By Emily Vidovich. Emily has a background in environmental journalism and sustainability and is a member of the George Washington University Class of 2019.

While there is an abundance of renewable energy sources on the surface of the ocean, including solar, wave, and wind power, methods for generating electricity within the ocean’s depths are less developed. A company called Seatrec is unlocking underwater energy production by designing and manufacturing technology that creates renewable energy from the naturally occurring temperature differences in ocean water. 

Seatrec’s modules are designed to be affixed to robots that move up and down the water column collecting data for oceanographers. The technology generates electricity by using phase change materials (PCMs)—substances that expand when heat changes them from solid to liquid. As the robots rise towards the surface and the water temperature increases, the solid wax PCM within Seatrec’s system melts and expands in volume. This change in volume causes the liquid wax to be pushed through a pipe system, and it spins a generator as it circulates. The rotating generator creates electricity, which is then stored in a rechargeable battery. 

A diagram showcasing how phase change materials turn a generator when they expand from solid to liquid. Credit: Seatrec

Since this system activates every time the robot it is attached to moves from cooler to warmer waters, robots rising to the surface are automatically able to regenerate the energy expended exploring the depths of the ocean. Consequently, having an attached, renewable source of electricity enables longer and more complex missions unhindered by energy limitations.

Yi Chao, the founder and CEO of Seatrec who holds a Ph.D. in Atmospheric and Ocean Sciences from Princeton University, is known as the “armchair oceanographer” due to his tendency towards seasickness. Chao jokes that he wants to send robots out to sea in a sustainable manner so that he doesn’t have to go himself.

According to Chao, powering underwater robots is one of the biggest challenges facing oceanographers. Typically, the robots and sensors used by oceanographers require batteries to operate, which means that either a ship must be deployed to facilitate battery changes or equipment is left in the sea once the battery is depleted. Both options are considerably costly and resource-intensive.

Seatrec’s SL1 creating renewable energy under the ocean’s surface. Credit: Seatrec

With Seatrec’s technology, there is now a third option. Providing a sustainable, unlimited power source that is attached to research equipment simultaneously removes the need to send out a research vessel and reduces the likelihood of equipment abandonment. Supplanting traditional batteries also benefits the marine environment by reducing battery pollution from unrecovered research equipment.

While the concept of transforming thermal energy to electricity using ocean temperature changes was originally developed by Henry Stommel in 1989, only over the past decade has science developed to the point where such a system could be built on the small scale necessary to affix it to an underwater robot. Seatrec’s main focus has been developing this technology to this end, but that is not the system’s only potential use. The United States Office of Naval Research has sponsored Seatrec’s research into increasing the energy output of their system so that it can be used to create large-scale submerged charging stations for underwater naval vessels.

Seatrec’s products are currently more expensive than the environmentally unfriendly traditional battery, a common problem emerging green technologies face as they attempt to supplant unsustainable alternatives. But as Seatrec transitions from the lab testing phase to commercial availability, Chao remains optimistic that the company can work with early adopters and government agencies to make their innovations more cost effective.

Ultimately, Chao’s vision is to use underwater renewable energy to power diverse industries, from research to defense to aquaculture. Above all, he hopes Seatrec’s technology can facilitate an expansion of environmental data collection and deep sea monitoring. He hopes to see tens of thousands of robots exploring the ocean powered by an energy source that is “renewable, unlimited, and sustainable.”

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