DIY Manual

14 | P a g e 10-543-1 REV A
DIY Manual
information on Voc and sizing the charge controller’s input. Voc is maximum when Isc is
at zero.
NOTE: Voc will increase in temps below the STC of 77
o
F, and decrease when temps are
above 77
o
F. In cold climates, Voc may increase to 125% of string voltage, so consider
that when designing a system. Refer to the MidNite Classic String Sizing Tool for help …
MidNite Solar - Classic Sizing Tool.
• Vmp – Maximum Power Voltage. Maximum voltage output when the PV module is
performing at the maximum power point on its Power (IV) Curve.
• Imp – Maximum Power Current. Associated with Vmp. Max current at same point.
• Isc – Short Circuit Current. Associated with Voc. Maximum output current when Voc is
zero.
NOTE: Panel values derived during STC testing rarely occur in the real world. You can
expect to see slightly lower values for volts, amps, and module wattage. Common
average performance of PV panels facing south and properly angled is 80% of the total
array wattage. If mounted flat (i.e., on an RV), then you can expect 50-65% of the total
array wattage.
Measuring Volts and Amps
You can measure voltage and current of the panel by itself without it being connected to the
entire solar system.
To measure voltage – Expose the solar panel to sunlight, connect multimeter red probe to the
panel’s positive wire, and multimeter negative probe to its negative wire. This is Voc.
To measure current – Cover the panel with a blanket and connect the panel’s positive wire to its
negative wire, forming a closed loop of the module itself. Using a clamp-on type of ammeter (or
a Fluke meter with appropriate amp circuit), measure current. This is Isc. Remove the blanket
to measure Imp.
NOTE: Use of blanket, before making electrical connection or disconnection, prevents sparking
at the MC-4 connectors. Voltage will be present (hence the spark), but no current flows.
Panels in Series: Voltage adds, Current stays the same.
Panels in Parallel: Current adds, Voltage stays the same.