Im not sure exactly how the loophole works that allows them to buy solar panels

I'm certainly no expert, but I had the impression that the big thing was if something they got required ongoing resources, leaving them beholden to outside the community beyond the initial transaction. They will trade with outside communities, just if that thing you buy now means you need to get gasoline every week or if that thing requires you to pay an electric company, then it's a liability. So buy a solar panel, ok, one and done. Now things that can run and charge from them may be fair game.

The bigger 'loophole' is phones. They generally have phones available, though they limit their availability. Notably the concept of a phone ringing disrupting a family meal is unacceptable, so they likely would confine phone usage to some outbuildings. Also meant only to facilitate things like business or emergencies, not for personal communication.