The Hanna MultiDrive
U.S. Patent 8,745,981
"Ocean Powered Take-off for Multiple Rotary Drives"
The simple sketch above, illustrates the Hanna direct drive power take-off (PTO) for wave energy conversion. The illustration is an artist's rendering that shows how this versatile primary drive might be utilized in a buoy application. The rendering is not an accurate representation of how the buoy would look. The actual buoy has a long hollow Tail Pipe (Acceleration Tube) suspended well below the surface. Inside the Tail Pipe is the Drive Float. This is the only PTO component that is immersed in sea water. For increased power capture, the buoy uses reactive phase control which is achieved by pneumatic "latching". This mechanism induces a resonant response delay, allowing the buoy and the Drive Float to move independently from each other for maximum energy absorption in normal or irregular wave periods. Lightweight, non-corrosive materials are integrated throughout the design.
To be successful, wave energy converters must be uncomplicated and easy to maintain. Only two gears are actively engaged during the up or down strokes. The final drive, a flywheel, spins multiple generators at high speeds for maximum power output. The system operates at low friction with only six bearings. All bearings and generators are off-the-shelf items.
The base of the Main Shaft is attached to an internal Drive Float which is contained inside the hollow Tail Pipe. The Pipe has openings below and above the water surface. Thus, the Tail Pipe is a typical Oscillating Water/Air Column system. However, the offshore buoy design is but one application for this versatile primary drive. Near or on shore MultiDrive PTO's can be built into a jetty or placed on top of monolithic, pre-cast concrete breakwaters. The PTO can be integrated into the design of off shore oil rigs and floating wind and wave harvesting structures.
The reciprocating Main Shaft is a linear rack gear that drives two rotary pinions. But this is by no means a common rack and pinion set up. By a proprietary arrangement of gears that are serially engaged, the bi-directional linear movement caused by waves is directly converted into a unidirectional rotary force. This rotational, one-way force efficiently drives multiple generators and/or hydraulic or seawater pumps in one continuous direction.
The Hanna PTO design is less complicated with greater energy capture than devices that use roller screw or variable winch designs. Variable winch designs rely on a spring mechanism that is tethered to the sea floor. Spring loaded systems have high maintenance demands. Long-term survivability is poor due to dynamic metal fatigue imposed by cyclic stresses on the mechanism.
Any developer or electric utility provider that wants to maximize power output and lower O&M costs, would benefit by using the MultiDrive system. It uses 100% of the wave cycle. With a favorable wave climate, the MultiDrive PTO will turn a plurality of generators continuously, in only one direction. The generators will produce a smooth and sustained power output. The design directly couples a unidirectional flywheel to the generators. The flywheel's mass and angular momentum provides high rotational speeds that will exceed the back torque (armature reaction) developed by the multiple generators under load.
An alternative to using multiple independent generators would be to eliminate the induction-type generators altogether and utilize the flywheel as a stand-alone permanent magnet synchronous generator (PMSG). Powerful magnets will be located in the flywheel's outer periphery. A fixed ring of windings wrap around the spinning magnets and will generate utility-scale power for the grid. The Hanna MultiDrive will use a specialized, low-speed generating topology which has been designed specifically for wave energy converters. The PMSG has the ability to maintain power regardless of fluctuating, low speeds and variable load conditions. This technology virtually eliminates the large unwanted magnetic attraction forces that exist in conventional generators.
The highly adaptive MultiDrive system can double its energy harvesting capabilities if used in conjunction with the patented Hanna Turbine (U.S. patent 8,358,026). The added turbine(s) could provide power to the grid or be used as a back up power source to charge batteries and other onboard energy needs. A buoy farm or shore-based power plant that leverages these combined technologies would have the greatest level of reliability and survivability of any other wave energy conversion system currently in the world market.
The videos shown above demonstrates how the rise and fall of ocean waves are converted into a rotational force. In the full-size, utility-grade device, the flywheel will turn freely under its own momentum between irregular wave sets. The flywheel's spinning mass will provide a sustained wave-to-wire efficiency over a wide range of sea conditions.
Contact WETGEN if you would like to learn more about this transformative wave energy technology. To read the Hanna MultiDrive patent, click HERE. There you can view computer generated videos of the device in action. The animated graphics show how the Hanna MultiDrive converts ocean waves into clean, renewable energy. A simple, cost-efficient system.
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