Grid-tied systems generally require SSEG registration with your municipality and a CoC signed by a qualified electrician. Off-grid/backup-only inverter systems still need a legal CoC but usually no feed-in registration. Requirements vary by municipality - your installer should handle the paperwork.
For essentials (lights, Wi-Fi, TV, fridge, security): 3-5kVA inverter with a 5kWh battery. To run geyser or stove too, budget 8kVA+ and 10kWh+ of storage.
A typical backup inverter + battery install takes 4-8 hours. A full hybrid solar system with roof panels typically takes 1-3 days including CoC sign-off.
Lithium (LiFePO4) lasts 8-15 years and cycles deeper daily; lead-acid is cheaper upfront but lasts 2-4 years under load-shedding duty. Lithium is the standard choice for daily-cycling backup.