Solar-driven water splitting at 13.8% solar-to-hydrogen efficiency

Re:Solar-driven water splitting at 13.8% solar-to-hydrogen e... by walrus01 on Thursday November 18, 2021 @10:51PM (#29273620)

> while hydrogen _IS_ light enough for an airplane

If you do the watt-hours per kilogram calculation the very best lithium ion batteries are something like 255Wh/kg right now.

Hydrogen fuel cell systems for small to medium sized UAS are somewhere in the 700-800Wh/kg range right now, including the weight of the (rather heavy, seriously engineered) ultra high pressure carbon fiber wrapped tanks needed for it, piping, and fuel cell.

Something like a tank of Jet-A fuel is >4000Wh/kg.

Hydrogen itself is light, the tankage systems needed to reliably contain a large volume of it on an aircraft are not.

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Re:Solar-driven water splitting at 13.8% solar-to-hydrogen e... by pjc50 on Friday November 19, 2021 @07:07AM (#29276379)

If you've got H2 on a plane it's probably lighter to just feed it to the jet engine directly rather than try to replace that with a fuel cell/motor combo which will not buy you enough efficiency gain to compensate for its weight.

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Re:Solar-driven water splitting at 13.8% solar-to-hydrogen e... by viernullvier on Friday November 19, 2021 @09:14AM (#29277310)

Or maybe not. It's not the weight of the fuel cell/motor combo that is the limiting factor, but the weight of the H2 storage tanks. An H2 jet engine will probably [0] be less efficient than a fuel cell + motor, so more H2 storage is required in order to reach a comparable performance.

[0] Considering the Carnot efficiency of a jet engine at ~30%, a combination of fuel cell (~60%), motor (~95%) and propeller (~80%) will still beat it by a factor of 1.5.

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