So recent experiments have shown that Vampires make poor sources of mana unless it can be harvested in a raw fashion. Stored the Vitae drops off and becomes near worthless.
So the solution would seem to be: Vampire Farming
So the idea would be to capture the little blood suckers, lock them in a cell, and throw "food" to them from time to time. Then when needed knock them out and bleed them. A nice renewable source of Mana.
I think I will start with 3 vamps. They shouldn't need arms or legs and that will make them more controllable. A simple steal head mask screwed on and some metal straps, and tada... a vampire blood bag is created. Then just dribble blood into the mask and take the vitae from them as needed.
A good experiment in renewable energy.