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Will Fast Charging Make Electric Vehicles Practical?

Improved chargers cut down on wait times, but they’re expensive, among other drawbacks.
September 24, 2012

It can take hours, even days, to recharge an electric car. That’s one reason GM added a backup gas-powered generator to its electric car, the Volt. Another option is the DC fast charger, which would allow cars to recharge up to 80 percent of the battery’s capacity in just half an hour.

Tesla Motors’ first DC fast-charging station, halfway between San Francisco and Los Angeles, will allow drivers to add 150 miles of range to their electric cars in half an hour—provided they have one of the higher-priced battery packages. Adding those miles would ordinarily take from several hours to more than a day, depending on the size of the battery and whether an ordinary outlet or a higher-voltage one is used.

But the impact of such charging stations will be limited by their high cost, and by the fact that fast-charging still takes far longer than it does to fill up a tank of gas. Conventional vehicles will remain the best option for people who regularly drive long distances; and those who purchase electric vehicles for commuting won’t need fast chargers—they can charge overnight at home or during the day at work.

For now, at least, the biggest barrier to electric-vehicle adoption is simply the high cost of the cars, which can cost twice as much as comparable gas-powered vehicles.

Most electric vehicles don’t require any special charging equipment. They come with on-board chargers that convert AC power from ordinary wall outlets to the DC power needed by the battery. But charging from a conventional 120-volt outlet is slow. It takes nearly a full day to charge the Nissan Leaf this way, and nearly three days to charge the version of Tesla’s Model S with a 300-mile range. EV owners often install special 240-volt connectors in their garages to shorten charging times to several hours—and almost all public charging stations charge at this rate.

DC fast chargers bypass a vehicle’s on-board charger—converting grid AC power to DC power outside the car—and deliver electricity directly to the battery at a higher rate than the on-board chargers would allow. A communications link incorporated into the charging cord allows the car’s battery management system to control the rate of charge to avoid damage to the battery. The system will, for example, slow down charging if the battery overheats or will typically stop charging when it reaches 80 percent of capacity.

The charging capacity of DC fast chargers varies. Some only deliver 20 kilowatts, but some experimental chargers deliver well over 100 kilowatts (in comparison, most 240-volt outlets will deliver 3.3 kilowatts). A 50-kilowatt charger would be more than enough to charge a Nissan Leaf to 80 percent capacity within half an hour (it has a 24-kilowatt-hour battery pack and less than 100-mile range). Charging times will vary widely depending on the temperature outside for the Leaf, but less so for other cars that have better battery cooling systems (see “Are Air-Cooled Batteries Hurting Nissan Leaf Range?”). But the standards for DC fast chargers are evolving—not all electric vehicles have fast-charging outlets (GM’s Volt doesn’t have one, for example), and adapters may be required for those that do. Only a couple of hundred have been installed so far in the United States.

The cost of the technology could prove a major obstacle. The equipment can cost tens of thousands of dollars, and installation costs can be triple the equipment costs, bringing the total to over $100,000 in some cases. Ecototality, which has installed 7,000 conventional, non-fast charging stations, is working with the U.S. Department of Energy to study whether drivers will use fast-charging stations enough for station owners to recoup the capital cost.

Another challenge is the fact that utilities will often charge a hefty “demand charge” per month because of the high load these chargers can put on the grid, says Arindam Maitra, a senior project manager at the Electric Power Research Institute. Fast charger owners will have to pay that fee even if no one uses the station. At least one DC fast-charging system charges $7 per charge, which is more expensive than buying gasoline for the equivalent range in a conventional car.

There are also reasons to doubt that electric vehicle owners will use fast chargers regularly. Most drivers in the U.S. travel less than 100 miles a day, and those who need to travel farther might find electric vehicles inconvenient, even with fast charging. Most of the electric vehicles on the market now and coming out in the next few months travel less than 100 miles on a charge. And cars with a larger range, like Tesla’s Model S—which costs $88,000 for the 300-mile version—are out of the price range of most drivers (see “Can Tesla Survive?”).

If battery costs come down significantly and 300-mile EVs become the norm, fast chargers located between cities such as Los Angeles and San Francisco and Boston and New York could be attractive. Pasquale Romano, CEO of Chargepoint, which has installed a network of about 10,000 conventional charging stations and is starting to add some fast chargers, says: “DC fast charging is very important in long-haul charging and occasional emergency charging. You’d drive a few hours, and stop and have lunch while you charge. They’re needed to make the ecosystem work.”

But Romano doesn’t see such fast chargers becoming common. “It’s not going to be a world where there’s DC everywhere and you’ve replaced gas stations,” he says, adding that most charging will be done at home or at 240-volt charging stations around town.

GM’s head of electric vehicle infrastructure development, Britta Gross, thinks 30 minutes is still too long to wait on a road trip. “Americans are very time-conscious,” she says. GM’s Volt doesn’t require fast-charging for long trips—it just uses the on-board gasoline generator to boost the range by about 300 miles (see “Teardown Reveals the Remarkable Complexity of Chevrolet’s Volt”). GM’s upcoming Spark EV, however, won’t have a gasoline generator to extend its range.

In terms of the adoption of these vehicles, Gross says, the first priority is having inexpensive 240-volt charging stations in people’s homes, followed by similar stations at workplaces for people who don’t have garages at home, both of which would allow electric vehicles to play to their strength—short commutes. She thinks DC fast chargers might have a niche market for those who live in cities and can’t charge at home or at work. They could use the cars to commute, charging up over lunch every few days.

Garrett Beauregard, senior vice president of engineering at Ecotality, is worried about another problem: building too many charging stations, conventional or otherwise, too quickly. “Overpopulation is bad. Some people oppose incentives that have allowed chargers to be installed,” he says. “We don’t want people pointing and saying, these things cost how much, and they haven’t been used in six months?”

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