United Kingdom

Hydrogen (H2) usage was 90 metric tonnes (Mt) in 2020 almost entirely for industrial and refining uses and generated almost completely from fossil fuels leading to nearly 900 Mt of carbon dioxide emissions. However there has been significant growth of H2 in recent years. Electrolysers' total capacity which are required to generate H2 from electricity has multiplied in the past years reaching more than 300 MW through 2021. Approximately 350 projects reportedly under construction could push total capacity to 54 GW by the year 2030. Some other 40 projects totalling output of more than 35 GW are in the planning phase. If each of these projects is completed global H2 production from electrolysers could exceed 8 Mt by 2030. It's an opportunity to take advantage of H2S prospects to be a crucial component of a clean safe and cost-effective sustainable future. This paper assesses the situation regarding H2 at the moment and provides recommendations for its potential future advancement. The study reveals that clean H2 is experiencing significant unparalleled commercial and political force with the amount of laws and projects all over the globe growing quickly. The paper concludes that in order to make H2 more widely employed it is crucial to significantly increase innovations and reduce costs. The practical and implementable suggestions provided to industries and governments will allow them to fully capitalise on this growing momentum.

The natural gas industry proposes carrying out trials on limited parts of the gas network using hydrogen as an alternative to natural gas as a fuel. Ahead of these trials it is important to establish whether the zones of negligible extent that are typically applied to natural gas systems could still be considered zones of negligible extent for hydrogen. The standard IGEM/UP/16 is commonly used by the natural gas industry to carry out area classification for low pressure gas systems for example as found in boiler houses. However IGEM/UP/16 is not applicable to hydrogen. Therefore IGEM commissioned HSE’s Science Division to develop some data that could be used to feed into an area classification assessment for the village trials.<br/>This report identifies two main elements of IGEM/UP/16 which may not apply to hydrogen and suggests values for hydrogen-specific alternatives. These are the ventilation rate requirements to allow a zone to be deemed of negligible extent and the definition of a confined space.

Britain’s Hydrogen Blending Delivery Plan which sets out how all five of Britain’s gas grid companies will meet the Government’s target for Britain’s network of gas pipes to be ready to deliver 20% hydrogen to homes and businesses from 2023 as a replacement for natural gas.

The transition to a low-carbon energy system can be depicted as a “great reconfiguration” from a socio-technical perspective that carries the risk of impact shifts. Electrification with the objective of achieving rapidly deep decarbonisation must be accompanied by effective efficiency and flexibility measures. Hydrogen can be a preferred option in the decarbonisation process where electrification of end-uses is difficult or impractical as well as for long-term storage in energy infrastructure characterised by a large penetration of renewable energy sources. Notwithstanding the current uncertainties regarding costs environmental impact and the inherent difficulties of increasing rapidly supply capacity hydrogen can represent a solution to be used in multi-energy systems with combined heat and power (CHP) in particular in urban energy districts. In fact while achieving carbon savings with natural gas fuelled CHP is not possible when low grid carbon intensity factors are present it may still be possible to use it to provide flexibility services and to reduce emissions further with switch from natural gas to hydrogen. In this paper a commercially established urban district energy scheme located in Southampton (United Kingdom) is analysed with the goal of exploring potential variations in its energy demand. The study proposes the use of scalable data-driven methods and probabilistic simulation to generate seasonal energy demand patterns representing the potential short-term and long-term evolution of the energy district.

