I recently took a test-drive in a Tesla Model 3. It was an impressive car, but the ride left me wondering: with all the electric horsepower under the hood, was it really better than a hybrid?

2019 Nissan Leaf. Photo: Nissan

The EPA has a dated, but functional website with all the fuel economy and energy efficiency information a driver could want on gasoline, hybrid, and electric vehicles. The EPA also has a unit of measure for electric vehicles called “MPGe”, an energy efficiency metric introduced in 2010 to compare the amount of energy consumed by alternative fuel vehicles to gasoline ones. The ratings are based on a formula that assumes that 33.7 kilowatt-hours (121 megajoules) of electricity is equivalent to one gallon of gasoline.

Regardless of where you live, the laws of nature say that one gallon of gasoline will produce about 20 pounds of carbon. In Minnesota, however, Xcel Energy produces electricity emitting 0.857 pounds of CO_{2} per killowatt-hour of electricity produced (on average for 2018). Put those numbers another way, with Xcel, 23.3 kilowatt-hours (84.0 magajoules) of electricity is equivalent to one gallon of gasoline in terms of carbon emissions.

I created an easy chart for comparing the pounds of CO_{2} per mile travelled, using a combination of EPA estimates and the Xcel Energy emissions data. You can see any vehicle’s fuel or electric economy at FuelEconomy.gov.

To calculate carbon per mile for a gasoline or hybrid car, take the figure 20.35 pounds of carbon per gallon of gasoline and divide by your fuel economy in miles per gallon. For my vehicle, a 2015 Prius, 20.35 / 45 = 0.452 pounds per mile.

To calculate carbon per mile for an electric car, take the FuelEconomy.gov kilowatt-hours per 100 miles, divide by 100, and multiply by your local area’s average for pounds of CO_{2} per kilowatt-hour. In Minnesota, with Xcel Energy, this is 0.857 pounds of CO_{2} per killowatt-hour of electricity produced. For a 2019 Nissan Leaf, we would calculate 31 / 100 × 0.857 = 0.266 pounds of CO_{2} per mile.

For all chart data, there is a public Google Spreadsheet.

Carbon emissions of select vehicles. Graphic: Author

*What wheels do you take around town? What steps do you take to reduce your carbon footprint? Share your adventures and your discoveries in the comments.*

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