Solar Cells Charge Robots Underwater
The ocean is a vast and mysterious place full of untapped energy potential. Huge machines have been built already to harness the power of waves and tides and groups are investigating the possibility of floating wind turbines. The U.S. Naval Research Laboratory is exploring another source: underwater sunlight.
Researchers there have built photovoltaic solar cells that are able to collect sunlight down to 30 feet below the surface and convert it to electricity. The energy could be used to power sensors or autonomous research devices designed to monitor ocean environments.
In the past, such devices have had to rely on long power cords or onboard batteries that die too fast or corrode in the salt water environment. Other sources of power include above-water solar cells built on platforms, which are cumbersome and costly.
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For this technology to work, the researchers, lead by Phil Jenkins, had to first analyze the kind of photons that were penetrating the water.
"We first studied the spectrum of filtered sunlight underwater and then designed a cell to best match the environment," Jenkins told Discovery News. Not surprisingly, a higher percentage of blue and green wavelengths of light made it below the water's surface.
Next, they had to figure out the best kind of solar cell for the job. Previous methods of collecting sunlight penetrating underwater relied on conventional crystalline silicon or amorphous silicon solar cells, which are designed to collect the full spectrum of lightwaves from the sun. Gallium indium phosphide solar cells (GaInP), are better suited for the blue and green spectrum and work in low light conditions.
To test the solar panels, Jenkins and his colleagues encased a gallium solar cell and a silicon solar cell in a glass sphere along with pressure sensors and a spectrometer, and then lowered it 30 feet into the ocean. The sensors measured the solar intensity and spectrum. The deeper into the water the GaInP cells went, the less interference they got from other wavelengths of light, making the collection of energy easier and more efficient.
So far, seven watts per square meter were collected from the cells at a depth of no more than 9.1 meters. This is enough energy to power a small AUV used by the laboratory for researching underwater ecosystems.
Because the solar cells work better in dark underwater conditions, solar-powered research vessels may be able to stay under longer. This isn't something that would directly affect consumers, but for scientists it's a big deal. Continuous solar power means more research time and less energy usage. And that means more time to research the ocean floor, the environment and to find even more of those creepy new species and organisms we keep hearing so much about.