University of Vermont

CEMS - The College of Engineering and Mathematical Sciences

Plug, unplug, drive

Release Date: 04-30-2008

Author: Joshua E. Brown
Email: joshua.brown@uvm.edu
Phone: 802/656-3039 Fax: (802) 656-3203

Plug-in
hybrid electric carRichard Watts pulls a plug out of a weatherproof socket. He rolls up the green extension cord. Then he yanks the other end out of a socket in the bumper of a car and tosses the cord in the trunk. "It's all charged," he says. "Ready to go?"

It's the right question. Sure, I'm ready to go on a drive in this nifty rechargeable Toyota Prius. But his question also applies more broadly to a new generation of plug-in hybrid electric cars like this one. Are they ready to go in cold and hilly Vermont? And, once they leave the lab and hit the showroom in 2010, how will they affect air pollution, the power grid, and consumer pocketbooks?

Watts, a researcher at UVM's Transportation Research Center, and Paul Hines, assistant professor of engineering, are launching a study to find out.

Different than flat
Like a conventional hybrid car, a plug-in hybrid runs on a battery pack when it can and then switches to a gasoline engine. But the plug-in hybrid doesn't just recharge its battery from the engine — it can also recharge by connecting to a standard electrical outlet.

As we ease out of the parking lot behind the research center, the car is delightfully quiet. Watts explains that this vehicle — donated by Central Vermont Public Service for research and customized with a high-capacity lithium-ion battery — should be able to go 20 miles on electric power alone before the gas engine kicks in.

For commuters, that means that a plug-in hybrid could run mostly on electricity — while today's conventional hybrid runs mostly on gas. A conventional hybrid gets equal to about 50 miles to the gallon. Plug-in hybrids can average around 100 mpg on the highway, and for shorter trips, get equal to 300 mpg or better, according to the California Cars Institute.

But Vermont is not California. Two plug-ins tested through the winter in Vermont ran at equal to 70 miles per gallon when the batteries were fully charged, according to a report issued this month by Green Mountain College and Central Vermont Public Service.

"It's different than flat around here," Watts says with a smile as we plunge down Colchester Avenue into Winooski. "Hills change the strain on an engine and the emissions coming out of the tailpipe. Cold weather has all sorts of effects on batteries." And snow tires and heating systems cut a plug-in's efficiency, said CVPS fleet manager Dan Mackey.

Consider $4 gas
Still, even in a Vermont January, a plug-in kicks the financial tires off a gasoline vehicle — and is cheaper to fuel than a conventional hybrid. With gas at $3.25 per gallon, a trip of 70 miles will cost you $13.38 in a Hummer, $4.46 in a Honda Civic hybrid and, with electricity at 12 cents a kilowatt, $3.97 in one of the CVPS plug-in hybrids. With $4-per-gallon gasoline anticipated this summer, the plug-in's fueling costs may start to look increasingly attractive.

Considering that there may be only three plug-in hybrids in Vermont today, these new cars shouldn't present any strain on the state's power system—yet. But, with General Motors and Toyota planning to bring out plug-in hybrids soon, that could quickly change. The Prius hybrids that CVPS had customized cost about $32,000 each, Mackey said. As the price of a plug-in comes into line with other cars, it may herald a "shift in demand from liquid fuels to electricity," Hines says.

Research in 2007 by UVM's Watts and Green Mountain College's Richard Letendre shows that the Vermont electricity grid can handle 50,000 plug-ins without any changes to the existing system. The number rises to more than 100,000 if people recharge the cars at night.

But many questions remain, which is why Watts and Hines are starting the second phase of research this July.

"If everyone plugged in at 8 in the morning and 6 at night that would be a disaster," Watts says, because that is the peak period of demand. The additional draw on the grid would force power providers to buy more expensive, dirtier power from outside the state — or might cause the grid or local circuits to fail.

"But there are valleys in use overnight," Watts says, and part of the new research will be exploring ways that drivers could be encouraged to recharge their plug-in cars at these off-peak times—and how regional policies and regulations might affect both car owners and power producers.

Energy arrows
Doesn't a plug-in hybrid just shift pollution from cars to power plants? Yes, but it's less pollution than a gasoline car even when accounting for emissions from the nation's coal-heavy power grid. And since Vermont's electricity supply is clean compared to most other states — it has a high proportion coming from hydro and nuclear power — cars that run on electricity could make a significant impact on the state's overall greenhouse gas emissions.

"Switching 50,000 existing vehicles from gasoline to plug-in hybrid electric vehicles would reduce carbon emissions by 31 percent," Watts and Letendre wrote in a report released this February.

Still, "right now, we're not sure if a plug-in reduces greenhouse gases compared to a conventional hybrid," Hines says, and, more broadly, the new study aims to understand the most effective way for consumers to direct their environmental dollars. "If people want to reduce greenhouse gas, how good a choice is a plug-in compared to, say, purchasing wind energy?" Hines asks.

The answer depends on "the complex interaction of the systems," from electrical to transportation to economic, he says. "One of the goals of this study is to quantify the uncertainty about which choices" will yield the most benefits. Nevertheless, he believes that if the electric grid shifts away from coal and natural gas to renewable sources by even a modest amount "in the next 10 years, plug-ins will be clearly superior technology."

To help gather data, Watts and other volunteers will be taking careful notes on the performance of UVM's new plug-in research car as they use it to commute. As we head out of Winooski, a dashboard computer screen shows energy flowing from the battery to the electric motor to the wheels. Watts steps hard on the accelerator, and the gas engine rumbles to life while the display shows an orange arrow from the engine to the electric motor.

Plug-in future
Not so long ago, General Motors killed its electric car program, and Toyota Motors discouraged Prius owners from modifying their vehicles to run as plug-ins. Now the arrows seem to be running the other direction. Today, GM is pushing to bring the plug-in Chevrolet Volt to the marketplace by 2010. Toyota may have a plug-in Prius available before that. And the California Air Resources Board last month demanded that manufacturers produce 58,000 plug-in hybrids in the next few years.

"Why I'm so interested is that plug-in hybrids allow you to choose your energy source," Watts says. "With a gas car you have only one choice. Whereas, in theory, with this car you could be plugged into wind power, or solar, or a wood chip plant. All these could power your car instead of oil."

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