How long does commercial solar take to pay back?

Payback is the installed cost divided by the yearly saving and income. It is simple, but the inputs are easy to get wrong.

What installers report

One UK installer's 2026 guide gives 3.5 to 6 years for most well-sized systems, with farms at 3.5 to 5 years and schools at 4 to 6. Its own worked examples contained inconsistencies, so view these as a marketing range, not a promise. We found no independent official figure.

The biggest factor: self-consumption

Every kWh you use on site saves you the full import price. Every kWh you export is paid at a much lower export rate (see selling surplus). A building busy in daylight, like a bakery or a workshop, does better than one empty on weekdays.

Worked example (our own assumptions)

Item	Assumption
System	50 kWp, installed cost £45,000
Generation	45,000 kWh a year
Used on site	80% = 36,000 kWh
Exported	20% = 9,000 kWh
Import price saved	26p/kWh
Export rate	8p/kWh (an assumption: export rates are set by each buyer, so get a real offer)

Savings: 36,000 x £0.26 = £9,360. Export income: 9,000 x £0.08 = £720. Total £10,080 a year.

Payback: £45,000 / £10,080 = about 4.5 years.

If only 50% is used on site: 22,500 x £0.26 = £5,850, plus 22,500 x £0.08 = £1,800, total £7,650. Payback: £45,000 / £7,650 = about 5.9 years. Same panels, noticeably slower.

Other things that change the answer

• Tariff. A fixed rate lower than today's market makes savings smaller.
• Ageing, cleaning and inverter replacement add costs over time.
• Roof ownership. Tenants need landlord consent and a lease long enough to recoup the cost.
• Tax. Solar equipment may qualify for capital allowances, which can reduce the net cost; which allowance applies depends on your business structure and spending, so get your accountant's view before relying on it.

Next steps

Gather 12 months of usage, ideally half-hourly, and ask for at least two quotes that state the assumed self-consumption. See commercial solar panels.

Quote-checking questions

1. What annual generation do you assume, and from what roof orientation?
2. What share do you expect me to use on site, and based on what data?
3. What import price are you assuming? Is it my actual contract rate?
4. What export rate, and is it guaranteed?
5. Are inverter replacement and maintenance in your numbers?

Sensitivity check

Run the same system at different prices. At 20p/kWh and 80% self-use: 36,000 x £0.20 = £7,200, plus £720 export = £7,920, so £45,000 / £7,920 = 5.7 years. At 30p: 36,000 x £0.30 = £10,800 plus £720 = £11,520, so £45,000 / £11,520 = 3.9 years. Prices matter nearly as much as self-consumption.

Is payback the right test?

Payback ignores what happens after year one. A rough return view: £10,080 a year on £45,000 is about 22% a year before degradation and maintenance. Compare it with other uses of the money, such as LED lighting, which may pay back faster for some sites.