WO2004090325A1

WO2004090325A1 - Reciprocating blade system for energy extraction from currents

Info

Publication number: WO2004090325A1
Application number: PCT/GB2004/001421
Authority: WO
Inventors: Lionel William Mills
Original assignee: Lionel William Mills
Priority date: 2003-04-08
Filing date: 2004-03-29
Publication date: 2004-10-21

Abstract

A multi-vane array apparatus suitable for use in a system for extracting energy from a defined water flow (2) is presented. The array (8) comprises a multiplicity of vanes (10) connected to upper and lower elongate vane carriers (16, 18) so as to be supported vertically. The vane carriers (16,18) are provided with anchoring devices (32-34) to anchor them in the water flow (2), so that they extend transversely thereacross. The vanes (10) are pivotally mounted on the vane carriers (8) for pivoting about a vertical axis, so as to be orientatable at an angle to the water flow (2) so as to be drivable, together with the vane carriers (16, 18), to and fro across the water flow. At least one of the vane carriers (16, 18) and the vanes (10) is provided with a control device (21) for retaining said vanes (10) in different ones of a plurality of different angles to the waterflow (2). The anchoring devices (32-34) are formed and arranged so that the multi-vane array (8) is displaceable longitudinally across the flow by the driving force thereof. At least one vane carrier (16, 18) is provided with a drive connection (20) to an energy conversion device (40-50) for converting mechanical power from the longitudinal displacement of the vane carriers (16, 18) into a remotely transmissible form of energy.

Description

RECIPROCATING BLADE SYSTEM FOR ENERGY EXTRACTION FROM CURRENTS

The present invention relates to the field of energy extraction more specifically to the extraction of energy from a flow of water.

There is a need to provide more efficient, cost effective and environmentally friendly alternatives to our present energy sources. Supplies of non-renewable energy sources such as oil, coal and gas will not last indefinitely and they are falling out of favour due to the adverse impact on the environment caused by burning fossil fuels. Nuclear power is plagued with safety hazards and existing methods of extracting solar energy are prohibitively expensive and unsuitable for large scale power plants or climates where sun is in short supply. Devices extracting energy from wind and wave, are being used more frequently but they have a number of drawbacks, an important one being that an equal amount of conventional generation capacity is required to stand idle on standby, in order to provide power when the necessary wind is absent.

The idea of generating power from tidal flow is not new, but to extract significant amounts of power, the method employed has to utilise as large a cross-section of the tidal stream as possible. This is because any energy extraction device will result in an increase in the static pressure locally and the effect of this is to cause the flow of water from upstream to change direction and go round the device which, as a result, then experiences a lower flow speed and hence extracts less power. Many rotating or oscillating vane devices also suffer from the problem that they require a multiplicity of units (each with its own power generation facility) to address the tidal cross-section. Even with such a multiplicity of devices there will in practice still be significant gaps through which the tidal flow may bypass the devices. Many of these devices are also very dependent on having clean aerodynamic surfaces to produce the best results but fouling will occur in the sea unless measures are taken to prevent or remove it. Prevention using antifouling paint is no longer an option in many situations because of the environmental impact of the toxins on sea life. This leaves mechanical removal as the preferred option but in strong tidal streams, it is very difficult and expensive to treat the large areas involved using divers.

EP 1071882 describes a device for extracting power from a current of water. The device has a prime -mover with a protruding control member which generates thrust as the control member and prime mover oscillate in a vertical direction, being driven by the current of water. The device is anchored to the seabed, hence getting power ashore is difficult. A significant problem exists because the mechanical and moving components, susceptible to wear and damage, are located underwater. Servicing and maintenance of the device necessitates divers operating underwater and it will be appreciated that installing and anchoring the device to the seabed, in strong tidal flows is difficult and expensive. The seabed may frequently be of sand or loose material which of course has a degree of buoyancy and loose material will also have water in the interstices, with the result that any large vertical oscillatory forces are likely to cause significant disturbance to the foundations unless they are very extensive and hence very expensive. Significant problems also arise with maintaining such a device in the strong current which is desirable in order to make energy extraction attractive, due to the dangerous working conditions for divers.. It is an object of the present invention to avoid or minimise one or more of the above-mentioned problems or disadvantages.

In a first aspect the present invention provides a system suitable for use in extracting energy from a defined water flow, said system comprising at least one multi-vane array in the form of a multiplicity of vanes connected at upper and lower end portions to upper and lower elongate vane carriers so as to be supported in a substantially vertical orientation and said upper and lower vane carriers being provided with anchoring devices formed and arranged so as to anchor said vane carriers in said defined water flow, in use of the system, so that they extend transversely across said defined water flow; said vanes being pivotally mounted on said vane carriers for pivoting about a substantially vertical axis, so as to be orientatable obliquely across the water flow so as to be drivable, together with the vane carriers, by the water flow, to and fro across the water flow, at least one of said vane carriers and said vanes being provided with control devices for retaining said vanes in different ones of plurality of different angle to the waterflow; said anchoring devices being formed and arranged so that said multi-vane array is displaceable longitudinally thereof, across the flow under the driving force of said water flow impinging on said obliquely directed vanes; at least one said vane carrier being provided with an energy conversion device for converting mechanical power from the longitudinal displacement of said vane carriers, into a remotely transmissible form of energy.

