to enable a predetermined electricity generation output, and at least one inactive period in which the vertical motion of the object is not sufficient to operate the pumping means to deliver water with a sufficient pressure to the electricity generating station to enable a predetermined electricity generation output. For example, an inactive period may occur around the tum-around point between the rising and falling of the vertical level of the body of water. The pumping means may cause water to be pumped directly to the electricity generating station during at least part of an active period.

In addition to this, or instead of, the pumping means may be operable to cause fluid to be pumped to a holding reservoir for subsequent delivery to the electricity generating station for the generation of electricity. The holding reservoir may be a gas container or cylinder in the case where the fluid is a gas.

In this respect, a cycle may comprise at least one active period in which the vertical motion of the object is sufficient to operate the pumping means to deliver fluid with a sufficient pressure to the holding reservoir, and at least one inactive period in which the vertical motion of the object is not sufficient to operate the pumping means to deliver fluid with a sufficient pressure to the holding reservoir. The pumping means may cause sufficient fluid to be pumped to the holding reservoir during an active period to maintain a sufficient amount or pressure of fluid in the holding reservoir to enable the generation of electricity from the water in the holding reservoir during at least part of an inactive period. The pumping means may cause a sufficient amount or pressure of fluid to be maintained in the holding reservoir to enable the generation of electricity from the water in the holding reservoir during the whole of the inactive period.

In the case where the fluid is water, the holding reservoir may be located at a vertical height above the electricity generating station. The vertical height may be sufficient to deliver water under its own weight to the electricity generating station with a sufficient pressure to enable a predetermined electricity generation output. Additional pressure may be applied to the water in the holding reservoir to achieve sufficient pressure of the water delivered to the electricity generating station. A weight pressing down on the water in the holding reservoir is employed to apply the additional pressure. The holding reservoir may be a cylinder and the weight may be a piston acted on by gravity.

The at least two bodies of water may be in separate docks in communication with an ocean, the vertical level of each body of water being caused to change by the operation of ocean tides.

The at least two bodies of water may also be in separate locks (for example, a river lock), the vertical level of each body of water being caused to change by water flowing into or out of the lock.

The vertical level of each body of water may also be controlled by the use of one or more gates across an opening to the dock or lock, as the case may be, which are operated to control the amount of water in the dock or lock, as the case may be.

The pumping means may be arranged between the object and an attachment the vertical level of which is not affected, at least as much as the object, by the change in vertical level of the body of water, the vertical motion of the object relative to the attachment operating the pumping means. The attachment may be disposed on the dock or lock side, as the case may be. The object may comprise a projection that overhangs the attachment on the dock or lock side, as the case may be, and the pumping means may be arranged between the attachment and the projection.

The pumping means may comprise at least one pump that is adapted to pump fluid for the generation of electricity when the level of the body of water is rising.

The pumping means may comprise at least one pump that is adapted to pump fluid for the generation of electricity when the level of the body of water is falling. The pumping means may comprise at least one pump that is adapted to pump fluid for the generation of electricity when the level of the body of water is rising or falling, for example a two-way pump.

The phase difference may be controlled so that an active period associated with one body of water at least partially overlaps with an inactive period associated with another body of water.

The phase difference may be controlled so that the respective cycles associated with the at least two such bodies of water do not experience an inactive period at the same time.

Another type of liquid other than water may be used as the fluid. At least two bodies of liquid other than water may be used.

According to a second aspect of the present invention, there is provided apparatus for generating electricity from a change in the vertical level of at least two bodies of water, comprising, for each body of water, an object floating on the water, means for pumping fluid operated in use by the resulting vertical motion of the object, and means for generating electricity from the pumped fluid, wherein the vertical level of each body of water changes in a cyclical manner, with the water rising during at least one part of a cycle and falling during at least one other part of that cycle, and wherein the respective cycles associated with the at least two bodies of water are arranged to be out of phase.

Reference will now be made, by way of example, to the accompanying drawings, in which:

Figures 1 A and IB are schematic diagrams for use in illustrating the operation of ocean tides;

Figure 2 is a schematic diagram illustrating one previously-considered scheme for harnessing the ocean tides to generate electricity; Figures 3 A and 3B schematically illustrate one previously-considered scheme for generating electricity from wave movement;

Figure 4 is a schematic diagram illustrating apparatus for generating electricity upon which an embodiment of the present invention is based;

Figure 5 is a graph showing the presence of active and inactive periods for a body of water affected by the tides;

Figure 6 is for illustrating the operation of an embodiment of the present invention in which two bodies of water with out-of-phase cycles are used to mask inactive periods; and

Figure 7 is a schematic diagram illustrating an embodiment of the present invention in plan view.

