The invention relates wind turbine apparatuses and particularly, but not exclusively to wind turbine apparatuses comprising a plurality of turbine modules.

It is known to arrange a plurality of vertical axis wind turbine (VAWT) modules within a frame to form a wind fence; see UK Patent No. 2476126, for example. Such an arrangement is shown in Figure 1 . As shown, the frame 1 is formed by upper and lower structural rails 3a, 3b and left and right side members 5a, 5b to form a rectangular frame. A plurality (four are shown) of wind turbine modules 7a-7d are located within the frame 1 and are spaced from one another along the width of the frame 1 . The modules 7a- 7d are affixed at either end to the upper and lower structural rails 3a, 3b. Each module 7a- 7d comprises a blade portion 9 and a generator 1 1 coupled thereto.

Figures 2 and 3 show an exemplary axial-flux generator 1 1 in further detail. As shown, the generator 1 1 comprises a rotor 13 and a stator 15. The rotor 13 is formed by an outer housing of the generator 1 1 which is connected to the blade portion 9 for rotation therewith. In contrast, the stator 15 is formed by a shaft 17 which is affixed to the lower rail 3b. The rotor 13 is rotatably mounted to the shaft 17 by upper and lower bearings 21 a, 21 b. The shaft 17 carries a disc 19 which has a plurality of coils 23 arranged in a circle. The rotor 13 carries a plurality of permanent magnets 25. The permanent magnets 25 are arranged in an upper circle and a lower circle which correspond with the circle of coils 23. The coils 23 are sandwiched between the upper and lower sets of magnets 25 with a small gap therebetween to allow free movement of the magnets 25 relative to the coils 23.

Rotation of the blade portion 9 in response to the force of wind causes rotation of the rotor 13. The movement of the magnets 25 relative to the coils 23 induces a current in the coils 23 which can be harnessed as useful electricity.

As described above, the rotor 13 is supported by a pair of bearings 21 a, 21 b which maintain alignment between the rotor 13 and the stator 15 such that the distance between the coils 23 and magnets 25 can be minimised, thereby improving efficiency. While such an arrangement addresses axial misalignment issues between the rotor 13 and stator 15, in order for the blade portion 9 and rotor 13 to rotate freely, the centre of the bearing supporting the upper end of the blade portion 9 (at the upper rail 3a) must lie on the axis defined by the centres of the two bearings 21 a, 21 b within the generator 1 1 . With this arrangement, sufficient alignment must be achieved in manufacture/assembly, and in all weather conditions during operation, to avoid the risk that at least some of these bearings bind, thus reducing system power output, and potentially causing excessive bearing wear or overheating. Achieving and maintaining such alignment is likely to lead to an excessive requirement for frame rigidity, blade stiffness, and/or a substantial common central shaft running the full height of the module, all with significant associated cost and weight penalties.

A flexible coupling between the blade portion 9 and the rotor 13 may be introduced to allow the rotation axis of the blade portion 9 to deviate slightly from that of the generator 1 1 without damaging either component. Such an arrangement can, however, create a new issue in that a high torque (perpendicular to the rotation axis) is generated on the lower rail 3b which supports the generator 1 1 .

Moreover, in order to carry the generated current away from the coils 23, it is necessary for the shaft 17 to be hollow so that suitable wiring can pass through the shaft 17. However, as described, the shaft 17 carries the weight of the generator 1 1 and must withstand in-service loads. As a result, such shafts are conventionally constructed from relatively high strength steel so as to give them the necessary strength and rigidity.

It is desirable to provide improved arrangements which address some or all of the issues associated with the prior art arrangements described above.

In accordance with an aspect of the invention, there is provided a wind turbine apparatus comprising: a blade portion; a generator comprising a stator having a plurality of coils and a rotor having a plurality of magnets, the rotor being connected to the blade portion such that rotation of the blade portion and rotor generates a current within the coils; wherein the blade portion is connected to the rotor by a yoke which extends around the generator and is connected to the base of the rotor such that the magnets of the rotor and the coils of the stator are disposed between the blade portion and the connection between the yoke and the rotor.

