G98 vs G99: Which Grid Connection Route Does Your Install Actually Need?

Every generator or battery that runs in parallel with the public network in Great Britain connects under one of two Energy Networks Association engineering recommendations. Which one applies decides something very practical: whether your installer can commission the system on the day and tell the network operator afterwards, or has to wait for a permission that can be refused.

The difference between G98 vs G99 comes down to a single number — sixteen amps per phase. This guide sets out where the threshold comes from, what it is actually applied to, and the two situations where an installation most homeowners would assume is straightforward turns out not to be.

The short answer

G98 is the connect-and-notify route for small-scale generation. Your installer fits the equipment, commissions it, and notifies the distribution network operator afterwards. There is no waiting and nothing to refuse.

G99 is the apply-first route for anything larger. The application goes in before the work starts, the DNO assesses what the local network can absorb, and it may come back with conditions, an export limit, or a refusal.

Both are published by the Energy Networks Association and implemented by every distribution network operator in Great Britain. Your installer handles the paperwork either way — but the route determines your timeline, so it is worth understanding before you sign anything.

Where the 16 A threshold comes from

G98 applies to equipment that meets the definition of a micro-generator. The ENA Distributed Generation Connection Guide (March 2025 edition) quotes that definition from EREC G98 as a source of electrical energy designed to operate in parallel with a public low voltage network "with nominal currents up to and including 16A per phase".

Anything above that is a power generating module and connects under EREC G99 instead.

Sixteen amps, not sixteen kilowatts

The limit is a current, not a power rating, and converting it depends on how many phases you have. The guide does the conversion explicitly: 16 A per phase corresponds to 3.68 kW on a single-phase low voltage supply and 11.04 kW on a three-phase one. Because the rule is defined in amps, the kilowatt figure that applies to your property follows directly from your supply type.

Single-phase and three-phase

Most British homes are single-phase, which is why 3.68 kW is the figure you see quoted everywhere. Three-phase supplies are found in larger detached properties and homes with heavy electrical demand, and they give considerably more headroom before G99 applies.

	G98	G99
Threshold	Up to 16 A per phase	Above 16 A per phase
Single-phase equivalent	Up to 3.68 kW	Above 3.68 kW
Three-phase equivalent	Up to 11.04 kW	Above 11.04 kW
Sequence	Install, commission, then notify	Apply and be approved, then install
Notification window	Within 28 days of commissioning	Agreed before work begins
Can it be refused?	No — it is a notification	Yes, or granted with conditions
Equipment requirement	Must be fully type tested	Type testing also applies

The threshold applies to the whole premises

The 16 A figure is not a per-device allowance. The ENA guide states that it "refers to the aggregate Micro-generator capacity installed in a single premises". Every piece of generating equipment at the property is counted together.

That reframes the question entirely. A 3.6 kW inverter is comfortably within G98 on its own. Add a second inverter of any meaningful size and the premises total moves above 16 A per phase, at which point the installation belongs under G99 — regardless of how modest each individual box looks on its datasheet.

It also explains a situation that comes up often: someone with an existing, properly notified solar array wants to add storage, and is told that the whole thing now needs a G99 application. That is the aggregate rule working as written, rather than an installer being cautious.

G98 in practice: connect, then notify

For a single premises within the threshold, there is no conversation with the DNO beforehand. The guide is unambiguous that you do not need to contact them in advance where combined capacity is 16 A or less per phase.

What follows the commissioning is not optional, though.

What gets submitted, and when

Your installer must notify the DNO within 28 days of commissioning, using the installation document set out as Form B in EREC G98. The ENA guide describes this in plain terms as a legal requirement, not a courtesy.

Two conditions sit alongside it. The equipment must be fully type tested — every micro-generator connecting under G98 has to be — and the work must be done by a competent installer with recognised electrical qualifications. Certified products and installers can be checked against the ENA Connect Direct type test register and the Microgeneration Certification Scheme.

G99 in practice: apply, then install

Above the threshold the order reverses, and so does the risk. The application goes in first, with a full system design, single-line diagram, protection settings and equipment detail. Only once the DNO responds can the installation proceed.

Timescales, conditions and refusals

The statutory window for a DNO to quote for a low voltage generation connection is 45 working days, rising to 65 for high voltage and above — obligations that flow from section 16 of the Electricity Act 1989.

What owners find harder than the wait is the outcome. A G99 application can come back with an export limit far below what the equipment could deliver, which is the recurring frustration in owner forums: a large inverter approved on condition that it exports a fraction of its rating. Where the local network is constrained, that is the DNO doing its job — but it is a possibility worth pricing in before you buy hardware sized for an unrestricted connection.

Why batteries complicate the picture

There is a persistent belief that storage sits outside all of this because a battery does not generate anything. The definition says otherwise, and says so deliberately: a micro-generator, in EREC G98's own words, includes electricity storage devices "for the avoidance of doubt".

