With the modern day pressure of global warming there has been an increasing impetus to develop alternative energy sources in favour of those that produce carbon dioxide emissions. In this regard, there have been many devices that have been developed which seek to harness the energy from the wind and turn this into mechanical energy which may then be converted into electrical energy if so desired.

The amount of power per square meter of wind is typically very small because the normal wind speeds on Earth are quite benign. Even so, it is not expected to be able to extract all of this power due to fundamental limits on efficiency for an ideal turbine which has been said to be 59%. This limit is further reduced by considering the effect of the rotation of the turbine. There are also further losses in electric generators and other parts of the energy conversion system. The current wind turbine technology achieves efficiencies that are close to this limit; hence further improvement in efficiency is likely to be marginal. Thus, the key question in considering a wind power technology is its ability to scale to very large surface areas. There are two basic approaches for scaling a plant to intercept large surface areas of wind: 1) build a larger turbine; and 2) use an array of turbines.

There are many variants and designs for wind power plants, but the dominant model is a Horizontal Axis Wind Turbine (HAWT) with three blades.

In the case of a HAWT, the power is extracted, from the area swept by the rotor. This area grows as the square of the diameter. Hence, by increasing the size of the rotor blade, the area grows as the square of the scaling factor. However, there are technical and economic limits for building larger rotors. For example, there are difficulties with the design, manufacture and transportation of very large blades. The dynamic forces on the system, such as centrifugal forces and wind sheer also become significant leading to reduced lifetime and increased OAM cost. Other effects such as vibrations, noise, visual impact, and the danger posed to avian life may also limit the size of the turbine. At this stage, we might be close to the practical limit and a significant increase in the size of turbines in the short to medium term may not be feasible.

Practically, therefore, we have no option but to move towards the second model for scaling which involves an array of turbines, also known as wind farms; It may appear that to scale wind power plants we should manufacture the HAWT of optimal size, and then deploy in a farm arrangement.

There are, however, limitations on how closely one can place wind turbines next to each other. This is because the rotation of blades creates a rotation of air flow in its vicinity and wake due to tip vortices and rotational torque imparted on air flow. The interference from these turbulence flows will reduce the efficiency of adjacent wind turbines at close distances. Consequently, the turbines must be spaced from each other and the power generated per square meter of land used becomes relatively fixed (around 10 Watts/m ² of land) and independent of the size of the rotor.

Accordingly, the present invention seeks to provide a wind energy conversion apparatus that addresses at least some of the disadvantages outlined above with respect to current arrangements.

Summary According to one aspect there is provided a wind energy conversion apparatus including:

a support frame;

an upper pair of axially spaced rotating members located in an upper portion of the support frame;

a lower pair of axially spaced rotating members located in a lower portion of the support frame, the upper and lower pair of axially spaced rotating members being in general vertical alignment;

two endless support means, each mounted around the vertically aligned upper and lower rotating members and configured to move in a circulating motion whereby movement of the endless support means rotates the upper and lower rotating members; and,

a plurality of aerofoils coupled between the two endless support means wherein each aerofoil is coupled between the two endless supports at

₍ opposed ends of the aerofoil at a position equal to, or forward of, the centre of mass of the aerofoil, wherein wind travelling past the plurality of aerofoils produces a translational force upon the aerofoil which in turn causes movement of the two endless support means and thereby rotation of the upper and lower rotating members.

In one form each aerofoil is coupled at a position that is forward of the centre of mass and behind the centre of pressure of the aerofoil. In one form each aerofoil is coupled at a position that is at least 10% forward of the centre of mass of the aerofoil. n a further form each aerofoil is coupled at a position that is at least 20% forward of the centre of mass of the aerofoil.

In one form each aerofoil includes a leading edge and a trailing edge and each aerofoil is coupled between the two endless supports at opposed ends of the aerofoil at a position between about 1/4 and about 3/7 along the distance between the leading edge and the trailing edge . In a further form the aerofoil is coupled at a position about 1/3 along the distance between the leading edge and the trailing edge. In one form each aerofoil is pivotally coupled between the two endless supports at opposed ends of the aerofoil. In a further form each aerofoil is able to pivot relative to the two endless support means to alter the angle of attack of the aerofoil. In one form each aerofoil is able to pivot relative to the two endless support means to alter the angle of attack of the aerofoil from between about positive 5° to about positive 20° and about negative 5° to about negative 20°. In a further form each aerofoil is able to pivot relative to the two endless supports to alter the angle of attack of the aerofoil from between about positive 8° to about positive 18° and about negative 8° to about negative 1 °. In yet a further form each aerofoil . is able to pivot relative to the two endless supports to alter the angle of attack of the aerofoil from between about positive 10° to about positive 16° and about negative 10° to about negative 16°. In one form each aerofoil is able to pivot freely relative to the two endless supports under the influence of the wind and/or gravity. In a further form, the aerofoil is able to pivot freely between a positive angle of attack in an upwind position on the two endless support means and a negative angle of attach in a downwind position on the two endless support means without the influence of another mechanism.

