Germany
Numerical Study on Shockwave Attenuation by Water Mist in Confined Spaces
Sep 2021
Publication
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.
Current Legislative Framework for Green Hydrogen Production by Electrolysis Plants in Germany
Mar 2022
Publication
(1) The German energy system transformation towards an entirely renewable supply is expected to incorporate the extensive use of green hydrogen. This carbon-free fuel allows the decarbonization of end-use sectors such as industrial high-temperature processes or heavy-duty transport that remain challenging to be covered by green electricity only. However it remains unclear whether the current legislative framework supports green hydrogen production or is an obstacle to its rollout. (2) This work analyzes the relevant laws and ordinances regarding their implications on potential hydrogen production plant operators. (3) Due to unbundling-related constraints potential operators from the group of electricity transport system and distribution system operators face lacking permission to operate production plants. Moreover ownership remains forbidden for them. The same applies to natural gas transport system operators. The case is less clear for natural gas distribution system operators where explicit regulation is missing. (4) It is finally analyzed if the production of green hydrogen is currently supported in competition with fossil hydrogen production not only by the legal framework but also by the National Hydrogen Strategy and the Amendment of the Renewable Energies Act. It can be concluded that in recent amendments of German energy legislation regulatory support for green hydrogen in Germany was found. The latest legislation has clarified crucial points concerning the ownership and operation of electrolyzers and the treatment of green hydrogen as a renewable energy carrier.
Storage System of Renewable Energy Generated Hydrogen for Chemical Industry
Nov 2012
Publication
Chemical industry is the base of the value chains and has strong influence on the competitiveness of almost all branches in economics. To develop the technologies for sustainability and climate protection and at the same time to guarantee the supply of raw material is a big challenge for chemical industry. In the project CO2RRECT (CO2 - Reaction using Regenerative Energies and Catalytic Technologies) funded by the German federal ministry of Education and Research carbon dioxide is used as the source of carbon for chemical products with certain chemical processes. Hydrogen that is needed in these processes is produced by electrolyzing water with renewable energy. To store a large amount of hydrogen different storage systems are studied in this project including liquid hydrogen tanks/cryo tanks high pressure tanks pipelines and salt cavities. These systems are analyzed and compared considering their storage capacity system costs advantages and disadvantages. To analyze capital and operational expenditure of the hydrogen storage systems a calculation methodology is also developed in this work.
System Analysis and Requirements Derivation of a Hydrogen-electric Aircraft Powertrain
Sep 2022
Publication
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.
Ammonia Production from Clean Hydrogen and the Implications for Global Natural Gas Demand
Jan 2023
Publication
Non-energy use of natural gas is gaining importance. Gas used for 183 million tons annual ammonia production represents 4% of total global gas supply. 1.5-degree pathways estimate an ammonia demand growth of 3–4-fold until 2050 as new markets in hydrogen transport shipping and power generation emerge. Ammonia production from hydrogen produced via water electrolysis with renewable power (green ammonia) and from natural gas with CO2 storage (blue ammonia) is gaining attention due to the potential role of ammonia in decarbonizing energy value chains and aiding nations in achieving their net-zero targets. This study assesses the technical and economic viability of different routes of ammonia production with an emphasis on a systems level perspective and related process integration. Additional cost reductions may be driven by optimum sizing of renewable power capacity reducing losses in the value chain technology learning and scale-up reducing risk and a lower cost of capital. Developing certification and standards will be necessary to ascertain the extent of greenhouse gas emissions throughout the supply chain as well as improving the enabling conditions including innovative finance and de-risking for facilitating international trade market creation and large-scale project development.
