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When comparing the life-cycle environmental performance of hydrogen energy systems, significant concerns arise due to potential methodological inconsistencies between case studies. In this regard, protocols for harmonised life cycle assessment (LCA) of hydrogen energy systems are currently available to mitigate these concerns. These protocols have already been applied to conventional hydrogen from steam methane reforming as well as to a large number of both fossil and renewable hydrogen options, allowing robust comparisons between them. However, harmonised life-cycle indicators of nuclear-based hydrogen options are not yet available in the literature. This study fills this gap by using the recently developed software GreenH 2 armony® to calculate the harmonised carbon, energy and acidification footprints of nuclear-based hydrogen produced through different pathways (viz., low-temperature electrolysis, high-temperature electrolysis, and thermochemical cycles). Overall, the harmonised case studies of nuclear-based hydrogen show a generally good performance in terms of carbon footprint and acidification, but an unfavourable performance in terms of non-renewable energy footprint. • Library of harmonised life-cycle indicators of hydrogen extended to nuclear options. • Nuclear and renewable hydrogen generally show a low harmonised carbon footprint. • Nuclear hydrogen generally shows a low harmonised acidification impact. • Nuclear and fossil hydrogen show an unfavourable non-renewable energy footprint. [ABSTRACT FROM AUTHOR]

Life cycle assessment (LCA) is a well-established methodology for the evaluation of the environmental performance of product systems. However, a large number of combinations of methodological choices is possible in LCA studies, threatening consistency when comparing different authors' studies. Regarding hydrogen, a specific LCA harmonisation initiative has recently been undertaken. Within the framework of this initiative, harmonisation protocols and libraries of life-cycle indicators of hydrogen have been developed in order to improve the robustness of comparative LCAs. Nevertheless, these libraries are currently affected by the lack of fossil-based hydrogen options. Hence, this study fills this gap by calculating harmonised carbon and energy footprints of hydrogen for a set of 15 new case studies involving relevant production pathways: gasification, reforming and autocatalytic decomposition of fossil feedstock, and electrolysis powered by fossil and grid electricity. Overall, the resulting extended library of harmonised life-cycle indicators stresses the role of renewable hydrogen as a key requirement in the path towards an environmentally-sustainable hydrogen economy. • Current library of harmonised life-cycle indicators of hydrogen extended to fossil options. • Fossil hydrogen generally linked to high harmonised carbon and energy footprints. • Especially unfavourable performance when compared to renewable hydrogen options. • Key role of renewable hydrogen as a requirement for a sustainable hydrogen economy. [ABSTRACT FROM AUTHOR]

This work uses harmonised life-cycle indicators of hydrogen to explore its role in the environmental performance of proton exchange membrane fuel cell (PEMFC) passenger vehicles. To that end, three hydrogen fuel options were considered: (i) conventional, fossil-based hydrogen from steam methane reforming; (ii) renewable hydrogen from biomass gasification; and (iii) renewable hydrogen from wind power electrolysis. In order to increase the robustness of the life-cycle study, the environmental profile of each hydrogen option was characterised by three harmonised indicators: carbon footprint, non-renewable energy footprint, and acidification footprint. When enlarging the scope of the assessment according to a well-to-wheels perspective, the results show that the choice of hydrogen fuel significantly affects the life-cycle performance of PEMFC vehicles. In this regard, the use of renewable hydrogen –instead of conventional hydrogen from steam methane reforming– is essential when pursuing low carbon and energy footprints. Nevertheless, the identification of the most favourable renewable hydrogen option was found to be conditioned by the prioritised life-cycle indicators. • Well-to-wheels assessment of PEMFC passenger vehicles with three hydrogen options. • Use of harmonised carbon, energy and acidification footprints of hydrogen. • High influence of the hydrogen fuel on the life-cycle performance of PEMFC vehicles. • Need for renewable hydrogen when pursuing low carbon and energy footprints. • Preferred renewable hydrogen option conditioned by the prioritised indicators. [ABSTRACT FROM AUTHOR]

