As major automakers like Nissan, Mitsubishi, General Motors, and others prepare to roll out mass-produced plug-in hybrid electric cars in the United States late this year, electric utilities are both salivating at the business opportunity and quietly fretting over potential outages that could mar the electric-vehicle rollout. The myth that thousands of EVs will seamlessly fold into the power grid by charging at night, using otherwise idle generating plants and power grids, is breaking down. Utilities worry that EV charging could black out the neighborhoods of some early EV adopters and give the emerging technology a black eye. Policy experts worry that the change in the grid's use could unintentionally muck up their green energy plans.
The urgency was palpable in comments by Saul Zambrano, director for clean air and transportation at San Francisco–based Pacific Gas & Electric Co. (PG&E), at a California Energy Commission conclave in October: "You've got to manage the runway. And from our perspective, we think the runway is getting short relative to the launch of these vehicles."
The EV wave looms largest for California utilities and their state regulators, thanks to the state's long-standing efforts to mandate zero-emissions vehicles and its abundance of wealthy green consumers. Californians buy 12 percent of new cars in the United States but 24 percent of its hybrid electric vehicles. According to the California Energy Commission, close to 5500 plug-in hybrid and pure battery EVs could be cruising the state next year, and state rules require large automakers to sell 20 000 more annually starting in 2012.
A few thousand EVs won't crash the California grid, but they could cause local trouble, explains Doug Kim, director of EV readiness efforts at Rosemead, Calif.–based Southern California Edison (SCE), PG&E's neighbor to the south. Kim expects EV buyers to be concentrated in certain communities. Star-studded Santa Monica is already on his watch list. "We need to make sure that our local neighborhood circuits, including the transformers, are robust enough to support those additional loads," says Kim.
EVs need lots of power, especially when charged quickly. Utilities bet that most buyers will want a 240-volt charger that can "fill the tank" of a modest-size EV in 2 to 3 hours, four times as fast as a standard 120-V charger can. Such "AC Level 2" chargers, as defined by the Society of Automotive Engineers' emerging J1772 standard, draw up to 6.6 kilowatts. Turning one on is like adding up to three homes to a neighborhood, and that's with the air conditioning, lights, and laundry running.
Turning on two or three Level 2 chargers could burn out the street-level transformers that are the distribution grid's weakest link. Most utilities employ undersized transformers, which are designed to cool overnight. Without time to cool, sustained excess current will eventually cook a transformer's copper windings, causing a short and blacking out the local loads it serves.
Ironically, electricity rates designed to discourage charging during the daytime threaten to intensify the night-charging challenge. For instance, customers with an AC Level 2 pay SCE a whopping 28 cents per kilowatt-hour to charge between noon and 9 p.m., but just 10 cents thereafter. That scheme protects the grid while it is normally peaking, but it invites new problems if EV owners plug in en masse at 9 p.m. "All of a sudden you've got an artificial peak and you've got transformers popping," says Zambrano, describing the nightmare scenario for the energy commission meeting.
SCE and PG&E are working with the Electric Power Research Institute to predict likely problem areas, and Kim and others are seeking to strengthen the grid before trouble starts. California's Public Utility Commission, meanwhile, is examining how utilities might use the smart meters they're installing to choreograph charging and avoid an early-evening EV-charging peak. The communication gear needed to allow smart meters to control EV charging can be integrated into vehicle chargers and will come standard in GM's Chevrolet Volt plug-in hybrid sedan.