The Role of Hydrogen in Energy Communities: Current Status, Challenges, and Future Developments

Abstract

Renewable hydrogen has become a versatile technology that can play a key role in the deployment of energy communities, although technological, economic, environmental, legal, and social challenges remain to be addressed. This study conducts a systematic review based on the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) methodology that analyzes the current state of technologies, the different applications, challenges and limitations, and future lines of research related to the enabling role of hydrogen in energy communities. Results from the bibliometric analysis show sustained growth in the number of publications over the last five years (2020–2025), with a predominance of applications in which hydrogen is combined with other energy carriers (58%). The versatility of hydrogen has prompted the evaluation of different applications, with particular emphasis on energy storage to capitalize on energy surpluses (51%), mobility (19%), and heating (20%). The main existing barriers come from the absence of stable long-term regulation, interoperability between components and technologies, and a lack of real data. Overcoming these challenges should be based on new technologies such as artificial intelligence and the construction and operation of pilot projects. In addition, a Strengths, Weaknesses, Opportunities and Threats (SWOT) analysis has been conducted building upon the SHARED-H2 SUDOE project, yielding particularly insightful results through the active involvement of stakeholders in the preparatory process. Based on all the points given above, the research concludes that it is necessary to improve long-term policies and increase training at all levels aimed at active end-user participation and a profound restructuring of the energy system.

1. Introduction

Society faces a multitude of energy, environmental, and technological challenges caused by the continuous increase in energy demand [1], as well as the constant rise in global temperatures [2]. This growth in energy demand is driven by the development of emerging economies [3] and the spread of new technologies such as Artificial Intelligence (AI) and digitization, which require large data storage and computing capacities, materialized in data centers [4]. According to the International Energy Agency (IEA) [5], annual electricity demand is expected to increase by 4%, which means that by 2027, global energy demand will be around 3500 TWh higher than in 2024. Despite the different plans for the electrification of the economy implemented by different countries [6,7,8], according to data from the Organization of Petroleum Exporting Countries (OPEC) in its World Oil Outlook 2050 report [9], global oil demand will increase by 10.3% by 2030 (103.0 mboe/d) compared to 2024 levels (94.3 mboe/d). Despite efforts to increase renewable energy production, estimated at 24.5% by 2030 (59.0 mboe/d) compared to the 2024 level (47.4 mboe/d), oil will still play a significant role in the energy matrix during the Clean Energy Transition (CET) [9].

The consequence of using fossil fuels such as oil or natural gas (NG), which contain carbon in their composition, is an increase in carbon dioxide (CO₂) emissions. According to the Climate Change 2023 Synthesis Report produced by the Intergovernmental Panel on Climate Change (IPCC), there is a direct correlation between the increase in anthropogenic emissions and global warming [10]. Global warming has a negative impact on health [11], generates more adverse and extreme weather events [12], affects biodiversity [13], and has a negative impact on energy resilience [14]. This creates a negative feedback loop between production, emissions, demand, and global warming.

In this context, solutions are needed to focus on reducing the use of fossil fuels and increasing energy generation through renewable energy sources [15]. Electrification is one of the most widely explored solutions [16]. However, there are sectors that are difficult to decarbonize through electrification [17], such as the thermal industrial energy demand [18] and mobility [19], due to the residual impact of electricity. Mobility is responsible for more than 25% of greenhouse gas (GHG) emissions [20]. In terms of energy consumption, the Heating, Ventilation and Air-Conditioning (HVAC) sector accounts for around 12% of final energy consumption worldwide [21], while mobility accounts for around 30% [22]. Therefore, the solutions proposed must not only focus on electrical applications using renewable energies such as solar or wind power but also include thermal applications and mobility in a holistic approach [23].

Renewable hydrogen, also commonly referred to in the recent literature as green hydrogen, is mainly produced through the electrolysis of water powered with renewable energies and is emerging as a versatile energy vector with the potential to enable the vertical integration of renewable energies into the decarbonization of multiple sectors [24]. Renewable hydrogen is therefore a strategic energy vector that allows surplus renewable energy, such as solar or wind power, to be stored for its use in transportation, thermal energy, raw materials for the industrial sector, and electricity production [25]. Within the context of energy communities, renewable hydrogen can be considered a local energy carrier, as its production is closely linked to the local availability of renewable resources and is typically intended for on-site storage and use [26]. Despite the versatility offered by renewable hydrogen, there are still many challenges to be overcome towards its effective integration into urban, rural, and industrial environments [27]. Although multiple financing instruments, such as the RedPowerEU program [28] and the NextGeneration funds [29], have been established, and numerous sectoral reports have highlighted both the benefits and challenges of renewable hydrogen [30,31], the rate of deployment remains below projected levels [32]. On the one hand, technological improvements are needed to increase the efficiency of the energy conversion process [33]. This improvement will directly enhance economic profitability and scalability [34], while increasing social acceptance [35] by offering a safe, clean, and resilient solution that supports local decarbonization and employment. On the other hand, regulations [36] and business models [37] need to be developed to effectively integrate hydrogen at the local level. Recent studies published in the journal Hydrogen analyze the different ways of producing renewable hydrogen and the challenges that need to be overcome for its effective integration into the energy infrastructures of different regions. Uzoagba C. E. J. et al. [37] analyzed the potential for renewable hydrogen development at both local and global levels. The results obtained in the review show that Africa could be a relevant stakeholder in the hydrogen sector due to its high solar and wind energy potential. Along the same lines, Vespa, M. and Hildebrand, J. [38] explored opportunities for hydrogen development in Luxembourg. Their research used qualitative analysis based on interviews with experts and professionals from different stakeholders in the renewable hydrogen sector. The main conclusions obtained show high expectations for the hydrogen sector in the country, but point to barriers such as cost and social acceptance, which can only be overcome through collaboration and effort by all stakeholders in communication and training.

In this regard, Energy Communities (ECs) included in Directive 2018/2001 of the European Parliament and of the Council, known as REDII from 2018 [39], represent a regulatory framework with the potential to accelerate the development of renewable hydrogen at the local level. REDII defines the concept of a Renewable Energy Community (REC) as an “autonomous and open legal entity controlled by partners or members located in the vicinity of the energy projects it develops” [40]. It follows that the goal is not economic performance, but rather to empower citizens and provide them with the tools to manage their own energy to mitigate their carbon footprint and increase their energy and economic savings [41]. Although the scope of RECs is more focused at the local and individual level, it also provides benefits at the global level. For example, they increase energy production and consumption in a distributed manner, taking advantage of local resources and reducing energy losses by bringing production and consumption closer together [42]. In turn, by involving citizens in the energy sector, they actively contribute to the CET, accelerating the process of transforming the current energy sector into a more distributed, intelligent, and resilient energy sector [43].

One of the main barriers to the expansion of ECs is the limited manageability of renewable resources, which constrains self-consumption and, consequently, reduces both profitability and stakeholder interest [44].

Storage, which allows for the management of the production-consumption balance, as well as increasing self-produced energy by taking advantage of surpluses, is a key technology for the viability of ECs [45]. Currently, the most widely used renewable energy in ECs is photovoltaic solar energy, being the objective to cover the electricity needs [46]. However, energy for thermal [47] and mobility uses [48] are very important and must be covered by other renewable energy vectors such as biomass [49], or geothermal [50]. In this context, recent research highlights the importance of hybrid storage solutions [51], which combine short-term storage such as batteries and supercapacitors with long-term storage such as hydrogen [52]. The aim of this combination is to increase the flexibility of the EC and improve overall efficiency through smart energy management [53]. Renewable hydrogen would offer added value over other storage technologies, as its flexibility would allow it to be used for several applications simultaneously [54]. Furthermore, if the characteristics of the EC required a multi-vector approach, hydrogen is the only energy vector that, apart from its direct use, has the technology to be transformed into electricity, gas, or sustainable fuels [55].

