Plug-in Hybrids

Fueling the Future

Inside this Article

General Motors’ concept plug-in hybrid electric vehicle, the Chevrolet Volt.
General Motors’ concept plug-in hybrid electric vehicle, the Chevrolet Volt.
Larry Brilliant, executive director, recharges the RechargeIT car.
Larry Brilliant, executive director, recharges the RechargeIT car.
Lithium-ion battery pack in CalCars’ EnergyCS/EDrive converted Prius.
Lithium-ion battery pack in CalCars’ EnergyCS/EDrive converted Prius.
General Motors’ concept plug-in hybrid electric vehicle, the Chevrolet Volt.
Larry Brilliant, executive director, recharges the RechargeIT car.
Lithium-ion battery pack in CalCars’ EnergyCS/EDrive converted Prius.

Last summer, (the philanthropic arm of the Internet giant) launched a plug-in hybrid car project and Web site called, proclaiming, “Recharge your car. Recharge the grid. Recharge the planet.” It could just as well have added, “Recharge your home.”

Plug-in cars, some that rely solely on electricity and some that marry an electric motor with a gasoline motor for better mileage and fewer emissions (plug-in hybrid-electric vehicles or PHEVs), are slowly making their way into the mainstream. 

And it’s not just because they replace most or all of the gasoline used to fuel the typical car with cleaner, cheaper, domestic electricity. The ability of electricity to flow into a car’s batteries and also to be pulled back out and returned to the electrical grid has caught the imagination of consumers and environmentalists alike. That return trip—commonly called vehicle-to-grid (V2G) technology—could power some of a home’s electrical appliances during a grid outage, or could be used by the electrical grid in ways that will increase the storage of and our access to clean, renewable energy.

An Electric Evolution

The story of plug-in hybrids has been unfolding within the past two decades or so, beginning with the battle over modern all-electric vehicles (EVs). General Motors unveiled an electric car in 1990, inspiring California’s clean-air regulators to demand that all the major car companies start producing zero-emission vehicles. Thousands of leased electric cars hit the roads, but a weakening of the clean-air mandate in 2003 allowed automakers to cancel the leases and destroy the cars, as documented in the 2006 film, Who Killed the Electric Car?

EVs are powered solely by an electric motor and a large bank of batteries—not by a gasoline engine. When the driver steps on the accelerator pedal, a controller sends electricity from the batteries to the motor, making the vehicle move. Regenerative braking systems use the electric motor to convert some of the car’s kinetic energy into electricity that gets fed back into the batteries as the vehicle slows down.

The plug is the best thing—and the worst thing—about EVs: On one hand, you get to plug them in (which is generally a cheaper and lower-emissions source of energy than gasoline), and on the other hand you have to plug them in to recharge their batteries after 30 to 200 miles of driving, depending on the car, driving conditions, and the battery type and size.

While the car companies were making EVs, they also began building hybrid gas-electric vehicles like the Toyota Prius, Honda Civic, and the Ford Escape. Hybrids are gasoline-dependent vehicles with internal combustion engines that also have an electric motor and a small bank of batteries. The electric-drive components work with the engine, providing boosts of power or increasing the overall fuel efficiency of the vehicle. The most popular hybrid, the Toyota Prius, typically gets 45 to 55 miles per gallon.

Hybrids on the market today aren’t designed to be plugged in. Instead they use the gas engine and, to a much lesser degree, the drive motor via regenerative braking, to recharge the batteries. Depending on a hybrid’s design, the gasoline engine may shut down when the electric motor can meet propulsion needs—saving energy and reducing emissions—and automatically restarts when more power is demanded. The fuel efficiency of hybrids depends on whether they are “full” hybrids that include all the hybrid features, or “hollow” hybrids that claim the name but incorporate minimal features, such as stopping the engine while idling but not using regenerative braking. Hollow hybrids may add merely 1 mpg in efficiency, and are often more about increased power than increased fuel efficiency.

Plug-In Promises

People are realizing that hybrids can be improved by adding more batteries and an AC charger that can be plugged into the grid. With overnight grid charging, a plug-in hybrid like the Prius can travel 100 miles on 1 gallon of gasoline and about 33 kilowatt-hours (KWH) of electricity. And PHEV drivers still don’t need to think about finding someplace to recharge the car if they want to drive long distances. If the owner forgets to plug in overnight, it’s no big deal—a plug-in hybrid then operates just like a conventional hybrid.

