Capital Allowances on Solar Panels UK

Solar PV systems installed at a UK business premises qualify as plant and machinery under HMRC capital allowances rules — meaning 100% Annual Investment Allowance up to £1,000,000 of qualifying expenditure per accounting period. For a profitable UK limited company at the 25% main rate of corporation tax, that translates to year-one tax relief equal to 25% of the install cost. This page covers the rules, the special rate pool considerations, the cash-basis treatment for sole traders, R&D credit interactions, and worked examples for £25k, £80k and £200k installs. For our canonical detailed page, see Annual Investment Allowance.

What capital allowances are and why they matter for solar

Capital allowances are HMRC's mechanism for giving tax relief on capital expenditure on plant and machinery. Without capital allowances, the cost of a £100,000 solar PV install would only be deductible from trading profits across its 25-year asset life — roughly £4,000 per year. With capital allowances, you can claim a substantial portion (or all, under AIA) of that capex against trading profits in the year the asset is brought into use. AIA is the single most important driver of commercial solar payback maths in 2026 — it converts a 7-year simple payback into a 5-year payback by reducing net effective capex by 25%. The HMRC published guidance on plant and machinery allowances is at gov.uk.

100% Annual Investment Allowance: the headline relief

AIA is the most common relief used on commercial solar PV. The rules in 2026: limited companies, sole traders, and partnerships can claim 100% AIA on qualifying plant and machinery expenditure up to £1,000,000 per accounting period. The £1m cap was made permanent in the Autumn Statement 2022 and remains in force in 2026. Solar PV qualifies as plant and machinery — the panels themselves, the mounting structure, inverters, DC and AC cabling, isolators and switchgear directly related to the PV system, and the installation labour are all qualifying expenditure. New ancillary roof construction (such as building a new roof solely to mount panels on, where the existing roof was structurally inadequate) generally also qualifies. Routine roof repair or remediation that would have been needed regardless of the PV install does NOT qualify and must be itemised separately on the invoice.

Above the £1m AIA cap: the 50% special-rate first-year allowance

A frequent error in commercial solar tax planning is assuming full expensing covers the spend above the AIA cap. It does not: full expensing (introduced April 2023, made permanent in the Autumn Statement 2023) applies to main-rate plant and machinery only, and solar PV is special-rate plant — a long-life asset with an expected useful life over 25 years. The correct mechanism for limited companies is the 50% First Year Allowance on special-rate expenditure: for a 1.5 MW commercial solar install at £1.05m turnkey, AIA covers the first £1m in full, and the 50% FYA relieves £25k of the £50k excess in year one, with the remaining £25k entering the special rate pool at a 6% writing-down allowance. Sole traders and partnerships cannot use the 50% FYA — they are limited to AIA. In practice, because most commercial installs sit well inside the £1m cap, AIA alone delivers 100% year-one relief on the whole system.

Worked example: £25,000 install for a small business

A 25 kW solar install on a small office or retail unit costs approximately £25,000 turnkey in 2026. The business is a UK limited company at the 25% main rate of corporation tax with sufficient trading profits to absorb the relief.

• Capex: £25,000
• AIA claim: £25,000 (full capex, well inside £1m cap)
• Year-one corporation tax saving: £25,000 × 25% = £6,250
• Net effective capex: £18,750
• Year-one savings (typical 25 kW install): £4,500–£6,000
• Simple payback on net capex: 3.1–4.2 years

Sole trader version: same maths but applied through self-assessment at the trader's marginal income tax rate. A sole trader at 40% gets £10,000 of year-one tax relief, dropping net capex to £15,000 and accelerating payback further.

Worked example: £80,000 install for a mid-size SME

An 80 kW solar install on a mid-size warehouse or manufacturing facility costs approximately £80,000 turnkey in 2026. The business is a UK limited company at the 25% main rate with strong trading profits.

• Capex: £80,000
• AIA claim: £80,000 (full capex)
• Year-one corporation tax saving: £80,000 × 25% = £20,000
• Net effective capex: £60,000
• Year-one savings (typical 80 kW install): £14,000–£18,000
• Simple payback on net capex: 3.3–4.3 years
• 25-year DCF NPV at 7%: £270,000–£310,000

This is the most common SME scenario in our portfolio — capex small enough to fund from cash flow or a single year's retained profit, large enough to deliver substantial tax relief and meaningful annual savings. See our cost page and commercial solar costs guide for full sub-vertical pricing.

Worked example: £200,000 install for a larger industrial site

A 250 kW solar install on a logistics warehouse or larger manufacturing site costs approximately £200,000 turnkey in 2026. The business is a UK limited company at the 25% main rate with sufficient trading profits.

