Although solar cells are proving indispensable for powering things such as electronic sensors on dry land, sensors located underwater have typically had to rely on batteries, or electricity piped in from photovoltaic panels situated above the surface. That could be changing, however, as scientists from the U.S. Naval Research Laboratory have recently developed functioning underwater solar cells.

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.

So far, it has been determined that GaInP cells placed at a maximum depth of 9.1 meters (29.9 feet) provide an output of 7 watts per square meter (10.8 sq ft) – enough to power a device such as an environmental sensor.