But what if instead of luring drivers to chargers, you could bring the chargers to the drivers? And make them solar-powered to boot?

"You can deploy this thing in five minutes," says Desmond Wheatley, Envision's chief executive, standing by an EV ARC he brought to an electric car conference in Palo Alto, California, in April. "There's zero environmental impact, and you pick this thing up and move it and you'll never know it's been there. At the end of the day, is it better to drive on sunshine or grid-powered electricity?"That's the idea behind the portable solar-powered parking space invented by Envision Solar out of San Diego. Called the EV ARC, the 9-by-16-foot structure fits on the back of a flatbed truck for delivery. It consists of a parking pad and a canopy of solar panels that charge a 21.6 kilowatt-hour battery. No power grid, construction, or permits needed. The big idea: Municipalities and businesses will buy the solar chargers and set them in parking spaces on city streets, parking lots and at retailers, moving them around as needed.

Envision's vision of a network of off-the-grid solar charging stations taps into a nascent trend. Installations of solar panels are exploding — the U.S. brought online 4,751 megawatts of photovoltaic power in 2013 alone, which accounted for nearly a third of new electricity capacity that year. For homeowners, using their solar arrays to charge their battery-powered cars with carbon-free electricity maximizes their investment in both. (Envision also makes "solar trees" with grid-connected chargers built into their trunks, which have been deployed around the U.S.)

"We know from the studies we've done that people really link together solar charging and electric vehicles," says Daniel Sperling, director of the Institute of Transportation Studies at the University of California, Davis. "You couple electric cars with solar and it's really a very compelling combination that sends all the right signals about the environment and energy independence."

"Economically it doesn't pencil out, given the high price of solar," he adds. "But if you put a standalone solar charger in a parking lot, a retail establishment or a workplace or somewhere it's going to be used during the day, it probably makes sense insofar as solar charging makes sense."

Why not just make the roof of the car out of solar panels?