Germany

The glass industry is part of the energy-intensive industry with most of the energy needed to melt the raw materials. To produce glass temperatures between 1000 and 1600 °C are necessary. Presently mostly fossil natural gas is the dominant energy source. As direct electrification is not always possible in this paper a Life Cycle Assessment (LCA) for specialty glass production is conducted where the conventional fossil-based reference process is compared to a hydrogen-fired furnace. This hydrogen can be produced on-site in an water electrolyzer using not only the hydrogen for the combustion but also the produced oxygen. Hydrogen can be produced alternatively off-site in a large scale electrolyzer to facilitate economy of scale. For the transport and distribution of this hydrogen different options are available. A rather new option are liquid organic hydrogen carriers (LOHC) which bind the hydrogen in a chemical substance. However temperatures around 300 °C are necessary to separate the hydrogen from the LOHC after transport. At the glass trough waste heat is available at the required temperature level to facilitate the dehydrogenation. The comparison is completed by the production of off-site hydrogen transported to the glass trough as conventional liquefied hydrogen in cooling tanks by truck or in hydrogen pipelines. In this assessment to power the electrolyzers the national grid mix of Germany is used. A time frame from 2020 till 2050 and its changing energy system towards defossilisation is analyzed. Regarding climate change on-site hydrogen production causes the least impact for specialty glass production in 2050. However negative trade-offs for other environmental impact categories e.g. Metal depletion are recorded.

This work evaluates the effectiveness of chemical-based solutions for storing large amounts of renewable electricity. Four “Power-to-X-to-Power” pathways are examined comprising hydrogen methane methanol and ammonia as energy carriers. The pathways are assessed using a model scenario where they are produced with electricity from an onshore wind farm stored in suitable facilities and then reconverted to electricity to meet the energy demand of a chemical site. An energy management and storage capacity estimation tool is used to calculate the annual load coverage resulting from each pathway. All four pathways offer a significant increase in load coverage compared to a scenario without storage solution (56.19%). The hydrogen-based pathway has the highest load coverage (71.88%) and round-trip efficiency (36.93%) followed by the ammonia-based (69.62% 31.37%) methanol-based (67.85% 27.00%) and methane-based (67.64% 26.47% respectively) pathways. The substantially larger storage capacity required for gaseous energy carriers to ensure a steady supply to the consumer could be a decisive factor. The hydrogen pathway requires a storage volume up to 10.93 times larger than ammonia and 16.87 times larger than methanol. Notably ammonia and methanol whose load coverages are only 2.26 and 4.03 percentage points lower than that of hydrogen offer the possibility of implementing site-specific storage solutions avoiding potential bottlenecks due to limited pipeline and cavern capacities.

Europe’s electricity transmission expansion suffers many delays despite its significance for integrating renewable electricity. A hydrogen network reusing the existing gas network could not only help to supply the demand for low-emission fuels but could also balance variations in wind and solar energies across the continent and thus avoid power grid expansion. Our investigation varies the allowed expansion of electricity and hydrogen grids in net-zero CO2 scenarios for a sector-coupled European energy system capturing transmission bottlenecks renewable supply and demand variability and pipeline retrofitting and geological storage potentials. We find that a hydrogen network connecting regions with low-cost and abundant renewable potentials to demand centers electrofuel production and cavern storage sites reduces system costs by up to 26 bnV/a (3.4%). Although expanding both networks together can achieve the largest cost reductions by 9.9% the expansion of neither is essential for a net-zero system as long as higher costs can be accepted and flexibility options allow managing transmission bottlenecks.

The results shown in this paper extend our research group’s previous work which presents the theoretically achievable hydrogen engine-out NOeo x (H2-NOeo x ) Pareto front of a hydrogen hybrid electric vehicle (H2-HEV). While the Pareto front is calculated offline which requires significant computing power and time this work presents an online-capable algorithm to tackle the energy management of a H2-HEV with explicit consideration of the H2-NOeo x trade-off. Through the inclusion of realistic predictive data on the upcoming driving mission a model predictive control algorithm (MPC) is utilized to effectively tackle the conflicting goal of achieving low hydrogen consumption while simultaneously minimizing NOeo x . In a case study it is shown that MPC is able to satisfy user-defined NOeo x limits over the course of various driving missions. Moreover a comparison with the optimal Pareto front highlights MPC’s ability to achieve close-to-optimal fuel performance for any desired cumulated NOeo x target on four realistic routes for passenger cars.

The realization of a carbon-neutral civilization which has been set as a goal for the coming decades goes directly hand-in-hand with the need for an energy system based on renewable energies (REs). Due to the strong weather-related daily and seasonal fluctuations in supply of REs suitable energy storage devices must be included for such energy systems. For this purpose an energy system model featuring hybrid energy storage consisting of a hydrogen unit (for long-term storage) and a lithium-ion storage device (for short-term storage) was developed. With a proper design such a system can ensure a year-round energy supply by using electricity generated by photovoltaics (PVs). In the energy system that was investigated hydrogen (H2) was produced by using an electrolyser (ELY) with a PV surplus during the summer months and then stored in an H2 tank. During the winter due to the lack of PV power the H2 is converted back into electricity and heat by a fuel cell (FC). While the components of such a system are expensive a resource- and cost-efficient layout is important. For this purpose a Matlab/Simulink model that enabled an energy balance analysis and a component lifetime forecast was developed. With this model the results of extensive parameter studies allowed an optimized system layout to be created for specific applications. The parameter studies covered different focal points. Several ELY and FC layouts different load characteristics different system scales different weather conditions and different load levels—especially in winter with variations in heating demand—were investigated.

With its ability to store and transport energy without releasing greenhouse gases hydrogen is considered an important driver for the decarbonisation of energy systems. As future hydrogen import prices from global markets are subject to large uncertainties it is unclear what impact different hydrogen and derivative import prices will have on the future German energy system. To answer that research question this paper explores the impact of three different import price scenarios for hydrogen and its derivatives on the German energy system in a climate-neutral setting for Europe in 2045 using three different energy system models. The analysis shows that the quantities of electricity generated as well as the installed capacities for electricity generation and electrolysis increase as the hydrogen import price rises. However the resulting differences between the import price scenarios vary across the models. The results further indicate that domestic German (and European) hydrogen production is often cost-efficient.

