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GoodWe ET PV string volts "jumping up"

nulled

New Member
Joined
Jan 20, 2025
Messages
10
Location
Australia
My Setup:

25kW GoodWe inverter + 28.8kWh Lynx F G2 battery

60 x 550W Canadian Solar Bifacial panels for a total of 33kW.

They are arranged in 4 strings, 18, 18, 10, 14. All panels aside from the 14 panel string face north, the 14 panel string faces south.

The inputs to the inverter are:

MPPT1-1: 18 panels

MPPT1-2: 18 panels

MPPT2: 10 panels

MPPT3: 14 panels

Now to my problem. I have noticed that sometimes the string voltage of MPPT1-1 and MPPT1-2 randomly shoots up by 100V which results in the current of the string dropping significantly. I can't seem to figure out why the voltage just "jumps" up for no reason. And I can't seem to figure out why or how it drops back down. This is probably best explained with a graph:

Blue line = MPPT1-1 (18 panels), Yellow line = MPPT1-2 (18 panels), Red line = MPPT2 (10 panels), Green line = MPPT3 (14 panels)

The volts normally hover around ~700V but then it goes to ~800V and you see a corresponding drop in current output. Also notice that when it's around the 700V mark, the line is thicker which I think is the MPPT logic constantly adjusting up/down to ensure it is at the right max power output. But at 800V it doesn't seem to be doing the same.

1737380956789.png

I don't think this is due to cloud cover and I get no shading from anything nearby. This can be seen by the same graph but with the other strings visible. See how on the 17 Jan, the current for the red and green strings are significantly higher than the blue and yellow?

1737380965408.png

As far as I can tell, I'm not exceeding any of the ratings of the MPPT inputs. I've actually disconnected all the strings and had only the 2x18 panels connected. When they are connected to MPPT1-1 and MPPT1-2 the volts are ~800V still however when I move one of the 18 panel strings onto another MPPT, they both drop down to 700V where they should be operating around.

Has anyone got any ideas as to what's happening?
 
It's the MPPT doing its job, hunting for the best power point by adjusting the current it pulls.
 
Yes but it looks like it's finding a point outside the optimum power output for the string. It's clear the operating voltage on MPPT1 is higher than it needs to be and results in current less than ideal. The current through all the strings should be about the same since all the panels are the same make and model with slight variation due to the face and tilt.
 
I'd want to see the calculated power before deciding that the current is less than ideal.
 
Here's a snapshot of the instantaneous readings from the SolarGo app.

PV1 (18 panels) = MPPT1-1 = 793.3 x 4 = 3173.2 = 176.29W/panel
PV4 (10 panels) = MPPT2 = 299.9 x 8.3 = 2489.17 = 248.917W/panel
PV6 (14 panels) = MPPT3 = 539.2 x 7.7 = 4151.84 = 296.56W/panel

1737415496900.png
 
Is your combined power close to the maximum rated for the inverter?
Here's a graph with the total PV power. I noticed that I can actually exceed the rated inverter capacity (25kW) due to having a battery connected. It sends anything above 25kW to charge the battery making full use of the PV output. I believe this is due to battery being able to be charged directly via the PV DC and the 25kW rating is the AC output rating.

1737420177937.png
 
A couple of thoughts:

If you are outside your MPPT input voltage tracking range, it may not be able to harvest much power.

How close to your maximum input are you?

Are 1-1 and 1-2 separate inputs, or two sets of wire connections to MPPT1?
 
Here's a graph with the total PV power. I noticed that I can actually exceed the rated inverter capacity (25kW) due to having a battery connected. It sends anything above 25kW to charge the battery making full use of the PV output.

I suspect you have maxed out the mppt's and the battery would be an unknown if I can accept the excess energy, the variations are likely the time it takes to adjust the mppts to the battery SOC?
 
A couple of thoughts:

If you are outside your MPPT input voltage tracking range, it may not be able to harvest much power.

