Yes it’s a lot more complicated than the people that sell solar will tell you. It’s not really possible to know what future utility rates will be, so your break-even/payback period can vary quite a lot. If you plan to stay in the house for a long time it might make more sense. Solar will add some value to the home, but probably not enough to recoup very much of what you paid to have it installed, especially if newer, better & more economical technology comes out. Having the solar with battery backup would be nice to have if you live some place where power outages occur frequently.
You're right that it adds value you your home, but not enough to recoup your costs. However, it might add value to your home enough to shorten your payback period. For example, I said that my payback point is 12 years. But perhaps if I sold my home at around 7 years, the increased value of the home from solar, plus the energy savings I'd accrued during those 7 years, might be enough for payback at 7 years. If I sell my house at 10 or 12 years, then I've made money with solar (through 10 years of energy savings plus increased value in my home).
You're correct that part of the payback calculation is based on the unknown of future costs. That's why I assume only a mild 3% inflation rate. Obviously if the Dims keep having their way, energy costs will keep increasing by way more than 3%.
And battery storage can make sense even if you live in an area with dependable power like I do. Part of my math is based on the real world numbers I'm experiencing now. I went from paying a high power bill + high natural gas bill + a lot at the pump from gasoline, to paying a low power bill + no natural gas bill + almost no gasoline cost + EV car payment + a HELOC payment (the loan I took out to pay for it all). To date it's saved my overall cash flow a total of $2,900 since my first solar install in May of 2021 (call it $1K per year). And as the HELOC balance is paid down, the HELOC payments go down too. Meanwhile the energy costs I avoid keep going up. So next year it'll cost me less money (lower HELOC payments) to save more money (higher energy costs I'm avoiding). And the next year it'll cost even less to save even more. Then the next year, and the next year, etc.
So my 12-year payback calculation includes paying interest on the HELOC during these years. But it doesn't include a positive: that $1K+ savings per year staying in my Roth IRA's growing interest free. (The main reason I did this energy project while the Dims were making the energy portion of my budget go through the roof.) In effect, my payback point is even sooner. And if the Dims keep making energy costs skyrocket my payback point is even sooner -- all while my retirement budget doesn't worry about energy cost inflation.