When do I need a G98 Stage 2 application?

The threshold matters because it is an aggregate, not a per-device figure. Engineering Recommendation G98 covers projects with a capacity of 16A per phase or less combined capacity per phase where multiple generation or storage units are connected at the same premises³. A household adding a battery alongside existing panels can therefore cross the line without installing anything larger than before.

Where the connection stays inside the limit, the installer notifies the distribution network operator after installation. Where it does not, the connection needs prior approval and takes the G99 route instead⁴. Stage 2 sits between the two: still a G98 application, but one that requires the network to be assessed before the connection can proceed.

What a G98 Stage 2 application is

EREC G98 is formally titled "Requirements for the connection of Fully Type Tested Micro-generators (up to and including 16 A per phase) in parallel with public Low Voltage Distribution Networks"⁸. It is a UK engineering standard written by the Energy Networks Association, and it replaced the earlier G83 standard². Its scope is deliberately narrow: smaller generation capacities of less than 16A per phase⁸.

The standard exists so that small, type-tested equipment can be connected without individual engineering study. A micro-generator that has passed type testing is treated as predictable, and the network operator accepts it on notification rather than application. That is the Fit and Inform principle, and it covers micro-scale systems up to 16 amps per phase⁹.

Stage 2 is what happens when that assumption fails. The connection is still within the G98 family, but the network cannot absorb it without further work. Northern Ireland Networks describes the split plainly: Stage 1 applies when a fully type-tested micro-generator can be connected under Fit and Inform without any reinforcement to the network, and Stage 2 applies when the proposed connection cannot be completed under Stage 1¹.

The distinction is not about the size of the installation alone. A connection inside the 16A limit can still need Stage 2 if the local network is constrained. Conversely, a connection at the limit may pass under Stage 1 if the network has headroom. The application process has been streamlined into two forms, the Stage 1 Commissioning form and the Stage 2 Application form⁵.

When the 16A per phase limit triggers Stage 2

The 16A per phase figure is the boundary of the whole G98 regime. G98 applies to all generation installations up to 16 amps per phase, which is single-phase systems up to 3.68kW and three-phase systems up to 11.04kW². The same limit appears in the Northern Ireland guidance, which covers micro-scale systems up to 16 amps per phase⁹.

The limit is expressed in amps because it is a current constraint on the connection point, not an energy constraint. A single-phase system is capped at 3.68kW, which is the figure that corresponds to 16A per phase. Three-phase connections spread the same current across three phases, which is why the capacity ceiling rises to 11.04kW².

Two things push a connection from Stage 1 into Stage 2. The first is aggregate capacity: where multiple generation or storage units connect at the same premises, the combined capacity per phase is what is measured against the 16A limit³. The second is network condition. A connection within the limit can still require assessment or reinforcement, and that is the definition of Stage 2¹.

The storage fast track process is relevant here. Ofgem's modification introduced a fast track process for storage applications of less than 16 Amp per phase, dated 30 November 2018¹⁰. Storage below the threshold is treated in the same family as generation below the threshold, which is why a battery addition is assessed on the same basis as a panel addition.

Adding to an existing installation: when the aggregate crosses the limit

The aggregate rule is the part most households miss. G98 covers 16A per phase or less combined capacity per phase where multiple generation or storage units are connected at the same premises³. Adding a second device does not reset the count; it adds to it.

A battery storage system needs a DNO application, and the process is the same as for solar panels, with the installer able to complete it⁷. Battery storage can be added to existing solar panels to maximise the benefits of the system¹¹. Neither of those facts changes the capacity arithmetic: the new device's contribution is added to what is already connected.

Northern Ireland Networks describes Stage 2 as covering multiple installations at one site⁵. That is the clearest statement of the aggregate principle in the guidance: one site, several devices, one combined figure measured against the limit.

The practical consequence is that a household planning a battery should establish the existing inverter rating before ordering. A system that was comfortably inside the limit on panels alone may not be once storage is added. The application is the installer's task, but the capacity figure is the household's to know.

Stage 2 versus G99: which route your installation takes

The dividing line between G98 and G99 is capacity. Anything larger than the G98 ceiling falls into a G99 application². Official guidance puts the same boundary at 3.68kWp: apply to connect is for larger installations exceeding 3.68kWp and requires a G99 application⁷. Installations over 3.68kWp require prior approval from the DNO and fall outside the G98 install and notify scope⁴.

The two routes differ in sequence as well as in threshold. G99 works on an apply then install basis, so approval is needed before installation¹². G98 works the other way round: the installer fits and commissions the generator, then registers the connection online¹. That sequencing is the practical difference a household feels, because a G99 application can hold up an installation while a G98 notification follows it.

The G99 Fast Track process has its own equipment rule. Any generating units, including electricity storage, connected through that process must use EREC G99 or G98 type tested inverters¹³. Units installed before April 27, 2019 can also use EREC G59 or G83 type tested inverters¹³. That grandfathering matters for older installations being extended.

For non-domestic installations, the Energy Networks Association directs applicants to the G98, G99 and G100 forms for non-domestic installations¹⁴. Domestic households at a single premises use the G98 Form B, which is designed for installations up to 16 amps per phase². G98 Form A covers installations of generation or storage at multiple premises⁴.

What the application must include and who submits it

The installer submits the application. For Stage 2, the household arranges for the installer to submit it using the G98/NI Stage 2 Application form⁶. Under Stage 1, the installer fits and commissions the generator, then registers the connection online¹. The household's role is to provide access and information, not to file the paperwork.

The core content of a G98 application is the generation capacity: the proposed total capacity of the installed generation in kW¹⁵. That single figure determines which route the connection takes, so it needs to reflect every unit at the site, not just the newest one.

Supporting documents include approved inverter type test certificates and a G100 declaration¹³. The G100 declaration is relevant where export is limited, and the G99 route requires the G99 application form or G100 if export is limited¹⁶. The application also needs site location details, installer contact details, details of each proposed micro-generator unit and schematic diagrams for each unit¹⁷.

The online form enforces completeness. Incomplete fields are highlighted in red and the submit button only appears once all required fields marked with an asterisk have been filled in¹⁷. That removes the common failure mode of a partially completed application sitting unsubmitted.

What happens after you apply: approval, commissioning and witness tests

Where Stage 2 requires reinforcement, the process has a defined sequence. Confirming the quote starts the pre-construction phase, covering survey, legal permissions and wayleaves, and then the construction phase⁶. A 20% deposit is needed to proceed with the quoted reinforcement work⁵.

The household has three options once a reinforcement quotation is issued: proceed with the reinforcement work, withdraw the application, or revise design loads to change the reinforcement required⁶. The same three options are set out in the support guidance: confirm the reinforcement work, change the design to reduce the reinforcement needed, or withdraw the application and remove the generation from the design¹⁸.

Once reinforcement work is complete, the installer has 30 days to submit a G98/NI Stage 1 Commissioning form with the details of the commissioned site⁶. For standard G98 notifications, the application form must be completed within 28 days of the solar panels being in place⁷.

The Fit and Inform process sets its own deadline: the installer submits the Stage 1 form and all relevant documentation within 30 days for approval¹⁹. Where the connection is part of a scheme with accreditation, the validity period matters too: once preliminary accreditation is granted, the installation must commission and an application for full accreditation be made within a certain time²⁰.

For a household, the sequence is: installer applies, network assesses, reinforcement is quoted if needed, deposit is paid, work is done, commissioning form is submitted, and the connection is registered. The independence this delivers is partial. The household generates and stores its own electricity, but the connection to the distribution network remains the network operator's to approve, and the export capacity remains capped by the standard the connection was made under.