Plug-ins, the Electric Grid and You

By Joe Wiesenfelder  on November 2, 2009
With mass-market plug-in electric cars getting closer to going on sale, automakers and utility companies are studying the demands on the electrical system and car buyers' homes with wide-ranging conclusions. At "The Business of Plugging-In" conference in Detroit, some participants estimated that preparing your home to charge your car was like preparing it to plug in a hair dryer. At least one high-profile speaker said it was like preparing to plug in three additional houses. The truth lies between these theories. It depends on what kind of car you're charging, where you live and how long you're willing to wait for a full charge. Today, we'll look at the electrical infrastructure's ability to handle plug-in cars.

"The impact from plug-in electric vehicles on the grid could be very substantial," said Peter Darbee, chairman and CEO of Pacific Gas and Electric Corp. Because his utility serves environmentally conscious northern California, Darbee expects a disproportionate adoption of plug-in cars. "There's more likelihood that the actual demand that we see from customers will be substantially higher than estimates," he said.

Currently, average electrical demand varies from one region to the next — as does the infrastructure currently in place to support that demand. "Adding an electric vehicle at 220 [volts] is like adding another home to the network or system — and that would be a home in the San Ramon area where people use a lot of air conditioning," Darbee said. In San Francisco where average electric use is lower, "It would be the equivalent of adding three homes."

The worst-case scenario, Darbee said, is a hot day with high electrical usage where residents would return from work, crank up their home air conditioners and plug in their cars. "You'd create a peak on top of the current peak load, the effect of which could be to bring down the electric system if you had a substantial concentration of electric cars," he said.

A proponent of so-called smart-grid technology, Darbee supports the proliferation of meters and charging stations that can ensure charging happens only at off-peak hours — between 11 p.m. and 5 a.m. — when it’s necessary for the local power grid.

Not all of the conference panelists were as cautionary as Darbee. Mike Ligett, director of emerging technology for Progress Energy Corp., said, "People who want to build out a smart grid on the backs of electric transportation aren't doing us any favors. We do not need a smart grid to make this work." Ligett said simple timers can be used to delay charging until off-peak hours. "It may be different if you serve San Francisco and your citizens don't have a place to plug in — there's no infrastructure and somebody's got to put it in," he allowed.

Progress Energy's electric utilities serve Florida and the Carolinas. "We have plenty of capacity; we have lots of off-peak energy," Ligett said. "Even we expect if three customers in the same cul de sac buy a battery-electric vehicle, we might have to upgrade a transformer, but we're not talking about anything like bringing down the grid. Did we have to replace some transformers when people put in air conditioners 20-30 years ago?" he said. "Yeah, we did."

"The worst thing we can do is confuse our customers and make it too complicated," Ligett said. "There's time for evolution. The market will evolve, the technology will evolve."

In some regards, both electrical utility execs are correct. Power requirements — for both the home and the grid — depend both on location and the type of plug-in car. Tomorrow, in Part II of this report, we'll address the costs and limitations a potential plug-in buyer might encounter.

Hybrids/Alternative Fuels

Executive Editor Joe Wiesenfelder, a launch veteran, leads the car evaluation effort. He owns a 1984 Mercedes 300D and a 2002 Mazda Miata SE.  Email Joe