Planning & Grid for Commercial Rooftop Solar

For most commercial rooftop arrays the planning question is now straightforward — and the grid connection is the hard part. The headline change owners most often hear about, the removal of the 1 MW cap on rooftop solar, is real and material. It was made on 21 December 2023 by SI 2023/1279. But “permitted development” does not mean “no process”: commercial rooftop solar sits under Class J of the General Permitted Development Order with a mandatory prior-approval step, and the parts of a scheme most likely to be refused or delayed are no longer in the planning system at all — they are at the Distribution Network Operator (DNO). This guide sets out where the genuine gates are in 2026, and how to sequence them so a deliverable array does not stall at the connection stage. It covers England only; Scotland, Wales and Northern Ireland have their own regimes.

The 1 MW cap was removed — what actually changed

Before 21 December 2023, the permitted-development right for solar on a commercial building was capped at 1 MW of installed capacity. Anything above that needed a full planning application — a process that added months and cost to exactly the large, high-load roofs (distribution sheds, manufacturing, big-box retail) where solar pays back fastest. SI 2023/1279 removed that ceiling for rooftop installations. A 2 MW or 3 MW array on a logistics warehouse can now proceed as permitted development rather than as a discretionary application.

That is a meaningful unlock for portfolio owners and for industrial and logistics property, where roof areas are large and roof-mounted capacity can run into several megawatts. But it changes the planning calculus, not the physics: a 2 MW rooftop array still needs a grid connection capable of taking it, and that — not the local planning authority — is now where the real constraint sits.

What did not change: the right is permitted development, which means it is conditional. It carries physical limits, a prior-approval procedure, and a list of exclusions. Treating “the cap is gone” as “anything goes” is the most common owner misconception we correct.

Permitted development under Class J — with prior approval

Rooftop commercial solar is permitted development under Class J of the GPDO, but most installations of any scale trigger a 56-day prior-approval step. Prior approval is a light-touch consent: the local planning authority cannot reconsider the principle of the development, only specific listed matters. For Class J solar, those matters are the design and external appearance of the equipment and — for installations that could affect aircraft or road users — glint and glare. The authority has 56 days to determine the prior-approval application; if it does not respond within that period, the development may proceed.

This is the distinction owners should hold onto: permitted development with prior approval is not a free pass, but it is also not a discretionary planning decision. The authority is not weighing whether solar is appropriate for the site — it is checking a defined set of technical points. A well-prepared prior-approval submission, with a roof layout drawing and a glint-and-glare assessment where one is needed, is rarely refused. But it is a step with a statutory clock, and it must be programmed in, not assumed away.

Class J physical limits

The permitted-development right applies only within defined dimensional limits. Exceed any of them and the right falls away, pushing the scheme into a full planning application:

The 1 m flat-roof height limit is the one that most often bites. Ballasted, tilted mounting systems on a flat commercial roof can approach or exceed 1 m at the rear of each row. Where a design pushes past that — for steeper tilt angles to lift winter yield, for example — the array may need a full application even though its capacity is well within permitted development. This is a design-coordination point to resolve early, not a surprise to discover at submission. We cover the structural and lifecycle side of this in owner’s due diligence.

Conservation areas and highway-fronting elevations

Historically, solar on a wall or roof slope fronting a highway within a conservation area fell outside permitted development. The 2023 changes relaxed this: such installations can now proceed as permitted development subject to prior approval, with the authority assessing the impact on the appearance of the conservation area. The principle is permitted; the appearance is checked. This matters for retail and mixed-use stock in town-centre conservation areas where roofs are visible from the street.

Car-park canopies — Class OA

Solar canopies over car parks are permitted development under Class OA, separately from the rooftop right. Class OA was introduced to support the build-out of car-park solar — the structures that shade parking bays while generating power and, increasingly, feeding EV charging. For owners, a solar car-park canopy is both a generation asset and a tenant-attraction amenity: covered parking plus EV charging is a leasing differentiator for offices, retail parks and industrial estates.

Class OA carries its own dimensional and locational limits and, like the rooftop right, a prior-approval step. The economics differ from rooftop — canopies carry steel-structure costs that roof-mounted arrays avoid — but on a site with surplus parking and a landlord-controlled supply, a canopy can pair generation with EV revenue. The cost picture for both routes is set out on the cost page.

What is excluded — listed buildings, scheduled monuments and Article 4

The permitted-development right does not reach everywhere. Three exclusions matter most to commercial owners:

• Listed buildings. Solar on a listed building is not permitted development. It requires listed building consent and, usually, planning permission, with the consenting authority weighing harm to the heritage asset. This does not make solar impossible on listed commercial stock — flat roofs hidden from view, or discreet rear slopes, are routinely consented — but it removes the permitted-development shortcut and adds heritage assessment.
• Scheduled monuments. Land that is, or contains, a scheduled monument is excluded outright.
• Article 4 Directions. A local planning authority can issue an Article 4 Direction that withdraws specified permitted-development rights in a defined area — often a conservation area or a sensitive townscape. Where an Article 4 Direction covers solar, a full planning application is required even though the national right would otherwise apply. These are local and must be checked property by property; a portfolio rollout cannot assume uniform permitted-development cover across all sites.

The practical consequence: planning status is a property-by-property check, not a portfolio-wide assumption. A REIT or fund running a multi-site programme should screen each asset’s designation and Article 4 status at the survey stage, before committing the array to a delivery programme.

