The National Academies: What You Need To Know About Energy

The National Academies

What You Need To Know About Energy

Electric Vehicles

Many new vehicle technologies have the goal of steering automobiles away from a dependence on fossil fuels. One vision is an all-electric vehicle (EV) that uses no gasoline or diesel fuel and does not emit any CO2. But affordable and reliable EVs will require advances in energy storage. At present, batteries that store enough electricity to give a vehicle acceptable driving range are expensive, large, and heavy. Yet technology may provide new options. For example, recent advances in nanotechnology, applied to the lithium ion battery, may permit significantly more energy to be stored in a smaller, lighter package.

PHEVs have conventional gasoline engines as well as batteries that can supply enough energy to travel 10 to 40 miles, depending on the kind of batteries used.

A compromise—plug-in hybrid electric vehicles (PHEVs)—may secure a significant place in the market sooner. PHEVs have conventional gasoline engines as well as batteries that can supply enough energy to travel 10 to 40 miles, depending on the kind of batteries used. They run on electric power until the batteries are discharged, then switch to gasoline for additional range. As of January 2008, no PHEVs were in production. But several major motor companies—including Toyota, General Motors, and Ford—have plans to introduce PHEVs within the next few years.

EV and PHEV batteries are recharged by plugging them into an electricity source while the vehicle is parked. This provides the immediate benefit of shifting some transportation energy demand from onboard petroleum-based fuels to the electrical grid. However, CO2 emissions would not decline proportionally because half of the electricity used to recharge the vehicle’s batteries is produced at coal-based plants.

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Energy Hands-on

What do you know about energy?

How much carbon dioxide is emitted by the average U.S. car driving one mile?

  • Sorry, that’s incorrect.

    The average U.S. car gets 21.4 mpg. About 19 pounds of carbon dioxide are emitted for every gallon burned, or 0.9 lb/mile.

  • Sorry, that’s incorrect.

    The average U.S. car gets 21.4 mpg. About 19 pounds of carbon dioxide are emitted for every gallon burned, or 0.9 lb/mile.

  • Correct!

    The average U.S. car gets 21.4 mpg. About 19 pounds of carbon dioxide are emitted for every gallon burned, or 0.9 lb/mile.

Energy Defined

Energy Density

The amount of energy stored within a system, typically measured either as energy per unit volume or energy per unit mass.

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