WO2010048152A1

WO2010048152A1 - Vertical axis wind turbine

Info

Publication number: WO2010048152A1
Application number: PCT/US2009/061286
Authority: WO
Inventors: Bradley E. Layton; David S. Paskman; Nicholas P. Haas; Matthew C. Morely; Jamal S. Khalife; Steven R. Helms
Original assignee: Drexel University
Priority date: 2008-10-20
Filing date: 2009-10-20
Publication date: 2010-04-29

Abstract

A vertical axis wind turbine is disclosed, including an axle and a plurality of blades circumferentially spaced about the axle and coupled to the axle. Each blade can include an outer surface and an inner surface, the outer surface and inner surface meeting at a leading edge and a trailing edge. Each blade can include a leading portion extending from the leading edge along the outer surface and the inner surface, the leading portion having, in longitudinal cross-section, an airfoil shape. Each blade can include at least one transverse channel located rearward of the leading portion. Each blade can include a trailing portion extending rearward from the channel to the trailing edge. Each channel can enhance wind turbine power output.

Description

VERTICAL AXIS WIND TURBINE

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to provisional U.S. patent application no. 61/106,840, filed October 20, 2008, and provisional U.S. patent application no. 61/232,210, filed August 7, 2009, the contents of which are incorporated herein by reference in their entirety.

TECHNICAL FIELD

[0002] The present invention relates to a vertical axis wind turbine for generating energy, particularly a vertical axis wind turbine that includes blades having one or more channels, scallop structures, tubercle structures, and/or vents.

BACKGROUND

[0003] Vertical axis wind turbines are well known in wind energy industries as generating rotational motion about an axis that is substantially vertical. Vertical wind turbines generally have the same efficiency regardless of wind direction, compared to horizontal wind turbines that are generally most efficient only when the wind has substantial velocity vector components in a direction parallel to the axis of rotation.

[0004] Darrieus turbine devices generate rotational motion based on lift principles, relying strictly on blade lift characteristics to generate a positive torque. A disadvantage of Darrieus devices is that these types of turbines may not reliably self-start, because they do not have sufficient stall surfaces normal to the direction of the wind flow to allow the blades to achieve enough momentum to maintain rotational motion. Therefore, these types of devices typically require an energy source to help the blades reach the required level of momentum to continue their rotational motion.

[0005] Savonius turbine devices generate rotational motion based on drag principles, relying on relatively large stall surfaces provided by cup-shaped blades. This type of device is relatively easy to self-start, because the stalling of wind into the surfaces that are normal to the wind flow allows the blades to generate sufficient momentum to maintain rotational motion. A disadvantage of Savonius devices is that these types of turbines are not very efficient, because as rotational speed increases, the large cup-shaped stall surfaces normal to the direction of the wind increasingly inhibit motion in the desired rotational direction.

[0006] It is desirable to develop an improved vertical axis wind turbine that has improved performance compared to the designs in the prior art.

SUMMARY

[0007] A vertical axis wind turbine is disclosed, including an axle and a plurality of blades circumferentially spaced about the axle and coupled to the axle. Each blade can include an outer surface and an inner surface, the outer surface and inner surface meeting at a leading edge and a trailing edge. Each blade can include a leading portion extending from the leading edge along the outer surface and the inner surface, the leading portion having, in longitudinal cross-section, an airfoil shape. Each blade can include at least one transverse channel located rearward of the leading portion. Each blade can include a trailing portion extending rearward from the channel to the trailing edge. Each channel can enhance wind turbine power output.

[0008] The airfoil shape of the leading portion of each blade, in longitudinal cross- section, can be a NACA standard airfoil shape. Each channel can enhance wind turbine power output by providing stall surfaces normal to the direction of an anticipated wind flow, such that drag forces can promote self-starting of the wind turbine. The vertical axis wind turbine can include a plurality of struts extending from the axle, each blade being coupled to the axle by corresponding struts. Each blade can define two Gaussian stress points, and each blade can be attached to two struts at the Gaussian stress points of the blade. Each blade can include a pair of opposing transverse channels. The trailing portion of each blade can taper to a sharp line at the trailing edge. Each blade can include at least one articulating panel that changes the shape of at least one of the outer surface and the inner surface depending on the angular speed of the wind turbine. The panel can be biased toward an open position such that centrifugal force actuates the panel to a closed position. The panel can substantially cover the channel in a closed position of the panel. Each blade can include at least one vent extending through the blade from the outer surface of the blade to the inner surface of the blade, wherein the panel substantially covers the vent in a closed position of the panel. Each blade can include two wind stagnation projections disposed at the top and bottom of the blade. The outer surface of each blade can define a camber, and the inner surface of each blade can define a camber that is different than the camber of the outer surface. The blades can define a circular path of rotation about the axle, and each blade can be oriented at a non-zero attack angle relative to a line tangent to the circular path of rotation. The attack angle of each blade can be between approximately 27 and 36 degrees. Each blade can include at least one tubercle structure at either or both o the leading edge and the trailing edge of the blade. Each blade can include at least one vent extending through the blade from the outer surface of the blade to the inner surface of the blade, and each tubercle structure can be located approximately at the same vertical position on the blade as a corresponding vent.

[0009] A vertical axis wind turbine is disclosed, including an axle and a plurality of blades circumferentially spaced about the axle and coupled to the axle. Each blade can include an outer surface and an inner surface, the outer surface and inner surface meeting at a leading edge and a trailing edge. Each blade can include a leading portion extending from the leading edge along the outer surface and the inner surface. Each blade can include plural scallops on each one of the outer surface and the inner surface, the scallops located rearward of the leading portion. Each blade can include a trailing portion extending rearward to the trailing edge from a leading scallop of the plural scallops on each one of the outer surface and the inner surface. Each scallop can enhance wind turbine power output.

[0010] Each scallop can enhance wind turbine power output by providing stall surfaces normal to the direction of an anticipated wind flow, such that drag forces can promote self- starting of the wind turbine. The vertical axis wind turbine can include a plurality of struts extending from the axle, each blade being coupled to the axle by corresponding struts. The leading portion of each blade can have, in longitudinal cross-section, an airfoil shape. The scallops can decrease in size from the leading portion to the trailing portion. Each blade can include at least one articulating panel that changes the shape of at least one of the outer surface and the inner surface depending on the angular orientation of the blade relative to the wind field velocity vectors. The panel can be biased toward a closed position such that a force applied by the wind field to the blade actuates the panel to an open position.

[0011] A method of harnessing wind energy by rotating a vertical axis wind turbine can include the steps of assembling the vertical axis wind turbine by coupling a plurality of blades to an axle, the blades being spaced circumferentially about the axle, exposing the blades to the wind so that the plurality of blades rotates about the axle, and changing the shape of at least one of an outer surface and an inner surface by moving an articulating panel from an open position to a closed position while the blades are rotating about the axle. Each blade can include an outer surface and an inner surface, the outer surface and inner surface meeting at a leading edge and a trailing edge. Each blade can include a leading portion extending from the leading edge along the outer surface and the inner surface. Each blade can include at least one transverse channel located rearward of the leading portion. Each blade can include a trailing portion extending rearward from the channel to the trailing edge. Each blade can include at least one articulating panel coupled to at least one of the outer surface and the inner surface.

[0012] The leading portion of each blade can have, in longitudinal cross-section, an airfoil shape. The articulating panel can move from the open position to the closed position due to centrifugal force acting on the panel while the blades are rotating about the axle. The articulating panel can move from the open position to the closed position due to a change in the angular orientation of the blade relative to the wind field velocity vectors. The method can further include orienting each blade at a non-zero attack angle relative to a line tangent to a circular path of rotation of the blades about the axle.

[0013] These and various other advantages and features are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to the accompanying descriptive matter, in which there are illustrated and described preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG. IA is a top view of a vertical axis wind turbine illustrating aspects of the invention;

[0015] FIG. IB is a perspective view of the turbine depicted in FIG. IA; [0016] FIG. 1C is a side elevation view of the turbine depicted in FIG. IA; [0017] FIG. 2A is a perspective view of a turbine blade having an airfoil profile;

[0018] FIG. 2B is a perspective view of a hybrid turbine blade having an airfoil profile and channels;

[0019] FIG. 2C is a perspective view of a hybrid turbine blade having an airfoil profile, channels, and vents;

[0020] FIG. 3 A is a top sectional view of the turbine blade depicted in FIG. 2A, taken along the line 3 A-3A;

[0021] FIG. 3B is a top sectional view of the turbine blade depicted in FIG. 2B, taken along the line 3B-3B; [0022] FIG. 3C is a top sectional view of the turbine blade depicted in FIG. 2C, taken along the line 3C-3C;

[0023] FIG. 4A is a computational fluid dynamics ("CFD") model showing the wind velocity profile resulting from an 8 mph wind flow field moving across a vertical axis wind turbine including blades depicted in FIG. 2 A;

[0024] FIG. 4B is a CFD model showing the wind velocity profile resulting from an 8 mph wind flow field moving across a vertical wind turbine including blades depicted in FIG. 2B;

[0025] FIG. 4C is a CFD model showing the wind velocity profile resulting from an 8 mph wind flow field moving across a vertical wind turbine including blades depicted in FIG. 2C;

[0026] FIG. 4D is a CFD model showing the wind pressure profile resulting from an 8 mph wind flow field moving across a vertical wind turbine including blades depicted in FIG. 2A;

[0027] FIG. 4E is a CFD model showing the wind pressure profile resulting from an 8 mph wind flow field moving across a vertical wind turbine including blades depicted in FIG. 2B;

[0028] FIG. 4F is a CFD model showing the wind pressure profile resulting from an 8 mph wind flow field moving across a vertical wind turbine including blades depicted in FIG. 2C;

[0029] FIG. 5A is a graph showing the simulated torque acting on the vertical wind turbine as a function of blade position resulting from a 2 mph wind flow field moving across each of three vertical wind turbines including the blades depicted in FIGs. 2A, 2B, and 2C, respectively;

[0030] FIG. 5B is a graph showing the simulated torque acting on the vertical wind turbine as a function of blade position resulting from a 2 mph wind flow field moving across each of three vertical wind turbines including alternative embodiments of the blades depicted in FIGs. 2A, 2B, and 2C, respectively;

[0031] FIG. 5C is a graph showing the simulated torque acting on the vertical wind turbine as a function of blade position resulting from an 8 mph wind flow field moving across each of three vertical wind turbines including the blades depicted in FIGs. 2 A, 2B, and 2C, respectively;

[0032] FIG. 5D is a graph showing the simulated torque acting on the vertical wind turbine as a function of blade position resulting from an 8 mph wind flow field moving across each of three vertical wind turbines including alternative embodiments of the blades depicted in FIGs. 2A, 2B, and 2C, respectively; [0033] FIG. 5E is a graph showing the simulated torque acting on the vertical wind turbine as a function of blade position resulting from a 14 mph wind flow field moving across each of three vertical wind turbines including the blades depicted in FIGs. 2 A, 2B, and 2C, respectively;

[0034] FIG. 5F is a graph showing the simulated torque acting on the vertical wind turbine as a function of blade position resulting from a 14 mph wind flow field moving across each of three vertical wind turbines including alternative embodiments of the blades depicted in FIGs. 2A, 2B, and 2C, respectively;

[0035] FIG. 5G is a graph showing the simulated torque acting on the vertical wind turbine as a function of blade position resulting from a 20 mph wind flow field moving across each of three vertical wind turbines including the blades depicted in FIGs. 2 A, 2B, and 2C, respectively;

[0036] FIG. 5H is a graph showing the simulated torque acting on the vertical wind turbine as a function of blade position resulting from a 20 mph wind flow field moving across each of three vertical wind turbines including alternative embodiments of the blades depicted in FIGs. 2A, 2B, and 2C, respectively;

[0037] FIG. 6 is a graph showing the simulated net work of six vertical wind turbines including blades as depicted in FIGs. 2A, 2B, and 2C, resulting from wind flow fields of 2, 8, 14, and 20 mph moving across the turbines;

[0038] FIG. 7 is a perspective view of a vertical axis wind turbine illustrating aspects of the invention;

[0039] FIG. 8A is a top sectional view of a turbine blade having an airfoil profile;

[0040] FIG. 8B is a top sectional view of an asymmetric hybrid turbine blade having an airfoil profile and a single channel;

[0041] FIG. 8C is a top sectional view of a hybrid turbine blade having an airfoil profile and channels;

[0042] FIG. 8D is a top sectional view of a hybrid turbine blade having an airfoil profile and scallop structures;

[0043] FIG. 8E is a top sectional view of a hybrid turbine blade having an elliptical profile and circular arc channels; [0044] FIG. 9A is a graph showing the simulated net tangential force (in the direction of rotation) acting on five 3-blade vertical wind turbines including blades as depicted in FIGs. 8A- 8E as a function of leading blade position, resulting from wind flow fields of 24.6 mph moving across the turbines;

[0045] FIG. 9B is a diagram showing the vector components of the net tangential force that is acting on each of the five 3-blade vertical wind turbines to produce the data that is depicted in FIG. 9 A;

[0046] FIG. 1OA is a top sectional view of a turbine blade having an asymmetric airfoil profile and a single articulating panel in an open position;

[0047] FIG. 1OB is a top sectional view of the turbine blade depicted in FIG. 1OA, with the single articulating panel in an intermediate position;

[0048] FIG. 1OC is a top sectional view of the turbine blade depicted in FIG. 1OA, with the single articulating panel in a closed position;

[0049] FIG. 1 IA is a top sectional view of a hybrid turbine blade having an airfoil profile, scallop cutouts, and two articulating wings in an open position;

[0050] FIG. 1 IB is a top sectional view of the hybrid turbine blade depicted in FIG. 1 IA, with the two articulating wings in a closed position;

[0051] FIG. 12A is a perspective view of a hybrid turbine blade having an airfoil profile, channels, and vents;

[0052] FIG. 12B is a graph showing the turbine speed (in RPM) as a function of wind speed for two 3-blade vertical wind turbine embodiments including blades as depicted in FIGs. 8C and 12A;

[0053] FIG. 13A is a perspective view of a hybrid turbine blade having an airfoil profile, channels, and rounded vents;

[0054] FIG. 13B is a perspective view of a hybrid turbine blade having an airfoil profile, channels, and rounded profile partial depth vents;

[0055] FIG. 13C is a perspective view of a hybrid turbine blade having an airfoil profile, channels, and rounded profile rounded depth vents;

[0056] FIG. 14A is a rear sectional view of a portion of a hybrid turbine blade having a vent with an articulating hinged flap in an open position; [0057] FIG. 14B is a rear sectional view of the portion of the hybrid turbine blade depicted in FIG. 14 A, with the articulating hinged flap in a closed position;

[0058] FIG. 14C is a side view of the portion of the hybrid turbine blade depicted in FIG. 14C, with the articulating hinged flap in a closed position;

[0059] FIG. 15A is a perspective view of a hybrid turbine blade having an airfoil profile, channels, and tubercle structures at the leading edge;

[0060] FIG. 15B is a perspective view of a hybrid turbine blade having an airfoil profile, channels, and tubercle structures at the trailing edge;

[0061] FIG. 15C is a perspective view of a hybrid turbine blade having an airfoil profile, channels, and tubercle structures at the leading and trailing edges;

[0062] FIG. 15D is a perspective view of a hybrid turbine blade having an airfoil profile, channels, tubercle structures at the leading edge, and vents located at the same vertical position as the tubercle structures.

[0063] FIG. 16A is a top sectional view of the turbine blade depicted in FIG. 15 A, taken along the line 15A- 15 A;

[0064] FIG. 16B is a top sectional view of the turbine blade depicted in FIG. 15B, taken along the line 15B-15B;

[0065] FIG. 16C is a top sectional view of the turbine blade depicted in FIG. 15C, taken along the line 15C-15C;

[0066] FIG. 16D is a top sectional view of the turbine blade depicted in FIG. 15D, taken along the line 15D-15D;

[0067] FIG. 17A is a top view of a vertical axis wind turbine illustrating inward and outward angles of attack of the turbine blades;

[0068] FIG. 17B is a graph showing the simulated net work produced by the rotation of five 3 -blade vertical wind turbines including blades having the various angles of attack shown in FIG. 17A as a function of the velocity of the wind field moving across the turbines; and

[0069] FIG. 17C is a graph showing the simulated net work produced by the rotation of a series of 3 -blade vertical wind turbines as a function of the angle of attack of the blades, resulting from wind flow fields of 15 mph moving across the turbines. DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0070] Referring to FIGs. IA, IB, and 1C, an exemplary vertical axis wind turbine 10 includes three blades 12, six struts 14, and an axle 16. Vertical wind turbine 10 preferably rotates about the axle 16 in a rotational direction Rl. Each blade 12 is spaced circumferentially about the axle 16, and each blade 12 has a leading edge 17, a trailing edge 18, an outer surface 19, an inner surface 20, and two wind stagnation projections 21. Each blade 12 has a height H {i.e., the total length of the leading edge 17 or the trailing edge 18 of each blade 12 or the distance between the two wind stagnation projections 21 of each blade 12), a length L {i.e., the linear distance from the leading edge 17 to the trailing edge 18 of each blade 12), and a maximum thickness T {i.e., the maximum linear distance from the outer surface 19 to the inner surface 20 of each blade 12), and each blade 12 rotates about the axle 16 in a substantially circular path having a diameter D.

