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.
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.
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.
Where would it be most useful?
Corn Ethanol
Mild blends are widely available. But E85—85 percent ethanol, 15 percent gas—is found only at about 1,500 filling stations in the United States., mostly in the Midwest. That number will grow, since the 2007 energy law mandates a fourfold increase in ethanol production by 2022.
Cellulosic Ethanol
Wherever it’s available. Once it’s produced, cellulosic ethanol will be the same as corn ethanol, fit for any flex-fuel vehicle capable of running on E85.
Biodiesel
For now, biodiesel seems most useful as a blend used in conventional diesel-powered automobiles. Some enthusiasts retrofit their cars to run on pure biodiesel—although that can void the warranty and cause other problems.
Clean Diesels
For large vehicles that generally get poor mileage and trucks used for heavy hauling. A number of states with the toughest emissions requirements—like California, New York, and Massachusetts—effectively ban older diesels, although clean diesels should meet their standards.
Hybrids
They’re great for people who take lots of short trips or drive frequently in traffic. At highway speeds, there’s less of a payoff, since the gas engine does most of the work. Hybrids perform better in warm climates than in cold ones, since low temps can degrade battery effectiveness.
Plug-In Hybrids
As with hybrids in general, plug-ins would be best for people who make a lot of short trips or commuters who drive frequently in traffic, since that’s when the battery-powered electric motor would be doing most of the work.
Electric Vehicles
They’d make most sense for commuters and others who typically drive short distances. Once the battery charge is depleted, there’s no real advantage to an EV—since it has to run on a gas engine or some other power source.
Hydrogen/Fuel Cells
Fuel cells make sense for most types of vehicles. One enduring challenge is "cold start"— the ability to power up at temps as low 30 below zero Fahrenheit—which means fuel cells are ill-suited for the coldest climates. That may be resolved by the time other technology matures.
How much will it cost?
Corn Ethanol
It’s often a bit cheaper than gas—but not a bargain, since mileage is lower. At $2.50 per gallon, for instance, it takes about $3.30 worth of E85 to drive the same distance as a gallon of $3 gas. Cars must also be specially outfitted to run on E85.
Cellulosic Ethanol
Unclear, because it’s not mass-produced yet, but estimates suggest it would be considerably cheaper than gas on a per-mile basis—perhaps less than $1 per gallon.
Biodiesel
Properly refined biodiesel tends to cost more than gasoline. But it varies. Some restaurants can be persuaded to give away used cooking oil, which will power certain cars. If production ramps up, costs should come down, but it’s not clear that will happen.
Clean Diesels
The price of diesel is usually a bit higher than gasoline, and new low-sulfur diesel is more expensive still. Diesel engines cost more, too. Some drivers might recoup the extra cost through better mileage.
Hybrids
They can be pricey. At about $23,000, for instance, the Honda Civic hybrid is roughly $4,000 more than a basic conventional model. The Lexus RX400h, at nearly $42,000, tops the comparable RX350 by about $5,000. But there’s always some payback from lower gas bills, fewer refueling stops, and, in some cases, tax breaks.
Plug-In Hybrids
Not sure, because the battery technology isn’t mature. But with the right batteries, plug-ins could be cheap to fuel. At overnight, off-peak rates, the cost of electricity might be one-fourth what an equivalent amount of gasoline would cost.
Electric Vehicles
The electric-powered Chevy Volt, due in 2010, will have a price tag of about $30,000—with GM most likely subsidizing the battery pack. Fueling it from home, however, could cost 80 percent less than filling a car with $3 gas.
Hydrogen/Fuel Cells
If mass-produced and widely distributed like gasoline, the cost of hydrogen fuel could be equivalent to $2 per gallon or less. Plus, fuel cells are about three times as efficient as gas engines, which means better mileage. But building an infrastructure to deliver hydrogen would cost billions, which would certainly add to consumers’ cost.
When's it coming?
