Germany

The global population is predicted to increase from ~7.3 billion to over 9 billion people by 2050.Together with rising economic growth this is forecast to result in a 50% increase in fueldemand which will have to be met while reducing carbon dioxide (CO 2 ) emissions by 50–80%to maintain social political energy and climate security. This tension between rising fuel demandand the requirement for rapid global decarbonization highlights the need to fast-track thecoordinated development and deployment of efficient cost-effective renewable technologies forthe production of CO 2 neutral energy. Currently only 20% of global energy is provided aselectricity while 80% is provided as fuel. Hydrogen (H 2) is the most advanced CO 2 -free fuel andprovides a ‘common’ energy currency as it can be produced via a range of renewabletechnologies including photovoltaic (PV) wind wave and biological systems such as microalgaeto power the next generation of H 2 fuel cells. Microalgae production systems for carbon-basedfuel (oil and ethanol) are now at the demonstration scale. This review focuses on evaluating thepotential of microalgal technologies for the commercial production of solar-driven H2 fromwater. It summarizes key global technology drivers the potential and theoretical limits ofmicroalgal H2 production systems emerging strategies to engineer next-generation systems andhow these fit into an evolving H 2 economy.

Public perceptions might determine the ease of the transition from a fossil-based to a green hydrogen-based production pathway in the industrial sector. The primary objective of this paper is to empirically identify the antecedents of the acceptance of two relevant industrial applications of green hydrogen: green methanol and green steel. The analysis relying on linear regression models utilises survey data from samples of residents near a chemical park and a steel plant (509 and 502 participants respectively) contrasting them with a representative sample of 1502 individuals in Germany. The findings suggest that acceptance of the transitions to green methanol and green steel is high both locally and nationally. In all surveys >59 % of the participants are in favour while the share of those who are opposed to the respective transitions is below 9 %. Key antecedents of acceptance which are conducive in all models relate to individuals’ attitudes towards green hydrogen and perceptions of the legitimacy of the industry actors involved with varying results across legitimacy types. In general the findings were similar across industrial applications and across levels of observation but varied across regions. This study highlights the importance of civil society perceptions and suggests that relationship management efforts aimed at maintaining positive perceptions of industrial hydrogen applications should consider their broader physical and social contexts.

We investigate the challenges and options for repurposing existing natural gas pipelines for hydrogen transportation. Challenges of re-purposing are mainly related to safety and due to the risk of hydrogen embrittlement of pipeline steels and the smaller molecular size of the gas. From an economic perspective the lower volumetric energy density of hydrogen compared to natural gas is a challenge. We investigate three pipeline repurposing options in depth: a) no modification to the pipeline but enhanced maintenance b) use of gaseous inhibitors and c) the pipe-in-pipe approach. The levelized costs of transportation of these options are compared for the case of the German Norddeutsche Erdgasleitung (NEL) pipeline. We find a similar cost range for all three options. This indicates that other criteria such as the sunk costs public acceptance and consumer requirements are likely to shape the decision making for gas pipeline repurposing.

This study uses a multi-method design to investigate the media’s role in shaping Germans’ attitudes toward green hydrogen. It combines an automatized content analysis of 7649 German newspaper articles published between July 2021 and June 2024 and a three-wave panel survey of the German population conducted between June 2023 and June 2024 with an initial sample of 2701 participants. The findings show that the intensity of media reporting on hydrogen was low compared to other energy-related topics. Nevertheless participants’ assessments of relative topic presence are rather accurate (rho: 0.50–0.80). A considerable number of participants were unable to position themselves toward the potential and challenges of hydrogen (23%–35%). Overall the results indicate that media and communication tend to stabilize or change existing attitudes rather than contribute to the formation or loss of attitudes leading to implications for the communication of relevant stakeholders.

In recent years new chemical release agents based on silane are being used in the tire industry. Silane is an inorganic chemical compound consisting of a silicon backbone and hydrogen. Silanes can be thermally decomposed into high-purity silicon and hydrogen. If silane is stored and transported in Intermediate Bulk Containers (IBCs) equipped with safety valves in vented semi-confined spaces such as ISO-Containers hydrogen can be accumulated and become explosive mixture with air. A conservative CFD analysis using the GASFLOW-MPI code has been carried out to assess the hydrogen risk inside the vented containers. Two types of containers with different natural ventilation systems were investigated under various hypothetical accident scenarios. A continuous release of hydrogen due to the chemical decomposition of silane from IBCs was studied as the reference case. The effect of the safety valves on hydrogen accumulation in the container which results in small pulsed releases of hydrogen was investigated. The external effects of the sun and wind on hydrogen distribution and ventilation were also evaluated. The results can provide detailed information on hydrogen dispersion and mixing within the vented enclosures and used to evaluate the hydrogen risks such as flammability. Based on the assumptions used in this study it indicates that the geometry of ventilation openings plays a key role in the efficiency of the indoor air exchange process. In addition the use of safety valves makes it possible to reduce the concentration of hydrogen by volume in air compared to the reference case. The effect of the sun which results in a temperature difference between two container walls allows a strong mixing of hydrogen and air which helps to obtain a concentration lower than both the base case and the case of the pulsed releases. But the best results for the venting process are obtained with the wind that can drive the mixture to the downwind wall vent holes.

The global push for sustainable energy has heightened the demand for green hydrogen which is crucial for decarbonizing heavy industry. However current electrolysis plant capacities are insufficient. This research addresses the challenge through optimizing large-scale electrolysis construction via standardization modularization process optimization and automation. This paper introduces H2Giga a project for mass-producing electrolyzers and HyPLANT100 investigating largescale electrolysis plant structure and construction processes. Modularizing electrolyzers enhances production efficiency and scalability. The integration of AutomationML facilitates seamless information exchange. A digital twin concept enables simulations optimizations and error identification before assembly. While construction site automation provides advantages tasks like connection technologies and handling cables tubes and hoses require pre-assembly. This study identifies key tasks suitable for automation and estimating required components. The Enapter Multicore electrolyzer serves as a case study showcasing robotic technology for tube fittings. In conclusion this research underscores the significance of standardization modularization and automation in boosting the electrolysis production capacity for green hydrogen contributing to ongoing efforts in decarbonizing the industrial sector and advancing the global energy transition.

