Implementation of energy harvesting system for powering thermal gliders for long duration ocean research

The exploration of the Earth's oceans is aided by autonomous underwater vehicles (AUVs). AUVs in use today include floats and gliders; they can be deployed to profile salinity, temperature and pressure of the ocean at depths of up to 2 km. Both the floats and gliders typically control buoyancy by filling and deflating an external bladder with a hydraulic fluid delivered by an electrical pump. The operation time of an AUV is limited by energy storage. For floats, such as the Argo float, the operating duration is approximately 5 years with the capability to dive once every 10 days. For electric gliders, such as the deep G2 Slocum, the mission duration can be up to one year with lithium primary batteries. An energy storage system has been developed that can harvest energy from the temperature differences at various depths of the ocean. This system was demonstrated on an Argo style float and has been implemented in a thermal version of the Slocum glider. The energy harvesting system is based on a phase change material with a freeze thaw cycle that pressurizes hydraulic oil that is converted to electrical energy. The thermal Slocum glider does not use an electrical pump, but harvested thermal energy to control buoyancy. The goal for the thermal Slocum glider is for persistent ocean operation for a duration of up to 10 years. A thermal powered glider with an energy harvesting system as described can collect conductivity, temperature, and pressure data and deliver it to the National Data Buoy Center (NDBC) Glider Data Monitoring System and the World Meteorological Organization (WMO) Global Telecommunications System (GTS). Feeding into operational modeling centers such as the National Centers for Environmental Prediction (NCEP) and the U.S. Naval Observatory (NAVO), this data will enable advanced climate predictions over a timespan not currently achievable with present technology. Current testing of the thermal powered Slocum glider is to determine the durability of the technology and quantify the glider system design. Previous issues with this technology included energy storage system management and glider mechanical limitations. Our objective is to learn how to fly an energy harvesting thermal glider that interacts with the ocean environment efficiently. We would also like to establish the latitudinal range of operation. This thermal powered Slocum glider, dubbed Clark, after the famous explorer duo Lewis and Clark, has been deployed off of St. Thomas for flight dynamics and durability testing. The following paper will discuss the deployment and testing of the thermal powered Slocum glider. We will also discuss the advantages of ocean energy harvesting technology for oceanographic research.