Study shows pollution index for electric cars dropping
The carbon emissions associated with that power vary greatly, depending on the local utility that provides it.
Now an updated study from the Union of Concerned Scientists calculates that in many US states, electric cars now have lower “wells-to-wheels” emissions per kilometre than they did just a year ago, Green Car Reports said.
So how’d they do that? The answer is that two things have changed.
First, the sales-weighted mix of electric cars sold has gotten slightly more efficient from December 2010, when the first one was sold, to June 2014.
An increase in the electric range of the Nissan Leaf from 177km (2011-2012 models) to 185km (2014-2015 models) accounts for part of this increase.
So does the May arrival of more efficient new models such as the BMW i3, which has the highest efficiency rating of any car sold in the US this year.
That means it takes fewer watt-hours per kilometre to drive than it used to.
Second, the UCS updated its “State of Charge” study in September, to use more recent data on the state-by-state mix of generating sources and the carbon dioxide — a greenhouse gas — associated with the production of each kilowatt-hour.
The previous edition of the study used 2009 plant emissions and generation data from US eGrid report. The latest version updates that by one year, to 2010 data; each was the most up-to-date breakout at the time.
The UCS points out that data from 2011 and 2012 (not yet included in the eGrid model) indicates a further reduction in coal generation.
The net effect is that the km/l equivalency figures for electric cars have risen from both more efficient use of every kilowatt-hour, and lower carbon emissions associated with each of those kWh.
In California, which buys up to half of the nation’s plug-in cars, a gasoline car would now have to deliver 95mpg (up from 78mpg) to be as low-emission as the average plug-in electric car.
And the UCS notes that the wells-to-wheels emissions per mile for plug-in electric cars has fallen in virtually every US region.
Three more states have entered the “Best” category, meaning the emissions from an electric car in those states are lower than those of a 50-mpg Toyota Prius — the most efficient gasoline car you can buy without a plug.
A variety of studies shows that electric cars are always cleaner than gasoline and diesel cars unless they’re recharged using electricity produced largely or entirely from coal.
Today, coal is less than 40 percent of the average US generation mix, and that percentage is expected to fall as utilities switch more of their mix to natural gas, while simultaneously boosting the capacity of renewable sources: wind, solar, and hydroelectric.
A Minnesota University study released recently found that charging electric cars off a grid where coal generates the power actually make the air dirtier, worsening global warming.
The study found that if the source of the electricity for all-electric cars comes from coal, the electric cars produce 3.6 times more soot and smog deaths than gas, because of the pollution made in generating the electricity.
“Unfortunately, when a wire is connected to an electric vehicle at one end and a coal-fired power plant at the other end, the environmental consequences are worse than driving a normal gasoline-powered car,” said Ken Caldeira of the Carnegie Institution for Science, who wasn’t part of the study but praised it.