Hydrogen System Research Articles

Hybrid renewable hydrogen systems in Saudi Arabia: A techno-economic evaluation for three diverse locations

This study presents a techno-economic evaluation of hybrid renewable hydrogen systems in Al Jouf, Yanbu, and Riyadh, Saudi Arabia, using HOMER software to model and optimize grid-connected and off-grid configurations. Grid-connected systems consistently demonstrate superior cost-effectiveness, achieving lower hydrogen (COH) and energy (COE) costs, particularly in resource-rich regions like Yanbu. Off-grid systems, while more expensive, offer crucial energy independence for remote areas or where grid reliability is a concern. Sensitivity analyses reveal that increasing solar irradiance reduces COH, COE, and net present cost (NPC), along with optimal PV array sizes, especially in grid-connected systems. Wind resources play a significant role in Yanbu, where abundant wind reduces reliance on solar energy. This emphasis on the role of wind resources in Yanbu provides the audience with specific regional factors affecting system design. Off-grid systems exhibit greater sensitivity to demand fluctuations due to their dependence on battery storage. The study highlights the importance of tailoring system designs to local resource availability, climate, and demand. Policy recommendations include promoting grid integration, supporting off-grid solutions in areas with limited grid access, investing in climate-resilient technologies, and fostering regional collaboration for a sustainable hydrogen economy in Saudi Arabia and the Arab region.

A zero-carbon emission approach for the reduction of refractory iron ores: Mineral phase, magnetic property and surface transformation in hydrogen system

In this study, a feasible strategy, named hydrogen mineral phase transformation (HMPT) technology, is proposed and employed to achieve efficient and clean recovery of Hainan Shilu refractory iron ore (HSRIO). The influences of HMPT roasting temperature, roasting time, and H2 concentration on the separation index of HSRIO are investigated. Under the optimal experimental conditions, the iron concentrate grade increases from 62.5% to 67.9%, and the iron recovery increases from 65.0% to 94.7% compared with the original beneficiation process. In addition, the evolution of mineral phases, magnetic properties, and mineral microstructures is analyzed using XRD, VSM, SEM, and high-temperature hot-stage microscopy. It is revealed that the transformation of hematite to magnetite occurs during the HMPT process, with the newly formed magnetite exhibiting a loose and porous reticulation structure. This study is of guiding significance for the development of Hainan Shilu refractory iron ore with high efficiency and zero-carbon emission.

Design considerations and preliminary hydrodynamic analysis of an offshore decentralised floating wind-hydrogen system

Despite the number of works on the techno-economics of offshore green hydrogen production, there is a lack of research on the design of floating platforms to concomitantly support hydrogen production facilities and wind power generation equipment. Indeed, previous studies on offshore decentralised configuration for hydrogen production, implicitly assume that a floating platform designed for wind power generation (FOWT) can be also suitable as a floating wind hydrogen system (FWHS). This work proposes a novel design for an offshore decentralised FWHS, and analyses the effects of the integration of the hydrogen facilities on the platform's dynamics and how this in turn affects the performances of the wind turbine and the hydrogen equipment. Our findings indicate that despite the reduction in platform's stability, the performance of the wind turbine is barely affected. Regarding the hydrogen system, our results aim at contributing to further assessment and design of this equipment for offshore conditions.

Design and Understanding of Adaptive Hydrogenation Catalysts Triggered by the H2/CO2-Formic Acid Equilibrium.

An adaptive catalytic system for selective hydrogenation was developed exploiting the H2+CO2HCOOH equilibrium for reversible, rapid, and robust on/off switch of the ketone hydrogenation activity of ruthenium nanoparticles (Ru NPs). The catalyst design was based on mechanistic studies and DFT calculations demonstrating that adsorption of formic acid to Ru NPs on silica results in surface formate species that prevent C═O hydrogenation. Ru NPs were immobilized on readily accessible silica supports modified with guanidinium-based ionic liquid phases (Ru@SILPGB) to generate in situ sufficient amounts of HCOOH when CO2 was introduced into the H2 feed gas for switching off ketone hydrogenation while maintaining the activity for hydrogenation of olefinic and aromatic C═C bonds. Upon shutting down the CO2 supply, the C═O hydrogenation activity was restored in real time due to the rapid decarboxylation of the surface formate species without the need for any changes in the reaction conditions. Thus, the newly developed Ru@SILPGB catalysts allow controlled and alternating production of either saturated alcohols or ketones from unsaturated substrates depending on the use of H2 or H2/CO2 as feed gas. The major prerequisite for design of adaptive catalytic systems based on CO2 as trigger is the ability to shift the H2+CO2HCOOH equilibrium sufficiently to exploit competing adsorption of surface formate and targeted functional groups. Thus, the concept can be expected to be more generally applicable beyond ruthenium as the active metal, paving the way for next-generation adaptive catalytic systems in hydrogenation reactions more broadly.

