G99 application pathway

Prior DNO assessment for generation or storage that does not qualify for G98.

G99 is the Great Britain connection standard for generating equipment that operates in parallel with a public distribution network and does not qualify for G98. For a typical home, that usually means the installation is above 16 A per phase or does not meet another G98 condition. Most G99 routes require the DNO to assess the design before the equipment is installed or commissioned.

The current standard is EREC G99 Issue 2, dated 10 March 2025. It covers installations far larger and more complex than domestic solar, but its Type A and Small Generation Installation procedures are the parts most likely to apply to a home or small business.

What decides whether G99 applies

For inverter-connected solar and storage, the starting figure is the inverter’s continuous AC rating. It is not the solar array’s DC peak power and it is not the battery’s energy capacity in kWh. Existing generating equipment at the same installation must also be included.

G98 is limited to an aggregate Registered Capacity of no more than 16A per phase. At 230V, that is 3.68kW on single phase or 11.04kW across three phases. G99 applies where the installation is above that threshold or otherwise fails the current G98 requirements.

Three terms need to be kept separate:

Intrinsic Design Capacity is the capacity built into a generating unit before any software restriction used for registration.
Registered Capacity is the capacity declared for the generating unit or module. In the Small Generation Installation procedures, it can be lower than the intrinsic capacity where a compliant device-level limitation is used and documented.
Maximum Export Limit is the net current the site may export through its connection point under a G100 customer limitation scheme.

A G100 export cap therefore does not, by itself, turn a larger installation into a G98 installation. G99 still assesses the generating equipment as well as the controlled export at the boundary.

The three Small Generation Installation procedures

G99 contains three streamlined procedures for fully type-tested generating units at an existing installation. The limits below are per phase and include new and existing generation and electricity storage.

Procedure	Each unit’s Intrinsic Design Capacity	Each unit’s Registered Capacity	Aggregate Registered Capacity	G100 limit	Paperwork
SGI-1	no more than 32A	no more than 16A	no more than 16A	not required	notify on Form A3-3
SGI-2	no more than 32A	no more than 16A	below 32A*	no more than 16A	apply on A1-2, then notify on A3-2
SGI-3	no more than 32A	no more than 32A	below 60A*	32A, unless aggregate Registered Capacity is no more than 32A	apply on A1-2, then notify on A3-2

*The Issue 2 summary table prints limits of no more than 32A and 60A, while the detailed SGI-2 and SGI-3 conditions say “less than” those figures. A design exactly on either boundary should be confirmed with the DNO rather than decided from the summary table alone.

SGI-1 is the exception to the usual description of G99 as an apply-before-install route. It is notification-only, but it applies only when all its conditions are met. SGI-2 and SGI-3 require an application and a DNO assessment before installation or commissioning.

Under the current standard, the DNO provides the result of an SGI-2 or SGI-3 initial assessment within 10 working days of receiving the application. That is a defined feature of these procedures, not a general promise for every G99 connection. The planned commissioning date on an SGI application is between 10 working days and three months from the application date.

The standard Type A route

Smaller installations that do not meet an SGI procedure can still use the simplified Type A application. National Grid Electricity Distribution’s published procedure uses Form A1-1 for aggregate capacity up to 17kW on single phase or 50kW on three phase. Above those figures it directs applicants to the Standard Application Form.

Those thresholds do not mean that a 17kW single-phase proposal will necessarily be accepted. They identify the application form. The DNO still studies the network and the proposed equipment before deciding what can connect.

What goes into the application

The exact portal varies by DNO, but a small G99 design normally needs:

the customer, installer, site and MPAN details
all existing and proposed generating units, including storage
each unit’s make, model, system reference and capacity
a circuit or single-line diagram showing how the equipment connects
a location plan and site layout
manufacturer specifications and type-test evidence
details of interface protection where this is not covered by type testing
the proposed Maximum Export Limit and G100 scheme, if export will be controlled

Type-tested equipment reduces the amount of project-specific compliance evidence, but it does not remove the application. Where equipment or interface protection is not fully type tested, additional verification and on-site testing may be required. The DNO may ask to witness commissioning, and its published procedure should say whether a fee applies.

What the DNO is deciding

The application is not simply a check that the inverter appears on a register. The DNO considers whether the proposed installation can operate without unacceptable effects on its network. The outcome may be the requested connection, a connection with conditions, a different export capacity, or a requirement for network work or further information.

An agreed G100 export limit can allow more generating capacity to be installed than the network can accept as continuous export. It is not automatic approval, and the DNO still considers the uncontrolled capacity, temporary excursions, protection, voltage and power-quality effects.

Do not install an apply-to-connect design on the assumption that the DNO will approve it unchanged. Government guidance makes the owner responsible for ensuring that the DNO has granted authorisation before work is carried out where the connection is classed as apply to connect.

After approval and commissioning

The installer must build and commission the installation in accordance with the accepted design and connection conditions. For Type A plant, Form A3-1 records the installed system. SGI-2 and SGI-3 use Form A3-2. Where tests are not witnessed, the current standard requires the Installation Document within 28 days of commissioning.

Keep the following with the handover records:

the submitted application and drawings
the DNO’s decision, offer or authorisation and its reference number
the final as-installed circuit diagram
system references and compliance evidence
the relevant G99 Installation Document
any G100 application and commissioning document
the programmed Registered Capacity and export-limit settings

If the design changes after approval, ask the DNO whether the change must be reassessed before installation. An apparently similar inverter can have a different Registered Capacity, type-test record or export-control arrangement.

Great Britain and Northern Ireland

The G99 process described here applies to England, Scotland and Wales. Northern Ireland uses G99/NI and NIE Networks’ own connection process. GB forms and response periods should not be assumed to apply there.

Applies to

Solar, Battery

Last reviewed

22 Jul 2026