Scientists make electricity from falling rainwater

April 18, 2025

Researchers from Singapore have developed a clever way to turn raindrops into electricity – enough to power 12 LEDs for 20 seconds using nothing more than a small vertical tube and some carefully timed droplets.

The study demonstrates how a phenomenon known as plug flow – in which all particles in a give cross-section have identical velocity and direction of motion – can dramatically boost electricity generation from falling water.

According to Siowling Soh, PhD, an associate professor at the National University of Singapore and the study’s corresponding author, when two materials come into contact, the charged entities on their surfaces get a slight nudge, similarly to the static electricity that builds up when you rub a balloon against your skin.

Since water flowing over certain surfaces can gain or lose charge, the team set out to harness this effect by generating electricity from rain-like droplets moving through a tube.

From raindrops to electricity

“Water that falls through a vertical tube generates a substantial amount of electricity by using a specific pattern of water flow: plug flow,” Soh explains. “This plug flow pattern could allow rain energy to be harvested for generating clean and renewable electricity.”

The chemical engineering expert explains that while running water can generate electricity by turning a turbine, hydroelectric power is limited to areas with abundant water sources, such as rivers.

That’s why for smaller and slower volumes of water, an alternative approach is to harness charge separation, which is a process that generates electrical charges as water flows through a channel lined with a conductive inner surface. However, this method has proven to be highly inefficient, as it only generates charge along the surface the water flows over.

In the past, scientists have attempted to boost its efficiency by increasing the surface area using micro- or nanoscale channels for continuous water flow. Yet, water doesn’t naturally pass through such tiny spaces, and forcing it through requires more energy than the system can produce.

To overcome this challenge, Soh and his team developed a straightforward setup using larger channels that rainwater could easily pass through.

In their design, water flowed from the bottom of a tower through a metallic needle, releasing rain-sized droplets into the opening of a 12-inch-tall (32-centimeter) and 2-millimeter-wide vertical polymer tube.

How it works

The device relies on the motion of rain-sized droplets falling into a slim vertical tube. When the droplets hit the top, they form short slugs of water separated by pockets of air, a pattern that enhances charge separation as the water moves downward.

This segmented flow allows electrical charges to build along the conductive inner surface of the tube. The water is then collected in a cup at the bottom, where wires at both ends capture the electricity generated during its descent.

Impressively, the system converts over 10 percent of the falling water’s energy into electricity, thus significantly outperforming the output from a continuous water stream by five orders of magnitude.

Although the droplet speeds used in the experiment were slower than natural rainfall, researchers believe the setup would be even more effective in real conditions. In follow-up tests, the researchers observed that moving water through two tubes, either simultaneously or sequentially, generated double the energy.

They then decided to put this insight into practice, and channeled water through four tubes. The system was then able to power 12 LEDs for 20 seconds, ultimately demonstrating its potential for simple, sustainable energy generation on rooftops and other urban surfaces.