FIELD OF THE INVENTION

The present invention is directed to the field of wind turbines, and more specifically to the components such as wind turbine blades that are moved by the wind to drive a turbine.

BACKGROUND TO THE INVENTION

Wind machines such as windmills and wind turbines convert wind energy to perform useful work by extracting power from a wind current by the use of blades mounted to a rotatable structure. The mass of a wind current impinging upon the blades and / or flowing around them transmits a force to the blades which is converted into a torque about the drive shaft (or other structure) upon which the blades rotate. The mechanical energy of the rotational movement of the drive shaft may be utilized for many purposes including, for example, to drive a turbine for electricity generation, or to power mechanical devices such as pumps, mills, or other machinery.

Wind machines have been developed over many years, and various useful designs have been implemented on an industrial scale. For example, some designs involve the use of propeller-like blades mounted on a hub which rotates upon a generally horizontal shaft. The propeller-like arrangement is orientated such that the axis of rotation of the blades is substantially parallel to the flow of the wind. However, it is necessary to orient the blades perpendicular to the direction of the wind in order to properly expose their surfaces to the wind current so that they will generate a rotational force. This directional sensitivity reduces the efficiency of this type of wind machine, especially in those areas having wind flows that are unpredictable or frequently changing. To optimize efficiency, the orientation of the device must be adjusted constantly to face the oncoming wind, and thus a steering mechanism must also be employed.

Other wind machine designs have a number of blades circularly mounted about a rotatable structure in a carousel fashion. The structure includes a shaft positioned with its axis generally parallel to the axis of the blades, and perpendicularly positioned with the wind flow. Such devices, commonly referred to as cross-wind axis wind turbines, are usually installed with the blades and shaft positioned vertically with the ground surface. In this configuration the blade surfaces are exposed to wind currents blowing from any direction, making them capable of capturing energy with a near instantaneous response from directionally changing winds, without need of a steering device sensitive to wind direction. Due to the vertical position of the rotating shaft it is unnecessary to mount a driven implement or a right angle drive, such as a gear box, at a high elevation on the supporting structure of the windmill. Further, cantilever forces upon the rotating shaft are significantly less than for wind machines with propeller-like blades and a horizontal shaft. Thus for vertical axis wind turbines, the bearings upon which the shaft turns may be smaller and less expensive.

For all types of wind machines, the blades extract power from the wind by slowing the free stream of the wind speed downstream of the blade. Typically, blades are designed to take advantage of a motive force generated from this wind speed change, thereby to provide torque about the rotating shaft.

Some wind turbines employ blades that take advantage of drag forces caused by the wind current impinging on the surface of the blades. Such a drag force is created by the transfer of kinetic energy from the moving wind mass to each blade as the wind current is slowed by contact with the surface of the blade as the wind flows around its form. Anemometers and some vertical axis wind turbines take advantage of drag forces. For example, Savonious wind turbines, of a type that is well known in the art, utilize scooped or curved blades connected together to define an S-shape cross-section (the axis of rotation being midway along the S-shape cross-section). Because of the curvature, the scoops experience less drag when moving against the wind than when moving with the wind. The differential drag causes the Savonious wind turbine to spin.

One advantage of drag type wind machines is that they are self-starting, and generally produce high torque from their starting mode through low rotational speeds. However, such devices have inherent limitations. For example, because of the way the energy is extracted from the wind, the speed of the rotating blade cannot be faster than the speed of the wind (usually it is somewhat less). This in turn, for any given wind speed, limits the maximum rotational velocity of the shaft to which the blades are affixed.

Depending upon the use of the wind machine, some form of a transmission may be required to obtain a desired shaft speed, which further reduces the efficiency of energy transfer.

The ratio of the blade tip speed to the wind speed is commonly known as the tip speed ratio. This value is used as a measure of the functional range of efficient operation of the wind machine. Generally, a drag-type machine will produce optimum power when the tip speed of its blades approaches that of the wind, meaning the tip speed ratio is close to one. However, a limit of the maximum tip speed attainable is also a limit to the amount of power which can be produced. A drag-type wind machine, being limited to a maximum ideal tip speed ratio of one, is thereby limited in its capability to produce power, and in its efficiency. The maximum efficiency obtainable with the drag-type wind machine is typically a moderate value of about 30%, often less.

