NL2008228C2

NL2008228C2 - Wind turbine having counter rotating blades.

Info

Publication number: NL2008228C2
Application number: NL2008228A
Authority: NL
Inventors: Dick Roest
Original assignee: Groundtracer B V
Priority date: 2012-02-03
Filing date: 2012-02-03
Publication date: 2014-06-24
Also published as: NL2008228A

Description

No. NLP190580A

Wind turbine having counter rotating blades BACKGROUND

The invention relates to a wind turbine comprising a rotor having a set of arms provided with foldable wind 5 engagement surfaces such as sails. Due to a growing demand for energy worldwide, interest in sustainable energy sources such as wind energy has peaked. In particular energy service company Alliander B.V. has invested in research in wind turbines for converting wind energy into rotational energy, 10 and is supporting this invention.

Wind turbines, or wind mills, having foldable wind engagement surfaces are known in the art, for instance from British patent no. 4085 which describes a windmill comprising four collapsible sails adapted for revolving 15 around a vertical axis of rotation. Each of the four sails opens out and collapses alternatively in their rotation as the force of the wind falls on the front or back of the sail. A drawback of the known windmill is that useful energy is lost during conversion of wind energy to rotational 20 energy. It is an object of the present invention to provide a wind turbine with foldable wind engagement surfaces, which more efficiently converts wind energy into rotational energy.

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SUMMARY OF THE INVENTION

According to a first aspect, the present invention 5 provides a wind turbine for converting a stream of wind blowing in a first direction into rotational energy, said wind turbine comprising a first rotor rotatable in a first direction of rotation around a first axis of rotation; a second rotor rotatable in a second direction of rotation 10 around a second axis of rotation substantially parallel to said first axis of rotation; wherein said first rotor and said second rotor are each provided with a set of arms extending substantially radially relative to its respective axis of rotation, each arm comprising a foldable wind 15 engagement surface having a folding line substantially in a plane normal to said axis of rotation; wherein said first direction of rotation is opposite to said second direction of rotation; and wherein said sets of arms of said first and second rotors are arranged for rotating in a substantially 2 0 common plane of rotation. Wind blowing between the axes of rotation thus engages wind engagement surfaces of both the first rotor and of the second rotor and is guided over said wind engagement surfaces substantially along the respective folding lines towards edges of the wind engagement surfaces 25 at the respective outer ends of the arms. Wind escaping over said edges of a wind engaging surface of the first rotor is thus directed towards its corresponding wind engagement surface of the second rotor, and vice versa. This increases the pressure of the stream of wind the first direction 30 incident on said wind engagement surfaces, which provides additional force for rotating the first and second rotors. Preferably, the rotors are arranged to rotate in phase, such that a first arm of said first rotor and a second arm of said second rotor are at a minimum distance to each other 35 when substantially coinciding with or intersecting a line between the first and second axis of rotation. The minimum distance is preferably substantially less than the length of 3 an arm of said first or second rotor, preferably less than one eighth thereof.

In an embodiment the first and second axes of rotation are arranged in a common substantially vertical 5 plane perpendicular to said common plane of rotation. The first axis of rotation and said second axis of rotation are thus both oriented either substantially horizontally, or are both oriented substantially vertically.

In an embodiment each of said engagement surfaces 10 is adapted for folding about its folding line between an unfolded position when said wind engagement surface is located substantially upstream from its arm and a folded position when said wind engagement surface is located substantially downstream from its arm. Preferably, the wind 15 engagement surfaces of first and second rotors substantially trail behind their associated arms along the respective direction of rotation of said rotor.

In an embodiment said first rotor and/or said second rotor comprises one or more additional sets of arms 20 spaced apart from said set of arms along its respective axis of rotation and extending substantially radially relative to said axis of rotation, each of said arms of said additional sets of arms comprising a foldable wind engagement surface having a folding line substantially in a plane normal to 25 said axis of rotation. By providing the rotors with additional sets of arms which are rotatable around the first and/or second axis of rotation, the total wind engagement surface is increased.

In an embodiment each of said foldable wind 30 engagement surfaces is arranged for folding about its folding line to an unfolded position due to said stream of wind when said wind engagement surface is located between said first and second axis of rotation, and preferably for folding about its folding line to an unfolded position 35 otherwise. The engagement surface presented to the wind stream by a wind engagement surface is thus substantially smaller when the wind engagement surface is in the folded 4 position than when it is in the unfolded position. Thus, when a first wind engagement surface of the first rotor and a second wind engagement surface of the second rotor are at a minimum distance from each other, the wind stream incident 5 on the first wind engagement surface is at least partially guided towards the second wind engagement surface and vice versa. As a result additional air pressure is exerted on said wind engagement surfaces which is at least partially converted into rotational energy.

