This Electric Bus Is Powered by the Road

A wireless charging pad embedded in the roadway sends electricity to the bus' battery, letting the vehicle run all day.
Nov 11, 2014·
Padma Nagappan is a multimedia journalist who writes about the environment, renewable energy, sustainability, agriculture, and biotechnology.

What if you could replace heavy-duty industrial trucks and buses that spew enormous amounts of carbon dioxide with electric vehicles that are charged from devices implanted in the road?

That’s the idea behind WAVE, a Salt Lake City start-up that has developed technology to wirelessly charge buses when they stop to drop off or pick up passengers. (WAVE stands for Wireless Advanced Vehicle Electrification.)

The company recently outfitted a University of Utah transit bus with the technology, which charges the vehicle’s battery when it makes five-minute stops.

“This does make for longer transit times, but as it charges during the day, you’re extending charge life and reducing the amount of charge a bus has to carry,” said James May, WAVE’s vice president of program management. “So you don’t need a huge battery to carry the big charge, and with a smaller battery, you can have a bus that’s lighter, smaller, more efficient.”

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Here’s how it works. The charging pad sits flush with the roadway and contains a magnet. A magnetic pad is also affixed to the bottom of the bus. The bus stops over the roadway pad, which creates an oscillating magnetic field that transfers the 50 kilowatt-hours (kWh) electromagnetic energy through the air to the vehicle. The electricity is then transferred to the bus’ battery.

It’s not a new concept—Nikola Tesla proposed the technology about a century ago. The challenge, though, was to figure out how to use magnets to generate a magnetic field and then channel electricity precisely to a target.

Electric buses need large and expensive batteries to generate enough electricity to allow them to run all day. Unlike a gas tank, a battery is heavy whether its full or empty.

A typical 355-kWh battery for an all-electric bus weighs about 8,000 pounds. A WAVE-powered bus only needs a 213-kWh battery pack.

The bus still needs to plug in at night to be fully charged. But range anxiety won’t be an issue, because the stops at wireless chargers keep the bus running throughout the day.

So how long can it go on a full charge?

“Good question, but it’s an old charging model question,” May said. “When you charge wirelessly, it’s all about opportunity—you can charge as long or as little as you want.”

For every minute it charges, the bus can travel half a mile. So if it charges for 60 minutes, then it can run for 30 miles.

The total lifetime cost for an electric bus can be less than that of a bus running on compressed natural gas or diesel, May said.

Transit agencies in California and Texas have placed orders with WAVE. The technology will work with cars but the company believes it is best suited for a niche market—transit agency buses, delivery vans, and heavily polluting industrial vehicles.

“Transit agencies love the idea since they all want to run electric buses and save money, but they’re also nervous about it because they run 150-mile routes on CNG, which is very reliable,” May said. “So they’re all in wait-and-see mode.”