Commissioning and functional testing
Solar Pv · Lesson 28 · Advanced
Purpose
Commission a grid-connected PV system through documented inspection, tests, functional proving and handover, not merely inverter startup.
Learning objectives
- Identify the governing boundary
- Trace energy and measurement paths
- Apply evidence in the required sequence
- Recognise unsafe assumptions
Commissioning establishes that the installed system matches design, is safe, performs required control functions and leaves durable evidence for the owner and future maintainers.
Core theory
Complete as-built drawings, string/module schedules, equipment records, labels, inspection, protective-conductor/bonding continuity where applicable, polarity, string Voc/current comparison and insulation-resistance testing with equipment limitations observed.
Verify AC protection, isolators, inverter/network settings, G98/G99 declarations or witnessed tests, G100 export-limitation response/failure behavior, shutdown, monitoring, alarms and storage/EPS modes where fitted.
Record instruments, results, tolerances, defects and corrective action. Hand over operating/shutdown/emergency instructions, warranties, maintenance plan, network approvals and metering/tariff boundaries.
| Term | Meaning | Symbol | Unit |
|---|---|---|---|
| Commissioning | Documented verification that an installed system satisfies design and functional requirements | Not applicable | Not applicable |
| String comparison | Comparison of like strings to identify polarity, wiring, shading or module anomalies | Not applicable | Not applicable |
| As-built | Record representing the installation actually constructed | Not applicable | Not applicable |
Assumptions: Values are supplied design inputs, not universal limits; Current DNO and product evidence will be checked.
- Compare: Three strings cluster within 2 V; one is about 50 V lower.
- Hold: Do not accept or parallel the anomalous string solely because the inverter starts.
- Investigate: Use safe isolation and documented tests to check module count, polarity, connections, shading and faults.
The 351 V string is anomalous and requires competent investigation and corrected evidence before acceptance.
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 normal inverter generation complete commissioning?
No. Inspection, electrical tests, network/export functions, documentation and handover are all required.
Answer: No. Inspection, electrical tests, network/export functions, documentation and handover are all required.
Practical exercise
Build a commissioning pack checklist and disposition three supplied anomalous test results.
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.