G98 applies to solar systems with an inverter output of 3.68kW or less per phase – which covers most homes. G99 applies to anything larger and requires formal DNO approval before you can install, adding 2-4 months to your timeline. You can often avoid G99 entirely by export-limiting a larger system to 3.68kW.
If you’ve been quoted a solar system and your installer has mentioned “G98 notification” or “G99 application,” it can feel like alphabet soup. But this genuinely matters – getting it wrong, or not understanding it, can delay your installation by months and add unexpected costs.
Here’s what’s actually going on, explained plainly.
What are G98 and G99?
G98 and G99 are the two engineering standards that govern how solar systems connect to the UK electricity grid. Think of them as two tiers of grid connection: one for smaller, everyday residential systems, and one for anything larger that needs more scrutiny.
Your Distribution Network Operator (DNO) – the company that manages the cables and infrastructure in your area – uses these standards to keep the grid stable. Too many systems pushing too much power into a local network can cause voltage problems. These standards are how the DNOs manage that risk.
The key difference is size. G98 is for systems up to 3.68kW per phase (16A). G99 is for everything above that. For most homeowners on a standard single-phase supply, that 3.68kW figure is the number to remember.
What the 3.68kW threshold actually means
This trips people up, so it’s worth being precise. The threshold is based on your inverter’s AC output, not the total panel capacity on your roof.
| Inverter setup | Standard |
|---|---|
| 5kW array connected to a 3.68kW inverter | G98 |
| 5kW array connected to a 5kW inverter (unrestricted) | G99 |
| 5kW inverter with export capped at 3.68kW | G98 |
Your battery capacity doesn’t factor in either. It’s purely the inverter output that counts.
On a three-phase supply, the limit triples to 11.04kW (3 x 3.68kW), which is why larger homes with three-phase electricity can often accommodate bigger systems without triggering G99.
G98: simple, fast, and free
For most residential installations, G98 is the relevant standard – and it’s refreshingly straightforward.
Your installer connects the system, commissions it, and then notifies your DNO within 28 days. You don’t need permission first. There’s no application fee. No waiting around. No technical assessment. The DNO acknowledges the notification (usually automatically), and that’s largely it.
The total additional delay to your installation: zero. That’s a big deal when you’re eager to start generating and cutting your bills.
Your installer handles all of this as part of a standard job – they submit the notification, provide the technical details, and manage any paperwork. As the homeowner, you mainly just need to supply your MPAN (the supply number on your electricity bill) and confirm whether you’re on a single or three-phase supply.
G99: more complex, more time, potentially more cost
G99 kicks in the moment your inverter output exceeds 3.68kW per phase. And the difference in process is significant.
Unlike G98 – which is notification after the fact – G99 requires formal approval before you can install anything. Your installer submits an application to the DNO, which then has 45 working days to assess it. In reality, that often stretches to 10-16 weeks. If the local network has capacity issues – common in rural areas or streets already dense with solar – it can run to 6 months or more.
Here’s roughly what that timeline looks like in practice:
| Scenario | Typical duration |
|---|---|
| No constraints; straightforward approval | 6-10 weeks |
| Minor assessment required | 10-16 weeks |
| Network constraints identified | 16-26 weeks |
| Reinforcement required | 6-12 months+ |
Costs under G99 are usually zero or modest – often just a small application fee, sometimes a witnessing fee if the DNO needs to attend commissioning. But if your local network needs reinforcing to accommodate your system, that cost can run into thousands of pounds, and it falls on you.
The DNO can also refuse the connection outright, or impose conditions – such as requiring you to cap your export anyway.
Export limiting: the smart middle ground
This is where most installers land for systems between roughly 4kW and 6.5kW. Export limiting lets you install a larger system while keeping it within G98 – by capping what you send back to the grid at 3.68kW.
Here’s how it works in practice. Say you install a 6kW system with a 5kW inverter. The inverter is programmed to export a maximum of 3.68kW to the grid at any one time. When you’re using electricity in the house, more of your generation goes to powering your home directly. When the house is quiet and generation is high – sunny summer midday – the inverter holds back anything above 3.68kW from being exported.
The benefit: you get a larger system, faster installation, no G99 delays, and you use the full generation capacity for your own consumption and battery charging.
