Save £450–£750 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 £6,400–£7,800 (the DESNZ MCS 2025/26 median-to-domestic-mean range) and can trim your bill by roughly £450–£750 a year, giving a payback of about 9–13 years. Check the performance warranty on any quote. Solar is 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 30 October 2026).

Realistically, a typical 4kW system saves about £620–£730 a year if it uses 30–50% of its output at home (our assumption), and nearer £470 in a poor case (3,000 kWh, 25% used at home), so about £450–£750 at 2026 prices — well short of £1,000. Savings come from two places: electricity you use yourself instead of buying (worth ~26p a unit at the October–December 2026 price cap) and surplus you export under the Smart Export Guarantee (around 12p with Octopus Outgoing, as at 30 October 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 by roughly £200–£300 a year, but so does the upfront cost (about £6,500 for 5 kWh on DESNZ retrofit figures).

Honest payback for UK domestic solar is typically 9–13 years, assuming a well-sited roof, sensible self-consumption and current energy prices — confirmed only at a proper survey. Panels commonly carry long performance warranties (check yours), so you should 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.

On our numbers a 4kWp system saves £620–£730 a year against £6,400–£7,800, which is roughly 8–11% a year in avoided bills before any inverter replacement or change in prices — but that's an estimate, not a guarantee. ROI improves the more electricity you use in daylight (self-consumed units are worth ~26p each versus ~12p exported, as at 30 October 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. Output is heavily weighted to summer and lowest in midwinter. On our assumption of 950 kWh per kWp, a 4kW system makes about 3,800 kWh across a whole year (PVGIS gives 886–1,131 kWh per kWp for south-facing roofs in 20 UK city centres). 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. Only suppliers with a SEG licence must offer an export tariff; each sets its own rate and terms, and the rate must be above zero. As at 30 October 2026 Octopus Outgoing pays 12p per kWh (variable) and Good Energy's Solar Savings pays 12p per kWh (variable); better fixed rates elsewhere are around 12–13p on comparison sites (indicative, checked 4–8 October 2026), and several suppliers pay only a few pence. For solar up to 50 kW you need an MCS certificate, and Octopus Outgoing also needs you to be an Octopus customer with a smart meter that sends half-hourly export readings. Don't over-value export, though: a unit you use yourself avoids ~26p 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.