Improved Efficiency. At an average fuel efficiency of 20 mpg, a conventional gasoline car needs 5 gallons of gas to travel 100 miles. The Toyota Prius hybrid needs about 2 gallons to go that distance. In comparison, Toyota’s RAV4-EV all-electric SUV goes 30% farther—about 130 miles—on the energy equivalent of just 1 gallon of gasoline (34 KWH). That’s half the energy required by a conventional Prius hybrid and one-fifth of the energy required by a standard gas-engine car. So how do PHEVs pencil out?

Using the average price for residential off-peak electricity in the United States—about 8 cents per KWH—the equivalent of 1 gallon of gasoline in energy (34 KWH) costs $2.72. Assuming that amount of electric energy can move a car at least 110 miles, driving on electricity costs about 2 cents per mile. In comparison, for a conventional hybrid that gets 50 mpg on gasoline costing $3 per gallon, each mile in a hybrid costs 6 cents—more than double the cost of fueling with electricity.

Terry Penney, manager of the National Renewable Energy Laboratory’s (NREL) FreedomCAR program, compared the costs associated with electricity rates and gasoline prices for a plug-in hybrid with enough batteries for a mere 10-mile all-electric range. He found that in 45 out of 50 states (all but the few states with the highest electricity rates), driving a plug-in hybrid would put money in the driver’s pocket: The fuel savings would more than offset a plug-in hybrid’s slightly higher projected sales price.

Cash-Back Cars. With vehicle-to-grid technology, a plug-in hybrid can become a “cash-back hybrid,” a term coined by Jon Wellinghoff, Federal Energy Regulatory Commission member. According to Wellinghoff, some electrical utilities and power aggregation companies have already expressed interest in the idea of contracting with plug-in hybrid owners to get occasional access to the electricity stored in their vehicles’ batteries. V2G on plug-in hybrids is likely to be used to supply electricity for what’s called “spinning reserves,” for times when it is difficult for the utilities to meet the instantaneous demand of the grid. They could also be used to shave peak loads by some individual V2G utility customers. That, says Wellinghoff, would make dollars and sense for a plug-in hybrid owner, especially if the owner also had a V2G contract. Wellinghoff says that, in the future, plug-in hybrid owners could conceivably make profits of $400 for spinning reserve V2G contracts and $2,700 per year for regulation contracts. The owner’s contract would specify how much energy may be drawn from the car’s batteries. For example, they could specify that their vehicle must retain at least 50% of its battery charge.

Reduced Pollution. While electric utilities are waking up to the possibilities of plug-in hybrids, some environmentalists are concerned about an increase in power plant pollution if everyone starts plugging in their cars. Most electricity in the United States is still generated by fossil-fueled (read: polluting) power plants and adding cars to the grid’s loads would increase electricity demands.

The data on plug-in hybrids, however, has calmed most environmentalists’ fears. Even plugged into the U.S. electrical grid, which gets more than half of its energy from coal, plug-in hybrids would produce 42% less carbon dioxide, and reduce emissions of other greenhouse gases and pollutants when compared to conventional fossil-fueled cars, according to NREL.

As more wind and solar generation is added to the grid mix, driving with grid electricity becomes cleaner still. Plug-in cars are synergistic with renewable energy, and V2G expands that synergy. For example, in many locations the wind blows mostly at night, when few people are awake to make use of wind energy. In fact, it’s estimated that there’s more than enough of an untapped wind resource in the United States to meet all current U.S. electrical needs, but there’s no place to store that wind energy during times of off-peak demand. However, nighttime is when people usually plug in to recharge their EV batteries, and the batteries could serve as distributed storage for that additional wind energy. The U.S. Department of Energy estimates that plug-in electric vehicles with V2G technology could increase America’s access to wind energy by a factor of three. And owners of off-grid RE-powered homes, which store renewable energy in batteries, could be driving cars that run partially on their surplus homemade renewable electricity and use the vehicle battery as further reserve capacity.

A Japanese Web site created in 2005 prominently showcases another important possibility of plug-in hybrid vehicles—providing a source of emergency backup electricity for a home during blackouts. It showed the plug-in Prius as an integral part of the “Toyota Dream House PAPI”—one example of environmentally friendly, energy saving, intelligent home design. The project suggested that if a hurricane or other disaster knocks out the electric grid, the car could supply electricity for some of a home’s critical electrical loads for up to 36 hours. 

Pulling for Plug-Ins

Unfortunately, while the merits of plug-ins have been pimped by the popular press and garnered the favor of an impressive aggregation of advocates, ranging from G. W. Bush to the activist environmental organization Rainforest Action Network, plug-in hybrids have yet to hit the mainstream market.

To convince automakers that there is a market for these cars, the City of Austin, Texas, launched a Plug-in Partners campaign and has gathered more than 8,000 advance “soft” (no financial commitment) orders for plug-in hybrids. Austin’s green energy comes from west Texas wind, and the city would like to use more of it. With plug-in hybrids, Austin aims to “replace Middle East oil with west Texas wind,” according to the campaign motto.

