Capital Allowances for Factory Solar Panels: The Accurate UK Tax Guide
Many websites — and some accountants — claim that factory solar panels qualify for "full expensing" at 100%. This is incorrect. Solar panels are special rate assets under HMRC guidance, and full expensing is explicitly unavailable to them. This guide sets the record straight and explains the three routes that do apply: the Annual Investment Allowance, the 50% First Year Allowance, and the Special Rate Writing Down Allowance.
Important notice
This guide reflects HMRC rules as of March 2026. Tax legislation can change. Always confirm your position with a qualified tax adviser before making capital allowance claims. References to HMRC guidance are provided throughout.
Capital Allowances at a Glance
Factory solar panels are special rate pool assets. The three available routes are:
| Route | Rate | Annual Limit | Best For |
|---|---|---|---|
| Annual Investment Allowance (AIA) | 100% | £1,000,000 | Most factories (systems under ~£1M) |
| 50% First Year Allowance (FYA) | 50% year 1 | No limit | Large systems over £1M |
| Special Rate WDA | 6%/year | No limit | Default if AIA/FYA not available |
Full expensing (100%) is not available for solar panels — it applies to main pool assets only.
The Industry Misinformation Problem
Since the government introduced "full expensing" in April 2023, a significant amount of incorrect guidance has spread across the solar industry. Numerous websites — including some operated by solar installers, finance brokers, and even general-purpose accounting resources — state that commercial solar panels qualify for 100% full expensing under the new rules.
This claim is wrong, and factory owners acting on it could make incorrect tax return filings.
What the incorrect claim looks like
"Solar panels qualify for full expensing — you can deduct 100% of the cost in year one with no annual limit."
This is incorrect. Full expensing applies only to main pool plant and machinery. Solar panels are special rate pool assets and are excluded.
What is actually correct
- Full expensing (Section 50AAB CAA 2001): Main pool assets only. Solar is excluded.
- AIA (Section 38A–39 CAA 2001): 100% relief up to £1M/year. Solar qualifies.
- 50% FYA for special rate assets (Section 45A CAA 2001): Solar qualifies. No monetary limit. Permanent since Autumn 2023.
- Special rate WDA: 6%/year. The default if other allowances not available.
The source of the confusion is understandable: both AIA and full expensing can produce a 100% deduction in year one. However, they are entirely different provisions with different eligibility rules. For solar, the 100% route is AIA — not full expensing. The distinction matters enormously when a factory's solar spend exceeds £1M, because full expensing has no monetary cap whereas AIA is capped at £1M per year.
What Are Solar Panels Classified As for Tax Purposes?
Solar panels are classified as special rate assets under the Capital Allowances Act 2001 (CAA 2001), specifically under Section 104A which defines the special rate pool. This is confirmed by HMRC in its Capital Allowances Manual at reference CA23153 and in the general business guidance at HMRC HS252.
The special rate pool covers assets that have longer expected useful lives or higher embedded carbon, including:
- Solar photovoltaic (PV) systems and solar thermal
- Integral features (electrical systems, cold water systems, lifts, air conditioning, heating systems)
- Assets with an expected useful life of 25 years or more when first used
- Thermal insulation added to existing buildings
Because solar panels typically have a 25-year-plus design life, they fall within the "long-life asset" category and are placed in the special rate pool — not the main pool. This is the fundamental reason why full expensing (which is confined to main pool assets) is unavailable.
Key HMRC references
- CA23153: Confirms solar panels as special rate pool assets — gov.uk/hmrc-internal-manuals/capital-allowances-manual/ca23153
- Section 104A CAA 2001: Defines the special rate pool and its contents
- HS252: HMRC's general capital allowances guidance for businesses, confirms the special rate classification
- Section 50AAB CAA 2001: Full expensing provisions — explicitly limited to main pool expenditure
The Three Tax Routes for Factory Solar Panels
Factory owners investing in solar have three capital allowances routes available. The right choice depends on the size of the investment and what other capital expenditure the business is making in the same year.
Route 1 — Annual Investment Allowance (AIA)
The Annual Investment Allowance is the most commonly used route for factory solar installations and will be the right choice for the vast majority of businesses. It allows a 100% deduction of qualifying expenditure in the year of purchase, subject to an annual monetary limit.
AIA key facts
- Allowance rate: 100% of qualifying expenditure
- Annual limit: £1,000,000 per year (permanent since April 2023)
- Eligible assets: Both main pool and special rate pool assets, including solar panels
- Timing: Must be claimed in the tax return for the accounting period in which expenditure is incurred
- Limit applies to group/associated companies: The £1M limit is shared between associated businesses, not available per company in a group
For most factory solar installations — which typically range from 50kW (around £37,500) to 1MW (around £750,000) — the full cost falls comfortably within the £1M AIA limit. This means the entire capital cost can be deducted against taxable profits in year one.
