Applications & Pathways

Proton exchange membrane fuel cells (PEMFCs) are attracting attention for their green energy-saving and high-efficiency advantages becoming one of the future development trends of renewable energy utilization. However there are still deficiencies in the gas supply system control strategy that plays a crucial role in PEMFCs which limits the rapid development and application of PEMFCs. This paper provides a comprehensive and in-depth review of the PEMFC air delivery system (ADS) and hydrogen delivery system (HDS) operations. For the ADS the advantages and disadvantages of the oxygen excess ratio (OER) oxygen pressure and their decoupling control strategies are systematically described by the following three aspects: single control hybrid control and intelligent algorithm control. Additionally the optimization strategies of the flow field or flow channel for oxygen supply speeds and distribution uniformity are compared and analyzed. For the HDS a systematic review of hydrogen recirculation control strategies purge strategies and hydrogen flow control strategies is conducted. These strategies contribute a lot to improving hydrogen utilization rates. Furthermore hydrogen supply pressure is summarized from the aspects of hybrid control and intelligent algorithm control. It is hoped to provide guidance or a reference for research on the HDS as well as the ADS control strategy and optimization strategy

To reduce carbon emissions generation of electricity from combustion systems is being replaced by renewable resources. However the most abundant renewable sources – solar and wind – are not dispatchable vary diurnally and are subject to intermittency and produce electricity at times in excess of demand (excess production). To manage this variability and capture the excess renewable energy energy storage technologies are being developed and deployed such as battery energy storage (BES) hydrogen production with electrolyzers (ELY) paired with hydrogen energy storage (HES) and fuel cells (FCs) and renewable natural gas (RNG) production. While BES may be better suited for short duration storage hydrogen is suited for long duration storage and RNG can decarbonize the natural gas system. California Senate Bill 100 (SB100) sets a goal that all retail electricity sold in the State must be sourced from renewable and zero-carbon resources by 2045 raising the questions of which set of technologies and in what proportion are required to meet the 2045 target in the required timeframe as well as the role of the natural gas infrastructure if any. To address these questions this study combines electric grid dispatch modeling and optimization to identify the energy storage and dispatchable technologies in 5-year increments from 2030 to 2045 required to transition from a 60% renewable electric grid in 2035 to a 100% renewable electric grid in 2045. The results show that by utilizing the established natural gas system to store and transmit hydrogen and RNG the deployment of battery energy storage is dramatically reduced. The required capacity for BES in 2045 for example is 40 times lower by leveraging the natural gas infrastructure with a concomitant reduction in cost and associated challenges to transform the electric grid.

Limiting global warming to 1.5 ◦C is crucial to prevent the worst effects of climate change. This entails also the decarbonization of the aviation sector which is considered to be a “hard-to-abate” sector and thus requires special attention regarding its sustainability transition. However transition pathways to a potentially climateneutral aviation sector are unclear with different stakeholders having diverse imaginations of the sector's future. This paper aims to analyze socio-technical imaginaries of climate-neutral aviation as different perceptions of various stakeholders on this issue have not been sufficiently explored so far. In that sense this work contributes to the current scientific debate on socio-technical imaginaries of energy transitions for the first time studying the case of the aviation sector. Drawing on six decarbonization reports composed by different interest groups (e.g. industry academia and environmental associations) three imaginaries were explored following the process of a thematic analysis: rethinking travel and behavioral change (travel innovation) radical modernization and technological progress (fleet innovation) and transition to alternative fuels and renewable energy sources (fuel innovation). The results reveal how different and partly conflicting socio-technical imaginaries are co-produced and how the emergence and enforceability of these imaginaries is influenced by the situatedness of their creators indicating that the sustainability transition of aviation also raises political issues. Essentially as socio-technical imaginaries act as a driver for change policymakers should acknowledge the existence of alternative and counter-hegemonic visions created by actors from civil society settings to take an inclusive and equitable approach to implementing pathways towards climate-neutral aviation.