In international regulations on explosion protection mechanical friction impact or abrasion is usually named as one of 13 ignition sources that must be avoided in hazardous zones with explosive atmospheres. In different studies it is even identified as one of the most frequent ignition sources in practice. The effectiveness of mechanical impacts as ignition source is dependent from several parameters including the minimum ignition energy of the explosive atmosphere the properties of the material pairing the kinetic impact energy or the impact velocity. By now there is no standard procedure to determine the effectiveness of mechanical impacts as ignition source. In some previous works test procedures with poor reproducibility or undefined kinetic impact energy were applied for this purpose. In other works only homogeneous material pairings were considered. In this work the effectiveness of mechanical impacts with defined and reproducible kinetic impact energy as ignition source for hydrogen containing atmospheres was studied systematically in dependence from the inhomogeneous material pairing considering materials with practical relevance like stainless steel low alloy steel concrete and non-iron-metals. It was found that ignition can be avoided if non-iron metals are used in combination with different metallic materials but in combination with concrete even the impact of non-iron-metals can be an effective ignition source if the kinetic impact energy is not further limited. Moreover the consequence of hydrogen admixture to natural gas on the effectiveness of mechanical impacts as ignition source was studied. In many cases ignition of atmospheres containing natural gas by mechanical impacts is rather unlikely. No influence could be observed for admixtures up to 25% hydrogen and even more. The results are mainly relevant in the context of repurposing the natural gas grid or adding hydrogen to the natural gas grid. Based on the test results it can be evaluated under which circumstances the use of tools made of non-iron-metals or other non-sparking materials can be an effective measure to avoid ignition sources in hazardous zones containing hydrogen for example during maintenance work.

Cost-effective hydrogen supply chains are crucial for accelerating hydrogen deployment and decarbonizing economies with the storage and transportation sectors representing major challenges. This study presents a systematic literature review of 81 papers to identify and analyze the main influencing factors on hydrogen storage and transportation costs with the aim of improving transparency across the hydrogen supply chain. The review identifies and assesses 25 technical nine economic and two environmental factors highlighting capital expenditure and capacity of storage and transport facilities as the primary drivers of storage and transportation costs. Furthermore transport distance for trucks and ships as well as the discount rate for pipelines are iden tified as additional critical cost-determining factors for the transportation sector.

Chapters:<br/>♦ Introduction by Rainer Quitzow and Yana Zabanova<br/>♦ The EU in the Global Hydrogen Race: Bringing Together Climate Action Energy Security and Industrial Policy by Yana Zabanova<br/>♦ Germany’s Hydrogen Strategy: Securing Industrial Leadership in a Carbon–Neutral Economy by Almudena Nunez and Rainer Quitzow<br/>♦ France’s Hydrogen Strategy: Focusing on Domestic Hydrogen Production to Decarbonise Industry and Mobility by Ines Bouacida<br/>♦ International Dimension of the Polish Hydrogen Strategy. Conditions and Potential for Future Development by Michał Smoleń and Wojciech Żelisko<br/>♦ Hydrogen Affairs in Hungary’s Politically Confined Ambition byJohn Szabo<br/>♦ Spain’s Hydrogen Ambition: Between Reindustrialisation and Export-Led Energy Integration with the EU by Ignacio Urbasos and Gonzalo Escribano<br/>♦  Italian Hydrogen Policy: Drivers Constraints and Recent Developments by Andrea Prontera<br/>♦  Hydrogen Policy in the Netherlands: Laying the Foundations for a Scalable Hydrogen Value Chain by Roelof Stam Coby van der Linde and Pier Stapersma<br/>♦ Hydrogen Strategy of Sweden: Unpacking the Multiple Drivers and Potential Barriers to Hydrogen Development by Stefan Ćetković and Janek Stockburger<br/>♦  Norway’s Hydrogen Strategy: Unveiling Green Opportunities and Blue Export Ambitions by Jon Birger Skjærseth Per Ove Eikeland Tor Håkon Jackson Inderberg and Mari Lie Larsen<br/>♦ The Geopolitics of Hydrogen in Europe: The Interplay between EU and Member State Policies by Rainer Quitzow and Yana Zabanova

Many developing countries seek to participate in the emerging global green hydrogen industry not only as exporters of green hydrogen and its derivatives to Europe and the Far East but also to use it for their own energy security and green transition. They hope that new development paths will lead to late-comer industrialisation. This article assesses corresponding prospects in Chile and Namibia two countries that pursue particularly ambitious plans on green hydrogen. To better understand the chances for path creation ex ante the authors draft an innovative framework that refers to context factors – that is structure – and three types of transformative agency. Against the backdrop of information from secondary sources and a series of expert interviews they uncover sound institutional reforms and initiatives of place-based leadership to promote the green hydrogen industry. However Chile and Namibia lack Schumpeterian entrepreneurship. It therefore remains to be seen whether new development paths will be inclusive contributing to in-country development. Typical downsides of extractive industries in resource peripheries might occur.

Public transport plays a prominent role with respect to mitigating transport-related environmental effects by improving passenger transport efficiency and the quality of life in cities. Batteries and fuel cells are at the forefront of the technological shift to zero-emission powertrains. Within the scope of the German-funded project BIC H2 corresponding systems analysis research focuses on the market introduction of fuel cell–electric buses in the Rhine–Ruhr Metropolitan Region through 2035. This study presents the related methods and major outcomes of this techno-economic research which spans spatially-resolved hydrogen demand modeling of all relevant sectors to hydrogen refueling stations and upstream infrastructure modeling to scenario-based analyses. The latter builds upon an empirical study supporting the development of the Hydrogen Roadmap of the State of North Rhine–Westphalia (NRW). Our results show that the demand in NRW alone is expected to account for one third of total German hydrogen use. Hydrogen bus refueling could substantially support market introduction during its early phases. In the long term however hydrogen demand in industry is significantly higher compared to that in the transport sector. Furthermore spatial analysis identifies regions with pronounced hydrogen demands that could therefore be candidates for initial infrastructure investments. With the Cologne area showing the highest hydrogen demand levels such regions can offer particularly high infrastructure utilization e.g. for bus refueling. On the infrastructure side trailers for transporting gaseous hydrogen to refueling stations are the most favorable option through 2035. Pipelines would be the preferred solution soon after 2035 due to increased hydrogen demand. If effectively deployed converted natural gas pipelines would be the most cost-effective option even earlier.

Hydrogen has become a key enabler for decarbonization as countries pledge to reach net zero carbon emissions by 2050. With hydrogen infrastructure expanding rapidly beyond its established applications there is a requirement for robust safety practices solutions and regulations. Since the 1980s considerable efforts have been undertaken by the nuclear community to address hydrogen safety issues because in severe accidents of water-cooled nuclear reactors a large amount of hydrogen can be produced from the oxidation of metallic components with steam. As evidenced in the Fukushima accident hydrogen combustion can cause severe damage to reactor building structures promoting the release of radioactive fission products to the environment. A number of large-scale experiments were conducted in the framework of national and international projects to understand the hydrogen dispersion and combustion behaviour under postulated accidental conditions. Empirical engineering models and numerical codes were developed and validated for safety analysis. Hydrogen recombiners known as Passive Autocatalytic Recombiner (PAR) were developed and have been widely installed in nuclear containments to mitigate hydrogen risk. Complementary actions and strategies were established as part of severe accident management guidelines to prevent or limit the consequences of hydrogen explosions. In addition hydrogen monitoring systems were developed and implemented in nuclear power plants. The experience and knowledge gained from the nuclear community on hydrogen safety is valuable and applicable for other industries involving hydrogen production transport storage and use.

