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Review

Renewable Energy Sources and Energy Production: A Bibliometric Analysis of the Last Five Years

by
Renzo Seminario-Córdova
* and
Raúl Rojas-Ortega
Training and Teaching Research Program, North Lima Campus, Cesar Vallejo University, Lima 15314, Peru
*
Author to whom correspondence should be addressed.
Sustainability 2023, 15(13), 10499; https://doi.org/10.3390/su151310499
Submission received: 2 June 2023 / Revised: 23 June 2023 / Accepted: 26 June 2023 / Published: 4 July 2023
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Abstract

:
Humanity has undertaken actions to decarbonize the main CO2-emitting industries, such as the energy industry. The solution to this problem has been to use renewable energy sources, with positive results in recent years. The objective of the present research was to analyze the scientific advances produced in research on renewable energy and energy production globally during the years 2019 and 2023. The purpose was to determine the current status and future trends in renewable energies in order to contribute to the scientific community by identifying potential risks and encouraging collaboration between authors, institutions, and countries. A bibliometric analysis was performed in the Scopus database using the keywords “renewable energies” and “energy production” within a search equation with a time limit of 2019 and 2023. Keyword co-occurrence and collaboration between authors and countries were performed with VOS Viewer software. It was determined, using per capita research analysis, that the leaders in this research were Cyprus, Denmark, Qatar, Norway, and Ireland. The leading institutions in this field of research are the Technical University of Denmark; Aalborg University; and the Ministry of Education, China. The predominant research topics were energy, engineering, and environmental sciences, related to energy sources such as biomass, hydrogen, or wave energy. The results described here have the potential to contribute to the scientific community, stimulating new research and identifying new needs in the existing literature.

1. Introduction

Climate change has become one of the main global problems of today [1]. Since it affects both ecosystems and human beings directly [2], it can cause a drop in crop yields and the loss of assets or livelihood opportunities [3]. In addition, it generates abrupt changes in ecosystem processes and characteristics, some of which may be irreversible [4]. According to numerous studies, the cause of climate change can be found in anthropogenic activity, causing an increase in global temperature [5] due to the emission of GHGs (greenhouse gases) [6]. For instance, global warming causes the evaporation of water, changes in precipitation patterns, and an increase in the frequency of droughts and floods [7]. Socially, it generates an increase in violence, political instability, and criminality [8].
As a result, it has become necessary to take an active stance towards this situation so that humanity can act to mitigate this issue, which affects society and ecosystems [9]. Therefore, in conjunction with Goal 7 of the Sustainable Development Goals, the use of renewable energy is being employed and promoted as a key strategy to confront environmental deterioration and the energy crisis [10]. Thus, the most viable solution is one that demands the presence of new sustainable energies, seeking better energy efficiency on a large scale along with changes in the fuel sources by switching from fossil fuels to renewable energies [11,12]. This is because the typical combustion reaction in an engine (fuel plus air (N2 + O2)) emits toxic gases such as carbon monoxide (CO), ozone (O3), nitrogen oxides, and volatile organic compounds, which are toxic to the human respiratory system [13] and are responsible for the increase in environmental temperature.
For this reason, some countries have taken actions towards reducing carbon emissions, such as Spain, which has reduced the use of coal as a source of electricity by up to 17% [14]. In addition, solutions such as hydrogen have the potential to initiate a new energy era with very low or almost zero carbon emissions [15]. Compared to natural gas (whose benefits are somewhat more complicated to calculate), hydrogen, as well as other clean energy sources, such as biomass or wave energies, can achieve the decoupling of some countries from fossil fuel sources [16]. This is evidenced by research [17] showing that, although Mexico has increased its use of natural gas for energy production, it is not enough to transform its electricity system into a low-carbon one. In contrast, biomass gasification has the potential to reduce harmful gases and has the potential to improve efficiency in the energy production process [18]; in fact, the research by Bildirici and Ersin [19] showed that biomass energy consumption influences economic growth in countries such as the U.S., Germany, and Great Britain. This is the driving force behind the use of renewable and clean energies as the only viable solution to keep the global temperature increase below 1.5 °C [20].
According to Sousa et al. [21], to achieve these changes, there is a need to invest in studies aimed at reducing CO2 emissions and improving economic growth. The current reality shows that the amount of energy generated from renewable sources is increasing worldwide [11] thanks to the advances achieved in recent years and the demands of Industry 4.0, which pushes countries to adopt these energy sources at a faster pace than they do today [22]. In view of this, the present study set out to corroborate the following hypotheses:
  • Research on renewable energies is multidisciplinary, which is why this topic is becoming one of the most important worldwide.
  • Renewable energies in energy production are of interest to all countries, but progress in this research varies for economic and geographic reasons.
  • The renewable energy sources that generate more interest worldwide are hydrogen, biomass, and solar energy, so there is a greater number of papers associated with these energy sources in the literature.
Therefore, the objective of the present research was to analyze the scientific advances produced in research on renewable energy and energy production globally during the years 2019 and 2023. The purpose was to determine the current status and future trends on renewable energies in order to contribute to the scientific community to identify potential risks and encourage collaboration between authors, institutions, and countries.

