16.01.2025

Life cycle assessments of the hydrogen infrastructure – an overview

When building a future hydrogen infrastructure, aspects of financing, approval, technological development and nationwide implementation are currently being considered. However, environmental aspects must also be taken into account in order to ensure a sustainable hydrogen infrastructure.

Hydrogen (H2) can be transported in various ways, among others as gaseous hydrogen (GH2) by pipeline or per ship as liquid hydrogen (LH2), ammonia (NH3) or liquid organic hydrogen carrier (LOHC). From an environmental perspective, this raises the question of the GHG emissions associated with the transport of these hydrogen carriers and modes of transport. Where are the ecological hotspots? And what reduction potentials are possible?

In order to answer these questions, the TransHyDE project System Analysis conducted a review on life cycle assessments of H₂ infrastructure, in which the results of past studies were analyzed. Figure 1 shows a summary of the life cycle assessment results from the literature. It shows the GHG potential (kg CO₂-eq.) of the hydrogen carriers and modes of transport examined in relation to the functional unit of one kilogram of hydrogen.

Figure 1: Life cycle emissions from H2 production to reconversion (own representation, based on [1, 2, 3, 4, 6, 7, 9, 12])

The results show a wide range. Firstly, this is due to the system boundaries of the studies examined, which vary in the assumptions considered, such as transport distance, modes of transport, used energy mix or the functional unit. Secondly, the data basis of the studies is associated with uncertainties, as the calculations are generally not based on primary data.

Although Figure 1 does not provide a clear answer to the question of the most environmentally friendly transport process, trends can be derived from an examination of the individual publications:

  • The carrier medium with the lowest environmental footprint for longer distances over 1000 km tends to be LH2 [1, 2, 3].
  • GH2 has comparable GHG emissions and has a lower environmental impact than LH2, especially for shorter transportation distances [4, 5].
  • H2 transport using chemical carrier media such as LOHC and NH3 is associated with higher GHG emissions [1, 6, 7]. However, NH3 tends to have the lowest environmental footprint [1, 8].

Emission hotspots differ depending on the hydrogen carrier. Energy-intensive conversion or reconversion steps are the main cause of the GHG emissions, particularly in the case of shorter transport distances. The following hotspots of transport emissions were identified for the carrier media and means of transport examined:

  • GH2 by truck: Transport emissions, particularly influenced by the assumed transport distance [7].
  • GH2 by pipeline: Electrical energy for the operation of compressor stations for injection and transport [2].
  • LH2: Energy-intensive liquefaction of hydrogen, especially when fossil grid electricity is used [11]. The use of electricity from wind power for liquefaction can contribute to a reduction in overall emissions [6]. For ship transport, the use of boil-off gas as fueling represents a potential for reducing emissions [1, 11].
  • LOHC: Heat requirement of dehydrogenation (reconversion to H2), especially if the heat requirement is covered by natural gas [1]. Using part of the transported hydrogen for dehydrogenation can reduce the GHG emissions [2, 6].
  • NH3: Ammonia cracking for reconversion into H2 [2]. Direct use of ammonia (without reconversion) can result in a reduction in overall emissions [2, 8].

The results of various sensitivity analyses show that the transport distance represents an essential influencing factor for the environmental sustainability of H2 imports. The total emissions increase with increasing transportation distance, regardless of the hydrogen carrier and mode of transport [2, 3, 4, 5]. This is due to the combustion of fuels as well as the electrical energy required for pipeline transport. The influence of transport on the GHG emissions differs in the energy content and transport capacities of the hydrogen carrier. For example, the emissions of LH2 transport increase less with the increasing distance than of GH2 transport by truck due to the higher energy content. The further the transport distance, the more advantageous is liquefaction [4, 5].

Another influencing factor is the composition of the energy mix used. If renewable energy, especially wind power, is used, transport emissions are significantly reduced compared to grid electricity [3, 6, 9,11]. The electricity supply is particularly relevant for the hydrogen carrier that requires a high amount of energy. For example, the GHG emissions per transported kg of hydrogen for LOHC & NH3 are 2.4 to 5 times higher when using grid electricity than when using wind power [3].

In conclusion, the environmental impacts of H2 transport differ in the literature, particularly due to differing system boundaries and data quality. Individual case studies are essential for concrete decision-making. A complete sustainability analysis in the sense of a life cycle assessment also requires the inclusion of other environmental impact categories, such as eutrophication or water consumption.

Literature:

[1] Arrigoni et al.: Environmental life cycle assessment (LCA) comparison of hydrogen delivery options within Europe. Luxemburg: Amt für Veröffentlichungen der Europäischen Union, 2024.

[2] Akhtar et al.: Life Cycle Assessment of Inland Green Hydrogen Supply Chain Networks with Current Challenges and Future Prospects in: ACS Sustainable Chemistry & Engineering, 2021.

[3] Noh et al.: Environmental and energy efficiency assessments of offshore hydrogen supply chains utilizing compressed gaseous hydrogen, liquefied hydrogen, liquid organic hydrogen carriers and ammonia in: International Journal of Hydrogen Energy, 2023.

[4] Frank et al.: Life-cycle analysis of greenhouse gas emissions from hydrogen delivery: A cost-guided analysis in: International Journal of Hydrogen Energy, 2021.

[5] Rödl et al.: Assessment of Selected Hydrogen Supply Chains—Factors Determining the Overall GHG Emissions, 2018.

[6] Wulf und Zapp: Assessment of system variations for hydrogen transport by liquid organic hydrogen carriers in: International Journal of Hydrogen Energy, 2018.

[7] Wulf et al: Life cycle assessment of hydrogen transport and distribution options in: Journal of Cleaner Production, 2018.

[8] Dickson et al.: Global transportation of green hydrogen via liquid carriers: economic and environmental sustainability analysis, policy implications, and future directions, 2022.

[9] Hermesmann et al.: The environmental impact of renewable hydrogen supply chains: Local vs. remote production and long-distance hydrogen transport in: Applied Energy, 2023.

[10] Kudoh et al.: Assessing Uncertainties of Life-Cycle CO2 Emissions Using Hydrogen Energy for Power Generation in: Environmental Aspects and Impacts of Hydrogen Technologies, 2021.

[11] Kolb et al.: Renewable hydrogen imports for the German energy transition – A comparative life cycle assessment in Journal of Cleaner Production, 2021.

[12] Kanz et al.: Life Cycle Global Warming Impact of Long-Distance Liquid Hydrogen Transport from Africa to Germany in: Hydrogen, 2023.