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Rudi Marais avatar image
Rudi Marais asked

Parallel MPPTs showing different yields

Hi Folks,

I have two SmartSolar 250/100 MMPTs feeding from separate PV strings into a common DC Bus bar.

Each string has the exact same quantity and model number PV panels feeding into each MPPT.

I have however noticed that the one MPPT produces a noticeably higher yield than the other one. If I then cut the PV supply to the highest yielding MPPT for a couple of seconds, and then reconnect it, that MPPTs yield will now be the lower one of the two.

The below screen from the VRM portal shows how MPPT1 / PV1 had the highest yield until around 14H00, after which I briefly cut the PV supply to it and then reconnected it. From that point onwards, MPPT2 continued to deliver the higher yield.

There are the odd instances where both MPPT yields are almost the same, but this is more an exception than a common occurrence.

Its almost appears like, whichever MPPT was switched on first, becomes the biggest contributor. Not sure if this is operating as intended, but I would have felt more comfortable if the two MPPTs yielded approximately the same value.

Both MPPTs are connected to a common CCGX via VE Direct cables and ESS and DVCC are enabled in thr GX in case you need to know. I also see a flickering network ICON displayed on each of the MPPTs display, whcih should mean that they are synchronised.

Any feedback will be greatly appreciated.


regards
Rudi



MPPT SmartSolar
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2 Answers
ejrossouw avatar image
ejrossouw answered ·

Hi @Rudi Marais It is not as simple as that. What are the loads and SOC of the batteries at the time? Much more info required, but in essence, the MPPTs will only ultimately produce to service what is required by the loads/charging, so it may well be the case that the master is telling the slave to back off as it already is producing the maximum and only requires a little from the slave. Also note assignment of a master is random in a smartnetwork if I recall correctly so this may help explain some of it. At least this is my understanding of it.

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Rudi Marais avatar image
Rudi Marais answered ·

Hi @ejrossouw , thank you for your reply and apologies if I did not provide sufficient detail.

My fairly low PV yield did not really concern me much and I do understand that the system will only generate what is required. My question really revolved around the fact that the MPPTs do not seem to contribute equal amounts to the overall PV yield.

If your comment regarding one MPPT taking a master role and then only taking the shortfall from the slave is correct, I can accept that. What however does not make sense is why the master would want to provide the total requirement and not rather request an equal contribution from the slave.

We had a nice sunny day yesterday and when I for example switched on a kettle, the combined PV yield could easily increase from 400W to 2,500W. From this, the master probably contributed 1800W on its own. There was thus ample opportunity for the master to actually supply the full PV requirement when no kettle was on, yet it still demanded a lower amount of power from the "slave".

The systems seems to be working well so I do not think I require any corrective action. I am really just keen to try and understand why the PV load is not shared equally between the 2 MPPTs, whatever the total load requirement from the system is.


Regards

Rudi


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