Will the 'clustering effect' of electric car owners harm the grid?

SARATOGA, Calif. -- In the long term, the move to electric cars may require an overhaul of the U.S. power grid. But in the immediate future, utilities and others are saying, the grid challenge is so small it barely registers.

This winter, and over the next five years, the first plug-in cars meant for mass production will hit showrooms. The cars will debut in many markets around the country, but they are expected to enjoy the most early success in the "Birkenstock Belt," a slang term for the regions where wealthy, educated environmentalists will pony up for a high-tech car, even if it's a fringe technology.

In researcher-speak, these are "early adopters," and they have an interesting habit: They cluster.

That means they live near each other, which means they use the same part of the grid. And if many have electric cars, they can strain the grid and possibly cause disruptions.

Here in California, the trends would seem to be locked on a collision course. The state sees itself on track for 1 million plug-in vehicles by 2020, and studies suggest these cars will overwhelmingly concentrate in upscale parts of the San Francisco Bay Area and the Los Angeles region.


But even here, experts aren't predicting much trouble. They think the grid can handle the first wave of electric vehicles because the early adopters will be few, in the tens of thousands rather than millions. And even in a largely old-fashioned grid, they say, EVs can probably get absorbed as air conditioners and plasma TVs did before them.

Even in the most optimistic scenario, there won't likely be more than 60,000 plug-ins nationwide in 2011, by Michael Kintner-Meyer's estimate. He's an engineer at Pacific Northwest National Laboratory who researches "smart" car chargers.

"Is this a big problem for the utilities? Most likely not," he said in an e-mail. "Smart charging technology will soon be working its way into the market and then you'll see much more load control strategies applied to mitigate these overloading issues."

For now, transformers carry the extra load

For now, the experts are putting their faith in an old workhorse of the grid: a bucket-shaped device called a transformer.

These gadgets hang at the top of utility poles with a single purpose: to convert the high voltage from the power lines to a level that's safe for human use. At the neighborhood level, a single transformer can serve five to six homes.

They're designed to last for 50 years -- long enough to save utility workers the trouble of replacement, but also long enough for electric loads to change. Fifty years ago, for example, household air conditioning wasn't commonplace; refrigerators had only been used for a few decades.

So grid planners have overdesigned these transformers for the increased workload they're likely to see in their lifetimes. Sunil Chhaya, senior manager for plug-in hybrid electric vehicle deployment programs at the Electric Power Research Institute (EPRI), said the new electric cars, if they're charged at medium speed, will use about half the electricity of a clothes dryer. That's well within the range of a typical transformer, which can handle about a 25 percent overload before bursting.

But what happens if all five, or even just two, of the houses sharing a transformer decide to get electric cars?

That is the question that everyone in the electric-car world -- carmakers, utilities, regulators, and parties like EPRI -- is studying. They want to predict where the cars will turn up and how they'll affect the grid, with enough accuracy that transformers won't explode.

The car companies have the clearest sense of where the very first buyers are, but they have been cagey about this data. Ford Motor Co., General Motors Co. and Nissan Motor Co. Ltd., all of which will release plug-in models in the next two years, either declined or didn't respond to requests for that information.

But the story of conventional hybrids, such as the Toyota Prius and Honda Civic, has gotten their attention. Since these cars have been available to the public for about 10 years, researchers have a good sense of where they've concentrated. Utilities, car companies and EPRI have used hybrid distribution as one way to model where EVs will land.

How many EVs will it take to blackout a neighborhood?

In the Los Angeles area, that forecast is Steve Powell's job. He's the manager of plug-in electric vehicle readiness at Southern California Edison (SCE), a utility serving about 14 million people.

Powell says it will be a while before those 14 million people have electric cars, but the near-term ramp-up is no joke: The utility expects 100,000 on its grid within five years.

SCE serves a 50,000-square-mile zone, so the utility knew the cars wouldn't be spread out evenly. Powell and his team looked at the hybrid data, and they saw the cars clustering near the coast at first, creeping inland only as time went on.

With a rough sketch of where the plug-in cars would be, the researchers began making up scenarios. If a neighborhood in Huntington Beach, for example, had a cluster of EVs, how would it affect their transformers, or the larger ones upstream? What would happen to wires and substations?

By and large, Powell found, there just wouldn't be enough cars in the early going to destabilize the grid. "On a system level, we don't expect any impacts," he said.

The result dovetails with other research around the country. Studies by other utilities have found that the cars will be too few and the transformers too robust to cause many, if any, sparks.

There is a 1-in-100,000 scenario, though: On the hottest day of the year, when every home's air conditioner is chugging and a crowd of EV drivers come home at the same time and plug in their cars, the old, local transformer could burst into flames.

Chhaya, the EPRI researcher, says this scenario is unlikely because people, and the machines they use, are diverse.

For one, they drive differently. Chhaya points out that a driver with a lead foot will enter the garage with a hotter battery; for safety reasons, its computer will delay charging, while the deliberate driver next door can start charging right away.

Another difference: Not everyone may want the same charging speed. Some will buy the faster-speed chargers that put more stress on the grid, but their thousand-dollar price tags may move other drivers to prefer the slow charge they get from a wall outlet.

A hazier view of large-scale use

If the "clustering effect" isn't much of a concern, EV experts say, the real challenge is the long-run preparation for hundreds of thousands, possibly millions, of EVs.

Few regions are as advanced as that of SCE, the L.A.-area utility. Powell, its plug-in chief, said the utility has had a pricing regime for electric cars for more than a decade. Some people can choose to pay more for charging at peak time versus off-peak time; others can choose to charge their car on an entirely separate meter.

An EV owner's choice can affect his utility bill as well as her grid -- and the climate. Charging at peak costs more money, but it also causes transformers to age more quickly. It increases the demand for peak power generation, which increases emissions.

SCE and utilities around the country want to shift to gradual, nighttime charges. There's plenty of spare power on the grid, since everyone's asleep, and this makes the power much cheaper. The utility doesn't have to make as many upgrades to the grid, and its existing grid equipment will last longer.

Jonathan Read, CEO of a company called ECOtality, thinks utilities need to think one step further -- and make this charging "smart" from the start.

ECOtality sells car chargers that can exchange information between the car and the utility. This way, Read says, both a customer and a utility can decide on the optimal way to use their money, electrons and equipment.

The company has received a DOE grant to deploy charging stations around the country -- about 16,000 total -- as public and private hot spots to see how people use them.

Read believes only a tiny minority of utilities and car companies have done the hard thinking about how people will actually charge the cars, and they will have some unexpected bumps as a result.

"You have a lot of utilities that are going to wake up with some surprises," he says. "And let's face it, vehicle manufacturers are there to sell cars; they're not really concerned about the grid. They've never really been concerned about Big Oil. It's just not in their chemistry."