Efficient Hydraulic-to-electric Energy Conversion for PCM-based Ocean Thermal Gradient Energy System to Power Uncrewed Underwater Vehicles

There have been numerous investigations into electrical energy storage types that use ocean thermal-to-electricity conversion techniques. Field tests have demonstrated that this technology is feasible for UUVs with long-term missions of over 3,000 km per deployment, most notably as vertical profiling sensors. Nonetheless, the energy generated by this method is not sufficient to meet the increasing energy requirements of Uncrewed Underwater Vehicles (UUVs) whose missions are expanding. The objective of this study is to design a highly effective ocean thermal gradient energy system to support long-term missions of a UUV. To enhance the performance of the thermal gradient energy system, we have developed a hybrid type (buoyancy regulation and electrical storage) Phase Change Material (PCM)-based energy harvesting system to facilitate efficient UUV operations. A prototype of the hydraulic-to-electric conversion system was developed, and experimental findings indicate that the hybrid system successfully delivers hydraulic energy for buoyancy change of profiling floats and improved efficiency of hydraulic-to-electric energy conversion, demonstrating its potential as a promising technology for supporting longer-term UUV missions that seek to increase the number of sensors and time at sea for data collection.