100kW Solar System Cost UK — 2026 Guide
A 100kW commercial solar system costs £80,000 to £95,000 fully installed in 2026 — £800–£950 per kWp. This is the most commonly installed commercial size in the UK, and the point where solar starts behaving like infrastructure rather than equipment.
Why 100kW is the UK's default commercial size
Three things converge at 100kW. The per-kWp price has fallen well below small-system rates. The roof area required — around 450–500 square metres — fits the standard portal-frame units that dominate UK industrial estates. And the output, 85,000–95,000 kWh a year, matches the consumption of a huge band of British businesses: precision manufacturers, food processors, cold stores, distribution operators, leisure centres and schools.
| Cost line | Typical 2026 range |
|---|---|
| Panels (~220 × 455W, tier-1) | £20,000–£26,000 |
| Inverters (2–3 string inverters) and protection | £6,000–£9,000 |
| Mounting system | £7,000–£9,500 |
| Electrical installation, DC/AC cabling, LV connection | £17,000–£22,000 |
| Access: scaffold towers, MEWPs, edge protection | £6,000–£10,000 |
| Design, G99, structural engineer, commissioning, witnessing | £5,000–£7,500 |
| Monitoring platform, export metering, O&M handover | £2,000–£3,000 |
The grid connection becomes a real workstream
At 100kW the G99 application stops being a formality. Your district network operator will assess whether the local transformer and feeder can absorb the export, and respond with one of three answers: a clean approval, an approval with export limitation, or a quotation for reinforcement works. The first two are common; the third is worth knowing about before you commit, which is why we recommend the DNO application go in at the fixed-price stage, not after contract.
Budget guidance: application and witnessing costs of £1,000–£2,500 are normal and should be inside the quote. Reinforcement, where required, is wildly site-specific — anything from £3,000 to £50,000 — and is the single best reason to get the DNO answer early.
Worked example: plastics manufacturer, Yorkshire
A plastics firm running two shifts installs 100kW at £86,500 on a trapezoidal roof with good access. Modelled yield: 91,000 kWh. Self-consumption hits 84% thanks to the second shift, displacing grid power at 25.8p/kWh — £19,700 a year — with export earning a further £1,100. The company claims the Annual Investment Allowance, cutting year-one corporation tax by about £21,600. Net effective cost ~£64,900; simple payback on net cost about 3.1 years; ROI over the 25-year panel warranty exceeds 500% even with conservative degradation and flat energy prices.
Comparing 100kW quotes properly
Two quotes £10,000 apart are usually not the same project. Check: panel wattage and tier, inverter brand and warranty length, whether scaffolding and the G99 are included, whether an export limitation device is priced, what structural verification is included, and whether out-of-hours installation (if your operation can't pause) is in scope. Our price factors guide walks through each line. If you're weighing up capital purchase against a funded route at this size, the finance vs purchase comparison includes a 100kW worked case. Larger roof? The kWp economics keep improving at 250kW.
100kW solar system — common questions
How big is a 100kW solar installation physically?
Around 215–225 panels at 450–460W, needing 450–500 square metres of clear roof. That is comfortably accommodated on a typical 1,000–1,500 square metre industrial unit once rooflights, plant and edge zones are excluded.
How long does a 100kW project take end to end?
Three to five months is normal: 1–2 weeks for desk feasibility, 2–4 weeks for survey and fixed pricing, 4–12 weeks for the G99 approval depending on DNO workload, then 2–3 weeks on site. The install itself is rarely the bottleneck — the grid application is.
What does a 100kW system save per year in 2026?
Yield is typically 85,000–95,000 kWh per year. A weekday business self-consuming 70% at 26p/kWh saves around £16,400 a year plus £1,300–£2,000 in export income. A seven-day operation self-consuming 90% saves over £21,000. Payback at 2026 prices is typically 4–6 years.
Will the DNO limit how much I can export?
Sometimes. In congested areas the DNO may offer a connection with limited or zero export rather than fund reinforcement. An export limitation device caps what flows to the grid while leaving on-site use untouched. For most daytime-heavy businesses the revenue impact is small — self-consumption is where the value is anyway.