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ahaz-alex avatar image
ahaz-alex asked

Multiplus II Ess behaviour, self consumption

Hey guys,

I'm looking for some help regarding my ess setup.

Installation:
1x Victron Multiplus II / 5000 via mk3
2x Victron MPPT Charger via Ve direct
Raspberry with Venus OS
400Ah 48V lead acid battery

All loads are connected to AC out 1, grid is available and connected to AC in.
Ess configured for self consumption.
Grid code is German, vde conform. No feed in to grid wanted. Grid setpoint is at 10W.
Charger in multiplus is disabled.

First problem is the morning, coming from the night in winter. SOC is low, inverter isn't running, supply from grid. So far so good. House needs about 300W.
Sunrise, solar power rises. What I expect: inverter starts, using all available power to support grid while PV power is low, then takes over completely when sun is high, and charging only with extra PV power. What happens: batteries are charged with all available PV power until soc is good again. Inverter isn't running half the day, starts in the late noon, when sunset is near. Now system runs on PV+batterie power til midnight, then soc is low again.
This seems totally ineffective. How can I prefer self consumption over charging? Would save a lot energy and battery lifetime.

Second problem is maybe because I change the soc if weather forecast is bad for a longer period. Then is set the soc to 80-90% at the last sunny day, so the batterie doesn't idle at low voltage.
But if I do so (ie soc is at 60% and I set it to 90, so the inverter would stop, grid can power loads and the PV can charge slowly to 90%) the Multiplus adds 20-100W charging power until soc is good again (even through the night). See picture, VenusOS adds "recharge" to the view and adds 22W (was at 100W when SOC was lower). How do I stop this? I never, never want to charge the battery with power from the grid. Charger tab in the multi is completely disabled.

Thanks for any good ideas :-)
Alex

screenshot-20221203-125406.png


Multiplus-IIESSSOC
screenshot-20221203-125406.png (199.5 KiB)
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3 Answers
jetlag avatar image
jetlag answered ·

I have the same behaviour. And in my understanding this is fine. I have LiFePo4 Batteries and my lower SoC state is currently 50% in winter. So in the morning the batteries are first charged to about 54% and then the inverter starts to support the consumption in the house first.

But independant from that, as long as no PV power is lost, in the sum all the power is consumed anyway. Maybe the inverter kicks in later, but then again is running for a longer time as the batteries have more energy stored. So in sum this should be still fine.

I have reduced the interverter power output to 500W as this is the point where the efficiency is more or less at the the peak. So it doesn't matter to me the system dischares e.g. 5kWh in 2 hours or in 10 hours. The sum of provided energy to the house is still the same, but maybe with some % of better efficiency.


Regarding your second point, - yes, you can reduce the power of the charger to 0W. Then no charging from the grid will be made.

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kivanov avatar image
kivanov answered ·

In ESS Optimized mode, once the min SOC is reached (and the ESS Low Soc bit is set), self consumption is disabled (disabling the inverter as well) and it gets enabled again after the SOC reaches at least 3% above the min SOC.

If you have your min SOC increased from the ESS menu, while you have already reached the previous min SOC value (and already have ESS Low Soc set), the system will either go into ESS Recharge mode (if the SOC was lower than 5% bellow the min SOC for more than 24h), or the system will start charging the battery with priority until reaching the new min SOC value + 3% before enabling the inverter and starts ESS self consumption again. Those are my observations and they are explained in the ESS manual Battery life section despite that those principles are valid also in Optimized mode without battery life.

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ahaz-alex avatar image
ahaz-alex answered ·

So there is no way to prefer self consumption over charging batteries?



screenshot-20221210-112720.png

There would be enough energy for 80% self consumption at the moment. But it's charging the battery which causes losses of about 20% roundtrip (lead acid). I would prefer to use all PV power for self consumption, and only charge the battery with extra energy. What happens if I use the lithium BMS assistant to disabled charge and discharge? Does the inverter start or goes everything to standby and I loose all PV power? Technical it should be possible, since the power assist does the same thing, only that the inverter should limit its power to the PV power available.


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ahaz-alex avatar image ahaz-alex commented ·
Even worse, the system is now in absorption, possible pv power would be around 1kW....
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nickdb avatar image nickdb ♦♦ commented ·
You have set an ESS minimum that is very high which is why it is in #1 state.

While it is like this loads will be serviced by grid and all solar will go to the battery until the SOC is 3-5% above the minimum you set.

That is how ESS works.

Set a lower minimum percentage.

If you can't operate without such a high minimum, then it is pointless to use ESS, You may as well set it to "keep charged" then surplus solar will go to loads.


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