EFFICIENT WIND ENERGY CONVERTOR WITHOUT GEARBOX OR MULTI-POLE GENERATOR

Abstract

A vertical axis turbine having a first rotor and at least one second rotor, the first rotor being configured to rotate around a first rotation axis that is vertical or more vertical than horizontal, in use. The first rotor may be configured to be driven and/or rotated by fluid motion, e.g. by wind or water flow. The at least one second rotor is provided on or coupled to the first rotor such that the first rotor is operable to move the second rotor through the fluid and thereby drive the second rotor upon rotation of the first rotor. The second rotor is operable to drive a power take off system. Optionally, rotation of the first rotor around the first rotation axis moves the second rotor around the first rotation axis. Each second rotor rotates around a respective second rotation axis that may be angled or perpendicular to the first rotation axis of the first rotor and is optionally a horizontal axis or at least an axis that is more horizontal than vertical, in use. The first and second rotors are configured so that the power take-off is by direct drive without the need for a gearbox or multi-pole generator. The first and second rotors are configured so that the power conversion of mechanical power at the first rotor is converted to mechanical power at the second rotors has high efficiency.

Claims

1. A vertical axis turbine comprising a first rotor and at least one second rotor; the first rotor being configured to rotate around a first rotation axis, wherein the first rotation axis is vertical or more vertical than horizontal in use; the at least one second rotor being provided on, comprised in or coupled to the first rotor such that the first rotor is operable to move the second rotor upon rotation of the first rotor; and the second rotor is operable to drive a power take off system.

2. The vertical axis turbine according to claim 1, wherein: the at least one second rotor in below rated wind speed has aerodynamic thrust coefficient (C.sub.T) to aerodynamic power coefficient (C.sub.P) ratio of more than 0.75 in use; and/or one or more or each of: the first rotor in below rated wind speed has a tip speed ratio in the range 4 to 5 in use; and/or the tip speed ratio in use at rated wind speed of the at least one or each second rotor is in the range 3 to 4; and/or the first and second rotor in below rated wind speed have a combined tip speed ratio) in a range from 14 to 16, such as 15; and/or the first rotor in below rated wind speed has an aerodynamic power coefficient (C.sub.pmax) within 5% of its maximum in use; and/or the maximum tip speed of blades of the at least one second rotor in use at its rated wind speed is in the range from 0.4 to 0.6 times the speed of sound; and/or the rated wind speed is in the range 11 m/s to 13.5 m/s in use

3. The vertical axis turbine of claim 1, wherein the power take-off system comprises an electricity generator.

4. The vertical axis turbine of claim 1, wherein the at least one second rotor comprises at least one second blade, and the rotation of the at least one second blade in use directly drives the power take-off system.

5. The vertical axis turbine of claim 1, wherein the first rotor comprises at least one upper blade and at least one lower blade.

6. The vertical axis turbine of claim 5, wherein the at least one second rotor is provided on or comprised in the lower blade or blades.

7. The vertical axis turbine of claim 5, wherein: the vertical axis turbine comprises a tower which supports the first rotor; the at least one upper blade projects generally upwards and away from the tower; and the at least one lower blade projects generally downwards and away from the tower.

8. The vertical axis turbine of claim 5, comprising two or more upper blades and two or more lower blades, wherein the upper blades and/or lower blades are rotationally symmetric around the rotation axis of the first rotor.

9. The vertical axis turbine of claim 5, wherein the overturning moment of the at least one upper blade acting on the first rotor in use acts in the opposite direction to the overturning moment of the at least one lower blade acting on the first rotor in use.

10. The vertical axis turbine of claim 5, wherein at least some of the at least one upper blade and/or the at least one lower blade are pitchable.

11. The vertical axis turbine of claim 5, wherein the upper and/or lower blades are free or unconnected at distal ends or tips thereof.

12. The vertical axis turbine of claim 1, wherein the one or more power take off systems are directly driven by the associated second rotor without being driven via a gearbox and/or first rotor rotates on a first bearing, and the first bearing does not comprise a drive-train.

13. The vertical axis turbine of claim 1 configured such that the second rotors are 25 m or less above the ground or sea level, in use, during the entire operation of the turbine.

14. The vertical axis turbine of claim 1, wherein turbine comprises a variable frequency transformer or electrical connection and the second rotor and/or the power take off are controllable by suitably controlling the variable frequency transformer or electrical connection.