Other cross-axis wind turbines known as Darrieus-type wind-turbines, as well as propeller-like wind turbines, use another type of motive force to propel the blades: a lift force, generated as the wind current flows past an aerofoil. The blades have the shape of an aerofoil positioned so that the movement of the wind current flowing over the blade generates a lift force to move the blade. A component of the lift force in the direction of rotation is applied through a rotor structure to the rotating shaft to create a torque about the shaft.

Lift-type wind-turbines, more especially propeller-like wind turbines, present some advantages over drag-type devices, including blade velocities much higher than that of the wind current turning the blades. In this way, the tip speed ratios may readily exceed one, and may be in the range of four to six. Higher tip speed ratios are achievable because blade speed is not directly dependent upon a wind velocity component, but rather on a lift force component, giving rise to high levels of efficiency at optimal wind speeds. However, lift-type wind turbines are less efficient at lower wind speeds and may stall if wind speed is insufficient or if the wind direction changes. Such inefficiencies make lift-type wind-turbines difficult to start. Indeed, power input to the driven shaft may be required to initiate rotation and bring the speed of the turbine up to a tip speed ratio sufficient for self-sufficient operation. Complex mechanical and electrical systems have been developed in the art to provide starting mechanisms, or to reduce the need for starting mechanisms.

Significant efforts and developments in the art have improved the efficiency and operation of wind turbines. However, there remains room for significant improvements in turbine design and turbine components. Ultimately, it is desired in the art to produce a wind turbine that is simple, reasonably efficient at most if not all stages of its operative cycle, and which in use requires minimal maintenance or energy input. SUMMARY OF THE INVENTION

It is an object of the present invention, at least in preferred embodiments, to provide a wind turbine blade, and / or a wind turbine comprising at least one blade, that is suitable for use in converting wind energy to mechanical energy.

Certain exemplary embodiments provide a wind turbine blade for connection to a rotor, hub or shaft of a wind turbine, to convert kinetic energy in a wind flow to mechanical energy for imparting rotational movement to the rotor, hub or shaft, the wind turbine blade comprising:

(a) a lift portion, such that exposure of the lift portion to said wind flow causes a difference in pressure on one side of the lift portion relative to an opposite side thereof, to generate a lift force suitable to move the blade; and

(b) a drag portion, such that exposure of the drag portion to said wind flow causes a mass of said wind flow to impinge upon a surface of the drag portion, to generate a drag force suitable to move the blade;

wherein the lift force and the drag force, or vectors thereof, are at least partially additive upon the blade which, when transferred to the rotor, hub or shaft, facilitates said rotational movement.

Certain other exemplary embodiments provide a wind turbine blade for connection to a hub, shaft or rotor of a wind turbine, to convert kinetic energy in a wind flow to mechanical energy for imparting rotational movement to the hub, shaft, or rotor, the wind turbine blade comprising:

a drag element having an concave surface for receiving said wind flow such that a mass of said wind flow impinges upon said concave surface thereby to generate a drag force upon the blade which, when transferred to the hub, shaft or rotor, causes rotation thereof; and

a lift element having a profile such that exposure to said wind flow causes a difference in air pressure on one side of the lift element relative to an opposite side thereof, to generate a lift force suitable to move the blade and impart said rotational movement.

Certain other exemplary embodiments provide a wind turbine comprising a hub, shaft or rotor, connected to which are one or more wind turbine blades for converting kinetic energy in a wind flow into mechanical energy for rotational movement of the hub, shaft, or rotor wherein:

at least one of the wind turbine blades comprises a lift portion, such that exposure of the lift portion to said wind flow causes a difference in air pressure on one side of the lift portion relative to an opposite side thereof, to generate a lift force suitable to move the blade; and

at least one of the wind turbine blades comprises a drag portion, such that exposure of the drag portion to said wind flow causes a mass of said wind flow to impinge upon a surface of the drag portion, to generate a drag force suitable to move the blade; wherein the lift force and the drag force are at least partially additive to facilitate said rotational movement of the hub, shaft or rotor.

These, and further exemplary embodiments will be apparent from the foregoing.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates an example wind turbine, in perspective view.

Figure 2 illustrates an example wind turbine blade in perspective view, with attached mounting arm(s).

