DESS Maximum charge power

Q&A and troubleshooting DESS
, , , ,
1

Hello!

I enabled DESS and its working fine.

My setup is:

  • 3 x Multiplus II 5000 in 3-phase operation
  • 1 x MTTP RS 450/200
  • 8 x Pylontech US5000

I have one problem with it: the system does not understand the Inverter limit.
In the cheap pricing hours its needed to charge the batteries with maximum power.
From both MPPT and grid.

If I set the “Maximum charge power” to 12kW (3x4kW from inverter) then in the daytime it will take everything from MPPT (6kW for example) and 6kW from inverter. But it should take 6kw + 12kw.

If I set the “Maximum charge power” to 23kW (12kW inverter+11kW MPPT) then the forecast is that it can charge the batteries from the grid at 23kW. Actually in the night-time it charges at 12kw and battery does not get full.

So the solution would be to separate “Maximum charge power” to “Maximum inverter charge power” and “Maximum batteries charge capability” or something similar.

Am I right?
Or is there some workaround to my problem?

2

The values in DESS are only for calculations. see here: DESS does not honor maximum charge/discharge power setting

3

Yes that’s correct.
Those values are for predictions.
I have also set grid input and output limits and those are also working well.

Problem is that the predictions needs inverter max charge capability and battery max charge capability (inverter+mppt).

4

@guystewart Do you understand the issue that I’m having?
Is there any fix planned for this?

5

The topic seems fairly quiet whereas I fully agree the soc forecast is completely incorrect due to this.
Most of the times, cheap rates are still a bit curved during sunny and windy days. It starts charging way too early and depending on the system and config it completes too soon. It should predict the combined charge capacity and continue to invert solar a bit longer before starting to charge.
Flip side is that by including RS charge power in the settings, it may start charging too late and does not finish as high as it could have.

I have been kind of requesting DESS to split AC and DC solar behaviour since late last year as I have both. Calculations are simply not the same. Neither is the nasty behaviour in the morning when DC solar is forced to go to battery in order to charge out of low-soc state. Only to invert to grid once it does (low-soc + 3%) and soc forecast has not been updated yet.