The invention relates to a wind power plant, comprising a rotor rotatable about a vertical rotational axis and having at least one wing flap which can be pivoted from an idle position in a direction about a horizontal axis.

Wind power has been utilised technically for many centuries. In the preindus- trial ages, it represented an energy potential that could not be achieved in any other way apart from hydraulic power. It was then displaced by power engines, but currently the utilisation of wind power has seen a renaissance in the past few decades, especially for regenerative power generation. For this purpose, wind turbines with aerodynamically shaped wings and horizontal rotational axis are used. Individual wind turbines of this configuration will achieve powers in the megawatt range. It is advantageous that the power of the wind power plant can be adjusted relatively easily to different wind conditions by simply twisting the rotor blades along its longitudinal axis, which is also known as blade adjustment. This blade adjustment can be used to protect the wind power plant from damage during strong winds and storms. It is disadvantageous in wind turbines with horizontal axis that the alignment of the axis needs to occur in the direction of the wind, for which purpose a yaw correction device is required. This poses problems especially for the utilisation of wind turbines of lower power, especially in form of a privately operated small-sized installations for the decentralised regenerative generation of energy for own use and or for supply to an energy supply network. In addition to the aforementioned wind turbines with a horizontally aligned axis, there are such wind turbines with a vertical axis which without any further active control are independent of the direction of the wind. The so-called Darrieus installations also comprise aerodynamically shaped rotor blades which utilise a lifting force. Wind turbines of the kind mentioned above differ from them in such a way that they are provided with wind flaps which are held to pivot about a horizontal axis and which are pressed away by the wind as a result of their air resistance. Since the wind flaps can only be pivoted in one direction from an idle position which is usually substantially vertical, they will apply their air resistance against the wind during movement thereof, whereas during movement towards the wind from the vertical idle position they will pivot into a substantially horizontal position and can be moved with lower air resistance against the wind. During further rotation into the direction of the wind, they will pivot into the vertical initial position again and will be moved further by the wind.

Wind turbines based on this fundamental principle are independent of the direc- tion of the wind, but can be adjusted only with difficulty to different wind conditions. A rotational speed limitation by a braking apparatus controlled by centrifugal force is known from the specification DE 2401214 A1 for the protection from destruction in the case of excessively strong winds. It protects the moved elements such as the rotating rotor and the connected generators for power generation from excessively destructive rotational speeds. However, it does not protect the wind power plant as such from the high wind load that is caused by strong winds.

It is therefore the object of the present invention to provide a wind power plant of the kind mentioned above which can be adjusted to different wind conditions in a simple way and therefore can also especially be protected from excessive wind loads. It is a further object to provide a method for the secure operation of wind power plant. This object is achieved by a wind power plant and an operating method for a wind power plant with the features of the independent claims. Advantageous embodiments and further developments are the subject matter of the respective dependent claims. A wind power plant of the kind mentioned above in accordance with the invention is characterized in that the rotor is displaceable in the direction of the vertical rotational axis. The wind speed is usually lower in the ground region than at exposed heights. The variation in the height of the rotor which is achieved by the displacement of the rotor in the vertical direction leads to an effect that regulates the rotational speed. Excessive rotational speeds which need to be avoided due to the large occurring centrifugal forces on the rotor and the increased load on the bearings can thereby be prevented even without any mechanical brake. In addition, the wind load on the wind power plant is also re- duced by lowering the rotor, which prevents damage. Furthermore, since the rotor can be lowered or lifted, the erection of the wind power plant and its maintenance is simplified.

A windbreaker is provided in an advantageous embodiment of the wind power plant which encloses the rotor in a lowered vertical position either in part or in full. The effect of the lowering of the rotor will additionally be supported by the windbreaker.

In a further advantageous embodiment, at least some of the wind flaps are covered with solar cells in full or in part on at least one of their surfaces. That way, additional electrical energy can be generated. It is particularly advantageous to transmit the electrical energy generated by the at least one solar cells from a rotating part of the wind power plant to a non-rotating part of the wind power plant via induction. This provides for a maintenance-free transmission from a rotating part of the wind power plant to a non-rotating part.