Figure 3 illustrates an example wind turbine blade as per Figure 2 in perspective view, but rotated through 180 degrees.

Figure 4 illustrates an example wind turbine blade as per Figures 2 and 3 in perspective view, viewed end-on with respect to the lift portion.

Figure 5 illustrates a cross-sectional view of the wind turbine blade as per Figures 2, 3, and 4.

Figure 6a illustrates an orbit cycle and orientation of a wind turbine blade of the invention when mounted to a vertical axis wind turbine in a carousel fashion, wherein the blades are rigidly mounted to support or mounting arms. Figure 6b illustrates an orbit cycle and orientation of a wind turbine blade of the invention when mounted to a vertical axis wind turbine in a carousel fashion, wherein the blades are rotatably mounted to support or mounting arms.

Figure 7 illustrates an example of a wind turbine blade in end perspective view.

Figure 8 illustrates an example of a wind turbine blade in cross-section.

Figure 9 illustrates an example of a wind turbine blade in cross-section.

Figure 10 illustrates an example of a wind turbine blade in cross-section.

Figure 11a illustrates another example wind turbine blade in perspective view, with attached mounting arm(s).

Figure lib illustrates another example wind turbine blade as per Figure 11a in

perspective view, but rotated through 180 degrees.

Figure 11c illustrates another example wind turbine blade as per Figures 11a and lib in perspective view, viewed end-on with respect to the lift portion.

Figure lid illustrates another example of a wind turbine blade as per Figures 11a and lib in end perspective view.

Figure lie illustrates another example of a wind turbine blade as per Figures 11a and lib in cross-section.

Figure 12 illustrates an example wind turbine blade in cross-section with example vortex generators.

DEFINITIONS:

Blade: (also wind turbine blade) refers to a wind turbine blade either of the prior art or as described herein.

Drag portion: refers to a part, element, or component of a wind turbine blade, which by virtue of its shape or configuration causes a wind flow to be slowed by or impinge upon surfaces of the drag portion thereby to exert a drag force on the blade upon exposure of the blade to a wind flow suitable to move the blade.

Leading edge: in relation to a lift portion of a wind turbine blade of the invention, refers to the leading edge of the lift portion relative to the orbiting motion of the blade when attached to or forming part of a wind turbine. The end opposite the leading edge is the trailing edge, which upon exposure of the blade to a wind flow may be the first edge encountered by the wind flow when the wind flow exerts a force upon the blade to move the blade.

Lift portion: refers to a part, element, or component of a wind turbine blade of the present invention, which by virtue of the exposure of the lift portion to a wind flow, causes a pressure differential across the lift portion thereby to generate a lift force suitable to move the blade.

Vortex generator: refers to any device or element forming part of or affixed to any surface of an wind turbine blade as described here, to break-up or create turbulence of any fluid (e.g. air or wind flow) passing over the blade surface.

Wind turbine: refers to a rotating machine which converts the kinetic energy of wind into mechanical energy. If the mechanical energy is used directly by machinery, such as a pump or grinding stones, the machine may be called a windmill. If the mechanical energy is instead converted to electricity, the machine may be called a wind generator, wind turbine, wind power unit (WPU), wind energy converter (WEC), or aerogenerator.

DETAILED DESCRIPTION OF SELECTED EMBODIMENTS

Increasingly, wind machines are helping to reduce our dependency upon fossil fuels and nuclear fission for the generation of electricity. Wind machine projects range from small wind turbines for domestic or household use, to large scale wind farms to supply power to the electrical grid. However, the continued and future success of wind machines for electricity generation depends largely upon their ability to convert the kinetic energy of wind into mechanical or electrical energy with a high degree of efficiency, regardless of wind speed and direction. Even small improvements in the efficiency of this energy conversion may improve the credibility of wind machines as a viable alternative to more traditional sources of energy.

The inventors of the present invention have deduced that wind turbine blade design is a key parameter for optimal extraction of energy from a given wind flow.

Moreover, the inventors have conducted meticulous research with the goal of developing a wind turbine blade that exhibits excellent energy conversion efficiency, with a capacity to extract useful kinetic energy from a range of different wind flows, regardless of their direction and speed, to covert this energy into a useful mechanical energy. At least in preferred embodiments, the wind turbine blades permit the production of wind turbines that start easily, exhibit excellent torque at low wind speeds, and excellent rotation speed and energy conversion efficiency at high wind speeds. Moreover, the wind turbine blades of the present invention are designed to be fitted to any type of wind turbine, including both windmill-style and carousel-style arrangements for the blade mountings, regardless of the orientation of the shaft or rotational axis relative to the ground.

