HK1080922B - Coupled vortex vertical axis wind turbine - Google Patents

Description

Coupled vortex vertical axis wind turbine

Technical Field

The present invention relates to the field of wind turbine engines, and more particularly to wind turbines that rotate about a vertical axis.

Background

Vertical-axis wind turbines have been known for many years. The most common configuration of vertical axis turbines is the Darrius turbine, which employs troposkien-shaped curved blades. Other vertical axis turbines employ straight blades that are connected to a vertical shaft by one or more blade support arms.

Modern vertical axis turbines employ airfoils that provide lift rather than aerodynamic drag to provide motive force to the rotor. The use of such lift-producing airfoils greatly improves the aerodynamic efficiency of the rotor as compared to drag-type devices. However, even with the use of lift-producing airfoils, conventional vertical axis turbines still suffer from a number of disadvantages compared to horizontal axis turbines. The peak aerodynamic efficiency achievable with most vertical-axis wind turbines is approximately 25-30%. Also vertical axis wind turbines are not inherently self-starting and require the application of a starting motor to start their rotation. Various improvements to such basic vertical-axis wind turbines have addressed these inherent problems.

A vertical axis, lift windmill is disclosed in us patent 4,115,027, the specification of which is incorporated herein by reference. Vertical airfoils providing aerodynamic lift are mounted to struts around a central shaft to form a rotor.

Various improvements to the windmill of us 4,115,027 are disclosed in us5,027,696 and 5,332,925, the specifications of which are incorporated herein by reference. The improvements include a new braking system, thick airfoil application, drive belt drive, two speed operation, and rotatable stator which improves efficiency during high winds and limits structural loads.

All of the wind turbines in the above-referenced patents employ stationary fairings outside the rotor to direct the wind flow through the rotor and improve efficiency. Although this method has been found to significantly improve the performance of wind turbines (aerodynamic efficiencies have been measured as high as 52%), it also results in additional structures that must be supported, increasing the plan area, which increases the wind loads on the structure during storm conditions. It would therefore be desirable to achieve similar performance improvements without the need for structural elements such as stationary fairings.

The wind turbine of the above-referenced patent also employs a mechanical braking system, which has been found to be reliable, but which also requires manual resetting after actuation. This can lead to high turbine downtime and reduced effectiveness if the operator is not present at all times. It is therefore desirable to introduce a braking system which automatically operates when a fault occurs in the turbine system and which automatically resets and restores the turbine to operation after the fault is cleared.

It is desirable to provide a vertical-axis wind turbine that achieves high aerodynamic efficiency while requiring minimal support structure. It is also desirable to provide a vertical-axis wind turbine that is adapted for application beneath an array of existing horizontal-axis wind turbines in a "shrub tree" type configuration to maximize energy production on a site. It is also desirable to provide a vertical axis wind turbine that incorporates a robust, reliable automatic aerodynamic and mechanical braking system that automatically resets after a fault is cleared. Moreover, it is also desirable to minimize the frequency and difficulty of repairs by providing simple access to components that require more frequent attention, such as gearboxes and engines. It is also desirable to simplify the turbine structure by applying a tie bar structure or a tie bar in combination with an external support frame, rather than an external support frame. An external pull wire configuration minimizes the number of parts required. These structures can also provide a clearer aerodynamic flow field to enhance the vortex effect of the turbine. It is also desirable to increase the swirl effect of the turbine and to increase the self-starting capability by applying a high solidity rotor.

Disclosure of Invention

The present invention provides a wind turbine with improved aerodynamic efficiency by interacting the vortices of two adjacent wind turbines and applying a high solidity rotor. The vortex interaction is a result of the close arrangement of adjacent turbines and their angular orientation relative to the prevailing wind direction. Adjacent turbines must also rotate in opposite directions to achieve coupled vortex interaction.

In a staggered configuration providing cable-to-cable and cable-to-rotor clearance, the drawbar arrangement may be closely arranged in a row configuration by employing three or four cable support point arrangements. The wind turbines may be arranged in a long row of coupled wind turbines with enhanced aerodynamic effects throughout the row of wind turbines. The direction of the turbines should be perpendicular to the prevailing wind direction. This orientation of the turbine is particularly suitable for those geographical locations where there is a strong prevailing wind direction and where little change in direction occurs.

