# Electric Vehicles

May 7, 2012, 6:19 pm
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The Tesla Roadster, which has a top speed of 125 mph and costs $101,500, represents the high end of the electric vehicle spectrum. Vehicles powered by electric motors or by a combination of gasoline engines and electric motors are becoming more commonplace. Such vehicles are highly efficient in the slow, stop-and-go traffic of cities, but are less advantageous for high-speed, long-distance travel. Battery technology limits the amount of energy that a vehicle can carry and thus its speed, range, and recharge time. Lead-acid batteries are inexpensive and reliable but are heavy and have low energy and power per size and weight. One of the manufacturers of these vehicles is developing a model equipped with lithium polymer batteries that will extend its range to 100 miles (161 km), but pricing and availability have yet to be determined. On the high end of the electric vehicle spectrum is a Tesla Roadster. For$101,500, one can purchase this electric-powered sports car that has a top speed of 125 mph, an acceleration from 0 mph to 60 mph in under 4 seconds, and a range of about 220 miles. This vehicle is equipped with 6831 lithium-ion cells, each about the size of an “AA” battery. [1] Together, they weigh 992 pounds (450 kg), have a service life that should extend beyond 100,000 miles (161,000 km), and cost more than \$30,000 retail. Recharge time is as short as 3.5 hours with a special, stationary charging unit and 8 hours or longer with a mobile unit.

Electric vehicles, despite their limited range, long recharge (refueling) times, and high costs, do have advantages over other types. Electric motors often achieve 90% conversion efficiency (the ratio of the input of electrical energy to the output of kinetic energy in the moving vehicle), and electric vehicles themselves emit no greenhouse gases. The power plants that generate the electricity to charge the vehicles may produce greenhouse gases, but large power plants are far more efficient than small engines and may enlist carbon capture and storage technologies. Moreover, electric vehicles usually recharge at night during the slack hours for electric power grids and thus, may not strain current generating capacities.  Most electric vehicles even work to charge themselves through regenerative braking, in which the electric motor driving the wheels also acts as a generator, which helps stop the vehicle by converting the kinetic energy of the moving vehicle into electricity that recharges its batteries.

Electric vehicles also have a certain appeal from a mechanical and engineering perspective. An electric motor provides high torque (rotational force down a shaft) over the full range of speeds, and therefore electric vehicles do not need gears, belts, or chains between the motor and the wheels. All the components in an electric vehicle operate at temperatures near room temperature. Consequently, electric vehicles require much less maintenance than gasoline- or diesel-powered vehicles. Typically, only the tires and brakes need regular service.

[1] Berdichevsky, G., K. Kelty, J. Straubel, and E. Toomre (2007) The Tesla Roadster Battery System, Tesla Motors, San Carlos, CA, http://www.teslamotors.com/display_data/TeslaRoadsterBatterySystem.pdf.

This is an excerpt from the book Global Climate Change: Convergence of Disciplines by Dr. Arnold J. Bloom and taken from UCVerse of the University of California.

©2010 Sinauer Associates and UC Regents

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