Researchers at MIT had recently developed a system capable of converting fluctuations in temperature which occur during the day-night cycle into electrical power.
Thermoelectric devices that generate power when one side of the device is a different temperature from the other have been widely discussed for a number of years now, but this is the first time such a system has been developed and demonstrated to work.
“We basically invented this concept out of whole cloth,” said study co-author Michael Strano, Carbon P. Dubbs Professor of Chemical Engineering at MIT. “We’ve built the first thermal resonator. It’s something that can sit on a desk and generate energy out of what seems like nothing.”
Since the device generates energy from ambient temperature changes, it remains unaffected by cloud cover, wind conditions, or other environmental factors. In fact, it can even be placed in the shade under a solar panel, thereby making it more efficient by drawing away waste heat.
The team’s thermal resonator has also been shown to be three times more efficient than an identically sized, commercial pyroelectric material – an established method for converting temperature fluctuations to electricity.
To build the device, the team had to first develop a material optimised for thermal effusivity – a property which combines thermal conduction and thermal capacity. The material is made of copper or nickel foam, which is then coated with a layer of grapheme to provide even greater thermal conductivity.
Finally, the foam is infused with octadecane, phase-change material, which changes between solid and liquid within a particular range of temperatures chosen for a given application.
In a test, a sample of the material managed to generate 350 millivolts of potential and 1.3 milliwatts of power – enough to power small-scale environmental sensors or communications systems – in response to a 10-degree-Celsius difference between night and day.
The new material could be used as part of a hybrid system of orthogonal energy sources, which could include fossil fuel generators and solar panels – as soon as one source fails, the others kicks in, even if just to send a distress signal.
In addition, the new material could prove useful in designing landers and rovers for the exploration of remote locations, including extra-terrestrial moons and planets, as much of the system could be made from local materials, thereby reducing the payload and attendant costs.