10 In an embodiment the wind turbine further comprises a support for supporting said first and second rotors, wherein said rotors are rotatable relative to said support around their respective axes of rotation and wherein said support is rotatable around a vertical axis. By 15 rotating the support around the vertical axis the wind turbine may be optimally aligned with the wind stream, i.e. such that the first and second axes of rotation are substantially perpendicular to the first direction of the wind stream.

2 0 In an embodiment the wind turbine further comprises a wind alignment member adapted for aligning the first axis of rotation and said second axis of rotation in a direction substantially perpendicular to said first direction. A suitable wind alignment member comprises a 25 substantially rigid surface, such as a wind vane, connected to the rotatable support. Another suitable alignment member comprises a motor for driving rotation of the support around its vertical axis based on the first direction.

In an embodiment said first rotor and said second 30 rotor are mirror symmetrical with respect to a plane parallel and equidistant to said first and second axes of rotation of said rotors. As the first and second rotors thus have substantially equal dimensions and mass the stability of the wind turbine, at least along the common plane of 35 rotation, is improved.

In an embodiment each of said wind engagement surfaces is adapted to form a substantially concave surface 5 facing said first direction of the wind stream with its concave side, at least when unfolded. A wind stream incident on the concave side of the wind engagement surface will provide a force on said wind engagement surface to fold to 5 the unfolded position. Preferably, when a wind stream is incident on a side of the wind engagement surface facing away from the wind stream, e.g. when the wind engagement surface is moving against the wind stream, the wind stream will cause the wind engagement surface to fold to the folded 10 position.

In an embodiment said wind engagement surfaces of said arms comprise a flexible material, preferably a flexible sheet. Such sheets provide cost effective wind engagement surfaces, similar to a sail.

15 In an embodiment said wind engagement surfaces of said arms comprise a resilient material. Preferably, when no force is exerted on the wind engagement surfaces the resiliency of the material causes the wind engagement surface to at least substantially fold. In particular when a 2 0 wind engagement surface is arranged downstream of its arm, the surface area of the wind engagement surface on which the wind stream is incident is substantially less than when the wind engagement surface is in the unfolded position.

In an embodiment said wind engagement surfaces of 25 said arms further comprise one or more reinforcement elements .

In an embodiment one or more of said wind engagement surfaces of an arm of said first and/or second rotor comprises a first portion adapted for engaging said 30 wind stream, said first portion foldably connected along a first edge to said arm; a second portion adapted for engaging said wind stream, said second portion foldably connected along a second edge to said arm.

In an embodiment said first and second portions 35 are hingeably connected to said arm. Preferably, the first and second portion are substantially rigid, at least to the extend that the material of the first and second portion is 6 not sufficiently flexible to allow folding in that material between a substantially unfolded and folded position.

In an embodiment said first rotor and/or said second rotor further comprises limiting structures for 5 limiting the opening angle of its wind engagement surfaces. The opening angle of the wind engagement surfaces in the unfolded position is thus limited, preferably to 180 degrees or less, such that the wind engagement surfaces maintain a greater surface are for engaging the wind when unfolded than 10 when folded.

In an embodiment said limiting structures comprise a link connecting sections of a wind engagement surface of an arm of said wind turbine on opposite sides of said arm to each other. The link, for instance a flexible link such as a 15 wire, preferably connects corner sections of said wind engagement surface to each other.

In an embodiment said limiting structures comprise a first link, connected to a first section of a wind engagement surface of an arm of said first rotor or said 20 second rotor, and a second link, connected to a second section of said wind engagement surface, wherein said first and second sections are arranged on opposite sides of said arm, and wherein said first and second links are connected to an arm neighboring said arm on said rotor in a direction 25 counter to the direction of rotation of said rotor. The limiting structures thus help in forming a wind scoop when the wind engagement surface is in the unfolded position.

In an embodiment said wind engagement surfaces of said arms are substantially symmetrical along their 30 respective arms. The force exerted by the wind engagement surfaces will thus typically be symmetrically distributed along the arm.

In an embodiment said arms each comprise a distal end at a far end from its axis of rotation, said wind 35 turbine further comprising one or more connecting elements connecting said distal ends of neighboring arms on a rotor to each other. The connecting elements preferably comprise 7 wires, e.g. metal wires or other wires with high tensile strength. By connecting the far ends of neighboring arms, which far ends are the ends of arms opposite to the ends of the arms proximate to their axis of rotation, the structural 5 strength of the rotor is increased.

In an embodiment the wind turbine further comprises an airlift structure for lifting the wind turbine from the ground, said airlift structure preferably comprising a balloon filed with a lighter-than-air 10 material. When the wind turbine is substantially floating in the air, the amount of ground surface required for placing and operating the wind turbine is substantially reduced.

In an embodiment the wind turbine comprises a 15 device which is driven by rotation of the rotors. The device preferably comprises a mechanical device such as a pump, e.g. for pumping water, or an electrical device such as dynamo, e.g. for generating electricity from said rotational movement of the rotors. Preferably, the device is comprised 20 on or within the support of the wind turbine.

