If your solar system is rated under 16 amps per phase, which works out at 3.68kW per phase, it falls under Engineering Recommendation G98: your installer fits it and notifies your Distribution Network Operator within 28 days of commissioning. Anything above that threshold falls under G99, and the application goes in before the system is connected. That single number decides how long your install takes to arrange, whether anyone can say no to it, and sometimes what size inverter you end up with. Northern Ireland runs its own version of the rules with a different deadline. Here is what each route involves and who actually does the paperwork.
What are G98 and G99?
They are the two Energy Networks Association engineering recommendations that set the technical rules for connecting a generator to the public electricity network, and every domestic solar install in Great Britain goes through one of them. Both came out of the EU network code 2016/631, Requirements for Generators, which was written into UK law and applies to equipment connected on or after 27 April 2019. Anything installed before that date sits under the older G83 and G59 documents instead.
- EREC G98 covers "the connection of Fully Type Tested Micro-generators (up to and including 16 A per phase) in parallel with public Low Voltage Distribution Networks".
- EREC G99 covers "the connection of generation equipment in parallel with public distribution networks", which in practice means everything larger.
The ENA states the split plainly: "A generator with a capacity less than 3.68kW/phase then EREC G98 applies" and "A generator with a capacity greater than 3.68kW/phase then EREC G99 applies". Source: Energy Networks Association, connecting generation to the electricity networks.
Your DNO is the company that owns the poles, cables and substations in your area, which is not the same thing as the company that bills you for electricity. You do not choose it, and it is the one that has to be told about your panels.
Which one applies to your solar system?
The number that decides it is the rated output of your inverter, not the peak rating of your panels. National Grid Electricity Distribution words its G98 qualifying criteria as "the rated output must be under 16A per phase for connection at low voltage". Sixteen amps at 230V is 3.68kW, which is why the same limit gets quoted both ways. A 4.5kWp array of panels feeding a 3.68kW inverter is still a 3.68kW generator as far as the network is concerned.
The threshold is per phase, so it scales with your supply:
| G98 | G99 | |
|---|---|---|
| Capacity | Less than 3.68kW per phase, which is under 16A per phase | Greater than 3.68kW per phase |
| Single-phase home | Up to 3.68kW total | Above 3.68kW |
| Three-phase supply | The limit applies to each phase separately. NIE Networks puts the equivalent NI ceiling at under 11.04kW across three phases | Above the per-phase limit on any phase |
| Process | Fit and notify. The install goes ahead, then the DNO is told | Apply first. The DNO assesses the connection before it is made |
| Deadline | Notify within 28 days of commissioning (Great Britain) | Application before connection; commissioning confirmation follows |
| Can the DNO refuse? | No assessment is required for a compliant install | Yes, or it can require network reinforcement or export limitation first |
Most standard UK domestic installs are deliberately sized to stay on the G98 side of the line, which is a large part of why 3.68kW inverters are so common on British roofs. It is also worth knowing that this is a per-phase rule and never a "4kW system" rule, whatever a sales quote might round it to.
Battery storage counts. The ENA's fast-track conditions measure "the total aggregate capacity of the generating units (including electricity storage devices)", and UK Power Networks handles solar and storage through the same notification route. If you are adding a battery to an existing array, the combined figure is what matters. Our solar battery storage guide covers the cost side of that decision.
How G98 works: fit first, notify within 28 days
Under G98 nobody has to approve your install in advance. The system goes in, and the notification follows within 28 days of commissioning. National Grid Electricity Distribution describes it as "a simple connection procedure for fully type tested installations under 16A per phase. Installations take place on a fit and notify basis", and states: "You must notify us of the generation installation within 28 days of commissioning." Source: National Grid Electricity Distribution, micro generation (G98).
NGED publishes the conditions an installation has to meet to qualify. Other DNOs word their criteria similarly, but check your own operator's page rather than assuming:
- Rated output under 16A per phase for connection at low voltage.
- Grid interface protection installed to local standards and functionally tested.
- The system shuts down during a power cut, so it cannot back-feed a dead network.
- An isolation switch capable of isolating all phases and lockable in the off position.
- A circuit diagram displayed on site.
- The installer "has not commissioned any other generation within the local geographic region within the last 28 days or plans to install more within this region in the next 28 days", in NGED's wording.
That last condition catches people out on new-build streets and group-buy schemes. Several installs clustered on one stretch of network stop being a one-off micro-generator and start being something the DNO wants to look at properly.
Equipment has to be type tested. Manufacturers lodge declarations of compliance in the ENA's LCT Register, and for G98 kit the ENA says manufacturers "must always lodge their declarations of full compliance" there. If your installer specifies a mainstream inverter this is already handled, but it is a fair question to ask when comparing quotes.
How G99 works: apply before you connect
Above 3.68kW per phase the order reverses. The application goes to the DNO first, and the connection only happens once it has been assessed. The DNO can study the impact on the local network, and it can require reinforcement work or an export limitation scheme as a condition of connecting.
For domestic-scale systems there is a shorter route. The ENA introduced revised fast-track procedures for small scale generation and storage inside G99 on 9 November 2022. The conditions include:
- The power generating modules are in a single installation.
- The total aggregate capacity of the generating units, including electricity storage devices, does not exceed 32A or 60A per phase, depending on which of the three procedures applies.
