Considerations on Renewable and Sustainable Energy in the Context of the Energy Transition: What Is New?

Abstract

Topics related to renewable and sustainable energy have been addressed by several scientific studies over the last few decades. Nonetheless, it is important to highlight what has already been done by the scientific community and what remains to be done in these fields to provide more insights for stakeholders, including policymakers, researchers, and economic operators. The literature survey showed that there are still gaps to be considered in the literature and novelties to be brought through different approaches, particularly those that take into account the several dimensions of these issues. From this perspective, this research aims to present the dimensions of renewable and sustainable energy explored in scientific documents, benchmarking past and future pathways in these domains. To achieve these objectives, a bibliometric analysis (focusing on scientific maturity) was carried out separately across different dimensions associated with this topic (this is one of the novelties of this study). Additionally, a targeted literature analysis based on bibliometric analysis was done, considering the most relevant documents. This research adopts a broad perspective in order to capture the context of energy transition, clean energy, and low-carbon development. The findings obtained show that the subject of renewable and sustainable energy has several topics and subtopics with different dynamics. Within these subtopics, it is worth mentioning the following: solar and wind energy are almost in the saturation phase (85.1% of potential development has already occurred); bioenergy, biomass, and hydroelectric power are at the beginning of the maturity phase (59.7% progress to saturation); tidal and wave energy are in the middle of the maturity phase (71.5% progress to saturation); green hydrogen and clean energy are in the saturation phase (99.0%); renewable energy and sustainable development goals are in the saturation phase (99.0%), and energy policy and technological innovation in renewable energy are in the middle of the maturity phase 68.0%). These results reflect the overlap between different topics rather than the individual scope of each field of research.

1. Introduction

Alternative sources of energy have motivated the scientific community worldwide [1] and, in certain circumstances, more focus has been placed on energy from solar, wind, and biomass sources [2] and less, for example, on the hydroenergy [3]. The interest of different stakeholders in renewable and sustainable sources of energy is explained through several factors, the world population growth [4] and environmental pollution [5] being some of these drivers. Climate change and severe droughts are other phenomena that promote the search for alternative energy sources [6]. The COVID-19 pandemic also impacted these contexts [7], in particular in terms of scientific research, opportunities to revitalise economies through green investment and improve energy efficiency, as well as the scarcity and prices of fossil fuel energy sources [8].

The increased importance of these topics is in line with the international trends of promoting a more sustainable development [9] in a framework of decarbonisation [10] under the green transition agenda [11], circular economy contexts [12], and clean energy evolution [13]. The renewable sources of energy are crucial to achieve the sustainable development goals (SDGs) [14], namely Goal 7 (affordable and clean energy), worldwide [15]. There is, however, a way to run for an effective green transition in the energy sector [16]. The United States, China, and the European Union have made a significant contribution to our understanding of renewable energy [17]. More specifically, when it comes to hydrogen energy, China has significant production capacity in these areas [18].

Several dimensions related to renewable and sustainable energy have been addressed by the literature, particularly the production, diffusion, storage, and resource management [19]. New paradigms associated with renewable power energies imply changes in the all systems, from conventional frameworks to more efficient processes, where new technologies related to digital transition [20] may bring important added value [21], as well as new and more adjusted approaches [22]. This is of principal importance due to the intermittency of some renewable sources [23]. Artificial intelligence is also important in predicting sustainable sources of energy [24], including machine learning techniques [25] and deep learning [26]. The most important themes and techniques in the linkages among the artificial intelligence and sustainable energies have been identified in the literature [27].

The bibliometric analysis, alongside the literature survey [28], appears in these domains as an approach that can contribute to bringing more insights into scientific trends, suggesting directions for the future [29], and supporting policymakers [30]. Sometimes, in some countries, research does not accompany the public interest in renewable energy [31]. There are significant differences among the studies carried out by lower- and higher-income countries (the higher-income countries consider more differentiated sources). On the other hand, the wind and solar power sources have deserved greater attention from the researchers focused on environmental sustainability [32].

Studies associated with renewable and sustainable energy, considering bibliometric analysis, have focused on various topics, including the importance of databases [33], research evolution [34], water desalination, renewable energies [35], and relationships between renewable power energy and project management [36]. International scientific collaboration is also highlighted as an interesting approach to combining skills and experiences, and, in this way, better deal with current world sustainability threats [37]. Energy efficiency and policy frameworks are emerging themes in the fields of green energy [38]. Green energy, like green hydrogen, still has fields to be better addressed, such as storage systems, combination with current energy infrastructures, risk control, and policy design [39].

The green transition is not exempt from bringing new challenges for the sustainability management, namely because of the increase in demand for some important resources [40]. Other important challenges are linked with processes integration, system management, energy supply [41], efficiency of the technology used [42], and location of renewable energy power plants [43]. In any case, energy is an important resource for supporting sustainable development [44], and renewable sources may contribute to a more balanced economic growth. These transitions towards a more sustainable energy production and use may play a crucial role in the transportation industry [45].

In general, the literature related to renewable and sustainable energy based on bibliometric analysis has focused on specific topics within this broad theme, showing that there is a field to be explored, offering opportunities to bring more insights into this issue. Much has already been written on this subject, including using bibliometric approaches, nonetheless, this study aims to provide a broader overview of the topic by exploring various subtopics using a similar methodology, so that the results obtained can be compared. It should be noted that the analysis is also (though not exclusively) based on topic combinations, capturing intersections and creating subtopics. In these cases, the results reflect research trends within the intersections and not for the entirety of each of the fields involved. The interpretation of the conclusions and results must be based on these assumptions. In this way, this study intends to highlight what was already done and what can still be explored in future research associated with different dimensions of renewable and sustainable energy. Therefore, a bibliometric analysis was carried out considering the following specific topics: general overview ((renew* W/1 energ*) OR (sustainab* W/1 energ*) OR (clean* W/1 energ*) OR (green* W/1 energ*) OR (low carbon W/1 energ*) OR (net zero W/1 energ*) OR (carbon neutral W/1 energ*) OR (carbon free W/1 energ*) OR (energ* W/1 transition*)); solar energy ((renew* W/1 energ*) OR (sustainab* W/1 energ*) OR (clean* W/1 energ*) OR (green* W/1 energ*) OR (low carbon W/1 energ*) OR (net zero W/1 energ*) OR (carbon neutral W/1 energ*) OR (carbon free W/1 energ*) OR (energ* W/1 transition*)) AND ((solar W/1 energ*) OR (photovoltaic) OR (solar W/1 power)); wind energy ((renew* W/1 energ*) OR (sustainab* W/1 energ*) OR (clean* W/1 energ*) OR (green* W/1 energ*) OR (low carbon W/1 energ*) OR (net zero W/1 energ*) OR (carbon neutral W/1 energ*) OR (carbon free W/1 energ*) OR (energ* W/1 transition*)) AND ((wind W/1 energ*) OR (wind W/1 power)); bioenergy and biomass ((renew* W/1 energ*) OR (sustainab* W/1 energ*) OR (clean* W/1 energ*) OR (green* W/1 energ*) OR (low carbon W/1 energ*) OR (net zero W/1 energ*) OR (carbon neutral W/1 energ*) OR (carbon free W/1 energ*) OR (energ* W/1 transition*)) AND ((bioenerg*) OR (biomass W/1 energ*) OR (biofuel*)); hydroelectric power ((renew* W/1 energ*) OR (sustainab* W/1 energ*) OR (clean* W/1 energ*) OR (green* W/1 energ*) OR (low carbon W/1 energ*) OR (net zero W/1 energ*) OR (carbon neutral W/1 energ*) OR (carbon free W/1 energ*) OR (energ* W/1 transition*)) AND ((hydro* W/1 energ*) OR (hydro* W/1 power) OR (hydropower)); tidal and wave energy ((renew* W/1 energ*) OR (sustainab* W/1 energ*) OR (clean* W/1 energ*) OR (green* W/1 energ*) OR (low carbon W/1 energ*) OR (net zero W/1 energ*) OR (carbon neutral W/1 energ*) OR (carbon free W/1 energ*) OR (energ* W/1 transition*)) AND ((tidal W/1 energ*) OR (tidal W/1 power) OR (tidal stream W/1 energ*) OR (tidal current W/1 energ*) OR (wave W/1 energ*) OR (wave W/1 power) OR (ocean wave W/1 energ*) OR (marine W/1 energ*)); green hydrogen and clean energy ((renew* W/1 energ*) OR (sustainab* W/1 energ*) OR (clean* W/1 energ*) OR (green* W/1 energ*) OR (low carbon W/1 energ*) OR (net zero W/1 energ*) OR (carbon neutral W/1 energ*) OR (carbon free W/1 energ*) OR (energ* W/1 transition*)) AND ((green* W/1 hydrogen) OR (hydrogen W/1 energ*)); renewable energy and sustainable development goals ((renew* W/1 energ*) OR (sustainab* W/1 energ*) OR (clean* W/1 energ*) OR (green* W/1 energ*) OR (low carbon W/1 energ*) OR (net zero W/1 energ*) OR (carbon neutral W/1 energ*) OR (carbon free W/1 energ*) OR (energ* W/1 transition*)) AND (“sustainable development goals” OR “SDG 7”); energy policy and economics ((renew* W/1 energ*) OR (sustainab* W/1 energ*) OR (clean* W/1 energ*) OR (green* W/1 energ*) OR (low carbon W/1 energ*) OR (net zero W/1 energ*) OR (carbon neutral W/1 energ*) OR (carbon free W/1 energ*) OR (energ* W/1 transition*)) AND ((polic*) OR (energ* W/1 polic*) OR (energ* W/1 economic*)); and technological innovation in renewable energy ((renew* W/1 energ*) OR (sustainab* W/1 energ*) OR (clean* W/1 energ*) OR (green* W/1 energ*) OR (low carbon W/1 energ*) OR (net zero W/1 energ*) OR (carbon neutral W/1 energ*) OR (carbon free W/1 energ*) OR (energ* W/1 transition*)) AND ((energ* W/1 technolog*) OR (clean* W/1 technolog*)). This bibliometric analysis was complemented with a focused literature analysis [46]. The inclusion of these search terms aims to consider the fields of renewable and sustainable energy from a broader perspective, including the literature relating to low-carbon and energy transition. For the bibliometric analysis, the documents obtained in a search carried out on 29 December 2025 using the Scopus [47] database were considered, and VOSviewer (version 1.6.20) [48,49,50] and Bibliometrix (Version: 5.3.0) [51] software procedures were taken into account. For each topic, the search was conducted without any restrictions, either in terms of time period or document type. The results were subjected to basic cleaning and standardisation in order to avoid inconsistencies/redundancies arising from variations in spelling or formatting, similarity to search terms (“renewable energy”, “renewable energy resources”, “renewable energies”, and “renewable energy source”) and generic terms such as “article”. Relying solely on the Scopus database for this research may be a weakness; however, the inclusion of a large number of documents in each sub-analysis potentially mitigates this limitation. It should be noted that although this study focuses on renewable and sustainable energy, the research incorporates concepts relating to the energy transition and policy frameworks.