Mathematical Modeling of Unstable Transport in Underground Hydrogen Storage
Apr 2015
Publication
Within the framework of energy transition hydrogen has a great potential as a clean energy carrier. The conversion of electricity into hydrogen for storage and transport is an efficient technological solution capable of significantly reducing the problem of energy shortage. Underground hydrogen storage (UHS) is the best solution to store the large amount of excess electrical energy arising from the excessive over-production of electricity with the objective of balancing the irregular and intermittent energy production typical of renewable sources such as windmills or solar. Earlier studies have demonstrated that UHS should be qualitatively identical to the underground storage of natural gas. Much later however it was revealed that UHS is bound to incur peculiar difficulties as the stored hydrogen is likely to be used by the microorganisms present in the rocks for their metabolism which may cause significant losses of hydrogen. This paper demonstrates that besides microbial activities the hydrodynamic behavior of UHS is very unique and different from that of a natural gas storage.
Sustainability Assessment and Engineering of Emerging Aircraft Technologies—Challenges, Methods and Tools
Jul 2020
Publication
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.
How Flexible Electricity Demand Stabilizes Wind and Solar Market Values: The Case of Hydrogen Electrolyzers
Nov 2021
Publication
Wind and solar energy are often expected to fall victim to their own success: the higher their share in electricity generation the more their revenue in electricity markets (their “market value”) declines. While market values may converge to zero in conventional power systems this study argues that “green” hydrogen production can effectively and permanently halt the decline by adding flexible electricity demand in low-price hours. To support this argument this article further develops the merit order model and uses price duration curves to include flexible hydrogen electrolysis and to derive an analytical formula for the minimum market value of renewables in the long-term market equilibrium. This hydrogen-induced minimum market value is quantified for a wide range of parameters using Monte Carlo simulations and complemented with results from a more detailed numerical electricity market model. It is shown that—due to flexible hydrogen production alone—market values across Europe will likely stabilize above €19 ± 9 MWh− 1 for solar energy and above €27 ± 8 MWh− 1 for wind energy in 2050 (annual mean estimate ± standard deviation). This is in the range of the projected levelized cost of renewables and other types of flexible electricity demand may further increase renewable market values. Market-based renewables may hence be within reach.
Blast Wave Generated by Delayed Ignition of Under-Expanded Hydrogen Free Jet at Ambient and Cryogenic Temperatures
Nov 2022
Publication
An under-expanded hydrogen jet from high-pressure equipment or storage tank is a potential incident scenario. Experiments demonstrated that the delayed ignition of a highly turbulent under-expanded hydrogen jet generates a blast wave able to harm people and damage property. There is a need for engineering tools to predict the pressure effects during such incidents to define hazard distances. The similitude analysis is applied to build a correlation using available experimental data. The dimensionless blast wave overpressure generated by delayed ignition and the follow-up deflagration or detonation of hydrogen jets at an any location from the jet ∆Pexp/P0 is correlated to the original dimensionless parameter composed of the product of the dimensionless ratio of storage pressure to atmospheric pressure Ps/P0 and the ratio of the jet release nozzle diameter to the distance from the centre of location of the fast-burning near-stoichiometric mixture on the jet axis (30% of hydrogen in the air by volume) to the location of a target (personnel or property) d/Rw. The correlation is built using the analysis of 78 experiments regarding this phenomenon in the wide range of hydrogen storage pressure of 0.5–65.0 MPa and release diameter of 0.5–52.5 mm. The correlation is applicable to hydrogen free jets at ambient and cryogenic temperatures. It is found that the generated blast wave decays inversely proportional to the square of the distance from the fast-burning portion of the jet. The correlation is used to calculate the hazard distances by harm thresholds for five typical hydrogen applications. It is observed that in the case of a vehicle with onboard storage tank at pressure 70 MPa the “no-harm” distance for humans reduces from 10.5 m to 2.6 m when a thermally activated pressure relief device (TPRD) diameter decreases from 2 mm to a diameter of 0.5 mm.
Effect of Heat Transfer through the Release of Pipe on Simulations of Cryogenic Hydrogen Jet Fires and Hazard Distances
Sep 2021
Publication
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.
