Solar for modular buildings: the complete supplier and installer
Solar for modular buildings is the discipline of putting working PV on roofs that were never engineered to carry it. Modular buildings — the volumetric, factory-built units that now house classrooms, clinics, offices and site facilities across the UK — have roofs rated for their own weight and the weather, typically 8-15 kg/m², not for a rooftop array. Conventional commercial solar weighs too much. The answer is a lightweight system engineered from the mounting up to deliver full generation at 8-12 kg/m² installed, verified to BS EN 1991 against the manufacturer's loading table.
We cover the whole of solar for modular buildings three ways, and you pick the one that fits. Supply-only: we provide the engineered lightweight mounting kit, modules, inverters and balance-of-system — including PV-ready kits for OEMs and main contractors to fit at factory stage. Install-only: you have the hardware, we deliver the structural assessment, planning, G99 and MCS-certified installation. Turnkey: we do everything from the first roof survey to the Scope 2 disclosure pack. Most enquiries are turnkey, but the supply route is what makes us useful to modular manufacturers building at volume — see the dedicated supplier section below.
Why modular buildings need a lightweight solar specialist
Modular and prefabricated buildings — Portakabin Solus, Algeco, McAvoy, Wernick, Elliott and the rest — are now a permanent fixture of the UK estate, not just temporary site huts. They house school classrooms, NHS administrative departments, local-authority neighbourhood offices, construction-site command centres, and energy and quarry-site facilities. What they almost all share is a roof structure engineered for the building's own weight and weather loads, not for an additional rooftop array. Typical modular roof loading capacity is 8-15 kg/m², against 30-60 kg/m² on a conventional steel-or-concrete-framed commercial building.
That single fact changes everything about the solar design. Drop a standard ballasted commercial array — 18-25 kg/m² with concrete ballast — onto a modular roof and you are outside the structural envelope before the first panel is energised. Lightweight solar is the answer: a system engineered from the mounting up to deliver the same generation at 8-12 kg/m² installed load. Get it right and a modular building decarbonises and cuts its energy bill exactly like any other; get it wrong and you risk the roof, the warranty, and the insurance. This is why a lightweight solar installer for modular buildings is a genuinely different specialism from a general commercial solar contractor. (For conventional commercial buildings with weak or near-capacity roofs that aren't modular, see lightweight solar panels for commercial buildings.)
Lightweight mounting systems for modular roofs
There are three mounting routes for solar on modular buildings, and the right one depends on the roof skin, the manufacturer's loading table, and whether the building will ever be relocated.
- Lightweight ballasted (10-12 kg/m²). Reduced-ballast tubs filled with recycled-polymer weights instead of concrete blocks. Penetration-free, so the roof membrane and its warranty stay intact, and the whole array is removable. Panel tilt is limited to 5-10° to keep wind uplift (and therefore ballast) down, which trims yield slightly versus a 10-15° conventional array — a trade we model explicitly in every proposal.
- Direct frame-fix (8-10 kg/m²). Mechanical fixings through the module roof skin into the steel frame beneath. The lightest option and the highest yield, but it requires the modular OEM's approval and a warranty endorsement. Best specified in collaboration with the manufacturer, ideally at module-build stage rather than retrofit.
- Standalone canopy or carport. An independent steel structure spanning between or beside modular buildings, or over adjacent parking. The PV load sits on the canopy, not the modules, so roof capacity is irrelevant. Higher capex but it removes the structural constraint entirely and is often the right answer for clusters of modular buildings on one site.
Modular solar mounting compared: ballasted vs frame-fix vs canopy
The same three routes, set side by side. For any building that might be relocated we steer toward ballasted from the outset; for a permanent building chasing maximum yield, frame-fix wins; for a cluster of units or a roof with no spare capacity, the canopy removes the constraint entirely. This is the comparison a lightweight solar installer for modular buildings walks every client through at feasibility.
