Germany

This paper aims to review existing energy-sector and hydrogen-energy-related legal policy and strategy documents in the ECOWAS region. To achieve this aim current renewable-energyrelated laws acts of parliament executive orders presidential decrees administrative orders and memoranda were analyzed. The study shows that ECOWAS countries have strived to design consistent legal instruments regarding renewable energy in developing comprehensive legislation and bylaws to consolidate it and to encourage investments in renewable energy. Despite all these countries having a legislative basis for regulating renewable energy there are still weaknesses that revolve around the law and policy regarding its possible application in green hydrogen production and use. The central conclusion of this review paper is that ECOWAS member states presently have no official hydrogen policies nor bylaws in place. The hydrogen rise presents a challenge and opportunity for members to play an important role in the fast-growing global hydrogen market. Therefore these countries need to reform their regulatory frameworks and align their policies by introducing green hydrogen production in order to accomplish their green economy transition for the future and to boost the continent’s sustainable development.

Hydrogen is a promising fuel to decarbonize aviation but macroeconomic studies are currently missing. Computable general equilibrium (CGE) models are suitable to conduct macroeconomic analyses and are frequently employed in hydrogen and aviation research. The main objective of this paper is to investigate existing CGE studies related to (a) hydrogen and (b) aviation to derive a macroeconomic research agenda for hydrogen-powered aviation. Therefore the well-established method of systematic literature review is conducted. First we provide an overview of 18 hydrogen-related and 27 aviation-related CGE studies and analyze the literature with respect to appropriate categories. Second we highlight key insights and identify research gaps for both the hydrogen and aviation-related CGE literature. Our findings comprise inter alia hydrogen’s current lack of cost competitiveness and the macroeconomic relevance of air transportation. Research gaps include among others a stronger focus on sustainable hydrogen and a more holistic perspective on the air transportation system. Third we derive implications for macroeconomic research on hydrogen-powered aviation including (I) the consideration of existing modeling approaches (II) the utilization of interdisciplinary data and scenarios (III) geographical suitability (IV) the application of diverse policy tools and (V) a holistic perspective. Our work contributes a meaningful foundation for macroeconomic studies on hydrogen-powered aviation. Moreover we recommend policymakers to address the macroeconomic perspectives of hydrogen use in air transportation.

One of the major advantages of SOFCs is their high fuel flexibility. Next to natural gas and hydrogen which are today’s most common fuels for SOFC-systems and cell-/stack-testing respectively various other fuels are applicable as well. In the literature a number of promising results show that available fuels as propane butane ammonia gasoline diesel etc. can be applied. Here the performance of an anode supported cell operated in specialized single cell test benches with different gaseous and liquid fuels and reformates thereof is presented. Fuels as ammonia dissolved urea (AddBlueTM) methane/steam and ethanol/water mixtures can directly be fed to the cell whereas propane and diesel require external reforming. It is shown that in case of a stable fuel supply the cell performance with such fuels is similar to that of appropriate mixtures of H2 N2 CO CO2 and steam if the impact of endothermic reforming or decomposition reactions is considered. Even though a stable fuel cell operation with such fuels is possible in a single cell test bench it should be pointed out that an appropriate fuel processing will be mandatory on the system level.

The goal of achieving water electrolysis on a gigawatt scale faces numerous challenges regarding technological feasibility and market application. Here the flexibility of operation scenarios such as load changes and capacity of electrolysis plays a key role. This raises the question of how flexible electrolysis systems currently are and what possibilities there are to increase flexibility. In order to be able to answer this question in the following a systematic literature research was carried out with the aim to show the current technical possibilities to adapt load and capacity of electrolysis technologies and to determine limits. The result of the systematic literature research is an overview matrix of the electrolysis types AEL PEMEL HTEL and AEMEL already applied in the market. Technical data on the operation of the respective electrolysis stacks as well as details and materials for the respective stack structure (cathode anode electrolyte) were summarized. The flexibility of the individual technologies is addressed by expressing it in values such as load flexibility and startup-times. The overview matrix contains values from various sour1ces in order to make electrolysis comparable at the stack level and to be able to make statements about flexibility. The result of the overview article shows the still open need for research and development to make electrolysis more flexible.

