Raindrop lights up 100 bulbs
Raindrop lights up 100 bulbs
“Generating electricity from raindrops efficiently has progressed one step ahead. A single raindrop can now power up 100 small LED light bulbs, completely setting a new milestone for energy-harvesting technologies”.
With current environmental changes, renewable energy with solar, wind, and water power is more important than ever. Currently, we depend on raindrop falling at high elevations and collecting into rivers to reach masses large enough to make turbine harvesting profitable.
Hydropower is nothing new. While 70% of Earth’s surface is covered by water, low-frequency kinetic energy that is contained in it is not efficiently transformed into electrical energy due to technological limitations.
For example, a conventional droplet energy generator based on the triboelectric effect can produce electricity provoked by electrostatic induction and contact electrification when a droplet hits a surface.
However, the amount of charges generated on the surface is defined by the interfacial effect, and as an outcome, the energy conversion efficiency is quite low.
A new device found by researchers to generate electricity by raindrop:
A research team led by scientists from the City University of Hong Kong (CityU) has developed a Droplet-based Electricity Generator (DEG): a device that can power up to 100 small LED bulbs just by controlling the power of a raindrop.
The device utilises a Field Effect Transistor (FET)-like structure that enables for high energy-conversion efficiency and its instant power density can reach up to 50.1 W/m2, thousands of times higher than other comparable devices without the use of FET-like design. And the energy conversion efficiency is considerably higher. This would support to advance scientific research of water energy production and tackle the energy crisis.
Professor Wang Zuankai from CityU pointed out that there are two crucial determinants for the invention. First, the team discovered that the continuous droplets hitting on Polytetrafluoroethylene (PTFE), an electret material with a quasi-permanent electric charge, gives a new route for the collection and storage of high-density surface charges.
They found that when water droplets repeatedly hit the surface of PTFE, the surface charges generated will collect and gradually reach a saturation. This discovery helped to win the bottleneck of low charge density found in previous work.
FET structure makes magic in the discovery:
Added key feature of their design is a novel set of structures similar to a FET, which is a Nobel Prize in Physics winning innovation in 1956 and has become the essential building block of modern electronic devices.
The device consists of an aluminium electrode, and an indium tin oxide (ITO) electrode with a film of PTFE deposited on it. The PTFE/ITO electrode is liable for the charge generation, storage, and induction.
When a falling water droplet hits and spreads on the PTFE/ITO surface, it significantly joints the aluminium electrode and the PTFE/ITO electrode, thus changing the original system into a closed-loop electric circuit.
The technology used to generate power from raindrop:
With this unique design, a high density of surface charges can be accumulated on the PTFE through continuous droplet hitting. Meanwhile, when the spreading water joins the two electrodes, all the stored charges on the PTFE can be completely released for the generation of electric current. As an outcome, both the instant power density and energy conversion efficiency are much higher.
The outcome of the research reveals that a raindrop of 100 microliters (1 microliter = one-millionth of a litre) of water discharged from a height of 15 centimetres can produce a voltage of over 140V and the power generated can light up 100 small LED light bulbs.
The increase in instant power density does not result from additional energy, but from the conversion of the kinetic energy of water itself.
The kinetic energy involved in falling water is due to gravity and can be observed as free and renewable. It should be properly used.
Additional data learned from the research:
The research also explains that the reduction in relative humidity does not change the efficiency of power generation. Moreover, both rainwater and seawater can be utilised to generate electricity.
The result of this research would benefit to harvest water energy to react to the global problem of renewable energy shortage.
“Generating power from raindrops instead of oil and nuclear energy can promote the sustainable development of the world”.
In the long run, the new design could be implemented and installed on different surfaces, where the liquid is in contact with solids, to completely use the low-frequency kinetic energy in water. This can vary from the mould surface of a ship or a coastline to the surface of umbrellas or even the insides of water bottles.
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