100kW Commercial Solar Cost
100kW Commercial Solar System Cost & Payback UK 2026
A 100kW commercial solar system fits mid-sized warehouses and similar properties with approximately 560 m² of usable roof. Annual savings £18,000–£25,000, payback in 4–6 years.
100kW
System size
~95k
Annual kWh
£18-25k
Annual saving
4-6yr
Payback
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, and supermarkets. This page sets out the 2026 cost, generation, savings, and payback for a typical 100kWp commercial installation, based on current UK market rates.
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: £75,000–£105,000 including VAT, design, supply, install, DNO, commissioning.
- First-year saving: £18,000–£25,000 (assumes 80% self-consumption, 20% export at SEG rates).
- Simple payback: 4–6 years before any AIA or finance is applied.
- 25-year lifetime savings: £712,000+ at current grid prices.
100kW Solar System Cost Breakdown
The £75,000–£105,000 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 4–6 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 (around 4 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, a good installer 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.
- 50% first-year allowance: full expensing does not apply to solar — HMRC classes solar PV as special rate expenditure — but spend above the AIA cap qualifies for a 50% first-year allowance, with the balance written down at 6% per annum.
For a £75,000–£105,000 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 an installer your last 12 months of half-hourly meter data plus a sketch (or postcode) of the building. You should get back:
- 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).
- Expect a fixed-price quote inclusive of design, supply, install, DNO application, commissioning and 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 £75,000–£105,000 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 £18,000–£25,000 per year, depending on grid tariff, self-consumption, and export rates. Over the system's 25-year warrantied life, lifetime savings are typically £500,000+ 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.
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