GB2477750A

GB2477750A - Combined vertical and horizontal axis wind generator

Info

Publication number: GB2477750A
Application number: GB1002277A
Authority: GB
Inventors: Roger Jeremy Baker
Original assignee: GLOBAL WIND IND Ltd
Current assignee: GLOBAL WIND IND Ltd
Priority date: 2010-02-11
Filing date: 2010-02-11
Publication date: 2011-08-17
Also published as: GB201002277D0

Abstract

A wind-driven power generator comprises a rotary structure carrying two or more drag-type wings 8 to rotate the structure about a vertical axis 2 under propulsion by the wind and carrying two or more horizontal axis wind turbines 26 for generating power as the structure rotates through the air. The asymmetric wings 8 concentrate airflow on the turbines 26 and extend horizontally in pairs with a one or more horizontal axis turbines 26 located in a gap 10 between each pair. The strut 9 supported wings may be of thin metal sheet, composites or plastics and honeycomb filled. A support frame 6 having vertical posts 34 and a main shaft supporting triangular tie bar arrangement 36 is located on only one side of the axis 2 and may be pivoted on a track 40 by vanes 42 about the axis 2 to remain always downwind of the generator.

Description

TITLE

Wind-driven power generators

DESCRIPTION

Technical Field

The invention relates to apparatus for harnessing wind power by the use of wind turbines in order to generate electricity.

Background of the invention

The demand for an increasing proportion of the world's energy to be provided from renewable sources has led to the rapid development of wind power technology.

Commonly used wind-driven power generators fall into two main types.

Horizontal axis wind turbines have been most widely employed for power generation on a large scale, suitable for supplying national electricity grids. They have a fan-type rotor that is mounted at the top of a mast for rotation about a horizontal axis. The efficiency of such turbines increases with rotor diameter so the masts are often I OOm or more tall. Because the working parts are all located high above the ground, construction and servicing of such turbines is difficult and expensive. The height of these structures makes them visually intrusive and can cause interference with television signals and aircraft radar. There is therefore a tendency towards siting them offshore, which adds further to the construction and maintenance costs. Means must be provided for turning the rotor to face the wind at all times in order to generate the maximum power but larger turbines are unable to react quickly to changes in wind direction.

Vertical axis wind turbines have blades arranged for rotation about a vertical shaft.

They have the great advantage that they can be driven by wind from any compass direction. The blades are normally thin strips that bow outwards between the top and bottom of the shaft (known as an "egg-beater" design) or that follow a helical path around the shaft. The blades have an aerofoil cross-section that generates lift as the wind blows over it, driving the rotation of the turbine. This arrangement lends itself to lightweight designs that can rotate rapidly, with the blades moving faster than the wind speed. They are thus used for power generation on a smaller, local scale, for example being mounted on the roof of a building to provide power to the occupants of that building.

There is a need for the development of further basic designs of wind turbine that can be used in situations that are not well suited to the established designs; and which can overcome some of the aforementioned disadvantages of the established designs.

Patent US 5151610 describes a wind-driven power generator in which a main rotor carries secondary rotors that are oriented to be driven by movement of the secondary rotors through the air during their circular motion about the main rotor axis. The principal example in that document is of a generator in which the main rotor is a horizontal axis turbine. A second example shows a vertical axis main rotor, in which the blades follow the "egg-beater" design and the secondary rotors are mounted on them, with radial struts for support. Those secondary rotors will be heavy and in that position will contribute a large moment of inertia to the rotating structure, which seems to be incompatible with the need for very rapid rotation in the "lift" mode of operation. The design therefore appears to be impractical so that, if it rotates at all, the power generated by the secondary rotors will not offset the reduced power generated by the main rotor.

Summary of the invention

The invention provides a wind-driven power generator comprising: a rotary structure mounted for rotation about a vertical axis; the rotary structure carrying two or more wings to r propulsion by the wind; the rotary structure further carrying two or more horizontal axis wind turbines for generating power as the structure rotates; the wings being shaped to concentrate airflow on the turbines.

G142.001.00.doc The invention maintains the principal advantage of vertical axis wind turbines, namely that it can be driven by wind from any direction. Its wings serve dual purposes, namely driving rotation of the rotary structure about its vertical axis and concentrating airflow on the turbines as that rotation carries the wings and turbines through the air. The turbines therefore experience an enhanced airspeed and/or mass flow and they generate more power for a given rate of rotation of the structure. By channelling and/or accelerating air onto the turbines, the effective amount of available wind power is increased.

The wings are preferably elongated in a substantially horizontal direction. This gives them a paddle-like configuration that is quite different from the "egg-beater" or helical designs used in conventional vertical axis generators. It relies on a "drag" mode of operation to effect rotation of the structure, rather than the "lift" mode of those earlier designs.

