IL315139B2 - Swept area regulated power generation system and method - Google Patents

Description

Swept Area Regulated Power Generation System and Method FIELD OF THE INVENTION The present invention relates to a power generator capable of regulating its swept area.

BACKGROUND OF THE INVENTION Installation of wind turbines on light platforms or structures, such as balloons, aerostats, tents is challenging because of the influence of the wind turbine on the platforms’ functionality and integrity, on the one hand, and on the other hand, because of the loads the wind forces create on the structure of the wind turbine itself. To allow this sort of application, there is a need for an ultralight wind turbine capable of surviving an entire range of wind speeds, without damaging its own structural integrity or that of the platform, carrying the turbine. To survive strong wind gusts the wind turbine must be capable of regulating wind load and power to a level that it can survive. To reduce the influence of the wind turbine on the carrying platform or structure, and to avoid disruption of the carrying platform or structure functionality and integrity thereof, the forces generated by the wind turbine must be controllable or adjustable, based on the requirements derived from the platform’s specification. We will assume that a balloon carries a wind turbine of the same weight as a payload but with a significantly larger front area. The buoyancy force of such a configuration will be the same but its drag force may be much higher and it may cause the balloon to lose altitude, until equilibrium between lift, drag and line tension forces is achieved. 20 If the altitude of the ballon is a functional requirement, such a solution may not be acceptable. The conclusion of this example is that for maintaining the altitude of the balloon, the wind turbine must either be able to reduce its drag force, by decreasing its swept area, or must be able to compensate for the drag force by an additional lift force, to keep the ratio of lift to drag forces of the entire system (balloon and payload) at the same level as before. Another major concern of implementing an ultralight wind turbine is its own ability to survive strong wind gusts over a broad range of wind speeds. Since an ultralight wind turbine is designed for minimal material, its ability to withstand strong wind gusts is limited and therefore the wind load must be regulated for the best fit between the turbine structure strength and power demand. Another significant requirement from wind turbines in general, and airborne wind turbines in particular, is their ability to harvest wind energy in a wide range of wind speeds, from lowest wind speed, under 2 meters per second, to highest wind speed, beyond 25 meters per second. The implications of this requirement are twofold: first, the turbine must be able to build a rotation torque from lowest possible wind speed, defined as a cut-in wind speed, to start generating power as early as possible; second, the turbine must be able to reduce the rotation torque at the high wind speed in order to survive and so to keep generating power beyond the wind speed currently defined as a cut-off wind speed (the wind speed at which the turbine is shut off). We will define this feature as wind adaptivity. Typically, the requirement to generate power over a wide range of wind speeds results in additional hardware and/or complexity. One example of this is the Harmony Wind Turbine, which is designed as a drag-based Savonius wind turbine with a complex mechanism for regulating the swept area of the blades as a function of the wind speed: in normal wind conditions the Harmony Wind Turbine rotates with fully opened blades, maximizing the exposed area to the wind for efficient energy generation; however, during high wind speeds, the blades fold back to decrease the swept area and lower the wind load on the structure of the wind turbine. The folding action of this wind turbine involves a complex gear mechanism, connecting the driver gear on the blade to the driven gear on the shaft. 30 Another example for generating power at low wide speed, is a hybrid wind turbine that combines Savonius blades inside the frame that carries Darrieus blades. The purpose of Savonius blades in this configuration is to reduce the cut-in speed. To build a rotation torque at a lower wind speed the common practice is to increase the swept area of the wind turbine. To keep generating power at extremely high wind speeds, the common practice is to decrease the swept area of the wind turbine. When an ultralight wind turbine that has a large swept area meets high wind speeds, its structure may not be able to survive the loads. Therefore, these requirements are mutually contradictory. US2010/0266412 discloses a horizontal wind turbine that includes turbine wheel carrying sailwing assemblies. Another variation of the sails wind turbine is shown in U.S. Pat. 9,051,916, which discloses a vertical wind turbine that uses sails to drive a frame. Additional configuration of the sails wind turbine is shown in US2014/0341736, which discloses a vertical sail wind turbine system that comprises rectangular sails in frames fixedly attached at the tip of parallel horizontal yardarms. Lanyards are used to limit the motion of the sails in a mechanical way and to introduce a braking system. More specifically, it is known in the prior art to provide overload protection that prevents damage to the sails in the event of strong winds, such as hurricanes. For example, EP 1 828 598 discloses a governor articulated to the sails for inducing rotation of the sails out of the path of excessive wind forces. U.S. Pat. No. 7,258,527 employs stop members adapted to limit a pivot angle of the airfoil, wherein each stop member is adapted to lift a pivot limitation of each airfoil for allowing the airfoil to pivot when the airfoil experiences a pushing force of the wind larger than a maximum resistance force thereof. The mechanical impact between the airfoil and the stop member produces significant noise, which is disruptive particularly when disposed in urban environments. The impact also increases the structural requirements of both the airfoil and the stop member. The wind turbines described in the above-mentioned publications allow the wind turbine’s blades to be formed of lightweight and inexpensive material. However, these advantages alone are not enough. The above-mentioned publications do not relate to the adaptivity of the wind turbine over a complete range of wind speeds, without compromising on performance and survivability.