The environmental sustainability of hydrogen energy systems is often evaluated through Life Cycle Assessment (LCA). In particular, environmental suitability is usually determined by comparing the life-cycle indicators calculated for a specific hydrogen energy system with those of a reference system (e.g., conventional hydrogen from steam methane reforming, SMR-H 2). In this respect, harmonisation protocols for comparative LCA of hydrogen energy systems have recently been developed in order to avoid misleading conclusions in terms of carbon footprints and cumulative energy demand. This article expands the scope of these harmonisation initiatives by addressing a new life-cycle indicator: acidification. A robust protocol for harmonising the acidification potential of hydrogen energy systems is developed and applied to both SMR-H 2 and a sample of case studies of renewable hydrogen. According to the results, unlike other energy systems, there is no correlation between acidification and carbon footprint in the case of hydrogen energy systems, which prevents the estimation of harmonised acidification results from available harmonised carbon footprints. Nevertheless, an initial library of harmonised life-cycle indicators of renewable hydrogen is now made available. • Harmonised carbon footprint, cumulative energy demand and acidification of hydrogen. • Library of harmonised results for steam-methane-reforming and renewable hydrogen. • Protocol for the harmonisation of the life-cycle acidification impact of hydrogen. • No correlation between carbon footprint and life-cycle acidification impact. • Identification and mitigation of misinterpretation concerns in comparative studies. [ABSTRACT FROM AUTHOR]

A significant number of case studies evaluating hydrogen through the Life Cycle Assessment (LCA) methodology are available in the scientific literature. However, inconsistencies in their methodological frameworks lead to potential misinterpretation concerns when it comes to comparing LCA results. In order to mitigate this risk, harmonisation protocols for life-cycle indicators arise as helpful tools. In this regard, a harmonisation protocol for the life-cycle global warming impact (GWP) of hydrogen has been recently developed. Taking this protocol as a starting point, this article expands the list of harmonised sustainability indicators of hydrogen by formulating a new protocol for the cumulative non-renewable energy demand (CED nr ) indicator. Furthermore, the protocol is applied to a sample of case studies of renewable hydrogen (harmonised CED nr ranging from 3 to 184 MJ kg −1 H 2 ) as well as to a reference case study of conventional hydrogen produced via steam methane reforming (harmonised CED nr of 201 MJ kg −1 H 2 ). The resultant library of harmonised CED nr consistently complements that of harmonised carbon footprints of hydrogen, showing a high correlation between GWP and CED nr (R 2 = 0.91). Overall, LCA harmonisation initiatives are found to mitigate misinterpretation concerns when comparing and ranking hydrogen energy systems both within the same technological category and between different technological categories (thermochemical, electrochemical, and biological). [ABSTRACT FROM AUTHOR]

An increasing number of studies addressing the Life Cycle Assessment (LCA) of hydrogen energy systems is found in the scientific literature. Most of these studies are comparative and show significant differences in terms of methodological choices. These differences significantly affect the results of the LCA studies and hamper their robust interpretation, especially when comparing results from different studies. Hence, harmonisation of the results under a consistent methodological framework is needed. This article defines a protocol for the harmonisation of the life-cycle global warming impact of hydrogen. Furthermore, the protocol is applied to renewable hydrogen based on a thorough literature survey of relevant LCA case studies classified by hydrogen-production technological category: thermochemical, electrochemical, and biological. In this sense, the two main outcomes of the study are the harmonisation protocol and the initial library of harmonised carbon footprints of renewable hydrogen for 71 case studies. Key methodological choices subject to harmonisation include (i) attributional approach, (ii) functional unit, (iii) system boundaries, and (iv) multifunctionality approach. Harmonisation is found to affect more significantly the thermochemical and biological categories than the electrochemical one. Nevertheless, risk of misinterpretation is found and exemplified in every technological category. The sources of potential misinterpretation are found to be usually linked to inconsistencies in terms of system boundaries (e.g., hydrogen compression) and, when applicable, multifunctionality approaches. Future LCA practitioners are highly recommended to use the proposed protocol to provide, along with their own results, the harmonised global warming impact of hydrogen in order to enhance current and future result interpretation when comparisons are made. [ABSTRACT FROM AUTHOR]