2. Literature Review

This section will be divided into different subsections addressing specific topics, based on the scientific literature relevant to the research carried out in this study.

2.1. Decarbonisation of Specific Sectors, Growing Energy Needs, and Hybrid Solutions

Energy efficiency improvement is a key element for promoting decarbonisation across economic sectors and processes, including in some specific contexts, such as the port dynamics [52]. The building sector is another context where concerns regarding reducing the environmental impacts from energy use are current and real [53]. Renewable energy power contributes to meeting the increased demand for energy [54] and mitigating environmental impacts [55]. This explains increased interest for the renewables worldwide [56], principally in China after the Renewables Law of 2006 [57]. The combination of wind and solar sources may reduce the uncertainty of these renewables when considered separately [58]. The consideration of hybrid solutions may potentially increase the energy generation, mitigate the intermittency [59], and mitigate environmental impacts [60]. The literature in these fields highlights the growing importance of hybrid decarbonisation strategies tailored to specific sectors. On the other hand, the studies reviewed appear to prioritise technological aspects at the expense of integrating socioeconomic and management considerations.

2.2. Integration of Renewable Energy Systems and New Technologies

Integration of renewable energy power in the existing grids brings new challenges [61], specifically in terms of voltage constancy, inertial answer, power quality and support, and frequency control [62]. Integration of renewable energy in microgrids needs adjusted and accurate predicting approaches. This is crucial for the energy sector planning and policy design [63]. Artificial intelligence methodologies may provide relevant contributions in these frameworks [64], namely improving the efficiency of the systems [65] through machine learning models [66] to analyse big data [67]. For solar power energy, artificial intelligence may potentially contribute to an increase of around 20% in efficiency and reduce 50% of the production costs [68]. These techniques may support stakeholders predict, for example, insulation, energy prices, and wind turbine conditions [69]. In the context of smart energy systems, the concept of IoE (Internet of Energy) has been considered to combine energy and information communication [70]. New technologies, such as compressed air energy storage, have appeared to deal with the fluctuation in the supply of some renewable energies [71]. In any case, batteries are the storage technology highlighted more in the literature, followed by hydrogen [72]. Hydrogen is important for handling the volatility of the generation of renewables; however, its consideration is not consensual [73]. Introduction of blockchain technologies in energy markets is another promising approach, though administrative and economic constraints remain [74]. Photonics-based systems are also an interesting technology created for offshore wind structures [75], as is the consideration of power electronic technologies in renewables [76]. Overall, the literature highlights technological advances that have been made, particularly in the fields of artificial intelligence and storage solutions. However, scientific contributions appear fragmented, which may limit the practical application of the proposed solutions.

2.3. Challenges and Opportunities for the Future in Renewable Energy and Regional Contexts

The future opens new opportunities to apply innovative technologies in the renewable energies sector [77], but also brings new challenges, particularly because of the uncertainty of climate change and extreme events. The impacts of these frameworks are expected to be asymmetric across regions with different characteristics [78]. This will be particularly visible in countries where renewable energies have greater importance, such as in the Brazilian context [79]. The transition towards a greener energy system must be accompanied by technological innovation that facilitates effective clean energy integration from both sides and more efficient processes in critical sectors, such as transportation, heating, cooling, and industry [80]. The potential of renewable energy in Europe has been assessed; however these analyses need to be clearer and careful, specifically to avoid great disparities in the results obtained [81]. Despite these worldwide trends to promote a green energy transition, in some cases ambitious [82], renewables represent, in general, a residual (or a smaller) part of the energy sector [83]. This is particularly visible in countries such as Australia, where only 6% of consumption was supplied by renewable energies [84]. The reviewed studies identify opportunities and challenges that need to be addressed. The diversity of regional conditions and the uncertainty surrounding climate change present additional and somewhat complex challenges.

2.4. Multidisciplinary Contexts and Stakeholder Engagement

The dynamics associated with the energy sector are multidisciplinary, and their assessment calls for the skills of researchers and experts from different fields of science to address several dimensions associated with these frameworks [85]. One important dimension related to the energy sector is the public acceptability of a greener transition. In general, the public is more willing to support broad initiatives of green energy transition than local projects [86]. Socioeconomic, technological, political, organisational, and environmental factors are among the main critical factors that influence the renewables initiatives [87]. The location of renewable generation plants is another critical point for the stakeholders [88]. The legislative context [89], the expertise available [90], the institutional framework [91], land use [92], market volatility [93], and public engagement [94] can also be a constraint for an effective implementation of renewable energy power initiatives if not properly addressed. Negative impact of renewables on the environment and nature may also hamper the adoption of the associated strategies in some contexts, such as Southeast Asia [95]. Additionally, some doubts remain about the real impact of the renewables on the carbon sequestration [96]. Reduction in solar energy generation efficiency dependence on temperature is another concern for the stakeholders [97]. Constraints associated with social, institutional, and environmental factors highlight the multidisciplinary nature of renewable and sustainable energy and the need for the scientific community to consider various dimensions in an integrated manner in order to implement holistic approaches.

2.5. Synthesis of the Literature Review and Research Gaps

The literature review carried out in the preceding subsections highlights the multidimensional nature of renewable and sustainable energy, encompassing aspects related to technology, the economy, the environment, and policy measures. Of particular note is the emphasis placed on technological advances, notably artificial intelligence and energy storage, with a view to improving system efficiency and optimising processes. Some aspects remain critical, such as system integration and grid stability, particularly in contexts where renewable sources are intermittent. There appears to be scope to explore issues related to socioeconomic dimensions and their interconnection with technological innovations.

Overall, the literature presents a fragmented picture with limited multidisciplinary integration, with research concentrated in certain regions of the world and specific technologies, notably solar and wind energy. There appear to be opportunities for studies that provide comparative analyses encompassing different dimensions related to renewable and sustainable energy. This study aims to contribute to addressing these gaps, using harmonised methodologies across different themes.

3. Metrics from the Scientific Literature

In this section, the first subsection related to a bibliometric general overview on renewable and sustainable energy will be provided and after that, subsections regarding the following subtopics—solar and wind energy; bioenergy, biomass and hydroelectric power; tidal and wave energy; green hydrogen and clean energy; renewable energy and sustainable development goals (SDGs); and energy policy and technological innovation in renewable energy—will be presented. These subtopics are considered for further analysis because of the number of documents found for each specific topic (solar energy, wind energy, bioenergy, biomass, etc.). To gather insights from various fields, in each subsection, the relevant topics will first be examined, followed by an analysis of the subtopic arising from the intersections of these topics. More specifically, to clarify the distinction between topics and subtopics, the following should be noted: topics refer to thematic domains identified using Boolean operators (solar energy, wind energy, bioenergy, or energy policy); subtopics refer to an intersection between two or more topics (solar and wind energy or energy policy and technological innovation).

3.1. General Overview

A total of 470,722 documents were found in the Scopus database for the general overview; specific topic and the main metric are presented in

Table 1. Metrics regarding the year, author name, subject area, and source title related to the specific topic—general overview.

Year		Author Name		Subject Area		Source Title
2025	65,678	Dincer, I.	440	Engineering	203,155	Energies	10,954
2024	61,063	Blaabjerg, F.	375	Energy	200,539	Renewable Energy	6398
2023	47,459	Guerrero, J.M.	341	Environmental science	95,854	Energy	6185
2022	40,128	Senjyu, T.	262	Computer science	70,399	Renewable and Sustainable Energy Reviews	6176
2021	33,375	Breyer, C.	226	Materials science	59,569	Sustainability Switzerland	5535
2020	27,505	Lin, B.	218	Physics and astronomy	56,321	International Journal of Hydrogen Energy	5355
2019	25,029	Chen, Z.	206	Chemistry	53,478	Applied Energy	4833
2018	20,995	Jurado, F.	205	Mathematics	51,012	Journal of Cleaner Production	4107
2017	18,342	Adebayo, T.S.	186	Chemical engineering	45,714	Energy Policy	4027
2016	15,231	Olabi, A.G.	186	Social sciences	38,059	Iop Conference Series Earth and Environmental Science	3167
2015	13,196	Mohammadi-Ivatloo, B.	183	Earth and planetary sciences	21,944	Energy Conversion and Management	2783
2014	12,608	Singh, B.	183	Business, management, and accounting	20,717	Aip Conference Proceedings	2746
2013	11,325	Sovacool, B.K.	182	Economics, econometrics, and finance	19,115	E3s Web of Conferences	2683
2012	10,152	Mekhilef, S.	175	Biochemistry, genetics, and molecular biology	14,944	Journal of Energy Storage	2593
2011	8799	Catalão, J.P.S.	173	Agricultural and biological sciences	14,682	IEEE Access	2571
2010	7275	Vale, Z.	167	Decision sciences	11,307	Energy Procedia	2505
2009	6737	Bansal, R.C.	163	Medicine	7332	Journal of Physics Conference Series	2424
2008	6181	Rosen, M.A.	161	Multidisciplinary	7322	Lecture Notes in Electrical Engineering	2187
2007	4378	Siano, P.	161	Immunology and microbiology	2797	Energy Reports	2183
2006	3461	Lund, H.	153	Arts and humanities	2697	Environmental Science and Pollution Research	2179

and

Table 2. Metrics related to keyword, affiliation, country, and language related to the specific topic—general overview.

