WO2008088921A2

WO2008088921A2 - Vertical windmills and methods of operating the same

Info

Publication number: WO2008088921A2
Application number: PCT/US2008/000847
Authority: WO
Inventors: Larry Frew; Raymond Browning; William B. Goldsworthy
Original assignee: Gift Technologies, Lp; Goldsworthy, Lois
Priority date: 2007-01-19
Filing date: 2008-01-22
Publication date: 2008-07-24
Also published as: WO2008088921A3

Abstract

A vertical windmill is provided including airfoils each having a leading edge, a trailing edge, a first surface between the leading edge and the trailing edge and a second surface between the leading edge and the trailing edge, where a thickness of each airfoil is defined between the two surfaces of each airfoil, and where each airfoil is symmetric about a plane intersecting both surfaces. Methods for operating vertical windmills are also provided.

Description

VERTICAL WINDMILLS AND METHODS OF OPERATING THE SAME

BACKGROUND OF THE INVENTION

[0001] The present invention relates generally to vertical windmills, and more particularly to a vertical windmill with a rotor supporting a plurality of blades, and more particularly to those blades utilizing the principle of lift to convert wind energy into rotational energy. [0002] Windmills and wind turbine machines of various designs are in use in converting wind energy to electrical energy. Design variations include windmills with horizontal axes, vertical axes, drag propulsion, aerodynamic lift, turbines and sails.

[0003] Horizontal axis wind turbines typically comprise a tall tower and a propeller or fan- like rotor mounted at the top of the tower for rotation about an axis substantially parallel to the earth's surface. Vertical windmills are more varied with cups, half cylinders, eggbeater- like blades, flat blades, paddles, blades, or turbines rotating around a vertical axis. The vertical windmill with blades may also have fixed or movable blades rotating on a central shaft directly or turbines which have a central rotor surrounded by stationary ring of vanes that serve to direct and compress air from the wind before it is directed at the rotor blades. Vertical axis wind turbines are divided generally into lift- and drag-types.

[0004] The advantage of the horizontal windmill is in the design of the propeller like turbine. The blades of the horizontal windmill are typically airfoils which provide lift. The lifting blades can spin faster than the air flow, and indeed may be supersonic at the tips, thus providing high efficiency and high rotation speed for generating electricity. [0005] A disadvantage of the horizontal axis wind turbine lies in the fact that the rotor must face either into or away from the direction of the wind and a yaw mechanism is required to rotate the rotor about the vertical axis of the tower to keep the rotor in proper alignment with the wind flow. Since a mechanical means of delivering power to the ground could cause the rotor to yaw out of alignment with the wind, energy conversion devices, such as generators; power transmission equipment; and related equipment are typically also mounted atop the tower. A structurally robust and costly tower is required to support the weight of the elevated equipment. Maintenance of horizontal axis turbines can be complex and costly because the equipment is located at the top of the tower. While horizontal axis wind turbine installations are relatively complex and expensive, they are the most common wind turbine configurations in current use. [0006] The advantage of the vertical axis windmill or turbine is that its exposure remains constant regardless of the wind direction and the system can be closer to the ground, including the generator which can be at ground level and linked mechanically to the windmill. [0007] While simple in conception and low in construction costs, the disadvantage with drag type windmills are that efficiencies are limited by geometry and opposing drag as the blades rotate in and out of the wind. Further, the torque typically changes as the blades rotate, in fact no torque will be produced to initiate rotation if the rotor is improperly aligned with the wind flow. Further, the maximum velocity of the cups or paddles of a drag-type turbine is substantially equal to the velocity of the wind. While this type of turbine can produce high torque and can be useful for pumping water and similar tasks, the speed of rotation is generally too slow for efficient production of electricity, a major use of commercial wind turbines. [0008] Lift-type vertical axis turbines rely on the lift force generated as the wind flows over an airfoil to obtain speeds exceeding the wind's velocity. The Darrieus wind turbine (i.e., the wind turbine described in U.S. Patent No. 1,835,018 to Darrieus) is the only vertical axis wind turbine manufactured commercially in volume. The most common Darrieus wind turbine looks like an eggbeater with C-shaped rotor blades attached at their top and bottom ends to a vertical central shaft. The Darrieus patent also includes a design for rectilinear blades arranged parallel to the shaft in a cylindrical drum. Darrieus turbines typically have two or three blades. Since lift forces provide the torque for rotation, the speed of the blades can exceed the speed of the wind. Darrieus wind turbines can have a speed ratio exceeding three making this type of turbine very suitable for electric power generation. The Darrieus C blade is bent and held in place at each end by its rotor. Typically for both types of Darrieus windmills the blades are airfoils that are approximately symmetrical on both surfaces and have a blunter leading edge and a sharper trailing edge. FIG. 1 shows an arrangement of such a Darrieus windmill. An airfoil 101 with a blunt leading edge 102 and a sharper trailing edge 103 is attached by a support 104 to a spindle 105 such that when the wind direction 106 is incident on the airfoil 101, lift is created in the direction 107 and the lift rotates the spindle 105 in the rotational direction 108. The airfoil 101 is aligned approximately tangentially to the axis of rotation of the spindle 105. If the airfoil 101 is directly on the windward or leeside of the windmill, no lift is generated. As the leading edge of the airfoil 101 rotates into the wind or out of the wind, lift is generated across the airfoil 101 into the rotational direction 108 providing power.

