UK Solar Panel Payback Calculator

How to use this calculator

1. Enter the system size in kWp and the installed cost from your quote.
2. Add any grant or rebate you are sure of. Most households have none, because there are no dedicated Government solar grants.
3. Check the yearly output per kWp. Your installer's estimate for your roof is better than the starting figure.
4. Set the share of the electricity you use at home. This moves the answer more than anything else, so try a few values.
5. Enter the price you pay per unit and the export rate your supplier offers. The payback period, the year-by-year table and the working appear straight away.

The result is a planning estimate, not a quote or financial advice. The starting figures were reviewed on 12 October 2026; prices and export rates change, so replace them with your own.

What do I need to enter?

• System size — the peak output in kWp from your quote, up to 100. It must be above 0.
• Installed cost and Grants and rebates — the quote price, and money you will definitely receive. Grants cannot exceed the cost.
• Yearly output per kWp — kWh made per kWp a year at your roof's angle and shading, up to 3,000. It must be above 0.
• Share used at home — 0% to 100% of the electricity you use yourself. The rest is exported.
• Electricity price you avoid — in pence per kWh, up to 200. It is what each unit you use yourself saves.
• Export rate — pence per kWh from your Smart Export Guarantee tariff, up to 200. It is held flat for 25 years.
• Yearly electricity price rise — 0% to 20% a year.
• Yearly panel degradation — 0% to 5% of output lost each year.
• Inverter replacement cost and Inverter replaced in — the cost, and the year from 1 to 25 it falls. Enter 0 for no replacement.

What do the results show?

• Payback period — the main figure, in years: when the total saved stays above the net cost, or Over 25 years if it never does.
• Payback in years and months — the same answer in plain words.
• Net cost after grants — installed cost less grants and rebates.
• Saving in year 1 and Total saved over 25 years — first-year bill savings plus export income, and the running total after the inverter bill.
• Table — each year's bill saving, export income and total saved so far.
• Summary — year 1 generation and savings, the cost and payback year, and payback at 20% to 60% used at home.

How is solar panel payback calculated?

Add up what the panels save each year until the total passes what the system cost. The payback is the point after which the savings stay ahead, so an inverter bill that puts a paid-back system back in the red moves the answer to when it recovers.

Take the calculator's defaults: a 4.6 kWp system costing £7,400, making 910 kWh per kWp a year. That is 4,186 kWh in year 1. With 30% used at home at 26.3p per kWh, the bill saving is £330; the rest is exported at 12p per kWh for £352, so year 1 saves £682. The electricity price rises 2% a year and the panels lose 0.5% of their output a year, and a £1,200 inverter replacement falls in year 12. The total saved stays above the £7,400 cost from year 13, after 12 years 3 months. Over 25 years it saves £16,999, a net gain of £9,599.

The £1,200 inverter replacement in year 12 is what moves the default payback from 10.6 years without it to 12.3 years with it. Set the cost to 0 to see the payback without it.

How long do solar panels take to pay for themselves in the UK?

Published examples run from about 9 to 12 years. They differ because they assume different costs, prices and amounts used at home, which is why the calculator lets you change each one.

What did Which? find?

Which? used a 4.6 kWp, ten-panel system on a south-facing roof, costing £7,400, with electricity at 25.8p per kWh (its June 2025 price) and a 12p export rate. Its London example saves £285 on bills and earns £370 from exports a year. It does not include maintenance or an inverter replacement.

What did the Energy Saving Trust find?

The Energy Saving Trust quotes a typical home system of around 4.5 kWp costing around £7,600. Its paybacks include export payments and use fuel prices from July 2026. The longer figure in each row is for a household that is out all day.

Both sources show the same pattern: the further north, the longer it takes, because there is less sunshine to turn into savings.

How much of the electricity will I use myself?

The electricity you use saves you the full unit price, while the electricity you export earns only the export rate, so the share you use at home drives the answer. A UCL study of 302 UK homes found they used 45% of their solar generation on average. The Which? London example implies about 26%: its £285 of bill savings at 25.8p is about 1,105 kWh used at home, against about 3,083 kWh exported for £370 at 12p. The table runs the default inputs at five different shares.

Being at home in the day, running a dishwasher or washing machine at midday, or adding a battery all raise the share. A battery also adds to the cost, so enter both changes together.

What is the Smart Export Guarantee?

Under Ofgem's Smart Export Guarantee (SEG), certain electricity suppliers must pay you for the electricity you export. The supplier sets the rate, the contract length and the other terms, but the rate must always be above zero, and payments are based on export meter readings.

• Rates vary widely. Which? found fixed rates from 1p to 16p per kWh in April 2026.
• You need an MCS-certified installation and a meter that gives half-hourly export readings, which usually means a smart meter.
• The scheme covers England, Scotland and Wales. In Northern Ireland, ask your supplier about an export tariff.

The calculator holds the export rate flat for 25 years, because supplier rates are not linked to inflation. Enter the rate you have been offered, not the best one you have seen, and remember it can change when the contract ends.

Is there VAT on solar panels, and are there grants?

HMRC's VAT Notice 708/6 zero-rates solar panels installed in residential accommodation from 1 May 2023 to 31 March 2027, and says the reduced rate of 5% applies from 1 April 2027. The cost on your quote already includes whichever applies, so there is no VAT field to fill in.

The Energy Saving Trust says there are no dedicated UK Government solar panel grants, although other schemes and some energy suppliers may offer support. The grants field starts at £0 for that reason.

When does the inverter need replacing?

The Energy Saving Trust says panels should last 25 years or more, but an inverter needs replacing after around 12 years. The calculator therefore deducts a replacement in year 12 by default. Change the cost and the year to match your inverter and warranty, or set the cost to 0 if you do not expect to replace it.

Panels also lose a little output each year. A review of field studies by NREL researchers, Photovoltaic Degradation Rates, found a median of 0.5% a year, which is the starting value.

What does this calculator not include?

• Roof direction, tilt and shading. They are inside the yearly output you enter.
• A battery, an electric car, or a time-of-use tariff.
• Loan interest or the return you could earn by investing the money instead.
• Cleaning, maintenance, insurance, or any change in the value of your home.
• Income tax on export payments or any change in your tax position.

To compare solar with another use of the money, use the ROI Calculator or the Compound Interest Calculator. Living in the US? Use the US Solar Panel Payback Calculator, which starts from US prices and explains net metering.

Sources for the figures on this page

• Which?: Are solar panels worth it?. The paybacks by city, and the £7,400, 25.8p and 12p assumptions.
• Energy Saving Trust: Solar panels. Typical size and cost, paybacks, grants and the 12-year inverter.
• Which?: Smart Export Guarantee explained. April 2026 rates and the MCS and meter requirements.
• Ofgem: Smart Export Guarantee (SEG). Suppliers set rates, which must be above zero.
• Ofgem: Energy price cap unit rates and standing charges. The 26.32p per kWh average for 1 October to 31 December 2026.
• GOV.UK: VAT on energy-saving materials and heating equipment (Notice 708/6). The zero rate to 31 March 2027 and 5% after.
• McKenna, Pless and Darby (UCL, 2018): Solar photovoltaic self-consumption in the UK residential sector. The 45% average across 302 homes.
• Jordan and Kurtz (NREL, 2013): Photovoltaic degradation rates, an analytical review. The 0.5% a year median.

This is general information, not financial or installation advice. Prices, export rates and tax rules change, so check the linked pages and get quotes from MCS-certified installers.

Frequently asked questions