The transport sector is considered to be a significant contributor to greenhouse gas emissions as this sector emits about one-fourth of global CO2 emissions. Transport emissions contribute toward climate change and have been linked to adverse health impacts. Therefore alternative and sustainable transport options are urgent for decarbonising the transport sector and mitigating those issues. Hydrogen fuel cell vehicles are a potential alternative to conventional vehicles which can play a significant role in decarbonising the future transport sector. This study critically analyses the recent works related to hydrogen fuel cell integration into vehicles modelling and experimental investigations of hydrogen fuel cell vehicles with various powertrains. This study also reviews and analyses the performance energy management strategies lifecycle cost and emissions of fuel cell vehicles. Previous literature suggested that the fuel consumption and well-to-wheel greenhouse gas emissions of hydrogen fuel cell-powered vehicles are significantly lower than that of conventional internal combustion vehicles. Hydrogen fuel cell vehicles consume about 29–66 % less energy and cause approximately 31–80 % less greenhouse gas emissions than conventional vehicles. Despite this the lifecycle cost of hydrogen fuel cell vehicles has been estimated to be 1.2–12.1 times higher than conventional vehicles. Even though there has been recent progress in energy management in hydrogen fuel cell electric vehicles there are a number of technical and economic challenges to the commercialisation of hydrogen fuel cell vehicles. This study presents current knowledge gaps and details future research directions in relation to the research advancement of hydrogen fuel cell vehicles.

In this podcast David Ledesma talks to Martin Lambert and Abdurahman Alsulaiman about the potential hydrogen import market particularly focusing on the EU which currently holds the largest and earliest hydrogen target. The podcast explores the emerging hydrogen trade market and considers numerous possibilities for its open up providing better clarity on policy statements and balance them against project announcements.

Throughout the podcast Martin and Abdulrahman delve into various key points – they shed light on the primary areas of focus for projects set to be completed by or before 2030 as well as the distinction between announcements and tangible progress such as projects currently at the Final Investment Decision stage or under construction.

Additionally they explore the EU’s role as one of the few countries to have publicly announced its requirements for hydrogen imports and its ambitious hydrogen import target. The EU is currently establishing a benchmark for the future hydrogen market. However in order for the EU to succeed in establishing future hydrogen supply lines with future trade partners it will be crucial to engage in open dialogues covering a wide range of topics.

Join us in this podcast as we uncover the potential of the hydrogen import market with a specific focus on the EU and discuss the necessary steps for its success.

The podcast can be found on their website.

Pursuing net-zero emission operations in the shipping industry are quintessential for this sector to mitigate the environmental impact caused by hydrocarbon fuel combustion. Significant contributions to this are expected from the substitution of conventional marine fuels by alternative emission-free fuels with lower emission footprints. This study aims to conduct a comprehensive literature review for delineating the main characteristics of the considered alternative fuels specifically focusing on hydrogen methanol and ammonia which have recently attracted attention from both industry and academia. This study comparatively assesses the potential of using these fuels in marine engines and their subsequent performance characteristics as well as the associated environmental benefits. In addition the required storage conditions space as well as the associated costs are reviewed. Special attention is given to the safety characteristics and requirements for each alternative fuel. The results of this study demonstrate that the environmental benefits gained from alternative fuel use are pronounced only when renewable energy is considerably exploited for their production whereas the feasibility of each fuel depends on the vessel type used and pertinent storage constraints. Hydrogen ammonia and methanol are considered best-fit solutions for small scale shipping requiring minimal on-board storage. In addition the need for comparative assessments between diesel and alternative fuels is highlighted and sheds light on marine engines’ operational characteristics. Moreover using combinations of alternative and diesel fuels is identified as a direction towards decarbonisation of the maritime sector; intensifying the need for optimisation studies on marine engine design and operation. This study concludes with recommendations for future research directions thus contributing to fuel research concepts that can facilitate the shipboard use of alternative fuels.

In August 2022 Shell started construction of Holland Hydrogen I (HH I) a 200 MW electrolyser plant in the port of Rotterdam’s industrial zone on Maasvlakte II in the Netherlands. HH I will produce up to 60000 kg of renewable hydrogen per day. The development and demonstration of a safe layout and plant design had been challenging due to ambitious HH I project premises many technical novelties common uncertainties in hydrogen leak effect prediction a lack of large-scale water electrolyzer operating history and limited standardization in this industry sector. This paper provides an industry perspective of the major challenges in commercial electrolyzer plant HSSE risk assessment and risk mitigation work processes required to develop and demonstrate a safe design and it describes lessons learned in this area during the HH I project. Furthermore the paper lists major common gaps in relevant knowledge engineering tools standards and OEM deliverables that need closure to enable future commercial electrolyzer plant projects to develop an economically viable and plant design and layout more efficiently and cost-effectively.