[0009] While vertical axis windmill installations are potentially less complex and costly than horizontal axis windmills, the lack of commercial success of vertical axis windmills is indicative of substantial drawbacks of this type of equipment. Since no tower is required, a major cost of a windmill installation is eliminated. However, wind speeds close to the ground are very low and turbulent due to boundary layer effects. As a result, the output of a vertical axis windmill, particularly the lower half of the rotor, is limited and the overall efficiency is relatively low. [0010] A great deal of the cost of windmills results from high strength materials that are used to withstand high stresses, which result from the high speed at which they operate. Windmills are also subject to very high amplitude and high frequency vibrations, which result in fatigue to the various components of the wind turbines. To minimize these vibrations, the blades and other rotational components of these systems must be perfectly balanced. Additionally, windmills are exposed to adverse weather conditions such as high winds, snow, ice and ultraviolet radiation. Substantial engineering and maintenance resources have to be devoted to the design and operation of these windmills so that they can withstand the multitude of forces, as well as the adverse conditions, to which they will be subjected. Windmills are often severely damaged by high wind conditions.

[0011] Windmills have a relatively small range of wind speeds within which they will operate efficiently, typically 20 to 40 miles per hour. At lower speeds the electricity generation is inefficient and at higher speeds the rotor is going too fast and must be damped electrically to prevent damage. Obviously, the necessity for such a high minimum wind speed greatly reduces the geographical areas where windmills can be used economically. Additionally, the necessity for providing the highest average wind speeds over the time of operation requires the windmills being set high above the ground on very tall masts. Tall masts further increase the cost of installation and maintenance and also make the spaces they are on unsightly. Additionally, another undesirable result of the tall masts is that bird kill is considerably increased. [0012] If windmills are sited too close together, then turbulence and shadowing of the wind occurs as the wind veers around an array of windmills. This limits the density of the windmills at any site. SUMMARY OF THE INVENTION

[0013] In an exemplary embodiment, the present invention relates generally to vertical windmills, and more particularly to a vertical windmill with a rotor supporting a plurality of airfoils, and more particularly to those airfoils utilizing the principle of lift to convert wind energy into rotational energy, and more particularly having the maximum lift from those airfoils near the windward and leeward sides of the rotor, and more particularly the airfoils of the vertical windmill are symmetrical airfoils with the symmetry between the leading and trailing edges, m another exemplary embodiment of the invention, the attack angle of the airfoils of the vertical windmill are positioned to maximize power derived from lift across the sum of the airfoils of the windmill. In another exemplary embodiment of the invention, lift on an individual airfoil is near maximum when the airfoil position is on the direct windward or leeward side of the windmill. In another exemplary embodiment of the invention, the transduction frommechanical to electric power is achieved by a linear electric generator or other electrical to mechanical power transducer. In a further exemplary embodiment of the invention, the mechanical to electrical power transducer may provide magnetic levitation for the bearing surface, hi another exemplary embodiment of the invention, the airfoils can be recessed in to a protective structure to provide a graduated decrease in airfoil area under higher wind conditions, hi another exemplary embodiment of the invention, the array of windmills is protected from high winds by recessing behind a protective structure. In another exemplary embodiment of the invention, the vertical windmills are closely arranged in an array of windmills minimizing the land area required and reducing the environmental impact. In another exemplary embodiment, the windmills are closely arranged in an array to minimize shadowing efforts, hi another exemplary embodiment of the invention, the windmill airfoils are formed by pultruding glass composites. In a further exemplary embodiment of the invention, the windmill airfoils are lightweight strong bent and stressed panels. In yet another exemplary embodiment, the windmill has pultruded glass fiber airfoils and airfoils which are strong lightweight bent panels under stress. In another exemplary embodiment of the invention, the rotor size of the vertical windmill may be expanded to include a large area with many airfoils firstly because the magnetic levitation and power transduction does not require a central spindle to support the rotor. [0014] In a further exemplary embodiment of the invention, the airfoils have supporting members between the airfoils to increase stiffness. In another exemplary embodiment of the invention, the airfoils have a smaller cross-section at the top and thus can be operated at very high wind speeds when the lower part of the airfoils are protected by a shield. [0015] In another exemplary embodiment, the windmill may be self-starting with three or more airfoils from any rotor position.

[0016] In an exemplary embodiment, the wind engine design is scalable, both in terms of overall size and in terms of the number of airfoils utilized. The wind engine design may be configured in a smaller radius for higher RPM operation, or larger diameter for lower RPM operation and higher torque, or it may be built on a very large scale for power-grid applications as no central spindle is required.