According to a second aspect the present invention provides a use of a wind turbine according to the invention, for driving a device, preferably a mechanical or electrical device. The rotational energy supplied by the wind turbine 25 may thus be used to drive a mechanical device such as a pump, e.g. for pumping water, or an electrical device such as dynamo, e.g. for generating electricity.

The various aspects and features described and shown in the specification can be applied, individually, 30 wherever possible. These individual aspects, in particular the aspects and features described in the attached dependent claims, can be made subject of divisional patent applications .

BRIEF DESCRIPTION OF THE DRAWINGS

35 8

The invention will be elucidated on the basis of an exemplary embodiment shown in the attached drawings, in which:

Figures 1A and IB schematically show a cross-5 sectional side view and a front view respectively of a wind turbine according to the present invention, figures 2A and 2B schematically show a side view and a top view respectively of an embodiment of the present invention, 10 figure 3 schematically shows a side view of a another embodiment of the present invention, figures 4A and 4B schematically show a side view and a top view of another embodiment of the present invention, 15 figures 4C and 4D schematically show side views of two alternative embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

20 Figure 1A schematically shows a cross-sectional side view of a wind turbine 1 according to the present invention. The wind turbine comprises a support 2 supporting a frame 3,5 which in turn supports a first rotor 100 and a second rotor 200. The support 2 is rotatable around a 25 vertical axis of rotation V to align the rotors 100,200 such that their axes of rotation L1,L2, which are substantially horizontal, are substantially normal to a wind stream blowing in a first direction W. In the embodiment shown, this alignment of the rotors 100,200 is achieved by means of 30 a substantially planar wind alignment surface 10 which is oriented substantially parallel to the first direction W and which is fixedly connected to the support via a beam 9.

The first rotor 100 is attached to an axle 140 which is rotatable relative to the frame 3,5 of the support 35 2 around first axis of rotation LI in direction R1. The first rotor 100 comprises a first set of arms 101,102,103 and 104 which comprise foldable wind engagement surfaces 9 111, 112,113 and 114 respectively. The wind engagement surfaces 111, 112, 113, 114 are foldable about respective folding lines substantially in a plane normal to the axis of rotation LI of the rotor 100. In the embodiment shown, the 5 folding line of each wind engagement surface 111,112,113,114 is substantially parallel to its corresponding arm 101,102,103,104. Though the wind engagement surfaces shown each comprise single sheet of a flexible and resilient material, wherein the flexibility of the material allows for 10 the wind engagement surface to fold or unfold, in an alternative embodiment, each of the wind engagement surfaces may comprise two portions of a plate like material, which two portions are arranged on either side of a corresponding arm and are attached to the arm by means of a hinge.

15 When a wind stream blows in a first direction W, it causes wind engagement surfaces 111,112 located substantially upstream of their arms 101,102 relative to the wind stream W to unfold to a position in which they form substantially concave surfaces facing the first direction W 2 0 with their concave sides. The force of the wind stream on these wind engagement surfaces 111 and 112 is converted into rotational energy, i.e. causes the first rotor 100 to rotate in direction R1 around its axis of rotation LI. At the same time, wind engagement surfaces 113 and 114 of the first 25 rotor 100 rotate against the first direction W of the wind stream, causing them to substantially fold along their folding lines such that the area with which they oppose the wind stream W is reduced, i.e. substantially less than the area with which the wind engagement surfaces 111,112 oppose 30 the wind stream. The force exerted by wind engagement surfaces 111 and 112 for making the rotor 100 rotate in the direction of rotation R1 is thus larger than the force exerted by wind engagement surfaces 113 and 114 on the rotor 100 in the opposite direction. An opening angle of each wind 35 engagement surface 111,112,113,114 is limited by limiting structures 121a,121b,122a,122b,123a,123b,124a, 124b in the form of wires, such that the wind engagement surfaces retain 10 their substantially concave shape when facing the wind stream W with their concave sides. In the embodiment shown, the wires 121a,121b and 122a,122b are substantially taut as their corresponding wind engagement surfaces 111, 112 are in 5 the unfolded position due to the wind acting thereon, and wires 123a,123b and 124a,124b are substantially slack as their corresponding wind engagement surfaces 113, 114 are in the folded position.

The second rotor 200 is attached to an axle 240 10 rotatable relative to said support 2 around axis of rotation L2, and comprises a first set of arms 201,202,203,204 which extend radially from said axis of rotation L2 and which are provided with wind engagement surfaces 211,212,213 and 214 respectively. The respective wind engagement surfaces 15 211,212,213 and 214 are foldable between a substantially folded position and a substantially unfolded position, along folding lines substantially in a plane normal to the second axis of rotation L2. Though the second rotor 200 is of a similar construction as the first rotor 100, it is arranged 2 0 to rotate in a direction of rotation R2 which is counter to the direction of rotation R1 of the first rotor. The wind engagement surfaces of both the first rotor 100 and of the second rotor 200 are thus arranged substantially for unfolding when located between the first axis of rotation LI 25 and the second axis of rotation L2. As each arm of the first rotor 100 is spaced apart by at least its length from the second axis of rotation L2, and each arm of the second rotor 200 is spaced apart by at least its length from the first axis of rotation LI, collisions between arms of the first 30 rotor and arms of the second rotor are prevented.