In one form a leading edge of each aerofoils is substantially symmetrical to a trailing edge of each aerofoil.

In one form an electric generator is configured to be driven from the rotation of at least one of the upper or lower rotating members.

In one form the wind speed passing the apparatus is between about 5 and 20 m/s. ,

In one form the two endless support means are in the form of a chain. In this form the plurality of aerofoils are each coupled to the endless support means via a connector.

Brief Description of the Figures

The present invention will become better understood from the following detailed description of preferred but non-limiting embodiments thereof, described in connection with the accompanying figures, wherein:

Figure 1 is a schematic diagram of a wind energy conversion apparatus in accordance with one embodiment;

Figure 2 is a schematic diagram of a wind energy conversion apparatus in accordance with a further embodiment;

Figure 3 is a schematic diagram of a wind energy conversion apparatus in accordance with yet a further embodiment; Figure 4 is a schematic diagram of a wind energy conversion apparatus in accordance with still a further embodiment;

Figure 5 is a detailed schematic diagram in accordance with an aspect of a wind energy conversion apparatus;

Figure 6 is a schematic diagram outlining a modular arrangement of a wind energy conversion apparatus in accordance with a further embodiment of the present invention;

Figure 7 is a schematic front elevation view of two wind energy conversion apparatus side by side in a modular arrangement in accordance with a further embodiment of the present application (the downwind aerofoils are not shown);

Figure 8 is a perspective view of a similar arrangement as that depicted in Figure 7; and,

Figure 9 is a photograph of a connector in accordance with an aspect of a wind energy conversion apparatus; Detailed Description and Preferred Embodiments

The foregoing describes only some embodiments of the present invention, and modifications and/or changes can be made thereto without departing from the scope and spirit of the invention, the embodiments being illustrative and not restrictive.

In the context of this specification, the word "comprising" means "including principally but not necessarily solely" or "having" or "including", and not "consisting only of. Variations of the word "comprising", such as "comprise" and "comprises" have correspondingly varied meanings.

The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as, an acknowledgement or admission or any form of suggestion that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

In the description, relative terms such as "upper", "lower", "vertical", "horizontal", "up", "down", "top" and "bottom" as well as derivatives thereof should be construed to refer to the orientation as then described or as shown in the attached figures. These relative terms are for convenience of the description and do not require the apparatus be constructed or operated in a particular orientation.

Referring to figure 1 there is shown a wind energy conversion apparatus 10 in accordance with one embodiment. The wind energy conversion apparatus consists of a support frame 15 which includes an upper and lower horizontal support and two side supports providing an orthogonal support frame which in figure I is shown as a generally rectangular shape and elongated in the vertical direction. The support frame 15 houses the moving parts of the wind energy conversion apparatus 10 and supports an upper pair of rotating members 40a, 40b, and a lower pair of rotating members 35a, 35b. The upper pair of rotating members 40a, 40b and the lower pair of rotating members 35a, 35b are spaced apart in an axial direction (where the rotating members rotate about the same axis point of rotation which is generally horizontal in orientation relative to the support frame 15) and each respective upper and lower rotating members 40a, 35a & 45b & 35b are in general vertical alignment positioned in the four corner areas of the support frame 15.

In the case of the upper rotating members 40a, 40b there is shown two individual rotating members attached to an upwind position and a downwind position of the support frame 15. In an alternative arrangement the upper rotating members 40a,40b can be replaced by one larger rotating member similar in size as that of the lower rotating members 35a, 35b. In either arrangement, the rotating members 40a, 40b & 35a, 35b can be coupled to an individual axle (as shown with the upper rotating members 40a, 40b) or to a common axle (as shown with the lower rotating members 35a, 35b).

