Solar Cells Use Underwater Sunlight for Electricity

Underwater sensors and systems are a huge help to scientists who are trying to monitor data from the ocean. Sticking an autonomous sensor in the water and leaving it to collect information -- from pollution levels to temperature and salinity -- is a lot easier than having to repeatedly go out on a boat and monitor it by hand. However, it is tough work to try and keep a full battery charged and running systems and sensors used underwater. Typically, these devices and systems rely on power created on dry land, or at least solar cells located up at the surface. However, the U.S. Naval Research Laboratory has made some interesting strides in being able to produce electricity using solar cells placed underwater.

Gizmag writes, "Water absorbs much of the spectrum of sunlight – blue-green light is the last portion of the spectrum to be absorbed, and thus penetrates the farthest below the surface. Because traditional topside silicon solar cells are designed around the full solar spectrum, this leaves them little to work with when placed underwater. It turns out, however, that gallium indium phosphide (GaInP) cells are highly efficient at converting light within the less intense blue-green wavelength into electricity. When used at depth underwater, GaInP cells receive nothing but the wavelength that they are optimized for, allowing them to perform much better than regular silicon cells under the same conditions."

"The use of autonomous systems to provide situational awareness and long-term environment monitoring underwater is increasing," said Phillip Jenkins, head, NRL Imagers and Detectors Section. "Although water absorbs sunlight, the technical challenge is to develop a solar cell that can efficiently convert these underwater photons to electricity."

The scientists have been able to get 7 watts per square meter from GalnP cells placed no deeper than 9.1 meters. This isn't much electricity, but it is enough to power a small device used by the Naval Research Laboratory. Perhaps this new type of solar cell will get ocean researchers a little closer to having autonomous sensors working for long stretches of time on clean energy.

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