The stator may comprise a shaft which is received by a supporting rail. The connection between the yoke and the rotor may be disposed between the supporting rail and the magnets and coils. The rotor may be rotatably mounted on the stator by a bearing, and the connection between the yoke and the rotor may be formed around the bearing.

The yoke may be compliant so as to allow the rotation axes of the blade portion and the rotor to be offset from one another.

The yoke may be connected to the blade portion and/or the rotor via a compliant coupling so as to allow the rotation axes of the blade portion and the rotor to be offset from one another. The yoke may be connected to the blade portion and/or the generator via a quick- release mechanism.

In accordance with another aspect of the invention, there is provided a wind turbine apparatus comprising: a blade portion; a generator comprising a stator having a plurality of coils and a rotor having a plurality of magnets, the rotor being connected to the blade portion such that rotation of the blade portion and the rotor generates a current within the coils; wherein the stator comprises a shaft, the shaft having a first terminal portion and a second terminal portion separated from one another by an insulator, the first and second terminal portions being electrically connected to the coils; wherein the shaft is received by openings provided in first and second conductive rails so as to support the generator and blade portion and such that the first and second terminal portions are electrically coupled to the first and second conductive rails respectively to carry the current from the coils. The holes in the first and second conductive rails may have complementary cross- sections to the first and second terminal portions.

The first terminal portion may be formed by a pin and the second terminal portion may be formed by a sleeve which surrounds the pin. The pin may project from the sleeve such that the pin is received by the second conductive rail when the sleeve is received by the first conductive rail. The pin and sleeve may be concentric.

The sleeve may have a first diameter and the pin may have a second diameter which is smaller than the first diameter. The openings of the first and second rails may be sized to receive the first and second diameters respectively.

The first and/or second rail may be provided with a retention member having or defining a hole sized to receive the first or second terminal portion. The retention member may be configured to be aligned with the rail so that the terminal portion is received by the hole of the retention member and the opening in the rail and wherein the retention member is translatable relative to the rail so as to draw the terminal portion against the rail, thereby mechanically connecting the stator to the rail. The first and/or second rails may be tubular defining a cavity which extends therethrough and the retention member may be received within the cavity.

An exterior profile of the retention member may be sized and/or shaped to ensure alignment of the hole of the retention member and the opening in the rail.

The exterior profile of the retention member may substantially correspond to (although may fit fairly loosely within) an interior profile of the cavity.

The retention member may be secured to the rail by a threaded fastener which translates the retention member relative to the rail as it is rotated.

The blade portion and the generator may form a turbine module and the apparatus may comprise a plurality of said modules. For a better understanding of the invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:-

Figure 1 is a front view of a prior art wind fence; Figure 2 is a front view of a prior art generator; Figure 3 is a cross-sectional view of the generator of Figure 2;

Figure 4 is a cross-sectional view of a wind turbine module according to an embodiment of the invention;

Figure 5 is a cross-sectional view of a wind turbine module according to another embodiment of the invention; Figure 6 is a perspective view of the wind turbine module of Figure 4 showing a yoke arrangement;

Figure 7 is a perspective view of the wind turbine module of Figure 4 following engagement with a lower rail;

Figure 8 is a perspective view of a generator according to an embodiment of the invention;

Figure 9 is a perspective view of a shaft of the generator;

Figure 10 is a cross-sectional view of the shaft;

Figure 1 1 is a perspective view showing the generator prior to engagement with a pair of conductive rails;

Figure 12 is a perspective view showing a pair of generators engaged with the conductive rails; and

Figure 13 is an exploded view showing a mechanical connection between the generator and the conductive rails.

Figure 4 shows a wind turbine module 2 according to an embodiment of the invention. The module 2 may be one of a plurality of similar modules arranged in a frame comprising an upper rail 4a and a lower rail 4b, in a similar manner to that shown in Figure 1 . The module 2 is connected at its upper end to the upper rail 4a and at its lower end to the lower rail 4b. The module 2 comprises a blade portion 6 and a generator 8. The generator 8 is an axial-flux generator which comprises a rotor 10 and a stator 12. The rotor 10 is formed by an outer housing of the generator 8 which is connected to the blade portion 6 for rotation therewith. In contrast, the stator 12 is formed by a shaft 14 which is affixed to the lower rail 4b. The rotor 10 is rotatably mounted to the shaft 14 by upper and lower bearings 16a, 16b. The shaft 14 carries a disc 18 which has a plurality of coils 20 arranged in a circle. The rotor 10 carries a plurality of permanent magnets 22. The permanent magnets 22 are arranged in an upper circle and a lower circle which correspond with the circle of coils 20. The coils 20 are sandwiched between the upper and lower sets of the magnets 22 with a small gap therebetween to allow free movement of the magnets 22 relative to the coils 20.