Two endless support means in the form of an endless belt 20, are attached around the outside circumference of the vertically aligned sets of rotating members 40a, 35a & 40b, 35b. The endless belt 20 is able to move around the rotating members 40, 35 in a circulating motion which thereby causes the rotating members 40, 35 to rotate about their horizontal axis points. In another form, the endless support means 20 may be in the form of a chain similar in construction to a bike chain wherein the outer circumferential surface of the upper and lower rotating members include teeth which meshingly engage with the spaces within the chain, such that movement of the chain thereby rotates the rotating members 40, 35. Coupled between the two endless support means 20 in a generally horizontal alignment are a plurality of aerofoils 25,30 which are coupled to the endless support means 20 on either an upwind side 25 or a downwind side 30 of the endless support means 20.

In operation, the action of the wind (generally indicated by the directional arrow on Figure 1) travelling past the upwind aerofoils 25 produces a translational lift force upon the upwind aerofoils 25 which in turn causes the endless support means 20 to move in a circulating motion which in turn rotates the rotating members 35,40. In addition, as the wind passes through the first set of upwind aerofoils 25 and proceeds to the downwind aerofoils 30, the profile of the downwind aerofoils 30 is inverted as it is circulated about the endless support means 20. (see figure 2) and the action of the wind on the downwind aerofoil 30 produces a translational lift force which also acts on the endless support means 20 in the opposite direction to that of the upwind aerofoils 25 and thereby causes the endless support means 20 to move in the same circulating direction. In this embodiment, the lower rotating members 35 are coupled to an axle 45 and the rotation of the rotating members 35 thereby causes the axle 45 to rotate which movement can then be used in the generation of electricity if so desired. In this form an electrical generator may be mechanically coupled to the rotating members 35 to generate electricity from the energy converted from the wind.

The approach adopted by the present invention is to abandon the rotary model (with its undesirable effects on creating turbulence in its vicinity and wake) and use a modular approach in building a large wind harvesting area. The apparatus 10 is preferably composed of a light support frame 15 that would be optionally mounted on a support tower or structural frame (not shown). As the endless support means 20 passes over the upper rotating members 40 and lower rotating members 35, the aerofoils will change side and orientation (ie change from upwind aerofoils to down wind aerofoils or vice versa).

Although not shown, the top and bottom and sides of the apparatus 10 may be covered using an aerodynamically shaped cover that guides the wind towards the centre of the apparatus 10 and enables the tips of the aerofoils and their flipping from an upwind to a downwind aerofoil at the upper region of the apparatus 10 and flipping from a downwind to an upwind aerofoil at the lower region of the apparatus to happen without being subjected to the wind.

Figure 2 shows a schematic diagram of one embodiment of the present invention where the upwind 25 and downwind aerofoils 30 are coupled on the endless support means 20 where the aerofoils have a zero angle of attack with respect to the wind direction. In this case, the lift force is due to the shape of the profile and is obtained using the following equation:

Where F] is the lift force and Ci is the coefficient of lift. As can be seen, the lift forces reinforce each other to move the endless support means 20 the belt in the direction of force. The total force applied to the endless support means 20 would be equal to the sum of lift forces on the aerofoils that are exposed to the wind. This force creates a torque across the endless support means causing rotation of the upper and lower rotating members 35, 40. When the downwind aerofoil is behind the upwind aerofoil (i.e. in its shadow), its lift force is reduced. Therefore, there may be a periodic reduction of the total force on the belt which may cause some vibrations. For this reason, in a preferred form of the present invention, the adjacent modules each including one apparatus of the present invention will position the aerofoils so that one module's arrangement of aerofoils has an offset with respect to the other. For example, if two modules are adjacent to each other, the aerofoils of one could be offset by one quarter of separation distance between successive aerofoils. This will reduce any variations of force on the system. This offset scheme can be extended to more than two adjacent modules.

Figure 7 and 8 show such an arrangement where two apparatus 10 are used to create a module wherein the two apparatus 10 share a common central endless support means 20 which rotates a common upper and lower rotating member 40c, 35c. In this embodiment the upwind aerofoils 25 and the downwind aerofoils 30 of the two apparatus are off set on the horizontal alignment on the endless support means such that when one apparatus downwind aerofoils 30 are in shadow, the downwind aerofoils 30 of the other apparatus are not. As such, this embodiment significantly reduces variations in the lift forces provided to the support means 20 as it circulates the rotating members 40 and 35.