The operation of an embodiment of the present invention will be described later with reference to Figures 6 and 7. Before that, a description of one example of the basic apparatus upon which an embodiment of the present invention is based will be provided with reference to Figure 4. The basic apparatus underlying an embodiment of the present invention as shown in Figure 4 is provided for generating electricity from a change in the vertical level of a single body of water 33 in a basin 34. In this example, the basin 34 is a dock in communication with an ocean, so that the vertical level of the body of water 33 is caused to change by the operation of ocean tides. As explained below, an embodiment of the present invention differs mainly in that more than one body of water 33 is used to generate electricity.

The apparatus of Figure 4 comprises an object 32 floating on the body of water 33, pumps 36, a cylinder 38, a piston 40, and an electricity generating station 42. The ocean tides cause the vertical level of the body of water 33 to change in a cyclical manner according to the ocean tides, with the water rising during the part of a cycle between a low tide and a high tide, and falling during the part of a cycle between a high tide and a low tide. The changing vertical level of the body of water 33 results in the vertical motion of the object 32, and this vertical motion of the object is employed to operate the pumps 36.

The pumps 36 operate under the pressure of the moving object 32 and are employed to pump water 44 from the body of water 33 in the basin 34 to the water cylinder 38. A piston 40 acting under gravity is arranged in the cylinder 38 to apply additional pressure to the water in the cylinder 38. In order to supply water to the cylinder 38, the pumps 36 must supply the water 44 at a pressure that is sufficient to raise both the water above the point of entry into the water cylinder 38 and the piston 40.

The water cylinder 38 is located at a vertical height above the electricity generating station 42 so that the hydrostatic head that is developed by virtue of the height of the water in the cylinder 38 above the electricity generating station 42, together with the additional weight of the piston 40, is sufficient to deliver water from the cylinder 38 to the electricity generating station 42 with a sufficient pressure to enable a predetermined electricity generation output. Electricity is generated at the electricity generating station from the pressure of the water 46 acting on turbines in the electricity generating station 42. In this respect, the electricity generating station 42 can be of a type known from existing hydroelectric power generation stations. The mass of the object 32 in this embodiment is of the order of tens of thousands of tons, and the mass of the piston 40 is of the order of tens of tons. After use in the electricity generating station 42, the water is preferably returned to the basin 34.

The pumps 36 are also operable to cause water 45 to be pumped directly to the electricity generating station 42 for the generation of electricity. When water 45 is pumped directly to the electricity generating station 42, the water 45 must be of sufficient pressure to drive the turbines if electricity generation is to be maintained at a predetermined output. The choice as to whether to deliver water to the electricity generating station 42 from the cylinder 38 or directly from the pumps 36 (or a combination of both) depends on the available pressure from the pumps 36, which in turn depends on the vertical motion of the object 32 on the body of water 33, as will now be explained. The ocean tides cause the vertical level of the body of water 33 in the basin 34 to change in a cyclical manner, as shown in Figure 5. The cycles comprise active periods A in which the vertical motion of the object 32 is sufficient to operate the pumps 36 to deliver water 45 with a sufficient pressure to the electricity generating station 42 to enable a predetermined electricity generation output. The cycles also comprise inactive periods I in which the vertical motion of the object 32 is not sufficient to operate the pumps 36 to deliver water 45 with a sufficient pressure to the electricity generating station 42 to enable a predetermined electricity generation output. The predetermined electricity generation output may be, for example, anything greater than zero, or may be any other threshold.

With the object 32 moving up and down with the water 33 as illustrated in Figure 5, the inactive periods I occur around the turn-around points between the rising and falling of the vertical level of the body of water 33. During the mactive periods I, the object 32 is not moving sufficiently to generate enough pressure in the water 45 delivered to the electricity generating station 42. On the other hand, during the active periods A, the pumps 36 are able to deliver sufficient pressure in the water 45 to generate electricity to a predetermined output level at the electricity generating station 42. In the absence of the water cylinder 38, this would result in an intermittent generation of electricity, with periods I in which no electricity is generated, or electricity is generated at an insufficient level of output.

