Readers’ forum: Electric vehicles and carbon emissions

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CLAIMS THAT replacing gasoline-powered vehicles with electric vehicles (EVs) will substantially reduce carbon emissions are unfounded.

The EV proponents claim (correctly) that most EV owners will opt to recharge the batteries at night when electric power costs are lower. This means they will be recharged with base-load electric power generation, which is primarily coal-fired.

The EV proponents argue that EVs are more efficient than gasoline-powered vehicles. While this is true, coal-fired generating plants have a conversion efficiency of only about 40 percent.

A few years ago, Southern California Edison Company conducted a study to determine the electrical energy consumption for some EVs under real-world driving conditions. They found that for the EVs tested, the average energy consumption was 0.42 kw-hr/mile. It is important to note that the EVs tested were all small vehicles, such as the Honda EV Plus and the Nissan Altra.

In 2006, the mileage traveled by passenger cars in the U.S. was 1.69 trillion miles. This figure does not include mileage traveled by pickups, vans, SUVs, and buses. Suppose that all of these passenger cars were replaced by EVs, and suppose the batteries on the EVs were recharged at night (off-peak) with coal-fired generation. What would be the effect on carbon dioxide emissions?

In 2006, the U.S. passenger car fleet consumed 1.76 billion barrels of gasoline and produced 644 million metric tons of carbon dioxide. The required electrical energy to power the EVs would consume 305 million tons of coal and produce 574 million metric tons of carbon dioxide. The reduction of 70 million metric tons of carbon dioxide represents a minuscule 1.2 percent of U.S. annual carbon dioxide emissions.

More importantly, since U.S. per-capita carbon dioxide emissions are about 19.8 metric tons, the 70 million metric tons are completely negated by population growth in 14 months. Furthermore, the EVs achieve the efficiency they do in part because they are small and lightweight. If they afforded the space and performance of the gasoline-powered fleet, they would provide no reduction in carbon emissions.

If the objective is a reduction in gasoline consumption, there are other options, such as compressed natural gas and methanol, that are less costly and would afford the public more choices.

Posted on May 27, 2010 · in USA

Tagged as: Carbon Dioxide • Carbon Emissions • EVs