Swiss startup develops a system that wirelessly charges electric buses through their tires

Wireless charging is not just about convenience. For electric buses, it can enable operators to prolong battery life, to achieve the same range with a smaller battery pack, and to charge the same number of vehicles with fewer charging stations, as a Momentum Dynamics exec (among others) explained to Charged.

The electrification of bus fleets is advancing swiftly in Europe, particularly in Switzerland, where a startup called Winduction, a spin-off from the respected technical university ETH Zurich, is taking a novel approach to inductive charging.

“We believe that electric buses can be operated much more cheaply if they are charged wirelessly and regularly during operation,” says ETH graduate and Winduction CEO Laurin Schwitter.

Most inductive charging systems transfer electricity from a coil in the ground to a second coil on the vehicle’s undercarriage—but there’s one weakness in this approach. The distance between the road and the undercarriage is relatively large, and varies from one vehicle model to another. This distance is important, as the efficiency of energy transfer decreases with increasing separation.

The three founders of Winduction believe they’ve found a better way. “In any vehicle, the only thing that’s always in contact with the ground are the wheels,” says Winduction CTO Sylvain Fricker.

The company’s system includes a set of induction coils housed in a ground plate set into the road surface, as in a typical setup. The second group of coils, however, is integrated into a specially developed bus tire.

“We minimize the transmission distance between the road and undercarriage by placing coils inside the wheel,” says Fricker. “From the ground into the vehicle, the Winduction system achieves an efficiency of over 90 percent. As our technology is also effective during short charging stops, the buses can make do with smaller batteries, making them significantly cheaper to buy and operate.”

However, putting inductive coils into tires presented its own challenge—conventional bus tires contain steel belts, which would react with the magnetic field and convert a large part of the power into heat.

“For our system to function, we work with partners to develop a completely new steel-free tire,” says CEO Schwitter.

Winduction demonstrated its system on the bus line between Zurich Airport and the city’s Oerlikon quarter. “Our calculations show substantial savings compared with depot charging. How large they are depends on the route. A feasibility study with transport operators is currently quantifying this,” Schwitter explains. 

Using Winduction’s system, operations on the route between Zurich Airport and Oerlikon should require charging plates only at 2 of 24 stops, at which the buses would charge for a total of 3 hours over the course of 16. For comparison, the electric buses used on this line currently charge simultaneously for 5 hours in the garage overnight, and need much more power to do so than they would with Winduction’s system.

Winduction is currently building real-world testing infrastructure in Winterthur, including a test lab and a test bus stop.

“In a subsequent stage of development, we want to bring all the components together in a form that’s geared towards the industry,” says Schwitter. “Our aim is to build a fully converted electric bus as quickly as possible that can also be used outside of our own private test area.” 

The founders plan to carry out the first pilot in 2028. Discussions are currently underway with several Swiss transport operators.

Source: ETH Zurich