How the floating droplet electric generator advances hydrovoltaic technology
Producing electricity from rain has long been one of the most ambitious goals in emerging energy research, a way to harness even the cloudiest days. The science is well established, yet existing devices are still too costly and bulky to scale effectively. A team at Nanjing University of Aeronautics and Astronautics is now addressing this gap with a new floating droplet electric generator that is lighter, more affordable, and capable of delivering performance comparable to conventional systems.
What is hydrovoltaic technology?
The field involved here is known as hydrovoltaic technology, a broad category of approaches that produce electricity through the direct interaction between water and functional materials.
One of the most active research lines focuses on droplet based electricity generators, or DEG. These devices represent an evolution of triboelectric nanogenerators, systems that harvest low frequency and low power energy by coupling triboelectrification with electrostatic induction.
More specifically, DEGs are solid liquid triboelectric nanogenerators that generate electricity when falling droplets make contact with a charged material. Traditional DEGs rely on a layered design in which a dielectric material is connected to an upper and a lower electrode, with the lower one resting on a rigid substrate. The working principle is described by the Chinese research team in their National Science Review paper:
“When a falling droplet strikes the dielectric layer, the support from the substrate enables it to spread at high speed and touch the upper electrode.” This triggers “an instantaneous charge transfer from the lower electrode to the upper one, driven by electrostatic induction, because the dielectric surface is generally negatively charged due to contact electrification, producing an electrical output.”
In simpler terms, each droplet that lands and spreads on the DEG surface acts as a temporary switch, closing the circuit and enabling the pre existing electrostatic field to generate current.
From DEG to water based W-DEG
On paper, this technology can produce hundreds of volts. In practice, its use has been limited by the rigid, expensive materials required for solid substrate devices.
This is where the team at Nanjing University of Aeronautics and Astronautics introduces a major design shift. The new device is engineered to float on water. In this configuration, the water itself serves as both the substrate and the lower electrode, significantly reducing weight and cutting costs in half.
To build the W-DEG, the researchers used a fluoropolymer dielectric film with a metal wire attached to the top to function as the upper electrode. The other end of the wire is placed directly in the water.
How the floating droplet electric generator works
“When a raindrop lands on the floating dielectric film, the underlying water provides the force needed to absorb the impact thanks to its incompressibility and surface tension. This allows the droplet to spread more effectively across the surface. At the same time, the ions in the water act as charge carriers, enabling the water layer to operate as a reliable electrode.”
The result is a device capable of delivering peak voltages of around 250 volts per droplet, matching the performance of solid substrate DEGs while weighing just one fifth as much.
The W-DEG also proved capable of operating across a wide range of ambient temperatures and salt concentrations.
Potential applications
The prototype tested by the team, a 0.3 square meter integrated unit, successfully powered 50 light emitting diodes simultaneously and charged capacitors to useful voltages within minutes.
“By allowing water itself to play both a structural and electrical role, we have opened a new pathway for lightweight, low cost, and scalable droplet based electricity generation,” said Prof. Wanlin Guo, corresponding author of the study. “This approach paves the way for hydrovoltaic systems that do not require solid ground and can integrate with other renewable technologies such as solar and wind.”
The findings are detailed in the article by Wei Deng, Zihao Wang, Jingmin Wang, Tao Hu, Xiao Wang, Xuemei Li, Jun Yin, and Wanlin Guo, Floating droplet electricity generator on water, National Science Review, Volume 12, Issue 11, November 2025, https://doi.org/10.1093/nsr/nwaf318