Save £400–£700 a Year on Electricity With Solar — Here's the Honest Maths

For most owner-occupiers with a decent roof, yes — but "worth it" depends on your bills, your roof direction and how much power you use during daylight. A typical 4kW system costs around £5,500–£8,000 and can trim a £1,500-a-year bill by roughly £400–£700, giving a payback of about 7–12 years on panels warrantied to last 25 years or more. They're least worth it if your bills are small, you're out all day with no battery, or you're planning to move soon. We quote ranges, not guarantees — the honest figure only comes from a survey of your specific home (as at July 2026).

Realistically, a typical 4kW system saves most UK homes about £400–£700 a year at 2026 prices — not the "£1,000+" some ads imply. Savings come from two places: electricity you use yourself instead of buying (worth ~26–28p a unit at the July 2026 price cap) and surplus you export under the Smart Export Guarantee (around 12p with Octopus Outgoing, as at July 2026). Because a self-used unit is worth roughly double an exported one, your savings hinge on using power in daylight — running the washing machine, dishwasher or a hot-water diverter while the sun's out. Add a battery and savings rise, but so does the upfront cost.

Honest payback for UK domestic solar is typically 7–12 years, assuming a well-sited roof, sensible self-consumption and current energy prices — confirmed only at a proper survey. Panels are warrantied to keep working for 25 years or more, so most homes see many years of near-free generation after payback. Payback is faster with high daytime usage, a south-facing roof and a low install price; slower if you're out all day, add an expensive battery, or have shading. Be wary of anyone quoting a single guaranteed figure like "5 years" — it ignores your usage, your roof and future changes to export rates. Ranges, not promises.

Domestic solar typically works out to the equivalent of a ~7–12% tax-free annual return over its life, based on 7–12 year paybacks and 25-year-plus warranties — but that's an estimate, not a guarantee. ROI improves the more electricity you use in daylight (self-consumed units are worth ~26–28p each versus ~12p exported, as at July 2026) and the lower your install cost. It weakens with shading, low daytime use, or an expensive battery that doesn't pay for itself. Rising energy prices push ROI up; falling export rates pull it down. Because it depends entirely on your home and habits, treat any headline ROI as a range to confirm at survey.

Yes, but less. Panels generate from daylight, not heat, so they still produce on overcast days — just at a fraction of peak. In the UK you'll typically get 60–70% of annual output between April and September, and only around 10–20% of summer levels in deep midwinter. A 4kW system might make ~3,400–4,200 kWh across a whole year, heavily weighted to summer. That's why solar rarely covers 100% of your needs and why you keep a grid connection for dark evenings and winter. Snow settling on panels stops output until it slides off. Honest planning assumes strong summers and weak winters, not steady year-round generation.

The Smart Export Guarantee (SEG) pays you for surplus electricity you send back to the grid. Every licensed supplier must offer a rate, but they vary widely: the mandatory floor is only ~4p, while competitive tariffs pay more — Octopus Outgoing is 12p (cut from 15p in March 2026) and Good Energy around 15p, as at July 2026. You need a smart meter and usually to be that supplier's import customer. Don't over-value export, though: a unit you use yourself avoids ~26–28p of import, so it's worth roughly double an exported one. The aim is to use more of your own power, then export what's left — not to chase export rates.