A grid-connected battery that can push power out to the network counts towards your premises total. It does not matter that the energy came from your roof or from an off-peak tariff rather than from a fuel.

The nuance worth holding on to is that capacity in kilowatt-hours is irrelevant here. What counts is the inverter's rated output in kilowatts. A large battery behind a modest inverter stays within the threshold; a small battery behind an oversized one does not.

The fast-track route for domestic storage

The ENA guide is candid about where this leaves most retrofits. Where storage is added alongside PV to offset consumption, it says, the total connected generation "is likely to be above 16A / phase and hence EREC G99 applies".

That sounds like a six-week delay for a job that takes a day. In practice it often is not, because DNOs operate a fast-track process for domestic-scale storage, submitted on G99 Form A1-2 under the Small Generation Installation Procedure. It cuts the DNO's response time from 45 days to ten days or less.

The backup-power trade-off worth knowing

There is one condition on that fast-track that is useful to know before shopping for a battery. The guide states that where the storage is designed to operate in island mode — that is, to keep supplying your home during a power cut — the fast-track process does not apply, and the standard G99 process is used instead.

So backup capability carries an administrative cost. A battery with an emergency power socket may well be the right choice, but choosing one moves the job off the ten-day route and onto the full application. That is a reasonable trade to make knowingly, and easier to plan for when it is understood before the project starts.

A worked example: adding an AC-coupled battery to an existing array

Take the most common British retrofit. A household already has rooftop solar, notified years ago under G98, and now wants storage so that the generation goes into the evening peak rather than out to the grid for very little in return.

An AC-coupled battery suits this because it connects on the alternating current side and leaves the existing inverter and panels untouched. The SolarFlow 3680 Mix AC+ and SolarFlow 2400 AC+ is built for exactly that job, and its numbers illustrate the rules above rather neatly.

What to check before you buy

A short list, in the order the questions actually arise.

Start with what is already connected. Any existing solar counts, so the honest starting figure is your current capacity plus whatever you are adding, not the new item in isolation.

Then confirm the equipment is on the type test register, and that whoever is installing it is qualified to do so. Battery systems of this kind are not consumer plug-in appliances: the AC+ requires installation by a qualified electrician working to BS 7671, and in England and Wales the work falls under Part P of the Building Regulations. Anyone suggesting you can simply plug one into a socket is not someone to buy from.

Finally, decide how much you value backup. If riding through a power cut matters, plan the project around the standard G99 timeline. If it does not, staying off island mode may keep the faster route open.

Getting the route right at the design stage is unglamorous, but it is what separates a system commissioned on schedule from one sitting in a garage awaiting a decision. It also has a bearing on the economics, since an export limit changes the arithmetic behind whether solar panels save money and how much of the benefit you can realistically capture by cutting your electricity bill at home.

Frequently asked questions

Does a home battery count towards the G98 limit?

Yes, if it can export to the network. EREC G98's definition of a micro-generator states that it includes electricity storage devices, so a grid-connected battery is counted alongside any other generation at the property. What matters is the inverter's rated output in kilowatts, not the battery's capacity in kilowatt-hours. Systems that genuinely cannot export are treated differently, which is one reason home battery storage without solar can follow a different path — confirm the position with your installer.

I already have solar. Do I need a new application to add a battery?

Almost certainly, yes. Because the threshold applies to the aggregate capacity at the premises, adding storage to an existing array usually takes the total above 16 A per phase. The ENA's own guidance says as much: where storage is combined with PV, G99 is the likely route. Your installer submits it, and the fast-track form often applies.

Can export limiting keep me under G98?

Not by itself, and this is where installers genuinely differ. Export limiting schemes have to comply with EREC G100, and following revisions to G99 those limiting devices must now be fully type tested. Limiting export can make a larger system acceptable to the DNO through the small generation route, but it does not simply reclassify a G99 installation as a G98 one. Ask your DNO or installer to confirm the position for your specific design.

How long does a G99 application take?

The statutory window for a DNO to provide a quotation for a low voltage generation connection is 45 working days. The fast-track route for domestic-scale storage reduces the DNO's confirmation time to ten days or less, but is unavailable where the equipment is designed to run in island mode during a power cut.

What happens if an installation is never notified?

Notification within 28 days of commissioning is a legal requirement, not an administrative nicety. Beyond compliance, an unnotified system creates practical problems: it complicates registering for an export tariff under the Smart Export Guarantee, it tends to surface during conveyancing when a buyer's solicitor asks for evidence, and the network operator is entitled to take issue with an unrecorded connection. Reputable installers handle it as a matter of course — ask for the paperwork.

Connection requirements are periodically revised by the Energy Networks Association and approved by Ofgem. Figures and procedures here reflect the ENA Distributed Generation Connection Guide, March 2025 edition; confirm the current position with your DNO or installer before making purchasing decisions. The relevant forms are published by each network operator, for example on SSEN's G98/G99 documents page.