“Managing energy efficiency and renewable energy in the residential sector: A bibliometric study”

The recent surge in publications addressing household energy efficiency and renewable energy highlights their vital roles in managing national decarbonization and green power transition. The study aims to analyze the research trends in this field to comprehend their significance in shaping residential decarbonization changes. Bibliometric and visualization analyses are applied to bridge existing knowledge gaps by focusing on technology and managerial mechanisms for implementing energy efficiency and renewable energy concepts. Leveraging the Scopus database and VOSviewer 1.6.19 software, the study covers energy efficiency publications from 1978 to 2023 and renewable energy papers from 1984 to 2023. The study clusters academic articles in two ways: keyword co-occurrence and co-authorship analyses. The first one reveals the merging of renewable energy and energy efficiency studies, covering sustainable development, heating/cooling mechanisms, and emerging technology trends. While both topics share commonalities like smart grids and the Internet of Things, renewable energy clusters spotlight specific areas such as bioenergy and wind/solar power. Co-authorship analysis highlights a notable increase in countries considering research topics, reflecting growing international collaboration. Leading contributors include the United States, the United Kingdom, China, Germany, and India. This study equips scientists with a systematic understanding of the evolution and latest research trends in managing household energy efficiency and renewable energy transformations. It aids in identifying promising research directions, further advancing these crucial fields.


INTRODUCTION
The escalating global concerns regarding climate change and its detrimental impacts on the planet necessitate revising energy production and consumption patterns (Koval et al., 2023;Melnyk et al., 2020;Sineviciene et al., 2019;Shpak et al., 2022). Transitioning toward sustainable energy practices at the household level by implementing energy efficiency improvements and renewable power technologies can significantly contribute to a sustainable future (Olczak et al., 2022;Pu et al., 2021;Sowa, 2020). There are several environmental, economic, and social reasons for that.
Firstly, the pressing need to reduce greenhouse gas emissions is a driving force behind this urgency. The residential sector is one of the main energy consumers and carbon dioxide emitters (Sotnyk et al., 2022a). Investing in energy-efficient measures and green power sources for households can substantially decrease the global carbon footprint and mitigate the adverse effects of climate change (Fasoranti et al., 2022;Kwilinski et al., 2023a;Nekrasenko et al., 2015). This approach aligns with international agreements like the Paris Agreement and national climate plans of the world's leading countries (Climate Action Tracker, n.d.; United Nations, n.d.), which call for urgent and ambitious action to limit global warming.
Secondly, residential energy consumption directly affects energy bills and overall economic stability. Energy-efficient measures can reduce power consumption, lowering home utility bills. Moreover, promoting renewable energy adoption creates opportunities for green jobs and stimulates economic growth in the green power sector, driving innovation and competitiveness (Janikowska & Jebreel, 2022;Lyndiuk et al., 2020;Trypolska, 2021;Vilchynska et al., 2023).
Thirdly, investing in energy efficiency and household green energy improves energy security. Overreliance on fossil fuels can lead to geopolitical tensions and price volatility. Diversifying energy sources and encouraging decentralized green power generation enhance energy independence and resilience (Chygryn &  Furthermore, managing energy-efficient measures and renewable energy in homes addresses energy poverty and social equity issues. In many regions, vulnerable communities struggle with high energy costs, leading to difficult choices between basic needs and utility payments. Implementing energy-efficient and green power programs can alleviate the burden on low-income households and enhance their quality of life (Fasoranti et al., 2022;Mentel et al., 2018).
Lastly, tackling residential energy issues can spur behavioral change and create a culture of sustainable living. When households adopt energy-efficient and renewable energy technologies, they become role models for their communities, inspiring broader adoption of sustainable habits (Rau et al., 2020;Vakulenko & Lieonov, 2022).
Given the above, energy-efficient and green power solutions for homes have a diverse and broad impact on society. However, their implementation requires encouraging state and local managerial mechanisms that should be scientifically grounded and consider the latest research developments in the field. Therefore, the systematization of modern scholar achievements on managing energy efficiency and renewable energy issues in the residential sector, determination of the research trends, leading contributor countries, and their international cooperation ties are vital to address these challenges.

