GB2489325A

GB2489325A - Vertical axis wind turbine with curved blades

Info

Publication number: GB2489325A
Application number: GB1205063.9A
Authority: GB
Inventors: John Timothy James Marshall
Original assignee: Individual
Current assignee: Individual
Priority date: 2011-03-22
Filing date: 2012-03-22
Publication date: 2012-09-26
Also published as: WO2012127239A2; WO2012127239A3; GB201104746D0; GB201205063D0

Abstract

A wind turbine blade comprising a curved frame supporting a tensioned membrane. Also claimed, is a vertical axis wind turbine comprising a mast and a rotor, wherein the rotor comprises a central hub and multiple arms 7 radiating from the central hub with a blade attached to each arm. Each blade comprises a curved frame supporting a tensioned membrane 8, wherein the outer ends of adjacent arms or adjacent blades are linked by stays and/or struts. Preferably each arm is attached to the frame of the blade on two opposite sides and the frame comprises arced ribs 10. There may be a vertical drive shaft coupled to a generator or pump at or near ground level and the mast may comprises a joint which allows the mast to be rotated between an erected position and a lowered position. A method of constructing a blade and erecting a mast are also claimed.

Description

Wind turbine This invention relates to a blade for a wind turbine and to a wind turbine comprising the blade. The invention is particularly suitable for vertical axis wind turbines.

A wind turbine conventionally has a plurality of blades which are caused to rotate by the wind. The blades may be distributed around either a horizontal or vertical axis.

Horizontal axis wind turbines have the disadvantage that they must be pointed into the wind. They also typically have most or all or their machinery (e.g. the electrical generator) on top of a tower or column. The resulting weight, coupled with the need for horizontal rotation of the rotor in response to changes in the wind direction, generally leads to substantial cost and complexity.

A first aspect of the present invention provides a blade for a wind turbine comprising a frame supporting a tensioned fabric membrane.

The blade of the present invention is both light and low cost.

The use of a fabric membrane has the additional benefit of noise reduction.

The frame may comprise a curved frame. The curved frame may have an arcuate cross section. In one embodiment, the blade has a longitudinal axis and a uniform cross section along the longitudinal axis.

The curved frame may comprise three parallel elongate members, defining the sides and apex of the curved frame. The two outer elongate members may be in a first plane and the central elongate member may be in a second plane spaced from the first plane.

The curved frame may comprise two or more arcuate ribs. Ribs may be attached between elongate members at each end and at one or more positions between the two ends.

The membrane may be a fabric membrane and may comprise either a woven or non woven fabric, for example polyester, polypropylene, glass fibre or polyethylene. The fabric membrane may comprise a smooth coating, such as a water repellent coating, for example PTF'E or PVC. Such a coating extends the life of the fabric and reduces wind drag.

The frame may comprise a strong material and may be metallic, for example galvanized steel. Other suitable materials include aluminium and carbon fibre. Suitable materials are preferably strong, light weight and resistant to deterioration due to weathering.

The light weight structure allows large blades to be used. The blade may be between im and 12m long. In one embodiment, the blades are between 3m and 6m long.

A second aspect of the invention provides a wind turbine comprising a mast and a rotor, wherein the rotor comprises a plurality of blades according to the invention.

The present invention has most of the mechanical components and the transmission unit located towards the base where they can be readily accessed for inspection and maintenance, while the supporting mast or structure and the rotor mechanism are relatively simple and light. Consequently the invention achieves a significant reduction in the cost, time and equipment required for installation and ongoing maintenance.

The rotor may comprise a central hub and a plurality of arms radiating from the central hub and wherein each blade is attached to an arm. Each arm may be attached to the frame of the blade on two opposite sides. This ensures a strong connection between the blade and the arm. The outer ends of adjacent arms or blades may be linked by stays and/or struts to enhance the rigidity of the rotor. The stays may be pre-tensioned, for example, pre-tensioned steel cables running between their outer ends. A strut may, for example, be a wooden or metal bar. Other structurai arrangements or frames and the like may also be used to link adjacent arms 7. The blades may be regularly spaced around the hub.

