When you are on an island with no coal, oil or gas and consumption is so low that you have to use small and inefficeint generators then it doesn't take much of a price drop for solar to be cheaper.
Hawaii does have a coal plant, but they have to ship the coal in, and they are big enough for the generators to be efficient, even though it doesn't leave much slack.
and probably would have imported some geothermal technology from NZ, Iceland or wherever a couple of decades ago.
If it was cheaper I would have expected them to do it just to improve their bottom line. Seems that they have one in Puna. Of course, it also mentions that the largest/most populated island, Oahu, isn't a good candidate for geothermal power. To the point that they're considering stringing a power cable undersea to connect the islands in order to transfer power between them, exploiting Big Island's geothermal plant for Oahu's benefit.
As for Alaska, hell no, save the oil for heating and selling down south. We have coal up here as well, we're currently in the process of trying to restart a coal power plant - it's even a 'clean coal' one that was built with the assistance of federal subsidies for the purpose of research.
Finally, I swear I've had a conversation similar to this before about Hawaii - Sure it's a special case, but that makes it a good candidate to look at for the potential problems the mainland could face if solar installs explode. IE look at where Hawaii is now to see where the southern US could be in 15-20 years.