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A generating apparatus for generating electrical power from a horizontal water flow comprises a fixed hub on a support structure and a power wheel arranged for rotation about a vertical axis about the hub. The power wheel includes rotor vanes adapted to cause rotation of the power wheel when the pow

A generating apparatus for generating electrical power from a horizontal water flow comprises a fixed hub on a support structure and a power wheel arranged for rotation about a vertical axis about the hub. The power wheel includes rotor vanes adapted to cause rotation of the power wheel when the power wheel is subject to a substantially horizontal water flow. One or more generators are provided on the hub to produce electrical power output from rotation of the power wheel relative to the hub. A shroud is rotationally mounted on the hub and arranged to cover at least some of the rotor vanes of the power wheel, so that the water flow is concentrated on the rotor vanes on one side only of the power wheel. A directional controller holds the shroud in a predetermined rotational position relative to the hub dependent on the direction of the water flow.

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1. A generating apparatus for converting kinetic energy from a substantially horizontal water flow to electrical energy, the apparatus comprising: a support structure;a hub which is rotationally fixed to the support structure;a hub level controller adapted to control the level of the hub on the supp

1. A generating apparatus for converting kinetic energy from a substantially horizontal water flow to electrical energy, the apparatus comprising: a support structure;a hub which is rotationally fixed to the support structure;a hub level controller adapted to control the level of the hub on the support structure;a power wheel arranged for rotation about a substantially vertical axis about the hub and provided with rotor vanes adapted to cause rotation of the power wheel when the power wheel is subject to a substantially horizontal water flow;a shroud rotationally mounted on the hub and arranged to cover at least some of the rotor vanes of the power wheel;a directional controller adapted to hold the shroud in a predetermined rotational position relative to the hub dependent on the direction of the substantially horizontal water flow; andat least one generator provided on the hub and adapted to produce electrical power output derived from rotation of the power wheel relative to the hub. 2. A generating apparatus according to claim 1, wherein the power wheel and the shroud each have controlled buoyancy. 3. A generating apparatus according to claim 1, wherein the shroud extends over at least 180° and substantially covers at least half of the rotor vanes of the power wheel at any instant. 4. A generating apparatus according to claim 1, wherein the shroud substantially covers at least some of the rotor vanes moving in a direction opposed to the direction of the substantially horizontal water flow. 5. A generating apparatus according to claim 1, wherein the shroud includes a plurality of vertically extending apertures adjacent to rotor vanes moving in a direction opposed to the direction of the substantially horizontal water flow. 6. A generating apparatus according to claim 1, wherein the shroud includes a plurality of shroud vanes adapted to divert water flow away from the vertical axis. 7. A generating apparatus according to claim 6, wherein the shroud vanes are adapted to create regions of low pressure adjacent to at least some of the rotor vanes moving in a direction opposed to the direction of the substantially horizontal water flow. 8. A generating apparatus according to claim 1, wherein the directional controller comprises a directional vane connected to the shroud and extending radially away from the shroud. 9. A generating apparatus according to claim 8, wherein the directional vane includes a trimming device adapted to trim the rotational position of the shroud. 10. A generating apparatus according to claim 8, wherein the directional controller comprises a flow separator connected to the shroud radially in a location substantially diametrically opposite the directional vane, the flow separator being shaped so as to divert at least part of the substantially horizontal water flow onto the rotor vanes of the power wheel. 11. A generating apparatus according to claim 1, wherein the support structure comprises a substantially vertical support column. 12. A generating apparatus according to claim 1, wherein the support structure comprises one or more guide means which engage with one or more key means on the hub to prevent relative rotation of the support structure and hub. 13. A generating apparatus according to claim 1, wherein the hub level controller comprises one or more floodable ballast chambers provided on the hub. 14. A generating apparatus according to claim 1, wherein each generator is provided in a generator chamber having an opening in a roof of said generator chamber and a removable cover sealably covering said opening. 15. A generating apparatus according to claim 14, further including a crane provided on the support structure and adapted to lift any one of said generators. 16. A generating apparatus according to claim 1, wherein the apparatus includes a plurality of transmissions provided on the hub, each transmission being adapted to transmit a driving force from the power wheel to drive one or more generators. 17. A generating apparatus according to claim 1, wherein the generating apparatus comprises a substantially vertical support column and a plurality of hubs, each hub being rotationally fixed to the support column, and each hub having an associated power wheel arranged for rotation about a substantially vertical axis about the hub and provided with rotor vanes adapted to cause rotation of the power wheel when the power wheel is subject to a substantially horizontal water flow to drive one or more generators provided on the hub. 18. A generating apparatus according to claim 1, the apparatus further comprising: a plurality of generators provided on the hub and adapted to produce electrical power output derived from rotation of the power wheel relative to the hub, each generator having an associated drive means driven by rotation of the power wheel; andgenerator control means adapted to selectively switch each of said plurality of generators between an active state and an inactive state. 19. A generating apparatus according to claim 18, wherein the generator control means includes an electrical controller adapted to selectively switch each of said plurality of generators on and off. 20. A generating apparatus according to claim 18, wherein the generator control means includes a sensor for detecting a speed parameter indicative of the relative rotational speed of the power wheel and the hub. 21. A generating apparatus according to claim 18, wherein the generator control means includes switching means adapted to switch each of said plurality of generators between an active state and an inactive state in response to the detected speed parameter. 