Hydrogen vs. conventional sector-coupling residential energy systems: An economic and environmental comparison based on multi-objective design optimization

Planning residential energy systems faces economic, environmental, and technical challenges, necessitating cost-effective and environmentally friendly solutions. Hydrogen technologies in districts have recently gained interest. However, their economic and environmental potential relative to conventional technologies remains largely unexplored. Therefore, we quantitatively compared the impacts of designing hydrogen-based and conventional sector-coupling systems on total costs and CO2 emissions.We developed a multi-objective optimization model for the design and operation of generation and storage units, aiming to minimize total costs and CO2 emissions. We created three energy system configurations for an exemplary German district, each involving photovoltaics, heat storage, and batteries, while varying the main heat supplier. The first configuration includes a gas combined heat and power unit, the second features a heat pump, and the third incorporates a fuel cell, an electrolyzer, and hydrogen storage.Our comparison of the Pareto fronts revealed that the hydrogen system’s cost is 83% higher than the gas-based system and 33% higher than the heat-pump-based system. Environmentally, the hydrogen system emits 11% less than the gas-based system but 47% more than the heat-pump-based system. In conclusion, hydrogen units offer environmental benefits through improved photovoltaic utilization but perform poorly economically due to high investment and operating costs.

Fragment quantum embedding using the Householder transformation: A multi-state extension based on ensembles

In recent studies by Yalouz et al. [J. Chem. Phys. 157, 214112 (2022)] and Sekaran et al. [Phys. Rev. B 104, 035121 (2021) and Computation 10, 45 (2022)], density matrix embedding theory (DMET) has been reformulated through the use of the Householder transformation as a novel tool to embed a fragment within extended systems. The transformation was applied to a reference non-interacting one-electron reduced density matrix to construct fragments’ bath orbitals, which are crucial for subsequent ground state calculations. In the present work, we expand upon these previous developments and extend the utilization of the Householder transformation to the description of multiple electronic states, including ground and excited states. Based on an ensemble noninteracting density matrix, we demonstrate the feasibility of achieving exact fragment embedding through successive Householder transformations, resulting in a larger set of bath orbitals. We analytically prove that the number of additional bath orbitals scales directly with the number of fractionally occupied natural orbitals in the reference ensemble density matrix. A connection with the regular DMET bath construction is also made. Then, we illustrate the use of this ensemble embedding tool in single-shot DMET calculations to describe both ground and first excited states in a Hubbard lattice model and an ab initio hydrogen system. Finally, we discuss avenues for enhancing ensemble embedding through self-consistency and explore potential future directions.

A Hybrid Machine Learning Approach: Analyzing Energy Potential and Designing Solar Fault Detection for an AIoT-Based Solar–Hydrogen System in a University Setting

This research aims to optimize the solar–hydrogen energy system at Kangwon National University’s Samcheok campus by leveraging the integration of artificial intelligence (AI), the Internet of Things (IoT), and machine learning. The primary objective is to enhance the efficiency and reliability of the renewable energy system through predictive modeling and advanced fault detection techniques. Key elements of the methodology include data collection from solar energy production and fault detection systems, energy potential analysis using Transformer models, and fault identification in solar panels using CNN and ResNet-50 architectures. The Transformer model was evaluated using metrics such as Mean Absolute Error (MAE), Mean Squared Error (MSE), and an additional variation of MAE (MAE2). Known for its ability to detect intricate time series patterns, the Transformer model exhibited solid predictive performance, with the MAE and MAE2 results reflecting consistent average errors, while the MSE pointed to areas with larger deviations requiring improvement. In fault detection, the ResNet-50 model outperformed VGG-16, achieving 85% accuracy and a 42% loss, as opposed to VGG-16’s 80% accuracy and 78% loss. This indicates that ResNet-50 is more adept at detecting and classifying complex faults in solar panels, although further refinement is needed to reduce error rates. This study demonstrates the potential for AI and IoT integration in renewable energy systems, particularly within academic institutions, to improve energy management and system reliability. Results suggest that the ResNet-50 model enhances fault detection accuracy, while the Transformer model provides valuable insights for strategic energy output forecasting. Future research could focus on incorporating real-time environmental data to improve prediction accuracy and developing automated AIoT-based monitoring systems to reduce the need for human intervention. This study provides critical insights into advancing the efficiency and sustainability of solar–hydrogen systems, supporting the growth of AI-driven renewable energy solutions in university settings.

