GB2478736A

GB2478736A - Power generation from water flow using venturi pump

Info

Publication number: GB2478736A
Application number: GB1004321A
Authority: GB
Inventors: Peter Miles Roberts
Original assignee: Verderg Ltd
Current assignee: Verderg Ltd
Priority date: 2010-03-16
Filing date: 2010-03-16
Publication date: 2011-09-21
Anticipated expiration: 2030-03-16
Also published as: GB2478736B; GB201004321D0

Abstract

An apparatus for generating electricity using fluid flow in a body of water comprises an array of spaced apart elements 24 defining a venturi section and downstream diffuser between each pair of elements. A series of holes 26 is spaced along each of the elements, so that fluid is drawn through the elements into the venturi section. The elements are connected to e.g. a manifold 14 to generate flow through a turbine 18. The elements may be arranged vertically or horizontally, and may have horizontal flow management vanes. The elements may be provided with a series of vertically positioned chambers, so that some of the holes 26 are separately connected to the manifold.

Description

Apparatus for Generating Power from Fluid Flow

Technical field

[0001] This invention relates to systems for converting wave, tidal or current energy in a body of water into a more useful form of energy. In particular this invention provides an apparatus for generating electricity using flows such as waves, tides or currents in a body of water.

Background art

[0002] They have been a number of proposals for converting current, wave or tidal flows into electricity as a non-polluting approach to power generation.

[0003] Previous systems for extracting energy from waves used the vertical movement of the water surface caused by the phase shift between the elliptical water particle paths along a wavelength. Typically, previous devices involved some form of float coupled to a mechanical arrangement or some form of trapped air body above the wave surface for converting the periodic vertical movement of the wave surface into some form of motion useful for electricity generation (usually rotary). Such systems are often mechanically complicated and to work effectively are tuned to resonate at a frequency at which the energy density of the ambient wave spectrum is expected to peak. Output can drop dramatically if the wave frequency differs from this design resonant frequency. Such systems are useless if there is only lateral flow (current or tide) with no oscillating vertical wave component.

[0004] Systems have been proposed for extracting energy in lateral flows. Such systems have involved the use of a vane which can be caused to oscillate by the flow, a mechanical transmission system converting this into rotary motion.

These systems face similar problems to wave-powered systems: mechanical complexity, inability to extract energy from other types of motion, etc. Other systems feature a large underwater propeller with an electrical power generator in the hub, analogous to a windmill but for water instead of wind flows. For the swept disc to gain exposure to the maximum incident current energy, the blades have to be very long which in turn requires sophisticated design and materials to accommodate the stresses at the blade root. Offshore tidal barrages seek to concentrate the incident energy of a large cross-section of water flow by trapping the flow behind a containing wall and funnelling it through turbines of much smaller cross-sectional area, as in a conventional dam. Such barrages, typically across a tidal estuary, are very expensive and environmentally disruptive and require the interaction of the tidal flow with the local topography of the estuary to amplify the tidal range.

[0005] One common problem for wave or flow systems is their ability to address a sufficiently large cross-section of the ocean for power generation to be possible on an industrial scale. Furthermore, end or edge effects can make it easier for the flow to go around any structure positioned in the flow to extract energy from it rather than to pass through the energy extraction system. This problem can be lessened by making an installation very large but this in turn can lead to further complexity and expense and may lead beyond the limits of current engineering capability.

[0006] W02008015047 discloses apparatus for converting energy from wave or current flows wherein a series of pipes are arranged such that venturis are defined between the pipes. Water flow between these pipes causes the venturis to act as pumps drawing water through the pipes which are fed by a manifolding flow conduit and driving a turbine. The series of pipes are arranged to form arrays with vertical planes which in turn are mounted on the sea bed to form barrages.

[0007] The invention seeks to provide alternative pipe arrangements to provide improved performances for such energy generating devices.

