Shorter-range electric cars meet the needs of almost all US drivers

Jonathan M. Gitlin

Nissan

The vast majority of American drivers could switch to battery electric vehicles (BEVs) tomorrow and carry on with their lives unaffected, according to a new study in Nature Energy. What's more, those BEVs need not be a $100,000 Tesla, either. That's the conclusion from a team at MIT and the Santa Fe Institute in New Mexico that looked at the potential for BEV adoption in the US in light of current driving patterns. Perhaps most interestingly, the study found that claim to be true for a wide range of cities with very distinct geography and even per-capita gasoline consumption.

The authors—led by MIT's Jessika Trancik—used the Nissan Leaf as their representative vehicle. The Leaf is one of the best-selling BEVs on the market, second only to the Tesla Model S in 2015 (10,990 sold vs 13,300 Teslas). But it's not particularly long-legged; although the vehicle got an optional battery bump from 24kWh to 30kWh for 2016, its quoted range is 107 miles on a full charge. You don't need to spend long browsing comment threads or car forums to discover that many drivers think this is too short a range for their particular use cases. Yet, Trancik and colleagues disagree.

The authors use the 24kWh Nissan Leaf as the basis for their calculations, based on a probabilistic model of BEV range based on driving behavior (rather than just looking at average commute distances and BEV range). This involved using information from the National Household Travel Survey, hourly temperature data for 16 US cities, and GPS data from travel surveys in California, Atlanta, and Houston (to calculate second-by-second speed profiles of different trip types).

As we all know, fuel economy figures published by the EPA rarely match the real-world, and quoted battery range often needs to be taken with a grain of salt. And this is true for the Leaf—using the GPS survey data the authors calculate that overwhelming majority of trips that match the EPA drive cycle in distance and duration have a greater energy intensity (0.23 kWh/mile for the EPA highway calculation, 0.24-0.33kWh/mile for 90 percent of trips). On top of that, most of us need to run the air conditioning or heater (which is where that hourly temperature data comes in), so the study factors this in, giving the 24kWh Leaf a real-world range of 73 miles (117km).

This almost matches the probabilistic model's calculation of 74 miles (119km) as the "distance for which half of all vehicle trips could be covered on one charge," illustrated in the reproduced figure below:

Enlarge / A reproduction of Figure 2 in Needell et al, 2016, showing the probability that a vehicle traveling a given daily distance exceeds a battery energy threshold (blue: 19.2kWh Nissan Leaf, red: 55.kWh ARPA-E target).

Nature Energy and Needell et al., 2016

Next, the authors used this model to examine how many US drivers could have their daily needs met by a BEV (again, based on the 2013 Nissan Leaf and real-world daily range of 73 miles on a single charge). In fact, 87 percent of all trips made by US drivers fall within this range. This is more than double the percentage found by the Union of Concerned Scientists in 2013, which found that 42 percent of US households could switch to EVs without much disruption.

Even in rural areas, 81 percent of drivers could switch to a BEV according to Needell et al., rising to above 90 percent for cities like Los Angeles, Phoenix, and Miami. The city-level comparisons are also rather illuminating. For instance, comparing the public transport paradise of New York City with the car-dependent sprawl of Houston revealed that the daily needs of drivers in both cities are within one percent of each other.

The fact that the study uses a 19.2kWh BEV (80 percent of the full 24kWh Leaf battery) as its representative vehicle should be even more encouraging for advocates of electrification. Batteries are getting cheaper and more energy-dense every year, and BEVs like the Chevrolet Bolt and Tesla Model 3 promise to double the Leaf's range for roughly the same price. A 55kWh battery should be capable of handling almost all our daily driving needs on a single charge, absent the cross-country road trip.

An accompanying commentary in Nature Energy finds it therefore mystifying that more people aren't making the switch to EVs. But as the National Academy of Science found last year, range isn't the only hurdle to adoption; long charging times, price (a Nissan Versa costs about half as much as the similar-but-electric Nissan Leaf), lack of infrastructure, and general confusion about the technology are all factors holding back EVs (whether they be plug-in hybrid or pure battery). With time, we can expect most of those factors will improve. For the meantime though, don't expect those internet commenters to stop complaining about how the electric car is a waste of time because they absolutely have to drive 200 miles to work every morning.

Nature Energy, 2016. DOI: 10.1038/nenergy.2016.112 (About DOIs).