Aston University · Web viewFor the network map of the competition between countries, four clusters are identified that cover the 50 countries with the most collaborative links in

International Association for Management of Technology IAMOT 2018 Conference Proceedings

CURRENT IN THE ENERGY FIELD 2014-2017: A BIBLIOMETRIC ANALYSIS OF SCIENTIFIC TRENDS

JAIRO BARRIOS VÁSQUEZ Universidad del Magdalena / Santa Marta, Colombia

[email protected]

GERARDO ANGULO-CUENTAS Universidad del Magdalena / Santa Marta, Colombia

[email protected]

SILVIA VALENZUELA MONGUA Universidad del Magdalena / Santa Marta, [email protected]

ABSTRACT

This study aims to build a global scientific production profile about the energy subject, which one is central to almost all major challenges and opportunities that face the world today. Whether for jobs, security, climate change, food production to increase incomes, access to energy for all essentials (un, 2015). For its development, it is carry out though a bibliometric analysis oriented to the identification of trends of the scientific research publications between 2014 and 2017, using 113.859 documents indexed by SCOPUS database. First, it is defined the search variable using keywords, and limited by documents type and years. Later it is made a metadata analysis of the documents, through processes of cleaning and standardization, measure a series of bibliometric indicators to develop scientific activity. As a result, it is shown the main trends in authors, topics, countries, institutions and journal. First one, it stands out Wang Y, Li Y, Zhang Y and Zang X as well their collaboration networks. The leading research topics are: energy efficiency, wind power, costs, power batteries, electrodes, and sustainable development. On the other hand, the countries with the largest publications in the subject are: China, Usa, India, United Kingdom, Germany and the main institutions are: Tsinghua University, North China Electric Power University, Chinese Academy of Sciences, Shanghai Jiaotong University. Finally, the journals of more publications about the subject are: Journal of Power Sources, Journal of Cleaner Production, International Journal of Hydrogen Energy. The main contribution of this study is bibliometrics indicators as an input for the strategic planning of science, technology and innovation in the energy field. Studying tendencies means understanding the opportunities for innovation and to provide to support the study of the scientific context on energy.

KEYWORDS

Bibliometrics analysis; Energy; Production trends scientific.

INTRODUCTION

The supply of energy is one of the concerns in different regions of the world. The components and underdeveloped define strategies and agreements to promote prosperity and protect the planet. In the current energy context, there are three major challenges: competitiveness, energy security and climate change (AENOR, 2011; K. Bunse, Vodicka, Schönsleben, Brülhart & Ernst, 2011; cited by Restrepo, S., Salazar, K., Ocampo, O., & Vergara, M. del C., 2014). Among the strategies for global,

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sustainable development objectives, the power of affordable and clean energy, seeks to combine efforts that guarantee energy for all, since, if things can be improved, higher levels of financing and policies will be needed. More daring commitments, in addition to the willingness of countries to adopt new technologies on a much broader scale. (ODS, 2017).

For its part, the mining-energy sector has been of great importance in macroeconomic stability in Colombia, due to the generation of foreign exchange, the country has been considered as one of the largest economies in Latin America, facing notably the global economic crisis (OECD, 2014). (Colciencias, 2005). Considering the Colombian energy matrix, there are guidelines in the National Energy Plan, such as: adapting the current supply of diesel with demand; reorient the demands through the Rational and Efficient Use -URE- of the resources; establish a clear policy and ensure supply through a diversified energy basket, among others (UPME, 2010). The sustainability of the energy matrix and the environmental impact has led the country to occupy the fifth position in the global energy competitiveness index. The development of the sector has been fundamental for the productive transformation, but the strengthening of Science, Technology and Innovation –ST&I-, is necessary, especially in unconventional sources of energy. Colombia in its strategy of regionalization of the ST&I, defined the strategic foci in ST&I of the departments in Colombia, alignment in planning is a priority to support the development of the country and address the challenges of the energy sector in terms of competitiveness, security and climate change. In Magdalena, energy is established as a strategic focus of the department (Colciencias, 2015), and this is where the present study contributes with an analysis of global scientific trends in the Energy area, based on the scientific production indexed in the Scopus database from the year 2014 until the year 2017.

