A team of researchers has discovered an ingenious way to convert falling water droplets, such as rain, into usable electricity. By directing droplets into narrow vertical tubes to create a "push flow," they were able to separate charges and harvest energy with surprising efficiency. This simple device not only overcomes the inefficiencies of traditional charge separation methods, but also generates enough power to light up 12 LEDs.
The innovative system has potential for applications on rooftops and in urban environments, providing a sustainable and low-cost alternative to hydroelectric power generation.
When two materials come into contact, charges on their surfaces are transferred—a common example is the static electricity created when a balloon rubs against skin. Likewise, when water flows over certain surfaces, it gains or loses electrical charge. Now, researchers reporting today (April 16) in ACS Central Science have harnessed this effect to generate electricity from raindrops flowing through thin tubes. The system generates enough electricity to light up 12 LED lights.
"Water falling through vertical pipes can generate large amounts of electrical energy through a specific water flow pattern called push flow," said Siowling Soh, corresponding author of the study. “This push-flow model can capture rain energy and use it to produce clean, renewable electricity.”
Water flows in short bursts, or plugs, through a thin polymer-coated tube, as shown in these illustrations and pictures, to generate electricity. Image source: Adapted from ACS Central Science 2025, DOI: 10.1021/acscentsci.4c02110
Traditional hydropower works by moving large amounts of water to drive turbines. But this only works in places with plenty of water, such as rivers. For smaller, slower flows, researchers explored an alternative: charge separation. When water flows through a channel with a conductive surface, the process generates electricity. However, this method is extremely inefficient because charge only accumulates on the surface where the water comes into contact.
To improve efficiency, scientists have tried using micron- and nanoscale channels to increase surface area. But these channels are too small for water to flow through easily—and pumping water through them takes more energy than the system can produce. To solve this problem, Soh, Chi Kit Ao and their team looked for a way to generate electricity using larger channels that would allow rainwater to flow through naturally.
The team designed a simple device in which water flows from the bottom of a tower through a metal needle, spraying raindrop-sized droplets into an opening in a 12-inch-high (32-centimeter), 2-millimetre-wide vertical polymer tube. The water droplets collide head-on at the top of the tube, creating a plug flow: a short column of water filled with air bubbles. As water flows through the tube, the charges separate. The water is then collected into a cup underneath the tube. Electrical energy is collected by wires placed on top of the tubes and in the cups.
The push flow system converts more than 10% of the energy of the water flowing through the pipe into electrical energy. Compared with continuous flow of water, the electrical energy generated by push flow is 5 orders of magnitude higher. Because the droplet speeds tested were much slower than rain, the researchers believe the system could be used to harvest electricity from falling raindrops.
In another experiment, the researchers observed that running water through two pipes simultaneously or sequentially doubled the amount of energy produced. Using this information, they flowed water through four pipes, and the device powered 12 LED lights continuously for 20 seconds. Researchers say push-flow energy could be simpler to install and maintain than hydroelectric plants, and could also be convenient for urban spaces like rooftops.
Compiled from /ScitechDaily