A Scoping Review of Renewable Energy, Sustainability and the Environment

The article aims to identify the latest trends in research on renewable energy, sustainability and the environment. A total of 92,873 publications from 123 Scopus sources for 2020–2021 are compared using the scoping review method. The results show that the most cited works in this sample are those by authors from the Asian region. The research of these authors focuses on the security, efficiency and reliability of separate elements in energy systems. Besides, the paper considers the problems regarding COVID disease along with the renewable energy sources, perovskite and organic solar panels, nanostructured materials and high energy density. Finally, the paper analyses applications of computer science methods in research on renewable energy, sustainability and the environment. The findings evidently show that recent advancements in computer science methods were not extensively used in the discussed research domain and give a great room for novel strategies of prognosing, simulation and processes optimisation.


Introduction
Researchers have been significantly interested in renewable energy, sustainable development and environmental protection in recent years. Constant changes in energy markets to increase green energy consumption stimulate studies and publication activity globally [1,2]. Governments of all countries face ambitious challenges for the goals of 2030 and the demands to counteract climate changes [3,4] and reduce greenhouse gas emissions [5,6]. The environmental component is an integral part of sustainable development, the impact of which is greatly enhanced due to the extensive use of fossil resources and insufficient environmental protection. Uncontrolled pollution of territories can lead to economic consequences and negatively impact the environment [7,8], causing ecological disasters and migration of the working population [9,10]. At the same time, the Paris Agreement 2015 contains regulated requirements that disturb the transformation of energy balances in terms of reducing the share of coal [11,12] and expanding green energy production in the energy sector [13]. Given this and considering the fluctuations of generating power based on most green energy sources [14,15], it does not seem strange to find ways to balance the growing share of renewable energy sources in conventional energy systems [16,17]. Unfortunately, the existing solutions have drawbacks.
The scientific community conducts discussions and studies of economic efficiency regarding renewable energy sources [18,19]. Given the criticism of the current approach to assessing economic efficiency, the criteria and methods for measuring it are widely discussed [20,21]. However, not all countries have been able to achieve certain efficiency targets so far. There is a gap between potential and actual energy generation from renewable energy sources [22,23] and indicators of its productivity [24,25]. A possible solution,

Materials and Methods
The concept of the study was based on an adapted approach to the scoping review, considering the methodologies outlined in several works [60,61]. Given the potential and comprehensive coverage of the scientific literature on renewable energy, the authors ask the following research question: 'What are the latest trends in research in the subject area, Renewable energy, sustainability and the environment?' The scoping review in this work was performed to analyse the scientific literature from the Scopus database as of 7 April 2021, and to maximise the coverage of promising research for 2015-2021. For the general estimation of tendencies in the chosen subject area, 363,255 publications were found by All Science Journal Classification Codes (ASJC) subject area: 'Renewable energy, sustainability and the environment', among which 270,382 units were excluded (by date and type of publications). During 2020-2021, the authors selected a total of 78,126 articles and 14,747 conference papers. The final database of the study contained 92,873 publications by 302,587 authors. Figure 1 shows the general methodology of the study.
Content analysis of publications was performed using analytical applications for data visualisation of scientific publications: SciVal (scival.com, Copyright © 2021 Elsevier B.V.; accessed on 7 April 2021) and VOSviewer 1.6.16 (vosviewer.com, Copyright © 2021 Centre for Science and Technology Studies, Leiden University, Leiden, The Netherlands; downloaded on 7 April 2021). Performance indicators, research of topics and topic clusters, works of authors and institutions in publications were analysed using the analytical solution SciVal. Network analysis of the observed topics and authors was performed applying VOSviewer 1.6.16.
Citation maps were built for the top 5 leading publications (by the number of citations). About 1548 works cite the top 5 leading publications. For these publications, VOSviewer 1.6.16 network maps of joint citation and topics of research networks of the authors of the works were formed. When constructing the maps, the association strength normalisation method was used. The authors merged small clusters using the min cluster size filter. Content analysis of publications was performed using analytical applications for data visualisation of scientific publications: SciVal (scival.com, Copyright © 2021 Elsevier B.V.; accessed on 7 April 2021) and VOSviewer 1.6.16 (vosviewer.com, Copyright © 2021 Centre for Science and Technology Studies, Leiden University, Leiden, The Netherlands; downloaded on 7 April 2021). Performance indicators, research of topics and topic clusters, works of authors and institutions in publications were analysed using the analytical solution SciVal. Network analysis of the observed topics and authors was performed applying VOSviewer 1.6.16.
Citation maps were built for the top 5 leading publications (by the number of citations). About 1548 works cite the top 5 leading publications. For these publications, VOSviewer 1.6.16 network maps of joint citation and topics of research networks of the authors of the works were formed. When constructing the maps, the association strength normalisation method was used. The authors merged small clusters using the min cluster size filter.

