Most everyone agrees that the next big leap in hybrids—the capacity to plug in to the grid and run mostly on electricity—will be expensive.

But that’s not stopping major automakers from pushing forward with plans for plug-in hybrids that promise dramatic increases in fuel efficiency.

Announcements about plug-ins continue to gain momentum. The Fisker Karma sporty plug-in hybrid sedan is due in mid-2010. General Motors says it’s on track to introduce the Chevy Volt plug-in hybrid sedan in late 2010. Hyundai plans to have a plug-in hybrid on sale by late 2012. Volvo said that its plug-in hybrid will be “a reality” by 2012. Toyota will begin commercial production of plug-in hybrids in 2012, producing between 20,000 and 30,000 units in the first year, according to media reports.

A plug-in hybrid car is similar to a conventional hybrid vehicle—both use a gasoline engine as well as an electric motor. However, plug-in hybrids use larger more expensive battery packs that can be recharged by connecting to common household electricity. Plug-in hybrids provide many of the benefits of an electric car, while maintaining the same driving range as conventional vehicles.

Staying in Stealth Mode

Many hybrid car drivers enjoy keeping the car in all-electric “stealth” mode, when the car is in slow stop-and-go traffic. Plug-ins would extend the stealth mode for the lion’s share of local driving.

The potential advantages are enormous. Consider:

• A hybrid gets about twice the fuel economy as a conventional car of the same size and capacity
• A plug-in hybrid will get about twice the fuel economy of a “conventional” gas-electric hybrid
• A plug-in hybrid, running on biofuel (e.g., 85 percent ethanol) could almost entirely eliminate its use of petroleum

What are the naysayers saying about plug-in hybrids? And how do Frank and Kramer respond?

• “The extra batteries will weigh too much.”
  Response: The extra weight of the batteries will be offset somewhat by the reduced weight of the gas engine. At high speeds in particular, fuel efficiency is affected primarily by aerodynamics—the added weight of the equivalent of one or two additional passengers has minimal impact on mileage.

• “The extra batteries will cost too much.”
  Response: If sold in high volumes by carmakers, vehicles using lithium ion batteries could be sold at prices only a few thousand dollars above that of today’s hybrids. Recharging will take place mostly at night during cheaper off-peak hours.

• “Producing power from the grid (to charge the cars) will produce additional emissions.”
  Response: What the industry calls "well-to-wheel" emissions (including greenhouse gases) for grid-powered vehicles is far lower than gasoline, even for the American power grid (which is about 50 percent coal). Cars charging off-peak will use power from plants that can't turn off at night. Many parts of the country get most of their power from cleaner sources such as natural gas and hydropower. It's far easier to improve centralized power stations than millions of aging cars. Finally, plug-in hybrids recharged from rooftop photovoltaic systems would have virtually zero emission.

While on the campaign trail, President Obama said he hoped to see 1 million plug-in hybrids on the road by 2015, a number beyond the most optimistic forecasts. Since Obama took office, the federal government has implemented a broad range of consumer and industry incentives to promote production and sales of plug-in vehicles.