Is Green Hydrogen an Environmentally and Socially Sound Solution for Decarbonizing Energy Systems Within a Circular Economy Transition?

Abstract

Green hydrogen (GH₂) is expected to play an important role in future energy systems in their fight against climate change. This study, after briefly recalling how GH₂ is produced and the main steps throughout its life cycle, analyses its current development, environmental and social impacts, and a series of case studies from selected literature showing its main applications as fuel in transportation and electricity sectors, as a heat producer in high energy intensive industries and residential and commercial buildings, and as an industrial feedstock for the production of other chemical products. The results show that the use of GH₂ in the three main areas of application has the potential of contributing to the decarbonization goals, although its generation of non-negligible impacts in other environmental categories requires attention. However, the integration of circular economy (CE) principles is important for the mitigation of these impacts. In social terms, the complexity of the value chain of GH₂ generates social impacts well beyond countries where GH₂ is produced and used. This aspect makes the GH₂ value chain complex and difficult to trace, somewhat undermining its renewability claims as well as its expected localness that the CE model is centred around.

1. Introduction

Hydrogen as an energy carrier has attracted the interest of scientists since the last century, particularly from 1970 onwards; this interest is driven by the worsening of environmental problems and concerns related to the reduced availability of fossil fuels [1,2,3,4,5]. More recently, the interest of research on particular subfields of hydrogen research, such as its production, has grown significantly [6]. Similarly, research in green hydrogen (hereafter referred to as GH₂) [7] has seen a particular increase over the last two years [8]. GH₂ is expected to play an important role in future decarbonizations scenarios [9,10,11] towards more sustainable energy systems mainly based on renewable sources [12]. In view of this, GH₂ produced by means of renewable electricity water electrolysis strengthens the role of renewables [13] and may become a necessary complement to meet both sustainability and energy security goals in national energy mixes [7], contributing to reducing the impacts of fossil electricity and transport sectors [13].

The transition to renewables is a necessary energetic choice to face the worsening of climate change [14] and, due to their abundance, to satisfy the global energy demand [15,16]. However, daily and seasonal variations limit the capacity of renewables to fully replace fossil electricity. Therefore, solutions to meet the daily and seasonal storage of electricity at global and local scales are urgently required [16] to speed the transition towards renewables [17]. Therefore, the role of GH₂ as an energy carrier capable of being stored in normal tanks becomes crucial compared to lithium–ion batteries [18]. The impacts of the latter are increasingly raising concerns and currently can only be partially mitigated by solutions integrating Circular Economy (CE) principles [19] and the consideration of social and environmental justice dimensions in policies or industrial strategies [20].

Aside from hydro, wind, and solar PV, GH₂ can be produced from other renewable feedstocks including biomasses not in competition with food production, such as household food, crop residues, livestock manure, and aquatic biomass [6]. With that, GH₂ production fully meets the principles of a CE [21].

The implementation of a future GH₂ economy faces several challenges due to the current higher production costs of GH₂ [10], the need to improve the efficiency and maturity of electrolyzers, and the investments needed for storage and transportation [6,22]. There are also uncertainties concerning the environmental impacts of decommissioning electrolyzers and some renewable energy technologies [23], as well as the contribution of GH₂ to the mitigation of other impact categories beyond GWP, such as abiotic resource depletion [24]. For these reasons, it is important to strengthen the research towards improving its economic competitiveness and environmental soundness [22,25]. According to Bloomberg forecasts, GH₂ should be able to compete with grey and blue hydrogen in Brazil, China, India, and some EU countries before the year 2050, depending on the scale up of more efficient electrolyzers. In the year 2023, the forecasts have been updated, limiting the 2050 competitiveness to only grey H₂ in China and India [24].

Recent literature [23,24,25,26,27,28], listed and analysed in Appendix A,

Table A1. Previous literature reviews resulting from the search of the literature according to the procedure explained in Section 3 (Materials and Methods).

Title of the Study	Goals/Main Focus	Primary Findings	Timeframe of the Selected Literature
Lagioia et al. [10]	This narrative literature review focused on the analysis of production technologies of blue and green hydrogen, as well as their management and applications in view of the hydrogen goals of the EU.	Green hydrogen is the only type that could play a role in future decarbonisation scenarios. For this to happen, blue hydrogen could pave the way for GH2, but there are uncertainties related to the development of CO2 carbon capture. GH2 produced by electrolysis is a mature technology. However, GH2 is also constrained by the availability of a surplus in the demand of electricity from renewables. The supply chain of GH2 should also be strengthened along with the use of certification schemes for CO2 emissions. In order to meet the future targets of the EU for hydrogen, the authors suggested the acceleration of investments in hydrogen innovation and its use in hard-to-abate sectors rather than e.g., in light-duty transport where hydrogen use is considered not efficient.	Not specified
Guareiro et al. [11]	Overview of several aspects associated with GH2, including the sources for its production, regulation, typologies of storage, transportation, and final uses. Critical analysis of the economic and environmental impacts, as well as the main challenges and opportunities it could have for chemistry.	In terms of the environmental impacts of GH2 production, the study shed light on the water required in the process (9 kg per kg of GH2). The water required for production of grey and blue hydrogen is half of that needed for GH2 production. The latter process is also much more energy-intensive and its production is currently not financially competitive. However, the authors, by reviewing the literature, also reported the results of studies performed in Brazil where the production of GH2, by using electricity from hydro and wind, achieved production costs comparable to that of grey hydrogen. The study also underlined the need for increasing the capacity of electrolysers for the development of a future hydrogen economy.	Not specified
Arsalis et al. [18]	Critical comparison of several characteristics (serice life, costs, recyclability, environmental impacts, safety issues, use and integration within energy systems) of two solar-powered energy systems: Lithium–Ion Batteries (PV-LIB) and Regenerative Hydrogen Fuel Cell (RHFC) energy systems.	The comparative analysis shows that, for example, hydrogen (within RHFC subsystems) produced through water electrolysis can be stored in high quantities in hydrogen storage units. The RHFC is then more suitable for long-term storage than short-term storage, while LIBs are more suitable for short-term storage. The refueling of RHFC subsystems is fast, requiring only a few minutes, while the recharging of LIBs is slow and needs several hours. In terms of costs, those related to LIBs are much decreased within the last decade while in the case of RHFC, the high costs of the electrolysers and fuel cell stacks limits their larger development.	Not specified
Sudalaimuthu and Sathyamurthy [21]	Overview of agro-waste for the production of GH2 and focusing on the thermochemical method of production.	The review highlighted several key findings such as, among others, the high energy content of hydrogen from agro-waste by gasification process. The H/C ratio is high, supporting the use of agro-waste instead of fossil fuels for hydrogen production. Thermochemical process resulted in a viable option among the analysed processes for converting agro-waste to hydrogen. Cellulose and lignin, as constituents of agro-waste, contributed to deciding the reaction temperature of gasification and the reaction temperature directly related to energy efficiency, process design, and technological and economic feasibility.	Not specified
Mokrzycki and Gawlik, [22]	Review of various aspects of the green hydrogen economy, including its advantages and disadvantages, risks, environmental impacts, and future water availability for hydrogen production.	Very strict relation between renewables and GH2 development. Costs, innovation in both technologies, GH2 storage and investments in transport, as well as efficiency improvements are key factors driving a faster GH2 development. A future acceleration to the green hydrogen economy will ultimately depend on widespread support and worldwide development as well as the willingness of the countries to perceive the goal of a future green hydrogen economy.	Not specified
Sola et al. [23]	Overview of the state of the art of LCA research on GH2 in the last five years, taking into account GHG emissions and other environmental categories (such as water use, critical materials use, and land use) and issues related to the large-scale production of GH2.	Increasing trend of LCA research on GH2. EU studies accounts for half of the literature sample. GHs have to be produced from renewable electricity to be claimed as a low emissions energy carrier. Water consumption and land use (due to the use of renewable energies) are important hotspots that could limit GH2 development in particular areas with scarcity of water, such as Saudi Arabia and Oman, that have high abundance of sun but are scarce in freshwater Rare metals and critical raw materials for electrolysers production (particularly PEM), such as iridium and platinum, and solar cells production serve as further hotspots Uncertainties related to the end-of-life disposal of electrolysers.	2019–2024
Ajeeb et al. [25]	Reviewed the recent literature on GH2 production in LCA studies, taking into account many factors such as the electrolysers technologies, renewable sources for GH2 production, the life cycle inventories, the local scale of GH2 production, and storage and environmental impacts.	Wind and solar energy resulted in the most appropriate sources for the production of GH2, with wind reporting a lower contribution to GWP compared to solar energy. PEM electrolysers have a potential contribution to GW that is lower than other technologies such as ALEL and SOEL Improvement of the energy efficiency and environmental impacts of the water electrolyser system can be realised by means of different strategies, including waste treatment strategies, such as the use of oxygen in industrial processes or the reuse of materials of the electrolysers.	2016–2024
Sebbagh et al. [26]	Evaluation of a wide range of aspects concerning GH2 from its production by means of electrolysis process and PEM, AEL, and SOEC electrolysers, benefits and costs, applications, environmental and economic analysis, and policy measures.	LCA as a key tool for policy decision making, particularly when considering cradle to cradle or cradle to grave boundaries of analysis. ISO/TS 19870:2023: https://www.iso.org/standard/65628.html (accessed online 19 May 2025) standard specifies how to assess the GHG emissions associated with the life cycle of hydrogen. GH2 has advantages in terms of lower carbon footprint compared to the other hydrogen colours, but it is important to consider that the electrolysis process requires a great amount of electricity and water. Advancement in the process and more efficient electrolysers are needed. Emissions should be accounted in the whole life cycle, taking into account storage and transport of the hydrogen, while other impacts such as land use and habitat loss are due to the large-scale development of renewables. LCAs should be comprehensive and consider land-use change and biodiversity loss besides the contribution to GWP	2020–2023
Singh et al. [27]	Analysed the production of GH2 hydrogen from biogas/landfilling gas by means of conventional reforming processes, such as dry methane reforming, steam methane reforming, partial oxidation reforming, and autothermal reforming. The review also considered the contribution to GWP (CO2 eq·kg−1 H2) emissions, as well as the economic aspects of the processes and their efficiencies.	The results of the reviewed studies showed that carbon footprint of biomethane reforming was lower than fossil methane reforming. The carbon footprint of biomethane from steam reforming was 4.8 kg CO2 eq./kg of hydrogen versus 11.2 kg CO2 eq./kg of hydrogen produced from steam reforming of natural gas. In other studies, harmonised carbon footprint of GH2 from biogas reforming resulted in 7.34 kg CO2 eq./kg of hydrogen , and the carbon footprint of GH2 produced from water electrolysis and electricity sourced by wind, solar thermal, solar PV, and hydro was 5 kg CO2 eq./kg of GH2, while electricity from the grid was 32 kg CO2 eq./kg of GH2. Finally, the study assessed the production of hydrogen from agricultural residues such as cheese whey, sugar beet molasses, and wine vinasses with wastewater treatment plant sludge and found that GHG emissions are the lowest for hydrogen produced from sugar beet molasses (3.56 kg CO2 eq./kg of hydrogen) compared to the other two feedstocks . Further LCA studies are suggested to validate the results provided in the existing research.	2015–2024
Shaya and Glöser-Chahoud [28]	Analysis of strengths and weaknesses of water electrolysis technologies, such as PEM, AEM, AWE, and SOEC, as well as their environmental impacts by reviewing the LCA literature on impact categories: GWP, AP, and EP, as well as recent technological progresses.	From the review of LCA studies emerged a variability of impacts on GWP across the four technologies for hydrogen production and, in particular, for PEMWE where the impacts range from 0.5 kg CO2 eq/kg of GH2 to 30 kg CO2 eq/kg of G H2. The impacts of hydrogen production are mainly affected by the source of electricity used for the electrolysis process, the efficiency of the electrolyser, and the materials used for its manufacturing. The use of renewable electricity can reduce the contribution to GWP as well as the advancement in the materials of catalysts and membranes. The review also offers an interesting analysis of the advantages and disadvantages of each water electrolyser technology with the inclusion of critical raw materials, technological maturity, and operational lifetime, among others. In this regard, AEMWE is the only one out of the four analysed water electrolyser technologies that is cirtical raw materials-free.	Not specified
Wang et al. [29]	Analysis of the evolution and development of policies supporting GH2 policies in the United States, the European Union, Japan, and China, and technological progress of electrolysis process from renewables as well as of GH2 produced from solar PV and wind. The study also integrated the environmental, social, and economic benefits of the different hydrogen pathways.	The USA was the first to introduce policies supporting hydrogen development, but all the four investigated areas/countries can be considered early adopters of hydrogen policies worldwide. Moreover, they all have strategies and goals for incentivising GH2 adoption. The results from the reviewed studies confirm that GH2 from wind electricity generates the lowest contribution to GWP and AP and has low energy costs (785 g CO2 eq./kg H2 and 10.5 MJ/kg of H2), while hydrogen produced using wind and solar electrolysis have the highest economic costs . Regarding electrolyses technologies, AWE has advantages in terms of costs, maturity, and wide application, while PEM is adaptable to the variability of renewables but has high costs, limiting its wider development. SOEC and AEM are still in the research and demonstration phase and have not yet been commercialised.	Not specified
Aravindan and Kumar [30]	Overview of GH2 production from renewable sources (solar, geothermal, biomass, wind, and technologies (e.g., water splitting), thermolysis, electrolysis, and photolysis), production costs, environmental impacts, and challenges in GH2 development.	The results include the analysis of studies evaluating the contribution to GWP of hydrogen from solar, wind, biomass and geothermal sources, and available technologies. Overall, wind-based production of hydrogen resulted in the lowest contribution to GWP ranging, according to the selected studies, from the value of 600 g CO2 eq./kg of GH2 to 970 g CO2 eq./kg of GH2. Production costs of GH2 from biomass were the lowest (1–3 $/kg hydrogen) while that of solar had the highest (7–10 $/kg GH2). In contrast, the efficiency of solar and wind in GH2 production (70–80%) is the highest compared to biomass and geothermal (50–60%).	Not specified
Incer-Valverde et al. [31]	Review of the different hydrogen colors, their environmental impacts, and costs in order to enhance their communication and understanding.	The most currently known hydrogen colours refer to green, grey, and blue. Worldwide, the national plans, strategies, or roadmaps on hydrogen are mainly based on a mix of these colours or only on one of them (green or blue). For example, India, Spain, and Sweden’s national plans are based on the development of green hydrogen. The analysis also showed the carbon intensities of the hydrogen colours and costs, showing an inverse relation between the carbon intensity and costs of each hydrogen colour. Grey, black, and brown have the highest carbon intensity and the lowest production costs.	Includes an analysis of reports from energy agencies from 2004 to 2024
Ishaq et al. [32]	Analysis of the state-of-the-art hydrogen production processes using renewable energy sources and other sources, uses of hydrogen as a fuel, typologies of storage, transportation, distribution and key challenges, and opportunities for a wider development of hydrogen.	Hydrogen is getting increased interest beyond its conventional role in the industrial sector for the production of ammonia and methanol since, for example, as a fuel, it offers the advantage of avoiding carbon dioxide emissions in the use stage. Notably, the production of GH2 by using electricity from renewable energies is considered the best option to overcome the intermittence of renewables. However, despite these advantages, there are many challenges for its large-scale adoption such the development of an environmentally clean production system for hydrogen on large scale, as well as the development of the needed infrastructures for its distribution, storage systems for stationery and vehicles applications, and reduction of the production costs.	Not specified
Jaradat et al. [33]	This review focused on the analysis of hydrogen production techniques and, in particular, on green hydrogen, providing an interesting analysis on the geographical areas most suited for renewables production. A bibliometric analysis on hydrogen research was also offered.	The shift to GH2 is relevant to meeting future decarbonisations goals, while the development of blue hydrogen is limited by the carbon capture and storage technology and by its permanent confinement. The transition to GH2 needs technological progresses, reduction in the costs of the electrolysers, more widespread infrastructures, policy support, and market incentives. The success of GH2 also depends on the further development of renewables worldwide and of processes such as solar-thermochemical and photo-electrochemical. The authors also suggested that, in the short term, the implementation of large-scale electrolysis systems is essential to enhance the market development of GH2 and create supply chains for its provisions from exporting to importing countries.	2000–January 2024
Saha et al. [34]	Assessment of hydrogen production methods and the ecological and financial impacts of three hydrogen colours (grey, blue, and green).	The review underscored the relevant role of hydrogen in decarbonising energy systems and, in particular, industrial and transport sectors, as well as its contribution to the stability of the energy systems by means of energy storage. Future development of hydrogen depends on the technological progresses, reduction of the costs of GH2, in particuar, and the supporting policies and regulations involved.	Not specified
Goren et al. [35]	Aimed to evaluate the environmental and economic impacts and efficiency of H2 produced from various feedstocks (fossil, biomass, and water) as well as advantages, possible drawbacks, and future directions for thermochemical and biological H2 production processes.	The results showed that methods using biomass as feedstock for hydrogen production (photo-fermentation, dark fermentation, and microbial electrolysis cell) are more environmentally sound compared to the others using fossil fuels as feedstock. Notably, photo-fermentation resulted in the lowest contribution to GWP (1.88 kg CO2 eq./kgH2) and AP (0.003 gSO2/kgH2). The high consumption of water in the conventional electrolysis process (about 9 kg of water consumed for 1 kg of hydrogen) can be reduced by using hydrogen as a fuel in the fuel cell systems and converted back to water and generating electricity. However, their analysis showed that hydrogen produced from fossil fuel-based (e.g., coal) gasification and steam–methane reforming processes has costs advantages compared to hydrogen from water electrolysis, while the process efficiency of water electrolysis is slightly lower than that of of the steam reforming process of natural gas and biomass.	1990–2022
Hren et al. [36]	Comparative analysis of the environmental impacts (GHG, AP, and EP) and energy footprint of 11 technologies in the production of hydrogen, as well as its storage and transport stages.	The analysis of the GHG footprint of the technologies for hydrogen production reveals that the lowest contribution comes from glycerol and alcohol waste steam reforming and water electrolysis, but using electricity from the EU27 mix revealed the highest GHGs emissions are associated to the water electrolysis process. The latter has also the highest values for the energy footprint indicator, while for acidification and eutrophication, the values are similar to that of natural gas steam reforming and higher than glycerol and alcohol waste steam reforming technologies, which reported the lowest values. Regarding storage, the gaseous hydrogen resulted in a lower GHG footprint than liquified hydrogen, while the transport of gaseous hydrogen by the pipeline had the smallest GHG footprint.	Not specified
Mehmod et al. [37]	Analysis of the existing literature assessing the contribution to GWP, AP, EP, and resource depletion categories related to GH2, as well as the evaluation of the technological maturity and efficiency of hydrogen production methods.	The contribution to GWP, AP, freshwater eutrophication, and resource depletion is the highest producing hydrogen from coal gasification, while the lowest is by producing GH2 from wind electricity. Electrolysis technologies: AEM, PEM, SOE, and advanced biomass gasification require more comprehensive impact assessments to understand their scalability and potential environmental impacts.	Excluded the literature before the year 2014
Maniscalco et al. [38]	Comprehensive analyses of LCA studies on hydrogen production technologies and impacts on GWP and other impact categories.	The results from the analysis of the selected LCA literature showed that the contributions to GWP from GH2 as well as that of blue, turquoise, and pink production are lower compared to hydrogen produced by steam reforming. Waste gasification has the worst performance compared to the different hydrogen colours. The contribution to AP has a similar pattern of GWP with a lower difference between yellow and green H2 due to the use of materials in both solar PV and wind systems. The hotspot analysis showed that in the electrolysis stage, the source of electricity and the specific and precious materials used for the production of the electrolysers affect the contributions to AP in AEM and PEM (nickel and gold) and to ADP due to the use of iridium and titanium. The inclusion of the end-of-life stage and the recycling of materials used for the electrolysers would mitigate the impacts to ADP but at present, the authors underlined that most of the LCA studies do not consider the recycling of precious materials due to lack of reliable data. For example, the process of recovery of platinum still faces industrial maturity issues, as well as high energy and economic costs.	Last 5 years
Buffi et al. [39]	Review of production pathways for producing hydrogen from biomass or biomass-derived sources (biogas, liquid bio-intermediates, sugars) also focusing on their maturity level, as well as the energy and environmental performances of the production pathways emerged from LCA studies.	The type of feedstock biomass influences the energy required for the process of hydrogen production. Energy requirements should be compared with each other under the same conditions of feedstock, production rates, and environmental conditions. From the analysis of the LCA literature emerged some of the studies following the ISO standard, while others proposed different methological approaches. Moreover, LCA studies differed on the system boundaries ranging from cradle to gate to cradle to grave. There are also different allocation assumptions. Regarding impact assessment, most of the studies adopted midpoint assessment methods and impact categories such as GWP, AP, and ODP.	Not specified
Angelico et al. [40]	Review of GH2 using the most cited papers and recent literature reviews published in energy- and hydrogen-focused journals.	The study showed the advantages and limitations of each GH2 production technologies (PEM, AWE, SOEC, AEM), as well as their efficiency, purity, and costs. The most important methods for GH2 production, storage and grid integration, environmental impacts, as well as challenges and research gaps are also reviewed along with the potential solutions to reducing the operating costs of GH2 production, storage, and distribution and to overcome any related challenges.	Not specified
Koshikwinja et al., [41]	Evaluation of the potential hydrogen life cycle in Africa in the stages of production and final uses, policies, infrastructures, and hydrogen logistics.	Africa has a great potential of developing a future GH2 economy due to large availability of renewables such as solar, wind, and hydro. The costs of GH2 are expected to decrease strongly to 1.5 Euro/kg by 2050. The mapping of hydrogen policies shows that some countries have clear hydrogen roadmaps, such as Morocco and South Africa.	January 2000– 15 May 2024
Dyantyi-Gwanya et al. [42]	Evaluation of the opportunities for a socio-economic development of GH2 involving its production, storage, and use in South Africa.	The analysis reveals that GH2 in South Africa has good prospects for GH2, both for the domestic use and export to other countries. The availability of renewables has an important role in the development of a green economy and could drive the demand of GH2, contributing to the reduction of the costs from 3.54 to 1.40 €/kgH2 and thus facilitating its larger production, use, and export.	1990–2021
Singh [43]	Analysis on how India is approaching three key areas such as: feedstock system, circular economy integration, and environmental impacts of hydrogen that are important for achieving the climate goals of the country.	The analysis underscored the huge availability of feedstocks for GH2 production of India playing a key role in its hydrogen mission. The government is committed to the green hydrogen mission, prioritising the circular economy transition across all the sectors. India has set initiatives to implement the circular economy model, while the transition toward the use of GH2 is in its infacy and requires political support. The CE framework suggests the elimination of GHG emissions from hydrogen production. However, it is important to support with stringent regulations and technological innovation the reduction of the GHG emissions. Green hydrogen will play a key role within the circular economy transition in reducing the GHG emissions necessary for the success of the hydrogen mission and the pursuing of the climate goals.	Not specified
Tasleem et al. [44]	Review of H2 colours, hydrogen strategies, and roadmaps worldwide, with ongoing large-scale advances in green, yellow, blue, white, and gold hydrogen production, with results from life cycle assessments, future perspectives, as well as challenges and solutions for hydrogen colours.	The study reported the results by [66] underlying the importance of taking into account the impacts of metal depletion and ecotoxicity due to the production of GH2. Results from other studies pointed out that the impacts of hydrogen production are mainly due (90%) to the source of electricity for the production of hydrogen. In this regard, the LCA by [118]of a solar-to-H2 plant, using AEM electrolysers in Poland, showed a low contribution to GWP of between 2.74 kg CO2 eq./kg of hydrogen and 4.34 kg CO2 eq./kg of hydrogen. Further results from LCA studies are provided.	Not specified
Anand et al. [45]	Provided an overview of GH2 production pathways, their efficiencies and environmental sustainability, characteristics of electrolysers, the materials used for their production and challenges, and final uses of GH2.	GH2 as an increasingly important element in global decarbonisation scenarios. AEL, PEM, and SOE electrolysers technologies still face costs and efficiency issues despite their consolidation. Collaborations with countries rich in renewable energies (wind and solar) and countries with scarcity of renewables serve as a possible pathway for GH2 development. Moreover, small-scale hydro plants or waste treatment plants serve as alternative for the production of GH2 at the local scale.	Not specified
Squadrito et al. [46]	Overview of the stateof-the-art hydrogen production technologies, and exploration of the most relevant geopolitical and economic aspects and implications of the hydrogen economy, including the water aspects.	The study pointed out the need fof the selected papers have been published since the year 2015or achieving a balance between distributed hydrogen systems and centralised systems, considering the advantages of producing GH2 locally, where it is water neutral (and CO2 neutral), and compared to the production of GH2 for the external market where transport generates carbon emissions. Furthermore, the energy and costs of producing GH2 from non-traditional water sources such as using wastewater would be lower compared to the production of GH2 with fresh water “Distributed hydrogen production is a powerful tool for maximising the social utility of the hydrogen economy, reducing household energy bills, increasing energy system efficiency and resilience, and reducing the environmental impact of city services. All these aspects must be considered in future energy policies”.	Not specified
Revinova et al. [47]	Review of the literature investigating the environmental and economic impacts of hydrogen storage and transportation technologies.	The analysis revealed that salt cavern and transportation by pipeline are the most economically competitive for transport hydrogen over long distances. Hydrogen stored and transported in gaseous form and by pipeline has lower impacts compared to other ways of storage and transport.	Not specified
Dash et al. [48]	Thorough analysis of GH2 with a particular focus on Alkaline Electrolyser, including its basic principles, materials of the components, the design of the electrolyser, integration of renewable energy sources, electrolyser costs, and environmental impacts.	The review reported the results of an Australian study evaluating a levelised cost of GH2 of 9.6 USD/kg GH2 produced while considering a solar electricity price between 38 and 65 USD/kg GH2. The production of GH2 by means of AEL requires a considerable amount of energy , water, and land for the installation of the electrolysis plants, as well as generates impacts in terms of land use and biodiversity loss. Moreover, the process generates waste such as spent electrodes and other materials.	Not specified
Almaraz et al. [49]	Identification of the social aspects concerning the development of the hydrogen economy, research gaps, and future research suggestions by using both bibliometric and systematic literature reviews.	The methodological approach identified, described and ranked 12 social aspects associated with hydrogen economy research. The most recurrent social aspects in the literature are accessibility, information, H2 markets, acceptability, and policies and regulations. Despite their importance, responsibility and technological safety were less occurrent in the analysed literature. Therefore, gaps in the literature or challenges to fulfil are the scarce use of social life cycle assessment in hydrogen research.	2000–August 2023
Vallejos-Romero et al. [50]	Analysis of the research on GH2 from the perspective of social impacts and challenges.	Social impacts of the life cycle of GH2 from production to storage and transport as well as social and environmental impacts of GH2 on local communities and indigenous groups are under research. During the investigation period, Europe and Asia mainly contributed to the research on social impacts of GH2.	1997–2022
Gatto et al. [51]	Critical overview concerning lithium and hydrogen technologies within the circular economy, sustainability, and social and environmental justice frameworks.	Both lithium and hydrogen can be used in future electromobility. The use of hydrogen in mobility has the advantage of the fast refuelling. However, hydrogen has costs disadvantages and the need for implementing an infrastructure. Its development depends on the political support received.	Not specified
Forastiero et al., [52]	Creation of the needed knowledge base about the environmental and social impacts due to the installation of offshore wind farms for supporting an appropriate regulatory framework for Uruguay in the implementation of offshore wind farms.	The environmental and social impacts emerged from the analysis of the literature review are studied in the context of the most favourable areas abundant in wind resources to understand the impacts on communities and ecosystems. The study concluded by underscoring the potentiality of Uruguay to rely on a stable availability of wind resources, recommending the adoption of a regulatory and participative framework before the implementation of the offshore wind farms.	Not specified
Handique et al. [53]	Analysed the state-of-the-art and trends in the literature on distributed hydrogen systems (DHS) with the aim of closing the gap due to the prevalence of studies dealing with centralised models of hydrogen production.	The analysis showed that there is an increasing interest in the subject of DHS. Almost 80% of the selected papers have been published since the year 2015. The review also covered the assessment of the energy, environmental, economic, and social benefits of DHS. These regarded the production of fuel on-site for the transport sector, the integration of water and energy sectors as well as the integration of electricity and mobility, reinforcement of the regional energetic system by the creation of synergies among electricity, thermal energy, and hydrogen, provision of energy access to isolated areas and islands, diversification of the energy mix from fossils to improve energy security, safer expansion of hydrogen supply chains compared to centralised systems, reduction of the dependence on the delivery of hydrogen by pipelines, and the improvement in public acceptance.	2000–2023

