You are right that this makes sense to store an energy surplus. The reason you see such a large gap between "41.5 kWh/kg" and "33.6 kWh/kg" is that the latter v

You are right that this makes sense to store an energy surplus. The reason you see such a large gap between "41.5 kWh/kg" and "33.6 kWh/kg" is that the latter value refers to what is called the lower heating value (LHV) [1]. The higher heating value (HHV) of hydrogen is 39.4 kWh/kg, and that's where the 95% efficiency claim comes from: 39.4 / 41.5 = 94.9%. This has a good explanation of higher and lower heating values for chemical fuels: https://en.wikipedia.org/wiki/Heat_of_combustion#Higher_heating_value https://en.wikipedia.org/wiki/Heat_of_combustion#Higher_heat... [1] https://en.wikipedia.org/wiki/Energy_density#In_chemical_reactions_(oxidation) https://en.wikipedia.org/wiki/Energy_density#In_chemical_rea...