Far better than trying to build an aircraft with huge insulated H2 tanks..use the H2 to make methanol. The other reagent is carbon monoxide. If you're getting the H2 from a
Solar Zinc process, the waste product is CO. Just pour it in the existing fleet and bob's yer uncle.
Get the carbon input to the SOLZINC from biomass (fast-growing Miscanthus grass, say) and the whole thing's CO2 neutral.