Solmetric PVA-1000S, User Manual

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7 Interpreting Measured I-V Curves
7-1
7 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 I-V curve represents the entire family of current and voltage pairs at which
the PV circuit can be operated or loaded. The PV analyzer’s mathematical models predict
the shape for this curve for thousands of different PV modules and configurations.
Occasionally the shape of the measured I-V curve will deviate substantially from the
shape predicted by the model. These substantial deviations from the predicted I-V curve
shape contain information about the performance of the PV System. This section
describes the most common patterns of deviation 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 model parameters stored in the PVA PC software
•
Number of PV modules in series
•
Number of PV modules or measured strings in parallel
•
Length and gauge of wire between the PV modules and the PV analyzer
•
Irradiance
•
PV cell temperature
•
Array azimuth and tilt
•
Latitude and longitude
•
Date, time, time zone, and daylight savings information
An inverter database is included in the PVA software only to display the inverter's max
power tracking range on the I-V curve graph. The inverter characteristics do not affect
the measurement of the I-V curves and are not used in creating the PV model.