Pittsburgh, Pennsylvania – Plug-in hybrid electric vehicles with small battery packs and lower driving ranges may be best for saving money, according to researchers at Carnegie Mellon University.  

The study, which will appear in the journal Energy Policy, finds that urban drivers who can charge their vehicles frequently, such as every 32 km or less, can simultaneously reduce petroleum consumption, greenhouse gases and expenses with a plug-in hybrid whose battery pack is sized for about 11 km of electric travel per charge. In contrast, vehicles with larger battery packs sized for 64 km or more of electric travel are too expensive for fuel savings to compensate, even in optimistic scenarios.

“Larger battery packs allow drivers to go longer distances on electric power,” said Professor Jeremy Michalek. “But batteries are heavy and expensive. We accounted for the effects of additional batteries on vehicle cost, weight and efficiency in order to understand the net implications on petroleum consumption, cost, and greenhouse gas emissions.”

Michalek said that over a range of scenarios, including fluctuating gas prices, new battery technologies or high taxes on carbon dioxide emissions, plug-ins with small battery packs are economically competitive with regular hybrid or conventional vehicles for drivers who charge frequently.

“Plug-in vehicles can reduce greenhouse gas emissions in general, but getting the most bang for the taxpayer buck means targeting the right vehicles to the right drivers,” Michalek said. “In fact, for drivers who charge their vehicles frequently, plug-in vehicles with small battery packs create fewer greenhouse gas emissions than plug-ins with large battery packs, because carrying extra weight makes vehicles less efficient. Plug-ins with large battery packs can still reduce greenhouse gas emissions for drivers who charge less frequently, as well as help shift air pollution away from population centres, but they won’t save drivers money unless batteries get very cheap.”

The study was funded by the National Science Foundation and the Teresa Heinz Scholars for Environmental Research Program.

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