, reviewed LCA studies concerning the production of GH₂ through electrolysis, shedding light on some life cycle impacts depending on the renewable sources used, the types of water electrolysis technologies, and the storage systems, before finally pointing out that wind and solar are the most favorable sources for GH₂ production, with potentially lower contributions to GWP when using wind power compared to solar PV [23,25].

These results have been confirmed by further literature reviews (Appendix A, Table A1, [29,30]) analysing the environmental impacts of GH_2, production as well as the economic impacts and policies supporting GH₂ development in some countries, including the EU [29]. However, the prospects could be more favorable in the future for solar-powered GH₂ due to the progressive decarbonization of the grid, leading to a reduction of the carbon intensity of the solar cells [23].

Other authors have explored the literature concerning the technological characteristics and environmental impacts of GH₂ production, comparing them with other hydrogen production patterns identified with different colours [9,10,11,31,32,33,34,35,36,37,38,39], integrating the analysis of economic impacts [11,34,35] and, in some cases, mapping the geographical areas most suitable for renewable energies and GH₂ development [11,33]. In areas rich with these sources, e.g., South Africa, GH₂ production could be used both for domestic use and exports [40,41,42]. Many countries have adopted hydrogen strategies and roadmaps [31,43,44], and some studies have also offered an overview of the latter and the current capacity and status of hydrogen projects within the framework of net zero emissions targets of the year 2050 [44], along with the analysis of the environmental impacts of GH₂ [43] and other hydrogen colors [31,44].

Some authors also focused on the comprehensive assessment of GH₂ production processes [21,45,46], storage and distribution modalities and their economic costs [47], and the analysis of specific electrolyzers such as AEL [48] that expand on basic principles and designs, materials for the components of the electrolyzers, the integration of renewable energy sources, electrolyzer costs, and environmental impacts [48].

A few literature reviews investigated the social aspects of hydrogen [49] or the social impacts of GH₂ production, storage, transportation, and distribution [50,51,52], integrating the analysis of the social impacts with that of the environmental impacts [52,53]. The low number of literature reviews confirms that social aspects/impacts are not yet included in most environmental and especially technical/economic assessments [50].

The economic costs are only one of several dimensions on how to decide GH₂ projects and strategies. Social aspects (particularly those related to the local population involved in the production of GH₂) should be much more integrated for a more comprehensive analysis useful for decision making [54]. There is a need for more research on the process of governance in the implementation of GH₂ technologies and their social acceptance [50].

This study aimed to contribute to the closing of this gap in the literature, evaluating the environmental and social impacts of GH₂ in the whole life cycle, as well as to improve our understanding of the effectiveness of GH₂ in reducing the contribution of energy systems to current environmental and social challenges.

The analysis is performed in light of the CE transition and the adoption of its principles aimed at changing the way products, materials, and food are designed, produced, and consumed [55] via a new model of circular local development [55]. The goal is to address the main research question that is as follows: Is Green Hydrogen an environmentally and socially sound solution for decarbonizing energy systems in the transition to a circular economy?

The novelty of the manuscript is as follows:

• Creation of a state-of-the-art framework composed of previous literature reviews useful to understanding the main current trends and gaps in the literature of GH₂;
• Strengthening the existing literature reviews on GH₂, enriching the understanding of the environmental and social impacts of the life cycle of GH₂ with the analysis of the most recently published articles;
• Assessment of the environmental and social impacts of GH₂ within the framework of the CE model and its principles to conceptualize the areas of relationship between CE and GH₂. This would clarify how GH₂ aligns with the CE framework and show how its implementation is consistent with the CE principles such as resource efficiency, closed-loop production, and local development.

This study develops over the next four sections. Section 2 analyses the relation between CE and GH₂, which is useful to understand its role in CE transition and the relevance of its principles in enabling a more environmentally and socially sound decarbonisation pathway. Section 3 provides details on the type of data used and the method adopted to extract them from the main international database. Section 4 presents the results of the narrative literature review, while Section 5 discusses the main results and presents the conclusions of this study.

2. Theoretical Framework: Circular Economy and Green Hydrogen

There is a strict link with the production of GH₂ and the CE model [47]. The CE promotes the vision of a new socio-economic system as well as sustainable production and consumption patterns [56] according to the three pillars of sustainable development [57]. Such a model suggests the elimination of waste and pollution by design and the continuous circulation of products and materials at their highest value by means of the most appropriate CE principles (such as “reduce, repair, reuse, recycling” and so on) [58] to tackle the need for extracting new raw materials [59].

The CE also promotes energy efficiency, lower energy use, and energy transition towards renewables [47,60]. These sources of energy continuously regenerate beyond human timescales and are part of the processes of the geobiosphere driven by the global power of solar, geothermal, and tidal energy [61]. Within this framework, the circulation of energy and the production of hydrogen from renewable sources may contribute to local and global decarbonization goals [62], avoiding the extraction and consumption of fossil fuels and related impacts, thereby supporting the independence from them [63].

On the other hand, the CE is a great opportunity to better ascertain the value of all local physical resources, be they natural or mined in the local urban systems [64]. Some authors provided evidence that the spatial distribution of renewable energies should be taken into account in decarbonization strategies, because some areas are richer in renewables compared to other areas or their geographical locations are more favorable towards solar or wind power [65]. This may likely have effects on GH₂ production and its environmental efficiency [66]. GH₂ can be considered a renewable fuel (a carrier of other renewable energies) because it can be produced indefinitely [22]. As a fuel, it is also more energy efficient per unit of mass compared to diesel and gas: the production of electricity with fuel cells powered by hydrogen achieves an efficiency of up to 65%, which is much higher than the efficiency achieved by, for example, a coal power plant (up to 35%) [22] or electricity generated from natural gas (45%) and oil (38%) [67].

The application of CE principles to renewable technologies (including green hydrogen), from the design stage, is absolutely required to reduce their impacts [68]. As a matter of fact, renewable technologies rely on finite materials for the production and store of energy [69], and for this reason, their lifecycle cannot be based on a linear approach [70]. This implies the designing of renewable technologies towards longer lifetimes, easier maintenance and repair, and the application of standardization and modularity in their design for disassembly at end-of-life [71]. Other CE solutions are full repowering, design for reuse and recycling, and, more broadly, the rethinking of the economics of renewable technologies [69] and supporting their development via policies and regulations such as those adopted in the European Union [72]. The adoption of certification schemes for encouraging more responsible supply chains in line with CE principles [10,73,74,75] under the EU Renewable Energy Directive and for renewable hydrogen [72], as well as the adoption of decision-making frameworks and standardized guidelines for reuse (e.g., for solar panels) [76], are also very important patterns for reducing the impacts on the whole life cycle of renewable energies and GH₂ [72].

3. Materials and Methods

This study mainly collected secondary data and information from the most recent international literature, although other sources and particular reports published by key stakeholders in the field of CE (such as the Ellen Mac Arthur Foundation) and the energy sector have been considered (European Hydrogen Observatory and International Energy Agency).

The method of the narrative literature review adopted by other scholars in the field of hydrogen research [10] has been considered appropriate for pursuing the goal of this study. The review has been conducted while taking into account the suggestions/guidelines for this type of narrative literature review [77,78]. In particular, Green et al. [77] emphasizes that the results should be presented in a “condensed format that typically summarizes the contents of each article”. Moreover, narrative literature reviews have the advantage of offering a broad overview of a topic, going through its history and evolution. Finally, these reviews “may be an excellent venue for presenting philosophical perspectives in a balanced manner” [77].

However, this type of literature review may be criticized when compared to the rigorousness of the method followed in systematic literature reviews [77]. In this regard, the method followed in this study has tried to reduce biases by considering guidelines from systematic literature reviews [78] in order to provide more reliable results and conclusions.

The keywords and query used for the searches, the database searched, and the criteria for selecting the articles are shown below. The method followed is more transparent and may be reproducible [78], adding scientific quality to the narrative literature review performed in this study.

Clarivate Web of Science has been selected as the main database to search the relevant literature in accordance with other authors who performed bibliometric analyses concerning hydrogen research [6].

The overall process started with the identification of the following keywords and query for searching the literature:

• Green Hydrogen AND Literature review;
• Green Hydrogen AND Circular economy;
• Green Hydrogen AND Environmental impacts;
• Green Hydrogen AND Life cycle assessment;
• Green Hydrogen AND Social life cycle assessment;
• Green Hydrogen AND Social impacts.

The criteria followed for the inclusion and exclusion of the literature are the temporal timeframe (2022 to 2025) and the coverage of the selected literature of the topics useful to address to the main research questions and understand if GH₂ could be an environmentally and socially sound solution for the main applications (as a fuel, heat producer, and a feedstock for other chemical products) in future energy systems.

Table 1. Description of the most important aspects used in searching and selecting the sample of articles of this study.

Keywords	Query	Results from All Databases	Inclusion	Exclusion	Number of Selected Articles
Green Hydrogen; Literature review	“Green Hydrogen” AND “Literature review”	63	Years 2022–2025 (28 March 2025) Literature reviews of LCA studies on GH2, reviews considering the analysis of the environmental impacts of GH2 life cycle, or environmental and social impacts and economic costs of GH2 life cycle Only literature reviews as document type	Years before 2022 Reviews only focused on financial or cost analysis of GH2 production/life cycle Document types beyond literature reviews	9
Green Hydrogen; Circular economy	“Green Hydrogen” AND “Circular economy”	94	Years 2022–2025 (28 March 2025) Articles/Reviews focused on LCA/analysis of environmental and social impacts and economic costs of GH2 production within CE framework	Years before 2022 Articles/Reviews only focused on financial or cost analysis of GH2 production within CE framework	10
Green Hydrogen; Environmental Impacts	“Green Hydrogen “AND “Environmental impacts”	109	Years 2022–2025 (28 March 2025) Articles/Reviews focused on LCA or analysis of environmental impacts of GH2 with other methods and eventually including the analysis of social impacts and cost of GH2 production	Years before 2022 Articles/Reviews focused only on financial or cost analysis of GH2 production	24
Green Hydrogen; Life cycle Assessment	“Green Hydrogen” AND “Life cycle Assessment”	239	Years 2022–2025 (28 March 2025) Articles/Reviews focused on LCA of GH2 life cycle or comparative LCA of GH2 and other hydrogen colours	Years before 2022 Articles/Reviews not focused on LCA of GH2 life cycle or comparative LCA of GH2 with other hydrogen colours	51
Green Hydrogen; Social Life cycle Assessment	“Green Hydrogen” AND “Social Life cycle Assessment”	2	Years 2022–2025 (28 March 2025) Articles focused on social life cycle assessment of GH2 production/life cycle	No criteria for the exclusion	2
Green Hydrogen; Social Impacts	“Green Hydrogen” AND “Social Impacts”	7	Years 2022–2025 (28 March 2025) Articles focused on social life cycle assessment or analysis of the social impacts of GH2 life cycle with other methods	Years before 2022 Articles not focused on the analysis of social impacts of GH2 life cycle	5
Duplicates					28
Total					73

summarises the keywords, the query, the results for each query, the criteria for the inclusion/exclusion of the searched articles, and the number of selected articles. The initial number of articles resulting from all the six queries was 514, and the total number of selected articles after the screening of the abstracts and content of the articles, as well as the removal of duplicates (28), resulted in 73. Some articles (20) listed in the note at the bottom of

Table A2. All the selected literature classified according to the year of publication, their goals, methods, and some results.