The blade portion 6 is connected to the rotor 10 by a yoke 24 which extends from the blade portion 6 to a lower side of the rotor 10. Specifically, the yoke 24 connects to the rotor 10 around the lower bearing 16b. The yoke 24 thus connects to the rotor 10 below the disc 18 of the stator 12 and its coils 20 and below the magnets 22 of the rotor 10 itself. In contrast to prior art arrangements where the blade portion is connected directly to the rotor (i.e. either rigidly or flexibly to the top of the rotor), the yoke 24 allows the connection to the rotor 10 to be placed lower down, closer to the lower rail 4b. The distance x between the coupling point and the neutral axis of the rail 4b in thus minimized. This reduces the levering effect of the wind loading on the rail 4b, via the rotor 10 or shaft 14, and thus minimises misalignment between the axes of rotation of the blade portion 6 and the rotor 10 for a given wind loading.

Further, as shown in Figure 5, the height of the generator 8 has no effect on the distance x such that stacked stator configurations can be used without increasing the levering effect.

It will be appreciated that the structure of the yoke 24 may take various forms, provided that it places the coupling point below the disc 18 of the stator 12 and its coils 20 and below the magnets 22 of the rotor 10 itself. However, Figures 6 and 7 show an exemplary yoke 24. As shown in Figures 6 and 7, the yoke 24 is formed as a metal band which is connected at either end to the base of the blade portion 6 such that it extends across the span (i.e. the width of the blade portion 6 when aligned with the frame) of the blade portion 6. Between each end, the band is bent away from the blade portion 6 to form a central section 26. The central section 26 is spaced from the blade portion 6 by a distance which is sufficient to receive the generator 8. The central section 26 comprises a hole which is received about a hub 28 formed at the base of the outer housing of the rotor 10. The diameter of the hole in the central section 26 of the yoke 24 is slightly larger than the external diameter of the hub 28 such that it fits loosely around the hub 28. The central section 26 is retained on the hub 28 by a lower collar 30 which is connected to the distal end of the hub 28. A plurality of elastomeric washers 32 are disposed on the upper and lower sides of the central section 26 between the central section 26 and a lower radial surface of the rotor 10 and between the central section 26 and the collar 30. The elastomeric washers 32 provide a compliant coupling between the blade portion 6 and the rotor 10 allow their orientations to vary under wind loading. A similar compliance may also be provided using other forms of flexible mounting, such as o-rings, springs, flexible struts or pillars. The yoke 24 may also be formed from flexible materials (e.g. polymers, glass reinforced composites, or aluminium or sheet steel) and/or articulated joints may be provided within the yoke 24 itself to provide compliance.

The yoke 24 may be detachable from the blade portion 6 and/or the rotor 10 using conventional bolts or quick release catches. This may allow the blade portion 6 and/or the generator 8 to be removed easily for maintenance or replacement. Alternatively, the entire module 2 may be removable using suitable brackets which attach to the frame.

As an illustration, an axial flux generator, constructed to match the output of a turbine with a swept area of ~0.75m ² , was mounted in a frame consisting of rectangular cross- section aluminium tubing, of cross-sectional outer dimensions 50mmx25mm. The top of the generator had a height of ~65mm above the neutral axis of the frame member, which thus corresponded to the minimum distance for a conventional coupling arrangement. In contrast, by using the yoke 24 described previously, the blade portion 6 can be attached between the generator and the lower rail 4b, at a distance of ~9mm from the surface of the beam, or <22mm from its neutral axis, corresponding to a reduction in torque (and hence tendency to twist) on the box-section frame member, of approximately 66%.