Worked example: 500kW factory solar system
System details
- System capacity: 500kW
- Capital cost: £375,000
- Corporation tax rate: 25%
- AIA claimed: £375,000
Tax outcome
- Taxable profit reduced by: £375,000
- Tax saving at 25%: £93,750
- Tax saving at 19% (small profits rate): £71,250
- Effective cost after tax (25%): £281,250
The tax saving is received via the corporation tax return, either as a reduced tax bill or a repayment where an advance payment has been made. The timing of the cash benefit is important — speak to your accountant about corporation tax instalment dates.
Worked example: 150kW factory solar system
System details
- System capacity: 150kW
- Capital cost: £112,500
- Corporation tax rate: 25%
- AIA claimed: £112,500
Tax outcome
- Tax saving at 25%: £28,125
- Net cost after tax relief: £84,375
- Typical annual energy saving: ~£30,000–£45,000
- Adjusted payback: approximately 2.0–2.8 years
The AIA is straightforward to claim. Your accountant will include it in the capital allowances computation attached to your corporation tax return (CT600) for the period in which you incurred the expenditure.
Route 2 — 50% First Year Allowance (FYA) for Special Rate Assets
The 50% First Year Allowance was introduced alongside full expensing in April 2023 and was made permanent in the Autumn 2023 Budget. It is specifically designed for special rate assets, which is exactly what solar panels are.
50% FYA key facts
- Allowance rate: 50% of qualifying expenditure in year one
- Annual monetary limit: None — applies to the full value of qualifying special rate expenditure
- Permanence: Made permanent from Autumn 2023. No planned end date.
- What qualifies: Special rate assets including solar panels, integral features, and long-life assets
- Remainder: The unrelieved 50% enters the special rate pool and is written down at 6%/year
- Exclusions: Cars, assets used for leasing, second-hand assets
The 50% FYA is the correct route for factory solar investments exceeding £1M, where the AIA limit is insufficient to cover the full cost. It is also available to companies that have already exhausted their AIA on other qualifying assets in the same year.
Worked example: £2M industrial solar installation
| Year | Event | Allowance | Tax saving (25%) |
|---|---|---|---|
| Year 1 | 50% FYA on £2M | £1,000,000 | £250,000 |
| Year 2 | 6% WDA on £1M pool balance | £60,000 | £15,000 |
| Year 3 | 6% WDA on £940,000 pool balance | £56,400 | £14,100 |
| Year 4+ | 6% WDA (reducing balance) | Declining each year | Declining |
On a £2M installation using the 50% FYA, the total NPV of tax relief over 25 years (at 25% tax and a 5% discount rate) is approximately £420,000–£450,000, with £250,000 received in year one.
Route 3 — Special Rate Writing Down Allowance (WDA)
The Special Rate Writing Down Allowance is the default position if you do not claim AIA or the 50% FYA. It provides relief at 6% per year on a reducing balance basis.
Special Rate WDA key facts
- Rate: 6% per year (reduced from 8% in April 2019)
- Basis: Reducing balance — 6% applied to the unrelieved pool balance each year
- Limit: No annual monetary limit
- Recovery timeline: Takes approximately 11 years to recover 50% of the original cost; over 35 years to recover 90%
- When to use: When AIA has already been used in full by other assets, or when the 50% FYA is not desirable for cash flow reasons
The WDA alone is a poor outcome for solar investment. On a £375,000 system, the year-one WDA is just £22,500 — compared to a £93,750 tax saving from AIA. Factory owners should always explore AIA and the 50% FYA before defaulting to the WDA.
What About Full Expensing?
Full expensing was introduced for companies on 1 April 2023 and made permanent from April 2024 (Finance Act 2024). It provides a 100% first-year allowance with no annual monetary limit. On paper, this sounds ideal for solar — but solar panels are excluded.
Why solar cannot use full expensing
- Full expensing applies under Section 50AAB CAA 2001, which is expressly limited to main pool expenditure.
- Solar panels are special rate pool assets. They are not main pool assets.
- HMRC's own guidance in the Capital Allowances Manual (CA23153) confirms solar is special rate.
- A separate provision — Section 50AAC — introduced a 50% first-year allowance for special rate assets, which is the provision that applies to solar.