The scientific production in the energy field is measurable in a global context, through a bibliometric analysis. The basis for studying a strategic area of technological and scientific sectors from sources of information, the evaluation of scientific activity is measured mainly through scientific publications, such as journals indexed in databases and patents, in addition to having in has a series of indicators to develop scientific activity. (Carrizo Sainero, G. 2000). In this article, we selected the potentially relevant bibliographic records of the SCOPUS database; this is the largest database of citations and abstracts of peer-reviewed literature: scientific journals, books and conference proceedings more than 60 million records and more of 130,000 books. Different statistical tools and processes were used to classify the information. The identification of trends was made through indicators such as: Number of documents indexed by author, keywords, journal, institution and country, as well as analysis of co-occurrence and contingency between them.

METHODOLOGY

The study was based on a quantitative study of the scientific production was indexed in the database Scopus in the period 2014-2017. Four phases were defined as shown in the Figure 1.

Planning Search Strategy

The first thing to define to make the analysis of the scientific production with respect to the thematic energy was the choice of the database. According to the scope of the research, Scopus was chosen which is the largest database of citations and summaries of peer-reviewed literature: scientific journals, books and conference proceedings of more than 60 million records and more than130.000 books. (Elsevier.com, 2017). This database has high volumes of information and it is

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Figure 1: Methodological design, source: Own elaboration

necessary to set the parameters to limit the information only to that which is potentially relevant to the subject of study, so it was determined to define a robust search equation, with Boolean’s operator that allows detecting energy-related records. The search parameters are shown in the Table 1.

Table 1: Search parameters.

Parameter Description

Documents typesThe database defines 16 type of documents, for the present study, four of this were chosen: Conference paper (cp), Article (ar), Article in press(ip) y Review (re)

Study period Refers to the years of study to be analysed, in this case there are four: 2014, 2015, 2016, 2017

Study area The database has a list of areas of all disciplines, within these is selected related to the topic that is the area of Energy.

Keyword Are the keywords defined by the academic expert, these are searched in the keywords of bibliographic records.

Source: Own elaboration

Bibliographic records processing

Once the search equation is defined, it is inserted in the Scopus database, obtaining the records that meet the parameters of the equation. These logs are discharged separated by commas from Scopus and processed in Microsoft Microsoft Excel® with advanced data tools. The variables to be identified in the processing are:

i. Citation Information (authors, title, year, Journal, document type and EID)ii. Bibliographical information (affiliations: Institutions and countries)

iii. Summary and keywordsA matrix is built in Microsoft Excel® with the above information, debugging is done to identify duplicated records, or lack of information.

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Definition and calculation of bibliometric indicators

In the third phase, the bibliometric indicators are defined, these can be of first order, the basic count of the variables or of second order, where the variables are combined. Once defined, we proceed to the calculation, using Microsoft Excel® and the VOSViewer® software in the case of second order indicators, which are presented in co-occurrence maps or contingency tables.

Scientific trends on the area of energy

The scientific trends on energy are presented by identifying the main results of each of the indicators calculated, the main authors, journals, keywords, institutions and countries that develop researches can be appreciated related to the energy issue.

RESULTS

Search parameters

The search equation resulted in a total of 113.860 documents. This was validated by the academic expert and then proceed with the download. The Table 2. Shows the results of search parameters:

Table 2: Information download bibliographic recordsParameter Description

Download date 17/01/2017

Search equation

KEY ("Costs" OR "Electric Batteries" OR "Energy Efficiency" OR "Reconfigurable Hardware" OR "Fuel Cells" OR "Sustainable Development" OR "Smart Power Grids" OR "Electric Inverters" OR "Energy Storage" OR "Commerce" OR "Power Converters" OR "Economics" OR "Investments" OR "Renewable Energies" OR "Electric Load Flow" OR "Cost Effectiveness" OR "Decision Making" OR "Stability" OR "Sensitivity Analysis" OR "Environmental Impact" OR "Biodiesel" OR "Uncertainty Analysis" OR "Climate Change" OR "Economic Analysis" OR "Biofuels" OR "Wind" OR "Energy Policy" OR "Distributed Power Generation" OR "Charging (batteries)" OR "Deregulation" OR "Energy Management" OR "Voltage Control" OR "Power Markets" OR "Smart Grid" OR "Risk Assessment" OR "System Stability" OR "Cybernetics" OR "Thin Films" OR "HVDC Power Transmission" OR "Mass Transfer" OR "Electric Vehicles" OR "Cost Benefit Analysis" OR "Solar") AND PUBYEAR > 2013 AND SUBJAREA ("ENER") AND DOCTYPE ("cp" OR "ar" OR "ip" OR "re" )

Period 2014-2017Initial result 113.860Final result 113.859Expert Ph. D. Gerardo Angulo Cuentas

Source: Own elaboration

Download, processing and debugging of bibliographic records.