Co-Design of a Wind–Hydrogen System: The Effect of Varying Wind Turbine Types on Techno-Economic Parameters

Green hydrogen is crucial for achieving climate neutrality and replacing fossil fuels in processes that are hard to electrify. Wind farms producing electricity and hydrogen can help mitigate stress on electricity grids and enable new markets for operators. While optimizing wind farms for electricity production is well-established, optimizing combined wind–hydrogen systems is a relatively new research field. This study examines the potential profit of wind–hydrogen systems by conducting a case study of an onshore wind farm near the North Sea. Varying turbine types from high wind-speed turbines (with high annual energy production) to low wind-speed turbines (with high full-load hours) are examined. Findings indicate that in a combined hydrogen system, the low wind-speed turbines, which are sub-optimal for mere electricity production, yield lower levelized costs of hydrogen at a higher hydrogen production. Although high wind-speed turbines generate higher profits under current market conditions, at high hydrogen prices and low electricity prices, low wind-speed turbines can yield higher total profit at this site. Therefore, an integrated optimization approach of wind–hydrogen systems can, in certain cases, lead to better results compared to an isolated, sequential optimization of each individual system.

Local Energy Community as a Small Hydrogen Valley – H2LEC

A Local energy community (LEC) is a vertically nested system in energy supply and an ecosystem with joint values and objectives. On-site integrated hydrogen-based systems connected to the grid, and consisting of electrolyser, hydrogen storage and fuel cell system - hydrogen prosumers - provide efficient balancing of local energy consumption and local production of renewable energy that can be extended over annual cycles. There is no transport of hydrogen needed. Thus, the H2LEC – Local energy community with integrated hydrogen systems - represents the carrier of dispersed energy and hydrogen production as a complement of concentrated energy and hydrogen production: on average, H2LEC will predictably achieve at least 75% self-supply. Additionally, with Combined Heat-and-Power systems, coupling to the thermal system adds to energy efficiency. H2LEC represents a virtual socio-economic system based on community values and thus engages initiative, innovation and capital of local actors, new technology start-ups and local industry; and represents opportunities for new disruptive business models. It brings into the energy supply system new players – prosumer who actively trade their flexibilities among themselves and on the external markets, and stimulates new enabling technologies - notably automated close-to-real time trading - thereby boosting end-to-end automated solutions. The H2LEC create the need and the market for smaller integrated hydrogen-based systems ranging from a few kWe for residential homes to a few MWe units for larger industrial companies or local districts with a complete range of capacities in between, for public or tertiary buildings and smaller enterprises. Thus, they provide an opening for participation of SMEs in local and international value chains and will create a strong complementary energy bottom-up pillar and hydrogen supply system locally and in Europe.

Hydrogen Infrastructure in the Future CO2‐Neutral European Energy System—How Does the Demand for Hydrogen Affect the Need for Infrastructure?

The fast rollout of hydrogen generation, transport, and storage infrastructure has become a top priority of the European Union and its member states. Planning hydrogen infrastructure requires a thorough understanding of the future role of hydrogen in the energy system. At the same time, there is still huge uncertainty about the future demand for hydrogen and its overall role. An energy systems analysis is conducted with high temporal and spatial as well as technological resolution under alternative demand scenarios. An energy system model is used to optimize the entire European energy system with hourly time resolution and high spatial consideration of renewable energy potentials. The hydrogen demand in the five scenarios ranges from about 700 TWh for mainly industrial uses to 2800 TWh in all sectors in the EU27 + UK by 2050. The results show that an integrated European hydrogen system is a robust element of the cost‐optimal system design in all scenarios. This encompasses flexible electrolyzers at the most favorable wind and solar locations, long‐distance hydrogen transport network, large‐scale seasonal underground storage, and electricity generation for peak demand periods. Conclusions about the individual components are provided and high‐resolution data on hydrogen demand are available for future research.

