Commercial solar PV ROI in 2026: what a 250 kWp roof actually returns

Short answer: A 250 kWp commercial rooftop solar system in 2026 costs roughly £180,000 installed and returns a net benefit of about £41,000 in year one for a business that uses most of its generation on site. That is a simple payback of a little over four years, falling below four years once the 50% first-year capital allowance is applied, and a conservative net return above £850,000 over a 25-year system life.

Most property and sustainability directors do not need persuading that solar makes sense. The question they actually ask is sharper: on our roof, with our electricity bill, what does the money do over 25 years, and when do we get the capital back?

This is a worked example for a 250 kWp commercial rooftop system in 2026. The numbers are illustrative, not a quote, but every assumption is stated so you can swap in your own figures. A firm number needs a structural survey, a half-hourly consumption profile and a Distribution Network Operator (DNO) check, all covered below.

Why 250 kWp is the commercial sweet spot

A 250 kWp array is the practical sweet spot for a mid-sized commercial roof: a distribution warehouse, a manufacturing unit, a large retail shed or a college sports hall. It needs roughly 1,250 to 1,500 square metres of usable roof and around 450 to 550 modern panels. It is large enough for the economics to be compelling, and small enough to sit under the grid thresholds where reinforcement cost starts to dominate.

The worked numbers

The headline is a net benefit of about £41,400 in year one against £180,000 of capital. The example assumes a south-facing roof in southern England, a business that operates through the day so most generation is used on site, and a commercial electricity price of 25p per kWh.

The annual generation figure uses about 900 kWh per kWp, the planning yield for a south-facing commercial roof in southern England under the MCS array-estimation method (MCS 024) and EU PVGIS irradiance data.

Line item	Assumption	Year 1 value
System size	250 kWp rooftop	-
Indicative installed cost	about £720 per kWp	£180,000
Annual generation	900 kWh per kWp	225,000 kWh
Self-consumed on site	70% of generation	157,500 kWh
Exported to grid	30% of generation	67,500 kWh
Grid electricity avoided	25p per kWh	£39,375
Export income (SEG at 6p)	6p per kWh	£4,050
Operation, monitoring, insurance	annual	-£2,000
Net year-1 benefit		about £41,400
Simple payback (before tax)		about 4.3 years

Before any tax treatment, that is a simple payback of a little over four years. The export income comes through a Smart Export Guarantee (SEG) tariff, the scheme regulated by Ofgem that obliges larger electricity suppliers to pay for exported generation.

Self-consumption is the lever, not panel price

The number that moves the answer most is not the price per panel. It is the split between what you use on site and what you export.

Every kWh you self-consume is worth the full 25p you would otherwise pay the grid. Every kWh you export earns around 6p under a SEG tariff. That is a four-to-one difference. The same array on two different buildings can return very differently purely on consumption profile.

Self-consumption scenarios for the same 250 kWp array

Self-consumption	Value of self-use	Export income	Net year-1 benefit	Simple payback
60% (135,000 kWh)	£33,750	£5,400	about £37,150	about 4.8 years
70% (157,500 kWh)	£39,375	£4,050	about £41,400	about 4.3 years
80% (180,000 kWh)	£45,000	£2,700	about £45,700	about 3.9 years

Bottom line: moving from 60% to 80% self-consumption improves the year-one return by about £8,500 with no change to the panels on the roof. Two things raise self-consumption:

1. Match the array to the daytime load. Oversizing a roof on a low-consumption building pushes generation into low-value export. The design follows the half-hourly consumption profile, not just the available roof area.
2. Add storage where the profile is peaky. Pairing PV with a battery energy storage system moves midday generation into the early evening, lifting self-consumption and shaving peak-rate import. On the right tariff it also opens grid-balancing revenue. It is a design decision driven by load shape, not a default.

The tax treatment most buyers miss

Commercial solar PV qualifies for capital allowances, and the 2026 rules are favourable. Solar PV sits in the special rate pool, so under the full expensing regime it attracts a 50% first-year allowance on the qualifying spend, with the balance written down at 6% a year thereafter. This is set out in HMRC guidance on capital allowances and the full expensing rules.