Power-to-X technologies that convert renewable electricity to chemically stored energy in “X” may provide a gaseous liquid or solid fuel that can be used in winter to provide both heat and electricity and thus replace fossil fuels that are currently used in many countries with cold winters. This contribution compares two options for power-to-X technologies for providing heat and electricity supply of buildings with high solar photovoltaic coverage at times of low solar availability. The option “compressed hydrogen” is based on water electrolysis that produces hydrogen on-site. This hydrogen is subsequently compressed and stored at high pressure (350 bar) for use in winter by a fuel cell. The option “aluminium redox-cycle” includes an inert electrode high temperature electrolysis process that is carried out at industrial scale. Produced aluminium is subseqeuntly transported to the site of use and converted to hydrogen and heat – and finally to electricity and heat - by aluminium-water reaction in combination with a fuel cell. Results of cost and LCA analysis show that the overall energetic efficiency of the compressed hydrogen process is slightly higher than for the aluminium redox cycle. However the aluminium redox-cycles needs far less on-site storage volume and is likely to become available at lower investment cost for the end user. Total annual cost of ownership and global warming potential of the two options are quite similar.

Hydrogen produced by water electrolysis and electrochemical batteries are widely considered as primary routes for the long- and short-term storage of photovoltaic (PV) energy. At the same time fast power ramps and idle periods in PV power generation may cause degradation of water splitting electrochemical (EC) cells. Implementation of batteries in PV-EC systems is a viable option for smoothening out intermittence of PV power. Notably the spreading of PV energy over the diurnal cycle reduces power of the EC cell and thus its overpotential loss. We study these potential advantages theoretically and experimentally for a simple parallel connected combination of PV EC and battery cells (PV-EC-B) operated without power management electronics. We show feasibility of the unaided operation of PV-EC-B device in a relevant duty cycle and explore how PV-EC-B system can operate at higher solar-to-hydrogen efficiency than the equivalent reference PV-EC system despite the losses caused by the battery.

This review describes recent research in the development of tank systems based on complex metal hydrides for thermolysis and hydrolysis. Commercial applications using complex metal hydrides are limited especially for thermolysis-based systems where so far only demonstration projects have been performed. Hydrolysis-based systems find their way in space naval military and defense applications due to their compatibility with proton exchange membrane (PEM) fuel cells. Tank design modeling and development for thermolysis and hydrolysis systems as well as commercial applications of hydrolysis systems are described in more detail in this review. For thermolysis mostly sodium aluminum hydride containing tanks were developed and only a few examples with nitrides ammonia borane and alane. For hydrolysis sodium borohydride was the preferred material whereas ammonia borane found less popularity. Recycling of the sodium borohydride spent fuel remains an important part for their commercial viability.

The technological lock-in of the transportation and industrial sector can be largely attributed to the limited availability of alternative fuel infrastructures. Herein a countrywide supply chain analysis of Germany spanning until 2050 is applied to investigate promising infrastructure development pathways and associated hydrogen distribution costs for each analyzed hydrogen market. Analyzed supply chain pathways include seasonal storage to balance fluctuating renewable power generation with necessary purification as well as trailer- and pipeline-based hydrogen delivery. The analysis encompasses green hydrogen feedstock in the chemical industry and fuel cell-based mobility applications such as local buses non-electrified regional trains material handling vehicles and trucks as well as passenger cars. Our results indicate that the utilization of low-cost long-term storage and improved refueling station utilization have the highest impact during the market introduction phase. We find that public transport and captive fleets offer a cost-efficient countrywide renewable hydrogen supply roll-out option. Furthermore we show that at comparable effective carbon tax resulting from the current energy tax rates in Germany hydrogen is cost-competitive in the transportation sector by the year 2025. Moreover we show that sector-specific CO2 taxes are required to provide a cost-competitive green hydrogen supply in both the transportation and industrial sectors.

Hydrogen safety has become the first consideration especially after fuel cell automobiles were pushed into commercial auto market. Tunnels are important parts of traffic infrastructure featured in confinement or semi-confinement. Hydrogen detonation is a potential accident scenario while hydrogen fuel cell vehicles are operated in a traffic tunnel with a confined space. Pressure shockwaves are mostly produced by hydrogen detonation and propagate along the tunnel. As a designed safety measure water mist injection is hopefully to mitigate the pressure loads of such shocks. To model the interaction between shockwaves and water droplets a droplet breakup model has been developed for the COM3D code which is a highly validated three-dimensional hydrogen explosion simulation code. By using the model the hydrogen detonation shockwave propagation in confined volumes is simulated in the study. The attenuation effects of water mist on the pressure shocks in the simulations are elaborated and discussed based on the simulation results.

