The problem with hydrogen is that it has abysmally low density, being a gas (8mg &#x2F; L at STP, 40 g &#x2F; L at 700 bar). Even liquid hydrogen has a density of only 70 g &#x2F; L. Compare jet fuel, which ranges around 800 g &#x2F; L. Hydrogen is a more efficient fuel per weight, but it really loses out when you compare volume. This inefficient use of volume is probably a more severe limiting factor than the weight.