2. Materials and Methods

2.1. Research Approach

This research corresponds to a bibliometric analysis which, according to Perea-Moreno et al. [23], is useful in scientific work since it provides an interesting overview of the scientific activity related to a particular topic at the international level and provides relevant and useful information for decision making in the scientific community [24]; likewise, bibliometric analysis provides a set of information from research results, how it has evolved, its visibility, and how it is structured [25]. In this sense, the aim was to evaluate the scientific activity and impact of research and its sources.

2.2. Search Strategies

The search strategy was defined by taking a set of keywords as a starting point, which were extracted from the UNESCO thesaurus [26]. During the first week of May 2023, the search process was carried out using Elsevier’s Scopus database, which is an interdisciplinary database that includes more than 36,000 titles in the fields of physical sciences, health, agriculture, social sciences, etc. [27] and publishes different types of scientific documents such as articles, books, or book chapters. Keywords were entered into the search engines of said database using a set of operators through the following search equation.
  • TITLE-ABS-KEY (renewable energy OR clean energy OR renewable energy integration) AND TITLE-ABS-KEY (energy production) AND PUBYEAR > 2018 AND PUBYEAR < 2024.
Furthermore, relevant gray literature was consulted in Google Scholar or similar databases such as EBSCO, IEE Xplore, or Scielo, with the purpose of searching for texts to reinforce the present research. Reference lists of relevant articles were also reviewed.

2.3. Inclusion and Exclusion Criteria

To perform the bibliometric analysis, a series of inclusion and exclusion criteria had to be met. The time range was set between 2019 and early 2023; therefore, articles published before this period were excluded. Regarding the publishing language, no restrictions were placed so that the survey would be as global as possible. Likewise, there was no territorial restriction; thus, there was no preference for any country, nor was there any kind of discrimination towards ethnicities or cultures.

2.4. Data Processing

Considering the guidelines of [28], the present study conducted an analysis of: (a) document types, (b) publishing language, (c) scientific production, (d) main scientific institutions with the highest production in the field, (e) collaboration between countries, (f) main authors, and (g) evolution in the use of keywords. This analysis was performed using the VOSViewer software (http://www.vosviewer.com/) (accessed on 11 May 2023), free software widely used to construct and visualize bibliometric networks using data obtained by searching large databases such as Scopus or Web of Science [29,30].
Figure 1 shows the process followed during this research to perform the bibliometric analysis.
(1)
Global search: three Scopus fields were used in this process: TITLE-ABS-KEY (renewable energy OR clean energy OR renewable energy OR renewable energy integration) AND TITLE-ABS-KEY (energy production) AND PUBYEAR > 2019 AND PUBYEAR < 2023. Then, the information was downloaded in an Excel file (.csv) in which categories such as years, author, type of document, country, cited by, source, and affiliation were included.
(2)
Bibliometric data analysis: this was performed independently, and each datum had its own analysis using Excel software.
(3)
Clustering: at this stage, all the information on authors, countries, and keywords was grouped using the VOSviewer ® software version 1.6.18. The results provided information about collaborations in the scientific community and countries, as well as research trends through keyword analysis.

3. Results

The quantification of scientific activity is performed through indicators such as the publications of an institution belonging to a particular country or area, in addition to the authors or year of publication [23,31]. The value of this information lies in making comparisons between institutions and providing a frame of reference to achieve the objective of the proposed research. For this reason, the scientific production was monitored over the last five years.

3.1. Current Status of the Last Five Years of Research on Renewable Energies in Power Production

The search resulted in a total of 2340 documents considering a large set of fields and document types for the period between 2019 and early 2023. Figure 2 shows the different types of publications found in this period on renewable energy and energy production.
There is a clear predominance of research articles representing 60.2% (1408 documents). These are followed by conferences (509 documents), reviews (265 documents), and book chapters (116 documents). In addition, a total of 39 documents, including books, editorials, and short documents, were registered.
The production per year of renewable energy and energy production was also identified (Figure 3).
This figure shows a trend towards an increase in research on renewable energies and energy production. During 2019, a total of 442 papers were published. This number increased until reaching its highest peak in 2022 (651 documents). The number of publications in 2023 is lower compared to other years, but this is because this survey was carried out only in the first four months of this year; therefore, it is expected that the percentage will continue to increase.
As for the predominant language in the publications found (Figure 4), it is evident that a considerable number of them were published in English (2277 documents), followed by Chinese (40) and German (6). The remaining languages total 23 documents, which included publications in French, Russian, Spanish, etc. The predominance of English was because this language is the predominant one for publications in Scopus [32].

3.2. Distribution of Scopus Thematic Areas and Journals on Renewable Energies and Energy Production

As a result of the bibliometric analysis, the publications were classified by subject area (Figure 5). This figure shows that 27.6% of the documents come under the thematic area “energy”. This is followed by documents related to engineering (21.84%) and environmental sciences (11.85%), as the three areas with the highest number of documents. Other subject areas such as mathematics, social sciences or business, management, and accounting represent 33.97% of the subject areas. Others include subject areas such as Biochemistry, Pharmacology, or Medicine. The variety of research areas demonstrates the current interest in implementing renewable energies in various areas and industries worldwide.
According to [23,31], the impact the publications have is not calculated immediately through citations since this is a measure that can only be calculated over the years. In this sense, the impact factor of the top 10 reviews in renewable energy and energy production research was used (Table 1).
The leading journal with the highest number of publications on renewable energy and energy production is the Energies journal (159 papers) with an H-Index of 132 and a JCR impact factor of 3.52. It is followed by Applied Energy (82 papers), with an H-Index of 264 and a JCR impact factor of 11.446, and Energy (66 papers), with an H-Index of 81 and a JCR impact factor of 8.857. Furthermore, all the journals belong to the Q1 quartile and that seven of the journals (70%) are from the United Kingdom.

