Researchers from the Woods Hole Oceanographic Institution (WHOI) and Webb Research Corporation (Falmouth, Mass.) have successfully deployed an "environmentally powered" marine robotic vehicle. The new robotic "glider" harvests ocean heat and uses the harvested energy to adjust buoyancy, sufficient to "glide" itself over great distances while collecting oceanographic data. See explanation below.
In December 2007, a research team led by oceanographers Dave Fratantoni of WHOI and Roy Watlington of the University of the Virgin Islands launched a prototype "thermal glider" off the coast of St. Thomas. The vehicle has been traveling uninterrupted ever since, crisscrossing the 4,000-meter-deep Virgin Islands Basin between St. Thomas and St Croix more than 20 times.
...Gliding underwater vehicles trace a saw-tooth profile through the ocean's layers, surfacing periodically to fix their positions via the Global Positioning System and to communicate via Iridium satellite to a shore lab.
...The new thermal glider draws its energy for propulsion from the differences in temperature—thermal stratification—between warm surface waters and colder, deeper layers of the ocean. The heat content of the ocean warms wax-filled tubes inside the engine. The expansion of the warming wax converts heat to mechanical energy, which is stored and used to push oil from a bladder inside the vehicle's hull to one outside, changing its buoyancy. Cooling of the wax at depth completes the cycle.
Should a Japanese factory ship mistake it for tasty source of sushi; or, should the glider become caught in a gill net, the GPS system would at least allow researchers to recover the expensive device.