A method in accordance with the invention for operating a wind power plant with a rotor that is rotatable about the vertical rotational axis is characterized in that the rotor is displaced in the vertical direction depending on its measured ro- tational speed. In an advantageous embodiment of the method, the rotor will be displaced in the vertical direction depending on a measured wind speed. The rotational speed and also the wind speed represent suitable criteria in order to automatically set the height of the rotor, thus providing secure operation of the wind power plant at all times.

The invention will be explained below in closer detail by reference to embodiments shown in the three drawings in closer detail, wherein: Fig. 1 shows a schematic sectional view of a wind power plant in a first embodiment;

Fig. 2 shows a schematic sectional view of a wind power plant in a second embodiment, and

Fig. 3 shows a schematic sectional view of a wind power plant in a third embodiment.

Fig. 1 shows a first embodiment of a wind power plant in a schematic sectional view, with the section being provided in this case in a vertical and central manner through the wind power plant.

The wind power plant comprises a central vertical mast 10 as the supporting element. It is anchored to the ground by means of a foundation (not shown), or it can alternatively be erected on a preferably movable (e.g. displaceable) platform. The mast 10 can be a carbon fibre tube, but other materials can also be used such as aluminium or steel, especially stainless steel. The cross section of the mast is preferably but not necessarily round. The longitudinal axis of the mast 10 represents a vertical rotational axis 1 1 for the wind power plant.

A supporting cylinder 30 is arranged concentrically in relation to the mast 10, which supporting cylinder is vertically movable by means of a vertical guide 12 cooperating with the mast 10 in the direction of the vertical rotational axis 1 1 . The vertical guide 12 can be a sliding guide in which respective sliding elements made of elastic or bronze for example will slide along respective surfaces on the mast 10. Roller bearings or recirculating ball bearings can be used in the vertical guide 12.

The wind power plant comprises a lifting apparatus 20 by means of which the supporting cylinder 30 can be vertically displaced. In the illustrated embodiment of Fig. 1 , the lifting apparatus 20 is integrated in the mast 10 and comprises a lifting cylinder 21 and a lifting rod 22 which can be moved in a hydraulic or pneumatic manner. The lifting cylinder 21 is connected to the mast 10 or the aforementioned foundation, whereas the lifting rod 22 acts on a crossbeam 23 which is connected to the supporting cylinder 30. The crossbeam 23 is guided on two opposite sides through the side wall of the mast 10, wherein said mast comprises respective vertical slit-like openings in order to enable a vertical movement of the crossbeam 23. Alternative lifting apparatuses are possible in addition to the illustrated hydraulic or pneumatic lifting apparatus 20, e.g. in form of a cable or chain drive, in which a traction cable or a chain which is elec- tromotively driven by a winch moves through or along said mast 10 and is guided over a deflection pulley at the end of the mast 10. The traction cable or the chain is connected to the supporting cylinder 30 with its free end. A lifting apparatus can also be provided whose drive is moved together with the supporting cylinder 30 and in which a gearwheel or a frictional wheel cooperates with a toothed rack or a friction face on the mast 10. Furthermore, a rotational cylinder 14 is provided which is rotatably mounted by means of pivot bearings 31 concentrically to the supporting cylinder 30 and is rotatable about said cylinder. Two pivot bearings 31 are shown by way of example in Fig. 1 , which pivot bearings are respectively positioned in the region of the upper and bottom end of the supporting cylinder and rotational cylinder 40. The supporting cylinder 30 and the rotational cylinder 40 are respectively provided with roughly the same height, which in the illustrated example is approximately half the height of the mast 10.

A ring generator 32 is arranged between the supporting cylinder 30 and the ro- tational cylinder 40, which ring generator generates electric power during rotation of the rotational cylinder 40 in relation to the supporting cylinder 30. For this purpose, a stator of the ring generator 32 is connected to the supporting cylinder 30 and a rotor of the ring generator 32 is connected to the rotational cylinder 40. The ring generator 32 is used for converting the wind energy acting on the wind power plant into electrical power. A generator with a central rotational axis can be used as an alternative to the ring generator 32. In this case, the generator is fixed to the supporting cylinder 30 and the rotational axis is coupled via a gearwheel, frictional wheel or belt drive with the rotational cylinder 40. It is also possible to transfer the rotational movement of the rotational cylin- der 40 via a shaft or any other mechanical type of transmission to a generator which is stationary relative to the foundation.