Present work investigates the potential of a long-range commercial blended wing body configuration powered by hydrogen combustion engines with future airframe and propulsion technologies. Future technologies include advanced materials load alleviation techniques boundary layer ingestion and ultra-high bypass ratio engines. The hydrogen combustion configuration was compared to the configuration powered by kerosene with respect to geometric properties performance characteristics energy demand equivalent CO2 emissions and Direct Operating Costs. In addition technology sensitivity studies were performed to assess the potential influence of each technology on the configuration. A multi-fidelity sizing methodology using low- and mid-fidelity methods for rapid configuration sizing was created to assess the configuration and perform robust analyses and multi-disciplinary optimizations. To assess potential uncertainties of the fidelity of aerodynamic analysis tools high-fidelity aerodynamic analysis and optimization framework MACHAero was used for additional verification. Comparison of hydrogen and kerosene blended wing body aircraft showed a potential reduction of equivalent CO2 emission by 15% and 81% for blue and green hydrogen compared to the kerosene blended wing body and by 44% and 88% with respect to a conventional B777-300ER aircraft. Advancements in future technologies also significantly affect the geometric layout of aircraft. Boundary layer ingestion and ultra-high bypass ratio engines demonstrated the highest potential for fuel reduction although both technologies conflict with each other. However operating costs of hydrogen aircraft could establish a significant problem if pessimistic and base hydrogen price scenarios are achieved for blue and green hydrogen respectively. Finally configurational problems featured by classical blended wing body aircraft are magnified for the hydrogen case due to the significant volume requirements to store hydrogen fuel.

Considerable progress has been made recently in the use of nanoporous materials for hydrogen storage. In this article the current status of the field and future challenges are discussed ranging from important open fundamental questions such as the density and volume of the adsorbed phase and its relationship to overall storage capacity to the development of new functional materials and complete storage system design. With regard to fundamentals the use of neutron scattering to study adsorbed H2 suitable adsorption isotherm equations and the accurate computational modelling and simulation of H2 adsorption are discussed. The new materials covered include flexible metal–organic frameworks core–shell materials and porous organic cage compounds. The article concludes with a discussion of the experimental investigation of real adsorptive hydrogen storage tanks the improvement in the thermal conductivity of storage beds and new storage system concepts and designs.

Especially the electrification of the industry sector is highly complex and challenging mainly due to process-specific requirements. In this context there are several industrial processes where the direct and indirect use of electricity is subject to technical restrictions. In order to achieve the national climate goals the fossil energy consumption remaining after the implementation of efficiency and sufficiency measures as well as direct electrification has to be substituted through hydrogen and synthetic gaseous liquid and solid hydrocarbons. As the main research object the role of synthetic fuels in industrial transformation paths is investigated and analyzed by combining individual greenhouse gas abatement measures within the Sector Model Industry. Sector Model Industry is an energy consumption model that performs discrete deterministic energy and emission dynamic calculations with a time horizon up to 2050 at macroeconomic level. The results indicate that the use of synthetic fuels can be expected with a high level of climate protection. The industrial CO2 target in the model makes it necessary to replace CO2 -intensive fossil with renewable fuels. The model uses a total of 163 TWh of synthetic fuels in the climate protection scenario and thus achieves an 88% decrease in CO2 emissions in 2050 compared to 1990. This means that the GHG abatement achieved in industry is within the range of the targeted CO2 mitigation of the overall system in Germany of between 80 and 95% in 2050 compared to 1990. Due to technical restrictions the model mainly uses synthetic methane instead of hydrogen (134 TWh). The results show that despite high costs synthetic fuels are crucial for defossilization as a fall back option in the industrial scenario considering high climate ambition. The scenario does not include hydrogen technologies for heat supply. Accordingly the climate protection scenario uses hydrogen only in the steel industry for the direct reduction of iron (21 TWh). 8 TWh of synthetic oil substitute the same amount of fossil oil in the climate protection scenario. A further analysis conducted on the basis of the model results shows that transformation in the energy system and the use of smart ideas concepts and technologies are a basic prerequisite for enabling the holistic defossilisation of industry. The findings in the research can contribute to the cost-efficient use of synthetic fuels in industry and thus serve as a basis for political decision making. Moreover the results may have a practical relevance not only serving as a solid comparison base for the outcome of other studies but also as input data for further simulation of energy system transformation paths.

Hydrogen as an energy carrier plays an important role in carbon neutrality and energy transition. Hydrogen is the lightest element with a density of only 0.08375 kg/m3 in gaseous form at standard temperature and pressure (STP); as a result hydrogen is usually stored and transported in a highly compressed form. It is prone to leakage and has a very low ignition energy of 0.017 mJ. Safety remains a challenge in the use of hydrogen as an energy source. This paper examines approximately 20 hydrogen-related accidents in China over a 20-year period focusing on the root causes consequences of the accidents and responses to them. These accidents occurred in the production storage transport and application of hydrogen with different causes in different locations and resulting in losses at different scales. Some statistical evaluations were conducted to learn lessons from the accidents. The main objective of this paper is (i) to retrieve a set of hydrogen related incidents from a region which is under-represented in incident repositories (ii) to contribute to a generalised lesson learned from them and (iii) to assist the definition of realistic scenarios for commonly occurring hydrogen accidents.

During a severe accident in a nuclear power plant one of the potential threats to the containment is the occurrence of energetic combustion events. In modern plants Severe Accident Management Guidelines (SAMG) as well as dedicated mitigation hardware are in place to minimize/mitigate this combustion risk and thus avoid the release of radioactive material into the environment. Advancements in SAMGs are in the focus of AMHYCO an EU-funded Horizon 2020 project officially launched on October 1st 2020. The project consortium consists of 12 organizations (from six European countries and one from Canada) and is coordinated by the Universidad Politécnica de Madrid (UPM). The progress made in the first two years of the AMHYCO project is here presented. A comprehensive bibliographic review has been conducted providing a common foundation to build the knowledge gained during the project. After an extensive set of accident transients simulated both for phases occurring inside and outside the reactor pressure vessel a set of challenging sequences from the combustion risk perspective for different power plant types were identified. At the same time three generic containment models for the three considered reactor designs have been created to provide the full containment analysis simulations with lumped parameter models 3-dimensional containment codes and CFD codes. In order to further consolidate the model base combustion experiments and performance tests on passive auto-catalytic recombiners under explosion prone H2/CO atmospheres were performed at CNRS (France) and FZJ (Germany). Finally it is worth saying that the experimental data and engineering models generated from the AMHYCO project are useful for other industries outside the nuclear one.

