Greentech Media

No matter how eco-auto savvy they are, customers won't be able to install the conversion system themselves, Hymotion warned. Drivers will have to turn to a developing network of certified installers. The first installers will be located in Los Angeles, San Francisco, Seattle, Boston, Minneapolis and Washington.

Thilo Koslowski, lead automotive analyst at Gartner, said he's intrigued by Hymotion's business model of selling kits into the aftermarket, instead of selling to automakers or manufacturing its own plug-in vehicles from scratch.

He likened the model to the secondary market that has risen to sell iPod accessories.

"We just haven't had this in the car industry," he said.

But tricking out a Prius will be a more extravagant indulgence than accessorizing an iPod.

"The cost is pretty high," Koslowski said.

Moreover, he said the launch timing isn't ideal in the softening economy. As a result, Koslowski said he doesn't expect a high sales volume for the conversion kits.

Still, big car manufactures will keep an eye on Hymotion, taking stock of the interest and demand from consumers, he said.

And the fact that a small company is willing to take the risk of entering the plug-in hybrid market could push the auto industry to move faster, he said.

But won’t increased competition be bad for Hymotion?

Kramer doesn’t think so, in any case.

"It's not correct to think there is some window of opportunity that will close once car makers are selling plug-in hybrids," he said.

While car manufacturers might take over the market for new plug-in hybrids, Kramer said he expects more than 1 million hybrids to be on the road by then, leaving Hymotion with enough of an aftermarket opportunity to carry on.

But before it can carry on, the company first needs to get started. If it can be the first to market with a kit that regular drivers can order online – and if can prove that car owners want plug-in hybrids, it could give the technology the kick start that advocates have been waiting for.