Engineers harvest cost effective, interruption-free electricity… from thin air

A team of engineers at the University of Massachusetts Amherst has shown that nearly any material can be turned into a device that continuously harvests electricity from humidity in the air. 

While this sounds completely extraordinary, the big news is the word ‘continuously’.  The fact that energy can be extracted from air isn’t of itself surprising when you consider the power of a lighting bolt. It’s doing so on demand and continuously that is the challenge.

‘The air contains an enormous amount of electricity,’ says Jun Yao, assistant professor of electrical and computer engineering in the College of Engineering at UMass Amherst, and the paper’s senior author. ‘Think of a cloud, which is nothing more than a mass of water droplets. Each of those droplets contains a charge, and when conditions are right, the cloud can produce a lightning bolt—but we don’t know how to reliably capture electricity from lightning. What we’ve done is to create a human-built, small-scale cloud that produces electricity for us predictably and continuously so that we can harvest it.’

In effect, what is happening is that energy is being extracted from humidity. Recently, other technologies have emerged that achieved this but none have produced a current output of longer than 48 hours.  The current output generated by this work ran beyond a 10 month test window.

The principle is based on the fact that a molecule of water in the air, travels around 100 nanometres (nm) before it bumps into another molecule. If you pass the ‘air’ through a material with holes smaller than that (1000 x thinner than a human hair) the molecules buffet into the material and each other, slowing their progress.

Professor Lau: ‘This means that the upper part of the layer would be bombarded with many more charge-carrying water molecules than the lower part, creating a charge imbalance, like that in a cloud, as the upper part increased its charge relative to the lower part. This would effectually create a battery—one that runs as long as there is any humidity in the air.’

Any kind of material can be used, which means, as Yao points out, ‘you could image harvesters made of one kind of material for rainforest environments, and another for more arid regions’. 

And because the material is incredibly thin, thousands can be stacked on top of each other to increase energy production, without making it noticeably bigger. It is anticipated that such a device would be capable of delivering kilowatt-level power for general electrical utility usage.

Photo: Derek Lovley/Ella Maru Studio