The sun reaches even where water filters it. At a depth of 10 meters in the South China Sea, a group of researchers tested photovoltaic cells capable of converting residual light into electricity. The results were published on September 11, 2026, in the journal *Joule*.
The test was conducted near the Weizhou Islands, off the southern coast of China. The modules, with a surface area of 115 square centimeters, generated 324 milliwatt-hours in two hours at a depth of 10 meters. At a depth of two meters, power output reached 1,416 milliwatt-hours. While this is a modest amount, it demonstrates that sunlight passing through water can power devices even at depths previously considered impractical.
The light that remains below the surface
The problem is physical. Water rapidly absorbs and scatters solar radiation, reducing the available energy. At a depth of 10 meters, only certain components of the spectrum reach the surface—specifically blue and green light. The research team has designed cells capable of harnessing those wavelengths. The technology uses wide-bandgap perovskites, photovoltaic materials different from the silicon used in most panels. In the device studied, the perovskite has properties that allow it to utilize the spectrum present at 10 meters.
In laboratory tests simulating those conditions, the cells achieved a conversion efficiency of 34.71%. This figure indicates what percentage of the light that reaches the cell is converted into electricity. The larger modules were then tested directly at sea.
From Batteries to Ocean Sensors
The main application proposed by the study involves equipment that must remain underwater for long periods. Oceanographic sensors, cameras, and communication systems are often far from power sources and rely on batteries. The modules powered lithium-ion batteries and LEDs, demonstrating the potential for integration with autonomous systems. According to Wen-Hua Zhang of Yunnan University and the Southwest United Graduate School in Kunming, “this work presents the first functional validation of submerged solar cells that actually operate at water depths of up to about 10 meters, significantly expanding their scope of application.” The statement was reported by Euronews.
The key issue is durability
The key issue remains durability. Accelerated testing recorded 48,094 equivalent operating hours and resulted in a T80 estimate of approximately 5.49 years at 10 meters. T80 indicates the time it takes for a device to decline to 80% of its initial performance. In laboratory tests, the cells also showed minimal performance loss after 1,160 hours under simulated underwater conditions.
The next step identified by the researchers will be to determine how deep this technology can continue to generate energy. Going deeper means dealing with even lower light levels and more challenging conditions in terms of efficiency and output. For now, the data collected at sea shows that at a depth of 10 meters, the photovoltaic system generated electricity even though the sunlight was already significantly attenuated.
