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Clusters of plug-in cars will tax local power grids

Utility executives are most concerned about neighborhoods with many electric cars maxing out local circuits, says the CEO of Pacific Gas & Electric.

DETROIT--If plug-in electric cars become popular in your neighborhood, you may face an electricity supply crunch when it comes to charging.

There have been a number of studies measuring whether the national power grid can fuel large numbers of electric vehicles. But the biggest concern regarding the impact of plug-ins is at the local level, where adding just a few vehicles could strain a local circuit, said Peter Darbee, the CEO of California utility Pacific Gas & Electric, during a talk at the Business of Plugging conference here Tuesday.

Darbee predicts that demand for plug-in vehicles will be very high, as turned out to be the case with cell phones. Based on early data, it's clear that purchasers of plug-in electric vehicles live near each other. Berkeley, California, for example, represents 18 percent of all customers in PG&E's territory while Fresno is only 2 percent.

PG&E CEO Peter Darbee; John Lauckner, General Motors' vice president of global program management; and George Pataki, former New York governor and counsel at Chadbourne & Parke, on a panel at the Business of Plugging In conference in Detroit. Martin LaMonica/CNET

But high concentrations of plug-in electric vehicles poses a serious challenge to utilities, Darbee said. Plug-in electric cars could draw electricity equivalent the amount needed to run one home, or up to three homes in certain places, he said.

"You can see if you have three or five electric cars arrive in a neighborhood, you're going to overload the local circuits, and that will lead to blackouts," Darbee said. "So we see it as an opportunity but we also see it as a challenge of significant proportions."

Darbee said that utilities need to work with auto companies and policy makers to ensure that customers have a smooth experience and that the grid is not stressed.The utility--considered one of the most progressive in the U.S.--is also taking a number of steps to avoid potential problems.

PG&E plans to recommend that consumers have a 220-volt charging point at home, which will allow most plug-in electric cars to recharge in two or three hours, rather than six or seven hours for a regular 110-volt outlet. Although it's more convenient for consumers, that higher-voltage charging significantly boosts the draw--as much as 6.6 kilowatts.

Darbee said that PG&E is a strong endorser of plug-in electric vehicle technology because it can significantly reduce carbon dioxide emissions and reduce imports of foreign oil. But there is a "nightmare" scenario for utilities. That's when large numbers drivers come home on a hot day when the load is already maxed out and they turn on air conditioners and lights, and plug in their cars.

"If that (charging) were at 220 (volts), the results would be pretty dramatic and pretty negative. You would create a peak on top of the current peak load. The effect would be to bring down the electrical system if you had substantial concentrations in the area," Darbee said.

To avoid that situation, PG&E plans to offer a 220-volt charger along with a timer. The consumer would be able to get off-peak rates--called dynamic pricing--by charging between 11:00 p.m. and 4:00 a.m.

Smart-grid technology, whereby homes are equipped with meters that can communicate with the utility, gives more flexibility. In that case, the utility could charge three electric cars in succession or at different rates overnight to ease the draw on a local circuit. Or the utility could offer consumers a menu of charging alternatives.

In about seven or 10 years, utilities are envisioning vehicle-to-grid capability in which a plug-in electric car owner would sell electricity from a battery back to the grid. A driver could program the system so that the stored energy is sold only at a certain price, Darbee said.

The costs of bulking up local electricity circuits should be shared by all people in a service territory, he argued. "Just like when there were hair dryers or electric driers, there was a shared cost," he said.