What has long been commonplace for cell phones and electric toothbrushes could soon become a reality for electric cars: wireless inductive charging. A transmitter coil in a base plate transfers energy via a magnetic field to a receiver coil in the car. This significantly increases convenience: The charging process starts automatically as soon as the car is parked correctly. At the same time, it opens up completely new possibilities. Parked electric cars would be automatically connected to the grid – and could contribute to the energy transition as mobile power storage devices in the future.
In the INLADE pilot project led by energy supplier Eniwa AG, Empa, together with other partners, tested wireless charging for the first time in Switzerland under real-life conditions. The project was supported by the Swiss Federal Office of Energy (SFOE) and the cantons of Zurich and Aargau. “The aim was to test the existing technology in everyday use, clarify technical and regulatory issues, and demonstrate its potential for the energy transition,” explains Mathias Huber from Empa's Chemical Energy Carriers and Vehicle Systems lab.
Same efficiency as cable charging
With Empa's new inductive charging station for the move mobility demonstrator, the converted electric car must be parked precisely. A screen shows the optimal position – in future, parking assistants will do this automatically. Once the vehicle is correctly positioned, the system recognizes the position above the base plate and starts the charging process. Before doing so, it checks whether there are any objects or living beings between the coils.
In the project, AMAG and other partners converted existing vehicles for wireless charging. To do this, receiver coils were installed and interfaces to the charging management and high-voltage systems were integrated. This was followed by extensive electromagnetic compatibility (EMC) measurements and safety tests. “The aim was to ensure that the magnetic field generated during inductive charging did not interfere with other devices inside or outside the vehicle, or with people,” explains Huber. The converted vehicles were then granted individual approval for use on Swiss roads, making them among the first electric cars worldwide with an inductive charging system suitable for everyday use. Conventional charging via cable remains possible, too.
The Empa researchers also investigated how inductive charging affects both the battery and the charging efficiency. Tests under real-world conditions – with snow, rain, temperature differences, and slight parking deviations – showed an efficiency of around 90 percent, comparable to charging via cable. “The technology works very reliably in practice and is similarly efficient to conventional charging systems,” Huber concluded.
Buffer for renewable energies
Like other vehicles, electric cars are immobile for an average of around 23 hours a day. If they were permanently connected to the power grid in parking lots or garages during this time, their batteries could serve as electricity storage devices, balancing fluctuations and thus promoting renewable energies. Bidirectional charging is technically possible with inductive charging technology. “The big advantage of an inductive system is that vehicles are connected to the grid much more frequently without the need for any active intervention – a plus for both convenience and the energy transition,” explains Huber.
But there are also economic advantages: Intelligent charging can reduce electricity costs, for example by charging at times when there is a high proportion of renewable electricity – especially during the day, when more and more photovoltaic systems will be feeding energy into the grid in the future.