In the present study Reynolds-Averaged Navier-Stokes simulations together with a novel flamelet generated manifold (FGM) hybrid combustion model incorporating preferential diffusion effects is utilised for the investigation of a hydrogen-blended diesel-hydrogen dual-fuel engine combustion process with high hydrogen energy share. The FGM hybrid combustion model was developed by coupling laminar flamelet databases obtained from diffusion flamelets and premixed flamelets. The model employed three control variables namely mixture fraction reaction progress variable and enthalpy. The preferential diffusion effects were included in the laminar flamelet calculations and in the diffusion terms in the transport equations of the control variables. The resulting model is then validated against an experimental diesel-hydrogen dual-fuel combustion engine. The results show that the FGM hybrid combustion model incorporating preferential diffusion effects in the flame chemistry and transport equations yields better predictions with good accuracy for the in-cylinder characteristics. The inclusion of preferential diffusion effects in the flame chemistry and transport equations was found to predict well several characteristics of the diesel-hydrogen dual-fuel combustion process: 1) ignition delay 2) start and end of combustion 3) faster flame propagation and quicker burning rate of hydrogen 4) high temperature combustion due to highly reactive nature of hydrogen radicals 5) peak values of the heat release rate due to high temperature combustion of the partially premixed pilot fuel spray with entrained hydrogen/air and then background hydrogen-air premixed mixture. The comparison between diesel-hydrogen dual-fuel combustion and diesel only combustion shows early start of combustion longer ignition delay time higher flame temperature and NOx emissions for dual-fuel combustion compared to diesel only combustion.

High-resolution direct numerical simulations are conducted for under-expanded cryogenic hydrogen gas jets to characterize the nearfield flow physics. The basic flow features and jet dynamics are analyzed in detail revealing the existence of four stages during early jet development namely (a) initial penetration (b) establishment of near-nozzle expansion (c) formation of downstream compression and (d) wave propagation. Complex acoustic waves are formed around the under-expanded jets. The jet expansion can also lead to conditions for local liquefaction from the pressurized cryogenic hydrogen gas release. A series of simulations are conducted with systematically varied nozzle pressure ratios and systematically changed exit diameters. The acoustic waves around the jets are found to waken with the decrease in the nozzle pressure ratio. The increase in the nozzle pressure ratio is found to accelerate hydrogen dispersion and widen the regions with hydrogen liquefaction potential. The increase in the nozzle exit diameter also widens the region with hydrogen liquefaction potential but slows down the evolution of the flow structures.

In response to the UK Government’s commitment to achieve net-zero carbon emissions by 2050 a range of research and demonstration projects are underway to investigate the feasibility of using hydrogen in place of natural gas within the national transmission and distribution system. In order for these projects to achieve their full scope of work a mechanism for performing hazardous area classification for hydrogen installations is required. At present IGEM/SR/25 is used to undertake such assessments for natural gas installations but the standard is not currently applicable to hydrogen or hydrogen/natural gas blends.<br/>This report presents updated data and a summary of the recommended methodologies for hazardous area classification of installations using hydrogen or blends of up to 20% hydrogen in natural gas. The contents of this report are intended to provide a technical commentary and the data for a hydrogen-specific supplement to IGEM/SR/25. The supplement will specifically cover 100% hydrogen and a 20/80% by volume blend of hydrogen/natural gas. Reference to intermediate blends is included in this report where appropriate to cover the anticipated step-wise introduction of hydrogen into the natural gas network.<br/>This report is divided into a series of appendices each of which covers a specific area of the IGEM standard. Each appendix includes a summary of specific recommendations made to enable IGEM/SR/25 to be applied to hydrogen and blends of up to 20% hydrogen in natural gas. The reader is encouraged to review the individual appendices for specific conclusions associated with the topic areas addressed in this report.<br/>In general the existing methodologies and approaches used for area classification in IGEM/SR/25 have been deemed appropriate for installations using either hydrogen or blends of up to 20% hydrogen in natural gas. Where necessary revised versions of the equations and zoning distances used in the standard are presented which account for the influence of material property differences between natural gas and the two alternative fuels considered in this work.

