Transmission, Distribution & Storage

Body-centered cubic (BCC) alloys are considered as promising materials for hydrogen storage with high theoretical storage capacity (H/M ratio of 2). Nonetheless they often suffer from sluggish kinetics of hydrogen absorption and high hydrogen desorption temperature. Carbon materials are efficient hydrogenation catalysts however their influence on the hydrogen storage properties of BCC alloy has not been comprehensively studied. Therefore in this paper composites obtained by milling of carbon catalysts (carbon nanotubes mesoporous carbon carbon nanofibers diamond powder graphite fullerene) and BCC alloy (Ti1.5V0.5) were extensively studied in the non-hydrogenated and hydrogenated state. The structure and microstructure of the obtained materials were studied by scanning and transmission electron microscopes X-ray diffraction (XRD) and Raman spectroscopy. XRD and Raman measurements showed that BCC alloy and carbon structures were in most cases intact after the composite synthesis. The hydrogenation/dehydrogenation studies showed that all of the used carbon catalysts significantly improve the hydrogenation kinetics reduce the activation energy of the dehydrogenation process and decrease the dehydrogenation temperature (by nearly 100 K). The superior kinetic properties were measured for the composite with 5 wt % of fullerene that absorbs 3.3 wt % of hydrogen within 1 min at room temperature.

The injection of pure hydrogen at a T-junction into a horizontal pipe carrying natural gas is analysed computationally to understand the influence of blending and pipe geometry (diameter ratio various 90 orientations) on mixing for a target of 4.8e20% volume fraction hydrogen blend. The strongly inhomogeneous distribution of hydrogen within the pipe flow and on the pipe walls could indicate the location of potential pipe material degradation including embrittlement effects. The low molecular mass of hydrogen reduces the penetration of a side-branch flow and increases the buoyancy forces leading to stratification with high hydrogen concentrations on the upper pipe surface downstream of the branch. Top-side injection leads to the hydrogen concentration remaining >40% for up to 8 pipe diameters from the injection point for volumetric dilutions ( D) less than 30%. Under-side injection promotes mixing within the flow interior and reduces wall concentration at the lower surface compared to top-side injection. The practical implications for these results in terms of mixing requirements and the contrasting constraint of codes of practice and energy demands are discussed.

Nanoporous carbons remain the most promising candidates for effective hydrogen storage by physisorption in currently foreseen hydrogen-based scenarios of the world’s energy future. An optimal sorbent meeting the current technological requirement has not been developed yet. Here we first review the storage limitations of currently available nanoporous carbons then we discuss possible ways to improve their storage performance. We focus on two fundamental parameters determining the storage (the surface accessible for adsorption and hydrogen adsorption energy). We define numerically the values nanoporous carbons have to show to satisfy mobile application requirements at pressures lower than 120 bar. Possible necessary modifications of the topology and chemical compositions of carbon nanostructures are proposed and discussed. We indicate that pore wall fragmentation (nano-size graphene scaffolds) is a partial solution only and chemical modifications of the carbon pore walls are required. The positive effects (and their limits) of the carbon substitutions by B and Be atoms are described. The experimental ‘proof of concept’ of the proposed strategies is also presented. We show that boron substituted nanoporous carbons prepared by a simple arc-discharge technique show a hydrogen adsorption energy twice as high as their pure carbon analogs. These preliminary results justify the continuation of the joint experimental and numerical research effort in this field.