3.3. Worldwide Distribution of Institutions

Identifying the leading institutions in renewable energy and energy production research, as well as the most used keywords, will provide insight into the current research trends in this field [31]. Table 2 presents the ten institutions with the highest production in renewable energy and energy production.
The leading research institution is the Technical University of Denmark (38 publications), followed by Aalborg University and the Ministry of Education, each with more than 30 publications. Norges Teknisk-Naturvitenskapelige Universitet ranks last with 20 publications.
Research at the Technical University of Denmark focuses mainly on wind energy as a renewable energy source. However, Denmark is not the only one interested in this energy source; China, Portugal, and Norway have also shown interest in wind energy. Likewise, the identification of renewable energy sources and resources has received interest from five institutions in Denmark, Italy, and Portugal. Chinese institutions show a marked interest in hydrogen production as a solution to their energy needs since the two Chinese institutions have hydrogen as a central area of research. Lastly, energy efficiency is another topic of interest, with two institutions having published research focused on this subject.

3.4. Articles with the Highest Number of Citations

The identification of the documents with the highest number of citations makes it possible to identify the interests of the scientific community and the trends that future research on renewable energies and energy production will follow. Table 3 shows the most cited papers during the period 2019–2023. There is a marked interest in hydrogen as a clean energy source.
Most of the twenty articles were reviews. Dawood et al. [33] stated that hydrogen is a CO2-emission-free energy source and represents a viable solution for sustainable and renewable energy storage [37]. However, to obtain the best results, there is a need to clean up the energy production pathway and the energy used to produce it [52]. Thus, it is necessary to integrate purification technologies into the production process. Similarly, Yue et al. [35] investigated the challenges facing the integration of hydrogen into energy systems. The authors identify that political support is key to moving towards a cost-effective hydrogen economy. Parra et al. [36] and Abdin and Mérida [50] performed economic evaluations of hydrogen-based power systems. The consensus reached by the authors is that hydrogen allows decarbonizing sectors such as transport, power, or heat while integrating them economically.
Other research seeks solutions [46] to problems such as long-term energy storage through molecules other than hydrogen, including the use of new technologies [40] or the efficient use of resources [41] for optimal energy storage [47]. The research of Smith et al. [34] sees ammonia as a clean solution to leave fossil fuels behind, employing a redefined Haber–Bosch process for this purpose. The research by Carrillo et al. [38] also addresses energy storage, but with concentrated solar power (CSP) as the source, which would allow continuous electricity generation even when there is not enough sunlight. Angulo et al. [39] conducted research with the objective of identifying opportunities in the bubbles present in energy transfer. While bubbles have an influence on the transfer, the authors described strategies to exploit them to enhance the electrochemical reactions. For their part, Alasi et al. [42] analyzed and evaluated in detail the advances in HVDC transmission systems, systems that, compared to HVAC systems, play a superior role in energy transmission, being also economically favorable.
Ding et al. [43] evaluated the impact of international trade, energy productivity, eco-innovation, and renewable energy consumption on carbon dioxide emissions. They showed that the listed factors are the main sources of CO2 emissions through the economic integration of the supply chain [45]. To reduce the emission of this gas and other GHGs, biofuels [50] can be used as substitutes to diversify the energy supply [44]. In Africa, the factors that would reduce CO2 emissions are renewable energies and human capital [51]. In turn, Fan et al. [48] stated that, in the short term, foreign direct investment causes changes in the consumption of renewable energies, but in the long term, a moderate slowdown in foreign direct investment will boost the use of such energies.

