Solmetric PVA-600, Руководство пользователя

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5 Interpreting Measured I-V Curves
5-12
PV Wiring Has Excess Resistance or Is Insufficiently Sized
The electrical resistance of the PV modules and their connecting cords are accounted for
in the models stored in the PV Analyzer module database. The resistance of additional
wire between the PV modules and the PV Analyzer should be accounted for by entering
the wire gauge and length in the Wiring section of the model.
To see the effect of wire resistance on the predicted I-V curve, enter 500 feet (1-way) of
#10 wire. This will add approximately 1 ohm of series resistance. Notice the change of
slope in the I-V curve near Voc.
The resistance of the primary test leads of the PV Analyzer is extremely low and can be
neglected. If additional test leads are attached to the primary leads, be sure that these test
leads are of a heavy gauge wire in order to add minimal resistance. Small-gauge test leads
can add significant resistance and corresponding measurement error.
Note that wire sizing guidelines for safety considerations (NEC tables, etc.) may not be
sufficient to minimize DC power losses from series resistance in cabling. Some sizing
guidelines call for a maximum 1% voltage drop due to cabling, which could result in
larger sized cabling than would be required to meet code safety considerations.
Electrical Interconnections in the Array Are Resistive
Electrical connections anywhere along the current path can add resistance to the circuit.
Assure that connectors between modules are fully inserted, and if using test leads with
alligator clips, be sure the clips have a good grip on a clean metal surface.
Series Resistance of PV Modules Has Increased
Certain degradation mechanisms can increase the amount of series resistance of a
particular module. Corrosion of metal terminals in the module connectors, in the module
junction box, or on the interconnects between cells may increase series resistance.
Corrosion damage is more common in aged modules in humid or coastal environments.
Manufacturing defects within the module can also result in poorly interconnected solar
cells. Before deciding that excess resistance comes from these sources, be sure to
properly account for PV wiring resistance in the model, and check the electrical
connections external to the PV modules for signs of damage or heating.