Germany

The hydrogen (H2) momentum affects the aviation sector. However a macroeconomic consideration is currently missing. To address this research gap the paper derives a methodology for evaluating macroeconomic effects of H2 in aviation and applies this approach to Germany. Three goals are addressed: (1) Construction of a German macroeconomic database. (2) Translation of H2 supply chains to the system of national accounts. (3) Implementation of H2-powered aviation into the macroeconomic data framework. The article presents an economy-wide database for analyzing H2-powered aviation. Subsequently the paper highlights three H2 supply pathways provides an exemplary techno-economic cost break-down for ten H2 components and translates them into the data framework. Eight relevant macroeconomic sectors for H2-powered aviation are identified and quantified. Overall the paper contributes on a suitable foundation to apply the macroeconomic dataset to and conduct macroeconomic analyses on H2-powered aviation. Finally the article highlights further research potential on job effects related to future H2 demand.

Appropriate climate change mitigation requires solutions for all actors of the energy system. The residential sector is a major part of the energy system and solutions for the implementation of a seasonal hydrogen storage system in residential houses has been increasingly discussed. A global analysis of prosumer systems including seasonal hydrogen storage with water electrolyser hydrogen compressor storage tank and a fuel cell studying the role of such a seasonal household storage in the upcoming decades is not available. This study aims to close this research gap via the improved LUT-PROSUME model which models a fully micro sector coupled residential photovoltaic prosumer system with linear optimisation for 145 regions globally. The modelling of the cost development of hydrogen storage components allows for the simulation of a residential system from 2020 until 2050 in 5-year steps in hourly resolution. The systems are cost-optimised for either on– or off-grid operation in eight scenarios including battery electric vehicles which can act as an additional vehicle-to-home electricity storage for the system. Results show that implementation of seasonal hydrogen systems only occurs in least cost solutions in high latitude countries when the system is forced to run in off-grid mode. In general a solar photovoltaic plus battery system including technologies that can cover the heat demand is the most economic choice and can even achieve lower cost than a full grid supply in off-grid operation for most regions until 2050. Additional parameters including the self-consumption ratio the demand cover ratio and the heat cover ratio can therefore not be improved by seasonal storage systems if economics is the main deciding factor for a respective system. Further research opportunities and possible limitations of the system are then identified.

One of aviation’s major challenges for the upcoming decades is the reduction in its climate impact. As synthetic kerosene and green hydrogen are two promising candidates their potentials in decreasing the climate impact is investigated for the mid-range segment. Evolutionary advancements for 2040 are applied first with an conventional and second with an advanced low-NOx and low-soot combustion chamber. Experts and methods from all relevant disciplines are involved starting from combustion turbofan engine overall aircraft design fleet level and climate impact assessment allowing a sophisticated and holistic evaluation. The main takeaway is that both energy carriers have the potential to strongly reduce the fleet level climate impact by more than 75% compared with the reference. Applying a flight-level constraint of 290 and a cruise Mach number of 0.75 causing 5% higher average Direct Operating Costs (DOC) the reduction is even more than 85%. The main levers to achieve this are the advanced combustion chamber an efficient contrail avoidance strategy in this case a pure flight-level constraint and the use of CO2 neutral energy carrier in a descending priority order. Although vehicle efficiency gains only lead to rather low impact reduction they are very important to compensate the increased costs of synthetic fuels or green hydrogen.

In this work a model of an energy system based on photovoltaics as the main energy source and a hybrid energy storage consisting of a short‐term lithium‐ion battery and hydrogen as the long‐term storage facility is presented. The electrical and the heat energy circuits and resulting flows have been modelled. Therefore the waste heat produced by the electrolyser and the fuel cell have been considered and a heat pump was considered to cover the residual heat demand. The model is designed for the analysis of a whole year energy flow by using a time series of loads weather and heat profile as input. This paper provides the main set of equations to derive the component properties and describes the implementation into MATLAB/Simulink. The novel model was created for an energy flow simulation over one year. The results of the simulation have been verified by comparing them with well‐established simulation results from HOMER Energy. It turns out that the novel model is well suited for the analysis of the dynamic system behaviour. Moreover different characteristics to achieve an energy balance an ideal dimensioning for the particular use case and further research possibilities of hydrogen use in the residential sector are covered by the novel model.

