Well, they are empty nesters (except for company) and live modestly. I think maybe he got rooked on the battery portion of his system. Hawaii electricity (they’re actually on Kauai) is expensive (diesel fuel) so they thought it would be a fair bargain, but I don’t think they will live long enough to see break-even (both in their 70s). Make sure you get a reputable vendor for your batteries. Those things can be dangerous. Put them in a well-ventilated area. You don’t want hydrogen gas building up.
I’m not even looking for break even. I’m obsessed with having electricity. If that grid goes down even for a year and you had to live without it at the very least your life would be a misery. None of us are pioneers. LOL!