GB2538548A

GB2538548A - Power take-off system for a wave energy device

Info

Publication number: GB2538548A
Application number: GB1508717.4A
Authority: GB
Inventors: Wilfrid Phillips John
Original assignee: PURE ENERGY PROFESSIONALS Ltd
Current assignee: PURE ENERGY PROFESSIONALS LIMITED
Priority date: 2015-05-21
Filing date: 2015-05-21
Publication date: 2016-11-23
Also published as: GB201508717D0

Abstract

A power take-off system 102 for a wave energy device uses a hydraulic or pneumatic transmission with a reciprocating output drive member 120 to drive a generator. The drive assembly may comprise a ram 104 with a piston 108 and cylinder 106. The reciprocating drive member 120 may be connected to a rotary generator 132 via a rack 124 126 and pinion 134, or it may drive a linear generator directly (figure 5).

Description

POWER TAKE-OFF SYSTEM FOR A WAVE ENERGY DEVICE

The present invention relates to a power take-off system for use with a wave energy device. The present invention also relates to a system for generating energy from the motion of waves comprising the same. The present invention further relates to a wave energy installation comprising the power take-off system.

Wave energy devices are well known in the art and are now being applied on a commercial scale. In general, wave energy devices operate to convert the movement of waves at the surface of a body of water, such as a sea or ocean, into energy. A wide range of arrangements for wave energy devices have been proposed in the art. The present invention relates to a power take-off system for use with a wave energy device that generates energy from the relative movement of two or more components of the device. Such movement is oscillatory in nature and is generated by the action of waves passing the wave energy device, herein referred to as 'incident waves'.

Known wave energy devices respond to the action of incident waves by generating relative movement between two or more components of the device. For efficient operation, the energy of a wave converted into relative movement of the two or more components of the wave energy device must be recovered by a take-off system as efficiently as possible.

It is known to employ a hydraulic power take-off system that operates to use the relative movement of two or more components of the wave energy device to generate a stream of pressurised hydraulic fluid, for example by the use of one or more hydraulic rams. The flow of pressurised fluid may then be used to power a hydraulic motor driving a generator, typically a rotary generator, to produce electrical energy.

In an alternative arrangement, the relative movement of two components of the wave energy device is used directly to drive a linear generator to produce electrical energy. This arrangement has the advantage of being more efficient in recovering energy from the relative movement of the components of the wave energy device than the aforementioned hydraulic system. However, the linear generator arrangement is generally specific to the type of wave energy device.

Power take-off systems have been investigated in the art. For example, WO 2005/045243 discloses a control system for wave energy devices comprising a rotary absorber receiving a stream of pressurised fluid generated by the action of the wave energy device. The control system operates to adjust the speed of rotation of the rotary absorber according to the velocity of fluid flowing through the absorber. In this way, the efficiency of the absorber may be optimised.

US 7,581,901 discloses a wave energy converter comprising a point absorber wave energy apparatus having first and second devices. The first device is arranged to float at the surface of the body of water. The second device is a submerged body. The converter comprises linkages between the first and second devices, whereby energy resulting from the relative movement of the first and second devices may be recovered. By allowing the second device to trap a volume of the surrounding water, the operation of the converter may be tuned to the prevailing conditions.

IE 2010/0469 concerns a wave energy converter. The converter comprises a wave energy absorber for absorbing energy from incident waves. A power take-off assembly is coupled to the wave energy absorber for recovering energy. The converter comprises an orientating mechanism operable to adjust the orientation of the power take-off assembly in response to changes in the orientation of the wave energy absorber.

A wave energy conversion system is described and shown in US 2012/139261. The system comprises a wave energy absorber for absorbing energy from incident waves. The wave energy absorber drives a switched reluctance machine. In this way, mechanical energy is converted into electrical energy. The switched reluctance machine has a generating mode and a monitoring mode. The system comprises a sensor for sensing an operating parameter of the wave energy absorber. The operating mode of the switched reluctance machine is controlled in response to the sensed operating parameter of the wave energy absorber. The system employs a mechanical linkage between the wave energy absorber and the switched reluctance machine. This is indicated in US 2012/139261 to avoid the need to use pneumatic or hydraulic systems, thereby increasing efficiency of the energy recovery.

