VERTICAL-AXIS WIND TURBINE Technical Field

The present invention relates to a vertical-axis wind turbine. Background Art Wind turbines with a vertical axis are known which are capable of supplying modest amounts of power to users by utilizing the kinetic energy of wind and are particularly suitable for so-called "distributed" applications, in which electric power is generated and consumed directly at the same site, without resorting to drawing power from the mains. Among currently commercially available turbines of this type, turbines are already known commercially as "Windside", which have a rotor provided with mutually opposite vertical vanes which are joined to each other on one side at the axis of rotation of the turbine and have a helical arrangement around their own longitudinal axis. Although such turbines allow to achieve higher efficiencies in converting the kinetic energy of wind into electric power with respect to turbines having a rotor with a horizontal axis with equal power rating, they are however not entirely satisfactory in the field of use as power generators for "distributed" applications. A drawback of "Windside" turbines consists in that the wind speed at which they are capable of generating power, known as "cut-in" speed, is rather high, and therefore their use is highly penalized in regions with limited windiness, such as for example urban areas, in which the presence of buildings makes it difficult for wind with an acceptable speed to develop. Another considerable drawback of turbines of this type resides in the shape of their vanes, which is rather complicated to manufacture, with consequent negative effects on the manufacturing costs of the turbine.

Turbines with a rotor having a vertical axis of the "Darrieus" type for small power levels are also known which have a substantially H-shaped configuration, with at least two vertical vanes which have a wing-like

profile, spaced laterally from the vertical rotation axis of the turbine and supported in a cantilever fashion, in an intermediate point of their longitudinal extension, by respective supporting arms which protrude radially from the axis of rotation of the turbine, on diametrically mutually opposite sides.

Although such types of turbines are constructively very simple, fairly efficient and relatively inexpensive, with respect to "Windside" turbines, they also suffer drawbacks.

Such turbines in fact have a rather high inertia, and therefore with low wind speeds they require an external source of motion to begin rotation, such source being constituted typically by an electric motor.

Another known solution is constituted by "Savonius" turbines, which have a rotor provided, in the simpler models, with two vanes which are arranged side by side and are semicylindrical and elongated vertically, with the concavity oriented oppositely with respect to the direction of rotation of the turbine and joined one another at the vertical axis of rotation of the turbine.

The operating principle of turbines of this type is conceptually similar to the principle of a cup anemometer, since they utilize the thrust applied in each instance by the wind during the rotation of the turbine to the concave portion of one of the vanes, while the other vane offers drag contrasting the rotation of the turbine.

Although "Savonius" turbines are structurally simpler than the turbines described above, they have efficiencies which are considerably penalized by the drag offered by the vanes during the rotation of the turbine. Disclosure of the Invention

The aim of the present invention is to provide a valid solution to the drawbacks cited above by providing a vertical-axis wind turbine which has an adequate efficiency and an extremely reduced rotational inertia, so as to allow to generate power even at extremely low wind speeds, so as to be

suitable for "distributed" applications as a decentralized power generator.

Within this aim, an object of the invention is to provide a vertical-axis wind turbine which, thanks to its particular constructive characteristics, is capable of offering the greatest assurances of reliability and safety in operation.

Another object of the present invention is to provide a turbine which is structurally very compact and dimensionally small, so that it can be installed easily on buildings or urban structures of different kinds.

Still another object of the present invention is to provide a vertical- axis wind turbine which is constructively very simple to provide and has an extremely low manufacturing cost.

This aim and these and other objects, which will become better apparent hereinafter, are achieved by a vertical-axis wind turbine according to the invention, characterized in that it comprises a rotor which has a frame which can rotate about a rotation axis which is substantially vertical and supports at least one vane array, which lies circumferentially around said rotation axis and comprises a plurality of vanes which are mutually angularly spaced and distributed along an annular region which is substantially concentric with respect to said axis of rotation. Brief Description of the Drawings

Further characteristics and advantages of the invention will become better apparent from the description of some preferred but not exclusive embodiments of the turbine according to the invention, illustrated by way of non-limiting example in the accompanying drawings, wherein: Figure 1 is a slightly perspective view of a first embodiment of the vertical-axis wind turbine according to the invention;

Figure 2 is a perspective view of a second embodiment of the vertical-axis wind turbine according to the invention;

Figure 3 is a perspective view of a third embodiment of the invention; Figure 4 is a perspective view of a fourth embodiment of the vertical-

axis wind turbine according to the invention;