Purpose: As a first step towards a consistent framework for both individual and comparative life cycle assessment (LCA) of hydrogen energy systems, this work performs a thorough literature review on the methodological choices made in LCA studies of these energy systems. Choices affecting the LCA stages 'goal and scope definition', 'life cycle inventory analysis' (LCI) and 'life cycle impact assessment' (LCIA) are targeted. Methods: This review considers 97 scientific papers published until December 2015, in which 509 original case studies of hydrogen energy systems are found. Based on the hydrogen production process, these case studies are classified into three technological categories: thermochemical, electrochemical and biological. A subdivision based on the scope of the studies is also applied, thus distinguishing case studies addressing hydrogen production only, hydrogen production and use in mobility and hydrogen production and use for power generation. Results and discussion: Most of the hydrogen energy systems apply cradle/gate-to-gate boundaries, while cradle/gate-to-grave boundaries are found mainly for hydrogen use in mobility. The functional unit is usually mass- or energy-based for cradle/gate-to-gate studies and travelled distance for cradle/gate-to-grave studies. Multifunctionality is addressed mainly through system expansion and, to a lesser extent, physical allocation. Regarding LCI, scientific literature and life cycle databases are the main data sources for both background and foreground processes. Regarding LCIA, the most common impact categories evaluated are global warming and energy consumption through the IPCC and VDI methods, respectively. The remaining indicators are often evaluated using the CML family methods. The level of agreement of these trends with the available FC-HyGuide guidelines for LCA of hydrogen energy systems depends on the specific methodological aspect considered. Conclusions: This review on LCA of hydrogen energy systems succeeded in finding relevant trends in methodological choices, especially regarding the frequent use of system expansion and secondary data under production-oriented attributional approaches. These trends are expected to facilitate methodological decision making in future LCA studies of hydrogen energy systems. Furthermore, this review may provide a basis for the definition of a methodological framework to harmonise the LCA results of hydrogen available so far in the literature. [ABSTRACT FROM AUTHOR]

The suitability of hydrogen as an energy management solution in a run-of-river hydropower plant in Central Italy is evaluated from a life-cycle perspective. Hydrogen production at off-peak hours via electrolysis is considered, as well as potential hydrogen storage in metal hydrides followed by hydrogen use at peak hours for power generation using fuel cell technology. Hydropower generation and hydrogen production are identified as the subsystems contributing most to the nine evaluated impact categories (e.g., global warming, abiotic depletion and cumulative energy demand). The renewable hydrogen produced shows a more favourable life-cycle environmental and energy performance than conventional hydrogen generated via steam methane reforming. Furthermore, when enlarging the system with hydrogen use for power generation, the renewable electricity product shows a better life-cycle profile than conventional electricity for the Italian electrical grid. Overall, under life-cycle aspects, hydrogen is found to be a suitable energy solution in hydropower plants both as a hydrogen product itself (e.g., for transportation) and as a feedstock for subsequent power generation at peak hours. [ABSTRACT FROM AUTHOR]