An embodiment of the shaft will now be described with reference to Figures 8 to 13. The shaft 1 14 shown therein may be used with the yoke arrangement described previously or may be used with conventional modules.

The shaft 1 14 comprises a central pin or rod 34 and an outer sleeve 36 within which the central pin 34 is disposed (see Figure 10).

The central pin 34 is cylindrical and substantially solid along its length. The outer sleeve 36 is tubular and has an internal diameter which is sized to receive the central pin 34 such that the central pin 34 and outer sleeve 36 are arranged concentrically. As shown, the central pin 34 has a greater axial length than the outer sleeve 36 such that a portion of the central pin 34 extends out of the outer sleeve 36. Both the central pin 34 and outer sleeve 36 (or at least a part thereof) are formed from conductive metals. For example, a medium/high strength aluminium alloy may be used, but other shaft materials including, but not limited to, copper, brass or steel may also be used. Disposed between the central pin 34 and the outer sleeve 36 is an insulating layer 38. The insulating layer 38 may be a discrete tubular element disposed between the central pin 34 and outer sleeve 36 or may be a layer formed on either (or both) of (or between) the central pin 34 and the outer sleeve 36. The insulating layer 38 extends along at least the axial length of the outer sleeve 36 and electrically insulates the central pin 34 from the outer sleeve 36. The insulating layer 38 may be a reinforced thermoplastic or thermoset material, such as a fibre-reinforced epoxy material, with the three components being bonded together, for example using an epoxy adhesive, to form a composite unit. The central pin 34 and outer sleeve 36 are connected to either end of the coils 20 to form connector terminals. The central pin 34 and outer sleeve 36 may be connected to the coils 20 either directly to provide an AC output or indirectly via a rectifier circuit to provide a DC output. Where a DC output is used, the connector terminals form positive and negative terminals. As shown in Figure 1 1 , the lower rail 4b is divided into a first (upper) lower rail 4b' and a second (lower) rail 4b". Each rail 4b', 4b" is formed by a hollow electrically conductive, structural box-section beam. The rails 4b', 4b" may be mechanically linked to one another with electrically insulating tie-pieces (not shown).

The first lower rail 4b' is provided with a plurality of holes 40' spaced along its length (two are shown, but any number may be provided to match the number of modules 2). The holes 40' are in fact each formed as a pair of coaxial holes in the upper and lower walls of the beam structure. The holes 40' have an internal diameter which is sized to receive (i.e. is slightly larger than) the outer sleeve 36 of the shaft 1 14. Similarly, the second rail 4b" is provided with a plurality of holes 40" spaced along its length and sized to receive the central pin 34. The holes 40" of the second rail 4b" thus have a smaller diameter compared to the holes 40'. The holes 40' of the first rail 4b' and the holes 40" of the second rail 4b" are coaxial. Therefore, as shown in Figure 12, when the shaft 1 14 is received by the lower rails 4b', 4b", the central pin 34 passes through one of the holes 40' in the first rail 4b' and is subsequently received by the corresponding hole 40" in the second rail 4b", at which point the outer sleeve 36 is received by the hole 40' of the first rail 4b'. The outer sleeve 36 contacts the first rail 4b' and the central pin 34 contacts the second rail 4b" to form electrical connections therewith. The first and second rails 4b', 4b" are thus able to carry the current generated in the generator 8 to which the shaft 1 14 is connected. As described, the shaft 1 14 is solid along its length. The shaft 1 14 is therefore stronger than conventional shafts which must be hollow to allow wires to pass therethrough. The shaft 1 14 can therefore be manufactured from lighter materials, such as aluminium. Figure 13 shows an arrangement which may be used to aid the electrical connection and to provide a mechanical connection between the shaft 1 14 and the rails 4b', 4b". Specifically, as shown, blocks 42 (retention members) may be disposed within the rails 4b' 4b". The blocks 42 have a cross-section which corresponds to that of the rails 4b', 4b" and thus in the present example are cuboid in shape. The blocks 42 are sized slightly smaller than the internal cavity of the rails 4b' 4b" such that they are loose when placed within the cavity. The blocks 42 are provided with holes 44', 44" which correspond to the holes 40', 40" of the respective rail 4b' 4b". A pair of threaded holes 46 are provided in each of the blocks 42. The threaded holes 46 are provided on the front (or rear) surface of the blocks 42 such that they are perpendicular to the holes 44', 44". Complementary holes 48', 48" are provided in a front surface of the rail 4b', 4b", such that a threaded fastener 50 (a bolt or the like) can be passed through the holes 48', 48" and received by the threaded holes 46 of the blocks 42, with the holes 44', 44" of the blocks 42 aligned with the holes 40', 40" of the rails 4b', 4b". As described previously, the blocks 42 are loose within the rails 4b', 4b" such that the threaded fasteners draw the blocks 42 towards the front surface of the rails 4b', 4b". This action locks the central pin 34 and outer sleeve 36 of the shaft 1 14 against the rail 4b', 4b" (between one wall of the holes 44', 44" in the blocks 42, and the opposite walls of the holes 40', 40" in the rails 4b', 4b") forming a solid mechanical and electrical connection. The blocks 42 may be electrically conductive to further aid the electrical connections between the shaft 1 14 and the rails 4b', 4b".