SUMMARY OF THE INVENTION An object of the present invention is to solve this contradiction and to allow harvesting the wind resource over a full range of wind speeds available at the site, thus maximizing the operation range and hence energy availability. To do so, without damaging the structure of the turbine, the wind turbine should be able to regulate its swept area as a function of the wind speed. For the purpose of the present invention, an ultralight weight is defined in terms of self-weight to swept area ratio. For example, a wind turbine having a ratio of weight to swept area of 1 kg per square meter, may be considered as ultralight weight. However, this definition should not be considered as limiting the scope of the invention. Other ratios, higher or lower, may be implemented as well, subject to characteristics of the application and subject to safety factor requirements. In case of installation of the ultralight weight wind turbine on the ground or on a marine platform, a higher safety factor can be considered and higher weight to swept area ratio can be accepted. In case of installation of the ultralight weight wind turbine on an airborne platform, a lower safety factor can be considered and lower weight to swept area ratio can be accepted. In accordance with one aspect of the present invention there is provided a system for energy generation comprising: a power converting device couplable to a support structure, a shaft coupled to the power converting device either directly or via a transmission, a first rotor located toward a first end of the shaft and being rotatable about a longitudinal axis of the shaft, a second rotor located toward a second end of the shaft and being rotatable about said axis, at least two vanes coupled to the first rotor and to the second rotor via respective coupling points, each vane being independently rotatable, under a force of a fluid directed to the system, about a line joining the respective coupling points, and first and second reactive elements, and at least one restraint associated with each vane, each restraint being configured to restrain the vane relative to the first and second rotors in a respective different power generative position, extended or folded, wherein the distance of the geometric center of the vane from the axis of the shaft at the extended position is significantly larger than at the folded position, whereby the swept area of the vane in the extended position is correspondingly larger than the swept area of the vane in the folded position. In some embodiments at the extended and folded positions the leading edge of the vane is directed in mutually opposite directions relative to the rotor. In some embodiments the power converting device is suspended from the support structure via a linking element. In other embodiments the power converting device is supported by the support structure. In some embodiments while the vane is located between the folded and extended positions, a chord line joining the leading and trailing edges is self-aligned relative to the fluid flow vector to minimize drag and while the vane is located at the folded or extended position, it generates significant torque caused by drag and lift forces induced by the fluid flow, wherein at the extended position the torque is significantly higher than at the folded position. In some embodiments the linking element is configured to allow the power converting device and the shaft, at least indirectly coupled thereto, to tilt in response to said force, thus changing the attack angle and regulating load on the system In some embodiments the linking element is freely rotating joint, whereby the attack angle is self-adjusted by the equilibrium between the load induced by the fluid flow and gravitational force acting on the system. In some embodiments the linking element is a freely rotating joint that is controlled by an actuator to allow adjustment of the attack angle In some embodiments the linking element is a freely rotating joint that is controlled by a spring to allow adjustment of the attack angle. In some embodiments the power converting device is at least indirectly coupled to blades that are configured for harvesting said force. In some embodiments the blades generate power as a function of attack angle. In some embodiments the first rotor, the second rotor and the shaft are rigidly coupled to a mast configured to drive the power converting device, directly or via a transmission. In other embodiments the first rotor, the second rotor and the shaft are configured to rotate about a mast that is at least indirectly coupled to the support structure, while either or both of the first and second rotors are configured to drive the power converting device, directly or via a transmission. In some embodiments the power converting device is any one of an electric generator, a pump, or any other form of mechanically driven device. In some embodiments a contact between the reactive elements and the respective restraints arrests the rotation of the vane. In some embodiments the reactive elements and the respective restraints support ferromagnetic material or permanent magnets or electromagnets, configured to create a magnetic force between the vane and the rotor. In some embodiments the magnetic force is any of the following forms: repulsive, attractive, or controllable attractive or repulsive. In other embodiments the support structure is airborne. In some embodiments the support structure carries a payload comprising at least one sensor. In other embodiments at least one sensor is configured for decoupling from the support structure and being directed to a designated target for carrying out a specified mission. In some embodiments the at least one sensor is configured for returning to the support structure after completion of said mission. In other embodiments the at least one sensor is carried by a drone. In accordance with another aspect of the invention there is provided a method of energy generation, the method comprising: directing a fluid flow against a system comprising at least two vanes rotatable about an axis of shaft, each configured to rotate about a respective vane rotation axis, whereby during a complete cycle of rotation the fluid flow impinges against different ones of the vanes causing the system to rotate about the axis of the shaft; and associating with each of the vanes, respective two reactive elements and their restraints, wherein the reactive elements and restraints are configured to create two power generative positions, extended and folded, which constitute the boundaries for vane to rotate within, about the line, wherein in each said position the vane harvest the energy of the fluid flow while moving downstream the fluid flow and in-between said positions the vane performs self-alignment to the fluid flow vector, to minimize the energy loss while moving upstream the fluid flow. In some embodiments the method including adjusting an attack angle thus to reduce the force induced by a high fluid flow on the system, to avoid an overload of the system. In some embodiments the method including adjusting the force of the fluid flow thus to drive the attack angle down for increasing the front area of the blades and the power generated by said blades.

BRIEF DESCRIPTION OF THE DRAWINGS To understand the invention and to see how it may be carried out in practice, embodiments will be described, by way of non-limiting example only, with reference to the accompanying drawings, in which: Figs. 1A is a schematic view of a power generation system according to an embodiment of the present invention; Fig. 1B shows a detail of the system shown in Fig. 1A; Figs. 2A, 2B and 2C are schematic views of the system of Fig. 1A responding to different fluid flow conditions; Figs. 3A, 3B and 3C show the system having a power converting device coupled to a support structure; Figs. 4A, 4B, 4C and 4D show variations of the system shown in Fig. 3A; Figs. 5A and 5B are front and cross-sectional views, respectively of a power generation system according to another embodiment of the invention; Fig. 6shows a system according to another embodiment of the invention; Fig. 7 shows a detail of the vanes and reaction elements during power generation; Fig. 8A shows a schematic view of an airborne configuration according to an embodiment of the invention; Fig. 8Bshows a top view of a payload of the system shown in Fig. 8A; Fig. 8C is a functional block diagram showing details of the payload for the system shown in Fig. 8B; and Fig. 9 shows schematically an embodiment having an air-buoyant structure carrying a sensor that is configured for decoupling from the support structure.

