Patent Publication Number: US-2009220339-A1

Title: Wind deflector for wind turbine and wind turbine incorporating same

Description:
BACKGROUND TO THE INVENTION 
     1. Field of the Invention 
     The present invention relates to wind turbines and in particular to a wind deflector for use with a wind turbine. 
     2. Background Information 
     Vertical axis wind turbines are well known in the art. In a vertical axis wind turbine the main rotor shaft is arranged vertically and has radially extending arms supporting vertically arranged wind engaging blades. In a lift-type vertical axis wind turbine the blades have an aerofoil shape such that most of the rotating force comes from aerodynamic forces generated by wind passing across the aerofoils. Because the turbine rotates the aerofoils engage the wind from continuously varying directions throughout a circular path and each blade experiences both positive and negative wind power within each revolution. This may cause the turbine to be less efficient than it might be. 
     SUMMARY OF THE INVENTION 
     It is one object of the present invention to provide a wind deflector for a wind turbine that overcomes or at least ameliorates the above problem, or to at least provide the art with a useful alternative. 
     According to a first aspect of the invention there is provided a wind deflector for a wind turbine, the wind deflector comprising a vertical wind deflecting surface located on a guide track or carousel and movable in a circular path about the wind turbine. 
     Preferably, the wind deflecting surface has a circumferential span of less than 30 degrees of the circular path. 
     Preferably, the wind deflecting surface has a circumferential span of between 5 and 30 degrees of the circular path. 
     Preferably, wherein the wind deflecting surface is curved in a horizontal direction. 
     Preferably, the wind deflector further comprises a control means for moving the wind deflecting surface to a position leading a prevailing wind direction by 30 degrees to. 
     According to a second aspect of the invention there is provided herein a wind turbine comprising a stationary core, a rotor rotatably supported about the core and having a plurality of radially extending rotor arms each bearing a rotor blade, and the wind deflector of claim  1 . 
     Preferably, the circular path is about the outer periphery of the rotor. 
     Preferably, the wind deflecting surface has a circumferential span of less than 30 degrees of the circular path. 
     Preferably, the wind deflecting surface has a horizontal span of between 5 and 30 degrees of the circular path. 
     Preferably, the wind deflecting surface has a vertical height longer than that of the rotor blade. 
     Preferably, the wind deflecting surface is straight or curved in a horizontal direction. 
     Preferably, the wind deflecting surface leads 30 degrees to the prevailing wind direction. 
     According to a third aspect of the invention there is provided herein a method of operating a vertical axis wind turbine comprising providing a vertical wind deflecting surface on a circular guide track or carousel having a circular path about the turbine rotor and moving the wind deflecting surface about the circular path to face a prevailing wind direction. 
     Preferably, the wind deflecting surface is moved about the circular path to lead 30 degrees to the prevailing wind direction. 
     Further aspects of the invention will become apparent from the following description, which is given by way of example only and is not intended to limit the scope of use or functionality of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An exemplary form of the present invention will now be described by way of example only and with reference to the accompanying drawings, in which: 
         FIG. 1  is a perspective illustration of a vertical axis wind turbine with a wind deflector, 
         FIG. 2  is an elevation illustration of the wind turbine with a wind deflector, viewing from the prevailing wind direction when the turbine is turning clockwise, 
         FIG. 3  is a plan illustration of the wind turbine with wind deflector, and 
         FIG. 4  is a perspective illustration of a second type of vertical axis wind turbine with which the wind deflector could be used. 
     
    
    
     DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
     In  FIG. 1  there is depicted a perspective illustration of a wind turbine with a wind deflector according to the invention. The scale of the wind turbine is not critical to the invention and it may be of any size from a small roof top wind turbine up to a large turbine having, for example, a diameter of 300 metres and a height of up to 500 metres. A wind turbine of this size has been proposed by the applicant in earlier patent applications. 
     The wind turbine of  FIG. 1  comprises a base housing an electricity generator  10 . A stationary turbine support frame  26  extends vertically from the base and encloses a vertical rotary shaft  11  coupled to the generator. The shaft  11  is connected to three radial blade structures each supporting lift-type aerofoil shaped blades  12 . The blades  12  are arranged 120 degrees apart about the rotary shaft  11 . The blades  12  are acted upon by wind causing the rotary shaft  11  to rotate for generating electricity as is known in the art. 
     The wind turbine has about its base a guide track  20  that defines a circular path about the circumferential path taken by the rotating blades  12 . A moveable frame  21  is located to travel on the circular track  20  and extends vertically to a height above the top of blades  12 . Two radially extending arms  22 ,  23  between the frame  21  and the turbine support frame  26  support the frame  21  at its top and an intermediate position. The two radial arms  22 ,  23  are vertically located at positions below and above the rotor blades  12  respectively. The frame  21  mounted on wheels or rollers (not shown) that allow it to freely travel along the circular track  20  and thus move about the perimeter of the wind turbine. A motorized drive system is provided at the frame base for moving the frame  21  along the circular track  20 . Located on an outer face of the frame  21  is a vertical wind deflecting surface  25 . The wind deflecting surface  25  has a width that spans approximately 10 degrees of the circular part circumference, and a vertical height B longer than the vertical length of the rotor blades  12 . The wind deflecting surface  25  is located on the frame such that its entire length B extends through the entire vertical height of the rotor blades  12 . The wind deflecting surface  25  is straight in the horizontal direction. In an alternative embodiment the wind deflecting surface  25  is curved in the horizontal direction. 
     Control means for the wind deflector include a wind direction sensor and deflector position control circuitry. In use, the direction of the prevailing wind acting on the wind turbine is determined and the position control means drives the frame  21  to a position such that the wind deflecting surface  25  is 30 degrees to the prevailing wind direction. In the drawings the circular track  20  is provided with position numbers  1  through  12  like the face of a clock. These numbers are for illustrative purposes only. They do not form part of the physical device and are not intended to limit the scope of use or functionality of the invention. As indicated on  FIG. 1 , in the illustrative embodiment the aerofoil shape of the turbines blades  12  is such that the turbine rotates in the clock-wise direction. The prevailing wind direction in the illustrated embodiment is from the 6 o&#39;clock position. Maximum efficiency and speed of rotation of the rotor is achieved if the wind deflecting surface  25  is located at a position that leads the prevailing wind direction by about 30 degrees. In the illustrated embodiment 30 degrees leading the wind direction is 5 o&#39;clock. The term leading refers to the fact that the rotor blades  12  passed behind the wind deflecting surface  25  30-degrees before they reach a position perpendicular to the prevailing wind direction. 
     Positioning a wind deflecting surface  25  having even a small circumferential span of 10 degrees at a position 30 degrees leading the prevailing wind direction substantially improves the speed and efficiency of rotation of the wind turbine for a given wind strength. The wind deflecting surface  25  causes the turbine to start rotation at a lower wind speed and to rotate at a faster speed for any given wind strength than when the wind deflecting surface  25  is absent. The optimum position for the wind deflecting surface  25  may varying from exactly 30 degrees depending on the dimensions of the wind deflecting surface and the type and size of the wind turbine rotor blades. 
     It should be appreciated that modifications and alterations obvious to those skilled in the art are not beyond the scope of the present invention. For example, in the preferred embodiment the horizontal span of the wind deflecting surface  25  is 10 degrees. However this is not essential to the invention and the span may be anywhere less than 30 degrees. Further, the inventors currently believe that the most effective position for the wind deflecting surface  25  is 30 degrees leading the prevailing wind direction. However, this is not essential to the invention and positions other than 30 degrees may provide acceptable results. Furthermore, it is anticipated that the most efficient position of the wind deflecting surface  25  might be related to the surface span. For example, if the span is increased from 10 degrees to, say, 30 degrees then the optimal position to the prevailing wind direction may vary from the preferred 30 degrees direction. 
       FIG. 4  depicts a large scale multi-stage wind turbine proposed by the applicant in earlier patent applications. The wind turbine depicted in  FIG. 4  has three independently rotatable turbine stages stack one above the other. This wind turbine may extend to a height of 300-500 meters. The wind experienced by different stages through the height of such a high wind turbine may vary slightly due to the effects of terrain. It is therefore desirable to have wind deflecting surfaces at each stage of the turbine that can be forced in slightly different directions to take account of slightly varying wind directions at different levels. In such an embodiment a carousel erected around the outer periphery of the wind turbine could carry a separate independently rotatable wind deflecting surface for each vertical stage of the wind turbine. The carousel would be made from tubular frame members so is not to unduly affect wind acting upon the wind turbine except in the area of the wind deflecting surface.