After a number of customers have asked, I put together this guide on how to test the output of used solar panels.
1) current
To test the short circuit current, plug the male connector into the female connector, intentionally short-circuiting the panel. Using a multimeter, clamp the sensor around the solar panels wires and measure the current.
On a bright shiny day, in full sunlight, tilting the solar panel so that it’s pointed perfectly at the sun, the current you measure here (in Amps) should approximately equal the “Short Circuit Current” spec provided by the manufacturer.
NOTE: You must use a multimeter with a clamp sensor, and you must use one that can measure DC current. Not all clamp multimeters have a DC setting, so consider yourself warned. I’ve had pretty good luck with this multimeter, and it has something like 8,000 positive reviews
https://amzn.to/4bWqwnv
NOTE 2: Short-circuiting the solar panel is not necessarily good for it. Most modern solar panels (especially high quality commercial ones) are built with enough protections in their control module that this won’t damage the panel. You should really only do this for a short period of time. Unplug the two connectors as soon as you are done with the test.
2) voltage
To test the open circuit voltage, take the same multimeter and probe the female and male MC4 connectors.
Again, on a bright shiny day, in full sunlight, tilting the solar panel so that it’s pointed perfectly at the sun, the voltage you measure here should approximately equal the “Open Circuit Voltage” spec provided by the manufacturer.
Here’s a video I shot showing how to do these tests.