DETAILED DESCRIPTION OF EMBODIMENTS In the following description of some embodiments, identical components that appear in more than one figure or that share similar functionality will be referenced by identical reference symbols. Fig. 1A shows a system 2 in an extended power generation position. The system 2 includes a power converting device 4 at least indirectly coupled to a support structure 6, either directly or via a linking element 8. A shaft 10 is adapted for coupling to a power converting device 4 either directly (not shown in the figures) or via a transmission 12. A first rotor 14 includes a hub and arms located toward a first end of the shaft 10 for rotation about a longitudinal axis of the shaft 10. A second rotor 18 located toward a second end of the shaft 10 for rotation about said axis. Vanes 20, each having a leading edge 22 and a trailing edge 24, are coupled to the first rotor 14 and to the second rotor 18 via respective coupling points 26. Each vane is independently rotatable, under a force of a fluid directed to the system, about a respective line 28 joining the coupling points 26, wherein the average distance between the leading edge 22 and the line 28 joining the coupling points 26 is significantly shorter than the average distance between the trailing edge 24 and the same line 28. Although four vanes 20 are shown in the system of a figure 1A two or more vanes may be used. It should be also stated that alternatively the leading edge 22 and the line 28 can be merged. Fig. 1B shows first 30 and second 32 reactive elements associated with each vane 20, each element configured to arrest the vane 20 relative to its rotors 14 and 18 in two different power generative positions – extended position (reactive element 30 abuts its restraint 36), or folded position (reactive element 32 abuts its restraint 36). Both positions are generally opposite to each other such that the leading edge 22 is directed in opposite directions at the two extremities defined by the extended and folded positions. The respective swept areas of the vanes in the extended and folded positions are significantly different. Fig. 1B shows both reactive elements 30 and 32 when they are distant from their restraints 36. Fig. 2A shows the swept area 34a of the system 2 at zero or negligible wind-speed. After being subjected to higher than cut-in speed, all the vanes 20 of the previously rotating system 2 start gradually rotating under the force of gravity about their respective axes 28 to the extended position, where their first reactive elements 30 (Fig. 1B) abut the respective restraints 36, as shown in Fig. 2A. At the extended position shown in Fig. 2A, the leading edges 22 of the vanes 20 are directed generally toward the center of the system 2. If the wind speed increases and exceeds its cut-in speed (above 0.5 meter per second) this will give rise to rotation torque about the axis of the shaft 10, generated by the vanes on the right side of the shaft 10 moving in a downstream direction (assuming that in Figs. 2A and 2B the wind vector is directed into the plane of the page), while the vanes on the left side of the shaft 10, will depart from their extended position of Fig. 2A while moving upstream and aligning themselves with the fluid flow vector, as shown in Fig. 2B. The transition from the state shown in Fig. 2A to the state shown in Fig. 2B represents a process of the startup. It should be noted that Fig. 2B shows the swept area 34b of the system 2 at low wind conditions, when the right-hand vanes 20 (relative to shaft 10) are in an extended position (the wind vector is directed into the figure plane) and the left-hand vanes move upstream while rotating between the boundaries defined by the extended and the folded positions, and aligning themselves with a fluid flow vector, by rotating about a respective axis 28, joining the coupling points 26. The term “fluid flow vector” refers to a vector sum of the wind vector and flow vector induced by the rotation of the vane about the axis of the shaft 10. The adoption of the vane 20 into either extended or folded power generative position depends on the fluid flow speed and the position of the vane 20 during the self- alignment process while moving upstream. If the fluid speed is low, but exceeds the cut-in speed, the induced forces will be significantly lower than the gravitational force, and the vane 20 will rotate about the axis 28 under the torque created by the gravity force into the extended position, as shown in Fig. 2B. At a certain fluid speed (for the purpose of description defined as an “intermediate speed”), the forces induced by the fluid will be higher than the gravitational force, and the vane will rotate about the axis 28 under the torque induced by the fluid flow in an opposite direction into the folded position shown in Fig. 2C. The swept area 34c in the folded position shown in Fig. 2C is smaller than the swept areas 34a or 34b, thus resulting in lower rotation torque (at the same fluid speed) generated by the vanes 20 on the right-side of the shaft 10. The folded position is created by the second reactive element 32 (Fig. 1B) meeting its restraint 36, which force the trailing edge 24 of the vane 20 to be directed, in general, to the center of the system. Fig. 3A shows a power converting device 4 suspended from a support structure via a linking element 8. Fig. 3B shows a power converting device 4 mounted on the support structure 6 in the form of a mast. In Fig. 3B the power converting device 4 is coupled to the second rotor 18 (the smaller one) and the linking element 8 is a spring capable of tilting under the force of the fluid flow, in the direction of the fluid flow vector 40, as shown in Fig. 3C. The power converting device 4 can be an electric generator, a pump, or any other form of mechanically driven device. The first and the second reactive elements, 30 and 32, and their respective restraints 36 define, respectively, the extended and the folded positions, which constitute the boundaries for an angular motion of the vane 20 through approximately 180 degrees, about a respective line 28 joining the coupling points 26. While the vane 20 is located in between the extended and folded positions during its upstream motion, it is aligned, in general, with the fluid flow vector and generates minimum possible power loss due to its interaction with the fluid, and while the vane 20 is located at the extended or folded position, it generates significant torque caused by drag and lift forces induced by the fluid flow. At the extended position the torque is significantly higher than at the folded position, thus compensating for the low power of the wind at the low wind-speed. This feature introduces a folding action, by using minimal material and introducing minimal complexity, that allows the vane 20 to start generating a rotational torque about the axis of the shaft 10 at a significantly lower cut-in speed, in an extended position, and then to switch at higher wind-speed to a folded position. Typically, this allows the cut-in speed to be reduced to under 1.5 meter per second – much lower than many other wind turbines. The linking element 8 shown in Fig. 3A is configured as a freely rotating joint, that allows the power converting device 4 and the shaft 10 coupled thereto, to tilt under the load created by the fluid or wind flow 40, thereby changing the attack angle 42 being the angle between the fluid flow 40 vector and the axis of the shaft 10, as shown in Figs. 4A and 4B. If the attack angle 42 is about 90 degrees (Fig. 4A), the load induced by the fluid flow 40 on the structure of the system 2 will be maximal. The lower the attack angle 42, the lower is the load induced by the fluid flow 40 on the structure of the system (Fig. 4B), and the higher is the lift force induced by the fluid flow 40 on the said system.

