Germany

Green hydrogen has the potential to contribute to the decarbonization of the fossil fuel industry and its development is expected to increase in the coming years. The social dynamics among the various actors in the green hydrogen sector are studied to understand their public perception. Using the technological innovation system research approach for the stakeholder analysis and the qualitative thematic analysis method for the interviews with experts this study presents an overview of the actors in the green hydrogen sector and their relations in Luxembourg. As a central European country with strategic political and geographic relevance Luxembourg offers a timely case for analyzing public perception before the large-scale implementation of green hydrogen. Observing this early stage allows for future comparative insights as the national hydrogen strategy progresses. Results show high expectations for green hydrogen in mobility and industry but concerns persist over infrastructure costs safety and public awareness. Regional stakeholders demonstrate a strong willingness to collaborate recognizing that local public acceptance still requires effort particularly in areas such as clear and inclusive communication sharing knowledge and fostering trust. These findings provide practical insights for stakeholder engagement strategies and theoretical contributions to the study of social dynamics in sustainability transitions.

Hydrogen can play a key role as short- and long-term energy storage solution in an energy grid with fluctuating renewable sources. In technologies using hydrogen there is always the risk of unintended leakages due to the low density of gaseous hydrogen. The risk becomes specifically high in confined areas where leaking hydrogen could easily mix with air and form flammable gas mixtures. In the maritime transportation large and congested geometries can be subject to accumulation of hydrogen. A mitigation measure for areas where venting is insufficient or even impossible is the installation of catalytic recombiners. The operational behavior can be described with numerical models which are required to optimize the location and to assess the efficiency of the mitigation solution. In the present study we established an experimental procedure in the REKO-4 facility a 5.5 m³ vessel to determine the recombination rate obtained from a recombiner. Based on the experimental data an engineering correlation was developed to be used for simulations in safety assessments.

For reaching the European greenhouse gas emission targets the phase-in of alternative technologies and energy carriers is crucial for all sectors. For the transport sector synthetic fuels are–next to electromobility–a promising option especially for long-distance shipping and air transport. Within this context the import of synthetic fuels from the Middle East and Northern Africa (MENA) region seems attractive due to low costs for renewable electricity in this region and low transport costs of synthetic fuels at the same time. Against this background this paper analyzes the role of the MENA region in meeting the future synthetic fuel demand in Europe using a cost-optimizing energy supply model. In this model the production storage and transport of electricity hydrogen and synthetic fuels by various technologies in both European and MENA countries in the period up to 2050 are explicitly modeled. Thereby different scenarios are analyzed to depict regional differences in investment risks: a base scenario that does not take into account regional differences in investments risks and three risk scenarios with different developments of regional investment risks. Sensitivity analyses are also carried out to derive conclusions about the robustness of results. Results show that meeting the future synthetic fuel demand in Europe to a large extent by imports from the MENA region can be an attractive option from an economic point of view. If investment risks are incorporated however lower import quotas of synthetic fuels are economically attractive for Europe: the higher generation costs are outweighed by the lower investments risks in Europe to a certain extent. Thereby investment risks outweigh other factors such as transport distance or renewable electricity generation costs in terms of exporting MENA regions and a synthetic fuel import is especially attractive from MENA countries with low investment risks. Concluding within this paper detailed export relations between MENA and EU considering investment risks were modeled for the first time. These model results should be complemented by a more in-depth analysis of the MENA countries including evaluating opportunities for local value chain development sustainability concerns (including social factors) and optimal site selection.