At least when in the unfolded position, the wind engagement surfaces 211,212,213 and 214 each form a substantially concave surface. Wires 221a,221b,222a,222b,223a,223b,224a,224b act as limiting 35 structures for limiting the extend to which the wind engagement surfaces 211,212,213 and 214 may unfold and function in the same manner as wires 11 121a,121b,122a,122b,123a,123b,124a,124b of the first rotor 100.

When the wind stream W engages the unfolded wind engagement surfaces 111 and 211, much of the wind stream is 5 first caught in the substantially concave shapes formed by the unfolded wind engagement surfaces 111,211 and 112,214, and is then guided towards and across the edges of the respective wind engagement surfaces 111,211. As the edges 111a,111b and 211a,211b of the wind engagement surfaces 111 10 and 211 at the distal ends of the arms 101 and 201 near line P are close to each other, the air pressure at the side of the wind engagements surfaces 111,211 facing the wind stream W, in particular near edges 111a,111b,211a,211b increases. As a result, a greater amount of wind energy is converted to 15 rotational energy than if the wind escaping over edges 111a,111b and 211a,211b would not at least partially be reused to drive rotation of said first and second rotors 100,200. In the embodiment shown the minimum distance between the wind engagement surface 111 of the first rotor 20 100 and the corresponding wind engagement surface 211 of the second rotor is less than one tenth the length of an arm. Both the first rotor 100 and the second rotor 200 are supported by the support 2 which is rotatable around a substantially vertical axis of rotation V.

25 The support 2 comprises an alignment member 10 for correctly aligning the rotors in the wind, i.e. such that the axes of rotation of the rotors are in a direction normal to the first direction of the wind stream W, and such that the wind engagement surfaces of the first and second rotors 30 fold towards the unfolded position when located between the first and second axes of rotation. The alignment member shown comprises the substantially planar wind alignment surface 10 which extends substantially perpendicular to the axes of rotation, and which is fixedly connected to the 35 support 2 by a beam 9. Though not shown, an alternative alignment member may be used instead, for instance comprising an electromotor adapted for rotating the support 12 around the vertical axis V based on the first direction of the wind. The frame 3,4,5,6 of the support 2 is shown in more detail in figure IB.

Figure IB schematically shows a front view of the 5 wind turbine 1 of figure 1A to the invention. The axles 140 and 240 of first rotor 100 and second rotor 200 respectively are supported by the support 2 and frame 3,4,5 for rotating around their respective axes of rotation LI and L2. The rotors 100,200 have been aligned using the planar wind 10 alignment surface 10 such that their axes of rotation LI and L2 are substantially perpendicular to the first direction of the wind stream, and such that the wind engagement surfaces of the rotors are arranged for unfolding when located between the axes of rotation L1,L2. Though for reasons of 15 clarity the wind alignment surface 10 and the beam 9 which connects the wind alignment surface 10 to the support 2 have been shown at an angle behind the support 2, the wind alignment surface would typically be at least substantially behind the support relative to the first direction of the 20 wind stream.

The rotors 100,200 each comprise a respective first set of arms 101,102,103, 104; 201,202,203,204 of which arms 101,103 and 201,203 have only been shown in figure IB for reasons of clarity. The arms are attached to their 25 respective axle 140 and 240, and extend radially from their respective axes of rotation L1,L2, each arm of the first sets of arms 101,102,103,104; and 201,202,203,204. Besides the first set of arms 101,102,103,104, rotor 100 comprises an additional set of arms spaced apart from the first set of 30 arms along the axis of rotation LI. For reasons of clarity only arms 105 and 107 of the additional set of arms are shown, though the person skilled in the art will appreciate that the additional set of arms typically comprises the same number of arms as the first set of arms, and is typically of 35 a same configuration as the first set of arms. Likewise, the second rotor comprises an additional set of arms spaced apart from its first set of arms along the second axis of 13 rotation L2, and of which additional set of arms only arms 205 and 207 are shown for reasons of clarity.

The first sets of arms 101, 102, 103, 104; 201,202,203,204 (see figure 1A) of the first and second 5 rotors 100,200 are arranged to rotate in a substantially common plane of rotation VI, which common plane VI is substantially vertical and extends perpendicular to both the first axis of rotation LI and the second axis of rotation L2 .

10 The additional sets of arms 105, 107; 205,207 of the first and second rotors 100,200 are arranged to rotate in a substantially common plane of rotation V2, which common plane is substantially vertical and extends perpendicular to both the first axis of rotation LI and the second axis of 15 rotation L2.

