Floating OTEC Plant—A Design and Coupled Dynamics

Ocean thermal energy conversion (OTEC) is a system that produces clean energy from the temperature differences in the ocean. Its power production is very stable and is expected to be implemented as a base-load power supply, despite using a natural energy source. In addition, this energy source would provide an attractive integration with other industries such as aquaculture with ocean nutrient enhancement, desalination, deep seawater cooling, and hydrogen production. Currently, a floating OTEC plant is in development toward a commercial-scale deployment. The floating plant is configured with a floating platform, mooring system, seawater intake pipe/inlet, and discharge pipe/duct. In particular, a cold water pipe (CWP) is the most challenging component in a commercial-scale OTEC. For a 100 MW-scale CWP, the length is 600–1000 m, and the diameter is over 10 m, designed to transport deep seawater at a flow rate of approximately 200 m3/s. Due to its size, there is a strong dynamic coupling between the floating platform and the mooring system, requiring a coupled analysis and an integrated design approach with other components. Meanwhile, one of the authors of this paper has proposed a 100 MW-net OTEC plantship for Indonesia, which utilizes a converted pre-owned ship to reduce capital costs. In this paper, a coupled dynamic analysis is performed for the preliminary design of the mooring system and CWP, along with a sensitivity analysis of the dynamic responses of the floating platform and CWP to design parameters. The results are used to discuss the dynamic characteristics and design methods for an OTEC floating plant, to improve reliability and further develop this floating structure concept.