In another aspect the present invention provides a multi-vane array apparatus suitable for use in a system for extracting energy from a defined water flow, said multi-vane array comprising a multiplicity of vanes connected at upper and lower end portions to upper and lower elongate vane carriers so as to be supported in a substantially vertical orientation and said upper and lower vane carriers being provided with anchoring devices formed and arranged so as to anchor said vane carriers in said defined water flow, in use of the system, so that they extend transversely across said defined water flow; said vanes being pivotally mounted on said vane carriers for pivoting about a substantially vertical axis, so as to be orientatable obliquely across the water flow so as to be drivable, together with the vane carriers, by the water flow, to and fro across the water flow, at least one of said vane carriers and said vanes being provided with control devices for retaining said vanes in different ones of plurality of different angles to the waterflow; said anchoring devices being formed and arranged so that said multi-vane array is displaceable longitudinally thereof, across the flow under the driving force of said water flow impinging on said obliquely directed vanes; at least one said vane carrier being provided with a drive connection for coupling thereof, in use of the apparatus, to an energy conversion device for converting mechanical power from the longitudinal displacement of said vane carriers, into a remotely transmissible form of energy.

The most advantageous water flow is a flow of water through a channel formed between opposed land masses which may be the banks of a river, for example a river estuary, or between an island and the mainland, or between two islands. Suitable defined water flows may also be found where the water flow is defined (at least partly) by submarine features, which may not actually break the surface under all or any tidal conditions . Advantageously the vane array apparatus of the invention, is formed and arranged so as to substantially occlude the water channel or other defined water flow with which it is intended to be used. It will of course be understood that in the case of wider channels, it may be preferred to subdivide the channel into a plurality of sections by nodes, with a multi- vane array in each section. The nodes could moreover be fixed structures or moored floating structures. Desirably the area of the multi-vane array (s) i.e. total length x total depth (corresponding generally to the total length of the vane array (s) x the average length of the vanes) is at least 60%, preferably at least 80%, and most preferably at least 90%, of the channel cross-section. Preferably the vanes are more or less substantially spaced apart so as to reduce interference therebetween whilst also ensuring that substantially all the water flow is deflected. Depending mainly on the vane profile selected, the vanes are disposed at a pitch corresponding to from 2 to 8 times, preferably 3 to 6 times, but most preferably from 3.5 to 5 times, for example, 4 times, the vane width.

It will be appreciated that the driving force component exerted longitudinally by the vane carriers will depend on the angle of the vanes to the resultant direction of flow of the water which depends on the water flow speed and the movement of the array. The drag exerted on the vane array by the flow will also depend on the angle at which the vanes are held relative to the resultant direction of flow of the water. The optimum angle for holding the vanes relative to the longitudinal axis of the vane array and the vane carriers thereof, is dependent on in ter alia the cross-sectional (foil) shape of the vanes. If the vanes are held at too great an angle, the vane array will stall and produce the high drag and low driving force. Typically, assuming the vane array extends substantially at right-angles to the water flow direction, it is preferred that the vanes are supported at an angle of from 5 to 18 degrees, e.g. 10 to 18 degrees, advantageously 8 to 15 degrees, e.g. 12 to 15 degrees, most preferably from 10 to 12 degrees, to the direction of the water flow during a principal part of the vane array displacement by the water flow - it being understood that there will inevitably be a finite delay at the beginning and end of each displacement stroke while the angle of the vanes relative to the water flow is being reversed, the vanes being rotated on their vertical pivots to present the other face to the oncoming stream at the end of each stroke, in order to reverse the direction of travel of the vanes and vane carriers .

The vane carriers may be of any suitable form capable of supporting the vanes and transmitting mechanical power resulting from their displacement. Thus, for example, the vane carriers could be in the form of flexible elongate members such as wire or chains which are capable of transmitting tensile forces. It will be appreciated that with such a flexible system only tension can be used to transmit energy from the moving vane carrier. Thus energy can only be abstracted at one end of the vane carrier, as the vane carrier moves away from the energy conversion device.

Thus, in order to maximise the energy that can be abstracted, it would normally be necessary to have an energy convers ion device at each end of a tension-mode operating vane carr ier which can alternately convert the mechanical energy as the vane carrier moves to and fro, transversely across the channel .

Alternatively, the vane carriers are formed and arranged, so as to be capable of transmitting both tension and thrust . Conveniently such a vane carrier is of substantially rigid material and construction. Where a tension and thrust transmitting vane carrier is used, only one energy conversion device need be provided per vane array for abstracting mechanical energy when the vane array moves to and fro relative to the energy conversion device. The energy conversion device can then be at the end closest to the electricity grid and quite possibly onshore. This simplifies and economises installation, maintenance and operation of the system.

Indeed it is a particular feature and benefit of the present invention, that, unlike with many other tidally driven power systems, the proximity of the reciprocally displacing ends of the vane array to the shore, allows the energy conversion devices to be mounted substantially entirely on shore, or at least substantially entirely above water, or protected by a bund or at least afloat in close proximity to shore, all of which provide greater or lesser degrees of reduced environmental attack, and improved ease of maintenance and servicing. In the preferred narrow tidal channels or in fast flowing rivers, there is frequently a need for bridges and the energy conversion device can then be located within the bridge structure which thereby conveniently forms part of the system device. In contrast many conventional designs have their energy conversion devices mounted underwater where they are susceptible to corrosion and other environmental attack, and/or out at sea where they are relatively inaccessible and thus difficult and expensive to service.

It will be appreciated that where both upper and lower vane carriers are coupled to energy conversion device means, they may be coupled individually to respective energy conversion devices, or may be coupled together to the same energy conversion device (s).