Perhaps most recently, GB 2519399 discloses a heaving buoy wave energy converter with an oscillating water column (OWC) power take-off assembly. The wave energy converter comprises a resonant having buoy point absorber having a surface piercing float. The absorber is coupled to an adjustable reference mass having a cavity for accommodating water. The buoy and the mass are arranged to move relative to one another in response to incident waves. A chamber is provided within the buoy and is in fluid communication with the surrounding water, so as to trap a volume of air above an enclosed volume of water. The height of the enclosed column of water varies as the point absorber reacts against its surface by means of an adjustable air-spring. A power take-off turbine is driven by a stream of pressurised air vented from the chamber, as the point absorber moves. The reference mass may be adjusted by varying the amount of water held therein.

Switched reluctance generators may be used to adjust the resistance of the turbine.

There is a need for an improved power take-off assembly for use with wave energy devices. It would be advantageous if the assembly could be employed with a variety of different designs of wave energy device with little or no modification. In addition, it would be advantageous if the power take-off assembly could be adjusted to suit the operation of the wave energy device and/or the prevailing conditions of operation, such as the frequency and intensity of the incident waves.

Surprisingly, it has been found that a most advantageous power take-off system is one employing a reciprocating output drive member for driving a generator, for example by means of a rack and pinion assembly. The output drive member, such as the rack of the rack and pinion assembly, is reciprocated under the action of a drive assembly, for example a ram, driven by a stream of pressurised fluid produced by the relative movement between two or more components of the wave energy device. The output drive member in turn drives the generator, for example the rack in turn drives one or more pinions, each attached to a generator, preferably a rotary generator, for generating electrical energy.

Accordingly, in a first aspect, the present invention provides a power take-off system for a wave energy device, the system comprising: a drive assembly, in use the drive assembly being driven by a stream of pressurised fluid produced by the operation of the wave energy device, the drive assembly having an output drive member moving, in use, in a reciprocating manner; and an electrical generator coupled to the output drive member.

The system of the present invention allows energy to be recovered from the wave energy device, and in turn the incident waves, at a high efficiency. The system is suitable for use with control methods and systems, which allow the operation of the energy recovery and generation assemblies to be optimised to the particular design of the wave energy device, its mode of operation and/or the prevailing conditions, such as the magnitude and frequency of the incident waves. In addition, the power take-off system of the present invention may be adapted with little or no modification for use with a wide range of different wave energy devices. Indeed, the system may be employed with any wave energy device that can generate a stream of pressurised fluid, for example by means of hydraulic ram, as described in more detail hereinafter.

The power take-off system of the present invention may be employed with any wave energy devices that are operable to generate a stream of pressurised fluid, for example by means of one or more hydraulic rams. Such wave energy devices are known in the art and examples are now being tested and applied on a commercial scale. The power take-off system may be mounted to the wave energy device. Alternatively, one or more components of the power take-off system may be located remote from the wave energy device. In this embodiment, the pressurised fluid is provided to the power take-off system from the wave energy device by suitable lines or conduits.

The system of the present invention may be employed with a wave energy device to capture energy from waves at the surface of any body of water. For example, the system may be employed to recover energy from the action of waves in seas, oceans or lakes.

The wave energy device is disposed in the body of water and responds to incident waves. The wave energy device may be disposed at or on the surface of the water. Alternatively, part or all of the wave energy device may be disposed below the surface. Suitable wave energy devices are known in the art.

As noted above, the power take-off system of the present invention employs a stream of pressurised fluid generated by the action of the wave energy device in response to incident waves. The stream of pressurised fluid may be a stream of compressed gas, such as air. More preferably, the pressurised fluid is a liquid, in particular a hydraulic liquid. Suitable hydraulic liquids for use in such systems are known in the art.

