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Future underwater robots could charge their batteries by eating fish poop

Luke Dormehl
The U.S. Navy wants to find a way to create underwater robots that can stay submerged for longer. Their idea? Giving it special batteries that can be recharged by eating fish poop.

The U.S. Navy is interested in underwater robots which could be used for a wide range of applications, from surveillance missions to carrying out inspection or exploration tasks. But, just as is the case with airborne drones, underwater robots face one of their biggest challenges in the limited amount of battery life that they possess. This severely limits certain possibilities, particularly when it comes to long-haul missions which require them to stay submerged for lengthy periods of time.

Fortunately, a solution may be on hand — and while it’s far from glamorous, it could nonetheless prove to be a game-changer for swimming robots when their power reserves run low. The idea: To utilize microbial fuel cells which feed on organic matter on the seabed. In practical terms, what this means is that it would power itself by chowing down on fish poop.

The microbial fuel cells would harvest this, err, material, which should be in plentiful supply in all but the deepest parts of the ocean, and then convert it into electricity. “It’s like a battery made by biology,” Meriah Arias-Thode at the Naval Information Warfare Center Pacific in San Diego, told New Scientist.

So far, the team showcased the use of three microbial fuel cells in powering an assortment of basic sensors, including one for monitoring water acidity levels. While these devices are ordinarily able to last just a few weeks underwater, a sensor powered using the microbial fuel cells meant that they could last for eight months.

It’s possible that this same technology could be used to power underwater robots entirely, rather than just their sensors. Because of the low power density of microbial fuel cells (it would take approximately one year for the current units to charge even a small underwater drone), an array of these fuel cells could be used. The Navy could also develop lower-powered underwater vehicles which do not have the same battery demands.

Possibly the most promising solution would be to develop large battery packs on the seabed, which could be used to charge underwater drones so that they could stay submerged for long periods of time. Watch this space.