Energy available (and cost) of hydrogen, as a gas or a liquid, is more easily indicated by mass than by the three gaseous variables; pressure, volume, and temperature. That is the reason marketing of hydrogen is by the kilogram.
For fleet vehicles or transit systems in continuous operation 24/7, liquid hydrogen could be used, stored in thin-walled but well insulated tanks at atmospheric pressure with some venting to assist refrigeration; rather than as a gas stored in high-pressure heavy steel tanks. The trade-off would be the additional energy needed to refrigerate and to maintain liquid hydrogen at fueling stations. Gene.