[0071] In some embodiments, each blade 12 or any of the other blades described herein can have a height H between 30 and 60 inches, for instance, 48 inches, a length L between 10 and 24 inches, for instance, 18 inches, and a maximum thickness T between 1.5 and 3.5 inches, for instance, 2.67 inches. In some embodiments, each blade 12 can be between 12 and 36 inches away from the axle 16, for instance, 24 inches away from the axle 16, resulting in a total vertical wind turbine 10 diameter D of between 24 and 72 inches, for instance, 48 inches. In other embodiments, the diameter of the vertical wind turbine 10 and particular features of each blade 12 can be of any size, depending on the desired performance characteristics of the vertical wind turbine 10. Without being bound by theory, it is believed that the ratio of the height H of each blade 12 to the diameter D of the vertical wind turbine 10 may be chosen to maximize the rotational torque produced by a particular wind flow, while minimizing the stress on the blades 12 and the vertical wind turbine 10.

[0072] In the embodiments shown, there is a single vertical wind turbine 10. However, in other embodiments (not shown), a network of wind turbines 10 can be employed, having any number of vertical wind turbines 10 used together. Multiple vertical wind turbines 10 can be preferable, depending on the particular desired performance characteristics of the network and the characteristics of the wind flow around each vertical wind turbine 10. For example, as described below with reference to FIGs. 4A-4C, a first vertical wind turbine 10 can produce localized areas of high wind speed, so it may be efficient to place a second vertical wind turbine 10 in a location where it can receive some of the excess energy from the high wind speed area. In some embodiments, multiple vertical wind turbines 10 can be stacked on top of each other, which can result in greater efficiency by allowing multiple vertical wind turbines 10 to be attached to the same axle 16 and/or the same electricity generator, though any arrangement of wind turbines is contemplated in accordance with certain aspects of the present invention.

[0073] In the embodiment shown in FIGs. 1A-1C, there are three blades 12, but any number of blades can be used in the vertical wind turbine 10 or in any of the other vertical wind turbines described herein. Preferably, there are an odd number of blades 12. For example, in some embodiments, there are 5, 1, 9, 11, and 15 blades 12. While not being bound by theory, it is believed that an odd number of blades 12 can improve the ability of the vertical wind turbine 10 to self- start, because a greater surface area of the blades 12 normal to the direction of the wind flow may be exposed to the higher velocity vectors in the wind flow than if an even number of blades 12 is used. However, the present invention is not intended to be limited to an odd number of blades 12, and in some embodiments, the vertical wind turbine 10 can include an even number of blades 12. In some embodiments (not shown), there can be multiple levels of blades 12 in a single vertical wind turbine 10. For example, there can be two vertically-stacked levels of blades 12 in a single vertical wind turbine 10, each level including three blades 12. In other embodiments, there can be any number of vertically-stacked levels of blades 12 in a single vertical wind turbine 10. Each level of blades 12 can have any number of blades, such as 5, 7, 9,

11, and 15 blades 12, and each vertically-stacked level can have a different number of blades 12 than the other levels.

[0074] In the embodiment shown in FIGs. IA- 1C, the vertical wind turbine can have three blades 12, each blade 12 extending through a 20-degree portion of the circular path that is traveled by each of the three blades 12. However, in other embodiments (not shown), each blade 12 can extend through any portion of the circular path that is traveled by each of the three blades

12, including 10, 15, 30, 45, or any portion of the circular path, depending on the desired amount of the surface area of the blades 12 that will be normal to the direction of the wind flow at particular desired rotational orientations of the blades 12.

[0075] Each blade 12 can be attached to the axle 16 via the struts 14 by any known mechanism, including, but not limited to, welding, bolting, clamping, or chemical bonding. Each blade 12 can also be integrally formed with the struts 14 and the axle 16, for example, in a single casting. Each blade 12 can be made of any material, such as foam, fiberglass, aluminum sheets, aluminum extrusions, steel, or a combination of materials, for example, with a lightweight material inside of the blade 12, such as a foam core, and a stronger, heavier material forming the outside shell of the blade 12, such as, but not limited to, fiberglass, aluminum sheets, or sheet metal. In some embodiments (not shown), each blade 12 may have a composite construction, including materials such as carbon-fiber composites and/or matrices of one or more materials. The axle 16 can be coupled to a shaft (not shown) via bearings that allow low friction rotation of the blades 12 about the axle 16 in the rotational direction Rl . The shaft can be mounted onto a support surface (not shown). The shaft (not shown) can also be coupled to an electric generator (not shown) to allow energy produced by the vertical wind turbine to be transferred for use with another apparatus coupled to the electric generator (not shown).

[0076] Each blade 12 is preferably attached to the axle 16 via two struts 14. In the embodiment shown in FIGs. 1A-1C, each strut 14 is attached to a respective blade 12 at the top and bottom ends of the blades 12, via the wind stagnation projections 21. However, it is preferable to attach the two struts 14 at the Gaussian stress points, in the middle of the inner surfaces 20 of the respective blades 12 (as shown, for example, in FIG. 7). The Gaussian stress points are the points along the inner surface 20 of each blade 12, where the bending stress experienced by each blade 12 (about an axis tangential to each blade 12) during rotation of the vertical wind turbine 10 in the direction Rl due to centrifugal force and the lift and drag forces across each blade 12 is minimized. In some embodiments, such as those including blades 12 having a constant cross-section along the height H, the Gaussian stress points G are located approximately 0.2071*H from the top and bottom of each blade 12. In the embodiments in which the two struts 14 are attached to each blade 12 at the Gaussian stress points, the struts 14 are attached to the inner surface 20 of each blade 12 by any known mechanism, including welding, bolting, clamping, or chemical bonding. In some embodiments, there can be a single strut 14 for each blade 12, or there can be greater than two struts 14 for each respective blade 12. For example, each blade 12 can be coupled to the axle 16 by 3, 4, 5, 6, or any number of struts 14.

[0077] In the embodiment shown in FIGs. IA- 1C, the struts 14 have a constant cross- section that is much smaller than the cross-section of each blade 12. In some embodiments (not shown), the struts 14 can have any other cross-sectional profile, such as an airfoil-like cross- section that may minimize drag, which may allow for greater energy-generation efficiency of the vertical wind turbine 10 when it rotates at high speeds. In some embodiments (not shown), the struts 14 can also include Savonius-style cup additions that may increase drag and enhance the self-starting capabilities of the vertical wind turbine 10. In some embodiments (not shown), the struts 14 can be variable in length, allowing the blades 12 to be dynamically positioned at different distances from the axle 16, depending on environmental conditions or the desired performance requirements of the vertical wind turbine 10.

[0078] Although in the embodiments shown, each blade 12 is coupled to the axle 16 by struts 14, in other embodiments (not shown), any other coupling mechanism can be used to couple the blades 12 to the axle 16. For example, each blade 12 can be coupled to the axle 16 by one or more solid discs, one or more discs including internal voids, circular, oval, or parabolic arc-shaped struts, or any other blade attachment mechanism that is known in the art.

[0079] It has been observed that a vertical wind turbine 10 having the design shown in FIGs. 1A-1C can combine lift and drag principles to allow the vertical wind turbine 10 to self- start and achieve sufficient angular momentum to maintain rotational velocity at low wind speeds, thereby preventing the need to rely on an external energy source. Without being bound by theory, it is believed that the vertical wind turbine 10 shown in FIGs. 1 A-IC can achieve increased efficiency in urban and suburban areas, given that wind in such areas tends to be unsteady, turbulent, and low-speed.

[0080] Referring to FIGs. 2 A and 3 A, an airfoil blade 12a suitable for use in any of the vertical wind turbines disclosed herein has a leading edge 17, a trailing edge 18, an outer surface 19, an inner surface 20, and a cross-sectional profile 22a. The cross-sectional profile 22a shows the airfoil shape of a cross-section of the airfoil blade 12a, perpendicular to outer surface 19 and the inner surface 20. In the embodiment shown in FIG. 2A, the blade 12a has a substantially constant cross-sectional profile 22a throughout the entire height H of the blade 12a (i.e., the total length of the leading edge 17 or the trailing edge 18 of the blade 12a). Cross-sectional profile 22a of the blade 12a preferably has a airfoil shape. The particular airfoil shape of cross-sectional profile 22a can be any airfoil shape, but in the embodiment shown in FIG. 3A, the cross- sectional profile 22a has the aspect ratio of a National Advisory Committee for Aeronautics ("NACA") 0015 airfoil, which has a maximum thickness 7 that is 15% of the length L. In other embodiments, a cross-sectional profile 22a having the aspect ratios of a NACA 0012 airfoil (which has a maximum thickness T that is 12% of the length L) was used (see, for example, FIGs. 5B, 5D, 5F, 5H, and 6, and TABLE 1 for simulated performance of blades 12 having an NACA 0012 aspect ratio). In the blade embodiments described herein that are based on one of the NACA airfoil shapes, the cross-sectional profile preferably has a trailing edge that defines a sharp point. In other embodiments, the cross-section of the trailing edge can have other geometries, including, for example, a straight line, a circular arc, an elliptical arc, or any other shape. [0081] In other embodiments (not shown), other airfoil shapes or other smoothly-varying shapes for cross-sectional profile 22a can be used. In some embodiments, cross-sectional profile 22a can have an airfoil-like (or substantially airfoil) shape that is capable of generating lift in the radial or circumferential direction, such lift being sufficient to generate a dynamic torque that is capable of generating and sustaining a rotational velocity of the vertical wind turbine 10. As can be seen in FIG. 3A, the cross-sectional profile 22a is preferably symmetrical about a centerline connecting the leading edge 17 with the trailing edge 18. In other embodiments (not shown), the cross-sectional profile 22a can be asymmetrical about the centerline, depending on the desired performance characteristics of the vertical wind turbine 10. For example, in some embodiments (not shown), the cross-sectional profile 22a can have a greater camber on the inner surface 20 than on the outer surface 19, or a greater camber on the outer surface 19 than on the inner surface 20, thereby potentially reducing stresses caused by bending of the blade 12a and shear induced at the intersection of the struts 14 and the blades 12a.

[0082] Referring to FIGs. 2B and 3B, a hybrid blade 12b suitable for use in any of the vertical wind turbines disclosed herein has a leading edge 17, a trailing edge 18, an outer surface 19, an inner surface 20, a cross-sectional profile 22b, an outer channel 24, and an inner channel 26. The cross-sectional profile 22b shows the hybrid shape of a cross-section of the airfoil blade 12b, perpendicular to outer surface 19 and the inner surface 20. In the embodiment shown in FIG. 2B, the blade 12b has a substantially constant cross-sectional profile 22b throughout the entire height H of the blade 12b (i.e., the total length of the leading edge 17 or the trailing edge 18 of the blade 12b or the distance between the optional wind stagnation projections 21 (not shown) of the blade 12b).

[0083] Cross-sectional profile 22b of the blade 12b preferably has an airfoil shape, with portions similar to the cross-sectional profile 22a of the blade 12a, but with portions removed corresponding to the outer channel 24 and the inner channel 26. As can be seen in FIG. 3B, the front of the cross-sectional profile 22b of the blade 12b near the leading edge 17 and the rear of the blade 12b near the trailing edge 18 adhere to an airfoil shape, but the portions of the cross- sectional profile 22b at the outer channel 24 and the inner channel 26 are carved out (or formed), preferably providing curved stall surfaces that can assist the vertical wind turbine 10 in self- starting. The exact shape of the outer channel 24 and the inner channel 26 can vary as desired, however, it is believed that the wind that approaches the blade 12b may be guided onto the curved surfaces that comprise the outer channel 24 and the inner channel 26. These curved surfaces in the channels 24 and 26 can provide wind stagnation locations along the airfoil blade 12b, which may increase the pressure on the blade 12b such that the majority of the wind's velocity energy is transferred into pressure on the blade 12b, thereby helping to initiate movement in the direction of the leading edge 17 (i.e., in the rotational direction Rl). These channels 24 and 26 may provide improved self-starting for the vertical wind turbine 10 having the blades 12b, while not substantially adding to the drag forces (thereby reducing positive torque and/or net work) at higher rotational speeds. As shown in FIGs. IA- 1C, the channels 24 and 26 can be bounded by the two wind stagnation projections 21, which are shown in FIG. IB as flat plates having substantially the same cross-sectional profile 22a the base airfoil-like profile of the blade 12, without portions carved out (or formed) at the top and bottom ends of the channels 24 and 26. In some embodiments (not shown), the two wind stagnation projections 21 may be tubercle-like projections from the outer surface 19 and/or the inner surface 20 of each blade 12. It is believed that the two wind stagnation projections 21 may improve the ability of the channels 24 and 26 to serve as wind stagnation locations along the airfoil blade 12b (as well as along the airfoil blade 12c shown in FIGs. 2C and 3C).

[0084] The particular airfoil shape of the portion of the cross-sectional profile 22b that is similar to the cross-sectional profile 22a can be any airfoil shape, but in the embodiment shown in FIG. 3B, the cross-sectional profile 22b has the aspect ratios of a NACA 0015 airfoil, but with portions of the cross-sectional profile 22b removed at the outer channel 24 and the inner channel 26. In other embodiments, such as that shown in FIGs. 5A-6 and TABLE 1, a cross-sectional profile 22b having the aspect ratios of a NACA 0012 airfoil was used (but also with portions of the cross-sectional profile 22b removed at the outer channel 24 and the inner channel 26). In other embodiments (not shown), other airfoil shapes or other smoothly- varying shapes for the airfoil portions of cross-sectional profile 22b can be used. In some embodiments, cross-sectional profile 22b can have an airfoil-like (or substantially airfoil) shape that is capable of generating lift in the radial or circumferential direction, such lift being sufficient to generate a dynamic torque that is capable of generating and sustaining a rotational velocity of the vertical wind turbine 10. As can be seen in FIG. 3B, the cross-sectional profile 22b is preferably symmetrical about a centerline connecting the leading edge 17 with the trailing edge 18. In other embodiments (not shown), the cross-sectional profile 22b can be asymmetrical about the centerline, depending on the desired performance characteristics of the vertical wind turbine 10. For example, in some embodiments (not shown), the cross-sectional profile 22b can have a greater camber on the inner surface 20 than on the outer surface 19, or a greater camber on the outer surface 19 than on the inner surface 20, thereby potentially reducing stresses caused by bending of the blade 12b and shear induced at the intersection of the struts 14 and the blades 12b.

[0085] Referring to FIGs. 2C and 3 C, a blade 12c suitable for use in any of the vertical wind turbines disclosed herein has a leading edge 17, a trailing edge 18, an outer surface 19, an inner surface 20, a cross-sectional profile 22c, an outer channel 24, an inner channel 26, and a plurality of vents 28 oriented at an angle α to the centerline connecting the leading edge 17 with the trailing edge 18. The cross-sectional profile 22c shows the hybrid shape of a cross-section of the airfoil blade 12c, perpendicular to outer surface 19 and the inner surface 20. As shown in FIGs. 2C and 3C, each of the plurality of vents 28 is an aperture, passing completely through the blade 12c from the outer surface 19 to the inner surface 20. In other embodiments (not shown), each of the plurality of vents 28 may pass partially through the blade 12c, from the outer surface 19 and/or the inner surface 20, or the vents 28 may be raised bumps, ridges, or tubercle-like protrusions, extending away from the outer surface 19 and/or the inner surface 20. In some embodiments, the tubercle-like protrusions may extend horizontally across the outer surface 19 and/or the inner surface 20, generally in the direction from the leading edge 17 towards the trailing edge 18 (i.e., along the length L of the blade 12c). Without being bound by theory, it is believed that such tubercle-like protrusions may help the wind flowing across the outer surface 19 and/or the inner surface 20 retain a uni-directional flow, thereby contributing to the lift forces acting on the blade 12c. As can be seen in FIG. 3 C, the blade 12c has a substantially constant cross-sectional profile 22c throughout the portions of the height H of the blade 12c that are not interrupted by the plurality of vents 28. In the portions of the height H of the blade 12c that include the plurality of vents 28, the cross-sectional profile 22c includes vents 28 carved through the cross-sectional profile 22c from the outer surface 19 to the inner surface 20.

[0086] The cross-sectional profile 22c of the blade 12c preferably has an airfoil shape, with portions similar to the cross-sectional profile 22a of the blade 12a, but with portions removed corresponding to the outer channel 24 and the inner channel 26, as well as portions removed corresponding to the plurality of vents 28. As can be seen in FIG. 3C, the front of the cross-sectional profile 22c of the blade 12c near the leading edge 17 and the rear of the blade 12c near the trailing edge 18 adhere to an airfoil shape, but the portions of the cross-sectional profile 22c at the outer channel 24 and the inner channel 26 are carved out (or formed), preferably forming curved stall surfaces as shown in FIG. 3C, and the portions of the cross-sectional profile 22c at the plurality of vents are carved out (or formed), preferably forming stall surfaces as well as allowing wind to pass through the blade 12c from the outer surface 19 to the inner surface 20. The exact shape of the outer channel 24, the inner channel 26, and the plurality of vents 28 can vary.

