Commercial solar system size calculator (UK)
Sizing a commercial solar system means balancing three constraints: your daytime electricity demand, your usable roof area, and your available capex. Use our free calculator to get an instant kWp recommendation, or read the sizing method below.
Sizing calculator at a glance
Best fit business types
- Any UK business exploring commercial solar
- Owner-occupiers weighing capex vs PPA
- Multi-site portfolios planning roll-out
- Facilities managers producing feasibility briefs
- Finance teams stress-testing payback
Design and spec notes
- Consumption-led sizing: 1 kWp per 1,000 kWh annual daytime consumption.
- Roof-led sizing: ~150 W/m² of usable south-facing roof.
- Budget-led sizing: capex ÷ £800/kWp ≈ system size.
- Cross-check all three before committing.
Related reading
FAQ — Sizing calculator systems
How accurate is the sizing calculator?
Within about 15% of a full feasibility study — enough to inform go/no-go decisions. A structural and DNO check is required before order.
What if my roof is smaller than my consumption suggests?
Fit the largest system the roof supports, then consider a solar carport or ground-mount for the residual — or a sleeved PPA for portfolio coverage.
Request your free feasibility review
Share a few details and our team will send a no-obligation review of your site — indicative system size, annual generation, savings and payback. Prefer to explore numbers yourself first? Run the calculator or contact us directly.
- MCS & RECC accredited installer
- Response within one working day
- No cost, no obligation