The present invention relates to a shaftless wind turbine which is particularly but not necessarily exclusively capable of self-starting. The invention further relates to a wind- deflector stator for a giromill-type wind turbine, and to a method of improving the efficiency of a vertical-axis wind turbine.

In the field of vertical-axis wind turbines, there are two main types of rotor construction available. There is the Darrieus or Giromill type arrangement, which has a plurality of vertical airfoils attached to a central shaft, and the Savonious design, which has a plurality of curved or v-shaped blades close to the centrally-rotating shaft, and will commonly be provided with a stator having a plurality of curved deflectors to channel air towards the rotor.

A Giromill generally has two or three rotor blades, shaped as airfoils, attached to a central shaft, and no stator is provided. This has many advantages, not least that the apparatus is lightweight and comparatively cheap to construct. There are, however, several disadvantages associated with the giromill arrangement.

Firstly, when the rotor is stationary, there can be no generation of a net rotational force. As such, a giromill is not self-starting. The rotor must already be spinning in order to generate torque.

Furthermore, the non-uniform angular shape of the rotor means that each individual blade has a sinusoidal power generation profile, which can lead to resonant rotational mode which can result in fracture. The overall structure also results in high centrifugal stresses on the mechanism, which can further lead to damage.

The presence of a shaft to support the rotor also creates turbulence in the centre of the giromill, leading to vortex shedding and subsequently disruption to the possible maximum power output by the rotor.

The present invention seeks to provide a stator arrangement for a wind turbine which increases the capability of a giromill rotor to self-start and produce viable amounts of electricity.

According to a first aspect of the invention there is provided a shaftless wind turbine comprising: a support member; a rotor engagable with the support member and rotatable relative thereto and including a rotor frame and a plurality of rotor blades engaged with the rotor frame, the rotor frame comprising an upper frame member and a lower frame member , the plurality of rotor blades extending between the upper and lower frame members; the rotor blades being airfoil blades arranged to be or substantially be tangentially-aligned to the circumference of the radial distance of the rotor; and wherein there is no wind-disrupting central shaft inside the rotor.

Optionally, at least one of the upper and lower frame members may be formed having a plurality of spokes.

Preferably, at least one of the upper and lower frame members may be formed having an annular frame member.

The rotor frame may be rotatable relative to the support member at at least one bearing.

Optionally the at least one bearing may include a generator for converting kinetic energy from the rotor into electrical energy.

Preferably, each airfoil blade may have a symmetric shape.

Each airfoil blade may have a NACA 0018 or 2418 shape.

The shaftless wind turbine may have a vertical-axis wind turbine.

Preferably, the support member may comprise a central pillar engagable with a base of the rotor.

The shaftless wind turbine may further comprise at least one buttress element engagable with the rotor frame or rotor blades.

Optionally, the support member may comprise a stator.

The shaftless wind turbine may further comprise a connector plate associated with a stator frame of the stator for stackable interconnection of at least one further said shaftless wind turbine.

Preferably, there may be at least one mounting element connected to the stator frame for attaching the wind turbine to a support structure. Optionally, the mounting element may comprise a plurality of feet engaged with the stator frame for attaching the wind turbine to a support structure.

The shaftless wind turbine may further comprise a generator configured to convert kinetic energy from the rotor into electrical energy, wherein the generator is mounted within a depth of the plurality of feet at or adjacent to the stator frame.

According to a second aspect of the invention, there is provided an electrical energy generation apparatus comprising a vertical structure and at least one shaftless wind turbine in accordance with at least one embodiment of the first aspect of the invention, wherein the or each shaftless wind turbine is attached to the vertical structure via the or each mounting element.

Optionally, the or each mounting element may attach to a side surface of the vertical structure.

Preferably, the vertical structure may be a telecommunications tower.

According to a third aspect of the invention, there is provided a method of improving the efficiency of a vertical-axis wind turbine, the method comprising the steps of: a] providing a support member; and b] via at least one bearing, engaging a rotor to the support member such that there is no wind-disrupting central shaft inside the rotor, the rotor including a rotor frame and a plurality of rotor blades engaged with the rotor frame, the rotor blades being arranged to be or substantially be tangentially-aligned to a rotational axis of the rotor.

