The finance directors who are changing their view of solar are not doing so because of net zero commitments or PR value. They are doing so because they have run the numbers carefully and found that commercial solar meets the investment criteria they apply to other capital projects — with better downside protection than most. This article sets out the financial framework they are using and the questions any FD should be asking before the next energy contract renewal.
The Capital Allocation Framework
Most FDs evaluate capital investment through a lens of payback period, IRR, net present value, and opportunity cost. Solar scores well on all four, particularly when assessed against the counterfactual of continuing to purchase electricity from the grid at rising rates rather than against a zero-cost baseline.
A commercial solar system typically has a payback period of four to eight years depending on system size, roof characteristics, consumption profile, and prevailing energy tariff. Over a 25-year system lifetime, the return multiple on the original capital investment is typically five to ten times — before accounting for energy price inflation, which improves the return further. Compare that to a fleet vehicle replacement cycle delivering functional depreciation, or IT infrastructure with a three to five year refresh cycle and no residual financial return, and solar starts to look structurally attractive.
4–8 yrs
typical commercial solar payback period
12–20%
typical IRR over a 25-year system lifetime
25+ yrs
expected operational life of commercial solar panels
The key insight for most FDs is that solar is not a cost item — it is a capital asset that generates a financial return. The framing matters for how it is evaluated, how it is financed, and how it appears on the balance sheet.
How Solar Affects EBITDA
EBITDA is the most widely used measure of business operating performance. Solar improves it directly by reducing energy expenditure, which flows straight through to operating profit. The mechanism is simple: every kilowatt-hour generated and consumed on-site is one fewer unit purchased from the grid. At current commercial electricity rates of 22 to 30p/kWh, that saving accumulates quickly.
A medium-sized commercial site consuming 150,000 kWh/year and self-generating 80,000 kWh through a 70 kWp rooftop solar installation might save £18,000 to £24,000 per year in avoided electricity costs. That saving flows directly to EBITDA. Over five years, the cumulative EBITDA improvement from this single investment is £90,000 to £120,000 — before accounting for energy price rises, which improve the return over time.
Illustrative EBITDA Impact — 70 kWp Commercial Installation
| Metric | Value |
|---|---|
| Annual generation | ~63,000 kWh |
| Self-consumption rate | 70–80% |
| Units offset from grid | ~44,000–50,000 kWh |
| Saving at 25p/kWh | £11,000–£12,500/yr |
| 5-year cumulative saving (flat rate) | ~£55,000–£62,500 |
| System cost (approximate) | £65,000–£85,000 |
| Payback period | 5–8 years |
Illustrative only. Actual figures depend on roof orientation, shading, consumption profile, and grid tariff.
Balance Sheet Treatment and Financing Options
How solar is financed determines how it appears on the balance sheet and what it does to key financial ratios. FDs have three primary routes, each with different accounting and cash flow implications.
Outright capital purchase
The system is capitalised as a fixed asset, depreciated over its useful life (typically 20–25 years under standard accounting treatment). The full capital allowance benefit is available in the year of purchase under the Annual Investment Allowance, effectively reducing the net cost by the corporation tax rate (25% from April 2023). This is typically the highest-return route for profitable businesses with available capital.
Asset finance or commercial loan
The capital outlay is financed over three to seven years, with monthly repayments structured to be lower than the monthly energy saving — creating positive cash flow from the outset. Interest charges are tax-deductible. This route preserves working capital and allows investment without drawing on reserves or credit facilities.
Power Purchase Agreement (PPA)
A third party owns and maintains the system; the business purchases the solar electricity at a fixed below-market rate, typically for 10 to 20 years. There is no capital outlay, no asset on the balance sheet, and no depreciation to manage. The trade-off is that the savings are lower than outright ownership and there is no residual value at contract end.
Energy Price Risk: The FD's Hidden Liability
Most businesses do not quantify their energy price risk in the same way they quantify interest rate risk, FX exposure, or credit risk. This is a gap in financial risk management that solar can partially close. A business spending £60,000 per year on electricity with no on-site generation is fully exposed to grid price movements. A business that has offset 60% of its consumption with on-site solar has reduced that exposure by 60% — permanently, for the life of the system.
