You are predicting exactly how much for solar (dollars per watt)? I have heard stories for years about 50 cents a watt, 25 cents a watt, etc. Right now panels are a dollar a watt same as 10 years ago.
I don’t calculate it that way. Dodgy salesmen use shoddy math like that to prove people can make money out of solar that way; they then find it’s pie in the sky, based on total guesswork.
The way I work it is, mental arithmetic. A flat rate 14.4p per kWh is typical, but it is creeping up. If I use on average 30kWh every day that’s £4.50 a day, or £31.50 a week, or £96 a month, £1150 ish per year - and that’s consistent with my quarterly bills before getting solar.
In other words, if I didn’t get solar, and if prices stay static for 7 years, after 7 years I’d have paid as much to the grid as I (overspent) last year on solar.
If I generate 60% of my own power over that seven year period, without reducing consumption, it’ll take just around 11.5 years to get to a point where the solar has paid not just for itself but for all the other works I had done at the same time, and for its maintenance.
In reality, the system is rated for 16 years minimum, and if it’s well maintained it should last for 22 years.
So, TCO over the lifetime amounts to a 20% cost reduction.
That’s if I generate only 60%, AND the price of using the grid doesn’t rise.
If I can get to a point where