G98 vs G99: connecting solar to the grid, explained

The threshold, exactly

Both documents are published by the Energy Networks Association. The copies we read are issue 2, dated 10 March 2025 on their title pages — with a caveat about the version that we set out at the foot of this page rather than burying.

G98’s own title sets the boundary: it covers the connection of “Fully Type Tested Micro-generators (up to and including 16 A per phase)”. And it converts that into power without leaving it to the reader:

For the purposes of this EREC G98 the Registered Capacity of 16 A per phase, single or multi-phase, 230/400 V AC corresponds to 3.68 kilowatts (kW) on a single-phase supply and 11.04 kW on a three-phase supply.

That is why 3.68 kW inverters are everywhere in British domestic solar. It is not a coincidence or a manufacturing convention — it is the largest single-phase inverter that keeps an installation inside the simpler process.

What each process actually requires

G99 is unambiguous about the sequence, and this is the sentence that matters if somebody offers to fit a large system and “sort the paperwork later”:

No Power Generating Modules should be installed or commissioned before this DNO assessment is complete and the Generator has been advised of the outcome of this assessment.

The middle ground most people miss

G99 is not one process. It contains three Small Generation Installation procedures for installations that are past the G98 threshold but still modest, and they are much lighter than a full application. These are where a typical domestic solar-plus-battery installation now lands, so they are worth knowing about.

Two things follow that are genuinely useful.

SGI-1 behaves like G98. If every unit is limited so the total registered capacity stays at or below 16 A per phase, you can “install and commission all the Power Generating Modules” and then notify. So adding a battery to an existing solar system does not automatically mean waiting for permission.

Export limitation buys you the simpler route. Export limitation under G100 is what makes SGI-2 and SGI-3 available: you may install more generating capacity than you are permitted to export, and use the difference yourself. Given that a used unit is worth roughly six times an exported one, that trade is often better than it sounds — see self-consumption.

Where G98 does not apply even below 16 A

Capacity is the main test but not the only one. G98 sends you to G99 where:

• the installation supplies two or more independent customers via a sharing agreement
• the plant is designed to run in parallel with the network only briefly — less than five minutes a month — or as an islanded installation
• the micro-generator is not fully type tested against G98’s requirements
• an integrated micro-generation and storage arrangement applies and the aggregate capacity exceeds 16 A per phase

G98 is candid about why the islanded case is excluded: “it is not possible to devise generic rules that will ensure safe operation under all operating conditions.”

The 800 W line, and where it comes from

G99 defines a Type A power generating module as one with a registered capacity of “0.8 kW or greater but less than 1 MW”.

That 0.8 kW figure is the same threshold that governs plug-in solar, where the interim product specification caps a device at 800 VA. It is not a coincidence: below 0.8 kW a generator falls outside the European connection-code categories the recommendations implement, which is precisely why a regime for very small devices could be built there at all.

The upper bands, for completeness and because they explain the vocabulary: Type B is 1 MW to under 10 MW, Type C and Type D are 10 MW and above or connected above 110 kV. No domestic installation is anywhere near them.

Notification is also required when you remove it

The obligation is symmetrical and this is the half people miss. G98 requires notification “no later than 28 days after de-commissioning all, or some of the Micro-generators in a Customer’s Installation”.

So if you take a system out, or reduce it, the network operator needs to know. Its model of what is connected to your street is only as good as the notifications it receives, and the records matter for everyone’s protection settings, not just yours.

Practical points

It is your installer’s job, but your obligation. The generator named on the form is you. Ask for a copy of the completed notification or application, and keep it — your SEG supplier may want evidence, and a future buyer’s surveyor certainly might.

A single connection point with several inverters is one plant. G98 says that where an installation has one connection point and more than one inverter with an aggregate registered capacity at or below 16 A per phase, “the installation shall be considered as a single Micro-generating Plant”. You cannot split an installation to stay under the threshold.

An existing G83 system is treated separately. Where a micro-generator was commissioned under the older G83, only the additional units need to conform to G98 — but if the total exceeds 16 A per phase, G99 applies and the operator must be consulted before work starts.

Notification is not the same as an export tariff. A G98 notification tells the network operator the system exists. Getting paid for exports needs a SEG tariff and a half-hourly export meter with an export MPAN , which is a separate arrangement with a supplier.

If you are told a large system needs no permission, that is wrong. Above 16 A per phase, installing before the assessment completes is contrary to G99. It is also a poor position to be in if the operator later requires changes.