[0087] The particular airfoil shape of the portion of the cross-sectional profile 22c that is similar to the cross-sectional profile 22a can be any airfoil shape, but in the embodiment shown in FIG. 3C, the cross-sectional profile 22c has the aspect ratios of a NACA 0015 airfoil, but with portions of the cross-sectional profile 22c removed at the outer channel 24, the inner channel 26, and the plurality of vents 28. In other embodiments, such as that shown in FIGs. 5A-6 and TABLE 1, a cross-sectional profile 22c having the aspect ratios of a NACA 0012 airfoil was used (but also with portions of the cross-sectional profile 22c removed at the outer channel 24, the inner channel 26, and the plurality of vents 28). In other embodiments (not shown), other airfoil shapes or other smoothly- varying shapes for the airfoil portions of cross-sectional profile 22c can be used. In some embodiments, cross-sectional profile 22c can have an airfoil-like (or substantially airfoil) shape that is capable of generating lift in the radial or circumferential direction, such lift being sufficient to generate a dynamic torque that is capable of generating and sustaining a rotational velocity of the vertical wind turbine 10. As can be seen in FIG. 3C, the cross-sectional profile 22c is preferably symmetrical about a centerline connecting the leading edge 17 with the trailing edge 18. In other embodiments (not shown), the cross-sectional profile 22c can be asymmetrical about the centerline, depending on the desired performance characteristics of the vertical wind turbine 10. For example, in some embodiments (not shown), the cross-sectional profile 22c can have a greater camber on the inner surface 20 than on the outer surface 19, or a greater camber on the outer surface 19 than on the inner surface 20, thereby potentially reducing stresses caused by bending of the blade 12c and shear induced at the intersection of the struts 14 and the blades 12c.

[0088] Although in the embodiments shown in FIGs. 1B-2C, each blade 12 has a substantially constant cross-sectional profile 22a, 22b, or 22c throughout the entire height H of the blade 12 (i.e., the total length of the leading edge 17 or the trailing edge 18 of the blade 12), in other embodiments (not shown), the cross-sectional profile 22 of each blade 12 can vary across the height H of the blade 12. For example, cross-sectional profile 22 of each blade 12 can be greatest in area in the center of each blade 12, and the cross-sectional profile 22 can taper at the ends of each blade 12, at which points the cross-sectional profile 22 will be smaller in area. While not being bound by theory, it is believed that varying the cross-sectional profile 22a, 22b, or 22c throughout the height H of each blade 12 may provide blades 12 having multiple stall characteristics, such that there may be net reactant forces at multiple wind speeds, depending on the particular cross-sectional profile of the blade 12. In such embodiments of the vertical wind turbine 10, some portions of the blades 12 having a first cross-sectional profile shape at particular locations along the height H may stall at different wind velocities than other portions of the blades 12 having a second cross-sectional profile shape. This variable cross-sectional profile feature of the blades 12 may allow such embodiments of the vertical wind turbine 10 to be able to self-start at a greater variety of wind speeds than embodiments having a constant cross-sectional profile throughout the height H of each blade 12. In other embodiments (not shown), the cross-sectional profile 22a, 22b, or 22c can also rotate about an axis parallel to the axle 16 along the height H of the blade 12, forming, for example, a helical vertical profile shape of the blade 12 (not shown). While not being bound by theory, it is believed that embodiments of the vertical wind turbine 10 having a helical vertical profile shape of the blade 12 may reduce vibration during rotation of the blades 12 about the axle 16.

[0089] Although in the embodiment shown in FIG. 1C, the outer surface 19 and the inner surface 20 of each blade 12 have a substantially rectangular projected shape when viewed from the side as in FIG. 1C, in other embodiments (not shown), the outer surface 19 and the inner surface 20 of each blade 12 can have other projected shapes. For example, the side-view projected shape of the outer surface 19 and the inner surface 20 of each blade 12 can itself resemble an airfoil shape, or the shape can be oval, trapezoidal, or any other shape that can achieve the particular desired performance characteristics of the vertical wind turbine 10.

[0090] The channels 24 and 26 may provide stall surfaces that allow a vertical wind turbine 10 including blades 12b or 12c to reliably self- start, because the stall surfaces provided by the channels 24 and 26 have sufficient area normal to the direction of the wind flow to allow the blades to achieve enough momentum to maintain rotational motion. In the blades 12b and 12c, the area of the stall surfaces provided by the channels 24 and 26 may be correlated to the amount of the cross-sectional profile 22b or 22c that is removed from the cross-sectional profile 22a (having the aspect ratio of a NACA 0015 airfoil). The greater the amount of the cross- sectional profile 22b or 22c that is removed from the cross-sectional profile 22a, the larger the area of the stall surfaces provided by the channels 24 and 26 may be.

[0091] In some embodiments, the stall surfaces provided by the channels 24 and 26 may have a cylindrical shape. In other embodiments, the stall surfaces provided by the channels 24 and 26 may have an ovoid shape. The exact shape and/or radius of curvature of the stall surfaces provided by the channels 24 and 26 may depend on the anticipated wind speed. While not being bound by theory, it is believed that where average wind speeds are lower, having a larger stall surface area provided by the channels 24 and 26 may allow the vertical wind turbine 10 to extract more energy out of a given wind field. As shown in FIGs. 2B and 2C, the channels 24 and 26 can extend through the entire height H of the blade 12b or 12c. However, in some embodiments (not shown), the channels 24 and/or 26 may only extend through a portion of the height H (or height fraction) of the blade 12b or 12c. The particular height fraction of the channels 24 and/or 26 for a blade 12b or 12c can be chosen based on the desired stall surface area for the blades 12b or 12c of the vertical wind turbine 10.

[0092] In some embodiments (not shown), there can be only an outer channel 24 or only an inner channel 26 on each blade 12b or 12c, or the location of the outer channel 24 be located at a different distances from the leading edge 17 than the location of the inner channel 26 (not shown). For example, each blade 12b or 12c may include at least one channel 24 or 26 extending along the blade 12b or 12c in a direction substantially parallel to the rotational axis {i.e., the axle 16) of the vertical wind turbine 10. In other embodiments (not shown), there can be a plurality of outer channels 24 and/or inner channels 26 on each blade 12b or 12c, and the locations of each channel 24 and 26 can vary along each blade 12b or 12c.

[0093] The plurality of vents 28 may allow wind to pass through the blade 12c from the outer surface 19 to the inner surface 20. As will be discussed below related to FIGs. 4A-4F, some of the wind that passes through the blade 12c may reduce the drag forces acting on portions of a leading blade 12c (i.e., a first blade 12c that a particular vector of wind reaches), and a portion of the wind that passes through the leading blade 12c may increase the drag forces acting on portions of a trailing blade 12c (i.e., a second blade 12c that is behind the first blade 12c substantially in the direction of the velocity vector of the portion of the wind that passes through the leading blade 12c). The combination of these wind pass-through effects on the leading blade 12c and the trailing blade 12c may reduce portions of the rotational travel of the blades 12c that result in a net negative torque acting on the vertical wind turbine 10 (i.e., a torque acting in a rotational direction opposite the rotational direction Rl).

[0094] Without being bound by theory, it is believed that at lower rotational velocities in the direction Rl, the plurality of vents 28 in the blade 12c reduces pressure on the leading blade 12c that may experience regions of negative torque, allowing the oncoming wind to stagnate on the trailing blade 12c (behind the leading blade 12c in the direction of the wind velocity vectors), rather than stagnating on the leading blade 12c. At higher rotational velocities in the direction Rl, it is believed that the boundary layer flow may inhibit pressure entry into the channels 24 and 26 and the plurality of vents 28, thereby allowing the lift-based characteristics of the airfoil blades 12c to dominate such that a net positive lift force is exerted on the wings in the rotational direction Rl . In some embodiments, the channels 24 and 26 and/or the plurality of vents 28 do not protrude outside the boundary of the base airfoil-like cross-sectional profile 22a of the blade 12b or 12c (i.e., the cross-sectional profile 22a from which portions may be removed to form the channels 24 and 26 and/or the plurality of vents 28). Without being bound by theory, it is believed that in such embodiments, at higher rotational velocities in the direction Rl, wind can move across each blade 12b or 12c and form a boundary flow that substantially seals off the channels 24 and 26 and the plurality of vents 28, such that the wind behaves in a similar manner as if the channels 24 and 26 and the plurality of vents 28 were not present.

[0095] The plurality of vents 28 may serve as additional stall surfaces in the blade 12c, between the outer surface 19 and the inner surface 20. As will be discussed below related to FIGs. 4A-6 and TABLE 1, some of the wind that passes through the blade 12c increase the forces acting on portions of a leading blade 12c (i.e., a first blade 12c that a particular vector of wind reaches). These additional stall surfaces in the blade 12c may help the vertical wind turbine 10 reliably self-start and may generate more torque at low rotational speeds, because the additional stall surfaces provided by the plurality of vents 28 have sufficient area normal to the direction of the wind flow to assist the blades in achieving enough momentum to maintain rotational motion.

[0096] In the embodiment shown in FIGs. 2C and 3C, the stall surfaces provided by the plurality of vents 28 between the outer surface 19 and the inner surface 20 are planar in shape. However, in other embodiments (not shown), the stall surfaces provided by the plurality of vents 28 between the outer surface 19 and the inner surface 20 can have other shapes, including, for example, a cup shape, a V-shape, or a channel shape (e.g., similar to the channel shape of the stall surfaces provided by the channels 24 and 26). In some embodiments (not shown), the stall surfaces provided by the plurality of vents 28 can have a channel shape having a semi-circular or semi-ovoid cross-section. A particular profile or shape of the stall surfaces provided by the plurality of vents 28 can be selected to produce a desired degree of drag force acting on the blade 12c. In the embodiment shown in FIG. 3C, the stall surfaces provided by the plurality of vents 28 are all planar in shape, but in some embodiments (not shown), some of the plurality of vents 28 can have planar stall surfaces, while others can have other shapes, such as a cup shape, a V- shape, or a channel shape.

[0097] In the embodiment shown in FIG. 2C, there are ten vents 28 (two substantially parallel rows each having 5 vents 28) in the blade 12c, and in the embodiment shown in FIGs. IB and 1C, there are sixteen vents 28 (two substantially parallel rows each having eight vents 28) in each blade 12. However, in other embodiments (not shown), there can be any number of vents 28, and they can be arranged in any pattern or any number of rows (which can be substantially parallel, perpendicular, or in any other relative orientation), depending on the particular dimensions of the blades 12c, the desired ratio of the solid surface area of the outer surface 19 and the inner surface 20 to the surface area removed from the outer surface 19 and the inner surface 20 by the vents 28, and the desired performance characteristics of the vertical wind turbine 10. For example, there can be 4, 5, 8, 12, 15, 20, or any number of vents 28, and they can be arranged in any geometric or row pattern, such as a V-pattern, a single row, three rows, a rectangular grid, or an irregularly-shaped grid.

[0098] In the embodiment shown in FIGs. 2C and 3C, each vent 28 is rectangular in cross-sectional shape (e.g., as viewed from the outer surface 19 or the inner surface 20). However, in other embodiments (not shown), the vents 28 can have any shape, including square, circular, oval, airfoil-shaped, triangular, trapezoidal, or any other shape, depending on the desired performance characteristics of the vertical wind turbine 10.

[0099] In the embodiment shown in FIGs. 2C and 3C, each blade 12c includes an outer channel 24, an inner channel 26, and a plurality of vents 28. However, in other embodiments (not shown), each blade 12c can include a plurality of vents 28, but each blade may not include an outer channel 24 and an inner channel 26. In some embodiments (not shown), each blade 12c can include a plurality of vents 28, but each blade may only include a single outer channel 24 or a single inner channel 26. For example, each blade 12c may include at least one channel 24 or 26 extending along the blade 12c in a direction substantially parallel to the rotational axis (i.e., the axle 16) of the vertical wind turbine 10.

[00100] As can be seen in FIG. 3C, the plurality of vents 28 are preferably oriented at an angle α to the centerline connecting the leading edge 17 with the trailing edge 18. As will be discussed below related to FIGs. 4A-6 and TABLE 1, an angle α can be chosen for a particular blade 12c to achieve a balance between the wind that passes through the blade 12c and the plurality of vents 28 serving as additional stall surfaces in the blade 12c. In the embodiment shown in FIG. 3 C, the angle α is approximately 50 degrees. However, in other embodiments, the angle α can be anywhere between approximately 15 and 165 degrees, more preferably an acute angle, for example, between approximately 30 and 70 degrees, depending on several factors, including, for example, the particular aspect ratio (i.e., the length Z/maximum thickness T ratio of the blade 12c) of the cross-sectional profile 22c of the blade 12c. For example, as will be discussed below related to FIGs. 5A-5H, a particular angle α can be selected to reduce the points in the motion of the blades 12c in the vertical wind turbine 10 that result in negative torque acting on the vertical wind turbine 10.

[00101] In the embodiment shown in FIG. 3C, each row of vents 28 has an angle α of approximately 50 degrees. However, in other embodiments (not shown), each row or a particular grouping of vents 28 can have an angle α that is different from the remaining vents 28. For example, in one embodiment (not shown), the row of vents 28 closest to the leading edge 17 of the blade 12c can have a first angle α, and the row of vents 28 closes to the trailing edge 18 can have a second angle α that is different from the first angle alpha.

[00102] Although in the embodiments shown in FIGs. IA- 1C, 2C, and 3C depict a plurality of vents 28 as holes penetrating completely through the blade 12c from the outer surface 19 to the inner surface 20, in other embodiments (not shown), the plurality of vents 28 may not penetrate completely through the blade 12c, or the plurality of vents 28 can be raised surface features, such as round bumps, ridge lines, or tubercle-like projections. It is believed that the inclusion of vents 28 that do not penetrate completely through the blade 12c or are raised features, extending from the outer surface 19 and the inner surface 20, may provide a benefit of increased torque from providing additional stall surfaces for the wind having velocity vectors normal to the stall surfaces to push against, as the blades 12c move in the rotational direction Rl . These additional embodiments of the plurality of vents 28 may enhance the laminar flow around the blades 12c, thereby improving positive torque and/or net work.

[00103] In some embodiments (not shown), the blades 12c can include end caps or other modifications (such as tubercle-like structures or projections) to the top and bottom of the outer surface 19 and the inner surface 20 (perpendicular to the outer surface 19 and the inner surface 20), in order to reduce wingtip losses and reduce turbulence at the end of the blades 12c, thereby improving positive torque and/or net work performance of the vertical wind turbine 10.

[00104] FIGs. 4A-4C are CFD models showing the wind velocity profile resulting from an 8 mph wind flow field moving across a vertical wind turbine including the blades depicted in FIGs. 2A-2C, respectively. Referring to FIGs. 4A-4C, CFD models 30, 32, and 34 respectively include an 8 mph wind W moving across a set of three blades 12a- 12c, respectively, attached to struts 14 and an axle 16 in a similar manner as for the embodiment shown in FIGs. IA- 1C. Each of the three blades 12 are at positions 1, 2, and 3, respectively, at which points each blade 12 is approximately 120 degrees apart from the other two blades 12, as in the embodiment depicted in FIGs. 1A-1C. The wind W includes regions of high velocity, W_H, that are higher than the initial far-field velocity of the wind W, and regions of low velocity, W_L, that are lower than the initial far-field velocity of the wind W.

[00105] As can be seen in FIG. 4A, the 8 mph far-field velocity wind W is blowing from right to left. The wind W reaches the leading blade 12a at position 1 (which in FIG. 4A is at an angular orientation approximately 30 degrees from a position normal to the velocity vectors of the wind W), leaving a low- velocity wind area W_L behind it {i.e., in the direction of the velocity vectors of the wind W). The blade 12a at position 1 causes a large velocity drop in the wind W from the outer surface 19 to the inner surface 20 of the blade 12a. The presence of the low- velocity wind area W_L behind the blade 12a at position 1 means that there is relatively little force on the blade 12a at position 2, which is substantially surrounded by the low-velocity wind area W_L- This force distribution on the blades 12a may result in a negative torque acting on the vertical wind turbine 10 when the blades 12a are in the orientation at positions 1, 2, and 3 as shown in FIG. 4A. The magnitude of the negative torque acting on the vertical wind turbine 10 when the blades 12a are in the position shown in FIG. 4A can be seen in FIGs. 5A-5H, depending on the speed of the wind W. Also in FIG. 4A, it can be seen that there is a high- velocity wind area W_H, which may be a beneficial location to locate one of the blades 12 of a second vertical wind turbine 10, in order to benefit from the excess energy that the first vertical wind turbine 10 (shown in FIG. 4A) has transferred to the wind area Wu-

[00106] As can be seen in FIG. 4B, the 8 mph far-field velocity wind W is blowing from right to left across three blades 12b, having channels 24 and 26. Not much difference can be seen in the magnitude of the velocity vectors of wind JFbetween FIGs. 4A and 4B, but it is believed that the vertical wind turbine 10 shown in FIG. 4B is capable of reliably self-starting and a producing higher net torque for each rotation of the blades 12b, due to the presence of the channels 24 and 26.

