Renewables are on the rise, coal is bleeding out, and natural gas is frustratingly cheap. While the energy sector fights it out for the future of the planet, researchers around the world are sneakily coming up with proof-of-concept technologies that may provide our gizmos with new sources of power further down the line.
Enter left stage, MIT’s thermal resonator. This rather magical-sounding device doesn’t need anything other than the ambient environment to generate electricity, which it does so by “harvesting” lingering thermal energy. This isn’t witchcraft, dear readers: this is the bleeding edge of engineering, and although we wouldn’t expect to own one anytime soon, it’s hard to argue that this isn’t extremely clever stuff.
Have you heard of the thermoelectric effect? It’s a neat quirk of physics that allows for the generation of a voltage when a specialized device known as a thermocouple is registering at different temperatures on either side of it. At the same time, if you add a voltage to the thermocouple, it’ll result in a temperature difference across the device.
Harvesting heat on the rooftop of MIT. Justin Raymond/MIT
Thermoelectric devices that utilize this effect aren’t new. They’re used in diesel engines, and occasionally in watches – wasted thermal energy escaping from the system is recaptured and transformed into electricity, making systems more energy efficient.
The problem with said devices is that a temperature difference has to be maintained across the device at all times. In the absence of anything causing this – sunlight fluctuations, say – no electricity can be generated, and this, according to an MIT-authored Nature Communications paper, is where their new device comes in.
They’ve concocted the world’s first thermal resonator, a device that they note can generate electricity based on small temperature fluctuations in the surrounding environment. As these happen everywhere, from the darkest shadows to the tops of mountains, this makes their device incredibly versatile.
How is this sorcery possible? Well, it’s all about the thermal effusivity, which describes a material’s ability to exchange thermal energy with its surroundings. Amp this up and you’ve got a very temperature-sensitive device.
This property is directly dependent on how well a material can store heat, as well as conduct it – and, as their paper notes, you often have materials that are only good at one or the other.
Combining a mixture of copper and nickel foams with that ferociously conductive wonder material, graphene, they’ve produced a material with high thermal conductivity, capacity and, therefore, effusivity.
Despite graphene’s legendary capabilities, the crown here goes to a special wax that readily switches between a solid and liquid state. This stores thermal energy, which is slowly effused to the other side of the device. This guarantees a slow-burn temperature difference and, consequently, an electric current.
Their device is so effective that, using standard temperature differences between night and day, it can generate enough to power a simple, portable communications system or sensor. Yes, so far it’s fairly primitive, but it’s early days: We wouldn’t be surprised if it’s used to power standalone devices or placed inside hybrid power systems for more complex systems in the near-future.
The study’s authors also explain that their device can “address the need for renewable energy sources that are not limited by intermittency, and capable of persistent operation.”
Lead author Anton Cottrill, an MIT graduate student, told IFLScience that “competing with solar and wind is definitely a tall order for this new renewable energy technology.” Instead, he described a future wherein all types exist side-by-side, perhaps even working together.
“Our thermal resonator device can actually exist underneath a solar cell,” where it will absorb any wasted heat from above to power itself.