G99 application for a home battery: when you need one and how long it takes

G98 or G99: count every inverter

The test is not the size of the battery in kWh. It is the combined output of every inverter at the property that can export, measured in amps per phase. G98 covers installations whose aggregate registered capacity is no greater than 16 A per phase. Anything above that is G99. On a single-phase supply at 230 V, 16 A is 3.68 kW; for a three-phase supply, SP Electricity North West puts the G98 limit at 11.04 kW. The ENA’s standard defines the registered capacity of an installation with an inverter as the lesser of the inverter’s rating and the rating of the energy source, and the solar inverter and the battery inverter count together.

The Powerwall 3 and EVO 10 figures come from Tesla’s UK datasheet, which allows 3.68 kW to 11.04 kW, and from the EVO’s published inverter versions of 5 kW to 10 kW. SP Energy Networks states the same line for batteries: all connections of energy storage in excess of 3.68 kW (16 A) per phase fall under G99.

The G98 route: fit first, notify after

For an installation within 16 A per phase the ENA’s G98 Issue 2, in effect from 10 March 2025, says the network operator needs no detailed study, and the installer must make the operator aware of the installation before commissioning or no later than 28 days after it, inclusive of the day of commissioning. The format is Form B, the installation document, which has a field for the energy storage capacity in kWh.

• The deadline: 28 days at National Grid Electricity Distribution, SSEN and UK Power Networks. SP Energy Networks words its own requirement as within 30 days of commissioning, so aim for 28 and treat 30 as the outer limit.
• The channel: ENA’s Connect Direct platform for connect and notify, which since Issue 2 needs a clear photograph of the cut-out with the application. Operators also take Form B by email: SP Electricity North West, for one, takes it at G98notifications@enwl.co.uk.
• Several installations nearby: if an installer plans, or has already done, other installations in a close geographic region within 28 days, the multiple-premises procedure applies instead, with Form A, and the operator approves before connection.
• If it is skipped: the standard says failure to comply may lead to the installation being disconnected under the Electricity Safety, Quality and Continuity Regulations.

The G99 route: three fast-track categories

Above 16 A per phase the installation needs the operator’s agreement first. For small generation and storage installations, National Grid Electricity Distribution and SSEN both publish a fast track with three categories of Small Generation Installation, SGI-1 to SGI-3. Every category needs fully type-tested equipment on an existing premises:

Once the application is in, SSEN aims to respond within 10 working days, and National Grid Electricity Distribution says you will hear back within 10 working days with the next steps. SSEN is explicit that you cannot connect until you receive confirmation that its assessment is complete; the installer then has up to three months to install and commission the generation and must submit Form A3-2 within 28 days of finishing. SSEN asks for a schematic showing the inverter’s rating, the live phases, neutral and earth and lockable isolators, the type test certificates, any export limitation scheme, and phase-to-neutral loop impedance; SGI-3 applications also need electrical measurements.

UK Power Networks works differently. It says that if the maximum export after any export limitation scheme is under 5 kW, it will automatically approve the application, and that notifying within 28 days is all that is needed for the smallest installations. An installation that falls outside fast track follows the operator’s formal G99 application process, which takes longer and may be priced; ask your installer for the operator’s current timescale.

The rules, network area by network area

Your network operator depends on where you live, and the first two digits of the 13-digit MPAN on your bill, the distributor ID, identify it. The Energy Networks Association’s find-my-network-operator tool does the same by postcode.

Operators’ pages read between 27 September and 7 October 2026. Where a page gives no figure, the table shows the ENA standard.

Northern Ireland has its own rules

NIE Networks runs a separate set: G98/NI applies where equipment exports a maximum of 3.68 kW on single phase or under 11.04 kW on three-phase, with the installer having 30 days from commissioning to submit the documentation and no application fee for Stage 1. G99/NI Fast Track covers solar or wind with battery storage up to 60 A per phase total installed capacity, 13.8 kW, with a maximum inverter size of 32 A (7.36 kW) and export limited to 16 A per phase. It is not fit-and-inform: approval must come before installation begins. NIE says the parameters changed on 1 May 2026, when the limit rose from 16 A per phase to 60 A. Export payments and funding differ too: see what else differs for a Northern Ireland battery.

Plug-in devices are a separate case

The plug-in solar devices that the 2026 regulations allow, solar only and rated at up to 800 W, sit outside G98 and G99 as such, and the regulations do not extend to a battery that plugs into a socket. Our page on plug-in solar batteries sets out what they say and what DESNZ is testing. A battery that is fitted by an installer is the case this guide covers.

Does a bigger connection pay?

An export limit trades against the saving, so it is fair to ask what a higher one is worth. In this site’s model, raising the export limit from 3.68 kW to 11.04 kW adds nothing for a single 13.5 kWh battery, in a London home using 3,000 kWh with 4 or 6 kWp of solar or one using 6,000 kWh with 6 kWp, all on Octopus Flux, because the battery empties inside the lower limit. For a 27 kWh system in the 6,000 kWh home with 6 kWp of solar it adds £141 a year (£1,071 against £931). On these figures a higher limit matters only for very large batteries; for a single battery of ordinary size the saving does not depend on it, though a larger inverter can still charge faster or power more in a cut.

What extra export is worth depends on the tariff. Export rates on Octopus’s tariffs range from 4.1p a unit to about 31p in the Flux peak, and at the G98 limit of 3.68 kW a battery can sell about 11 kWh in a three-hour evening window.

What to ask your installer

1. The combined inverter rating in amps per phase and kW, solar and battery together.
2. Which route that makes it: a G98 notification, a fast-track category or a standard G99 application.
3. Who applies and when, and a copy of the operator’s confirmation before any work starts.
4. Whether an export limit is needed, and what it does to the saving.
5. The operator’s current response time, and what happens to the installation date if it runs over.
6. Who submits the commissioning form within 28 days, and that you receive a copy.

The same questions belong on every written quote; our checklist for comparing battery storage quotes puts the network route on its own line, and the installation timeline shows where this step sits. Once you know your route, get battery storage quotes (we reply by email) and compare them on the same specification.

If you are adding a battery to existing panels, the retrofit solar battery page explains why both inverters count together and what the usual AC-coupled route costs.

Ask where the battery will go as well: PAS 63100 rules out some of the places that look easiest, and a location that fails it changes the cable run and the quote.