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A comment on Seawater split to produce green hydrogen with nearly 100% efficiency. Parent comment

Re:Seawater split to produce green hydrogen with nearly 100%... by hannob on Friday February 03, 2023 @02:00AM (#34638023)
It should be said that the overall efficiency of airplanes is also terrible. It's just that there's no drop-in replacement, and therefore people are looking at e-fuels for planes. But this doesn't change a simple fact: This is very inefficient and won't be cheap.
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Re:Seawater split to produce green hydrogen with nearly 100%... by rstuart4133 on Saturday February 04, 2023 @05:45AM (#34653433)
This seemed ... odd. Surely being crammed in like a cow in an abattoir truck gets airplanes something. So I looked it up https://en.wikipedia.org/wiki/Energy_efficiency_in_transport

For the curious: Boeing 747-400: 3.1 litres / passenger 100km, or 91 passenger miles per US gallon.

Better than ICE car with 1 person in it, and modern planes do better. It turns out the lower temperatures at 10km above sea level helps both the Carnot efficiency and drag. But the 747-400 travels just under the speed of sound, which hurts. Slower airplanes (but still faster than any land based transport), get you a 2 or 3 fold improvement.

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