Field of the Invention

[0001 ] The present invention relates to vertical axis wind turbines.

Background to the Invention

[0002] Vertical axis wind turbines (more broadly defined as wind turbines having an axis which is transverse relative to wind direction) fall into two types: those relying on drag such as Savonius rotors and those relying on lift such as Darrieus rotors.

[0003] Savonius rotors and similar designs have curved blades extending outwardly from a central axle. The curved blades have uniform concavity; that is, they have a concave side arranged to ‘catch’ wind and a convex side arranged to move into the wind. The drag on the concave side is significantly higher than on the convex side, and this differential in drag causes the rotor to spin under the action of wind.

[0004] Traditional Savonius rotors have a number of inefficiencies. The drag on the convex side of each blade limits the power available. This can be partially addressed by increasing the width of the blades, but such an increase can result in unacceptable shear forces between blades and the axle. Increasing the length of the blades can result in significant variations in torque along the blade, and unacceptably large bending moments being induced.

[0005] The present invention seeks to provide a drag-style vertical axis wind turbine which addresses some of these concerns, at least in part.

Summary of the Invention

[0006] According to one aspect of the present invention there is provided a rotor for a wind turbine, the rotor having a plurality of blades, each blade having a width in a generally radial direction, each blade being curved along at least part of its width, each blade having an outer end, a concave outer portion, an intermediate portion, a convex inner portion, and an inner end, wherein the intermediate portion is located between the concave outer portion and the concave inner portion; the inner end of each blade being fixed to the intermediate portion of an adjacent blade.

[0007] The intermediate portion may be straight. Alternatively, the intermediate portion may be concave or convex. The intermediate portion may act as an extension of the concave outer portion or of the convex inner portion.

[0008] Each blade may include a straight innermost portion extending between the inner end and the convex inner portion. The straight innermost portion of one blade is preferably oriented at about 90° relative to the intermediate portion of the adjacent blade to which it is fixed.

[0009] The convex inner portion of each blade preferably curves through about 130°; that is, the initial straight portion and the intermediate straight portion of a blade are preferably oriented at about 130° relative to each other.

[0010] The concave outer portion preferably curves through about 90°.

[0011 ] It will be appreciated that the convex inner portions and innermost portions of the plurality of blades combine to form a closed curve around an axle of the rotor. It is preferred that an average radius of the closed curve is about half of a radius of the rotor.

[0012] It will be appreciated that the closed curve shields the axle of the rotor from the wind. The convex side of the convex inner portions are similarly shielded from the wind.

[0013] Advantageously, the creation of the closed curve provides the rotor with significant rigidity. In addition, the construction results in significant noise reduction when compared with many prior art turbines.

[0014] It will be appreciated that rotors of the present invention can be assembled in modular fashion along a common axis. Brief discussion of Prior Art

[0015] Prior art searching has revealed a number of vertical axis wind turbines which employ broadly S-shaped blades.

[0016] In some instances, the S-shaped blades extend across an axle of the turbine, thus acting as two simple concave blades. Examples of this arrangement include Korean patent publication number 101 ,001 ,812; US patent number 9,494,136; and US patent application number 20120235418.

[0017] In other instances, the S-shaped blade is located on one radial side of an axle, with the convex portion arranged to deflect wind either into the concave portion or else to another blade. Examples of this arrangement include those of US Patent number 1 ,367,766 and international publication numbers WO 2012/082953 and WO 2019/172792.

[0018] These prior art arrangements do not suggest the connection of successive blades so as to create a robust structure.

Brief Description of the Drawings

[0019] It will be convenient to further describe the invention with reference to preferred embodiments of the present invention. Other embodiments are possible, and consequently the particularity of the following discussion is not to be understood as superseding the generality of the preceding description of the invention. In the drawings:

[0020] Figure 1 is a first perspective of a rotor for a wind turbine in accordance with the present invention;

[0021 ] Figure 2 is a second perspective of the rotor of Figure 1 ;

[0022] Figure 3 is a cross section through a first embodiment of a rotor for a wind turbine in accordance with the present invention;

[0023] Figure 4 is a cross section through a second embodiment of a rotor for a wind turbine in accordance with the present invention; [0024] Figure 5 is a side view of the rotor of Figure 3;

[0025] Figure 6 is a side view of the rotor of Figure 4;

[0026] Figure 7 is a base plate from within the rotor of Figure 3;

[0027] Figure 8 is a base plate from within the rotor of Figure 4;

[0028] Figure 9 is a perspective of a turbine comprising three of the rotors of Figure 3 axially aligned;

[0029] Figure 10 is a side cross section of the turbine of Figure 9;

[0030] Figure 11 is a perspective of a turbine comprising three of the rotors of Figure 4 axially aligned; and

[0031 ] Figure 12 is a side cross section of the turbine of Figure 11 .