T The large-scale implementation of solar hydrogen production requires an optimal combination of photovoltaic systems with suitably-designed electrochemical cells possibly avoiding power electronics for DC-DC conversion to decrease costs. Here a stable solar-driven water splitting system is presented obtained through the direct connection of a state-of-the-art proton exchange membrane (PEM) electrolyzer to a bifacial silicon hetero junction (SHJ) solar module of three cells in series with total area of 730 cm2 . The bifaciality of the solar module has been optimized through modeling in terms of the number of cells module height and inclination. During outdoor operation in the standard monofacial configuration the system is able to produce 3.7 gr of H2 h 1 m 2 with an irradiation of 1000 W m 2 and a solar-to-hydrogen efficiency (STH) of 11.55%. The same system operating in bifacial mode gives rise to a higher H2 flux and STH efficiency reaching values of 4.2 gr of H2 h 1 m 2 and STH of 13.5%. Such a noticeable difference is achieved through the collection of albedo radiation from the ground by the bifacial PV system. The system has been tested outdoors for more than 55 h exhibiting very good endurance with no appreciable change in production and eff

The worsening climate crisis has increased the urgency of transitioning energy systems from fossil fuels to renewable sources. However many industrialized countries are struggling to meet their growing demand for renewable energy (RE) through domestic production alone and therefore seek to import additional RE using carriers such as hydrogen ammonia or metals. The pressing question for RE importers is therefore how to select trading partners i.e. RE exporting countries. Recent research has identified a plethora of different selection criteria reflecting the complexity of energy systems and international cooperation. However there is little guidance on how to reduce this complexity to more manageable levels as well as a lack of tools for effective partner evaluation. This article aims to fill these gaps. It proposes a new multidimensional framework for evaluating and comparing potential RE trading partners based on four dimensions: economy and technology environment and development regulation and governance and innovation and cooperation. Focusing on Germany as an RE importer an exploratory factor analysis is used to identify a consolidated set of composite selection criteria across these dimensions. The results suggest that Germany’s neighboring developed countries and current net energy exporters such as Canada and Australia are among the most attractive RE trading partners for Germany. A dashboard tool has been developed to provide the framework and composite criteria including adjustable weights to reflect the varying preferences of decision-makers and stakeholders. The framework and the dashboard can provide helpful guidance and transparency for partner selection processes facilitating the creation of RE trade networks that are essential for a successful energy transition.

Mitigating anthropogenic climate change and achieving the Paris climate goals is one of the greatest challenges of the twenty-first century. To meet the Paris climate goals sector-specific transformation pathways need to be defined. The different transformation pathways are used to hypothetically quantify whether a defined climate target is achievable or not. For this reason a bottom-up model was developed to assess the extent of selected industrial decarbonization options compared to conventionally used technologies from an emissions perspective. Thereby the bottom-up model is used to analyze the German container and flat glass industries as an example. The results show that no transformation pathway can be compatible with the 1.5 °C based strict carbon dioxide budget target. Even the best case scenario exceeds the 1.5 °C based target by approximately +200%. The 2 °C based loose carbon dioxide budget target is only achievable via fuel switching the complete phase-out from natural gas to renewable energy carriers. Furthermore the results of hydrogen for flat glass production demonstrate that missing investments in renewable energy carriers may lead to the non-compliance with actually achievable 2 °C based carbon dioxide budget targets. In conclusion the phase-out from natural gas to renewable energies should be executed at the end of the life of any existing furnace and process emissions should be avoided in the long term to contribute to 1.5 °C based strict carbon dioxide budget target.

In this paper the broader perspective of green hydrogen (H2) supply and refueling systems for aircraft is provided as an enabling technology brick for more climate friendly H2-powered aviation. For this two H2 demand scenarios at exemplary airports are determined for 2050. Then general requirements for liquid hydrogen (LH2) refueling setups in an airport environment are derived and techno-economic models for LH2 storage liquefaction and transportation to the aircraft are designed. Finally a cost tradeoff study is undertaken for the design of the LH2 setup including LH2 refueling trucks and a LH2 pipeline and hydrant system. It is found that for airports with less than 125 ktLH2 annual demand a LH2 refueling truck setup is the more economic choice. At airports with higher annual LH2 demands a LH2 pipeline & hydrant system can lead to slight cost reductions and enable safer and faster refueling. However in all demand scenarios the refueling system costs only mark 3 to 4% of the total supply costs of LH2. The latter are dominated by the costs for green H2 produced offsite followed by the costs for liquefaction of H2 at an airport. While cost reducing scaling effects are likely to be achieved for H2 liquefaction plants other component capacities would already be designed at maximum capacities for medium-sized airports. Furthermore with annual LH2 demands of 100 ktLH2 and more medium and larger airports could take a special H2 hub role by 2050 dominating regional H2 consumption. Finally technology demonstrators are required to reduce uncertainty around major techno-economic parameters such as the investment costs for LH2 pipeline & hydrant systems.

Modern arc processes such as the modified spray arc (Mod. SA) have been developed for gas metal arc welding of high-strength structural steels with which even narrow weld seams can be welded. High-strength joints are subjected to increasingly stringent requirements in terms of welding processing and the resulting component performance. In the present work this challenge is to be met by clarifying the influences on hydrogen-assisted cracking (HAC) in a high-strength structural steel S960QL. Adapted samples analogous to the self-restraint TEKKEN test are used and analyzed with respect to crack formation microstructure diffusible hydrogen concentration and residual stresses. The variation of the seam opening angle of the test seams is between 30° and 60°. To prevent HAC the effectiveness of a dehydrogenation heat treatment (DHT) from the welding heat is investigated. As a result the weld metals produced at reduced weld opening angle show slightly higher hydrogen concentrations on average. In addition increased micro- as well as macro-crack formation can be observed on these weld metal samples. On all samples without DHT cracks in the root notch occur due to HAC which can be prevented by DHT immediately after welding.

This paper is based on a position paper of the German Industry Association Concentrated Solar Power e.V. to the German government and discusses options on how to decarbonize the heat demand of the domestic industry. Among other option concentration solar collectors are a suitable option in Germany which has not been expected by many experts. The paper derives requirements that are needed to ensure a quick and sustainable way to decarbonize industrial heat demand. They are considered to also be relevant for many other countries that follow the same ambition to become climate neutral in the next decades. They major statements are: A mix of different renewable energy technologies in conjunction with efficiency measures is needed to ensure a secure climate-friendly and cost-efficient heat supply for the industry; The different technology options for the provision of heat from renewable sources through electrification and through hydrogen can and must be combined and integrated with each other. In this context concentrating solar thermal represents an important part of the hybrid supply portfolio of a decarbonized industry This requires: The definition of an expansion target for process heat and the flanking measures; Ensuring the equivalence of renewable heat renewable electricity and green hydrogen - also as hybrid solutions; The promotion of concentrating solar thermal reference projects as an impetus for market ramp-up in Germany; The launch of an information campaign for heat consumers and the establishment of a pool of consultants.

