Is Business Solar Worth It in 2026? The Honest Maths

“Is it worth it” is the right question, but it does not have a single answer. Business solar is worth it for a manufacturer running machinery through the day and paying 30p a unit; it can be marginal for an office that empties at five and uses little power when the sun is up. The honest position is that solar pays back well for most UK businesses with a genuine daytime load, and the 2026 numbers back that up, but the return is driven almost entirely by how much of the power you use on site. This guide sets out the real maths for 2026, the tax and export income that shape it, and, just as importantly, the situations where it does not stack up.

The headline numbers for 2026

For a well-matched system, simple payback in 2026 typically lands at about four to seven years before any tax relief, and roughly three and a half to five years once the year-one Annual Investment Allowance cuts the net cost. After that, the system generates for another fifteen to twenty years or more, because panels lose only around 0.3 to 0.5 per cent of output a year and are usually warrantied to hold 80 to 92 per cent of their nameplate at year 25.

Expressed as a return, an unleveraged project commonly shows an internal rate of return of 10 to 20 per cent, and high-self-consumption sites are sometimes quoted 15 to 25 per cent. Treat anything above 20 per cent as best-case and check it per project rather than taking it as a given. A 10 to 20 per cent IRR from an asset with a twenty-five-year life is a strong result against most alternative uses of business capital, which is why the underlying case is sound for the majority of buyers.

Why self-consumption is the whole game

The economics of business solar do not come from generation, they come from what you do with it. A unit of electricity you use on site displaces grid power priced at roughly 26 to 32p in 2026. A unit you export to the grid earns roughly 12 to 16p under the Smart Export Guarantee. Using your own power is worth more than double exporting it, so the single biggest driver of your return is your self-consumption rate, the share of generation you actually use rather than spill back to the grid.

A well-matched daytime load achieves about 50 to 80 per cent self-consumption. Sizing to your on-site demand, not to how much roof you have, is therefore the most important decision in the whole project. An oversized system that generates far more than you can use during daylight will export the surplus at the lower rate and drag your payback out; a right-sized system that consumes most of what it makes will pay back fast. This is why two businesses with identical roofs can see very different returns, and why a proper look at your half-hourly consumption matters more than the panel spec.

The tax relief that shortens payback

The tax position is where a lot of the 2026 saving is made, and it is also where the market gets it wrong most often, so it is worth being precise.

For the great majority of installs the relevant relief is the Annual Investment Allowance, which gives 100 per cent first-year relief on qualifying plant up to £1,000,000 a year. Solar qualifies, and because most business installs cost well under £1m, the AIA usually writes off the whole system against your profits in year one. At a 25 per cent corporation-tax rate that returns roughly 25p of tax for every £1 spent, in the first year, which is what pulls post-relief payback down from the pre-tax four-to-seven-year range into the three-and-a-half-to-five-year range.

The point businesses get wrong is assuming solar attracts 100 per cent full expensing. It does not. Solar PV is special-rate plant under HMRC’s rules (manual reference CA22335), and full expensing, along with the new 40 per cent first-year allowance from January 2026, applies only to main-rate assets. Solar spend above the £1m AIA cap can use the 50 per cent special-rate first-year allowance, with the balance written down at 6 per cent a year. The Autumn Budget 2025 cut the main-rate writing-down allowance from 18 to 14 per cent from April 2026, but left the special-rate 6 per cent unchanged. Plan around the AIA, not around full expensing, and confirm your own position with your accountant. There is more detail on the tax relief on the grants and funding page.

Two further items help the maths. If you are VAT-registered, the 20 per cent VAT on a commercial install is reclaimable through your normal VAT return, so for most firms it is a timing item rather than a real cost. And in England, qualifying rooftop solar for self-consumption is 100 per cent exempt from business rates from April 2022 to March 2035, so it will not raise your rateable value in that window. Scotland and Wales run separate regimes, so check locally.

A worked example

Consider a representative owner-managed engineering firm in the West Midlands running CNC machinery on a single daytime shift. It fits a 48 kWp rooftop array generating around 46,000 kWh a year. About 78 per cent of that is used on site, displacing power at 28p, and the rest is exported at 15p, giving a gross annual benefit near £12,400.

On a full capital purchase, and after the roughly £12,000 of year-one AIA relief brings the net cost down, a system like this shows a simple payback of a little under five years, then generates for two decades more. Funded instead on a seven-year green loan, the repayments run to roughly £9,800 a year, so the project is over £2,500 a year cash-positive from the start, before counting the tax relief, and the full saving flows to the bottom line once the loan clears. These are representative, indicative 2026 figures, not a named client, but they show how a right-sized system on a strong daytime load pays for itself.

You can run the same shape of calculation on your own bill. The finance calculator models the payment against the saving for each funding route, and the payback and ROI page walks through the figures for different system sizes.

When it is not worth it

An honest resource has to say when the answer is no, or not yet. Solar does not suit every business, and there are four situations where it either fails to stack up or needs a hard second look.

Your daytime demand is low. This is the big one. If your business uses little electricity between roughly 9am and 4pm, when the panels are producing, you will export most of the generation at 12 to 16p rather than displace grid power at 26 to 32p. A pure-office operation that empties in the evening, or a business whose main load is overnight, will see self-consumption fall well below 50 per cent and payback stretch out accordingly. A battery can help shift some of that load, but it adds cost and rarely rescues a fundamentally poor consumption match on its own.

Your roof or site is unsuitable. A north-facing, heavily shaded or structurally weak roof cuts generation and can add cost, and if you rent your building on a short lease you may not hold it long enough to see the payback, or be able to get landlord consent. In these cases the honest answer is to fix the constraint first or look at a funder-owned route where you do not carry the asset.

You have a better use for the capital and cannot finance. If buying outright is the only route open to you and that capital would earn more deployed in the business, the opportunity cost can outweigh the solar return. This is usually an argument for financing rather than for not doing solar at all, since a green loan or hire purchase lets you keep the cash and still own the system, but if finance is not available the sums may not favour tying up the money.

The system is oversized for your load. A system sized to fill the roof rather than match your demand will look impressive on generation and disappointing on return. If a quote proposes far more capacity than your consumption can absorb during daylight, that is a red flag worth challenging before you sign anything.

The thread running through all four is the same: solar rewards a business that uses the power it makes, holds its building long enough to benefit, and sizes the system to its load rather than its roof. Where those conditions hold, the 2026 maths is strongly positive. Where they do not, no funding route fixes an underlying mismatch.

Making the decision

If you have a real daytime load and a suitable building, the 2026 numbers say solar is worth it, and the main remaining question is not whether but how to pay for it, which is what the funding routes and the finance calculator are for. If your load is uncertain, the most valuable first step is to look at your half-hourly consumption data so you can estimate your self-consumption rate honestly before anyone quotes you a system.

When you are ready to firm up the figures for your own building, our sibling resource lets you request costed quotes from vetted installers, or you can start a quote here. Take the resulting numbers to your accountant, sense-check the self-consumption assumption, and decide on evidence rather than on a headline payback figure that may not reflect how your business actually uses power.