I-V curve tracing measures the current–voltage characteristic of a PV string or module on site and compares it with the expected curve. It reveals underperformance that a simple voltage or current check misses — mismatch, shading, soiling, damaged modules and bypass diode faults — and gives evidence for commissioning sign-off.
Key Takeaways
- A full curve shows faults that open-circuit voltage alone cannot.
- Measured curves are translated to standard conditions for comparison.
- Curve shape points to the cause: steps, slopes and low current each mean something.
- Measured-versus-modelled comparison supports performance acceptance.
What the Curve Tells You
Each string's I-V curve is measured together with irradiance and module temperature, then translated to standard test conditions and compared with the expected curve. IEC 61829 covers on-site measurement of I-V characteristics.
Reading the Shape
Steps in the curve often indicate shading or bypass diode operation; a lower current across the curve suggests soiling or irradiance effects; a changed slope can point to series resistance problems in connections or cables. These are faults a simple Voc or Isc check can miss.
At Scale
On utility-scale 1500 V plants, including bifacial and tracker systems, testing needs analysers rated for the array voltage and a sampling plan that covers every inverter block. We use our own Solmetric PVA-1500 analysers, with a PVA-1000 for module-level diagnostics.
Beyond the Curve
I-V tracing works best alongside infrared thermography — including aerial thermal inspection — and earthing and electrical tests, all reported against acceptance limits.
Into Operation
The commissioning curves become the plant's baseline. Repeated during O&M, they show degradation, soiling and cleaning effectiveness over time.
Frequently Asked Questions
Do we need to test every string?
The sampling plan is agreed in the commissioning scope; testing every string gives the most complete baseline.
Can I-V tracing verify a performance guarantee?
It provides key evidence. Performance guarantee testing combines measured performance with the agreed method and conditions.
References and Further Reading
Use the applicable standard edition, equipment requirements and local rules agreed in the project design basis.
