Heatpump performance will depend on how the unit is sized relative to the needs of the house, along with outdoor temps.
The cooler it is out the less heat the unit will put it. For air temperature, likely 15 to 30F warmer than return air vs the 40-60ish you would get out of a modern gas furnace.
The heatpump by design moves more air than a furnace relative to heating capacity.
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Questions before proceeding with this project:
1. How is the place heated now? Electric, gas, propane, etc.
2. What is the cost per delivered kwh, therm or otherwise
3. How much will this heatpump retrofit cost? is there a roi? Are you looking at heatpump just because you have an array?
Generally heating is an inefficient way to use it. Power produced from PV is very expensive power, you just payed for it all in one go. Heating even with a heatpump is not an efficient use at all.
Your typical 3 ton heatpump, 14 seer/8 hspf may draw 2.5-3.5kw provide and run for 6-24 hours per day depending on how cold it is. The production from pv won't offset this unless there's a huge array. It may be better to keep the credit accumulated and use it during the a/c season.
Straight electric would be far worse, whopping 10.6kw being consumed to supply the same amount of heat as a 3 ton hp at 47f outdoor.
4. What configuration is best?
Heatpumps can be installed as retrofit on top of fossil fueled furnace (dual fuel) or as all electric, with the backup heat consuming copious amounts of electricity when the heatpump can't keep up or when its just plain too cold to get much heat out of it.
With the all electric you get to run the heatpump below the balance point, taking advantage of potentially cheap heat (if you have a low rate like 5 cents per kwh) but if much backup heat is needed, you could be better off with dual fuel.
Depends on costs, rates, balance points. A load calculation needs to be done and heat output of a heatpump compared with heat loss.
Got to compare costs at various temps.