Once the search equation was defined, the 113.860 bibliographic records were downloaded. Following the downloading of the documents a matrix was obtained with the information to be analysed. These data were submitted to a debug process where duplicate documents were deleted, and the total data was verified. Finally, a total of 113.859 documents were selected for analysis.

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Bibliometric indicators

The bibliometric indicators to be calculated are of two types:

i. Basic or first-order analysis and a coarse or second-order analysis of the information, the first order is composed of 6 indicators:

a. Number of documents by document type. b. Number of documents by journal.c. Number of documents by country.d. Number of documents by author.e. Number of documents by institution.f. Number of documents by keywords.

ii. Thick or second-order analysis of the information were used:a. Co-occurrence indicators with the VOSViewer® Software and Microsoft Excel®; The

co-occurrence of two statistical variables refers to a relationship of necessity or a positive correlation to study in cases where one can appear without the other.

b. Contingency indicators with Microsoft Excel®, using the function Dynamics tables, which are used to register and analyse the association between two or more variables.

Scientific trends in energy.

Number of documents by type.

This research covers the period between 2014 to 2017, it is evidenced that the highest percentage of indexed documents is 36% of the total data corresponding to 41.221 publications in the year 2015, in 2016 34% is 38.214, in 2014 about 27% is 30.864 publications of the first month in the year 2017 is 3% of the total number of documents indexed by SCOPUS per year with 3.560 publications. (see Figure 2.)

Figure 2: Timeline of publications, source: Own elaboration from Scopus database, note: Published documents until date 17/01/2017

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It is possible to observe the increase of 33% with respect to the year 2014 to 2015, in the year 2016 there was a decrease 7,26% in the publications of scientific documents in the topic of energy.

The bibliometric analysis shows that most indexed documents are articles, (see Table 3.) with a total of 69.067 articles. In 2017 there is a low number of registrations because the consultation date was in the first quarter of the year.

Table 3. Total indexed documents by document type

Document Type Count % % Accumulated Article 69.067 60,66 60,66Conference Paper 37.440 32,88 93,54Review 3.939 3,46 97,00Article in Press 3.413 3,00 100,00

Total 113.859 100,00 -

Source: Own elaboration from Scopus database, note: Published documents until date 17/01/2017

The used search equation is segregated by document type, of the 4 types selected for this analysis, the document type with less number of publications are the articles in press with a total of 3.413.

The percentage of published documents, it is notorious that more than 50% of the total number of documents are scientific articles, (see Table 3.) which demonstrates that scientific activity in the field of energy can promote new publications of student articles, Professors, research groups, etc.

Number of documents by country

For this analysis a ranking of the first 15 countries with the highest scientific production in the energy field was taken, with 103.935 documents, it means 91% of the total data, with an average of 6.495,93 per country. The country with the largest number of publications is China with a total of 27.096 documents indexed by SCOPUS, followed by the United States with 19.550, India with 8.139, United Kingdom with 6.199 and Germany with 6.170 documents. (see Table 4.)

However, the native country of this research, Colombia, was taken as a reference so that make a worldwide comparison, where it occupies the position 44 with a total of 462 publications, 0,44% of total documents indexed by SCOPUS. In the year 2014 Colombia published a total of 141 documents, for 2015 and 2016 were published 184 and 124 documents respectively and the first month of 2017 have been published 13 documents.

Table 4: Top 15 most productive countries 2014 -2017Rank Country Count % % Accumulated

1 China 27.096 23,80 23,802 United States 19.550 17,17 40,973 India 8.139 7,15 48,124 United Kingdom 6.199 5,44 53,565 Germany 6.170 5,42 58,986 Italy 4.992 4,38 63,36

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Rank Country Count % % Accumulated7 South Korea 4.322 3,80 67,168 Japan 4.220 3,71 70,879 Spain 4.044 3,55 74,42

10 Canada 3.911 3,43 77,8511 Australia 3.748 3,29 81,1512 France 3.310 2,91 84,0513 Iran 3.306 2,90 86,9614 Brazil 2.383 2,09 89,0515 Malaysia 2.083 1,83 90,88

44* Colombia 462 0,41 91,28 Total 103.935 91,28

Source: Own elaboration from Scopus database, note: Published documents until date 17/01/2017

In an international context, Asia is the continent with the highest scientific production, with a total of 6 leading countries in the Energy area, which are: China, India, South Korea, Japan, Iran and Malaysia. Secondly, it identified the European continent and the country with the highest number of publications in the field of energy is United Kingdom, followed by Germany with a difference of 0,4% of total research, countries such as Italy, Spain and France are also identified. Meanwhile, in the American continent is led by 3 countries, United States, Canada and Brazil. Currently, Australia is the country with the highest scientific activity in the Oceania continent, and the African continent does not have at least one country in the top 15.

