- The new droplet-based electricity generator provides instantaneous power density along with incredible energy-conversion efficiency.
- The device can produce a voltage of 140V using just a 0.1-milliliter drop of water (released from a height of 5.9 inches).
Hydropower became a source for generating electricity in the late 19th century. It a green process in which power is derived from the energy of falling or fast-running water.
More than 70% of the Earth’s surface is water-covered. Yet existing technologies are incapable of using kinetic energy contained in tides and waves to convert it into electric energy efficiently.
Although significant efforts have been made to utilize energy from ocean waves, rivers, tides, and even raindrops, energy conversion efficiency (of water to electricity) has remained quite low.
To increase this conversion efficiency, a team led by researchers at the City University of Hong Kong has built a droplet-based electricity generator (DEG) that delivers instantaneous power density along with incredible energy-conversion efficiency.
Unlike existing droplet energy generators that rely on the triboelectric effect, the new DEG features a field-effect transistor-like structure to provide superior power density (up to 50.1 W/m2) and substantially higher energy-conversion efficiency.
How Does It Work?
The invention is based on two main parameters –
- Continuous droplets impinging on a synthetic fluoropolymer called polytetrafluoroethylene (PTFE).
- A new device comprising of an indium tin oxide (ITO) electrode, an aluminum electrode, and a film of PTFE deposited on it.
PTFE is a synthetic fluoropolymer of tetrafluoroethylene with a quasi-permanent electric charge. When drops of water continuously hit the PTFE, the charges on its surface accumulate and eventually reach a saturation point. This provides a new way of accumulating and storing high-density surface charges.
The second key parameter of the invention is a unique set of structures similar to a field-effect transistor. It contains two electrodes and a film of PTFE deposited on it. When drops of water hit and spread on the PTFE surface, it ‘bridges’ the ITO and aluminum electrode, converting the device into a closed-loop electric circuit.
A diagram of DEG (left) and the optical image showing four parallel DEG devices fabricated on a glass substrate (right) | Source: CityU
When water droplets connect two electrodes, the charges stored on the PTFE’s surface can be released for generating electric current. Since the device fully releases high-density charges, both energy conversion efficiency and instantaneous power density are much greater.
The findings show that a 0.1-milliliter drop of water released from a height of 5.9 inches can produce a voltage of 140V, which is enough to light up 100 small LED bulbs.
The impressive instantaneous power density comes from the water falling on the surface of the PTFE. According to the researchers, this free and renewable kinetic energy of the water should be better utilized.
What more impressive is, both seawater and rainwater can be used for electricity generation. The decrease in relative humidity doesn’t impact power generation efficiency. The research team believes that their device will help in reducing the global problem of renewable energy shortage.