Since the publication of the REDII directive, there is still considerable disparity and heterogeneity in its implementation across the different member states [56]. During this period, developments in research into both EC and renewable hydrogen have been significant and have been explored jointly, as demonstrated in this research. However, there are few critical and systematic reviews that explore deeper into advances in this area. The database obtained and refined according to the methodology in Section 2 includes only five studies in the review category in which hydrogen is not the central topic of the research but is analyzed in conjunction with other technologies. Zhou, Y. [57] analyzed the energy transition of urban districts towards a carbon-neutral energy model. Their study analyzed two energy vectors: direct electrification and hydrogen. The results obtained indicate that hydrogen is a vector more focused on large districts and heavy mobility. The research focuses on a comparison between electrification and hydrogenation, focusing primarily on electrical energy and mobility, while thermal purposes are only transversally proposed. El-Eman, Rami. S et al. [58] analyzed advances in hybrid renewable energy and nuclear energy systems in multipurpose energy systems. In this case, hydrogen is mentioned as one of the ways to store energy in distributed systems, but it does not focus specifically on energy communities, nor is hydrogen the key topic of the review. Rossi, M. et al. [59] analyzed energy and micro-energy hubs within integrated energy communities. The results obtained show that hydrogen plays a key role in sector coupling and multi-vector systems due to its versatility in terms of technologies and uses. However, although it is one of the energy vectors analyzed in the document, hydrogen is not the main topic. Bahloul, M. et al. [60] reviewed batteries and key technologies for successfully integrating energy storage systems for citizens. Hydrogen is treated as one of the three technologies analyzed, along with batteries and thermal storage. However, the hydrogen analyzed was firstly used in the residential sector for power-to-power production and, secondly, for heating. Gharibvand, H. et al. [61] analyzed the different flexibility mechanisms, how to evaluate them, and the different effects of energy storage. In this regard, hydrogen was analyzed as one of the storage systems, concluding that efficiency and cost improvements are needed to make hydrogen production profitable.

Literature reviews on the integration of renewable hydrogen in energy communities do not analyze the role of hydrogen in a central way. Furthermore, hydrogen technologies are not at the same stage of development, being essential to analyze the possible uses of hydrogen both separately and in combination with other energy carriers. Therefore, a specific literature review is needed to compile developments in the different uses of hydrogen within an energy community, identify barriers and research gaps, and establish a series of recommendations to ensure that future research addresses the specific issues of its integration into ECs. This review aims to answer the following research questions: (i) What uses and technologies of renewable hydrogen are applicable in ECs? (ii) What challenges are being identified in the literature? (iii) What solutions are being proposed? (iv) What lines of research and future developments are recommended?

Despite numerous reviews in this field, no previous study has explicitly analyzed the role of renewable hydrogen within energy communities (ECs) in a comprehensive manner. This research therefore provides a holistic and original analysis of how renewable hydrogen can be integrated in ECs across different possible uses: single-use, multi-application, and multi-vector configurations. The study goes beyond existing reviews by not only analyzing technological applications but also identifying barriers, challenges, and future research directions that remain unexplored. Specifically, the novel contributions of this work include the following:

• A systematic review of 103 research papers published between 2019 and 2025, providing the most up-to-date overview of renewable hydrogen in ECs.
• A bibliometric analysis of the different uses of renewable hydrogen within a low-carbon economy, beyond seasonal storage, identifying the most common hydrogen technologies based on their use.
• A structured classification of hydrogen applications into single-use, multi-application, and multi-vector, along with an analysis of the associated barriers and recommendations for future research.
• Strengths, Weaknesses, Opportunities and Threats (SWOT) analysis was development thought Focus Groups transnational (France, Spain, and Portugal).

Altogether, this research offers a unique, integrative perspective on renewable hydrogen in ECs, combining technological, operational, and socio-economic dimensions that have not been addressed simultaneously in the previous literature.

The paper is organized as follows. Section 2 describes the database and method used to ensure the review can be replicated. Section 3 presents the results including the current state of the art, key challenges, and future directions. Section 4 discusses the main findings, and the results of SWOT matrix. Finally, Section 5 summarizes the main conclusions of the research.

2. Materials and Methods

This section outlines the methodology used to conduct a systematic literature review aimed at comprehensively addressing the research questions formulated in Section 1. This review includes studies that apply hydrogen technologies to energy communities. Table 1 sets out the potential uses of hydrogen within an energy community, identifying the different technologies involved and grouping them, according to their functional role in energy system, as commonly adopted in the literature [62,63].

Table 1. Description of the main hydrogen uses included in the systematic review. Abbreviations: Power-to-Liquid (PtL); Direct Reduced Iron (DRI); Power-to-Power (PtP); Power-to-Gas (PtG); Fuel Cell (FC); Internal Combustion Engine adapted for hydrogen (ICE-H₂); Gas Turbine (GT); Hydrogen Refueling Station (HRS); Compressed Hydrogen (CH₂); Liquid Hydrogen (LH₂); Combined Heat and Power (CHP); Solid Oxide Fuel Cell (SOFC); Micro Gas Turbine (MGT).

Hydrogen Use	Description	Technology Involved	Maturity Level	Ref.
Feedstock	Raw material in industrial processes: refineries, ammonia and methanol synthesis, sustainable fuel production, and steel industry	1-Electrolyzer 2-Biomass gasification 3-DRI 4-PtL	1-Commercial 2-Laboratory scale 3-Demonstration 4-Demonstration	[64,65,66]
Mobility	Transport fuel: light road transport, heavy road-transport, railway, marine transport and aircrafts	1-FC 2-ICE-H2 3-GT 4-HRS 5-CH2 (350, 700 bar) 6-LH2 storage	1-Emerging market 2-Laboratory scale 3-Laboratory scale 4-Commercial 5-Commercial 6-Laboratory scale	[67]
Combustion	Fuel for industrial thermal processes such as industrial heaters or steam turbines	1-Hydrogen combustion chambers 2-Hydrogen burners	1-Demonstration 2-Demonstration	[68]
Power generation /energy storage	Storage and use of surplus renewable energy (PtP)	1-FC 2-CH2 (350, 700 bar) 3-Electrolyzer 4-Hydrogen Compressor	1-Emerging market 2-Commercial 3-Commercial 4-Commercial	[69]
Back-up emergency system	Back-up emergency system in critical facilities such as hospital or telecommunication applications	1-FC 2-CH2 (350, 700 bar) 3-ICE-H2 4-MGT	1-Emerging market 2-Commercial 3-Commercial 4-Laboratory scale	[70]
Heating	Individual domestic heating or district heating (Pure or mixed with natural gas)	1-Hydrogen boilers 2-Micro-CHP 3-SOFC 4-MGT	1-Demonstration 2-Emerging market 3-Demonstration 4-Demonstration	[71]
Blending /energy distribution	Injection of hydrogen into natural gas networks (PtG) or pure hydrogen networks.	1-Pipeline adapted for hydrogen 2-Gas pipeline adapted for hydrogen 3-Injection system 4-Compression stations 5-Leakage hydrogen detection	1-Demonstration 2-Demonstration 3-Laboratory scale /Demonstration 4-Emerging market 5-Emerging market	[72]

This classification provides an overview of the status of potential uses to support a clearer understanding of the conclusions of the research conducted. The maturity level classification distinguishes among five categories: research, laboratory scale, demonstration, emerging market, and commercial. A type of technology is considered commercially mature when it is proven, demonstrated, and widely available for commercial uses. Emerging market technology is proven and demonstrated, but its application is limited in the market. Demonstration scale technology is a technology that has been tested in relevant real-world environments such as a pilot plant or a specific application. In contrast, laboratory scale is considered a developing technology that has been validated in controlled environments or at the prototype level but lacks standardized application. Finally, technologies in the initial research phase are those that have no application beyond concept or simulations. Additionally, based on the set of criteria defined in Table 1, a classification framework has been established to organize the articles included in the review. Accordingly, and as will be explained in the following section, the reviewed studies are classified into single-use, multi-application, and multi-vector systems, depending on whether hydrogen is used for a single application, multiple applications, or in combination with other energy vectors as a sector coupler.

Scopus and Web of Science (WoS) have been used as reference databases. The search strategy consisted of an initial global search that included all terms referring to energy communities and different synonyms referring to hydrogen. The specific queries were as follows:

• Energy communities: TITLE-ABS-KEY (“energy communit*” OR “energy cooperative*” OR “citizen energy” OR “local energy system*” OR “community energy project*” OR “renewable energy communit*”).
• Hydrogen: TITLE-ABS-KEY (“hydrogen” OR “hydrogen energy” OR “green hydrogen” OR “hydrogen fuel” OR “renewable hydrogen”).

