Like electricity, hydrogen is a secondary energy and it cannot be pumped out of the ground like oil. Since it never occurs alone, but only in a compound form, it must be split from the hydrogen-rich source material with the help of energy. So hydrogen comes in different colours, depending on the source material – curious?
In contrast to the universe, hydrogen rarely exists in atomic form on earth. Two atoms bond to become the molecule H2, a colourless, tasteless, odourless gas (What is hydrogen?). A great deal of energy is needed to split the molecule and bring it into an atomic form. Among others, the following source materials can be used:
Splitting hydrogen requires a great deal of energy. If water in hydrogen and oxygen is split with the help of electric power, we refer to this process as electrolysis.
In principle, what occurs in a fuel cell is the reverse process. As an element, hydrogen is able to convert back into water together with oxygen. The energy stored in the hydrogen is emitted as electricity that can then drive an electric motor.
Electricity from hydrogen is not green per se. Today, around 90 million tonnes of hydrogen are produced each year. However, most of it comes from natural gas, according to the IEA about 70 million tonnes. Per tonne of hydrogen, ten tonnes of CO2 occur as a by-product. The proportion of green hydrogen – that which is produced by means of electrolysis from renewable energy – is still very small.
However, if hydrogen is to make a decisive contribution to climate protection and lead to less dependency on fossil energy sources, plant capacities that produce power from renewable sources must be massively developed on a global scale.
Major challenges must be mastered before "little" hydrogen can play out its all-rounder talent for our climate.
Hydrogen theory of colours
Electricity from hydrogen is not green per se. Depending on the production method, hydrogen is assigned a different colour. Theory of colour:
Green hydrogen is produced by means of water electrolysis. To do so
electricity from renewable energy sources such as hydropower, wind or solar energy is used. Green hydrogen is therefore low in CO2.
Grey hydrogen is produced by means of steam reformation, usually using natural gas. In this process about 10 tonnes of CO2 per tonne of hydrogen occur. The CO2 is emitted into the atmosphere. Steam reformation is the most widely used process in Europe.
Blue hydrogen is grey hydrogen where some of the CO2 is captured and stored (carbon capture and storage, CCS) in the ground.
Turquoise hydrogen is generated through the thermal splitting of methane (methane pyrolysis). Solid carbon is produced in the place of CO2. The process of methane pyrolysis is still in the developmental stage.
Yellow hydrogen is hydrogen that is generated from the existing power mix in the grid. In Switzerland, this electricity mainly comes from hydropower or nuclear power.
Pink hydrogen is produced with nuclear power. Nuclear power is nearly CO2 free in its operation, but its energy source is not renewable.
If you are interested in hydrogen technology and what Axpo is doing in this area, have a look at our "Hydrogen" knowledge dossier and learn more.