Ground-mount vs roof-mount commercial solar — which suits your site?

The default for commercial solar is the roof — it's dead space you already own, and it's usually the cheapest, simplest option. But it's not the only one, and it isn't always the best. If you have spare land, or a roof that can't take panels, ground-mount is worth understanding.

This guide is about where the array physically sits. It's a different question from which way the panels point once they're there — that's covered in south-facing vs east-west arrays, and it applies to both mounting types. Decide the location first, using the tests below; orientation is the next decision, not this one.

Roof-mount: the sensible default

In its favour:

• No land cost. You're using space that's otherwise doing nothing.
• Usually no planning application. Since the 1MW cap was removed in 2023, most commercial rooftop solar is permitted development (see planning permission).
• Shorter cabling runs from panels to your switchgear, and the array sits right where the power is used — so less cable, less trenching, and marginally lower transmission losses.
• Generally lower cost per kWp for a straightforward install — no groundworks, foundations, or fencing.

The constraints:

• The roof limits the system size. You can only fit what the roof holds, which may be less than your consumption justifies.
• Roof condition and structure matter. An old roof, a weak structure, or awkward orientation/shading can rule it out or add cost (see the site survey).
• Maintenance access is harder. Cleaning and repairs mean working at height, which means access equipment and a higher day rate.
• It's tied to the roof's life. If you re-roof in ten years, the panels have to come off and go back on — budget roughly £40–£80 per panel for a strip-and-refit, and check who carries that cost in your contract.

Ground-mount: when land changes the picture

In its favour:

• Scale. The system is limited by land, not roof area, so you can build bigger — useful if your demand outstrips what the roof can supply.
• Optimal orientation and tilt. Ground arrays can be set at the ideal angle rather than being dictated by the roof's shape, typically winning back 5–10% yield versus a compromised roof pitch.
• Easy access. Maintenance, cleaning, and repairs are at ground level — cheaper and simpler over the system's life, with no access equipment to hire.
• Roof-independent. No structural worries, and re-roofing never disturbs the array.

The costs and catches:

• It uses land that might have other value (parking, expansion, yard space).
• Groundworks and foundations, perimeter security/fencing, and longer cabling/trenching back to your building all add cost.
• It usually needs planning permission. Unlike rooftop, ground-mount beyond a very small size is not permitted development and requires a full planning application — adding time and uncertainty.

How much land does it actually take?

This is the question that decides most site conversations, and it's rarely answered plainly.

A ground-mounted array needs far more area than the panels themselves, because the rows have to be spaced to stop them shading each other through the winter months when the sun is low. The standard UK planning rule of thumb is roughly 4 to 5 acres per MWp — about 2 hectares — for a conventional fixed-tilt ground array.

Scaled to the sizes SMEs actually build:

• 100 kWp — roughly half an acre (~0.2 ha)
• 250 kWp — roughly 1 to 1.25 acres (~0.5 ha)
• 500 kWp — roughly 2 to 2.5 acres (~1 ha)

Compare that with roof-mount, where the same 250 kWp needs around 1,200–1,500 m² of usable roof — because panels sit flat to the roof plane with little or no inter-row spacing. That's the core trade: the ground needs three to four times the footprint for the same capacity. If your "spare land" is a corner of the yard, run those numbers before anyone gets excited.

The cost gap, honestly

Per-kWp costs move with scale and site conditions, so treat these as shape rather than a quote:

• Roof-mount, 30–250 kWp: around £900/kWp installed is a reasonable planning figure for a straightforward commercial roof.
• Ground-mount at small scale (under ~150 kWp): typically 10–25% more than the equivalent roof array. Foundations, fencing and trenching are largely fixed costs, so they hurt most when spread over few panels.
• Ground-mount at larger scale (400 kWp+): the gap narrows and can invert, because those fixed costs spread across more capacity and the install itself is faster per panel on open ground than at height.

So the intuitive answer — "the ground must be cheaper, there's no working at height" — is usually wrong for the sizes most SMEs build, and only becomes right once you're building at a scale where the groundworks amortise. On top of the capex, budget for the planning application itself: £600–£3,000+ in fees and consultant time for a small commercial scheme, plus any ecology or landscape surveys the council asks for.

Planning: the timeline that catches people out

Rooftop is usually permitted development and you can move at the speed of your installer. Ground-mount is a full application, and the calendar is not negotiable:

• Statutory determination period: 8 weeks for a minor application, 13 weeks for a major one. A ground array over 0.5 hectares is commonly treated as major.
• In practice: allow 3 to 6 months from first drawing to decision once you include pre-application advice, validation, consultee responses and the committee cycle.
• Common conditions: landscape screening, ecology mitigation, glint-and-glare assessment near an airfield or major road, and a decommissioning plan.

None of that is a reason to avoid ground-mount. It's a reason not to promise the board an install date before you have a decision, and a reason to start the planning conversation in parallel with — not after — the DNO connection application, which has its own timescale and is the more common true bottleneck.

The hybrid worth knowing: solar carports

If your "spare land" is a car park, solar carports (canopies) are a third option: panels on raised structures over parking. You get ground-mount's access and orientation benefits, keep the land's primary use, provide shade and shelter, and create a natural home for EV charging fed by your own solar (see EV charging and solar).

The catch is cost. The steelwork is doing two jobs — carrying panels and spanning parking bays — so carports typically run £1,400–£2,000/kWp, comfortably the most expensive of the three. They earn that back only where the car park is genuinely surplus to nothing, the shelter has real amenity value, or EV charging is going in anyway and the groundworks can be shared. Price it as a car-park upgrade that happens to generate, not as a cheap way to add solar.

How to decide

Work through it in order:

1. Is your roof suitable — sound structure, reasonable orientation, not heavily shaded, with years of life left? If yes, start there; it's usually cheapest and avoids planning.
2. Is the roof big enough for the system your consumption justifies? If the roof caps you well below your demand, ground-mount (or a roof-plus-ground mix) lets you build to the right size.
3. Do you have land you can spare — at the three-to-four-times footprint the rows actually need, not the panel area? And the appetite for a 3–6 month planning process?
4. Got a big car park and EV plans? Price a solar carport against both.

A roof-plus-ground hybrid is often the honest answer for a growing site: build the roof now because it's quick and unplanned, and hold the land option for when demand justifies phase two.

Sanity-check

1. Roof condition and remaining life — confirmed by survey, with the strip-and-refit cost understood if you re-roof mid-life?
2. Roof capacity vs your demand — does the roof alone meet your needs, or does it cap you well short?
3. Spare land — genuinely available at 4–5 acres per MWp, or earmarked for parking, storage or expansion?
4. Planning — have you factored 3–6 months and £600–£3,000+ for a ground array, and started the DNO application in parallel?
5. Scale — under ~150 kWp, is ground-mount actually costing you 10–25% more for no yield gain?

The bottom line

For most SMEs the roof is the right answer: cheapest, fastest, usually no planning. Reach for ground-mount when the roof is unsuitable or too small for the system you need — accepting that you're trading the roof's simplicity for three-to-four times the footprint, groundworks, and a planning process measured in months. The cost advantage people assume ground-mount has doesn't appear until you're building at several hundred kWp. And if you've a large car park, let a solar carport into the comparison — but price it honestly, because it's the dearest option per kWp by some distance.

To size a system against your usage, run the calculator. For which way the panels should face once you've chosen where they sit, see south-facing vs east-west arrays; for the planning and DNO detail, planning permission for commercial solar. Monthly intel: the Brief.

General information. Land-area and cost figures are planning rules of thumb — confirm roof suitability by survey, land area by measured site plan, and planning status with your local authority.