There are several processes to obtain hydrogen. Most important are two, Natural Gas Reforming and Electrolysis. In Natural Gas Reforming, hydrogen is produced by reacting natural gas with high-temperature steam. This method is the cheapest, most efficient and most common process for obtaining hydrogen. However, this process is not “clean”, because CO2 is produced in the process and usually vented to the atmosphere. In the other method, Electrolysis, an electric current splits water into hydrogen and oxygen. If the electricity comes from renewable sources, such as solar or wind, then the resulting hydrogen is considered renewable.