[00107] As can be seen in FIG. 4C, the 8 mph far-field velocity wind W is blowing from right to left across three blades 12c, having channels 24 and 26 and a plurality of vents 28. The wind W reaches the leading blade 12a at position 1, leaving a low- velocity wind area W_L behind it, but the velocity drop in the wind W from the outer surface 19 to the inner surface 20 of the blade 12c at position 1 is smaller than the blade 12a at position 1 in FIGs. 4A and 4B. This higher resulting velocity in the low- velocity wind area W_L behind the blade 12c at position 1 means that there is an increased force on the blade 12c at position 2, compared to the force on the blade 12a at position 2 in FIGs. 4A and 4B. This modified force distribution on the blades 12c may result in a positive torque or lower negative torque acting on the vertical wind turbine 10 when the blades 12c are in the orientation at positions 1, 2, and 3 as shown in FIG. 4C.

[00108] The magnitude of the positive torque or lower negative torque acting on the vertical wind turbine 10 when the blades 12c are in the position shown in FIG. 4C can be seen in FIGs. 5A-5H, depending on the speed of the wind W. It is believed that the presence of the plurality of vents 28 in the blade 12c at position 1 may be responsible for the higher resulting velocity in the low- velocity wind area W_L, because some of the wind from wind area W is permitted to pass through the blade 12c at position 1 via the plurality of vents 28, thereby retaining some of the initial velocity in the same direction.

[00109] FIGs. 4D-4F are CFD models showing the wind pressure profile resulting from an 8 mph wind flow field moving across a vertical wind turbine including the blade depicted in FIGs. 2A-2C, respectively. Referring to FIGs. 4D-4F, CFD models 36, 37, and 38 respectively include an 8 mph wind having a base pressure P moving across a set of three blades 12a- 12c, respectively, attached to struts 14 and an axle 16 in a similar manner as for the embodiment shown in FIGs. 1A-1C. Each of the three blades 12 are at positions 4, 5, and 6, respectively, at which points each blade 12 is approximately 120 degrees apart from the other two blades 12, as in the embodiment depicted in FIGs. 1A-1C. The wind at base pressure P includes regions of low pressure, P_L and P_L , that are lower than the initial far-field pressure P of the wind.

[00110] As can be seen in FIG. 4D, the 8 mph far field velocity wind having a pressure P is blowing from right to left, in a similar manner as in FIG. 4A. The wind having a pressure P reaches the leading blade 12a at position 4 and the trailing blade 12a at position 6 (the blades are positioned such that the blade 12a at position 5 is at an angular orientation approximately 70 degrees from a position normal to the pressure gradient vectors of the wind having a pressure P), leaving low-pressure areas P_L and P_L behind the blades 12a at positions 4 and 6, respectively. The blades 12a at positions 4 and 6 cause large pressure drops in the wind having a pressure P from the outer surface 19 to the inner surface 20 of the blade 12a at position 4 and from the inner surface 20 to the outer surface 19 of the blade 12a at position 6. These pressure drops across the blades 12a at positions 4 and 6 create a force distribution on the blades 12a that may result in a negative torque acting on the vertical wind turbine 10 when the blades 12a are in the orientation at positions 4, 5, and 6 as shown in FIG. 4D. The magnitude of the negative torque acting on the vertical wind turbine 10 when the blades 12a are in the position shown in FIG. 4D can be seen in FIGs. 5A-5H, depending on the speed of the wind having a pressure P.

[00111] As can be seen in FIG. 4E, the 8 mph far field velocity wind having a pressure P is blowing from right to left across three blades 12b, having channels 24 and 26, in positions 4, 5, and 6. Although some difference can be seen in the magnitude of the pressure gradient vectors of the wind having a pressure P between FIGs. 4D and 4E, there are still low-pressure areas P_L and P_L behind the blades 12b at positions 4 and 6, which may result in a negative torque acting on the vertical wind turbine 10 when the blades 12b are in the orientation at positions 4, 5, and 6 shown in FIG. 4E. However, there may be an improved ability of the vertical wind turbine 10 shown in FIG. 4E to achieve self-starting and a higher net torque produced for each rotation of the blades 12b, due to the presence of the channels 24 and 26.

[00112] As can be seen in FIG. 4F, the 8 mph far field velocity wind having a pressure P is blowing from right to left across three blades 12c, having channels 24 and 26 and a plurality of vents 28, in positions 4, 5, and 6. In FIG. 4F, it appears that the areas of relative low pressure P_L and P_L have been substantially eliminated. This lower resulting pressure gradient change across the blades 12c in positions 4 and 6 can produce a positive torque or lower negative torque acting on the vertical wind turbine 10 when the blades 12c are in the positions shown in FIG. 4F.

[00113] The magnitude of the positive torque or lower negative torque acting on the vertical wind turbine 10 when the blades 12c are in the position shown in FIG. 4F can be seen in FIGs. 5A-5H, depending on the speed of the wind W. Without being bound by theory, it is believed that the presence of the plurality of vents 28 in the blade 12c at positions 4, 5, and 6 may be responsible for the higher resulting pressure in the area behind the blades 12c at positions 4 and 6, relative to the more substantial pressure drops across the blades 12a and 12b at positions 4 and 6 as shown in FIGs. 4D and 4E, because some of the wind having a pressure P is permitted to pass through the blades 12c via the plurality of vents 28, thereby retaining more of the initial pressure level.

[00114] Referring to FIG. 5A, line 41a represents the simulated total torque acting on all three blades 12a having a cross-sectional profile 22a with the same aspect ratio as the NACA 0015 blade profile, at twelve different angular positions ranging from the first blade 12a (farthest to the right in FIG. 4A) being at an initial position of zero degrees {i.e., fully normal to the direction of the wind flowing from right to left) to intermediate rotational positions in 10-degree increments in a rotational direction Rl as shown in FIG. IA, to a final position of 120 degrees, at which point a second blade 12a has moved to the initial position of the first blade 12a. Line 41b represents the total torque acting on all three blades 12b (having channels 24 and 26) at the same angular positions as line 41a, and line 41c represents the total torque acting on all three blades 12c (having channels 24 and 26 and a plurality of vents 28) at the same angular positions as the line 41a.

[00115] As can be seen in FIG. 5A, lines 41a and 41b show blades 12a and 12b exhibiting negative torque regions, the most substantial being at approximately the 15-45 degree positions and the 65-75 degree positions. This likely means that blades 12a and 12b may not be able to self-start, so they may need a motor or other energy input to attain sufficient momentum to keep spinning in a rotational direction Rl as shown in FIG. IA. Although both lines 41a and 41b have substantial negative torque regions, line 41b (blade 12b with channels 24 and 26) has two areas, near 60 degrees and 100 degrees, where the positive torque is higher than line 41a (blade 12a), so the net work (integral of the torque curve over the entire 120-degree rotational distance) will be higher for line 41b than 41a, which likely means that blade 12b may be capable of extracting more energy out of a given wind flow than blade 12a. The net work resulting from each of the curves shown in FIGs. 5A-5H are shown in FIG. 6 and TABLE 1.

[00116] As can be seen in FIG. 5A, line 41c shows blade 12c exhibiting less substantial negative torque regions than lines 41a and 41b, the most substantial being at approximately the 100-120 degree position. However, the large negative torque region in lines 41a and 41b at approximately the 15-45 degree position has been converted to a positive torque region. It is believed that this reduction in the degree of negative torque with blade 12c is due to the presence of the plurality of vents 28, which may allow a reduction in the pressure gradient across the blades 12c and a resultant reduction in some of the forces that contribute to negative torque. This likely means that blade 12c may have an improved ability to self- start compared to blades 12a and 12b. Also, the net work is higher for line 41c than either 41a or 41b (which can be seen in FIG. 6 and TABLE 1), which likely means that blade 12c may be capable of extracting more energy out of a given wind flow than either blade 12a or blade 12b.

[00117] Referring to FIG. 5B, lines 42a, 42b, and 42c are similar to lines 41a, 41b, and 41c, except the lines 42a, 42b, and 42c represent the total torque acting on all three blades 12a, 12b, and 12c having cross-sectional profiles 22a, 22b, and 22c with the same aspect ratio as the NACA 0012 blade profile, rather than the NACA 0015 blade profile. Compared to the NACA 0015 blade profile, the NACA 0012 blade profile has an aspect ratio that is narrower (i.e., smaller maximum thickness T between the outer surface 19 and the inner surface 20) for a given blade 12 length L (i.e., a given distance between the leading edge 17 and the trailing edge 18).

[00118] Just as in FIG. 5A, the lines 42a, 42b, and 42c in FIG. 5B show an increased positive torque of line 42b compared to 42a, and a less substantial negative torque region in line 42c compared to lines 42a and 42b that may result in an improved ability for the 12c blade with the NACA 0012 aspect ratio of the cross-sectional blade profile 22c to self-start. However, as will be discussed below relative to FIG. 6 and TABLE 1, line 42b has a higher net work than lines 42a and 42c, implying that in a 2 mph wind field, the 12b blade (with channels 24 and 26) with the NACA 0012 aspect ratio may extract more energy than the 12c blade (with channels 24 and 26 and the plurality of vents 28) with the NACA 0012 aspect ratio.

[00119] FIGs. 5C, 5E, and 5G show the predicted torque as a function of blade position resulting from the computer simulations of a 8 mph, 14 mph, and 20 mph wind flow field moving across each of three vertical wind turbines including the blades depicted in FIGs. 2A, 2B, and 2C, respectively, each blade having the NACA 0015 aspect ratio of the cross-sectional blade profile 22. FIGs. 5D, 5F, and 5H show the predicted torque as a function of blade position resulting from the computer simulations of a 8 mph, 14 mph, and 20 mph wind flow field moving across each of three vertical wind turbines including the blades depicted in FIGs. 2A, 2B, and 2C, respectively, each blade having the NACA 0012 aspect ratio of the cross-sectional blade profile 22. FIGs. 5C-5H show that the 12b blade may improve some of the positive torque regions relative to the 12a blade, and they also show that the 12c blade may improve some of the negative torque regions relative to the 12a and 12b blades. However, it is easier to determine which blade extracts the most energy from a given wind field by referring to FIG. 6 and TABLE 1.

[00120] FIG. 6 is a graph showing the simulated net work resulting from wind flow fields of 2, 8, 14, and 20 mph, moving across each of six vertical wind turbines including alternative embodiments of the blades depicted in FIGs. 2A, 2B, and 2C. TABLE 1 is a table showing the data depicted graphically in FIG. 6. Referring to FIG. 6, the net work for each of the six vertical wind turbines including alternative embodiments of the blades depicted in FIGs. 2 A, 2B, and 2C is shown. The net work shown in FIG. 6 is the integral over 120 degrees of the torque lines 41a through 48c shown in FIGs. 5A-5H, but with an adjustment that subtracts the estimated friction loss (e.g., from the bearings coupled to the axle 16) from the result of the integral.

Work (FT-LB) /1/3 revolution = Torque Energy minus Friction

Wind Speed NACA0015 NACA0015-1 NACA0015-2 NACA0012 NACA0012-1 NACA0012-2 2 0.002 0.008 0.016 0.001 0.008 0.003

8 0.010 0.077 0.268 0.068 0.126 0.153

14 0.092 0.270 0.801 0.042 0.562 0.467

20 0.211 0.477 1.803 0.008 0.810 0.899

TABLE 1 [00121] As can be seen in FIG. 6, the three embodiments of the blades 12a, 12b, and 12c depicted in FIGs. 2A, 2B, and 2C, respectively, that have a cross-sectional profile 22 with the same aspect ratio as the NACA 0015 blade profile are shown as blade profiles 51a, 51b, and 51c, respectively. The three embodiments of the blades 12a, 12b, and 12c depicted in FIGs. 2A, 2B, and 2C, respectively, that have a cross-sectional profile 22 with the same aspect ratio as the NACA 0012 blade profile (having a narrower aspect ratio than the NACA 0015 blade profile) are shown as blade profiles 52a, 52b, and 52c, respectively.

[00122] The net work data shown in FIG. 6 can allow a comparison of which embodiments of the invention allow harvesting of the most energy from a given wind area having a particular wind speed. FIG. 6 shows that at all wind speeds that were simulated, the blade 12c having a NACA 0015 aspect ratio profile with a cross-sectional profile 22c (having channels 24 and 26 and a plurality of vents 28) produced the highest net work. Although the blade 12b having a NACA 0015 aspect ratio profile with a cross-sectional profile 22b (having channels 24 and 26) produced less total work than the blade 12c, the blade 12b produced more total work than the blade 12a.

[00123] Among the blades 12 having a NACA 0012 aspect ratio profile, the benefits of the channels 24 and 26 and the plurality of vents 28 were still substantial, but less of a dramatic improvement than the blades 12 having a NACA 0015 (less narrow) aspect ratio profile. While not being bound by theory, it is believed that the blades 12 having a NACA 0015 (less narrow) aspect ratio profile may have received more benefit from the plurality of vents 28 (compared to the blades 12 having a NACA 0012 aspect ratio profile), because of the higher relative thickness of the blades based on the NACA 0015 profile, which may provide a greater stall surface area inside the vents 28 for a blade 12c of a given length L and height H. Comparing blade profiles 52a, 52b, and 52c, the blade 12c (having channels 24 and 26 and the plurality of vents 28) had the highest net work at 8 mph and 20 mph, but the blade 12b (having channels 24 and 26) had the highest net work at 2 mph and 14 mph. Both the blades 12b and 12c had a higher net work than the blade 12a, which had neither the channels 24 and 26 nor the plurality of vents 28.

[00124] Comparing the blade profiles 51b and 52b, the blade 12b with the NACA 0012 aspect ratio profile (having channels 24 and 26) had the highest net work at all wind speeds, but comparing the blade profiles 51c and 52c, the blade 12c with the NACA 0015 aspect ratio profile (having channels 24 and 26 and the plurality of vents 28) had the highest net work at all wind speeds. These results suggest that there are competing design considerations that may be taken into consideration when designing the blade 12 cross-sectional profile 22 for a particular set of blades 12 for a particular vertical wind turbine 10.

[00125] FIG. 7 illustrates the mechanical connection among components of an exemplary vertical wind turbine 60 that includes three blades 62, six struts 64, and an axle 66. Vertical wind turbine 60 preferably rotates about the axle 66 in a rotational direction Rl . Each blade 62 is spaced circumferentially about the axle 66, and each blade 62 has a leading edge 67, a trailing edge 68, an outer surface 69, and an inner surface 70. Each blade 62 has a height H2 {i.e., the total length of the leading edge 67 or the trailing edge 68 of each blade 62), a length L2 (i.e., the linear distance from the leading edge 67 to the trailing edge 68 of each blade 12), and a maximum thickness T2 (i.e., the maximum linear distance from the outer surface 69 to the inner surface 70 of each blade 62).

[00126] Each blade 62 is preferably attached to the axle 66 via two struts 64. In the embodiment shown in FIG. 7, each strut 64 is attached to a respective blade 62 at the Gaussian stress points, in the middle of the inner surfaces 70 of the respective blades 62. In some embodiments, such as those including blades 62 having a constant cross-section along the height H2, the Gaussian stress points G are located approximately 0.2071 *H2 from the top and bottom of each blade 62. The struts 64 can be attached to the inner surface 70 of each blade 62 by any known mechanism, including welding, bolting, clamping, or chemical bonding. In some embodiments, there can be a single strut 64 for each blade 62, or there can be greater than two struts 64 for each respective blade 62. For example, each blade 62 can be coupled to the axle 66 by 3, 4, 5, 6, or any number of struts 64. The arrangement of the components shown in FIG. 7 can be employed with any blade configuration described herein.

[00127] It has been observed that a vertical wind turbine 60 having the design shown in FIG. 7 and blades disclosed herein can combine lift and drag principles to allow the vertical wind turbine 60 to self-start and achieve sufficient angular momentum to maintain rotational velocity at low wind speeds, thereby preventing the need to rely on an external energy source. Without being bound by theory, it is believed that the vertical wind turbine 60 shown in FIG. 7 can achieve increased efficiency in urban and suburban areas, given that wind in such areas tends to be unsteady, turbulent, and low-speed.

[00128] Referring to FIG. 8A, an airfoil blade 62a suitable for use in any of the vertical wind turbines disclosed herein has a leading edge 67, a trailing edge 68, an outer surface 69, an inner surface 70, and a cross-sectional profile 72a. The cross-sectional profile 72a shows the airfoil shape of a cross-section of the airfoil blade 62a, perpendicular to outer surface 69 and the inner surface 70. In the embodiment shown in FIG. 8A, the blade 62a has a substantially constant cross-sectional profile 72a throughout the entire height of the blade 62a (i.e., the total length of the leading edge 67 or the trailing edge 68 of the blade 62a). In the embodiment shown in FIG. 8 A, the cross-sectional profile 72a has the aspect ratio of a National Advisory Committee for Aeronautics ("NACA") 0012 airfoil, which has a maximum thickness that is 12% of the length. In some embodiments, cross-sectional profile 72a can have an airfoil-like (or substantially airfoil) shape that is capable of generating lift in the radial or circumferential direction, such lift being sufficient to generate a dynamic torque that is capable of generating and sustaining a rotational velocity of the vertical wind turbine 60. As can be seen in FIG. 8A, the cross-sectional profile 72a is preferably symmetrical about a centerline connecting the leading edge 67 with the trailing edge 68.