Figure 3: The top 15 most productive countries (2014- 2017), source: Own elaboration from Scopus database, note: Published documents until date 17/01/2017

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Number of documents by institution

For this indicator was carried out with the same methodology of a ranking of the first 15 institutions, to know which is of greater production making a comparison (see Table 5.), mostly are institutions of China, except two universities of Denmark Aalborg University and Danmarks Tekniske Universitet 1, and one from Sweden, Harbin Institute of Technology.2

The percentage that represents this indicator with respect to the total indexed documents is 10,9%.

Table 5: The top 15 most productive intitutions (2014- 2017)Rank Institution Country Count % Accumulated %

1 Chinese Academy of Sciences China 2.158 1,90 1,902 Tsinghua University China 1.655 1,46 3,36

3North China Electric Power University

China 1.341 1,18 4,54

4 Shanghai Jiao Tong University China 948 0,83 5,375 Zhejiang University China 877 0,77 6,14

6China Electric Power Research Institute

China 826 0,73 6,87

7 Tianjin University China 755 0,66 7,54

8Huazhong University of Science and Technology

China 706 0,62 8,16

9South China University of Technology

China 694 0,61 8,77

10 Danmarks Tekniske Universitet Denmark 685 0,60 9,3711 Aalborg University Denmark 673 0,59 9,9612 Xi'an Jiaotong University China 625 0,55 10,5113 Harbin Institute of Technology Sweden 563 0,50 11,0114 Chongqing University China 547 0,48 11,4915 National Institute of Technology China 545 0,48 11,97

Total 12.757 - -Source: Own elaboration from Scopus database, note: Published documents until date 17/01/2017

The institution with the largest number of documents indexed by SCOPUS is Chinese Academy of Sciences with 2.158 publications, followed by Tsinghua University, North China Electric Power, Shanghai Jiao Tong University and Zhejiang University with 1.655, 1.341, 948 and 877 documents respectively. In the year 2015 there was an increase of 42%, a significantly increase respect 2014, on the other hand, in 2016 decreased 3% respect 2015, it can then be said that the scientific production has increased on an average of 27%.

Number of documents by author

1KTH Royal Institute of Technology in Stockholm KTH, (2017) [online] Source: https://www.kth.se/en [25 Jun 2017]2 Danmarks Tekniske Universitet - DTU. (2017). [online] Source: http://www.dtu.dk/ [25 Jun. 2017].

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For this classification, the 15 authors with the highest number of publications indexed by SCOPUS were identified (see Table 6.). Getting in the top 5 authors of Chinese origin, first Wang Y. has 1.369 publications, the second place was Li Y. with 1.283, the third one was Zhang Y. with 1.212, and the fourth and fifth places were Zhang X. with 1.100 and Wang X. with 1.090 documents respectively.

Table 6: Top 15 the most productive authors 2014 - 2017Rank Autor País 2014 2015 2016 2017 Total %

1 Wang Y. China 327 463 536 43 1.369 1,202 Li Y. China 314 457 470 42 1.283 1,133 Zhang Y. China 277 428 465 42 1.212 1,064 Zhang X. China 274 391 406 29 1.100 0,975 Wang X. China 263 403 382 42 1.090 0,966 Wang J. China 251 413 382 26 1.072 0,947 Li J. China 243 345 385 33 1.006 0,888 Liu Y. China 247 376 348 30 1.001 0,889 Li X. China 227 341 365 31 964 0,85

10 Zhang J. China 274 345 315 18 952 0,8411 Liu J. China 210 289 306 31 836 0,7312 Wang Z. China 212 255 300 26 793 0,7013 Zhang L. China 186 274 302 27 789 0,6914 Wang H. China 201 291 265 24 781 0,6915 Wang L. China 191 232 285 26 734 0,64

