G100 export limitation

DNO-agreed control schemes that limit net export or import at a connection point.

G100 is the Great Britain technical standard for a Customer Export or Import Limitation Scheme. The scheme measures current at a property’s connection point and controls selected generation or loads so that net export or import stays within limits agreed with the DNO.

The current standard is EREC G100 Issue 2 Amendment 2, published in 2023. It covers both export and import limitation. “Export limitation scheme” is still widely used for an export-only arrangement; the standard uses “customer limitation scheme” (CLS) for the broader category.

G100 is not a connection permission and it is not an alternative name for G98 or G99. It specifies how the limiting scheme must behave. The generation and storage behind it must still follow G98 or G99 as applicable, and the DNO must agree the connection and the limit.

Installed capacity and exported power are different

An export limit applies to the net flow through the connection point. It does not necessarily equal the combined rating of the inverters behind it.

For example, solar could be producing 5kW while the home uses 2kW. Net export is then 3kW. A correctly designed scheme responds to the measured flow at the boundary, not simply to the solar inverter’s headline output. How it allocates control between solar, storage and loads depends on the approved design.

This distinction matters when choosing the connection route:

Registered Capacity describes the generating equipment declared under G98 or G99.
Maximum Export Limit (MEL) is the maximum current agreed with the DNO for export through the connection point.
Maximum Import Limit (MIL) is the corresponding agreed import limit.

A site-level G100 cap does not automatically reduce Registered Capacity and does not by itself make a larger installation eligible for G98. Some generating devices can instead have a lower, documented Registered Capacity than their Intrinsic Design Capacity. That is a device-level limitation with its own compliance evidence, not the same thing as measuring and controlling net site export.

What a G100 scheme contains

A typical export scheme has a current-measuring device near the connection boundary, a controller and a reliable control path to the inverters or other devices being managed. The exact arrangement can be integrated into one manufacturer’s system or assembled from compatible components.

The standard requires the design to explain:

which generation, storage and loads are controlled
how current at the connection point is measured
the requested export and import limits
how the controller changes device output or demand
how communication, component and power-supply failures are detected
how the installation moves to a fail-safe condition
how operation, failures and resets are recorded

G100 Issue 2 allows short excursions beyond the normal limit while the scheme responds, but it restricts their magnitude, duration and frequency. Persistent or repeated excursions trigger the fail-safe state. The DNO assesses the temporary current, voltage, protection and power-quality effects, so the amount of equipment behind a G100 scheme is not unlimited merely because continuous export is capped.

Fail-safe does not mean “carry on at full output”

Fail-safe means the scheme can bring export or import back to the agreed limit despite a component failure or a loss of communication between the controller and controlled devices. The approved response might reduce output, change demand or disconnect relevant equipment, depending on the design.

This is why a casual software setting that the owner can alter is not enough. National Grid Electricity Distribution states that commissioned CLS settings cannot be changed by the customer and may be changed only with written DNO agreement. It requires protection against unauthorised access, such as a password, PIN or sealable physical control.

The fail-safe behaviour should be understood before purchase. An owner should know what remains operational if the meter, controller, communications link or internet connection fails. Internet access is not inherently required by the standard, but a particular product design may use networked services for monitoring or support.

Application before installation

Where a G100 scheme is proposed, its information is submitted with the relevant generation application. Government guidance classifies export-limited devices as apply to connect: the DNO must receive the application before installation and grant authorisation before the work is carried out.

G100 includes three core documents:

Form A describes the proposed CLS, capacities, requested limits, schematic and fail-safe operation.
Form B is the manufacturer’s compliance verification report. For a fully type-tested scheme on the ENA Type Test Register, the system reference can be used instead of supplying the full product declaration.
Form C records the installed equipment and commissioning checks.

DNO portals may wrap these forms into their own online process. The label used by a portal is less important than ensuring that the proposal, manufacturer evidence and final commissioning record all refer to the same scheme and settings.

How G100 appears in small solar and battery applications

The current G99 Small Generation Installation procedures use G100 explicitly. SGI-2 combines fully type-tested units within its capacity limits with export capped at 16A per phase. SGI-3 normally caps export at 32A per phase, unless its aggregate Registered Capacity is no more than 32A.

National Grid also describes a common single-phase storage case: G98-compliant solar up to 16A plus G98-compliant storage up to 16A, behind a G100 scheme limiting export to 16A. The complete installation follows the G99 fast-track application route. It is not two independent G98 notifications.

Coupling affects the capacity calculation. A DC-coupled battery behind the same hybrid inverter does not add a second AC inverter rating. An AC-coupled battery has its own inverter, so its capacity is counted alongside the solar inverter. The DNO application should show the real electrical arrangement rather than relying on a marketing description such as “hybrid” or “non-exporting”.

Commissioning and records

After the DNO accepts the proposal, the installer builds and tests the scheme. The DNO may require its own representative to witness some commissioning checks. National Grid’s published process requires its installation and commissioning form within 28 days after commissioning; installers should follow the deadline and method stated by the relevant DNO.

Keep:

the DNO’s accepted export or import limit
the approved schematic and equipment schedule
the G100 system reference or Form B evidence
the completed Form C or DNO equivalent
commissioning and fail-safe test results
the protected settings and instructions for fault or lockout conditions
records of any later DNO-approved change

Replacing an inverter, sensor, controller or communications component can affect the approved scheme. Do not assume that an equivalent-looking replacement can be fitted without review.

Cost and lost export

There is no dependable generic G100 price. Cost depends on whether limitation is built into compatible equipment, whether an external controller and sensors are needed, the complexity of the site, DNO study requirements and any witness testing. Limitation equipment, commissioning, DNO charges and network work are separate cost components.

The energy curtailed by a limit depends on generation, on-site demand, storage behaviour and the actual agreed limit. Percentage uplifts and reinforcement-cost examples from unrelated projects do not establish either cost or lost export for a particular home.