What is blue hydrogen? Worldwide, hydrogen is now regarded as a promising energy carrier. Why? The reason is that its combustion produces only water as a byproduct. But since pure hydrogen does not occur in sufficient quantities in nature, it has to be produced.
Until now, this has been done by using fossil fuels, first and foremost natural gas. For every ton of hydrogen produced, around 10 tons of climate-damaging CO2 are released into the atmosphere. The hydrogen produced in this way is called "gray hydrogen."
Blue hydrogen is basically the same as gray hydrogen, because it is also produced from natural gas. With one difference: During production, the CO2 produced is captured and stored – for example in former oil or gas fields. This process is also known as "carbon capture and storage" and means that the CO2 is only released in small quantities. Compared with gray hydrogen, blue hydrogen is therefore low in emissions and prevents the greenhouse effect from worsening. It is therefore also referred to as decarbonized hydrogen.
While gray hydrogen is produced with the release of CO2 and blue hydrogen with almost no emissions, green hydrogen is produced by electrolysis of water. Only electricity from renewable sources is used for the electrolysis process used in each case. This means that the production of green hydrogen is 100 percent CO2-free.
Turquoise hydrogen is obtained by the thermal cracking of methane. Instead of CO2, solid carbon is produced during this process. In order to make the process CO2-neutral, the high-temperature reactor must be supplied with heat from renewable energies and the carbon must be permanently bound.
Only the production of green hydrogen – that is, the production of hydrogen by means of electrolysis from renewable electricity – avoids the release of climate-damaging CO2 by 100 percent. The production of all other types of hydrogen results in methane or CO2 emissions – at least in small quantities – being released into the atmosphere.
The future therefore lies in green hydrogen. However, since this is not yet available in large quantities today, it makes sense to use blue hydrogen until the green hydrogen economy is sufficiently developed. In order to drive forward the energy transition, blue hydrogen could then gradually be replaced by green hydrogen.
But how long can that take? In what quantities is green hydrogen already available today? In Germany, electrolysis plants with a total capacity of 10 gigawatts are already being planned, which should be able to produce around 30 terawatt hours of green hydrogen a year by 2030. Since this is only equivalent to the gas consumption of about eight cold days, the sole supply of green hydrogen will not be sufficient in the coming years either.
In addition to its low-CO2 production, the great advantage of blue hydrogen is that – unlike green hydrogen – it is available at short notice. The technology of CO2 capture and storage is mature and has been used by many manufacturers for years.
No, but in view of the medium-term scarcity of green hydrogen and the fact that blue hydrogen is nevertheless produced with quite low CO2 emissions, blue hydrogen thus represents a so-called "bridge technology". In this sense, the use of blue hydrogen supports the development of the hydrogen infrastructure – towards green hydrogen.
The CO2 emissions resulting from the production of blue hydrogen range from 23 to 150 grams per kilowatt hour. However, the captured CO2 can be reused or is stored in geological formations. Whether for storing green electricity in the natural gas grid or as an energy supplier for generating electricity and heat – the hydrogen produced is available for various applications.
Hydrogen also plays an important role as a fuel in the transportation sector. Here it can be harnessed as stored energy in fuel cell technology. Both the hydrogen fuel cell and the direct methanol fuel cell utilize an electrochemical process that converts chemical energy into electrical energy and heat. Hydrogen-powered vehicles represent a viable alternative to e-vehicles – especially for longer distances and in local public transport.
In contrast to conventional gray hydrogen, the carbon dioxide produced in the production of blue hydrogen is not emitted, but either stored or further processed for industrial purposes. Green hydrogen is even more environmentally friendly than blue hydrogen. Until it is available in the required quantities, important industrial sectors can be decarbonized with blue hydrogen.