The use of the water cylinder 38 enables sufficient water to be pumped into the cylinder 38 to enable the generation of electricity from the water in the cylinder 38 during at least part of the inactive periods I, and preferably during the whole of the inactive periods I. This enables a continuous supply of electricity from the electricity generating station 42. Of course, because of the requirement for water 44 delivered from the pumps 36 to the cylinder 38 to be of a sufficient pressure to fill the cylinder 38, there are also active and inactive periods associated with the pumping of water into the cylinder 38. Therefore, sufficient water 44 should be pumped into the cylinder 38 during the active periods of the cylinder 38 to maintain electricity generation at a predetermined output level during the inactive periods. In this example, where the vertical level of the body of water 33 is determined by the ocean tides, a cycle lasts for approximately 12 hours, with the time between a high and a low being approximately 6 hours. It can be expected, therefore, that an inactive period, which occurs around the turn-around point between the rising and falling of the tides, would be approximately 2.5 hours long.

In this example the pumps 36 are two-way pumps which operate to pump water in the same direction when the object 32 rises and when the object 32 falls. Two pumps 36 are used, arranged on opposite sides of the object 32 so as to stabilise the object as it rises and falls, with substantially equal reaction forces between the object 32 and the pump 36 on both sides of the object 32. The object 32 comprises a projection that overhangs an attachment on the basin 34, with the pump 36 arranged between the attachment and the projection.

Although the example described above with reference to Figure 4 was described in relation to a body of water 33 in communication with an ocean, so that the basin 34 is a dock, it will be appreciated that an embodiment of the present invention can operate in a similar manner when the body of water is in a lock, for example a river lock, where the vertical level of the body of water 33 is caused to change by water flowing into or out of the lock. The vertical level of the body of water 33 is controlled by the use of one or more gates across an opening to the lock which are operated to control the amount of water in the lock. With such an embodiment, the height of the water in the lock can be controlled to any profile, not necessarily that shown in Figure 5. For example, the profile may be saw-shaped; with such a profile, there is a minimal turn-around time between the rising and falling of the body of water 33 and therefore the inactive periods described above with reference to Figure 5 will be much shorter. With shorter inactive periods, the cylinder 38 can be much smaller so as to maintain a much smaller amount of water for use in generating electricity during the inactive periods.

Although the example described above with reference to Figure 4 made use of two pumps, it will of course be appreciated that any number of pumps may be used. The more pumps that are used, the more water that can be pumped. Even the use of one pump is possible, with appropriate means for stabilising the object 32 in the water 33. It will also be appreciated that the use of two-way pumps is not essential. For example, if two pumps are used, one could be a one-way pump acting when the object 32 is rising, and the other pump could be a one-way pump acting when the object 32 is falling. Even a single one-way pump would be possible, using an appropriate scheme to maintain the electricity supply above a certain level as described above, if required. The electricity generating station 42 is preferably located close to the electricity grid for ease of supply thereto.

The use of a piston 40 to apply additional pressure to the water in the cylinder 38 is also not essential. If the cylinder 38 is located at a sufficient height, the potential energy of the water itself being converted to kinetic energy by the time it reaches the electricity generating station 42 would be sufficient to apply enough pressure to the turbines of the electricity generating station 42 so as to generate sufficient electricity.

In an embodiment of the present invention, as an alternative to, or as well as, the use of a water cylinder 38 to maintain the generation of electricity at a predetermined level, two or more bodies of water 33 are employed in a similar way as described above to generate electricity, as will now be explained with reference to Figures 6 and 7.

Figure 6 is a graph showing the water height profiles associated with the use of two bodies of water to generate electricity. The respective heights of the first and second bodies of water are illustrated as changing in a manner similar to that shown in Figure 5. However, the respective cycles associated with the two bodies of water are arranged to be out of phase, with the phase being controlled so that an active period associated with one body of water completely covers an inactive period associated with the other body of water. In this way, when the pressure of water from the pumps associated with the first body of water is insufficient to drive directly the turbines or fill the cylinder 38, the pressure of water from the pumps associated with the other body of water is sufficient, thereby enabling the generation of electricity to be maintained at a predetermined level.