HyResponder is a European Hydrogen Train the Trainer programme for responders. This paper describes the key outputs of the project and the steps taken to develop and implement a long-term sustainable train the trainer programme in hydrogen safety for responders across Europe and beyond. This FCH2 JU (now Clean Hydrogen Joint Undertaking) funded project has built on the successful outcomes of the previous HyResponse project. HyResponder has developed further and updated educational operational and virtual reality training for trainers of responders to reflect the state-of-the-art in hydrogen safety including liquid hydrogen and expand the programme across Europe and specifically within the 10 countries represented directly within the project consortium: Austria Belgium the Czech Republic France Germany Italy Norway Spain Switzerland and the United Kingdom. For the first time four levels of educational materials from fire fighter through to specialist have been developed. The digital training resources are available on the e-Platform (https://hyresponder.eu/e-platform/). The revised European Emergency Response Guide is now available to all stakeholders. The resources are intended to be used to support national training programs. They are available in 8 languages: Czech Dutch English French German Italian Norwegian and Spanish. Through the HyResponder activities trainers from across Europe have undertaken joint actions which are in turn being used to inform the delivery of regional and national training both within and beyond the project. The established pan-European network of trainers is shaping the future in the important for inherently safer deployment of hydrogen systems and infrastructure across Europe and enhancing the reach and impact of the programme.

Proton exchange membrane electrolytic cells (PEMECs) have the potential to provide green Hydrogen as a sustainable energy source. PEMEC has already been applied at an industrially relevant scale. However it still faces challenges regarding reliability and durability especially in long-term operation. This review emphasizes the need for standardizing the cell configuration the testing protocols and the evaluation procedures to attain the optimum operation settings and eventually precisely evaluating the degradation rate. Potential physicochemical and electrical operational health indicators are described to identify the degradation of a distinct cell component in a running PEMEC. The reliable evaluation of degradation rate via operational health indicators with a robust supervisory system under stringent operating conditions is likely to diagnose the degradation mechanism. By developing incremental empirical degradation models via mapping a correlation between the history of proposed operational health indicators the instantaneous degradation rate can be quantified. This approach in turn enables us to determine the state-of-operation of an electrolyzer during service thereby benchmarking the durability of PEMEC. Finally with the target of scaling up and fulfilling the commercial demands for PEMEC the significance and literature contributions regarding operation management and prog nostics are expressed.

Globally a green hydrogen economy rush is underway and many companies investors governments and environmentalists consider it as an energy source that could foster the global energy transition. The enormous potential for hydrogen production for domestic use and export places Africa in the spotlight in the green hydrogen economy discourse. This discourse remains unsettled regarding how natural resources such as land and water can be sustainably utilized for such a resource-intensive project and what implications this would have. This review argues that green hydrogen production (GHP) in Africa has consequences where land resources (and their associated natural resources) are concerned. It discusses the current trends in GHP in Africa and the possibilities for reducing any potential pressures it may put on land and other resource use on the continent. The approach of the review is interpretive and hinges on answering three questions concerning the what why and how of GHP and its land consequences in Africa. The review is based on 41 studies identified from Google Scholar and sources identified via snowballed recommendations from experts. The GHP implications identified relate to land and water use mining-related land stress and environmental ecological and land-related socioeconomic consequences. The paper concludes that GHP may not foster the global energy transition as is being opined by many renewable energy enthusiasts but rather could help foster this transition as part of a greener energy mix. It notes that African countries that have the potential for GHP require the institutionalization of or a change in their existing approaches to land-related energy governance systems in order to achieve success.

A series of unconfined hydrogen detonation bench-mark experiments are analyzed with respect to CFD code validation and safety measures development. 1-Dimensional in-house code COM1D was applied for validation against experimental data for unconfined detonation of a hemispherical envelope of about 3- and 5-m radius with hydrogen-air mixtures from 20 to 30% hydrogen in air. The code demonstrates a very good agreement with experimental data and allows an adequate simulation of the unconfined hydrogen detonation. All calculated data were scaled in Sachs coordinates to compare with experimental data and to approximate the data for practical evaluation of safety distances. Numerical experiments with different hydrogen inventories from 50 g to 50 kg and different sizes of the cloud from 1 to 2 m radius of the same amount of hydrogen 50g were carried out to clarify the problem of energy of gaseous explosion responsible for the strength of blast wave. Additionally a comparison of hydrogen-air explosion pressure with blast wave properties from the hypothetical cloud of hot compressed combustion products (P=Picc; T=Ticc) and simply a hot air of the same initial pressure and temperature as combustion products showed very good agreement of shock wave strength at far distances beyond the cloud. This confirms the governing role of energy of combustion on blast wave propagation and its ability to scale the strength of blast waves. The dynamics of the explosion process and combustion product expansion were also analyzed experimentally and numerically to evaluate the dimension of the heat radiation zone and heat flux from combustion products. To demonstrate the capability of tested COM1D code the modeling and analysis of high-pressure hydrogen tanks rupture at 350 and 700 bar were conducted to investigate blast wave strength and evaluate the safety distances.

Subcooled liquid hydrogen (sLH2) is an onboard storage as well as a hydrogen refueling technology that is currently being developed by Daimler Truck and Linde to boost the mileage of heavy-duty trucks while also improving performance and reducing the complexity of hydrogen refueling stations. In this article the key technical aspects advantages challenges and future developments of sLH2 at vehicle and infrastructure levels will be explored and highlighted.

In many industries low-carbon hydrogen will substitute fossil fuels in the course of the transformation to climate neutrality. This paper contributes to understanding this transformation. This paper provides an overview of energy- and emission-intensive industry sectors with great potential to defossilize their production processes with hydrogen. An assessment of future hydrogen demand for various defossilization strategies in Germany that rely on hydrogen as a feedstock or as an energy carrier to a different extent in the sectors steel chemicals cement lime glass as well as pulp and paper is carried out. Results indicate that aggregate industrial hydrogen demand in those industries would range between 197 TWh and 298 TWh if production did not relocate abroad for any industry sector. The range for hydrogen demand is mainly due to differences in the extent of hydrogen utilization as compared to alternative transformation paths for example based on electrification. The attractiveness of production abroad is then assessed based on the prospective comparative cost advantage of relocating parts of the value chain to excellent production sites for low-carbon hydrogen. Case studies are provided for the steel industry as well as the chemical industry with ethylene production through methanol and the production of urea on the basis of ammonia. The energy cost of the respective value chains in Germany is then compared to the case of value chains partly located in regions with excellent conditions for renewable energies and hydrogen production. The results illustrate that at least for some processes – as ammonia production – relocation to those favorable regions may occur due to substantial comparative cost advantages.