Authors	Year of Publication	Goals	Method	Some Results
Anand et al. [45]	2025	Provided an overview of GH2 production technologies, their efficiencies and environmental sustainability, characteristics of electrolysers, the materials used for their production and challenges, and final uses of GH2	Literature review	GH2 as an important element in global decarbonisation scenarios. AEL PEM, and SOE electrolysers still face costs and efficiency issues. Collaborations with countries rich in renewables (wind and solar) and those with low availability for GH2 development. Small-scale hydro plants or local biomass from waste treatment plants serve as alternatives for the production of GH2 at the local scale.
Angelico et al. [40]	2025	Reviewed the most cited papers and recent literature reviews published in energy- and hydrogen- focused journals	Literature review	The study showed the advantages and limitations of each GH2 electrolyser technologies (PEM, AWE, SOEC, AEM), as well as their efficiency, purity, and costs. The most important methods for GH2 production, storage, and grid integration, and their environmental impacts, challenges, and research gaps are also reviewed along with the potential solutions to reduce the operating costs of GH2 production, storage, distribution, and solutions to overcome the related challenges.
Bonesso et al. [108]	2025	Conducted a social and economic analysis of GH2 produced from an integrated wind-based electrolysis plant in Southern Italy	Social and economic analysis	The levelised cost of energy resulted in 3.60 €/kg of GH2 in the base scenario while in the alternative scenarios, it comprised between 3.20 and 4 €/kg of GH2. In the survey, the results from most of the respondents (72%) of the sample did not to know the difference between green and blue hydrogen.
Dyantyi-Gwanya et al. [42]	2025	Evaluation of the opportunities for the socio-economic development of GH2 involving its production, storage, and use in South Africa	Literature review	South Africa has good prospects for GH2 both for the domestic use and export to other countries. The availability of renewables has an important role in the development of a green economy and could drive the demand of GH2 and contributing to the reduction of the costs from 3.54 to 1.40 €/kg H2, facilitating its larger production, use, and export.
Gabbar and Ramadan [97]	2025	Proposed the analysis of environmental and economic sustainability of scenarios applied to buildings combining renewable energies and GH2 production.	Environmental and socio-economic analysis	The scenario integrating wind turbine and solar PV panels covers up to 63% of the electricity lighting needs of the building, avoiding the supply from the utility grid and thus achieving socio-economic benefits.
Gatto et al. [51]	2025	Critical overview concerning lithium and hydrogen technologies within circular economy, sustainability, and social and environmental justice frameworks.	Literature review	Both lithium and hydrogen can be used in the future electromobility. The use of hydrogen in mobility has the advantage of the fast refuelling. However, hydrogen has costs disadvantages and the need for implementing an infrastructure. Its development depends on the political support received.
Guven [124]	2025	One of the goals is the assessment of the environmental impacts and costs by means of LCA and LCC of GH2 production from floating PV system and its use in the selected ferry line in Turkey.	Life cycle assessment and Life cycle costing	GH2 fuel resulted the most environmentally sound compared to marine diesel oil for fuelling the inland ferry lines, reducing the contribution to GWP by 77.5 % and releasing less PM10 emissions by 91.7 % and 57.3 % less SOx. The costs of GH2 in the three scenarios range from 6.66 $/kg of GH2 to 6.99 $/kg of GH2, making them financially uncompetitive with diesel and requiring the support of financial incentives such as the reduction of corporate tax by 10%.
Hoppe and Minke [133]	2025	Assessment of the assembly of a 5 MW AWE and the environmental impacts on the manufacturing stage following the recycling and reuse of materials at the end-of-life.	Life cycle assessment	The use of recycled materials for the manufacturing of the AWE system reduces the impacts to GWP by about 50% compared to the use of virgin materials. Further reduction of the impacts can be achieved by adopting design for repair, reuse, repurposing, and remanufacturing.
Koshikwinja et al. [41]	2025	Evaluation of the potential hydrogen life cycle in Africa in the stages of production and final uses, policies, possible infrastructures, and facilities for hydrogen logistics.	Literature review	Africa has a great potential of developing a future GH2 economy due to large availability of renewables such as solar, wind, and hydro. The costs of GH2 are expected to decrease strongly to 1.5 Euro/kg by 2050. The mapping of hydrogen policies shows that some countries, such as Morocco and South Africa, have clear hydrogen roadmaps.
Mehmod et al. [37]	2025	Analysis of the existing literature assessing the contribution to GWP, AP, EP, and resource depletion categories related to GH2 and other hydrogen colours and the technological maturity and efficiency of hydrogen production methods.	Literature review	The contribution to GWP, AP, FETP, and resource depletion is the highest-producing hydrogen from coal gasification while the lowest by producing GH2 from wind electricity. Electrolysis technologies: AEM, PEM, SOE, and advanced biomass gasification require more comprehensive impact assessments to understand their scalability and potential environmental impacts.
Mokrzycki and Gawlik [22]	2025	Review of various aspects of GH2 economy including its advantages and disadvantages, risks, environmental impacts, and future water availability for hydrogen production,.	Literature review	Key factors for the acceleration of the GH2 development are reduced costs, innovation in renewables and GH2 technologies, GH2 storage and investments in transport, as well as efficiency improvements. The GH2 economy will ultimately depend on widespread support and development.
Nelson et al. [121]	2025	Assess the environmental performances of hydrogen produced by photocatalysis.	Life cycle assessment	More than 98% of all environmental emissions are due to the construction of the photoreactor. Most of the contribution to the normalised 19 investigated impact categories comes from stainless steel and, to a lesser extent, from glass and concrete. Glass and steel are the two main contributors to ODP.
Nguyen et al. [128]	2025	Comparison of the impacts of alternative (blue and green ammonia and blue and green hydrogen) and conventional fuels to be used in internal combustion engines in marine applications.	Life cycle assessment	Blue ammonia with on-board reforming (0.312 kg/kWh of fuel) and without on-board reforming (0.354 kg/kWh) show higher values compared to green ammonia with (0.144 kg/kWh) and without on-board reforming (0.189 kg/kWh), with green hydrogen (0.14 kg/kWh) emerging as the best alternative compared to the fossil fuel case (0.65 kg/kWh).
Schlehuber et al. [131]	2025	Analysis of the environmental and economic performances (from manufacturing, operating, and disposal) of the autonomous-driving, hydrogen-powered boats (AHB) and comparison of the AHB with the different types of trucks analysed in the literature.	Life cycle assessment and life cycle costing	AHBs, due to their small size, can be used in the river network and potentially replace transport by trucks characterised by higher emissions. Scenario 2 is the optimal one, incorporating a better balance between the environmental impacts (0.33 kg CO2 eq./km) and total costs (0.58 €/km). With that, the AHB can be considered the cost-optimal option for distances beyond 624 km.
Singh et al. [27]	2025	Analyse the production of GH2 hydrogen from biogas/landfilling gas by means of conventional reforming processes, such as dry methane reforming, steam methane reforming, partial oxidation reforming, and autothermal reforming. The review also considered the contribution to GWP (CO2 eq·kg−1 H2) emissions, as well as the economic aspects of the processes and their efficiencies	Literature review	The results of the reviewed studies showed that carbon footprint of biomethane reforming was lower than fossil methane reforming. The carbon footprint of biomethane from steam reforming was 4.8 kg CO2 eq./kg of hydrogen versus 11.2 kg CO2 eq./kg of hydrogen produced from steam reforming of natural gas. In other studies, harmonised carbon footprint of GH2 from biogas reforming resulted in 7.34 kg CO2 eq./kg of hydrogen and the carbon footprint of GH2 produced from water electrolysis and electricity sourced by wind, solar thermal, solar PV, and hydro was 5 kg CO2 eq./kg of GH2, while that of electricity from the grid was 32 kg CO2 eq./kg of GH2. Finally, a study assessed the production of hydrogen from agricultural residues such as cheese whey, sugar beet molasses, and wine vinasses with wastewater treatment plant sludge, and found that GHG emissions are the lowest for hydrogen produced from sugar beet molasses (3.56 kg CO2 eq./kg of hydrogen) compared to the other two feedstocks . Further LCA studies are suggested to validate the results provided in the existing research.
Sola et al. [23]	2025	State-of-the-art LCA research on GH2 in the last five years taking into account GHG emissions and other environmental categories (such as water use, critical materials use, and land use) and large-scale GH2 development	Literature review	Increasing trend of LCA research on GH2. Water consumption and land use (due to the use of renewable energies) in important hotspots that could limit GH2 development, particularly in areas scarce in water such as Saudi Arabia and Oman that have high abundance of sun but are scarce in freshwater. Rare metals and critical raw materials for electrolysers production (particularly PEM) such as iridium and platinum, as well as solar cells production, serve as further hotspots. Uncertainties related to the end-of-life disposal of electrolysers.
Tabrizi et al. [125]	2025	Analysis of the carbon footprint of GH2 production through an AEL system with electricity sourced by PV or wind in Italy and the UK.	Life cycle assessment	The results show that the updating of the baseline scenario (to consider the advances in the solar PV and wind technologies) leads to a reduction in the carbon footprint for Italy and the United Kingdom. The contributions to GWP for GH2 produced in Italy using solar PV (single-SI modules) electricity in the lower bound is 1.76 kg CO2 eq./kg GH2. The carbon footprint of onshore and offshore wind shows values in the lower bound that are well below 1 kg CO2 eq./kg GH2. both for Italy and the UK in all the scenarios and plants. The study also confirmed that the source of electricity (solar or wind) is the most relevant factor in determining the carbon footprint of GH2.
Tasleem et al. [44]	2025	Review of H2 colours, hydrogen strategies and roadmaps worldwide, currently ongoing large-scale advances in green, yellow, blue, white, and gold hydrogen production, results from life cycle assessments, future perspectives, as well as challenges and solutions for hydrogen colours.	Literature review	The study reported the results by [66], underlying the importance of taking into account the impacts of metal depletion and ecotoxicity due to the production of GH2. Results from other studies pointed out that the impacts of hydrogen production are mainly due (90%) to the source of electricity for the production of hydrogen. in this regard, the LCA by [118] of a solar-to-H2 plant, using AEM electrolysers in Poland, shows a low contribution to GWP between 2.74 kg CO2 eq./kg of Hydrogen and 4.34 kg CO2 eq./kg of hydrogen. Further results from LCA studies are provided.
Affandi et al. [116]	2024	Assessing the environmental and economic viability of three case studies of GH2 production in Malaysia and Thailand by means of PEM and AEL electrolyser powered by a solar PV system from cradle to grave (extraction of raw materials, transportation, construction, use phase, disposal and recycling phase) Results are measured in terms of greenhouse gas emissions and levelised cost of hydrogen and other financial indicators.	Life cycle assessment	The GHG emissions of GH2 produced using PEM electrolysers resulted comprised, depending on the case studies, between 2.26 and 4.46 kg CO₂ eq/kg GH₂ while that related to AEL electrolysers are between 2.61 and 5.15 kg CO₂ eq/kg GH₂. The LCOH ranges changed across the three case studies from $5.64/kg H2 to $5.12/kg H2 and $510.82/kg H2 (case with AEL electrolyser) to $7.31/kg H2, $6.38/kg H2 and $14.23/kg H2 (case with PEM electrolyser) and is higher than fossil-derived hydrogen ($1–$2/kg H2). For the GHG emission, the most important factors are the energy mix and the specific context where the electrolysers plant operates, while the capital costs of the electrolysers and the capacity of the PV systems are relevant in affecting the LCOH of GH2.
Ajeeb et al. [25]	2024a	Reviewed the recent literature on GH2 production in LCA studies, taking into account many factors such as the electrolysers technologies, renewable sources for GH2 production, the life cycle inventories, the local scale of GH2 production, storage, and environmental impacts.	Literature review	Wind and solar energy resulted in the most appropriate sources for the production of GH2, with wind reporting a lower contribution to GWP compared to solar energy. PEM electrolysers have a potential contribution to GW lower than the other technologies such as ALEL and SOEL. Improvement of the energy efficiency and environmental impacts of the water electrolyser system can be realised by means of different strategies, including waste treatment strategies such as the use of oxygen in industrial processes or the reuse of materials of the electrolyser.
Ajeeb et al. [114]	2024b	Identified the most adequate and environmentally sound electrolysis hydrogen option between two ALE technologies such as ALE-Pressurised and ALE-Capillary sourced by renewables in Portugal. The production of GH2 is based on 50% electricity from solar PV and 50% from wind in Portugal. The goal was to identify the most appropriate and environmentally sound electrolysis hydrogen production system between the two ALE technologies (ALE-P and ALE-C).	Life cycle assessment	The ALE-Capillary system resulted in the generation of lower impacts than the ALE-Pressurised within the 16 analysed environmental impacts categories. The source of electricity (the energy mix of wind and solar PV) in the life cycle of GH2 generated most of the impacts ranging from 92% fpr ODP, 96% fpr mineral fossil resource depletion, and 98% for the other investigated impact categories (including GWP). The contribution to GWP resulted in 1.98 kg CO2 eq./kg GH2 for ALE-C and 2.39 kg CO2 eq./kg GH2 for ALE-P.
Al-Ghussain [137]	2024	Analysed the techno-economic feasibility and the life cycle GHG emissions of GH2 production (wind and solar-based electricity) and the influence of geographical variations of wind and solar, ambient conditions, and PEM electrolyser size on the carbon intensity and costs of both renewables and GH2.	Techno-economic and environmental analysis	The study underlined the importance of optimising the size of the PEM electrolyser and the use of hourly-based models for the purpose as well as for the analysis of the production costs and carbon intensity of GH2. The geographical location of renewables influences the carbon intensity (CI) of GH2 and costs. The CI ranges from 0.3 to 1.9 kg CO2 eq./kg GH2 CO2 eq./kg GH2 (wind-based electricity), with peaks of 4.34 CO2 eq./kg GH2 for central regions. GH2 produced using solar electricity has a high variability ranging from 1.58 to 2.95 kg CO2 eq./kg GH2. GH2 production costs comprised between 1.5 and 15 USD/kg GH2 for wind-based systems and 3.0 and 5.2 USD/kg H2 for the solar PV-based systems. Geographical differences and ambient conditions have an important role in affecting the costs of GH2 as well as the CI of electricity from renewables and of GH2.
Alghool et al. [89]	2024	Assessing the environmental contributions to GWP of 18 different blue hydrogen processes throughout their life cycle. The study also considered the comparison of the contribution to GWP with GH2 produced by using solar collectors.	Life cycle assessment	The LCA results showed that the NH3 process has the least environmental impact, releasing 2.12 kg CO2 eq./kg H2 compared to the other 18 blue hydrogen processes. NH3 process produces hydrogen from ATR technology in combination with carbon capture and storage of the CO2 with hydrogen that could be delivered as ammonia to consumers.
Almaraz et al. [49]	2024	Identification of the social aspects concerning the development of the hydrogen economy, research gaps, and future research suggestions by using both bibliometric and systematic literature reviews.	Literature review	The methodological approach identified, described, and ranked 12 social aspects associated to the hydrogen economy research. The most recurrent social aspects in the literature results are accessibility, information, H2 markets, acceptability, and policies and regulations. Despite their importance, responsibility and technological safety are less occurrent in the analysed literature. Therefore, gaps in the literature or challenges to fulfil are the scarce use of social life cycle assessment in hydrogen research.
Arrigoni et al. [123]	2024	Evaluation and comparison of the potential environmental impacts of different hydrogen storage and delivery options for an industrial cluster located in northern Europe and expected to be operative after 2030.	Life cycle assessment	The hydrogen production process and the type of delivery affect the environmental performances of hydrogen delivery options. Lowest impacts are due to hydrogen produced on-site by relying on abundant renewable energies. The import of GH2 can be less impactful than grey hydrogen or hydrogen produced by electrolysis with electricity sourced partially by the grid.
Awad et al. [130]	2024	Analysis of the impacts on CO2 emissions and costs due to the use of grey and green hydrogen as fuels for buses in Dubai.	Environmental analysis and life cycle costing	The optimal option is replacing the Dubai bus diesel fleet at end of lifetime with mixed fuel hydrogen. This allows the usage of existing grey hydrogen fuel available at reasonable costs compared to green hydrogen. Energy consumption mainly contributes to the high cost of hydrogen fuel produced from electrolysis. A reduction in the costs can be obtained by improving the efficiency of the technology and by using solar power plants.
Barghash et al. [110]	2024	Comparison of the impacts to Midpoint and Endpoint impact categories of dark fermentation (DF) and electrolysis hydrogen production processes in the light of achieving Oman’s Vision 2040. The goal was to evaluate the impacts of treating water for biohydrogen production by considering two sources of electricity.	Life cycle assessment	The dark fermentation method uses sludge as feedstock while electrolysis uses the treated water. The results show that both processes contribute to GWP. However, the contributions to GWP can be reduced by integrating a solar power plant for the provision of energy to both processes.
Castagnoli et al. [119]	2024	Assessment of the potential environmental impacts of waste to methanol technology that jointly integrates waste gasification and methanol synthesis for the recovery of the chemical carbon and hydrogen available in municipal solid waste.	Life cycle assessment	The results showed that the scenario of waste to methanol and GH2 system has a lower global impact compared to the conventional waste to energy scenario. The waste to methanol process produced 1366 kg of methanol per ton of refused derived fuel by converting the CO2 contained in the waste extending the value of the by-products and improving the economic viability of the process.
Currie et al. [102]	2024	Assessment of the financial viability of integrating GH2 in electrical grid of South Australia, enabling the presence of a higher share of renewable energies in the electrical system.	Techno-economic and environmental analysis	The analysis confirmed that GH2 would improve the reliability and security of the electricity system in the presence of wind and solar variability or in the impossibility of storing the surplus energy from these sources in an efficient way. However, considering only financial indicators, the proposed project would not be viable and would require economic subsidies.
Dash et al. [48]	2024	Thorough analysis of GH2 with a particular focus on Alkaline Electrolyser including its basic principles, materials of the components, the design of the electrolyser, and integration of renewable energy sources.	Literature review	The review reported the results of an Australian study evaluating a levelised cost of GH2 of 9.6 USD/kg GH2 produced while considering a solar electricity price between 38 and 65 USD/kg GH2. The production of GH2 by means of AEL requires a considerable amount of energy, water, and land for the installation of the electrolysis plants, impacting land use and biodiversity loss . Moreover, the process generates waste such as spent electrodes and other materials.
Dos Reis et al. [141]	2024	Performed a S-LCA of GH2 in order to evaluate the impacts of its life cycle by using both PSILCA and SHDB database for the S-LCA.	Social life cycle assessment	Social impacts in the extraction and processing of the raw materials resulted in the most significant stage in both databases. China and South Africa are the areas that mainly contribute to the social impacts due to the extraction of iridium and titanium in South Africa and naflon production in China.
Du et al. [138]	2024	Evaluation of the potential environmental impacts in terms of GHG emissions throughout the life cycle of GH2 from cradle to gate (extraction of the resources to transportation of GH2) and the LCOH.	Environmental and cost analysis	The GHG emissions associated with the life cycle of GH2 produced from wind and solar PV power resulted in between 2.07 and 4.59 kgCO2 eq./kg GH2 in the year 2020. The study predicted a further reduction by the year 2030 to 1.57 and 3.78 kg CO2 eq./kg GH2.
Eshkaftaki et al. [120]	2024	The study assessed the potential environmental impacts (as GWP, AP, ODP, HT, Fine particulate matter formation) of integrating GH2 into the steel production process from cradle to gate.	Life cycle assessment	The life cycle assessment results showed a potential contribution to GWP of 93 kg CO2 per second of steel produced, with the electric arc furnace contributing significantly to the environmental impacts in terms of GWP and fine particle formation.
Forastiero et al. [52]	2024	Creation of the needed knowledge base about the environmental and social impacts for the installation in Uruguay of offshore wind farms for the production of electricity for GH2 (in line with the hydrogen roadmap) and by this supporting an appropriate regulatory framework for Uruguay.	Literature review	The environmental and social impacts emerged from the analysis of the literature review were studied in the context of the most favourable areas abundant of wind resources to understand the impacts on communities and ecosystems in Uruguay. The study concluded by underscoring the potentiality of Uruguay to rely on a stable availability of wind resources, recommending the adoption of a regulatory and participative framework before the implementation of offshore wind farms.
Gandiglio and Morocco [99]	2024	Overview of the funded projects and other initiatives regarding the development of hydrogen in Italy detailing their location, sector of application and funds received.	Perspective	The study collected data of about 150 funded initiatives. The priority in the allocation of the funds of PNNR has been given to sectors where the electrification is not yet technically or economically viable. Priority sectors are: production of GH2 in brownfield areas (local use and transport of GH2 to promote the so-called hydrogen valleys), use of hydrogen in hard-to-abate sectors, manufacturing of the electrolysers, hydrogen production plants, and storage and refuelling stations for road and railway lines.
Martin-Gamboa et al. [142]	2024	Identified the social hotspots in two value chains of GH2 in EU: the production on-site and use in the country and the production and compression of GH2 outside the country of use.	Social life cycle assessment	Production and use of GH2 value chain in the same country resulted in better social performances than the off-site production outside of the country. The worst performances of the off-site production are due to the higher complexity of the value chain. The scenario analysis confirmed the better performances of on-site production and use in two of the indicators such as child labour and fair salary. In contrast, the performances of the off-site production are better when considering the social impacts of the indicator and contribution to economic development.
Guven [126]	2024	Assessment of the environmental impacts and costs of producing GH2 from electricity generated by an offshore wind system located in the Eagen Sea. Identification of the most adequate economic tools for supporting GH2 production.	Life cycle assessment and life cycle costing	The contribution resulted in between 0.7 kg CO2-eq./kg GH2 and 0.753 kg CO2eq./kg GH2 for GWP-20 and GWP-100, respectively, while that to Fine Particulate Matter Formation 0.24 gPM2.5/kgH2 for FPMF-20 and 0.53 gPM2.5/kg GH2 for FPMF-100. The results of the LCC shows a LCOH of $4.36/kg GH2.
Handique et al. [53]	2024	Analysed the state-of-the-art and trends of the literature on distributed hydrogen systems (DHS) with the aim of closing the gap due to the prevalence of studies dealing with centralised models of hydrogen production.	Literature review	The analysis showed that there is an increasing interest in the subject of DHSs. Almost 80% of the selected papers have been published since the year 2015. The review also covered the assessment of the energy, environmental, economic, and social benefits of DHS. These regarded the production of fuel on-site for the transport sector, the reduction of the GHGs emissions, the integration of water and energy sectors as well as the integration of electricity and mobility, reinforcement of the regional energetic system by the creation of synergies among electricity, thermal energy, and hydrogen, provision of energy access to isolated areas and islands, diversification of the energy mix from fossils improving energy security, safer expansion of hydrogen supply chains compared to centralised systems, reduction of the dependence on the delivery of hydrogen by pipelines, and improvement of public acceptance.
Hassan et al. [96]	2024	Assessment of the technical and financial performances of a commercial hydrogen battery in rooftop solar systems (4.5 kWp) in comparison with the performances with Li–Ion battery.	Technical, environmental and cost analysis	The analysis showed that both types of batteries reduces the dependence of electricity from the grid and its costs. In terms of technical performances, the Li–Ion battery has lower roundtrip energy losses while the hydrogen battery increases the life of the battery, allowing a longer duration of energy storage. On the other hand, hydrogen batteries are not the best choice in areas with scarcity of water and Li–Ion batteries are sensitive to high temperatures.
Jaradat et al. [33]	2024	Overview of the current state of green hydrogen research with the latest progresses in GH2 production technologies, supporting policies, and global research trends through bibliometric analysis	Literature review	The transition to GH2 needs technological progresses and reduction of the costs in the electrolysers, more widespread infrastructures, policy support, and market incentives. The success of GH2 also depends on the further development of renewables worldwide and processes such as solar-thermochemical and photo-electrochemical.
Khan et al. [127]	2024	Evaluated the total life cycle impacts of GH2 from cradle to grave including the production of the electrolyser, its transport and installation, and the end-of-life by means of a case study in Australia	Life cycle assessment	GH2 produced by means of PEM electrolyser and wind electricity has lower impacts than GH2 from AEL electrolyser and solar PV power. The most significant stage result was during the operation stage when considering GWP due to the use of electricity and the impacts of the construction of wind and solar PV plants. The impacts in the other categories such as water depletion, fossil fuel, and metal depletion saw relatively lower results in the case study. However, from the perspective of scalability, the impacts can be mitigated by manufacturing electrolysers with renewable energies and recycled materials and making them recyclable. Moreover, further mitigation strategies for reducing the impacts regard the life cycle of the electricity used for the electrolysis process and a more sustainable use of water.
Kugemann and Poladis [107]	2024	The study developed a new integrated Multi Criteria Decision Analysis framework to rank several alternative fuels for buses and types of buses on the basis of technical, environmental, social, and economic dimensions. The framework is applied to the public transport system of the island of Gotland (Sweden).	Multicriteria assessment	The results evidenced that the most preferred fuel for buses is biogas (particularly that produced by waste resources) andplug-in hybrid electric biogas. Battery electric and hybrid electric hydrogen fuel cell resulted in interesting alternatives from the perspective that they are produced locally. However, the most preferred option is for biogas as a fuel despite assuming a further development of wind capacity and the improvement of the capacity of GH2 towards the achievement of energy self-sufficiency as well as the use of subsidies to support the development of GH2.
Maestre et al. [17]	2024	Monitoring the performances of a hybrid solar PV-based GH2 demonstrative pilot plant, useful to ensure the total annual coverage of electricity needs of a social housing unit.	Techno-economic and environmental analysis	The results showed the environmental, economic, and social benefits achieved by the hybrid solar PV–hydrogen pilot plant after two years of monitoring. The economic benefits such as avoided electricity costs are particularly relevant for the people living in social housing, as they are at potential risk of energy poverty. The monitoring and control system implemented for the pilot plant allow the analysis of variables and energy performances. The control system has shown to work effectively since the electrolyser or the fuel cells entered into operation when there is a surplus of energy or when the batteries and the solar PV plant do not meet the energy demand of the social housing.
Maniscalco et al. [38]	2024	Comprehensive overview of hydrogen production technologies and impacts generated to the different categories including GWP.	Literature review	The results from the analysis of the selected LCA literature showed that the impacts to GWP from GH2 as well as that of blue, turquoise, and pink production are lower compared to hydrogen produced by steam reforming. Waste gasification has the worst performances compared to the different hydrogen colours. The contribution to AP has a similar pattern of GWP with a lower difference between yellow and GH2 due to the use of materials in both solar PV and wind systems. The hotspot analysis shows that in the electrolysis stage, the source of electricity and the specific and precious materials used for the production of the electrolysers affect the contributions to AP in AEM and PEM (nickel and gold) and to ADP due to the use of iridium and titanium. The inclusion of the end-of-life stage and the recycling of materials used for the electrolysers would mitigate the impacts to ADP, but at present, the authors underlined that most of the LCA studies do not consider the recycling of the precious materials due to lack of reliable data. For example, the process of recovery of platinum still faces industrial maturity issues, as well as high energy and economic costs.
Martelli et al. [101]	2024	Comparison of the life cycle impacts of a traditional diesel-powered tractor, a fuel cell hybrid tractor using grey hydrogen, and a fuel cell hybrid tractor powered by GH2.	Life cycle assessment	The fuel cell hybrid tractor showed much lower impacts in all the investigated impact categories with the exception of FFP, where the impacts compared to the traditional tractors are lower by 4.55%. In the life cycle of a traditional tractor, the most critical step is the use stage, while in the fuel-cell tractor, it is the manufacturing stage. The comparison with the fuel cell hybrid tractor using GH2 to the traditional tractor shows a strong reduction ointhe impacts to GWP and other impact categories except TETP and FETP. The comparison between the fuel cell hybrid tractor powered with GH2 and that using grey hydrogen shows a worsening of the performances in almost all the impact categories except for GWP and FFP.
Martinez-Ramon et al. [122]	2024	Evaluating the environmental impacts and identification of the hotspots in the production of hydrogen from biogas by means of chemical looping dry reforming methane technology and compared with the green hydrogen performances (3.38 or 3 kg of CO2 eq./kg of H2).	Life cycle assessment	The results showed that the contribution to GWP is 10.76 kg CO2 eq./kg of hydrogen while the potential contribution to the other impact categories are: 3.19E-02 kg mol H+ eq (AP), 1.35E-04 kg PO4-3- eq. (FEP), 7.81E-06 kg Sb eq. (ADP), 9.92E-08 kg CFC-11 eq. (ODP), 4.52E-02 kg NMVOC eq. (POFP). The contribution to GWP, in particular, is well above 3 kg and cannot be qualified as GH2 according to the Commission Delegated Regulation (EU) 2021/2139 of 4 June 2021. The contribution to GWP is dominated by the processes related to biogas production while the contributions to ADP are mainly caused by the production of copper and other metals used for the two catalysts (LTS and HTS).
Mertens et al. [143]	2024	The commentary focused on the analysis of mitigation strategies for reducing the supply chain risks vulnerability with regard to critical raw materials needed for the production of solar photovoltaics, wind turbines, Li–Ion batteries, and water electrolysers.	Critical raw material analysis	The mitigation strategies comprise material efficiency, material replacement, recycling and eco-design, relocation of mining activities, and renewable production activities. The analysis showed that the highest supply chain risk is for solar PV because of the important role of China in the manufacturing of solar PV panels.
Mio et al. [109]	2024	Assessment and comparison of the impacts of different methods for hydrogen production with the goal of identifying the most environmentally sustainable performance: GH2 from water electrolysis with renewable electricity, grid hydrogen produced from water electrolysis and grid electricity, grey hydrogen from steam reforming of natural gas, blue hydrogen by steam reforming of natural gas and carbon capture and storage. The analysis considered the Energy Return on Energy Invested, the levelised cost of hydrogen and LCA assessment. The study evaluated the use of hydrogen for 2 trips per day of a medium size ferryboat to navigate full electric for 7 h in the Adriatic Sea.	Life cycle assessment, energy and costs analysis	The analysis showed that GH2 produced by water electrolysis and renewable electricity (from floating solar OV system) achieved the best performances both with regard to the energy indicators and GWP (4.32 kg CO2 eq./kg of GH2 versus 1.26E+01 kg CO2 eq./kg of grey hydrogen and 2.35E+01 kg CO2 eq./kg of grid hydrogen), even if further improvement should be considered to reduce the impacts beyond the GWP such as that related to FETP, METP, TETP, HTP, ODP, SOP, LOP, and WCP. For these impact categories, the impacts of GH2 production are higher than blue and grey hydrogen, while that of WCP is greater than the grid hydrogen.
Nhien et al. [106]	2024	Potentiality of wind–fuel cell hybrid systems in providing an adequate energy supply. Focus on the efficient hydrogen production/storage/use to minimise energy costs and maximise the renewable use in the local electricity grid.	Energy, environmental, and cost analysis	The optimal plant configuration for renewable and GH2 production and the best geographical locations are identified. Calculated the potential annual electricity generation and benefits in terms of avoided CO2 emissions and the created new green spaces.
Oyewole et al. [98]	2024	The study evaluated the techno-economic viability of an energy system based on renewables (wind and solar PV), used as a peaker plant and an on-site GH2 refuelling station. This way, the complementarity of both technologies in the energy systems helps to mitigate the high costs of production of GH2 that would have been incurred in a standalone station.	Techno-economic and environmental analysis	The assessment of the energy system was performed for three selected cities and showed itself to be a viable option for producing electricity and hydrogen fuel. The levelised cost of hydrogen at Johannesburg, Pretoria and Cape Town for a 2 MW grid resulted in 74.2 $/MWh, 76.3 $/MWh and 50 $/MWh, respectively, and are competitive with the LCOE of natural gas plants generally used as peaking plants. The results also showed the CO2 equivalent emissions and the related carbon taxes ($) avoided for the energy systems in the three cities. The LCOE of hydrogen at Johannesburg, Pretoria and Cape Town energy systems resulted in 5.85 $/kg, 5.97 $/kg, and 4.45 $/kg, respectively.
