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What will solar cost you, and when does it pay back?

Every assumption below is on screen and editable. If you think one of them is wrong for your house, change it — that is the point. Payback on solar is a range, and a site that shows you the six inputs behind the range is more use than one asserting a single year.

Runs entirely on your device. Nothing you type is sent to us or to anyone else.

Your system

Roughly one panel per 2 m² of usable roof.

Put your actual quote in here if you have one.

Your household

kWh per kWp per year

proportion

GBP per kWh

GBP per kWh

proportion per year

GBP, once at year 12

Pays for itself in year 11

A 4.4 kWp system at £6,900, generating about 3,740 kWh in its first year.

Year one saving
£404
Year one export
£269
Year one total
£673
Net at year 25
£7,758
Year 1Year 25

Bars show your cumulative position. Amber is money still out; green is money ahead.

What each assumption means, and when to change it

The assumptions behind every figure on this page

AssumptionDefault Why, and when to change it
Annual yield 850 kWh per kWp per year A south-facing, unshaded roof at a typical UK latitude. East/west split roofs lose roughly 15%, and heavy shading far more. Set your own figure if you have a real MCS estimate.
Share of generation used at home 0.4 proportion Without a battery, a household that is out on weekdays typically self-consumes 30–40%. A battery, an EV or someone home in the day pushes it to 60–80%. This is the input that moves payback most, which is why it is not hidden.
Electricity you avoid buying 0.27 GBP per kWh Roughly the price cap unit rate. Every unit you use yourself is worth this; every unit you export is worth the export rate, which is far less. That gap is the whole economics of a battery.
Export rate 0.12 GBP per kWh The best widely available untied flat rate at the time of writing. Check the current table at /smart-export-guarantee/rates/ — this number moves.
Annual panel degradation 0.005 proportion per year Typical manufacturer warranty terms imply about 0.5% a year.
Inverter replacement 1200 GBP, once at year 12 Included because leaving it out overstates lifetime return. Set it to zero to see how much difference it makes.

What the install itself costs

Installed cost by system size

SystemPanelsRoof area Typical installed costUsually suits
3.5 kWp 8 16 m² £5,000–£6,500 A 1–2 bedroom home, or a low-usage household
4.4 kWp 10 20 m² £6,000–£7,800 The UK median installation — a 3 bedroom semi
5.3 kWp 12 24 m² £7,000–£9,000 A 3–4 bedroom home with a heat pump or an EV
6.2 kWp 14 28 m² £8,000–£10,500 A 4+ bedroom home, high daytime usage
7 kWp 16 32 m² £9,000–£12,000 Large detached, usually needing G99 approval

These bands have not yet been rebuilt from an MCS extraction, so no data month is shown. Ranges are indicative, not a quote.

These bands are indicative and have not yet been rebuilt from an MCS extraction, so no data month is shown. Use your own quote in the calculator above for a real answer.

The costs that are usually left off the first quote

ItemTypical cost When it appliesWhat to watch
Scaffolding £300–£1,200 Almost always Varies with height, access and whether the scaffold has to go over a conservatory or a neighbour’s land. Some quotes exclude it entirely — check.
Consumer unit upgrade £400–£800 Where the existing board cannot take the circuit Older boards frequently cannot. It is a legitimate cost, but it should appear on the quote rather than on the invoice.
Bird proofing £500–£900 Recommended, rarely quoted upfront Pigeons nesting under an array is the single most common post-install complaint. Retrofitting mesh costs more than fitting it on day one.
Roof remediation up to £3,000 Where the roof needs work first A 25-year array on a roof with 8 years left is a false economy. A survey should establish this before you sign.
Inverter replacement £800–£1,800 Year 10–15 Panels outlast inverters. Payback models that run 25 years and never replace the inverter are wrong by roughly one replacement.
DNO G99 application up to £400 Systems above 3.68kW per phase Usually handled by the installer, and usually free, but approval takes 4–8 weeks and can come back with conditions.

These bands have not yet been rebuilt from an MCS extraction, so no data month is shown. Ranges are indicative, not a quote.

Common questions

Why does your payback figure differ from the one an installer gave me?
Usually because of self-consumption. A model assuming 70% home use produces a much shorter payback than one assuming 40%. Set the slider to match when your household uses electricity.
Why is there no electricity price inflation in the model?
Future electricity prices cannot be forecast reliably. Leaving inflation out keeps the calculation conservative. You can test a higher future price by changing the import-price input.
Does it include the inverter replacement?
Yes, £1,200 at year 12 by default, and you can set it to zero to see the difference. Panels outlast inverters, so a 25-year model that never replaces one is wrong by roughly one replacement.
Is my data sent anywhere?
No. The calculation runs entirely in your browser. Nothing you type is transmitted to us or to anyone else, and there is no sign-up.

Work out the number before anyone quotes you

Every assumption editable, nothing sent anywhere, no email. It will not give you a quote, but it will tell you whether one is fair.

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