How long solar panels take to pay for themselves is the question every solar site answers with one confident number and no working. This page gives you the Energy Saving Trust's figures untouched, then does the sum itself with all five inputs linked to the document each came from. Nobody is going to ring you.
One rule governs this page above the others on the site: no input to any calculation is assumed. If we could not find a published figure for something, there is no sum, and the page says which figure is missing. As it turns out, every input has one. The answer they give is not the answer you have been reading elsewhere, and the receipts are below so you can see why.
The Energy Saving Trust publishes payback in years, by city and by how much of the day someone is at home. These are its figures exactly as published. We have not reworked them.
| City | Home all day | Home half the day | Out all day |
|---|---|---|---|
| London | 9 | 9 | 9 |
| Manchester | 10 | 10 | 11 |
| Aberystwyth | 9 | 9 | 10 |
| Stirling | 11 | 11 | 12 |
How long the Energy Saving Trust reckons a system takes to pay for itself, by city and by how much you are at home, based on fuel prices as at July 2026. Worth noting they now publish this in years rather than annual savings, so if a site quotes you an Energy Saving Trust pound figure, it is working from a table that no longer exists.
London 9/9/9 · Manchester 10/10/11 · Aberystwyth 9/9/10 · Stirling 11/11/12 years, fuel prices as at July 2026
years to payback (home all day / home half day / out all day)
Page dated 27 August 2026.
Source: Energy Saving Trust · checked 2026-09-08 · JSON
No figures in this section, on purpose. The sum has five parts, and every site that gives you one number has picked a value for each of them without telling you.
Divide the cost by the yearly saving and you have the payback. Simple sum, five guesses, one confident number. Which of the five do the official sources actually publish?
Every input below is a published figure, linked. The arithmetic is ours and is labelled as ours. We have kept to a 4 kW system with no battery and no shade, in the four cities the Energy Saving Trust uses, in its three occupancy cases, so the two sets of figures can sit side by side. We run it twice, once at the best export rate open to anyone and once at the rate the Trust assumes, which several suppliers pay to their own customers.
4 kW at £2,108.65/kW comes to £8,435, our arithmetic from the DESNZ retrofit mean for existing homes. That is the government's mean for certified installations on existing homes in the small band, times the system size, and nothing else. No battery, no scaffolding surprises.
£2,108.65/kW mean, existing homes only
pounds per kW of total installed capacity (TIC), domestic retrofit installations only (existing homes, not new builds)
Covers 1 April 2025 to 31 March 2026.
Source: DESNZ (from the MCS Installation Database) · checked 2026-09-08 · JSON
This is the sum every MCS-certified installer has to give you in writing before you sign, and the standard says it must come with a warning that output "is impossible to predict with certainty". We use the same sum, with the shade factor at 1.00, which is the standard's own value for a roof with nothing in the way.
Annual output in kWh = system size in kWp x the zone's kWh per kWp figure x a shade factor, which is 1.00 where nothing shades the roof
formula, MIS 3002 Issue 5.0 Appendix B, the estimate every MCS installer must give in writing before contract
Page dated 10 May 2023.
MCS's table gives a figure for every pitch and every direction. We do not pick one, because that would be a guess about your roof. We take two figures the table hands us without a choice: the flat-roof figure, which is the same whichever way the roof faces, and the best cell in the zone. A pitched roof facing south sits near the top of that range, one facing east or west sits lower.
| City | MCS zone | Output per kW of panels, flat roof to best-placed roof |
|---|---|---|
| London | zone 1 (London) | 828 to 985 kWh per kWp a year |
| Manchester | zone 7E (Manchester) | 735 to 866 kWh per kWp a year |
| Aberystwyth | zone 13 (Aberystwyth) | 789 to 922 kWh per kWp a year |
| Stirling | zone 14 (Stirling) | 701 to 835 kWh per kWp a year |
828 to 985 kWh per kWp a year
kWh per kWp of panels, from a flat roof (the table's orientation-free figure) to the table's best cell (south-facing at 37 to 39 degrees), before any shading
Page dated 26 February 2025.
735 to 866 kWh per kWp a year
kWh per kWp of panels, from a flat roof (the table's orientation-free figure) to the table's best cell (south-facing at 37 to 39 degrees), before any shading
Page dated 26 February 2025.
789 to 922 kWh per kWp a year
kWh per kWp of panels, from a flat roof (the table's orientation-free figure) to the table's best cell (south-facing at 35 to 36 degrees), before any shading
Page dated 26 February 2025.
