@MattMastodon@Sodis Careful about labels. »Renewables« often includes biomass (which is just fast-track fossil tbh) and hydro (which is not so volatile). I'm talking about wind and solar specifically (volatiles).
40% is roughly the mean capacity factor of a good mix of volatiles. This is what you can directly feed to the user from the windmill/panel, without storage. You can expand a bit by massive overbuilding, but you can't overbuild your way out of no wind at night.