Ground-mount is a different and tighter regime — Class K

If a scheme cannot fit the available roof and an owner looks to ground-mounted solar on adjacent land, the permitted-development position is far more restrictive. Standalone ground-mount falls under Class K, which is tightly limited — broadly to a single installation, with a 9 sqm footprint limit for the permitted-development right on most land, and significant exclusions. In practice, anything beyond a token ground array needs a full planning application. For commercial owners the message is simple: the rooftop and car-park rights are generous; the ground-mount right is not. Land-based solar of any meaningful scale is a planning project, not a permitted-development one.

The grid is the real gate — G99 connections

For any commercial array above roughly 50 kW, the binding constraint in 2026 is the DNO grid connection, not planning. Generation that exports to, or runs in parallel with, the distribution network must connect under the Engineering Recommendation G99 process. Below the 3.68 kW-per-phase G98 threshold a connection can be notified and energised; commercial arrays sit well above that and so require a full G99 application to the DNO, which must be approved before the system is energised.

The reason this is now the critical path is capacity. Large parts of the distribution network are at or near their limit for accepting new generation. A G99 application can come back in one of three ways: an offer to connect at the requested capacity; an offer conditional on network reinforcement (which can carry a five- or six-figure cost and a multi-month — sometimes multi-year — programme); or a constrained offer that limits how much the site may export. Owners who treat the connection as a formality to handle after the panels are specified routinely find the timeline, the cost, or the achievable size of the array dictated by the DNO, not by the roof.

Reinforcement, curtailment and the size of the offer

Where the local network has headroom, a G99 offer can be straightforward and inexpensive. Where it does not, the DNO may require reinforcement — upgrading a substation, transformer or cable — and pass a share of that cost to the connecting party. On a constrained part of the network, the offer may instead cap the array’s export, or require active management. Either outcome changes the project economics. A roof that could physically carry 500 kWp may only be worth installing at 300 kWp if that is what the network will accept without prohibitive reinforcement — or the full array may still make sense if most of the output is self-consumed on site rather than exported.

Export limitation under G100 — making a bigger array fit

Where the constraint is export rather than generation, an export-limitation scheme under Engineering Recommendation G100 can let a larger array connect. G100 allows a site to install more generation capacity than its export agreement permits, provided a certified control system guarantees that export to the grid never exceeds the agreed limit — typically by throttling the inverters or diverting surplus. For a commercial property with high on-site daytime demand, this is often the route that makes the asset-led case work: the array is sized to the load, self-consumption is maximised, and export is capped to whatever the DNO will accept. Self-consumption is the principal return driver for commercial solar in any case, so a G100-limited connection frequently costs little in lost revenue while unlocking a much larger, more economic installation.

Sequence the connection first

The single most important sequencing decision is to start the grid conversation early — ideally before the array is finally specified. A realistic order of operations:

1. Establish the site’s existing supply capacity and the landlord-controlled versus tenant-metered position.
2. Make an early-stage capacity enquiry or full G99 application to the DNO to understand headroom, likely reinforcement and any export constraint.
3. Size the array to the connection offer and the on-site load, applying G100 export limitation if it lets a larger, better-economic system fit.
4. Run the Class J (or Class OA) prior-approval submission in parallel, including a glint-and-glare assessment where the location requires one.
5. Coordinate the structural roof survey and any re-roof timing alongside both, so the build is a single programme.

Done in that order, the connection result shapes the array before money is committed to a design the network cannot accept. Done in the reverse order — panels first, grid last — the DNO answer becomes an expensive surprise. To start that process for a specific asset, request a quote with the site address and current supply details, and the connection enquiry can be run alongside the design.

Frequently asked questions

Does removing the 1 MW cap mean my rooftop array needs no planning at all?

No. The 1 MW cap was removed by SI 2023/1279 on 21 December 2023, so larger rooftop arrays are now permitted development rather than full planning applications. But the right under Class J still carries a 56-day prior-approval step covering design, external appearance and — where relevant — glint and glare, plus physical limits and a list of exclusions. It is permitted development with prior approval, not an exemption from the planning system. Listed buildings, scheduled monuments and any property under an Article 4 Direction fall outside the right entirely.

What is the real bottleneck if planning is now easier?

The grid connection. For any commercial array above roughly 50 kW, the binding constraint is the G99 application to the DNO, which must be approved before the system can be energised. Large parts of the distribution network are at or near capacity for new generation, so a connection offer may require costly reinforcement, may limit how much the site can export, or may take many months to programme. We routinely see the achievable size, cost and timeline of an array set by the DNO rather than by the roof, which is why the connection enquiry should be run before the design is finalised.

Can I install a bigger array than the grid will let me export?

Yes, using an export-limitation scheme under Engineering Recommendation G100. G100 lets a site install more generation than its export agreement allows, provided a certified control system ensures grid export never exceeds the agreed limit — usually by throttling the inverters. For a property with strong on-site daytime demand this is often the route that makes the asset-led case work, because the array is sized to the load and most output is self-consumed rather than exported. Since self-consumption is the main return driver for commercial solar, a G100-limited connection typically sacrifices little revenue while unlocking a much larger, more economic system.

Do I need planning permission for a solar car-park canopy?

Solar car-park canopies are permitted development under Class OA, separately from the rooftop right under Class J, subject to their own dimensional limits and a prior-approval step. That makes canopies a viable route on sites with surplus parking, and pairing a canopy with EV charging turns it into a tenant-attraction amenity as well as a generation asset. The economics differ from rooftop because the steel structure adds cost that a roof-mounted array avoids, so a canopy makes most sense where there is a landlord-controlled supply to consume the output. The structural, consent and lifecycle checks are set out in owner’s due diligence.