Total 3.023 4.286 4.454 374 12.137 10,66Source: Own elaboration from Scopus database, note: Published documents until date 17/01/2017

In the Table 6, it can be seen that the country with the largest number of publications is China, the authors of this country are at the forefront in this area, according to World Health Organization (WHO, 2017), China continues to be the country with the greatest atmospheric pollution. Their cities literally suffocate because of carbon dioxide. The Beijing authorities made the decision to decrease by 2017 the amount of carbon used in energy production by 30%. Pollution levels in large Chinese cities sometimes exceed 500 micrograms per cubic metre. But if we speak of average figures, Saudi Arabia surpasses all nations, which is not within the ranking of countries with scientific participation in this area.

In addition, authors with the largest number of publications cover 10.65% of all publications indexed by SCOPUS around energy.

At the Figure 4, it is identified that the 10 most productive authors are the same 10 that have been cited the most times.

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Figure 4: The most

productive authors vs

the publications

output perfomance authors of

Energy field 2014 – 2017, source: Own elaboration from Scopus

database, note: Published documents until date 17/01/2017

Compared to the number of citations the most productive authors have not the same places in terms of their major research impact authors such as Wang J., Wang Y. and Liu J. whose production has an average of 884 indexed documents, their academic impact is approximately four times their number of publications.

Number of documents by journals

Figure 5: Top 15 of indexed journals in the

Energy area (2014-2017), source: Own elaboration from Scopus

database, note:

Published documents until date

17/01/2017This indicator selected a ranking of the 15 journals with the highest number of publications (see Figure 5.) The total of these publications in the energy area is 40.392 documents indexed by SCOPUS, it can be inferred from the same way that the total number of documents have increased each year, in 2015 increase 28,6% with respect 2014, the year 2016 increase 10% with respect 2015.

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The bibliometric analysis shows that most indexed documents are articles with 61% of the total documents. The 5 journals with the most publications are: Journal of Power Sources, Journal of Cleaner Production, International Journal of Hydrogen Energy, Energy Procedia and Applied Energy.

Number of documents by Keywords

This indicator identified the 15 most used keywords by the authors in their publications, that represent a percentage of 56.2% of the total documents. First, the Energy efficiency has 9.187 documents, the research on Wind power has a total of 7.545, the Costs of energy has an estimated of 7.396, the Electric batteries has 6.927 publications and finally the Electrodes with 6.624. These five topics are the global trends in the energy field currently.

The Table 7 shows that the most productive year was 2015 with a total of 37.122 publications, a significant increase compared to 2014 of 75,72%, although for 2016 there was a decrease of 6,95%. The query date of the search equation was January 17 th of 2017; so far this year the topic of major scientific production is Sustainable development. In this analysis it can also differentiate how fossil fuels are a trend due to the impact they generate on the environment.

Table 7: The top 15 most frequent keywords (2014 – 2017)Rank Keywords 2014 2015 2016 2017

1 Energy efficiency 2.487 3.448 2.932 3202 Wind power 2.215 2.775 2.359 1963 Costs 1.664 2.693 2.766 2734 Electric batteries 858 3.065 2.828 1765 Electrodes 847 2.711 2.872 1946 Sustainable development 1.589 2.406 2.219 4077 Electric power transmission networks 923 3.151 2.364 1278 Optimization 1.697 2.357 2.286 1929 Renewable energy resources 1.295 2.394 2.100 182

10 Fuel cells 976 2.323 2.417 10411 Solar cells 1.503 2.098 1.988 22012 Solar energy 1.472 2.171 1.939 20013 Carbon dioxide 1.546 1.636 2.166 29314 Carbon 852 2.104 1.872 19415 Wind turbines 1.201 1.790 1.599 123

Total 21.125 37.122 34.707 3.201Source: Own elaboration from Scopus database, note: Published documents until date 17/01/2017

At the Figure 6, it took the top of the most productive countries and the top of the keywords, it was observed that the most of the topics of China are Electric batteries, Electrodes and Wind power, while in United States are publications about Electric batteries, Costs and Sustainable development. On the other hand, India has the most documents about Energy efficiency, Wind power and Optimization. Germany, carries out its recent studies about Solar cells, Electric batteries and Electrodes, finally United Kingdom focuses its research about Energy efficiency, Wind power and the Costs.