| Mounting route | Installed load (kg/m²) | Relative yield | Relocatable? | Roof penetration / warranty | Best for |
|---|---|---|---|---|---|
| Lightweight ballasted | 10-12 | Good (5-10° tilt) | Yes — 1-2 day dismount | Penetration-free; warranty intact | Relocatable, temporary and warranty-sensitive roofs |
| Direct frame-fix | 8-10 | Highest (10-15° tilt) | Harder — reseal penetrations | Penetrates skin; needs OEM endorsement | Permanent buildings, max yield, factory-stage fit |
| Standalone canopy / carport | 0 on the roof | Highest (optimal tilt) | Structure is fixed; PV reusable | None on the modular roof at all | Unit clusters, near-capacity roofs, dual-use parking |
Structural loading — what we check before we quote
Every lightweight solar project on a modular building opens with a structural loading assessment to BS EN 1991-1-1 (dead loads) and BS EN 1991-1-4 (wind loads), checked against the modular manufacturer's published per-module roof loading table. Modular OEMs publish these figures; we obtain them at feasibility and design the array to sit comfortably inside the envelope with margin for wind uplift and maintenance access loads. Where the building has been on site long enough that the original loading documentation is lost, we commission a structural engineer's inspection rather than guess. No lightweight system goes on a roof we haven't verified.
Lightweight solar installer and supplier — both halves of the job
Most enquiries we get for modular buildings fall into one of two shapes, and we cover both. As a lightweight solar supplier for modular buildings, we provide the engineered mounting system, modules, inverters and balance-of-system — including PV-ready kits that modular OEMs and main contractors fit during factory build, which is materially cheaper than retrofitting after the building is craned into place. As a lightweight solar installer for modular buildings, we deliver the full turnkey project: structural assessment, fixed-price proposal, planning route confirmation, DNO G99 application, MCS-certified installation with the correct lightweight mounting for the building, IEC 62446 commissioning, and a Scope 2 disclosure pack for ESG reporting. You can engage us for supply only, install only, or end to end.
Solar for modular buildings supplier: PV-ready kits and factory fit-out
As a solar for modular buildings supplier we sell the engineered system, not just the install. The supply-only offer is built for modular OEMs and main contractors who want a PV-ready building coming off the production line, and for estate operators self-delivering with their own electrical contractor. It covers the lightweight mounting kit matched to your roof skin and loading table, high-efficiency mono-PERC or n-type modules, string or hybrid inverters, and the full balance-of-system — DC cabling, isolators, monitoring and protection.
The strongest version of this is factory fit-out: we specify PV-ready mounting points, roof reinforcement detail and cable routing into the building at design freeze, so the unit leaves the factory ready to energise. Fitting at factory stage is materially cheaper than retrofit — no second mobilisation, no working at height on an occupied building, no second access plan. For OEMs running a product line, or a contractor placing a programme order, we supply a standardised lightweight specification at volume pricing that drops straight onto your structural drawings. This is what separates a supplier who understands modular construction from a generic panel distributor: the kit is engineered to your loading table, not bought off a shelf.
PV systems for modular construction: design for manufacture and assembly
A PV system for modular construction belongs in the DfMA workflow, not bolted on afterwards. Volumetric and panelised construction win on speed and cost precisely because as much as possible is resolved before the modules are built — and solar is no exception. Brought in at design stage, the PV scope integrates cleanly: mounting points designed into the roof cassette, cable routes coordinated with the M&E first-fix, grid provisioning and the G99 application started in parallel with the build programme, and the array layout reconciled against the modular OEM's structural loading table before steel is cut.
The alternative — designing PV after the building is craned into place — forces compromises: surface-run cabling, ballast added to compensate for fixings that were never detailed, and a separate site visit that the off-site model was meant to eliminate. Coordinating with the OEM's engineers at design freeze lets us confirm exactly how much load each roof module can take and where, then size the array to sit inside that envelope with margin. Whether the units are fitted out off-site or topped out on arrival, designing the PV into the manufacturing sequence is how modular construction keeps its speed-and-certainty advantage while still hitting net-zero and MEES targets.
Typical system sizing for modular buildings
Modular buildings are usually single-storey with a 200-2,000 m² footprint, so arrays are smaller than on conventional offices — but the economics still stack up, especially with high daytime occupancy in schools, clinics and offices.
