Researchers from the EPFL (École polytechnique fédérale de Lausanne) Energy Center and Industrial Electronics Lab, along with partners from the Swiss Federal Laboratories for Materials Science and Technology (EMPA), are demonstrating a new type of energy storage that could be the solution to quick electric vehicle charging.
While the storage capacity of batteries is improving, electric vehicle owners are faced with the harsh reality that the power grid remains weak: how could it ever charge thousands of cars at the same time, especially when it comes to ultra-fast charging, which requires 10 times more power.
In an attempt to find a charging solution that would be the equivalent of filling up a tank of gas, EPFL researchers proposed intermediate storage.
If an electric vehicle charged for as long as it took to fill up an ordinary car’s tank with gas, it wouldn’t get very far. According to EPFL, such a quick charge would require 4.5 MW of power – equivalent of about 4,500 washing machines, which would bring down the power grid.
“We came up with a system of intermediate storage,” says Alfred Rufer, a researcher in EPFL’s Industrial Electronics Lab. “With this buffer storage, charging stations can be disconnected from the grid while still providing a high charge level for cars.” And this can be done using the low-voltage grid (used for residential electricity needs) or the medium-voltage grid (used for regional power distribution), which significantly reduces the required investment.
The team’s intermediate storage idea is achieved using a Lithium-ion battery the size of a shipping container, which is constantly charging at a low level of power from the grid. When a car needs a quick charge, the buffer battery promptly transfers the stored electricity to the vehicle, so that the grid is not even used.
The demonstrator that’s being worked on currently looks like a trailer and is holding the intermediate storage battery. It draws power from the low-voltage grid and provides the 20 to 30 kWh needed to charge a standard electric car battery, in just 15 minutes.
“Our aim was to get under the psychological threshold of a half hour. But there is room for improvement,” says Massimiliano Capezzali, deputy director of the Energy Center, who coordinated the project.
After conducting demonstrations, EPFL found their concept to be completely realistic. A station capable of charging 200 cars per day would need an intermediate storage capacity of 2.2 MWh, which is about the same magnitude as the energy consumed by one home in one year, and the equivalent of four of the team’s shipping container batteries.
“Electric cars will change our habits. It’s clear that, in the future, several types of charging systems – such as slow charging at home and ultra-fast charging for long-distance travel – will co-exist,” says Dr. Capezzali.