To ensure the replicability of this review and allow for updates progresses on the research topic, this research follows the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) methodology [73]. Figure 1 shows the selection and refinement process of the research included in the literature review.

Figure 1. PRISMA flowchart for selection and refinement of studies.

An initial total of 431 documents (SCOPUS: 195 and WoS: 236) was retrieved based on the search terms without applying restrictions. This systematic review focuses on recent advances, so the analysis period has been limited to publications from the last six years to date (2019–2025). This filtering resulted in a total of 334 relevant documents (SCOPUS: 168 and WoS: 166). This initial restriction step shows that more than 77% of the research has been published in the past six years to date, highlighting both the emerging nature and increasing significance of the topic. Papers indexed in the reference databases as “Book Chapter”, “Original review”, ‘Article’ and “Conference Paper” and using English as language, were taken into account. Following the initial identification, 39 documents were excluded (SCOPUS: 27 and WoS: 12). The database was limited to fields focusing on the application of renewable hydrogen as an energy carrier (electricity or thermal) or feedstock. Other subject areas such as “Medicine”, “Chemical Engineering” and “Chemistry” were excluded. Duplicate publications in the database were analyzed and removed. The 91 duplicate documents were eliminated, resulting in an eligibility-prepared database of 189 records.

Finally, all sections of the 189 selected articles were reviewed. As a result of this review, it was determined that 86 studies were outside the scope of the review. A study was considered outside the scope when (i) renewable hydrogen was not key to the work and was only mentioned as one alternative among others, and (ii) it focused on renewable hydrogen but in local applications other than an energy community, such as a hydrogen valley. Therefore, 103 studies were reviewed in detail and included in the systematic review. All authors of the articles participated independently in the process of including or excluding publications from the database. The consistency and transparency of the process were ensured using a shared document. Discrepancies between the results of each author in the refinement process were analyzed individually and resolved through regular meetings. Therefore, the final selection of reviewed articles was the result of the consolidation of individual analyses and the agreement by all authors with them.

3. Results

Following the PRISMA refinement process, 103 full-text articles were analyzed in depth. These research works were classified according to the simultaneity of hydrogen applications:

(i)

Single-use: Hydrogen is used for a single application.

(ii)

Multi-application: Hydrogen is used for two or more applications simultaneously.

(iii)

Multi-vector: Hydrogen is used simultaneously with other vectors, in such a way that hydrogen is used as a sector coupler.

The Section 3 has been divided into two subsections to provide a comprehensive review, both quantitative (Section 3.1) and qualitative (Section 3.2). Section 3.1 presents a bibliometric analysis with the aim of quantitatively analyzing research trends, search keywords, and the most relevant bibliographic sources. Section 3.2 provides a qualitative review of the different studies analyzed. This review is divided according to the simultaneity of hydrogen applications. In this way, the potential uses of hydrogen that are most widely researched in the literature and the most explored combination of technologies are identified, with the aim of identifying challenges and making recommendations for future research.

3.1. Bibliometric Analysis

Bibliometric analysis has been structured according to the recommendations set out in the study published by Donthu, N. et al. in 2021 [74]. The objective of the bibliometric analysis is to perform a quantitative analysis of recent publications to identify topic trends, research gaps, the most influential publishers, and journals in the field (Section 3.1.1. Performance Analysis), and the interconnections between different areas of study (Section 3.1.2. Science Mapping).

3.1.1. Performance Analysis

Performance analysis is very useful for detecting trends and lines of research in a specific field, as well as the evolution of technology and the interest of the scientific community. Figure 2 shows the number of publications classified according to the simultaneity of hydrogen applications defined above and the number of citations per year.

Figure 2. Number of publications and citations per year on the integration of renewable hydrogen in ECs.

Figure 2 shows an upward trend in the number of publications between 2020 and 2024. The year 2019 falls within the scope of the systematic review, but no publications addressing the integration of renewable hydrogen in ECs were found in the databases analyzed. It was not until 2020 that the EU’s reconstruction strategy was established, with renewable hydrogen beginning to be proposed as one of the key energy pillars due to its versatility and its combination with other existing vectors. For this reason, during the period of 2020–2022, most published studies focused on the integration of hydrogen in combination with other vectors. From 2022 onwards, a slight change in trend can be observed in the distribution of topics. Multi-vector applications are declining slightly due to the technological complexity of operating several systems at once with different operational requirements. Therefore, research efforts are beginning to shift towards using hydrogen for a single purpose or for several applications, but without focusing on interaction with other vectors. The goal is to increase design accuracy and produce the amount of renewable hydrogen necessary for the selected demand. This allows for maximum utilization of hydrogen and better control over profitability. Over the last year, there has been a slight decline in the number of publications on these topics. There are no further data to conclude whether this is a trend or simply a slight decline due to the complexity of the technology and the fact that regulations are advancing more slowly than expected, reducing interest and eagerness for technological developments.

Figure 3 shows the percentage distribution of hydrogen uses in each category defined. The aim is to identify the main lines of research developed and to determine which hydrogen uses (Table 1) are most important based on the categories into which the research has been classified.

Figure 3. Percentage distribution of the number of publications classified according to the hydrogen uses established in Table 1 and degree of simultaneity (inner ring: single-use, middle ring: multi-application, and outer ring: multi-vector).

The inner ring corresponds to the single-use category. As shown, most of the hydrogen use corresponds to PtP (62%), followed by mobility (17%) and feedstock (15%). This trend is justified by the greater maturity of the market for the technologies involved and the greater efficiency of the energy transformation process. The use of renewable hydrogen as a raw material to replace the current gray hydrogen is one of the most relevant uses of hydrogen, but these industries are placed in specific locations and are often not located near urban environments, where ECs are usually established. The middle ring shows the uses of the multi-application category. The trend is similar, although heating applications are particularly significant, occupying third place in the ranking led by PtP (39%), mobility (22%), and heating (18%). This trend is due to the need to increase the hours of use of hydrogen equipment to improve profitability. As shown in Section 3.2.2, CHP stands out, as it allows for the design of integrated and efficient systems capable of adapting to different demand curves. Finally, although the year abroad was dedicated to multi-vector research, with PtP (50%), heating (21%), and mobility (21%) continuing to dominate, there was a significant reduction in the use of hydrogen as a feedstock. This highlights the technological complexity of managing residential and industrial energy systems in conjunction with other energy vectors such as electricity or gas. Applications specifically addressing hydrogen as a backup system are not considered, as the focus of ECs lies in collaborative energy management. Consequently, critical facilities requiring continuous power supply are integrated into the EC energy management system rather than treated as standalone solutions.

Table 2 presents the annual distribution of publications by publisher and journal. More than half of the articles reviewed are published by Elsevier (54.8%), with particular emphasis on the journals Applied Energy (16 articles), Energy Conversion and Management (8 articles), and Energy (7 articles). These journals are recognized for their multidisciplinary nature within the field of energy, but above all for their strong focus on applied energy research. The Multidisciplinary Digital Publishing Institute (MDPI) is also a very relevant publisher for the integration of hydrogen in EC (21.1%), with its Energies journal standing out with 15 articles. The Energies journal also has a section specifically focused on hydrogen research. Finally, the Institute of Electrical and Electronics Engineers (IEEE) is distinguished for its collections of international conferences and congresses of great relevance to the sector (14.4%). As discussed in Section 3.2, one of the barriers identified is training, which is why conferences, where interaction is synchronous and direct, are one of the most important tools for disseminating results.

Table 2. Yearly distribution of included papers (2020–2025), by publisher (in bold) and journal (in regular font), related to the integration of renewable hydrogen in EC.