- Small managed modular office (300 m²): 20-40 kWp typical
- Mid-size modular block (1,000 m²): 60-120 kWp typical
- Large modular complex (2,000 m²+): 120-300 kWp typical
| Modular building size | Typical kWp | Indicative cost (£1,000-£1,400/kWp) | Typical annual generation | Indicative payback |
|---|---|---|---|---|
| Small modular office (300 m²) | 20-40 kWp | £20,000-£56,000 | 17,000-34,000 kWh | 6-9 years |
| Mid block (1,000 m²) | 60-120 kWp | £60,000-£168,000 | 51,000-102,000 kWh | 6-8 years |
| Large complex (2,000 m²+) | 120-300 kWp | £120,000-£420,000 | 102,000-255,000 kWh | 5-8 years |
Indicative figures for UK modular roofs at ~850 kWh/kWp and strong daytime self-consumption; confirmed per building at feasibility. Payback shown before grants and before the Annual Investment Allowance.
Cost per kWp on modular runs £1,000-£1,400/kWp, above the £700-£1,000/kWp of conventional flat-roof commercial solar, reflecting the smaller scale and the lightweight hardware. Even so, payback on a well-sited modular array with strong daytime self-consumption is typically 6-9 years before grants, and the Annual Investment Allowance returns 100% of the capital cost as a first-year tax deduction for most businesses. For the full finance picture — cash purchase, asset finance, operating lease and PPA — see our finance options, and use the solar cost calculator to model your own numbers.
Modular solar payback: how the numbers work
Three variables decide the payback on solar for modular buildings: how much you generate, how much of it you use on site, and the price you would otherwise pay for grid electricity. Modular education, healthcare and office buildings are unusually strong on the second variable — their 9-5 occupancy means 80-90% of generation is consumed on site during the day rather than exported at a low rate, which is what drives payback down toward the bottom of the 6-9 year band. The table above gives indicative system sizes and paybacks by building size; the worked logic is simple. A 60 kWp mid-block array generating ~51,000 kWh a year, self-consuming 85% of it at a 28p/kWh commercial rate, saves roughly £12,100 a year before any export income or grant. Against an £66,000-£84,000 install that is a 5.5-7 year simple payback, shortened further by the Annual Investment Allowance returning 100% of the capital as a first-year tax deduction. Rather than embed a throwaway widget, we model your exact figures in the fixed-price proposal and you can sense-check them against the table above or the site-wide solar payback calculator.
Where modular buildings are deployed in 2026
Modular construction has matured well beyond the temporary cabin. The deployments where we see the most lightweight solar demand:
- Education estate — modular classroom and admin blocks, often becoming permanent through extended planning consents
- NHS administrative and clinical-support buildings on hospital sites
- Construction-site offices and welfare facilities (typically 2-5 year deployments, ideal for relocatable arrays)
- Local-government estate — neighbourhood offices and satellite admin buildings
- Mining, energy, water and quarry-site offices
- Emergency-response and resilience infrastructure (Environment Agency, DEFRA, civil-contingency centres)
The same lightweight approach covers everything in this family of structures. Prefab buildings — factory-assembled and craned into place — share the modular roof-loading constraint exactly, as do temporary buildings such as site cabins, welfare blocks and pop-up classrooms on short deployments. Whether you call it a portable office, a relocatable unit or a permanent volumetric building, a PV system for modular construction is engineered the same way: low installed load, structural verification against the manufacturer's table, and a ballasted layout that lifts off cleanly when the building moves. Prefabricated, portable and temporary all sit inside one lightweight design discipline.
Solar PV for prefab buildings: same constraint, same lightweight discipline
Solar PV for prefab buildings follows exactly the same rules as volumetric modular. Prefab, panelised and pre-engineered buildings are all built off-site and assembled on a prepared base, and they all share the defining constraint: a lightweight roof structure rated well below a conventional steel-framed commercial building. A prefab classroom, a panelised healthcare unit, an office pod or a welfare cabin will typically carry 8-15 kg/m², so the conventional concrete-ballasted array is off the table from the start.