The system of the present invention comprises a drive assembly. In operation, the drive assembly receives and is driven by the stream of pressurised fluid generated by the wave energy device. The drive assembly comprises an output drive member. Operation of the drive assembly under the action of the pressurised fluid produces an oscillating motion of the output drive member. Preferably, the drive assembly operates to produce a reciprocating motion of the output drive member.

The drive assembly may be of any configuration that generates an oscillating, preferably reciprocating, motion in an output drive member from a stream of pressurised fluid. In a preferred embodiment, the drive assembly comprises a ram assembly. The ram assembly comprises a piston, in particular a piston moveable in a reciprocating manner in a cylinder, the output drive member being connected directly or indirectly to the piston. In one preferred arrangement, the output drive member is connected directly to the piston.

In operation, the pressurised fluid from the wave energy device is supplied to the ram assembly so as to act on the piston and move the piston in a reciprocating manner. Suitable ram assemblies for use in the drive assembly of the system are known in the art and are commercially available.

As noted, the power take-off system of the present invention employs a stream of pressurised fluid, produced by the action of the wave energy device in response to incident waves. The power take-off system may comprise a master ram assembly for generating the stream of pressurised fluid from the relative movement of two or more components of the wave energy device, the pressurised fluid being supplied to the drive assembly of the system, as described above. The master ram assembly is preferably mounted to and forms part of the wave energy device. Again, suitable arrangements for providing a master ram assembly for generating a stream of pressurised fluid from the action of the wave energy device are known in the art.

In one embodiment, the power take-off system comprises a first or master ram assembly, operated by the wave energy device to generate a stream of pressurised fluid, and a second or slave ram assembly forming the drive assembly of the power take-off system and receiving the pressurised fluid, as hereinbefore described. The first and second ram assemblies may be coupled together by suitable conduits or lines to allow for the flow of pressurised fluid between the ram assemblies.

The use of a pressurised fluid as the means for transferring drive from the wave energy device to the drive assembly of the power take-off system provides a significant degree of design freedom. In particular, this allows the drive assembly and the generator to be remote from the wave energy device. This in turn means that the orientation of the components, such as the rack of a rack and pinion of a drive linkage, is not dependent upon the arrangement of components, such as the master ram assembly, on the wave energy device.

In addition, the use of a pressurised fluid system to transfer drive from the wave energy device to the motor of the power take-off system allows the installation to be protected against adverse conditions, such as large waves and heavy seas.

For example, the system of the wave energy device generating the pressurised fluid, such as a master ram assembly, may be locked in position in adverse conditions, under which damage to components of the installation may arise. The drive assembly, such as a slave ram assembly, may be decoupled from the system of the wave energy device generating the pressurised fluid, so as stop drive to the generator. Further safety features may also be included in the pressurised fluid system, for example one or more pressure relief valves, to prevent damage to either one or both of the wave energy device and the power take-off system. Such a use of pressure relief valves in pressurised fluid systems is known in the art.

The output drive member of the drive assembly is coupled to a generator. In one embodiment, the output drive member is coupled directly to the generator. Alternatively, the output drive member indirectly coupled to the generator, for example by means of a drive linkage. The drive linkage may be any assembly that transfers drive from the reciprocating output drive member to the generator. For example, the drive linkage may comprise a chain.

In one preferred embodiment, the drive linkage comprises: a rack connected to the output drive member of the drive assembly, reciprocation of the output drive member generating a reciprocating, substantially linear motion of the rack; and a pinion engaging with the rack, whereby movement of the rack induces rotation of the pinion.

The generator is coupled to the pinion, whereby rotation of the pinion provides drive to the generator.

