Hydrogen is a gas found in large quantities in our environment, but rarely in its pure state (combined with oxygen in water or with carbon in methane).
To create it you therefore need to use processes to separate it from the other elements. Nowadays, the majority of hydrogen production is from fossil fuels: by cracking methane, or by gasifying charcoal. Such hydrogen is therefore described as “grey”.
“Green” hydrogen can chiefly be obtained by the electrolysis of water, taking advantage
of the surplus electricity generated from renewable sources (wind power, solar etc.).
Once obtained, the hydrogen can be used to supply fuel cells, or it can be reinjected into the grid. It can be combined with CO2 via the process known as methanation to produce synthetic methane (Power to CH4).