Solar is worth it for most UK homes with a decent roof — but "most" is doing real work in that sentence. Here is how to work out which side of the line your house falls on.
The maths, stripped back
Three things decide it:
- What the system costs you — typically £5,500-£9,500 for a 3-5 kWp domestic install.
- How much you generate — roughly 850-950 kWh per kWp per year on an unshaded south-facing UK roof.
- How much of it you use yourself — because a self-consumed unit is worth 3-5 times an exported one.
Point three is where most online payback calculators quietly flatter the answer.
When solar clearly is worth it
- You are home during the day, or work from home. Self-consumption above 50% transforms the numbers.
- You have an EV and can charge it during daylight hours.
- You have or plan a heat pump. It raises your electricity demand, which raises the value of every generated unit.
- You have a battery. Self-consumption typically goes from ~40% to 70%+.
- Your roof faces south, east or west with little shading.
- You plan to stay put for at least eight years.
When solar is marginal or not worth it
- A heavily shaded roof. Trees, chimneys, dormers or a neighbouring building can cut output by a third or more.
- A north-facing only roof. Do not.
- Very low electricity use — a low-occupancy flat using 1,500 kWh a year has little to displace.
- You are moving within two or three years. Solar adds some value to a property but rarely the full install cost.
- A roof that needs replacing soon. Do the roof first; removing and refitting panels costs real money.
- A listed building or conservation area where planning constraints force expensive compromises.
Realistic payback
For a typical unshaded 4 kWp installation on an occupied 3-bed home:
| Scenario | Annual benefit | Rough payback |
|---|---|---|
| Out all day, no battery | £450 - £600 | 11 - 15 years |
| Home during the day, no battery | £650 - £900 | 8 - 11 years |
| With battery and EV | £900 - £1,300 | 9 - 12 years (higher upfront) |
Panels are typically warrantied for 25 years with a performance guarantee around 85% at year 25. Inverters usually need replacing once, at £800-£1,500, which honest payback figures should include.
Things that improve the answer
- Zero-rated VAT on domestic installations reduces the upfront cost.
- A good Smart Export Guarantee rate. Rates vary widely between suppliers, and you can take an export tariff from a different supplier to your import one. It is worth shopping around after installation.
- Time-of-use tariffs. With a battery, buying cheap overnight electricity and using it at peak adds a second income stream independent of the sun.
The non-financial part
Plenty of households install solar knowing the payback is ten years, because it insulates them from price volatility, reduces carbon, and — with a battery — keeps the lights on during outages. Those are legitimate reasons. Just make the decision knowing the actual numbers rather than a salesperson's best case.
How to check your own case in ten minutes
- Find your annual kWh from a recent bill.
- Look at your roof on a satellite map: orientation, area, shading.
- Get three quotes and compare the stated annual generation and the assumed self-consumption rate.
- Divide the installed cost by the realistic annual benefit. If it comes out under 12 years, it is a sound investment on a 25-year asset.
Read next: solar panels for a 3-bedroom house and Smart Export Guarantee rates.