Export limitation and smart export tariffs
Solar Pv · Lesson 23 · Advanced
Purpose
Design export limitation as a fail-safe network-control function, distinct from a smart export tariff.
Learning objectives
- Identify the governing boundary
- Trace energy and measurement paths
- Apply evidence in the required sequence
- Recognise unsafe assumptions
A G100 export-limitation scheme measures power at the agreed boundary and controls generation or storage so export remains within an approved limit. Its safety and failure behavior matter as much as its normal setpoint.
Core theory
Confirm CT/meter location, phase coverage, orientation, communications, response time, control hierarchy, inaccessible settings and behavior on sensor, communications or controller failure.
Include every generator and storage device that can affect boundary export. Prove the scheme across import, export, rapid load loss, full generation and credible failure states.
DNO approval and any witness/type-test evidence are separate from the commercial export tariff. A tariff cannot increase approved network export capacity.
| Term | Meaning | Symbol | Unit |
|---|---|---|---|
| G100 | ENA recommendation for customer export-limitation schemes | Not applicable | Not applicable |
| Fail-safe | Moving to a defined safe state on a credible failure | Not applicable | Not applicable |
| Export limit | Maximum permitted power flow from customer installation to network | Not applicable | Not applicable |
Assumptions: Values are supplied design inputs, not universal limits; Current DNO and product evidence will be checked.
- Uncontrolled: Boundary export would be 8 − 3 = 5 kW.
- Required control: At least 1 kW of generation must be curtailed or absorbed.
- Verify: Test rapid load loss and sensor/control failure, not only this steady state.
The controller must reduce boundary export by at least 1 kW in this state and remain compliant during transitions/failures.
Reasonableness check: The conclusion follows the connection point, aggregate plant and declared equipment rather than a marketing label.
- Treating 3.68 kW as a timeless universal threshold
- Assessing each inverter separately instead of aggregate behavior at the connection point
- Confusing a portal reading with settlement-grade metering
Where this appears in practice
A complete PV installation coordinates mechanical support, DC design, network permission, export control, metering, inspection, testing and handover.
Knowledge check
Does an export tariff prove G100 compliance?
No. Commercial payment and the approved technical export-limitation scheme are separate.
Answer: No. Commercial payment and the approved technical export-limitation scheme are separate.
Practical exercise
Draw a G100 measurement/control diagram and a failure-state test table for PV plus battery storage.
Summary
- Use the current rule and exact product record
- Assess the whole installation at the connection point
- Commissioning evidence is broader than successful generation
Sources and review
- Engineering Recommendation G98: Energy Networks Association; Current issue and amendment must be confirmed; Great Britain
- Engineering Recommendations G99 and G100 / Type Test Register guidance: Energy Networks Association; Current issue and Connect Direct status must be confirmed; Great Britain
- IEC 62446-1:2016: PV systems: documentation, commissioning tests and inspection: IEC; 2016 + AMD1:2018; International
- Health and safety in roof work (HSG33): HSE; Fifth edition; Great Britain
Editorial review date: 2026-08-22. Professional electrical review is pending.