Patent Application
20120007366
Embodiments of the present invention relate generally to wind power generation, and more specifically to vertical axis wind turbines.
Over 87% of the land mass of the Earth experiences Class 2 wind speeds, which are too weak to cost effectively generate energy with existing wind turbine technology. Class 2 winds, which blow at 4.5 meters per second, contain approximately 100 to 150 Watts of usable power per square meter. By comparison, Class 6 winds, required for most conventional turbines to operate cost effectively, contain 1,000 Watts of power per square meter.
A vertical axis wind turbine according to an embodiment of the present invention includes a hub configured to rotate about an axis of rotation substantially aligned with a gravitational force, a first rotor arm rigidly coupled to the hub, a second rotor arm rigidly coupled to the hub, a first rotor blade pivotably coupled to the first rotor arm at a first hinge joint, such that the first rotor blade rotates freely about the first rotor arm at the first hinge joint, the first rotor blade having a first upper end and a first lower end, and a second rotor blade pivotably coupled to the second rotor arm at a second hinge joint, such that the second rotor blade rotates freely about the second rotor arm at the second hinge joint, the second rotor blade having a second upper end and a second lower end. According to such embodiment, a first length of the first rotor blade from the hinge joint to the first lower end is longer than a second length of the first rotor blade from the hinge joint to the first upper end, a third length of the second rotor blade from the hinge joint to the second lower end is longer than a fourth length of the second rotor blade from the hinge joint to the second upper end, the first hinge joint is the only point of contact between the first rotor blade and any other part of the vertical axis wind turbine, and the second hinge joint is the only point of contact between the second rotor blade and any other part of the vertical axis wind turbine.
While multiple embodiments are disclosed, still other embodiments of the present invention will become apparent to those skilled in the art from the following detailed description, which shows and describes illustrative embodiments of the invention. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not restrictive.
While the invention is amenable to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and are described in detail below. The intention, however, is not to limit the invention to the particular embodiments described. On the contrary, the invention is intended to cover all modifications, equivalents, and alternatives falling within the scope of the invention as defined by the appended claims.
To generate the same amount of energy in Class 2 winds as can be generated in Class 6 winds, a much larger rotor area, or “capture area,” is employed. The power output of a wind generator is proportional to the swept area of the rotor, such that when the swept area is doubled, the power output will also double, for a given wind speed. The power output of a wind generator is also proportional to the cube of the wind speed, such that doubling the wind speed causes the power output to increase by a factor of eight, for a given swept area. This example illustrates that even relatively small increases in wind speed for a given rotor swept area can result in very large power increases, and hence very large increases in wind forces experienced by the rotors and other hardware. As such, most existing wind generators are unable to operate across multiple categories of wind speeds without a significant risk of failure.
According to an embodiment of the present invention, a wind turbine changes its rotor area (e.g. “swept area”), in order to match and/or accommodate wind speed changes.
Turbine 100 further includes one or more rotor arms 4 coupled to the hub 3, according to embodiments of the present invention. For example, the rotor arms 4 may be rigidly coupled to the hub 3 via one or more attachment bolts 10. The hub 3 may be an alternator, and/or may be part of an alternator, such that rotation of the rotor arms 4 rotates the alternator 3 and generates electrical energy, according to embodiments of the present invention. The hub 3 may be coupled to a mounting plate 2, and the mounting plate 2 may be coupled and/or formed integrally with a support post 1 or tower, and the support post may be coupled and/or formed integrally with a mount 13, according to embodiments of the present invention. Hub 3 may also be a gearing device used to drive mechanical equipment such as, for example, a water pump or other rotating machinery.
As used herein, the term “coupled” is used in its broadest sense to refer to elements which are connected, attached, and/or engaged, either directly or integrally or indirectly via other elements, and either permanently, temporarily, or removably. As used herein, the terms “rotatably coupled” and “pivotably coupled” are used in their broadest sense to refer to elements which are coupled in a way that permits one element to rotate or pivot with respect to another element.
A rotor blade 6 may be rotatably and/or pivotably coupled to the rotor arm 4. The pivotable coupling between rotor blade 6 and rotor arm 4 may be accomplished with a hinge joint 5, according to embodiments of the present invention. The rotor blade 6 rotates freely about the rotor arm 4 at the hinge joint 5, according to embodiments of the present invention. The rotor blade 6 rotates from an upright or vertical position, shown in solid lines in
The rotor blade 6 includes a top length 14 extending between the hinge pivot point 5 and the top 15 of the rotor blade 4, and also a bottom length 16 extending between the hinge pivot point 5 and the bottom 17 of the rotor blade 4, according to embodiments of the present invention. The length D of the bottom length 16 is larger than the length C of the top length 14, according to embodiments of the present invention. This has the effect of unbalancing the weight of the blade so that one end, as measured from the hinge pivot 5, is heavier than the other. The rotor blade 6 is attached to the rotor arm 4 in such a way that the long end (heavy end) is in the downward position.