On £180,000 of capital, that is a £90,000 deduction in year one. For a company paying the 25% main rate of corporation tax, that is about £22,500 of cash tax saved in the first year, with further relief on the remaining balance over time. That pulls the effective payback in from about 4.3 years to under four.

Capital allowance positions vary by company, so confirm the treatment with your accountant before it goes in a board paper. The point stands: the tax line is material and it is often left out of the back-of-envelope sums.

What the return looks like over 25 years

Over a 25-year life the same system returns a conservative net benefit of more than £850,000 on the £180,000 invested, an indicative internal rate of return of around 18%.

Panels carry performance warranties of 25 to 30 years and degrade slowly, about 0.4 to 0.5% a year. Budget for one inverter replacement around year 12 to 15, in the region of £12,000 to £15,000. Holding electricity prices flat and netting off degradation, maintenance and that inverter replacement gives the £850,000-plus figure. If commercial electricity prices rise over the period, as they have for most of the last decade, the lifetime return is materially higher. Few capital projects with this little operational risk return at that level.

What would change these numbers on your site

Five things move the answer, and all five are checked during design rather than guessed:

1. Roof condition and structure. A roof with under 15 years of life left, or one that cannot take the load, changes the scope before a single panel goes up. A structural survey comes first.
2. Orientation and pitch. East-west roofs generate less at peak but spread output across the day, which can raise self-consumption. South maximises total yield. Which is better depends on your load.
3. The DNO connection. A 250 kWp system needs a G99 application to your Distribution Network Operator under the Energy Networks Association Engineering Recommendation G99. At this scale the DNO may require export limitation or reinforcement, and its response time is usually the longest item in the programme.
4. Your actual tariff and consumption profile. Half-hourly metering data is the single most useful input. It gives the real self-consumption rate instead of an assumed 70%.
5. Metering and MCS. Systems installed to Microgeneration Certification Scheme (MCS) standards qualify for SEG export payments and give a documented quality baseline. Rossair designs and installs to MCS.

How Rossair approaches a commercial PV project

Rossair designs and installs commercial solar PV as part of an in-house renewable energy capability that also covers air source heat pumps and battery storage. The work is done by the same directly-employed engineering team that delivers our mechanical and electrical projects, so the electrical infrastructure, the DNO application and the controls are handled under one contract rather than passed between subcontractors.

For estates already looking at decarbonisation, PV rarely stands alone. It pairs naturally with heat pump electrification, where the array offsets the additional electrical load that electrified heating creates. That is the same logic behind the gas-removal work Rossair delivered at Wembley Health Centre for the NHS. Solar, storage and heat are one system, and they are most efficient when designed together.

Frequently asked questions

What is the payback period on commercial solar PV in 2026?

For a well-sited 250 kWp commercial rooftop system with strong daytime self-consumption, a simple payback of roughly four to five years is realistic in 2026. The 50% first-year capital allowance brings the effective payback closer to four years for a company paying corporation tax. Self-consumption is the biggest single variable.

How much does a 250 kWp commercial solar PV system cost in 2026?

A 250 kWp system typically costs £160,000 to £200,000 installed, or about £640 to £800 per kWp, depending on roof type, fixing method, inverter specification and any grid reinforcement. A structural and electrical survey is needed before any figure is firm.

How much electricity does a 250 kWp solar array generate per year?

Roughly 215,000 to 240,000 kWh in year one in the UK, depending on location and orientation. Rossair plans on about 900 kWh per kWp for a south-facing commercial roof in southern England. Output falls about 0.4 to 0.5% a year as panels age.

Does a commercial solar PV system need DNO approval?

Yes. A 250 kWp system needs a G99 connection application, and the DNO may require export limitation or reinforcement at this scale. The DNO response is usually the longest item in the programme, so it goes in early. Rossair handles the G99 application and export limitation design as part of the works.

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Thinking about solar on a commercial estate? See how Rossair delivers commercial solar PV and renewable energy. We will run these numbers against your actual roof, tariff and consumption profile, not a generic assumption.