The accident at Japan's Fukushima Daiichi nuclear power plant in March 2011 caused by an earthquake and a subsequent tsunami resulted in a failure of the power systems that are needed to cool the reactors at the plant. The accident progression in the absence of heat removal systems caused Units 1-3 to undergo fuel melting. Containment pressurization and hydrogen explosions ultimately resulted in the escape of radioactivity from reactor containments into the atmosphere and ocean. Problems in containment venting operation leakage from primary containment boundary to the reactor building improper functioning of standby gas treatment system (SGTS) unmitigated hydrogen accumulation in the reactor building were identified as some of the reasons those added-up in the severity of the accident. The Fukushima accident not only initiated worldwide demand for installation of adequate control and mitigation measures to minimize the potential source term to the environment but also advocated assessment of the existing mitigation systems performance behavior under a wide range of postulated accident scenarios. The uncertainty in estimating the released fraction of the radionuclides due to the Fukushima accident also underlined the need for comprehensive understanding of fission product behavior as a function of the thermal hydraulic conditions and the type of gaseous aqueous and solid materials available for interaction e.g. gas components decontamination paint aerosols and water pools. In the light of the Fukushima accident additional experimental needs identified for hydrogen and fission product issues need to be investigated in an integrated and optimized way. Additionally as more and more passive safety systems such as passive autocatalytic recombiners and filtered containment venting systems are being retrofitted in current reactors and also planned for future reactors identified hydrogen and fission product issues will need to be coupled with the operation of passive safety systems in phenomena oriented and coupled effects experiments. In the present paper potential hydrogen and fission product issues raised by the Fukushima accident are discussed. The discussion focuses on hydrogen and fission product behavior inside nuclear power plant containments under severe accident conditions. The relevant experimental investigations conducted in the technical scale containment THAI (thermal hydraulics hydrogen aerosols and iodine) test facility (9.2 m high 3.2 m in diameter and 60 m3 volume) are discussed in the light of the Fukushima accident.

Using electricity for heating can contribute to decarbonization and provide flexibility to integrate variable renewable energy. We analyze the case of electric storage heaters in German 2030 scenarios with an open-source electricity sector model. We find that flexible electric heaters generally increase the use of generation technologies with low variable costs which are not necessarily renewables. Yet making customary night-time storage heaters temporally more flexible offers only moderate benefits because renewable availability during daytime is limited in the heating season. Respective investment costs accordingly have to be very low in order to realize total system cost benefits. As storage heaters feature only short-term heat storage they also cannot reconcile the seasonal mismatch of heat demand in winter and high renewable availability in summer. Future research should evaluate the benefits of longer-term heat storage.

Greenhouse gas emissions need to be drastically reduced to mitigate the environmental impacts caused by climate change and to lead to a transformation of the European energy system. A model landscape consisting of four final energy consumption sector models with high spatial (NUTS-3) and temporal (hourly) resolution and the multi-energy system model ISAaR is extended and applied to investigate the transformation pathway of the European energy sector in the deep emission mitigation scenario solidEU. The solidEU scenario describes not only the techno-economic but also the socio-political contexts and it includes the EU27 + UK Norway and Switzerland. The scenario analysis shows that volatile renewable energy sources (vRES) dominate the energy system in 2050. In addition the share of flexible sector coupling technologies increases to balance electricity generation from vRES. Seasonal differences are balanced by hydrogen storage with a seasonal storage profile. The deployment rates of vRES in solidEU show that a fast profound energy transition is necessary to achieve European climate protection goals.

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. 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 in a 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 circumstance the turbulence intensified by the water injection can prompt hydrogen combustion which is a negative side-effect of the spray.

Dynamically-operated water electrolyzers enable the production of green hydrogen for cross-sector applications while simultaneously stabilizing power grids. In this study the start-up phase of polymer electrolyte membrane (PEM) water electrolyzers is investigated in the context of intermittent renewable energy sources. During the start-up of the electrolysis system the temperature increases which directly influences hydrogen production efficiency. Experiments on a 100 kWel electrolyzer combined with simulations of electrolyzers with up to 1 MWel were used to analyze the start-up phase and assess its implications for operators and system designers. It is shown that part-load start-up at intermediate cell voltages of 1.80 V yields the highest efficiencies of 74.0 %LHV compared to heat-up using resistive electrical heating elements which reaches maximum efficiencies of 60.9 %LHV. The results further indicate that large-scale electrolyzers with electrical heaters may serve as flexible sinks in electrical grids for durations of up to 15 min.