After that, it can be affirmed that a great increase was generated in the studies about renewable energies and the batteries, these topics are currently a key piece in the scientific production. The use

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of these alternative sources to obtain energy is a matter of global competitiveness, which is why the costs are a pillar of the experts to research on sustainable development. (see Figure 6 )

Figure 6: Trends by country, source: Own elaboration from Scopus database, note: Published documents until date 17/01/2017

At the Figure 7, it is observed that the trends in countries and institutions are Energy efficiency, Wind power, Costs, Electric batteries, Electrodes and Electric power transmission networks, it can be concluded that the Chinese Academy of Sciences studies mostly electrodes. While, the Tsinghua University and the North China Electric Power University publish in greater quantity about the Wind power, likewise Shanghai Jiao Tong University Energy efficiency, something similar happens in the China Electric Power Research Institute where the trend is Electric power transmission networks.

By carrying out a forecast analysis using the information of indexed documents in the years 2014 - 2017, it can be inferred that, by the end of the year 2018, there will be an average increase of 8% in the publications on energy subject.

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Figure 7: Trends by Institution, source: Own elaboration from Scopus database, note: Published documents until date 17/01/2017

Co-occurrence Keywords Vs Keywords

Starting the analysis of second order indicators, maps of co-occurrence networks of the keywords, countries and authors were used, the size of the nodes is proportional to the number of occurrence of the terms, and their location is determined by the algorithm of Kernel used by VOSViewer® that locates them according to the similarities and analogies of the terms, the greater similarity, the greater the closeness between the nodes. (Van Eeck, Ness Jan & Waltman, Ludo, 2013).

The Keyword study was worked with 1.225 keywords, which were analyzed in VOSViewer® for the construction of the network map shown in Figure 8, in which four clusters are detected: among the main themes of each are observed Optimization (red) , Electric Batteries (green), Sustainable development (blue) and Energy efficiency (yellow). (see Figure 8.)

On the map, it can be seen a high interactivity between the clusters, which indicates a great complementarity between the research topics. The size of the nodes of greater circumference is similar, which are related to each other and to the smaller ones.

In the Optimization cluster it was classified into 360 keywords, correlations are identified with research topics such as Wind Power, Energy storage, Energy management, Power converters, which indicates that investigations are being carried out, such as optimization in energy storage or conversion of wind energy to electric power.

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In the Optimization cluster were classified 360 keywords, correlations are identified with research topics such as Wind Power, Energy storage, Energy management, Power converters, which indicates that investigations are being carried out, such as optimization in energy storage or conversion of wind energy to electric power.

In the second cluster, Electric Batteries, were detected 323 keywords, among these are Electrodes, Lithium, efficiency, Methanol, Fuel Cells, Carbon, this means that the studies carried out are about the efficiency of alternative electric batteries with elements such as lithium, Methanol, Hydrogen, Solar cells.

Figure 8: Co-ocurrence network of the 1225 high frequency keyword, source: Own elaboration from Scopus database using VOSviewer® (17/01/2017)

Regarding the remaining clusters, Sustainable Development has 312 related keywords such as Costs, Carbon dioxide, Environmental impact, Greenhouse gases, Combustion. This shows that worldwide research is carried out on the environmental impact caused by the greenhouse gases as well as the costs and investments generated in the countries, guaranteeing the sustainable development of present and future generations. The last cluster Energy efficiency contains 230 topics of collaboration, are identified Solar energy, Solar power generation, Heat transfer, Thermal energy, Temperature, Geometry, from the above then, it can be said that recent research publications are about energy efficiency solar and the heat transfer that it generates, in addition to the efficiency of alternative energies such as Thermal and Geothermal Energy.

Co-occurrence Country vs Country

For the network map of the competition between countries, four clusters are identified that cover the 50 countries with the most collaborative links in the energy field, in the Figure 9, the nodes of greater size are distinguished, these are the countries with the greatest number of collaborations in the different research topics already analysed. (see Figure 9.)

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Figure 9: Network map co-ocurrence Country vs. Country, source: Own elaboration from Scopus database using VOSviewer® (17/01/2017)

Now, the largest cluster is the Red one with a total of 19 countries mostly European, this represents that they have a greater correlation with the other clusters, it is also identified by the number of connection lines. The next cluster is the Green one, which is comprised of 15 countries, the blue and yellow clusters contain 11 and 5 countries respectively. In the green and blue clusters can be seen smaller nodes are separated from the larger node, which means less interaction of these with other countries of the other clusters.