[00129] Referring to FIG. 8B, a hybrid airfoil blade 62b suitable for use in any of the vertical wind turbines disclosed herein has a leading edge 67, a trailing edge 68, an outer surface 69, an inner surface 70, a cross-sectional profile 72b, and an inner channel 76. The cross- sectional profile 72b shows the hybrid shape of a cross-section of the airfoil blade 12b, perpendicular to outer surface 69 and the inner surface 70. In the embodiment shown in FIG. 8B, the blade 62b has a substantially constant cross-sectional profile 72b throughout the entire height of the blade 62b. In some embodiments, the hybrid airfoil blade 62b can have a single outer channel 74 in place of the single inner channel 76, depending on the desired design and performance characteristics of the vertical wind turbine 60.

[00130] Cross-sectional profile 72b of the blade 62b preferably has a airfoil shape, with portions similar to the cross-sectional profile 72a of the blade 62a, but with a portion removed corresponding to the inner channel 76. As can be seen in FIG. 8B, the front of the cross- sectional profile 72b of the blade 62b near the leading edge 67 and the rear of the blade 62b near the trailing edge 68 adhere to an airfoil shape, but the portion of the cross-sectional profile 72b at inner channel 76 is carved out (or formed), preferably providing a curved stall surface that can assist the vertical wind turbine 60 in self-starting. The curved surface in the inner channel 26 can provide a wind stagnation location along the airfoil blade 62b, which may increase the pressure on the blade 62b such that the majority of the wind's velocity energy is transferred into pressure on the blade 62b, thereby helping to initiate movement in the direction of the leading edge 67 (i.e., in the rotational direction Rl). The inner channel 76 may provide improved self-starting for the vertical wind turbine 60 having the blades 62b, while not substantially adding to the drag forces (thereby reducing positive torque and/or net work) at higher rotational speeds. In some embodiments, the inner channel 76 can be bounded by two wind stagnation projections, which are shown in FIG. IB, for example, as flat plates having substantially the same cross-sectional profile as the base airfoil-like profile of the blade, without portions carved out (or formed) at the top and bottom ends of the inner channel 76.

[00131] The particular airfoil shape of the portion of the cross-sectional profile 72b that is similar to the cross-sectional profile 72a can be any airfoil shape, but in the embodiment shown in FIG. 8B, the cross-sectional profile 72b has the aspect ratios of a NACA 0012 airfoil, but with portions of the cross-sectional profile 72b removed at the inner channel 76. As can be seen in FIG. 8B, the cross-sectional profile 72b is preferably asymmetrical about a centerline connecting the leading edge 67 with the trailing edge 68.

[00132] Referring to FIG. 8C, a hybrid blade 62c suitable for use in any of the vertical wind turbines disclosed herein has a leading edge 67, a trailing edge 68, an outer surface 69, an inner surface 70, a cross-sectional profile 72c, an outer channel 74, and an inner channel 76. The cross-sectional profile 72c shows the hybrid shape of a cross-section of the airfoil blade 62c, perpendicular to outer surface 69 and the inner surface 70. In the embodiment shown in FIG. 8C, the blade 62c has a substantially constant cross-sectional profile 72c throughout the entire height of the blade.

[00133] Cross-sectional profile 72c of the blade 62c preferably has an airfoil shape, with portions similar to the cross-sectional profile 72a of the blade 62a, but with portions removed corresponding to the outer channel 74 and the inner channel 76. As can be seen in FIG. 8C, the front of the cross-sectional profile 72c of the blade 62c near the leading edge 77 and the rear of the blade 62c near the trailing edge 68 adhere to an airfoil shape, but the portions of the cross- sectional profile 72c at the outer channel 74 and the inner channel 76 are carved out (or formed), preferably providing curved stall surfaces that can assist the vertical wind turbine 60 in self- starting. The curved surfaces in the channels 74 and 76 can provide wind stagnation locations along the airfoil blade 62c, which may increase the pressure on the blade 62c such that the majority of the wind's velocity energy is transferred into pressure on the blade 62c, thereby helping to initiate movement in the direction of the leading edge 67 (i.e., in the rotational direction Rl). These channels 24 and 26 may provide improved self-starting for the vertical wind turbine 60 having the blades 62c, while not substantially adding to the drag forces (thereby reducing positive torque and/or net work) at higher rotational speeds. In some embodiments, the channels 74 and 76 can be bounded by two wind stagnation projections, which are shown in FIG. IB, for example, as flat plates having substantially the same cross-sectional profile as the base airfoil-like profile of the blade, without portions carved out (or formed) at the top and bottom ends of the channels 74 and 76.

[00134] The particular airfoil shape of the portion of the cross-sectional profile 72c that is similar to the cross-sectional profile 72a can be any airfoil shape, but in the embodiment shown in FIG. 8C, the cross-sectional profile 72c has the aspect ratios of a NACA 0012 airfoil, but with portions of the cross-sectional profile 72c removed at the outer channel 74 and the inner channel 76. As can be seen in FIG. 8C, the cross-sectional profile 72c is preferably symmetrical about a centerline connecting the leading edge 67 with the trailing edge 68.

[00135] Referring to FIG. 8D, a hybrid blade 62d suitable for use in any of the vertical wind turbines disclosed herein has a leading edge 67, a trailing edge 68, an outer surface 69, an inner surface 70, a cross-sectional profile 72d, outer scallops 74', 74", and 74'", and inner scallops 76', 76", and 76'". The cross-sectional profile 72d shows the hybrid shape of a cross- section of the airfoil blade 62d, perpendicular to outer surface 69 and the inner surface 70. In the embodiment shown in FIG. 8D, the blade 62d has a substantially constant cross-sectional profile 72d throughout the entire height of the blade. As used herein, a scallop is one of a plurality of channels located on an inner surface or an outer surface of a turbine blade. A scallop or a channel can have any of the sizes, shapes, or locations along an inner surface or an outer surface of a turbine blade that are disclosed herein. A scallop in any one embodiment can have the same size, shape, or location of a channel in another embodiment, and a channel in any one embodiment can have the same size, shape, or location of a scallop in another embodiment.

[00136] Cross-sectional profile 72d of the blade 62d preferably has an airfoil shape, with portions similar to the cross-sectional profile 72a of the blade 62a, but with portions removed corresponding to the outer scallops 74', 74", and 74'", and the inner scallops 76', 76", and 76'". As can be seen in FIG. 8D, the front of the cross-sectional profile 72d of the blade 62d near the leading edge 77 adheres to an airfoil shape, but the portions of the cross-sectional profile 72d at the outer scallops 74', 74", and 74'", and the inner scallops 76', 76", and 76'" are carved out (or formed), preferably providing curved stall surfaces that can assist the vertical wind turbine 60 in self-starting. The curved surfaces in the outer scallops 74', 74", and 74'" and the inner scallops 76', 76", and 76'" can provide wind stagnation locations along the airfoil blade 62d, which may increase the pressure on the blade 62d such that the majority of the wind's velocity energy is transferred into pressure on the blade 62d, thereby helping to initiate movement in the direction of the leading edge 67 (i.e., in the rotational direction Rl). These outer scallops 74', 74", and 74'", and inner scallops 76', 76", and 76'" may provide improved self-starting for the vertical wind turbine 60 having the blades 62d, while not substantially adding to the drag forces (thereby reducing positive torque and/or net work) at higher rotational speeds. In some embodiments, the outer scallops 74', 74", and 74'", and the inner scallops 76', 76", and 76'" can be bounded by two wind stagnation projections, which are shown in FIG. IB, for example, as flat plates having substantially the same cross-sectional profile as the base airfoil-like profile of the blade, without portions carved out (or formed) at the top and bottom ends of the outer scallops 74', 74", and 74'", and the inner scallops 76', 76", and 76'".

[00137] The particular airfoil shape of the portion of the cross-sectional profile 72d that is similar to the cross-sectional profile 72a can be any airfoil shape, but in the embodiment shown in FIG. 8D, the cross-sectional profile 72d has the aspect ratios of a NACA 0012 airfoil, but with portions of the cross-sectional profile 72d removed at the outer scallops 74', 74", and 74'", and the inner scallops 76', 76", and 76'". As can be seen in FIG. 8D, the cross-sectional profile 72d is preferably symmetrical about a centerline connecting the leading edge 67 with the trailing edge 68. In some embodiments, the cross-sectional profile 72d can be asymmetrical about the centerline. For example, there may be a single outer scallop 74' and three inner scallops 76', 76", and 76'". In embodiments with equal numbers of outer scallops and inner scallops, the outer scallops 74', 74", and 74'", and the inner scallops 76', 76", and 76'" may be positioned at different locations along the cross-sectional profile 72d. For example, the leading inner scallop 76' may be closer to the leading edge 67 than the leading outer scallop 74'.

[00138] Referring to FIG. 8E, a hybrid blade 62e suitable for use in any of the vertical wind turbines disclosed herein has a elliptical leading edge 67e, a rounded trailing edge 68e, an outer surface 69, an inner surface 70, a cross-sectional profile 72e, an outer circular channel 74e, and an inner circular channel 76e. The cross-sectional profile 72e shows the hybrid shape of a cross-section of the airfoil blade 62e, perpendicular to outer surface 69 and the inner surface 70. In the embodiment shown in FIG. 8E, the blade 62e has a substantially constant cross-sectional profile 72e throughout the entire height of the blade. As can be seen in FIG. 8E, the cross- sectional profile 72e is symmetrical about a centerline connecting the leading edge 67 with the trailing edge 68. The hybrid blade 62e shown in FIG. 8E is based on the disclosure in U.S. Patent Application Pub. No. 2008/0273978.

[00139] Referring to FIG. 9A, a graph 80 shows the simulated net tangential force (in the direction of rotation) acting on each of the five 3 -blade vertical wind turbines including alternative embodiments of the blades as depicted in FIGs. 8A-8E as a function of leading blade position. The net tangential force data shown in FIG. 9 A can allow a comparison of which embodiments of the invention allow harvesting of the most work or energy from an example 24.6 mph wind field.

[00140] The net tangential force experienced by the five embodiments of the blades 62a, 62b, 62c, 62d, and 62e depicted in FIGs. 8A-8E, respectively, are shown as curves 82a, 82b, 82c, 82d, and 82e, respectively. The net tangential force shown in graph 80 is the sum of the net tangential force acting on all three blades of each turbine, resulting from wind flow fields of 24.6 mph moving across the turbines, as the leading blade (the blade that is closest to the direction from which the wind is blowing) moves from an initial position where the longitudinal axis is perpendicular to the direction of the wind to a final position that is 120° rotated about the axis 66.

[00141] Referring to FIG. 9B, the diagram 83 shows the vector components of the net tangential force 84 that is acting on each of the five 3 -blade vertical wind turbines to produce the data that is depicted in FIG. 9A. The net tangential force 84 is a circumferentially directed component of the vector sum of the lift force 85 and the drag force 86 produced by a wind field acting on a turbine blade 62 at an angular orientation 87 relative to the direction of the wind. The net tangential force 84 can be calculated via the following formula: T = -D*cosθ + L*sinθ, where T is the net tangential force 84, L is the lift force 85, D is the drag force 86, and θ is the angular orientation 87 (or angle of attack) of the blade 62 relative to the direction of the wind. The net tangential force 84 is tangent to a circle defined by the blades 62 as they rotate about the axle 66 in a substantially circular path, for example, shown as the diameter D in FIG. IA.

[00142] Referring again to FIG. 9A, graph 80 shows that at all rotational positions that were simulated, the blade 62d having a NACA 0012 aspect ratio profile with a cross-sectional profile 72d (having outer scallops 74', 74", and 74'", and inner scallops 76', 76", and 76'") produced the highest net tangential force. The blade 62c having a NACA 0012 aspect ratio profile with a cross-sectional profile 72c (having an outer channel 74 and an inner channel 76) produced the next highest net tangential force at all rotational positions, and it can be seen in FIG. 9A that the curve 82c representing the blade 62c is approximately 10% lower than the curve 82d representing the scalloped blade 62d.

[00143] The blade 62b having a NACA 0012 aspect ratio profile with a cross-sectional profile 72b (having a single inner channel 76) and the blade 62e having an elliptical aspect ratio profile with a cross-sectional profile 72e (having an outer circular channel 74e and an inner circular channel 76e) appear in FIG. 9A to have produced approximately the same net tangential force at some rotational positions, although at most rotational positions, the curve 82b representing the blade 62b is higher than the curve 82e representing the blade 62e. As can be seen below in TABLE 2, the asymmetric blade 62b produced approximately 21% less net work than the scalloped blade 62d, and the elliptical blade 62e produced approximately 29% less net work than the scalloped blade 62d.

[00144] The blade 62a having a NACA 0012 aspect ratio profile with a cross-sectional profile 72a produced a substantially lower (approximately 30-50% lower) net tangential force at all rotational positions than the scalloped blade 62d, and it can be seen in FIG. 9 A that the curve 82a representing the blade 62a is lower than the other four curves at all rotational positions.

[00145] TABLE 2 is a table showing the net work produced by each turbine including a respective embodiment of the blades depicted in FIGs. 8A-8E, without subtracting the estimated friction loss (however, the estimated friction loss was subtracted when the data for FIG. 6 and TABLE 1 was calculated). For example, the friction loss due to transferring the kinetic energy of a vertical wind turbine to an attached electric generator can be estimated to be 2-3% from the gears and 5-10% from the motor. The net work produced by each turbine including a respective embodiment of the blades depicted in FIGs. 8A-8E can be calculated by integrating the force value over 120°. If a first turbine including a first blade embodiment experiences a higher net tangential force than a second turbine including a second blade embodiment throughout a 120° path of rotation, then the net work produced by the first turbine will be greater than the net work produced by the second turbine. TABLE 2 shows a similar relative performance among the 5 blade designs that are shown in FIG. 9.

TABLE 2

[00146] Among the blades 62 having a NACA 0012 aspect ratio profile, the benefits of the blades 62b and 62c having one or more channels 24 and 26 were substantial compared to the blade 62a without the channels 74 or 76, but less of a dramatic improvement than the blade 62d having outer scallops 74', 74", and 74'", and inner scallops 76', 76", and 76'". Among the blades 62 having channels 74 and/or 76 or scallops 74', 74", 74'", 76', 76", and 76'", the benefits of the blades 62b, 62c, and 62d having the NACA 0012 aspect ratio profile were substantial compared to the blade 62e having an elliptical aspect ratio profile. These results suggest that there are competing design considerations that may be taken into consideration when designing the blade 62 cross-sectional profile 72 for a particular set of blades 62 for a particular vertical wind turbine 60.

[00147] Referring to FIG. 1OA, a hybrid airfoil blade 92 suitable for use in any of the vertical wind turbines disclosed herein has a leading edge 97, a trailing edge 98, an outer surface 99, an inner surface 100, an open position cross-sectional profile 102, and an articulating panel 105. The articulating panel 105 includes an inner channel 106 and an airfoil portion 107. The articulating panel 105 defines a center of inertia 108. The articulating panel 105 is rotatable relative to the remainder of the blade 92 by pivoting about a pivot axis 109.

[00148] The cross-sectional profile 102 shows the hybrid asymmetric shape of a cross- section of the airfoil blade 92, perpendicular to outer surface 99 and the inner surface 100. In the embodiment shown in FIG. 1OA, the blade 92 has a substantially constant cross-sectional profile 102 throughout the entire height of the blade 92. In some embodiments, the hybrid airfoil blade 92 can have a single outer channel in place of the single inner channel 106, depending on the desired design and performance characteristics of the vertical wind turbine 60.

[00149] Cross-sectional profile 102 of the blade 92 preferably has an airfoil shape, with portions similar to the cross-sectional profile 72a of the blade 62a, but with a portion removed corresponding to the inner channel 106. Cross-sectional profile 102 of the blade 92 shown in FIG. 1OA is similar to cross-sectional profile 72b of the blade 62b that is shown in FIG. 8B, and the blade 92 can have a similar self-starting behavior, wherein the inner channel 106 preferably provides a curved stall surface that can assist the vertical wind turbine 60 in self-starting.

[00150] In some embodiments, the inner channel 106 can be bounded by two wind stagnation projections, which are shown in FIG. IB, for example, as flat plates having substantially the same cross-sectional profile as the base airfoil-like profile of the blade, without portions carved out (or formed) at the top and bottom ends of the inner channel 106.

[00151] The particular airfoil shape of the portion of the cross-sectional profile 102 that is similar to the cross-sectional profile 72a can be any airfoil shape, but in the embodiment shown in FIG. 1OA, the cross-sectional profile 102 has the aspect ratios of a NACA 0012 airfoil, but with portions of the cross-sectional profile 102 removed at the inner channel 106. As can be seen in FIG. 1OA, the cross-sectional profile 102 is preferably asymmetrical about a centerline connecting the leading edge 97 with the trailing edge 98.