Disclosure of the invention

[0008] A first aspect of the invention provides an apparatus for generating electricity using fluid flow in a body of water comprising: -an array of spaced apart elements, each array element defining an elongate flow passage having an upstream side and a downstream side, each element being provided with a series of holes spaced along its length and the downstream side extending and tapering away in the direction of flow, wherein the array elements are arranged side by side such that opposing walls of adjacent array elements define a venturi section and a first diffuser section extending downstream from the venturi section; -a flow conduit having an inlet and an outlet; -a turbine located in the flow conduit; and -a generator connected to the turbine; wherein the flow passages are connected to the outlet of the flow conduit such that the flow of water through the venturi sections causes water to be drawn through the flow conduit out via the holes the resulting flow driving the turbine [0009] The upstream end of each element can extend and taper away from the holes such that when the array elements are arranged side by side opposing walls of adjacent elements define a second diffuser section extending upstream from the venturi section. The profile of the upstream side and the downstream side can be substantially symmetrical.

[0010] The profiles of each array element include substantially hexagonal shapes extending in the direction of the fluid flow and substantially elliptical shapes extending in the direction of the fluid flow.

[0011] In one embodiment the profile of the upstream side and the profile of the downstream side are substantially different.

[0012] The outer surface of the array elements defining the diffuser section can be roughened to induce turbulence in the diffuser section.

[0013] The apparatus can further comprise spacer elements located within the diffuser section. The spacer elements can be moveable within the diffuser section relative to the array elements.

[0014] The downstream end of the array elements can comprise a plurality of holes.

The downstream end can comprise a flow control valve to provide a flow path between the downstream end and the flow passage.

[0015] In one embodiment the downstream side includes a buoyancy section.

[0016] In one embodiment the array elements are substantially vertical. The elements are connected to a horizontal manifold at their lower end; the manifold being connected to the flow conduit.

[0017] The apparatus can further comprise horizontal flow management vanes arranged horizontally across the array elements. Each flow passage can comprise a series of chambers positioned vertically down the flow passage; and a feeder tube extending from each chamber and having an inlet located below the series of chambers.

[0018] In another embodiment the array elements are substantially horizontal. The array elements are connected to a vertical manifold; the manifold being connected to the flow conduit.

[0019] Each manifold can comprise a series of chambers, each chamber positioned adjacent the end of a flow passage; and a feeder tube extending from the chamber and having an inlet located below the series of chambers.

[0020] A second aspect of the invention comprises an array element for use in an apparatus for generating electricity using fluid flow in a body of water; the array element defining an elongate flow passage and having an upstream side and a downstream side, the element being provided with a series of holes spaced along its length, the downstream side extending and tapering in the direction of flow, such that when array elements are placed side by side opposing walls of adjacent elements define a venturi section and a diffuser section extending downstream from the venturi section.

Brief description of the drawings

[0021] The invention will now be described by way of example with reference to the accompanying drawings: Figure 1 shows an embodiment of the apparatus according to the invention aligned across a current flow; Figure 2 shows a schematic plan view of an arrangement of pipes according to the invention across a current flow; Figure 3 shows an embodiment of the invention having horizontally arranged pipes; Figure 4 shows details of a horizontal pipe for use with the invention; Figure 5 shows a cross sectional side view of an embodiment of the invention having horizontally arranged pipes Figure 6-1 1 shows examples of transverse cross sections of pipes for use in the apparatus of the invention; Figures 12-16 are examples of transverse cross sections of pipes for use in the apparatus of the invention; Figure 17 shows a schematic transverse cross section of a pipe for use in an embodiment of the invention; Figure 18 shows a schematic of an embodiment of the invention having horizontal vanes; Figure 19 shows a schematic of an embodiment of the invention having vertically arranged pipes with internal segmentation; Figure 20 shows a schematic of an embodiment of the invention having horizontally arranged pipes; Figure 21 shows a schematic view of one embodiment of the invention having vertical pipes; Figure 22 shows a cut away view of the embodiment of Figure 21; Figure 23 shows another cut away view of the embodiment of Figure 21; Figure 24 shows a schematic of an embodiment of the invention installed across part of the width of a body of water; and Figure 25 shows a side view of Figure 24.

Mode(s) for carrying out the invention [0022] The invention is broadly based on the technology disclosed in W02008/01 5047, which describes an apparatus comprising an arrangement of first and second pipes for generating electricity using tidal, wave or current flow in a body of water. The first pipes are provided with a series of holes spaced along its length and are connected to a flow conduit having an inlet into the body of water. The venturis defined between adjacent pipes acts as venturi pumps inducing flow from inside the first pipes through the holes so as to draw water through the flow conduit and drive a turbine connected to a generator.