The turbine may comprise a vertical drive shaft coupled to the rotor and to a generator or pump at ground level.

In one embodiment, the mast or a mount for the mast comprises a joint which allows the mast to be rotated between an erected position (with the mast vertical) and a lowered position (with the mast horizontal or near horizontal) . In its lowered position, the rotor is easily accessible for maintenance. The wind turbine may comprise one or more base plates, wherein the mast and base plate have a hinged connection. The base plate may further comprise anchors (for example stakes) for fixing to the ground.

The mast may bifurcate towards its lower end.

The hub and parts of the coupling assembly beneath the drive shaft may be constructed from salvaged commercial vehicle rear axle components. The wind turbine thus not only produces energy from a sustainable source but can be manufactured using recycled components.

The wind turbine may further comprise stays to support the mast in its erected position. The stays may be secured into the ground by ground anchors. This method of supporting the mast enables the wind turbine to be easily moved to different positions, making it particularly suitable for short term installation. In addition, the stays can also be used to erect the mast. The wind turbine is thus easily relocatable due to its ease of installation and removal.

Alternatively, the wind turbine may comprise a clamping device suitable for securing the mast to a building. In this case, the clamping device will replace some or all of the stays and ground anchors. As before, a joint allows ease of access to the rotor and upper end of the mast.

The wind turbine may comprise a generator or pump which is releasably mountable at or near the base. The generator or pump may be skid mounted.

The primary uses of the invention are likely to include small-scale installations for electricity generation, water pumping and irrigation. Turbines may be located on open ground or secured to the corner or side of a building.

The large surface area of the blades makes this design particularly effective in areas with lighter winds.

A third aspect of the present invention provides a method of constructing a blade for a wind turbine comprising the steps of: forming a frame to define the shape of the blade; stretching a fabric membrane over the frame, so that the fabric membrane is tensioned; and securing the tensioned fabric membrane to the frame.

A fourth aspect of the present invention provides a method of erecting a wind turbine comprising a mast and rotor wherein the mast or a mount for the mast comprises a joint, the method comprising the steps of: attaching two or more stays to the mast and securing these stays to the ground; using another stay to pull the mast into a vertical position about the joint; and securing the remaining stay or stays to the ground.

The method optionally includes the step of locking the joint.

Preferred features of the second, third and fourth aspects of the invention may be as described above in connection with the first aspect.

Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of the words, for example "comprising" and "comprises", mean "including but not limited to", and do not exclude other moieties, additives, components, integers or steps.

Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Other features of the present invention will become apparent from the following example. Generally speaking the invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims and drawings) . Thus features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith.

Moreover unless stated otherwise, any feature disclosed herein may be replaced by an alternative feature serving the same or a similar purpose.

The present invention will now be described by way of example only and with reference to the accompanying illustrative drawings.

Figure 1 shows a side view of the wind turbine without the stays; Figure 2 shows the blade detail; Figure 3 shows a plan view of the rotor blades; and Figure 4 shows the mast, rotor and stays.

In the embodiment shown in Figures 1 and 4, the wind turbine is sited on open ground and the mast is supported by stays 12 which are connected to ground anchors (not shown) . The mast 1 is hinged at the base and the stays can be used with a gin pole to raise and lower the mast for installation and maintenance.

Figure 1 shows a base plate 5 which could be made from steel and staked to the ground. It incorporates vertical brackets through which one or more pins pass, creating a hinge.

A metal mast 1 is secured to the base plate 5 by the hinge pins (not shown), and is held in a vertical position by stays 12, passing from the upper parts of the mast 1 to ground anchors (not shown) some distance out from the base plate 5. Running beside the mast 1 is a vertical drive shaft 2 which turns a generator or pump 4.

