Sir Chris Llewellyn Smith and team's modeling in the UK for that archipelago state in northern Europe's weather system finds that every ten years a gray doldrums sets in which almost eliminates wind and solar generation. That requires bridging with some sort of once every ten years solution because they are an island and so interconnections with HVDC are more expensive.

In the continent-scale of North America, regions have to intentionally isolate themselves — hello, Texas — in order to not have significant advantages over archipelagos in terms of geographical spread of generation and ability to move electrons from where they are created to where they are needed. Hence, energy reliability in the end game requiring a lot of two-week energy supply is a once every hundred year requirement.