Transmission, Distribution & Storage

Hydrogen is emerging as a promising future energy medium in a wide range of industries. For mobile applica tions it is commonly stored in a gaseous state within high-pressure composite overwrapped pressure vessels (COPVs). The current state of the art pressure vessel technology known as Type V eliminates the internal polymer gas barrier used in Type IV vessels and instead relies on carbon fibre laminate to provide structural properties and prevent gas leakage. Achieving this functionality at high pressure poses several engineering challenges that have thus far prohibited commercial application. Additionally the traditional manufacturing process for COPVs filament winding has several constraints that limit the design space. Automated fibre placement (AFP) a highly flexible robotic composites manufacturing technique has the potential to replace filament winding for composite pressure vessel manufacturing and provide pathways for further vessel optimi sation. A combination of both AFP and Type V technology could provide an avenue for a new generation of highperformance composite pressure vessels. This critical review presents key work on industry-standard Type IV vessels alongside the current state of Type V CPV technology including manufacturing developments challenges cost relevance to commercial standards and future fabrication solutions using AFP. Additionally a novel Type V CPV design concept for a two-piece AFP produced vessel is presented.

The storage of excess electrical generation enabled through the electrolytic production of hydrogen from water would allow “load-shifting” of power generation. This paves the way for hydrogen as an energy carrier to be further used as a zero‑carbon fuel for land air and sea transportation. However challenges in hydrogen storage and transportation ultimately pose restrictions on its wider adaption along horizontal and vertical vectors. This paper investigates chemical energy carriers ranging from small molecules such as ammonia and methane to formic acid as well as other more complex hydrocarbons in response to this timely engineering problem. The hydrogenation and dehydrogenation of such carrier molecules require energy lowering the effective net heating value of hydrogen up to 32 %. Different carrier approaches are discussed in the light of availability energetics water requirements and suitability for applications in power generation shipping trucking and aviation supplemented by a comprehensive safety review making this study unique in its field. It is found that hydrogen delivered without a carrier is ideal for power generation applications due to the large quantities required. Aviation would benefit from either ammonia or hydrogen and is generally a field challenging to decarbonize. Ammonia appears also to be a good medium for shipping hydrogen between continents and to power container ships due to its high energy density and lower liquid temperature compared with hydrogen. At the same time ammonia can also be used to power the ship's engine. Long-haul trucking would benefit the most from cryogenic or compressed hydrogen due to the lower quantities required and purity requirements of the fuel cells.

Because of their high surface areas crystallinity and tunable propertiesmetal−organic frameworks (MOFs) have attracted intense interest as next-generationmaterials for gas capture and storage. While much effort has been devoted to thediscovery of new MOFs a vast catalog of existing MOFs resides within the CambridgeStructural Database (CSD) many of whose gas uptake properties have not beenassessed. Here we employ data mining and automated structure analysis to identify“cleanup” and rapidly predict the hydrogen storage properties of these compounds.Approximately 20 000 candidate compounds were generated from the CSD using analgorithm that removes solvent/guest molecules. These compounds were thencharacterized with respect to their surface area and porosity. Employing the empiricalrelationship between excess H2 uptake and surface area we predict the theoretical total hydrogen storage capacity for the subsetof ∼4000 compounds exhibiting nontrivial internal porosity. Our screening identifies several overlooked compounds having hightheoretical capacities; these compounds are suggested as targets of opportunity for additional experimental characterization.More importantly screening reveals that the relationship between gravimetric and volumetric H2 density is concave downwardwith maximal volumetric performance occurring for surface areas of 3100−4800 m2 /g. We conclude that H2 storage in MOFswill not benefit from further improvements in surface area alone. Rather discovery efforts should aim to achieve moderate massdensities and surface areas simultaneously while ensuring framework stability upon solvent removal.

