It’s widely assumed that charging an EV is a much less expensive way to power a car than pumping gas. But most studies take an overly simplistic approach. However, a team of researchers from the US Department of Energy labs took a comprehensive look at the multiple, interrelated factors. Their detailed assessment of EV charging costs was published this week in the journal Joule.

There’s no single number for annual EV charging costs because it depends a lot on when, where, and how an electric vehicle is charged. Nonetheless, the researchers say the current national average for electric vehicle fuel in the US is $0.15/kWh for light-duty EVs and $0.14/kWh for light-duty plug-in hybrids.

Regional costs vary from an average of $0.10 per kilowatt-hour in Oregon to $0.23 per kWh in Massachusetts. Most states fall between $0.12/kWh and $0.16/kWh range.

An efficient EV goes about 4 miles per kilowatt-hour. So you can start to do your own calculations for annual (or lifetime) EV fueling costs, but that’s a simplistic evaluation based mostly on the cost of electricity. You also need to consider variations in charging behavior, vehicle use, time of day, power level, and retail electricity rates ­– as well as the cost of buying, installing, and maintaining a charging station. 

These factors widen the range of cost to between $0.08/kWh to $0.27/kWh for EVs.

This map shows the cost per kWh of electricity to charge an EV.

Another major factor is how much charging an EV driver does at home versus at work or a DC quick charger. The researchers from the National Renewable Energy Laboratory and the Idaho National Laboratory made assumptions about the mix of charging that’s residential, workplace/public, and DC quick charging. 

  • EVs: 81% residential, 14% workplace/public L2, and 5% DCFC (84% of residential charging uses Level 2)
  • Plug-in Hybrids: 81% residential, 19% workplace/public L2 (50% of residential charging uses Level 2)

Now, spread the costs and variabilities over 15 years. That’s how the researchers determined that the projected expenses saving as low as $3,078 and as high as $10,445 compared with gasoline vehicles.

Previous studies have tried to pinpoint EV charging costs over the lifetime of the vehicle. But the DOE researchers say the new study is more comprehensive. They took into account such factors as the availability and usage of residential time-of-use rates and residential charging using Level 1 versus Level 2.

Here are just a few examples of how these factors could affect EV charging costs:

  • The ubiquitous use of L1 EVSE at home reduces the cost by 24% ($0.11/kWh)
  • Utilizing low cost, off-peak time-of-use rates range from a 14% reduction ($0.13/kWh) to a 17% increase ($0.17/kWh) in a “business as usual” case
  • Reducing lifetime vehicle-miles-traveled to 100,000 miles increases charging costs by 15% (∼$0.17/kWh). The costs of EV charging equipment are amortized over fewer miles.

Complicated enough? No. Each factor also interacts with the others, producing a wide range of possible cost values. So the researchers present “best case” and “worst-case” scenarios. Strictly based on cost, the best case is charging at home using Level 1 during off-peak, time-of-use pricing. The worst case is charging exclusively at DC fast-charging stations.

But assuming a common mix of home and public charging, this map shows how much money you could expect to save in an EV versus gas car based on where you live.

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