The downside: during peak summer generation, you may be curtailing – effectively wasting – some output that you could otherwise export and get paid for via the Smart Export Guarantee (SEG). How much this matters depends on how much electricity you use during the day. If you work from home, run a heat pump, or have a battery to soak up the excess, it’s barely noticeable.
For most households, export limiting is the pragmatic choice. You get a bigger, more capable system on your roof without the months of waiting.
Which standard will apply to your installation?
Here’s a practical guide based on common system sizes:
| System size | Typical standard | Notes |
|---|---|---|
| 8-10 panels (3-4kW) | G98 | Standard small system; no complications |
| 10-12 panels (4-5kW) | G98 with export limit | Very common approach |
| 12-16 panels (5-6.5kW) | G98 with export limit | Popular for families with higher usage |
| 16+ panels (6.5kW+) | G98 with limit or G99 | Depends on whether you want uncapped export |
If you’re adding a battery to your solar system, the same principle applies – the hybrid inverter’s AC output is what the DNO cares about. A 5kW hybrid inverter with export capped to 3.68kW stays comfortably within G98.
Who handles the application?
Your MCS-certified installer handles almost everything. They:
- Determine which standard applies
- Prepare and submit the notification or application
- Provide technical documentation to the DNO
- Manage any back-and-forth
- Handle commissioning paperwork
As the homeowner, you’ll need to:
- Provide your MPAN (on your electricity bill)
- Confirm single or three-phase supply
- Sign the application if required (G99)
- Accept the connection offer (G99 only)
- Pay any applicable fees
If your installer hasn’t mentioned G98 or G99 at all, don’t panic – reputable installers handle this routinely. But it’s worth asking which standard your system falls under, so you have realistic expectations for your installation timeline.
Network constraints: what can go wrong with G99
The main risk with G99 is network constraints. If many homes in your street or village already have solar, the local transformer or cable infrastructure may be at or near capacity. In that case, the DNO may:
- Require you to export-limit anyway (making the G99 process somewhat moot)
- Ask for network reinforcement works before connecting you
- Refuse the connection at the requested capacity
Rural areas and properties at the end of long cable runs tend to be most affected. If you’re in an area like this, your installer should be able to check the DNO’s heat maps – most DNOs publish network capacity data online – before submitting any application.
If constraints look likely, export limiting to stay within G98 is often the more reliable route.
Frequently asked questions
Does the number of solar panels determine G98 or G99?
No. The standard is determined by your inverter’s AC output, not the number of panels or total panel capacity. You can have 5kW of panels connected to a 3.68kW inverter and remain under G98.
How long does G98 take?
There’s no delay to your installation. Your installer installs the system, commissions it, and then notifies the DNO within 28 days afterwards. You’re generating power immediately.
How long does G99 take?
The DNO has 45 working days to assess a G99 application, but real-world timelines are usually 10-16 weeks. If your local network has constraints, it can take significantly longer.
Does a battery system require G99?
Not necessarily. It depends on your hybrid inverter’s AC output. A 5kW hybrid inverter with export limited to 3.68kW stays within G98. Your installer will confirm which applies.
Can I avoid G99 by export limiting?
Yes, in most cases. If your inverter can be programmed to cap export at 3.68kW, you remain within G98 regardless of the inverter’s total output capacity. Most modern inverters support this.
Will I lose money by export limiting?
Potentially a small amount during peak summer generation. If your home uses most of its generation directly – or you have a battery – the impact is minimal. For most households, the faster installation and simpler process outweigh the occasional curtailment.
Who submits the G99 application?
Your MCS installer. You don’t need to contact the DNO directly. Understanding the process helps you set realistic expectations and make informed decisions about system sizing.
For the vast majority of homes, G98 is the relevant standard. Your installer notifies the DNO after the job is done, and you’re generating from day one. Clean, simple, no delays.
If you’re looking at a larger system – anything with an inverter output above 3.68kW – talk to your installer about export limiting before assuming you need to go through a G99 application. In most residential cases, capping your export is the faster, simpler option, with very little real-world downside.
If you do need G99, build at least 10-16 weeks into your project timeline and ask your installer to check local network capacity before applying. The earlier you start, the sooner you’re generating.