Potentials of Hydrogen Technologies for Sustainable Factory Systems
Mar 2021
Publication
The industrial sector is the world’s second largest emitter of greenhouse gases hence a methodology for decarbonizing factory systems is crucial for achieving global climate goals. Hydrogen is an important medium for the transition towards carbon neutral factories due to its broad applicability within the factory including its use in electricity and heat generation and as a process gas or fuel. One of the main challenges is the identification of economically and environmentally suitable design scenarios such as for the entire value chain for hydrogen generation and application. For example the infrastructure for renewable electricity hydrogen generation hydrogen conversion (e.g. into synthetic fuels) storage and transport systems as well as application in the factory. Due to the high volatility of energy generation and the related dynamic interdependencies within a factory system a valid technical economic and environmental evaluation of benefits induced by hydrogen technologies can only be achieved using digital factory models. In this paper we present a framework to integrate hydrogen technologies into factory systems. This enables decision makers to identify promising measures according to their expected impact and collect data for appropriate factory modelling. Furthermore a concept for factory modelling and simulation is presented and demonstrated in a case study from the electronics industry assessing the use of hydrogen for decentralized power and heat generation.
Life Cycle Assessment of Improved High Pressure Alkaline Electrolysis
Aug 2015
Publication
This paper investigates environmental impacts of high pressure alkaline water electrolysis systems. An advanced system with membranes on polymer basis is compared to a state-of-the-art system with asbestos membranes using a Life Cycle Assessment (LCA) approach. For the advanced system a new improved membrane technology has been investigated within the EU research project “ELYGRID”. Results indicate that most environmental impacts are caused by the electricity supply necessary for operation. During the construction phase cell stacks are the main contributor to environmental impacts. New improved membranes have relatively small contributions to impacts caused by cell construction within the advanced systems. As main outcome the systems comparison illustrates a better ecological performance of the new developed system
Site-Dependent Environmental Impacts of Industrial Hydrogen Production by Alkaline Water Electrolysis
Jun 2017
Publication
Industrial hydrogen production via alkaline water electrolysis (AEL) is a mature hydrogen production method. One argument in favor of AEL when supplied with renewable energy is its environmental superiority against conventional fossil-based hydrogen production. However today electricity from the national grid is widely utilized for industrial applications of AEL. Also the ban on asbestos membranes led to a change in performance patterns making a detailed assessment necessary. This study presents a comparative Life Cycle Assessment (LCA) using the GaBi software (version 6.115 thinkstep Leinfelden-Echterdingen Germany) revealing inventory data and environmental impacts for industrial hydrogen production by latest AELs (6 MW Zirfon membranes) in three different countries (Austria Germany and Spain) with corresponding grid mixes. The results confirm the dependence of most environmental effects from the operation phase and specifically the site-dependent electricity mix. Construction of system components and the replacement of cell stacks make a minor contribution. At present considering the three countries AEL can be operated in the most environmentally friendly fashion in Austria. Concerning the construction of AEL plants the materials nickel and polytetrafluoroethylene in particular used for cell manufacturing revealed significant contributions to the environmental burden.
Future Hydrogen Markets for Transportation and Industry: The Impact of CO2 Taxes
Dec 2019
Publication
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.
Simulation of Coupled Power and Gas Systems with Hydrogen-Enriched Natural Gas
Nov 2021
Publication
Due to the increasing share of renewable energy sources in the electrical network the focus on decarbonization has extended into other energy sectors. The gas sector is of special interest because it can offer seasonal storage capacity and additional flexibility to the electricity sector. In this paper we present a new simulation method designed for hydrogen-enriched natural gas network simulation. It can handle different gas compositions and is thus able to accurately analyze the impact of hydrogen injections into natural gas pipelines. After describing the newly defined simulation method we demonstrate how the simulation tool can be used to analyze a hydrogen-enriched gas pipeline network. An exemplary co-simulation of coupled power and gas networks shows that hydrogen injections are severely constrained by the gas pipeline network highlighting the importance and necessity of considering different gas compositions in the simulation.
Transient Reversible Solid Oxide Cell Reactor Operation – Experimentally Validated Modeling and Analysis
Oct 2018
Publication
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.
