A robotics startup has developed underwater drones powered by renewable energy harvested from temperature differentials in the water — part of a vision to, as the company's chief executive says, save the ocean "one battery at a time."
California-based Seatrec was founded in 2012 to commercialise Dr. Yi Chao's energy harvesting technology, originally developed at NASA's Jet Propulsion Laboratory. "Our goal is to deploy our energy harvesting system to use renewable energy to power those robots [performing monitoring tasks at sea]," explains Chao in an interview with IEEE Spectrum. "We're going to save one battery at a time, so hopefully we're going to not to dispose more toxic batteries in the ocean."
The company's key product is the SL1 Thermal Energy Harvesting System. As the name suggests, it captures energy from temperature differences in the thermocline — a layer within the water in which the temperature changes more rapidly than elsewhere. As the pod moves up and down a tether, it charges an internal battery — and the company is working on modifying drones to use the same system.
"We just attach the backpack to the robots," Chao tells IEEE Spectrum, "we give them a cable providing power, and they go into the ocean."
The energy harvesting system works through a phase-change material which shifts as it is exposed to the different temperatures throughout the thermocline — harvesting energy from both the transition from solid to liquid and from liquid to gas, with the energy then recovered as the phase-change material is cooled and returns to a solid again.
The SLG Thermal Energy Harvesting System is the drone-based equivalent to the SL1. Designed in an underwater glider form-factor, and to be made available as a modular retrofit for existing drones, the SLG is a fully autonomous drone capable of operating as deep as 1,000m and able to generate 20kJ of energy per cycle — up from 8kJ in the SL1.
More information on the company's work is available on the official website.