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5 Interpreting Measured I-V Curves
5-1
5 Interpreting Measured I-V Curves
Introduction
A PV module, string, or array has a characteristic curve of current versus voltage; the ―I-
V curve‖. The PV Analyzer‘s mathematical models predict the ideal shape for this curve
for thousands of different PV modules and configurations. Occasionally the shape of the
measured I-V curve will deviate from the shape predicted by the model. These changes
from the ideal shape contain information about the performance of the PV System. This
section describes the most common deviations and identifies possible causes for these
deviations.
Inputs to the PV Model
The modeling features of the PV Analyzer predict the shape of the I-V curve for
comparison with measured results. For the prediction to be valid, the inputs to the model
must be valid. The model inputs are:

PV module characteristics (available for over 2000 model numbers)

Number of PV modules in series

Number of PV modules or strings in parallel

Length and gauge of wire between the string and the PV Analyzer

Irradiance

Cell temperature

For some instrument modes it is also necessary to provide: latitude, longitude, time
zone, and array orientation.
Inverter characteristics are used only to illustrate the maximum power tracking range.
They do not affect the PV array model.