The Cluster Analysis
The authors analysed the clusters and topics included in the subject area 'Renewable Energy, Sustainability and the Environment' for works published in 2020-2021. All publications during this period can be grouped into 20 clusters, three of which belonged to

The Cluster Analysis
The authors analysed the clusters and topics included in the subject area 'Renewable Energy, Sustainability and the Environment' for works published in 2020-2021. All publications during this period can be grouped into 20 clusters, three of which belonged to the top 1% of worldwide clusters by prominence in the Scopus database. These are such ASJC topic clusters (TC) as TC. 30 According to the analytical platform SciVal, this sample of publications contained a total of 825 ASJC topics, 135 topics of which were in the top 1% of worldwide topics by prominence. Among the topics in the sample, one topic had 100% prominence ( Figure 2, Table 2). This is T.20 (TC.8), which is related to the study of perovskite photovoltaic cells for solar panels. This topic is prospective and developing rapidly.
the top 1% of worldwide clusters by prominence in the Scopus database. These are such ASJC topic clusters (TC) as TC.30, TC.28, TC.81 ( Table 1). The TC.30 contains 52 topics, the most important in terms of prominence percentile are topics (T) T.4025, T.1727, T.6, T.350 and T.5899. In the TC.28, topics T.257, T.200, T.5522 should be distinguished by prominence, and in the TC.81-topics T.5457, T.2456, T.3285. It is clear that the subject of these publications mainly relates to such areas as energy, materials science, chemistry. Although research within these clusters is being conducted worldwide, scientists from China and the United States have made the most significant progress.
According to the analytical platform SciVal, this sample of publications contained a total of 825 ASJC topics, 135 topics of which were in the top 1% of worldwide topics by prominence. Among the topics in the sample, one topic had 100% prominence ( Figure 2, Table 2). This is T.20 (TC.8), which is related to the study of perovskite photovoltaic cells for solar panels. This topic is prospective and developing rapidly.  In general, the most cited publications in the research topics ( Table 2) were prepared by both small teams and quite powerful ones, consisting of 30 people. Moreover, about 27% of all teams were international ( Figure 3). However, at the same time, only 3% of coauthors had both an academic and a corporate affiliation, which may be a symptom of some slowdown in the commercialisation of innovations.  In general, the most cited publications in the research topics (Table 2) were prepared by both small teams and quite powerful ones, consisting of 30 people. Moreover, about 27% of all teams were international ( Figure 3). However, at the same time, only 3% of co-authors had both an academic and a corporate affiliation, which may be a symptom of some slowdown in the commercialisation of innovations.    At the same time, 31% of publications in the sample belonged to the top 10% of journals. Most publications were published in 5 journals (Table 3) Table A1).

Institutions' Research Performance
In terms of quantitative indicators of institutions for scientific publications in this area, the absolute leaders are Chinese institutions, which in the top ten occupy nine places in terms of the number of publications. However, if we study the number of citations per one publication, the picture will be completely different. According to this metric, the top five institutions include Fluxim AG (Switzerland), International Union for Conservation of Nature and Natural Resources (Switzerland), Royal Swedish Academy of Sciences (Sweden), Valparaiso University (USA), Cag University (Turkey). These institutions belong to different countries and regions, and to different sectors. The top five includes government, corporate and academic institutions. It is worth noting that according to this metric, only institutions with a few highly cited works were in the top (Table 4). Assessing the level of international cooperation in writing scientific publications, it is clear that Chinese institutions prevail. Two Chinese institutions (Chinese Academy of Sciences, and Ministry of Education, China) and one French institution (Center national de la recherche scientifique, CNRS) had the largest number of publications co-authored with employees of foreign institutions in 2020-2021. The Sankey chart provides information on the affiliation of the leading foreign co-authors of these institutions (Figure 4). One can see several directions of geographical orientation: Asian (besides China, you can also name Hong Kong, Singapore, Japan), American (USA and Canada), European (except France, also Great Britain, Denmark, Spain), Australian and African (Tunisia).