What changes between prefab build systems is the roof skin and the fixing detail, and that decides the mounting route. A prefab with a robust steel roof cassette and OEM approval can take direct frame-fix at 8-10 kg/m² for maximum yield. A panelised roof with a membrane finish, or any prefab where penetration would compromise the warranty, gets lightweight ballasted at 10-12 kg/m² instead. We read the manufacturer's loading table for the specific prefab system, verify it on site, and pick the mounting that keeps the array comfortably inside the envelope. The design discipline — survey, verify, size to the table, keep it removable where relocation is likely — is identical to volumetric modular; only the build system in front of us differs.
Solar PV for temporary buildings: relocatable and construction-site arrays
Solar PV for temporary buildings is a decision about permanence as much as about panels. The first question is whether the building — and therefore the array — needs to move. For a permanent modular building, frame-fix and maximum yield make sense. For a temporary building on a 2-5 year deployment — a construction-site office, a welfare block, a decant classroom while a permanent building is rebuilt — a relocatable lightweight ballasted array is almost always the right call. It dismounts, transports and re-installs in 1-2 days, with relocation costing roughly 15-25% of the original install, and it transfers cleanly to the next site or the next phase.
Construction-site deployments add a second dimension: resilience. Site offices and welfare facilities on remote or early-phase sites often run on a constrained or interrupted grid connection, so pairing the lightweight array with a battery keeps lighting, heating and welfare running through supply interruptions and trims generator hours and diesel cost. Over a typical 2-5 year deployment a relocatable lightweight array is usually cash-positive before you even count the value of reuse on the next project — which is exactly why temporary and construction-site buildings, far from being too short-lived for solar, are some of the strongest cases for it. Pair it with battery storage for grid-interruption resilience, and confirm the planning route — most temporary arrays under 50 kWp are Permitted Development.
Lightweight solar for modular buildings in London
We install lightweight solar on modular buildings across Greater London and the Home Counties, and it is one of our busiest modular markets — London's land pressure pushes schools, NHS trusts and councils toward modular blocks on constrained sites, and those organisations are under the most acute net-zero and MEES pressure. A London modular solar project under 50 kWp is almost always Permitted Development; grid connection runs through UK Power Networks across most of the capital, or SSEN in parts of west and south-west London. We confirm the exact planning and DNO route for any London postcode at feasibility stage, and we coordinate with borough estates teams on access, parking suspensions and out-of-hours craneage where a constrained site demands it. Whether you need a lightweight solar installer for modular buildings in London or a supplier for a factory-fit programme, the lightweight engineering is identical — only the logistics change. Modular buildings on business parks and construction sites frequently pair solar with EV charging for fleet and visitor parking, which we can design into the same scheme.
Relocation and removability
Because modular buildings can be relocated, the solar on them often needs to move too — particularly on construction-site offices and other temporary deployments. Lightweight ballasted systems are built for exactly this: the array dismounts, transports and re-installs in 1-2 days, with relocation costing roughly 15-25% of the original install. Direct-fix systems are more involved to move (the roof penetrations must be resealed on dismount and the structure reattached at the new site), so for any building likely to relocate we steer toward ballasted from the outset. Over a 2-5 year deployment a relocatable lightweight array is usually cash-positive even before the value of reuse at the next site.
Working with modular OEMs at specification stage
For new modular buildings still in procurement, integrating PV-ready mounting points and cable routing at the OEM's specification stage is far cheaper than retrofitting after delivery. Most major UK modular manufacturers offer a PV-ready specification as a paid upgrade, and we supply the lightweight kit to match. If you are a modular OEM or a main contractor specifying a building, talk to us before the design freezes — factory-fit lightweight solar avoids a second mobilisation, a second access plan, and the cost premium of working on a finished, occupied building.
Recent lightweight modular solar installs
A 2025 project for a multi-academy trust: 48 kWp lightweight ballasted array across two Portakabin-built modular classroom blocks in the South East. Recycled-polymer ballast at 11 kg/m², verified against the manufacturer's loading table. Generation 41,000 kWh/year, ~88% self-consumed during school hours. Annual saving £15,000; AIA claimed in full. Zero roof penetrations, warranty intact.
A 2025 construction-site command office on a major infrastructure programme: 36 kWp relocatable lightweight system on an Algeco modular complex, specified for reuse across three sequential site phases. Designed for 1-day dismount/remount. Combined with a small battery to run the welfare facilities through grid-supply interruptions on a remote site.
