you have to make sure you're at 4 or less shields.
So after you've got ENERGIZED!!!!!!! you cast your shield 4 times (takes a while). any more than that and it cycles back through. IE if you use it five times it will be just like if you hadn't at all, 6 times and you're one cast on the way to being energized and so forth.
That's a terrible explanation. I hope you get it though.
Edit: Oh! And if you cast your shield 3 times it's like you've done 3/5. Anyway, the point is to cast shield four times while energized so you're 4/5 charges. You cast tibbers to rofl stun putting you at 5/5. You cast incinerate to make people angry.
What I try for is 3 shields so 3/5 of the way there, tibbers for aoe stun 4/5, disintegrate main target 5/5, and incinerate next for two aoe stuns in one fight. Suck it TF.
that way you aren't wasting stun time too by casting two stuns right on top of each other.