Solar Panel Payback Calculator
Panels pay for themselves out of electricity you stop buying, not out of electricity you generate. The share you use yourself while the sun is up is worth several times the share you export, which is why two identical installations can have very different payback periods.
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Self-consumption is where the money is
A kilowatt-hour you use as it is generated saves the full retail price — often 0.30 or more once network charges and tax are counted. The same kilowatt-hour exported earns whatever the export rate is, frequently a fifth of that.
So the single most important figure here is the share you use yourself. A house that is empty all day exports most of its generation and takes far longer to break even than one with someone home, a heat pump running, or a car charging in the afternoon.
Generation depends on where you are
A kilowatt-peak of panels produces roughly 900 to 1,000 kWh a year in northern Europe, around 1,100 in the middle, and 1,300 to 1,500 around the Mediterranean. Orientation and pitch matter too: a south-facing roof at about 35 degrees is the reference, and east-west arrangements give up perhaps a sixth of the total while spreading it more evenly across the day, which can raise self-consumption enough to compensate.
A battery changes the calculation, not always for the better
Storage lifts self-consumption from a third to two thirds or more, which is a large gain. It also costs money and has a shorter life than the panels. Add its cost here and raise the self-use share to see whether it earns its place; frequently it lengthens payback rather than shortening it.
Rising prices shorten payback
The saving is measured in electricity you do not buy, so it grows with the price of electricity. The figures here hold today's price constant, which is the conservative choice. If prices rise faster than inflation, real payback comes sooner than shown.
What is not counted
Inverter replacement, usually needed once in a 25-year life. Cleaning and occasional repair. Any effect on what the house is worth. And the value of the roof space itself, which matters if the roof needs replacing during the panels' life — that is the moment to install, not five years before.
Frequently asked questions
What self-consumption share should I assume?
Around a third for a house that is empty on weekdays, half or more with a heat pump, an electric car charged at home, or a battery.
Which electricity price do I enter?
The all-in price from your bill: the total divided by the kilowatt-hours used. Using the energy component alone understates the saving substantially.
Is a battery worth adding?
Add its cost and raise the self-use share to find out. It often lengthens payback rather than shortening it, because storage is expensive and wears out sooner than the panels.
Do panels stop working after 25 years?
No. Output declines slowly, typically around half a percent a year, and most panels still produce well beyond the period counted here.