(cabriphoto.com / September 28, 2012)

Environmental impact

The Union of Concerned Scientists, a nonprofit advocacy group founded in 1969 at MIT, uses scientific analysis to address social issues such as climate change, energy, transportation, sustainable agriculture and scientific integrity. According to a study released last month by the group, the impact of driving a Nissan Leaf in Hampton Roads or Northeast North Carolina on global warming is at the same level as that of driving a gas-powered vehicle that returns 55 mpg in combined city/highway driving. For the Mitsubishi i, the gas-powered car would have to return 63 mpg to match the i's impact. According to the EPA figures, not a single car meets these standards.

This is despite electric utilities' reliance on coal.

Even when coal's dominance as an electric power source is considered, gas vehicles contribute more to global warming than EVs. The UCS study cites not just vehicle emissions, but the "wells to wheels" emissions generated by extracting, refining and delivering petroleum to the vehicle. By contrast, electric cars have no emissions; the only emissions come from power plants.

And, if a power plant increases its use of renewable energy, such as wind or solar, the reduction in greenhouse gas emissions can be significant. Considering that the average gas-powered compact car in the United States returns 27 mpg, charging an electric car on average has a greenhouse gas impact of 30 mpg nationwide, according to the UCS. But, if the power plant is fired by natural gas, that score would be 54 mpg; wind, 3,900 mpg.

How efficient?

Just like some gas cars travel further on a gallon of gas, some electric cars go farther off a kilowatt-hour of electricity. The Mitsubishi i is the most efficient, using 0.3 kWh/mile or the equivalent of 112 mpg, according to the EPA. The Leaf rates 0.34 kWh/mile or 99 mpg-e, while the Volt measures 0.36 kWh/mile or 94 mpg-e.

The cost

Electric vehicles, such as the Nissan Leaf and Mitsubishi i, and gas-electric hybrids cost more than your typical vehicle. The Leaf starts at $35,200, the i at $29,125 and the Volt at $39,145. All of them are eligible for a $7,500 federal tax credit.

Assuming these vehicles are driven 11,000 miles annually - or 30 miles a day - the Leaf driver would save $1,180 a year in Hampton Roads; the i driver, $1,210, according to UCS analysis. This assumes a gas price of $3.50 a gallon.

According to an analysis by the Society of Automotive Engineers, Chevrolet Volt drivers use electricity for 64 percent of their travel. Assuming that, you'd save $857 annually, assuming a premium gas price of $3.70.

If you drive more than 11,000 miles a year, the savings will be greater.

Or, put another way, the Leaf and i drivers save 400 gallons of gas annually, the Volt driver 260 gallons vs. your average gas car, which returns 27 mpg in combined city/highway driving.

Still, there's one more cost to consider: battery replacement. According to Consumer Reports, the Volt's batteries are estimated to cost $8,000, the Leaf's approximately $18,000. Thankfully, both EVs have 8-year/100,000-mile warranties on their battery packs and related components.

Final thoughts

Given the positive environmental impact and the savings versus conventionally powered vehicles, an electric car is a viable solution for those who can live with its limited driving range. And the costs reported by the UCS show that while recharging an EV will raise your electric bill, it's still less than the price paid at the pump, in the air and overseas.