The confusion arises because installers and generic finance websites often simplify the message to: "solar qualifies for 100% allowances." This is only true for amounts within the AIA limit. It is never true under the full expensing provisions, which do not cover solar at all.
| Allowance | Rate | Applies to Solar? | Reason |
|---|---|---|---|
| Full Expensing (s.50AAB) | 100%, no limit | No | Main pool assets only. Solar is special rate. |
| AIA (s.38A) | 100%, up to £1M | Yes | Covers both main pool and special rate assets. |
| 50% FYA (s.45A / s.50AAC) | 50%, no limit | Yes | Designed specifically for special rate assets. |
| Special Rate WDA | 6%/year | Yes | Default for all special rate pool assets. |
Worked Examples for UK Factory Owners
The following examples illustrate how capital allowances interact with different system sizes and installation budgets. All examples assume the company pays corporation tax at 25% (main rate, applicable to profits over £250,000). The 19% small profits rate applies to profits below £50,000; marginal relief applies between £50,000 and £250,000.
Example 1: Small manufacturing unit — 150kW system
A family-run manufacturing business with annual profits of £500,000 installs a 150kW rooftop solar system.
Capital cost
£112,500
AIA deduction
£112,500 (100%)
Tax saving (25%)
£28,125
- Net cost after tax relief: £84,375
- Estimated annual energy saving: £30,000–£42,000
- Adjusted payback period: approximately 2.0–2.8 years
- Route: AIA (full expenditure within £1M limit)
Example 2: Mid-size factory — 500kW system
A medium-sized food manufacturer installs a 500kW system on its main production building.
Capital cost
£375,000
AIA deduction
£375,000 (100%)
Tax saving (25%)
£93,750
- Net cost after tax relief: £281,250
- Estimated annual energy saving: £95,000–£130,000
- Adjusted payback period: approximately 2.2–3.0 years
- Route: AIA (well within £1M limit)
Example 3: Large industrial site — £2.5M solar installation
A large automotive parts manufacturer installs a 3MW solar array across three factory roofs. Total capital cost: £2,500,000. The business has not used AIA on any other assets this year.
| Portion of cost | Route | Year 1 deduction | Tax saving at 25% |
|---|---|---|---|
| First £1,000,000 | AIA | £1,000,000 | £250,000 |
| Next £750,000 (50% of £1.5M) | 50% FYA | £750,000 | £187,500 |
| Remaining £750,000 (enters special rate pool) | 6% WDA from year 2 | £0 (year 1) | £0 (year 1) |
| Total year 1 | £1,750,000 | £437,500 |
Year 2 onwards: The £750,000 special rate pool balance attracts WDA at 6% per year (reducing balance). Year 2 WDA: £45,000, tax saving £11,250. Year 3 WDA: £42,300, and so on.
Business Rates Exemption — an Often-Missed Saving
Alongside capital allowances, rooftop solar installations on non-domestic buildings benefit from a permanent business rates exemption. This is a separate financial benefit that many factory owners overlook entirely when calculating the return on a solar investment.
Business rates exemption: the key rules
- Applies to: Rooftop solar on non-domestic buildings (factories, warehouses, offices)
- Does not apply to: Ground-mounted solar arrays (these attract separate business rates assessments)
- Permanence: The exemption is permanent and has been in place since 2012
- Effect: The presence of solar panels does not increase the rateable value of your factory building
- Annual saving: Estimated £2,000–£15,000+ per year depending on system size and local multiplier
Without this exemption, a large rooftop solar system could theoretically increase a factory's rateable value, triggering higher annual business rates. The exemption removes this risk entirely. Over a 25-year system life, the compounded value of this exemption can be substantial — for a £5,000/year saving, the undiscounted total is £125,000.
Note that the business rates exemption applies independently of and in addition to the capital allowances regime described above.
VAT on Factory Solar Panels
The VAT position on factory solar is time-sensitive and represents a significant additional financial consideration.
Current VAT rates for solar installation
- Until 31 March 2027: 0% VAT on solar panel supply and installation (confirmed)
- From 1 April 2027: 20% standard rate is currently proposed to apply
- Saving for qualifying installations before April 2027: 20% of total supply and installation cost
For a factory spending £500,000 on solar before 31 March 2027, the 0% VAT rate saves £100,000 compared to the standard 20% rate. For a £1M installation, the VAT saving is £200,000.
Businesses that are fully VAT-registered and make wholly taxable supplies would normally recover VAT on purchases regardless of the rate. However, where a business has partial exemption or cannot recover VAT (for example, certain financial services businesses, NHS trusts, or businesses with significant exempt supplies), the 0% rate is a genuine cost saving.
Even for fully VAT-registered businesses with full input tax recovery, the 0% rate removes the cash flow cost of paying VAT and then reclaiming it — which, for large installations, can represent a meaningful working capital benefit.