Among the different hydrogen premixed combustion concepts direct injection (DI) is one of the most promising for internal combustion engine (ICE) applications. However to fully exploit the benefits of this solution the optimization of the mixture preparation process is a crucial factor. In the present work a study of the hydrogenair mixture formation process in a DI H2-ICE for off-road applications was performed through 3D-CFD simulations. First a sensitivity analysis on the injection timing was carried out to select the optimal injection operating window capable of maximizing mixture homogeneity without a significant volumetric efficiency reduction. Then different spray injector guiding caps were tested to assess their effect on in-cylinder dynamics and mixture characteristics consequently. Finally the impact of swirl intensity on hydrogen distribution has been assessed. The optimization of the combustion chamber geometry has allowed the achievement of significant improvements in terms of mixture homogeneity.

With the aim of reducing carbon emissions and seeking independence from Russian gas in the wake of the conflict in Ukraine the use of hydrogen in the European Union is expected to rise in the future. In this regard hydrogen transport via pipeline will become increasingly crucial either through the utilization of existing natural gas infrastructure or the construction of new dedicated hydrogen pipelines. This study investigates the effects of hydrogen blending in existing pipelines on the European energy system by the year 2050 by introducing hydrogen blending sensitivities to the Global Energy System Model (GENeSYS-MOD). Results indicate that hydrogen demand in Europe is inelastic and limited by its high costs and specific use cases with hydrogen production increasing by 0.17% for 100%-blending allowed compared to no blending allowed. The availability of hydrogen blending has been found to impact regional hydrogen production and trade with countries that can utilize existing natural gas pipelines such as Norway experiencing an increase in hydrogen and synthetic gas exports from 44.0 TWh up to 105.9 TWh in 2050 as the proportion of blending increases. Although the influence of blending on the overall production and consumption of hydrogen in Europe is minimal the impacts on the location of production and dependence on imports must be thoroughly evaluated in future planning efforts.

Synthetic current density profiles with wind and photovoltaic power characteristics were calculated by autoregressive-moving-average (ARMA) models for the experimental evaluation of dynamic operating concepts for alkaline water electrolyzers powered by renewable energy. The selected operating concepts included switching between mixed and split electrolyte cycles and adapting the liquid electrolyte volume flow rate depending on the current density. All experiments were carried out at a pressure of 7 bar a temperature of 60 °C and with an aqueous potassium hydroxide solution with 32 wt.% KOH as the electrolyte. The dynamic operating concepts were compared to stationary experiments with mixed electrolyte cycles and the experimental evaluation showed that the selected operating concepts were able to reduce the gas impurity compared to the reference operating conditions without a noticeable increase of the cell potential. Therefore the overall system efficiency and process safety could be enhanced by this approach.

A transition towards zero-emission fuels is required in the mobility sector in order to reach the climate goals. Here (green) renewable hydrogen for use in fuel cells will play an important role especially for heavy duty applications such as trucks. However there are still challenges to overcome regarding efficient storage infrastructure integration and optimization of the refuelling process. A key aspect is to reduce the refuelling duration as much as possible while staying below the maximum allowed temperature of 85 C. Experimental tests for the refuelling of a 320 l type III tank were conducted at different operating conditions and the tank gas temperature measured at the front and back ends. The results indicate a strongly inhomogeneous temperature field where measuring and verifying the actual maximum temperatures proves difficult. Furthermore a simulation approach is provided to calculate the average tank gas temperature at the end of the refuelling process.

An exemplary techno-economic and environmental assessment of carbon-negative hydrogen (H2) production is carried out in this work. It is based on the so-called “dark photosynthesis” with carbon dioxide (CO2) capture and geological storage. As a special feature of the assessment the economic consequences due to the impact on the global climate are taken into account. The results indicate that the example project would be capable of generating negative GHG emissions under the assumptions made. The amount is estimated to be 17.72 kgCO2 to be removed from the atmosphere per kilogram of H2 produced. The levelized costs of carbon-negative hydrogen are obtained considering the economic impact of greenhouse gas emissions and removals. They are estimated to be 0.013 EUR/kWhH2. Compared to grey hydrogen from natural gas (0.12 EUR/kWhH2) and green hydrogen from electrolysis using renewable electricity (0.18 EUR/kWhH2) this shows a potential environmental-economic advantage of the considered example. Even without internalization of GHG impacts an economic advantage of the project (0.12 EUR/kWhH2) over green hydrogen (0.17 EUR/kWhH2) is indicated. Compared to other NETs the GHG removal efficiency is at the lower end of both BECCS and DACCS approaches.

Beyond its role as an energy vector a growing number of natural hydrogen sources and reservoirs are being discovered all over the globe which could represent a clean energy source. Although the hydrogen amounts in reservoirs are uncertain they could be vast and they could help decarbonize energy-intensive economic sectors and facilitate the energy transition. Natural hydrogen is mainly produced through a geochemical process known as serpentinization which involves the reaction of water with low-silica ferrous minerals. In favorable locations the hydrogen produced can become trapped by impermeable rocks on its way to the atmosphere forming a reservoir. The safe exploitation of numerous natural hydrogen reservoirs seems feasible with current technology and several demonstration plants are being commissioned. Natural hydrogen may show variable composition and require custom separation purification storage and distribution facilities depending on the location and intended use. By investing in research in the mid-term more hydrogen sources could become exploitable and geochemical processes could be artificially stimulated in new locations. In the long term it may be possible to leverage or engineer the interplay between microorganisms and geological substrates to obtain hydrogen and other chemicals in a sustainable manner.

In the context of the German Energiewende the current government intends to install six million heat pumps by 2030. Replacing gas heating by power has significant implications on the infrastructure. One of the biggest advantages of using gas is the existing storage portfolio. It has not been clarified yet how power demand should be structured on an annual level—especially since power storage is already a problem and solar power is widely promoted to fuel heat pumps despite having an inverse profile. In this article three different solutions namely hydrogen batteries and carbon capture and storage are discussed with respect to resources energy and financial demand. It shows that relying solely on batteries or hydrogen is not solving the structuring problem. A combination of all existing technologies (including fossil fuels) is required to structure the newly generated electricity demand

Meeting the Paris Agreement's goal to limit global warming to well below 2 °C and pursuing efforts towards 1.5 °C is likely to require more rapid and fundamental energy system changes than the previously-agreed 2 °C target. Here we assess over 200 integrated assessment model scenarios which achieve 2 °C and well-below 2 °C targets drawn from the IPCC's fifth assessment report database combined with a set of 1.5 °C scenarios produced in recent years. We specifically assess differences in a range of near-term indicators describing CO2 emissions reductions pathways changes in primary energy and final energy across the economy's major sectors in addition to more detailed metrics around the use of carbon capture and storage (CCS) negative emissions low-carbon electricity and hydrogen.

