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CALCULATOR · Finance

Solar Panel Payback Calculator

Net cost, year-1 savings and simple payback for a rooftop PV system — with lifetime returns and LCOE.

Show formula
production = size × yield · savings = self-used × electricity price + exported × export price · payback = net cost ÷ year-1 savings

Inputs

The installed price from the quotation, before grants — panels, inverter, mounting and labour. Comparing quotes per kWp keeps different sizes honest.

One-time grants, rebates or tax credits that come straight off the invoice. Payback divides the net figure — what you actually paid.

The system's peak output in kWp — 6 kWp is roughly 14–16 panels on a family roof. Installers quote it first.

kWh each installed kWp produces per year at your site: 900–1,400 across most of Europe, 1,400–1,800 in sunny US states. Take it from the installer's estimate or a simulation report.

Your price for one kWh bought from the grid — the unit rate on your electricity bill. Every kWh you use yourself saves exactly this much.

What the grid pays for one kWh you feed in. Many small systems export unpaid — leave 0 and the exports earn nothing.

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Share of generation used as it is produced. Without a battery a typical home sits near 30%; a battery, or shifting loads into the sun, pushes it far higher.

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Yearly loss of output as panels age. Warranties guarantee 84–87% of day-one output after 25 years — about 0.5–0.7% a year.

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How many years the returns are accumulated over. 25 years is the standard panel warranty horizon; an inverter may need replacing once inside it.

Result

Your result appears here

Enter System cost and the result fills in as you type.

How it works

  1. Enter the installed price from the quotation and any grant or rebate that comes straight off it — the payback divides the net figure, because that is what you actually paid.
  2. Fill in the roof: the size in kWp and the specific yield per kWp per year from your installer’s estimate or a simulation report. Then the two prices — what you pay per kWh from the grid and, if anything, what you are paid for exporting.
  3. Read the simple payback, plus the year-1 savings it is built from, the cost after the subsidy, the lifetime return at each year’s own output, and the system’s lifetime cost per kWh.

Frequently asked questions

What is specific yield and where do I find it?

It is the kWh one installed kWp produces per year at your site, and it carries everything the location decides — sun, tilt, orientation, shading, temperature. Your installer’s yield estimate or a free simulation (PVWatts, PVGIS) states it directly; typical figures run 900–1,400 kWh/kWp across most of Europe and 1,400–1,800 in the sunnier US states. It is the one input that scales the whole answer linearly, so doubling it halves the payback.

What does self-consumption mean here?

The share of your generation you use as it is produced, displacing electricity you would have bought at the retail price; the rest is exported at the feed-in tariff. Without a battery a typical home self-consumes about 30%, and a battery — or simply running the dishwasher at noon — pushes it far higher. If exports go unpaid, self-consumption is everything your savings stand on, which is why storage so often shortens the payback more than an extra panel does.

Why simple payback — no price rises, inverter replacement or discounting?

Because every extra assumption is another number you would have to guess. Simple payback uses only figures you can read off a quotation and a bill, so it stays checkable — rising prices can only shorten it, and a mid-life inverter or a repair can only lengthen it. Treat the lifetime return the same way: a floor built from today’s prices, not a forecast.

Examples

6 kWp at 1,100 kWh/kWp: a 9,000 quotation with a 2,000 grant, electricity at 0.30, exports paid 0.05, defaults elsewhere
6,600 kWh a year — 1,980 self-used and 4,620 exported — earns 825.00 in year 1; the net 7,000 pays back in 8.5 years. Across 25 years at 0.5% degradation: 155,469.28 kWh, 19,433.66 saved, 12,433.66 net — a 177.6% return and 0.045 per kWh of its own energy.
A 14,000 quotation for 10 kWp at 1,400 kWh/kWp, no grant: electricity at 0.25, exports paid 0.08, a 25% self-consumption share, over 30 years
14,000 kWh a year splits into 3,500 self-used and 10,500 exported — 1,715.00 in year 1, so the 14,000 pays back in 8.2 years. Over 30 years: 390,924.26 kWh, 47,888.22 saved, 33,888.22 net — a 242.1% return and 0.036 per kWh.

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