As the rotor blade 6 and rotor arm 4 rotate about the axis 12, a centrifugal force is applied to the rotor blade 6; when the rotor blade 6 is of uniform cross section and density (which also corresponds to the simplest and lowest cost rotor blade 6 construction), this centrifugal force may be modeled as applied to the midpoint of the rotor blade 6 between the top 15 and bottom 17, in a direction away from the axis of rotation 12. Because length D is larger than length C, the midpoint of the rotor blade 6 occurs below the hinge pivot point 5, which causes the bottom length 16 to rotate outwardly (e.g. away from axis 12) and the top length 14 to rotate inwardly (e.g. toward axis 12) as the centrifugal force is increased. The centrifugal force is increased as the rotational velocity of the rotor arms 4 increases, which is in turn caused by increased wind speeds. Thus, at higher wind speeds, the top 15 of the rotor blade 6 rotates inwardly toward the axis of rotation 12, thereby reducing the swept area or the rotor area 18, according to embodiments of the present invention. This configuration permits a relatively steady energy generation over a wide range of wind speeds, as a result of the rotor blades 6 automatically adjusting the rotor area as described, according to embodiments of the present invention.
According to embodiments of the present invention, the automatic adjustment of the angle of the rotor blades 6 with respect to the rotor arms 4 is completely passive, and involves a minimal amount of hardware. According to embodiments of the present invention, the hinge joint 5 is the only point of contact between the rotor blade 6 and any other part of the vertical axis wind turbine 100, including the rotor arm 4, hub 3, and/or base 1. According to such embodiments, there are no stabilizers or wires or frames that attach to the rotor blade 6; instead, the sole mechanism that governs and/or constrains the movement of the rotor blade 6 is the hinge 5.
Although a particular hinge joint 20 is illustrated, one of ordinary skill in the art, based on the present disclosure, will appreciate the numerous other ways for pivotably coupling the rotor blade 6 with the rotor arm 4, according to embodiments of the present invention. For example, a single-sided bracket may be used instead of a U-shaped bracket 9. Also, the U-shaped bracket may instead extend from the rotor arm 4 and mate with a bearing element that is coupled with or attached to the rotor blade 6, according to embodiments of the present invention. A shaft and/or pin and/or the like may be used instead of a bolt 7 and nut 21 combination, according to embodiments of the present invention. According to some embodiments of the present invention, the bearing element 8 is omitted, and the bolt 7 or shaft simply rotates within an aperture in the rotor arm 4.
The rotor blade 6 includes a leading edge 22, a trailing edge 23, an inner surface 24 extending from the leading edge 22 to the trailing edge 23, and an outer surface 25 extending from the leading edge 22 to the trailing edge 23, according to embodiments of the present invention. According to embodiments of the present invention, the outer surface 25 is longer than the inner surface 24 between the leading edge 22 and trailing edge 23 in a plane orthogonal to the axis of rotation (such as, for example, the plane according to which the view of
Because the vertical axis wind turbine 100 shown in
According to embodiments of the present invention, device 100 is totally controlled by natural forces of wind and gravity; such a configuration minimizes wear of accessory controls and minimizes unbalance of the rotating member 3, because additional accessories and complicated support and/or stabilization mechanisms are not included in the system.
Embodiments of the present invention accomplishes rotor area change using only one moving part (e.g. the rotor blade 6), whose angle and area change are accomplished using only the natural forces. This permits production of energy in low wind speed areas and in extreme high wind conditions, and also greatly reduces the parts count, complexity, and cost of manufacturing and maintenance for wind turbine 100, according to embodiments of the present invention. Embodiments of the present invention make it possible to generate energy in all classes of wind from Class 1 to Class 7 and in typhoon and hurricane areas, without damage or damage to the point of failure, with its ability to use much larger rotor area for low wind areas and to control or reduce the rotor area for higher wind conditions. The variable area performance reduces the exposed rotor area for high wind conditions, which allows installation much closer to actual loads in lower or higher wind speeds, according to embodiments of the present invention.
The plurality of rotor arms 4 can be any number of rotor arms, depending on the specific wind regime. The attachment of the rotor blade 6 to the rotor arm 4 may be accomplished in several ways. The rotor blades 6, hinges 20, and rotor arms 4 are attached to the hub 3 in such a manner that they are mechanically balanced and rotate freely around the axis 12, according to embodiments of the present invention. A rotational dampener may optionally be incorporated in the hinge 20. Such a rotational dampener may impart a rotational friction, located at or on the rotor hinge pin (for example, at the bolt 7), with rotational friction dampening operation similar to a Scott Model Tail wheel used on many popular aircraft. The various components of the turbine 100 may be constructed with fiberglass, aluminum, steel, or other structural materials in nearly any combination.
