Isn't Hawaii a special case because of its isolation?

If so many people install solar in Southern California or Arizona that the local utility has more power coming in during the day than it can use or store, it can sell the excess via the national grid to someplace that can use it.

As far as I've been able to determine from the internet, there is no connection between Hawaii power grids and the mainland. In fact, it looks like the grids of each island might be isolated from the others.