Tony Markel drives a plug-in hybrid that runs 50 miles per charge, goes 100 miles per gallon and gets power from the sun. If he has his way, you’ll drive one too before long. His 2006 Prius has a lithium-ion battery six times more powerful than the nickel-metal hydride pack Toyota put in it. But what makes the car really cool is the solar panel on the roof. It generates enough juice to go 5 miles. Markel is a senior engineer at the National Renewable Energy Laboratory. He and his colleagues have been experimenting with the car for about a year in a quest to make lithium-ion batteries cheaper and more durable. ‘Those are the barriers — battery cost and battery life,’ he says. ‘That’s the main thing holding the technology back.’ The way he sees it, though, the barriers won’t stand much longer. Automakers are chipping away at those barriers as well, and the lab hopes its research hastens the day when electricity supplants petroleum in our cars. ‘The landscape is changing quickly,’ he says, with plug-in hybrids and electric cars from General Motors, Toyota and Nissan looming on the horizon as early as 2010. […]