Annual Investment Allowance for Data Centre Solar (2026)

The Annual Investment Allowance (AIA) was made permanent at £1 million a year from the Autumn Statement 2023. If you last costed a data centre solar project before then, your post-tax numbers may be out of date. This article explains how the allowance applies to a rooftop PV project, what it is worth in cash, and the structuring mistakes that waste it. It is general information, not tax advice: your tax adviser must confirm the qualifying proportion and the treatment for your company.

What the AIA is, and what it is not

The AIA lets a business deduct 100% of qualifying plant and machinery spend, up to £1 million a year, from taxable profits in the year the spend is incurred. It is a deduction, so the cash value is the deduction multiplied by your tax rate. For a UK company paying corporation tax at the main rate of 25%, every £1 deducted saves 25p of tax.

Full expensing, the separate 100% regime for company spend on main-rate plant, is a different allowance. The guidance this site follows treats solar PV and the electrical systems that serve it as special-rate expenditure, so full expensing is not the route; the AIA is, and above the cap the 50% first-year allowance for special-rate spend applies. Confirm the classification of each cost line with your adviser before you rely on either.

Source for the AIA rules and the £1m limit: GOV.UK, Annual Investment Allowance. First-year allowances: GOV.UK, first-year allowances.

What usually qualifies, and what usually does not

Usually qualifying plant and machinery on a PV project: modules, inverters, mounting structures, DC cabling, AC switchgear and metering, battery storage where installed, protection relays and export-limiting equipment, and monitoring hardware.

Usually not qualifying: structural roof repair or re-roofing, asbestos removal, scaffolding treated as a revenue cost, and any DNO network reinforcement that sits on the network operator’s side of the connection. Ask the contractor to split the quote so your adviser can see the qualifying share. Splits of 85–90% qualifying are common in quotes, but the figure is project-specific.

A worked illustration (modelled, not a quote)

Take a £500,000 project of which £450,000 is qualifying plant, bought outright by a company paying 25% corporation tax.

Line	Amount
Total project cost	£500,000
Qualifying plant	£450,000
Deduction under the AIA (within the £1m cap)	£450,000
Corporation tax saved at 25%	£112,500
Net cost after tax relief	£387,500

The tax saving arrives through your corporation tax return and payments for the year, not on the day you pay the contractor, so model the cash timing. Because the saving is received as a reduction in tax, it only has value if the company has taxable profit to deduct it from.

Above the £1m cap

AIA headroom is shared across all qualifying plant and machinery spend in the accounting period, not just solar. If the same year includes a UPS upgrade, a CRAC replacement or a hall fit-out, those compete for the same £1m. Spend above the cap on special-rate assets can qualify for the 50% first-year allowance, with the remainder going into the special-rate writing-down pool at 6% a year. Check current rates on GOV.UK before modelling.

Planning point: where a project would breach the cap, moving other plant spend into the next accounting period, or phasing the PV installation across two periods, can recover more relief than a single oversized year.

Timing and ownership traps

• First use. Allowances are generally given for the period in which the expenditure is incurred and the asset is brought into use. A system commissioned just after your year end moves the relief a year later.
• Leases and PPAs. If a funder owns the asset, the funder claims the allowances, not you. That is a real trade-off against outright purchase; see the on-site PPA guide and the cost page.
• Hire purchase. Under HP, the buyer can usually claim the allowances on the asset; confirm the structure with your adviser.
• No taxable profit. Entities with no corporation tax liability, or with losses, cannot use the deduction immediately.

Where to go next

The cost and payback page sets out the modelled assumptions, and the grants and funding page covers the other routes. To compare installer quotes side by side, request matched quotes.