A row of coupled vortex turbines may be disposed below a row of horizontal axis turbines. This "bush" type structure maximizes the capture energy available at a site. The aerodynamic performance of the horizontal axis turbine can be improved due to the fact that the vertical axis turbine is arranged below the horizontal axis turbine. The row of vertical axis turbines may also create a vertical mixing effect such that high energy wind flow enters the wind flow field of the horizontal axis wind turbine.

The turbine employs a pneumatic braking system that automatically shuts down and resumes operation of the turbine after the fault has cleared. The pneumatic brake is biased by a counterweight so that the brake is normally applied by the counterweight and is disengaged when the pneumatic cylinder is pressurized to lift the brake and counterweight. Normally closed solenoid valves control the air pressure applied to the pneumatic cylinders. The valve is current actuated. When the power is off, the solenoid valve opens to release air pressure to the pneumatic cylinder. When power is restored, the solenoid valve closes and the compressor pressurizes the cylinder to lift the counterweight and disengage the brake. This ensures that in the event of a power failure, the brake will be applied to stop the turbine and will be released when power is restored. A toggle switch is provided for opening the solenoid valve if the power supply is not disconnected but the engine is disabled for some reason.

A linkage connects the mechanical brake to a system for adjusting blade pitch. When the brake is applied, the blades are tilted at a 45 degree angle to act as a drag brake. In this way, the turbine has a redundant mechanical and aerodynamic braking, thus guaranteeing a higher reliability.

Turbine components that are subject to high wear and require maintenance are located at ground level. The tie rod of the turbine is supported by a pair of bearings located at the bottom of the tie rod. The two bearings are separated by approximately 0.914 meters (3 feet) in the vertical direction. The uppermost one of the two bearings remains in a fixed position and supports only the static weight of the main shaft. The lowermost bearing is free to slide in the horizontal direction, allowing the drawbar to rock. The lower bearing supports the weight of the blade and the vertical forces from the aerodynamic drag skin on the rotor. The load on the upper bearing is sufficiently small that the bearing extends the life of the turbine. The lower bearing is provided where it can be easily removed for replacement of the bearing housing. The lower bearing support can be made freely movable in the horizontal direction by using a simple bracket of ball bearings.

In one embodiment, the axes of the pair of wind turbines are spaced apart from each other by a distance greater than twice the radius, but less than twice the radius plus 3.048 meters (10 feet).

In another embodiment, the axes of the pair of wind turbines are separated from each other by a distance greater than twice the radius, but less than twice the radius plus 1.524 meters (5 feet).

In a preferred embodiment of the invention, the turbine comprises three sets of blades in three stacked modules. During a braking operation, only the blades in the lowermost module are pitched. The bottom set of blades is easily accessible from the ground for maintenance. It is expected that the tiltable set of blades will require more maintenance than the other two fixed-pitch sets of blades due to the tilting motion during braking. The wear state of the set of blades is not estimated to be high because braking does not occur relatively often. The two upper modules use blades connected by yoke-like attachments that include wear resistant pin connections for inhibiting pitch motion and minimizing wear of the blades.

The bearing atop the draw bar is encased in a cable attachment box and protected from environmental exposure. This will reduce the need for oil bleed and will minimize wear.

Drawings

Other features and advantages of the present invention will become apparent from the following more detailed description, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a perspective view of a guyed vertical axis wind turbine according to the present invention.

Fig. 2 is a perspective view of a second preferred embodiment of the present invention.

FIG. 3 is a perspective view of two wind turbines arranged in a coupled vortex configuration according to the present invention.

FIG. 4 is a top schematic view of a pair of vertical axis wind turbines arranged in a coupled vortex configuration according to the present invention.

FIG. 5 is a perspective view of a plurality of vertical-axis wind turbines arranged in a row in a coupled vortex configuration in accordance with the present invention.

FIG. 6 is a schematic top view of a plurality of vertical axis wind turbines arranged in a row in a coupled vortex configuration according to the present invention.

FIG. 7 is a perspective view of a row of vertical-axis wind turbines aligned in a coupled vortex configuration with a row of horizontal-axis wind turbines in a bush configuration.

Fig. 8 is a diagrammatic elevational view of a drive train and engine according to the present invention.

Fig. 9 is a schematic front view of a braking system and a blade driving device according to the present invention.

FIG. 10 is a diagrammatic elevational view of a brake system and blade drive according to the present invention with the brake in an active condition.

Fig. 11 is a plan view of a brake system disconnect switch according to the present invention.

FIG. 12 is a perspective view of a roller bearing curve.

