Our next-door neighbors recently installed a 7 KW photovoltaic system, and then they replaced their home's old (broken) air-conditioning system with a new one. (The owner said it was broken for the last few years because they couldn't afford to run it anyway.) Now they run their high-efficiency A/C system almost constantly because it's "free". This is almost literally constantly because our neighborhood homes lack insulation, energy-efficient windows, and other ways to maintain a temperature difference. But it's free energy so they don't have to care, right?
Someday our grandkids will probably wonder why anyone would try to conserve energy.
Perhaps I'm ignorant on the topic, but why is this a problem? If they have a self-sustaining power supply that is using the sun's energy that is beating down on us anyways, why should they or anyone care about running the AC constantly? I don't believe there's an environmental impact if it's a properly installed central AC unit.
From your perspective of the self-sustaining power supply, it's not a problem. Like the old snack-food slogan, "Eat all you want-- we'll make more!"
However from a thermodynamics perspective they're cooling a space which lacks insulation. Instead of investing a few thousand bucks on permanent passive cooling, they're burning hundreds of kilowatt-hours on active cooling (as long as their A/C plant lasts). Regardless of the price (free!), they're wasting energy and resources.
Hawaii homes from the 1980s are built of single-wall or double-wall construction with no insulation. Zero. None. Single-wall designs are board & batten. Double-wall designs (most of our neighborhood) are 2x4 studs with drywall on one side, Masonite siding on the other, and just air in between. Single-pane windows. The roofs are plywood sheathing with asphalt shingles.
More modern homes (since about 2005) are usually built with more insulation, but there's no mandate. The state passed a law in 2010 requiring all new homes to be built with solar water heaters, and even that initiative was bitterly opposed. (Especially by the island's small businesses which retrofitted solar water heating to older homes.) However there are still thousands of homes on the islands heating their water with electricity.
We've extensively remodeled our 1980s home over the last 15 years. I'm sitting 50 feet away from the neighbor's uninsulated air-conditioned bubble. Our house has a roof with heat-reflective shingles and two inches of icynene foam insulation and reflective foil, our attics have solar-powered exhaust fans, our walls have shredded denim batts and reflective foil, and we use low-e double-pane tinted windows. Our house cools off at night (open windows) and during the day doesn't start to warm up until well into the afternoon. Their house probably cools off at night, yet their attic must heat up to at least 125 degrees by noon. At 1 PM in May, the outside ambient air temperature is 76 degrees. They have all of their windows shut and the air conditioning is running flat out to keep the house cool.
A rough analogy would be living in a winter climate surrounded by a sustainably-managed forest. You have more firewood than you'll ever need because you can grow it faster than you have to harvest it-- but would you open the home's doors & windows in December and just have a huge woodstove roaring away in every room?
Sustainable or not, even when it's free, they're wasting energy. Just like keeping a Nissan Leaf interior chilled by A/C while the car's battery is recharging.