One of the more challenging ways to use clean energy is in fueling our cars. Advanced transportation technologies—including fuel cells, electric motors, advanced engines, improved materials, and other technologies—aim to reduce pollution and minimize petroleum fuel use in cars, trucks, buses, fleet vehicles, and public transportation.
Compared to current commercial vehicles, advanced vehicles achieve higher fuel economies and make greater use of alternative fuels. The most common alternative fuels in use are biodiesel, ethanol, hydrogen, methanol and natural gas.
Ethanol is the primary U.S. fuel made from renewable energy sources. Ethanol produced from corn is used as a gasoline additive to provide additional oxygenation in cities that have trouble meeting air quality standards for ozone. Corn— like other plants, trees, and organic materials—is considered a “biomass” energy source.
To make greater use of ethanol, “flex fuel” vehicles are now available that can be fueled with either gasoline or E85—a mixture of 85% ethanol and 15% gasoline.
This flexibility allows you to use E85 where it’s available, but still fuel your car with gasoline in areas where E85 is not available.
One issue with producing ethanol from corn is its limited ability to meet our transportation energy needs. All the corn produced in the country would not generate enough ethanol to fuel our vehicles. To address this issue, new technologies are being developed to convert other biomass sources into ethanol. For instance, the ability to convert not only corn, but also crop residues such as cornstalks and cobs into ethanol, will greatly expand the production of ethanol from corn, and also improve its economics. In the future, there will be dedicated energy crops that will supply our nation’s vehicles with ethanol.
Researchers have also developed the technology to convert other forms of biomass—such as wood chips, food waste, grass, or even trash—into ethanol.
In addition to ethanol, a wide variety of energy sources other than gasoline or petroleum diesel fuel can be used to fuel vehicles—these are clean fuels, but most of them are not renewable.
Natural gas vehicles are ideal urban commuter cars, because many cities now offer a number of natural gas refueling stations. The vehicles operate efficiently, with very low tailpipe emissions. Natural gas is also ideal for public transportation, such as buses, taxis, limousines, or shuttles.
Methanol is another alternative fuel, and like ethanol, it is usually mixed with 15% gasoline to form a fuel called M85. Methanol is currently produced from natural gas, although it can also be produced from biomass sources.
More renewable fuels are being developed and will be available in increasing quantities in the coming years. For diesel engines, biodiesel fuels have been developed from vegetable oils and animal fats. These renewable source fuels have the benefit of burning cleaner and with less soot than regular diesel fuel.
The fuel cell is a device that converts the chemical energy of a fuel directly into usable electricity and heat without combustion. Fuel cells are similar to batteries in that both produce a DC current by means of an electrochemical process. Unlike batteries, however, fuel cells use reactants that are stored externally and operate continuously as long as they are supplied with fuel. Any hydrogen-rich material can theoretically serve as a source of hydrogen for fuel cells. These currently include natural gas and petroleum distillates, as well as renewable fuels such as methanol, ethanol, or hydrogen.
Fuel cell vehicles have the potential to reduce harmful emissions and consumption of nonrenewable energy sources because they are clean and efficient. Fuel cells are a technology that could change our future – a device that could power automobiles with little or no tailpipe emissions, provide energy to homes and factories with virtually no smokestack pollution — and use renewable, domestic energy at high efficiency while creating thousands of jobs.
Fuel cells are one of the three power system technologies currently being considered for an 80-miles-per-gallon vehicle under the Partnership for a New Generation of Vehicles. Many of the major automakers have demonstrated direct hydrogen fuel cell systems that should have the potential to be competitive with internal combustion engine propulsion systems.
Electricity is considered an alternative fuel when it is used to charge an electric vehicle. Today, electric vehicles are available from most major automakers. Ford Motor Company, for instance, recently received an order from the U.S. Postal Service for 500 electric vehicles—the largest U.S. order for electric vehicles in history.
The real question for electric cars is, where does the electricity come from? It’s possible for the electricity to come from renewable energy sources, making the electric car a clean car in many ways.
The simplest way is to purchase 100% green power to recharge the car. Some cities have also installed recharging stations with roofs to shelter the cars as they refuel. These roofs are covered with photovoltaic solar panels, so that they actually generate the electricity to refuel the cars.
As we move toward vehicles that run on renewable fuels, it’s also important to reduce the amount of fuel used by vehicles. While saving energy, fuel efficient cars also produce less air pollution.
One approach to increasing automotive efficiency is the hybrid electric vehicle. These vehicles are powered by both an engine and an electric motor, and include a battery pack large enough to continue providing power to the electric motor under most normal driving conditions. The electricity needed to maintain the charge of the batteries is generated by the engine, so unlike electric vehicles, hybrid electric vehicles do not need to be plugged in.
The year 2000 marked a turning point for hybrid electric vehicles in the United States, with the first sale of hybrid electric cars by Honda. The Honda Insight, initially released as a two seat vehicle, combines a three cylinder gasoline engine with an electric motor that provides an extra boost while accelerating and climbing hills. The Insight achieves a remarkable 70 miles to the gallon on the highway, according to U.S. Environmental Protection Agency mileage estimates.
The Toyota Prius, a four door sedan, combines a four-cylinder gasoline engine with an electric motor, working in tandem to save energy. DaimlerChrysler, Ford, and General Motors are expected to follow suit with their own hybrid electric cars in the near future.
One key to the high efficiency of hybrid electric vehicles is the fact that although a lot of power is needed to accelerate a car, a relatively small amount is needed to keep it rolling at a constant speed. Standard gasoline or diesel cars need a large, powerful engine for acceleration, but suffer an efficiency penalty when that same large engine is used to cruise at highway speeds. A hybrid electric vehicle uses just a small engine for cruising, but boosts its power with the electric motor during acceleration.
Another key to high efficiency in these vehicles is power management, which is really the tricky part. The motor and engine must be switched on and off as they are needed, and enough energy must be drawn from the engine to keep the batteries charged over the course of a day’s drive. To help keep the batteries charged, especially in stop-and-go city driving, “regenerative” braking actually generates electricity while braking the car.
All of the hybrid electric cars planned or in production now include either a gasoline or diesel engine, but there’s no technical reason why a hybrid electric vehicle couldn’t someday make use of renewable energy sources by fueling up with ethanol or methanol. And the diesel models that Ford and General Motors are developing could potentially be fueled from cleane rburning biodiesel fuels. So someday soon, you may be driving a clean, efficient car powered by renewable fuels.