Detailed Description

As shown in fig. 1, the present invention consists of a wind turbine 1 having a main shaft 2 rotating about a vertical axis 1. The main shaft 2 is preferably made of steel tubing of sufficient size and thickness to withstand the compressive, torsional and bending loads during operation of the turbine and high winds, as the turbine may stop rotating. There are four blades 3 connected to the main shaft 2. The number of blades may vary as a design choice, although the chord length and rotor size need to be adjusted to ensure the desired solidity. Four blades are the preferred embodiment. Each blade 3 is connected to the main shaft 2 by a pair of blade arms 4. Although it is conceivable to apply one separate blade arm 4 for each blade 3, a preferred embodiment is to apply two blade arms 4 for each blade 3. Another preferred embodiment is that the blade arm 4 is movably connected to each blade 3 at the end of the blade 3, thereby reducing the aerodynamic tip effect on the blade and preventing the blade 3 from bending stresses at the connection point of the blade arm 4. Preferably, the blade 3 is connected to the arm 4 by an instantaneous articulated connection, for example a pin connection.

The height H of the rotor is determined according to the length of the blades 3. The diameter D of the rotor is twice the distance from the centre line of the shaft 2 to the chord line of the blade 3. The area swept by the rotor is determined as the rotor height H times the rotor diameter D. Each blade 3 has a plan area equal to the chord width C of the blade multiplied by the blade height H. Since there are four blades in the rotor, the sum of all blade plane areas equals four times the single blade plane area. The sum of all blade plane areas divided by the area swept by the rotor is considered the solidity of the rotor. For the present invention, the solidity of the rotor is preferably 33%. For a drag windmill the solidity will be much higher than 33%, typically 100%. Experiments have shown that a rotor solidity of 30-40% provides the best performance, preferably a solidity of 33%.

The main shaft 2 is supported at its lower end in a drive chain case 5 and at its upper end by a bearing 6. The upper bearing is supported by a set of stay cables 7. Because the main shaft 2 extends up beyond the top set of blade arms 4 by a distance greater than the length of one blade arm 4, the pull cable 7 can be extended at a 45 degree angle to a base 8 buried in the ground. Figure 1 shows a belt with three pull cables, although four or more pull cables may be used if desired, depending on local soil conditions, terrain and other factors.

Fig. 2 shows a second preferred embodiment according to the invention, in which the rotor comprises three modules 9 placed on top of each other. Each module 9 has four blades 3 connected to the main shaft 2 by blade arms 4. In the second preferred embodiment, each module 9 is similar to the rotor of the first preferred embodiment. The solidity of each rotor module 9 is between 30% and 40%, preferably 33%. The three modules 9 shown in fig. 2 are all connected to a common main shaft 2 so that they can rotate together. The blades 3 of the three modules 9 are staggered at an angle of 30 degrees between the modules. By staggering the blades, the output of the wind turbine is smooth. Although three modules are shown in fig. 2, it may include two modules, or it is contemplated to include four or more modules.

If two wind turbines 1 are located in close proximity to each other, as shown in fig. 3, the linear flow and the vortex flow emanating from the two rotors combine, and thus the efficiency of both rotors is improved. Fig. 4 shows a plan view of the two wind turbines, and it can be seen that the centre lines of the turbines with the rotor diameter D are at a distance L apart. If L is slightly larger than D, the rotors are spaced apart from each other by a distance s equal to L minus D. The spacing s between the two rotors should be kept as small as possible, taking into account suitable mechanical and manual safety. Preferably about 0.914 meters (3 feet) apart. This close arrangement of adjacent rotors is classified as a coupled eddy current configuration. In this coupled vortex configuration, the two rotors should rotate in opposite directions to achieve the desired improvement in aerodynamic efficiency. The direction of rotation of the two rotors is indicated by arrows in fig. 4.

In such a coupled vortex configuration, the wind turbines should be oriented such that a line connecting the two wind turbine centerlines is perpendicular to the prevailing wind direction. Ideally, the wind direction should not exceed 20 degrees at most, relative to the direction shown in fig. 4. Such a wind direction is found to be available in places with strong prevailing wind directions, for example at mountains. However, such coupled vortex arrangements for the rotor do not work well where there is no dominant wind force.