Various forms of energy conversion device may be used in accordance with the present invention, depending on, in ter alia , the form and arrangement of the vanes and vane carriers used and to what extent these are capable of transmitting thrust or are restricted to transmitting only tension. Having regard to the reciprocating generally (recti-) linear motion of the vane carriers it is particularly convenient to use an energy conversion device which converts linear motion substantially directly into a remotely transmissible form of energy. Thus, for example, the energy conversion device may take the form of a device for converting motion of the vane carrier (s) directly to electrical energy using, for example, a linear electrical generator. Where this is not possible, it is preferable for the energy conversion device to utilise a hydraulic system. Preferably one or more hydraulic piston and cylinder devices which drive hydraulic fluid under high pressure to produce hydraulic power, is used. The hydraulic power generated can be used in accordance with conventional practice to drive an electrical generator.

Alternatively a hydraulic digital pump or motor such as those available from Artemis Intelligent Power Ltd of Edinburgh, UK, could be used as part of the said energy conversion device. These hydraulic digital pumps and motors are particularly convenient because the resistance of the pumps can be readily adjusted as required. This can accommodate changes in the strength of the flow of water and allows the movement of the vanes and vane carrier to accelerate rapidly to an optimum speed at the beginning of each forward and reverse stroke, and continue to move at that speed during the majority of the period of the stroke. It will be appreciated in this connection, that the water flow will usually vary with time to a greater or lesser extent, even in rivers, and as the vanes generate more power at the optimum speed, it is important to be able to adjust the resistance of the energy conversion system so as to allow the vane assembly to reach optimum operating speed quickly and then to travel at this speed during the remainder of its stroke.

Where it is desired to convert the reciprocating recti-linear vane carrier motion into a rotary motion, for example, in order to drive a dynamo or alternator to generate electricity, or a rotary pump to pump fluid, then this can conveniently be effected by means of conventional devices such as rack and pinion gear devices etc.

Where the energy conversion process involves pressurised fluid, this can be used to drive an electrical generator directly either via a hydraulic motor, or turbine.

Additionally or alternatively, the pressurised fluid could be used indirectly: for example some or all of the pressurised fluid could be conducted to a pumped storage (gravity type) reservoir or held under pressure in a pressurised reservoir, before being used to generate electrical power at a later time .

In general, the drive produced by the vanes is passed to the vane carrier which then acts on one or more hydraulic piston and cylinder devices. Where water speed and hence the driving force is low, the resistance (to the displacement of the piston inside the cylinder), may be adjusted in various different ways. Thus, for example, where two or more piston and cylinder devices are provided, some may be selectively disabled for part or all of the stroke e.g. by either opening valves which prevent pressure building up in the cylinder or simply disconnecting the cylinder (s) mechanically, until the vane carrier reaches the desired speed. In most cases, once the water flow speed in the channel is known, suitable calculations can be used to predict the required resistance which can be adjusted prior to the start of movement. This enables the necessary resistance adjustment to be made prior to the drive loads building up.

It is also possible to adjust resistance in individual piston and cylinder devices, without disabling them entirely, by, for example providing valved or throttled, bypass or relief, passages connecting opposite sides of the piston, and/or by providing variable diameter piston rods, e.g. of telescopic construction, so as to vary the effective cross-sectional area of the piston - in terms of the difference in cross- sectional area of the cylinder occupied by hydraulic fluid at opposite sides of the piston. Further details of such arrangements are discussed in more detail herein below with reference to the detailed description of some preferred embodiments of the invention.

Where two or more hydraulic cylinders are used, it may be advantageous to position them at opposite ends of the vane carrier so that one set is acting in tension and one compression. This reduces the stresses on the carrier when both are in use.; however, these cylinders will normally have a different resistance in compression compared to tension because of the area taken up by the connecting rod. Having said that, it is possible to use piston and cylinder arrangements with somewhat more complex piston rod configurations in order to facilitate adjustment of flow resistance by means of adjusting the volume of fluid displaced for a given piston displacement or to enable the power generation system to be sited at one end only. Thus, for example, the connecting rod may be hollow and will then connect the two pressure-sides of the cylinders via a transfer valve which may be closed and opened automatically according to the direction of movement of the connecting rod relative to the cylinder. Such a transfer valve can allow the vane array to accelerate up to operating speed before it begins to move the piston.

The upper vane carrier may be provided with a buoyancy support. Thus part or all of the upper vane carrier may conveniently be in the form of (or attached to) a floating pontoon with the vanes effectively suspended therefrom above the bottom of the channel, as this can help restrict waterflow bypassing above the vanes. The sides of this pontoon (and the vane carriers in general) are advantageously shaped to direct the water flow smoothly onto the vanes but the upper surface of the pontoon could be used for other purposes such as the support for a bridge (mounted on rollers to allow the pontoon to move to and fro without affecting traffic) .

Although most or all of the energy conversion equipment (typically hydraulic and electrical equipment) would advantageously be on shore, some or all of the energy conversion equipment could instead be mounted on a service pontoon moored to the shore, and coupled, in a suitable manner, to the vane carrier. Such a service pontoon together with said equipment can then all be built in a shipyard rather than at a site selected purely for its high power potential and which could well be a long way from roads and accommodation . Whether the energy conversion equipment is mounted above or below water, however, there generally needs to be a mechanical connection to the shore or a seabed or riverbed anchorage. The drag loads on the vanes can, however, be very high and some movement in the direction of the water flow is usually inevitable notwithstanding the anchoring arrangements. Thrust guides in the plane of the vane array are therefore desirably provided in order to ensure that the piston and connecting rods remain in alignment and thus prevent wear of these components and the hydraulic pressure seals where fitted. Conveniently guide rails are used at each cylinder, in order to ensure that the hydraulic cylinder stays located correctly relative to the array. These guides merely ensure piston alignment, they do not react the heavy drag loads on the vanes caused by the water flow. These loads are reacted by the mooring points which are preferably sited out of the water flow current and if possible at or on each shore.

