Chinese Researchers Test Solar Panels That Work 10 Meters Underwater

Researchers in China have tested solar panels that generate electricity 10 meters (32 feet) beneath the surface of the South China Sea, using a solar cell specially designed for the dim, blue-green light that survives underwater. A team led by Wen-Hua Zhang of Yunnan University lowered a small underwater robot carrying the solar modules off China's Weizhou Island and left it there for two hours. The modules delivered 324 milliwatt-hours of energy into lithium-ion batteries, enough to later power an LED panel. The study is published in the journal Joule.

Sunlight changes as it passes through water. Red and infrared wavelengths fade quickly, so by a depth of 5 to 10 meters, the light that remains is dominated by blue-green wavelengths of roughly 400 to 600 nanometers. An ordinary solar cell, built for the full spectrum of sunlight on land, wastes much of its potential underwater. The researchers instead built a wide-band-gap perovskite solar cell, with a band gap of about 1.96 electron volts, tuned to respond strongly to that surviving blue-green light. They also added a polymer called PHMG, which helped the perovskite form a more stable crystal structure and reduced defects that can drain its electrical performance.

In laboratory tests designed to mimic sunlight 10 meters underwater, the small solar cells converted 34.71% of the light reaching them into electricity, compared with 17.08% under standard surface sunlight. The cells did not produce more electricity underwater overall, since far less sunlight reaches that depth in the first place; they were simply better at using the blue-green light that remained. A 2020 analysis in Joule had already calculated that underwater solar cells with a wider band gap could remain useful to depths of about 50 meters in very clear water.

Zhang said the practical operating depth will also depend on marine biofouling, floating debris and seawater corrosion, not light intensity alone. His team believes the technology could work at depths of 20 to 30 meters, and experiments are underway to test that. Zhang said underwater solar cells could become one part of a broader push toward "smart ocean" infrastructure, including autonomous underwater vehicles that need a steady source of power.