Wind flaps 50, which are pivotable about a horizontal pivoting axis 51 in one di- rection, face radially to the outside away from the rotational cylinder 40. In the embodiment as shown in Fig. 1 , several wind flaps 50 (five in this case) arranged above one another form a blade. Two opposite blades of these blades are shown in Fig. 1 . The embodiment comprises four blades in total, which are arranged evenly about the rotational cylinder 40, so that the angle between them is 90°. Both the number of four blades and the number of five wind flaps per blade are provided by way of example and shall not be limiting in any way. The number of blades can be different in other embodiments and preferably lies between two and six, and especially preferably three or four. The number of the wind flaps per blade can also vary in other embodiments. It is also possible in particular that a single wind flap 50 represents one blade. The rotational cylinder 40 and all elements that are connected to said cylinder and rotate with said cylinder, especially the blades and the wind flaps 50, will be referred to below in a summarising manner as the rotor of the wind power plant. In the example of Fig. 1 , every blade comprises horizontally aligned extension arms 41 which face outwardly radially away from the rotational cylinder 40, with one respective extension arm being arranged in the upper region of the blade and one in the bottom region. The upper and bottom extension arms 41 of each blade are connected at the outer ends by a vertical brace 42. A frame is there- fore formed for each blade in which the five respective wind flaps 50 are inserted.

The wind flaps 50 are respectively pivotably held in the upper region on one side in the rotational cylinder 40 and on the other side in the vertical brace 42, with their respective bottom end either resting on a limit stop on the rotational cylinder 40 and/or the vertical brace 42 or on the respective wind flap 50 disposed below, so that the wind flaps 50 can only be pivoted in one direction. If the wind impinges from one direction onto the blade, the wind flaps 50 will close and the blade or wind flaps 50 will have a high wind resistance and are respec- tively subjected to a wind pressure which leads to a rotation of the rotational cylinder 40. If the wind impinges on the opposite side of the blade, e.g. when the blade moves against the direction of the wind during the rotation of the rotor, the wind flaps 50 will pivot up and the blade will have a lower wind resis- tance. Consequently, a torque will be obtained on the rotor independently from the direction of the wind which leads to its rotation in the wind. This rotational movement can be converted into electrical power via the ring generator 32.

The wind power plant that operates according to this fundamental principle does not initially require any active control because the wind flaps 50 can be pivoted open or closed in a purely passive way by the wind itself.

A rotational speed of the rotor is obtained during the operation of the wind power plant which is dependent on the wind intensity and dependent on the re- sistance of the ring generator 32 that is applied against the rotation of the rotational cylinder 40 under load. If the wind intensity becomes too large and/or the ring generator 32 is unable to supply power because the downstream energy storage units are filled and energy supply to a load or an energy supply network is not desired or provided, the lifting apparatus 20 can be used in accordance with the application to lower the rotor. Usually, the wind speed in the region of the ground is lower than at exposed heights. The variation in the height of the supporting cylinder 30 and therefore the rotor consequently already leads to a speed-regulating effect. Excessive rotational speeds must be avoided due to the large occurring centrifugal force on the rotor and the increased load on the bearings. In addition, an excessive wind intensity (especially when occurring in gusts) may cause damage to the wind flaps 50 and its pivoting mechanism and optionally also other elements due to excessive wind intensity irrespective of the rotational speed of the rotor. Finally, there is a likelihood that the mast 10 will break or tear away from its bracing.

