I-V characteristic curve

The I-V characteristic curve describes how the output current of a PV module or string relates to its output voltage. To measure it, the string is held at a range of voltages and the current at each voltage is recorded. The curve runs from the short-circuit current at one end to the open-circuit voltage at the other. Values read from the curve include maximum power voltage, current and power, open-circuit voltage, short-circuit current, and the fill factor, which describes the shape of the curve. Some inverters use their built-in MPPT to trace the curve for each MPP tracker or string. This avoids the time and cost of a separate measuring instrument. The same data can be plotted as a P-V characteristic curve, which shows power against voltage. Compare the measured curve with the ideal curve, or with earlier curves taken in similar conditions. Deviations can point to installation errors, faults or damage in the array. This makes I-V curve checks useful at commissioning, during scheduled maintenance and when diagnosing faults.

<!-- review notes

• sentence 2: support check: partial - The sweep at different voltages and the bounds are stated, but not the specific direction (short-circuit current at one end, open-circuit voltage at the other), nor that the string is 'held' at each voltage.
• sentence 4: support check: partial - Inverter MPPT is used to measure the curve and it replaces expensive specialized devices, but 'some inverters' and the per-tracker or per-string scope are only loosely stated, and 'time and cost' is stated as the traditional drawback rather than explicitly avoided. -->