Keyword		Affiliation		Country		Language
Energy	36,500	Ministry of Education of the People’s Republic of China	9177	China	109,603	English	450,203
Energy efficiency	33,600	Chinese Academy of Sciences	7908	United States	60,982	Chinese	12,560
Sustainable development	32,985	Tsinghua University	5181	India	50,940	German	2223
Solar energy	32,464	North China Electric Power University	4297	United Kingdom	26,180	Spanish	1160
Wind power	30,796	Xi’an Jiaotong University	3393	Germany	24,807	French	844
Alternative energy	29,259	CNRS Centre National de la Recherche Scientifique	3127	Italy	18,568	Japanese	822
Energy policy	27,528	University of Chinese Academy of Sciences	3095	Australia	14,483	Russian	793
Carbon dioxide	25,027	Zhejiang University	3087	Spain	14,050	Korean	626
Energy utilisation	24,728	State Grid Corporation of China	3060	Japan	13,196	Polish	573
Carbon	21,067	Shanghai Jiao Tong University	2918	Canada	12,937	Portuguese	443
Solar power generation	20,524	Tianjin University	2683	The Republic of Korea	12,514	Italian	319
Electric power transmission networks	20,414	Aalborg University	2491	Saudi Arabia	12,196	Ukrainian	234
Fossil fuels	20,026	National Renewable Energy Laboratory	2460	France	11,813	Turkish	160
Energy storage	19,558	Huazhong University of Science and Technology	2284	Iran	11,410	Czech	113
Optimisation	19,276	China Electric Power Research Institute	2236	Turkey	11,139	Persian	99
Climate change	18,835	Southeast University	2227	Malaysia	11,121	Croatian	41
Investments	17,544	Technical University of Denmark	2115	Pakistan	8670	Slovak	41
Biomass	17,052	King Saud University	1964	Poland	8316	Romanian
Power	15,757	Shandong University	1962	Brazil	8001	Slovenian	38
Greenhouse gases	15,345	Harbin Institute of Technology	1842	The Netherlands	7805	Lithuanian	37

. It should be noted that, for example, in Table 2, the total for the column relating to language is higher than the total number of documents analysed. This is because some documents are associated with more than one language. Although the number of renewable energy studies has increased in recent years (Table 1), the scientific literature remains concentrated in engineering studies, in a group of productive authors (Dincer, I.; Blaabjerg, F.; Guerrero, J.M.; Senjyu, T.; and Breyer, C.) and disseminated principally through specific journals (Energies, Renewable Energy, Energy, and Renewable and Sustainable Energy Reviews) and conference proceedings (Iop Conference Series Earth and Environmental Science, for example). Significant gaps remain in socioeconomic analysis, practical evidence, sector linkages, and impact assessment. This suggests that there is a need for more interdisciplinary, empirically-based, and context research. The results also indicate that topics related to socioeconomic and management dimensions, although extremely important, are often overlooked in these analyses.

Renewable energy studies are led by English-language documents, with China and the United States being the most productive countries of affiliation. The greatest contributions come from institutions such as the Chinese Academy of Sciences and Tsinghua University (Table 2). Renewable energy studies are quickly increasing, solar energy, wind, efficiency, and sustainability being the most relevant themes. Despite the rapid growth of renewable energy studies, significant gaps also remain in terms of geographic distribution, energy storage and grid integration, socioeconomic and policy dimensions consideration, and sector interrelationships, with current literature profoundly focused, for example, on solar and wind technologies in a small number of countries. It will be important to consider the significance of various renewable energy sources from a global perspective.

3.2. Solar and Wind Energy

For the specific topics of solar energy and wind power, 90,667 and 45,417 documents, respectively, were found in the Scopus database. The bibliometric analysis reveals an increasing growth in renewable energy assessment in recent years, where engineering and energy related studies have relevance and are clustered in productive authors (Dincer, I.; Senjyu, T.; and Singh, B.). Research production is led by China and India, with an asymmetric global distribution, considering that outputs from Africa, Latin America, and other environmentally vulnerable regions remain low. Subject area distribution reveals a focus on technology, with social sciences having only a residual contribution. In this way, despite the maturity and production volume of the field, key gaps remain. These gaps are related to interdisciplinary combinations, policy impact evaluation, and research addressing social engagement. These insights reveals that there is a field to be explored, namely to shift the research from technical modelling towards broader, empirically instructed, and socio technical studies (

Table 3. Metrics related to the specific topic of solar energy.

Year		Author Name		Subject Area		Country
2025	12,708	Dincer, I.	203	Engineering	47,690	China	17,028
2024	12,650	Senjyu, T.	139	Energy	47,391	India	14,201
2023	9757	Singh, B.	136	Computer science	19,209	United States	9195
2022	8334	Jurado, F.	105	Environmental science	15,694	Italy	3677
2021	6929	Breyer, C.	102	Mathematics	13,634	United Kingdom	3662
2020	5739	Blaabjerg, F.	96	Materials science	10,504	Saudi Arabia	3281
2019	5181	Mekhilef, S.	89	Physics and astronomy	9444	Germany	3223
2018	4356	Bansal, R.C.	81	Chemical engineering	6075	Spain	2995
2017	3751	Guerrero, J.M.	80	Social sciences	5649	Iran	2821
2016	2927	Kamel, S.	75	Chemistry	5084	Australia	2784
2015	2540	Yona, A.	75	Earth and planetary sciences	3115	Malaysia	2760
2014	2435	Pearce, J.M.	71	Decision sciences	3034	Japan	2494
2013	2092	Sopian, K.	70	Business, management, and accounting	2951	Turkey	2357
2012	1881	Khalid, M.	69	Economics, econometrics, and finance	2077	Canada	2191
2011	1614	Funabashi, T.	65	Multidisciplinary	1500	The Republic of Korea	2149
2010	1187	Rosen, M.A.	65	Agricultural and biological sciences	1429	Egypt	2115
2009	1085	Leva, S.	64	Medicine	1326	France	1838
2008	933	Bajaj, M.	60	Biochemistry, genetics, and molecular biology	1225	Pakistan	1704
2007	620	Padmanaban, S.	59	Arts and humanities	309	Indonesia	1677
2006	450	Yan, J.	57	Pharmacology, toxicology, and pharmaceutics	148	Algeria	1453

). Socioeconomic factors play a central role in these issues and could be properly addressed.

In

Table 4. Metrics related to the specific topic of wind energy.

Year		Author Name		Subject Area		Country
2025	5100	Senjyu, T.	93	Energy	24,798	China	10,298
2024	5255	Breyer, C.	77	Engineering	24,663	India	5671
2023	4180	Chen, Z.	71	Computer science	9373	The United States	4975
2022	3934	Dincer, I.	67	Environmental science	8282	The United Kingdom	2447
2021	3201	Blaabjerg, F.	64	Mathematics	7042	Germany	2212
2020	2834	Funabashi, T.	64	Physics and astronomy	3134	Spain	1436
2019	2573	Singh, B.	53	Social sciences	2995	Iran	1352
2018	2154	Muljadi, E.	52	Materials science	2577	Canada	1229
2017	1940	Mohammadi-Ivatloo, B.	51	Earth and planetary sciences	2090	Australia	1162
2016	1745	Yona, A.	51	Business, management, and accounting	1726	Italy	1160
2015	1534	Lund, H.	47	Chemical engineering	1674	Turkey	1136
2014	1558	Roy, P.K.	44	Decision sciences	1492	Japan	1124
2013	1296	Omer, A.M.	43	Economics, econometrics, and finance	1349	Denmark	1084
2012	1277	Wang, X.	43	Agricultural and biological sciences	767	Saudi Arabia	993
2011	1060	Rehman, S.	42	Chemistry	764	Egypt	850
2010	993	Jurado, F.	41	Multidisciplinary	671	The Republic of Korea	839
2009	896	Khalid, M.	41	Medicine	510	Malaysia	797
2008	793	Bogdanov, D.	39	Biochemistry, genetics, and molecular biology	274	France	784
2007	618	Huang, Q.	37	Arts and humanities	140	Brazil	745
2006	394	Kaldellis, J.K.	36	Neuroscience	51	The Russian Federation	651

, overall, the data indicate an unbalanced expansion of renewable energy studies from 2006 to 2025, with a clear concentration of documents in recent years, led by a group of productive authors (Senjyu, T.; Breyer, C.; and Chen, Z.). Subject area distribution is dominated by energy, engineering, computer science, and related quantitative fields. On the other hand, social sciences, economics, business, and humanities have lower contributions. Geographically, China, India, the United States, and a few European countries contribute to the number of publications. Participation from developing and environmentally vulnerable regions is still relatively reduced. These frameworks suggests key gaps: inadequate interdisciplinary studies, limited socioeconomic and policy studies, and few regional studies. Renewable energy plays a very significant role in the European context, which may be thoroughly examined in future research.

Considering the solar energy and wind power search queries together (with the Boolean operator and between the two groups of queries), 16,486 documents were obtained regarding subtopic solar and wind energy. Figure 1 shows that this subtopic is in the maturity phase with the growth becoming slower.

