On Thursday, Consumer Reports released figures from testing the Leaf and Volt showing that both have lower per-mile operating costs than gasoline cars. The savings come from the higher efficiency of electric vehicles, and the lower relative cost for electricity versus gasoline. Their calculations left out a few cost-of-ownership factors, but it is in line with other studies of electric vehicle operating costs. For example a few months ago the New Zealand government declared the iMiev (the only production electric car being imported to that country) was the cheapest to operate.
According to CR's figures the Nissan Leaf costs 3.5 cents per mile to operate based on the national average electricity cost of 11 cents per kilowatt-hour. Of course electricity costs vary from place to place and it's your cost per kilowatt-hour that determines your cost per mile. This cost is less than half what CR calculates it costs to run a Prius. The Chevrolet Volt is a little heavier and costs a bit more electricity to run, and when in electric drive mode it will cost you 3.8 cents per mile. When it switches to gasoline mode (the Volt is a plug-in serial hybrid design), because it requires Premium gas its cost per mile is higher than even typical gasoline cars.
CR's report did not say this, but the comparison is also based on the cost for gasoline. A cost which varies from place to place and from day to day. Over time the cost of electricity is a lot more stable than gas prices, and in the long run we expect gas prices to continue going up, because of the effects of peak oil discussed in ExxonMobil predicts electrified vehicles will be mainstream by 2040.
The costs work out this way because of the greater efficiency of electric drive trains over gasoline. To understand this lets look at a few figures.
Gallons Gasoline Equivalent: This is a measure developed by the EPA to compare between fuels based on the energy content. A gallon of gasoline has 114,000 BTU's, a gallon of Diesel #2 has 129,500 BTU's, a gallon of Liquefied petroleum gas has 84,300 BTU's and so forth. Hence it takes 0.88 gallons of Diesel #2 to equal a gallon of gasoline, and 1.35 gallons of LPG to do the same. Using the same conversion method it takes 33.41 kilowatt-hours of electricity to equal the energy content of a gallon of gasoline.
The Nissan Leaf, with its 24 kilowatt-hour battery pack carries on-board the energy equivalent of 0.71 gallons of gasoline, yet it goes 90-100 miles per charge. For comparison, a fuel efficient car getting 40 miles/gallon would go maybe 29 miles on that small amount (0.71 gallons) of gasoline.
Miles per Gallon Gasoline Equivalent: Electricity comes in coulombs, and gasoline comes in gallons, and as your high school chemistry teacher probably said it is a bad idea to compare apples to oranges, or in this case gallons to coulombs. But with 100 years of societal history understanding miles per gallon, we will feel most comfortable converting electric vehicle efficiency to the familiar miles per gallon units. The powers-that-be (the EPA and NHTSA) have gone through several iterations of ways to inform buyers about the relative fuel efficiency of electric or gasoline cars. They developed a formula, based on the Gallons Gasoline Equivalence numbers, to calculate the miles per gallon equivalency (MPGe) figure that is reported on electric car stickers.
In the Consumer Reports testing they found the Volt got 2.93 miles per kilowatt-hour, while the Leaf got 3.16 miles/kilowatt-hour. Hence the Leaf is more efficient at using its electricity than the Volt, and has a lower cost per mile for electricity.
Fuel Cost per Mile: This being Consumer Reports, we are sure they drove cars around a test track and carefully measured energy consumption. The figures so far should help you understand how they arrived at these figures. But it's straight-forward of CR to, with careful measurement, calculate the cost per mile based on the energy consumption they measure and the cost to buy that energy.
They based this on averages, average electricity and gas prices. And of course both do vary from time to time, but a key difference is that electricity costs are set by utility commissions and change slowly whereas gasoline prices are set by market forces and swing wildly.
The cost to recharge an electric car isn't always the cost of electricity. At your home, with your charging station, the cost to recharge is the cost your utility company charges you for electricity. However when you're away from home the situation is muddier.
Some public charging stations offer free electric car charging. In some cases a store will install chargers in the store parking lot with free charging, because they know a customer whose car is charging might stay longer in the store and might end up buying more things. In some cases businesses are installing chargers for use of their employees who own electric cars. In some cases a parking garage will have chargers where it's free to use the charger, but still costs the driver to park in the garage.
Some public charging stations are a commercial business where a company like Coulomb Technologies or Ecotality wants to profit from operating an electric car charging network. They'll charge you money for the privilege and convenience of charging your car while on the go. These companies will almost certainly charge you more than the cost of the electricity if only because their own costs are more than the cost of the electricity.
In other words, your actual fuel cost per mile with an electric car will vary based on these factors.
Other costs of ownership: The Consumer Reports chart skips over a bunch of other costs of ownership, and only focused on the fuel cost per mile. Electric cars are much simpler and are expected to require much less maintenance. No oil changes every 3-5,000 miles, no spark plugs to change, etc. The biggest cost of ownership question looming on the horizon is the cost to replace the battery pack. The current battery packs are expected to last 5 years or so, but the cars themselves should last 8-10 years or more, which means the Leaf owner will face the question of replacing that pack in a few years. It's not known what the cost of that will be.
The savings based on lower cost per mile operating costs will, over time, pay for the higher up-front cost of buying the electric car. This is just like buying a compact fluorescent or LED light bulb, where the purchase cost is higher but pays for itself over time because the CFL and LED bulbs costs less to run and last longer. As a smart informed consumer it pays to understand the bigger picture of what you're buying and the long term costs of ownership.