100kWp commercial solar PV cost in the UK (2026)
At 2026 prices, a 100 kWp commercial solar PV system costs £80,000 - £100,000 installed (excl. VAT). After 100% Full Expensing for limited companies, net cost is around 25% lower. Typical post-tax payback: 3.2-4.1 years.
100 kWp cost summary
| System size | 100 kWp |
| Installed cost range (2026, excl. VAT) | £80,000 - £100,000 |
| £ per Wp | £0.80 - £1.00 |
| Number of panels (450W modules) | ~220 |
| Roof area required | ~560 m² |
| Annual generation (UK avg) | 95,000 kWh |
| Best fit for | medium factory, hotel, office complex, school, dairy farm, retail park anchor unit |
| Best grant stack | Full Expensing (limited co) or AIA (partnership) + SEG + regional grant £5k-£15k |
Year-1 maths breakdown
Worked example for a limited company at the 25% main corporation tax rate, with typical self-consumption assumptions for this system size.
| Gross capex (mid) | £90,000 |
| 100% Full Expensing tax saving (25% CT) | -£22,500 |
| Net effective cost | £67,500 |
| Annual self-consumption (60%) | 57,000 kWh saving £15,390/year |
| Annual SEG export (40%) | 38,000 kWh earning £1,140 - £5,700/year |
| Total year-1 savings/revenue | £16,530 - £21,090 |
| Post-tax payback | 3.2 - 4.1 years |
Typical roof & site requirements for 100 kWp
- Unshaded roof area: ~560 m² needed for 220 × 450W panels
- Roof condition: 15+ years remaining life expected — older roofs may need refurbishment first (adds £30-300k depending on size)
- Roof structure: imposed load 12-25 kg/m² — modern portal-frame and composite roofs typically fine; some 1960s-80s structures need Cat 2 survey
- Electrical service: three-phase G99 connection required; rural sites may need DNO capacity study (5-11 weeks lead time)
- Planning: typically permitted development for commercial rooftop solar; listed buildings and conservation areas require consent
- Insurance: notify your insurer before installation; typical premium impact £150-£800/year additional
Best grant fit for 100 kWp
Recommended grant stack
Full Expensing (limited co) or AIA (partnership) + SEG + regional grant £5k-£15k
Use the free eligibility calculator for a personalised grant match against your specific sector, postcode and ownership structure.
Generation & savings model
This page uses conservative 2026 assumptions:
- UK average insolation: 950 kWh/kWp/year
- Tier 1 panel pricing: £0.18/Wp landed
- Inverter pricing: £0.07/Wp
- Mounting + BOS: £0.18/Wp
- Install + DNO: £0.15-£0.30/Wp depending on roof type
- SEG floor: 3p/kWh (regulatory minimum)
- SEG ceiling: 15p/kWh (best 2026 fixed-tariff rate)
- Self-consumption rate: typical for medium factory, hotel, office complex, school, dairy farm, retail park anchor unit load profile
100 kWp commercial solar · FAQs
How much does a 100 kWp commercial solar system cost in 2026?
At 2026 prices, a 100 kWp commercial solar PV system costs approximately £80,000 - £100,000 installed (excl. VAT). After 100% Full Expensing tax relief for a limited company at the 25% main CT rate, net cost is around £60,000 - £75,000.
What is the payback period for a 100 kWp commercial solar system?
With 60% self-consumption and SEG export tariffs of 3p-15p/kWh, a 100 kWp system typically pays back in 3.2-4.1 years post-tax (limited company at 25% CT). Higher tax rates (sole trader at 45%) compress payback further.
What size roof is needed for a 100 kWp system?
A 100 kWp system requires approximately 560 m² of unshaded roof area — around 220 modern 450W solar panels. Modern industrial portal-frame buildings, large warehouses and big-box retail typically accommodate this comfortably.
How much electricity will a 100 kWp system generate?
In the UK (average insolation), a 100 kWp system generates approximately 95,000 kWh per year. Self-consumption rate depends on your load profile — 60% is typical for medium factory, hotel, office complex, school, dairy farm, retail park anchor unit.
Which grants apply to a 100 kWp system?
Best grant fit for this size: Full Expensing (limited co) or AIA (partnership) + SEG + regional grant £5k-£15k. Always use the eligibility calculator for a personalised match.
Can I get finance for a 100 kWp solar system?
Yes — at this scale, asset finance / hire purchase is the most common route (5-7 year terms at 7-11% APR in 2026). For systems above 250kWp, operating lease and PPA are also viable. See finance routes.
Get a sized quote for your 100 kWp project
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