Solar fuel, wind power integration, clean energy, energy systems, microgrid, photovoltaics, and carbon are emerging topics (

Table 5. Trend terms (all keywords) related to the subtopic of solar and wind energy.

Term	Year (Median)
Old Terms
Agricultural engineering	1981
Solar energy—applications	1984
Wind power—applications	1985
Heating—solar	1986
Photovoltaic conversion	1996
Solar radiation—collectors	1986
Diesel electric power plants	1991
Straw	1994
Developing country	2004
Water power	2002
Emerging Terms
Carbon	2022
Photovoltaics	2023
Microgrid	2023
Energy systems	2023
Energy	2024
Power	2024
Clean energy	2024
Hybrid power	2025
Wind power integration	2025
Solar fuels	2025

). On the other hand, alternative energy, energy policy, optimisation, fossil fuels, energy efficiency, electric power transmission networks, energy storage, photovoltaic cells, wind turbines, and natural resources are motor themes (important and well developed). Energy systems, economic analysis, clean energy, hydrogen storage, and hydrogen production are examples of emerging or declining themes (

Table 6. Thematic clusters related to the subtopic of solar and wind energy.

Words	Cluster
Alternative energy	Motor themes
Energy policy	Motor themes
Optimisation	Motor themes
Fossil fuels	Motor themes
Energy efficiency	Motor themes
Energy systems	Emerging or declining themes
Economic analysis	Emerging or declining themes
Clean energy	Emerging or declining themes
Hydrogen storage	Emerging or declining themes
Hydrogen production	Emerging or declining themes
Electric power transmission networks	Motor themes
Energy storage	Motor themes
Photovoltaic cells	Motor themes
Wind turbines	Motor themes
Natural resources	Motor themes
Electric load dispatching	Emerging or declining themes
Stochastic systems	Emerging or declining themes
Uncertainty	Emerging or declining themes
Forecasting	Emerging or declining themes
Uncertainty analysis	Emerging or declining themes

).

Table 7. Factorial analysis (Multiple Correspondence Analysis) results related to the subtopic of solar and wind energy.

Word	Dim1	Dim2	Cluster
Wind turbines	−0.04	−0.48	1
Photovoltaic cells	−0.04	−0.44	1
Energy systems	0.02	−0.06	1
Hydrogen storage	0.03	−0.64	1
Energy management	0.04	−0.19	1
Clean energy	−0.39	0.69	2
Photovoltaic	−0.35	0.04	2
Energy storage	0.24	0.25	2
Optimisation	0.54	0.41	2
Hydroelectric power	0.98	0.01	2
Power generation	1.19	0.72	3
Alternative energy	1.55	1.05	3
Solar power	1.57	0.83	3
Photovoltaic system	1.60	1.30	3
Electricity generation	2.02	0.45	3

shows that energy systems is a central term and that different terms may be grouped in three clusters. One specialised cluster is related to electricity generation and photovoltaic systems. This means that these themes have not been central to the literature produced on issues related to this subtopic. The other is associated with clean energy, optimisation, microgrid, and hydroelectric power and another is related to sustainable development, natural resources, energy use, and energy management.

China, the USA, Saudi Arabia, the United Kingdom, India, and Germany are the most structural influencing countries in the network, revealing their importance and centrality for the international collaboration (

Table 8. Collaboration network related to the subtopic of solar and wind energy.

Node	Cluster	Betweenness	Closeness	PageRank
China	1	56.629	0.020	0.078
The USA	1	62.035	0.020	0.070
Saudi Arabia	2	30.039	0.020	0.047
The United Kingdom	3	31.670	0.020	0.044
India	2	32.742	0.020	0.043
Germany	3	22.545	0.019	0.035
Australia	1	15.319	0.018	0.033
Egypt	2	9.520	0.018	0.032
Spain	3	17.867	0.019	0.031
Malaysia	2	10.923	0.017	0.027
Italy	3	11.229	0.018	0.026
Canada	1	7.587	0.019	0.025
Iran	1	5.866	0.018	0.024
France	3	12.184	0.018	0.024
Denmark	3	4.298	0.017	0.024

). These countries could play an important role in promoting international networking on this issue.

3.3. Bioenergy, Biomass, and Hydroelectric Power

From the Scopus database, 22,288, 23,979, and 1359 documents, respectively, were found for the specific topics bioenergy and biomass and hydroelectric power, and for the subtopic bioenergy, biomass, and hydroelectric power (for this subtopic, the two specific topic search queries were considered together with the Boolean operator AND between the two sets of queries). Energy, environmental science, engineering, and agricultural and biological sciences are the most dominant subject areas for the specific topic of bioenergy and biomass (

Table 9. Metrics related to the specific topic of bioenergy and biomass.

Year		Author Name		Subject Area		Country
2025	2630	Thrän, D.	66	Energy	10,326	India	3219
2024	2321	Chen, W.H.	45	Environmental science	8811	The United States	3125
2023	1908	Murphy, J.D.	44	Engineering	6037	China	2778
2022	1637	Show, P.L.	37	Chemical engineering	3821	The United Kingdom	1285
2021	1569	Ong, H.C.	34	Agricultural and biological sciences	3270	Brazil	1119
2020	1216	Tippayawong, N.	32	Biochemistry, genetics, and molecular biology	2153	Germany	1108
2019	1144	Chang, J.S.	31	Chemistry	1965	Italy	997
2018	1029	Junginger, M.	31	Social sciences	1541	Malaysia	938
2017	963	Kumar, G.	31	Materials science	1150	Canada	698
2016	899	Pandey, A.	30	Mathematics	1148	Spain	679
2015	840	Omer, A.M.	28	Computer science	1100	Australia	639
2014	814	Dincer, I.	27	Business, management, and accounting	969	Turkey	592
2013	841	Nizami, A.S.	27	Physics and astronomy	948	The Republic of Korea	590
2012	687	Faaij, A.	25	Earth and planetary sciences	930	Poland	557
2011	659	Lam, S.S.	25	Immunology and microbiology	829	Indonesia	554
2010	595	Angelidaki, I.	24	Economics, econometrics, and finance	807	Saudi Arabia	524
2009	668	Dalai, A.K.	24	Medicine	537	Pakistan	511
2008	471	Nanda, S.	24	Multidisciplinary	422	Sweden	466
2007	279	Olabi, A.G.	24	Decision sciences	189	Japan	454
2006	180	Gupta, V.K.	23	Pharmacology, toxicology, and pharmaceutics	168	The Netherlands	436

). Brazil appears to have a relevant contribution to this topic. Regarding the topic of hydroelectric power, physics and astronomy, material sciences, and mathematics appear before the social sciences and the agricultural and biological sciences, for example (

Table 10. Metrics related to the specific topic of hydroelectric power.

Year		Author Name		Subject Area		Country
2025	3972	Dincer, I.	99	Energy	13,266	China	7068
2024	3621	Cheng, C.	59	Engineering	9862	The United States	2325
2023	2703	Bernitsas, M.M.	34	Environmental science	5569	India	2186
2022	2232	Jurasz, J.	33	Physics and astronomy	3331	The United Kingdom	1055
2021	1719	Chen, D.	31	Materials science	2460	Germany	1018
2020	1246	Liu, P.	28	Mathematics	2452	Turkey	829
2019	1023	Ramos, H.M.	28	Computer science	2430	Italy	775
2018	852	Breyer, C.	27	Chemical engineering	2360	Australia	748
2017	759	Ming, B.	27	Chemistry	2173	Canada	714
2016	585	Sun, H.	24	Social sciences	1587	The Republic of Korea	627
2015	520	Yang, W.	24	Earth and planetary sciences	1347	Spain	627
2014	545	Wu, Z.	23	Business, management, and accounting	890	Japan	608
2013	469	Ding, T.	22	Economics, econometrics, and finance	766	Saudi Arabia	587
2012	475	Liu, B.	22	Agricultural and biological sciences	510	Iran	574
2011	419	Olabi, A.G.	22	Biochemistry, genetics, and molecular biology	476	Malaysia	550
2010	341	Rosen, M.A.	22	Decision sciences	448	Brazil	506
2009	312	Saini, R.P.	22	Multidisciplinary	344	The Russian Federation	489
2008	286	Duić, N.	21	Medicine	217	Pakistan	436
2007	234	Jurado, F.	21	Arts and humanities	95	Indonesia	425
2006	198	Bamisile, O.	20	Pharmacology, toxicology, and pharmaceutics	39	Norway	407

). The cost-effectiveness and socioeconomic impact of alternative solutions as sources of renewable energy are of paramount importance for their adoption by stakeholders; therefore, it is suggested to increase scientific contributions in these areas.

The subtopic of bioenergy, biomass, and hydroelectric power is at the beginning of the maturity phase, showing that there is a filed to be explored (Figure 2). Wind power integration, windmill, solar fuels, hydrogen storage, clean energy, sustainable energy, and carbon dioxide are the emerging terms (

Table 11. Trend terms (all keywords) related to the subtopic of bioenergy, biomass, and hydroelectric power.

Term	Year (Median)
Old Terms
Societies and institutions	2006
Wood fuels	2006
Eurasia	2007
Asia	2007
Development strategy	2007
Europe	2008
Fuels	2008
Biological materials	2008
Animalia	2009
Greenhouses	2009
Emerging Terms
Carbon dioxide	2022
Hydrogen production	2023
Sustainability	2023
Sustainable energy	2023
Energy	2024
Clean energy	2024
Hydrogen storage	2024
Solar fuels	2025
Windmill	2025
Wind power integration	2025

). The presence of hydrogen here is explained by the broader perspective of the search query used for the hydroelectric power. Climate change, biofuel, carbon dioxide, environmental impact, energy policy, and sustainable development are motor themes, and hydrogen production, clean energy, and hydrogen storage are emerging or declining themes (

Table 12. Thematic clusters related to the subtopic of bioenergy, biomass, and hydroelectric power.