Embodiments of the present invention, using only the natural centrifugal/centripetal forces, together with the forces of the wind on the rotor blade 6/aerofoil, controls the area of the rotor exposed to the wind, which in turn controls the power output and the stresses applied by the wind. The rotor area exposed to the wind determines power production, and is also a source of stress and wind loading on a wind machine. Embodiments of the present invention control the area of the rotor blades exposed to the wind, which in turn controls the exponentially increasing, and potentially damaging, forces applied to, or on, the machine from the wind and other forces.
This method of wind turbine 100 construction permits the use of a much larger rotor area, which makes it feasible and commercially viable in Class 2 (9.8 mph/4.5 mps) as well as higher wind areas, including Class 7 (9.4 mps). This results in stress loads from the wind and other forces being held nearly constant throughout the operational range of the turbine 100 (for example, over all wind speeds).
Embodiments of the present invention feature a reduced component part count and reduced complexity compared with existing turbine designs, which often require brakes, braces, and complex control systems to avoid excess speed and/or to halt rotation in lower wind speeds. According to embodiments of the present invention, device 100 does not require either blade feathering or external braking. Fewer numbers of parts also reduces overall maintenance. Existing vertical axis wind turbines suffer from extreme centrifugal forces as wind speeds increase, which, in turn, requires substantial bracing on the rotor blades to counteract such forces and to attempt to prevent the rotor blade from buckling at the mounting point. However, embodiments of the present invention such forces are re-directed; in high wind speeds (and thus high rotational speeds of the rotor blades 6 about the axis 12), the rotor blades 6 run substantially parallel to the centrifugal forces and the rotor blades 6 become, when horizontal, much like helicopter blades. The centrifugal forces then become a large component of the strength and/or stability and/or balance of the rotor blades 6, according to embodiments of the present invention.
The natural rotational balance of the rotor blades 6 is not restricted by bracing of any type or form, according to embodiments of the present invention. Bracing is not required because, in high wind speeds, the rotor blade 6 strength is increased in much the same way as a helicopter rotor. According to some embodiments of the present invention, a locking mechanism may optionally be used to hold the rotor blades 6 in a substantially vertical position until the rotor arms 4 reach a selected rotational speed, at which point the rotor blade 6 will be released from the locking mechanism and permitted to automatically adjust its angle as described, above. Such a locking/release mechanism may be activated by centrifugal forces, and may be similar to a gate-latch type latching mechanism commonly used for fence gates, according to embodiments of the present invention.
Embodiments of the present invention allow the rotor blade 6 to continuously change its angle to meet the demands of the wind loading on the machine 100 by reducing the cross sectional area (e.g. the area exposed to the wind), thereby allowing only enough exposed area to generate the desired amount of energy and relieving any stress above that which is required for optimum power output.
According to one embodiment of the present invention, the turbine 100 includes a stop, either mounted to the rotor arm 4, the rotor blade 6, and/or included within the hinge joint 20, which is configured to prevent rotation of the lower end 17 of the rotor blade 6 toward the axis of rotation 12 beyond a substantially vertical position of the rotor blade 6.
According to one embodiment of the present invention, the turbine 100 includes a spring (such as, for example, a torsion spring positioned at the pivot point 5) that is configured to bias the rotor blade toward 6 a substantially upright position (as illustrated in the solid lines of
According to embodiments of the present invention, rotation of the rotor blade 6 about the rotor arm 4 is neither controlled nor facilitated by a computer or electronic control system. According to embodiments of the present invention, rotation of the hub 3 is neither controlled nor facilitated by a computer or electronic control system. According to embodiments of the present invention, the only forces acting on the rotor blade 6 during operation are those of gravity, wind, centripetal forces, and friction at the first hinge joint 20, with such centripetal forces being created due to the rotation of the rotor arms 4 by the wind. In other words, in some embodiments of the present invention, there are no springs or cables acting on the rotor blade 6.
Various modifications and additions can be made to the exemplary embodiments discussed without departing from the scope of the present invention. For example, while the embodiments described above refer to particular features, the scope of this invention also includes embodiments having different combinations of features and embodiments that do not include all of the described features. Accordingly, the scope of the present invention is intended to embrace all such alternatives, modifications, and variations as fall within the scope of the claims, together with all equivalents thereof.
This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/210,673, filed on Mar. 20, 2009, and entitled “Variable Area Vertical Axis Wind Turbine,” the contents of which are incorporated herein by reference.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US10/28015 | 3/19/2010 | WO | 00 | 9/20/2011 |
| Number | Date | Country | |
|---|---|---|---|
| 61210673 | Mar 2009 | US |
