I would think long term Geothermal and a passive solar house would make the most sense in the south.
A house with three foot overhangs. 10-12’ ceilings. A geothermal heat pump to take advantage of the fact that the ground temp is 55 degrees.
Then super insulate with an air to air heat exchanger.
Some of those old adobe houses built in the desert of AZ stay cool even when it is 110 degrees. Just like some of those 700 year old stone houses in Sicily stay cool in the summer. Of course, the walls are 3’ thick.
True that. Key words being "long term". IMHO there's a long time to get the ROI -- too much time for things to break down.
Contrarily, if my system keeps working as it has been the past 3 years (really basing it on data from the past year and a half since I added onto it in the fall of 2022), with the expected decline in throughput based on the warranties of each component, and with a reasonable 3% inflation rate on the energy prices I'm mostly avoiding, then I'm looking at a payback timepoint of about 9 years from now (2033), which is 11 years after the upgrade. That means 9 years from now I'll have saved a total in energy costs equal to how much I still owe on the HELOC loan I took out to buy and install the equipment. But my solar panels will still have 14 more years (25 year warranty, guaranteed to still be producing 70% as much power in the final year) and my batteries will still have 8 more years (19 year / 50%). And because it was cheap enough to put into a low interest loan, what we're really talking about is I had little up-front cost (meaning, that money and all the money I save each month by not having sky high power, natural gas, and gasoline expenses is money that stays in our Roth IRAs growing tax free all this time until I eventually have to take some of it out to pay off the HELOC).
I just don't think I could have done that with the much larger cost of geothermal.