Even with a body of water 33 in a dock, with the vertical level being affected by the ocean tides, it is possible to control the level of the body of water 33 by the use of one or more gates across an opening to the dock which are operated to control the amount of water in the dock. This would enable two such docks to be used with the relative water level cycles of the two docks being controlled in a similar manner to that shown in Figure 6. This could be achieved with two docks as follows. As the tide turns from a high point and starts to fall, the gates of the first dock would be closed to hold water in the dock, while the water level in the second dock is allowed to fall. As the water level in the second dock approaches the level associated with an inactive period, the gates of the first dock would be opened to allow the water level in the first dock to fall. By the time the level of water in the first dock reaches a point associated with an inactive period, the water level in the second dock will have started to rise above the point associated with the end of the inactive period of that dock. Such a process would be repeated to maintain the generation of electricity above a predetermined output level.

A particular embodiment of the present invention operating according to the above principles will now be described with reference to Figure 7. The apparatus comprises four basins 34A, 34B, 34C and 34D. Basins 34A and 34B respectively contain two bodies of water 33A and 33B on which two objects 32A and 32B are respectively floating. The objects 32A and 32B rise and fall according to the vertical level of the respective bodies of water 33A and 33B, and this motion is used to operate pumps 36. Tidal water is supplied from the ocean 17.

As described above, the pumps 36 are caused by this motion to pump a fluid such as water, although in this embodiment the fluid being pumped by the pumps is a gas such as ordinary air. The pumped gas is fed to a gas container or holding reservoir analogous to the cylinder 38 described above, where it is stored under compression. The compressed gas is subsequently used to drive the generators to generate electricity at the electricity generating station 42. The capacity of the gas cylinder can be chosen according to how much potential energy it is required to store in order to meet the energy requirements and to maintain electricity production above a predetermined level. The number of pumps 36 used can also be varied according to demand and electricity production requirements.

The manner of filling and emptying the basins 34A, 34B, 34C and 34D will now be described (referring to these in short-hand simply as A, B, C and D). For this description, the following starting point will be assumed. The ocean 17 is at high tide, with water in basins A, B and C being held at a high tide level (substantially full) and the water in basin D being held at a low tide level (substantially empty). To enable this, sluice gates are provided between basins A and C, basins B and D, as well as between respective basins A and B and the ocean 17. Sluice gates are also provided between basins A and D and between basins B and C. All sluice gates are initially closed.

Next, the sluice gates between basins A and D are opened to allow water to empty from basin A into basin D. Basins C and D are of a much greater capacity than basins A and B to allow for this. The falling level of the body of water 33 A in basin A causes the floating object 32 A to drop, and this in turn operates the pumps 36 to supply more compressed air to the gas cylinder 38. The sluice gates between basins A and D are then closed.

When basin A is emptied by the above process, the sluice gates between basins B and D are opened to allow water to empty from basin B into basin D. Again, the falling level of the body of water 33B in basin B causes the floating object 32B to drop, and this in turn operates the pumps 36 to supply more compressed air to the gas cylinder 38. The sluice gates between basins B and D are then closed.

After the above process of emptying basins A and B into basin D, basins A and B will be substantially empty, or at a level comparable to that in basin D. At this stage, the tide will still be high enough to allow basins A and B to be re-filled by opening the sluice gates between respective basins A and B and the ocean 17 and again closing them when the basins are full. The rising level of the bodies of water 33A and 33B in respective basins A and B will cause the floating objects 32A and 32B to rise, and this in turn operates the pumps 36 to supply more compressed air to the gas cylinder 38.

Of course, the re-filling of basin A can be overlapped with the emptying of basin B, and vice-versa, to provide a more continuous supply of compressed gas to the cylinder 38. When basin A is again full, the above process is repeated to empty basin A into basin D. Likewise, when basin B is again full, the above process is repeated to empty basin B into basin D.

The emptying of basins A and B into D and subsequent re-filling of basins A and B from the ocean 17 continues until the tide has fallen to a level such that it is unable to re-fill basins A and B sufficiently. When this occurs, the water in basin C (which is initially held at high tide level) is instead used to top up basins A and B during the above process, making use of the sluice gates between basin C and basins A and B. Likewise, if the level of water in basin D has risen to an extent that it is higher than the ocean water 17, basins A and B can be emptied into the ocean 17 instead of basin D in the above process.

