Mention renewable energy and most people will instantly think of hydro, solar, and wind power. However, not only sunlight, wind and large amounts of water can be harnessed to generate electricity. So can natural phenomena such as the evaporation of water. Or raindrops, for that matter.
Scientists at the City University of Hong Kong have devised a way to harness the kinetic energy of the falling drops. Thanks to a special device, they can generate enough power from a single raindrop to power 100 small LED bulbs, according to a new study published in the journal Nature.
"Our research shows that a 100 microliter drop of water released from a height of 15 centimeters can generate a voltage of more than 140 V, and the energy generated can light up 100 small LED lights," explains biomedical engineer Wang Zuankai, who led the research.
Rain drops can be harnessed to generate energy due to triboelectric effect, a form of contact electrification by which certain materials become electrically charged after coming into contact with a different material.
However, the amount of energy previously obtained in this way was quite low. To improve the conversion efficiency, the university research team has created a specially designed drop-based electricity generator (DEG), which has a polytetrafluoroethylene (PTFE) film attached so that it can maintain a surface charge while being bombarded. by drops of water, as in the rain.
When water droplets hit the surface, they act as a "bridge" connecting two electrodes, one made of aluminum and the other made of indium tin oxide (ITO), which is mounted on a glass base. Thanks to its device, a high surface charge density can be accumulated from the falling raindrops, so the stored charges can be released to generate electric current in a highly efficient way.
Although the device is still in its early stages, it could one day be installed on different surfaces where liquid frequently comes into contact with a solid. "This can range from the surface of the hull of a ferry to the surface of umbrellas or even inside bottles of water," the scientists explain.