Testing solar panels for current output

[electricthot]

I have been led to believe solar panels degrade over time. I have some panels in my array that are 20 years old. I tried to test them for current output, and I got very low readings. However, I am unsure of my testing method. I tested them inline, interrupting the positive lead from each panel, while they were contributing to the system. Also, my charge controller  was in float mode when I tested them, so the current going into my batteries from the controller was minimal. Should they be isolated from the system when checking for amperage output?

[Bratster]

Yes you would need to test them while they're isolated from the system. That way you can be sure that there's nothing else going on that would cause less current to be drawn than panel is capable of producing. Such as your batteries being fully charged.

Connect an ammeter straight across the panels output.
Make sure you're using a meter that has a high enough current range that it can handle the full short circuit current of the solar panel.

Sent from my Nexus 6 using Tapatalk

[Seekonk]

Short circuit is a good test, but I had a couple panels with bad sections where the current measured fine. The 12V panel had become a 6V panel with one section passing current through the bypass diode.  Calculate a resistor from the power point voltage and current. Choose a value resistance just a bit higher and use that for a final test.

[TerraHertz]

Or if you want to get fancy you can use an electronic load, to graph the V-I curve and hence the point of maximum power output. Like here: http://everist.org/NobLog/20160504_solar_panels_vs_emp.htm

[PTR_1275]

Irradiance plays a massive part. How do you know what amount of sunlight is hitting your panels? Specs say 5 amps, you test 3.8 (for example) how do you know you’re getting 1000 w/m2 to make a useful comparison to the test conditions that he pane was rated to.

If you’re testing all the panels under identical conditions you will be able to see if one is dramatically less than the others though.

As seekonk said, testing under load is also needed to make sure the panel can output good voltage. I’ve had lots that would put out current, but the usable voltage was too low for battery charging due to cracks in the cells or the tabbing between the cells.

[DougSpindler]

I thought only way to test pannels output properly is in a labratory.  Or test at the equator at noon.  But even at the equator the amount of solar energy from the sun varies from day to day even on a clear day.

Isn’t the best he can do is do a comparison test between his panels?  Ther is no way for him to compare to max rated output of the pannel to see how much they have degraded.

[james_s]

If you have a newish reference panel of known output then that ought to work, perhaps a calibrated light meter? You'll need some way to establish a baseline but it shouldn't be too hard to determine whether the output is in the right ballpark.