The wind turbine 1 comprises coupling elements 51,51a, 52,53,54, 54a, 55, 56, 57 and 58 for coupling the rotors 100,2 00 such that they rotate counter to each other and at substantially the same speed. In the embodiment shown the 20 coupling elements comprise a first wheel 51 fixedly connected to the axle 140 of the first rotor 100 and connected via a belt 51a to second wheel 52. The second wheel 52 is rotation-fixedly connected to a gear 53 and to a drive axle 57 of a dynamo 58 for converting rotational 25 energy of the drive axle 57 into electrical energy. The coupling elements further comprise a third wheel 54 fixedly connected to axle 240 of the second rotor 200, connected via a belt 54a to a fourth wheel 55. The fourth wheel is rotation fixedly connected to a gear 55, which gear 55 30 engages said gear 53, such that said gears 53, 55 rotate in opposite directions. The coupling elements rotationally couple the rotors 100, 200 to each other such that they rotate at substantially the same speed, and such that at any time a distance between corresponding arms of the first 35 rotor 100 and of the second rotor 200 to a line P halfway between the first axis of rotation LI and the second axis L2 and parallel thereto, is substantially the same. For 14 instance, corresponding arms 101 and 201 have the same angular velocity, and at any time during their rotation, a distance between arm 101 and the line P is substantially the same as a distance between arm 201 and the line P. Thus, 5 when the wind engagement surfaces 111,112 of both arms 101,201 are at a location close to said line P as shown in figure IB, a stream of wind engaging said surface 111 may at least partially escape said surface 111 over edges 111a,111b and provide an extra force on wind engagement surface 211. 10 Likewise, wind escaping over edges 211a,211b of wind engagement surface 211 provides an extra force on wind engagement surface 111.

Figures 2A and 2B schematically show a side view and a top view respectively of an embodiment of a wind 15 turbine 400 according to the present invention. The wind turbine comprises 400 a support 402 which is mounted rotatably around a vertical axis of rotation V on a base 408. The support 402 comprises a frame 403,404 supporting a first rotor 500 comprising an axle 540 rotatable around a 20 vertical axis of rotation L3, and a second rotor 600 comprising an axle 640 rotatable around a vertical axis of rotation L4. The first rotor 500 comprises a first set of arms 501,503 attached and a second set of arms 505, 507. Though for reasons of clarity figure 2A shows each set of 25 arms to comprise only two arms, it will be appreciated that each set will typically comprise a larger number of arms extending radially from its axis of rotation. Both sets of arms 501,503; 505, 507 are attached to the axle 540. The first rotor 500 is rotationally coupled with the second 30 rotor 600, preferably using coupling elements as described in figure 1A, such that the first rotor 500 rotates substantially at the same speed as the second rotor 600, but in a direction of rotation counter to the direction of rotation of the second rotor 500. A device, e.g. a dynamo or 35 a pump can be arranged in the support 402, for converting rotational energy of the rotors 500,600 into electrical or mechanical energy respectively. Such a device is preferably 15 coupled to the coupling elements instead of directly to the axles 540 or 640.

Each of the arms 501,503; 505, 507 of the first rotor comprises a foldable wind engagement surface 511,513; 5 515,517, wherein each of said wind engagement surfaces is foldable around a folding line substantially in a respective plane normal to its axis of rotation L3. Likewise, the second rotor 600 comprises two sets of arms 601,603; 605,607, each arm comprising a foldable wind engagement 10 surface 611,613,-615,617, wherein each of said wind engagement surfaces is foldable around a folding line substantially in a respective plane normal to its axis of rotation L4. The arms of the first sets 501,503; 601,603 are arranged for rotating in a common horizontal plane of 15 rotation HI, and the arms of the second sets 505,507; 605, 607 are arranged for rotating in a common horizontal plane of rotation H2.

Wind alignment member 410, comprising a substantially planar wind alignment surface 410 extending 2 0 perpendicular to the axes of rotation L3,L4 and which is fixedly connected to the support 402 by beam 409, is adapted for orienting the support 402 such that the vertical axes of rotation L3,L4 of the first and second rotor 400,500 respectively are substantially perpendicular to a first 25 direction W in which a wind stream is directed (see figure 2B) .

Because the wind engagement surfaces of the first rotor 500 and second rotor 600 are arranged for folding to the unfolded position when within the frame 403,404, or 30 alternatively when located between the axes of rotation L3 and L4, the wind stream which escapes one rotor provides additional wind pressure for driving rotation of the other rotor. For instance, wind escaping across edges 511a,511b of wind engagement surface 511 farthest from the axle 540 to 35 which arm 501 of said wind engagement surface 511 is connected, at least partially flows towards edges 611a,611b of wind engagement surface 611, such that at a point 16 substantially halfway between the axes of rotation L3,L4 the air pressure is increased, providing an additional force on the wind engagement surfaces 511,611 for driving rotation of the respective first and second rotor. The edges 611a,611b 5 are the edges of the wind engagement surface 611 arranged farthest from axle 640 to which the arm 601 of the wind engagement 611 surface is connected.