According to a fourth aspect of the invention, there is provided a rotor for a shaftless wind turbine comprising: a rotor frame comprising an upper frame member and a lower frame member; and a plurality of rotor blades engaged with the rotor frame, the plurality of rotor blades extending between the upper and lower frame members; the rotor blades being airfoil blades arranged to be or substantially be tangentially-aligned to the circumference of the radial distance of the rotor; and there being no wind-disrupting central shaft inside the rotor .

According to a fifth aspect of the invention, there is provided a shaftless wind turbine comprising: a stator including a stator frame and a plurality of deflector blades engaged with the stator frame, the stator frame comprising an upper frame member and a lower frame member each having a plurality of radially-extending spokes, the plurality of deflector blades extending between the radially-extending spokes of the upper and lower frame members, wherein each of the deflector blades is formed as a planar plate aligned to radius of the stator; and only one rotor receivable within the stator and rotatable relative thereto and including a rotor frame and a plurality of rotor blades engaged with the rotor frame, the rotor frame comprising an upper frame member and a lower frame member each having a plurality of radially-extending spokes, the plurality of rotor blades extending between the radially-extending spokes of the upper and lower frame members; the plurality of deflector blades being arranged to direct incident wind towards the rotor; the rotor blades being airfoil blades arranged to be or substantially be tangentially- aligned to the circumference of the radial distance of the rotor; and wherein there is no wind-disrupting central shaft inside the rotor.

The construction of a shaftless wind turbine has many advantages, not least that a cleaner wind flow path is provided through the turbine. This negates vortex shedding associated with traditional shaft-based giromill turbines, whilst also minimising the pressure drop inside the rotor. An improved power conversion can therefore be achieved compared with shafted turbines. Furthermore, the presence of the stator can mitigate the effects of stall angles, allowing the rotor to be self-starting. Not only does this improve power conversion, but the arrangement has been found to result in reduced noise generation compared with shaft-based or Savonious type turbines.

Optionally, a total number of deflector blades of the plurality of deflector blades may be greater than a total number of rotor blades of the plurality of rotor blades. The total number of deflector blades may be at least twice the total number of rotor blades, and in one preferred embodiment, there may be eight deflector blades and three rotor blades.

The preferred arrangement of the shaftless wind turbine includes sufficient wind deflectors to provide an optimum flow acceleration to improve the angle of attack of the wind for the rotor. However, there is a balance to be considered so that wind access to the rotor blades is not inhibited. A total of eight deflector blades has been found to offer a convenient arrangement for a three-bladed rotor, though evidently other configurations are feasible.

Optionally, the plurality of deflector blades may be equi-angularly spaced around the rotor. Equi-angular spacing of the deflector blades ensures a uniformity of operation of the shaftless wind turbine regardless of the direction of incident wind.

Preferably, the upper and lower frame members may be formed as plates.

Upper and lower plates allow for a sandwich-like stator configuration to be formed, defining, with the deflector blades, a stator cage around the rotor. This is then robust and vibrationally resistant.

Optionally, the rotor frame may be rotatable relative to the stator frame at at least one bearing.

A bearing arrangement, preferably at the upper and lower respective frame elements, allows for one version of a shaftless arrangement to be realised. No shaft is required if there is at least one bearing between the stator and rotor, though two bearings are preferred for stability reasons.

Each airfoil blade may have a symmetric shape, such as a NACA 0018 shape.

Airfoil blades are preferred for the rotor, since this is a form which is appropriate for a giromill type of turbine. Many arrangements in the art use more complicated impeller- type configurations, but the present invention is a much simpler construction.

The shaftless wind turbine may preferably be a vertical-axis wind turbine.

A vertical-axis turbine is preferred, since the turbine is then operable from all potential horizontal wind directions.

Preferably, only one said rotor may be provided.

The shaftless wind turbine may preferably further comprise a connector plate associated with the stator frame for stackable interconnection of at least one further said shaftless wind turbine.

The modular stacking of the shaftless wind turbines allow for easy upscaling of a wind generator installation to improve power generation. The shaftless wind turbine may further comprise at least one mounting element connected to the stator frame for attaching the wind turbine to a support structure.

The provision of the stator is an advantage from a mounting perspective, since the removal of the shaft allows for a wider and more stable base portion of the wind turbine to be provided. Mounting elements therefore allow mounting of the turbine to a variety of structures.

The mounting element may comprise a plurality of feet engaged with the stator frame for attaching the wind turbine to a support structure.

The shaftless wind turbine may further comprise a generator configured to convert kinetic energy from the rotor into electrical energy, and preferably the generator may be mounted within a depth of the plurality of feet at or adjacent to the stator frame.