[0023] The term Spectral Marine Energy Convertor' (SMEC) is used to define such technology. The word "spectral" signifies that energy is extracted from any water movement between the pipes irrespective of the frequency at which the the ambient wave spectrum is expected to peak. SMEC is "pan-spectral". It works well even at near-zero frequency i.e. in tidal flows and unidirectional (river) flows.

[0024] The basic principle of the invention is to provide a SMEC apparatus wherein the pipes have at least one tapered side such that a diffuser section is formed between adjacent pipes. Figure 1 shows part of an apparatus comprising a series of pipes set across a current flow. Figure 2 shows a plan view of a pipe arrangement to demonstrate the principle of operation.

[0025] The arrangement comprises an array of pipes 10 arranged vertically in a parallel spaced side-by-side arrangement in essentially the same plane with a venturi 12 defined between adjacent pipes. The lower ends of the pipes are connected to a common horizontal manifold structure 14 which is connected to the flow conduit 16 housing the turbine 18. The turbine 18 is connected to the generator via a drive shaft. Each pipe 10 comprises a downstream tapered side 20, and upstream side 22, a flow passage 24 and rows of holes 26 spaced along the length of the pipe. Adjacent pipes 10 are positioned such that a venturi section 12 and a diffuser section 28 are defined by the opposing walls of adjacent pipes 10. The holes 26 are positioned such that they are in fluid communication with the flow passage 24 and located at or near the venturi section 12.

[0026] Water enters the flow conduit 16 via the inlet 32 and the pipes 10 are connected to the outlets 34 of the flow conduit such that a primary flow 36 of water past the arrangement of pipes causes the venturi 12 to act as venturi pumps inducing flow 38 from inside of the pipes out through the holes 26 so as to draw water 40 through the flow conduit and drive the turbine. A head drop from the upstream water surface head to the downstream water level is caused by the venturi effect. As the current flows through the venturi between the pipes an amplified head loss occurs in the venturi. This induces the flow 38 of water out through the holes 26. This amplified head drop across the pipes, flow conduit and turbine induces a high velocity secondary flow 38 through the manifold piping with a volume smaller than the primary flow which can be used to drive the turbine.

[0027] Figure 3 shows a different arrangement of pipes 50 for the SMEC apparatus, which is installed across an entrance of a body of water 62. In this case the pipes 50 of the apparatus are arranged substantially horizontally having a substantially vertical plane and connected to a vertical manifold 64. The horizontal pipes 50 are arranged in a parallel spaced apart side-by-side array in essentially the same plane such that the opposing walls of adjacent pipes define a venturi and a diffuser section.

[0028] With reference to Figure 4 and 5 each pipe 50 comprises a tapered side 56, a flow passage 58 and holes 60 spaced along the length of the pipe 50. Adjacent pipes 50 are positioned such that a venturi section 66 and a diffuser section 68 are defined between the opposing walls of adjacent pipes. Water 62 enters the flow conduit via the inlet and the pipes 50 are connected to the outlets of the manifold 64 such that flow of water past the arrangement of pipes causes the venturi to act as venturi pumps inducing flow from inside the pipes through the holes so as to draw water through the flow conduit and drive the turbine.

[0029] A horizontal arrangement of venturi pipes can help isolate the induced low pressure in the venturi from the free surface of the primary flow. This helps maintain the low pressure formed in the venturi, which drives the secondary flow and thereby helps maintain the potential useful power output that can be achieved.

[0030] Energy losses through the venturi can occur as a result of reintegration of the secondary flow with the primary flow inside the venturi. The theoretical maximum amount of useful work that can be extracted from the secondary flow is a function of the geometry of SMEC apparatus. The geometry of the profile of the venturi can affect the energy losses in the venturi.

[0031] Figures 6-1 1 show examples of profiles of the pipes that can be used for forming the apparatus for use in unidirectional flows.

[0032] Each pipe 70 forming the array comprises an upstream side 72 and a downstream side 74. A flow passage 76 is positioned between the upstream side 72 and the downstream side 74. A series of holes or slots 78 are defined along the length of the flow passage 76 positioned so that they will be at or near the venturi section 80 formed between adjacent pipes. In pipes 76 for use in unidirectional flow 82 the profile of the upstream and downstream sides of the pipes can be different with the entrance 84 to the venturi 80 being shorter than the diffuser section 86 downstream of the venturi 80.

