Solar panel payback period in the UK: the official figures, then the sum with every input linked

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.

Figures on this page last checked 24 October 2026. Each carries its own receipt with its own date.

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.

What the Energy Saving Trust says

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.

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.

How payback is actually worked out

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.

• What the system costs to buy and fit.
• What the panels generate in a year, which depends on where you live, which way the roof faces, how steep it is and what shades it.
• How much of that you use yourself instead of buying from the grid. This is the one that moves everything, and it depends on whether anyone is in during the day.
• What you are paid for the rest, the export rate, which is set by whichever supplier you choose to pay you.
• How your bill changes: every unit you use yourself is a unit you did not buy, at whatever your tariff charges.

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?

• Cost: published. The government records what certified installations on existing homes cost per kW, by system size. It is on the cost page.
• Generation: published, as a method. MCS, the certification scheme every installer works to, publishes a table of output per kW for every postcode zone and a formula every installer must use in the written estimate before you sign.
• Self-use: published, as a method. MCS publishes tables of how much of the output a home keeps, by how much electricity it uses and whether anyone is in during the day, and says which column to use when the household's own figures are not known.
• The price of a unit: published, for the cap. Ofgem publishes the unit rate under the price cap each quarter. Your own tariff is on your bill, and nobody publishes that but your supplier.
• Export rate: published, by each supplier. They are all on the export rates table, sorted by who can have them.
• How your bill changes: not published by anyone, because it is the product of the four above and your own house. Anyone who gives you it is giving you their guesses multiplied together.

The sum, with receipts

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.

Input 1: the cost

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.

Input 2: what the panels generate

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.

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.

Input 3: how much of it you use yourself

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.

Input 4: what a unit costs you

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, 26.32p/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.

Input 5: what you are paid for the rest

We use three rows from the export rates table and name them all. First, Fuse Energy's tariff Single Rate Variable Export at 13p/kWh, the highest rate open to anyone on our table when we last read the suppliers' pages. Fuse Energy says in writing that you can take it while buying your electricity from someone else. Second, E.ON Next's tariff Next Flex Export v1 at 6p/kWh, also open to anyone, from one of the large suppliers. The open-to-anyone tier ran 2p/kWh to 13p/kWh when we last read the suppliers' pages, so where your own rate sits in that range moves every figure below. Third, 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. Our supplier pages set out what each asks for before you apply: the E.ON Next page and Octopus page.

The arithmetic, one case in full

London, someone home all day, flat roof, at E.ON Next's 6p/kWh. Every other cell in the tables below is the same four lines with different inputs.

• Generation: 4 kW × 828 kWh per kWp × 1.00 = 3,312 kWh a year.
• Used at home: 32% of 3,312 kWh = 1,060 kWh. Sent out: 2,252 kWh.
• Saved: 1,060 kWh × 26.32p/kWh = £279. Paid: 2,252 kWh × 6p/kWh = £135. Together £414 a year.
• Payback: £8,435 ÷ £414 = about 20 years.

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.

Two export scenarios, not promises

These are two scenarios, not a forecast and not a promise. The only thing that changes between them is who pays you for what you send to the grid. Scenario A is Fuse Energy at 13p/kWh. Scenario B is E.ON Next at 6p/kWh. Both are open to anyone, both are variable, which means the supplier can change them, and both are from the supplier's own page, linked above. Here is the working for the case walked through above, one line per scenario.

Every pound in that table is our arithmetic from the DESNZ retrofit mean for existing homes and the MCS, Ofgem and supplier figures above, not a published figure. A variable export rate can move whenever the supplier says so, and the sum is rebuilt when it does. Your own roof, bill and habits will give a different answer.

Scenario A: every city, at Fuse Energy's 13p/kWh

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, Fuse Energy's export rate of 13p/kWh.

Our arithmetic from the five inputs above, rounded to whole years. A scenario, not a promise.

Scenario B: every city, at E.ON Next's 6p/kWh

The same sum with one change: E.ON Next's open export rate of 6p/kWh.

Our arithmetic from the five inputs above, rounded to whole years. A scenario, not a promise.

The result, if your own supplier pays you 12p/kWh

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.

Our arithmetic from the same inputs with the export rate changed, rounded to whole years.

You will have noticed that scenario B, 18 to 31 years, is a long way from the Energy Saving Trust's, and that scenario A, 13 to 19 years, and the customer-rate table, 13 to 20 years, narrow 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 customer-rate table exists: it runs our sum at that rate, taken from a supplier that actually pays it, and scenario A runs it at a rate just above it that anyone can have. 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.

What moves payback most

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:

• Being in during the day. Every unit used at home is worth the full unit rate. Every unit sent out is worth the export rate, a fraction of it. MCS's tables above show the gap between the "home all day" and "out all day" columns, and it is the biggest single lever you have. Running the washing machine at noon is not a joke; it is the sum.
• A battery. It moves output from the export column to the home column. MCS's tables show the share rising with battery size, and the battery has a cost of its own: MCS's average for one is on the cost page. We have not done the battery sum here because it needs a battery size, and picking one would be our guess.
• The export rate. The three tables above are the same house at three rates, and the table runs wider than that, depending on who you are to the supplier. If you are switching supplier anyway, the export rate is part of the price of the switch.
• The VAT change. Solar is zero-rated for now and goes to the reduced rate on a date set in law. The countdown is below. It moves the cost, which moves everything.
• Panels getting older. MCS's method takes no account of panels getting older, and its output estimate is for the first year. Neither MCS document states how fast panels lose output, so we do not either. If someone gives you a rate, ask where it came from.

Where to go from here

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.

Questions people actually ask

Where to go next

• Export rates: what each supplier pays for your exported power.
• Solar panel cost: what a solar system costs.
• Solar panel grants: which grants actually pay for panels.
• All the figures Hearthsum keeps: the hub, with every page on it.