The Sol Invictus is a massive power source. It basically a mini sun trapped inside a containment field. It radiates its light on solar panels that collect its power. (Similar to a Dyson Sphere but miniaturized.)
It has a very long life time on its own but with increased use, it runs out very quickly as the "sun" can be made to fuse materials quicker by reinputting some of its own power to increase the temperature of the "sun."