In the energy transition from fossil fuels to renewables hydrogen is a realistic alternative to achieving the decarbonization target. However its chemical and physical properties make its storage and transport expensive. To ensure the cost-effective H2 usage as an energy vector other chemicals are getting attention as H2 carriers. Among them ammonia is the most promising candidate. The value chain of NH3 as a H2 carrier considering the long-distance ship transport includes NH3 synthesis and storage at the loading terminal NH3 storage at the unloading terminal and its cracking to release H2. NH3 synthesis and cracking are the cost drivers of the value chain. Also the NH3 cracking at large scale is not a mature technology and a significant effort has to be made in intensifying the process as much as possible. In this respect this work reviews the available technologies for NH3 cracking critically analyzing them in view of the scale up to the industrial level.

To achieve carbon neutrality by 2060 decarbonization in the energy sector is crucial. Hydrogen is expected to be vital for achieving the aim of carbon neutrality for two reasons: use of power-to-hydrogen (P2H) can avoid carbon emissions from hydrogen production which is traditionally performed using fossil fuels; Hydrogen from P2H can be stored for long durations in large scales and then delivered as industrial raw material or fed back to the power system depending on the demand. In this study we focus on the analysis and evaluation of hydrogen value in terms of improvement in the flexibility of the energy system particularly that derived from hydrogen storage. An electricity–hydrogen coupled energy model is proposed to realize the hourly-level operation simulation and capacity planning optimization aiming at the lowest cost of energy. Based on this model and considering Northwest China as the region of study the potential of improvement in the flexibility of hydrogen storage is determined through optimization calculations in a series of study cases with various hydrogen demand levels. The results of the quantitative calculations prove that effective hydrogen storage can improve the system flexibility by promoting the energy demand balance over a long term contributing toward reducing the investment cost of both generators and battery storage and thus the total energy cost. This advantage can be further improved when the hydrogen demand rises. However a cost reduction by 20% is required for hydrogen-related technologies to initiate hydrogen storage as long-term energy storage for power systems. This study provides a suggestion and reference for the advancement and planning of hydrogen storage development in regions with rich sources of renewable energy.

Underground hydrogen storage in depleted hydrocarbon reservoirs and aquifers has been proposed as a potential long-term solution to storing intermittently produced renewable electricity as the subsurface formations provide secure and large storage space. Various phenomena can lead to hydrogen loss in subsurface systems with the key cause being the trapping especially during the withdrawal cycle. Capillary trapping in particular is strongly related to the hysteresis phenomena observed in the capillary pressure/saturation and relative-permeability/saturation curves. This paper address two key points: (1) the sole impact of hysteresis in capillary pressure on hydrogen trapping during withdrawal cycles and (2) the dependency of optimal operational parameters (injection/withdrawal flow rate) and the reservoir characteristics such as permeability thickness and wettability of the porous medium on the remaining hydrogen saturation.<br/>Model<br/>To study the capillary hysteresis during underground hydrogen storage Killough [1] model was implemented in the MRST toolbox [2]. A comparative study was performed to quantify the impact of changes in capillary pressure behaviour by including and excluding the hysteresis and scanning curves. Additionally this study investigates the impact of injection/withdrawal rates and the aquifer permeability for various capillary and Bond numbers in a homogeneous system.<br/>Findings<br/>It was found that although the hydrogen storage efficiency is not considerably impacted by the inclusion of the capillary-pressure scanning curves the impact of capillary pressure on the well properties (withdrawal rate and pressure) can become significant. Higher injection and withdrawal rates does not necessarily lead to a better performance in terms of productivity. The productivity enhancement depends on the competition between gravitational capillary and viscous forces. The observed water upconing at relatively high capillary numbers resulted in low hydrogen productivity. highlighting the importance of well design and placement.

