California-based Seatrec Inc. has come up with the first energy source for underwater robots that is completely powered by the environment and allows the devices to operate in the open ocean indefinitely, without any intervention. For ways to generate power, the company's engineers settled on phase-transition materials - that is, substances that transition between phases - typically between a solid and a liquid at certain desired temperatures. For the development, the engineering team chose a common material in the industrial-grade paraffin family with a melting point of about 50°F, which is between a typical deep ocean temperature of about 40°F and a surface temperature of about 70°F. The idea behind the development is that Seatrec's 2 SL1 modules attach to a robotic float and generate power through the volume changes that phase transition materials undergo as the float rises from colder deep water to warmer surface water. Seatrec plans to commercialize the system for underwater gliders. In the future, the company hopes to develop a power plant that will move phase transition material from liquid to gas through the depths of the ocean, creating an order of magnitude more energy that could recharge more power-hungry robots at sea.