The vane carrier anchoring devices are generally formed and arranged so that the vane carriers are held against the drag of the water flow whilst still being capable of displacement transversely to the flow under the driving force of the water flowing through the multi-vane array.

The primary vane carrier anchorages (which may typically be heavy chain or linked steel bars connected to the mooring points) have to react the whole of the drag load of the array and hence are advantageously arranged as opposed upstream and downstream catenaries whose final directions as they connect to the mooring points are approximately aligned with the water flow (i.e. unloaded, each catenary would be very slack) . These catenaries may be sited a considerable distance upstream and downstream of the array to which they are connected by tension members which lead eventually to the upper and lower vanes, or the vane carriers, or the elements which link the vanes and vane carriers. The distance to the mooring (and hence the length of these tension members) allows the designed stroke of the array to take place without significant displacement of the array up or downstream, for example, for a 10m stroke, with tension members 100m long, the above displacement would be only 0.14m parallel to the tidal direction and this may be capable of being accommodated in the design of the thrust carriages and cylinders, with or without the use of the piston alignment guide rails mentioned above. The catenaries are heavier than water and therefore hang in mid water from the mooring points. The buoyancy of the tension members may be adjusted where necessary by buoyancy control devices (weights and/or buoyancy floats) so that despite their length, they neither drag on the bottom nor reach close enough to the surface to impede navigation.

In some cases, it may be preferable to eliminate the long tension members and have the catenaries linked to the array using very short tension members. In this case, the reciprocating movement of the vane carriers relative to the stationary catenaries may conveniently be accommodated by arranging for the upper and lower vane carriers to run on rails and rollers at their attachment to the catenary tension members so that there is no need for any significant movement of the catenaries themselves. Where these shorter tension members are used it is preferable to have four catenaries rather than the two catenaries described herein above.

By using the catenaries to react the drag loads in this way, the vane carriers can be constructed relatively lightly and/or in flexibly joined sections, and yet still be capable of transmitting high thrust loads without buckling. Indeed, the vane carriers may even be constructed in short sections with couplings there-between formed and arranged to resist any buckling loads (which can then be more or less fully reacted by the up- and down-stream anchorages) .

Where the upper vane carrier must be kept submerged below the water surface, the upper vane carrier can be made more nearly neutrally buoyant, with the balance of the loading necessary to maintain its depth in the water being provided either by thrust guide rails at either side and/or by buoyancy compensation guideways attached to the underside of the lower vane carrier along which can run "cars" connected to ballast or the seabed at one or more points below the vane array, thus allowing the vane carrier to move to and fro at a set distance from the seabed. When this approach is adopted, the power conversion equipment must also be fixed (i.e. not move up and down with the tide) , so in these cases, the power conversion equipment can be sited ashore and if necessary, camouflaged. It is then possible, by using a buried electrical cable and camouflaged powerhouse, to abstract power and yet leave no visible trace on what may be a beautiful natural scene.

Further preferred features and advantages of the invention will appear from the following detailed description given by way of example of a preferred embodiment illustrated with reference to the accompanying drawings in which: Fig. 1 is a general perspective view of a system of the invention for extracting energy from a tidal water flow through a channel;

Fig. 2 is a detail vertical sectional view of the coupling between the vane array of the system of Fig. 1 and a service pontoon mounting the energy conversion equipment thereof; Fig. 3 is a schematic detail sectional view of one form of piston and cylinder arrangement for use in the energy conversion equipment of Fig. 2;

Fig. 4 is a vertical sectional view illustrating an alternative form of vane array anchorage suitable for use with a system of the invention;

Fig. 5 is a flow diagram indicating fluid flows in another embodiment with variable energy conversion equipment resistance;

Fig. 6 is a similar flow diagram of a further embodiment; Fig. 7 is a schematic perspective view of a multi-vane array installation in a wide channel with synchronised vane array displacement; and

Fig. 8 is a corresponding view of a similar installation with out-of-phase vane array displacement.

Fig. 1 shows a perspective view of a system, represented generally by reference number 1, of the present invention for extracting energy from a tidal water flow 2, the direction of flow of which is indicated by the arrow 4. The tidal water 2 flows through a channel β which is approximately 200m wide and 25m deep. The water 2 generally flows through the channel 6 at up to 3ms^-1.

The system 1 comprises a multi-vane array 8 in the form of twenty vanes 10 (only ten of which are shown for clarity) which are pivotally connected at their upper edge 12 and lower edge 14 to an upper vane carrier 16 and a lower vane carrier 18, respectively. The vane carriers 16, 18 are in the form of rigid elongate members 19. The lower vane carrier 18 house a control device 21 for cyclically changing the angle of the vanes 10 relative to the water flow during operation of the apparatus. The vane carriers 16, 18 transversely span the channel 6 and each end portion 20, of the upper vane carrier is connected to a power pontoon 22, each of which is moored to land 24 on either side of the channel 6 via pontoon moorings 26.

