G98 vs G99: how solar and batteries connect to the grid

When we design a solar or battery system, one of the jobs you’ll rarely see is the paperwork with your local electricity network. Every system that runs connected to the grid goes through one of two routes, G98 or G99, and which one applies changes what has to happen before your installation.

We handle all DNO notifications or applications required for your installation as standard. Here’s how G98 vs G99 works, and what it means for you.

G98 vs G99 at a glance

	G98	G99
Covers	Fully type-tested systems in a single home, up to 16 amps per phase in total	Anything above 16 amps per phase, or equipment not type-tested under G98
In kW	Up to 3.68 kW on a single-phase supply, or 11.04 kW on three-phase	Above those figures
Before installation	Usually nothing needed from the DNO	An application, assessed and approved by the DNO
Conditions	None to agree in advance	A connection offer sets the conditions and any connection charge
After commissioning	Notify the DNO within 28 days	Commission­ing paperwork on the day if the DNO witnesses the tests, otherwise within 28 days
Batteries	Count towards the total	Count towards the total

Who the DNO is

Your Distribution Network Operator (DNO) owns and maintains the local electricity network: the cables and substations that bring power to your street. It isn’t your energy supplier, the company you pay for the electricity you use. There are six DNOs in Great Britain, each covering its own regions.

Christchurch, Bournemouth and Poole all sit in Scottish and Southern Electricity Networks’ (SSEN) southern England area. Parts of west Dorset are covered by National Grid Electricity Distribution instead. Your postcode decides which, and the Energy Networks Association (ENA) has a postcode lookup if you’d like to check yours. Either way, on our solar PV installs across Dorset the notification or application is ours to send, not yours.

Where the G98 and G99 rules come from

G98 and G99 are Engineering Recommendations published by the ENA. Generation connecting to the distribution network in Great Britain has to connect under one or the other, and that includes home solar panels and batteries. Fully type-tested equipment carries a reference from the ENA’s type test register, which goes on the paperwork.

G98: fit, then notify

G98 covers small systems in a single home: fully type-tested equipment with a combined capacity of no more than 16 amps per phase. That’s 3.68 kW on a single-phase supply, or 11.04 kW on a three-phase supply. Type-tested means the equipment has been tested to show it meets the standard.

In most cases a system that size has very little effect on the network, so the ENA sums up the process as “fit and inform”. You don’t need to talk to the DNO before the equipment is commissioned. Instead, the installer must notify the DNO within 28 days of commissioning, counting the commissioning day itself. That’s a legal requirement.

The notification tells the DNO:

• where the system is, including the meter details,
• who owns it,
• what it is, including its capacity, type-test reference and energy source,
• who installed it, and their qualifications,

along with a signed declaration that the installation meets G98.

Local rules can add to that. SSEN, the DNO for Christchurch, Bournemouth and Poole, asks for an application before connection, even for a small system, if there’s more than one generator at a single property, if the same installer has fitted generation at another property with the same postcode (ignoring its last two characters) within the last 28 days, or if the total generation goes over the G98 limits.

G99: apply first, install after

Anything above 16 amps per phase, or equipment that isn’t type-tested under G98, comes under G99. Here, the order is reversed.

The application goes to the DNO before installation begins. The DNO assesses the impact your system could have on its network, then comes back with a connection offer setting out the conditions for connecting and any connection charge. Those conditions can include a limit on how much the system exports to the grid. If the network needs work before it can take your system, that work has to be done first.

The system can only be connected once the DNO has approved the application and any work needed for the connection is finished. After commissioning, the paperwork goes to the DNO on the day if the DNO witnesses the tests, or within 28 days if it doesn’t.

Why batteries change the picture

Two details catch people out.

Batteries count. The G98 limit applies to everything generating at the property added together, and the ENA’s definition includes electricity storage. DNOs treat a battery as generation when it’s exporting to the network.

The inverter rating is what counts. For panels and batteries connected through an inverter, the ENA treats the inverter’s rating as the system’s rating, or the rating of the energy source if that’s lower. It isn’t simply the total wattage of the panels on your roof. That’s why the inverter you choose matters, whether it’s one of the Fox ESS hybrid inverters we fit or another make.

Put those together and a combined solar and battery system is likely to come to more than 16 amps per phase, which puts it under G99. The ENA notes that DNOs run a fast-track application for some home-scale storage, depending on the total connected generation, which cuts the time for the DNO to confirm whether the connection is acceptable from 45 days to 10 days or less.

It works the same way if you add a battery later. The new battery is added to what’s already connected, so a battery retrofit can need a G99 application even if your panels went in under G98. Our guide to adding a battery to existing solar panels covers the rest of a retrofit.

G98 or G99: which applies to you?

Your system is likely to be G98 if:

• it’s in a single home,
• everything generating there, batteries included, adds up to no more than 16 amps per phase,
• the equipment is fully type-tested.

It will need an application first if:

• the total is above 16 amps per phase, which a combined solar and battery system is likely to be, putting it under G99,
• the equipment isn’t type-tested under G98,
• you’re adding to an existing system and the new total goes over the limit,
• your DNO is SSEN and one of its triggers above applies, such as more than one generator at the property.

Ready to talk it through? Talk to us about a free home survey and we’ll tell you which route your system needs before any work is agreed.

Why the paperwork matters to you

The route affects your timing. A G99 application has to be assessed and approved before your system is connected, so it can affect when your installation goes ahead. We’ll tell you at the design stage which route you’re on.

It also affects your export tariff. SSEN says most energy suppliers ask for its “DNO response”, the email confirming it has logged your commissioning documents, before you can apply for an export tariff. Getting the notification or application right is part of getting your system working for you.

What G98 vs G99 means for your installation

We work out which route your system needs at the design stage, before any work begins.

• Under G98, we install and commission your system, and the DNO is notified within the time the rules allow.
• Under G99, the application goes in first, and nothing is connected until the DNO has approved it.

Either way, it’s handled as standard, and there’s no separate form for you to fill in. It’s the same on all our solar PV installations across Dorset and Hampshire, from solar installations in Christchurch near our base and Highcliffe solar PV a short drive away, to solar panels across Poole, and on the battery storage systems we design. System size starts with your roof and your usage, as our guide to how many solar panels you need explains, and we check your supply on every solar panel survey.

Good to know G98 is a notification after the work is done, while G99 needs the network operator’s approval before anything is connected.

G98 vs G99: the short version

G98 is fit, then notify; G99 is apply, then fit. Batteries count towards the total, and the inverter rating is what counts. You don’t need to work out which applies to you, because we do it at the design stage and handle the G98 notification or the G99 application as standard. Book a free home survey to get started.