In just one example, Figure 1 illustrates an embodiment of a wind turbine of the present invention, which incorporates a wind turbine blade of the present invention. The wind turbine is of a type similar to those disclosed in international patent publication WO2007/121563 published November 1, 2007, the entirety of which is incorporated herein by reference.

In Figure 1, the wind turbine is shown generally at 10, mounted atop vertically extending cylindrical pole 11 supported by optional cables 12. Ring-shaped permanent magnet generator 13 is integrated with cylindrical pole 11. In this embodiment, wind turbine blades 14 are coupled via arms 15 directly to an outer casing associated with a rotating current-inducing set of permanent magnets or rotor 16 for rotation about a stationary current-inducing stator (not shown) which is rigidly affixed to cylindrical pole 11. The outer casing of rotor 16 includes bearings (not shown) at the top and bottom which allow the rotor to rotate smoothly about the stator. When the magnetic field of the rotor cuts through the conductors of the stator a voltage is induced in the conductors. Current generated by the device may be used immediately to power a device requiring electricity or alternatively may be stored in a battery pack or other charge storage device.

The precise arrangement of the rotor and stator, and other components of the wind turbine, may be varied significantly from Figure 1, to form alternative configurations for electricity generation that are known in the art. For example, the generator need not necessarily be mounted generally atop the cylindrical pole, but a shaft about which the blades orbit may be operatively linked via a geared mechanism to the generator.

Moreover, the energy of the rotating shaft may be utilized for purposes other than electricity generation, including for example the transfer of mechanical energy for useful work (e.g. grinding, pumping etc.).

Each blade 14 has a particular configuration that is better understood by reference to Figures 2, 3 and 4 and the foregoing discussion. In these Figures, a single blade 14 is illustrated still attached to arm 15 for mounting the blade as a component of a wind turbine, as shown in Figure 1. The blade includes a lift portion 20, which in the illustrated embodiment takes the form of an elongate planar or sheet-like member of generally uniform width and cross-section extending the length of the blade. The lift portion 20 is constructed of a material that is at least substantially rigid such that the material is at least substantially inflexible when exposed to a wind flow. Moreover, lift portion 20 is of a form such that a wind flow flowing around or over the lift portion causes a pressure differential on one side or planar surface of the lift portion relative to the other side or planar surface. This pressure differential generates a lift force on the lift portion, wherein at least a vector of the lift force is sufficient to cause the blade to turn about its orbit when mounted to a shaft or other rotatable components of a wind turbine.

In addition to the lift portion 20, the blade comprises a drag portion 21 which, at least in the embodiment illustrated in Figures 2, 3 and 4, takes the form of an elongate curved sheet-like member of generally uniform thickness and cross-section. Drag portion 21 also extends the length of the blade, with the concave side 22 of the drag portion (not visible in Figures 2 and 3 but visible in Figure 4) facing leading edge 24 of the lift portion 20, and with the convex side 23 of the drag portion (visible in Figures 2 and 3 but not visible in Figure 4) facing away from the lift portion 20. Thus, in the configuration shown in Figures 2, 3 and 4, the leading edge 24 of lift portion 20 extends towards the concave surface 22 of the drag portion 21, whereas the trailing edge 25 of lift portion 20 extends away from the drag portion 21.

Wind flow about the blade impinges upon the surfaces of the drag portion.

However, in a manner that is known in the art the wind flow typically exerts a higher pressure upon the concave side 22 of the drag portion 21 relative to the convex side 23, in part because the wind flow can flow more easily over and around convex surface 23 when it faces the oncoming wind. In this way the mass of the wind flow impinging upon the concave side 22 causes a drag force on the drag portion, wherein at least a vector of the drag force is suitable to move the blade about its orbit, with the convex side 23 leading the direction of movement.

