MPPT Peculiar Feedback Behaviour - 20% Energy loss

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jsmvanwyk asked Sep 18, '19

MPPT Peculiar Feedback Behaviour - 20% Energy loss

Good day,

I have a Victron 2x Multiplus 5000 paralleled with a set of East and West Facing panels. I have a total of 18*315W Panels East and 12x355W panels West. The East panels are on a 150/100 MPPT and the West panels on a 250/100 MPPT. The Multiplus Firmwares are on 2624459. The CCGX is on 2.33 and the MPPT's are on 1.42

I have 1 x ZBM2 from Redflow and I can feed back into the grid. My problem is that I have long suspected I'm not getting the full available yield from my system due to some throttling of the MPPT's.

I have played with the Grid reference point and I've now seen today that if I set the grid reference point to -2000W I have today actually managed to generate 20% more yield from my East MPPT. (Yesterday the 17th I generated 19.2 kWh and today over 24 kWH). Both mornings were sunny without clouds. Unfortunately it became cloudy in the afternoon and the West MPPT was not observed so I couldn't see the full impact on the total system in the afternoon.

I have attached the graph from the Portal here for the last 3 days and you can clearly see that when my West MPPT is starting to receive sunlight it is starting to throttle back the East MPPT. However, today when I put the grid reference point to -2000W at about 7:30am I almost had a clean PV distribution curve on my East MPPT.

I also have taken the last 7 day's hourly profile and plotted that onto each other and you can clearly see the massive difference that I've seen today.

And for the full system:

I honestly believe that for some reason ESS is not allowing the full potential of feedback to happen and really would appreciate if someone at Victron could investigate the cause of this. A loss of 20% is quite substantial and I dont' want to have to every day set my system manually into a negative grid reference point to get the max from my system.

Any thoughts on this issue?

Kind regards

Marius

MPPT Controllers CCGX Color Control grid multigrid

3-days.png (45.9 KiB)

7-days.png (88.1 KiB)

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Answer 1 · 2019-09-20T09:25:12Z

Phil Gavin answered · Sep 20, 2019 at 09:25 AM

Ok, I use 3rd party MPPT's, but I set them to a slightly higher voltage than my Quattro charges.

This is my experience.

If I set a negative grid point the quattro throttles the MPPT's to the grid set point as the DC voltage is raised.

If I allow "export excess solar to grid" the negative "grid set point" is ignored and I get the full export curve at a lower DC voltage.

It just works.

I can't imagine that it should be more difficult with actual Victron MPPT's.

Edit:

One more thing, I had to do:

I set scheduling charging to happen at night, so the batteries don't discharge overnight and I also adjusted things so I don't get an absorb cycle during the day. (That messes up the export curve as well).

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jsmvanwyk commented · Sep 23, 2019 at 08:38 AM

Thanks for the pointers,

however, my problem is slightly different. That is that I have grid feedback switched on, and without forcing the grid reference point to a higher negative my system is not exporting all "it can" to the grid, unless as per my post, I actually set the Grid reference point very high. Due to the fact that I have a self consumption setup whereby I run my whole house from my system and therefore during the mornings I'm always charging my battery as well as providing energy to my loads I should be getting the max available from the system....which I'm not, as I said, by forcing a higher feedback to the grid.

So I'm actually preventing throttling because of this..

also, my MPPT's are controlled by the BMS (canbus) but I believe due to the fact that setting this high negative grid reference point it is not the problem. I believe there is fundamentally something in the way ESS is running that is creating this issue.

I've now run this for the last 5 days in this manner and generated an extra 19% of kWh on average over the 5 days when compared to the previous 5 days.

If I look at the size of my system that means I've "lost" a potential of around 2000kWh over the year...

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Phil Gavin jsmvanwyk commented · Sep 23, 2019 at 06:35 PM

If I don't set my 3rd party MPPT's at a slightly higher voltage than the quattro settings I also don't export up to full potential.

But I have no BMS.

So maybe doing what you are doing, is a way of achieving the same thing when a BMS is involved?

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