Hydrogen as a suitable and clean energy carrier has been long considered a primary fuel or in combination with other conventional fuels such as gasoline and diesel. Since the density of hydrogen is very low in port fuel-injection configuration the engine’s volumetric efficiency reduces due to the replacement of hydrogen by intake air. Therefore hydrogen direct in-cylinder injection (injection after the intake valve closes) can be a suitable solution for hydrogen utilization in spark ignition (SI) engines. In this study the effects of hydrogen direct injection with different hydrogen energy shares (HES) on the performance and emissions characteristics of a gasoline port-injection SI engine are investigated based on reactive computational fluid dynamics. Three different injection timings of hydrogen together with five different HES are applied at low and full load on a hydrogen– gasoline dual-fuel SI engine. The results show that retarded hydrogen injection timing increases the concentration of hydrogen near the spark plug resulting in areas with higher average temperatures which led to NOX emission deterioration at −120 Crank angle degree After Top Dead Center (CAD aTDC) start of injection (SOI) compared to the other modes. At −120 CAD aTDC SOI for 50% HES the amount of NOX was 26% higher than −140 CAD aTDC SOI. In the meanwhile an advanced hydrogen injection timing formed a homogeneous mixture of hydrogen which decreased the HC and soot concentration so that −140 CAD aTDC SOI implied the lowest amount of HC and soot. Moreover with the increase in the amount of HES the concentrations of CO CO2 and soot were reduced. Having the HES by 50% at −140 CAD aTDC SOI the concentrations of particulate matter (PM) CO and CO2 were reduced by 96.3% 90% and 46% respectively. However due to more complete combustion and an elevated combustion average temperature the amount of NOX emission increased drastically.

In this fifth episode  Steffan Eldred and Neelam Mughal from Innovate UK KTN discuss how the glass industry is driving new hydrogen developments and research and explore the hydrogen transition opportunities and challenges in this sector alongside their special guest Rob Ireson Innovation and Partnerships Manager at Glass Futures Ltd.

The podcast can be found on their website

The UK oil and gas sector is mature and a combination of a dwindling resource base and a move towards decarbonisation has led to lower investments and an increasing decommissioning bill. Many existing offshore assets are in the vicinity of potential renewable energy developments or low-carbon facilities. We propose a technical evaluation process to understand whether pipelines might be repurposed to reduce the costs of low-carbon energy investment and oil decommissioning. We identify survival analysis as an effective method to investigate the potential of pipelines repurposing based on historical failure records as it deals with acceptable levels of data gaps and does not require associated field costs for detailed inspection. It provides a close estimate of the anticipated remaining life when compared to feasibility studies. We use survival analysis to examine several repurposing case studies for low-carbon investments. It also demonstrates that several pipeline systems have the potential to operate safely beyond their design life. Detailed records of failure will allow for further development of this methodology in the future.

DNV has carried out an investigation into potential uses for smart gas meter data as part of Phase 1 of the Modernising Energy Data Applications competition as funded by UK Research & Innovation. In particular a series of calculations have been carried out to investigate the possibility of differentiating accidental gas leaks from normal appliance use in domestic properties. This is primarily with the aim of preventing explosions but the detection of leaks also has environmental and financial benefits.

Three gases have been considered in this study:

• A representative UK natural gas composition.
• A blend of 80% natural gas and 20% hydrogen.
• Pure hydrogen.

