Production of hydrogen
The theory of colours
Companies want to be able to manufacture green products from hydrogen and market them accordingly (e.g. green steel), are involved in EU emissions trading or have committed themselves to energy and climate targets. Anyone who buys hydrogen therefore wants to know how this hydrogen was produced.
There are several ways to reliably provide this information, from simple labelling to a linked system of guarantees of origin and sustainability certificates. The types of production and associated CO2 emissions play a major role here.
The “colours” of hydrogen denote the respective production paths and have been established by various market participants for better description. While known technologies are thus uniformly recognisable by their colours, different colours are used by different parties for new technologies.
An overview of the most common hydrogen colours:
The current production of one kilogram of "grey" hydrogen from natural gas (via steam reformation) generates 11 to 12 kg of CO2-equivalent greenhouse gas emissions, even in very efficient plants.
If the CO2 emissions produced during steam reformation are captured and permanently stored, this is referred to as " blue" hydrogen.
In the case of " turquoise" hydrogen, the carbon is separated from natural gas by pyrolysis and the rest is hydrogen. The process requires additional energy (electricity, heat). There are currently no pyrolysis plants of this type in commercial operation.
Additional challenges associated with the natural gas-based production of hydrogen are emissions during the production and transport of the natural gas (CO2, CH4) and the fact that the capture of CO2 cannot yet be achieved completely, but to an extent of 90 to 95%. Residual emissions from these production routes are therefore to be expected for the foreseeable future.
This category also includes the production of hydrogen from coal, which is associated with even higher CO2 emissions than natural gas.
Electrolysis, the splitting of water with electrical energy in a redox reaction, is the only technology currently commercially available and used on the market to produce "green" hydrogen. However, in order for hydrogen to qualify as such, a number of other criteria must be met. First and foremost, the electricity used must come from renewable sources.
Various technologies are available for electrolysis (market-ready or in the demonstration stage):
- Alkaline electrolysis
- PEM electrolysis
- SOFC (Solid Oxide Fuel Cells / high temperature fuel cells)
A number of electrolysis plants are already in operation or being planned in Austria. An overview of the current status can be found here.
The individual technologies have distinct advantages and therefore different areas of application. They differ according to the number of operating hours, added value on balancing energy markets, use of water vapour, direct use of seawater. However, the origin (share of renewables, certificates and guarantees of origin) and costs of the electricity used, which - in the case of green hydrogen - must in any case come from renewable sources, are of decisive importance.
Green hydrogen can also be produced by gasifying biomass. At the end of the process, the carbon is present in numerous solid, liquid and gaseous by-products. The value chains and cycles must be taken into account here. By using sustainable biomass, negative CO2 emissions can also be achieved, i.e. CO2 can be removed from the atmosphere.
Biomethane from biogas plants can be converted into hydrogen using technological options, but these processes compete with the requirements and areas of application for biomethane as a renewable gas.
The direct utilisation of photon energy from sunlight is a promising option, but one that can only be realised in the long term. Fundamental issues in materials research (stability) must be resolved by 2030 in order to prevent the gap in efficiency and costs from becoming too large in the further development of what is likely to be a very successful combination of PV electrolysis by then.
There are also other varieties. In the case of "pink" hydrogen, for example, the electricity for electrolysis comes from nuclear power plants, although this is sometimes also known as yellow or violet hydrogen.