Publisher/Journal	2020	2021	2022	2023	2024	2025
Aalborg University Open Publishing.				1	1
International Journal of Sustainable Energy Planning and Management				1	1
Elsevier	1	5	10	12	12	16
Applied Energy		3	2	3	4	4
Energy			1	1	2	3
Energy and Buildings					2	2
Energy Conversion and Management		1	1	3	1	1
Energy Policy		1
Energy Storage and Saving						1
e-Prime—Advances in Electrical Engineering, Electronics and Energy				1	1
International Journal of Hydrogen Energy			1	1	1	1
Journal of Cleaner Production				1
Journal of Energy Storage			1		1	1
Renewable And Sustainable Energy Reviews			1			1
Renewable Energy	1		1	1	2
Renewable Energy Focus						1
Scientific Reports				1
Smart Energy			1
Sustainable Cities and Society			1
Sustainable Energy, Grids and Networks						1
Energy Proceedings	2				1
Energy Proceedings	2				1
Frontiers		1		1
Frontiers in Energy Research		1		1
IEEE		2	2	5	5	1
2025 13th icSmartGrid						1
2023 IEEE 6th CIEEC				1
2023 IEEE PES ISGT EUROPE				1
2024 3rd SyNERGY MED					1
2024 EEEIC/I&CPS Europe and 2024 PES ISGT EUROPE					1
2024 IEEE PES ISGT EUROPE					1
2021 INTERNATIONAL CONFERENCE ON SEST		1
2022 17TH INTERNATIONAL CONFERENCE PMAPS			1
2023 EEEIC/I&CPS Europe and 2023 PES ISGT EUROPE				1
2024 IEEE PES ISGT EUROPE					1
Conference Record of the IEEE Photovoltaic Specialists					1
IEEE Access				2
IEEE Power and Energy Society General Meeting			1
IET Conference Proceedings		1
IOP Publishing					1
Journal of Physics: Conference Series					1
MDPI	1	3	4	4	6	5
Applied Sciences (Switzerland)		1	1	1	1
Clean Technologies		1
Energies		1	3	3	5	3
Processes						1
Sustainability (Switzerland)	1	1				1
Springer			1
Power Systems			1
Total Articles Published per Year	4	11	17	22	27	23

3.1.2. Science Mapping

Science mapping is a type of analysis useful for identifying connections between different keywords, allowing the detection of connections between keywords and allowing the definition of trends and methodologies used in research [74]. VOSviewer 1.6.20 [75] was employed to analyze the generated database and carry out keyword co-occurrence analysis. The full counting method in VOSviewer has been used for this analysis. The minimum keyword occurrence is set to 8. As a result, 37 keywords met this criterion, while 997 were filtered out, as shown in Figure 4.

Figure 4. Keyword co-occurrence network for research on the role of renewable hydrogen in ECs. The colors represent thematic groups: gray is assigned to “single-use”, blue to “multiple applications”, and green to “multi-vector”.

Figure 4 presents a keyword co-occurrence network, where each node represents one of the 37 identified keywords. The terms “single-use”, “multi-application,” and “multi-vector” do not appear in the original database. These keywords were introduced after carefully reviewing and classifying the different studies. The objective is to identify which keywords appear most frequently in each category defined. The dimensions of the nodes correspond to the number of occurrences of each keyword in the database, while the links indicate co-occurrence within the same document. The thickness of the links represents the strength of this co-occurrence, with thicker links denoting greater frequency. The colors represent thematic groups: gray is assigned to “single-use,” blue to “multiple applications,” and green to “multi-vector,” which correspond to the classification used in the review, as shown in Figure 2.

Table 3 shows the three groups into which the keywords have been grouped. The objective of the cluster analysis is to detect the most relevant points based on the simultaneity of hydrogen applications and the relationships between them.

Table 3. Clustering hotspot in the role of renewable hydrogen in ECs.

Cluster	Cluster Research Hotspot	Keyworks in the Cluster
1 (Grey color)	Single-use	Battery storage; digital storage: economic analysis; energy; energy community; hydrogen; hydrogen production; hydrogen storage; integer programming; investments; local energy; multi-objectives optimization; power; solar power generation; wind power
2 (Blue color)	Multi-application	Decarbonization; electric energy storage; multi-objectives optimization; renewable energy communities; renewable energy resources
3 (Green color)	Multi-vector	Alternative energy; carbon; clean energy; energy management; energy storage; energy systems; multi energy; optimization; renewable energies; smart grid; uncertainty

3.2. Current Status, Challenges and Future Developments

This section compiles a qualitative analysis of the role of renewable hydrogen in ECs, identifying the most developed applications, the main technologies involved, and the main challenges identified in the literature. It is structured according to the simultaneity of hydrogen applications established throughout the article as follows: Section 3.2.1 presents research in which hydrogen is focused on a single use. Section 3.2.2 analyzes research in which hydrogen combines two or more uses simultaneously. Finally, Section 3.2.3 compiles research in which hydrogen is combined with other energy carriers such as electricity or NG, in many cases playing a key role as a sector coupler.

3.2.1. Single-Use Hydrogen

A review of the existing literature reveals that approximately 67% of studies focus on applications directly linked to energy balancing, emphasizing hydrogen’s role as an energy storage or conversion medium. Among the remaining applications, primary energy production and mobility each account for approximately 15% of single-use hydrogen studies, reflecting their relevance for renewable energy integration and decarbonization. In contrast, heating applications represent the smallest contribution, yet they offer opportunities for operational flexibility and cost optimization through hybrid heating systems and coordinated control strategies.

Analyzing firstly the contributions linked to the energy balance applications, recent research has focused on robust and adaptive optimization frameworks to manage uncertainties in renewable generation, demand, and market prices within Local Energy Communities (LECs). Khojasteh, M. et al. proposed an adaptive robust optimization approach for joint energy and regulation service management, integrating community-scale batteries and hydrogen storage systems to ensure resilience under uncertainty, while simultaneously enhancing operational flexibility, cost efficiency, and sustainability by maximizing local renewable energy use and reducing reliance on fossil electricity [76]. Similarly, Dorahaki, S. et al. developed an adaptive bi-level optimization model based on Stackelberg game theory to coordinate community energy storage and prosumer participation in multiple markets [77]. Earlier, Khojasteh, M. et al. introduced a robust max–min optimization strategy for hydrogen-integrated LECs, confirming that hydrogen enhances operational flexibility and reduces total energy costs by up to 38%, while also supporting sustainability by increasing the utilization of locally generated renewable energy and promoting a more environmentally friendly energy management [78]. Complementary approaches, such as cooperative Model Predictive Control (MPC), have also been applied to mitigate energy resilience risks in networked microgrids, demonstrating the increasing use of advanced control and optimization tools for resilient community energy management [79].

Building upon these frameworks, other works have explored multi-level management strategies to combine short- and long-term coordination of hybrid systems. Fu, A. and Cvetković, M. presented a four-stage receding-horizon strategy that integrates photovoltaics, batteries, and hydrogen components (electrolyzer and fuel cell) across yearly, monthly, day-ahead, and intraday horizons [80]. The approach distinguishes between seasonal hydrogen storage and daily battery use, enhancing self-sufficiency and flexibility. Similarly, Fu et al. demonstrated a local energy hub for urban environments implementing a comparable multi-scale coordination scheme, while Nistor. A. S. et al. validated through simulation that integrating hydrogen generators with smart SCADA systems enables improved grid interaction and renewable utilization at community level [81,82].

A common thread across these studies is the recognition of hydrogen as a long-term energy balancing and flexibility vector in energy communities. Multiple works demonstrate that integrating electrolyzers, fuel cells, and hydrogen storage enhances the system’s ability to balance renewable variability and provide ancillary services but also promoting sustainability by maximizing local renewable energy use and reducing dependence on fossil-based electricity [83,84]. Bianchi, F. R. et al. employed Reversible Solid Oxide Cells (rSOCs) to optimize transitions between electrolysis and fuel-cell modes, showing hydrogen’s dual role in power-to-gas and power-to-power pathways. By storing surplus renewable electricity as hydrogen and converting it back when needed, their approach not only enhances operational flexibility but could potentially avoid a significant reduction in CO₂ emissions (around 5 tons of CO₂ per year per 100 kWh/day of surplus PV generation), supporting decarbonization and increasing the effective use of clean, locally generated energy [85]. Other studies have validated hydrogen’s contribution to islanded or off-grid operation, such as Jin, L. et al. who compared hydrogen versus battery storage in a hydropower-based community [86], and Nastasi, B. and Mazzoni, S. who explored renewable hydrogen energy community layouts for autonomous operation using solar-driven electrolysis [87].

