Comment by pfdietz

Just eyeballing that, it's 2 grams of hydrogen per 30 grams of carbohydrate. So, about 1 tonne/acre/year, or maybe half a kilogram per gallon. The hydrogen right now almost certainly is tapped off existing industrial supply, which comes from natural gas, but there's no reason one couldn't use "green hydrogen" from renewable-powered electrolysis instead. PV produces much more energy/acre than biomass does (and can produce it even outside the growing season), so this wouldn't increase land use very much.