Solar panel payback and savings calculator
Would solar panels pay off on your roof? Enter your system size, cost and where you live, and see how much they could make, save on bills and earn from export, plus whether charging your EV from them helps. Results update as you type.
Your inputs
Typical home system 4.5 kWp, about 12 panels (Energy Saving Trust)
Energy Saving Trust typical cost for 4.5 kWp: about £7,600. Use your quote.
PVGIS 5.3, south-facing, 35° tilt, 14% system losses
East/west: 15–20% less than south (EST); we use 17.5%
Higher if someone is home in the day or you run appliances on timers
Ofgem cap average Oct–Dec 2026, GB, 0% VAT
Outgoing Octopus flat rate 12p; EST says “around 12p”
Only possible if the car is home and plugged in during the day. 0 if no EV.
Use your night rate if you are on an EV tariff, e.g. 6.5p (Intelligent Octopus Go, from 6.5p, checked 31 Oct 2026)
Our assumption; check your panel warranty
EST: replace the inverter after about 12 years. Cost is our estimate.
Result
Adjust inputs to calculate
Breakdown
Cumulative net position over 25 years
Starts at minus the system cost, then adds each year's saving (with panel degradation) and subtracts an inverter replacement in year 12.
What your result means: the headline is the estimated saving in year one. Divide the system cost by it for a rough payback time; the chart shows when you break even over 25 years, allowing for panels slowly losing output and a new inverter in year 12. Using more of your own power (rather than exporting it) usually shortens payback.
Estimates for information only, not financial advice. Prices, grants and rates change, so check them with the supplier or installer before you decide. Get at least three quotes from MCS-certified installers. See our terms.
How we calculate
- Generation: system size (kWp) × yearly yield for your region (kWh per kWp, from PVGIS 5.3 for a south-facing 35° roof with 14% losses) × a direction factor (100% south, 95% south-east/west, 82.5% east or west). Output falls by the degradation rate each year.
- Self-use: the share you use at home saves the import price on each kWh.
- EV charging from solar: spare solar (after home use) sent to your car saves what you would otherwise pay to charge it, but you lose the export payment for those kWh. If your night EV rate (for example 6.5p) is below your export rate (12p), exporting and charging overnight is worth more, and the calculator tells you.
- Export: everything left is exported at your Smart Export Guarantee rate.
- Payback: the first year in which the cumulative savings, minus the installed cost and the year-12 inverter replacement, reach zero. Prices are held flat (today's money); no interest, financing or maintenance costs are included.
Sources and last updated
All figures checked on 27 October 2026 unless stated. Every default can be changed.
| Figure | Default | Source (date) |
|---|---|---|
| Import price | 26.32p/kWh | Ofgem price cap, 1 Oct–31 Dec 2026, published 26 Aug 2026. GB average, Direct Debit; 0% VAT on domestic electricity 1 Oct 2026–30 Jun 2027 (HMRC VAT Notice 701/19, checked 2 Nov 2026). |
| System size and cost | 4.5 kWp, £7,600 | Energy Saving Trust: Solar panels |
| Yield by region | 859–1,122 kWh/kWp | EU JRC PVGIS 5.3 (SARAH-3 data), queried 27 Oct 2026 for each city listed, south-facing, 35° tilt, 14% losses |
| East/west penalty | 17.5% | Energy Saving Trust: Solar panels (“around 15–20% less”) |
| Export rate | 12p/kWh | Octopus Energy: Outgoing Octopus (flat 12p); EST “around 12p” |
| Inverter life | ~12 years | Energy Saving Trust: Solar panels |
| Self-use 40%, degradation 0.5%/yr, inverter £1,000 | — | Our assumptions, not from a published source. Change them to match your quote. |
Frequently asked questions
What about Guernsey?
The GB figures here (Ofgem cap, Smart Export Guarantee, PVGIS regions) do not apply in Guernsey. Guernsey Electricity's Standard tariff is 26.01p/kWh (checked 3 Oct 2026), close to the GB cap, and Guernsey gets more sun than most of the UK. Plymouth (1,121 kWh/kWp) is the nearest region in the list. Guernsey Electricity's buy-back rate is 9.9p/kWh (no VAT or GST; checked 2 Nov 2026), so enter 9.9p as the export rate.
How long do solar panels take to pay back in the UK?
With the defaults (4.5 kWp, £7,600, London, 40% self-use, 12p export, 26.32p import) the calculator shows about 9 years. The Energy Saving Trust gives 9 to 12 years depending on location and how much you are at home (fuel prices as of July 2026). Your roof, quote and tariff matter most.
Is it worth charging my EV from solar?
It depends on what you would otherwise pay. Spare solar sent to the car saves your charging rate but loses the export payment. If you would otherwise charge at the 26.32p cap rate, solar charging is worth about 14p per kWh more than exporting at 12p. If you are on an EV tariff at about 6.5p overnight, exporting at 12p and charging at night is worth more.
What is the Smart Export Guarantee?
A scheme in England, Scotland and Wales under which larger suppliers must offer a payment for electricity you export. Rates are set by each supplier; Outgoing Octopus pays a flat 12p per kWh (checked 27 Oct 2026). You need a smart meter and usually an MCS-certified installation.
Do I need planning permission?
Usually not: rooftop solar is normally permitted development, but listed buildings, conservation areas and national parks can have restrictions. Your installer registers the system with your network operator (EST).
More in the solar panel payback guide and the other home-energy tools. Your inputs stay in your browser; see our privacy notice.