The vanes 10 are held in a vertical orientation between the upper vane carrier 16 and the lower vane carrier 18 and can pivot about a vertical axis via their points of connection 28 to the upper and lower vane carriers 16, 18. The vanes 10 can be rotated to a suitable oblique angle to the direction of the flow of water 4 and retained thereat. The angle at which the vanes 10 are held is controlled by a computer system which is programmed to provide the optimum angle, which is dependent on in ter alia the water flow speed, cross- sectional shape of the vanes etc, on the basis of trials conducted at the commissioning stage of the system, continuous feedback, and/or other suitable means.

The vanes 10 are constructed of pre-stressed glass reinforced concrete and have a standard cross-sectional shape (NACA 0012 symmetrical foils i.e. the breadth of the vane cross-section is 12% of the width of the vane cross-section) . The breadth, width and vertical length of the vanes 10 being 0.3, 2.5m and 25 (or 30)m, respectively.

When the vanes 10 are orientated obliquely across the tidal water flow 2, the water impinging on the vanes 10 results in a force which drives the vanes 10 and the connected upper and lower vane carriers 16, 18 across the channel 6. The vanes 10 and vane carriers 16, 18 travel about 10m across the channel 6, at a speed of about 5ms^-1 when at maximum speed. The angle of the vanes 10 across the tidal flow 2 is changed cyclically to produce a repeating to and fro motion across the tidal flow 2, each stroke being approximately 10m. The vane carriers 16, 18 are connected at catenaries 30, 32 which extend across the channel 6. The catenaries 30, 32 are located upstream and downstream, respectively, of the vanes 10 and vane carriers 16, 18. The catenaries 30, 32 are anchored (via catenary moorings 33) to the land 24 on either side of the channel 6 and the catenaries 30, 32 and vanes 10 are connected to each other by tension members 34 in the form of chains 36 which are approximately 100m long.

Fig. 2 shows the connections of the multi-vane array 8 to the power pontoon 22 and the pontoon mooring 26, in more detail. The upper vane carrier 16 is connected to the piston 40 of one or more hydraulic cylinders 42. A single cylinder is shown for clarity and this is approximately 13m long with an internal bore of around 1 m. As the multi-vane carrier array 8 moves to and fro across the channel 6 the piston 40 is driven alternatively inwards and outwards of the hydraulic cylinder 42 which drives hydraulic fluid 44 within the cylinder 42 under high pressure to drive an electrical generator 46, downstream of a hydraulic accumulator 48 and hydraulic motor 50, according to conventional practice. Using the approximate parameter figures described above it has been estimated that 16MW of power could be generated using a single cylinder at each end of the multi-vane array. However, it will be appreciated that the number and/or size of the cylinders used can be varied depending on the area of vanes, speed of the tidal flow etc.

The power pontoon 22 may be connected to the pontoon mooring 26 via link members 52 and universal joints 54. This allows the floating power pontoon 22 a degree of freedom to move vertically and longitudinally of the channel 6 in concert with the motion of the multi-vane array 8 according to tidal variations, drag etc, thus maintaining alignment of the piston 40 with the cylinder 42.

In the embodiment of the invention shown in Fig. 1 a power pontoon 22 and pontoon mooring 26 are provided at both ends of the multi-vane array 8 and power can, therefore, be extracted from both of the power pontoons 22 during each, stroke.

It is also possible to arrange the relationship of the pistons 40 and cylinders 42 with the motor 50 and electrical generator 46 so that a motor 50 and generator 46 need only be situated at a single location at one end of the multi-vane array 8, while still being capable of extracting power during both strokes of the multi-vane array 8. An example of such an arrangement is shown in Fig. 3. It will be appreciated that this arrangement is advantageous because it reduces construction and maintenance costs which would be incurred if a motor and generator was required at both ends of the multi- vane array.

In Fig. 3 a longitudinal cross-section of the cylinders 42 at the left hand (L) and right hand (R) ends of the multi-vane array 8 are shown for a stroke moving from right to left (Fig. 3A) and a return stroke moving from left to right (Fig. 3B) , as indicated by the bold arrow.

The pistons 40 of the cylinders 42 at the left and right hand ends of the vane array (not shown here) have hollow piston connecting rods 56 which are connected to each other by a pipe 57 so that the working fluid 58 can be transmitted from the right hand cylinder to the left hand cylinder during forward and return strokes thereof. As may be seen from the drawing, the piston 40 is slidably mounted on the tubular piston rod 56 for displacement between an end stop 60 and a secondary stop 61 set back from the end stop 60. An annular flange 62, through which the piston rod 56 can slide, is set still further back and substantially spaced apart from the secondary stop 61 and is formed and arranged so as to act as a flap valve closure for an annular fluid inlet opening 63 at the proximal end 64 of the cylinder 42. The tubular piston rod 56 is provided with openings 65 between the end stop 60 and the secondary stop 61 so that when the slidable piston 40 is retracted from the end stop 60 back to the secondary stop 61 during a forward (right to left as viewed in Fig. 3A) stroke, high pressure working fluid 66 inside the tubular piston rod 56 in front 67 of the piston 40 is isolated from low pressure working fluid 68 to the rear 69 of the piston 40, whilst during the return stroke (see Fig. 3B) the high pressure working fluid 66 inside the tubular piston rod 56 is isolated from low pressure working fluid 70 to the front (LHS) 67 of the piston. Correspondingly the high pressure working fluid 66 inside the tubular piston rod 56 is in communication with the front (LHS) 67 of the piston 40 during the forward stroke, and the rear (RHS) 69 of the piston 40 during the return stroke.

