The Office of Naval Research is funding a project called “SOLO-TREC” (Sounding Oceanographic Lagrangian Observer — Thermal RECharging), that uses the temperature difference in layers of the ocean to generate electricity and propel a ship theoretically indefinitely.
SOLO-TREC has a series of tubes full of waxy phase-change materials, which expand when the float encounters warm temperature near the surface of the ocean. The materials contract when waters get cooler, as the float dives into the ocean. This expansion/contraction of the material pressurizes oil, driving a hydraulic motor.
This motor generates about 1.6 watt-hours of electricity, recharging the batteries, which power a pump. The pump can change the float’s buoyancy, moving it up and down the water column.
“In theory what you have now is unlimited endurance for something that has this type of engine,” said Thomas Swean Jr., team leader for ocean engineering and marine systems at the Office of Naval Research, which funded the project. “Other things can break, but as far as the energy source, it will only stop working if the ocean ran out of energy, which is unlikely to happen … One of the Navy’s goals is to have a persistent presence in the world’s oceans. This is the type of technology that leads you to that.”
SOLO-TREC has been launched last November, and has just been approved for an extended research mission.The thermal engine behind SOLO-TREC has been designed by NASA’s Jet Propulsion Laboratory and the ONR, while the University of California at San Diego designed the 180 pounds scuba tank-looking vessel.
Up to now, SOLO-TREC dived 430 times to about 500 meters, each time producing enough energy to power its onboard instruments, buoyancy pump, GPS receiver and satellite communication devices. You can track the current position of SOLO-TREC here.
In theory, this thermal engine could run as long as there is a temperature gradient in the ocean, and even in the oceans of other planets or moons, like Saturn’s Europa, toward which NASA targeted their interests. Still, there’s a lot of research to be done on this type of engine, but the results so far look encouraging.