For those tired of winter, you’re not alone. Electric cars hate the cold, too. Researchers have conducted the first investigation into how electric vehicles fare in different U.S. climates. The verdict: Electric car buyers in the chilly Midwest and sizzling Southwest get less bang for their buck, where poor energy efficiency and coal power plants unite to turn electric vehicles into bigger polluters.
Scientists at Carnegie Mellon University (CMU) in Pittsburgh, Pennsylvania, began their research by pulling public data from FleetCarma, a company that tracks vehicle performance among car fleets operated by governments and businesses. The study looked at 7000 all-electric Nissan Leafs across the country and how their driving ranges varied with temperature. Cold reduces a battery’s oomph whether it lives in your car or smart phone. “We then combined those performances with regional reports on weather and drivers’ habits to build a nationwide map of car efficiency for every hour of every day within a typical year,” says co-author and CMU mechanical engineer Jeremy Michalek.
In terms of driving range, electric cars in California and the Deep South travel the farthest, as the balmy temperatures yield the best energy efficiency and therefore longer trips before they must be plugged in again. (That’s a lucky break for Golden Staters, who also purchase the most green vehicles in the nation.) Vehicles in cold places, in contrast, have less battery capacity and thus shorter range. The average range of a Nissan Leaf on the coldest day drops from 112 km in San Francisco to less than 72 km in Minneapolis, according to the study, published online this month in Environmental Science & Technology.
The reason is straightforward. When batteries are cold, they have a lower electrical capacity, which limits the duration in which they can pump power. But extremely hot cities, like Phoenix, were almost as bad as chilly towns. Heat improves battery efficiency, but too much can degrade its overall life span and output.
These temperature extremes require drivers to charge their cars for longer. So the team measured the greenhouse gas emissions that would be generated by power grids as a result of plugging in electric vehicles at home. Average energy consumption by electric cars was 15% higher in the upper Midwest and Southwest versus the Pacific Coast.
“We knew that vehicle range was influenced by AC and heater use in extreme climes, but I was surprised by the size of the cold weather effect on battery efficiency,” says David Greene, an energy and environmental policy expert at the University of Tennessee, Knoxville, who was not involved with the study.
But future electric car owners shouldn’t be discouraged by these environmental shortcomings, Greene says. Electric vehicles are still in their infancy, and the findings offer policymakers new insights into how best to introduce electric cars across the country. For example, he says, America’s power plants are “the biggest source of greenhouse gas emissions” in the country. Cleaning up the grid would be the cheapest way to cut greenhouse gases, Greene says (along with the U.S. Environmental Protection Agency), and lower the climate impact of electric vehicles. In the meantime, policymakers could push incentives, like access to high-occupancy vehicle lanes or tax breaks for charging stations, in regions where electric cars already perform well (such as the Southeast and Pacific Coast) and spend less effort outside those regions. Such incentives could boost electric car sales overall. “More money equals a greater investment into technology, like improved batteries and power stations, which reduces barriers for all consumers,” Greene says.