3.5. Global Distribution of Publications for the Period 2019–2023

Global scientific production by country is illustrated in Figure 6. The number of publications is represented by the intensity of the colors; blue indicates a higher number of publications, while gray indicates no publications. The largest number of publications (306 documents) is evidenced in China, followed by Italy (257), the United States (244), Germany (189), India (152), the United Kingdom (137), Spain (114), France (91), Denmark (83) and Australia (77). These represent the countries with the highest number of publications in the period 2019–2023.
However, if the number of inhabitants of each country is considered, the number of research projects in each country varies. Therefore, an analysis was made of the number of research papers per capita in ten countries (Table 4). The calculation is made by dividing the publications registered in a country by the total population of the country in question. This value is used to determine exactly which country is leading in each field of research.
The calculation of total research per capita identified Cyprus (15.27) as the leader in research on renewable energies and energy production, followed by Denmark (14.17), Qatar (8.93), Norway (8.32), and Ireland (6.95). The last of these ten countries is Switzerland (5.17). Among these countries, Qatar stands out, with an energy consumption using fossil fuels that is very close to 100%. This reality has led to research being carried out in the last five years [54], seeking to integrate renewable energies, such as solar energy, into its energy system [55] with favorable results and good social acceptance.
In contrast, Table 5 shows the countries with the highest number of publications without considering the number of inhabitants.
The data allow us to state that China and India do not perform the best in terms of renewable energy research and energy production, as their research per capita is 0.22 and 0.11, respectively. The table shows that the leader of these ten countries is Denmark (and it ranks second among the countries overall). It is followed by Italy (4.35), Australia (2.99), Spain (2.40), Germany (2.27), the United Kingdom (2.18), France (1.34), and the United States (0.74).
Figure 7 shows the collaborative relationships between countries. The colors determine to which group each country belongs. The size of the circles is an indication of how important a country is based on the number of publications on renewable energy and energy production. The lines represent which countries have collaborated with each other to form a cluster.
Eleven collaboration groups between countries were identified, six of which are the most relevant and have the largest number of publications (Figure 7 and Table 6). The main countries are China, Italy, the United States, Germany, India, Spain, France, and Spain. From these, the red cluster is the one with the highest number of collaborations and with the greatest presence in the network. Within this cluster, the leading country is China, followed by the United States and Germany. The next most important cluster is the green one, led by India, and includes countries such as Iraq, Malaysia, Saudi Arabia, and the United Arab Emirates. These are followed by the clusters led by Italy (blue), Spain (yellow), France (violet), and Canada (turquoise).
Collaborations can be observed between countries belonging to the same geographical area, such as the ones between Brazil, Colombia, and Venezuela (South American countries) or the countries in the green cluster. These collaborations were also economically motivated, such as in the case of the United States, which did not necessarily collaborate with countries in North America (such as Canada, which collaborated with Egypt and Chile) but instead collaborated with countries in other continents. Thus, it can be stated that there are two forms of collaboration between countries: based on their geographical location and based on economic relations.

3.6. Analysis of Scientific Communities and Keywords

Another helpful factor in understanding the research trends for a particular topic (in this case renewable energy and energy production) is the identification of the most prominent authors [31]. Therefore, Table 7 and Figure 8 show information on the five most productive authors on this topic, as well as the number of papers published between 2019 and 2023.
The most prominent author in the publications on renewable energies and energy production is Maréchal, F. (with an H-Index of 58 and 14 papers published in the study period). He is followed by Díncer, L. (with an H-Index of 116 and 11 papers). Figure 9 shows that in the year 2022, three of the five authors had the highest number of publications, this year also being the most productive regarding this topic.
Once the main authors have been identified, the next step is to identify the scientific communities that represent the connections between authors and a central core, which would be the most significant elements of the community [23,56]. The importance of identifying scientific communities, according to [23,31], lies in the fact that it allows the identification of current research trends, collaboration between authors, and areas of knowledge. In addition, community detection has been successfully performed in other areas such as medicine [57], education [27], and energy [30]. Figure 9 shows the bibliometric network of scientific communities representing the relationships between authors grouped under the same color. Likewise, the fact that the clusters are close to each other is evidence of a close relationship between them, while the clusters that are farther apart in the network show the least relationship with other communities.
The bibliometric network allowed the identification of 22 clusters, which represent the number of scientific communities. The largest of these communities is represented by the red cluster, with 47 authors, led by Liu, Y. This is followed by the community represented by the green color, with 45 authors, led by Li, Y. It is important to mention that although Li, Y. has more contributions than Liu, Y., the red cluster is the largest in terms of number of nodes. Then, the third community with the largest presence is represented by the blue color, with 39 authors, led by Chen, H. The community with the smallest number of authors has only six authors and is led by Kong, L.
The next analysis conducted in the present study was focused on keywords. According to [31], the importance of identifying keywords lies in the fact that they are used as research instruments, refine search equations and, most importantly, identify trends in lines of research. Figure 10 shows the keyword cloud of research on renewable energy and energy production over the last five years. The size of each term is related to the frequency of occurrence.
The bibliometric analysis determined that the most used keyword during the last five years in research on renewable energies and energy production is “Renewable energy resources” (490 mentions), followed by “Renewable energies” (408 mentions), “Renewable energy” (365 mentions), “Electric Power Transmission Networks” (289), and “Alternative Energy” (285 mentions). This cloud helps to identify versions of the same keyword (such as “Renewable energies” or “Renewable energy”), which are only a reflection of how the authors express themselves towards the same idea.
Once the main keywords were identified, the evolution over time of five of them was analyzed (Figure 11). This analysis was useful to identify the individual trends for each year.
A clear growth trend is evident for these keywords, as their presence increased considerably by 2022. However, the graph reveals that these numbers decreased by 2023. This would be because this bibliometric analysis was carried out during the first four months of 2023. It is also worth noting that the use of these keywords slightly decreased during 2020, which would correspond to the year in which the COVID-19 pandemic, declared by the WHO, began, a year in which research was focused on this disease. Even so, given the need to mitigate climate growth, research into renewable energy and energy production has continued to increase.
The keywords are also useful for identifying groups and areas of research (which are represented by clusters in the bibliometric networks). Figure 12 shows the network of emerging areas in renewable energy and energy production research in the period 2019–2023.
Based on the analysis of the bibliometric network, a total of 19 emerging areas or clusters (highly related to each other, given the marked proximity between them) in research on renewable energies and energy production were identified. Out of these 19, 5 clusters stand out for their number and their relationships. Table 8 shows some characteristics of the five main emerging research areas (Figure 12).
By analyzing the bibliometric network and its components (Figure 12 and Table 8), it is possible to identify solar energy as the main subject (red cluster). This is evidenced not only by the size of its components but also by the number of nodes and the close relationship between them. In this group, the research by Carrillo et al. [38], which reviews the advances in storage proposals for this type of energy and the potential materials for storing thermochemical energy, is noteworthy. Similarly, other research in this group focuses on the use of this type of energy to reduce CO2 emissions [47] or the challenges to be overcome for its full integration into energy systems [58]. Likewise, the presence of keywords such as Spain, Italy, or Europe, confirms that this research topic is of great interest to the European scientific community.
The second group, represented by the green cluster, addresses the issue of hydrogen as a sustainable clean energy source. The use of this source has been gaining relevance and interest in the scientific community as a solution to mitigate CO2 emissions and stabilize global temperature [33]. As shown in Table 4, research on hydrogen has a considerable number of citations [35], making it one of the three main sustainable energy alternatives, with results that can be verified better than other sources such as natural gas [15].
The third group, represented by the blue cluster, addresses the impacts of changing the energy model to a sustainable one. This group includes research involving comparative evaluations of renewable energy sources [36]. Likewise, research on biofuels is also found in this group, such as the research carried out by Vu et al. [59]. The yellow cluster addresses research on thermal energy and energy conservation. It is also worth mentioning the research by Bagherian and Mehranzamir [60], which reviewed how renewable energies have been integrated for combined heat and power production.
Finally, the purple cluster represents research on wave energy. The presence of the keyword “Australia” indicates that this country is interested in wave energy as a research topic [61], in which the authors aimed to integrate wave, solar, and wind energy with positive results in electricity production.

