We noticed you're browsing in private or incognito mode.

To continue reading this article, please exit incognito mode or log in.

Not an Insider? Subscribe now for unlimited access to online articles.

Sustainable Energy

Electric Buses Get a Jump Start

A GM-funded bus could reduce transit agencies’ fuel bills by 80 percent.

The electric-bus startup Proterra has raised $30 million in new funding, including $6 million from GM Ventures. The company uses relatively small battery packs to keep down costs, intending them to be recharged frequently at rapid-charging stations that can replenish them in less than 10 minutes.

Electric bus: Proterra’s buses, including the one shown here, are being used in small numbers by transit agencies.

Fuel-saving technology is important to transit agencies, especially now that diesel prices are high and volatile—a gallon of diesel costs a dollar more that it did a year ago. Proterra CEO Jeff Granato says each bus will save the transit agency $600,000 in fuel costs over the 12-year life of the vehicle, plus another $70,000 to $95,000 in maintenance costs. Electricity to charge the buses costs about 18 cents per mile, compared with about $1 a mile for diesel fuel.  Granato says these savings make the total cost of an electric bus comparable to that of a diesel bus over the life of the vehicle, even though the electric bus costs more up front. (The company won’t say how much the buses cost, but they do, apparently, need nearly $700,000 in fuel and maintenance savings to break even with diesel buses.)

In general, the main problem with electric vehicles is the high cost of the battery packs. Batteries are the most expensive part of electric cars, and they’re an important reason GM’s Volt costs twice as much as a comparably sized gasoline-powered vehicle and the Nissan Leaf has a small battery pack that limits the car’s range to around 70 miles per charge. The Proterra bus has a range of only 30 to 40 miles. Achieving even the modest range of the Leaf would add roughly $60,000 to a bus’s price, according to analyst estimates of current automotive battery costs. (Proterra also isn’t saying what its batteries cost.) Although its short range would be inconvenient in a car, it is more practical in a transit bus, which runs a predictable route and can regularly pull into a charging station.

Proterra uses a type of battery chemistry—lithium titanate—that it says allows the batteries to be recharged in less than 10 minutes every few hours all day and still last eight years or more. Such frequent and fast charging would damage other lithium-ion batteries, rendering them useless after just a few years, Granato says. Proterra has also developed an automated charging system. As the bus approaches a charging station, it communicates wirelessly with an overhead charging arm, which takes control of the motion of the bus as it passes underneath, stopping it when the charger is in place. The bus can charge as passengers get on and off. If the bus travels a route that doesn’t completely deplete the battery, it can be topped off in just a couple of minutes, Granato says.

Proterra’s other key innovation is building its buses out of composite materials, saving thousands of pounds to offset the weight of the batteries and make the buses more efficient.

A similar fast-charging system has been developed by Sinautec Automobile Technologies, based in Arlington, Virginia, and its Chinese partner, Shanghai Aowei Technology Development Company. Their buses use ultracapacitors that can be charged even more quickly than the lithium-titanate batteries. But they only hold enough charge to go several city blocks, requiring charging stations at many bus stops along a route. The Proterra system could allow buses to charge just once per route, reducing the number of chargers needed (which it says cost about $50,000 apiece). The Chinese automaker BYD is also marketing fast-charging buses, but its system requires 30 minutes to charge to 50 percent capacity.

The high up-front cost of electric buses continues to limit their appeal, even to transit agencies in the United States that can get the federal government to cover 80 percent of the cost of new buses, says Bill Van Amburg, senior vice president at CalStart, an organization that promotes heavy-duty hybrid and electric vehicles. Another problem is that new chemistries like lithium titanate have yet to be proved to last in buses. Finally, Van Amburg says, transit agencies, which are used to buying buses that can ply any of the routes on their system, would probably need to make some adjustments to accommodate buses that have to charge one or more times per route.

So far Proterra has made about 10 buses, and these are in use by transit agencies in states including California and Texas. The company plans  to use its new funding to scale up production capacity and drive down costs. 

Tech Obsessive?
Become an Insider to get the story behind the story — and before anyone else.

Subscribe today
More from Sustainable Energy

Can we sustainably provide food, water, and energy to a growing population during a climate crisis?

Want more award-winning journalism? Subscribe to Insider Plus.
  • Insider Plus {! insider.prices.plus !}*

    {! insider.display.menuOptionsLabel !}

    Everything included in Insider Basic, plus the digital magazine, extensive archive, ad-free web experience, and discounts to partner offerings and MIT Technology Review events.

    See details+

    What's Included

    Unlimited 24/7 access to MIT Technology Review’s website

    The Download: our daily newsletter of what's important in technology and innovation

    Bimonthly print magazine (6 issues per year)

    Bimonthly digital/PDF edition

    Access to the magazine PDF archive—thousands of articles going back to 1899 at your fingertips

    Special interest publications

    Discount to MIT Technology Review events

    Special discounts to select partner offerings

    Ad-free web experience

You've read of three free articles this month. for unlimited online access. You've read of three free articles this month. for unlimited online access. This is your last free article this month. for unlimited online access. You've read all your free articles this month. for unlimited online access. You've read of three free articles this month. for more, or for unlimited online access. for two more free articles, or for unlimited online access.