Patent Publication Number: US-2009220342-A1

Title: Shaftless vertical axis wind turbine

Description:
BACKGROUND TO THE INVENTION  
     1. Field of the Invention 
     The current invention relates to wind turbines and more particularly to vertical axis wind turbines. 
     2. Background Information 
     With the continuing increase in demand for energy, especially in developing countries, and a realisation that traditional fossil fuel supplies are limited, there is increasing interest in new and improved ways to harness renewable energy sources such as sunlight, wind, rain (water), tides and geothermal heat, which are naturally replenished. Hydro-electricity generation has been a mainstay of renewable energy for many decades. However, with greater importance being placed on the environmental impact of damming waterways and the realisation that clean fresh drinking water is an important commodity, hydro-generation schemes are becoming less desirable. Attention has now turned to wind as a source of future large scale electricity generation. 
     Wind turbines can be characterised as either horizontal axis or vertical axis turbines. Horizontal axis turbines typically comprise a tower with a large fan-like blade rotating around a horizontal axis much like a windmill. Hitherto the largest horizontal axis wind turbines are about the height of a 40-storey building and have a blade diameter of approximately 126 metres. In order to produce sufficient electricity for supply to a public electricity network, horizontal axis wind turbines are located in large wind farms that can comprise hundreds of wind turbines spread over a large area. Although they use an abounded renewable energy source these wind farms occupy large areas of land and are unsightly. 
     Conventional vertical axis wind turbines have a main rotor shaft extending vertically. The main advantage of vertical axis turbines is that the generator and gearbox can be placed at the bottom of the shaft near the ground meaning that the tower does not need to support this weight. Additionally, a vertical shaft wind turbine can accept wind from any direction and does not need to turn, or yaw, about its vertical axis, to face the prevailing wind direction. However, there is a significant amount of lateral force applied to the vertical shaft and turbine structure due to the larger surface area that vertical axis turbines presents to the wind. Thus, there is a practical size limit on vertical axis wind turbines known hitherto. Additionally, because the rotor in a vertical axis wind turbine spins about a vertical axis the wind part of the rotor is moving with the wind while a diametrically opposite part of the rotor is moving towards the wind and must counter the oncoming force of the wind. 
     It is an object of the present invention to provide a shaftless vertical axis wind turbine that can be made to a taller and larger scale than wind turbines known hitherto in order to greater harness wind energy. It is another object of the present invention to provide a vertical axis wind turbine that overcomes or at least ameliorates disadvantages with known wind turbines, or at least to provide the public with a useful alternative. 
     SUMMARY OF THE INVENTION  
     According to the invention there is provided a shaftless vertical axis wind turbine comprising:
         a stationary hollow core having inner and outer circular walls with a void between the inner and outer walls, and   a rotor rotatably supported about the core and having a plurality of radially extending rotor arms each having a wind engaging rotor blade located at a distal end.       

     Preferably, the wind turbine further comprises a plurality of vertical ribs within the void and connecting the inner and outer walls. 
     Preferably, the wind turbine further comprises two or more rotors located one above the other for independent rotation about the core. 
     Preferably, each one of the rotors is mechanically connected with an electric generator. 
     Preferably, there is a generator driven by each one of the rotors. 
     Preferably, the generator is a direct drive type generator. 
     Preferably, the wind turbine further comprises a pair of electricity generating windings located on the core and rotor respectively for generating electricity during relative movement between the core and rotor, without the use of any mechanical gearing system. 
     Preferably, the rotor is supported on a ledge extending about the outer wall of the core. 
     Preferably, the outer wall of the core is stepped to define the ledge. 
     Preferably, the rotor comprises upper rollers or wheels that rotatably support the rotor on the ledge, and lower rollers or wheels that rotatably support the rotor about the outer wall of the core. 
     Preferably, the rotor further comprises second upper rollers or wheels that rotatably support the rotor about the outer wall of the core. 
     Preferably, the ledge has an abutment and at least one of the upper wheels or second upper wheels engage against the abutment. 
     Preferably, the radially extending rotor arms comprises tie-stayed truss members. 
     Preferably, the radially extending rotor arms are tapered towards the distal ends. 
     Preferably, the wind engaging blades are lift-type rotor blades, and the rotor arms further comprises a drag type rotor blade located adjacent the core. 
