Generation and export metering
Solar Pv · Lesson 24 · Advanced
Purpose
Distinguish generation, import/export and product-monitoring measurements by boundary, direction and legal purpose.
Learning objectives
- Identify the governing boundary
- Trace energy and measurement paths
- Apply evidence in the required sequence
- Recognise unsafe assumptions
A generation meter measures generated energy at a defined internal point; an import/export meter measures exchange with the public network; an inverter portal estimates product energy for operation. These readings need not match.
Core theory
Document each meter boundary, phase coverage, sign convention, CT ratio/orientation, accuracy class, communications and who owns/reads it.
Settlement, tariff, certification and incentive arrangements may require approved/MID or supplier-installed equipment under current scheme rules; confirm rather than infer from the display.
Reconcile readings using direct self-consumption, storage losses, auxiliary loads, clipping, curtailment and measurement uncertainty. Never substitute a portal for the required revenue meter.
| Term | Meaning | Symbol | Unit |
|---|---|---|---|
| Generation meter | Meter at a defined internal generation boundary | Not applicable | Not applicable |
| Import/export meter | Bidirectional meter at the network exchange boundary | Not applicable | Not applicable |
| CT | Current transformer used to sense current magnitude and direction | Not applicable | Not applicable |
Assumptions: Values are supplied design inputs, not universal limits; Current DNO and product evidence will be checked.
- Boundary: Generation is measured before site consumption; export after it.
- Balance: Direct site use = 6 − 2 = 4 kWh.
- Qualify: Real reconciliation includes timing, storage, auxiliaries, losses and meter uncertainty.
Illustrative direct self-consumption is 4 kWh.
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
Should an inverter portal be assumed to be the revenue meter?
No. It has a different boundary and purpose unless the scheme explicitly establishes otherwise.
Answer: No. It has a different boundary and purpose unless the scheme explicitly establishes otherwise.
Practical exercise
Create a meter schedule and energy-balance diagram for PV, battery, loads and grid.
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.