The feet provide a suitable location for mounting a generator, particularly at the base of a stack of turbines.

According to a sixth aspect of the invention, there is provided an electrical energy generation apparatus comprising a vertical structure and at least one shaftless wind turbine in accordance with at least one embodiment of the fifth aspect of the ivnention, wherein the or each shaftless wind turbine is attached to the vertical structure via the or each mounting element.

Optionally, the or each mounting element may attach to a side surface of the vertical structure.

In a preferable arrangement, the vertical structure may be a telecommunications tower.

According to a seventh aspect of the invention, there is provided a wind-deflector stator for a giromill-type wind turbine, the wind-deflector stator comprising: a stator frame having upper and lower frame members, each of the upper and lower frame members having a bearing or bearing receiver positioned thereon for receiving a giromill-type wind turbine within the stator frame; and a plurality of deflector blades extending around a perimeter of the stator frame between the upper and lower frame members, the plurality of deflector blades being arranged along or substantially to a radius of the stator frame. It may be advantageous to provide many of the desirable effects described in relation to the above-defined stator to giromill installations which are already in situ. This could result in efficiency improvements to a wide variety of existing wind turbines.

Preferably, each of the plurality of deflector blades may be planar.

Optionally, the plurality of deflector blades may be equi-angularly spaced around a perimeter of the stator frame.

According to a eighth aspect of the invention, there is provided a method of improving the efficiency of a vertical-axis wind turbine, the method comprising the steps of: a] providing a stator having stator frame and a plurality of inwardly-directed deflector blades thereon; and b] via at least one bearing, engaging a rotor to the stator frame such that there is no wind-disrupting central shaft inside the stator, the rotor including a rotor frame and a plurality of rotor blades engaged with the rotor frame, the rotor blades being arranged to be or substantially be tangentially-aligned to a rotational axis of the rotor.

According to a ninth aspect of the invention, there is provided a shaftless wind turbine comprising: a stator including a stator frame and a plurality of deflector blades engaged with the stator frame; and a rotor receivable within the stator and rotatable relative thereto and including a rotor frame and a plurality of rotor blades engaged with the rotor frame; the plurality of deflector blades being arranged to direct incident wind towards the rotor; and the rotor blades being arranged to be or substantially be tangentially-aligned to a rotational axis of the rotor.

Preferably, each of the plurality of deflector blades may be planar.

Planar blades are simple to construct and do not impart any unnecessary or unhelpful directionality to the flow into the rotor region. This is preferred for a giromill configuration of rotor.

Each of the plurality of deflector blades may be aligned to a radius of the stator.

Again, radial alignment of the blades eliminates directionality of wind flow, which may be requisite for achieving optimum flow acceleration at or adjacent to the rotor blades.

The stator frame may comprise an upper frame member and a lower frame member, the plurality of deflector blades extending between the upper and lower frame members. The provision of upper and lower frame members serves to stabilise the rotor, reducing the effect of vibrations or resonant forces which may otherwise arise for a traditional giromill.

In one preferable arrangement, the rotor frame may comprise an upper frame member and a lower frame member, the plurality of rotor blades extending between the upper and lower frame members.

Similarly to the stator, the provision of upper and lower frame members for the rotor stabilises and strengthens the rotor, reducing the prospect of vibrational collisions between the stator and rotor. This is particularly important in the instant invention, in which the rotor blades rotate very close to the deflector blades of the stator.

Preferably, each of the plurality of rotor blades may be an airfoil blade.

The invention will now be more particularly described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 shows a perspective representation of a first embodiment of a shaftless wind turbine in accordance with the first aspect of the invention;

Figure 2 shows a plan view of the shaftless wind turbine of Figure 1 ;

Figure 3 shows a side view of the shaftless wind turbine of Figure 1;

Figure 4 shows a diagrammatic plan representation of wind velocity through the stator of the shaftless wind turbine of Figure 1 , with incident wind flow from left to right;

Figure 5 shows a perspective representation one embodiment of an electrical energy generation apparatus in accordance with the second aspect of the invention;

Figure 6 shows a perspective representation of a stacked pair of wind turbines used with the electrical energy generation apparatus of Figure 5;

Figure 7 shows a perspective representation of a second embodiment of a rotor for use with a shaftless wind turbine in accordance with the first aspect of the invention; and Figure 8 shows a perspective representation of a second embodiment of a shaftless wind turbine in accordance with first aspect of the invention utilising the rotor of Figure 7.

