Electricity from tyres could keep electric vehicles running 10% longer

What’s a nanogenerator? It is, we are told, a device or technology that converts mechanical or thermal energy into electricity. The technology has already found its way into automotive and tyre applications, and now the University of Wisconsin-Madison reports that a group of its engineers have, together with a “collaborator from China”, developed a nanogenerator that could increase an electric vehicle’s mileage by around ten per cent.

The researchers claim their Triboelectric nanogenerator (TENG) development is the first of its kind and have published their findings in the journal Nano Energy. Researcher and paper co-author Xudong Wang, an associate professor of materials science and engineering at the university, explains that the nanogenerator relies on the triboelectric effect to harness energy from the changing electric potential between the road surface and a vehicle’s wheels. The triboelectric effect is the electric charge that results when two dissimilar objects rub together or come into contact.

According to Wang, the nanogenerator offers an excellent way to take advantage of energy usually lost due to friction. “The friction between the tyre and the ground consumes about ten per cent of a vehicle’s fuel. That energy is wasted. So if we can convert that energy, it could give us very good improvement in fuel efficiency.”

Tests the research team carried out using a single-electrode triboelectric nanogenerator (S-TENG) on a toy car’s rubber wheel, which was coated with a rough PDMS film to simulate a tyre tread surface, showed a monotonic increase in S-TENG electric output as speed and weight load upon the wheel rose. According to the abstract of Wang and his colleagues’ paper, which is titled ‘Single-electrode triboelectric nanogenerator for scavenging friction energy from rolling tires’, the maximum instantaneous power obtained was 1.79 mW at a load resistance of 10 MΩ, which corresponds an energy conversion efficiency as high as 10.4 per cent.

For testing purposes, Wang and his colleagues connected an electrode in the toy car’s wheel to six green LED lights, and the movement of electrons caused by friction was sufficient to power these lights. “Regardless of the energy being wasted, we can reclaim it, and this makes things more efficient,” says Wang. “I think that’s the most exciting part of this, and is something I’m always looking for: how to save the energy from consumption.”

The researchers believe their demonstration provides a “promising solution to scavenge the wasted friction energy from rolling tyres,” a solution with the potential for improving the fuel efficiency or range of electric vehicles. “There’s big potential with this type of energy,” Wang commented. “I think the impact could be huge.”