As shown in FIG. 5, a longer row of wind turbines may be arranged in a coupled vortex configuration. When a long row of wind turbines is so arranged, the centre line of each rotor is spaced from the centre line of the adjacent rotor by a distance L which is slightly larger than the rotor diameter D, so that there is a small spacing s between each pair of rotors. As shown in fig. 6, each rotor should rotate in the opposite direction to its neighboring rotor. Thus, each second turbine rotates clockwise when viewed from above, while the turbines in between rotate counterclockwise.

As shown in fig. 7, the exhaust turbine may be located below a row of horizontal axis turbines to form a "bush" type structure. This can result in a greater energy output at one location. It may also improve the performance of horizontal axis wind turbines by mixing low energy air from a lower level with high energy air from a higher level, or replacing low energy air from a lower level with high energy air from a higher level. Another possible synergy of this brush-off configuration is that the base for the horizontal axis turbine may be modified to serve as anchor points for the guy wires supporting the vertical axis wind turbine in a coupled vortex arrangement. This configuration is particularly suitable for those locations where there is unidirectional dominant wind.

The drive train for a wind turbine according to the invention is similar to that described in US5,027,696 or US5,332,925, both of which are incorporated herein by reference. As shown briefly in fig. 8, the drive train consists of a shaft mounted to a gearbox 10, which gearbox 10 is used to increase the rotational speed of the main shaft 2 to a speed suitable for driving the generator. The belt drive 11 transfers energy from the gearbox 10 to the generator 12. The belt drive 11 can provide additional speed increase and it also introduces some flexibility to the drive train for eliminating torque spikes. The gearbox 10 is shaft mounted and, unless restrained, will rotate in a torque direction. In a preferred embodiment, the rotation of the gearbox 10 is limited to a small angular increase, such that the belt tension goes from slack (no drop) to tight. This angle increase is adjustable. A damper 13 constrains the angular rotational rate of the gearbox 10 in the positive torque direction for stabilizing the drive train during start-up and preventing torque spikes. In a preferred embodiment, a standard pickup truck shock absorber is used.

Although the belt drive 11 is included in the preferred embodiment, it may be eliminated from the drive train. In the preferred embodiment, the generator 12 is a standard asynchronous induction generator. Other types of generators or alternators operating at constant or variable speed may also be employed.

The brake system for a wind turbine shown in simplified form in fig. 9 and 10 is an important component. In fig. 9 the brake system is shown in the disconnected position, in which the turbine may be operated. FIG. 10 shows the braking system in the operating position for shutting down the turbine. In the event that the electrical grid is no longer functional, or the generator or generator control fails to limit the wind turbine rotor speed, the wind turbine's braking system must ensure that the wind turbine does not lose control to damaging speeds. The braking system must also ensure that it is able to bring the wind turbine to a standstill in a short time in the event of a malfunction or other problem of the wind turbine.

As shown in fig. 9 and 10, the braking system comprises a brake disc 14 which is located above a bottom flange 15 of the spindle 2. The inner diameter of the brake disc 14 is slightly larger than the outer diameter of the spindle 2, so that the disc 14 can both rotate and move up and down. The rotational movement of the disc 14 with respect to the spindle 2 is limited by several pins 16 fitted vertically through the bottom flange 15, the brake disc 14 and a flange 17 identical to the bottom flange 15. The flanges 15 and 17 are welded to the main shaft 2 and their outer diameter (which are the same size) is much smaller than the outer diameter of the brake disc 14. The brake disc 14 is free to move vertically between the flanges 15 and 17. There are two sets of brake pads, an upper set of fixed brake pads 18 and a lower set of movable brake pads 19. The movable brake shoe 19 is free to move vertically and to rotate freely in a vertical plane. The movable brake shoe 19 is mounted to the short end of a brake arm 20 which pivots in the vertical plane of the fulcrum pin shaft 21. A counterweight 22 is provided at the end of the brake arm 20 to provide a braking force. The fulcrum pin 21 is arranged so that its distance to the end of the brake arm 20 supporting the counterweight 22 is ten times its distance to the centre of the movable brake shoe 19. There are two parallel brake arms 20, one mounted on each side of the spindle 2. When the long end of the brake arm 20 is lower than the fulcrum 21, the short end rises so that the movable brake shoe 19 moves upward. The movable brake pad 19 is located below the brake disc 14 and thus contacts the brake disc 14 when the movable brake pad 19 is raised. As the long end of the brake arm 20 is lowered further, the brake disc 14 is raised until it contacts the upper fixed brake shoe 18. The brake disc 14 is then clamped between the upper and lower brake pads 18, 19. This state is shown in fig. 10. The braking force is then the mechanical advantage of the counterweight 22 times the lever or ten times the counterweight 22.

