Solar panels vs no solar in 2026: does the cashflow stack up?

The 2026 maths in one paragraph

A standard 4 kW UK solar PV install (10–12 panels, no battery) costs around £6,500 today. A south-facing roof at typical UK pitch generates ~3,400 kWh a year. About half of that is used directly in the home — offsetting electricity at full retail rate (~30p/kWh) — saving roughly £420/year. The other half gets exported and paid at the SEG rate (3–15p/kWh; ~10p midpoint) — earning about £170/year. Total Year-1 net benefit: £590. The system pays for itself in ~11 years and earns £14,750 net over its 25-year lifespan. Year 26 onward it’s free electricity.

The “do nothing” baseline

Doing nothing means paying full retail electricity rates for every kWh used, for the next 25 years, with rates likely to rise (UK retail electricity has compounded at ~6%/year since 2015 in nominal terms). A house using 3,800 kWh of electricity per year at 30p/kWh spends £1,140/year today. Over 25 years with 4% real inflation that’s £47,500 in real terms. Even partial offset from solar materially shifts that envelope.

When solar doesn’t pay back

Three configurations push payback past 15 years and may not be worth it:

• Pure north-facing roof — output drops 30–40% vs south. Payback pushes to 14–18 years. Look at the south face of an outbuilding or a ground-mount option instead.
• Heavy shading from neighbours / trees for more than 4 hours per day during peak generation (10am–4pm). Microinverters or DC optimisers can partially compensate but add £800–£1,500 to the install.
• Properties you plan to leave within 7 years. The system holds resale value (estate agents quote £3,000–£6,000 uplift) but doesn’t pay back the full install before you exit. Make the decision deliberate.

Does adding a battery change the answer?

A 5 kWh battery costs £2,500–£4,000 installed (additional to panels). It shifts your self-consumption ratio from 50% to about 80% — most of your evening usage comes from the battery rather than the grid. Annual benefit lifts by ~£150–£250 from higher self-consumption + lower export. So a £3,000 battery adds maybe £200/year of value — 15-year payback on the battery alone, dragging the system’s overall payback from 11 to 13 years.

Worth doing if: you spend >£1,500/year on electricity, have a heat pump or EV (high evening + winter draw), or value resilience against grid outages. Skip if: you’re on a tight budget — get panels first, add a battery later when prices drop further (battery prices have fallen 25% since 2023).

The SEG tariff matters more than people realise

SEG rates vary 5× between UK suppliers. At 3p/kWh (minimum-compliance suppliers) a 4 kW system earns £50/year on export. At 15p/kWh (Octopus + a few competitors) the same system earns £255/year. That’s £200/year of difference for a 30-second tariff-switch decision. Worth re-evaluating every year — SEG rates compete for your business in a way that the old Feed-in-Tariff regime didn’t.

Bottom line

For most UK homeowners with a south-or-near-south facing roof and limited shading, 2026 is a “yes” on solar — the payback is faster than UK fixed-term savings rates can match, and the carbon and resale upside come free. The pre-survey check at propertoasty.com/checkuses the Google Solar API’s roof segmentation to give a property-specific answer: panel count, expected kWh/yr, payback in years.