701 to 835 kWh per kWp a year
kWh per kWp of panels, from a flat roof (the table's orientation-free figure) to the table's best cell (south-facing at 39 to 40 degrees), before any shading
Page dated 26 February 2025.
MCS publishes tables for this, by how much electricity the home uses and whether anyone is in during the day. The tables are for a home with no battery, and they fall as the system grows, because a bigger system makes more at midday than an empty house can use. We read the column for a home using 3,500 kWh a year, which is the figure MCS says to use when the household's own bills are not to hand.
| Who is in | Share of the output used at home, MCS table |
|---|---|
| Home all day | 29% to 36% of what the panels make, home all day, no battery |
| Home half the day | 23% to 29% of what the panels make, home half the day, no battery |
| Out all day | 15% to 19% of what the panels make, out all day, no battery |
3,500 kWh a year
kWh of electricity a year, MGD 003 clause 4.3.5, used when the household's own bills are not to hand
Page dated 1 April 2022.
29% to 36% of what the panels make, home all day, no battery
percent of annual generation used in the home, PV only, for a home using 3,500 to 3,999 kWh a year, across generation bands from 2,700 to 4,199 kWh
Page dated 1 April 2022.
23% to 29% of what the panels make, home half the day, no battery
percent of annual generation used in the home, PV only, for a home using 3,500 to 3,999 kWh a year, across generation bands from 2,700 to 4,199 kWh
Page dated 1 April 2022.
15% to 19% of what the panels make, out all day, no battery
percent of annual generation used in the home, PV only, for a home using 3,500 to 3,999 kWh a year, across generation bands from 2,700 to 4,199 kWh
Page dated 1 April 2022.
Every unit you use from the roof is a unit you did not buy. We price it at the electricity unit rate under Ofgem's price cap, 26.11p/kWh, because it is the one published price. What a supplier on the price cap can charge for a unit of electricity this quarter, Great Britain average, paying by direct debit. Ofgem resets it every three months and this page is rebuilt when it does. Your own tariff is the number that matters for you, and it is on your bill. Ofgem has already published the rate for the quarter starting 1 October 2026: 26.32p/kWh. The sum on this page is rebuilt from it when that quarter starts.
26.11p/kWh
pence per kWh of electricity under the price cap, Great Britain average, paying by direct debit, 1 July to 30 September 2026
Covers 1 July 2026 to 30 September 2026.
We use two rows from the export rates table and name them both. First, E.ON Next's tariff Next Flex Export v1 at 6p/kWh, which was the top of the open-to-anyone tier when we last read the suppliers' pages. The bottom of that tier was 2p/kWh, and using it would lengthen every figure below. Second, Octopus's tariff Outgoing Octopus at 12p/kWh, which needs you to buy your electricity from Octopus. We run the sum at that rate because it is the one the Energy Saving Trust assumes, and because it is what a supplier's own customers are actually paid. British Gas's Export Premium, ScottishPower's SmartGen Premium, Good Energy's Solar Savings and OVO's SEG Beyond Exclusive pay their own customers the same rate, as we last read their pages, so this table is the one to read if your electricity comes from any of them. Every row is on the table.
6p/kWh
pence per kWh exported
The source page carries no date. Read 8 September 2026.
12p/kWh
pence per kWh exported
The source page carries no date. Read 8 September 2026.
Source: Octopus Energy · checked 2026-09-08 · JSON
London, someone home all day, flat roof, at the open rate. Every other cell in the tables below is the same four lines with different inputs.
Those pounds are our arithmetic from the DESNZ retrofit mean for existing homes and the MCS, Ofgem and supplier figures above, not published figures. The unit rate changes every quarter and the export rate whenever the supplier says so, so the sum is rebuilt when either does.
Each cell runs from the zone's best-placed roof to a flat one. 4 kW, no battery, no shade, a home using 3,500 kWh a year, this quarter's cap rate, E.ON Next's open export rate of 6p/kWh.
| City | Home all day | Home half the day | Out all day |
|---|---|---|---|
| London | 18 to 20 years | 20 to 23 years | 24 to 27 years |
| Manchester | 20 to 22 years | 22 to 24 years | 26 to 29 years |
| Aberystwyth | 19 to 21 years | 21 to 23 years | 25 to 28 years |
| Stirling | 20 to 23 years | 23 to 25 years | 27 to 31 years |
Our arithmetic from the five inputs above, rounded to whole years.
