Wrenches,
As time passeth, we're bumping more into older PVs/arrays that have
questionable outputs. After minimizing the variables (dust, temps, sun
angle, wiring, expected deterioration with age, etc) and still coming up
with low numbers. Testing individual PVs' Voc and Isc don't seem to tell
the whole story as they often look good.
Would not a definitive test be to wire a suspect PV to an
inexpensive mppt CC (oxymoron?) and then to an orphaned battery. The
battery would have to have a mondo (surplus) rheostat paralleled to it to
maintain a steady voltage during the test. With appropriate metering in
place, you would then have Vmmp and Immp as the rheostat is tweaked to hold
a steady batt voltage and the CC finds the knee.
Help me here. I know its a little spendy to cobble up but the value
of nailing an offender might be worth it. Am I missing something? Is it
common for inverters to fall off in output gradually?
Bill
Feather River Solar Electric
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