This works out how long solar panels would take to pay for themselves in your house. It asks six questions, shows every step of the arithmetic, and collects nothing from you.
It will also tell you when the answer is no, which is the part most calculators leave out.
Before you use it
Three things to know, because they explain why this gives a longer answer than most.
The costs come from government data, not from quotes. DESNZ publishes what people actually paid across roughly 177,000 domestic installations. Those figures run higher than the ranges most sites use, which we set out on our solar cost page.
We do not assume electricity prices will rise. There is a checkbox for it, switched off. Assuming 5% a year for twenty years transforms any payback figure, and that assumption is doing the work rather than the panels. Prices probably will rise, which makes the real answer better than ours. We would rather be wrong in that direction.
On typical settings this returns thirteen to sixteen years. Across every combination of occupancy and export rate, the full range runs from about ten years to over twenty, which we set out in the table on are solar panels worth it. Where you land inside that range is what the calculator is for.
It asks whether anyone is home during the day. That single question moves payback by years, because electricity you use yourself is worth 26.32p while electricity you export may be worth 4p. Almost no other calculator asks it.
Change anything you disagree with. The working updates as you go, so you can see exactly which assumption produced which number. That is the point of it: not to give you a figure, but to let you check ours and substitute your own.
One practical note. Get your quotes first if you can, then put the real figure into the installed cost box. The calculator prefills the official average for your system size, which is a reasonable starting point but not your price. And run it before the calculator, not after it, because a payback figure is far more useful while you can still change what you are buying.
Your roof and your household
Around 9 panels at 430W each.
This decides more than anything else on the page. Electricity you use yourself is worth 26.32p. Electricity you export is worth a fraction of that.
Smart Export Guarantee rates vary hugely by supplier. Check yours rather than assuming.
Off by default. Assuming prices rise shortens every payback figure, and it is a guess about the future rather than a fact about your house.
What the arithmetic says
The working
| Estimated generation | |
| Used in the house | |
| Exported to the grid | |
| Total benefit a year | |
| Installed cost |
Why does another calculator say nine years?
Because of three assumptions, all of them defensible in isolation and all of them favourable.
A generous efficiency or generation figure. Heat pump calculators often default to a seasonal efficiency of 4.0 when the real-world break-even against gas is 2.8. Solar calculators sometimes assume an unshaded south-facing roof in the south of England.
Compounding energy price inflation. Assume prices rise 5% a year for twenty years and almost any efficiency measure looks transformative. That assumption, not the technology, is doing the work. We leave it switched off by default.
Bundling several technologies together. Switch on solar, a battery, a heat pump and smart car charging at once and the strong parts of the case carry the weak ones. You never find out which part paid.
We are not saying those calculators are dishonest. Their inputs are usually visible and adjustable. But defaults are what most people accept, and theirs point one way.
Estimates only, not a quote. Import price 26.32p per kWh from the Ofgem price cap for 1 October to 31 December 2026. Installed costs from DESNZ Solar PV cost data, 2025/26 release, declared net capacity basis. Generation follows the MCS MIS 3002 method of system size multiplied by a location value and a shade factor; the regional values used here are approximations derived from published MCS and Energy Saving Trust figures, not the full MCS location table, so treat them as indicative. Self-consumption bands are our own estimates. The range shown reflects roughly plus or minus 8% on generation to allow for shading, pitch and year-to-year weather.
What to do with the answer
If it says under fifteen years, that is a normal result for a decent roof and it is a reasonable purchase. Panels are usually warranted for twenty five years, so the last decade is generating free electricity.
If it says fifteen to twenty years, look at the two free levers before anything else. Shifting your electricity use into daylight hours costs nothing and raises self-consumption. Choosing a better export tariff costs nothing and can be worth thousands over the life of the system. Between them they will usually move the answer more than negotiating on the quote will. Our guide to solar export rates explains why published rate comparisons contradict each other and how to find what you would actually be paid.
If it says over twenty years, something specific is wrong rather than solar being wrong. Usually it is a north-facing or heavily shaded roof, an empty house on a poor export rate, or a quote well above the official average. Each of those has a different answer, and none of them is “buy anyway”.
If you are thinking about a battery, run the numbers separately. A battery costs as much as the panels on many quotes, and counterintuitively a good export rate makes the case for one worse rather than better. We set out why on our batteries page.
What this calculator does not do
Being clear about the limits, since a number on a screen carries more authority than it deserves.
- It does not survey your roof. Shading is the largest single variable in generation and it cannot be assessed remotely. An MCS installer will give you a shade factor, and you should ask for it.
- It uses approximate regional figures. MCS publishes exact generation values for every location, orientation and pitch. Ours are interpolated from published figures, which is good enough to decide whether to proceed and not good enough to plan around.
- It ignores the inverter replacement you will probably need after ten to fifteen years. That is a real cost inside the payback period and it would lengthen every figure here.
- It assumes your circumstances stay the same. Retirement, an electric car, working from home or moving all change the answer substantially.
- It is not a quote, and we are not installers. We do not sell solar panels and nobody pays to appear here.
Why our figures are longer than other calculators
You will find calculators returning seven or nine year paybacks. They are not lying, and their inputs are usually visible. The difference is in the defaults, and there are three of them.
Optimistic performance assumptions. A high generation figure, or in heat pump calculators a seasonal efficiency of 4.0 when the real-world break-even against gas is 2.8.
Compounding price inflation. Assume electricity rises 5% a year for two decades and the twenty year comparison becomes enormous. That assumption produces most of the headline saving.
Bundled technologies. Solar, a battery, a heat pump and smart car charging all switched on together. The parts that pay well carry the parts that do not, and you never learn which was which.
We have made the opposite choice on all three. That produces a less encouraging number, and we think it is the more useful one. If you would rather see the cheerful version, switch on the price inflation checkbox and you will get some way there, with the assumption stated rather than hidden.
Last updated 18 September 2026. Import electricity price of 26.32p per kWh from the Ofgem price cap for 1 October to 31 December 2026. Installed costs from DESNZ Solar PV cost data, 2025/26 release published 28 May 2026, declared net capacity basis, domestic installations. Generation follows the MCS MIS 3002 method; the regional values used are approximations derived from published MCS and Energy Saving Trust figures rather than the full MCS location table, and are labelled as indicative. Self-consumption bands are our own estimates. Export rates are not capped or centrally published. This is an estimate and not a quote. Written by Ben Jardine.