Lotus‑Leaf‑Inspired Carbon Fiber Generator Harvests Raindrop Energy for Self‑Powered Systems

Researchers at the Department of Mechanical Engineering, Ulsan National Institute of Science and Technology (UNIST), have announced a breakthrough technology that harvests electrical energy from raindrops falling on rooftops. The system—named the *S‑FRP‑DEG* (Static‑Field Rod‑Composite Droplet Electricity Generator)—uses a lotus‑leaf‑inspired coating on a carbon‑fiber composite substrate to produce useful voltage and current without any external power source. **Mimicking Nature’s Hydrophobic Surfaces** The lotus leaf remains pristine in rain due to its microscopic, densely packed protrusions that range from 3 to 10 µm in height. These structures reduce the liquid–surface contact area, causing water droplets to bead and roll off. The UNIST team replicated this effect on a carbon‑fiber composite by etching irregularities into the surface and applying a hydrophobic, high‑dielectric coating. When a raindrop lands, the bead‑shaped droplet briefly touches the composite, allowing the opposing charge of the drop and the surface to interact. **Static‑Like Charge Separation** The operation of the generator is rooted in electrostatic charge transfer. A raindrop, carrying a net positive charge, contacts the negatively charged composite surface. As the bead rapidly detaches—within microseconds—the two oppositely charged bodies separate, driving the excess charge through the conductive carbon fibers. This transient event creates an electrical current, analogous to the familiar static discharge phenomenon. In laboratory tests, a single 92‑µL drop produced up to 60 V and several microamperes of current. When four units were serially connected, their cumulative voltage was sufficient to light 144 LED bulbs instantly, demonstrating a practical conversion of rain energy into visible power. **Material Advantages for Outdoor Deployment** Traditional droplet generators built from metal surfaces suffered rapid corrosion when exposed to acidic or pollutant‑laden rainwater. By employing carbon‑fiber composites—known for their high strength‑to‑weight ratio and inherent corrosion resistance—UNIST eliminated this limitation. The lightweight yet robust substrate is compatible with roofing applications and can serve as a structural element itself. Moreover, the lotus‑leaf‑derived coating resists adhesion of soot and other urban pollutants. This ensures that the generator’s performance remains stable over long periods of exposure to harsh city environments. **Real‑Time Rainfall Sensing** Beyond power generation, the team demonstrated a rain‑detection principle by attaching the generators to roof edges and drainage ducts. Because the frequency of electrical signals emitted by the generator is directly proportional to the rainfall rate, the system can function as an instant sensor, enabling automated control of drainage systems or fire‑alarm triggers during heavy precipitation. "With no external power requirement, buildings, bridges, and other urban infrastructure could be monitored and protected against flooding simply by harvesting rainwater," Professor Park Young‑bin, lead researcher, said during a press briefing. **Future Directions** The group plans to explore the integration of the S‑FRP‑DEG into mobile platforms where carbon‑fiber composites are already standard, such as lightweight aircraft and high‑speed vehicles. In these contexts, the generator could supply self‑powered auxiliary systems, reducing overall energy consumption. This innovative work was funded by the National Research Foundation of Korea (NRF) under the Mid‑career Researcher Program and was published online on November 20 in the peer‑reviewed journal *Advanced Functional Materials*. --- Dr. Lee Sung‑hwan and researcher Kim Jae‑jin served as co‑first authors on the study, reflecting the collaborative effort across multiple disciplines within UNIST. The breakthrough represents a significant step toward harnessing ambient mechanical energy for sustainable, self‑regulated urban infrastructure.