German Hydrogen Core Network: 90 per cent Reduction in Climate Impact Possible

With the planned conversion of large parts of the current natural gas transmission network to hydrogen, a central component of the German energy transition is materialising: the hydrogen core network. Against this backdrop, a key question is emerging: What emissions will be produced due to the mere operation of this network – irrespective of the actual generation or use of energy? In view of the ongoing political decision-making process regarding the development of the hydrogen infrastructure, a well-founded assessment of the potential climate effects of grid operation is particularly important.

For the first time, a recent article by the Wuppertal Institute now provides a detailed analysis of grid emissions – and the associated climate impact of switching the German transmission gas grid from natural gas to hydrogen. The analysis focuses solely on the operation of the infrastructure, i.e. the transport of gases through the network, without taking into account the hydrogen's origin. The authors analyse the emissions along various network components such as compressor stations, fittings and pipelines. They come to a clear conclusion: Climate-relevant emissions also occur during the transport of hydrogen, for example due to leaks where hydrogen escapes into the atmosphere. Compared to today's natural gas transmission network, however, the climate impact of network operation can be reduced by up to 90 per cent by switching to hydrogen. At the same time, the researchers point out that the conversion to a climate-friendly hydrogen network can only succeed if, in addition to network operation, hydrogen generation and the surrounding infrastructure are also decarbonised. This includes processes in the upstream chain – including imports – as well as a future climate-neutral electricity grid in Germany, for example for the operation of compressor stations.

Scientific background to the climate impact of hydrogen

Like the well-known greenhouse gases CO2 or methane, hydrogen also has an impact on the climate – albeit indirectly: Although hydrogen itself has no infrared-absorbing properties, it does influence chemical processes in the atmosphere. For example, it delays the decomposition of methane and thus increases its greenhouse gas effect, which indirectly contributes to global warming. One particular focus of the study is therefore on classifying the climate impact of hydrogen, expressed as Global Warming Potential (GWP). While CO2 is assigned a GWP of 1 as a reference value, the GWP of hydrogen is between 4 and 12, according to the available studies. By comparison, methane has a GWP of around 30 over a period of 100 years. The indirect effects of hydrogen are therefore lower than those of methane, but significantly higher than those of CO2 – at least if only the GWP is taken into account.

At the same time, the research team warns against misinterpreting these figures. The aim of the study is therefore also to provide differentiated information and prevent premature conclusions on the climate impact of hydrogen and the associated infrastructure. This is because the GWP is a mass-based indicator that describes the climate impact per kilogramme of gas emitted. However, as hydrogen is the gas with the highest gravimetric energy density, one kilogramme of hydrogen contains significantly more energy than the same mass of other energy sources – such as natural gas, whose main component is methane. Comparisons of climate impact based solely on GWP per kilogramme are therefore misleading as long as they are not set in relation to the amount of energy transported.

The article "From natural gas to hydrogen: Climate impacts of current and future gas transmission networks in Germany" was published in the journal Frontiers in Energy Research as part of the Special Issue "Climate Implications of Hydrogen Energy Systems". The article can be downloaded free of charge via the link below.