Abstract:
A power generation system that generates power in low flow situations is disclosed. The system includes a set of vanes, wherein each vane is mounted on a corresponding mast, so as to selectively transmit energy from the flow medium to a rotor shaft or to freely deflect in the direction of flow, depending on whether the flow impinges on the vanes in an energy-producing or a non-energy-producing direction. This is achieved by mounting each vane on its mast, so that it deflects in the flow direction when the vane is subjected to non-energy-producing flow energy, and also coupling each vane to the mast of an adjacent vane, so that the vane exerts a pull force on the mast of the adjacent vane, when the vane is capturing energy-producing flow energy.

Description:
This application claims priority from U.S. Provisional Applications 61/209,105, filed on Mar. 2, 2009, and 61/286,045, filed on Dec. 14, 2009. 
    
    
     BACKGROUND INFORMATION 
     1. Field of the Invention 
     The present invention relates to the field of power generation from a renewable power source. More particularly, the invention relates to the use of a rotor and vanes in a flowpath of a flow medium, for generating electrical power. 
     2. Description of the Prior Art 
     Humans have extracted power from the energy of flowing streams for centuries. Typically, this is done by forcing the water over a dam and using the head pressure from the drop to turn a turbine. Building a dam is a very costly effort and the barrier to flow caused by the dam typically has serious negative consequences for wildlife and, particularly, for migrating species of fish. As a result, people have tried many different ways of extracting energy from flowing water simply by relying on the kinetic energy of a flowing stream. Wind turbines rely on the flow of air and are becoming ever more popular as a source of clean energy. One type of wind turbine is the Savonius wind turbine, which is a drag-type vertical axis wind turbine generator that typically has a very low efficiency, around 15%. As a result, the Savonius wind turbine is generally not deemed suitable for electricity generation, except for small-scale production. This type of turbine is also used in installations that require slow rotation and high torque, such as in pumping water or grinding grain. 
     What is needed therefore is apparatus for and a method of extracting energy from a flow medium. What is further needed is such apparatus and method that is mechanically uncomplicated, yet efficient. What is yet further needed is such apparatus and method that is suitable for extracting energy from very low flow currents, with high efficiency and low impact on the natural environment and wildlife. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention is a power generating system comprising a rotor and a system of vanes that are placed in the flowpath of a fluid. The vanes may also be referred to as paddles or blades. The power generation system according to the invention is most typically placed in the flowpath of water, such as in a stream or river, or in a tidal zone, in which case the system is referred to as a tidal in-stream energy conversion device (TISEC), but generally, the power generation system may be operated successfully and effectively in the path of just about any type of flow medium, be it liquid or gaseous. For purposes of simplicity and illustration only, reference may be made hereinafter to a flowing stream and also to water as the flow medium. This is not intended to be limiting and it is understood that the power generation system according to the invention may be placed in the flowpath of a fluid other than water, such as air, oil, photons, planetary atmosphere, etc. 
     The vanes are mounted on masts and the masts are rigidly attached to the shaft of a rotor. The flowpath of the flow medium urges the vanes to move in the flow direction, i.e., in the downstream direction. The rotor includes a rotor shaft that rotates in one direction only and which transmits the rotation to the rotor, which, in turn, is connected to an electric generator that generates electricity as the rotor rotates. The movement of the vanes is selectively constrained, so that some of the vanes are allowed to deflect freely in the direction of flow, while the rest of the vanes are constrained to receive the force of the flow, which is then transmitted to the rotor, causing it to rotate. Thus, the flow impinging on the vanes, although flowing in the downstream direction, includes a flow component that is a forward or power-generating flow and a flow component that is a reverse or non-power-generating flow. In the course of rotation of the rotor shaft, each of the vanes is at some point subjected to a greater return flow force than a power-generating flow force. Those vanes receiving a greater power-generating flow than a non-power-generating flow transmit force to the rotor shaft; those vanes receiving a greater reverse flow than the power-generating flow deflect more or less in the downstream direction. As a result, those vanes that are deflecting in the downstream direction allow flow through the power generation system, and therefore allow marine life to pass through the system unharmed. This aspect also reduces significantly the drag on the system, because the deflecting vanes present a minimal strike zone or area. 
     As with conventional Savonius type rotors, the rotor of the power generation system according to the invention cannot rotate at a velocity that exceeds the velocity of the current. This limitation is offset, with regard to efficiency, by the fact that the rotor requires very low flow to rotate. Preliminary tests have shown that the power generation system according to the invention begins capturing energy and generating power at flows as low as 0.3 m/s and has an optimal Tip-Speed-Ratio (TSR) in the range of 0.3 to 0.5. This is in contrast to typical TSR values in the range of about 1.0 to 5.0 for conventional turbines. The low flow rate and low TSR indicate that the system does not suffer from the disadvantages mentioned above with regard to conventional turbines, including Savonius and other types. In other words, the power generation system according to the invention does not lie fallow in low-flow periods. The power generation system will operate at very low tidal flows, rather than just at peak flow. The low operating speed may also have a positive effect on fish mortality rates, reducing the mortality significantly over the mortality rates associated with conventional TISEC systems. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is described with reference to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements. The drawings are not drawn to scale. 
