I am new to the solar arena and I would appreciate someone informing me as to how to check a panel to see if it generating the proper amount of power.
Thanks
Dave

I'm also looking for a good way to check my panels. I have 90 BP Solar MST-50's hooked up to 3 STXR-UPG's ( 2-1500, 1-2500). I've noticed the 2-1500's always show about 100 watts less than the 2500 unit. Aslo when the local power company came out to do their annual check, they indicated a couple of strings were reading less than the others. I have 5 panels per array, 6 arrays per inverter. Can I use a clamp on amp meter to measure each panel, or do I need to disconnect the panel from the array to make the measurement.

It's raining here today in Tucson, but there shoud be some sun tomorrow for me to make some measurements.

Thanks
Kendall

If you have a clamp-on DC amp meter, that would work. Most clamp-ons are AC only though.

You need to shade the strings, or use the master disconnect, to kill the current flow. If there are amps flowing, removeing a wire, to connect an inline ampmeter, will generate a nice welding arc. so:
disconnect current flow
wire in ampmeter
re-establish current flow & measure for 5 min (as panels change temp, the current may change)
Check each string for amps this way.
If no strings are in parallel, you can readily check voltages while panels are under load.

I am not an electrician. Any wires you melt are still yours. Your mileage may vary. contents may settle while shipping. Batteries not included. Superman cape does not enable wearer to fly.

DC current clamps seem to start around $400-$500 from Fluke (List price):

Fluke Current Probes

You can also try with an AC current clamp measuring the Inverter's AC output current (and voltage) to see what the VA output is (you need a watt-meter to measure AC watts directly)... 100 watts is within the +/- 10% or so that you would expect with solar panels. Also, it is possible that the meters on the Inverters may not be perfectly calibrated either.

-Bill

Not with these panels
http://home.comcast.net/~steveb13/solar ... -panel.pdf

Couple of things,

Even with perfect panels, having a 7% difference ( 100 watts ) is well within the specs of most solar panels. And if your modules are the Old BP Asi's your 30 panels are all parallel to work with the Suntie, so thats a boat load of wire all more than likely on an undersized home run. Unless the inverters are next to the panels, you probably have different home runs lenghts ( end of panels parralled to the Suntie ) and that will account for some difference.

Not sure how the "power company" would check 30 parallel panels but from what you have said so far nothing seems out of line. Also, Asi is really bad at long term performance, the MST's only had a 10 year warranty, since your using Suntins, the system must be at least 3 years old, my guess much older.

Check the wiring, and come back with some more detailed data and maybe we can better understand what you have

Well, I purchased a clamp on dc amp meter from Graingers for about $170, and checked the output of each panel. I found that I had 8 panels (4 on each inverter) with no output. I also checked for open circuit voltage and read about 0vdc. So it looked like there was a problem with the panel connections. I contacted Tucson Electric Power company, who I purchased the SunShare Kits from, and who I have a warranty with thru 2012. I requested a repair for the bad panels. They sent someone out who replaced the 8 panels with new ones. The two 1500's are now reporting about the same power as the 2500 inverter. TEP seemed very concerned that so many panels failed for a system from 2002, but as I now have a clamp-on meter, I'll keep checking them thru the year 2012 for free replacement units. After 2012, it may be time to upgrade to more efficent units. I might also look into a ground based tracking system. I getting tired of dragging the hose onto the roof to wash the 90 panles up there.

Thanks for the advice from this Forum.

Kendall Head
Tucson AZ

Wow, thats a great deal, they come and change out the panels!, I've never heard of this before. Thats the best 170.00 spent, as it makes your power company live upto there warranty and you get new panels to boot

ASI panels have been constantly plagued by failures and everyone except unisolar has thrown in the towel in producing them. For small panels, made from other countrys with 2 year warrants there is still ASI, But I would never buy them for my own system

Yes, roof mount systems are a royal pain to work on, if its going on the roof, get the best panel money can buy so your not having to be up there changing out bad panels every year