The wings may be arranged in pairs with a gap between each pair of wings, the horizontal axis turbines being located in such gaps. Thus the large surface area of two wings concentrates airflow onto each turbine. Each pair of wings is preferably symmetrical about the gap between them, which should ensure that the combined airflow from the two wings is aligned with the turbine, rather than from one side.

A front surface of each wing preferably has at least a majority of its surface area angled towards the gap, in order to deflect air towards the gap as the wing passes through the air. This may be achieved in an aerodynamic fashion by making the front surface convex and asymmetrical in cross-section with respect to the direction of rotation of the wing.

A rear surface of each wing is preferably concave and substantially symmetrical in cross-section with respect to the direction of rotation of the wing. This is an efficient shape for catching the wind to drive rotation of the structure.

In a further aspect of the invention, an upper part of the rotary structure is held in position by a support frame, the support frame extending to the ground on only one side of the rotary structure. The support frame can therefore be arranged such that it lies wholly on the downwind side of the rotary structure and does not disrupt the wind flowing onto the wings.

Such a support frame can be made to pivot about the axis of the rotary structure so that it can be manually or automatically placed to on the downwind side.

In this specification, the terms "vertical" and "horizontal" refer to the orientation of the power generator relative to the ground. It may be possible to operate the apparatus when tilted through a small angle from the true vertical, for example on an upslope in which the prevailing wind is not strictly horizontal.

Brief description of the drawings

Figure 1 is a vertical elevation of a power generator in accordance with the invention.

Figure 2 is a plan view of the power generator of Figure 1.

Figure 3 is a cross section through a pair of wings and a wind turbine of Figure 1.

The illustrated power generator comprises a vertical shaft 2 that is mounted for rotation about a vertical axis between a base 4 and a support frame 6. The base 4 is shown to have an arch-like structure that raises the shaft 2 off the ground but that is not essential. Instead the shaft 2 may extend down to ground level so that the weight of the structure is borne at its centre.

Extending generally horizontally from the shaft 2 are four wings 8, arranged in pairs one above the other. Each wing 8 may have one or more struts 9 along its length to stiffen it and help support its weight. A first pair of wings 8 on one side of the shaft 2 is balanced by a second pair of wings 8 on the opposite side of the shaft 2. Between each pair of wings 8 is a horizontal gap 10. Roughly speaking, each wing 8 lies in a vertical plane so that the configuration of the wings in relation to the shaft 2 is like a paddlewheel.

More precisely, each wing 8 curves out of that vertical plane in both the horizontal and vertical directions. As seen best in Figure 2, the wing 8 curves backwards along its length so, as the rotary structure turns in the direction shown by an arrow 12, the tip 16 of the wing trails the rest of the wing 8. This shape helps to catch the wind when it is behind the wing 8 and to shed the wind when it is in front of the wing 8.

The net force on two wings 8 mounted on opposite sides of the shaft 2 thus causes the shaft 2 to rotate under wind propulsion. As best seen in Figure 3, the wing 8 also curves backwards along its vertical cross section. A rear surface 18 of the wing has a io concave cross section and is generally symmetrical about the horizontal plane, which is the best shape to catch the wind when it is behind the wing 8. A front surface 20 of the wing has a convex cross section, which is the best shape to shed the wind when it is in front of the wing 8. The difference between the two surfaces thus enhances the ability of the wing 8 to rotate the shaft 2 under wind propulsion.

Unlike the rear surface 18, the front surface 20 of each individual wing is not symmetrical about the horizontal plane. The leading edge 22 of the wing is far above or below the centreline and the majority of the area of the front surface 20 is angled back from that leading edge towards the gap 10. The two wings 8 of the pair are mirror images of one another, arranged symmetrically about the gap 10. As the wings rotate about the shaft 2 and sweep through the air, the majority of the air mass that comes into contact with the front surfaces 20 of the wings is deflected by the mutually inclined surfaces 20 towards and through the gap 10, as shown by arrows 24. The symmetrical arrangement imparts no net upward or downward component to the combined airflow through the gap 10.

A wind turbine 26 is mounted in the gap 10 between each pair of wings 8. By "in the gap" it is meant that the turbine 26 lies in the airstream passing through the gap 10. It does not have to lie directly between the wings 8 and, as illustrated, is preferably mounted a short distance behind them. The turbine 26 may be supported, as shown, on a yoke 28 extending vertically between the two wings 8, or in any other suitable fashion that provides sufficient structural support while minimizing disruption to the airflow. The wind turbine 26 is oriented with its axis horizontal and generally tangential to the path swept out by the turbine 26 as it orbits the vertical shaft 2. The rotor blades 32 of the turbine 26 face towards the gap 10 and the diameter of the rotor blades 32 is comparable to the size of the gap 10. The wind turbine 26 is mounted relatively close to the tips 16 of the wings 8 but not so close that its rotor blades 32 project beyond the wing tips 16. Any suitable wind turbine 26 may be used, depending on the scale of the apparatus and the expected airspeed through the turbine 26. The number of rotor blades 32 may be varied and they may or may not rotate within a shroud.

