It's funny how this is brought up again and again. Actually the one energy form that needs the most "backup" (a very imprecise word) is nuclear. Because nuclear

It's funny how this is brought up again and again. Actually the one energy form that needs the most "backup" (a very imprecise word) is nuclear. Because nuclear is very slow to adjust you need either massive overproduction and somehow "dump" this when you don't need it (the reason why Belgium had all their highways brightly lit, I remember being amazed by this when we travelled during the night between countries) or what you call "backup" from e.g. gas. If you have a large enough modern grid (and that is not the case right now due to massive underinvestments) renewable good power 100% with very little overproduction (you obviously need capability i.e. overcapacity). There have been several studies on this (some are mentioned here https://www.vox.com/2015/6/9/8748081/us-100-percent-renewable-energy https://www.vox.com/2015/6/9/8748081/us-100-percent-renewabl...)