July 31, 2008 | Op-ed

Plug-in Hybrids: The Cars that will Recharge America

While biofuels offer a drop-in alternative to oil in the short run, the long-term energy security of this country requires us to leverage technological innovations to achieve greater efficiency. In their 2008 book Apollo's Fire, Jay Inslee and Bracken Hendricks make a persuasive case that efficiency should be one of our first priorities in securing America's supply of energy. “Fifty thousand air conditioners running on one less kilowatt each because of increased efficiency are just as powerful as a power plant churning out 50,000 kilowatts of power,” they write. “The only difference is that the conserved energy is quieter, safer, and almost always cheaper.”

One technology that offers greater efficiency in the transportation sector-and also promises to diversify our sources of energy in that sector-is the plug-in hybrid electric vehicle (PHEV). Like the conventional hybrids that have gained so much popularity in recent years, PHEVs combine an electric motor with an internal combustion engine. The critical difference is that PHEVs can literally be “plugged in” to the U.S.'s electrical grid-running off electricity for a number of miles before burning a drop of petroleum. Because the U.S. has “a vast infrastructure for generating electric power,” and because electric vehicles are far more efficient than those relying on internal combustion engines, Brookings Institution energy and environment scholar David Sandalow describes PHEVs in his book Freedom from Oil as a “game-changing technology.” Indeed, PHEVs have the potential to dramatically decrease our dependence on oil and yield significant environmental benefits.

The Technology

 

PHEVs represent the next major leap in automotive technology following hybrid vehicles, which were themselves revolutionary. By utilizing electricity generated from the car's engine and brakes, hybrids were able to attain impressive fuel efficiency. For example, the Toyota Prius-the world's most recognizable hybrid-gets 48 mpg, head and shoulders above the 22.4 mpg average for all consumer cars in 2006.

Though more than a million hybrids have been sold worldwide, car manufacturers are already preparing to sell PHEVs as the next generation of electric vehicles. Automakers will incorporate either one high-capacity or a cluster of lower-capacity batteries into the car's traditional drivetrain architecture, thus allowing the vehicles to store electricity when they are connected to the grid.

The current generation of PHEV batteries has a nickel-metal hydride (NiMH) base. NiMH batteries are a significant improvement over the lead-acid batteries that powered the first generation of electric vehicles, such as the EV1 that General Motors introduced in California in the 1990s. One advantage to NiMH batteries is their durability. Sherry Boschert notes in her 2006 book Plug-in Hybrids that by 2003, “data from Ford and others showed that NiMH batteries lasted 2,000-3,000 cycles, meaning that a pack should last 130,000-150,000 miles … essentially for the life of the car.” Nonetheless, NiMH batteries still have a relatively low capacity, likely limiting this generation of PHEVs to a range of somewhere between 10 and 60 miles per charge (after which the internal combustion engine kicks in, and the car runs as a regular hybrid).

PHEVs will likely be improved by further technological breakthroughs in battery technology. Lithium-ion (Li-ion) batteries are already commonly used in cell phones and laptops, and Green Car Congress reports that in May 2007, A123Systems “introduced its automotive-class, large-format 32-series Li-Ion cells specifically designed for Hybrid Electric Vehicle (HEV) and Plug-in Hybrid Electric Vehicle (PHEV) use.” Lithium-ion batteries are smaller and lighter than NiMH batteries, and Boschert notes that they “provide 25-30% more power and energy storage.” Though automakers will likely shy away from their use until there is more data on the batteries' cycle life and longevity, lithium-ion batteries have the potential to cheaply and efficiently power the American auto fleet one day.

Sodium-nickel-chloride Zebra batteries are also promising. Boschert notes that they “fall in between NiMH and Li-ion in power and energy characteristics and are available in vehicle-sized versions at less cost.” Meridian International Research considers sodium-nickel-chloride batteries the most promising for electrification of the energy sector for a variety of reasons, including the fact that their materials are “[a]vailable, cheap and plentiful.” However, not all observers are convinced that sodium-nickel-chloride would be suitable for PHEVs.

While it is too early to say what kind of electric car battery will emerge as the victor, it is clear that this technology has great promise. This potential that has not escaped the notice of key politicians, as evidenced by John McCain's proposal to offer a $300 million prize for development of a battery that can “leapfrog” current hybrid and electric car capabilities.

Regardless of which battery system they use, PHEVs can be recharged virtually anywhere (including from wall sockets in a garage) by using what amounts to a long extension cord. Because PHEVs have both an electric motor and internal combustion engine, they do not have the driving range limitations of vehicles that run solely from electric power, such as the EV1. Once the electric charge has run out, the cars can simply run off gasoline. (However, various national studies indicate that around 60% of Americans travel 30 miles or less every day, putting them within the electric motor's range for many PHEVs.)

Strategic Implications for Oil Dependence

PHEVs can dramatically reduce our dependence on oil. Just as hybrids represented a major leap in fuel efficiency over conventional internal combustion vehicles, PHEVs may be able to double the gas mileage of the first generation of hybrids. As Boschert writes, “[b]y plugging into a regular wall socket overnight while the owner is sleeping, a plug-in Prius can get over 100 miles (160 km) per gallon of gasoline plus a small amount of cheap electricity.”

