Closed Cycle Hydrogen Fuel Cell Question

[DaltonS]

Murphy’s Rules: I’ve heard of fuel efficiency, but…
Blurb: In GURPS Spaceships, at TL7 a Chemical Refinery (p.19) can produce 4× the rocket fuel that a Fuel Cell (p.20) needs to power it.
Details:
In GURPS Spaceships, a TL7 Fuel Cell (p.20) using hydrogen and liquid oxygen rocket fuel can produce 1 Power Point for three hours on internal fuel plus four times that (12 hours) for each fuel tank … which can filled by a Chemical Refinery (p.19) in 3 to 3 1/3 hours for 1 power point and a tank of water. Thus, each Power Point Hour of fuel cell energy can process up to four Power Point Hours worth of fuel. Since this is a closed system, if the fuel cell’s tanks are filled it can operate indefinitely and still provide power for other systems 72%-75% of the time. (And this is just at TL7; fuel cell efficiency doubles for each of the next three tech levels.)

Dalton “Yeah, I know it's unrealistic, but that's the point!” Spence