Connecting Solar to the Grid: G98 and G99 Explained

Connecting a solar array to the grid is not a matter of wiring it up and switching on. Any generating equipment that runs in parallel with the low-voltage distribution network has to meet an Energy Networks Association engineering recommendation, and which one applies depends almost entirely on size. G98 covers small-scale generation of 3.68kW or less per phase, and works as a notification: the installer tells the distribution network operator (DNO) within 28 days of commissioning¹. G99 covers everything above that, and is an application that needs written acceptance before the system is energised³.

The threshold is the single most useful number for a householder to know. On a standard single-phase supply, 3.68kWp is the ceiling for the notification route, and most residential solar systems sit under it⁵. On a three-phase supply the equivalent G98 limit is 11.04kWp⁶. Above either figure, the connection falls under G99 and the process changes from telling the network to asking it.

Both standards exist for the same reason: to stop embedded generation from destabilising the network it sits on. The inverter must disconnect when voltage or frequency drifts outside set limits, must not reconnect until the supply is stable, and must be certified to the standard before it is installed⁷. That is what makes a grid-connected array safe to run alongside everyone else's, and it is also what defines the boundary of a household's independence: the array can supply the home and export the surplus, but it stays tied to the network's rules and the network's permission.

What G98 and G99 actually are

G98 is a UK engineering standard written by the Energy Networks Association, and it replaced the earlier G83⁴. It sets the technical requirements for connecting small-scale generation, such as solar panels or wind turbines, with a capacity of 3.68kW or less per phase, and for running that generation in parallel with the low-voltage distribution network¹. The obligation behind it sits in the Electricity, Safety, Quality and Continuity Regulations 2002, which is why the process is not optional⁴.

G99 is the companion document for larger connections. Where G98 is a notification, G99 is an application: the DNO assesses the proposed connection against the network's capacity and issues acceptance before the system can be commissioned¹¹. The current published basis for compliance testing is Engineering Recommendation G99 Issue 1, Amendment 9, dated 3 October 2022⁸. An earlier amendment, Issue 1 Amendment 8 dated 1 September 2021, appears on equipment datasheets as the compliance reference for specific inverters¹².

The distinction matters because it determines who does what and when. Under G98 the equipment is installed, then the DNO is told. Under G99 the DNO is asked first, and the answer can be no, or yes with conditions such as export limitation. The product being installed, usually the solar PV inverter or the electrical energy storage system, must be fully G98 or G99 compliant for either route to be available⁷.

The figures that decide the route

Three numbers separate a notification from an application. The first is 3.68kW per phase, the G98 capacity limit for small-scale generation on a single-phase supply¹. The second is 11.04kWp, the equivalent limit where the connection is three-phase⁶. The third is 28 days, the window in which a system exporting up to 3.68kWp must be notified to the DNO after installation².

The 11.04kWp figure is not a domestic threshold in the ordinary sense. It appears in connection guidance as the G98 limit for buildings other than dwellings, and as the three-phase export limit for export-capable connections⁶. For a house on a single-phase supply, the practical ceiling is 3.68kWp, which is why so many domestic arrays are sized at or just under it.

The 28-day notification window is a deadline, not a grace period, and it applies to the export capability of the system rather than to its total panel rating. A system with the ability to export up to 3.68kWp can be notified to the DNO within 28 days of being installed². Where export is limited to below that figure by a device setting, the notification still applies, but the network sees a smaller export figure.

What drives the choice between them

Size drives the route, but size is not only about panels. The figure the DNO cares about is the generation capacity in kW, described in application guidance as the proposed total capacity of the installed generation³. That is the inverter's output rating, not the sum of the module nameplate figures, and it is the number that decides whether the installation is notified or applied for.

Battery storage changes the calculation. Storage connections in the UK are governed through technical requirements including G98 and G99, so an inverter and battery combination has to be certified as a unit¹⁴. A hybrid inverter that charges a battery from the grid and discharges to the home is a generating unit in the network's terms, and its export capability counts toward the threshold.

Adding capacity later triggers the same test again. A worked example describes a householder applying to the DNO via a G99 application for permission to connect a further 2.5kWp of solar, because the addition took the installation past what the existing connection allowed⁵. The lesson is that the connection agreement attaches to the installation as a whole, not to the original array.

Certification is the other driver. The product being installed, usually the solar PV inverter or electrical energy storage system, must be fully G98 or G99 compliant⁷. Manufacturers publish the certification alongside the model: the SolaX UK X3-HYBRID G4 materials list G98 and G99 certification, and Victron's MultiPlus-II carries G98 and G99 certification for the 48/3000 to 48/10000 models only¹⁴. A model without the certificate cannot be connected under either route, whatever its output.