Austria is committed to the net-zero climate goal along with the European Union. This requires all sectors to be decarbonized. Hereby hydrogen plays a vital role as stated in the national hydrogen strategy. A report commissioned by the Austrian government predicts a minimum hydrogen demand of 16 TWh per year in Austria in 2040. Besides hydrogen imports domestic production can ensure supply. Hence this study analyses the levelized cost of hydrogen for an off-grid production plant including a proton exchange membrane electrolyzer wind power and solar photovoltaics in Austria. In the first step the capacity factors of the renewable electricity sources are determined by conducting a geographic information system analysis. Secondly the levelized cost of electricity for wind power and solarphotovoltaics plants in Austria is calculated. Thirdly the most cost-efficient portfolio of wind power and solar photovoltaics plants is determined using electricity generation profiles with a 10-min granularity. The modelled system variants differ among location capacity factors of the renewable electricity sources and the full load hours of the electrolyzer. Finally selected variables are tested for their sensitivities. With the applied model the hydrogen production cost for decentralized production plants can be calculated for any specific location. The levelized cost of hydrogen estimates range from 3.08 EUR/kg to 13.12 EUR/kg of hydrogen whereas it was found that the costs are most sensitive to the capacity factors of the renewable electricity sources and the full load hours of the electrolyzer. The novelty of the paper stems from the model applied that calculates the levelized cost of renewable hydrogen in an off-grid hydrogen production system. The model finds a cost-efficient portfolio of directly coupled wind power and solar photovoltaics systems for 80 different variants in an Austria-specific context.

The valorization of integrated steelworks process off-gases as feedstock for synthesizing methane and methanol is in line with European Green Deal challenges. However this target can be generally achieved only through process off-gases enrichment with hydrogen and use of cutting-edge syntheses reactors coupled to advanced control systems. These aspects are addressed in the RFCS project i3 upgrade and the central role of hydrogen was evident from the first stages of the project. First stationary scenario analyses showed that the required hydrogen amount is significant and existing renewable hydrogen production technologies are not ready to satisfy the demand in an economic perspective. The poor availability of low-cost green hydrogen as one of the main barriers for producing methane and methanol from process off-gases is further highlighted in the application of an ad-hoc developed dispatch controller for managing hydrogen intensified syntheses in integrated steelworks. The dispatch controller considers both economic and environmental impacts in the cost function and although significant environmental benefits are obtainable by exploiting process off-gases in the syntheses the current hydrogen costs highly affect the dispatch controller decisions. This underlines the need for big scale green hydrogen production processes and dedicated green markets for hydrogen-intensive industries which would ensure easy access to this fundamental gas paving the way for a C-lean and more sustainable steel production.

Chile abundant in solar and wind energy resources presents significant potential for the production of green hydrogen a promising renewable energy vector. However realizing this potential requires an understanding of the most suitable locations for the installation of green hydrogen industries. This study proposes a quantitative methodology that identifies and ranks potential public lands for industrial use based on a range of technical parameters (such as solar and wind availability) and socio-environmental considerations (including land use restrictions and population density). The results reveal optimal locations that can facilitate informed sustainable decision-making for large-scale green hydrogen implementation in Chile. While this methodology does not replace project-specific technical or environmental impact studies it provides a flexible general classification to guide initial site selection. Notably this approach can be applied to other regions worldwide with abundant solar and wind resources such as Australia and Northern Africa promoting more effective and sustainable global decision-making for green hydrogen production.

Hydrogen refueling stations (HRS) can cause a significant fraction of the hydrogen refueling cost. The main cost contributor is the currently used mechanical compressor. Electrochemical hydrogen compression (EHC) has recently been proposed as an alternative. However its optimal integration in an HRS has yet to be investigated. In this study we compare the performance of a gaseous HRS equipped with different compressors. First we develop dynamic models of three process configurations which differ in the compressor technology: mechanical vs. electrochemical vs. combined. Then the design and operation of the compressors are optimized by solving multi-stage dynamic optimization problems. The optimization results show that the three configurations lead to comparable hydrogen dispensing costs because the electrochemical configuration exhibits lower capital cost but higher energy demand and thus operating cost than the mechanical configuration. The combined configuration is a trade-off with intermediate capital and operating cost.

The shipping industry faces the dual challenge of reducing emissions to meet net-zero targets by 2050 and transporting green energy sources like hydrogen and its derivatives. Green shipping corridors provide experimental routes for lowcarbon solutions with the Suez Canal uniquely positioned to lead. This paper examines the canal’s evolving role as a dynamic energy space where diverse actors and networks intersect shaping spatial power relations and aligning with green capitalism interests. It explores the Suez Canal’s potential to serve as a model for hydrogen initiatives and its capacity to influence global energy governance and geopolitical dynamics in the transition to a sustainable shipping future. The canal also represents a microcosm of broader global shifts toward a future hydrogen economy where numerous stakeholders vie for power and influence.

Demand for hydrogen is expected to increase in the coming years to defossilize hard-to-abate sectors. In the European Union the question remains in which quantities and at what cost hydrogen can be produced to satisfy the growing demand. This paper applies different approaches to model costs and potentials of off-grid hydrogen production within the European Union. The modeled approaches distinguish the effects of different spatial and technological resolutions on hydrogen production potentials costs and prices. According to the results the hydrogen potential within the European Union is above 6800 TWh. This figure far surpasses the expected demand range of 1423 to 1707 TWh in 2050. The cost of satisfying the demand exceeds 100 billion euro at marginal costs of hydrogen below 85 euro per megawatt-hour. Additionally the results show that an integrated European Union market would reduce the overall system costs notably compared to a setup in which each country covers its own hydrogen demand domestically. Just a few countries would be able to supply the entire European Union’s hydrogen demand in the case of an integrated market. This finding leads to the conclusion that an international hydrogen infrastructure seems advantageous.

Electric arc furnace slag is a major by-product of steelmaking yet its industrial utilization remains limited due to its complex chemical and mineralogical composition. This study presents a hydrogen-based approach to recover metallic components from EAF slag for potential reuse in steelmaking. Laboratory experiments were conducted by melting 50 g of industrial slag samples at 1600 ◦C and injecting hydrogen gas through a ceramic tube into the liquid slag. After cooling both the slag and the metallic phases were analyzed for their chemical and phase compositions. Additionally the reduction process was modeled using a combination of approaches including the thermochemical software FactSage 8.1 models for density surface tension and viscosity as well as a diffusion model. The injection of hydrogen resulted in the reduction of up to 40% of the iron oxide content in the liquid slag. In addition the fraction of reacted hydrogen gas was calculated.

