Recently, a research team at the Ulsan National Institute of Science and Technology (UNIST) in South Korea developed a droplet generator based on carbon fiber-reinforced polymer (CFRP) that converts the impact of raindrops into electrical energy to power rainwater management systems.
CFRP is lightweight and durable, widely used in aerospace and construction for its strength and corrosion resistance. These properties make it ideal for long-term outdoor installation on rooftops and other exposed urban structures.
Professor Young-Bin Park’s team from UNIST’s Department of Mechanical Engineering developed a superhydrophobic fiber-reinforced polymer-based droplet generator (S-FRP-DEG) using CFRP. This device converts rainfall impacts into electrical signals, enabling rainwater management systems to operate without external power sources.
Fiber-reinforced polymer (FRP) consists of carbon fiber fabric, carbon fiber tow (CFT), glass fiber fabric, and epoxy resin, offering a high strength-to-weight ratio and corrosion resistance.
Coating FRP with polydimethylsiloxane and polytetrafluoroethylene particles creates a superhydrophobic surface with a 167° water contact angle, enabling rapid droplet contact and large-area separation. The coating possesses self-cleaning capabilities, forming a negatively charged surface that enhances energy harvesting performance.
The power generation principle relies on electrostatic effects: when positively charged raindrops contact the negatively charged superhydrophobic surface, charges transfer along the rolling droplets, inducing current flow through embedded carbon fiber tow for instantaneous electricity generation.
Compared to traditional metal-based droplet generators susceptible to corrosion from humidity and urban pollution, this CFRP-based device overcomes these issues with superior durability and stability. The S-FRP-DEG exhibits enhanced resistance to moisture and contaminant corrosion. The research team further enhanced water repellency and reduced dirt accumulation by incorporating textured surfaces and a biomimetic lotus-leaf coating.
In laboratory tests, a single raindrop with a volume of approximately 92 microliters generated up to 60 volts and several microamperes of current. When four units were connected in series, the system briefly powered 144 LED lights, demonstrating its scalability.
The team also validated the technology’s practical application by installing the device on building roofs and drainage pipes. As rainfall intensity increases, electrical signals become stronger and more frequent, enabling the system to distinguish between light, moderate, and heavy rain and automatically activate drainage pumps when necessary.
The research findings have been published in Advanced Functional Materials. Professor Young-Bin Park stated that this technology holds promise for urban flood early warning systems and can be extended to energy harvesting systems for transportation vehicles such as automobiles and aircraft.