Export Limitation for Commercial Solar PV: How G100 Schemes Work

Updated 20 October 2026 · SEO Dons Editorial

Why would a network operator cap a site's export?

Every connection has limits on how much power can flow through it without overloading network equipment or pushing voltages too high. When a business wants to export more than the local network can absorb, the network operator may need to reinforce it, which takes time and money. National Grid Electricity Distribution (NGED) describes export limitation as the alternative: customers who want more generation or storage, but have been told that extra export capacity needs costly or time-bound upstream reinforcement, may choose to restrict the net export of their connection rather than wait for, or contribute to, that reinforcement.

NGED adds that these schemes let network operators keep supplies secure for existing customers while still connecting new generation and storage. NIE Networks, which has adopted ENA Engineering Recommendation G100 to connect customer demand or generation larger than the agreed maximum import or export capacity, explains the risk being managed: flows outside the agreed limits could cause unintended operation of network equipment such as a service fuse or an upstream control relay. Operating above an agreed import or export capacity is therefore treated as unsafe for the network's equipment.

What is G100, and what does an export limitation scheme do?

G100 is the Energy Networks Association's engineering recommendation for customer limitation schemes, and network operators build their own requirements on it. NGED's description is the clearest summary: an export limitation scheme measures power at the exit point of the installation and uses that measurement to restrict generation or storage output, or to increase customer demand, so the agreed export capacity is not exceeded.

NGED's earlier standard technique SD1E/4, issued in October 2018 under the Western Power Distribution name and based on G100, gives a precise definition: a system of one or more items of equipment, sensors, control systems and control signals that interfaces with the customer's generation or load to keep the net flow of electricity into the distribution system below an agreed value. Its purpose, in the document's own words, is to allow parallel generation with an installed capacity above the site's agreed export capacity.

The agreed export capacity is the number everything turns on. SD1E/4 defines it as the maximum power, expressed in kVA, permitted at the connection point when power flows into the distribution system, and notes that in some circumstances it may be zero. Electricity North West makes the same point from the other side: export limitations are defined in the customer's connection agreement.

How fast must a scheme respond, and what does fail-safe mean?

NGED's current connection guidance sets two headline requirements. The scheme must bring exported active power down to the maximum export capacity or below within 5 seconds. And it must be fail-safe: if any component or signalling system in the scheme fails or loses power, the scheme must reduce export in the same way within the same time.

SD1E/4 shows what that means in practice. It is a 2018 document, so the current G100 issue and the operator's latest requirements should be checked for any live project, but its principles make a useful checklist:

Discrete units should be connected by metallic or fibre-optic cables. Radio links are acceptable only on frequencies licensed by Ofcom with a planned availability of 99.9% or higher.
If the communication path fails, generation output must be reduced immediately so the agreed export capacity is not exceeded.
Above 16 A per phase of installed generation, the scheme must be fail-safe, fully restricting excess export if any single component or communication link fails or loses power.
Once commissioned, settings should not be readily alterable by the customer and may only be changed with the network operator's written agreement.
HV connections with a limitation scheme need additional reverse power protection as back-up.
A functional description, the settings and a single line diagram must be displayed on site.

Zero export or limited export: which design fits?

A limited-export design lets some surplus flow to the grid, up to the agreed figure, so the array can be sized somewhat beyond the building's coincident demand. A zero-export design sets the agreed export capacity at zero, so every kilowatt-hour the building cannot use at that moment is curtailed. In both cases the half-hourly demand profile becomes the main sizing tool: the more generation that coincides with on-site demand, the less is lost to curtailment, and the yield model should state that curtailment explicitly.

Export limitation does not remove every ceiling. SD1E/4 explains that although a scheme allows installed generation to exceed the agreed export capacity, there is still a limit on the maximum generation that can be installed, because a scheme takes a finite time to detect an excursion and bring export back down. The installed capacity is restricted so that protection does not mal-operate and equipment voltage ratings are not exceeded during that operating time, and G100 itself includes worked examples of the calculation. The network operator assesses this for each application.

How do batteries and on-site demand change the design?

A limitation scheme has two levers: hold back generation, or raise demand. SD1E/4 notes that schemes are often, but not always, installed as part of a battery storage scheme, and that storage counts as demand when charging and generation when discharging. That makes a battery the natural partner for an export-limited array: midday surplus that would otherwise be curtailed charges the battery, and the stored energy is used on site later.

Controllable loads can do a similar job. Vehicle charging, water heating or process loads that can move into the middle of the day all raise demand when the array peaks. The design must cover the moments when that demand is not there: SD1E/4 requires a scheme that relies on extra demand to reduce or disconnect the generation if the demand is not available. For the economics of adding storage, see battery storage with commercial solar PV.

Which equipment does the scheme control?

For a PV array, the generation a scheme restricts is the inverter output, so inverter choice and export limitation have to be designed together. The inverters must accept the control signal and respond within the required time, and the measuring device at the connection point and the links between them must meet the fail-safe rules above. Our guide to string, central and optimiser inverters covers the inverter side. Separately, NGED notes that generation, including energy storage, must also meet ENA Engineering Recommendations G98 and G99 as applicable, and that installers submit an export limitation application alongside the generation forms.

What should a proposal show about export limitation?

The agreed export capacity used in the design, and whether the network operator has confirmed it or it is assumed.
The modelled annual energy curtailed by the scheme, alongside self-consumption and any battery throughput.
The limitation device or controller, the requirements it is built to, and how it measures at the connection point.
The fail-safe behaviour on loss of communication, sensor or power, and the response time.
Commissioning tests: NGED's installation and commissioning form asks installers to confirm the scheme is fail-safe if any unit or communication link fails, and that settings are password protected or sealed against customer access.

Export limits change the shape of the business case more than the hardware cost, so they belong in the first design conversation, not the last. The commercial PV systems guide sets out what a full specification should include, and you can request quotes through the site's enquiry form.

Sources

Export Limitation, National Grid Electricity Distribution, checked 20 October 2026
Standard Technique SD1E/4: Technical Requirements for Customer Export Limiting Schemes, Western Power Distribution (now NGED), October 2018, checked 20 October 2026
Export Limitation Scheme installation and commissioning tests form, NGED, checked 20 October 2026
Over installs, NIE Networks, checked 20 October 2026
EREC G98 and EREC G99 frequently asked questions, Electricity North West, checked 20 October 2026

Common questions

Is a zero-export commercial solar system allowed?

Yes, where it is agreed with the network operator. SD1E/4 notes that a site's agreed export capacity may be zero in some circumstances, and the limitation scheme then has to keep net export at that level, curtailing any generation the building cannot use.

Does export limitation waste solar energy?

Only when generation exceeds on-site demand plus the export allowance. Good sizing, a battery or loads that can be shifted into the middle of the day reduce that loss, and the yield model should show how much energy is expected to be curtailed.

Can a limitation scheme be added when a business expands an existing system?

Often, yes. NGED presents export limitation as an option for customers seeking to increase the generation or storage installed without waiting for network reinforcement, and the installer submits an export limitation application alongside the generation forms.

Who sets a site's agreed export capacity?

The distribution network operator, through the connection agreement. SD1E/4 notes that every connection with a site-specific connection agreement has an agreed export capacity, and Electricity North West states that export limitations are defined in the connection agreement.