When the wind blows from any direction, as previously described it will exert a stronger force on the rear surfaces 18 than on the front surfaces 20 of the wings 8 and there will be a net moment causing the wings 8 and the shaft 2 to rotate about the vertical axis. The broad area of the wings 8 will allow this rotation to occur even in light winds and should allow the wind to begin turning the structure even from a stationary start. The moment of inertia provided by the relatively heavy wind turbines 26 at a substantial radius from the axis is beneficial because it provides the momentum required to continue the rotation smoothly through the points in the cycle where the length of the wings 8 is parallel to the wind direction and they generate little turning force. The rotation of the vertical shaft 2 may itself be used to drive an electrical generator (not shown) in the conventional manner for vertical axis wind turbines. However, such a generator necessarily imparts a retarding force to the shaft and the power drawn should not be so high that this adversely affects the operation of the orbiting wind turbines 26.

As the structure rotates about the axis, the wind turbines 26 are carried through the air along a circular path. This movement relative to the ambient air causes an airflow through the turbines 26, which turns them and causes their inbuilt generators to generate electrical power. The current from the generators is fed by suitable conductors (not shown), via the shaft 2, to equipment that can either supply the electricity for use immediately or store its energy for use at a later time. The means for converting, supplying or storing the electrical power do not form part of the present invention and will not be described further.

The wind turbines 26 orbit the vertical axis at a roughly constant ground speed, ignoring small variations around the orbit due to differences in the turning force exerted by the wind when the wings 8 are aligned parallel or transverse to it.

However, such rotation only occurs when wind is blowing over the site so there is one half of the orbit in which the turbines 26 are moving against the wind direction and one half of the orbit in which the turbines 26 are moving with the wind direction.

Because of the "drag" design of the apparatus, it is expected that the ground speed of the turbines will be somewhat less than the current wind speed. Therefore over the small sector of the orbit (much less than half) where the movement of the turbine 26 is approximately parallel to the wind, the ambient wind is moving faster than the turbine 26 and would tend to operate the turbine in reverse. However, because the wings 8 deflect a much greater airflow through the gap 10, the localized airflow through the turbine 26 will be increased and should always remain positive. The reactive force on the air striking the front surfaces 20 of the wings increases the kinetic energy of the air mass passing through gap 10, which is available for conversion to mechanical and ultimately electrical energy by rotation of the turbine 26. Because the wind turbines 26 are paired on opposite sides of the shaft 2, when one of them is at the point in the orbit that produces the minimum amount of power, the other is at the point in the orbit that produces its maximum amount of power and the overall output of the wind-driven power generator is thereby smoothed.

In order to increase the power output of the apparatus and to provide further smoothing of it, the number of pairs of wings 8 and the number of associated wind turbines 26 need not be limited to two. Any greater number of wing pairs 8 and turbines 26 may be evenly spaced around the shaft 2, until a point is reached at which the sets of wings are too close together, whereby the airflow through one turbine 26 is adversely affected by the wake from the preceding wings 8 and turbine 26. To avoid this problem, the pairs of wings 8 could be arranged in more than one tier along an elongated shaft 2. In particular, two pairs of wings 8 carrying two turbines 26, as shown in the drawings, could be supplemented by a second, similar structure mounted above and offset through 900. The structure is likely to be simpler if each tier contains an even number of wing pairs, so that each wing 8 can be counterbalanced by a corresponding wing on the opposite side of the shaft.

More than one wind turbine 26 could be arrayed along a single gap 10. Optionally, the inner turbine(s) could be of reduced capacity to reflect the lower air speed expected from their rotation closer to the axis.

io The wings 8 are illustrated with a uniform height over the whole of their length but that is not necessarily so. In particular, the wings 8 may taper towards the shaft 2 andlor may be absent from a region adjacent to the shaft 2, except for the strut 9 or such other structural component as may be required to attach the wings 8 to the shaft 2. Similarly, the gap 10 need not be of uniform width. The wing tips 16 may be provided with fins (not illustrated) or other appendages to control the formation of vortices. More radically different designs of wing could be considered, for example with the length of the wings and the length of the gap between them aligned vertically. Instead of each pair of wings with an elongate gap between them, a single, funnel-shaped wing could channel air towards the turbine through a generally circular central aperture.

