Part 2 From Site Arrival to System Energization – Field Testing for PV Module Integrity
Ahmed Hamdy
"Power Generation & Renewable Energy | Operations & Maintenance Manager | Project Management | Solar PV & CCPP Specialist | Commissioning & Startup | Safety Management"
This post will cover "Site Testing (Incoming Goods / Pre-Installation)" and "Construction & Commissioning Testing," integrating the relevant "Test Execution" details. "Welcome to Part 2 of our deep dive into PV module testing!
After rigorous Factory Acceptance Testing (see Part 1), the focus shifts to ensuring module integrity upon arrival at the site and throughout the construction and commissioning phases.
1. Site Testing (Incoming Goods / Pre-Installation): Assessing Transit & Handling Integrity
Purpose: To identify any damage incurred during transportation, handling, or storage at the site before modules are installed. Early detection prevents costly rework and ensures that only sound modules are integrated into the array.
Key Tests (often on a statistical sampling basis):
A. Visual Inspection:
Methodology: Meticulously checking pallets and a sample of modules for shipping damage (crushed boxes, torn packaging), cracked glass (especially edges and corners), bent or dented frames, and any signs of compromised packaging that might indicate rough handling.
Acceptance: Zero tolerance for cracked glass. Minor cosmetic frame damage might be acceptable based on predefined criteria, but structural damage is a cause for rejection.
B. IV Curve Tracing (Outdoor):
Equipment: Calibrated portable IV curve tracer, pyranometer (for in-plane irradiance), module temperature sensor.
Test Procedure:
1. Safety: Ensure the area is secure, use PPE.
2. Connect the tracer to the module terminals.
3. Simultaneously measure real-time irradiance and module temperature.
4. Perform IV trace.
5. Correct measured Pmax, Voc, Isc, Vmpp, Impp, FF to STC using IEC 60891 procedures.
Purpose: Verifies electrical parameters under prevailing site conditions and compares them to FAT data (flash lists). Significant deviations can indicate damage or degradation not visible externally.
Acceptance: Pmax typically should align with FAT data within measurement uncertainty (e.g., ±5%). Significant drops in FF or Voc can point to cell damage.
C. Insulation Resistance (IR) Test (Module Level):
Equipment: Calibrated Megohmmeter.
Test Procedure:
1. Safety: Isolate module, use PPE.
2. Short positive and negative leads. Connect megohmmeter between shorted leads and module frame.
3. Apply test voltage (e.g., 1000V or as per site protocol).
4. Measure resistance after 1 minute.
Purpose: Confirms insulation hasn't been compromised by impact or moisture during transit.
Acceptance: Typically >40 MΩ·m² (e.g., >80 MΩ for a 2m² module) or as specified.
D. Electroluminescence (EL) Imaging (Mobile):
Equipment: Mobile EL testing unit (camera, power supply, dark enclosure or performed at night).
Procedure: Forward bias the sampled module with current (e.g., Isc or lower) in a dark environment and capture the EL image.
Purpose: Highly effective for detecting new microcracks, cell damage, or finger interruptions due to rough handling or transit stresses that are invisible to the naked eye.
Acceptance: Based on predefined EL defect classification (e.g., no new critical cracks, limits on number/severity of minor cracks).
Applicable Standards for Site Testing Guidance:
IEC 62446-1 (Grid-connected PV systems – Part 1: Documentation, commissioning tests and inspection): Provides a framework for initial verification.
2. Construction & Commissioning Testing: Ensuring System Integrity
Purpose: To verify that modules and strings are correctly installed, wired, and functioning as part of the larger PV system before grid connection. This phase catches installation errors and confirms array performance.
Key Tests:
A. String IV Curve Tracing:
Equipment & Procedure: Similar to module IV tracing, but applied to entire strings.
Purpose: Measures the performance of entire strings to identify module mismatches, significant soiling on some modules within a string, wiring issues (high resistance connections), or systematically underperforming modules. The shape of the string IV curve can be diagnostic.
Acceptance: String Pmax should be consistent across similar strings (accounting for orientation/shading differences). The shape of IV curve should be smooth without significant steps or dips indicative of module/diode issues.
B. String Insulation Resistance (IR) Test:
Equipment & Procedure: Megohmmeter applied between the combined positive and negative conductors of a string (or array section) and ground. Test voltage as per IEC 62446-1 (e.g., 250V, 500V, 1000V depending on Uoc max).
Purpose: Checks the insulation integrity of the entire DC cabling system from modules to inverters, including connectors, combiners, and wiring. Catches damaged cable insulation, water ingress in connectors, or faulty module insulation.
Acceptance (IEC 62446-1): R_iso > 1 MΩ (for test voltages < 500V), or R_iso > (U_oc_stc_max_system_voltage / 1000) MΩ (min 0.5 MΩ). Higher site-specific values are often required.
C. Thermal Imaging (Thermography):
Equipment: Calibrated thermal imaging camera (< 50 mK NETD).
Procedure: Performed during or immediately after initial energization (modules under load, ideally >600 W/m² irradiance, clear skies, low wind). Scan modules, junction boxes, AC and DC connections.
Purpose: To detect hotspots in modules (faulty cells, active bypass diodes due to partial shading or internal cell issues), junction boxes (diode failures, poor connections), or DC wiring connections (high resistance).
Acceptance (IEC TS 62446-3 guidance):
* Normal: ΔT <5°C.
* Observation: ΔT 5-20°C.
* Critical: ΔT >20-40°C (requires immediate investigation).
D. Polarity Checks:
Methodology: Using a voltmeter to verify correct positive and negative connections at string level, combiner boxes, and inverter inputs before energization.
Purpose: Prevents equipment damage and safety hazards from reverse polarity connections.
E. Continuity and Grounding Checks:
Methodology: Using a multimeter (low resistance ohmmeter for grounding) to verify continuity of all DC circuits, protective earthing (PE) conductors, and bonding of module frames and mounting structures.
Purpose: Ensures all electrical paths are complete for current flow and that safety grounding is correctly implemented according to design and local codes.
Applicable Standards for Construction & Commissioning:
IEC 62446-1: Core standard for commissioning tests.
IEC TS 62446-3: Grid-connected PV systems – Part 3: Outdoor thermography of PV modules and plants.
Conclusion:
"Thorough site, construction, and commissioning tests are indispensable for bridging the gap between factory quality and operational readiness. These field verifications confirm that modules have survived transit, are installed correctly, and the system as a whole is safe and performing as expected before it begins its long-term generation.
Join us for Part 3, where we'll discuss long-term O&M testing strategies and delve into failure analysis when issues do arise.
Technical References:
IEC 62446-1: Grid-connected PV systems – Part 1: Documentation, commissioning tests and inspection.
IEC TS 62446-3: Grid-connected PV systems – Part 3: Outdoor thermography of PV modules and plants.
IEC 60891: Photovoltaic devices - Procedures for temperature and irradiance corrections to measured I-V characteristics.
Local electrical codes and installation guidelines.For more interesting topics about energy Kindly, check our newsletter...👇
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Ahmed Hamdy Abd Elrahman........✍️✍️✍️
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