Green hydrogen produced from surplus electricity during peak production can be injected into subsurface reservoirs and retrieved during high-demand periods. In this study X-ray tomography was employed to examine hysteresis resulting from repeated hydrogen injection and withdrawal. An unsteady state experiment was performed to evaluate the distribution of hydrogen and brine after drainage and imbibition cycles: images of the pore-space configuration of fluids were taken immediately once injection had stopped and after waiting for a period of 16 h with no flow. A Bentheimer sandstone sample with a length of 60 mm and diameter of 12.8 mm was used and hydrogen was injected at ambient temperature and a pore pressure of 1 MPa. The gas flow rate was decreased from 2 ml/min to 0.08 ml/min over three cycles of gas injection followed by water flooding while the brine injection rate was kept constant. The results showed the presence of capillary pressure hysteresis and hydrogen migration through Ostwald ripening due to the diffusion of gas dissolved in the brine. These phenomena were characterized through analysis of interfacial curvature area connectivity and pore occupancy. The hydrogen tended to reside in the larger pore spaces consistent with water-wet conditions. 16 h after flow had stopped the hydrogen aggregated into larger ganglia with a single large connected ganglion dominating the volume. Moreover the Euler characteristic decreased after 16 h indicating an improvement in connectivity. The work implies that Ostwald ripening – mass transport of dissolved gas – leads to less hysteresis and better connectivity than would be assumed ignoring this effect as done in assessments of hydrocarbon flow and trapping.

Implementation of the hydrogen economy for emission reduction will require storage facilitiesand underground hydrogen storage (UHS) in porous media offers a readily available large-scale option. Lack ofstudies on multiphase hydrogen flow in porous media is one of the several barriers for accurate predictions ofUHS. This paper reports for the first time measurements of hysteresis in hydrogen-water relative permeabilityin a sandstone core under shallow storage conditions. We use the steady state technique to measure primarydrainage imbibition and secondary drainage relative permeabilities and extend laboratory measurements withnumerical history matching and capillary pressure measurements to cover the whole mobile saturation range.We observe that gas and water relative permeabilities show strong hysteresis and nitrogen as substitute forhydrogen in laboratory assessments should be used with care. Our results serve as calibrated input to field scalenumerical modeling of hydrogen injection and withdrawal processes during porous media UHS.

Hydrogen and electricity derived from renewable sources present feasible alternative energy options for the decarbonisation of the transportation and power sectors. This study presents the utilisation of hydrogen generated from solar and wind energy resources as a clean fuel for mobility and backup storage for stationary applications under economic and environmental uncertainties. This is achieved by developing a detailed technoeconomic model of an integrated system consisting of a hydrogen refuelling station and an electric power generation system using Mixed Integer Quadratic Constrained Programming (MIQCP) which is further relaxed to Mixed Integer Linear Programming (MILP). The model is implemented in the Advanced Interactive Multidi mensional Modelling Software (AIMMS) and considering the inherent uncertainties in the wind resource solar resource costs and discount rate the total cost of the three configurations (Hybrid PV-Wind Standalone PV and Standalone wind energy system) was minimised using robust optimisation technique and the corresponding optimal sizes of the components levelised cost of energy (LCOE) excess energy greenhouse emission avoided and carbon tax were evaluated. The levelised cost of the deterministic optimisation solution for all the config uration ranges between 0.0702 $/kWh to 0.0786 $/kWh while the levelised cost of the robust optimisation solution ranges between 0.07188 $/kWh to 0.1125 $/kWh. The proposed integration has the advantages of affordable hydrogen and electricity prices minimisation of carbon emissions and grid export of excess energy.

We perform a simulation study of hydrogen injection in a depleted gas reservoir to assess the geomechanical impact of hydrogen storage relative to other commonly injected gases (methane CO2). A key finding is that the differences in hydrogen density compressibility viscosity and thermal properties compared to the other gases result in significantly less thermal perturbation at reservoir level. The risks of fault reactivation and wellbore fractures due to thermally-induced stress changes are significantly lower when storing hydrogen compared to results observed in CO2 scenarios. This implies that hydrogen injection and production has a much smaller geomechanical footprint with benefits for operational safety. We also find that use of nitrogen cushion gas ensures efficient deliverability and phase separation in the reservoir. However in this study a large fraction of cushion gas was back-produced in each cycle demonstrating the need for further studies of the surface processing requirements and economic implications.