In this work we examine the possibility of converting a light propeller-driven aircraft powered by a spark-ignition reciprocating piston and internal combustion engine running on AVGAS into one powered by an electric motor driven by a proton exchange membrane fuel cell stack running on hydrogen. Our studies suggest that storing hydrogen cryogenically is a better option than storing hydrogen under pressure. In comparison to cryogenic tanks high-pressure tanks are extremely heavy and unacceptable for light aircraft. We show that the modified aircraft (including batteries) is no heavier than the original and that the layout of the major components results in lower movement of the aircraft center-of-gravity as the aircraft consumes hydrogen. However we acknowledge that our fuel cell aircraft cannot store the same amount of energy as the original running on AVGAS. Therefore despite the fact that the fuel cell stack is markedly more efficient than an internal combustion engine there is a reduction in the range of the fuel cell aircraft. One of our most important findings is that the quantity of energy that we need to dissipate to the surroundings via heat transfer is significantly greater from a fuel cell stack than from an internal combustion engine. This is particularly the case when we attempt to run the fuel cell stack at high current densities. To control this problem our strategy during the cruise phase is to run the fuel cell stack at its maximum efficiency where the current density is low. We size the fuel cell stack to produce at least enough power for cruise and when we require excess power we add the energy stored in batteries to make up the difference.

Utilizing renewable energy sources to produce hydrogen is essential for promoting cleaner production and improving power utilization especially considering the growing use of fossil fuels and their impact on the environment. Selecting the most efficient method for distributing power and capacity is a critical issue when developing hybrid systems from scratch. The main objective of this study is to determine how a backup system affects the performance of a microgrid system. The study focuses on power and hydrogen production using renewable energy resources particularly solar and wind. Based on photovoltaics (PVs) wind turbines (WTs) and their combinations including battery storage systems (BSSs) and hydrogen technologies two renewable energy systems were examined. The proposed location for this study is the northwestern coast of Saudi Arabia (KSA). To simulate the optimal size of system components and determine their cost-effective configuration the study utilized the Hybrid Optimization Model for Multiple Energy Resources (HOMER) software (Version 3.16.2). The results showed that when considering the minimum cost of energy (COE) the integration of WTs PVs a battery bank an electrolyzer and a hydrogen tank brought the cost of energy to almost 0.60 USD/kWh in the system A. However without a battery bank the COE increased to 0.72 USD/kWh in the same location because of the capital cost of system components. In addition the results showed that the operational life of the fuel cell decreased significantly in system B due to the high hours of operation which will add additional costs. These results imply that long-term energy storage in off-grid energy systems can be economically benefited by using hydrogen with a backup system.

As subsidies for renewable energy are progressively reduced worldwide electric vehicle charging stations (EVCSs) powered by renewable energy must adopt market-driven approaches to stay competitive. The unpredictable nature of renewable energy production poses major challenges for strategic planning. To tackle the uncertainties stemming from forecast inaccuracies of renewable energy this study introduces a peer-to-peer (P2P) energy trading strategy based on game theory for solar-hydrogen-battery storage electric vehicle charging stations (SHS-EVCSs). Firstly the incorporation of prediction errors in renewable energy forecasts within four SHS-EVCSs enhances the resilience and efficiency of energy management. Secondly employing game theory’s optimization principles this work presents a day-ahead P2P interactive energy trading model specifically designed for mitigating the variability issues associated with renewable energy sources. Thirdly the model is converted into a mixed integer linear programming (MILP) problem through dual theory allowing for resolution via CPLEX optimization techniques. Case study results demonstrate that the method not only increases SHS-EVCS revenue by up to 24.6% through P2P transactions but also helps manage operational and maintenance expenses contributing to the growth of the renewable energy sector.

As an important piece of equipment for hydrogen energy application the hydrogen internal combustion engine is helpful for the realization of zero carbon emissions where the aluminum connecting rod is one of the key core components. A semi-solid forging forming process for the 7075 aluminum alloy connecting rod is proposed in this work. The influence of process parameters such as the forging ratio sustaining temperature and duration time on the microstructures of the semi-solid blank is experimentally investigated. The macroscopic morphology metallographic structure and physical properties of the connecting-rod parts are analyzed. Reasonable process parameters for preparing the semi-solid blank are obtained from the experimental results. Under the reasonable parameters the average grain size is 41.48~42.57 µm and the average shape factor is 0.80~0.81. The yield strength and tensile strength improvement ratio of the connecting rod produced by the proposed process are 47.07% and 20.89% respectively.

