A practical guide to help UK business owners assess roof orientation, pitch, shading, load capacity, and remaining roof life before committing to a commercial solar installation.
A commercial solar installation is a long-term asset. Panels typically carry product warranties of 20 to 25 years, according to the Energy Saving Trust and Which?, so the roof beneath them needs to be in good shape for at least as long. Choosing the right system size, layout, and mounting approach all depend on what your roof can realistically offer.
The UK government's Solar Roadmap notes that 1.5 million homes already have solar installed, and commercial rooftops represent a major share of the untapped potential. For business owners, the key question is not simply whether solar works on roofs in general, but whether your specific roof can support a system that earns its keep. A structural survey and a shading analysis done early can prevent costly changes later.
The sections below cover each factor in turn: orientation and pitch, structural load, shading, roof condition and age, and the planning and permitting rules that apply to commercial buildings.
Current vs potential solar capacity on UK commercial rooftops (GW)
| Currently installed | 5 gw |
|---|---|
| Potential capacity | 60 gw |
The gap between what is already installed and what is technically achievable shows the scale of the commercial rooftop opportunity still available.
Solar energy has a critical role to play in the UK’s energy transition, and commercial real estate has the potential to be a major player in the generation of rooftop solar.
South-facing roof sections at a pitch of between 30 and 40 degrees produce the highest annual output in the UK. East- and west-facing roofs still perform well and can extend generation into the morning and evening, which suits businesses with spread consumption patterns. North-facing slopes are generally avoided as the primary array position.
Flat roofs, which are common on warehouses, retail units, and office buildings, are well suited to commercial solar. Panels are mounted on angled ballast frames, typically set to 10 to 15 degrees, so orientation can be chosen regardless of which way the building faces. This flexibility is one reason flat roof solar panels are a popular choice for commercial premises.
Pitch also affects cleaning and maintenance access. Steeper pitches shed rain and dirt more readily, while flat or low-pitch arrays may need more frequent cleaning to maintain output. Ask any installer to include access and cleaning requirements in their proposal.
A commercial solar array adds a continuous load to the roof structure. Each panel typically weighs around 10 to 12 kg, and ballasted flat-roof mounting systems add further weight from the frames and ballast blocks. A 100 kW system, for example, involves a significant number of panels spread across a large area, and the combined load must sit within the roof's permitted limit.
Before any installation, a structural engineer should assess the roof's load-bearing capacity. This is particularly important for older industrial buildings and any roof where the original design specification is unknown. Your installer should either carry out this assessment or require one before finalising a system design.
Roof penetrations, used when panels are mechanically fixed rather than ballasted, require waterproofing details that meet building regulations. A reputable installer will provide a full waterproofing warranty alongside the panel warranty. Ask to see both before you sign a contract.
Shading is one of the most significant factors in commercial solar output. Rooftop plant rooms, air-handling units, lift shafts, and parapet walls all cast shadows that shift throughout the day and across the seasons. Even partial shading on a single panel can reduce the output of the entire string it belongs to, unless the system uses optimisers or microinverters to isolate the effect.
A professional shading analysis, often carried out using software such as PVsyst or similar tools, maps shadow paths across the roof throughout the year. This analysis should be included in any serious commercial solar assessment. If your installer does not offer one, that is worth noting as a gap in their proposal.
Shading cannot always be eliminated, but it can be managed. Careful array layout, row spacing to reduce inter-row shading, and the choice of inverter technology all affect how well a shaded site performs. Carry out the analysis before finalising system size, not after.
Fitting solar panels to a roof that needs replacing in five years is poor planning. Removing and reinstalling an array adds cost and downtime, so the condition and remaining life of the roof membrane, covering, or structure should be assessed before any installation goes ahead.
For flat commercial roofs, membrane condition is critical. A roofing contractor can inspect the membrane and give an honest assessment of remaining life. If the membrane has fewer than ten to fifteen years left, replacing it before panel installation is usually the more cost-effective path. Many commercial solar installers work alongside roofing contractors and can coordinate the sequencing.