[00152] In other embodiments, the cross-sectional profile 102 can be symmetrical about a centerline connecting the leading edge 97 with the trailing edge 98. For example, the cross- sectional profile 102 can include a second articulating panel opposite a first articulating panel 105, such that in the open position, the cross-sectional profile 102 includes an outer channel as well as the inner channel 106.

[00153] In other embodiments, the cross-sectional profile 102 can include a plurality of articulating panels 105 on each of the outer surface 99 and the inner surface 100, such that, in an open position, the outer surface 99 and the inner surface 100 can define outer scallops 74', 74", and 74'", and inner scallops 76', 76", and 76'" in a manner similar to the cross-sectional profile 72d that is shown in FIG. 8D.

[00154] Referring to FIG. 1OB, the hybrid airfoil blade 92 has an intermediate position cross-sectional profile 102', in which the articulating panel 105 has moved from the initial position shown in FIG. 1OA to an intermediate position.

[00155] To move from the initial position shown in FIG. 1 OA to the intermediate position shown in FIG. 1OB, the articulating panel 105 rotates about the pivot axis 109 in a clockwise direction. As shown, the articulating panel 105 has a center of inertia 108 that is initially positioned radially inward of the pivot axis 109 in FIG. 1OA. As the blades 92 rotate about the axle 66 of the vertical wind turbine 60 (or any other impeller disclosed herein), a centrifugal force causes the articulating panel 105 to rotate about the pivot axis 109 such that the center of inertia 108 moves from a position that is radially inward of the pivot axis 109 towards a position that is radially outward of the pivot axis 109. As shown in FIG. 1OB, the center of inertia 108 has begin to move radially outward relative to the pivot axis 109, causing the articulating panel 105 to rotate in a clockwise direction relative to the pivot axis 109.

[00156] Referring to FIG. 1OC, the hybrid airfoil blade 92 has a closed position cross- sectional profile 102", in which the articulating panel 105 has moved from the intermediate position shown in FIG. 1OB to a closed position.

[00157] To move from the intermediate position shown in FIG. 1OB to the closed position shown in FIG. 1OC, the articulating panel 105 continues to rotate about the pivot axis 109 in a clockwise direction. As the blades 92 rotate about the axle 66 of the vertical wind turbine 60 (or any other impeller disclosed herein), a centrifugal force continues to cause the articulating panel 105 to rotate about the pivot axis 109 such that the center of inertia 108 moves from a position that is radially inward of the pivot axis 109 towards a position that is radially outward of the pivot axis 109. As shown in FIG. 1OC, the center of inertia 108 has reached a position that is located radially outward relative to the pivot axis 109, causing the articulating panel 105 to be positioned such that the airfoil portion 107 is located along the inner surface 100, while the inner channel 106 has rotated to a position inside the remainder of the blade 92.

[00158] In the embodiment shown in FIG. 1OC, the cross-sectional profile 102" has the aspect ratio of a National Advisory Committee for Aeronautics ("NACA") 0012 airfoil, which has a maximum thickness that is 12% of the length. As can be seen in FIG. 1OC, the cross- sectional profile 102" is preferably symmetrical about a centerline connecting the leading edge 97 with the trailing edge 98. Cross-sectional profile 102" of the blade 92 shown in FIG. 1OC is similar to cross-sectional profile 72a of the blade 62a that is shown in FIG. 8 A, and the blade 92 can have a similar Darrieus-like lift force behavior as the blade 62a.

[00159] The blade 92 can be designed such that at lower wind speeds, the blade 92 has an open position cross-sectional profile 102 in which the inner channel 106 is positioned along the inner surface 100, while at higher wind speeds, the blade 92 has a closed position cross-sectional profile 102" in which the airfoil portion 107 is positioned along the inner surface 100. When the articulating panel 105 pivots about the pivot axis 109 from the open position to the closed position due to centrifugal force, the pivoting of the articulating panel 105 can be stopped when the articulating panel 105 reaches the closed position by designing an interference between the airfoil portion 107 and the remainder of the inner surface 100. Such an interference between the airfoil portion 107 and the remainder of the inner surface 100 can cause the airfoil portion 107 to be locked in position against the remainder of the inner surface 100, so long as a sufficient centrifugal force is continued to be applied to the blade 92 from rotation of the blade 92 about the axle 66.

[00160] When the wind velocity decreases or when the blade 92 begins to rotate at a lower angular velocity about the axle 66, such that the centrifugal force that is applied to the blade 92 drops below a predetermined threshold, the articulating panel 105 can rotate counterclockwise from the closed position shown in FIG. 1OC to the open position shown in FIG. 1OA. Any mechanism can be used to return the articulating panel 105 from the closed position back to the open position when the centrifugal force is reduced, including, for example, a torsional spring or a gravitational cam- like spring that is biased towards forcing the articulating panel 105 to the open position shown in FIG. 1OA. [00161] Referring to FIG. 1 IA, a hybrid airfoil blade 112 suitable for use in any of the vertical wind turbines disclosed herein has a leading edge 117, a trailing edge 118, an outer surface 119, an inner surface 120, an open position cross-sectional profile 122, an outer articulating wing 123, and an inner articulating wing 125. When the articulating wings 123 and 125 are in the open position, the outer articulating wing 123 and the outer surface 119 define an outer pocket 124, and the inner articulating wing 125 and the inner surface 120 define an inner pocket 126. In the embodiment shown in FIG. 1 IA, the blade 112 has a substantially constant cross-sectional profile 122 throughout the entire height of the blade. In some embodiments, the cross-sectional profile 122 can include a plurality of articulating wings 123 and/or 125 on each of the outer surface 119 and/or the inner surface 120.

[00162] When the outer articulating wing 123 is in the open position, the outer articulating wing 123 and the outer surface 119 further define outer scallop portions 124a and 124b, and outer scallops 124", and 124'". When the inner articulating wing 125 is in the open position, the inner articulating wing 125 and the inner surface 120 further define inner scallop portions 126a and 126b, and inner scallops 126", and 126'".

[00163] The cross-sectional profile 122 shows the hybrid shape of a cross-section of the airfoil blade 112, perpendicular to outer surface 119 and the inner surface 120. In the embodiment shown in FIG. 1 IA, the blade 112 has a substantially constant cross-sectional profile 122 throughout the entire height of the blade 112. The articulating wings 123 and 125 are rotatable relative to the remainder of the blade 112 by pivoting about respective pivot points located at the front portions of the articulating wings 123 and 125 closest to the leading edge 117 of the blade 112.

[00164] Cross-sectional profile 122 of the blade 112 preferably has an airfoil shape, with portions similar to the cross-sectional profile 72a of the blade 62a, but with portions removed corresponding to the outer scallop portions 124a and 124b, the outer scallops 124" and 124'", the inner scallop portions 126a and 126b, and the inner scallops 126" and 126'". Cross-sectional profile 122 of the blade 112 shown in FIG. 1 IA is similar to cross-sectional profile 72d of the blade 62d that is shown in FIG. 8D, but with the addition of the articulating wings 123 and 125.

[00165] In some embodiments, the outer scallop portion 124a, the outer scallops 124" and 124'", the inner scallop portion 126a, and the inner scallops 126" and 126'" can be bounded by two wind stagnation projections, which are shown in FIG. IB, for example, as flat plates having substantially the same cross-sectional profile as the base airfoil-like profile of the blade, without portions carved out (or formed) at the top and bottom ends of the outer scallop portion 124a, the outer scallops 124" and 124'", the inner scallop portion 126a, and the inner scallops 126" and 126'".

[00166] The particular airfoil shape of the portion of the cross-sectional profile 122 that is similar to the cross-sectional profile 72a can be any airfoil shape, but in the embodiment shown in FIG. 1 IA, the cross-sectional profile 122 has the aspect ratios of a NACA 0012 airfoil, but with portions of the cross-sectional profile 122 removed at the outer scallop portions 124a and 124b, the outer scallops 124" and 124'", the inner scallop portions 126a and 126b, and the inner scallops 126" and 126'". As can be seen in FIG. 1 IA, the cross-sectional profile 122 is preferably about a centerline connecting the leading edge 117 with the trailing edge 118.

[00167] In some embodiments, the cross-sectional profile 122 can be asymmetrical about the centerline. For example, the hybrid airfoil blade 112 can have a single outer articulating wing 123 or a single inner articulating wing 125, depending on the desired design and performance characteristics of the vertical wind turbine 60. The outer articulating wing 123 and the inner articulating wing 125 can be positioned at different locations along the cross-sectional profile 122. For example, the inner articulating wing 125 can be closer to the leading edge 117 than the outer articulating wing 123. In some embodiments, there may be a single outer scallop 124' and two inner scallops 126' and 126". In embodiments with equal numbers of outer scallops and inner scallops, the outer scallops 124' and 124", and the inner scallops 126' and 126" may be positioned at different locations along the cross-sectional profile 122. For example, the leading inner scallop 126' may be closer to the leading edge 117 than the leading outer scallop 124'.

[00168] Referring to FIG. 1 IB, the hybrid airfoil blade 112 has a closed position cross- sectional profile 122', in which the articulating wings 123 and 125 have moved from the open position shown in FIG. 1 IA to a closed position. When the articulating wings 123 and 125 are in the closed position, the outer articulating wing 123 and the outer surface 119 define an outer scallop 124' (formed by outer scallop portions 124a and 124b), and the inner articulating wing 125 and the inner surface 120 define an inner scallop 126' (formed by inner scallop portions 126a and 126b).

[00169] To move from the open position shown in FIG. 1 IA to the closed position shown in FIG. 1 IB, the articulating wings 123 and 125 rotate relative to the remainder of the blade 112 by pivoting about respective pivot points located at the front portions of the articulating wings 123 and 125 closest to the leading edge 117 of the blade 112. [00170] The blade 112 can be designed such that when the wind field has a net vector velocity component that is directed longitudinally along the blade 112 from the leading edge 117 to the trailing edge 118 of the blade 112, the blade 112 has an closed position cross-sectional profile 122' in which the articulating wings 123 and 125 are flush against the respective outer and inner surfaces 119 and 120, as shown in FIG. 1 IB. When the blade 112 is in the closed position because the wind field has a net vector component directed from the leading edge 117 to the trailing edge 118 of the blade 112, the wind can flow from the leading edge 117 to the trailing edge 118, producing a Darrieus-like lift force to help keep the blades 112 rotating about an axle 66.

[00171] When the wind field has a net velocity vector component that is directed longitudinally along the blade 112 from the trailing edge 118 to the leading edge 117 of the blade 112, the blade 112 has an open position cross-sectional profile 122 in which the articulating wings 123 and 125 are extended from the respective outer and inner surfaces 119 and 120, forming the respective pockets 124 and 126, as shown in FIG. 1 IA. When the blade 112 is in the open position because the wind field has a net vector component directed from the trailing edge 118 to the leading edge 117 of the blade 112, the blade 112 can exhibit a self-starting behavior, wherein the pockets 124 and 126, as well as the outer scallop portions 124a and 124b, the outer scallops 124" and 124'", the inner scallop portions 126a and 126b, and the inner scallops 126" and 126'" preferably provide stall surfaces that can assist the vertical wind turbine 60 (or any of the other vertical wind turbines disclosed herein) in self-starting.

[00172] Depending on the particular wind velocity vector components at any moment in time, a vertical wind turbine 60 including three blades 112 may have a first blade 112 disposed in an open position (i.e., with articulating wings 123 and 125 extended away from the respective outer and inner surfaces 119 and 120), while having a second blade 112 disposed in a closed position (i.e., with articulating wings 123 and 125 located flush against the respective outer and inner surfaces 119 and 120).

[00173] Depending on the particular wind velocity vector components at any moment in time, a vertical wind turbine 60 including three blades 112 may have a first blade 112 disposed in an open position at a first circumferential position relative to an origin located at the axle 66, and the first blade 112 may be disposed in a closed position at a second circumferential location. In such a situation, the articulating wings 123 and 125 may undergo an opening and a closing during each rotation of the first blade 112 about the axle 66. [00174] Any mechanism can be used to move the articulating wings 123 and 125 between the open and closed positions, including, for example, a torsional spring or a gravitational cam- like spring that is biased towards forcing the articulating wings to the open position shown in FIG. 1 IA or the closed position shown in FIG. 1 IB. In some embodiments, a torsion spring may be used to dampen the motion of the articulating wings 123 and 125 between the open and closed positions, for example, in order to minimize the force of the impact between the articulating wings 123 and 125 and the respective outer and inner surfaces 119 and 120.

[00175] Referring to FIG. 12A, a hybrid blade 132 suitable for use in any of the vertical wind turbines disclosed herein has a leading edge 137, a trailing edge 138, an outer surface 139, an inner surface 140, a cross-sectional profile 142, an outer channel 144, an inner channel 146, transverse vents 148a oriented substantially perpendicularly to the longitudinal axis of the blade 132, and longitudinal vents 148b oriented substantially parallel to the longitudinal axis of the blade 132. In some embodiments, the vents 148a and 148b may be oriented at an angle to the center line connecting the leading edge 137 with the trailing edge 138, in a manner similar to that shown in FIGs. 2C and 3C, wherein the vents 28 are oriented at an angle α to the centerline connecting the leading edge 17 with the trailing edge 18. The vents 148a and 148b are not limited to the size and orientation shown in FIG. 12A. In some embodiments, the vents 148a and 148b can have any shape and orientation relative to the leading edge 137 and the trailing edge 138.

[00176] The cross-sectional profile 142 of the blade 132 preferably has an airfoil shape, with portions similar to the cross-sectional profile 72a of the blade 62a shown in FIG. 8 A, but with portions removed corresponding to the outer channel 144, the inner channel 146, the transverse vents 148a, and the longitudinal vents 148b. As can be seen in FIG. 12A, the front of the cross-sectional profile 142 of the blade 132 near the leading edge 137 and the rear of the blade 132 near the trailing edge 138 adhere to an airfoil shape, but the portions of the cross- sectional profile 142 at the outer channel 144 and, the inner channel 146, the transverse vents 148a, and the longitudinal vents 148b are carved out (or formed), preferably providing stall surfaces that can assist the vertical wind turbine 60 (or any of the vertical wind turbines described herein) in self- starting. In some embodiments, the channels 144 and 146 can be bounded by two wind stagnation projections, which are shown in FIG. IB, for example, as flat plates having substantially the same cross-sectional profile as the base airfoil-like profile of the blade, without portions carved out (or formed) at the top and bottom ends of the channels 144 and 146. [00177] The particular airfoil shape of the portion of the cross-sectional profile 144 that is similar to the cross-sectional profile 72a shown in FIG. 8A can be any airfoil shape, but in the embodiment shown in FIG. 12A, the cross-sectional profile 144 has the aspect ratios of a NACA 0012 airfoil, but with portions of the cross-sectional profile 142 removed at the channels 144 and 146 and the vents 148a and 148b. As can be seen in FIG. 12A, the cross-sectional profile 142 is preferably symmetrical about a centerline connecting the leading edge 137 with the trailing edge 138. In other embodiments, the cross-sectional profile 142 can be asymmetrical about the centerline, depending on the desired performance characteristics of the vertical wind turbine 60. For example, in some embodiments, there may be only an outer channel 144 or only an inner channel 146 on each blade 132, or the location of the outer channel 144 be located at a different distance from the leading edge 137 than the location of the inner channel 146.

[00178] As shown in FIG. 12A, each of the vents 148a and 148b is an aperture, passing completely through the blade 132 from the outer surface 139 to the inner surface 140. In other embodiments, each of the plurality of vents 148a and 148b may pass partially through the blade 132, from the outer surface 139 and/or the inner surface 140, or the vents 148a and 148b may be raised bumps, ridges, or tubercle-like protrusions, extending away from the outer surface 139 and/or the inner surface 140. As can be seen in FIG. 12A, the blade 132 has a substantially constant cross-sectional profile 142 throughout the portions of the height H of the blade 132 that are not interrupted by the vents 148a and 148b.

[00179] The vents 148a and 148b may allow wind to pass through the blade 132 from the outer surface 139 to the inner surface 140. As discussed above related to FIGs. 4A-4F, some of the wind that passes through the blade may reduce the drag forces acting on portions of a leading blade (i.e., a first blade that a particular vector of wind reaches), and a portion of the wind that passes through the leading blade may increase the drag forces acting on portions of a trailing blade (i.e., a second blade that is behind the first blade substantially in the direction of the velocity vector of the portion of the wind that passes through the leading blade). The combination of these wind pass-through effects on the leading blade and the trailing blade may reduce portions of the rotational travel of the blades that result in a net negative torque acting on the vertical wind turbine (i.e., a torque acting in a rotational direction opposite the rotational direction Rl).

[00180] Referring to FIG. 12B, a graph 133 shows turbine speed (in RPM) as a function of wind speed for two 3-blade vertical wind turbine embodiments, a first best fit line 133a representing blade 62c (airfoil profile with channels) shown in FIG. 8C, and a second best fit line 133b representing blade 132 (airfoil profile with channels and vents) shown in FIG. 12A. As can be seen in FIG. 12B, the blade 62c shown in FIG. 8C performed substantially better than the blade 132 shown in FIG. 12A.

