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SolarG98 and G99 explained: which one applies to your system
Two forms, one threshold, and you will never fill in either of them yourself. Here is what your installer sends to the network operator, when it goes in, and how long it holds things up.
Updated 4 August 2026 · from the OVO Solar & Battery team
The short answer
G98 and G99 are the two routes for connecting a home generator to the electricity network. G98 covers smaller systems and works on a fit first, tell them after basis. G99 covers larger ones and requires permission before any work starts. One number decides which route you are on: the AC rating of the inverter, measured per phase.
3.68kW per phase is the line
At or below 3.68kW per phase, which is 16A per phase, your system goes down the G98 route and gets notified after commissioning. Above it, you are into G99 and the network operator has to approve the design before the scaffold goes up.
Who your DNO is, and why they get a say
Your Distribution Network Operator owns and runs the cables and substations that bring electricity to your street. Great Britain has 14 licensed DNO areas between six groups, and you do not choose yours any more than you choose your postcode. Because a solar system pushes power back into their network, they get a say in what connects to it. Your regional partner deals with the same DNO every week and handles the whole process for you, and you can find yours on the coverage page.
- Use the Energy Networks Association postcode tool to look it up in seconds.
- Call 105, the free national number, and ask.
- Read the first two digits of the bottom line of your MPAN, printed on your electricity bill.
G98: fit first, notify within 28 days
G98 is a notification, not a request. The system is designed, installed and commissioned, and the installer then submits the G98 form to the DNO within 28 days. There is no waiting period built into your project and no approval to chase. This is the route most single phase homes take, which is why a 3.68kW inverter is the standard specification on a typical UK domestic install.
A properly completed G98 cannot be refused
If the system sits inside the threshold and the paperwork is filled in correctly, the DNO has no grounds to reject it. That is the whole point of the connect and notify route, and it is why the vast majority of domestic installations never involve a wait.
G99: apply first, then fit
Above 3.68kW per phase, the order reverses. The installer submits a G99 application and the DNO assesses whether the local network can take the extra generation before anything is fitted. A standard determination usually takes around 4 to 8 weeks. Fast track routes can come back in about 2 weeks, and genuinely complex cases can run to 12. The application itself is free, though installers may charge an admin fee for preparing it, and in rare cases the DNO can require network reinforcement that carries a cost.
| G98 | G99 | |
|---|---|---|
| Applies when | Inverter is 3.68kW per phase or less, which is 16A per phase | Inverter is above 3.68kW per phase, or above 11.04kW on three phase |
| Permission first | No. Fit, commission, then notify | Yes. Nothing is installed until the DNO responds |
| Timing | Form submitted within 28 days of commissioning | Around 4 to 8 weeks for a standard decision, about 2 on a fast track |
| Can it be refused | No, not if it is properly completed | Yes, and reinforcement work can be required |
| Who submits it | Your installer | Your installer |
Both thresholds refer to the AC rating of the inverter, per phase, not to the panel capacity on the roof.
Your local OVO expert will tell you on the call which route your system takes and what it adds to the timeline. The 45 minute video design is free and there is no home visit.
Get your free quote →The threshold is the inverter, not the panels
This is the part that surprises people. The 3.68kW figure is the inverter's AC output rating, so it does not cap how many panels go on the roof. Arrays are routinely oversized relative to the inverter, with industry practice putting the ratio somewhere between 1.10 and 1.30, and you can comfortably sit well above 4kWp of panels on a 3.68kW inverter and still be a G98 job. Extra panels are cheaper than a bigger inverter once the scaffold and the crew are paid for, which is the argument in our guide to filling the roof first time and in the cost guide. Where a battery is in the design, the sizing order changes again, and that is covered in the solar and battery strategy.
Single phase or three phase changes the ceiling
Know what is at stake
Most UK homes are single phase and capped at 3.68kW of inverter under G98. A three phase home gets 11.04kW under the same connect and notify rule, which is a very different system before anyone applies for anything.
Find the service head
It is the sealed unit where the supply cable enters the property, normally next to or just below the meter.
Count the fuses and the wires
Single phase typically shows one cut-out fuse and two wires, a live and a neutral. Three phase shows three 100A fuses and four wires, three lives and a neutral.