Hydrogen is currently being promoted because of its advantages as an energy vector, its potential to decarbonise the economy, and strategical implications in terms of energy security. Hydrogen from high-temperature electrolysis coupled with concentrated solar power (CSP) is especially interesting since it enhances the last two aspects and could benefit from significant technological progress in the coming years. However, there is a lack of studies assessing its future environmental performance. This work fills this gap by carrying out a prospective life cycle assessment based on the expected values of key performance parameters in 2030. The results show that parabolic trough CSP coupled with a solid oxide electrolyser is a promising solution under environmental aspects. It leads to a prospective hydrogen carbon footprint (1.85 kg CO 2 eq/kg H 2) which could be classified as low-carbon according to current standards. The benchmarking study for the year 2030 shows that the assessed system significantly decreases the hydrogen carbon footprint compared to future hydrogen from steam methane reforming (81% reduction) and grid electrolysis (51%), even under a considerable penetration of renewable energy sources. • Life-cycle profile of renewable hydrogen from solid oxide electrolysis in 2030 is assessed. • A simulation model with concentrated solar power integration is built for data supply. • Prospective carbon footprint shows that hydrogen from this system qualifies as green. • In solar-only mode, solar infrastructure becomes an environmental hotspot. • Solar plant scale arises as a key factor affecting the life-cycle profile of hydrogen. [ABSTRACT FROM AUTHOR]

The Life Cycle Assessment (LCA) methodology is often used to check the environmental suitability of hydrogen energy systems, usually involving comparative studies. However, these comparative studies are typically affected by inconsistent methodological choices between the case studies under comparison. In this regard, protocols for the harmonisation of methodological choices in LCA of hydrogen are available. The step-by-step application of these protocols to a large number of case studies has already resulted in libraries of harmonised carbon, energy, and acidification footprints of hydrogen. In order to foster the applicability of these harmonisation protocols, a web-based software for the calculation of harmonised life-cycle indicators of hydrogen has recently been developed. This work addresses—for the first time—the validation of such a tool by checking the deviation between the available libraries of harmonised carbon, energy, and acidification footprints of hydrogen and the corresponding tool-based harmonised results. A high correlation (R2 > 0.999) was found between the library- and tool-based harmonised life-cycle indicators of hydrogen, thereby successfully validating the software. Hence, this tool has the potential to effectively promote the use of harmonised life-cycle indicators for robust comparative LCA studies of hydrogen energy systems, significantly mitigating misinterpretation. [ABSTRACT FROM AUTHOR]

The high expectations placed on hydrogen as a clean fuel have led to a growing amount of life-cycle assessment (LCA) studies of hydrogen-related systems. The multiple methodological choices and diverse technical characteristics contribute to a broad set of practices, resulting in significant variability even among similar systems. This study sets the basis for the development of harmonised guidelines for LCA of fuel cells and hydrogen (FCH) systems by analysing current LCA practices. The reviewed literature suggests that previous efforts on harmonisation of LCA methodological choices have led to common practices for certain choices, e.g. functional unit. However, an incomplete definition of some parameters hinders the interpretability of LCA results and hides the potential sources of variability in terms of LCA estimates. In this work, in addition to a systematic literature review of LCA of FCH systems to identify current practices and gaps, sources of variability were investigated for the life-cycle greenhouse gas emissions of hydrogen production systems through a meta-regression analysis (MRA). The MRA results show that the variability of LCA estimates in the literature can be explained by a limited set of qualitative (e.g. implementation of CO 2 capture, among other technological choices) and quantitative (e.g. electricity consumption for hydrogen processing) variables. Although a certain progress towards common methodological choices in LCA of FCH systems was identified, further work is still needed to harmonise practices, as well as to extend the application of the proposed MRA approach to other life-cycle indicators for both identification of main drivers and harmonisation of LCA impact scores. • 100 LCA studies of hydrogen systems are systematically reviewed. • Key and emerging LCA aspects and choices are identified and analysed. • A meta-regression model is built for the carbon footprint of produced hydrogen. • Determinants of produced hydrogen CO 2 eq emissions are analysed. • A set of variables is proposed to explain the variability of CO 2 eq emissions. [ABSTRACT FROM AUTHOR]

