Off grid tesla powerwall, customer want to add additional storage using a multiplus

DIY
, ,
1

I have a customer who has a tesla powerwall 2 on a stand alone/remote power system.

He wants to utilise a 2nd battery bank - non tesla that he already owns.

connecting a multiplus 2 with cerbo GX and a Lynx shunt and using the powerwall as the grid.

Issues I see are that frequency shift could be a problem if I try to charge the 2nd bank via the multiplus - ie, one or the other battery inverters would cause frequency shift and drop out the solar inverters resulting in undercharged battery banks

open to suggestions.

My background is 20 years doing remote power systems but Ive never done anything with tesla powerwalls.

cheers

2

If the Victron inverter is smaller than the 5kW power wall, then using this downstream should work ok.

If the system is grid connected, then there won’t / should not be any frequency shift while the grid is on.

The Tesla powerwall should have a modbus map accessible over the local network for accessing battery state of charge, this could be used by the cerbo to control charging / discharging of the second system.

AC coupled PV inverters will usually end up being controlled by modbus TCP/IP over the network, it may be necessary to introduce a subnet group to allow control by either the Tesla or the Cerbo, but not both.

Hope this helps.

3

Cheers, will be stand alone - no utility grid.

I was possibly going to go down the path of using the powerwall as the ‘grid’ and have a grid setpoint of 1kW in the Multiplus.

I figured this would make the powerwall discharge first before the multiplus starts to supply battery power from its own bank.

Multiplus batteries would be DC coupled, not the most efficient way I know as there will be times when the Powerwalls PV will be dormant but the multiplus batteries will still be charging and could possibly do with the additional charge source. (if that makes sence).

Im interested in the modbus map beng used by the cerbo but dont have the first idea on how to program that.

Im an electrician and although can bash my way through setting up basic systems, once we start going down this path with multiple inverters talking to each other Im very green.