Thus, in accordance with the embodiment illustrated, the wind flow interacts with both the lift portion and the drag portion of the blade such that the blade experiences both a lift force and a drag force. Importantly, when the blade is mounted to a wind turbine, both the lift force and the drag force may at times contribute to the movement of the blade about its orbit. The invention encompasses any wind turbine blade of any configuration in which the wind turbine blade includes one or more elements or components configured to cause a lift force, and one or more elements or components configured to generate a drag force upon the blade. However, such components may not necessarily be shaped, configured or mounted relative to one another in the manner shown in Figures 2, 3, and 4. Indeed, the wind turbine blades of the present invention include those in which the lift components and drag components are mounted entirely separately from one another upon the blade. Furthermore, the present invention encompasses wind turbines that include blades wherein each blade separately includes either a lift component or a drag component so that each blade is either a lift blade or a drag blade, with all lift blades and drag blades contributing to the rotation of the wind turbine upon exposure to a wind flow.

Regardless, the invention encompasses the combined use of lift and drag components (either within the same blade or within the same wind turbine) to convert kinetic energy in the wind flow to mechanical energy suitable to cause rotation of a shaft or other components of the wind turbine. It is one intention of the blade designs disclosed herein to optimize extraction of energy from the wind flow by taking advantage of both lift and drag forces, wherein the lift and drag forces are at least partially additive to facilitate rotation of the wind turbine. However, in particularly preferred

embodiments, for example as shown in Figures 2, 3, and 4, the structural and function relationship between the lift and drag portions may further contribute to the energy conversion efficiency.

As illustrated with reference to Figures 2, 3, and 4, lift portion 20 extends generally close to drag portion 21, and parallel with a symmetrical axis of drag portion 21. Figure 5 shows a cross section of the blade, again showing how leading edge 24 of lift portion 20 extends towards drag portion 21. In use, a wind flow flowing generally from left to right in Figure 5 flows around lift portion 20 (to cause a pressure differential between each side of the lift portion 20) and the wind flow will then be directed at least in part by lift portion 20 towards drag portion 21. Thus the lift portion 20 effectively performs at least two useful functions by (1) causing a lift force in the wind flow and (2) helping air flowing about and emanating from the lift portion to flow towards the drag portion 21 so that a mass of the air impinges upon concave surface 22 thereof. In this way, there is at least some degree of synergy between the function of lift and drag portions because the lift portion 20 helps to concentrate or to direct wind flow onto appropriate surfaces of the drag portion 21 to facilitate the drag force.

In selected embodiments the lift portion 20 may exhibit additional functions. For example, with reference once again to the wind turbine illustrated in Figure 1, each blade 14 is mounted to arms 15, which are connected to rotor 16. Figure 4 best illustrates the nature of the mounting connections 30 between blade 14 and arm 16. Each blade 14 may be mounted rigidly to each arm 15. Alternatively each blade 14 may be mounted rotatably to each arm 15 such that at least some degree of rotational movement 31 is permitted by each blade at the end of each arm, about an axis 32 generally parallel to the elongate profile of each blade. In this latter embodiment, the lift portion 20 of each blade may help to orientate each blade about its rotational movement such that in use each lift portion 20 extends substantially parallel with the direction of flow of the wind. This in turn causes drag portion 21 to be oriented such that concave surface 22 faces fully into the wind flow, increasing the potential for a mass of the wind flow to impinge upon concave surface 22 thus increasing the drag force on the blade.

Thus, in such embodiments the lift portion 20 functions effectively as an orientation device to increase the capacity of the drag portion to extract energy from the wind flow. Compared to rigid mounting of the blades 14 to arms 15, rotational mounting combined with the presence of the lift portion causes the blade to maintain an

orientation in line the wind flow for a longer portion of the blade orbit cycle. This is better understood with reference to Figures 6a and 6b, which illustrate plan views of selected wind turbines of the present invention (for the sake of simplicity only the carousel of arms and attached blades are shown, with the rotor or shaft assemblies not shown). In each Figure, the direction of wind flow is shown generally by arrows 33. The wind flow causes rotation of the carousel carrying the blades 14 about an orbit cycle as shown by arrows 34, such that blades positioned on the left side of each Figure generate a drag force in the wind flow.

