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.