Authors' Topic Research
In the context of the scientific achievements in the subject area 'Renewable Energy, Sustainability and the Environment' it is also reasonable to analyse the authors' contribution. If we observe the top 10 most cited publications in this field in 2020, it is possible to see the geographical distribution of the relationship between publications ( Figure 5). According to the results of spatial clustering, five clusters of countries were identified, the researchers of which have joint publications. The first cluster consisted of 15 countries, and related to assessing the stability of perovskite solar cells. The second cluster included studies of solar cells and modules, but included scientists from 4 countries: Australia, Germany, Italy and Japan. The third cluster of countries included researchers from the United States who had the largest number of links with foreign partners (22 links in this sample of publications). The fourth and fifth clusters included two countries each, China and Hong Kong in the fourth cluster, and India and Turkey in the fifth.  In general, the most cited works dealt with the security, efficiency and reliability of separate elements of energy systems in 2020-2021. Most works of the different areas studied energy storage issues, solar cells and their components (Table 5). It can be seen in more detail by looking at the topics of research networks.  In general, the most cited works dealt with the security, efficiency and reliability of separate elements of energy systems in 2020-2021. Most works of the different areas studied energy storage issues, solar cells and their components (Table 5). It can be seen in more detail by looking at the topics of research networks. To this end, the authors identified 1548 works citing the top 5 leading publications. For these publications, VOSviewer 1.6.16 network maps of joint citation ( Figure 6) and topics of research networks of the authors of the works (Figure 7) were formed. The online citation map visually shows 59 authors who cited the top 5 leading publications more than 15 times in 2020-2021. The most prominent author in this regard was the Chinese scientist Li Y., who had a binding force of 118 for 54 documents. The author's network focused on collaboration with colleagues from the College of Materials Science and Engineering, Hunan University (China), studying high-density potassium ion batteries.  As a result of the contextual analysis (Figure 7), a separate research direction in the first cluster was identified. Some works included in the first cluster observed the causes (SARS-CoV-2), results and consequences of coronavirus disease (COVID-19) along with the use of renewable energy sources. In combination with the sustainable development  As a result of the contextual analysis (Figure 7), a separate research direction in the first cluster was identified. Some works included in the first cluster observed the causes (SARS-CoV-2), results and consequences of coronavirus disease (COVID-19) along with the use of renewable energy sources. In combination with the sustainable developmen As a result of the contextual analysis (Figure 7), a separate research direction in the first cluster was identified. Some works included in the first cluster observed the causes (SARS-CoV-2), results and consequences of coronavirus disease (COVID-19) along with the use of renewable energy sources. In combination with the sustainable development goals research, scientists tried to find an ecological footprint of the pandemic, better to manage waste and to form new trends in ecological research.
The terms included in the research of perovskite solar panels are concentrated in the second cluster. These terms had the most significant impact on the sample (total link strength was 2458 units). In combination with the main topic, the scientist paid attention to efficiency, measurement of degradation, defects and limitations of solar panels. The topics of long-term and operational stability of elements, photovoltaic devices, optoelectronic technologies [62,63] were also studied.
The third cluster contained works focusing on the study of semiconductors, silicone, nanostructured materials, nanofluidics. Performance assessments for green energy transformation were evaluated.
The fourth cluster considered various technologies to use batteries and accumulators of clean energy, capacity retention, assessment and ensuring the stability of space in the management of high-energy densities.
The fifth cluster included studies of energy gaps that the authors tried to bridge with efficient energy conversion technologies. Most works in the cluster were related to the development of organic solar panels.