Rigid mounting of blades 14 to arms 15 is shown in Figure 6a. As a result of the rigid mounting, each lift portion of each blade remains generally perpendicular to each arm 15 throughout each orbit cycle of the carousel (shown by arrows 34). As a result, the drag portions are in an optimal position to be impinged upon by the wind flow only when in the position 14a, because in this position the wind flow flows directly past the lift portion 20 to interact with concave surface 22 of drag portion 21, and drag portion 21 faces fully into the wind. Whilst the blades in positions 14b and 14c are still able to generate some drag force by virtue of the wind flow 33, the orientation of each drag portion is not optimal, and thus the drag force generated is less than for position 14a.

By contrast, rotational mounting of blades 14 to arms 15 is shown in Figure 6b. The rotational mounting permits each lift portion to be forced by the wind flow into an orientation at least substantially in line with a direction of the wind flow. Thus, in Figure 6b as a blade moves as per arrows 34 the blade adopts a position as shown in 14b, and maintains this orientation relative to the wind flow through most if not all of the left side portion of rotation 34, as shown at positions 14a and 14c. As the blade moves to the right side portion of rotation 34, convex side 23 turns to face the oncoming wind flow 33, and is kept in an optimal orientation for the wind flow to flow over and beyond convex side 23 by virtue of lift portion 20, which again maintains the blade in an orientation with the lift portion 20 at least substantially parallel to wind flow 33.

Without wishing to be bound by theory, the inventors believe that rigid mounting of the blades to the arms, as shown in Figure 6a, increases the lift forces upon each blade, because there is an increased opportunity for each lift portion of each blade to benefit from a pressure differential on each side thereof, at various positions around orbit cycle 34. In contrast, the rotational mounting of the blades to the arms, as shown in Figure 6b, increases the drag forces upon each blade, because the lift portion 20 orients the blade for increased drag for a longer period of time through the orbit cycle 34. However, since with rotational mounting the lift portion of each blade functions as an orientation device, there is perhaps less opportunity for each lift portion to benefit from a pressure differential across its opposite sides, and thus less opportunity to generate lift forces suitable to facilitate the orbiting of the blades.

The invention thus further encompasses the use of blades that comprise both a lift portion and a drag portion, wherein the blades have a limited or restricted rotational range of motion when mounted to other components of the turbine (e.g. arms), with the intention of optimizing the energy extraction from the wind flow by the lift and drag portions through the orbit cycle of the carousel. Still further, the limited pivotal movement may be biased as required, for example so that in an unbiased position the lift portion of the blade extends in a direction at least substantially perpendicular to the arm to which it is mounted (at least in the embodiments illustrated in Figures 6a and 6b).

In the wind turbine blades of the invention, the shape, length, configuration, and orientation of the lift and drag portions, and the positioning of the lift and drag portions relative to one another, can vary significantly from the illustrated embodiments. For example, the lift portion may take any configuration suitable to generate a lift force upon exposure to a wind flow. From Figures 2, 3, and 4 it will be noted that lift portion 20 at its leading edge 24 does not extend all the way to contact drag portion 21. Instead, a gap 26 of generally uniform width extends between leading edge 24 and drag portion 21 (gap 26 is best seen in the perspective view provided by Figure 7). This gap is an optional feature of selected blades, and permits wind flow and air movement about the leading and trailing edges of lift portion 20. In selected embodiments the turbine blades may have larger or smaller gaps 26 extending between the lift and drag portions. In the embodiments illustrated the lift portion 20 extends via its leading edge 24 into a partial lumen formed by the curvature of drag portion 21. In selected embodiments the lift portion 20 may extend to virtually contact drag portion (leaving a small gap 26 of width from 0.1 to 5cm), or in still further embodiments the lift portion 20 may extend all the way to contact drag portion 21, effectively eliminating leading edge 24 and gap 26.

In still further embodiments the lift portion 20 may be spatially separated from drag portion 21, such that gap 26 is from 5cm to 100cm in width. Furthermore, lift portion 20 may be offset or angled relative to drag portion 21 as shown for example in Figures 8 and 9 respectively. The offset distance a or the angle β may vary according to the design of the wind turbine blade and the prevailing conditions for which the blade will be used. In further selected embodiments, the invention encompasses blades in which the offset distance a and / or the angle β may be varied whilst the blade is in use, for example during each orbit of the blade, or according to changes in wind flow speed or direction.