A decrease in a load, on the one hand, and on the other hand, an increase in a lift force, allows to keep the ratio of lift to drag forces of the entire system (balloon and payload) at the same level as before installing the system 2. To allow regulating the load on the structure of the system 2, by tilting the system and changing its attack angle 42, the linking element 8 can be configured in different ways: In the configuration of Fig. 3A, wherein the linking element 8 is a freely rotating joint, the attack angle is defined by the equilibrium between the load induced by the fluid flow 40 and the gravitational force acting on the system. In the configuration of Fig. 4A and 4B, wherein the linking element 8 is a rotating joint controlled by an actuator 46 (e.g. electric, hydraulic or pneumatic) at least indirectly coupled to the shaft 10, the attack angle 42 is defined by the position of the actuator 46. In the configuration of Fig. 4C and 4D, wherein a rotating linking element 8 is controlled by a spring 48, the attack angle is defined by the equilibrium between the torque generated by the load induced by the fluid flow 40 and the torque generated by the spring 48 - both torques about the rotation axis of the linking element 8. A low stiffness spring 48 will allow the system 2 to achieve a balance under the fluid flow 40 at a lower attack angle 42. A high stiffness spring will allow the system 2 to achieve a balance under the fluid flow 40 at an attack angle closer to 90 degrees. If the attack angle 42 is reduced, overload of the system 2 can be avoided. This feature introduces a tilt regulation action, while maintaining minimal material and complexity, that allows the system 2 to achieve a significantly higher cut- off speed by regulating its front area against the wind. Figs. 5A and 5B show in front elevation and cross section, respectively, a system for power generation with a power converting device 4 having a hollow shaft coupled to blades 50 via a shaft adaptor 50a, at one end, and coupled via a transmission 12 to the rotor 14 (comprises a hub 14a and arms 14b attached thereto), at the other end. In this embodiment the power converting device 4 and the transmission 12 are enclosed within the transmission’s housing 12a. Blades 50 are configured for harvesting the fluid flow energy at low attack angles. The blades 50 generate power directly dependent on the attack angle: the lower the attack angle, the higher the front area of the blades and power harvested by these blades. The shape and the size of the blades 50 are configured to withstand the highest fluid or wind speed, thus, to allow the system 2 to continue generating power at high fluid speed without exceeding the strength limits of the vanes , shaft 10, rotors 14 and 18 and other components of the system 2. This feature introduces a compensation action, while maintaining minimal material and complexity, that allows the system 2 to maintain productivity at high wind speeds. Fig. 6 shows a system 2 for power generation with the first rotor, the second rotor and the shaft rigidly coupled to a mast 52, which is configured to be an extension of the shaft 10 for driving the power converting device 4, either directly or via a transmission 12. The functionality and the interfaces of the mast 52, while configured as an extension of the shaft 10, are the same as of the shaft 10. By such means, the coupling of the mast to the linking element 8 is equivalent to the coupling of the shaft 10 to the same linking element 8 in the previous embodiments. In this embodiment the mast 52 is rotatably supported on the structure 6 via bearings (not shown). It should be noted that each one of the reactive elements 30 and 32 (Fig. 1B) is configured as a mechanical contact stopper that arrests the rotation of the vane 20 when it abuts its restraint or restraints 36, coupled to the first rotor 14. Alternatively, the reactive elements 30 and 32 can be coupled to the rotors (14 or 18), while the restraints 36 are coupled to the vane 20 (this configuration is not shown). It will also be noted that while in Fig. 1B a single restraint 36 is shown, which is operative to arrest or restrain the reactive elements 30 and 32 on opposing sides of a common restraint, in practice in all embodiments separate restraints may be provided: one for each of the two reactive elements. The interaction between the reactive elements 30, 32 and their restraints 36 can be also contactless. In the contactless configuration, elements 30 and 32 can carry within the slots 44 (Fig. 1B) reactive targets which are made of either metal or permanent magnets that are configured to interact with reactive targets chosen from the group of permanent magnets 56 or electromagnets 58 carried by the restraints 36 in its slots, to create a magnetic force between the vane 20 and the rotor 14. The magnetic force may be any of the following forms: repulsive, attractive, or controllable attractive or repulsive. In accordance with the above-mentioned description, energy is generated by directing a fluid flow 40 against the system 2 comprising at least two vanes 20 rotatable about an axis of shaft 10, each configured to rotate about a respective vane rotation axis 28, whereby during a complete cycle of rotation the fluid flow 40 impinges against different ones of the vanes 20 causing the system 2 to rotate about the axis of the shaft . Associated with each of the vanes 20 are two respective reactive elements 30 and and complementary restraints 36, the reactive elements and their restraints being configured to create two power generative positions, extended and folded, which constitute boundaries or extremities within which the vane 20 to rotate about the axis 28. In each position the vane 20 harvests the energy of the fluid flow while moving downstream of the fluid flow, while at intermediate positions between the two extremities the vane 20 is capable of aligning itself with the fluid flow vector, by rotating about a respective line 28 joining the coupling points 26, to minimize the energy loss while moving upstream of the fluid flow. The direction of the rotation of the vane 20 toward said extended or folded position depends on the fluid flow speed level. The following description provides a more detailed understanding of the system structure and action. The transmission housing 12a can optionally be configured as a linking element 8, either tiltable or rigid. As shown in Fig. 5B, the first rotor 14 comprises a hub 14a and arms 14b attached thereto. The second rotor 18 may be similar to the first rotor structure but of different dimensions. The vane 20 can be formed of fabric coupled at a first end to a boom 20b (shown in Fig. 3A) rotatable at a first coupling point 26 about line 28 and stretched by its second end to the second coupling point 26 (Fig. 1A). The shape of the fabric 20a can be characterized by a triangular geometry (not shown), trapezoid geometry (Fig. 1A), or other geometries that may require some rigid elements to be integrated into the fabric. The shape of the vane 20 can have a geometry of wing or of blade, with a complex profile (not shown). The first rotor 14 arms 14a support restraints 36, which interact with reactive elements 30 and 32 attached directly to the vanes 20 (not shown) or to the boom 20b, as shown in Fig. 1B. 30 Magnets 56 inserted into slots 44 (shown in Fig. 1B) of the reactive elements 30, and restraints 36 co-operate to induce a repulsive force between the vanes 20 and the rotor 14. From the structural perspective, each rotation axis 28 can be implemented by a cord (not shown) connected at both ends to coupling points 26. The centerlines of the cords can serve as an axis about which the respective vanes 20 rotate independently of each other. Each cord can support a vane 20 that is rotatable about the axis of the cord. The reactive elements 30 and 32 are configured to interact with the restraints 36 so as to create a reactive force which, depending on the direction of the wind against the vane, impedes or enhances rotation of the vane 20 about the cord when the vane 20 is in close proximity to the reactive elements 30 or 32. The interaction between the reactive elements 30 and and their restraints 36 can be effected mechanically, but is preferably contactless based on mutually attractive or repulsive magnetic or electrostatic forces, in a similar manner to the prior art. In some embodiments, the reactive elements 30 and 32 include first magnets 56 that repel second magnets 56 included in the restraints 36 attached to the boom 20b or directly to the vane 20. The magnetic interaction between the materials inserted into the slots 44 of the reactive elements 30, 32 and the restraints 36, can be of any of the following forms: repulsive, attractive (can be also achieved by including in the reactive element a target of a ferromagnetic material such an iron), and controllable attractive or repulsive. For the sake of simplicity and for the purpose of this description it will be assumed that both the reactive elements 30 and 32 and the restraints 36 are carrying permanent magnets whose polarities are configured to create a mutually repulsive force. Fig. 1A shows an initial disposition of the vanes 20 and will serve to explain the response of the system 2 to calm weather, where the fluid flow speed is either zero or very low, below the cut-in speed, and therefore cannot move the vanes 20 from their equilibrium position where the orientation of all vanes 20 relative to the shaft 10 is substantially identical. For the sake of clarity, it should be noted that the fluid can be either gaseous or liquid and that the system can operate in both environments. Because of the angle between the line 28 and the vertical axis of the shaft 10, in calm weather gravitational forces of the vanes 20 will lead them to reach an extended position resulting in maximal swept area 34a as shown in Fig. 1A, where the reactive elements 30 and their restraints 36 are in close proximity. Owing to the repulsive force between the pairs of magnets 56 inserted into the reactive element 30 and its restraint 36, the vanes 20 are unable to remain in the plane defined by the line 28 and the axis of shaft 10. As a result, all the vanes 20 will be slightly rotated about the line 28 as shown in Fig. 3A. It will be appreciated that the direction of this rotation as shown in the figure is by way of example only. Fig. 2B shows the system 2 subjected to low-speed fluid flow 40. At low fluid speed at least one vane 20w will harvest the fluid flow energy, staying in the extended position and moving in a downstream direction, while at least one other vane 20y will align itself with a fluid flow vector, driven in an upstream direction, via the shaft 10, by the power harvested by the vane 20w. In an extended position the swept area achieved 34a is the maximum possible. The reactive elements 30 and their restraints 36 may interact by contact, or contactlessly, if magnets 56 are inserted into the slots 44 of the reactive elements 30 and their restraints 36. The other vanes, 20x and 20z, may function as the previously described vanes, respectively – vane 20x may harvest fluid flow energy in a downstream direction and vane 20z may align itself with a fluid flow vector in an upstream direction. The reaction elements 30 and 32 of the vanes 20y and 20z that align themselves with the fluid flow vector while moving in an upstream direction, will be displaced from their restraints 36. These vanes rotate about the lines 28 in the range of about 180 degrees between the boundaries defined by the restraints 36, and they neither contribute to power generation, nor significantly oppose it. The vanes that are moving in a downstream direction harvest fluid energy by virtue of being arrested either in an extended or a folded position. During the rotation about the axis of the shaft 10, each vane 20 cyclically alters its state between an extended or folded position and a state of self-alignment, owing to changes in the net torque about the line 28. At intermediate fluid speed (Fig. 2C) at least one vane 20w will harvest the fluid flow energy, maintaining the folded position and moving in a downstream direction, while at least one other vane 20y will align itself with a fluid flow vector, driven in an upstream direction, via the shaft 10, by the power harvested by the vane 20w. In the folded position, the swept area achieved 34c is significantly smaller than the maximum possible. The reactive elements 30 and their restraints 36 may interact by contact or contactlessly, if magnets 56 are inserted into the slots 44 of the reactive elements 30 and their restraints 36. The other vanes, 20x and 20z, may function as the previously mentioned vanes, respectively – vane 20x may harvest fluid flow energy in a downstream direction and vane 20z may align itself with a fluid flow vector in an upstream direction. The number of vanes 20 and arms 14b in the figures is for illustration only. Any number of such, equal to or greater than two, may be employed. Figs. 2B and 2C show the system 2 facing a fluid flow vector normal to and into the page. This view demonstrates an advantage of having two different power generating positions. As can be seen, while to the right of the shaft 10 the projection of the area of the vane 20w arrested in an extended position (Fig. 2B) in the direction of flow 40 is maximal. Alternatively, the projection of the same vane 20w arrested in the folded position (Fig. 2C) in the direction of flow 40 is minimal. Since the power generated by the fluid flow is proportional to the projection of the area impacted by the wind, the system 2 will start harvesting fluid energy earlier, thus increasing power availability. It will also be understood that opposing vanes operate in a mutually opposed manner, whereby one vane is active and contributes to power generation while the other is inactive and plays no part in the current generation cycle. These two vanes will exchange their functionalities during every half-revolution (180 ) about the axis of the shaft. The following description relates to operation of the reactive elements of the vanes: a. A controlled attractive force can be achieved by inserting into one of the reactive elements a ferromagnetic material and into its restraint an electromagnet. The electromagnet can be controlled by a controller (constituting a first controller, not shown) that may be triggered by proximity sensor switches (not shown) that are configured to turn the electromagnet ON when the vane 20 rotates within range of the complementary reactive element thereby maintaining the vane in the arrested state, and OFF when the vane has accomplished its power generating function for the current cycle. For the complementary inactive vane, the attractive force between its respective reactive elements is deactivated to allow the vane to rotate in between the boundaries set by the extended and folded positions. It will be appreciated that other sensors may be used to trigger or activate the controller. For example, an angular encoder can be used to provide a measure of angular rotation relative to a predetermined origin, the controller being responsive to the encoder signals for energizing or de-energizing the electromagnets. b. Alternatively, a controlled repulsive force can be achieved by inserting into the one of the reactive elements a permanent magnet 56 and into its restraints an electromagnet (not shown) controlled by a controller (constituting a second controller, not shown) responsive to sensors as explained above. c. A controlled attractive or repulsive force can be achieved by interaction between a permanent magnet 56 and an electromagnet controlled by a controller in like manner. The controller is responsive to sensor signals for changing the polarity of the electromagnet during the power generative state, thereby increasing the power generation efficiency of the system 2 by controlling the duration of the power generation state relative to duration of the self-alignment state. As in the previous configuration, during the last state the electromagnet will be switched to OFF; however, during the power generation state the interaction can start with a repulsive polarity and then be switched to the attractive polarity to delay the timing of the state switching from power generation to self-alignment. The mast 52 can either be rotatable, as shown in Fig. 6, or static, as shown in Fig. 3C (static mast 52 is equivalent to structure 6). If the mast 52 is rotatable, the rotors 14 and 18 are rigidly coupled via the shaft 10 to the mast 52, which is configured to rotate in a support structure 6 carried by bearings 60 (not shown) and driving a power converting device 4 either directly or via transmission gears 12. The support structure 6 may be coupled to a building, a static structure, to the ground or to the mobile platform – vehicle, marine vessel or aerostat (Fig. 9). To prevent overload of the system 2 under extreme conditions, such as extreme rotational speed or an extreme fluid flow 40, for example in harsh weather conditions, the system 2 can be allowed tilting to a small attack angle in which all the vanes 20 cannot enter neither extended nor folded position but can keep aligning themself with the fluid flow vector without providing power to the power converting device 4. 30 Although the vanes 20 illustrated in the figures are of a planar shape, it will be understood that they may also be of other forms, such as blade, wing, or sail, and they may be made of rigid, flexible, or combined materials. If the vanes 20 have the form of a wing, their profile may be either symmetric, or alternatively, it may be asymmetric (not shown). The connection between the wing- shaped vanes 20 and the coupling points 26 on the rotors 14 and 18 can be effected either by a cord 28a fixedly attached to the rotors 14 and 18 and rotatably coupled to the vane or by a cord 28a fixedly attached to the vane 20 and rotatably coupled to the rotors and 18 (not shown). Fig. 1A shows a vane 20 made of a sail cloth of trapezoid shape. Fig. 3A shows the sail cloth, wherein one edge of the vane is tied via attachment points 64 to a first boom 20b while the second edge of the vane 20a is tied via the attachment points 66 to a second boom (not shown). The boom 20b is rotatable about the line 28 and attached to the coupling point 26. The second boom is rotatable about the line 28 and attached to the other coupling point 26. It should be noted that each vane may carry more than one reactive element and 32 which interacts with an equal number of restraints 36 supported by any one or more of the first rotor 14, the second rotor 18 and the shaft 10. It should further be noted that the cord 28a can be chosen from any of the following groups: cables, ropes, wires, rods, bars, and they may be made of rigid or flexible material. Moreover, the cords can be an independent component, or can be combined with the vanes 20 into a unitary structure. It should also be noted that the system 2 is not limited by dimensions, scale, geometry, or shape. The shape of the system may be generally conical, with a base facing either up or down, cylindrical, or any other shape that meets the functionality or the purpose of the system 2. To understand operation of the system 2 operating as a wind turbine, the method of energy generation will now be explained. Fig. 1A shows the system 2 in calm weather (i.e., with substantially zero wind force), during which the vanes 20 are subject solely to the influence of gravity. The position that all the vanes 20 will adopt is as shown in Fig. 1A – generally, the trailing edges 24 are directed towards the exterior of the system 2, while being slightly deflected in a clockwise direction (Fig. 7) due to the repulsive magnetic force between the magnets 56 inserted into the slots 44 of the reactive elements and their restraints 36. The rotation of the rotors 14 and 18 about the axis of the shaft under the action of the fluid flow 40 will be in a direction opposite to the direction of the deflection: if the vanes are deflected in a clockwise direction as seen from above, the rotors 14 and 18 will rotate in a counterclockwise direction, and vice versa. Fig. 7 shows an upper view of the right-side part of the system 2 rotating in a counterclockwise direction while subjected to low-speed fluid flow 40. Under the action of the fluid flow 40, vanes 20w and 20x move downstream, in the general direction of the flow and are arrested by contact or contactless interaction between the reactive elements 30 and their respective restraints 36. In this condition, the vanes 20w and 20x generate power and rotate the rotatable components of the system 2 about the axis of the shaft 10. At the same time, the vanes 20y and 20z (not shown in Fig. 7) move upstream, against the general direction of the flow, freely rotating about the line 28, while keeping away from the restraints 36. While the orientation of the vanes 20w and 20x that are moving with the flow 40 is such that brings their lift and drag forces to maximum, the orientation of the vanes 20y and 20z that move against the flow 40 is such that minimizes their drag forces. As a result, energy losses of the system 2 are reduced and the efficiency of the power generation is increased. Rotational energy harvested from the fluid flow 40 is provided either directly to power converting device 4, or indirectly, via transmission gear 12. The power converting device 4 may be an electric generator, pump, or a mechanically driven device. During the rotation each of the vanes 20 cyclically alternates between the power generative extended or folded position and the self-alignment position, driven by the fluid flow. Operation of the three-position turbine generator (two power generative and one self-aligned) is such that it does not depend on the direction of the flow. It should be noted that the system 2 is not limited to vertical orientation one only. Other orientations of the system, such as horizontal, tilted, upside down and others, are applicable as well. It will be appreciated that although reference is made to first and second controllers, their functionalities may be combined and may optionally be implemented by a suitably programmed computer.