Check the meter markings
Labels reading L1, L2 and L3 are a reliable sign of a three phase supply.
Take a photo for your design call
One clear picture of the meter and service head lets your regional partner confirm the phase and the connection route while you are still on the video call.
If the DNO turns the application down
- Pay for the network reinforcement the DNO has specified, if the quoted cost is proportionate to the system.
- Cap the inverter at 3.68kW, or apply export limitation, so the design drops back under the G98 threshold.
- Decline the connection and redesign the system around a smaller inverter with more panels behind it.
- Reapply later, because local network capacity changes as reinforcement work is carried out in the area.
Get a written quote on the call, with the grid application route already worked out for your property. Book a free 45 minute video design with your regional partner.
Get your free quote →OVO SEG Install Exclusive pays 20p per kWh where OVO installs both solar and battery, or 15p per kWh for solar only. The exclusive rates require you to take your electricity supply from OVO and are subject to system size limits. OVO's standard SEG rate of 4p per kWh is open to customers of any supplier. Rates correct at August 2026 and subject to change. Full conditions are in our export rate guide.
Grid connection questions, answered
Do I have to fill in a G98 or G99 form myself?
No. On a standard certified installation the installer handles the whole process end to end, from working out which route applies to submitting the paperwork and dealing with the DNO's questions. Your local OVO expert does it as part of the job, and you will not be asked to sign a network application yourself.
How long does a G99 application take?
A standard determination usually takes around 4 to 8 weeks from submission. Fast track routes can come back in roughly 2 weeks, and complex cases where the local network is already constrained can stretch to about 12 weeks. Nothing is installed until the answer arrives, so it is worth having the design call early if you suspect you are over the threshold.
Can I fit more than 4kW of panels and stay on G98?
Yes. The threshold applies to the inverter's AC rating, not to the panel capacity on the roof. Oversizing an array relative to the inverter is normal practice, with typical ratios between 1.10 and 1.30, so a 3.68kW inverter can sit behind meaningfully more than 4kWp of panels and remain a connect and notify job.
Does the application cost anything?
The application itself is free. Some installers charge an admin fee for preparing and submitting it, and in the rare cases where the DNO requires network reinforcement before it will accept the connection, that work carries a cost which is quoted separately.
How do I find out who my DNO is?
Great Britain has 14 licensed DNO areas owned by six groups, and yours is set by where you live. You can use the Energy Networks Association postcode tool, call 105 free of charge, or read the first two digits of the bottom line of the MPAN on your electricity bill.
Can a G98 notification be rejected?
Not if it is properly completed and the system genuinely sits within the 3.68kW per phase limit. G98 is a notification rather than a request, which is the reason most domestic installations go ahead without any waiting on the network operator.
What is the maximum I can install without prior approval?
3.68kW of inverter on a single phase supply, or 11.04kW on three phase. Above those figures you need a G99 approval before installation. Whether your home is single or three phase therefore has a much bigger effect on system size than most people expect.
Figures and specifications in this guide are sourced below and were checked on the date shown. Rates and product specifications change; we confirm the current picture on your free design call.
Sources
- G98 connect and notify process, the 28 day notification window, and that a completed notification cannot be rejected sunsave.energy
- G99 approval requirement, 4 to 8 week standard determination, fast track and complex case timescales, free application and refusal options sunsave.energy
- Threshold applies to inverter AC rating rather than panel capacity, and the 3.68kW single phase and 11.04kW three phase limits sunsave.energy, spiritenergy.co.uk
- What a DNO is, the 14 licensed areas across six groups, the 105 number and the MPAN lookup ovoenergy.com, uw.co.uk
- Identifying a single phase or three phase supply from the service head, fuses and meter markings ukpowernetworks.co.uk
- Inverter loading ratios of 1.10 to 1.30 and the case for oversizing an array relative to the inverter aurorasolar.com, freedomforever.com
- OVO SEG rates and eligibility conditions ovoenergy.com
Read next
How solar panels work, and why they work here
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Read the guide →What solar costs in 2026, and what drives the price
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Read the guide →Adding a battery to solar you already have
Your panels stay untouched. The grid application is the part that catches people out.
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