4. Discussion

The analysis of the characteristics of the 2340 documents found in the bibliometrics allowed us to identify that the most published type of document was the article (Figure 2) and that the production on renewable energies and energy production significantly advanced in the last five years (Figure 3). Other bibliometric studies on renewable energies obtained similar results. In fact, there is a growth trend in renewable energy research between 2020 and 2022 [62,63], showing that the level of awareness on this topic has been progressing over time [64], which is evidenced by the increased presence of hybrid/integrated energy systems along with a decrease in individual technologies [65]. Likewise, the main study categories were energy, engineering, and environmental sciences (Figure 4). Analyses by [23,31] also identify energy and environmental sciences, respectively, as their main study categories, responding to the focus of the papers analyzed, which seek to employ renewable energies to produce different types of energy and protect the environment.
Regarding the journals with the highest number of publications (Table 1), the role of scientific journals in contributing to the literature on renewable energies and energy production can be observed. The journals Energies, Applied Energy, and Energy stand out. Furthermore, regarding the nationality of the journals, it is evident that most of them are from the United Kingdom (7 of the top 10), Switzerland (2), and the Netherlands. In other bibliometric studies, the journal Energies also leads in the scientific contribution to renewable energies or at least in the top 10 journals [31,63,64]; Energy is also among the top 10 journals [23,66]. As for the institutions with the highest scientific production, the Technical University of Denmark and Aalborg University were identified as the leaders in this field, both of Danish origin (Table 2). Only one previous study [23] mentions the Technical University of Denmark; in fact, there is a clear predominance of various Chinese institutions, including the Chinese Academy of Sciences, North China Electric Power University or Chinese Ministry of Education, which in this study are among the top five institutions but do not lead in scientific production on renewable energies for energy production. These differences, however, are probably due to the approach of this study, which was general and sought to address all renewable energies. In studies focused on analyzing the scientific production of an energy source such as solar energy, hydrogen, or biomass, the leading institution was the Chinese Academy of Sciences [23,67,68].
As for the country with the highest scientific production, an analysis of the number of research studies per capita (Table 4) identified Cyprus as the leading country (per capita research of 15.27). This was followed by Denmark (14.17), Qatar (8.93), Norway (8.32), and Ireland (6.95). According to the International Energy Agency (IEA) [53], the share of renewable energy in the energy consumption of Cyprus is 12.0%. The interest of this country in changing its energy system, which, until less than five years ago, covered its energy demand with 93% fossil fuels [69], was driven by the European Union’s goal of having 40% of its energy production covered by renewable energies [70]. In Denmark, the share of renewable energies is 37.5% [53]. It is in this country that there is a marked interest in migrating to 100% renewable energy systems [71,72], coinciding with the nationality of the leading research institutions (Table 3). Likewise, of the ten countries leading in the amount of research, the presence of renewable energies in Norway is 62.4% [53], a country that has managed to exceed its national renewable energy target and become the European leader in new renewable energy [73].
In other bibliometric studies, China is identified as the country with the highest number of publications on renewable energy [64,66,67] or within the top three [23,31,62,63,65]. Considering only the number of articles, the study also identified that the articles found were mainly of Chinese and Italian origin (Figure 6). However, when calculating the amount of research per capita (Table 5), this study identified China as one of the countries with the lowest performance in this aspect. In fact, considering the population of the countries, Cyprus (population of 1.244 million) has published sixty times more than China (population of 1 400 million) and three times more than Italy (population of 5.11 million). Another country that has been considered a leader in renewable energy research is the USA, but considering the same criteria, the research performance of this country is not the best either (population of 331.9 million), being surpassed almost twenty times more by Cyprus. This statement coincides with IEA data [53], since Norway, Denmark, Finland, Switzerland, and Cyprus are some of the countries leading in the integration of renewable energies in their energy systems, while China, the USA, and the United Kingdom are the main CO2 emitters.
The analysis of the most frequent keywords (Figure 10 and Figure 11) revealed that, among the general keywords such as “Renewable energies” or “Renewable energy resources”, there is a revealing one: “Alternative Energy”. This term encompasses different alternative energies such as biomass, solar energy, and hydropower, whose presence has gained relevance in various countries worldwide. It has been recorded that biomass is widely used to produce energy [74] and that its use in energy consumption influences the economic growth of some industrialized countries [19]. It is also a carbon-neutral form of energy with the potential to replace oil and other fossil fuels [44]. In the case of solar and wind energy, given their intermittent nature, storage systems need to be implemented to supply energy around the clock without interruption, among which the Thermochemical Heat Storage Systems [38] and the Conventional Compressed Air Energy Storage System [75] stand out, both capable of increasing the efficiency of energy production and avoiding energy losses in the long term.
Regarding the co-occurrence bibliometric network (Figure 12 and Table 8), studies on solar energy in energy systems were grouped in the first group. This result reveals the interest that this energy source has garnered worldwide, coming to be considered as the main driver of the global growth of the share of renewable energy in all sectors that can be considered [76] and playing an important role in achieving zero carbon emissions by 2050. The second group corresponds to hydrogen-related keywords. In fact, 5 of the 20 most cited articles (Table 3) study hydrogen, responding to claims that it is one of the most promising solutions for storing clean and renewable energy [33,35]. However, according to IEA data [53], in the share of renewable energy consumption worldwide, solar energy barely covers 1%, while only 0.1% of hydrogen worldwide is produced by water electrolysis, the rest being produced by non-renewable sources.
The third group includes research on clean energy and sustainable development. One of the main drivers in the integration of renewable energies in various sectors is Industry 4.0, which encourages the switch to clean energies at a faster pace, seeking to reduce carbon emissions, in contrast to global policies that still show poor results [22]. This group also includes biomass, which in some countries covers up to 10% of the energy supply [53]. The fourth group contains keywords related to geothermal energy, which has a presence of only 0.2% of world energy consumption since this type of energy is limited to countries with high subsoil temperatures (areas with active volcanoes, for example), but this problem has been solved with closed-loop geothermal systems, seeking to make this energy source reach global scales [77]. Finally, the last group contains keywords related to wave energy; the increase in research on this energy source is because it was the largest untapped renewable resource in 2019 since its exploitation technologies did not achieve reliable and economical energy production on a global scale [78]. This demonstrates the need for new energy systems based on clean energy to be economically sustainable so that the energy transition can take place at a faster pace than has been the case to achieve zero carbon emission targets.