[0033] The number, shape and arrangement of holes defined along the length of the flow passage can vary. The term holes can include apertures, slots, continuous slots, elongate holes and any other suitable opening into the flow passage [0034] Figure 6 shows one profile of a venturi pipe 70 for use in the apparatus. The hollow venturi pipe 70 comprises a short substantially semicircular upstream side 72 tapering to an elongate downstream side 74 forming a substantially teardrop shape. A flow passage 76 forming part of the secondary flow path extends along the length of the pipe 70. Holes 78 are located between the upstream 72 and downstream 74 sides along the length of the pipe 70. The pipe can be strengthened with the addition of internal bracing struts 88.

[0035] Figure 7 shows a profile for a venturi pipe for unidirectional flow. The hollow venturi pipe 70 has a substantially hexagonal cross sectional shape having a short pointed upstream side 72 and an elongate downstream side 74 with a flow passage 76 extending along the length of the pipe 70. Holes 78 are located between the upstream and downstream sides along the length of the pipe.

[0036] Figures 8 and 9 shows transverse cross sectional shapes of venturi pipes having a hollow centre with differing arrangement of struts and bracing 88. The pipes 70 have a tapering elongate downstream side 74 and a shorter semicircular upstream side 72. The semicircular upstream side 72 has a wider diameter than the downstream side 74. Holes 78 are located along the length of the pipe 70 on the upstream side 72 at the boundary with the downstream side 74.

[0037] Figures 10 and 11 show different embodiments of the pipes for the apparatus having differing bracings, struts and plate arrangements to provide strengthening to the pipes. The cross section shape of the pipe 70 has a short tapering upstream side 72 forming the flow passage 76 for the secondary flow path. The pipe 70 has a tapered elongated downstream side 74 which is longer then the upstream side 72 and closed off from the upstream side 72. Holes 78 are located along the length of the pipe7o in the upstream side 72 near the boundary with the downstream side 74 for secondary flow from the flow passage 76 into the venturi. The closed off downstream side 74 can include a buoyancy section 90.

[0038] The primary flow 82 accelerates into the venturi 80 between the pipes 70, flows through the venturi section 80 and then diverges out between the walls of the pipes that defines the diffuser section 86.

[0039] Providing a tapered section on the downstream side of the pipes helps aid pressure recovery as the primary flow decelerates out of the venturi. For optimal functioning of the venturi pump the low pressure regime is required to be preserved inside the venturi section in accordance with Bernoulli's theorem. In order to meet this requirement the primary flow needs to decelerate smoothly through the diffuser section lying downstream of the venturi section to give pressure recovery back up towards the ambient free stream head.

[0040] A blunter shorter upstream side to the pipe can be used in unidirectional flow with the positive pressure gradient in the entry throat of the venturi promoting good flow conditioning.

[0041] When the apparatus is to be used in bodies of water having bi-directional flow the pipe can have a substantially the same profile shape as shown in Figures 12, 13 and 14.

[0042] Pipes 100 for use in bi-directional flow 102a, 102b have a tapered downstream side 104 and upstream side 106, such that two diffusers sections 108a, 108b are defined between adjacent pipes 100 separated by the venturi section 110.

The symmetrical shape of the pipes allows the entrance throat 108b of the venturi 110 to become the diffuser section when the direction of flow I 02a is reversed 102b. The secondary flow 112a, 112b will join the primary flow 102a, 102b as it leaves the pipes 100 through the holes. As shown in Figure 12 the bi-directional pipes 100 can have a substantially elliptical shape extending parallel to the direction of the water flow 102. Further examples of cross section shapes for pipes for use in bi-directional flow are shown in Figure 13, the bi-directional pipes 100 can have a substantially hexagonal shape extending parallel to the direction of the water flow 102.

[0043] In order to achieve a low diffuser angle a pipe with a long chord length is obtained. Figure 14 shows an array of bi-directional pipes 100 with spacers elements 114 located within the diffuser sections 1 08a, I 08b formed by adjacent pipes 100. Spacer elements 114 can be positioned within the diffuser section to allow a short chord length over the whole assembly to be used whilst still preserving a small effective angle to aid pressure recovery. The change in the direction of the primary flow 102 as it passes through the diffuser section 108a with the spacer elements 114 promotes flow mixing and aids pressure recovery.

