Researchers at Nanjing University of Aeronautics and Astronautics in China have developed a floating device that can harvest energy from falling raindrops.
Raindrops are more than just a source of fresh water – they also carry untapped energy that falls freely from the sky. Scientists have long sought to capture this natural resource, but traditional droplet electricity generators face challenges such as low efficiency, heavy materials and limited scalability.
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The new device directly incorporates natural water as part of its structure, offering a lightweight, cost-effective and environmentally friendly approach to renewable energy.
Conventional droplet electricity generators typically rely on a rigid substrate and a metal bottom electrode to produce electricity when raindrops strike a dielectric film. While capable of generating hundreds of volts, these designs are heavy, expensive and limited by the use of solid construction materials. By contrast, the new water-integrated device floats directly on a body of water, with the water itself serving as both the supporting substrate and the conductive electrode. This nature-integrated design reduces material weight by about 80 per cent and cost by about 50 per cent compared to conventional systems, while delivering comparable electrical performance.
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When raindrops fall onto the floating dielectric film, the incompressibility and high surface tension of water provide the mechanical strength needed to support the impact, allowing droplets to spread effectively. At the same time, ions in the water act as efficient charge carriers, enabling the water to function as a reliable electrode. Together, these properties ensure that the floating generator produces high peak output voltages – around 250 volts per droplet – on par with conventional devices that rely on metal electrodes and rigid substrates.
Durability is another strength of the design. Tests showed that the generator maintained performance across a wide range of conditions, including varying temperatures, salt concentrations and even exposure to outdoor lake water with biofouling. Unlike many energy devices that degrade in harsh environments, the floating generator continued to operate stably thanks to the chemical inertness of its dielectric layer and the resilience of its water-based structure.
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To further enhance stability, the team exploited water’s high surface tension to design drainage holes that allow water to pass downward but not upward, creating a self-regulating system for removing excess droplets. This innovation ensures that the device avoids water accumulation, which could otherwise reduce output.
The device also offers impressive potential for scalability. The researchers demonstrated a 0.3-square-metre integrated device – significantly larger than previously reported droplet generators – that could power 50 LEDs simultaneously. The integrated system also charged capacitors to useful voltages within minutes, showing the potential to power small electronics and wireless sensors. With further development, such systems could be deployed across lakes, reservoirs, or coastal regions, where they would harvest renewable electricity without occupying valuable land resources.
‘By letting water itself play both structural and electrical roles, we’ve unlocked a new strategy for droplet electricity generation that is lightweight, cost-effective and scalable,’ said Professor Wanlin Guo. ‘This opens the door to land-free hydro-voltaic systems that can complement other renewable technologies such as solar and wind.’
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The implications of this work extend beyond rainwater harvesting. Because the device floats naturally on water surfaces, it could be deployed in diverse aquatic environments for powering environmental monitoring systems, such as sensors that track water quality, salinity, or pollution. In regions with frequent rainfall, it could provide a distributed energy solution that supplements local grids or powers off-grid applications. Moreover, the concept of ‘nature-integrated design’ – using abundant natural materials such as water as functional components – could inspire new approaches in green technology.
The researchers note that while the laboratory results are promising, challenges remain before large-scale deployment. Real raindrops vary in size and velocity, which could affect performance, and ensuring the integrity of large dielectric films in dynamic outdoor conditions will require further engineering. Still, the demonstration of a durable, efficient and scalable prototype marks an important step toward practical applications.
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The research has been published in National Science Review.