22. A generating apparatus according to claim 21, wherein the generator control means is adapted to switch more generators to an active state when the detected speed parameter is indicative of an increase in the relative rotational speed of the power wheel and the hub. 23. A generating apparatus according to claim 21, wherein the generator control means is adapted to switch a generator to an active state when the detected speed parameter is indicative that the relative rotational speed of the power wheel and the hub has reached a predetermined upper trigger value. 24. A generating apparatus according to claim 21, wherein the generator control means is adapted to switch a generator to an inactive state when the detected speed parameter is indicative that the relative rotational speed of the power wheel and the hub has reached a predetermined lower trigger value. 25. A generating apparatus according to claim 24, wherein the apparatus includes a primary transmission comprising a ring gear fixed to the power wheel and adapted to drive each of the primary drivers. 26. A generating apparatus according to claim 18, wherein each drive means comprises: a primary driver driven by the power wheel;a drive shaft for driving the associated generator; anda transmission coupled between the primary driver and the drive shaft. 27. A generating apparatus according to claim 26, wherein each drive means includes a clutch to selectively engage or disengage the generator from the drive shaft. 28. A method of generating electricity from a substantially horizontal water flow in a body of water using a generating apparatus including a power wheel arranged for rotation about a substantially vertical axis about a hub rotationally fixed to a support structure, the power wheel having a plurality of rotor vanes, the method comprising the steps of: providing a shroud rotationally mounted on the hub and arranged to cover at least some of the rotor vanes of the power wheel; moving the hub in a vertical direction on the support structure to an operating position in the substantially horizontal water flow;fixing the hub in an operating position in the substantially horizontal water flow; aligning the shroud with the substantially horizontal water flow such that the rotor vanes on a first side of the generating apparatus are not covered by the shroud and are subject to hydrodynamic forces from the substantially horizontal water flow, and such that the rotor vanes on a second side of the generating apparatus are at least partially covered by the shroud so as to at least partially shield the rotor vanes from hydrodynamic forces from the substantially horizontal water flow;driving the power wheel to rotate about the hub by means of the hydrodynamic forces from the substantially horizontal water flow on the rotor vanes provided on the power wheel; anddriving one or more generators provided on the hub from the rotation of the power wheel,wherein the generating apparatus is a generating apparatus according to claim 1. 29. A method of generating electricity from a substantially horizontal water flow in a body of water using a generating apparatus including a power wheel arranged for rotation about a substantially vertical axis about a hub rotationally fixed to a support structure, the power wheel having a plurality of rotor vanes, the method comprising the steps of: providing a shroud rotationally mounted on the hub and arranged to cover at least some of the rotor vanes of the power wheel;moving the hub in a vertical direction on the support structure to an operating position in the substantially horizontal water flow;fixing the hub in an operating position in the substantially horizontal water flow;aligning the shroud with the substantially horizontal water flow such that the rotor vanes on a first side of the generating apparatus are not covered by the shroud and are subject to hydrodynamic forces from the substantially horizontal water flow, and such that the rotor vanes on a second side of the generating apparatus are at least partially covered by the shroud so as to at least partially shield the rotor vanes from hydrodynamic forces from the substantially horizontal water flow;driving the power wheel to rotate about the hub by means of the hydrodynamic forces from the substantially horizontal water flow on the rotor vanes provided on the power wheel; anddriving one or more generators provided on the hub from the rotation of the power wheel. 30. A method according to claim 29, wherein the step of aligning the shroud is carried out by providing a directional controller on the shroud adapted to hold the shroud in a predetermined rotational position relative to the hub dependent on the direction of the substantially horizontal water flow. 31. A method according to claim 29, wherein the directional controller comprises a directional vane connected to the shroud and extending radially away from the shroud, and the step of aligning the shroud includes allowing the shroud to adopt an equilibrium position such that the directional vane is substantially aligned with the substantially horizontal water flow. 32. A method according to claim 29, wherein the step of aligning the shroud includes the further step of trimming the rotational position of the shroud by adjusting the position of a pivotable flange at the trailing edge of the directional vane. 33. A method according to claim 29, including the further step of separating the substantially horizontal water flow at the generating apparatus so as to divert at least part of the substantially horizontal water flow onto the rotor vanes of the power wheel on the first side of the generating apparatus and to divert at least part of the substantially horizontal water flow past the shroud on the second side of the generating apparatus. 34. A method according to claim 33, wherein the separating step is carried out by a flow separator connected to the shroud radially in a location substantially diametrically opposite the directional vane. 35. A method according to claim 29, including the step of providing a plurality of vertically extending apertures adjacent to rotor vanes moving in a direction opposed to the direction of the substantially horizontal water flow and creating a region of reduced pressure adjacent to at least some of the plurality of vertically extending apertures. 36. A method according to claim 29, including the step of providing a plurality of shroud vanes and creating regions of low pressure adjacent to at least some of the rotor vanes moving in a direction opposed to the direction of the substantially horizontal water flow. 37. A method according to claim 29, further including the step of selecting an optimum level in the substantially horizontal water flow and moving the hub in a vertical direction on the support structure to an operating position at said level. 38. A method according to claim 29, wherein the step of moving the hub to an operating position includes flooding one or more floodable ballast chambers provided on the hub. 39. A method according to claim 29, further including the step of lifting the hub in a vertical direction on the support structure to a maintenance position in which at least part of the generating apparatus is above the surface of the body of water. 40. A method according to claim 39, wherein the step of lifting the hub to a maintenance position includes displacing water from one or more floodable ballast chambers provided on the hub.