Home Battery Separate from PV Battery

JayBee66

I have an all-in-one PV inverter and battery. I am toying with the idea of additional battery storage but don't want to pay €2000 plus for another PV battery.

Is it possible to get a house battery that works separately to the PV battery or do they have to communicate with each other with regards to powering the house? As far as charging is concerned I would automate that in relation to the PV battery being full or at night during the winter. Maybe the option to dump its charge (keeping within the 5KW limit) to take advantage of future agile pricing.

Thoughts and ideas welcome.

graememk

https://www.boards.ie/discussion/2058343073/home-battery-separate-from-pv-battery

If you know what you're doing, you could just connect any other 16s LFP battery (I'm assuming the original one is 16s, some dryness is 15s) to another and no communication is necessary, the new battery will just keep in step with the original one

Not staying within the NC6 limits, a me3000 + a 15kWh battery for under 2K. Control it via modbus.

JayBee66

https://www.boards.ie/discussion/comment/121929874#Comment_121929874

The aim is to have a standalone house battery that is unaware of the PV system. I'm a little vague on how a house battery would work when there's a PV system doing its own thing.

unkel

https://www.boards.ie/discussion/comment/121930026#Comment_121930026

Two separate battery / inverter systems is problematic. Charging is simple, one could charge from the grid and or PV and the other could just charge from the grid. But discharging is the problem. How would each battery know how much to discharge into your load?

That's why you can't easily have two separate battery / inverter systems. You can have two separate batteries alright, but best to have them in parallel, with only one inverter and only one of the batteries taking the lead and doing all the comms with the inverter. As @graememk described

JayBee66

https://www.boards.ie/discussion/comment/121944705#Comment_121944705

I understand. I am probably back to square one and having to get an additional battery from the same manufacturer as I doubt the inverter is capable of handling two different ones.

unkel

https://www.boards.ie/discussion/comment/121945675#Comment_121945675

What system do you have (battery / inverter)? We might give you some upgrade ideas

JayBee66

https://www.boards.ie/discussion/comment/121946038#Comment_121946038

KStar BluE-S 5000D with integrated CATL 5kW battery. The OEM of the Libbi.

unkel

https://www.boards.ie/discussion/comment/121947668#Comment_121947668

Wow, unusual choice. Fairly upmarket, at least price wise. Maybe ping myenergi, see if they would have a solution for you expanding your KStar system. Or more obvious I guess, ping KStar, their system should be modular, right? You should be able to add another 5kWh module?

bullit_dodger

https://www.boards.ie/discussion/2058343073/home-battery-separate-from-pv-battery

It's a bit "hacky", but you could let the batteries discharge in separate time windows.

E.g. Noon -> 6pm battery1 is allowed to discharge and then 6pm->midnight Battery 2 is allow to discharge. Changing the time zones as required. Could easily set that up in most inverter settings, but if you have a way in controlling it via automation, you could query the SOC on both batteris and then set which battery is "on" and turn the other one off.

Disadvantage of course is that you couldn't easily get the discharge rate of the two batteries combined, but in theory you would have access to the full capacity.

unkel

You could do that, but you would unneccessarily have a buy an expensive second hybrid inverter that way (while you already have one). I'd nearly be inclined if you couldn't upgrade the battery for the existing system for reasonable money, to sell the lot and buy a more suitable (bigger) system. Will almost certainly be financially wiser and less troublesome to setup

The great benefit of having a DIY battery is that you can easily double or triple the battery size, you wouldn't even need a new BMS, new inverter, nothing but a few extra busbars and of course the raw battery cells themselves