In addition to the mechanical braking force applied to the brake pads 18 and 19 on the brake disc 14, the wind turbine also comprises a system for pitching the blades 3 to provide aerodynamic braking. The aerodynamic braking system comprises a blade activation disc 23 located on the main shaft 2 at a height adjacent the lower set of blade arms 4. The blade activation disc 23 has an inner diameter slightly larger than the outer diameter of the main shaft 2 so that the disc 23 can rotate around the main shaft and move up and down along the main shaft 2. A set of blade pitch cables 24 and 25 are connected to the blade brake disc. The first set of cables 24 is connected to the leading edge of the blade 3. The second set of cables 25 is connected to the trailing edge of the blade 3. Four of each cable 24 and 25 are provided so that when the blade activation disc 23 is rotated relative to the main shaft 2, the leading edge of the blade moves away from the main shaft 2 and the trailing edge moves towards the main shaft 2, thereby pitching the blade 3. The blade 3 is pivotally mounted to a blade arm 4 at a position intermediate its leading edge and center of gravity. Because the center of gravity is forward of the pivot location, the blades tend to tilt unless they are restrained by the cable 24.

The blade activation disk 23 is rotated while the mechanical brake is applied. A set of tappets 26 is located at the top of the brake disc 14 and extends up to the underside of the blade activation disc 23. The tappet 26 is guided and defined in a hole between the flange 17 and a further flange 27, the flange 27 being located just below the blade activation disc 23. The holes in the flanges 17 and 27 are oversized to enable the tappet to move vertically in the hole. When the mechanical brake is applied, the brake disc 14 moves upwardly. This upward movement of the brake disc 14 is transmitted to the blade activation disc 23 through the tappet 26, so that the blade activation disc 23 also moves upward. The first set of stops 28 inhibits rotational movement of the brake 29 relative to the main shaft 2, wherein the brake 29 is connected to the blade activation disc 23. However, when the tappet 26 moves the blade activation disc 23 upward, the stopper 29 on the blade activation disc 23 is not moved by the stopper 28. The centrifugal force generated from the blade pulls the cables 24 and 25 and thus the blade activation disk 23 to a new position where the brake 29 engages the second set of stops 30. The first set of stops 28 corresponds to blade pitch positions for operating the turbine and the second set of stops 30 corresponds to blade pitch positions for aerodynamic braking. Ideally, the vanes are angled approximately 45 degrees between stops 28 and 30. A set of springs 31 pull the blade activation disc 23 back to the transport position with the detents 29 engaging the stops 28. When the rotor speed drops, the centrifugal force generated by the blades is not high enough to overcome the force generated by the spring 31 and the blades return to their operating position. When the mechanical brake is disengaged, the tappets 26 move downwards, allowing the brakes 29 to drop to a position where they are held by the stops 28. Thus, during braking operation, the blades are pitched to provide aerodynamic braking, but they automatically return to their operating position when the brake is disengaged. The aerodynamic brakes are shown in their operating position in fig. 9 and in their rest position accompanying the blade pitch in fig. 10.

In the embodiment shown in fig. 2, the wind turbine comprises three stacked modules, the aerodynamic brake preferably being comprised only on the bottom module. The spacing of the blades on the other two modules is fixed to minimize wear and maintenance of the upper module.