Growing renewable energy deployment worldwide has sparked a shift in the energy landscape with far-reaching geopolitical ramifications. Hydrogen’s role as an energy carrier is central to this change facilitating global trade and the decarbonisation of hard-to-abate sectors. This analysis offers a new method for optimally sizing solar/wind-to-hydrogen systems in specifically suitable locations. These locations are limited to the onshore and offshore regions of selected countries as determined by a bespoke geospatial analysis developed to be location-agnostic. Furthermore the research focuses on determining the best configurations for such systems that minimise the cost of producing hydrogen with the optimisation algorithm expanding from the detailed computation of the classic levelised cost of hydrogen. One of the study’s main conclusions is that the best hybrid configurations obtained provide up to 70% cost savings in some areas. Such findings represent unprecedented achievements for Italy and Portugal and can be a valuable asset for economic studies of this kind carried out by local and national governments across the globe. These results validate the optimisation model’s initial premise significantly improving the credibility of this work by constructively challenging the standard way of assessing large-scale green hydrogen projects.

This paper presents a method for estimating Well-to-Wheel (WTW) energy use and greenhouse gas (GHG) emissions attributed to the advanced railway propulsion systems implemented in conjunction with different energy carriers and their production pathways. The analysis encompasses diesel-electric multiple unit vehicles converted to their hybrid-electric plug-in hybrid-electric fuel cell hybrid-electric or battery-electric counterparts combined with biodiesel or hydrotreated vegetable oil (HVO) as the first and second generation biofuels liquefied natural gas (LNG) hydrogen and/or electricity. The method is demonstrated using non-electrified regional railway network with heterogeneous vehicle fleet in the Netherlands as a case. Battery-electric system utilizing green electricity is identified as the only configuration leading to emission-free transport while offering the highest energy use reduction by 65–71% compared to the current diesel-powered hybrid-electric system. When using grey electricity based on the EU2030 production mix these savings are reduced to about 27–39% in WTW energy use and around 68–73% in WTW GHG emissions. Significant reductions in overall energy use and emissions are obtained for the plug-in hybrid-electric concept when combining diesel LNG or waste cooking oil-based HVO with electricity. The remaining configurations that reduce energy use and GHG emissions are hybrid-electric systems running on LNG or HVO from waste cooking oil. The latter led to approximately 88% lower WTW emissions than the baseline for each vehicle type. When produced from natural gas or EU2030-mix-based electrolysis hydrogen negatively affected both aspects irrespective of the prime mover technology. However when produced via green electricity it offers a GHG reduction of approximately 90% for hybrid-electric and fuel cell hybrid-electric configurations with a further reduction of up to 92–93% if combined with green electricity in plug-in hybrid-electric systems. The results indicate that HVO from waste cooking oil could be an effective and instantly implementable transition solution towards carbon–neutral regional trains allowing for a smooth transition and development of supporting infrastructure required for more energy-efficient and environment-friendly technologies.

To reach the decarbonisation goals a zero CO2 emissions large ship propulsion system is proposed in this work. The ship selected is a large ferry propelled by an internal combustion engine fuelled by an ammonia-hydrogen blend. The only fuel loaded in the vessel will be ammonia. The hydrogen required for the combustion in the engine will be produced onboard employing ammonia decomposition. The heat required for this decomposition section will be supplied by using the hot flue gases of the combustion engine. To address the issues regarding NOx emissions a selective catalytic reduction (SCR) reactor was designed. The main operating variables for all the equipment were computed for engine load values of 25% 50% 75% and 100%. Considering the lowest SCR removal rate (91% at an engine load of 100%) the NOx emissions of the vessel were less than 0.5 g/kWh lower than the IMO requirements. An energy analysis of the system proposed to transform ammonia into energy for shipping was conducted. The global energy and exergy efficiencies were 42.4% and 48.1%. In addition an economic analysis of the system was performed. The total capital cost (CAPEX) for the system can be estimated at 8.66 M€ (784 €/kW) while the operating cost (OPEX) ranges between 210 €/MWh (engine load 100%) and 243 €/MWh (engine load of 25%). Finally a sensitivity analysis for the price of ammonia was performed resulting in the feasibility of reducing the operating cost to below 150 €/MWh in the near horizon.

