Ask this question and you’ll get answers ranging from “five years” to “never”. The truth sits in between, and it depends on three numbers you can check yourself. The Energy Saving Trust puts typical payback at nine to twelve years across the UK once export payments are included (figures based on July 2026 fuel prices) — nine years in London, up to twelve in Stirling. Here’s the maths behind that, laid out honestly.
The three numbers that decide it
Every solar payback calculation comes down to:
- What the system costs to install.
- How much electricity it generates each year.
- What each unit is worth — and that depends on whether you use it or export it.
Get those three right and the rest is division.
Number one: what the system costs
The Energy Saving Trust says a typical domestic system is around 4.5kWp and costs around £7,600 to install. Roof access, panel choice and whether the roof covering needs work all move that figure, so treat it as a midpoint rather than a promise.
One genuine help: solar panel and battery installations on homes currently carry 0% VAT, running until 31 March 2027, after which the rate reverts to 5%. That zero rate is already reflected in the prices you’ll be quoted.
Number two: what it generates
Generation depends on system size, roof orientation, shading and where you live — the Energy Saving Trust notes that areas further south get more direct sunlight, which is good news here in East Kent.
For the worked example below we’ll use 4,000kWh a year from a 4.5kWp system. That’s a representative round figure for a well-oriented, unshaded roof in the far south east — not a prediction for your house. A proper MCS quote includes a site-specific generation estimate based on your actual roof, and that’s the number you should hold your installer to.
Number three: self-use vs export — where the money really is
This is the part most sales pitches skate over. A unit of solar electricity is worth one of two amounts:
- Used in your home: it replaces a unit you’d have bought from the grid. Under the current Ofgem price cap (1 July to 30 September 2026), the average electricity unit rate is 26.11p/kWh — call it 26p.
- Exported to the grid: you’re paid via the Smart Export Guarantee, and rates vary hugely — from around 1p to 25p per kWh depending on tariff. As a real reference point, Outgoing Octopus currently pays 12p/kWh on its variable tariff.
A self-used unit is worth roughly double an exported one. That’s why when you use electricity matters as much as how much you generate.
One eligibility point worth knowing: SEG payments require an MCS-certified installation and a meter capable of half-hourly export readings — typically a smart meter. It’s one practical reason to insist on an MCS-accredited installer, whoever you use.
The worked example
These are round, representative figures — not a quote. Your roof, usage pattern and tariff will move every line.
| Item | Figure |
|---|---|
| System size | 4.5kWp |
| Installed cost | £7,600 |
| Annual generation | 4,000kWh |
| Self-used (assume 40%) | 1,600kWh × 26p = £416 |
| Exported (60%) | 2,400kWh × 12p = £288 |
| Annual benefit | £704 |
| Simple payback | £7,600 ÷ £704 ≈ 11 years |
That 40% self-use figure is an assumption for a household with someone in for part of the day. Shift it and the answer shifts too:
- Out all day (25% self-use): £260 saved + £360 exported = £620 a year, so about 12 years.
- Home most days, or shifting washing and dishwasher runs into daylight (70% self-use): £728 + £144 = £872 a year, so under 9 years — before any battery cost.
A battery pushes self-use up further, but it also adds thousands to the install cost, so it doesn’t automatically shorten payback. It’s a separate sum worth doing properly.
Reassuringly, our rough 9–12 year range lands right where the Energy Saving Trust’s own payback table does.
What the simple sum leaves out
Honesty cuts both ways, so here’s what “cost ÷ annual saving” ignores — the Energy Saving Trust itself cautions against leaning too hard on simple payback:
- Electricity prices move. The cap rose from 24.67p to 26.11p per kWh in July 2026. If prices rise, payback shortens; if they fall, it stretches.
- The inverter won’t last as long as the panels. Panels should run 25 years or more, but expect to replace the inverter after around 12 years.
- Export rates aren’t guaranteed. SEG tariffs only have to be above zero, and suppliers change them.
- The standing charge stays. Solar cuts your unit consumption, not the daily 57.19p standing charge.
The honest bottom line
For a typical UK home, solar pays for itself in roughly nine to twelve years, then keeps generating for a decade or more beyond that. The single biggest lever you control is self-use: every unit you consume in daylight is worth about twice what an exported one earns. Run the sums with your own annual usage and a site-specific generation estimate before you sign anything — and if an installer’s payback claim looks dramatically better than the maths above, ask them to show their working. Our own Sigenergy and Fox ESS packages are priced up front, subject to survey, so you can run the same sums on them.