The lifting apparatus 20 further simplifies the installation of the wind power plant and its maintenance. Smaller wind power plants which are designed for private use often have heights in the region of 20 m and more in order to move out of the wind shadow of ambient buildings or trees. The lifting apparatus 20 allows avoiding the use of a crane or the like during installation or maintenance. Installation is therefore facilitated and made possible in inaccessible areas for example. A windbreaker 60 is additionally provided in the embodiment as shown in Fig. 1 , which windbreaker provides a windshield for the lowered rotor. In the illustrated example, the windbreaker 60 is arranged as an upwardly open cylinder which rests on the ground into which the rotor of the wind power plant can travel in a substantially complete way. The windbreaker 60 further prevents that persons can enter the region of the rotor of the wind power plant and therefore reduces the likelihood of injury by the rotating rotor, especially when the wind power plant is not provided with such a large height that contact with the rotor per se is avoided. As a result, the presented wind power plant is especially suitable as a smaller installation, e.g. for use on private land such as a garden for example. It can be provided that the windbreaker 60 comprises removable elements or flaps or the like, so that maintenance and repair work can be performed in the lowered state of the rotor. The windshield provided by the wind- breaker 60 reduces the likelihood of accidents by a rotor that rotates in the wind. In addition, it is obvious that an arresting mechanism can be provided which prevents the rotation of the rotor.

The lifting apparatus 20 will be triggered by a control apparatus not shown in Fig. 1 . It can be provided to consider several factors in the control of the height of the rotor on the mast 10. These factors can include the rotational speed of the rotor for example which is determined by a speed sensor, with the ring generator 32 being used as a speed sensor in the case of a suitable arrangement of said generator. Furthermore, a separately measured wind speed that is measured by an anemometer can be considered for example. Forecast weather information that is obtained via a network connection for example can also be considered. Furthermore timer control by a timer can also be considered. Finally, a possibility for manual control is also provided. In addition to the described lowering of the rotor in the case of an excessively large wind speed, it can additionally be provided to lower the rotor during a period of calm or very low wind speed, i.e. in cases in which utilisation of wind power is not possible. The windbreaker 60 finally offers the possibility to arrange further supplementary components of the wind power plant in a visually protected or theft-proof manner either on an inside wall of the windbreaker 60 or in a bottom region be- neath a completely lowered rotor. Such components can especially be system components such as an inverted rectifier which converts the current supplied by the ring generator 32 into a current of suitable frequency and phase position which is suitable for supply to an energy supply network. It is further possible that energy storage units are provided as system components which allows us- ing the wind power plant as a power supply installation in an insular position separated from an energy supply network, or which intermediately store the energy in connection with an energy supply network in order to supply said energy to the energy supply network during periods of high demand. Batteries can be used as energy storage units for example, or also a device for the electroly- sis of water and the subsequent storage of the decomposition products of hydrogen and oxygen. The decomposition products can be brought to reaction with each other in fuel cells under supply of current. Even when a windbreaker 60 is not provided, such system components can be integrated in the wind power plant, e.g. in a base or a foundation of the wind power plant.

Fig. 2 shows a second embodiment of a wind power plant in accordance with the invention in an illustration similar to Fig. 1 . In this and the following drawings, the same reference numerals designate the same or similarly acting elements as in Fig. 1 .

The wind power plant again comprises a rotor with a vertical rotational axis 1 1 , about which a rotational cylinder 40 can rotate with radially outwardly facing blades. The rotor corresponds to the one of the first embodiment. Reference is therefore made to the explanations made in connection with Fig. 1 .

A lifting apparatus 20 is provided in order to displace the rotor in its height above the ground or foundation. The lifting apparatus 20 is arranged as above in a hydraulic or pneumatic manner with a lifting cylinder 21 and a lifting piston 22. In contrast to the first embodiment, the lifting piston 22 is fixed in a station- ary manner to the foundation and the lifting cylinder 21 is displaceable. Moreover, the lifting piston 22 simultaneously forms a mast 10 of the wind power plant and the lifting cylinder 21 represents a supporting cylinder 30 around which the rotational cylinder 40 is rotatably mounted. An upper vertical guide 12 is fixed in a stationary manner to the lifting cylinder 22 and comprises a seal for the operating medium of the lifting cylinder 21 , e.g. a shaft seal. A bottom vertical guide 12 moves together with the lifting cylinder 21 .

The arrangement is compact and saves material, and offers the further advan- tage that the mast 10 will not protrude upwardly when the rotor is lowered. In a further development of the illustrated embodiment, a multiple extendable lifting cylinder, i.e. also known as a stepped or telescopic cylinder, can be used.

Fig. 3 shows a further embodiment of a wind power plant according to the ap- plication. It is shown in contrast to Fig. 1 in a horizontal sectional view.

