By Ysabel Yates
It sounds like a child’s question: can you generate solar power underwater? The answer, according to Phillip Jenkins and his team at the US Naval Research Laboratory, is yes. The researchers recently demonstrated a method for harvesting solar power underwater at depths of 30 feet.
Currently, the only option for underwater energy is batteries, which shortens the amount of time an underwater system can be powered. Having a source of renewable energy underwater opens up the possibility for long-term installations of autonomous systems, including systems for communication, environmental monitoring and networks of sensors.
Jenkins says the technology is meant to be “a new tool in the toolbox,” opening up further possibilities in renewable energy, and new options for powering underwater systems.
To date, the solar cells are capable of generating 7 watts of energy per square meter at depths of 9.1 meters, which is enough to demonstrate the technology’s potential for use in shallow water, such as in the areas near shorelines. (Above ground solar cells typically generate about 110-220 watts per square meter.)
To achieve this breakthrough in efficiency, the researchers needed a solar cell optimized to absorb the narrow wavelength spectrum of visible light available underwater. Instead of crystalline silicon solar cells or amorphous silicon cells, the researchers opted for high-quality gallium indium phosphide (GaInP) cells. GaInP cells are better at absorbing wavelengths in the blue/green spectrum, making them ideal for capturing light that has been filtered through water.
The researchers’ next step is to test how the technology will fare during long-term deployment. This includes understanding how water quality variations affect performance. “You see it in rivers” says Jenkins. “One day they’re murky, and one day they’re clear. Water quality varies all over the world, and we have to take this into consideration.”
In addition to understanding how water quality affects energy harvesting, the researchers need to test how the system will age and degrade. Speaking to the permanence of these solar installations, Jenkins says there is no reason why they couldn’t last a long time, providing they can withstand potential biofouling and sedimentation.
The development of efficient underwater solar cells is about creating options, because other renewable energy systems are not one-size-fits-all solutions. For example, other water-related renewables, such as wave power, operate at the water’s surface, limiting the scope of the power’s reach. Jenkins and his team aim to generate power at the bottom, which requires an underwater system.
This breakthrough has the potential to help everything from monitoring pollution levels to learning more about underwater creatures than ever before. Although underwater solar cells still have far to go before they are developed at the commercial scale, this development put the option of long-term underwater installations on the table, which is an exciting prospect for the future.