Corn Ethanol
Ethanol has been around for many years but hasn’t caught on because the fuel isn’t widely available, and for most drivers it’s more expensive on a per-mile basis. Virtually all cars can run on mild blends like E10, and most automakers build E85-capable cars or plan to.
Cellulosic Ethanol
Five years, perhaps. It’s not quite around the corner, but it’s probably closer than hydrogen-powered cars. Backing by big companies like General Motors—and the possibility of technology breakthroughs—could speed adoption.
Biodiesel
Refiners already produce about 250 million gallons of biodiesel per year—but that’s barely 1 percent of all diesel consumed in the United States. And diesels themselves represent a small portion of the car market here. The industry could gather steam if there are tax breaks or other subsidies.
Clean Diesels
A couple of clean diesels, like the Mercedes-Benz E320 sedan, are on the market now, with other models from automakers such as Volkswagen, Audi, and Hyundai on the way.
Hybrids
By the end of 2008, there will be nearly two dozen hybrids on the market, including sedans, crossovers, luxury makes, full-size SUVs, and pickup trucks.
Plug-In Hybrids
Unknown. There’s not yet an affordable battery that can handle the deep charges and discharges that would occur under normal use in a plug-in. Prototype lithium ion batteries—like those in power tools and laptops—are promising, but it’s not clear if they can be scaled up for something as big as a car.
Electric Vehicles
GM built an electric car in the 1990s—the EV1—that flopped because it had limited range, with no backup engine, and carried just two people. Tiny Tesla Motors is building a $100,000 all-electric car, due in 2008, using several thousand laptop-style lithium-ion batteries strung together. Stay tuned.
Hydrogen/Fuel Cells
Could still be 10 or 20 years away. There are major technical hurdles in terms of producing the fuel, distributing it widely, and storing it in cars.
What’s taking so long?
Corn Ethanol
In some farm states, where the corn is grown, there are plenty of ethanol stations. But there are no pipelines from there to major population centers, and the fuel hasn’t caught on nationwide because it doesn’t really save drivers money.
Cellulosic Ethanol
It’s more difficult to break down the cellulose in plants than the starch that generates corn ethanol. Researchers are working on new enzymes and manufacturing processes to make it easier and cheaper to produce cellulosic ethanol.
Biodiesel
Demand for biodiesel isn’t as strong as for other oil alternatives, partly because diesel engines represent a small portion of the American car market. Even in Europe, where diesel cars are far more popular, biodiesel fervor has faded because raising the right crops might cause deforestation.
Clean Diesels
Diesels are popular in Europe, where gas is more expensive, but in the United States, pollution problems have relegated them to a small sliver of the car market. If clean diesels pass muster in California—which sets the standards for several other states—the technology could make a comeback.
Hybrids
They’re available now. The next step will be "dual-mode" hybrids that have two electric motors, are more efficient, and are more suitable for big SUVs and pickups that have four-wheel drive and heavy towing capability. The first dual-mode hybrids are the Chevy Tahoe and GMC Yukon SUVs.
Plug-In Hybrids
The battery technology. The nickel-metal hydride batteries used in today’s hybrids don’t hold enough energy to be viable for plug-ins and can’t handle the deep charges and discharges needed. Lithium-ion batteries might work, but nobody has mass-produced one that’s safe, reliable, and potent enough for a car.
Electric Vehicles
The batteries. An EV battery pack must be able to withstand thousand of deep charges and discharges. Lithium-ion batteries like those used in laptops, cell phones and power tools have the most potential—but nobody’s mass-produced one big enough to power a car safely and reliably.
Hydrogen/Fuel Cells
Researchers are still searching for cost effective ways to produce the fuel, transport it, and store it in a car. An even bigger problem is building a hydrogen infrastructure comparable to a gas station on every corner, which would cost billions and require the unprecedented cooperation of automakers, energy companies, and the government.
Who’s doing it?