Referring to Figures 1 to 3, there is shown a shaftless wind turbine, indicated globally at 10, for use in the generation of electrical energy from incident wind thereon.

The shaftless wind turbine 10 comprises a stator 12 and a rotor 14 positioned within the stator 12. The rotor 14 is preferably of a shaftless giromill-type or Darrieus design of vertical axis wind turbine, and the stator 12 is thus configured to optimise or improve the wind flow onto the rotor 14.

The stator 12 comprises a stator frame 16, here having upper and lower frame members 18a, 18b vertically spaced apart from one another. Each of the upper and lower frame members 18a, 18b is preferably formed as a plate, and may have the spoked wheel arrangement comprising a plurality of radially-extending spokes, as shown with a plurality of radial voids which reduce the total weight of the stator frame 16 without significantly affecting rigidity. It may be preferred that the stator frame 16 as a whole form the shape of a cylinder.

A plurality of deflector blades 20 are also provided which extend between the upper and lower frame members 18a, 18b, acting as in-use vertical deflectors for wind. Preferably, each of the deflector blades 20 is planar, and may be aligned to a radius of the stator 12 as measured from the rotational axis of the rotor 14. In certain embodiments of the invention, however, the deflector blades may be slightly angled with respect to the radial direction of the stator.

For the depicted stator 12 for which calculations have been made, the stator 12 has a diameter of 2.4m, whilst each of the deflector blades 20 has a height of 1m and a width of 150mm. A total of eight equi-angularly spaced apart deflector blades 20 is provided, which provides significant flow adjustment capability without completely blocking flow into the centre of the stator frame 16.

The deflector blades 20 may preferably be planar, but can be formed as any appropriate deflection member such as a paddle, baffle or wind-guide, provided that flow acceleration or optimisation is achieved into the central rotor-containing portion of the stator 12 cage. The rotor 14 is formed having a rotor frame 22 having upper and lower frame members 24a, 24b which are respectively rotatably engagable with the upper and lower frame members 18a, 18b of the stator frame 16. To avoid the provision of a shaft or spindle for the rotor 14, it is preferred that upper and lower bearings 26 are provided to allow for engagement between the stator frame 16 and rotor frame 22.

The total dimensions of the rotor 14 are preferably matched to an inner cylindrical volume of the stator 12, thereby allowing the rotor 14 to rotate freely within the stator 12 without impinging on the deflector blades 20.

The rotor frame 22 is preferably formed so as to have a plurality of radially-extending spokes. Each of the upper and lower frame members 24a, 24b may have a number of spokes equal to a number of blades of the rotor 14. Here, three spokes are provided, with no additional framework, in order to minimise the weight of the rotor 14.

The rotor 14 also includes a plurality of rotor blades 28, tangentially aligned, or substantially so, to the rotational axis of the rotor 14, and which are preferably formed as airfoil blades. The depicted embodiment shows airfoil blades having a National Advisory Committee for Aeronautics (NACA) value of 0018, which refers to the shape of a symmetric airfoil in accordance with the following equation. y _t = 51 [0.2969Vx- 0.1260X -0.3516x ² + 0.2843x ³ - 0.1015x ⁴ ], where:

• x is the position along the chord from 0 to 1.00;

• y _t is the half-thickness at a given value of x (centreline to surface); and

• t is the maximum thickness as a fraction of the chord (and therefore 0.18 in this instance).

The rotor blades 28 are preferably positioned at the perimeter edges of the upper and lower rotor frame members 24a, 24b, so as to rotate close to the inner edges of the deflector blades 20 and thereby obtain the maximum benefit of the wind-deflection capabilities thereof. In most applications, the rotor blades 28 would be vertically aligned, though helically bladed configurations are also known in the art. The shaftless wind turbine 10 may be provided with a generator 30, as is shown in Figure 3, which is engaged with one of the bearings 26, and via which the kinetic energy generated by rotation of the rotor 14 can be converted into electrical energy.

Since the wind turbine 10 is shaftless, it may be desirable to provide one or more mounting elements 32 connected to the stator frame for attaching the wind turbine 10 to a support structure. Such mounting elements 32 may be provided, for example, as feet connected to the lower stator frame member 18b, and may be equi-angularly positioned therearound for uniform support.

