PNAS Study: Promise of EVs Depends Critically on Electricity Generation Sources

Shifting to electric vehicles in the future will reduce emissions due to less burning of gasoline in internal combustion engines. But a significant share of this benefit will continue to be offset without complementary policies designed to lower emissions from the sources of electricity that come online to meet additional demand. That’s the finding of a new study co-authored by Yale School of the Environment Economics Professor Matthew Kotchen.

The study published in PNAS is the first to show an increase in marginal emissions in electricity generation stemming from an increased reliance on coal to meet additional demand for electricity.

“Even though average emissions decreased by 28% over the last decade, marginal emissions increased by 7% largely due to a greater reliance on coal to satisfy shifts in electricity use,’’ the study found.

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Using these metrics, the authors also evaluated the Biden Administration’s goal of having electric vehicles make up 50% of new vehicle sales by 2030 and found that the increase in emissions to meet that target would likely undo more than half of the emissions reductions from fewer gasoline-fueled vehicles.

“Average emissions are sometimes used for policy evaluation despite the fact that shifts in electricity demand are associated with different sources of generation than what characterizes the grid on average,’’ the study noted.

Calculations on the potential for emissions reductions from electric vehicles that rely only on average emissions and don’t include marginal emissions will overestimate the reductions by 27-114%, the study states.

The authors said policies need to address lowering both average and marginal emissions and eliminating coal fired generation will be key to both.

In the past, coal was used to meet base-load demand for electricity and natural gas was used to ramp up and down demand shifts, but in the past decade that has switched because natural gas has gotten cheaper. Coal is now becoming more of the marginal fuel source for generating electricity.

“We need to be careful not to let EVs be the lifeline for continued existence of coal plants,’’ said Kotchen.

Nine percent of new cars sold in the U.S. last year were electric, up from 2.5% in 2019, according to the International Energy Agency.

“It’s important to recognize electric vehicles are still going to be cleaner than internal combustion engines, but we can make them even cleaner with complementary policies that promote electricity generation from lower-emission sources of energy’’ says Kotchen.