Publications

In the ongoing effort to reduce carbon emissions on a worldwide scale green hydrogen which is generated through environmentally responsible processes has emerged as a significant driving force. As the demand for clean energy continues to rise it is becoming increasingly important to have a solid understanding of the technological and economic elements of modern techniques of producing green hydrogen. In the context of green hydrogen generation understanding green hydrogen production's techno-economic features is necessary to reduce carbon emissions and transition to a low-carbon economy. associated with breakthroughs in technology the present study examines the most fascinating and relevant aspects of techno-economic analysis. Despite challenges green hydrogen can help the world move to a cleaner more sustainable energy future with solid analytical frameworks and legislation.

Hydrogen refuelling stations are an important part of the infrastructure for promoting the hydrogen economy. Since hydrogen is a flammable and explosive gas hydrogen released from high-pressure hydrogen storage equipment in hydrogen refuelling stations will likely cause combustion or explosion accidents. Studying high-pressure hydrogen leakage in hydrogen refuelling stations is a prerequisite for promoting hydrogen fuel cell vehicles and hydrogen refuelling stations. In this work an actual-size hydrogen refuelling station model was established on the ANSYS FLUENT software platform. The computational fluid dynamics (CFD) models for hydrogen leakage simulation were validated by comparing the simulation results with experimental data in the literature. The effects of ambient wind speed wind direction leakage rate and leakage direction on the diffusion behaviors of the released hydrogen were investigated. The spreading distances of the flammable hydrogen cloud were predicted using an artificial neural network for horizontal leakage. The results show that the leak direction strongly affected the flammable cloud flow. The ambient wind speed has complicated effects on spreading the flammable cloud. The wind makes the flammable cloud move in certain directions and the higher wind speed accelerates the diffusion of the flammable gas in the air. The results of the study can be used as a reference for the study of high-pressure hydrogen leakage in hydrogen refuelling stations.

Fighting climate change has become a major task worldwide. One of the key energy sectors to emit greenhouse gases is transportation. Therefore long term strategies all over the world have been set up to reduce on-road combustion emissions. In this context the road freight sector faces significant challenges in decarbonization driven by its limited availability of low-emission fuels and commercialized zero-emission vehicles compared with its high energy demand. In this work we develop the Mobility and Energy Transportation Analysis (META) Model a python-based optimization model to quantify the impact of transportation projected policies on freight transport by projecting conventional and alternative fuel technologies market acceptance as well as greenhouse gas (GHG) emissions. Along with introducing e-fuels as an alternative refueling option for conventional vehicles META investigates the market opportunities of Mobile Carbon Capture (MCC) until 2050. To accurately assess this technology a techno-economic analysis is essential to compare MCC abatement cost to alternative decarbonization technologies such as electric trucks. The novelty of this work comes from the detailed cost categories taken into consideration in the analysis including intangible costs associated with heavy-duty technologies such as recharging/refueling time cargo capacity limitations and consumer acceptance towards emerging technologies across different regions. Based on the study results the competitive total cost of ownership (TCO) and marginal abatement cost (MAC) values of MCC make it an economically promising alternative option to decarbonize the freight transport sector. Both in the KSA and EU MCC options could reach greater than 50% market shares of all ICE vehicle sales equivalent to a combined 35% of all new sales shares by 2035.

A sudden release of compressed gases and the formation of a jet flow can occur in nature and various engineering applications. In particular high-pressure hydrogen jets can spontaneously ignite when released into an environment that contains oxygen. For some scenarios these high-pressure hydrogen jets can be released into a mixture containing hydrogen and oxygen. This scenario can possibly lead to a wide range of combustion regimes such as jet flames slow or fast deflagrations or even hazardous detonations. Each combustion regime is characterized by typical pressures and temperatures however fast transition between regimes is also possible.<br/>A common project between Tel Aviv University (TAU) Nuclear Research Center Negev (NRCN) and Commissariat à l’Energie Atomique et aux énergies alternatives (CEA) has been recently launched in order to understand these phenomena from experimental modelling and numerical points of view. The main goal is to investigate the dynamics and combustion regimes that arise once a pressurized hydrogen jet is released into a reactive environment that contains inhomogeneous concentrations of hydrogen steam and air.<br/>In this paper we present the first numerical results describing high-pressure hydrogen release obtained using a massively parallel compressible structured-grid flow solver. The experimental arrangements devoted to this phenomenon will also be described.

Historically it has been a challenge to simulate the experimentally observed cellular structures and marginal behavior of multidimensional hydrogen-oxygen detonations in the presence of losses even with detailed chemistry models. Very recently a quasi-two-dimensional inviscid approach was pursued where losses due to viscous boundary layers were modeled by the inclusion of an equivalent mass divergence in the lateral direction using Fay’s source term formulation with Mirels’ compressible boundary layer solutions. The same approach was used for this study along with the inclusion of thermally perfect detailed chemistry in order to capture the correct ignition sensitivity of the gas to dynamic changes in the thermodynamic state behind the detonation front. In addition the strength of transverse waves and their impact on the detonation front was investigated. Here the detailed San Diego mechanism was applied and it has been found that the detonation cell sizes can be accurately predicted without the need to prescribe specific parameters for the combustion model. For marginal cases where the detonation waves approach their failure limit quasi-stable mode behavior was observed where the number of transverse waves monotonically decreased to a single strong wave over a long enough distance. The strong transverse waves were also found to be slightly weaker than the detonation front indicating that they are not overdriven in agreement with recent studies.

