The short version
- A 4kW system costs roughly £6,000–£8,000 installed, at 0% VAT.
- It generates around 3,400–4,000 kWh a year on a decent south-facing roof.
- Realistic payback is 10–15 years, depending mostly on your export tariff.
- Panels are warranted for 25 years and typically still produce ~85% of their rated output at that point.
- Choosing the right SEG tariff can be worth £200 a year. Most people never look.
Solar in Britain suffers from two opposite bad arguments. One says it is pointless because we do not get enough sun. The other says it pays for itself in five years. Neither is true.
Here are the actual numbers.
What a UK roof actually produces
Britain gets meaningfully less irradiance than southern Europe, but solar panels work on daylight rather than heat — and they are in fact slightly more efficient in cooler conditions. A well-oriented 4kW system in England or Wales generates roughly 3,400 to 4,000 kWh a year.
What moves that figure:
- Orientation. South is best. East or west typically costs you 15–20%, though it spreads generation across the morning and evening, which can suit your usage better.
- Pitch. Around 30–40° is close to optimal.
- Shading. The one that ruins systems. A chimney or tree shading part of an array can cut output disproportionately unless the design accounts for it with optimisers or microinverters.
- Latitude. Cornwall outperforms Cumbria, but less than people assume — roughly 10–15% across England and Wales.
What that generation is worth
This is where most estimates go wrong, because a generated kWh is worth two very different amounts depending on whether you use it or export it.
- Electricity you use yourself replaces a unit you would have bought at 26.11p.
- Electricity you export earns whatever your Smart Export Guarantee tariff pays — typically 6p to 15p.
Without a battery, a typical household self-consumes only 30–50% of what it generates, because peak production is midday when the house is often empty.
A worked example
A 4kW system generating 3,700 kWh a year, with 35% self-consumption:
| SEG tariff | Self-used (1,295 kWh) | Exported (2,405 kWh) | Total per year | Payback on £7,000 |
|---|---|---|---|---|
| Low (6p) | £338 | £144 | £482 | 14.5 years |
| Average (13p) | £338 | £313 | £651 | 10.8 years |
| Strong (15.1p) | £338 | £363 | £701 | 10.0 years |
The panels are identical in all three rows. The only variable is the export tariff, and it moves payback by four and a half years.
The most underrated decision in domestic solar is which supplier you export to. SEG rates are not regulated to a floor beyond being above zero, and the spread across the market is enormous. Some suppliers pay around 1–4p. The best widely available flat rates are around 15p. Switching costs you an afternoon.
Do you need a battery?
A battery raises self-consumption from around 35% to 70% or more, by storing midday generation for the evening. On the example above that lifts annual value from roughly £700 to roughly £840.
But a system with storage costs £10,000–£14,000 rather than £7,000. So the battery adds about £140 a year of solar value for £3,000–£7,000 of cost. On solar self-consumption alone, a battery usually lengthens payback rather than shortening it.
Batteries can still be a sound purchase — but usually for reasons other than solar: cheap overnight electricity on a time-of-use tariff, export arbitrage on tariffs that pay a premium at peak hours, or backup during outages. Judge a battery on those merits, not on the solar arithmetic.
When solar is not worth it
Being straight about this matters more than the sales pitch:
- Heavily shaded roofs. Optimisers help, but they do not manufacture sunlight.
- North-facing only. Output drops far enough that payback stretches past the warranty.
- A roof needing replacement within a few years. Do the roof first — removing and refitting an array is an avoidable expense.
- Moving house soon. Solar adds some value to a property, but rarely the full installed cost.
- Very low electricity use. If you use 1,500 kWh a year, most generation is exported at export rates and the economics weaken considerably.
The 0% VAT window
Domestic solar, battery storage and installation currently attract 0% VAT instead of 20%. On a £7,000 system that is worth around £1,170.
This relief is due to end on 31 March 2027. If it does, the same installation becomes materially more expensive overnight, and the payback figures above stretch accordingly.
Solar and heat pumps together
These work better in combination than either does alone. A heat pump substantially increases your electricity consumption, which raises the share of your solar generation you use yourself — and self-used units are worth 26.11p rather than an export rate.
The caveat is seasonal mismatch: your heat pump works hardest in December, when your panels produce least. Solar will not power your heating through winter. What it does well is cover hot water and shoulder-season heating, and lift self-consumption across the year. Our running-cost comparison covers the heat pump side.
Where ByEco stands right now. Boiler Upgrade Scheme applications can only be submitted by an MCS-certified installer. ByEco is currently going through MCS and TrustMark certification, so we cannot lodge a BUS application for you yet. If you are planning work, talk to us about timing — we will tell you honestly whether we can help on your schedule or whether you are better off going elsewhere.
The verdict
For a household with a reasonable roof, decent daytime electricity use and a sensible export tariff, solar in the UK pays back in roughly ten to twelve years and then produces close to free electricity for another fifteen. That is a solid long-term return, not a quick win.
Anyone quoting you a five-year payback is either assuming a battery arbitrage strategy they have not explained, or they are wrong.
Sources
Every figure on this page was checked against primary sources on 22 August 2026. Grant rules and energy prices change — if you are reading this much later, verify before acting.
- Ofgem — Energy price cap unit rates and standing charges
- Ofgem — Smart Export Guarantee (SEG)
- Which? — Smart Export Guarantee rates compared
Talk it through
Every home is different, and the honest answer to “is this worth it?” depends on your heat demand, your insulation and your tariff. Send us your postcode and we will give you a realistic figure rather than a hopeful one.