In all embodiments of the invention, system components can be formed of lightweight materials, such as carbon fiber tubes and plastic, and the vanes 20 can be formed of a lightweight fabric, with an area density as low as 25 g/m, thus providing very low overall weight to swept area ratio and facilitating lightweight portable and airborne configurations. Fig. 8A shows a general view of an energy-independent tethered aerostat system having a wind power generation system 2. The support structure 6 is anchored to a tether and is held aloft by an air-buoyant structure 72 such as an aerostat or a balloon. The top view of the payload carried by the aerostat 72 is shown in Fig. 8B, and once again as a functional block diagram in Fig. 8C. Wind 40 energy harvested by the sails 20 at the altitude of a few hundred meters above the ground (where the wind speed is significantly higher than on the ground) drives the power converting device 4 either directly (not shown) or via transmission gears 12. The power generated by the converting device 4 is then fed into an electronic circuit which is responsible for charging an onboard battery 82 and feeding power to a sensor module 84 (which may contain one or more sensors, such as camera, acoustic sensor, rotational encoder, etc.) and a communication module 86. The size and volume of the aerostat 72 is not affected by the weight of the system 2, as it is fully compensated for by the reduction in the battery weight onboard the aerostat – the higher the energy generated by the system 2, the lower the energy demand from the onboard battery. The information gathered by the sensor module 84 can be transferred via the communication module either to the cloud (not shown), or to a ground terminal 78, which can include a smartphone and/or a computer. Given a sufficient wind power at the operating altitude, the aerostat system 72 can be functional for as long as the aerostat 72 can stay in the air (weeks or months). In areas with sufficient solar energy, stabilization surfaces 74 and 76 made from a photovoltaic foil can be added to augment the power source. In this case the electronic circuit 80 is provided with an additional power port (not shown) for the photovoltaic foil power supply. Although the configuration shown in Figs. 8A to 8C includes a single power converting device 4 anchored to a common support structure 6, in an alternative embodiment of an airborne system, a pair of power converting device 4 may be anchored to the support structure 6 to similar effect. In another aspect of the invention, the system 2 according to all embodiments may have a dual use: while detached from the power converting device 4, for example via clutch (not shown), it can act as a high-precision anemometer. This feature allows evaluating wind power potential at different altitudes for long periods of time, without the need for additional hardware. In this case, the sensor module 84 can measure the rotation velocity of the shaft 10 (via an electro-optic or magnetic encoder 88), which is in general proportional to the wind 40 speed. In addition to measuring the anemometer rotation velocity, the sensor module 84 may also gather other meteorological metrics (e.g. temperature, humidity, pressure). It should be stated that the sensor module 84 encompasses a broad range of sensing technologies and is not limited to only the examples described above. Fig. 9 shows schematically an embodiment wherein the support structure 6, carried by an air-buoyant structure 72, such as an aerostat or a balloon, supports at least mechanically, either directly or via a docking device 90, a light-weight drone 92. The drone carries a camera 84 operating as an alternative sensor module, while a battery of the drone (not shown) is charged by the system 2 via an electronic circuit 80 to keep it always fully charged. One advantage of this configuration is the ability of the drone 92, and specifically its camera 84, to operate continuously 24/7, either while being stationary and at least indirectly coupled to structure 6, charged by the power supplied from the system 2 without running the motors of the drone, or while flying to a target detected during the stationary phase or elsehow, or while flying back to the docking device 90. The information gathered by the camera 84 can be transferred via a communication module of the drone (equivalent to module 86) either to the cloud (not shown), or to a ground terminal 78, which can include a smartphone and/or a computer. Optionally, an operator on the ground can take control of the drone 92 via the ground terminal 78. The functional continuity of this arrangement provides great flexibility to those who are willing to have a continuous observation, for most of the time from the above, and in a case of a need for an investigation, from a short distance to the target. The ability of the drone 92 to leave the docking device 90 and to return later, allows the drone 92, equipped with a sufficient gas canister 94 (Fig. 9), to refill gas (e.g. helium) into the aerostat 72. The interface between the gas container 94 and the interior of the aerostat 72 can be effected by the docking device 90, equipped with a suffusion gas coupling mechanism (not shown). The ability of the system 2 to provide energy to an embedded payload (constituted in some embodiments by the camera 84 or any other on-board sensor module 84 and the communication module 86), or to an external payload (drone 92 in Fig. 9), along with the ability of an aerostat 72 to be refilled with gas (e.g. helium) in order to compensate for gas leakage over time, allows the aerostat 72 and its payload (84 and 86, or 92) to be operational at a predetermined altitude for an unlimited time, subject to a sufficient natural resources availability (wind 40 and optionally sun radiation), and subject to periodic refill of the canister 94 on the ground or in the air. The refill of the canister on the ground can be performed automatically by using a similar docking device connected to a gas tank 96 as shown in Fig. 9, while directing the drone 92 to a remote gas tank 96 for remote refill can be triggered automatically by a reduction in gas pressure in the aerostat 72. Although optimally the leading edges of the vanes subtend an angle of 180° when moving between the two extremities from folded to extended positions and vice versa, in practice acceptable operational efficiency may be achieved even when the angle subtended by the vanes is somewhat less or more than 180°. For example, high efficiency can be obtained even if the leading edges of the vanes move through an angle of 165° between extremities and fairly good efficiency is still obtained even when they subtend a maximum angle of only 145°. Within the context of the description and the appended claims, terms such as “generally”, “about”, “substantially” and “approximately” encompass a departure from optimal of ± 20%. It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrated embodiments and that the present invention may be embodied in other specific forms without departing from the scope of the appended claims. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being defined by the appended claims rather than by the foregoing description.

