Solar irradiance goes up voltage goes down...

[Windfiend]

Newbie here, my company has recently taken over a solar site and I have been tasked with fixing the inverter which is a Schneider Zantrex GT500. Support from Schneider has been poor. Anyway, after troubleshooting the AC breaker failure, determined that the under voltage coil was bad so I sent it out to be repaired and tested. The inverter would try to close in the AC side and would fail. I just recently got it back and installed it however while waiting for start up DC voltage(which is 440VDC), I noticed that as irradiance increased my total DC voltage on the controller was dropping. I started around 432VDC at about 670 wm2 and as it got sunnier my voltage lowered to about 414VDC around 1032 wm2. There are 8 combiner boxes with 24 strings each with 12 panels per string. I tested VOC on each string on a few boxes to determine if i had a bad panel somewhere and I did see lower voltages on some strings but I couldn't find any bad panels. I do know that I have to do much more testing but I was curious if anyone has found a problem similar to this where when it gets sunnier and voltage decreases? Just looking for some suggestions as I am new to Solar and very new to DC to AC inverters. I though maybe the MPPT might be malfunctioning but I don't know how to test this. Any help would be greatly appreciated.

 

[whinmoor]

It may seem strange but higher temperatures push down voltage. Lower temperatures push up voltage.

System design needs to factor in possible extreme temperatures.

In other words, when panels get hot, the voltage is lower, so what you're seeing is perfectly normal.

 

[Windfiend]

It may seem strange but higher temperatures push down voltage. Lower temperatures push up voltage.

System design needs to factor in possible extreme temperatures.

In other words, when panels get hot, the voltage is lower, so what you're seeing is perfectly normal.

Thanks for the reply... It does seem antithetical. However, one of our sites nearby, say a 10 minute drive with exactly same weather conditions was producing just fine although a different inverter manufacturer. I would agree that this should have been in the design of the array to account for this. I am located in Michigan and we're not known to have extreme temps(except for cold haha!) Perhaps this is the wrong type of inverter for this design, or rather under powered. I appreciate the input.