Most promising source of sustainable energy is ocean currents as the flow of water provides frequent and predictable energy. Ocean currents have excellent potential towards future renewable energy resources. There are various oceanic energy forms such as wave, marine currents, tidal currents, and thermal energy. In contrast the research and development are technically challenging and potentially expensive.
The Kuroshio current is a stout ocean current in the western North Pacific Ocean which tide steadily closer the Japanese seaside. This current was forenamed as an energy resource with only small fluctuations in flow, regardless of the time of day or the season and flow is almost 500 meter deep and 100 kilometer wide with a flow speed of 1 to 1.5 m/s. This materializes to be a fain slow flow, merely sufficient for generating electricity because the density of water is 800 times higher than that of air. Also Kuroshio current is said to has power density equivalent to that of a wind flow at 9 to 14 m/s.
Dr. Katsutoshi Shirasawa and colleagues from Okinawa Institute of Science and Technology Graduate University and Hiroshima University in Japan proposed a new ocean-current turbine which was designed with a float at its top and a counterweight at its bottom. Payable to buoyancy and gravity, the turbine maintains a stable position. Ocean-current turbine has many advantages for power production which includes stability, availability of large water flow, predictability of flow speeds and paths and no visual impact.
The research team experimented by attaching the turbine with a strut to a small fishing boat and towed to simulate an ocean current. Before towing, part of the float was slightly above the sea surface. The depth of the towing point was two metre below the surface. The tow rope was connected to the float and nacelle. In order for the turbine to operate in water, the rope connected to the float had a forward-bent posture. The output cable from the electric generator was connected to a resistive load on the boat. The electrical output was rectified from three-phase alternating current to direct current. The voltage and current of the load were then measured to determine output power
The authors study depicted the owing experiments bring to vindicate the float and counterweight configuration off and also to show that the results bear hydrostatic stability and electric power generation for the proposed turbine out. The ocean current turbine was operated within the flow to convert the kinetic energy of an ocean current into electricity.
After several experiments, they proposed a new marine current turbine with high hydrostatic stability. The rotor torque developed when the turbine was operated in the middle layer of machine current should be cancelled. Hence, they employed a turbine with a float at its top and a weight at its bottom. Thereby the kinetic energy of currents at sea is harnessed by the proposed marine current turbine to achieve stable power generation. Lately, optimization of the entire turbine system will be analysed using computational fluid dynamics.
Katsutoshi Shirasawa 1, Kohei Tokunaga2, Hidetsugu Iwashita2, Tsumoru Shintake1, Experimental verification of a floating ocean-current turbine with a single rotor for use in Kuroshio currents, Renewable Energy, Volume 91, 2016, Pages 189–195.
- Okinawa Institute of Science and Technology Graduate University, Onna, Okinawa 904-0495, Japan.
- Graduate School of Engineering, Hiroshima University, 1-4-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8527, Japan.
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