I think much depends on what weapon your turret is using. If you have cannon/cannon or beam/cannon in the turret, it makes a whole heck of a lot of sense to have the turret barrel and base generating as much power as possible, up to the per second power consumption of the weapon (turret barrel and base combined). If however you have something like a missile/beam in the turret, storing the power for 45 seconds worth of generation is going to be a problem for anything other than the smallest missiles. You are in that case better off generating the power in the main ship body where the power can be stored in a large set of batteries, which will gain from the size boost. (The more battery modules that are contiguous to one another, the more each one will hold.)
Turrets will draw power from their parent, both from battery and generation. As far as I know however, it does not work in reverse. If your turret is generating more power than it can use, it will not feed that excess power into the batteries of it's parent, such as the main ship hull. Any surplus generated power will be lost. It can I suppose still be worth while having a little bit of power generation inside such turrets and their bases, at least a tad over 1000 power a second, as the power modules can store 50K on their own.