Keywords

1 Introduction

In recent decades, there has been growing public awareness of the impact of greenhouse gas emissions on the Earth's climate and the need to reduce dependence on fossil fuels [1,2,3,4,5]. As a result, renewable energy sources have become one of the most important elements of the energy policy of many countries, including Poland and Slovakia [6,7,8,9,10,11,12].

Renewable energy sources, such as solar, wind and hydropower, are gaining increasing importance worldwide as an alternative to fossil fuels [13,14,15,16]. The European Union's energy policy imposes an obligation on member countries to increase the share of energy from renewable sources in the overall energy mix [17,18,19]. Poland and Slovakia, as countries with a similar energy structure, are following this trend and intensifying investments in renewable energy sources.

Figure 1 shows the share of renewable energy in Poland and Slovakia from 2004 to 2021, according to Eurostat data [20].

Fig. 1.
figure 1

Share of renewable energy in Poland and Slovakia according to Eurostat data [20].

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Analyzing the chart above, it can be seen that Poland and Slovakia are characterized by very similar growth in the share of renewable energy. In 2021, Poland's renewable energy sources share was 15.6%, while Slovakia’s was 17.4%. In 2020, both countries reached the target set by the European Union. Poland achieved the required 15%, while Slovakia achieved 14% of the renewable energy sources share in the energy mix.

Figure 2 shows the percentage share of each renewable energy source in Poland and Slovakia.

Fig. 2.
figure 2

Structure of renewable energy in a) Poland, b) Slovakia.

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Despite the similar rate of development of renewable energy sources in Poland and Slovakia, the structure of energy generation from individual renewable sources is different (Fig. 2). The main renewable energy source for Poland is photovoltaics, which account for 54% of installed capacity. In Slovakia, the main source of renewable energy is hydroelectric power, which accounts for 77%. Table 1 shows the installed capacity of each renewable source in 2022.

Table 1. Installed capacity in renewable energy sources
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When comparing the installed capacity of renewable energy sources, it is important to consider the total installed capacity of all power plants. In Poland, the total installed capacity is about 60 GW, while in Slovakia it is about 8 GW. This means that the total installed capacity of renewable energy sources in Poland is about 37% of the total installed capacity, while in Slovakia it is 41%. It should be noted, however, that energy from renewable sources such as photovoltaics and wind power is characterized by high variability and largely depends on weather conditions. Hydroelectric power plants, on the other hand, very often operate as peaking power plants, i.e. they work only during periods of peak energy demand. As a result, the actual energy obtained from renewable sources is lower than the installed capacity value would suggest.

The article presents a bibliometric analysis of research on renewable energy sources in Poland and Slovakia. The study was based on publications indexed in the Scopus database. The analysis covered the period from 1990 to 2023. The paper analyzes research topics related to renewable energy sources and examines the most cited publications by authors from the analyzed countries and the main research centers.

2 Bibliometric Analysis of the Literature

Bibliometric analysis is a method of studying scientific publications that is based on the use of statistical techniques to collect, process and analyze bibliographic data. The purpose of bibliometric analysis is to assess the impact of scientific publications on the development of a particular scientific field and to identify the most important authors, journals, topics and research centers [21,22,23].

For the analysis, CiteSpace software was used, which allows analysis of publications and citations and creates visualizations showing the network of connections between publications, authors, institutions and keywords. CiteSpace allows the generation of maps and graphs that show connections between scientific publications in a given research area. The program can detect trends and patterns in scientific publications, as well as identify key authors, institutions, research topics and scientific journals. CiteSpace allows analysis of bibliometric data from a variety of sources, including databases such as Web of Science, Scopus, PubMed and others.

This publication uses data from the Scopus database. “Renewable Energy” was used as the search criterion. Then, through filters, the country was set to Poland and then to Slovakia.

2.1 Bibliometric Analysis for Poland

Figure 3 shows an analysis of publications by authors’ affiliations. Through this analysis, it is possible to determine which institutes are most involved in renewable energy research.

Based on Fig. 3, Table 2 was made, which shows the 15 centers with the highest number of publications and the corresponding centrality coefficient. The centrality coefficient in bibliometric analysis signifies how important a node is in the network and its role in connecting other nodes. In the case of bibliometric analysis, this coefficient can help identify authors, universities or publications that play a central role in a particular field of scientific research. This means that publications from universities with the highest centrality index, characterize the greatest innovation and are the most frequently cited.

