Payback isn’t cost ÷ savings — energy prices rise and panels degrade. This calculator models both across 25 warrantied years and gives you the honest break-even year and lifetime profit.
Installed cost and annual benefit in — payback year, 25-year profit and effective return out.
Dividing £6,000 by £800 says 7.5 years — but if energy prices rise 3%/yr, real payback lands nearer 6.8, and 25-year profit swells well past the naive figure. Conversely, ignoring 0.4–0.6%/yr panel degradation slightly flatters late-life output. Model both; the calculator above does.
Typical UK results: 4kWp at £5,500–£6,500 with £700–£900 annual benefit pays back in 6.5–9 years, delivering £14,000–£22,000 25-year profit. Larger systems on high-usage homes with strong export rates land at the fast end. Anything an installer quotes under 5 years deserves scrutiny of the assumptions; over 12 suggests the wrong roof or the wrong price.
Three levers: price (competitive quotes vary 20–30% for identical hardware — our one-installer match keeps this honest), self-use (shift dishwasher/laundry/EV charging into daylight; a battery systemises it), and export rate (a mid-teens SEG rate versus a default few pence is worth £150+/yr — see SEG guide). Grant-eligible? WH:LG funded solar makes payback instant.
Facts checked 21 August 2026. We link to official sources and show when facts were last verified. If a scheme changes, we update the page.
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