The shaft 1 14 may be secured using different forms of retention member. For example, a bolt may pass through the walls of the rails 4b', 4b" into a hole in the shaft 1 14 or simply against the outer surface of the shaft 1 14.

From an electrical perspective, the structure of the shaft 1 14 described above, comprising two mutually isolated conductors, would be useful in carrying single phase AC from a suitably designed stator to an external conductive clamping/support mechanism for example of the type described above. Alternatively, the same design of shaft could be used to carry DC, for example from rectifiers within the generator.

Other variants on the above shaft design could be used, for example, to carry 3 phase AC, by the construction of a 5 layer shaft of alternating concentric conductors and insulating layers to a support structure comprising, for example, three electrically conductive rails, one above the other, with corresponding holes to receive the 3 mutually isolated electrically conductive concentric tubes/cylinders of such a shaft.

A plurality of generators may feed DC current or AC current (if suitably synchronised) into the lower rails which act as busbars to convey the electricity. This frame of the apparatus may be supplied and installed prior to fitting any of the modules 2. The design of the shaft 1 14 allows such a frame to be populated with wind turbine modules 2 in a very rapid and efficient manner, without any wiring connections whatsoever being made between the generators 8 and any other part of the system, and with no wiring being required within, nor running along, the frame.

The shaft 1 14 and its constituent elements need not be circular in cross-section. For example, the shaft 1 14 may have a square cross-section which may prevent rotation of the shaft 1 14. Further, although the two conductors of the shaft 1 14 have been described as being located one within the other, it will be appreciated that other arrangements may be used where the conductors (terminal portions) are provided in other positions, but still mutually isolated from one another. For example, the conductors may each have complementary semi-circular cross-sections. Further, the central pin 34 may have the same outer diameter as the outer sleeve 36 over the portion extending below the sleeve 36 (for example, with a ring of insulating material or an air gap between the radial surfaces of the central pin 34 and the sleeve 36). The holes in each of the rails 4b', 4b" may therefore have the same diameter.

Further, although the aspects described previously are particularly beneficial for an apparatus comprising a plurality of wind turbine modules, they may also be used with an apparatus comprising a single turbine.

The above description focuses on axial-flux generators; however, it will be appreciated that the concepts may also be extended to radial-flux generators. Further, the generator need not be provided at the bottom of the module and may instead be at the top of the module or a generator provided at either end. Moreover, the wind turbine module may be arranged such that the blade portion has its axis of rotation oriented horizontally, but perpendicular to the wind direction such that the generator is at either or both sides. Consequently, references to relative positions (e.g. "below" and the like) should be construed accordingly.

To avoid unnecessary duplication of effort and repetition of text in the specification, certain features are described in relation to only one or several aspects or embodiments of the invention. However, it is to be understood that, where it is technically possible, features described in relation to any aspect or embodiment of the invention may also be used with any other aspect or embodiment of the invention. The invention is not limited to the embodiments described herein, and may be modified or adapted without departing from the scope of the present invention.