The term 'hydrogen economy' refers to the proposed large-scale use of hydrogen in place of fossil fuels to eliminate carbon dioxide emissions from activities that are difficult to electrify, such as long-distance transportation and the production of cement and steel. This gaseous element is an infinitely renewable resource whose combustion releases only water vapor into the atmosphere, and it can be obtained from water using wave, wind, solar and other renewable energy sources.
Hydrogen is currently obtained from four main sources: natural gas, petroleum, coal, and water. It is being used in growing quantities in a variety of applications, including metal welding, production of electronic components, plastics and fertilizers manufacturing, and textile dying. It is also being used to a small but increasing extent to power buses and railway vehicles both by using fuel cells and with internal combustion engines.
The main obstacles to creating a hydrogen economy include developing techniques for producing, storing and transporting the hydrogen on a large scale safely, at low cost and with minimal environmental effects. Safety remains a major concern because hydrogen is extremely flammable and explosive in the presence of air, and leaks would be particularly serious in enclosed areas such as underground parking garages and tunnels. Moreover, leaks can be difficult to detect because hydrogen is odorless and its flames are nearly invisible to the naked eye.