Greentech Media

While the grid already is strained in some places, a U.S. Department of Energy study released in December found the current system could accommodate 170 million plug-in hybrids. How's that? Most owners would charge at night, when electricity is in surplus.

Of course, the grid is hardly a mosaic of greenie goodness at the moment. It's mostly powered by natural gas and coal today. But Brown's vision is to power the plug-in hybrids with wind power, which peaks at night.

It's an attractive idea because plug-in hybrids would reduce fuel costs for drivers if they plug in, yet allow them to fuel up as usual if they don't. And wind power is a proven technology that's already cheaper than conventional electricity in some places.

But others say the scenario is unrealistic. First of all, wind isn't consistent, and Vinod Khosla, founder of Khosla Ventures (and a co-founder of Sun Microsystems), says utilities need to be able to supply customers with extra power when they want it. "They can't say, 'We can't supply power now because the wind isn't blowing or the sun isn't shining'," he says. "Regulators would come down pretty damn hard on utilities that said that."

Brown counters that at large scales - if wind power were evenly distributed nationally, for example - wind power is as reliable as conventional electricity. Also, he says, the plug-in hybrids' batteries could act as backup storage to even the flow of electricity. Utilities could pull from those batteries to avoid an outage in a crisis, and drivers wouldn't be stranded because the cars work as regular hybrids if they aren't charged. (Two California utilities, Pacific Gas and Electric and San Diego Gas and Electric, have demonstrated plug-in hybrid technology in the last few months.)

Even so, plug-in hybrids are too expensive to reverse climate change, Khosla says. According to the DOE report, plug-in hybrids are expected to cost $6,000 to $10,000 more per vehicle than conventional cars. Even at just $20,000 a car, it would cost more than $4 trillion to switch over America's 220 million-plus cars. "A few trillion dollars, and sure, we can solve the problem," Khosla says.

It's true that cars have decade-long lifespans, meaning it would take years for the world's fleet to make the switch even if every new car sold were a plug-in hybrid - even assuming they were readily available. But if plug-in hybrids catch on, they could well play a role in reducing oil use - and possibly in boosting wind power.