Patel et al. [111]	2024	The goal of the study was the comparison of the climate change impacts and their main influencing factors of different hydrogen production pathways such as: grey hydrogen (steam methane reforming with natural gas), blue hydrogen (steam methane reforming and carbon capture and storage of released CO2), turquoise hydrogen (pyrolysis with natural gas), and GH2 (PEM electrolysis and a mix of renewable electricity from solar and wind). Scenarios of natural gas delivered by Russia by pipeline and from the USA by means of LNG. The study also investigated the factors that drives the contribution to GWP.	Life cycle assessment	The results indicate that GH2 generate the lowest potential contribution to GWP (0.6 kg CO2 eq./kg H2 using wind power and 2.5 kg CO2 eq./kg H2 with solar PV power) compared to the other hydrogen pathways. Grey hydrogen potential contribution resulted in 13.9 kg CO2 eq. per kg H2. The delivery by LNG option has higher impacts compared to the pipeline route for all the hydrogen pathways. The study pointed out the relevance of including the upstream processes related to natural gas and LNG life cycle since they affect the environmental impacts of grey and blue hydrogen and the comparison with GH2.
Pellegrini et al. [105]	2024	Analysis of the techno-economic and environmental impacts sustainability of integrating a solar photovoltaic to an electrolyser within an aluminium fluoride production plant. In particular, the goal was to assess the costs of converting natural gas to GH2 for one of the burners of a chemical plant.	Techno-economic and environmental analysis	The proposed solution showed itse;f to be technically feasible and beneficial for the environment in terms of reduction of CO2 and other pollutants, as well as reduction of energy consumed both from the use of renewables and GH2. In financial terms, the investment has a high payback period and a low profitability. The analysis also showed that energy efficiency certificates are not adequate to support the investments for GH2, while the support up to 4.5 Euro/kg provided within the EU Hydrogen Bank Action would be more suitable. (https://ec.europa.eu/commission/presscorner/detail/en/ip_23_5982 (accessed on 19 May 2025).).
Revinova et al. [47]	2024	Reviewed the literature investigating the environmental and economic impacts of hydrogen storage and transportation technologies.	Literature review	The analysis reveals that salt cavern and transportation by pipeline are the most economically competitive for transport hydrogen over long distances. Hydrogen stored and transported in gaseous form and by pipeline has lower impacts compared to other ways of storage and transport.
Rodrigues et al. [40]	2024	Evaluation of the potential role and impacts of GH2 development in southern Africa also by means of a case study of a stand-alone application	Causal network approach, interviews	Africa has a good potential of producing GH2 for the country and for exports due to its potential of producing GH2 by using electricity from solar PV. Some African countries such as South Africa have already introduced policies in favour of GH2 development. The concept of “agrivoltaic” is proposed to meet the food–energy–water nexus. The viability and impacts of GH2 and its storage capacity in stand-alone energy systems and agrivoltaic has to be evaluated in future research.
Saha et al. [34]	2024	Assessment of hydrogen production methods and the ecological and financial impacts of three key hydrogen colors (grey, blue, and green).	Literature review	The review underscored the relevant role of hydrogen in decarbonising energy systems and, in particular, industrial and transport sectors as well as contributing to the stability of the energy systems by means of energy storage. Future development of hydrogen depends on the technological progresses, reduction of the costs, particularly that of GH2, and the supporting policies and regulations.
Sayer et al. [147]	2024	The study analyses the environmental impacts and costs of four production pathways (grey, blue, yellow, and green) and two transportation modes (by pipeline and by ship) for the delivery of hydrogen from North Africa to Europe. The goal is the identifying the production pathway of hydrogen with the lowest impacts and costs.	Environmental and cost analysis	The production of grey hydrogen has the lowest total costs compared to the other options but it is more appropriate to consider in the accounting the externalities in terms of CO2 emissions. The environmental assessment shows that GH2 produced using wind electricity and imported from Tunisia (1.39 kg CO2 eq./kg H2) and GH2 produced using solar PV electricity imported from Morocco (1.16 kg CO2 eq./kg H2) have the lowest emissions compared to grey (12.49 kg CO2 eq./kg H2), blue (9.24 kg CO2 eq./kg H2), and yellow hydrogen (5.76 kg CO2 eq./kg H2) produced locally. In actuality, GH2 produced locally is assumed to generate zero CO2 emissions and would be the best option from an environmental point of view. The emissions considered in this study are the emissions related to the production of hydrogen, the upstream emissions, and that of transport in case it is imported (in agreement with the Directive 2018/2001, which states “Electricity qualifying as fully renewable according to the methodology set out in Directive 2018/2001, shall be attributed zero greenhouse gas emissions”.
Sebbagh et al. [26]	2024	Evaluation of a wide range of aspects concerning GH2 from its production by means of electrolysis process and PEM, AEL, and SOEC electrolysers, benefits and costs, applications, environmental and economic analysis, and policy measures.	Literature review	LCA as a key tool for policy decision making, particularly when considering cradle to cradle or cradle to grave boundaries of analysis. ISO/TS 19870:2023 https://www.iso.org/standard/65628.html (accessed online 19 May 2025) standard specifies how to assess the GHGs emissions associated to the life cycle of hydrogen. GH2 has advantages in terms of lower carbon footprint compared to the other hydrogen colours, but it is important to consider that the electrolysis process requires a great amount of electricity and water. Advancements in the process and more efficient electrolysers are needed. Emissions should be accounted in the whole life cycle, taking into account storage and transport of the hydrogen, while other impacts such as land use and habitat loss are due to large-scale development of renewables. LCAs should be comprehensive and consider land use change and biodiversity loss besides the contribution to GWP.
Shen et al. [112]	2024	Evaluation of the climate impacts and the other environmental impacts of a hydrogen economy for the EU energy system and its climate goals, comparison of the climate impacts of different hydrogen pathways (GH2, blue and others), assessment of the impacts in monetary terms, and comparison between GH2 and blue hydrogen production.	Life cycle assessment	The comparison of the life cycle climate impacts among grey, half-blue, blue, and GH2 shows that the impacts of the latter are much lower than that of the other hydrogen production pathways. The impacts of GH2 production are mainly due to the electricity supply compared to the other pathways where most of the impacts are associated to the process and natural gas supply. The contribution of GH2 production is also lower when considering other impact categories such as resource use, ODP, and AP but not in the case of HTP (cancer effects), IRP (human health), land use, water scarcity, resource use, mineral and metals, and eutrophication potential (freshwater) compared to blue hydrogen.
Singh [43]	2024	Analysis on how India is approaching three key areas such as feedstock system, circular economy integration, and environmental impacts of hydrogen that are important for achieving the climate goals of the country.	Literature review	The analysis underscored the huge availability of feedstocks for GH2 production of India playing a key role in its hydrogen mission. The government is committed towards the green hydrogen mission putting at the centre the circular economy transition in all the sectors. India has set initiatives to implement the circular economy model while the transition toward the use of GH2 is at the beginning and requires political support. The CE framework suggests the elimination of GHG emissions from hydrogen production. However, it is important to support with stringent regulations and technological innovation the reduction of the GHG emissions. Green hydrogen will play a key role within the circular economy transition in reducing the GHG emissions necessary for the success of the hydrogen mission and the pursuing of the climate goals.
Singhla et al. [136]	2024	Analysis of the environmental and economic impacts of three types of hydrogen production pathways such as grey, blue, and green hydrogen and the barriers to the adoption of fuel cells.	Environmental and cost analysis	The study confirmed that the impacts of the hydrogen production pathway are influenced by the type of production process and the electricity source. The authors also suggested the importance of establishing a market for hydrogen in order to facilitate its trading. Ideally, it would be required a market for each hydrogen colour.
Sudalaimuthu and Sathyamurthy [21]	2024	Provided an overview of agro-waste for the production of GH2 and focusing on the thermochemical method of production.	Literature review	The review highlighted several findings such as, among others, the high energy content of hydrogen from agro-waste by gasification. The H/C ratio is high, supporting the use of agro-waste instead of fossil fuels for hydrogen production. Thermo-chemical process resulted in a viable option among the analysed processes for converting agro-waste to hydrogen. Cellulose and lignin as constituents of agro-waste contributed to deciding the reaction temperature of gasification and the reaction temperature directly related to energy efficiency, process design, and technological and economic feasibility.
Shaya and Glöser-Chahoud [28]	2024	Assessment of the LCA studies focused on hydrogen production technologies such as AWE, PEMWE, SOEC, AEMWE, their environmental impacts, and recent technological progresses.	Literature review	From the review of LCA studies emerged a variability of impacts on GWP across the four technologies for hydrogen production and, in particular, for PEMWE where the impacts range from 0.5 kg CO2 eq./kg of GH2 to 30 kg CO2 eq./kg of G H2. The impacts of hydrogen production are mainly affected by the source of electricity used for the electrolysis process, the efficiency of the electrolyser, and the materials used for its manufacturing. The use of renewable electricity can reduce the contribution to GWP as well as the advancement in the materials of catalysts and membranes. The review also offers an interesting analysis of the advantages and disadvantages of each water electrolyser technology with the inclusion of critical raw materials, technological maturity, operational lifetime among others. In this regard, AEMWE is the only one within the four analysed water electrolyser technologies that is critical raw materials free.
Simoes and Santos [13]	2024	The study adopted the framework of a SWOT (Strengths, Weaknesses, Opportunities, and Threat) analysis to investigate the current state of affairs of GH2 market.	SWOT Analysis	The main strength of GH2 is its low environmental contribution to GWP. Moreover, a further strength are the global policies that have incentivised over the years the transition towards more clean and renewable energy sources such as the UN Development Goals, the Paris Agreement, and the European Green Deal. Policies and regulations, programmes, strategies and roadmaps favouring the increased use of GH2 or hydrogen have been adopted in various countries such as Germany, Spain, Denmark, Japan, and Australia. However, internal factors related to the hydrogen technology and external factors are obstacles to GH2 development such as the lack of international standards, carbon taxes as the primary tool for supporting decarbonisation, the future development of renewable energies, and the associated environmental and social impacts, and the problem of scarcity of freshwater.
Tomos et al. [129]	2024	Comparison of the life cycle GHG emissions of several fuel options having the highest potential of reducing the contributions to GWP such as green and blue hydrogen, green and blue ammonia, e-methanol, bio-methanol, fatty acid methyl ester (FAME) biodiesel, and bio-methane. All these alternatives are compared to heavy fuel oil that is mainly used in international shipping.	Life cycle assessment	The results show that GH2, FAME biodiesel, and bio-methanol generated the lowest impacts to GWP compared to the other alternatives. These fuels have the best decarbonisation potentials. However, the use of these alternative fuels is still very low and there is a lack of initiatives aimed at accelerating their use, undermining their potential of decarbonizing on time the international shipping fleet.
Torrubia et al. [60]	2024	Evaluation of the impacts of copper recovery in three cases of easte electrical and electronic equipments, WEEE (scraps, mix, and waste printed circuit boards), through three scenarios: conventional, green hydrogen, and hydrogen from grid electricity in order to assess for the last case the impact of electricity mix for the production of hydrogen.	Life cycle assessment	The results show that the carbon footprint of copper recovered from WEEE is much lower than the carbon footprint of primary copper. The contribution to GWP from the recovery of copper in WEEE is further reduced by using GH2 produced from renewable electricity from the grid (wind power) compared to the scenario where the electricity from the grid is produced from non-renewable energies.
Wang et al. [29]	2024	Analysis of the evolution and development of policies supporting GH2 policies in the United States, the European Union, Japan, and China, and technological progress of electrolysis process from renewables as well as of GH2 produced from solar PV and wind. The study also integrates the environmental, social, and economic benefits of the different hydrogen pathways.	Literature review	The USA has been the first to introduce policies supporting hydrogen development, but all the four investigated areas/countries can be considered early adopters of hydrogen policies worldwide. Moreover, they all have strategies and goals for incentivising GH2 adoption. The results from the reviewed studies confirm that GH2 from wind electricity generate the lowest contribution to GWP and AP and low energy costs (785 g CO2 eq./kg H2 and 10.5 MJ/kg of H2) while hydrogen produced by using wind and solar electrolysis had the highest economic costs. Out of the electrolyses technologies, AWE has advantages in terms of costs, maturity and wide application while PEM is adaptable to the variability of renewables but has high costs limiting its wider development. SOEC and AEM are still in the research and demonstration phase and have not yet been commercialised.
Wei et al. [117]	2024	Comparison of the environmental emissions of four water electrolysers technologies such as AEL, AEM, PEM, and SOE. The assessment also expands on the materials and energy used for the manufacturing of each electrolyser technology for identifying their environmental contribution.	Life cycle assessment	The results reveal the impacts to the investigated impact categories generated in the manufacturing process of each water electrolyser technology as well as the factors that mainly contribute to the impacts of the production of hydrogen and the operativity of the electrolyser system. The results reveal that in the manufacturing process of the electrolysers materials such as nickel, steel, and platinum mainly contribute to most of the investigated impact categories. For example, in AEM, the bipolar plate is mainly made of steel and the latter contributes to almost 80% of the contributions to CC. With regard to the impacts at a system level in the operation stage, the results evidenced that the lowest impacts come from the production of GH2 by AEM electrolyser using electricity from wind. On the contrary, AEL electrolyser with electricity from hydropower provided the highest contributions to CC. Further important categories considered in the LCA are: Human Health, Ecosystem Quality, and Abiotic Stock Resources.
Agostinho et al. [103]	2023	This LCA and Emergy Accounting study analyses the environmental impacts of replacing diesel with H2 produced by means of grid electricity (83% from renewables such as hydro and biomass) in urban buses. Emergy Accounting and life cycle assessment (LCA) are applied to obtain complementary environmental indicators.	Life cycle assessment and emergy accounting	The comparison of the hydrogen scenario (functional unit: km person) with other urban buses scenarios shows that the hydrogen scenario has worst performances compared to buses fuelled by diesel, electricity, LPG, and biodiesel in the fossil energy depletion category, but performs better compared to GWP, AP, and PMFP. The results by emergy accounting show that the operational stage requires 95.6% of the total emergy use with the highest shares as electricity (51.2%) and labor (44.4%). Hydrogen energy source has a higher renewability (41.49%) compared to diesel (0.05%) and biodiesel (18.83%), lower emergy loading ratio and higher emergy sustainability index.
Akhtar et al. [140]	2023	This study performs a cradle to gate social life cycle assessment pf hydrogen produced from water electrolysis by means of solar PV and wind electricity in 7 countries. The main goal is identifying the social hotspots in the GH2 supply chain. Moreover, a further goal is the comparison of the social hotspots with hydrogen produced from natural gas, and assess the impacts of GH2 on SDGs for policy purposes and future recommendations for a large-scale development of a GH2 economy	Social life cycle assessment	The results of the study show that the production of GH2 in South Africa presents the highest risks to most of the social indicators and in particular child labor, fair salary, unemployment, association and bargaining rights and gender wage gap. The risk in the other countries can be mitigated by avoiding the imports of the renewable and electrolysis technologies from other countries and manufacturing them domestically. The implications for policy regard the adoption of better working conditions and of international regulations in order to avoid that more polluting activities are exported towards developing and emerging countries.
Aravindan and Kumar [30]	2023	Overview of GH2 production from renewable sources (solar, geothermal, biomass, wind and technologies (e.g., water splitting: thermolysis, electrolysis and photolysis), production costs, environmental impacts and challenges in GH2 development	Literature review	The results include the analysis of studies evaluating the contribution to GWP of hydrogen from solar, wind, biomass and geothermal sources and available technologies. In overall, wind-based production of hydrogen resulted to provide the lowest contribution to GWP ranging according to the selected studies from the value of 600 g CO2 eq./kg of GH2 to 970 g CO2 eq./kg of GH2 . Production costs of GH2 from biomass were the lowest (1–3 $/kg hydrogen) while that of solar the highest (7–10 $/kg GH2). On the contrary the efficiency of solar and wind in GH2 production (70–80%) is the highest compared to biomass and geothermal (50–60%).
Arcos and Santos [83]	2023	Analysis and technical and economic comparison of the different hydrogen production pathways in order to understand their current feasibility	Techno-economic and environmental analysis	Grey, black/brown and blue hydrogen are the least environmentally friendly but those with the lower production costs (ranging from 0.67 to 2.05 USD/kgH2 respectively). Green Hydrogen is the most environmentally friendly but has one of the highest production costs ranging from 2.28–7.39 USD/kgH2. Yellow hydrogen resulted with the highest production costs (6.06–8.81 USD/kg H2) but these latter as the CO2 emissions depend on the location as well as on the electricity mix of the specific location.
Blohm and Dettner [54]	2023	Development of sustainability criteria for the production of GH2 in order to contribute to reinforce the social dimension of sustainability in hydrogen decision-making and base decision not only on the economic criteria.	literature review and Interviews	The proposed framework consists of 16 sustainability criteria developed over six impact categories (Environment, Basic Needs, Socio-Economy, Electricity Supply, Project Planning, Energy transition) and offer a useful framework for orienting decision making in the assessment of GH2 projects and strategies.
Boulmrharj et al. [135]	2023	Assessment of the techno-economic feasibility and GHG emissions of hybrid systems for the production of hydrogen and electricity required for public transport and street lighting in three cities in Morocco	Techno-economic and environmental analysis	The GHG emissions of the assessed hybrid systems configurations mainly derive from the use of the PV panels (74% of the total emissions) as well as from PEM electrolyzers and storage tanks and are lower in the second configuration due to the lower production of electricity. The GHG emissions per kWh produced are 0.017 kg CO2eq/kWh on average and are lower than the GHG emissions of the national grid. The financial analysis shows that the profitability of the proposed system depends on the size of the city in the case of the second configuration. Further factors that affect the financial performances are the capital costs, income tax, the hydrogen and oxygen selling prices.
De Kleijne et al. [113]	2023	Assessment of how the impacts in terms of GHG of GH2 are influenced by three factors: the (future) electricity source; the multi-functionality approach; the grey or blue hydrogen benchmark for comparing the emissions. The focus is on the production of GH2 by water elecrolysis (PEM electrolyser considered more efficient and less material intensive than AEL electrolysers)	Life cycle assessment	Off-shore wind based GH2 resulted to have the lowest GHG footprint ranging from 0.4–0.8 kg CO2eq./kg of GH2. Hydrogen produced by using the electricity from the grid of the EU 2020 resulted to have GHG emissions in a range 6.3–16.6 kgCO2eq./kg H2 with the maximum value higher than grey hydrogen. The authors also investigated if the production of GH2 is the best use of renewable electricity founding that alternative uses of electricity could have the priority over the production of GH2 in case of maximisation of the climate benefits. In the case of additional renewable capacity GH2 has better environmental performances than fossil-based hydrogen. GH2 “can be produced, when combined with hydrogen storage, when demand for renewable electricity elsewhere is low. This leaves opportunities for hydrogen production in areas with large renewable energy potentials, including renewable capacity without grid connection”. The authors also found that the GHG intensity of the electricity mix mainly affect the variation in the GHG footprint.
Goren et al. [35]	2023	Aims to evaluate the environmental and economic impacts and efficiency of H2 produced from various feedstocks (fossil, biomass and water) as well as advantages, possible drawbacks and future directions for thermochemical and biological H2 production processes	Literature review	The results show that methods using biomass as feedstock for hydrogen production (photo-fermentation, dark fermentation and microbial electrolysis cell) are more environmentally sound compared to the others using fossil fuels as feedstock. In particular, photo-fermentation resulted with the lowest contribution to GWP (1.88 kg CO2 eq./kg H2) and AP (0.003 gSO2/kg H2). The high consumption of water in the conventional electrolysis process (about 9 kg of water consumed for 1 kg of hydrogen) can be reduced by using hydrogen as a fuel in the fuel cell systems and converted back to water and generating electricity. However, their analysis show that hydrogen produced from fossil fuel-based (e.g., coal) gasification and steam-methane reforming processes has costs advantages compared to hydrogen from water electrolysis while the process efficiency of water electrolysis is slightly lower than that of the process of steam reforming of natural gas and biomass.
Hren et al. [36]	2023	Comparative analysis of the environmental impacts (GHG, AP and EP) and energy footprint of 11 technologies for the production of hydrogen and storage and transport stages	Literature review	The analysis of the GHG footprint of the technologies for hydrogen production reveals that the lowest contribution comes from glycerol and alcohol waste steam reforming and water electrolysis but using electricity from the EU27 mix the highest GHG emissions are associated to the water electrolysis process. The latter has also the highest values for the energy footprint indicator while for acidification and eutrophication the values are similar to that of natural gas steam reforming and higher than glycerol and alcohol waste steam reforming technologies that reported the lowest values. Regarding the storage, the gaseous hydrogen resulted with a lower GHG footprint than liquified hydrogen while the transport of gaseous hydrogen by pipeline had the smallest GHG footprint.
Incer-Valverde et al. [31]	2023	Review of the different hydrogen colors, their environmental impacts and costs in order to enhance their communication and understanding.	Literature review	The most current known hydrogen colours refer to green, grey and blue. Worldwide the National Plans, Strategies or Roadmaps on Hydrogen are mainly based on a mix of these colours or only on one of them (green or blue). For example, India, Spain and Sweden National Plans are based on the development of Green Hydrogen. The analysis also shows the carbon intensities of the hydrogen colours and costs showing an inverse relation between the carbon intensity and costs of each hydrogen colours. Grey, black and brown have the highest carbon intensity and the lowest production costs.
Lagioia et al. [10]	2023	This narrative literature review focuses on the analysis of production technologies of blue and green hydrogen as well as their management and applications in view of the hydrogen goals of the EU	Literature review	Green hydrogen is the only type that could play a role in the future decarbonisation scenarios. For this to happen, blue hydrogen could pave the way to GH2 but there are uncertainties related to the development of CO2 carbon capture. GH2 produced by electrolysis is a mature technology. However, GH2 is also constrained by the availability of a surplus in the demand of electricity from renewables. The supply chain of GH2 should also be strengthen along with the use of certification schemes for CO2 emissions. In order to meet the future targets of the EU for hydrogen the authors suggest the acceleration of investments in hydrogen innovation and its use in hard-to-abate sectors rather than , for example, in light-duty transport where hydrogen use is considered not efficient.
Maciel et al. [139]	2023	Assessment of the GHG emissions and contribution to GWP of hydrogen produced by water electrolysis using electricity from wind, solar and hydro sources.	Environmental analysis	The study found that GH2 produced by hydroelectricity has the lowest contribution to GWP followed by wind and solar PV. The analysis of the life cycle of electricity from the three sources show that relevant for wind source is the contribution of steel to the impacts since it is used for the production of the rotor and the tower while for solar PV the elaboration of silicon wafers in electronic degree is the least efficient stage and for hydro the main impacting factor is the reservoir while the dam in the case of Small Hydroelectric Centre and the use of concrete and steel used in the construction stage.
Maddaloni et al. [144]	2023	Analysis of the use of four different streams of treated municipal wastewaters as feedstock for SOEC electrolyser.	Environmental analysis	The simulation analysis shows that two of the wastewater streams could be effectively evaporated and treated within the cell without generating waste liquids containing excessive pollutant concentrations. The energy efficiency of the electrolysers achieved a value of 85% that is comparable to that of the other types of electrolysers such as PEM and AEL.
Marouani et al. [146]	2023	Analysis of the concept of GH2 and its production process in several countries having a relevant potential of GH2 production such as Australia, the European Union, India, Canada, China, Russia, the United States, South Korea, South Africa, Japan, and other nations in North Africa.	Environmental and cost analysis	GH2 development has many benefits but many challenges to face. The article focuses on many aspects that are important to take into account for its integration in the future energy systems such as the environmental impacts, the technological progresses, the development of the infrastructures for its storage and delivery, the necessary policy frameworks for accelerating the investments in hydrogen technologies and support its demand, financial viability, and workforce transition.
Pawlowski et al. [118]	2023	Calculation of the carbon footprint and financial indicators of GH2 produced by water electrolysis and AEM technology using electricity from solar PV panels. The PV plant with 5 MW of peak power is located in Poland.	Life cycle assessment and life cycle costing	The carbon footprint resulted comprised between 2.73 and 3.85 kg CO2 eq./kg H2. The financial analysis evidenced that the investment in the project is sustainable only in the presence of external subsidies. In this case, the net present value is positive and the payback period is 8 years.
Squadrito et al. [46]	2023	Overview of the state of the art of hydrogen production technologies, and exploration of the most relevant geopolitical and economic aspects and implications of the hydrogen economy development, including the water aspects.	Literature review	The study points out the need for achieving a balance between distributed hydrogen systems and centralised systems and considering the advantages of producing GH2 locally, where it is water neutral (and CO2 neutral), compared to the production of GH2 for the external market where transport generates carbon emissions. Further, the energy and costs of producing GH2 from non-traditional water sources such as e.g., using wastewater would be lower compared to the production of GH2 with fresh water “Distributed hydrogen production is a powerful tool for maximising the social utility of the hydrogen economy, reducing household energy bills, increasing energy system efficiency and resilience, and reducing the environmental impact of city services. All these aspects must be considered in future energy policies”.
Vallejos-Romero et al. [50]	2023	Analysis of the research on GH2 from the perspective of social impacts and challenges	Literature review	Social impacts of the life cycle of GH2 from production to storage and transport as well as social and environmental impacts of GH2 on local communities and indigenous groups are under researched. In the investigated period Europe and Asia mainly contributed to the research on social impacts of GH2.
Weidner et al. [66]	2023	Assessment of the environmental impacts of different options to produce 500 Mt/yr of hydrogen involving green (from solar PV or wind power), blue and grey hydrogen pathways.	Life cycle assessment	The impacts to GW show the surpassing of the planetary boundaries for blue and grey hydrogen while not for green hydrogen produced by using wind electricity.
Zhang et al. [115]	2023	Identifying the most suitable and environmentally sound method for hydrogen produced from water electrolysis among the seven processes combining three types of electrolysers (AEL, PEM and SOEC) and onshore and offshore wind electricity	Life cycle assessment	The production of GH2 by using electricity from onshore wind and PEM electrolyzer technology generate the lowest contribution to GWP by 0.0936 kg CO2-eq. The impacts are also lower for such combination with regard to AP, ODP and EP impact categories.
Arsalis et al. [18]	2022	Critical comparison of several characteristics (service life, costs, recyclability, environmental impacts, safety issues, use and integration within energy systems) of two solar powered energy systems: Lithium–Ion Batteries (PV-LIB) and Regenerative Hydrogen Fuel Cell (RHFC) energy systems	Literature review	The comparative analysis shows that, for example, hydrogen (within RHFC subsystems) produced through water electrolysis can be stored in high quantities in hydrogen storage units. The RHFC is then more suitable for long-term storage than short-term storage, while LIBs are more suitable for short-term storage. The refuelling of RHFC subsystems is fast, requiring only a few minutes, while the recharging of a LIBs is slow and needs several hours. In terms of costs, those related to LIBs are much decreased within the last decade while in the case of RHFC the high costs of the electrolyzers and fuel cell stacks limits their larger development.
Barghash et al. [87]	2022	Evaluation of technical and economic feasibility of producing GH2 in Oman and exploration of the benefits of using treated effluent from wastewater treatment.	Cost–benefit analysis	The results of the study show the technical and economic feasibility of using treated effluents from wastewater for the production of GH2. Moreover, the selling of GH2 provides a source of economic revenue by which cover the initial investments costs.
Buffi et al. [39]	2022	Review of production pathways for producing hydrogen from biomass or biomass-derived sources (biogas, liquid bio-intermediates, sugars) while also focusing on their maturity level, as well as the energy and environmental performances of the production pathways emerged from LCA studies.	Literature review	The type of feedstock biomass influences the energy required for the process of hydrogen production. Energy requirements should be compared with each other under the same conditions of feedstock, production rates and environmental conditions. From the analysis of the LCA literature emerges that some of the studies followed the ISO standard while others proposed different methodological approaches. Moreover, LCA studies differ on the system boundaries ranging from cradle to gate to cradle to grave. There are also different allocation assumptions. Regarding impact assessment, most of the studies adopt midpoint assessment methods and impact categories such as GWP, AP and ODP.
Gandiglio et al. [132]	2022	Evaluation and comparison of the environmental impacts of electricity in the island of Ginostra produced by two energy systems: a diesel-based energy system (Reference scenario) and a proposed RES-based energy system (Renewable scenario). The study also aims to identify the processes or components that mainly contribute to the environmental impacts and evaluate the possible future improvements.	Life cycle assessment	The renewable scenario is composed of a solar PV plant and a hydrogen battery energy storage. The results (referred to a time horizon of 25 years) underlined that for the production of 1 kWh, the impacts are higher for the current diesel-based system for most of the categories investigated. Therefore, the renewable scenario improves the current scenario in such categories. The exceptions are for EP, freshwater; Ecotoxicity potential, freshwater; Water use and Resource use, minerals and metals where the impacts of the renewable scenario are slightly higher than the reference scenario.
Guareiro et al. [11]	2022	Overview of several aspects associated with GH2 including the sources for its production, regulation, typologies of storage, transportation, and final uses. Critical analysis of the economic and environmental impacts and the main challenges and opportunities it could have for chemistry.	Literature review	In terms of environmental impacts of GH2 production, the study shed light on the water required in the process (9 kg per kg of GH2). The water required for production of grey and blue hydrogen is half of that needed for GH2 production. The latter process is also much more energy-intensive and, currently, its production is not financially competitive. However, the authors, by reviewing the literature, also reported the results of studies performed in Brazil where the production of GH2 by using electricity from hydro and wind achieved production costs comparable to that of grey hydrogen. The study also underlined the need for increasing the capacity of electrolysers for the development of a future hydrogen economy.
Ishaq et al. [32]	2022	Analysis of the state-of-the-art hydrogen production processes using renewable energy sources and other sources, uses of hydrogen as a fuel, typologies of storage, transportation, distribution, and key challenges and opportunities for a wider development of Hydrogen.	Literature review	Hydrogen is getting increased interest beyond its conventional role in industrial sector for the production of ammonia and methanol since, for example, as a fuel, it offers the advantage of avoiding carbon dioxide emissions in the use stage. In particular, the production of GH2 by using electricity from renewable energies is considered the best option to overcome the intermittence of renewables. However, despite these advantages, there are many challenges for its large-scale adoption such as those related to the development of an environmentally clean production system for hydrogen at a large scale, as well as the development of the needed infrastructures for its distribution, storage systems for stationery and vehicle applications, and reduction of the production costs.
Lykas et al. [104]	2022	Analysis of energy, exergy, and financial performances of the production of GH2 from excess solar electricity in a Greek island.	Energy, exergy, and cost analysis	The analysis proposed a configuration involving a solar parabolic collector plant generating electricity and heat. The electricity in excess that cannot be received by the local grid is delivered to a PEM water electrolyser for the production of GH2. The latter is assumed to be compressed, stored in tanks, and eventually used as a fuel for vehicles or ferries. The results showed that the proposed system can satisfy the annual diverse energy needs of the island, producing 210 MWh and 2356.5 kg of GH2 with a good financial return, resulting in an investment payback period of less than 7 years and a positive net present value.