The front end wall 71 of the cylinder 42 (remote from the piston rod 56) has a central fluid inlet aperture 72 which is occluded by a flap valve closure 73 or the like during the forward stroke of the piston 40, and opens during the return stroke. First and second high pressure fluid outlets 74, 75 with one-way valves 76 are provided at front and rear end portions 77, 78 of the cylinder 42 for exhausting high pressure fluid from front and rear sides 67, 69 of the piston 40 during the forward and return strokes thereof, respectively. The outlets 74, 75 are connected 79 to a common supply pipe 80 which transmits high pressure working fluid to the electrical generator 46. As indicated schematically, the fluid inlet openings 63 and 72 at respective ends 78, 77 of the cylinder 42 are in communication with the channel water 81 so that when the respective valve closures 62, 73 open, channel water 81 is drawn into the respective cylinder 42 at the respective side of the piston 40.

In use of the system, it may be seen that at the end of the return stroke the piston 40 will be held against the end stop

60 on the piston rod 56. Then, as the vane array changes direction and begins to drive forward the piston rod 56, the piston 40 will remain in place until the piston rod 56 has moved so far ahead of the piston 40 that the secondary stop

61 engages it. Since the piston 40 is not trying to displace any fluid during this period, it will be appreciated that forward movement of the piston rod 56 will be subject to only relatively low resistance. This allows the vane array and piston rods to build up speed and momentum relatively easily, up to an initial level, whereupon the secondary stop 61 then comes into engagement with the piston 40 and begins to drive it forward and displace pressurised working fluid 66 inside the cylinder at the front side 67 of the piston 40 to be driven out of the forward end outlet 74 towards the generator 46 for driving thereof.

When the piston 40 and piston rod 56 reach the end of the forward stroke and the direction of movement of the vane array, and thus of the piston rod 56, changes, a similar process occurs with the piston rod 56 initially moving without the piston 40, allowing momentum to build up easily, and then subsequently engaging with it and driving high pressure working fluid out through the rear end outlet 75 of the cylinder via the one way valve 76.

As may be seen in the drawing, when the piston 40 at the left-hand side (energy conversion side of the channel) is undergoing a forward stroke, the one at the right-hand side (remote side of the channel) undergoes a return stroke, and vice versa.

In Fig. 4 a multi-vane array 8 is shown in which the lower vane carrier 18 has an elongate downwardly depending housing 82 along the inside of which a small bogie 84 runs. The bogie 84 is connected to an anchor 86 embedded in the seabed 88 by anchor connection members 90 so that the bogie 84 remains in a fixed position as the housing 82 runs back and forth relative to it when the vanes 10 and vane carriers 16, 18 move to and fro across the water channel 6. (If required, the stroke of the multi-vane array 8 could be limited by the end walls 92 of the housing engaging the bogie 84 or other convenient means (not shown) .^' This arrangement anchors the multi-vane array 8, while a degree of flexibility of movement can be introduced by using anchor connection members 90 of appropriate flexibility.

It will be appreciated that various refinements may be included if required to reduce wear and tear in various parts of the system, depending on the forces involved, and in particular any forces tending to distort part of the system. Thus, for example, where the piston cylinder device is mounted on land (as opposed to on a pontoon or other floating support), the cylinders 42 of the energy conversion device may be mounted using bearing mounts 94 permitting vertically upward and downward motion of the cylinders 42 with rising and falling water levels during the tidal cycle, the cylinder being connected to the fluid motor etc by flexible hoses.

Fig. 5 is a schematic flow diagram of another embodiment with variable resistance, with like parts corresponding to those in Figs. 2 and 3 being indicated by like reference numbers. In this simplified drawing there is shown a piston and cylinder device 40, 42 driven by the vane array 8, to transmit pressurised fluid out through a supply pipe 80 to a hydro-electric generator 46 via a pumped storage reservoir or pressurised fluid accumulator 96. The supply pipe 80 is provided with a dump valve 98 arranged so that when it is opened, pressurised fluid transmitted from the cylinder 42 is dumped (conveniently returned to the main body of water 81 in the channel 2) , thereby substantially reducing the resistance to displacement of the piston 40 and so allowing speed and momentum of the piston 40 and vane array 8 to be built up easily - as is desirable at the beginning of a stroke. Once a suitable level of speed and momentum has built up, then the control valve 98 is closed and the piston 40 then used to transmit fluid to the reservoir 96.

The speed of movement of the vane array 8 is fed to a computer 100 which uses this speed to modulate opening of the control valve 98, the angle of the vanes in the vane array 8, the number and pressure of the hydraulic cylinders in operation, as well as the generator operating parameters etc. The computer 100 is advantageously programmed with intelligent feedback monitoring and analysis software so that it effectively learns from experience by trying slightly different settings of these various parameters (especially the vane angle and the resistance to motion) and then comparing the results with the best previously achieved. To optimise the power extracted from the flow, it is highly desirable that the blade array moves at the optimum speed (which is dependant on the tide speed) . In an oscillating system, however, the only period at constant speed can be the middle period after the acceleration and before the deceleration periods which must necessarily be at lower and less efficient speeds. The array needs to be of relatively substantial construction and will thus be quite heavy. So despite the high power being extracted from the tidal flow, the array will take time to reach the optimum operating speed and energy will be lost during the less efficient acceleration and deceleration periods. To reduce these losses, the array is desirably arranged to compress a resilient buffer at each end of its stroke e.g. by using a buffer which compresses a volume of gas. This is illustrated in the modified embodiment of Fig. 6 which is a schematic flow chart similar to that of Fig. 5, and in which like parts corresponding to those in Fig. 5, are indicated by like reference numbers.

