Commercial Solar Cost UK 2026: Per Watt & Per kW

Commercial Solar Cost: Per Watt & Per kW at a Glance

The headline number businesses ask for is cost per watt (or per kWp — kilowatt-peak). The table below shows total installed cost, cost per watt, and cost per kWp across the most common UK commercial system sizes in 2026. Per-watt cost falls as system size rises, because fixed costs (scaffolding, design, DNO application, commissioning) spread across more capacity.

* 500kWp per-kWp cost is £700–£850/kWp. All figures are supply-and-install (panels, inverters, mounting, scaffolding, electrical works, G99 application, commissioning) and exclude VAT. Actual cost varies by roof type, location, and DNO connection complexity.

What Is the Installed Cost Per Watt for Commercial Solar?

For 2026, UK commercial solar installs at £0.75–£1.05 per watt for typical 50–250kWp rooftop projects. The cost-per-watt metric is how most installers and energy managers compare quotes, because it normalises for system size. Key reference points:

• Small (10–30kWp): £0.85–£1.30/W — fixed costs (scaffold, design, DNO) weigh heavily on small systems.
• Mid (50–250kWp): £0.72–£1.05/W — the sweet spot for most commercial rooftops.
• Large (500kWp–1MWp+): £0.65–£0.85/W — economies of scale on procurement and labour.

If a quote comes in materially above £1.20/W for a mid-size system, ask what's driving it — it may reflect a difficult roof (fragile, asbestos, steep pitch), an expensive DNO reinforcement, or simply an uncompetitive margin. Our guide to evaluating a commercial solar quote covers what a fair quote should contain.

How Much Does a 100kW Commercial Solar System Cost?

A 100kWp commercial solar system costs £75,000–£105,000 fully installed in 2026 (£750–£1,050 per kWp). It generates around 90,000–100,000 kWh per year depending on location and roof orientation, displacing roughly £18,000–£25,000 of grid electricity annually at current commercial rates of 20–27p/kWh. That puts simple payback at 4–6 years before incentives.

After claiming the Annual Investment Allowance (AIA) at the 25% corporation tax rate, a £100,000 system returns £25,000 in first-year tax relief, cutting the net cost to £75,000 and shortening payback to roughly 3.5–4.5 years. A 100kWp array typically needs 450–600m² of unshaded roof — a fit for a mid-size warehouse, factory, or large office.

What Affects Commercial Solar Installation Cost?

Several factors move the final price within (and occasionally outside) the per-watt ranges above:

• System size: the single biggest driver of per-watt cost — bigger is cheaper per watt.
• Roof type and condition: standing-seam and trapezoidal metal roofs are quick and cheap to mount; fragile, asbestos, or aged felt roofs add cost (overcladding or remediation). Pitched and tiled roofs cost more than flat.
• Mounting system: ballasted flat-roof systems vs penetrative fixings vs lightweight non-penetrating systems for low-load-capacity roofs.
• Inverter strategy: central string inverters (cheapest), or optimisers/microinverters where shading or complex roofs demand it.
• DNO grid connection: a straightforward G99 acceptance adds little; a constrained network needing reinforcement can add thousands and months. See our DNO connection guide.
• Scaffolding and access: multi-storey or restricted-access sites cost more.
• Battery storage: optional, adds £400–£600/kWh but lifts self-consumption and unlocks extra savings.

What's Included in a Commercial Solar Price?

A fixed-price commercial solar quote should be supply-and-install and cover: MCS-accredited solar panels (Tier-1 modules, e.g. JA Solar, Trina, Longi); inverters (e.g. SMA, Huawei, Sungrow, Solis); the mounting/racking system; DC and AC electrical works and isolation; a G99/G98 protection device and the DNO application; scaffolding and access; structural sign-off; commissioning, MCS certification and handover; and monitoring. Beware quotes that exclude scaffolding, the DNO application, or the structural report — these can add 10–20% if billed later.

Financial Incentives That Reduce the Net Cost

The sticker price is not the net cost. UK businesses can stack several incentives:

• Annual Investment Allowance (AIA): 100% first-year tax deduction on qualifying plant including solar — up to £1,000,000 per year. At 25% corporation tax, that returns 25p in the pound. See solar capital allowances.
• Smart Export Guarantee (SEG): get paid 8–20p/kWh for surplus electricity exported to the grid.
• Industrial Energy Transformation Fund (IETF): grants of 30–60% for energy-intensive manufacturers. See commercial solar grants.
• 0% VAT on qualifying installations with a residential element; recoverable VAT for VAT-registered businesses on pure commercial installs.

For a full ROI picture including these incentives, see our commercial solar payback period guide or try the commercial solar calculator.

How to Finance Commercial Solar

Three common routes, each with a different cash-flow profile:

• Outright purchase: best lifetime ROI, full AIA benefit, you own the asset and all the savings. Best when capital is available.
• Asset finance / leasing: spread the cost over 5–10 years; monthly repayments are often lower than the energy savings, so the system is cash-flow positive from day one. See commercial solar financing.
• Power Purchase Agreement (PPA): a third party funds, owns, and maintains the system; you buy the electricity it generates at a fixed rate below grid price, with zero capital outlay. See commercial solar PPA.

Worked Example: Business With a £50,000 Annual Electricity Bill

A business paying £50,000/year for electricity at 25p/kWh uses around 200,000 kWh annually. A 150kWp solar system (cost ~£120,000–£150,000) generates ~140,000 kWh/year, covering 60–70% of daytime demand. At 80% self-consumption, that saves roughly £28,000–£32,000/year. After AIA tax relief (~£35,000 at 25% CT), the net cost is around £100,000, giving a payback of 3.5–4 years and a 25-year saving exceeding £700,000. Add a battery and self-consumption rises toward 90%, improving the return further.

Cost by Building Type

Different commercial buildings carry different typical system sizes and costs. For sector-specific cost guidance see factories, warehouses, farms, and offices. For a breakdown of what goes into the installation itself — labour, scaffolding, grid connection, commissioning — see our installation cost breakdown.