CLAIMS: 1. A system (2) for energy generation, the system comprising: a power converting device (4) couplable to a support structure (6); a shaft (10) coupled to the power converting device either directly or via a transmission (12); a first rotor (14) located toward a first end of the shaft and being rotatable about a longitudinal axis of the shaft; a second rotor (18) located toward a second end of the shaft and being rotatable about said axis; at least two vanes (20) coupled to the first rotor and to the second rotor via respective coupling points (26), each vane being independently rotatable, under a force of a fluid directed to the system, about a line (28) joining the respective coupling points; and first and second reactive elements (30, 32) and at least one restraint (36) associated with each vane, each restraint being configured to restrain the vane relative to the first and second rotors in a respective different power generative position, extended or folded, wherein the distance of the geometric center of the vane from the axis of the shaft at the extended position is significantly larger than at the folded position, whereby the swept area (34a, 34b) of the vane in the extended position is correspondingly larger than the swept area (34c) of the vane in the folded position. 2. The system as claimed in claim 1 , wherein at the extended and folded positions the leading edge of the vane is directed in mutually opposite directions relative to the rotor. 3. The system as claimed in claim 1 or 2 , wherein the power converting device is suspended from the support structure (6) via a linking element (8). 4. The system as claimed in claim 1 or 2 , wherein the power converting device is supported by the support structure.