Note: The following have been extracted from the references of the selected articles and integrated to the articles retrieved from the search on Web of Science: [18,36,40,51,53,96,97,98,99,102,103,104,105,106,107,108,123,132,133,143].

of Appendix A have been extracted from the references of the selected articles and integrated into the articles retrieved from the search on Web of Science, because they have been considered useful for this study. The total number of articles is therefore 93. The latter are all listed on the basis of the year of publication in Table A2 of Appendix A and presented according to the author/s, main goal, method, and results.

Figure 1 shows that more than half of the selected articles consist of literature reviews and life cycle assessment studies. This latter method is, in some cases, combined to Life Cycle Costing or Emergy Accounting. The rest of the sample are studies that apply different methods, such as techno-economic and environmental analysis, environmental and cost analysis, and social life cycle assessment.

4. Results

4.1. Hydrogen and Green Hydrogen Production

Hydrogen is a very abundant element in the universe, composing 75% by weight according to [79], while also being widespread on Earth, where is never available in its molecular form (H₂) due to its high reactivity. Instead, it is a fundamental constituent of complex molecules of biological origin, organic salts, and water [80].

In order to separate hydrogen from the other elements, it must be “extracted” by providing energy (be it renewable, fossil, or nuclear) for the separation process leading to different economic costs and environmental impacts, depending on the source of extraction [9]. For this reason, hydrogen is considered an energy vector and not an energy source as with wind or solar [81].

Currently, most of the hydrogen worldwide is obtained by using fossil fuels as feedstocks, the processes of steam reforming of natural gas, and coal gasification [82]. Figure 2, listing the colours attributed to hydrogen according to the kind of energy needed for its production, shows that, in the case of both brown/black hydrogen and grey hydrogen, their production is accompanied with the release of CO₂ emissions. A fraction of the latter can be captured and stored underground in the production process of blue hydrogen [83].

Turquoise hydrogen is also produced from natural gas as blue and grey hydrogen but involves the process of methane pyrolysis, which produces turquoise hydrogen and solid carbon. The latter can be sold and reused in various production processes. Going further, red and purple/pink hydrogen are produced with electrolysis or thermochemical processes by using nuclear electricity [83].

Yellow hydrogen is obtained by means of the water electrolysis process driven by solar electricity, while GH₂ is also from water electrolysis driven by renewables other than solar. The carbon footprint of GH₂ approaches closer to zero compared to the other types of hydrogen derived from fossil fuels, which release CO₂ in the production stage [23,31,32,44,83].

For the purposes of determining the environmental impacts of hydrogen, it is appropriate not to limit the analysis of direct emissions in the usage stage, as shown in Figure 2. Therefore, when GH₂ is burned as a fuel in a traditional engine or in fuel cells, the upstream hydrogen production process should also be considered [31]. The impacts of these different steps will be further analysed in Section Policy and Practical Recommendations.

Renewable energies such as wind, solar PV, geothermal, hydro, tidal, and biomass can be used to produce the electricity required for the electrolysis process [32], as well as to decompose water into its constituent elements (hydrogen and oxygen): “Electrolytic water splitting is driven by passing the electrical current through the water, where conversion of the electrical energy to chemical energy takes place at the electrode-solution interface through charge transfer reactions in a unit called an electrolyzer. Water reacts at the anode to form oxygen and protons, whereas a hydrogen evolution reaction takes place at the cathode” [85].

Agricultural residues, by means of biological fermentation, electrolysis, and thermochemical processes, can also be used to produce GH₂. Residues have a relevant content of lignocellulose, leading to a higher H/C ratio compared to fossil fuels. For example, H/C of wood biomass ranges from 1.7 to 2, while that of bituminous coal comprised between 0.1 and 0.3 [21]. The higher the H/C ratio, the higher the energy efficiency of the fuel and the lower the CO₂ emissions from combustion [86]. Furthermore, GH₂ can also be derived from food and transportation industries.

Some authors have also highlighted the benefits of producing GH₂ by using part of the treated effluents from a wastewater plant for the production of GH₂ by water electrolysis and electricity produced from solar PV panels. In a case study located in Oman, the economic analysis, in particular, shows that reusing the wastewater instead of discharging it into the sea generates further revenues due to the selling of the produced GH₂. The revenues would cover the initial investment costs within a short amount of time [87].

Given the variety of renewable sources from which GH₂ can be produced, some authors suggested to further characterise the greenness of GH₂ into new colours such as “dark green” for GH₂ coming from the electrolysis process and “light green” obtained from other production approaches [46].

The European Commission has defined renewable hydrogen as a fuel of non-biological origin and identified two criteria to assess its renewability (additionality and temporal and geographic correlation). The first criteria: “Additionality ensures that increased hydrogen production goes hand in hand with new renewable electricity generation capacity. Hydrogen producers must therefore conclude power purchase agreements with new and unsupported renewable electricity generation capacity”. while the second ensure that hydrogen is produced “when and where renewable electricity is available to avoid the demand for renewable electricity for hydrogen production incentivize more fossil electricity generation” [88].

