5 Interpreting Measured I-V Curves
5-3
Figure 46. Effect of series and shunt losses on the shape of the I-V curve
The fill factor is the ratio of two areas defined by the I-V curve. These areas represent
electrical power (watts) because they are the product of a voltage and a current. Fill factor
is the area represented by the max power point, divided by the area represented by Isc
and Voc. In an ideal (but unrealizable) PV module, the two areas would be identical and a
fill factor of 1.0 would result.
The Shape of a Normal I-V Curve
Figure 47 shows a normal I-V curve (red line), as a starting point for the discussion. The
predicted I-V curve shape is shown by the five dots. The power versus voltage curve is
also visible (blue line). Power is calculated as the product of measured current and
voltage at each I-V point.
Figure 47. A normal I-V curve for the parallel combination of two strings of eight
175-watt modules, showing conformance with five points predicted by the PV
model.
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