The burning boxes needed to heat the towers to produce those 3 buckets consume 2,400 L/minute...
Generating 512 EU/t (assuming no losses and free distilled water) requires 3.2 buckets per minute.
BC Fuel isn't the only burnable thing you get out of the Towers, and as I said the Towers are more than self-sustaining regarding the Fuels they output. You will get much more Energy out of the whole thing than you expect.
And don't forget that unless your Oil Tanker has Infinite Oil, you will run out of it quickly.
These work while my PC is turned off?
That kind of timeskip is something I would never allow, especially since there are computers with fucked up System Clocks. (I know two Computers of that kind)