Calculate the right battery bank size for your solar system based on daily usage, battery chemistry and required autonomy.
Typical NZ home: 15–25 kWh/day
For a typical NZ home using 20 kWh/day with 2 days of autonomy and LiFePO4 batteries (90% DoD), you need approximately 44 kWh of gross battery capacity — about 9 × 5.12 kWh units. This calculator works it out automatically.
Depth of discharge is how much of the battery's capacity you can use before recharging. LiFePO4 batteries typically allow 90% DoD, meaning you can use 9 kWh from a 10 kWh battery. Lead-acid AGM batteries are limited to 50% DoD to preserve cycle life.
Divide your daily energy consumption by the location's peak sun hours and system efficiency (typically 80%). For a 20 kWh/day home in Auckland (4.2 PSH): 20 / (4.2 × 0.80) ≈ 6 kW of solar panels.