In certain embodiments the angle of attack of the aerofoils may be increased which has been found to change and increase the associated lift force provided by the wind passing the aerofoil. The coefficient of lift increases almost linearly with the angle of attack up to around 8 to 18 degrees and preferably 10 to 16 degrees. The drag, ^" however, remains almost negligible for angles of attack less than 10 degrees. Therefore according to one embodiment it is preferable to have a large enough angle of attack without significant increase in drag. However, it was found that a fixed connection of the end of the aerofoils to the endless support means 20 with a fixed positive angle of attack may not provide the most desirable outcome as the lift forces of the upwind aerofoils 25 will be in the same direction as the lift forces provided by the wind on the downwind aerofoils 30 as illustrated in Figure 3. Accordingly in another embodiment the upwind aerofoils 25 are provided with a positive angle of attack and the downwind aerofoils are provided with a negative angle of attack. In a preferred form, the aerofoils 25 coupled to the upwind section of the endless support means have a positive angle of attack of between about 5° and about 20° and preferably about 8° to about 18°, and more preferably about 10° to about 16°. In this form, it is preferred that aerofoils 30 coupled to the downwind section of the endless support means have a negative angle of attack. In a preferred form the aerofoils coupled to the downwind section of the endless support means have a negative angle of attack of between about 5° and about 20° and preferably about 8° to about 18°, and more preferably about 10° to about 16°.

In certain embodiments it was found that when the aerofoils are coupled to the endless support means 20 at a point which is forward of the centre of mass of the aerofoils but behind the centre of pressure a significantly improved amount of lift force and efficiency of wind energy conversion was achieved. In a preferred form, the aerofoils were coupled between the two endless support means at a position on each end of the aerofoil that was at least 10% forward of the centre of mass of the aerofoil. In a further preferred form, the aerofoils were coupled between the two endless support means at a position on each end of the aerofoil that was at least 20% forward of the centre of mass of the aerofoil.

Each aerofoil includes a leading edge and a trailing edge and in an alternative arrangement each aerofoil is coupled between the two endless supports at opposed ends of the aerofoil at a position between about 1/4 and about 3/7 along the distance between the leading edge and the trailing edge of the aerofoil. In a further preferred form, the aerofoil is coupled at a position about 1/3 along the distance between the leading edge and the trailing edge.

In a certain embodiments, it was surprisingly found that when the aerofoils are coupled whereby they are able to pivot or rotate freely about the coupling between the aerofoil and the endless support such that the aerofoils are able to pivot and move under the influence of gravity and or the wind, the aerofoils have a tendency to move between a positive angle of attack when on the upwind section of the endless support means and a negative angle of attack when on the downwind section of the endless support means. Without wishing to be bound by theory it is believed the combination of weight and lift force create a pitch moment that keeps each aerofoil in the appropriate angle of attack as illustrated in Figure 4. The angle also automatically is adjusted as the blade changes orientation at the top and bottom of the module with the assistance of gravity. In a preferred form of this embodiment, each aerofoil is able to pivot relative to the two endless support means to alter the angle of attack of the aerofoil from between about positive 5° to about positive 20° and about negative 5° to about negative 20°. In a preferred form each aerofoil is able to pivot relative to the two endless supports to alter the angle of attack of the aerofoil from between about positive 8° to about positive 18° and about negative 8° to about negative 18°. In yet a further preferred form each aerofoil is able to pivot relative to the two endless supports to alter the angle of attack of the aerofoil from between about positive 10° to about positive 16° and about negative 10° to about negative 16°.

In one embodiment, the aerofoil is able to pivot freely between a positive angle of attack in an upwind position on the two endless support means and a negative angle of attach in a downwind position on the two endless support means under the influence of the wind and/or gravity only and without the influence of another active mechanical mechanism. By not requiring an active mechanical mechanism or other influence aside from wind and/or gravity the wind energy apparatus as herein described provides an arrangement that is significantly more simplified than current designs of linear wind energy conversion arrangements.

In one form, the coupling between the end of the aerofoil and the endless support means allows the aerofoil to pivot in the desired range allowing the aerofoil to move between a positive angle of attach and a negative angle of attack. In one example embodiment depicted in Figure 9, the endless support means is in the form of a chain (not shown) and the coupling 100 is fixed at an opening 1 10 to an end of an aerofoil (not shown). The coupling 100 may be threaded onto a chain through a main chain receiving channel 120 and attached in a manner that allows the coupling (and the attached aerofoil) to move or pivot relative to the chain which thereby provides the coupling (and attached aerofoil) the desired degree of movement as described above. For example, the coupling may include corresponding openings 121 , 122 which receive two pins (not shown) which pass though the chain thereby attaching the coupling thereto. One of the openings 122 does not allow a pin to move once located therein in a significant manner, but the other opening 121 provides a degree of movement which allows the coupling to pivot about the other opening 122.

