Rooftop vs Ground-Mount vs Solar Carport

Most commercial solar lands on the roof, but the roof is not always the right answer. A building with a tired membrane, a small footprint, or a large car park may generate more, sooner, and at a better return from the ground or over the parking bays. The three siting options — rooftop, ground-mount and solar carport — differ on cost per kWp, planning route, how much generation you can fit, and the secondary value they unlock. This guide compares them so you can decide where the array should go before you commission a feasibility study.

The decision is rarely binary. Larger sites mix siting types — roof for the cheapest kWp, a carport over staff parking for EV amenity, ground-mount on a spare paddock if the roof and car park together cannot meet demand. What matters is matching siting to the asset: roof condition, available land, parking, the half-hourly load profile and your G99 grid headroom. Get those right and the cost per kWp and payback follow.

The three options at a glance

Figures are indicative and ex-VAT (0% VAT on commercial solar since April 2022). Always confirm against a site-specific feasibility study.

Rooftop: the default, and usually the cheapest

For most commercial buildings the roof is the lowest cost per kWp because the supporting structure already exists — you are buying panels, mounting and inverters, not land or steel. Flat roofs typically use ballasted systems that sit on the membrane without penetration, preserving any membrane warranty; pitched, metal-deck and standing-seam roofs use clamped mounts. Either way a structural roof-loading survey to BS EN 1991 is a precondition, because the added dead and wind load must be within the roof’s capacity.

Planning is now straightforward for most schemes. The 1 MW cap on commercial rooftop permitted development was removed on 21 December 2023 (SI 2023/1279), so larger arrays proceed under Class J permitted development with a 56-day prior approval — not a free pass, but a far shorter route than full planning. The constraint that catches owners out is roof age: if the membrane has under 15 years of life left, you should re-roof and install solar in one project rather than fix panels to a roof you will strip in a decade.

Rooftop is the right starting point when the roof is sound, the orientation is workable and the building’s daytime load is high enough to self-consume the output. The detail on mounting and roof types sits in our commercial solar roof types guide.

Ground-mount: when you have land, not roof

Ground-mount makes sense when the roof cannot carry an array, the building is listed or has a fragile membrane, or daytime demand outstrips what the roof and car park can supply. It also gives full control over tilt and orientation, which lifts yield per panel above a sub-optimal roof.

The trade-offs are land and planning. A megawatt of ground-mount needs roughly four to five acres, so this is for owners with spare paddock, yard or brownfield. On planning, the permitted development route (Class K) is narrow and capped, so most commercial ground-mount needs full planning permission — a longer, less certain process involving landscape, ecology and glint-and-glare assessment. Civils, frames and longer cable runs also push the cost per kWp above rooftop, though at scale the per-kWp panel cost still falls.

Ground-mount suits sites with genuine surplus land and a high, steady load — think manufacturing, industrial and logistics estates or rural commercial holdings. Where land is the binding constraint, pairing a smaller ground array with rooftop and a carport often beats trying to site everything in one place.

Solar carport: parking into generation, plus EV

A solar carport puts the array on a steel canopy over parking bays. It costs more per kWp than rooftop because you are also paying for the structure, but it earns that back in three ways: it generates where you have no usable roof, it provides weather cover for vehicles, and it pairs naturally with EV charging — the canopy carries the panels and the chargers in one structure, and smart charging can soak up daytime solar directly.

Planning improved here too. Class OA permitted development now covers car-park solar canopies in England, subject to prior approval, with limits including a maximum height of 4 metres and a 10-metre standoff from any dwelling; glare is assessed at prior-approval stage. That makes a carport a far quicker consent than ground-mount for many sites. The catch is the same one that governs every option above ~50kW: the G99 DNO connection is usually the real bottleneck, not planning, so check grid headroom early.

Carports are the best fit for owners with a sizeable, well-used car park — retail parks, offices, leisure and destination sites — especially where EV charging is becoming an expectation. For the structural detail and EV pairing see our solar carports for commercial property guide and the dedicated solar car parks and canopies resource.

How to choose

Work through the asset in order. Is the roof sound with over 15 years of membrane life and adequate structural capacity? If yes, rooftop is almost always the cheapest route and your default. If the roof is weak, listed or too small for your load, do you have a sizeable, used car park? A carport converts that into generation and EV amenity under Class OA. Only if neither roof nor car park can carry enough — and you hold spare land — does ground-mount with full planning earn its place.

Two factors sit across all three. First, self-consumption drives the return: every unit you use on site saves ~24–28p versus the ~12–16p SEG export rate, so siting that matches generation to your daytime load beats raw capacity. Second, the G99 connection above ~50kW determines what you can actually export and often what you can install — settle that with your DNO before committing to a siting strategy. The wider consent and grid picture is covered in our planning and grid guide, and you can pressure-test the numbers with our cost guide or request a feasibility study.

Frequently asked questions

Is rooftop always cheaper than ground-mount or a carport?

Per kWp, almost always — the building already provides the structure, so you avoid the cost of land prep, frames or a steel canopy. Rooftop typically runs around £700–1,100/kWp falling with scale, while ground-mount adds civils and cabling and carports add the canopy structure (often 30–60% more than rooftop). The exception is when the roof needs replacing first or cannot take the load, at which point another siting type may give a better whole-project return.

Do I need full planning permission for each option?

It depends on the route. Rooftop now proceeds under Class J permitted development (prior approval) since the 1 MW cap was removed on 21 December 2023, and car-park canopies fall under Class OA permitted development (also prior approval). Ground-mount has only a narrow, capped permitted development route (Class K), so most commercial ground arrays need full planning. None of these is a guaranteed pass — prior approval still assesses matters like glare — and above ~50kW the G99 DNO connection is usually the bigger hurdle.

Can I combine more than one siting type on a single site?

Yes, and larger sites often should. A common pattern is roof for the cheapest kWp, a carport over staff or customer parking for EV amenity, and ground-mount only if the first two cannot meet demand and you hold spare land. The right mix is set by roof condition, available land, parking and your half-hourly load profile — a feasibility study sizes each element against your grid headroom.