...What happens if you plug in a bunch of hungry electric cars in a neighborhood?
"We found that they could handle one to two to maybe three vehicles per home pretty easily if they are charged slowly, the same voltage that you have in your home for appliances, 120 volts," says engineer Carl Imhoff at the Pacific Northwest National Laboratory. Slowly means about eight hours. Imhoff says the grid could handle tens of millions of electric cars at that rate.
But people will want faster charging, which will require bigger transformers and heavy-duty power outlets that deliver 240 volts. And running the grid will get more complicated.
Here's why: Grid operators have to match supply and demand 24/7 because they can't store electricity easily. So when demand drops, they have to turn off power plants somewhere. If demand spikes -- say, a hot day in Texas -- they need to fire up extra generators.
The Power-Sharing Tango
Adding millions of cars to the demand side is like tossing a juggler another ball in mid-juggle. Imhoff says one way to keep the system balanced is to use "smart" chargers that tell grid operators how much juice these cars need.
"If you use smart charging," he says, "you can actually cycle the charge -- turn the charge off, turn it on, turn it off, turn it on -- to serve the local conditions of the power system."
Nighttime is a good time to charge cars, when there are lots of power plants sitting idle and electricity is cheaper. And for drivers who care about where their electrons are coming from, that's the most common time for utilities to get energy from wind turbines.
Eventually, grid operators could theoretically draw power from cars when they're hooked up, say, to satisfy a surge in demand somewhere else on the grid. Cars themselves would become sources of energy.
"Presumably," says Mark Lauby, with the North American Electric Reliability Corporation, the grid operators' organization, "the automobiles are going to be smart enough to tell me, 'Hey, I'm here and I want to be charged,' or 'Hey, I'm here and I have energy available if you want it.' "
This kind of power-sharing tango between utilities and drivers could make the grid more efficient, but it's also fraught with difficulties. No one wants to wake up to a drained battery, and to get power back from cars, engineers would have to install equipment to convert the batteries' direct current to alternating current.
So for now, grid engineers are waiting to see if drivers come over to electric cars. If they do, they will build. Copyright 2010 National Public Radio. To see more, visit
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