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jocano2000

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Reply with quote  #1 
Hi everybody,


I have a 8.8 kW system showing low performance for a long time. Checking at the monitoring system, I only see a strange behavior in voltage that I'm not used to. The voltage has two peaks on a regular basis (every day) and then drops to a constant value (150 V) which is the same for every day regardless of radiation. Here is a graph to illustrate the problem.

I'd appreciate your insights about this problem that I need to identify.
Here is the details of the system:

DC size: 8.8 kWdc installed
AC size: 7.6 kWac (Inverter fronius)

More details in the attached graph

240445 - Drop in Voltage.png Regards,

Jose Cano

Rick H Parker

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Reply with quote  #2 
Too much information on one page, we cannot read the graphs.
Can you put the graphs in a high resolution pdf and attach it.
Or break up the graphs to separate pages.

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Rick H Parker
Kansas, USA
Electronics Engineering Technologist
stmbtwle

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Reply with quote  #3 
It LOOKS like something is tripping out due to overload, over voltage, or whatever.  I would suspect the inverter but I can't speculate as to why.

The layout diagram seems to show two strings of 13 panels each, and 2 strings of 4 panels each. Strange, unless it is actually two strings of 17 panels each.

It also shows two different roof layouts. if they face in different directions and are on the same inverter, that may cause a problem, as the two sections would be producing different voltages/current.  

What are the specs on the panels? The inverter?

I'd talk to Fronius or the installer.



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Willie, Tampa Bay
jocano2000

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Reply with quote  #4 
Thanks Rick H Parker and stmbtwle.

I attached the graphs in separate files so that you can look at them better.
As the string layout shows, the strings are not combining different roofs, however they could be connected in the same MPPT (two different roof's strings in the same MPPT).

stmbtwle, after looking at these new graphs, do you still think that is tripping out due to overload/voltage?

The specifications are in the following link: 
https://d1819pwkf4ncw.cloudfront.net/files/documents/sedsfroniusprimousawith1015682691snapshot-328025.pdf
check at the PRIMO 7.6-1 model.

Thanks so much for your insights,

Jose Cano
240445 - Drop in Voltage (Cloudy-winter).png  240445 - Drop in Voltage (Sunny-summer).png  240445 - Drop in Voltage (Sunny-winter).png  240445 - String layout.png

Rick H Parker

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Reply with quote  #5 
I think the panels are miss-wired, neither channel is operating in the MPP range of 250V-480V.

Can you take a closeup picture of the MPPT terminal block and post it?  It is where the solar panels connect to the charge controller.



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Rick H Parker
Kansas, USA
Electronics Engineering Technologist
Rick H Parker

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Reply with quote  #6 
Do you have any information on the panels? ... Make, Model, specs and quantity. 


1 According to the layout diagram you have two 13-panel strings and two 4-panel strings. Thats a BIG difference in voltage. Depending on your inverter and how it's connected, that could be a problem.

Can go either way. This unit has two MPPT charge controllers.
The two can be wired to harvest two different sized arrays or can be wired to split the voltage of one big string array. I thinking somebody got confused by the dual MPPT and the two ways they can be configured.

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Rick H Parker
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stmbtwle

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Reply with quote  #7 
I can't tell the cause, but I do think something is causing the inverter to go into a 'safe' mode. I agree with Rick that the panels may be mis-wired or mis-configured. However that's not something I can determine from here. I think you need to have a solar-qualified electrician check it out.

A couple things concern me.

1 Accordind to the layout diagram you have two 13-panel strings and two 4-panel strings. Thats a BIG difference in voltage. Depending on your inverter and how it's connected, that could be a problem.

However if there are two inverters as Rick says, this would make sense.

2 My other issue is that it looks like you have a "hip" style roof with one hip facing east and one facing south. As the sun rises, the east side panels catch the sun. Some time later the sun is high enough to produce output in the south panels, and I'll bet that's about when everything goes "south". It's not a problem with microinverters, but I've been told that panels facing in a different direction needed a separate inverter. That was 8 years ago, things may have changed. Fronius should be able to tell you, and it might even be in the installation manual. This is what I can glean from the diagrams; if all your panels face the same direction it shouldn't be a problem.

I think the two voltage spikes are the voltage ramping up in the morning before the inverter turns on, then the load pulls the voltage down to 150v more or less. It seems like a lot to me, but it may be as designed. The second spike is when the inverter turns off. What does Fronius have to say?

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Willie, Tampa Bay
Rick H Parker

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Reply with quote  #8 
I think the two voltage spikes are the voltage ramping up in the morning before the inverter turns on, then the load pulls the voltage down to 150v more or less.

Each MPPT has a 16A limit, MPPT1 may be dropping the voltage to balance the power equation for 16A. This would make sense if the panels on MPPT1 wired on a lower voltage series-parallel configeration that has the capacity to deliver more then 16A.  If you look at both MPP1 and MPP2 they are both about 150V. The Unit is designed for about twice that, MPP range 250V-480V.

If Jose uploads a picture of the MPPT terminal block, I might be able to spot the problem. Read the last page notes, "System is producing low power since inverter (7.6kWac), my interpretation is that the problems started when the charge controller/inverter combo was replaced. I'm betting that the solar panels where wired to the new unit incorrectly when the new unit was installed. If there are four banks of PV panels and four power leads going to the unit, this is a real possibility, the numbers support my theory.


2(150V*16A) = 4800W, which is real close to the 4.2kW in the note. To get the full 8.8 kW at 16A per channel the panels need to be wired to produce about twice the voltage input to the MPPTs.

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Rick H Parker
Kansas, USA
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Rick H Parker

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Reply with quote  #9 
I think the two voltage spikes are the voltage ramping up in the morning before the inverter turns on, then the load pulls the voltage down to 150v more or less.

Another possibility is that a short string got wired in parallel with a longer string on Mpp1. When no current flows you see the voltage of the longer string, when current starts flowing the voltage drops to the voltage of the short string. Look at the graphs, the voltage on Mpp1 drops when Mpp1 current starts flowing the rises when Mpp1 current stops. 

A full profile of the panels would be helpful.

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Rick H Parker
Kansas, USA
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stmbtwle

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Reply with quote  #10 
Very possible, Rick.

I'm looking at the layout and even with two inverters I don't see how it can possibly be wired correctly. Three inverters, maybe. But there's simply not enough information. I don't know which strings are connected to which inverter nor what the panel specs are. Nor is there any performance curve from the other inverter (or from before the problem started) to make a comparison.

Need to find someone locally to check it out.

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Willie, Tampa Bay
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