Background: Naval trafc is highly dependent on depleting fossil resources and causes signifcant greenhouse gas emissions. At the same time marine transportation is a major backbone of world trade. Thus alternative fuel concepts are highly needed. Diferent fuels such as ammonia methanol liquefed natural gas and hydrogen have been proposed. For some of them frst prototype vessels have been in operation. However practical experience is still limited. Most studies so far focus on aspects such as efciency and economics. However particularly in marine applications reliability of propulsion systems is of utmost importance because failures on essential ship components at sea pose a huge safety risk. If the respective components lose their functionality repair can be much more challenging due to large distances to dockyards and the complicated transport of spare parts to the ship. Consequently evaluation of reliability should be a core element of system analysis for new marine fuels. Results: In this study reliability was studied for four potential fuels. The analysis involved several steps: estimation of overall failure rates identifcation of most vulnerable components and assessment of criticality by including severity of fault events. On the level of overall failure rate ammonia is shown to be very promising. Extending the view over a pure failure rate-based evaluation shows that other approaches such as LOHC or methanol can be competitive in terms of reliability and risk. As diferent scenarios require diferent weightings of the diferent reliability criteria the conclusion on the best technology can difer. Relevant aspects for this decision can be the availability of technical staf high-sea or coastal operation the presence of non-naval personnel onboard and other factors. Conclusions: The analysis allowed to compare diferent alternative marine fuel concepts regarding reliability. However the analysis is not limited to assessment of overall failure rates but can also help to identify critical elements that deserve attention to avoid fault events. As a last step severity of the individual failure modes was included. For the example of ammonia it is shown that the decomposition unit and the fuel cell should be subject to measures for increasing safety and reducing failure rates.

The paper presents the first outcomes of the experimental numerical and theoretical studies performed in the funded by Fuel Cell and Hydrogen Joint Undertaking (FCH2 JU) project HyTunnel-CS. The project aims to conduct pre-normative research (PNR) to close relevant knowledge gaps and technological bottlenecks in the provision of safety of hydrogen vehicles in underground transportation systems. Pre normative research performed in the project will ultimately result in three main outputs: harmonised recommendations on response to hydrogen accidents recommendations for inherently safer use of hydrogen vehicles in underground traffic systems and recommendations for RCS. The overall concept behind this project is to use inter-disciplinary and inter-sectoral prenormative research by bringing together theoretical modelling and experimental studies to maximise the impact. The originality of the overall project concept is the consideration of hydrogen vehicle and underground traffic structure as a single system with integrated safety approach. The project strives to develop and offer safety strategies reducing or completely excluding hydrogen-specific risks to drivers passengers public and first responders in case of hydrogen vehicle accidents within the currently available infrastructure.

Hydrogen storage in depleted gas fields is a promising option for the large-scale storage of excess renewable energy. In the framework of the hydrogen storage assessment for the “Underground Sun Storage” project we conduct a multi-step geochemical modelling approach to study fluid–rock interactions by means of equilibrium and kinetic batch simulations. With the equilibrium approach we estimate the long-term consequences of hydrogen storage whereas kinetic models are used to investigate the interactions between hydrogen and the formation on the time scales of typical storage cycles. The kinetic approach suggests that reactions of hydrogen with minerals become only relevant over timescales much longer than the considered storage cycles. The final kinetic model considers both mineral reactions and hydrogen dissolution to be kinetically controlled. Interactions among hydrogen and aqueous-phase components seem to be dominant within the storage-relevant time span. Additionally sensitivity analyses of hydrogen dissolution kinetics which we consider to be the controlling parameter of the overall reaction system were performed. Reliable data on the kinetic rates of mineral dissolution and precipitation reactions specifically in the presence of hydrogen are scarce and often not representative of the studied conditions. These uncertainties in the kinetic rates for minerals such as pyrite and pyrrhotite were investigated and are discussed in the present work. The proposed geochemical workflow provides valuable insight into controlling mechanisms and risk evaluation of hydrogen storage projects and may serve as a guideline for future investigations.

