Could Rain Generate Electricity? A New Device Harvests Energy From Raindrops

For centuries, civilizations have harnessed energy from moving water. However, traditional hydroelectric power generally requires large bodies of water, such as rivers, to move heavy machinery. A new approach asks a different question: Could raindrops striking a rooftop generate useful electricity?

Researchers are exploring that possibility with a technology called a droplet-based triboelectric nanogenerator, or D-TENG. These devices use the triboelectric effect, in which electrical charges develop when two materials come into contact and then separate.

How raindrops can produce electricity

A familiar example of the triboelectric effect occurs when a balloon is rubbed against hair. The balloon and hair develop opposite electrical charges, causing the hair to stand up and stick to the balloon.

D-TENGs apply a similar principle to falling or sliding water. As a raindrop moves across a negatively charged surface, positive charge collects near the surface while negative charge is released. When the droplet reaches a metal electrode, the negative charges flow into an external circuit and generate electricity.

Traditional D-TENG designs have a drawback: water can remain on the electrode surface. The accumulated water blocks later droplets, reduces performance and may contribute to corrosion.

A needle-shaped electrode improves water removal

Researchers from China’s Three Gorges University and the Chinese Academy of Sciences addressed this problem by changing the shape of the electrode. Instead of using a flat strip, they proposed a needle-shaped electrode that could help droplets separate more quickly and allow the device to use less expensive components.

The resulting device is called a needle-electrode droplet-based triboelectric nanogenerator, or NED-TENG.

How the NED-TENG was built

To construct the NED-TENG, the researchers prepared a water-repellent plastic film made with polytetrafluoroethylene, or PTFE. The material served as the negatively charged surface.

A copper wire was inserted into the center of the film to create a needle-like electrode. The needle extended 3 millimeters, or about 0.1 inch, from the front of the film so that it could come into contact with raindrops. The researchers placed copper foil on the back of the film as a second electrode, completing the circuit.

They connected both electrodes to equipment that measured the device’s electrical performance, mounted the components on an acrylic plate and sealed them with waterproof tape.

Testing the rain-powered generator

To simulate raindrops, the team tilted the NED-TENG at a 50-degree angle and released tap-water droplets from a height of 30 centimeters, or about 12 inches, above the film.

Like a conventional D-TENG, the device generated electricity when a droplet slid across the film and touched the needle electrode. However, the needle contacted only a small portion of the water. As a result, the droplet could detach easily instead of pooling on the surface.

NED-TENG produced higher voltage and current

The researchers evaluated the device using two key electrical measurements: voltage and current. Voltage describes the force that drives charge through a circuit, while current describes the rate at which that charge moves.

Compared with a conventional D-TENG, the NED-TENG produced approximately 564 volts and 5 milliamps of current. That was nearly twice the voltage and three times the current produced by the traditional design. According to the researchers, the output was enough to power small electronic devices such as indicator lights.

The team also varied the height from which droplets were released. Increasing the height from 10 to 30 centimeters, or about 4 to 12 inches, increased both voltage and current. The device reached peak values of approximately 543 volts and 4 milliamps at a release height of 30 centimeters.

At greater heights, the droplets struck the surface too forcefully. The impact caused them to bounce or splash, disrupting the sliding and charging process.

The best angle was 50 degrees

The researchers tested tilt angles ranging from 10 to 70 degrees. Electrical performance increased as the angle became steeper, reaching a peak at 50 degrees with approximately 521 volts and 3 milliamps.

However, steeper angles also reduced the amount of time that each droplet remained in contact with the surface, which limited the electrical output. The researchers noted that triboelectric materials are highly sensitive, so measurements can vary slightly between experiments. This explains why individual peak values were lower than the device’s overall maximum output.

Multiple devices powered 200 LED lights

To examine how the technology might perform in a rooftop installation, the researchers connected multiple NED-TENG units. Combining the devices helped reduce fluctuations in the generated power.

Ten connected NED-TENGs charged small energy-storage components and powered 200 LED lights within two minutes.

Could rooftops become rain-powered generators?

Overall, the NED-TENG shed water more effectively, was easier to construct and produced more power than the conventional D-TENG design. The results suggest that needle-shaped electrodes could help overcome one of the main challenges facing droplet-based triboelectric generators: water buildup on the device surface.

The technology is not yet a replacement for conventional electricity generation or a solution for powering an entire home. However, it could eventually support small electronic devices and low-power systems in locations that receive regular rainfall.

The researchers said future, larger-scale studies should investigate how rooftop systems can direct rainwater to the devices at optimal heights. They also need to study how droplets interact with different surfaces over time to improve long-term performance.

With further development, low-cost NED-TENG systems could turn rooftops into small generators powered by daily rainfall.

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