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Axpert Parallel - producing different solar Kw


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I am not sure if I am going crazy or not, I hope not :)

 

I have 2 Axpert Kings installed in parallel, however for some reason the one Axpert is always producing roughly half of the what the other inverter is doing. This is regardless of what is happening in the system, full batteries, charging batteries, mixing between grid and solar, full load.

 

Both panel setups are on the same roof, facing north orientation, same pitch currently set up as 3 strings of 4 Panels (Will be changing this back to 4 strings of 3 panels) going into each Axpert. No shade covering the panels during the day. 

 

Any ideas of where I can start tinkering to find out the problem? 

 

Setup as follows:

 

Axpert King x2 - parallel

12v Narada batteries  x12 (connected in 48v)

Renewys Solar panels 270W x 24 (12 on one inverter, 12 on other inverter)

 

 

Pics I took:

 

17a

98v

IMG_20200714_135330.thumb.jpg.44062612fd1f46fde4586d90cc87ab6e.jpg

 

 

32a

114V

IMG_20200714_135333.thumb.jpg.44833098514cd1e75d20b4889eae293f.jpg

 

 

IMG_20200714_135333.jpg

IMG_20200714_135330.jpg

Edited by Blowdart18
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I see from the above that the battery is fully charged, when this is happening what is the load on the system as from the display it would seem low. 

I had the same issue with my King when first installed, the unit will only draw the PV power required... i.e. If the battery is full and the load only requires 2.63kw, that is all it will draw, irrespective of there is more available.

From the load indicator, this would make 100% sense as presumably you have 2x Axpert King 5K units, which look like they are under 25% load.. i.e. a combined 2.5kw, hence not pulling more than 2.63kw when taking into account system losses.

Why it is not pulling even from both, who knows but you will most likely find that the load is not being evenly pulled either and this may explain the disproportionate PV. 

 

Easy way to test.. increase the load and see what happens to the PV generation :) 

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Posted (edited)

Hi Jay-dee, thanks for the insight, however I pretty much ruled that out too.

See below pics when I had half batteries and half load, and it was still only giving me 50% of what it should be giving. 

 

 

IMG_20200712_101644.jpg

IMG_20200712_101637.jpg

Edited by Blowdart18
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22 minutes ago, Blowdart18 said:

Hi Jay-dee, thanks for the insight, however I pretty much ruled that out too.

See below pics when I had half batteries and half load, and it was still only giving me 50% of what it should be giving. 

Sorry, then my insight is exhausted here :( 

Some troubleshooting ideas

1 - If you change the PV's around... does the HS/Master unit still stay half of the Slave? i.e. is it the PV install or the Inverters

2 - If you shut down the slave unit and just run the primary... does it stay at same value or increase? i.e. confirming if it is a Parallel issue

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43 minutes ago, Jay-Dee said:

Sorry, then my insight is exhausted here :( 

Some troubleshooting ideas

1 - If you change the PV's around... does the HS/Master unit still stay half of the Slave? i.e. is it the PV install or the Inverters

2 - If you shut down the slave unit and just run the primary... does it stay at same value or increase? i.e. confirming if it is a Parallel issue

Very True - thanks for the advise Jay-Dee, let me try that and then I can revert :)

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A thought: do the battery voltage readings of the two inverters agree fairly closely?

I have a similar issue with my Axpert MKS PF0.8s; when not much solar is needed, one provides about twice the other. But when more is needed, they both pull their weight.

I did attempt to calibrate the battery voltages a while back. Either that reverted, or I did it wrong, or it depends on load somehow. I'll play with that again when I have more time.

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@Coulomb sorry some how missed your post here.

The funny thing is I left late for work on Wednesday and made sure to get everything running before I left, tumble dryer, washing machine, dish washer, and literally everything I could to pull power throughout the morning. And still the one inverter chugs along at half of the production it should be doing.

This week has been a bit hectic but I still want to swap the PV cables coming in, its rather easy considering I can do it at the fuse box, and see if that makes a difference. 