[0017] In another exemplary embodiment, a vertical windmill is provided including a generally vertical rotation axis, and a plurality of airfoils spaced apart from said generally vertical axis and rotating about said generally vertical axis, wherein each airfoil includes a central longitudinal axis, wherein each airfoil is symmetric about a plane along said central longitudinal axis, and wherein each airfoil comprises a concave surface opposite a convex surface. In a further exemplary embodiment, a vertical windmill is provided including a generally vertical rotation axis, and a plurality of airfoils spaced apart from said generally vertical axis and rotating about said generally vertical axis, wherein each airfoil comprises a central longitudinal axis, wherein each airfoil central longitudinal axis is not perpendicular to a plane perpendicular to said rotation axis. In yet a further exemplary embodiment, a vertical windmill is provided including a generally vertical rotation axis, a plurality of airfoils spaced apart from said generally vertical axis and rotating about said generally vertical axis, and a magnetic levitation bearing, wherein the windmill rotates about the magnetic levitation bearing. In yet another exemplary embodiment, the magnetic levitation bearing is a mechanical to electrical transducer for converting the rotational energy of the windmill into electrical energy. [0018] In another exemplary embodiment, a vertical windmill is provided. The vertical windmill has a generally vertical rotational axis and a plurality of airfoils spaced apart from the generally vertical rotational axis. The plurality of airfoils rotates about the generally vertical rotational axis. Each airfoil includes a central longitudinal axis such that each airfoil is symmetrical about a plane along each central longitudinal axis. Furthermore, each airfoil includes a concave surface opposite a convex surface. In yet another exemplary embodiment, a vertical windmill is provided having a generally vertical rotational axis and a plurality of airfoils spaced apart from the generally vertical rotational axis and rotating about the generally vertical rotational axis. Each airfoil includes a central longitudinal axis such that each airfoil's central longitudinal axis is not perpendicular to a plane perpendicular to the generally vertical rotational axis.

[0019] In yet a further exemplary embodiment, a vertical windmill is provided, including a generally vertical rotational axis and a plurality of airfoils spaced apart from the generally vertical rotational axis and rotating about the generally vertical rotational axis. The vertical windmill also includes a magnetic levitation bearing such that the windmill rotates about the such magnetic levitation bearing. In yet a further exemplary embodiment, the magnetic levitation bearing may be part of a mechanical to electrical transducer for converting the rotational energy of the windmill into electrical energy.

[0020] In yet another exemplary embodiment, a vertical windmill is provided including a vertical rotational axis and a plurality of airfoils spaced apart from the generally vertical rotational axis and rotating about the generally vertical rotational axis. With this exemplary embodiment, each of the airfoils is a bent stress panel bent along its longitudinal axis. [0021] In another exemplary embodiment, a vertical windmill is provided including a generally vertical rotation axis, and a plurality of airfoils spaced apart from said generally vertical axis and rotating about said generally vertical axis, wherein each of said airfoils is a bent stress panel bent along its longitudinal axis.

[0022] In an exemplary embodiment a vertical windmill is provided including a generally vertical axis of rotation and a plurality of airfoils rotating about the axis of rotation. Each of the airfoils includes a leading edge and a trailing edge such that the leading edge of each airfoil is further from the axis or rotation than the trailing edge of each airfoil. Each airfoil includes a first surface extending between its leading and trailing edges and a second surface between its leading and trailing edges and a thickness between the first and second surfaces. Each airfoil is symmetric in cross-section about a plane intersecting its first and second surfaces. In another exemplary embodiment, each airfoil has a leading edge identical to its trailing edge. In yet another exemplary embodiment, the plane divides each airfoil in half. In a further exemplary embodiment, the windmill includes an upper end over a lower end, and at least one of the airfoils generates a force including a component directed toward the lower end. In yet a further exemplary embodiment, the central longitudinal axis of at least one airfoil is generally parallel to the axis of rotation. In another exemplary embodiment, the axis of the at least one airfoil is not parallel to the axis of rotation. In yet another exemplary embodiment, each airfoil includes an upper end and a lower end and a length there between, and at least one of the airfoils is linear along the length. In yet a further exemplary embodiment, each airfoil includes an upper end and a lower end and a length there between, and at least one of the airfoils curves along said length. In one exemplary embodiment, at least one of the airfoils is a bent panel. In another exemplary embodiment, the leading and trailing edges of each of the airfoils each intersect a separate radius extending from the axis of rotation. In yet another exemplary embodiment the first surface of each airfoil is convex and the second surface of each airfoil is concave. In yet a further exemplary embodiment the windmill also includes a plate on which the airfoils are mounted, and each of the airfoils is retained on the plate by at least a guy connected to the airfoils and the plate. In another exemplary embodiment, the windmill further includes a plate supporting the airfoils and a magnetic levitation bearing which includes an inner portion including a first magnetic section within an outer portion including a second magnetic portion, whereby the inner portion is rotatable relative to the outer portion. Moreover the first and second magnetic sections repel each other, and wherein the plate is coupled to one of the inner and outer portions and the other of the inner and outer portions is coupled to a support for supporting the windmill. In a further exemplary embodiment, the first and second magnetic sections are part of a transducer for converting rotational energy to electrical energy. In another exemplary embodiment, the outer portion includes a V-shaped section and the inner portion includes a V-shaped section such that one of the V-shaped sections is nested within the other of the V-shaped sections, hi a yet a further exemplary embodiment, the windmill includes a shield structure and the airfoils are part of a rotor, and the rotor is retractable in and extendible from the shield structure in response to a wind strength to which the rotor is exposed or in response to a rotational speed of the rotor, hi another exemplary embodiment the airfoils are part of a rotor and the windmill further includes a gantry supporting the rotor. In yet another exemplary embodiment one of the airfoils includes a chord extending from its leading edge to its trailing edge such that the chord is at a 45° angle relative to a radius extending from the axis of rotation and intersecting a midpoint of the chord. In yet a further exemplary embodiment one or both of the leading and trailing edges of an airfoil is non-uniform.