Corn Ethanol
General Motors, Ford, and Chrysler build the most "flex-fuel vehicles," able to run on gas or any ethanol blend up to E85. Converting new cars to FFVs on the assembly line costs less than $100; third-party shops can convert existing cars for $1,500 or less.
Cellulosic Ethanol
Many small companies are producing it in labs, with the first large-scale plant set to start running this year. Venture capitalists are interested, while General Motors and other automakers may also invest in companies producing this fuel.
Biodiesel
The strongest support for biodiesel comes from agricultural interests, such as the soybean industry. Most of the big automakers haven’t shown significant interest.
Clean Diesels
Mercedes, Audi, VW, and other carmakers from Europe—where diesels are most popular—have the most advanced clean-diesel technology. General Motors, Ford, and Chrysler use diesel engines in their pickup trucks. Others plan to introduce clean diesels, too.
Hybrids
Toyota and Honda dominated the hybrid market for several years, but now virtually all manufacturers plan to offer a lineup of hybrids.
Plug-In Hybrids
Toyota, Ford, and other automakers are testing prototypes. Google, some municipalities, and a few utilities are also working to convert conventional hybrids into plug-ins, along with enthusiasts retrofitting their hybrids with lithium-ion batteries. (But don’t try this at home.)
Electric Vehicles
GM has the most at stake, with multimillions of research dollars—and its credibility—committed to delivering the Chevy Volt by 2010. Toyota and other carmakers are also doing extensive battery research, as are battery suppliers.
Hydrogen/Fuel Cells
Most of the big automakers have fuel-cell programs. GM has recruited ordinary consumers to test a fleet of 100 fuel cell vehicles on the east and west coasts. Honda plans to lease a fuel-cell car, for about $600 per month, to a few consumers in 2008. Others could announce similar programs.
Could it be a silver bullet?
Corn Ethanol
Highly unlikely. Corn ethanol helps reduce greenhouse gases and is a renewable energy source. But it’s a less potent form of energy than gasoline—and doesn’t really save drivers money, at current prices.
Cellulosic Ethanol
Maybe half a bullet. It’s renewable, would cut greenhouse gas emissions, and ought to be affordable—if the technology develops. It still generates some pollution but far less than oil-based fuels do.
Biodiesel
No. Even if production grew rapidly, it would still be limited to use in cars with diesel engines or unusual modifications, and the benefits aren’t as promising as those of cellulosic ethanol or other alternatives. But biodiesel could still help reduce greenhouse gases and petroleum use.
Clean Diesels
No. Since it’s a fossil fuel, even clean diesels are not an alternative to hydrocarbons.
Hybrids
Probably not. Today’s hybrids still require a gasoline-fed engine and two drive systems, which is less efficient than a single power source. But hybrids are helping drive up fuel economy, propel battery technology, and make consumers comfortable with newfangled cars.
Plug-In Hybrids
Should the battery technology mature and plug-ins become viable, the math would be very compelling. Some experts think plug-ins could get the equivalent of 100 miles per gallon. Powering them from the grid would bring further savings, cutting the cost of fueling by 75 percent or more.
Electric Vehicles
Researchers have their fingers crossed. If the battery technology matures, lithium-powered electric vehicles could be a game-changer, with great driving characteristics, low tailpipe emissions, and super cheap fuel. But big backers like GM. have guessed wrong before.
Hydrogen/Fuel Cells
Maybe. If the technology matures, costs fall, and hydrogen fuel becomes widely available, it would solve several problems: Hydrogen could come from renewable sources and generates no tailpipe emissions. And theoretically, it would be affordable—maybe even cheap.
TopPrimary sources: Automotive News, Union of Concerned Scientists, dieselforum.org, Department of Energy, Environmental Protection Agency, General Motors, Honda, Toyota, American Automobile Association, Renewable Fuels Association, Natural Resources Defense Council, National Biodiesel Board, Center for Automotive Research
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.