The effect of the stator 12 in use on the wind flow and speed is shown in Figure 4. Wind flow is directed from right to left, with an initial linear flow velocity of approximately 5m/s.

For wind flow passing directly through the centre of the stator 12, there is minimal disruption to the velocity until the wind contacts the rearmost rotor blade 28 shown in inset A. There is no turbulence created by the stator 12 in the central portion due to the absence of a shaft.

As can be seen in insets B of the diagram, the deflector blades 20 cause wind velocity modification at deflector blades 20 which are not parallel with the wind flow direction. This is particularly noticeable for deflector blades 20 at or substantially at 45° to the wind flow direction, causing significant changes to the wind velocity profile at the rotor blades 28. Indeed, the manifestation of the irregular wind velocity at the rotor blades 28 has the advantage of producing non-uniform forces on the rotor blades 28, allowing for a self starting condition to be achieved.

This effectively achieves a scenario in which there is never a 0° angle of attack for the rotor, that is, the condition in which self-start cannot occur.

The wind-deflector stator 12 also has the advantage of forming a support cage for the rotor 14, and therefore minimises vibrations or torque fluctuations. This acts to stabilise the shaftless wind turbine 10.

The power output of the shaftless wind turbine 10 has been modelled extensively using, in particular, two-dimensional power calculations. Table 1 below indicates some of the relevant data obtained from such modelling calculations for the present design. It is noted that Figure 4 corresponds with load case 5 in Table 1 Table 1

From the modelling data, it can be seen that the coefficient of power (CP), that is, the actual fraction of power achieved with respect to the maximum power theoretically possible, is between approximately 30% and 40%, and in some load cases, in excess of 40%. This provides excellent power output which far exceeds that of traditional giromill wind turbines.

A shaftless wind turbine which is approximately 1 m tall is illustrated, but it will be apparent that it is possible to extend the height of the wind turbine along the rotational axis in order to increase the power output thereof.

Whilst upper and lower plates are described for each of the stator and the rotor, it will be appreciated that it may be possible to provide an unbounded rotor or stator, such that there was only a bearing at an upper or lower end thereof. This may lead to vibrational issues, but may be suitable for some specific applications.

Whilst the shaftless wind turbine has hereto been described as a full operational unit capable of generating power in its own capacity, it will be apparent that the wind-deflector stator as described couple readily be used in conjunction with existing giromill arrangements, shaftless or otherwise, and therefore the stator could be provided as a retrofittable apparatus in its own right.

It is therefore possible to provide a shaftless wind turbine having a stator and a rotor, in which the stator has a velocity-modifying effect to rotor blades therein, so that a differential pressure can be created to self-start the turbine. This overcomes many of the advantages of the giromill type arrangement of wind turbines.

An electrical energy generation apparatus 100 is illustrated in Figure 5. The electrical energy generation apparatus 100 comprises a vertical structure 102, and a plurality of wind turbines 10 as previously described. The vertical structure 102 is preferably a telecommunications tower, allowing for power generation capabilities for the tower without impeding the communications capabilities.

In a preferred embodiment, a plurality of turbine modules 104, such as that shown in Figure 6, may be provided spaced around the vertical structure 102, potentially at different heights to maximise wind capture possibility in different atmospheric conditions. A helical configuration is shown in Figure 5.

The turbine modules 104 are formed from at least one wind turbine 10, and in this instance, are formed from a pair of stacked wind turbines 10. Preferably, the wind turbines 10 are connected via a connector plate at or adjacent to the upper or lower stator frames 18a, 18b, though this is not shown in Figure 6. Alternative fasteners, such as brackets or flanged connectors, could be provided instead, however, to permit modular assembly of the wind turbines 10 into turbine modules 104 for assembly onto the vertical structure 102.

To mount the turbine modules 104 to the vertical structure 102, there may be provided dedicated mounting elements 132, here in the form of base plates which couple to one end of the stator 12 of a wind turbine, and which can then be directly mounted onto the vertical structure 102 via one or more fasteners, such as bolts. A preferred separation between the vertical structure 102 and the turbine modules 104 is approximately 1.0 to 1.2m. The dimensions of the turbine module here is 5.5m height, 3m diameter, and a radial width of the stator 12 is 0.2m. Each wind turbine is 2.5m height, with the auxiliary equipment, here shown combined with the mounting element 132, is 0.5m height.