[00181] In some respects, the data shown in FIG. 12B may conflict with the simulated data shown in FIG. 6, in which a vertical wind turbine having three blades including channels and a plurality vents was simulated to produced a higher net work in some designs than a vertical wind turbine having only channels. The data may suggest that the particular size, shape, and location of the vents 148a and 148b in the blade 132 was not optimal for harnessing energy from a given wind field. These results may suggest that there are competing design considerations that may be taken into consideration when determining if and/or where to place vents in a given blade design. While not being bound by theory, it may be possible to improve the energy harnessing performance of a given vented blade design by including one or more mechanisms that can prevent wind from passing through the blades when the blades are rotating at a higher rotational velocity, such as the mechanisms shown and described below with reference to FIGs. 14A-14C.

[00182] Referring to FIG. 13A, a hybrid blade 132a suitable for use in any of the vertical wind turbines disclosed herein has a leading edge 137, a trailing edge 138, an outer surface 139, an inner surface 140, inner and outer channels, and transverse vents 135a oriented substantially parallel to the longitudinal axis of the blade 132a. Transverse vents 135a have a rounded (e.g., oval) profile in a longitudinal plane penetrating the leading edge 137 and a trailing edge 138. Transverse vents 135a penetrate completely through the blade 132a from the outer surface 139 to the inner surface 140.

[00183] While not being bound by theory, having a relatively large number of vents (e.g., 15 vents as shown in FIG. 13A), each with a relatively small cross-sectional area (e.g., 1-2% of the area of the outer surface 139) may allow some wind to pass through a leading blade 132a to reach a trailing blade 132a, when the blades 132a are rotating at a low rotational velocity, and may provide additional stall surfaces to help a vertical wind turbine including blades 132a start spinning. However, the small cross-sectional area of each vent 135a may help prevent some of the loss of Darrieus-like lift behavior that may have reduced the net work produced by the blades 132 shown in FIG. 12A in the experiments discussed above with reference to FIG. 12A.

[00184] Referring to FIG. 13B, a hybrid blade 132b suitable for use in any of the vertical wind turbines disclosed herein has a leading edge 137, a trailing edge 138, an outer surface 139, an inner surface 140, inner and outer channels, and transverse vents 135b oriented substantially parallel to the longitudinal axis of the blade 132b. Transverse vents 135b have a rounded (e.g., oval) profile in a longitudinal plane penetrating the leading edge 137 and the trailing edge 138. Transverse vents 135b penetrate partially through the blade 132b (e.g., 10-20% through) from the respective outer surface 139 and inner surface 140. As shown in FIG. 13B, there are 15 transverse vents 135b penetrating partially through the blade 132b from the outer surface 139 and 15 transverse vents 135b penetrating partially through the blade 132b from the inner surface 140. As shown in FIG. 13B, each vent 135b has a flat bottom that defines a plane that is substantially parallel to a longitudinal plane penetrating the leading edge 137 and the trailing edge 138.

[00185] While not being bound by theory, having a plurality of vents (e.g., 30 vents as shown in FIG. 13B), each with a relatively small cross-sectional area (e.g., 1-2% of the area of the outer surface 139) may provide additional stall surfaces to help a vertical wind turbine including blades 132b start spinning. However, having each vent 135b only partially penetrate through he blade 132b may help prevent some of the loss of Darrieus-like lift behavior that may have reduced the net work produced by the blades 132 shown in FIG. 12A in the experiments discussed above with reference to FIG. 12A.

[00186] Referring to FIG. 13C, a hybrid blade 132c suitable for use in any of the vertical wind turbines disclosed herein has a leading edge 137, a trailing edge 138, an outer surface 139, an inner surface 140, inner and outer channels, and transverse vents 135c oriented substantially parallel to the longitudinal axis of the blade 132c. Transverse vents 135c have a rounded (e.g., oval) profile in a longitudinal plane penetrating the leading edge 137 and the trailing edge 138. Transverse vents 135c penetrate partially through the blade 132c (e.g., 10-20% through) from the respective outer surface 139 and inner surface 140. As shown in FIG. 13C, there are 15 transverse vents 135c penetrating partially through the blade 132c from the outer surface 139 and 15 transverse vents 135c penetrating partially through the blade 132c from the inner surface 140. As shown in FIG. 13 C, each vent 135c has a curved or rounded bottom, the deepest portion of each vent 135c being substantially tangent to a longitudinal plane penetrating the leading edge 137 and the trailing edge 138.

[00187] While not being bound by theory, having a plurality of vents (e.g., 30 vents as shown in FIG. 13B), each with a relatively small cross-sectional area (e.g., 1-2% of the area of the outer surface 139) may provide additional stall surfaces to help a vertical wind turbine including blades 132c start spinning. However, having each vent 135c only partially penetrate through the blade 132c, with a rounded bottom, may help prevent some of the loss of Darrieus- like lift behavior that may have reduced the net work produced by the blades 132 shown in FIG. 12A in the experiments discussed above with reference to FIG. 12A.

[00188] Referring to FIGs. 14A-14C, a rear sectional view 132' of a portion of a hybrid turbine blade having a vent with an articulating hinged flap in an open position, suitable for use in any of the vertical wind turbines disclosed herein, has a trailing edge 138, an outer surface 139, an inner surface 140, a longitudinal vent 148b' oriented substantially parallel to the longitudinal axis of the blade 132', and an articulating flap 149a coupled to the vent 148b' by a hinge 149b.

[00189] The blade 132' can be designed such that at lower wind speeds, the articulating flap 149a is disposed in a partially open position as shown in FIG. 14A or in a fully open position, thereby allowing wind to pass through the blade 132' from the outer surface 139 to the inner surface 140. At higher wind speeds, the articulating flap 149a can be disposed in a closed position as shown in FIG. 14B, thereby preventing wind from passing through the blade 132'.

[00190] When the articulating flap 149a pivots about the hinge 149b from the open position to the closed position due to centrifugal force, the pivoting of the articulating flap 149a can be stopped when the reaches the closed position by designing an interference between the articulating flap 149a and the remainder of the outer surface 139. Such an interference between the articulating flap 149a and the remainder of the outer surface 139 can cause the articulating flap 149a to be locked in position against the remainder of the outer surface 139, so long as a sufficient centrifugal force is continued to be applied to the blade 132' from rotation of the blade 132' about the axle 66.

[00191] When the wind velocity decreases or when the blade 132' begins to rotate at a lower angular velocity about the axle 66, such that the centrifugal force that is applied to the blade 132' drops below a predetermined threshold, the articulating flap 149a can rotate inward from the closed position shown in FIG. 14B to an intermediate position shown in FIG. 14A, and then to a fully open position. Any mechanism can be used to return the articulating flap 149a from the closed position back to the open position when the centrifugal force is reduced, including, for example, a torsional spring or a gravitational cam-like spring that is biased towards forcing the articulating flap 149a to the fully open position.

[00192] The ability of one or more vents 148b' to be open or closed, depending on the wind speed and/or the rotational velocity of the vertical wind turbine 60 (or any of the other vertical wind turbines disclosed herein) may initially allow wind to pass through the blade 132' from the outer surface 139 to the inner surface 140 when it may be helpful to assist the vertical wind turbine 60 in self-starting, while later preventing wind from passing through the blade 132' when it may be more desirable for the blade 132' to display a Darrieus-like lift behavior.

[00193] As discussed above related to FIGs. 4A-4F, allowing some wind to pass through a leading blade 132' to reach a trailing blade 132', when the blades 132' are rotating at a low rotational velocity, may provide additional stall surfaces to help a vertical wind turbine including blades 132' start spinning. However, preventing wind from passing through a leading blade 132', when the blades 132' are rotating at a high rotational velocity, may help prevent some of the loss of Darrieus-like lift behavior that may have reduced the net work produced by the blades 132 shown in FIG. 12A in the experiments discussed above with reference to FIG. 12A.

[00194] Referring to FIGs. 15A and 15A, a hybrid blade 152a suitable for use in any of the vertical wind turbines disclosed herein has a leading edge 157, a trailing edge 158, an outer surface 159, an inner surface 160, a cross-sectional profile 162a, an outer channel 164, and an inner channel 166. The leading edge 157 includes tubercle structures 157a and notches 157b. The notches 157b penetrate from the leading edge 157 into the blade cross-sectional profile 162a up to a notch base 157'. The cross-sectional profile 162a shows the hybrid shape of a cross- section of the airfoil blade 152a, perpendicular to the outer surface 159 and the inner surface 160.

[00195] The cross-sectional profile 162a of the blade 152a preferably has an airfoil shape, but with portions removed corresponding to the outer channel 164 and the inner channel 166. As shown in FIGs. 1 A-IC, the channels 164 and 166 can be bounded by two wind stagnation projections, which are shown in FIG. IB as flat plates having substantially the same cross- sectional profile 162a the base airfoil-like profile of the blade 152a. The particular airfoil shape of the portion of the cross-sectional profile 162a that is similar to the cross-sectional profile 72a shown in FIG. 8 A can be any airfoil shape, but in the embodiment shown in FIG. 16A, the cross- sectional profile 162a has the aspect ratios of a NACA 0012 airfoil, but with portions of the cross-sectional profile 162a removed at the outer channel 164 and the inner channel 166. In other embodiments, a cross-sectional profile 162a having the aspect ratios of a NACA 0015 airfoil or a cross-sectional profile 162a having other smoothly-varying shapes for the airfoil portions of cross-sectional profile 162a can be used. As can be seen in FIG. 16A, the cross- sectional profile 162a is preferably symmetrical about a centerline connecting the leading edge 157 with the trailing edge 158. In other embodiments, the cross-sectional profile 162a can be asymmetrical about the centerline, depending on the desired performance characteristics of the vertical wind turbine.

[00196] The tubercle structures 157a and notches 157b extend horizontally across the outer surface 159 and/or the inner surface 160, generally in the direction from the leading edge 157 towards the trailing edge 158. Without being bound by theory, it is believed that such tubercle-like protrusions may help the wind flowing across the outer surface 159 and/or the inner surface 160 retain a uni-directional flow, thereby contributing to the lift forces acting on the blade 152a. Without being bound by theory, it is believed that such tubercle-like protrusions may create channels of greater fluid velocity across the blade surfaces 159 and 160 than if the blade surface did not include the tubercle-like protrusions, thereby contributing to the lift forces acting on the blade 152a. These tubercle structures 157a and notches 157b may enhance the laminar flow around the blades 152a as they rotate about an axle 66, thereby improving positive torque and/or net work. Although six tubercle structures 157a and five notches 157b are shown in FIG. 15A, any number of tubercle structures 157a and notches 157b can be used. Although the notches 157b are shown in FIG. 16A as penetrating into the blade cross-sectional profile 162a up to a notch base 157', the notches 157b can penetrate into the blade cross-section up to any location within the blade cross-sectional profile 162a.

[00197] Referring to FIGs. 15B and 15B, a hybrid blade 152b suitable for use in any of the vertical wind turbines disclosed herein has a leading edge 157, a trailing edge 158, an outer surface 159, an inner surface 160, a cross-sectional profile 162b, an outer channel 164, and an inner channel 166. The trailing edge 158 includes tubercle structures 158a and notches 158b. The notches 158b penetrate from the trailing edge 158 into the blade cross-sectional profile 162b up to a notch base 158'. The cross-sectional profile 162b shows the hybrid shape of a cross- section of the airfoil blade 152b, perpendicular to the outer surface 159 and the inner surface 160.

[00198] The cross-sectional profile 162b of the blade 152b preferably has an airfoil shape, but with portions removed corresponding to the outer channel 164 and the inner channel 166. As shown in FIGs. 1 A-IC, the channels 164 and 166 can be bounded by two wind stagnation projections, which are shown in FIG. IB as flat plates having substantially the same cross- sectional profile 162b the base airfoil-like profile of the blade 152b. The particular airfoil shape of the portion of the cross-sectional profile 162b that is similar to the cross-sectional profile 72a shown in FIG. 8 A can be any airfoil shape, but in the embodiment shown in FIG. 16B, the cross- sectional profile 162b has the aspect ratios of a NACA 0012 airfoil, but with portions of the cross-sectional profile 162b removed at the outer channel 164 and the inner channel 166. In other embodiments, a cross-sectional profile 162b having the aspect ratios of a NACA 0015 airfoil or a cross-sectional profile 162b having other smoothly- varying shapes for the airfoil portions of cross-sectional profile 162b can be used. As can be seen in FIG. 16B, the cross- sectional profile 162b is preferably symmetrical about a centerline connecting the leading edge

157 with the trailing edge 158. In other embodiments, the cross-sectional profile 162b can be asymmetrical about the centerline, depending on the desired performance characteristics of the vertical wind turbine.

[00199] The tubercle structures 158a and notches 158b extend horizontally across the outer surface 159 and/or the inner surface 160, generally in the direction from the trailing edge

158 towards the leading edge 157. Without being bound by theory, it is believed that such tubercle-like protrusions may help the wind flowing across the outer surface 159 and/or the inner surface 160 retain a uni-directional flow, thereby contributing to the lift forces acting on the blade 152b. Without being bound by theory, it is believed that such tubercle-like protrusions may create channels of greater fluid velocity across the blade surfaces 159 and 160 than if the blade surface did not include the tubercle-like protrusions, thereby contributing to the lift forces acting on the blade 152b. These tubercle structures 158a and notches 158b may enhance the laminar flow around the blades 152b as they rotate about an axle 66, thereby improving positive torque and/or net work.

[00200] Although six tubercle structures 158a and five notches 158b are shown in FIG. 15B, any number of tubercle structures 158a and notches 158b can be used. Although the notches 158b are shown in FIG. 16B as penetrating into the blade cross-sectional profile 162b up to a notch base 158', the notches 158b can penetrate into the blade up to any location within the blade cross-sectional profile 162b.

[00201] Referring to FIGs. 15C and 15C, a hybrid blade 152c suitable for use in any of the vertical wind turbines disclosed herein has a leading edge 157, a trailing edge 158, an outer surface 159, an inner surface 160, a cross-sectional profile 162c, an outer channel 164, and an inner channel 166. The leading edge 157 includes tubercle structures 157a and notches 157b. The notches 157b penetrate from the leading edge 157 into the blade cross-sectional profile 162c up to a notch base 157'. The trailing edge 158 includes tubercle structures 158a and notches 158b. The notches 158b penetrate from the trailing edge 158 into the blade cross-sectional profile 162b up to a notch base 158'. The cross-sectional profile 162c shows the hybrid shape of a cross-section of the airfoil blade 152c, perpendicular to the outer surface 159 and the inner surface 160. [00202] The cross-sectional profile 162c of the blade 152c preferably has an airfoil shape, but with portions removed corresponding to the outer channel 164 and the inner channel 166. As shown in FIGs. 1 A-IC, the channels 164 and 166 can be bounded by two wind stagnation projections, which are shown in FIG. IB as flat plates having substantially the same cross- sectional profile 162c the base airfoil-like profile of the blade 152c. The particular airfoil shape of the portion of the cross-sectional profile 162c that is similar to the cross-sectional profile 72a shown in FIG. 8 A can be any airfoil shape, but in the embodiment shown in FIG. 16C, the cross- sectional profile 162c has the aspect ratios of a NACA 0012 airfoil, but with portions of the cross-sectional profile 162c removed at the outer channel 164 and the inner channel 166. In other embodiments, a cross-sectional profile 162c having the aspect ratios of a NACA 0015 airfoil or a cross-sectional profile 162c having other smoothly-varying shapes for the airfoil portions of cross-sectional profile 162c can be used. As can be seen in FIG. 16C, the cross- sectional profile 162c is preferably symmetrical about a centerline connecting the leading edge 157 with the trailing edge 158. In other embodiments, the cross-sectional profile 162c can be asymmetrical about the centerline, depending on the desired performance characteristics of the vertical wind turbine.

[00203] The tubercle structures 157a and notches 157b extend horizontally across the outer surface 159 and/or the inner surface 160, generally in the direction from the leading edge 157 towards the trailing edge 158. The tubercle structures 158a and notches 158b extend horizontally across the outer surface 159 and/or the inner surface 160, generally in the direction from the trailing edge 158 towards the leading edge 157. Without being bound by theory, it is believed that such tubercle-like protrusions may help the wind flowing across the outer surface 159 and/or the inner surface 160 retain a unidirectional flow, thereby contributing to the lift forces acting on the blade 152c. Without being bound by theory, it is believed that such tubercle-like protrusions may create channels of greater fluid velocity across the blade surfaces 159 and 160 than if the blade surface did not include the tubercle-like protrusions, thereby contributing to the lift forces acting on the blade 152c. These tubercle structures 157a and 158a and notches 157b and 158b may enhance the laminar flow around the blades 152c as they rotate about an axle 66, thereby improving positive torque and/or net work.

