A further update. After 3 months the batteries have cut the bought in power by 25%. This means a just under 12 year payback based on the part of the year with least sunshine. Despite that we have seen days with nearly no bought in power.
Today after a few sunny days we started on battery power and have bought in 360 kWh vs a usage of 11 KWh. The payback so far is under 12 years and I'm sure will get below 6 easily over a full year.
JohnV6 2022 CX Plus Four 2025 MG ZS EV aka Trigger