← All guides · 2026-06-17

Solar Payback Period: How to Calculate It Honestly

The honest formula

Simple payback = net system cost ÷ annual savings. The subtlety is entirely in 'annual savings': it is (self-consumed kWh × retail price) + (exported kWh × export price) − maintenance. Because export prices are usually far below retail prices, two identical roofs can have paybacks years apart depending on how much of the production is used on-site.

Typical numbers in 2026

Residential turnkey costs run $900–1,500 per kWp in most competitive markets. With retail electricity at $0.15–0.35/kWh, typical honest paybacks are: southern Europe and Australia 4–7 years, central Europe 7–11 years, sunny US states 6–10 years (before incentives). Utility-scale projects work differently — they compete on LCOE and PPAs rather than retail offsets.

What most calculators hide

Watch for four omissions: panel degradation (~0.4%/year, so lifetime output is ~90% of year-one), inverter replacement around year 12–15 ($0.10–0.15 per Wp), electricity price inflation (helps you — historically 2–5%/year), and the discount rate if you care about NPV rather than simple payback. Our AI planner includes all four and researches your country's current prices and incentives before computing.

When payback is the wrong metric

For a 25–30 year asset, internal rate of return (IRR) tells you more than payback. A system with a 9-year payback and 25-year life yields an IRR around 10–12% — hard to match with comparable low-risk investments. Payback answers 'when am I whole'; IRR answers 'was this a good use of money'.

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