For pitched commercial roofs, tiles or sheets should be checked for damage, and any underlying timber or steel structure assessed for corrosion or rot. A roof in sound condition that has been recently inspected gives your installer a solid foundation to work from, and gives you confidence that the system life will match the warranty period.
Most commercial rooftop solar installations are covered under permitted development rights, meaning planning permission is not required in many cases. However, there are important exceptions. If the building is listed, in a conservation area, or the installation would project more than one metre above the roofline, full planning permission is likely to be needed. Rules were updated under the General Permitted Development Order, and local planning authorities can add conditions on top.
For larger ground-mounted or frame-mounted systems on commercial sites, planning permission is almost always required regardless of location. The planning rules for commercial solar are covered in detail on our page on planning permission for commercial solar panels, which is worth reading before you speak to an installer.
Building regulations approval is separate from planning permission and applies to structural changes and electrical work. Your installer must notify your Distribution Network Operator (DNO) before connecting any generation equipment to the grid. This notification is the installer's responsibility, but it is worth confirming the process is under way before installation begins.
Commercial system costs vary widely with size. According to renewableenergyhub.co.uk (2026), a small 25 kW system costs around £25,000, a medium 100 kW system ranges from £85,000 to £130,000, and a large 1 MW installation runs from £750,000 upwards. Roof type, mounting method, distance to the distribution board, and DNO connection requirements all influence the final figure.
Payback depends on how much of the generated electricity the business uses directly. The Energy Saving Trust reports a typical payback period of 9 to 12 years on an ideal roof, with longer periods for east-facing or shaded installations. High daytime electricity consumption, such as in manufacturing, cold storage, or hospitality, shortens payback because more generated power is used on-site rather than exported at a lower rate.
Businesses that export surplus electricity can receive payment under the Smart Export Guarantee. For further detail on export payments and VAT treatment for commercial systems, the hub page on commercial solar covers these topics in full.
Illustrative cumulative savings against upfront cost (£)
| 2027 | -218,750 £ |
|---|---|
| 2029 | -156,250 £ |
| 2030 | -125,000 £ |
| 2032 | -62,500 £ |
| 2033 | -31,250 £ |
| 2034 | 0 £ |
| 2035 | 31,250 £ |
| 2036 | 62,500 £ |
Assumed: system cost £250,000, annual savings of £31,250 (based on up to 70% reduction in daytime electricity costs applied to a typical bill). This is an illustration only; actual returns depend on energy use, tariffs and roof conditions. Illustrative example, calculated from the assumptions in the text, not figures from a source.
Illustrative example
The trade-offs, in short.
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Answers to the most common questions.
South-facing roofs at a pitch of 30 to 40 degrees deliver the highest annual output. East- and west-facing roofs still perform well and suit businesses with morning or evening consumption. Flat roofs offer the most flexibility because panels are mounted on angled frames and can face any direction.
A structural assessment is strongly recommended and most reputable installers will require one. It confirms the roof can carry the combined weight of panels, frames, and any ballast. Older industrial buildings and any roof where the original load specification is unavailable should always be assessed by a qualified structural engineer.
There is no fixed age limit, but if your roof membrane or covering has fewer than ten to fifteen years of serviceable life remaining, replacing it before installation is usually the more cost-effective choice. Removing and reinstalling an array adds significant cost, so coordinating a re-roof with the solar installation avoids that expense later.
It can, particularly in systems where panels share a single inverter string. Rooftop obstructions such as plant rooms, lift shafts, and parapet walls should all be included in a professional shading analysis. Optimisers or microinverters can limit the impact by isolating shaded panels from the rest of the array.
Many commercial rooftop installations fall under permitted development and do not need planning permission. Exceptions include listed buildings, conservation areas, and systems projecting more than one metre above the roofline. Ground-mounted and large frame-mounted systems on commercial sites typically require full planning permission regardless of location.
Collect quotes from several MCS-certified installers who have commercial experience. Ask each one for a shading analysis, a structural load assessment, and a clear breakdown of costs, expected output, and payback assumptions. Comparing at least three detailed proposals gives you a reliable picture of what your roof can achieve.