[0044] With reference to Figure 15 the spacers 114 can be moveable in and out of the diffuser sections 1 08a, I 08b. Movement of the spacers 114 changes the blockage ratio which can help performance in a tidal flow where the primary flow velocity is continuously variable. Movement of the spacers from a position close to the venturi section to a position further downstream decreases the blockage ratio.

[0045] Further changes can be made to the SMEC apparatus to improve flow conditioning to obtain the appropriate flow profile. In one embodiment as shown in Figure 16 the spacers I 14a, I 14b can be connected by a septum 116 within the venturi section. This can help prevent flow dividing around the spacer unevenly and can help flow conditioning.

[0046] The blockage ratio can influence the performance of the apparatus. The blockage ratio is formed by dividing the distance between the centrelines of two adjacent venturi pipes by the gap between adjacent pipes at the venturi section.

[0047] The outer surface of the pipes that defines the diffuser section can comprises a roughened area. The roughened surface helps to promote turbulent flow in the boundary layer which can promote mixing and aid pressure recovery. The surface can have an unsmooth surface, such as a dimpled surface. The surface may be formed onto the pipe during its manufacture or can be allowed to develop on the pipe during use by allowing natural accretion of marine growth or similar over time.

[0048] Figure 17 shows a profile of a pipe 120 for use in a SMEC apparatus comprising perforations 122 in the downstream side 124. Perforations 122 can be formed in the end of the downstream side 124 of the pipes and a flow control valve 126 can be located within the downstream side 124 to control flow of water from the boundary layer of the diffuser section into the flow passage 128.

The flow control valve 126 can be used to draw water from the boundary layer of the diffuser section into the pipe 120 helping prevent or delay flow separation.

[0049] Figure 18 shows an embodiment of the invention having flow management vanes 132 extending horizontally across the vertically arranged pipes 134 connected to a manifold 136. The apparatus comprises an array of vertical pipes 134 with one or more flow management vanes 132 positioned horizontally across the vertically arranged array of pipes. The horizontal vanes can be flat to keep the flow substantially horizontal as it passes through the venturi.

[0050] The water surface at the top of each venturi gap is at the free surface of a water column that has accelerated forward up to a high velocity over the short length of the venturi prior to a deceleration as it exits into the diffuser section. The elevation of the free water surface is dictated by the complex force balance resulting from its total head, the rate of change of its momentum and the atmospheric pressure acting on it. The free water surface elevation remains at a higher elevation than its locally reduced total head would indicate were it quasi-static. Any tendency for the free surface to depress in the pipe can have a detrimental effect on the performance of the device. By positioning management vanes across the pipes depression of the free surface can be inhibited.

[0051] When the pipes themselves are horizontal such as shown in Figure 3 the horizontal arrangement of the pipes inherently provides the same effect to the apparatus as horizontal management vanes can provide to vertical pipe arrangements.

[0052] In situations where the apparatus is located in a tidal flow, the free surface of the primary flow water can have a variable elevation. Figure 19 shows a cross section view of a part of an apparatus having vertical pipes 140 connected to a horizontal manifold 142. In a further embodiment of the invention each pipe 140 is divided into a plurality of chambers 144 arranged vertically along the length of the pipe. A feeder tube 146 is connected to each chamber 144 and extends to below the minimum free surface level 148 that the free surface of the secondary flow water will reach. The number of chambers required will depend on the variation in water level that the pipes are exposed to, the length of the pipes and the frequency of the holes 150 in the pipes.

[0053] In tidal flows as the water level falls the uppermost holes can become exposed to the atmosphere which exposes the water inside the pipes to atmospheric pressure. The water level inside the venturi pipes will then fall and the less power cane be generated since fewer holes along the pipe are active. Internal segmentation of the pipes to create a series of chambers each in fluid communication with the lower end of the pipe via a tube, enables all the holes below the primary flow surface to be utilised even at low water levels.