This study investigates the impact of delayed and accelerated expansion of the volatile renewable energy sources (vRES) onshore wind offshore wind and photovoltaics on Europe’s (EU27 United Kingdom Norway and Switzerland) demand for hydrogen imports and its derivatives to meet demand from final energy consumption sectors and to comply with European greenhouse gas (GHG) emission targets. Using the multi-energy system model ISAaR we analyze fourteen scenarios with different levels of vRES expansion including an evaluation of the resulting hydrogen prices. The load-weighted average European hydrogen price in the BASE scenario decreases from 4.1 €/kg in 2030 to 3.3 €/kg by 2050. Results show that delaying the expansion of vRES significantly increases the demand for imports of hydrogen and its derivatives and thus increases the risk of not meeting GHG emission targets for two reasons: (1) higher import volumes to meet GHG emission targets increase dependence on third parties and lead to higher risk in terms of security of supply; (2) at the same time lower vRES expansion in combination with higher import volumes leads to higher resulting hydrogen prices which in turn affects the economic viability of the energy transition. In contrast an accelerated expansion of vRES reduces dependency on imports and stabilizes hydrogen prices below 3 €/kg in 2050 which increases planning security for hydrogen off-takers. The study underlines the importance of timely and strategic progress in the expansion of vRES and investment in hydrogen production storage and transport networks to minimize dependence on imports and effectively meet the European climate targets.

Novel hydrogen-based aircraft concepts pose significant challenges for the system development process. This paper proposes a generic adaptable and multidisciplinary framework for integrated model-based systems engineering (MBSE) and model-based safety assessment (MBSA) for the conceptual design of complex systems. The framework employs a multi-granularity modelcentric approach whereby the architectural specification is utilized for design as well as query purposes as part of a qualitative and quantitative graphbased preliminary safety assessment. For the qualitative assessment design and safety rules based on existing standards and best practices are formalized in the model and applied to a graph-based architecture representation. Consequently the remaining architectures are quantitatively assessed using automated fault trees. This safety-integrated approach is applied to the conceptual design of a liquid hydrogen fuel system architecture as a novel uncertain and complex system with many unknown system interrelations. This paper illustrates the potential of a combined MBSE-MBSA framework to streamline complex early-stage system design and demonstrates that all qualitatively down-selected hydrogen system architecture variants also satisfy quantitative assessment. Furthermore it is shown that the design space of novel systems is also constrained by safety and certification requirements significantly reducing the number of actual feasible solutions.

To enable hydrogen-powered aircraft operations liquid hydrogen infrastructure has to be planned well in advance. This study analyses the transition pathway of liquid hydrogen supply infrastructure from the initial development phase to market penetration optimizing the design and dispatch of the system. The findings reveal that the single-year approach used in previous studies significantly underestimates the costs associated with supply infrastructure. During the transition phase substantial investments are required in specific years leading to high supply costs particularly in the early years. Off-take agreements could be used to achieve a more balanced cost distribution. For the considered location of a generic airport on-site liquid hydrogen supply costs range between 3.83 and 5.03 USD/kgH2 assuming a long-term supply agreement. At a less favourable airport supply costs are 29% higher compared to a favourable location. However costs could be reduced by up to 12% if hydrogen is imported via vessels or the European Hydrogen Backbone. The primary factors influencing supply costs are the availability of renewable energy resources and the distances to the nearest port as well as hydrogen production hubs. Therefore the optimal supply chain must be assessed individually for each airport. Overall this study provides insights and a methodology that can support the development of future liquid hydrogen infrastructure roadmaps for hydrogen-powered aviation.

Climate change and global warming concerns promote interest in alternative fuels especially zero-carbon fuels like hydrogen. Modifying existing combustion engines for dual-fuel operation can decrease emissions of vehicles that are already on the road. The procedure of a deep learning-based model predictive control as a machine learning implementation practical for complex nonlinear systems with input and state constraints has been developed and tested on a hydrogen/diesel dual-fuel (HDDF) engine application. A nonlinear model predictive controller (NMPC) utilizing a deep neural network (DNN) process model is proposed to control the injected hydrogen and diesel. This DNN model has eight inputs and four outputs and has a short computational time compared to the physics-based model. The architecture and hyperparameters of the DNN model of the HDDF process are optimized through a two-stage Bayesian optimization to achieve high accuracy while minimizing the complexity of the model described. The final DNN architecture has two hidden layers with 31 and 23 neurons. A modified engine capable of HDDF operation is compared to standard diesel operation to evaluate the engine performance and emissions. During experimental engine testing the controller required an average computational time of 2 ms per cycle on a low-cost processor satisfying the real-time requirements and was faster than recurrent networks. The control performance of the DNN-NMPC for the HDDF engine showed a mean absolute error of 0.19 bar in load tracking while maximizing average hydrogen energy share (68%) and reducing emissions. Specifically the particulate matter emissions decrease by 87% compared to diesel operation.

In recent years numerous hydrogen-powered rail vehicles have been developed and their deployment within public transport is steadily increasing. To avoid disadvantages compared to diesel vehicles refueling times of 15 min are stated in the industry as target independent of climate zones or vehicle configurations. As refueling time varies with these parameters this work presents the corresponding refueling times and defines optimization potentials. A simulation model was set up and parametrized with a reference vehicle and hydrogen refueling station from the FCH2RAIL project. Measurement data from this station and vehicle were analyzed and compared to simulation results for model validation. The results show that at high ambient temperature pre-cooling reduces refueling time by 71 % and type 4 tanks increase refueling time by 20 % compared to type 3. Overall optimized tank design and thermal management reduce the refueling time for rail vehicles from over 2 h to 15 min.

Hydrogen emissions arise from leakage during its production transport storage and use leading to an increase in atmospheric hydrogen concentrations. These emissions also cause an indirect climate effect which has been quantified in the literature with a global warming potential over 100 years (GWP100) of about 11.6 placing hydrogen between carbon dioxide (1) and methane (29.8). There is increasing debate about the climate impact of an energy transition based on hydrogen. As a case study we have therefore evaluated the expected climate impact of switching from the long-distance natural gas transmission network to the outlined future “hydrogen core network” in Germany. Our analysis focuses on the relevant sources and network components of emissions. Our results show that the emissions from the network itself represent only about 1.8% of total emissions from the transmission of hydrogen with 98% attributed to energy-related compressor emissions and only 2% to fugitive and operational hydrogen leakage. Compared to the current natural gas transmission network we calculate a 99% reduction in total network emissions and a 97% reduction in specific emissions per transported unit of energy. In the discussion we show that when considering the entire life cycle which also includes emissions from the upstream and end-use phases the switch to hydrogen reduces the overall climate impact by almost 90%. However while our results show a significantly lower climate impact of hydrogen compared to natural gas minimising any remaining emissions remains crucial to achieve carbon neutrality by 2045 as set in Germany’s Federal Climate Action Act. Hence we recommend further reducing the emissions intensity of hydrogen supply and minimising the indirect emissions associated with the energy supply of compressors.

