Having done the conversion twice now. You have pretty much a trade off scale one side how efficient the heat pump is at a given outside temp combined with your costs of electricity vs cost of oil. What that boils down to an an outside temp that you switch to using oil, and most of the time in CT it's way warmer than that.

Now combine that with solar. For the first few years when your paying off your panels thats probably in the 20's with a modern heat pump and oil > 2 bucks a gallon. Then you're price of electricity drops to 0 for what your panels put out so rapidly it's a question of still using less than you generate overall and what the heat pump can deal with. Think you need oil NG propane or something as a backup heat source in CT, cheaper and more efficient than a generator that can run heat pumps when we lose power for a week.