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BATTERY ELECTRIC VEHICLES have zero tailpipe emissions. However, the production of their batteries, the supply of their electricity and their eventual disposal affect the environment. Such life-cycle analyses, from cradle to grave, tell a more nuanced story.
I’ve read BEV tradeoff articles before, but this time around, my principal reference isn’t some fringe anti-EV group, it’s Science magazine published by the American Association for the Advancement of Science.
In the Research section of Science, May 20, 2016, Nicholas S. Wigginton offers “Life-cycle Tradeoffs of Plug-ins.” Briefly, he notes, “Shifting to electric passenger vehicles ideally will reduce the carbon footprint of the transportation sector. Two recent studies, however, show that the greenhouse gas emissions produced over the life cycle of electric vehicles, from productions through use, may not always be less than those of gasoline-burning vehicles.”
The two articles Wigginton cites are both published in Environmental Research Letters, a quarterly scientific journal that’s electronic-only, peer-reviewed and open-access. (This last aspect implies its papers are free to all readers, funded by publication charges.)
Research for “The Size and Range Effect: Lifecycle Greenhouse Gas Emissions of Electric Vehicles” was performed by Linda Ager-Wick Ellingsen et al, Industrial Ecology Programme and Department of Energy and Process Engineering, Norwegian University of Science and Technology, Trondheim, Norway. As described in their Abstract, the researchers “compile cradle-to-grave inventories for EVs in four size segments to determine their climate change potential…. Furthermore, a sensitivity analysis assesses the change in lifecycle emissions when electricity with various energy sources powers the EVs.”
The four European BEV classes analyzed were the A-segment typified by the Mitsubishi iMiev; C-segment with the Kia Soul EV; D-segment represented by the Mercedes-Benz B Class Electric; and F-segment exemplified by the Tesla Model S with its two battery choices.
As expected, increasingly large cars of all types had greater average energy requirements, as measured on the NEDC, the New European Driving Cycle, the EU’s counterpart of the U.S. Environmental Protection Agency’s combined City/Highway Cycles.
The chart at left displays GHG (Greenhouse Gas) emissions, in CO2-equivalent tons, for vehicles during production, use and end-of-life. The gray shaded area, called the fossil envelope by researchers, shows lifecycle emissions of conventional vehicles. The thin blue lines are for the four BEVs considered.
The bar graphs on the right show the distribution of BEV emissions, depending on car size, split among battery production, vehicle production, use and end-of-life.
As shown, with my red annotations for emphasis, researchers found that “larger EVs can have higher lifecycle GHG emissions than smaller conventional vehicles. Thus, at the current state of the technology, finding the right balance between battery size and charging infrastructure is an important element in maximising the climate change mitigation of EVs.”
The other research paper cited in Science is “Effect of Regional Grid Mix, Driving Patterns and Climate on the Comparative Carbon Footprint of Gasoline and Plug-in Electric Vehicles in the United States,” by Tugce Yuksel, Department of Mechanical Engineering, Carnegie Mellon University, and colleagues at CMU and the Department of Industrial Engineering and Operations Research, University of the Philippines-Diliman.
The research identified interesting differences in life-cycle GHG emissions, depending upon where and how the cars are used. For example, in urban counties of California, Florida and Texas, the Nissan Leaf BEV had a smaller carbon footprint than the Toyota Prius hybrid, the most efficient of gasoline vehicles. On the other hand, the Prius’s footprint was smaller in the Midwest and South.
The Leaf beat the conventional Mazda 3 in most urban counties, but the Mazda’s total life-cycle GHG was lower in the rural Midwest.
The Chevrolet Volt plug-in hybrid had a larger carbon footprint than the Prius throughout the continental U.S., but the Volt had a cleaner cradle-to-grave than the Mazda 3 in many urban counties.
The researchers conclude, “Regional grid mix, temperature, driving conditions, and vehicle model all have substantial implications for identifying which technology has the lower carbon footprint, whereas regional patterns of VMT [vehicle miles traveled] have a much smaller effect. Given the variation in relative GHG implications, it is unlikely that blunt policy instruments that favor specific technology categories can ensure emission reductions universally.”
As Yogi Berra observed, “It ain’t over till it’s over.” And science is never over. ds
© Dennis Simanaitis, SimanaitisSays.com, 2016