A vertical mast 10 is provided again, on which a supporting cylinder 30 can be moved up and down in the vertical direction guided by vertical guides 12. The vertical movement of the supporting cylinder 30 is achieved by a lifting appara- tus which is realised in this case via three traction cables 24. The traction cables 24 are respectively guided on one side along the mast 10, extend at the upper end over a deflection pulley and are guided on the opposite side back to the supporting cylinder 30 again, to which they are connected. A rotational cylinder 40 is arranged concentrically about the supporting cylinder 30 and is mounted to be rotatable about said cylinder, of which four blades are arranged to extend radially to the outside in an evenly distributed manner about the circumference. The blades respectively comprise wind flaps 50 which are pivotable about a respective horizontal pivoting axis 51 . The elements which ro- tate about the vertical rotational axis are referred to in a summarising manner as the rotor of the wind power plant. As in the previously described embodiment, several wind flaps 50 are respectively preferably arranged in several planes above one another in this case too. The wind flaps 50 are fixed to a horizontal shaft 52 extending along the horizontal pivoting axis 51 . A limit stop is provided which allows a movement of each wind flap 50 from a substantially vertical idle position only in one direction. Said limit stop can either act on the wing flap 50 per se or on the horizontal shaft 52. Respectively opposing wind flaps 50 are coupled with each other in such a way that they are twisted by approximately 90° against one another about the horizontal pivoting axis 51 . This coupling supports the upward pivoting of the wind flaps 50. The coupling is achieved by means of a control rod assembly not shown in the drawing, which acts on levers 53 which are respectively arranged on the horizontal shafts 52. In Fig. 3, all wind flaps 50 are therefore shown to be pivoted about approximately 45° out of their vertical idle position. The illustration shows that the wind flaps 50 are not provided with a rectangular basic shape, but are sloped in a curve-like manner especially in the region of the mast 10. Collisions with wind flaps 50 disposed in the same plane can be pre- vented in this way.

A supporting frame is formed about the wind flaps 50, which is formed by horizontal extension arms (not shown in the drawing) and one respective vertical brace 42 (cf. the extension arm 41 of Fig. 1 ). The horizontal shafts 52 are held at their ends in bearings 44a, 44c which are fixed to the rotational cylinder 40 or the vertical brace 52. The frame elements which enclose the wind flaps 50, i.e. the horizontal extension arms and the vertical brace 42, are preferably shaped in an aerodynamic manner, thereby leading to additional torque in the rotational direction of the rotor of the wind power plant.

A wind guide element 43 is arranged about the rotational cylinder 40, which guide element touches the rotational cylinder 40 in a region between the wind flaps 50 and is fixed to said cylinder by connecting elements such as screws. The wind guide element 43 is spaced from the rotational cylinder 40 towards the wind flaps 50, wherein it reaches its maximum distance at the positions of the wind flap 50. Openings are provided at these positions through which the horizontal shafts 52 are guided, with a further bearing 44b being provided at these positions for the support of the horizontal shafts 52. A concave surface configuration of the wind guide element 43 is therefore obtained in the region between the wind flaps 50. It is preferably not arranged in a symmetrical way, but is provided with a lower ascending gradient on the side facing the wind than on the side facing away from the wind. As a result of the asymmetric configuration of the shape, the wind guide element 43 will also guide air flows which move towards the mast 10 and which therefore would not lead to a torque to the (closed) wind flap 50 facing the wind, which is therefore subjected to a higher wind pressure, thus leading to an increase in the efficiency of the wind power plant. It is further possible in smaller wind turbines to omit the external bearing of the horizontal shafts 52 and therefore the vertical brace 52 and the horizontal extension arm, and to pivotably fix the wind flaps 50 only by way of the inner bearings 44a, 44b arranged on the rotational cylinder 40 or on the wind guide element 43.

In the region of the horizontal shafts 52 which are covered by the wind guide element 43, levers 53 are additionally arranged in the illustrated embodiment, said levers being actuated by the control rod assembly extending substantially parallel to the mast 10. Said assembly can further be displaced by a further cyl- inder or any other drive device in its longitudinal direction, by means of which the pivoting angle of the wind flaps 50 can be set. An active adjustment of the wind flaps 50 can be performed in this way in a supporting manner or alternatively to the passive pivoting of the wind flaps 50 about the pivoting axis 51 . An active pivoting of the wind flaps 50 offers the advantage in low wind that the wind flaps 50 running against the wind can be brought into a completely horizontal position or one that is disposed in the wind direction, and they will therefore offer the lowest possible wind resistance when moving towards the wind.

