Run the check for your building
The check uses the same four datasets as the tables below. It needs only a roof area and your nearest city; add the floor area and your unit rate for the share of use and the value. The estimate shows on the page as you type. Sending it is optional.
How the estimate is worked out
- Clear roof area = roof area × the share clear of plant (70%, 50% or 30% from your answer). This is an assumption you can change by choosing a different option.
- System size (kWp) = clear area ÷ 5 m² per kWp (5.5 m² on mixed roofs). Modern modules of around 430 W are a little under 2 m² each; the allowance covers gaps, walkways and row spacing.
- Yearly generation = kWp × the PVGIS yield for your nearest office market and roof type (flat roofs as a 10° east-west layout, pitched roofs at 30° south, mixed roofs at 10° south).
- Share of use = generation ÷ (floor area × 95 kWh per m², the CIBSE TM46 general-office electricity benchmark).
- Cost reference = kWp × the DESNZ 2025/26 non-domestic average (mean) for that size band, up to 50 kW. Above 50 kW the check states the 10-50 kW average as a reference only.
- Planning route = the Class J tests for England (listed status, size over or under 50 kW, Article 4 note for conservation areas), or the devolved class that applies instead: Part 43 Class A in Wales, Class 6J in Scotland or Part 37 Class A in Northern Ireland.
Dataset 1: solar yield for 13 UK office markets
Pulled from the European Commission's PVGIS v5.2 on 18 October 2026 for 1 kWp of crystalline silicon panels on a free-standing rack with 14% system losses, using the PVGIS-SARAH2 radiation database. The last column scales the east-west figure to 100 m² of clear flat roof at 5 m² per kWp, which is 20 kWp.
| Office market | Nation | Network operator | 10° east-west | 10° south | 30° south | kWh a year per 100 m² clear flat roof |
|---|---|---|---|---|---|---|
| Cardiff | Wales | National Grid Electricity Distribution | 853 | 933 | 1021 | 17,060 |
| Reading | England | SSEN (Southern Electric) | 849 | 929 | 1017 | 16,980 |
| London (City) | England | UK Power Networks | 848 | 928 | 1018 | 16,960 |
| Bristol | England | National Grid Electricity Distribution | 848 | 927 | 1014 | 16,960 |
| Cambridge | England | UK Power Networks | 846 | 930 | 1027 | 16,920 |
| Birmingham | England | National Grid Electricity Distribution | 805 | 880 | 964 | 16,100 |
| Nottingham | England | National Grid Electricity Distribution | 804 | 881 | 969 | 16,080 |
| Leeds | England | Northern Powergrid | 775 | 850 | 938 | 15,500 |
| Newcastle | England | Northern Powergrid | 762 | 841 | 936 | 15,240 |
| Belfast | Northern Ireland | NIE Networks | 756 | 828 | 910 | 15,120 |
| Manchester | England | Electricity North West | 742 | 807 | 880 | 14,840 |
| Edinburgh | Scotland | SP Energy Networks | 740 | 816 | 905 | 14,800 |
| Glasgow | Scotland | SP Energy Networks | 707 | 771 | 843 | 14,140 |
Source: PVGIS v5.2 PVcalc, European Commission Joint Research Centre (re.jrc.ec.europa.eu). Sorted by the east-west column. Coordinates are city-centre points; shading and module choice change real output.
Three things stand out for office owners. First, the spread is real but not decisive: Cardiff tops the east-west column at 853 kWh per kWp and Glasgow is lowest at 707, a gap of about 17%. A Glasgow office with a clear roof still out-generates a London office whose roof is crowded with plant. Second, Leeds (775) beats Manchester (742) despite being further north, which is why a city-specific figure matters more than a north-south rule of thumb. Third, on a flat roof in central London, south-facing rows at 10° yield about 9% more per kWp than an east-west layout (928 against 848 kWh), but east-west rows need far less spacing and pack more panels into the same area, which is why so many office roofs use them.
Dataset 2: how far the roof goes, by number of storeys
This is the question estates teams ask first: what share of the building's electricity can the roof supply? Holding everything else equal (a roof half clear of plant, 5 m² per kWp, the east-west yield and the TM46 benchmark of 95 kWh per m² of floor), the answer is driven by the number of storeys, because each extra floor adds demand but no roof.
| Storeys | Central London | Manchester | Glasgow |
|---|---|---|---|
| 1 | 89% | 78% | 74% |
| 2 | 45% | 39% | 37% |
| 4 | 22% | 20% | 19% |
| 8 | 11% | 10% | 9% |
Calculated from PVGIS v5.2 yields and the CIBSE TM46 general-office electricity benchmark (95 kWh/m²). A building with lower use than the benchmark, or a clearer roof, covers more.
The practical reading: single-storey business-park offices can cover most of their daytime use from the roof, while a mid-rise city office should size the array to displace daytime demand and look to a car-park canopy, a PPA or efficiency measures for the rest. Neither case needs a battery to use the output, because an office's use runs through the working day.
Dataset 3: what the official statistics say about cost
DESNZ publishes the UK's only official solar cost series, built from Microgeneration Certification Scheme records. The 2025/26 release covers April 2025 to March 2026 and was published on 28 May 2026. It reports 88,788 non-domestic installations, 4,368 of them in the 10-50 kW band.
| Size band | Non-domestic (mean) | All installations (median) |
|---|---|---|
| 0-4 kW | £1,892 | £1,780 |
| 4-10 kW | £1,533 | £1,697 |
| 10-50 kW | £1,259 | £1,262 |
Source: DESNZ, Solar PV cost data 2025/26 (declared net capacity basis). Includes equipment, installation, grid connection and VAT where applicable; excludes battery storage. DESNZ gives the non-domestic breakdown as a mean and publishes medians only for all installations combined, so the two columns are different statistics. No official series exists above 50 kW.