Alternative fuels of low or zero carbon content can decarbonise the shipping operations. This study aims at assessing the lifetime environmental-economic sustainability of ammonia and hydrogen as alternatives to diesel fuel for short sea shipping cargo vessels. A model is employed to calculate key performance indicators representing the lifetime financial sustainability and environmental footprint of the case ship using a realistic operating profile and considering several scenarios with different diesel substitution rates. Scenarios meeting the carbon emissions reduction targets set by the International Maritime Organisation (IMO) for 2030 are identified whereas policy measures for their implementation including the emissions taxation are discussed. The derived results demonstrate that the future implementation of carbon emissions taxation in the ranges of 136–965 €/t for hydrogen and 356–2647 €/t for ammonia can support these fuels financial sustainability in shipping. This study provides insights for adopting zero-carbon fuels and as such impacts the de-risking of shipping decarbonisation.

Accelerated decarbonisation of steelmaking oil refining and petrochemical industries is essential for climate change mitigation. Drawing on three longitudinal case studies of these industries in the UK this synthesis article makes a comparative analysis of their varying low-carbon reorientation speeds. The paper uses the triple embeddedness framework to analyse five factors (policy support international competition financial health technical feasibility corporate strategy and mindset) that explain why UK oil refineries have in recent years been comparatively the fastest in their low-carbon reorientation and UK steelmakers the slowest. We find that policy support has been more beneficial for refining and petrochemicals than for steel although recent government deals with steelmakers addressed this imbalance. International competition has been high for steel and petrochemicals and comparatively lower for refining (meaning that decarbonisation costs are less detrimental for international competitiveness). Financial performance has comparatively been worst for steel and best for oil refining which shapes the economic feasibility of low-carbon options. Hydrogen and carbon-capture-and-storage are technologically feasible for refining and petrochemicals while Electric Arc Furnaces are technically feasible for steelmakers but face wider feasibility problems (with scrap steel supply electricity grids and electricity prices) which is why we question the recent government deals. Corporate strategy and perceptions changed in oil refining with firms seeing economic opportunities in decarbonisation while steelmakers and petrochemical firms still mostly see decarbonisation as a burden and threat. The paper ends with comparative conclusions a discussion of political considerations and future outlooks for the three UK industries policy and research.

Blending hydrogen to existing fuel mix represents a major opportunity for decarbonisation. One important consideration for this application is the chemical interaction between hydrogen and hydrocarbon fuels arising from their different combustion chemistries and varying considerably with combustion processes. This paper conducted an exploratory study of hydrogen’s impact on autoignition in several combustion processes where hydrogen is used as a blending component or the main fuel. Case studies are presented for spark ignition engines (H2/natural gas) compression ignition engines (H2/diesel) moderate or intense low-oxygen dilution (MILD) combustors (H2/natural gas) and rotational detonation engines (H2/natural gas). Autoignition reactivity as a function of the hydrogen blending level is investigated numerically using the ignition delay iso-contours and state-of-the-art kinetic models at time scales representative of each application. The results revealed drastically different impact of hydrogen blending on autoignition due to different reaction temperature pressure and time scale involved in these applications leaving hydrocarbon interacting with hydrogen at different ignition branches where the negative pressure/temperature dependency of oxidation kinetics could take place. The resulted non-linear and at times non-monotonic behaviours indicate a rich topic for combustion chemistry and also demonstrates ignition delay iso-contour as a useful tool to scope autoignition reactivity for a wide range of applications.

Hydrogen is becoming increasingly popular as a clean secure and affordable energy source for the future. This study develops an approach for designing a PV–battery–electrolyzer–fuel cell energy system that utilizes hydrogen as a long-term storage medium and battery as a short-term storage medium. The system is designed to supply load demand primarily through direct electricity generation in the summer and indirect electricity generation through hydrogen in the winter. The sizing of system components is based on the direct electricity and indirect hydrogen demand with a key input parameter being the load sizing factor which determines the extent to which hydrogen is used to meet seasonal imbalance. Technical and financial indicators are used to assess the performance of the designed system. Simulation results indicate that the energy system can effectively balance the seasonal variation of renewable generation and load demand with the use of hydrogen. Additionally guidelines for achieving self-sufficiency and system sustainability for providing enough power in the following years are provided to determine the appropriate component size. The sensitivity analysis indicates that the energy system can achieve self-sufficiency and system sustainability with a proper load sizing factor from a technical perspective. From an economic perspective the levelized cost of energy is relatively high because of the high costs of hydrogen-related components at this moment. However it has great economic potential for future self-sufficient energy systems with the maturity of hydrogen technologies.

