Coils In The Road Could Charge EVs While Driving

One of the primary issues with EVs is that you need to pull over and stop to get a charge. If there isn't a high-speed DC charger available, this can mean waiting for hours while your battery tops up.

It's been the major bugbear of electric vehicles since they started hitting the road in real numbers. However, a new wireless charging setup could allow you to juice up on the go.

Over the years, many proposals have been made to power or charge electric vehicles as they drive down the road. Many are similar to the way we commonly charge phones these days, using inductive power transfer via magnetic coils. The theory is simple. Power is delivered to coils in the roadway, and then picked up via induction by a coil on the moving vehicle.

Taking these ideas from concept into reality is difficult, though. When it comes to charging an electric vehicle, huge power levels are required, in the range of tens to hundreds of kilowatts. And, while a phone can sit neatly on top of a charging pad, EVs typically require a fair bit of ground clearance for safely navigating the road. Plus, since cars move at quite a rapid pace, an inductive charging system that could handle this dynamic condition would require huge numbers of coils buried repeatedly into the road bed.

Despite these challenges, the idea has been proven in the real world to a limited extent. The Online Electric Vehicle, or OLEV, was developed by the Korea Advanced Institute of Technology (KAIST), and used to power a shuttle bus in 2009. The system slowly expanded to four lines by 2016, with the buses charging wirelessly thanks to inductive power transmitters buried in the road along the bus's route.

The second-generation of the system used on the buses transmits 100 kW of power wirelessly across an air gap of 17 cm at a power efficiency of 85%. This is achieved by using multiple power pickup coils mounted on a single vehicle. Much research went into finding the optimum coil geometries and electrical parameters to enable the system to run at this level. With power delivered from the road surface, the buses can rely on smaller batteries to get around, saving weight and improving efficiency. The system is buried in 5-15% of the roadway on the bus routes, and a vehicle detection system powers down the induction coils when not in use. While some of the routes have since closed, a shuttle service still operates at KAIST using the technology.

Other companies are also working in this space, too. Startup Magment is named for a portmanteau of "magnetic cement," and is working on a special inductive road demonstration with the Indiana Department of Transport. Details are scarce, but the company is pioneering a special method of mixing ferromagnetic materials in with cement to produce a more cost-effective and efficient wireless charging road system. The company intends to use the system for non-road applications, too, like forklifts and electric scooters.

Another standout is Israel-based company Electreon operating a pilot program in Gotland, Sweden. First deployed in December 2020, the project has successfully run a 40-ton truck on a 1.65-km long test section of road. Again using copper coils buried in the road surface, it's able to deliver around 70 kW of power to a moving vehicle at speeds up to 80 km/h. The company is also working on other pilot programs around the world, including a facility with Ford Motor Company to be installed near Detroit's Michigan Central Terminal.

The problem for such systems remains cost. For a start, burying power transmission lines and fancy coils in the road surface itself costs a lot to do in the first place. It's expensive enough for new roads, and even worse when you need to dig up an existing road to put the hardware in afterwards. Estimates for one Swedish project indicated that a wireless system like Electreon's would cost on the order of $2 million USD per km in a new build. This cost comes in around twice as much to install as more traditional methods of power transfer, like simple rails or overhead wires, while delivering much less power to boot. The latter are already proving their value in trucking tests in several locations around the world.

Maintenance is also a major issue. Burying anything in a roadway means that it's a huge job to repair it if something goes wrong. At the least, it will require shutting down the road, and at worst, it will mean digging it up. Upgrading to higher-performance technology will similarly require invasive work to remove the old hardware and reinstall the new.

Finally, there's the issue of standardization. Powering vehicles via inductive coils in the road is great, but cars and trucks will need special pickups fitted to receive this energy. The inductive pickup must be carefully tuned to the coils in the road, so there's little chance of retrofitting a one-size-fits-all pickup that can traverse multiple electric roadway systems. Thus, in order to make such systems practical, one company's system would have to be rolled out across broad sections of roadway, to the point where it became economically worthwhile for individual and commercial users to contemplate fitting their vehicles with pickup hardware.

It seems unlikely that we’ll be digging up our roads to fit charging coils anytime soon. After all, we’ve barely equipped our cities and towns with regular EV chargers, and they’re already a mature and established technology. However, in some applications, such as specialist bus or trucking routes, the technology may just catch on. From there, it could spread further, but only if the heavy investment makes sense.