Every solar or battery job in Great Britain ends at the same desk. The distribution network operator, the DNO, has to know the system is there. What changes with size is how much the operator needs to know, and whether it needs to know before you install or after.
This guide is the map. One table sets out every band, from a 3.68 kW home system to a farm above 50 MW. Each part of the series then takes one band and walks through the form, the wait, and what happens after the switch-on.
Two questions decide everything
Every DNO application answers the same two questions.
- Do you apply first, or connect and notify afterwards? Under 16 A per phase you install, then tell the operator within 28 days. Above it, you wait for an answer before a panel goes on the roof.
- Which form? The ENA publishes one set of forms for the whole of Great Britain. The operator's own portal or email address changes; the form does not.
Both answers come from capacity per phase, measured in amps at 230 V. That is the unit the standards are written in. 16 A per phase is 3.68 kW on a single-phase supply and 11.04 kW across three phases.
The size ladder in one table
| Band | Single-phase | Three-phase | Route | Before you install | After commissioning |
|---|---|---|---|---|---|
| Every unit 16 A or under, site 16 A or under per phase | up to 3.68 kW | up to 11.04 kW | G98 | Nothing | G98 Form B within 28 days |
| Units rated up to 32 A, each set down to 16 A, site 16 A or under | up to 3.68 kW set | up to 11.04 kW set | G99 SGI-1 | Nothing | Form A3-3 |
| Units up to 32 A, each set to 16 A, site under 32 A, export limited to 16 A | under 7.36 kW | under 22.08 kW | G99 SGI-2 | Form A1-2, 10 working days | Form A3-2 |
| Units up to 32 A, site 32 A or under (or under 60 A with export limited to 32 A) | up to 7.36 kW (13.8 kW limited) | up to 22.08 kW (41.4 kW limited) | G99 SGI-3 | Form A1-2, 10 working days | Form A3-2 |
| Up to 17 kW single-phase or under 50 kW three-phase, not on an SGI lane | up to 17 kW | under 50 kW | G99 Type A, Form A1-1 | Form A1-1, then the answer | Form A3-1 |
| 50 kW up to 1 MW | — | 50 kW to 999 kW | G99 Type A, Standard Application Form | The SAF, an offer, acceptance | Commissioning tests, Form A3-1 |
| 1 MW up to 10 MW | — | 1 MW to 9.99 MW | G99 Type B | The SAF with Parts 4 and 5, compliance documents | Witnessed tests, Form B3 |
| 10 MW up to 50 MW, or 50 MW and above | — | — | G99 Type C and D | As Type B, with wider studies | Witnessed tests, operational notifications |
The amp figures are the standard's own. The kW figures are those amps at 230 V, rounded to two decimal places. A 5 kW inverter draws 21.7 A on one phase, so it is never G98.
How the size is measured
The operator counts three things, and it is easy to confuse them.
Intrinsic design capacity is what the unit can do: the rating on the data sheet and on the ENA register. Registered capacity is what you have set it to. A 5 kW hybrid turned down to 3.68 kW has an intrinsic capacity of 21.7 A and a registered capacity of 16 A. The small generation lanes in part 2 exist because of that gap.
The aggregate is every generating unit on the supply added together, per phase. That includes the battery's inverter, the solar already on the roof from another installer, and the diesel set in the yard. A second system on a home can push the whole property from G98 into G99.
Single-phase units on a three-phase supply are judged on the phase they sit on. Two 5 kW inverters on the same phase are 43.5 A on that phase, not 14.5 A spread across three.
The G99 types
Above 16 A per phase everything is EREC G99, and G99 sorts generating modules by registered capacity.
| Type | Registered capacity | Connection point |
|---|---|---|
| A | 0.8 kW up to, but not including, 1 MW | below 110 kV |
| B | 1 MW up to, but not including, 10 MW | below 110 kV |
| C | 10 MW up to, but not including, 50 MW | below 110 kV |
| D | 50 MW and above | any, or below 50 MW at 110 kV and above |
The whole rooftop book, domestic and commercial, is Type A. Within Type A the form changes at 50 kW three-phase: the short forms below it, the Standard Application Form above it.
The waits, side by side
- G98 and SGI-1. No wait. Install, commission, notify within 28 days.
- SGI-2, SGI-3 and Form A1-1. The standard gives the operator 10 working days for the SGI lanes. Most operators run the A1-1 as a fast track on a similar clock, though some quote longer.
- The Standard Application Form. Tens of working days, set by Ofgem's guaranteed standards for the operator and the voltage, then an offer you accept and, sometimes, pay for.
- Type B and above. Months. The compliance documents, the studies and the witnessed tests each carry their own notice periods.
The forms, plainly named
Form codes are easy to muddle, so here is every one you will meet.
- G98 Form B — the notification for a micro-generator, after commissioning.
- G98 Form A — the application when one installer plans several micro-generators close together.
- Form A1-1 — the short G99 application under 50 kW three-phase or 17 kW single-phase.
- Form A1-2 — the short G99 application for the small generation lanes, where every unit is on the ENA register.
- Form A1-3 — as A1-1, where the output is shared between two or more customers.
- The Standard Application Form (SAF) — the full G99 application from 50 kW. Type A jobs complete Parts 1, 1a, 2 and 3.
- Form A2-4 — the site compliance and commissioning tests for a Type A module that is not fully type tested, which is every module above 50 kW.
- Form A3-1 — the installation document after a G99 Type A commissioning.
- Form A3-2 — the notification after an A1-2 application.
- Form A3-3 — the notification for a unit set down to 16 A.
- Forms B2-1, B2-2 and B3 — the Type B compliance document, its witnessed tests and its installation document.
- Form D1 — the notice when generation is removed.
What the series covers
- G98: solar under 16 A per phase, connect and notify. The 3.68 kW line, the 28-day rule, Connect Direct and what tips a home out of G98.
- SGI-1, SGI-2 and SGI-3: G99 for bigger home inverters. A 5 kW hybrid, set down or not, with or without an export limiter.
- G99 Form A1-1: the short application under 50 kW. Three-phase homes and small business roofs.
- 50 kW to 1 MW: the G99 Standard Application Form. The full form, the offer, the works and the witness test.
- Above 1 MW: G99 Type B, C and D connections. Compliance dossiers, studies and the transmission step.
- Before the DNO application: operator, MPAN and what counts. Which operator, which MPAN, batteries, existing solar and the headroom question.
Questions installers ask
Is a 5 kW inverter G98?
No. 5 kW on one phase is 21.7 A, above the 16 A line. It is G99, on one of the small generation lanes in part 2 if the inverter is on the ENA register. Set it down to 16 A and it becomes SGI-1, which connects and notifies like G98.
Does the battery count?
Yes. The operator counts the AC rating of every generating unit on the supply, and a battery inverter is a generating unit. A battery with no solar is still a G99 application above 16 A.
Is it kW or kWp?
The DNO works in the AC registered capacity of the inverters, in amps per phase. Panel kWp is a design number, not a DNO number. A 6 kWp array on a 3.68 kW inverter is a 16 A system.
Do the forms differ by operator?
The forms are ENA standards and are the same everywhere in Great Britain. What differs is where they go: Connect Direct, an operator's own portal, or an email address. Northern Ireland has its own versions, G98/NI and G99/NI.
Solar Engine reads the band off the design as you draw it: the inverters, their settings, the phases and any generation already declared. The DNO tab names the lane, the form and the wait before the first panel is placed, and the CRM files the forms from the same record.