Comment on “How green is blue hydrogen?”

Matteo C. Romano*, Cristina Antonini, André Bardow, Valentin Bertsch, Nigel P. Brandon, Jack Brouwer, Stefano Campanari, Luigi Crema, Paul E. Dodds, Stefania Gardarsdottir, Matteo Gazzani, Gert Jan Kramer, Peter D. Lund, Niall Mac Dowell, Emanuele Martelli, Luca Mastropasqua, Russell C. McKenna, Juliana Garcia Moretz Sohn Monteiro, Nicola Paltrinieri, Bruno G. PolletJeffrey G. Reed, Thomas J. Schmidt, Jaap Vente, Dianne Wiley

*Corresponding author for this work

Research output: Contribution to journalComment/debateScientific

24 Citations (Scopus)
44 Downloads (Pure)


This paper is written in response to the paper “How green is blue hydrogen?” by R. W. Howarth and M. Z. Jacobson. It aims at highlighting and discussing the method and assumptions of that paper, and thereby providing a more balanced perspective on blue hydrogen, which is in line with current best available practices and future plant specifications aiming at low CO2 emissions. More specifically, in this paper, we show that: (i) the simplified method that Howarth and Jacobson used to compute the energy balance of blue hydrogen plants leads to significant overestimation of CO2 emissions and natural gas (NG) consumption and (ii) the assumed methane leakage rate is at the high end of the estimated emissions from current NG production in the United States and cannot be considered representative of all-NG and blue hydrogen value chains globally. By starting from the detailed and rigorously calculated mass and energy balances of two blue hydrogen plants in the literature, we show the impact that methane leakage rate has on the equivalent CO2 emissions of blue hydrogen. On the basis of our analysis, we show that it is possible for blue hydrogen to have significantly lower equivalent CO2 emissions than the direct use of NG, provided that hydrogen production processes and CO2 capture technologies are implemented that ensure a high CO2 capture rate, preferably above 90%, and a low-emission NG supply chain.

Original languageEnglish
Pages (from-to)1944-1954
Number of pages11
JournalEnergy Science and Engineering
Issue number7
Early online date29 Mar 2022
Publication statusPublished - Jul 2022
MoE publication typeB1 Non-refereed journal articles


  • carbon capture
  • CCS
  • hydrogen
  • natural gas


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