"How much cash could a PowerSat make? If it lasted ~ 30 years - a common assumption - and the energy was sold at $0.05 /kW.hr, that's roughly ~ 263,000 hours x $0.05 x 10^6 kW = $13.15 billion "

If you could buy electrical power in Space at $0.05 /kW.hr, the energy cost to convert water into rocket fuel would be very cheap.
"The energy required to produce hydrogen by electrolysis is about 32.9 kW-hr/kg." http://www.h2cars.biz/artman/publish/printer_467.shtml

For each kg of hydrogen created from water 8 kg of oxygen is made. So from 9 kg of water using 33 kW hr you split into 8 kg O2 and 1 kg H2. Or about 3.7 kW needed per kg of water converted. For rocket fuel I believe you run rich, so instead of 8 to 1, you use 6 to 1. You could store the extra Oxygen or you vent it for part of the cooling process, this affectly adds about 25% to energy cost of making 1 kg of LH2 & LOX, so instead it it's about 4.5 kW per kg and for a nice round number, let say it cost 5 kW hrs of energy to split, and liquidify the Hydrogen and Oxygen (LH2 & LOX). A power source providing of 1 megawatt, would provide enough energy to make 4.8 tonnes per day and 144 tonnes every 30 days.
If instead of charging .05 /kW hr, you charged say $25.00/kw hr, you would be providing power at a much lower cost than what is currently available in Space. You would get 1/2 of the gross of your $13.15 billion number [though 30 year life is fairly unreasonable, 15 year would more realistic, so 1/4 of your number], but you are building powerplant with 1/1000th the capability, roughly 1/1000th of it's mass. You wouldn't need to beam the power to earth and have lose energy in transmission. And currently 5 cent a kW hr is too expensive in terms of wholesale energy costs in regard to grid power- though for energy needs not on the grid [in remote locations], this could be a fairly good price.

Currently there isn't a market for this much rocket fuel in space [144 tonnes per month], but for start up operation you could looking at something which 1/10th or 1/20th this power, but within a decade or so, a market could developed which needed this much electrical power.