Subcooled liquid hydrogen (sLH2) is an onboard storage as well as a hydrogen refueling technology that is currently being developed by Daimler Truck and Linde to boost the mileage of heavy-duty trucks while also improving performance and reducing the complexity of hydrogen refueling stations. In this article the key technical aspects advantages challenges and future developments of sLH2 at vehicle and infrastructure levels will be explored and highlighted.

Air compressors in hydrogen fuel cell vehicles play a crucial role in ensuring the stability of the cathode air system. However they currently face challenges related to low efficiency and poor stability. To address these issues the experimental setup for the pneumatic performance of air compressors is established. The effects of operational parameters on energy consumption efficiency and mass flow rate of the air compressor are revealed based on a Morris global sensitivity analysis. Considering a higher flow rate larger efficiency and lower energy consumption simultaneously the optimal operating combination of the air compressor is determined based on grey relational multi-objective optimization. The optimal combination of operational parameters consisted of a speed of 80000 rpm a pressure ratio of 1.8 and an inlet temperature of 18.3 °C. Compared to the average values the isentropic efficiency achieved a 48.23% increase and the mass flow rate rose by 78.88% under the optimal operational combination. These findings hold significant value in guiding the efficient and stable operation of air compressors. The comprehensive methodology employed in this study is applicable further to investigate air compressors for hydrogen fuel cell vehicles.

The present paper offers a thorough examination of the safety measures enforced at hydrogen filling stations emphasizing their crucial significance in the wider endeavor to advocate for hydrogen as a sustainable and reliable substitute for conventional fuels. The analysis reveals a wide range of crucial safety aspects in hydrogen refueling stations including regulated hydrogen dispensing leak detection accurate hydrogen flow measurement emergency shutdown systems fire-suppression mechanisms hydrogen distribution and pressure management and appropriate hydrogen storage and cooling for secure refueling operations. The paper therefore explores several aspects including the sophisticated architecture of hydrogen dispensers reliable leak-detection systems emergency shut-off mechanisms and the implementation of fire-suppression tactics. Furthermore it emphasizes that the safety and effectiveness of hydrogen filling stations are closely connected to the accuracy in the creation and upkeep of hydrogen dispensers. It highlights the need for materials and systems that can endure severe circumstances of elevated pressure and temperature while maintaining safety. The use of sophisticated leak-detection technology is crucial for rapidly detecting and reducing possible threats therefore improving the overall safety of these facilities. Moreover the research elucidates the complexities of emergency shut-off systems and fire-suppression tactics. These components are crucial not just for promptly managing hazards but also for maintaining the station’s structural soundness in unanticipated circumstances. In addition the study provides observations about recent technical progress in the industry. These advances effectively tackle current safety obstacles and provide the foundation for future breakthroughs in hydrogen fueling infrastructure. The integration of cutting-edge technology and materials together with the development of upgraded safety measures suggests a positive trajectory towards improved efficiency dependability and safety in hydrogen refueling stations.

Hydrogen is the most promising alternative fuel in the field of engines. Exhaust heat assisted methanol dissociation is an attractive approach for generating hydrogen. In this work simulations are conducted on a compression ignition engine fueled with different proportions of diesel-dissociated methanol gas (DMG) blends at intermediate engine speed full load and 0% EGR ratio. The results reveal that the indicated thermal efficiency and indicated mean effective pressure are greatly enhanced combustion efficiency is increased and regular emissions of CO HC and soot are reduced while NOx emissions are reduced with increased DMG substitution. In addition a simulation is conducted at an intermediate engine speed full load 15% DMG substitution ratio and varying EGR ratios of 0–20%. The results indicate that the dual-fuel engine outperforms the original engine with respect to power fuel economy and regular emissions once an optimal EGR rate is adopted.