The price of constructing hydrogen generation units is very high and sometimes it is not possible to build them in the desired location so the transfer of hydrogen from the hydrogen generation system to the units that need it is justified. Since the storage of hydrogen gas needs a large volume and its transportation is very complex so if hydrogen is stored in liquid form this problem can be resolved. In transporting liquid hydrogen (LH2) over long distances owing to heat transfer to the environment the LH2 vaporizes forming boil-off gas (BOG). Herein in lieu of only reliquifying the BOG this study proposes and assesses a system employing the BOG partially as feed for a novel liquefaction process and also the remaining utilized in a proton exchange membrane fuel cell (PEMFC) to generate power. Using the cold energy of the onsite liquid oxygen utility of the LH2 cargo vessel the mixed refrigerant liquefaction cycle is further cooled down. In this regard by using 130 kg/h BOG as input 60.37 kg/h of liquid hydrogen is produced and the rest enters PEMFC with 552.7 kg/h oxygen to produce 1592 kW of power. The total thermal efficiency of the integrated system and electrical efficiency of the PEMFC is 83.18% and 68.76% respectively. Regarding the liquefaction cycle its specific power consumption (SPC) and coefficient of performance (COP) were achieved at 3.203 kWh/kgLH2 and 0.1876 respectively. The results of exergy analysis show that the exergy destruction of the whole system is 937.4 kW and also its exergy efficiency is calculated to be 58.38%. Exergoeconomic and Markov analyses have also been applied to the integrated system. Also by changing the important parameters of PEMFC its optimal performance has been extracted.

A significant contribution to the reduction of carbon emissions will be enabled through the transition from a centralised fossil fuel system to a decentralised renewable electricity system. However due to the intermittent nature of renewable energy storage is required to provide a suitable response to dynamic loads and manage the excess generated electricity with utilisation during periods of low generation. This paper investigates the use of stationary hydrogen-based energy storage systems for microgrids and distributed energy resource systems. An exploratory study was conducted in Australia based on a mixed methodology. Ten Australian industry experts were interviewed to determine use cases for hydrogen-based energy storage systems’ requirements barriers methods and recommendations. This study suggests that the current cost of the electrolyser fuel cell and storage medium and the current low round-trip efficiency are the main elements inhibiting hydrogen-based energy storage systems. Limited industry and practical experience are barriers to the implementation of hydrogen storage systems. Government support could help scale hydrogen-based energy storage systems among early adopters and enablers. Furthermore collaboration and knowledge sharing could reduce risks allowing the involvement of more stakeholders. Competition and innovation could ultimately reduce the costs increasing the uptake of hydrogen storage systems.

Transporting green hydrogen by existing natural gas networks has become a practical means to accommodate curtailed wind and solar power. Restricted by pipe materials and pressure levels there is an upper limit on the hydrogen blending ratio of hydrogen-enriched compressed natural gas (HCNG) that can be transported by natural gas pipelines which affects whether the natural gas network can supply energy safely and reliably. To this end this paper investigates the effects of the intermittent and fluctuating green hydrogen produced by different types of renewable energy on the dynamic distribution of hydrogen concentration after it is blended into natural gas pipelines. Based on the isothermal steady-state simulation results of the natural gas network two convection–diffusion models for the dynamic simulation of hydrogen injections are proposed. Finally the dynamic changes of hydrogen concentration in the pipelines under scenarios of multiple green hydrogen types and multiple injection nodes are simulated on a seven-node natural gas network. The simulation results indicate that compared with the solar-power-dominated hydrogen productionblending scenario the hydrogen concentrations in the natural gas pipelines are more uniformly distributed in the wind-power-dominated scenario and the solar–wind power balance scenario. To be specific in the solar-power-dominated scenario the hydrogen concentration exceeds the limit for more time whilst the overall hydrogen production is low and the local hydrogen concentration in the natural gas network exceeds the limit for nearly 50% of the time in a day. By comparison in the wind-power-dominated scenario all pipelines can work under safe conditions. The hydrogen concentration overrun time in the solar–wind power balance scenario is also improved compared with the solar-power-dominated scenario and the limit-exceeding time of the hydrogen concentration in Pipe 5 and Pipe 6 is reduced to 91.24% and 91.99% of the solar-power-dominated scenario. This work can help verify the day-ahead scheduling strategy of the electricity-HCNG integrated energy system (IES) and provide a reference for the design of local hydrogen production-blending systems.

