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Larger batteries work against EV efficiency

Bigger isn’t necessarily better when it comes to electric vehicles because their efficiencies diminish as their battery packs get bigger, says a recent study from Carnegie Mellon University (CMU).

In a study appearing in the Proceedings of the National Academy of Sciences, Jeremy J. Michalek argues that electrified vehicles with smaller battery packs are more efficient in reducing societal costs for health care, environmental damages and oil consumption.

“Current government policy provides larger subsidies for vehicles with larger battery packs, assuming that larger is better,” says Michalek, an associate professor of engineering and public policy and mechanical engineering at CMU. “While larger battery packs allow plug-in vehicles to drive longer distances on electric power, they are also expensive and heavy, are underutilized when the battery capacity is larger than needed for a typical trip, require more charging infrastructure and they produce more emissions during manufacturing.”

Michalek’s research is aimed at understanding trade offs in the capabilities of new technologies and to predict what near- and long-term strategies should be.

“It’s possible that future plug-in vehicles with large battery packs might offer the largest benefits at competitive costs if the right factors fall into place, including sufficiently low cost batteries, high gasoline prices, low emission electricity and long battery life,” added study co-author Mikhail Chester, assistant professor of sustainable engineering at Arizona State University. “But such a future is not certain, and in the near term, HEVs and plug-in vehicles with small battery packs provide more emissions benefits and oil displacement benefits per dollar spent.”

The American Recovery and Reinvestment Act of 2009 provides up to $7,500 in tax credits for up to 200,000 plug-in vehicles.

“Because vehicles with larger battery packs are more expensive, fewer of them can be subsidized, and that can result in lower total benefits,” said Michalek, who recently received a $400,000 grant from the National Science Foundation (NSF) to analyze how public policy could help determine the types of vehicles built in coming years and how consumers might respond to these vehicles.

“Given the major spending cuts under debate in Washington, it is important that we get the most benefits out of spending designed to improve the environment and energy security,” Michalek said. “More research on batteries — especially lowering cost — and a transition to a cleaner electricity grid are needed to pursue a future where large battery packs may also be able to help address climate change, air pollution and oil dependency at competitive costs.”

Source: Autonet