Hydrogen is a high-quality energy carrier that can be employed with high conversion efficiency and essentially zero emissions at the point of use. Hydrogen can be made from a variety of widely available primary energy sources, including natural gas, coal, biomass (agricultural or forestry residues or energy crops), wastes, solar, wind, or nuclear power. Technologies for production, storage, and transmission of hydrogen are well established in the chemical industries. Hydrogen transportation, heating, and power generation systems have been technically demonstrated, and in principle, hydrogen could replace current fuels in all their present uses. If hydrogen is made from renewable or decarbonized fossil sources, it would be possible to produce and use energy on a large scale system with essentially no emissions of air pollutants (nitrogen oxides, carbon monoxide, sulfur oxides, volatile hydrocarbons or particulates) or greenhouse gases during fuel production, transmission, or use. Because of hydrogen's desirable environmental...