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New full LCA highlights complexity of environmental advantages and disadvantages of EVs relative to ICE vehicles; the importance of life cycle thinking
7 October 2012
Researchers at the Norwegian University of Science and Technology (NTNU) have compared the emissions resulting from the production, use, and end-of-life of electric and internal combustion engine vehicles (EVs and ICEVs) in a full life-cycle analysis (LCA). They found that electric vehicles (EVs) powered by the present European electricity mix offer a 10% to 24% decrease in global warming potential (GWP) relative to conventional diesel or gasoline vehicles assuming lifetimes of 150,000 km (93,206 miles).
However, they also found that EVs exhibit the potential for significant increases in human toxicity, freshwater eco-toxicity, freshwater eutrophication, and metal depletion impacts, largely resulting from the vehicle supply chain. Their results, they cautioned in an open-access paper published in the Journal of Industrial Ecology, are sensitive to assumptions regarding electricity source, use-phase energy consumption, vehicle lifetime, and battery replacement schedules.
Because the production impacts of EVs are more significant than for conventional vehicles, a vehicle lifetime of 200,000 km (124,274 miles) would increase the GWP benefits of EVs to 27% to 29% relative to gasoline vehicles or 17% to 20% relative to diesel. However, a lifetime of 100,000 km decreases the benefit of EVs to 9% to 14% with respect to gasoline vehicles and results in impacts indistinguishable from those of a diesel vehicle.
EVs offer advantages in terms of powertrain efficiency, maintenance requirements, and zero tailpipe emissions, the last of which contributes to reducing urban air pollution relative to conventional internal combustion engine vehicles (ICEVs). This has led to a general perception of EVs as an environmentally benign technology. The reality is more complex, requiring a more complete account of impacts throughout the vehicle’s life cycle. Consistent comparisons between emerging technologies such as EVs and their conventional counterparts are necessary to support policy development, sound research, and investment decisions.
...The production phase of EVs proved substantially more environmentally intensive. Nonetheless, substantial overall improvements in regard to GWP, TAP [terrestrial acidification], and other impacts may be achieved by EVs powered with appropriate energy sources relative to comparable ICEVs. However, it is counterproductive to promote EVs in regions where electricity is produced from oil, coal, and lignite combustion.
The electrification of transportation should be accompanied by a sharpened policy focus with regard to life cycle management, and thus counter potential setbacks in terms of water pollution and toxicity. EVs are poised to link the personal transportation sector together with the electricity, the electronic, and the metal industry sectors in an unprecedented way. Therefore the developments of these sectors must be jointly and consistently addressed in order for EVs to contribute positively to pollution mitigation efforts.—Hawkins et al.
To be able to compare EVs to ICEVs, the researchers had to create their inventory with more detail than they could readily obtained from prior public inventories; the study thus also contributes a higher-resolution, transparent comparison of an ICEV and an EV to the publicly available literature.
The new study offers significantly more resolution regarding the manufacture of vehicle components, full transparency, consideration of a range of battery technologies, and includes a broader array of environmental impacts than prior works, the researchers suggested.
The researchers established a common generic vehicle glider and customized powertrains for gasoline, diesel, and EVs. They investigated two types of batteries in the EV case: LiFePO4 and LiNCM. In the use phase, they tracked electricity and fuel consumption, together with their full supply chains. Use phase energy requirements were based on the performance of the Mercedes A-series ICEV and the Nissan Leaf EV, vehicles of comparable size, mass, and power. For the end of life, they modeled treatment and disposal of the vehicle and batteries.
In the study, they assessed six transportation technologies in terms of ten life cycle environmental impact categories: an LiNCM or LiFePO4 EV powered by European average electricity (Euro); an LiNCM EV powered by either natural gas (NG) or coal (C) electricity; and an ICEV powered by either gasoline (G) or diesel (D).
Among the other high-level findings of the study:
For all scenarios, human toxicity potential (HTP), mineral depletion potential (MDP), and freshwater eco-toxicity potential (FETP) are caused primarily by the supply chains involved in the production of the vehicles.
The use phase dominates for GWP, terrestrial eco-toxicity potential (TETP), and fossil depletion potential (FDP).
End-of-life treatment adds only a marginal contribution across all impact categories.
The EV production phase is more environmentally intensive than that of ICEVs for all impact categories with the exception of terrestrial acidification potential (TAP).
The supply chains involved in the production of electric powertrains and traction batteries add significantly to the environmental impacts of vehicle production. For some environmental impact categories, lower emissions during the use phase compensate for the additional burden caused during the production phase of EVs, depending on the electricity mix. However, this is not always the case.
The shift in emissions that EVs are poised to bring about— an elimination of tailpipe emissions at the expense of increased emissions in the vehicle and electricity production chains— brings new opportunities and risks for policy makers and stakeholders. On the one hand, EVs would aggregate emissions at a few point sources (power plants, mines, etc.) instead of millions of mobile sources, making it conceptually easier to control and optimize societies’ transportation systems. On the other hand, the indirect nature of these emissions— which are embodied in internationally traded commodities such as copper, nickel, and electricity— challenges us as a society. It poses the question of how serious are we about life cycle thinking, and how much control and oversight we, customers, and policy makers believe should be exerted across production chains.—Hawkins et al.
Hawkins, T. R., Singh, B., Majeau-Bettez, G. and Strømman, A. H. (2012), Comparative Environmental Life Cycle Assessment of Conventional and Electric Vehicles. Journal of Industrial Ecology. doi: 10.1111/j.1530-9290.2012.00532.x
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