AUTONEWS

Tyres instead of a plug: electric buses that charge during operation

The back wheel of the slightly ageing post bus stands on a plate about the size of a shopping trolley. Suddenly, the bus’s battery begins to charge. 10 percent, 20, 30 – the battery indicator climbs steadily, with no need for a cable to connect the bus to the plate. The underlying technology was developed by the ETH spin-off Winduction. As the company’s first prototype, the electric bus is intended to solve a challenge that is becoming increasingly significant in public transport. 

The electrification of bus fleets is advancing in Switzerland and Europe. At present, transport companies primarily rely on a combination of large batteries and powerful charging stations involving thick cables. Both are expensive to purchase and maintain. Moreover, charging takes place at night in the depot using electricity that is not yet derived entirely from renewable sources – and the enormous batteries make the bus heavy, which leads to greater wear on individual components, as well as taking up valuable space.  

How can electric buses be charged inductively and much more cost-effectively? It is precisely this approach that is being explored by Sonam Bhuka, Sylvain Fricker and Laurin Schwitter, the three founders of Winduction. “We believe that electric buses can be operated much more cheaply if they are charged wirelessly and regularly during operation,” says ETH graduate Laurin Schwitter, CEO of the ETH spin-off.  

Known in technical terms as inductive charging, this is not fundamentally a new technology. For example, mobile phones can be charged by lying them on small plates that are available for desks or bedside tables, and electric cars can now also be charged wirelessly. However, most systems seek to transfer electricity directly from a coil in the ground to a second coil on the vehicle’s undercarriage. The power is transmitted by an invisible magnetic field that links the two coils.  

Yet there is one major 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 a key factor for inductive charging systems, as the efficiency of energy transfer decreases with increasing separation. 

Much smaller batteries and less power loss...The three founders of Winduction therefore take a different approach. “In any vehicle, the only thing that’s always in contact with the ground are the wheels,” says ETH alumnus Sylvain Fricker, who is in charge of technology at the fledgling company. This simple observation gave rise to the idea from which the spin-off takes its name: Winduction stands for “wheel-based induction.” 

The technology works using magnetically coupled coil systems. The first induction coils are housed in a ground plate that is set into the road surface. These coils are connected to the power grid and produce a magnetic field. A second group of coils, integrated into a specially developed bus tyre, picks up the energy when the bus stops and passes it on to the vehicle battery. 

“We minimize the large 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 – in other words, less than 10 percent of the power fed in through the ground plate is lost. “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,” adds the ETH graduate.

Bus tyres without steel...However, the new system with the tyre as a relay also presented a challenge for the three founders of Winduction. Specifically, conventional bus tyres contain steel belts that provide stability, but this steel would react with the magnetic field and convert a large part of the power into heat instead of transferring it.  

“For our system to function, we work with partners to develop a completely new steel-free tyre,” says Schwitter, the company’s CEO. Although this change leads to greater costs for an individual bus tyre, the increase is almost negligible in the context of the overall acquisition and operating costs of a bus. 

Lower costs over the lifetime of a bus line...It is precisely in terms of the costs that the three founders see the biggest advantage of their technology. Transport companies are less interested in the price of individual vehicle components than in the total costs over the lifetime of a bus line. These costs include the acquisition of the vehicles, energy consumption, maintenance and infrastructure as well as personnel and financing costs. 

According to Winduction’s calculations, the total costs could decrease significantly with the new charging system. The founders demonstrate this using 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,” explains Schwitter.  

Charging during the day, reducing the burden on the grid...The reasons for this are manifold. Buses with smaller batteries are cheaper and can transport more people. Winduction’s ground plates are also relatively cheap compared with classical charging infrastructure. Another advantage is that the buses repeatedly recharge during the day. On the route between Zurich Airport and Oerlikon, charging plates would only be necessary at 2 of 24 stops, at which the buses would charge for a total of 3 hours over the course of 16. This, in turn, would also reduce the number of reserve vehicles needed. 

For comparison, the electric buses used on this line currently charge simultaneously for five hours in the garage overnight and need much more power to do so than they would with the system from Winduction. The lower power consumption would be even more important in the future, as electricity is becoming increasingly affordable in the daytime thanks to the expansion of photovoltaics. At the same time, peak loads in the power grid are reduced, as it is no longer necessary for all buses to be charged at the same time overnight, further reducing costs. 

Pilot operation at Zurich Airport from 2028...The ETH spin-off Winduction is currently building realistic testing infrastructure in Winterthur, supported by the Federal Office of Transport and the Swiss Climate Foundation. This includes both a test lab and the company’s own 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. One example is the region around Zurich Airport, where the bus is to be tested in real operating conditions and will also transport passengers for the first time. The passengers will be none the wiser as the ground plate transfers power quietly and wirelessly into the battery.  

Winduction, an ETH Zurich spin-off company, has created a wireless charging system that powers electric buses through their wheels during normal route stops.

How the system works:

• Road Plates: A charging plate sits flat on the street at a regular bus stop.

• Tire Transfer: When a bus stops, electricity flows from the road plate directly through the tires and into the vehicle's battery.

• No Plugs: Buses do not need heavy cables or manual plug-ins during the day.

The steel-free tire challenge:

• The Problem: Normal bus tires use internal steel belts for strength. Steel reacts badly with magnetic fields and turns electrical energy into waste heat instead of sending it to the battery.

• The Solution: Winduction partnered with manufacturers to build a brand new, completely steel-free bus tire.

• The Cost: While these special tires cost a bit more to make, the price difference is very small compared to the overall cost of running a bus line.

Key benefits:

• Smaller Batteries: Buses carry smaller, lighter batteries because they charge often during the day.

• Lower Costs: Lighter vehicles cause less road wear, and buying smaller batteries lowers the starting price of the bus.

• Cleaner Energy: Daytime charging uses cheap solar power and avoids overloading the electric grid at night.

Timeline and Testing

• Testing Phase: Winduction is building a test lab and a mock bus stop in Winterthur, Switzerland.

• Pilot Launch: Real-world testing on the route between Zurich Airport and Oerlikon is planned to start in 2028

by ETH Zurich