Good morning,
Recently, I expanded the existing battery system at home by adding a 3-phase Victron system with 3x MP6k5, so that we are now also protected against power outages. However, I am running into a few challenges at the control level.
The system:
Solar inverters:
1x SOLAX G4 15kW hybrid (18000Wp facing SSE) + 129kWh battery
1x SOLAX G2 X3 6kW (10650Wp facing NNW)
1x SOLAX G2 X3 8kW (3280Wp facing SE, Planned: 7620Wp facing W)
Victron system
3x Multiplus 6k5 + 48x 628AH EVE MB56 + 3x JK300A BMS
How the Solax inverter is controlled
The Solax hybrid inverter has several operating modes:
“Self use” – The Solax energy meter is kept at 0; all loads are powered from the battery and all solar power is stored, up to a maximum power of 14.5kW.
“Feed in prio” – Solar energy left over after supplying the household loads is exported to the grid. In the absence of sunlight, the loads are supplied from the battery.
Force discharge – Forced battery discharge
Force charge – Forced battery charging
How the complete system works
The idea is to put Victron DESS in charge and let it determine what should happen with the batteries and so on.
what currently works:
The Solax hybrid inverter follows the DESS strategy and adjusts its operating mode accordingly. I programmed all of this via Node-RED.
The issue I am running into is providing DESS with the correct information. Via Node-RED, I have added all the solar inverters so that they are visible in VRM. The HV battery is also included. The apparent limitation is that Victron does not handle having two batteries very well. You can add a second battery, but in the DESS planning it only takes one battery into account. The workaround I am currently using is that I created one large virtual battery that combines the SOC of both batteries, and DESS now accepts this.
The problem is that I cannot add a second battery charger to the system, so DESS does not understand that a lot of solar energy is being used to charge the HV battery. This results in a negative DC load. I have already applied a correction to the generated solar energy so that only the PV power that does not go into the HV battery is shown in the system as power. The correct generation in kWh is still passed on to the system, so that part is working properly.
The part that does not work properly is the calculation of the energy used in the house. This particularly goes wrong when DESS charges from the grid: the Solax switches over neatly and also charges via the grid. The disadvantage is that the system sees this as an AC load in the house and therefore effectively as consumption.
Is there a way to add a virtual second inverter that charges the battery, so that the energy flows in VRM are reasonably accurate? Alternatively, an AC charger + MPPT DC charger would also work.