Solar payback

Free. No account, no email, nothing uploaded.

Estimated annual generation, kWh

Installed cost, £

The generation figure is on every MCS-certified quote. This tool will not invent one: it depends on your latitude, orientation, pitch, shading and the local weather record.

Used in the house rather than exported, 40% The lever that costs nothing. Every point is worth £4.00 a year on your figures.

You pay to import, p/kWh

You are paid to export, p/kWh

Import defaults to the Ofgem cap. Export is an input: it varies by supplier and none has been verified at source here, so put in what you are actually offered.

With a battery Raises self-consumption, and adds cost. Judge it on its own.

Electricity rises, % a year

Life, years

Leave inflation at 0 for the answer that does not depend on a forecast.

Payback £699.98 in year one

10.2 yrs

on £7,000.00 spent, and £9,488.78 ahead over 25 years.

A used unit against an exported one

1.7 times the value: 26.11p saved against 15p earned. Every extra point of self-consumption is worth £4.00 a year and costs nothing, which is more than most of the things people are sold to improve a system.

Year one

Used in the house	1440 kWh, saving £375.98
Exported	2160 kWh, earning £324.00
Benefit	£699.98

Over 25 years

Spent	£7,000.00
Total benefit	£16,488.78
Ahead	£9,488.78

Generation comes off your quote and is never estimated here. Nothing uploaded.

Worth knowing

A UNIT YOU USE IS WORTH 1.7 TIMES A UNIT YOU EXPORT. Using it saves you the import price of 26.11p; exporting it earns you 15p. Self-consumption is the biggest lever you can pull for NOTHING: more generation costs money, and running the dishwasher at noon does not. It is decided by when you are at home and what you run, rather than by the panels.
On your figures every extra percentage point of self-consumption is worth £4 a year. Moving from 40% to 50% is worth £40 a year, which is free: it is timing the washing machine, the dishwasher and anything with a timer to run in the middle of the day.
The generation figure is yours, off the quote, and this tool deliberately does not estimate one. Annual output depends on latitude, orientation, pitch, shading and the local weather record. Comparing two quotes on their stated generation, for the same roof, is a far more useful exercise than any calculator, and a quote that will not state one is telling you something.
Payback at 10.2 years, and over 25 years the total benefit is £16,489 against £7,000 spent, so £9,489 ahead. PAYBACK IS NOT A RETURN: it says nothing about year 12 onwards, and nothing about the money being tied up in a roof in the meantime. The lifetime figure is the one that answers the question people actually mean.
Electricity price rises are set to zero, so nothing here depends on a forecast. That is the conservative version. If you want to see how much of the case rests on prices rising, put a figure in and watch the payback move.
Panels lose about 0.5% of their output a year, which is in the arithmetic above. The inverter is the part that usually needs replacing first and it is rarely in a payback figure at all, so ask what its warranty is and add a replacement to your own numbers.
Import price defaults to the Ofgem cap of 26.11p, which changes on 1 October. Export rates are an input because they vary by supplier and tariff and none has been verified at source for this site: put in what you are actually being offered rather than a headline rate.

Worked out on this device, by this page. Nothing you typed was sent anywhere or stored, and closing the tab loses it.

Next in the same job

Energy bill estimator

Split into the part that using less changes, and the part it does not.

EV charging cost

Home off-peak against a public rapid, against petrol, and against the mileage rate.

Appliance running cost

Your appliance and your rate, not the nameplate watts times hours.

The gap between what you save and what you earn

Generate a unit and use it in the house, and you save the import price: around 26p under the current cap. Generate one and export it, and you earn the export rate, which is a considerably smaller number set by whatever tariff you are on.

That gap is the entire economics of a domestic solar system, and it is why two identical installations on two identical roofs can have paybacks years apart. One household is in during the day and the other is not.

Be careful with the version of this claim you usually hear

"Self-consumption matters more than system size" is repeated everywhere and it is not quite right. A bigger system raises the units you use and the units you export, so 10% more generation is usually worth more than 10 points more self-consumption.

