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solarhome avatar image
solarhome asked

ESS mode - cycle battery

Hello technical specialist,
ESS mode, BMZ-battery, AC-output Fronius Primo, MPPT Smart Solar. All the latest updates.
The system works to offset surpluses and as a backup system with minimal SOC maintenance.
It is normal to see graphs that the battery cycles by +/- 3%.
If I have a minimum SOC of 60%, then the MPPT Solar power goes to the battery at about 63%.
Then the battery will be consumed and again 60% will start again.
Is this a normal system property of the ESS system?

Thank you for your time
Ondra

battery chargingESSBMV Battery MonitorSOC
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3 Answers
boekel avatar image
boekel answered ·

What is set as battery monitor? and what are the parameters from the bms?
I -think- your battery is fully charged but SOC not correct.

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Guy Stewart (Victron Community Manager) avatar image
Guy Stewart (Victron Community Manager) answered ·

Hello Solarhome,

I will be conducting a thorough real world test and updating the documentation for the BMZ some time in the next month, perhaps sooner. The battery should arrive to me tomorrow.

I should be able to give you some much better advice then.

In the mean time, would you mind if I look through the VRM for your site to see more closely what is going on?

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solarhome avatar image solarhome commented ·

Hello Guy,
please write me your email:

Thank You for your time and support
Ondrej Dlabaja

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solarhome avatar image
solarhome answered ·

the same problem with another installation and another battery manufacturer.
If I have a minimum SOC of 30%, then the MPPT Solar power goes to the battery at about 33%.
Then the battery will be consumed and again 30% will start again.
Is this a normal system property of the ESS system?



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boekel avatar image boekel ♦ commented ·

You'll really need to provide more information..
-battery manufacturer / type or BMS brand / type
-show the BMS parameters when this happens
-what is your grid setpoint

Also: you've cropped the screenshots so we can't see the current.

it -might- be normal operation, battery get's charged a bit (I'd say 1,2V..), than discharge is allowed again until lower SOC setpoint is reached, etc.

The battery seems to react very fast in voltage VS current, is it lead-acid?

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rogio avatar image rogio commented ·

Hello,

It looks like this behaviour is still around in the wild.


Whenever the solar input is lower than the loads, and the battery goes down to the "minimum SOC unless grid fails".


Then the DC connected solar is used only to bring the battery 3% up, using the grid in that time to feed the loads.


When the battery is again 3% above the "Minimum SOC unless grid fails" the battery and the DC connected solar is used for loads - again until the minimum SOC until grid fails "mark" - where it again shows the ESS #1 (and "External control") - and this is running the battery in 3% cycles - as long as there is some solar input and that solar input is still under the level of the loads requirements (or under that level in average).


(example start at 30% SOC "Unless grid fails" mark (with ESS #1 and "external control" shown) - "constant" 1kW solar, 2kW loads - charging the battery with 1kW DC solar, running the loads from grid, then at SOC+3% (The ESS #1 goes away) system starts feeding the loads with the 1kW DC solar and discharging 1kW from the battery until the "mark" to start the cycle again. This results in "pushing like 50% of the solar through the battery" in this exercises - charging and discharging the 3% - In like 7 such cycles seen for example two days ago).


Not using the solar PRIMARY for the loads - as it says in the manuals, just part of such time (DC solar < loads) feeding DC solar to the battery, feeding loads from grid and when SOC+3% turning to battery + DC solar feeding loads until down to SOC again - to repeat the cycle of SOC to SOC+3% to SOC to SOC+3% ...)


Wondering why the setup can't just leave the battery on SOC mark ("unless grid fails") in peace and just use the DC connected solar to participate in satisfying (mostly major part) of the loads needs without this "+-3% games" with battery acting as 3% of its charge capacity as "capacitor".


(in this ESS case the battery is US3000C Pylontech connected to Cerbo. Optimised without battery life. External, Cerbo GX connected grid meter (even not necessary) where all the loads and the DC connected solar (Victron MPPTS - also Cerbo connected) are "behind" the inverters.)

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