Great PV system!
If you decide to go the heat pump route, make sure you find a very experienced installer.
- The data shows that heat pumps are very efficient; however, they are so often poorly installed that the efficiency is generally reduced by 50% due to several common installation deficiencies.
- They are also very expensive.
If you have an electric hot water heater, perhaps going combined hydronic heating would be a very efficient choice. The conventional hot water tank would be hooked up to a variable-speed air handler and a forced-air duct system would be installed. Then you can install a conventional Energy Star-rated (14 SEER) 1.5 ton a/c condensor that can also run off your PV.
No matter what, make sure that you have a duct-blaster test to ensure that the ducts are tight. Less than 3% leakage is acceptable.
For more information:
Read Rick Goyette's Q&A "Should I go with an air source heat pump or electric radiant floor heat?"
Also, read Florian Speier's Q&A "Can I configure an electric tankless water heater to run a baseboard hot-water heating system?"