Charging electric cars without any cables

Inductive charging in a practical test: Wireless charging stations are to be tes
Inductive charging in a practical test: Wireless charging stations are to be tested in everyday operation at Empa. Photo: Empa
Eight stakeholders from business, science and the public sector launched the first project for wireless charging of electric vehicles in Switzerland at the end of November 2023. The project team is investigating the technical feasibility of inductive charging under everyday conditions, determining the advantages and disadvantages compared to conventional charging systems and clarifying the approval process. Empa is part of the project team, which is supported by the Swiss Federal Office of Energy (SFoe).

Inductive charging has long been used for toothbrushes and cell phones, for example. The principle is the same for electric vehicles: A receiver plate is mounted on the underside of the vehicle, and when parked in a parking space with a charging plate, the energy is transferred to the battery in the car by using a magnetic field. The technology comes from the US partner company WiTricity.

The initial focus of the approximately two-year project lies on retrofitting the vehicles with prototypes of the inductive charging system and vehicle registration. Later, the use of converted vehicles in e-car sharing is planned. Among other things, Empa is investigating the energy efficiency and reliability of the new system. "We are looking at how charging works under different environmental conditions compared to conventional, conductive charging and analyzing the charging efficiency and the effects of both systems on the power grid," explains Miriam Elser, Group Leader Vehicle Systems at Empa.

While Empa is taking care of the technical analysis, researchers from the Institute for Sustainable Development at the ZHAW School of Engineering are investigating the experiences of vehicle users. The project is being led by the energy supply company Eniwa AG from Buchs. Other partners are the municipal utility alliance Swisspower, Energie Thun AG and BRUGG eConnect AG.

The project envisages the installation and operation of six to seven charging stations and vehicles - one of them at Empa as part of the "move" mobility demonstrator. The project participants hope that wireless charging will increase convenience for vehicle users and further reduce the barriers to switching to electromobility. At least three stations for use in e-car sharing should prove this. To this end, Eniwa is still looking for further locations and innovative partners who would like to participate in this lighthouse project.

In the future, electric car batteries could play a major role in regulating the electricity grid, namely in so-called bidirectional charging. In doing so, the car battery is used as a storage unit that releases part of the energy back into the grid when it is not needed for driving. For energy suppliers such as Eniwa, it is highly relevant to know how reliably vehicle batteries can be used to regulate the electricity grid. "When the batteries are practically full, vehicles are generally not connected to the charging station, although in this state they would be predestined to temporarily make some of their energy available to the power grid," explains Samuel Pfaffen, Head of Corporate Development at Eniwa. With wireless charging stations, there is no need to connect the vehicles to the charging station manually, which makes it much easier to access the vehicles’ battery storage systems.