LITERATURE REVIEW
The number of publications on energy efficiency and green power in households in the Scopus database has increased significantly over several decades, especially in the last 20 years. Such growth suggests that scientists are considering the residential sector as an essential contributor to the decarbonization of the economy through introducing and managing energy-efficient changes and renewable energy technologies.
The most popular recent topics on energy efficiency in the residential sector cover households' energy-saving behavior ( Overall, there is a great diversity of research on residential energy efficiency and green power issues. However, there is a lack of papers summarizing and systematizing current developments and managing trends in the field. In particular, Andor and Fels (2018) considered 44 international studies and analyzed the available empirical evidence on non-price interventions encouraging energy conservation behavior among private households. They confirmed that instruments like social comparison, commitment devices, goal setting, and labeling might substantially decrease home power consumption, although their effects vary significantly.
Corsini et al. (2019) performed a bibliometric analysis that utilized practice theories within sustainable energy consumption studies. The study detected the changes in the field, namely, the shift from researching 'consumer identity' to investigating the 'household energy' topic under the sharing and circular economy. Ingeborgrud et al. (2020) studied the evolution and current developments in energy-related social sciences and humanities research. The scholars revealed that recent research concentrates on new technologies, for example, smart meters, household power demand management, energy-efficient initiatives of communities, energy poverty, energy justice, and relevant social and economic policies.
Buckley (2020) analyzed 52 studies considering the effects of different incentives for energy efficiency in households. The article indicated that despite advancements in the quality of recent studies, the analysis underscores the significance of methodological rigor when conducting and reporting the effects of incentives.
Jensen et al. (2019) reviewed 1067 Sustainable Energy Consumption Initiatives (SECIs) to curb residential power usage across 30 European nations. The authors developed a problem-framing typology, categorizing initiatives into four types: 1) technology changes, 2) individual behavior changes, 3) everyday life situation changes, and 4) complex interaction changes. The analysis revealed a bias toward technocratic and consumer behavioral strategies (75% in categories 1 and 2). Addressing and managing technology-business-culture-life interactions is proposed for more effective, lasting transformation. Sotnyk et al. (2023) explore the progress and contemporary household energy efficiency and green power research patterns. The study identifies the nations, institutions, and authors contributing to the field alongside discerning avenues of global cooperation. Using the SciVal platform and Scopus "Analyze search results" tool, the authors highlight that the current focal areas encompass environmental, economic, and social implications, as well as management strategies to adopt pioneering energy-efficient and renewable energy technologies in households. These technologies include smart meters, grids, and the Internet of Things. However, the study focuses primarily on analyzing current research trends and general features of their evolution without a deep insight into research genesis. In addition, the intricate progression of international cooperation ties in the field has yet to be thoroughly examined in the temporal dimension.
Overall, there is a lack of papers compiling the evolution and current state of scientific developments in the residential energy efficiency and green pow-er field. It reduces the effectiveness of sectoral strategies and policies based on disintegrated approaches to their formation. In turn, it impedes energy efficiency and renewable energy advancement in households, decreasing the social, economic, and environmental effectiveness of state and local management mechanisms. Therefore, there is a need to cover the knowledge gap in identifying the evolution trends and current and prospective research directions in managing residential energy-efficient and green power changes, as well as their main contributors worldwide.
The study aims to analyze the genesis of the research on the energy-efficient and renewable energy technologies and management mechanisms for their deployment in households and reveal the perspective directions for further consideration to combat climate change, promote economic stability, enhance energy security, and foster social equity. The paper uses publications from the Scopus database and the VOSviewer package to perform the bibliometric analysis. The novelty is to offer lucid insights into the evolution and recent trends of household energy efficiency and green power studies. Additionally, it sheds light on the most influential countries contributing to this field and the directions of international collaboration in the temporal dimension.

