Could Pure Electrics Emit More Than Hybrids?

Jeremy Michalek says the biggest electric vehicle subsidies are going to the wrong cars. After studying the life cycle of electrified cars -- from the first moment of raw material mining to the final day in the car's life -- Michalek and fellow researchers have concluded that hybrids with smaller batteries pollute less than pure EVs.

That, of course, flies in the face of everything we now believe. Today, cars with bigger lithium-ion batteries receive three times as much in federal subsidies than hybrids with smaller batteries. Those subsidies, however, are based on the idea that big-battery EVs pollute less, which may not necessarily be so, Michalek says.

A battery electric vehicle (shown as "BEV240") could be responsible for more social damage in the form of emissions than a plug-in hybrid, largely as a result of battery size.
(Source: Carnegie Mellon University)

"As the battery pack gets larger, the emissions associated with manufacturing can be quite significant," Michalek, an associate professor of mechanical engineering and public policy at Carnegie Mellon University, said in an interview. "You have to look at the entire supply chain. Some of the emissions come from the facility where the battery is assembled, but a portion of it is upstream. Some of it comes from the powerplants used to create the electricity that runs the equipment."

Michalek's conclusions were recently published in an article in Issues and Science and Technology, a publication of the National Academies. They were also unveiled in a separate study titled "Valuation of plug-in vehicle life-cycle air emissions and oil displacement benefits," in 2011. For both papers, Michalek teamed with researchers from Arizona State University and the Rand Corporation.

The gist of the studies' conclusions is that there's more to emissions than what comes out of the tailpipe. This is especially so when it comes to vehicles with big lithium-ion batteries. According to the studies, a battery-electric car with a 240 km (144 mile) range is responsible for between $4,000 and $5,000 worth of "social damages" over its lifetime. The figure is similar to conventional gas-burning vehicles, but higher than that of hybrids.

A plug-in hybrid with a 20 km (12 mile) all-electric range, for example, comes in at less than $4,000. In arriving at the numbers, researchers considered emissions caused by vehicle operation, as well as by electricity production, gasoline production, battery production, and vehicle production.

The bottom line of the study is that smaller battery size is important. Although the studies didn't mention any specific vehicle models, their findings indicate that a Prius PHV plug-in hybrid with a 4.4 kWh battery would emit less than a Chevy Volt with a 16 kWh battery. Similarly, a Volt would emit less than a pure electric car with a big battery.