. The system as claimed in any one of the preceding claims, wherein while the vane is located between the folded and extended positions, a chord line joining the leading and 30 trailing edges is self-aligned relative to the fluid flow vector to minimize drag and while the vane is located at the folded or extended position, it generates significant torque caused by drag and lift forces induced by the fluid flow, wherein at the extended position the torque is significantly higher than at the folded position. 6. The system as claimed in claim 3, wherein the linking element is configured to allow the power converting device and the shaft, at least indirectly coupled thereto, to tilt in response to said force, thus changing the attack angle and regulating load on the system. 7. The system as claimed in claim 6, wherein the linking element is freely rotating joint, whereby the attack angle is self-adjusted by the equilibrium between the load induced by the fluid flow and gravitational force acting on the system. 8. The system as claimed in claim 6, wherein the linking element is a freely rotating joint that is controlled by an actuator to allow adjustment of the attack angle. 9. The system as claimed in claim 6, wherein the linking element is a freely rotating joint that is controlled by a spring to allow adjustment of the attack angle.

. The system as claimed in any one of the preceding claims, wherein the power converting device is at least indirectly coupled to blades (50) that are configured for harvesting said force. 11. The system as claimed in claim 10, wherein the blades generate power as a function of attack angle. 12. The system as claimed in any one of the preceding claims, wherein the first rotor, the second rotor and the shaft are rigidly coupled to a mast configured to drive the power converting device, directly or via a transmission. 13. The system as claimed in claim 3 or 4, wherein the first rotor, the second rotor and the shaft are configured to rotate about a mast that is at least indirectly coupled to the support structure, while either or both of the first and second rotors are configured to drive the power converting device, directly or via a transmission. 14. The system as claimed in any one of the preceding claims, wherein the power converting device is any one of an electric generator, a pump, or any other form of mechanically driven device.

. The system as claimed in any one of the preceding claims, wherein contact between the reactive elements and the respective restraints arrests the rotation of the vane. 16. The system as claimed in any one of claims 1 to 14, wherein the reactive elements and the respective restraints support ferromagnetic material or permanent magnets or electromagnets, configured to create a magnetic force between the vane and the rotor. 17. The system as claimed in claim 16, wherein the magnetic force is any of the following forms: repulsive, attractive, or controllable attractive or repulsive. 18. The system according to any one of the preceding claims, wherein the support structure (6) is airborne. 19. The system according to claim 18, wherein the support structure (6) carries a payload comprising at least one sensor (84).

