‘Little’ Errors Add Up: What an Electric Vehicles Study Gets Right, and What It Gets Wrong

December 21, 2016
David Reichmuth
Senior Engineer, Clean Transportation Program

A new study by consulting firm Arthur D. Little (ADL) claims that the benefits of electric cars, both environmental and economic, are lower than others, including UCS, have shown. However, the differences are largely due to questionable assumptions about battery replacements and the use of electric vehicles as a gasoline car replacement.

What they get right

EVs on average have lower overall greenhouse gas emissions and lower costs to fuel than gasoline cars now, and these benefits are likely to increase over time. This is the conclusion of our report and also the ADL analysis. In our report, “Cleaner Cars from Cradle to Grave”, we found that the average electric vehicle results in about half the climate changing emissions than a comparable gasoline car, even when the manufacturing emissions are included. The ADL study finds a lower benefit, about 20 percent, due to assumptions discussed below. However, they also note that the emissions savings will likely grow over time as electricity generation becomes cleaner, consistent with our findings.

What they get wrong about emissions

The ADL analysis and the UCS analysis of greenhouse gas emissions is largely the same except for two factors: battery replacement and the need for a replacement gasoline car to accompany the electric car. These two factors account for nearly 40 percent of the ADL estimate of emissions from a battery electric car and therefore are critical to understanding the benefits of electric vehicles.

The ADL study assumes that all EVs will need a replacement battery after seven to ten years of use. The study cites the fact that “this is consistent with the warranty that BEV manufacturers offer on their vehicles’ battery packs” to bolster this claim. However, by analogy, gasoline cars would be expected to need a new engine and/or transmission after the expiration of a five-year powertrain warranty. We don’t know what the true lifetime and failure rate for electric car batteries are, especially for today’s second generation battery systems since they’ve only been on the market for a few years. But assuming a battery replacement at 7-10 years is a 100 percent failure rate for the battery system. Making this assumption would require some proof, and yet there’s no evidence that this is the case for battery lifetime.

The largest factor inflating the ADL estimates of emissions is the assertion that drivers of electric vehicles would 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 questionable assumption is critical to the lower electric car benefits seen in the ADL report: it increases their emission estimates from an electric vehicle like the Nissan LEAF by 28 tons, while the baseline estimate of  LEAF manufacturing and electricity use only totals 69 tons.

The ADL study chooses an unlikely scenario — that an EV buyer would purchase a vehicle that covers only 75 percent of their trips — to arrive at their emissions estimate, rather than doing a straight up mile for mile comparison. This argument is based primarily on early electric vehicle use data from Idaho National Laboratory that showed Nissan LEAF drivers drove on average 9,700 miles per year, while gasoline cars average around 12,000 miles per year. But since that data was collected, charging infrastructure has improved and electric car drivers are going farther. Per California Air Resources Board data, drivers of 2013 and 2014 Nissan LEAFs are going an average of 11,000 miles per year. But perhaps more important, it looks like at least some of the lower mileage in electric cars is not due to the technology, but instead the lease terms that many electric car buyers choose. Auto companies have offered very attractive low-mileage lease terms for electric vehicles, with 10,000 – 12,000 miles per year included in the lease contract. Nissan LEAF drivers that chose a 12,000 mile or lower lease drove on average 9,000 miles per year, while those on a 15,000 mile lease drove over 12,000 miles per year on average. If the lower annual driving for an electric vehicle is not due to technical limitations, then there is no basis for adding gasoline vehicle use to the emissions analysis of electric cars.

However, even if electric cars were being driven fewer miles, the assumption that additional gasoline miles would be needed is biased. Drivers will choose electric cars with a range and capability that meets their travel needs. Someone who requires the ability to regularly drive long distances without refueling is unlikely to choose a short-range battery electric car as a replacement for a gasoline car. That’s not to say that they couldn’t drive electric; however, they would likely choose a longer-range electric vehicle. The comparison chosen in the ADL study overestimates emissions from assumptions about the behavior of the drivers, not the actual emissions from making or using the vehicles.

What they get wrong about costs

While our report focused on the climate-changing emissions from cars, the ADL study also attempts to estimate the difference in costs between electric and gasoline cars. The same choices (100% battery replacement rate and the need for a rental gasoline car) that inflated the emissions estimates also have a large impact on the economic estimates. For example, the cost of the rental gasoline car to make up for miles driven below the national average adds over $10,000 to the ADL estimate of the lifetime electric car cost and adds over 15 percent to the cost estimate. As noted above, these costs are unlikely to occur because a consumer who needs to rent a car 25 percent of the time is not likely to choose a short range EV to begin with.

The next generation of electric cars will be even better

The next generation of electric cars are already starting to show up on dealership lots. Starting with the Chevy Bolt, there are likely to be several battery electric cars that combine longer range, the ability to quickly recharge, and at a more affordable price. These features will make it cheaper to use an electric car and also allow displacement of even more miles that are currently driven using gasoline. Combined with cleaner sources of power, electric cars will likely show even more benefits in the future compared to gasoline vehicles.