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A new assessment suggests more than we think, outside of a few large cities.

by Jonathan M. Gitlin - Jul 16, 2015 12:00 pm UTC

Tesla vs Mad Max vs Aurich

Last week, we took a look at the role incentives can play in encouraging people to buy electric vehicles (EVs). Today, we bring you a paper from the National Bureau of Economic Research that attempts to calculate the environmental benefits of EVs versus conventional vehicles in light of those subsidies. Is it as desirable to encourage EV use in a state where the electricity comes from burning coal as it is in a state where that electricity comes from natural gas or nuclear power?

The authors, four economists from the University of North Carolina (UNC) Greensboro, Dartmouth College, Middlebury College, and UNC Chapel Hill have created what they describe as "a powerful and unprecedented modeling framework for analyzing electric vehicle policy." They do this with three different components. First, a model of consumer choice between EVs and gasoline-powered cars. Next, they incorporate the effect of EV charging on air pollution from individual power stations. Finally their model compares the emissions from these power stations with the emissions internal combustion vehicles would produce at the same location.

The analysis uses some quite complicated formulae to calculate the damages that result from emissions per mile from 11 different battery EVs on sale in 2014, compared to the closest internal combustion engine-powered equivalent, independent of price. Where possible they've compared like models, so the EV Ford Focus vs a regular Focus, a Fiat 500e vs a regular Fiat 500, and so on. For cars where there isn't a conventional model (Nissan Leaf, Mitsubishi i-MiEV, Tesla's Model Ss) the authors picked cars they believed were equivalent in features (Toyota Prius, Chevrolet Spark, BMW 7-series). Then they compared the EVs' kWh/mile rating with the gasoline cars' fuel economy, as well as pollution from nitrogen oxides, sulfur dioxide, small particulates, and volatile organic compounds.

EPA city and highway mileage figures are used to calculate the effects of gasoline vehicles in urban and rural areas (their model goes down to the county level). For EVs, the authors start with EPA's MPGe figures and then adjust this for the temperature profile for each county. Then they factor in the amount of each of the pollutants listed above at each of 1,486 power stations across the country per kWh of electricity (the data is from 2010 to 2012). Those pollution estimates then get modified again by an assumed daily charging profile to calculate the emissions per mile of each power plant for any given county in the US.

The US electricity grid consists of three main regions (East, West, and Texas), which the authors further split into nine smaller regions as defined by the North American Electricity Reliability Corporation (NERC). Apparently there isn't much transmission of electricity between the main regions, but the authors assume that within the nine NERC subregions, the pollution from an EV charging will be the same regardless of the county. Finally, monetary values for the social costs of pollution come from the EPA for carbon dioxide  and the AP2 mode l for local pollutants. And in case that wasn't enough, they weighed the statistics for vehicle miles traveled in each county to get a sense of how important driving distances are.

The result of all this complex mathematics is that, outside of a number of Californian and Texan cities, driving an EV may result in more damage from pollution than driving an equivalent conventional car. In Los Angeles, which has a lot of traffic and which benefits from relatively clean electricity, an EV is the right choice, they argue. Alternatively, the rural midwest is the opposite story, since the low population density means comparatively little air pollution from traffic, but electricity comes from lots of coal power stations. But even Chicago and New York fare badly under their model, despite both cities paying a hefty price from conventional traffic pollution.

The paper also suggests that EVs export pollution across a much larger geographical area than a gasoline vehicle. This is something that local governments don't take into account with subsidies in their view, and that the hefty EV subsidies in states like Georgia ($5,000 per EV) are based on an incomplete picture of the problem.

The conclusions are sure to be welcome news to EV skeptics; if recent discussion threads for EVs here at Ars are anything to go by, there are plenty of people out there who want to see battery-powered vehicles fail. However, there are quite a lot of assumptions made in the paper. The estimates are based on traveling 15,000 miles a year (24,000km), which is fifty percent greater than the current average for cars. And as they note, the data for power stations is now several years old, and electricity generation is becoming ever-cleaner in the US. They also haven't calculated the various impacts from mining or extracting the fuel for power stations and cars or the materials for batteries, nor the benefits to encouraging adoption of EVs now to spur the market to develop and refine powertrains and battery technology, something we're definitely seeing happen .

Promoted Comments

One massive benefit of electric cars in cities, is that the pollution isn't occurring at the point of use.

European cities have tough environmental targets to reach by 2020, and many won't make it. London, for example. Pollution within London is estimated to cause 9000+ premature deaths each year, and reduce life expectancy by over a year. Some major shopping streets have terrible NO2 levels, and solving these is paramount.