Carbon management technology pathways for reaching a U.S. Economy-Wide net-Zero emissions goal

The Carbon Management Study Group of the 37th Energy Modeling Forum (EMF 37) designed seven scenarios to explore the role of three potentially key technology suites – point source carbon dioxide capture and storage (PSCCS), direct air capture of carbon dioxide (DACCS), and hydrogen systems (H2) – in shaping the broader technology pathways to reaching net-zero carbon dioxide (CO2) emissions in United States by 2050. Each scenario was run by up to 13 models participating in the EMF 37 study. Results show that carbon dioxide removal technologies were consistently a major part of successful pathways to net-zero U.S. CO2 emissions in 2050. Achieving this net-zero CO2 goal without any form of carbon dioxide capture and storage was found to be impossible for most models; some models also found it impossible to reach net-zero without DACCS. The marginal cost of achieving net-zero CO2 emissions in 2050 was between two and 10 times higher without PSCCS and/or DACCS available. The carbon price at which DACCS was deployed as a backstop technology depended upon the assumed cost at which DACCS was available at scale. Carbon prices were between $250 and $500 per ton CO2 when DACCS deployed as a backstop. The average CO2 capture rate across all models in 2050 in the central net-zero scenario was 1.3 GtCO2/year, which implies a substantial upscaling of capacity to move and store CO2. Hydrogen sensitivity scenarios showed that H2 typically constituted a relatively small share of the overall U.S. energy system; however, H2 deployed in applications that are considered hard to decarbonize, facilitating transition towards net-zero emissions.

Hydrogen adsorption on fcc metal surfaces towards the rational design of electrode materials

The successful large-scale implementation of hydrogen as an energy vector requires high performance electrodes and catalysts made of abundant materials. Rational materials design strategies are the most efficient means of reaching this goal. Here we present a study on the adsorption of H-atoms onto fcc transition metal surfaces and propose descriptors for the rational design of electrodes and catalysts by means of correlations between fundamental properties of the materials and among other properties, their experimentally measured performance as hydrogen evolution electrodes (HEE). A large set of quantum mechanical modelling data at the DFT level was produced, covering the adsorption of H-atoms onto the most stable surfaces (100), (110) and (111) of: Ag, Au, Co, Cu, Ir, Ni, Pd, Pt and Rh. For each material and surface, a coverage dependent set of minimum energy structures was produced and chemical potentials for adsorption of H-atoms were obtained. Averaging procedures are here proposed to approach modelling to the experiments. Several correlations between the computed data and experimentally measured quantities are done to validate our methodology: surface plane dependent adsorption energies, chemical potentials and experimentally determined surface energies and work functions. We search for descriptors of catalytic activity by testing correlations between the DFT data obtained from our averaging procedures and experimental data on HEE performance. Our methodology allows us to obtain linear correlations between the adsorption energy of H-atoms and the exchange current density (i0) in a HEE, avoiding the volcano-like plots. We show that the chemical potential has limitations as a descriptor of i0 because it reaches an early plateau in terms of i0. Simple quantities obtained from database data such as the first stage electronegativity (χ) as devised by Mulliken has a strong linear correlation i0. With a quantity we denominate modified second-stage electronegativity (χ2m) we can reproduce the typical volcano plot in a correlation with i0. A theoretical and conceptual framework is presented. It shows that both χ and χ2m, that depend on the first ionization potential, second ionization potential and electron affinity of the elements can be used as descriptors in rational design of electrodes or of catalysts for hydrogen systems.

Optimization of Residential Hydrogen Facilities with Waste Heat Recovery: Economic Feasibility across Various European Cities

The European Union has established ambitious targets for lowering carbon dioxide emissions in the residential sector, aiming for all new buildings to be “zero-emission” by 2030. Integrating solar generators with hydrogen storage systems is emerging as a viable solution for achieving these goals in homes. This paper introduces a linear programming optimization algorithm aimed at improving the installation capacity of residential solar–hydrogen systems, which also utilize waste heat recovery from electrolyzers and fuel cells to increase the overall efficiency of the system. Analyzing six European cities with diverse climate conditions, our techno-economic assessments show that optimized configurations of these systems can lead to significant net present cost savings for electricity and heat over a 20-year period, with potential savings up to EUR 63,000, which amounts to a 26% cost reduction, especially in Southern Europe due to its abundant solar resources. Furthermore, these systems enhance sustainability and viability in the residential sector by significantly reducing carbon emissions. Our study does not account for the potential economic benefits from EU subsidies. Instead, we propose a novel incentive policy that allows owners of solar–hydrogen systems to inject up to 20% of their total solar power output directly into the grid, bypassing hydrogen storage. This strategy provides two key advantages: first, it enables owners to profit by selling the excess photovoltaic power during peak midday hours, rather than curtailing production; second, it facilitates a reduction in the size—and therefore cost—of the electrolyzer.