As one of the most promising renewable green energies hydrogen power is a popularly accepted option to drive automobiles. Commercial application of fuel cell vehicles has been started since 2015. More and more hydrogen safety concerns have been considered for years. Tunnels are an important part of traffic infrastructure with a mostly confined feature. A hydrogen leak followed possibly by a hydrogen fire is a potential accident scenario which can be triggered trivially by a car accident while hydrogen-powered vehicles operate in a tunnel. Water spray is recommended traditionally as a mitigation measure against tunnel fires. The interaction between water spray and hydrogen fire is studied by way of numerical simulations. By using the computer program of Fire Dynamics Simulator (FDS) tunnel fires of released hydrogen in different scales are simulated coupled with water droplet injections featured in different droplet sizes or varying mass flow rates. The cooling effect of spray on hot gases of hydrogen fires is apparently observed in the simulations. However in some circumstances the turbulence intensified by the water injection can prompt hydrogen combustion which is a negative side effect of the spray.

Offshore green hydrogen production lacks of flexible and scalable supervisory control approaches for multistack electrolyzers raising the need for extendable and high-performance solutions. This work presents a two-stage nonlinear model predictive control (MPC) method. First an MPC stage generates a discrete on-off electrolyzer switching decision through algebraic relaxation of a Boolean signal. The second MPC stage receives the stack’s on-off operation decision and optimizes hydrogen production. This is a novel approach for solving a mixed-integer nonlinear program (MINP) in multi-stack electrolyzer control applications. In order to realize the MPC the advantages of the implicit multilinear time-invariant (iMTI) model class are exploited for the first time for proton exchange membrane (PEM) electrolyzer models. A modular flexible and scalable framework in MATLAB is built. The tensor based iMTI model in canonical polyadic (CP) decomposed form breaks the curse of dimensionality and enables effective model composition for electrolyzers. Simulation results show an appropriate multilinear model representation of the nonlinear system dynamics in the operation region. A sensitivity analysis identified three numeric factors as decisive for the effectiveness of the MPC approach. The classic rule-based control methods Daisy Chain and Equal serve as reference. Over two weeks and under a wind power input profile the MPC strategy performs better regarding the objective of hydrogen production compared to the Daisy Chain (4.60 %) and Equal (0.43 %) power distribution controllers. As a side effect of the optimization a convergence of the degradation states is observed.

This study examines the pricing and assesses resilience methods in hydrogen supply chains by thoroughly analyzing two main disruption scenarios. The model examines a scenario in which a hydrogen production company depends on a Renewable Power plant (RP) for its electricity supply. Ensuring a steady and efficient hydrogen supply chain is crucial but outages at renewable power sources provide substantial obstacles to sustainability and operational continuity. Therefore in the event of disruptions at the RP the company has two options for maintaining resilience: either sourcing electricity from a Fossil fuel Power plant (FP) through a grid network to continue hydrogen production or purchasing hydrogen directly from another company and utilizing third-party transportation for delivery. Using a game theoretic approach we examine how different methods affect demand satisfaction cost implications and environmental sustainability. The study employs sensitivity analysis to evaluate the impact of different disruption probabilities on each scenario. In addition a unique sensitivity analysis is performed to examine the resilience of transmission security to withstand disruptions. This study evaluates how investments in security measures affect the strength and stability of the supply chain in various scenarios of disruption. Our research suggests that the first scenario offers greater reliability and cost-effectiveness along with a higher resilience rate compared to the second scenario. Furthermore the examination of the environmental impact shows that the first scenario has a smaller amount of CO2 emissions per kg of hydrogen. This study offers important insights for supply chain managers to optimize resilience measures hence improving reliability reducing costs and minimizing environmental effects.

Currently local regulations governing hydrogen installations vary by geographical region and by country leading to discrepancies in safety and separation distance requirements for similar hydrogen systems. This work carried out in the frame of IEA TCP H2 Task 43 (IEA TCP H2 2022) aims to provide an overview of various methodologies and recommendations established for risk management and consequence assessment in the event of accidental scenarios. It focuses on a case study involving industrial electrolyzers utilizing alkaline and PEM technologies. The research incorporates lessons learned from past incidents offers recommendations for mitigation measures reviews existing methodologies and highlights areas of divergence. Additionally it proposes strategies for harmonization. The study also emphasizes the most significant scenarios and the corresponding leakage sizes