[0023] In another exemplary embodiment a vertical windmill is provided including a generally vertical axis of rotation and a plurality of airfoils rotating about the axis or rotation. Each airfoil includes a leading edge and a trailing edge and the leading edge of each airfoil is further from the axis of rotation than the trailing edge of each of each airfoil. A first surface extends between the leading and trailing edge of each airfoil, and a second surface extends between the leading and trailing edges of each airfoil, and the trailing edge of each airfoil is a mirror image of the leading edge of such airfoil.

[0024] In yet another exemplary embodiment a vertical windmill is providing including a rotor including a plurality of airfoils rotating about an axis of rotation of the rotor and a shield surrounding the rotor for protecting the rotor from strong winds, wherein the rotor is retractable within the shield and extendible from the shield.

[0025] In a further exemplary embodiment a method of operating a vertical windmill is provided. The method includes providing a plurality of airfoils on a rotor of the windmill for providing a lift force for rotating the rotor when exposed to wind; positioning at least one of the airfoils so as to generate a lift force having a downward component when the rotor is rotating, and exposing the rotor to the wind whereby the airfoils cause said rotor to rotate and the at least one airfoil of the plurality of airfoils to generate a lift force having a downward component whereby the downward component reduces vibrations of the windmill. In yet a further exemplary embodiment, the method further includes retracting the rotor in a shield when the wind has a speed above a predetermined level or the windmill rotates at a rotational speed above a predetermined level. In yet another exemplary embodiment positioning at least one of the plurality of airfoils so as to generate a lift force having a downward component includes positioning the at least one airfoil at an angle whereby the at least one airfoil is at a non-vertical incline. In yet a further exemplary embodiment, the method further includes selecting the angle as a function of a desired level of the downward component.

[0026] In another exemplary embodiment a method is provided for operating a vertical windmill. The method includes providing a plurality of airfoils on a rotor of the windmill for providing a lift force for rotating the rotor when exposed to wind. The method further includes exposing the rotor to the wind whereby the airfoils cause said rotor to rotate, and retracting at least partially the airfoils in a shield when a rotational speed of the rotor exceeds a first level or when the wind has a speed exceeding a second level. In yet another exemplary embodiment, the method further includes further retracting the airfoils within the shield when the rotor rotational speed exceeds a third level or when the wind has a speed exceeding a fourth level, where the third level is greater than the first level and where the fourth level is greater than the second level.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0027] The invention will be better understood and the objects and advantages of the present invention will become apparent when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawings wherein:

[0028] FIG. 1 is a partial top view of the airfoil action for a Darrieus windmill;

[0029] FIG. 2 is a cross-sectional view of a symmetrical airfoil;

[0030] FIG. 3 A in a plan view of a plurality of airfoils arranged on a rotor in an exemplary embodiment vertical windmill;

[0031] FIG. 3B is a plan view of a plurality of airfoils arranged on a rotor of another exemplary embodiment vertical windmill.

[0032] FIG. 4 in a partial elevation view of an airfoil placed on a rotor in an exemplary embodiment vertical windmill;

[0033] FIG. 5 illustrates a relative direction of lift for an inclined airfoil;

[0034] FIG. 6 illustrates a plurality of exemplary embodiment airfoils attached to a bottom and top plate of a rotor; [0035] FIG. 7 is a side view of a plurality of foils attached to a rotor and supported by a gantry;

[0036] FIG. 8 is a side view of a rotor cage with magnetic levitation bearings;

[0037] FIG. 9 is a perspective view of a large area airfoil carousel;

[0038] FIG. 1OA illustrates a flat panel that can be bent to form the airfoils shown in FIGS.