METHODS
Two publication sets downloaded from the Scopus database as of August 10, 2023, were used for the research. The first one included papers on energy efficiency in households for the period 1978-2023. The second set contained publications on renewable energy issues in the residential sector dated 1984-2023. These two arrays of documents were formed using the keyword search function in the Scopus database, namely, the "title, abstract, keywords" option. The keywords "energy efficiency" and "household" were applied to select publications on the energy efficiency topic. In contrast, the keywords "renewable energy" and "household" were used to form the dataset on the green power theme.
Initially, the publication search did not involve time constraints. However, the time frames for the selected publications were determined automatically by the availability of relevant papers in the Scopus database. To specify the formed document set, additional filters were applied to the publication type (article and conference paper), language (English), and publication stage (final). Two final paper sets included 4,544 Scopus publications on energy efficiency and 3,842 documents on renewable energy in the residential sector.
The following research stage involved the content analysis of the selected publications in VOSviewer 1.6.19 and the visualization of the results. It was applied separately for household energy efficiency and green power topics. The bibliometric study in VOSviewer was conducted in two directions: keyword co-occurrence and co-authorship analyses. The software uses the clustering method for both types of analyses. VOSviewer allows dividing a publication set into several clusters and presenting them as network and overlay dynamic maps to conduct a deeper analysis of the development  trends in the selected field. Figure 1 illustrates the research algorithm. In addition, comparative analysis and generalization methods were used to conduct the discussion and make conclusions.

RESULTS AND DISCUSSION
The keyword co-occurrence analysis in VOSviewer included investigating the recent research directions on managing energy efficiency and renewable energy transformations in the residential sector and their changes over time. The co-authorship analysis studied the leading countries in energy efficiency and renewable energy research and their international cooperation ties at present and in evolutionary terms.