Figure 3 schematically shows a side view of a wind turbine 1000 according to the invention, comprising a 10 support 1002 which is rotatable relative to a ground plane 1010 around a vertical axis of rotation V. The support 1002 comprises an annular base 1006, which is rotatable around the axis of rotation V relative to the ground plane 1010 using a wheel drive comprising wheels 1007,1008 and a motor 15 for driving rotation of the wheel 1008. The support 1002 comprises a first substantially upright support element 1004 and a second substantially upright support element 1005, both protruding from the annular base 1006, between which upright support elements 1004,1005 a first rotor 1100 and a 20 second rotor 1200 are supported. The first rotor 1100 and second rotor 1200 are rotationally coupled for rotating around their respective axes of rotation L5, L6 at substantially equal speeds but in opposite directions R5 and R4. The rotors 1100, 1200 are arranged such that the wind 25 engagement surfaces of their arms substantially unfold when located between the axis of rotation L5 of the first rotor 1100 and the axis of rotation L6 of the second rotor, i.e. when located proximate or closest to line P2 which is parallel to the axes of rotation L5,L6 and arranged halfway 30 between those axes. The line P2 lies in an plane which is parallel and equidistant to said axes of rotation L5,L6.

Each rotor comprises multiple sets of arms 1101a, 1103a; 1101m, 1103m; HOlv, 1103v, 1201a, 1203a; 1201m, 1203m; 1201v, 1203v, wherein the sets of arms of each 35 respective rotor 1100,1200 are spaced apart from each other along the axis of rotation of the rotor. In the embodiment shown, the first and second rotors each comprise twentytwo 17 sets of arms. The arms of corresponding sets of arms of the first and second rotor are adapted for rotation around their respective axis of rotation R5,R6 in a vertical plane which is substantially common for each arm in both sets. For 5 instance, arms 1101a, 1103a of a first set of arms of the first rotor and arms 1201a, 1203a of a corresponding first set of arms of the second rotor are arranged for rotating in a substantially common vertical plane.

Though for reasons of clarity each set of arms is 10 shown comprising only two arms, it will be appreciated that each set of arms will typically comprise more than two arms, e.g. three to six arms in a common plane normal to the axis of rotation. The arms of the set of arms 1201m, 1203m and of the set of arms 1101m, 1103m will be described next, though 15 the description holds for the other arms of the first and second rotors as well. Arms 1101m,1103m and 1201m, 1203m each comprise a foldable wind engagement surface 1111m, 1113m, 1211m and 1213m respectively, of a same construction as described for the previous embodiments. Wind engagement 20 surfaces 1111m and 1211m which are located upstream relative to their arms 1101m, 1201m, in figure 3 shown between the axes of rotation L5,L6, are in a substantially unfolded position in which they form substantially concave surfaces for facing a stream of wind. The wind engagement surfaces 25 1113m,1213m are substantially downstream of their arms 1103m, 1203m and are in a folded position. The wind engagement surfaces between the axes of rotation L5,L6, at least during a part of their rotation, are arranged for trapping a substantial part of a wind stream which passes 30 between the axes of rotation.

A dynamo 1058 is adapted for converting rotation of said rotors 1100,1200 into electrical energy.

Figures 4A and 4B show a schematic side view, and a schematic top view respectively of an embodiment of a wind 35 turbine 2000 according to the present invention. The wind turbine comprises a support 2003 for supporting a first rotor 2100 and a second rotor 2200, each comprising multiple 18 sets of arms as described for the previous embodiments. The first rotor 2100 and second rotor 2200 comprise axles 2140 and 2240 respectively to which the arms are connected, which axles 2140,2240 are rotatably connected to the support 2003 5 for rotating relative to the support 2003 in opposite directions R7, R8 at substantially equal speeds around substantially horizontal axes of rotation L7 and L8 respectively. The rotors 2100,2200 are arranged such that the wind engagement surfaces of their arms substantially 10 unfold when located between the axis of rotation L7 of the first rotor 2100 and the axis of rotation L8 of the second rotor 2200, i.e. when located proximate or closest to line P3 which is parallel to the axes of rotation L7,L8 and arranged halfway between those axes. The line P3 lies in an 15 plane which is parallel and equidistant to said axes of rotation L7,L8.

The support 2003 comprises a first support element 2004 and a second support element 2005, between which the first rotor 2100 and the second rotor 2200 are located. The 20 support 2003 further comprises reinforcement rods 2007 and 2008 which increase the structural integrity of the support 2003.

