Series of articles concerning hydrogen: Life cycle assessment of hydrogen

In the course of the last few years, an immense dynamic can be felt in the field of hydrogen. At the same time, great progress has been made in research and development at many points along the hydrogen value chain and important findings have been made. In the first series of articles on hydrogen, the basics of the gas were explained along its value chain from production to transport and storage to application.

In this second series, individual focus topics are dealt with in detail and the current state of knowledge is summarized. The third article deals with the greenhouse gas emissions (GHG emissions) of hydrogen and their accounting.

Overview of the topics in the hydrogen series

  1. Use of hydrogen in steel production
  2. Raw material demand for hydrogen production
  3. Life cycle assessment of hydrogen
  4. Electrolyzer operating modes
  5. Efficiency of hydrogen transport
  6. Roadmaps for developing a hydrogen infrastructure

The emission of hydrogen is a topic that frequently incites considerable discussion. Primarily, it is regarded as a more accurate metric for assessing hydrogen’s sustainability, surpassing the conventional color-based classification system. However, the process of determining these emissions is not without its ambiguities, leading to significantly divergent outcomes. This article summarizes the work of the FfE in the context of hydrogen emission balancing in recent months and is thus intended to provide assistance in classifying emission balances and interpreting their results.

Types of emissions accounting for hydrogen

Renewably produced hydrogen is climate-neutral, i.e. it has a CO2 footprint of 0 kg CO2 eq./kg H2 – at least, that is the assumption and idea behind the term “green hydrogen”. However, this is not correct for all variants of emissions accounting. A basic distinction is made here between the balancing of direct emissions and emissions according to the Life Cycle Assessment (LCA) method. In the LCA, zero emissions in the production of hydrogen are not possible due to the consideration of emissions over the entire life cycle.

The LCA includes all expenses incurred in the upstream chain in the environmental impact of hydrogen production. This includes, in particular, the construction of plants to generate renewable electricity. In the discussion paper “Hydrogen Carbon Footprint in the Context of Clean Hydrogen Standards”, we showed that this can lead to very different results depending on the electricity-generation technology and the database used. The following graphic illustrates this once again.

Figure 1: Emission factor of hydrogen depending on the emission factor of the electricity used

The differences become clear when looking at the renewable power generation technologies wind and photovoltaics (PV). While the emission factor of wind-based hydrogen is generally less than 1 kg CO2-eq./kg H2, the range of PV-based hydrogen extends from less than 1 kg CO2-eq./kg H2 to around 4 kg CO2-eq./kg H2. These large differences are due to the influences of different locations and the associated full load hours on the one hand and different technologies on the other.

If only direct, i.e. combustion-related emissions in the upstream chain are considered, electricity from renewable energies is balanced with zero. When burning gas, for example, no emissions are accounted for in the upstream chain of the gas. Although this significantly simplifies the accounting, it neglects emissions that are indirectly related to hydrogen production. In both cases, however, it is crucial that the limit values to be complied with are adapted to the accounting method.

Method and limit values of various guidelines

Various institutions have already set limits for the CO2 intensity of sustainable hydrogen. Above all, in the course of the adoption of the Delegated Act (DA) on Article 25 of the Renewable Energy Directive II (RED II), it was decided that the emission intensity of sustainable hydrogen may not exceed 30% of the value of conventional hydrogen, i.e. 3.41 kg CO2 eq./kg H2. The methodology also stipulates that the construction of plants is excluded from the calculation of emissions. Accordingly, electricity from renewable energies such as wind and PV is accounted for as zero. However, this is accompanied by a problem in the assessment of sustainability according to the EU taxonomy, which leaves the choice open between DA and LCA accounting. The concrete implications of this are illustrated in the paper “Relevance of Emission Accounting Methods for the Classification of Green Hydrogen”, as shown in Figure 2.

Figure 2: Global warming potential of hydrogen according to the LCA methods and the DA for Art. 25 and Art. 28 of RED II in the context of the limit value of the EU taxonomy

It can be seen that in the case of the EU taxonomy, in addition to different methods, different databases can also lead to widely divergent results. Depending on whether the values for PV modules are taken from the ecoinvent database or those of the Federal Environment Agency, the limit value is either reached or not. A clear framework needs to be established here regarding which methods and which databases should be used.

However, these differences do not only occur within the EU. Limit values for sustainable hydrogen are currently being defined worldwide. Both the limit values and the underlying methods vary greatly. The following table lists some examples of important regulations with the respective methods and limit values.

Label Region Limit value
in kg CO2-Eq./kg H2
DA Art. 28(5) RED II EU 3,4 LCA without plant construction
EU Taxonomy EU 3,0 LCA or acc. to DA Art. 28(5) RED II
Inflation Reduction Act (IRA) USA min. 0,45; max. 4,0 tba; based on the GREET model
UK Low Carbon Hydrogen Standard UK 2,4 LCA without plant construction
Green Hydrogen Organisation* International 1,0 LCA without plant construction
CertifHy* EU 4,4 LCA without plant construction
TÜV Süd* International 3,4 LCA without plant construction

*Private Organisation

From a European perspective, the simple applicability of the IRA in the context of sustainable hydrogen is regularly pointed out. However, the accounting method is still pending and is expected in mid-2023.


The relevance of accounting for the GHG emissions of hydrogen has increased due to the application of emission intensity benchmarks. These benchmarks are intended to determine whether hydrogen is sustainable and thus form the basis for the price at which it can be sold. However, to ensure certainty regarding the underlying business models in hydrogen production, the methods and databases must also be clear. In order to be able to provide evidence of low emissions intensity, the methods must be easy to apply in addition to the basic know-how regarding emissions accounting within the companies.