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colj avatar image
colj asked

Problem with Solar PV, Quattro and running Offgrid

Hi All,

Just has a 'problem' running off grid and would like to understand if some of this was expected behaviour and if there's something I should be doing to avoid this happening again please.

Running offgrid, Solar PV producing 2kW, background use 500w wanted to use excess to charge batteries (started at c90% SoC).

All looked good to start with. After about an hour I noticed that the PV yield was saying zero though still full sun.

Looked at the VRM and could see that the PV yield was oscillating between 2kW and 0 (and then after a while, the PV RCD had tripped - a separate problem).


Looking at the logs I'm guessing that when the battery charging went from bulk to absorption, the Quattro started frequency shifting to try to control the charging with the excess PV. Should mention here that I have an old Sunnyboy inverter (no direct control) with a wired AC sensor to the Cerbo GX measuring PV yield. Why was the PV output dropped to zero (such that the battery was then discharged to satisfy the 500W load? Can this situation be avoided please?

Separately, I'm guessing that my old Sunnyboy PV inverter didn't cope with the oscillating frequency shifting causing it's RCD to trip?

Appreciate some guidance/suggestions please?

Colin

offgridsolar
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5 Answers
colj avatar image
colj answered ·

Trying to answer my own question I have a possible theory.

In the ESS frequency configuration for the Quattro to control the PV output, the default values are 51,52,53Hz.

Aside: Does anyone happen to know if the last frequency (disconnection) is actually a 'greater than' (per the ESS help) or a 'greater than or equal to' (which seems more likely) please?

Looking at the specifications for more modern Sunnyboys (and assuming my old model is the same), then the frequency at which the PV will start being decreased is > 51Hz and disconnect at >= 52Hz. So, is it possible that the Quattro set a frequency of >=52Hz to downrate the PV, which happened to turn it off, then immediately reverted to a 'normal' frequency. Whilst the Sunnyboy was restarting, there was no PV output so the background loads discharged the battery. When the Sunnyboy was up, immediately there was 2kW of PV, causing the cycle to be repeated. Eventually, the timings of this on/off caused the RCD on the PV circuit to trip.

Does this sound plausible please?

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ahtrimble avatar image
ahtrimble answered ·

I guess I am a little confused, what charge controller are you using and do you have the right settings in the charge controller? It's your charge controller (CC) that will control the charging of your batteries. And when the CC hits its settings for bulk, absorption, and float it will adjust the PV output to match. When the batteries hit 100% SOC, based on voltage, the CC will shut down its output till it hits its restart voltage. The CC will also go into absorption and float according to its settings as well. On nice sunny days with low power consumption it is not unusual for my CC to shut down because the batteries are 100% SOC.


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colj avatar image colj commented ·

I have Leoch batteries (own BMS) canbus? attached to Cerbo GX. Batteries reached about 93% SoC in bulk mode then changed to absorption which (from the logs) seemed to trigger the behavior described.

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ahtrimble avatar image ahtrimble colj commented ·

That didn't answer "I guess I am a little confused, what charge controller are you using and do you have the right settings in the charge controller? "

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PeterM avatar image
PeterM answered ·

You have to make sure the SMA freq shift parameters are compatible with Victron . Out the box they are not ( AT least in South Africa ) - it might depend where your are and what the grid code settings are . What are your freq limits on your victron and the SMA - in the SMA the setings are seen here 1670659231224.png


1670659231224.png (17.4 KiB)
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colj avatar image colj commented ·

My SMA Sunnyboy is 12 years old. Not sure I could even find those settings it it had them! However i did find some American (i'm in the UK so 50Hz) SMA documentation that graphically showed the frequency shifting (and as you suggested), this doesn't match the default settings in the Quattro.

1670661455090.png

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1670661455090.png (174.4 KiB)
colj avatar image colj commented ·
Thanks for the pointer - I finally got into my SMA3000 to see the settings. Fortunately (12 years ago) the installer didn't change the default password! Nothing immediately looks inconsistent. However I did try the system again 'offgrid' (with updated frequency shift values) and it still kept shutting down. Monitoring the SMA3000, it looked like it was disconnecting whenever the 'Island' voltage dropped below 230VAC - struggling to see a parameter in the setup that would cause that especially as 230VAC is set as the country nominal voltage.
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PeterM avatar image
PeterM answered ·

It too me a long while how to work out what freq paramete rthe SMA responds to . Mine is the SB4000-TL21. It is not the obvious ones as indicated by that freq graph . It starts reducing power responding to either ( or maybe both? ) "difference between reset freq and grid freq " or "difference between starting frequency and grid freq" - in my case both are set to 0.2 Hz. Now the Frequency at which no power is produced is determined by the "Active power gradient" and the start frequency ( as described earlier ) so in my case start of power reduction is 50.2 Hz . Power is reduced at a rate of 75% / HZ to at 51.2 Hz power is reduced by 75% with zero power at 51.53 Hz. I have my Multiplus set to start power reduction at 50.2 Hz , Minimum power 51.5 Hz and disconnect freq 52.5 Hz . Do not use the two wire BMS assistant in the Multiplus with ESS when you are AC coupled - I find it often gets into a Freq locked state and you need to reboot the Multi when grid power is lost

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PeterM avatar image
PeterM answered ·

BTW to change any of the frequency values you need an installer Grid code in addition to the password. If you don't have the grid code password you can still view the values and then set the Victron accordingly


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