An established method was used to calculate the gas outflow rate from leaks into buildings downstream of the meter regulator. These gas leak rates were compared with the gas use by typical domestic appliances and these leaks were considered in the context of the smart gas meter data that is currently available in 30-minute periods. A representative set of gas accumulation calculations was performed. It was found that the following three general cases apply to all three gases:

• Small holes of up to 1 mm rarely reach flammable gas/air concentrations for any gas except under the most unfavourable conditions such as small volumes combined with low ventilation rates. These releases would likely be detected within 6 to 12 hours.
• Medium holes between 1 mm and 6 mm give outflow rates equivalent to a moderate to high level of gas use by appliances. The ability to detect these leaks is highly dependent on the hole size the time at which the leak begins and the normal gas use profile in the building. The larger leaks in this category would be detected within 30 to 60 minutes while the smaller leaks could take several hours to be clearly differentiated from appliance use. This is quick enough to prevent some explosions.
• Large holes of over 6 mm give leak rates greater than any gas use by appliances. These releases rapidly reach a flammable gas/air mixture in most cases but would typically be detected within the first 30-minute meter output period. Again some explosions could be prevented in this timescale.

An event tree has been used to quantify the approximate success rate of detecting and preventing explosion events. Using the currently available 30-minute smart meter data and functionality it is estimated that around 7% of explosions could be prevented with a slight variation depending on the gas type in use. Additional functionality could be included in the meter to improve this performance. Typically one of the risk mitigation measures in isolation increases the explosion prevention rate to around 15%. If multiple improvements are made then the detection rate is predicted to increase to around 30%.

An examination of detailed historical incident information suggests that the explosions that lead to fatalities or significant damage to houses are typically of the type that would be more likely to be detected and prevented. It is estimated that between 25% and 75% of the more severe explosions could be prevented depending on which potential improvements are implemented.

Based on the conservative estimates of explosion prevention a cost benefit analysis suggests that it is justifiable to spend between around £1 and £10 per meter installed to implement the proposed technology. This is based purely on lives saved and does not take account of other benefits.

With the rising threat of climate change green hydrogen is increasingly seen as the high-capacity energy storage and transport medium of the future. This creates an opportunity for low- and middle-income countries to leverage their high renewable energy potential to produce use and export low-cost green hydrogen creating environmental and economic development benefits. While identifying ideal locations for green hydrogen production is critical for countries when defining their green hydrogen strategies there has been a paucity of adequate geospatial planning approaches suitable to low- and middle-income countries. It is essential for these countries to identify green hydrogen production sites which match demand to expected use cases such that their strategies are economically sustainable. This paper therefore develops a novel geospatial cost modelling method to optimize the location of green hydrogen production across different use cases with a focus on suitability to low- and middle-income countries. This method is applied in Kenya to investigate the potential hydrogen supply chain for three use cases: ammonia-based fertilizer freight transport and export. We find hydrogen production costs of e3.7–9.9/kgH2 are currently achievable across Kenya depending on the production location chosen. The cheapest production locations are identified to the south and south-east of Lake Turkana. We show that ammonia produced in Kenya can be cost-competitive given the current energy crisis and that Kenya could export hydrogen to Rotterdam with costs of e7/kgH2 undercutting current market prices regardless of the carrier medium. With expected techno-economic improvements hydrogen production costs across Kenya could drop to e1.8–3.0/kgH2 by 2030.

In this podcast David Ledesma talks with Rahmat Poudineh Senior Research Fellow and Aliaksei Patonia Research Fellow on issues and options with respect to long distance transportation of the hydrogen.

Hydrogen currently is mainly a local or regional commodity. If hydrogen is to become a truly global-traded commodity it needs to be transported over long transoceanic distances in an economical way. However unlike natural gas shipping compressed or liquefied hydrogen over long distances is very inefficient and expensive. At the same time hydrogen can be converted into multiple carriers with a higher energy density and higher transport capacity such as liquid ammonia toluene/methylcyclohexane (MCH) or methanol. These chemicals have their own advantages and drawbacks and their techno-economic characteristics in terms of boil-off gas and thermodynamic and conversion losses play a key role in the efficiency of transoceanic transportation of the hydrogen.

On the other hand apart from techno-economic features there are other factors to consider for long distance transportation of the hydrogen via its careers. Here such issues as safety public acceptance as well as legal and regulatory constraints may come into play. Another factor is the availability of the industries and infrastructures already developed around any of possible hydrogen carriers as well as their potential industrial applicability beyond hydrogen. Finally technological progress in other decarbonization applications and most importantly full commercialization of CCUS solutions is likely to dramatically change the approach towards long distance hydrogen transportation.

