Germany

The intermittent production of the renewable energy imposes the necessity to temporarily store it. Large amounts of exceeding electricity can be stored in geological strata in the form of hydrogen. The conversion of hydrogen to electricity and vice versa can be performed in electrolyzers and fuel elements by chemical methods. The nowadays technical solution accepted by the European industry consists of injecting small concentrations of hydrogen in the existing storages of natural gas. The progressive development of this technology will finally lead to the creation of underground storages of pure hydrogen. Due to the low viscosity and low density of hydrogen it is expected that the problem of an unstable displacement including viscous fingering and gravity overriding will be more pronounced. Additionally the injection of hydrogen in geological strata could encounter chemical reactivity induced by various species of microorganisms that consume hydrogen for their metabolism. One of the products of such reactions is methane produced from Sabatier reaction between H2 and CO2. Other hydrogenotrophic reactions could be caused by acetogenic archaea sulfate-reducing bacteria and iron-reducing bacteria. In the present paper a mathematical model is presented which is capable to reflect the coupled hydrodynamic and bio-chemical processes in UHS. The model has been numerically implemented by using the open source code DuMuX developed by the University of Stuttgart. The obtained bio-chemical version of DuMuX was used to model the evolution of a hypothetical underground storage of hydrogen. We have revealed that the behavior of an underground hydrogen storage is different than that of a natural gas storage. Both the hydrodynamic and the bio-chemical effects contribute to the different characteristics.

Subsurface porous media hydrogen storage could be a viable option to mitigate shortages in energy supply from renewable sources. In this work a scenario for such a storage is developed and the operation is simulated using a numerical model. A hypothetical storage site is developed based on an actual geological structure. The results of the simulations show that the storage can supply about 20 % of the average demand in electrical energy of the state of Schleswig-Holstein Germany for a week-long period.

Germany the European Union member state with the largest fiscal space and its leading manufacturer of industrial goods is pursuing an ambitious hydrogen strategy aiming at establishing itself as a major technology provider and importer of green hydrogen. The success of its hydrogen strategy represents not only a key element in realizing the European vision of climate neutrality but also a central driver of an emerging global hydrogen economy. This article provides a detailed review of German policy highlighting its prominent international dimension and its implications for the development of a global renewable hydrogen economy. It provides an overview of the strategy’s central goals and how these have evolved since the launch of the strategy in 2020. Next it moves on to provide an overview of the strategy’s main areas of intervention and highlights corresponding policy instruments. For this we draw on a comprehensive assessment of hydrogen policy instruments which have been systematically analyzed and coded. This was complemented by a detailed analysis of policy documents and information gathered in six interviews with government officials and staff of key implementing agencies. The article places particular emphasis on the strategy’s international dimension. While less significant in financial terms than domestic hydrogen-related spending it represents a defining feature of the German hydrogen strategy setting it apart from strategies in other major economies. The article closes with a reflection on the key features of the strategy compared to other important countries identifies gaps of the strategy and discusses important avenues for future research.

Green hydrogen promises to be critical in achieving a sustainable and renewable energy transition. As green hydrogen is produced with renewables green hydrogen could become an energy storage medium of the future and even substitute the current unsustainable grey or blue hydrogen used in the industry. Bringing this transition into reality for instance in Germany there are visions to rapidly build hydrogen facilities in Africa and export the produced green hydrogen to Europe. One problem however is that these visions presumably conflict with the visions of actors within Africa. Therefore this study aims to provide an initial assessment of African stakeholders’ visions for future energy exports and renewable energy expectations. By comparing visions from Germany and Africa this assessment was conducted to identify differences in green energy and hydrogen visions that could lead to conflict and similarities that could be the basis for cooperation. The National Hydrogen Strategy outlines the German visions which clarifies that Germany will have to import green hydrogen to meet its green transition target. In this context of future energy export demand a partnership between German and African researchers on assessing green hydrogen potentials in Africa started. The African visions were explored by surveying the partners from different African countries working on the project. The results revealed that while both sides see the need for an immediate transition to renewable energy the African side is not envisioning the immediate export of green hydrogen. Based on the responses the partners are primarily concerned with improving the continent’s still deficient energy access for both the population and industry. Nevertheless this African perspective greatly emphasises cross-border cooperation where both sides can realise their visions. In the case of Germany that German investment could build infrastructure which would benefit the receiving African country or countries and open up the possibility for the envisioned green hydrogen export to Europe.

Aviation contributes to anthropogenic climate change by emitting both carbon dioxide (CO2) and non-CO2 emissions through the combustion of fossil fuels. One approach to reduce the climate impact of aviation is the use of hydrogen as an alternative fuel. Two distinct technological options are presently under consideration for the implementation of hydrogen in aviation: hydrogen fuel cell architectures and the direct combustion of hydrogen. In this study a hydrogen demand model is developed that considers anticipated advancements in liquid hydrogen aircraft technologies forecasted aviation demand and aircraft startup and retirement cycles. The analysis indicates that global demand for liquid hydrogen in aviation could potentially reach 17 million tons by 2050 leading to a 9% reduction in CO2 emissions from global aviation. Thus the total potential of hydrogen in aviation extends beyond this considering that the total market share of hydrogen aircraft on suitable routes in the model is projected to be only 27% in 2050 due to aircraft retirement cycles. Additionally it is shown that achieving the potential demand for hydrogen in aviation depends on specific market prices. With anticipated declines in current production costs hydrogen fuel costs would need to reach about 70 EUR/MWh by 2050 to fulfill full demand in aviation assuming biofuels provide the cheapest option for decarbonization alongside hydrogen. If e-fuels are the sole option for decarbonization alongside hydrogen which is the more probable scenario the entire hydrogen demand potential in aviation would be satisfied according to this study’s estimates at significantly higher hydrogen prices approximately 180 EUR/MWh.

