Rain = Energy??

Researchers have developed a raindrop electricity generator that uses a field-effect transistor-style structure to instantly produce a surprisingly high voltage from water drops. It can produce 140V from just one drop of rain, enough to power 140 small LED bulbs.

In order to improve the conversion efficiency, the research team has spent two years developing the droplet-based electricity generator (DEG). It’s instantaneous power density can reach up to 50.1 W/m2­, thousands of times higher than similar devices without the use of the FET-like design. The energy conversion efficiency is also markedly higher.

The raindrop electricity generator consists of an aluminium electrode and an indium tin oxide electrode layered with a film of PTFE, a material with a ‘quasi-permanent’ electric charge. The PTFE/ITO electrode is responsible for the charge generation, storage, and induction. When drop hits the surface, it bridges the aluminium electrode and the PTFE/ITO electrode and creates a closed-loop electric circuit.


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‘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 Auankai, lead researcher from cityU’s department of mechanical engineering.

Their findings were published in the latest issue of the highly prestigious scientific journal nature under the tile ‘a droplet-based electricity generator with high instantaneous power density‘. 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 believes that in the long run, the raindrop electricity generator 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.

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