for price of heat pump you can buy 3-6 times bigger PV array. heatpumps are not expensive but they are not cheap COMPARED to other alternative. cop is not cons

for price of heat pump you can buy 3-6 times bigger PV array. heatpumps are not expensive but they are not cheap COMPARED to other alternative. cop is not constant, it changes. closer the outside temperature and indoor temperate is, less work is needed / higher COP heat pump provides. buying 4 times more panels gives you always 4 times more energy. in -40F you get 4 times more energy from 4 times bigger pv array. heat pump will probably just start running integrated resistive heater IN THESE temperatures. heat pump can be configured in a way that it not only heats but also cools, so yes in that situation heat pump can be cheaper. then not having one and be less comfortable / productive because of it. you can buy PV system and after it paid itself, it still works, still generates electricity. gas can not be 0 $. so depends what / how you calculate things.