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Firstly, the energy density of hydrogen is a lie. Yes, the fuel itself has the highest know energy content per mass, but it's nearly useless as a gas. To reach
by yholio 5y ago
Firstly, the energy density of hydrogen is a lie. Yes, the fuel itself has the highest know energy content per mass, but it's nearly useless as a gas.
To reach any useful volume density you need a high pressure COPV tank that weights an other of magnitude more than the fuel it contains. To generate electricity you need a bulky fuel cell with low efficiency, which in turn requires a very beefy cooling system, larger than the one used on an ICE vehicle since the fuel cell is so much sensitive to overheating.
If you add it all up, you get something that's comparable with a battery in terms of energy density, but with half the round trip efficiency, expensive and dangerous refueling, larger upfront costs and lower lifetime.
It's no surprise then that the range record for a hydrogen car is actually lower than the corresponding BEV car.
The only genuine advantage of fuel cells is faster refill, but with advances in battery chemistry and ubiquity of charging spots, this becomes less of an issue.
As for the mineral scarcity issue, fuel cells have it much worse, each requiring a small fortune in platinum or other rare minerals. The lithium content for batteries is dropping and a somewhat lower performance sodium ion chemistry is available, with practically limitless supply.
- _hypx 5y agoA COPV has about 6% hydrogen by mass. At 33.3 kWh/kg, that’s ~2000 Wh/kg. This is far beyond the theoretical limits of li-ion batteries. Platinum is not a critical component, only necessary in current PEM fuel cells. Future fuel cells should eventually do away with platinum altogether. As hydrogen is effectively limitless too this is never going to be a resource concern.
- yholio 5y agoA typical Mirai fuel consumption is 0.76kg/100km in similar driving conditions with a Tesla doing 15kWh/100km, so real world fuel density is 20kWh/kg - with a corresponding decrease in COPV density. You would then almost halve that density to take into consideration the whole electricity generating system, cell + cooling + the supercap or NiMH assembly that handle transients and regen braking etc. So the density advantage of Hydrogen is limited, half to a third the battery mass with comparable volume. Not a game changer in 2010, and certainly not now, when everything else is against it. The much improved and high performance fuel cells have been just around the corner for two decades. In the meantime, BEV sales have outstripped H2EVs one thousand to one, growing exponentially every year. How could anyone even consider buying a H2EV when the reliability of infrastructure is a joke even in the most mature US market [1]? Considering electric chargers are becoming ubiquitous and anyone can install one in their own home? I think one needs to smell the roses, it's not a festive occasion for H2EVs. [1] https://www.motortrend.com/reviews/2021-toyota-mirai-long-term-test-review-update-3-dispatches-hydrogen-fuelpocalypse/ https://www.motortrend.com/reviews/2021-toyota-mirai-long-te...
- _hypx 5y agoWhich is still something like 1200 Wh/kg. Worlds beyond li-ion...
- yholio 5y agoFor the COPV alone. If we can ignore the associated hardware, a flask with some lithium could do 11kWh/Kg, if only it were to combust with the surrounding air in a spontaneous Li-Air cell. Aside from mass, volume is fundamental on a terrestrial EV, it reduces storage capacity, comfort and range at highway speeds. That's why a Tesla can have two trunks, while the Mirai is limited to just 5 Kg of fuel.
- _hypx 5y agoEven with everything included, that's still 600 Wh/kg or so. BTW, an EV with everything included really only has around 140-160 Wh/kg. It's still far short of what hydrogen can do. The Mirai also stores around 186 kWh of LHV energy (220 kWh HHV). It's storing a fundamentally larger quantity of energy than comparable EVs.
- yholio 5y agoIndeed, but it does so by filling every inch of space. There's no front trunk, and the backseats and trunk are relatively cramped. Further improving on that pits you against the laws of physics: even if you could, say, safely double the pressure in the bottles, you waste more and more energy - compression is already a big part of the round-trip inefficiency of H2EV. Meanwhile, EV already exist today with similar range - Model S or Mercedes EQS, with something like 90% solar cell to wheel efficiency, and battery chemistries are only getting better.
- _hypx 5y agoIt’s a modified Lexus in the end. It’s not optimized. If well designed you’ll get more room and range compared to a similar EV. The Hyundai Nexo is an example. Also, not every EV has a frunk, like the EQS.