Quote:
Originally Posted by Mailanka
I suppose in your specific case, you might be able to trap the water being burned by the fuel cell for the purposes of making fuel-cell fuel, and then feed it to the refinery to make more fuel-cell fuel. I suppose that's what you mean by a perpetual motion machine?
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Yes, you can. It's one of a general category where certain components are made somewhat cinematically good so they're actually an interesting option for PCs, plus the way power accounting is done usually tracks fuel use based on average rather than peak power use.
Looking at this realistically, water has a heat of formation of about -16 MJ/kg, so converting a short ton of water into hydrogen and oxygen takes 14.4 GJ or 4 MWh, meaning the SM+5 fuel processor requires a minimum of 2 MW (plus additional for liquefying). 1 EP, based on other items, is somewhere in the 50-100 kW/ton (of ship) range, or 1.5-3 MW. That's pretty high given its
size, but the actual efficiency isn't absurd if we go with the higher estimate for an EP.
However, a fuel cell is
grossly unrealistic. A 1 EP fuel cell producing 3 MW and weighing 1.125 tons has a power density of 2.7 kW/kg, which is order of magnitude higher than any realistic device. At realistic TL 7 efficiencies, it should produce 2-3 MWh per ton of fuel; with 0.375 tons of internal fuel, it should run out of fuel in 20-30 minutes, not 3 hours, and even TL 10 reactors should last less than an hour.