Closed Cycle Hydrogen Fuel Cell Question

[Anthony]

Originally Posted by DaltonS

Ah, but there are no high energy systems that use a fractional power point. We would need at least four fuel cells to power even a smaller high energy system. That was the reason for my sig: an actual RW definition of a Power Point in kW/ton of ship would be very helpful.

We can derive it from two sources: power output of weapons, and power output of electric drives.

Based on the performance of weapons, a SM +5 (30 ton) ship has a 10 megajoule beam weapon, and an improved beam weapon can fire once per 10 seconds, so that's 1 megawatts per 30 tons or 33 kW/ton. The efficiency of beam weapons is unspecified, but in prior editions of the rules didn't exceed 50% (realistic is hard to gauge, actual current figures are <1%, but viable weapons probably require 10%), so it's at least 66 kW/ton and likely more.

For a reaction engine, power requirement is 0.5 * thrust * exhaust velocity. A mass driver engine produces 0.3 mps per tank, corresponding to an exhaust velocity of 6 mps or 9,600 m/s, and has a thrust of 0.01G or 90N/ton, for a power output of 432 kW/ton. An ion drive produces 1/20 the thrust with 10x the exhaust velocity, or 216 kW/ton. David Pulver has admitted to giving drives unrealistic performance for the sake of being more interesting.

Overall, I'd assume 1 ep is somewhere around 100 kW/ton, which is on a par with a reasonable performance ground car (though said car probably isn't spending only 5% of its mass on its power plant).