An anonymous reader writes about a new robot submersible that uses temperature differences in the sea to power operation for more than twice as long as previous, battery-dependent vehicles. "The torpedo-shaped glider moves through the ocean by changing its buoyancy to dive and surface, unlike motorized, propeller-driven undersea vehicles. To power its propulsion, the submersible gathers thermal energy from the ocean. When it moves from cooler water to warmer areas, internal tubes of wax are heated up and expand, pushing out the gas in surrounding tanks and increasing its pressure. The compressed gas stores potential energy, like a squeezed spring, that can be used to power the vehicle. To rise, oil is pushed from inside the vehicle to external bladders, thus increasing the glider's volume without changing its mass, making it less dense. The oil can be shifted inside to increase the density and sink the vehicle."