In Fig. 6 the dump valve is replaced by a control valve 101. As the array reaches the end of its stroke, the control valve

101 switches the hydraulic flow to an accumulator cylinder

102 containing a trapped gas volume 103 above a piston 104. The incoming hydraulic fluid flow displaces the piston 104 and thereby compresses the trapped gas volume which is subjected to progressively higher pressures as it is adiabatically compressed. (Insulation 106, is provided between the working fluid 105 and gas 103, and around the accumulator 102 in order to limit energy losses due to heat exchange) . The rising gas pressure produces an increase in the fluid pressure and this in turn increases the load on the piston rod 56 of the energy conversion device so that the array is slowed to a halt. By suitably arranging the accumulator cylinder shape, gas volume and pressure, it is possible to bring the array to rest at the end of its stroke. Thereafter, the hydraulic pressure on the piston rod driven by the expansion of the gas 103 will help to accelerate the array back up to optimum operating speed for the return stroke. By storing and returning the kinetic energy of the array in this way, it is possible to extend the time the array is moving at the optimum speed and reduce the acceleration and deceleration phases, thus making the reciprocating action much more efficient.

The embodiment of Fig. 6 also differs from Fig 5 in some further respects. Seawater tends to be corrosive and where fresh water is readily available, this may be preferable for use as the hydraulic fluid. It is non-polluting and is a far less corrosive medium and accordingly in many applications fresh water will be preferred. Thus the piston and cylinder 40, 42 of the energy conversion device, together with the generator 46 and reservoir 96 may form a fresh-water circuit 107 which is isolated from the seawater in which the array is working. Also instead of using a single-acting piston and cylinder unit at each end of the array, on some sites, it is possible to use a double-acting piston and cylinder unit 108 at just one end (whichever is the most convenient) , of the array, together with suitable valved 109 fluid conduit connections 110, to each end 111, 112 of the cylinder 42.

Fig. 7 shows an energy extraction system 113 of the invention suitable for a wide channel 114, which comprises a series 115 of vane arrays 8 mounted in respective channel sections 116 defined between a series of nodes 117. The upper and lower vane carriers 12,14 respectively, are coupled together 118 at each end 119,120, to piston and cylinder energy conversion devices 121 mounted mid-height (relative to the vane arrays 8) on the nodes 117 and all arranged for energy extraction operation in tension only. In this case the displacement of the vane arrays 8 at opposite sides of a given node 117, is synchronised so that the forces (indicated by the bold arrows 122) exerted on the node 117 therebetween are balanced, and there is no significant net displacement force exerted on the node 117. This allows for a relatively simple form of mooring arrangement with just a single mooring point 123 connected by mooring chains 124 to the node 117 being required at each of the upstream and downstream sides 125,

126, thereof. As with the embodiment of Fig. 1, the vanes 10 (only a few shown schematically) of each array 8, are supported by catenaries 32 (only one shown for clarity) extending between the mooring points 123, and connected to the vanes 10 by tension members 34. The energy extracted at each of the nodes 117, is transferred out therefrom by a transmission line 127 connected 128 to the energy conversion devices 121 thereat.

Fig. 8 shows a similar system 129 in which, in order to provide a smoother extracted energy level to the transmission line 127, the vane arrays 8 are controlled (via the angling of the vanes 10), so that the vane array displacements (as indicated by the bold arrows 130) of neighbouring vane arrays 8, are out of phase with each other. It will be appreciated that this will result in fluctuating net displacement forces being exerted on the nodes 117, which will therefore require additional support in order to maintain the positions of the nodes 117. This is provided by using additional mooring chains 124 to connect each node 117 to additional, spaced apart, mooring points 123. (It will be appreciated that, as with Fig.7, various parts of the system have been omitted for the sake of clarity.) It will be appreciated that various modifications may be made to the abovedescribed embodiments. Thus, for example, in order to reduce the need for maintenance by divers, the vanes 10 may be provided with mechanical cleaning devices, conveniently in the form of a sliding fit collar 131 (see Fig.2) mounted on the vane 10 and formed and arranged to be propelled up and down the vanes 10 for scraping and/or brushing them clean - conveniently using some energy diverted from the generator 46 of the energy conversion device.

Various advantages of the invention over the prior art will be apparent from the above. Yet another advantage that may be mentioned is the relative friendliness of the system of the present invention to large fish and mammals e.g. seals, with its relatively large, blunt and relatively slow moving foils unlike propellers and ^'underwater windmills' whose blade tips are both fast-moving and sharp.

Claims

1. A multi-vane array apparatus suitable for use in a system for extracting energy from a defined water flow, said multi- vane array comprising a multiplicity of vanes connected at upper and lower end portions to upper and lower elongate vane carriers so as to be supported in a substantially vertical orientation and said upper and lower vane carriers being provided with anchoring devices formed and arranged so as to anchor said vane carriers in said defined water flow, in use of the system, so that they extend transversely across said defined water flow; said vanes being pivotally mounted on said vane carriers for pivoting about a substantially vertical axis, so as to be orientatable obliquely across the water flow so as to be drivable, together with the vane carriers, by the water flow, to and fro across the water flow, at least one of said vane carriers and said vanes being provided with control devices for retaining said vanes in different ones of plurality of different angles to the waterflow; said anchoring devices being formed and arranged so that said multi-vane array is displaceable longitudinally thereof, across the flow under the driving force of said water flow impinging on said obliquely directed vanes; at least one said vane carrier being provided with a drive connection for coupling thereof, in use of the apparatus, to an energy conversion device for converting mechanical power from the longitudinal displacement of said vane carriers, into a remotely transmissible form of energy.