Detailed Description of Preferred Embodiments

[0032] Figures 1 and 2 show a rotor 10 comprised of a plurality of blades 12. In the embodiment of the drawings there are nine blades 12.

[0033] Each blade 12 has a “windward” side 14 and a “leeward” side 16.

[0034] Each blade 12 is broadly “S” shaped. In other words, each blade 12 has a concave outer portion 18 and a convex inner portion 20 when viewed from the windward side 14.

[0035] The precise geometry of each blade 12 will now be described.

[0036] The blade 12 has an inner end 22 and an outer end 24. The blade 12 has an initial straight portion 26 which extends from the inner end 22. The blade then has a first curved portion 28 which curves through about 130° towards the leeward side 16. The initial straight portion 26 and the first curved portion 28 combine to form the convex inner portion 20. The length of the initial straight portion 26 is similar to the arc length of the first curved portion 28.

[0037] An intermediate straight portion 30 extends tangentially away from the first curved portion 28. It will be appreciated that the intermediate straight portion 30 is angled at 130° with respect to the initial straight portion 26.

[0038] The intermediate straight portion 30 has a length about twice that of the initial straight portion 26.

[0039] A second curved portion 32 curves through about 90° towards the windward side 14 to form the concave outer portion 18. The second curved portion 32 terminates at the outer end 24. The radius of curvature of the second curved portion 32 is similar to that of the first curved portion 28.

[0040] The blades 12 are fixed to each other by suitable means such as bolting or welding. The arrangement is such that the inner end 22 of one blade 12 is fixed to the intermediate straight portion 30 of an adjacent blade 12 at an angle of 90°, forming a join 34.

[0041 ] It will be seen that the initial straight portion 26 of the blade 12 forms an angle of about 140° relative to the initial straight portion 26 of the adjacent blade 12.

[0042] When all nine blades 12 are thus assembled, it will be appreciated that the convex inner portions 20 combine to form a closed curve 36. The closed curve 36 has a varying radius, with the joins 34 representing the maximum radius and the junctions of the initial straight portions 26 and first curved portions 28 representing the minimum radius.

[0043] The average radius of the closed curve is about half the radius of the rotor 10; that is the distance from a central axis to the outer ends 24 of the blades 12. [0044] The blades 12 are arranged to be fixed together as described above and then mounted onto a base plate 40 as seen in Figure 7 or a base plate 50 as seen in Figure 8.

[0045] The base plate 40 is circular, having a central protruding cylinder 42. A plurality of reinforcing blades 44 extend between the central protruding cylinder 42 and an upper surface of the base plate 40. The base plate 40 has mounting points 46 spaced around its circumference, arranged to receive joins 34. The base plate 40 has connection points 48 spaced around an inner circumference of the central protruding cylinder 42.

[0046] The base plate 50 is circular, having a central axle 52. A plurality of reinforcing blades 54 extend between the central axle 52 and an upper surface of the base plate 50. The base plate 50 has mounting points 56 spaced around its circumference, arranged to receive joins 34.

[0047] In use, wind travelling towards the rotor 10 is caught by the concave outer portions 18 of the blades 12, and causes the rotor 10 to spin. The convex inner portions 20 of the blades 12 are all located within the closed curve, and thus are not presented to the wind.

[0048] Wind forces are concentrated at the joins 34, driving the rotor 10.

[0049] The closed curve acts as a monocoque structure, adding significant rigidity to the rotor 10. The connection of blades 12 at a radially spaced location from the central protruding cylinder 42 or central axle 52 dramatically reduces the applied shear forces when compared to traditional Savonius rotors.

[0050] It will be appreciated that a number of rotors 10 can be mounted along a single axis in a generally modular fashion as shown in Figures 9 to 12 to form a turbine. [0051 ] Where a base plate 40 of the first embodiment is used, a lowermost base plate 60 can be mounted beneath the rotor 10 as shown in Figures 9 and 10. In this embodiment the central protruding cylinder 42 of the lowermost base plate 60 is arranged to act as an outer rotor generator, with a stator positioned within the central protruding cylinder 42 and arranged to generate electrical power. Alternatively, the lowermost base plate 60 can be directly attached to a bespoke generator.

[0052] Where a base plate 50 of the second embodiment is used, a lowermost base plate 62 can be mounted beneath the rotor 10 as shown in Figures 11 and 12. In this embodiment the central axle 52 of the lowermost base plate 62 is arranged to act as an inner rotor generator, with a stator positioned outside the central axle 52 and arranged to generate electrical power. Alternatively, the lowermost base plate 62 can be directly attached to a bespoke generator

[0053] Modifications and variations as would be apparent to a skilled addressee are deemed to be within the scope of the present invention.