Affordable, Scalable, Ocean Energy Harvesting System

The proposed ocean thermal energy harvesting approach is applicable to Slocum gliders, fixed-site power plants, and drifting or moored UUV charging stations. The temperature-induced buoyancy changes are driven by high-surface-area Shape Memory Alloy material that undergoes crystalline structure changes (Austinite - Martensite) when warmed or cooled by seawater. SMA produces useful linear strains of 5 to 8%. The strains can be directly used to create temperature-induced buoyancy changes by compressing and expanding a number of small spheres. SMA buoyancy engines have the potential to create a 19% buoyancy change over a 20 degree C temperature change when used in a closed thin spherical shell that is gas-precharged. Unlike a liquid-solid phase changes, the crystalline phase change contracts when heated and expands when cooled. As a result, the buoyancy changes are directly useful in ocean thermal energy harvesting. There is no need to pump a fluid in and out of a pressure vessel to get the temperature change in phase with the volume change. The high surface area per unit mass of thin shelled SMA spheres allows very high rates of heat transfer thereby dramatically improving the power output of a system that harvests ocean thermal energy.