Is the hydrogen still green after the renewable power-hydrogen-methanol-hydrogen route?

The storage and transportation challenges hinder the application of green hydrogen gas (H2). Methanol can be served as a liquid intermediate for H2, however, whether H2 keeps green after this “transit journey” is questionable. In this work, a green power-hydrogen-methanol-hydrogen (PHMH) integrated system was proposed, and the energy conversion and CO2 emission characteristics were studied. Four modules—water electrolysis, methanol synthesis, methanol reforming, and hydrogen purification—were simulated. H2 purity, transport distance, carbon emission, energy efficiency, and exergy efficiency were analyzed for PHMH system. When hydrogen purity was 99.99 %, transport distance was 1500 km, methanol synthesis was conducted at 220 °C and 50 bar, and methanol reforming was conducted at 230 °C and 12 bar, the energy efficiency and exergy efficiency of PHMH system are, respectively, 52.9 % and 56.7 %. Water electrolysis is the primary energy-consuming module. The carbon intensity of a typical PHMH route is 6.3 kgCO2e/kgH2, classifying the produced hydrogen as low-carbon hydrogen rather than green hydrogen. Transport distance has less effect on the equivalent carbon emission; whereas H2 purity affects it importantly. The carbon intensity will fall to 5.5 kgCO2e/kgH2 if H2 purity is 90 %, H2 product remains low-carbon hydrogen, according to the standards issued by the China Hydrogen Alliance.