Thermodynamic and Ecological Preselection of Synthetic Fuel Intermediates from Biogas at Farm Sites
Jan 2020
Publication
Background: Synthetic fuels based on renewable hydrogen and CO2 are a currently highly discussed piece of the puzzle to defossilize the transport sector. In this regard CO2 can play a positive role in shaping a sustainable future. Large potentials are available as a product of biogas production however occurring in small scales and in thin spatial distributions. This work aims to evaluate suitable synthetic fuel products to be produced at farm sites.<br/>Methods: A thermodynamic analysis to assess the energetic efficiency of synthesis pathways and a qualitative assessment of product handling issues is carried out.<br/>Results: Regarding the technical and safety-related advantages in storage liquid products are the superior option for fuel production at decentralized sites. Due to the economy of scale multi-stage synthesis processes lose economic performance with rising complexity. A method was shown which covers a principle sketch of all necessary reaction separation steps and all compression and heat exchanger units. The figures showed that methanol and butanol are the most suitable candidates in contrast to OME3-5 for implementation in existing transportation and fuel systems. These results were underpin by a Gibbs energy analysis.<br/>Conclusions: As long as safety regulations are met and the farm can guarantee safe storage and transport farm-site production for all intermediates can be realized technically. Ultimately this work points out that the process must be kept as simple as possible favoring methanol production at farm site and its further processing to more complicated fuels in large units for several fuel pathways.
Alternative Energy Technologies as a Cultural Endeavor: A Case Study of Hydrogen and Fuel Cell Development in Germany
Feb 2012
Publication
Background: The wider background to this article is the shift in the energy paradigm from fossil energy sources to renewable sources which should occur in the twenty-first century. This transformation requires the development of alternative energy technologies that enable the deployment of renewable energy sources in transportation heating and electricity. Among others hydrogen and fuel cell technologies have the potential to fulfill this requirement and to contribute to a sustainable and emission-free transport and energy system. However whether they will ever reach broad societal acceptance will not only depend on technical issues alone. The aim of our study is to reveal the importance of nontechnical issues. Therefore the article at hand presents a case study of hydrogen and fuel cells in Germany and aims at highlighting the cultural context that affects their development.<br/>Methods: Our results were obtained from a rich pool of data generated in various research projects through more than 30 in-depth interviews direct observations and document analyses.<br/>Results: We found that individual and collective actors developed five specific supportive practices which they deploy in five diverse arenas of meaning in order to attach certain values to hydrogen and fuel cell technologies.<br/>Conclusions: Based on the results we drew more general conclusions and deducted an overall model for the analysis of culture in technological innovations that is outlined at the end of the article. It constitutes our contribution to the interdisciplinary collaboration required for tackling the shift in this energy paradigm.
Reliable Off-grid Power Supply Utilizing Green Hydrogen
Jun 2021
Publication
Green hydrogen produced from wind solar or hydro power is a suitable electricity storage medium. Hydrogen is typically employed as mid- to long-term energy storage whereas batteries cover short-term energy storage. Green hydrogen can be produced by any available electrolyser technology [alkaline electrolysis cell (AEC) polymer electrolyte membrane (PEM) anion exchange membrane (AEM) solid oxide electrolysis cell (SOEC)] if the electrolysis is fed by renewable electricity. If the electrolysis operates under elevated pressure the simplest way to store the gaseous hydrogen is to feed it directly into an ordinary pressure vessel without any external compression. The most efficient way to generate electricity from hydrogen is by utilizing a fuel cell. PEM fuel cells seem to be the most favourable way to do so. To increase the capacity factor of fuel cells and electrolysers both functionalities can be integrated into one device by using the same stack. Within this article different reversible technologies as well as their advantages and readiness levels are presented and their potential limitations are also discussed.
Is Blue Hydrogen a Bridging Technology? - The Limits of a CO2 Price and the Role of State-induced Price Components for Green Hydrogen Production in Germany
Jun 2022
Publication
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.
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