For decades, hydropower has been synonymous with massive dams and giant turbines. Research from Singapore, however, points to a far simpler approach: raindrops falling through a small plastic tube can generate electricity. In laboratory tests, the system was even able to power 12 LED lights for 20 seconds.
The study, conducted by a team of scientists from the National University of Singapore, exploits a specific flow pattern known as plug flow. Unlike continuous water flow in ordinary pipes, plug flow forms short columns of water separated by pockets of air as the droplets fall through a vertical tube. This rhythmic pattern turns out to be the key to electricity generation.
The findings were published in the journal National Science Review and are described as a breakthrough that could open new ways of harvesting renewable energy from rainfall.
How Can Raindrops Generate Electricity?
The device itself is remarkably simple: a plastic tube measuring 32 centimeters in height with an inner diameter of just 2 millimeters. At the top, water droplets comparable in size to rain are fed into the tube.
Instead of forming a continuous stream, the water organizes itself into bead-like segments separated by air. This configuration enables electrical charge separation between the water and the inner surface of the tube. The principle is similar to static electricity generated when two different surfaces come into contact.
As water flows along a solid surface, charge exchange occurs through a process known as contact electrification. Negative ions tend to adhere to the tube’s surface, while positive charges move along with the flowing water.
Until now, electricity generation based on water–solid contact has been considered inefficient, because charge separation only occurs within an extremely thin region at the liquid–solid interface, known as the electric double layer.
This physical limitation—defined by the Debye length—means that power output from conventional continuous water flow is very small, especially in channels larger than the micrometer scale.
The plug-flow pattern overcomes this constraint. Using a tube 32 centimeters long and 2 millimeters in diameter, the system achieved an energy conversion efficiency of more than 10 percent and a power density of around 100 watts per square meter—about five orders of magnitude higher than conventional continuous-flow approaches.
In experiments, a single tube generated approximately 440 microwatts. When four tubes were operated in parallel, the combined output was sufficient to power 12 LED lights.
Energy Potential from Rooftops
The main advantage of this system lies in its simplicity. No dams, turbines, or large-scale infrastructure are required. It relies solely on gravity and a stable flow of water—resources that are naturally available in regions with high rainfall, or even from runoff collected on building rooftops.
Tests show that the system functions reliably with various types of water, including tap water, saltwater, hot water, and cold water. Power output also increases linearly as more tubes are added, making the concept inherently scalable.
Interestingly, natural raindrops reach a higher terminal velocity than the controlled flows used in laboratory experiments. In theory, this means the actual energy potential under real rainfall conditions could be even greater.
The discovery also offers a fresh perspective on atmospheric electrical phenomena, such as the negative charges commonly observed around waterfalls or breaking ocean waves, effects that may involve similar intermittent flow patterns.
That said, further studies are still needed to assess material durability, integration with building systems, and the consistency of electricity generation under real-world weather conditions.
Even so, the findings point to a compelling possibility: rain, long viewed merely as part of the water cycle, also carries mechanical energy that can be converted into clean electricity.
