This patent application relates to hydrokinetic turbines, and more particularly to arrays of hydrokinetic turbines.
Hydrokinetic turbines are a type of renewable energy device, designed to gain the energy of flowing water without the need for conventional hydroelectric facilities such as dams. Hydrokinetic turbine systems may be installed in natural streams, such as rivers, ocean currents, tidal estuaries, and also in some human-made waterways and canals. Hydrokinetic turbine systems may also be used in ocean-energy structures, which can extract energy from tidal and marine currents.
The hydrokinetic turbines are designed to be installed underwater, in floating, fixed, anchored, or towed configurations. The turbines drive a rotor connected to a generator. These systems may be in any place where the effective water flow has a sufficient minimum speed to generate energy.
Hydrokinetic turbines can be characterized by their rotational axis orientation relative to the water flow direction. One type is an axial flow turbine, with a horizontal axis, parallel to the water flow. The second type, a cross flow turbine, has either a horizontal axis or a vertical axis, perpendicular to the flow direction.
Most axial-flow hydrokinetic turbines are “lift-based” as opposed to “drag-based”. Lift-based, axial-flow turbines generally use the same principles as aircraft wings, propellers, and wind turbines.
A more complete understanding of the present embodiments and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings, in which like reference numbers indicate like features, and wherein:
The following description is directed to a modular hydrokinetic turbine system, having an axial rotor configuration. Multiple blade modules are arranged in series on a single rotor shaft. The modular approach allows for high power per installation, minimal downtime for module swaps due to damage, high economy of scale at low installation volumes, and flexibility in source customization with standardized equipment. Reaction and hydraulic forces acting on the turbine system are low, allowing a design with a minimized support structure. This drives manufacturing costs down.
Modular turbine system 10 is comprised of blade modules 11 and support modules 12. Blade modules 11 are installed atop support modules 12 to result in a series of assembled turbine system modules that run lengthwise down the water stream.
In the example of
Each blade module 11 has a blade set 11a and a rotor shaft portion 11b. When system 10 is assembled, the rotor shaft portions 11b are connected lengthwise to provide a rotor shaft, which drives a generator 13 to generate electrical power. The power is delivered to whatever infrastructure is appropriate for the hydrokinetic application.
The blade modules 11 and the generator 13 are supported by the support modules 12, which rest on the bottom of the water stream. System 10 may be installed by first laying support modules 12 onto the stream bed and connecting them together. The blade modules 11 are then attached atop support modules 12. However, there are various installation alternatives such as by first connecting all support modules 12 then laying them onto the stream bed, or by first assembling each blade module 11 to one or more support modules 12 and then connecting those module sets together in the water stream.
As is evident from the description herein, the modular hydrokinetic turbine system 10 mitigates support requirements for both length and width by utilizing the length inherent in the structure, reducing cross-sectional profile. It requires mainly shear at the surface of the stream bed, thereby reducing the force normal.
As illustrated, the water flow presents to the blade set 11a of a first blade module 11. Each additional blade set 11a faces the water flow. As further described below, the blade modules 11 are spaced apart so that wake losses are minimized and activation of the blades of each module is optimized.
Each blade module 11 has a blade set 11a, a rotor shaft portion 11b, and a rotor shaft coupling 35. Rotor shaft couplings 35 attach rotor shaft portions 11b of the blade modules 11 together, resulting in a rigid rotor shaft that runs the length of the system 10, from the first blade module 11 to the generator 13, and uses the energy from all blade sets 11a to drive the generator.
Each blade set 11a comprises a number of lift-type axial rotor blades. In the example of this description, each blade set 11a has three blades, but more or fewer could be used.
As discussed below in connection with
A single generator 13 is aft of the last blade module 11. Generator 13 is generally cylindrical, thereby having a rounded face toward the water flow direction. This face has a small area relative to the water flow, resulting in minimal reactive force from the presence of the generator in the flow. In other embodiments, generator 13 may be fore of the first blade module 11.
In the example of this description, each support module 12 has rigid parallel rails and rigid angled truss members, securely attached to each other. The parallel rails rest on the bottom of the stream bed, and the angled truss members support the rotor shaft. This results in a triangular or “A-shaped” support frame, but other configurations are possible. Common features of the support modules 12 are that each support module 12 has at least one horizontal bottom piece that secures the system on the bottom of the stream bed and at least one upright piece to which the blade modules may be attached in a manner that allows the blades to properly rotate.
The ends of the various pieces of the support modules 12 have support module couplings 36, which allow easy connection of a number of support modules 12 in series. As stated above, the support modules 12 allow the entire support frame of turbine system 10 to be assembled and installed independently of the blade modules 11 if desired.
The water flow presented to the first blade set 11a has a mean flow velocity, u. This blade set 11a results in a wake and a mean flow velocity deficit.
The mean flow velocity deficit decreases with the wake distance. In the example of
In the example of
Various features may be added to subdue loading on the turbine blades. Specifically, the incidence angle of the blades can be made to passively vary depending on current velocity. This will help prevent blade failure when the current velocity is high.
Each bushing 93 holds the blade 91 in place with a rotor seat 101. A spring 102 is placed between the rotor seat 101 and a stopper 103. The spring 102 is preloaded using the hydrokinetic load as calculated from maximum current velocity. A net load exceeding the spring force represents a safety margin. If desired, for low current energy conversion, springs may be used on both sides of the rotor seat.
Thrust mitigation may be provided with a thrust bearing in the generator 13 or with thrust mitigation at the support modules 12.