Last week's heat wave prompted another eruption of that perennial question: Won't electric cars that recharge from grid power overload the nation's electricity system?

Or put more bluntly: Will electric vehicles bring down the U.S. power grid?

The answer, equally bluntly, is: No. They won't.

(And we rather wish that certain news organizations--we're talkin' to you, The New York Times--could add a bit more perspective before writing about the topic in the predictable maybe-yes-but-maybe-no format.)

Study by unlikely partners

A comprehensive and wide-ranging two-volume study from 2007, Environmental Assessment of Plug-In Hybrid Vehicles, looked at the impact of plug-in vehicles on the U.S. electrical grid. It also analyzed the "wells-to-wheels" carbon emissions of plug-ins versus gasoline cars.

The study is well regarded, in part because of its authors. It was a joint effort by two somewhat unlikely partners: the Electric Power Research Institute (EPRI), which is the utility industry's research arm, and the Natural Resources Defense Council (NRDC).

It looks at the consequences of drivers charging plug-in vehicles at different times during the day. And it assumes a gradual rollout of electric vehicles into the current U.S. fleet of 300 million vehicles. GM, for example, will only sell 10,000 Chevy Volts during all of 2011.

1 EV = 4 plasma TVs

In practice, this means electric cars will only impose marginal increases on the electric grid. The load of one plug-in recharging (about 2 kilowatts) is roughly the same as that of four or five plasma television sets. Plasma TVs hardly brought worries about grid crashes.

Auto analyst J.D. Power projects that by 2015, global production of plug-in electric vehicles--for all markets, not just the U.S.--will total 500,000 per year, half in China. If they all charged at the same time, that's no more than the load of 2 million plasma TV sets, globally.

Even if the U.S. alone has half a million plug-ins to recharge (out of 300 million vehicles on the road, remember) within a few years, utility executives aren't losing any sleep. In fact, they're happy. They love the idea of selling you "fuel" for your vehicle.

Off-peak charging incentives

They will, however, offer strong incentives to get you to charge overnight, when demand on their generating capacity plummets. They have tons of unused power capacity then, and they'd like nothing better than to sell you some of that power, even at special cheap rates.

Even before "smart grid" applications arrive, owners will be able to direct their electric cars when to recharge. The driver of a 2011 Volt, for example, can plug it in as soon as she returns from work, but set the car to charge only when cheaper nighttime rates kick in--after 11 pm, say.

Knowing all this, the EPRI-NRDC study concluded--not surprisingly--that plug-in vehicles won’t strain the grid. Two earlier, more limited studies from the Pacific Northwest National Laboratory and Oak Ridge National Laboratory concluded essentially the same thing.

'Prius clusters' a worry

A more realistic worry for utility executives is that early adopters who buy plug-in vehicles will live in concentrated groups, informally known as "Prius clusters" (more than half the buyers who've put down deposits on the 2011 Nissan Leaf now own Toyota Prius hybrids).

The result is that neighborhood transformers may have to be upgraded if, for example, two or three homes on a particular cul-de-sac install EV chargers.

Upgrading local distribution equipment is a manageable problem, one that utilities plan for all the time as household electric usage inches up due to new consumer electronics and other equipment.

Knowing where it may occur is key, which is why utilities are working hard asking likely EV buyers to raise their hands ahead of time.

But in short, the extra load on the grid from charging upcoming plug-in cars will be relatively slow to grow, predictable, and highly localized in its early years. Electric vehicles will not "bring down the grid" under any circumstances.

[IEEE Spectrum; photo by Flickr user achouro]