A team of Chinese and Swiss scientists say they have developed solar cells that can function 10 metres underwater, paving the way for submerged sensors, cameras, and communications systems to be powered by the sun while out at sea.
The researchers, writing in a study published in the journal Joule, explain that underwater solar energy harvesting currently remains an “unresolved challenge” due to what they describe as the “strong spectral attenuation of sunlight in water.”
Solar cells traditionally can only work in very shallow water – up to around two metres – therefore limiting practical applications in bodies of water.
“Very few studies have been reported on underwater solar cells, and all of them are focused on very shallow water depths of only two meters or less, a scenario far from catering for requirements of practical application,” said Wen-Hua Zhang, an author of the study from the Yunnan University and Southwest United Graduate School in Kunming, China.
“This work presents the first functional validation of submerged solar cells practically operating at a water depth of up to about 10 meters, greatly broadening their application scope.”
Utilising lead halide perovskite solar cells with absorption spectrally matched to the underwater solar spectrum at a depth of 10 metres, the scientists first undertook lab experiments, proving their solar cells were able to absorb blue to orange light.
After being stored in an oxygen-free glovebox for 300 days the solar cells were shown to retain about 96 per cent of their initial efficiency. The cells also showed almost no degradation after 1,160 hours under simulated conditions at a depth of 10 metres.
Taking their solar cells out of the lab, the researchers next submerged the solar cells aboard underwater robots off the Weizhou Islands in the South China Sea. Deployed at a depth of 10 meters, the solar cells exhibited “exceptional” long-term operational stability.
“What surprised us most was so much electrical energy our large-area modules generated under real-world conditions at 10-meter water depth for only two hours,” said Zhang.
“Moreover, we have achieved scaling from small‑area laboratory cells to large‑size modules.
“The combination of the laboratory investigations and the in-field experiments provides strong evidence for the operation of underwater photovoltaics.”
Zhang’s team will now move to test perovskite solar cells at deeper water depths in an attempt to determine the limit at which solar cells can operate, and to establish standardised testing protocols for underwater solar cells.
Even though the focus of solar PV electricity generation has been weaning humanity off fossil fuel sources on land, the researchers believe that there remain practical applications for solar cells to operate offshore underwater.
Applications such as monitoring aquaculture or offshore communication systems could both benefit from submerged solar generation.
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Joshua S Hill
Joshua S. Hill is a Melbourne-based journalist who has been writing about climate change, clean technology, and electric vehicles for over 15 years. He has been reporting on electric vehicles and clean technologies for Renew Economy and The Driven since 2012. His preferred mode of transport is his feet.
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