Industrial & Manufacturing Unit Flat Roofs

Why manufacturing gives the fastest solar payback

The economics of solar on a factory roof are driven by one thing: a high, steady daytime electrical load. Compressors, extraction and ventilation, refrigeration, ovens and kilns, CNC and process machinery run through the working day, and that demand matches the solar generation curve almost perfectly. The result is the highest self-consumption of any sector — often 80 to 90 percent of the generation is used on site as it is produced, rather than exported — and self-consumption is where the money is, because every unit you generate and use is a unit you no longer buy at the full commercial rate. That is why a manufacturing array frequently pays back faster than any other flat-roof project, commonly in the region of five and a half years.

On a roof of 1,500 to 10,000 square metres, a system of 150 kW to 1 MW is typical, sized not to fill the roof but to match the load — there is usually little point generating far more than the process can consume unless a battery or a strong export position justifies it.

Older roofs, asbestos and the survey that comes first

Manufacturing units are often older than the sleek distribution sheds, and that changes the survey. Many were built with profiled-metal or asbestos-cement roofs, and any building from before 2000 needs an asbestos survey under the Control of Asbestos Regulations 2012 before any intrusive fixing. The felt or single-ply covering itself is usually fine; the real risk is legacy asbestos-cement sheets, rooflights or insulating board at penetrations, which must be managed by a licensed contractor where present. We flag this before anyone lifts a fixing, so it is dealt with properly rather than discovered mid-job.

The deck matters just as much. An older profiled-metal or concrete roof may have less residual capacity than a modern portal frame, so a structural engineer confirms it can carry the array’s 15 to 25 kilograms per square metre plus wind uplift before design. Where capacity is tight, a lighter low-ballast or mechanically-fixed system, or some strengthening, keeps the project viable.

Working around plant, rooflights and a live operation

A manufacturing roof is rarely a clear field. Extraction stacks, roof plant, rooflights and service penetrations break up the usable area, so the layout is designed around them rather than assuming the whole footprint is available. And the factory keeps running: the works happen on the roof above the slab while production continues below, phased so nothing on the floor stops. Where hot works over a sensitive process are a concern, the mounting and any roof detailing are specified to remove naked-flame risk.

Ballasted mounting and the wind calculation

As on any flat roof, the default is a ballasted, penetration-free system that never pierces the membrane and keeps the waterproofing guarantee intact, with the ballast weight and its heavier perimeter and corner zones set by a wind-uplift calculation to BS EN 1991-1-4. On a marginal deck, or where the membrane manufacturer will not accept ballast point loads, a sealed mechanically-fixed system is detailed to the manufacturer’s specification so the guarantee still holds. The choice follows the deck, the membrane and the wind zone, not a price list.

Self-consumption modelled from real data, and batteries

Because self-consumption drives the return, the system is sized from your half-hourly consumption data, not a rule of thumb. We model how much of the generation your process would actually use hour by hour across the year, and where a meaningful surplus would otherwise be exported cheaply, we size a battery to store it and lift the share used on site — or to shift load away from the most expensive grid periods. On a strong continuous load a battery is not always needed; on a more variable one it can transform the economics. We model it rather than assume it.

Capital allowances and funding

Commercial solar is eligible for capital allowances via the Annual Investment Allowance — it is special-rate plant, so the route is the AIA, not full expensing, which your accountant confirms. The array can be funded from capital, through asset finance or leasing, or under a PPA with no upfront cost. Where the site is public-sector — a research or training facility, for example — a fabric-and-generation project can sometimes fall within the Public Sector Decarbonisation Scheme, though that funds public bodies only and runs in competitive time-limited rounds.

What we do

We model the system from your consumption data, survey the roof including any asbestos and structural questions, design the ballast and layout to BS EN 1991-1-4, handle the G99 grid application, and install around your production. Every proposal is itemised in writing, with the self-consumption model, the structural sign-off and the DNO position set out in full — and we will tell you honestly if the roof needs attention before a 25-year array goes on.