my system consists of a Multiplus-II, Cerbo-GX, 500A-Shunt, some MPPTs (450/100, 250/60, 145/45) and a DIY battery (16S LiFePo4, 13,5kWh)
The system is configured as ESS and generally works well. For safety reasons and durability of the batteries I don’t want to exceed the charge current for more than 40A even if the cells are capable of being charged with more power, but anyway.
In conjunction with DVCC this works very well, BUT if the option “DC-feed-in” within ESS is set, this current limit is ineffective then and leads to very high currents if the MPPTs are capable to deliver the power. This fact is also stated in the manual and thus I actually shouldn’t ask it in the forum here, but for me it doesn’t make sense and could possibly changed by Victron…
During the day the PV delivers energy which is divided into internal power usage in the house and charging of the battery, controlled in turn by DVCC to limit the battery current. This is done by adjusting the battery charge voltage. When the battery is full (and the charge current falls below a threshold), grid feed becomes slowly active.
Why isn’t it possible to devide the power between charging the battery with limited current and feed in the rest? I can “simulate” this increasing the grid setpoint. Then it is quite possible to realize grid feed in AND charging the batteries with current limit. Of course this is only static and must be controlled in a similar way how ESS controls all energy flows.
Is anybody who has the same problem? Is it solvable by Victron? Is anybody here who has a “trick” to get around this?
I have a very similar setup and am facing the exact same issue and frustration. I don’t understand why this option doesn’t exist.
In my case, on a sunny day, my batteries (10 kWh capacity) are fully charged by 11:00 AM (in this period. Probably during summer it will be way earlier ), and only after that, any excess energy is injected into the grid. From my perspective, this puts full strain on the batteries due to as-rapid-as-possible charging in the morning, followed by full strain on the inverter for the rest of the day, while the batteries just stay fully charged—leading to additional wear and tear.
If there were an option to limit the charging power/current of the batteries, while injecting the excess into the grid and whithout limiting the PV production, it would help reduce wear on both the batteries and the inverter.
I’ve searched extensively for a solution but haven’t had any success. Maybe, hopefully, Victron is aware of this need and is working on some options soon.
Spot on! You stress the core point of the problem, short and concise.
For me the problem will even get worse, when the new strings with ~4kWp + 3kWp will be connected soon. Then the 450/100 would then charge the batteries with currents far beyond 100 Amps, which will be dangerous and thus impossible. So I must do without grid-feed-in then, not to overcharge the battery.
Nonetheless, sometimes when I’m at home, I experiment with increasing the grid setpoint to values of 1000W or similar to simulate an intelligent control. (Grid-feed-in option switched off, DVCC set to 40A max). The ESS control is then able to limit the current as well as feeding power to the grid simultaneously! So it’s definitely possible to realise technically!
If one would “crafting” a NodeRed-Flow workaround, it should be possible to to overcome this problem temporarily in the same manner by splitting the power distribution of both, battery and grid power. On top of that with “soft-switches” on the dashboard it could be possible to adapt quickly to different situations then.
By the way a similar thing I do, when I am facing heavily varying loads over the day: I set the grid setpoint to similar values, to be always in “selling conditions” when the control loop is to slow to compensate the switched-on load, not to pay for these poorly controlled phases of the stupid control loop. Of course only an option when you expect these conditions over hours.
Would be fine if someone has an idea about this.
But Victron should definitely think about a solution on that, looking at Fronius and how smooth their ESS control works.
The fact that DVCC “Limit charge current” setting is not working when feed-in is enabled is not only “slightly sub-optimal” (read: very bad) Victron feature, but I find it even quite dangerous.
What I’m observing on my setup, when battery is not reaching 100% SOC yet and so charge not being limited by voltage: I see charge current not only above the DVCC “Limit charge current” (as unfortunately expected with feed-in enabled ), but I see it going high enough even above the “Discharge Current Limit” that battery BMS reports (as seen under Battery / Parameters on the Cerbo console). That does not look good to me at all, could lead to battery damage !
