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Just how efficient are the new-generation vehicles?

HENRY PETROSKI - Batteries are costly and heavy. Producing hydrogen fuel cells will require energy. In their desire to appeal to the good environmental intentions of potential new-car buyers, automobile manufacturers have been eager to introduce new models, accessories, and features that signal alternative energy and fuel economy. But what makes good advertising copy does not necessarily translate into savings or even into sensible behavior.

The Toyota Prius is probably the most conspicuous example of a "green" car, but some early Prius owners have told me that they practically had to relearn how to use the gas pedal in order to achieve the fuel economy that is promised of the hybrid. Unless a driver accelerates carefully and attentively, advertised fuel savings may not materialize in any automobile.

Plug-in hybrids are supposed to be the next wave. The Chevy Volt plug-in has been advertised to get 150 or more miles per gallon of gasoline, and it is said to be able to travel about 40 miles on a fully charged battery pack. For about 75 percent of the U.S. population, this could be sufficient for commuting to and from work without using any gasoline. The plug-in is designed to be recharged overnight in the owner's garage or during the day in an employee parking lot.

All-electric cars are the next logical step, of course, but battery technology - albeit centuries old - has not yet quite caught up with green dreams. The all-electric Tesla Roadster is being made in limited quantities, but its more-than-$100,000 price tag puts it out of reach of the average citizen. Its lithium-ion battery pack, which alone costs about $10,000 and weighs half a ton, suggests why all-electric cars of any kind tend to be pricey - and heavy.

It has been suggested that the energy stored in an electric car's battery pack might also be fed into the regional power grid during periods of peak demand, but the existing grid might not be up to having millions of vehicles hooked up to it and feeding from it simultaneously. And a power plant in every green-car owner's garage or parking space would require a grid smarter than presently exists.

Some green automobile features seem to be more silly than sensible. Ford announced that its new Fusion hybrid would have a "Zen-like instrument panel" whose electronic display would reward fuel-efficient drivers with multiplying "images of green leaves." That's nice, but should it be necessary?

Toyota's third-generation Prius can be fitted with an optional solar roof, which powers a fan designed to lower the temperature inside a parked car. However, as the small print in one advertisement notes, the system "must be turned on prior to leaving vehicle," which is reasonable, and the car must also be "parked in direct sunlight," which is counterproductive. Of course, the same cooling effect might be achieved by just parking in the shade, which works even without throwing a switch.

Green cars, like virtually any other kind of conventional or alternative technology, cannot escape being part of a much larger thermodynamical system. Someday, mainstream vehicles powered by long-promised hydrogen-driven and water-emitting fuel cells may move silently along our highways, but the fuel will still have to be produced somewhere by some energy-consuming (and possibly polluting) process. And the hydrogen will have to be made available at filling stations that are at least as conveniently located as diesel stations are today.

Automobiles may be self-propelled vehicles, but that is not to say that they do not consume energy in one form or another. Trying to make them out to be more than they are promises to be a continuing frustration to marketers working within the grand technological system in which we all move.

Henry Petroski is the Aleksandar S. Vesic Professor of Civil Engineering and a professor of history at Duke University. His new book, The Essential Engineer: Why Science Alone Will Not Solve Our Global Problems, will be published in February.




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