Scientists at the U.S. Naval Research Laboratory in Washington, said underwater autonomous systems and sensor platforms are severely limited by the lack of power sources, having to rely on on-shore power, batteries or solar power supplied by an above-water platform.
Attempts to use photovoltaic solar cells have had limited success due to the lack of penetrating sunlight, as most current solar cells are optimized to use the terrestrial solar spectrum, they said.
"Although water absorbs sunlight, the technical challenge is to develop a solar cell that can efficiently convert these underwater photons to electricity," Phillip Jenkins of the NRL Imagers and Detectors Section said.
The filtered spectrum of the sun underwater is biased toward the blue/green portion of the spectrum, researchers said, requiring solar cells well matched to the wavelength range.
Using high-quality gallium indium phosphide cells, researchers said they've managed outputs of 7 watts per square meter, sufficient to harvest useful solar power at depths commonly found in nearshore zones.