Earlier quoted context omitted.
Japan is quite long (North-South). It's comparable to the East coast of Australia, which has a single grid/energy market. Also, wind and solar are often (not always) complementary energy sources.
Is whether the sun is shining in the north sufficiently decoupled from sun shining in the south? Is the wind blowing in the north decoupled from the wind blowing in the south? I’m suggesting that the distance is not large enough for that to be the case. Which makes it a very different situation to a nuclear plant taken offline for maintenance. Not to mention that afaik they don’t take the entire plant offline. They’l…
Interestingly for any type of generation - Japan runs two different grid frequencies, which limits cross-flow from one half to the other half. They do have HVDC interconnects, but are rather limited (they're building more, in no small part as a result of Fukushima)