Some authors [89] underline that, in the transition to GH₂, the role of blue hydrogen is important since it could use the existing infrastructure of natural gas accelerating the general adoption of hydrogen. These authors have compared, by means of LCA, different pathways for the life cycle of blue hydrogen (obtained by the process of steam reforming and two new processes such as Partial Oxidation of Methane and Auto-Thermal Reforming) and found that the production of hydrogen via auto-thermal reforming and delivery of ammonia to consumers has the lowest contributions to GWP, i.e., 2.12 kg CO₂ eq./kg of hydrogen. The study also jointly evaluated the life cycle contributions to GWP of blue hydrogen pathways with that of GH₂ (produced with water electrolysis and electricity sourced by concentrated solar PV collectors) and found that the integration of GH₂ strongly reduces the impacts in all the considered pathways that provide H₂ as a final product.

Concerning the levelized production costs of the different hydrogens, in the year 2023, the costs of grey hydrogen by SMR was the most financially competitive in the EU (being 3.76 €/kg of hydrogen), while the average costs of blue hydrogen by SMR with carbon capture were 4.41 €/kg of H₂. Figure 3 shows the levelised production costs of GH₂ in the EU. These ranged from 4.13 €/kg of H₂ to 9.30 €/kg of H₂, with an average of 6.61 €/kg of H₂ and a median of 6.20 €/kg of H₂ [90].

It is also important to note that the levelized production cost is a financial indicator [91] and that the “lower” values of the indicators for grey and blue hydrogen do not account for the negative external costs related to the CO₂ released into the natural environment and the society involved in the production process. Conversely, the positive externalities, due to the avoidance of CO₂ emissions, are not accounted for in the “highest” value of levelized cost of production of GH_2. Therefore, the levelized production costs should be integrated by further analysis for a more comprehensive accounting of the social costs of the different hydrogens [92].

For the production of GH₂, four types of electrolysers were mainly analysed by the literature: proton-exchange membrane (PEM), alkaline water electrolysis (AWE), solid oxide electrolysis cell (SOEC), and anion exchange membrane (AEM) [9,45,48,83]. The latter are a less consolidated technology compared to the former three [9,83]. Each type of electrolyser has its advantages and limitations in terms of Faradaic efficiency, hydrogen purity, costs, and materials used for their manufacturing. For example, the PEM electrolyser has a high efficiency in terms of hydrogen produced per unit of electricity used in the reaction and achieves the highest purity (99.99%) compared to the other three, but its manufacturing requires precious and expensive materials such as platinum and iridium [9]. The high costs of the catalyst prevent a larger-scale application of the PEM electrolyzer [83]. AWE is made of less costly materials but has a lower efficiency and the hydrogen purity is lower (99.5%) [83].

The IEA [93] underlined those financial decisions for investments (FIDs) in carbon capture and storage involved in large-scale projects for the production of hydrogen from fossil fuels has grown, particularly in North America and EU in the year 2023. The IEA [93] also reported that FID for increasing electrolyser capacity have achieved 6.5 GW worldwide in the year 2024. China is emerging as an important player in electrolyser capacity, accounting about 40% of the global FIDs, and is further strengthening its manufacturing role, that is, 60% of the global electrolysers’ manufacturing capacity. However, final investments’ decisions for electrolysis projects have reached more than 2 GW in the EU as well, while in India, the decisions have reached a capacity of 1.3 GW.

4.2. Storage and Distribution of Hydrogen and Green Hydrogen

After production, the life cycle of hydrogen encompasses several processes before it can be used for its final applications. The latter affect the ways hydrogen can be stored and distributed [94]. Purification processes could be also required in case hydrogen is used, for example, in fuel cells. Hydrogen can be stored in different ways (liquid, compressed gas, or bounded in physical or chemical terms in a suitable solid-state material) and the choice of one method over the other depends on various factors such as the geographical location, weight constraints, the demand [94], costs, environmental impacts, and safety issues [47]. Therefore, each storage method has its advantages and disadvantages [47].

Currently, hydrogen is mainly stored aboveground in small and medium metal tanks by the industry in the form of compressed gas or in liquid form stored at very low temperatures (so-called cryogenic storage) [95]. Moreover, hydrogen is mainly produced and consumed on-site without the need to be delivered by transportations means or infrastructures [93]. The transport requirements could increase in the future due to the particularly higher demand of GH₂ and the need to link locations of GH₂ production where there is a high availability of renewable resources with locations where there is a demand for consuming GH₂.

Gas compression has the advantage of reducing the volume of hydrogen but entails high energy costs and the use of cylinders that can safely support high pressures, which are typically made of high-cost materials [94]. There is an increasing interest in storing large quantities (up to several tons) of hydrogen in gaseous form in unused geological repositories [11,47,94]. Underground storage of hydrogen in gaseous form in salt caverns, aquifers, depleted hydrocarbon deposits, as well as in specially designed rock caverns, is possible for hydrogen at pressures up to about 150 bar [94]. Salt caverns, in particular, have proven to be a viable storage solution [11,47] and are used to store hydrogen in the United States and United Kingdom [93].

The distribution of hydrogen as compressed gas or in liquid and solid forms on the road by truck is considered optimal for small stations [94] and is the most common distribution means today [82]. However, this option seems to have a higher environmental impact compared to the pipeline distribution [47].

The transport of hydrogen as compressed gas or in liquid and solid forms by ship might be a cost-efficient solution for hydrogen (in the form of ammonia, methanol, and LOHC or liquid hydrogen) over long distances [93], but this transport option has not yet achieved a commercial scale and has the disadvantage of relevant energy losses [61]. Ideally, the distribution in pipeline networks under a gaseous state seems essential in the future and in view of the potential large-scale use of hydrogen [47]. The EU is supporting the development of hydrogen infrastructure by means of the European Hydrogen Backbone [95]. The latter is an initiative joining together 33 energy operators in the field of energy infrastructures. The mission is speeding the decarbonisation of the EU while recognising the relevant role of hydrogen infrastructures (existing and new ones) in driving the development of a pan-European, low-carbon hydrogen market [95].

In this regard, the existing natural gas distribution networks could serve for the transport of hydrogen–natural gas blends or pure hydrogen [47]. In this case, the distribution of hydrogen up to distances of 2500–3000 km at quantities of hydrogen above 200 kt per year seems the less costly way of distribution for repurposed pipelines; currently, about 5000 km of hydrogen pipelines are already functioning around the world [93]. However, in the case of dedicated new pipelines, they require very high capital investments [47].

Finally, some authors have analysed and compared the performances of hydrogen batteries [96] and fuel cells and lithium–ion batteries [18] for storing energy for short and longer periods in PV solar systems [96]. Hassan et al. [96] compared lithium–ion batteries and hydrogen batteries while considering their technical and financial performances. Their results seem favour the lithium–ion batteries that would also have better financial performances due to the lower payback period compared to hydrogen batteries. However, green hydrogen batteries have a longer service life for a longer energy storage than lithium–ion batteries [18].

4.3. Final Uses of Hydrogen

Figure 4 shows that hydrogen can be used for the following three main purposes:

• Fuel for the most adopted transportation means such as cars, buses, airplanes, trains, and tractors [97]. As a fuel, it can also be stored for electricity production in order to help satisfy the peak demand [98].
• Production of heat needed in industrial processes and residential and commercial buildings [97]. In particular, the use of GH₂ in “hard-to-abate” systems would be relevant, i.e., in industrial sectors where electrification is technically difficult and not very competitive. This is the case with the production of steel, ceramics, or cement, as well as in the chemical industry and foundries. These sectors need a large amount of energy, and it is difficult to reduce their GHG emissions [99].
• Raw material for the production of chemicals such as ammonia (needed for the production of fertilizers) and methanol used in the chemical industry to produce other compounds, fuels, and additives [22,82,97], as well as in refineries to remove impurities and upgrade heavy oil fractions into lighter products [22,82].

In the year 2023, the data from [100] provided evidence that hydrogen consumed in the EU amounted to 7.9 Mt. The highest share of total hydrogen demand was used by refineries (57%) and by the ammonia industry (25%). Globally, these two sectors accounted for 82% of all the hydrogen demand. The rest of the hydrogen is used in the chemical industry (11%) and other industrial uses (3%) and emerging hydrogen applications (less than 0.1%) as clean hydrogen in mobility, steel production, and e-fuels [93].

4.4. Case Studies of Application of Green Hydrogen

Table 2. Features of GH₂ case studies from literature.

	Authors and Geographical Scale	Case Study Goal	Key Findings	Success Factors	Limitations
Industrial processes involving GH2	Pellegrini et al. [105], Cagliari (Italy)	Analysis of the techno-economic sustainability of integrating a solar photovoltaic to an electrolyser within an aluminium fluoride production plant. In particular, the goal is assessing the costs of converting natural gas to GH2 for one of the burners of a chemical plant.	The proposed solution showed itself to be technically feasible and beneficial for the environment. In financial terms, the investment has a high payback period and a low profitability. The analysis also showed that energy efficiency certificates are not adequate to support the investments for GH2, while the support up to 4.5 Euro/kg provided within the EU Hydrogen Bank Action would be more suitable. https://ec.europa.eu/commission/presscorner/detail/en/ip_23_5982 (accessed on 19 May 2025). )	The research performs an important first step in the evaluation of the environmental and techno-economic viability of introducing GH2 in hard-to-abate industries where there is the potential of achieving relevant reductions of CO2 emissions.	The main limitation of the investments in power-to-hydrogen integration are the lack of financial feasibility. In that regard, further analysis are needed to explore more comprehensively the socio-economic benefits of such investments.
	Torrubia et al. [60], Germany	Evaluation of copper recovery in three types of waste electrical and electronic equipments, WEEEs (scraps, mix, and waste-printed circuit boards), through three scenarios for shredding, reduction, and oxidation, fire refining and electrorefining. The first one is driven by power from fossil fuels, and the second and third ones by GH2 from renewable (wind) electricity.	The results show that the carbon footprint of copper recovered from WEEE is much lower than the carbon footprint of primary copper. The contribution to GWP from the recovery of copper in WEEE is further reduced by using GH2 produced from renewable electricity from the grid (wind power) compared to the scenario where the electricity from the grid is produced from non-renewable energies.	The study shows the environmental benefits to GWP and other impact categories coming from the recycling of copper and the use of GH2, underscoring the central role of energy transition and renewable energies in the CE model and transition.	The development of GH2 is facing several challenges and, therefore, the results of the study are conditioned by the improvement of the technical and economic viability of GH2 production, storage, as well as the limitations of renewable energies.
USE of GH2 as a fuel for transport	Kugemann and Poladis [107], Gotland (Sweden)	The study developed a new integrated Multi Criteria Decision Analysis framework to classify several alternative fuel buses on the basis of technical, environmental, social, and economic dimensions.	The analysis assessed seven types of fuels for buses (bioethanol, biodiesel, biogas, plug-in hybrid electric biodiesel, plug-in hybrid electric biogas, battery electric, and hybrid electric hydrogen fuel cell). The results provide evidence that the most preferred fuel is biogas (particularly those produced by waste resources) and as buses that of Plug-in hybrid electric biogas. Battery electric and hybrid electric hydrogen fuel cell resulted in interesting alternatives from the perspective they are produced locally. However, even when assuming a further development of wind capacity and the improvement of the capacity of GH2 towards the achievement of energy self-sufficiency, as well as the use of subsidies to support the development of GH2, the most preferred option is for biogas as a fuel.	The study has been tailored on the basis of the local needs of the island and identified the most important aspects improving the awareness of the alternatives for buses and fuels. The analysis also enriched the evaluation process by enhancing the understanding of the different opinions of the stakeholders participating to the analysis.	Lack of standardisation of the method, particularly with regard to the social criteria and the focus of the latter dimension on negative impacts rather than positive. The analysis examines only some alternative buses and fuels most viable for the island. The ranking is based on individual preferences.
	Agostinho et al. [103], Brazil	This LCA and emergy accounting study analyses the impacts of replacing diesel with H2 produced by means of grid electricity (83% from renewables such as hydro and biomass) in urban buses. Emergy accounting and life cycle assessment (LCA) are applied to obtain complementary environmental indicators.	The comparison of the hydrogen scenario (functional unit: km person) with other urban bus scenarios shows that the hydrogen scenario has worst performance compared to buses fuelled by diesel, electricity, LPG, and biodiesel in the fossil energy depletion category, but performs better compared to GWP, AP, and PMFP. The results by emergy accounting show that the operational stage requires 95.6% of total emergy use, with the highest shares being electricity (51.2%) and labour (44.4%). Hydrogen energy source has a higher renewability (41.49%) compared to diesel (0.05%) and biodiesel (18.83%), with lower emergy loading ratio and higher emergy sustainability index.	The study focuses on LCA and Emergy, considering them as individually and complementary to avoid the so-called “entropy trap” and trade-offs between the results of the LCA and that of emergy accounting.	The limitations reported by the authors regard the boundaries of the system that do not include the end-of-life for the materials or components such as batteries. Moreover, there is still a lack of LCA studies and emergy accounting research on the topic, preventing a broader discussion of the results of the study.
	Martelli et al. [101], Italy	Analysis and comparison of the life cycle impacts of a traditional diesel-powered tractor, a fuel cell hybrid tractor using grey hydrogen and a fuel cell hybrid tractor powered by GH2.	The fuel cell hybrid tractor shows much lower impacts in all the investigated impact categories with the exception of FFP, where the impacts, compared to the traditional tractors, are lower by 4.55%. In the life cycle of a traditional tractor, the most critical step is the use stage, while in the fuel cell tractor is the manufacturing stage. The comparison with the fuel cell hybrid tractor using GH2 with the traditional tractor shows a strong reduction of the contributions to GWP and other impact categories except TETP and FETP. The comparison between the fuel cell hybrid tractor powered with GH2 and that using grey hydrogen shows a worsening performance in almost all the impact categories except GWP and FFP.	The literature still lacks a complete LCA from cradle to grave, and this study covers this void by improving the knowledge on the impacts of replacing traditional diesel-powered tractors with alternatives based on GH2 and fuel cells.	Future research should further explore the impacts following the adoption of further mitigating strategies such as the design of fuel cells, the use of more sustainable materials and energy mix for GH2 production.
Techno-economic viability of integrated processes of production and use of GH2 from renewable sources	Bonesso et al. [108], Southern Italy	Analysis of the levelized cost of energy of GH2 produced from an electrolysis plant with electricity sourced by wind. Perception of GH2 suitability in citizens, assessed by means of a questionnaire survey.	The levelized cost of hydrogen resulted in 3.60 euro/kg of GH2 in the base scenario, while in the alternative scenarios, it comprised between 3.20 and 4 euro/kg of GH2. The sensitivity analysis revealed that the most significant factor influencing the LCOH is the capacity factor. Most of the respondents (72%) of the sample appeared to not know the difference between green and blue hydrogen. In the sample, those with the highest knowledge on hydrogen production were men of 35 years of age. However, provided the required knowledge about blue and green hydrogen, the respondents showed an increasing willingness to pay for the installation of the plants.	The study provides important information to policy makers and other stakeholders about the role of GH2 in contributing to more sustainable and flexible energy systems.	One of the limits is that the methodological approach does not include the analysis of the environmental sustainability of GH2 produced in the case study. Large-scale projects could require the verification of the results with a live experiment.
	Oyewole et al. [98], Johannesburg, Pretoria and Cape Town (South Africa)	The study evaluated the techno-economic viability of an energy system based on renewables (wind and solar PV) used as a peaker plant and an on-site green hydrogen refuelling station. The goal is to reduce the electricity costs of the system and amplify its reliability.	The assessment of the energy system was performed for three selected cities and showed itself to be a viable option for producing electricity and hydrogen fuel. The levelized cost of electricity at Johannesburg, Pretoria and Cape Town for a 2 MW grid resulted in 74.2 $/MWh, 76.3 $/MWh, and 50 $/MWh, respectively, and competes with the LCOE of natural gas plants generally used as peaking plants. The results also showed the CO₂ equivalent emissions and the related carbon taxes ($) avoided for the energy systems in the three cities. The levelized cost of hydrogen at Johannesburg, Pretoria and Cape Town energy systems resulted in 5.85 $/kg, 5.97 $/kg, and 4.45 $/kg, respectively.	The analysis showed the environmental and economic benefits of optimising the urban energy systems with the use of GH2. The proposed solution based on the complementarity of both technologies helps to mitigate the high costs of production of GH2 in a standalone station.	There are some methodological limits due to the assumptions made in the modelling of the study. For example, the progressive ageing of the components before the achievement of the service life is not considered in the model.
	Currie et al. [102], South Australia	Assessment of the financial viability of integrating GH2 in an electrical grid of South Australia, enabling the presence of a higher share of renewable energies in the electrical system.	The analysis confirmed that GH2 would improve the reliability and security of the electricity system in the presence of wind and solar variability or in the impossibility of storing the surplus energy from these sources in an efficient way. GH2 would be produced in gaseous form by using surplus renewable electricity, a water aquifer, and a PEM electrolyser. The electricity would be produced by means of a gas turbine and be sent back to the grid. However, considering only financial indicators, the proposed project would not be viable, requiring economic subsidies.	The research shows how to improve the seasonal storage of the electrical system and through this, its reliability in satisfying the demand of electricity.	The study underlines limitations in the modelling of the research, such as the assumed storage type, data availability, and the limited focus on financial costs disregarding environmental and social impacts.
	Lykas et al. [104], Kythnos (Greece)	Analysis of energy, exergy, and financial performances of the production of GH2 from excess solar electricity in a Greek island.	The analysis proposed a configuration involving a solar parabolic collector plant generating electricity and heat. The electricity in excess that cannot be received by the local grid is delivered to a PEM water electrolyser for the production of GH2. The latter is assumed to be compressed, stored in tanks, and eventually used as a fuel for vehicles or ferries. The results showed that the proposed system can satisfy the annual diverse energy needs of the island, producing 210 MWh and 2356.5 kg of GH2 with a good financial return, resulting in an investment payback period of less than 7 years and a positive net present value.	The innovativeness of the study is the application of two technologies for storing energy such as the solar thermal energy storage tank and the compressed hydrogen.	Future research can evaluate more broadly the environmental and social benefits of the proposed installation and investments.
Application of renewable energies for GH2 production to provide heat and electricity in buildings	Gabbar and Ramadan. [97], Canada	Analysis and comparison of seven scenarios, among which a business-as-usual scenario meeting all the energy needs (electric, thermal, and gas) by means of the utility grid. The other energy scenarios evaluate the partial replacement of the grid supply by the local production of solar PV panels or wind turbine or fuel cells or their integration, as well as the use of a GH2 system.	The scenario integrating wind turbine and solar PV panels covers until 63% of the electricity lighting needs of the building, avoiding the supply from the utility grid and the achievement of economic benefits. The integration of the green hydrogen–fuel propane blend system for the thermal needs further widens the economic benefits and generate environmental benefits in terms of CO2 savings per year.	The study contributes in covering a relevant gap in the literature, showing the benefits of the integration of renewables and GH2 production in buildings to replace fossil fuels	One of the possible limits could be the small scale of the project and the need for evaluating the potential scalability of the analysis and its effects on the results of the study.
	Nhien et al. [106] Swedish cities (Visby, Helsingborg, Lund and others)	This study assessed the potential of wind–fuel cell hydrogen energy system to generate a sustainable and reliable energy in meeting households’ demand.	The system was centred on a wind farm integrated with a PEM electrolyser and reverse osmosis desalination units for the production of electricity, hydrogen, and freshwater. The system includes PEM fuel cells equipped with a hydrogen tank to meet the demand and overcome the intermittency of wind power. The analysis confirms the great potential of Sweden in electricity production from wind due to its abundance of coastlines, particularly in the cities of Visby and Helsingborg. The results show that, in the city of Visby and in the other analysed cities, the proposed energy system would provide a sustainable energy supply to 4500 households.	The analysis is particularly meaningful in social terms, showing the possibility of reducing the dependence on fossil fuels and rely on a renewable local source of energy.	Future research could consider the analysis of further areas with a high potential of wind power production and conduct an LCA in order to understand the environmental impacts of the energy system and its components.
	Meastre et al. [17], Spain	Monitoring the performances of a hybrid, solar PV-based GH2 demonstrative pilot plant, which is useful to ensure the total annual coverage of electricity needs of a social housing unit.	The results show the environmental, economic, and social benefits achieved by the hybrid solar PV–hydrogen pilot plant after two years of monitoring. The economic benefits of reduced electricity costs are particularly relevant for the people living in social housing or at potential risk of energy poverty. The monitoring and control system implemented for the pilot plant allow the analysis of variables and energy performances. The control system has shown itself to work effectively since the electrolyser or the fuel cells enter into operation when there is a surplus of energy or when the batteries and the solar PV plant do not meet the energy demand of the social housing.	The study shows a modular and scalable solution that integrates the production of GH2. It is possible to satisfy the electricity and thermal needs of isolated residential systems, adding value to the building and realize multiple benefits.	The analysis could be extended by assessing further impact categories beyond CO2 and primary energy savings.

lists several cases of application of GH₂ as a fuel and as a heat producer selected from the analysed literature. Each case study is analysed according to its goal/main focus, key findings, success factors, and limitations. These cases evaluated the environmental impacts of the use of GH₂ by means of different methods such as LCA [17,60,101] or its technical and financial performances [102]. Some studies combined LCA and Emergy Accounting [103] or technical/energy/exergy analyses [104], while others assessed the technical and financial viability of GH₂ projects, adding to the evaluation of the environmental benefits [98,105]. Other studies also investigated the optimal geographical location of GH₂ projects [106] or the preferences for different types of fuel, including GH₂ [107], and the financial analysis of GH₂, integrating them with citizens perception assessment [108]. In general, the cases show the environmental benefits of using GH₂ as a fuel in transport [101,103] and industrial hard-to-abate sectors [105], contributing to the decarbonisation goals but sometimes worsening other impact categories such as TETP and FETP [101] or FD [103]. With regard to financial feasibility, the investigated cases show that it depends on local factors, such as the integration of a GH₂ plant with other uses (e.g., peaker plants) [98] or the availability of more tailored policy tools, or other factors such as the prices of natural gas [105]. In this regard, it is important to complement financial analyses with social cost–benefit analyses, as well as to more broadly evaluate the socio-economic feasibility and welfare of GH₂ projects.

