Thursday, June 14, 2012

Navy Invents Underwater Solar Cells

By Jason Mick (blog), June 11, 2012

Humans learn the secret that kelp has enjoyed for millions of years

Whether it’s underwater research buoys or reconnaissance submersibles, a key challenge facing all small autonomous floaters/divers is power. Batteries, after all, only carry so much charge and any kind of moving parts or broadcast hardware can rapidly deplete that charge.

Researchers at the U.S. Naval Research Laboratory (NRL) are looking to borrow a page from Mother Nature's playbook and develop solar cells optimized for underwater devices. Currently such devices have three options -- batteries, on-shore power, or attached solar cells that float on the ocean's surface.

Phillip Jenkins, head, NRL Imagers and Detectors Section, headed the study to make underwater cells that can produce a decent amount of power. He explains the challenges, commenting, "The use of autonomous systems to provide situational awareness and long-term environment monitoring underwater is increasing. Although water absorbs sunlight, the technical challenge is to develop a solar cell that can efficiently convert these underwater photons to electricity."

While underwater light is less intense, it is in a narrower band of spectrum, so underwater cells do have the advantage of only having to capture a narrower color range -- a common source of inefficiency in terrestrial cells.

The NRL team has completed preliminary testing and has shown that gallium indium phosphide (GaInP) cells handily outperform their silicon-based counterparts.

The GaInP photovoltaics are very efficient at harvest light of wavelengths between 400 and 700 nm -- in the realm where most ocean light is concentrated.  Further, they are enhanced by a low dark current, which allows them to operate efficiently erven in low light conditions.

At a depth of 9.1 meters, the GaInP cels were nearly three times as efficient.  The NRL team estimates that at that depth a one meter panel could produce seven watts of power, demonstrating its feasibility for numerous applications.

 While the price of the GaInP cells might bre slightly to substantially higher than silicon panels, depending on the film design, for the Navy, efficiency might trump cost.

It would be easy to imagine these cells to power small, unmanned submersibles that patrol the waters for long periods without rest, similar to continuously-airborne solar-powered UAV fliers, another current field of military research.  Both applications could see drones deployed for months or even years without having to be touched by human hands.

And who knows, maybe some day these cells could be employed to power shallow-sea ocean colonies (popular science fiction fodder).

Source: U.S. Navy Research Lab

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