15. The vertical axis turbine of claim 1, wherein the turbine is operable to analyse the variation of power generated by the at least one second rotor and associated power take off system in order to determine the direction of the prevailing wind.

16. A method of generating power using the vertical axis turbine of claim 1, comprising: providing the turbine such that fluid acts against the upper blades and/or lower blades to drive the first rotor such that: rotation of the first rotor drives the at least one second rotor though the fluid; and fluid acts against the at least one second rotor to drive the at least one second rotor.

17. The method of claim 16, wherein the fluid is air and/or water.

18. The method of claim 16, wherein the power generated is generated by and/or extracted from the rotation of the at least one second rotor.

19. The method of claim 16, wherein the power generated is electricity.

20. A method of controlling the rotation of the first rotor of the vertical axis turbine of claim 1 in use, comprising: pitching at least some of the blades; and/or varying a frequency of an electrical connection or variable frequency transformer coupled to the power take off system.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0115] At least one embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0116] FIG. 1 shows a perspective view of a vertical axis turbine;

[0117] FIG. 2 shows a plane view of a vertical axis turbine;

[0118] FIG. 3 shows a wind farm of the vertical axis turbines; and

[0119] FIG. 4 shows planforms of upper, lower and second blades.

DETAILED DESCRIPTION OF THE DRAWINGS

[0120] Throughout the following description, identical reference numerals will be used to identify identical parts.

[0121] FIG. 1 shows a vertical axis turbine 5 with a tower 10 and a first rotor 12. The first rotor 12 is attached to the tower 10 at a first bearing 13. The first rotor 12 rotates on the first bearing 13. The first bearing 13 is at the top of the tower 10. The first rotor 12 has a support member 15. The first rotor 12 is attached to the first bearing 13 in the centre of the support member 15.

[0122] Two upper blades 20 are attached to the support member 15, and the upper blades 20 project obliquely upwards and away from the tower 10. Two lower blades 25 are attached to the support member 15, and the lower blades project obliquely down and away from the tower 10. The upper blades 20 and the lower blades 25 are attached to the support member 15 by attachment points 30. The attachment points 30 for the upper blades 20 include actuators which can pitch the upper blades 20. As the first rotor 12 rotates relatively slowly in use, the pitching of the upper blades 20 is also relatively slow, and so the duty cycle of the actuators is low. The actuators therefore have low maintenance costs.

[0123] The lower blades 25 include respective second rotors 35 and associated electricity generators 37 at the ends of the lower blades 25. The second rotors 35 include second blades 40. The second rotors 35 are each configured to drive the associated electricity generator 37. The second rotors 35 face in opposing directions, so that rotation of the first rotor 12 results in both second rotors 35 being driven along the same path in the same orientation in use.

[0124] The upper blades 20, lower blades 25 and support member 15 are configured such that when wind blows against the vertical axis turbine 5, the first rotor 12 rotates clockwise around the first bearing 13 (although it will be appreciated that a configuration in which the rotation direction is reversed could be provided). This rotation drives the second rotors 35 through the air. The air acts against the second blades 40 of the second rotors 35, which causes the second rotors 35 to rotate. This in turn powers the electricity generators 37 driven by the second rotors 35. Thus, the first rotor 12 acts to rotate the second rotors 35, and the rotation of the second rotors 35 drives the generators 37. As such it is the rotation of the second rotors 35 rather than the first rotor 12 that primarily drives the generators 37.

[0125] The horizontal axis second rotors 35 are unusually designed to operate with a low value of C.sub.P and high C.sub.P to C.sub.T ratio and a low blade tip speed ratio, in contrast to conventional horizontal axis wind turbines. The second rotors 35 are also designed to operate with a high blade tip speed, of the order of 160 m/s. If the blade tip speed of the second rotor 25 were much higher, the second rotor 35 would become incompatible with the required high-lift and low-drag aerodynamic characteristics.

[0126] As the second rotors operate at relatively high blade tip speed with relatively short second blade 40, the second rotors 35 rotate at high speed, e.g. up to 50 rad/s. This results in each of the second rotors 35 being able to directly drive the respective associated electricity generator 37 without the need for a gearbox or multi-pole generator. This simplifies the second rotor 35 and therefore reduces the cost of the second rotor 35.

[0127] As there is no power take-off system at the first bearing 13, there is no need for a large, heavy and expensive drive-train at the first bearing 13. This greatly simplifies the vertical axis turbine 5 and greatly reduces its cost.