1OB and 1OC;

[0039] FIG. 1OB is a side view of an exemplary stress panel airfoil for use in an exemplary embodiment vertical windmill;

[0040] FIG. 1OC is a side view of another exemplary embodiment stress panel airfoil for use in an exemplary embodiment vertical windmill;

[0041] FIG. 1OD is a front view of another exemplary embodiment airfoil of the present invention;

[0042] FIG. 11 is a top view of an array of windmills;

[0043] FIG. 12 is a side view of an exemplary embodiment recessing windmill with a cylindrical wind shield structure; and

[0044] FIG. 13 is a partially cut away view of a magnetic levitation bearing supporting a vertical windmill.

DETAILED DESCRIPTION OF THE INVENTION

[0045] In an exemplary embodiment, the invention provides a windmill generating electricity. An exemplary embodiment invention is characterized by a vertical windmill with a rotor supporting a plurality airfoils, hi another exemplary embodiment, these airfoils utilize the principle of lift to convert wind energy into rotational energy, and more particularly they have the maximum lift near the windward and leeward sides of the rotor. In an exemplary embodiment, the airfoils of the vertical windmill are symmetrical airfoils with the symmetry between the leading and trailing edges. The windmill may be further characterized by a rotor assembly holding the airfoils which retracts into a protective structure under high wind conditions. The windmill may be further characterized by having a mechanical to electrical power transducer that also acts as a magnetic levitation bearing.

[0046] FIG. 2 illustrates a cross-section of a symmetrical airfoil 201. The leading edge 202 of the symmetrical airfoil 210 is essentially the same shape as the trailing edge 203. This essential fact can apply to airfoils of a wide variety of actual shape: from the thicker airfoil shown in FIG. 2, to airfoils with thinner cross-sections, or airfoils formed from bent flat panels, or even fabrics such as in a sail. The direction of the wind 204 perpendicular, i.e., at a 0° angle of attack to the mirror axis, i.e., the axis of symmetry 206, gives a resultant lift direction 205 along the axis of symmetry 206. Thus, wind from either direction perpendicular to the axis of symmetry gives the same resultant lift.

[0047] FIG. 3 A illustrates in plan how a plurality of symmetric airfoils 301 are preferably arranged on a rotor 302 in a vertical windmill. The plurality of airfoils radiate outwardly from a central shaft 303. The symmetric airfoils 301 are preferably all of the same size and style and are equidistantly spaced around the central shaft 303. The symmetrical airfoils 301 are arranged so that the direction across the symmetric airfoils 301 from their leading edge to their trailing edge is approximately in line with the shaft 303. Some deviation from this direction may be found in certain arrangement of airfoils to be more optimum due to the combination of effects over the configurations of airfoils 301, but in an exemplary embodiment the direction of the airfoils 301 is directly out from the center of the rotor. The direction of rotation 304 of the assembly including the airfoils 301, the rotor 302, and the shaft 303 in a wind blowing in the direction 305 is towards the convex side of the airfoils 301. In an exemplary embodiment, the preferred number of airfoils 301 arranged on a rotor is greater than three. In another exemplary embodiment, the symmetrical airfoils 301 are arranged so that the angle between a chord 320 connecting the leading edge to the trailing edge of each airfoil is at an angle of 45° to a radius 324 intersecting a midpoint 326 of the chord of such airfoil, as for example shown in FIG. 3B. [0048] FIG. 4 illustrates in elevation how an airfoil 401 is placed for attachment to a rotor 402 in a vertical windmill with rotation around a vertical axis 403. The airfoil 401 can be of any length and as illustrated in FIG. 4, it can be attached perpendicular to the plane of the rotor 403 and in the same direction as the axis of rotation 403 which is nominally vertical. [0049] FIG. 5 illustrates the relative direction of lift 501 for an inclined airfoil 502. With an inclined airfoil 502 attached to a rotor 503 at an angle 504 less than a right angle, the resultant direction of lift 501 for a wind blowing into the page in the direction 505 has a component of force downwards. By selecting the angle 504, this downward component of force can be arranged to oppose any unbalancing couple or resultant forces created by the drag forces on other airfoils attached to the rotor. This balance of forces then reduces vibration and shock to the rotor spindle or rotating shaft during wind gusting and helps prevent the rotor assembly lifting off its bearings in a high wind.

[0050] FIG. 6 illustrates a plurality of airfoils 601a, b, c attached with a top plate 602 and a bottom plate 603 that would accept a spindle through apertures 604a, b to form a rotating assembly 605. The top plate and bottom plates hold the airfoils 601a, b, c in a fixed relative position around the assembly 605 and in a fixed relative orientation to the axis of rotation 606. [0051] FIG. 7 illustrates a plurality of foils 701a, b attached to a top plate 702 and a bottom plate 703 connected by a spindle 704 to form a rotor assembly 705. The top of the assembly is supported by a gantry 706 having a top arm 707 with a bearing holding the spindle 704 in a fixed direction to the vertical. The bottom of the rotor assembly 705 is supported by a bearing and gear assembly 708 that can be connected to an electrical generator. The rotor assembly 705 as it is not self-supporting in an exemplary embodiment, can be made very lightweight and thus can spin at high speeds. The gantry can be made of scaffolding and need not cause significant turbulence when directly to the windward of the rotator assembly. It can be appreciated by those ordinarily skilled in the art that a number of gantry designs would be suitable in different circumstances.