Hydrogen is a promising energy carrier for decarbonizing maritime and stationary applications. However using 100% hydrogen in large-bore engines introduces combustion challenges such as pre-ignition and backfire. These statistically occurring combustion anomalies particularly their spatial and temporal behavior cannot be fully understood through thermodynamic data alone. This study applies optical diagnostics to a medium-speed single-cylinder research engine (bore: 350 mm stroke: 440 mm displacement: 42.3 dm3 ) operated with 100% hydrogen exceeding 20 bar IMEP. By varying the air–fuel equivalence ratio between 2.3 and 4.0 and comparing active pre-chamber and open combustion chamber ignition systems backfire-induced operating limits are identified. High-speed flame imaging through two endoscopic accesses and up to three cameras captures both visible and UV (308 nm) flame chemiluminescence. An implemented visual vibration compensation method using fiber optics enables tracking of flame origins and propagation. The recordings show that 65% of ignition events initiate near one intake valve suggesting local hydrogen enrichment confirmed via 3D-CFD simulations. This is linked to intake manifold geometry which leads to mixture inhomogeneity up to −260◦ CA BTDC. At loads above 15 bar IMEP the localized enrichment reduces or shifts attributed to increased turbulence and intake mass flow. CFD simulations also reveal that gas temperatures under the intake valves exceeding the ignition temperature of hydrogen as early as 300◦ CA BTDC create the risk of backfire in the early gas phase. Additionally glowing oil droplets and ignition zones near the piston were observed indicating that lube oil ignition may be a cause of later (after −290◦ CA BTDC) backfire events. These findings contribute to the understanding of hydrogen combustion anomalies and support future experimental and modeling-based optimization of large-bore hydrogen engines.

Green hydrogen is gaining global attention as a zero-carbon energy carrier with the potential to drive sustainable energy transitions particularly in regions facing rising fossil fuel costs and resource depletion. In sub-Saharan Africa financing mechanisms and structured off-take agreements are critical to attracting investment across the green hydrogen value chain from advisory and pilot stages to full-scale deployment. While substantial funding is required to support a green economic transition success will depend on the effective mobilization of capital through smart public policies and innovative financial instruments. This review evaluates financing mechanisms relevant to sub-Saharan Africa including green bonds public–private partnerships foreign direct investment venture capital grants and loans multilateral and bilateral funding and government subsidies. Despite their potential current capital flows remain insufficient and must be significantly scaled up to meet green energy transition targets. This study employs a mixed-methods approach drawing on primary data from utility firms under the H2Atlas-Africa project and secondary data from international organizations and the peer-reviewed literature. The analysis identifies that transitioning toward Net-Zero emissions economies through hydrogen development in sub-Saharan Africa presents both significant opportunities and measurable risks. Specifically the results indicate an estimated investment risk factor of 35% reflecting potential challenges such as financing infrastructure and policy readiness. Nevertheless the findings underscore that green hydrogen is a viable alternative to fossil fuels in subSaharan Africa particularly if supported by targeted financing strategies and robust policy frameworks. This study offers practical insights for policymakers financial institutions and development partners seeking to structure bankable projects and accelerate green hydrogen adoption across the region.

This study examines the economic and regulatory implications of the development of Germany’s hydrogen core network. Using a mathematical-economic model of the amortization account and a reproduction of the network topology based on the German transmission system operators’ draft proposals the analysis evaluates the impact of delaying the network expansion with completion postponed from 2032 to 2037. The proposed phased approach prioritizes geographically clustered regions and ensures sufficient demand alignment during each expansion stage. The results demonstrate that strategic adjustments to the network size and timing significantly enhance cost-efficiency. In the initially reduced and delayed scenario uncapped network tariffs remain below €15/ kWh/h/a suggesting that under specific conditions the amortization account may become redundant while maintaining supply security and supporting the market ramp-up of hydrogen. These findings highlight the potential for demand-driven phased hydrogen infrastructure development to reduce financial burdens and foster a sustainable transition to a hydrogen-based energy system.

Liquid hydrogen (LH2) is a promising energy carrier to decrease the climate impact of aviation. However the inevitable formation of hydrogen boil-off gas (BOG) is a main drawback of LH2. As the venting of BOG reduces the overall efficiency and implies a safety risk at the airport means for capturing and re-using should be implemented. Metal hydrides (MHs) offer promising approaches for BOG recovery as they can directly absorb the BOG at ambient pressures and temperatures. Hence this study elaborates a design concept for such an MH-based BOG recovery system at hydrogen-ready airports. The conceptual design involves the following process steps: identify the requirements establish a functional structure determine working principles and combine the working principles to generate a promising solution.

The Middle East and North Africa region has not played a major role in climate action so far and several countries depend economically on fossil fuel exports. However this is a region with vast solar energy resources which can be exploited affordably for power generation and hydrogen production at scale to eventually reach carbon neutrality. In this paper we elaborate on the case of the United Arab Emirates and explore the aspirations and feasibility of its net-zero by 2050 target. While we affirm the concept per se we also highlight the technological complexity and economic dimensions that accompany such transformation. We expect the UAE’s electricity demand to triple between today and 2050 and the annual green hydrogen production is expected to reach 3.5 Mt accounting for over 40% of the electricity consumption. Green hydrogen will provide power-to-fuel solutions for aviation maritime transport and hard-to-abate industries. At the same time electrification will intensify—most importantly in road transport and low-temperature heat demands. The UAE can meet its future electricity demands primarily with solar power followed by natural gas power plants with carbon capture utilization and storage while the role of nuclear power in the long term is unclear at this stage.