Of all the solutions we've seen to extend the range of EVs, this might be the most unique. A company in Wakarusa, Indiana, has designed a self-propelled trailer that contains an electric generator and batteries that keep an EV charged.

Electric Motors and Vehicles (EMAV) founder and president Wil Cashen thinks that the United States doesn't have a robust enough infrastructure to keep the coming fleet of EVs charged in the near term. So, he's developed the Pru – short for Power Regeneration Unit – as what he calls a "rolling infrastructure" that always has power at hand to charge an EV in any situation.

"We decided that this thing has to be completely self-powered and guided by the host vehicle," Cashen said. "It couldn't be in a position where it's being towed. We designed something called the Smart Hitch – the brains behind the entire Pru vehicle. It sends a signal to the speed controller based on the pulling, tugging or tension that's delivered to the hitch when the host vehicle moves."

With the hitch in place, the Pru always propels itself with an internal 240V DC motor to match the car's speed so there is no stress on the EV. "We made it so it never taxes the electric car, so that the electric car never has to tow anything," Cashen said. A GPS unit uses data from Google Earth to determine topographic variations that may affect the battery's duty cycle.

Connected to an EV with a hundred-mile range, Cashen estimated the Pru's combined lithium-ion batteries and four-cylinder, 750-cc diesel generator could provide a range of 700 miles on six gallons of gas – or a 116-mpg equivalent. The Pru has the ability to deliver up to 400 volts and can also be used as a standalone charging unit wherever power is unavailable.

Cashen, who was the CEO of Electric Motors until he was ousted in January, envisions the weekend outdoor enthusiast or frequent road-trip vacationer as the ideal customer for the Pru.

"We're looking at people who want to be a one-car family, " Cashen said. "During the week, they're driving short distances, but if they're going somewhere on the weekend." Of the six-foot trailer, only a quarter of the space is taken up by generator and batteries. "We made room so that people can put their gear in it," he said.

EMAV already has experience designing campers and trailers, having developed and manufactured the Mopar - Jeep Tech Camper/Trailer products as a tier two supplier. Cashen says that Chrysler is keeping an eye on this project, too. "Obviously, they're interested because they're going to be building an electric car," he said.

So far, the entire project is theoretical, as there's no prototype yet. Still, Cashen said the first Pru units would be sized to follow behind small and midsize cars and may be ready by the first part of 2011. That's just in time for the Nissan Leaf and Chrysler's upcoming Fiat 500 EV. The cost is estimated at $15,000 – about eight times the price of a six-foot trailer without a battery and generator on board.

Images: EMAV