[0052] An alternative exemplary embodiment of a rotor assembly which is self-supporting but still lightweight is illustrated in FIG. 8. A top plate 801 is attached to a bottom plate 802 using a plurality of struts 803a, b, c and guys 804 to form a cage in which airfoils can be attached between the top plate 801 and the bottom plate 802. The rotor cage has no central spindle and the bottom plate 802 is supported by a circular magnetic levitation bearing 805 allowing it to rotate freely.

[0053] A large rotor cage that is a carousel for mounting a large plurality of airfoils is illustrated in FIG. 9. An annular top plate 901 is attached to an annular bottom plate 902 using a plurality of rigid supports 903 and braced by a system of guy wires 904. The guy wires 904 may be used in a variety of configurations with the rigid supports 903, the annular top plate 901, and the annular bottom plate 902 to form a self-supporting stiff carousel that a large plurality of airfoils can be attached to. A single exemplary airfoil 905 is shown attached between the annular top plate 901 and the annular bottom plate 902. Multiple such airfoils may be inserted between the top and bottom annular plates. The carousel has no central spindle and can be mounted upon a magnetic levitation bearing allowing it to rotate freely.

[0054] It will be apparent to those ordinarily skilled in the art that the wind turbine apparatus of the invention can be made in a large variety of desired sizes. The apparatus may have a diameter from several feet to hundreds of feet or even greater, if desired. The height may also vary, for example, from about 1 foot to 30 feet, or more. As the lift from the airfoils is on the windward and leeward sides of the windmill, a large number of airfoils mounted on a large carousel will not interfere significantly with each other and the airfoils can thus be spaced close together improving wind collection efficiency.

[0055] hi a further exemplary embodiment, lightweight, yet strong airfoils can be formed by bent stressed panels of fiberglass or similar materials. A flat panel 1001 as shown in

FIG. 1 OA which may be a fiberglass panel or a ribbed material with stays like a sail can be bent to form a lightweight symmetric stress panel airfoil 1002 as shown in FIG. 1OB that can be attached in this shape to a top and bottom plate of a rotor assembly. Other variations of the airfoil shape can be implemented including a panel with a double bend leading to a complex stress panel airfoil 1003, as for example shown in FIG. 1OC which when mounted on an exemplary embodiment vertical windmill of the present invention, would have a resultant downward force in a cross wind. In yet a further exemplary embodiment, the leading and/or trailing edges 1020 of the airfoil 1004 may be non-uniform, as for example they be scalloped as shown in FIG. 10D. Applicants believe that the non-uniform edges will reduce the drag of the airfoil as they reduce the surface area of the airfoil. Consequently, the drag on the windmill is reduced. In addition, they reduce the wind generated noise as the windmill rotates by affecting the frequency of the noise.

[0056] Exemplary embodiment airfoils may be made from various materials. For example they may be formed a metallic material, a matrix material, and/or a composite material as for example a material including glass fibers. These blades may be formed by various methods including pultrusion.

[0057] Because the lift is derived from the directly windward and leeward sides of the windmill, there is an important geometric consideration in the arrangement of windmills in an array. In FIG. 11, a plurality of vertical windmills 1102 are arranged in an array 1101. Windmills are often sited in areas with a prevailing wind. This wind will veer from the prevailing direction by a quarter circle. The array 1101 is thus sited such that the vertical windmills 1102 form an approximate line perpendicular to the prevailing wind direction and the likely wind veer directions 1103. If a Darrieus type machine is used, then the spacing of the windmills must be sufficient to prevent the shadowing of the windmills by other windmills as the wind veers around. With an exemplary embodiment, the vertical windmills described herein have a spacing 1104 which can be very close. The wind as it veers over a quarter to each side of the prevailing direction still is incident on the lifting airfoils because they are on the windward and leeward sides and unshadowed by the nearest neighbor windmill. In an exemplary embodiment, the array of exemplary windmills can thus be spaced less than two diameters apart with little effect on the efficiency of the array.

