Annual Investment Allowance for Solar PV — 2026 UK Tax Guide

Annual Investment Allowance (AIA) is the most material tax incentive for UK commercial solar in 2026. It allows full deduction of solar PV capital cost from taxable profit in the year of installation — for most commercial buyers, that's a 25% reduction in post-tax effective system cost. Full Expensing extends similar treatment for limited companies. Here's how it works.

What Qualifies as AIA-Eligible Solar Expenditure

• Solar PV panels
• Inverters (string, central, microinverters, optimisers)
• Mounting and racking systems
• DC and AC cabling
• Junction boxes, isolators, fuses
• Monitoring systems
• Design and engineering fees (HMRC accepts these as part of capital expenditure)
• DNO connection costs
• Installation labour
• Commissioning costs
• Battery storage where installed alongside solar (under HMRC's 2024 confirmation)

What Does NOT Qualify

• Roof repairs unrelated to solar (separately treated)
• Site groundworks unrelated to solar (e.g. car park resurfacing)
• Solar PPA payments (these are operating expenditure, not capital)
• Insurance premiums for the solar system
• O&M contract fees (operating cost)

How AIA Works — Worked Example

Limited company installs a 100kW solar system at £100,000 capital cost.

• Year-1 taxable profit (before AIA): £400,000
• AIA claimed against solar: £100,000
• Year-1 taxable profit (after AIA): £300,000
• Year-1 corporation tax (25%): £75,000 (vs £100,000 without AIA)
• Tax saving from AIA: £25,000
• Post-tax effective cost of solar: £100,000 − £25,000 = £75,000

AIA Cap and Annual Limit

• 2026 AIA cap: £1,000,000 per year (per company / group)
• Solar systems above £1m capital cost split across more than one tax year, or use Full Expensing for limited companies.
• The £1m cap is shared across all qualifying capital expenditure (not just solar).

Full Expensing — The Extension

Full Expensing (made permanent in 2024) allows limited companies to claim 100% deduction on main-pool plant and machinery — including solar PV — without the £1m cap. Effectively, FE replaces AIA for limited companies on solar PV (and most other commercial capital):

• 100% first-year deduction
• No cap
• Available to limited companies (not sole traders or partnerships)
• Permanent (post-2024 reforms)

Sole Trader and Partnership AIA

• AIA still applies (£1m cap).
• Full Expensing not available — limited to incorporated companies.
• Income tax rate at the top: up to 45% (Scotland: 47%) — depending on personal income, the post-tax effective cost can drop further than for limited companies.

Battery Storage and AIA — Important Update

HMRC confirmed in 2024 that battery storage installed alongside (and operationally integrated with) solar PV qualifies for AIA / Full Expensing. Standalone batteries (no solar) have a more nuanced position. We work with our clients' accountants on the specific qualifying status.

How to Claim AIA on Solar

1. Confirm with your accountant the company's qualifying status.
2. Complete capital expenditure pages of the company's CT600 corporation tax return.
3. Maintain detailed install invoice + commissioning evidence (we provide this as standard).
4. Submit return; AIA is claimed in the period of expenditure.
5. Tax saving accrues in the same accounting period.

Frequently Asked Questions

Does commercial solar qualify for AIA?

Yes. UK commercial solar PV qualifies for Annual Investment Allowance, providing 100% first-year deduction against taxable profit up to £1m per year. Full Expensing extends this for limited companies.

What's the difference between AIA and Full Expensing?

AIA: £1m annual cap, available to all businesses. Full Expensing: no cap, available to limited companies only. Both provide 100% first-year deduction on qualifying solar capital. Limited companies typically use Full Expensing above the AIA cap.

Can AIA be claimed on solar batteries?

Yes — HMRC confirmed in 2024 that battery storage installed alongside solar PV qualifies for AIA / Full Expensing. Standalone batteries without solar have a more nuanced position; consult your accountant.

What about VAT on commercial solar?

Commercial solar PV currently attracts 0% VAT under the 2022–2027 zero-rating extension. This is separate from AIA and applies regardless of business structure.

Can a sole trader claim AIA on solar?

Yes — sole traders and partnerships can claim AIA up to the £1m cap. Sole traders cannot use Full Expensing (limited to incorporated companies). Income tax rates may make sole-trader AIA highly tax-effective at the upper income brackets.

Related Guides

• Solar capital allowances
• Commercial solar grants
• Solar finance options
• Solar ROI calculator