The locally occurring mechanisms of hydrogen embrittlement significantly influence the fatigue behaviour of a material which was shown in previous research on two different AISI 300-series austenitic stainless steels with different austenite stabilities. In this preliminary work an enhanced fatigue crack growth as well as changes in crack initiation sites and morphology caused by hydrogen were observed. To further analyze the results obtained in this previous research in the present work the local cyclic deformation behaviour of the material volume was analyzed by using cyclic indentation testing. Moreover these results were correlated to the local dislocation structures obtained with transmission electron microscopy (TEM) in the vicinity of fatigue cracks. The cyclic indentation tests show a decreased cyclic hardening potential as well as an increased dislocation mobility for the conditions precharged with hydrogen which correlates to the TEM analysis revealing courser dislocation cells in the vicinity of the fatigue crack tip. Consequently the presented results indicate that the hydrogen enhanced localized plasticity (HELP) mechanism leads to accelerated crack growth and change in crack morphology for the materials investigated. In summary the cyclic indentation tests show a high potential for an analysis of the effects of hydrogen on the local cyclic deformation behaviour.

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.

The use of fossil fuels as an energy supply becomes increasingly problematic from the point of view of both environmental emissions and energy sustainability. As an alternative hydrogen is widely regarded as a key element for a potential energy solution. However differently from fossil fuels such as oil gas and coal the production of hydrogen requires energy. Alternative and intermittent renewable energy sources such as solar power wind power etc. present multiple advantages for the production of hydrogen. On the one hand the renewable sources contribute to a remarkable reduction of pollutants released to the air and on the other hand they significantly enhance the sustainability of energy supply. In addition the storage of energy in form of hydrogen has a huge potential to balance an effective and synergetic utilization of renewable energy sources. In this regard hydrogen storage technology is a key technology towards the practical application of hydrogen as “energy carrier”. Among the methods available to store hydrogen solid-state storage is the most attractive alternative from both the safety and the volumetric energy density points of view. Because of their appealing hydrogen content complex hydrides and complex hydride-based systems have attracted considerable attention as potential energy vectors for mobile and stationary applications. In this review the progresses made over the last century on the synthesis and development of tetrahydroborates and tetrahydroborate-based systems for hydrogen storage purposes are summarized.

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.

Driven by concerns regarding the sustainability of aviation and the continued growth of air traffic increasing interest is given to emerging aircraft technologies. Although new technologies such as battery-electric propulsion systems have the potential to minimise in-flight emissions and noise environmental burdens are possibly shifted to other stages of the aircraft’s life cycle and new socio-economic challenges may arise. Therefore a life-cycle-oriented sustainability assessment is required to identify these hotspots and problem shifts and to derive recommendations for action for aircraft development at an early stage. This paper proposes a framework for the modelling and assessment of future aircraft technologies and provides an overview of the challenges and available methods and tools in this field. A structured search and screening process is used to determine which aspects of the proposed framework are already addressed in the scientific literature and in which areas research is still needed. For this purpose a total of 66 related articles are identified and systematically analysed. Firstly an overview of statistics of papers dealing with life-cycle-oriented analysis of conventional and emerging aircraft propulsion systems is given classifying them according to the technologies considered the sustainability dimensions and indicators investigated and the assessment methods applied. Secondly a detailed analysis of the articles is conducted to derive answers to the defined research questions. It illustrates that the assessment of environmental aspects of alternative fuels is a dominating research theme while novel approaches that integrate socio-economic aspects and broaden the scope to battery-powered fuel-cell-based or hybrid-electric aircraft are emerging. It also provides insights by what extent future aviation technologies can contribute to more sustainable and energy-efficient aviation. The findings underline the need to harmonise existing methods into an integrated modelling and assessment approach that considers the specifics of upcoming technological developments in aviation.

Hydrogen safety issues attract focuses increasingly as more and more hydrogen powered vehicles are going to be operated in traffic infrastructures of different kinds like tunnels. Due to the confinement feature of traffic tunnels hydrogen deflagration may pose a risk when a hydrogen leak event occurs in a tunnel e.g. failure of the hydrogen storage system caused by a car accident in a tunnel. A water injection system can be designed in tunnels as a mitigation measure to suppress the pressure and thermal loads of hydrogen combustion in accident scenarios. The COM3D is a fully verified three-dimensional finite-difference turbulent flow combustion code which models gas mixing hydrogen combustion and detonation in nuclear containment with mitigation device or other confined facilities like vacuum vessel of fusion and semi-confined hydrogen facilities in industry such as traffic tunnels hydrogen refueling station etc. Therefore by supporting of the European HyTunnel-CS project the COM3D is applied to simulate numerically the hydrogen deflagration accident in a tunnel model being suppressed by water mist injection. The suppression effect of water mist and the suppression mechanism is elaborated and discussed in the study.