[0058] FIG. 12 illustrates a recessing windmill and cylindrical wind shield structure. A windmill 1201 is mounted within a cylindrical wind shield structure 1202 such that the windmill 1201 can be elevated up and down in the vertical direction 1203. In low wind conditions the windmill 1201 can be fully elevated out of the windshield structure 1202 and can be gradually recessed as the wind strengthens. In a full storm, the windmill 1201 can be fully recessed into the wind shield structure 1202 for protection. The elevation and retraction of the windmill out and into the shield may be automated such that the amount of elevation is a function of the rotational speed of the windmill. For example, as the rotational speed increases beyond a predetermined first level, the windmill is retracted to a desired level within the shield so as to reduce the rotational speed of the windmill. If the windmill speed exceeds another desired level, the windmill may be further retracted within the shield so as to prevent the windmill from rotating at speeds that may be catastrophic to the windmill. The elevating action not only protects the windmill 1201 from damage but serves to regulate the speed of its rotor assembly from low to high wind speeds. It will be appreciated that the wind shield structure 1202 can be constructed in many different shapes, styles and materials without altering the fundamental nature of the invention. [0059] hi another exemplary embodiment, an exemplary embodiment vertical windmill 1302 is supported by magnetic levitation bearings, as for example shown in FIG. 13. In an exemplary embodiment, the magnetic levitation bearing 1303 includes an outer portion 1304 formed around an inner portion 1306. The two portions repel each other. In the shown exemplary embodiment, the outer portion is an annular member having an upper end surface 1307 and a lower end surface 1308 extended radially inward and toward each other defining a V-shaped section in cross-section. The inner portion also has an upper annular surface 1310 and a lower annular surface 1312 which extend radially outward in a direction away from each other also defining a V-shaped section in cross-section complementary to the V- shaped section defined by the upper and lower end surfaces of the outer portion. In this regard, the outer portion V-shaped section nests within the inner portion V-shaped section improving the stability of the bearing during operation. In the shown exemplary embodiment, the outer member upper surface is complementary to the inner member upper surface, and the outer member lower surface is complementary to the inner member lower surface. In another exemplary embodiment, the orientation of the V-shaped sections of the inner and outer portions may be reversed such that the inner portion V-shaped section nests within the outer portion V-shaped section. [0060] Magnets 1316 are mounted on the upper and lower surfaces of the outer member. Repelling magnets 1318 from those mounted on the outer member are mounted on the inner and lower surface of the inner member. In this regard, the magnets repel each other causing the inner member to remain separate and suspended from the outer member and allowing it to freely rotate relative to the outer member without any friction between the two members. In an exemplary embodiment, magnets 1316 and 1318 are rare earth magnets with a field strength of at least about 13,000 Gauss. In another exemplary embodiment, the V-shaped sections themselves are magnetic and repel each other. [0061] In the shown exemplary embodiment, the inner member is mounted on a shaft or spindle 1319 of the vertical windmill, while the outer member may be mounted to a stationary structure. In the exemplary embodiment, two magnetic levitation bearings may be used, an upper bearing 1320 and a lower bearing 1322, which may be the same as the upper bearing, as for example shown in FIG. 13. In yet a further exemplary embodiment, the portion of the inner section of the bearing defining the upper surface may be separate from the portion defining the lower surface. In another exemplary embodiment, the exemplary embodiment upper and lower magnetic levitation bearings 1320 and 1322 may be incorporated in a mechanical to electrical transducer 1340 which is used to convert the mechanical rotational energy generated by the vertical windmill into electrical energy.

[0062] The apparatus of this invention is fully functional for generating electrical energy even in very high wind conditions. Yet, the apparatus is capable of generating electrical energy even at low wind speeds.

[0063] While there is provided herein a disclosure of exemplary embodiments of this invention, it is not desired to limit the invention to the exact construction, dimensional relationships and operation shown and described. Various modifications, alternative constructions, changes and equivalents will readily occur to those skilled in the art and may be employed, as suitable, without departing from the true spirit and scope of the invention. Such changes might involve alternative materials, components, structural arrangements, sizes, shapes, forms, functions, operational features or the like.

Claims

CLAIMS:

1. A vertical windmill comprising: a generally vertical axis of rotation; a plurality of airfoils rotating about said axis, each of said airfoils comprising a leading edge and a trailing edge wherein the leading edge of each of said airfoils is further from said axis than the trailing edge of each of said airfoils, wherein a first surface extends between said leading and trailing edges of each of said airfoils, and wherein a second surface extends between said leading and trailing edges of each of said airfoils, wherein a thickness of each of said airfoils is defined between said first and second surfaces of each of said airfoils, and wherein each of said airfoils has a cross-section symmetric about a plane intersecting said first and second surfaces of each of said airfoils.

2. The windmill as recited in claim 1 wherein for each of said airfoils, said leading edge is identical to said trailing edge.

3. The windmill as recited in claim 1 wherein for each of said airfoils, said plane divides each of said airfoil in half.

4. The windmill as recited in claim 1 comprising an upper end over a lower end, wherein at least one of said airfoils generates a force comprising a component directed toward the lower end.

5. The windmill as recited in claim 1 wherein at least one of said airfoils comprises a central longitudinal axis, wherein the central longitudinal axis of said least one of said airfoils is generally parallel to said axis of rotation.

6. The windmill as recited in claim 1 wherein at least one of said airfoils comprises a central longitudinal axis, wherein the central longitudinal axis of said at least one of said airfoils is not parallel to said axis of rotation.