In parallel, several studies evaluate the techno-economic feasibility of integrating hydrogen into community-scale energy systems. Pera, L. et al. found that hydrogen storage becomes increasingly profitable as technology costs decrease [88], while Bekele, E. et al. emphasized the strong influence of electrolyzer investment costs on overall system feasibility [89]. Both studies also highlight that integrating hydrogen can increase renewable energy utilization and reduce reliance on fossil-based electricity, potentially avoiding several tons of CO₂ per year per community, thereby combining techno-economic benefits with tangible environmental impacts. Similarly, Ciancio, A. and De Santoli, L.; Spazzafumo, G. and Raimondi, G.; and Raimondi, G. and Spazzafumo, G. demonstrated that hydrogen integration can significantly enhance self-sufficiency in renewable energy communities, although economic viability is still constrained by current technology costs [90,91,92]. Overall, these works highlight the importance of cost reduction and optimal system design for the widespread adoption of hydrogen-based solutions in energy communities.

In addition, the integration of hydrogen value chains within community-scale and regional systems has been increasingly explored to support decarbonization and energy independence. Katsaprakakis, D. A. et al. presented the Sifnos Energy Community as a pilot case for energy transition in insular systems, coupling hydrogen with pumped hydro storage and fostering local economic development [93]. By enabling the island to cover most of its electricity demand from renewable sources and hydrogen storage, this approach enhances energy autonomy, reduces reliance on imported fossil fuels, and could avoid tens of tons of CO₂ per year, thereby contributing to the decarbonization and environmental sustainability of the local energy system. Sołtysik, M. et al.; and Böhringer, M. et al., also demonstrated how hydrogen integration in LECs and energy clusters enhances self-sufficiency and grid resilience, though economic viability still depends on technological maturity and policy support [94,95]. Finally, uncertainty in renewable production, load demand, and prices remains a key challenge in LEC operations. Tostado-Véliz, M. et al. addressed this using Information Gap Decision Theory (IGDT) for day-ahead scheduling in hydrogen-enabled energy communities, improving both self-sufficiency and resilience under uncertain conditions [96]. Li, N. et al. applied multi-objective optimization to assess hydrogen integration under various grid connection limits, revealing trade-offs between energy independence and grid stability. These contributions complement robust and bi-level optimization approaches, highlighting diverse methodological frameworks for addressing uncertainty in community-scale energy systems [97].

On the other hand, in relation to studies focusing on hydrogen production from primary energy sources, these works mainly explore the use of renewable energy and waste resources as feedstocks for renewable hydrogen generation, emphasizing techno-economic optimization and energy efficiency. Mojtahed, A. et al. proposed a landfill gas-based hydrogen system combining electrolysis, methane reforming, and a supercritical CO₂ heat pump, achieving high energy efficiency and reduced hydrogen costs. In addition to these techno-economic benefits, the system converts methane from landfill gas into hydrogen, reducing net greenhouse gas emissions and supporting decarbonization efforts while improving overall environmental sustainability [98]. Pizzuti, I. et al. demonstrated that offshore wind integrated with PEM electrolyzers and battery storage can directly supply hydrogen for industrial applications while minimizing intermediate storage needs. By leveraging offshore wind, their system achieves high renewable utilization and avoids approximately 268 kt CO₂ per year from wind energy use and an additional ~520 kt CO₂ per year through green hydrogen [99]. Amin, A. et al.; and Bekele, E. et al. analyzed hybrid PtG and PtL systems within rural communities and emerging Hydrogen Valleys, showing improved renewable energy utilization, reduced CO₂ emissions, and potential economic viability, with Bekele et al. reporting a 29.5% decrease in emissions compared to a business-as-usual scenario [100,101]. Finally, within this use, Jodry, A. et al. addressed industrial hydrogen hubs, integrating electrolysis with natural gas and biomethane, highlighting the importance of multi-vector energy integration and local renewable resources for cost-effective and flexible hydrogen deployment [102].

Hydrogen utilization represents a strategic pathway to enhance renewable energy integration and support decarbonization in community-scale mobility systems. Salehizadeh, M. et al. developed a sequential optimization framework that allocates excess residential PV generation to hydrogen production for FCEVs, coupled with community energy storage to manage demand response, achieving improved electricity cost savings and enhanced local energy flexibility [103]. Guo, M. et al. proposed a density- and correlation-based methodology to structure highway energy communities integrating traffic-power coupling networks with hydrogen refueling infrastructure, effectively managing stochastic energy demand induced by traffic flows. By optimizing the interaction between traffic-induced loads and local renewable energy sources, their approach enhances energy efficiency and can contribute to reductions in transportation-related CO₂ emissions, highlighting the potential environmental benefits of integrating hydrogen and renewables in mobility-focused energy communities [102]. Additionally, Gronier, T. et al. investigated collective hydrogen production for bus fleets within energy communities, developing optimal grid interaction and hydrogen allocation strategies that balance economic performance with mobility requirements [104]. In urban zero-energy communities, Liu, J. and Yang, H. analyzed hybrid renewable energy systems with stationary batteries and mobile hydrogen vehicles, demonstrating significant improvements in renewable self-consumption, economic performance, and load coverage compared to battery-only configurations. Their results show that systems with hydrogen vehicles achieve renewable self-consumption ratios up to 94.45% and substantial reductions in CO₂ emissions (≈75.96%) compared to baseline scenarios without hydrogen integration [105,106].

Finally, as mentioned before, hydrogen integration in heating systems represents the smallest contribution within single-use hydrogen applications. In this sense, Wang, Y. et al. investigated a hybrid heating network combining a dual-source heat pump with district heating, evaluating multiple control strategies based on cost optimization and low-temperature prioritization. Dynamic simulations demonstrated that strategies leveraging hourly electricity pricing and waste heat from hydrogen production significantly reduce annual energy costs, while tariff structures and price dynamics were identified as critical factors influencing system performance. This work illustrates the potential of coordinated control of multiple heat sources, including hydrogen-derived waste heat, to achieve efficient and economically viable heating in community-scale energy networks [107].

In order to provide an integrated overview of the analyzed literature, Table 4 summarizes the reviewed works according to their main technology and energy system configuration, the scale, and key limitations.

Table 4. Summary of the main contributions within single-use hydrogen applications.

Category	References	Technology	Limitations/Challenges
Energy Balance—LECs with H2 and battery storage	[76,77,78,80,82,83,88,89]	Battery energy storage systems + hydrogen (electrolyzer, H2 storage, fuel cell), photovoltaics, wind	High computational complexity Sensitivity to forecasting errors Scalability concerns
Energy Balance—Microgrids and networked systems	[79,81,84,90,97]	Photovoltaics, wind, hydrogen seasonal storage, batteries	Coordination complexity Communication delays Idealized forecasting and scalability limitations
Energy Balance PtP/Industrial and off-grid systems	[85,86,87,91,92,93,94,95,96]	Photovoltaics, wind, small hydro, reversible SOCs, electrolyzer + fuel cell + H2 storage	Geographic/climatic specificity Limited real-time market modeling Scalability concerns
Primary Energy Hydrogen production from renewable and waste sources	[98,99,100,101,102]	Landfill gas, offshore wind, photovoltaics + wind + battery, PtG/PtL, electrolysis + natural gas + biomethane	Constant efficiency assumptions Limited real-time market considerations
Heat Production Hybrid heating systems	[107]	Dual-source heat pump + district heating + H2 waste heat	Assumed constant component efficiency Results dependent on tariff variations
Mobility Hydrogen for Transport and Storage	[103,104,105,106,108]	PV + hydrogen + FCV, Traffic-power coupled networks, hybrid renewable + battery/H2 vehicles	Idealized forecasting Limited scalability Dependency on policy/support frameworks

3.2.2. Several Uses of Hydrogen

The simultaneous use of hydrogen in several applications is a research line focus to increase the operating hours of hydrogen production facilities to increase profitability and reduce the cost of hydrogen production. In this regard, recent research focuses on finding the combination of applications that provides the greatest benefit to the EC. It should be borne in mind that the principle of EC management is based on the complementarity of consumption profiles, so those applications with consumption profiles that are out of sync in time will be those that, a priori, offer greater profitability.

