Professional-services office: 30 kWp bought outright with full year-one AIA relief

A well-capitalised professional-services firm occupying its own three-storey office wanted to cut a rising electricity bill and put idle cash reserves to better use than the near-nothing they earned on deposit. With a strong daytime load from lighting, servers, air conditioning and a busy open-plan floor, and no plans to move building, the numbers pointed clearly at buying the system outright.

The funding structure

The firm paid the full installed cost of a 30 kWp rooftop system from its own reserves and owned the asset from the day it was commissioned. As a VAT-registered business it reclaimed the 20% input VAT through its normal return, so the effective outlay was the ex-VAT price. Because it bought outright there was no lender, no interest and no finance term to manage.

At an indicative 2026 installed cost of around £850 per kWp, the 30 kWp system came to roughly £25,500 before VAT. There was no monthly payment to weigh against the saving here, so the decision rested on one question: did the return on that cash beat the return on the next best use of it.

The numbers

The system generates about 28,500 kWh a year in this part of the South East. With the office occupied through the working day, self-consumption sits near the top of the range at about 75%, so roughly 21,400 kWh is used on site displacing grid power at 28p a unit, worth about £5,990. The remaining 7,100 kWh is exported under the Smart Export Guarantee at an indicative 15p, adding about £1,065. Together that is a gross annual benefit near £7,300.

On the tax side, the whole cost fell comfortably under the £1m Annual Investment Allowance cap, so the firm claimed 100% first-year relief on the qualifying spend. At 25% corporation tax that returned roughly £6,400 against its tax bill in year one, cutting the net cost of the system to about £19,100 once the AIA relief and reclaimed VAT are counted.

Against that reduced net cost, a gross benefit of around £7,300 a year gives a simple payback of a little under three years, or close to four years measured against the full pre-relief price. From then on the system keeps generating for two decades or more with no finance cost attached, and every unit it produces flows straight to the bottom line.

Why this route suited them

Buying outright is the most expensive route on day one and the cheapest over the system’s life, and it only makes sense when a business has cash it can spare without starving the rest of the operation. This firm did. It had reserves earning very little, a settled building it would hold for the long term, and a tax bill large enough to absorb the year-one allowance in full. Ownership meant it kept every pound of saving, all the export income and the entire capital allowance, with no lender margin quietly eroding the return. For a cash-comfortable owner who wants the maximum lifetime return and has no better use for the money, no route beats it.

Model this against your own electricity spend in the finance calculator, then get costed quotes when you are ready.