Words	Cluster
Climate change	Motor themes
Biofuel	Motor themes
Carbon dioxide	Motor themes
Environmental impact	Motor themes
Fossil fuel	Motor themes
Solar energy	Motor themes
Wind power	Motor themes
Geothermal energy	Motor themes
Energy policy	Motor themes
Sustainable development	Motor themes
Hydrogen production	Emerging or declining themes
Clean energy	Emerging or declining themes
Hydrogen storage	Emerging or declining themes
Solar fuels	Emerging or declining themes
Hydrogen energy	Emerging or declining themes
Alternative energy	Emerging or declining themes
Electricity generation	Emerging or declining themes
Solar power	Emerging or declining themes
Optimisation	Emerging or declining themes
Energy use	Emerging or declining themes

). Clean energy is a central topic, and fossil fuels, sustainable development, and investments are specialised topics (

Table 13. Factorial analysis (Multiple Correspondence Analysis) results related to the subtopic of bioenergy, biomass, and hydroelectric power.

Word	Dim1	Dim2	Cluster
Clean energy	−0.16	−0.16	1
Energy	0.01	−0.05	1
Sustainability	0.34	0.62	1
Alternative energy	0.48	1.07	1
Energy efficiency	0.58	0.43	1
Solar power generation	0.65	−0.51	2
Sustainable development	0.78	0.10	2
Geothermal energy	0.90	−0.55	2
Energy policy	0.90	−0.14	2
Investments	1.00	−0.06	2
Biofuel	−0.02	1.64	3
Energy resource	0.60	1.98	3
Fossil fuel	0.99	1.98	3

). A deeper assessment of the obtained results reveals that hydrogen, energy efficiency, sustainability, and climate change appear in the same cluster. Wind energy, solar power, biomass, economic, and greenhouse gas emissions occur in the other cluster. In future research, it would be important to understand, for example, the role of biofuels in the context of renewable energy, as well as their centrality and relevance to related themes.

The most important and central countries in the network collaboration are China, the USA, the United Kingdom, India, Saudi Arabia, Malaysia, Germany, Turkey, Pakistan, Egypt, Italy, Australia, Canada, Poland, and Iraq (

Table 14. Collaboration network related to the subtopic of bioenergy, biomass, and hydroelectric power.

Node	Cluster	Betweenness	Closeness	PageRank
China	1	145.878	0.015	0.078
The USA	2	177.103	0.016	0.075
The United Kingdom	2	128.915	0.015	0.056
India	1	73.131	0.014	0.052
Saudi Arabia	1	36.813	0.014	0.043
Malaysia	1	41.056	0.013	0.038
Germany	4	95.568	0.014	0.037
Turkey	3	19.411	0.013	0.033
Pakistan	1	7.874	0.013	0.029
Egypt	1	19.948	0.012	0.029
Italy	2	29.137	0.014	0.029
Australia	1	12.837	0.013	0.025
Canada	1	8.338	0.012	0.025
Poland	4	28.888	0.013	0.025
Iraq	1	2.055	0.012	0.024

). China, the United States, and the United Kingdom could play an important role in fostering greater collaboration in these domains.

3.4. Tidal and Wave Energy

Engineering, energy, environmental sciences, computer science, and Earth and planetary sciences appear among the most dominant subject areas for the specific and subtopic tidal and wave energy (

Table 15. Metrics related to the specific topic of tidal and wave energy.

Year		Author Name		Subject Area		Country
2025	991	Iglesias, G.	65	Engineering	4860	China	1441
2024	810	Wang, Z.L.	52	Energy	3715	The United Kingdom	1310
2023	760	Ringwood, J.V.	50	Environmental science	2162	The United States	1175
2022	658	Mattiazzo, G.	49	Computer science	908	India	550
2021	583	Bernitsas, M.M.	41	Earth and planetary sciences	900	Spain	416
2020	487	Johanning, L.	39	Mathematics	852	Italy	368
2019	436	Leijon, M.	38	Materials science	593	France	361
2018	420	Taveira-Pinto, F.	37	Physics and astronomy	580	Australia	311
2017	394	Rosa-Santos, P.	36	Social sciences	434	Ireland	308
2016	309	Thies, P.R.	34	Agricultural and biological sciences	366	Portugal	246
2015	312	Bracco, G.	30	Chemical engineering	340	Japan	235
2014	288	Neill, S.P.	30	Chemistry	217	Canada	218
2013	257	Faedo, N.	29	Business, management, and accounting	157	Malaysia	213
2012	216	Garrido, I.	28	Economics, econometrics, and finance	142	The Republic of Korea	205
2011	197	Greaves, D.	27	Decision sciences	135	Iran	190
2010	207	Lavidas, G.	27	Multidisciplinary	87	Sweden	166
2009	154	Masters, I.	27	Biochemistry, genetics, and molecular biology	70	Indonesia	163
2008	125	Rusu, E.	27	Medicine	61	Germany	141
2007	81	Angeloudis, A.	26	Arts and humanities	35	Turkey	130
2006	51	Garrido, A.J.	26	Immunology and microbiology	13	Norway	127

). For this topic, 8206 documents were found. Iglesias, G., Wang, Z.L. and Ringwood, J.V. are the most productive authors. This is a subtopic with specific characteristics that requires its own approaches.

This subtopic is in the middle of the maturity phase (Figure 3), and the main emerging terms are the following (

Table 16. Trend terms (all keywords) related to the subtopic of tidal and wave energy.

Term	Year (Median)
Old Terms
Water waves—wave energy conversion	1984
Water waves—wave energy conversion	1989
Energy resources—renewable	1989
Water power	2004
Marketing	2003
Renewable electricity generation	2001
Contracts	2002
Rotors	2004
Industrial economics	2006
Societies and institutions	2006
Emerging terms
Offshore winds	2023
Alternative energy	2022
Offshore oil well production	2022
Hydroelectric power	2025
Nanogenerators	2023
Energy	2024
Power	2024
Clean energy	2024
Windmill	2025
Solar fuels	2025

): solar fuels, windmill, clean energy, nanogenerators, hydroelectric power, and offshore winds. Marine environment and offshore oil well production are motor themes, and energy harvesting and energy conversion are emerging or declining themes (

Table 17. Thematic clusters related to the subtopic of tidal and wave energy.

Words	Cluster
Oceanography	Emerging or declining themes
Energy harvesting	Emerging or declining themes
Energy conversion	Emerging or declining themes
Oscillating water column	Emerging or declining themes
Power take-offs	Emerging or declining themes
Ocean currents	Emerging or declining themes
Turbines	Emerging or declining themes
Hydrodynamics	Emerging or declining themes
Optimisation	Emerging or declining themes
Computational fluid dynamics	Emerging or declining themes
Energy policy	Motor themes
Solar energy	Motor themes
Fossil fuels	Motor themes
Climate change	Motor themes
Energy efficiency	Motor themes
Alternative energy	Motor themes
Offshore oil well production	Motor themes
Environmental impact	Motor themes
Wind turbines	Motor themes
Marine environment	Motor themes
Electricity generation	Motor themes

). Turbines, tidal currents, solar energy, and geothermal power are specialised topics in specialised clusters. Alternative energy and energy efficiency are central terms (

Table 18. Factorial analysis (Multiple Correspondence Analysis) results related to the subtopic of tidal and wave energy.

Word	Dim1	Dim2	Cluster
Alternative energy	−0.04	0.11	1
Energy efficiency	−0.01	−0.45s	1
Computational fluid dynamics	−0.01	0.90	1
Clean energy	0.16	−0.28	1
Ocean currents	0.29	0.88	1
Solar power generation	0.65	−2.31	2
Solar energy	0.86	−2.22	2
Geothermal energy	1.28	−2.63	2
Turbines	0.83	1.03	3
Tidal currents	1.24	1.57	3

). These results demonstrate the interdependence among various renewable energy sources. Considering these sources in isolation may compromise the robustness of the obtained results.

The United Kingdom, China, the USA, Spain, France, Australia, Ireland, Italy, and Portugal are the most relevant and central countries in the world network related to this subtopic (

Table 19. Collaboration network related to the subtopic of tidal and wave energy.

Node	Cluster	Betweenness	Closeness	PageRank
The United Kingdom	2	140.777	0.019	0.105
China	1	107.643	0.018	0.081
The USA	1	70.920	0.018	0.070
Spain	2	34.937	0.016	0.044
France	2	44.078	0.017	0.044
Australia	1	31.299	0.017	0.042
Ireland	2	10.984	0.015	0.040
Italy	2	25.837	0.016	0.033
Portugal	2	6.323	0.015	0.031
Canada	1	19.936	0.017	0.029
India	1	27.997	0.017	0.027
Iran	1	6.380	0.016	0.023
Malaysia	1	8.697	0.015	0.022
Sweden	2	3.404	0.015	0.021
Denmark	2	3.744	0.015	0.021

). Sweden and Denmark also appear among the top structural influencing countries, but with less importance and centrality. These energy sources do, in fact, have their own specific characteristics that explain the interest shown by the scientific community in the countries identified as the most relevant and pivotal.

3.5. Green Hydrogen and Clean Energy

For this specific subtopic, 14,085 documents were found. As in subtopics analysed before, Dincer, I. appears among the most productive authors. These results once again demonstrate the interconnection of various renewable energy sources. Energy, engineering, physics and astronomy, chemistry, environmental science, and chemical engineering are among the dominant subject areas (

Table 20. Metrics related to the specific topic of green hydrogen and clean energy.

