Plug-in hybrid electric vehicles (PHEVs) are taking off as the next big thing in energyefficient automaking. Essentially hybrids with extension cords and larger batteries, PHEVs can go up to 40 miles on electricity alone. That might not sound like a lot, but more than 60 percent of American drivers travel fewer than 31 miles each day. 

Plugging in also shifts most emissions from the tailpipes of individual vehicles to smokestacks at centralized power plants, making pollutants easier to capture. But before ecophiles reach for their wallets, they should know that plug-ins may only be nominally better for the environment than hybrids, according to a study in Environmental Science and Technology that compared total life cycle greenhouse gas emissions of PHEVs, hybrids, and conventional vehicles.

That’s because total emissions depend heavily on how the electricity a PHEV runs on is generated. If the electricity comes from a coal-burning power plant, then plugins can actually contribute more greenhouse gases than regular hybrids. But if the US incorporates more renewables like wind into its energy mix, plug-ins would have the lowest emissions, the study’s authors say. “There’s a real opportunity to have very large greenhouse gas–emission reductions,” says Constantine Samaras, a coauthor, “but that’s only if we can develop low-carbon electricity sources.” The graph below shows how PHEVs stack up against hybrids and conventional cars.

Story by Jessica A Knoblauch. This article originally appeared in Plenty in October 2008.

Copyright Environ Press 2008

Plug-in hybrids
Adding renewable energy to the grid will make PHEVs cleaner.