I am NO expert, but here is what I do for a quick check... This is certainly not exhaustive testing and doesn't begin to check things like thermal cycling issues, voltage leaking, arcing, etc. But it's quick and easy to do.
On a very sunny summer day around solar-noon local time, I place my test panel in the sun, pointing directly at it.
I place a short stick (~1ft) with a square flat end, perpendicular to the face of the panel, and set up the panel so the stick casts no shadow.
1) I measure Voc using my multi-meter set to DC volts.
No connection to the panel other than my meter is used. Voltage should be near Voc as stated on the back.
This measurement is not very sensitive to panel angle. NOTE: temperature affects Voc, and the expected value can adjusted using information on the back. Look for temperature coefficient value.
2) I measure short circuit current (Isc) using my multi-meter set to highest DC Amps setting.
a) I cover the solar panel with an opaque object like a blanket or cardboard. This prevents a large spark from damaging your panel connectors or meter leads when I connect the meter in step d.
b) I verify that my meter has the input current capacity in excess of the max solar panel current.
c) I configure my multi-meter to DC measure current (by moving red probe to current input).
d) I connect my meter leads to MC4 connectors, which has the effect of shorting out the panel, and allows me to measure Isc.
e) I remove the cover on the panel and make the Isc reading. The Isc reading is very sensitive to panel angle (and panel condition).
f) I put the cover back on the panel and remove my meter connections.
g) I try really hard not to forget to move my red meter probe back to the voltage input so the next time I use my meter I am not shorting out what I am measuring!! It has happened.
Note: I only use the procedure described here on a single panel! I would never do this using 2 or more panels as the voltages could become lethal!
If anyone knows of better procedures, please post a follow up. This procedure is actually a bit time consuming now that I think about it and can't be done indoors.