4.5. Environmental Impacts of the Life Cycle of Green Hydrogen

The Table A2 in Appendix A lists all the LCA studies included in our literature review. For each study, the goal and some results are provided. The next Section 4.5.1, Section 4.5.2 and Section 4.5.3 analyse in detail the goals of the LCA studies, the system boundaries, and the main results in terms of environmental impacts. Further key aspects such as the functional units, the impact assessment methods, and impact categories are dealt with in Section 4.5.4.

4.5.1. Goal and Scope of Reviewed GH₂ LCA Studies

“Goal and Scope” is the first step in an LCA study according to the ISO standards 14,040 and 14,044, and its relevance is crucial, since it defines the approach to be adopted. Some of the main aspects that must defined in this stage are the final objective and the context of the study, namely a number of important characteristics, such as the functional unit, the system boundaries, the type of data (foreground or background), the exclusion of some life cycle stages or inputs, and the selected impact indicators and characterization factors.

The goal of the selected LCA studies regards, in many cases, the assessment and comparison of the impacts of the production of various hydrogen pathways (or “colours”) such as green, blue, and grey hydrogen [66,89,109,110,111,112,113]. Selected studies also aimed to identify the most environmentally sound electrolysis technology (AEL, PEM, SOEC, AEM) for GH₂ production [114,115,116,117,118] or to assess the impacts of integrating the production of GH₂ in industrial processes [60,119,120].

The goal of some LCAs was evaluating the impacts of hydrogen production by means of specific processes, such as photocatalysis [121], or substrates, such as biogas, or by means of chemical looping, dry reforming methane technology [122] as well as comparing the impacts of delivering hydrogen through various types of hydrogen storage (e.g., liquid and compressed hydrogen) and delivery options (by pipeline or by ship) [123]. Furthermore, the goals of other LCA studies were the evaluation of GH₂ produced by water electrolysis and renewable electricity such as a floating PV system [124], offshore or onshore wind and solar PV plants in Italy and the UK [125], an offshore wind plant located in the Eagen Sea [126], and the whole life cycle from cradle to grave using PEM electrolyser and wind electricity as well as AEL electrolyser and solar PV power [127].

Finally, another non-negligible goal of some reviewed LCA studies has been the comparison of the impacts of conventional and alternative fuels used in internal combustion engines in marine applications [128,129], or in urban buses such as the use of diesel and H₂ produced by using electricity from the grid in Brazil [103] or in Dubai [130]. The comparison of the impacts has also involved autonomous-driving, hydrogen-powered boats and long-haul tracking [131], traditional and fuel cells hybrid tractors powered by GH₂ [101], or systems for producing electricity such as a diesel-based energy system and a proposed RES-based energy system that also include the production of hydrogen [132].

A few LCA studies [110,133] have a specific goal associated with the circular economy. The first one was aimed at assessing the environmental impacts of the electrolyser on the manufacturing stage by considering the use of recycled and reused materials, while the second one assessed the environmental impacts of producing hydrogen by dark fermentation and electrolysis. In the case of the latter process, the use of treated wastewater was evaluated and two scenarios of electrolysis with/without a solar PV plant have been also considered.

4.5.2. System Boundaries of LCA Studies

Figure 5 shows the whole life cycle of GH₂, encompassing all the “cradle to grave” processes within the boundaries of the investigated hydrogen system. Basically, the whole life cycle consists of upstream and downstream phases before and after the operation stage of production of GH₂ by means of the water electrolysis process. The upstream processes comprise the extraction and processing of the raw materials and energy needed for the manufacturing of the renewable energy technologies (PV, hydro, and wind power plants), and the electrolyser required for the water electrolysis process. The downstream processes involve the end-of-life stages of renewable technologies and electrolyser, consisting of their decommissioning/dismantling and the reuse/refurbishing/repurposing of their components [133] along with the recycling of remaining materials [101,110,114,127,133]. Moreover, the LCA approach “cradle to grave” is still not fully circular because a fraction of solid waste is disposed of in landfill [114] or treated by the incinerator [133].

Table 3. Summary of some key aspects of the selected LCA literature.

Author/s	Publication Year	System Boundaries	F.U.	Impact Assessment	Impact Categories	Use of Other Methods/Indicators	Electrolyser	RE Source
[124]	2025	Cradle to gate	1 kg of GH2	Intergovernmental Panel on Climate Change, 2021	GWP, particulate matter formation, NOx and SOx emissions, and water consumption	LCCA	PEM	Floating PV
[133]	2025	Construction and end-of-life recycling	5 MW of AWE system	ReCiPe (2016)	GWP, Mineral Resource Scarcity, Human Toxicity Potential for cancer (HTPc)	NO	AWE	NO
[121]	2025	Cradle to gate	0.01 MJ hydrogen energy	Environmental Footprint (Mid-point Indicator)	19 impact categories, including climate change	NO	NO	Solar energy (componds parabolic concentrator)
[128]	2025	Cradle to grave	1 kWh of engine energy output	ReCiPe 2016 Midpoint, CML-IA, IPCC	18 impact categories of ReCiPe 2016 Midpoint	NO		Onshore wind
[131]	2025	Cradle to grave	1 km of AHB travel	Environmental footprint 3.1	GWP100	Cost Assessment
[125]	2025	Cradle to gate	1 kg of GH2	Environmental Footprint 3.0	Acidification, fossil resource use, mineral and metal resource use	NO	AEL	Solar PV and offshore and onshore wind
[116]	2024	Cradle to grave	1 kg of GH2		GHG emissions	Financial analysis	AEL, PEM	Solar PV
[114]	2024	Cradle to grave	1 kg of GH2	ILCD 2011 Midpoint method	GWP and 15 impact categories	NO	ALE-P and aLE-C	Solar PV and wind energy
[89]	2024	Cradle to grave	1 kg of H2	CML 2001–January 2016	GWP	NO		Concentrated photovoltaic collectors
[123]	2024	Cradle to utilization	Delivery of 1 Mt of H2 in 1 year	EF impact assessment method (European Commission, 2021)	16 impact categories, including climate change	NO	PEM	Energy mix of the grid
[110]	2024	Cradle to gate		ReCiPe (H)	GWP100, FDP, WDP	NO	PEM	Solar PV
[119]	2024	Cradle to grave	300.000 t of RDF producible from residual MSW	ReCiPe 2016	All impact categories of ReCiPe 2016 Midpoint		PEM	Solar PV
[120]	2024	Cradle to grave	1 kg of H2	CML 2001, ReCiPe 2016 Endpoint, and EPS 2015 d	GWP, FPMF, Asthma Cases, Water consumption, OFP, EP	NO	SOE	Solar PV
[126]	2024	Cradle to gate	1 kg of H2	ReCiPe2016	GWP-100 years, GWP-20 years, FPMF-20 years, FPMF-100 years	Life cycle Costing Assessment	PEM	Offshore Wind
[127]	2024	Cradle to grave	1000 tons of H2	ReCiPe 2016	GWP, WDP, FDP, MDP, ODP, HTP, TAP	NO	AEL, PEM	Solar PV and wind
[101]	2024	Cradle to grave	1 kg/vehicle/year	ReCiPe 2016 V. 1.03	10 impact categories of ReCiPe 2016	NO	PEM	Solar PV
[122]	2024	Cradle to gate	1 kg of H2	Environmental Footprint 3.1 method	GWP, AP, FEP, ODP, POFP, ADP
[109]	2024	Cradle to gate	1 kg of H2	ReCiPe 2016 Midpoint (H)	All the environmental categories of Recipe, including GWP	Energy analysis (EROI), financial analysis, LCOH	AEC Alkaline electrolysis cell	Floating photovoltaic
[111]	2024	Cradle to gate	1 kg of H2		GWP100 and GWP20	NO		Wind and solar energy
[112]	2024	Cradle to utilisation	1 kWh fuel use		Climate change, water use, human toxicity, eco-toxicity, resource depletion and land use	Environmental costs	PEM	European electricity mix with renewables for PEM
[129]	2024	Cradle to gate	5.3 EJ/year	ReCiPe 2016 Hierarchal	GWP100	NO	PEM	Renewable energies
[60]	2024	Cradle to utilisation	1 kg of copper	CML 2001–January 2016	ADP, abiotic depletion-fossil fuels, Acidification, Eutrophication, Freshwater Acquatic Ecotoxicity, GWP, HT, MT, OLD, PO, TT	NO		Wind
[117]	2024	Cradle to gate	1 MJ of hydrogen production at 1 bar pressure in Europe in 2023	IPCC, ImpactWorld+, EPS2000	CC, Human Health, Ecosystem Quality, Abiotic resource depletion	NO	AEL, AEM, PEM, and SOE	Solar PV, Wind, Hydro power
[103]	2023	Well to Wheel	Kilometer–person		Embodied fossil energy, GWP, AP, Particulate matter	Emergy accounting and emergy indicators		80% of the electricity mix of Brazil is sourced by renewables
[113]	2023	Cradle to gate	1 kg of H2		GHG emissions		PEM	Solar PV, offsfore wind
[118]	2023	Cradle to gate	1 kg of H2, 99.8% purity, 1 bar pressure	IPCC GWP 100a	GHG emissions	Financial analysis (net present value and payback period	AEM	Solar PV
[66]	2023	Cradle to utilisation	500 Mt/yr of hydrogen	Planetary Boundaries framework LCIA, ReCiPe 2016 (Midpoint) Hierarchist, Environmental Footprint 3.0 (Midpoint), CML-IA baseline 4.8 from 2016 (Midpoint)	CC and other impact categories			Solar PV and wind
[115]	2023	Cradle to gate	1 kg of H2		GWP, AP, ODP, EP	NO	AEL, PEM, SOEC	Onshore and offshore wind
[132]	2022	Cradle to utilisation	1 kWh of electricity	Environmental Footprint (EF) 3.0 method	CC, ODP, POFP, PM; AP, FEP, TEP, MEP, Ecotoxicity Freshwater, water use, Resource use, fossils, Resource use, minerals and metals.	Economic analysis already performed	Alkaline electrolyzer	Solar PV

Note: The empty cells refer to missing information in the articles.

evidences that 9 out of 29 LCA studies of this literature review adopted a “cradle to grave” approach, involving all the stages of the life cycle of renewable technologies and the electrolysers, while 13 followed a “cradle to gate” approach excluding the use stage and end-of-life, 5 used a “cradle to use” procedure, and 1 used “Well to Wheel”. Only one study considered the construction and end-of-life stages.

The end-of-life stage of the electrolyser still represents a challenge for LCA practitioners and the recycling industry because of the lack of reliable data and the low level of maturity of the recycling processes [38]. Advancements in the end-of-life stages, particularly for the electrolyser, are necessary for a transition to the CE model and for an improvement in the impacts during the manufacturing stage of such technology.

4.5.3. Analysis/Interpretation of the Environmental Impacts

The analysis of the results of the selected LCAs shows that the production of GH₂ by water electrolysis using renewable electricity presents more favourable results if using wind electricity compared to solar PV.

In this regard, Tabrizi et al. [125] assessed the production of GH₂ in Italy and the UK, calculating a carbon footprint for wind-based hydrogen lower than solar-based GH₂. Moreover_, the carbon footprint differs depending on the location. The values for wind off-shore-based hydrogen for the UK are lower (0.62–1.06 kg CO₂ eq./kg H₂) compared to Italy (0.8–1.36 kg CO₂ eq./kg H₂). For solar-based hydrogen, the carbon footprint for Italy is between 1.76 and 2.25 kg CO₂ eq./kg H₂ by using electricity from single-SI modules, while for the UK, it is between 2.65 and 2.77 kg CO₂ eq./kg H₂. The authors pointed out that the source of electricity of the electrolyser generates the highest contributions to the carbon footprint of hydrogen. In the case of solar PV-based GH₂, the PV modules are responsible for the large share of the carbon footprint of the PV plant due to the fact that the cells are mainly manufactured in China by means of the still coal-based electricity used in this country. Therefore, a reduction of the production of solar PV-based GH₂ could only happen following a decarbonisation of the Chinese electricity mix [125].

Other authors also confirmed that a large share of the contribution to GWP for the production of GH₂ comes from the production of electricity. Pawłowski et al. [118] evaluated the impacts of GH₂ produced by an AEM electrolyser and a 5 MW solar PV plant located in Poland, calculating a carbon footprint between 2.73 and 3.85 kg CO₂ eq/kg H₂ (PV tracker) as well as 3.01 and 4.34 kg CO₂ eq/kg H₂ (PV standing). Similarly, Ajeeb et al. [114] also found in their Portugal case study that the electricity mix (solar and wind) of the AEL electrolyser is responsible for the largest impacts in the production of GH₂, ranging from 92% for ODP, 96% for mineral fossil resource depletion, and 98% for the other investigated impact categories (including GWP).

Furthermore, Affandi et al. [116] showed that the GHG emissions of GH₂ produced using PEM electrolyser and solar PV electricity were between 2.26 and 4.46 kg CO₂ eq/kg GH₂, while those related to AEL electrolyser were between 2.61 and 5.15 kg CO₂ eq/kg GH₂. Zhang et al. [115], comparing the impacts of three water electrolysis technologies (AEL, PEM, and SOEC), calculated that onshore wind and the use of PEM for GH₂ production generate the lowest contributions to the selected impact categories (GWP, AP, EP, ODP), with values of 0.0936 kg CO₂ eq./kg of H₂ (GWP), 2.97 × 10⁻⁴ kg SO₂ eq./kg of H₂ (AP), 2.86 × 10⁻⁵ kg Phosphate eq./kg H₂ (EP), and 4.22 × 10⁻¹⁵ kg R11 eq./kg H₂ (ODP).

Other authors have compared the environmental impacts of hydrogen produced by means of different feedstocks and processes. Patel et al. [111] showed that the production of GH₂ from wind power generate the lowest emissions (0.6 kg CO₂ eq./kg H₂) compared to GH₂ produced from solar PV electricity (2.5 kg CO₂ eq./kg H₂), as well as the hydrogen from fossil fuels delivered in two pathways by pipeline from Russia and LNG routes from USA. In particular, grey hydrogen produced by SMR released 13.9 kg CO₂ eq./kg H₂ and 12.3 kg CO₂ eq./kg H₂, blue hydrogen produced by SMR-CCS emitted 7.6 kg CO₂ eq./kg H₂ and 9.3 kg CO₂ eq./kg H₂, and turquoise hydrogen emitted 6.1 kg CO₂ eq./kg H₂ and 8.3 kg CO₂ eq./kg H₂. Moreover, if the production of GH₂ occurs by using electricity from the grid connected to both solar and wind at the same percentage (50% wind and 50% solar), most of the contribution to GWP comes from solar electricity (1.2 kg CO₂ eq. per kg H₂) while wind has a lower impact (0.3 kg CO₂ eq. per kg H₂).

These results are in line with the study by De Kleijne et al. [113], who assessed that GH₂ from electricity by offshore wind has the lowest GHG footprint, ranging from 0.4–0.8 kg CO₂eq./kg of GH₂, while that from solar PV leads to a higher GHG footprint at 1.7–4.4 kg CO₂eq./kg of GH_2. The use of electricity from the present EU grid worsens the GHG footprint to 6.3–16.6 kg CO₂eq./kg of GH₂, assuming the transition towards a cleaner EU electricity mix reduces the GHGs footprint to 2.1–5.6 kg CO₂eq./kgH₂.

Shen et al. [112] assessed the impacts of four decarbonisation scenarios by the year 2050 for the European industry hard-to-abate sectors as well as transport. The four scenarios are as follows: blue hydrogen replacing fossil fuels, GH₂ replacing fossil fuels, decarbonisation without GH₂, and business as usual without changes in the energy mix. Their results show that GH₂ scenarios have much lower impacts than the other three scenarios in terms of CC, fossil resource depletion, photochemical ozone formation, and acidification. On the other hand, the performances of GH₂-based scenarios compared to the others are worse for land use, water scarcity, mineral resource depletion, particulate matter, eutrophication freshwater, human toxicity, ecotoxicity, and ionising radiation. The Shen et al. [112] study concluded with evidence that the production of electricity from renewables (wind and solar) will have to increase by 50% to support the decarbonisation of industry and transport by 2050, thus requiring further infrastructures. This would cause the increase of the contribution to other impact categories such as human health, mineral resource use, and ecosystem damage [112].

Finally, Mio et al. [109] found that in the comparison among grey, blue, grid, and green hydrogens, the latter has lower environmental contributions to GWP and to the other air pollutants. In other impact categories, the impacts of GH₂ production are higher (such as in the case of LOP and WCP) or lower than the grid electricity-based hydrogen that have resulted in the worst performances across almost all impact categories due to the impacts coming from the electricity mix of the grid. The impacts of GH₂ production to land use seem to not be a concern, particularly when mitigated by the installation of an offshore plant or rooftop solutions.

4.5.4. Most Relevant Factors Affecting the Environmental Impacts

As evident in the previous section, the environmental impacts of the life cycle of GH₂ depend on different factors such as the source of renewable electricity (e.g., wind or solar), the local context, and the type of electrolysis technology. Further influencing factors are the assumptions related to the efficiency and lifetime of the electrolyser [113].

In the life cycle of GH₂, the operation stage of the electrolyser, due to the source of electricity used for the electrolysis process, generates the highest contribution to GWP of GH₂ [114,116,134]. Some authors have underlined that, given the high contribution of the operativity stage of the electrolyser, it is difficult to identify the specific contribution of the manufacturing stage of the electrolyser as well as the impacts of the end-of-life within a recycling scenario. They underlined that if a production method of H₂ with lower impacts is used, both the impacts of manufacturing and end-of-life stages can be more visible and comparable to the operating stage of the electrolyser [134]. However, the results of the LCA when adopting a “cradle to grave” approach show that even in the case of production of GH₂, the impacts of manufacturing and end-of-life stages seems less relevant compared to the operation stage of the electrolyser [127]. Khan et al. [127] showed that the inclusion of the end-of-life recycling and the remanufacturing of the electrolyser with recycled materials lead to a reduction of the GWP of the whole life cycle of GH₂ by 5–12%, FDP by 5–8%, and by 3–20% for MDP [127].

Of course, regarding the end-of-life recycling scenario, the reduction of the impacts during the manufacturing stage of the electrolyser is significant for the AEL electrolyser compared to the PEM electrolyser due to the higher quantity of assumed recyclable materials. The contributions to GWP decrease by 70%, while those of FDP decrease by 65% and MDP decrease by 59% [127].

Hoppe and Minke [133] investigated the LCA impacts on the manufacturing and end-of-life stages of a 5 MW AWE, confirming the relevant reductions of GWP (−50%) obtained by manufacturing an AWE electrolyser (5 MW) with recycling materials compared to the use of virgin materials. The authors also underlined that about 77% of the materials comprising the electrolyser can be reused or recycled.

Wei et al. [117] focused on the analysis of the manufacturing process of four electrolysers depending on the materials and input used in the process. An AEL electrolyser with electricity sourced by hydro as well as an AEM electrolyser sourced by hydropower emerged as those with the highest potential contributions to CC at 0.083 kg CO₂ eq./MJ H₂ and 0.075 kg CO₂ eq./MJ H₂. The results reveal that in the manufacturing of 1 kW of AEL electrolyser and particularly in the anode production, nickel contributes to almost half of the total contributions to CC. On the other hand, the scenario with PEM (0.009 kg CO₂ eq./MJ H₂) and AEM (0.008 kg CO₂ eq./MJ H₂) electrolysers powered by wind electricity resulted in them having the lowest contribution to CC. With regard to the analysis of the other impact categories of the electrolyser system, such as human health, ecosystem quality, and abiotic stock resource impacts, the most impacting scenarios were those with AEL electrolyser and electricity sourced by solar PV and AEL with hydropower [117].

4.5.5. Analysis of the Results of Techno-Economic and Environmental Studies

The analysis of the environmental impacts has been also performed by further selected studies available in Table A2 of Appendix A. Most of the studies conducted a techno-economic analysis in combination with an environmental analysis in order to evaluate the technical and financial viability and environmental benefits of decarbonisation projects by integrating renewable energies and the production of hydrogen. Currie et al. [102], in an Australian case study, found that the integration of GH₂ in the electricity system improves the reliability and security of the system, overcoming the variability of renewable sources such as wind and solar PV and thus providing the opportunity of storing the energy surplus from these sources in an efficient way. However, in order to ensure its financial viability, the project should be supported by subsidies [102].

Oyewole et al. [98] analysed an energy system based on renewables (wind and solar PV) used as a peaker plant and an on-site GH₂ refuelling station. They showed that it is a viable option for producing electricity and hydrogen fuel at competitive costs compared with those of natural gas plants generally used as peaking plants in the urban context of three cities in South Africa [98]. In Morocco, Boulmrharj et al. [135] calculated the GHG emissions of a hybrid system for the production of hydrogen and electricity required for public transport and street lighting in three cities. The GHG₂ emissions were lower (0.017 kg CO₂eq./kWh) than the GHG emissions from the grid electricity [135].

With regard to the applications in buildings concerning the implementation of a hybrid PV–hydrogen demonstrative pilot plant in Spain, Maestre et al. [17] showed that it is possible to achieve independence from grid electricity, thus obtaining CO₂ emissions savings and socio-economic benefits in terms of avoided electricity costs [17].