How close to your maximum input are you?

Are 1-1 and 1-2 separate inputs, or two sets of wire connections to MPPT1?
Yeah that might be a possibility. It's nominal input voltage is 620V

1737421549959.png

1-1 and 1-2 are separate inputs.
 
Yeah that might be a possibility. It's nominal input voltage is 620V

View attachment 271632

1-1 and 1-2 are separate inputs.
OK, so your tracking range goes up to 850V, so that's not the problem. Well, shouldn't be the problem. Still something anomalous going on there.

But the above says you have 3 trackers and 2 strings per tracker, so 1-1 and 1-2 are not separate. It looks like the voltage is exactly the same, but the current varies?

Are the three strings facing North all in the same plane?

How hard would it be to take one panel out of each of the 18-string arrays, just bypass it for a few days. I mean it _feels_ like you are exceeding the MPPT control range, even though the spec sheet says it's 200-850V
 
Will see what it's like as I haven't been up on the roof to check how the panels were installed. The whole system was installed by an installer. They didn't have much of an idea as to what's going on and have passed me onto Goodwe to follow up...which I'm yet to get a hold of.

Here's a sketch of the inputs into the MPPTs, there's separate connectors for each string.

1737425077109.png

All the north facing panels are on the same plane. Here's a sketch of the PV arrays:
1737425356051.png
 
Hmm:

/*
The two input strings per MPPT should be of the same type, the same number of modules, the same tilt and angle to ensure the best efficiency.
*/

On page 112 it talks about 'PV Connect Mode", what's that set to?

Your Voc is 49.6, 18 times that is 892.8V, and your MPPT operating range only goes to 850V, so it feels like you are going out of range and the tracker gets confused. Except where your voltage readings (from the inverter?) are within spec.

Do you have a DVM that'll go to 1000Vdc? If not, don't measure anything, but if you do, see if the MPPT input voltages match the inverter readings.

What's the temperature there? Looks like the PV input went from zero to 800V at 7:20AM?

Could be wiring problems. Could be your installer should be on the hook for design, configuration, and diagnostics...

#GraspingAtStraws
 
Haha yes it's all very strange.

The PV connect mode is set to Standalone - I actually don't even know how you can even wire the panels in the other ways the manual says?

I'll see if I can measure the panels later. As for the PV input going from 0-800V, it was because I had isolated all the panels overnight and switched them back on at 7:20AM.

If I parallel the 18 panels and the 14 panels into MPPT1, will that do anything or prove anything? Would that be the equivalent of removing panels?
 
If I parallel the 18 panels and the 14 panels into MPPT1, will that do anything or prove anything? Would that be the equivalent of removing panels?
That was going to be my next thought, but if the pairs of MPPT inputs are forced to remain at the same voltage, your production on the longer strings will drop.

It’s very strange that the manual does not detail the operation or connection of the MPPT inputs.
 
I've found some documentation on a different inverter series (Goodwe SMT) with some other MPPT requirements:


2.1 PV Module Series Design Principles
For SMT series models, the following string design requirements are proposed, while fulfilling four conditions:
(1) The maximum Voc of the string is lower than the maximum input voltage of the inverter (≤1100V).
(2) The MPPT voltage of PV modules connected in the series is within the inverter full load MPPT voltage range (510V~860V).
(3) The voltage difference between different MPPTs is less than 120V.
(4) When the inverter is connected to multiple strings, the strings should be dispersed into each MPPT as far as possible.

I jumped onto the Goodwe PV design software and intriguingly it says this:

Warning:
The voltage between MPPT trackers being too high may trigger the inverter's derating logic.
Solution:
Adjust the number of modules in the strings to reduce the voltage difference between MPPT trackers.
1737448188456.png

This doesn't explain why when I disconnect all other strings and only 2x18 panels into MPPT1 the volts can still go high. Perhaps it needs some sort of reference string???
 

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