[0054] In another embodiment of the invention when the apparatus comprises horizontal pipes 160, the vertical manifold 164 can be segmented. Figure 20 shows a cross section of part of an apparatus having horizontal venturi pipes provided with a series of holes 162 and extending between vertical manifolds 164. The manifold 164 is connected to a flow conduit 166 housing an turbine 168 connected to a drive shaft to drive a generator 170. The vertical manifold pipe 164 is divided into a plurality of chambers 172 arranged vertically along the length of at least part of the manifold. A tube 174 is connected to each chamber and extends from the chamber to below the minimum free surface level 176 that the free surface of the secondary flow water will reach. Each chamber 172 is positioned to correspond with a horizontal pipe 160 extending from the vertical manifold 164. The number of chambers required will depend on the variation in water level that the pipes are exposed to. It is not necessary that all venturi pipes are associated with an individual chamber.

[0055] Figures 21, 22, and 23 show a further embodiment of the SMEC apparatus. In which the apparatus comprises an array of vertical pipes 200 have a tapered downstream side 202 and a flow passage 204 having holes 206 positioned along its length. The pipes 200 are connected to a common horizontal manifold 208 which in turn is connected to a vertical flow conduit 210. The flow conduit 210 has inlets 212 for receiving water from the body of water and one or more turbines 214 located within the flow conduit 210 connected to a generator 216 via a drive shaft. Horizontal manifolds 218 are positioned across the pipes 200 and flow conduit 210.

[0056] The method of installing the SMEC apparatus can vary depending on the type of apparatus and where the apparatus is to be installed. Methods can include floating the sections of the apparatus into position, lowering the apparatus into position by controlled flood and/or lowering the apparatus into position by cranes. The SMEC apparatus can be installed to span an entire body of water, i.e. from bank to bank of a river or strait, or may be installed only partially across a body of water.

[0057] Locks can be incorporated into the SMEC apparatus as for conventional barrages to permit the passage of shipping. Gaps may be incorporated into the SMEC apparatus to permit the passage of water crafts, fish or marine mammals up and down the river.

[0058] Where the apparatus is placed in a flow with a larger cross section than the apparatus the presence of free edges permits the primary flow to divert around the apparatus rather than passing through the pipes. The longer the apparatus relative to the body of water the less the losses are as a percentage of the useful potentially available output energy.

[0059] In order to reduce the effect of edge losses the apparatus can run across the entire body of moving water, such as from bank to bank of a river or from one coast to another coast. As shown in Figure 24 and Figure 25 where the apparatus 180 does not intercept the entire body of water 182 edge losses can be minimised. In order to minimise edge losses in such an arrangement, a surface 184 can be attached to the free end of the apparatus extending at right angles upstream of the apparatus 180. The surface 184 can help direct water through the pipes 186 and minimise flow around the edge. The inlet 188 for the secondary flow 190 can be located at the free edges to encourage the primary flow 192 to pass between the pipes 186 rather than around the free edges.

[0060] Frictional losses occurring through the secondary flow path can cause a fall in pressure at a number of points throughout the flow path resulting in a decrease in maximum output that can be obtained. Frictional losses can occur through the intake to the turbines as the water enters the turbine. These losses can be minimised by using a smoothly contoured entry duct.

[0061] The hydrodynamic efficiency of the power offtake turbines can affect the overall performance of the apparatus. The use of controllable-pitch turbines can help maximise performance. Turbine types suitable for SMEC include Axial flow and Kaplan turbine types. Frictional losses can all be minimised by reducing sharp edges and employing smooth internal surface of the parts of the turbine in contact with the water. The turbine can be positioned low in the water, this increases the ambient operating pressure and helps suppress and performance degradation from cavitation over the blade surfaces. Positioning the generator above the water surfaces reduces the chance of water coming into contact with any electrical machinery. This can be achieved with a sufficiently long drive shaft between the turbine and the generator.

[0062] The exhaust from the turbine can be subjected to flow conditioning. This can be achieved by locating an outwardly tapered bell mouth downstream of the turbine forming a diffuser. This will help sustain a reduced pressure drop downstream of the turbine which increases the power that can be extracted from the secondary flow.

[0063] For an apparatus with vertical pipes extending from the horizontal manifold, the volumetric flow rate reduces as water flows up into each subsequent venturi pipe. Therefore in one embodiment of the invention the cross section area of the manifold can be decreased along the flow path to give a constant flow velocity along the length of the manifold at a value above the critical value for sediment deposition. Such flow condition can also help prevent energy wasting eddies forming in the manifold.