The podcast can be found on their website. 

Policy Connect Carbon Connect and sector and Parliamentary experts have collaborated to present options for the gas grid to play a useful role in the UK’s transition to a low carbon energy system through the widespread use of low carbon gas. The report calls on Government to support the transition to a more flexible gas grid that uses various forms of gas including low carbon gases such as hydrogen and biomethane.

Global climate targets have highlighted the need for a whole-systems approach to decarbonisation one that includes targeted national policy and industry specific change. Situated within this context this research examines policy and pricing barriers to decarbonisation of the UK steel industry. Here the techno-economic modelling of UK green steelmaking provides a technical contribution to analysis of pricing barriers and policy solutions to these barriers in the UK specifically but also to the broader industrial decarbonisation literature. Estimated costs and associated emissions projections reveal relevant opportunities for UK steel in contributing to national climate and emissions targets. Modelling demonstrates that green steelmaking options have been put at price disadvantages compared to emissions-intensive incumbents and that fossil-free hydrogen-based steel-making has lower emissions and lower levelised costs than carbon capture and storage options including top gas recycling blast furnace (TGR-BF) with CCS and HIsarna smelter with CCS. Two primary policy recommendations are made: the removal of carbon pricing discrepancies and reductions in industrial electricity prices that would level the playing field for green steel producers in the UK. The research also provides relevant policy considerations for the international community in other industrial decarbonisation efforts and the policies that must accompany these decarbonisation choices.

The pathway to zero carbon emissions passing through carbon emissions reduction is mandatory in the shipping industry. Regarding the various methodologies and technologies reviewed for this purpose Life Cycle Cost Analysis (LCCA) has been used as an excellent tool to determine economic feasibility and sustainability and to present directions. However insufficient commercial applications cause a conflict of opinion on which fuel is the key to decarbonisation. Many LCCA comparison studies about eco-friendly ship propulsion claim different results. In order to overcome this and discover the key factors that affect the overall comparative analysis and results in the maritime field it is necessary to conduct the comparative analysis considering more diverse case ships case routes and various types that combine each system. This study aims to analyse which greener fuels are most economically beneficial for the shipping sector and prove the factors influencing different results in LCCA. This study was conducted on hydrogen ammonia and electric energy which are carbon-free fuels among various alternative fuels that are currently in the limelight. As the power source a PEMFC and battery were used as the main power source and a solar PV system was installed as an auxiliary power source to compare economic feasibility. Several cost data for LCCA were selected from various feasible case studies. As the difficulty caused by the storage and transportation of hydrogen and ammonia should not be underestimated in this study the LCCA considers not only the CapEx and OpEx but also fuel transport costs. As a result fuel cell propulsion systems with hydrogen as fuel proved financial effectiveness for short-distance ferries as they are more inexpensive than ammonia-fuelled PEMFCs and batteries. The fuel cost takes around half of the total life-cycle cost during the life span.

In this work geochemical modelling using PhreeqC was carried out to evaluate the effects of geochemical reactions on the performance of underground hydrogen storage (UHS). Equilibrium exchange and mineral reactions were considered in the model. Moreover reaction kinetics were considered to evaluate the geochemical effect on underground hydrogen storage over an extended period of 30 years. The developed model was first validated against experimental data adopted from the published literature by comparing the modelling and literature values of H2 and CO2 solubility in water at varying conditions. Furthermore the effects of pressure temperature salinity and CO2% on the H2 and CO2 inventory and rock properties in a typical sandstone reservoir were evaluated over 30 years. Results show that H2 loss over 30 years is negligible (maximum 2%) through the studied range of conditions. The relative loss of CO2 is much more pronounced compared to H2 gas with losses of up to 72%. Therefore the role of CO2 as a cushion gas will be affected by the CO2 gas losses as time passes. Hence remedial CO2 gas injections should be considered to maintain the reservoir pressure throughout the injection and withdrawal processes. Moreover the relative volume of CO2 increases with the increase in temperature and decrease in pressure. Furthermore the reservoir rock properties porosity and permeability are affected by the underground hydrogen storage process and more specifically by the presence of CO2 gas. CO2 dissolves carbonate minerals inside the reservoir rock causing an increase in the rock’s porosity and permeability. Consequently the rock’s gas storage capacity and flow properties are enhanced