This continues until the tide reaches the low point. Basin D is then emptied into the ocean 17 through a channel under or around basin B (or optionally through basin B itself).

A similar process is then performed as the tide starts to rise. Due to its large capacity, basin C is still able to fill basins A and B as the tide rises, with those basins emptying into the ocean 17. When the tide has reached a sufficiently high level, basins A and B can instead be filled from the ocean 17, emptying into basin D. The emptying and filling of basins A and B is again performed with overlapping cycles to ensure a continuous supply of compressed gas to the cylinder 38.

At high tide, basin C is filled from the ocean water 17 through a channel under or around basin A (or optionally through basin B itself), and due to the large capacity of basin D it remains at a low level. This returns the basins to the state described at the start of the process, allowing the process to be repeated time after time.

With an embodiment of the present invention as described with reference to Figure 7, the pressure of compressed air being supplied by the pumps 36 to the gas cylinder 38 can be arranged so as always to be higher than the pressure of air leaving the cylinder 38 to drive the turbines. This allows a continuous feed of compressed air into the cylinder 38 which in turn allows a continuous supply of compressed air to the turbines and in turn a continuous supply of electricity. The pressure can be monitored to regulate the pressure of gas supplied to the turbines. If necessary, a reserve cyhnder can be provided which is charged up during periods where supply of compressed gas exceeds demand, and this reserve cylinder can be used to top up the main gas cylinder (the pressure in the reserve cylinder being higher than that in the main cylinder) during periods where demand is exceeding supply or when the level of water in basin C is not sufficiently high to enable supply at a predetermined level. The reserve cylinder could also be used to drive the turbines directly.

It will be appreciated that the positioning of the basins is not limited to that shown in Figure 7. For example, basins A and B could be provided to the sides of basins C and D respectively, allowing direct access from basins C and D to the ocean. Other arrangements are possible. It will also be appreciated that a more than two object- containing basins could be used, and/or more than one object provided in each such basin, and also more than two basins such as basins C and D could be provided if necessary.

Claims

CLAIMS:

1. A method of generating electricity from a change in the vertical level of at least two bodies of water by, for each body of water, floating an object on the water, employing the resulting vertical motion of the object to operate means for pumping fluid, and employing the pumped fluid to generate electricity at an electricity generating station, wherein the vertical level of each body of water changes in a cyclical manner, with the water rising during at least one part of a cycle and falling during at least one other part of that cycle, and wherein the respective cycles associated with the at least two bodies of water are arranged to be out of phase.

2. A method as claimed in claim 1, wherein electricity is generated from the pressure of the pumped fluid at the electricity generating station.

3. A method as claimed in claim 1 or 2, wherein the vertical level of each body of water changes in a cyclical manner, with the water rising during at least one part of a cycle and falling during at least one other part of that cycle.

4. A method as claimed in claim 3, wherein the vertical level of each body of water changes in a predetermined manner.

5. A method as claimed in any preceding claim, wherein the pumped fluid comprises a gas.

6. A method as claimed in any preceding claim, wherein the pumped fluid comprises water.

7. A method as claimed in claim 6, wherein the pumping means cause water to be pumped from the body of water itself.

8. A method as claimed in claim 6 or 7, wherein the pumping means are operable to cause water to be pumped directly to the electricity generating station for the generation of electricity.

9. A method as claimed in claim 8, wherein a cycle comprises at least one active period in which the vertical motion of the object is sufficient to operate the pumping means to deliver water with a sufficient pressure to the electricity generating station to enable a predetermined electricity generation output, and at least one inactive period in which the vertical motion of the object is not sufficient to operate the pumping means to deliver water with a sufficient pressure to the electricity generating station to enable a predetermined electricity generation output.

10. A method as claimed in claim 9, wherein an inactive period occurs around the turn-around point between the rising and falling of the vertical level of the body of water.

11. A method as claimed in claim 9 or 10, wherein the pumping means cause water to be pumped directly to the electricity generating station during at least part of an active period.

12. A method as claimed in any preceding claim, wherein the pumping means are operable to cause fluid to be pumped to a holding reservoir for subsequent delivery to the electricity generating station for the generation of electricity.

13. A method as claimed in claim 12, wherein a cycle comprises at least one active period in which the vertical motion of the object is sufficient to operate the pumping means to deliver fluid with a sufficient pressure to the holding reservoir, and at least one inactive period in which the vertical motion of the object is not sufficient to operate the pumping means to deliver fluid with a sufficient pressure to the holding reservoir.

