Copyright 2003 by the American Association for the Advancement of Science. All rights reserved.
June 30, 2003
The Bush Administration has instituted a program—known as the FreedomCar and Fuel Initiative—to replace gasoline-powered automobiles with ones powered by hydrogen fuel cells, an advance that could bring increased efficiency, an end to dependence on foreign oil, cleaner air, and reduced greenhouse gas emissions.
The administration has painted an enticing picture of a hydrogen-based economy that will free the nation from its energy-related problems. This ambitious vision faces numerous obstacles, however, and even its most optimistic proponents expect it to take over 15 years to achieve.
What follows is a brief outline of the hydrogen technologies under development, their potential benefits, and the hurdles faced in making the hydrogen economy a reality.
A hydrogen fuel cell is a device that produces electricity from the reaction between hydrogen and oxygen. The only byproduct of this reaction is water. Fuel cells thus offer a zero emission power source. Fuel cells are also inherently more efficient than the internal combustion engines used in today's cars. Internal combustion engines can convert up to 30 percent of the energy in the gasoline they consume into usable power whereas fuel cells have the potential to operate at up to 55 percent efficiency.
Several types of fuel cells are currently in use. The phosphoric acid fuel cell is the most well-developed and is used in commercial applications such as providing grid support and back-up power, and powering large vehicles such as buses. Alkaline fuel cells, meanwhile, have been used by NASA to provide electricity on the space shuttle. A third source still under development, polymer electrolyte membrane fuel cells, may have the most promise for transportation applications.
However, fuel cell manufacturers still need to achieve major improvements in cost and durability before their technologies can see widespread use in automobiles. David K. Garman, the assistant secretary of energy for energy efficiency and renewable energy, recently told the Senate Science, Technology, and Space Subcommittee that fuel cells will need to come down in cost by "an order of magnitude." The Department of Energy (DOE) has set a goal of developing a polymer electrolyte membrane fuel cell that will operate at a cost of $45 per kilowatt by 2010. Current gasoline engines, by comparison, operate at $35 per kilowatt.
Fuel cell cars will also require the development of supporting technologies, such as electric motors. Other witnesses at the May 7 Senate hearing noted that many of these technologies are currently being developed for hybrid electric vehicles, thus emphasizing the importance of continued investment in hybrids.
Storage of hydrogen on board a vehicle may be the most significant obstacle to mass production of hydrogen-powered cars, according to Mr. Garman. Hydrogen can be stored as a gas, as a liquid, or in a solid state as part of chemical compounds called metal hydrides. Storage as a gas is the most mature technology, but requires the hydrogen to be compressed to high pressures, since the natural density of hydrogen is very low. Liquid storage, on the other hand, can be achieved at ambient pressures and uses less volume, but requires very low-temperature cryogenic containers and the use of large quantities of energy to convert gaseous hydrogen to a liquid. Metal hydrides may turn out to be the best solution because they do not require extreme pressures or temperatures, but development is much farther down the road.
While hydrogen is currently produced primarily in decentralized locations for use on-site, 17 percent is produced for sale and distribution by about 80 centralized plants. This hydrogen is transported through pipelines and by trucks. Hydrogen pipelines are currently operated in Texas, Louisiana, California, and Indiana.
Developing a hydrogen infrastructure is one of the major challenges of a conversion to hydrogen-powered cars. Market incentives to build such an infrastructure will not exist until hydrogen-powered cars are on the roads, but hydrogen-powered cars will not be attractive to consumers until a viable infrastructure is in place. DOE's hydrogen initiative aims to address this "chicken-and-egg" problem by ensuring that vehicle and infrastructure technologies are developed simultaneously.
Although hydrogen is the most abundant element in the universe, it is not present on Earth in its pure form. It must be obtained from compounds that contain it, such as fossil fuels and water. Thus, hydrogen is not itself an energy source, but is an energy carrier, much like electricity—it is a mechanism for storing energy produced from a wide variety of sources.
Currently, nine million tons of hydrogen are produced each year mainly for use in chemicals, petroleum refining, metals, and electronics. 95 percent is produced from natural gas by steam reforming. In this process, the natural gas reacts chemically with steam, producing hydrogen and carbon dioxide. Hydrogen can also be produced by electrolysis, where electricity is used to split water into hydrogen and oxygen. Since carbon dioxide is a greenhouse gas, the latter method would be preferable, but would require increased generation of electricity from either nuclear power plants or renewable sources such as wind and solar power. Technologies are also under development for producing hydrogen from biomass and coal.
The production methods used will ultimately determine whether hydrogen can provide environmental benefits. If it is produced primarily through steam reforming, it will not necessarily provide any reduction in greenhouse gases. However, if it is produced from clean sources such as wind and solar power, it could have a major impact on global warming.
An additional area of concern for the hoped-for transition to hydrogen is safety. Safety risks both real and perceived will need to be addressed as the technology progresses, an issue that came up at a May 20 hearing of the House Energy and Commerce Committee. In response to a question from Rep. Steve Buyer (R-IN), Mr. Garman indicated that safety was not as big an obstacle as some perceive it to be. The main safety concern is flammability, he said, and since hydrogen is very light, it dissipates quickly and may actually be less dangerous than gasoline. He noted that hydrogen gas is not toxic, although a leak can cause suffocation in an enclosed space.
Reaction in Congress to President Bush's hydrogen initiative has been enthusiastic, with most members supporting the vision of a hydrogen economy. Most of the criticism it has faced is that the program is too small, or does not include sufficient parallel efforts in areas such as hybrid technology and renewable energy sources. Sen. Byron Dorgan (D-ND), for example, says it will require a technology development program on the scale of the Apollo space program that put humans on the moon, and he has proposed a plan to spend $6.5 billion on the hydrogen effort.
Others, meanwhile, argue that a transition to a hydrogen economy presents a daunting challenge that will require a set of coordinated federal government policies. "Developing the technology is not enough," said Dr. David J. Friedman, an engineer with the Union of Concerned Scientists, at the Senate hearing. "A fuel cell vehicle Apollo-like project must also include clear vehicle production and fuel supply goals, performance targets and timelines along with the resources to make the program successful." ••• [an error occurred while processing this directive]
Copyright 2003 by the American Association for the Advancement of Science. All rights reserved. |