The colours of hydrogen

Hydrogen has many colours, and we frequently refer to green, turquoise, blue and grey hydrogen. Since this versatile energy carrier is actually a colourless gas, one might well ask what these colours actually mean. We show what colours hydrogen is classified as, what the meaning behind these colours is, and how they are related to climate protection.

What colours does hydrogen come in?

Hydrogen itself is has no colour. The colourless gas is an efficient, climate-neutral energy source for heating, as it has a much higher thermal value than, for example, fuel oil or natural gas, and its combustion does not produce any substances that are harmful to the environment or the climate. Hydrogen is also easy to store, allowing surplus electricity to be put to good use. Despite these positive characteristics and the major contributions that hydrogen makes to climate protection, hydrogen production needs to be examined more closely with respect to climate protection. The subdivision of hydrogen into different colours is intended to provide information about how the hydrogen is produced, the energy sources used and the climate neutrality of the hydrogen.

Infographics: Green Hydrogen

Green hydrogen

Green hydrogen is the term used to describe hydrogen that is produced on a CO2-neutral basis through the electrolysis of water. During electrolysis, water is split into its constituent elements of oxygen and hydrogen. The electricity this requires is generated from renewable energy sources, for example wind energy, hydropower or solar energy. Since neither the production of green hydrogen nor the end products hydrogen and oxygen are harmful to the environment or the climate, green hydrogen is climate-neutral. That is why EWE is focusing on this variant.

In order to produce large amounts of green hydrogen, we need considerably larger electricity generation capacities from renewable energies. In addition, electricity prices must be affordable so that green hydrogen is also economically competitive. An important lever for achieving this would be the reform of the charges and levies on electricity.

Infographics: Turquoise Hydrogen

Turquoise hydrogen

Turquoise hydrogen is created by a thermal process in which natural gas is broken down with the help of methane pyrolysis into hydrogen and solid carbon. If the carbon remains permanently bound and is not combusted during further processing, this process is also CO2-neutral. The reactors or blast furnaces used to split the methane would also have to be powered by renewable energies. Another factor in the analysis of turquoise hydrogen is that the extraction of the raw material, natural gas, often also produces emissions. As a result, turquoise hydrogen is usually not completely climate-neutral when it comes to the entire production process and the downstream processing of carbon as a by-product.

Infographics: Blue Hydrogen

Blue hydrogen

Blue hydrogen is generated from the steam reduction of natural gas. During this process, natural gas is split into hydrogen and CO2. In this steam reforming process, however, the carbon dioxide is not emitted into the atmosphere; instead, it is stored or processed industrially. Carbon Capture and Storage (CSS) technology can be used to store CO2 underground. This means that blue hydrogen does not produce any CO2 emissions either. However, the long-term impacts of storage are uncertain and leakage can still negatively affect the environment and climate.

Infographics: Grey Hydrogen

Grey hydrogen

Grey hydrogen is the exact opposite of green hydrogen, as it is not climate neutral. Grey hydrogen is obtained by steam reforming fossil fuels such as natural gas or coal. In this process, the waste product CO2 is released directly into the atmosphere. Ten tonnes of carbon dioxide are produced for each tonne of hydrogen extracted, so grey hydrogen is harmful to the climate. Grey hydrogen is also the term used when electricity from fossil fuels and non-renewable energy sources is used instead of eco-power for the electrolysis of water.

Other colours of hydrogen

Sometimes other colours are ascribed to hydrogen, based on how it is produced. For red, pink and violet hydrogen, the electrolysers are driven by nuclear power. Yellow hydrogen refers to hydrogen production from a mixture of renewable energies and fossil fuels. Hydrogen that is merely a waste product of other chemical processes is referred to as white hydrogen. The use of coal as a fuel produces brown hydrogen.

The colours of hydrogen and climate protection

Hydrogen is considered to be an efficient, climate-neutral energy carrier. Only water vapour is produced during combustion and no environmentally harmful substances are released. Hydrogen is also easy to store, so electrolysers can use surplus electricity, such as from renewable energies, for the viable production of hydrogen. This makes hydrogen a promising and sustainable energy carrier in terms of environmental and climate protection. However, we need to undertake a more sophisticated approach to the production and extraction of hydrogen.

The differing processes, by-products and energy sources used influence how climate-neutral hydrogen production actually is. The classification of hydrogen by colour into green, turquoise, blue and grey hydrogen makes it possible to draw conclusions about how climate-neutral the hydrogen is in each case. Both industry and companies should expand the use of renewable energies so that they can increasingly make use of green hydrogen in the future. This is the only option that is absolutely climate-neutral and serves to effectively protect the climate.

FAQs about the colours
What colours are used to classify hydrogen and what do they mean?

Hydrogen is primarily divided into the colours green, turquoise, blue and grey. These colours provide information about how hydrogen is produced, the energy carriers and energy sources used, and whether it is climate-neutral:

  • Green hydrogen: produced from electrolysis of water with oxygen as a by-product, using electricity from renewable energy sources > 100% climate-neutral
  • Turquoise hydrogen: produced by splitting methane with solid carbon as a by-product; depending on the energy source, extraction of the natural gas and further processing of the solid carbon, emissions may occur > not 100% climate-neutral
  • Blue hydrogen: produced by splitting methane with CO2 as a by-product, which is stored and not emitted > climate-neutral, but long-term effect of CO2 storage uncertain
  • Grey hydrogen: produced by splitting fossil fuels and electricity from fossil energies > 100% climate-damaging
What is the difference between green and blue hydrogen?

The difference between green and blue hydrogen is that blue hydrogen produces CO2 as a by-product. In the case of green hydrogen, oxygen is the only by-product of the electrolysis of water, making green hydrogen completely climate-neutral. The production of blue hydrogen is also basically emissions-free and climate-neutral. However, the carbon dioxide produced must be stored underground and can result in environmental damage through leakage. The long-term effects of underground storage are also still uncertain. Green hydrogen is for this reason the safer alternative compared to blue hydrogen, as well as the most effective in terms of climate protection.

Which hydrogen colour is best?

In terms of climate protection and climate neutrality, green hydrogen is by far the best option. Green hydrogen is produced using only renewable energy and does not generate any problematic or harmful by-products. As such, green hydrogen is completely climate-neutral. Turquoise and blue hydrogen are produced from natural gas. In this process, the extraction of the natural gas itself may be associated with environmental damage and emissions. The storage or downstream processing of the by-products in question, CO2 and carbon, can also work against the climate neutrality of turquoise and blue hydrogen. In hydrogen production, consideration must also be given to whether the electricity required for turquoise and blue hydrogen comes from renewable or fossil fuel sources. EWE is placing its focus clearly on green hydrogen.

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