Recommended usable capacity
– kWh
Balanced
Nominal capacity (incl. DoD)
– kWh
Assumes 95% DoD (LFP)
Power requirement
– kW
Battery/inverter continuous ≥ avg; surge ≥ peak.
PV charge time (indicative)
– hrs
Assumes 0.75 × PV kW as midday charge power.
How many batteries?
| Common battery size | Usable per unit | Units needed |
|---|
Engineering notes (short version)
- Usable kWh = Avg backup load (kW) × backup hours ÷ (RTE × DoD), then add design headroom.
- Nominal kWh = usable ÷ DoD.
- Power (kW): choose a system with continuous ≥ avg backup load and surge ≥ peak load.
- PV charge time is a sanity check using 0.75 × PV kW as typical mid‑day net charge power.
What size is "about right"?
For a typical Aussie home (18–22 kWh/day) wanting overnight backup of essentials (~0.8–1.2 kW), 10–13.5 kWh usable is a common sweet spot. Go larger if you want longer outages, all‑of‑home coverage, or to soak more solar on low FiT.