Computer Science Research Domain in Renewable Energy, Sustainability and the Environment
Emerging research on renewable energy, sustainability and the environment coincide with a dynamic development of information technologies and computer science methods, which support the conducted research by modelling, prognosis, optimisation and computer simulations solutions. According to SCOPUS sources, for the last two years (2020-2021), only a very selected number (443) of documents covered simultaneously all the aspects, namely renewable energy, sustainability and the environment, with the aid of computer science techniques. On the other hand, bilateral correlations between computer science and individual subdomains: renewable energy, sustainability and the environment, respectively, have a much greater representation, reaching tens of thousands of scholarly outputs, in the last two years.
Considering synergy between renewable energy and computer science research domains, the most cited scholarly outputs, considering this research field, investigate photovoltaic cells parameters optimisation. The power system frequency stabilisation subdomain was the most cited [64]. Another research subdomain, second in citation order, covers renewable energy smart grid systems [65]. The most extensively exploited computer science methods encompass machine learning techniques, blockchain technology and edge computing, which increase the intelligence of smart grid nodes, support the security of energy systems and reduce a transferred data stream.
Analogically, the computer science research domain, in the context of sustainability, encompasses thousands of scholarly outputs. The most cited prevailing problems regard blockchain and machine learning techniques in sustainable supply chains and transportation policies [66][67][68]. The research subdomain also puts a particular interest in the exploitation of big data techniques and Edge-IoT systems for ecosystems monitoring [69], damage detection [70] and livestock or crops monitoring [71]. Surprisingly, sustainable human-centric healthcare and distant education systems [72,73], which intuitively may inspire scientists, due to the recent pandemic situation, in the last two years, give way to the logistics-related problems. Data science techniques and artificial intelligence can support ecological design, which accelerates the transition towards a regenerative approach [74] or can support energy management and sharing among base stations [75].
According to the SCOPUS sources, the most extensive scope of scholarly outputs regards exploiting computer science techniques and methods in environmental engineering-related problems. The dominating research subdomain considers wireless networks [76]. It might be caused by the growing importance of the 5G/6G technologies in communication and IoT distributed [77,78], covering edge computing and industrial sensors clouds. Second, in citation rate, research problems concern computer science techniques in autonomous vehicles software [79]. Besides widely explored aspects of roads static vicinity (i.e., signposts) analysis [80], geo-localisation and route planning [81], the most challenging and at the same time revealing great room for research-based impact refers to predicting the behaviour of a dynamic, unpredictably changing environment [82].
Artificial intelligence techniques for energy consumption or savings prediction [83] are among the most cited problems in the renewable energy engineering research domains. They are almost as much investigated as the aspects of robust grid energy management or optimal deployment of zero-net-energy systems [84,85].
The maps of pairwise research topics, encompassing computer science methods in selected subdomains are presented in Figure 8. Although individual research subdomains are developing very dynamically, their interdependences are relatively limited. Based on this, it can be concluded that the application of IT methods in the field of green energy and sustainability will steadily increase in the coming years.
Energies 2021, 14,4490 clouds. Second, in citation rate, research problems concern computer scienc in autonomous vehicles software [79]. Besides widely explored aspects of ro cinity (i.e., signposts) analysis [80], geo-localisation and route planning [81], th lenging and at the same time revealing great room for research-based imp predicting the behaviour of a dynamic, unpredictably changing environmen Artificial intelligence techniques for energy consumption or savings pr are among the most cited problems in the renewable energy engineering mains. They are almost as much investigated as the aspects of robust grid agement or optimal deployment of zero-net-energy systems [84,85].
The maps of pairwise research topics, encompassing computer science selected subdomains are presented in Figure 8. Although individual research are developing very dynamically, their interdependences are relatively limit this, it can be concluded that the application of IT methods in the field of g and sustainability will steadily increase in the coming years. (a)

Conclusions
The study aimed to identify the general trends in research in the subject ar able energy, sustainability and the environment'. The general research que swered by exploring the scientific publications for 2020-2021. To this end, 92,8 tions by 302,587 authors, published in 123 sources and indexed by the Scopus of 7 April 2021, were analysed. Applications of visualisation of scientific p

Conclusions
The study aimed to identify the general trends in research in the subject area 'Renewable energy, sustainability and the environment'. The general research question is answered by exploring the scientific publications for 2020-2021. To this end, 92,873 publications by 302,587 authors, published in 123 sources and indexed by the Scopus database as of 7 April 2021, were analysed. Applications of visualisation of scientific publications data-SciVal and VOSviewer were used for the analysis of the newest subjects and clusters, research of establishments and the leading authors of analytical works.
The data showed that all publications during this period were grouped into 20 clusters (ASJC), three of which belonged to the top 1% of the world's clusters by popularity: TC.30, TC.28, TC.81. Among the topics in the sample, one topic had the 100% prominence, related to the study of perovskite photovoltaic cells for solar panels (T.20). About 31% of publications in the sample belonged to the top 10% of journals. However, at the same time, only 3% of co-authors had both an academic and a corporate affiliation, which may be a symptom of some slowdown in the commercialisation of innovations.
In terms of the number of scientific publications in this field, the absolute leaders are Chinese institutions. They take nine places in the top ten in terms of the number of published works for 2020-2021. The largest number of publications co-authored with employees from foreign institutions in 2020-2021 had two Chinese institutions (Chinese Academy of Sciences, and Ministry of Education, China) and one French (CNRS).
In general, in 2020-2021, the most cited works were those mainly by authors from the Asian region, which were devoted to security, efficiency and reliability of individual elements in the energy systems, the study of COVID disease along with the renewable energy sources, perovskite and organic solar panels, nanostructured materials and high energy density.
The review is enhanced by a contextual analysis of areas of collaboration between two rapidly growing disciplines: computer science and the fields of renewable energy, sustainability and environmental engineering. Its results clearly show that the undeveloped space of cooperation between the disciplines will be a stimulator of their mutual development and a source of many new solutions in the coming years. Acknowledgments: Authors appreciate the copyright holder: © Elsevier B.V. as well as the source of the extracted data which is SciVal @ www.scival.com (accessed on 7 April 2021).

Conflicts of Interest:
The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.