In order to achieve gradual but timely decarbonisation of the transport sector, it is essential to evaluate which types of vehicles provide a suitable environmental performance while allowing the use of hydrogen as a fuel. This work compares the environmental life-cycle performance of three different passenger cars fuelled by hydrogen: a fuel cell electric vehicle, an internal combustion engine car, and a hybrid electric vehicle. Besides, two vehicles that use hydrogen in a mixture with natural gas or gasoline were considered. In all cases, hydrogen produced by wind power electrolysis was assumed. The resultant life-cycle profiles were benchmarked against those of a compressed natural gas car and a hybrid electric vehicle fed with natural gas. Vehicle infrastructure was identified as the main source of environmental burdens. Nevertheless, the three pure hydrogen vehicles were all found to be excellent decarbonisation solutions, whereas vehicles that use hydrogen mixed with natural gas or gasoline represent good opportunities to encourage the use of hydrogen in the short term while reducing emissions compared to ordinary vehicles. • Environmental performance comparison between different hydrogen-powered vehicles. • Comparison between fuel cell and hydrogen internal combustion engine vehicles. • Life cycle assessment of hybrid electric vehicles fed with hydrogen. • Natural gas-hydrogen and gasoline-hydrogen vehicles are assessed. • Vehicles fuelled with renewable hydrogen are excellent decarbonisation solutions. [ABSTRACT FROM AUTHOR]

Worldwide, the road transport sector typically arises as one of the main sources of air pollutants due to its high energy intensity and the use of fossil fuels. Thus, governments and social agents work on the development and prospective planning of decarbonisation strategies oriented towards sustainable transport. In this regard, the increase in the use of alternative fuels is the recurrent approach to energy planning, e.g. through the promotion of electric vehicles, biofuels, natural gas, liquefied petroleum gas, etc. However, there is a lack of comprehensive information on the techno-economic performance of production pathways for alternative fuels. The acquisition of robust techno-economic data is still a challenge for energy planners, modellers, analysts and policy-makers when building their prospective models to support decision-making processes. Hence, this article aims to fill this gap through a deep literature review including the most representative production routes for a wide range of road transportation fuels. This led to the development of datasets including investment costs, operating and maintenance costs, and transformation efficiencies for more than 40 production pathways. The techno-economic data presented in this work are expected to be especially useful to those energy actors interested in performing long-term studies on the transition to a sustainable transport system. • Comprehensive literature review of alternative fuels for road transport. • LPG, natural gas, biofuels, electricity and hydrogen as alternative fuels. • Techno-economic data of conventional and alternative fuel production pathways. • Efficiency and investment and operating costs for more than 40 production pathways. • Intended use of the techno-economic database for energy systems modelling. [ABSTRACT FROM AUTHOR]

• National energy systems model on the production of alternative fuels for road transport. • Second-generation biofuels would play a key role in satisfying the biofuel demand. • Electric vehicles would mainly involve renewable power generation. • Clean hydrogen for transport would be produced via electrolysis. • Alternative fuel implementation highly contributes to decarbonising road transport. Road transport is one of the main sources of greenhouse gas emissions due to the current dependence on fossil fuels such as diesel and gasoline. This situation needs to be changed through the retirement of fossil fuels and the implementation of alternative fuels and vehicles such as biofuels, battery electric vehicles, and fuel cell electric vehicles fuelled by hydrogen. Nevertheless, the environmental suitability of alternative fuels is conditioned by how they are produced. Through the case study of Spain, this article prospectively assesses – from a techno-economic and carbon footprint perspective– the production technology mix of alternative fuels from 2020 to 2050. The proposed energy systems optimisation model includes a large number of production technologies regarding biofuels (bioethanol, biodiesel, synthetic diesel/gasoline, and hydrotreated vegetable oil), electricity, and hydrogen. The combined study of these fuels provides a relevant framework to discuss the targets established for the road transport sector with a high level of detail not only regarding fuel type but also technology breakdown. The results show the relevance of second-generation biofuel production technologies in fulfilling the future biofuel demand. Regarding the extra electricity demand associated with the penetration of electric vehicles, the results suggest a key role of wind- and solar-based technologies in meeting such a need. Concerning hydrogen as an option to decarbonise the transport system, even though steam methane reforming is the most mature and cost-competitive production technology, hydrogen production would be satisfied through electrolysis in order to avoid relying on fossil resources as the main feedstock. Overall, this integrated approach to the long-term production technology mix of alternative fuels for road transport is expected to be relevant to a wide range of decision-makers willing to prospectively assess road transport systems from a technology perspective. [ABSTRACT FROM AUTHOR]