The wind turbine 2000 further comprises an airlift structure comprising a zeppelin or blimp 2010 filed with a 25 lighter-than-air gas, i.e. a gas having a lower density than the air surrounding the zeppelin, e.g. helium or heated air. The zeppelin 2010 comprises a longitudinal axis Lz which is parallel to the first direction of the wind stream W (see figure 3C) and is provided with wind alignment members in 30 the form of fins 2011 for aligning the zeppelin with a front side 2012 into the direction in which the wind stream W is blowing. The axes of rotation L7,L8 of the wind turbine are oriented substantially perpendicular to the longitudinal axis Lz of the zeppelin. The zeppelin thus forms a wind 35 alignment structure for aligning the axis of rotation L7,L8 of the wind turbine substantially perpendicular to the first direction W.

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The support 2003 is suspended from the zeppelin 2010 by means of a rigid frame 2006 which rotation fixedly connects the support 2003 to the zeppelin 2010. The wind turbine 2000 is mechanically connected to the ground 1010 by 5 a wire 2021. The wire 2021 functions to at least substantially fix the location of the wind turbine 2000 with respect to the ground 1010. Moreover, the wire 2021 comprises an electrical conductor for conducting electricity generated by dynamo 2 058 of the wind turbine to a location 10 remote from the wind turbine.

Figure 4C schematically shows yet another embodiment according to the invention. The wind turbine 3000 according to this embodiment comprises airlift means 3010 in the form of a balloon filled with a lighter-than-air gas. 15 The wind turbine further comprises a frame 3003,3004,3005,3007,3008 for supporting a first rotor 3100 and a second rotor 3200, comprises respective axles 3140,3240 rotatable relative to the support around respective substantially horizontal axes of rotation L9,L10 20 in opposite directions R9,R10. The rotors 3100,3200 are rotationally coupled in the same manner as described for the previous embodiments. The first rotor 3100 and the second rotor 3200 each comprises a plurality of arms with foldable wind engagement surfaces as described for the embodiments 25 above. The rotors 3100,3200 are arranged such that the wind engagement surfaces of their arms substantially unfold when located between the axis of rotation L9 of the first rotor 3100 and the axis of rotation L10 of the second rotor 3200, i.e. when located proximate or closest to line 43 which is 30 parallel to the axes of rotation L9,L10 and arranged halfway between those axes. The line P4 lies in an plane which is parallel and equidistant to said axes of rotation L9,L10.

The wind turbine 3000 is connected to the ground 1010 by means of at least two wires or ropes 3021,3022 which 35 connect two respective sides of the frame 3005,3004 which are spaced apart along the axis of rotation L9 to poles 1011,1012 embedded into the ground. The wires 3021,3022 are 20 substantially taut, such that they substantially restrain changes in orientation of the wind turbine 3000 relative to the ground 1010 around a vertical axis of rotation V of the wind turbine 3000. In case the wind direction changes, one 5 or both of the wires 3021,3022 is uncoupled from the poles 1011,1012 and attached to another pole, for instance to pole 1013, such that the wires 3021, 3022 are substantially taut and such that the support 1003 is rotated relative to the ground 1010 for changing its orientation to the wind 10 direction. Wire 3021 also comprises an electrical conductor for conducting electrical energy generated by dynamo 3058 of the wind turbine 3000 away from the wind turbine.

Typically the wires 3021,3022 are attached to poles such that the direction of the wind stream is 15 substantially normal to a vertical plane defined by the first and second axes of rotation L9,L10. Though in the embodiment shown the wind turbine is aligned using poles 1011,1012,1013,1014 and wires 3021,3022 it will be apparent that alignment of the wind turbine 3000 by be achieved using 20 other means.

Figure 4C shows another embodiment of a wind turbine according to the invention. The wind turbine 4000 comprises airlift means in the form of a kite 4010, which is rotation-freely connected via a wire 4012 to a frame 25 4003,4004,4005. The frame supports a first rotor 4100 and a second rotor 4200, each of said rotors comprising an axle 4140, 4240 to which a plurality of arms with foldable wind engagement surfaces is attached. The axles 4140,4240 of the rotors 4100,4200 are rotationally coupled for rotating 30 around their respective axis of rotation L11,L12 in opposite directions R11,R12 and at the same velocity.

The foldable wind engagement surfaces are arranged for unfolding when located between the axes of rotation L11,L12. For keeping the rotors aligned with their axis of 35 rotation perpendicular to the wind, two wires 4021,4022 are attached respectively on either side 4005,4004 of the frame along the axis of rotation and connect said frame 21 4003,4004,4005 to the ground 1010. When the wires 4021,4022 are taut, as shown, they limit a change in orientation of the frame with respect to the wind. Moreover, the wire comprises an electrical conductor for conducting electrical 5 energy generated by dynamo 4 058 away from the wind turbine 4000.

It is to be understood that the above description is included to illustrate the operation of the preferred embodiments and is not meant to limit the scope of the 10 invention. From the above discussion, many variations will be apparent to one skilled in the art that would yet be encompassed by the spirit and scope of the present invention. In particular it is envisaged that a wind turbine according to the invention is further provided with an 15 electrical generator, e.g. a dynamo, adapted for converting rotational movement of said rotors into electrical energy.

