Looking farther into the future, renewable energy and natural gas also are linked through their role in preparing for a renewable hydrogen economy. As a fuel, hydrogen produces virtually no pollution; its principal combustion by-product is water.50 While most hydrogen is currently made from natural gas, it can be produced by gasifying biomass or by electrolyzing water with current generated by renewable energy. Because hydrogen can be stored, it frees intermittent renewable energy technologies from reliance on backup power from conventional energy sources. For the same reason, it provides a channel through which renewable energy can serve the transportation sector. Technologies using hydrogen have not yet reached the general market, in contrast to the other renewable energy technologies described in this paper. However, several energy analysts tout hydrogen produced with renewable energy as the ideal fuel of the future-an emissions-free, greenhouse-safe "hydrocarbon without the carbon."51
Natural gas is linked to this potential hydrogen future in three ways. First, it now serves as a feedstock for most of the hydrogen produced, and hydrogen derived from gas likely will provide the initial basis for any large-scale penetration of hydrogen into the energy market. Second, fuel cells that run on natural gas also can use hydrogen, and may do so in the future. Third and more speculatively, hydrogen might someday flow through the pipeline system that has been constructed for natural gas. This will require solving some technical problems: hydrogen tends to embrittle certain steels and, since it is lighter than natural gas, existing pipelines would require new compressors.