Seasonal energy storage is the last thing, but that also means it's the last caveat, as far as I can tell. If we figure out seasonal energy storage, that's it. Solar just wins. There's no further need for fossil fuels. We're done.

I guess there's still aircraft.

Fuel cells are a possible solution (especially if one can build a dual mode electrolyzer/fuel cell), but combined cycle power plants burning hydrogen would also work, if only at very large scale (but then economical hydrogen storage likely requires large scale).