A range of existing and newly developed hydrogen standards certification and labelling (SCL) schemes aim to promote the role of ‘renewable’ ‘clean’ or ‘green’ hydrogen in decarbonising energy transitions. This paper analyses a sample of these SCLs to assess their role in the scaling up of renewable hydrogen and its derivatives. To analyse these hydrogen SCLs we embellish a novel conceptual framework that brings together Sustainability Systems Thinking and Governance (SSG) literatures. The results reveal noteworthy scheme differences in motivation approach criteria and governance; highlighting the complex interconnected and dynamic reality within which energy systems are embedded. We consider whether the sustainable utilisation of renewable hydrogen is well-served by the proliferation of SCLs and recommend an SSG-informed approach. An SSG approach will better promote collaboration towards an authoritative global multistakeholder compromise on hydrogen certification that balances economic considerations with social and environmental dimensions.

Russia’s invasion of Ukraine has reaffirmed the importance of scaling up renewable energy to decarbonise Europe’s economy while rapidly reducing its exposure to foreign fossil fuel suppliers. Therefore the question of sources of flexibility to support a fully decarbonised European energy system is becoming even more critical in light of a renewable-dominated energy system. We developed and used a Pan-European energy system model to systematically assess and quantify sources of flexibility to meet deep decarbonisation targets. The electricity supply sector and electricity-based end-use technologies are crucial in achieving deep decarbonisation. Other low-carbon energy sources like biomethane hydrogen synthetic e-fuels and bioenergy with carbon capture and storage will also play a role. To support a fully decarbonised European energy system by 2050 both temporal and spatial flexibility will be needed. Spatial flexibility achieved through investments in national electricity networks and cross-border interconnections is crucial to support the aggressive roll-out of variable renewable energy sources. Cross-border trade in electricity is expected to increase and in deep decarbonisation scenarios the electricity transmission capacity will be larger than that of natural gas. Hydrogen storage and green hydrogen production will play a key role in providing traditional inter-seasonal flexibility and intraday flexibility will be provided by a combination of electrical energy storage hydrogen-based storage solutions (e.g. liquid H2 and pressurised storage) and hybrid heat pumps. Hydrogen networks and storage will become more critical as we move towards the highest decarbonisation scenario. Still the need for natural gas networks and storage will decrease substantially.

The MultHyFuel project aims to develop evidence-based guidelines for the safe implementation of Hydrogen Refueling Stations (HRS) in a multi-fuel context. As a part of the generation of good practice guidelines for HRS Hazardous Area Classification (HAC) methodologies were analyzed and applied to case studies representing example configurations of HRS. It has been anticipated that Negligible Extent (NE) classifications might be applicable for sections of the HRS for instance a hydrogen generator. A NE zone requires that an ignition of a flammable cloud would result in negligible consequences. In addition depending on the pressure of the system IEC 60079-10-1:2020 establishes specific requirements in order to classify the hazardous area as being of NE. One such requirement is that a zone of NE shall not be applied for releases from flammable gas systems at pressures above 2000 kPag (20 barg) unless a specific detailed risk assessment is documented. However there is no definition within the standard as to the requirements of the specific detailed risk assessment. In this work an example for a specific detailed risk assessment for the NE classification is presented:<br/>• Firstly the requirements of cloud volume dilution and background concentration for a zone of NE classification from IEC 60079-10-1:2020 are analyzed for hydrogen releases from equipment placed in a mechanically ventilated enclosure.<br/>• Secondly the consequences arising from the ignition of the localized cloud are estimated and compared to acceptable harm criteria in order to assess if negligible consequences are obtained from the scenario.<br/>• In addition a specific qualitative risk assessment for the ignition of the cloud in the enclosure was considered incorporating the estimated consequences and analyzing the available safeguards in the example system.<br/>Recommendations for the specific detailed risk assessment are proposed for this scenario with the intention to support improved definition of the requirement in future revisions of IEC 60079-10-1.

Hydrogen produced using renewable energy from offshore wind provides a versatile method of energy storage and power-to-gas concepts. However few dedicated floating offshore electrolyser facilities currently exist and therefore conditions of the offshore environment on hydrogen production cost and efficiency remain uncertain. Therefore this review focuses on the conversion of electrical energy to hydrogen using water electrolysis located in offshore areas. The challenges associated with the remote locations fluctuating power and harsh conditions are highlighted and recommendations for future electrolysis system designs are suggested. The latest research in polymer electrolyte membrane alkaline and membraneless electrolysis are evaluated in order to understand their capital costs efficiency and current research status for achieving scaled manufacturing to the GW scale required in the next three decades. Operating fundamentals that govern the performance of each device are investigated and future recommendations of research specifically for the integration of water electrolysers with offshore wind turbines is presented.

During the driving of a fuel cell car the expansion of the hydrogen along the emptying of the high pressure storage tank produces a cooling of the gas. The hydrogen vessel can experience a fast depressurization during acceleration or under an emergency release. This can result on the one hand in exceeding the low safety temperature limit of 40 C inside the on-board compressed hydrogen tank and on the other hand in the cooling of its walls. In the present paper defueling experiments of two different types of on-board hydrogen tanks (Type III and Type IV) have been performed in all the range of expected defueling rates. The lowest temperatures have been found on the bottom part of the Type IV tank in very fast defuelings. For average driving conditions in both types of vessels the inside gas temperature gets closer to that of the walls and the tank would arrive to the refuelling station at a temperature significantly lower than the ambient temperature.