In selected embodiments the wind turbine blade includes at least some means to physically connect its lift portion to its drag portion. In the embodiments illustrated in Figure 2, 3, 4, and 7 the blade includes brackets 27 with end brackets 27a and further brackets 27b, which maintain a desired distance between lift portion 20 and drag portion 21. Brackets 27 further improve the structural integrity of the blade, and resist distortion of the blade or relative movement of the lift and drag portions upon exposure of the blade to wind flows. The brackets illustrated have a generally teardrop shape. However, the brackets or other means to connect the lift and drag portions may take any shape and form suitable to provide the desired spatial relationship between the components of the blade. In further embodiments, the connection between the lift and drag portions may be provided by the arms 15 or other members to which the lift and drag portions are mounted to produce a useful blade structure.

Furthermore, the lift portion 20 may take any shape and form suitable to generate a lift force in a wind flow for at least part of an orbit cycle for the blade. Typically, the lift portion is required to achieve a temporary pressure differential from one side of the lift portion compared to the other side, when the lift portion is exposed to a wind flow, thereby to generate a lift force on the lift portion in a direction of the side with the lower pressure. In most of the illustrated embodiments the lift portion is shown as a generally flat or planar blade-like member. However, the invention is not limited in this regard. The lift portion may be elongate or otherwise, of uniform width and cross-section or otherwise. In selected embodiments the lift portion may take the form of an aerofoil, with an aerofoil-like cross section. Such embodiments are in some instances preferred, because it is well known in the art that an aerofoil shape generates a desired pressure differential when a wind flow passes under and over it. One example of a blade design that incorporates an aerofoil is shown in Figure 10, which illustrates another cross-section through a blade design of the invention. In this embodiment the drag portion 21 takes a form that is equivalent to previous described embodiments. However, in contrast to other embodiments (e.g. Figure 5) the lift portion 20 has an aerofoil cross-section, with lower pressure side 28, and higher pressure side 29. Upon exposure to a wind flow flowing from left to right across the Figure, the flow of the air over the aerofoil will generate a lift force in a manner well known in the art, in a direction approximately equivalent to arrow 40. A vector of this lift force and a drag force generated in the same wind flow, illustrated by arrow 41, are at least partially additive thereby to achieve a combined force suitable to facilitate movement of the blade. The orientation and / or direction of the aerofoil relative to the drag portion may be changed and / or reversed as required.

The drag portion 21 may also take any form suitable to generate a drag force. Many such drag devices or components are known in the art. Illustrated in the Figures are drag portions that typically have an elongate form and substantially uniform width and cross-sectional profile. Typically, though not necessarily, a drag portion will include some form of concave surface, or hollowed-out section to "catch" the wind flow, so that the wind flow can impinge upon interior surfaces of the concave surface adjacent a partial lumen created by the concave surface. In this way, kinetic energy in the wind flow is transferred to the blade, to turn the blade.

Further modifications to blade design, and the interaction of the lift and drag portions of the blade, may be beneficial for blades intended for windmill-type wind turbines that comprise a shaft or rotor rotating about an axis at least substantially perpendicular to the ground, with the blades extending radially away from the centre of rotation. The lift portion and the drag portion may take any form (as described) but further considerations may help improve the functioning of the turbine blades. For example, the lift portion, if in planar or aerofoil form, may benefit from a flair towards the portions extending away from the axis of rotation, which will inevitably have an increased airspeed during operation. Such arrangements are well known in the art to provide a substantially even lift force along the length of the blade. Likewise, the drag portion may need to be adapted in selected embodiments, to provide an even drag force along the length of the blade. For example, the depth of any concave side of an elongate drag portion (extending outward along the blade from the central axis) may be reduced to provide reduced drag force on the outer portions of the blade, which turn the fastest in the wind flow.

For greater certainty, the lift elements or lift portions 20 of the wind turbine blades disclosed herein are typically illustrated to include an elongate, generally planar member. Figure 10 illustrates one variant of such members which has an aerofoil cross- section. However, the embodiments are not limited in the regard. The wind turbine blades disclosed herein may include any lift elements or lift portions of any cross- sectional profile, or with any uniform or non-uniform cross-sectional profile, suitable to generate a lift force resulting from a pressure differential upon exposure to a wind flow from one or more directions. In selected embodiments the cross-sectional profile of the lift elements or lift portions may differ from a planar or an aerofoil cross section to include curved, tapered, parabolic, concave, convex, wedge-shaped or any other cross- sectional profile, whether uniform or non-uniform, along a length of the lift element or lift portion.