Operators of public electricity grids today are faced with the challenge of integrating increasing numbers of renewable and decentralized energy sources such as wind turbines and photovoltaic power plants into their grids. These sources produce electricity in a very inconstant manner due to the volatility of wind and solar power which further complicates power grid control and management. One key component that is required for modern energy infrastructures is the capacity to store large amounts of energy in an economically feasible way.<br/>One solution that is being discussed in this context is “power-to-gas” i.e. the use of surplus electricity to produce hydrogen (or even methane with an additional methanation process) which is then injected into the public natural gas grid. The huge storage capacity of the gas grid would serve as a buffer offering benefits with regards to sustainability and climate protection while also being cost-effective since the required infrastructure is already in place.<br/>One consequence would be however that the distributed natural gas could contain larger and fluctuating amounts of hydrogen. There is some uncertainty how different gas-fired applications and processes react to these changes. While there have already been several investigations for domestic appliances (generally finding that moderate amounts of H2 do not pose any safety risks which is the primary focus of domestic gas utilization) there are still open questions concerning large-scale industrial gas utilization. Here in addition to operational safety factors like efficiency pollutant emissions (NOX) process stability and of course product quality have to be taken into account.<br/>In a German research project Gas- und Wärme-Institut Essen e. V. (GWI) investigated the impact of higher and fluctuating hydrogen contents (up to 50 vol.-% much higher than what is currently envisioned) on a variety of industrial combustion systems using both numerical and experimental methods. The effects on operational aspects such as combustion behavior flame monitoring and pollutant emissions were analyzed.<br/>Some results of these investigations will be presented in this contribution.

Hydrogen storage is expected to play a crucial role in the comprehensive defossilization of energy systems. In this context the focus is typically on underground hydrogen storage (e.g. in salt caverns). However aboveground storage which is independent of geological conditions and might offer other technical advantages could provide systemic benefits and thereby gain shares in the hydrogen storage market. Against this background this paper examines the market relevance of aboveground compared to underground hydrogen storage. Using the opensource energy system model and optimization framework of Europe PyPSA-Eur the influence of geological independence storage cost relations and technical storage characteristics (i.e. efficiencies) on mentioned market relevance of aboveground hydrogen storage are investigated. Further the expectable market relevance based on current cost projections for the future is assessed. The studies show that in terms of hydrogen capacities aboveground hydrogen storage plays a considerably smaller role compared to underground hydrogen storage. Even when assuming comparatively low aboveground storage cost it will not exceed 1.7% (1.9 TWhH2LHV) of total hydrogen storage capacities in a cost-optimal European energy system. Regarding the amounts of annually stored hydrogen aboveground storage could play a larger role reaching a maximum share of 32.5% (168 TWhH2 LHV a-1) of total stored hydrogen throughout Europe. However these shares are only achievable for low cost storage in particularly suited energy system supply configurations. For higher aboveground storage costs or lower efficiencies shares drop below 10% sharply. The analysis identifies some especially influential factors for achieving higher market relevance. Besides storage costs the demand-orientation of a particular aboveground storage system (e.g. hydrogen storage at demand pressure levels) plays an essential role in market relevance. Further overall efficiency can be a beneficial factor. Still current projections of future techno-economic characteristics show that aboveground hydrogen storage is too expensive or too inefficient compared to underground storage. Therefore to achieve notable market relevance rather drastic cost reductions beyond current expectations would be needed for all assessed aboveground hydrogen storage technologies.

Replacing fossil fuels with energy sources and carriers that are sustainable environmentally benign and affordable is amongst the most pressing challenges for future socio-economic development. To that goal hydrogen is presumed to be the most promising energy carrier. Electrocatalytic water splitting if driven by green electricity would provide hydrogen with minimal CO2 footprint. The viability of water electrolysis still hinges on the availability of durable earth-abundant electrocatalyst materials and the overall process efficiency. This review spans from the fundamentals of electrocatalytically initiated water splitting to the very latest scientific findings from university and institutional research also covering specifications and special features of the current industrial processes and those processes currently being tested in large-scale applications. Recently developed strategies are described for the optimisation and discovery of active and durable materials for electrodes that ever-increasingly harness first principles calculations and machine learning. In addition a technoeconomic analysis of water electrolysis is included that allows an assessment of the extent to which a large-scale implementation of water splitting can help to combat climate change. This review article is intended to cross-pollinate and strengthen efforts from fundamental understanding to technical implementation and to improve the ‘junctions’ between the field’s physical chemists materials scientists and engineers as well as stimulate much-needed exchange among these groups on challenges encountered in the different domains.

The Carbon2Chem project aims to convert exhaust gases from the steel industry into chemicals such as methanol to reduce CO2 emissions. Here H2 is required for the conversion of CO2 into methanol. Although much effort is put to produce H2 from renewables the use of fossil fuels especially natural gas seems to be fundamental in the short term. For this reason the development of clean technologies for the processing of natural gas with a low environmental impact has become a topic of utmost importance. In this context methane pyrolysis has received special attention to produce CO2-free H2.

