The Pros and Cons of 8 Green Fuels

Our dossiers detail which fuels are overrated—and which could power your next car

By Rick Newman
Posted January 11, 2008

After years of talk, rising oil prices—combined with global-warming concerns and a disdain for foreign oil—have finally set the stage for breakthroughs in alternative fuels. To see how the hottest new technologies stack up, click on each fuel for a rundown of its attributes and flaws, or click on the topics on the left to see how various fuels compare:

Corn Ethanol: A fuel derived from the sugars in corn and other plants. Pure ethanol is usually blended with gasoline. "E10"—10 percent ethanol—is common today. E85—85 percent ethanol—is the highest practical blend; some gas is still required for combustion in most climates.

Cellulosic Ethanol: A biofuel refined from cellulose, the fibrous material that makes up most of the plant matter in wheat, switch grass, corn stalks, rice straw, and even wood chips.

Biodiesel: A renewable fuel made from vegetable oil or animal fats, including soybeans, canola oil, and even used cooking oil. It’s sometimes mixed with conventional, petroleum-based diesel to help cut down on tailpipe emissions.

Clean Diesels: Diesel is refined from petroleum, like gasoline, but the pollution it produces is harder to control. "Clean diesel" vehicles burn the fuel more efficiently and trap pollutants better. New low-sulfur diesel fuel also pollutes less—much like unleaded gasoline, compared with leaded.

Hybrids: There are several kinds of hybrids. In general, today’s models have a battery-powered electric motor that drives the car at slower speeds and a gas engine that kicks in at higher speeds. The engine also helps recharge the battery, along with energy captured from the rotation of the wheels during deceleration.

Plug-In Hybrids: Same principle as for ordinary hybrids: There’s an electric motor and a gas engine, except that the battery powering the motor would be recharged from an electrical outlet, at home or someplace else. The motor would power the car until battery power waned. Then the gas engine or another secondary power source would kick in.

Electric Vehicles: Any car with a battery-powered motor—including every variety of hybrid—is an electric vehicle to some extent. A pure electric vehicle would be run entirely by the battery-powered motor.

Hydrogen/Fuel Cells: The concept is similar to hybrids: an electric motor would drive the car much of the time. In this case, the motor would be charged by something under the hood called a fuel-cell stack, which converts hydrogen and oxygen into electricity that flows to the battery. The on-board fuel would be hydrogen.

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