Another place where it could make sense is trains. Building overhead power lines could be expensive, especially if we are talking about high speed trains. Becau

Another place where it could make sense is trains. Building overhead power lines could be expensive, especially if we are talking about high speed trains. Because of the square cube law, large pressurized tanks could be economically quite efficient. A train could carry an extra car with a pressurized tank at 700 bar. At this pressure the hydrogen density is 42 kg/m3. A typical oil car has a volume of 131 m3, so assuming the same volume, we'd get about 5.5 tons of hydrogen. Hydrogen has about 3 times the energy density of diesel fuel, and hydrogen cells about twice the efficiency of diesel engines, so all in all 5.5 tons of hydrogen would be the equivalent of about 33 tons of diesel. That's more than enough to move a train from one train station to another one, even if the stations are hundreds of miles apart.