Hydrogen can serve multiple purposes within the energy system, from flexibility provider, to decarbonizing hard-to-abate sectors, to chemical feedstock. A range of model paradigms have been developed to assess the potential for hydrogen energy systems while accounting for the unique characteristics of hydrogen. This study proposes a taxonomy to classify models of hydrogen energy systems. The taxonomy is based on a review of 29 studies that proposed a taxonomy for energy models in general. This review identified 124 categories that are commonly used to map models, which were grouped into six major categories. This general taxonomy was then adapted to hydrogen, leaving only 32 categories in four major categories. Nine hydrogen archetypes that cover the entire spectrum of studies of hydrogen energy systems were identified. Each of these archetypes was mapped against the categories defined which allowed identifying common gaps across archetypes and degree of interrelationship between them. The environmental and high spatial resolution aspects are only covered by one archetype. The correlation between archetypes assessed in this study can be used to identify opportunities for soft-linking. All the archetypes provide partial answers and using a modeling suite composed of various models could address shortcomings of individual archetypes. All models have a strong focus on technology and costs, with other aspects such as the innovation cycle, market design and policy levers to promote deployment receiving little focus. Capturing these dynamics in the hydrogen archetypes would enable a more holistic analysis and would also facilitate subsequent action. • A taxonomy to classify hydrogen models is proposed based on a review of 29 studies. • Nine hydrogen archetypes covering the entire range of studies are defined. • Each archetype is characterized using the hydrogen taxonomy. • Challenges for each archetype are discussed together with potential solutions. [ABSTRACT FROM AUTHOR]

• Techno-economic and environmental optimisation of the hydrogen production mix in Spain. • Analysis of scenarios using energy systems modelling and carbon footprint restrictions. • Steam reforming of natural gas as the main production technology in the short term. • Key role of water electrolysis and biomass gasification in the medium-to-long term. • Savings >50 Mt CO 2 eq in 2050 for the scenarios with carbon footprint restrictions. Fuel cell electric vehicles arise as an alternative to conventional vehicles in the road transport sector. They could contribute to decarbonising the transport system because they have no direct CO 2 emissions during the use phase. In fact, the life-cycle environmental performance of hydrogen as a transportation fuel focuses on its production. In this sense, through the case study of Spain, this article prospectively assesses the techno-economic and environmental performance of a national hydrogen production mix by following a methodological framework based on energy systems modelling enriched with endogenous carbon footprint indicators. Taking into account the need for a hydrogen economy based on clean options, alternative scenarios characterised by carbon footprint restrictions with respect to a fossil-based scenario dominated by steam methane reforming are evaluated. In these scenarios, the steam reforming of natural gas still arises as the key hydrogen production technology in the short term, whereas water electrolysis is the main technology in the medium and long term. Furthermore, in scenarios with very restrictive carbon footprint limits, biomass gasification also appears as a key hydrogen production technology in the long term. In the alternative scenarios assessed, the functional substitution of hydrogen for conventional fossil fuels in the road transport sector could lead to high greenhouse gas emission savings, ranging from 36 to 58 Mt CO 2 eq in 2050. Overall, these findings and the model structure and characterisation developed for the assessment of hydrogen energy scenarios are expected to be relevant not only to the specific case study of Spain but also to analysts and decision-makers in a large number of countries facing similar concerns. [ABSTRACT FROM AUTHOR]