Evolution of the conceptualization of hydrogen through knowledge maps, energy return on investment (EROI) and national policy strategies

Abstract

In order to address Climate Change and energy dependency challenges, hydrogen (H-2) is emerging as a promising energy carrier. Studies related to its production have conceptualized it as green (GH(2)), clean, renewable (RH2), ecological, and sustainable (SH2). The aim of this research is to deepen the understanding of the GH(2) concept and to state boundaries between different terms. To reach this objective, a bibliometric analysis of publications indexed in SCOPUS is launched. Also, in order to assess the potential of renewable energy sources (RES) for GH(2) production, a review of the meta-analysis literature on the Energy Return on Energy Invested (EROI) ratio as regards these RES is performed. Additionally, an analysis of main national strategies on GH(2) is launched. Results indicate that the GH(2) concept is gaining remarkable relevance, while the keyword maps show no significant differences between SH2, RH2 and GH(2). EROI reveals low average values for the different biomass energy production processes. For their part, GH(2) national strategies focus mainly on solar and wind technologies, albeit leaving the door open to biomass, where EROI could become an adequate metric to guide these strategies towards a low carbon energy path. Although the role of biomass may become fundamental in this energy transition process, given its low EROI values and considering that it is not a totally clean RES, it should be indexed as RH2, but not always as GH(2). Finally, a proposal that guides a more appropriate use of the term GH(2) is made.