I’d like to use the pool year round. I know I’m not going to drain it. I have solar on my roof so I could use that time to heat it but am not sure how cold it would get at night. I moved here in April/ May and used the pool then. My wife would set foo in it until June, July
So you are quite right, we do not winterize pools here in AZ. We certainly do not drain them. Most pools remain "open" in the winter but by "open" it's really just the pump running on a very light schedule and minimal chlorination and pH control.
You can't (easily or economically) use a pool all year round here. Sorry, the water gets too cold and if you tried to heat it you will wreck the heater in short order. Heatpumps are not efficient at all when the air temps are below 50F and that is especially true around here because the humidity is so low. There simply isn't enough heat energy to extract out of the cold, dry air. Likewise, gas heaters cannot be run when the water temps are below 60F and the air temps are very low. The combustion condensate that would be created by the heater would be so corrosive that the heat exchanger would rot out quickly. Not to mention, the cost of gas to constantly heat a mass of water that large to any swimmable temperature would be outrageous even in this part of the country where gas is cheap. Solar wouldn't work either as the system would radiate heat away more so than absorb it.
Realistically, the best you can do around here is start heating a pool in March and keep it going through October, maybe mid-November. But in that scenario, the only heat source that makes sense to use is rooftop solar heating. In order to do that, you'll need to be able to run pipes from your equipment pad up to your roof on a south-facing exposure to get the maximum benefit. You can use a gas heater in lieu of solar OR in combination with solar. You'll also need an automation controller to automate the valves in the solar loop so that they open and close when the roof top temperatures are right. People try to manually do that and inevitably leave the solar running too long or at the wrong time and cause all sorts of trouble.
Most importantly, none of this will work efficiently unless the pool is covered in the overnight hours. A roof top solar system can certainly add several degrees to the pool over the course of a day. but, if left uncovered, all the heat will be gone by the morning. Evaporative cooling is greatest in these parts because the dew point temperatures are always super-low (often 20-30 degrees below the day time temps). Water evaporates like crazy around here and if you don't control it, all the heating will do is cause the pool to lose water to evaporation which you will have to make up with fill water.
Anyway, hopefully that gives you something to think about. Anything you do is going to cost significant investment. The pictures don't show the entire property but it looks like the equipment pad is pretty far away from the house and the backyard looks well finished. That being the case, adding any new services will involve lots of digging.
Good luck.
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