A subset of the electric vehicle (EV), the plug-in hybrid electric vehicle (PHEV) combines the battery-stored power of an EV with an internal combustion engine.
The car runs on stored electricity until its charge depletes, at which point the internal combustion engine kicks in. At this point a PHEV can function as a traditional hybrid or a plain old gas-powered car.
Pure EVs are limited by the storage capacity of their batteries, which might have a driving range of 100-200 miles before they need to be recharged. The PHEV offers the advantage of unlimited range, because you can just fill the gas tank as necessary. 100-200 miles is more than most of us drive in an average day, but the PHEV has an advantage on longer trips.
The PHEV is being embraced by traditional automakers as an interim step that will allow them to continue making cars with similar bodies and internal combustion engines until they master EV and eventually hydrogen technologies.
Department of Energy research conducted at the Pacific National Laboratory shows that converting 84% of US cars to PHEVs would result in a 27% reduction in CO2 emissions from transportation. (Keep in mind that electricity generation is not emissions free, since electricity is generated primarily from fossil fuels.)
Between 75% and 85% of cars in the US could be replaced with PHEVs without increasing electric generating capacity, by developing a Smart Grid and Smart Chargers that will allow PHEVs to draw electricity off-peak and actually put electricity back into the grid during periods of peak demand.
So, When Can I Buy One?
The first commercial PHEV available to the general public was released in early 2009 by Chinese automaker BYD. Currently BYD's plug-in, the F3DM, is only available in China, though BYD has said it plans to put the vehicle on the international market by 2011.
Though plug-in conversion kits are available for drivers of traditional hybrids like Toyota's Prius, PHEVs currently remain out of reach for car-buyers in the U.S.. Several start-up automakers seeking to corner the PHEV market have recently announced plug-in models to be released in the next few years.
In 2007, one of these start-ups, California-based Fisker Automotive, revealed plans to build a luxury plug-in hybrid with an all-electric range of 50 miles. Founder Henrik Fisker has stated that he plans to begin selling the PHEV, called the Karma, in late 2009 at a base price around $80,000. If released on schedule, the Karma will be the first PHEV available on the American market.
The highly anticipated Chevrolet Volt, tentatively slated for a November 2010 release, will be the first plug-in hybrid to be mass-produced by one of America's Big Three automakers (General Motors, Ford, and Chrysler). Aiming to put the Volt within reach of the typical American car buyer, GM has tentatively set the base price at $40,000, with government tax incentives bringing the cost down to around $32,500.