A common starting question from UK warehouse operators: how many panels will fit on my roof? The answer depends on roof area, mounting system, sprinkler clearances, and panel size. This guide walks through the math with worked examples for typical UK warehouse buildings.
Modern panel size and density
Utility-grade Tier-1 panels in 2026 are typically 2.0-2.4 sqm each (1700×1130 mm to 2278×1133 mm) at 405-560W per panel. Mounting density on flat warehouse roofs is typically 5-7 sqm per kW installed (panel area + tilt spacing + walkway clearances). Modern profiled steel roofs achieve denser packing than membrane roofs (which require larger ballast spacing).
Sprinkler and roof obstruction reductions
LPC sprinkler clearances reduce usable roof area by 8-15% typically (1m clear to deflector, 0.6m at high-bay). Rooflights, M&E plant, and roof access walkways reduce usable area further — typically another 10-25%. After these deductions, usable PV area is typically 60-80% of nominal roof area.
Worked examples
50,000 sqft warehouse (4,650 sqm gross roof): usable PV area ~3,500 sqm. PV capacity at 6 sqm/kW = 580 kW (~1,100 panels at 530W).
100,000 sqft warehouse (9,300 sqm gross roof): usable PV area ~6,500 sqm. PV capacity ~1.1 MW (~2,000 panels).
200,000 sqft warehouse (18,600 sqm gross roof): usable PV area ~13,500 sqm. PV capacity ~2.2 MW (~4,200 panels).
400,000 sqft warehouse (37,200 sqm gross roof): usable PV area ~26,500 sqm. PV capacity ~4.4 MW (~8,300 panels).
When DNO capacity is the binding constraint
For warehouses above 1.5-2 MW capacity, DNO grid connection often becomes the binding constraint rather than roof area. Sites with grid headroom can install up to physical roof capacity; sites with grid constraints may be limited to 1-3 MW. We pre-check DNO capacity during structural survey.
When to install less than maximum capacity
Maximum roof PV capacity isn't always the optimum. Self-consumption ratio drops rapidly above 100% of daytime baseload — excess generation exports at SEG (5-15p/kWh) versus avoided grid retail (22p/kWh). For most warehouse types, we size to 90-110% of metered daytime baseload, not to roof maximum.