Hydrogen is widely viewed by environmentalists, as well as by many large corporations, as a panacea to air pollution, global warming and shrinking petroleum supplies. This view has been endorsed by President Bush who, in his 2003 State of the Union Address stated, "The first car driven by a child born today could be powered by hydrogen and pollution free."
Hydrogen-powered cars and trucks that use fuel cells to drive electric motors instead of internal-combustion engines could potentially eliminate tail-pipe pollution and dependence on foreign oil. But hydrogen is not an energy source. It is only an energy carrier that must be produced from a primary energy source, such as natural gas, coal, nuclear fuel, wind or solar radiation.
There are two main methods for making hydrogen. The dominant commercial method uses natural gas and steam to produce ultimately hydrogen and carbon dioxide. In this process, called steam reforming, less than 80 percent of the input energy is left in the hydrogen; then another 15 percent or more is lost converting the hydrogen to liquid or compressed gas. Thus, at most only two-thirds of the original energy ends up as useful hydrogen. Moreover, natural gas is an expensive non-renewable fossil fuel that is in short supply. Furthermore, natural gas has many other important uses, such as heating our homes and serving as a feedstock for many chemicals.
The other main way of making hydrogen is by electrolysis. This process is straightforward, but costs three times as much as steam reforming to make the same amount of hydrogen. It uses an electrolyzer, in which a current is passed through water, to split the water into hydrogen and oxygen.
An electrolyzer is essentially a fuel cell operating in reverse. But the electricity must first be produced from a primary energy source. At the very best, only half as much electricity can be obtained from the hydrogen as is consumed to make it. If electricity from the grid were used to produce the hydrogen, over 50 percent of the electric energy would come from coal-fired power plants, which are the most polluting source. If hydrogen produced by electrolysis were used as fuel, the president's statement should be amended from a "pollution-free car" to a "pollute elsewhere car."
Environmentalists recommend using solar energy or wind to generate electricity for a "renewable hydrogen economy." We have been staunch supporters of renewable energy for half a century and recently some renewable options have achieved economic competitiveness in favorable locations. But the renewable hydrogen path to electricity would more than double the cost of electricity, and probably would set back deployment of renewable electric power for decades. Wind, solar and biomass should be used for heat and power generation, not for making hydrogen.
The nuclear industry argues that reactors are the preferred option to make hydrogen for fuel cells, because they do not generate greenhouse gases. If the public is willing to accept the risks associated with transport and storage of nuclear waste, nuclear power is an available option. But, using nuclear-generated electricity to make hydrogen, from which to make electricity, is a waste of energy and money.
Petroleum engineers predict that worldwide petroleum production will peak in 10 to 30 years. Once production begins to decrease, it will be necessary to supplement oil with some other fuel or to reduce consumption by conservation measures, such as increased mileage of the vehicle fleet and using mass transport. Both of these changes will take time, and we must begin to plan now.
Fortunately, there are several technologies to reduce petroleum consumption. The most obvious is to increase the mileage of the auto and pickup fleet. This can be achieved by building smaller cars and hybrid vehicles, such as the Toyota Prius and Ford Escape. Hybrids use a small gasoline or diesel engine that always runs at maximum efficiency and charges on-board batteries when it produces excess power; when needed, the hybrid draws energy from the batteries to run an electric-drive motor.
Battery technology has improved enormously in the past decade, and state-of-the-art batteries in hybrids increase mileage. But even greater reductions in fuel consumption and pollution can be achieved with "plug-in," electric-gasoline or diesel hybrids, by charging their batteries overnight when excess electrical capacity is available. Demonstration-model plug-in hybrids are on the road and need no new technology for their large-scale deployment. It has been estimated that plug-in hybrids could approach and perhaps even exceed 100 miles per gallon of fuel used. It is also possible to replace petroleum-based fuels with liquid fuels made from coal or biomass, further reducing our dependence on imported petroleum.
There are no huge technical obstacles to making hydrogen and using it as a fuel. But a hydrogen economy would be more expensive and use more primary energy than other options. Moreover, it would require many hundreds of billions of dollars to build a storage and transport infrastructure. We should not accept President Bush's statement that hydrogen will replace oil without examining other options that are more economical and for which the technology and infrastructure already exist.
Frank Kreith and Ron West are retired engineering professors from the University of Colorado, Boulder, and both live in Boulder. Kreith also served as Branch Chief at the Solar Energy Research Institute for 10 years.
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