GREEN power may no longer be as fickle as the weather, thanks to a device that can generate electricity in any conditions – be it sun, wind or rain.

Most forms of renewable energy are intermittent, says Elias Siores at the Institute for Materials Research and Innovation at the University of Bolton in the UK – the wind doesn’t always blow and the skies aren’t always cloud-free. “What we wanted was something that can take energy from different elements,” he says.

So, together with his colleagues, Siores has done just that. First, he created 20-centimetre-long flexible ribbons made of a piezoelectric polymer that generates electrical currents when perturbed, either by wind or when rain drops fall on it. The team chose a polymer called polyvinylidene fluoride over ceramic piezoelectric materials because in wind tunnel tests and simulated rain it deformed more, creating higher peak voltages. That means more energy per rain drop or gust of wind, says Siores.

Next, the team coated the ribbons with a flexible photovoltaic (PV) film, and attached a pair of electrodes with which to harvest this solar-induced current. Siores says that 10 square centimetres of the PV film can generate 1 to 2 watts of solar energy at its peak. The work will appear in Smart Materials and Structures.


It makes sense to combine different forms of renewable energy because they complement each other so well, says Hod Lipson at Cornell University in Ithaca, New York. But such hybrid generators would likely be limited to small-scale applications, because piezoelectric materials aren’t very energy-dense. “Their benefit would be more for powering very low power devices,” he says.

“Combining different forms of renewable energy makes sense because they complement each other”

Siores agrees that each hybrid ribbon would only generate a few milliwatts consistently, perhaps enough to charge a cellphone. He envisages building pine cone-like structures made up of many flat “needles” that oscillate with the wind and rain, while simultaneously having a high surface area to harvest the sun’s energy.

A similar technique using standard nylon could also be used to make energy-generating clothing, Siores says: “We can turn nylon into piezoelectric nylon.” His team achieves this by extruding it into fibre form in the presence of a strong electric field. The fibres are then coated with a conducting electrode material, followed by a PV layer and then another electrode layer. The result, says Siores, can be woven into fabrics to make garments that generate energy as we move or soak up sunshine.

Journal reference: Smart Materials and Structures (DOI:10.1088/0964-1726/20/5/055019)