With a growing need for replacing fossil fuels with cleaner alternatives hydrogen has emerged as a viable candidate for providing heat and power. However stable and safe combustion of hydrogen is not simple and as such a number of key issues have been identified that need to be understood for a safe design of combustion chambers. One such issue is the higher propensity of hydrogen flames to flashback compared to that for methane flames. The flashback problem is coupled with higher burner temperatures that could cause strong thermal stresses in burners and could hinder their performance. In order to systematically investigate flashback in premixed hydrogen-air flames for finding a global flashback criteria in this study we use numerical simulations as a basic tool to study flashback limits of slit burners. Flashback limits are found for varying geometrical parameters and equivalence ratios and the sensitivity of each parameter on the flashback limit and burner temperatures are identified and analyzed. It is shown that the conventional flashback correlation with critical velocity gradient does not collapse the flashback data as it does not take into account stretch induced preferential diffusion effects. A new Karlovitz number definition is introduced with physical insights that collapses the flashback data at all tested conditions in an excellent manner.

Hydrogen delivered at hydrogen refuelling station must be compliant with requirements stated in different standards which require specialized sampling device and personnel to operate it. Currently different strategies are implemented in different parts of the world and these strategies have already been used to perform 100s of hydrogen fuel sampling in USA EU and Japan. However these strategies have never been compared on a large systematic study. The purpose of this paper is to describe and compare the different strategies for sampling hydrogen at the nozzle and summarize the key aspects of all the existing hydrogen fuel sampling including discussion on material compatibility with the impurities that must be assessed. This review highlights the fact it is currently difficult to evaluate the impact or the difference these strategies would have on the hydrogen fuel quality assessment. Therefore comparative sampling studies are required to evaluate the equivalence between the different sampling strategies. This is the first step to support the standardization of hydrogen fuel sampling and to identify future research and development area for hydrogen fuel sampling.

Hydrogen mobility is one option for reducing local emissions avoiding greenhouse gas (GHG) emissions and moving away from a mainly oil-based transport system towards a diversification of energy sources. As hydrogen production can be based on a broad variety of technologies already existing or under development a comprehensive assessment of the different supply chains is necessary regarding not only costs but also diverse environmental impacts. Therefore in this paper a broad variety of hydrogen production technologies using different energy sources renewable and fossil are exemplarily assessed with the help of a Life Cycle Assessment and a cost assessment for Germany. As environmental impacts along with the impact category Climate change five more advanced impact categories are assessed. The results show that from an environmental point of view PEM and alkaline electrolysis are characterized by the lowest results in five out of six impact categories. Supply chains using fossil fuels in contrast have the lowest supply costs; this is true e.g. for steam methane reforming. Solar powered hydrogen production shows low impacts during hydrogen production but high impacts for transport and distribution to Germany. There is no single supply chain that is the most promising for every aspect assessed here. Either costs have to be lowered further or supply chains with selected environmental impacts have to be modified.

The concept of sector coupling has been gaining increased momentum in political discourses during 18 the past few years but it has only recently received the attention of international academics. The 19 private sector is particularly relevant to foster sector coupling through entrepreneurial action – 20 specifically innovative business models for more sustainable technologies are needed to promote a 21 transition towards more sustainability. So far however the literature on business models from a 22 sector coupling perspective is scarce yet strongly emerging. To address the identified research gaps 23 and enhance the current knowledge on the emerging hydrogen vehicle industry and sector coupling 24 this study adopts a qualitative and exploratory research approach and builds on information gained 25 in 103 semi-structured interviews to discuss emerging business models in Germany. In particular 33 26 business cases have been analyzed. Anchoring business model theory to the concept of sector 27 coupling this study identifies 12 business model archetypes in the emerging hydrogen vehicle 28 industry and its value chain. It can be shown that while the market is still emerging and the market 29 players are not defined and are evolving companies are currently engaged in finding their position 30 along the value chain fostering vertical integration and promoting cooperation between the 31 different sectors. While this study is relevant for both the academia and the industry it is particularly 2 32 interesting for policy makers shaping the future of sustainable development specifically considering 33 integrated energy systems.

Aircraft powered by green hydrogen (H2) are a lever for the aviation sector to reduce the climate impact. Previous research already focused on evaluations of H2 aircraft technology but analyses on infrastructure related cost factors are rarely undertaken. Therefore this paper aims to provide a holistic overview of previous efforts and introduces an approach to assess the importance of a H2 infrastructure for aviation. A short and a medium-range aircraft are modelled and modified for H2 propulsion. Based on these a detailed cost analysis is used to compare both aircraft and infrastructure related direct operating costs (DOC). Overall it is shown that the economy of H2 aviation highly depends on the availability of low-cost green liquid hydrogen (LH2) supply infrastructure. While total DOC might even slightly decrease in a best LH2 cost case total DOC could also increase between 10 and 70% (short-range) and 15e102% (medium-range) due to LH2 costs alone.

The anticipated upscaling of hydrogen energy applications will involve the storage and transport of hydrogen at cryogenic conditions. Understanding the potential hazard arising from leaks in high-pressure cryogenic storage is needed to improve hydrogen safety. The manuscript reports a series of numerical simulations with detailed chemistry for the transient evolution of ignited high-pressure cryogenic hydrogen jets. The study aims to gain insight of the ignition processes flame structures and dynamics associated with the transient flame evolution. Numerical simulations were firstly conducted for an unignited jet released under the same cryogenic temperature of 80 K and pressure of 200 bar as the considered ignited jets. The predicted hydrogen concentrations were found to be in good agreement with the experimental measurements. The results informed the subsequent simulations of the ignited jets involving four different ignition locations. The predicted time series snapshots of temperature hydrogen mass fraction and the flame index are analyzed to study the transient evolution and structure of the flame. The results show that a diffusion combustion layer is developed along the outer boundary of the jet and a side diffusion flame is formed for the near-field ignition. For the far-field ignition an envelope flame is observed. The flame structure contains a diffusion flame on the outer edge and a premixed flame inside the jet. Due to the complex interactions between turbulence fuel-air mixing at cryogenic temperature and chemical reactions localized spontaneous ignition and transient flame extinguishment are observed. The predictions also captured the experimentally observed deflagration waves in the far-field ignited jets.

