Willett Kempton drives an uncommon car.

The body is a Toyota Scion. The innards have been stripped of their "greasy parts," and replaced by massive batteries and other electrical components.

The resulting vehicle, developed by Kempton, a renewable-energy professor at the University of Delaware, can hit 95 miles an hour and go 120 miles before charging.

As impressive as those numbers are, the car's real benefit is that it's not just a user of energy.

It's also a provider.

The battery in this new breed of electric car can both give and receive, taking a charge and then, through the same electrical cord, sending some of its stored energy back to a hungry electricity grid, as needed.

Kempton's is currently the only such two-way electric car in a regional grid that spans Pennsylvania, New Jersey, and some or all of 11 other states, along with the District of Columbia.

But add a few million more - as Kempton and others predict will happen, perhaps within the decade - and things begin to look a whole lot different.

Suddenly, the nation's automobiles are no longer just a transportation option, but a network of mini-storage devices for electricity.

One car might even power a few nearby homes for a while if the wires go down in a storm.

"Energy storage is not only a nexis between these two titans - the energy and auto industries - it's a game-changer," said Edward Kjaer, director of electric transportation for the Southern California Edison utility.

He spoke last week at an electric-car summit at the Valley Forge offices of PJM Interconnection, the region's grid operator.

More than a dozen electric utilities were there along with three other grid operators, two automakers, plus a bevy of think tanks, government agencies, and other electric organizations.

They touted the plug-in car as a way to reduce emissions that cause global warming, save customers money, and wean the U.S. off foreign oil.

But most of all, they focused on how the next generation of plug-ins could solve a problem that has plagued the electricity industry: energy storage.

Unlike the water supply system, which has reservoirs to balance supply and demand, the electric system must balance input and output on a near-instantaneous basis.

Right now, the wizardlike grid operator sends pulses of information every two to four seconds to coal-fired and natural-gas plants in the system, telling them to rev up production. Or slow down.

That prevents the plants from operating most efficiently, much the way a car guzzles more gas when it speeds up and slows down constantly instead of cruising in its sweet spot of fuel efficiency.

Supporters see the new plug-in vehicles as a stabilizing addition. They envision thousands or millions of car batteries taking electricity from the grid during low-demand periods, such as overnight, and sending electricity back into the grid at times of heavy demand.

It could help the industry shave the peaks - important, because the whole system has to be sized for the highest demands to avoid brownouts - and fill the valleys, when some power plants might otherwise be slow.

This ability will become far more important, experts say, as the nation moves to increased power from fickle wind and solar sources, which fluctuate with every gust and passing cloud.

How many cars will it take? Even thousands would be a good start, said PJM's president and chief executive officer, Terry Boston. At the top end, his grid system, which serves 51 million people, could handle 25 million cars in its off-peak hours.

Kempton's car is a research project owned by the University of Delaware. It's dubbed the MAGICC car - after the initials of the Mid-Atlantic Grid Interactive Cars Consortium, formed to further develop, test and demonstrate the technology.

It was a star at last week's summit, ensconced in a big tent in the parking lot.

The car was plugged in and sucking juice. Then, a PJM official sent out a signal from a grid computer just a few feet away, and within a second a nearby meter started spinning backward. The car was giving electricity back.

As a custom job, the car cost about $70,000, Kempton said. But he estimated that on the mass market, such a car would cost about $5,000 more than its gas counterpart.

What gives it a financial edge is that electric "fuel" costs a fraction of gasoline.

Better still, the car owners could be paid for the electricity they return, perhaps enough to earn back the cost of the car in a few years.

Most owners use their cars just one hour a day. In a "vehicle-to-grid" world, "the other 23 hours, that device belongs to the system," said Jon Wellinghoff, chairman of the Federal Energy Regulatory Commission (FERC).

Last week's supporters cited a confluence of events that are boosting the advent of electric vehicles.

Towns are planning. Austin, Texas, is considering adding plugs to its parking meters. San Francisco, Oakland and San Jose have announced plans to pursue a joint charging infrastructure.

The technology is getting there. Chevrolet is coming out with its first plug-in vehicle, the Volt ("more than just a car" is its slogan), in November 2010. (It won't be able to give back, but future versions likely will.)

By one official's count, about 15 other electric-car projects are due out between then and 2012.

President Obama was surely the first to refer to the grid in an inaugural address.

"It's gone beyond the nice science fair project," said Arshad Mansoor, a vice president of the nonprofit Electric Power Research Institute.

To be sure, the fuel of the future has yet to be chosen.

Both car companies represented at last week's summit, Ford and Chevrolet, said they were continuing research on hydrogen and natural gas.

And there are more hurdles than anyone cares to count.

Foremost among them is the battery.

The technology has progressed from lead acid to lithium ion, but the batteries are still massive, heavy and expensive. Until a few weeks ago, when GM announced a deal to open a manufacturing plant for its Chevy Volt batteries in Michigan, all were made abroad.

It put promoters in the uncomfortable position of wondering whether they were just going to replace foreign oil with foreign batteries.

But the United States is ahead in developing new batteries using nanotechnology, they said.

The technology requires more of a "smart grid," capable of more two-way conversations. That, too, is coming.

A recent FERC report said about 8 percent of U.S. consumers now participate in some type of "demand response" program, which allows a utility to turn off electrical equipment during periods of peak demand.

A big question is emissions, said Michael Ligett, director of market and energy services for Progress Energy, a Southeastern utility. "As we change . . . from millions of tailpipes to hundreds of smokestacks, our emissions will go up," and utilities worry they could be penalized.

But society's emissions would go down. For the first time in about a century, drivers could be breathing easier.

Contact staff writer Sandy Bauers at 215-854-5147 or sbauers@phillynews.com. To post a comment, visit her blog at http://go.philly.com/greenspace.