Traffic lights under a concrete bridge

Contactless charging: how electric vehicles recharge at red traffic lights


Contactless charging: how electric vehicles recharge at red traffic lights

June 3, 2019

No searching for an available charging station. No long charging times when you can’t use your electric vehicle. Instead stop and recharge the battery where you have to wait anyway: at red traffic lights. This is exactly the type of mobility that contactless charging intends to create in the future.

Discover here: 

  • How electric vehicles recharge without cables
  • Where electric buses already charge contactlessly
  • What “snack charging” is and how it benefits you
  • Why you won't even have to stop to charge your electric vehicle in future

Energy companies, suppliers and major automotive manufacturers are working to develop a technology that allows batteries in electric cars to be recharged quickly and without the need for charging cables. Specifically, they are developing contactless charging systems and standardising them with the vision of a future in which the charging process can be easily integrated into the everyday lives of electric car drivers.

Research has long since proven that the technology works: while conductive charging of electric vehicles uses a cable to transfer energy from the vehicle to the power grid, contactless charging works wirelessly via electromagnetic fields. The underlying principle: a stationary coil embedded in the ground creates a magnetic field with another coil that is attached to the bottom of the vehicle. This enables the current to flow into the electric car. In Braunschweig, inductive electric buses are already in service. The 200 kW contactless charging at the bus terminal is so fast that the bus driver's break time is sufficient.


“Snack charging”: brief charging more often

Contactless charging technology also provides a solution for an existing dilemma surrounding electric mobility in cars – short range and sometimes long distances between charging stations. This is because passenger vehicles require much lower charging performance than buses. These days, eleven kilowatts are enough to charge batteries just as quickly as quick-charging stations. Scientists are already working on a 20 kW enhancement.

As a result, wireless charging is possible not only at traffic lights but also at many locations where drivers temporarily park their vehicles. For example in the parking lot at the supermarket or outside the doctor's office, in car parks, on motorway service areas or at petrol stations. The lithium-ion battery is briefly charged during short stops, also known as “snack charging”. Achieving a 60 to 70 percent battery charge while driving in city traffic is realistic. The advantage of the short charging cycles: four to five charges per day increase the battery’s service life. The electric vehicles only have to be docked with the charger, known as the supercharger, for long distances.



“Snack charging” means using brief stops for charging.
A man plugs a charging cable into an charging station
Short charging stops are sufficient for driving in the city; the electric car only needs more extensive charging when driving longer distances.

Wireless charging: implementation is a long way off

However, making wireless battery charging equally and comprehensively available to everyone requires a network of contactless charging stations. Charging panels have to be installed in the ground. In addition, the coils in the underbody of the electric car and the coil geometry of the ground panel have to be standardised. Car manufacturers are currently planning to release the first plug-in hybrids with a wireless charging option. In these models, the charging panel and coil of the electric car are still individually matched to each other; models from other manufacturers will not be able to recharge at these contactless charging stations.

The industry has already agreed on a number of common standards. The energy is transmitted at 85 kilohertz and Wi-Fi enables communication with the electric vehicle. One challenge lies in developing a charging panel that allows the greatest possible tolerance when parking the vehicle. In order to transmit energy efficiently, the car currently has to be parked precisely above the panel. In addition, a standardised system has to take into account the different vehicle sizes and the different receiver coils.

Contactless charging at 100 km/h

Dynamic charging of electric vehicles goes one step further. This solution is already being tested. In Jinan, China, for example, there is a two-kilometre-long section of highway with solar panels integrated into the road surface. This means that electric cars can be charged wirelessly while driving. But good things take time. The high-end solution – contactless charging while driving – still has a long road ahead before it becomes part of everyday life on German roads. However, the network of quick-charging stations continues to grow and the on-going development of e-charging options will further simplify charging your electric car. Eventually, you will no longer have to worry about it at all.