NASA, US Navy and university researchers have successfully demonstrated the first robotic underwater vehicle to be powered entirely by ocean thermal energy. The Sounding Oceanographic Lagrangrian Observer Thermal RECharging (SOLO-TREC) autonomous underwater vehicle uses a novel thermal recharging engine powered by the natural temperature differences found at different ocean depths.
Special Phase Change Materials (PCMs) contained in 10 external tubes on-board the SOLO-TREC expand about 13% when heated above 10 °C and then correspondingly contract when cooled below 10 °C. This expansion/contraction produces a high pressure oil that can be collected and periodically released to drive a hydraulic motor for electricity generation and battery recharging.
Since its deployment, SOLO-TREC has completed more than 300 dives from the ocean surface to a depth of 500 meters (1,640 feet). Its thermal recharging engine produced about 1.7 watt-hours, or 6,100 joules, of energy per dive, enough electricity to operate the vehicle’s science instruments, GPS receiver, communications device and buoyancy-control pump.
Scalable for use on most robotic oceanographic vehicles, this technology could usher in a new generation of autonomous underwater vehicles capable of virtually indefinite ocean monitoring for climate and marine animal studies, exploration and surveillance.
Researchers at NASA’s Jet Propulsion Laboratory, Pasadena, Calif.; and the Scripps Institution of Oceanography, University of California, San Diego, completed the first three months of an ocean endurance test of the prototype vehicle off the coast of Hawaii in March.
People have long dreamed of a machine that produces more energy than it consumes and runs indefinitely. While not a true perpetual motion machine, since we actually consume some environmental energy, the prototype system demonstrated by JPL and its partners can continuously monitor the ocean without a limit on its lifetime imposed by energy supply.—Jack Jones, a JPL principal engineer and SOLO-TREC co-principal investigator
SOLO-TREC is now in an extended mission. The JPL/Scripps team plans to operate SOLO-TREC for many more months, if not years.
The present thermal engine shows the great promise in harvesting ocean thermal energy. With further engineering refinement, SOLO-TREC has the potential to augment ocean monitoring currently done by the 3,200 battery-powered Argo floats.—Russ Davis, a Scripps oceanographer
The international Argo array, supported in part by the National Oceanic and Atmospheric Administration, measures temperature, salinity and velocity across the world’s ocean. NASA and the US Navy also plan to apply this thermal recharging technology to the next generation of submersible vehicles.