Roof Not Suitable? Solar Carport or Roof Solar for Business
Carport or rooftop? For many commercial sites the answer is both. Here's the head-to-head comparison covering economics, planning, EV integration, and visibility.
Per-kWp install cost
Typical UK ranges. Rooftop: £700-£900/kWp turnkey. Carport: £950-£1,300/kWp turnkey. The 25-35% premium for carport reflects: structural steel (vs free rooftop), foundations and groundworks, planning permission overhead, longer DC and AC cable runs.
Annual yield
Rooftop (south-facing 35° tilt): 968 kWh/kWp/yr in Birmingham on PVGIS v5.3. Carport at a 10° pitch: 875 kWh/kWp/yr in Birmingham, ranging from 946 in Cardiff to 772 in Glasgow — a shallow canopy gives up 9.5-11.5% against a 35° array. A bifacial uplift of 5-12% from tarmac reflection applies on top of the canopy figure, not on top of the rooftop one.
Available area
Rooftop: limited to roof footprint (and often only ~60% of roof is usable after vents, plant, edge zones, skylights, MGA). Carport: limited to car park footprint, but typically gives more useful area than the building's roof. Some sites have more car park area than roof area.
Structural overhead
Rooftop: requires structural survey of existing roof. Many UK commercial roofs (asbestos, lightweight membrane, old steel) cannot take PV load without strengthening. Carport: builds own structure; no constraint from existing building.
Planning
Rooftop: typically Permitted Development (Class A or J, GPDO 2015). Carport: permitted development under Part 14 Class OA subject to prior approval, which the authority has 56 days to determine — a full application only where the canopy exceeds 4 m, sits within 10 m of the curtilage of housing, or is in a listed building's curtilage. Budget 8-12 weeks either way, because the DNO connection usually sets the programme. See solar carports.
EV integration
Rooftop: difficult — chargers go in car park, panels on roof, requiring AC cable run between them. Carport: built-in — DC stubs at column bases, cable runs are short and integral to carport design.
Visibility and brand
Rooftop: typically not visible from ground level. Carport: highly visible — visible from car park, often from street. Strong sustainability marketing surface.
Combine both
A common pattern for decarbonisation: install rooftop first (faster, cheaper), then add carport as a second phase. Where the car park area exceeds the roof area, the result can be materially more on-site solar than rooftop alone could deliver.
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Related reading: the Class OA planning route · the capital allowances position · car park solar panels.
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