[0064] In a further embodiment the turbine and generator can be designed to run in reverse as a pump to back flush any debris or contamination out of the apparatus. Conventional anti-fouling treatment and mechanical cleaning tools can also be incorporated into the apparatus to minimise the effect that marine fouling and sedimentation can have on the performance of the apparatus.

[0065] Variations can be made to the invention. The aspect ratio of the profile of the pipes can be varied to provide the optimum performance of the array. The aspect ratio of the profile of the pipe is ratio of the length of L of the profile and of the width W of the profile at its widest point.

[0066] Further changes can be made within the scope of the invention.

Claims

Claims 1. An apparatus for generating electricity using fluid flow in a body of water comprising: -an array of spaced apart elements, each array element defining an elongate flow passage and having, an upstream side and a downstream side, each element being provided with a series of holes spaced along its length and the downstream side extending and tapering away in the direction of flow, wherein the array elements are arranged side by side such that opposing walls of adjacent array elements define a venturi section and a first diffuser section extending downstream from the venturi section; -a flow conduit having an inlet and an outlet; -a turbine located in the flow conduit; and -a generator connected to the turbine; wherein the flow passages are connected to the outlet of the flow conduit such that the flow of water through the venturi sections causes water to be drawn through the flow conduit and out via the holes the resulting flow driving the turbine.
2. An apparatus as claimed in claim I wherein the upstream side of each element extends and tapers away from the holes such that when the array elements are arranged side by side opposing walls of adjacent array elements define a second diffuser section extending upstream from the venturi section.
3. An apparatus as claimed in claim 2 wherein the profile of the upstream side and the profile of the downstream side are substantially the same.
4. An apparatus as claimed in any of claims I to 3 wherein the profile of each array element is substantially hexagonal in the direction of the fluid flow.
5. An apparatus as claimed in any of claims I to 3 wherein the profile of each array element is substantially elliptical in the direction of the fluid flow.
6. An apparatus as claimed in claim I or 2 wherein the profile of the upstream side and the profile of the downstream side are substantially different.
7. An apparatus as claimed in any preceding claim wherein the outer surface of each array element defining the diffuser section is roughened to induce turbulence flow through the diffuser section.
8. An apparatus as claimed any preceding claim further comprising a spacer element located within the diffuser section.
9. An apparatus as claimed in claim 8 wherein the spacer elements are moveable within the diffuser section relative to each array element.
10. An apparatus as claimed any preceding claim wherein the downstream side of each array element comprise a plurality of holes.
11. An apparatus as claimed in claim 10 wherein the downstream side comprises a flow control valve to provide a flow path between the downstream side and the flow passage.
12. An apparatus as claimed any preceding claim wherein the downstream side includes a buoyancy section.
13. An apparatus as claimed any preceding claim wherein the array elements are arranged substantially vertically.
14. An apparatus as claimed in claim 13 wherein each array element is connected to a horizontal manifold at its lower end; the manifold being connected to the flow conduit.
15. An apparatus as claimed in claim 13 or claim 14 further comprising horizontal flow management vanes arranged horizontally across the array elements.
16. An apparatus as claimed in any of claims 13, 14 or 15 wherein each flow passage comprises a series of chambers positioned vertically down the flow passage; and a feeder tube extending from each chamber and having an inlet located below the series of chambers.
17. An apparatus as claimed in any of claims 1-12 wherein the array elements are arranged substantially horizontally.
18. An apparatus as claimed in claim 17 wherein each array element is connected to a vertical manifold; the manifold being connected to the flow conduit.
19. An apparatus as claimed in claim 17 or claim 20 wherein each manifold comprises a series of chambers, each chamber positioned adjacent the end of a flow passage; and a feeder tube extending from the chamber and having an inlet located below the series of chambers.
20. An array element for use in an apparatus for generating electricity using fluid flow in a body of water; the array element defining an elongate flow passage and having an upstream side and a downstream side, the element being provided with a series of holes spaced along its length, the downstream side extending and tapering in the direction of flow, such that when array elements are placed side by side opposing walls of adjacent elements define a venturi section and a diffuser section extending downstream from the venturi section.