And another famous Texan is helping drive the plug-in revolution: The day after his State of the Union speech in January 2007, President Bush issued an executive order saying that when plug-in hybrids become available, federal fleets with 20 or more vehicles must buy them. With the stroke of a pen, he signified his administration’s support for these cars.

Are automakers listening? Maybe.

Several automakers developed plug-in hybrid prototypes in the 1990s, but cast them aside during their battle to weaken California’s Zero Emission Vehicle mandate. Stung by bad publicity from Who Killed the Electric Car?, at least one automaker has started to reverse its course. At the 2007 North American International Auto Show in Detroit, General Motors showcased its prototype plug-in hybrid—aptly named the Volt. With electricity stored in a lithium-ion (Li-ion) battery pack, this car purportedly can deliver 40 miles before the flex-fuel (gasoline, E85, petrodiesel, or biodiesel) engine turns on to recharge the batteries and extend the car’s range to 640 miles.

In the past year, at least five other major car companies have said they’re developing plug-in vehicles. But the automakers are quick to say that plug-in hybrids won’t hit the market until more research is done on advanced Li-ion batteries (see Better Batteries sidebar).

Move for the Future

The same day that Google switched on a 1.6-megawatt solar-electric array at its California headquarters—the largest PV installation on a corporate campus in North America— made another strong move toward energy independence, launching They unveiled five plug-in hybrid conversions and plans to build a fleet of up to 100 plug-in hybrids for employee use. The company also awarded a $150,000 grant for a large-scale V2G planning and implementation research project, and is set to take proposals for $10 million in funding for companies focused on plug-in hybrids, electric vehicles, batteries, and V2G technology, demonstrating that where there’s a will (and some substantial financial backing), there’s a way.

In the meantime, plug-ins might not be hitting the showroom floor soon, but you can still support the push for these resource-efficient vehicles. Here’s how:

  • Support plug-in hybrids by joining Austin’s Plug-in Partners campaign, and by using collective buying power as leverage. Plug In America lists the phone numbers of the major automakers on its Web site and urges consumers to call them. “Tell the automakers that you won’t buy a new car unless it has a plug on it,” says EV driver and Plug In America cofounder Marc Geller.
  • Push for government incentives or interventions to help plug-in hybrids get to market. Plug In America and other advocates have been lobbying the California Air Resources Board—which this year is revising its weakened Zero Emission Vehicle Mandate—to put some teeth back into clean-car regulations.
  • Do it yourself. If you have some experience in high-voltage electronics, you can convert a conventional hybrid to a plug-in hybrid. Costs vary widely depending on components and the type and number of batteries. And there’s no standard conversion kit available yet, so be prepared to do lots of research first. (See Plug-In Pioneers sidebar.)


Sherry Boschert is the author of Plug-in Hybrids: The Cars that Will Recharge America (New Society Publishers) and is on the steering committee of Plug In America.

California Cars Initiative •

Do-it-yourself plug-in hybrid conversions • 

Electric Auto Association • 

Plug In America •

Plug-in Partners • •’s initiative to reduce CO2 emissions, cut oil use & stabilize the electrical grid by accelerating the adoption of PHEVs

Toyota Dream House PAPI:

Comments (3)

Kevin Marshall's picture

I was just going over to renew but with this article? When it comes to electric cars no one has moved the big 3 and the press into the lime light like Elon Musk and his Tesla! I can not believe the Tesla was not mentioned! The Model S just got 2013 Motor Trend Car of the Year! I would have thought your magazine would be behind with full support of Tesla. Especially since no one in 50 years has be successful in mass producing a car to challenge the big 3 since Tucker. Bit disappointed Home Power.

Scott Russell's picture

We're always sorry to hear of a disappointed reader, of course, Kevin. But in this case, I hope our explanation is a suitable one. The article you happened across was originally published in late 2007 (with very minor updates since), well before the Tesla Model S was released. It can be difficult to know where to draw the line on keeping online articles available. Although there's still valuable and relevant information in this one, perhaps it has reached the end of its lifespan. Thanks for taking the time to post. -Scott for HP

Jim and Elaine Stack's picture

You can convert a FULL HYBRID, Like the prius to a plugin with a kit from or both make a hybrid even better. Or have a local PLUG IN company do the conversion for you.

It cost about 10 Kwh $1 to go 57 miles in my 100% electric Nissan LEAF. Most cars would take 2 or 3 gallons of gas to do that at $7-12 so you can see how you can save a lot by plugging in !.

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