. The system according to claim 19, wherein at least one sensor is configured for decoupling from the support structure (6) and being directed to a designated target for carrying out a specified mission. 21. The system according to claim 20, wherein the at least one sensor is configured for returning to the support structure (6) after completion of said mission. 22. The system according to claim 20 or 21, wherein the at least one sensor is carried by a drone. 23. A method for generating energy, the method comprising: directing a fluid flow against a system comprising at least two vanes rotatable about an axis of shaft, each configured to rotate about a respective vane rotation axis, whereby during a complete cycle of rotation the fluid flow impinges against different ones of the vanes causing the system to rotate about the axis of the shaft; and associating with each of the vanes, respective two reactive elements and their restraints, wherein the reactive elements and restraints are configured to create two power generative positions, extended and folded, which constitute the boundaries for vane to rotate within, about the line, wherein in each said position the vane harvest the energy of the fluid flow while moving downstream the fluid flow and in-between said positions the vane performs self-alignment to the fluid flow vector, to minimize the energy loss while moving upstream the fluid flow. 24. The method as claimed in claim 23, including adjusting an attack angle thus to reduce the force induced by a high fluid flow on the system, to avoid an overload of the system.

. The method as claimed in claim 23 or 24, including adjusting the force of the fluid flow thus to drive the attack angle down for increasing the front area of the blades and the power generated by said blades.

Claims (25)

- 1 - CLAIMS:

1. A system (2) for energy generation, the system comprising: a power converting device (4) couplable to a support structure (6); a shaft (10) coupled to the power converting device either directly or via a transmission (12); a first rotor (14) located toward a first end of the shaft and being rotatable about a longitudinal axis of the shaft; a second rotor (18) located toward a second end of the shaft and being rotatable about said axis; at least two vanes (20) coupled to the first rotor and to the second rotor via respective coupling points (26), each vane being independently rotatable, under a force of a fluid directed to the system, about a line (28) joining the respective coupling points; and first and second reactive elements (30, 32) and at least one restraint (36) associated with each vane, each restraint being configured to restrain the vane relative to the first and second rotors in a respective different power generative position, extended or folded, wherein the distance of the geometric center of the vane from the axis of the shaft at the extended position is significantly larger than at the folded position, whereby the swept area (34a, 34b) of the vane in the extended position is correspondingly larger than the swept area (34c) of the vane in the folded position.

2. The system as claimed in claim 1 , wherein at the extended and folded positions the leading edge of the vane is directed in mutually opposite directions relative to the rotor.

3. The system as claimed in claim 1 or 2 , wherein the power converting device is suspended from the support structure (6) via a linking element (8).

4. The system as claimed in claim 1 or 2 , wherein the power converting device is supported by the support structure. - 2 -

5. The system as claimed in any one of the preceding claims, wherein while the vane is located between the folded and extended positions, a chord line joining the leading and trailing edges is self-aligned relative to the fluid flow vector to minimize drag and while the vane is located at the folded or extended position, it generates significant torque caused by drag and lift forces induced by the fluid flow, wherein at the extended position the torque is significantly higher than at the folded position.

6. The system as claimed in claim 3, wherein the linking element is configured to allow the power converting device and the shaft, at least indirectly coupled thereto, to tilt in response to said force, thus changing the attack angle and regulating load on the system.

7. The system as claimed in claim 6, wherein the linking element is freely rotating joint, whereby the attack angle is self-adjusted by the equilibrium between the load induced by the fluid flow and gravitational force acting on the system.

8. The system as claimed in claim 6, wherein the linking element is a freely rotating joint that is controlled by an actuator to allow adjustment of the attack angle.

9. The system as claimed in claim 6, wherein the linking element is a freely rotating joint that is controlled by a spring to allow adjustment of the attack angle.

10. The system as claimed in any one of the preceding claims, wherein the power converting device is at least indirectly coupled to blades (50) that are configured for harvesting said force.

11. The system as claimed in claim 10, wherein the blades generate power as a function of attack angle.

12. The system as claimed in any one of the preceding claims, wherein the first rotor, the second rotor and the shaft are rigidly coupled to a mast configured to drive the power converting device, directly or via a transmission.

13. The system as claimed in claim 3 or 4, wherein the first rotor, the second rotor and the shaft are configured to rotate about a mast that is at least indirectly coupled to the - 3 - support structure, while either or both of the first and second rotors are configured to drive the power converting device, directly or via a transmission.

14. The system as claimed in any one of the preceding claims, wherein the power converting device is any one of an electric generator, a pump, or any other form of mechanically driven device.

15. The system as claimed in any one of the preceding claims, wherein contact between the reactive elements and the respective restraints arrests the rotation of the vane.

16. The system as claimed in any one of claims 1 to 14, wherein the reactive elements and the respective restraints support ferromagnetic material or permanent magnets or electromagnets, configured to create a magnetic force between the vane and the rotor.

17. The system as claimed in claim 16, wherein the magnetic force is any of the following forms: repulsive, attractive, or controllable attractive or repulsive.

18. The system according to any one of the preceding claims, wherein the support structure (6) is airborne.

19. The system according to claim 18, wherein the support structure (6) carries a payload comprising at least one sensor (84).

20. The system according to claim 19, wherein at least one sensor is configured for decoupling from the support structure (6) and being directed to a designated target for carrying out a specified mission.

21. The system according to claim 20, wherein the at least one sensor is configured for returning to the support structure (6) after completion of said mission.

22. The system according to claim 20 or 21, wherein the at least one sensor is carried by a drone.

23. A method for generating energy, the method comprising: directing a fluid flow against a system comprising at least two vanes rotatable about an axis of shaft, each configured to rotate about a respective vane rotation axis, - 4 - whereby during a complete cycle of rotation the fluid flow impinges against different ones of the vanes causing the system to rotate about the axis of the shaft; and associating with each of the vanes, respective two reactive elements and their restraints, wherein the reactive elements and restraints are configured to create two power generative positions, extended and folded, which constitute the boundaries for vane to rotate within, about the line, wherein in each said position the vane harvest the energy of the fluid flow while moving downstream the fluid flow and in-between said positions the vane performs self-alignment to the fluid flow vector, to minimize the energy loss while moving upstream the fluid flow.

24. The method as claimed in claim 23, including adjusting an attack angle thus to reduce the force induced by a high fluid flow on the system, to avoid an overload of the system.

25. The method as claimed in claim 23 or 24, including adjusting the force of the fluid flow thus to drive the attack angle down for increasing the front area of the blades and the power generated by said blades.