Techno-economic synergy analysis of integrated electric power and hydrogen system

This study introduces an integrated renewable-penetrated electric power and hydrogen energy system (IRPHS) framework to address the integration challenges of renewable energy sources (RESs) through the development of a hydrogen-based multi-carrier energy system. The IRPHS combines a renewable-penetrated electric power system (RP-EPS) with hydrogen energy system (HES), integrating urban transportation systems (UTSs), and incorporating short and long-term hydrogen storage. By employing scenario-based stochastic programming and the alternating direction method of multipliers (ADMM), the study tackles uncertainties of renewable power and complexities of IRPHS problem. The research evaluates benefits of integrated versus stand-alone operation, focusing on flexibility across hydrogen generation, transportation, and storage. Findings highlight cost-efficient hydrogen generation, enhanced efficiency, and economic benefits in RES deployment, particularly with long-term hydrogen storage.

Leveraging normalizing flows for orbital-free density functional theory

Abstract Orbital-free density functional theory (OF-DFT) for real-space systems has historically depended on Lagrange optimization techniques, primarily due to the inability of previously proposed electron density approaches to ensure the normalization constraint. This study illustrates how leveraging contemporary generative models, notably normalizing flows (NFs), can surmount this challenge. We develop a Lagrangian-free optimization framework by employing these machine learning models for the electron density. This diverse approach also integrates cutting-edge variational inference techniques and equivariant deep learning models, offering an innovative reformulation to the OF-DFT problem. We demonstrate the versatility of our framework by simulating a one-dimensional diatomic system, LiH, and comprehensive simulations of hydrogen, lithium hydride, water, and four hydrocarbon molecules. The inherent flexibility of NFs facilitates initialization with promolecular densities, markedly enhancing the efficiency of the optimization process.

Comprehensive 3E -energetic, economic, and environmental-analysis of a hybrid solar dish-Brayton engine and fuel cell system for green hydrogen and power generation

This work aims to assess the energy, economic, and environmental performance of a novel hybrid solar dish Bryton engine and fuel cell (SDBE-FC) system for generating green hydrogen and electricity. The system includes solar dish units, fuel cells, an electrolyzer, a converter, and a hydrogen storage tank. The study introduces a novel SDBE-FC system, replacing typical photovoltaic/fuel cell setups, to achieve higher efficiency and improved financial and environmental competitiveness. A vigorous energy-enviro-economic analysis is carried out using MATLAB/Simulink® to model system components. Key parameters have been analyzed, including the electrolyzer efficiency, flow rate, power, and the SDBE plant and FC stack's power, area, and efficiency. The total levelized cost of energy (LCOE) and the reduction in CO2 emissions are also calculated. Results showed that using 50 stacked fuel cells achieved an efficiency of 7%, increasing the number of staked fuel cells to 400 increased the efficiency by eightfold achieving a peak power of 297 kW. The efficiency and power output of the fuel cell decreased by 16% and 22.2%, respectively, when the operational temperature increased from 40 °C to 80 °C. Furthermore, LCOE as low as 0.218 US$/kWh was achieved using 25 SDBE units at 1100 °C. At 30 kW, the SDBE system produces 750 kW of power with 18.3% efficiency and occupies 4099.8 m2 as the temperature (Th) reaches to 1100 °C. The SDBE, with a rated power range of 15 kW–30 kW, achieved a 390.8% CO2 emissions reduction, amounting to 34,120.76 tons of CO2, when 25 SDBE units were utilized.