The current study presents a comprehensive investigation of different energy system configurations for a remote village community in India with entirely renewable electricity. Excess electricity generated by the systems has been stored using two types of energy storage options: lithium-ion batteries and green hydrogen production through the electrolysers. The hybrid renewable energy system (HRES) configurations have been sized by minimising the levelised cost of energy (LCOE). In order to identify the best-performing HRES configuration economic and environmental performance indicators has been analysed using the multi-criteria decision-making method (MCDM) TOPSIS. Among the evaluated system configurations system-1 with a photovoltaic panel (PV) size of 310.24 kW a wind turbine (WT) size of 690 kW a biogas generator (BG) size of 100 kW a battery (BAT) size of 174 kWh an electrolyser (ELEC) size of 150 kW a hydrogen tank (HT) size of 120 kg and a converter (CONV) size of 106.24 kW has been found to be the best-performing system since it provides the highest relative closeness (RC) value (∼0.817) and also has the lowest fuel consumption rate of 2.31 kg/kWh. However system-6 shows the highest amount of CO2 (143.97 kg/year) among all the studied system configurations. Furthermore a detailed technical economic and environmental analysis has been conducted on the optimal HRES configuration. The minimum net present cost (NPC) LCOE and cost of hydrogen (COH) for system 1 has been estimated to be $1960584 $0.44/kWh and $22.3/kg respectively.

Developing an effective energy transition roadmap is crucial in the face of global commitments to achieve net zero emissions. While renewable power generation systems are expanding challenges such as curtailments and grid constraints can lead to energy loss. To address this surplus electricity can be converted into green hydrogen serving as a key component in the energy transition. This research explores the use of renewable solar energy for powering a proton exchange membrane electrolyser to produce green hydrogen while a downdraft gasifier fed by municipal solid waste generates hydrogen-enriched syngas. The blended fuel is then used to feed a Solid Oxide Fuel Cell (SOFC) system. The study investigates the impact of hydrogen content on the performance of the fuel cell-based power plant from thermodynamics and exergoeconomic perspectives. Multiobjective optimisation using a genetic algorithm identifies optimal operating conditions for the system. Results show that blending hydrogen with syngas increases combined heat and power efficiency by up to 3% but also raises remarkably the unit product cost and reduces carbon dioxide emissions. Therefore the optimal values for hydrogen content current density temperatures and other parameters are determined. These findings contribute to the design and operation of an efficient and sustainable energy generation system.

As a versatile energy carrier hydrogen possesses tremendous potential to reduce greenhouse emissions and promote energy transition. Global interest in producing hydrogen from renewable energy sources and transporting storing and utilizing hydrogen is rising rapidly. However the high costs of producing clean hydrogen and the uncertain application scenarios for hydrogen energy result in its relatively limited utilization worldwide. It is necessary to find new promising technological paths to drive the development of hydrogen energy. As part of technological innovation emerging technologies have vital features such as prominent impact novelty relatively fast growth etc. Identifying emerging hydrogen-energy-related technologies is important for discovering innovation opportunities during the energy transition. Existing research lacks analysis of the characteristics of emerging technologies. Thus this paper proposes a method combining the latent Dirichlet allocation topic model and hydrogen-energy expert group decision-making. This is used to identify emerging hydrogen-related technology regarding two features of emerging technologies novelty and prominent impact. After data processing topic modeling and analysis the patent dataset was divided into twenty topics. Six emerging topics possess novelty and prominent impact among twenty topics. The results show that the current hotspots aim to promote the application of hydrogen energy by improving the performance of production catalysts overcoming the wide power fluctuations and large-scale instability of renewable energy power generation and developing advanced hydrogen safety technologies. This method efficiently identifies emerging technologies from patents and studies their development trends. It fills a gap in the research on emerging technologies in hydrogen-related energy. Research achievements could support the selection of technology pathways during the low-carbon energy transition.

