Publications

To meet the new regulation for the deployment of alternative fuels infrastructure which sets targets for electric recharging and hydrogen refuelling infrastructure by 2025 or 2030 a large infrastructure comprising trucksuitable hydrogen refuelling stations will soon be required. However further standardisation is required to support the uptake of hydrogen for heavy-duty transport for Europe’s green energy future. Hydrogen-powered vehicles require pure hydrogen as some contaminants can reduce the performance of the fuel cell even at very low levels. Even if previous projects have paved the way for the development of the European quality infrastructure for hydrogen conformity assessment sampling systems and methods have yet to be developed for heavy-duty hydrogen refuelling stations (HD-HRS). This study reviews different aspects of the sampling of hydrogen at heavy-duty hydrogen refuelling stations for purity assessment with a focus on the current and future specifications and operations at HD-HRS. This study describes the state-of-the art of sampling systems currently under development for use at HD-HRS and highlights a number of aspects which must be taken into consideration to ensure safe and accurate sampling: risk assessment for the whole sampling exercise selection of cylinders methods to prepare cylinders before the sampling filling pressure and venting of the sampling systems.

In order to study the flow blending and transporting process of hydrogen that injects into the natural gas pipelines a three-dimensional T-pipe blending model is established and the flow characteristics are investigated systematically by the large eddy simulation (LES). Firstly the mathematical formulation of hydrogen-methane blending process is provided and the LES method is introduced and validated by a benchmark gas blending model having experimental data. Subsequently the T-pipe blending model is presented and the effects of key parameters such as the velocity of main pipe hydrogen blending ratio diameter of hydrogen injection pipeline diameter of main pipe and operating pressure on the hydrogen-methane blending process are studied systematically. The results show that under certain conditions the gas mixture will be stratified downstream of the blending point with hydrogen at the top of the pipeline and methane at the bottom of the pipeline. For the no-stratified scenarios the distance required for uniformly mixing downstream the injection point increases when the hydrogen mixing ratio decreases the diameter of the hydrogen injection pipe and the main pipe increase. Finally based on the numerical results the underlying physics of the stratification phenomenon during the blending process are explored and an indicator for stratification is proposed using the ratio between the Reynolds numbers of the natural gas and hydrogen.

Hydrogen crossover limits the load range of alkaline water electrolyzers hindering their integration with renewable energy. This study examines the impact of the electrode-diaphragm gap on crossover focusing on diffusive transport. Both finite-gap and zero-gap designs employing the state-of-the-art Zirfon UTP Perl 500 and UTP 220 diaphragms were investigated at room temperature and with a 12 wt% KOH electrolyte. Experimental results reveal a relatively high crossover for a zero-gap configuration which corresponds to supersaturation levels at the diaphragm-electrolyte interface of 8–80 with significant fluctuations over time and between experiments due to an imperfect zero-gap design. In contrast a finite-gap (500 μm) has a significantly smaller crossover corresponding to supersaturation levels of 2–4. Introducing a cathode gap strongly decreases crossover unlike an anode gap. Our results suggest that adding a small cathode-gap can significantly decrease gas impurity potentially increase the operating range of alkaline electrolyzers while maintaining good efficiency.

A proton exchange membrane electrolyzer can effectively utilize the electricity generated by intermittent solar power. Different methods of generating electricity may have different efficiencies and hydrogen production rates. Two coupled systems namely PV/T- and CPV/T-coupling PEMEC respectively are presented and compared in this study. A maximum power point tracking algorithm for the photovoltaic system is employed and simulations are conducted based on the solar irradiation intensity and ambient temperature of a specific location on a particular day. The simulation results indicate that the hydrogen production is relatively high between 11:00 and 16:00 with a peak between 12:00 and 13:00. The maximum hydrogen production rate is 99.11 g/s and 29.02 g/s for the CPV/T-PEM and PV/T-PEM systems. The maximum energy efficiency of hydrogen production in CPV/T-PEM and PV/T-PEM systems is 66.7% and 70.6%. Under conditions of high solar irradiation intensity and ambient temperature the system demonstrates higher total efficiency and greater hydrogen production. The CPV/T-PEM system achieves a maximum hydrogen production rate of 2240.41 kg/d with a standard coal saving rate of 15.5 tons/day and a CO2 reduction rate of 38.0 tons/day. Compared to the PV/T-PEM system the CPV/T-PEM system exhibits a higher hydrogen production rate. These findings provide valuable insights into the engineering application of photovoltaic/thermal-coupled hydrogen production technology and contribute to the advancement of this field.

Hydrogen storage plays a crucial role in achieving net-zero emissions by enabling large-scale energy storage balancing renewable energy fluctuations and ensuring a stable supply for various applications. This study provides a comprehensive analysis of hydrogen storage technologies with a particular focus on underground storage in geological formations such as salt caverns depleted gas reservoirs and aquifers. These formations offer high-capacity storage solutions with salt caverns capable of holding up to 6 TWh of hydrogen and depleted gas reservoirs exceeding 1 TWh per site. Case studies from leading projects demonstrate the feasibility of underground hydrogen storage (UHS) in reducing energy intermittency and enhancing supply security. Challenges such as hydrogen leakage groundwater contamination induced seismicity and economic constraints remain critical concerns. Our findings highlight the technical economic and regulatory considerations for integrating UHS into the oil and gas industry emphasizing its role in sustainable energy transition and decarbonization strategies.