• Capex: £200,000
• AIA claim: £200,000 (full capex, inside £1m cap)
• Year-one corporation tax saving: £200,000 × 25% = £50,000
• Net effective capex: £150,000
• Year-one savings (typical 250 kW install): £40,000–£55,000
• Simple payback on net capex: 2.7–3.75 years
• 25-year DCF NPV at 7%: £680,000–£760,000

At this scale, the AIA relief alone (£50,000) often exceeds the deposit on an asset finance package. Companies sometimes use AIA-claimed cash to fund the deposit on a second project, multiplying their capex deployment in a single tax year.

Sole trader and partnership treatment

Sole traders and partnerships have two routes for solar capital allowances. Accruals basis accounting uses the standard AIA at 100% up to £1m per accounting period, identical to the corporate route but applied through self-assessment at the sole trader's or partner's marginal income tax rate. A higher-rate taxpayer at 40% on a £40,000 install gets £16,000 of tax relief in year one. Cash-basis accounting (allowable for sole traders and partnerships with turnover under £150,000) treats the full capex as a deductible expense in the year of payment — economically equivalent to 100% AIA but applied through the cash-basis rules. Sole traders with significant other capex in the same year may prefer to spread relief by electing not to claim full AIA — this is rare for solar but possible. Partnerships claim AIA at the partnership level and split relief among partners according to profit-sharing ratios.

Special rate pool considerations

Solar PV is technically classified as a long-life asset (expected useful life over 25 years) which under the standard rules sits in the special rate pool with 6% writing-down allowance. However, AIA is available for both main-rate and special-rate pool assets up to the £1m annual cap — and note that full expensing does not apply to solar, because it covers main-rate plant only. For limited companies on capex above £1m, the 50% First Year Allowance (FYA) for special rate pool assets is the relevant relief, with the remaining 50% added to the special rate pool at 6% WDA. In practice, the vast majority of commercial solar installs sit inside the £1m AIA cap and use AIA exclusively. Only the largest projects (multi-MW utility-scale arrays) hit the cap and need to consider FYA mechanics.

R&D tax credit interactions

Standard commercial solar PV installs are not R&D — they deploy mature, commercially-available technology in a routine engineering pattern. But businesses claiming R&D enhanced expenditure on other activities (manufacturing process R&D, new product development, software R&D) need to sequence their capital allowances carefully. The general principle: AIA on solar should be claimed first against trading profits, reducing taxable profit before R&D enhanced expenditure is applied. Reversing the sequence can waste relief because R&D enhancement creates losses that AIA can't offset against — losses created by R&D enhanced expenditure can be surrendered for an R&D credit, but unused AIA cannot. Always confirm sequencing with your accountant or R&D specialist before submitting the CT600.

Battery storage and capital allowances

Battery storage installed alongside solar PV qualifies as plant and machinery on the same basis as the PV system itself — 100% AIA up to the £1m cap, with the 50% special-rate first-year allowance for limited-company spend above it. This includes the battery cabinet, hybrid or AC-coupled inverter, battery management system, fire suppression, switchgear, cabling and installation labour. A combined PV-plus-battery install at £150,000 (£95k PV + £55k battery) sits comfortably inside the AIA cap and delivers £37,500 of year-one corporation tax relief. See our battery storage page for full sizing and economics.

Practical claim mechanics

Three things to get right when claiming. First, the invoice from the installer must itemise plant and machinery costs separately from any non-qualifying ancillary spend (new roof construction not required for the PV, structural alterations beyond what's needed to mount the array, business interruption costs). Every quote we issue itemises in this format by default. Second, the asset must be brought into use in the accounting period the AIA is claimed — meaning the system has to be commissioned and generating, not just delivered to site. Third, the CT600 (for limited companies) or self-assessment (for sole traders and partnerships) needs the AIA claimed in the correct box — capital allowances in the corporation tax computation, with the £1m cap applied at company level and shared across group companies under common control. See HMRC's published guidance at gov.uk.

VAT treatment alongside capital allowances

Commercial solar PV in the UK is subject to 20% VAT at standard rate (the 0% domestic rate introduced in April 2022 applies only to residential installations — commercial sites are not eligible). VAT-registered businesses recover the input VAT in full through the next quarterly VAT return, so the cash impact is timing rather than absolute. The AIA claim is calculated on the net-of-VAT cost (the actual cost to the business after VAT recovery). Non-VAT-registered businesses include the VAT in the AIA-eligible capex. Partial-exemption businesses recover VAT on the proportion of the install attributable to taxable activity — typically irrelevant for trading businesses, occasionally relevant for charities, education and certain financial services.