Hypothesis.<br/>The large-scale implementation of hydrogen economy requires immense storage spaces to facilitate the periodic storage/production cycles. Extensive modelling of hydrogen transport in porous media is required to comprehend the hydrogen-induced complexities prior to storage to avoid energy loss. Wettability of hydrogen-brine-rock systems influence flow properties (e.g. capillary pressure and relative permeability curves) and the residual saturations which are all essential for subsurface hydrogen systems.<br/>Model.<br/>This study aims to understand which parameters critically control the contact angle for hydrogen-brine-rock systems using the surface force analysis following the DLVO theory and sensitivity analysis. Furthermore the effect of roughness is studied using the Cassie-Baxter model.<br/>Findings.<br/>Our results reveal no considerable difference between H2 and other gases such as N2. Besides the inclusion of roughness highly affects the observed apparent contact angles and even lead to water-repelling features. It was observed that contact angle does not vary significantly with variations of surface charge and density at high salinity which is representative for reservoir conditions. Based on the analysis it is speculated that the influence of roughness on contact angle becomes significant at low water saturation (i.e. high capillary pressure).

The RePowerEU plan [1] and the European Hydrogen Strategy [2] recognise the important role that the transport of hydrogen will play in enabling the penetration of renewable hydrogen in Europe. To implement the European Hydrogen Strategy it is important to understand whether the transport of hydrogen is cost effective or whether hydrogen should be produced where it is used. If transporting hydrogen makes sense a second open question is how long the transport route should be for the cost of the hydrogen to still be competitive with locally produced hydrogen. JRC has performed a comprehensive study regarding the transport of hydrogen. To investigate which renewable hydrogen delivery pathways are favourable in terms of energy demand and costs JRC has developed a database and an analytical tool to assess each step of the pathways and used it to assess two case studies. The study reveals that there is no single optimal hydrogen delivery solution across every transport scenario. The most cost effective way to deliver renewable hydrogen depends on distance amount final use and whether there is infrastructure already available. For distances compatible with the European territory compressed and liquefied hydrogen solutions and especially compressed hydrogen pipelines offer lower costs than chemical carriers do. The repurposing of existing natural gas pipelines for hydrogen use is expected to significantly lower the delivery cost making the pipeline option even more competitive in the future. By contrast chemical carriers become more competitive the longer the delivery distance (due to their lower transport costs) and open up import options from suppliers located for example in Chile or Australia.

Subsurface porous formations provide large capacities for underground hydrogen storage (UHS). Successful utilization of these porous reservoirs for UHS depends on accurate quantification of the hydrogen transport characteristics at continuum (macro) scale specially in contact with other reservoir fluids. Relative-permeability and capillary-pressure curves are among the macro-scale transport characteristics which play crucial roles in quantification of the storage capacity and efficiency. For a given rock sample these functions can be determined if pore-scale (micro-scale) surface properties specially contact angles are known. For hydrogen/brine/rock system these properties are yet to a large extent unknown. In this study we characterize the contact angles of hydrogen in contact with brine and Bentheimer and Berea sandstones at various pressure temperature and brine salinity using captive-bubble method. The experiments are conducted close to the in-situ conditions which resulted in water-wet intrinsic contact angles about 25 to 45 degrees. Moreover no meaningful correlation was found with changing tested parameters. We monitor the bubbles over time and report the average contact angles with their minimum and maximum variations. Given rock pore structures using the contact angles reported in this study one can define relative-permeability and capillary-pressure functions for reservoir-scale simulations and storage optimization.

Among the numerous envisioned applications for hydrogen in the decarbonization of the energy system seasonal energy storage is usually regarded as one of the most likely options. Although long-term energy storage is usually considered at grid-scale level given the increasing diffusion of distributed energy systems and the expected cost reduction in hydrogen related components some companies are starting to offer residential systems with PV modules and batteries that rely on hydrogen for seasonal storage of electrical energy. Such hydrogen storage systems are generally composed by water electrolysers hydrogen storage vessels and fuel cells.<br/>The aim of this work is to investigate such systems and their possible applications for different geographical conditions in Italy. On-grid and off-grid systems are considered and compared to systems without hydrogen in terms of self-consumption ratio size of components and economic investment. Each different option has been assessed from a techno-economic point of view via MESS (Multi Energy Systems Simulator) an analytical programming tool for the analysis of local energy systems.<br/>Results have identified the optimal sizing of the system's components and have shown how such systems are not in general economically competitive for a single dwelling although they can in some cases ensure energy independence.