Solar Panel Payback Calculator

How to use

1. Enter installed cost and system size from any quote.
2. Set your peak sun hours (4–6 typical) and electricity rate.
3. Read payback years and projected 25-year savings; tweak inflation to stress-test the quote.

About this tool

Rooftop yield ≈ system kW × peak sun hours × 365 × 0.80 performance ratio. Yearly saving = yield × tariff (plus exported surplus where net-metering applies). Payback = installed cost ÷ saving; 25-year net saving compounds with a modest annual tariff-inflation assumption you control. Quotes vary wildly by roof and region — treat this as a sanity check against salesperson numbers, which is exactly what it's for.

FAQ

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The Solar Payback Formula (Worked Example)

Solar panel repayment is the time your electricity savings take to equal the system's net cost. The formula: Payback years = (Total installed cost − incentives) ÷ (annual generation × self-use value + export earnings − annual maintenance). Worked example: a 5 kW system costs 12,000 in total, with a 2,000 incentive applied. It generates 6,500 units a year; you self-consume 60% at a 0.28 tariff (1,092 saved) and export 40% at a 0.08 rate (208 earned), minus 60 maintenance. Net annual benefit ≈ 1,240, so payback ≈ 10,000 ÷ 1,240 ≈ 8 years. Enter your own numbers in the calculator above — the two inputs that move the result most are self-consumption share and your actual daytime tariff.

Typical Payback Ranges by System Size

Ranges reflect common residential tariffs and installed costs; your quote and usage decide the real figure. Bigger systems only pay back faster when the extra generation is actually consumed or fairly compensated — sizing to your daytime load beats sizing to your roof.

What Shortens — or Stretches — Your Repayment

• Self-consumption first: every unit you use directly offsets a full retail tariff, usually 3–4× the export rate. Shift washing, dishwashing and EV charging into daylight hours.
• Panel orientation and shading: south-facing (northern hemisphere) at roof pitch is ideal; even one shaded panel can drag a whole string's output down unless optimisers are fitted.
• Incentives and net metering: tax credits, rebates and honest export tariffs can cut payback by 2–4 years; policy changes cut both ways, so check current rules before signing.
• Degradation and maintenance: quality panels lose ~0.5% output a year; inverter replacement around year 10–12 is the one cost to budget for.
• Financing: cash purchases pay back fastest; loan interest adds to the net cost, while lease models trade payback for zero-upfront.

Run the calculator with optimistic and pessimistic tariff pairs to see the payback band — a decision made on the band survives tariff changes far better than a single-number answer.