Solar panel payback
Cornwall generates about 30% more than the Scottish Highlands from identical panels, so a national average is close to useless. This uses your region.
4 kWp is about 10 panels
50% typical, 75% with a battery
£756 a year in The Midlands, against about £5,600 installed. Over 25 years you would be roughly £13,311 ahead.
The number that decides it is self-consumption
Electricity you use yourself is worth the full unit price you would otherwise pay. Electricity you export earns you only the export rate, which is usually less than half that. So the same panels pay back much faster for someone at home during the day, or with an EV or heat pump soaking up the middle of the day, than for someone out at work.
The default here assumes half of what you generate gets used at home, which is typical without a battery. With a battery it can reach 70–80%.
What is not included
- Scaffolding on an awkward roof, which can add several hundred pounds.
- An inverter replacement at roughly year 12–15, typically £800–£1,500.
- Panel degradation, which is slow — around 0.5% a year.
- Future electricity price rises, which would shorten the payback.