One reason that PHEVs can attain such improvements in fuel economy over internal combustion engines is that they make far more efficient use of energy. As Sandalow notes, internal combustion engines are startlingly inefficient:

With hundreds of moving parts constantly creating friction, an internal combustion engine wastes much of its energy in the form of excess heat. (That's the reason for your car's cooling system.) The “thermal efficiency” of an internal combustion engine-its ability to convert fuel to useful work-is roughly 20%. The thermal efficiency of even an old-fashioned coal plant is roughly 33 to 34%. Newer coal units have efficiencies of more than 40%.

Electric vehicles are estimated to be about four times as efficient as gasoline vehicles. Drivers will experience significant cost savings due to this efficiency, coupled with the fact that power from the electric grid costs less than liquid fuels. Former CIA director R. James Woolsey estimates that when a PHEV is running in electric mode, “you will be driving at a cost of between a penny and three cents a mile,” far less than the current cost of gasoline. The power required to run plug-in hybrids while in electric mode would come from domestic sources, an obvious improvement over the status quo.

Scientists at the Pacific Northwest National Laboratory estimate that PHEVs have the technical potential to displace 6.5 million barrels of oil equivalent per day, which is about 52% of the U.S.'s oil imports. Plug-in hybrids that are also flexible-fuel vehicles can do even more to reduce our dependence on oil. Woolsey writes that a PHEV that uses 85% ethanol fuel (E85) can get around 500 miles per gallon of gasoline used. U.S. automaker General Motors has promised to be the first company to introduce a plug-in and flex-fuel vehicle.

Environmental Benefits

The introduction of PHEVs can also minimize the environmental harm associated with the internal combustion engine. Some skeptics do not immediately recognize this fact: the New York Times, for example, tersely dismissed the environmental benefits of electric cars in a recent puff piece on hydrogen vehicles because electricity “is often produced by coal-burning power plants.”

It is true that about 50% of America's electricity is currently generated from coal-fired plants, which are a significant source of greenhouse gases. Despite this, the greater efficiencies of PHEVs mean that they emit far fewer greenhouse gases than either standard internal combustion engines or conventional hybrids. Sandalow provides a concise summary comparing the carbon dioxide emissions of a gasoline-powered car to those of a PHEV running off power generated entirely from coal:

1. Burning a gallon of gasoline releases roughly 20 pounds of carbon dioxide into the atmosphere.
2. A gallon of gasoline moves the average U.S. vehicle roughly 21 miles.
3. That means the average car releases just under 1 pound of carbon dioxide for each mile traveled.
4. Generating a kilowatt-hour of energy at the average U.S. coal plant releases roughly 2.1 pounds of carbon dioxide into the atmosphere.
5. A kilowatt-hour moves a first generation PHEV roughly 3 miles.
6. That means a first-generation PHEV recharged with energy from a coal-fired power plant will release roughly 0.7 pounds of carbon dioxide per mile when driving on its electric motor.

Joseph J. Romm, a senior official in the Clinton administration's Department of Energy, similarly concludes that even if “the entire grid were coal, … you'd still have far lower CO2 emissions from a plug-in Prius than from the average new car on the road running on gasoline.” Of course, the assumptions that Sandalow and Romm make are unrealistically pessimistic in order to prove their point. The fact is that the entire grid is not powered by coal, and according to a number of studies PHEVs reduce greenhouse gases between 27 to 37% based on current electrical grid and driving patterns.

Nor would PHEVs require a great deal of new electricity generation capacity in the near future since most of these cars will be plugged in during off-peak hours. Boschert explains:

Plug-in cars get recharged mainly at night, when many plants either waste the energy they produce or power down without shutting off completely, because there's less demand than during the day. This “excess capacity” at night (the amount of power that could be generated) was enough in 2000 to accommodate more than 43 million electric vehicles, the US Department of Energy estimated. Since plug-in hybrids would recharge with a quarter or half of the amount of electricity needed by electric vehicles, we wouldn't need any new power plants until well over 80 million of them are on the road.

In the future, PHEVs can yield even greater environmental benefits as the grid becomes cleaner-for example, through the introduction of more renewable energy. Romm believes that PHEVs can potentially offer “zero life-cycle emissions in the long term as the grid gets cleaner.”

Conclusion

PHEVs will hit the market faster than many readers realize: both Toyota and General Motors plan to introduce models around 2010. These cars will likely be sold to government agencies and corporations before they are offered to average consumers.

In order to maximize the strategic and environmental benefits of PHEVs, the federal government should undertake policies to help them attain market penetration. Sandalow offers two such policies that should be adopted. First, he notes that the federal government purchases 65,000 new cars annually, and recommends that “the federal government issue an open order for 30,000 plug-in hybrid vehicles, offering to pay an $8,000 premium for each one.” He advocates that the General Services Administration should commit to repeating this order each year after the initial delivery, with the premiums decreasing over time. Second, he recommends that the federal government provide tax credits for the first 2 million or so PHEVs purchased.

By making more efficient use of energy and diversifying the sources of power for our transportation sector (by putting the entire electrical grid into play), PHEVs can play a critical role in moving us past the current energy crisis. They can also play an important role in addressing another generation-defining challenge, the threat of global warming.