Energy Department Launches Confusing New Electric Car Fuel Calculator

By · June 11, 2013

DoE Cost Caluclator

How much does it cost to fill an electric car? The answer can vary according to where you live, where your electricity comes from, and what car you’re driving. On average, an electric car is about three times cheaper to run than a gasoline car, but it can be difficult to make a precise comparison of fueling costs between your existing gasoline car and the electric one you’re hoping to buy.

Enter the U.S. Department of Energy and its new fuel calculator designed to help you figure out how much money you can save by making the switch to electric. The calculator works by looking up the average price of a gallon of gasoline in your home state, and comparing it with the average cost of electricity, which is displayed as an eGallon.

But what is an eGallon? According to the D.O..E., it’s an easier way tomake the direct comparison between electric fuel and gasoline—essentially a rebranding of the term "gallon of gasoline equivalent" or G.G.E. Like its Miles Per Gallon equivalent (M.P.G.e.) calculation used to generate efficiency ratings for plug-in cars however, the eGallon is a convoluted beast—and adds to the alphabet soup of alternative terms used to describe non-liquid fuels.

“The eGallon is measured as an ‘implicit’ cost of a gallon of gasoline,” writes the D.O.E. in its eGallon Methodology paper. “It is calculated by multiplying the average U.S. residential electricity price (EP) by the average comparable passenger car's adjusted combined fuel economy (FE) by the average fuel consumption of popular electric vehicles (EC).”

Or for readers with a math mind, eGallon ($/gal) = EP * FE * EC.

Misleading, Confusing

While the intention of the U.S. D.O.E. is to make it easier to compare the cost of owning an electric car and a gasoline car, the methodology is mixed up. Not only does the calculation make gross generalizations about the U.S. car market, but it invents an entirely new unit of measurement where none is required.

For a start, the eGallon is calculated using a combination of averages, dramatically decreasing the accuracy of the figures displayed. Second, while it focuses on cost rather than gas mileage, it doesn’t give real world consumption figures. Instead, it gives a fabricated eGallon figure as a comparison to something drivers are already familiar with—the price they pay per gallon at the fuel pump. Apparently, the D.O.E. is betting that drivers will be motivated by thinking of using electricity as some kind of equivalent of a buck-fifty gas (or something close to it.)

While this illustrates the fact that plug-in cars are cheaper to drive than gasoline ones, it does nothing to communicate the real-world, everyday cost in terms of cost per distance traveled. A far more sensible and accurate option would be to offer a calculation based on how much each car costs per mile.

With its large database of official E.P.A. ratings, and knowledge of fuel and electricity prices across the U.S., the Energy Department should build a calculator that allows customers to input their car make, model, and year, where they live, and how many miles they travel on average per day. It could then give them a price per mile breakdown compared with any number of popular plug-in cars, offering a true, easy-to-understand cost per mile analysis.

As gas prices rise, and electricity prices remain relatively stable, the analysis per mile could give consumers all the incentive they need to make the switch to electric.

New to EVs? Start here

  1. Seven Things To Know About Buying a Plug-In Car
    A few simple tips before you visit the dealership.
  2. Incentives for Plug-in Hybrids and Electric Cars
    Take advantage of credits and rebates to reduce EV costs.
  3. Buying Your First Home EV Charger
    You'll want a home charger. Here's how to buy the right one.