Developing clean and renewable energy instead of the ones related to hydrocarbon resources has been known as one of the different ways to guarantee reduced greenhouse gas emissions. Geothermal systems and native hydrogen exploration could represent an opportunity to diversify the global energy matrix and lower carbon-related emissions. All of these natural energy sources require a well to be drilled for its access and/or extractions similar to the petroleum industry. The main focuses of this technical–scientific contribution and research are (i) to evaluate the global energy matrix; (ii) to show the context over the years and future perspectives on geothermal systems and natural hydrogen exploration; and (iii) to present and analyze the importance of developing technologies on drilling process optimization aiming at accessing these natural energy resources. In 2022 the global energy matrix was composed mainly of nonrenewable sources such as oil natural gas and coal where the combustion of fossil fuels produced approximately 37.15 billion tons of CO2 in the same year. In 2023 USD 1740 billion was invested globally in renewable energy to reduce CO2 emissions and combat greenhouse gas emissions. In this context currently about 353 geothermal power units are in operation worldwide with a capacity of 16335 MW. In addition globally there are 35 geothermal power units under pre-construction (project phase) 93 already being constructed and recently 45 announced. Concerning hydrogen the industry announced 680 large-scale project proposals valued at USD 240 billion in direct investment by 2030. In Brazil the energy company Petroleo Brasileiro SA (Petrobras Rio de Janeiro Brazil) will invest in the coming years nearly USD 4 million in research involving natural hydrogen generation and since the exploration and access to natural energy resources (oil and gas natural hydrogen and geothermal systems among others) are achieved through the drilling of wells this document presents a technical–scientific contextualization of social interest.

This article provides an overview of the requirements for a grid-oriented integration of hydrogen energy storage (HES) and components into the power grid. Considering the general definition of HES and the possible components this paper presents future hydrogen demand electrolysis performance and storage capacity. These parameters were determined through various overall system studies aiming for climate neutrality by the year 2045. In Germany the targeted expansion of renewable energy generation capacity necessitates grid expansion to transport electricity from north to south and due to existing grid congestions. Therefore electrolysis systems could be used to improve the integration of renewable energy systems by reducing energy curtailment and providing grid services when needed. Currently however there are hardly any incentives for a grid-friendly allocation and operation of electrolysis or power-to-gas plants. Two possible locations for hydrogen plants from two current research projects HyCavMobil (Hydrogen Cavern for Mobility) and H2-ReNoWe (Hydrogen Region of north-western Lower Saxony) are presented as practical examples. Using power grid models the integration of electrolysis systems at these locations in the current high and extra-high voltage grid is examined. The presented results of load flow calculations assess power line utilization and sensitivity for different case scenarios. Firstly the results show that power lines in these locations will not be overloaded which would mean an uncritical operation of the power grid. While the overall grid stability remains unaffected in this case selecting suitable locations is vital to prevent negative effects on the local grid.

Hydrogen is a promising candidate for addressing environmental challenges in aviation yet its use in structural validation tests for Wing Structure-Integrated highpressure Hydrogen Tanks (SWITHs) remains underexplored. To the best of the authors’ knowledge this study represents the first attempt to assess the feasibility of conducting such tests with hydrogen at aircraft scales. It first introduces hydrogen’s general properties followed by a detailed exploration of the potential hazards associated with its use substantiated by experimental and simulation results. Key factors triggering risks such as ignition and detonation are identified and methods to mitigate these risks are presented. While the findings affirm that hydrogen can be used safely in aviation if responsibly managed they caution against immediate large-scale experimental testing of SWITHs due to current knowledge and technology limitations. To address this a roadmap with two long-term objectives is outlined as follows: first enabling structural validation tests at scales equivalent to large aircraft for certification; second advancing simulation techniques to complement and eventually reduce reliance on costly experiments while ensuring sufficient accuracy for SWITH certification. This roadmap begins with smaller-scale experimental and numerical studies as an initial step.

Japan and other industrialized countries rely on the import of green hydrogen (H2 ) as they lack the resources to meet their own demand. In contrast countries such as Australia have the potential to produce hydrogen and its derivatives using wind and solar energy. Solar energy can be harnessed to produce electricity using photovoltaic systems or to generate thermal energy by concentrating solar irradiation. Thus thermal and electrical energy can be used in a solid oxide electrolysis process for low-cost hydrogen production. The operation of a solid oxide electrolysis cell (SOEC) stack integrated with solar energy is experimentally investigated and further analyzed using a validated simulation model. Furthermore a techno-economic assessment is conducted to estimate the hydrogen production costs including the expenses associated with liquefaction and transportation from Australia to Japan. High conversion efficiencies and low-cost SOECs are projected to result in production costs below 4 USD/kg.

Hydrogen plays a key role in many industrial applications and is currently seen as one of the most promising energy vectors. Many efforts are being made to produce hydrogen with zero CO 2 footprint via water electrolysis powered by renewable energies. Nevertheless the use of fossil fuels is essentialin the short term. The conventional coal gasification and steam methane reforming processes for hydrogen production are undesirable due to the huge CO2 emissions. A cleaner technologybased on natural gas that has received special attention in recent years is methane pyrolysis. The thermal decomposition of methane gives rise to hydrogen and solid carbon and thus the release of greenhouse gases is prevented. Therefore methane pyrolysis is a CO2-free technology that can serve as a bridge from fossil fuels torenewable energies.

A key factor in reducing the cost of green hydrogen production projects using water electrolysis systems is to minimize the degradation of the electrolyzer stacks as this impacts the lifetime of the stacks and therefore the frequency of their replacement. To create a better understanding of the economics of stack degradation we present a linear optimization approach minimizing the costs of a green hydrogen supply chain including an electrolyzer with degradation modeling. By calculating the levelized cost of hydrogen depending on a variable degradation threshold the cost optimal time for stack replacement can be identified. We further study how this optimal time of replacement is affected by sensitivities such as the degradation scale the load-dependency of both degradation and energy demand and the costs of the electrolyzer. The variation of the identified major sensitivity degradation scale results in a difference of up to 9 years regarding the cost optimal time for stack replacement respectively lifetime of the stacks. Therefore a better understanding of the degradation impact is imperative for project cost reductions which in turn would support a proceeding hydrogen market ramp-up.