Auxiliary flaps 54 also offer a supporting effect for the complete upward pivoting of the wind flaps 50, of which one each is arranged on each of the horizontal shafts 52. The auxiliary flaps 54 are fixed in an asymmetric manner to the horizontal shafts 52 like the wind flaps 50, so that impinging wind exerts a torque on the horizontal shafts 52, by means of which they are rotated and will upwardly pivot the wind flaps 50. The auxiliary flaps 52 are connected to the wind flaps 50 in a twisted manner with respect to the same in such a way that said auxiliary flaps will follow the wind flaps 50 with respect to the upward pivoting movement and will exert the largest torque on the horizontal shafts 52 when they have already been partly pivoted out of the substantially vertical idle posi- tion. The rotational angle about which the auxiliary flaps 54 will follow the wind flaps 50 lies in the range of 20 to 90° and preferably in the range of 30 to 70°. In the illustrated example the angle is 45°. The auxiliary flaps are arranged in the present case in a semi-spherical way, or they can also be flat. It can be provided in a further advantageous further development of the wind power plant that the surface of the wind flaps 50 is covered with solar cells. They will contribute additional regenerative energy during the operation of the wind power plant by the conversion of solar power into electrical power. It can be provided to actively pivot the wind flaps 50 during a calm period or low wind in such a way with respect to their pivoting direction that the highest possible maximum yield of solar energy is obtained. It is also possible that in the case of low wind intensities optimisation is provided in the respect that the total energy, i.e. the sum total of wind and solar power, is maximised. It is optionally possible that a position of the wind flaps 50 is assumed which is not optimal for the utili- sation of wind energy but which is provided for the benefit of increased solar power conversion. In the case of calm or very low wind speeds in which substantially only solar power is generated, it can be provided to lower the rotor of the wind power plant. It can further be provided to actively turn the rotational cylinder 40 around during a calm period or low wind in such a way that the highest possible maximum yield of solar energy is obtained. This is particularly expedient if not all of the wind flaps 50 are provided with solar cells. In one embodiment, the ring generator 32 can act as a motor and be used to actively turn the rotational cylinder 40. For transmitting the electrical energy generated by the solar cells from a rotating part of the wind power plant, e.g. the rotational cylinder 40, to a non-rotating part of the wind power plant, e.g. the supporting cylinder 30 or the central mast 10, sliding contacts can be used. In an alternative embodiment, the direct- current (DC) generated by the solar cells can first be converted into alternating current (AC) by an inverter and then be transmitted via induction. This provides for a maintenance-free transmission from a rotating part to a non-rotating part. Inverters often comprise an output transformer for generating AC-current suitable for feeding into a power grid. In a preferred embodiment, such transformer can be designed with coils that can rotate against each other. That way, the transformer used in the inverter can be applied to transmit the generated electrical power from a rotating part to a non-rotating part of the power plant. It is also possible to use coils of the ring generator 32, e.g. of its rotor and its stator, for transmitting the electrical energy generated by the solar cells. The ring generator 32 then acts as a transformer.

As in the embodiment of Fig. 1 , a windbreaker 60 is provided which encloses the wind power plant in the bottom region up to a predetermined height, e.g. up to a height of 2.5 m for example. Three of the blades and the windbreaker 60 are only partly shown in Fig. 3 for reasons of better clarity of the illustration.

List of reference numerals

10 Mast

1 1 Vertical rotational axis

12 Vertical guide

20 Lifting apparatus

21 Lifting cylinder

22 Lifting rod

23 Crossbeam

24 Traction cable

30 Supporting cylinder

31 Rotational bearing

32 Ring generator

40 Rotational cylinder

41 Extension arm

42 Vertical brace

43 Wind guide element

44 a-c Bearing

50 Wind flap

51 Horizontal pivoting axis

52 Horizontal shaft

53 Lever

54 Auxiliary flap

60 Windbreaker