The present study explores the potential of integrating the NET Zero Cycle (NZC) with hydrogen production by alkaline electrolyzers. To achieve this an Aspen Plus model was developed for the NZC and its accuracy was first confirmed by comparing it with literature data. The creation of a model for an alkaline electrolyzer was achieved using Aspen Custom Modeler and later imported into Aspen Plus. A comprehensive simulation was conducted in Aspen Plus to examine the synergies between the NZC and the alkaline electrolyzer. In this integration the oxygen demand of the NZC is met by a combination of an air separation unit (ASU) and the electrolyzer. The electrolyzer not only partially fulfills the oxygen requirements but also acts as an external heat supplier for the regenerator. Additionally the NZC supplies deionized water to the electrolyzer. A thermodynamic analysis in dicates that the integration of the NZC and alkaline electrolyzers results in a higher efficiency of 56.5 % compared to the stand-alone NZC an improvement of 2.3 %. Assuming that the NZC and alkaline electrolyzer operate at the same power production and input levels the alkaline electrolyzer can generate substantial oxygen to reduce the energy consumption of the ASU significantly. This aspect represents one of the primary reasons for the enhanced efficiency observed in this study. However the ASU still needs to be operated to provide the full oxygen demands of the process. To identify the key parameters influencing the integration of the NZC and alkaline electrolyzers a sensitivity analysis was performed. To enhance the system efficiency a comprehensive investigation was conducted to analyze the influence of key parameters such as combustor outlet temperature (COT) turbine outlet pressure (TOP) and combustor outlet pressure (COP) on the thermodynamic first law efficiency of the cycle. An increase in electrolyzer input power and a reduction in electrolyzer inlet feed were associated with a higher cycle effi ciency. The results also highlight that the TOP COT and the electrolyzer input power have a more significant impact on the cycle thermodynamic first law efficiency within the range of 5.7 4.0 and 2.6 % respectively while COP only causes a 0.4 % change in cycle efficiency. The integrated system demonstrates an impressive system first law thermodynamic efficiency of 62.5 % and exergy efficiency of 60.6 %.

Developing countries including Ghana face challenges ensuring access to clean and reliable cooking fuels and technologies. Traditional biomass sources mainly used in most developing countries for cooking contribute to deforestation and indoor air pollution necessitating a shift towards environmentally friendly alternatives. The study’s primary objective is to evaluate the economic viability of using solar PV-based green hydrogen as a sustainable fuel for cooking in Ghana. The study adopted well-established equations to investigate the economic performance of the proposed system. The findings revealed that the levelized cost of hydrogen using the discounted cash flow approach is about 89% 155% and 190% more than electricity liquefied petroleum gas (LPG) and charcoal. This implies that using the hydrogen produced for cooking fuel is not cost-competitive compared to LPG charcoal and electricity. However with sufficient capital subsidies to lower the upfront costs the analysis suggests solar PV-based hydrogen could become an attractive alternative cooking fuel. In addition switching from firewood to solar PVbased hydrogen for cooking yields the highest carbon dioxide (CO2) emissions savings across the cities analysed. Likewise replacing charcoal with hydrogen also offers substantial CO2 emissions savings though lower than switching from firewood. Correspondingly switching from LPG to hydrogen produces lower CO2 emissions savings than firewood and charcoal. The study findings could contribute to the growing body of knowledge on sustainable energy solutions offering practical insights for policymakers researchers and industry stakeholders seeking to promote clean cooking adoption in developing economies.

In the present study pilot simulations of the phenomena of blast wave and fireball generated by the rupture of a high-pressure (35 MPa) hydrogen tank (volume 72 L) due to fire were carried out. The computational fluid dynamics (CFD) model includes the realizable k-ε model for turbulence and the eddy dissipation model coupled with the one-step chemical reaction mechanism for combustion. The simulation results were compared with experimental data on a stand-alone hydrogen tank rupture in a bonfire test. The simulations provided insights into the interaction between the blast wave propagation and combustion process. The simulated blast wave decay is approximately identical to the experimental data concerning pressure at various distances. Fireball is first ignited at the ground level which is considered to be due to stagnation flow conditions. Subsequently the flame propagates toward the interface between hydrogen and air.

Studies estimating the production cost of hydrogen-based fuels known as e-fuels often use renewable power profile time series obtained from open-source simulation tools that rely on meteorological reanalysis and satellite data such as Renewables.ninja or PVGIS. These simulated time series contain errors compared to real on-site measured data which are reflected in e-fuels cost estimates plant design and operational performance increasing the risk of inaccurate plant design and business models. Focusing on solar-powered e-fuels this study aims to quantify these errors using high-quality on-site power production data. A state-of-the-art optimization techno-economic model was used to estimate e-fuel production costs by utilizing either simulated or high-quality measured PV power profiles across four sites with different climates. The results indicate that in cloudy climates relying on simulated data instead of measured data can lead to an underestimation of the fuel production costs by 36 % for a hydrogen user requiring a constant supply considering an original error of 1.2 % in the annual average capacity factor. The cost underestimation can reach 25 % for a hydrogen user operating between 40 % and 100 % load and 17.5 % for a fully flexible user. For comparison cost differences around 20 % could also result from increasing the electrolyser or PV plant costs by around 55 % which highlights the importance of using high-quality renewable power profiles. To support this an open-source collaborative repository was developed to facilitate the sharing of measured renewable power profiles and provide tools for both time series analysis and green hydrogen techno-economic assessments.

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.