Breakthrough invention creates electricity from daily temperature swings

16 Feb 2018

With the predictability of the day-night cycle, the thermal resonator can create renewable energy. Image: Mike Pellinni/Shutterstock

When it comes to passive electricity-producing technology, a new invention could be the breakthrough we’ve been looking for.

When thinking of new renewable energy technologies, a concept such as thermoelectric generation – which generates power when one side of the device is a different temperature from the other – could be hugely beneficial.

On that note, a team from MIT has unveiled a new device that expands on this idea by converting daily temperature fluctuations during the day-night cycle into electrical power, without needing two different temperature inputs at the same time.

Called a thermal resonator, the device could enable a continuous, years-long operation of remote sensing systems, making it ideal for technologies as part of the internet of things (IoT).

Detailing the device in a paper published to Nature Communications, the MIT team said that the whole concept is a potentially untapped source of energy that could one day sit on someone’s desk while being able to power a range of different devices from what seems like nothing.

So far, the early build of the device only generates a modest amount of power, but it doesn’t need to be in direct sunlight and can generate energy while in any conditions, including shade.

That means it is unaffected by short-term changes in cloud cover, wind conditions or other environmental conditions, and can be located anywhere that’s convenient.

Thermal resonator

The team’s test device, which has been deployed on the roof of an MIT building for several months, was used to prove the principle behind its new energy-harvesting concept. Image: Justin Raymond

The power of graphene

When compared to identically sized commercial pyroelectric material – the most popular method of generating electricity from passive temperature changes – the thermal resonator was able to outperform it by a factor of three in terms of power per area.

To actually create the device, the breakthrough moment came when the team realised it needed a material optimised for a little-recognised characteristic called thermal effusivity, which determines how readily it can draw and release heat from its surroundings.

The problem is that many materials – such as ceramics – are able to have a high thermal capacity but have low conduction, making them unsuitable.

But by tailoring the team’s own materials, made of a metal foam comprising copper or nickel and coated with graphene and a wax called octadecane, it could provide significant thermal conductivity.

In response to a 10C temperature change, a tiny amount of the material was able to produce 350 millivolts of potential power and 1.3 milliwatts of power, giving it enough juice to power small sensors and communication systems.

While so far the design has been tested on the day-night cycle, it could be possible to expand it to other temperature fluctuations found in everyday objects, such as refrigerators.

Colm Gorey was a senior journalist with Silicon Republic