In this embodiment, the power take-off system further comprises a rack and pinion assembly. The rack of the rack and pinion assembly is connected either directly or indirectly to the output drive member of the drive assembly, whereby in operation, the rack is reciprocated in a substantially linear manner. In one embodiment, the rack is connected directly to the output drive member of the drive assembly. The pinion of the rack and pinion assembly is arranged in conventional manner to engage with the rack, whereby substantially linear movement of the rack causes the pinion to rotate.

In one embodiment, a single pinion is provided, for example driving a single generator. More preferably, two or more pinions are provided, each pinion engaging with the rack to be driven by the movement of the rack. In a preferred embodiment, the system comprises a first pinion engaging with a first side of the rack and a second pinion engaging with a second side of the rack, opposite to the first side.

Each of the first and second pinions may be coupled to the same or to different generators.

The rack and pinion assembly provides a number of technical advantages. In particular, allowing the generator to operate at a higher speed. For example, a greater relative velocity between the stator and the rotor of a rotary electrical generator can be achieved than would normally be possible using a linear drive system, such as is used in the prior art.

The power take-off system of the present invention further comprises a generator. The generator is driven directly or indirectly by the output drive member of the drive assembly and produces electricity. The generator may be a linear generator. More preferably, the generator is a rotary generator. Suitable generators are known in the art and are commercially available.

As noted, the generator may be a linear generator. A linear generator comprises a stator and a reciprocating rod, movement of the rod within the stator generating electrical energy. The linear generator may be coupled to the output drive member of the drive assembly by a drive linkage. In one embodiment, the rod of the linear generator is coupled directly to the output drive member of the drive assembly.

In preferred embodiment, the generator is a rotary generator. The rotary generator may be coupled to the ouput drive member of the drive assembly by a drive linkage. In a preferred arrangement, the drive linkage comprises a rack and pinion, as described above. The rotary electrical generator is coupled to the pinion, whereby rotation of the pinion is employed to generate electrical energy. The generator may be coupled directly to the pinion. Alternatively, the pinion may transfer its drive to the generator via one or more gears, such as arranged in a gearbox.

The use of a rotary electrical generator provides a number of advantages, for example by avoiding the structural problem of maintaining a stable air gap between the moving and stationary components of the machine. In addition, the stroke of the oscillating or reciprocating components of the system, such as the rack, may be varied, without requiring any modification of the generator. This allows the system to be optimised for use with a specific design of wave energy device and/or the conditions prevailing at a particular location or site, without significant modification to the system.

Any suitable rotary electrical generator may be employed in the system of the present invention and suitable generators are known in the art. One particularly preferred rotary electrical generator is a switched reluctance generator. Switched reluctance generators can operate over a very wide range of speeds, while maintaining an efficiency close to their maximum. As a result, switched reluctance generators can operate efficiently over a wide range of different wave conditions and be used for a wide range of different designs of wave energy device.

The power take-off system of the present invention may employ a control system for the generator to optimise the generation of electrical energy. For example, the switched reluctance generator employs a control system to control the reluctance in the stator windings. The control system employs reluctance switching of the switched reluctance generator.

For example, the resistance torque, that is the resistance of the generator to rotation of the rotor, may be adjusted by the control system to match the behaviour of the wave energy device and the prevailing conditions. The torque of the generator may be adjusted continuously or intermittently, as required, in order to maximise the power output of the power take-off system.

The control system may be arranged to respond to one or more operating parameters of the power take-off system and/or the wave energy device. For example, the control system may monitor and respond to the position and speed of movement of the rack.

Again, the use of a control system allows the power take-off system to be tuned and optimised to a particular design of wave energy device and/or the prevailing conditions. The control system may be programmed, for example with software, appropriate to the wave energy device and/or the conditions likely to prevail at the deployment site. Again, this can be achieved with little or no modification to the components of the power take-off system.

Solid state control systems, preferably with no moving parts, are particularly preferred for reasons of robustness and reliability.

In operation, the electrical generator may be employed transitorily as a motor, that is to drive components of the power take-off system, for example to implement advanced control algorithms. In addition or alternatively, the generator may be used to move components of the drive assembly, for example the piston of a ram assembly, or components of the wave energy device, for example the piston of a master ram assembly, to a desired position, such as the centre of a stroke.