7. The windmill as recited in claim 1 wherein at least one of said airfoils comprises an upper end and a lower end and a length there between, wherein said at least one of said airfoils is linear along said length.

8. The windmill as recited in claim 1 wherein at least one of said airfoils comprises an upper end and a lower end and a length there between, wherein said at least one of said airfoils curves along said length.

9. The windmill as recited in claim 1 wherein at least one of said airfoils is a bent panel.

10. The windmill as recited in claim 1 wherein the trailing and leading edges of each of said airfoils intersect a separate radius extending from said axis of rotation.

11. The windmill as recited in claim 1 wherein the first surface is convex and the second surface is concave.

12. The windmill as recited in claim 1 wherein said leading edge is a mirror image of trailing edge and wherein the first surface is convex and the second surface is concave.

13. The windmill as recited in claim 1 further comprising a plate on which said airfoils are mounted, wherein each of said airfoils is retained on the plate by at least a guy connected to the airfoils and the plate.

14. The windmill as recited in claim 1 further comprising: a plate supporting said plurality of airfoils; and a magnetic levitation bearing comprising an inner portion comprising a first magnetic section within an outer portion comprising a second magnetic section, said inner portion being rotatable relative to said outer portion, wherein said first and second magnetic sections repel each other, and wherein said plate is coupled to one of said inner and outer portions and said other of said inner and outer portions is coupled to a support for supporting said windmill.

15. The windmill as recited in claim 14 wherein said first and second magnetic sections are part of a transducer for converting rotational energy to electrical energy.

16. The windmill as recited in claim 14 wherein said outer portion comprises a V- shaped section and said inner portion comprises a V-shaped section, wherein one of said V- shaped sections is nested within the other of said V-shaped sections.

17. The windmill as recited in claim 1 further comprising a shield structure, wherein said plurality of airfoils are part of a rotor, and wherein said rotor is retractable in and extendible from said shield structure in response to at least one of said wind strength to which said rotor is exposed and said rotational speed of said rotor.

18. The windmill as recited in claim 1 wherein said plurality of airfoils are part of a rotor and wherein said windmill further comprises a gantry supporting said rotor.

19. The windmill as recited in claim 1 wherein one of said airfoils comprises a chord extending from said leading edge to said trailing edge of said airfoil, wherein said chord is at a 45° angle relative to a radius extending from said axis of rotation and intersecting a midpoint of said chord.

20. The windmill as recited in claim 1 wherein at least one of said leading and trailing edges is non-uniform.

21. The windmill as recited in claim 20 wherein the other of said leading and trailing edges is non-uniform.

22. A vertical windmill comprising: a generally vertical axis of rotation; a plurality of airfoils rotating about said axis, each of said airfoils comprising a leading edge and a trailing edge wherein the leading edge of each of said airfoils is further from said axis than the trailing edge of each of said airfoils, wherein a first surface extends between said leading and trailing edges of each of said airfoils, and wherein a second surface extends between said leading and trailing edges of each of said airfoils, wherein each of said airfoil trailing edge is a mirror image of said each of said airfoil leading edge.

23. A vertical windmill comprising: a rotor comprising a plurality of airfoils rotating about an axis of rotation; and a shield surrounding said rotor for protecting said rotor from strong winds, wherein said rotor is retractable within said shield and extendible from said shield.

24. A method of operating a vertical windmill comprising: providing a plurality of airfoils on a rotor of said windmill for providing a lift force for rotating said rotor when exposed to wind; positioning at least one of said plurality of airfoils so as to generate a lift force having a downward component when said rotor is rotating; and exposing said rotor to the wind whereby said airfoils cause said rotor to rotate and said at least one airfoil of said plurality of airfoils to generate a lift force having a downward component whereby said downward component reduces vibrations in said windmill.

25. The method as recited in claim 24 further comprising retracting said rotor in a shield when said wind comprises a speed above a predetermined level or said windmill rotates at a rotational speed above a predetermined level.

26. The method as recited in claim 24 wherein positioning at least one of said plurality of airfoils so as to generate a lift force having a downward component comprises positioning said at least one airfoil at an angle whereby said at least one airfoil is at a non- vertical incline.

27. The method as recited in claim 26 further comprising selecting said angle as a function of a desired level of said downward component.

28. A method of operating a vertical windmill comprising: providing a plurality of airfoils on rotor of said windmill for providing a lift force for rotating a rotor of said rotor when exposed to wind; exposing said rotor to the wind whereby said airfoils cause said rotor to rotate; and retracting at least partially said plurality of airfoils in a shield when a rotational speed of said rotor exceeds a first level or when said wind has a speed exceeding a second level.

29. The method as recited in claim 28 further comprising further retracting said plurality of airfoils within said shield when said rotor exceeds a third level or when said wind has a speed exceeding a fourth level, wherein said third level is greater than said first level and said fourth level is greater than said second level.