Solar has a hard upper limit on how much power it can produce. If you want any more than that, you'll have to look elsewhere. Fusion is an obvious candidate, assuming it can be made economical.
Pretty big assumption, I realize, but note that fusion doesn't have the huge safety and liability problems that make fission power plants obscenely expensive, so it may yet work out.
I know they're using heavy hydrogen, but I assume it has the same storage problems as light hydrogen.