You're not thinking very big, or in terribly deep timescales. There's not a lot of easy-to-access hydrogen in the solar system, and most of it is at the bottom of steep gravity wells. (The gas giants)
On the other hand, if you put your solar collector well inside Mercury's orbit, where the solar flux is dramatically higher, then you get plenty of power, without having to maintain and fuel a reactor.
On the other hand, if you put your solar collector well inside Mercury's orbit, where the solar flux is dramatically higher, then you get plenty of power, without having to maintain and fuel a reactor.