A review of the existing literature reveals that approximately 40% of studies combine electricity production with thermal energy (CHP). In relation to other applications, energy storage combined with mobility (20%) in residential EC or with industrial use of hydrogen (20%) stands out. The remaining studies included in the multi-application category focus on the use of hydrogen as a feedstock and its combination with mobility or to provide grid regulation services in low-power distributed energy systems.

Decarbonization of mobility is a fundamental aspect of ECs, as it has a significant impact at the local level on health and quality of life in urban environments. FCV integration represents a completely zero-emission solution, which, combined with the speed of the refueling process, offers a solid alternative to mobility systems based on fossil fuels or batteries. However, vehicle usage patterns are highly random, which makes it difficult to efficiently design and manage production facilities. For this reason, and in order to increase profitability, it is vitally important that mobility-based solutions are combined with other uses that reduce this variability and guarantee sufficient operating hours to make the operation profitable. Ghasemnajad, H. et al. [109] analyzed the effect of mobility randomness on the design and management of an EC. Their research proposes an optimization framework based on Information Gap Decision Theory (IGDT) in which the uncertainty of consumption patterns can be analyzed through the variability of the distance traveled or refueling ranges. Mobility is combined with energy sharing models among community members, as well as with the thermal comfort of homes. The model generated is optimized with Mixed-Integer Linear Programming (MILP) with the aim of sizing the most economical PV, electrolyzer, and storage system located in parking lots. The results obtained indicate that they are robust, as they can tolerate up to 50% variability in the distance traveled. However, there are no experimental data from pilot cases available to validate the results obtained and improve the models. Alam, Md, M. et al. [110] proposed a framework based on AI and intelligent optimization algorithms for designing and operating low-voltage LEC microgrids. The framework they created is based on a two-level approach. The first level uses a clustering algorithm (K-means) to extract and classify demand patterns from the data; the second level uses this algorithm for optimization (MILP + Particle Swarm Optimization (PSO)) in design and operating costs. It uses a real LEC in Australia as a case study. In this case, hydrogen is used as a storage system to manage the variability of the renewable energies considered (PV, wind, and small hydro) and as fuel in FCVs. The results obtained show not only a significant improvement in costs (47.03–57.73%) compared to the grid-connected scenario, but also a 98.23% reduction in emissions compared to a coal-based reference scenario. However, the application of AI requires the acquisition of quality data. Sanz-Cuadrado, C. et al. [111] investigates the application of hydrogen as a raw material in rural ECs to reverse depopulation. The case study analyzed is a region of Spain in the vicinity of Calatayud. The research is based on a comparison of three scenarios to valorize the surpluses from the existing 4 MW facility in the municipalities: (i) the direct sale of energy, (ii) storage in batteries, and (iii) advanced uses of hydrogen in hydrogen refueling stations (HRS) and feedstock production for fertilizers. The results obtained show that the most profitable option in the short term is the direct sale of energy. The hydrogen-based scenario shows that the high cost of the technology reduces profitability, although it offers significant advantages in the long term, especially in the social sphere, which is one of the central pillars of the research.

CHP is one of the most relevant topics in the integration of hydrogen in ECs due to several advantages: (i) it improves system efficiency, since part of the hydrogen energy that cannot be used in the form of electricity is used in the form of heat; (ii) it reduces the complexity of management systems, since both electrical and thermal energy production are coupled in one system, requiring fewer components and technologies to be controlled; and (iii) it simultaneously addresses two of the most relevant consumption areas in the building sector by producing energy and heat together. Of note in this area are the studies by Gabbar, H.A. and Ramadan, A. [112], who propose a hybrid system combining renewable energies (PV and/or wind) and hydrogen in buildings. They compare several scenarios in a large building located in Oshawa, Canada. The comparison is made using simulations carried out in TRNSYS 16, in which hydrogen covers part of the electricity needs through FC, while heating needs are covered by direct combustion of hydrogen mixtures with NG. One of the peculiarities of this study is that it analyzes the risks of integrating hydrogen into an urban environment, in addition to the techno-economic study. The results show that the incorporation of hydrogen amplifies the decarbonization introduced by renewable energies, especially due to the reduction in NG use, achieving reductions from 540 to 324 tCO₂/year, which represents an economic saving of around CAD 251,406 in carbon emission allowances. Despite the advantages, the authors identify that further research is needed on the scalability of these systems. Capuder, T. et al. [113] go one step further by creating a framework capable of optimizing the operation of a fuel cell in isolation, considering not only the energy criteria but also introducing dynamic regulation. A comparison of three different systems is made, one of which is hydrogen-based. The proposed hydrogen installation involves the use of an electrolyzer to produce hydrogen that will be used in a fuel cell focused on meeting heat needs as its primary objective and electricity second. The results show that the inclusion of dynamic stability in the optimization framework can increase costs by 6.2%. The dynamic stability analysis highlights the difficulty of integrating the main components into the grid, such as the electrolyzer and fuel cell, as they do not contribute to the stability of a small grid. Another very relevant approach is that taken by Martinez-Reverte, I. et al. [114], whose objective is to determine the impact of introducing FC in a cogeneration system in 4194 homes in Valencia (Spain) supplied by the NG network. Eight configurations are analyzed, varying different parameters such as thermal and electrical power, different operating modes, and different distributions. The selected configuration corresponds to a 4 MW central Phosphoric Acid Fuel Cell (PAFC), operating in thermal mode in winter and in electrical mode in summer. The investment in a system of this type is around EUR 15.2 million. Large investment required demonstrates the need for more research that takes into account different business models and incentives, such as that carried out by Caramanico, N. et al. [115]. The authors propose a techno-economic analysis of micro-CHP systems for use in buildings. Two technologies are compared, NG-SOFC and rSOFC, under different incentive schemes and different external environmental parameters. They use as a case study a set of simulated buildings using TRNSYS located in the city of Milan (Italy). Although it is not completely environmentally friendly, the most competitive technology is NG-SOFC, although rSOFC offers good results in ECs. This is because it reduces the number of components and increases the hours of use, which improves the distribution of investment among the different members.

Hydrogen can also add value to industrial ECs. Rosén, S. et al. [116] explored the role of hydrogen in an industrial region in Sweden, where there are three large hubs with hydrogen-intensive industries such as oil refineries and chemical plants. The aim of the research is to analyze the advantages of building a hydrogen transport pipeline linking the three hubs compared to a distributed system based on ECs. The results obtained indicate cost reductions in the price of hydrogen of between 12 and 17% due to the construction of the pipeline. This research is highly relevant as it also demonstrates the effect of scale in hydrogen-based systems and the importance of the distribution and transport stage. Similarly, Vokony, I. [117] presented a feasibility analysis of hydrogen integration in a real EC located in Hungary, which has the potential to become a pilot project serving as a testing laboratory. In this case, hydrogen would be used to meet the electrical and thermal energy needs of different industries, taking advantage of surplus renewable energy and technologies such as piston engines or MGTs. Another application analyzed is the use of hydrogen and natural gas mixtures in vehicles that allow for such fuel flexibility. However, the author points out that this specific application is prohibited in Hungary.

Finally, Sun, D. et al. [118] have conducted an in-depth analysis of the dynamic behavior of a hybrid EC that combines a wind farm with a hydrogen plant intended for direct sale through the NG network or for refueling vehicles. The proposed model was developed in Matlab/Simulink, which can be subjected to different wind speed scenarios or numbers of electrolyzers in operation. The results obtained indicate that the introduction of a hydrogen production plant in an appropriate manner provides stability to the system in the event of sudden changes in the grid. For example, in the event of a sudden drop of 15 MW, they have achieved frequency variations of 0.34 Hz, which is a very promising value.

Table 5 summarizes the key challenges and the dominant technologies associated with each hydrogen multi-application use category identified in the literature review.

Table 5. Summary of the main contributions within multi-application hydrogen use.