This study aimed to simulate the sector-coupled energy system of Germany in 2030 with the restriction on CO2 emission levels and to observe how the system evolves with decreasing emissions. Moreover the study presented an analysis of the interconnection between electricity heat and hydrogen and how technologies providing flexibility will react when restricting CO2 emissions levels. This investigation has not yet been carried out with the technologies under consideration in this study. It shows how the energy system behaves under different set boundaries of CO2 emissions and how the costs and technologies change with different emission levels. The study results show that the installed capacities of renewable technologies constantly increase with higher limitations on emissions. However their usage rates decreases with low CO2 emission levels in response to higher curtailed energy. The sector-coupled technologies behave differently in this regard. Heat pumps show similar behaviour while the electrolysers usage rate increases with more renewable energy penetration. The system flexibility is not primarily driven by the hydrogen sector but in low CO2 emission level scenarios the flexibility shifts towards the heating sector and electrical batteries.

Hydrogen has set high hopes for decarbonization due to its flexibility and ability to decarbonize sectors of the economy where direct electrification appears unviable. Broad hydrogen policies have therefore started to emerge. Nevertheless it is still a rather niche technology not integrated or adopted at scale and not regulated through particular policy provisions. The involved stakeholders are thus still rushing to set the agenda over the issue. All this plays out publicly and shapes the public discourse. This paper explores how the composition of stakeholders their positions and the overall discourse structure have developed and accompanied the political agenda-setting in the early public debate on hydrogen in Germany. We use discourse network analysis of media where stakeholders' claims-making is documented and their positions can be tracked over time. The public discourse on hydrogen in Germany shows the expected evolution of statements in connection with the two milestones chosen for the analyses the initiation of the Gas 2030 Dialogue and the publication of the National Hydrogen Strategy. Interestingly the discourse was comparatively feeble in the immediate aftermath of the respective milestones but intensified in a consolidation phase around half a year later. Sequencing the discourse and contextualizing its content relative to political societal and economic conditions in a diachronic way is essential because it helps to avoid misinterpreting the development of stakeholders' standpoints as conflict-driven rather than mere repositioning. Thus we observed no discourse “polarization” even though potentially polarizing issues were already present in the debate.

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.

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.

The goal of the European energy policy is to achieve climate neutrality. The long-term energy strategies of various European countries include additional targets such as the diversification of energy sources maintenance of security of supply and reduction of import dependency. When optimizing energy systems these strategic policy targets are often only considered in a rudimentary manner and thus the understanding of the corresponding interdependencies is lacking. Moreover hydrogen is considered as a key component of a fully decarbonized energy system but its role in the power sector remains unclear due to the low round-trip efficiencies. This study reveals how fully decarbonized European power systems can benefit from hydrogen in terms of overall system costs and the achievement of strategic policy targets. We analyzed a broad spectrum of scenarios using an energy system optimization model and varied model constraints that reflect strategic policy targets. Our results are threefold. First compared to power systems without hydrogen systems using hydrogen realize savings of 14–16% in terms of the total system costs. Second the implementation of a hydrogen infrastructure reduces the number of infeasible scenarios when structural policy targets are considered within the power system. Third the role of hydrogen is highly diverse at a national level. Particularly in countries with low renewable energy potential hydrogen plays a crucial role. Here high levels of self-sufficiency and security of supply are achieved by deploying hydrogen-based power generation of up to 46% of their annual electricity demand realized via imports of green hydrogen.

To abate climate change and ameliorate the air quality in urban areas innovative solutions are required to reduce CO2 and pollutant emissions from traffic. Alternative fuels made from biomass or CO2 and hydrogen can contribute to these goals by substituting fossil gasoline or diesel in combustion engines. Using a conjoint analysis approach the current study investigates preferences of laypeople (n = 303) for fuel production facilities in terms of siting location plant size raw material used in the production and raw material transport. The location was most decision-relevant followed by raw material transport whereas plant size and type of raw material played a less prominent role for the preference choice. The best-case scenario from the point of view of acceptance would be the installation of a rather small bio-hybrid fuel production plant in an industrial area (instead of an agricultural or pristine environment). No transport or transport via underground pipeline were preferred over truck/tank car or overground pipeline. The findings can be used as a basis for planning and decision-making for designing production networks for new fuel types.

The European Commission aims to establish green hydrogen produced through electrolysis using renewable electricity and in a transition phase hydrogen produced in a low-carbon process or blue hydrogen. In an extensive cost analysis for Germany up to 2050 based on scenario data and a component-based learning rate approach we find that blue hydrogen is likely to establish itself as the most cost-effective option and not only as a medium-term low-carbon alternative. We find that expected CO2 prices below €480/tCO2 have a limited impact on the economic feasibility of electrolysis and show that substantial increases in excise tax on natural gas could lead blue hydrogen to reach a sufficient cost level for electrolysed hydrogen. Unless alternatives for green hydrogen supply through infrastructure and imports become available at lower cost electrolysed hydrogen may require long-term subsidies. As blue hydrogen comprises fugitive methane emissions and financing needs for green hydrogen support have implications for society and competition in the internal market we suggest that policymakers rely on hydrogen for decarbonising only essential energy applications. We recommend further investigations into the cost of hydrogen infrastructure and import options as well as efficient subsidy frameworks.

The global transition to a clean and sustainable energy infrastructure does not stop at aviation. The European Commission defined a set of environmental goals for the “Flight Path 2050”: 75% CO2 reduction 90% NOx reduction and 65% perceived noise reduction. Hydrogen as an energy carrier fulfills these needs while it would also offer a tenable and flexible solution for intermittent large-scale energy storage for renewable energy networks. If hydrogen is used as an energy carrier there is no better device than a fuel cell to convert its stored chemical energy. In order to design fuel cell systems for passenger aircraft it is necessary to specify the requirements that the system has to fulfill. In this paper a statistical approach to analyze these requirements is presented which accounts for variations in the flight mission profile. Starting from a subset of flight data within the desired class (e.g. mid-range inter-European flights) a stochastic model of the random mission profile is inferred. This model allows for subsequent predictions under uncertainty as part of the aircraft design process. By using Monte Carlo-based sampling of flight mission profiles the range of necessary component sizes as well as optimal degrees of hybridization with a battery is explored and design options are evaluated. Furthermore Monte Carlo-based sensitivity analysis of performance parameters explores the potential of future technological developments. Results suggest that the improvement of the specific power of the fuel cell is the deciding factor for lowering the energy system mass. The specific energy of the battery has a low influence but acts in conjunction with the specific power of the fuel cell.