Hydrogen is seen as a prime choice for complete replacement of gasoline so as to achieve zero-emissions energy and mobility. Combining the use of this alternative fuel with a circular economy approach for giving new life to the existing fleet of passenger cars ensures further benefits in terms of cost competitiveness. Transforming spark ignition (SI) engines to H2 power requires relatively minor changes and limited added components. Within this framework the conversion of a small-size passenger car to hydrogen fueling was evaluated based on 0D/1D simulation. One of the methods to improve efficiency is to apply exhaust gas recirculation (EGR) which also lowers NOx emissions. Therefore the previous version of the quasi-dimensional model was modified to include EGR and its effects on combustion. A dedicated laminar flame speed model was implemented for the specific properties of hydrogen and a purpose-built sub-routine was implemented to correctly model the effects of residual gas at the start of combustion. Simulations were performed in several operating points representative of urban and highway driving. One of the main conclusions was that highpressure recirculation was severely limited by the minimum flow requirements of the compressor. Low-pressure EGR ensured wider applicability and significant improvement of efficiency especially during partial-load operation specific to urban use. Another benefit of recirculation was that pressure rise rates were predicted to be more contained and closer to the values expected for gasoline fueling. This was possible due to the high tolerance of H2 to the presence of residual gas.

China’s coal chemical sector uses coal as both a fuel and feedstock and its increasing greenhouse gas (GHG) emissions are hard to abate by electrification alone. Here we explore the GHG mitigation potential and costs for onsite deployment of green H2 and O2 in China’s coal chemical sector using a lifecycle assessment and techno-economic analyses. We estimate that China’s coal chemical production resulted in GHG emissions of 1.1 gigaton CO2 equivalent (GtCO2eq) in 2020 equal to 9% of national emissions. We project GHG emissions from China’s coal chemical production in 2030 to be 1.3 GtCO2eq ~50% of which can be reduced by using solar or wind power-based electrolytic H2 and O2 to replace coal-based H2 and air separation-based O2 at a cost of 10 or 153 Chinese Yuan (CNY)/tCO2eq respectively. We suggest that provincial regions determine whether to use solar or wind power for water electrolysis based on lowest cost options which collectively reduce 53% of the 2030 baseline GHG emissions at a cost of 9 CNY/tCO2eq. Inner Mongolia Shaanxi Ningxia and Xinjiang collectively account for 52% of total GHG mitigation with net cost reductions. These regions are well suited for pilot policies to advance demonstration projects.

The production of hydrogen-based dense energy carriers (DECs) has been proposed as a combined solution for the storage and dispatch of power generated through intermittent renewables. Frameworks that model and optimize the production storage and dispatch of generated energy are important for data-driven decision making in the energy systems space. The proposed multiperiod framework considers the evolution of technology costs under different levels of promotion through research and targeted policies using the year 2021 as a baseline. Furthermore carbon credits are included as proposed by the 45Q tax amendment for the capture sequestration and utilization of carbon. The implementation of the mixed-integer linear programming (MILP) framework is illustrated through computational case studies to meet set hydrogen demands. The trade-offs between different technology pathways and contributions to system expenditure are elucidated and promising configurations and technology niches are identified. It is found that while carbon credits can subsidize carbon capture utilization and sequestration (CCUS) pathways substantial reductions in the cost of novel processes are needed to compete with extant technology pathways. Further research and policy push can reduce the levelized cost of hydrogen (LCOH) by upwards of 2 USD/kg.

The Integrated Energy System (IES) that coordinates multiple energy sources can effectively improve energy utilization and is of great significance to achieving energy conservation and emission reduction goals. In this context a low-carbon and economic dispatch model for IES is proposed. Firstly a hydrogen energy-based IES (H2-IES) is constructed to refine the utilization process of hydrogen energy. Secondly the carbon emissions of different energy chains throughout their life cycle are analyzed using the life cycle assessment method (LCA) and the carbon emissions of the entire energy supply and demand chain are considered. Finally a staged carbon trading mechanism is adopted to promote energy conservation and emission reduction. Based on this an IES low-carbon and economic dispatch model is constructed with the optimization goal of minimizing the sum of carbon trading costs energy procurement costs and hydrogen sales revenue while considering network constraints and constraints on key equipment. By analyzing the model under different scenarios the introduction of life cycle assessment staged carbon trading and hydrogen energy utilization is shown to promote low-carbon and economic development of the comprehensive energy system.