Ohh, i guess i understand what you said, but then it still doesn’t solve it completely.
You have to set the charge/discharge power above the maximum your system can actually get?
So that would solve the most of the hours, but still in the last hour you will always have a discrepancy because it is impossible to get every day exactly the amount of energy needed to fill that last hour.
Maybe it is way more complicated for Victron than i wrote it, but i can’t see how it is that hard to get something in the code that says, after reaching SOC, return to normal operation.
I’m not a programmer and can’t answer these questions. I didn’t write, just increase the charging rate a bit and you’ll have no more problems. I wrote, check your parameters and enter the most realistic values possible, and I stand by that. Otherwise, the system works strictly according to its forecast data. Whether you can or should keep a certain reserve for this is a different discussion. The disadvantage would be that battery capacity would be tied up. Many things have advantages and disadvantages that you don’t always notice right away. I’ve been with DESS for 18 months now and have made a lot of progress and even more setbacks. Since October 2024, it has been running non-stop without any major incidents. You have to spend some time with the system to understand it. What it can and can’t do.
Most realistic sounds to me an amount that it certainly can achieve.
I have that at this moment, but it stops discharging ten minutes before the hour ends.
Maybe over time the system will learn to correct that.
I’m also curious why they charge or discharge to a percentage by the hour instead of just by targeting the end percentage it wants to discharge to, and let it continues do that. Sounds to me that they make it more complicated than it has to be.
Has Victron ever commented about those things before?
I just checked my data. I have three MP2 48/3000/35 batteries and my maximum charging rate is set to 5.3 kW. It worked very well. But that applies to my system and only for charging. It also depends somewhat on the battery and the charging parameters. I limit my charging to 120 A; on average, that’s 110 A with some fluctuations. Multiplied by 50 V, that roughly equals 5.5 or 5.3 kW.
No. That’s not how it works. Let’s be practical. My system calculates that it has an additional requirement of 12 kWh at night. Now it knows that it needs to charge fully for 2 hours and for 1 hour at reduced power. Now it looks for a time window when it can achieve this. It charges at full power during the 2 most favorable hours. In my case that would be 10.6 kWh if all goes well. It charges the remaining 1.4 kWh before or after. After that it’s not a problem, the system could possibly correct itself. But if the system buys the full 1.4 kWh before the 2 hours because of the prices, but only manages 4.5 kWh per hour because of my incorrect settings, it looks like an error. The other way around, it charges for 1 hour with 6 kW and I only specified 3 kW as the charging power. Then at some point the system realizes that I have far too much power and releases it again. I know that the parameters are not that easy to determine, especially because the charging power is not linear even in the upper Soc range. But for the DESS in its current form, these parameters are important. The last 50 W certainly don’t matter, but they should be roughly correct.
But the system doesn’t charge or discharge by amount of energy, it charges by SOC. Every hour it has a set SOC in mind that it wants to achieve, if it reaches that, it stops and waits till the next hour to charge or discharge further.
If it just doesn’t set the SOC every hour, but just sets an end SOC, and works to that, in the best hours, then it wouldn’t stop every hour and sit in a waiting stage where it does things we do not want. Like using grid or battery on the wrong moments.
The system calculates the target SoC based on the amount of energy it can discharge or charge. The amount of energy that can be discharged or charged is not random; it’s determined by the operator in the parameters.
I don’t want to argue. Try it with the charging rate, or not. I wanted to help, nothing more, nothing less. My DESS is running smoothly at the moment, although I can imagine some improvements. Good luck.
Thanks all for the good discussion regarding this subject!
I think we can conclude the behavior as discussed it tunable by setting the correct charging power (in relation to what your system can achieve). Nonetheless, DESS would benefit from some safeguards/guardrails strategies to prevent the behavior from happening once target SOC is reached before the hour.
Of course it is calculating it by the amount of energy it needs. But it charges by percentages of the SOC.
It just doesn’t work really well to charge every hour to a certain percentage, in my opinion it would work better when they just set a end target SOC and set the hours it has to do that, then there won’t be any problem with using grid or battery at moments you do not want it to.
Then at the end when it reaches the target SOC, it can resume more easily the normal operation cycle and you don’t get strange things.
And you now also lose every hour 10 minutes of charging or discharging time at the best hours.
It could be more efficient.
But maybe my vision on that is just wrong and is that impossible to do?
No worries, i appreciate it!
I understand from you that there can be some tweaking done to optimize it a bit more, but i just hope there is someone that can explain why it isn’t possible to change it on Victron their end so everyone can benefit from it and doesn’t have to tweak things a lot to get somewhat decent results.
That’s not entirely true either. The amount of energy is, of course, crucial for the calculation. With prices changing hourly, it’s crucial to get the maximum at the optimal hour and a smaller portion at off-peak times. Or even to skip it altogether because battery costs or conversion losses are too high. We haven’t even discussed the most crucial factor yet: When does it actually make sense to purchase how much energy, when do I use the available energy? And so on and so forth…
Well, it is not only the SOC, but also the restrictions:
0 - No restrictions between battery and the grid 1 - Grid to battery energy flow is restricted 2 - Battery to grid energy flow is restricted 3 - No energy flow between battery and grid
and the strategy:
0 - Target SOC 1 - Self-consumption
Of course tweaking of the charge power might help, but it should not be necessary. I’m a software engineer, and this sort of “repairs” does not make the system stable.
Problems should be analyzed and the root cause should be repaired thoroughly.
This behavior of charging and discharging during one hour with the same price is not correct and should be prevented by a strategy that only allows or charging or discharging.