To improve access to the vertical drive shaft 2, the lower section of the mast 1 may bifurcate and the generator 4 may be skid mounted. For a bifurcated mast two base plates may be provided, with the generator skid mounted in between.

The generator (or pump) may be skid mounted to the base or alternatively near the base.

On top of the mast 1 is a rotor 3 which is turned by the wind, causing the drive shaft 2 to rotate.

The turbine is raised or lowered by connecting one of the stays 12 to a winch or tractor and using other stays 12 to restrict movement.

Figure 2 shows the frame 8 of each blade, which consists of a pair of tubes 9, several arcuate ribs 10 and a spreader 11. One tube 9 is attached at its mid point to the end of the arm 7 at 90°. The other tube 9 is attached at its mid point to the arm 7, also at 90°, at a position towards (but not at) the other end of the arm 7.

Arcuate ribs 10 link the tubes 9 at various positions above and below the arm 7.

A fabric cover is stretched very tightly over the frame 8.

Tension eliminates any flapping movement, similar to a drum skin.

Suitable materials for this cover may include PVC coated polyester and other outdoor fabrics used for temporary structures, road transport and marine applications.

A spreader 11 connects the top and bottom ribs 10 to prevent them bending inwards. The spreader 11 may also include a unifying feature, similar in function to a zip, allowing the cover to be made in two pieces.

Figure 3 shows a plan view of the rotor 3, configured for clockwise rotation. A mirror image would enable it to rotate counter-clockwise. The hub 6 has two or more equally spaced sockets which are horizontal or near-horizontal when the turbine is erected. Arms 7 slide into these sockets and are secured, with nuts and bolts for example. The arms 7 could attach to these sockets in different ways if preferred. The arms 7 are rigid once assembled and should not pivot, twist or flex. Stays or struts 13 may be used to link adjacent arms 7 -for example, the stays may be tensioned steel cables running between their outer ends.

A strut may, for example, be a wooden or metal bar. Other structural frames and the like may also be used to link adjacent arms 7.

At the other end of the arms 7 are blade assemblies 8 which are curved about a vertical or near-vertical axis. The number of blades 8 can vary -six are shown in this illustration. The blade assemblies 8 once assembled are rigid and should not pivot, twist or flex. The whole structure comprising the hub 6, arms 7 and blades 8, once assembled, is rigid and should not pivot, twist or flex.

Figure 4 shows the mast 1 and rotor 3 supported by four stays 12.

More may be used if required.

In an alternative embodiment of the blade, the ends of the blade are capped to prevent wind spillage. The ends may be filled with fabric (e.g. the same fabric as used in the blade) Alternatively, the frame may include closed ends.