Hey Victron, this is something you should either improve some reasonable way, or at least provide a help / workaround how to prevent that from happening. To me also (as someone already noted above) seems this should be technically doable. At least the “Discharge Current Limit” which battery BMS reports should be respected. (Note: I see that with a battery which is officially supported, Pylontech ones).
A battery charger without current limit is a no-go! (here in conjunction with a complete ESS system). It’s an essential feature which must work to prevent fire or extraordinary wear on the batteries.
The question is “how PV surplus control works” at all and why there is a need to omit current limiting then. How solar surplus is detected and drained to the grid?
Because the basic current limiting itself should be an easy task to do: limiting the charge voltage coming from the MPPTs as soon as the current limit is reached and adjusting it to a constant value with a control loop. The same as the inverter does at the grid side to limit and control the inverter power.
So, it should be an independent loop to control the current for the batteries. it should not be the customer’s responsibility to ensure security
I sized my system correctly after reading the manual. I have a mix of MPPT and grid-tied AC inverters. DVCC is excellent in ESS it only works on the inverter AC charger allowing you to capture all the MPPT charge current and export all the grid-tied solar which is most efficient.
I have a 100A charger 36kwh battery and can charge from 0% to 100% with a day of full sun.
I use a mix of AC and DC charging using node-red by setting DVCC to a certain current based on voltage. It gradually tapers down to 0 as the voltage rises. I also use a load dump in the morning that sets the grid setpoint negative and exports the solar if the SOC is greater than 60%.
You can current limit the MPPT by going to the settings using Bluetooth. If you have a charger with 100A and you only want to charge with 50A you can set it to 50A. But that will not export just limit the MPPT current if you are worried about safety.
If you need help with node red let me know. If you are handy with code I can post my flow to set the grid setpoint but it might be more complex than you need as I have 2 phases and 2x grid-tied AC inverters. It will give you some ideas and some handy functions to get you started and maybe you can improve it its not perfect but works.
Thank you very much for the well-founded and useful post!
…and congrats for the well balanced setup you’ve built. I oversized my PV to have enough power to charge the batteries also on partly sunny days resp. to compensate the typical house consumption even if there is rather bad weather, so the charge currents at full sun are higher than recommended for a balanced setup. Therefore my need for limiting the charge current.
When I would adjust down the maximum MPPT currents via bluetooth, also the usable power for the Multiplus would go down, what is not my intention of course, but you’re right so far.
Btw in another thread I finally just found a post that confirms that current limit to the batteries is not done by adjusting the voltage carefully, but by limiting the DC output current of the MPPTs. In this case it’s obvious, that in case of “DC-feed-in” the maximum current is needed for the Multiplus then and thus can’t be limited anymore. → Build 55 Victron Feed-in questions - #4 by kleini - victron - Batrium Community
Anyway, I am absolutely interested in getting help with your Node-Red scripts as a template for my setup here. I mentioned that I played with adjusting the grid-setpoint for that reason and I’m happy, that you successfully applied this method to control the power-flow within your system.The only problem I have at the moment is, that I have lost access to NodeRed on the CerboGX due to an issue with the internal match of my credentials. This would be a topic for another thread. I used NodeRed to control the balancer for the DIY batteries in the recent past and its a great tool for customizing the system to your needs.
Down the bottom of this thread, I posted my flow to export excess solar in the morning if the SOC is above 60%. The problem I have is the grid export limit per phase of 5000W. I have so much solar that the battery can be charged at 10 am and this is when the AC grid-tied PV inverters are also pumping out 5000w so I can’t export anything. Dumping the excess in the morning allows me to send 6-8 kWh to the grid before I hit my export limit.
There is some handy functions there to get power and do things at certain times of the day. You should be able to use some of it and either use MPPT power or current to set the - setpoint to reduce the battery charge.
about this.