In order to minimize emissions of the aerospace sector and thus its impact on the climate several novel concepts of propulsion systems for aircraft are being developed. Many of these concepts do not use an energy source based on the combustion of hydrocarbons but other means of energy generation and storage like hydrogen fuel cells and corresponding hydrogen storage systems. The use of hydrogen as a primary energy carrier in aircraft poses novel and different hazards when compared to conventional propulsion and fuel storage systems. The study described in the present paper identifies analyzes and evaluates failure conditions and corresponding hazards that are associated with the electrified propulsion systems. Mitigation strategies to prevent failures to occur or decrease their severity are recommended. The effects of the assessed failures on aircraft crew and occupants are classified as catastrophic hazardous or major as defined in the according Certification Specifications. Failure Conditions occurring at the aircraft system and subsystem levels are considered and their effect on the aircraft and propulsion system is assessed. The hazards identified mostly emerge due to the properties of the gaseous or liquid hydrogen. They include the flammability of gaseous hydrogen and the very low temperatures of cryogenic liquid hydrogen as well as the installation of high voltage power infrastructure and high capacity heat exchangers.

A two-stage system is used for hydrogen (H2) and methane (CH4) production from sucrose wastewater. The H2- producing reactor is operated at pH temperature (T) and hydraulic retention time (HRT) of 5.5 35 ◦C 24 h respectively. While operating conditions of 7–8 pH 35 ◦C T and 144 h HRT are used to conduct the CH4 production stage. The effects of two different parameters as sucrose concentration (5 10 and 20 g/L) and addition of ferrous ions (60 and 120 mg/L) are investigated. Both H2 and CH4 productions are increased at high sucrose concentrations. However the optimum H2 and CH4 yields of 163.2 mL-H2/g-sucrose and 211.8 mL-CH4/g-TVS are obtained at 5 g-sucrose/L. At 5 g-sucrose/L addition of Fe2+ increases the H2 yield to 192.5 and 176.2 mLH2/g-sucrose corresponding to 60 and 120 mg-Fe2+/L respectively. Higher removal efficiencies and total energy recovery are measured using the two-stage system than the single-stage reactor.

Hydrogen is the energy carrier for a sustainable future without fossil fuels. As this requires a reliable transportation infrastructure the conversion of existing natural gas (NG) grids is an essential part of the worldwide individual national hydrogen strategies in addition to newly erected pipelines. In view of the known effect of hydrogen embrittlement the compatibility of the materials already in use (typically low-alloy steels in a wide range of strengths and thicknesses) must be investigated. Initial comprehensive studies on the hydrogen compatibility of pipeline materials indicate that these materials can be used to a certain extent. Nevertheless the material compatibility for hydrogen service is currently of great importance. However pipelines require frequent maintenance and repair work. In some cases it is necessary to carry out welding work on pipelines while they are under pressure e.g. the well-known tapping of NG grids. This in-service welding brings additional challenges for hydrogen operations in terms of additional hydrogen absorption during welding and material compatibility. The challenge can be roughly divided into two parts: (1) the possible austenitization of the inner piping material exposed to hydrogen which can lead to additional hydrogen absorption and (2) the welding itself causes an increased temperature range. Both lead to a significantly increased hydrogen solubility in the respective materials compared to room temperature. In that connection the knowledge on hot tapping on hydrogen pipelines is rare so far due to the missing service experiences. Fundamental experimental investigations are required to investigate the possible transferability of the state-of-the-art concepts from NG to hydrogen pipeline grids. This is necessary to ensure that no critical material degradation occurs due to the potentially increased hydrogen uptake. For this reason the paper introduces the state of the art in pipeline hot tapping encompassing current research projects and their individual solution strategies for the problems that may arise for future hydrogen service. Methods of material testing their limitations and possible solutions will be presented and discussed.