One such embodiment is illustrated with reference to Figure 11, which includes a lift portion 20 which is of generally uniform width but which has a curved profile. Figures 11a, lib, 11c and lid corresponding respectively to Figures 2, 3, 4 and 7. The general format and structure of the wind turbine blade shown generally at 14 is similar to that previous described with respect to Figure 2, 3, 4 and 7 except for the shape of lift portion 20, which extends in a curved manner from trailing edge 25 to leading edge 24. A cross- section through blade 14 is shown in Figure lie, which presents a similar view to Figure 5 and 10 for the blade 14 illustrated in Figure 11a to lid. It may be seen from Figure lie that lift portion 20 in cross-section has a generally uniform width in a similar manner to that shown in Figure 5. However, in contrast to Figure 5 the lift portion illustrated in Figure lie has a curved profile. Embodiments such as is shown in Figure 11 may present especially useful lift and drag characteristics. Although a particular curved profile is illustrated in Figure 11, any other curved profile, including variable curved profiles, parabolic, aerofoil-type, and other curves of any radius may be used according to the preferred blade design and application, wind-conditions and turbine positioning.

Moreover, in selected embodiments the nature of the curved profile may be the same regardless of the position of cross-section of the blade. In other embodiments, the nature of the curved profile for the lift portion may vary along a length of the blade. For example, the radius, shape or flare of the curve may increase or decrease along a length of the blade, and the blade may include both planar (non-curved) and curved portions for the lift portion of the blade.

For greater clarity, the drag portions or elements of a wind turbine blade as described herein may take any form or configuration suitable to cause a drag force upon the blade upon exposure to a wind flow. Typically, though not necessarily, a drag portion or element may include a convex surface to receive a mass of wind flow such that the flow impinges upon and imparts a drag force to internal surfaces of the convex surface. However, a drag portion may also include planar surfaces to receive the wind flow, or may include both planar and convex surfaces.

In still further embodiments, any wind turbine blade as described herein optionally may include one or more vortex generators forming part of or attached to any blade surface or portion thereof. If present, the purpose of such vortex generators may be to break-up or create turbulence of any fluid (e.g. air or wind flow) passing over the blade surface. This may be desired according to the blade design and application, to alter or tweak the functionality of the blade, or the orientation and operation of a blade in various wind flows. Thus, the precise nature, configuration, shape, degree of protrusion, number, spacing and positioning of vortex generators may vary considerably according to the application. Moreover, the vortex generators may take any shape and form including but not limited to aerofoil, circle, tear-drop, dorsal (shark-fin), knife-edge or other symmetrical or asymmetric shapes protruding from any lift portion or drag portion blade surface. Just one illustrative embodiment is shown in Figure 12 in which there is shown a cross-section of a blade design similar to that shown in Figure 5. However, in addition two protrusions in the form of vortex generators 50 and 51 are shown on the surfaces of the lift portion 20 and the drag portion 21 respectively. Such vortex generators are carefully positioned and refined to modify the wind flow about the surfaces of the blade during operation, thus to facilitate and optimize the blade's operative functionality.

Table 1 attached hereto presents a significant quantity of experimental data in the form of field test results for wind turbine blades of dimensions 72" by 24" by 12" mounted to a vertical axis wind turbine. For many of the tests ambient temperature, due point, barometric pressure, air densiy, wind speed and direction are noted, and the wind turbine operated for a period of time to measure output from the turbine.

Measurements included average wattage, peak wattage, and kilowatt-hours of power generation.

Whilst the methods of the present invention are herein defined according to specifically recited embodiments and examples, a skilled artisan will appreciate that further embodiments are implicit from the present disclosure. It is Applicant's intention to encompass all embodiments, whether explicitly or implicitly inferred from the present disclosure, within the scope of the appended claims.

Performance Data of Present (72"x24"xl2")Multi Element Blade

TABLE 1

Performance Data of Present (72"x24"xl2")Multi Element Blade

TABLE 1

Performance Data of Present (72"x24"xl2")Multi Element Blade

TABLE 1

Performance Data of Present (72"x24"xl2")Multi Element Blade

TABLE 1

Performance Data of Present (72"x24"xl2")Multi Element Blade

TABLE 1