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matejs avatar image
matejs asked

Occasionally unstable ESS

Hi,

for more than 2 years I have a simple system: grid-tied, one phase, MultiPlus II 48/3000/35-32, SmartSolar MPPT 150/35, 4x150Ah AGM batteries (w/ balancer), ESS enabled, Keep Batteries charged mode, no feed-in of excess power, AC grid setpoint 75W

Most of the time it works nicely, however time to time it becomes unstable. And this bugs me a lot.

For example: perfect sunny day outside, AC load cca 1kW, battery full, but suddenly MPPT is not producing. Strange behaviour is that MPPT is switching from bulk to absorption mode (1/3Hz frequency). MPPT production cycles and tries to ramp up, eg.. 0W, 5W, 16W, 60W, 80W... and than back to 0W.

Battery power jumps from e.g. -200W... to 200W... and back.

This takes for cca 20minutes and then it is back to normal. I have not found out what causes this. It looks like something trips the whole system into unstable mode.


Any ideas?


Thanks,

Matej

ESS
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3 Answers
seb71 avatar image
seb71 answered ·

ESS works better if you allow it to use the battery.

So try "Optimized with BatteryLife" and a high value for "Minimum SOC", such as 85% if you want to always have battery close to fully charged, instead of "Keep batteries charged".


If a load suddenly turns on, the inverter can quickly draw energy from the battery, because it takes a while for the solar charger to ramp up.

Similarly, when a load is turned off, the excess energy from the PV array can be diverged into the not fully charged battery, until the solar charger ramps down.


See if this makes any difference.


Also, do you know that when using ESS, the solar charger internal algorithm is disabled and the inverter controls the charging, even from the Sun?

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matejs avatar image matejs commented ·

I have tried "Optimized with Battery" before. I got the feeling that this was happening even more frequently.

Yes, I know that solar charger is out of control. This is why I am surprised why is this happening at all. What I would implement is: if battery SOC is within 100% to 95% do not use battery at all (no charging, no power out of battery). When it falls below 95%, charge to 100%. Basically I would make hysteresis larger - opposed to "Keep battery charged" that keep 100% all the time (and might cause troubles when the battery is near full - and it is not easy to determine "full")!

"Optimized with Battery" is not exactly what I have described above since it would use battery power - I do not want that. I want batteries to be used only in case of power outage. AGM batteries are too expensive (opposed to electricity cost) to be used in ESS system.

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seb71 avatar image seb71 matejs commented ·
I do not want that. I want batteries to be used only in case of power outage. AGM batteries are too expensive (opposed to electricity cost) to be used in ESS system.

In that case, I don't understand your complain.

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matejs avatar image matejs seb71 commented ·

Complain is: sunny outside, battery full, lots of AC load but PV gives 0W.

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tozz avatar image tozz matejs commented ·

You said no feed-in or excess power. If this happens when your batteries are charged.. could it be that there is simply no power demand?

Batteries don't accept any more charge. And if there is no (meaningfull) load on the system, there is nowhere the power can go to. So the MPTT will shutdown.

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matejs avatar image matejs tozz commented ·

There is a lot of demand when this happens, e.g. 2x more that my PV peak.I will take a screenshot when this happens.

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laurentiupitran avatar image
laurentiupitran answered ·

hello,

what about this comparation on the data delivered by Victron equipments and separate measurements in a ESS system, three phase?compare Victron consumption.png


compare-victron-consumption.png (160.2 KiB)
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lm-31 avatar image
lm-31 answered ·

Hi @matejS ,

Have you found any solution to your problem of instability?

I have some pretty close behaviour with my two 150/45 MPPT, one is ramping up then power drops to zero, the other then ramps up, etc... They are controlled by the ESS.

It only happens when my PV production is high enough (>1500w or so).

It has to be noted that my Multiplus is simply used as a grid-tied inverter (PV in, power out through AC-in, to the grid and my house).

Thanks!

Louis

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