MIT researchers have found a way to generate small amounts of electricity from condensation, by having electrically-charged droplets jump between superhydrophobic (water-repelling) and hydrophilic (water-attracting) metal plates. The advance could be especially useful in remote areas or developing countries, not least because it produces clean water as a side product.

While pulling electricity out of thin air is a physical impossibility, producing it from water droplets in the atmosphere is very much within our reach. We have known for years that droplets are capable of carrying an electric charge, so properly harnessing this phenomenon under controlled conditions could lead to an exciting new source of renewable energy.

Now, a team led by Nenad Miljkovic at MIT seem to have done just that, by finding a way to generate electricity simply by harnessing the humidity in the air.

Last year, Miljkovic and colleagues found that droplets on a superhydrophobic surface will on occasion spontaneously jump away of their own accord and, in the process, gain a small electric charge.

The researchers have used this phenomenon to generate electricity. To do so, they have used a series of conductive plates, alternating between water-repelling copper oxide and water-attracting copper. As droplets spontaneously separate from one plate, they gain a charge and travel all the way to the other plate. The moving charges generate electricity.

False-color time-lapse images captured via high-speed imaging show a droplet jumping from a superhydrophobic copper oxide fin to a hydrophilic copper fin (Image: Nenad Miljkovic and Daniel J. Preston/MIT)

During initial testing, the device only produced a very modest 15 picowatts per square centimeter of metal plate. However, according to the scientists, the process could easily be improved almost 70-fold to achieve at least one microwatt per square centimeter. At that rate, a generator about the size of a camping cooler could fully charge your phone in approximately 12 hours.

For the system to work, the crucial factor is a temperature differential between the device itself and the surrounding air, which will allow condensation to form. According to the researchers, any area where dew forms would be enough to generate power for at least a few hours in the morning.

Though the device only has the potential to produce a relatively modest amount of power, it should still find use with people living in the developing world, or perhaps to power remote automated environmental sensors. Moreover, a generator that uses this principle should be quite cheap to produce, since the plates can be made out of any conductive metal.

A paper on the advance appears in the journal Applied Physics Letters.

Source: MIT