The same sum with one change: the export rate is Octopus's Outgoing Octopus at 12p/kWh, the rate the Energy Saving Trust assumes. British Gas's Export Premium, ScottishPower's SmartGen Premium, Good Energy's Solar Savings and OVO's SEG Beyond Exclusive pay their own customers the same rate, as we last read their pages, so this table is the one to read if your electricity comes from any of them.
| City | Home all day | Home half the day | Out all day |
|---|---|---|---|
| London | 13 to 15 years | 14 to 16 years | 15 to 18 years |
| Manchester | 15 to 17 years | 16 to 18 years | 17 to 20 years |
| Aberystwyth | 14 to 16 years | 15 to 17 years | 16 to 18 years |
| Stirling | 15 to 18 years | 16 to 19 years | 18 to 20 years |
Our arithmetic from the same inputs with the export rate changed, rounded to whole years.
Change any input and the answer moves. That is why nobody honest gives you one number.
You will have noticed that our first table, 18 to 31 years, is a long way from the Energy Saving Trust's, and that the second, 13 to 20 years, narrows it. We have not reworked the Trust's figures and we are not calling them wrong. Two of its inputs are on its page, and both differ from ours. It assumes an export rate of about 12p/kWh, which is why the second table exists: it runs our sum at that rate, taken from a supplier that actually pays it. And its worked example costs around £7,600 for a 4.5 kWp system, which sits below the £8,435 our sum pays for a 4 kW one, because the Trust's cost is a modelled example and ours is the government's mean of what existing homes actually paid. What the Trust assumes for generation, and for the share of it used at home, is not on its page, so the rest of the gap cannot be pinned on anything, and we would rather leave it unexplained than guess. What we can say is that a home using more electricity in daylight than MCS's default, or a battery, would each pull our figures down further. Those are the things worth asking about, and the next section is about them.
About 12p/kWh
pence per kWh exported, the Smart Export Guarantee rate the Energy Saving Trust's payback modelling assumes
Page dated 27 August 2026.
Source: Energy Saving Trust · checked 2026-09-08 · JSON
Around £7,600 for a 4.5 kWp system
pounds per whole installation
Page dated 27 August 2026.
Source: Energy Saving Trust · checked 2026-09-08 · JSON
No figures in this section either, except where a source publishes one and it is elsewhere on the site. In rough order of how much they matter:
No adjustment for the age of the panels
MGD 003 clause 4.4.2, as applied to the self-use estimate
Page dated 1 April 2022.
0% until 31 March 2027, then 5% from 1 April 2027
percent, on installation in residential accommodation
Covers 1 April 2022 to 31 March 2027.
The cost page has the government's figures by system size, with and without a battery. The export rates table has every supplier's rate, sorted by who can have it. The grants page has what actually pays towards panels, nation by nation, which is the one thing that shortens payback more than any of the above, if you qualify.
The Energy Saving Trust's table reads London 9/9/9 · Manchester 10/10/11 · Aberystwyth 9/9/10 · Stirling 11/11/12 years, fuel prices as at July 2026: three figures for each city, for someone home all day, home half the day and out all day. Our own sum, with every input published and linked above, comes out at 13 to 31 years for a 4 kW system with no battery, depending on the city, who is in, the roof and which export rate you can get. The gap between those two answers is the honest answer: it depends on inputs nobody can publish for your house.
Partly the export rate. The Trust assumes about 12p/kWh, our first table uses the best rate open to anyone, and our second table uses a supplier's own-customer rate at the Trust's figure, which narrows the gap. Partly the cost: the Trust's example is around £7,600 for a 4.5 kWp system, and ours is the government's mean for existing homes. The rest we cannot attribute, because the Trust's page does not say what it assumes for generation or for the share used at home, and we would rather show you a longer figure with receipts than a shorter one without.
It moves output from the export rate to the full unit rate, and MCS's tables show the home's share rising with battery size. It also costs just around £9,000 on MCS's average of every battery fitted last year. Whether the first outweighs the second depends on the battery size, which is why there is no battery sum on this page.
The best row on the table that you actually qualify for. The open tier runs 2p/kWh to 6p/kWh as we last read it, and several suppliers pay their own customers 12p/kWh, which is the rate our second table uses. Each row links to the supplier's own page with the date we read it.
Yes, in one direction. Solar is zero-rated until 31 March 2027 and goes to the reduced rate the day after, so the same system bought later costs more against the same saving and takes longer to pay back.