The comparison in 2026
UK farm rooftops typically have pitches of 5-15° — substantially below the theoretical optimum of 30-35° for UK latitude. Should racking be designed to optimise tilt (using sloping mounts) or follow the existing roof pitch? The choice affects cost, generation, and structural complexity.
Detailed comparison
Following roof pitch (typical 10° farm roof). Simpler racking; lower wind loading; lower visual impact; cheaper to install. Generation impact: a 10° south-facing pitch vs 30° optimum loses approximately 6-8% annual generation. Optimised tilt (30° racking mounts on a 10° roof). More complex mounting; higher wind loading (especially in coastal locations); slightly more expensive to install — typically £100-£150/kW additional racking cost. Captures the full theoretical optimum (35° tilt). Net economics. For a 200 kW install: roof-pitch following generates approximately 180,000 kWh/year; optimised tilt 192,000 kWh/year. Difference 12,000 kWh/year worth approximately £2,500/year. Racking premium: £20-30,000. Payback on the racking premium: 8-12 years. When optimised tilt wins. Shallow flat roofs where tilt adds substantially to generation (e.g., 0-5° roofs); ground-mount installations where structural cost increase is small; installations where peak summer generation matters less than year-round consistency; installations on sites where SEG export is a key income stream. When roof-pitch following wins. Standard pitched UK farm roofs (5-15° pitch); cost-sensitive installs; coastal locations where wind loading matters most; installations where install speed and simplicity are valued. Flat-roof case (specifically). Almost always justifies optimised tilt — the generation gap between 0° (flat) and 30° (optimum) is 12-15% annual generation. Tilted ballasted racking standard on flat farm rooftops. Recommendation. For most UK farm installs with pitched roofs (5-15°): follow the roof pitch. For flat roofs: optimised tilt. For ground-mount: optimised tilt.
How to decide for your specific install
The right choice depends on the specifics of your farm: roof geometry; load profile; capital sensitivity; future expansion plans; long-term operational priorities. We model multiple specification scenarios in every feasibility study where the choice is material. Send us your half-hourly meter data and building dimensions — we deliver a free desk feasibility within 7 working days, including specification recommendations with clear rationale.
Common questions
What do you typically recommend?
Depends on the specifics of the site. Our default approach is documented in the comparison above; we model alternative scenarios where the project requirements suggest different specification choices.
How material is the difference in practice?
Most specification differences sit at the margin of project economics — typically 2-10% impact on overall 25-year NPV. The fundamental decision (whether to install PV at all) is far more material than the specification choice within PV.
Can we change specification later?
Some changes possible without complete reinstall (e.g., battery brand, inverter replacement at end of life). Other choices (e.g., optimised tilt vs roof-pitch following) are baked in at install. Specification decisions for permanent elements should be made carefully at design stage.
Do you have a preferred manufacturer or product?
We're independent of any specific manufacturer. Every quote includes specification recommendations specific to the site geometry, the farm's strategic priorities, and current market pricing. We never push a specific brand without rationale.