The Pros and Cons of 8 Green Fuels

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

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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:

  • What is it?
  • What’s good about it?
  • What’s bad about it?
  • Where would it be most useful?
  • How much will it cost?
  • When’s it coming?
  • What’s taking so long?
  • Who’s doing it?
  • Could it be a silver bullet?
  • What is it?

    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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    What's good about it?

    Corn Ethanol
    It’s renewable, and corn is plentiful in the United States. Burning corn ethanol can cut greenhouse-gas emissions by as much as 20 percent, compared with gasoline. Producing ethanol generates fewer emissions, too.
    Cellulosic Ethanol
    A lot. It’s renewable and can be made from nonfood plants. It also has much greater "energy bounce" than gasoline or corn ethanol, which means it generates far more energy than it takes to produce. Greenhouse-gas emissions are lower than those from gas, too.
    Biodiesel
    Biodiesel is renewable, from domestic sources, and can be used with any diesel engine. It also has more energy than gasoline, which raises mileage. Like ordinary diesel, it offers good torque characteristics in cars, which drivers notice as power and acceleration.
    Clean Diesels
    Diesel contains more energy than gasoline, so cars get about 30 percent better mileage—with greater torque, which drivers feel as low-end acceleration. The extra energy also makes diesels ideal for towing heavy loads, which is why many trucks are diesel-powered.
    Hybrids
    Hybrid mileage can be 25 to 30 percent higher than that of ordinary gas-powered cars. That’s because the electric motor, which requires no gas, does most of the work during driving conditions where the gas engine is least efficient—like stop-and-go urban driving. Since they burn less fuel, hybrids emit fewer greenhouse gases, too.
    Plug-In Hybrids
    Powering the battery from the electrical grid could be much cheaper than gasoline. If owners charged up overnight, they’d be tapping into off-peak power that costs utilities less—so some savings could be passed on to consumers. Plug-ins could also get higher mileage than today’s hybrids, with fewer emissions.
    Electric Vehicles
    As with plug-in hybrids, electric vehicles could be cheap to fuel, given the relatively low cost of electricity drawn from the power grid through an ordinary outlet. Power drawn overnight at off-peak rates could cost one-fourth the equivalent of gasoline.
    Hydrogen/Fuel Cells
    Many things. Hydrogen is widely available, in natural gas and water, for instance. The only tailpipe emission is water. Pound for pound, hydrogen fuel has more inherent energy than gasoline, which could mean higher mileage: A prototype Honda fuel-cell vehicle gets the equivalent of nearly 70 miles per gallon.
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