Water turbine

Abstract

A turbine for use in extracting energy from within a water flow comprises: an array of turbine blades formed and arranged for rotation, in use, about an axis substantially normal to the direction of water flow; wherein at least one turbine blade of the array is formed to be adjustable, in use, from a first, driving, configuration when moving with the direction of water flow, to a second, return, configuration when moving against the direction of water flow, and wherein the surface area of the turbine blade presented to the direction of water flow is reduced when in the return configuration.

1 .- 22 . (canceled) 
     
     
         23 . A turbine for use in extracting energy from within a water flow comprising: an array of turbine blades formed and arranged for rotation, in use, about an axis substantially normal to the direction of water flow; wherein at least one turbine blade of the array is formed to be adjustable, in use, from a first, driving, configuration when moving with the direction of water flow, to a second, return, configuration when moving against the direction of water flow, and wherein the surface area of the turbine blade presented to the direction of water flow is reduced when in the return configuration. 
     
     
         24 . A turbine according to  claim 23 , wherein in use the turbine rotates as a consequence of a greater force of water flow acting on the turbine blade when in the driving configuration. 
     
     
         25 . A turbine according to  claim 23 , wherein said at least one turbine blade comprises at least one hydrofoil. 
     
     
         26 . A turbine according to  claim 25 , wherein the or each hydrofoil is arranged so that in operation the hydrofoil generates lift during at least part of the rotation of the turbine. 
     
     
         27 . A turbine according to  claim 26 , wherein the or each hydrofoil is arranged to generate lift in operation when in the return configuration. 
     
     
         28 . A turbine according to  claim 25 , further comprising constraining means for constraining the movement of the or each hydrofoil. 
     
     
         29 . A turbine according to  claim 28 , wherein the constraining means is configured to constrain the or each hydrofoil to have a desired orientation during at least part of each rotation of the turbine. 
     
     
         30 . A turbine according to  claim 29 , wherein the desired orientation is a desired orientation relative to the direction of water flow. 
     
     
         31 . A turbine according to  claim 29 , wherein in the desired orientation the or each hydrofoil is held substantially tangential to the direction of rotation of the turbine. 
     
     
         32 . A turbine according to  claim 28  wherein the constraining means comprises at least one guide device attached to or forming part of the or each hydrofoil, wherein the at least one guide device is arranged to engage with at least one track during at least part of the rotation of the turbine. 
     
     
         33 . A turbine according to  claim 23 , wherein said at least one turbine blade is formed and arranged to generate lift in operation to rotate the turbine. 
     
     
         34 . A turbine according to  claim 33 , wherein said at least one turbine blade is formed and arranged to generate lift when in the return configuration to rotate the turbine. 
     
     
         35 . A turbine according to  claim 23 , wherein said at least one turbine blade is formed and arranged to experience a drag force from water flow acting on the turbine blade when in the first, driving configuration, the drag force acting to rotate the turbine. 
     
     
         36 . A turbine according to  claim 35 , wherein in operation the drag force acting on the turbine blade in the first, driving configuration is greater than a drag force acting on the turbine blade when in the second, return configuration. 
     
     
         37 . A turbine according to  claim 23 , wherein the turbine blades are spaced radially outwardly from the centre of rotation of the turbine, thereby providing a central space radially inward of the turbine blades. 
     
     
         38 . A turbine according to  claim 37 , wherein in operation water flows through the central space. 
     
     
         39 . A turbine according to  claim 37 , wherein the turbine blades are arranged so that in operation water contacts at least one of the turbine blades after flowing through the central space. 
     
     
         40 . A turbine according to  claim 39 , wherein said at least one turbine blade is arranged to generate lift from contact with water that has flowed through the central space. 
     
     
         41 . A turbine according to  claim 23 , wherein at least one adjustable turbine blade is provided with one or more flap portions, which in operation move to increase or decrease the surface area of the turbine blade presented to the direction of water flow when moving from the driving configuration to the return configuration. 
     
     
         42 . A turbine according to  claim 41 , wherein at least one of the flap portions is shaped to form a hydrofoil. 
     
     
         43 . A turbine according to claim  22 , further comprise latching means for releasably holding the or each turbine blade in the first configuration during at least part of rotation of the turbine. 
     
     
         44 . A method of extracting energy from within a water flow comprising: locating at least one turbine in a body of water; and extracting energy from the rotation of the said turbine, wherein the said turbine comprises an array of turbine blades formed and arranged for rotation, in use, about an axis substantially normal to the direction of water flow; wherein at least one turbine blade of the array is formed to be adjustable, in use, from a first driving configuration when moving with the direction of water flow, to a second return configuration when moving against the direction of water flow, and wherein the surface area of the turbine blade presented to the direction of water flow is reduced when in the return configuration.