Surprisingly efficient and inexpensive: How to easily generate electricity from rain.

A research team from Singapore has developed a promising method to generate electricity from falling rain - and surprisingly efficient at that.

The new technique is based on vertically standing, conductive-coated tubes through which rainwater flows intermittently. This so-called plug-flow movement generates significantly more electricity than a steady stream of water.

In the experimental setup, scientists used tubes with a height of 32 centimeters and an inner diameter of two millimeters. Inside, a special polymer ensures electrical conductivity. Raindrop-sized droplets are supplied from above, forming short columns of water with air bubbles upon impact in the tube. This irregular, discontinuous movement causes the electrically charged particles in the water - positively charged H+ ions and negatively charged OH- ions - to separate more spatially. This creates a voltage that can be measured and used via electrodes on the tube.

Compared to previous experiments with continuous water flow, the new system achieves significantly higher efficiency. Researchers speak of a theoretical power density of around 100 watts per square meter - a value that is about five orders of magnitude above previous rain-based experiments.

The key to success lies in the flow behavior: the abrupt movement allows ions to move further away from the surface of the tube than would be possible with a steady stream of water. This surpasses a previously considered physical limit, the so-called Debye length. This discovery is a breakthrough, as the low contact area of water with solid surfaces was previously seen as a limiting factor for energy generation from precipitation.

In practical tests, four of the tested tubes provided enough power to permanently light a dozen LEDs. The tests also showed that the system can be easily scaled. Combining two tubes - side by side or end-to-end - doubles the amount of energy produced. However, the effect does not increase with tube lengths exceeding 32 centimeters.

The new technology could be used in the future as a cost-effective and environmentally friendly supplement to conventional hydropower. Unlike large dams or turbine systems, the system does not require large amounts of water or complex infrastructure. Instead, it is particularly suitable for urban areas, such as rooftops or gutters, as well as remote areas without access to the power grid. The researchers see their development as a practical solution for decentralized power generation and a new way to use precipitation as a renewable energy source. The system is not only technically convincing but also easy to install and low maintenance - and could help advance the energy transition.