14. A method as claimed in claim 13, wherein the pumping means cause sufficient fluid to be pumped to the holding reservoir during an active period to maintain a sufficient amount of fluid in the holding reservoir to enable the generation of electricity from the fluid in the holding reservoir during at least part of an inactive period.

15. A method as claimed in claim 14, wherein the pumping means cause a sufficient amount of fluid to be maintained in the holding reservoir to enable the generation of electricity from the fluid in the holding reservoir during the whole of the inactive period.

16. A method as claimed in any one of claims 12 to 15, when dependent on claim 5, wherein the holding reservoir is a gas container for holding the pumped gas under pressure.

17. A method as claimed in any one of claims 12 to 15, when dependent on claim 6, wherein the holding reservoir is located at a vertical height above the electricity generating station.

18. A method as claimed in claim 17, wherein the vertical height is sufficient to deliver water under its own weight to the electricity generating station with a sufficient pressure to enable a predetermined electricity generation output.

19. A method as claimed in claim 17 or 18, wherein additional pressure is applied to the water in the holding reservoir to achieve sufficient pressure of the water delivered to the electricity generating station.

20. A method as claimed in claim 19, wherein a weight pressing down on the water in the holding reservoir is employed to apply the additional pressure.

21. A method as claimed in claim 20, wherein the holding reservoir is a cylinder and the weight is a piston acted on by gravity.

22. A method as claimed in any preceding claim, wherein the at least two bodies of water are in separate docks in communication with an ocean, the vertical level of each body of water being caused to change by the operation of ocean tides.

23. A method as claimed in any one of claims 1 to 21 , wherein the at least two bodies of water are in separate locks, the vertical level of each body of water being caused to change by water flowing into or out of the lock.

24. A method as claimed in claim 22 or 23 , wherein the vertical level of each body of water is also controlled by the use of one or more gates across an opening to the dock or lock, as the case may be, which are operated to control the amount of water in the dock or lock, as the case may be.

25. A method as claimed in any preceding claim, wherein the pumping means are arranged between the object and an attachment the vertical level of which is not affected, at least as much as the object, by the change in vertical level of the body of water, the vertical motion of the object relative to the attachment operating the pumping means.

26. A method as claimed in claim 25, when dependent on claim 22 or 23, wherein the attachment is disposed on the dock or lock side, as the case may be.

27. A method as claimed in claim 26, wherein the object comprises a projection that overhangs the attachment on the dock or lock side, as the case may be, and the pumping means are arranged between the attachment and the projection.

28. A method as claimed in any preceding claim, wherein the pumping means comprise at least one pump that is adapted to pump fluid for the generation of electricity when the level of the body of water is rising.

29. A method as claimed in any preceding claim, wherein the pumping means comprise at least one pump that is adapted to pump fluid for the generation of electricity when the level of the body of water is falling.

30. A method as claimed in any preceding claim, wherein the pumping means comprise at least one pump that is adapted to pump fluid for the generation of electricity when the level of the body of water is rising or falling.

31. A method as claimed in claim 30, wherein said at least one pump that is adapted to pump fluid for the generation of electricity when the level of the body of water is rising or falling is a two-way pump.

32. A method as claimed in any preceding claim, when read as appended to claim 9 or 13, wherein the phase difference is controlled so that an active period associated with one body of water at least partially overlaps with an inactive period associated with an other body of water.

33. A method as claimed in claim 32, wherein the phase difference is controlled so that the respective cycles associated with the at least two such bodies of water do not experience an inactive period at the same time.

34. A method as claimed in any preceding claim, when dependent on claim 6, modified in that another type of fluid other than water is used.

35. A method as claimed in any preceding claim, modified in that at least two bodies of liquid other than water are used.

36. Apparatus for generating electricity from a change in the vertical level of at least two bodies of water, comprising, for each body of water, an object floating on the water, means for pumping fluid operated in use by the resulting vertical motion of the object, and means for generating electricity from the pumped fluid, wherein the vertical level of each body of water changes in a cyclical manner, with the water rising during at least one part of a cycle and falling during at least one other part of that cycle, and wherem the respective cycles associated with the at least two bodies of water are arranged to be out of phase.