In a further aspect, the present invention provides a method for taking power off a wave energy device, the method comprising: generating a stream of pressurised fluid by exposing a wave energy device to waves at the surface of a body of water; supplying the stream of pressurised fluid to a drive assembly, the drive assembly moving an output drive member in a reciprocating manner; employing the output drive member to drive a generator.

As noted above, in one preferred embodiment, the drive assembly comprises a rack, whereby reciprocation of the output drive member generates a reciprocating, substantially linear motion of the rack; the method further comprising: employing the reciprocating, substantially linear motion of the rack to drive a pinion, whereby movement of the rack induces rotation of the pinion; and employing rotation of the pinion to drive the electrical generator, thereby producing electrical energy.

Aspects and features of the method of the present invention are as described hereinbefore.

In a further aspect, the present invention provides an installation for generating electrical energy from the action of waves at the surface of a body of water, the installation comprising: a wave energy assembly operable under the action of incident waves to generate a stream of pressurised fluid; and a power take-off system as described hereinbefore.

The wave energy assembly may comprise a single wave energy device.

Alternatively, the wave energy assembly may comprise a plurality of two or more wave energy devices, known in the art as a 'wave farm'. Each wave energy device may have a dedicated power take-off system. Alternatively, the two or more wave energy devices may be connected to a common system for transporting pressurised fluid to one or more power take-off systems. In this way, variations or irregularities in the supply of pressurised fluid to the or each power take-off system may be smoothed.

A single wave energy device may be arranged to provide pressurised fluid to one or more power take-off assemblies.

The or each wave energy device may be connected directly to one or more power take-off systems, such that pressurised fluid is supplied directly to the or each power take-off system from the respective wave energy device. Alternatively, the installation may comprise an accumulator for storing pressurised fluid, the or each wave energy device providing pressurised fluid to the accumulator and the or each power take-off system drawing pressurised fluid from the accumulator.

In embodiments in which the installation comprises a plurality of power take-off systems, for example when a plurality of wave energy devices are used, such as in a 'wave farm', the systems may be connected to a common electrical output, such as a bus. This allows the electrical energy output to be smoothed. In addition, individual power take-off systems may draw electrical energy from the bus, for example when it is required to operate the generator as a motor to drive the power take-off system, as described hereinbefore.

Embodiments of the present invention will now be described, by way of example only, having reference to the accompanying drawings, in which: Figure 1 is a diagrammatical representation of a wave energy installation incorporating a power take-off system of the present invention; Figures 2a to 2f are diagrammatical representations of examples of wave energy devices that may be employed in the wave energy installation; Figure 3 is a diagrammatical representation of one embodiment of a power take-off system of the present invention; Figure 4 is a simplified schematic representation of one embodiment of a hydraulic circuit for use with the power take-off system of Figure 3; and Figure 5 is a diagrammatical representation of a second embodiment of a power take-off system of the present invention.

Turning to Figure 1, there is shown a wave energy installation. The installation, generally indicated as 2, is shown deployed in a body of water 4, such as a lake, ocean or sea, having a surface 6 with waves 8 and a bed 10.

The installation 2 comprises a wave energy device 20 disposed to be acted upon by the action of the waves 8 at the surface 6 of the body of water 4. The wave energy device 20 comprises two components 22a and 22b that are moved relative to each other by the action of incident waves 8. The wave energy device 20 is shown tethered to the bed 10, by way of example. The wave energy device 20 is further operable to generate a stream of pressurised fluid from the relative movement of the two components 22a and 22b. In the embodiment shown in Figure 1, the wave energy device 20 comprises a master ram assembly 24 operable to generate a stream of pressurised hydraulic fluid.

The installation 2 further comprises a power take-off system 30. Pressurised fluid generated by the wave energy device 20 is provided to the power take-off system 30 by means of a fluid line 32. Fluid is returned to the wave energy device from the power take-off system 30 by a fluid return line 34.