Claims

Claims 1. A vertical axis wind turbine comprising a mast and a rotor, wherein the rotor comprises a central hub and a plurality of arms radiating from the central hub and wherein a blade is attached to each arm, wherein each blade comprises a curved frame supporting a tensioned membrane and wherein the outer ends of adjacent arms or adjacent blades are linked by stays and/or struts.
2. A wind turbine according to claim 1 wherein each arm is attached to the frame of the blade on two opposite sides.
3. A wind turbine according to claim 1 or 2, wherein the stays are pre-tensioned.
4. A wind turbine according to any one of claims 1 to 3, wherein the blades are regularly spaced around the hub.
5. A wind turbine according to any one of claims 1 to 4, further comprising a vertical drive shaft coupled to a generator or pump at or near ground level.
6. A wind turbine according to any one of claims 1 to 5, wherein the mast or a mount for the mast comprises a joint which allows the mast to be rotated between an erected position and a lowered position.
7. A wind turbine according to any one of claims 1 to 6 further comprising one or more base plates, wherein the mast and base plate have a hinged connection.
8. A wind turbine according to claim 7 wherein the base plate further comprises anchors for fixing to the ground.
9. A wind turbine according to any one of claims 1 to 8 wherein the mast bifurcates towards its lower end.
10. A wind turbine according to any one of claims 1 to 9 further comprising stays to support the mast in its erected position.
11. A wind turbine according to any one of claims 1 to 10 further comprising a generator or pump which is releasably mountable at or near the base.
12. A wind turbine according to claim 11 wherein the generator or pump is skid, wheel or roller mounted at or near the base.
13. A wind turbine according to any one of the preceding claims wherein the curved frame of the blade has an arcuate cross section.
14. A wind turbine according to any one of the preceding claims, wherein the blade has a longitudinal axis and a substantially uniform cross section along the longitudinal axis.
15. A wind turbine according to any one of the preceding claims wherein the curved frame comprises three parallel elongate members, defining the sides and apex of the curved frame.
16. A wind turbine according to claim 15, wherein the two outer elongate members are in a first plane and the central elongate member is in a second plane spaced from the first plane.
17. A wind turbine according to any one of the preceding claims wherein the curved frame comprises two or more arcuate ribs.
18. A wind turbine according to any one of claims 15 or 16 and claim 17, wherein each rib is attached to an elongate member at each end at a position between the two ends.
19. A wind turbine according to any one of the claims 1 to 18, wherein the outer ends of the blade are capped.
20. A wind turbine according to any one of the preceding claims, wherein the membrane comprises a woven fabric.
21. A wind turbine according to claim 20 wherein the fabric comprises polyester.
22. A wind turbine according to any one of claims 1 to 18, wherein the fabric comprises a non woven fabric.
23. A wind turbine according to any one of the preceding claims, wherein the membrane comprises a smooth coating.
24. A wind turbine according to any one of the preceding claims wherein the frame comprises a metallic material.
25. A wind turbine according to any one of the preceding claims wherein the blade is between lm and 12m long.
26. A method of constructing a blade for a wind turbine comprising the steps of: (i) forming a frame to define the shape of the blade; (ii) stretching a membrane over the frame, so that the membrane is tensioned; and (iii) securing the tensioned membrane to the frame.
27. A method of erecting a wind turbine comprising a mast and rotor wherein the mast or a mount for the mast comprises a joint, the method comprising the steps of: (i) attaching two or more stays to the mast and securing the two or more stays to the ground; (ii) using a further stay or stays to pull the mast into a vertical position about the joint; and (iii) securing the further stay or stays to the ground.
28. A method according to claim 27 further comprising the step of locking the joint.
29. A blade for a wind turbine comprising a curved frame supporting a tensioned membrane.
30. A blade according to claim 29 wherein the curved frame has an arcuate cross section.
31. A blade according to claim 29 or 30, wherein the blade has a longitudinal axis and a substantially uniform cross section along the longitudinal axis.
32. A blade according to any one of claims 29 to 31 wherein the curved frame comprises three parallel elongate members, defining the sides and apex of the curved frame.
33. A blade according to claim 32, wherein the two outer elongate members are in a first plane and the central elongate member is in a second plane spaced from the first plane.
34. A blade according to any one of claims 29 to 33 wherein the curved frame comprises two or more arcuate ribs.
35. A blade according to any one of claims 32 or 33 and claim 34, wherein each rib is attached to an elongate member at each end at a position between the two ends.
36. A blade according to any one of claims 29 to 35, wherein the outer ends of the blade are capped.
37. A blade according to any one of claims 29 to 36, wherein the membrane comprises a woven fabric.
38. A blade according to claim 37 wherein the fabric comprises polyester.
39. A blade according to any one of claims 29 to 36, wherein the fabric comprises a non woven fabric.
40. A blade according to any one of claims 29 to 39, wherein the membrane comprises a smooth coating.
41. A blade according to any one of claims 29 to 40 wherein the frame comprises a metallic material.
42. A blade according to any one of claims 29 to 41 wherein the blade is between lm and 12m long.
43. A blade for a wind turbine substantially as herein described with reference to the accompanying illustrative drawings.
44. A wind turbine substantially as herein described with reference to the accompanying illustrative drawings.