G99 Application Guide 2026: Commercial Solar Step by Step

The short answer

If you are putting solar or a battery on a commercial building in Great Britain, you will almost certainly need a G99 application. G99 is the Energy Networks Association's Engineering Recommendation for connecting generation to the distribution network, and it applies to anything above 16A per phase. The rule is simple: apply first, connect after the DNO says yes. This guide walks through what goes into the application, how the DNO assesses it and what slows it down. If you would rather hand it over, our grid connection consultancy prepares and submits it for every KMM project.

G98, G99 and G100 compared

Who G99 applies to

Any generating equipment above 16A per phase connected to a DNO's network, which covers nearly every commercial solar installation: factory and warehouse roofs, farm buildings, solar carports and ground mounts. It also covers battery storage that can export, and several smaller systems on one site whose combined output crosses the threshold.

Power-generating module types

G99 sorts generation into types by size, and the paperwork grows with each step. In Great Britain, Type A runs from 0.8 kW up to 1 MW, Type B from 1 MW up to 10 MW, Type C from 10 MW up to 50 MW, and Type D is 50 MW and above or anything connected at 110 kV or more. Almost all rooftop commercial solar is Type A; large ground mounts can reach Type B, which brings extra technical requirements and testing.

What goes into the application

• Your supply details: the MPAN, the agreed supply capacity in kVA and whether the supply is single- or three-phase.
• The system design: inverter makes, models and ratings, battery capacity if any, and the total generation capacity.
• A single-line diagram showing how the generation connects to your board and where the protection sits.
• Type-test evidence for the inverters, usually by reference to the ENA type-test register.
• The export you want: full export, or a lower limit managed under G100.
• A site location plan so the DNO can find the right part of its network.

Most of the delay we see comes from incomplete applications, so it pays to get this right first time. Our DNO application template lists what to gather.

The process, step by step

1. Check capacity. Look at the existing supply and, for bigger systems, ask the DNO for a budget estimate or a pre-application discussion.
2. Design the system around your load and the likely export position.
3. Submit the G99 application with the design, diagram and type-test evidence.
4. DNO assessment. The DNO studies the impact on its network and replies with a connection offer, which may include an export limit or a cost for reinforcement.
5. Accept the offer and install.
6. Commission and notify. Larger systems may need the DNO to witness testing; the commissioning paperwork goes back to the DNO before the system is signed off.

What 16A per phase means in kilowatts

The G98 limit is written in amps because that is how the network sees it. On a single-phase 230V supply, 16A works out at about 3.68 kW of inverter output. On a three-phase supply the same 16A applies to each phase, so the ceiling is about 11 kW in total, as long as the output is balanced across the phases. A typical commercial roof of 30 kW, 100 kW or more is far above either figure, which is why commercial projects go through G99. The limit is about inverter output, not panel capacity, so a site can sometimes fit more panels than the inverter rating, but it cannot dodge G99 by doing so.

What a connection offer contains

If the DNO accepts the application, it replies with a connection offer. Read it before you commit to the rest of the project. It usually sets out:

• The generation and export capacity the DNO will allow, which may be lower than you asked for.
• Any export limit and whether a G100 scheme is needed to enforce it.
• Any works and charges on the network side, such as reinforcement or new equipment, and who pays.
• Conditions and timescales, including how long you have to accept the offer and any testing the DNO wants to witness.

An offer with a reinforcement charge or a tight export limit is not the end of the project. It usually means re-sizing the system, adding a battery or designing around the limit; that is the conversation our grid connection consultancy has with the DNO.

Common reasons applications stall

• Missing or inconsistent information: the supply capacity, the MPAN or the inverter models do not match across the forms.
• No single-line diagram, or one that does not show the protection and the point of connection.
• Inverters that are not on the ENA type-test register, so the DNO asks for extra evidence.
• Asking for full export on a part of the network that cannot take it, instead of proposing a limit up front.
• Applying late, after the system has been ordered, so the DNO's timescale becomes the project's critical path.

Export limits and G100

When the local network cannot take everything your system could export, the DNO may offer a lower export capacity. G100 lets you install more panels than that export figure by fitting a control system that keeps export under the agreed limit. On a site with a strong daytime load, which describes most factories and warehouses, very little is exported anyway, so an export limit often costs little. Our G99 vs G100 guide covers when it is worth it.

How long it takes, and what slows it down

Timescales depend on the DNO, the size of the system and how busy that part of the network is. Small, complete applications on uncongested networks move quickest; large schemes, high-voltage connections and congested areas take far longer, and some need network studies before an offer can be made. Our DNO application timelines post covers what we see in practice. The things that most often add delay are missing information, an export request the network cannot take, and applications sent late in the project instead of at the start.

Adding EV chargers or a battery

EV chargers add demand that the DNO will want to know about, and a battery that can export is generation in its own right. Put them in the same application as the solar where you can, so the DNO assesses the whole site once. See our EV chargepoint consultancy page if chargers are part of the plan.

G99 in the East Midlands

Most of the East Midlands is in National Grid Electricity Distribution's East Midlands licence area, and the far north of Lincolnshire is Northern Powergrid. The rules are the same everywhere in Great Britain, but each DNO runs its own application portal and its own queue. Our East Midlands commercial solar page has the regional yields and grid notes.

G99 application FAQs