The third cluster (blue) contains the two largest nodes in the network map, which means that they are the countries with the highest co-occurrences, United States and China. It is observed that the node that represents Hong Kong, is further away and smaller, which refers to having a low correlation amount with the other countries. Meanwhile, in the Green cluster, the largest nodes and with the largest number of lines of relationship with the other clusters are France and Canada, which indicates a high correlation between these countries with nodes of the same size, as well as United States, Germany, and Italy.

Emphasizing in the yellow cluster, three countries in South America with the highest scientific production are clearly identified according to the analysis carried out in Brazil, Colombia and Chile, related to Spain and Mexico, it can be deduced that it is by the native language of the countries, one more classification Extensive of this research could contain the language of the authors.

Co-occurrence author vs author.

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For this indicator, six clusters containing the 120 authors with the highest scientific output that were identified. It shows greater nodes are similar, the proximity between them and the number of connection lines, it means, the indicator Number of documents by author showed that most authors are Chinese, for that reason, are related by country, institution and publication journals. (see Figure10.)

The clusters are classified by colors, the red cluster with greatest magnitude with 25 co-occurrences, which indicates that authors like Wang Y. Zhang Y., among others who are identify with the largest nodes, have a high correlation among them. The correlation lines demonstrate a strong collaborative work between the authors with the highest number of Scopus publications in the energy field.

Figure 10: Network map Concurrence author vs author, source: Own elaboration from Scopus database using VOSviewer® (17/01/2017)

CONCLUSION

The methodology used to carry out this research is quantitative. From the search equation, a total of 113.860 documents indexed by SCOPUS were obtained in the energy area between 2014 and 2017, one duplicate was eliminated to complete 113.859 publications to be analysed.

During a period between 2014 to 2017. There is evidence of an increase in scientific production of 33% with respect to the year 2014 to 2015, in 2016 there was a decrease of 7.26% in the publication of scientific documents about energy.

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The bibliometric analysis shows that most indexed documents are articles with 61% of the total documents. The five journals with the most publications are: Journal of Power Sources, Journal of Cleaner Production, International Journal of Hydrogen Energy, Energy Procedia and Applied Energy.

The five countries with the highest number of publications were China, United States, India, United Kingdom and Germany. Colombia ranks 44th with 462 publications, that is, 0.44% of all documents indexed in SCOPUS. In 2014, Colombia published 141 documents; for 2015 and 2016, 184 and 124 documents were published respectively, and in the first month of 2017, 13 documents were published.

In an international context, Asia is the continent with the highest scientific production, with six leading countries in the Energy area, which are: China, India, South Korea, Japan, Iran and Malaysia. Secondly, it identified the European continent and the country with the highest number of publications in the field of energy is United Kingdom, followed by Germany with a difference of 0,4% of total research, countries such as Italy, Spain and France are also identified. Meanwhile, in the American continent is led by three countries, United States, Canada and Brazil. Currently, Australia is the only one country of the Oceania continent, and the African continent does not have at least one country in the top 15.

Three countries are clearly identified in South America with the highest scientific production according to the analysis carried out in Brazil, Colombia and Chile, related to Spain and Mexico, it can be deduced that it is the native language of the countries.

In addition, the 15 authors with the highest number of publications cover 10,65% of all publications indexed by SCOPUS in the energy area. The five authors of Chinese origin, Wang Y., Li Y., Zhang Y., Zhang X. and Wang X., reflect the leadership of institutions such as: Chinese Academy of Sciences and Tsinghua University in the energy field.

The top 15 most productive institutions represent a percentage of 10,9% with respect to the total of indexed documents. The five institutions with the highest scientific output are: Chinese Academy of Sciences, Tsinghua University, North China Electric Power University, Shanghai Jiao Tong University and Zhejiang University.

The countries and institutions trends identified in the top of the highest scientific production are Energy efficiency, Wind power, Costs, Electric batteries, Electrodes and Electric power transmission networks. Different central issues are detected as Optimization with support topics such as Wind Power, Energy storage, Energy management, Power converters. The second central topic Electric Batteries investigating Electrodes, Lithium, efficiency, Methanol, Fuel Cells, Carbon, followed by Sustainable Development that contains keywords related to Costs, Carbon dioxide, environmental impact, greenhouse gases, Costs, Combustion. And finally, Energy efficiency with collaborative research in Solar energy, Solar power generation, Heat transfer, Thermal energy, Temperature, Geometry.

REFERENCES

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