Harnessing the Energy of Aluminium

Batteries built for the sea have the power needed for underwater drones and ocean sensors.
23 March, 2017
Underwater UUV drones are necessary for defense applications and private industry – think offshore oil and gas operations.
Even so, their use has always been limited by less than optimal battery technology. There's never been a solution that made it easy and cost effective to just launch a UUV from shore and eliminate the need for a support vessel and crew to deploy, operate and retrieve the drone.

For example, the distance from the mainland to oil and gas operations in the Gulf of Mexico far exceeds the current UUV range. For a standard, out and back UUV about 53 centimeters long, the usable range limits the usefulness of the device to near-shore pockets near Houston, Texas, and in and around New Orleans in southern Louisiana. Yet most pipelines and offshore platforms located much farther out than that, with many in the 300 to 400 kilometer ranges. While the drone technology exists – and so do the advantages – there's just no good way to power them over these long distances.
Image: Linkedin
"Despite roughly order-of-magnitude increases in power and energy offered by new technologies, power and energy are still an issue for torpedo-like AUVs," was the conclusion of one RAND study of defense capabilities that lamented the current reality. "Power and energy technologies for traditional, torpedo-like AUVs are deemed immature."

That's the problem that an American company has been working on, and now they have developed an alternative battery based on aluminium with the potential to deliver 10 times the battery life and range than alkaline, lead-acid and other battery combinations that have historically limited use of the drones.
Built by Open Water Power (OWP), the batteries rely on cells that have a block of aluminium as the anode and use nickel as the cathode. As they alternate in an electrolyte bath derived from the seawater itself, they deliver the energy needed for undersea views and operations delivered through the UUV. There's some potassium hydroxide dissolved into the solution too, which is important because it prevents the anodes from getting clogged with aluminium hydroxide produced in the chemical reaction.
The clogs always cut short the battery life in previous attempts to design a viable underwater battery, but the OWP team, which began its work at Massachusetts Institute of Technology, thinks they have it figured out. Their version includes a foam rubber plug held in a separate chamber of the battery.

The plugs are ejected when they are full of the aluminium hydroxide they've collected, and a fresh one begins its work. There are enough plugs loaded into the device to match the lifespan of the aluminium supply, giving the battery a vastly extended life cycle to support a range of underwater UUV missions. Using the potassium hydroxide instead of pure water cuts the speed at which the clogs are formed too.
Preliminary safety tests conducted by the United States military found that the batteries met their match, performing well over "a range of abusive conditions that would typically cause lithium-ion and even silver-zinc batteries to fail dangerously."

The next test of OWP's technology will come this summer, when the firm will fit batteries into UUVs built by Riptide Autonomous Solutions. Those tests will look at real-world operational ranges for the oil and gas industry, which OWP expects can be extended to cover nearly the entire northern part of the Gulf of Mexico, from Texas to Florida.
Banner image: Saab Group