Willmer Guevara Ramírez¹, Rosa-María Río-Belver¹ and Itziar Martínez de Alegría¹

¹ University of the Basque Country (UPV/EHU) Faculty of Engineering in Vitoria-Gasteiz Industrial Organization and Management Engineering Department C/ Nieves Cano 12, 01007 Vitoria, Spain.

willmer.guevara@inacapmail.cl

Keywords: Sustainable hydrogen, Renewable hydrogen, Photovoltaic electricity potential, Bibliometric.

1. Introduction

Green hydrogen production can come from different renewable energy sources, the literature describes solar energy as one of the most promising due to the wide availability of this natural resource [1], [2]. This has resulted in the name of solar hydrogen and which has focused the attention of many researchers, organizations, and countries, resulting in the generation of important knowledge that can contribute to the rapid massification of these technologies.

In this context, the objective of this research is to map the research trends related to green-solar hydrogen, through a bibliometric analysis of the publications indexed in SCOPUS, identifying the most mature and emerging topics, as well as the authors keys and their level of collaboration. In addition, the relationship between the potential of photovoltaic electricity and the volume of research documents related to green-solar hydrogen is analyzed, which also correlates with the solar electricity generation capacity of the leading countries.

2. Methodology

The research used the SCOPUS database to index a greater number of documents of high scientific rigor. The exploration carried out covered terms that characterize the trend of solar hydrogen production, such as clean, sustainable, renewable, and green. We searched for keywords as exact phrases and resulted in 1305 documents up to the year 2020.

Key indicators such as the number of citations, the number of documents and the citations per document were used in the analysis [3]. The co-authorship maps at the different levels of authorship, and the co-occurrence of keywords, were constructed using VOSviewer, which is a software that has gained relevance within the framework of bibliometric studies [3]–[5].

At the same time, the correlation between the scientific production of the leading countries in the green hydrogen-solar and their production of solar electric energy is analyzed [6].

3. Results

Publications related to the concept of green hydrogen date back to 1982, with a discrete record until 2004, when it began to grow exponentially until the present. Scientific production on the concept of green hydrogen has been led by China and the USA, with more than 215 papers and 100 collaborations with other countries. Germany, Italy, India, Spain, United Kingdom and Japan are also notable for their productivity and networking. The latter, despite significant output, has only collaborated on 29 occasions. There is also a more discreet participation of certain countries from less developed regions such as Africa, Latin America, and Asia.

Only the United States is among the countries with high PVOUT and leads in green hydrogen research. Other countries with very high PVOUT such as Chile, Mexico, South Africa, and the Arab countries have a discrete scientific production on the subject.

On the other hand, the country’s leading research on green hydrogen are those that currently lead the world in the production of electricity from solar energy. Pearson correlation coefficient shows a high correlation between the two variables, with ρ=0.86 and a p-value of 0.0013. Many of these nations have a medium or moderate PVOUT, which implies that they require greater efforts and technological development to achieve better efficiency levels.

The co-occurrence of the author keywords has made it possible to identify the hottest topics and their maturity or relevance over time (Fig. 6). A total of 2,477 was included, of which 127 appear 5 or more times. The word “solar hydrogen” stands out due to its frequency (200) and number of links (311), and it is also a term that has reached a certain maturity since its average converges in 2012. There are also 21 keywords close to it, such as “solar hydrogen production or generation”, which in total add up to 365 appearances with 1,522 networks. On the other hand, the word “solar” accompanied by other terms appears 651 times and generates 2,835 links, adding the terms close to “photo*” such as “photochemical”, “photoelectrochemical”, “photoelectrolysis”, “photocatalysis” among others add up to 453 frequencies and 1,991 links. This shows the relevance of solar research to produce green hydrogen. Especially the words close to “photocatalysis*”, defined as a more emerging word, and being among the most co-occurring and with strong links to the terms “solar hydrogen” and “water splitting”. The latter is in the middle range of maturity and is notable for its frequency (140), but more so because it has many links with the main names of the techniques used to produce green hydrogen.

Co-authorship and productivity are led by Japanese researchers Ph. D Yutaka Tamaura and Ph. D Hiroshi Kaneko, with 25 and 23 papers and 58 and 61 collaborations respectively, both belonging to the same research cluster. A total of 12 clusters were identified, including the one led by Ph. D Kazunari Domen with 18 papers and 42 collaborations and the one led by Ph. D Xinchen Wang with 22 papers and 37 collaborations.

4. Conclusions

It is expected that studies on green-solar hydrogen will become more relevant in the coming years since several countries have defined specific strategies for the development of this fuel. At the same time, it is expected that researchers from countries with higher PVOUT will play a greater scientific role, which will be reflected in the number of publications and/or patents.

Most of the studies on the concept of green-solar hydrogen focus on production through different techniques with the aim of achieving sustainable production, producing a deficit of research that addresses problems such as the supply chain, international marketing, impact on the carbon footprint, among others.

There are countries with high PVOUT and little scientific development on the subject, and that have opted to massify their green hydrogen production using solar energy, for which it would be very useful to establish alliances with the leading researchers and organizations identified in this research.

References

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2. G. Kakoulaki, I. Kougias, N. Taylor, F. Dolci, J. Moya, and A. Jäger-Waldau, “Green hydrogen in Europe – A regional assessment: Substituting existing production with electrolysis powered by renewables,” Energy Convers. Manag., vol. 228, p. 113649, Jan. 2021, doi: 10.1016/j.enconman.2020.113649.
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6. IRENA, Renewable capacity statistics 2020, Internatio. Abu Dhabi: International Renewable Energy Agency (IRENA), 2020.