As shown in fig. 9 and 10, the braking system is driven by a pneumatic cylinder 32 that raises and lowers the counterweight 22 and the end of the brake arm 20. When the lower end of cylinder 32 is pressurized, the internal piston is driven to lift weight 22 and brake arm 20 upward. The pneumatic cylinder 32 must be pressurized to disengage the brake and when the pressure in the pneumatic cylinder is released, the brake is applied. The compressed air supply 33 to the pneumatic cylinder 32 is controlled to control the brake system. An air compressor 34 supplies compressed air to the pneumatic cylinder 32. In the preferred embodiment, one compressor 34 supplies compressed air to the pneumatic cylinders 32 on several adjacent wind turbines. The flow of air into and out of the pneumatic cylinder is controlled by a solenoid valve 35. The solenoid valve 35 is energized by a circuit 36, which circuit 36 also supplies voltage to the motor 12, so that the brake is energized if the voltage applied to the motor is interrupted. A compressed air line 33 is open between the pneumatic cylinder 32 and the compressor 34. When the power applied to the solenoid valve 33 is interrupted, the solenoid valve 33 closes the passage between the compressor 34 and the pneumatic cylinder 32 and discharges the compressed gas from the pneumatic cylinder 32, thereby lowering the weight 22 and the brake arm 20 and activating the brake system. This is a failsafe design because loss of voltage will cause the solenoid valve 35 to de-energise, releasing pressure in the air line 33 supplying air to the pneumatic cylinder 32, causing the brake to actuate. The power supplied to the valve 35 may be interrupted due to a failure in the turbine circuit or in the active supply. The solenoid 36 and compressor circuit 37 may also be manually powered off using a brake switch 38. In addition to manual shut-off, a toggle switch 39 in the electromagnetic circuit 36 may be closed with a trip lever 40, which trip lever 40 moves into the path of the toggle switch 39 causing it to close. The trip lever 40 and toggle switch 39 are shown in fig. 11. The manual switch 38 and the toggle switch 39 must be reset either manually or by control software. If a fault occurs in the actual circuit, the brake will engage, and when the current is restored, it will automatically shut off.

As shown in fig. 11, the toggle switch 39 is actuated by a trip lever 40. The trip lever 40 is mounted to the spindle flange 15. The trip lever 40 is free to rotate away from the main shaft 2 but is constrained by a spring 41. The tension of the spring 41 may be such that when the rotor speed is above the allowable speed (i.e. slightly above the engine speed), the trip lever 40 moves to a position where the toggle switch 39 is disengaged. The trip lever 40 is preferably steel to provide a sufficiently high weight to provide sufficient centrifugal force. In alternative embodiments, the toggle switch 39 may be actuated by a solid state speed sensor or a PLC controller.

Although the brake system comprises a lot of mechanical and aerodynamic braking and the excitation system is fail-safe, experience in the field of wind turbines has shown that it is desirable to include another double brake disconnect system in order to avoid a runaway wind turbine. A dual rotor speed regulation system is shown in figures 9 and 10. A set of counterweight arms 42 are supported mounted at the top ends of the blade arms 4 of the bottom rotor module. In the preferred embodiment two arms 42 are used. When the rotor is at rest, the arms 42 hang downward. As the rotor speed increases, the arms 42 are thrown upwardly and outwardly. A cable 43 is connected to each arm 42 at a suitable distance from the arm pivot point and is connected to the top end of the blade activation disc 23. When the rotor speed exceeds the off speed of the toggle switch 39, the cable 43 creates sufficient tension to cause the disc 23 to lift off its first set of stops 28. The blades 3 are then free to pitch to a pitch angle of 45 degrees. The aerodynamic braking effect keeps the rotor speed within a structurally safe range. This is a fault protection system that protects the rotor.

As shown in fig. 8, the lower end of the main shaft 2 is supported by two bottom bearing blocks 44 and 45. A main or upper bearing 44 is mounted to a main support beam 46 above the gearbox 10 and bedplate. The shaft system comprises a main shaft 2 and a drive shaft 47. Such a shaft system may rotate about the main bearing 44. Both bearings are self-aligning. The shaft system comprising the main shaft 2 and the drive shaft 47 is swaying because the stay cable 7 is elongated under load. The bottom bearing 45 must be able to move in the horizontal plane to relieve bending stresses in the drive shaft 47. The bearing 45 is smaller than the main bearing 44. The drive shaft is stepped at the bottom to accommodate the bearing 45 so that the bearing 45 can carry axial loads with the main bearing 44. The lower bearing is retained on a plate 48 and the plate 48 is retained on a rolling bearing surface 49 as shown in figure 12. The rolling bearing surface 49 allows the bearing support plate 48 to move freely in the horizontal plane, thereby mitigating bending of the drive shaft 47. All these plates are supported on the base 50 by means of several plates held in a horizontal position by anchor bolts protruding from the base 50. The lower bearing 45 is supported by the base 50. The lower bearing 45 is held on the plate 48 by adjustable bearing bolts 51 which can be adjusted to share a particular load between the main bearing 44 and the lower bearing 45.

Figure 12 shows that the rolling bearing surface 49 is a surface formed by a row of balls 52 held in a frame 53. All of the balls 52 have the same diameter. The diameter of the balls 52 is greater than the thickness of the frame 53 so that the steel plate above the balls 52 remains on the ball bearings. The top bearing plate 48 is able to roll on the balls 52. The top plate 48 and bottom plate 51 are oiled on their surfaces adjacent the balls 52.

