Arizona is one of the states where a solar tax credit survives the end of the federal one. The Arizona Department of Revenue describes its Credit for Solar Energy Devices (Form 310) as a nonrefundable individual tax credit for someone who installs a solar energy device in their residence in Arizona.
Two words in that description do a lot of work. “Nonrefundable” means the credit can reduce your Arizona tax bill to zero but will not pay you anything beyond it — if your state liability is small, so is the benefit. And a credit is claimed on your return, not deducted from the installer's invoice, so you pay the full price up front and recover later. Ask a tax professional what it is actually worth in your situation before letting it into a payback calculation.
We have deliberately not quoted a percentage or a cap here. Those change, and the authoritative statement of them is the current year's Form 310 instructions on the Department of Revenue site — check them rather than an installer's summary.
On the equipment side, Arizona's electricity-to-gas ratio favors a heat pump, and in this climate the system is doing far more cooling than heating anyway — which is the case a heat pump wins most comfortably.