Forget the payback period conversation. It misses the point.
A 4kW solar system costs around £5,500 installed. At current electricity prices it saves £900 to £1,400 a year.
Borrow £5,500 at five percent over ten years: monthly repayment £58. Monthly bill saving £100. You are £42 ahead. Every month. From day one. The panels pay for themselves before you finish paying for them.
This is cash flow positive immediately. Not eventually. Now.
The reason millions haven't done this is not financial. The maths works right now at commercial lending rates with no subsidy.
The reason is that nobody told them. No letter from the municipality. No conversation at the mortgage appointment. No default that makes it the obvious choice.
The information gap is the policy failure. Not the technology. Not the economics.
Spring is when the case is strongest. Bills still high. Solar generation climbing. Pain live. Window open.
The municipality sends the letter. The bank has the product. The installer is local. The household does the maths and says yes. That's the whole plan. No summit required.