     Preferably, the rotor comprises a tubular carousel rotatably supported about the core with the plurality of rotor arms extending from the carousel. 
     Preferably, the wind engaging blades are lift-type rotor blades, and the rotor further comprises a plurality of drag type rotor blade located about the carousel. 
     Preferably, the wind turbine further comprises a pump reserve hydro electricity generation system. 
     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 section elevation illustration of a first embodiment of a multi-stage wind turbine according to the invention, 
         FIG. 2  is a section plan illustration through A-A of  FIG. 1 , 
         FIG. 3  is a section plan illustration through B-B of  FIG. 1 , 
         FIG. 4  is a section elevation illustration of a rotor arm and blade of the first embodiment wind turbine, 
         FIG. 5  is an illustration of the rotor mounting and generator arrangement of the first embodiment wind turbine, 
         FIG. 6  is an illustration of an alternative embodiment for the generator of the first embodiment wind turbine, 
         FIG. 7  is an illustration of a second arrangement for mounting the rotor in the first embodiment wind turbine, 
         FIG. 8  is an illustration of a third arrangement for mounting the rotor in the first embodiment wind turbine, 
         FIG. 9  is a section elevation illustration of a second embodiment of a multi stage wind turbine according to the invention having a different rotor arm construction, 
         FIG. 10  is a section plan illustration through C-C of  FIG. 9 , 
         FIG. 11  is a section plan illustration through D-D of  FIG. 9 , 
         FIG. 12  is a section elevation illustration of a pair of rotor arms and a blade of the second embodiment wind turbine, 
         FIG. 13  is a section plan illustration through an upper truss arm of the second embodiment wind turbine, 
         FIG. 14  is a section plan illustration through a lower truss arm of the second embodiment wind turbine, 
         FIG. 15  is an illustration of an arrangement for mounting the rotor in the second embodiment wind turbine, 
         FIG. 16  is an enlarged illustration of the top roller set of the arrangement illustrated in  FIG. 15 , 
         FIG. 17  is a section plan illustration at C-C in the second embodiment illustrated in  FIG. 15 , 
         FIG. 18  is a section plan illustration at D-D in the second embodiment illustrated in  FIG. 15 , 
         FIG. 19  is a section plan illustration, at the top of the rotor, of a third embodiment of a multi stage wind turbine according to the invention having a different rotor arm design and a plurality of drag-type rotor fins about the rotor carousel, and 
         FIG. 20  is a section plan illustration, at the bottom of the rotor, for the embodiment of  FIG. 19 . 
     
    
    
     DESCRIPTION OF THE EXEMPLARY EMBODIMENTS  
     The invention will now be described as practiced in a large size, i.e. tall building sized, shaftless vertical axis multi-stage wind turbine. The design of the wind turbine is such that it can be made to a very large size and in particular much larger than known wind turbines. Hitherto the largest wind turbines are horizontal shaft wind turbines having a blade diameter of up to 126 metres. By large scale the inventors intend that a wind turbine according to the invention could have a diameter, or width, at its base of between 250 and 350 metres and a vertical height of between 300 and 500 metres or higher. This is, however, not intended to limit the use or functionality of the invention and a skilled addressee will appreciate that principles of the invention can be applied to a wind turbine of any size, bigger or smaller. 
     Because a wind turbine according to the invention can be made to such a large scale it can capture a large area of wind at greater heights where wind velocity is higher. The power (P) potentially available in the wind is given by ½ρAv 3  where ρ is the density of air, A is the swept area of the turbine rotor, and v is the velocity of wind. Therefore, the amount of power that can be generated by a wind turbine increases proportionally to the area swept out by its rotors and increases to the cubic power of wind speed. Being up to 350 metres wide the wind turbine has a large area swept out by its rotors. Being able to reach heights of 500 metres or more means that the wind turbine is exposed to winds of higher velocity and thus a wind turbine according to the invention is able to tap greater energy potential of the wind. 
     Construction of a wind turbine of the size referred to above may use well known building construction and large scale engineering techniques. Numerous tall buildings of up to 500 or more metres have been constructed in most countries of the world and the building and construction techniques for such structures are easily within the know-how of the skilled addressee. The individual structural elements and features of the wind turbine described herein lend themselves to such known construction techniques. 
