Rooftop vs Ground-Mount Solar for Manufacturing Sites

Most UK manufacturers weighing up solar assume the decision is simply “put panels on the roof”. For many sites that is the right answer, but not all. Roof condition, available land, the size of your daytime electrical load and your growth plans all change the maths. This guide compares rooftop and ground-mount solar across the five factors that actually decide it, gives you a side-by-side table, and sets out the cases where combining both is the strongest option.

Why the choice matters for manufacturing

Solar for a manufacturing plant is sized to your daytime baseload, not to how much roof you have. Compressors, motors, process heat, refrigeration and machinery draw a strong, daytime-weighted load that lines up well with the solar generation curve, which is why a correctly sized array can self-supply 30 to 60 percent of a plant’s annual demand. The working rule is to install 70 to 90 percent of peak daytime demand to maximise self-consumption and avoid spilling cheap exports onto the grid.

Where you mount the panels changes how easily you can hit that target. Rooftop uses space you already own and pushes generation right next to the load. Ground-mount frees you from roof constraints and can scale well beyond what a roof holds. The right answer depends on your site, so let us take the deciding factors one at a time.

Planning and permitting

Rooftop solar is the lighter path through planning. Permitted Development Rights under Class A Part 14 of the GPDO 2015 generally cover rooftop PV on industrial and manufacturing buildings, subject to size limits, provided the building is not listed or in a conservation area. Planning permission is only required where panels project more than 200mm above the roof plane, on principal elevations of certain heritage buildings, or on listed mill structures. For a typical portal-frame factory that means no planning application at all.

Ground-mount is a different regime. A field or yard array almost always needs full planning permission, and larger schemes attract scrutiny on landscape, ecology, glint and glare, and agricultural land classification. That adds months to the programme and a real risk of refusal or conditions. Neither route removes the grid-connection hurdle: a G99 application is required for connections above 17 kW per phase, typical DNO study responses run to around 65 working days, and actual connection dates land at 6 to 18 months on capacity-constrained networks. Apply early whichever mounting you choose, because the connection is usually the longest item in the programme. The official Smart Export Guarantee rules apply equally to both once you are MCS certified.

Land use and roof condition independence

This is where the two options diverge most sharply. Rooftop solar uses otherwise dead space, so it consumes no land you could use for expansion, yard, or parking. That is a genuine advantage on a tight industrial site. The catch is that rooftop depends entirely on the roof beneath it. Roof condition on pre-2000 industrial buildings is often unknown, and metal or asbestos-cement roofs may need refurbishment before any PV can be fixed. Asbestos-cement roofs cannot be retrofitted at all and must be replaced with a modern membrane first, and most pre-2000 industrial roofs need engineer sign-off before ballast or rail loading.

Ground-mount sidesteps the roof entirely. If your roof is aged, structurally marginal, cluttered with rooftop plant, or simply too small, a ground array on spare land or a yard delivers the same generation without touching the building. It also makes future re-roofing far simpler because you are not working around a live rooftop array. The trade-off is that it needs land you are willing to commit for 25 years or more, which many urban manufacturing sites do not have.

Self-consumption and generation

For a daytime-heavy manufacturing load, both mounting types feed the same meter, so the self-consumption story is similar in principle. The difference is in siting quality. Rooftop panels sit directly above the load with short cable runs, but their orientation is fixed by the roof pitch and they can be shaded by parapets, rooftop plant and adjacent buildings, which is why we run a 3D shading study before sizing. Ground-mount can be set at the optimum tilt and orientation and laid out to avoid shading, so per-panel yield is often a little higher.

Rooftop is more space-efficient per kilowatt of usable roof: roughly 5 to 6 square metres of roof per kW using 450W-plus panels, so a 500 kW system needs around 2,500 to 3,000 square metres of unobstructed roof. Ground-mount needs more total land per kW because of inter-row spacing to prevent self-shading, but land is often the thing you have spare when roof is the thing you do not. For an energy-intensive site where rooftop alone offsets only 30 to 60 percent of annual consumption, ground-mount capacity can close more of the gap before you reach for a green PPA or battery storage.