Hydrogen fuel cell vehicles can complement other electric vehicle technologies as a zeroemission technology and contribute to global efforts to achieve the emission reduction targets. This article spotlights the current deployment status of fuel cells in road transport. For this purpose data collection was performed by the Advanced Fuel Cells Technology Collaboration Programme. Moreover the available incentives for purchasing a fuel cell vehicle in different countries were reviewed and future perspectives summarized. Based on the collected information the development trends in the last five years were analyzed and possible further trends that could see the realization of the defined goals derived. The number of registered vehicles was estimated to be 51437 units with South Korea leading the market with 90% of the vehicles being concentrated in four countries. A total of 729 hydrogen refueling stations were in operation with Japan having the highest number of these. The analysis results clearly indicate a very positive development trend for fuel cell vehicles and hydrogen refueling stations in 2021 with the highest number of new vehicles and stations in a single year paralleling the year’s overall economic recovery. Yet a more ambitious ramp-up in the coming years is required to achieve the set targets.

The production of fat steel products is commonly linked to highly integrated sites which include hot metal generation via the blast furnace basic oxygen furnace (BOF) continuous casting and subsequent hot-rolling. In order to reach carbon neutrality a shift away from traditional carbon-based metallurgy is required within the next decades. Direct reduction (DR) plants are capable to support this transition and allow even a stepwise reduction in CO2 emissions. Nevertheless the implementation of these DR plants into integrated metallurgical plants includes various challenges. Besides metallurgy product quality and logistics special attention is given on future energy demand. On the basis of carbon footprint methodology (ISO 14067:2019) diferent scenarios of a stepwise transition are evaluated and values of possible CO2equivalent (CO2eq) reduction are coupled with the demand of hydrogen electricity natural gas and coal. While the traditional blast furnace—BOF route delivers a surplus of electricity in the range of 0.7 MJ/kg hot-rolled coil; this surplus turns into a defcit of about 17 MJ/ kg hot-rolled coil for a hydrogen-based direct reduction with an integrated electric melting unit. On the other hand while the product carbon footprint of the blast furnace-related production route is 2.1 kg CO2eq/kg hot-rolled coil; this footprint can be reduced to 0.76 kg CO2eq/kg hot-rolled coil for the hydrogen-related route provided that the electricity input is from renewable energies. Thereby the direct impact of the processes of the integrated site can even be reduced to 0.15 kg CO2eq/ kg hot-rolled coil. Yet if the electricity input has a carbon footprint of the current German or European electricity grid mix the respective carbon footprint of hot-rolled coil even increases up to 3.0 kg CO2eq/kg hot-rolled coil. This underlines the importance of the availability of renewable energies.

In contrast to sustainable aviation fuels for use in conventional combustion engines hydrogen-electric powertrains constitute a fundamentally novel approach that requires extensive effort from various engineering disciplines. A transient system analysis has been applied to a 500 kW shaft-power-class powertrain. The model was fed with high-level system requirements to gain a fundamental understanding of the interaction between sub-systems and components. Transient effects such as delays in pressure build up heat transfer and valve operation substantially impact the safe and continuous operation of the propulsion system throughout a typical mission profile which is based on the Daher TBM850. The lumped-parameters network solver provides results quickly which are used to derive requirements for subsystems and components which support their in-depth future development. E.g. heat exchanger transfer rates and pressure drop of the motor's novel hydrogen cooling system are established. Furthermore improvements to the system architecture such as a compartmentalization of the tank are identified.

Hydrogen is one of the most promising power sources for meeting the aviation sector’s long-term decarbonization goals. Although on-board hydrogen systems namely fuel cells are extensively researched the maintenance repair and overhaul (MRO) perspective remains mostly unaddressed. This paper analyzes fuel cells from an MRO standpoint based on a literature review and comparison with the automotive sector. It also examines how well the business models and key resources of MRO providers are currently suited to provide future MRO services. It is shown that fuel cells require extensive MRO activities and that these are needed to meet the aviation sector’s requirements for price safety and especially durability. To some extent experience from the automotive sector can be built upon particularly with respect to facility requirements and qualification of personnel. Yet MRO providers’ existing resources only partially allow them to provide these services. MRO providers’ underlying business models must adapt to the implementation of fuel cells in the aviation sector. MRO providers and services should therefore be considered and act as enablers for the introduction of fuel cells in the aviation industry.