     The apparatus of the preferred embodiment is “multi-stage” in that a plurality of independent turbines, each with a respective rotor, are stacked vertically about a common vertical cylindrical supporting structure. Each turbine is associated with its own electrical generator, either by direct drive, gearing or other transmission means. As the vertical wind turbine may extend to a height of several hundred metres it may experience different wind directions and velocities at different levels through its height. Each turbine is free to rotate in response to the wind that it experiences independently of a generator at a different level which may be experiencing different wind conditions. However, this is not essential to the invention and the wind turbine may be made to have just a single rotor. 
     A wind turbine according to the invention is shaftless. In this document “shaftless” refers to the fact that each rotor of the wind turbine is a freely rotating structure. There is no shaft coaxial with the rotor to transmit torque to a generator, as is the case in conventional rotating electrical machines and known vertical and horizontal shaft wind turbines. 
     FIRST PREFERRED EMBODIMENT  
       FIGS. 1-5  depicted a first embodiment of a shaftless vertical multi-stage wind turbine  1  according to the invention. Although not critical to the invention in terms of scale, the turbine has a diameter of 350 metres and a height of up to 500 metres. The wind turbine  1  comprises three basic functional parts, namely a vertical supporting structure, at least one wind driven rotor located about the structure and a generator driven by the rotor for the generation of electricity. In the preferred embodiment there is plurality of vertically stacked independently rotating rotors. The rotors are stacked vertically one above the other and are each coupled with a corresponding power transmission and generation units located with the vertical supporting structure. 
     The vertical supporting structure comprises a vertically extending cylindrical tower forming the core of the wind turbine  1  and typically has a diameter of between 15% and 40% of the total wind turbine diameter. In the preferred embodiment the diameter of the core tower is 25% of the wind turbine diameter and so for a wind turbine having a diameter of 300 meters the diameter of the core tower is 75 meters. The core tower extends the full height of the wind turbine and may be caped with a roof (not shown) that is either flat, pitched or domed. The core tower is constructed with two concentric circular walls  5 ,  6  having a void  7  between them. A plurality of ribs  8  extend vertically within the void  7  at spaced apart circumferential locations connecting the inner and outer walls  5 ,  6 . The vertical ribs  8  separate the void  7  between the walls into a plurality of cells. In the preferred embodiment the distance between the inner and outer tower walls  5 ,  6  is several meters providing sufficient room for a lift shaft  9 , stairwell  10  and machine room at each rotor level for accommodating generation equipment all within the wall void  7 . The area within the inner wall  6  of the core is generally hollow creating a large centre void  11  within the structure. The core tower is made from reinforced concrete and may be constructed using known construction techniques. The double wall cellular structure of the core tower gives the tower strength to withstand large lateral forces generated by wind. 
     Each stage of the wind turbine includes a rotor  19 ,  20 ,  21 ,  22  located and freely rotatable about the core tower. The rotors at each stage can be of the same size or different sizes. The rotors  19 ,  20 ,  21 ,  22  comprise a fully trussed tubular carousel structure  23  rotatably supported about the core. A plurality of tie-stayed trussed arms  26  extend radially from the bottom  232  of the carousel  23 . The radial truss arms  26  are stayed by tie members  27  extending from top  231  of the carousel  23  to the distal end of the radial truss arm  26 . At the distal ends of each radial truss arm  26  is a generally aerofoil shaped lift-type blade  28 . The blade  28  is located on a sub-frame  24  pivotally affixed to the radial truss arm  26  at a hinge  25 . The blade  28  pivots about hinge joint  25  to have an actively varying “pitch” angle (depicted by arrow E in  FIG. 2 ) to the wind so as to turn more efficiently under a wide range of wind conditions. In the preferred embodiment there are three symmetrically spaced trussed radial arms  26  and blades  28  on each rotor, however this is not meant to limit the scope of use or functionality of the invention. The skilled addressee will appreciate that 2, 4, 5, 6 or more blades may be used with varying degrees of power and efficiency. 
