Researchers from City University of Hong Kong (CityU) have recently developed a new type of generator that uses rain to create electricity. It features a field-effect transistor (FET)-like structure that allows for high energy conversion efficiency, and its instantaneous power density is increased by thousands of times compared to its counterparts without FET-like structure.
A conventional droplet energy generator based on the triboelectric effect can generate electricity induced by contact electrification and electrostatic induction when a droplet hits a surface. However, the amount of charge generated on the surface is limited by the interfacial effect, and as a result, the energy conversion efficiency is quite low.
In order to improve the conversion efficiency, the research team has spent two years developing the DEG. Its instantaneous power density can reach up to 50.1 W/m2, thousands of times higher than similar devices without the use of the FETlike design. The energy conversion efficiency is also markedly higher.
“Our research shows that a drop of 100 microlitres (1 microlitre = one-millionth litre) of water released from a height of 15 cm can generate a voltage of over 140V, and the power generated can light up 100 small LED lights,” said Professor Wang, an author of the research paper.
Professor Wang said he hoped that the outcome of this research would help to harvest water energy to respond to the global problem of renewable energy shortage. He believed that in the long run, the new design could be applied and installed on different surfaces, where liquid is in contact with a solid, to fully utilise the low-frequency kinetic energy in water. This can range from the hull surface of a ferry to the surface of umbrellas or even inside water bottles.
He also pointed out that there are two crucial factors for the invention. First, the team found that the continuous droplets impinging on PTFE, an electret material with a quasipermanent electric charge, provides a new route for the accumulation and storage of high-density surface charges. They found that when water droplets continuously hit the surface of PTFE, the surface charge generated will accumulate and gradually reach saturation. This new discovery has helped to overcome the bottleneck of the low-charge density encountered in previous work.