Solar farm vs rooftop solar: when each makes sense in 2026
UK commercial solar has two principal deployment modes: rooftop on existing commercial property, and ground-mount (solar farm) on agricultural or industrial land. The two have very different economics, planning, and operational characteristics. This guide covers when each makes sense.
Side-by-side comparison
| Feature | Rooftop solar | Solar farm (ground-mount) |
|---|---|---|
| Typical scale | 10 kWp - 5 MWp | 1 MWp - 350 MWp+ |
| £/Wp installed | £0.60-£1.20 | £0.45-£0.75 (utility scale) |
| Planning | Mostly permitted development | Full planning consent required |
| Land use | Existing roof | 0.5-1 acre per 250 kWp |
| BMV agricultural land | N/A | Strong planning presumption against |
| NSIP threshold | N/A | Above 50 MWp = nationally significant |
| Self-consumption | 20-95% typical | Usually 0% (wholesale market) |
| DNO connection | Property's existing supply | New connection required, often substantial cost |
| Construction time | 2-6 weeks | 6-12 months |
| Income type | Self-consumption + SEG + REGO | Wholesale PPA + REGO |
| IRR (typical) | 12-22% | 8-14% |
Which one for your business? Real scenarios
Commercial property with adequate roof
Recommendation: Rooftop solar. Higher IRR, faster delivery, no planning consent required, immediate self-consumption value.
Farm with marginal land + barn roofs
Recommendation: Combination. Maximise rooftop on barn buildings (FETF-eligible); add ground-mount on marginal land for additional generation. Best both worlds.
Investor / utility-scale developer
Recommendation: Solar farm. Scale economics favour large ground-mount. Multi-acre sites with wholesale PPA secured to a long-term buyer.
Commercial property with constrained roof but adjacent land
Recommendation: Combined. Maximise rooftop; supplement with on-site ground-mount where land permits. Behind-the-meter ground-mount captures self-consumption value.
Public sector estate with land available
Recommendation: Combine. Schools and councils with multiple roofs and grounds achieve best economics combining rooftop self-consumption with ground-mount export. PSDS funding routes available for both.
Key deciding factors
- Rooftop solar IRR (12-22%) consistently beats ground-mount IRR (8-14%) — self-consumption captures retail electricity rate (~28p) vs ground-mount captures wholesale rate (~8-12p).
- Solar farm above 50 MWp is a Nationally Significant Infrastructure Project — Secretary of State approval, 18-30 month consent timeline.
- BMV agricultural land (Grade 1, 2, 3a) faces strong planning presumption against ground-mount. Grade 3b, 4, 5 are typically easier.
- AONBs, National Parks: ground-mount solar almost always refused.
- Solar canopies over car parks combine ground-mount-equivalent generation with retained land use — sometimes the optimal compromise.
- Rooftop project is typically delivered in 4-8 months end-to-end; solar farm 18-36 months.
Comparison FAQs
Why is rooftop solar IRR higher than ground-mount?
Self-consumption captures retail electricity rate (~28p/kWh). Ground-mount exports at wholesale (~8-12p/kWh). The 16-20p/kWh difference compounds over 25 years.
Can I install solar farm on my farm land?
Subject to planning. Grade 1-3a agricultural land is heavily protected. Grade 3b, 4, 5 land is more permissible. Local plan and ecology assessment material.
What is the NSIP threshold?
50 MWp in England (was 350 MWp before recent reforms). Solar farms above this threshold need DCO consent via the Secretary of State — 18-30 month process.
Should I do rooftop + ground-mount combined?
Yes if both opportunities exist. Maximise rooftop first (highest IRR), then add ground-mount for additional generation. Strong economics for sites with land + roof.
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