The co-occurrence analysis
The co-occurrence analysis used a threshold of eight keyword occurrences to cluster the publications. On the household energy efficiency research topic, VOSviewer identified six interdisciplinary clusters ( Figure 2) with 493 items, including four large (red, green, blue, and yellow) and two small (lilac and turquoise) clusters closely connected. Based on the keywords, the large red cluster consists of 137 items and could be named "Energy efficiency as part of sustainable development." It covers different aspects of sustainable energy development, like carbon emissions and global warming threats, urbanization and economic growth impacts, public health, carbon footprint, waste management, green power sources (biomass, biogas, agricultural wastes) for homes, and others. The cluster's keyword "sustainable development" has 298 occurrences and a total link strength of 2141.
The second (green) cluster combines 120 items and could be named "New trends in energy-efficient technologies." It includes issues on energy storage and utilization, smart and microgrids, the Internet of Things, intelligent buildings, smart homes, electric vehicles, photovoltaic cells, hybrid systems, and managerial and organizational aspects of their implementation in the residential sector. The most significant keywords of the clus-  The third (blue) cluster consists of 113 items united by the topic "Energy use and policy in the residential sector." The cluster covers mostly social, economic, and management issues of home energy, such as power consumption patterns and energy-efficient behavior, power market, energy conservation, household energy demand, energy efficiency gaps, and investments. The most important keywords include "housing" (846 occurrences with a total link strength of 6870), "household energy" (785 and 6348, respectively), "energy policy" (646 and 5149), "energy conservation" (637 and 4900), and "energy use" (531 and 4413).
The fourth (yellow) cluster combines 85 items and could be named "Energy-efficient heating and cooling." It considers the technical and economic aspects of heating and conditioning in buildings, energy-efficient heating systems for homes, including using green power sources (geothermal, solar energy, heat pumps), passive house standards, lifecycle cost of energy-efficient heating projects, etc. The most significant keywords of the cluster are "energy utilization" (1327 occurrences with a total link strength of 9928), "heating" (791 and 6151, respectively), and "air conditioning" (219 and 1790).
The fifth (lilac) cluster includes 30 items and covers power market (emphasizing electricity) issues connecting to home energy efficiency. The papers from this cluster study energy demand and its elasticity, pricing policy in the residential sector, demand-side management, electricity consumption and costs. The main keywords include "costs" (309 occurrences with a total link strength of 2686), "electricity consumption" (284 and 2252, respectively), and "demand-side management" (106 and 1007).
The last (turquoise) cluster has eight items considering energy-efficient lighting. The most significant keywords are "lighting" (91 occurrences with a total link strength of 651) and "light emitting diodes "(47 and 309, respectively).  Analyzing the keywords co-occurrence in the publications on the household green power topic, VOSviewer formed five interdisciplinary clusters ( Figure 4) with 275 items. The red cluster contains 74 research papers on the economic, managerial, social, and environmental aspects of renewable energy, including those for the residential sector.
It covers various issues such as green power policy and low carbon economy development, management of energy transitions, renewable energy planning, pricing, consumption patterns, and willingness to pay for green power in households. The cluster's keyword "renewable energies" has 1011 occurrences and a total link strength of 5132. Other popular keywords include "alternative energy "(518 occurrences and a total link strength of 2751), "investment" (318 and 1851, respectively), "decision-making" (118 and 647), and "emission control" (128 and 818).
The second (green) cluster consists of 69 items focusing on different bioenergy technologies, their environmental impacts, and the mechanisms of their influence on the household sector. It includes research papers on biogas, biomass, biodiesel, wood, and wastes, and estimations of the consequences of their use for climate change, sustainable development, greenhouse gases, quality of life, regional planning, homes, etc. The main keywords of the cluster are "biogas" (193 occurrences and a total link strength of 1057), "biomass" (197 and 998, respectively), "greenhouse gases" (204 and 1307), and "sustainable development" (295 and 1502).
The third (blue) cluster combines 68 items, studying the latest trends in green power technologies  The fourth (yellow) cluster combines 39 items and focuses mainly on solar and wind energy issues. In addition, it includes papers on hydrogen, geothermal, and tidal power technologies, as well as their economic efficiency, optimization, management, and monitoring in the residential sector. The most significant keywords of the cluster are "solar power generation" (337 occurrences with a total link strength of 2038), "photovoltaic cells" (283 and 1593, respectively), "wind power" (244 and 1284), and "economic analysis" (212 and 1298).
The fifth (lilac) cluster identifies 25 items and covers home heating and cooling mechanisms using green power technologies. The latter involves solar, waste, geothermal power, and other renewa-ble energy sources. Moreover, the cluster contains papers on decarbonization, district heating, heat storage, refrigerators, and zero-energy buildings. The main keywords include "heating" (444 occurrences with a total link strength of 2563) and "energy utilization" (537 and 2800, respectively).

Figure 5. Overlay visualization of keyword co-occurrence analysis on household renewable energy research
The results of the co-occurrence analysis show that some clusters for energy efficiency and green power topics are very similar. Energy efficiency and renewable energy red clusters consider the economic, managerial, social, and environmental impacts of these technologies' development. Energy efficiency green and renewable energy blue clusters include new technological trends. Energy efficiency yellow and renewable energy lilac clusters contain studies on home heating and cooling issues. Specific renewable energy clusters are those considering bioenergy and solar and wind issues.
Overall, the co-occurrence analysis in VOSviewer

The co-authorship analysis
The co-authorship analysis studied the leading countries in energy efficiency and green power research (with a minimum of 10 papers per country). Moreover, the leading organizations and authors, having more than four papers worldwide, were checked. In addition, the research links among the countries were studied in detail.
Concerning energy efficiency research in the residential sector, the countries' network includes all continents and is presented by nine clusters in different colors in Figure 6. The broad scientific collaboration of the United States and the United Kingdom with researchers from all continents is worth noting. However, their most extensive interactions include European partnerships. China primarily cooperates with scientists from Europe but also has close  Concerning household renewable energy research, the countries' network is presented by eight clusters indicated in different colors in Figure 8.  Latvia, and Lithuania but also has joint publications with researchers from Germany, the United Kingdom, Switzerland, and China.
The study revealed a rising trend of countries participating in household energy efficiency and renewable energy research and publishing on vari-ous relevant issues. Additionally, there is a noteworthy increase in international cooperation within this field, contributing significantly to its advancement. The results confirmed the previous findings indicating that the United States, China, and European countries are leading in residential energy efficiency and green power research.