Where would it be most useful?
Corn Ethanol
Mild blends are widely available. But E85—85 percent ethanol, 15 percent gas—is found only at about 1,500 filling stations in the United States., mostly in the Midwest. That number will grow, since the 2007 energy law mandates a fourfold increase in ethanol production by 2022.
Cellulosic Ethanol
Wherever it’s available. Once it’s produced, cellulosic ethanol will be the same as corn ethanol, fit for any flex-fuel vehicle capable of running on E85.
Biodiesel
For now, biodiesel seems most useful as a blend used in conventional diesel-powered automobiles. Some enthusiasts retrofit their cars to run on pure biodiesel—although that can void the warranty and cause other problems.
Clean Diesels
For large vehicles that generally get poor mileage and trucks used for heavy hauling. A number of states with the toughest emissions requirements—like California, New York, and Massachusetts—effectively ban older diesels, although clean diesels should meet their standards.
Hybrids
They’re great for people who take lots of short trips or drive frequently in traffic. At highway speeds, there’s less of a payoff, since the gas engine does most of the work. Hybrids perform better in warm climates than in cold ones, since low temps can degrade battery effectiveness.
Plug-In Hybrids
As with hybrids in general, plug-ins would be best for people who make a lot of short trips or commuters who drive frequently in traffic, since that’s when the battery-powered electric motor would be doing most of the work.
Electric Vehicles
They’d make most sense for commuters and others who typically drive short distances. Once the battery charge is depleted, there’s no real advantage to an EV—since it has to run on a gas engine or some other power source.
Hydrogen/Fuel Cells
Fuel cells make sense for most types of vehicles. One enduring challenge is "cold start"— the ability to power up at temps as low 30 below zero Fahrenheit—which means fuel cells are ill-suited for the coldest climates. That may be resolved by the time other technology matures.
How much will it cost?
Corn Ethanol
It’s often a bit cheaper than gas—but not a bargain, since mileage is lower. At $2.50 per gallon, for instance, it takes about $3.30 worth of E85 to drive the same distance as a gallon of $3 gas. Cars must also be specially outfitted to run on E85.
Cellulosic Ethanol
Unclear, because it’s not mass-produced yet, but estimates suggest it would be considerably cheaper than gas on a per-mile basis—perhaps less than $1 per gallon.
Biodiesel
Properly refined biodiesel tends to cost more than gasoline. But it varies. Some restaurants can be persuaded to give away used cooking oil, which will power certain cars. If production ramps up, costs should come down, but it’s not clear that will happen.
Clean Diesels
The price of diesel is usually a bit higher than gasoline, and new low-sulfur diesel is more expensive still. Diesel engines cost more, too. Some drivers might recoup the extra cost through better mileage.
Hybrids
They can be pricey. At about $23,000, for instance, the Honda Civic hybrid is roughly $4,000 more than a basic conventional model. The Lexus RX400h, at nearly $42,000, tops the comparable RX350 by about $5,000. But there’s always some payback from lower gas bills, fewer refueling stops, and, in some cases, tax breaks.
Plug-In Hybrids
Not sure, because the battery technology isn’t mature. But with the right batteries, plug-ins could be cheap to fuel. At overnight, off-peak rates, the cost of electricity might be one-fourth what an equivalent amount of gasoline would cost.
Electric Vehicles
The electric-powered Chevy Volt, due in 2010, will have a price tag of about $30,000—with GM most likely subsidizing the battery pack. Fueling it from home, however, could cost 80 percent less than filling a car with $3 gas.
Hydrogen/Fuel Cells
If mass-produced and widely distributed like gasoline, the cost of hydrogen fuel could be equivalent to $2 per gallon or less. Plus, fuel cells are about three times as efficient as gas engines, which means better mileage. But building an infrastructure to deliver hydrogen would cost billions, which would certainly add to consumers’ cost.
When's it coming?