Larger wind turbines 10 can be utilised however, and 4m diameter, 4m height wind turbines 10 would appear to work well, leading to 8.5m turbine modules 104.

Where a plurality of turbine modules 104 is provided around a vertical structure 102. For a square structure, with turbine modules 104 being mounted on each of the flat or substantially flat side faces, electricity generation will occur well when incident wind is directed towards a single face, thereby generating power primarily from the turbine module 104 on that face. However, improved energy generation is achieved when the incident wind approaches on the corners of the vertical structure 102, since two turbine modules 104 will be active at once, as the respective stators 12 direct the wind towards the rotors 14 on the corresponding wind turbines 10.

An improved way of utilising telecommunication towers can therefore be provided by the use of modular, easily assembleable wind turbines, to thereby produce power from otherwise unused space. The wind turbines are low-profile, and therefore do not interfere with the telecommunications, and therefore significant energy generation capabilities can be realised.

Figures 7 and 8 show an alternative embodiment of the rotor previously described which may obviate the need to provide a stator. The rotor, referenced globally at 214, is indicated in detail at Figure 7, whilst the shaftless wind turbine 210 is shown in full in Figure 8. The rotor 214 has a plurality of rotor blades 228, which are formed preferably as defined in respect of the first embodiment, as airfoil blades arranged to be or substantially be tangentially-aligned to the circumference of the radial distance of the rotor 214. A preferred number of airfoil blades is three.

The rotor frame 222 comprises a lower frame member 224b which has a plurality of radially extending spokes 234, each of which connects with a lower portion of a corresponding rotor blade 228. The spokes 234 meet at a central hub 236 which forms or houses a bearing for connection to an associated support member. The support member could be a stator as described in connection with the previous embodiment, though will be preferably described as the central pillar 238 or similar structure as referenced in Figure 8. The stator is no longer necessary, as a rotor 214 having this form can be self-sustaining without requiring the deflector blades of a stator.

The upper frame member 224a of the rotor frame 222 is now formed as an annulus or similar ring structure, referred to as a halo ring, which can support the rotor blades 228 from deflecting outwards as they spin, whilst also minimising air resistance.

With reference to Figure 8, the rotor 214 can be mounted directly to a shaft 238 of a central pillar 240 or similar support member. One or more buttress elements 242 may be provided associated with each spoke 234 or rotor blade 228 which couple to the support member at the shaft 238 to further limit the outward buckling effect of the rotor blades 228 as the rotor 214 spins. The generator for the shaftless wind turbine can be integrated into the central pillar 240.

Modelling of the energy output has been conducted, using NACA 2418 blade having a 50cm chord length, with the rotor 214 being somewhere between 6m and 8m in diameter, and being 7.25m in diameter in the tested embodiment, and 5.5m in height. It is anticipated that this turbine size will produce 10kW of power at 10m/s wind speed, having a rated thrust of 2.7kN and a rated speed of 100rpm. It has a cut-in speed of 3m/s and a cut-out speed of 20m/s, and is controlled so as to be stall regulated.

This data has been collated using turbine simulations based on an idealised rotor, using a BEM model, which predicts performance by simulating the lift and drag of the airfoils at difference angles of attack. The predicted power coefficient peak is calculated as 0.45, though an expected reduction in the power coefficient is anticipated as being around 20- 30% due to dynamic stall effects, three-dimensional geometry, tip losses, and/or parasitic drag. This yields an average energy production for an average wind speed of 5m/s of approximately 23,400kWh. It is therefore anticipated that the turbine 210 be primarily installed in sites with average windspeeds of greater than 6m/s, and preferably in sites which permit close-proximity packing, since there is no steering requirement for directional capture, nor is the increase in noise significant. Large energy gains can be made in small physical spaces.

The material construction of the rotor 214 is anticipated as being primarily from aluminium or carbon-fibre reinforced polymer (CFRP), though the upper frame member 224a may need to be formed from a CFRP flat sheet.

This improved rotor design can obviate the need for a dedicated stator, and can also advantageously improve the resilience of the overall shaftless wind turbine to buckling of the rotor blades outwardly, during the rotation, which would otherwise be mitigated by the presence of a central shaft.

The words ‘comprises/comprising’ and the words ‘having/including’ when used herein with reference to the present invention are used to specify the presence of stated features, integers, steps or components, but do not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination.

The embodiments described above are provided by way of examples only, and various other modifications will be apparent to persons skilled in the field without departing from the scope of the invention as defined herein.