If you're contemplating buying a plug-in hybrid vehicle, the main question on your mind is probably how much it will cost to keep the batteries charged relative to the cost of the gas that you normally put into an internal combustion engine vehicle. To help you make the comparison, the Environmental Protection Agency (EPA) has come up with a new measurement called the Petroleum-Equivalent Fuel Economy Calculation or PEF. It allows you to compare the fuel economy of a hybrid or electric vehicle with a car that runs on a gas engine. The calculations that go into the PEF are complicated (you can read about them on the EPA Web site), but in practice all you need to do is to compare the PEF with the normal EPA fuel-efficiency figures to see how much electric "fuel" your hybrid needs to go a given number of miles. For instance, the PEF for the Chevy Volt plug-in hybrid is 230 miles per gallon (97.8 kilometers per liter), making it the first production car with a three-digit EPA rating [source: Valdes-Dapena]. Of course, it's not actually going to be using gallons of gas except when the 40-mile (64.4-kilometer) battery range is exceeded, but this gives you a rough idea of how its fuel efficiency compares with other cars that do use gasoline.
Perhaps a better way of looking at this is that General Motors estimates that it will cost 80 cents to give the Volt a full 40-mile (64.4-kilometer) charge using house current. Hymotion estimates that its plug-in for the Prius will cost even less, about 50 cents per 40-mile recharge. Further, GM says the Volt will run 100 miles (160.9 kilometers) on $2.75 worth of electricity, or about 3 cents per mile. Obviously this is going to vary according to how much your local power company charges for electricity and it'll vary according to whether you charge at peak hours or off-peak hours, but it's considerably cheaper than gasoline would cost for an equivalent distance. Another figure offered by GM estimates that a Volt driven for 15,000 miles (24,140 kilometers) per year without ever exceeding the battery-only range would use $300 worth of electricity annually. By comparison, a car with an internal combustion engine that average 30 miles per gallon (12.8 kilometers per liter) would cost $1,500 annually for the same amount of driving.
This is, in fact, the major advantage of driving a plug-in hybrid. These vehicles may have a limited range and take a long time to charge, but they'll be about the cheapest ride you can get until fully electric vehicles are available.
For more information about the plug-in hybrids and other related topics, follow the links on the next page.