A robotic underwater glider deployed by the Woods Hole Oceanographic Institution and the Webb Research Corporation keeps itself powered in a way that's bound to make Mother Nature happy while gathering oceanographic information — using changes in water temperature.
Known as thermal stratification, bodies of water tend to be warmer toward the top, where the sun's light penetrates its layers, and get colder the deeper you go. The thermal glider's engine contains wax tubes that, when warmed by the heat of the water, expand and that expansion is converted into mechanical energy. That energy then pushes oil from an internal reservoir to an external bladder, forcing a change in buoyancy and helping the glider dive. At the chilly depths, the wax compresses and oil once more enters the internal reservoir, causing the glider to rise.
The thermal glider has made several successful trips in the waters surrounding the Virgin Islands, and is equipped with GPS software just in case it gets lost or runs afoul of fishing nets.