Year		Author Name		Subject Area		Country
2025	3628	Dincer, I.	87	Energy	8109	China	5033
2024	3096	Boretti, A.	26	Engineering	5011	India	1240
2023	1995	Rosen, M.A.	26	Physics and astronomy	3314	The United States	1143
2022	1413	Wu, Z.	25	Chemistry	2466	Germany	729
2021	822	Ahmad, T.	20	Environmental science	2372	The United Kingdom	637
2020	444	Hassan, Q.	20	Chemical engineering	2345	The Republic of Korea	627
2019	319	Wang, L.	20	Materials science	2343	Italy	612
2018	227	Shao, Z.	19	Mathematics	1139	Australia	567
2017	165	Olabi, A.G.	18	Computer science	1021	Saudi Arabia	561
2016	131	Wang, L.	18	Social sciences	526	Turkey	447
2015	118	You, S.	18	Earth and planetary sciences	464	Japan	424
2014	161	Yuan, T.	17	Business, management, and accounting	405	Canada	423
2013	139	Abdelkareem, M.A.	16	Biochemistry, genetics, and molecular biology	358	Spain	391
2012	180	Allakhverdiev, S.I.	16	Economics, econometrics, and finance	242	Iran	351
2011	139	Aziz, M.	16	Multidisciplinary	195	Egypt	295
2010	79	Lin, J.	16	Decision sciences	152	France	282
2009	115	Pollet, B.G.	16	Agricultural and biological sciences	133	The Russian Federation	272
2008	124	Veziroglu, T.N.	16	Medicine	111	Malaysia	264
2007	95	Acar, C.	15	Pharmacology, toxicology, and pharmaceutics	36	Pakistan	255
2006	87	Fang, J.	15	Arts and humanities	34	Brazil	219

), highlighting the importance of these issues for this subtopic. This topic achieved the saturation phase (Figure 4), and degradation model, oxygen evolution, hydrogen economy, electrolysis, and hydrogen production are the emerging topics (

Table 21. Trend terms (all keywords) related to the subtopic of green hydrogen and clean energy.

Term	Year (Median)
Old Terms
Automotive fuels	2004
Thermal effects	2004
Research and development management	2005
Air pollution control	2005
Societies and institutions	2005
Mathematical models	2006
Project management	2006
Crude petroleum	2006
Protons	2007
Eurasia	2007
Emerging Terms
Hydrogen production	2023
Hydrogen	2023
Hydrogen storage	2023
Renewable energy	2024
Electrolysis	2024
Green hydrogen	2024
Hydrogen economy	2025
Controlled study	2025
Oxygen evolution	2025
Degradation model	2026

). Hydrogen evolution reaction and electrolysis are still niche themes (

Table 22. Thematic map related to the subtopic green hydrogen and clean energy.

Words	Cluster
Hydrogen production	Basic themes
Hydrogen storage	Basic themes
Green hydrogen	Basic themes
Solar power generation	Basic themes
Clean energy	Basic themes
Electrolysis	Niche themes
Electrocatalysts	Niche themes
Hydrogen evolution reaction	Niche themes
Water splitting	Niche themes
Water electrolysis	Niche themes

), and hydrogen production and hydrogen storage are the basic themes (important themes, but not well developed). Water splitting, oxygen evolution reaction, electrolysis, and cost-effectiveness are specialised terms, and sustainable energy, energy efficiency, and hydrogen production are the central terms (

Table 23. Factorial analysis (Multiple Correspondence Analysis) related to the subtopic of green hydrogen and clean energy.

Word	Dim1	Dim2	Cluster
Carbon	−0.05	−0.34	1
Sustainable energy	−0.05	−0.05	1
Hydrogen production	−0.04	−0.71	1
Energy efficiency	0.24	−0.75	1
Electrolyzers	0.35	−1.17	1
Water electrolysis	−0.86	−1.15	2
Electrolysis	−0.81	−1.12	2
Cost-effectiveness	−0.50	−1.08	2
Electrolytic cells	0.14	−1.62	2
Oxygen evolution reaction	−2.46	−0.82	3
Catalyst activity	−2.25	−0.69	3
Electrocatalysts	−2.18	−0.78	3
Oxygen	−1.73	−1.14	3
Water splitting	−1.64	−0.37	3

). China, the USA, and Saudi Arabia are structural influencing countries in the international collaboration network (

Table 24. Collaboration network related to the subtopic of green hydrogen and clean energy.

Node	Cluster	Betweenness	Closeness	PageRank
China	1	95.582	0.020	0.109
The USA	1	42.187	0.020	0.057
Saudi Arabia	2	31.359	0.019	0.056
The United Kingdom	3	33.399	0.020	0.051
India	2	25.291	0.020	0.046
Australia	1	15.125	0.019	0.038
Germany	3	25.691	0.020	0.036
The Republic of Korea	2	6.449	0.019	0.034
Italy	3	20.024	0.019	0.028
Spain	3	30.877	0.019	0.027
France	3	15.293	0.018	0.027
Egypt	2	4.632	0.017	0.026
Japan	1	7.142	0.017	0.025
Pakistan	2	2.784	0.017	0.025
Canada	4	5.184	0.019	0.025

). Although the production and storage of hydrogen are important and even central to certain findings, these are the themes that still need to be explored in greater depth in the scientific literature.

3.6. Renewable Energy and Sustainable Development Goals (SDGs)

A total of 7166 documents were found for this specific subtopic. Energy, environmental science, engineering, social sciences, computer science, and economics and business domains are subject areas with relevant contributions for the topic (

Table 25. Metrics related to the specific topic of renewable energy and sustainable development goals.

Year		Author Name		Subject Area		Country
2025	2263	Adebayo, T.S.	47	Energy	3149	China	1292
2024	1719	Bekun, F.V.	41	Environmental science	2941	India	1224
2023	1045	Raman, R.	34	Engineering	1943	The United Kingdom	617
2022	763	Alola, A.A.	27	Social sciences	1839	The United States	567
2021	512	Pata, U.K.	27	Computer science	980	Turkey	540
2020	337	Sinha, A.	26	Economics, econometrics, and finance	913	Pakistan	441
2019	162	Balsalobre-Lorente, D.	25	Business, management, and accounting	805	Malaysia	422
2018	98	Anwar, A.	24	Mathematics	579	Saudi Arabia	374
2017	64	Caglar, A.E.	24	Earth and planetary sciences	442	Australia	307
2016	30	Ahmed, Z.	23	Chemical engineering	386	Spain	264
2015	14	Gyamfi, B.A.	23	Agricultural and biological sciences	317	Italy	263
2014	2	Murshed, M.	23	Chemistry	273	Germany	261
2013	1	Nedungadi, P.	23	Physics and astronomy	272	South Africa	255
2012	2	Sharif, A.	22	Materials science	268	Nigeria	247
2011	4	Olabi, A.G.	21	Decision sciences	231	Poland	236
2010	6	Usman, M.	21	Multidisciplinary	215	Bangladesh	219
2008	2	Abdelkareem, M.A.	19	Medicine	175	Indonesia	200
2007	4	Kirikkaleli, D.	18	Biochemistry, genetics, and molecular biology	147	Brazil	194
2006	1	Obaideen, K.	17	Arts and humanities	73	Canada	189
2000	1	Ozturk, I.	16	Psychology	49	The Russian Federation	187

), showing the importance attached to socioeconomic factors, for example, in these subjects. This topic is in the saturation phase (Figure 5). Artificial intelligence, green economy, sustainable development, climate change, and COVID-19 are among the emerging terms (

Table 26. Trend terms (all keywords) related to the subtopic of renewable energy and sustainable development goals.

Term	Year (Median)
Old Terms
Health hazard	2017
Catering service	2018
Priority journal	2019
Analysis	2019
Electric load management	2019
Wellbeing	2020
Proven reserves	2020
Conservation of energy resources	2020
Planning	2021
Electric power generation	2021
Emerging Terms
COVID-19	2022
Climate change	2023
Carbon dioxide	2023
United Nations	2023
Sustainable development	2024
Sustainable development goal	2024
Sustainable development goals	2024
Green development	2025
Green economy	2025
Artificial intelligence	2025

). Economic development and environmental protection are motor themes, and climate change and environmental impact are emerging or declining themes (

Table 27. Thematic maps related to the subtopic of renewable energy and sustainable development goals.

Words	Cluster
Clean energy	Central themes
Energy policy	Central themes
Energy efficiency	Central themes
Investments	Central themes
Economics	Central themes
Alternative energy	Motor themes
Sustainability	Motor themes
Economic growth	Motor themes
Economic development	Motor themes
Environmental protection	Motor themes
Climate change	Emerging or declining themes
Environmental impact	Emerging or declining themes
Greenhouse gases	Emerging or declining themes
Circular economy	Emerging or declining themes
Global warming	Emerging or declining themes

). Circular economy and energy transition are central terms, and alternative energy, innovation, economic growth, environmental economics, and planning are specialised topics (

Table 28. Factorial analysis (Multiple Correspondence Analysis) related to the subtopic of renewable energy and sustainable development goals.

Word	Dim1	Dim2	Cluster
Circular economy	−0.08	0.04	1
Biomass	0.05	−0.06	1
Energy transition	0.14	−0.53	1
Energy efficiency	0.23	−0.49	1
Decision-making	0.28	−0.65	1
Alternative energy	0.91	0.37	2
Innovation	0.94	1.06	2
Environmental sustainability	1.19	0.41	2
Economic growth	1.46	0.93	2
Environmental economics	1.67	1.11	2
Energy transitions	0.37	−0.98	3
Developing countries	0.42	−0.79	3
Energy conservation	0.45	−1.03	3
Planning	0.57	−1.30	3
Energy policy	0.57	−1.22	3

). The structural influencing countries are China, Turkey, and India (

Table 29. Collaboration network related to the subtopic of renewable energy and sustainable development goals.

