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SolarG98 vs G99: the 28-day form and the eight-week wait, in plain English
Two connection standards decide whether your solar install is a formality or a four to eight week wait. The dividing line is one number on your quote, and it is not the number most people expect.
Updated 4 August 2026 · written by the Clearline guidance team
The dividing line
G98 applies when inverter capacity is 3.68kW per phase or less, which is 16A per phase. G99 applies above that, which on a three phase supply means above 11.04kW. Everything else follows from which side of that line your system sits on.
The number being measured is the inverter's AC rating, not the panel capacity on the roof. You can hang well over 4kWp of panels on a 3.68kW inverter and stay firmly within G98. That is not a loophole, it is how UK residential solar is routinely designed, and we explain the engineering behind it in inverter sizing explained.
Panels do not count. The inverter does.
Homeowners are regularly told there is a four panel or a ten panel limit. There is no such thing. The connection standard regulates how much AC power your system can push into the network at once, which is set by the inverter, and the panels above that rating simply extend your generating day.
G98: fit first, tell them after
G98 is a connect-and-notify process. The installer fits the system, commissions it, and then submits the G98 form to your Distribution Network Operator within 28 days of commissioning. No waiting, no approval stage, no risk of the project stalling.
The important detail is that a properly completed G98 notification cannot be rejected. Below the threshold, the DNO does not have discretion over whether you connect. This is why the standard UK single phase design has settled around 3.68kW of inverter with a fuller roof of panels behind it.
G99: ask first, wait, then fit
Above the threshold, the process reverses. The installer submits a G99 application and the DNO makes a determination before any installation work happens. A standard determination takes roughly four to eight weeks. Fast-track routes run at around two weeks, and complex cases can stretch to twelve.
The application itself is free, although installers may charge an administration fee for preparing and submitting it. In rare cases the DNO can require paid network reinforcement, which is a genuine cost risk worth establishing early on a large system.
| 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 |
| Order of events | Fit, commission, then notify | Apply, wait for a determination, then fit |
| Timescale | Form submitted within 28 days of commissioning | Roughly four to eight weeks standard, around two weeks fast-track, up to twelve for complex cases |
| Can it be refused? | No, not when properly completed | Yes, or approved with conditions |
| Cost | Free application, installer may charge an admin fee | Free application, installer may charge an admin fee, plus possible network reinforcement in rare cases |
| Who files it | The installer | The installer |
G98 and G99 process and threshold guidance, accessed August 2026.
If a G99 is refused
Refusal is not the usual outcome, but it happens, and there are four routes from there.
- Fund the network upgrade. Viable when the reinforcement cost is modest relative to the system.
- Cap the inverter at 3.68kW. Export limitation brings the system back under the G98 threshold. You keep the panels and the self-consumption; you limit what flows out.
- Decline the connection. Rare, and usually a signal to redesign rather than abandon.
- Reapply later. Local network conditions change as reinforcement projects complete elsewhere.
Export limitation is not the disaster it sounds like
Capping the inverter limits what you can push to the grid, not what your panels generate or what your house can use. Given that self-consumed electricity is worth the rate you avoid paying and exported electricity is worth your export tariff, a cap costs you the difference on the exported units only. Our tariffs guide covers what those rates currently are.
Which one will apply to you
Start with your supply type. Most UK homes are single phase, where the ceiling is 3.68kW. If you have three phase, the same rule applies per phase and the ceiling is 11.04kW, which puts most residential systems comfortably inside G98. Our single phase versus three phase guide covers the sixty-second check at your fuse board.
Check your supply
One cut-out fuse and two wires is single phase. Three 100A fuses and four wires, or L1 L2 L3 on the meter, is three phase.
Find the inverter rating on your quote
It is a kW figure, separate from the panel kWp. On single phase quotes it is very often 3.68kW precisely because of this threshold.
Compare the two
At or under 3.68kW per phase, you are in G98 territory and the timeline is unaffected. Above it, budget four to eight weeks before installation.
Ask about reinforcement risk
Only relevant on a G99. It is rare, but it is the one outcome that carries a potentially significant unbudgeted cost.
You will not be filling in either form
In a standard installation carried out by an MCS-certified installation team for your area, the homeowner never files any of this. The installation team handles G98 and G99 end to end. What you should get is a clear answer on which process applies, and if it is G99, a realistic date rather than an optimistic one.
That paperwork also matters afterwards. Some suppliers require proof of grid connection from the DNO before they will pay you for exported electricity, alongside your MCS certificate and a smart meter capable of half-hourly export readings. Getting the connection documentation right is part of getting paid.
A free design call will tell you which process your system falls under, how long it realistically takes, and whether a slightly smaller inverter would save you two months.
Get your free quote →Every county page on this site carries a calculator for that area, so you can test different inverter sizes against your own usage before committing. Start at your county page, or read what a DNO is for the background on who is making these decisions.
G98 and G99, answered
What is the difference between G98 and G99?
G98 is a connect-and-notify process for systems with an inverter of 3.68kW per phase or less, where the installation happens first and the form is submitted within 28 days of commissioning. G99 applies above that threshold and requires the network operator's approval before any installation work begins. The dividing line is the inverter's AC rating per phase.
How long does a G99 application take?
A standard determination takes roughly four to eight weeks. Fast-track routes run at around two weeks, and complex cases can stretch to twelve. Timescales vary between the 14 network operator areas, so treat any national figure as a guide rather than a promise.
Can I install more than 3.68kW of solar?
Yes. The 3.68kW threshold applies to the inverter's AC output per phase, not to panel capacity, so a system with well over 4kWp of panels can sit within G98. If you want inverter capacity above the threshold, that is a G99 application rather than a prohibition.
Does a G98 or G99 application cost anything?
The application itself is free, though installers may charge an administration fee for handling it. On a G99, the network operator can in rare cases require paid network reinforcement, which is a separate and potentially significant cost. That risk should be raised before you sign anything on a large system.
What happens if my G99 is refused?
There are four routes: fund the network upgrade, cap the inverter at 3.68kW using export limitation, decline the connection, or reapply later when local network conditions have changed. Capping the inverter is the most common practical answer, and it limits what you export rather than what your home can use.
Do I need to fill in the form myself?
No. In a standard installation the installer handles both processes end to end, from application to commissioning paperwork. What you should ask for is confirmation of which process applies and, on a G99, a realistic installation date.
Do I need the connection paperwork to get paid for exports?
Some suppliers require proof of grid connection from your network operator before enrolling you on an export tariff, alongside MCS certification and a smart meter that records export every 30 minutes. Keeping the commissioning documentation is worth doing properly. It is what unlocks the payments.
See the numbers next: LONGi 530 W panels, installed, or the solar panels guide.
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 application: 3.68kW per phase threshold, 16A per phase, 28 day submission after commissioning, cannot be rejected when properly completed, installer files it sunsave.energy
- G99 application: prior approval, four to eight week standard determination, around two weeks fast-track, up to twelve weeks complex, free application, admin fees, reinforcement risk, refusal options sunsave.energy
- The threshold governs inverter AC rating, not panel kWp sunsave.energy
- Three phase connect and notify limit of 11.04kW blog.spiritenergy.co.uk
- Single phase and three phase supply identification ukpowernetworks.co.uk
- Supplier requirements for export payment including G98 or G99 proof of grid connection and half-hourly export metering britishgas.co.uk
- Smart Export Guarantee scheme rules and metering requirements ofgem.gov.uk
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