Well, there are ways to produce MJ and store it... But I don't think you can use it to power your armor. I still think the easiest way to power your suit is with an IC2 energy storage (BatBox, MFS, MFSU) and just put it in there to charge your power armor.
It's been a while. But if you don't have IC2 in your modpack, you might have Thermal Expansion. If so, use an Energetic Infuser. If you don't well. Look for a different block that allows to charge items and use that one. Gl