Researchers assess pros and cons of hybrid electric vehicles

Credit: Adelaide Cole/Art Editor Credit: Adelaide Cole/Art Editor

Carnegie Mellon researchers have released new findings claiming that the use of battery electric vehicles (BEVs, or “all-electric vehicles”) and plug-in hybrid electric vehicles (PHEVs) with large battery packs today are actually more expensive in the long run.

The research conducted by Jeremy Michaelek, a professor in the departments of mechanical engineering and engineering and public policy, and his colleagues also suggests that BEVs and PHEVs offer diminishing returns on social benefits per dollar spent as compared to conventional hybrid electric vehicles (HEVs) and PHEVs with small battery packs. A summary of their findings was recently published in the scientific journal Proceedings of the National Academy of Sciences.

The researchers’ conclusions came after an in-depth assessment into a wide range of factors influencing the aggregate costs and environmental impact of BEVs, including greenhouse gas emissions from electricity generation, gas prices, the financial and air emissions costs of battery production, limitations of current battery technology, and more.

Various degrees of these factors were also taken into consideration to account for best and worst case scenarios for BEV utilization. For example, the researchers indicated that in a world with high gas prices, durable BEV batteries that had a lifetime of 12 years and were charged by a hydroelectric power grid were optimistic conditions for justifying the use of BEVs. In these scenarios, BEVs presented an aggregate premium (private ownership cost, air emissions damages costs, and oil premium costs combined) of about $3,000 and $5,000 lower than HEVs and gas-powered vehicles, respectively.

However, a drastically different picture is painted in the pessimistic case: Assuming BEV batteries last just six years and are powered by electricity from a coal-fired power plant in a world with low gas prices, the net premium of a standard BEV jumps to over $50,000 more than that of HEVs and gas-powered vehicles.
In regard to air pollution costs specifically, while a BEV could reduce these costs by $100 compared to an HEV in the optimistic case, costs could also increase by as much as $5,000 in the pessimistic case.

Even in the researchers’ base case — with average gas prices, a typical power grid, and the use of batteries with a lifetime of 12 years — BEVs still presented a $20,000 net cost over HEVs and conventional vehicles. PHEVs with large battery packs were almost $10,000 more expensive.

“Current government policy provides larger subsidies for vehicles with larger battery packs, assuming that larger is better,” Michalek observed in a press release on, referring to the tax credit of up to $7,500 available for purchasers of electric vehicles. “While larger battery packs allow plug-in vehicles to drive longer distances on electric power instead of gasoline, they are also expensive and heavy, they are underutilized when the battery capacity is larger than needed for a typical trip, they require more charging infrastructure, and they produce more emissions during manufacturing.”

The typical American is not oblivious to the disadvantages of BEVs, either. While a 2006 poll indicated that over 50 percent of Americans would buy a hybrid vehicle, a Gallup poll conducted earlier this year in May revealed that 57 percent of Americans would never buy an all-electric car, no matter how high gas prices go.

These views seemed to resonate with Benjamin Pious, a Carnegie Mellon junior studying business administration and psychology.

“I wouldn’t buy one of the ones you plug into the walls,” said Pious. “The thing with those cars is that they’re fundamentally impractical. You can’t actually get where you need to go with them. But [my dad’s Prius] is pretty marvelous. The gas mileage is actually considerably higher than what Toyota quotes.”

Though there are plans for a 2012 Prius PHEV model, Toyota Priuses fall for now under the category of conventional HEVs, since they never need to be plugged in to charge their built-in electric batteries. They are instead charged by the car’s gasoline engine and regenerative braking system, both of which allow for greater gas mileage. PHEVs, such as the Chevrolet Volt, include similar technologies, but also allow their batteries to be recharged via an electric outlet.

Researchers are scrutinizing BEVs such as the Tesla Roadster or Nissan Leaf, which have no fuel cells, fuel tanks, or internal combustion engine, and are powered solely by their internal battery packs. The researchers’ data offers greater context for properly analyzing the role BEVs should play in our society.