Solar Panel Savings and Payback Calculator

What Does the Solar Panel Payback Calculator Work Out?

The solar panel payback calculator works out four figures for your home: your yearly saving on bills, your yearly export income, the years it takes to pay back the cost, and a 25-year net figure, plus a Good fit, Borderline or Poor fit verdict. The table below lists each output with its meaning and unit.

Payback is counted in years and savings in pounds a year, and the card keeps the two apart.

This calculator starts from a cost you already have: an installer's quote, or our estimate for a system size. It suits a reader holding a quote. A reader starting from the home itself gets cost, savings and payback in one calculator on the home page, which sizes and prices the system first. Both tools run on one engine and one data table, and both sit with the output and battery tools among our UK solar calculators. Each output above needs a few inputs from you.

What You Need to Run the Payback Calculator

You need five things: the installed cost (or our estimate), your postcode, your roof direction and shade, your yearly electricity use or monthly bill, and your unit and export rates; every one has a default you can keep. The calculator estimates from the defaults until you change them, and the table shows where each default comes from.

The unit rate is the price you pay for each kWh you buy. A monthly bill typed in place of the yearly use is converted to kWh at your unit rate, after the standing charge is taken off. System size is entered in kWp (kilowatt peak), the rated output of the panels. The yearly kWh a roof generates at a postcode is the subject of our UK solar power calculator, which shows that figure alone.

A Northern Ireland postcode changes the default rates, because the price cap does not apply there. The first input, the cost, has two routes.

Your Installed Cost: Quote or Our Estimate?

Use your quote if you have one, because it is the price you would actually pay; use our estimate if you do not. The two routes differ in where the cost comes from.

We give the estimate and installers give the quote, after a survey of your own roof. With the cost and your use entered, the calculator builds the yearly saving.

How the Calculator Works Out Your Yearly Saving and Export Income

The calculator splits what your panels generate in a year into the electricity you use at home, valued at your unit rate, and the electricity you export, valued at your export rate; the two together are your yearly benefit. The table shows the three parts in order, with the line for a 4 kWp reference home: no battery, 2,500 kWh of yearly use, home some of the day, no postcode (so the stand-in generation figure), a south roof at 35 degrees with no shade, and the default unit and export rates.

The share of your generation used at home comes from three answers: when you use most electricity, how your generation compares with your yearly use, and the battery choice. Electricity used at home is worth more than electricity exported while your unit rate (26.32p per kWh by default) is above your export rate (13p per kWh by default). Solar does not reduce the standing charge of 54.83p a day, so the saving leaves it out.

Export income needs an export tariff under the Smart Export Guarantee, which started on 1 January 2020 and covers Great Britain. The scheme asks for the installation and installer to be MCS certified or equivalent, and for a meter that records your exports. It is not the Feed-in Tariff, which closed to new applicants on 1 April 2019. The calculator assumes your network operator sets no export limit; an export limit lowers export income. The saving plus the export income is the bottom line of the payback sum.

How to Calculate Solar Panel Payback

To calculate solar panel payback, divide the installed cost by the yearly benefit (saving on bills plus export income); the answer is the number of years. The sum has four lines.

1. Generation (kWh) = system size (kWp) x yield (kWh per kWp) x shade factor
2. Yearly saving (£) = kWh used at home x unit rate
3. Export income (£) = kWh exported x export rate
4. Payback (years) = installed cost divided by (yearly saving + export income)

The result is simple payback at today's prices. The calculator holds the unit rate and the export rate flat for every year and does not forecast them. A line under the result shows the payback at a unit rate 20% lower and 20% higher, so the effect of a price change is visible without a forecast. The years that savings take to cover the cost across UK homes are the subject of our guide to the payback period for solar panels. The same four lines fit in a spreadsheet.

Solar Panel Payback in a Spreadsheet

The payback sum fits in eight rows of a spreadsheet, one input per row and the payback in the last. The table gives each row, its formula in words and an illustration for the same reference home, with the share used at home that our self-use table gives it.

A spreadsheet gives the same simple payback as the calculator. It does not give the 25-year figure, the verdict or the VAT clock, and it has no shade factor unless you add one. The calculator does the same sum and shows it on the result card.

