How long does commercial solar installation take?
A UK commercial solar installation takes 2–12 weeks on-site depending on system size. Including DNO G99 approval, structural survey and commissioning, the full project timeline from signed order to first generation is typically 3–6 months. A 100 kWp rooftop system takes about 3–4 weeks on-site; a 1 MWp system takes 8–12 weeks.
Last updated 26 July 2026.
Key facts at a glance
| 50 kWp system | 1–2 weeks on-site |
|---|---|
| 100 kWp system | 3–4 weeks on-site |
| 250 kWp system | 4–6 weeks on-site |
| 500 kWp system | 6–8 weeks on-site |
| 1 MWp+ system | 8–12 weeks on-site |
| DNO G99 approval | 45 working days statutory |
| Signed order → energisation | 3–6 months typical |
The commercial solar project timeline
The gating item is usually DNO G99 approval, not the physical install. Structural survey (2–3 weeks), design and DNO application (2 weeks), DNO response (up to 45 working days), materials lead time (2–6 weeks) and install run in parallel where possible.
What extends the timeline
Anything requiring a new HV connection or substation upgrade adds 3–9 months. Listed buildings, conservation-area planning applications, or asbestos re-roofs each add 6–12 weeks. Requesting DNO early — during feasibility, not after design — usually eliminates the biggest risk.
Related reading
FAQ
Can commercial solar be installed while the business is operating?
Almost always yes. Most warehouse, factory and office solar installs happen with zero downtime — scaffolding and roof work run outside operational hours where needed. Final grid tie-in requires a short (typically 2–4 hour) power-down.
How long until the system generates electricity?
From physical completion, energisation is typically 1–2 weeks — the time to complete DNO commissioning tests and switch on export.
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