How much does a 100 kW commercial solar system cost?

A 100 kW commercial solar system in the UK costs £85,000-£110,000 turnkey in 2026. The variation comes down to roof type, whether you need a three-phase upgrade, panel tier, optimiser specification, and whether the install triggers a G99 DNO application. The midpoint figure of around £92,000 covers a clean install on a single-pitch metal roof with three-phase already on site, Tier 1 panels, SolarEdge optimisers, MCS commissioning, and a 10-year insurance-backed workmanship warranty.

What 100 kW physically looks like

A 100 kW system uses around 185 panels (assuming 540 W modern modules) covering roughly 600 m² of roof. That fits comfortably on most light-industrial unit roofs, larger office buildings, retail showroom roofs, or detached garden centre buildings. On the typical 1990s steel-portal warehouse with 800-1,200 m² of roof, a 100 kW system uses around half the available roof — leaving headroom for future expansion.

You’ll need either three-phase electrical supply (standard on industrial sites) or a three-phase upgrade (£2,500-£8,000) before commissioning. 100 kW on single-phase is not technically possible — UK distribution rules cap single-phase G98 installs at around 3.68 kW (16 A per phase), and even the streamlined G99 fast-track caps a single phase at 17 kW.

Cost breakdown — typical 100 kW SME install

Component	Approximate cost
185 x Tier 1 540W panels	£29,000
Inverters (e.g. 2 x SMA 50 kW or SolarEdge equivalent)	£14,500
Power optimisers (185 units)	£18,000
Mounting system (clip-fix or rail)	£6,500
AC/DC cabling, isolators, switchgear	£5,500
Scaffolding/access	£3,500
Structural roof survey	£900
DNO application (G99 if applicable)	£2,500
MCS commissioning + building control	£1,800
Smart export meter	£350
Project management	£4,500
Subtotal	£87,050
10-year IWA workmanship warranty	£2,400
Turnkey before VAT	£89,450

Annual generation and savings

A well-sited 100 kW system in the UK Midlands generates 88,000-95,000 kWh per year (lower in the north, higher in the south-west). For a daytime-occupied office or light-industrial unit, expect:

• Self-consumption: 60-75% of generation displaces grid electricity at ~38p/kWh
• Export: 25-40% sold via SEG at 4–12p/kWh (Octopus Outgoing Fixed pays 12p as at July 2026)
• Annual saving: £18,000-£25,000

After 100% AIA tax relief, a £92,000 install costs a profitable limited company £69,000 net. With £22,000/year savings, payback drops to around 3.1 years.

What pushes the price toward £110,000

• Pitched tile or slate roof (panels need penetrating fixings + flashings)
• Three-phase supply upgrade required
• Asbestos roof that must be over-clad before install
• Heritage considerations or planning conditions
• Battery storage included (add £25,000-£45,000 for a 50 kWh battery)
• Constrained DNO area requiring transformer upgrade

Common misconceptions

“100 kW pays back in 6-7 years” — that was true in 2021 when grid electricity was 14p/kWh. At today’s 38p commercial rates, payback for a daytime-occupied site is closer to 4 years. Conversely, watch out for installers quoting 3-year paybacks on weekend-only or evening-occupied sites — without battery storage, self-consumption falls below 30% and payback stretches to 7+ years.

Another misconception: that 100 kW is the cap for “small” commercial. The G98/G99 boundary is 16 A per phase — about 3.68 kW on single-phase, or roughly 11 kW across three phases. Above that everything is G99, though fully type-tested systems up to 17 kW per phase (roughly 50 kW three-phase) take a streamlined fast-track. A 100 kW install is past both, so it always requires a full G99 application, which adds 6-18 months to the DNO connection timeline. Plan accordingly.

Next steps

For a fixed-price 100 kW quote based on your meter data and roof drawings, contact us. For wider cost context, see cost guide and grants and funding. Related FAQs: cost per kW, system size sizing, payback period.