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.

Hydrogen has the potential to decarbonize a variety of energy-intensive sectors including steel production. Using the life cycle assessment (LCA) methodology the state of the art is given for current hydrogen production with a focus on the hydrogen carbon footprint. Beside the state of the art the outlook on different European scenarios up to the year 2040 is presented. A case study of the transformation of steel production from coal-based towards hydrogen- and electricity-based metallurgy is presented. Direct reduction plants with integrated electric arc furnaces enable steel production which is almost exclusively based on hydrogen and electricity or rather on electricity alone if hydrogen stems from electrolysis. Thus an integrated steel site has a demand of 4.9 kWh of electric energy per kilogram of steel. The carbon footprint of steel considering a European sustainable development scenario concerning the electricity mix is 0.75 kg CO2eq/kg steel in 2040. From a novel perspective a break-even analysis is given comparing the use of natural gas and hydrogen using different electricity mixes. The results concerning hydrogen production presented in this paper can also be transferred to application fields other than steel.

Power-to-X processes where renewable energy is converted into storable liquids or gases are considered to be one of the key approaches for decarbonizing energy systems and compensating for the volatility involved in generating electricity from renewable sources. In this context the production of “green” hydrogen and hydrogen-based derivatives is being discussed and tested as a possible solution for the energy-intensive industry sector in particular. Given the sharp ongoing increases in electricity and gas prices and the need for sustainable energy supplies in production systems non-energy-intensive companies should also be taken into account when considering possible utilization paths for hydrogen. This work focuses on the following three utilization paths: “hydrogen as an energy storage system that can be reconverted into electricity” “hydrogen mobility” for company vehicles and “direct hydrogen use”. These three paths are developed modeled simulated and subsequently evaluated in terms of economic and environmental viability. Different photovoltaic system configurations are set up for the tests with nominal power ratings ranging from 300 kWp to 1000 kWp. Each system is assigned an electrolyzer with a power output ranging between 200 kW and 700 kW and a fuel cell with a power output ranging between 5 kW and 75 kW. There are also additional variations in relation to the battery storage systems within these basic configurations. Furthermore a reference variant without battery storage and hydrogen technologies is simulated for each photovoltaic system size. This means that there are ultimately 16 variants to be simulated for each utilization path. The results show that these utilization paths already constitute a reasonable alternative to fossil fuels in terms of costs in variants with a suitable energy system design. For the “hydrogen as an energy storage system” path electricity production costs of between 43 and 79 ct/kWh can be achieved with the 750 kWp photovoltaic system. The “hydrogen mobility” is associated with costs of 12 to 15 ct/km while the “direct hydrogen use” path resulted in costs of 8.2 €/kg. Environmental benefits are achieved in all three paths by replacing the German electricity mix with renewable energy sources produced on site or by substituting hydrogen for fossil fuels. The results confirm that using hydrogen as a storage medium in manufacturing companies could be economically and environmentally viable. These results also form the basis for further studies e.g. on detailed operating strategies for hydrogen technologies in scenarios involving a combination of multiple utilization paths. The work also presents the simulation-based method developed in this project which can be transferred to comparable applications in further studies.

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.

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.

Background: The widespread use of sustainable energy technologies is a key element in the transformation of the energy system from fossil-based to zero-carbon. In line with this technology acceptance is of great importance as resistance from the public can slow down or hinder the construction of energy technology projects. The current study assesses the social acceptance of three energy technologies relevant for the German energy transition: stationary battery storage biofuel production plants and hydrogen fuel station. Methods: An online survey was conducted to examine the public’s general and local acceptance of energy technologies. Explored factors included general and local acceptance public concerns trust in relevant stakeholders and attitudes towards financial support. Results: The results indicate that general acceptance for all technologies is slightly higher than local acceptance. In addition we discuss which public concerns exist with regard to the respective technologies and how they are more strongly associated with local than general acceptance. Further we show that trust in stakeholders and attitudes towards fnancial support is relatively high across the technologies discussed. Conclusions: Taken together the study provides evidence for the existence of a “general–local” gap despite measuring general and local acceptance at the same level of specifcity using a public sample. In addition the collected data can provide stakeholders with an overview of worries that might need to be addressed when planning to implement a certain energy project.

The importing of renewable energy will be one part of the process of defossilizing the energy systems of countries and regions which are currently heavily dependent on the import of fossil-based energy carriers. This study investigates the possibility of importing renewable methanol comprised of hydrogen and carbon dioxide. Based on a methanol synthesis simulation model the net production costs of methanol are derived as a function of hydrogen and carbon dioxide expenses. These findings enable a comparison of the import costs of methanol and hydrogen. For this the hydrogen production and distribution costs for 2030 as reported in a recent study for four different origin/destination country combinations are considered. With the predicted hydrogen production costs of 1.35–2 €/kg and additional shipping costs methanol can be imported for 370–600 €/t if renewable or process-related carbon dioxide is available at costs of 100 €/t or below in the hydrogen-producing country. Compared to the current fossil market price of approximately 400 €/t renewable methanol could therefore become cost-competitive. Within the range of carbon dioxide prices of 30–100 €/t both hydrogen and methanol exhibit comparable energy-specific import costs of 18–30 €/GJ. Hence the additional costs for upgrading hydrogen to methanol are balanced out by the lower shipping costs of methanol compared to hydrogen. Lastly a comparison for producing methanol in the hydrogen’s origin or destination country indicates that carbon dioxide in the destination country must be 181–228 €/t less expensive than that in the origin country to balance out the more expensive shipping costs for hydrogen.

The increasing demand for renewable energy storage may position hydrogen as one of the major players in the future energy system. However to introduce such technology high level of safety must be offered. In particular for the accident scenarios with combustion or explosion of the unintendedly released hydrogen in partially or fully confined volumes such as e.g. road tunnel the effective countermeasures preventing or reducing the risk of equipment damages and person injuries should be established. A mitigation strategy could be the use of existing fire suppression system which can inject water as a spray. The shock waves resulted from hydrogen explosion could be weakened by the water droplets met on the shock path. In the presented work an attenuation effect of water droplets presence on the strength of the passing shock was studied. The analysis of the different attenuation mechanisms was performed and estimation of the effect of spray parameters such as droplet size and spray density on the shock wave was carried out. For the quantitative evaluation of the attenuation potential a numerical model for the COM3D combustion code was developed. The novel model for the droplet behavior accounting for the realistic correlations for the fluid (water) particle drag force linked with the corresponding droplet breakup model describing droplet atomization is presented. The model was validated against literature experimental data and was used for the blind simulations of the hydrogen test facility in KIT.

