A new way of generating clean power could run your lights with rain.
Hydropower typically relies on the movement of water to create electricity through mechanical energy, such as spinning turbines in a dam. But a new method, described April 16 in ACS Central Science, skips the mechanics and harnesses tiny bursts of energy sparked when rain plunks into a narrow tube.
“There is a lot of energy in rain,” says Siowling Soh, an engineer at the National University of Singapore. “If we can tap into this vast amount of energy, we can move toward a more sustainable society.”
Soh and colleagues’ technique relies on charge separation, a process where oppositely charged particles become spatially divided, creating a voltage between them. It’s the same phenomenon as shuffling across a rug then getting zapped when touching a light switch.
Power wash
Water flowing in a tube can build up an electrical charge, sometimes large enough to harness for energy. But there are many ways the water can move — depending on the width of the tube compared to the flow and whether air ends up interspersed with the water. The panels below show five flow scenarios, each illustrated and photographed, ordered from most electrical power generated (left) to least (right).
Previous experiments have found that water running through a conductive tube also creates charge separation. As the water flows, negatively charged hydroxide molecules accumulate on the tube’s surface, leaving an excess of positively charged hydrogen ions in the water. But the amount of charge separation is negligible, and the energy produced is outweighed by the power needed to pump water through the system. Soh wanted to find a way around that.
Instead of using a continuous flow of water, he and his team dripped rainlike drops into a tube two millimeters wide, about the width of a grain of rice. Inside the tube, the water driblets flowed with air pockets between them, creating a movement pattern called a plug flow. Plug flows trigger higher amounts of charge separation than continuous flows, Soh says, resulting in roughly 100,000 times as much energy.
After traveling the length of the tube, each charged droplet fell into a stainless steel cup. Wires connected to the tube and the cup allowed the built-up charge in each to power circuits, creating an electric current. The plug flow from four 32-centimeter-long tubes for 20 seconds produced enough electricity to continuously power 12 LED lightbulbs during that time.
“We think it will be helpful in rainy places, including tropical countries like Singapore,” Soh says.
The method could be scaled up by installing rain-catching tubes on roofs or next to water sources that create spurts of water ideal for plug flow, such as waterfalls.