Figure 5 is a partial sectional perspective top view of a vane of the turbine according to the invention in the embodiment of Figure 3, taken along a horizontal plane; Figure 6 is a sectional view, taken along a horizontal plane, of a vane of the wind turbine according to the invention in its first embodiment of Figure 1;

Figure 7 is a schematic sectional view of the first embodiment of the turbine according to the invention, taken along a plane which is perpendicular to the axis of rotation of the rotor. Ways of carrying out the Invention

With reference to the figures, the vertical-axis wind turbine, according to the invention, generally designated by the reference numeral 1, comprises a rotor 2, which is constituted by a frame 3 designed to be supported so that it can rotate about a substantially vertical rotation axis 3a and to be connected, by means of a shaft 4 arranged coaxially to the rotation axis 3a, to a user device, constituted typically by an alternator.

The frame 3 of the rotor 2 supports, so as to rotate rigidly therewith, at least one vane array 5, which lies circumferentially around the rotation axis 3 a and is constituted by a plurality of vanes 6, which are mutually angularly spaced and are distributed along an annular region which is substantially concentric with respect to the rotation axis 3 a.

More particularly, the vane array 5 delimits peripherally an internal cavity 7 of the rotor 2, which is arranged coaxially with respect to the rotation axis 3 a.

Advantageously, the vanes 6 are distributed with a constant spacing about the rotation axis 3 a, so as to form, in the space comprised between them, a plurality of channels 8 which are substantially identical to each other, are open toward the internal cavity 7 of the rotor 2, and are designed to be crossed by the fluid in relative motion with respect to the turbine in

order to apply thrust to the vanes 6.

Conveniently, the vanes 6 are constituted by laminas whose longitudinal extension is substantially parallel to the axis of rotation 3a, as in the example of Figure 1. As an alternative, as shown in Figures 2, 3 and 4, the vanes 6 may also have a spiral arrangement around the rotation axis 3a, in order to reduce the noise of the turbine at high wind speeds.

Optionally, the vanes 6 can be wound in a helix about their corresponding longitudinal axis, at an angle preferably ranging from 0° to 360°, as in the embodiments shown in Figures 2, 3 and 4.

Moreover, each vane 6 can conveniently be extended longitudinally, from an intermediate portion thereof toward the corresponding ends, progressively toward the rotation axis 3a, as in the examples of Figures 2, 3 and 4. Such a configuration of the vanes 6 allows to achieve a reduction of the moment of inertia of the rotor 2 with respect to the rotation axis 3 a, with a consequent reduction of the cut-in wind speed required to start the rotation of the rotor 2.

Advantageously, the vanes 6 can have, in a transverse cross-section, a curved shape, preferably a circular arc-like shape, with a concavity which is oriented in the opposite direction with respect to the direction of rotation of the rotor 2.

As an alternative, the vanes 6 may also have a transverse cross- section which is shaped like a wing profile, so as to achieve, with respect to the preceding solution, a better performance in terms of turbine efficiency.

The number of vanes 6 provided along the vane array 5 may conveniently be varied from 4 to 100, depending on the power rating of the turbine.

It should be noted that a large number of vanes 6 along the vane array 5 also allows to achieve significant reductions in the cut-in wind speed and

therefore to extend the operating range of the turbine, allowing its use at sites which have limited wind.

Advantageously, as shown in particular in Figure 6, each vane 6 forms, substantially at its longitudinal edge 6a directed toward the outside of the rotor 2, an angle α which ranges substantially from -90° to 90°, with respect to an imaginary radial plane which passes through the rotation axis

3 a and through the longitudinal edge 6a.

It should be noted that the angle α in practice provides the angle at which the wind enters the channels 8 formed by the vanes 6 which, in each instance, face the direction from which the wind arrives, during the rotation of the rotor about the rotation axis 3 a.

Conveniently, each vane 6 further forms, substantially at its longitudinal edge 6b directed toward the inside of the rotor 2, an angle β which ranges substantially from -90° to 90°, with respect to a radial plane which passes through the rotation axis 3 a and through the longitudinal edge

6b.

In practice, the angle β constitutes the exit angle from the channels 8 which is imposed by the vanes 6 to the fluid which enters the internal cavity 7 ofthe rotor 2. It should be noted that angles α and β which are small in absolute value are preferable if the turbine is located in sites with limited wind, whereas instead, when the turbine is placed in very windy sites, angles α and β which are larger in absolute value, are preferably usable.

