I have to disagree with the Dyson sphere . This amount of material would  take mining many thousand of planets to construct. Obviously there will be a way to harness this energy just not near as obvious  as a huge Dyson sphere,(reply>), @What Tech Review Wont Tell You Anything is a possibility in my opinion a civilization that old would have a much easier way of doing this. I am not smart enough to think that far ahead, but maybe a way to build a structure with the already existing atoms around the star. I am sure they would still need to use the light , heat and other energy from the star. So the structure could collect energy but still let the light through and energy for photosynthesis and such. IDK i am not smart enough for this  stuff.,(reply>), Well if there is a civilisation which came a million years before us, for a civilisation like that, it doesnt seem like an impossibility.