5. Conclusions

The bibliometric analysis of the 2340 publications allowed us to corroborate the hypotheses put forward at the beginning of this research. Thus, the following conclusions can be drawn:
The predominant publication type was the research article. This was because, even though Scopus lists multiple types of documents, articles are the predominant form of publication. There has been a growing trend over the last five years in research on renewable energies and energy production, 2022 being the most representative year, with the highest number of publications. It is anticipated that 2023 will surpass the previous year in the coming months.
Considering the number of inhabitants of each country, an analysis of per capita research was carried out, which showed that the country leading in research on renewable energy and energy production is Cyprus, followed by Denmark, Qatar, and Norway. The objectives set by the EU are the main motivators for countries to accelerate the implementation of renewable energies in various industries. The analysis of international collaboration showed that there are two forms of collaboration between countries: one based on their geographic location and the other based on economic relations.
The main subject areas addressed by the publications analyzed were energy, engineering, and environmental sciences. Other fields such as eco-economics, mathematics, or medicine showed that interest in renewable energies is multidisciplinary.
Based on the keyword analysis, the following energy sources were identified as research trends of international interest: solar energy, hydrogen, evaluation of renewable energies such as biomass, thermal energy, and wave energy. Specifically, this analysis revealed that solar energy is a topic of interest in European countries, while Australia shows interest in wave energy.
The results obtained in this study may be useful for those interested in the development prospects of the financial investment logic and the investigation of the risk of renewable energy-based projects. In addition, it represents a step forward in reducing carbon footprints as it presents to future researchers the advances that are currently being made in trying to integrate renewable energy systems.
Finally, this study was conducted in the Scopus database, and only five publication years were considered (2019–2023). Therefore, it is recommended to analyze the scientific production in other databases (such as Web of Science) and to cover a longer period to show the evolution of the use of renewable energies in energy systems. Likewise, the analysis carried out in this study was a retrospective one; it is recommended that a prospective study be carried out using projections of industrialized and developing countries in terms of the consumption of renewable energies that they expect to achieve in the coming years.

Author Contributions

Conceptualization, R.S.-C. and R.R.-O.; methodology, R.S.-C. and R.R.-O.; software, R.R.-O.; validation, R.S.-C. and R.R.-O.; formal analysis, R.S.-C.; investigation, R.S.-C.; resources, R.S.-C. and R.R.-O.; data curation, R.S.-C. and R.R.-O.; writing—original draft preparation, R.R.-O.; writing—review and editing, R.S.-C. All authors have read and agreed to the published version of the manuscript.

