There are too many variables to provide a definitive answer
To ask the question is ignorant and irrelevant
There are too many variables to provide a definitive answer
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True... but here is one answer.
The cheapest energy is the energy you don’t need to buy. I have a bungalow that is about 2,800 square feet... about half of it is an addition that I put on and when it was built, I went significantly beyond what was required for insulation and the overall heating bill only went up 10% when I was done with it, even though the house square footage doubled. Mind you, I also increased the attic insulation in the original part of the house when I put the addition on.
About 15 years ago, I decided to increase the insulation of the original part of the house.... the entire house has a full 8 foot high basement and while the exterior of the foundation on the addition I put on was insulated (polystyrene), the original part of the house only had some insulation on the inside of the foundation to accommodate some finished basement rooms. As a summer project, I dug up the entire foundation wall for the original part of the house right down to the footings and insulated it with 5 inches of polystyrene... managed to snag an excellent deal on some factory seconds that had a ripple in them but were perfect for what I wanted. This was not a small undertaking but I worked on when I could and over a couple of months, it was done. The top of the insulation is covered with some formed aluminum flashing and caulked to the top of the foundation wall about one inch below the bottom row bricks. This has made a huge difference... not just the drop in energy costs but due to the amount of thermal mass on the inside of the insulation, it enables the house to ‘ride through’ periods of no heat (in the event of a power outage) without a serious (rapid) drop in temperature.
As good as this has been, my next house will be better... it will be completely off grid for everything.
Just as a side note, I recommend folks see the interview that Tucker Carlson did the other day with Dennis Quaid. Quaid has made it a bit of a mission to warn folks about the possibility of a complete electric grid failure due to a Carrington Event.... https://twitter.com/TuckerCarlson/status/1746215532833947700
Don’t know what a Carrington Event is? It’s a geomagnetic storm....
https://en.wikipedia.org/wiki/Carrington_Event B