Similarly, Hassan et al. [96], in a case study assessing the use of a commercial hydrogen battery in rooftop solar systems, indicated that hydrogen batteries reduce the dependence on grid electricity and its costs [96]. Moreover, the hydrogen battery, compared to the Li–Ion battery, increases the life of the battery and thereby achieving a longer duration of energy storage [51,96]. In terms of costs, Arsalis et al. [18] pointed out that those related to LIBs have decreased significantly within the last decade, while in the case of RHFC, the high costs of the electrolysers and fuel cells stacks limit their larger development [18].

Arcos and Santos [83] as well as Singhla et al. [136], assessing the CO₂ emissions and production costs of various hydrogen production methods, have found that grey, black/brown, and blue hydrogens are the least environmentally friendly [83,136] but have lower production costs (ranging from 0.67 to 2.05 USD/kgH₂, respectively) [83]. Green hydrogen is the most environmentally friendly but has one of the highest production costs, ranging from 2.28 to 7.39 USD/kgH₂ [83]. In the European context, the case study by Bonesso et al. [108] in Italy calculated a levelized cost of wind-based hydrogen at 3.60 euro/kg of GH2 in the base scenario, while in the alternative scenarios, it comprised between 3.20 and 4 euro/kg of GH₂ [108].

Awad et al. [130] suggested that the best solutions for the decarbonisation of the Dubai bus fleet would be to replace the diesel buses with those using mixed hydrogen as a fuel in order to benefit from the existing grey hydrogen being available at lower costs. Boulmrharj et al. [135], meanwhile, pointed out that the analysed hybrid systems producing hydrogen and electricity for transportation and lighting services in cities in Morocco would be profitable only in cities of medium size or are not profitable at all regardless of the size. They could become more profitable in the future due to the reduction of income taxes and the expected increase in selling prices of hydrogen and oxygen. The latter study has found some of the most relevant factors affecting the profitability of the hybrid systems [135].

Al-Ghussain et al. [137] have confirmed that the geographical location of renewables is a relevant factor influencing the carbon intensity (CI) of GH₂ and its costs [137]. The CI comprised between 0.3 and 1.9 kg CO₂ eq./kg GH₂ (wind-based electricity) while the CI when using solar electricity is between 1.58 and 2.95 kg CO₂ eq./kg GH₂. The production costs comprised between 1.5 and 15 USD/kg GH₂ for wind-based systems and 3.0 and 5.2 USD/kg H₂ for the solar PV-based systems [137]. Du et al. [138] underlined scenarios that GH₂ production in China would be competitive with hydrogen produced with conventional production methods by the year 2030.

Finally, in a further study by Bollini Braga Miciel et al. [139], GH₂ produced by hydroelectricity has the lowest contribution to GWP, followed by wind and solar PV [139]. The analysis of the life cycle impacts of electricity for the three sources show that for wind source, the manufacturing stage of the rotor and the tower is the most significant because of the large use of steel; for solar PV, the elaboration of silicon wafers in electronic degree is the least efficient stage; and for hydro, the dam with the use of concrete and steel in the construction stage has the largest contribution to the impacts [139].

4.6. Social Impacts of the Life Cycle of Green Hydrogen

According to Akhtar et al. [140], the supply chain of GH₂, compared to conventional hydrogen from fossil fuels, is rather complex due to the need for purchasing components from various parts of the world [140]. This fact also has social implications in terms of distribution of the social impacts, e.g., the production of components and products such as the electrolyser. Akhtar et al. [140] have performed a social life cycle assessment of GH₂ produced via water electrolysis and electricity from wind and solar energy in several exporting countries of hydrogen equipments (USA, Chile, South Africa, Saudi Arabia, Oman, Australia, China), finding that GH₂ production generates impacts in most of the social indicators investigated (child labour, unemployment, gender wage gap). The results show that these social impacts can be strongly reduced by developing a domestic production industry of GH₂ instead of importing the products from other countries. The authors suggest that it is important to improve the working conditions in the energy sector and develop international regulations to avoid carbon-intensive activities being outsourced to other countries.

Dos Reis et al. [141] have analysed, by means of S-LCA, the life cycle of production of GH₂ in Portugal considering the system boundaries in the extraction and processing of materials for the electrolyser, its production, as well as that of GH₂. The extraction and processing of the materials for the electrolysers resulted in the generation of the highest impacts among most of the social impact indicators including child labour, risks of conflicts, association, and bargaining rights. Depending on the extraction and processing stage of the materials for the electrolyser, for both databases used (PSILCA and SHDB), the largest contribution to the social impact indicators come mainly from the production of naflon and, to a lesser extent, iridium and titanium. China and South Africa are the countries that contribute the most to these social impacts. Portugal emerged as the most important contributor in the PSILCA database to the social indicators “Frequency of forced labour”, “Weekly hours of work per employee”, “Non-fatal accidents”, and “Trade unionism” for the manufacturing of the electrolyser. The authors underlined that the life cycle of GH₂ in Portugal generates social impacts internationally and at the domestic level.

Considering these premises, it has clearly emerged that the traceability of GH₂, in its value chain to gather more data on its social impacts, is crucial for policy purposes [142]. Martin-Gamboa et al. [142] have assessed two value chains of GH₂ in the European Union: on-site and off-site. The functional unit is the delivery of 1 Mt of GH₂ to the final user located in Western Europe. On-site scenario refers to the production of GH₂ from wind electricity in Western Europe, while the second scenario (off-site) comprises GH₂ produced in Southern Europe by using electricity from solar PV panels, before being compressed and stored in a salt cavern, and delivered by ship to Western Europe, where it is stored again and supplied to the final user. The off-site GH₂ production is assumed to occur in Northern Africa and Southern Asia due to their climate conditions, logistics, and regulations [142].

The results show that the off-site scenario is more complex than the on-site scenario due to the presence of more processes. In both scenarios, the stages of assembly/construction, operation, and maintenance occur in Western Europe where GH₂ is consumed, while the stages of component manufacturing and extraction and processing of raw materials implies a progressive widening of the geographical distribution of social impacts beyond the EU. In the on-site scenario, wind turbines are assumed to be produced in Western Europe where there is a relevant market share for this product, while in the off-site scenario, the contribution of eastern and southern Asia is expected to be higher due to their dominance in the manufacturing of solar PV components (cells, modules, and so on). In both scenarios, the analysis of the extraction and processing of raw materials stage show the dependence of the EU on other countries (southern Africa and east and southern Asia) for the availability of key materials needed for the production of solar and wind systems as well as electrolysers such as silicon, rare earths, titanium, platinum, and iridium [142].

The social hotspots analysis reveals that in both scenarios, the major risks in child labour are due to the component manufacturing stage as well as during the extraction and processing of raw materials. There is a higher contribution from eastern Asia, particularly China, to the risk of child labour, particularly in the solar PV production, in the off-site scenario. The on-site scenario for GH₂ production resulted in better social performances in the analysed social impact categories “child labor” and “fair salary” while showing less favourable social performances in the category “contribution to economic development”. Finally, it is important to underline that in the off-site scenario, the value chain is longer, with more processes performed outside the EU, resulting in more challenges for their monitoring and analysis from a policy perspective [142].

Finally, it is important to be aware of the potential social risks of GH₂ beyond the consideration of the technological and climate aspects, and to evaluate its transition within the wider framework of environmental and social justice [54] and policies involving all the stakeholders in order to reduce the potential social impacts [52].

4.7. The Circularity of Green Hydrogen

The CE concept suggests a more efficient use of resources and the circulation over multiple lifecycles of the materials, products, and components to preserve their value as much as possible [133]. As evidenced in Section 2, the product design has a central role in assuring that such aspects are met while considering the CE principles as targets in the design of renewable technologies and electrolysers.

Table 4 summarises the strategies that should be applied in order for GH₂ to be in line with the CE principles, as well as the challenges in applying such strategies on the basis of the analysis of the selected literature in this study. The strategies imply the incorporation of innovative design approaches in the life cycle of GH₂ aimed at, for example, reducing the material intensity of the electrolysers [143] or designing their components for repair, reuse, or refurbishing [133]. Moreover, another important aspect is the strategic material selection in order to replace the use of critical materials [133] as well as design materials for recyclability at the end-of -life [38]. The life cycle of GH₂ should be designed to eliminate or minimize all forms of waste (solid and emissions to air, water and soil) and limit their hazardousness to enhance more cleaner production processes [43].

Anand et al. [45] suggested the reuse of treated wastewater for the production of hydrogen at a particularly small scale to avoid the use of freshwater [45]. Solid Oxide Electrolysis Cells are not a mature electrolyser technology but have the advantage of allowing the use of impure water [144].

Another important aspect is the integration of the principle of renewability to the production of GH₂ and its whole life cycle. As we have seen in the previous sections, the source of electricity for feeding the electrolyser affects the renewability of GH₂. Thus, it is important to ensure the renewability of the source by reducing the impacts of the renewable technologies plants because their manufacturing could involve electricity produced from fossils [125] as well as having several social hotspots [140,141,142].

The principle of renewability goes hand in hand with that of localness since, for example, the carbon intensity of GH₂ depends on the local production of renewables [137] and these are not distributed equally [33] because some geographical areas are richer in wind [106,125] or solar [125] or hydro [11]. However, importing hydrogen from other countries has a higher carbon footprint [123,144], and the production of GH₂ at the local scale improves the security of the local electricity system or that of single buildings [53]. Clearly, the creation of a surplus at the local scale in cities [98] or islands [104] is easier than at the larger scale of a nation, and some studies show that the production of GH₂ is viable in technical and financial terms [98,104]. In the short term, de Kleijne et al. [113] suggested that the surplus of electricity should first be used to decarbonise the heat and transport sectors, while hydrogen production should be a second option [113]. Therefore, it is relevant to monitor and evaluate the impacts of GH₂ and adopt policies supporting research projects to understand the alignment of GH₂ development and technologies to the CE principles and the decarbonisation goals [43].

Table 4. Principles of CE and the strategies applying them to GH_2.

Principles of CE	Application to GH2	Challenges
Circular Design	Innovative design approaches to reduce the use of natural resources in the electrolysers [133,142] and reduce/eliminate emissions and other forms of waste in the life cycle of GH2 [43].	Costs and durability of catalysts in AWE electrolyzers [48]
	Considering for electrolysers the substitution of critical materials as well as designing their components for repair, reuse, refurbishing and their materials for recyclability [133]. Designing electrolysers’ components for repair, reuse, and refurbishing [133].
Reduction	Reduction in material intensity to improve the resource efficiency of the electrolysers [143]	Costs and durability of catalysts in AWE electrolyzers [48]
Reuse	Reuse of wastewater in the electrolysis process at the small local scale to avoid the use of freshwater [22,25] and competition with other water uses [46,145]. Tertiary effluents require low investments compared to seawater desalination systems and are a secure water supply compared to stormwater [46,145]. Reuse of oxygen from the electrolysis process for wastewater treatment and industrial processes. This strategy could reduce the cost of hydrogen and the environmental footprint of wastewater [22] because oxygen is re-used for the treatment of wastewater [46]. Recovery of water as a byproduct of the use of hydrogen for energy purposes (e.g., use in fuel cells, internal combustion engines). This process releases pure water independently from the type of water used as an input for the electrolysis process (freshwater, seawater, wastewater) [46]. Countries with scarce availability of water could find more appeal in importing hydrogen than ex-porting due to the fact they import both energy and water [46].	Production pathways of GH2 and treatment of wastewater such as biological treatment. Anaerobic membrane bioreactors are characterised by a low hydrogen production yield and a low efficiency in COD removal [144].
	Solid Oxide Electrolysis Cell are an interesting solution for producing GH2 as they can use impure water sources as feedstock [144]
Recycling	About 77% of the materials contained in a AWE can be recycled or reused [133]. Recycling the materials composing of electrolysers at the end-of-life [133].	Most LCA studies do not include the recycling stage of precious materials of the electrolyzers due to lack of reliable data [38].
Renewability	Production of GH2 from renewables (wind, solar, hydro) [25,146]; Buses using GH2 as a fuel, compared with buses fuelled by diesel, electricity, LPG, and biodiesel, have a higher renewability and other better emergy indicators such as emergy sustainability index and environmental loading ratio [103].	Improving the share of electricity from renewables to create a surplus of electricity for GH2 production [10,33]; The electrolyzers and renewables technologies are currently manufactured by using the electricity mix, with contributions from fossil energy [126].
Localness/local scale	GH2 produced from renewable electricity contributes to the diversification of the electricity mix from fossils, thereby improving energy security [53].	Balance between distributed and centralised hydrogen systems [46].
	Implementation of small-scale hydro plants or using local biomass from waste treatment plants for GH2 production [45].

Table 4. Principles of CE and the strategies applying them to GH_2.

Principles of CE	Application to GH2	Challenges
Circular Design	Innovative design approaches to reduce the use of natural resources in the electrolysers [133,142] and reduce/eliminate emissions and other forms of waste in the life cycle of GH2 [43].	Costs and durability of catalysts in AWE electrolyzers [48]
	Considering for electrolysers the substitution of critical materials as well as designing their components for repair, reuse, refurbishing and their materials for recyclability [133]. Designing electrolysers’ components for repair, reuse, and refurbishing [133].
Reduction	Reduction in material intensity to improve the resource efficiency of the electrolysers [143]	Costs and durability of catalysts in AWE electrolyzers [48]
Reuse	Reuse of wastewater in the electrolysis process at the small local scale to avoid the use of freshwater [22,25] and competition with other water uses [46,145]. Tertiary effluents require low investments compared to seawater desalination systems and are a secure water supply compared to stormwater [46,145]. Reuse of oxygen from the electrolysis process for wastewater treatment and industrial processes. This strategy could reduce the cost of hydrogen and the environmental footprint of wastewater [22] because oxygen is re-used for the treatment of wastewater [46]. Recovery of water as a byproduct of the use of hydrogen for energy purposes (e.g., use in fuel cells, internal combustion engines). This process releases pure water independently from the type of water used as an input for the electrolysis process (freshwater, seawater, wastewater) [46]. Countries with scarce availability of water could find more appeal in importing hydrogen than ex-porting due to the fact they import both energy and water [46].	Production pathways of GH2 and treatment of wastewater such as biological treatment. Anaerobic membrane bioreactors are characterised by a low hydrogen production yield and a low efficiency in COD removal [144].
	Solid Oxide Electrolysis Cell are an interesting solution for producing GH2 as they can use impure water sources as feedstock [144]
Recycling	About 77% of the materials contained in a AWE can be recycled or reused [133]. Recycling the materials composing of electrolysers at the end-of-life [133].	Most LCA studies do not include the recycling stage of precious materials of the electrolyzers due to lack of reliable data [38].
Renewability	Production of GH2 from renewables (wind, solar, hydro) [25,146]; Buses using GH2 as a fuel, compared with buses fuelled by diesel, electricity, LPG, and biodiesel, have a higher renewability and other better emergy indicators such as emergy sustainability index and environmental loading ratio [103].	Improving the share of electricity from renewables to create a surplus of electricity for GH2 production [10,33]; The electrolyzers and renewables technologies are currently manufactured by using the electricity mix, with contributions from fossil energy [126].
Localness/local scale	GH2 produced from renewable electricity contributes to the diversification of the electricity mix from fossils, thereby improving energy security [53].	Balance between distributed and centralised hydrogen systems [46].
	Implementation of small-scale hydro plants or using local biomass from waste treatment plants for GH2 production [45].

5. Concluding Remarks

The goal of this review study is to understand if GH₂ could be an environmentally and socially sustainable option for decarbonising energy systems in the transition to CE. The research comprised the analysis of the environmental and social impacts of GH₂ in its life cycle, with special focus on the impacts associated with the use of GH₂ for its main three final applications (fuel, heat producer, and feedstock), by means of several case studies from the selected literature. The latter contained literature reviews as well as LCA, LCA and LCC, LCA and Emergy Accounting, Social LCA, environmental, technical, and financial and cost analysis studies. This way, the main research question has been evaluated on the basis of different approaches and dimensions of sustainable development.

The results from the assessed LCAs and environmental analyses show that the production of GH₂, compared to other hydrogen typologies (so-called “colours”) from fossils or grid electricity, has lower contributions to GWP, FPMF, and TAP [109]. Contributions of GH₂ to other impact categories are mainly caused by the sources of electricity (wind, solar, or hydro) used for the electrolysis process and the impacts associated with the electricity mix and materials necessary for the manufacturing of the solar PV panels [125] and wind turbines [139]. Moreover, several LCAs point out that wind-based GH₂ has lower contributions to GWP than solar-based GH₂ [111,113,115,125,127]. With that, this study confirms the results from previous literature reviews [25].

Compared to previous literature reviews, this research has also integrated the results from the small number of existing S-LCA literature. The results show the complexity of the value chain of GH₂ and the uneven geographical distribution of the social impacts (particularly the child labour impact category) in the countries contributing to the extraction and provision of materials, as well as the components required for the manufacturing of electrolysers and renewable power plants, such as the wind turbines and the solar PV panels in the EU [142,143,144]. These results also show the dependence of the EU on foreign countries (particularly southern Africa and East and southern Asia) for the availability of key materials such as silicon, rare earths, titanium, platinum, and iridium [142] and the difficulties of applying traceability to the GH₂ life cycle and the concept of circular local development [55,64]. The creation of a domestic production industry for the components of the electrolysers and renewable power plants would mitigate the impacts, avoiding that the most impacting activities are outsourced outside the EU [140].

This study has also explored how GH₂ is coherent with the principles of CE such as circular design, reduction, reuse, recycling, renewability, and localness/local scale. The application of the CE principles is important in mitigating some of the impacts related to the use of natural resources and critical raw materials, the consumption of water in the electrolysis process, and the production of waste [48]. Some studies also confirm the technical viability as well as the economic profitability behind the use of wastewater [87]. The latter is proposed as a feedstock for SOEC electrolysers [144]. This type of electrolyser technology is not yet as mature as the AEL but can also use impure water [144]. Some authors also underlined the importance of circular water use in the hydrogen life cycle, considering that the use of hydrogen as a fuel generates pure water as a by-product that can be reused in the electrolysis process [46].

Regarding the principles of localness or circular local development, this research assessed various case studies of the application of GH₂ in final uses (Section 4.4), providing evidence of the environmental performance of GH₂ as well as its main success factors and limitations. In general, the investigated case studies show that GH₂ has the potential to contribute to the decarbonisation objectives by reducing the contributions to GWP and other impact categories of conventional transport tools such as buses [103] and agricultural tractors [101], of chemical industries [105], and of residential buildings by satisfying their electricity and heat demands, thus making them self-sufficient and independent from fossil fuel sources [17,97]. Moreover, GH₂’s integration in the electricity system may improve its seasonality and reliability in satisfying electric demand [102].

Being an energy carrier and a potential effective energy storage, GH₂ is strictly associated with the development of renewable energies. According to some authors, in the short term, “while the grid can still be further decarbonised and electrification of heat and transport is still in progress, these applications of renewable electricity may take priority over green hydrogen production, if climate benefits are to be maximised. Only when (local) renewable electricity demand for the alternatives has been met, would green hydrogen production be effective in contributing to emission reductions” [113].

GH₂ production is not in competition with other uses of renewable electricity since it can be produced in combination of renewable energies. Its main expected contribution to the global energy system should be to strengthen the role of renewable energies in the electricity system overcoming their fluctuating nature. Hydrogen can be stored when and where there is a high production of solar or wind electricity and a low demand by stakeholders.

Recent GH₂ literature shows the great interest that it is growing worldwide and the commitment of the scientific and technological community in making GH₂ easier to produce and stored as well as be economically cheaper. Despite the technological and economic challenges on one side and the environmental and social challenges on the other, the development of GH₂ in a selected number of sectors seems attainable on the basis of the case studies analysis included in this study.

Undoubtedly, GH₂ can be considered a new and potentially effective tool, among others, in the current global energy market, where the relevance of fossil fuels is being progressively replaced by more distributed renewable energies.

Policy and Practical Recommendations

The results of the present study show that GH₂ may represent an important technological innovation to achieve the decarbonisation goals worldwide [45]. Its production generates a lower contribution to GWP throughout its whole life cycle compared to other hydrogen production patterns from fossils. Moreover, its use as a fuel has the advantage of releasing just water as a by-product [46], which is an important advantage not to be disregarded, if we think about the impacts on human health and total urban environment presently generated by fossil fuels use.

Many reviewed studies have shown that GH₂ is going to be competitive on a pure financial basis in terms of costs, net present value, and the indicator of levelized cost of hydrogen in presence of subsidies or other tools [45,102,105,118]. The EU has already adopted the levelized cost of hydrogen for the evaluation of its economic competitiveness [82]. Clearly, the use of this indicator is somehow limited and further methodological approaches and indicators are needed to capture the total economic value and benefits of its production and use.

Further research should be performed to better understand how the advantages of GH₂ can be maximised while the environmental and socially negative impacts in the supply chains be minimised and eliminated. The effectiveness of more responsible and certified supply chains should also be evaluated and monitored.

Several case studies in this review also show that investments in GH₂ require identifying the most suitable policy tools for supporting its development in hard-to-abate sectors where the integration of GH₂ production has the potential of relevant reductions in CO₂ emissions.

Finally, the present study has also showed that the adoption of CE principles is considered in only a low number of LCAs [101,110,114,127,133]. Therefore, it is important to strengthen the research in this field to assess the impacts of mitigation strategies and GH₂ improvement scenarios. Furthermore, LCAs should be integrated with other assessment methods such as Emergy accounting, material flow accounting, social cost–benefit analysis, S-LCA, and social impact assessments to provide feedbacks useful to policy makers and stakeholders, to improve the knowledge and transparency on the impacts, and to promote a roadmap towards the implementation of GH₂ and renewable energies that meet the imperatives of CE, climate change, sustainability, and social justice.