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."
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.
California's regulators also envision smart charging to help EVs synchronize with the state's wind farms, which tend to provide most of their energy overnight. That would help EVs secure something that remains hotly contested by energy experts: their environmental benefit, something that is both complex to calculate and regional.
For their part, regulators at the California Air Resources Board predict that a kilometer's worth of EV charge should result, on average, in just 43 percent as much carbon dioxide as burning a kilometer's worth of gasoline. They consider EVs a key tool in their goal to reduce greenhouse-gas emissions to 1990 levels by 2020.
But things are different for the United States as a whole. Whereas carbon-heavy coal provides just 16 percent of California's electricity, it meets fully half of U.S. power demand. That U.S. reliance on coal-fired power (along with the energy intensiveness of battery manufacturing) negates the EV's on-road efficiency advantage over gasoline-powered cars, according to the U.S. National Research Council.
The effects of EVs are even more vexing farther up the coast from California. Thanks to hydropower, British Columbia's power sector released the equivalent of just 22 metric tons of CO2 per gigawatt-hour in 2007—squeaky clean relative to the U.S. average of roughly 600 metric tons per GWh. However, taking advantage of that low-carbon energy to charge EVs overnight may be pricey, according to a study of British Columbia's grid readiness released in November by the Pacific Institute for Climate Solutions.
British Columbia is in a bind because provincial utility BC Hydro imports cheap coal-fired power from Alberta to meet its nighttime demand, saving up hydroelectric energy for lucrative daytime exports to California and elsewhere. Shifting to hydropower at night to make EV charging green would mean forgoing a significant income stream that keeps power costs low for British Columbia consumers. And the loss of the province's hydropower exports could make it harder for California to meet its carbon-emissions goals. "The BC Hydro mandate for carbon-neutral power generation by 2020 can be either facilitated or aggravated by the growth of [plug-in vehicles]," according to the energy systems engineers at the University of Victoria who wrote the report.