Electrical energy produced by the power take-off system 30 leaves through a cable 36. In the embodiment shown in Figure 1, the cable 36 is electrically connected to a bus 38.

The power take-off system 30 may be mounted to the wave energy device 20 or positioned remotely therefrom, as indicated in Figure 1.

Referring to Figures 2a to 2f, there is shown diagrammatical representations of examples of wave energy devices that may be used to generate a stream of pressurised fluid.

The wave energy devices in Figures 2a to 2f, generally indicated as 52a to 52f, are different in configuration. However, each of the devices 52a to 52f employs a first member 54a to 54f moveable by the action of incident waves and a second member 56a to 56f. The second member 56a to 56f may be a moveable member or be part of a fixed structure. A master ram assembly 58a to 58f is disposed between the first member 54a to 54f and the second member 56a to 56f, whereby relative movement between the first and second members operates the master ram assembly to generate a stream of pressurised hydraulic fluid, as is known in the art.

The devices of Figures 2a to 2f are as follows: Figure 2a: a terminator, often referred to as a 'clam'; Figure 2b: a float operated attenuator; Figure 2c: a type of clam attenuator; Figure 2d: a hinged raft attenuator; Figure 2e: an oscillating wave surge converter; and Figure 2f: a heaving point absorber.

Turning to Figure 3, there is shown one embodiment of a power take-off system of the present invention for use in the installation of Figure 1. The power take-off system, generally indicated as 102, comprises a drive assembly comprising a ram assembly 104 having a cylinder 106 and a piston 108 moveable longitudinally within the cylinder. The cylinder comprises a first fluid port 110 and a second fluid port 112 displaced from the first port. The ports 110, 112 are arranged such that the piston 108 reciprocates therebetween.

The cylinder 106 is secured by mounts 114.

A drive member in the form of a rod 120 is connected at a first end to the piston 108 and for reciprocating movement therewith. A second end of the rod 120 is connected to a rack 122 having opposing upper and lower (as viewed in Figure 3) surfaces 124, 126 provided with a plurality of teeth.

First and second rotary electrical generator assemblies 130a, 130b are provided. Each generator assembly 130a, 130b comprises an electrical generator 132a, 132b, the shaft of which is connected to a respective pinion 134a, 134b in contact with a respective one of the upper and lower surfaces 124, 126 of the rack.

In operation, pressurised fluid is supplied from the wave energy device 20 to one of the first and second fluid ports 110, 112 via the fluid line 32, causing the piston 108 to move in a first direction within the cylinder 106. Once the piston has completed its stroke, the supply of pressurised fluid is provided to the other of the first and second fluid ports 110, 112, causing the piston to move in the reverse direction. Fluid is exhausted from the cylinder 106 by appropriate opening of the fluid ports 110, 112.

The reciprocating movement of the piston 108 is transferred by the rod 120 to the rack 122, the action of which is to drive each of the pinions 134a, 134b of the generator assemblies 130a, 130b. The generators 132a, 132b output electrical energy to the cable 36.

In the arrangement shown in Figure 3, electrical energy is produced during both the forward and reverse movements of the piston 108, the rod 120 and the rack 20 122.

Should it be required, for example to position the piston 108 within the cylinder 106, electrical energy may be supplied to one or both of the generators 132a, 132b, which then act as motors to rotate the respective pinion 134a, 134b and the rack 122.

Figure 4 shows a simplified schematic representation of a hydraulic circuit for use with the power take-off system of Figure 3.

The hydraulic circuit, generally indicated as 202, comprises hydraulic fluid lines interconnecting a master ram assembly 204 operated by the wave energy device, for example in one of the arrangements shown in Figures 2a to 2f, and a slave ram assembly 206 comprised in the drive assembly of the power take-off system. Non-return valves 208 in the hydraulic fluid lines control the flow of hydraulic fluid. Air/hydraulic fluid accumulators 210 each hold a body of hydraulic fluid and ensure that the hydraulic circuit remains filled with fluid. Pressure relief valves 212 are provided in the circuit to provide a safeguard against large forces acting on the master ram assembly 204 damaging components of the system.