[00204] Although six tubercle structures 157a and 158a and five notches 157b and 158b are shown in FIG. 15C, any number of tubercle structures 157a and 158a and notches 157b and 158b can be used. Although the notches 157b are shown in FIG. 16C as penetrating into the blade cross-sectional profile 162c up to a notch base 157', the notches 157b can penetrate into the blade up to any location within the blade cross-sectional profile 162c. Although the notches 158b are shown in FIG. 16C as penetrating into the blade cross-sectional profile 162b up to a notch base 158', the notches 158b can penetrate into the blade up to any location within the blade cross-sectional profile 162b.

[00205] Referring to FIGs. 15D and 15D, a hybrid blade 152d suitable for use in any of the vertical wind turbines disclosed herein has a leading edge 157, a trailing edge 158, an outer surface 159, an inner surface 160, a cross-sectional profile 162d, an outer channel 164, an inner channel 166, and vents 168. The leading edge 157 includes tubercle structures 157a and notches 157b. The notches 157b penetrate from the leading edge 157 into the blade cross-sectional profile 162d up to a notch base 157'. The trailing edge 158 includes tubercle structures 158a and notches 158b. The notches 158b penetrate from the trailing edge 158 into the blade cross- sectional profile 162b up to a notch base 158'. The cross-sectional profile 162d shows the hybrid shape of a cross-section of the airfoil blade 152d, perpendicular to the outer surface 159 and the inner surface 160. The vents 168 are located approximately at the same vertical position on the blade 152d as the tubercle structures 157a and 158a.

[00206] The cross-sectional profile 162d of the blade 152d preferably has an airfoil shape, but with portions removed corresponding to the outer channel 164 and the inner channel 166. As shown in FIGs. 1 A-IC, the channels 164 and 166 can be bounded by two wind stagnation projections, which are shown in FIG. IB as flat plates having substantially the same cross- sectional profile 162d the base airfoil-like profile of the blade 152d. The particular airfoil shape of the portion of the cross-sectional profile 162d that is similar to the cross-sectional profile 72a shown in FIG. 8 A can be any airfoil shape, but in the embodiment shown in FIG. 16D, the cross- sectional profile 162d has the aspect ratios of a NACA 0012 airfoil, but with portions of the cross-sectional profile 162d removed at the outer channel 164 and the inner channel 166. In other embodiments, a cross-sectional profile 162d having the aspect ratios of a NACA 0015 airfoil or a cross-sectional profile 162d having other smoothly- varying shapes for the airfoil portions of cross-sectional profile 162d can be used. As can be seen in FIG. 16D, the cross- sectional profile 162d is preferably symmetrical about a centerline connecting the leading edge 157 with the trailing edge 158. In other embodiments, the cross-sectional profile 162d can be asymmetrical about the centerline, depending on the desired performance characteristics of the vertical wind turbine.

[00207] The tubercle structures 157a and notches 157b extend horizontally across the outer surface 159 and/or the inner surface 160, generally in the direction from the leading edge 157 towards the trailing edge 158. The tubercle structures 158a and notches 158b extend horizontally across the outer surface 159 and/or the inner surface 160, generally in the direction from the trailing edge 158 towards the leading edge 157. Without being bound by theory, it is believed that such tubercle-like protrusions may help the wind flowing across the outer surface 159 and/or the inner surface 160 retain a uni-directional flow, thereby contributing to the lift forces acting on the blade 152d. Without being bound by theory, it is believed that such tubercle-like protrusions may create channels of greater fluid velocity across the blade surfaces 159 and 160 than if the blade surface did not include the tubercle-like protrusions, thereby contributing to the lift forces acting on the blade 152d. These tubercle structures 157a and 158a and notches 157b and 158b may enhance the laminar flow around the blades 152d as they rotate about an axle 66, thereby improving positive torque and/or net work.

[00208] Although four tubercle structures 157a and 158a and three notches 157b and 158b are shown in FIG. 15D, any number of tubercle structures 157a and 158a and notches 157b and 158b can be used. Although the notches 157b are shown in FIG. 16D as penetrating into the blade cross-sectional profile 162d up to a notch base 157', the notches 157b can penetrate into the blade up to any location within the blade cross-sectional profile 162d. Although the notches 158b are shown in FIG. 16D as penetrating into the blade cross-sectional profile 162b up to a notch base 158', the notches 158b can penetrate into the blade up to any location within the blade cross-sectional profile 162b. Although the inner two tubercle structures 157a and 158a are shown as extending along a greater portion of the respective leading edge 157 and trailing edge

158 than the outer two tubercle structures 157a and 158a, in some embodiments, all of the tubercle structures 157a and 158a can extend along approximately the same portion of the respective leading edge 157 and trailing edge 158.

[00209] As can be seen in FIG. 15D, the vents 168 are located approximately at the same vertical position on the blade 152d as the tubercle structures 157a and 158a. Without being bound by theory, it is believed that having the vents 168 located at approximately the same vertical position on the blade 152d as the tubercle structures 157a and 158a will allow a greater amount of air to be diverted by the notches 157b and 158b onto the portion of the blade surface that does not have the vents 168, which may improve the Darrieus-like lift characteristics of the non-vented portions of the blade surfaces 159 and 160.

[00210] Referring to FIG. 17 A, an exemplary vertical wind turbine 170 includes three blades 172, six struts 174, and an axle 176. Vertical wind turbine 170 preferably rotates about the axle 176 in a rotational direction Rl. Each blade 172 is spaced circumferentially about the axle 176, and each blade 172 has a leading edge 177, a trailing edge 178, an outer surface 179, and an inner surface 180. Each blade 172 is preferably attached to the axle 176 via two struts 174. In the embodiment shown in FIG. 17A, each strut 174 is attached to a respective blade 172 at the Gaussian stress points, in the middle of the inner surfaces 180 of the respective blades 172.

[00211] As shown in FIG. 17A, each blade 172 has a cross-sectional profile 182 that is the same as the cross-sectional profile 72c shown in FIG. 8C. In other embodiments the cross- sectional profile 182 can be any cross-sectional profile disclosed herein, including, for example, cross-sectional profile 72d shown in FIG. 8D. Each blade 172 is oriented at an angle of attack β relative to an axis that is tangent to the circumference of a circle defined by the path traveled by the blades 172 as they move in the rotational direction Rl about the axle 176. For example, an angle of attack β of 12° for a blade 172 means that the leading edge 177 is located at a greater radial distance away from the axle 176 than the trailing edge 178, and the longitudinal axis of the blade 172 (running between the leading edge 177 and the trailing edge 178) is oriented at a 12° angle to the tangent of the circle defined by the rotation path of the blades 172.

[00212] In some embodiments, the angle of attack β of the blades 172 may vary as a function of angular velocity of the vertical wind turbine 170. For example, the angle of attack β of the blades 172 may initially be set to 0° when the angular velocity of the vertical wind turbine 170 is zero. As the angular velocity of the vertical wind turbine 170 increases, the angle of attack β of the blades 172 may increase in proportion to the angular velocity (e.g., in linear proportion or exponential proportion), up to a maximum angle of attack β of 27° at a high angular velocity of the vertical wind turbine 170. As the angular velocity of the turbine 170 slows down, the angle of attack β of the blades 172 may decrease, for example, in linear proportion or exponential proportion to the angular velocity. Such a variable angle of attack β of the blades 172 may be controlled by any mechanism, including, for example, centrifugal force increasing the angle of attack β of the blades 172 at higher angular velocities, and a torsional spring biased to decrease the angle of attack β of the blades 172 back to 0° as the centrifugal force decreases at lower angular velocities of the turbine 170.

[00213] Referring to FIG. 17B, a graph 190 shows the simulated net work (per revolution of the turbine) acting on each of five 3 -blade vertical wind turbines including alternative angles of attack β of the blades as depicted in FIG. 17A as a function of wind velocity. The work data shown in FIG. 17B can allow a comparison of which angle of attack β embodiments of the invention allow harvesting of the most work or energy from a range of wind field velocities. [00214] The net work harnessed by the five embodiments including alternative angles of attack β of the blades depicted in FIG. 17A are shown as lines 191a (β=12°), 191b (β=6°), 191c (β=0°), 191d (β=-6°), and 191e (β=-12°). The net work values shown in graph 190 is the integral of the sum of the net tangential force acting on all three blades 172 of each turbine 170, resulting from wind flow fields of 5-20 mph moving across the turbines 170, as the leading blade 172 (the blade that is closest to the direction from which the wind is blowing) moves from an initial position where the longitudinal axis is perpendicular to the direction of the wind to a final position that is 120° rotated about the axle 176. The net work values shown in graph 190 include adjustment that subtracts the estimated friction loss (e.g., from the bearings coupled to the axle 176) from the result of the integral.

[00215] The graph 190 shows that at all angles of attack β of the blades 172 that were simulated, the blades having angles of attack β of 12° produced the highest net work, followed by the blades having angles of attack β of 6° that produced the next highest net work, followed by the blades having angles of attack β of 0°. The embodiments including blades having negative angles of attack β (i.e., -6° and -12°) had negative net work values, meaning that the turbines with these blades spun backwards relative to the blades having zero or positive angles of attack β.

[00216] Referring to FIG. 17C, a graph 192 shows the simulated net work (per revolution of the turbine) acting on each of seventeen 3 -blade vertical wind turbines including alternative angles of attack β of the blades (each successive embodiment has an angle of attack β that is approximately 3° greater than the previous embodiment) as a function angle of attack β, in a simulated wind field having a velocity of 15 mph.

[00217] The net work harnessed by the various embodiments including alternative angles of attack β of the blades is shown as line 193. The net work values shown in graph 192 is the integral of the sum of the net tangential force acting on all three blades 172 of each turbine 170, resulting from a wind flow fields of 15 mph moving across the turbines 170, as the leading blade 172 (the blade that is closest to the direction from which the wind is blowing) moves from an initial position where the longitudinal axis is perpendicular to the direction of the wind to a final position that is 120° rotated about the axle 176. The net work values shown in graph 192 include adjustment that subtracts the estimated friction loss (e.g., from the bearings coupled to the axle 176) from the result of the integral.

[00218] The graph 192 shows that the net work is highest with embodiments having angles of attack β of the blades between 27 and 36 degrees. The net work increases as a function angle of attack β of the blades up until an angle of attack β of approximately 27°, and the net work decreases as a function of angle of attack β of the blades after an angle of attack β of approximately 32°. These results suggest that there may be competing design considerations that can be taken into consideration when designing the blade 172 cross-sectional profile 182 for a particular set of blades 172 for a particular vertical wind turbine 170.

[00219] The foregoing description is provided for the purpose of explanation and is not to be construed as limiting the invention. While the invention has been described with reference to preferred embodiments or preferred methods, it is understood that the words which have been used herein are words of description and illustration, rather than words of limitation. Furthermore, although the invention has been described herein with reference to particular structure, methods, and embodiments, the invention is not intended to be limited to the particulars disclosed herein, as the invention extends to all structures, methods and uses that are within the scope of the appended claims. Further, several advantages have been described that flow from the structure and methods; the present invention is not limited to structure and methods that encompass any or all of these advantages. Those skilled in the relevant art, having the benefit of the teachings of this specification, may effect numerous modifications to the invention as described herein, and changes can be made without departing from the scope and spirit of the invention as defined by the appended claims. Furthermore, any features of one described embodiment can be applicable to the other embodiments described herein. For example, any features or advantages related to the cross-sectional profile of a blade, channels, vents, and/or tubercle structures with respect to discussion of a particular blade embodiment can be applicable to any of the other blade embodiments described herein.

Claims

What is Claimed:

1. A vertical axis wind turbine, comprising: an axle; and a plurality of blades circumferentially spaced about the axle and coupled to the axle, each blade including: an outer surface and an inner surface, the outer surface and inner surface meeting at a leading edge and a trailing edge, a leading portion extending from the leading edge along the outer surface and the inner surface, the leading portion having, in longitudinal cross-section, an airfoil shape, at least one transverse channel located rearward of the leading portion, and a trailing portion extending rearward from the channel to the trailing edge; whereby each channel enhances wind turbine power output.

2. The vertical axis wind turbine of claim 1, wherein the airfoil shape of the leading portion of each blade, in longitudinal cross-section, is a NACA standard airfoil shape.

3. The vertical axis wind turbine of claim 1, wherein each channel enhances wind turbine power output by providing stall surfaces normal to the direction of an anticipated wind flow, such that drag forces promote self-starting of the wind turbine.

4. The vertical axis wind turbine of claim 1 , further comprising a plurality of struts extending from the axle, wherein each blade is coupled to the axle by corresponding struts.

5. The vertical axis wind turbine of claim 4, wherein each blade further defines two Gaussian stress points, and each blade is attached to two struts at the Gaussian stress points of the blade.

6. The vertical axis wind turbine of claim 1 , wherein each blade has a pair of opposing transverse channels.

7. The vertical axis wind turbine of claim 1 , wherein the trailing portion of each blade tapers to a sharp line at the trailing edge.

8. The vertical axis wind turbine of claim 1, wherein each blade further includes at least one articulating panel that changes the shape of at least one of the outer surface and the inner surface depending on the angular speed of the wind turbine.

9. The vertical axis wind turbine of claim 8 wherein the panel is biased toward an open position such that centrifugal force actuates the panel to a closed position.

10. The vertical axis wind turbine of claim 9 wherein the panel substantially covers the channel in a closed position of the panel.

11. The vertical axis wind turbine of claim 8, wherein each blade further includes at least one vent extending through the blade from the outer surface of the blade to the inner surface of the blade, and the panel substantially covers the vent in a closed position of the panel.

12. The vertical axis wind turbine of claim 1 , wherein each blade further includes two wind stagnation projections disposed at the top and bottom of the blade.

13. The vertical axis wind turbine of claim 1 , wherein the outer surface of each blade defines a camber and the inner surface of each blade defines a camber that is different than the camber of the outer surface.

14. The vertical axis wind turbine of claim 1 , wherein the blades define a circular path of rotation about the axle, and each blade is oriented at a non-zero attack angle relative to a line tangent to the circular path of rotation.

15. The vertical axis wind turbine of claim 14, wherein the attack angle of each blade is between approximately 27 and 36 degrees.

16. The vertical axis wind turbine of claim 1, wherein each blade further includes at least one tubercle structure at either or both of the leading edge and the trailing edge of the blade.

17. The vertical axis wind turbine of claim 16, wherein each blade further includes at least one vent extending through the blade from the outer surface of the blade to the inner surface of the blade, and each tubercle structure is located approximately at the same vertical position on the blade as a corresponding vent.

18. A vertical axis wind turbine, comprising: an axle; and a plurality of blades circumferentially spaced about the axle and coupled to the axle, each blade including: an outer surface and an inner surface, the outer surface and inner surface meeting at a leading edge and a trailing edge, a leading portion extending from the leading edge along the outer surface and the inner surface, plural scallops on each one of the outer surface and the inner surface, the scallops located rearward of the leading portion, and a trailing portion extending rearward to the trailing edge from a leading scallop of the plural scallops on each one of the outer surface and the inner surface; whereby each scallop enhances wind turbine power output.

19. The vertical axis wind turbine of claim 18, wherein each scallop enhances wind turbine power output by providing stall surfaces normal to the direction of an anticipated wind flow, such that drag forces promote self-starting of the wind turbine.

20. The vertical axis wind turbine of claim 18, further comprising a plurality of struts extending from the axle, wherein each blade is coupled to the axle by corresponding struts.

21. The vertical axis wind turbine of claim 18, wherein the leading portion of each blade has, in longitudinal cross-section, an airfoil shape.

22. The vertical axis wind turbine of claim 18, wherein the scallops decrease in size from the leading portion to the trailing portion.

23. The vertical axis wind turbine of claim 18, wherein each blade further includes at least one articulating panel that changes the shape of at least one of the outer surface and the inner surface depending on the angular orientation of the blade relative to the wind field velocity vectors.

24. The vertical axis wind turbine of claim 18 wherein the panel is biased toward a closed position such that a force applied by the wind field to the blade actuates the panel to an open position.

25. A method of harnessing wind energy by rotating a vertical axis wind turbine, the method comprising: assembling the vertical axis wind turbine by coupling a plurality of blades to an axle, the blades being spaced circumferentially about the axle, each blade including: an outer surface and an inner surface, the outer surface and inner surface meeting at a leading edge and a trailing edge, a leading portion extending from the leading edge along the outer surface and the inner surface, at least one transverse channel located rearward of the leading portion, a trailing portion extending rearward from the channel to the trailing edge, and at least one articulating panel coupled to at least one of the outer surface and the inner surface; exposing the blades to the wind so that the plurality of blades rotates about the axle; changing the shape of at least one of the outer surface and the inner surface by moving the articulating panel from an open position to a closed position while the blades are rotating about the axle.

26. The method of claim 25, wherein the leading portion of each blade has, in longitudinal cross-section, an airfoil shape.

27. The method of claim 25, wherein the articulating panel moves from the open position to the closed position due to centrifugal force acting on the panel while the blades are rotating about the axle.

28. The method of claim 25, wherein the articulating panel moves from the open position to the closed position due to a change in the angular orientation of the blade relative to the wind field velocity vectors.

29. The method of claim 25, further comprising orienting each blade at a non-zero attack angle relative to a line tangent to a circular path of rotation of the blades about the axle.