Taking charge: Toyota Prius plug-in hybrid

Several companies have begun converting Toyota Priuses and Ford Escape Hybrids to plug-in vehicles. Having watched this aftermarket industry develop, we have had our Prius Touring converted to a plug-in for evaluation, sacrificing a factory warranty for science. Toyota, too, has taken notice and developed its own plug-in Prius, which it showed at the Los Angeles Auto Show last November. The company plans to offer a production plug-in Prius based on the next-generation car by 2012.

Like today's hybrids, plug-ins improve gas mileage by using both electricity and a gasoline engine to power the car. However, plug-ins have bigger batteries than ordinary hybrids, and the batteries can't be recharged by the engine alone. They have to be recharged by being plugged in, much like a cell phone or laptop. Automakers and automotive engineering organizations say that electricity is a much more efficient power source for a car—as much as three times more efficient than a gas engine. So when the cars run on electricity, they can save money on operating costs compared with burning gasoline. To be truly green in terms of emissions, however, the source of your electricity also needs to be "clean" (that is, not from a coal-burning powerplant)

Most plug-in hybrids are rated according to how many miles they can drive on electric power without using the gas engine. Some future models, such as the Chevrolet Volt and the Fisker Karma, can drive up to 40 miles (according to the manufacturers) without ever using the gas engine. Chrysler has recently shown prototypes making similar claims.

Toyota says its factory Prius conversion has an electric range of just seven miles. It has an additional 6.5 amp/hour battery pack in the spare tire well. Unlike in our converted car, there is no spare tire.

I had a chance to drive the Toyota version of a current Prius (which is still not for sale) on a trip to Portland last week to attend the Toyota Sustainable Mobility Seminar. The iridescent green and gray version we drove in Portland wasn't fully charged when we got in. (Charging takes three to four hours from a 110-volt household outlet.) With the EV-mode button switched on, we were able to drive all around downtown Portland on a trip of about four miles, and the gas engine never started during normal driving. It sparked to life only when I intentionally accelerated hard once to see what would happen. Even pulling out into traffic from an uphill ramp out of a parking garage, the engine didn't turn on. Toyota claims their plug-in Prius will go 60 mph in EV mode before starting the engine. We didn't have a chance to test that claim.

While Toyota's plug-in Prius was impressive, and may represent the way many future cars will operate, don't expect to find it at dealerships, ever. The real promised plug-in Prius will be a new, next-generation design, and it may be smaller than the current body-style Prius we drove.

—Eric Evarts

Read our "Green tour of the Detroit auto show" and "We plug in our Toyota Prius hybrid."