Fig. 3.
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Cooperation between universities.

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Table 2. Number of publications and centrality by university
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Based on the analysis performed, it can be concluded that for the adopted criteria, the highest number of publications is shown by AGH University of Krakow, while the highest centrality coefficient, which indicates the key role in research on renewable energy sources, has the Polish Academy of Sciences, which means that the research done by its scientists is most often cited.

Figure 4 shows an analysis of citations by major areas of interest to researchers.

Fig. 4.
figure 4

Citation analysis.

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Based on the analysis seen in Fig. 4, the CiteSpace program can analyze publications for the citation burst indicator. This indicator is used to identify articles that have gained a significant number of citations in a short period of time. Citation burst can be used to identify articles with high scientific value and those that have influenced the further development of the field. Figure 5 shows the 10 publications with the highest citation burst.

Fig. 5.
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Top 10 references with the strongest citation burst.

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Analyzing the publications with the highest citation burst, it can be seen that the highest number of citations are articles relating to the issues of Poland's energy transformation, which currently obtains most of its energy from coal [24,25,26,27,28]. An important aspect of these studies is the impact of renewable energy sources on Poland's energy security and the problems of implementing renewable energy sources in Poland, such as the law defining minimum distances of wind turbines from buildings. Attention was also given to the problem of implementing low-carbon technologies in rural areas [29]. This problem is particularly evident during the heating season, when many households use solid fuel stoves to heat their homes. However, due to the lack of access to the gas grid and the costliness of installing heating systems based on renewable energy sources, rural residents continue to use old and environmentally unfriendly solutions.

2.2 Bibliometric Analysis for Slovakia

Figure 5 shows the analysis in terms of authors’ affiliations performed for publications from Slovakia (Fig. 6).

Fig. 6.
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Cooperation between universities.

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Table 3 shows the 10 institutes with the highest number of publications and their corresponding centrality coefficient. The analysis shows that the largest number of publications on renewable energy sources is published by scientists from the Technical University of Košice. Based on the centrality coefficient, it can be concluded that the highest number of citations and the greatest influence on other scientists are characterized by the works of scientists from the Slovak Academy of Sciences.

Table 3. Number of publications and centrality by university
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Figure 7 shows an analysis of citations by the main areas of interest for scientists from Slovakia.

Fig. 7.
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Citation analysis

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Figure 8 shows the 5 publications with the highest citation burst rate.

Fig. 8.
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Top 5 references with the strongest citation burst.

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Analyzing the results obtained, it can be concluded that the highest number of citations in a short period of time was obtained by research on photovoltaic installations. The authors of the research present maximum power point tracking (MPPT) algorithms that will increase the efficiency of photovoltaic panels [30, 31]. The authors also discuss problems related to DC-DC converters and their impact over the performance of renewable energy systems.

3 Conclusion

The article presents a bibliometric analysis of research on renewable energy sources in Poland and Slovakia. Thanks to the use of programs such as CiteSpace, it is possible to identify the scientific centers that constitute the most important links in research on renewable energy sources. The analysis shows that in Poland and Slovakia, the key centers in terms of innovation and number of citations are the Polish and Slovak Academy of Sciences. On the other hand, the number of publications in a given field largely depends on the size of the academic center and the number of scientists working in them, and does not indicate the innovativeness of a given scientific center.

Analyzing specific publications and links between them, it can be concluded that in the case of Poland, publications on Poland's energy transformation have the highest number of citations. Currently, most of Poland's energy is obtained from coal, and the use of renewable energy sources is critical to Poland's energy security. One of the main problems is the implementation of renewable energy sources, including the problem of minimum distances of wind turbines from buildings, as specified in the law. In addition, the problem of implementing low-carbon technologies in rural areas was also studied. This analysis provides a better understanding of the problems of energy transition in Poland and can help develop effective solutions for future generations. In the case of Slovakia, the most cited publications relate to increasing the efficiency of photovoltaic installations through improved hardware, such as DC-DC converters. However, there is still a need for further research in certain areas, such as energy storage, smart grid technologies, and the use of renewable energy in transport.

The results of the bibliometric analysis can guide researchers and investors who make decisions about the direction of renewable energy research and investment. The analysis can also be used to assess the performance and effectiveness of scientific activities, which is important for making decisions related to their funding and assessing their impact on society.