     Referring to  FIG. 5 , the outer wall of the core tower is stepped at the level of each rotor stage  19 ,  20 ,  21 ,  22  to provide ledges  30  about the outer periphery of the core tower. Each rotor is rotatably supported about the core tower on the respective ledges  30  located around the outer periphery of the core tower. The outer edge of each ledge  30  has an abutment  35 . An inwardly extending hook frame portion  233  of the rotor locates over the ledge  30 . There are sets of wheels or rollers  31  located circumferentially about the inner edge of the inwardly extending frame portion  233  that run horizontally on a circular track  351  affixed to the inward face of the abutment  35 . Second sets of wheels or rollers  32  are also located circumferentially about the inner edge of underside of the frame portion  233  and vertically on a second circular track  352  affixed to the upward face of the abutment  35 . The upper wheels rollers sets  31 ,  32  provide vertical and horizontal lateral support to the rotor against the outer periphery of the concrete core tower. There is also a plurality of thrust rollers  33  located about the inner periphery of the bottom  232  of the rotor carousel  23 . The trust rollers  33  run on a circular track  353  affixed to the outer wall  5  of the core to provide lateral support for the lower part of the rotor against the outer periphery of the core tower. Thus each rotor is suspended vertically at a top part of its frame from a ledge  30  and is provided with vertical and horizontal lateral supports by the cooperation of the upper wheels and rollers  31 ,  32  and the thrust rollers  33 . The rotor rotates about the core tower under the effect of wind interaction with the aerofoil shaped blades at the distal ends of the rotor arms. 
     Movement of the rotor is used to mechanically turn a generator  40  located with the core tower by means of gearing located adjacent the roller thrust roller  33 . A pair of gears  42 ,  43  is rotatably located in an opening in the core tower outer wall. The smaller gear  42  is engaged by a ring gear  44  located below the thrust roller  33  about the inner periphery of the lower annular member  232  and rotates the smaller gear  42  with movement of the rotor. The smaller gear is fixed with the larger gear  43  which engages a generator gear  41  to turn the generator  40 . 
     Alternative Arrangement for the Generator 
     The mechanically turned generator  40  is not essential to the invention. Any type of suitable power transmission and/or generation system known in the art may be used to convert rotational energy of the rotors into electricity. For example, direct drive (gearless) generator systems, without the use of any mechanical gearing, may be used. In a direct drive generator system, there is a set of stationary components and another set of rotating components. One of the components contains the electro magnetic winding, or in case permanent magnets are used, the permanent magnets and their holders and the other components contain the conductive windings. Electricity is produced by the relative movement of the rotating component through or about the static component.  FIG. 6  illustrates such a direct drive system wherein permanent magnet field poles  61  are attached to the upper edge of the inwardly extending portion  233  of the rotor carousel  23  and the stator winding part  60  thereof is affixed to the outer wall  5 . 
     Alternative Arrangement for the Rotor Supports 
       FIG. 7  illustrates a second arrangement for mounting the rotor from the tower ledges  30 . The ledge  30  has a chamfered abutment  29  at its outer edge. A lateral stabilisation wheel  311  is provided to run against a track  354  affixed to the face of the chamfered abutment  29  providing lateral stabilisation for the rotating rotor.  FIG. 8  illustrates yet another embodiment the outer wall of the core tower which is cylindrical without steps and the rotors are mounted on corbel-type roller track beam  34  located around the outer periphery of the core tower and fixed thereto. 
     SECOND PREFERRED EMBODIMENT HAVING AN ALTERNATIVE ROTOR ARM CONSTRUCTION  
       FIGS. 9-14  depict a second preferred embodiment of a wind turbine according to the invention which has an alternative rotor arm arrangement. In this embodiment the rotor blades are supported about the rotor carousel by four radially extending trussed arms  461 ,  462 ,  261 ,  262 . The upper part of the blade  28  is supported by a first pair of horizontally spaced apart trussed arms  461 ,  462  extending radially from the top  231  of the rotor carousel  23 . The bottom part of the blade  28  is supported by a corresponding second pair of horizontally spaced part trussed arms  261 ,  262  extending radially from bottom  232  of the rotor carousel  23 . In between the upper and lower pairs of trussed arms  461 ,  462 ,  261 ,  262  there are diagonal tie-stay arms  48  extending from the inner end of the upper set of radial trussed arms  461 ,  462  to the distal end of the lower set of radial trussed arms  261 ,  262 . The leading truss arms  461 ,  261  in each pair may also be tie-stayed by stays  481  in the horizontal plane to the rotor carousel  23  to provide additional stability. 
