Delta and Luke, fission IS the gap closer to fusion and the logical choice. There are many techs available and in development that could get us there - if only the mostly faux public fear of nuclear would allow these new plants to be built. Check this out:
https://www.technologyreview.com/2019/02/27/136920/the-new-safer-nuclear-reactors-that-might-help-stop-climate-change/
I think we need a serious breakthrough in both solar and battery tech for it to really make a dent. Of course continue using hydro and tidal where it makes sense. Geothermal is interesting, but don't know tons about that. Wind? Sure clean, but ugly and impedes our radar.