Spring overcurrent panel production makes both of my inverters trip

[Spanish Flyer]

Good morning to you all..

I have mentioned this on other threads, but still haven´t sorted out my problem.
It is a fact and now I come to learn about it that during these periods, when we have clear skies or even with slight white cloud presence, and the temperatures are still low in early Spring, that the panels can and will overproduce higher current that what is stated on their specs... So if you, like I did, calculate the total number of panels and their size following the figures given by the panel manufacturer, you can find yourself producing moce CC PV voltage than what your inverters can handle and of course they will trip to protect their hardware.

The problem with removing one or more panels amongst other things is that you will miss the extra power you had during the rest of the year, basically in winter.
In my case I have two strings where I have this problem; I have separated them into two identical inverters and as before one inverter with both strings kept tripping, now both inverters trip, so now instead of reducing my problem I have actually doubled it!!

I am now searching for a dedicated PV adjustable String Circuit breaker where you can adjust it to trip just before the inverter does (FYI, when my inverter trips, both its MPPT's fail to deliver and it can take as much as 5 minutes for the inverter to rearm); with the string circuit breaker I would only loose one string and the inverter would not suffer from so many PV CC current overloads.

I have actually found a breaker that might just solve my problem, at least partially because it doesn't rearm and I would have to connect it every time it trips, but at least I'm protecting the inverter and only one string goes, not both...
The mentioned breaker is: an EATON PKZ-SOL12 https://www.eibabo.com/en/eaton/dc-string-circuit-breaker-12a-pkz-sol12-eb10782548
Maybe someone has has experience with it.... Pitty though that it doesn't rearm after some time, but I have to sort out my problem ASAP, so if I can't find one that rearms itself, I will go for these...

Best regards

 

[SeaGal]

You refer to overcurrent and higher current, but then say the inverters are tripping as the panels produce more voltage?

Current should not be an issue - an inverter will simply draw what current it needs to produce its maximum output. That is commonly done and is known as over-panelling.

Overvoltage is a different issue and is one that will damage your inverter if you exceed its maximum input voltage.

The simple solution would be to parallel the panels into two circuits, but it seems you have done that, albeit using two inverters.

I am wondering therefore if the tripping is actually caused by a different issue than the one you have assumed?

 

[sunshine_eggo]

Good morning to you all..

I have mentioned this on other threads, but still haven´t sorted out my problem.
It is a fact and now I come to learn about it that during these periods, when we have clear skies or even with slight white cloud presence, and the temperatures are still low in early Spring, that the panels can and will overproduce higher current that what is stated on their specs... So if you, like I did, calculate the total number of panels and their size following the figures given by the panel manufacturer, you can find yourself producing moce CC PV voltage than what your inverters can handle and of course they will trip to protect their hardware.

Which is it? What is tripping the inverter? Voltage or current?

Panels at lower temperature actually produce lower current, not higher.

If it's voltage, then someone designed the system incorrectly. You don't size for panel Voc and MPPT max voltage, you size for panel Voc, MPPT max voltage and lowest temperature. Generally speaking, most regions needs at least a ~15% buffer between panel Voc and max MPPT voltage to ensure they stay safely under voltage limit in cool/cold weather.

If this is the case, a panel should be removed from the string.

 

[Spanish Flyer]

You refer to overcurrent and higher current, but then say the inverters are tripping as the panels produce more voltage?

Current should not be an issue - an inverter will simply draw what current it needs to produce its maximum output. That is commonly done and is known as over-panelling.

Overvoltage is a different issue and is one that will damage your inverter if you exceed its maximum input voltage.

The simple solution would be to parallel the panels into two circuits, but it seems you have done that, albeit using two inverters.

I am wondering therefore if the tripping is actually caused by a different issue than the one you have assumed?

Hi SeaGat, That is another puzzling problem I can't understand, because the Voltage checked with a good tester NEVER reads over the 600V DC that both Kostal MP Plus 5.02; it actually reaches around 520-530 DC voltage when it trips in the case of both inverters. The watts should reach 5000W, but again both inverters trip at about 4300W, when in theory they should be able to reach over the 5000W mark. In case you wonder about the state of these already 2 year old units, I have two more brand new same inverters out of the box... and tried one and also tripped...
And all my strings are set in series, as shown on this rather complicated image hope you understand. I actually have 4 inverters, but my problem is only with both Kostal inverters....
Thanks for your comments

 

[timselectric]

Current is not the issue.
Voltage is.

 

[Spanish Flyer]

Which is it? What is tripping the inverter? Voltage or current?

Panels at lower temperature actually produce lower current, not higher.

If it's voltage, then someone designed the system incorrectly. You don't size for panel Voc and MPPT max voltage, you size for panel Voc, MPPT max voltage and lowest temperature. Generally speaking, most regions needs at least a ~15% buffer between panel Voc and max MPPT voltage to ensure they stay safely under voltage limit in cool/cold weather.

If this is the case, a panel should be removed from the string.

"Generally speaking, most regions needs at least a ~15% buffer between panel Voc and max MPPT voltage" I believe that is the case; the installer never took into account that 15%... I have now been trying to read all readings and even though it was almost impossible to achieve, including the phone, I did get a reading where the values were as follows: 8.9 A 530 V and 4950 W; just after that, the inverter failed. The problem is none of those figures exceeded the limit values of the inverter
Thanks a lot...
The thing is, I'd rather keep the panels untouched and try the Adjustable String Limiter Circuit Breaker ..or something similar (if it at all exists..

 

[timselectric]

It's high DC bus voltage that is shutting it down.
No need to make it complicated.
Remove one panel from each string.
Hopefully you can make another string from the extra panels.