       FIGS. 15 and 16  illustrates an arrangement for mounting the rotor from the tower ledges  30 , which can be used with the second preferred embodiment of a wind turbine. There is no abutment  35 . The upper lateral stabilisation wheel  31  is provided to run against a track  351  that is affixed to the outer circumferential face of the core.  FIGS. 17 and 18  are plan views of this arrangement. 
       FIGS. 19 and 20  illustrates a further alternative design of the rotor arm in which the arm is tapered from the carousel  23  towards the rotor blade  28 . Tapering provides the rotor arm with a lot more strength to resist flexing and blending in a lateral direction during rotation of the rotor. 
     In addition, the inventors envisage that the rotor arm in this and other embodiments may be enclosed by a aerodynamically shaped skin in order to reduce drag of the rotor arm as it moves through the air. 
     THIRD PREFERRED EMBODIMENT HAVING A COMBO BLADE ARRANGEMENT  
     One of the disadvantages of lift-type vertical axis wind turbines is that there is a (negative power) drag against the rotational direction when the blades  28  of the rotor rotate into the wind. They require sufficiently high wind speed across the blade surface in order to generate the aerodynamic forces needed to start the rotor. To overcome the above difficulties, in a further embodiment of the present invention, curved fins are added about the rotor carousel  23  to create a combo wind turbine.  FIGS. 9-14  illustrate the preferred embodiment of this combo wind turbine. The curved fins are located between the upper and lower pairs of trussed arms ( 461 ,  462 ), ( 261 ,  262 ). The fins  45  act like drag-type rotor blades in capturing the wind and help to start the rotor turning. As the rotor speed increases the aerodynamic forces generated at the aerofoil type blades  28  also increase and contribute to turning forces on the rotor. At normal rotor speeds, the predominant rotational force comes from the aerofoil type blades  28 . 
     Although the embodiment illustrated in  FIGS. 9-14  has three curved fins  45  all located in between the upper and lower radial truss arms pairs, this is not essential to the invention and the curved fins  45  may be of any number and of any size about the perimeter of the rotor carousel  23  so long if they are sufficient to begin turning the rotor at a desired wind speed. 
       FIGS. 19 and 20  show an alternative version of the combination blade arrangement wherein a plurality of fins  45  are arranged about the rotor carousel  23  independently of the rotor arms. This greater number of fins  45  than in the embodiment depicted in  FIGS. 9-14  allows the fins  45  to be of smaller size thus causing less drag at higher speeds when the rotor is operating substantially by the lift effect of the outer rotor blades  28 . 
     Pumped Reserve System 
       FIG. 1  also illustrates an important, although not essential, feature available in a wind turbine according to the current invention. The height and size of the wind turbine make it feasible to store large volumes of water at significant height in the core tower. A significant volume of water can be stored in the upper void  7  between the inner and outer walls of the core tower without the need for significant additional strengthening of the upper parts of the tower. Likewise, no significant additional strengthening of the tower is needed to store water in the lower centre core void  11  of the tower. Such water can be moved between these upper and lower storage reservoirs by a riser pipe within the wall void or on the inner surface of the inner wall. Water is pumped by electric pump from the lower reservoir to the upper reservoir at times when the wind conditions allow more electricity to be generated than is needed for supply to the electricity grid or local power consumption. When conditions reverse or during peak load times, or when the wind is low, water is released from the upper reservoir back to the lower reservoir through a hydro generator to supplement wind generation alone. Although pumped reserve systems are known in the art, hitherto it has not been possible to incorporate a hydro pump reserve system into wind generator due to limitations on the physical size and strength of wind turbine towers and wind generation capacity of a single tower. The tower of the current invention overcomes such problems by providing a strong tall and large tower and through the incorporation of large stacked rotors to enable large generation capacity from a single tower. 
     Where in the foregoing description reference has been made to integers or elements having known equivalents then such are included as if individually set forth herein. 
     Embodiments of the invention have been described, however it is understood that variations, improvements or modifications can take place without departure from the spirit of the invention or scope of the appended claims.