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Plug 'n play: Could plug-in hybrid cars help the energy crisis?

POSTED 29 NOVEMBER 2007


Plugging in the hybrid car
A plug-in hybrid builds on the existing efficiency advantages of today's hybrid cars, like the Toyota Prius:

Sky blue four-door car parked in front of garage, large battery pack rests on drivewayAt slow speeds, the electric motor can move the car without burning gasoline.

The gasoline engine can turn off to save energy while parking, in a traffic jam or at a traffic light.

The electric motor can aid with acceleration and hill climbing, so the gasoline motor can be smaller and more efficient.

Energy recovered during braking can be stored in the battery.

By adding a big, beefy battery and associated electronics, this conventional hybrid is being converted into a plug-in hybrid. Gotta wonder: Where did they stash all the tools when snapping the pic? Photo: Wisconsin Public Power, Inc.

The essential difference in a plug-in hybrid is the addition of a jumbo battery, which increases the electric range and further reduces energy use. Electric motors are, after all, more efficient than gasoline engines: They need less energy to do the same amount of work.

So even accounting for fuel burned to generate electricity for the battery, experts say plug-in hybrids will significantly reduce fuel use and carbon dioxide pollution, and thus help brake global warming.


Hybrids lead to significant reductions in carbon dioxide pollution and global warming. If a big battery can power 60 miles of driving, most of the carbon dioxide created by the car comes from the "fuel cycle" -- meaning the electric generating plant. Getting that electricity from solar or wind power would zero out carbon dioxide pollution. Data: National Renewable Energy Laboratory

Save gallons, save bucks?
Driving on electricity is also significantly cheaper than driving on gas. According to Argonne National Laboratory, $1 buys enough electricity to drive as far as one gallon of gas -- at today's prices.

The actual cost could be much cheaper if the charger juices up the battery with electricity generated at night. Some utilities already discount their "off-peak" power, to help level out the demand for electricity and reduce their costs. And it's just possible that the price of gas is heading higher, which would further increase the hybrid advantage.

All potential savings, of course, must be measured against the premium price for the plug-in hybrid. Experts say a conventional hybrid carries a $3,000-$4,000 premium, and the plug-in (when it hits the market) might cost that much again -- a potential price jack-up of $6,000 to $8,000. For all hybrids, however, significant market competition and demand may lead to economies of scale and cost cutting.

5 schematic diagrams showing flow of energy through a hybrid in different circumstances
In conventional hybrids, the energy flow between the energy, battery and wheels depends on conditions. In a plug-in hybrid, electricity energy also enters the battery from a wall plug. Modified graphic from original at Wikipedia.

Save bucks, save a planet?
The second plug-in payoff is more complicated, more significant, and more remote: Using batteries in millions of plug-in hybrids to store low-cost, night-time electricity and return it to the grid during the juice-hungry daytime. Using this so-called "vehicle-to-grid" technology, car owners could recoup costs by selling electricity back to the utility, and (theoretically) still enjoy some all-electric miles on the car.

Although vehicle-to-grid will not appear on the first plug-in hybrids, Andrew Frank, a hybrid expert at the University of California at Davis, sees it as revolutionary. "This is much more than cars, they are also energy storage on a societal scale."

Wind farms, he notes, need backup generators for calm days. "Instead, we should be storing the energy generated when the wind blew in the batteries, and taking it out when needed." We shall return to the idea that cars -- of all things! -- could actually help us dig out of the looming energy crisis...

Diagram of a car, sections of the trunk and engine are highlighted in green
The big battery in the plug-in hybrid can be charged by the gasoline engine or the electric grid. The wheels can get power from the battery (through the electric motor), and/or from the engine. The power electronics negotiate complicated, ever-changing matters of supply and demand. Diagram: Argonne National Laboratory

Let a million hybrids bloom!
Years before plug-in hybrids hit the market, they have already gathered "strange-bedfellow" supporters:

Advocates of energy conservation and renewable energy

Electric utilities eying an expanded market

National-security types worried about mounting oil imports

The latter group includes self-described "cheap hawks" like Frank Gaffney, Jr., former assistant secretary of defense under Ronald Reagan. In testimony to Congress last summer, Gaffney warned that China is locking up oil supplies through a worldwide series of contracts. Gaffney, who is president of the Center for Security Policy, observed that the "... electrification of the transportation sector is a key element of the effort to reduce our consumption of oil. Automobiles and other vehicles that can use electricity to provide some or all of their fuel can make a real contribution to weaning us from our oil addiction and diminishing the national security vulnerabilities that arise therefrom."

Sounds good. So where are the plug-in hybrids?

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Megan Anderson, project assistant; Terry Devitt, editor; S.V. Medaris, designer/illustrator; David Tenenbaum, feature writer; Amy Toburen, content development executive

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