MIL-101(Cr) entrapped polyol-synthesized iron promoted platinum bimetallic nanoparticles system for synergistic selective hydrogenation of cinnamaldehyde

The interfacial characteristics of platinum (Pt) metal catalysts can be systematically regulated by interacting them with electropositive metals, leading to synergistic interactions for extensive catalytic applications. In this study, an evenly dispersed polyol-synthesized iron (Fe)-promoted Pt bimetallic nanoparticle (BNPs) system was embedded in MIL-101(Cr). The PtFe2@MIL-101(Cr) catalyst unveiled remarkable activity (86%) and selectivity (89%) for the superior hydrogenation of the targeted CO bond of cinnamaldehyde (CAL). The exceptional hydrogenation performance can be credited to the interplay of the geometric and electronic properties arising from charge shuttling between Fe and Pt within the homogenously distributed Pt–Fe bimetallic nanoparticle system. The experimental results indicate enhanced valence electrons in the Pt d-band through the mutual synergetic interface between the Pt and Fe BNPs. Consequently, these Fe–Pt sites functioned as interfacial electrophilic and nucleophilic (Lewis acid-base) sites, enhancing H2 activation and facilitating CO bond conversion to yield unsaturated cinnamal alcohols (COL). Additionally, the narrow pores of MIL-101(Cr) encapsulating the Pt–Fe BNPs induced steric hindrance, allowing only CO bond hydrogenation. Furthermore, the PtFe2@MIL-101(Cr) catalyst maintained its optimal hydrogenation performance over five cycles, demonstrating no substantial loss in either CAL conversion or COL yield, thus endorsing the universal practical applicability of the catalyst.

Optimal operation for P2H system with 100% renewable energy concerning thermal-electric properties

Power to hydrogen (P2H) system with renewable energy sources is an important research point for sustainable development. Developing a comprehensive model to accurately capture the thermal-electric characteristics of an electrolyzer and utilizing it to optimize the system’s performance pose a significant challenge. In this paper, we develop an energy conversion model of the Alkaline Water Electrolyzer (AWE), describing the impact of temperature on AWE’s operation. Then, using experimental fitting methods, we fit the important formulas of the model: the maximum power (MMP) function and the efficiency function. Subsequently, based on the proposed energy conversion model, we propose an active variable temperature (AVT) operation strategy for the P2H system with renewable energy aimed at maximizing hydrogen production. At last, cases for both the day-ahead and hour-ahead situations are conducted with real photovoltaic power. The simulation results show that the AVT operation strategy achieves up to 3% higher hydrogen production and nearly 100% renewable energy utilization rates.

Integration Assessment of Renewable Energy Sources (RESs) and Hydrogen Technologies in Fish Farms: A Techno-Economical Model Dispatch for an Estonian Fish Farm

A fundamental aspect of fish farms is their energy consumption, which is essential for various activities like water supply, pool aeration, thermal conditioning, lighting, filtration, and recirculation systems. Due to volatile prices and rising energy use, costs have surged, requiring energy-optimization solutions for economic viability and pollution reduction. In this context, this study aims to evaluate renewable energy integration in these installations based on real data, assessing current operations, proposing renewable energy optimization, and exploring hydrogen systems for energy needs, using HOMER PRO® to analyze different scenarios. For this purpose, it targets a rainbow trout farm in Estonia, and by simulating the various hybrid configurations proposed, it aims to optimize its energy production and storage, ensuring feasibility and technical integration. The results of the simulations primarily demonstrate the potential for using the byproduct of electrolysis to cover the oxygen demand in these types of processes, reducing the demand for raw materials. Additionally, it is observed that storage enhances performance in isolated systems; however, the economically viable integration of hydrogen technology requires three assumptions: a regulatory framework allowing surplus energy sales to the grid, an existing infrastructure for hydrogen trading, and high energy purchase prices.

Risks in the design of regional hydrogen hub systems: A review and commentary.

Early investments in regional hydrogen systems carry two distinct types of risk: (1) economic risk that projects will not be financially viable, resulting in stranded capital, and (2) environmental risk that projects will not deliver deep reductions in greenhouse gas emissions and through leaks, perhaps even contribute to climate change. This article systematically reviews the literature and performs analysis to describe both types of risk in the context of recent efforts in the United States and worldwide to support the development of "hydrogen hubs" or regional systems of hydrogen production and use. We review estimates of hydrogen production costs and projections of how future costs are likely to change over time for different production routes, environmental impacts related to hydrogen and methane leaks, and the availability and effectiveness of carbon capture and sequestration. Finally, we consider system-wide risks associated with evolving regional industrial structures, including job displacement and underinvestment in shared components, such as refueling. We conclude by suggesting a set of design principles that should be applied in developing early hydrogen hubs if they are to be a successful step toward creating a decarbonized energy system.