Corn Ethanol
Ethanol has been around for many years but hasn’t caught on because the fuel isn’t widely available, and for most drivers it’s more expensive on a per-mile basis. Virtually all cars can run on mild blends like E10, and most automakers build E85-capable cars or plan to.
Cellulosic Ethanol
Five years, perhaps. It’s not quite around the corner, but it’s probably closer than hydrogen-powered cars. Backing by big companies like General Motors—and the possibility of technology breakthroughs—could speed adoption.
Biodiesel
Refiners already produce about 250 million gallons of biodiesel per year—but that’s barely 1 percent of all diesel consumed in the United States. And diesels themselves represent a small portion of the car market here. The industry could gather steam if there are tax breaks or other subsidies.
Clean Diesels
A couple of clean diesels, like the Mercedes-Benz E320 sedan, are on the market now, with other models from automakers such as Volkswagen, Audi, and Hyundai on the way.
Hybrids
By the end of 2008, there will be nearly two dozen hybrids on the market, including sedans, crossovers, luxury makes, full-size SUVs, and pickup trucks.
Plug-In Hybrids
Unknown. There’s not yet an affordable battery that can handle the deep charges and discharges that would occur under normal use in a plug-in. Prototype lithium ion batteries—like those in power tools and laptops—are promising, but it’s not clear if they can be scaled up for something as big as a car.
Electric Vehicles
GM built an electric car in the 1990s—the EV1—that flopped because it had limited range, with no backup engine, and carried just two people. Tiny Tesla Motors is building a $100,000 all-electric car, due in 2008, using several thousand laptop-style lithium-ion batteries strung together. Stay tuned.
Hydrogen/Fuel Cells
Could still be 10 or 20 years away. There are major technical hurdles in terms of producing the fuel, distributing it widely, and storing it in cars.
What’s taking so long?
Corn Ethanol
In some farm states, where the corn is grown, there are plenty of ethanol stations. But there are no pipelines from there to major population centers, and the fuel hasn’t caught on nationwide because it doesn’t really save drivers money.
Cellulosic Ethanol
It’s more difficult to break down the cellulose in plants than the starch that generates corn ethanol. Researchers are working on new enzymes and manufacturing processes to make it easier and cheaper to produce cellulosic ethanol.
Biodiesel
Demand for biodiesel isn’t as strong as for other oil alternatives, partly because diesel engines represent a small portion of the American car market. Even in Europe, where diesel cars are far more popular, biodiesel fervor has faded because raising the right crops might cause deforestation.
Clean Diesels
Diesels are popular in Europe, where gas is more expensive, but in the United States, pollution problems have relegated them to a small sliver of the car market. If clean diesels pass muster in California—which sets the standards for several other states—the technology could make a comeback.
Hybrids
They’re available now. The next step will be "dual-mode" hybrids that have two electric motors, are more efficient, and are more suitable for big SUVs and pickups that have four-wheel drive and heavy towing capability. The first dual-mode hybrids are the Chevy Tahoe and GMC Yukon SUVs.
Plug-In Hybrids
The battery technology. The nickel-metal hydride batteries used in today’s hybrids don’t hold enough energy to be viable for plug-ins and can’t handle the deep charges and discharges needed. Lithium-ion batteries might work, but nobody has mass-produced one that’s safe, reliable, and potent enough for a car.
Electric Vehicles
The batteries. An EV battery pack must be able to withstand thousand of deep charges and discharges. Lithium-ion batteries like those used in laptops, cell phones and power tools have the most potential—but nobody’s mass-produced one big enough to power a car safely and reliably.
Hydrogen/Fuel Cells
Researchers are still searching for cost effective ways to produce the fuel, transport it, and store it in a car. An even bigger problem is building a hydrogen infrastructure comparable to a gas station on every corner, which would cost billions and require the unprecedented cooperation of automakers, energy companies, and the government.
Who’s doing it?