A 2024 NHS modular admin building on a hospital campus: 72 kWp direct frame-fix array, specified with the modular OEM and warranty-endorsed at build stage. Generation 63,000 kWh/year feeding the trust's Scope 2 reporting and Greening Government Commitments evidence. Salix PSDS funding (see our grants and funding guide) covered a third of the capital cost. Schools, NHS trusts and councils are our busiest modular audience — see public-sector solar for the funding and procurement detail, and more proof on our case studies.
From feasibility to commissioning: the modular solar process
Every modular project runs through the same six stages, whether it is a single classroom block or a fleet of site offices. The full company-wide method is on our process page; here is how it applies to a lightweight modular install.
- Structural loading assessment. We survey the roof to BS EN 1991-1-1 (dead loads) and BS EN 1991-1-4 (wind loads) and check the result against the modular manufacturer's published per-module loading table. No system goes on a roof we have not verified.
- Fixed-price proposal. Within 7 working days we issue a fixed-price proposal with the mounting route, system size, generation, self-consumption and payback modelled, and all four finance routes — cash, asset finance, operating lease and PPA — set out.
- Planning and DNO G99. We confirm the planning route (Permitted Development under 50 kWp in most cases) and submit the G99 grid-connection application to the relevant DNO.
- MCS-certified installation. We install with the correct lightweight mounting for the building, keeping installed load inside the verified 8-12 kg/m² envelope, with NICEIC electrical sign-off.
- IEC 62446 commissioning. We commission and test to IEC 62446 and hand over the full documentation set.
- Scope 2 disclosure pack. We issue a Scope 2 emissions disclosure pack for ESG, SECR and — for public bodies — Greening Government Commitments reporting. See ESG reporting for how this feeds your disclosures, and MEES 2030 for the EPC B compliance driver behind much of the modular school, NHS and council estate.
Lightweight solar for modular buildings — common questions
The questions estate managers, OEMs and main contractors ask most.
Can you install lightweight solar on a modular building?
Yes. Modular and prefabricated buildings typically have roof structures rated 8-15 kg/m² — lighter than the 30-60 kg/m² of conventional commercial roofs. We use lightweight PV systems (high-efficiency mono-PERC or n-type modules on recycled-polymer ballast tubs or direct frame-fix mounting) that install at 8-12 kg/m², staying inside the modular structural envelope. Every project starts with a structural loading assessment to BS EN 1991 against the modular manufacturer's published roof loading table.
Are you a lightweight solar installer and supplier, or just one?
Both. We supply the lightweight mounting system, modules and inverters, and we install and commission the system end to end (MCS-certified, NICEIC electrical sign-off, IEC 62446 commissioning). For modular OEMs and main contractors we can also supply PV-ready kits for factory fit-out before the building leaves the production line, which is cheaper than retrofit.
How much does lightweight solar for a modular building cost?
Lightweight systems run slightly higher per kWp than conventional commercial solar — typically £1,000-£1,400/kWp installed versus £700-£1,000/kWp on a standard flat roof — because the arrays are smaller and the lightweight mounting hardware costs more. A typical 60 kWp modular install lands around £66,000-£84,000 before grants and capital allowances. Annual Investment Allowance gives 100% first-year tax relief on the full cost for most businesses.
Can the solar system be moved if the modular building relocates?
Yes — this is one of the main reasons lightweight ballasted systems suit modular buildings. The array dismounts, transports and re-installs in 1-2 days at a new site. Relocation typically costs 15-25% of the original install. For temporary or construction-site modular offices on a 2-5 year deployment, a relocatable lightweight array is usually cash-positive over the deployment even before any second-site reuse.
Do you supply lightweight solar for modular buildings in London?
Yes. We install lightweight solar on modular buildings across Greater London and the Home Counties — education modular blocks, NHS modular admin, construction-site offices, and local-authority satellite buildings. London modular projects are usually Permitted Development under 50 kWp; UK Power Networks (or SSEN in west/south-west London) handles the G99 grid connection. We confirm the planning and DNO route for any London postcode at feasibility stage.