How the process runs, step by step

The sequence is short but the order matters, because connecting before acceptance is a breach of the connection obligation.

1. Establish the generation capacity in kW, which is the proposed total capacity of the installed generation³.
2. Confirm the inverter or storage system holds current G98 or G99 certification for the model being fitted⁷.
3. For G98, install and commission, then notify the DNO within 28 days².
4. For G99, submit the application and wait for written acceptance before energising¹¹.
5. Keep the notification or acceptance with the installation records, alongside the electrical certificate.

For most domestic solar installations under G98/NI, Stage 1 is the standard process, with Stage 2 reserved for cases that need more assessment¹⁰. In Great Britain the equivalent split is between notification and application, and the DNO for the area handles it: new solar panel and battery storage grid connections in Crawley, for example, require notification to UK Power Networks under the G98/G99 process¹¹.

The information the DNO wants is consistent. Generation capacity is the proposed total capacity of the installed generation in kW, and it sits alongside the address, the connection type and the protection settings³. Where the network cannot accept the full export, the acceptance may be conditional on export limitation, which is a separate device and a separate set of settings.

Protection settings the inverter must hold

The technical heart of both standards is what the inverter does when the grid misbehaves. A compliant power generating unit disconnects from the grid when voltage or frequency leaves the permitted window, and stays disconnected until the supply returns to normal. Test data for a compliant unit records no reconnection at 1.16 pu, 0.78 pu, 47.4 Hz and 52.1 Hz, and active power ceasing within 5 seconds of an instruction being received⁸.

Loss of mains protection is tested to BS EN 62116, and the recorded run-on time in one test was 351 ms⁸. A separate figure of 357 ms appears in the same test documentation, and the two are not reconciled; where a specific run-on time matters, the test report for the exact model is the reference. The unit in that test used an electromechanical relay to disconnect from the grid, with no solid-state switching device available⁸.

The interface requirements are equally specific. A compliant unit provides an input port that can be used to shut down the module, with a high-level description of the logic interface covering whether the signal is AC or DC⁸. The maximum signal values recorded are 240 V AC and 110 V DC, and the relay status convention is 1 for closed and 0 for open⁸. Cyber security compliance is declared by the manufacturer against the requirements in section 9.1.7 of the standard⁸.

These are not settings a householder chooses. They are built into the certified firmware of the inverter, and they are the reason a grid-connected array cannot be used to back-feed a dead network during a power cut.

Across the four nations: where G98 does not reach

Engineering Recommendation G98 applies to Great Britain only⁹. That single sentence changes the process for households in Northern Ireland, which has its own connection arrangements administered through NIE Networks, including a G98 NI route with a Stage 1 and Stage 2 process¹⁰. Stage 1 is described as the standard process for most domestic solar installations under G98/NI¹⁰.

The Northern Ireland position also differs at the building regulations level. Part F of the building regulations in Northern Ireland has been consulted on separately, and the supporting documentation sits with the Northern Ireland departments rather than with the Great Britain framework⁶. A householder in Belfast is therefore working to a different set of documents from one in Bristol, even where the physical installation is identical.

Scotland, Wales and England sit within the Great Britain framework, so G98 and G99 apply as written, and the DNO for the area administers them. The differences that remain are commercial and administrative rather than technical: which network operator covers the postcode, how quickly it turns applications around, and whether the local network has headroom for the export proposed.

What the connection means for energy independence

A grid connection is what makes a domestic array economically useful, and it is also what limits how independent the household can become. The connection allows surplus generation to be exported and paid for, and it allows the home to draw power when the array is not producing. It also means the installation operates under the network's rules, at the network's thresholds, and with the network's permission.

The scale of what domestic solar now contributes is substantial. National solar generation averaged 109.7 GWh per day across 21 to 22 June 2026, scaled from a domestic solar capacity of 6.3 GW within 23 GW of total national solar capacity¹⁶. Solar's share of Great Britain's power reached 9.6% in July 2025, up from 9.6% a year earlier¹⁷. For a household, the connection is the mechanism by which its own generation joins that total.

Self-sufficiency is measured, in the industry's own definition, as the percentage of electricity consumed in the property over a year which is met by either behind the meter solar or electrical energy storage¹⁸. That definition is the honest one for this subject: it counts what the home supplies itself, and it excludes what the grid supplies. A G98 connection with no battery will show a lower figure than the same array with storage, because export happens instead of self-consumption.

The dependence that remains is structural. The array needs the grid to export to, needs a supplier to be paid through, and needs the DNO's acceptance to be connected at all. Where the network cannot accept the export, the connection is granted on condition that export is limited, which reduces the household's ability to sell surplus. The engineering recommendations are the terms on which a home becomes a small generator, and they are worth reading before the panels go on the roof rather than after.