Factbox: Hydrogen - energy's rainbow renewable

(Reuters) - Energy producer BP Plc on Thursday announced plans to develop the UK’s largest blue hydrogen production facility.

FILE PHOTO: BP signage is seen at a service station near Brighton, Britain, January 30, 2021. REUTERS/Toby Melville

Sectors including energy, steel and chemicals are looking to develop large-scale hydrogen applications to help reduce carbon emissions and avert global warming.

Hydrogen falls into several categories denoted by colour, with the ultimate aim being green hydrogen, where renewable energy such as wind or solar powers the extraction of hydrogen.

Here are details about green, grey, blue and turquoise hydrogen:

1. Green hydrogen

Derived from renewable sources which could include offshore wind powering floating electrolysis plants.

Green hydrogen can be stored, piped, or carried by tankers to consumers, for example to serve hydrogen filling stations.

Hydrogen can also be turned into synthetic methane with qualities identical to natural gas, but this process is at an early stage.

Biomethane derived from fermented crops can also play a role.

2. Grey hydrogen

Using steam-methane reforming, currently the standard industry process, it involves extracting hydrogen from fossil fuels such as coal or gas while releasing carbon monoxide and carbon dioxide.

3. Blue hydrogen

Blue hydrogen is grey hydrogen but captures the CO2 emissions for placement in underground or subsea storage. Seen as a transitional approach while green hydrogen cannot fully meet demand, some environmentalists oppose this option.

4. Turquoise hydrogen

Also called low-carbon hydrogen and so far very small scale, this is hydrogen generated from natural gas but using pyrolysis where the gas is passed through molten metal, producing solid carbon as a byproduct with useful applications.

Editing by Vera Eckert and Jason Neely