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Comment by nytesky | Hacker News Reader

Aren’t these fuel cells? Not gaseous hydrogen you combust?

They should be pretty high density from my googling, and they were a core shuttle technology.

“In common energy sources, the energy density (specific energy) is rough as follows: hydrogen fuel (142Mj/Kg) > natural gas (55Mj/Kg) > petrol (46Mj/Kg) > coal (30Mj/Kg) > lithium batteries (generally no more than 1.8Mj/Kg)”

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1 kg of hydrogen is roughly 40 kwh of energy - lets assume 50% efficiency to electricity, to reach the energy of a Tesla battery (roughly 100 kwh) you’d need roughly 5 kg of hydrogen. That seems extremely viable as a power source for a car, it can’t be that difficult to compress a few kilograms of hydrogen into a tank..

How much volume does 5kg of hydrogen take up?

Hydrogen at 20C and 1 ATM (ambient gas, basically) has a density of 0.083 kg/m³. So, a 1 cubic meter tank (about the size of a large refrigerator) would have .083 kg of hydrogen at ambient temperature and pressure. If you could increase the density (via increasing pressure, for example) 60x, that would be ~5 KG in a 1 cubic meter tank. 60 ATM is about 800 PSI, or about the pressure of a CO2 cartridge. From Wikipedia, though, car companies are trying to amp the pressure way up to 10x that, presumably to get the tank size down or increase the total energy.

https://en.wikipedia.org/wiki/Hydrogen_storage

142mj/kg is great, but not if you need a bus size volume to hold 1kg

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