100kW Commercial Solar System Cost & Payback UK 2026

A 100kW commercial solar system is one of the most common UK rooftop sizes — sized for mid-sized warehouses, secondary schools, mid-tier hotels, mid-sized factories, distribution depots, larger offices, supermarkets. This page gives you the live 2026 cost, generation, savings, and payback numbers, taken directly from our installed fleet. No marketing fluff: real numbers from real installs.

100kW Solar System — Quick Numbers (UK 2026)

Here is what a 100kW commercial solar PV system typically delivers across the UK in 2026:

• Typical panel count: ~220 panels at 455 Wp tier-1 monocrystalline.
• Roof area required: approximately 560 m² of usable, south-facing or east/west roof.
• Annual generation: ~95,000 kWh per year (UK national average — Midlands).
• Installed cost: £90,000–£115,000 including VAT, design, supply, install, DNO, commissioning.
• First-year saving: £27,500–£28,500 (assumes 80% self-consumption, 20% export at SEG rates).
• Simple payback: 3.2–4.2 years before any AIA or finance is applied.
• 25-year lifetime savings: £712,000+ at current grid prices.

100kW Solar System Cost Breakdown

The £90,000–£115,000 install range for a 100kW system breaks down approximately as:

• Panels (45%): tier-1 monocrystalline panels (JA Solar, Trina, Longi, Jinko) — £40,500–£51,750
• Inverters (15%): string or central inverters (SolarEdge, SMA, Huawei) — £13,500–£17,250
• Mounting & cabling (12%): roof-rated mounting hardware, DC cable, AC cable — £10,800–£13,800
• Installation labour (15%): rigging, electrical, MCS commissioning — £13,500–£17,250
• Design, DNO & paperwork (8%): structural sign-off, G99 application, MCS pack — £7,200–£9,200
• Contingency (5%): scaffolding, weather, late-stage variations — £4,500–£5,750

100kW Solar System Payback Analysis

A 100kW system installed in 2026 pays back in approximately 3.2–4.2 years for most UK businesses. The exact figure depends on three factors:

• Self-consumption ratio. Higher daytime electricity use = faster payback. A 100kW system feeding a 24/7 industrial load pays back ~6–8 months faster than one feeding a 9-to-5 office.
• Grid tariff. Businesses paying 30p+/kWh see paybacks at the lower end (3.2 years); businesses on legacy contracts at 18–22p/kWh see paybacks at the upper end.
• Finance route. Capital purchase has the fastest paper payback. PPA gives day-one cashflow positive without capital outlay. Asset finance over 7 years often gives a net-positive monthly position from month one.

What Properties Suit a 100kW System?

A 100kW commercial solar system is a strong fit for mid-sized warehouses, secondary schools, mid-tier hotels, mid-sized factories, distribution depots, larger offices, supermarkets. The roof must offer approximately 560 m² of usable space — clear of significant shading, plant rooms, skylights, and rooflights. Roof age matters: panels carry 25-year warranties and are typically not lifted off mid-life, so the underlying roof should have ≥10 years of remaining life. Where the roof is older, our team specs a coordinated roof-and-solar refurbishment.

Tax Treatment of a 100kW Solar Investment

For UK companies, a 100kW solar system qualifies for either:

• Annual Investment Allowance (AIA): 100% first-year capital allowance up to the AIA cap (£1m as at 2026). For most 100kW systems, 100% of the install cost can be written off against the company's taxable profit in year one.
• Full Expensing: 100% deduction on main-pool plant for limited companies. Full Expensing is now permanent for solar PV under HMRC's 2024–2026 capital allowances reform.

For a £90,000–£115,000 install at 25% corporation tax, the post-tax effective cost reduces to £67,500–£86,250. Always confirm allowances with your accountant before committing.

Get a Fixed-Price 100kW Solar Quote

Send us your last 12 months of half-hourly meter data plus a sketch (or postcode) of the building. We will return:

• A specific 100kW system design tailored to your roof — panel count, layout, orientation, inverter sizing.
• An accurate annual generation forecast modelled in PVSyst from your local irradiance data.
• A first-year and 25-year saving forecast based on your actual tariff structure (not generic averages).
• A fixed-price quote inclusive of design, supply, install, DNO, commissioning, MCS handover.

The desk feasibility takes 3–5 working days and is free. From signed proposal to commissioned system: typically 8–14 weeks.

Frequently Asked Questions

What is a 100kW solar system?

A 100kW (kilowatt) commercial solar PV system uses approximately 220 solar panels with a combined nameplate capacity of 100 kilowatts. It generates around 95,000 kWh of electricity per year in the UK, enough to offset 60–90% of typical commercial electricity usage.

How much does a 100kW solar system cost in the UK?

As of 2026, a 100kW commercial solar system costs £90,000–£115,000 fully installed in the UK. This includes panels, inverters, mounting, cabling, electrical work, design, DNO application, MCS commissioning, and 25-year output warranty.

How much will a 100kW solar system save me?

A 100kW system typically saves £27,500–£28,500 per year, depending on grid tariff, self-consumption, and export rates. Over the system's 25-year warrantied life, lifetime savings are typically £627,000+ even after accounting for panel degradation.

How long does a 100kW solar install take?

From signed contract to commissioning: typically 8–14 weeks for a 100kW rooftop system. This includes 1–2 weeks design and DNO submission, 4–8 weeks lead time for panels and inverters, 1–3 weeks of on-site install, and final MCS commissioning.

What roof size do I need for a 100kW system?

A 100kW solar system requires approximately 560 m² of usable roof. The roof should be south, east, or west facing, with no major shading from neighbouring buildings or trees. Flat roofs work well using ballasted mounting at 10–15° tilt; pitched roofs use rail-mounted in-line systems.

Related Guides

• Commercial solar panel cost — full UK guide
• How a commercial solar install works step by step
• Commercial solar grants and incentives
• Solar finance, PPA and lease options
• AIA and Full Expensing on commercial solar
• Get a fixed-price solar quote