CONCLUSION
The study examines the origins of research on energy efficiency and renewable energy technologies and managing their implementation in households. It involves 4,544 publications on the residential energy efficiency topic and 3,842 papers on the home green power topic extracted from the Scopus database to perform the bibliometric analysis using the VOSviewer 1.6.19 software package. The paper provides clear insights into the evolution of studies on household energy efficiency and renewable energy issues, highlights recent trends and the leading nations contributing to this field, and unveils patterns of international collaboration over time. The conclusions are outlined below.
First, recognizing the residential sector's substantial role in managing national economies' decarbonization and green energy transition has increased the interest of researchers in investigating energy efficiency and renewable energy issues in households, especially over the last 20 years. Publication analysis reveals two key attributes characterizing many works in the field: their interdisciplinary nature and robust international collaboration. Rather than solely addressing technical aspects, the scholars prominently delve into the social, economic, managerial, and environmental dimensions of home energy efficiency and green power matters, creating international research teams. Notably, the adoption, use, and management of new information technologies to improve energy efficiency and implement renewable energy in households is the special focus of recent studies, which get the highest citing.
Second, the conducted keyword co-occurrence cluster analysis in VOSviewer showed a close interrelation of green power and energy efficiency research issues, causing similar directions in their development. For instance, both renewable energy and energy efficiency clusters contain publication sets devoted to (1) social, economic, managerial, and environmental issues (sustainable development), (2) heating and cooling, and (3) new technological trends in the field. Moreover, the latter includes the same technologies as smart grids, the Internet of Things, and electric vehicles. However, the renewable energy clusters have specific ones, considering bioenergy and wind and solar power issues.
Third, during the last eight years, evolutional changes in the prevailing directions of household energy efficiency and green power research have occurred. While the scholars focused on the environmental impacts of energy-efficient technologies and home energy conservation in 2014-2015, power optimization and residential energy efficiency policy gained popularity in 2016-2017. The latest trends include studies on new energy-efficient technologies and management mechanisms of their implementation in the household sector. As for the evolution of green power research, it moved from investigating bio-, wind energy, and renewable energy planning in homes to considering green power transition issues and innovative technologies, ensuring these changes, along with investment, demand management, and other economic and managerial mechanisms to support sustainable transformations.
Fourth, the co-authorship analysis focused on identifying prominent nations in the residential energy efficiency and renewable energy field and their interconnected relationships. Future studies should acknowledge certain limitations of this analysis. First, the latter utilized publications from the Scopus database, applying co-authorship and co-occurrence analyses with the VOSviewer tool. Expanding the scope of future investigations could involve alternative review techniques and software. Second, enhancing the co-occurrence analysis could entail a broader range of keywords for comprehensive exploration or a more focused selection to delineate specific research trends. Third, this study concentrated on English-language articles and conference papers within the Scopus database. Future exploration might encompass various publication types (book chapters or reviews), languages, and databases, particularly Web of Science. The identified limitations offer promising avenues for further scholarly inquiry.
Overall, the research revealed new trends in renewable energy and energy efficiency development to consider for improving the residential sector's relevant policies and managerial mechanisms. The outputs of the keyword co-occurrence and co-authorship clustering analyses may be used for creating innovative and highly effective energy policy strategies and instruments. Broader speaking, the study's results may help build long-term management mechanisms for green power and energy efficiency deployment in many countries to reform their residential sector toward decarbonization and greening the economies.

ACKNOWLEDGMENTS
The publication was prepared in the framework of the research project "Formation of economic mechanisms to increase energy efficiency and provide sustainable development of renewable energy in Ukraine's households" (No. 0122U001233), funded by the National Research Foundation of Ukraine.