Special to MIT TECHNOLOGY REVIEW by C. Caruso
Electric vehicles promise to free us from our dependence on gasoline, but there’s a catch: most models can’t travel as far as their internal-combustion counterparts without recharging. As a result, whenever widespread adoption of electrics comes up, the conversation almost always turns to “range anxiety.”
New research suggests the concern is overblown. By analyzing people’s driving habits across the country, Jessika Trancik at MIT and colleagues found that currently available electric cars could replace 87 percent of the personal vehicles on the road and still get us where we need to go (and back again). Assuming battery technology improves in line with government estimates, by 2020 up to 98 percent of vehicles could be replaced.
You don’t have to pony up for a Tesla, either. In their analysis, the team used performance metrics for the Nissan Leaf, which starts around $29,000. According to the researchers, the Leaf’s range averages 74 miles per charge, which includes a buffer of 10 percent of charge left in the battery, though that depends on things like whether you often drive in heavy traffic and how hard you tend to lean on the accelerator.
The researchers’ model used self-reported data on how Americans travel, taken from the 2009 National Household Travel Survey. They paired that with GPS data from car trips around the country, as well as fuel economy data, and air temperature readings. The model assumed that people only recharged their cars overnight.
Replacing 87 percent of vehicles with Nissan Leafs would, predictably, have a huge impact on fuel consumption. The researchers say it would slash our national gas-guzzling habit by 61 percent and have a dramatic impact on carbon emissions. If batteries improve in line with expectations laid out by the U.S. Department of Energy’s ARPA-E agency, those numbers would increase to 98 percent replacement, which would account for 88 percent of our gasoline consumption.
Perhaps most interesting is the high potential for replacement across a wide variation in climate, urban planning, and population. Sprawling Houston, for example, has the potential for 88 percent replacement, compared with 87 percent in New York City. Even in rural settings, the model indicates that 81 percent of vehicles could be replaced.
The researchers are currently working on getting the model into the hands of consumers to help them make more informed decisions about whether an electric car can meet their needs, either overall or on a particular day of driving.
“It’s taking the approach of empowering people with information, which often today they don’t have,” Trancik says. “These changes can happen from the ground. And I think the area of personal transportation is just so exciting for that reason, because private citizens can really make a difference today.”
Getting electric cars widely adopted still presents challenges. The biggest is dealing with the remaining 13 percent of cars making trips that are too long for today’s electric vehicles. People need to have a convenient alternative on their “high-energy days,” Trancik says, or they will never purchase an electric vehicle. Sharing of gas-powered vehicles is one potential solution, and down the road, quick-charging stations or battery swapping may become more realistic options.
Installing overnight charging stations at home can also be logistically difficult. Robert Green, a computer scientist at Bowling Green State University who studies electric cars and power system reliability, points out that we must consider how the charging demands of more electric cars will affect the power grid. He considers the newer, more complex data set used by the model to be the study’s biggest contribution. “Better data gives you a more accurate picture of what life with electric vehicles looks like,” he says.
“Every time I see a paper like this, the major takeaway is Hey, you don’t actually have to be scared about these—the math works out,” he says. “But there is that issue when you are driving long-haul or vacation or whatever it happens to be.”