[0128] Power electronics 41 are included at the base of the tower 10 and are easily accessible. As the power electronics 41 are easily accessible, maintenance costs are relatively low. The power electronics 41 are used to monitor and control the vertical axis turbine 5 and the power the vertical axis turbine 5 generates.

[0129] The power electronics 41 are connected to a power connector 42. The power connector 42 connects the vertical axis turbine 5 to a power system 43, such as a national power grid.

[0130] As the power electronics 41 are located at a low height, they can easily be accessed from the level of the base of the tower 10. This provides for easy and low cost maintenance.

[0131] FIG. 2 shows the planar view of the vertical axis turbine 5 of FIG. 1. The rotation axis of the first rotor 45 is shown by the dashed line.

[0132] The tips of the upper blades 20 and the lower blades 25 are the same distance from the rotation axis of the first rotor 45 and rotate at the same radius from the rotation axis of the first rotor 45. The second rotors 35 are at the tips of the lower blades 25.

[0133] The second rotors 35 are the same height from base of the tower 10. The second rotors 25 are the same distance from the rotation axis of the first rotor 45 and rotate at the same radius from the rotation axis of the first rotor 45.

[0134] As the second rotors 35 are located at a low height (e.g. 25 m or 20 m or less from the ground or sea level), they can easily be accessed from the level of the base of the tower 10. As the second rotors 35 are also lightweight and replaceable, the second rotors 35 can easily be replaced. This provides for easy and low cost maintenance.

[0135] The upper blades 20 make a smaller acute angle to the vertical than the lower blades 25. The upper blades 20, the lower blades 25 and the support member 15 lie in a plane.

[0136] FIG. 3 shows an off-shore wind farm 105 of the vertical axis turbines 5. The tower 10 supports the first rotor 12 above the sea 110. The tower 10 may be supported by a floating platform or secured to the sea bed.

[0137] The lower blades 25 project downwards towards the sea 110, and the second rotors 35 are at the tips of the lower blades 25. The second rotors 35 are therefore at relatively low height and relatively close to the surface of the sea 110. Maintenance and/or replacement of the second rotors 35 is therefore relatively straightforward from a boat, as the second rotors 35 are not at a significant height.

[0138] FIG. 4a shows planforms of an upper blade 20 and a lower blade 25. Both the upper blade 20 and the lower blade 25 are thicker at the base than at the tip. The base of the lower blade 25 is thicker than the base of the upper blade 20. The upper blade 20 is longer than the lower blade 25.

[0139] FIG. 4b shows a planform of a second blade 40. The second blade 40 has a similar planform to the lower blade 25, but the second blade 40 is much smaller than the lower blade 25.

[0140] In examples described above, the first and second rotors are configured so that the power take-off is by direct drive without the need for a gearbox or multi-pole generator. The first and second rotors are configured so that the power conversion of mechanical power at the first rotor is converted to mechanical power at the second rotors has high efficiency.

[0141] Although various examples have been provided above, it will be appreciated that the present invention is not limited to these specific examples but is instead defined by the claims. For example, it will be appreciated by one skilled in the art that the turbine may be scaled up or down to different sizes, and the sizes given here are exemplary only. Similarly, it will be appreciated that geometric terms are to be construed purposively. For example, the blades are 3-dimensional objections, and that they may be linear and/or straight does not prohibit, for example, tapering along the blade length. Upper and lower blade pairs may be planar, but it will be understood that the upper and lower blade pair will not exist solely in a 2-dimensional plane, but may nevertheless be planar as real 3-dimensional objects. The rotational axis of the first rotor is described as substantially vertical in use, and it will be understood that this relates to a rotational axis in use which may deviate from being completely vertical in use, for example makes an angle to the vertical of less than 15°.

[0142] It will be appreciated by one skilled in the art that the turbines disclosed above are equally applicable as on-shore and off-shore wind turbines, and that the turbine described may be used elsewhere, for example as a tidal stream turbine. Furthermore, if the turbine disclosed above were to be used as a wave turbine, it will be appreciated that minor modifications of the embodiments shown in the Figures may be necessary, such modifications falling within the scope of the disclosure. For example, the first rotor of FIG. 1 may have to be inversed horizontally, such that the second rotors are on the upper blades and not the lower blades. This would advantageously bring the second rotors closer to the surface of the water, which would provide the benefit of easier access and lower maintenance costs.