Export limiting explained
An export limit sounds like a penalty and is usually the opposite: it is what lets you install more panels than your connection would otherwise allow. Because a unit you use is worth roughly six times a unit you export, capping the smaller number costs much less than it appears to.
An export limit caps how much power leaves your property at any instant — not how much you generate, and not how much you use.
It is usually offered as an alternative to refusal or reinforcement, and it is usually worth taking. Under G99 ’s simplified procedures a G100 -compliant limitation scheme is what makes the lighter application routes available at all.
The economics are the reason it stings less than it sounds. A unit you use is worth your import rate; a unit you export earns your SEG rate, often around a sixth as much. A limit constrains the cheap half.
What the scheme actually does
G100 governs customer limitation schemes, covering both directions of flow. The export side works from a Maximum Export Limit — the MEL — agreed with your DNO.
The scheme monitors the net flow at the connection point and acts to keep it inside that limit. Net is the important word: it is measuring what crosses the boundary of your property, so anything the house is consuming at that moment reduces what needs to be curtailed.
Key parameters, as ENA describes the document:
| Requirement | Specification |
|---|---|
| Default maximum response time | 1 minute to bring flow back within the limit |
| Extended response time | 3 minutes for certain technologies such as reciprocating gas engines and micro hydro, where there is no adverse voltage effect |
| Measurement tolerance | ±2% of the greater of the export or import limit |
| Fully type tested | The design meets G100’s requirements and the manufacturer declares all similar schemes will be built to the same standards with the same performance |
A minute is a long time in electrical terms and a very short one in solar terms. Cloud edges move output faster than that, which is why the limit is enforced as a control loop rather than a hard trip.
When you will meet one
As a condition of connection. The most common route: the DNO assesses your application, finds the network cannot absorb your full output, and offers a limit rather than refusing outright or requiring reinforcement.
As the price of the simpler process. This is the part that gets missed. G99’s small generation installation procedures require one:
- SGI-2 requires “an EREC G100 Fully Type Tested export limitation scheme is present that limits the export from the Generator’s Installation to the Distribution Network to no more than 16 A per phase”
- SGI-3 requires the same limiting export to 32 A per phase, waived where the generating units total no more than 32 A
So a limitation scheme can be what keeps a battery-plus-solar installation inside a 10-working-day assessment instead of a full standard application.
On a shared or constrained supply. Flats, converted properties and long rural feeders all turn up here more often.
You can install considerably more panel capacity than you are permitted to export. The difference is not wasted — it is consumed on site, stored, or curtailed only in the hours the limit actually binds.
This is the same principle as the DC:AC ratio, applied at the property boundary instead of at the inverter.
How much output does a limit actually cost?
Less than people assume, for three compounding reasons.
It binds for very few hours. A UK array reaches its rated output rarely — our modelling puts peak in-plane irradiance on a London roof in June at about 60% of the 1,000 W/m² a panel is rated at. A limit set near your inverter’s rating is inactive almost all year.
It is net of consumption. Whatever the house is drawing at that moment comes off the exported figure first. A limit of 3.68 kW with a 1 kW load running is effectively 4.68 kW of generation.
It only touches the cheap half. Every kilowatt hour you consume is untouched, and those are the valuable ones.
Put together: on a system generating more than the household uses — which is most 4 kWp systems, as our rooftop calculator will show you — the marginal unit at midday in June was going to be exported at around 4p anyway.
Zero export
At the extreme, some connections are offered only on a zero-export basis. The system serves the property and nothing crosses the boundary.
That is a real constraint and worth being clear about:
- You earn nothing under SEG. There is nothing to pay you for.
- All the value comes from avoided import, at your import rate — which is the more valuable half.
- Sizing changes completely. There is no point installing capacity you cannot consume or store, so the system should be matched to your daytime demand rather than your annual demand.
- A battery becomes much more attractive, because storing surplus is the only alternative to discarding it.
Zero export is a bad deal presented as a good one if you were sold a system sized for export. It is a perfectly reasonable deal if the system was sized for the constraint from the start.
Questions worth asking
What limit would you accept? Ask before assuming the answer is no. This turns a refusal into a number.
Is the scheme fully type tested to G100? G99’s simplified procedures require it, and a scheme that is not adds a compliance exercise to your application.
Where is it measuring? At the connection point, netting off household load — not at the inverter. The difference is worth real output.
What happens if it fails? G100 requires fail-safe behaviour, tested at commissioning. Ask what the system does on loss of communication.
Does this let me use a simpler application route? If accepting a limit moves you from a standard application into SGI-2 or SGI-3, that is weeks of difference.
What would it take to lift it later? Networks get reinforced. Under G99 a modification affecting technical capability has to be notified and may trigger retesting, so lifting a limit is an application, not a settings change.
Sources
- ENA EREC G100 issue 2 amendment 2, Technical Requirements for Customer Export and Import Limitation Schemes (19 April 2023) We could not obtain this document directly — see the note on sourcing below.
- Engineering Recommendation G99, issue 2 (10 March 2025) Free to download.
- Engineering Recommendation G98, issue 2 (10 March 2025) Free to download.
- Smart Export Guarantee Annual Report — SEG Year 5
Contains public sector information licensed under the Open Government Licence v3.0.
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