Guide · Commercial solar payback
Commercial solar payback: the honest numbers.
Every installer quotes a payback figure. Very few explain what actually drives it. Here is the equation, a worked West Midlands example you can check line by line, and the things that quietly add years to the answer.
The equation
It is simpler than the sales deck suggests.
Payback is the net installed cost divided by the annual value of the electricity the system produces. That is the whole calculation, everything else nudges the inputs. Three numbers move the answer, and only one of them is really about the roof.
Ex-VAT, for straightforward commercial roof work. Small arrays on awkward roofs sit at the top of that range; a clean 250 kWp warehouse roof near the bottom. Cost per kWp falls with scale, so doubling the array rarely doubles the bill.
What you pay per unit today. Half-hourly industrial sites sit at the low end, micro-business contracts at the high end. Every unit you generate and use is a unit you never buy — so the higher your rate, the faster solar pays.
The one that actually decides the answer. A unit you use on site is worth your full import rate. A unit you export earns a Smart Export Guarantee tariff — typically around a third of it. Two identical arrays can be years apart on payback for this reason alone.
A note on VAT before the numbers: the 0% domestic rate does not apply to commercial premises. A VAT-registered business normally recovers the VAT as input tax, so commercial payback should always be modelled on the ex-VAT figure. Every number on this page is ex-VAT.
Worked example
100 kWp on a West Midlands warehouse.
A single-shift distribution warehouse near Oldbury, clean south-facing roof, typical 9-to-5 demand curve. Illustrative figures, ex-VAT, excluding finance costs and assuming no roof or grid works.
Where the "three-year payback" figure comes from
Push self-consumption from 70% to around 90%: a two-shift operation, workplace EV charging, or a battery soaking up the midday surplus: and the same array displaces roughly 85 MWh a year instead of 66. At a 24p import rate that is about £21,000 of avoided electricity annually, against a net cost of roughly £64,000 after Annual Investment Allowance relief.
That is a payback just under three years. It is a real number, but it belongs to a specific kind of site, one that uses nearly everything it makes. It is not a promise that applies to every roof, and we will say so plainly if yours is not that site.
Read the detail on the tax side in our guide to commercial solar capital allowances, and on the export side in the Smart Export Guarantee for business.
Load shape
Why a 9-to-5 business beats a night-heavy one.
Solar generation is a bell curve: it climbs from mid-morning, peaks around the middle of the day and fades by late afternoon, strongest from April to September. Payback is decided by how much of your demand curve sits underneath that shape.
A single-shift manufacturer, a warehouse picking through the day, a school, an office running air conditioning through a July afternoon, their demand lines up almost perfectly with generation. Self-consumption of 70% to 90% is achievable without a battery, and payback lands in the good part of the band.
A night-shift operation, a cold store that pulls hardest overnight, a venue that opens at six in the evening, generation and demand barely overlap. Self-consumption might be 30% to 40%, and the rest leaves the site at roughly a third of its value. Same roof, same equipment, payback potentially twice as long.
That is why every Green Tech Hub commercial proposal starts with twelve months of half-hourly consumption data, not a tape measure on the roof. The overlap between your load and the generation forecast decides whether an array is a three-year investment or a seven-year one, and it is knowable before you spend anything.
Proof on a real roof
A 154 kWp rooftop array with 64 kWh of battery storage, sized to the daytime machinery load so generation is used the moment it is made.
Sized to the site's daytime machinery load, the array was matched to the consumption, not to the available roof area. That is the whole difference.
What moves the date
What lengthens payback, and what shortens it.
Adds years
- Low daytime consumption — the single biggest lever, and the one no amount of good engineering fixes.
- Shading from rooflights, plant, flues, neighbouring buildings or trees. Optimisers recover much of the yield, but they add cost.
- Structural works: an older portal frame may need a structural report and strengthening before it carries an array.
- Asbestos-cement roof sheets, which cannot simply be drilled — expect licensed handling, non-penetrative mounting, or an overclad.
- A roof covering near the end of its own life. Putting a 25-year array on a 5-year roof is a false economy.
- Grid reinforcement: if the G99 connection offer requires network works to export at full capacity, you either fund them or accept an export limit.
- Oversizing beyond what the site can actually use, which converts expensive kWp into cheap exported units.
Takes years off
- Battery storage — moves midday surplus into your evening and early-morning demand, converting exported units back into self-consumed ones.
- Workplace, fleet or visitor EV charging, which creates genuine new daytime load exactly when the array is generating.
