Commercial solar payback in the UK — what 2026 numbers actually look like

Commercial solar payback in the UK currently sits in a band most businesses find surprising: seven to nine years on south-facing roofs in southern England, stretching to ten or eleven in northern regions, on a £900-per-kWp installation cost. After payback, the remaining sixteen to eighteen years of the panels' warrantied life is essentially profit.

That's the headline. The numbers underneath are where the decision actually gets made.

The three inputs that move the answer most

Payback isn't one number — it's the output of a small handful of inputs that combine in obvious ways. The three that matter:

1. Your electricity tariff. Every penny you pay per kWh is a penny you save by generating it yourself. At Ofgem's Q1 2026 non-domestic benchmark of around £0.28/kWh, solar is straightforwardly economic for most south-facing UK buildings. If you're on a legacy contract at £0.15/kWh — rare in 2026, but it happens — payback stretches by 50% or more.

2. Your self-consumption rate. Solar is most valuable when you use the electricity on-site (offsetting £0.28/kWh) rather than exporting it (£0.05–£0.07/kWh under the Smart Export Guarantee). A warehouse running daytime operations might self-consume 80% of generation; a building only occupied evenings might self-consume 30%. That difference doubles payback.

3. Where you are. Southern England produces roughly 950 kWh per kWp per year on a well-oriented roof. Scotland drops to around 780. That's a 17% spread, and it pulls payback in line.

Everything else — capital allowances, SEG rates, panel choice, inverter brand — moves the answer by months at the margin, not years.

A representative case

A mid-sized warehouse in the South East with a £24,000 annual electricity bill, south-facing pitched roof, full daytime operations:

• System size: 125 kWp (roughly 275 panels, ~600 m² of roof)
• Annual generation: ~119,000 kWh
• Self-consumption: 72%, offsetting £24,000/year of bill
• Export income: ~£2,000/year (33,000 kWh @ £0.06/kWh SEG)
• Total annual benefit: ~£26,000
• Installed cost: ~£113,000 ex VAT (£900/kWp)
• Simple payback: 4.3 years

That's an unusually quick payback because the bill is large enough to support a system sized for total daytime self-consumption. A smaller business with a £6,000 annual bill would size at perhaps 30 kWp, install for around £27,000, and pay back over closer to 7 years — still strong, but the headline shifts.

You can run the numbers for your own building on our calculator. The defaults reflect current UK benchmarks; you can override the tariff and system size if you know your specifics.

What changes the answer in 2027 and beyond

Three forward-looking shifts worth modelling if you're deciding now:

• Electricity prices. Commercial rates have eased from the 2022 peak but remain elevated. Most credible long-run forecasts assume 3–5% annual inflation in non-domestic electricity through 2030. Higher inflation makes solar more attractive, not less.
• Panel costs. Module prices have fallen consistently for two decades. The 2026 commercial installed cost of ~£900/kWp is already 30% below 2020 levels. If you can wait a year, you might pay £830/kWp — but you'll also pay another £24,000 in electricity bills meanwhile. The maths almost always argues for proceeding.
• The SEG. The Smart Export Guarantee is supplier-discretionary and rates move. Conservative modelling assumes £0.05–£0.07/kWh; some suppliers currently pay more for variable exports. This affects export income, which for most commercial systems is 20–30% of total benefit.

The bit installers underplay

Three things rarely featured prominently in commercial proposals:

• Inverter replacement. Inverters typically need replacing at year 12–15 — budget £6,000–£15,000 for a system of this size. A well-prepared proposal will model this; many don't.
• Cleaning. UK rainfall handles most of it, but expect to budget £200–£500/year for a periodic clean on a 100+ kWp system. Not material to the case, but real.
• Roof condition. Panels last 25+ years. If your roof needs work within the next decade, do it before you install. Removing and refitting panels for re-roofing costs £30–£60 per panel — non-trivial.

None of these change whether commercial solar is a good investment. They change the precision of the payback number, which is why we model them in the figures above and why we'd recommend you push installers to do the same.

How to sanity-check any quote

If you're sitting in front of an installer's proposal:

1. Check the assumed yield. A 100 kWp south-facing system in the South East should generate 95,000–100,000 kWh/year. Numbers materially above that are optimistic; numbers materially below need explaining.
2. Check the self-consumption assumption. Installers sometimes assume 90%+ self-consumption to flatter payback. Reality for most commercial buildings is 65–80%. Push back if it's 85+ without a credible operational explanation.
3. Check the capital allowances treatment. Commercial solar qualifies for the Annual Investment Allowance (AIA) — 100% first-year deduction up to £1m. A serious quote will model the post-tax payback, not just the gross one. We cover the tax reliefs in full in our guide to commercial solar grants and funding in 2026.
4. Check the SEG rate. In 2026, business export tariffs run from about 8.5p to 15p/kWh depending on supplier and whether the rate is fixed or variable. Modelling 5–8p is genuinely conservative; 10–15p is achievable on the best fixed tariffs but assumes you switch and lock in. Anything above 15p is optimistic.

Run those four checks and you'll know whether the proposal in front of you is conservative, realistic, or wishful.

What to do next

If you want the monthly intel on UK commercial solar — benchmarks, policy shifts, real costs from the field — subscribe to the Brief. One email a month, written for finance directors, never for installers.

If you want the figures for your own building first, the calculator is the fastest way to get a sense of the scale of decision you're looking at.