Corn Ethanol
General Motors, Ford, and Chrysler build the most "flex-fuel vehicles," able to run on gas or any ethanol blend up to E85. Converting new cars to FFVs on the assembly line costs less than $100; third-party shops can convert existing cars for $1,500 or less.
Cellulosic Ethanol
Many small companies are producing it in labs, with the first large-scale plant set to start running this year. Venture capitalists are interested, while General Motors and other automakers may also invest in companies producing this fuel.
Biodiesel
The strongest support for biodiesel comes from agricultural interests, such as the soybean industry. Most of the big automakers haven’t shown significant interest.
Clean Diesels
Mercedes, Audi, VW, and other carmakers from Europe—where diesels are most popular—have the most advanced clean-diesel technology. General Motors, Ford, and Chrysler use diesel engines in their pickup trucks. Others plan to introduce clean diesels, too.
Hybrids
Toyota and Honda dominated the hybrid market for several years, but now virtually all manufacturers plan to offer a lineup of hybrids.
Plug-In Hybrids
Toyota, Ford, and other automakers are testing prototypes. Google, some municipalities, and a few utilities are also working to convert conventional hybrids into plug-ins, along with enthusiasts retrofitting their hybrids with lithium-ion batteries. (But don’t try this at home.)
Electric Vehicles
GM has the most at stake, with multimillions of research dollars—and its credibility—committed to delivering the Chevy Volt by 2010. Toyota and other carmakers are also doing extensive battery research, as are battery suppliers.
Hydrogen/Fuel Cells
Most of the big automakers have fuel-cell programs. GM has recruited ordinary consumers to test a fleet of 100 fuel cell vehicles on the east and west coasts. Honda plans to lease a fuel-cell car, for about $600 per month, to a few consumers in 2008. Others could announce similar programs.
Could it be a silver bullet?
Corn Ethanol
Highly unlikely. Corn ethanol helps reduce greenhouse gases and is a renewable energy source. But it’s a less potent form of energy than gasoline—and doesn’t really save drivers money, at current prices.
Cellulosic Ethanol
Maybe half a bullet. It’s renewable, would cut greenhouse gas emissions, and ought to be affordable—if the technology develops. It still generates some pollution but far less than oil-based fuels do.
Biodiesel
No. Even if production grew rapidly, it would still be limited to use in cars with diesel engines or unusual modifications, and the benefits aren’t as promising as those of cellulosic ethanol or other alternatives. But biodiesel could still help reduce greenhouse gases and petroleum use.
Clean Diesels
No. Since it’s a fossil fuel, even clean diesels are not an alternative to hydrocarbons.
Hybrids
Probably not. Today’s hybrids still require a gasoline-fed engine and two drive systems, which is less efficient than a single power source. But hybrids are helping drive up fuel economy, propel battery technology, and make consumers comfortable with newfangled cars.
Plug-In Hybrids
Should the battery technology mature and plug-ins become viable, the math would be very compelling. Some experts think plug-ins could get the equivalent of 100 miles per gallon. Powering them from the grid would bring further savings, cutting the cost of fueling by 75 percent or more.
Electric Vehicles
Researchers have their fingers crossed. If the battery technology matures, lithium-powered electric vehicles could be a game-changer, with great driving characteristics, low tailpipe emissions, and super cheap fuel. But big backers like GM. have guessed wrong before.
Hydrogen/Fuel Cells
Maybe. If the technology matures, costs fall, and hydrogen fuel becomes widely available, it would solve several problems: Hydrogen could come from renewable sources and generates no tailpipe emissions. And theoretically, it would be affordable—maybe even cheap.
TopPrimary sources: Automotive News, Union of Concerned Scientists, dieselforum.org, Department of Energy, Environmental Protection Agency, General Motors, Honda, Toyota, American Automobile Association, Renewable Fuels Association, Natural Resources Defense Council, National Biodiesel Board, Center for Automotive Research
