What size solar system does my business need?
Size a commercial solar system to match your daytime electricity demand, not your total annual bill. A good starting rule: 1 kWp of solar per 1,000 kWh of annual daytime consumption. A business using 250,000 kWh/year with 60% daytime demand needs roughly 150 kWp — enough to cover most on-site load without heavy export.
Last updated 26 July 2026.
Key facts at a glance
| Sizing rule of thumb | 1 kWp per 1,000 kWh annual daytime consumption |
|---|---|
| Space per kWp (rooftop) | ~5–7 m² of usable roof |
| Space per kWp (ground-mount) | ~12–15 m² |
| Target self-consumption | 60–80% |
| Small business (10–30 staff) | 20–50 kWp typical |
| Mid-size warehouse / factory | 150–500 kWp typical |
| Large DC / 24-7 site | 500 kWp–2 MWp |
Start from consumption, not roof area
The most common sizing mistake is filling the roof. Over-sizing pushes generation into low-value export (typically 4–6p/kWh under SEG vs 24–28p saved on self-consumed grid units) and can trigger a costly HV grid upgrade. Match kWp to daytime demand first.
When to over-size deliberately
If you plan EV charging, electrification of heat (heat pumps), or 24/7 shift extension within 3–5 years, size for future load. Similarly for on-site battery storage or a private-wire arrangement across an estate.
Related reading
FAQ
How many panels for a 100 kWp system?
About 220 panels at 460 W each, or 200 panels at 500 W. Modern 550 W commercial panels need roughly 180 panels for 100 kWp.
How much roof space for 100 kWp?
Around 500–700 m² of usable roof (approximately 5,400–7,500 sq ft) for a standard rooftop install.
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