         FIG. 1  is a plane view of the power generation system according to the invention, illustrating how the vanes are coupled to the masts. 
         FIG. 2  is a side elevational view of the power generation system of  FIG. 1 . 
         FIG. 3  is a top plane view of the power generation system according to the invention, with the rotor shaft oriented parallel to the flowpath of the flow medium. 
         FIG. 4  illustrates a first alternative motion-restraint means. 
         FIG. 5  illustrates a second alternative motion-restraint means. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will now be described more fully in detail with reference to the accompanying drawings, in which the preferred embodiments of the invention are shown. This invention should not, however, be construed as limited to the embodiments set forth herein; rather, they are provided so that this disclosure will be complete and will fully convey the scope of the invention to those skilled in the art. 
       FIGS. 1 and 2  are schematic illustrations of a power generation system  100  according to the invention. The power generation system  100  comprises power generation means for transmitting rotational motion to an electrical generator and energy-capture means for capturing kinetic energy from a flow medium, such as a liquid or a gas. The power generation means  110  includes a rotor shaft  112  that is attached at one end to a generator  114 . The generator  114  is a conventional piece of equipment and is not described in any detail herein. Also, the generator  114  is shown mounted at the bottom of the power generation system, but it can just as well be mounted at the top. The energy-capture means  120  comprises a set of foils or vanes  122  and masts  124 , each vane  122  being fastened to a corresponding mast  124 . A set of four vanes  122  is shown in the figures, but this is for illustration purposes only. It is understood, that the power generation system  100  may be constructed with any suitable odd or even number of vanes. The vanes  122  may be paddle-like, as shown in  FIGS. 1-3 , or may be curved as is known to do with conventional Savonius-type wind turbines, so as to reduce drag, etc. 
     The power generation system  100  may be installed in the flowpath of a flow medium, such that the rotor shaft  112  is oriented orthogonal or parallel to the direction of flow. In a first installation, the power generation system  100  is installed in a riverbed, for example, with the rotor shaft  112  oriented orthogonal to the direction of flow of the water, i.e., set vertical with reference to the ground. This set-up is deemed the optimal one in situations in which the rate of flow is relatively slow, such as in bodies of water with slow moving currents or ocean tides, or in the presence of low wind velocities. In this orientation,  FIG. 1  is a top plane view of the power generation system  100 . For purposes of illustration only, all four vanes  122  are shown fully extended, so as to illustrate how the vanes  122  are coupled to the masts  124 . Each vane  122  is pivotably coupled along one edge of the vane to the corresponding mast  124  with an attachment means  128  such that the vane  122  may swing about the mast  124  when a flow pressure from the flow medium is exerted against the vane. Various suitable means of attachment are conceivable. In the embodiment shown, the attachment means  128  comprises a plurality of rings that are attached to the upper edge of the body of the vane  122  and that allow the vane to swing freely about the mast  124 . The energy-capture means  120  further comprises motion restraint means  126  which serves to convert the motion of a vane under forward flow conditions to rotational motion on the rotor shaft  112 . There are many ways in which this can be accomplished.  FIGS. 1-3  illustrate a first embodiment of the motion-restraint means  126 , which is a system of flexible connectors that connects each vane  122  to an adjacent mast  124 . By “flexible connector” is meant a coupling means that is capable of exerting a pull force, but incapable of exerting a push force. Thus, for example,  FIG. 1  shows four vanes  122 , designated individually  122 A,  122 B,  122 C, and  122 D, and four corresponding masts, designated individually  124 A,  124 B,  124 C, and  124 D. The plurality of flexible connectors  126  are similarly designated  126 A,  126 B,  126 C, and  126 D. Each flexible connector  124  couples a lower edge  122 X of one vane with the outer end  124 X of the mast  124  of an adjacent vane  122 . Thus, for example, a first flexible connector  126 A flexibly couples the lower end  122 X of the vane  122 D with the outer end  124 X of the mast  124 A. Additional embodiments of the motion-restraint means  126  are discussed below in conjunction with  FIGS. 4 and 5 . 
