I have a 8 kW (16x 360 w panels) system with a 10 kW Sunsync inverter and 4x Pylontech US3000 C battery storage. Connected to the grid but not able to feed into the grid in Makhanda / EC. My question: why do the lights dim and flicker when we lose the grid/utility in the middle of the day with full sun or in the evening with fully charged batteries. Everytime the utility power is cut the lights start dimming/flickering although there is plenty of solar power or battery available. My installer has made some changes but it does not really make a difference. Any advice would be much appreciated. Thank you

What type of lights? Halogen or Led?

Voltages between Life & Neutral.

Then mainly, voltage between Neutral and Earth at that stage.

If proper Neutral_Earth bond when in Island mode, there should be no voltage between N&E.