Last updated May 7, 2018 at 2:59 pm
The gentle undulations of leaves in a breeze has long been a source of poetic inspiration, but soon it could also be a source of electric power.
Critics of renewables often point out that the sun doesn’t always shine and the wind doesn’t always blow, researchers have now developed a system that exploits those very changes to generate power.
As proof of concept, researchers from Linköping University in Sweden show that electricity can be generated by a leafy twig blowing in breezes created by a fan.
The key to the technology rests with earlier research done by the same group that led to the development of nano-antennas designed to be incorporated into window glass.
The devices, described in the journal Nano Letters, absorb even weak solar radiation and deploy it to successfully reduce cold downdrafts, offering a substantial energy saving associated with heating buildings.
The swarm principle
The latest work takes the invention one step further, by combining the antennas with a pyroelectric film, creating tiny optical generators just 160 nanometres in size.
Pyroelectric substances generate voltages because of changes to input. Thus, a charge is created as they move from being warm to cool, or the other way around – as would happen, for instance, if they were repeatedly dappled with light and shade.
And while each little generator produces only a tiny charge, it is the nature of nanotechnology to operate on a swarm principle.
“The nano-antennas can be manufactured across large areas, with billions of the small discs uniformly distributed over the surface,” says research team leader Magnus Jonsson.
“The spacing between discs in our case is approximately 0.3 micrometres. We have used gold and silver, but they can also be manufactured from aluminium or copper.”
To demonstrate the concept, co-author Mina Shiran Chaharsoughi created an experiment that used a leaf-covered twig, blown about by a fan, with an optical generator positioned beneath it.
As the leaves flapped about, throwing light and shade on the generator, enough electrical pulses were generated to power a small external circuit.
If the technology proves to be both economic and scalable, the world might soon have yet another reason to refrain from cutting down forests.
“The research is at an early stage, but we may in the future be able to use the natural fluctuations between sunshine and shade in trees to harvest energy,” says Jonsson.
The research paper was published in Advanced Optical Materials.