Will solar void my modular building warranty?
Not if it is specified correctly. Direct-fix mounting requires the modular OEM's approval and a warranty endorsement, which we obtain as part of design. Lightweight ballasted mounting avoids penetrating the roof skin entirely, so it generally sits outside warranty-affecting works — but we always confirm with the manufacturer and your building insurer at design stage, because modular roof warranties often carry specific roof-addition clauses.
Are you a solar supplier for modular buildings or do you install too?
Both, and you can engage us for either half or the whole job. As a supplier we provide the engineered lightweight mounting system, modules, inverters and balance-of-system — including PV-ready kits for modular OEMs and main contractors to fit at factory build stage. As an installer we deliver the full turnkey project: structural assessment, fixed-price proposal, planning and G99 application, MCS-certified install, IEC 62446 commissioning and a Scope 2 disclosure pack. Supply-only, install-only or end to end — your choice.
Can you supply a PV-ready kit for our modular building at factory build stage?
Yes. PV-ready supply at factory build is the cheapest route to a solar-enabled modular building. We supply the lightweight mounting points, cable routing, roof reinforcement detail and DC infrastructure to fit before the unit leaves the production line, specified against your structural loading table. Fitting at the factory avoids a second site mobilisation, a second access plan and the cost premium of working on a finished, occupied building once it has been craned into place.
Does solar PV work for prefab and panelised construction the same as volumetric modular?
Yes — prefab, panelised and volumetric construction all share the modular low-load roof constraint, typically 8-15 kg/m2, so the same lightweight design discipline applies. We choose ballasted or frame-fix mounting per the specific prefab build system and its roof skin: a prefab classroom, a panelised healthcare unit, an office pod or a welfare block each gets the mounting route that stays inside its published loading table. The engineering is identical; only the build system and roof detail change.
Can you fit solar PV to a temporary or construction-site building?
Yes. Temporary and construction-site buildings on 2-5 year deployments are an ideal fit for relocatable lightweight ballasted arrays. The penetration-free array dismounts, transports and re-installs in 1-2 days, so it moves with the building or transfers to the next site. Pairing it with a battery gives welfare and command facilities resilience through grid-supply interruptions on remote sites. Over the deployment a relocatable array is usually cash-positive even before counting the value of reuse at the next site.
Is a PV system viable on modular construction with such a low roof loading?
Yes. Modular roof loading of 8-15 kg/m2 rules out conventional concrete-ballasted arrays at 18-25 kg/m2, but our lightweight systems install at 8-12 kg/m2 and deliver the same generation per panel. Every system is engineered from the mounting up and verified to BS EN 1991 against the manufacturer's loading table before any panel goes on the roof. Low roof loading constrains the mounting choice, not the viability of solar itself.
What is the payback on solar for a modular building?
Typically 6-9 years before grants for a well-sited modular array with strong daytime self-consumption — schools, clinics and offices with 9-5 occupancy self-consume 80-90% of generation, which shortens payback. Modular costs £1,000-£1,400/kWp installed, above the £700-£1,000/kWp of conventional flat-roof solar, because arrays are smaller and the lightweight hardware costs more. The Annual Investment Allowance returns 100% of the capital cost as a first-year tax deduction for most businesses, materially improving the effective payback.
Do temporary modular building solar arrays qualify for capital allowances if relocated?
In most cases yes — solar PV plant generally qualifies for the Annual Investment Allowance (100% first-year deduction) for businesses, and a relocatable array does not lose that simply because it can be moved. Relocation costs (typically 15-25% of the original install) are normally treated as further qualifying expenditure when the array is re-commissioned at the next site. Capital-allowance treatment depends on your specific tax position, so confirm the detail with your accountant; we provide the full asset and cost documentation to support the claim.
Can you supply solar across a fleet of modular buildings on different sites?
Yes. Fleet and programme supply is a core part of what we do for modular OEMs, main contractors and estate operators. We supply a standardised lightweight specification across multiple buildings and sites at volume pricing, with per-site structural verification and a single point of coordination. Whether it is a rollout of school modular blocks, a construction company's site-office fleet, or a public-sector estate of relocatable units, one engineered kit specification scales across the whole programme.