Electricity is one energy carrier that can be produced sustainably from renewable resources. Commercial power plants now convert solar, wind, biomass, and geothermal energy directly into electricity. Taken together, these renewable resources now supply over 15,000 megawatts to the nation's electrical grid.⁹ Once generated, electricity can be moved through transmission lines and used in a wide variety of energy applications without producing pollution.

Unfortunately, little progress has been made in using electricity generated from this centralized power grid in transportation, despite a promising beginning a century ago. In 1900, electric cars outnumbered gasoline vehicles by a factor of two to one; an electric race car held the world land speed record. Their quiet, smooth ride and the absence of difficult and dangerous hand-crank starters made electric vehicles the car of choice, especially among the urban social elite. Early in this century there were more than one hundred electric vehicle manufacturers.¹⁰

The weight, space requirements, long recharging time, and poor durability of electric batteries undercut the ability of electric cars to compete with much more energy-dense gasoline, an energy carrier manufactured from crude oil. One pound of gasoline contained as much chemical energy as the electricity held in one hundred pounds of the lead acid batteries then in use. Refueling a car with gasoline was measured in minutes, on-board storage was a snap, supplies appeared to be limitless, and long-distance fuel delivery was relatively cheap and easy. With these attributes, gasoline dominated the fuel marketplace. By 1920, electric cars had virtually disappeared.

As environmental and resource depletion issues take their toll on the oil-dominated transportation system nearly a century later, electric cars are now making a comeback. In December 1996, General Motors began selling the EV-1, the first electric car to be produced by a major automotive manufacturer in more than 70 years. Hundreds of other companies worldwide have spent the last decade in frenetic electric vehicle research, development, and commercialization. The critical issues of battery weight, volume, and recharging, however, continue to present major obstacles to the commercial success of vehicles recharged with electricity from a grid. These impediments thwart attempts to bring renewable energy resources into the transportation marketplace through a connection to centralized power generation.

Hydrogen is another carrier of energy that, like electricity, can be produced from various renewable and nonrenewable resources. It offers an alternative to electricity generated at centralized powerplants. Hydrogen also displays many of the attributes of centrally generated electricity and minimizes most of the problems of using centrally generated electricity in transportation applications. Molecular hydrogen (consisting of two bonded hydrogen atoms) is a potent fuel, containing three times more energy per pound than gasoline and six times more energy per pound than coal. About 93% of the known universe consists of hydrogen atoms, but most of the hydrogen on Earth appears in combination with other elements. Just as electricity is generated from the energy in other resources, molecular hydrogen is produced by extracting hydrogen atoms from compounds that contain other elements.

Once manufactured in pure form, the energy in hydrogen can be released by burning or it can be converted without combustion to electricity in fuel cells. An electrochemical device with no moving parts, a fuel cell uses catalysts, electrodes, semi-permeable membranes and electrolytic substances to control the combination of hydrogen and oxygen to form water. The energy released by the chemical reaction is captured electrochemically as electricity. Because no combustion occurs and little of the chemical energy escapes as waste heat, fuel cells are highly efficient electrical generators. Efficiencies of 50% are achievable today. Emerging fuel cell technologies should surpass 60% efficiency rates. These efficiencies compare to those of an automotive internal combustion engine, which currently converts less than 20% of the energy in gasoline into motion. Although invented in 1839, fuel cells were not developed commercially until the 1960s, when their suitability for generating electricity aboard space craft was recognized. Every space vehicle in the Apollo, Gemini, and Shuttle space programs has been powered in part by hydrogen fuel cells.¹¹

Whether the energy in hydrogen is released as heat through combustion or converted into electricity in a fuel cell, little or no pollution is produced when the chemical energy in hydrogen is tapped. The sole byproduct of the chemical combination of hydrogen and oxygen is water. No carbon dioxide, hydrocarbons, carbon monoxide, sulfur compounds or toxic air pollutants are released. Because they operate at low temperatures, fuel cells also produce no nitrogen oxides. Hydrogen combustion produces some nitrogen oxide air pollution because of the high temperatures involved. Tests to date indicate that nitrogen oxide concentrations from hydrogen-burning engines can be kept very low, meeting the proposed California equivalent zero emission vehicle standard.

Air pollution from hydrogen production is potentially very small as well. If fossil fuels are used in the hydrogen production process, as they are in the steam reforming of natural gas (discussed below), then some environmental impacts could be associated with the production, processing, distribution of these fossil fuels. The major environmental problems associated with hydrogen produced from renewable resources are due to the materials used in technologies to produce hydrogen, or in the fuel cells that use these materials. Carcinogenic asbestos membranes and potent potassium hydroxide, for example, are currently used in hydrogen-generating electrolyzers. Other environmental concerns stem from land use considerations associated with large-scale renewable resource development, and with air and water pollution from biomass production and use.

Furthermore, a variety of toxic metals are used as catalysts or electrodes in some advanced hydrogen production technologies and in fuel cells. Recovery and reuse of these expensive materials is important to improving the economics of these technologies, however, so that zero environmental damage can be achieved in most cases.

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