Node	Cluster	Betweenness	Closeness	PageRank
China	1	32.011	0.020	0.082
Turkey	1	7.825	0.020	0.048
India	2	9.634	0.020	0.048
The United Kingdom	3	19.460	0.020	0.048
Pakistan	1	5.627	0.020	0.044
The USA	3	10.940	0.020	0.043
Malaysia	2	4.678	0.020	0.040
Saudi Arabia	2	2.392	0.020	0.038
Australia	3	3.854	0.020	0.030
Germany	3	4.105	0.020	0.025
The Republic of Korea	1	1.092	0.020	0.024
Azerbaijan	1	1.545	0.018	0.024
Poland	1	11.107	0.020	0.022
Spain	3	3.955	0.020	0.022
United Arab Emirates	2	1.226	0.020	0.021

). Although the socio-economic aspects deserve more in-depth consideration in this subtopic, they need to be explored more prominently within it.

3.7. Energy Policy and Technological Innovation in Renewable Energy

The search in the Scopus database obtained, respectively, 78,245, 32,560, and 8728 documents for the specific topics of energy policy and technological innovation in renewable energy, and for the subtopic considering these two specific topics together the Boolean operator AND was considered to find the 8728 documents for the subtopic. Social, economic, and business sciences are among the dominant subject areas for the energy policy topic (

Table 30. Metrics related to the specific topic of energy policy.

Year		Author Name		Subject Area		Country
2025	13,888	Lin, B.	166	Energy	40,778	China	16,931
2024	10,386	Adebayo, T.S.	158	Environmental science	27,130	The United States	9651
2023	7995	Sovacool, B.K.	137	Engineering	25,381	The United Kingdom	6299
2022	6701	Shahbaz, M.	110	Social sciences	14,628	India	6152
2021	5619	Murshed, M.	105	Computer science	9037	Germany	4248
2020	4457	Alola, A.A.	100	Economics, econometrics, and finance	8884	Italy	3529
2019	3874	Bekun, F.V.	100	Mathematics	7679	Turkey	3136
2018	3375	Kirikkaleli, D.	100	Business, management, and accounting	7414	Australia	2990
2017	2932	Ozturk, I.	93	Earth and planetary sciences	4149	Spain	2521
2016	2460	Streimikiene, D.	93	Chemical engineering	2985	Pakistan	2441
2015	2087	Balsalobre-Lorente, D.	86	Physics and astronomy	2806	Malaysia	2283
2014	2031	Taghizadeh-Hesary, F.	84	Materials science	2775	Canada	2112
2013	1798	Breyer, C.	80	Agricultural and biological sciences	2433	Saudi Arabia	2018
2012	1664	Sharif, A.	80	Decision sciences	1988	The Netherlands	2014
2011	1449	Radulescu, M.	79	Chemistry	1610	Poland	1948
2010	1190	Pata, U.K.	67	Multidisciplinary	1370	France	1783
2009	921	Usman, M.	66	Medicine	1129	The Republic of Korea	1773
2008	741	Wang, Q.	66	Arts and humanities	760	Japan	1688
2007	656	Raihan, A.	64	Biochemistry, genetics, and molecular biology	755	Iran	1492
2006	471	Blumberga, D.	63	Psychology	420	Indonesia	1366

). Material sciences, chemistry, and chemical engineering are among the subject areas that deserved more attention for the technological and innovation specific topic (

Table 31. Metrics related to the specific topic of technological innovation in renewable energy.

Year		Author Name		Subject Area		Country
2025	5637	Omer, A.M.	72	Energy	15,566	China	8004
2024	4597	Breyer, C.	42	Engineering	12,713	The United States	4383
2023	3162	Duić, N.	40	Environmental science	7914	India	3520
2022	2585	Dincer, I.	35	Materials science	4657	The United Kingdom	2362
2021	2210	Adebayo, T.S.	34	Chemistry	3681	Germany	1370
2020	1808	Lin, B.	32	Computer science	3471	Italy	1236
2019	1589	Streimikiene, D.	31	Chemical engineering	3434	Australia	1197
2018	1364	Olabi, A.G.	29	Social sciences	3203	Saudi Arabia	1064
2017	1241	Sovacool, B.K.	27	Physics and astronomy	2970	The Republic of Korea	1016
2016	968	Hasanuzzaman, M.	26	Mathematics	2722	Malaysia	999
2015	825	Klemeš, J.J.	26	Business, management, and accounting	1910	Canada	976
2014	871	Mohammadi-Ivatloo, B.	26	Economics, econometrics, and finance	1792	Turkey	944
2013	788	Rosen, M.A.	26	Earth and planetary sciences	1596	Spain	940
2012	710	Brent, A.C.	25	Biochemistry, genetics, and molecular biology	689	Pakistan	837
2011	657	Schmidt, T.S.	25	Agricultural and biological sciences	678	Japan	756
2010	535	Shao, Z.	24	Decision sciences	652	Iran	625
2009	421	Psarras, J.	23	Multidisciplinary	497	The Netherlands	607
2008	359	Chen, H.	22	Medicine	383	The Russian Federation	553
2007	291	Kirikkaleli, D.	22	Arts and humanities	229	South Africa	545
2006	237	Raihan, A.	22	Psychology	134	France	540

). This subtopic is almost in the middle of the maturity phase (Figure 6). Green development, energy economics, energy transition, economic development, and economic growth are the emerging terms (

Table 32. Trend terms (all keywords) related to the subtopic of energy policy and technological innovation in renewable energy.

Term	Year (Median)
Old Terms
Global climate change	1998
Renewable energy technologies (ret)	2000
Law	2002
Crude petroleum	2003
Kerosene	2004
Marketing	2005
Air pollution control	2005
Research and development management	2005
Greenhouse effect	2006
Societies and institutions	2006
Emerging Terms
Alternative energy	2022
China	2023
Economic growth	2023
Economic development	2023
Energy	2024
Clean energy	2024
Energy transition	2024
Energy economics	2025
Circular economy	2025
Green development	2025

). Energy transition as an emerging topic is confirmed by

Table 33. Thematic map related to the subtopic of energy policy and technological innovation in renewable energy.

Words	Cluster
Energy efficiency	Motor themes
Investments	Motor themes
Energy utilisation	Motor themes
Economics	Motor themes
Energy conservation	Motor themes
Sustainable development	Motor themes
Climate change	Motor themes
Environmental technology	Motor themes
Clean energy	Motor themes
Emission control	Motor themes
Alternative energy	Emerging or declining themes
Electricity generation	Emerging or declining themes
Power generation	Emerging or declining themes
Energy planning	Emerging or declining themes
Energy market	Emerging or declining themes
Greenhouse gases	Emerging or declining themes
Energy transition	Emerging or declining themes
Environmental impact	Emerging or declining themes
Energy transitions	Emerging or declining themes
Gas emissions	Emerging or declining themes

. This term is also a central topic (

Table 34. Factorial analysis (Multiple Correspondence Analysis) related to the subtopic of energy policy and technological innovation in renewable energy.

Word	Dim1	Dim2	Cluster
Energy transitions	−0.06	0.11	1
Sustainability	0.00	0.93	1
Alternative energy	0.19	0.64	1
Decision-making	0.23	−0.47	1
Solar power generation	0.24	−1.16	1
Economic growth	0.35	1.84	2
Environmental policy	0.49	1.46	2
Environmental protection	1.12	0.56	2
Carbon dioxide	1.18	1.16	2
Emission control	1.30	0.93	2
Global warming	1.58	0.19	3
Greenhouse gases	1.93	−0.25	3
Gas emissions	2.26	−0.25	3

) and global warming is a specialised term. China, the United Kingdom, the USA, and Turkey are important and central countries in network collaboration (

Table 35. Collaboration network related to the subtopic of energy policy and technological innovation in renewable energy.

Node	Cluster	Betweenness	Closeness	PageRank
China	1	103.096	0.020	0.088
The United Kingdom	2	55.750	0.020	0.062
The USA	2	38.296	0.020	0.056
Turkey	1	21.722	0.019	0.040
Pakistan	1	10.288	0.019	0.039
Saudi Arabia	1	19.950	0.018	0.037
India	1	15.103	0.019	0.035
Malaysia	1	7.217	0.017	0.034
Germany	2	11.122	0.018	0.033
Australia	1	8.807	0.019	0.028
Italy	2	5.293	0.017	0.025
Spain	2	13.446	0.018	0.025
The Netherlands	2	2.345	0.016	0.024
Canada	2	4.812	0.019	0.022
The Republic of Korea	1	2.136	0.017	0.020

). Global warming, for example, is an emerging challenge for humanity that needs to be addressed more prominently in the specialist literature in these fields.

4. Targeted Literature Discussion Based on Bibliometric Insights

Table 36 presents the top 10 documents with the highest total link strength, considering bibliographic data and bibliographic coupling links from the documents found for the subtopic solar energy and wind power. This subtopic was considered because of the importance of solar energy and wind power for renewable and sustainable energy both for the energy sector and for the scientific community. Figure 7 illustrates the approach adopted for the focused analysis of influential documents, which considers the PRISMA protocol as a reference guide and is based on the bibliometric analysis [98,99]. This criterion (total link strength of bibliographic coupling links), which reflects the degree of connectivity of each document within the network, was chosen because it captures the structural relevance of the document within the field of research.

The literature associated with renewable and sustainable energy focused on the combination of different energy power sources in optimised and hybrid [100] approaches, namely to reduce costs and to complement each other [101]. The problem with some renewable energies is the instability and the costs of investment and maintenance [102]. These hybrid systems may combine solar energy, wind power [103], geothermal sources [104], and battery storage. The optimal sizing of these hybrid systems is impacted by socio-demographic factors [105] and is another concern for the scientific community [106]. The availability of data and the consideration of adjusted methodologies of analysis are crucial [107] for successful sustainable development. Integration of renewable and sustainable energy into systems brings new challenges [108] and new technologies may provide added value to finding solutions. In the contexts of renewables, hydrogen has assumed increased importance [109].

