Storm is controlled chaos. It is a blast on teams, but solo a lot of it's potential is wasted. For Energy blast, the single target damage is great, but AoE is very lacking. That being said, the best advise I can give is to simply play around with it until you get the feel for it and what it needs.
I like storm as a controller secondary, simply so you can control the scatter and stack the controls or fill control gaps. Most of Storm's powers are great at 3 or 4 slots. It does have one of the steeper learning curves though.
As a defender, your secondary effects are going to be stronger than any other AT. I personally would not do energy blast if you're going to neuter the secondary effect. I get it, Energy sucks on teams if the user isn't actively using the knockback to get things back to the group's tank. I'd suggest dark, sonic, radiation, or ice for blasts. Those offer secondary effects that will help your debuffing game while giving you more tools to deal with things on your way to the AVs