While the preferred embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various changes may be made therein without departing from the scope of the invention. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed.

Claims (18)

1. A pair of lift-based wind turbines, wherein each wind turbine comprises:

a shaft rotatable about a vertical axis;

a blade connected to the shaft for rotation therewith, wherein the blade is disposed radially outward from the shaft at a predetermined radius; and

a braking system which applies aerodynamic braking when the system is activated;

wherein the axes of the pair of lift-based wind turbines are separated from each other by a distance less than three times the radius and greater than two times the radius, wherein the axis of a first wind turbine of the pair of lift-based wind turbines rotates in a first predetermined direction and the axis of a second wind turbine of the pair of lift-based wind turbines rotates in a direction opposite to the direction in which the one wind turbine rotates.

2. A wind turbine according to claim 1, wherein the axes of the pair of wind turbines are spaced from each other by a distance greater than twice said radius but less than twice said radius plus 3.048 meters.

3. A wind turbine according to claim 2, wherein the axes of the pair of wind turbines are spaced from each other by a distance greater than twice said radius but less than twice said radius plus 1.524 meters.

4. A wind turbine according to claim 2, wherein the axes of the pair of wind turbines are separated from each other by a distance substantially equal to two times said radius plus 0.914 meters.

5. The wind turbine of claim 1, wherein the wind turbine has a rotor solidity of greater than 30% and less than 40%.

6. A wind turbine according to claim 5, characterized in that the rotor solidity of the wind turbine is substantially 33%.

7. The wind turbine of claim 1, wherein the braking system is a fail-safe braking system.

8. The wind turbine of claim 7, wherein the braking system is automatically reset.

9. The wind turbine of claim 7, wherein said braking system comprises a pneumatic actuator.

10. A wind turbine according to claim 9, wherein in the pair of wind turbines there is a separate air compressor for providing compressed air to the aerodynamic devices of both wind turbines.

11. The wind turbine of claim 1, further comprising a third wind turbine, wherein the third wind turbine comprises:

a tower;

a shaft rotatable about a substantially horizontal axis;

a vane connected to the shaft for rotation therewith, wherein the path swept by the vane defines a rotor having upper and lower extreme heights; and

wherein the horizontal-axis wind turbine is disposed adjacent to the pair of vertical-axis wind turbines such that a lower ultimate height of the horizontal-axis wind turbine is higher than a top of the vertical-axis wind turbines.

12. A wind turbine according to claim 1, characterized in that said wind turbine is mounted in a position having a prevailing wind direction and that the line between the shafts of the pair of wind turbines is substantially perpendicular to said prevailing wind direction.

13. A wind turbine according to claim 1 adapted to generate substantially unobstructed wind flow between the wind turbines.

14. A pair of lift-based wind turbines, each wind turbine comprising:

a shaft rotatable about a vertical axis;

a vane connected to and rotatable with the shaft, wherein the vane is disposed at a predetermined radius radially outward from the shaft, and

a braking system that applies aerodynamic braking when activated;

wherein the axes of the pair of lift-based wind turbines are spaced apart from each other by a distance less than three times said radius, the axis of a first wind turbine of said pair of lift-based wind turbines rotating in a first predetermined direction and the axis of a second wind turbine of said pair of lift-based wind turbines rotating in a direction opposite to said one wind turbine rotating direction, said pair of lift-based wind turbines being adapted to generate a substantially unobstructed wind flow between the turbines.

15. A wind turbine according to claim 14, characterized in that the wind turbine is mounted in a position having a main wind direction, wherein a line between the shafts of the pair of wind turbines is substantially perpendicular to the main wind direction.

16. The wind turbine of claim 14, further comprising a third wind turbine, wherein the third wind turbine comprises:

a tower;

a shaft rotatable about a substantially horizontal axis;

a vane connected to the shaft for rotation therewith, wherein the path swept by the vane defines a rotor having upper and lower extreme heights; and

wherein the horizontal-axis wind turbine is disposed adjacent to the pair of vertical-axis wind turbines such that a lower ultimate height of the horizontal-axis wind turbine is equal to a top of the vertical-axis wind turbines.

17. The wind turbine of claim 14 wherein said wind turbine further comprises a fail-safe braking system.

18. The wind turbine of claim 17, wherein the braking system is automatically reset.