So even if the power comes from coal, that's coal burning outside the city, thus improving the air

quality within the city (over a diesel or petrol car).

Other solutions require political willpower and intelligence, so it's not worth hoping that they will happen. For example Oxford Street has a bus and taxi problem (all diesel, and too many of them). A tram along the road and terminating buses early (or rerouting them) could solve the issues here. Luckily they are installing electric buses elsewhere in London now, but not in Oxford Street. Taxis should be electric soon too, but there is lifespan to consider here.

690 posts | registered Sep 30, 2006 puppies Ars Centurion jump to post

Really not surprising that cost/benefit varies by region. By extension it should not be surprising that the math will favor EVs more assuming power generation gets cleaner in the future. (which is hopefully the case).

This should not be seen as an indictment of EVs biut rather of the continued use of coal for power generation in many regions.

375 posts | registered Jul 8, 2013 Power_Struggle Smack-Fu Master, in training jump to post

The article basically says that EVs are only as green as the production of their electricity.

Oddly enough, not everybody likes this conclusion.

Considering that EVs can be great at absorbing 'unreliable' green electicity,

considering that PV and wind are already on cost parity with fossil fuels,

considering that fossil fuels are 'too cheap' today because the externalities are unaccounted for,

I would say that the future of EVs looks pretty bright.

93 posts | registered May 22, 2013 Thunder005 Wise, Aged Ars Veteran jump to post

This ARS article was greatly conveyed. but the study itself is completely flawed in their comparisons.

I read this study last week when it broke out and couldn't wait to discuss on Ars. The study is comparing Gasoline to Power generation to get the EPA value of a car. THIS IS A FLAWED COMPARISON.

You can not compare in this way. The only way you could compare if you are doing emissions from a Gasoline engine, is to directly compare the different cars. an All electric car makes zero emissions, so it wins, end of study.

if you want to take one step back and see how the electric car gets it power, then you also have to take one step back at how the Gasoline car (ICE Car) gets its power. I live in southeast texas, where some order of 20-40% of the countries oil supply is processed into Gasoline for the USA, diesel fuel, Jet fuel, and NG is liquefied with additives to be shipped as LNG, and or imported from all reaches of the planet.

These processing plants require HUGE sums of power and pollute unimpeded by the EPA. I don't have any figures but to create one gallon of nice rich 93 octane Gasoline for your pretty BMW-7 series that also produces emissions once it burns it in its own engine, then you also need to take into account the emission produced by the Fracking and oil drilling process, the Shipping vessel to bring it to port, the enormous amounts of power generation required to power the processing plant, the processing plant itself, which uses Coal and other products to produce the gas, the enormous amount of energy it takes to run the pumping station to pump the product to Baytown, TX, then the even large amount of energy to pump that to all parts of the country. And once it gets there, each gas station company adds its own additive and then it has to be trucked to the gas-station it gets picked up at.

so since a coal fired plant can directly mine/extract the coal and then fire it in a fairly clean fired coal plant. (clean compared to years past, even the coal industry says they are getting cleaner). I'd take power generation directly to zero emission vehicle over ICE car any day, with orders of magnitude cleaner emissions if you considered the facts for what they were.

Just use a quantitative value by adding all the emissions to get your one gallon, so it can be included in the ICE comparison since this was done for the EV's.

The Telsa batteries come with an 8 year warranty, so I would have to replace them every 8 years at $12,000. Mabye I would get lucky and wear them out before the 8 years is up, but I doubt it is a replacement value warranty. It is most likely a percentage of life left, which means I would be paying sooner with all the miles I drive.

Battery longevity is directly related to temperature, depth of discharge, and time spent at particularly high and particularly low states of charge. As a result, EV manufacturers lock out the highest and lowest states of charge. At 60% depth of discharge which corresponds to an average of 150 miles of range, and avoiding high and low states of charge, Panasonic has shown similar NCA cells to last over 3,000 charge cycles with a degradation to about 88%. 150 * 3,000 = 450,000 miles. Using a 90% DoD with 1,200 charge cycles, we are looking at about 250,000 miles. At 250,000 miles, at 20,000 miles a year, that's 12.5 years. That's why the unlimited mile warranty with the 85 kWh battery pack in the 8 year term. You'd have to drive over 30,000 miles a year to even start to test the limits of longevity in 8 years, and it is likely that the mean is going to be somewhere around 40,000 to 45,000 miles a year to drop the battery down to the mid 80% capacity. At that point, you can still choose to drive the car.

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