The answer may lie with hydrogen-powered fuel cells, a model of which is shown to the left. One future envisioned by many far-sighted experts is a sustainable solar/hydrogen system that would gradually replace our current fossil-fuel system. In such a scenario, energy from the sun would be utilized in various forms to produce hydrogen (H2) gas for use in fuel cells. Fuel cells are efficient and versatile (They can be used to power items from cell phones to vehicles to large buildings.) and emit only water as a byproduct. Most fuel cells that are currently in use rely on H2 that is manufactured from fossil fuels such as natural gas through a process called "reforming." Although this "reforming" process does produce the greenhouse gas CO2, the amount produced is far less than that produced from traditional fossil fuel combustion. In the short term, we could utilize the existing natural gas pipeline infrastructure to deliver natural gas to "reforming" stations that could be placed around the country, perhaps at existing gas stations. Alternatively, several of the fuel-cell vehicles that are being developed carry on-board "reformers" that convert fossil fuels to hydrogen fuel. These vehicles can simply be refueled with standard gasoline or other liquid fuels.
Eventually, however, our infrastructure and technology could be converted such that sustainable techniques, relying on solar power, could be utilized to produce H2. For example, technologies are currently being developed that utilize the direct light of the sun to split H2O into H2 and O2 (photolysis). Alternatively, solar energy can be captured by photovoltaic cells, which produce electricity. This solar-produced electricity can be sent through H2O, causing it to split into H2 and O2 (electrolysis). Electricity generated by wind turbines could also be used to perform the electrolysis of water to produce H2 gas. Because it is the unequal heating of the earth's atmosphere by the sun that causes the wind to blow, wind turbines are ultimately relying on solar energy. Biomass, which also ultimately traces its origins back to the solar energy that drives photosynthesis, can be utilized to produce H2 gas. An outline of some of the sustainable paths to H2 production is illustrated below: