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A range of existing and newly developed hydrogen standards, certification and labelling (SCL) schemes aim to promote the role of 'renewable', 'clean' or 'green' hydrogen in decarbonising energy transitions. This paper analyses a sample of these SCLs to assess their role in the scaling up of renewable hydrogen and its derivatives. To analyse these hydrogen SCLs, we embellish a novel conceptual framework that brings together Sustainability, Systems Thinking, and Governance (SSG) literatures. The results reveal noteworthy scheme differences in motivation, approach, criteria, and governance; highlighting the complex, interconnected, and dynamic reality within which energy systems are embedded. We consider whether the sustainable utilisation of renewable hydrogen is well-served by the proliferation of SCLs and recommend an SSG-informed approach. An SSG approach will better promote collaboration towards an authoritative, global, multistakeholder, compromise on hydrogen certification that balances economic considerations with social, and environmental dimensions. [Display omitted] • There is a proliferation of hydrogen standards, certification and labelling (SCL) schemes. • We analyse a sample of SCLs to investigate their role in scaling green hydrogen. • We employ a Sustainability, Systems Thinking, and Governance (SSG) approach. • We recommend an SSG lens to help craft a global multistakeholder initiative. [ABSTRACT FROM AUTHOR]

Sustainable energy demand drives innovation in energy production. Electrolysis of water can produce carbon-free hydrogen from renewable sources. This paper presents a bibliometric analysis of recent and highly referenced research on hydrogen electrolysers utilising the Scopus database to shed insight into future trends and applications. It has been discovered that the most frequently published type of study for top-ranked papers is the formulation of problems and simulations (38.3%), followed by a study of the state-of-the-art technology assessment (32.5%), laboratory research, design, and performance evaluation (24.2%), and reviews (5%). In general, 33.33% of articles focused on controlling hydrogen electrolyser efficiency. This study used different case studies from the global literature to conduct a complete evaluation of the electrolyser statistical analysis of the present state of the art, models or modes of operation, key challenges, outstanding issues, and future research. This evaluation will aid researchers in building a commercially successful hydrogen electrolyser. • A comprehensive review on hydrogen electrolyser is analysed for future research directions. • The problems, state-of-the-art technology, design, and performance evaluation is reviewed. • The control strategies are significantly boost the efficiency of hydrogen electrolysers. • A statistical analysis on electrolyser models, open issues, and future research trend is investigated. • This review will contribute to improve the efficiency and sustainability of electrolyser technology. [ABSTRACT FROM AUTHOR]

Given global warming, which limits the use of classical energy sources, renewables can provide a solution to the dilemma between environmental protection and sustainable economic growth. In this complex and changing context, green hydrogen can become a promising link between renewable energy sources and end users. However, although hydrogen has a high gravitational energy density, it has a very low volumetric energy density. This challenge requires hydrogen compression at several stages in the supply chain from electrolysis units to conversion, storage, and distribution. Recently, many studies have focused on hydrogen compression technologies. This paper provides an overview of recent advances in large-scale hydrogen compression. First, the role of hydrogen compression in providing clean energy for the future is explored. Then the thermodynamic concept of hydrogen compression is investigated. Gaining a proper understanding of compressor operating conditions in various operations in the large hydrogen industry is the next focus of this paper. Later, the capabilities and limitations of available mechanical compressors for the hydrogen industry, including reciprocation and centrifugal, are summarized. Finally, research gap and recommended new areas in this field are recognized. The presented insightful concepts provide students, experts, researchers, and decision-making working on large-scale hydrogen industry with the state of the art in hydrogen compressors industry. • Green hydrogen is a promising link between production and use of renewables. • Low molecular weight of hydrogen makes compression a crucial step in the green hydrogen chain. • Various operations in this industry need compressors with output pressures of 20 bar–200 bar. • Only reciprocating and centrifugal compressors can handle the required capacity in this industry. • Review of resources proves rapid progress in the design and reliability of hydrogen compressors. [ABSTRACT FROM AUTHOR]

This study aims to investigate the gasification potential of olive pomace with using different fixed-bed gasifier systems. Olive pomace as a dried form was supplied from a chemical industry plant working on olive oil soap, located in Izmir, Türkiye. After a complete characterization of olive pomace, gasification experiments by using fixed bed reactor systems were done at three different gasifier temperatures as 700, 800 and 900 °C. As a gasification agent, dry air was used with four different flowrates (0.4, 0.2, 0.1, 0.05 L/min) while pure oxygen experiments were carried out with a flow rate of 0.01 L/min. Syngas with H 2 content of 48% and 45% (volumetric) were obtained in updraft and downdraft gasifiers, respectively, by using dried air as a gasifying agent. Heating value of syngas was around 12.4 MJ/Nm3. In the pure oxygen atmosphere, H 2 contents of the syngas were measured as 53% and 39%vol. In the updraft and downdraft gasifiers. This paper presents the research results on the olive pomace gasification study as a part of a large-scale research project and discuss them in the context of hydrogen production from the fixed bed reactors. [Display omitted] • Pomace gasification process was carried out in two different fixed bed reactors. • The volumetric percentage of H 2 gas was found to be in the range of 40–50%. • The maximum volume of methane was measured approximately as 20%. • The maximum volume of CO was measured in the range of 20–30% in both reactors. • The maximum volume of hydrogen in the updraft gasifier was measured as 48%. [ABSTRACT FROM AUTHOR]

The paper considers the task of creating an instrumental system for optimizing the exchange of active power of the trunk and distribution networks, taking into account the price indicators of electricity in a joint and separate mode of operation. As part of the development of a simulation model of the automated control system of the local intelligent power system MicroGrid, the results of modeling the exchange of active power of the power connection from the main network of the main South of Russia main electrical networks and the distribution network of the university campus (in which classical sources of generation are combined with solar, wind and hydrogen energy) are presented. In a single model, the electrical mode of operation of networks is simulated in the voltage range of 0.4–500 kV. Simulation is carried out in steady state and transient mode. Slow, real and fast time modes are available. Simulation of emergency control systems has been implemented. The modes of synchronization of the main and distribution networks in normal and emergency circuits are considered. Reliability control and monitoring of the main operating parameters are carried out. The active power exchange module created on the basis of the results of the simulation as part of the software package « RETREN » will make it possible to use this complex to automate the management of local power system. The energy system, in addition to power from the grid, includes gas generation, solar panels installed on the roofs of campus buildings, wind turbines and stationary hydrogen power plants operating on hydrogen fuel cells. The complex of designers allows organizing human-machine interfaces of any complexity on completely domestic software products. [ABSTRACT FROM AUTHOR]

Green hydrogen is increasingly considered a vital element for the long-term decarbonization of the global energy system. For regions with scarce land resources, this means importing significant volumes of green hydrogen from regions with abundance of renewable energy. In producing countries, this raises significant sustainability questions related to production and export. To assess these sustainability-related opportunities and challenges, the authors first present a review of renewable energy deployment in the electricity sector, and then extend it to the foreseeable opportunities and risks of green hydrogen production in exporting countries. The paper finds that questions of freshwater and land availability are critical from an environmental and a socio-economic point of view, and that the development of international standards for the governance of hydrogen-related projects will be crucial. These should also address potential conflicts between the deployment of renewable energy for the decarbonization of local power grids, and the export of green hydrogen. • Production and export of GH raise questions of sustainability and climate justice. • Land and freshwater availability are key risks for local communities. • Community engagement is needed to mitigate local environmental risks factors. • International standards for governance of hydrogen projects are key to sustainability. • Climate-related risks should be included in sustainability standards. [ABSTRACT FROM AUTHOR]

Sector coupling will play a key role in the future energy system to realise greenhouse gas emission reductions. A major factor will be green hydrogen based on renewable energies to defossilise consumption sectors. Related business models of power to gas are not yet implemented on the market. However, given the urgency of the change, this is essential. This paper investigates hydrogen business models under current market conditions of high power prices, no existing market for green hydrogen and the given regulatory framework with no levies for green hydrogen production in the German market. For this purpose, an open-source business model evaluation tool for sector coupling, which enables a simple and generic evaluation of sector coupling business models including production and possible transportation infrastructure, is developed and applied. Furthermore, the impact of changes of the input parameters like power prices and the influence of regulatory changes on profitability are assessed. The results show that X-to-power business cases can be already profitable due to high power prices on the wholesale market. However, power-to-X business models like hydrogen production still have negative net present values and the net present value is worsened when infrastructure for hydrogen transportation is considered. Key parameters for the negative result are investment costs and low hydrogen prices. Nevertheless, it must be considered that higher hydrogen prices have a negative impact on the X-to-power business model. To allow for profitable business cases, the market conditions need to be adjusted to ensure sufficiently high prices for green hydrogen. Furthermore, subsidies on investment or operational and maintenance costs can support the integration of power-to-X into the market. Transportation infrastructure has a significant impact on profitability. Given these facts, it is necessary to create the required framework conditions to ensure the realisation of sector coupling. • Presentation of an open-source approach to assessing sector coupling business models. • Case study on hydrogen including renewables, transportation infrastructure, and regulatory and market conditions in Germany. • No market-based introduction of power-to-X business models without subsidies. • X-to-power business models profitable due to high power prices. • Power-to-X and X-to-Power jeopardise each other as they require opposing hydrogen and electricity prices. [ABSTRACT FROM AUTHOR]

This paper aims to holistically study hydrogen production options essential for a sustainable and carbon-free future. This study also outlines the benefits and challenges of hydrogen production methods to provide sustainable alternatives to fossil fuels by meeting the global energy demand and net-zero targets. In this study, sixteen hydrogen production methods are selected for sustainability investigation based on seven different criteria. The criteria selected in the comparative evaluation cover various dimensions of hydrogen production in terms of economic, technical, environmental, and thermodynamic aspects for better sustainability. The current study results show that steam methane reforming with carbon capture could provide sustainable hydrogen in the near future while the other technologies' maturity levels increase and the costs decrease. In the medium- and long-terms, photonic and thermal-based hydrogen production methods can be the key to sustainable hydrogen production. [Display omitted] • A holistic study of hydrogen production options for a sustainable and carbon-free future. • It outlines the benefits and challenges of hydrogen production methods. • Sixteen methods are selected for sustainability investigation based on seven different criteria. • It covers economic, technical, environmental, and thermodynamic aspects of sustainability. • It can help stakeholders deploy a hydrogen roadmap for a more sustainable future. [ABSTRACT FROM AUTHOR]

This paper uses established and recently introduced methods from the applied mathematics and statistics literature to study trends in the propagation and capacity of low-carbon hydrogen projects over the past two decades. First, we judiciously apply a regression model to estimate the association between various predictors and the capacity of global hydrogen projects. Next, we turn to the geographic propagation of low-carbon hydrogen projects, where we apply a recently introduced method to explore the geographic variance of hydrogen projects over time. Then, we demonstrate that most geographic regions display linear growth in cumulative plants and apply distance correlation to determine the nonlinear dependence between the two most prolific regions - North America and Europe. Finally, we study relationships between the propagation and capacity of green vs blue hydrogen over time, specifically, the time-varying regional consistency between the contribution of green vs blue plants to the total number and capacity of hydrogen plants. • We study a low-carbon hydrogen project database from the International Energy Agency. • An exponential increase in green hydrogen plant capacity is highlighted. • A dramatic closing between the capacity of green and non-green plants is revealed. • New insights revealing spatio-temporal trends in hydrogen propagation are shown. • Relationships between green and fossil-fuelled hydrogen plants are studied over time. [ABSTRACT FROM AUTHOR]

The potential role of hydrogen as a tool for the decarbonization of the energy sector is widely recognized. In this paper, a comprehensive analysis of the marginal utility of increasing the hydrogen penetration on the energy and environmental performances of a multi-energy system is developed to assess its potential. A distributed energy system satisfying the energy requirements for an existing building is chosen as test case, assumed as representative of a wide set of applications. Starting from real energy consumption profiles, representative scenarios and optimized design configurations are defined using a methodology that takes into account uncertainties both in demand and renewable production profiles and in techno-economic parameters assumptions. For each multi energy system configuration, an optimal dispatch control strategy is achieved through a mixed-integer linear programming method to maximize the building self-independence from the grid. Results show how an increase of hydrogen technologies penetration allows a reduction of the specific carbon footprint of the system down to 100 grCO 2 /kWh while increasing the system resilience up to 85%. Detailed information about the marginal effect of H 2 technologies on resilience, carbon footprint, and fossil energy savings are presented and can be used for extensions to similar applications. • Resilience up to 85% is achieved through hydrogen integrated multi-energy system. • Specific carbon footprint is reduced up to 100grCO 2 /kWh. • Uncertainties are accounted through a coupled clustering-Montecarlo approach. • Hydrogen seasonal storage is crucial for decarbonization of the energy system. [ABSTRACT FROM AUTHOR]

This paper is a critical review of selected real-world energy storage systems based on hydrogen, ranging from lab-scale systems to full-scale systems in continuous operation. 15 projects are presented with a critical overview of their concept and performance. A review of research related to power electronics, control systems and energy management strategies has been added to integrate the findings with outlooks usually described in separate literature. Results show that while hydrogen energy storage systems are technically feasible, they still require large cost reductions to become commercially attractive. A challenge that affects the cost per unit of energy is the low energy efficiency of some of the system components in real-world operating conditions. Due to losses in the conversion and storage processes, hydrogen energy storage systems lose anywhere between 60 and 85% of the incoming electricity with current technology. However, there are currently very few alternatives for long-term storage of electricity in power systems so the interest in hydrogen for this application remains high from both industry and academia. Additionally, it is expected that the share of intermittent renewable energy in power systems will increase in the coming decades. This could lead to technology development and cost reductions within hydrogen technology if this technology is needed to store excess renewable energy. Results from the reviewed projects indicate that the best solution from a technical viewpoint consists in hybrid systems where hydrogen is combined with short-term energy storage technologies like batteries and supercapacitors. In these hybrid systems the advantages with each storage technology can be fully exploited to maximize efficiency if the system is specifically tailored to the given situation. The disadvantage is that this will obviously increase the complexity and total cost of the energy system. Therefore, control systems and energy management strategies are important factors to achieve optimal results, both in terms of efficiency and cost. By considering the reviewed projects and evaluating operation modes and control systems, new hybrid energy systems could be tailored to fit each situation and to reduce energy losses. • Review of 15 projects that use hydrogen as energy storage in a power system. • Hydrogen is one of very few alternatives for long-term electricity storage. • Hydrogen storage should in most cases be combined with battery storage. • Power-to-gas-to-power for hydrogen still has a low energy efficiency (15–40%). • Intermittent in-flow of energy and high costs are big challenges for these systems. [ABSTRACT FROM AUTHOR]

This paper presents techno-economic modelling results of a nationwide hydrogen fuel supply chain (HFSC) that includes renewable hydrogen production, transportation, and dispensing systems for fuel cell electric buses (FCEBs) in Ireland. Hydrogen is generated by electrolysers located at each existing Irish wind farm using curtailed or available wind electricity. Additional electricity is supplied by on-site photovoltaic (PV) arrays and stored using lithium-ion batteries. At each wind farm, sizing of the electrolyser, PV array and battery is optimised system design to obtain the minimum levelised cost of hydrogen (LCOH). Results show the average electrolyser capacity factor is 64% after the integration of wind farm-based electrolysers with PV arrays and batteries. A location-allocation algorithm in a geographic information system (GIS) environment optimises the distributed hydrogen supply chain from each wind farm to a hypothetical hydrogen refuelling station in the nearest city. Results show that hydrogen produced, transported, and dispensed using this system can meet the entire current bus fuel demand for all the studied cities, at a potential LCOH of 5–10 €/kg by using available wind electricity. At this LCOH, the future operational cost of FCEBs in Belfast, Cork and Dublin can be competitive with public buses fuelled by diesel, especially under carbon taxes more reflective of the environmental impact of fossil fuels. [Display omitted] • The H₂ demand for H₂ bus in 6 cities in Ireland is 13.7 kilotonnes/year. • Integration of renewables increases the electrolyser capacity factor to maximum 73%. • Share of wind, solar & battery to electrolyser are 79%, 16%, & 5%, respectively. • The total H₂ fuel cost from the distributed supply chain is between 5 & 10 €/kg. • Operational cost parity of diesel & H₂-fuelled bus can be met by 2030 in Dublin. [ABSTRACT FROM AUTHOR]

This paper studies the potentials of green hydrogen production from hydropower energy and its application in electricity regeneration and replacement of petroleum products from the transportation sector in Nepal. The potential surplus hydroelectric energy, and hydrogen production potential from the surplus energy considering different scenarios, is forecasted for the study period (2022–2030). The results showed that hydrogen production potential ranges from 63,072 tons to 3,153,360 tons with the utilization of surplus energy at 20% and 100% respectively, in 2030. The economic analysis of hydrogen from hydropower projects that electricity is valued based on per kg of hydrogen when the surplus electricity is provided at feasible lower price values compared to the US $1.17. This study concludes that hydrogen production from spilled hydro energy and its use in the transportation sector and independent electricity generation is a niche opportunity to lead the country towards sustainable energy solutions and an economy running on hydrogen. • Methodological study for quantification of excess hydropower and hydrogen production. • Cost projections scenarios from green hydrogen from surplus hydropower electricity. • Identification of role of green hydrogen in multiple end-use areas of developing nation. • Potential replacement of conventional fuel with hydrogen in transportation sector. [ABSTRACT FROM AUTHOR]

This paper investigates the optimal planning of microgrids including the hydrogen energy system through mixed-integer linear programming model. A real case study is analyzed by extending the only microgrid lab facility in Austria. The case study considers the hydrogen production via electrolysis, seasonal storage and fueling station for meeting the hydrogen fuel demand of fuel cell vehicles, busses and trucks. The optimization is performed relative to two different reference cases which satisfy the mobility demand by diesel fuel and utility electricity based hydrogen fuel production respectively. The key results indicate that the low emission hydrogen mobility framework is achieved by high share of renewable energy sources and seasonal hydrogen storage in the microgrid. The investment optimization scenarios provide at least 66% and at most 99% carbon emission savings at increased costs of 30% and 100% respectively relative to the costs of the diesel reference case (current situation). • A MILP model for renewable based hydrogen production, seasonal storage and mobility. • A real case study is analyzed by extending a microgrid lab facility in Austria. • Multiple investment optimization scenarios relative to two distinct reference cases. • CO 2 reduction by at least 66% and at most 99% relative to the diesel reference case. • Introducing carbon prices to bridge the cost gap between hydrogen and diesel fuel. [ABSTRACT FROM AUTHOR]

Storing energy in the form of hydrogen is a promising green alternative. Thus, there is a high interest to analyze the status quo of the different storage options. This paper focuses on the large-scale compressed hydrogen storage options with respect to three categories: storage vessels, geological storage, and other underground storage alternatives. In this study, we investigated a wide variety of compressed hydrogen storage technologies, discussing in fair detail their theory of operation, potential, and challenges. The analysis confirms that a techno-economic chain analysis is required to evaluate the viability of one storage option over another for a case by case. Some of the discussed technologies are immature; however, this does not rule out these technologies; rather, it portrays the research opportunities in the field and the foreseen potential of these technologies. Furthermore, we see that hydrogen would have a significant role in balancing intermittent renewable electricity production. • Limitations and challenges of large-scale hydrogen storage. • A coverage for all technologies for the compressed hydrogen storage. • Reviewing the concerns of hydrogen blending into the natural gas infrastructure. • Compares the technologies with respect to; storage time, losses, size, and cost. • To evaluate the storage alternatives, a techno-economic chain analysis is required. [ABSTRACT FROM AUTHOR]

Clean fuels are the critical requirement for industrialized world to combat emission of greenhouse gas. Hydrogen is one of the cleanest fuels that generates water as a result of combustion. Production of hydrogen from renewable and nonpolluting resources is an imperative task for sustainable clean fuel production. Biological processes provide an opportunity to produce hydrogen from renewable and economical bio-resources like biomass and solar energy through various processes such as direct/indirect photolysis, photo-fermentation, dark-fermentation, and CO gas-fermentation. This paper provides a comprehensive review on biological hydrogen production including organisms, type of substrates and their concentrations, role of chemical addition, operation conditions such as temperature, pH, and agitation, as well as illumination systems in case of light dependent processes. Further discussions in this work comprise various configuration of integrated biological processes of photolysis, dark, and photo-fermentation such as two component and three-component systems. • Presentation of recent progresses on biological hydrogen production processes. • Discussion of challenges on applications of biological hydrogen routes. • Comparisons of various configurations of integrated biohydrogen generation systems. [ABSTRACT FROM AUTHOR]

Hydrogen has an important role as a smart solution for Smart Grid, as it can play as an energy vector, a storage medium, and a clean fuel cell. The integration of Hydrogen and Smart Grid can minimize the impact on the environment while maximizing sustainability, which indicates that we are developing toward a hydrogen society. There have been already many studies on different aspects of this topic. For a better understanding of the related work, this paper proposed a comprehensive overview of the related work on the integration of Hydrogen and Smart Grid. Related literature is organized and analyzed from four categories, including Hydrogen energy in smart grids, Hydrogen fuel cell electric vehicles, Hydrogen economy in smart grids, and Models for energy system in smart grids. And each subject has been introduced more carefully. What's more, for a clear understanding for readers, we provide overall scenario views for the organization of the related work. • The integration of Hydrogen and Smart Grid is a trend. • The integration will help boost new economy and form hydrogen society. • Four different viewpoints include grid, vehicle, economy and system models. • More than 100 publications are reviewed for the integration. [ABSTRACT FROM AUTHOR]

This paper presents high-performance Ni-YSZ tubular catalysts for CO 2 methanation prepared by the extrusion molding. We fabricated tubular-shaped Ni-YSZ catalysts with various Ni contents (25–100 wt% NiO) and investigated the effect of Ni content on CO 2 methanation performance under various temperatures and gas flow rates. Catalysts with Ni contents >75 wt% showed CH 4 yields >91% above 270 °C with high CH 4 selectivities (>99%). High CH 4 yields were also observed under high GHSVs at 300 °C: 93% and 92% at 8700 and 17,500 h−1, respectively. Investigation of methanation with the catalysts revealed that CO 2 methanation was accelerated by a localized hotspot at the reactor inlet arising from the interaction between reaction kinetics and heat generation. Using a numerical simulation, we considered the optimum arrangement of catalytic activity in the reactor to avoid hotspot generation and realize a stable high CO 2 methanation performance. We can simultaneously achieve high CH 4 production and prevent hotspot formation by properly arranging catalysts with different activities. • Ni content >75% gave CH 4 yields >91% above 270 °C with selectivities >99%. • Inlet hotspot arises from interaction of heat generation and reaction acceleration. • Increasing catalytic activity along reactor length can avoid hotspot formation. [ABSTRACT FROM AUTHOR]

One of the objectives of the research project at Hawaii Natural Energy Institute (HNEI) is to demonstrate long-term durability of the electrolyzer when operated under cyclic operation for frequency regulation on an Island grid system. In this paper, a Hydrogen Energy System with an electrolyzer is analyzed as a potential grid management tool. A simulation tool developed with a validated model of the hydrogen energy system and Island of Hawaii grid model is presented and employed for this investigation. The simulation study uses realistic measured solar and wind power profiles to understand what optimal electrolyzer size would be required to achieve the maximum level of grid frequency stabilization. The simulation results give insight into critical information when designing a hydrogen energy system for grid management applications and the economic impact it has when operated as a pure grid management scheme or as a limitless hydrogen production system. • Hydrogen energy system (HES) is analyzed as a potential grid management tool. • A simulation tool is presented and employed for grid management investigation. • Framework for electrolyzer long-term degradation study under renewable cyclic load. • Insight into critical fact when designing HES for grid management application. • The impact of operating HES as a pure grid frequency stabilizer is also presented. [ABSTRACT FROM AUTHOR]

The reliance on fossil fuels is one of the most challenging problems that need to be dealt with vigorously in recent times. This is because using them is not sustainable and leads to serious environmental issues, such as: air pollution and global warming. This condition affects economic security and development. An alternative to fossil fuel is highly possible which will be more environmentally friendly, sustainable and efficient as well. Among all the different technologies associated with renewable energy, fuel cell technologies represent one of the most promising technological advancement to curb the situation. In this paper, an overview of the technology and its advantages and disadvantages compared with competitive technologies was revealed. The application of different fuel cell types in the stationary and portable sectors was covered. Furthermore, recent challenges and promising developments of current fuel cell technologies in different studied applications were reviewed. Some possible solutions to the challenges were named in this paper for both the portable and stationary fuel cell applications. The paper further seeks to expose the world to the current progress made in the fuel cell industry up to date and possible areas that needs intensified research and modifications to make the fuel cell industry more vibrant and buoyant. [ABSTRACT FROM AUTHOR]

Abstract Heavy fossil fuels consumption has raised concerns over the energy security and climate change while hydrogen is regarded as the fuel of future to decarbonize global energy use. Hydrogen is commonly used as feedstocks in chemical industries and has a wide range of energy applications such as vehicle fuel, boiler fuel, and energy storage. However, the development of hydrogen energy in Malaysia is sluggish despite the predefined targets in hydrogen roadmap. This paper aims to study the future directions of hydrogen economy in Malaysia considering a variety of hydrogen applications. The potential approaches for hydrogen production, storage, distribution and application in Malaysia have been reviewed and the challenges of hydrogen economy are discussed. A conceptual framework for the accomplishment of hydrogen economy has been proposed where renewable hydrogen could penetrate Malaysia market in three phases. In the first phase, the market should aim to utilize the hydrogen as feedstock for chemical industries. Once the hydrogen production side is matured in the second phase, hydrogen should be used as fuel in internal combustion engines or burners. In the final phase hydrogen should be used as fuel for automobiles (using fuel cell), fuel-cell combined heat and power (CHP) and as energy storage. Highlights • Biomass and solar pathways for hydrogen production could be feasible in Malaysia. • Hydrogen can be used as transportation fuel, heating fuel and energy storage. • Hydrogen economy in Malaysia faces technical, economic and social challenges. • Renewable hydrogen could be commercialized in 3 phases via the proposed framework. [ABSTRACT FROM AUTHOR]

Abstract: Nowadays, renewable power system solutions are widely investigated for residential applications. Grid-connected systems including energy storage elements are designed. Advanced research is actually focused on improving the reliability and energy density of renewable systems reducing the whole utility cost. Source and load modeling, power architectures and algorithms are only a few topics to be addressed. Designers have to carefully deal with each subtopic prior to design efficient renewable energy systems. In the literature, each topic is separately discussed and the lack of a unique reference guide is clear to power electronics designers. In this paper, each design step including source and load modeling, hybrid supply architectures and power algorithms, is carefully addressed. A review of existing solutions is presented. The correlation between each topic is deeply analyzed. Guidelines for system design are given. This paper can be referenced as a detailed review of renewable energy system design issues and solutions. [Copyright &y& Elsevier]

Abstract: This paper presents a novel hourly energy management system (EMS) for a stand-alone hybrid renewable energy system (HRES). The HRES is composed of a wind turbine (WT) and photovoltaic (PV) solar panels as primary energy sources, and two energy storage systems (ESS), which are a hydrogen subsystem and a battery. The WT and PV panels are made to work at maximum power point, whereas the battery and the hydrogen subsystem, which is composed of fuel cell (FC), electrolyzer and hydrogen storage tank, act as support and storage system. The EMS uses a fuzzy logic control to satisfy the energy demanded by the load and maintain the state-of-charge (SOC) of the battery and the hydrogen tank level between certain target margins, while trying to optimize the utilization cost and lifetime of the ESS. Commercial available components and an expected life of the HRES of 25 years were considered in this study. Simulation results show that the proposed control meets the objectives established for the EMS of the HRES, and achieves a total cost saving of 13% over other simpler EMS based on control states presented in this paper. [Copyright &y& Elsevier]

In this paper, the hybrid concept to use renewable electricity to produce hydrogen with an electrolyser in combination with a battery is introduced and analysed. This hybrid system opens the possibility to optimise operation and to increase operation times of the system and thus to improve the techno-economic performance. To analyse the performance, a model has been developed, which designs and operates a single or hybrid power-to-gas system in a cost optimal manner. The underlying method is a mixed integer linear programming (MILP) approach, which minimises total system costs. The cost optimisation modelling is performed by a case study for a hybrid electrolyser/battery system directly coupled with a large PV power plant without grid connection. The results show, that batteries can support electrolyser operation in a reasonable way. This is however associated with higher hydrogen production costs and not competitive compared to the installation of additional electrolyser capacity or curtailment of electricity. [ABSTRACT FROM AUTHOR]

This paper presents a framework for the design and assessment of a renewable energy sources (RES)-based hydrogen supply system. We generate an integrated renewable hydrogen supply (IRHS) system that includes various types of RES and hydrogen technologies such as production, storage, and transportation. We then develop a multi-period deterministic optimization model for the IRHS system by using a mixed integer linear programming (MILP) technique. The proposed model optimizes the configuration and operational strategy of the IRHS system. The capability of the proposed model is demonstrated through its application to the design problem of Korea's future hydrogen economy. We perform an economic evaluation to identify the major parameters for the required cost of the energy system infrastructure. [ABSTRACT FROM AUTHOR]

Abstract: There is an increasing need for new and greater sources of energy for future global transportation applications. One recognized possibility for a renewable, clean source of transportation fuels is solar radiation collected and converted into useable forms of electrical and/or chemical (hydrogen) energy. This paper describes methods for utilizing and combining existing technologies into systems that optimize solar energy collection and conversion into useful transportation fuels. Photovoltaic (PV)-electrolysis (solar hydrogen) and PV-battery charging systems described in this paper overcome inefficiencies inherent in past concepts, where DC power from the PV system was first converted to AC current and then used to power electrical devices at the point of generation, or fed back to the grid to reduce electricity costs. These past, non-optimized concepts included efficiency losses in power conversion and unnecessary costs. These drawbacks can be avoided by capitalizing on the unique feature of solar photovoltaic devices that match their maximum power point to the operating point of an electrolyzer or a battery charger without intervening power transformers. This concept is illustrated for two systems designed, built, and tested by General Motors for fueling a fuel cell electric vehicle and charging an automotive propulsion battery. Based on this research, we propose a scenario in which individual home-owners, businesses, or sites at remote locations with no grid electricity, can capture solar energy, store it as hydrogen generated via water electrolysis, or as electrical energy used to charge storage batteries. Such a decentralized energy system provides a home refueling option for drivers who only travel limited distances each day. [Copyright &y& Elsevier]

Abstract: While the dominant role of hydrogen in a sustainable energy future is widely accepted, the strategies for the transition from fossil-based to hydrogen economy are still actively debated. This paper emphasizes the role of carbon-neutral technologies and fuels during the transition period. To satisfy the world''s growing appetite for energy and keep our planet healthy, at least 10TW (or terawatt) of carbon-free power has to be produced by mid-century. Three prominent options discussed in the literature include: decarbonization of fossil energy, nuclear energy and renewable energy sources. These options are analyzed in this paper with a special emphasis on the role of hydrogen as a carbon-free energy carrier. In particular, the authors compare various fossil decarbonization strategies and evaluate the potential of nuclear and renewable energy resources to meet the 10TW target. An overview of state-of-the-art technologies for production of carbon-free energy carriers and transportation fuels, and the assessment of their commercial potential is provided. It is shown that neither of these three options alone could provide 10TW of carbon-neutral power without major changes in the existing infrastructure, and/or technological breakthroughs in many areas, and/or a considerable environmental risk. The authors propose a scenario for the transition from current fossil-based to hydrogen economy that includes two key elements: (i) changing the fossil decarbonization strategy from one based on CO2 sequestration to one that involves sequestration and/or utilization of solid carbon, and (ii) producing carbon-neutral synthetic fuels from bio-carbon and hydrogen generated from water using carbon-free sources (nuclear, solar, wind, geothermal). This strategy would allow taking advantage of the existing fuel infrastructure without an adverse environmental impact, and it would secure a smooth carbon-neutral transition from fossil-based to future hydrogen economy. [Copyright &y& Elsevier]

This paper considers the technical and economic feasibility of using renewable energy with hydrogen as the energy storage medium for two remote communities in Bhutan, selected to illustrate two common scenarios presenting different challenges. The Royal Government of Bhutan has published plans to provide electricity to all households in the next 20 years, but the practical problems of extending the grid over long distances and mountainous terrain will make that target difficult and expensive to achieve. Consequently, the possibility of using natural energy and diversified generation is attractive. This paper examines the use of hydro power in one community and photovoltaics with wind power in another. Hydrogen is the proposed energy storage medium in both cases. Analysis suggests that it is technically possible to use renewable energy and hydrogen for diversified power supplies and that where, as here, the costs of grid extension are high, it may also be financially viable. Thus we argue that there is a good case for establishing a test and demonstration system near the capital Thimphu for further investigation prior to use in remote locations. [Copyright &y& Elsevier]

Hydrogen production via steam methane reforming (SMR) dominates the supply to refining complexes worldwide, resulting in significant greenhouse gas (GHG) emissions. There is a considerable demand for clean hydrogen pathways that are economically competitive with SMR. The development of a 563 MW integrated wind-hydrogen model with energy storage is proposed. The model utilizes real-time wind energy data to ascertain the optimal size of the electrolyser, the number of electrolyser units and the battery (energy storage) capacity that will yield a minimum hydrogen production cost, whilst functioning in a liberalized electricity market with dynamic prices. The optimal plant configuration consists of 81 units of a 3496 kW (760 Nm 3 /hr) electrolyser and 360 MWh (60 units) of battery capacity. For the minimum hydrogen production cost determined ($9.00//kg H 2 ), the wind farm accounts for 63% of this cost. Hence, if existing wind farm assets are used, such that the investment cost of building the wind-hydrogen plant does not include the wind farm costs, the hydrogen production cost is reduced to $3.37/kg H 2 . For a particular electrolyser-battery configuration, it was observed that the minimum hydrogen production cost occurs when their respective capacity factors are approximately equivalent. The benefits of energy storage are limited by the decrease in overall plant efficiency, which results from the use of the battery. For the techno-economic conditions considered in this paper, hydrogen production costs from wind powered electrolysis ($3.37 to $9.00/kg H 2 ) are uncompetitive with SMR/SMR-CCS ($1.87 to $2.60/kg H 2 ). [ABSTRACT FROM AUTHOR]

This paper presents the technical study of a commercial sailboat conversion, originally manufactured with an internal combustion engine (ICE), into electrical hybrid propulsion system with fuel cell and batteries. Batteries are charged with electrical energy from grid when boat remains at port. The used hydrogen is generated with the electrolysis of water using energy provided through the on-board renewable system (eolic, photovoltaic and marine generation). In order to check the viability of conversion mathematical modelling is used. Firstly, hull hydrodynamic resistance is obtained through Free!Ship software. Then, this result is implemented into a global model which is developed under Matlab/Simulink ® environment. Furthermore, renewable energy and power systems are developed as Simulink ® models and a logic controller manages them. In this study, the selection of all energy and power elements is shown. Real operation sailboat under real conditions is simulated. Finally, results obtained are compared with Spanish Navigation Normative to study a possible technical feasibility. [ABSTRACT FROM AUTHOR]

In order to improve the production of environmental friendly hydrogen, new advanced alkaline electrolyzers must be designed to optimize their combination with renewable energies. In pursuing this goal, modeling of alkaline electrolyzers becomes a powerful design tool. In this paper is presented a mathematical model that describes the behavior of an alkaline electrolysis cell. Unlike most of the existing models in literature, the proposed model simulates the influence of both electrode/diaphragm distance and electrolyte concentration in regular operation. The role of these aspects is crucial when designing alkaline electrolyzers since the process efficiency is found to be very sensitive to them. The computations done with the model presented here were validated with in situ experimental data, reporting a great accuracy: the maximum error was around 1% from all polarization curves studied. Combination with renewable energies was also studied by introducing a solar PV profile and the error reported never exceeds 3%. The influence of the considered variables (temperature, electrode/diaphragm distance and electrolyte concentration) was quantified using sensitivity analysis. [ABSTRACT FROM AUTHOR]

Abstract: This paper addresses the fundamental question of where hydrogen might fit into a global sustainable energy strategy for the 21st century that confronts the three-pronged challenge of irreversible climate change, uncertain oil supply, and rising pollution. We re-envision the role of hydrogen at national and international strategic levels, relying entirely on renewable energy and energy efficiency. It is suggested the time for an exclusive ‘hydrogen economy’ has passed, since electricity and batteries would be used extensively as well. Yet hydrogen would still play a crucial role: in road and rail vehicles requiring a range comparable to today’s petrol and diesel vehicles; in coastal and international shipping; in air transport; and for longer-term seasonal storage on electricity grids relying mainly on renewables. Hydrogen fuel cell vehicles are proposed where medium and long distance trips are required, with plug-in battery electric vehicles reserved for just short trips. A hierarchy of spatially-distributed hydrogen production, storage and distribution centers relying on local renewable energy sources and feedstocks would be created to limit the required hydrogen pipeline network to the main metropolitan areas and regions by complementary use of electricity as a major energy vector. Bulk hydrogen storage would provide the strategic energy reserve to guarantee national and global energy security in a world relying increasingly on renewable energy. It is recommended that this vision next be applied to specific countries by conducting detailed energy-economic-environmental modeling to quantify its net benefits. [Copyright &y& Elsevier]

Abstract: The residential sector accounts for about a third of the total world energy consumption. Energy efficiency, Renewable Energy Sources and Hydrogen can play an important role in reducing the consumptions and the emissions and improving the energy security if integrated (Efficiency, Res, Hydrogen) systems are developed and experimented. The paper analyzes a real residential 100 square meters house, where energy efficiency measures and RES technologies have been applied, sizing a hydrogen system (electrolyzer, metal hydrides and fuel cell) for power backup, taking into consideration its dynamic behavior, experimentally determined. The technologies used are already available in the market and, except hydrogen technologies, sufficiently mature. Through energy efficiency technologies (insulation, absorbers, etc), the maximum electrical and thermal power needed decreases from 4.4 kW e to 1.7 kW e (annual consumption from 5000 kWh to 1200 kWh) and from 5.2 kW t to 1.6 kW t (annual consumption from 14,600 kWh to 4500 kWh) respectively. With these reduced values it has been possible to supply the consumptions entirely by small photovoltaic and solar thermal plants (less than 10 m2 each). The hydrogen backup even if remains the most expensive (versus traditional batteries and gasoline generator), satisfying all the electric needs for one day, increases the security and allows net metering. Moreover the low-pressure hydrogen storage system through metal hydrides guarantees system safety too. Finally the system modularity can also satisfy higher energy production. [Copyright &y& Elsevier]

Abstract: This paper concerns the impacts of the meteorological data, the choice of the load profile, and the time simulation (1–11 years) on the energy flows and on the H2/O2/H2O storage sizing in a photovoltaic/fuel cell/electrolyzer hybrid system (PEPITE project). The simulations were computed with the ORIENTE software. 4 load profiles have been investigated (3 diurnal and one nocturnal) with an identical daily consumption (26 kWh). According to load profiles, the gap observed between the most favorable and the most disadvantageous years induces H2 storage variations rates between 45.5% and 55.3%. Furthermore, if we compare the most penalizing meteorological year with the sizing when we simulate several successive years, we also obtain variation rates (ration between the standard deviation and the corresponding averaged value) ranges from 24.4 to 37.9% for the 3 diurnal profiles. The nocturnal profile presents specific results because it is unsustainable. The main conclusion of this work is the great importance to consider several consecutive years of tilted irradiation data, 7 in our case, to size the H2/O2/H2O storages. [ABSTRACT FROM AUTHOR]

Abstract: PEPITE is a project funded by the French ANR PAN-H research program. This project concerns, among various other tasks, a demonstration of a weather station electricity supply with help of a PV/FC/EL hybrid system located at the CEA center of Cadarache (France). To design a relevant sizing for this demonstration system, a complete sizing tool has been developed via a new numerical optimizing code named ORIENTE. It uses Matlab software based on sequential running time. The demonstration system will be composed of a PV array, a PEM fuel cell system and a PEM electrolyzer, batteries, storage tanks for H2, O2 and H2O, as well as associated converters. This paper presents the obtained optimal sizing curves for the hybrid system (Ppv [kWp], [kg]) by taking into account the predefined constant load (6.5kW) functioning 24/24hours and the system energy balance for a loss-of-load probability LLP=0. These results give the sizes of each subsystem and will make possible to build the best energy flows control mode. [Copyright &y& Elsevier]

Abstract: Hydrogen as an energy currency, carrier and storage medium may be a key component of the solution to problems of global warming, poor air quality and dwindling reserves of liquid hydrocarbon fuels. Hydrogen is a flexible storage medium and can be generated by the electrolysis of water. It is particularly advantageous if an electrolyser may be simply and efficiently coupled to a source of renewable electrical energy. This paper examines direct coupling of a polymer electrolyte membrane (PEM) electrolyser to a matched solar photovoltaic (PV) source for hydrogen generation and storage. Such direct coupling with minimum interfacing electronics would lead to substantial cost reduction and thereby enhance the economic viability of solar-hydrogen systems. The electrolyser is designed for fail-safe operation with multiple levels of safety and operational redundancy. A control system in the electrolyser unit provides for disconnection when required and for auto-start in the morning and auto shut-down at night, simultaneously addressing the goals of minimum energy loss and maximum safety. The PV system is a 2.4kW array (20.4m2 total area) comprising 30, 12V, 80W, Solarex polycrystalline modules in a series–parallel configuration. The integrated system has been operated for approximately 60 days over a 4-month period from September 2007 to January 2008 with many periods of unattended operation for multiple days, experiencing weather ranging from hot and sunny (above 40°C) to cool and cloudy. The principle and practicality of direct coupling of a suitably matched PV array and PEM electrolyser have been successfully demonstrated. Details of electrolyser operation coupled to a PV array along with modelling work to match current–voltage characteristics of the electrolyser and PV system are described. [Copyright &y& Elsevier]

Abstract: Many island power systems are powered by diesel generators or long underwater cables, which result in greater operating costs or losses than stand-alone systems. It is therefore desirable to integrate renewable energy (RE) sources into these mini grids. The main objective of the paper is to describe, analyse and present a more unified approach for assessing the technical feasibility/potential of different energy scenarios for the islands of Malta. In this study, three different scenarios are analysed. Integrating RE sources (RES) in energy systems reduces losses, cuts fossil fuel consumption whilst maintaining system stability and increasing job opportunities. Hydrogen conversion and storage methods are also analysed as a method for greenhouse gas (GHG) reduction in the transport sector and as a way to reduce excess electricity produced from RE. [Copyright &y& Elsevier]

Abstract: While the world energy demand is steadily growing, the concern for the environmental aspects of energy use and natural resource exploitation has increased. A new market has emerged for renewable energy, often referred to as “green energy”. This paper presents an optimization model developed as part of a feasibility study on the idea of exporting renewable energy in the form of hydrogen, from Iceland to the continent of Europe. The goal is to find the most economical ways of producing hydrogen solely via electrolysis from water, using electricity from hydro and geothermal power. The mixed integer programming model presented here facilitates the search for optimal choices from the 23 potential power plants, 11 of which are based on geothermal sources, and 12 are hydropower stations. The best locations for hydrogen production are in the southwest region of Iceland and the least expensive hydrogen production is at energy demand between 2 and 4TWh/yr. At lower demand, the cost of energy is relatively higher, due to inefficient use of power plants and transfer lines. At higher demand, the cost of constructing new power transfer lines increases, leading to higher overall energy costs. [Copyright &y& Elsevier]

Abstract: This paper examines a comparative assessment in terms of CO2 emissions from a hydrogen passenger train in Ontario, Canada, particularly comparing four specific propulsion technologies: (1) conventional diesel internal combustion engine (ICE), (2) electrified train, (3) hydrogen ICE, and (4) hydrogen PEM fuel cell (PEMFC) train. For the electrified train, greenhouse gases from electricity generation by natural gas and coal-burning power plants are taken into consideration. Several hydrogen production methods are also considered in this analysis, i.e., (1) steam methane reforming (SMR), (2) thermochemical copper–chlorine (Cu–Cl) cycle supplied partly by waste heat from a nuclear plant, (3) renewable energies (solar and wind power) and (4) a combined renewable energy and copper–chlorine cycle. The results show that a PEMFC powertrain fueled by hydrogen produced from combined wind energy and a copper–chlorine plant is the most environmentally friendly method, with CO2 emissions of about 9% of a conventional diesel train or electrified train that uses a coal-burning power plant to generate electricity. Hydrogen produced with a thermochemical cycle is a promising alternative to further reduce the greenhouse gas emissions. By replacing a conventional diesel train with hydrogen ICE or PEMFC trains fueled by Cu-Cl based-hydrogen, the annual CO2 emissions are reduced by 2260 and 3318 tonnes, respectively. A comparison with different types of automobile commuting scenarios to carry an equivalent number of people as a train is also conducted. On an average basis, only an electric car using renewable energy-based electricity that carries more than three people may be competitive with hydrogen trains. [Copyright &y& Elsevier]

Abstract: A stand-alone renewable-energy system employing a hydrogen-based energy store is now being commissioned within the HaRI project at West Beacon Farm, Leicestershire, UK. The interconnection of the various generators, loads and storage system is made through a central DC busbar: an arrangement that is believed to be unique within systems of this type and scale. The rotating generators, such as the wind turbines, are connected through standard industrial drives operating in regenerative mode, while the DC devices—electrolyser, fuel cell and solar photovoltaic array—employ custom DC–DC converters. This paper reviews the design philosophy of the electrical system and the various converters required. Modelling and simulation of the system is discussed along with practical lessons learnt from its implementation and some initial results are presented. [Copyright &y& Elsevier]

Abstract: Hong Kong is highly vulnerable to energy and economic security due to the heavy dependence on imported fossil fuels. The combustion of fossil fuels also causes serious environmental pollution. Therefore, it is important to explore the opportunities for clean renewable energy for long-term energy supply. Hong Kong has the potential to develop clean renewable hydrogen energy to improve the environmental performance. This paper reviews the recent development of hydrogen production technologies, followed by an overview of the renewable energy sources and a discussion about potential applications for renewable hydrogen production in Hong Kong. The results show that although renewable energy resources cannot entirely satisfy the energy demand in Hong Kong, solar energy, wind power, and biomass are available renewable sources for significant hydrogen production. A system consisting of wind turbines and photovoltaic (PV) panels coupled with electrolyzers is a promising design to produce hydrogen. Biomass, especially organic waste, offers an economical, environmental-friendly way for renewable hydrogen production. The achievable hydrogen energy output would be as much as 40% of the total energy consumption in transportation. [Copyright &y& Elsevier]