Funding

This research received funding from Cesar Vallejo University (Perú).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Methodology used in the bibliometric analysis.
Figure 1. Methodology used in the bibliometric analysis.
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Figure 2. Distribution of different types of publications during 2019–2023.
Figure 2. Distribution of different types of publications during 2019–2023.
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Figure 3. Publications on renewable energy and energy production in 2019–2023.
Figure 3. Publications on renewable energy and energy production in 2019–2023.
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Figure 4. Distribution of publication languages during 2019–2023.
Figure 4. Distribution of publication languages during 2019–2023.
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Figure 5. Subject areas of publications produced in 2019–2023.
Figure 5. Subject areas of publications produced in 2019–2023.
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Figure 6. Renewable energy research on energy production by country of origin (period 2019–2023).
Figure 6. Renewable energy research on energy production by country of origin (period 2019–2023).
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Figure 7. Clusters of collaboration between countries in the period 2019–2023.
Figure 7. Clusters of collaboration between countries in the period 2019–2023.
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Figure 8. Number of publications of the five main authors per year.
Figure 8. Number of publications of the five main authors per year.
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Figure 9. Bibliometric network of scientific communities on renewable energies and energy production.
Figure 9. Bibliometric network of scientific communities on renewable energies and energy production.
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Figure 10. Cloud of the main keywords related to renewable energies and energy production.
Figure 10. Cloud of the main keywords related to renewable energies and energy production.
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Figure 11. Evolution on the use of the top five keywords during the period 2019–2023.
Figure 11. Evolution on the use of the top five keywords during the period 2019–2023.
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Figure 12. Bibliometric network of keyword co-occurrence.
Figure 12. Bibliometric network of keyword co-occurrence.
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Table
Table 1. SJR, H-Index, and JCR impact factor of the 10 journals with the highest number of publications on renewable energies and energy production.
Table 1. SJR, H-Index, and JCR impact factor of the 10 journals with the highest number of publications on renewable energies and energy production.
JournalQuartileSJRH-IndexJCRTotal CitesCites/Doc (2 Years)DocumentsCountry
EnergiesQ10.6321323.25220,0253.66159Switzerland
Applied EnergyQ12.90726411.44693,82012.1982United Kingdom
EnergyQ11.989818.85771,89610.1166United Kingdom
Energy Conversion and ManagementQ12.51423211.53341,64911.4664United Kingdom
Journal Of Cleaner ProductionQ11.98126811.072177,78211.9060United Kingdom
Renewable and Sustainable Energy ReviewsQ13.23237816.79947,24817.4255United Kingdom
International Journal of Hydrogen EnergyQ11.3182487.13968,0817.6753United Kingdom
Renewable EnergyQ11.8152328.63456,8649.7447United Kingdom
Sustainability SwitzerlandQ10.664373.889145,3044.3940Switzerland
Journal Of Energy StorageQ11.456818.90725,9599.9430Netherlands
Table
Table 2. Scientific production and most used keywords on renewable energies and energy production by the top ten international institutions.
Table 2. Scientific production and most used keywords on renewable energies and energy production by the top ten international institutions.
InstitutionCountryDocumentsMain Keywords
123
Technical University of DenmarkDenmark38Wind powerRenewable energy resourcesRenewable energy source
Aalborg UniversityDenmark36Renewable energy resourcesElectric power transmission networksRenewable energies
Ministry of EducationChina30Hydrogen productionAlternative energyWind power
Politecnico di TorinoItaly28Renewable energiesRenewable energy resourcesRenewable energy source
Chinese Academy of SciencesChina26Hydrogen productionEnergy efficiencyEnergy utilization
Politecnico di MilanoItaly26IntegrationRenewable energy resourcesCosts
Universidade de LisboaPortugal23Energy storageRenewable energy resourcesWind power
Technische Universität MünchenGermany22Energy efficiencyPowerRenewable energies
Delft University of TechnologyNetherlands21Renewable energiesSolar power generationAlternative energy
Norges Teknisk-Naturvitenskapelige UniversitetNorway20Electric power generationWind powerCarbon dioxide
Table
Table 3. Most cited papers during the period 2019–2023.
Table 3. Most cited papers during the period 2019–2023.
Document TitleYearJournalCited byReference
Hydrogen production for energy: An overview2020International Journal of Hydrogen Energy905[33]
Current and future role of Haber–Bosch ammonia in a carbon-free energy landscape2020Energy and Environmental Science460[34]
Hydrogen energy systems: A critical review of technologies, applications, trends and challenges2021Renewable and Sustainable Energy Reviews350[35]
A review on the role, cost and value of hydrogen energy systems for deep decarbonization2019Renewable and Sustainable Energy Reviews267[36]
A review and comparative evaluation of thermochemical water splitting cycles for hydrogen production2020Energy Conversion and Management262[37]
Solar Energy on Demand: A Review on High Temperature Thermochemical Heat Storage Systems and Materials2019Chemical Reviews251[38]
Influence of Bubbles on the Energy Conversion Efficiency of Electrochemical Reactors2020Joule218[39]