     Referring to the description above, with the rotor shaft installed vertical to the ground,  FIG. 2  is an elevational view of the power generation system  100  according to the invention. The power generation system  100  is installed in the flowpath of a body of water that has a rather strong current, such as a stream or river. The flow direction FD is into the plane of the drawing sheet, as indicated by the tail of an arrow FD. The vanes  124 A and  124 C are aligned perpendicular and the vanes  124 B and  124 D aligned parallel to the flow direction FD. Flow pressure against the vanes  122 A and  122 C exerts a force on the body of the vanes in the flow direction FD. Vane  122 C appears foreshortened, because the flow is forcing it to swing about the mast and extend downstream in the flow direction at some angle from the vertical. The flexible connector  126 D, which couples the lower edge of vane  122 C with the outer end of the mast  124 D, obscured from view by the rotor shaft  112 , is incapable of exerting a push on the mast  124 D and, thus, the pressure exerted on vane  122 C is not transmitted as a force to the mast  124 D. The body of the vane  122 A is constrained by the flexible connector  126 B from moving in the downstream direction. This places the flexible connector  126 B in tension, which exerts a pull to the right on the mast  124 B, which in turn transmits a rotational force to the rotor shaft  112  in the direction indicated by arrow RD. The vanes  122 B and  122 D, being oriented essentially parallel to the direction of flow in this view, do not exert any pull forces on the adjacent masts  124 C and  124 A. If the direction of flow were reversed, the flow force would push against the rear side of vane  122 C, which would be constrained from swinging about its mast  124 C by the motion-restraint means  126 D. This would effectively pull the mast  124 D (obscured from view) toward the left, again transmitting a rotational force to the rotor shaft  112  in the same direction indicated by arrow RD. In this manner, pressure from the flow medium past the vanes  122 , regardless of direction of flow, causes the rotor shaft  112  to rotate in a single direction. 
     Now referring to  FIG. 3 , the power generation system  100  is installed with the rotor shaft oriented parallel to the flowpath of the flow medium. This parallel set-up is particularly suitable for installations in which the rate of flow is relatively fast, such as in the presence of high wind velocities, high pressure resulting from a waterfall, etc., because the rotor shaft  112  does not have to withstand the high wind velocities.  FIG. 3  is a top plane view of the power generation system  100  in this parallel set-up, under conditions of high flow, with the vanes  122  extending in the downstream flow direction. Each vane deflects in the downstream direction, which places each some tension force on each of the flexible connectors  126 A- 126 D, which in turn exerts a rotational force on each of the masts  124 A- 124 D. Assuming the flow medium flows with even strength over the power generation system  100 , each vane  122  deflects approximately to the same degree, thereby exerting approximately the same amount of force on each mast  124 , which in turn forces a rotation of the rotor shaft  112 . The power generation system  100  in this parallel orientation may also be used as a brake for water- and aircraft. 
       FIGS. 4 and 5  illustrate additional embodiments of the motion-restraint means  126 . In the first embodiment discussed above, the motion-restraint means  126 ′ is a flexible connector that links the outer lower corner of one vane with the outer portion of the mast of an adjacent vane. It is also possible to have a motion-restraint means  126  that is mounted either on the respective mast  124  or on the rotor shaft  112  such that the restraint allows the respective vane  122  to swing about the mast  124  in one direction, yet restrains the vane from swinging in the opposite direction. Such motion-restraint means  126  encompass rigid fixtures or frames that are mounted on the masts or on the rotor shaft and may be combined with the attachment means  128 , for example, the attachment means may allow rotational motion in one direction only.  FIG. 4  illustrates motion-restraint means  126 ′, that include rigid stops or bars that are mounted on the respective masts  124 A- 124 D. The stops or bars are mounted on the mast so that they are behind the vane with respect to the desired direction of rotation.  FIG. 4  illustrates an instantaneous view of the power generation system  100 , showing a set of bars  126 C′ mounted on the front side of the vane  122 C, a set of bars  126 A′ mounted on the rear side of the vane  122 A, and a set of bars  126 B′ mounted on the left side of the vane  122 B. Vane  122 C appears foreshortened, because is extends downstream as indicated by the flow direction arrow FD.  FIG. 5  illustrates the motion-restraint means  126  mounted on or incorporated into the construction of the rotor shaft  112 , whereby the vanes  122  are in the same position as in  FIG. 4 . Again, the motion-restraint means  126 ′ are provided behind the particular vane  122  with regard to the desired direction of rotation. 
     One of the advantages of the power generation system  100  according to the invention is that the direction of flow is not critical to efficient functioning of the system. Should the direction of flow of the flow medium be other than parallel or perpendicular to the presenting surfaces of the vanes, the motion-restraint means  126  that couples the vanes  122  to the masts  124  ensures that the flow pressure exerted on the vanes will be transmitted as a rotational force to the rotor shaft  112 . The forward flow and the reverse flow components, whether in parallel and perpendicular orientation to the rotor shaft, will contribute proportionally to the rotational force. This ability makes the power generation system  100  particularly suitable for use in turbulent flowpaths in which flow direction changes rapidly and radically. A further advantage of power generation system  100  according to the invention is that electrical power generating components may be mounted on the system above or below the waterline. In areas that are not view sensitive, for example, it is desirable to mount the rotor, generator, and electrical energy transmission equipment above the water line and/or remote from the energy capture means, for cost reasons. Equipment that is not submerged in water is easier to install and maintain, and, consequently, less costly. 
     It is understood that the embodiments described herein are merely illustrative of the present invention. Variations in the construction of the power generation system may be contemplated by one skilled in the art without limiting the intended scope of the invention herein disclosed and as defined by the following claims.