Challenging Arthur Little study on electric-car emissions: questionable assumptions

Transitions into new technologies always generate confusion and misinformation, and certainly that has been the case with modern electric cars.

Buyers, automakers, and analysts debate their cost, suitability, real-world range, wells-to-wheels carbon footprint, and recyclability, among other issues.

Six years after the first modern electric cars launched, the volume of misinformation has slowed somewhat as sober analysis replaces rhetoric.

But consensus in many of those debates has not necessarily been achieved, and new analyses and articles still emerge that can paint a distorted picture of complex issues.

Take, for example, a study published by long-established consulting firm Arthur D. Little.

Titled Battery Electric Vehicles vs. Internal Combustion Engine Vehicles^[1], it was published in November—and quickly promoted by skeptics of electric cars.

Lower emissions, higher cost

The study concluded that, over its lifecycle, an electric car would generate 23 percent fewer greenhouse-gas emissions than a gasoline-powered car.

That sounds good, no? Apparently not.

If every car on earth were electric, the study continued, that reduction would translate to just a 1.8-percent decline in total emissions.

But the study also concluded that even small electric cars would cost $20,000 more for owners to operate than comparable gasoline-powered cars.

And, their total "human toxicity" (largely due to heavy metals and graphite) would be three to five times greater.

Cue the ominous background music.

Assumptions and methodology

The challenge with all such studies, of course, is in looking at their assumptions and methodology.

An electric car with a higher purchase price would definitely be much more expensive for an owner who kept it only a couple of years and put very few miles on it, for example.

Last month, the Union of Concerned Scientists critiqued the ADL study, summarizing its findings in a post entitled "'Little' Errors Add Up: What an Electric Vehicles Study Gets Right, and What It Gets Wrong ^[2]."

(That's a pun. Get it?)

The UCS notes that its own studies and the ADL report both agree that plug-in electric cars cost less to fuel than gasoline or diesel cars.

And both also agree that they have lower overall emissions of greenhouse gases, and that those reductions will increase over time as the grid gets cleaner—although the two differ in the amount of the savings.

Tesla Model S lithium-ion battery pack in rolling chassis [photo: Martin Gillet via Flickr]

Enlarge Photo ^[3]

Every battery replaced

The group goes on to note, however, that the Arthur D. Little study makes two critical assumptions that together account for fully 40 percent of the emissions attributed to the electric car.

First, it assumes that every electric car will need a replacement battery pack after 7 to 10 years—apparently based on the length of time those batteries are warranted against failure by carmakers.

This assertion is highly debatable. With the very first modern plug-in cars just six years old, the data simply isn't there yet.

Differences in retained battery capacity for modern lithium-ion packs may exist between different models, and between battery-electric and plug-in hybrid vehicles.

"Assuming a battery replacement at 7-10 years is a 100-percent failure rate for the battery system," notes the UCS.

"Making this assumption would require some proof, and yet there's no evidence that this is the case for battery lifetime."

Adding gasoline miles

Second, the ADL study assumes that all electric-car users will "require a replacement gasoline car for about a quarter of all miles driven, because electric vehicles are driven fewer miles per year than gasoline cars."

This increases total emissions attributed to a Nissan Leaf from 69 tons to 97 tons, the UCS notes—a very large boost based on a "questionable assumption."

The Arthur D. Little study does not, in other words, compare emissions for an electric car to those for a gasoline car driven the same distance. It adds miles driven on gasoline to the electric car's emissions.

The study makes this assumption based on early data from Idaho National Laboratory that showed Nissan Leaf drivers covering an average of 9,700 miles per year, while gasoline cars averaged about 12,000 miles.