Category	References	Technology	Limitations/Challenges
Mobility and Energy Balance	[109,110]	HRS; electrolyzers; hydrogen storage and PV plant	Lack of experimental validation data Uncertainty in assumptions Quantity and quality in the data acquisition process
Mobility and feedstock	[111]	PV plant; Electrolyzer; HRS and ammonia synthesis	Difficulty obtaining individualized data Lack of long-term vision Low hydrogen production. EC scale too small
CHP	[112,113,114,115]	FC; PV; hydrogen storage, heat storage; rSOFC; NG-SOFC, blending; PAFC	Scalability Lack of experimental validation data Technological maturity in integration. Grid-following components Lack of long-term vision Influence of external parameters that cannot be controlled in the long term
Industry and Energy Balance	[116,117]	PV plants; electrolyzers; hydrogen pipelines; Underground Hydrogen storage (UHS); compressed hydrogen storage	Difficulty in forecasting long-term hydrogen consumption Absence of specific regulation of hydrogen in the industrial sector
Frequency grid regulation and feedstock	[118]	FCV; Alkaline Electrolyzers (AEL); wind	Low understanding of the dynamic behavior of hydrogen components.

3.2.3. Hydrogen Integrated into a Multi-Vector System

Multi-vector energy systems are a step in the evolution towards integrated models; they are able to combine electricity, gas, heat, and alternative fuels to improve the resilience, efficiency, and sustainability of the energy system. Hydrogen stands as key enabler for sector coupling, allowing the connection between independent sectors such as mobility, heating and electricity generation and consequently obtaining more efficient systems than when analyzed independently [119]; studies have shown that hydrogen can improve flexibility of the electricity grid [120], facilitate stationary energy storage [121], present an efficient integration in hybrid electricity–gas networks [122] and supply auxiliary services to the system [123].

Hydrogen performs multiple functions within a multi-vector energy system: long-term energy storage, being a complement to battery storage [124]; sector coupling, according to its processing through electrolysis or methanation [125]; decarbonization of hardly electrifiable sectors such as industry, aviation and heavy transport [126]; and participation in auxiliary systems and demand response [127].

The integration of hydrogen with renewable energies is one of the pillars of modern multi-vector energy systems. Coupling via electrolyzers mitigates renewable variability and improves the utilization of wind and solar resources. Recent studies have shown that electrolyzers can operate efficiently under dynamic renewable generation conditions [120,127,128].

In addition, integrated planning projects indicate that PV–H₂ hybrid systems can reduce operating costs and emissions compared to exclusively electrical solutions [129]. Lei, L. and Wu, N. have demonstrated that collaborative multi-energy models complemented by optimization models can achieve a 17.67% reduction in emissions, with total system cost reductions of 16.59% [130]. The optimal expansion of hydrogen systems in scenarios with high renewable penetration has also been analyzed [60,131].

Many studies have focused on the modelling and optimization of multi-vector energy systems with hydrogen. In this field, stochastic and scenario-based optimization models have gained relevance, including models for optimal dispatch, infrastructure planning, and real-time operation. Several studies have developed complex mathematical models that integrate electrolyzers, fuel cells, storage, and thermal networks [122,132,133].

Some research has developed multi-objective optimization models to capture trade-offs between efficiency, costs and emissions. For example, Xie, C. et al. [126] demonstrated that the efficient integration of multi-vector energy systems could improve emissions reduction (59.9%) compared to single-vector systems that do not use batteries as storage systems (38.6%), while others have addressed the predictive control of multi-vector systems with hydrogen [134,135].

On the other hand, hydrogen stands out as a seasonal storage solution in combination with batteries to cover long time horizons. Hybrid battery–H₂ architectures have been proposed that improve system resilience [124,136].

Recent studies also analyze the role of storage in smoothing demand peaks in urban contexts [137] and in isolated microgrids [123]. Regarding the latter, smart electrical systems are evolving towards multi-vector platforms that integrate hydrogen as a flexible resource. Some studies show that fuel cells can participate in primary and secondary regulation [119,138]; other proposals analyze hydrogen as a resource for alleviating grid congestion [139].

Hydrogen also allows renewable surpluses to be managed by converting them into higher-density energy products such as synthetic methane or liquid fuels [140,141]. These products can be used for electricity generation, and for heating and mobility, where hydrogen can also be directly used. Hydrogen-based mobility can play an important role in system stability thanks to the H₂-based vehicle-to-grid (H₂-V2G) concept. Studies in recent years have shown promising integration into public transport and logistics fleets [125,142].

Table 6 summarizes the key challenges and the dominant technologies associated with each hydrogen multi-vector use category identified in the literature review.

Table 6. Summary of the main contributions within multi-vector hydrogen applications.

Category	References	Technology	Limitations/Challenges
Mobility	[120,132,137,143,144,145,146]	Electricity, heat, gas, water, hydrogen	Lack of flexibility in existing optimization models Impulse Circular Economy initiatives to support biomethane and hydrogen production Uncertainties in hydrogen loads complicate the management of multienergy systems Uncertainties in energy availability due to climate change complicate the economic evaluation
Feedstock and blending	[121]	Electricity, heat, hydrogen	Heterogeneous data sources Need for refinement of management models
Heating	[122]	Electricity, heat, gas, water, hydrogen	Commercialization of oxygen as a byproduct of the hydrogen generation to increase profitability
Heating and Mobility	[147,148]	Electricity, bioenergy	Hydrogen implies higher costs for decarbonization than all-electric scenarios
Blending and Power generation	[136,140,149,150]	Carbon Capture and Storage (CCS), Use, PtG, ORC, Ice Storage Air Conditioning (ISAC)	Increasing flexibility of hydrogen fuel cells to respond to rapid changes in the demand Strengthening impacts on carbon emissions of the whole life cycle
Blending and Heating	[151,152]	Electricity, gas, hydrogen	High renewable energy potential areas are required for hydrogen and blending to be more effective than batteries for excess storage Low electrolyzer efficiency reduces performance for energy storage
Power generation, Mobility and Heating	[119,124,153,154,155,156]	Electricity, heat, gas, hydrogen	Reducing uncertainty in prices and energy availability prediction
Power generation	[60,123,125,126,127,128,129,131,133,134,138,141,142,157,158,159,160,161,162,163,164,165,166,167]	Electricity, heat, hydrogen	Improving resilience of the model to system disturbances Advanced control strategies to enable real-time coordination among electricity, thermal, and hydrogen subsystems Reduction in technological costs for a sustainable business model Dependence on RES potential for the economic viability of hydrogen production
Power generation and Mobility	[139,168,169,170]	Electricity, hydrogen	Development of decision-making solutions to improve the coordination between energy systems during emergencies
Power generation and Heating	[130,135,171,172,173,174,175]	Electricity, heat, gas, hydrogen	Incorporation of sociological aspects in the alliance cooperation to ensure its stability Reducing uncertainty in prices and energy availability prediction

4. Discussion

Section 3 provides an in-depth analysis of the various studies published in relevant scientific journals. This review has made it possible to identify the main lines of research, the main challenges and limitations, and the value that renewable hydrogen brings to a low-carbon economy and its interactions with other energy carriers. It can be observed that in the different categories evaluated (single-use, multi-application, and multi-vector), the barriers to hydrogen integration are similar. The lack of real data is a barrier to design optimization, as well as adjusting hydrogen installation to present and future needs. The low availability of real data also has a negative impact on the development of efficient models and algorithms for the management and integration of a hydrogen facilities within an EC. Both barriers have an impact on the profitability of the final facilities, reducing social interest in and social acceptance of this technology.

In this regard, initiatives promoted by various supranational institutions such as the European Union (EU) are essential for introducing renewable hydrogen into ECs across different locations and configurations, and generating real success. The objective is to have a testing laboratory under real conditions that allows for the generation of knowledge and databases to provide a solid foundation for developing new business models that can be extrapolated to other ECs with different characteristics. Initiatives such as the SHARED-H2 SUDOE project entitled “Renewable hydrogen: a solution for flexible and distributed energy storage in LEC,” funded by the Interreg SUDOE program and co-funded by the EU, work to integrate renewable hydrogen within the regions included in the SUDOE territory. The SUDOE territory is composed of 26 NUTS-II regions across four States: three EU Member States: France, Spain and Portugal, and Andorra as a third country. Specifically, in France, this includes the regions of Nouvelle-Aquitaine, Occitanie, and Auvergne; in Spain, all territories except the Canary Islands; and in Portugal, only the mainland is included.