Two cautions. The figures include VAT where it applied, so compare like with like when you read a quotation. And because most office systems are larger than 50 kW, the honest use of these numbers is as an upper reference for a first budget line. A proposal priced from your meter data and a roof survey replaces it.
Dataset 4: the planning route, situation by situation
For England, the rules are in Class J of Part 14, Schedule 2 of the Town and Country Planning (General Permitted Development) (England) Order 2015, checked against the latest revised text on legislation.gov.uk on 18 October 2026.
| Situation | Route | What it means in practice |
|---|---|---|
| Rooftop system up to 50 kW, building not listed | Permitted development, Class J | No application, provided panels stay within 1 m of the highest part of a flat roof (0.2 m beyond a pitched slope) and at least 1 m from the roof edge |
| Rooftop system above 50 kW | Class J(c) with prior approval | Apply to the council, which considers design, external appearance and glare on neighbours and has 56 days to decide |
| Listed building, or within its curtilage | Not permitted development | Listed building consent, and usually planning permission |
| Scheduled monument site | Not permitted development | A planning application and scheduled monument consent |
| Conservation area, not listed | Class J still applies to roofs: the roof-slope-fronting-a-highway exclusion on article 2(3) land (J.1(d)) was omitted on 21 December 2023 (S.I. 2023/1279, art. 6(2)) | Check whether an Article 4 direction removes the right in your area |
| Very large rooftop system | No capacity cap | The 1 MW limit in J.3 was omitted on 21 December 2023 (S.I. 2023/1279, art. 6(3)) |
| Wales, Scotland or Northern Ireland | Devolved rules | Class J is England only; check your nation's permitted development order with the council |
Source: GPDO 2015 Sch. 2 Pt 14 Class J (J.1, J.2, J.4), latest revised version on legislation.gov.uk. This is a summary, not legal advice; the council's view decides.
The detail behind each route, including Article 4 directions and listed offices, is in the planning permission guide for commercial buildings.
Before the numbers: who confirms each roof check
| Check | Why it matters on an office | Who confirms it |
|---|---|---|
| Remaining roof life | Lifting an array to re-roof costs money and downtime | Roofing contractor or building surveyor |
| Load and wind uplift | Ballast adds weight; lightweight and modular offices are the usual limit (see modular offices) | Structural engineer |
| Plant and rooflights | Chillers, AHUs and lift rooms cut the usable area | Facilities manager, with a roof plan |
| Shading | Taller neighbours to the south can take a large share of output | Yield model with a shading survey |
| Fire strategy and access | Cable routes, isolation and safe access affect design and insurance | Fire engineer and the building's insurer |
| Grid connection | G98 covers small systems; most office arrays need a G99 application | Your distribution network operator |
For flat roofs specifically, the flat-roof office guide covers ballast and membrane questions, and the guide to how many panels an office needs goes deeper on sizing from meter data.
Use and cite this data
The tables on this page may be quoted with a link. Cite as: Office roof solar check, solarpanelsforofficebuildings.co.uk, last verified 18 October 2026; yields from PVGIS v5.2 (European Commission JRC), costs from DESNZ Solar PV cost data 2025/26, demand from CIBSE TM46, planning from the GPDO 2015 on legislation.gov.uk. We re-pull the yields and re-check the cost release and the legislation when they change. This site is an independent guide published by SEO Dons Ltd; it is not an installer.
Questions about office roofs and solar
Frequently Asked Questions
How do I know if my office roof is suitable for solar panels?
Check five things in this order: the roof covering has plenty of life left, a structural engineer confirms it can carry the extra load and wind uplift, there is enough clear area once plant, rooflights and a 1 m edge zone are excluded, nearby buildings do not shade it heavily, and the grid connection is workable. The office solar check on this page turns the clear area and your nearest city into a system size and yearly generation.
How much electricity does a solar panel system on an office roof generate?
PVGIS v5.2 gives between 707 kWh (Glasgow) and 853 kWh (Cardiff) per kWp a year for a flat-roof 10° east-west layout across the 13 UK office markets in the table, and 1018 kWh per kWp in central London for a pitched roof at 30° facing south. Multiply by the system size in kWp for a yearly figure.
What share of an office building's electricity can rooftop solar cover?
It depends mostly on the number of storeys. Using the CIBSE TM46 general-office benchmark of 95 kWh per m² and a roof half clear of plant, a single-storey office in central London could cover about 89% of its use, a four-storey office about 22% and an eight-storey office about 11%.
How much does office rooftop solar cost per kW?
The official benchmark is DESNZ Solar PV cost data. For 2025/26 the average (mean) installed cost for non-domestic systems of 10-50 kW was £1,259 per kW. DESNZ publishes no series above 50 kW, where prices per kW are usually lower, so use the 10-50 kW average as a reference rather than a quote.
Does office rooftop solar need planning permission?
In England, Class J of Part 14 of the GPDO 2015 makes rooftop solar on non-domestic buildings permitted development, except on listed buildings and scheduled monuments and subject to height and 1 m edge limits. Above 50 kW, Class J(c) needs prior approval from the council on design, external appearance and glare, decided within 56 days. Wales, Scotland and Northern Ireland have their own rules.