How to Read Your Payback Result

Your result card shows the payback in years beside the unit rate, export rate and cost it used, so you can see what the number depends on. The table explains each field on the card.

The VAT clock looks ahead to 1 April 2027. Home solar and batteries carry 0% VAT until 31 March 2027 and 5% from 1 April 2027 (HMRC VAT Notice 708/6). The card shows your cost at 5% VAT, rounded, and the longer payback next to today's.

Read the payback years against the life of the system. Solar panels "should last 25 years or more" (Energy Saving Trust, page updated 1 October 2026), so a payback well inside 25 years leaves years of saving after the cost is covered. The verdict turns that reading into one of three words.

What Good Fit, Borderline and Poor Fit Mean

Good fit means the payback sits inside our Good fit range with no Poor fit trigger; Borderline means a longer payback that is still inside our Borderline range. Poor fit means longer than that, or a trigger such as a north-facing roof or heavy shade. The verdict decides what the card shows next.

A north-facing roof is a Poor fit in this calculator whatever the payback years, because it generates the least of the eight directions. The verdict for solar on a UK home in general, across roof, use and years in the home, is on our page about whether solar panels are worth it in the UK. One field on the card looks past the payback year.

What the 25-Year Figure Includes

The 25-year figure adds up each year's saving and export income for 25 years, minus the installed cost and one inverter replacement, with output falling a little each year. It rests on three assumptions.

• Output loss of 0.5% a year, from the second year (our assumption)
• One inverter replacement at around £800 (Energy Saving Trust, last updated 13 August 2026)
• Unit rate and export rate held at today's values for all 25 years

The payback years leave the inverter out; only the 25-year figure counts it. A result is one set of inputs, and changing one input gives a second result to compare.

Change One Input and Run It Again

Change one input at a time and run it again; the four reruns below show which choice moves your payback most.

• Switch the battery between none, add one and show both
• Replace the default export rate with the rate on your own tariff
• Move the answer about when you use most electricity
• Swap your quote for our estimate, or the other way round

The result updates after each change, and the address bar keeps your answers (never your postcode) so a rerun can be shared. Two reruns need a note.

With and Without a Battery

Choose "Show both" to see panels alone and panels with a battery side by side; the battery raises the share you use at home but adds cost, so payback can go up or down. The battery column adds the battery price to the cost of the panels.

A battery price always appears with its size in kWh, and the panels stay in kWp. The price is worked on the DESNZ median per kWh for the battery's size band and rounded to the nearest £100, and the card names the median and its period. The battery column counts charging from your own panels only. Charging on a cheaper overnight rate is not in the sum, and a replacement battery inside the 25 years is not counted. The fitted price of the two together is on our page about solar panels with a battery.

Your Export Tariff

Enter the export rate on your own tariff; the default is 13p per kWh. That default is our calculation from Ofgem figures: Smart Export Guarantee payments divided by the kWh exported, 1 April 2024 to 31 March 2025. Each supplier sets its own export rate, so your tariff's rate replaces the default.

Rerun the calculator at your tariff's rate and read the export income line again. A tariff that asks you to buy your electricity from the same supplier changes two inputs, so enter that supplier's unit rate as well. The rules for payment, meters and certificates are on our page about how the Smart Export Guarantee works. A rerun that still says Good fit or Borderline leads to the next step, a survey.

Get a Free Survey From MCS-Registered Installers After Your Result

A Good fit or Borderline result shows the survey step. We give the estimate, Leads 2 Trade arranges the survey and installers give you a quote after the visit. The request has three steps.

1. You request a survey under your result.
2. Leads 2 Trade arranges the survey.
3. Installers give you the quote after the visit.

Leads 2 Trade says a solar panel installer must be MCS registered to join its supplier network.

You will get phone calls. That is how surveys are arranged. We are paid by Leads 2 Trade Limited when a homeowner we refer asks for a survey. You are never charged. It does not change our figures.

We do not refer tenants, people who are only researching, or Poor fit results. The request form is not open on this site yet. Before you ask: check your roof for solar.

Solar Payback Calculator Questions