The sea's thermal energy is powering a new submersible vehicle: the Sounding Oceanographic Lagrangrian Observer Thermal Recharging vehicle, or just Solo-Trec.
After five years of research between NASA's Jet Propulsion Laboratory, the U.S. Navy and USCD's Scripps Institute of Oceanography, an underwater robot has covered a total of 100 miles of sea floor off the coast of Hawaii. The automotive vehicle runs completely on energy collected from the change of water temperatures between different ocean depths. Solo-Trec's trek is shown in the image below.
Traveling between the surface and 1,640 feet down, Solo-Trec produces about 1.7 Watt-hours each dive. This power fuels the vehicle's on-board sensors, GPS, communication device and buoyancy-control pump. Starting at the end of November, the 183-pound robot made around 3 to 4 dives each day, totaling more than 300 trips.
Solo-Trec has 10 external tubes that contain phase-change materials (PCMs). These waxy substances either expand or contract as Solo-Trec moves between shallow, warmer waters or deep, cooler waters. Rising toward the sea's surface, the vehicle's PCMs melt and expand, pressurizing an oil held within the float. The oil drives a hydraulic motor that generates electricity and charges the Solo-Trec's batteries. The batteries then operate the float's hydraulic system.
JPL Engineer Jack Jones says in a statement:
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.
Among the military applications, non-stop data collection and surveillance could come in handy for climate monitoring, biological research and mapping the bottom of the sea.