An important advantage of the wind conversion apparatus as herein described is that the aerofoils do not rotate in the wind but are only experiencing a translational motion (up or down). All the points on an aerofoil move at the same speed and as such, the aerofoil does not impart a torque on the air flow. In addition, the tips of the aerofoils are out of wind and covered so the tip vortices are likely to be small with little chance of interfering with neighbouring apparatus of the same design. Consequently, many of the apparatus of the present invention can be placed next to each other without significant loss of efficiency to build a large wind collection array such as that depicted in Figure 6.

The dynamic forces on a collection array made up of many of the apparatus in accordance with the present invention are small and not synchronized with each other. For example, centrifugal forces are negligible, wind sheer would have no effect as the apparatus at the top and bottom of the array are independent. Other vibrations are likely to be local to each individual apparatus and at different frequencies and phases. So they would not lead to a resonant structure-scale vibration.

The same basic design is used for any scale with the same manufacturing procedure and materials. Hence, mass production of large arrays is likely to reduce the overall cost per apparatus. According to a preferred embodiment of the present invention to apply an aerodynamic break to the apparatus 10 there are at least two mechanisms for slowing down (or stopping) the rotation of the endless support means, (i) to reduce the angle of attack and (ii) to disable the capability of aerofoils to adjust the angle of attack in each rotation as described. Both of these can be enabled by progressively squeezing together the rubber cushions 50 constraining the aerofoil tips as shown in Figure 5.

As the rubber cushions 50 are squeezed together, the angle of attack is decreased as the aerofoil pivots around point 55. The active yaw system, or deviation around its vertical axis, in HAWTs is required to yaw the whole turbine in the desired direction. The modular approach in the present invention enables us to control the yaw motion of the apparatus with finer adjustment. At the limit, each modular apparatus may have its own yaw controller. This would be appropriate for situations when the change in wind direction frora the predominant direction is relatively small (up to around 45 degrees). If larger yaw movement is required, it is possible to apply the yaw motion to a number of modules connected to a common larger support structure that are placed horizontally next to each other. This will increase the downwind separation between the modules and improve efficiency (see Figure 6).

As shown in Figure 6 the modules may be mounted on a traditional wind power tower. Alternatively, the arrangement of modules may take many forms and shapes. For example, due to reduced noise and vibration, it may be possible to put a row of modules on top (or the side) of apartment blocks and tal l buildings and blend it architecturally with the surrounds.

The wind energy conversion apparatus as herein described will become better understood from the following example of a preferred but non-limiting embodiment thereof.

Example

A wind energy conversion apparatus as herein described was prepared with the dimensions of the support frame being 2 m X 2 m and including 12 aerofoils arranged around the two endless support means in the form of a chain with the connector coupling the chain with the aerofoils allowing the aerofoils to pivot between a positive angle of attach of 12 - 16 degrees when on the upwind side of the apparatus and a negative angle of attach of 12 to 16 degrees when on the down wind side of the apparatus. The wind energy conversion apparatus was placed in a Wind tunnel. The module was connected to a generator via a torque sensor and a gearbox. An electrical load variation/measurement system was also connected to the generator. The torque sensor provided data for power output before the losses due to gearbox and generator. The electrical power output was also measured after these losses. Measurements were conducted for wind speeds of 4, 6, 8, 10, 12 and 14 m/s. During each run, the wind energy conversion apparatus was allowed to attain a steady state with no load. Then the load was gradually increased until the apparatus slowed down significantly. The electrical power output at each instant was measured using a measurement system. The raw data was later analysed to estimate the power output at various wind speeds.

Results

Table 1 and Figure 1 show the efficiency and output efficiency for different wind speeds in tabular and line graph forms.

Table 1 : Summary of experimental and calculated data

Efficiency

Output Efficiency

8 10 12 14

Figure 1 : Efficiency and output efficiency as a function of wind speed

The overall trend in the efficiency curve is according to expectation. At low wind speeds, there is little power available and hence the fixed component of loss dominates. As the wind speed increases, efficiency improves very quickly and it reaches optimum operating conditions.

Finally, it can be understood that the inventive concept in any of its aspects can be incorporated in many different constructions so that generality of the preceding description is not superseded by the particularity of the attached drawings. Various alterations, modifications and/or additions may be incorporated into the various constructions and arrangements of parts without departing from the spirit or ambit of the present invention.