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.
