Green Hydrogen
Green hydrogen is hydrogen produced by splitting water through electrolysis using renewable electricity, so its production emits no fossil carbon dioxide. It is seen as a route to decarbonise industries that are hard to electrify directly, such as steel, ammonia and high-temperature heat.
Hydrogen is classed by how it is made. Most hydrogen today is 'grey', produced from natural gas with associated carbon emissions. Green hydrogen instead uses an electrolyser powered by wind, solar or other renewable electricity to separate water into hydrogen and oxygen, so the carbon footprint depends on the electricity source rather than on fossil feedstock.
Its appeal is in applications where direct electrification is difficult: as a chemical feedstock for ammonia and refining, as a reducing agent in steelmaking, and as a fuel for high-temperature process heat and some heavy transport.
The main constraints are cost and the availability of cheap renewable power, since electrolysis is energy-intensive. Green hydrogen is therefore generally targeted at sectors with few alternatives rather than uses that can be electrified more cheaply and directly.