Turning now to Figure 5, there is shown a second embodiment of a power take-off system of the present invention for use in the installation of Figure 1. The power take-off system, generally indicated as 302, comprises a drive assembly comprising a ram assembly 304 having a cylinder 306 and a piston 308 moveable longitudinally within the cylinder. The cylinder 306 comprises a first fluid port 310 and a second fluid port 312 displaced from the first port. The ports 310, 312 are arranged such that the piston 308 reciprocates therebetween.

The cylinder 306 is secured by mounts 314.

A drive member in the form of a rod 320 is connected at a first end to the piston 308 and for reciprocating movement therewith. A second end of the rod 320 is connected to the rod 322 of a linear electrical generator 324. As a result, reciprocating movement of the rod 320 generates a corresponding reciprocating motion of the rod 322 of the linear generator 324.

In operation, pressurised fluid is supplied from the wave energy device 20 to one of the first and second fluid ports 310, 312 via the fluid line 32, causing the piston 308 to move in a first direction within the cylinder 306. Once the piston 308 has completed its stroke, the supply of pressurised fluid is provided to the other of the first and second fluid ports 310, 312, by appropriate operation of the hydraulic circuit, causing the piston 308 to move in the reverse direction. Fluid is exhausted from the cylinder 306 by appropriate opening of the fluid ports 310, 312.

The reciprocating movement of the piston 308 is transferred by the rod 320 to the rod 322. The generator 324 outputs electrical energy to the cable 36, shown in Figure 1.

In the arrangement shown in Figure 5, electrical energy is produced during both the forward and reverse movements of the piston 308, the rod 320 and the rod 322 of the generator.

Should it be required, for example to position the piston 308 within the cylinder 306, electrical energy may be supplied to the linear generator 324, which then acts as a motor.

