An Energy Self-Sufficient Underwater Profiling Buoy Powered by Ocean Thermal Energy

Abstract Unmanned underwater vehicles play an important role in ocean observation and exploration; however, they do not have long endurance due to energy limitations. This paper proposes an energy self-sufficient underwater profiling buoy that uses ocean thermal energy for buoyancy propulsion and as a power supply, to enable long-term ocean observations. Based on the principle of operation of the proposed buoy, an energy balance model is established that is used to calculate the energy captured by the heat exchangers and the energy consumption of the devices on board. The energy self-sufficiency rate is defined as an indicator for evaluating the impact of the key configuration parameters of the buoy on the energy self-sufficiency performance, which depends on the diving speed, diving depth, and system pressure of the accumulator. In addition, a buoyancy compensation unit with two accumulators is installed on the buoy to compensate for the impact of variations in seawater density on the buoyancy propulsion performance and to overcome buoyancy loss. When the diving speed of the buoy is around 0.24 m/s and the diving depth is above 900 m, the accumulator has an initial pressure of 10 MPa, a driving pressure of 11.1–17.9 MPa, and a charging pressure of 20 MPa, and the energy self-sufficiency rate of the buoy exceeds 100%. This work provides theoretical guidance for realising energy self-sufficiency for other unmanned underwater vehicles.