Smart Export Guarantee (SEG) — Income from Surplus Export
The Smart Export Guarantee (SEG) requires licensed electricity suppliers with 150,000 or more domestic customers to offer export tariffs to eligible generators. This is an additional income stream for factory solar owners, above and beyond energy cost savings.
SEG at a glance
- Typical export rates: 15p–24p per kWh (varies by supplier and tariff)
- Eligibility: Systems up to 5MW with an MCS-certified installation
- What is exported: Electricity generated but not consumed on site
- Tax treatment: SEG income is taxable as trading income or a miscellaneous receipt
- Typical factory export rate: 20–35% of total generation (depending on working hours and energy profile)
Factory-sized solar systems typically export less than domestic systems because factories are large consumers with the generation capacity usually sized to match daytime demand. Nevertheless, evening, weekend, and holiday generation typically results in meaningful export.
| System Size | Annual Generation | Est. Export (25%) | SEG Income (18p/kWh) |
|---|---|---|---|
| 100kW | ~85,000 kWh | ~21,250 kWh | ~£3,825/yr |
| 500kW | ~425,000 kWh | ~106,250 kWh | ~£19,125/yr |
| 1,000kW | ~850,000 kWh | ~212,500 kWh | ~£38,250/yr |
SEG income is taxable, which slightly reduces the net benefit. At 25% corporation tax, £19,125 of SEG income results in approximately £14,344 after tax. Even so, this is meaningful additional income that contributes to the overall payback calculation. For more on the financial return from factory solar overall, see our industrial solar ROI calculator.
The Full Financial Picture: Combining All Benefits
Capital allowances do not exist in isolation. They are one component of a wider financial case for factory solar. The table below shows all key financial benefits for a typical 500kW factory installation.
| Benefit | Estimated Value | Timing |
|---|---|---|
| AIA tax relief (25% on £375,000) | £93,750 | Year 1 (tax return) |
| Annual electricity cost saving | £95,000–£130,000/yr | Ongoing (25+ years) |
| SEG export income (net of tax) | ~£14,000–£19,000/yr | Ongoing |
| Business rates exemption (rooftop) | £3,000–£10,000/yr | Ongoing |
| VAT saving (if partially exempt) | Up to £75,000 | Year 1 (if before Apr 2027) |
Capital Allowances FAQ for Factory Solar
Can we claim full expensing on our solar panels?
No. Full expensing (the 100% first-year allowance introduced in April 2023) applies only to main pool plant and machinery. Solar panels are classified as special rate assets and are explicitly excluded from full expensing provisions. Many websites incorrectly claim otherwise. The correct 100% route for solar is the Annual Investment Allowance (AIA), which has a £1M annual limit. For amounts over £1M, the 50% First Year Allowance applies. See HMRC Capital Allowances Manual CA23153 for confirmation of solar's classification.
What is the AIA limit for the current tax year?
The AIA is currently £1,000,000 per year and has been at this level since 1 January 2016 (made permanent from April 2023 by the Finance Act 2023). The limit is per business, not per asset. Where businesses are associated (broadly, under common control), the £1M must be shared. Most factory solar installations fall within the £1M limit.
Do we need to choose between AIA and the 50% FYA?
Yes. These are separate provisions and you must elect one or the other for a given piece of expenditure — they cannot both apply to the same asset. For most factories with a solar cost below £1M and available AIA headroom, AIA is the better choice (100% relief vs 50%). For systems over £1M, it makes sense to use AIA on the first £1M and the 50% FYA on the remainder. Your accountant will determine the optimal allocation considering all capital expenditure in the year.
How does the 50% FYA interact with our regular capital allowances pool?
When you claim the 50% FYA, you deduct 50% of the qualifying expenditure in year one. The remaining 50% is added to your special rate pool, which is entirely separate from your main pool. From year two, the special rate pool balance is written down at 6% per year on a reducing balance. The main pool (for other plant and machinery) is unaffected and continues to attract WDA at 18%/year.
What happens to the balance after claiming 50% FYA?
The unreduced 50% enters your special rate pool. It then receives writing down allowances at 6% per year on a reducing balance. For example, if you claim 50% FYA on a £2M installation, £1M enters the pool. Year 2 WDA: £60,000. Year 3 WDA: £56,400 (6% of £940,000 remaining balance). This continues over many years. The full theoretical relief is eventually available, but the reducing balance method means recovery is slow.
Is the 50% FYA permanent?
Yes. The 50% First Year Allowance for special rate assets was made permanent in the Autumn 2023 Budget (Finance Act 2024). There is no scheduled end date. It applies to qualifying expenditure incurred on or after 1 April 2023 (for corporation tax) and 6 April 2023 (for income tax, i.e. sole traders and partnerships). Future Budgets could in theory change this, but the permanence signals strong policy commitment.
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