Watching the Andy’s Off-Grid Garage videos in youtube, I have seen that its is possible serialize MPII and use the Power Assist and relay features to control how they have to work together.(https://youtu.be/SsTkgoN6ENM?si=QIE6MJlqDA4Vxvx1)
I think that this option could help me.
I have the following off-grid system (no option to connect to the grid): MPII 5kw with 2xPylontech US5000 plus solar charger and Cerbo.
I want to install a heat pump in the house and this will require perhaps some more power but mainly a much larger battery bank as I want to assure 2 days without solar production due to cloudy days. PV production is not a problem as I have unlimited space and I live in catalonia where I can get quite good solar production in winter.
Battery is the main issue as I will need between 30kw and 50kw to assure 2 days without solar production. I can not expand this capacity using Pylontech as they are expensive and I am thinking to build my DIY batteries using lifepo4 prismatic cells with JK Inverter BMSs.
On the other hand, I have been told that actually a Victron system can only manage 1 battery bank, not two, and I would not like discard my actual Pylontech batteries.
I was thinking in the following design by using the basics of Andy’s design by serializing inverters:
1 - Connect heat pump to AC-Out2 of my actual MPII. AC-Out1 will be for the rest of house loads and AC-Out2 will be dedicated only to heat pump.
2 - Install a new MPII (3kw or 5kw) and connect its AC-Out1 to AC-In of my actual MPII
3 - Connect the generator relay of my actual MPII to the on/off relay of new MPII
4- Connect the new battery bank (30kw to 50kw) to the new inverter plus a new RS SmartSolar Charger 450/200 and a new Cerbo for this new system.
5 - Configure the AC-Out2 relay assistant to turn on the new MPII when the AC-Out2 load is higher than the standby load of the heat pump and when AC-Out2 load goes down, then turn-off the new MPII. When the heat pump starts, then the relay will start the new MPII and when heat pump stops the relay will stop the new MPII.
This design would allow me to have an integrated system and use both batteries. The main system (the actual one with MPII+pylontech+loads) will be controlled and monitorized with the actual Cerbo and the new Cerbo will allow to control and monitorize the second MPII and the DIY batteries and the new solar charge.
As I have been looking for this desing in the community and I have not found any mention, I have some doubts about its feasibility.
Does this design work?
Is there any other alternative?
is there any major risk/issue?
Thanks