I don't see where that number comes from. Also, "good grid" means "perfect national transmission", which is a wildly optimistic assumption. The US is currently

I don't see where that number comes from. Also, "good grid" means "perfect national transmission", which is a wildly optimistic assumption. The US is currently split into multiple grids, with ties being able to handle less than 1% of their generation capacity. Moreover, that's just the US. Here is what the link has to say about countries less blessed with landmass and latitude: > Indeed, in smaller countries, substantial gaps (>30% of demand for >20 h per year; pale orange curves in Fig. 4) remain in systems even with 12 h of energy storage and annual generation that is 3x annual demand. Or this, directly referring to extensive overbuilding required to meet demand: > For instance, historical solar and wind resources data in Germany reveal that there were nearly 2 weeks in which dispatchable generation had to cover practically all of the demand because of a period with very low solar and wind power availability (called “dark doldrums”)27. Although with vast enough wind and solar capacity it might still be possible to meet demand in all hours, the required capacity increases exponentially after a point that depends on the renewable resources of that country, and it is this geophysically-dependent point that will largely determine the cost-effectiveness of highly-reliable, renewables-based electricity systems.