Moving a unit from export to self-use gains you only the difference between the two rates, not the whole import price. The honest point is different and better: self-consumption is the biggest lever you can pull for nothing. More generation costs thousands. Running the washing machine at noon costs nothing at all, and the tool tells you exactly what each percentage point is worth on your own figures.

Why there is no generation estimate here

Annual output depends on latitude, orientation, roof pitch, shading and the local weather record. It is a genuinely modelled number and this tool has no business inventing one, in exactly the same way the boiler and radiator tools refuse to invent a heat loss.

You already have the figure. Every MCS-certified quote states an estimated annual generation. That is the number to put in, and comparing two quotes on their stated generation for the same roof is a more useful exercise than any calculator. A quote that will not state one is telling you something.

Batteries, judged on their own

A battery raises self-consumption, which as established is the right lever. It also costs several thousand pounds, and on most current numbers that makes the payback longer, not shorter.

The tool works out the same system with and without the battery so you can see the difference rather than argue about it. If a battery lengthens your payback by three years, that is not an argument against having one, it is just the honest price of the other things it gives you: resilience in a cut, and the ability to shift cheap overnight electricity.

One thing that is almost never in a quote: a battery's warranty is measured in cyclesrather than years, and that is the number that runs out. A twenty five year comparison containing a battery is quietly assuming a replacement nobody has costed.

Payback is not a return

"Pays back in nine years" is the figure everybody asks for and it answers less than it appears to. It says nothing about year ten onwards, and nothing about several thousand pounds being tied up in a roof in the meantime.

So the tool gives you the payback, because that is what people want, and also the lifetime total: what the system delivers across its assumed life against what it cost. That second figure answers the question people mean when they ask about payback.

The two assumptions worth playing with

Electricity price inflation. Leave it at zero and you get the answer that depends on no forecast at all. Put a figure in and watch the payback shorten. The difference between the two is the size of the bet you are making about the next twenty five years. See it plainly rather than have it built into a headline number by somebody selling panels.

Degradation. Panels lose a little output every year, typically around half a percent, and that is in the arithmetic here. The bigger omission in most calculations is the inverter, which usually needs replacing well inside the panels' life and rarely appears in a payback figure at all. Ask what its warranty is, and add a replacement to your own numbers before deciding.

Common questions

Why does self-consumption matter so much?

Because a unit you use saves you the import price, currently around 26p, and a unit you export earns you the export rate, which is a much smaller number. The gap between those two is what a unit is worth moving. Crucially it is the biggest lever you can pull for nothing: more generation costs money, and running the dishwasher at noon does not.

Is more self-consumption better than a bigger system?

Not straightforwardly, and the loose version of that claim is wrong. A bigger system raises both the units you use and the units you export, so 10% more generation is usually worth more than 10 points more self-consumption. Moving a unit from export to self-use gains only the difference between the two rates, not the whole import price. The point is that self-consumption is free.

Why will this not estimate my generation?

Because annual output depends on your latitude, orientation, roof pitch, shading and the local weather record, and that is a real modelled figure rather than something to guess at. You already have it: every MCS-certified quote states an estimated annual generation. Comparing two quotes on their stated generation for the same roof is a more useful exercise than any calculator.

Does a battery improve payback?

Usually it makes payback longer, not shorter. A battery raises self-consumption, which is the right lever, but at current prices it adds more cost than the extra self-use is worth. It can still earn its place for resilience or for shifting cheap overnight electricity. Judge it on whether the extra self-consumption pays for the battery, not on whether the whole system pays back.

What is missing from a typical payback figure?

The inverter. It usually needs replacing first, well within the panels' life, and it is rarely in anybody's payback calculation. Ask what its warranty is and add a replacement to your own numbers. If there is a battery, its warranty is in cycles rather than years, and that is the number that runs out.

Should I assume electricity prices will rise?

You can, and you should know how much of the case rests on it. Leave the inflation figure at zero and you get the answer that does not depend on a forecast. Put a figure in and the difference between the two is the size of the bet you are making about the next twenty five years.