Roof-mounted solar on farm buildings: Class J
The rules that apply to barns, sheds, grain stores and other non-domestic buildings in England are in Class J of Part 14 of the General Permitted Development Order 2015 — not the householder Classes A and B that most online guides quote. Class J covers microgeneration solar PV (up to 50 kW) on a building, and "other solar PV equipment" on the roof of a building, which is how larger farm arrays are treated. Development is not permitted if:
- • panels on a pitched roof would protrude more than 0.2 m beyond the plane of the roof slope;
- • panels on a flat roof would rise more than 1 m above the highest part of the roof;
- • any equipment would sit within 1 m of the roof's external edge;
- • the building is listed, is within the curtilage of a listed building, or the site is a scheduled monument.
No capacity cap. The old limit on rooftop capacity was omitted on 21 December 2023 by S.I. 2023/1279. Prior approval above 50 kW. Roof arrays larger than microgeneration need a prior approval application to the local planning authority about design and external appearance, in particular the impact of glare on neighbouring land; the council has 56 days to decide. Designated land. In conservation areas, National Parks, National Landscapes (AONBs) and similar article 2(3) land, Class J's extra restriction is on wall-mounted equipment fronting a highway — roof arrays remain permitted development if they meet the limits above.
Our guide to solar panels on farm buildings covers the building checks that sit alongside planning — structure, asbestos roofs and generation.
Field and ground-mounted arrays: full planning
Permitted development for stand-alone solar on non-domestic land is Class K, and it is narrow: one array per curtilage, no more than 9 m² of panels, no dimension over 3 m, no more than 4 m high and at least 5 m from the boundary. Anything sized to run a farm needs full planning permission from the local planning authority.
At the other end of the scale, the Infrastructure Planning (Onshore Wind and Solar Generation) Order 2025 made onshore solar in England a nationally significant infrastructure project only above 100 MW from 31 December 2025, up from 50 MW. That old line is why so many English solar farms were built at 49.9 MW — see the biggest solar farms in the UK. For the practical side of a field array, see ground-mounted solar panels for farms.
What planners look at on a farm solar application
- • Agricultural land quality. Best and most versatile land is grades 1, 2 and 3a. The Solar Roadmap (June 2025) says lower-quality land should be preferred and proposals on BMV land must justify it and avoid, mitigate and, where necessary, compensate for impacts. Councils must consult Natural England on proposals likely to lose 20 hectares or more of BMV land that are not in line with the development plan.
- • Landscape and visual impact. Views from homes, roads and rights of way, screening, and glint and glare.
- • Heritage. The setting of listed buildings and conservation areas.
- • Biodiversity. Mandatory Biodiversity Net Gain applies to most planning applications in England; wildflower ground cover and hedgerows under and around an array can help deliver it.
- • Continuing farm use. A documented grazing or cropping plan strengthens the case — see agrivoltaics in the UK.
- • Grid connection. Not a planning test, but a scheme without a realistic G99 connection offer rarely gets built; see G98 and G99 explained.
How long it takes
| Route | Statutory period | Applies to |
|---|---|---|
| Class J permitted development | None | Roof arrays up to 50 kW within the limits |
| Class J prior approval | 56 days | Roof arrays above 50 kW |
| Planning application | 8 weeks | Smaller ground-mounted arrays and other non-major schemes |
| Major development | 13 weeks (16 with an environmental statement) | Includes any site of 1 hectare or more |
| Development consent order | National process | Onshore solar above 100 MW in England |
Statutory periods are the targets councils work to; pre-application advice, surveys and any extension agreed with the council add to them.
Wales, Scotland and Northern Ireland
Planning is devolved. Scotland has its own permitted development order, with a separate class for solar on non-domestic buildings. Wales has its own permitted development rules and its own regime for larger energy projects. Northern Ireland has a separate planning system run by its councils and the Department for Infrastructure. The England rules on this page do not apply in those nations, so check the relevant government guidance before relying on permitted development there. For Scottish farms, see farm solar in Scotland.
Getting a planning check
A good installer checks the permitted development position as part of the desk feasibility and tells you early whether a roof needs prior approval or a field needs a full application. For full applications, they usually work with a planning consultant on the landscape, ecology, heritage and glint-and-glare assessments. Ask who prepares and pays for each report before you commit.