In a period of long-term energy price volatility, this risk reduction has real financial value. A business that can demonstrate to investors, lenders, or acquirers that it has structurally reduced its exposure to energy price rises is, all else equal, a more predictable and defensible business. That has implications for cost of capital, covenant headroom, and valuation multiples.
The tax treatment adds further clarity. The Super Deduction has been replaced by a 100% First Year Allowance for new plant and machinery through most capital allowance categories applicable to solar equipment. A business investing £80,000 in a commercial solar installation in a 25% corporation tax environment effectively reduces the net cost by £20,000 in the year of investment, improving both the payback period and the IRR.
Making the Internal Case for Solar Investment
For FDs building the business case internally, the most effective structure focuses on financials first and sustainability second — because the financial case is stronger and more defensible. The following framework covers the key components of a robust board-level submission.
- 1
Establish the baseline: current annual energy spend, average unit rate, and consumption profile by time of day. Request half-hourly data from your supplier if not already available.
- 2
Commission a feasibility study: a qualified commercial solar installer should provide generation modelling, self-consumption estimates, system sizing options, and indicative capital costs. Omni3 provides this at no charge.
- 3
Model three scenarios: outright purchase (showing Annual Investment Allowance benefit and payback), asset finance (showing monthly cash flow from day one), and PPA (showing risk-free cost reduction with no capex).
- 4
Quantify the energy risk reduction: express the current grid exposure as a percentage of annual energy spend and show how solar reduces that exposure over the system lifetime.
- 5
Include the ESG and reporting angle: for businesses subject to TNFD, TCFD, or supply chain sustainability requirements, on-site renewable generation provides measurable, auditable carbon reduction data. This has increasing commercial value in tender processes and financing relationships.
Frequently Asked Questions
How is commercial solar treated for corporation tax?
Solar equipment qualifies as plant and machinery for capital allowance purposes. Under the Annual Investment Allowance, the full cost can be written off against taxable profits in the year of investment, up to the AIA limit (currently £1 million). This effectively reduces the net cost by the prevailing corporation tax rate (25% for most companies) in year one, materially improving the payback period and IRR.
Does solar appear on the balance sheet?
Under outright ownership, yes — as a fixed asset (plant and machinery) subject to depreciation over its useful life. Under a PPA structure, the system is owned by the third party and does not appear on your balance sheet. Asset finance arrangements create both an asset and a corresponding liability. The appropriate treatment depends on the financing structure and should be confirmed with your auditors.
Can solar improve our EBITDA in year one?
Yes, if financed correctly. Annual energy savings begin from the moment the system is commissioned. Under asset finance, where monthly repayments are structured below the monthly energy saving, there is a positive EBITDA contribution from month one. Under outright purchase, the EBITDA improvement is immediate but the capital has already been deployed.
How does solar affect business valuation?
Solar improves EBITDA, which is typically the primary driver of business valuation for SMEs (valued at an EBITDA multiple). A £20,000 annual energy saving at a 5x multiple adds £100,000 to enterprise value. Beyond the direct EBITDA effect, demonstrable energy cost reduction and ESG credentials can be attractive to acquirers focused on operational resilience and sustainability.
What is the typical IRR for a commercial solar installation?
For a well-designed commercial installation, the IRR typically falls in the 12–20% range over a 25-year lifetime at current energy prices. The return improves if energy prices rise above the base case. It is less sensitive to energy price falls because the system generates returns from the first year and most of the return is front-loaded in years one to ten.
Related pages
Important disclaimer. The financial figures and projections in this article are illustrative only. Actual returns depend on system size, consumption profile, energy tariff, and financing structure. Tax treatment described is based on UK corporation tax rules current as of June 2026 and may change. This article does not constitute financial, tax, or investment advice. Independent professional advice should be sought before making capital investment decisions. Last updated June 2026.