The wings 8 themselves are generally of a lightweight construction and may be formed from thin metal sheet or may be moulded from materials such as plastics or composites. They may be solid but the space between the front and rear surfaces 18,20 is preferably either hollow or filled by a lightweight material such as a honeycomb to add rigidity.

A separate aspect of the invention, which could be used with the wind-driven power generator previously described or with any vertical axis turbine, concerns the support frame 6. To prevent oscillation of the shaft 2 as it rotates under the influence of changing forces, the shaft 2 must be held in position at its top as well as at its bottom.

The support frame 6 comprises a pair of vertical posts 34, spaced at approximately 1200 apart from one another with respect to the axis and positioned at a radius from the axis greater than the length of the wings 8. The tops of the posts 34 and the top of the shaft 2 are connected to each other by a triangular arrangement of tie beams 36, which form a rigid structure that prevents the top of the shaft 2 from moving.

Because the posts 34 are all on one side of the axis -i.e. within a span of 180° relative to the axis -they can be positioned all on the downwind side of the rotary structure so that the posts maintain "clean air", i.e. they do not block or disrupt the wind before it reaches the rotary structure and adversely affect its capacity to generate power.

Additional posts or other support arrangements may be provided, while maintaining the principle that they are all located on one side of the axis.

In some sites, the prevailing wind direction may be so constant (or the wind be so weak when blowing from the opposite direction) that the posts 34 can be fixed in position on the downwind side of the generator. Alternatively, and as shown in the drawings, the support frame 6 can be made to rotate about the axis so that the posts 34 are moved to the downwind side when the wind direction changes. The base 4 of the support frame 6 has an arched form with three legs 38 at 120° angles to each other, two of which carry the posts 34. The legs 38 can slide or roll in circular tracks 40 to position the posts 34 as desired. Preferably, the positioning is done automatically when the wind direction changes. This could be achieved by providing vanes 42 on the posts 34, which use the force of the wind to move them. Alternatively, a traditional fantail system could be employed, in which the fantail is rotated by the wind when it is not aligned with the wind then and drives a system of gears to turn the support frame 6 in the appropriate direction. A further alternative would be a simple wind vane to sense the wind direction and a motor to move the frame in response to changing signals from the wind vane.

Power generation apparatus may be made to work at various scales by varying parameters such as the number, length, height and degree of curvature of the wings; the size and shape of the gap between the wings; the capacity of the orbiting horizontal-axis turbines; and the degree of power taken from the rotating vertical shaft. A typical installation might have a radius of 1 Om and a rotational period of lOs during average wind conditions. This would fill a niche between the giant, industrial, horizontal axis turbines and the small, roof-top vertical axis turbines of the prior art.

The generators could be grouped together to form a wind farm sharing electricity conversion and storage facilities. Their low height would minimize the visual impact.

Claims

CLAIMS1. A wind-driven power generator comprising: a rotary structure mounted for rotation about a vertical axis; the rotary structure carrying two or more wings to rotate the structure under propulsion by the wind; the rotary structure further carrying two or more horizontal axis wind turbines for generating power as the structure rotates; the wings being shaped to concentrate airflow on the turbines.
2. A power generator according to claim 1, wherein the wings are elongated in a substantially horizontal direction.
3. A power generator according to claim 2, wherein the wings are curved along their length so that an outer tip of the wing trails as the structure rotates.
4. A power generator according to any preceding claim, wherein the wings are arranged in pairs with a gap between each pair of wings, the horizontal axis turbines being located in such gaps.
5. A power generator according to claim 4, wherein each pair of wings is symmetrical about the gap between them.
6. A power generator according to claim 4 or claim 5, wherein a front surface of each wing has at least a majority of its surface area angled towards the gap.
7. A power generator according to claim 6, wherein the front surface is convex and asymmetrical in cross-section with respect to the direction of rotation of the wing.
8. A power generator according to any preceding claim, wherein each wing has a concave rear surface, which is substantially symmetrical in cross-section with respect to the direction of rotation of the wing.

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9. A power generator according to any preceding claim, wherein an upper part of the rotary structure is held in position by a support frame, the support frame extending to the ground on only one side of the rotary structure.
10. A power generator according to claim 9, wherein the support frame can be pivoted about the axis of the rotary structure to remain on the downwind side of the structure.
11. A power generator according to claim 10, wherein the support frame carries vanes that cause it to pivot automatically to the downwind side of the structure.
12. A power generator according to any of claims 9 to 11, wherein the support frame comprises two posts spaced at approximately 1200 apart with respect to the vertical axis.
13. A power generator substantially as described herein with reference to the drawings.