Smart energy networks provide an effective means to accommodate high penetrations of variable renewable energy sources like solar and wind which are key for the deep decarbonisation of energy production. However given the variability of the renewables as well as the energy demand it is imperative to develop effective control and energy storage schemes to manage the variable energy generation and achieve desired system economics and environmental goals. In this paper we introduce a hybrid energy storage system composed of battery and hydrogen energy storage to handle the uncertainties related to electricity prices renewable energy production and consumption. We aim to improve renewable energy utilisation and minimise energy costs and carbon emissions while ensuring energy reliability and stability within the network. To achieve this we propose a multi-agent deep deterministic policy gradient approach which is a deep reinforcement learning-based control strategy to optimise the scheduling of the hybrid energy storage system and energy demand in real time. The proposed approach is model-free and does not require explicit knowledge and rigorous mathematical models of the smart energy network environment. Simulation results based on real-world data show that (i) integration and optimised operation of the hybrid energy storage system and energy demand reduce carbon emissions by 78.69% improve cost savings by 23.5% and improve renewable energy utilisation by over 13.2% compared to other baseline models; and (ii) the proposed algorithm outperforms the state-of-the-art self-learning algorithms like the deep-Q network.

With the unprecedented development of green and renewable energy sources the proportion of clean hydrogen (H2 ) applications grows rapidly. Since H2 has physicochemical properties of being highly permeable and combustible high-performance H2 sensors to detect and monitor hydrogen concentration are essential. This review discusses a variety of fiber-optic-based H2 sensor technologies since the year 1984 including: interferometer technology fiber grating technology surface plasma resonance (SPR) technology micro lens technology evanescent field technology integrated optical waveguide technology direct transmission/reflection detection technology etc. These technologies have been evolving from simply pursuing high sensitivity and low detection limits (LDL) to focusing on multiple performance parameters to match various application demands such as: high temperature resistance fast response speed fast recovery speed large concentration range low cross sensitivity excellent long-term stability etc. On the basis of palladium (Pd)-sensitive material alloy metals catalysts or nanoparticles are proposed to improve the performance of fiberoptic-based H2 sensors including gold (Au) silver (Ag) platinum (Pt) zinc oxide (ZnO) titanium oxide (TiO2 ) tungsten oxide (WO3 ) Mg70Ti30 polydimethylsiloxane (PDMS) graphene oxide (GO) etc. Various microstructure processes of the side and end of optical fiber H2 sensors are also discussed in this review.

This review presents state-of-the-art for representative sampling of hydrogen from hydrogen refueling stations. Documented sampling strategies are presented as well as examples of commercially available equipment for sampling at the hydrogen refueling nozzle. Filter media used for sampling is listed and the performance of some of the filters evaluated. It was found that the filtration efficiency of 0.2 and 5 mm filters were not significantly different when exposed to 200 and 300 nm particles. Several procedures for gravimetric analysis are presented and some of the challenges are identified to be filter degradation pinhole formation and conditioning of the filter prior to measurement. Lack of standardization of procedures was identified as a limitation for result comparison. Finally the review summarizes results including particulate concentration in hydrogen fuel quality data published. It was found that less than 10% of the samples were in violation with the tolerance limit.

This narrative document sets out the main rationale for hydrogen storage development at scale in the UK: - To meet net zero the UK will need considerable energy storage - Hydrogen storage will be a major and essential part of this - Physical hydrogen storage is needed in the UK - Only geological hydrogen storage can deliver at the scale needed within the timescales for net zero - Geological hydrogen storage should be supported through a viable business model now to ensure it comes online in the 2030s.