AC Coupled System with Fronius, optimal ESS settings?

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micmak asked Apr 15 2022 at 10:58 AM

AC Coupled System with Fronius, optimal ESS settings?

Hi,

First, please accept my apologies in advance for the long post. I tried to find answers as much as possible from the documentation.

A local installer recently installed an AC coupling solution for my home, consisting of a Quattro 8k, Fronius 8.2, Cerbo GX with touchscreen, 24kwh BYD LVS Premium and 14*535W panels.

I am still connected to the grid which is still cheap where I live, but I only get that 2-3 hours a day, and it doesn't support (for now) feeding back to the grid. It is still a good option to have especially during the night and very cloudy days. But anything fed back is being counted towards my bill as usage.

It is configured as ESS, but its mode is set to "keep batteries charged", so I don't see any of the settings for zero feed-in with Fronius and whatnot, I only see "Grid feed-in" menu, active changed to yes but this screenshot was during a grid outage:

That's not working very well. During the day with 100% battery and it's sunny, I still feed-in around 1kwh in the short 1-2 hours the grid is available (which I am paying for as usage).

I am thinking that an Optimized mode is better. Like the below example from the wiki:

But I am not sure which one to set, with or without battery life? Then I turn on "Fronius Zero feed-in" and have the "minimum Discharge SoC" to a high number, maybe 80%?

I also assume I need to have "Feed-in excess solarcharger power" to off? What's the recommended settings for my setup?

Side question #1: I only had the system for a couple of days, but I am getting a high voltage alarm briefly every time the batteries reach 100% during the day and I see there is a 0.25V difference between minimum cell and maximum cell voltage. Is this something to worry about?

Side question #2: is there a way to get a time to go value for this setup? (like the one in the smartshunt?)

ESS Fronius BYD

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Answer 1 · 2022-04-15T11:31:47Z

Alexandra answered · Apr 15 2022 at 11:31 AM

@micmak

You don't want to feed into the Grid but you have it enabled? Switch it off there.

Battery life is explained here. During periods of poor weather when solar energy is reduced, BatteryLife will dynamically raise the Low SoC limit which has been set. So if that is what you want then use it. I prefer it on as with lithium they need full charges to balance regularly.

If you are off grid mostly then when grid does come on then it will charge from grid to the SOC you set. For at least the first week or so do keep your batteries at full charge, on initial install it is always a good idea with a new bank.

Answer 2 · 2022-04-15T11:40:38Z

micmak answered · Apr 15 2022 at 11:40 AM

@Alexandra thanks a lot for taking the time to reply.

You mean I should switch off "AC coupled PV - Feed in excess" and that's it? I wonder why the installer went with what I have below then...

What's the difference between that and enabling optimize with batterylife then using Fronius zero feed-in option?

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Alexandra ♦ commented · Apr 16 2022 at 5:55 AM

@micmak

Normally it is not on if no feedback is wanted at all. If you disable it, does the fronius get 'lazy' and not cover the loads? If it does that may be why he has done it. Is paying for overshoot feedback a problem for you? Some people aren't bothered as they are already saving more.

We are not allowed to feedback at all, the grid meters go into tamper mode, so we always have to be pulling 100w or 200w from the grid. And do not enable feedback.

The optimize with battery life is for something separate. We usually have ours at 95% or 90% soc with optimized on as letting the batteries work a bit means the system work more in self consumption.

But if the bank is smaller than the full nightly needs on systems we keep them charged so they go into the evening with as much capacity as possible in case of grid faliure.

At this point you and your installer will be working out where is best based on your useage. So a bit of experimental changes will be in order. And your needs and yeilds and setup will change between winter and summer so give it time and you will get to know how to drive it.

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micmak Alexandra ♦ commented · Apr 16 2022 at 9:10 AM

Wih AC coupled feed-in off, I see the same behavior, it's oscillating between feeding back and using the grid. The behavior was when grid become online: fronius went into WAIT then LOADING with 0 output, then starting giving back and taking from the grid, up to 1kw feed-in is seen. I also see the feed-in limit active in the grid feed-in menu? Is there something I need to restart after the change?

PS: the forum is not allowing me to paste images anymore for some reason

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Alexandra ♦ commented · Apr 16 2022 at 5:58 AM

Questions #2

With BYD there is no time to go. But you can work it out based on your loads.

And the BYDs while they are settling in do give the high voltage alarms. On all the systems we have installed we have seen that. They calm down after a bit. Keep them fully charged for about a week or a bit more if you are being forced to cycle due to power outages.

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micmak Alexandra ♦ commented · Apr 16 2022 at 9:19 AM

that's not possible as I only get the grid 2 hours a day, and if that's outside the sunny hours, then I can keep them for 4-8 hours a day fully charged maybe. Do I need to wait longer for them to balance out or do I need to find a way to give them electricity for 1 week?

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Answer 3 · 2022-04-15T13:48:59Z

Matthias Lange - DE answered · Apr 15 2022 at 1:48 PM

Is the Fronius configured to be controlled by the GX device?

https://www.victronenergy.com/live/ac_coupling:fronius

Answer 4 · 2022-04-15T15:52:02Z

micmak answered · Apr 15 2022 at 3:52 PM

Hi @Matthias Lange - DE , that’s correct, and ess is configured. Byd bmu, fronius and quattro are all connected to the gx. If I change the mode to optimize then I can see the fronius zero feedin option. Also it's connected to the AC out of the quattro.

Answer 5 · 2022-04-16T02:30:06Z

shaneyake answered · Apr 16 2022 at 2:30 AM

I would set the system to keep batteries charge for about the first week and then switch to Optimized with Battery Life. The first week gives the system time to balance out all the cells.

You should have feed-in AC coupled PV turned off and DC coupled PV turned off.

Side question #1: This is because the systems hasn't had enough time to fully balance.

Side question #2: No, probably in the future but currently you need a Smartshunt.

What is the purpose of the batteries? For outage prevention/backup or for grid usage reduction?
If for backup then 90% to keep batteries charged is a good option. If for usage reduction then you can go as low as 20% and for something in the middle 40-60% is a good option.

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AC Coupled System with Fronius, optimal ESS settings?

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