Claims

CLAIMS1. A power take-off system for a wave energy device, the system comprising: a drive assembly, in use the drive assembly being driven by a stream of pressurised fluid produced by the operation of the wave energy device, the drive assembly having an output drive member moving, in use, in a reciprocating manner; and an electrical generator coupled to the output drive member.
2. The power take-off system according to claim 1, wherein the drive assembly is arranged to be driven by a stream of pressurised liquid.
3. The power take-off system according to any preceding claim, wherein the drive assembly comprises a ram assembly.
4. The power take-off system according to claim 3, wherein the ram assembly comprises a piston moveable within a cylinder, the output drive member being coupled directly or indirectly to the piston.
5. The power take-off system according to claim 4, wherein the output drive member is coupled directly to the piston.
6. The power take-off system according to any of claims 3 to 5, wherein the power take-off system comprises a master ram assembly and the ram assembly of the drive assembly is a slave ram assembly.
7. The power take-off system according to claim 6, wherein the master ram assembly and the slave ram assembly are hydraulically coupled together by a fluid conduit.
8. The power take-off system according to either of claims 6 or 7, wherein the master ram assembly is mounted to the wave energy device.
9. The power take-off system according to any preceding claim, wherein the output drive member is coupled directly to the generator.
10. The power take-off system according to any of claims 1 to 8, wherein the output drive member is indirectly coupled to the generator by a drive linkage.
11. The power take-off system according to claim 10, wherein the drive linkage comprises: a rack connected to the output drive member of the drive assembly, reciprocation of the output drive member generating a reciprocating, substantially linear motion of the rack; and a pinion engaging with the rack, whereby movement of the rack induces rotation of the pinion; the generator being coupled to the pinion.
12. The power take-off system according to claim 11, wherein the generator is coupled directly to the pinion of the rack and pinion.
13. The power take-off system according to either of claims 11 or 12, wherein the rack of the rack and pinion is coupled directly to the output drive member.
14. The power take-off system according to any of claims 11 to 13, wherein the rack and pinion comprises a plurality of pinions.
15. The power take-off system according to claim 14, wherein a first pinion engages with one side of the rack and a second pinion engages with the opposite side of the rack.
16. The power take-off system according to any preceding claim, wherein the generator is a linear generator.
17. The power take-off system according to any of claims 1 to 15, wherein the generator is a rotary generator.
18. The power take-off system according to claim 17, wherein the rotary generator is a switched reluctance generator.
19. The power take-off system according to any preceding claim, further comprising a control system.
20. The power take-off system according to claim 19, wherein the control system is arranged to respond to one or more operating parameters of the power take-off system.
21. An installation for generating electrical energy from the action of waves at the surface of a body of water, the installation comprising: a wave energy assembly operable under the action of incident waves to generate a stream of pressurised fluid; and a power take-off system as claimed in any preceding claim.
22. The installation according to claim 21, wherein at least part of the power take-off system is remote from the wave energy assembly.
23. The installation according to either of claims 21 or 22, comprising a plurality of wave energy assemblies.
24. The installation according to any of claims 21 to 23, comprising a plurality of power take-off systems.
25. The installation according to claim 24, wherein the power take-off systems are connected to an electrical bus for receiving the electrical energy output by the power take-off systems.
26. A method for taking power off a wave energy device, the method comprising: generating a stream of pressurised fluid by exposing a wave energy device to waves at the surface of a body of water; supplying the stream of pressurised fluid to a drive assembly, the drive assembly moving an output drive member in a reciprocating manner; employing the output drive member to drive a generator.
27. The method according to claim 26, wherein the drive assembly comprises a ram assembly.
28. The method according to claim 27, wherein the ram assembly comprises a piston moveable within a cylinder, the output drive member being coupled directly or indirectly to the piston.
29. The method according to claim 28, wherein the output drive member is coupled directly to the piston.
30. The method according to any of claims 27 to 29, wherein the power take-off system comprises a master ram assembly and the ram assembly of the drive assembly is a slave ram assembly.
31. The method according to claim 30, wherein the master ram assembly and the slave ram assembly are hydraulically coupled together by a fluid conduit.
32. The method according to either of claims 30 or 31, wherein the master ram assembly is mounted to the wave energy device.
33. The method according to any of claims 26 to 32, wherein the output drive member is coupled directly to the generator.
34. The method according to any of claims 26 to 33, wherein the output drive member is indirectly coupled to the generator by a drive linkage.
35. The method system according to claim 34, wherein the drive linkage comprises a rack, whereby reciprocation of the output drive member generates a reciprocating, substantially linear motion of the rack; the method further comprising: employing the reciprocating, substantially linear motion of the rack to drive a pinion, whereby movement of the rack induces rotation of the pinion; and employing rotation of the pinion to drive the electrical generator, thereby producing electrical energy.
36. The method according to any of claims 26 to 35, wherein the generator is a linear generator.
37. The method according to any of claims 26 to 35, wherein the generator is a rotary generator.
38. The method according to claim 37, wherein the rotary generator is a switched reluctance generator.
39. The method according to claim 38, wherein the method comprises adjusting the resistance torque of the switched reluctance generator.
40. The method according to claim 39, wherein the resistance torque is adjusted in response to one or more operating parameters of the power take-off assembly.
41. The method according to any of claims 26 to 40, wherein the generator is transitorily used as a motor to move one or more components of the power take-off assembly.
42. A power take-off assembly for a wave energy device substantially as hereinbefore described having reference to any one of Figures 1 to 5.
43. An installation for generating electrical energy from the action of waves at the surface of a body of water substantially as hereinbefore described having reference to any one of Figures 1 to 5.
44. A method of generating electrical energy from the action of waves at the surface of a body of water substantially as hereinbefore described having reference to any one of Figures 1 to 5.