Hybrids could be more efficient

Credit: J.W. Ramp/Publisher Credit: J.W. Ramp/Publisher

Not all hybrids are created equal, reported a team of Carnegie Mellon researchers upon testing the efficiency of large- and small-capacity battery packs used to operate plug-in hybrid vehicles. An electric vehicle with a large, heavy battery pack will require 10 percent more energy per mile than a similar vehicle with a smaller battery pack.

“We wanted to find out if the reduced vehicle efficiency caused by the additional weight of the heavy batteries used to store electrical energy in a PHEV [plug-in hybrid electric vehicle] would be significant,” said Jeremy Michalek, an assistant professor of mechanical engineering and leader of the research team. “We knew others were ignoring this, and we knew as mechanical engineers that extra mass causes extra losses. We wanted to see if the effect was enough to matter.”

The other members of the team were Carnegie Mellon researchers Constantine Samaras and C.S. Norman Shiau. The research was funded by a grant from the National Science Foundation.

Michalek believes the results of the study will have implications for automakers, consumers, and policymakers. Once the technology is cost-effective, it will become more mainstream, drastically increasing its impact. Small-capacity PHEVs may prove to be ideal for commuters, enabling them to save money while reducing oil consumption and greenhouse gas emissions.

This is hardly a niche market — studies show that more than 50 percent of car owners drive less than 20 miles a day, according to a Feb. 26 press release issued by Carnegie Mellon’s Design Decisions Laboratory.

In addition, such use may increase the demand for these vehicles among all consumers and lead to technological advances that could make larger-capacity PHEVs more competitive in the future.

“There are reasons we may still want to pursue the larger capacity plug-in vehicles in parallel, but when setting policy, I don’t think we should ignore the potential of the small-capacity plug-ins for building a market now,” Michalek said.

One large-capacity PHEV on the market today is GM’s Chevy Volt, with a battery pack that could accommodate an estimated 40 miles of travel. Small-capacity PHEVs, such as GM’s Saturn VUE or the PHEV version of the Toyota Prius, are sized for saven miles and 10–12 miles worth of batteries, respectively.

The battery of a small-capacity PHEV costs around $3000; the battery of a large-capacity PHEV costs close to $16,000. In comparison, the cost of the battery of a conventional Toyota Prius is $1300.

While switching from a Prius to a small-capacity PHEV will cost the consumer $1700, Michalek estimates that the car owner will save about $5400 in fuel costs alone over a 150,000-mile lifespan, which more than makes up for the $1700 premium.

However, switching to a large-capacity PHEV from a Prius will cost the consumer $14,700.

While the owner will save $5100 in fuel costs, it’s not enough to cover the $14,700 premium. In other words, large-capacity PHEV owners will lose $9600, while small-capacity PHEV owners will actually make $3700.

The results of the study may help achieve President Barack Obama’s goal of having a million electric cars on the roads by 2012.
However, some Carnegie Mellon students remain skeptical of the benefits of electric vehicles.

“Hybrid-electric cars can be seen as a part of the solution to reducing carbon emissions, and saving money, but we have to remember that a car economy like the one we’ve enjoyed for the last century will not reduce emissions that much,” said Austin Redwood, a junior art and creative writing major and president of the student environmental organization Sustainable Earth. “We’ll still be using coal to power the cars and nickel for the batteries — two resources that need to be mined, then shipped all over the world for manufacture and distribution,” Redwood said. “If we don’t focus on conservation and reduction, hybrid-electric could only shift a lot of those emissions to the extraction of other natural resources, creating similar problems in supply/demand cycles, surplus, and scarce resources.”

Julia Kennedy, a junior art major, and Nathan Frank, a junior business major, expressed similar sentiments.

“Although my father owns a hybrid car, I have heard that they are no more energy efficient than regular vehicles because of the number of batteries you need to replace during their life cycle,” Kennedy said.
“Hybrid-electric cars are good, but I don’t think they are the best option for alternative automotive fuel sources,” Frank said. “Government funds should go towards the most efficient option in my opinion: Hydrogen cars that exhaust water. This is a better use of research money.”

Sean McMillan, a junior policy and management major, disagreed.

“I think beyond the environmental benefits, electric cars are just dope. I felt like Buzz Lightyear when I rode in a Prius,” he said.

But the work’s not over yet.

“We are continuing to work on a range of issues associated with economic and environmental impact of alternative transportation and the influence of technical tradeoffs, market forces, and public policy in determining the direction we go,” Michalek said.