Full Expensing vs AIA for Solar Panels
It doesn't apply to solar — here's what does.
Full expensing versus Annual Investment Allowance for UK commercial solar — and the short answer up front: full expensing does not apply to solar. Here is the claim that does.
Full expensing versus Annual Investment Allowance for UK commercial solar — and the short answer up front: full expensing does not apply to solar. Here is the claim that does.
The short answer: full expensing does not apply to solar
A surprising amount of commercial solar marketing gets this wrong, so let's be precise. Full expensing (made permanent in 2024) gives incorporated companies a 100% first-year deduction on qualifying main rate plant and machinery. Solar PV is classed by HMRC as special rate expenditure — which means it is excluded from full expensing. If a proposal or article tells you to claim full expensing on solar panels, it is working from the wrong asset classification.
The relief that actually applies is just as good for most projects: the Annual Investment Allowance (AIA) delivers a 100% first-year deduction on solar up to £1m of qualifying spend per year, for every business structure. For incorporated companies spending beyond the AIA in a year, a 50% first-year allowance applies to the special-rate excess, with the balance written down through the special rate pool at 6% per annum. This post sets out the current state of play for UK commercial property owners, facilities directors, and finance teams in 2026.
Market context
The UK commercial solar PV market entered a sustained growth phase from 2021 onwards as grid retail electricity prices more than doubled, corporate and public-sector net zero commitments brought forward decarbonisation timelines, and the supply chain matured to support installations at scale. UK installed commercial solar capacity exceeded 2.5 GW in 2024 and is projected to add 1 GW per year through 2030 under current policy trajectories.
Against that market backdrop, the topic of this post sits at the centre of the practical decisions UK commercial property owners face in 2026. The economics, the compliance environment, and the financing landscape have all shifted in ways that materially affect commercial solar project planning.
Detailed analysis
Three primary factors drive the current state of the UK commercial solar market relevant to the AIA-versus-full-expensing question (and remember: full expensing does not apply to solar). First, the underlying economics — UK commercial grid retail electricity averages 22–28p/kWh in 2026 versus commercial solar LCOE of 6–10p/kWh, meaning every kWh self-consumed from on-site generation saves the marginal grid retail tariff. Second, the regulatory environment — UK building regulations, MEES (Minimum Energy Efficiency Standards), SECR (Streamlined Energy and Carbon Reporting), and net zero commitments increasingly require demonstrable energy efficiency and Scope 2 emissions reductions. Third, the financing environment — three distinct funding routes (capital purchase plus AIA, asset finance, PPA) plus capital grants for public sector and manufacturing estates.
For UK commercial decision-makers, this means the 2026 commercial solar market is more mature, more scrutinised, and more strategically embedded than at any previous point. Generalist solar installers running domestic work as their core business and commercial as a side line are increasingly outcompeted by specialist commercial installers with deeper compliance, design, and aftersales infrastructure.
Real-world examples
To make this concrete, consider three representative UK commercial project profiles:
- 300 kW rooftop install on a Tier-1 automotive supplier in the West Midlands. Annual electricity demand 1.4 GWh against £140k+ quarterly bills. 92% self-consumption, 4.8-year payback, second-phase 200 kW battery contract within 18 months.
- 120 kW roof install on a multi-academy trust secondary school in the East Midlands. 100% PSDS grant funded after Low Carbon Skills Fund feasibility. Live monitoring dashboard integrated into curriculum. Trust scaled the model to 5 further sites within 24 months.
- 650 kW PPA install on a logistics distribution centre in the South East. 12,000 sqm regional distribution centre. Zero capital, fixed 11p/kWh energy rate for 20 years (vs 22p grid). 130 tonnes/year carbon reduction reportable in ESG annual report from year one.
Practical guidance
For UK commercial decision-makers acting on the analysis above, three practical steps de-risk the decision. First, start with a proper desk-based feasibility study from half-hourly meter data — sizing systems to actual demand rather than to roof capacity is the single biggest determinant of project ROI. Second, engage a commercial-only specialist installer rather than a generalist running domestic work as their core business — the gap in compliance and design quality is wider than the headline price difference suggests. Third, map the funding stack early — combining AIA, capital grants where applicable, and the right financing route can improve project IRR by 4–6 percentage points.
Cross-references
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