- All generating units are connected via fully type tested inverters.
- The units will not operate during a loss of mains.
- Where required, an EREC G100 compliant export limitation scheme is fitted.
The application uses G99 Form A1-2, and the ENA requires that "the planned commissioning date stated on the application form shall be between 10 working days and three months from the date that the application is submitted to the DNO". Ten working days is therefore the realistic floor for a fast-track job, not the typical wait. Commissioning is then confirmed on Form A3-2 no later than 28 days after commissioning where the tests were not witnessed.
Individual DNOs put their own front end on this. UK Power Networks runs the three fast-track categories as Small Generation Installations, SGI-1 to SGI-3, through its Smart Connect installer portal, and says that "if the maximum export of your installation after any export limitation scheme is under 5kW we will automatically approve your application". Between 5kW and 50kW the application still goes through the same portal but a person reviews it. Sources: UK Power Networks, G99 fast track process and SGIs; UK Power Networks, solar and storage.
A full G99 application outside the fast-track categories means a network study, and the timescale depends on your DNO and on what it finds. If reinforcement is needed, that is when a quote for the work appears.
Export limitation: how bigger systems stay simple
An export limitation scheme caps how much your system can push onto the network, which lets a physically larger array sit inside a lower connection category. The relevant document is EREC G100, "Technical Guidance for Customers' Export and Import Limitation Schemes". The device monitors the flow at your meter and throttles the inverter or diverts to a battery before the export limit is breached.
Raise it with installers if your roof has space for a bigger array than your supply comfortably allows. There is a catch. You are capping your own export, so on a bright Saturday in June the system throttles back and that generation is simply lost unless a battery or a hot water diverter can absorb it. Whether the trade is worth making depends on how much you use during the day and what you are paid for export, which we work through in the Smart Export Guarantee rates comparison.
Northern Ireland runs a different process
In Northern Ireland the rules are G98/NI and G99/NI, administered by NIE Networks, and the notification deadline is 30 days rather than 28. NIE Networks describes G98/NI as a "Fit and Inform" process and sets the boundary as: "If your new equipment exports a maximum of 3.68 kW on single phase, or under 11.04 kW on three-phase, or under 16 Amps per phase then G98/NI will apply, above this value then the G99/NI set of rules will apply."
The practical differences for a NI household:
- Two stages, not one. Stage 1 is a single installation at one site and uses the Fit and Inform route. Stage 2 covers multiple installations at one site and is assessed against the local network first.
- 30 days to submit. Your installer has 30 days from the date of commissioning to submit the Stage 1 commissioning documentation.
- No application fee for a G98/NI Stage 1 connection. Fees only arise if Stage 2 reinforcement work is needed.
- Metering follows. NIE Networks arranges an import and export meter if the site does not already have one, and you then take out an export contract with an electricity supplier. NIE Networks is not part of that contract.
Source: NIE Networks, G98/NI installations. The export side differs too: the Smart Export Guarantee covers Great Britain only, so NI households need to ask suppliers directly what export terms they offer, as set out in our SEG and Feed-in Tariff comparison.
Who actually fills in the forms?
Your installer does, in almost every case, and some DNOs will not accept the paperwork from anyone else. The Energy Saving Trust puts it simply: "If you're planning to install a solar panel system in your home, you must register it with your Distribution Network Operator (DNO). The DNO is the company responsible for bringing electricity to your home. Usually, your installer will register the device with the DNO for you." In Northern Ireland the installer registers the system with NIE Networks. Source: Energy Saving Trust, solar panels.
UK Power Networks goes further and states that "only installers can notify us on behalf of customers", handling it through the Smart Connect portal. Even so, the ENA is clear about where responsibility sits: "Compliance is the responsibility of the customer who is quite often, but not always, the owner of the generation." The installer files it, but it is your installation that has to comply.
Worth settling before you sign anything:
- Ask which route your system falls under and get the answer in writing on the quote, G98 or G99, along with the inverter's rated output.
- Ask who submits the notification and when. Any competent MCS-certified installer will treat this as routine, and MCS certification is separately required for a Smart Export Guarantee tariff.
- Ask for a copy of the submitted form and the DNO acknowledgement. You will want it when you apply for an export tariff, and if you sell the house.
Grid notification is a different thing from planning permission, and one does not cover the other. Most roof-mounted domestic solar is permitted development, but the limits differ by nation, which we set out in the planning permission guide.
How this shapes the system you buy
For most homes the connection rules are a paperwork step handled by the installer, not a constraint on what you can fit. A typical 4.5kWp system costing around £7,600 will usually be arranged to sit inside G98 or a fast-track G99 category, and the notification happens after the scaffolding comes down. A 1930s semi in Leeds with a single-phase supply and twelve panels on the back roof will almost never run into any of this.
The rules start to bite in three situations: a large array on a single-phase supply, a battery added to a system that was originally sized right up to the old limit, and several homes on the same stretch of network installing within weeks of each other.
If a quote proposes a system meaningfully above 3.68kW of inverter capacity, ask what the connection route is and what happens if the DNO requires export limitation. That answer can change the payback maths, and it is the sort of thing a good quote spells out. Size-by-size costs are in our solar panel costs guide.