2. An apparatus as claimed in claim 1 wherein the vanes are arranged in said vane array at a pitch of from 2 to 8 times the vane width.

3. An apparatus as claimed in claim 2 wherein the vanes are arranged in said vane array at a pitch of from 3 to 6 times the vane width.

4. An apparatus as claimed in any one of claims 1 to 3 wherein the vanes are mounted and controlled so as to be disposable at an angle of from 5 to 18 degrees to the direction of the water flow, during a principal part of the vane array displacement by the water flow.

5. An apparatus as claimed in claim 4 wherein said angle is from 10 to 12 degrees.

6. An apparatus as claimed in any one of claims 1 to 5 wherein the vane carriers are comprised by tensile force transmitting flexible elongate members.

7. An apparatus as claimed in claim 6 wherein said elongate members are selected from wires and chains .

8. An apparatus as claimed in any one of claims 1 to 5 wherein the vane carriers are comprised by tensile and thrust force transmitting rigid elongate members.

9. An apparatus as claimed in any one of claims 1 to 8 wherein each of said upper and lower vane carriers is provided with a drive connection for coupling thereof, in use of the apparatus, to a respective energy conversion device.

10. An apparatus as claimed in any one of claims 1 to 8 wherein said upper and lower vane carriers are provided with a common drive connection for coupling thereof together, in use of the apparatus, to an energy conversion device.

11. An apparatus as claimed in any one of claims 1 to 10 wherein the upper vane carrier is provided with a buoyancy support .

12. An apparatus as claimed in claim 11 wherein said vane carrier and buoyancy support include a pontoon having sides formed and arranged for directing water flow smoothly onto the vanes.

13. An apparatus as claimed in any one of claims 1 to 10 wherein the upper vane carrier is provided with limited buoyancy close to neutral buoyancy.

14. An apparatus as claimed in claim 13 wherein the balance of the loading necessary to maintain the upper vane carrier submerged is provided by at least one of thrust guide rails at either side and buoyancy compensation guideways attached to the underside of the lower vane carrier along which can run "cars" connected to at least one of ballast and the bed of the channel below the vane array, thereby allowing the vane carrier to move to and fro at a set distance from the bed.

15. A system suitable for use in extracting energy from a defined water flow, said system comprising at least one multi-vane array in the form of a multiplicity of vanes connected at upper and lower end portions to upper and lower elongate vane carriers so as to be supported in a substantially vertical orientation and said upper and lower vane carriers being provided with anchoring devices formed and arranged so as to anchor said vane carriers in said defined water flow, in use of the system, so that they extend transversely across said defined water flow; said vanes being pivotally mounted on said vane carriers for pivoting about a substantially vertical axis, so as to be orientatable obliquely across the water flow so as to be drivable, together with the vane carriers, by the water flow, to and fro across the water flow, at least one of said vane carriers and said vanes being provided with control devices for retaining said vanes in different ones of plurality of different angle to the waterflow; said anchoring devices being formed and arranged so that said multi-vane array is displaceable longitudinally thereof, across the flow under the driving force of said water flow impinging on said obliquely directed vanes; at least one said vane carrier being provided with an energy conversion device for converting mechanical power from the longitudinal displacement of said vane carriers, into a remotely transmissible form of energy.

16. An apparatus as claimed in claim 15 suitable for use in a wide channel wherein is provided a series of multi-vane arrays mounted in channel sections defined between nodes subdividing the channel into a plurality of sections, with a multi-vane array in each section.

17. An apparatus as claimed in claim 16 wherein the nodes are fixed structures or moored floating structures.

18. An apparatus as claimed in any one of claims 15 to 17 wherein the area of the multi-vane array(s) i.e. total Length x total depth (corresponding generally to the total length of the vane array (s) x the average length of the vanes) is at least 60% of the channel cross-section.

19. An apparatus as claimed in claim 18 wherein said area is at least 90% of the channel cross-section.

20. An apparatus as claimed in any one of claims 15 to 19 wherein are used primary vane carrier anchorages for reacting substantially the whole of the drag load of the array, which comprise opposed upstream and downstream catenaries whose final directions as they connect to the mooring points are approximately aligned with the water flow.

21. An apparatus as claimed in any one of claims 15 to 20 wherein said energy conversion device is provided with a controlled variable resistance for reducing the resistance of the energy conversion device at the beginning of each stroke of the vane-carrier.

22. An apparatus as claimed in any one of claims 15 to 21 wherein said energy conversion device comprises a linear electrical generator.

23. An apparatus as claimed in any one of claims 15 to 21 wherein said energy conversion device comprises a hydraulic device.

24. An apparatus as claimed in claim 23 wherein said hydraulic device includes a device for converting rectilinear to rotary drive.

25. An apparatus as claimed in claim 24 wherein said rotary drdive is used to drive a pump or motor.

26. An apparatus as claimed in any one of claims 15 to 25 wherein is included an energy storage reservoir selected from a compressed gas reservoir and a pumped (gravity) storage reservoir.