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05.07

Saving Energy with Plug-in Hybrid Electric Vehicles

By Cliff Lau

With gasoline prices averaging more than $3.00 per gallon today, and with the global warming issue heating up in Congress and in public awareness, it's not surprising to see plug-in hybrid electric vehicles (PHEV) making headlines. Car buyers are wondering, when can we buy a plug-in electric vehicle? Electrical, mechanical and automotive engineers are working feverishly to bring these cars to the market. Since many of these engineers are IEEE members, it makes sense for us to strongly support the development of plug-in hybrids.

What is PHEV?

Simply put, a plug-in hybrid electric vehicle is a vehicle that can be driven by an electric motor for at least 10 miles without consuming any gasoline, and its battery system can be recharged by plugging it into the wall outlet.

PHEVs differ from today’s hybrids, such as the Toyota Prius and the Honda Civic Hybrid, in that these conventional hybrids cannot be driven by the electric motor alone. Such cars are powered by gasoline engines, with the electric motors providing an assist in acceleration. During deceleration, electricity is generated to recharge the battery. The important difference is that PHEVs can be plugged into the wall outlet to recharge the battery storage system which can drive the vehicle for at least 10 miles without consuming a drop of gasoline. Still, PHEVs are not entirely electric cars, like an electric golf cart, or like other electric vehicles like the new Tesla Roadster. A PHEV is a hybrid that utilizes a gasoline engine for long-range driving.

The April 2007 issue of IEEE Spectrum has an article that describes the top 10 technology-laden cars [www.spectrum.ieee.org/apr07/5012]. One PHEV is the Chevrolet Volt, a concept car with a 120 KW electric motor and a 3-cylinder turbocharged gasoline motor. In the all-electric mode, the Volt can be driven for about 40 miles, with a recharging time of approximately 6.5 hours. Such a PHEV would be ideal for commuters with short round-trip driving distances.

Why PHEV?

Concerned about a looming energy crisis and global warming caused by the burning of fossil fuel, Congress took action. On 6 March 2007, the House of Representative introduced H.R. 1331 to amend the Internal Revenue Code to provide tax credits for new qualified plug-in hybrid motor vehicles. The qualified vehicles are defined as any new hybrid motor vehicle that: (1) is a passenger automobile or light truck with a gross vehicle weight rating of not more than 8,500 pounds; (2) meets or exceeds EPA emission standards; (3) draws propulsion energy from a traction battery of not less than 4 KWh; and (4) is equipped with a means of recharging its energy storage system from an external source of electricity.

Today’s hybrid vehicles are already making significant impacts on our overall gasoline consumption. The average conventional light-duty vehicle weight, at 4,000 lbs. in 1976, dropped to 3,200 lbs. by 1981, but was back to 4,000 lbs. in 2005. Over the same period, the time to go from 0 to 60 mph dropped from over 14 seconds to less than 10 seconds [chart, page 5 at www.epa.gov/otaq/cert/mpg/fetrends/420s06003.pdf]. The official EPA mileage table gives a good comparison of how much gasoline the hybrids can save, although actual mileage can be lower than the EPA estimates for both hybrid cars and for conventional gasoline engine cars. EPA's Web site for this analysis is www.fueleconomy.gov/feg/download.shtml.

Using 2006 data for otherwise identical models of hybrid and non-hybrid cars and SUVs, the hybrids show combined mileage between 20 percent and 47 percent better than the corresponding gasoline model. The Toyota Prius, at 47 percent, is currently the leader, but other manufacturers are catching up rapidly. Similarly, the 2007 data showed mileage improvement between 16 percent and 40 percent. If one compares cars that are specifically designed as hybrid, the mileage improvement is even more significant, approaching 50 percent, even though the comparison is not on otherwise identical models.

Reducing gasoline consumption can save consumers a bundle of money. If we assume the gasoline price at $3.00 per gallon, and the car is driven between 12,000 and 15,000 miles per year, the cost savings can be significant — between $140 and $720 using the above EPA estimates. The following table shows the economics of operating a purely electric powered vehicle, such as the new Tesla Roadster scheduled for delivery in 2008, against a conventional gasoline engine vehicle [http://en.wikipedia.org/wiki/Tesla_Roadster].

Table 1 - Economic comparison of electric (Tesla) and gasoline vehicles

Reducing the consumption of gasoline and our dependence on foreign oil has tremendous impact on our economic and national security. In the past, the petroleum producing cartels have essentially held the United States hostage by creating artificial gasoline shortages. Many of us remember the long gasoline lines in the 1970s. Even when no shortage exists, gasoline prices continue to climb, creating economic hardship in certain sectors of the economy. In the case of extreme shortage or even complete shutdown of gasoline supply, or in the case of extreme gasoline price hike, PHEVs would allow us to drive to work, shopping and other regular business, minimizing economic disruptions. In terms of national security, PHEVs would reduce our overall dependence on foreign oil.

Obviously, integrating a large number of plug-in electric vehicles into the electric power grid is no small matter. It is necessary to examine the impact of a substantial increase in demand for electricity. To a first approximation, it is likely that these electric vehicles would be charged at night when the marginal units are the most efficient. Generally, demand for electricity is low at night after primetime. It is very likely that the use of these PHEVs would not impose requirements for additional electrical capacity, but it requires further study. Detailed analysis, considering all factors, as well as both the advantages and the disadvantages, is necessary to facilitate the large-scale deployment of PHEVs.

IEEE-USA position

IEEE-USA, representing a significant number of electrical engineers in the United States, is in a good position to promote the use of PHEVs. IEEE-USA supports the development of PHEVs, and recommends the following:

• Speed up the development and widespread use of plug-in hybrid electric vehicles to add resilience to our transportation system, and to increase energy independence

• Promote research and development efforts and programs to improve batteries for the plug-in vehicles

• Utilize appropriate government incentives to encourage a greater adoption and penetration in the consumer market for plug-in hybrid electric vehicles

• Encourage the introduction of sophisticated electricity metering and pricing by electric utilities that will permit the full realization of all the benefits of advanced battery charging systems

• Promote research on the integration and impact of PHEVs on the electric power grid and the development of standards to facilitate the development of the industry

In summary, IEEE-USA is committed to promoting the research and development of PHEVs to achieve economic and national security benefits. Today, the most efficient hybrids are already cutting gasoline consumption by as much as 40 percent. PHEVs can cut gasoline consumption further, to as much as 50 percent or more.

Dr. Cliff Lau is a research staff member at the Institute for Defense Analyses, and is currently the IEEE-USA Vice President for Technology Policy. Comments may be submitted to todaysengineer@ieee.org.