G98 and G99 DNO applications

G98 and G99 are the Energy Networks Association engineering recommendations that govern connecting generation to the distribution network. The dividing line is capacity. Where total generation capacity is 16A or less per phase at low voltage — approximately 3.68kW on a single-phase 230V supply, or 11.04kW across three phases at 400V — G98 applies, the Distribution Network Operator does not have to be contacted in advance, and the installer submits an Installation Commissioning Confirmation within 28 days of commissioning. Above that threshold, a G99 application must be made and approved before installation goes ahead.

Why the network cares

The distribution network was designed to move electricity in one direction: from substations to houses. Embedded generation reverses that flow on a local circuit, and enough of it in one street changes voltage and loading conditions for everyone connected to that transformer.

G98 and G99 exist so the DNO knows what is connected, where, and at what capacity. Under G98 the volume is small enough that notification after the fact is acceptable. Under G99 the DNO wants to assess the effect on the local network before it happens, and may impose conditions or require network reinforcement.

The G98 route

This covers most domestic single-phase installations.

The sequence is simple: design, install, commission, then notify. The installer submits the Installation Commissioning Confirmation within 28 days of commissioning, recording what has been connected and where. There is no waiting period and no approval to obtain first, which is why a straightforward domestic array can be surveyed and installed within a normal lead time.

It is a notification, not a formality to be skipped. An unnotified installation is a compliance failure, it complicates any future work on the property, and it can surface awkwardly during a sale.

The G99 route

Above the threshold, the process runs the other way round.

The installer prepares an application with the proposed capacity, inverter details and protection settings, and submits it to the DNO. The DNO assesses the local network and responds — with an approval, an approval subject to conditions, or an offer that involves connection charges for network reinforcement.

Only once that approval is in place can the installation be booked. Timescales vary by DNO and by how loaded the local network is. In a constrained area an application can come back with an export limit rather than an unrestricted approval, or with a cost attached.

None of that is a reason to avoid a larger system. It is a reason to start the application early and to build the wait into your expectations rather than discovering it after signing.

Export limitation

Where the network cannot accept the full output of a system, an export limitation scheme is often the answer. The inverter and its control system are configured to restrict how much can flow out to the grid, while the system remains free to supply the house at full output.

For a household with high self-consumption — storage, an EV, a heat pump — an export-limited system can behave very much like an unrestricted one in day-to-day use. It is worth understanding the distinction before assuming a constrained network rules out the design you wanted.

Where storage complicates things

A battery that can discharge to the grid is generation capacity from the network’s point of view. So a house with an existing G98-notified array can move above the threshold simply by adding storage, and that pushes the whole installation into G99 territory.

Two consequences follow. First, a battery retrofit is not always the quick job it appears. Second, if you know storage is on the horizon, it is far better to establish the network position at the design stage of the original array than to discover it two years later.

Three-phase supplies

Three-phase is comparatively rare domestically but common on larger properties, barn conversions and anything with a workshop. The G98 threshold across three phases at 400V is approximately 11.04kW, which allows a considerably larger array before G99 applies. Where a property already has three-phase, or where an upgrade is being considered for other reasons, it changes the design options meaningfully.

What we do

We establish the supply type and existing generation at survey, size the design with the threshold in mind, and tell you plainly which route your system falls under and what that means for timescales. For G98 work we submit the commissioning confirmation within the 28-day window and put a copy in your handover pack. For G99 work we make and manage the application, and we do not book installation until approval is in hand.