Smart technologies for promotion of energy efficiency, utilization of sustainable resources and waste management2019Journal of Cleaner Production198[40]
Energy for desalination: A state-of-the-art review2020Desalination183[41]
HVDC Transmission: Technology Review, Market Trends and Future Outlook2019Renewable and Sustainable Energy Reviews177[42]
Towards sustainable production and consumption: Assessing the impact of energy productivity and eco-innovation on consumption-based carbon dioxide emissions (CCO2) in G-7 nations2021Sustainable Production and Consumption174[43]
Integrated process of lignocellulosic biomass torrefaction and pyrolysis for upgrading bio-oil production: A state-of-the-art review2019Renewable and Sustainable Energy Reviews166[44]
Linking international trade and foreign direct investment to CO2 emissions: Any differences between developed and developing countries?2020Science of the Total Environment163[45]
Mapping the sustainable development goals relationships2020Sustainability159[46]
The role of energy storage in deep decarbonization of electricity production2019Nature Communications153[47]
An empirical research on the relationship amongst renewable energy consumption, economic growth and foreign direct investment in China2020Renewable Energy150[48]
Valorization of hydrothermal liquefaction aqueous phase: pathways towards commercial viability2020Progress in Energy and Combustion Science144[49]
Hybrid energy systems for off-grid power supply and hydrogen production based on renewable energy: A techno-economic analysis2019Energy Conversion and Management140[50]
Innovation, trade openness and CO2 emissions in selected countries in Africa2021Journal of Cleaner Production139[51]
Mixed proton and electron conducting double perovskite anodes for stable and efficient tubular proton ceramic electrolysers2019Nature Materials139[52]
Table
Table 4. Research per capita for the country’s leading in the number of documents published.
Table 4. Research per capita for the country’s leading in the number of documents published.
CountryDocumentsPopulation
(Millions)		Renewable Energy Consumption (IEA)Per Capita Research *
Cyprus191.24412.0%15.27
Denmark835.85737.5%14.17
Qatar242.6880.1%8.93
Norway425.04862.4%8.32
Ireland355.03312.3%6.95
Finland355.54145.8%6.32
Croatia273.89931.6%6.92
Portugal6110.3328.2%5.91
Latvia111.88441.5%5.84
Switzerland458.70324.8%5.17
Note. * Decimals have been adjusted for better understanding. IEA: International Energy Agency, data extracted from [53].
Table
Table 5. Number of publications per capita for ten countries.
Table 5. Number of publications per capita for ten countries.
CountryDocumentsPopulation
(Millions)		Renewable Energy Consumption (IEA)Per Capita Research *
China3061 40014.4%0.22
Italy25759.1117.3%4.35
United States244331.910.4%0.74
Germany18983.217.2%2.27
India152140 832.9%0.11
United Kingdom14767.3312.2%2.18
Spain11447.4217.3%2.40
France9167.7515.5%1.34
Denmark835.85737.5%14.17
Australia7726.6910.1%2.99
Note: * Decimals have been adjusted for better understanding. IEA: International Energy Agency, data extracted from [53].
Table
Table 6. Main clusters of international collaboration in renewable energies and energy production.
Table 6. Main clusters of international collaboration in renewable energies and energy production.
GroupColorCountry
1RedChina, United States, Germany, Portugal, Iran, Switzerland, Norway
2GreenIndia, Iraq, Saudi Arabia, Malaysia, United Arab. Emirates, Yemen, Oman
3BlueItaly, Greece, Czech Republic, Lithuania, Romania
4YellowSpain, Brazil, Colombia, Costa Rica, Venezuela
5VioletFrance, Morocco, Rwanda, South Africa, Kenya,
6TurquoiseCanada, Egypt, Algeria, Chile, Panama
Table
Table 7. Information on the top five authors in 2019–2023.
Table 7. Information on the top five authors in 2019–2023.
Author
(Country)		AffiliationH-IndexInvestigation LineDocuments
Maréchal, F.
(Switzerland)		Ecole Polytechnique Fédérale de Lausanne58Energy14
Dincer, I.
(Canada)		Ontario Tech University116Energy11
Duić, N.
(Croatia)		University of Zagreb54Energy9
Ghorbani, B.
(Iran)		Amol University of Special Modern Technologies33Energy8
Barelli, L.
(Italy)		Università degli Studi di Perugia31Energy7
Table
Table 8. Main keywords and clusters identified in renewable energy and energy production research.
Table 8. Main keywords and clusters identified in renewable energy and energy production research.
ClusterColorMain KeywordsTopic
1Redrenewable energies, renewable energy resources, alternative energy, solar energy, solar power generationSolar energy
2Greenhydrogen production, carbon dioxide, hydrogen, electrolysis, natural gas, ammoniaHydrogen
3Bluesustainable development, environmental impact, biomass, biofuels, economic and social effects, energy sustainableRenewable energy and sustainability
4Yellowheat storage, energy conservation, thermal energy, heating, geothermal energyThermal energy
5Purplewave energy conversion, wave energy, levelized costs, tidal power, wave power, risk assessmentWave energy
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Seminario-Córdova, R.; Rojas-Ortega, R. Renewable Energy Sources and Energy Production: A Bibliometric Analysis of the Last Five Years. Sustainability 2023, 15, 10499. https://doi.org/10.3390/su151310499

AMA Style

Seminario-Córdova R, Rojas-Ortega R. Renewable Energy Sources and Energy Production: A Bibliometric Analysis of the Last Five Years. Sustainability. 2023; 15(13):10499. https://doi.org/10.3390/su151310499

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Seminario-Córdova, Renzo, and Raúl Rojas-Ortega. 2023. "Renewable Energy Sources and Energy Production: A Bibliometric Analysis of the Last Five Years" Sustainability 15, no. 13: 10499. https://doi.org/10.3390/su151310499

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