Table 36. Top documents with the highest total link strength.

Label	URL	Total Link Strength	Normalised Citations	Publication Year
Elma (2012) [101]	https://doi.org/10.1016/j.apenergy.2012.02.080	267	1.5093	2012
Kaabeche (2011) [106]	https://doi.org/10.1016/j.energy.2010.11.024	222	6.9453	2011
Addo (2014) [100]	https://doi.org/10.1109/iciea.2014.6931410	205	0.0793	2014
Tito (2016) [105]	https://doi.org/10.1016/j.solener.2016.07.036	187	2.8074	2016
Ismail (2014) [104]	https://doi.org/10.1109/inmic.2014.7097399	181	0.1785	2014
Hosseinzadeh (2017) [103]	https://doi.org/10.1109/icciautom.2017.8258709	179	0.1083	2017
Mohamed (2017) [107]	https://doi.org/10.1016/j.rser.2017.04.048	177	3.0594	2017
Liu (2022) [108]	https://doi.org/10.3390/app12042194	164	0.3447	2022
Mansir (2026) [109]	https://doi.org/10.1177/0958305x241248373	150	0.8885	2024
Senjyu (2006) [102]	https://doi.org/10.1109/tec.2006.874250	149	2.2052	2006

Table 36. Top documents with the highest total link strength.

Label	URL	Total Link Strength	Normalised Citations	Publication Year
Elma (2012) [101]	https://doi.org/10.1016/j.apenergy.2012.02.080	267	1.5093	2012
Kaabeche (2011) [106]	https://doi.org/10.1016/j.energy.2010.11.024	222	6.9453	2011
Addo (2014) [100]	https://doi.org/10.1109/iciea.2014.6931410	205	0.0793	2014
Tito (2016) [105]	https://doi.org/10.1016/j.solener.2016.07.036	187	2.8074	2016
Ismail (2014) [104]	https://doi.org/10.1109/inmic.2014.7097399	181	0.1785	2014
Hosseinzadeh (2017) [103]	https://doi.org/10.1109/icciautom.2017.8258709	179	0.1083	2017
Mohamed (2017) [107]	https://doi.org/10.1016/j.rser.2017.04.048	177	3.0594	2017
Liu (2022) [108]	https://doi.org/10.3390/app12042194	164	0.3447	2022
Mansir (2026) [109]	https://doi.org/10.1177/0958305x241248373	150	0.8885	2024
Senjyu (2006) [102]	https://doi.org/10.1109/tec.2006.874250	149	2.2052	2006

5. Main Insights and Discussion

Population growth [4], environmental challenges [5], climate change [6], pandemics [7], and the traditional energy markets dynamics [8] have motivated several stakeholders to pay more attention to renewable and sustainable energy, in line with the international goals [14]. Solar and wind energy sources have deserved more attention of the scientific community [2], with the United States, China and some European Union countries having relevant contributions for the understanding of the renewables sector [17]. The concentration of scientific output in a small number of countries can be explained by the availability of funding for scientific research and access to technological resources and bibliographic information. In any case, this leads to a bias in the scientific literature produced, leaving out realities relating to developing countries that are, in certain cases, more vulnerable to climate change. Digital transition plays a crucial role in the changes towards renewables [21]. The importance of the available data [33], international collaboration [37], energy efficiency and policy [38], adjusted storage systems, hybrid structures and risk monitoring [39], location of power plants [43], and integration processes [41] were also highlighted. There is a wide range of technological topics identified, which the literature appears to address in a fragmented manner, in some cases. The lack of integration between technology, socioeconomic contexts, and policy measures may limit the practical application of the solutions identified.

Transportation systems [52] and the building sector [53] are contexts where renewables may contribute to mitigating environmental impacts. The uncertainty [58] and intermittency [59] of the renewable systems have promoted the consideration of hybrid solutions. Voltage constancy, inertial response, and frequency control are other concerns [62]. Transition to renewable energy is not without its challenges, particularly in terms of grid stability and reliability, highlighting the need for integrated solutions. Artificial intelligence may bring added value to these frameworks, particularly for forecasting insulation, market conditions, and wind turbine dynamics [69]. Other new technologies, such as compressed air energy storage [71], new batteries [72], blockchain [74], and photonics [75] have been referred to in the literature. The emergence of digital technologies opens up new opportunities but also raises new concerns regarding cost–benefit and environmental impacts, which need to be explored in greater depth in the literature. Despite stakeholders’ interest in renewables, this sector remains residual in the world’s energy consumption. This suggests that structural barriers remain, particularly in terms of economic constraints and infrastructure limitations. Another dimension that may deserve deeper focus in future research is public engagement with the greener transition [86]. The energy transition requires social acceptance, and this needs to be properly addressed, taking a multidisciplinary approach. In any case, some doubts remain on the real implication of renewables about carbon emissions mitigation [96]. This becomes particularly important when indirect emissions, life cycle analyses, and rebound effects are taken into account.

The bibliometric analysis highlights that there are significant differences in the literature regarding several subtopics related to renewables. These subtopics are associated with the following combinations: solar and wind energy, bioenergy, biomass and hydroelectric power, tidal and wave energy, green hydrogen and clean energy, renewable energy and sustainable development goals, and energy policy and technological innovation in renewable energy. In general, research related to renewables increased strongly after 2020, and this literature is focused on engineering studies, concentrated on a reduced number of authors and published by specific sources. This disciplinary concentration suggests an imbalance in the knowledge produced, which is not adequately complemented by socioeconomic and policy insights. Socioeconomic analysis, empirical evidence, policy impact research, and interdisciplinary research are gaps that could be addressed in future studies. China and the United States are the countries with the greatest contribution to the renewables topic, and solar energy, wind power, efficiency, and sustainability are the most relevant themes. It is suggested that a more balanced geographic distribution of the scientific production deserves deeper attention from the researchers, as well as some themes, such as energy storage, grid integration, and socioeconomic and policy assessments. These limitations pose challenges for the development of region-specific solutions and carry the risk of implementing strategies that are not tailored to local conditions and needs. Solar and wind energy research is led by China, India, the United States, and some European countries, being focused on technological subject areas and almost in saturation phase, suggesting the need for change in future research, particularly in terms of integration and optimisation. Bioenergy, biomass, and hydroelectric power are concentrated on environmental, engineering, agricultural, material, and quantitative sciences, and are in the beginning of the maturity phase, showing that there is a field to be explored. There are, however, certain factors to bear in mind in these areas, particularly with regard to land use, biodiversity, and competition for resources. Tidal and wave energy is focused on engineering, environmental, computer, and earth sciences, and is in the middle of the maturity phase. The associated costs and technical complexity may explain why these fields have been developed more slowly. Green hydrogen and clean energy are in the saturation phase, as well as the renewable energy and sustainable development goals subtopic. Despite the level of saturation observed, there are aspects that need to be better addressed, such as the economic viability of the associated solutions and the technological requirements. Energy policy and technological innovation in renewable energy are almost in the middle of the maturity phase. This demonstrates recognition of the importance of policy measures for the energy transition.

What is new (what are the main gaps and what can be done in future research):

-

In general: increase the research about socioeconomic analysis, empirical research, sector interrelationships, policy assessment, energy storage, grid integration, promote more balanced geographical distribution of the research (increasing the contributions from Africa, Latin America and environmentally vulnerable countries), and encourage interdisciplinary and social participation.

-

Solar and wind power: develop emerging themes, such as wind power integration and microgrid; address emerging or declining themes related to solar power generation, stochastic systems, electricity generation and photovoltaic systems.

-

Bioenergy, biomass, and hydroelectric power: develop emerging topics associated with wind power integration, windmill, solar fuels, hydrogen storage, and sustainable energy; consider emerging or declining themes related to biofuels, electricity generation, greenhouse gas emissions, and economic dimensions.

-

Tidal and wave energy: address emerging themes, such as solar fuels, windmills, nanogenerators, and offshore winds; consider specialised topics associated with turbines, tidal currents and geothermal power.

-

Green hydrogen and clean energy: consider basic and emerging themes related to degradation model, oxygen evolution, hydrogen economy, electrolysis, hydrogen production, and hydrogen storage; address specialised terms, such as water splitting, oxygen reaction, and cost-effectiveness.

-

Renewable energy and sustainable development goals (SDGs): develop emerging topics, such as artificial intelligence, green economy, sustainable development, and climate change; consider specialised themes associated with environmental protection, carbon emissions, economic development, and growth.

-

Energy policy and technological innovation in renewable energy: develop emerging themes related to green development, energy economics, energy transition, and economic development; take into account specialised themes, such as global warming in these contexts.

6. Conclusions

This study adopts a broad conceptual approach, encompassing various fields related to renewable and sustainable energy. In terms of practical implications, it is important to better understand renewable energy markets, better address the other renewables beyond solar and wind power, and increase the scientific production related to contexts associated with Africa, Latin America, and other vulnerable countries to the current environmental challenges. It is also relevant to enhance the contributions about datasets, analysis methodologies (artificial intelligence and life cycle sustainability assessment, for example), stakeholder mapping and engagement, storage systems, hybrid structures, microgrid and integration processes. More insights about new technologies for the renewable energy sector are additionally important, such as compressed air storage, batteries, blockchain, and photonics. It is also relevant to better address the real contributions of renewables to carbon sequestration. For policy recommendations, it is suggested to convince the national, European, and International organisations to consider the findings obtained with this study to design research programmes that specifically address the gaps identified, specifically to promote the research in emerging, specialised, and basic topics. For future research, it would be important to bring more contributions to identify the different dimensions and subtopics inside the renewable and sustainable energy topic.