> Volume wise, ugh. H- 8 MJ/L, Gasoline - 32 MJ/L In practice, hydrogen @10 kpsi/70 MPa is currently a bit over 1 MJ/L when including the tanks. Gasoline is m

> Volume wise, ugh. H- 8 MJ/L, Gasoline - 32 MJ/L In practice, hydrogen @10 kpsi/70 MPa is currently a bit over 1 MJ/L when including the tanks. Gasoline is misleading as well, because a fuel cell is easily twice as efficient as a gas engine and up to 3x. Li-ion batteries are anywhere from .5 to 2.5 MJ/L, for reference. Thing is, volumetric efficiency is all but irrelevant for most applications. Even airplanes have huge amounts of empty space that could accommodate tanks; container ships would be less efficient but that's about it. > You need ~5-10 kilograms of H2 to deal with light duty vehicles. 5 kg will take a Toyota Mirai over 300 miles. > Training and retraining all the gas station attendants to deal with cryogenic materials is no small undertaking. This is not a thing. Attendants don't need to do anything with cryogenic anything. > Hydrogen penetrates metals. Makes metals the enemy and things can wear down unexpectedly. Scary stuff. Preventative maintenance is complicated. This is an issue when you're trying to build electron microscopes, not when you're fueling cars. The diffusion rate of hydrogen is negligible for everyday purposes like safety. Certain parts need to be designed to avoid embrittlement, but it's a minor problem- embrittlement is only really an issue at VERY high temperatures. If the steel isn't glowing, it's a minor issue, and for most other metals it's even less of an issue. > Pumping hydrogen into a vehicle is done slowly from my recollection. It's as fast as a highway pump, and often slightly faster. It's pretty hard to pump slowly when 10 kpsi is involved, after all. > Hydrogen's flames are invisible. It's a pale blue flame that's difficult to see during the day. Typically it just explodes, unfortunately. Hydrogen is always at such high pressure that it spreads out rapidly and sustained flames are very unlikely, and then there's the fact that the energy density causes things to break. > The efficiency of manufacturing hydrogen for fuel usage is probably like 10% to 30%. Can't imagine it being more than that. Commercial processes are ~60% and non-commercial are above 80%.