I am trying to work out if I can utilize the V2L functionality of our cars (both MG ZS EV) to charge our home battery, a Tesla powerwall 2 with backup gateway on days where the power need exceeds the useable capacity during the daytime and peak cost rate. This is typical in the winter months where solar generation is low and the demand means the battery runs out before it can recharge at the off peak rate.
Tesla support literature says you can combine both solar and other microgeneration such as wind turbine so long as the second is connected to the non backup circuit. This is AC coupled so runs at 240v.
I’m not convinced this is a workable solution as the V2L is not earthed and although it seems on the MG at least the output power is limited to 2.2kw by a resistor in the lead I don’t know how that works in practice as the Tesla powerwall could try and pull it’s max charge rate of 5kw.
If it is possible what potential issues are there?
This is a little misleading. It doesn’t technically combine the solar and other AC sources, but rather enables both to be used independently. The alternative source, such as a backup generator or V2L, is connected to the non-backup circuit. So it’s not being used to power the backup loads (which is essentially what you require). The backup gateway only has one AC source connection, which is used for the grid connection (or a generator in a permanent off-grid system). It cannot manage multiple AC sources like dedicated off-grid multi-mode inverters.
As far as I know, the only way to use V2L as a backup is using an Automatic Transfer Switch (ATS) or a manual Changeover switch (As shown in the V2L explained article). The ATS could be triggered by the Powerwall signalling a changeover to the backup source (generator or V2L). Then, your home backup circuits could be powered by the alternative AC source.
However, you cannot charge the Powerwall battery directly from the alternative AC source. Once in backup mode, the Powerwall will charge from the solar while your home runs off the V2L.
Regarding earthing, this is very important and can be problematic when using a V2L source. Being an off-grid system designer, I am not experienced with the Powerwall and connecting alternative backup sources. But the Powerwall installation manual (Page. 22) does provide some technical details about general earthing requirements.