The use of fossil fuels has caused many environmental issues including greenhouse gas emissions and associated climate change. Several studies have focused on mitigating this problem. One dynamic direction for emerging sources of future renewable energy is the use of hydrogen energy. In this research we evaluate the sourcing decision for a hydrogen supply chain in the context of a case study in Thailand using group decision making analysis for policy implications. We use an integrative multi-criteria decision analysis (MCDA) tool which includes an analytic hierarchy process (AHP) fuzzy AHP (FAHP) and data envelopment analysis (DEA) to analyze weighted criteria and sourcing alternatives using data collected from a group of selected experts. A list of criteria related to sustainability paradigms and sourcing decisions for possible use of hydrogen energy including natural gas coal biomass and water are evaluated. Our results reveal that political acceptance is considered the most important criterion with a global weight of 0.514 in the context of Thailand. Additionally natural gas is found to be the foreseeable source for hydrogen production in Thailand with a global weight of 0.313. We also note that the analysis is based on specific data inputs and that an alternative with a lower score does not imply that the source is not worth exploring.

Green liquid hydrogen (LH2) could play an essential role as a zero-carbon aircraft fuel to reach long-term sustainable aviation. Excluding challenges such as electrolysis transportation and use of renewable energy in setting up hydrogen (H2) fuel infrastructure this paper investigates the interface between refueling systems and aircraft and the impacts on fuel distribution at the airport. Furthermore it provides an overview of key technology design decisions for LH2 refueling procedures and their effects on the turnaround times as well as on aircraft design. Based on a comparison to Jet A-1 refueling new LH2 refueling procedures are described and evaluated. Process steps under consideration are connecting/disconnecting purging chill-down and refueling. The actual refueling flow of LH2 is limited to a simplified Reynolds term of v · d = 2.35 m2/s. A mass flow rate of 20 kg/s is reached with an inner hose diameter of 152.4 mm. The previous and subsequent processes (without refueling) require 9 min with purging and 6 min without purging. For the assessment of impacts on LH2 aircraft operation process changes on the level of ground support equipment are compared to current procedures with Jet A-1. The technical challenges at the airport for refueling trucks as well as pipeline systems and dispensers are presented. In addition to the technological solutions explosion protection as applicable safety regulations are analyzed and the overall refueling process is validated. The thermodynamic properties of LH2 as a real compressible fluid are considered to derive implications for airport-side infrastructure. The advantages and disadvantages of a subcooled liquid are evaluated and cost impacts are elaborated. Behind the airport storage tank LH2 must be cooled to at least 19 K to prevent two-phase phenomena and a mass flow reduction during distribution. Implications on LH2 aircraft design are investigated by understanding the thermodynamic properties including calculation methods for the aircraft tank volume and problems such as cavitation and two-phase flows. In conclusion the work presented shows that LH2 refueling procedure is feasible compliant with the applicable explosion protection standards and hence does not impact the turnaround procedure. A turnaround time comparison shows that refueling with LH2 in most cases takes less time than with Jet A-1. The turnaround at the airport can be performed by a fuel truck or a pipeline dispenser system without generating direct losses i.e. venting to the atmosphere.

Carbon neutrality (or climate neutrality) has been a global consensus and international experience exchange is essential. Given the differences in the degree of social development resource endowment and technological level each country should build a carbon-neutral plan based on its national conditions. Compared with other major developed countries (e.g. Germany the United States and Japan) China's carbon neutrality has much bigger challenges including a heavy and time-pressured carbon reduction task and the current energy structure that is over-dependent on fossil fuels. Here we provide a comprehensive review of the status and prospects of the key technologies for low-carbon near-zero carbon and negative carbon emissions. Technological innovations associated with coal oil-gas and hydrogen industries and their future potential in reducing carbon emissions are particularly explained and assessed. Based on integrated analysis of international experience from the world's major developed countries in-depth knowledge of the current and future technologies and China's energy and ecological resources potential five lessons for the implementation of China's carbon neutrality are proposed: (1) transformation of energy production pattern from a coal-dominated pattern to a diversified renewable energy pattern; (2) renewable power-to-X and large-scale underground energy storage; (3) integration of green hydrogen production storage transport and utilization; (4) construction of clean energy systems based on smart sector coupling (ENSYSCO); (5) improvement of ecosystem carbon sinks both in nationwide forest land and potential desert in Northwest China. This paper provides an international perspective for a better understanding of the challenges and opportunities of carbon neutrality in China and can serve as a theoretical foundation for medium-long term carbon neutral policy formulation.

The rising demand for energy and the aim of moving away from fossil fuels and to low-carbon power have led many countries to move to alternative sources including solar energy wind geothermal energy biomass and hydrogen. Hydrogen is often considered a “missing link” in guaranteeing the energy transition providing storage and covering the volatility and intermittency of renewable energy generation. However due to potential injustice with regard to the distribution of risks benefits and costs (i.e. in regard to competing for land use) the large-scale deployment of hydrogen is a contested policy issue. This paper draws from a historical analysis of past energy projects to contribute to a more informed policy-making process toward a more just transition to the hydrogen economy. We perform a systematic literature review to identify relevant conflict factors that can influence the outcome of hydrogen energy transition projects in selected Economic Community of West African States countries namely Nigeria and Mali. To better address potential challenges policymakers must not only facilitate technology development access and market structures for hydrogen energy policies but also focus on energy access to affected communities. Further research should monitor hydrogen implementation with a special focus on societal impacts in producing countries.

Jet flames originated by cryo-compressed ignited hydrogen releases can cause life-threatening conditions in their surroundings. Validated models are needed to accurately predict thermal hazards from a jet fire. Numerical simulations of cryogenic hydrogen flow in the release pipe are performed to assess the effect of heat transfer through the pipe walls on jet parameters. Notional nozzle exit diameter is calculated based on the simulated real nozzle parameters and used in CFD simulations as a boundary condition to model jet fires. The CFD model was previously validated against experiments with vertical cryogenic hydrogen jet fires with release pressures up to 0.5 MPa (abs) release diameter 1.25 mm and temperatures as low as 50 K. This study validates the CFD model in a wider domain of experimental release conditions - horizontal cryogenic jets at exhaust pipe temperature 80 K pressure up to 2 MPa abs and release diameters up to 4 mm. Simulation results are compared against experimentally measured parameters as hydrogen mass flow rate flame length and radiative heat flux at several locations from the jet fire. The CFD model reproduces well experiments with reasonable engineering accuracy. Jet fire hazard distances established using three different criteria - temperature thermal radiation and thermal dose - are compared and discussed based on CFD simulation results.

