K Lin, YH Joo, S Helkin C Ham
This paper describes a novel design of a wave energy harvest device that utilizes a flywheel energy storage (FES) system to yield increased power generation. The buoy design is moored to the ocean floor via a cable; as the buoy is heaved vertically by ocean waves, the cable rotates a pulley which in turn drives the rotor of an onboard generator. A ratchet within the pulley allows the rotor to only be turned in one direction. To prevent large tensions from begin imposed on the cable by the back torque from the generator, a flywheel energy storage system is used. As the buoy is heaved vertically by incident waves, the electric load on the generator is removed, resulting in all of the energy extracted by the buoy to be stored in the flywheel system. Consequently the buoy is less restricted by high tensions and able to closely follow the motion of the waves, even while using a large generator with a high back torque coefficient. As the buoy moves downward after being heaved, the load is re-coupled to the generator, transferring the energy stored by the flywheel to the generator. Essentially the FES system trades power generation time for improved buoy motion. The focus of the paper is not to optimize the design of the buoy, but rather demonstrate the effectiveness of the FES system for the buoy design with arbitrary parameters. Simple simulations for a small buoy confirm the effectiveness of the proposed flywheel energy storage system—without it the wave energy harvest device produced only 90.0watts of power, but with it the device produced 180.3watts—an improvement of 100%. This improvement is based on a small generator with low back torque coefficient; for a large-scale design and stronger generator, the benefits are expected to be even greater.