Comment on “How green is blue hydrogen?”

This paper is written in response to the paper“How green is blue hydrogen?”byR. W. Howarth and M. Z. Jacobson. It aims at highlighting and discussing the method and assumptions of that paper, and thereby providing a more balancedperspective on blue hydrogen, which is in line with current best availablepractices and future plant specifications aiming at low CO2emissions. Morespecifically, in this paper, we show that: (i) the simplified method that Howarthand Jacobson used to compute the energy balance of blue hydrogen plants leadsto significant overestimation of CO2emissions and natural gas (NG)consumption and (ii) the assumed methane leakage rate is at the high end ofthe estimated emissions from current NG production in the United States andcannot be considered representative of all‐NG and blue hydrogen value chainsglobally. By starting from the detailed and rigorously calculated mass andenergy balances of two blue hydrogen plants in the literature, we show theimpact that methane leakage rate has on the equivalent CO2emissions of bluehydrogen. On the basis of our analysis, we show that it is possible for bluehydrogen to have significantly lower equivalent CO2emissions than the directuse of NG, provided that hydrogen production processes and CO2capturetechnologies are implemented that ensure a high CO2capture rate, preferablyabove 90%, and a low‐emission NG supply chain.