Scale and cost

Rooftop capacity is capped by the roof. Once you have filled the usable area, you are done, and for many manufacturers that ceiling still comfortably covers the daytime baseload. Across our manufacturing work, typical rooftop systems run from 150 kW for an engineering workshop up to 2,000 kW for a large automotive plant on a 3,000 to 12,000 square metre roof. Where the roof is the limit rather than the load, ground-mount lets you keep going.

On cost per kilowatt the two are broadly comparable at manufacturing scale. Installed cost is usually £750 to £950 per kW for systems above 250 kW, falling towards £600 per kW above 1 MW, and most projects reach simple payback in 5 to 7 years. Ground-mount saves on roof-fixing and access equipment but adds groundworks, fencing, security and often a longer cable run and civils, so the totals tend to converge. The capital is normally fully expensed in year one under the Annual Investment Allowance, which covers the first £1m of qualifying spend at 100 percent under the government’s capital allowances guidance. See our cost breakdown for the full modelling and our grants and funding guide for the IETF and Climate Change Agreement routes.

Rooftop vs ground-mount at a glance

Factor	Rooftop	Ground-mount
Planning	Usually Permitted Development on industrial buildings	Almost always full planning permission needed
Land use	Uses dead roof space, frees no land	Commits spare land or yard for 25 years plus
Roof condition	Depends on a sound roof; asbestos-cement must be replaced first	Independent of the roof entirely
Siting and yield	Fixed by roof pitch; shading from plant and parapets	Optimum tilt and orientation, easier to avoid shading
Space efficiency	High: 5 to 6 sqm of roof per kW	Lower per kW due to inter-row spacing
Scale ceiling	Capped by usable roof area	Scales with available land, past roof limits
Cost per kW	£750 to £950 above 250 kW, towards £600 above 1 MW	Broadly comparable; groundworks offset roof-fixing savings
Grid connection	G99 above 17 kW per phase, 6 to 18 months	Same G99 process and timescales

When a manufacturer should do both

Combining rooftop and ground-mount is not a compromise, it is often the best design. Consider it when:

• Your load exceeds your roof. An energy-intensive site whose rooftop array offsets only part of the baseload can add a ground array to push self-consumption higher before turning to a PPA. This is common on food and beverage sites where refrigeration, chilling and ovens run close to 24/7, giving exceptional self-consumption that a bigger system can serve. See our food and beverage manufacturing page.
• Part of your roof is not fit for PV. Where some roof bays are sound and others need replacing, you can install rooftop on the good bays now and make up the shortfall with ground-mount, rather than waiting on a full re-roof.
• You are phasing the investment. Fit the roof first for the fastest payback on space you already own, then add a ground array in a later phase as budget, land use or grid capacity allow.
• You are adding EV or fleet charging. Daytime charging of forklifts, plant vehicles and staff EVs absorbs generation at 100 percent self-consumption, and a combined rooftop and ground system gives you the headroom to feed both the plant and the chargers.

For sites where export capacity will not arrive in time, we phase the design with battery storage so you get immediate self-consumption while waiting for the export agreement, and battery starts to pay above roughly 250 kW where night shifts run or DUoS red-band charges are heavy.

How we decide it for your site

Every project starts with the same evidence base rather than a preference for one mounting type. We pull at least 12 months of half-hourly meter data to model your load shift by shift, run a structural survey and roofing-condition assessment, carry out a 3D shading study, and assess any spare land for a ground option. From that we recommend rooftop, ground-mount, or a combination, and share the full model so your finance team can stress-test the payback and IRR. Use of an MCS-certified installer is what keeps the roof warranty and SEG eligibility intact, and you can verify accreditation directly with MCS Certified.

If you know your annual electricity spend and roughly how much roof or land you have, that is enough for us to sketch the right approach. Request a free feasibility study and quote and we will come back with a sized, priced proposal, rooftop, ground-mount or both, within 7 working days.