 

[SeaGal]

... I have now been trying to read all readings and even though it was almost impossible to achieve, including the phone, I did get a reading where the values were as follows: 8.9 A 530 V and 4950 W

Electrician's gloves and better insulated probes would be advisable too

 

[hwy17]

I have heard of installers casually overvolting in Italy too. Inverters must be a lot more hardened to it over there, or we are too cautious and too paranoid here.

Look at that 16 panel string.

 

[Steve_S]

KOSTAL Downloads: Brochures, manuals & more..

KOSTAL Downloads – Information & brochures

KOSTAL Downloads: Data sheets for our inverters ✓ Brochures ✓ Information flyers ✓ Additional information ► Download info now!

www.kostal-solar-electric.com

From their Manual - Page 44 English Version.
It does appear that these have a similar condition like the MPP & Growatt Units with multiple MPPT Solar Controllers within. Their documentation is "ODD" but that may be a result of multi-language translations and that certainly doesn't help much.

When setting up Solar Panel Arrays one has to account for High VOC conditions as mentioned above. Panels can generate above their ratings provided the conditions are "just so" and while it may not last too long, it can be enough to fry your electronics if not taken into account.

Panels in Series increase Voltage while panels in Parallel increase Amperage.
If you can have 600V Input and you are using a 48V Battery Bank then "technically" you can only have up to 540VDC as you have to leave an extra 60V space for overproduction. There are different ways to work out VOC overages.

As noted above, MPP/Growatt and most other AIO's also have limits with multiple MPPT Controllers. Some will limit array size if Both MPPT controllers are used and that means lower voltage & amperage.

 

[bones1]

It's high DC bus voltage that is shutting it down.
No need to make it complicated.
Remove one panel from each string.
Hopefully you can make another string from the extra panels.

My setup seems to shut down when my panels are producing at their max as well. My two strings of 5 250-watt panels each can do only about 5A or 170 volts each, the most output total I have seen is 2100 watts total so I don't know what is shutting my two EG6500's off, they stay running with no output and the batteries have the red fault lights on. These inverters have way more input capacity than that. Solar Assistant shows bus voltage at 436.

 

[Solar Guppy]

From the image showing a VMP of 484.5 Volts I think your VOC is the issue. Voltage Maximum Power aka VMP is where the panel produces the most wattage, but this isn't the unloaded Voltage Open Circuit aka VOC.

Many trackers do sweeps that start with no load on the array, and this is likely your issue. Typically VMP is ~ 77% of VOC so that would put your array ~630V which exceeds the maximum operational voltage.

 

[timselectric]

My setup seems to shut down when my panels are producing at their max as well. My two strings of 5 250-watt panels each can do only about 5A or 170 volts each, the most output total I have seen is 2100 watts total so I don't know what is shutting my two EG6500's off, they stay running with no output and the batteries have the red fault lights on. These inverters have way more input capacity than that. Solar Assistant shows bus voltage at 436.

When battery is full and panels are in full sun. The array voltage runs high. Which increases the DC bus voltage.

 

[bones1]

Thanks, Tim. Do you think the bus voltage could be why my inverters are shutting down? The highest pv voltage I have ever seen is about 190v per string, per inverter.. with fully charged batteries and little load. I can't find what the max bus voltage should be on these EG4 6500s, I do see max pv at 450-500 on the sticker. My Solar Assistant app shows right now the total bus voltage at 370V but it looks like it's only reading one inverter, don't get that either. Don't know if that's both inverters combined or just the one it seems to be reading. The bus voltage did go up to 475V a few times in the last few days as you said it would earlier.

 

[timselectric]

Thanks, Tim. Do you think the bus voltage could be why my inverters are shutting down? The highest pv voltage I have ever seen is about 190v per string, per inverter.. with fully charged batteries and little load. I can't find what the max bus voltage should be on these EG4 6500s, I do see max pv at 450-500 on the sticker. My Solar Assistant app shows right now the total bus voltage at 370V but it looks like it's only reading one inverter, don't get that either. Don't know if that's both inverters combined or just the one it seems to be reading. The bus voltage did go up to 475V a few times in the last few days as you said it would earlier.

I had the same issue. And once I removed one panel from each string. I never had the problem again.

 

[bones1]

I will give that a try, thanks, Tim.

 

[RCinFLA]

Before SCC wakes up and starts to draw from PV array, they often check PV array Voc voltage. If it is too high the SCC controller will not start up.

MOSFET breakdown voltage spec is based on conditions under switching dynamics. Their Vds breakdown voltage is higher when in static, inactive state so checking voltage first helps prevent SCC damage from high Voc.

Some SCC's have a hard contact relay that isolates DC to DC converter from PV array until controller closes relay after making PV array Voc measurements.

Worse case for high Voc is usually cold morning as sun starts to rise.

 

[bones1]

I cut down on the panels and the bus voltages were about 20 volts lower than yesterday's peak of 475. The inverters have not shut off yet today but one has now developed a fluctuating output from 105- 126 and so on. Lights starting flickering and I checked and saw the irratic output on one inverter, the other is steady 120. Turned the solar off and on and the output returned to 120v. Never a dull moment with this junk

 

[LydMekk]

One thing is max PV voltage but you need to consider max MPPT charge volts...
475V sounds way too high.
Most other inverters in that class has 425V as absolute maximum.
I think you're still too high vs. the volts.
If it were me I would have gone with strings not over 400V VoC.

 

[bones1]

Thanks for the help. I have two strings of panels, 5 250 watt panels, in series in each string. My pv voltage never gets over 190 volts per string. Very low power array. I have one string for each inverter. I understand these inverters can handle 450+ per input. I can't see how this is too much pv coming in. The 475 numbers I am referring to are bus voltages and I'm not sure what they should be to be in spec.