alt Hacker News> or heck at least it's a well understood, solved problem.
It is not. As a case in my point, Spain had a blackout last year (and I completely believe they are competent professionals - the task is just hard).
> It's just that those interconnections haven't been built yet.
They haven't been built because the grid isn't just a technical problem. It's also a socioeconomic problem, and adding new interconnections would require finding who needs to pay for it ; and currently, that question has no answer.
Hard is relative. Sure, it's hard, but it's a lot simpler problem than something like being able to consume tropical fruit in a temperate country in the middle of winter.
The difference of course is that the invisible hand of the market gets that fruit into grocery stores. For various relatively good reasons, power is driven by very visible hands.