Claims

A wind turbine for converting a wind stream that blows into rotational energy in a first direction, the wind turbine comprising: a first rotor rotatable in a first direction of rotation about a first axis of rotation; a second rotor rotatable in a second direction of rotation about a second axis of rotation substantially parallel to the first axis of rotation; wherein the first rotor and the second rotor are each provided with a set of arms extending substantially radially with respect to its respective axis of rotation, each arm comprising a foldable wind engagement surface with a fold line substantially in a plane normal to the axis of rotation; Wherein the first direction of rotation is opposite to the second direction of rotation; and wherein the sets of arms of the first and second rotors are arranged to rotate in a substantially common plane of rotation.

2. Wind turbine according to claim 1, wherein the first and second rotation axes are arranged in a joint substantially vertical plane perpendicular to the joint plane of rotation.

3. Wind turbine according to claim 1 or claim 2, wherein each of the engagement surfaces is adapted to fold its folding line between an unfolded position when the wind engagement surface is positioned substantially upstream of its arm and a folded position when the wind engagement surface is substantially downstream of his arm.

4. Wind turbine as claimed in any of the foregoing claims, wherein the first rotor and / or the second rotor comprise one or more additional sets of arms that are spaced apart from its set of arms along its respective axis of rotation and extend substantially radially with respect to the axis of rotation, wherein each of the arms of the additional sets of arms comprises a foldable wind engagement surface with a fold line substantially in a plane normal to the axis of rotation.

5. Wind turbine according to any one of the preceding claims, wherein each of the foldable wind engagement surfaces is adapted to fold due to the wind flow around its folding line to an unfolded position when the wind engagement surface is placed between the first and second rotation axes.

6. Wind turbine according to any one of the preceding claims, further comprising a support for supporting the first and second rotors, wherein the rotors are rotatable relative to the support about their respective axis of rotation and wherein the support is rotatable about a vertical axis .

A wind turbine according to any one of the preceding claims, further comprising a wind alignment element adapted to align the first axis of rotation and the second axis of rotation in a direction substantially perpendicular to the first direction.

A wind turbine according to any one of the preceding claims, wherein the first rotor and the second rotor are mirror-symmetrical with respect to a plane parallel to and equidistant from the first and second rotational axes of the rotors.

A wind turbine according to any one of the preceding claims, wherein, when unfolded, each of the wind engaging surfaces is adapted to form a substantially hollow surface that faces its first side of the wind stream with its hollow side.

10. Wind turbine as claimed in any of the foregoing claims, wherein the wind-engaging surfaces of the arms comprise a flexible material, preferably a flexible sheet.

11. Wind turbine as claimed in any of the foregoing claims, wherein the wind-engaging surfaces of the arms comprise a resilient material.

A wind turbine according to any one of the preceding claims, wherein the wind engagement surfaces of the arms further comprise one or more reinforcing elements.

13. Wind turbine as claimed in any of the foregoing claims, wherein one or more of the wind-engaging surfaces of an arm of the first and / or second rotor comprises: a first part adapted to grip the wind flow, the first part foldable along a first edge is connected to the arm; 15 a second portion adapted to engage the wind flow, the second portion being foldably connected to the arm along a second edge.

14. Wind turbine according to claim 13, wherein the first and second parts are hingedly connected to the arm.

A wind turbine according to any one of the preceding claims, wherein the first rotor and / or the second rotor further comprises restriction structures for limiting the opening angle of its wind engagement surfaces.

The wind turbine of claim 15, wherein the restraint structures comprise a link connecting sections of a wind grip surface of an arm of the wind turbine on opposite sides of the arm.

17. Wind turbine according to claim 15 or claim 16, wherein the restriction structures comprise: a first link connected to a first section of a wind grip surface of an arm of the first rotor or the second rotor, and a second link connected to a second section of the wind engagement surface, wherein the first and second sections are arranged on opposite sides of the arm, and wherein the first and second links are connected to an arm adjacent to the arm of the rotor in a direction opposite to the direction of rotation of rotor.

A wind turbine according to any one of the preceding claims, wherein the wind engagement surfaces of the arms 5 are substantially symmetrical along their respective arms.

19. Wind turbine according to any of the preceding claims, wherein the arms comprise a distal end at their far end of the axis of rotation, wherein the wind turbine 10 further comprises one or more connecting elements which connect the distal ends of neighboring arms on a rotor.

20. Wind turbine as claimed in any of the foregoing claims, further comprising a wind turbine in the air lifting structure for lifting from the ground, wherein in the air lifting structure preferably a balloon is filled with a material that is lighter than air.

A wind turbine according to any one of the preceding claims, further comprising a device driven by rotation of the rotors. 2 0

Use of a wind turbine according to any one of the preceding claims for driving a device.

The use of claim 22, wherein the device comprises a pump or a dynamo. -o-o-o-o-o-o-o-