ESS system switches between charging and discharging

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question

Eric asked May 27, '24

ESS system switches between charging and discharging

ESS system switches between changing and discharging when the house load combined with charging load is greater than the available PV power.

The system works perfectly with full sun.

I have a MultiPlus-II 48/3000/35-32, Energy Meter VM-3P75CT, the Multiplus is connected in parallel with a Fronius 5KW solar system.

ESS is set to charge batteries if solar is greater than the load (only charges with solar) grid set point is set to 100w.

The problem only happens while PV is less than the house load and charging load combined.

For example if there is no one home the standby load of the house is approximately 300w.

If the battery is @ 50% SOC and there is 4kw of PV the system will charge the battery with 1730 watts and works well.

If the battery is @ 50% SOC and there is 1.5kw of PV the system will charge the battery with 1730 watts and then switch to discharge because there is more load than PV.

After 2 seconds of not charging it will try and charge again, this continues switch between charge and discharge.

If I then limit the charge current to 500w the system behaves normally.

The issue only occurs while PV is less than the house and charging load combined.

The problem is that the Multiplus does not try to automatically limit the charge current to a value less than the available PV, How can I fix this?

Please see video for a demonstration of the problem.

ess settings

img-4075.mov (31.7 MiB)

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Alexandra ♦ commented · May 27 at 07:10 AM

What is the min soc set in case of grid faliure? Is peak shaving under minimum allowed?

Do you have anything on the output of the inverter?

"ESS is set to charge batteries if solar is greater than the load (only charges with solar) grid set point is set to 100w."

How have you set up for this?

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Eric Alexandra ♦ commented · May 28 at 07:29 AM

Min SOC is 10%.

No Peak shaving.

All load are in parallel to input/output 1, no loads on priority output.

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Answer 1 · 2024-05-27T07:03:25Z

nickdb answered · May 27 at 07:03 AM

That is how an ESS works.

As long as you are above minimum ESS SOC, the battery supplies the delta and is later topped up by PV when there is surplus.

I would encourage you to do the ESS training and thoroughly go through the manual, it will fill in the blanks.

When systems are imbalanced, or during poor weather, this is what it does.

Putting inverting limits in place is a good option, if you want to lean on grid.

Limiting DC charging also restricts power to loads from MPPT's.

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Eric commented · May 28 at 07:56 AM

Hi Nickdb, thanks for your answer, re reading my question I think I could have asked it better, what I really want to know is how can I control the battery charge current so that it does not exceed the available PV power. I use the Multiplus to charge the batteries and I have an AC coupled system, so the Multiplus internal battery charger appears as a load.

Basically this is how my system is built, I want to configure the Victron built in charger so that it automatically limits its self to the available surplus PV power, this is to prevent the issue I first mentioned. "MY ESS system switches between charging and discharging when the house load combined with charging load is greater than the available PV power".

Using grid power is fine when PV and Battery is insufficient for my load but I want to automatically adjust the battery charging current based on available surplus PV power.?

So far I haven't been able to find any information on this?

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