Merely by way of example, according to a preferred embodiment which is particularly valid if the turbine according to the invention is applied in urban areas, the angle α has a breadth ranging from 45° to 85°, while the angle β ranges from -30° to 60°.

Advantageously, the frame 3 of the rotor 2 comprises at least two vane supporting disks, respectively a lower vane supporting disk 9a and an upper vane supporting disk 9b, which mutually connect the ends of the

vanes 6.

In particular, at least one or more preferably each of the vane supporting disks 9a, 9b is coupled axially to the shaft 4, which can pass through the internal cavity 7 of the rotor 2 along the rotation axis 3a. Conveniently, the vane supporting disks 9a, 9b are perforated or spoked so as to achieve a reduction of their moment of inertia with respect to the rotation axis 3 a.

It should be noted that the vanes 6 can be connected to the vane supporting disks 9a, 9b by welding or by way of detachable connection means, constituted by screw elements 10 or the like, so as to allow easy disassembly of the rotor 2 and consequently its easy transport.

Preferably, the rotor 2 is mounted so that it can rotate on a base 11 which is designed to be fixed, by means of threaded connections 12 or connections of another similar type, to the structure of a building in general. It should be noted that the turbine can be made of metallic material or, at least partially, of plastics by thermoformation or injection molding, so as to contain both the overall weight of the turbine and its production costs.

Operation of the turbine according to the invention is as follows.

Wind strikes the rotor 2 with a component of relative motion which is substantially perpendicular to the rotation axis 3 a and crosses the rotor 2 transversely, acting on the vane array 5 in two successive instants.

In particular, a first interaction between the wind and the vane array 5 occurs in the region of the vane array 5 which, during the rotation of the rotor 2, is in a front position with respect to the wind advancement direction, while a second interaction between the wind and the vane array 5 occurs in the region of the vane array 5 which, with respect to the wind advancement direction, is arranged at the rear and is therefore struck by the flow of wind which is confined within the internal cavity 7 of the rotor and has already been the subject of the first interaction with the vane array 5. The first interaction between the wind and the vane array 5 has the

effect of generating part of the net mechanical power, minimizing the effect of drag.

The second interaction is aimed at obtaining another substantial fraction of the net power, by utilizing the residual kinetic energy of the wind after the first interaction, again minimizing drag.

More particularly, the first interaction and the second interaction between the wind and the vane array 5 occur in the following manner.

The wind enters the rotor 2 through the channels 8 delimited by the vanes 6 which in each instance face, during the rotation of the rotor 2, the direction from which the wind arrives, which is at right angles to the rotation axis 3a.

Once it has been directed along the channels 8, the wind applies to the vanes 6 a thrust action which is substantially tangent to the extension of the vane array 5, so as to initiate or maintain the rotation of the rotor 2, and then exits from the vane array 5, entering the internal cavity 7 of the rotor 2.

After entering the internal cavity 7 of the rotor 2, the wind still has speed and continues its advancement, entering the channels 8 delimited by the vanes 6 which are on the opposite side with respect to the direction from which the wind arrives and providing a further thrust action on the vane array 5 before exiting finally from the rotor 2.

In practice it has been found that the invention achieves, in all of its embodiments, its intended aim and objects, since by way of the double interaction between the wind and the vane array of the rotor of the turbine, energy efficiencies approximately 30% higher than those of conventional turbines are achieved.

Moreover, the turbine according to the invention has the advantage of having, for an equal delivered power, an extremely smaller footprint and therefore an extremely lower environmental impact than current turbines.

Moreover, it has been determined experimentally that thanks to its particular structure and the possibility to adopt a large number of vanes, the

turbine according to the invention allows to reduce significantly the cut-in speed with respect to turbines of the known type, bringing it to values even lower than 1.5-2 m/s.

All the characteristics of the invention described above as advantageous, convenient or the like may also be omitted or be replaced with equivalents.

The individual characteristics described with reference to general teachings or to particular embodiments may all be present in other embodiments or may replace characteristics in these embodiments. The invention thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the appended claims.

In practice, the materials used, so long as they are compatible with the specific use, as well as the shapes and dimensions, may be any according to requirements.

All the details may further be replaced with other technically equivalent elements.

The disclosures in Italian Patent Application No. VR2007 AOOOO 10 from which this application claims priority are incorporated herein by reference.

Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly, such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.