- A high import tariff. The more you pay the grid, the more each generated unit is worth.
- Capital allowances — the Annual Investment Allowance or the 50% special-rate first-year allowance can take a year or more off the payback date.
- The England business rates exemption on onsite renewable generation and storage, which runs to 31 March 2035 and is applied automatically at valuation.
- Funded routes. A power purchase agreement removes the capital cost entirely, which changes the question from payback to price per unit.
Two of those levers have their own pages: commercial battery storage, which is the usual answer when a site is exporting too much of what it makes, and fully funded and PPA installs, which remove the capital cost from the equation altogether on systems above 100kW.
The honest caveats
The bits most quotes leave out.
Inverters are not panels
Panels are the long-life component, 25 to 30 years of service, with a 25-year performance warranty on the tier-one modules we specify. Inverters and batteries are power electronics, and a working life of 10 to 12 years is the realistic planning assumption. A replacement in that window belongs in the model. On a three-to-five-year payback the array has already repaid itself several times over before that bill arrives, so it changes the lifetime return rather than the payback date, but it should be written down, not quietly omitted.
Tariffs move, in both directions
Payback is calculated against your current import rate: if power gets dearer it shortens, if it gets cheaper it lengthens. We model on your actual contracted rate rather than an optimistic forecast, and show the sensitivity so you can see how much of the case rests on that assumption.
Export income is not guaranteed income
Under the Smart Export Guarantee, licensed suppliers must offer an export tariff for installations up to 5MW, but they set the rate, and rates move. Claiming it also requires half-hourly export metering and MCS or equivalent certification, one practical reason our installs are MCS-certified under NIC-600049. Treat export as upside; build the case on self-consumption.
Programme, not just price
Most commercial rooftop solar in England is permitted development, the 1MW rooftop cap was removed in 2023, but systems above 50kW involve a prior-approval application, and listed buildings and conservation areas are the exception. Export also needs a G99 application to the DNO, which in the West Midlands is National Grid Electricity Distribution. Neither changes the arithmetic; both change when the savings start.
Questions
Payback, answered.
Anything else. Call and speak to a director, not a sales team.
What is a realistic payback for commercial solar in the West Midlands?
For a straightforward rooftop array on a business that uses most of its generation during the working day, four to six years gross is the honest starting band, falling to roughly three to four once capital allowances are applied. Sites with very high daytime demand and a high import tariff can beat three years; a night-heavy operation without storage can run past seven. Anyone quoting a single number before seeing your half-hourly data is guessing.
Can my business claim full expensing on solar panels?
No. Solar PV is special rate plant, and special rate expenditure is excluded from full expensing. The routes that do apply are the Annual Investment Allowance, which gives 100% relief on qualifying plant including special rate assets up to £1 million a year, or the 50% special-rate first-year allowance, with the balance going into the special rate pool. Treat this as general information and confirm the treatment with your accountant.
Does exporting to the grid pay for the system?
Rarely. Licensed suppliers must offer an export tariff for installations up to 5MW under the Smart Export Guarantee, and it is real income, but the rate is typically a fraction of what you pay to import — a self-consumed unit is worth roughly three times an exported one. Export is the consolation prize, not the business case. You also need half-hourly export metering and MCS or equivalent certification to claim it.
Should inverter replacement be in the payback calculation?
Yes. Panels are the long-life component at 25 to 30 years, and ours carry a 25-year performance warranty, but inverters and batteries are electronics with a working life nearer 10 to 12 years. A replacement in that window belongs in any honest model. It normally lands long after the system has paid for itself, so it changes the lifetime return rather than the payback date.
Does a battery make payback faster or slower?
It depends entirely on your load shape. A battery adds capital cost, so on a site already self-consuming 85% of its generation it usually lengthens payback. On a site exporting a third of everything it makes, storing that surplus and using it at your import rate instead of selling it at the export rate can shorten payback materially. Your half-hourly data settles the question before you spend anything.
Do roof or grid works change the numbers much?
They can dominate them. Asbestos-cement sheeting, a roof covering near the end of its life, structural strengthening on an older frame, or a DNO connection offer that requires network reinforcement are all capital costs that sit on top of the array itself. We identify them at survey stage rather than at installation stage, because finding them late is what turns a four-year payback into a seven-year one.
Get your actual number.
The free Business Energy Survey pulls your half-hourly consumption, models the array in CAD against your real load, and returns a fully costed proposal with the payback maths shown. No obligation.
More on commercial solar PV — Rooftop & ground-mount PV, designed around your load profile and roof.