Most UK commercial rooftop solar pays back in roughly four to eight years. A 509 kWp warehouse roof paying 25p/kWh and using 80% of its generation on site pays back in 4.6 years. The biggest single factor is not the price of panels but how much of the electricity you use on site rather than export.
What payback actually means
Payback is the point where the money solar has saved you equals what the system cost. After that, the savings are yours. It is the simplest measure of a solar investment and the one most finance teams ask for first, but it is a blunt one: it says nothing about what happens in the twenty years after you break even, which is where most of the value sits.
Our calculator reports simple payback: cumulative savings against the installed cost, with no discounting. We also show net benefit over 25 years, which is the better number for comparing solar against other uses of the same capital.
The five things that move payback
- How much you use on site. The single biggest factor. Electricity you use yourself displaces the full import price. Electricity you export earns a few pence. A site that uses 80% of its generation pays back far faster than one that uses 40%.
- What you pay for electricity. Payback is driven by the price you avoid, not the price of panels. A site on 30p/kWh pays back considerably sooner than an identical site on 18p/kWh.
- Where you are. A kWp in the South West generates around 20% more than the same kWp in Scotland. See how much electricity commercial solar generates.
- How it is mounted. Pitched roof is the cheapest per kWp; carports cost roughly 65% more. See what commercial solar costs.
- How you pay for it. Buying outright gives the fastest payback and the most total benefit. A PPA has no payback period at all, because you spend nothing upfront. See how to pay for commercial solar.
A worked example
A 3,200 m² pitched warehouse roof, UK average sunshine, paying 25p/kWh and using 80% of generation on site. These are the calculator's own figures:
| Usable roof area | 3,200 m² |
|---|---|
| System size | 508.98 kWp (998 panels) |
| Installed cost | £458,082 |
| Generation, year 1 | 456,021 kWh |
| Saving, year 1 | £95,764 |
| Payback | 4.6 years |
| Net benefit over 25 years | £2,793,299 |
Change one input and the answer moves. At 18p/kWh the same roof takes closer to six and a half years. In Scotland, with its lower sunshine, it takes longer again. That is why a generic payback figure is close to useless: the number that matters is the one for your roof, your region and your electricity price.
What the payback figure includes
Our figure includes the installed cost of the system, the value of electricity you use on site, export income at a flat 5p/kWh, electricity price inflation at 3% a year, panel degradation of 1% in year one and 0.4% a year after that, and an allowance for one inverter replacement in year 13.
It does not include finance costs if you borrow, your own staff time, roof repairs needed before installation, or any grid connection reinforcement your distribution network operator may charge for. Those last two can be significant and are site-specific, which is why an estimate is not a quotation. See planning, grid connection and other hurdles.
How to shorten payback
- Size the system to your demand, not your roof. A smaller array that you use entirely often pays back faster than a larger one that exports half its output.
- Shift load into daylight hours where the process allows it. Every kWh moved from night to midday is worth the difference between the import price and the export price.
- Claim the capital allowances. Solar qualifies for the special rate pool, and companies can use full expensing on qualifying plant, which pulls relief forward.
- Check the business rates position. Plant used to generate renewable power has been exempt from business rates in England since April 2022.
- Consider a battery only if the numbers work. A battery raises the share you use on site but adds capital cost, so it can lengthen payback even while it increases total savings.
Common questions
How long does commercial solar take to pay back?
Most UK commercial rooftop systems pay back in roughly four to eight years. The worked example on this page, a 509 kWp warehouse roof at 25p/kWh using 80% of its generation on site, pays back in 4.6 years. Sites with a lower electricity price, less daytime demand or less sunshine take longer.
Is payback the right way to judge a solar investment?
It is a useful first filter but an incomplete one. Payback ignores everything that happens after you break even, which for a 25-year asset is where most of the value sits. Net benefit over the life of the system, and return on investment, are better measures for comparing solar against other uses of the same capital.
Does a battery make payback faster?
Usually not. A battery increases the share of generation you use on site, which increases total savings, but it also adds capital cost. In most commercial cases it raises lifetime savings while lengthening payback. The calculator lets you model it both ways.