What G99 covers
ENA Engineering Recommendation G99 governs the connection of generation above 16A per phase — anything larger than the micro-generation systems that fall under G98.
In practice that means:
- Single phase above roughly 3.68kW
- Three phase above roughly 11.04kW
- Most systems with battery storage, regardless of solar array size
- Any site where cumulative existing generation pushes the total over the threshold
The threshold is inverter output, not array capacity. A 5kWp array on a 3.68kW inverter stays in G98. A 3kWp array on a 6kW hybrid inverter with a battery does not.
G99 types
G99 bands generation by capacity, and the requirements step up sharply as you move through them.
Almost all rooftop solar, domestic and commercial, sits here. Requirements are proportionate: type test evidence, protection settings, single-line diagram, export arrangement.
Larger commercial rooftop and ground mount. Significantly heavier technical evidence, more detailed protection and control requirements, and a longer assessment.
Utility scale.
Transmission-adjacent.
Most installers only ever see Type A. If you're moving into larger commercial portfolios, the jump from Type A to Type B is the point at which in-house handling usually stops being viable — the technical pack is a different order of work.
Fast track and full assessment
Not every G99 application goes through the full assessment. Smaller Type A systems can qualify for a fast track route, where the network operator applies a simplified assessment on the basis that the system is small enough and the local network unconstrained enough not to need detailed study.
Whether a job qualifies depends on capacity, phase configuration, the operator's own thresholds and what's already connected on the local network. It isn't something you elect — the operator determines it — but how the application is presented affects whether it's identified correctly at the outset. Applications that should have been fast tracked and weren't are one of the quieter causes of delay.
What goes into a G99 application
Site and supply
- Full address and postcode
- Import MPAN
- Phase configuration and supply capacity
- All existing generation on site, declared
Generation equipment
- Inverter manufacturer, model, quantity
- Rated output in kW and A per phase
- G99 type test certificate reference — current, not superseded
- Total array capacity in kWp
- Battery manufacturer, model, capacity and inverter rating where fitted
Protection
- Protection settings schedule
- Loss of mains protection type and settings
- Interface protection arrangement where applicable
Export arrangement & drawings
- Whether export limited, and to what
- The export limitation scheme, device and G100 compliance evidence
- Single-line diagram showing generation, protection, metering and point of connection
The single-line diagram and the protection settings schedule are the two items that most often turn a G99 application into a fortnight of back-and-forth. They're also the two that get left until last.
How long a G99 takes
The network operator has a statutory window to respond — commonly up to 45 working days for a standard distributed generation application, though this varies by operator and by application type. Fast-tracked Type A systems frequently come back considerably sooner. Constrained networks, Type B applications and anything requiring detailed study run longer.
Where the assessment identifies that network reinforcement is needed, you move into a different conversation entirely: a connection offer with a capital contribution attached, which the customer has to accept and pay before the connection proceeds. That can add months. It's rare on domestic rooftop and not rare at all on commercial sites in constrained areas.
Schedule accordingly. A G99 application should go in at the point the job is won, not the week before the scaffold arrives.
Why G99 applications get rejected or stall
Superseded type test reference
Inverter firmware revisions supersede certificates. The reference that worked six months ago may not work now.
Missing or inadequate single-line diagram
Every G99 needs one. A sketch won't clear assessment.
Export limitation asserted rather than evidenced
Stating a system is limited to 3.68kW isn't sufficient. The scheme, the device and the G100 compliance evidence all have to be there.
Undeclared existing generation
The operator has visibility of what's already connected. Omitting it looks like an error at best.
Combined rating miscalculated on hybrid systems
Solar inverter and battery inverter ratings interact in ways that aren't always obvious, particularly on AC-coupled retrofits.
Unanswered queries
The most common failure of all. The operator asks a question, nobody sees the email, and the application quietly drops out of the queue. Nothing is rejected. It just stops.
Can you handle G99 in-house?
Yes, and plenty of installers do. There's no qualification required and the forms are publicly available.
The honest picture: a routine Type A G99 for straightforward domestic solar is around 90 minutes to two hours once you're fluent, and closer to three or four the first several times. Add a battery, an export limiter or an AC-coupled retrofit and it climbs. Add query handling across the assessment period and export MPAN chasing afterwards and you're realistically at three to four hours of attention per job, spread across six weeks.
The problem isn't the difficulty. It's the interruption pattern. G99 applications generate queries at unpredictable intervals during a window when you've moved on to other jobs, and the cost of missing one is a restart rather than a delay.
For commercial work the calculation is different again. Type B applications need technical input that most installation businesses don't carry in-house, and the margin on a stalled commercial job disappears quickly.
We're not going to pretend you can't do this. We'd rather you knew exactly what you're handing over.
Our G99 service
You send
Address, MPAN, inverter details, array size, phase, battery details, export arrangement, customer contact.
We do
- Route assessment — G98 or G99, Type A or Type B, fast track eligibility
- Full application preparation including protection settings schedule
- Single-line diagram preparation where you don't have one
- Submission to the correct network operator
- Query handling throughout the assessment window
- Approval and export MPAN retrieval
- Full audit trail returned to you — submission reference, every DNO exchange, the approval itself
Flat fee per application. All six GB network operator groups. Seven day average submission-to-you turnaround, with the assessment window being the operator's, not ours.
Send us your next G99
Route assessment, technical pack, submission and query handling — all in the flat fee.
Frequently asked questions
What's the difference between G98 and G99?
G98 covers micro-generation up to 16A per phase and is a notification you make within 28 days of commissioning. G99 covers everything above that and is an application requiring approval before you install. Roughly, 3.68kW single phase and 11.04kW three phase is the dividing line.
Can I install before G99 approval?
No. If the network operator imposes conditions — an export limit, a different connection arrangement, a reinforcement contribution — you'd be modifying a commissioned system at your own cost.
How long does G99 approval take?
Commonly up to 45 working days for the operator's response on a standard application, though fast-tracked smaller systems are often quicker and constrained sites take longer. Where reinforcement is required, considerably longer.
Does a battery require a G99 application?
Usually. Batteries count as generation and the combined inverter rating typically exceeds the G98 threshold. Adding storage to an existing G98-notified solar system generally requires a fresh G99 application.
What is G99 fast track?
A simplified assessment route the network operator can apply to smaller Type A systems on unconstrained networks. It's determined by the operator, not elected by the applicant, though how the application is presented affects whether eligibility is identified early.
Do I need a single-line diagram for G99?
Yes. It's a standard requirement and one of the most common reasons applications stall. We prepare them where you don't have one.
What is a Type A G99 application?
Generation between 0.8kW and 1MW. It covers essentially all rooftop solar including commercial, and has proportionate technical requirements compared with the Type B, C and D bands above it.
Do you handle Type B applications?
Yes. Type B covers 1MW to 10MW and carries substantially heavier technical evidence requirements. Talk to us about commercial portfolio work.