Use this to eliminate the possibility of 1) Inverter, 2) Cabling or 3) the panel setup - something I have not been technically inclined to check. 

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Posted (edited)

Problem is it is difficult to rely on ICC as it only picks up the feed of the one inverter too :( So you have to be at home to pick up the readings off the inverter itself. 

However one thing I have noticed if i check the production for the day, the load also tends to differ between the two. Not so much in the pic, but it has been up to a 2kwh difference before.

 

IMG_20200720_174348.jpg

IMG_20200720_174344.jpg

Edited by Blowdart18
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20 hours ago, Blowdart18 said:

one thing I have noticed if i check the production for the day, the load also tends to differ between the two.

That suggests a possible problem with the AC-out cabling. Do they have their own breakers between the inverters and the load? Perhaps check that all the connections are all tight. I found out one of mine was a little loose when the breaker tripped for no immediately apparent reason. It turns out the heat of the looser connection conducted into the thermal cutoff part of the breaker, and tripped it. That was an embarrassing day 😯.

The inverters are supposed to adjust their output voltage to share the current about equally. As loads change, one can temporarily be taking a lot more of the load. So this also may not mean much.

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So some feedback with regards to the system, Thursday night I swapped the 2 systems in terms of PV input and would you guess what happened... 

The problem moved with the inverter, so the inverter that was producing maximum PV was now only producing half.

Didn't change any other settings, so next step is to check if there is something wrong with the panels in terms of wiring. etc etc.

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On 2020/07/21 at 4:07 AM, Coulomb said:

A thought: do the battery voltage readings of the two inverters agree fairly closely?

I have a similar issue with my Axpert MKS PF0.8s; when not much solar is needed, one provides about twice the other. But when more is needed, they both pull their weight.

I did attempt to calibrate the battery voltages a while back. Either that reverted, or I did it wrong, or it depends on load somehow. I'll play with that again when I have more time.

@Coulomb How do you calibrate the axpert inverters?

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On 2020/07/23 at 4:35 PM, Blowdart18 said:

Problem is it is difficult to rely on ICC as it only picks up the feed of the one inverter too :( So you have to be at home to pick up the readings off the inverter itself. 

However one thing I have noticed if i check the production for the day, the load also tends to differ between the two. Not so much in the pic, but it has been up to a 2kwh difference before.

 

I monitor both my Axpert MKS II inverters with ICC.  The cable goes into either one and "axpert parallel" is selected in ICC.  Then it shows both.

In terms of different loads: this doesn't solve any problems, but just for further insight: with PV turned of or at night, let it run from grid and check what the load watts on each inverter.  It should be very similar as the power is just flowing through from the grid. If it's not the same, your AC cable lengths may be different. The breakers could have different internal resistance.  Your neutrals might be connected together before the neutral bus instead of after.

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  • 2 weeks later...

 

So in reply to this topic, remember to check your controller settings or as people put it your display version with the Axperts. 

 

Mine was different versions which meant that the 2 Axperts were not speaking nicely with one another, so in essence they did not know how to work together to maximize PV production.

Once updated each Axpert is producing the exact amount of PV Kw now.  Lesson learnt. 

 

IMG_20200731_182207.thumb.jpg.d44a698cf6eed544c342e8c5292078d8.jpg

IMG_20200731_182204.thumb.jpg.0eed335ab1548c9f87a82151c4bbc3bc.jpg

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Hi 
As the AC input and output and even the battery DC side is bridged out in the parallel config, my opinion is that the issue is in one of the PV input sets.
If I recall correctly, you have posted 98V and 114V of the 2 PV inputs. If the 270W panels operate at around 30V, the 114 seem OK (depending on the time of day). The 98 V set is suspect, how does the 'open circuit' voltages test? You can perhaps measure the sets and strings and panels, the should give similar readings each time. 
Hopefully just a connection issue in one string.. ((Just measure and check connections safely - it can be a 'shocking' experience ☺️)

Let us know please - I run a similar setup, but the power drawn from the PV sets are equal, even with the 2 uneven sets I have. 

Greetings 

Jaco P

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