The liquid hydrogen demand particularly driven by clean energy applications will rise in the near future. As industrial large scale liquefiers will play a major role within the hydrogen supply chain production capacity will have to increase by a multiple of today’s typical sizes. The main goal is to reduce the total cost of ownership for these plants by increasing energy efficiency with innovative and simple process designs optimized in capital expenditure. New concepts must ensure a manageable plant complexity and flexible operability. In the phase of process development and selection a dimensioning of key equipment for large scale liquefiers such as turbines and compressors as well as heat exchangers must be performed iteratively to ensure technological feasibility and maturity. Further critical aspects related to hydrogen liquefaction e.g. fluid properties ortho-para hydrogen conversion and coldbox configuration must be analysed in detail. This paper provides an overview on the approach challenges and preliminary results in the development of efficient as well as economically viable concepts for large-scale hydrogen liquefaction.

With the growth of aviation traffic and the demand for emission reduction alternative fuels like the so-called electrofuels could comprise a sustainable solution. Electrofuels are understood as those that use renewable energy for fuel synthesis and that are carbon-neutral with respect to greenhouse gas emission. In this study five potential electrofuels are discussed with respect to the potential application as aviation fuels being n-octane methanol methane hydrogen and ammonia and compared to conventional Jet A-1 fuel. Three important aspects are illuminated. Firstly the synthesis process of the electrofuel is described with its technological paths its energy efficiency and the maturity or research need of the production. Secondly the physico-chemical properties are compared with respect to specific energy energy density as well as those properties relevant to the combustion of the fuels i.e. autoignition delay time adiabatic flame temperature laminar flame speed and extinction strain rate. Results show that the physical and combustion properties significantly differ from jet fuel except for n-octane. The results describe how the different electrofuels perform with respect to important aspects such as fuel and air mass flow rates. In addition the results help determine mixture properties of the exhaust gas for each electrofuel. Thirdly a turbine configuration is investigated at a constant operating point to further analyze the drop-in potential of electrofuels in aircraft engines. It is found that electrofuels can generally substitute conventional kerosene-based fuels but have some downsides in the form of higher structural loads and potentially lower efficiencies. Finally a preliminary comparative evaluation matrix is developed. It contains specifically those fields for the different proposed electrofuels where special challenges and problematic points are seen that need more research for potential application. Synthetically-produced n-octane is seen as a potential candidate for a future electrofuel where even a drop-in capability is given. For the other fuels more issues need further research to allow the application as electrofuels in aviation. Specifically interesting could be the combination of hydrogen with ammonia in the far future; however the research is just at the beginning stage.

Hydrogen energy applications often require that systems are used indoors (e.g. industrial trucks for materials handling in a warehouse facility fuel cells located in a room or hydrogen stored and distributed from a gas cabinet). It may also be necessary or desirable to locate some hydrogen system components/equipment inside indoor or outdoor enclosures for security or safety reasons to isolate them from the end-user and the public or from weather conditions.<br/>Using of hydrogen in confined environments requires detailed assessments of hazards and associated risks including potential risk prevention and mitigation features. The release of hydrogen can potentially lead to the accumulation of hydrogen and the formation of a flammable hydrogen-air mixture or can result in jet-fires. Within Hyindoor European Project carried out for the EU Fuel Cells and Hydrogen Joint Undertaking safety design guidelines and engineering tools have been developed to prevent and mitigate hazardous consequences of hydrogen release in confined environments. Three main areas are considered: Hydrogen release conditions and accumulation vented deflagrations jet fires and including under-ventilated flame regimes (e.g. extinguishment or oscillating flames and steady burns). Potential RCS recommendations are also identified.

Liquid hydrogen (LH2) compared to compressed gaseous hydrogen offers advantages for large-scale transport and storage of hydrogen with higher densities. Although the gas industry has good experience with LH2 only little experience is available for the new applications of LH2 as an energy carrier. Therefore the European FCH JU funded project PRESLHY conducted pre-normative research for the safe use of cryogenic LH2 in non-industrial settings. The central research consisted of a broad experimental program combined with analytical work modelling and simulations belonging to the three key phenomena of the accident chain: release and mixing ignition and combustion. The presented results improve the general understanding of the behavior of LH2 in accidents and provide some design guidelines and engineering tools for safer use of LH2. Recommendations for improvement of current international standards are derived.

For a green economy to be possible in the near future hydrogen production from water is a sought-after alternative to fossil fuels. It is however important to put things into context with respect to global CO2 emission and the role of hydrogen in curbing it. The present world annual production of hydrogen is about 70 million metric tons of which almost 50% is used to make ammonia NH3 (that is mostly used for fertilizers) and about 15% is used for other chemicals [1]. The hydrogen produced worldwide is largely made by steam CH4 reforming (SMR) which is one of the most energy-intensive processes in the chemical industry [2]. It releases based on reaction stoichiometry 5.5 kg of CO2 per 1 kg of H2 (CH4+ 2 H2O → CO2 + 4 H2). When the process itself is taken into account in addition the production [3] becomes about 9 kg of CO2 per kg of H2 and this ratio can be as high as 12 [4]. This results in the production of about one billion tons/year of CO2. The world annual CO2 emission from fossil fuels is however much larger: it is about 36 billion tons of which roughly 25% is emitted while generating electricity and heat 20% due to transport activity and 20% from other industrial processes. Because of the link between global warming and CO2 emissions there is an increasing move towards finding alternative approaches for energy vectors and their applications.