The development of SHARED-H2 SUDOE is structured around three pilot actions with different characteristics and uses of hydrogen: (i) Pilot 1 (Spain) integration of renewable hydrogen in an industrial EC where hydrogen would be used in rural activities in the surrounding area; (ii) Pilot 2 (France) is part of an existing self-consumption facility, where hydrogen would be used to take advantage of surpluses for both energy storage and to supply hydrogen to a set of fuel cell bicycles; (iii) Pilot 3 (Portugal) is a demonstration laboratory where application simulations will be carried out to adopt solutions for real cases, urban and regional mobility.

One of the main results of the project obtained during the first year is a situational diagnosis of the introduction of renewable hydrogen technologies in LEC. The diagnosis was developed through a SWOT analysis. A SWOT analysis is a very common tool in preliminary analyses and strategic planning [176,177], which allows for the identification of internal and external factors that are influencing the introduction of hydrogen in ECs. A series of focus groups were held with the aim of obtaining an evidence-based diagnosis that accurately represents the reality of the entire SUDOE territory and is not biased by the knowledge of the project members. A focus group consists of a group meeting led by a moderator using a script of topics. The aim is to encourage interaction between participants as a method of generating information [178].

A total of nine focus groups were organized, corresponding to each of the participating countries (three) and pilot actions (three). The 84 unique stakeholders who attended came from different countries within the SUDOE territory and represented the business sector (21%), professional associations (21%), public administrations and agencies (48%), universities (4%), and technology centers (6%) related to the energy and hydrogen fields. The moderation was carried out by the University of Salamanca, which was responsible for preparing the script with the appropriate questions, as well as ensuring a balance of participation among the different attendees. The questions were grouped into five thematic blocks: technological, economic–financial, environmental, legal–administrative, and social. This topic structure allowed for a holistic approach to the feasibility of integrating renewable hydrogen into EC. In turn, each of the blocks consisted of a balanced number of questions and was given a similar amount of time, with the aim of ensuring that the results were balanced, representative, and extrapolatable to other regions. The broad spectrum of attendees ensured that the results included not only the opinions of field experts, but also reflected the perceptions of all stakeholders involved, even if they did not have in-depth knowledge of the technology.

Figure 5 shows the main results of the SWOT analysis. No significant differences were detected between the different countries. It can therefore be concluded that the current situation and barriers to the introduction of renewable hydrogen are very similar. In terms of strength, S1 and S3 stand out. Renewable hydrogen is perceived as an energy vector capable of harnessing surpluses in multiple applications that would otherwise be fed into the electricity grid with limited remuneration. W1 and W3 are the most significant weaknesses, both related to the economic sphere. On the one hand, due to low technological maturity and limited implementation, Capital Expenditures (CAPEX) and Operational Expenditures (OPEX) of renewable hydrogen technologies are high. On the other hand, it is observed that financing programs prioritize large-scale hydrogen production projects and volumes, while the budget allocated to small-scale EC projects being limited. Renewable hydrogen represents a significant medium to long-term opportunity, as its flexibility and technological advantages over other storage systems, such as batteries, enable more effective use of local resources, reduce dependence on third parties (O2), and increase the Self-Sufficiency Ratio (SSR). However, the lack of political stability and long-term strategies for decarbonization and hydrogen integration (T1) constrains its safe deployment in EC-scale projects and discourages R&D on standardized, interoperable energy systems across technologies and suppliers (T2).

Figure 5. SWOT matrix for renewable hydrogen in EC.

Analyzing jointly the literature review in Section 3 and the SWOT matrix shown in Figure 5, research carried out in the field of renewable hydrogen within an energy community delves deeper into opportunities and strengths, as it explores different uses aimed at exploiting surpluses and increasing energy independence, both in terms of electricity and gas. The scope of the research carried out is focused on overcoming the weaknesses detected in the SWOT analysis, as much of the research included in the review performs techno-economic analyses with the aim of detecting the most profitable uses and developing more efficient and robust management models. However, much more research is needed on the development of long-term policies and on establishing strategies that encourage investment in this type of project. Training at all levels is key to increasing knowledge about the urban and safe use of hydrogen and preventing public opinion from becoming a threat to this business model.

5. Conclusions and Future Directions

Energy communities (ECs), introduced in the REDII regulations in 2018, aim to improve energy system efficiency through decentralization, decarbonization, and active citizen participation. Central to ECs is the combination of efficient energy management and local use of renewable resources, where renewable hydrogen can play a key role. Hydrogen, produced via water electrolysis using surplus renewable energy, is a sustainable vector aligned with 2050 decarbonization targets. It can be applied in single-use, multi-application, or multi-vector configurations across applications such as PtP, CHP, mobility, and feedstock within energy communities. However, technical, economic, and social barriers (such as integration challenges, high component costs, limited real-world data, and regulatory gaps) hinder pilot projects and adoption. A holistic approach addressing technical, economic, environmental, regulatory, and social factors is therefore essential for successful implementation and active citizen participation in ECs.

In this research, the systematic review of 103 peer-reviewed studies published between 2020 and 2025 offers a comprehensive overview of the role that renewable hydrogen can play within an ECs. The most common and mature applications, as well as the main challenges and limitations being addressed by the scientific community, have been identified and analyzed. The review has been divided into two clearly differentiated parts. A quantitative analysis has been carried out through a bibliometric assessment that combines a performance analysis with science mapping techniques, and a qualitative analysis in which the main research published on the subject in the last six years has been reviewed and analyzed in depth. The research carried out demonstrates a growing and sustained interest in the integration of renewable hydrogen as a flexible energy vector capable of harnessing surplus renewable energy in different applications, either in isolation or in combination with other energy vectors. It has been shown that the main application of hydrogen is as a storage system to manage the intermittent production inherent in renewable energies such as PV and wind power (single-use: 62%; multi-application: 39%; multi-vector: 50%). However, other uses of hydrogen such as mobility (single-use: 17%; multi-application: 22%; multi-vector: 19%) or heating (single-use: 6%; multi-application: 18%; multi-vector: 24%) are also widely explored. In the case of heating, there are notable differences between single-use and combination with other uses and energy vectors. This is probably due to the low efficiency and profitability of direct hydrogen combustion in boilers, which means that as an isolated application it is not particularly attractive compared to other applications such as PtP or mobility. On the other hand, in the case of multi-application or multi-vector, joint use in CHP systems or as a fuel mixed with NG increases the efficiency of the overall system and reduces emissions.

Despite the maturity of hydrogen technologies (Table 1), high component costs and limited demonstration projects hinder real-world integration and the generation of experience and data for scaling up. This also slows societal understanding of hydrogen’s benefits. In this regard, the SWOT analysis carried out in the SHARED-H2 SUDOE project offers very interesting results by involving different stakeholders in the preparation process. Takeaways show that societal weaknesses and threats align closely with the challenges addressed in current research, confirming that the scientific community is correctly focused on overcoming barriers to hydrogen integration in energy communities (ECs). However, based on the analysis carried out, the following three priority lines of research are proposed to be addressed in the short term (five years):

• Development of a design tool with low human–machine interaction and a high degree of automation using AI-based optimization and data integration techniques. A key limitation identified is the shortage of qualified professionals, which creates pressure on the labor market and limits the participation of small and medium-sized enterprises (often the entities most familiar with local realities and driving ECs). Web-based platforms could democratize knowledge and support early-stage decision-making, enabling holistic and transparent comparisons between hydrogen technologies and other energy vectors.
• Development of full-scale pilot projects in different locations and with different applications for hydrogen use. The objective is twofold: to generate data that will enable the refinement of theoretical research and improvement of the models being developed, and to bring the technology closer to society so that it naturally and gradually becomes a real technological alternative demanded by the end user.
• Training programs, both highly specialized to train professionals working in the energy sector who are promoters of CE, and dissemination and outreach activities aimed at people with low technical qualifications. It should not be forgotten that CE is geared towards the active participation of the end user, so the degree of expertise should not be a barrier to most of the population becoming familiar with hydrogen technology and existing applications and their safe use.

Finally, it should be noted that the literature review is limited to papers written in English up to the year 2025 and indexed in SCOPUS and WoS. Rapid technological advances in the coming years could provide additional insights into the analysis carried out.