I'm in a similar situation to youMy PV array has a 3.6kWh inverter & 6.7kW of storage batteries. This is powered directly from the incoming mains supply but before the house consumer unit. Likewise with the Zappi.
I also have a separate 3.6kWh inverter powering 9.6kW of Pylontech batteries, this is connected to the consumer unit upstream of the PV inverter.
Using the Zappi with Eco+ & as long as the PV batteries are full/export generation exceeds 1.4kWh then the car(s) will charge using solar. However when charging overnight using IO & Fast mode this will drain approx 3kWh from the PV batteries & take the remainder from grid.
(the other inverter/Pylontech batteries are unaffected by car charging & they are only drained by house usage).
This arrangement is OK because from Mar-Sept almost all car charging is from solar & on the few occasions IO is needed I’m not bothered too much about the PV battery drain as it will inevitably re-fill the next day anyway.
Basically, the low rate IO period gets very little use at this time of year but in winter It’s used extensively including charging the Pylontechs overnight. They power the house during the day & excess PV generation part fills the other batteries.
So in short, yes charging the car overnight on IO will drain your PV batteries but the solution I also use in winter is to block discharge 23.30-05.30 via my PV inverter ‘local mode’. This simple step means all power draw is taken from grid during the low cost period and battery SOC is unaffected.
I currently have a 3.6kWh inverter with 4.8kW battery and a Zappi (using Eco+ whenever I can)
As I'm currently on GO (Expires 25th Dec), I charge the storage batteries enough to make sure the charge in the battery will last long enough until the sun comes out. I also make sure that any overnight charging of the car doesn't currently come out of the PV batteries (due to the known fixed timeslots)
How do you work IO + Zappi so that
- I can still charge the PV batteries on the cheap rate (is the 6 hour cheap rate slot guaranteed?)
- IO charging (outside of 6 hour slot) doesn't flatten the PV batteries
- I can still charge the car using ECO+
- I can charge my daughters car (Not IO compatible)