The European Union set a 2050 decarbonization target in the Paris Agreement to reduce carbon emissions by 90–95% relative to 1990 emission levels. The path toward achieving those deep decarbonization targets can take various shapes but will surely include a portfolio of economy-wide low-carbon energy technologies/options. The growth of the intermittent renewable power sources in the grid mix has helped reduce the carbon footprint of the electric power sector. Under the need for decarbonizing the electric power sector we simulated a low-carbon power system. We investigated the role of hydrogen for future electric power systems under current cost projections. The model optimizes the power generation mix economically for a given carbon constraint. The generation mix consists of intermittent renewable power sources (solar and wind) and dispatchable gas turbine and combined cycle units fuelled by natural gas with carbon capture and sequestration as well as hydrogen. We created several scenarios with battery storage options pumped hydro hydrogen storage and demand-side response (DSR). The results show that energy storage replaces power generation and pumped hydro entirely replaces battery storage under given conditions. The availability of pumped hydro storage and demand-side response reduced the total cost as well as the combination of solar photovoltaic and pumped hydro storage. Demand-side response reduces relatively costly dispatchable power generation reduces annual power generation halves the shadow carbon price and is a viable alternative to energy storage. The carbon constrain defines the generation mix and initializes the integration of hydrogen (H₂). Although the model rates power to gas with hydrogen as not economically viable in this power system under the given conditions and assumptions hydrogen is important for hard-to-abate sectors and enables sector coupling in a real energy system. This study discusses the potential for hydrogen beyond this model approach and shows the differences between cost optimization models and real-world feasibility.

High-strength steels with yield strength of 960 MPa are susceptible to hydrogen-assisted cracking (HAC) during welding processing. In the present paper the implant test is used to study HAC in a quenched and tempered steel S960QL and a high-strength steel produced by thermo-mechanical controlled process S960MC. Welding is performed using the gas-metal arc welding process. Furthermore diffusible hydrogen concentration (H_D) in arc weld metal is determined. Based on the implant test results lower critical stress (LCS) for complete fracture critical implant stress (σ_krit) for crack initiation and embrittlement index (EI) are determined. At HD of 1.66 ml/100 g LCS is 605 MPa and 817 MPa for S960QL and S960MC respectively. EI is 0.30 and 0.46 for S960QL and S960MC respectively. Fracture surfaces of S960QL show higher degradation with reduced deformation. Both higher EI of S960MC and fractography show better resistance to HAC in the HAZ of S960MC compared to S960QL.

Fully decarbonizing global industry is essential to achieving climate stabilization and reaching net zero greenhouse gas emissions by 2050–2070 is necessary to limit global warming to 2 °C. This paper assembles and evaluates technical and policy interventions both on the supply side and on the demand side. It identifies measures that employed together can achieve net zero industrial emissions in the required timeframe. Key supply-side technologies include energy efficiency (especially at the system level) carbon capture electrification and zero-carbon hydrogen as a heat source and chemical feedstock. There are also promising technologies specific to each of the three top-emitting industries: cement iron & steel and chemicals & plastics. These include cement admixtures and alternative chemistries several technological routes for zero-carbon steelmaking and novel chemical catalysts and separation technologies. Crucial demand-side approaches include material-efficient design reductions in material waste substituting low-carbon for high-carbon materials and circular economy interventions (such as improving product longevity reusability ease of refurbishment and recyclability). Strategic well-designed policy can accelerate innovation and provide incentives for technology deployment. High-value policies include carbon pricing with border adjustments or other price signals; robust government support for research development and deployment; and energy efficiency or emissions standards. These core policies should be supported by labeling and government procurement of low-carbon products data collection and disclosure requirements and recycling incentives. In implementing these policies care must be taken to ensure a just transition for displaced workers and affected communities. Similarly decarbonization must complement the human and economic development of low- and middle-income countries.

A reversible solid oxide cell (rSOC) reactor can operate efficiently in both electrolysis mode and in fuel cell mode. The bidirectional operability enables rSOC reactors to play a central role as an efficient energy conversion system for energy storage and sector coupling for a renewable energy driven society. A combined system for electrolysis and fuel cell operation can result in complex system configurations that should be able to switch between the two modes as quickly as possible. This can lead to temperature profiles within the reactor that can potentially lead to the failure of the reactor and eventually the system. Hence the behavior of the reactor during the mode switch should be analyzed and optimal transition strategies should be taken into account during the process system design stage. In this paper a one dimensional transient reversible solid oxide cell model was built and experimentally validated using a commercially available reactor. A simple hydrogen based system model was built employing the validated reactor model to study reactor behavior during the mode switch. The simple design leads to a system efficiency of 49% in fuel cell operation and 87% in electrolysis operation where the electrolysis process is slightly endothermic. Three transient operation strategies were studied. It is shown that the voltage response to transient operation is very fast provided the reactant flows are changed equally fast. A possible solution to ensure a safe mode switch by controlling the reactant inlet temperatures is presented. By keeping the rate of change of reactant inlet temperatures five to ten times slower than the mode switch a safe transition can be ensured.

“Linking the power and transport sectors—Part 1” describes the general principle of “sector coupling” (SC) develops a working definition intended of the concept to be of utility to the international scientific community contains a literature review that provides an overview of relevant scientific papers on this topic and conducts a rudimentary analysis of the linking of the power and transport sectors on a worldwide EU and German level. The aim of this follow-on paper is to outline an approach to the modelling of SC. Therefore a study of Germany as a case study was conducted. This study assumes a high share of renewable energy sources (RES) contributing to the grid and significant proportion of fuel cell vehicles (FCVs) in the year 2050 along with a dedicated hydrogen pipeline grid to meet hydrogen demand. To construct a model of this nature the model environment “METIS” (models for energy transformation and integration systems) we developed will be described in more detail in this paper. Within this framework a detailed model of the power and transport sector in Germany will be presented in this paper and the rationale behind its assumptions described. Furthermore an intensive result analysis for the power surplus utilization of electrolysis hydrogen pipeline and economic considerations has been conducted to show the potential outcomes of modelling SC. It is hoped that this will serve as a basis for researchers to apply this framework in future to models and analysis with an international focus.

Green hydrogen is a key solution for reducing CO2 emissions in various industrial applications but high production costs continue to hinder its market penetration today. Better competitiveness is linked to lower investment costs and higher efficiency of the conversion technologies among which polymer electrolyte membrane electrolysis seems to be attractive. Although new manufacturing techniques and materials can help achieve these goals a less frequently investigated approach is the optimization of the design point and operating strategy of electrolyzers. This means in particular that the questions of how often a system should be operated and which cell voltage should be applied must be answered. As existing techno-economic models feature gaps which means that these questions cannot be adequately answered a modified model is introduced here. In this model different technical parameters are implemented and correlated to each other in order to simulate the lowest possible levelized cost of hydrogen and extract the required designs and strategies from this. In each case investigated the recommended cost-based cell voltage that should be applied to the system is surprisingly low compared to the assumptions made in previous publications. Depending on the case the cell voltage is in a range between 1.6 V and 1.8 V with an annual operation of 2000e8000 h. The wide range of results clearly indicate how individual the design and operation must be but with efficiency gains of several percent the effect of optimization will be indispensable in the future.